Resonance Detecting Method of Traveling-Wave Type Ultrasonic Motor with Piezoelectric Element Sensor

Abstract

The driving force of ultrasonic motors (USMs) is the frictional force between the ultrasonic vibrating stator and the rotor. A mechanical resonance of the stator is utilized for expanding the amplitude of stator vibration. The mechanical resonant frequency of USMs is variable according to the temperature rise of USMs and the change of load applied to them. In order to drive and control USMs stably, the driving frequency of a high-frequency power source must track or match the resonant frequency of USMs. Therefore, detection of resonant state on USM is required. This paper describes a resonance detecting method of the USM with a piezoelectric element sensor mounted on the stator. The phase difference between the generated voltage by this sensor and the applied voltage to the USM indicates the resonant state of the USM, which is derived from the fundamental equations of electromechanical conversion theory and piezoelectric effect. This effective resonance detecting method is experimentally demonstrated using a computer-based measuring system.