Two-Phase Direct Vibration Modal Control of Ultrasonic Motors Based on Active Disturbance Rejection Observer

With the advancement of traveling-wave ultrasonic motors and their increasing use in robotics, aerospace, and high-precision instruments, improving their output characteristics and system stability has become a key research focus. Uncertainty in system parameters causes unobservable effects on output characteristics due to changes in microscopic vibration modes, which cannot be measured in real time. From a dynamic perspective, it is desirable for the two-phase drive of an ultrasonic motor to generate pure traveling waves at the stator surface, resulting in elliptical motion. However, in practice, factors such as temperature fluctuations, two-phase asymmetry, and piezoelectric ceramic nonlinearities cause variations in system parameters. As a result, forced oscillations do not produce equal amplitudes in both phases, even when the two-phase drive voltages are equal. This paper proposes a direct control method for the two-phase modes of ultrasonic motors based on an active disturbance rejection observer (ADRO). The method utilizes self-impedance control to vibrate in real time as the system parameters change, compensating for disturbances without the need for sensors. It then directly controls the two-phase modes, ensuring equal amplitudes and a 90-degree phase difference, through fuzzy PID voltage regulation. This approach synthesizes the two-phase standing waves into a pure traveling wave, resulting in increased torque and more stable speed.