This paper presents an approach for position sensorless control in piezoelectric actuators. To achieve high-precision positioning with a piezoelectric actuator, a feedback control system using a high-resolution position sensor should be used to mitigate nonlinearities and disturbances. Sensorless control is desirable to reduce the cost and space utilization in micro- and nano-positioning systems. In this paper, actuator position is estimated based on the capacitance of the actuator because the displacement is propotionate to the capacitance. To measure the capacitance, a reference voltage with a high frequency component is injected into the actuator. On the basis of the reference voltage and current, the capacitance is estimated through the discrete Fourier transform. The displacement of the actuator is calculated using the relationship between displacement and capacitance. The position feedback controller is designed based on the estimated displacement signal. The proposed sensorless control approach is verified by conducting experiments using a bimorph-type piezoelectric actuator.
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