Author name cluster

Steven Dubowsky

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.

47 papers

1 author row

ICRA Conference 2012 Conference Paper

Lithium hydride powered PEM fuel cells for long-duration small mobile robotic missions

Jekanthan Thangavelautham
Daniel Strawser
Mei Yi Cheung
Steven Dubowsky

This paper reports on a study to develop power supplies for small mobile robots performing long duration missions. It investigates the use of fuel cells to achieve this objective, and in particular Proton Exchange Membrane (PEM) fuel cells. It is shown through a representative case study that, in theory, fuel cell based power supplies will provide much longer range than the best current rechargeable battery technology. It also briefly discusses an important limitation that prevents fuel cells from achieving their ideal performance, namely a practical method to store their fuel (hydrogen) in a form that is compatible with small mobile field robots. A very efficient fuel storage concept based on water activated lithium hydride (LiH) is proposed that releases hydrogen on demand. This concept is very attractive because water vapor from the air is passively extracted or waste water from the fuel cell is recycled and transferred to the lithium hydride where the hydrogen is “stripped” from water and is returned to the fuel cell to form more water. This results in higher hydrogen storage efficiencies than conventional storage methods. Experimental results are presented that demonstrate the effectiveness of the approach.

ICRA Conference 2009 Conference Paper

A study of cooperative control of self-assembling robots in space with experimental validation

Chiara Toglia
Daniel T. Kettler
Fred Kennedy
Steven Dubowsky

Modular self-assembling on-orbit robotic and satellite systems can be more reliable, have lower launch costs, and be more easily repaired and refueled. However, when individual modules assemble, many challenges and opportunities make the control of the assembled system complex. These issues include changes in inertial properties, and redundancy of actuators and sensors. Optimal control methods may be used to coordinate the control of the modules after assembly, insure good performance, and best utilize the combined resources of the assembly of modules. Simulation and experimental results compare this Cooperative algorithm's performance to that of an approach in which the control of the individual modules is not coordinated. Cooperative optimal control methods prove well-suited for controlling redundant, modular space systems.

ICRA Conference 2008 Conference Paper

Experimental validation of a fuel-efficient robotic maneuver control algorithm for very large flexible space structures

Masahiro Ono
Peggy Boning
Tatsuro Nohara
Steven Dubowsky

The robotic maneuvering of large space structures is key to a number of future orbital missions. In this paper a large space structure maneuver control algorithm, recently proposed, is extended and experimentally validated. The method uses space robots’ manipulators to control the vibration of the structures being maneuvered and their reaction jets perform the large motion maneuvers. The algorithm quickly damps out the vibrations and requires less fuel than reaction jet-based vibration control methods. The approach is called maneuver decoupled control. Its performance is demonstrated and quantitatively evaluated in simulation and experiments.

ICRA Conference 2008 Conference Paper

The experimental study of a precision parallel manipulator with binary actuation: With application to MRI cancer treatment

Kenjiro Tadakuma
Lauren M. DeVita
Jean-Sébastien Plante
Shaoze Yan
Steven Dubowsky

In this paper the performance of a high-precision parallel robot manipulator with bistable actuation is experimentally evaluated. The manipulator is for performing prostate cancer biopsy and treatment within the bore of a magnetic resonance imaging (MRI) system. The analysis and simulations have shown that this bistable manipulator is able to perform well with dielectric elastomer actuators that have been shown to be compatible with the high magnetic fields of an MRI. In this work an experimental prototype system was developed and tested. The results show that it provides the precise needle placement required by the medical task.

ICRA Conference 2007 Conference Paper

Mobility and Power Feasibility of a Microbot Team System for Extraterrestrial Cave Exploration

Samuel B. Kesner
Jean-Sébastien Plante
Penelope J. Boston
Tibor Fábián
Steven Dubowsky

Planetary scientists are greatly interested in the caves present on the Moon and Mars, however these areas present major challenges to current space robots. A new space robotics concept, microbots, is presented and a possible reference mission to Mars is discussed. The feasibility of the mobility and power systems of the microbot are analyzed within the context of the reference mission. The results of this analysis are that the microbot system is a feasible concept for a development timeline of approximately 10 years.

