An experimental investigation of actuators for space robots

Abstract

A two degree of freedom robot joint module was designed and built for the space environment, and evaluated in a thermal vacuum chamber at NASA's Johnson Space Center. The hypothesis was that servo dynamics would change across the wide temperature range of space, and a series of chamber experiments showed thermal adaptation is required to maintain response and stability over the EVA range of 223-373 K. A key finding was that control parameters selected for optimum dynamic response at room temperature were found to be inappropriate across the thermal vacuum range. At cold temperatures (233 K) the nominal gains were found to produce a critically damped response with large steady state error. At warm temperatures, the response was underdamped with significant overshoot, and at hot temperatures (353 K) the system went unstable, using gains that were optimal at room temperature. At each of seven thermal vacuum states, gains were found to deliver the desired dynamic response, and those settings were recorded.