An Open-Loop Positioning Method for Reduction of Influence of Nonlinearities in Piezoelectric Actuator

A unique driving method of piezoelectric actuator to reduce influences of hysteresis and creep is represented in the paper. It is for point-to-point (PTP) open-loop positioning. In the method, when an object is stepwise positioned using the piezoelectric actuator, the input voltage to the actuator is raised up to maximum value and pulled down to 0V sinusoidally in order to initialize the actuator condition, and then it is returned to a constant starting point at the beginning of every step. Finally it is raised up to appropriate step height with some overshoot. Both influences of hysteresis and creep characteristics are reduced drastically using the method. Stepwise positioning of 2 mu m step height with 0.2 mu m accuracy is realized using the basic method. For nano-meter order positioning accuracy, creep behavior of the actuator is serious problem. It is found that multi-cycle large sinusoidal drive which is called initializing drive can reduce creep motion significantly. Eventually, less than 5nm accuracy for 20nm stepwise PTP positioning is realized.