In this paper, a new longitudinal and torsional type ultrasonic motor with two stators is presented and investigated. Normally, such a motor consists of one rotor and one stator, and two types of transducers that are longitudinal PZT and torsional PZT are used to generate the desired elliptical locus on the stator surface. The operating frequency is at the resonance frequency of torsional transducer. In order to enhance the efficiency of the motor, however, the resonance frequencies of both transducers should be closed to each other. For the purpose of matching the resonance frequencies, a symmetrical structure is adopted in design of the motor. Furthermore, two rings are added to the stators in order to adjust the resonance frequencies of these two transducers. A finite element model is developed and ANSYS software is used to analyze the resonance frequencies of longitudinal vibration and torsional vibration as well as optimize the motor geometry. According to the FE results, an experimental prototype is fabricated and the experimental results agree well with the theoretical predictions.

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. r

This paper deals with an ultrasonic motor, which consist of one rotor and two stators. The main parts of each stator are one longitudinal and one torsional piezoceramic actuator, which are used to generate the desired elliptical orbit on the stator surface. For the purpose of a high efficiency, the longitudinal and the torsional resonant frequency should ideally coincide with the operational frequency. To match the resonant frequencies, two adjustable rings are added to the stators. The influence of the mass and the position of the rings on the first longitudinal and the first torsional eigenfrequency and their mode shapes is investigated. The experimental results fit very well with the theoretical predictions and show that the adjusting rings can be used to match the eigenfrequencies of the two mode shapes.

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