Spacecraft gimbal control system design for precision pointing applications must take into consideration a host of non-linear disturbance torques. Included in this category are cable restraint torques, cogging torques, magnetic drag, and bearing friction torques. Of these, bearing friction torque has the greatest impact on precision pointing. The more traditional approach for compensating the friction torque disturbance relies on laboratory measurement of friction torques and 'open loop' or feed forward compensation using the measured values. This is a satisfactory approach as long as one can assume that the boost, deployment and the orbital environments will not drastically alter the measured value. In this paper, methods of friction compensation which are based upon on-line friction torque estimation and corresponding control system adaptation are considered and compared with the open loop method. Note that only a single degree of freedom gimbal is considered; in practice this technique can be replicated for a multiple degree of freedom gimbal. The open loop compensator makes use of a friction torque model, fed by the commanded gimbal rate, to increase the Proportional plus Integral plus Derivative (PID) controller's commanded torque to overcome friction. Note that both methods accept acceleration commands, and make use of encoder measured gimbal angle in closing their loops through a PID control law.
Examination of adaptive control-based approaches to friction compensation in spacecraft gimbal control systems
Untersuchung einer adaptiv, geregelten Loesung der Reibungskompensation in Weltraum-Kreiselsteuerungs-Systemen
Proc. of the 24th IEEE Conf. on Decision and Control ; 1 ; 642-646
1985
5 Seiten, 7 Bilder, 2 Quellen
Conference paper
English
Spacecraft Attitude Control Using a Double-Gimbal Control Moment Gyro
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