Compensating for some errors related to time delay in a charge-coupled-device-based fast steering mirror control system using a feedforward loop

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Abstract
In many control systems, the most effective method to improve the performance of the closed-loop system is by enhancing the gain of the control system, which results in a wide control bandwidth. However, in the control system of a charge-coupled-device-based tracking loop for a fast steering mirror, the bandwidth of the closed loop is greatly limited by the large time delay of the TV tracker. Additionally, the time delay leads to instability of the system when the closed-loop system has high gain. We propose a new feedforward control to compensate some errors related to the time delay of the tracker, meanwhile improving the performance of the closed-loop fast steering mirror system. The control structure we propose includes two closed loops; a tracking loop and a fast position loop. The fast position loop is produced using an eddy current sensor, and the tracking loop is the outer loop, enveloping the fast position loop. The feedforward signal is estimated from the signal of the eddy current sensor and the TV tracker, which is added to the input of the fast position loop. Experimental results show that our proposed feedforward system can effectively enhance trajectory tracking and pointing performance.