Wear mode control of drive tip of ultrasonic motor for precision positioning

A precision positioning stage driven by ultrasonic motor, (USM) with Al2O3 drive tip and Al2O3 driven rail has been developed for the electron beam (EB) direct-write system. Wear of a drive tip should be kept in mild wear mode for a stable precision positioning by retaining the minimum slip in the contact interface between a drive tip and a driven rail since the stage is driven by friction force generated in the contact interface. In this investigation, selecting method of the optimum preload of USM and the optimum gains of PID controller are proposed experimentally in order to keep wear mode of drive tip in mild wear mode. The optimum preload W-c is given in the condition when the maximum stage velocity is given in open loop control. In the condition of preload above W-c macroscopic slip between drive tip and driven rail is restrained. The optimum gains of PID controller are given when the amount of fluctuation of operating voltage E-f, which is the monitoring parameter of slip in the contact interface between drive tip and driven rail, is the minimum value. Selecting these optimum preload and gains of PID controller is verified to keep wear mode of Al2O3 drive tip of USM in mild wear mode experimentally. (C) 2003 Elsevier B.V. All rights reserved.