Lonnie J. Love

Environment estimation for enhanced impedance control

Impedance control is a popular method of controlling the dynamic response a robot has to external forces. The advantage of such a control paradigm is the ability to manipulate in both unconstrained and constrained environments. Unlike hybrid control methods that attempt to control forces and motions in orthogonal directions, impedance control consists of a single control law that accommodates external forces. One problem associated with such a controller is the selection of the robots target impedance. This paper illustrates, through analysis and experimentation, the shortcoming of improper target impedance selection. The integration of a real time estimate of the robots environment with the impedance controller resolves this problem. Experimental results illustrate improved performance during the transition from unconstrained to constrained manipulation.

A novel teleoperated long-reach manipulator testbed and its remote capabilities via the Internet

During the 1995 DOE Robotics Forum at Albuquerque, New Mexico, Georgia Techs Intelligent Machine Dynamics Laboratory demonstrated remote display capabilities of its telemanipulated long-reach manipulator testbed through the Internet. This paper describes the testbed and addresses the methods, limitations, and capabilities of remote operations.

A comparison of joint control algorithms for teleoperated pick and place tasks using a flexible manipulator

This paper presents initial results of an on going study of robot control algorithms used for teleoperation of long reach manipulators. The focus of the paper is the effect of the slave robot control algorithm on the performance of a teleoperation schemes that uses long reach, flexible manipulators. This study investigates the influence of PD, PD with input shaping, and PD with modified command filtering on pick and place teleoperation tasks. Data from 90 trials using 6 operators is used in an attempt to identify any increase in performance resulting from the use of any of the above control schemes. The results of this investigation indicate an increase in performance, based upon a combination of interaction forces and task execution time, of teleoperated pick and place tasks when a flexible robot uses either PD with input shaping or PD with modified command filtering.<<ETX>>

Waste tank cleanup manipulator modeling and control

Waste tank cleanup is a current application area for robotics in the United States. As a result of tank access restrictions, designs for several current waste cleanup manipulator systems have long links with small cross-sections and variable lengths. In addition, as a result of anticipated payload capacity, these manipulator designs are hydraulically actuated. This paper takes two approaches to investigating the problem of the control of manipulators having variable-length flexible links and hydraulic actuators. First, a simulation of a hydraulically actuated, 2-DOF, polar (r-/spl Theta/), manipulator with one flexible link is used to illustrate the problem of applying controllers successfully developed for hydraulically actuated, fixed-length flexible manipulators to hydraulically-actuated, variable-length systems. Next, based upon the simulation results, simple controller modifications are proposed and are shown to work on a full-scale experimental test bed. Motion control of hydraulically actuated, variable-length flexible-link manipulators is the focus of this paper.

Adaptive Impedance Control for Bilateral Teleoperation of Long Reach, Flexible Manipulators

Abstract Current applications in the field of telerobotics, such as space based assembly and nuclear waste remediation, require the use of long reach manipulators. These robots are characterized by their large workspace and reduced mass. Unfortunately, this reduction in mass increases structural compliance making these robots susceptible to vibration. Until recently, no attempt has been made to provide the operator any type of force reflection due to the compliance of the slave robot. This research addresses the control of bilateral teleoperation systems that use long reach flexible manipulators. Experiments indicate that the compliance of the slave robot directly affects the stability of the teleoperation system. Our study suggests that this may be controlled by increasing the damping on the master robot. This increase in target damping increases the effort an operator must exert during the execution of a task. To circumvent this limitation, the authors propose an adaptive impedance control paradigm. A new teleoperation strategy adapts the target impedance of the master robot to variations in the identified impedance of the remote environment coupled to the slave robot. Experiments suggest increased performance due to a decrease in the power the operator must provide during the execution of a task.

Command filtering and path planning for remote manipulation of a long reach flexible robot

We focus on the fusion of autonomous and teleoperated commands. This combination provides full use of the robots workspace without requiring large motion amplification between a master and slave robot. Combining autonomous and teleoperated commands provides the potential for large variations in the commanded momentum of the flexible robot. These variations excite the lightly damped, low resonant frequencies associated with these manipulators. Two techniques are proposed to reduce the vibration during sudden stops in the commanded motion of a flexible manipulator. First a new command filtering approach that permits shorter delay times than standard input shaping methods is presented. Next, we propose dynamic alteration of the desired trajectory. Our investigation shows that filtering techniques exhibit an oscillatory response, more so than standard PD control algorithms, during hard stopping conditions. However the shorter time delay filtering algorithm has less vibration than standard input shaping techniques. Furthermore, any vibration may be eliminated by commanding the robot to decelerate instead of immediately stopping the motion.

Modeling Teleoperated Tank Waste Removal at Oak Ridge National Laboratory

ABSTRACTOne of the pervasive problems facing the Department of Energys (DOE) national research facilities are the large volumes of stored radioactive waste. Historically, much of this waste, generated during the cold war, is contained in under ground storage tanks. Unfortunately, many of these tanks are showing signs of aging and fatigue. Subsequently, there is an aggressive DOE program directed at identifying existing technologies that can safely remove material from these facilities for storage in more stable environments. Oak Ridge National Laboratory (ORNL), teaming with industry and other laboratories, has designed, developed, and integrated a remotely operated waste removal system. This manuscript describes this system as well as the modeling and simulation effort performed prior to system integration and operation. The modeling effort includes a novel dynamic model of multiple robots coupled by an elastic hose. The result of a simulation study, presented in the latter part of the manuscript, provi...