Robust digital control of nonlinear microelectro-mechanical actuators using sliding-mode control

This paper presents an overview of high precision robust digital control of MEMS nonlinear actuators, in particular torsional electrostatic actuators, using sliding-mode control [N. Yazdi et al. (2003), H. Sane et al. (2004)]. Sliding-mode control enables compact realization of a robust controller tolerant of device characteristic variations, nonlinearities and many types of inherent instabilities. Application of 1^st order SMC to the control of dual-axis torsional actuators beyond their pull-in limit is demonstrated. Also a modified SMC scheme which uses adaptive switching of the sliding-mode variable differential gain to improve control precision is presented. The modified scheme has resulted in average reduction of 44-56% in output chatter and 70-91% when used for control of several 2-axis gimbaled beam steering micromirrors with a wide range of mechanical characteristics.