A miniature cylindrical piezoelectric motor with an asymmetric vibrator

In this paper, a miniature cylindrical-type traveling wave piezoelectric motor with an asymmetric vibrator is reported. The proposed piezoelectric motor uses only a single piezoelectric plate that is asymmetrically bonded on a cylindrical tube, but it still can excite two bidirectional traveling waves by changing the driving signal frequencies. Typical elliptic motions are observed by using the finite element method (FEM). A prototype motor, whose stator was 8 mm in diameter and 31 mm in length, was fabricated to verify this idea. Our experiments showed that the prototype motor can rotate anticlockwise around the frequency of 21 kHz, at which it works in two degenerated B₂ bending coupling modes, and clockwise around 32.7 kHz in two degenerated B₂₂ flexural coupling modes. The results coincide well with our FEM prediction. Finally, further miniaturization was carried out, and a micromotor with 1 mm diameter was constructed, which shows a tunable rotation direction by adjusting the driving signal frequencies. This research has provided a way for piezo-motor miniaturization, with advantages of simple structure and easy driving and control strategy.