PRACTICAL CONTROL METHOD FOR NANO POSITIONING USING A LANGEVIN ULTRASONIC MOTOR IN VACUUM ENVIRONMENT

摘要

This paper presents an investigation about the practical control method of noble linear positioning stage for the vacuum environment use. The stage is driven by the hybrid bolt clamped Langivin (BCL) type ultrasonic linear motor which is excited with its different modes of natural frequencies in both lateral and longitudinal directions. This stage system has various variables to drive such as driving frequency, magnitude of preload, phase difference of each mode, and exciting voltage and current etc. In this paper, to obtain the robust driving condition of the motor, the parameters of motor are designed by using Taguchi method. In addition, because the accurate model of motor in vacuum environment is hard to find, nominal characteristic trajectory following (NCTF) control method was adopted. To achieve the fine control performance in vacuum environment the feedback control parameters were also optimized by Taguchi method. Finally the stage is operated in high vacuum condition, and the operating performances are investigated comparing with air environment. As a result, the robustness of point to point (PTP) positioning was accomplished in high vacuum condition with nanometer level accuracy.