Ultrasonic piezomotor with longitudinally oscillating amplitude-transforming resonator

An ultrasonic piezoelectric motor concept is presented that is based on the transformation of the longitudinal oscillations of a rod-shaped resonator into continuous motion by arranging the resonator diagonally to a drum. The efficiency of the motor was enhanced by increasing the amplitude of motion at the point of motion transfer by tapering the resonator. To optimize the resonator design, the validity of the predictions derived from the one-dimensional analytical theory for longitudinal ultrasonic resonators was tested with respect to this application by means of finite-element calculations. The one-dimensional calculation turned out to be hardly applicable at all to real resonators. The finite-element calculations showed that maximum final amplitude is attained when the resonator tapers as steeply as possible, no preference being shown for any special mathematical form of cross-sectional reduction. Efficiencies of 35% and torques of 25 N-cm were attained at 150 r/min.<>