Author name cluster

Máximo A. Roa

Possible papers associated with this exact author name in Arrow. This page groups case-insensitive exact name matches and is not a full identity disambiguation profile.

41 papers

1 author row

IROS Conference 2025 Conference Paper

CageCoOpt: Enhancing Manipulation Robustness through Caging-Guided Morphology and Policy Co-Optimization

Yifei Dong 0007
Shaohang Han
Xianyi Cheng
Werner Friedl
Rafael I. Cabral Muchacho
Máximo A. Roa
Jana Tumova
Florian T. Pokorny

Uncertainties in contact dynamics and object geometry remain significant barriers to robust robotic manipulation. Caging helps mitigate these uncertainties by constraining an object’s mobility without requiring precise contact modeling. Existing caging research often treats morphology and policy optimization as separate problems, overlooking their synergy. In this paper, we introduce CageCoOpt, a hierarchical framework that jointly optimizes manipulator morphology and control policy for robust caging-based manipulation. The framework employs reinforcement learning for policy optimization at the lower level and multitask Bayesian optimization for morphology optimization at the upper level. We incorporate a caging metric into both optimization levels to encourage caging configurations and thereby improve manipulation robustness. The evaluation consists of four manipulation tasks and demonstrates that co-optimizing morphology and policy improves task performance under uncertainties, establishing caging-guided co-optimization as a viable approach for robust manipulation.

IROS Conference 2024 Conference Paper

Perception-aware Full Body Trajectory Planning for Autonomous Systems using Motion Primitives

Moritz Kuhne
Riccardo Giubilato
Martin J. Schuster
Máximo A. Roa

Many robotic systems rely on visual sensing to accomplish simultaneously the tasks of state estimation, mapping, and path planning. One one hand, the usage of camera sensors represents a power-efficient and lightweight option for solving this problem. On the other hand, these tasks pose requirements on the quality of the visual input (e. g. number of tracked features for Visual Odometry) that are often in contrast to the optimal viewpoint planning for local mapping and obstacle avoidance. Dealing with this constraint is actively researched in the field of perception-aware planning. The approaches delivered by this field mostly concern Micro air vehicles (MAVs), but could be applied to a larger group of robotic systems. We propose a perception-aware trajectory planner for a class of robotic systems that can orient their cameras independently from their direction of travel. By using motion primitives, our planner does not require differentiable models for motion and perception objectives. We evaluate our method in simulation, showing increased capabilities in localization-aware motions around obstacles, and demonstrate its run-time capability on a real planetary rover. The code is released publicly under github.com/DLR-RM/palp.

ICRA Conference 2023 Conference Paper

Task-Oriented Stiffness Setting for a Variable Stiffness Hand

Ana Elvira H. Martin
Ashok M. Sundaram
Werner Friedl
Virginia Ruiz Garate
Máximo A. Roa

The integration of variable stiffness actuators (VSA) in robotic systems endows them with intrinsic flexibility and therefore robustness to unknown disturbances. However, this characteristic presents a challenge: choosing the best intrinsic stiffness setting guaranteeing the required force ap-plication capability while keeping the system as adaptable to uncertainties as possible. This paper proposes a method to set the optimal stiffness for a multi-finger VSA hand to perform a desired manipulation task. The task is generically represented as a force (with unknown magnitude) applied along a reference direction. According to the force application's direction and the hand's kinematic state, the fingers assume a certain role to split the collective force application. We employ the endpoint stiffness ellipsoid to analyze the required finger stiffness to fulfill the task. We evaluate the optimized stiffness settings in a door opening application with an iterative adaption of the stiffness behavior to handle the unknown force requirement. The results show a successful collective behavior of the fingers, where the stiffness setting considers a task-oriented force-adaptability trade-off and effective use of independent VSA fingers.

IROS Conference 2022 Conference Paper

Influence of Variable Leg Elasticity on the Stability of Quadrupedal Gaits

Federico Del Fatti
Anna Sesselmann
Máximo A. Roa

Several template models have been developed to facilitate the analysis of limit-cycles for quadrupedal locomotion. The parameters in the model are usually fixed; however, biology shows that animals change their leg stiffness according to the locomotion velocity, and this adaptability invariably affects the stability of the gait. This paper provides an analysis of the influence of this variable leg stiffness on the stability of different quadrupedal gaits. The analysis exploits a simplified quadrupedal model with compliant legs and shoulder joints represented as torsional springs. This model can reproduce the most common quadrupedal gaits observed in nature. The stability of such emerging gaits is then checked. Afterward, an optimization process is used to search for the system parameters that guarantee maximum gait stability. Our study shows that using the highest feasible leg swing frequency and adopting a leg stiffness that increases with the speed of locomotion noticeably improves the gait stability over a wide range of horizontal velocities while reducing the oscillations of the trunk. This insight can be applied in the design of novel elastic quadrupedal robots, where variable stiffness actuators could be employed to improve the overall locomotion behavior.

