SPEED TRACKING SERVOCONTROL SYSTEM WITH SPEED RIPPLE REDUCTION SCHEMEFOR TRAVELING-WAVE-TYPE ULTRASONIC MOTOR

Recently, as an area of application of ultrasonic waves to the energy- related subject, technical development of ultrasonic motors is expecte d. To date, the principles and characteristics of several types of ult rasonic motors have been reported. Components taking advantage of the characteristic features of the ultrasonic motor have been in part redu ced to practice. Further, several methods have been reported on the dr iving control method for the ultrasonic motor. In the speed tracking s ervocontrol system using the ultrasonic motor, the effect of the load torque and the control characteristics of the speed tracking are only partly reported and are insufficient for practical applications. Furth er, the fluctuation of the speed, or the speed ripple, caused by the m anufacturing process of the ultrasonic motor has not been studied care fully. In this paper, a new speed servocontrol system is proposed in w hich the speed ripple reduction, load torque characteristics, and spee d tracking are taken into consideration. The proposed system uses two control loops. A speed control loop using a variable gain is construct ed in the driving frequency control section. Further, only the speed r ipple is extracted from the revolving speed detection signal and is us ed for feedback compensation to the constant voltage control loop in t he applied voltage control section. A test experiment is carried out a nd the experimental results are used to determine the effectiveness of the proposed speed servocontrol system. (C) 1998 Scripta Technica, El ectron Comm Jpn Pt 3, 81(9): 1-9, 1998.