Researches on frequency tracking technology of utrasonic motor

Ultrasonic motors continuous operation can make stator generate heat, the natural frequency of stator operational modal drifts about under the high temperature, and the output performance of the ultrasonic motor is reduced. Because of these reasons, it is an effective means to adopt suitable technology to follow the natural frequency of stator operational modal to guarantee the ultrasonic motor steady operation, and many researchers have carried on research to this. In the paper, it is analyzed that frequency-tracking based on the single-electrode feedback voltage and the impedance characteristic of the stator, the tracking principle, tracking mode and tracking effect are all researched. The results show that the frequency tracking of the single-electrode feedback voltage increases complexity of the ultrasonic motor structure, reduces the flexibility of the ultrasonic motor speed control, and hinders the ultrasonic motor output performance to maximum. Although the frequency tracking of the phase difference between the single-electrode feedback voltage and an input voltage increases complexity of the ultrasonic motors, the ultrasonic motor output performance is brought into play extremely. The frequency-tracking based on admittance of the stator is a high-efficient technology, because it simplifies the ultrasonic motor structure, enhances the flexibility of the ultrasonic motor speed control, and the ultrasonic motor output performance is implemented to the most.