ICRA Conference 2022 Conference Paper

Kinematic Transfer Learning of Sampling Distributions for Manipulator Motion Planning

Peter Lehner
Máximo A. Roa
Alin Albu-Schäffer

Recent research has shown that guiding sampling-based planners with sampling distributions, learned from previous experiences via density estimation, can significantly decrease computation times for motion planning. We propose an algorithm that can estimate the density from the experiences of a robot with different kinematic structure, on the same task. The method allows to generalize collected data from one source manipulator to similarly designed target manipulators, significantly reducing the computation time for new queries for the target manipulator. We evaluate the algorithm in two experiments, including a constrained manipulation task with five different collaborative robots, and show that transferring information can significantly decrease planning time.

ICRA Conference 2021 Conference Paper

Automated Planning of Workcell Layouts Considering Task Sequences

Timo Bachmann
Korbinian Nottensteiner
Máximo A. Roa

The initial design of a robotic workcell layout has a large impact on the feasibility and performance of the intended robotic tasks. We define this layout design as a constrained nonlinear optimization problem that aims to optimize the placement of workcell components by minimizing the distance traveled between task sequences while maximizing the robot’s manipulability. Suitable constraints guarantee the reachability as well as the absence of collisions. We solve this optimization problem via a genetic algorithm, and demonstrate it in three scenarios for a dual-arm robotic system that assembles product variants out of aluminum profiles.

IROS Conference 2021 Conference Paper

Embedding a Nonlinear Strict Oscillatory Mode into a Segmented Leg

Anna Sesselmann
Florian Loeffl
Cosimo Della Santina
Máximo A. Roa
Alin Albu-Schäffer

Robotic legs often lag behind the performance of their biological counterparts. The inherent passive dynamics of natural legs largely influences the locomotion and can be abstracted through the spring-loaded inverted pendulum (SLIP) model. This model is often approximated in physical robotic legs using a leg with minimal mass. Our work aims to embed the SLIP dynamics by using a nonlinear strict oscillatory mode into a segmented robotic leg with significant mass, to minimize the control required for achieving periodic motions. For the first time, we provide a realization of a nonlinear oscillatory mode in a robotic leg prototype. This is achieved by decoupling the polar task dynamics and fulfilling the resulting conditions with the physical leg design. Extensive experiments validate that the robotic leg effectively embodies the strict mode. The decoupled leg-length dynamic is exhibited in leg configurations corresponding to the stance and flight phases of the locomotion task, both for the passive system and when actuating the motors. We additionally show that the leg retains this behavior while performing jumping in place experiments.

IROS Conference 2021 Conference Paper

Quadrupedal template model for parametric stability analysis of trotting gaits

Lorenzo Boffa
Anna Sesselmann
Máximo A. Roa

Simple template models have proven useful for understanding the underlying dynamics of legged locomotion. The most common one, the SLIP model, considers the legs as linear springs with constant stiffness, and it explains well the radial dynamics of the legs. However, in order to study the influence of the leg swing dynamics and leg segmentation on gait stability, more complex models are required. This paper introduces a novel template model for quadrupedal gait, which considers these additional aspects. The dynamic behavior of the model is analyzed via numerical simulation, using a continuation approach. By conducting a parametric analysis on the trotting gait and analyzing its stability, we identify the influence of the main model parameters, leading to marginally unstable limit cycles. These numerical results are applicable to the design of more efficient elastic quadrupedal robots.

IROS Conference 2020 Conference Paper

Environment-Aware Grasp Strategy Planning in Clutter for a Variable Stiffness Hand

Ashok M. Sundaram
Werner Friedl
Máximo A. Roa

This paper deals with the problem of planning grasp strategies on constrained and cluttered scenarios. The planner sequences the objects for grasping by considering multiple factors: (i) possible environmental constraints that can be exploited to grasp an object, (ii) object neighborhood, (iii) capability of the arm, and (iv) confidence score of the vision algorithm. To successfully exploit the environmental constraints, this work uses the CLASH hand, a compliant hand that can vary its passive stiffness. The hand can be softened such that it can comply with the object shape, or it can be stiffened to pierce between the objects in clutter. A stiffness decision tree is introduced to choose the best stiffness setting for each particular scenario. In highly cluttered scenarios, a finger position planner is used to find a suitable orientation for the hand such that the fingers can slide in the free regions around the object. Thus, the grasp strategy planner predicts not only the sequence in which the objects can be grasped, but also the required stiffness of the end effector, and the appropriate positions for the fingers around the object. Different experiments are carried out in the context of grocery handling to test the performance of the planner in scenarios that require different grasping strategies.

