Darwin G. Caldwell

TMLR Journal 2026 Journal Article

Incremental3D: Real-time Incremental 3D Scene Generation with Scene Graphs

• Penggang GAO
• Yonas Teodros Tefera
• Darwin G. Caldwell
• Nikhil Deshpande

Realistic 3D environments are important for a wide range of applications, including robotics, simulation, virtual reality, and video games. The goal of 3D scene generation is to create spatially structured, semantically meaningful, and visually realistic environments that capture objects and their relationships in space. Graph-based 3D scene generation approaches represent environments as scene graphs, where nodes correspond to objects and edges encode their semantic and spatial relationships. However, existing methods become inefficient when the 3D scene graph evolves incrementally, because they are fundamentally single-shot: inserting even a single new object requires regenerating the entire scene. This global re-computation incurs prohibitive latency and scalability limitations. To address this limitation, we propose Incremental3D, a framework for incremental 3D scene generation in real-time from evolving scene graphs. Incremental3D augments the scene graph with a global context node that captures a holistic representation of the evolving environment. At each update step, this node aggregates information from new nodes and edges to form a global embedding. Newly inserted objects are then generated by conditioning on both this embedding and their local features, enabling geometry synthesis and spatial prediction without recomputing unchanged regions. Extensive experiments demonstrate that Incremental3D achieves a generation rate of 38 Hz, while maintaining high spatial and geometric accuracy, indicating its potential for real-time and latency-sensitive applications.

IROS Conference 2025 Conference Paper

ManiDP: Manipulability-Aware Diffusion Policy for Posture-Dependent Bimanual Manipulation

• Zhuo Li 0018
• Junjia Liu
• Dianxi Li
• Tao Teng
• Miao Li 0002
• Sylvain Calinon
• Darwin G. Caldwell
• Fei Chen 0007

Recent work has demonstrated the potential of diffusion models in robot bimanual skill learning. However, existing methods ignore the learning of posture-dependent task features, which are crucial for adapting dual-arm configurations to meet specific force and velocity requirements in dexterous bimanual manipulation. To address this limitation, we propose Manipulability-Aware Diffusion Policy (ManiDP), a novel imitation learning method that not only generates plausible bimanual trajectories, but also optimizes dual-arm configurations to better satisfy posture-dependent task requirements. ManiDP achieves this by extracting bimanual manipulability from expert demonstrations and encoding the encapsulated posture features using Riemannian-based probabilistic models. These encoded posture features are then incorporated into a conditional diffusion process to guide the generation of task-compatible bimanual motion sequences. We evaluate ManiDP on six real-world bimanual tasks, where the experimental results demonstrate a 39. 33% increase in average manipulation success rate and a 0. 45 improvement in task compatibility compared to baseline methods. This work highlights the importance of integrating posture-relevant robotic priors into bimanual skill diffusion to enable human-like adaptability and dexterity.

ICRA Conference 2024 Conference Paper

Assessment and Benchmarking of XoNLI: a Natural Language Processing Interface for Industrial Exoskeletons

• Olmo A. Moreno-Franco
• Raajshekhar Parameswari
• Christian Di Natali
• Darwin G. Caldwell
• Jesús Ortiz 0001

Industrial exoskeletons are a potential solution for reducing work-related musculoskeletal disorders during carrying or lifting tasks. Having sensors, electrical/pneumatic actuators, and control systems, active exoskeletons present a more versatile control system because it is possible to select different assistive strategies based on the performed task. From this perspective, human-machine interaction is required to safely open basic exoskeleton domains to the user and provide an adaptable setup system. This article presents the assessment and benchmarking of the novel XoLab Natural Language Interface, a voice user interface for interaction and configuration of industrial active exoskeletons. The evaluation of the novel interface was performed by 17 participants who completed the setup and operational activities while wearing the XoTrunk exoskeleton. The benchmark consisted of a comparison of the presented device with previous adaptable interfaces for the exoskeleton: the user command interface and the monitor system interface. The results showed that although the novel interface demonstrated a considerable lag in the time response, it was more attractive, stimulating and novel than the standard one. However, the standard interface obtained favourable results over the user command interface and the voice interface perspicuity and efficiency.

IROS Conference 2023 Conference Paper

Human-in-the-Loop Optimization of Active Back-Support Exoskeleton Assistance Via Lumbosacral Joint Torque Estimation

• Andreas Sochopoulos
• Tommaso Poliero
• Darwin G. Caldwell
• Jesús Ortiz 0001
• Christian Di Natali

The assistive profile of an active back support exoskeleton is strongly dependent on the manual tuning of controller gains based on previous experience and trial-and-error. Human-in-the-loop (HIL) optimization allows for automatic tuning of assistive profiles to different subjects. Most HIL methods make use of intrusive sensors that could affect out-of-the-lab exoskeleton adoption. Therefore, we propose a HIL-based assistive controller architecture using only one single IMU that can be easily embedded in any exoskeleton system. To validate our algorithm we recruited 3 subjects and asked them to perform a series of successive load liftings. Meanwhile, we analysed the back-muscles activations focusing on cumulative activation (iEMG), and median activation. We also monitored the total torque generated by the exoskeleton. With respect to an assistance-less condition, the proposed controller resulted in up to 19% reduction of the back-muscles activity. Moreover, compared to a state-of-the-art controller that produced up to 15% reduction of the back-muscles activity, the new controller also required generation of 4% less exoskeleton torque.

IROS Conference 2023 Conference Paper

Kinematically-Decoupled Impedance Control for Fast Object Visual Servoing and Grasping on Quadruped Manipulators

• Riccardo Parosi
• Mattia Risiglione
• Darwin G. Caldwell
• Claudio Semini
• Victor Barasuol

We propose a control pipeline for SAG (Searching, Approaching, and Grasping) of objects, based on a decoupled arm kinematic chain and impedance control, which integrates image-based visual servoing (IBVS). The kinematic decoupling allows for fast end-effector motions and recovery that leads to robust visual servoing. The whole approach and pipeline can be generalized for any mobile platform (wheeled or tracked vehicles), but is most suitable for dynamically moving quadruped manipulators thanks to their reactivity against disturbances. The compliance of the impedance controller makes the robot safer for interactions with humans and the environment. We demonstrate the performance and robustness of the proposed approach with various experiments on our 140 kg HyQReal quadruped robot equipped with a 7-DoF manipulator arm. The experiments consider dynamic locomotion, tracking under external disturbances, and fast motions of the target object.

IROS Conference 2022 Conference Paper

A Whole-Body Controller Based on a Simplified Template for Rendering Impedances in Quadruped Manipulators

• Mattia Risiglione
• Victor Barasuol
• Darwin G. Caldwell
• Claudio Semini

Quadrupedal manipulators require to be compliant when dealing with external forces during autonomous manipulation, tele-operation or physical human-robot interaction. This paper presents a whole-body controller that allows for the implementation of a Cartesian impedance control to coordinate tracking performance and desired compliance for the robot base and manipulator arm. The controller is formulated through an optimization problem using Quadratic Programming (QP) to impose a desired behavior for the system while satisfying friction cone constraints, unilateral force constraints, joint and torque limits. The presented strategy decouples the arm and the base of the platform, enforcing the behavior of a linear double-mass spring damper system, and allows to independently tune their inertia, stiffness and damping properties. The control architecture is validated through an extensive simulation study using the 90kg HyQ robot equipped with a 7-DoF manipulator arm. Simulation results show the impedance rendering performance when external forces are applied at the arm's end-effector. The paper presents results for full stance condition (all legs on the ground) and, for the first time, also shows how the impedance rendering is affected by the contact conditions during a dynamic gait.

ICRA Conference 2021 Conference Paper

Vision Based Adaptation to Kernelized Synergies for Human Inspired Robotic Manipulation

• Sunny Katyara
• Fanny Ficuciello
• Fei Chen 0007
• Bruno Siciliano
• Darwin G. Caldwell

Humans in contrast to robots are excellent in performing fine manipulation tasks owing to their remarkable dexterity and sensorimotor organization. Enabling robots to acquire such capabilities, necessitates a framework that not only replicates the human behaviour but also integrates the multi-sensory information for autonomous object interaction. To address such limitations, this research proposes to augment the previously developed kernelized synergies framework with visual perception to automatically adapt to the unknown objects. The kernelized synergies, inspired from humans, retain the same reduced subspace for object grasping and manipulation. To detect object in the scene, a simplified perception pipeline is used that leverages the RANSAC algorithm with Euclidean clustering and SVM for object segmentation and recognition respectively. Further, the comparative analysis of kernelized synergies with other state of art approaches is made to confirm their flexibility and effectiveness on the robotic manipulation tasks. The experiments conducted on the robot hand confirm the robustness of modified kernelized synergies framework against the uncertainties related to the perception of environment.

ICRA Conference 2020 Conference Paper

A Linearly Constrained Nonparametric Framework for Imitation Learning

• Yanlong Huang
• Darwin G. Caldwell

In recent years, a myriad of advanced results have been reported in the community of imitation learning, ranging from parametric to non-parametric, probabilistic to non-probabilistic and Bayesian to frequentist approaches. Meanwhile, ample applications (e. g. , grasping tasks and humanrobot collaborations) further show the applicability of imitation learning in a wide range of domains. While numerous literature is dedicated to the learning of human skills in unconstrained environments, the problem of learning constrained motor skills, however, has not received equal attention. In fact, constrained skills exist widely in robotic systems. For instance, when a robot is demanded to write letters on a board, its end-effector trajectory must comply with the plane constraint from the board. In this paper, we propose linearly constrained kernelized movement primitives (LC-KMP) to tackle the problem of imitation learning with linear constraints. Specifically, we propose to exploit the probabilistic properties of multiple demonstrations, and subsequently incorporate them into a linearly constrained optimization problem, which finally leads to a non-parametric solution. In addition, a connection between our framework and the classical model predictive control is provided. Several examples including simulated writing and locomotion tasks are presented to show the effectiveness of our framework.

ICRA Conference 2020 Conference Paper

Agile Legged-Wheeled Reconfigurable Navigation Planner Applied on the CENTAURO Robot

• Vignesh Sushrutha Raghavan
• Dimitrios Kanoulas
• Darwin G. Caldwell
• Nikos G. Tsagarakis

Hybrid legged-wheeled robots such as the CEN-TAURO, are capable of varying their footprint polygon to carry out various agile motions. This property can be advantageous for wheeled-only planning in cluttered spaces, which is our focus. In this paper, we present an improved algorithm that builds upon our previously introduced preliminary footprint varying A* planner, which was based on the rectangular symmetry of the foot support polygon. In particular, we introduce a Theta* based planner with trapezium-like search, which aims to further reduce the limitations imposed upon the wheeled-only navigation of the CENTAURO robot by the low-dimensional search space, maintaining the real-time computational efficiency. The method is tested on the simulated and real full-size CENTAURO robot in cluttered environments.

IROS Conference 2020 Conference Paper

Line Walking and Balancing for Legged Robots with Point Feet

• Carlos Gonzalez
• Victor Barasuol
• Marco Frigerio
• Roy Featherstone
• Darwin G. Caldwell
• Claudio Semini

The ability of legged systems to traverse highly- constrained environments depends by and large on the performance of their motion and balance controllers. This paper presents a controller that excels in a scenario that most state- of-the-art balance controllers have not yet addressed: line walking, or walking on nearly null support regions. Our approach uses a low-dimensional virtual model (2-DoF) to generate balancing actions through a previously derived four- term balance controller and transforms them to the robot through a derived kinematic mapping. The capabilities of this controller are tested in simulation, where we show the 90kg quadruped robot HyQ crossing a bridge of only 6 cm width (compared to its 4 cm diameter spherical foot), by balancing on two feet at any time while moving along a line. Additional simulations are carried to test the performance of the controller and the effect of external disturbances. Lastly, we present our preliminary experimental results showing HyQ balancing on two legs while being disturbed.

IROS Conference 2020 Conference Paper

Modeling Cable-Driven Joint Dynamics and Friction: a Bond-Graph Approach

• Daniele Ludovico
• Paolo Guardiani
• Alessandro Pistone
• Jinoh Lee
• Ferdinando Cannella
• Darwin G. Caldwell
• Carlo Canali

Cable-driven joints proved to be an effective solution in a wide variety of applications ranging from medical to industrial fields where light structures, interaction with unstructured and constrained environments and precise motion are required. These requirements are achieved by moving the actuators from joints to the robot chassis. Despite these positive properties a cable-driven robotic arm requires a complex cable routing within the entire structure to transmit motion to all joints. The main effect of this routing is a friction phenomenon which reduces the accuracy of the motion of the robotic device. In this paper a bond-graph approach is presented to model a family of cable-driven joints including a novel friction model that can be easily implemented into a control algorithm to compensate the friction forces induced by the rope sliding into bushings.

ICRA Conference 2020 Conference Paper

MPC-based Controller with Terrain Insight for Dynamic Legged Locomotion

• Octavio Villarreal
• Victor Barasuol
• Patrick M. Wensing
• Darwin G. Caldwell
• Claudio Semini

We present a novel control strategy for dynamic legged locomotion in complex scenarios that considers information about the morphology of the terrain in contexts when only on-board mapping and computation are available. The strategy is built on top of two main elements: first a contact sequence task that provides safe foothold locations based on a convolutional neural network to perform fast and continuous evaluation of the terrain in search of safe foothold locations; then a model predictive controller that considers the foothold locations given by the contact sequence task to optimize target ground reaction forces. We assess the performance of our strategy through simulations of the hydraulically actuated quadruped robot HyQReal traversing rough terrain under realistic on-board sensing and computing conditions.

IROS Conference 2020 Conference Paper

Pattern Analysis and Parameters Optimization of Dynamic Movement Primitives for Learning Unknown Trajectories

• Mantian Li
• Zeguo Yang
• Fusheng Zha
• Xin Wang 0041
• Pengfei Wang 0001
• Wei Guo 0015
• Darwin G. Caldwell
• Fei Chen 0007

A robot in the future may initially has a good learning capability but an empty library of movements. It gradually enriches its library of movements through human demonstrations. Dynamic Movement Primitives (DMPs) has been proved to be an effective way to represent trajectories. Trajectories are classified into discrete and rhythmic ones, and parameters are set for each demonstrated trajectory. However, what kind of trajectory will be provided by robot users is sometimes unknown to robot developers, so trajectory pattern and the parameters can not be determined in advance. It's also impossible for non-technical robot users to set these parameters and determine the pattern of movements they are going to demonstrate. To make it easier for non-expert robot users to programme their robots by demonstration, this work presents an efficient way to deal with these two problems. The effectiveness of the proposed methodology is proved by teaching a robot to clean the whiteboard in different ways and stack a set of cubic boxes in specific order.

ICRA Conference 2019 Conference Paper

Generalized Orientation Learning in Robot Task Space

• Yanlong Huang
• Fares J. Abu-Dakka
• João Silvério
• Darwin G. Caldwell

In the context of imitation learning, several approaches have been developed so as to transfer human skills to robots, with demonstrations often represented in Cartesian or joint space. While learning Cartesian positions suffices for many applications, the end-effector orientation is required in many others. However, several crucial issues arising from learning orientations have not been adequately addressed yet. For instance, how can demonstrated orientations be adapted to pass through arbitrary desired points that comprise orientations and angular velocities? In this paper, we propose an approach that is capable of learning multiple orientation trajectories and adapting learned orientation skills to new situations (e. g. , via-point and end-point), where both orientation and angular velocity are addressed. Specifically, we introduce a kernelized treatment to alleviate explicit basis functions when learning orientations. Several examples including comparison with the state-of-the-art dynamic movement primitives are provided to verify the effectiveness of our method.

IROS Conference 2019 Conference Paper

Hierarchical Reinforcement Learning for Concurrent Discovery of Compound and Composable Policies

• Domingo Esteban
• Leonel Rozo
• Darwin G. Caldwell

A common strategy to deal with the expensive reinforcement learning (RL) of complex tasks is to decompose them into a collection of subtasks that are usually simpler to learn as well as reusable for new problems. However, when a robot learns the policies for these subtasks, common approaches treat every policy learning process separately. Therefore, all these individual (composable) policies need to be learned before tackling the learning process of the complex task through policies composition. Moreover, such composition of individual policies is usually performed sequentially, which is not suitable for tasks that require to perform the subtasks concurrently. In this paper, we propose to combine a set of composable Gaussian policies corresponding to these subtasks using a set of activation vectors, resulting in a complex Gaussian policy that is a function of the means and covariances matrices of the composable policies. Moreover, we propose an algorithm for learning both compound and composable policies within the same learning process by exploiting the off-policy data generated from the compound policy. The algorithm is built on a maximum entropy RL approach to favor exploration during the learning process. The results of the experiments show that the experience collected with the compound policy permits not only to solve the complex task but also to obtain useful composable policies that successfully perform in their corresponding subtasks.

ICRA Conference 2019 Conference Paper

Non-parametric Imitation Learning of Robot Motor Skills

• Yanlong Huang
• Leonel Rozo
• João Silvério
• Darwin G. Caldwell

Unstructured environments impose several challenges when robots are required to perform different tasks and adapt to unseen situations. In this context, a relevant problem arises: how can robots learn to perform various tasks and adapt to different conditions? A potential solution is to endow robots with learning capabilities. In this line, imitation learning emerges as an intuitive way to teach robots different motor skills. This learning approach typically mimics human demonstrations by extracting invariant motion patterns and subsequently applies these patterns to new situations. In this paper, we propose a novel kernel treatment of imitation learning, which endows the robot with imitative and adaptive capabilities. In particular, due to the kernel treatment, the proposed approach is capable of learning human skills associated with high-dimensional inputs. Furthermore, we study a new concept of correlation-adaptive imitation learning, which allows for the adaptation of correlations exhibited in high-dimensional demonstrated skills. Several toy examples and a collaborative task with a real robot are provided to verify the effectiveness of our approach.

IROS Conference 2019 Conference Paper

Uncertainty-Aware Imitation Learning using Kernelized Movement Primitives

• João Silvério
• Yanlong Huang
• Fares J. Abu-Dakka
• Leonel Rozo
• Darwin G. Caldwell

During the past few years, probabilistic approaches to imitation learning have earned a relevant place in the robotics literature. One of their most prominent features is that, in addition to extracting a mean trajectory from task demonstrations, they provide a variance estimation. The intuitive meaning of this variance, however, changes across different techniques, indicating either variability or uncertainty. In this paper we leverage kernelized movement primitives (KMP) to provide a new perspective on imitation learning by predicting variability, correlations and uncertainty using a single model. This rich set of information is used in combination with the fusion of optimal controllers to learn robot actions from data, with two main advantages: i) robots become safe when uncertain about their actions and ii) they are able to leverage partial demonstrations, given as elementary sub-tasks, to optimally perform a higher level, more complex task. We showcase our approach in a painting task, where a human user and a KUKA robot collaborate to paint a wooden board. The task is divided into two sub-tasks and we show that the robot becomes compliant (hence safe) outside the training regions and executes the two sub-tasks with optimal gains otherwise.

IROS Conference 2019 Conference Paper

Variable Configuration Planner for Legged-Rolling Obstacle Negotiation Locomotion: Application on the CENTAURO Robot

• Vignesh Sushrutha Raghavan
• Dimitrios Kanoulas
• Arturo Laurenzi
• Darwin G. Caldwell
• Nikos G. Tsagarakis

Hybrid legged-wheeled robots are able to adapt their leg configuration and height to vary their footprint polygons and go over obstacles or traverse narrow spaces. In this paper, we present a variable configuration wheeled motion planner based on the A* algorithm. It takes advantage of the agility of hybrid wheeled-legged robots and plans paths over low-lying obstacles and in narrow spaces. By imposing a symmetry on the robot polygon, the computed plans lie in a low-dimensional search space that provides the robot with configurations to safely negotiate obstacles by expanding or shrinking its footprint polygon. The introduced autonomous planner is demonstrated using simulations and real-world experiments with the CENTAURO robot.

IROS Conference 2018 Conference Paper

An Uncertainty-Aware Minimal Intervention Control Strategy Learned from Demonstrations

• João Silvério
• Yanlong Huang
• Leonel Rozo
• Darwin G. Caldwell

Motivated by the desire to have robots physically present in human environments, in recent years we have witnessed an emergence of different approaches for learning active compliance. Some of the most compelling solutions exploit a minimal intervention control principle, correcting deviations from a goal only when necessary, and among those who follow this concept, several probabilistic techniques have stood out from the rest. However, these approaches are prone to requiring several task demonstrations for proper gain estimation and to generating unpredictable robot motions in the face of uncertainty. Here we present a Programming by Demonstration approach for uncertainty-aware impedance regulation, aimed at making the robot compliant - and safe to interact with - when the uncertainty about its predicted actions is high. Moreover, we propose a data-efficient strategy, based on the energy observed during demonstrations, to achieve minimal intervention control, when the uncertainty is low. The approach is validated in an experimental scenario, where a human collaboratively moves an object with a 7-DoF torque-controlled robot.

ICRA Conference 2018 Conference Paper

Enhanced Tele-interaction in Unknown Environments Using Semi-Autonomous Motion and Impedance Regulation Principles

• Luca Muratore
• Arturo Laurenzi
• Enrico Mingo Hoffman
• Lorenzo Baccelliere
• Navvab Kashiri
• Darwin G. Caldwell
• Nikos G. Tsagarakis

Robotics teleoperation has been extensively studied and considered in the past in several task scenarios where direct human intervention is not possible due to the hazardous environments. In such applications, both communication degradation and reduced perception of the remote environment are practical issues that can challenge the human operator while controlling the robot and attempting to physically interact within the remote workspace. To address this challenge, we introduce a novel shared-autonomy Tele-Interaction control approach that blends the motion commands from the pilot (master side) with locally (slave side) executed autonomous motion and impedance modulators. This enables a remote robot to handle and autonomously avoid physical obstacles during manoeuvring, reduce interaction forces during contacts, and finally accommodate different payload conditions while at the same time operating with a “default” low impedance setting. We implemented and experimentally validated the proposed method both on simulation and on a real robot platform called CENTAURO. A series of tasks, such as maneuvering through the physical constraints of the remote environment in an autonomous manner, pushing and lifting heavy objects with autonomous impedance regulation and colliding with the rigid geometry of the remote environment were executed. The obtained results demonstrate the effectiveness of the shared-autonomy control principles that eventually aim to reduce the level of attention and stress of human pilot while manoeuvring the slave robot, and at the same time to enhance the robustness of the robot during physical interactions even if accidentally occurred.

ICRA Conference 2018 Conference Paper

Footstep Planning in Rough Terrain for Bipedal Robots Using Curved Contact Patches

• Dimitrios Kanoulas
• Alexander Stumpf
• Vignesh Sushrutha Raghavan
• Chengxu Zhou
• Alexia Toumpa
• Oskar von Stryk
• Darwin G. Caldwell
• Nikos G. Tsagarakis

Bipedal robots have gained a lot of locomotion capabilities the past few years, especially in the control level. Navigation over complex and unstructured environments using exteroceptive perception, is still an active research topic. In this paper, we present a footstep planning system to produce foothold placements, using visual perception and proper environment modeling, given a black box walking controller. In particular, we extend a state-of-the-art search-based planning approach (ARA*) that produces 6DoF footstep sequences in 3D space for flat uneven terrain, to also handle rough curved surfaces, e. g. rocks. This is achieved by integrating both a curved patch modeling system for rough local terrain surfaces and a flat foothold contact analysis based on visual range input data, into the existing planning framework. The system is experimentally validated using real-world point clouds, while rough terrain stepping demonstrations are presented on the WALK-MAN humanoid robot, in simulation.

ICRA Conference 2018 Conference Paper

Generalized Task-Parameterized Skill Learning

• Yanlong Huang
• João Silvério
• Leonel Rozo
• Darwin G. Caldwell

Programming by demonstration has recently gained much attention due to its user-friendly and natural way to transfer human skills to robots. In order to facilitate the learning of multiple demonstrations and meanwhile generalize to new situations, a task-parameterized Gaussian mixture model (TP-GMM) has been recently developed. This model has achieved reliable performance in areas such as human-robot collaboration and dual-arm manipulation. However, the crucial task frames and associated parameters in this learning framework are often set by the human teacher, which renders three problems that have not been addressed yet: (i) task frames are treated equally, without considering their individual importance, (ii) task parameters are defined without taking into account additional task constraints, such as robot joint limits and motion smoothness, and (iii) a fixed number of task frames are pre-defined regardless of whether some of them may be redundant or even irrelevant for the task at hand. In this paper, we generalize the task-parameterized learning by addressing the aforementioned problems. Moreover, we provide a novel learning perspective which allows the robot to refine and adapt previously learned skills in a low dimensional space. Several examples are studied in both simulated and real robotic systems, showing the applicability of our approach.

