Sensorless adaptive sliding mode position control for piezoelectric actuators with charge leakage

Position control of piezoelectric actuators is greatly affected by nonlinearities such as hysteresis and creep. Therefore, precise position sensors must be utilized which have high cost and complicated structures in micro scales. Charge-based position estimation is an alternative method which resorts to piezoelectric linear charge-position property to estimate the actuator position, but in low-impedance actuators, there is a charge leakage caused by actuator internal resistance which deteriorates the position estimation and closed-loop control performance. In this article, the leakage is considered as a sensor fault. Therefore, a combination of charge measurement method and an appropriate observer is designed to detect and isolate the mentioned fault and estimate the actuator position properly. In addition, an adaptive sliding mode control procedure is proposed for trajectory tracking in the presence of estimated states. The required analysis is carried out to guarantee the closed-loop stability. Finally, experimental results show the effectiveness of the proposed method.