ICRA Conference 2019 Conference Paper

A Benchmarking Framework for Systematic Evaluation of Robotic Pick-and-Place Systems in an Industrial Grocery Setting

Pavlos Triantafyllou
Hussein Mnyusiwalla
Panagiotis Sotiropoulos
Máximo A. Roa
Duncan Russell
Graham E. Deacon

Robotic manipulation is a very active field of research nowadays; however, pick-and-place operations constitute the majority of today's industrial robotic applications. In order to adopt a robotic solution for an industrial setting, proper evaluation processes should be defined to assess the system's performance. A number of benchmarks have been proposed in the literature focusing mainly on individual components needed to perform the task, like grasping, perception and motion planning; thus, they do not provide enough information on the performance of the entire robotic system. To address this, we propose a benchmarking framework for a pick-and-place task inspired by a use case for picking fruits and vegetables in an industrial setting. To foster reproducible research and comparison of different robotic systems, the benchmarking framework uses surrogate objects with instructions on how to build them, an easy-to-reproduce environment, and guidelines for object placement. The proposed benchmark is applied to evaluate the performance of two variants of a robotic system with different end-effectors.

ICRA Conference 2019 Conference Paper

Experiments with Human-inspired Behaviors in a Humanoid Robot: Quasi-static Balancing using Toe-off Motion and Stretched Knees

Bernd Henze
Máximo A. Roa
Alexander Werner
Alexander Dietrich
Christian Ott 0001
Alin Albu-Schäffer

Humanoid robots typically display locomotion patterns that include walking with flat foot-ground contact, and knees slightly bent. However, analysis of human gait indicate that several physiological mechanisms like stretched knees, heel-strike and toe push-off increase the step length and energetic efficiency of locomotion. This paper presents an implementation of two of those mechanisms, namely stretched knees and push-off, on a quasi-static whole-body balancing controller. The influence of such mechanisms on the kinematic capabilities of the DLR humanoid robot TORO is analyzed in different experiments, and their benefits are thoroughly discussed. As a result, the energetic savings of balancing with stretched knees are shown to be of reduced magnitude with respect to the overall power consumption of the robot, and the ability of TORO for negotiating stairs is greatly enhanced.

IROS Conference 2018 Conference Paper

CLASH: Compliant Low Cost Antagonistic Servo Hands

Werner Friedl
Hannes Höppner
Florian Schmidt 0001
Máximo A. Roa
Markus Grebenstein

This paper presents the first two members of the new generation of CLASH hands, which exploit low cost actuation and rapid prototyping to create antagonistic modular and lightweight hands and grippers. The hands approach the robustness of the DLR Awiwi hand with a much lower complexity and cost. To reduce the number of required actuators, a differential coupling mechanism for underactuated fingers was developed, along with a new mechanism that uses variable stiffness actuation in order to increase the workspace of underactuated fingers. The hands provide a research platform for both hand-in-hand and robotic grasping. Design aspects are discussed, and an initial experimental validation verifies the hands' performance.

ICRA Conference 2018 Conference Paper

Evaluating the Quality of Non-Prehensile Balancing Grasps

Robert Krug 0002
Yasemin Bekiroglu
Danica Kragic
Máximo A. Roa

Assessing grasp quality and, subsequently, predicting grasp success is useful for avoiding failures in many autonomous robotic applications. In addition, interest in nonprehensile grasping and manipulation has been growing as it offers the potential for a large increase in dexterity. However, while force-closure grasping has been the subject of intense study for many years, few existing works have considered quality metrics for non-prehensile grasps. Furthermore, no studies exist to validate them in practice. In this work we use a real-world data set of non-prehensile balancing grasps and use it to experimentally validate a wrench-based quality metric by means of its grasp success prediction capability. The overall accuracy of up to 84 % is encouraging and in line with existing results for force-closure grasps.

