A method for matching the eigenfrequencies of longitudinal and torsional vibrations in a hybrid piezoelectric motor

A hybrid piezoelectric motor is investigated, which uses a longitudinal transducer and a tangential transducer to generate the desired elliptical trajectories on the surface of the stator. In general, such a motor consists of one stator and one rotor. The frequency at which it is driven is the resonance frequency of the tangential motion of the stator. For the purpose of enlarging the micro displacement generated by the ultrasonic vibration and obtaining a large torque and a higher efficiency, the resonance frequency of the longitudinal vibration and torsional vibration should coincide. However, it is difficult to match these two resonance frequencies of the two transducers with an identical geometry size. In this paper, a new prototype of a hybrid piezoelectric motor is proposed, in which two stators are used to increase the contact area between the rotor and the stator. Besides, two adjusting rings are added to the stators to adjust the resonance frequencies of both vibrations in such a way that they coincide. A theoretical model and a FE model are used to optimize the geometry of the motor and to investigate the effects of matching the eigenfrequencies.