Full-gap tracking system for parallel plate electrostatic actuators using closed-loop control

Abstract

Bi-directional full-gap tracking on parallel-plate electrostatic actuators using closed-loop control is demonstrated in this paper. On-Off control is explored, where the actuator position is controlled by actuating or releasing the actuator based on the actual position (weather it is above or below the desired position). Noise and delays introduced by the readout circuit compromise the performance of this control law working at 5MHz sampling frequency. A Proportional-Integral-Derivative control law with feedback linearization is also implemented. This second control law is more complex than the on-off control and requires extensive data processing. In addition, in order to effectively control the actuator, the structure characteristics need to be available as well as the response of the readout circuit (voltage/distance converter). In order to decrease the steady-state error and the overshoot of the structure position, various proportional-integral-derivative (PID) gains are tested. Both controllers are implemented using a FPGA (Field-programmable gate array), which increases the performance of the controller. The experimental results, for both the controllers, show bi-directional tracking of several wave forms at frequencies up to 1kHz (limited by the dynamics of the actuators). The extension of the travel range is about 88.9% of the full-gap available (due to the mechanical stoppers present in the structure). This corresponds to a displacement range extension of 267%.