Longitudinal And Torsional Composite Type Ultrasonic Motor Design And Experimental Research

Ultrasonic motor is a new type motor in the recent two decades, which has different operating principles than traditional electromagnetic motors. It utilizes the converse piezoelectric effect of piezoelectric ceramics to make the stator induce ultrasonic vibration, then the rotor move rotationally or linearly through the friction forces between the stator and rotor. It has such unique characteristics as low speed, high torque, simple structure, driving directly, good electromagnetic compatibility (EMC), and self-lock function at turning off power, which makes the ultrasonic motor have an important role in certain special fields.Ultrasonic motor has many patterns, and two important patterns are developed to be miniaturization or big torque. The Longitudinal-torsional composite type ultrasonic motor has a bright perspective for its big torque. In this paper, the characteristics of longitudinal-torsional composite type ultrasonic motors are studied from the aspects of the drive mechanism, design theory and frequency annexing.The main research results are summarized as follow:In chapter 1, the development of ultrasonic motors at home and abroad is reviewed. The ultrasonic motor's structure, classification, and basic principle are systematically summarized. Then, the longitudinal-torsional composite type ultrasonic motor is mainly introduced from its feature, development history and present situation.In chapter 2, the relative basic theory about the longitudinal-torsional composite type ultrasonic motor is introduced. The formation of an elliptic trajectory is analyzed, and its driving mechanism is also stated.In chapter 3, an electromechanical equivalent model for ultrasonic motor is used to analyze the resonance frequency of longitudinal vibration or torsional vibration respectively. Based on it, a new simplified method is proposed to calculate the resonance frequency of longitudinal-torsional composite type ultrasonic motor by combinations of the longitudinal vibration and torsional vibration. From the comparison of two methods, the new method is effective for calculating the resonance frequency of the longitudinal-torsional composite type ultrasonic motor.In chapter 4, the frequency annexing about longitudinal vibration and torsional vibration of motors is studied. A method by increasing the depth of piezoelectric ceramic in the longitudinal vibration is proposed to solve the problems on longitudinal vibration's small amplitude, small pre-tightening force and low frequency output. The method is also proved to play a certain role in the frequency annexing. It can be found that the analysis results are essentially identical to the experiment results.In chapter 5, the experiments are carried out to test the performances of a longitudinal-torsional composite type ultrasonic motor. The influences of driving frequency, driving voltage and pre-pressure between the stator and rotator on the motor's output characteristics are given.