ICRA Conference 2006 Conference Paper

Identification of Actuation Efforts using Limited Sensory Information for Space Robots

Peggy Boning
Steven Dubowsky

Autonomous space robots are needed for future missions such as satellite capture and large space structure construction. Precise control of these space robots is important for space missions but real world factors such as unpredictable actuator behavior can degrade performance. Sensing capabilities in space robots to measure and compensate for this uncertainty are limited by the practical issues of issues of weight, complexity and reliability. This paper presents a method that does multi-actuator sensing with a reduced number of actuators. A force/torque sensor is mounted between a space robot's spacecraft and its manipulators and is used to identify manipulator joint actuator outputs while simultaneously estimating spacecraft thruster forces and moments. Theoretical development and simulation results are presented

ICRA Conference 2006 Conference Paper

The Design of a Friction Compensation Control Architecture for a Heavy Lift Precision Manipulator in Contact with the Environment

Justin R. Garretson
William T. Becker
Steven Dubowsky

Joint friction is a major obstacle in heavy-lift precision manipulator performance. Friction compensation is vital to the performance of these manipulators. This paper presents a friction compensation architecture for a six degree-of-freedom heavy lift manipulator which utilizes sensor-based compensation in some joints, and a combination of adaptive, and model-based compensation in the remaining joints. The adaptive approach is used when the manipulator is not in contact with the environment, and the model-based compensation is used when the manipulator or its payload nears the environment. The parameters of the model-based approach are updated by the adaptive compensation during the non-contact phase of the task. This approach is validated in simulation

ICRA Conference 2005 Conference Paper

Shape, Motion, and Parameter Estimation of Large Flexible Space Structures using Range Images

Matthew D. Lichter
Steven Dubowsky

Future space missions are expected to use robotic systems to assemble, inspect, and maintain large space structures in orbit. To carry out these tasks, robots need to know the deformations and motions of the structures with which they interact. This paper presents a method for efficiently estimating the shape, motion, and dynamic model parameters of a vibrating space structure using range imaging sensors. The method assumes that the mode shapes are approximately known a priori. A Kalman filter exploits a mechanics-based dynamic model to extract the modal frequencies and damping as well as the modal coefficients and their time rate of change. This paper presents theoretical development as well as simulation and experimental results. Results on computational efficiency are included.

ICRA Conference 2005 Conference Paper

Vibration-based Terrain Analysis for Mobile Robots

Christopher A. Brooks 0002
Karl Iagnemma
Steven Dubowsky

Safe, autonomous mobility in rough terrain is an important requirement for planetary exploration rovers. Knowledge of local terrain properties is critical to ensure a rover’s safety on slopes and uneven surfaces. This paper presents a method to classify terrain based on vibrations induced in the rover structure by wheel-terrain interaction during driving. Vibrations are measured using an accelerometer on the rover structure. The classifier is trained using labeled vibration data during an off-line learning phase. Linear discriminant analysis is used for on-line identification of terrain classes such as sand, gravel, or clay. This approach is experimentally validated on a laboratory testbed.

ICRA Conference 2004 Conference Paper

Manipulation in MRI Devices using Electrostrictive Polymer Actuators: with an Application to Reconfigurable Imaging Coils

John Vogan
Andreas Wingert
Jean-Sébastien Plante
Steven Dubowsky
Moustapha Hafez
Daniel F. Kacher
Ferenc A. Jolesz

MRI (magnetic resonance imaging) is a powerful medical diagnostic tool. Its value would be greatly increased if it were possible to physically manipulate objects within the MRI during imaging. However, the extraordinarily strong magnetic fields used by the MRI make conventional electromagnetic components, such as actuators and sensors, unusable. In this paper, it is shown that devices constructed using binary polymer based actuators, called electrostrictive polymer actuators (EPAM) are able to function effectively within the MRI without degrading its imaging performance. These actuators eliminate the need for conventional electromagnetic actuators and their associated electronics. The binary nature of the actuators eliminates the need for feedback sensors to control the devices motion. The basic concept called digital mechatronics is briefly summarized in this paper. Its application to a reconfigurable MRI surface-imaging coil (RMIC) is also presented. Experimental results are presented that show the EPAM RMIC is completely compatible in the MRI and can be used to enhance the diagnostic capabilities of MRI. The paper also suggests other applications of binary EPAM based actuators for use in MRI systems.

ICRA Conference 2004 Conference Paper

Probabilistic Modeling and Analysis of High-speed Rough-terrain Mobile Robots

Dariusz Golda
Karl Iagnemma
Steven Dubowsky

Mobile robots have important applications in high speed, rough-terrain scenarios. It would be desirable to construct accurate models of these systems. However, due to the system complexity, accurate modeling is difficult. In This work a high-speed rough-terrain robot model is presented. Experiments show that this model can accurately predict robot performance in simple, well-known terrain. However in unstructured, rough terrain, performance prediction is less accurate. A stochastic method for analyzing system performance in spite of model parameter uncertainty is presented. A method for studying model sensitivity to parameter uncertainty is also presented. It is shown that stochastic analysis can be used effectively for model-based analysis of real-world rough-terrain robotic systems.

