FE analysis and experimental evaluation of the performance of a travelling wave rotary motor driven by high power ultrasonic transducers

Ultrasonic motors have been exploited mainly in low power and low duty cycle applications. In aerospace and automotive applications, there is also the need for motors able to provide high torque but employed at very low duty cycle. In this work numerical simulations and experimental measurements carried out on a high power ultrasonic motor are presented. The proposed motor is composed of a annular shaped stator and two light cone shaped rotors. The rotors are pressed in contact to the borders of the inner surface of the stator by means of an opportune pre-stress system. A travelling rotating wave is generated in the stator by two and four Bolted Langevin Transducers, opportunely placed on the lateral surface of the stator. Each transducer is designed to excite in the ring radial nonaxisymmetric modes. The effective generation of the travelling wave in the stator, with both two and four driving transducers, has been accurately simulated with a FEM software. A prototype of the motor has been constructed and experimentally characterized. Comparisons between simulation and measurements have shown a satisfactory agreement. The improvement of motor performances achieved by increasing the number of driving transducers is analyzed and discussed.