A modified sensorless position estimation approach for piezoelectric bending actuators

Abstract

Piezoelectric bending actuators are widely used in micro positioning tasks. Due to material nonlinearities such as hysteresis and creep, the position-force control of these actuators is necessary. However, position sensors for micro scale applications are expensive and require a complex configuration. Sensorless approaches are alternative methods in which by resorting to the linear charge-position characteristic, the actuator position can be estimated. But, in piezoelectric actuators with small impedances, due to charge leakage caused by piezoelectric internal resistance, the charge-position characteristic is not linear. Due to nonlinear behavior of piezoelectric internal resistance, its compensation would be more complicated. This paper targets at a modified procedure in which with the help of nonlinear functions for the internal resistance, the linear charge-position characteristic can be obtained. To this purpose, a modified active Prandtl-Ishlinskii (PI) operator is proposed which estimates and compensates the charge leakage. As a result, the ideal linear mapping can be achieved and actuator position can be appropriately estimated. The results are finally validated by experiments and compared with previous methods.