A 'center-wobbling' ultrasonic rotary motor using a metal tube-piezoelectric plate composite stator

This paper demonstrates a new type of compact ultrasonic motor that operates using a wobbling mode of motion. The motor was driven by a piezoelectric composite stator that consisted of a hollow metal cylinder whose outside surface was flattened on two sides at 90° to each other, upon which two rectangular piezoelectric plates were bonded. A wobbling motion was generated at both ends and at the center of the stator upon application of a sinusoidal voltage to each piezoelectric plate (which were phase shifted by90° with each other). Results showed that the flexural displacement at the stator's center was ∼ 4× that at its ends. Consequently, the stator could drive a rotor using a center wobbling motion. Our prototype motor had a significantly higher driving force than conventional end driven stators. The prototype was 4.7 mm in diameter and 20 mm in length, having a rotor 20 mm in diameter. The prototype operated at 46 kHz, had a maximum torque output of ∼50 mNm, and had a no-load rotational speed of 70 rpm in both directions. The prototype was also found to be suitable for precision actuation applications.