This paper addresses the control problem of extending the travel range of a MEMS electrostatic actuator through a closed-loop voltage control scheme. Since the electrostatic actuator is inherently unstable due to its pull-in limit, one of the major control goals is to stabilize the actuator system beyond the limit. In addition, the controller has to be robust against external disturbances and noise. After comparing and analyzing the advanced controllers being reported, an active disturbance rejection controller (ADRC) is originally employed to the micro actuator to solve the control problem. The ADRC mainly consists of an extended state observer (ESO) and a PD controller. The ESO is used to estimate system states and the external disturbance, which can be taken as an augmented state of the ESO. The PD controller based on the observed states drives the displacement output of the actuator to a desired level. The ADRC is successfully simulated onto a parallel-plate electrostatic actuator. The simulation results verified the effectiveness of the controller through extending the travel range of the actuator to 99% of the initial gap between two plates in the presences of noise and disturbance.
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