A novel hollow type of traveling wave rotary ultrasonic motor is proposed, optimized, fabricated, and tested in this study. Unlike conventional ultrasonic motors, this novel ultrasonic motor adopts a bran-new preloading method that preload is applied from the bottom of the stator through a wave spring, which can not only enhance the anti-overload ability but also extend the working life of the motor. According to this motor, a three-dimensional finite element model has been built by the commercial finite element software ADINA. In terms of the friction material and the preload, a detailed further optimization procedure is given after the initial design. Finally, the appropriate size and location of the friction layer and a proper preload for this motor have been determined. Almost all of the motor’s mechanical capacities, such as rotational speed, torque, and deformation, can be obtained by simulations in ADINA, which have good agreement with experimental results.

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 $\alpha$ , 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.