ICRA Conference 2004 Conference Paper

State, Shape, and Parameter Estimation of Space Objects from Range Images

Matthew D. Lichter
Steven Dubowsky

An architecture for the estimation of dynamic state, geometric shape, and model parameters of objects in orbit using on-orbit cooperative 3-D vision sensors is presented. This has application in many current and projected space missions, such as automated satellite capture and servicing, debris capture and mitigation, and large space structure assembly and maintenance. The method presented here consists of three parts: (1) kinematic data fusion, which condenses sensory data into coarse kinematic surrogate measurements; (2) Kalman filtering, which filters these surrogate measurements and extracts the full dynamic state and model parameters of the target; and (3) shape estimation, which uses filtered pose information and the raw sensory data to build a body-fixed probabilistic map of the target's shape. This method does not rely on feature detection, optical flow, or model matching, but rather exploits the well-modeled dynamics of objects in space using the Kalman filter. The architecture is computationally fast since only coarse measurements need to be provided to the Kalman filter. This paper illustrates the three steps of the architecture in the context of rigid body (satellite and debris) estimation and flexible structure estimation.

ICRA Conference 2002 Conference Paper

Analysis and Design of an Omnidirectional Platform for Operation on Non-Ideal Floors

Matthew Spenko
Haoyong Yu
Steven Dubowsky

An omnidirectional platform with an active offset split caster (ASOC) is described and its ability to operate on non-ideal floors is studied. It is shown that all of its driven wheels of the platform will remain in contact with an uneven floor at all times, a condition necessary to maintain good traction and dead-reckoning capabilities. It is shown that planning algorithms developed for an ideally flat floor perform adequately for a realistic uneven floor. Furthermore, it is shown that the ASOC design consumes less power than other conventional wheel omnidirectional designs and is more suitable for heavier loads. Analytical and experimental results are presented.

ICRA Conference 2002 Conference Paper

Computational Issues in the Planning and Kinematics of Binary Robots

Matthew D. Lichter
Vivek A. Sujan 0002
Steven Dubowsky

To meet the objectives of many future missions, robots will need to be adaptable and reconfigurable. A concept for such a robotic system has been proposed previously based on using a large number of simple binary actuators. Previous researchers have addressed some of the issues brought up by robots with a few binary actuators. This paper examines the computational feasibility of controlling and planning such binary robotic systems with a large number of actuators, including computation of their workspace, forward kinematics, inverse kinematics and trajectory following. Methods are proposed and evaluated by simulation. A detailed error analysis and computational requirements are presented. An example of the planning for a binary walking robot is presented.

ICRA Conference 2002 Conference Paper

On-Line Terrain Parameter Estimation for Planetary Rovers

Karl Iagnemma
Hassan Shibly
Steven Dubowsky

Future planetary exploration missions will require rovers to traverse very rough terrain with limited human supervision. Wheel-terrain interaction plays a critical role in rough-terrain mobility. In this paper an on-line estimation method that identifies key terrain parameters using on-board rover sensors is presented. These parameters can be used for accurate traversability prediction or in a traction control algorithm. These parameters are also valuable indicators of planetary surface soil composition. Simulation and experimental results show that the terrain estimation algorithm can accurately and efficiently identify key terrain parameters for loose sand.

ICRA Conference 2002 Conference Paper

Optimized Binary Modular Reconfigurable Robotic Devices

Moustapha Hafez
Matthew D. Lichter
Steven Dubowsky

Binary robotic devices with large numbers of degrees of freedom have been proposed by a number of researchers. However, experimental implementations of these concepts have been built with conventional components. These physical systems are heavy, complex, and far from being practical devices. In this paper, a lightweight, compliant mechanism driven by optimized magnet-coil actuators is proposed and developed as an element for modular hyper-redundant robotic systems. Such elements could be used in a number of applications and would replace conventional, complex, and heavy components. The device has a parallel kinematics structure. Its binary actuation simplifies its control architecture. Analytical and experimental results for a practical prototype system are presented.

ICRA Conference 2002 Conference Paper

Visually Built Task Models for Robot Teams in Unstructured Environments

Vivek A. Sujan 0002
Steven Dubowsky

In field environments it is not usually possible to provide robotic systems with valid geometric models of the task and environment. The robot or robot teams will need to create these models by performing appropriate sensor actions. Here, an algorithm based on iterative sensor planning and sensor redundancy is proposed to enable them to efficiently build 3D models of the environment and task. The method assumes stationary robotic vehicles with cameras carried by articulated mounts. The algorithm uses the measured scene information to find new camera mount poses based on information content. Issues addressed include model-based multiple sensor data fusion, and uncertainty and vehicle suspension motion compensation. Simulations show the effectiveness of this algorithm.

