Servo speed control of traveling-wave ultrasonic motors using pulse width modulation

With the advantages of lightweight, compact size, fast response, power-off holding torque and high-torque low-speed characteristics, the traveling-wav e ultrasonic motor (TUSM) is becoming attractive for servo application. Thi s paper presents a new pulse Width modulation (PWM) method for servo speed control of a TUSM. The key is to digitally control the pulse width, hence t he fundamental value, of the bipolar 2-phase voltages feeding into the TUSM . This method takes a definite advantage of minimum audible noise compared with those available methods, such as phase-difference control, frequency c ontrol, and on-off PWM control. Experimental results confirm that the propo sed speed controller can offer good steady-state and transient performances and can significantly suppress the audible noise occurred at speed variati ons.