Fault-tolerant joint development for the Space Shuttle remote manipulator system: analysis and experiment

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