IROS Conference 2018 Conference Paper

Hierarchical Path Planner Using Workspace Decomposition and Parallel Task-Space RRTs

George Mesesan
Máximo A. Roa
Esra Icer
Matthias Althoff

This paper presents a hierarchical path planner consisting of two stages: a global planner that uses workspace information to create collision-free paths for the robot end-effector to follow, and multiple local planners running in parallel that verify the paths in the configuration space by expanding a task-space rapidly-exploring random tree (RRT). We demonstrate the practicality of our approach by comparing it with state-of-the-art planners in several challenging path planning problems. While using a single tree, our planner outperforms other single tree approaches in task-space or configuration space (C-space), while its performance and robustness are comparable to or better than that of parallelized bidirectional C-space planners.

IROS Conference 2018 Conference Paper

Humanoid Teleoperation Using Task-Relevant Haptic Feedback

Firas Abi-Farraj
Bernd Henze
Alexander Werner
Michael Panzirsch
Christian Ott 0001
Máximo A. Roa

Robotic teleoperation is a key technology for a wide variety of fields. Teleoperating a humanoid in particular is essential as it allows the user to act remotely on an interface designed especially for humans, e. g. , in a space station, or operating tools and machinery in disaster scenarios. This paper presents a ‘task-relevant’ haptic interface for humanoid teleoperation, which bridges the gap between the task at hand and the balance of the robot. The operator is given command over the humanoid's hands and is informed through haptic cues about the impact of her/his potential actions on the robot’ stability. Moreover, a null-space autonomous controller acts in the operator's null-space to provide her/him with a wider workspace and help in the successful execution of the task. The architecture is designed to top an existing compliance controller for a torque-controlled humanoid robot. Experiments on the humanoid robot TORO are reported to demonstrate the feasibility and effectiveness of the approach.

ICRA Conference 2017 Conference Paper

Grasp quality evaluation done right: How assumed contact force bounds affect Wrench-based quality metrics

Robert Krug 0002
Yasemin Bekiroglu
Máximo A. Roa

Wrench-based quality metrics play an important role in many applications such as grasp planning or grasp success prediction. In this work, we study the following discrepancy which is frequently overlooked in practice: the quality metrics are commonly computed under the assumption of sum-magnitude bounded contact forces, but the corresponding grasps are executed by a fully actuated device where the contact forces are limited independently. By means of experiments carried out in simulation and on real hardware, we show that in this setting the values of these metrics are severely underestimated. This can lead to erroneous conclusions regarding the actual capabilities of the grasps under consideration. Our findings highlight the importance of matching the physical properties of the task and the grasping device with the chosen quality metrics.

IROS Conference 2017 Conference Paper

Multi-contact balancing of humanoid robots in confined spaces: Utilizing knee contacts

Bernd Henze
Alexander Dietrich
Máximo A. Roa
Christian Ott 0001

Introducing humanoid robots in areas where space is limited, for example in search-and-rescue scenarios or industrial manufacturing, represents a huge challenge, especially when the environment is cluttered and unknown. The robot should be capable of utilizing multiple contact points distributed across the entire body and not just its feet and hands. Extra contacts on the whole body, for instance including the knees and elbows, enable the robot to increase its agility and robustness by enhancing the support polygon. This paper applies our passivity-based approach for hierarchical whole-body control including balancing to scenarios involving contacts distributed all over the body of the robot as required in confined spaces. The approach is experimentally validated on the torque-controlled humanoid robot TORO to demonstrate the general applicability of the presented framework.

ICRA Conference 2016 Conference Paper

Flexible, semi-autonomous grasping for assistive robotics

Jörn Vogel
Katharina Hertkorn
Rohit U. Menon
Máximo A. Roa

This paper proposes a scheme to provide flexible semi-autonomous grasping capabilities to an assistive robotic manipulator. The testbed consists of a five-finger robotic hand mounted on a robotic arm. During teleoperation, the position of the hand is continuously controlled in the three translational degrees of freedom, and the user has no direct influence over the rotational behavior. The proposed semi-autonomy scheme assists the user for moving and orienting the hand towards the object, and automates the grasping process when it is triggered. The velocity commands issued by the user are enhanced using virtual fixtures, which are not preprogrammed to support one approach direction to the (known) object, but are adapted online according to the intended movement. The approach is validated with a psycho-physical user study where the participants grasp objects in a simulation environment using a SpaceMouse interface. This setting serves as a testbed for the target application in which disabled subjects will control the real robotic system with an interface based on bio-signals. The user study compares the semi-autonomous and the pure teleoperation modes in terms of objective and subjective measures, showing an increase in performance and a decrease in workload for the proposed semi-autonomous mode.

