Analysis of the post-fault behavior of robotic manipulators, An

Includes bibliographical references.Operations in hazardous or remote environments are invariably performed by robots. The hostile nature of the environments, however, increase the likelihood of failures for robots used in such applications. The difficulty and delay in the detection and consequent correction of these faults makes the post-fault performance of the robots particularly important. This work investigates the behavior of robots experiencing undetected locked-joint failures in a general class of tasks characterized by point-to-point motion. The robot is considered to have "converged" to a task position and orientation if all its joints come to rest when the end-effector is at that position. It is seen that the post-fault behavior may be classified into three categories: 1) The robot converges to the task position; 2) the robot converges to a position other than the task position; or 3) the robot does not converge, but keeps moving forever. The specific conditions for convergence are identified, and the different behaviors illustrated with examples of simple planar manipulators.This work was supported by Sandia National Laboratories under contract number AL-3011

Undetected locked-joint failures in kinematically redundant manipulators: a workspace analysis

Includes bibliographical references.Robots are frequently used for operations in hostile environments. The very nature of these environments, however, increases the likelihood of robot failures. Common failure tolerance techniques rely on effective failure detection. Since a failure may not always be successfully detected, or even if detected, may not be detected soon enough, it becomes important to consider the behavior of manipulators with undetected failures. This work focuses on developing techniques to analyze a manipulator's workspace and identify regions in which tasks, characterized by sequences of point-to-point moves, can be completed even with such failures. Measures of fault tolerance are formulated to allow for the evaluation of the workspace.This work was supported by Sandia National Labs under contract no. AL-3011 and by NSF under contract no. MIP-9708309

Failure tolerant teleoperation of a kinematically redundant manipulator: an experimental study

Includes bibliographical references (page 765).Teleoperated robots in harsh environments have a significant likelihood of failures. It has been shown in previous work that a common type of failure such as that of a joint "locking up," when unidentified by the robot controller, can cause considerable performance degradation in the local behavior of the manipulator even for simple point-to-point motion tasks. The effects of a failure become more critical for a system with a human in the loop, where unpredictable behavior of the robotic arm can completely disorient the operator. In this experimental study involving teleoperation of a graphically simulated kinematically redundant manipulator, two control schemes, the pseudoinverse and a proposed failure-tolerant inverse, were randomly presented under both nonfailure and failure scenarios to a group of operators. Based on performance measures derived from the recorded trajectory data and operator ratings of task difficulty, it is seen that the failure-tolerant inverse kinematic control scheme improved the performance of the human/robot system

Advancing automation and robotics technology for the Space Station Freedom and for the US economy

The progress made by levels 1, 2, and 3 of the Office of Space Station in developing and applying advanced automation and robotics technology is described. Emphasis is placed upon the Space Station Freedom Program responses to specific recommendations made in the Advanced Technology Advisory Committee (ATAC) progress report 10, the flight telerobotic servicer, and the Advanced Development Program. Assessments are presented for these and other areas as they apply to the advancement of automation and robotics technology for the Space Station Freedom

Real-time failure-tolerant control of kinematically redundant manipulators

Includes bibliographical references (pages 1115-1116).This work considers real-time fault-tolerant control of kinematically redundant manipulators to single locked-joint failures. The fault-tolerance measure used is a worst-case quantity, given by the minimum, over all single joint failures, of the minimum singular value of the post-failure Jacobians. Given any end-effector trajectory, the goal is to continuously follow this trajectory with the manipulator in configurations that maximize the fault-tolerance measure. The computation required to track these optimal configurations with brute-force methods is prohibitive for real-time implementation. We address this issue by presenting algorithms that quickly compute estimates of the worst-case fault-tolerance measure and its gradient. Comparisons show that the performance of the best method is indistinguishable from that of brute-force implementations. An example demonstrating the real-time performance of the algorithm on a commercially available seven degree-of-freedom manipulator is presented

An intelligent, free-flying robot

The ground based demonstration of the extensive extravehicular activity (EVA) Retriever, a voice-supervised, intelligent, free flying robot, is designed to evaluate the capability to retrieve objects (astronauts, equipment, and tools) which have accidentally separated from the Space Station. The major objective of the EVA Retriever Project is to design, develop, and evaluate an integrated robotic hardware and on-board software system which autonomously: (1) performs system activation and check-out; (2) searches for and acquires the target; (3) plans and executes a rendezvous while continuously tracking the target; (4) avoids stationary and moving obstacles; (5) reaches for and grapples the target; (6) returns to transfer the object; and (7) returns to base

NASA space station automation: AI-based technology review

Research and Development projects in automation for the Space Station are discussed. Artificial Intelligence (AI) based automation technologies are planned to enhance crew safety through reduced need for EVA, increase crew productivity through the reduction of routine operations, increase space station autonomy, and augment space station capability through the use of teleoperation and robotics. AI technology will also be developed for the servicing of satellites at the Space Station, system monitoring and diagnosis, space manufacturing, and the assembly of large space structures

Failure tolerant teleoperation of a kinematically redundant manipulator: an experimental study

Includes bibliographical references (page 880).Teleoperated robots in harsh environments have a significant likelihood of failures. It has been shown in previous work that a common type of failure such as that of a joint "locking up", when unidentified by the robot controller, can cause considerable performance degradation in the local behavior of the manipulator even for simple point-to-point motion tasks. The effects of a failure become more critical for a system with a human in the loop, where unpredictable behavior of the robotic arm can completely disorient the operator. In this experimental study involving teleoperation of a graphically simulated kinematically redundant manipulator, two control schemes, the pseudoinverse and a proposed failure-tolerant inverse, were randomly presented under both non-failure and failure scenarios to a group of operators. Based on performance measures derived from the recorded trajectory data and operator responses, it is seen that the failure tolerant inverse kinematic control scheme improved the performance of the human/robot system