Force Accommodation Control Of The Space Shuttle Remote Manipulator System: Experimental Results

Abstract

Force accommodation control technology has been applied to the Shuttle Remote Manipulator System (SRMS). Unique characteristics of the SRMS such as seuctural jlexibilities, large payloads, servo saturation limits, joint friction, low sampling rate, and limited access to rhe servo interface have been shown to influence the stability, limit the peqormance and dictate ihe type of a candidate force feedback control scheme. This paper first describes the linear analysis for a single link SRMS model where the cffects of gearbox flexibility, link flexibility, payload and environment stifness are discussed. A jbrce control law is then designed based on this model using classical control appproaches. Next, the effects of non-linearities, such as: gearbox backlash, friction, and servo saturation limits, on rhe stability of the control law are discussed using describing function technique. The control is then applied to a real-time SRMS simulation facility, called the Space System Automated Integration and Assembly Facility (SSAIAF) at the Johnson Space Center. The facility houses a 6-DOF Stewart table that is controlled via a man-in-the-loop to follow a real-time, high fidelity iiynamic model of the SRMS. Docking hardware is mounted on the table to provide real contact jbrces for studying the Stationlshuttle docking task. Force feedback control was implemented and tested for one of the docking scenarios. Experimental results are presented in the last section.