Affects of pre-pressure on ultrasonic motor output performance

When the rotary traveling wave type ultrasonic motor working, the piezoelectric ceramic excites the stator vibration to produce traveling wave, then the elliptical motion of the particle is formed. Under the function of the pre-pressure between the rotors and stator, the rotor rotates by the friction between the rotors and the stator; finally it realizes that the rotational speed and the torque of the motor are taken out. Therefore, the pre-pressure between the rotors and stator has essential influence on the ultrasonic motor performance,many researchers have carried on research to these. According to the documents, it is indicated by most scholars that the pre-pressure has effect on the contact between the rotor and stator, and the conclusion is difference from the experiment because it is neglected that the pre-pressure has effect on the stator vibration. In the paper, the ultrasonic motor model is derived from analyzing the force on the interface between the rotors and stator and founding stator dynamic equations and rotor dynamic equations. Under different pre-pressure, the stator vibration characteristic and the ultrasonic motor output performance are studied by means of the motor model. The result shows that the pre-pressure affects the ultrasonic motor output performance, because it changes the contact area between the stator and the rotor, and the other that the pre-pressure has influence on the performance with the resonant frequency of the stator increasing, the stator vibration changing and the contact area varying. It is indicated from the result that no-load speed and the stall torque are non-monotonic changing with the pre-pressure increasing, and the changing law is connected with the frequency of the excitation voltage on the stator.