ICRA Conference 2000 Conference Paper

Action Module Planning and its Application to an Experimental Climbing Robot

David M. Bevly
Shane Farritor
Steven Dubowsky

This paper presents the application of an action module planning method to an experimental climbing robot named LIBRA. The method searches for a sequence of physically realizable actions, called action modules, to produce a plan for a given task. The search is performed with a hierarchical selection process that uses task and configuration filters to reduce the action module inventory to a reasonable search space. Then, a genetic algorithm search finds a sequence of actions that allows the robot to complete the task without violating any physical constraints. The results for the LIBRA climbing robot show the method is able to produce effective plans.

ICRA Conference 2000 Conference Paper

An Analytical Method to Eliminate the Redundant Parameters in Robot Calibration

Marco A. Meggiolaro
Steven Dubowsky

Model based error compensation of a robotic manipulator, also known as robot calibration, requires the identification of its generalized errors. These errors are found from measured data and used to predict, and compensate for, the end-point errors as a function of configuration. However, the generalized error formulation introduces redundant parameters, often non-intuitive, that may compromise the robustness of the calibration. The existing numerical methods to eliminate such errors are formulated on a case-by-case basis. In this paper, the general analytical expressions and physical interpretation of the redundant parameters are developed for any serial link manipulator, expressed through its Denavit-Hartenberg parameters. These expressions are used to eliminate the redundant parameters from the error model of any manipulator prior to the identification process, allowing for systematic robot calibration with improved accuracy. Simulations are conducted to verify the theory presented in the paper.

ICRA Conference 2000 Conference Paper

Application of a Model-Free Algorithm for the Packing of Irregular Shaped Objects in Semiconductor Manufacture

Vivek A. Sujan 0002
Steven Dubowsky

A robotic system has been developed to automate the crucible packing process in the CZ semiconductor wafer production. It requires the delicate manipulation and packing of highly irregular shaped polycrystalline silicon nuggets, into a fragile glass crucible. An online algorithm is presented to plan the packing. It uses a method called virtual trial and error. The online algorithm handles large numbers of highly irregularly shaped object of different sizes without requiring the object models. Working with the 3D range maps of objects, it is computationally fast enough to be applied in real-time to practical industrial applications, such as the CZ wafer manufacture. Simulation results show that it compares well with the human performance. The integrated system is shown to achieve high production rates, required precision and cost effectiveness.

ICRA Conference 2000 Conference Paper

Design and Implementation of a Robot Assisted Crucible Charging System

Vivek A. Sujan 0002
Steven Dubowsky
Yoshiaki Ohkami

A robotic system is developed to automate the packing of polycrystalline silicon nuggets into a fragile fused silica crucible in CZ semiconductor wafer production. The highly irregular shapes of the nuggets make this a difficult and challenging task. In this system, nugget grasping is done with a three-cup suction gripper and nugget manipulation is attained with a 7-DOF SCARA manipulator. An optical 3D vision system, based on active laser triangulation, measures the nugget and crucible profiles. A model-free virtual trial and error packing algorithm determines optimal nugget placement in real time. A hybrid position-force control scheme has been implemented and tested for physical nugget placement. The integrated system achieves high production rates, required precision and cost effectiveness.

ICRA Conference 2000 Conference Paper

PAMM - A Robotic Aid to the Elderly for Mobility Assistance and Monitoring: A Helping-Hand for the Elderly

Steven Dubowsky
Frank Génot
Sara Godding
Hisamitsu Kozono
Adam Skwersky
Haoyong Yu
Long Shen Yu

Meeting the needs of the elderly presents important technical challenges. In this research, a system concept for a robotic aid to provide mobility assistance and monitoring for the elderly and its enabling technologies are being developed. The system, called PAMM (personal aid for mobility and monitoring), is intended to assist the elderly living independently or in senior assisted living facilities. It provides physical support and guidance, and it monitors the user's basic vital signs. An experimental test-bed used to evaluate the PAMM technology is described. This test-bed has a cane based configuration with a nonholonomic drive. Preliminary field trials at an Eldercare Facility are presented.