ICRA Conference 2018 Conference Paper

Hybrid Probabilistic Trajectory Optimization Using Null-Space Exploration

• Yanlong Huang
• João Silvério
• Leonel Rozo
• Darwin G. Caldwell

In the context of learning from demonstration, human examples are usually imitated in either Cartesian or joint space. However, this treatment might result in undesired movement trajectories in either space. This is particularly important for motion skills such as striking, which typically imposes motion constraints in both spaces. In order to address this issue, we consider a probabilistic formulation of dynamic movement primitives, and apply it to adapt trajectories in Cartesian and joint spaces simultaneously. The probabilistic treatment allows the robot to capture the variability of multiple demonstrations and facilitates the mixture of trajectory constraints from both spaces. In addition to this proposed hybrid space learning, the robot often needs to consider additional constraints such as motion smoothness and joint limits. On the basis of Jacobian-based inverse kinematics, we propose to exploit robot null-space so as to unify trajectory constraints from Cartesian and joint spaces while satisfying additional constraints. Evaluations of hand-shaking and striking tasks carried out with a humanoid robot demonstrate the applicability of our approach.

ICRA Conference 2018 Conference Paper

Multi-Priority Cartesian Impedance Control Based on Quadratic Programming Optimization

• Enrico Mingo Hoffman
• Arturo Laurenzi
• Luca Muratore
• Nikos G. Tsagarakis
• Darwin G. Caldwell

In this work we introduced a prioritized Cartesian impedance control under the framework of the Quadratic Programming (QP) optimization. In particular, we present a formulation which is simpler than full inverse dynamics, avoids any matrix pseudo-inversion, inverse kinematics computation and considers strict priorities among tasks. Our formulation is based on QP optimization permitting to take into account also explicit inequality constraints. We compare in simulation the tracking results obtained with a classical algebraic implementation against those derived from the proposed QP implementation taking into account joint torque limits. We consider the classical Cartesian impedance controller and a simplified version, also known as Virtual Model Control. Finally the proposed method was implemented and validated on a humanoid upper-body torque controlled robot. Experimental trials involving various physical interaction conditions were executed to demonstrate the performance of the proposed method.

IROS Conference 2018 Conference Paper

On the Orientation Planning with Constrained Angular Velocity and Acceleration at Endpoints

• Mohammad Shahbazi
• Navvab Kashiri
• Darwin G. Caldwell
• Nikos G. Tsagarakis

This paper presents orientation planning algorithms respecting the requirements of task space trajectory generation, particularly in robotics applications. The proposed algorithms fulfill the following conditions: (i) permitting to impose constraints at angular velocity and acceleration in addition to orientation at endpoints; (ii) rendering continuous acceleration profiles even when interpolating multiple orientations; and (iii) being computationally fast enough for realtime implementation. The generated spline trajectories are essentially a concatenation of polynomial in time curves parameterized by quaternion coefficients. To impose the unitariness condition critically required for quaternion representation of orientation, we develop an on-line update mechanism which successively reparameterizes the polynomials constructing the spline, towards suppressing distortions that the normalization operation might incur. Experiments on an anthropomorphic robot upper-body are carried out to demonstrate the efficacy and real-time compatibility of the proposed algorithms in comparison with a standard spherical interpolation method.

ICRA Conference 2018 Conference Paper

Online Falling-Over Control of Humanoids Exploiting Energy Shaping and Distribution Methods

• Rajesh Subburaman
• Jinoh Lee
• Darwin G. Caldwell
• Nikos G. Tsagarakis

This paper proposes a novel fall control technique based on energy concepts, which can be applied online to mitigate the impact forces incurred during the falling over of humanoids. The technique reduces the total energy using a nonlinear control tool, called energy shaping (ES), and further distributes the reduced energy over multiple contacts by means of energy distribution polygons (EDP). We also include an effective orientation control to safeguard the end-effectors in the event of ground impacts. The performance of the proposed method is numerically evaluated by dynamic simulations under the sudden falling over scenario of the humanoid robot for both lateral and sagittal falls. The effectiveness of the proposed ES and EDP concepts are verified by diverse comparative simulations with total energy, distribution, and impact forces.

IROS Conference 2018 Conference Paper

Probabilistic Learning of Torque Controllers from Kinematic and Force Constraints

• João Silvério
• Yanlong Huang
• Leonel Rozo
• Sylvain Calinon
• Darwin G. Caldwell

When learning skills from demonstrations, one is often required to think in advance about the appropriate task representation (usually in either operational or configuration space). We here propose a probabilistic approach for simultaneously learning and synthesizing torque control commands which take into account task space, joint space and force constraints. We treat the problem by considering different torque controllers acting on the robot, whose relevance is learned probabilistically from demonstrations. This information is used to combine the controllers by exploiting the properties of Gaussian distributions, generating new torque commands that satisfy the important features of the task. We validate the approach in two experimental scenarios using 7- DoF torque-controlled manipulators, with tasks that require the consideration of different controllers to be properly executed.

IROS Conference 2018 Conference Paper

Towards Minimal Intervention Control with Competing Constraints

• Yanlong Huang
• João Silvério
• Darwin G. Caldwell

As many imitation learning algorithms focus on pure trajectory generation in either Cartesian space or joint space, the problem of considering competing trajectory constraints from both spaces still presents several challenges. In particular, when perturbations are applied to the robot, the underlying controller should take into account the importance of each space for the task execution, and compute the control effort accordingly. However, no such controller formulation exists. In this paper, we provide a minimal intervention control strategy that simultaneously addresses the problems of optimal control and competing constraints between Cartesian and joint spaces. In light of the inconsistency between Cartesian and joint constraints, we exploit the robot null space from an information-theory perspective so as to reduce the corresponding conflict. An optimal solution to the aforementioned controller is derived and furthermore a connection to the classical finite horizon linear quadratic regulator (LQR) is provided. Finally, a writing task in a simulated robot verifies the effectiveness of our approach.

ICRA Conference 2018 Conference Paper

Translating Videos to Commands for Robotic Manipulation with Deep Recurrent Neural Networks

• Anh Nguyen 0003
• Dimitrios Kanoulas
• Luca Muratore
• Darwin G. Caldwell
• Nikos G. Tsagarakis

We present a new method to translate videos to commands for robotic manipulation using Deep Recurrent Neural Networks (RNN). Our framework first extracts deep features from the input video frames with a deep Convolutional Neural Networks (CNN). Two RNN layers with an encoder-decoder architecture are then used to encode the visual features and sequentially generate the output words as the command. We demonstrate that the translation accuracy can be improved by allowing a smooth transaction between two RNN layers and using the state-of-the-art feature extractor. The experimental results on our new challenging dataset show that our approach outperforms recent methods by a fair margin. Furthermore, we combine the proposed translation module with the vision and planning system to let a robot perform various manipulation tasks. Finally, we demonstrate the effectiveness of our framework on a full-size humanoid robot WALK-MAN.

IROS Conference 2018 Conference Paper

VARO-Fi: A Variable Orientable Gripper to Obtain In-Hand Manipulation

• Nahian Rahman
• Darwin G. Caldwell
• Ferdinando Cannella

This paper proposes a novel gripper or end-effector named VARO-fi (VARiable Orientable fingers with translation), with the aim of obtaining human like prehensile manoeuvre such as, in-hand manipulation. The 4 fingered VARO-fi consists of 9 degrees of freedom and it can perform several in-hand manipulation tasks which have been described in this paper. Moreover, the gripper is a simplification of previously proposed gripper platform called Dexclar. The derivation of VARO-fi has been presented and its capabilities have been demonstrated by experiments. Although a generic convex payload is considered as a primitive in the design of VARO-fi however, it is capable to address manipulation for other regular shaped payloads, which has been proven by experiments. A comparison is also illustrated in order to underline the strength of the novel gripper with respect to the state of the art.

ICRA Conference 2017 Conference Paper

A self-adaptive variable impedance actuator based on intrinsic non-linear compliance and damping principles

• Navvab Kashiri
• Darwin G. Caldwell
• Nikos G. Tsagarakis

Despite the growing focus on the design of compliant mechanisms for robotics actuators that manifest several advantages in terms of robustness and interaction-related characteristics, the incorporation of elasticity in the actuation drive renders under-damped vibration modes and reduces the bandwidth of the system. The addition of damping principles into compliant systems can address such impediments to accuracy and stability, and enhance the passivity characteristics of the controlled compliant actuator. However, passive damping mechanisms integrated into compliant systems to exhibit user-defined passive dissipation profiles have not been realized. This paper proposes a non-linear stiffness compliant module, and introduces a novel non-linear damper which complements the elastic element. The cam-follower mechanism was employed for rendering the user-defined non-linear behaviour. While the passive compliance of the module is replicated using a curved leaf spring, the passive damping is generated by rolling/sliding motion of a rigid cylinder on an elastomer. The design of the module is described, the theoretical modelling is presented, and experimental results validating the functionality of the proposed design in dissipating under-damped oscillations are demonstrated.

IROS Conference 2017 Conference Paper

Dexclar: A gripper platform for payload-centric manipulation and dexterous applications

• Nahian Rahman
• Luca Carbonari
• Carlo Canali
• Darwin G. Caldwell
• Ferdinando Cannella

Developing grasping devices with the capabilities to carry out dexterous tasks similar to human hand are being studied for many decades. To this aim, mathematical analysis such as control of multi-fingered gripper, grasp synthesis algorithms, contact types and their interactions have been explicitly addressed by many researchers. Since human hands are dexterous due to the complex integration of control and numerous sensors, hence they are naturally adaptable to grasp, in-hand manipulation of plurality of object by their construction. On the other hand, artificial grippers require priori knowledge of the payload geometry and configuration to maneuver grasping and manipulation tasks at the very first place. Moreover, theoretical analysis, such as contact kinematics, grasp stability cannot predict the nonholonomic behaviors, and therefore, uncertainties are always present to restrict a maneuver, even though the gripper is kinematically feasible of doing the task. Hence, in general, industrial grippers do exploit simpler mechanisms with least number of fingers and tend to avoid soft materials in the construction primarily to achieve dexterity, reliability, repeatability and speed in the process. However, in-hand manipulation of objects urges certain degrees of flexibility in the gripper design; which is difficult to obtain from a rigid structure and also the use of non-rigid materials reduce speed, accuracy and performance. In this research, a gripper platform named Dexclar (DEXterous reConfigurable moduLAR) is proposed, which addresses the dilemma by combining mechanism and modularity, evaluating payload centric requirements.

IROS Conference 2017 Conference Paper

FLEGX: A bioinspired design for a jumping humanoid leg

• Mariapaola D'Imperio
• Daniele Ludovico
• Cristiano Pizzamiglio
• Carlo Canali
• Darwin G. Caldwell
• Ferdinando Cannella

Robotics in the last decades is moving towards bioinspired solutions in order to develop systems increasingly integrated with the human environment. Among them, legged robots fascinates more and more researchers thanks to their ability of moving in unstructured environment such as the ones typical of earthquakes, where in the near future robots are planned to be send to help humans while performing dangerous tasks. On the base of this findings, the authors propose a novel concept for a jumping humanoid leg, based on the key role played from the structural flexibility. The geometric and dynamic features of this leg have been selected thanks to a targeted set of numerical simulations. An extensive campaign of experimental tests useful for the validation of the numerical model here presented will be a matter of future works.

IROS Conference 2017 Conference Paper

Inverse dynamics control of bimanual object manipulation using orthogonal decomposition: An analytic approach

• Mohammad Shahbazi
• Jinoh Lee
• Darwin G. Caldwell
• Nikos G. Tsagarakis

In this paper, the well-known problem of codependence between inverse dynamics torque and contact force in bimanual object manipulation is addressed. The common contact constraint, namely rigid grasping, is exploited to decompose the set of dynamics equations into two orthogonally decoupled sets. Subsequently, the inverse dynamics control is formulated in a sub-manifold that is independent of the contact force, leading to analytically correct solutions that do not need to resort to common approximations for the aforementioned codependence problem. The contact force is also analytically computed and, therefore, can be optimally distributed using the torque redundancy. Relying on this prediction is most significant in situations where a force sensor at the end-effector is not present or is faulty. Even in the availability of sensory data, the predicted force may be used to correct typically noisy or delayed when filtered measurements, resulting in improved robustness. Simulation experiments on a planar bimanual manipulation model are presented.

IROS Conference 2017 Conference Paper

Learning manipulability ellipsoids for task compatibility in robot manipulation

• Leonel Rozo
• Noémie Jaquier
• Sylvain Calinon
• Darwin G. Caldwell

Posture body variation is one of the ways in which humans skillfully and naturally augment their motion and strength capabilities along specific task-space directions in order to successfully perform complex manipulation tasks. Posture variation also has a significant role in robot manipulation, where manipulability arises as a useful criterion to analyze and control the robot dexterity as a function of its joint configuration. In this context, this paper introduces the promising idea of manipulability transfer, a method that allows robots to learn and reproduce desired manipulability ellipsoids from expert demonstrations. The proposed framework is built on a tensor-based formulation of Gaussian mixture model that takes into account that manipulability ellipsoids lie on the manifold of symmetric positive definite matrices. This geometry-aware method is used to design a manipulability-based redundancy resolution that allows the robot to modify its posture so that its manipulability ellipsoid coincides with the desired one. Experiments in simulation validate the functionality of the proposed approach, which extends the robot learning capability beyond trajectory, force and impedance learning approaches.

IROS Conference 2017 Conference Paper

Learning task-space synergies using Riemannian geometry

• Martijn J. A. Zeestraten
• Ioannis Havoutis
• Sylvain Calinon
• Darwin G. Caldwell

In the context of robotic control, synergies can form elementary units of behavior. By specifying task-dependent coordination behaviors at a low control level, one can achieve task-specific disturbance rejection. In this work we present an approach to learn the parameters of such low-level controllers by demonstration. We identify a synergy by extracting covariance information from demonstration data. The extracted synergy is used to derive a time-invariant state feedback controller through optimal control. To cope with the non-Euclidean nature of robot poses, we utilize Riemannian geometry, where both estimation of the covariance and the associated controller take into account the geometry of the pose manifold. We demonstrate the efficacy of the approach experimentally in a bimanual manipulation task.

IROS Conference 2017 Conference Paper

Object-based affordances detection with Convolutional Neural Networks and dense Conditional Random Fields

• Anh Nguyen 0003
• Dimitrios Kanoulas
• Darwin G. Caldwell
• Nikos G. Tsagarakis

We present a new method to detect object affordances in real-world scenes using deep Convolutional Neural Networks (CNN), an object detector and dense Conditional Random Fields (CRF). Our system first trains an object detector to generate bounding box candidates from the images. A deep CNN is then used to learn the depth features from these bounding boxes. Finally, these feature maps are post-processed with dense CRF to improve the prediction along class boundaries. The experimental results on our new challenging dataset show that the proposed approach outperforms recent state-of-the-art methods by a substantial margin. Furthermore, from the detected affordances we introduce a grasping method that is robust to noisy data. We demonstrate the effectiveness of our framework on the full-size humanoid robot WALK-MAN using different objects in real-world scenarios.

IROS Conference 2017 Conference Paper

Online payload identification for quadruped robots

• Guido Tournois
• Michele Focchi
• Andrea Del Prete
• Romeo Orsolino
• Darwin G. Caldwell
• Claudio Semini

The identification of inertial parameters is crucial to achieve high-performance model-based control of legged robots. The inertial parameters of the legs are typically not altered during expeditions and therefore are best identified offline. On the other hand, the trunk parameters depend on the modules mounted on the robot, like a motor to provide the hydraulic power, or different sets of cameras for perception. This motivates the use of recursive approaches to identify online mass and the position of the Center of Mass (CoM) of the robot trunk, when a payload change occurs. We propose two such approaches and analyze their robustness in simulation. Furthermore, experimental trials on our 80-kg quadruped robot HyQ show the applicability of our strategies during locomotion to cope with large payload changes that would otherwise severely compromise the balance of the robot.

ICRA Conference 2017 Conference Paper

Trajectory and foothold optimization using low-dimensional models for rough terrain locomotion

• Carlos Mastalli
• Michele Focchi
• Ioannis Havoutis
• Andreea Radulescu
• Sylvain Calinon
• Jonas Buchli
• Darwin G. Caldwell
• Claudio Semini

We present a trajectory optimization framework for legged locomotion on rough terrain. We jointly optimize the center of mass motion and the foothold locations, while considering terrain conditions. We use a terrain costmap to quantify the desirability of a foothold location. We increase the gait's adaptability to the terrain by optimizing the step phase duration and modulating the trunk attitude, resulting in motions with guaranteed stability. We show that the combination of parametric models, stochastic-based exploration and receding horizon planning allows us to handle the many local minima associated with different terrain conditions and walking patterns. This combination delivers robust motion plans without the need for warm-starting. Moreover, we use soft-constraints to allow for increased flexibility when searching in the cost landscape of our problem. We showcase the performance of our trajectory optimization framework on multiple terrain conditions and validate our method in realistic simulation scenarios and experimental trials on a hydraulic, torque controlled quadruped robot.

IROS Conference 2017 Conference Paper

Viscosity-based height reflex for workspace augmentation for quadrupedal locomotion on rough terrain

• Michele Focchi
• Roy Featherstone
• Romeo Orsolino
• Darwin G. Caldwell
• Claudio Semini

We propose a reactive locomotion strategy, called height reflex, that is useful to address big elevation changes in the terrain (e. g. when a quadruped robot has to step down from a high platform). In these cases the swing leg can lose mobility creating issues in the subsequent steps. The height reflex is a foot trajectory replanning strategy that redistributes the swing motion (in a smart way) to the stance legs to “lower” the whole trunk and to aid the foothold searching motion. To spread the motion we exploit a massless link model of the robot with virtual dampers at the joints, which is used to replan the feet trajectories. The proposed approach is able to incorporate kinematic limits, it is easy-to-tune, computationally efficient and suitable for real-time implementations. The reflex is implemented and experimentally evaluated on the 80 kg hydraulic quadruped HyQ. With our approach we were able to address high steps, up to 24 cm which is 30% of HyQ leg length and 53% of its retractable leg range.

IROS Conference 2017 Conference Paper

What is the torque bandwidth of this actuator?

• Jörn Malzahn
• Navvab Kashiri
• Wesley Roozing
• Nikos G. Tsagarakis
• Darwin G. Caldwell

The paper proposes a method to assess the feasible torque bandwidth for electrically driven torque controllable actuators over its entire torque amplitude range. The method solely relies on the knowledge of hardware parameters and thereby determines the physically feasible torque control bandwidth at a given torque amplitude, independent of a controller. The method yields torque-frequency diagrams that are suitable to benchmark torque controllers, formulate actuator design specifications and compare as well as select actuators for a specific torque control application. The paper exemplifies the method on a WALK-MAN leg actuator with locked actuator output and the more practical case of a varying load inertia.

ICRA Conference 2017 Conference Paper

Whole-body trajectory optimization for non-periodic dynamic motions on quadrupedal systems

• Andreea Radulescu
• Ioannis Havoutis
• Darwin G. Caldwell
• Claudio Semini

Autonomous legged robots will be required to handle a wide range of tasks in complex environments. While a lot of research has focused on developing their abilities for periodic locomotion tasks, less effort has been invested in devising generalized strategies for dynamic, non-periodic movements. Motion design approaches are frequently enlisted in the form of teleoperation or predefined heuristics in such scenarios. We employ a realistic simulation of the hydraulically actuated HyQ2Max quadrupedal system for investigations on two distinctive tasks: rearing and posture recovery. We present a whole-body optimization methodology for non-periodic tasks on quadrupedal systems. This approach delivers solutions involving multiple contacts without the need for predefined feet placements. The results obtained show the potential of optimization approaches for motion synthesis in the context of complex tasks.

IROS Conference 2016 Conference Paper

Balance and impedance optimization control for COmpliant huMANoid stepping

• Emmanouil Spyrakos-Papastavridis
• Darwin G. Caldwell
• Nikos G. Tsagarakis

The work presented herein, attempts to address the problem of designing stepping recovery controllers for compliantly actuated humanoid robots. Based on the decomposition of the stepping procedure into three distinct phases, which are characterized by unique combinations of configurations and impedance levels, the contrivance of a Linear Quadratic Regulator (LQR) optimization process allows for the production of a corresponding number of controllers. The penalties associated with the proposed cost functions, which account for compliant dynamics and balance-related parameters alike, are selected in a systematic manner that facilitates the generation of the appropriate impedance levels required for each particular phase of the stepping motion. Subsequently, the superimposition of gravity compensation control, onto the original LQR controllers, renders them nonlinear and theoretically capable of tracking referential stepping trajectories. The associated referential motor positions are then generated by exploiting a formula relating the Centre-of-Pressure (CoP) to the compliant ankle dynamics, thereby satisfying the balancing constraints whilst also accounting for the system's inherent under-actuation. Thus, the technique's novelty stems from its explicit consideration of flexible joint dynamics and deflection torques, for the design of the desired impedance levels and joint stepping trajectories. The Series Elastic Actuator (SEA) powered COmpliant huMANoid (COMAN), has served as an avatar of the stepping recovery methodology that is expounded in the paper.

IROS Conference 2016 Conference Paper

Comparison of open-loop and closed-loop disturbance observers for series elastic actuators

• Wesley Roozing
• Jörn Malzahn
• Darwin G. Caldwell
• Nikos G. Tsagarakis

This contribution compares two approaches for applying disturbance observers (DOBs) to the torque control problem of series elastic actuators (SEAs). It is demonstrated that they are in fact equivalent for linear models in terms of their ability to reject disturbances and enforce nominal model dynamics. The closed loop and error transfer functions for the DOB-based approaches are compared to a fully linear plant and a nonlinear plant without DOB. Simulations demonstrate that the DOBs are able to increase the bandwidth of the nonlinear plant significantly, up to that of the linear plant. Furthermore, the DOBs significantly increase the tracking accuracy at low frequencies.

ICRA Conference 2016 Conference Paper

Design of a variable compliant humanoid foot with a new toe mechanism

• Wooseok Choi
• Gustavo A. Medrano-Cerda
• Darwin G. Caldwell
• Nikos G. Tsagarakis

The general approach to humanoid feet design considers the use of rectangular plate sole structures that are relatively stiff and compatible for flat terrain locomotion. Although this can be adequate the inability of these stiff feet to cope with small terrain irregularities, it makes them inappropriate for rough terrains. Toward improvement of humanoids feet this paper presents mechanism of new variable compliant humanoid feet which can provide functionality and adaptability to humanoids locomotion on uneven terrains. The proposed feet design introduces new toe mechanism in the feet with variable stiffness implemented using a leaf spring and rubber balls in series. We present the mechanism design and the implementation of the sensor, and discuss the estimation of variable stiffness range and coefficient of damping at sole. A prototype of the feet was built and experimental results are included to validate the feet design.

IROS Conference 2016 Conference Paper

Detecting object affordances with Convolutional Neural Networks

• Anh Nguyen 0003
• Dimitrios Kanoulas
• Darwin G. Caldwell
• Nikos G. Tsagarakis

We present a novel and real-time method to detect object affordances from RGB-D images. Our method trains a deep Convolutional Neural Network (CNN) to learn deep features from the input data in an end-to-end manner. The CNN has an encoder-decoder architecture in order to obtain smooth label predictions. The input data are represented as multiple modalities to let the network learn the features more effectively. Our method sets a new benchmark on detecting object affordances, improving the accuracy by 20% in comparison with the state-of-the-art methods that use hand-designed geometric features. Furthermore, we apply our detection method on a full-size humanoid robot (WALK-MAN) to demonstrate that the robot is able to perform grasps after efficiently detecting the object affordances.

IROS Conference 2016 Conference Paper

Enhancing bilateral teleoperation using camera-based online virtual fixtures generation

• Mario Selvaggio
• Gennaro Notomista
• Fei Chen 0007
• Boyang Gao
• Francesco Trapani
• Darwin G. Caldwell

In this paper we present an interactive system to enhance bilateral teleoperation through online virtual fixtures generation and task switching. This is achieved using a stereo camera system which provides accurate information of the surrounding environment of the robot and of the tasks that have to be performed in it. The use of the proposed approach aims at improving the performances of bilateral teleoperation systems by reducing the human operator workload and increasing both the implementation and the execution efficiency. In fact, using our method virtual guidances do not need to be programmed a priori but they can be instead automatically generated and updated making the system suitable for unstructured environments. We strengthen the proposed method using passivity control in order to safely switch between different tasks while teleoperating under active constraints. A series of experiments emulating real industrial scenarios are used to show that the switch between multiple tasks can be passively and safely achieved and handled by the system.

IROS Conference 2016 Conference Paper

HEXOTRAC: A highly under-actuated hand exoskeleton for finger tracking and force feedback

• Ioannis Sarakoglou
• Anais Brygo
• Dario Mazzanti
• Nadia Vanessa Garcia-Hernandez
• Darwin G. Caldwell
• Nikos G. Tsagarakis

Exoskeletons offer an intuitive method for actuating multiple DOF of the body; this makes them attractive for applications where generation and coupling of artificial forces to the limbs is needed. Force feedback hand exoskeletons have been continuously considered for whole hand haptic interaction in virtual reality simulators, in teleoperation setups and for rehabilitation. In hand exoskeletons finger tracking, actuation and transmission systems must be embedded in confined spaces, matching at the same time the profound dexterity of the hand transparently and without causing a burden. Most of the design approaches for such systems have remained largely experimental due to hardware limitations, impacting heavily on important functional and ergonomic factors. This paper presents the design of a novel 3-digit hand exoskeleton, which addresses the issues of finger tracking and force feedback. It proposes a new approach for the application of the feedback force with a single attachment at the fingertip through a 6DoF kinematic chain. This kinematic linkage allows for unconstrained reach of the fingers within their full workspace and facilitates a sensor system for high resolution 6DOF tracking of the fingertips. At the same time the highly under-actuated mechanism permits application of a bidirectional feedback force at the fingertips. The hand exoskeleton fits an large range of hand sizes and requires no mechanical alignment between the linkage and the fingers, whatsoever. Preliminary results show the efficacy of this system as a tracking and force feedback device for the hand.

