Precise contour motion of XY stage driven by ultrasonic linear motors in a high vacuum environment

Abstract

This paper presents the effect of a vacuum environment on the precise motion control of an XY stage driven by an ultrasonic linear motor. Hybrid, bolt-clamped Langevin-type (hybrid BLT) ultrasonic linear motors that operate at the resonance frequencies of the third longitudinal and sixth lateral modes were adopted in the XY stage. The vacuum environment affects the friction characteristics of the ultrasonic motor system’s driving elements significantly. In this study, the system was characterized according to the vacuum level in terms of the resonance frequency of the ultrasonic motor, the slope of the NCT curve in the micro-dynamics and macrodynamics regimes, the range of the micro-dynamics, and the range of the dead zone. In accordance with the variations in the resonance frequency, the frequency was adjusted to match the resonance frequencies of the longitudinal and lateral modes using an external inductor. Based on the variations in the dead zone and dynamic characteristics, a control algorithm was designed by continuously employing nominal characteristics trajectory following (NCTF) control, feedforward control, and switching control based on the micro-dynamics and macro-dynamics Ultraprecision level of motion accuracy was achieved by the developed system in a high vacuum environment.