Modal frequency adjustment of a traveling wave type rod shape ultrasonic motor

As far as a bolted Langevin-type rod shape ultrasonic motor is concerned, the modal frequencies of two bending vibration modes usually disagree with each other. As a result, motor efficiency, performance and speed stability are affected. A modal frequency adjustment technique was proposed to solve this problem. According to dynamic equations of the stator and the K. A. Stetson's structural perturbation theory, the modal frequencies of the updated stator were calculated. Finite element analysis of the stator was employed to determine the stator appropriate position for modification. Meanwhile, the influence of stator modification on the bending vibration modal frequency was analyzed. A stator prototype was fabricated and its frequency magnitude characteristic was tested. The modal frequency difference of two phases was 170 Hz. After chamfered portions had been formed on the stator, the difference was reduced to 70 Hz, which met the requirements of the engineering project. The validity of the proposed method is verified using experimentation. © 2010 Chin. Soc. for Elec. Eng.