IROS Conference 2016 Conference Paper

Grasp quality evaluation in underactuated robotic hands

Maria Pozzi
Ashok M. Sundaram
Monica Malvezzi
Domenico Prattichizzo
Máximo A. Roa

Underactuated and synergy-driven hands are gaining attention in the grasping community mainly due to their simple kinematics, intrinsic compliance and versatility for grasping objects even in non structured scenarios. The evaluation of the grasping capabilities of such hands is a challenging task. This paper revisits some traditional quality measures developed for multi-fingered, fully actuated hands, and applies them to the case of underactuated hands. The extension of quality metrics for synergy-driven hands for the case of underactuated grasping is also presented. The performance of both types of measures is evaluated with simulated examples, concluding with a comparative discussion of their main features.

IROS Conference 2016 Conference Paper

Multi-contact planning and control for a torque-controlled humanoid robot

Alexander Werner
Bernd Henze
Diego A. Rodriguez
Jonathan Gabaret
Oliver Porges
Máximo A. Roa

Humanoid robots that need to traverse constrained and uncertain environments require a suitable combination of perception, planning and control. This paper presents an integrated pipeline that allows the robot to autonomously acquire visual information, define step locations, compute feasible multi-contact stances using hands and feet, and generate a motion plan to reach the desired goal even going through different contact states. The execution of the desired path is guaranteed through a passivity-based multi-contact controller. The approach is evaluated in simulations and experiments in different scenarios using the humanoid robot TORO.

ICRA Conference 2015 Conference Paper

An adaptive compliant multi-finger approach-to-grasp strategy for objects with position uncertainties

Zhaopeng Chen
Thomas Wimböck
Máximo A. Roa
Benedikt Pleintinger
Miguel Neves 0002
Christian Ott 0001
Christoph Borst 0001
Neal Y. Lii

This paper presents an adaptive and compliant approach-to-grasp strategy for multi-finger robotic hands, to improve the performance of autonomous grasping when encountering object position uncertainties. With the proposed approach-to-grasp strategy, the first robot finger to experience unexpected impact would pause its movement in a compliant manner, and remains in contact with the object to minimize the unplanned motion of the target object. At the same time, the remainder of the fingers continuously, adaptively move toward re-adjusted grasping positions with respect to the first finger in contact with the object, without the need for on-line re-planning or re-grasping. An adaptive grasp control strategy based on spatial virtual spring framework is proposed to achieve local (e. g. not resorting to the robotic arm) in-hand adjustments of the fingers not yet in contact. As such, these fingers can be adaptively driven to the adjusted desired position to accomplish the grasp. Experimental results demonstrate that significantly larger position errors with respect to the hand workspace can be accommodated with the proposed adaptive compliant grasp control strategy. As much as 391% increase in position error area coverage has been achieved. Finally, beyond the quantitative analysis, additional observations during the extensive experiment trials are discussed qualitatively, to help examine several open issues, and further understand the approach-to-grasp phases of the robot hand tasks.

ICRA Conference 2015 Conference Paper

Determining independent contacts regions to immobilize 2D articulated objects

Noe Alvarado
Raúl Suárez
Máximo A. Roa

This paper deals with the problem of determining independent contacts regions (ICRs) on 2D articulated objects, such that a finger contact in each region guarantees a force-closure (FC) immobilization, independently of the exact position of the finger. These regions allow a robust finger or fixture placement on the links of the articulated object, despite of possible errors in the position of the contacts. The proposal defines a generalized wrench space for articulated objects and then computes the ICRs starting from an initial FC grasp, considering frictional contacts. The approach has been implemented, and some illustrative examples are provided.

ICRA Conference 2015 Conference Paper

Functional power grasps transferred through warping and replanning

Theodoros Stouraitis
Ulrich Hillenbrand
Máximo A. Roa

This paper presents a method to transfer functional grasps among objects of the same category through contact warping and local replanning. The method transfers implicit knowledge that enables an action on a class of objects for which no explicit grasp or task information has been given in advance. Contact points on the source object are warped based on global and local shape similarities to the target object. These warped contacts are then used to define a hand posture that reaches close to them, while at the same time provides the desired functionality on the object. The approach is tested on different sets of objects with a success rate of 87. 5%, and large benefits are shown when compared to a naive technique that only transfers a suitable hand pose to the novel object.

IROS Conference 2015 Conference Paper

Simultaneous and realistic contact and force planning in grasping

Katharina Hertkorn
Máximo A. Roa
Thomas Wimböck
Christoph Borst 0001

Traditional approaches in grasping consider separately the planning of contact points and forces. This often leads to optimally simulated grasps that fail in a real execution when the forces applied at the chosen contact points cannot resist expected perturbations like the own object weight. This paper presents a method that combines a grasp planner with the computation of grasp forces, which provides contact points and contact forces that take into account joint and torque limits of the robotic hand for fingertip grasps. The planner starts with a given hand pose relative to the object, and uses the concept of reachable independent contact regions to obtain a set of force closure grasps. Within this set, the grasp that best counteracts a given external wrench is chosen. The evaluation examples illustrate how the capabilities of the robotic hand can be used more effectively by this joint planning approach.

