The measurement on vibration friction coefficient of ultrasonic motor

An ultrasonic motor (USM) of the friction type is driven by the friction force between the stator and the rotor. However the classical Coulomb friction law can not be used to explain the driven mechanism of an ultrasonic motor under the condition of high frequency vibration between the stator and the rotor. In our early study[1], a vibration friction model was offered to explain a phenomenon in an experiment of an ultrasonic motor, in which the friction coefficient was considered as a function of the vibration amplitude. In this paper, we show some experimental results to verify our vibration friction model. The vibration amplitude of the stator is measured by using a laser vibrometer, and the results show that it is proportional to the input voltage. The tangential friction force between the stator and the rotor is measured by changing the input voltages under various normal pre-load. The friction coefficient is calculated according to its definition, namely the tangential friction force divide by the normal force. With the increasing of the input voltage or says the amplitude, it is found that the vibration friction coefficient decreases. The experimental results are in a good agreement with the theoretical calculations. The vibration friction model would be used to explain the driven mechanism of an ultrasonic motor in a further work.