QUICK AND PRECISE POSITION CONTROL OF ULTRASONIC MOTORS WITH 2 CONTROL INPUTS

Ultrasonic motor (USM) has an excellent performance and many useful fe atures. Since this motor is superior in holding torque and high respon se characteristic. it has been expected to use as position servomotor for small motors. There have been reported some mathematical models of the ultrasonic motor. however, these models are too complex to apply for control of the motor. Therefore position controllers based on PI c ontrol or fuzzy control have I,een proposed ill recent, years. It is d ifficult to control the ultrasonic motor with high-performance using s uch controllers, thus simple and convenient mathematical model is nece ssary for precise control. This paper presents a new position control scheme of ultrasonic motor, it consists of a PI controller and an adap tive controller which compensates the speed characteristic variations with online parameter identification. Moreover. this system controls b oth driving frequency and phase difference in order to achieve a quick and precise position control. The effectiveness of proposed central s cheme is demonstrated by experiments.