Evaluation of Temperature Dependency for Displacement Estimation in Piezoelectric Stack Actuators

In the position control system using the piezo-electric actuators, sensorless displacement control is an attractive approach that avoids the use of expensive and bulky displacement sensors. An estimation approach that uses the relationship between the capacitance and displacement has been proposed, where a high-frequency injection signal is applied to the actuator as a superimposed signal. The discrete Fourier transform is performed using the voltage and current generated by the superimposed signal to obtain the capacitance of the actuator. However, the change in the actuator characteristics that result from high-frequency injection have not been sufficiently investigated. The purpose of this paper is to investigate the effect of continuous high-frequency injection on the temperature change and estimation performance. The relationship between the temperature and capacitance changes during long-duration high-frequency signal injection is experimentally investigated by attaching a thermocouple to the surface of the actuator. To improve the estimation accuracy, the capacitance change is compensated using a model based on the relationship between the temperature and capacitance changes. The validity of the approach is verified by conducting the experiments using the piezoelectric stack actuator.