Using Input Shaping to Minimize Residual Vibration in Flexible Space Structures

Input shaping is examined as a technique to reduce the residual vibration in flexible space structures. As part of a NASA program, a nonlinear threedimensional model of the Shuttle's Remote Manipulator System (SRMS) was used to test the interactions between feedback and feedforward control techniques. The problem of changing geometry systems was also examined in detail. As these systems move, their geometries change, and thus the system characteristics change. This often leads to problems with controlling such a structure. If a feedback controller is optimized for certain frequencies, then a large move encompassing many frequencies might lead to more residual vibration than usual. These systems also pose interesting problems for input shaping. An input shaper is usually designed for one main frequency. If that frequency is shifting during the move, what frequency do you shape for? This thesis addresses this problem. Results from using input shaping with feedback controllers on the SRMS show that input shaping does improve performance for small slews over just feedback control alone. For longer slews using a trapezoidal velocity profile, input shaping only helps if the settling criterion is very small. Runs done using the Draper Remote Simulation showed that the response of the system depended very heavily on what type of payload was being moved. For the unloaded case, the SRMS settled very quickly and a quick, insensitive input shaper improved the performance the most. For a midsize payload, the SRMS frequencies are much lower and performance is thus degraded. A more insensitive input shaper gave the best performance increase here. For a very large payload, the system frequencies are around 0.4 Hz. The unshaped SRMS response settled very slowly, but input shaping could not overcome the nonlinearities and did not provide any performance increase. Thesis Supervisor: Warren Seering Title: Professor of Mechanical Engineering