Single Phase Drive Ultrasonic Motor Using LiNbO3 Rectangular Vibrator

A miniature thin-plate ultrasonic motor fabricated from LiNbO3 was studied. To obtain a single phase drive motor, we used a coupling mode which combined a longitudinal and flexural in-plane vibrations. In our previous study, the coupling modes were achieved in a parallelogram vibrator by the effect of additional external mass. Instead of deforming the outer shape, this study uses an internal coupling effect resulting from the crystal anisotropy. We confirmed that a rectangular plate vibrator made of X-rotated Y-cut LiNbO3 with additional y'-axis rotation has coupling modes and can operate as the stator of a single phase motor. In this paper, we describe the design of the vibrator with finite element method analysis and the experimental results from the ultrasonic motor using a LiNbO3 rectangular plate 10 mm in length. The motor with a rotor shaft 1 mm in diameter demonstrated the following characteristics: a speed of 1000 rpm and torque of 25 µN m in counter-clockwise (CCW) revolution, and of 5000 rpm and 12 µN m in clockwise (CW) revolution. We obtained the reverse rotation experimentally; however, the different characteristics between CW and CCW operation, which are obstacle to practical use, are subjects for future study.