Design of a Linear Ultrasonic Piezoelectric Motor

Abstract

A new geometrically unique ultrasonic motor (USM) was designed, prototyped, and tested. USMs operate by vibrating a drive tip in an elliptical motion while in periodic contact with a driven surface. Piezoelectric elements are used to create the elliptical motions and are driven at near resonance frequencies to create the needed displacements for the motor to operate. The motor in this article consists of an arched frame, a center ground, and two piezoelectric elements connected to the center ground. Several finite element models were developed to design the motor and to predict performance. The models predicted a linear motor capable of pushing up to 5 N and a maximum speed of 0.4 m/s. A prototype frame was built out of tool steel and run against an oxide ceramic plate. The prototype motor achieved a maximum speed of 55.6 mm/s and a push force of 0.348 N at a preload of 6 N. The prototype frame’s steady-state displacements were approximately 20% of the expected output from the finite element models. Reasons for these discrepancies are discussed and investigated.