A Self-Sensing Wedge-Wave Ultrasonic Motor Using Modal Sensors

Abstract

This paper experimentally and computationally examines the modal sensors integrated with a recently developed rotary ultrasonic motor (USM) driven by continuous wedge waves of the fundamental modes with the integer circumferential modal number. The traveling wave is formed from constructive interference of two equal-intensity standing waves induced by two comb transducers using dual sinusoidal excitations in 90 degree phase difference. The transducers and modal sensors are segmented in strips around the circumference of piezoelectric tube in the circular wedge-like motor stator. The latter are used to monitor the dynamic response of the stator during operation. The response of USM acquired by the proposed modal sensors has distinct vital characteristics in different frequency bands. The high-pass signals are used not only to note the variation in phase difference between excitations but to detect the resonant frequency, which is altered by payload, wear situation, etc. The low-pass signal reveals the revolution speed and dynamic reaction of the motor stator exerted by frictions and contact forces because of the rotor. The time-frequency response of stator is further characterized during the period in which the revolving direction of rotor is switched over.