A failure tolerant joint design 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 was studied. The mathematical model of the differential system was developed and the inherent nonlinear dynamic characteristics for the differential were reduced to linear state equations through variable substitutions. Other nonlinear phenomena in the system were also included in the model. Simulations were performed for various joint failure conditions, and results of these simulations demonstrated the capability of the drive system to sustain a single failure while remaining operational. A scaled-down hardware testbed was subsequently designed and built to validate the analytical results. The experimental failure transient responses were consistent with the simulation results. The test demonstrated a very useful design for a space-based robot joint which will be capable of sustaining a single failure and absorbing the failure disturbance, deactivating and locking-up the failed drive unit, and continuing to be operational with the remaining single drive mode