Contact dynamic modeling of hollow-type ultrasonic motor considering the microscopic viscous effect

A microscopic contact model for annular traveling wave ultrasonic motors (ATWUMs) is proposed in this paper, aiming to deeply investigate the dynamic contact behavior between the stator and rotor as well as their friction-driven mechanisms. Compared with traditional contact models of annular traveling wave ultrasonic motors, the LuGre's microscopic dynamic friction theory is introduced into this model, and the influence of the stator tooth structure is fully taken into account. Additionally, estimation methods for key parameters in the contact model are provided. Based on this model, systematic analysis and evaluation of the normal stress, tangential stress, and mechanical output characteristics within the motor are conducted. Subsequently, the torque-speed characteristics of the prototype are measured through experiments and compared with the simulation results. Experimental results show that the simulated values are highly consistent with the measured ones, thereby validating the effectiveness of the proposed microscopic contact model. To further evaluate the model performance, a comparative analysis between this model and traditional contact models that use Coulomb's law of friction while neglecting the influence of stator teeth (assuming continuous tooth surfaces) is performed. The comparison results indicate that the proposed model is recognized as superior to traditional models in terms of accuracy.