ICRA Conference 2016 Conference Paper

Hierarchical planning of dynamic movements without scheduled contact sequences

• Carlos Mastalli
• Ioannis Havoutis
• Michele Focchi
• Darwin G. Caldwell
• Claudio Semini

Most animal and human locomotion behaviors for solving complex tasks involve dynamic motions and rich contact interaction. In fact, complex maneuvers need to consider dynamic movement and contact events at the same time. We present a hierarchical trajectory optimization approach for planning dynamic movements with unscheduled contact sequences. We compute whole-body motions that achieve goals that cannot be reached in a kinematic fashion. First, we find a feasible CoM motion according to the centroidal dynamics of the robot. Then, we refine the solution by applying the robot's full-dynamics model, where the feasible CoM trajectory is used as a warm-start point. To accomplish the unscheduled contact behavior, we use complementarity constraints to describe the contact model, i. e. environment geometry and non-sliding active contacts. Both optimization phases are posed as Mathematical Program with Complementarity Constraints (MPCC). Experimental trials demonstrate the performance of our planning approach in a set of challenging tasks.

IROS Conference 2016 Conference Paper

Preparatory object reorientation for task-oriented grasping

• Anh Nguyen 0003
• Dimitrios Kanoulas
• Darwin G. Caldwell
• Nikos G. Tsagarakis

This paper describes a new task-oriented grasping method to reorient a rigid object to its nominal pose, which is defined as the configuration that it needs to be grasped from, in order to successfully execute a particular manipulation task. Our method combines two key insights: (1) a visual 6 Degree-of-Freedom (DoF) pose estimation technique based on 2D-3D point correspondences is used to estimate the object pose in real-time and (2) the rigid transformation from the current to the nominal pose is computed online and the object is reoriented over a sequence of steps. The outcome of this work is a novel method that can be effectively used in the preparatory phase of a manipulation task, to permit a robot to start from arbitrary object placements and configure the manipulated objects to the nominal pose, as required for the execution of a subsequent task. We experimentally demonstrate the effectiveness of our approach on a full-size humanoid robot (WALK-MAN) using different objects with various pose settings under real-time constraints.

ICRA Conference 2016 Conference Paper

Robust and adaptive whole-body controller for humanoids with multiple tasks under uncertain disturbances

• Jinoh Lee
• Houman Dallali
• Maolin Jin
• Darwin G. Caldwell
• Nikos G. Tsagarakis

This paper focuses on the development of a dynamic model-free whole-body controller for a humanoid robot with high kinematic redundancy. The proposed controller is based on force-level operational-space control framework, which computes joint torques for the required forces of prioritized multiple tasks. While typical approaches based on this framework require to obtain an accurate robot dynamics model, which has been generally recognized as a major hurdle to overcome for implementation in real humanoid robots, the proposed controller incorporates adaptive sliding-mode and online dynamics estimation schemes; thus, it can be easily realized on a humanoid without identifying complex robot dynamic parameters. As a result, the gains of the proposed controller are adaptively adjusted to assure the control accuracy, when the humanoid robot changes its posture and undergoes uncertain disturbances. Experiments with a 23-DoFs humanoid under uncertain disturbances verify that the proposed controller can robustly perform multiple tasks with high accuracy.

ICRA Conference 2016 Conference Paper

Synergy-based interface for bilateral tele-manipulations of a master-slave system with large asymmetries

• Anais Brygo
• Ioannis Sarakoglou
• Arash Ajoudani
• Nadia Vanessa Garcia-Hernandez
• Giorgio Grioli
• Manuel G. Catalano
• Darwin G. Caldwell
• Nikos G. Tsagarakis

In this work a novel synergy-based bilateral tele-manipulation strategy is introduced. The proposed algorithm has been primarily developed to remotely control the Pisa/IIT SoftHand (SH) using a 3-finger hand exoskeleton as master device. With a single actuator and a sensory system limited to a position encoder and a current sensor, the SH minimalist design promotes robustness but challenges traditional teleoperation strategies.

ICRA Conference 2016 Conference Paper

Towards a multi-legged mobile manipulator

• Bilal Ur Rehman
• Michele Focchi
• Jinoh Lee
• Houman Dallali
• Darwin G. Caldwell
• Claudio Semini

A common disadvantage of multi-legged robots is that they often lack the manipulation capability. To overcome this limitation, an arm can be added to the body of the multi-legged robot, to perform manipulation tasks and provide assistance for locomotion. First, we proposed an attachment configuration of the arm for a multi-legged robot that provide a uniform workspace in front, below and above the base robot trunk. Second, an integrated control framework promises to keep the mobility and the balance of the mobile platform and provides precise manipulation capability of the arm incorporating a payload estimation scheme. Finally, we verify an integrated control framework with experimental results of a static and walking mobile platform while moving the arm.

ICRA Conference 2016 Conference Paper

Variable duration movement encoding with minimal intervention control

• Martijn J. A. Zeestraten
• Sylvain Calinon
• Darwin G. Caldwell

Programming by Demonstration (PbD) offers a user-friendly way to transfer skills from human to robot. Typically, demonstration data do not contain the control inputs required to reproduce the demonstrated skill. These can be obtained from a low-level controller that tracks the modeled movement. We present a PbD approach for minimal intervention control — a control strategy that only corrects perturbations that interfere with task performance. The novelty of our approach is the probabilistic encoding of the movement duration, providing a performance measure that enables minimal intervention control in a temporal sense. This is achieved by combining a probabilistic movement encoding based on Hidden Semi-Markov Model (HSMM) with Model Predictive Control (MPC). The probabilistic model is used to construct an objective function, hereby assuming that variance is a measure for task performance. The proposed method is demonstrated in a robot experiment and compared with our earlier work.

ICRA Conference 2016 Conference Paper

WALK-MAN humanoid lower body design optimization for enhanced physical performance

• Francesca Negrello
• Manolo Garabini
• Manuel G. Catalano
• Przemyslaw Kryczka
• Wooseok Choi
• Darwin G. Caldwell
• Antonio Bicchi
• Nikos G. Tsagarakis

The deployment of robots to assist in environments hostile for humans during emergency scenarios require robots to demonstrate enhanced physical performance, that includes adequate power, adaptability and robustness to physical interactions and efficient operation. This work presents the design and development of the lower body of the new high performance humanoid WALK-MAN, a robot developed recently to assist in disaster response scenarios. The paper introduces the details of the WALK-MAN lower-body, highlighting the innovative design optimization features considered to maximize the leg performance. Starting from the general lower body specifications the objectives of the design and how they were addressed are introduced, including the selection of the leg kinematics, the arrangement of the actuators and their integration with the leg structure to maximize the range of motion, reduce the leg mass and inertia, and shape the leg mass distribution for better dynamic performance. Physical robustness is ensured with the integration of elastic transmission and impact energy absorbing covers. Experimental walking trials demonstrate the correct operation of the legs while executing a walking gait.

IROS Conference 2015 Conference Paper

A new foot sole design for humanoids robots based on viscous air damping mechanism

• Wooseok Choi
• Chengxu Zhou
• Gustavo A. Medrano-Cerda
• Darwin G. Caldwell
• Nikos G. Tsagarakis

The work presents the development and evaluation of a novel foot sole for humanoid robots. For humanoid locomotion the foot sole is important for absorbing impacts. In contrast to the simple planar rubber pad foot sole that is conventionally used in humanoid robots this paper introduces a new foot sole design in which the dissipation of energy during collision is done effectively using a viscous air damping sole mechanism that provides better reduction of the ground impact forces. The paper describes the principle of the foot sole and provides details of its design and implementation. Experimental trials were performed with the child size humanoid robot, COMAN, wearing the proposed feet to validate their performance during landing and walking. The results demonstrate that the proposed new passive damping mechanism can reduce effectively the ground reaction impact forces and oscillations while maintaining the foot/body posture.

IROS Conference 2015 Conference Paper

Active control of under-actuated foot tilting for humanoid push recovery

• Zhibin Li 0001
• Chengxu Zhou
• Qiuguo Zhu
• Rong Xiong
• Nikos G. Tsagarakis
• Darwin G. Caldwell

We propose a novel control framework to demonstrate a unique foot tilting maneuver based on ankle torque control for humanoid balance recovery. The framework consists of the variable impedance regulation at the center of mass of the robot based on the ankle torque control, the virtual stoppers to prevent over tilting of the feet, and the body attitude control. The scope of our paper focuses on the sagittal scenario as the first proof of concept on the balance recovery by means of active foot tilting without losing stability. Our study demonstrates the success of the control implementation for the humanoid push recovery and the feasibility of having actively controlled foot tilting. The experimental data are presented and analyzed.

ICRA Conference 2015 Conference Paper

Damping control of variable damping compliant actuators

• Navvab Kashiri
• Gustavo A. Medrano-Cerda
• Nikos G. Tsagarakis
• Matteo Laffranchi
• Darwin G. Caldwell

The development of variable impedance actuators (VIAs) has highlighted the need for proper control of passive impedance to attain suitable interaction performance. Until recently the regulation of the intrinsic impedance in VIAs is achieved in an open-loop model-based manner, mainly due to the lack of physical sensors capable of measuring impedance components such as stiffness and damping. Hence, the estimation of variable stiffness and damping has been explored, with the target to provide monitoring and feedback for potential closed loop control schemes. However, the use of the output of these estimators in the feedback control of variable impedance actuators has never been implemented/demonstrated in practice. This work contributes to the field with the development and experimental evaluation of a novel damping feedback control for a class of variable impedance compliant actuators able to realize a variable physical damping principle. The scheme is based on non-model-based damping estimation feedback to compensate model uncertainties in the action of an inner controller that uses a model-based friction estimator. Experimental results demonstrate the ability of the proposed scheme to replicate with good fidelity constant and time-varying damping levels.

ICRA Conference 2015 Conference Paper

Encoderless position control of a two-link robot manipulator

• Petar Kormushev
• Yiannis Demiris
• Darwin G. Caldwell

Encoders have been an inseparable part of robots since the very beginning of modern robotics in the 1950s. As a result, the foundations of robot control are built on the concepts of kinematics and dynamics of articulated rigid bodies, which rely on explicitly measuring the robot configuration in terms of joint angles - done by encoders.

IROS Conference 2015 Conference Paper

Exploiting the redundancy for humanoid robots to dynamically step over a large obstacle

• Chengxu Zhou
• Xin Wang 0041
• Zhibin Li 0001
• Darwin G. Caldwell
• Nikos G. Tsagarakis

In this paper, we resolve the issue of stepping over a large obstacle by exploiting the redundancy of pelvis rotation and the versatility of foot trajectories for the humanoids. The control framework consists of a motion pattern that exploits the redundancy of pelvis rotation to enlarge the kinematic workspace, a generic foot trajectory generation which can be modified by a parametric interface to adapt to a specific task as well as utilizing the hip abduction to avoid obstacle collision. Moreover, the compensation strategies are also presented for reducing the discrepancies to implement the dynamic stepping motion on a real robot. The effectiveness is validated by COMAN's capability of dynamically stepping over a large obstacle of 10cm height by 5cm width which is almost 20% of its leg length in both simulation and experiment.

ICRA Conference 2015 Conference Paper

Fall Prediction of legged robots based on energy state and its implication of balance augmentation: A study on the humanoid

• Zhibin Li 0001
• Chengxu Zhou
• Juan Alejandro Castano
• Xin Wang 0041
• Francesca Negrello
• Nikos G. Tsagarakis
• Darwin G. Caldwell

In this paper, we propose an Energy based Fall Prediction (EFP) which observes the real-time balance status of a humanoid robot during standing. The EFP provides an analytic and quantitative measure of the level of balance. Both simulation and experimental studies were conducted and compared with the previously proposed indicators, such as Capture Point (CP) and Foot Rotation Indicator (FRI). The EFP also suggests the balance augmentation by active foot tilting to create larger potential barriers. As a proof of concept, a hybrid balance controller was designed to stabilize the robot including under-actuation phases so the robot can also balance with shoes. Our study reveals that both EFP and CP successfully predict falling about 0. 2s in advance for the tested robot, while the FRI fails due to the light weight of the foot and limited resolution of the force/torque measurement.

ICRA Conference 2015 Conference Paper

Feed forward incision control for laser microsurgery of soft tissue

• Loris Fichera
• Diego Pardo
• Placido Illiano
• Darwin G. Caldwell
• Leonardo S. Mattos

In this paper we present a feed forward controller to regulate the depth of laser incisions in soft tissue. Such a controller is compatible with the requirements of laser microsurgery, where space constraints limit the use of sensing devices. The controller is based on an inverse model that maps the desired incision depth to the required laser exposure time. This model is extracted from experimental data through the use of statistical learning methods. To prove the concept, the controller is implemented in a robot-assisted laser microsurgery system that enables precision control of exposure time and laser motion. The validity and the accuracy of the controller is verified experimentally on ex-vivo muscle tissue (chicken breast), revealing an RMSE of 0. 12 mm for incisions ranging up to 1 mm. In addition, we demonstrate how the model can be used to implement the automatic ablation of entire volumes of tissue, through the superposition of controlled laser incisions.

IROS Conference 2015 Conference Paper

From one-legged hopping to bipedal running and walking: A unified foot placement control based on regression analysis

• Yangwei You
• Zhibin Li 0001
• Darwin G. Caldwell
• Nikos G. Tsagarakis

This paper aims at developing a unified and adaptive foot placement control for legged robots. The locomotion control of legged robots can be classified into three parts as body height control, body attitude control, and forward velocity control. In our study, the body attitude is controlled at stance phase by the hip actuator, and the height is controlled by the motion of the stance leg. In this case, the foot placement has a nearly linear correlation with forward velocity. Hereby, a generic foot placement controller is developed to control the forward velocity based on the online linear regression analysis of their coupled correlation. Our proposed algorithm is capable of adjusting the control parameters automatically, and is featured by good adaptability and higher control accuracy that outperforms the empirical tuning. The very same controller is able to produce stable hopping with accurate forward velocity tracking even with unknown mass offset, as well as stable bipedal running and walking with accurate velocity tracking.

ICRA Conference 2015 Conference Paper

Kinematic analysis and design considerations for optimal base frame arrangement of humanoid shoulders

• Mostafa Bagheri
• Arash Ajoudani
• Jinoh Lee
• Darwin G. Caldwell
• Nikos G. Tsagarakis

It is well known that kinematics can significantly affect the manipulation capabilities of robotic arms, traditionally illustrated by performance indices such as workspace volume, kinematic and force manipulability, and isotropy within the arm workspace. In the case of dual-arm systems and bimanual manipulation tasks, the kinematics effects to the above indices becomes even more apparent. However, in spite of the large number of dual-arm systems developed in the past, there is a little literature on the kinematic design analysis for the development of such systems. Particularly, the effects of configuration/ orientation of the shoulders' placement with respect to the torso structure have not sufficiently studied or considered, while many dual-arm systems with upward and/or forward tilt angle in shoulder base frame have been introduced. This paper addresses this problem and quantifies the effect of shoulders base frame orientation in a dual-arm manipulation system by looking at its effect on several important manipulation indices, such as the overall and common workspace, redundancy, global isotropy, dual-arm manipulability, and inertia ellipsoid index within the common workspace of the two arms. Consequently, a range of upward and forward tilt angles for the shoulder frames is identified for the design of a dual-arm torso system to render the most desired manipulation performance.

IROS Conference 2015 Conference Paper

Kinematic-free position control of a 2-DOF planar robot arm

• Petar Kormushev
• Yiannis Demiris
• Darwin G. Caldwell

This paper challenges the well-established assumption in robotics that in order to control a robot it is necessary to know its kinematic information, that is, the arrangement of links and joints, the link dimensions and the joint positions. We propose a kinematic-free robot control concept that does not require any prior kinematic knowledge. The concept is based on our hypothesis that it is possible to control a robot without explicitly measuring its joint angles, by measuring instead the effects of the actuation on its end-effector. We implement a proof-of-concept encoderless robot controller and apply it for the position control of a physical 2-DOF planar robot arm. The prototype controller is able to successfully control the robot to reach a reference position, as well as to track a continuous reference trajectory. Notably, we demonstrate how this novel controller can cope with something that traditional control approaches fail to do: adapt to drastic kinematic changes such as 100% elongation of a link, 35-degree angular offset of a joint, and even a complete overhaul of the kinematics involving the addition of new joints and links.

IROS Conference 2015 Conference Paper

Learning bimanual end-effector poses from demonstrations using task-parameterized dynamical systems

• João Silvério
• Leonel Rozo
• Sylvain Calinon
• Darwin G. Caldwell

Very often, when addressing the problem of human-robot skill transfer in task space, only the Cartesian position of the end-effector is encoded by the learning algorithms, instead of the full pose. However, orientation is just as important as position, if not more, when it comes to successfully performing a manipulation task. In this paper, we present a framework that allows robots to learn the full poses of their end-effectors in a task-parameterized manner. Our approach permits the encoding of complex skills, such as those found in bimanual manipulation scenarios, where the generalized coordination patterns between end-effectors (i. e. position and orientation patterns) need to be considered. The proposed framework combines a dynamical systems formulation of the demonstrated trajectories, both in ℝ 3 and SO(3), and task-parameterized probabilistic models that build local task representations in both spaces, based on which it is possible to extract the relevant features of the demonstrated skill. We validate our approach with an experiment in which two 7-DoF WAM robots learn to perform a bimanual sweeping task.

IROS Conference 2015 Conference Paper

Learning optimal controllers in human-robot cooperative transportation tasks with position and force constraints

• Leonel Rozo
• Danilo Bruno
• Sylvain Calinon
• Darwin G. Caldwell

Human-robot collaboration seeks to have humans and robots closely interacting in everyday situations. For some tasks, physical contact between the user and the robot may occur, originating significant challenges at safety, cognition, perception and control levels, among others. This paper focuses on robot motion adaptation to parameters of a collaborative task, extraction of the desired robot behavior, and variable impedance control for human-safe interaction. We propose to teach a robot cooperative behaviors from demonstrations, which are probabilistically encoded by a task-parametrized formulation of a Gaussian mixture model. Such encoding is later used for specifying both the desired state of the robot, and an optimal feedback control law that exploits the variability in position, velocity and force spaces observed during the demonstrations. The whole framework allows the robot to modify its movements as a function of parameters of the task, while showing different impedance behaviors. Tests were successfully carried out in a scenario where a 7 DOF backdrivable manipulator learns to cooperate with a human to transport an object.

ICRA Conference 2015 Conference Paper

Learning symbolic representations of actions from human demonstrations

• Seyed Reza Ahmadzadeh
• Ali Paikan
• Fulvio Mastrogiovanni
• Lorenzo Natale
• Petar Kormushev
• Darwin G. Caldwell

In this paper, a robot learning approach is proposed which integrates Visuospatial Skill Learning, Imitation Learning, and conventional planning methods. In our approach, the sensorimotor skills (i. e. , actions) are learned through a learning from demonstration strategy. The sequence of performed actions is learned through demonstrations using Visuospatial Skill Learning. A standard action-level planner is used to represent a symbolic description of the skill, which allows the system to represent the skill in a discrete, symbolic form. The Visuospatial Skill Learning module identifies the underlying constraints of the task and extracts symbolic predicates (i. e. , action preconditions and effects), thereby updating the planner representation while the skills are being learned. Therefore the planner maintains a generalized representation of each skill as a reusable action, which can be planned and performed independently during the learning phase. Preliminary experimental results on the iCub robot are presented.

ICRA Conference 2015 Conference Paper

New motorized micromanipulator for robot-assisted laser phonomicrosurgery

• Nikhil Deshpande
• Leonardo S. Mattos
• Darwin G. Caldwell

In laser-based laryngeal surgeries, motorized laser scanners offer greater aiming accuracy and efficiency. In this paper, a new motorized laser micromanipulator is presented, which is based on a spherical orienting device. It is a 2 degrees-of-freedom roll/pitch mechanism which actuates the laser beamsplitter mirror for improved aiming control and automated intraoperative planning. The combination of this device with state-of-the-art reflective laser focusing optics overcomes the drawbacks of an earlier prototype, providing increased operating distance and surgical range. This makes the device more suitable to real surgical scenarios in the operating room (OR). Improved system accuracy and usability is successfully demonstrated through comparative user trials against the traditional manual laser micromanipulator. The new device offers greater than 57% improvement in accuracy demonstrating its safety and usability. Preliminary ex-vivo trials were also performed with expert surgeons with the new mechanism. The surgeons evaluated the system positively and provided valuable and favourable feedback pointing to the suitability of the device for the OR and its potential to enhance the capacity of laser-based transoral microsurgeries.

IROS Conference 2015 Conference Paper

Online regeneration of bipedal walking gait pattern optimizing footstep placement and timing

• Przemyslaw Kryczka
• Petar Kormushev
• Nikos G. Tsagarakis
• Darwin G. Caldwell

We propose a new algorithm capable of online regeneration of gait patterns. The algorithm uses a nonlinear optimization technique to find step parameters that will bring the robot from the present state to a desired state. It modifies online not only the footstep positions, but also the step timing in order to maintain dynamic stability during walking. Inclusion of step time modification extends the robustness against rarely addressed disturbances, such as pushes towards the stance foot. The controller is able to recover dynamic stability regardless of the source of the disturbance (e. g. model inaccuracy, reference tracking error or external disturbance). We describe the robot state estimation and center-of-mass feedback controller necessary to realize stable locomotion on our humanoid platform COMAN. We also present a set of experiments performed on the platform that show the performance of the feedback controller and of the gait pattern regenerator. We show how the robot is able to cope with series of pushes, by adjusting step times and positions.

ICRA Conference 2015 Conference Paper

OpenSoT: A whole-body control library for the compliant humanoid robot COMAN

• Alessio Rocchi
• Enrico Mingo Hoffman
• Darwin G. Caldwell
• Nikos G. Tsagarakis

A fundamental aspect of controlling humanoid robots lies in the capability to exploit the whole body to perform tasks. This work introduces a novel whole body control library called OpenSoT. OpenSoT is combined with joint impedance control to create a framework that can effectively generate complex whole body motion behaviors for humanoids according to the needs of the interaction level of the tasks. OpenSoT gives an easy way to implement tasks, constraints, bounds and solvers by providing common interfaces. We present the mathematical foundation of the library and validate it on the compliant humanoid robot COMAN to execute multiple motion tasks under a number of constraints. The framework is able to solve hierarchies of tasks of arbitrary complexity in a robust and reliable way.

ICRA Conference 2015 Conference Paper

Planning and execution of dynamic whole-body locomotion for a hydraulic quadruped on challenging terrain

• Alexander W. Winkler
• Carlos Mastalli
• Ioannis Havoutis
• Michele Focchi
• Darwin G. Caldwell
• Claudio Semini

We present a framework for dynamic quadrupedal locomotion over challenging terrain, where the choice of appropriate footholds is crucial for the success of the behaviour. We build a model of the environment on-line and on-board using an efficient occupancy grid representation. We use Any-time-Repairing A* (ARA*) to search over a tree of possible actions, choose a rough body path and select the locally-best footholds accordingly. We run a n-step lookahead optimization of the body trajectory using a dynamic stability metric, the Zero Moment Point (ZMP), that generates natural dynamic whole-body motions. A combination of floating-base inverse dynamics and virtual model control accurately executes the desired motions on an actively compliant system. Experimental trials show that this framework allows us to traverse terrains at nearly 6 times the speed of our previous work, evaluated over the same set of trials.

IROS Conference 2015 Conference Paper

Reactive trotting with foot placement corrections through visual pattern classification

• Victor Barasuol
• Marco Camurri
• Stéphane Bazeille
• Darwin G. Caldwell
• Claudio Semini

Agile robot locomotion on rough terrain is highly dependent on the ability to perceive the environment. In this paper, we show how the interaction between a reactive control framework and an online mapping system can significantly improve the trotting performance on irregular terrain. In particular, this new locomotion controller increases the stability of the robot and reduces frontal leg and shin collisions with obstacles by correcting in realtime the foothold locations. The mapping system uses an RGB-D sensor and a motion capture system to build a three dimensional map of the surroundings of the robot. While the robot is trotting, the control framework requests in advance a local heightmap around the next nominal foothold position. Then, an optimized foot placement location is estimated by applying visual pattern classification on the acquired heightmaps, and the leg endpoint trajectory is modified accordingly. The foothold correction is performed independently for each leg. To show the effectiveness of our approach the controller was tested both in simulation and experimentally with our 80 kg hydraulic quadruped robot, HyQ. The results show that visual based reaction through pattern classification is a promising approach to increase locomotion robustness over challenging terrain.

