Contact characteristics of a traveling wave ultrasonic motor based on an electric contact method

The electric contact method is an effective method to evaluate the contact state by experiment, but the method is applied when the motor is stalled. It is not suitable for evaluating contact state when the rotor is rotating, e.g. rotary contact state. To solve this problem, the electric contact method is improved so that it can evaluate the rotary contact state. The relative contact lengths of both stalling state and unload state of ultrasonic motor are tested. The results show that the relative contact length of unload state is much smaller than that of stalled state. The maximum difference is about 36%. It indicates that load has a significant impact on contact between stator and rotor. Finally, the relative contact length of unload state is calculated based on visco-elasticity contact model and the calculated results shows good agreement with the measured results. The improved electric contact method can evaluate the motor rotary contact state effectively.