IROS Conference 2014 Conference Paper

Posture and balance control for humanoid robots in multi-contact scenarios based on Model Predictive Control

Bernd Henze
Christian Ott 0001
Máximo A. Roa

This work presents a new approach to whole-body control for balancing and posture stabilization of humanoid robots utilizing an optimization of contact forces in combination with Model Predictive Control. To perform tasks that require multiple contacts, like manipulation or crawling, the controller allows the robot to use a subset of its end effectors to apply a desired wrench to the environment. The remaining end effectors are used for balancing while taking into account the wrenches originating from the manipulation. Due to the prediction the controller is able to react to changes in the control inputs in advance. This approach is evaluated in simulation with the humanoid robot TORO.

ICRA Conference 2014 Conference Paper

Towards a functional evaluation of manipulation performance in dexterous robotic hand design

Máximo A. Roa
Zhaopeng Chen
Irene C. Staal
Jared N. Muirhead
Annika Maier
Benedikt Pleintinger
Christoph Borst 0001
Neal Y. Lii

Dexterous multifingered hands are the most complex and versatile variants of robotic end effectors. Compared to simpler grippers and underactuated hands, they should be more capable of grasping and, especially, manipulating different objects. This paper explores the relationship between kinematic design and manipulation performance of robotic hands. Some evaluation criteria frequently used by hand designers to verify kinematic configurations are revisited. The results from these criteria are scrutinized and compared with the evaluation of the manipulation workspace and the ranges of motion of inhand manipulation for a set of predefined objects. Simulations and actual manipulation experiments are carried out with different kinematic configurations on a modular dexterous hand. The results show some disconnection between perceived good designs through common evaluation criteria and their actual, realizable manipulation performance. This work finally gives some insight toward a more holistic approach to design hands that better address grasp and manipulation for the intended tasks and applications.

IROS Conference 2013 Conference Paper

Extended independent contact regions for grasping applications

Bao-Anh Dang-Vu
Máximo A. Roa
Christoph Borst 0001

Independent contact regions have been proposed as a way to overcome possible errors in finger positioning for grasping an object. Efficient implementations for their computation have been developed, that even allow their usage in real-time telemanipulation applications. However, the main problems in the computation of contact regions are that they strongly depend on the initial grasp used as an starting point, and that for a given initial grasp there is not a unique set of contact regions. This paper analyzes the optimality of current approaches for ICR computation in 2D, where the optimal regions are still easily computable, and proposes an algorithm to obtain contact regions closer to the optimal ones. The approach is implemented and analyzed for 2D and 3D objects with any number of contact points.

ICRA Conference 2013 Conference Paper

Planning in-hand object manipulation with multifingered hands considering task constraints

Katharina Hertkorn
Máximo A. Roa
Christoph Borst 0001

In-hand manipulation with a multifinger hand is defined as changing the object pose from an initial to a final grasp configuration, while maintaining the fingertip contacts on the object surface. Given only the task constraints, represented as a desired motion of the object and an external force to be applied or resisted, the problem can be expressed as finding a good set of contact points on the object and a corresponding hand configuration compatible with the task to be executed. This paper presents a method for solving such problem, taking into account the kinematic structure and torque limits of the hand, the force closure condition (which must be guaranteed during the whole trajectory), and task compatibility. The feasibility of such method is tested in simulation of 2D and 3D examples.

IROS Conference 2013 Conference Paper

Sequential trajectory re-planning with tactile information gain for dexterous grasping under object-pose uncertainty

Claudio Zito
Marek Sewer Kopicki
Rustam Stolkin
Christoph Borst 0001
Florian Schmidt 0001
Máximo A. Roa
Jeremy L. Wyatt

Dexterous grasping of objects with uncertain pose is a hard unsolved problem in robotics. This paper solves this problem using information gain re-planning. First we show how tactile information, acquired during a failed attempt to grasp an object can be used to refine the estimate of that object's pose. Second, we show how this information can be used to replan new reach to grasp trajectories for successive grasp attempts. Finally we show how reach-to-grasp trajectories can be modified, so that they maximise the expected tactile information gain, while simultaneously delivering the hand to the grasp configuration that is most likely to succeed. Our main novel outcome is thus to enable tactile information gain planning for Dexterous, high degree of freedom (DoFs) manipulators. We achieve this using a combination of information gain planning, hierarchical probabilistic roadmap planning, and belief updating from tactile sensors for objects with non-Gaussian pose uncertainty in 6 dimensions. The method is demonstrated in trials with simulated robots. Sequential replanning is shown to achieve a greater success rate than single grasp attempts, and trajectories that maximise information gain require fewer re-planning iterations than conventional planning methods before a grasp is achieved.

