Travelling wave ultrasonic motor using the B08 flexural mode of a circular membrane

This paper describes the design, construction, and performance of a piezoelectric motor that uses the travelling B₀₈ mode of an 80-mm diameter circular membrane to drive a rotor by frictional contact. The motor is of a thin planar design, giving high torque of up to 0.33 Nm at low speed and has been developed as a design that can be made with lithographic techniques for miniaturization. Investigations of the free stator with a vibration pattern imager and impedance analyser gave the resonance frequency, mode, and electromechanical coupling of the stator. Motor speed as a function of frequency for a constant voltage and performance charts of speed, output power, and efficiency against torque are presented for a particular input voltage and rotor pre-load. The effects of two different lead zirconate titanate (PZT) ring dimensions have been investigated. Excitation of the B₀₉ mode has been observed, incommensurate with the piezoelectric excitation of the stator. This is discussed with relation to edge-clamping of the stator. Single standing wave motoring was observed, believed to arise from asymmetry of the stator and its perturbation of the B₀₈ resonance mode. Sources of power loss, including frame vibration and friction interface slip, are considered and discussed