Inertial sensor-based multiloop control of fast steering mirror for line of sight stabilization

Abstract

, "Inertial sensor-based multiloop control of fast steering mirror for line of sight stabilization," Opt. Eng. 55 (11) Abstract. 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.

MEMS Inertial Sensors-Based Multi-Loop Control Enhanced by Disturbance Observation and Compensation for Fast Steering Mirror System

“…Therefore, the FSM acceleration controlled model including a quadratic differential can be expressed as follows [9,15,21,23]: $G_a(s)=\frac{\ddot{\theta }(s)}{U(s)}=\frac{K}{\frac{s^2}{{\varpi }_n{}^2}+\frac{2\xi }{{\varpi }_n}s+1}\cdot \frac{s^2}{T_{e}s+1}$…”

“…The classical stabilization control structure of multi-loop feedback control in FSM system is shown in Figure 2 [9,15]. …”

“…To avoid the inaccurate control in acceleration closed loop, the acceleration controller is designed as follows [15]: $C_a=\frac{260}{s}\times \frac{0.0011s+1}{0.00092s+1}$…”

“…Therefore, the traditional PI controller can meet the velocity closed-loop and also the position closed-loop [15]. …”

“…To avoid the saturation of double integration, Tang designed the controller as a band-pass filter and combined a CCD and accelerometers to implement dual closed-loop control [14]. Tian used a CCD, gyroscopes and accelerometers to implement a three-closed-loop control model, and a lag controller was used to accomplish acceleration control, which improved the disturbance suppression performance powerfully [9,15]. But the error rejection ability of the FSM system is still not adequate when suffering some uncertain disturbances, because of the mechanical resonances, CCD time delay and the drift noise in MEMS inertial sensors [14].…”