High-precision positioning considering vibration and disturbance suppression in piezo-driven stage systems

This paper presents a controller design approach to compensate for the disturbances and achieve robust vibration suppression against variations in the resonant frequency in a piezo-driven stage system. Disturbances such as nonlinearities due to hysteresis and creep phenomena are inherent in piezoelectric actuators, resulting in a low control performance of positioning or low tracking accuracy. Although various types of modeling and model-based approaches have been proposed to compensate for the nonlinearities, these approaches have limitations such as substantial modeling complexity, time-consuming modeling process, and high computational cost required for their evaluation and implementation. Moreover, resonant vibration modes in the mechanism lead to residual vibrations in the positioning or may even destabilize the system. In particular, the vibrational dynamics tend to have a low stability margin in piezo-driven systems because of sharp resonant peaks associated with the low structural damping. In this study, a state observer is employed to estimate the disturbance and vibration mode signals, wherein the observer is designed to suppress the disturbance and the vibration by using the estimated signals. Considering the hysterisis as an input disturbance to the linear plant renders complex modeling processes unnecessary. To compensate for the mechanical vibrations, pole-assignment method is used to achieve the gain-peak reductions and robustness against variations in the resonant frequency. The effectiveness of the proposed approach was verified by conducting experiments on a piezo-driven stage system.