ICRA Conference 2015 Conference Paper

Underwater robot-object contact perception using machine learning on force/torque sensor feedback

• Nawid Jamali
• Petar Kormushev
• Arnau Carrera
• Marc Carreras
• Darwin G. Caldwell

Autonomous manipulation of objects requires reliable information on robot-object contact state. Underwater environments can adversely affect sensing modalities such as vision, making them unreliable. In this paper we investigate underwater robot-object contact perception between an autonomous underwater vehicle and a T-bar valve using a force/torque sensor and the robot's proprioceptive information. We present an approach in which machine learning is used to learn a classifier for different contact states, namely, a contact aligned with the central axis of the valve, an edge contact and no contact. To distinguish between different contact states, the robot performs an exploratory behavior that produces distinct patterns in the force/torque sensor. The sensor output forms a multidimensional time-series. A probabilistic clustering algorithm is used to analyze the time-series. The algorithm dissects the multidimensional time-series into clusters, producing a one-dimensional sequence of symbols. The symbols are used to train a hidden Markov model, which is subsequently used to predict novel contact conditions. We show that the learned classifier can successfully distinguish the three contact states with an accuracy of 72% ± 12 %.

JBHI Journal 2014 Journal Article

A Fully Automated System for Adherent Cells Microinjection

• Gabriele Becattini
• Leonardo S. Mattos
• Darwin G. Caldwell

This paper proposes an automated robotic system to perform cell microinjections to relieve human operators from this highly difficult and tedious manual procedure. The system, which uses commercial equipment currently found on most biomanipulation laboratories, consists of a multitask software framework combining computer vision and robotic control elements. The vision part features an injection pipette tracker and an automatic cell targeting system that is responsible for defining injection points within the contours of adherent cells in culture. The main challenge is the use of bright-field microscopy only, without the need for chemical markers normally employed to highlight the cells. Here, cells are identified and segmented using a threshold-based image processing technique working on defocused images. Fast and precise microinjection pipette positioning over the automatically defined targets is performed by a two-stage robotic system which achieves an average injection rate of 7. 6 cells/min with a pipette positioning precision of 0. 23 μm. The consistency of these microinjections and the performance of the visual targeting framework were experimentally evaluated using two cell lines (CHO-K1 and HEK) and over 500 cells. In these trials, the cells were automatically targeted and injected with a fluorescent marker, resulting in a correct cell detection rate of 87% and a successful marker delivery rate of 67. 5%. These results demonstrate that the new system is capable of better performances than expert operators, highlighting its benefits and potential for large-scale application.

ICRA Conference 2014 Conference Paper

A passivity based compliance stabilizer for humanoid robots

• Chengxu Zhou
• Zhibin Li 0001
• Juan Alejandro Castano
• Houman Dallali
• Nikos G. Tsagarakis
• Darwin G. Caldwell

This paper presents a passivity based compliance stabilizer for humanoid robots. The proposed stabilizer is an admittance controller that uses the force/torque sensing in feet to actively regulate the compliance for the position controlled system. The low stiffness provided by the stabilizer permits compliant interaction with external forces, and the active damping control guarantees the passivity by dissipating the excessive energy delivered by disturbances. Both the theoretical work and simulation validations are presented. The effectiveness of the stabilizer is demonstrated by the simulations of a simplified cart-table model and the multi-body model of a humanoid under impulsive/periodic force perturbations during standing and walking in place. Simulation data show the quantitative evaluation of the stabilization effect by comparing the responses of body attitude, center of mass, center of pressure without and with the stabilizer.

IROS Conference 2014 Conference Paper

A study on data-driven in-hand twisting process using a novel dexterous robotic gripper for assembly automation

• Fei Chen 0007
• Ferdinando Cannella
• Carlo Canali
• Mariapaola D'Imperio
• Traveler Hauptman
• Giuseppe Sofia
• Darwin G. Caldwell

In electronic manufacturing system, the design of the robotic hand with sufficient dexterity and configuration is important for the successful accomplishment of the assembly task. It is significant that the robot can grasp assembly parts and do some simple in-hand manipulation so as to fit them with the package slots. In this research, we study the process of precise in-hand posture transition problem using a novel jaw like gripper with human-sized anthropomorphic features. We transform the in-hand manipulation problem into a series of static grasping problems. Then we study the successful twisting condition on each grasp frame by analyzing its dynamic performance and requirements. Based on this data-driven idea, simulation and experimental data is obtained from both successful and failed trials. Finally, we create the distribution of parameters grasp map for successful twisting.

ICRA Conference 2014 Conference Paper

A task-parameterized probabilistic model with minimal intervention control

• Sylvain Calinon
• Danilo Bruno
• Darwin G. Caldwell

We present a task-parameterized probabilistic model encoding movements in the form of virtual spring-damper systems acting in multiple frames of reference. Each candidate coordinate system observes a set of demonstrations from its own perspective, by extracting an attractor path whose variations depend on the relevance of the frame at each step of the task. This information is exploited to generate new attractor paths in new situations (new position and orientation of the frames), with the predicted covariances used to estimate the varying stiffness and damping of the spring-damper systems, resulting in a minimal intervention control strategy. The approach is tested with a 7-DOFs Barrett WAM manipulator whose movement and impedance behavior need to be modulated in regard to the position and orientation of two external objects varying during demonstration and reproduction.

ICRA Conference 2014 Conference Paper

Development of a hybrid actuator with controllable mechanical damping

• Ioannis Sarakoglou
• Nikos G. Tsagarakis
• Darwin G. Caldwell

This paper presents a novel hybrid actuator with controllable mechanical damping. It has been developed to provide subsequently the actuation means for haptic interfaces that can demonstrate intrinsic passive performance when rendering hard contacts. The overall actuator is a dual actuation system where one actuator is responsible for generating the joint motion while the second is dedicated to regulating the physical damping through a semi-active friction mechanism. This semi active friction mechanism applies a purely dissipative torque on the joint, which can be continuously controlled to render damping levels ranging from completely free to heavily damped and even a completely locked joint. The present work focuses mainly on the mechatronic details of the actuator design and in particular on the modelling and control of the damper. The proposed variable damping mechanism is evaluated in a simple 1-DOF joint. Experimental results are presented to demonstrate that the unit is capable of replicating physical damping with adequate performance.

ICRA Conference 2014 Conference Paper

Dynamically transitioning between surfaces of varying inclinations to achieve uneven-terrain walking

• Luca Colasanto
• Nicolas Perrin-Gilbert
• Nikos G. Tsagarakis
• Darwin G. Caldwell

This paper focuses on how to generate dynamic transitions in order to make our robot COMAN (COmpliant huMANoid) dynamically traverse inclined terrains. The novel approach addresses dynamic walking on inclined surfaces by dividing the walking motion into two phases: transition and incline walking. During the transition phase, the humanoid robot performs a 3-dimensional movement in order to transfer its body between surfaces of different inclinations, which is then followed by the incline-walking phase. The transition phase is less trivial to execute than the incline walking itself. In this paper, we first formulate the equations of a 3D (non linear) Inverted Pendulum, and then we derive an equivalent model. Subsequently, we introduce a trajectory generator based on this model and validate it experimentally by performing, with COMAN, dynamic transitions from the horizontal ground to a 10° slope.

ICRA Conference 2014 Conference Paper

Enhanced computer-assisted laser microsurgeries with a "virtual microscope" based surgical system

• Nikhil Deshpande
• Jesús Ortiz 0001
• Darwin G. Caldwell
• Leonardo S. Mattos

Ergonomic and human-centered approaches are increasingly important in the design of surgeon-machine interfaces. In the case of microsurgeries, the procedures suffer from susceptibility to variation in surgeon skill and equipment characteristics. This paper presents a novel, computer-assisted surgical interface for laser-based microsurgeries, called the “μRALP Surgical System”. With the system, surgeries can be performed with improved safety and precision using a three-part architecture: (i) a 3D viewer device providing stereoscopic visualization; (ii) a graphics stylus that controls a motorized micromanipulator for laser aiming and activation; and (iii) a configuration interface allowing system setup and modifications in real-time. The system combines the advantages of a computer-assisted platform while respecting the visualization and manipulation requirements of a microsurgical procedure. The features include intraoperative planning for automatic laser incisions and ablations as well as safety regions based on virtual overlays in the surgeon's field-of-view. A comparative evaluation of the proposed system against the traditional system points to the clear superiority of the new interface. The quantitative comparison shows that the proposed interface is safer, more precise, and better controlled. The qualitative comparison demonstrates that the interface is easier to use, easier to learn, and has a minimal training requirement. The technological advances presented here shall lead to enhanced interfaces, increasing the capacity of surgical systems through user-centered design approaches.

IROS Conference 2014 Conference Paper

Haptic exploration of unknown surfaces with discontinuities

• Rodrigo S. Jamisola
• Petar Kormushev
• Antonio Bicchi
• Darwin G. Caldwell

This work presents an approach for exploring unknown surfaces with discontinuities using only force/torque information. The motivation is to build an information map of an unknown object or environment by performing a fully-autonomous haptic exploration. Examples of discontinuities considered here are contours with sharp turns (such as wall corners) and abrupt dips (such as cliffs). Compliant motion control using force information has the ability to conform to unknown, smooth surfaces but not to discontinuous surfaces. This paper investigates solutions to address the limitation in compliant motion control over discontinuities while maintaining a desired normal force along the surface. We propose two methods to address the problem: (1) superposition of motion and force control and (2) rotation of axes for force and motion control. The theoretical principles are discussed and experimental results with a KUKA lightweight arm moving in 2D space are presented. Both approaches successfully negotiate objects with sharp 90-degree and 120-degree turns while still maintaining good tracking of the desired force.

ICRA Conference 2014 Conference Paper

In-hand precise twisting and positioning by a novel dexterous robotic gripper for industrial high-speed assembly

• Fei Chen 0007
• Ferdinando Cannella
• Carlo Canali
• Traveler Hauptman
• Giuseppe Sofia
• Darwin G. Caldwell

In electronic manufacturing system, the design of the robotic hand with sufficient dexterity and configuration is important for the successful accomplishment of the assembly task. Due to the growing demand from high-mix manufacturing industry, it is difficult for the traditional robot to grasp a large number of assembly parts or tools having cylinder shapes with correct postures. In this research, a novel jaw like gripper with human-sized anthropomorphic features is designed for in-hand precise positioning and twisting online. It retains the simplicity feature of traditional industrial grippers and dexterity features of dexterous grippers. It can apply a constant gripping force on assembly parts and performs reliable twisting movement within limited time to meet the industrial requirements. Manipulating several cylindrical assembly parts by robot, as an experimental case in this paper, is studied to evaluate its performance. The effectiveness of proposed gripper design and mechanical analysis is proved by the simulation and experimental results.

ICRA Conference 2014 Conference Paper

Learning from demonstrations with partially observable task parameters

• Tohid Alizadeh
• Sylvain Calinon
• Darwin G. Caldwell

Robot learning from demonstrations requires the robot to learn and adapt movements to new situations, often characterized by position and orientation of objects or landmarks in the robot's environment. In the task-parameterized Gaussian mixture model framework, the movements are considered to be modulated with respect to a set of candidate frames of reference (coordinate systems) attached to a set of objects in the robot workspace. Following a similar approach, this paper addresses the problem of having missing candidate frames during the demonstrations and reproductions, which can happen in various situations such as visual occlusion, sensor unavailability, or tasks with a variable number of descriptive features. We study this problem with a dust sweeping task in which the robot requires to consider a variable amount of dust areas to clean for each reproduction trial.

IROS Conference 2014 Conference Paper

Lyapunov Stability Margins for humanoid robot balancing

• Emmanouil Spyrakos-Papastavridis
• Nicolas Perrin-Gilbert
• Nikos G. Tsagarakis
• Jian S. Dai 0001
• Darwin G. Caldwell

This work introduces a novel balance monitoring strategy for humanoid robots. The proposed method addresses the problem of ensuring the balance maintenance of a humanoid robot, through the online monitoring of its state of balance by means of a Lyapunov (energy) function. The proposed method involves the use of dynamical models accounting for both the link and motor states. Energy limits corresponding to the front and rear edges of the support polygon are computed using a closed-loop Lyapunov function. Therefore, this method focuses on the resolution of two issues through a single control scheme, namely, guaranteeing asymptotical stability of the robot at the joint level, in addition to ensuring that it maintains its dynamical balance. A mathematical proof of the previous claims, as well as of the method's validity, is provided in the paper, whereby a direct relationship between the CoP and the system's energy has been established for the first time. Experimental results of step recovery and walking tests performed on the COmpliant huMANoid (COMAN) corroborate the method's applicability and performance as a balance monitor.

ICRA Conference 2014 Conference Paper

Model-free force tracking control of piezoelectric actuators: Application to variable damping actuator

• Jinoh Lee
• Matteo Laffranchi
• Navvab Kashiri
• Nikos G. Tsagarakis
• Darwin G. Caldwell

On a new demand of safe human-robot interaction for robotic applications, the Compact Compliant Actuator, named CompAct TM, is recently developed with physical compliance and active variable damping. In this mechanism, a desired physical damping behavior is realized by generating a friction force which is actively controlled by piezoelectric actuators (PEAs). However, nonlinearities such as hysteresis and creep effect make difficult to precisely control the generated piezoelectric force. This paper focuses on a development of precise force tracking controller for PEAs. A time delay estimation (TDE) using a force feedback is newly proposed to compensate a hysteretic behavior of the PEA and external uncertainties without a mathematical model. Thanks to the force-based TDE, the proposed control is accurate, computationally efficient and easily implementable on the real PEA system. The proposed control scheme is experimentally verified on the CompAct TM. Root-mean-square values of the steady-state error for step commands are kept as less than error ratio of 0. 13 % and the closed-loop system bandwidth for sinusoidal commands of 20 N stroke is confirmed as about 11 Hz under 100 N payload. In addition, the stability of the proposed control is proved to be bounded-input-bounded-output (BIBO) stable.

ICRA Conference 2014 Conference Paper

Null space redundancy learning for a flexible surgical robot

• Danilo Bruno
• Sylvain Calinon
• Darwin G. Caldwell

A new challenge for surgical robotics is placed in the use of flexible manipulators, to perform procedures that are impossible for currently available rigid robots. Since the surgeon only controls the end-effector of the manipulator, new control strategies need to be developed to correctly move its flexible body without damaging the surrounding environment. This paper shows how a positional controller for a new surgical robot (STIFF-FLOP) can be learnt from the demonstrations given by an expert user. The proposed algorithm exploits the variability of the task to comply with the constraints only when needed, by implementing a minimal intervention principle control strategy. The results are applied to scenarios involving movements inside a constrained environment and disturbance rejection.

ICRA Conference 2014 Conference Paper

Online discovery of AUV control policies to overcome thruster failures

• Seyed Reza Ahmadzadeh
• Matteo Leonetti
• Arnau Carrera
• Marc Carreras
• Petar Kormushev
• Darwin G. Caldwell

We investigate methods to improve fault-tolerance of Autonomous Underwater Vehicles (AUVs) to increase their reliability and persistent autonomy. We propose a learning-based approach that is able to discover new control policies to overcome thruster failures as they happen. The proposed approach is a model-based direct policy search that learns on an on-board simulated model of the AUV. The model is adapted to a new condition when a fault is detected and isolated. Since the approach generates an optimal trajectory, the learned fault-tolerant policy is able to navigate the AUV towards a specified target with minimum cost. Finally, the learned policy is executed on the real robot in a closed-loop using the state feedback of the AUV. Unlike most existing methods which rely on the redundancy of thrusters, our approach is also applicable when the AUV becomes under-actuated in the presence of a fault. To validate the feasibility and efficiency of the presented approach, we evaluate it with three learning algorithms and three policy representations with increasing complexity. The proposed method is tested on a real AUV, Girona500.

ICRA Conference 2014 Conference Paper

Path planning with force-based foothold adaptation and virtual model control for torque controlled quadruped robots

• Alexander W. Winkler
• Ioannis Havoutis
• Stéphane Bazeille
• Jesús Ortiz 0001
• Michele Focchi
• Rüdiger Dillmann
• Darwin G. Caldwell
• Claudio Semini

We present a framework for quadrupedal locomotion over highly challenging terrain where the choice of appropriate footholds is crucial for the success of the behaviour. We use a path planning approach which shares many similarities with the results of the DARPA Learning Locomotion challenge and extend it to allow more flexibility and increased robustness. During execution we incorporate an on-line force-based foothold adaptation mechanism that updates the planned motion according to the perceived state of the environment. This way we exploit the active compliance of our system to smoothly interact with the environment, even when this is inaccurately perceived or dynamically changing, and update the planned path on-the-fly. In tandem we use a virtual model controller that provides the feed-forward torques that allow increased accuracy together with highly compliant behaviour on an otherwise naturally very stiff robotic system. We leverage the full set of benefits that a high performance torque controlled quadruped robot can provide and demonstrate the flexibility and robustness of our approach on a set of experimental trials of increasing difficulty.

ICRA Conference 2014 Conference Paper

Physical interaction detection and control of compliant manipulators equipped with friction clutches

• Navvab Kashiri
• Matteo Laffranchi
• Nikos G. Tsagarakis
• Alessio Margan
• Darwin G. Caldwell

This work focuses on the modeling and control of robotic manipulators powered by compliant actuation systems equipped with clutches for providing friction torque on demand. A novel control scheme is proposed for modulating the clutch friction torque in this particular class of compliant actuators to make the robot operate in “Rigid mode” when it does not interact with the environment to achieve high accuracy, bandwidth and controllability; meanwhile ensuring that the robot maximum static force is constrained to a maximum threshold permitting flexible reactions in potentially risky scenarios. The robot autonomously switches to “Compliant mode” (clutches off) when it interacts with external agents to exploit the advantages of compliance during contacts. Experimental results are presented to show the effectiveness of proposed approach in improving the robot performance (tracking accuracy) while still guaranteeing an interaction-friendly behavior when contact occurs.

ICRA Conference 2014 Conference Paper

Power efficient balancing control for humanoids based on approximate optimal ankle compliance regulation

• Mohamad Mosadeghzad
• Nikos G. Tsagarakis
• Gustavo A. Medrano-Cerda
• Darwin G. Caldwell

The balance control of humanoid robots against external perturbations is a fundamental prerequisite for operating in unstructured environments where physical interaction may unexpectedly occur. These balancing actions can be very demanding in terms of power and torque requirements for ankle joints especially after strong and sudden impacts. In this work, an optimal control problem is formulated for the linearized inverted pendulum model to reduce the peak power requirements during ankle balancing strategy. This optimal control which reduces peak torque and power is computed numerically and approximated by a piecewise linear function of the states called the approximate optimal compliance regulator. The balancing ability of this compliance regulator is evaluated against other optimal compliance methods. The stability of the linearly switching approximated optimal compliance regulator is determined from practical perspective using quadratic stability and parameter dependent Lyapunov functions. The efficacy of the proposed stabilizer is validated for a compliant humanoid.

ICRA Conference 2014 Conference Paper

Real-time damping estimation for variable impedance actuators

• Navvab Kashiri
• Matteo Laffranchi
• Jinoh Lee
• Nikos G. Tsagarakis
• Lisha Chen
• Darwin G. Caldwell

Recently-developed variable damping mechanisms have been exploited as a complement to compliant actuators. While accurate knowledge and control of generated damping is essential for achieving the desired performance, no physical sensor measuring the damping exists. This work introduces a novel non-model-based approach for the estimation of time-variant damping for variable impedance actuation systems. The approach is based only on torque and position/velocity measurements; without the knowledge of system's inputs, to ensure the estimation of both intentional and unintentional changes. Hence, a recursive least square estimator, modified for achieving a proper convergence for the estimation of time-variant parameters, is exploited. Experiments on a variable physical damping actuator are also presented to validate the performance of proposed approach.

ICRA Conference 2014 Conference Paper

Robot-object contact perception using symbolic temporal pattern learning

• Nawid Jamali
• Petar Kormushev
• Darwin G. Caldwell

This paper investigates application of machine learning to the problem of contact perception between a robot's gripper and an object. The input data comprises a multidimensional time-series produced by a force/torque sensor at the robot's wrist, the robot's proprioceptive information, namely, the position of the end-effector, as well as the robot's control command. These data are used to train a hidden Markov model (HMM) classifier. The output of the classifier is a prediction of the contact state, which includes no contact, a contact aligned with the central axis of the valve, and an edge contact. To distinguish between contact states, the robot performs exploratory behaviors that produce distinct patterns in the time-series data. The patterns are discovered by first analyzing the data using a probabilistic clustering algorithm that transforms the multidimensional data into a one-dimensional sequence of symbols. The symbols produced by the clustering algorithm are used to train the HMM classifier. We examined two exploratory behaviors: a rotation around the x-axis, and a rotation around the y-axis of the gripper. We show that using these two exploratory behaviors we can successfully predict a contact state with an accuracy of 88 ± 5 % and 81 ± 10 %, respectively.

IROS Conference 2014 Conference Paper

Terminal sliding-mode based force tracking control of piezoelectric actuators for variable physical damping system

• Jinoh Lee
• Maolin Jin
• Nikos G. Tsagarakis
• Darwin G. Caldwell

The need for safe human-robot interaction in emerging robotic applications has recently driven the development of new range of actuation systems spanning from variable stiffness drives to variable damping or full variable impedance joints. Concerning the provision of variable physical damping in compliant actuators, the main objective is to improve the control of compliant joint. In a particular class of these variable physical damping actuators (VPDAs), the level of generated damping is realized by creating a friction force which is actively controlled by piezoelectric actuators (PEAs). Therefore, to effectively control the damping output, the accurate force control of the PEAs is required. However, difficulties to precisely control the generated piezoelectric force stem from its highly nonlinear behavior such as hysteresis and creep effect. This paper presents a novel practical force tracking controller for PEAs with unknown hysteresis behavior. The proposed control consists of two elements: terminal sliding-mode based desired dynamics injection and model-free compensation for nonlinear dynamics of PEAs, which allow fast convergence and extraordinary robustness to the closed-loop system. The stability of the overall system is proved in the sense of Lyapunov. On the real prototype of VPDA, the proposed control scheme is experimentally verified and analyzed by comparison to other controllers, demonstrating improved force tracking performance of PEAs in VPDA system.

IROS Conference 2013 Conference Paper

A compliant humanoid walking strategy based on the switching of state feedback gravity compensation controllers

• Emmanouil Spyrakos-Papastavridis
• Gustavo A. Medrano-Cerda
• Nikos G. Tsagarakis
• Jian S. Dai 0001
• Darwin G. Caldwell

This paper provides stability analyses for two different types of desired gravity compensation controllers, employing both motor and link feedback, and describes a means by which these controllers can be used to control a compliant humanoid robot in order to ensure the successful execution of walking trajectories. Given the challenging task of controlling compliant bipedal systems, owing to their possession of underactuated degrees of freedom, the full actuator and link dynamics are accounted for. The proposed walking strategy involves a process of switching between three distinct controllers which is contingent upon the force feedback provided by the force/torque sensors embedded in the robot's feet. These controllers were tuned using a simulation model of the robot and were then implemented on the compliant COMAN legs, whose performance of walking confirms the controllers' stability, in addition to the walking scheme's efficacy.

IROS Conference 2013 Conference Paper

A pragmatic bio-inspired approach to the design of octopus-inspired arms

• Emanuele Guglielmino
• Isuru S. Godage
• Letizia Zullo
• Darwin G. Caldwell

This paper presents the results of a multidisciplinary project where biologists, mechanical engineers and electronic engineers worked together to develop bio-inspired soft continuum arms, whose design captures and takes advantage of key features of the octopus anatomy and control. The cross-integration of such diverse expertise was channelled towards the design of soft continuum arms whose characteristics were inspired by nature, but with a focus on readily available engineering technologies and their effective integration from a system viewpoint. On one side the mechanical structure and the control was designed looking at the animal, in particular at the coupling between its anatomy and control system that allows the animal to survive in its ecosystem. On the other side engineering issues and constraints were carefully accounted for, namely material softness, intrinsic safety, energy efficiency, cost effectiveness and manufacturing aspects. The design evolution is presented through three different generations of prototypes where both bio-inspiration and engineering requirements are appropriately blended.

ICRA Conference 2013 Conference Paper

A reactive controller framework for quadrupedal locomotion on challenging terrain

• Victor Barasuol
• Jonas Buchli
• Claudio Semini
• Marco Frigerio
• Edson R. de Pieri
• Darwin G. Caldwell

We propose a reactive controller framework for robust quadrupedal locomotion, designed to cope with terrain irregularities, trajectory tracking errors and poor state estimation. The framework comprises two main modules: One related to the generation of elliptic trajectories for the feet and the other for control of the stability of the whole robot. We propose a task space CPG-based trajectory generation that can be modulated according to terrain irregularities and the posture of the robot trunk. To improve the robot's stability, we implemented a null space based attitude control for the trunk and a push recovery algorithm based on the concept of capture points. Simulations and experimental results on the hydraulically actuated quadruped robot HyQ will be presented to demonstrate the effectiveness of our framework.

