Design of an ultrasonic motor with multi-vibrators

Abstract

This paper presents and verifies a new idea for constructing an ultrasonic motor (USM). The stator contains several vibrators fabricated by bonding piezoelectric ceramics (PZTs) to a metal base. When two alternating current (AC) voltages with a 90° phase difference are applied to the PZTs, longitudinal and bending modes are excited in the vibrator. The bending vibrations of the vibrators are stacked to form the torsional vibration of the stator, ultimately generating longitudinal-torsional composite vibration. Both vibrators and the stator are excited to the resonance state. A standing wave is formed by superposition of longitudinal and torsional modes. The proposed motor is an in-plane vibration motor because the vibrations of the stator are in the circumferential plane. The finite element method (FEM) is used to validate the feasibility of the proposed motor. The fabricated stator contains five vibrators. The tested resonance frequencies of longitudinal and torsional modes are 44.42 kHz and 43.83 kHz, respectively. The stall torque is 0.3 N·m and no-load speed is 45 r/min. The highest efficiency is 30%. The applied driving voltage is 100 V<inf>o-p</inf> (peak voltage) at 43.9 kHz. The designed motor is a parallel-actuated integral motor. It allows the vibrators to operate synchronously, and overcomes asynchronous issues that occur in traditional multi-vibrator motors.