Displacement Estimation and Control Based on High Frequency Injection and Bridge Circuit in Piezoelectric Actuators

In the position control system using the piezoelectric actuators, a feedback control system is indispensable to improve the positioning/tracking accuracy by compensating for nonlinearities in the actuator. However, a high-resolution displacement sensor poses the problems of cost and installation space. In this paper, a feedback control system without the displacement sensor is designed by combining displacement estimation based on capacitance detection with vibration control by a bridge circuit. The superimposed signal with a high frequency component is injected to the actuator. Based on the voltage and the current generated by the injection signal, the capacitance is computed by performing the discrete Fourier transform. The displacement is estimated using linear relationship between the capacitance and the displacement. In addition, a minor-loop is designed to suppress the resonant vibration using a detected signal through the bridge circuit. The designed control system is evaluated by conducting numerical simulations and experiments using a piezoelectric cantilevered actuator.