IROS Conference 2013 Conference Paper

An asymmetric compliant antagonistic joint design for high performance mobility

• Nikos G. Tsagarakis
• Stephen Morfey
• Houman Dallali
• Gustavo A. Medrano-Cerda
• Darwin G. Caldwell

This paper presents the design of a novel compliant joint for high performance mobility. The design principle of the joint is based on an asymmetric compliant antagonistic scheme which is actuated by two motors of different power capability and efficiency. Torques from the two motors are transmitted to the joint through two elastic elements of different stiffness and energy storage capacity. The proposed compliant joint design combines high power performance, large energy storage capacity and physical resilience all necessary features for performing high performance mobility such as agile locomotion. The paper introduces the principle of operation, the design and mechanical implementation of the joint. Preliminary experimental trials demonstrate the joint performance in a single degree of freedom leg prototype system.

ICRA Conference 2013 Conference Paper

Autonomous robotic valve turning: A hierarchical learning approach

• Seyed Reza Ahmadzadeh
• Petar Kormushev
• Darwin G. Caldwell

Autonomous valve turning is an extremely challenging task for an Autonomous Underwater Vehicle (AUV). To resolve this challenge, this paper proposes a set of different computational techniques integrated in a three-layer hierarchical scheme. Each layer realizes specific subtasks to improve the persistent autonomy of the system. In the first layer, the robot acquires the motor skills of approaching and grasping the valve by kinesthetic teaching. A Reactive Fuzzy Decision Maker (RFDM) is devised in the second layer which reacts to the relative movement between the valve and the AUV, and alters the robot's movement accordingly. Apprenticeship learning method, implemented in the third layer, performs tuning of the RFDM based on expert knowledge. Although the long-term goal is to perform the valve turning task on a real AUV, as a first step the proposed approach is tested in a laboratory environment.

IROS Conference 2013 Conference Paper

Comparative usability and performance evaluation of surgeon interfaces in laser phonomicrosurgery

• Giacinto Barresi
• Nikhil Deshpande
• Leonardo S. Mattos
• Andrea Brogni
• Luca Guastini
• Giorgio Peretti
• Darwin G. Caldwell

Robot-assisted surgical procedures, such as Laser Phonomicrosurgery (LP), suffer from susceptibility to variation in surgeon skill and equipment characteristics. Ergonomic and human-centered approaches acquire increased importance in the design of surgeon-machine interfaces. This paper proposes a protocol for comparative evaluation of surgeon-machine interfaces based on two criteria: (i) the subjective evaluation of their usability using questionnaires, and (ii) the objective evaluation of their performance using an imaging-based feature extraction method. Two interfaces in LP, the traditional (“AcuBlade”) interface and the novel (“Virtual Scalpel”) interface, were evaluated to demonstrate the effectiveness of the proposed scheme. A series of experimental trials were conducted using the interfaces in surgery-like tasks in a controlled environment. The subjective evaluation pointed to the superiority of the Virtual Scalpel interface (score: 83. 06) in terms of confidence and ease of use, and learnability, over the AcuBlade interface (score: 65. 56). The objective evaluation showed the Virtual Scalpel interface having an overall score (55. 96) significantly superior to the AcuBlade (51. 37). It is thus shown that the multidimensional evaluation approach allowed to clearly distinguish between levels of perceived usability and effective performance of surgeon-machine interfaces from a user-centered perspective.

IROS Conference 2013 Conference Paper

Compliant attitude control and stepping strategy for balance recovery with the humanoid COMAN

• Nicolas Perrin-Gilbert
• Nikos G. Tsagarakis
• Darwin G. Caldwell

In this paper we describe an approach for hu-manoid robot balance recovery that combines a novel attitude control algorithm adding compliance to the robot's behavior and increasing the smoothness of its motion, and an omnidirectional stepping strategy that can trigger one or two steps based on a measured disturbance vector. The proposed method is validated through experiments with the inherently compliant humanoid COMAN.

ICRA Conference 2013 Conference Paper

COMpliant huMANoid COMAN: Optimal joint stiffness tuning for modal frequency control

• Nikos G. Tsagarakis
• Stephen Morfey
• Gustavo A. Medrano-Cerda
• Zhibin Li 0001
• Darwin G. Caldwell

The incorporation of passive compliance in robotic systems could improve their performance during interactions and impacts, for energy storage and efficiency, and for general safety for both the robots and humans. This paper presents the recently developed COMpliant huMANoid COMAN. COMAN is actuated by passive compliance actuators based on the series elastic actuation principle (SEA). The design and implementation of the overall body of the robot is discussed including the realization of the different body segments and the tuning of the joint distributed passive elasticity. This joint stiffness tuning is a critical parameter in the performance of compliant systems. A novel systematic method to optimally tune the joint elasticity of multi-dof SEA robots based on resonance analysis and energy storage maximization criteria forms one of the key contributions of this work. The paper will show this method being applied to the selection of the passive elasticity of COMAN legs. The first completed robot prototype is presented accompanied by experimental walking trials to demonstrate its operation.

ICRA Conference 2013 Conference Paper

Computing with a muscular-hydrostat system

• Kohei Nakajima
• Helmut Hauser
• Rongjie Kang
• Emanuele Guglielmino
• Darwin G. Caldwell
• Rolf Pfeifer

Octopus arms, as well as elephant trunks, squid tentacles, and vertebrate tongues are termed muscular-hydrostats. In such structures, the volume of the organ remains constant during their motions, enabling diverse, complex, and highly controlled movements without the support of a skeleton. Such flexible structures show major advantages over articulated arms that have a rigid skeleton and joints. These advantages have been attracting roboticists aiming to apply these material properties to soft robot controls. In this paper, we show that the muscular-hydrostat system itself has the computational capacity to achieve a complex nonlinear computation. By using a 3D dynamic simulator of the system inspired by the octopus, we actually demonstrate that the system is capable of emulating complex nonlinear dynamical systems by exploiting its elastic body dynamics as a computational resource. In addition, we systematically analyze its computational power in terms of memory capacity, and show that the system has an intrinsic and characteristic short term memory profile. Finally, the implications for soft robot control and future application scenarios are discussed.

IROS Conference 2013 Conference Paper

Dynamic trot-walking with the hydraulic quadruped robot - HyQ: Analytical trajectory generation and active compliance control

• Barkan Ugurlu
• Ioannis Havoutis
• Claudio Semini
• Darwin G. Caldwell

This paper presents a trajectory generator and an active compliance control scheme, unified in a framework to synthesize dynamic, feasible and compliant trot-walking locomotion cycles for a stiff-by-nature hydraulically actuated quadruped robot. At the outset, a CoP-based trajectory generator that is constructed using an analytical solution is implemented to obtain feasible and dynamically balanced motion references in a systematic manner. Initial conditions are uniquely determined for symmetrical motion patterns, enforcing that trajectories are seamlessly connected both in position, velocity and acceleration levels, regardless of the given support phase. The active compliance controller, used simultaneously, is responsible for sufficient joint position/force regulation. An admittance block is utilized to compute joint displacements that correspond to joint force errors. In addition to position feedback, these joint displacements are inserted to the position control loop as a secondary feedback term. In doing so, active compliance control is achieved, while the position/force trade-off is modulated via the virtual admittance parameters. Various trot-walking experiments are conducted with the proposed framework using HyQ, a ∼ 75kg hydraulically actuated quadruped robot. We present results of repetitive, continuous, and dynamically equilibrated trot-walking locomotion cycles, both on level surface and uneven surface walking experiments.

ICRA Conference 2013 Conference Paper

Gravity compensation control of compliant joint systems with multiple drives

• Emmanouil Spyrakos-Papastavridis
• Gustavo A. Medrano-Cerda
• Nikos G. Tsagarakis
• Jian S. Dai 0001
• Darwin G. Caldwell

This paper presents a sufficient condition to establish the existence of unique equilibrium points for three types of gravity compensation controller when applied to over-actuated systems. As compared to the existing work, this paper extends the current theory by introducing feedback gain matrices that are not constrained to being diagonal and positive definite. The inherently COmpliant huMANoid (COMAN) served as a platform for the validation of the designed gravity compensation controller that employed reference link positions. The displayed experimental results provide evidence of successful link tracking of sinusoidal references on a humanoid system composed of series elastic actuators.

ICRA Conference 2013 Conference Paper

Imaging based metrics for performance assessment in laser phonomicrosurgery

• Nikhil Deshpande
• Leonardo S. Mattos
• Giacinto Barresi
• Andrea Brogni
• Giulio Dagnino
• Luca Guastini
• Giorgio Peretti
• Darwin G. Caldwell

State-of-the-art laser phonomicrosurgery (LP) used for the treatment of laryngeal abnormalities involves complex otolaryngological surgical techniques. It relies heavily on surgeon dexterity, requiring significant psychomotor skills. Equipment scale and size, laser operative distance, and the anatomically small nature of the vocal folds all combine to compound the surgical challenges. An objective measurement is therefore necessary to understand the impact of equipment design, its usability, surgeon skill, and learning, on performing LP effectively. This paper introduces imaging based feature extraction as a method to establish metrics to assess surgical performance in LP. Experimental analysis demonstrates the utility of these metrics in measuring surgical task execution vis-à-vis the task objectives. The metrics also provide for a combined rating scale giving a robust quantitative classification of the levels of surgical performance.

IROS Conference 2013 Conference Paper

Improving the energy efficiency of autonomous underwater vehicles by learning to model disturbances

• Petar Kormushev
• Darwin G. Caldwell

Energy efficiency is one of the main challenges for long-term autonomy of AUVs (Autonomous Underwater Vehicles). We propose a novel approach for improving the energy efficiency of AUV controllers based on the ability to learn which external disturbances can safely be ignored. The proposed learning approach uses adaptive oscillators that are able to learn online the frequency, amplitude and phase of zero-mean periodic external disturbances. Such disturbances occur naturally in open water due to waves, currents, and gravity, but also can be caused by the dynamics and hydrodynamics of the AUV itself. We formulate the theoretical basis of the approach, and demonstrate its abilities on a number of input signals. Further experimental evaluation is conducted using a dynamic model of the Girona 500 AUV in simulation on two important underwater scenarios: hovering and trajectory tracking. The proposed approach shows significant energy-saving capabilities while at the same time maintaining high controller gains. The approach is generic and applicable not only for AUV control, but also for other type of control where periodic disturbances exist and could be accounted for by the controller.

IROS Conference 2013 Conference Paper

Link position control of a compliant actuator with unknown transmission friction torque

• Lisha Chen
• Matteo Laffranchi
• Jinoh Lee
• Navvab Kashiri
• Nikos G. Tsagarakis
• Darwin G. Caldwell

This paper proposes a control strategy for a compliant actuator, the CompAct™ actuator, which is equipped with semi active friction dampers in its transmission system. Both the transmission flexibility and the nonlinearity of the friction based damping torque makes the control of this actuator not a trivial task. This paper studies model of the presented actuator and the control problem of accurate link position tracking based on sliding mode approach that considers the friction torque as an uncertainty. Stability analysis and simulations highlight the effectiveness of the proposed controller in compensating for the deflections and unknown friction torque of the actuator. The performance of the controller is also validated by experiment results that demonstrate the tracking performance of the CompAct™ actuator achieved by the presented control strategy.

ICRA Conference 2013 Conference Paper

Octopus inspired walking robot: Design, control and experimental validation

• Tianjiang Zheng
• Isuru S. Godage
• David T. Branson
• Rongjie Kang
• Emanuele Guglielmino
• Gustavo A. Medrano-Cerda
• Darwin G. Caldwell

This paper presents an Octopus inspired walking robot with pneumatic muscle actuator (PMA) driven continuum arms. Each arm is made up of 4 longitudinally arranged PMAs, consistent with octopus arm anatomy. We first present the design and construction of a single continuum arm followed by its modeling and experimental validation. The design of the walking robot is then presented followed by details of extended dynamic model describing the full walking robot with four arms. Basic control architecture is introduced for the robot to achieve walking motion and experimental results analyzed. Initial results show good agreement between the experimental results and simulation results.

IROS Conference 2013 Conference Paper

On improving the extrapolation capability of task-parameterized movement models

• Sylvain Calinon
• Tohid Alizadeh
• Darwin G. Caldwell

Gestures are characterized by intermediary or final landmarks (real or virtual) in task space or joint space that can change during the course of the motion, and that are described by varying accuracy and correlation constraints. Generalizing these trajectories in robot learning by imitation is challenging, because of the small number of demonstrations provided by the user. We present an approach to statistically encode movements in a task-parameterized mixture model, and derive an expectation-maximization (EM) algorithm to train it. The model automatically extracts the relevance of candidate coordinate systems during the task, and exploits this information during reproduction to adapt the movement in real-time to changing position and orientation of landmarks or objects. The approach is tested with a robotic arm learning to roll out a pizza dough. It is compared to three categories of task-parameterized models: 1) Gaussian process regression (GPR) with a trajectory models database; 2) Multi-streams approach with models trained in several frames of reference; and 3) Parametric Gaussian mixture model (PGMM) modulating the Gaussian centers with the task parameters. We show that the extrapolation capability of the proposed approach outperforms existing methods, by extracting the local structures of the task instead of relying on interpolation principles.

IROS Conference 2013 Conference Paper

On-line identification of autonomous underwater vehicles through global derivative-free optimization

• George C. Karras
• Charalampos P. Bechlioulis
• Matteo Leonetti
• Narcís Palomeras
• Petar Kormushev
• Kostas J. Kyriakopoulos
• Darwin G. Caldwell

We describe the design and implementation of an on-line identification scheme for Autonomous Underwater Vehicles (AUVs). The proposed method estimates the dynamic parameters of the vehicle based on a global derivative-free optimization algorithm. It is not sensitive to initial conditions, unlike other on-line identification schemes, and does not depend on the differentiability of the model with respect to the parameters. The identification scheme consists of three distinct modules: a) System Excitation, b) Metric Calculator and c) Optimization Algorithm. The System Excitation module sends excitation inputs to the vehicle. The Optimization Algorithm module calculates a candidate parameter vector, which is fed to the Metric Calculator module. The Metric Calculator module evaluates the candidate parameter vector, using a metric based on the residual of the actual and the predicted commands. The predicted commands are calculated utilizing the candidate parameter vector and the vehicle state vector, which is available via a complete navigation module. Then, the metric is directly fed back to the Optimization Algorithm module, and it is used to correct the estimated parameter vector. The procedure continues iteratively until the convergence properties are met. The proposed method is generic, demonstrates quick convergence and does not require a linear formulation of the model with respect to the parameter vector. The applicability and performance of the proposed algorithm is experimentally verified using the AUV Girona 500.

IROS Conference 2013 Conference Paper

Onboard perception-based trotting and crawling with the Hydraulic Quadruped Robot (HyQ)

• Ioannis Havoutis
• Jesús Ortiz 0001
• Stéphane Bazeille
• Victor Barasuol
• Claudio Semini
• Darwin G. Caldwell

This paper presents a framework developed to increase the autonomy and versatility of a large (∼75kg) hydraulically actuated quadrupedal robot. It combines onboard perception with two locomotion strategies, a dynamic trot and a static crawl gait. This way the robot can perceive its environment and arbitrate between the two behaviours according to the situation at hand. All computations are performed on-board and are carried out in two separate computers, one handles the high-level processes while the other is concerned with the low-level hard real-time control. The perception and subsequently the appropriate gait modifications are performed autonomously. We present outdoor experimental trials of the robot trotting over unknown terrain, perceiving a large obstacle, altering its behaviour to the cautious crawl gait and stepping onto the obstacle. This allows the robot to locomote quickly on relatively flat terrain and gives the robot the ability to overcome large irregular obstacles when required.

IROS Conference 2013 Conference Paper

Optimal ankle compliance regulation for humanoid balancing control

• Mohamad Mosadeghzad
• Zhibin Li 0001
• Nikos G. Tsagarakis
• Gustavo A. Medrano-Cerda
• Houman Dallali
• Darwin G. Caldwell

Keeping balance is the main concern for humanoids in standing and walking tasks. This paper endeavors to acquire optimal ankle stabilization methods for humanoids with passive and active compliance and explain ankle balancing strategy from the compliance regulation perspective. Unlike classical stiff humanoids, the compliant ones can control both impedance and position during task operation. Optimal compliance regulation is resolved to maximize the stability of the humanoids. The linearized model is proposed to obtain the optimal ankle impedance for stabilizing against impacts. The nonlinear model is proposed as well and compared with the linear one. The proposed methods are validated by experiments on an intrinsically compliant humanoid using passivity based admittance and impedance controllers both in joint and Cartesian space.

ICRA Conference 2013 Conference Paper

Optimal control for maximizing velocity of the CompAct™ compliant actuator

• Lisha Chen
• Manolo Garabini
• Matteo Laffranchi
• Navvab Kashiri
• Nikos G. Tsagarakis
• Antonio Bicchi
• Darwin G. Caldwell

The CompAct™ actuator features a clutch mechanism placed in parallel with its passive series elastic transmission element and can therefore benefit from the advantages of both series elastic actuators (SEA) and rigid actuators. The actuator is capable of effectively managing the storage and release of the potential energy of the compliant element by the appropriate control of the clutch subsystem. Controlling the timing of the energy storage/release in the elastic element is exploited for improving motion control in this research. This paper analyses how this class of actuation systems can be used to maximize the link velocity of the joint. The dynamic model of the joint is derived and an optimal control strategy is proposed to identify optimal input reference profiles for the actuator (motor position/velocity and clutch activation timing) which permit the link velocity maximization. The effect of compliance of the joint on the performance of the system is studied and the optimal stiffness is analyzed.

IROS Conference 2013 Conference Paper

Skills transfer across dissimilar robots by learning context-dependent rewards

• Milad Malekzadeh Shafaroudi
• Danilo Bruno
• Sylvain Calinon
• Thrishantha Nanayakkara
• Darwin G. Caldwell

Robot programming by demonstration encompasses a wide range of learning strategies, from simple mimicking of the demonstrator's actions to the higher level extraction of the underlying intent. By focusing on this last form, we study the problem of extracting the reward function explaining the demonstrations from a set of candidate reward functions, and using this information for self-refinement of the skill. This definition of the problem has links with inverse reinforcement learning problems in which the robot autonomously extracts an optimal reward function that defines the goal of the task. By relying on Gaussian mixture models, the proposed approach learns how the different candidate reward functions are combined, and in which contexts or phases of the task they are relevant for explaining the user's demonstrations. The extracted reward profile is then exploited to improve the skill with a self-refinement approach based on expectation-maximization, allowing the imitator to reach a skill level that goes beyond the demonstrations. The approach can be used to reproduce a skill in different ways or to transfer tasks across robots of different structures. The proposed approach is tested in simulation with a new type of continuum robot (STIFF-FLOP), using kinesthetic demonstrations from a Barrett WAM manipulator.

IROS Conference 2013 Conference Paper

Stability and performance of the compliance controller of the quadruped robot HyQ

• Thiago Boaventura
• Gustavo A. Medrano-Cerda
• Claudio Semini
• Jonas Buchli
• Darwin G. Caldwell

A legged robot has to deal with environmental contacts every time it takes a step. To properly handle these interactions, it is desirable to be able to set the foot compliance. For an actively-compliant legged robot, in order to ensure a stable contact with the environment the robot leg has to be passive at the contact point. In this work, we asses some passivity and stability issues of the actively-compliant leg of the quadruped robot HyQ, which employs a highperformance cascade compliance controller. We demonstrate that both the nested torque loop performance as well as the actuator bandwidth have a strong influence in the range of virtual impedances that can be passively rendered by the robot leg. Based on the stability analyses and experimental results, we propose a procedure for designing cascade compliance controllers. Furthermore, we experimentally demonstrate that the HyQ's actively-compliant leg is able to reproduce the compliant behavior presented by an identical but passively-compliant version of the same leg.

IROS Conference 2013 Conference Paper

Stabilizing humanoids on slopes using terrain inclination estimation

• Zhibin Li 0001
• Nikos G. Tsagarakis
• Darwin G. Caldwell

This paper presents an integrated control framework for balancing humanoids on uneven terrains combining stabilization control and terrain inclination estimation. The stabilization is realized by passivity based admittance control that utilizes the force/torque feedback in feet to actively regulate the compliance. The logic-based terrain estimation algorithm exploits feet to probe the terrain inclination and deals with underactuation when feet tilt on the contact surface. The equilibrium position in the admittance control is thereby adapted for recovering balance on the slope. Both the theoretical work and experimental validation are presented. The method is implemented and validated on the real humanoid by demonstrating the capability of estimating terrain inclination, balancing on the slope with varying gradient, and maintaining upright posture in the meantime. Experimental data such as inclination estimation in the comparison study, center of pressure measurement, and body attitude compensation are presented and analyzed.

ICRA Conference 2013 Conference Paper

Tele-Impedance based stiffness and motion augmentation for a knee exoskeleton device

• Nikos Karavas
• Arash Ajoudani
• Nikos G. Tsagarakis
• Jody Alessandro Saglia
• Antonio Bicchi
• Darwin G. Caldwell

In this paper, a knee exoskeleton device and its Tele-Impedance based assistive control scheme is presented. The exoskeleton device is an inherently compliant actuated system that was implemented based on the series elastic actuation (SEA) to provide improved and intrinsically soft interaction behaviour. Details of the exoskeleton design are presented. A detailed musculoskeletal model was developed and experimentally identified in order to map electromyographic signals to the antagonistic muscle torques, acting on the human knee joint. The estimated muscle torques are used in order to determine the user's intent and joint stiffness trend. These reference signals are exploited by a novel Tele-Impedance controller which is applied to a knee exoskeleton device to provide assistance and stiffness augmentation to the user's knee joint. Experimental trials of a standing-up motion task were carried out for evaluation of the proposed control strategy. The results indicate that the proposed knee exoskeleton device and control scheme can effectively generate assistive actions that are intrinsically and naturally controlled by the user muscle activity.

IROS Conference 2013 Conference Paper

The use of a hydraulic DC-DC converter in the actuation of a robotic leg

• Shuang Peng 0001
• Helmut Kogler
• Emanuele Guglielmino
• Rudolf Scheidl
• David T. Branson
• Darwin G. Caldwell

This paper presents the application of a hydraulic DC-DC converter, namely a step down Buck Converter to the actuation of a robot leg that is part of the quadruped robot HyQ. The use of a Hydraulic Buck Converter (HBC) offers significant advantages in terms of improved efficiency of hydraulic actuation systems analogously to an electric switching DC-DC converter as opposed to a rheostatic-type system. In this paper, a HBC consisting of two digital valves and two check valves is introduced to improve the efficiency performance of a singl leg of a hydraulic quadruped robot (HyQ). This type of hydraulic buck converter is able to support the locomotion in two directions. The HBC operates at a switching frequency of 100 Hz in pulse-width-modulation. The better energy performance compared to proportional control is achieved by the use of fast check valves. The performance of the system with a 3-way-4-position proportional valve is compared with the HBC drive. A test rig is set up to investigate the performance of HBC with two different controllers and a Hydraulic Proportional Drive (HPD) system, based on proportional valves which control flow, by throttling it, in a dissipative manner. The performance of position tracking and energy consumption is evaluated. The experimental results indicate that HBC systems can achieve similar position tracking with relatively less consumed energy.

IROS Conference 2013 Conference Paper

Visuospatial skill learning for object reconfiguration tasks

• Seyed Reza Ahmadzadeh
• Petar Kormushev
• Darwin G. Caldwell

We present a novel robot learning approach based on visual perception that allows a robot to acquire new skills by observing a demonstration from a tutor. Unlike most existing learning from demonstration approaches, where the focus is placed on the trajectories, in our approach the focus is on achieving a desired goal configuration of objects relative to one another. Our approach is based on visual perception which captures the object's context for each demonstrated action. This context is the basis of the visuospatial representation and encodes implicitly the relative positioning of the object with respect to multiple other objects simultaneously. The proposed approach is capable of learning and generalizing multi-operation skills from a single demonstration, while requiring minimum a priori knowledge about the environment. The learned skills comprise a sequence of operations that aim to achieve the desired goal configuration using the given objects. We illustrate the capabilities of our approach using three object reconfiguration tasks with a Barrett WAM robot.

ICRA Conference 2012 Conference Paper

A compact tactile display suitable for integration in VR and teleoperation

• Ioannis Sarakoglou
• Nikos G. Tsagarakis
• Darwin G. Caldwell

Haptic feedback should integrate kinaesthetic and tactile feedback. However current haptic displays do not satisfy the stringent performance and design requirements for integration in teleoperation and VR. This work presents the development of a compact, high performance tactile display for the fingertip. The compact design, high performance, reliability, and simple connectivity of this display make it suitable for immediate integration in current VR and master-slave haptic systems. In terms of performance this display achieves an excellent combination of force, amplitude and spatiotemporal resolution at the tactors, surpassing the performance of devices of a similar footprint. Its operation is based on the display of surface shape to an area of the fingertip through a 4×4 array of vertically moving tactors. The tactors are spring loaded and are actuated remotely by dc motors through a flexible tendon transmission. This work presents the overall design, control and performance of the device. A preliminary analysis of the transmission system is presented and is used to compensate for output errors induced by component elasticity.