ICRA Conference 1999 Conference Paper

Achieving Fine Absolute Positioning Accuracy in Large Powerful Manipulators

Marco A. Meggiolaro
Peter C. L. Jaffe
Steven Dubowsky

High accuracy is generally unattainable in manipulators capable of producing high task forces due to such factors as high joint, actuator, and transmission friction and link elastic and geometric distortions. A method called base sensor control has been developed to compensate for nonlinear joint characteristics, such as high joint friction, to improve system repeatability. A method to identify and compensate for system geometric and elastic distortion positioning errors in large manipulators has also been proposed to improve absolute accuracy in systems with good repeatability using a wrist force/torque sensor. This technique is called geometric and elastic error compensation. Here, it is shown experimentally that the two techniques can be effectively combined to enable strong manipulators to achieve high absolute positioning accuracy while performing tasks requiring high forces.

ICRA Conference 1999 Conference Paper

Rapid Physics-Based Rough-Terrain Rover Planning with Sensor and Control Uncertainty

Karl Iagnemma
Frank Génot
Steven Dubowsky

In future planetary exploration missions, rovers will be required to autonomously traverse challenging environments. Much of the previous work in robot motion planning cannot be successfully applied to the rough-terrain planning problem. A model-based planning method is presented in this paper that is computationally efficient and takes into account uncertainty in the robot model, terrain model, range sensor data, and rover path following errors. It is based on rapid path planning through the visible terrain map with a simple graph-search algorithm, followed by a physics-based evaluation of the path with a rover model. Simulation results are presented which demonstrate the effectiveness of the method presented.

ICRA Conference 1999 Conference Paper

Shaped Objects: With Application to CZ Semiconductor Manufacture

Vivek A. Sujan 0002
Steven Dubowsky

A robotic system is being developed to automate the crucible packing process in CZ semiconductor wafer production. It requires the delicate manipulation and packing of highly irregular polycrystalline silicon nuggets, into a fragile fused silica crucible. For this application, a dual optical 3D surface geometry measuring system that uses active laser triangulation has been developed and successfully tested. One part of the system measures the geometry profile of a nugget being packed and the other the profile of the nuggets already in the crucible. A resolution of 1 mm with 15 KHz sampling frequency is achieved. Data from the system is used by a packing algorithm to determine optimal nugget placement. The system is shown to achieve high production rates, required precision and cost effectiveness.

ICRA Conference 1998 Conference Paper

A Base Force/Torque Sensor Approach to Robot Manipulator Inertial Parameter Estimation

Guangjun Liu
Karl Iagnemma
Steven Dubowsky
Guillaume Morel

A practical method is proposed for estimating the inertial parameters of robot manipulators with substantial unmodeled joint friction and actuator dynamics. The manipulator is mounted on a six-axis force/torque sensor. Sensor measurements and joint velocities recorded during manipulator motion are used to identify the inertial parameters. The unmodeled joint friction and actuator dynamics do not degrade the estimation results, as in conventional methods. The estimation algorithm does not require difficult-to-measure acceleration measurements. Experimental results presented show that an accurate estimation of inertia parameters is attainable. Since the sensor is external to the manipulator, the same sensor can be used for parameter estimation for a number of different systems.

ICRA Conference 1998 Conference Paper

Physics-Based Planning for Planetary Exploration

Shane Farritor
Hervé Hacot
Steven Dubowsky

Recently a planetary rover returned important scientific information from Mars. More ambitious missions are planned. New planning methods are required that allow rovers to explore challenging areas with a high level of autonomy. This paper presents a planning methodology based on a physics-based model of the rover and environment. Plans are developed that allow a rover to perform a mission while explicitly considering constraints such as power, actuator, wheel slip, and vehicle stability limits. Results obtained from detailed rover simulations are presented.

ICRA Conference 1997 Conference Paper

A systematic error analysis of robotic manipulators: application to a high performance medical robot

Constantinos Mavroidis
Steven Dubowsky
Ph. Drouet
J. Hintersteiner
J. Flanz

A systematic methodology to calculate the end-effector position and orientation errors of a robotic manipulator is presented. The method treats the physical error sources in a unified manner during the system's design so that the effect they have on the end-effector positioning accuracy can be compared and the dominant sources identified. Based on this methodology, a computer program has been developed that can perform the error analysis on any serial link manipulator. This methodology and the software are applied here to the error analysis of a six degree of freedom high performance medical manipulator, for positioning in proton therapy.

ICRA Conference 1996 Conference Paper

A systems-level modular design approach to field robotics

Shane Farritor
Steven Dubowsky
Nathan Rutman
Jeffrey Cole

Long development times and high costs prevent robots from being practical for use in many important field missions. Here a modular design approach is proposed to produce a rapidly deployable low cost field robotic system. An inventory of components such as actuated joints, links, power supplies, and software modules are assembled to produce a field robotic system for a specified task. The proposed design method uses a hierarchical selection process combined with a genetic algorithm to select a robot configuration and action plan for a given task. This method is applied to an inspection task required for the preservation of the USS Constitution, an historic naval ship.

