A contact model based on multi-scale rough surface of ultrasonic motor

The working of the ultrasonic motor directly relies on the micron-amplitude & high-frequency vibrations of the stator in contact with the friction layer. Therefore, the multi-scale rough surface features on the contact surface, which are also at the micron level, cannot be neglected. A novel contact model considering rough surface of different scales is proposed in this paper, and the impact of different scale features on output characteristics is studied. First, the equivalent stiffness coefficient and surface clearance value related to the applied preload on the contact surface are derived using the probability statistics method. Then, the surface data collected by the profilometer are decomposed into microscopic roughness and mesoscopic waviness using wavelet transform. The roughness data are substituted into the probability statistics method, and the waviness is used to adjust the amplitude function. Subsequently, the time-varying working dead zone is obtained using the discrete method, and the output characteristics are obtained by Coulomb friction. The influence of model variables such as microscopic roughness, mesoscopic waviness, preload, stator amplitude, and material properties on the output characteristics is analyzed through simulation analysis. The collected experimental data of the mechanical characteristic curve are highly consistent with the simulation results, verifying the accuracy of the proposed multi-scale contact model. This model can be applied to other types of ultrasonic motors and provides a new perspective for improving motor performance, as well as a theoretical foundation for the study of contact surface texture.