ICRA Conference 2012 Conference Paper

A position and stiffness control strategy for variable stiffness actuators

• Irene Sardellitti
• Gustavo A. Medrano-Cerda
• Nikos G. Tsagarakis
• Amir Jafari
• Darwin G. Caldwell

Variable stiffness actuators (VSAs) have been introduced to improve, at the design level, the safety and the energy efficiency of the new generation of robots that have to interact closely with humans. A wide variety of design solutions have recently been proposed, and a common factor in most of the VSAs is the introduction of a flexible transmission with varying stiffness. This, from the control perspective, usually implies a nonlinear actuation plant with varying dynamics following time-varying parameters, which requires more complex control strategies with respect to those developed for flexible joints with a constant stiffness. For this reason, this paper proposes an approach for controlling the link position and stiffness of a VSA. The link positioning relies on a LQR-based gain scheduling approach useful for continuously adjusting the control effort based on the current stiffness of the flexible transmission. The stiffness perceived at the output link is adjusted to match the varying task requirements through the combination of the positioning gains and the mechanical stiffness. The stability of the overall strategy is briefly discussed. The effectiveness of the controller in terms of tracking performance and stiffness adjustment is verified through experiments on the Actuator with Adjustable Stiffness (AwAS).

IROS Conference 2012 Conference Paper

Bio-inspired crawling locomotion of a multi-arm octopus-like continuum system

• Rongjie Kang
• Emanuele Guglielmino
• David T. Branson
• Darwin G. Caldwell

This paper presents a control algorithm to achieve crawling locomotion for a multi-arm robotic system inspired by live octopuses. First the paper introduces a dynamic model of a continuum arm. The model accounts for the key features relevant to crawling locomotion, namely longitudinal muscles and suckers that provide force interaction with the surrounding environment. This single arm model is then validated against live octopus data and expanded to an 8-arm system. Appropriate coordination algorithms of the eight arms result in crawling locomotion. The results of this work can be used to study the motor control schemes for both multiple continuum arm robots and live octopuses.

IROS Conference 2012 Conference Paper

Code generation of algebraic quantities for robot controllers

• Marco Frigerio
• Jonas Buchli
• Darwin G. Caldwell

Controllers for articulated robots such as an arm or a humanoid commonly need to continuously calculate complex algebraic quantities, such as the joint space inertia matrix or Jacobians. An effective and fast implementation of the calculation of these quantities is crucial to achieve complex, yet robust controllers and thus enable sophisticated behaviors in robots. Although the nature of these algebraic quantities is very well known in robotics, they do not lend themselves easily to manual implementation, because of ambiguities and the complexity in their development and use. We propose an approach that addresses this issue by relying on automatic code generation, thus relieving the user from hand crafted development. Our approach also addresses efficiency and speed, in order to satisfy the strict requirements of real time robot controllers, yet it is easy to use. We show the effectiveness of our method by means of some preliminary comparisons.

ICRA Conference 2012 Conference Paper

Control architecture for robots with continuum arms inspired by octopus vulgaris neurophysiology

• David T. Branson
• Rongjie Kang
• Emanuele Guglielmino
• Darwin G. Caldwell

Conventional rigid body robots typically use few degrees of freedom (DOF). This results in a manipulator that lacks flexibility and maneuverability when compared to continuum robots that utilize a much higher number of DOF. However, due to their continuous nature, the difficulty of measuring and controlling a large number of actuated DOF, and their high degree of nonlinearity, the development of control algorithms for continuum robot manipulators is an ongoing challenge. This paper presents an algorithm inspired by biological solutions from live octopus that utilizes division of functionality to achieve simple and robust control of continuum arm based systems. Simulated results for single and multiple dynamic continuum arms show the controller is capable of producing motions similar to that of octopus. The resulting controller is also computationally efficient enough for real-time implementation. In future this work will be implemented on a prototype robot with multiple continuum arms.

ICRA Conference 2012 Conference Paper

Dynamic continuum arm model for use with underwater robotic manipulators inspired by octopus vulgaris

• Tianjiang Zheng
• David T. Branson
• Rongjie Kang
• Matteo Cianchetti
• Emanuele Guglielmino
• Maurizio Follador
• Gustavo A. Medrano-Cerda
• Isuru S. Godage

Continuum structures with a very high or infinite number of degrees of freedom (DOF) are very interesting structures in nature. Mimicking this kind of structures artificially is challenging due to the high number of required DOF. This paper presents a kinematic and dynamic model for an underwater robotic manipulator inspired by Octopus vulgaris. Then, a prototype arm inspired by live octopus is presented and the model validated experimentally. Initial comparisons of simulated and experimental results show good agreement.

ICRA Conference 2012 Conference Paper

Dynamic torque control of a hydraulic quadruped robot

• Thiago Boaventura
• Claudio Semini
• Jonas Buchli
• Marco Frigerio
• Michele Focchi
• Darwin G. Caldwell

Legged robots have the potential to serve as versatile and useful autonomous robotic platforms for use in unstructured environments such as disaster sites. They need to be both capable of fast dynamic locomotion and precise movements. However, there is a lack of platforms with suitable mechanical properties and adequate controllers to advance the research in this direction. In this paper we are presenting results on the novel research platform HyQ, a torque controlled hydraulic quadruped robot. We identify the requirements for versatile robotic legged locomotion and show that HyQ is fulfilling most of these specifications. We show that HyQ is able to do both static and dynamic movements and is able to cope with the mechanical requirements of dynamic movements and locomotion, such as jumping and trotting. The required control, both on hydraulic level (force/torque control) and whole body level (rigid model based control) is discussed.

ICRA Conference 2012 Conference Paper

Efficient human-like walking for the compliant huMANoid COMAN based on linematic Motion Primitives (kMPs)

• Federico L. Moro
• Nikos G. Tsagarakis
• Darwin G. Caldwell

Research in humanoid robotics in recent years has led to significant advances in terms of the ability to walk and even run. Yet, despite the general achievements in locomotion and control, energy efficiency is still one important area that requires further attention, especially as it is one of the major steeping stones leading to increased autonomy. This paper examines, and quantifies, the energetic benefits of introducing passive compliance into bipedal locomotion using COMAN, an intrinsically COmpliant huMANoid robot. The novelty of the method proposed consists of: i) the use of a method of gait synthesis based on kinematic Motion Primitives (kMPs) extracted from human, ii) the frequency tuning of the resultant trajectories, to excite the physical elasticity of the system, and the subsequent analysis of the energetic performance of the robot. The motivation is to assess the possible effects of using dynamic human-like, and human derived, trajectories, with significant Center of Mass (CoM) vertical displacement, regulated in frequency around the frequency band of the system resonances, on the excitation of the compliant actuators, and subsequently to measure and verify any energetic benefit. Experimental results show that if the gait frequency is close to one of the main resonant frequencies of the robot, then the total work contribution of the elastic compliant element to the overall motion of the robot is positive (15% of the work required is generated by the springs).

ICRA Conference 2012 Conference Paper

Hopping at the resonance frequency: A trajectory generation technique for bipedal robots with elastic joints

• Barkan Ugurlu
• Jody Alessandro Saglia
• Nikos G. Tsagarakis
• Darwin G. Caldwell

It is known that bipedal robots with passive compliant structures have obvious advantages over stiff robots, as they are able to handle the potential energy management. Therefore, this paper is aimed at presenting a jumping pattern generation method that takes advantage of this property via the utilization of the base resonance frequency, which is of special importance. To begin with, the resonance frequency is determined through a system identification procedure on our actual robot. Consequentially, the vertical component of the CoM is generated via a periodic function in which the resonance frequency is employed. The horizontal component of the CoM is obtained using the ZMP criterion to guarantee the dynamic balance. Having obtained the necessary elements of the CoM trajectory within an analytical manner, joint motions are computed with the help of translational and angular momenta constraints. In order to validate the method, two legged jumping experiments are conducted on our actual compliant robot. In conclusion, we observed repetitive, continuous, and dynamically equilibrated jumping cycles with feasible landing phases.

ICRA Conference 2012 Conference Paper

How design can affect the energy required to regulate the stiffness in variable stiffness actuators

• Amir Jafari
• Nikos G. Tsagarakis
• Irene Sardellitti
• Darwin G. Caldwell

Variable stiffness actuators have been developed based on different design solutions which can be arranged into two groups: antagonistic and series design. In both the cases two actuation units are combined with passive elastic elements to adjust both the stiffness and the equilibrium position of the actuated joint. To regulate the stiffness, mechanical work is required to be done which depending on the design principle of the actuator results in certain energy consumption. In this paper different variable stiffness design approaches with different types of springs (linear, quadratic, exponential and cubic) are analyzed and compared with respect to the energy required to regulate the stiffness. The results give some insights about the design parameters which mostly affect the energy consumption for the stiffness adjustment. In this work, it is shown that among different design and spring arrangements, the variable stiffness in series design which uses linear springs with constant pretension, requires the minimum energy consumption to adjust the stiffness.

IROS Conference 2012 Conference Paper

Integration of a tactile display in teleoperation of a soft robotic finger using model based tactile feedback

• Ioannis Sarakoglou
• Nadia Vanessa Garcia-Hernandez
• Nikos G. Tsagarakis
• Darwin G. Caldwell

Tactile feedback is a key modality in object exploration and manipulation. However it has not been satisfactorily addressed in master-slave teleoperation. One of the reasons is that current tactile displays do not satisfy the stringent performance and design requirements for integration in master haptic devices. This paper presents the integration of a compact, high performance tactile display in a teleoperation setup. In this scenario the tactile display provides tactile feedback while remote objects are being contacted through a soft robotic finger. The display is mounted on a force feedback master device, which controls a manipulator equipped with a force sensor and a soft finger. Force feedback and tactile feedback are combined in a hybrid approach. Force feedback on the master reflects the measured remote interaction forces while tactile feedback is model based. This hybrid feedback method can provide force and tactile information in cases of highly structured teleoperation scenes where tactile sensing is absent or rudimentary while accurate environment models exist. An experiment is presented where users teleoperated the robot finger in a 3D contour following task with and without tactile feedback. Subjects' performances indicate an improvement in teleoperation when both tactile and force feedback are present.

IROS Conference 2012 Conference Paper

Internal model control for improving the gait tracking of a compliant humanoid robot

• Luca Colasanto
• Nikos G. Tsagarakis
• Zhibin Li 0001
• Darwin G. Caldwell

This paper reports on the modelling and trajectory generation of an intrinsically compliant humanoid robot. To achieve adequate gait tracking performance in a compliant robot is not trivial and cannot be addressed with the traditional control approaches used for stiff robots. To permit the development of effective gait generators which take into account the additional dynamic effects due to intrinsic compliance, an appropriate model which can predict the robot motion dynamics is required. In this work, we propose a model which combines the inverted pendulum model approach with a compliant model (Cartesian) at the level of the COM. Based on this model which permits to predict the motion of the centre of mass (COM) of the compliant robot an Internal Model Control strategy is adopted to improve the gait tracking performance. The derivation of the model is introduced followed by experimental validation which demonstrates the tracking performance achieved by the proposed reduced model. The Internal Model Control is subsequently discussed and validated on the COmpliant huMANoid COMAN using a series of ZMP based walking gaits.

IROS Conference 2012 Conference Paper

Locomotion with continuum limbs

• Isuru S. Godage
• Thrishantha Nanayakkara
• Darwin G. Caldwell

This paper presents the kinematics, dynamics, and experimental results for a novel quadruped robot using continuum limbs. We propose soft continuum limbs as a new paradigm for robotic locomotion in unstructured environments due to their potential to generate a wide array of locomotion behaviors ranging from walking, trotting, crawling, and propelling to whole arm grasping as a means of negotiating difficult obstacles. A straightforward method to derive the kinematics and dynamics for the proposed quadruped has been demonstrated through numerical simulations. Initial experiments on a prototype continuum quadruped demonstrate the ability to stand up from a flat-belly stance, absorb external disturbances such as maintaining stability after dropping from a height and after being perturbed by a collision, and crawling on flat and cluttered environments. Experiment results provide evidence that locomotion with soft continuum limbs are feasible and usable in unstructured environments for variety of applications.

IROS Conference 2012 Conference Paper

On the role of load motion compensation in high-performance force control

• Thiago Boaventura
• Michele Focchi
• Marco Frigerio
• Jonas Buchli
• Claudio Semini
• Gustavo A. Medrano-Cerda
• Darwin G. Caldwell

Robots are frequently modeled as rigid body systems, having torques as input to their dynamics. A high-performance low-level torque source allows us to control the robot/environment interaction and to straightforwardly take advantage of many model-based control techniques. In this paper, we define a general 1-DOF framework, using basic physical principles, to show that there exists an intrinsic velocity feedback in the generalized force dynamics, independently of the actuation technology. We illustrate this phenomena using three different systems: a generic spring-mass system, a hydraulic actuator, and an electric motor. This analogy helps to clarify important common aspects regarding torque/force control that can be useful when designing and controlling a robot. We demonstrate, using simulations and experimental data, that it is possible to compensate for the load motion influence and to increase the torque tracking capabilities.

ICRA Conference 2012 Conference Paper

Pneumatic muscle actuated continuum arms: Modelling and experimental assessment

• Isuru S. Godage
• David T. Branson
• Emanuele Guglielmino
• Darwin G. Caldwell

This paper presents an improved mode shape function-based 3D dynamic model for pneumatic muscle actuated continuum arms, and validates the model and simulation results through experimental testing. The model also facilitates the direct control of pneumatic muscle actuated continuum arms through the use of input pressure. This is achieved without additional intermediary transformations and does not have singularity problems present in previous models. The proposed arm model uses a new pneumatic muscle actuator (PMA) dynamic model with hysteresis that is capable of modelling both extending and contracting PMAs. The proposed hysteric model is simple, easily adaptable, and validated experimentally. The PMA model can be applied to dynamically model any PMA based system as well as PMA actuated continuum arms utilizing different actuator configurations.

ICRA Conference 2012 Conference Paper

Stabilization for the compliant humanoid robot COMAN exploiting intrinsic and controlled compliance

• Zhibin Li 0001
• Bram Vanderborght
• Nikos G. Tsagarakis
• Luca Colasanto
• Darwin G. Caldwell

The work presents the standing stabilization of a compliant humanoid robot against external force disturbances and variations of the terrain inclination. The novel contribution is the proposed control scheme which consists of three strategies named compliance control in the transversal plane, body attitude control, and potential energy control, all combined with the intrinsic passive compliance in the robot. The physical compliant elements of the robot are exploited to react at the first instance of the impact while the active compliance control is applied to further absorb the impact and dissipate the elastic energy stored in springs preventing the high rate of spring recoil. The body attitude controller meanwhile regulates the spin angular momentum to provide more agile reactions by changing body inclination. The potential energy control module constrains the robot center of mass (COM) in a virtual slope to convert the excessive kinetic energy into potential energy to prevent falling. Experiments were carried out with the proposed balance stabilization control demonstrating superior balance performance. The compliant humanoid was capable of recovering from external force disturbances and moderate or even abrupt variations of the terrain inclination. Experimental data such as the impulse forces, real COM, center of pressure (COP) and the spring elastic energy are presented and analyzed.

IROS Conference 2012 Conference Paper

The anatomy of a fall: Automated real-time analysis of raw force sensor data from bipedal walking robots and humans

• Petar Kormushev
• Barkan Ugurlu
• Luca Colasanto
• Nikos G. Tsagarakis
• Darwin G. Caldwell

An automated approach is proposed which can analyze ground reaction force data from bipedal walking robots and humans. The input of the automated analysis is the raw data from force sensors mounted in the feet of a robot. The output is detailed information, such as detected single support, double support, and swing phases, their durations, timings of events like heel strikes, properties of the phase transitions and of the robot itself. The proposed approach is generic, parameter-free, model-free, robust, computationally efficient, and applicable for real-time use during walking. It can detect early indications of instability that could lead to a fall of the robot. Three real-world experiments are presented: with a compliant bipedal robot, with a stiff humanoid robot, and with a human subject.

ICRA Conference 2012 Conference Paper

The application of embodiment theory to the design and control of an octopus-like robotic arm

• Emanuele Guglielmino
• Letizia Zullo
• Matteo Cianchetti
• Maurizio Follador
• David T. Branson
• Darwin G. Caldwell

This paper examines the design and control of a robotic arm inspired by the anatomy and neurophysiology of Octopus vulgaris in light of embodiment theory. Embodiment in an animal is defined as the dynamic coupling between sensorymotor control, anatomy, materials, and the environment that allows for the animal to achieve effective behaviour. Octopuses in particular are highly embodied and dexterous animals: their arms are fully flexible, can bend in any direction, grasp objects and modulate stiffness along their length.

IROS Conference 2012 Conference Paper

The role of physical damping in compliant actuation systems

• Matteo Laffranchi
• Lisha Chen
• Nikos G. Tsagarakis
• Darwin G. Caldwell

Recently, compliance has been considered as one of the key physical properties that a robot should incorporate to be able to physically interact with humans and uncertain environments. Apart from the improved ability of interaction, mechanical robustness and higher safety-related performances, compliance introduces underdamped oscillatory modes and reduces the mechanical natural frequency of the plant to be controlled making its control much more complex than that of conventional stiff actuators. To overcome these drawbacks, some recent works focus on the incorporation of physical damping within compliant actuators. This work presents an analysis for the quantitative evaluation of the effects of physical damping in compliant robotic joints to demonstrate the improvements (dynamic performance, stability, controllability, tracking precision and energy efficiency) which can be gained by incorporating physical damping in such flexible transmission systems. Simulation and experimental results validate that these benefits can effectively be achieved on an existing compliant actuator prototype with variable physical damping.

IROS Conference 2012 Conference Paper

Variable impedance actuators: Moving the robots of tomorrow

• Bram Vanderborght
• Alin Albu-Schäffer
• Antonio Bicchi
• Etienne Burdet
• Darwin G. Caldwell
• Raffaella Carloni
• Manuel G. Catalano
• Gowrishankar Ganesh

Most of today's robots have rigid structures and actuators requiring complex software control algorithms and sophisticated sensor systems in order to behave in a compliant and safe way adapted to contact with unknown environments and humans. By studying and constructing variable impedance actuators and their control, we contribute to the development of actuation units which can match the intrinsic safety, motion performance and energy efficiency of biological systems and in particular the human. As such, this may lead to a new generation of robots that can co-exist and co-operate with people and get closer to the human manipulation and locomotion performance than is possible with current robots.

ICRA Conference 2012 Conference Paper

Walking trajectory generation for humanoid robots with compliant joints: Experimentation with COMAN humanoid

• Zhibin Li 0001
• Nikos G. Tsagarakis
• Darwin G. Caldwell

This work introduces a walking pattern generator suitable for humanoids with inherent joint compliance. The proposed walking pattern generator computes the desired center of mass (COM) references on-line based on the COM state feedback. The position and velocity of the COM are the feedback variables, and the constraint ground reaction force (GRF), which is limited by the support polygon, is the control effort to drive the COM states to track the desired ones. The zero moment point (ZMP) is obtained naturally as a result of GRF interaction with robot feet. The proposed COM tracking scheme demands a lower bandwidth from the controller compared to the ZMP tracking schemes. Experimental data of the real compliant humanoid, such as ZMP, COM motion, and GRF are presented to demonstrate the validation of the proposed gait generation method.

ICRA Conference 2011 Conference Paper

A 3D dynamic model for continuum robots inspired by an octopus arm

• Tianjiang Zheng
• David T. Branson
• Emanuele Guglielmino
• Darwin G. Caldwell

Continuum robotic arms are based on non-rigid components that result in a nearly infinite number of degrees of freedom (DOF). Due to this reason it can be very complex to establish mathematical models for continuum robotic arms. This paper presents a 3D dynamic model of an arm based on octopus anatomy that utilizes 4 longitudinal and 4 radial muscles. The arm is composed of a multi-segment structure having distributed stiffness and damping to represent the muscles. The simulations are applied to a multi-segment arm, and results mimic several typical octopus arm motions.

ICRA Conference 2011 Conference Paper

A compact compliant actuator (CompAct™) with variable physical damping

• Matteo Laffranchi
• Nikos G. Tsagarakis
• Darwin G. Caldwell

The new areas of technical exploitation of robotics systems has recently set new trends for the robotic actuation by demanding more versatile systems which can cope with unpredictable interactions within not well defined environments and work in close vicinity with the human. Following these trends, this work presents the development of a new actuation system with embodied characteristics such as passive compliance and variable physical damping. Compared to the other existing compliant linear or rotary actuators the proposed CompAct unit has the ability to regulate the oscillations induced by the introduction of the compliance by means of a variable physical damping actuator (VPDA) unit. Apart from facilitating the control the VPDA unit can assist in managing the energy transfer from/to the compliant module. The mechatronics, model and control scheme of the CompAct are analysed. The overall system is evaluated with experimental trials performed using a prototype unit. Preliminary results are presented to show that the unit and the proposed control scheme are capable of regulating the impedance components (stiffness and damping) within a wide range and with good fidelity.

IROS Conference 2011 Conference Paper

A new variable stiffness actuator (CompAct-VSA): Design and modelling

• Nikos G. Tsagarakis
• Irene Sardellitti
• Darwin G. Caldwell

This paper describes the design and modelling of a new variable stiffness actuator (CompAct-VSA). The principle of operation of CompAct-VSA is based on a lever arm mechanism with a continuously regulated pivot point. The proposed concept allows for the development of an actuation unit with a wide range of stiffness and a fast stiffness regulation response. The implementation of the actuator makes use of a cam shaped lever arm with a variable pivot axis actuated by a rack and pinion transmission system. This realization results in a highly integrated and modular assembly. Size and weight are indeed an open issue in the VSAs design, which ultimately limit their implementation in multi-dof robotic systems. The paper introduces the mechanics, the principle of operation and the model of the actuator. Preliminary results are presented to demonstrate the fast stiffness regulation response and the wide range of stiffness achieved by the proposed CompAct-VSA design.

IROS Conference 2011 Conference Paper

A nonlinear series elastic actuator for highly dynamic motions

• Ivar Thorson
• Darwin G. Caldwell

A novel revolute nonlinear series elastic actuator called the HypoSEA is presented. The actuator uses a hypocycloid mechanism to stretch a linear spring in a nonlinear way. The actuator is optimized for highly dynamic tasks such as running and jumping, as it features a 120Nm torque capability and more than 30J of passive energy storage. When combined with a suitable controller, using the spring as an energy buffer can greatly reduce the work done by the rotor during periodic motions. The design has exceptionally low reflected mechanical impedance, making it robust against repeated impact loads. The nonlinear stiffening spring is optimized for the nonlinearities typically found in revolute-jointed hopping robots, and may be adjusted offline using a pretensioning mechanism. Finally, the low effective stiffness around the zero-torque equilibrium allows for extremely sensitive force control.

IROS Conference 2011 Conference Paper

A virtual scalpel system for computer-assisted laser microsurgery

• Leonardo S. Mattos
• Giulio Dagnino
• Gabriele Becattini
• Massimo Dellepiane
• Darwin G. Caldwell

A medical robotic system for teleoperated laser microsurgery based on a concept we have called “virtual scalpel” is presented in this paper. This system allows surgeries to be safely and precisely performed using a graphics pen directly over a live video from the surgical site. This is shown to eliminate hand-eye coordination problems that affect other microsurgery systems and to make full use of the operator's manual dexterity without requiring extra training. The implementation of this system, which is based on a tablet PC and a new motorized laser micromanipulator offering 1µm aiming accuracy within the traditional line-of-sight 2D operative space, is fully described. This includes details on the system's hardware and software structures and on its calibration process, which is essential for guaranteeing precise matching between a point touched on the live video and the laser aiming point at the surgical site. Together, the new hardware and software structures make both the calibration parameters and the laser aiming accuracy (on any plane orthogonal to the imaging axis) independent of the target distance and of its motions. Automatic laser control based on new intraoperative planning software and safety improvements based on virtual features are also described in this paper, which concludes by presenting results from sets of path following evaluation experiments conducted with 10 different subjects. These demonstrate an error reduction of almost 50% when using the virtual scalpel system versus the traditional laser microsurgery setup, and an 80% error reduction when using the automatic laser control routines, evidencing great improvements in terms of precision and controllability, and suggesting that the technological advances presented herein will lead to a significantly enhanced capacity for treating a variety of internal human pathologies.

ICRA Conference 2011 Conference Paper

AwAS-II: A new Actuator with Adjustable Stiffness based on the novel principle of adaptable pivot point and variable lever ratio

• Amir Jafari
• Nikos G. Tsagarakis
• Darwin G. Caldwell

The Actuator with Adjustable Stiffness (AwAS) is an actuator which can independently control equilibrium position and stiffness by two motors. The first motor controls the equilibrium position while the second motor regulates the compliance. This paper describes the design and development of AwAS-II which is an improved version of the original realization. AwAS tuned the stiffness by controlling the location of the springs and adjusting its arm, length. Instead AwAS-II regulates the compliance by implementing a force amplifier based on a lever mechanism on which a pivot point can adjust the force amplification ratio from zero to infinitive. As in the first implementation, the actuator which is responsible for adjusting the stiffness in AwAS II is not working against the spring forces. Its displacement is perpendicular to the force generated by springs which makes changing the stiffness energetically efficient. As the force amplification ratio can theoretically change from zero to infinitive consequently the level of stiffness can tune from very soft to completely rigid. Because this range does not depends on the spring's rate and length of the lever, thus soft springs and small lever can be used which result in a lighter and more compact setup. Furthermore as the lever arm is shorter the time required for the stiffness regulation is smaller.

