| The ultrasonic motor(USM)is a new type of actuator that use piezoelectric material and its reverse piezoelectric effect to convert electric energy into mechanical energy.The converted mechanical energy exists in the stator as a vibration form.The vibration drives the rotor or slider to rotate or translate through the friction between rotor and stator.The working principle of USM endows it the merits of compact structure,high precision,low speed and large torque,quick response,electromagnetic compatibility,self-locking on power off.These advantages make the USM suitable to apply in many occasions that traditional electromagnetic motors do not satisfy the working conditions.Consequently,the USM can be applied in many extensive areas such as medical instruments,precise stage,auto-zooming/focusing,and robotics.The USM is a typical interdisciplinary science that involves aspects such as vibration mechanism,tribology,electrics/electronics,material science,and control theory.In this thesis,we analyzed how the piezoelectric material and its reverse piezoelectric effect produce bending deformation,generating mechanical power.The mechanism of how in-plane modes work and form elliptic motion in the stator was studied.The mechanism of how the helical motion was generated by the thread contact is also studied.Based on the above knowledge,the following problems were studied.(1)With piezoelectric constitutive equations and thin plate model,the mechanical quality factor,and effective electromechanical coupling factor of a bending piezoelectric transducer were calculated to view dependence of the length of bonded piezoelectric plate.The theoretical results show that product of the two parameter K_eff~2Q_m reachs the peak value when the bonded PZT occupies 0.4-0.5 times the statorsurface.Four stators with different amount of piezoelectric plates were designed,fabricated,and tested experimentally.The results show that the stator with 4 PZT plates output the largest speed and energy efficiency.The performance is consistent with the variation trend of K_eff~2Q_m.Thus K_eff~2Q_m can be selected as an target parameter tooptimize the overall performance of the ultrasonic motor,so that the motor can output large power and maintain high energy rate at the same time.(2)A nut-type ultrasonic motor that can be driven with single signal was proposed.A method using single channel laser dopler vibrometer to measure vibration phase was proposed.The method takes the input exciting signal as the reference signal to calculate the vibration phase.Together with the measured amplitude,a complete travelling wave can be described by the method.Using the proposed measuring method,the vibration phase of the single signal drive nut-type ultrasonic motor was measured and recorded.The result shows that a single signal generated a traveling wave in the stator.The feasibility of using single signal drive to excite a travelling wave was deduced theoretically.The phase response of the damped vibration of a circular structure was calculated.From the result,it can be concluded that the single signal drive can generate a traveling wave in the circular structure,when the mode split happens and internal damping exists.(3)It is explored to apply the nut-type motor in a high temperature superconductor filter.The nut-type motor was minimized and redesigned to fit the application condition.The newly developed structure of the stator is a cup-like nut-type stator.Since a fixing base with bolt hole was added to the nut-type stator,the new cup-type motor can be fixed easily onto the application system with a bolt,so that the motor can be fixed conveniently without any assistant parts.Then,a prototype cup-like nut-type motor and superconductor filter were fabricated and assembled into an adjustable filter.The adjustable filter was tested in a cryogenic vacuum cavity,and the cup-like nut-type motor successfully tuned the center frequency by 6%.It's the first tunable HTFS using ultrasonic motor to change the center frequency mechanically. |
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