IROS Conference 2013 Conference Paper

Virtual reality support for teleoperation using online grasp planning

Katharina Hertkorn
Máximo A. Roa
Manuel Brucker
Philipp Kremer
Christoph Borst 0001

Classic telepresence approaches allow a human to interact with a remote or a virtual reality environment (VR) with force feedback. Coupling with a remote robot can be used to work in dangerous environments without the human being on-site. The coupling with a VR system can be used for training and verification of task sequences or robotic actions.

ICRA Conference 2012 Conference Paper

Identification of contact formations: Resolving ambiguous force torque information

Katharina Hertkorn
Máximo A. Roa
Carsten Preusche
Christoph Borst 0001
Gerhard Hirzinger

This paper presents the identification of contact formations using force torque information. As force torque measurements do not map uniquely to their corresponding contact formations, three steps are performed: Initially, the wrench space for each contact formation is computed automatically. Then, a contact formation graph is augmented with a similarity index that reflects the similarity of contact formations with respect to their spanned wrench spaces. A particle filter is used to represent the likeliness of a contact formation given a force torque measurement. Finally, this probability distribution is resolved taking the similarity index, the transitions of the contact formation graph and the history of identified contact formations into account. This allows the recognition of the order of demonstrated contact formations by a measured set of forces and torques. The approach is verified by experiments.

ICRA Conference 2012 Conference Paper

Power grasp planning for anthropomorphic robot hands

Máximo A. Roa
Max Argus
Daniel Leidner
Christoph Borst 0001
Gerhard Hirzinger

This paper presents an approach for computing power grasps for hands with kinematic structure similar to the human hand, which allows the implementation of strategies inspired in human grasping actions. The proposed method first samples the object surface to look for the best spots for creating an opposing grasp with two or three fingers, and then aligns the other fingers to match the local curvature of the object surface. Different grasp strategies are considered, depending on the relative size of the object with respect to the hand, and on the location of potential obstacles in the environment. Several application examples are provided with two different hand models.

IROS Conference 2012 Conference Paper

Transferring functional grasps through contact warping and local replanning

Ulrich Hillenbrand
Máximo A. Roa

We present a method for transferring grasps between objects of the same functional category. This transfer is intended to preserve the functionality of a grasp constructed for one of the objects, thus enabling the analogous action to be performed on a novel object for which no grasp has been specified. Manipulation knowledge is hence generalized from a single example to a class of objects with a significant amount of shape variability. The transfer is achieved through warping the surface geometry of the source object onto the target object, and along with it the contact points of a grasp. The warped contacts are locally replanned, if necessary, to ensure grasp stability, and a suitable grasp pose is computed. We present extensive results of experiments with a database of four-finger grasps, designed to systematically cover variations on grasping the mugs of the Princeton Shape Benchmark.

IROS Conference 2011 Conference Paper

Bipedal walking control based on Capture Point dynamics

Johannes Englsberger
Christian Ott 0001
Máximo A. Roa
Alin Albu-Schäffer
Gerhard Hirzinger

This paper builds up on the Capture Point concept and exploits the simple form of the dynamical equations of the Linear Inverted Pendulum model when formulated in terms of the center of mass and the Capture Point. The presented methods include (i) the derivation of a Capture Point (CP) control principle based on the natural dynamics of the linear inverted pendulum (LIP), which stabilizes the walking robot and motivates (ii) the design of a CP tracking and a CP end-of-step controller. The exponential stability of the CP control law is proven. Tilting is avoided by proper projection of the commanded zero moment point. The robustness of the derived control algorithms is analyzed analytically and verified in simulation and experiments.

IROS Conference 2011 Conference Paper

Graspability map: A tool for evaluating grasp capabilities

Máximo A. Roa
Katharina Hertkorn
Franziska Zacharias
Christoph Borst 0001
Gerhard Hirzinger

This paper presents the graspability map, a novel approach to represent for a particular object the positions and orientations that a given mechanical hand can adopt to achieve a force closure precision grasp. The algorithm is based on the intersection between the fingertip workspaces and the object, plus the verification of a necessary condition for force closure grasps. The maps are computed offline and can be used for comparing the grasp capabilities of different mechanical hands with respect to some benchmark objects. The maps have also potential applications in online grasp and manipulation planning.