IROS Conference 2011 Conference Paper

Bilateral physical interaction with a robot manipulator through a weighted combination of flow fields

• Antonio Pistillo
• Sylvain Calinon
• Darwin G. Caldwell

When collaboration between human users and robots involves physical interaction, the importance of the safety issue arises. We propose a method to transfer to robots several tasks demonstrated by the user through kinesthetic teaching and subsequently learned using a weighted combination of dynamical systems (DS). The approach used to encode the desired skills ensures a safe robot behavior during the task reproduction, allowing physical interaction with the user who can employ the manipulator as a tangible interface. By using a force sensor-less impedance controller with a back-drivable robot, this concept is exploited in two physical human-robot interaction (pHRI) scenarios. The first considers an emergency situation in which the user can stop or pause a task execution by grasping and moving the robot away from the region of space associated to the skill. The second studies the possibility to select one among several learned tasks and switch to its execution by physically guiding the robot towards the task region.

IROS Conference 2011 Conference Paper

Bipedal walking energy minimization by reinforcement learning with evolving policy parameterization

• Petar Kormushev
• Barkan Ugurlu
• Sylvain Calinon
• Nikos G. Tsagarakis
• Darwin G. Caldwell

We present a learning-based approach for minimizing the electric energy consumption during walking of a passively-compliant bipedal robot. The energy consumption is reduced by learning a varying-height center-of-mass trajectory which uses efficiently the robot's passive compliance. To do this, we propose a reinforcement learning method which evolves the policy parameterization dynamically during the learning process and thus manages to find better policies faster than by using fixed parameterization. The method is first tested on a function approximation task, and then applied to the humanoid robot COMAN where it achieves significant energy reduction.

IROS Conference 2011 Conference Paper

Dynamic model of a hyper-redundant, octopus-like manipulator for underwater applications

• Rongjie Kang
• Asimina Kazakidi
• Emanuele Guglielmino
• David T. Branson
• Dimitris P. Tsakiris
• John A. Ekaterinaris
• Darwin G. Caldwell

The octopus arm is a unique tool that combines strength and flexibility. It can shorten, elongate and bend at any point along its length. To model this behavior, a hyper-redundant manipulator composed of multiple segments is proposed. Each segment is a parallel robotic mechanism with redundant actuation. The kinematics and dynamics of this manipulator are analyzed and simulated utilizing a modular computational modeling method. Simulation results for some primitive movements are presented, and the effect of hydrodynamic forces is included.

IROS Conference 2011 Conference Paper

Encoding the time and space constraints of a task in explicit-duration Hidden Markov Model

• Sylvain Calinon
• Antonio Pistillo
• Darwin G. Caldwell

We study the use of different weighting mechanisms in robot learning to represent a movement as a combination of linear systems. Kinesthetic teaching is used to acquire a skill from demonstrations which is then reproduced by the robot. The behaviors of the systems are analyzed when the robot faces perturbation introduced by the user physically interacting with the robot to momentarily stop the task. We propose the use of a Hidden Semi-Markov Model (HSMM) representation to encapsulate duration and position information in a robust manner with parameterization on the involvement of time and space constraints. The approach is tested in simulation and in two robot experiments, where a 7 DOFs manipulator is taught to play a melody by pressing three big keys and to pull a model train on its track.

ICRA Conference 2011 Conference Paper

Exploiting natural dynamics for energy minimization using an Actuator with Adjustable Stiffness (AwAS)

• Amir Jafari
• Nikos G. Tsagarakis
• Darwin G. Caldwell

In repetitive trajectories, adaptable compliance actuators can minimize energy consumption thanks to their ability to adjust the level of stiffness which allows the exploitation of the natural dynamics of their link based on the desired motion's frequency. However for most of these actuators in case of a variable frequency motion, it is not energetically beneficial to exploit the natural dynamics in the real time due to the considerably high amount of energy needed to change the stiffness. AwAS (Actuator with Adjustable Stiffness) achieves the stiffness regulation not through the control of the spring pretension (as in most of the existing variable stiffness joints) but by controlling the location of the spring elements. An important consequence of this mechanism is that the displacement needed to change the stiffness is perpendicular to the forces generated by the springs which in turn helps to minimize the energy/power required to regulate the stiffness. It is experimentally shown that AwAS is capable of minimizing energy consumption through exploiting the natural dynamics in real time for both fixed and variable frequency motions.

IROS Conference 2011 Conference Paper

Novel modal approach for kinematics of multisection continuum arms

• Isuru S. Godage
• Emanuele Guglielmino
• David T. Branson
• Gustavo A. Medrano-Cerda
• Darwin G. Caldwell

This paper presents a new three dimensional (3D) kinematic model based on mode shape functions (MSF) for multisection continuum arms. It solves the singularity problems associated with previous models and introduces a novel approach for intuitively deriving exact, singularity-free MSFs, thus avoiding mode switching schemes and simplifying error models. The model is able to simulate spatial bending, pure elongation/contraction, and introduces inverse orientation kinematics for the first time to multisection continuum arms. Also, it carefully accounts for physical constraints in the joint space to provide enhanced insight into practical mechanics, and produces correct results for both forward and inverse kinematics. The model is validated through simulations, based on a prototype continuum robotic arm. Proposed approach is applicable to a broad spectrum of continuum robotic arm designs.

ICRA Conference 2011 Conference Paper

Shape function-based kinematics and dynamics for variable length continuum robotic arms

• Isuru S. Godage
• David T. Branson
• Emanuele Guglielmino
• Gustavo A. Medrano-Cerda
• Darwin G. Caldwell

This paper presents a new three dimensional kinematic and dynamic model for variable length continuum arm robotic structures using a novel shape function-based approach. The model incorporates geometrically constrained structure of the arm to derive its deformation shape function. It is able to simulate spatial bending, pure elongation, and incorporates a new stiffness control feature. The model is validated through numerical simulations, based on a prototype continuum arm, that yields physically accurate results.

ICRA Conference 2011 Conference Paper

The design of the lower body of the compliant humanoid robot "cCub"

• Nikos G. Tsagarakis
• Zhibin Li 0001
• Jody Alessandro Saglia
• Darwin G. Caldwell

The “iCub ”is a robotic platform that was developed by the RobotCub [1] consortium to provide the cognition research community with an open “child-like ”humanoid platform for understanding and development of cognitive systems [1]. In this paper we present the mechanical realization of the lower body developed for the “cCub ”humanoid robot, a derivative of the original “iCub”, which has passive compliance in the major joints of the legs. It is hypothesized that this will give to the robot high versatility to cope with unpredictable disturbance ranging from small uneven terrain variations to unexpected collisions or even accidental falls. As part of the AMARSI European project, the passive compliance of this newly developed robot will be exploited for safer interaction, energy efficient and more aggressive damage-safe learning. The passive compliant actuation module used is a compact unit based on the series elastic actuator principle (SEA). In addition to the passive compliance the “cCub ”design includes other significant updates over the original prototype such as full joint state sensing including joint torque sensing and improved range of motion and torque capabilities. In this paper, the new leg mechanisms of the “cCub ”robot are introduced.

ICRA Conference 2011 Conference Paper

Upper-body kinesthetic teaching of a free-standing humanoid robot

• Petar Kormushev
• Dragomir N. Nenchev
• Sylvain Calinon
• Darwin G. Caldwell

We present an integrated approach allowing a free-standing humanoid robot to acquire new motor skills by kinesthetic teaching. The proposed method controls simultaneously the upper and lower body of the robot with different control strategies. Imitation learning is used for training the upper body of the humanoid robot via kinesthetic teaching, while at the same time Reaction Null Space method is used for keeping the balance of the robot. During demonstration, a force/torque sensor is used to record the exerted forces, and during reproduction, we use a hybrid position/force controller to apply the learned trajectories in terms of positions and forces to the end effector. The proposed method is tested on a 25-DOF Fujitsu HOAP-2 humanoid robot with a surface cleaning task.

IROS Conference 2010 Conference Paper

A 3-way valve-controlled spring assisted rotary actuator

• Yousheng Yang
• Emanuele Guglielmino
• Claudio Semini
• Jian S. Dai 0001
• Darwin G. Caldwell

Hydraulic actuators are characterized by fast dynamics, high power density, high stiffness, large output force/torque, and in recent years are becoming increasingly attractive in the field of robotics. This paper presents the study of a 3-way proportional valve controlled, spring assisted electro-hydraulic rotary actuator, which consists of a 3-way proportional valve, a linear cylinder and a reciprocal spring. The operating principle is presented and a mathematical model is developed. Comparison analysis is made between the new actuator and a traditional one with an application to a hydraulically actuated legged robot.

IROS Conference 2010 Conference Paper

A novel actuator with adjustable stiffness (AwAS)

• Amir Jafari
• Nikos G. Tsagarakis
• Bram Vanderborght
• Darwin G. Caldwell

This paper describes the design and development of a new actuator with adjustable stiffness (AwAS) which can be used in robots which are necessary to work close to or physically interact with humans, e. g. humanoids and exoskeletons. The actuator presented in this work can independently control equilibrium position and stiffness by two motors. The first motor controls the equilibrium position while the second motor regulates the compliance. The novelty of the proposed design with respect to the existing systems is on the principle used to regulate the compliance. This is done not through the tuning of the pretension of the elastic element as in the majority of existing system but by controlling the fixation of the elastic elements (springs) using a linear drive. An important consequence of this approach is that the displacement needed to change the stiffness is perpendicular to the forces generated by the springs, thus this helps to minimize the energy/power required to change the stiffness. This permits the use of a small motor for the stiffness adjustment resulting in a lighter setup. Experimental results are presented to show the ability of AwAS to control position and regulate the stiffness independently.

ICRA Conference 2010 Conference Paper

A variable physical damping actuator (VPDA) for compliant robotic joints

• Matteo Laffranchi
• Nikos G. Tsagarakis
• Darwin G. Caldwell

This paper introduces the development of a semi-active friction based variable physical damping actuator (VPDA) unit. The realization of this unit aims to facilitate the control of compliant robotic joints by providing physical variable damping on demand assisting on the regulation of the oscillations induced by the introduction of compliance. The mechatronics details and the dynamic model of the damper are introduced. The proposed variable damper mechanism is evaluated on a simple 1-DOF compliant joint linked to the ground through a torsion spring. This flexible connection emulates a compliant joint, generating oscillations when the link is perturbed. Preliminary results are presented to show that the unit and the proposed control scheme are capable of replicating simulated relative damping values with good fidelity.

IROS Conference 2010 Conference Paper

An octopus anatomy-inspired robotic arm

• Emanuele Guglielmino
• Nikos G. Tsagarakis
• Darwin G. Caldwell

This paper focuses on the design of a robotic arm inspired to the anatomy and morphology of an octopus arm. The octopus is a boneless animal and its amazing dexterity is due to its muscular structure where longitudinal (axial), transverse (radial) and oblique muscles seamlessly interact while preserving hydrostaticity i. e. volume conservation (“muscular hydrostat”). Mimicking some features of the octopus is instrumental to design a dexterous and compliant system. After analysing the relevant anatomical and morphological characteristics of the octopus arm, the key biomechanical features of interest to the design of a robotic arm have been identified. A design methodology has been developed based on the analysis of the muscular hydrostat properties. A prototype arm has been built using bespoke contracting pneumatic muscles and expanding elements. In the current stage of development the system has 15 actuated degrees of motion (DOM) and 8 degrees of freedom (DOF), all independently controllable through valves and a dedicated electronics and software interface. Pros and cons of the current design as well as practical prototyping trade-offs are thoroughly described.

IROS Conference 2010 Conference Paper

Antagonistically actuated compliant joint: Torque and stiffness control

• Irene Sardellitti
• Gianluca Palli
• Nikos G. Tsagarakis
• Darwin G. Caldwell

The current research effort in the design of lightweight and safe robots is resulting in increased interest for the development of variable stiffness actuators. Antagonistic pneumatic muscle actuators (pMAs) have been proposed for this purpose, due to their inherent nonlinear spring behavior resulting from both air compressibility and their nonlinear force-length relation. This paper addresses the simultaneous torque and stiffness control of an antagonistically actuated joint with pneumatic muscles driven by compact, fast-switching solenoid valves. This strategy allows compensation of unmodeled joint dynamics while adjusting the joint stiffness depending on the task requirements. The proposed controller is based on a sliding mode force control applied to an average model of the valve-pneumatic muscle system. This was necessary to cope with both the well known model uncertainties of the pMA and the discontinuous on-off behavior of the solenoid valves. Preliminary experimental results verified the effectiveness of the proposed implementation.

ICRA Conference 2010 Conference Paper

Control of a hydraulically-actuated quadruped robot leg

• Michele Focchi
• Emanuele Guglielmino
• Claudio Semini
• Thiago Boaventura
• Yousheng Yang
• Darwin G. Caldwell

This paper is focussed on the modelling and control of a hydraulically-driven biologically-inspired robotic leg. The study is part of a larger project aiming at the development of an autonomous quadruped robot (hyQ) for outdoor operations. The leg has two hydraulically-actuated degrees of freedom (DOF), the hip and knee joints. The actuation system is composed of proportional valves and asymmetric cylinders. After a brief description of the prototype leg, the paper shows the development of a comprehensive model of the leg where critical parameters have been experimentally identified. Subsequently the leg control design is presented. The core of this work is the experimental assessment of the pros and cons of single-input single-output (SISO) vs. multiple-input multiple-output (MIMO) and linear vs. nonlinear control algorithms in this application (the leg is a coupled multivariable system driven by nonlinear actuators). The control schemes developed are a conventional PID (linear SISO), a Linear Quadratic Regulator (LQR) controller (linear MIMO) and a Feedback Linearisation (FL) controller (nonlinear MIMO). LQR performs well at low frequency but its behaviour worsens at higher frequencies. FL produces the fastest response in simulation, but when implemented is sensitive to parameters uncertainty and needs to be properly modified to achieve equally good performance also in the practical implementation.

ICRA Conference 2010 Conference Paper

Control strategies for ankle rehabilitation using a high performance ankle exerciser

• Jody Alessandro Saglia
• Nikos G. Tsagarakis
• Jian S. Dai 0001
• Darwin G. Caldwell

This paper presents the control architecture and preliminary experimental results of a high performance parallel robot used for ankle rehabilitation. The goal of this work was to design suitable control algorithms for diagnostic, training and rehabilitation of the ankle in presence of musculoskeletal injuries. A position control scheme is used for patient-passive exercises while an admittance control technique is used to perform patient-active exercises with and without motion assistance. The design of the control algorithms is based on the analysis of the rehabilitation protocol taking into account the dynamics of the system and the dynamics of the interaction between the human and the robot. Electromyographic (EMG) signals are used to evaluate patient's effort during training/exercising. The results indicate the great potential of the rehabilitation device as a tool to fasten and improve the ankle therapies outcome.

IROS Conference 2010 Conference Paper

Design and experimental evaluation of the hydraulically actuated prototype leg of the HyQ robot

• Claudio Semini
• Nikos G. Tsagarakis
• Emanuele Guglielmino
• Darwin G. Caldwell

This paper focuses on the design and experimental evaluation of a hydraulically actuated robot leg. The evaluation of the leg prototype is an important milestone in the development of HyQ, a Hydraulically actuated Quadruped robot. The prototype features two rotary joints actuated by hydraulic cylinders and has a mass of 4. 5kg. We performed several experiments with the leg prototype attached to a vertical slider to tests the robustness of the mechanical design and the hydraulic actuation system. Besides the experimental evaluation of the hydraulic components, we also extensively studied the sensor data of the leg during periodic hopping. The results show that hydraulic actuation is suitable for legged robots because of its high power-to-weight ratio, fast response and ability to cope with high impact force peaks. Furthermore, we compare the cylinder force data obtained by the load cell with the calculated value based on the cylinder pressures to analyze if it is possible to eliminate this sensory system redundancy in the future. Through these studies, weaknesses of the design were identified and suggestions on how to improve them are presented.

ICRA Conference 2010 Conference Paper

Evaluation of a probabilistic approach to learn and reproduce gestures by imitation

• Sylvain Calinon
• Eric L. Sauser
• Aude Billard
• Darwin G. Caldwell

We present an approach based on Hidden Markov Model (HMM) and Gaussian Mixture Regression (GMR) to learning robust models of human motion through imitation. The proposed approach allows us to extract redundancies across multiple demonstrations and build time-independent models to reproduce the dynamics of the demonstrated movements. The approach is systematically evaluated by using automatically generated trajectories sharing similarities with human gestures. The proposed approach is contrasted with four state-of-the-art methods previously proposed in robotics to learn and reproduce new skills by imitation. An experiment with a 7 DOFs robotic arm learning and reproducing the motion of hitting a ball with a table tennis racket is then presented to illustrate the approach.

IROS Conference 2010 Conference Paper

Learning-based control strategy for safe human-robot interaction exploiting task and robot redundancies

• Sylvain Calinon
• Irene Sardellitti
• Darwin G. Caldwell

We propose a control strategy for a robotic manipulator operating in an unstructured environment while interacting with a human operator. The proposed system takes into account the important characteristics of the task and the redundancy of the robot to determine a controller that is safe for the user. The constraints of the task are first extracted using several examples of the skill demonstrated to the robot through kinesthetic teaching. An active control strategy based on task-space control with variable stiffness is proposed, and combined with a safety strategy for tasks requiring humans to move in the vicinity of robots. A risk indicator for human-robot collision is defined, which modulates a repulsive force distorting the spatial and temporal characteristics of the movement according to the task constraints. We illustrate the approach with two human-robot interaction experiments, where the user teaches the robot first how to move a tray, and then shows it how to iron a napkin.

IROS Conference 2010 Conference Paper

Power hydraulics - switched mode control of hydraulic actuation

• Emanuele Guglielmino
• Claudio Semini
• Helmut Kogler
• Rudolf Scheidl
• Darwin G. Caldwell

This paper is concerned with the application of switching technology to hydraulic actuation. Over the last 50 years with advances in power electronics, faster and faster static switches have been developed and applied to the control of motors. Hydraulic technology evolved in the opposite direction: switching control was not considered, and more and more accurate proportional flow/pressure control devices (servovalves etc) were developed. However despite the sophistication of such valves, from an energetic viewpoint proportional control is dissipative and inefficient. Indeed, by analogy it can be seen as the equivalent of resistive (rheostatic) motor control. In robotic applications where high power density, ruggedness and reliability are key requirements hydraulic actuation can be a sensible choice. However, the low efficiency of proportional control can be a limitation and it is necessary to go beyond the paradigm of proportional flow/pressure control. One response to this challenge is to revisit traditional on-off hydraulic technology and develop "power hydraulic" devices that behave in analogous manner to their power electronic counterparts. "Power hydraulics" is a challenging and little explored technology due to the markedly non-linear behaviour of hydraulic systems and the need of components with dynamic specifications that are not readily available off-the-shelf. After an analysis of the real on-off characteristics of a valve, a prototype hydraulic switching converter, inspired by the electric DC-DC Buck converter, is presented and its performance in pressure control mode, relative to a classical proportional valve-controlled system, are assessed. An energy saving of 75% is achieved. Merits and limitations of the current design are identified.

IROS Conference 2010 Conference Paper

Robot motor skill coordination with EM-based Reinforcement Learning

• Petar Kormushev
• Sylvain Calinon
• Darwin G. Caldwell

We present an approach allowing a robot to acquire new motor skills by learning the couplings across motor control variables. The demonstrated skill is first encoded in a compact form through a modified version of Dynamic Movement Primitives (DMP) which encapsulates correlation information. Expectation-Maximization based Reinforcement Learning is then used to modulate the mixture of dynamical systems initialized from the user's demonstration. The approach is evaluated on a torque-controlled 7 DOFs Barrett WAM robotic arm. Two skill learning experiments are conducted: a reaching task where the robot needs to adapt the learned movement to avoid an obstacle, and a dynamic pancake-flipping task.

IROS Conference 2010 Conference Paper

The design of an anthropomorphic dexterous humanoid foot

• Steve Davis 0001
• Darwin G. Caldwell

The human foot serves three main functions; adapts to contours of ground, absorbs shock impacts and stores and releases energy. Despite significant development of humanoid robots the foot has seen little research and as a result most bipeds do not walk in a humanlike manner. In this work a study of the human foot is conducted to determine how each of these is achieved. The paper then describes the design, construction and testing of a fully articulated humanoid foot which has the same functionality as the human foot.

IROS Conference 2010 Conference Paper

Water/air performance analysis of a fluidic muscle

• Michele Focchi
• Emanuele Guglielmino
• Claudio Semini
• Alberto Parmiggiani
• Nikos G. Tsagarakis
• Bram Vanderborght
• Darwin G. Caldwell

This paper deals with a comparative study on using water and air as actuation means for the control of a fluidic muscle (designed for air) and assesses the performance, particularly from a dynamic and energetic point of view. A medium with higher bulk modulus such as oil/water is believed to increase pressure and force bandwidths and reduce sensitivity to load variations, as is the case with conventional hydraulic stiff actuation systems. However in this application the inherent flexibility of the muscle plays a major role. Water has been chosen because of its non-flammability, environmental friendliness and the low solubility of air in it. The operating pressure range of the pneumatic muscle is 0-6 bar (typical range of a pneumatic system) that is well below typical operating pressures of hydraulic systems (typically over 100 bar). At such low pressures the dynamic behaviour of water is less predictable because of the higher likelihood of entrapped air in the water which physically occurs when operating at low pressures. This can majorly affect water bulk modulus and hence its dynamic performance. Therefore, the behaviour of the system in this unconventional pressure range for a liquid must be more thoroughly investigated. Theoretical and experimental analyses on a dedicated test rig have been carried out to assess these assumptions.

ICRA Conference 2009 Conference Paper

A compact soft actuator unit for small scale human friendly robots

• Nikos G. Tsagarakis
• Matteo Laffranchi
• Bram Vanderborght
• Darwin G. Caldwell

This paper presents the development of a new compact soft actuation unit intended to be used in multi degree of freedom and small scale robotic systems such as the child humanoid robot “iCub” [1]. Compared to the other existing series elastic linear or rotary implementations the proposed design shows high integration density and wider passive deflection. The miniaturization of the newly developed high performance unit was achieved with a use of a new rotary spring module based on a novel arrangement of linear springs.

ICRA Conference 2009 Conference Paper

A high performance 2-dof over-actuated parallel mechanism for ankle rehabilitation

• Jody Alessandro Saglia
• Nikos G. Tsagarakis
• Jian S. Dai 0001
• Darwin G. Caldwell

This paper presents the mechanical design of an ankle rehabilitation robotic device based on a 2-dof, redundantly actuated parallel mechanism. The parallel mechanism introduced in this paper has the advantage of mechanical and kinematic simplicity when compared to existing platforms while at the same time it is fully capable of carrying out all the exercises required by ankle rehabilitation protocols. The proposed device makes use of actuation redundancy to eliminate singularity and greatly improve the workspace dexterity. In addition, the requirements for high torque capacity and back-drivability are satisfied with the employment of a custom made cable driven linear electric actuator that combines the high force capacity with excellent back-drivability. The analysis undergoes the optimal design towards the maximization of manipulator workspace, dexterity, torque output and compactness of the device. Finally, the performance of the custom linear actuator and the prototype of the rehabilitation device are shown.

IROS Conference 2009 Conference Paper

Antagonistic and series elastic actuators: a comparative analysis on the energy consumption

• Matteo Laffranchi
• Nikos G. Tsagarakis
• Ferdinando Cannella
• Darwin G. Caldwell

Recent investigations show that compliant systems can be more safe and energy-efficient than conventional stiff actuated systems. As a result, researchers are increasingly implementing compliance within actuation systems using a variety of mechanisms. In general, these actuators can be grouped in 2 main categories. The first category includes all the actuation systems with a compliant element connected in series (SEA), while the second group contains all those systems that employ two actuators placed antagonistically. In both designs the ability to regulate the stiffness is essential in order to meet safety and/or performance demands. Energy consumption is a very important aspect to be considered, especially in autonomous robots. This paper presents a theoretical study on the energy consumption of variable stiffness actuators, comparing the amount of energy required in order to perform a certain task.

IROS Conference 2009 Conference Paper

Leg mechanisms for hydraulically actuated robots

• Yousheng Yang
• Claudio Semini
• Nikos G. Tsagarakis
• Emanuele Guglielmino
• Darwin G. Caldwell

The performance of highly dynamic robotic machines is directly associated with both the actuation means and the specific mechanical properties/configuration of the system. Hydraulic actuation demonstrates significant competitive advantages when minimum weight and volume, large forces and wide range of speeds are required and this makes it very suitable for systems such as legged robots. The geometry and design of leg mechanisms have great effect on the actuation system performance such as the required flow, which directly determines the size/weight and power density, in turn affecting the performance of the robot. This paper describes the mechanism and operation principle of two 2-DOF legs considered for HyQ, a hydraulically actuated quadruped robot. Numerical studies have been done to investigate the required flow, the pressure in the actuator chambers and the efficiency of the two leg mechanisms. The results show that the second leg design reduces the required flow significantly with less pressure-jump in the actuator and higher efficiency.

