Robust Controller Design for an Electrostatic Micromechanical Actuator

In this paper, a robust feedback controller is developed on an electrostatic micromechanical actuator to extend the travel range of it beyond pull-in limit. The actuator system is linearized at multiple operating points, and the controller is constructed based on the linearized model. Two kinds of controller designs are developed for set-point tracking of the actuator despite the presences of sensor noise and external disturbance. One of them is a regular fourth order Active Disturbance Rejection Controller (ADRC) and is able to achieve 97% of the maximum travel range. And the other one is a novel multi-loop controller with a second order ADRC in an inner loop and a PI controller in an outer loop. The multi-loop controller can achieve 99% of the maximum travel range. Transfer function representations of both controller designs are developed. The controllers are successfully applied and simulated on a parallel-plate electrostatic actuator model. The simulation results and frequency domain analyses verified the effectiveness of the controllers in extending the travel range of the actuator, in disturbance rejection, and in noise attenuation.