ICRA Conference 1996 Conference Paper

Impact dynamics of Space long reach manipulators

Kazuya Yoshida
Constantinos Mavroidis
Steven Dubowsky

The problem of impact dynamics of Space robotic systems that consist of a rigid manipulator supported by a flexible deployable structure is addressed. Due to joint back-drivability and the dynamic coupling between the manipulator and its supporting structure, unknown motion of the system occurs after it makes impulsive contact with the environment. A method that uses the system's dynamic model is proposed to estimate the motion of the system after impact. This method which can be used to find ways to minimize the impact effect and vibrations of the supporting structure due to impact, is verified experimentally using the MIT Vehicle Emulation System (VES II). The experimental results show that the impact force and the system motion after impact can be reduced if the manipulator configuration prior to impact and the controller gains are properly selected.

ICRA Conference 1996 Conference Paper

The precise control of manipulators with joint friction: a base force/torque sensor method

Guillaume Morel
Steven Dubowsky

Joint friction is a major problem in accurately controlling robot position during manipulator tasks involving small and slow motions. Previous research in this field suggests the use of either complex modeling and identification techniques, or expensive and delicate torque sensors that must be integrated into the manipulator. This paper proposes a simple, cost-effective method for compensating the effect of joint friction, which utilizes a six-axis force/torque sensor mounted on the base of the manipulator. From the base wrench measurements, the joint torques are estimated and fed back through a torque controller, that virtually eliminates friction and gravity effects. With such high-quality torque control, a simple PD position controller is sufficient to provide high precision motion control even at very low speed and small motions. Theoretical and practical aspects of the torque estimation are first discussed. Next, the control design and tuning is shown. Experimental results for an industrial Puma manipulator, with high Coulomb friction in its gear trains, show the effectiveness of the method. The achieved precision is substantially greater than for conventional methods and approaches the resolution of the Puma's encoders.

ICRA Conference 1996 Conference Paper

Vibration control of deployment structures' long-reach space manipulators: The P-PED method

Miguel A. Torres
Steven Dubowsky
Attilio Pisoni

This paper presents a control method called the pseudo-passive energy dissipation (P-PED) method. The P-PED method is a closed-loop control scheme for increasing the overall damping characteristics of an elastically-mounted space manipulator system. It reduces degrading base vibrations resulting from external disturbances or motion of the manipulator, thereby decreasing the time necessary to perform maneuvers. A methodology for computing the optimal P-PED gains is presented. Experimental results are presented which show that the P-PED method is viable for practical implementation.

IROS Conference 1995 Conference Paper

Inferred end-point control of long reach manipulators

Constantinos Mavroidis
P. Rowe
Steven Dubowsky

The problem of the end-point control of long reach manipulator systems, consisting of a dexterous manipulator carried by deployable structures, is addressed. Such systems can be important where a manipulator must perform a task in a difficult to reach location. Power line maintenance systems and the Space Station Freedom's external maintenance robot are examples. Their supporting deployable structures can exhibit substantial vibrations, making the system very difficult to control. Here, a sensor based control algorithm, called inferred end-point control is proposed. Simulation and experimental results show that it yields stable and accurate manipulator end-effector positioning control despite of vibrations of the system's supporting structure using easily obtained strain measurements.

ICRA Conference 1994 Conference Paper

A Coordinated Jacobian Transpose Control for Mobile Multi-Limbed Robotic Systems

Craig Sunada
Dalila Argaez
Steven Dubowsky
Constantinos Mavroidis

This analytic and experimental study proposes a control algorithm based on Jacobian control for coordinated position and force control for autonomous multi-limbed mobile robotic systems. The technique is called coordinated Jacobian transpose control, or CJTC. Such position/force control algorithms will be required if future robotic systems are to operate effectively in unstructured environments. Generalized control variables, GCV's, express in a consistent and coordinated manner the desired behavior of the forces exerted by the multi-limbed robot on the environment and a system's motions. The effectiveness of this algorithm is demonstrated in simulation and laboratory experiments on a climbing system. >

IROS Conference 1994 Conference Paper

A laboratory test bed for space robotics: the VES II

Steven Dubowsky
William Durfee
Thomas Corrigan
Andrew Kuklinski
Uwe Müller

The dynamic interaction between a space robotic manipulator and its base in micro-gravity can make it difficult to control and lead to system performance degradation. Control and planning algorithms proposed in the past to compensate for this dynamic interaction have lacked sufficient experimental evaluation. A laboratory test bed is described which was developed and built to emulate the dynamic behavior of space robotic systems and investigate proposed planning and control algorithms. Two methods for removing the effects of gravity in the laboratory are presented. Experimental results demonstrate the effectiveness of this test bed in studying the dynamic coupling between a space manipulator and its spacecraft. >