ICRA Conference 2009 Conference Paper

MACCEPA 2. 0: Adjustable compliant actuator with stiffening characteristic for energy efficient hopping

• Bram Vanderborght
• Nikos G. Tsagarakis
• Claudio Semini
• Ronald Van Ham
• Darwin G. Caldwell

The MACCEPA (Mechanically Adjustable Compliance and Controllable Equilibrium Position Actuator) is an electric actuator of which the compliance and equilibrium position are fully independently controllable and both are set by a dedicated servomotor. In this paper an improvement of the actuator is proposed where the torque-angle curve and consequently the stiffness-angle curve can be modified by choosing an appropriate shape of a profile disk, which replaces the lever arm of the former design. The actuator has a large joint angle, torque and stiffness range and these properties can be made beneficial for safe human robot interaction and the construction of energy efficient walking, hopping and running robots. The ability to store and release energy is shown by simulations on a 1DOF hopping robot. Its hopping height is much higher compared to a configuration in which the same motor is used in a traditional stiff setup. The stiffness of the actuator has a stiffening characteristic so the leg stiffness resembles more a linear stiffness as found in humans.

IROS Conference 2009 Conference Paper

Safe human robot interaction via energy regulation control

• Matteo Laffranchi
• Nikos G. Tsagarakis
• Darwin G. Caldwell

This paper presents an energy-based control strategy to be used in robotic systems working closely or cooperating with humans. The presented method bounds the dangerous behavior of the robot during the first instants of the impact by limiting the energy stored into the system to a maximum imposed value. Two critical physical human robot interaction (pHRI) cases are studied, these are the collision either against a free or a clamped head. Safe energy values that can be used as reference were retrieved by analysing experimental data of energy absorption to failure of cranium bones and cervical spinal cords. The energy regulation control is implemented in a series elastic actuator prototype joint. The model and the control scheme of the system are analysed. The proposed control scheme is a position-based controller that adjusts the position trajectory reference in function of the maximum energy value imposed by the user. Preliminary results are presented to show that the actuator unit and this control scheme are capable of limiting the energy to a maximum imposed value.

IROS Conference 2009 Conference Paper

The mechanical design of the new lower body for the child humanoid robot 'iCub'

• Nikos G. Tsagarakis
• Bram Vanderborght
• Matteo Laffranchi
• Darwin G. Caldwell

The “iCub” is a robotic platform that was developed within the RobotCub European project to provide the cognition research community with an open “child-like” humanoid platform for understanding and development of cognitive systems [1]. In this paper we present the mechanical realization of the new lower body developed for the “iCub” child humanoid robot in order to keep up with the latest technology and solve mechatronic problems found in the previous version. The new lower body assembly demonstrates significant improvements over the old prototype including higher modularity, full joint state sensing and improved range of motion and torque capabilities. In particular the new leg and waist mechanisms to match the size and physical abilities of a 3 year old human child are introduced.

IROS Conference 2008 Conference Paper

2D motion coordination enhancement for 'Ataxia' impaired users using a haptic device

• Nikos G. Tsagarakis
• Martin Gube
• Darwin G. Caldwell

This paper examines the application of a force feedback interface to minimize the effect of the pathological absence of control on the upper limb motion of impaired users. The haptic device used in this research is a two degree of freedom (DOF) Pantograph planar device. Force sensing is employed to detect the user indentation of motion while assistive impedance based techniques were used to develop a clumsy motion suppression control system. The erratic motion suppression techniques and the experimental system setup were evaluated in two dimensional tracking tasks using a human subject with failure of the gross coordination of the upper limb muscle movements resulted by a disorder named dasiaMuscle Ataxiapsila. The preliminary results obtained from these experiments depict that the proposed system can be used to enhance the motion coordination for muscle ataxia impaired subjects in two dimensional tracking tasks, similar to computer mouse interactions.

ICRA Conference 2007 Conference Paper

Automated Handling, Assembly and Packaging of Highly Variable Compliant Food Products - Making a Sandwich

• Steve Davis 0001
• M. G. King
• John W. Casson
• John O. Gray
• Darwin G. Caldwell

This paper describes the design, construction and testing of an automated system for the assembly and packaging of triangular sandwiches. This process is currently highly labour intensive with little automated machinery available. This paper analyses the current manual production techniques and develops a number of modular workstations which can be incorporated into an existing line in place of human operators. The machine developed completes the final assembly of the sandwich and then cuts and packages it into a plastic skillet (container) for dispatch. To test the overall performance of the system real plant trials were conducted with the machine in a sandwich production factory and the results of these trials are reported here

ICRA Conference 2007 Conference Paper

Design of an Automated Handling System for Limp, Flexible Sheet Lasagna Pasta

• René J. Moreno Masey
• Darwin G. Caldwell

The manipulation of flexible and limp sheet materials is a common requirement in many industrial manufacturing processes, however automation of even simple tasks involving these difficult to handle materials tends to be particularly problematic. The industrial manufacture of lasagne ready meals is one example of a process that has been almost completely automated except for the handling of the flexible lasagna pasta, which remains a highly repetitive and labour intensive manual task. In this paper a robotic end-effector is developed to enable the automatic handling of lasagna pasta sheets. The design of the end-effector is described and its performance evaluated through testing using a robot arm. The concept was further developed into a low cost fixed automation machine suitable for industrial use. The pneumatic pick and place type machine was able to pick a pasta sheet from a moving conveyor and place it into a plastic tray with a cycle time of less than 4 seconds.

IROS Conference 2007 Conference Paper

Lower body realization of the baby humanoid - 'iCub'

• Nikos G. Tsagarakis
• Francesco Becchi
• Ludovic Righetti
• Auke Jan Ijspeert
• Darwin G. Caldwell

Nowadays, the understanding of the human cognition and it application to robotic systems forms a great challenge of research. The iCub is a robotic platform that was developed within the RobotCub European project to provide the cognition research community with an open baby- humanoid platform for understanding and development of cognitive systems. In this paper we present the design requirements and mechanical realization of the lower body developed for the "iCub". In particular the leg and the waist mechanisms adopted for lower body to match the size and physical abilities of a 2 frac12 year old human baby are introduced.

IROS Conference 2006 Conference Paper

Free to Touch: A Portable Tactile Display For 3D Surface Texture Exploration

• Ioannis Sarakoglou
• Milan Bezdicek
• Nikos G. Tsagarakis
• Darwin G. Caldwell

The development of successful tactile displays can be assisted by the capacity to assess their performance in integrated virtual reality applications. The design of single tactor or desktop tactile displays has been useful for scientific analysis of the mechanisms of touch. Nevertheless, it does not provide useful information about the quality of immersion in VR environments integrated with tactile feedback where user mobility and comfort are paramount. The present work introduces a new wireless portable tactile display for the finger. This new device demonstrates excellent levels of force output combined with good bandwidth in a configuration of a wearable 4times4 array of vertically moving tactors. The focus of this design is small size, comfort, mobility and ultimately integration into a complete Virtual Reality system for tactile surface texture exploration with 6DOF in the finger's work envelope

IROS Conference 2006 Conference Paper

Tele-Operated High Speed Anthropomorphic Dextrous Hands with Object Shape and Texture Identification

• Ping Yong Chua
• Milan Bezdicek
• Steve Davis 0001
• Darwin G. Caldwell
• John O. Gray

This paper reports on the development of two number of robotic hands have been developed which focus on tele-operated high speed anthropomorphic dextrous robotic hands. The aim of developing these hands was to achieve a system that seamlessly interfaced between humans and robots. To provide sensory feedback, to a remote operator tactile sensors were developed to be mounted on the robotic hands. Two systems were developed, the first, being a skin sensor capable of shape reconstruction placed on the palm of the hand to feed back the shape of objects grasped and the second is a highly sensitive tactile array for surface texture identification

IROS Conference 2004 Conference Paper

Occupational and physical therapy using a hand exoskeleton based exerciser

• Ioannis Sarakoglou
• Nikos G. Tsagarakis
• Darwin G. Caldwell

Hand therapy is a major sector of physiotherapy and one of great importance. The impairment of the hand and generally of the upper limbs can be the cause of social and financial hardship and a serious cause of physical and emotional deterioration. Major efforts are directed into developing therapy methods and procedures in order to standardise and therefore successfully apply treatment regimes in a wide scale. Although, the lack of scientific measurements of statistical value that the current methods suffer due to the mostly empirical nature of examination, assessment and treatment does not assist this endeavour. This paper presents an exoskeleton based system for the physical and occupational therapy of the hand in an interactive VR environment. This system enhances the existing therapy methods with the introduction of accurate and repeatable finger motion and force measurement, interactivity, potential for great exercise assortment and statistical registration and evaluation.

ICRA Conference 2002 Conference Paper

Enhanced Dynamic Performance in Pneumatic Muscle Actuators

• Steve Davis 0001
• J. Canderle
• P. Artrit
• Nikos G. Tsagarakis
• Darwin G. Caldwell

Pneumatic muscle actuators based on McKibben muscles have performance characteristics that may be of considerable significance in robotics due to their power/weight ratio and use as user friendly soft drives. However, the dynamic response (bandwidth) has been inferior to electric systems, with a secondary concern over system stiffness. In this paper, the bandwidth limit is addressed from two perspectives; air flow effects and the physical structure of the actuator. It is shown that by reducing the dead volume within the muscle structure (by the addition of a variety of filler materials) the bandwidth can be increased by up to 400%, with similar increases in system stiffness. At the same time the air volume used to power the actuator can be reduced by up to 80-90%. The methods of achieving these improvements are fully assessed. Also, by ensuring effective air flow rates, it is shown that bandwidth limits can be increased by several 100% and potentially increases of 1000s% are possible.

ICRA Conference 2000 Conference Paper

Improved Modelling and Assessment of Pneumatic Muscle Actuators

• Nikos G. Tsagarakis
• Darwin G. Caldwell

Traditional robotic/mechatronic design has successfully exploited the attributes of heavy mechanical systems engineering, but future scientific trends suggest a need for technology that will emulate natural systems. Among the most pressing of the requirements are actuation systems that can interact in a safer and more natural way. Pneumatic technology has many of the compliance forms needed for this softer interaction and a number of new systems based on McKibben muscles have been developed in recent years. In this paper a new model of operation of pneumatic muscle systems is developed. In particular, the model considers the distortion effects at the termination nodes and the radial pressure loss due to rubber elasticity. The new model is compared experimentation on a very large actuator and shows how this new model improves the assessment of forces and displacement that can be achieved by the actuator. The new model is compared against previous systems models.

ICRA Conference 1999 Conference Paper

An Integrated Tactile/Shear Feedback Array for Stimulation of Finger Mechanoreceptor

• Darwin G. Caldwell
• Nikos G. Tsagarakis
• C. Giesler

VR and telepresence applications have placed increasing demands on the need for effective user interfaces. To date most of the interfaces have emphasised the use of visual and audio effects but tactile feedback has been identified as a leading feature for future systems where there will be an increased desire to truly interact with the virtual/remote world rather than being observational. The paper focuses on the cutaneous aspects of tactile feedback describing the design and construction of pneumatically powered tactile and shear feedback modules. It is shown that by incorporating a range of novel features into this design it is possible to stimulate all the mechano-receptive nerves (SAI, SAII, RAI, and RAII) with localised signals from DC to 400 Hz. All this is shown in a fully integrated, ultra-light and comfortable package. The design control and performance results are all presented.

ICRA Conference 1999 Conference Paper

Development of a Pneumatic Muscle Actuator Driven Manipulator Rig for Nuclear Waste Retrieval Operations

• Darwin G. Caldwell
• Nikos G. Tsagarakis
• Gustavo A. Medrano-Cerda
• J. Schofield
• S. Brown

The processes of nuclear clean-up, dismantling and decontamination are highly hazardous, but in many instances, particularly where the facility is older there has been little provision for automation, and human intervention is necessary. The paper describes a prototype design of a teleoperational rig for retrieval of radioactive material (spent Magnox fuel) from underwater storage ponds. The system uses a combination of the traditional man-handled manipulation pole combined with new pneumatic muscle actuators. The paper considers the design requirement, the technology and the system performance in dry test operations.

ICRA Conference 1998 Conference Paper

Dextrous Exploration of a Virtual World for Improved Prototyping

• Darwin G. Caldwell
• C. Favede
• Nikos G. Tsagarakis

The capability of visualising and touching models of new products or new environments is a key factor in the design to production process. Usually this requires the construction of a physical model of the environment but production of the model can be costly and time consuming. Use of CAD packages can assist with the visualisation process, but proprioceptive and tactile sensations are required to augment this and provide the opportunity to feel the object. This work shows design, construction and testing in a virtual world of a generic 18 DOF proprioceptive input and feedback exoskeleton to monitor the motions of the human arm from sternum/spine to wrist and feedback tactile sensation generated during contact within a virtual world. The design is light, comfortable, and easy to wear for long periods providing an almost complete, unhampered range of input options. The proprioceptive inputs are augmented by tactile feedback of contact pressure (8 sensation points) to the upper and lower arm segments and pressure, texture, slip, edges/ridges/corners and thermal parameters to the hand. The paper shows how the input/feedback exoskeleton can be used to explore CAD designs generated in a commercial package (AutoCad) and imparted directly into a virtual world (WorldToolKit) permitting testing of products/processes before production and thereby improving the design-production process through the enhanced used of concurrent engineering techniques.

ICRA Conference 1998 Conference Paper

Pneumatic Muscle Actuator Technology a Light Weight Power System for a Humanoid Robot

• Darwin G. Caldwell
• Nikos G. Tsagarakis
• D. Badihi
• Gustavo A. Medrano-Cerda

This work reports on the construction of components for a humanoid robot powered by a new low mass, high power weight and volume actuation system, called the pneumatic muscle actuator (PMA). In addition to their power and force capabilities the PMA, being pneumatic, produces a more natural human muscle like contact and as such can be considered a soft actuation system with the inherent safety implication when working in close proximity to humans. The integration and testing of the performance of the component sections is also considered to show how these structures and actuators can be combined to produce the various systems needed for a low mass humanoid and the potential for future application in humanoid and other robotic fields.

ICRA Conference 1997 Conference Paper

Investigation of bipedal robot locomotion using pneumatic muscle actuators

• Darwin G. Caldwell
• Gustavo A. Medrano-Cerda
• Colin J. Bowler

Bipedal locomotion and particularly the human gait is a highly automated and complex process involving large numbers of actuators. Unfortunately actuator technology is an area of robotics with many conflicting requirements such as: high power density, high power to weight ratio, rapid response, accurate repeatable control, cleanliness, high efficiency, and low cost, which make selection complex. Pneumatic muscle actuators (PMA) [based on the McKibben Muscle] which can provide position and force control better than 1% have been applied to upper limbs with some success and with contractile forces in excess of 1000N (in units weighing less than 50g) there is considerable potential for use in bipedal locomotion. This paper will explore the design of a bipedal robot to take advantage of the potential of these actuators. Muscle co-ordination and control sequences will be considered for striding and standing activities and it will be shown that in terms of the energy requirements PMAs are very capable of providing a reliable bipedal drive source with linear actuation, low mass, fast response, compliant energy storage and simple construction.

ICRA Conference 1997 Conference Paper

Mechano thermo and proprioceptor feedback for integrated haptic feedback

• Darwin G. Caldwell
• Nikos G. Tsagarakis
• Andrew Wardle

Haptic sensation has two complex components; skin (cutaneous) sensing which is mediated by a variety of sensing organs that respond to pressure, vibration, displacement and temperature and kinaesthetic/proprioceptive sensing (muscles and joints) which responds to motions and forces exerted by the interaction of the body with the external environment. Although haptic interaction has been identified as being crucial for many applications, achieving realism in haptic feedback has not been possible due to physical, understanding and modelling problems. This paper explores the sensation of touch from a physiological and technological perspective and shows how this can be combined with an integrated touch/force reflecting system to produce a 'realistic' haptic rendering.

IROS Conference 1996 Conference Paper

Multi-modal cutaneous tactile feedback

• Darwin G. Caldwell
• S. Lawther
• Andrew Wardle

Haptic cues are the forms of information that can be acquired by the human sensory system through touching or handling an object. Some cues require active exploration while others are passively received. A basic taxonomy of haptic cues and the role that each cue plays in grasping and manipulation is illustrated in this paper. An initial analysis considers all forms of sensing and feedback (visual, audio, smell and taste) but attention is focused on global tactile requirements (kinaesthetic) and the local tactile (cutaneous) sensory cues. A multi-modal feedback system is shown which can stimulate a range of tactile nerves (mid/mid and low frequency plus thermal), together with the test results. Particular attention is applied to the use of mid-high frequency stimulation, where interesting sensations have been recorded which have a direct bearing on the ability of a user to use this form of system for prolonged periods.

ICRA Conference 1996 Conference Paper

Sensory requirements and performance assessment of tele-presence controlled robots

• Darwin G. Caldwell
• K. Reddy
• Osman Kocak
• Andrew Wardle

Robots have most successfully been applied in repetitive operations, but often when the task involves complex variable operations in unstructured environments teleoperation is preferred. As the complexity of these human supervisory tasks has increased the trend has been towards greater sensory feedback and more intuitive input control. This paper reports on the relative effectiveness of and need for sensory feedback systems for operator control in telepresence applications. In particular, studies were made of the performance of manipulation and navigation planning operations on a twin armed mobile robot using a variety of visual and audio cues and input systems. The performance was measured by experimentation with a range of subjects at a number of difficulty levels to test the effectiveness of the telepresence controller in a series of technical scenarios.

ICRA Conference 1996 Conference Paper

Tactile perception and its application to the design of multi-modal cutaneous feedback systems

• Darwin G. Caldwell
• S. Lawther
• Andrew Wardle

Applications in telepresence, virtual reality and virtual environments have highlighted the need for an advanced realistic user interface to remote and virtual entities. Vision and audition have been well developed leaving touch as a key sensory parameter which is presently under-utilised. In this paper a detailed study of the present knowledge of the human sensory nervous system relating to the 'sense of touch and feeling' is undertaken. Using this knowledge of the operation of tactile nerves a multi-modal cutaneous tactile feedback glove has been designed and tested. The construction of this system which feeds back data on texture/slip motion, edges/ridges and surface contours, contact force and thermal parameters is detailed with the test results and system assessment.

IROS Conference 1995 Conference Paper

Adaptive position control of antagonistic pneumatic muscle actuators

• Gustavo A. Medrano-Cerda
• Colin J. Bowler
• Darwin G. Caldwell

Problems with the control and compliance of pneumatic systems have prevented their widespread use in advanced robotics. However, their compactness, power/weight ratio and inherent safety are factors that could potentially be exploited in sophisticated dexterous manipulator designs. These advantages have lead to the development of novel actuators such as the McKibben Muscle, Rubbertuator, Flexator, Romac and pneumatic muscle actuators (PMA). However, the nonlinearities in these systems still limit their controllability. This paper considers the development of an adaptive controller for bi-muscular PMA system. Control of these muscles is explored via adaptive pole-placement controllers. Experimental results indicate that accurate position control /spl plusmn/2/spl deg/ is feasible, with power/weight outputs in excess of 1 kW/kg at 250 kPa being possible.

IROS Conference 1995 Conference Paper

Multi-armed dexterous manipulator operation using glove/exoskeleton control and sensory feedback

• Darwin G. Caldwell
• Osman Kocak
• U. Andersen

Developments in telepresence have served to demonstrate the requirements for an advanced realistic user interface to remote and virtual entities. Most of these applications have concentrated on visual and audio feedback but recent research has highlighted the need for tactile input, control and feedback. This paper reports on the operator input/feedback robot sensory/control aspects of a dexterous manipulation system possessed of two arms (left and right) and two dexterous multi-jointed skeletal 'hands'. The operator input units developed include a light weight 7 degree of freedom arm exoskeleton combined with a cutaneous tactile feedback glove providing finger input control and tactile feedback of contact force, vibrational and thermal data in a system with an overall mass of less than 0. 75 kg. This provides a user friendly system that can be used for extended periods without excessive strain.

IROS Conference 1994 Conference Paper

A chemo-pneumatic drive source for flexible operation of pneumatic muscle actuators

• Darwin G. Caldwell
• R. K. Reddy

Hydraulic, pneumatic and electrical systems form the principle power sources that have been used to operate robots in industrial environments. However, when considering the needs of advanced robotics, one of the most fundamental requirements and problems is the provision of a suitable energy source to power the robot in a nonindustrial, often remote site. This work is aimed at designing a portable power supply that will operate efficiently and effectively in an untethered environment using a chemical fuel. Initially a feasibility study was undertaken to identify the different energy sources that are most widely used in the field of industrial robots, noting their relative advantages and disadvantages. Subsequently, the report focuses on the design, implementation and testing of an internal combustion based system that will be used to provide the drive source to a compressor which in turn will produce a constant air supply via a clutch and a series of gear mechanisms. Development and application of the mobile power supply is detailed. The silencing of the system is also analysed to reduce the noise level and allow operation in an enclosed/restricted environment as well as in the open atmosphere. This chemo-pneumatic power source is subsequently shown in operation driving pneumatic muscle actuators used in the construction of a high power/weight dexterous (3 finger 1 thumb) hand. >

ICRA Conference 1994 Conference Paper

Characteristics and adaptive control of pneumatic muscle actuators for a robotic elbow

• Darwin G. Caldwell
• Gustavo A. Medrano-Cerda
• Michael Goodwin

Problems with the control and compliance of pneumatic systems have prevented their widespread use in advanced robotics. However, their compactness, power/weight ratio and inherent safety are factors that could potentially be exploited in sophisticated dexterous manipulator designs. This paper considers the development of a new high power/weight and power/volume braided pneumatic muscle actuator (PMA) having considerable power output potential, combined with controllable motion and inherent compliance to prevent damage to handled objects. Control of these muscles is explored via adaptive pole-placement controllers. Experimental results indicate that accurate position control /spl plusmn/1/spl deg/ is feasible with power/weight outputs in excess of 1 kW/kg at 200 kPa being possible. >

IROS Conference 1994 Conference Paper

Tele-presence: feedback and control of a twin armed mobile robot

• Darwin G. Caldwell
• Andrew Wardle

Robots are often required to function in areas that are too dangerous or expensive for direct human labour. Unfortunately the unstructured nature of many of these environments and complexity of the task make autonomous operation impossible and tele-operation is essential. A variety of tele-operated devices are available to assist the operator, but in general control of the actions is not truly intuitive. Ideally the operator would wish to input body motions (from legs, arm, hand and head) which the robot would duplicate, and receive from the remote sensors, feedback of a quality and form comparable with that normally sensed. This work considers the development and testing of enhanced input, control and feedback (visual audio and tactile) systems for a twin armed mobile robot to be used in tele-presence applications. In particular the authors focus on the performance of the operator in controlled motion and manipulation tasks. These tests involve assessment of the usefulness of tactile, video and audio feedback parameters including: wide/narrow angle field of view, colour/monochrome, stereo/mono vision and audio. The performance is assessed in terms of the ease of training, time to perform simple functions and accuracy of task completion. >

ICRA Conference 1994 Conference Paper

Tele-Presence: Visual, Audio and Tactile Feedback and Control of a Twin-Armed Mobile Robot

• Darwin G. Caldwell
• Andrew Wardle
• Michael Goodwin

Robots are often required to function in environments which would be extremely dangerous or expensive when using direct human labour, however, computer control and intelligence are not sufficiently developed to permit the robots to perform these advanced technical tasks under their own initiative, and there is always a human operative in the loop. Ideally the operator would wish to input body motions (from legs, arm, hand and head) which the robot would duplicate, and receive from the remote sensors full visual, audio and tactile feedback of a quality and form comparable with that normally produced by the eyes, ears and skin. This work considers the development of input, control and feedback (visual, audio and tactile) systems (man-machine interface) for a twin armed mobile robot to be used in tele-presence applications. This multi-purpose human-machine interface provides the user with an enhanced degree of true control of and 'feel' for the task. >

IROS Conference 1993 Conference Paper

Multi-modal tactile sensing and feedback (tele-taction) for enhanced tele-manipulator control

• Darwin G. Caldwell
• Clarence Gosney

Describes the development of a multi-sensor tactile digit. This instrumented finger has the ability to detect contact pressure/force, hardness, texture, temperature, slip, surface profile/shape, and thermal conductivity. This information is subsequently transferred directly from the robot to the skin of the remote operator using tactile feedback units based on piezo, vibro and thermal effects. This multipurpose human-machine interface (tele-taction) provides the user with an enhanced degree of true feel for a grasped object.

IROS Conference 1992 Conference Paper

Multi-sensor Tactile Perception For Object Manipulation/identification

• Darwin G. Caldwell
• Alexander Buysse
• Zhou Weizhan

IROS Conference 1992 Conference Paper

Polymeric Gels: Pseudo Muscular Actuators And Variable Compliance Tendons

• Darwin G. Caldwell