Research On Frequency Tracking Technology Of Traveling Wave Type Ultrasonic Motor

Ultrasound motor(USM)is a micro-motor with new type of driving method,It uses the high-frequency vibration generated by the inverse piezoelectric effect of piezoelectric ceramic as the direct driving force,and drives the movement of the rotor through the friction between the rotor and the stator.Compared with the traditional electromagnetic motor,it has the characteristics of low speed,large torque,no electromagnetic interference,no noise and self-locking,etc.so it is widely used in many fields.Due to the specific operating principle and operation mode of the ultrasonic motor,temperature and load changes are likely to cause the ultrasonic motor to be unstable and its speed fluctuates.Closed-loop control based on speed feedback usually requires the installation of a speed sensor,which increases the size of the entire system,increases the cost of the input,and limits the application in some applications.To solve this problem,a Frequency tracking method based on phase difference feedback is introduced in this paper.Firstly,the type of phase difference was selected by the sensitivity to the temperature and load;Secondly,aiming to the interference of mechanical and harmonic noises,the correlation phase extraction method was proposed to improve the accuracy of phase difference between driving voltage and monitor electrode voltage;Lastly,the Frequency automatic tracking strategy was given according to the changes of temperature and load respectively.Experiment results indicate that this method can reduce the speed fluctuations caused by the changes of temperature and load,and improve the speed stability of motor system.Because only two voltage signals are needed to be recorded,this method is easy for implement.