ICRA Conference 1994 Conference Paper

Path-Planning for Elastically-Mounted Space Manipulators: Experimental Evaluation of the Coupling Map

Miguel A. Torres
Steven Dubowsky
Attilio Pisoni

The Coupling Map has been proposed as an analytical tool to describe the dynamic interaction between space manipulators which are either elastically mounted or carried by free-flying spacecraft. The Coupling Map has yielded a number of path-planning algorithms which have been successfully demonstrated in simulation to improve system performance. This paper presents an experimental evaluation of the Coupling Map and some of its path-planning algorithms. These experimental results show that the Coupling Map based path-planning algorithms are valid and viable candidates for practical implementation on space manipulator systems. >

ICRA Conference 1992 Conference Paper

Motion planning of mobile multi-limb robotic systems subject to force and friction constraints

Akhil Madhani
Steven Dubowsky

A method is presented to generate motions for a class of multilimb robotic systems enabling them to apply large static forces over large ranges of motion without saturating actuator effort limits, system-environment friction constraints, kinematic joint limits, or geometric workspace obstacles. The approach, termed the force-workspace (FW) approach, maps these constraints into the system C-space to form constraint obstacles using a recursive subdivision process. To generate motions along which actuator efforts can be specified without violating system constraints, paths are planned that avoid these constraint obstacles. The method permits the shape of the paths to be controlled using any configuration-dependent performance criterion. The FW approach was applied to a proposed three-limb planar climbing robot whose task is to climb upwards between two vertical walls by pushing outwards to generate frictional support. >

ICRA Conference 1992 Conference Paper

The experimental performance of a mobile manipulator control algorithm

Norbert Hootsmans
Steven Dubowsky
Patrick Z. Mo

Results of an experimental study of a motion control algorithm for mobile manipulators are presented. The dynamic interactions between a mobile manipulator and its vehicle are shown to lead to poor performance when a conventional fixed-base controller, which neglects these interactions, is used. The mobile manipulator control algorithm, which accounts for dynamic vehicle motions caused by manipulator motions, is shown to be stable and to perform well, while using only limited sensory data, such as would be practically available in highly unstructured field environments. >

ICRA Conference 1991 Conference Paper

Coordinated manipulator/spacecraft motion control for space robotic systems

Evangelos Papadopoulos
Steven Dubowsky

The coordinated control of space manipulators and their spacecraft is investigated. The dynamics of free-flying space robotic systems are written compactly as functions of the system barycentric vectors. A control technique is developed that includes requirements on a spacecraft's position and orientation as well as on its manipulator. This control scheme has the double advantage of allowing a system's motion to be planned to avoid impacts with is environment, and of maintaining a favorable manipulator configuration during the end-effector's motion. In addition, since a system's spacecraft can be moved, the workspace of its manipulator becomes unlimited. A transposed-Jacobian type controller with inertial feedback is developed, and an example is used to demonstrate this technique. >

ICRA Conference 1991 Conference Paper

Large motion control of mobile manipulators including vehicle suspension characteristics

Norbert Hootsmans
Steven Dubowsky

Conventional fixed-base controllers are shown not to perform well on mobile manipulators due to the dynamic interactions between a manipulator and its vehicle. An extended Jacobian transpose control algorithm is developed to improve the performance of such manipulator systems. It is shown to perform well in the presence of modeling errors and the practical limitations imposed by the sensory information available for control in highly unstructured field environments. >

ICRA Conference 1990 Conference Paper

On the nature of control algorithms for space manipulators

Evangelos Papadopoulos
Steven Dubowsky

A study of the characteristics of control algorithms that can be applied to the motion control of space manipulators is reported. The results obtained show that nearly any control algorithm that can be applied to conventional terrestrial fixed-base manipulators, with a few additional conditions, can be directly applied to free-floating space manipulators. Barycenters are used to formulate efficiently the kinematic and dynamic equations of free-floating space manipulators. A control algorithm for a space manipulator system is designed to demonstrate the value of the analysis. >

ICRA Conference 1989 Conference Paper

A method for estimating the mass properties of a manipulator by measuring the reaction moments at its base

