Finite Element Modeling of Surface Traveling Wave Friction Driven for Rotary Ultrasonic Motor

Abstract

Finite element modeling (FEM) is a critical tool in the design and analysis of piezoelectric devices, offering detailed numerical simulations that guide various applications. While traditionally applied to eigenfrequency analysis and time-dependent studies for predicting excitation eigenfrequencies and estimating traveling wave amplitudes, FEM's potential extends to more sophisticated tasks. Advanced FEM applications, such as modeling friction-driven dynamic motion and reaction forces, are essential for accurately simulating the complex behaviors of piezoelectric actuators under real-world conditions. This paper presents a comprehensive motor model that encompasses the coupling dynamics between the stator and rotor in a piezoelectric ultrasonic motor (USM). Utilizing contact theory, the model simulates the complex conditions encountered during the USM's initial start-up phase and its transition to steady-state operation. Implemented in COMSOL Multiphysics, the model provides an in-depth analysis of a rotary piezoelectric actuator, capturing the dynamic interactions and reaction forces that influence its performance. The introduction of this FEM-based model represents a significant advancement in the simulation and understanding of piezoelectric actuators. By offering a more complete picture of the motor's behavior from start-up to steady state, this study enables more accurate control and optimization of piezoelectric devices, enhancing their efficiency and reliability in practical applications.

Figures (14)

• Figure 1: (Left) Modeling geometry and component definition. (Right) Component mesh with extra fine on the contacting surface, and normal on the rest of the component.
• Figure 2: Displacement profile of the rotor current position compared to the initial position.
• Figure 3: Normal reaction force (green) and friction force (purple) intensity. The simulation was performed under 4$^{th}$ mode so 4 peaks are shown in the figure. The friction was tangential along the rotor circumference to drive it to rotate.
• Figure 4: (Left) Results of an x-component velocity probe placed on the rotor. Velocity reaches a settle-down status at approximately 1.5ms. (Right) Carvalho et al. developed a stator simulation with the z-axis displacement reaching a settle-down status of around 1.4ms. Image reproduced from carvalhomultiphysics.
• Figure 5: Result of an x-component displacement probe placed on the rotor. It reaches over 65$\mu m$ at the end of the simulation.