Control of a MEMS Fast Steering Mirror With Improved Quasi-Static Performance

Abstract

This paper presents a control algorithm for a novel micro-electro-mechanical system (MEMS) fast steering mirror (FSM), whose performance is poor in open loop control mode. Based on the characterization and parameter identification of MEMS FSM, an improved double step algorithm is proposed to shorten the settling time and improve its quasi-static working bandwidth. A characterization system is set up, in which optical sensor is utilized to monitor the tilt angle of FSM. The performance of the FSM in the time and frequency domain are both acquired, while the key parameters of the FSM model are identified. Finally, the closed-loop experiments for the FSM are done to verify the effectiveness of the control algorithm. The experimental results demonstrate that the settling time (98%) of the FSM is effectively reduced from 398 ms to 0.4 ms under the improved double step control mode, which has a better tracking performance and tiny overshoot, comparing with the open loop control mode.INDEX TERMS MEMS, micro mirror, tracking control, improved double step algorithm I. INTRODUCTIONFast steering mirror (FSM) is an optical device for quickly and accurately adjusting the direction of the reflected laser, which, as a significant component, can therefore acquire and track the optical signal to provide a stable communication link [1][2][3][4][5] . FSM is mainly divided into voice coil motor FSM, piezoelectric ceramic FSM, and MEMS FSM. The eigenfrequency of the voice coil motor FSM is usually in the range of 100 Hz to 700 Hz [6] . Therefore, the voice coil motor is prone to resonate. The hysteresis is a difficulty for piezoelectric ceramic FSM control, which will become pronounced, especially under high driving voltages [7] . This characteristic leads to the nonlinearity of FSM, so a compensation algorithm is necessary to be implemented in the driver [8] . Micro-electro-mechanical system (MEMS) mirrors, as a class of integrated chip-based mirrors, can be flexibly designed in materials and structure for different applications. Thus, the MEMS FSM can be designed to avoid some of these difficulties in a certain