POINTING CONTROL AND VIBRATION SUPPRESSION OF A SLEWING FLEXIBLE FRAME

An analytical and experimental control system design for a slewing fra me containing active members is presented. This testbed is a model for the slewing of dynamically complex structures such as solar arrays an d space trusses. Two of the frame's passive members are replaced by ac tive elements that contain piezoceramic material. The active members a re integral in suppressing vibrations because the torsional vibrations are difficult to control with the slewing actuator. The design is per formed with a finite element-based model that contains significant err or; therefore, both control loops must have performance and stability robustness. Suppression of the torsional motion is accomplished with a n active member in a positive position feedback (PPF) loop designed wi th frequency domain and Nyquist techniques. The pointing controller is designed using mu synthesis to maximize the robustness of the control law. This compensator slews the structure with a two second settling time, 7 % overshoot, and less than a 2 % steady-state error due to sta tic friction. With the supplementary PPF control loop closed, the sett ling time of the torsional vibrations is reduced from over 30 s to app roximately 6 s. Thus, vibration suppression and satisfactory step resp onse is obtained using robust control laws in multiple feedback loops.