The design and fabrication of electrostatic actuators for micro-mirror systems in telecommunications, scanning, and display applications has advanced enormously over the past few years. These advances were largely stimulated by the telecommunication bubble of the early 2000's. Early micro-mirror systems utilized parallel plate actuation schemes that suffered from inherent pull-in stabilities and required high operation voltages of several hundred Volts. The continuous need for micro-mirror systems that deflect at high angles with low voltage drives (< 50 V) have resulted in a number of solutions. Innovative techniques such as the utilization of parametric analog torque amplification, raised side electrodes that suppress pull-in and magnify torque, high energy density vertical comb drives, and mechanical motion multiplication schemes all contribute toward these goals. This paper reviews recent progress in this area and discusses current technical challenges.
This paper presents high-resolution control of torsional electrostatic micromirrors beyond their inherent pull-in instability using robust sliding-mode control (SMC). The objectives of this paper are two-fold - firstly, to demonstrate the applicability of SMC for MEMS devices; secondly - to present a modified SMC algorithm that yields improved control accuracy. SMC enables compact realization of a robust controller tolerant of device characteristic variations and nonlinearities. Robustness of the control loop is demonstrated through extensive simulations and measurements on MEMS with a wide range in their characteristics. Control of two-axis gimbaled micromirrors beyond their pull-in instability with overall 10-bit pointing accuracy is confirmed experimentally. In addition, this paper presents an analysis of the sources of errors in discrete-time implementation of the control algorithm. To minimize these errors, we present an adaptive version of the SMC algorithm that yields substantial performance improvement without considerably increasing implementation complexity.
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