Development of precision pointing controllers with and without vibration suppression for the NPS precision pointing hexapod

Abstract

Satellite optical payloads demand better vibration control and finer precision pointing than ever before. Fortunately, the Stewart-Gough platform offers the potential of accomplishing both of these simultaneously. Using the Precision Pointing Hexapod at NPS (a Stewart-Gough platform), several controllers for precision pointing, with and without vibration disturbances, were developed. Unlike the traditional means of pointing a hexapod, (i.e. sensing and controlling strut length to orient payload), this research used the payload orientation derived from payload mounted position sensors to determine orientation and provide feedback to the actuator controller. Small and large angle controllers were developed and evaluated for accuracy using static pointing and dynamic tracking tasks. The pointing controllers were then added to an Adaptive Disturbance Canceller and evaluated for pointing accuracy and vibration suppression performance given a single tone disturbance. The results showed a static pointing accuracy of Å 0.008Ê» and a dynamic pointing accuracy ranging from Å 0.05Ê» to Å 0.2Ê», depending on the size and speed of the circular trajectory. Vibration suppression down to the noise floor was achieved in all static orientations tested. As for dynamic circle-tracking performance, at least a 20 dB reduction in the fundamental disturbance was obtained without degradation in pointing accuracy.