Space Station is an international joint development project sponsored by the United States, Canada, Europe, and Japan. The Canadian designed special purpose dexterous manipulator (SPDM) is scheduled to maintain the Space Station and perform the on orbit replaceable unit (ORU) removal/insertion tasks. Johnson Space Center (JSC) of National Aeronautics and Space Administration (NASA) has been assigned as the lead center to integrate all Space Station sub-systems and to perform the ground testing of Space Station ORUs for robotic compatibilities. The Track Task robotic testing facility for ORUs was established for this purpose. The facility consists of a pair of hydraulic manipulators, special end-effectors and tools, video sub-system, multiprocessors controller, and the display and control workstation. This paper discusses the design and implementation of this facility.>

Describes a hierarchical robot controller designed and built at NASA's Johnson Space Center. The robot used is a six degree-of-freedom hydraulic manipulator equipped with joint position sensors and a wrist force/torque sensor. The objective of the project is to emulate the performance characteristics of the Space Station's Special Purpose Dexterous Manipulator (SPDM), which will perform various telerobotic external maintenance tasks. Some features implemented in the controller include a resolved position control algorithm, force/moment accommodation, and gravity compensation. This multiple-processor control system is divided, by processor, into a servo controller, a force/moment data filter, a Cartesian-space controller, a host/traffic controller and a network communication controller. This paper describes the functions of each individual processor and the design of their inter-processor communication.>

The feasibility of space-based fault-tolerant robot joint design with a dual-motor, single-output differential-based mechanical drive system is investigated. The mathematical model of the differential system is developed, and the inherent nonlinear dynamic characteristics for the differential are reduced to linear state equations through variable substitutions. Nonlinear phenomena such as gearbox forward/backdrive efficiency, motor friction/stiction, and torque limiting are included. Simulations have been performed for various joint failure conditions. A scaled-down differential testbed has been designed and built to validate the analytical results. Simulation and test results demonstrate that the design is capable of sustaining a single failure and absorbing the failure disturbance, and continuing to be operational with the remaining single drive mode.>

An analysis of an improved joint drive system for the shuttle remote manipulator system (SRMS), capable of sustaining a single actuator failure, is presented. This system employs a differential gear train with dual input actuators driving a single load. The mathematical model for the drive system includes: gearbox flexibility and damping, motor damping, high gear ratio, and high load impedance. The nonlinear dynamic equations for the system reduce to linear form without approximation. Effects of gearbox placement and load sharing are examined. A feedback system that improves overall response is discussed. Simulation results show that the design is able to sustain a single electromechanical actuator failure without impeding the joint's performance. Plans for a hardware implementation to verify the system are given.>