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The application of ultrasonic motor (USM) has been seriously restricted by its relatively low efficiency. The energy loss caused by the radial sliding on the contact surface of the motor is considered as one of the major reasons for the low efficiency of USM. In this report, the solution is proposed to reduce the radial sliding by optimizing the stator comb-teeth of the traveling wave rotary ultrasonic motor (TWUSM). Theoretical analysis, simulation, and experiments were conducted in PMR60 type TWUSM (motor model) to verify the optimized method. The results indicate that the friction angle α, which represents the degree of radial sliding, can be efficiently reduced by chamfering the teeth on the stator of motor. The maximum efficiency of 44.3% is obtained in the modified motor of which the stator chamfer size is 1.0 mm × 45°, which is nearly two times higher than that of the nonmodified motor (25%). Therefore, it is a feasible and simple pathway to improve the efficiency of the USM.

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