Nonlinear Positioning Compensation of Thin-Disc Ultrasonic Motor Using Fuzzy Sliding-Mode Control

The study intends to focus on the design of a thin-disc piezoceramic-driving ultrasonic actuator dedicated to discrete stepping motors. By the improved design and construction, the innovative ultrasonic actuator was developed and used as a stator. The electromechanical coupling characteristics based on the composite structure would produce the flexural wave on the stator, which consisted of a piezoceramic membrane bonded on a metal sheet. Due to the converse piezoelectric effect, the driving ability of the actuator came from the vibration of extension-shrinkage of a metal sheet corresponding to the frequency of a single-phase AC power. Under constraints at the specific geometry positions on the metal sheet, the varying behaviors of flexural waves were formed. The simple structure of an actuator demonstrated that the mechanical design of the actuator and the rotor could be separated, depending on what we need in pragmatic applications. And, its positioning accuracy could be reached through a closed loop servo control, i.e. Fuzzy Sliding Mode Control (FSMC). FSMC was used to automatically compensate nonlinearly mechanical behaviors such as dead-zone and hysteresis phenomena. Furthermore, FSMC scheme has successfully overcome the high frequency chattering phenomena with lower control effort while the motor is applied to position tracking, and also has been proven in the excellent robust ability for noise rejection.