Harry West
Evangelos Papadopoulos
Steven Dubowsky
Hanson Cheah

Emulating on Earth the weightlessness of a manipulator floating in space requires knowledge of the manipulator's mass properties. A method for calculating these properties by measuring the reaction forces and moments at the base of the manipulator is described. A manipulator is mounted on a six-degree-of-freedom sensor, and the reaction forces and moments at its base are measured for different positions of the links of the manipulator as well as for different orientations of its base. A procedure is developed to calculate from these measurements some combinations of the mass properties of the manipulator. The mass properties identified are not sufficiently complete for computed torque and other dynamic control techniques, but do allow compensation for the gravitational load on the links of the manipulator, and for simulation of weightless conditions on a space emulator. The algorithm has been experimentally demonstrated on a PUMA 260 and used to measure the independent combinations of the sixteen mass parameters of the base and three proximal links of the manipulator. >

ICRA Conference 1989 Conference Paper

Planning mobile manipulator motions considering vehicle dynamic stability constraints

Steven Dubowsky
E. E. Vance

The high-speed motions of mobile manipulators can dynamically disturb their vehicles, even to the point where they can cause a vehicle to tip over. A planning method is presented which insures that such dynamic disturbances do not exceed the capabilities of a vehicle, and compromise its stability, while permitting a mobile manipulator to perform its tasks quickly. The method is an extension of an algorithm for fixed-base manipulators and has been implemented in a CAD system with extensive computer graphics. The technique can also determine if any proposed manipulator motion plan, optimal or conventional, results in dynamic forces which exceed the capabilities of a vehicle and result in either a statistically or dynamically unstable system. The technique is applied to a representative system in which there is significant friction between the vehicle and ground. The results suggest that the algorithm may be an effective planning tool for such mobile manipulators. The technique has also been found to be effective for planning the motions of spacecraft-mounted manipulators. >

ICRA Conference 1988 Conference Paper

Global time optimal motions of robotic manipulators in the presence of obstacles

Zvi Shiller
Steven Dubowsky

A practical method to obtain the global time optimal motions of robotic manipulators is presented. This method takes into account the nonlinear manipulator dynamics, actuator constraints, joint limits, and obstacles. Previously developed methods of optimizing manipulator motions along given paths and a local path optimization are utilized. A set of best paths is obtained first in a global search over the manipulator workspace, using graph search and hierarchical pruning techniques. These paths are used as initial conditions for a continuous path optimization to yield the global optimal motion. Examples of optimized motions of a six-degree-of-freedom manipulator, operating in a three-dimensional space with obstacles, are presented. >

ICRA Conference 1987 Conference Paper

On the dynamics of manipulators in space using the virtual manipulator approach

Z. Vafa
Steven Dubowsky

Robotic manipulators carried by future spacecraft are expected to perform important tasks in space, like servicing satellites. Such applications will encounter problems due to the dynamic coupling between the manipulator and the spacecraft. A Virtual Manipulator (VM) concept has been developed recently for the modelling of manipulators working in space. This paper shows that the VM facilitates planning and control of the motions of manipulators mounted on spacecraft, that minimizes the degrading consequences of manipulator/vehicle dynamic interactions. The VM is a new theoretical approach for the design and development of future space manipulator systems.

ICRA Conference 1986 Conference Paper

Time optimal trajectory planning for robotic manipulators with obstacle avoidance: A CAD approach

Steven Dubowsky
M. A. Norris
Zvi Shiller

A method is presented which finds the minimum time motions for a manipulator between given end states. The method considers the full nonlinear manipulator dynamics, actuator saturation characteristics, and accounts for both the presence of obstacles in the work space and restrictions on the motions of the manipulator's joints. The method is computationally practical and has been implemented in a Computer Aided Design (CAD) software package, OPTARM II, which facilitates its use. Examples of its application to a six degree-of-freedom articulated manipulator, performing tasks in a typical environment, are presented. The results show that substantial improvements in system performance can be achieved with the technique.

ICRA Conference 1985 Conference Paper

On the optimal control of robotic manipulators with actuator and end-effector constraints

Zvi Shiller
Steven Dubowsky

The motion of current industrial manipulators is typically controlled so that tasks are not done in a minimum time optimal manner. The result is substantially lower productivity than that potentially possible. Recently a computationally efficient algorithm has been developed to find the true minimum time optimal motion for a manipulator moving along a specified path in space that uses both the full nonlinear dynamic character of the manipulator and the constraints imposed by its actuators. A Computer Aided Design (CAD) implementation of the algorithm called OPTARM is described which can treat practically general six degree-of-freedom manipulators. Examples are presented which show OPTARM to be a useful design tool for manipulators, their tasks and work places. The algorithm is extended in OPTARM to include the constraints imposed by manipulator payloads and end-effectors.