In a charge-coupled device (CCD)-based fast steering mirror (FSM) tracking control system, high control bandwidth is the most effective way to enhance the closed-loop performance. However, the control system usually suffers a great deal from mechanical resonances and time delays induced by the low sampling rate of CCDs. To meet the requirements of high precision and load restriction, fiber-optic gyroscopes (FOGs) are usually used in traditional FSM tracking control systems. In recent years, the MEMS accelerometer and gyroscope are becoming smaller and lighter and their performance have improved gradually, so that they can be used in a fast steering mirror (FSM) to realize the stabilization of the line-of-sight (LOS) of the control system. Therefore, a tentative approach to implement a CCD-based FSM tracking control system, which uses MEMS accelerometers and gyroscopes as feedback components and contains an acceleration loop, a velocity loop and a position loop, is proposed. The disturbance suppression of the proposed method is the product of the error attenuation of the acceleration loop, the velocity loop and the position loop. Extensive experimental results show that the MEMS accelerometers and gyroscopes can act the similar role as the FOG with lower cost for stabilizing the LOS of the FSM tracking control system.

In the ground-based astronomical telescope, the imaging quality is usually affected by tip-tilt vibrations induced by the telescope structure. Long exposure time of the image sensor is usually required for a good signal-to-noise ratio, which brings the amount of time delays into the control loop of the tip-tilt mirror. Thus, a low control bandwidth is insufficient to compensate telescope vibrations. In this paper, an improved disturbance observer (DOB) control based on only the image sensor is proposed to reject structural vibrations. This new DOB controller is added into the original loop in the tip-tilt mirror control system, so the closed-loop performance can be optimized by designing an appropriate Q-filter. An improved Q-filter is presented to reject large-magnitude vibrations and also to reduce amplifications induced by this controller at nondisturbance frequencies. This proposed controller can achieve a satisfying result in vibration mitigations when vibration frequencies are provided to design the Q-filter. Furthermore, in the tilt-tilt mirror control system, this improved DOB is not restricted by an accurate model such that noise in the loop cannot provide serious influence on vibration mitigation. Both simulations and extensive experiments are carried out to demonstrate that the DOB can earn an extra improvement on the control performance in comparisons with the conventional feedback controller.

In the charge-coupled device (CCD)-based tracking control system of fast steering mirrors (FSMs), high control bandwidth is the most effective method to enhance closed-loop performance, which, however, usually suffers a great deal from time delay induced by a low CCD sampling rate. Moreover, mechanical resonances also limit high control bandwidth. Therefore, a tentative approach to implementing a CCD-based tracking control system for an FSM with inertial sensor-based cascade feedback is proposed, which is made up of acceleration feedback, velocity feedback, and position feedback. Accelerometers and gyroscopes are all the inertial sensors, sensing vibrations induced by platforms, in turn, which can contribute to disturbance supersession. In theory, the acceleration open-loop frequency response of the FSM includes a quadratic differential, and it is very difficult to compensate a quadratic differential with a double-integral algorithm. A lag controller is used to solve this problem and accomplish acceleration closed-loop control. The disturbance suppression of the proposed method is the product of the error attenuation of the acceleration loop, the velocity loop, and the position loop. Extensive experimental results show that the improved control mode can effectively enhance the error attenuation performance of the line of sight (LOS) for the CCD-based tracking control system.

We propose a simple PID (proportional integral differential)-I controller to improve the performance of a CCD-based (charge coupled device) control system for fast steering mirror, which consists of adding an integrator in series to a PID controller, resulting in two integrators in the control loop. The conditions for implementing the PID-I controller into the control system of the fast steering mirror are presented mainly in terms of the closed-loop stability and error attenuation. A model of CCD-based control loop is made to analyze the characteristics of the control loop. Although the error attenuation bandwidth with PID-I controller is a little smaller than that with an integral controller, the error attenuation at low frequency is greatly enhanced. The experimental results are in accordance with the theoretical analysis.

High control bandwidth is usually restricted in a finite sampling rate of a charge-coupled device (CCD)-based tracking loop, which hinders a good closed-loop performance. Conventionally, a rate feedforward controller is usually used to improve the control performance; however, it is restricted by the line-of-sight (LOS) rate, which is required to be estimated due to only the LOS error available in the CCD-based tracking control system. Besides that, it is also affected by the inverse of the control model. A new error-based feedforward (EBF) control mode is proposed to overcome these difficulties. Due to being plugged into an existing feedback control loop, the closed-loop performance of the CCD-based control system can be minimized by optimizing a Q-filter. The closed-loop stability and robustness with this EBF control system are investigated on the condition of the gain margin and the phase margin of the open-loop transfer function. Furthermore, this paper proposes a new criterion to enhance the robustness of the EBF control system and reveals the sensitivity function property. Because of not being restricted by an accurate model, this new feedforward controller cannot lead to a compromise between error attenuation and noise propagation in the control loop. Simulations and experiments are both used to testify the effectiveness of the improved control mode.