Acceleration feedback of a CCD-based tracking loop for fast steering mirror

Abstract

In the control system of a CCD-based tracking loop for a fast steering mirror (FSM), the most effective method often employed to improve pointing performance is to increase high gain of the control system for a high bandwidth, which, however, usually suffers a great deal from a low CCD sampling rate and the mechanics of the FSM. Moreover, the amount of time delay engendered by sampling and data processing can significantly reduce the performance of a closed-loop system. Therefore, a tentative approach to the implementation of a CCD-based tracking control system with acceleration feedback is proposed. In theory, the position open loop is made of double integrators with a high bandwidth of the acceleration feedback loop; in fact, however, the acceleration open loop of the FSM response includes a quadratic differential, and it is very difficult to compensate a quadratic differential with an integral algorithm. To solve this problem, a novel acceleration closed system such as a bandpass filter is proposed. The position is reconstructed into a simple first-order filter instead of a third-order control system. In addition experimental results show that the acceleration feedback proposed here can effectively enhance the bandwidth of the closed-loop system and its trajectory tracking and pointing performance. (C) 2009 Society of Photo-Optical Instrumentation Engineers. [DOI: 10.1117/1.3065500]