| The ultrasonic motor is a new type motor that has been developed in recent twenty years. It is different from traditional electromagnetic motors in principle. Ultrasonic vibration is excited by the conversely piezoelectric effect of piezoelectric materials and magnified by the elastic body. With the friction coupling, the rotation of the rotor or moving of the slider is generated. Ultrasonic motor is characterized by low speed, high torque, direct load-driving and simple structure. It isn't disturbed by the electromagnetic field. Ultrasonic motor can carry out self-holding without electric power. All of these characters make ultrasonic motor promising in some special application areas.Ultrasonic motor has various forms. Among the ultrasonic motors, the longitudinal-torsional composite type ultrasonic motor can output the torque ten times as the traveling wave type ultrasonic motor with the same diameter. It also has better controllability. So the study of longitudinal-torsional composite type ultrasonic motor can expend the application of ultrasonic motor. Several years ago, the research of ultrasonic motor with torque more than 1Nm and high positioning accuracy was mainly in Japan, and our country wasn't engaged in this area. But recently, many research agencies in our country begin to pay great attention to the research of the longitudinal-torsional composite type ultrasonic motor, such as Zhe-Jiang University, Nanjing University of aero and astro, Tsing-Hua University. In this thesis, we analyze the friction driving model, vibration mode, the choose of the frictional materials, the structural design and optimization, the measurement and control system on the ultrasonic motor, and so on. On the basis of the research above, two sample motor are manufactured. Both of them can output the torque more than lONm, and the positioning accuracy can reach 0.025 degree. From the description above, we can drew the conclusion that the basis of theory and experiment research about the longitudinal-torsional composite type ultrasonic motor with large torque and high precision has been founded.The research work and creative achievements of this thesis are as following:1. Deduce the resonance frequency equations of longitudinal and torsional vibrations of ultrasonic motor using the Mason equivalent circuit, which gives the relationship between physical dimension and the resonance frequency. After that, the design theory of longitudinal and torsional vibrators has been founded.2. By using the method of equivalent circuit and FEM, the longitudinal and torsional vibrators of the ultrasonic motor are designed, and better precision is obtained. Combined with the experimental study, the key factors which have much influence on the output torque are deeply analyzed for the first time, and some usefulconclusions are drawn, such as the double end of the piezoelectric vibrator should be forced, the longitudinal vibrator should locate near the nodal plane of the longitudinal vibration. Also the frictional material of the ultrasonic motor is deeply probed in the paper, and the conclusion that the viscid and coating type frictional material suited for longitudinal-torsional composite type ultrasonic motor is drawn. Finally, the longitudinal-torsional composite type ultrasonic motor is designed hollow in the middle, and the greater output torque is attained.3. The force passing model of longitudinal-torsional composite type ultrasonic motor is put forward. By using the momentum and energy conservation law and the other mechanics principle, the equation about contact angle and output torque are founded. By using the of the equation above, The inter-relationship between contact angle, output torque with pre-stressing, longitudinal and torsional vibration amplitude, the frictional material characteristic are displayed. It quicken up the foundation of the theory of the longitudinal-torsional composite type ultrasonic motor .4. The driving circuits with not only the shift between zero degree and 180 degree on he two...
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