ICRA Conference 2011 Conference Paper

Influence of contact types and uncertainties in the computation of Independent Contact Regions

Máximo A. Roa
Raúl Suárez

Independent Contact Regions provide robustness in front of finger positioning errors during an object grasping. However, different sources of uncertainty may be present like, for instance, the friction model used in grasp planning, indetermination of the friction coefficients, and errors in the model of the object that affect the positions of the boundary points as well as the direction normal to the object surface. These sources have not been previously considered in the computation of the Independent Contact Regions. This paper discusses how to take into account these factors when computing the Independent Contact Regions for discretized objects, i. e. objects described with a cloud or a mesh of points. The considerations provided allow a more robust result for application in grasp synthesis and regrasp planning.

ICRA Conference 2011 Conference Paper

Reachable Independent Contact Regions for precision grasps

Máximo A. Roa
Katharina Hertkorn
Christoph Borst 0001
Gerhard Hirzinger

Independent Contact Regions allow a robust finger placement on the object, despite of potential errors in finger position. They are computed without considering the kinematics of the end-effector, and are usually applied to off-line grasp planners. This paper presents an approach to obtain Reachable Independent Contact Regions by including the hand kinematics in the computational loop. The regions are computed in a short time, which allows real-time applications in virtual grasping. Potential applications of the proposed approach include regrasp planning, and dual-hand manipulation of objects.

IROS Conference 2009 Conference Paper

Regrasp planning in the grasp space using independent regions

Máximo A. Roa
Raúl Suárez

This paper presents an approach for quasi-static regrasp planning using n fingers, taking advantage of a method that quickly explores the grasp space for discrete objects. The approach relies on a sampling method, which provides samples of force-closure or non force-closure grasps used to compute regions of the graspable or non-graspable space, respectively. The regrasp contact points generated assure that a force-closure grasp is always possible when performing the regrasp motions. Application examples are included to show the relevance of the results.

IROS Conference 2008 Conference Paper

Grasp space generation using sampling and computation of independent regions

Máximo A. Roa
Raúl Suárez
Jan Rosell

This paper presents the use of independent contact and non-graspable regions to generate the grasp space for 2D and 3D discrete objects. The grasp space is constructed via a sampling method, which provides samples of force-closure or non force-closure grasps, used to compute regions of the graspable or non-graspable space, respectively. The method provides a reliable procedure for an efficient generation of the whole grasp space for n-finger grasps on discrete objects; two examples on 2D objects are provided to illustrate its performance. The approach has several applications in manipulation and regrasping of objects, as it provides a large number of force-closure and non force-closure grasps in a short time.

ICRA Conference 2008 Conference Paper

Independent contact regions for frictional grasps on 3D objects

Máximo A. Roa
Raúl Suárez

This paper presents an efficient algorithm to compute independent contact regions on the surface of complex 3D objects such that a finger contact anywhere inside each of these regions assures a force-closure grasp despite the exact contact position. Independent contact regions provide robustness in front of finger positioning errors during an object grasping, and give relevant information for finger repositioning during the object manipulation. The object is described with a mesh of surface points, so the procedure is applicable to objects of any arbitrary shape. The proposed approach uses information from the wrench space, and generates the independent regions by growing them around the contact points of a given starting grasp. A two-phase approach is also provided to find a locally optimum force-closure grasp that serves as starting grasp, considering as grasp quality measure the largest perturbation wrench that the grasp can resist with independence of the perturbation direction. The approach has been implemented and several examples are provided to illustrate its performance.

IROS Conference 2007 Conference Paper

Geometrical approach for grasp synthesis on discretized 3D objects applied to repeatable test methods

Máximo A. Roa
Raúl Suárez

Grasp synthesis on real 3D objects is a critical problem in grasp and manipulation planning. This paper presents a geometrical approach to compute force closure (FC) grasps, with or without friction and with any number of fingers. The object's surface is discretized in a cloud of points, so the algorithm is applicable to objects of any arbitrary shape. One or more FC grasps are obtained with a geometrical approach, which embeds the FC test in the algorithm to simplify achieving the force-closure property. This initial FC grasp may be improved with a complementary optimization algorithm. The grasp quality is measured considering the largest perturbation wrench that the grasp can resist with independence of the perturbation direction. The efficiency of both algorithms is illustrated through numerical examples.