Study On The Exciting Technology Of Rectangular Shaped Vibrators For Ultrasonic Motors

The ultrasonic motors which utilize the mechanism of friction drive are quite differentwith the conventional electric motors. They utilize the friction force between the resonantvibrators and the rotors to drive. They are characterized as high torque at low speed, hightorque volume ratio, precise and accurate positioning, no electromagnetic interference andself-breaking without extra energy consumption, thus meeting the requirements ofmicrominiaturization, high precision and intellectualization in the areas of direct drive,precise drive and non-magnetic drive.To successfully design an ultrasonic motor, and to get better motor performance, it isrequired to investigate the exciting technologies of vibrator for ultrasonic motors. When thepre-force and the load are fixed, the work that the vibrator does to the mover is determined bythe motion trajectory of the contact point. The motion trajectory of the contact point onvibrator surface is the coupling between working vibration modes. So how to effectivelyexcite the working vibration mode and successfully couple the working vibration modes arethe key issues in the design of ultrasonic motors. They are also the key to achieve betterperformances of ultrasonic motors.For the specific piezoelectric vibrator, the motion trajectory of the contact point onvibrator surface depends on the type of working vibration mode, the coupling betweenworking vibration modes, the amplitude of the exciting voltage, the frequency of the excitingvoltage and the exciting location on vibrator. This dissertation focuses on how to effectively excite and successfully couple the working vibration modes of ultrasonic motor vibrator, andit investigates the exciting technologies of vibration shape of ultrasonic motors in threeaspects:(a) the coupling of working vibration modes (b) the regulation method of thefrequency difference between working vibration modes (c) the method of determining theoptimal exciting location on vibrator.The main research contents are as follows:1. A dual-frequency modal superposition exciting method for ultrasonic motor withrectangular shaped vibrator has been proposed and realized. The requirements forsuperposition of two vibration modes are obtained. There are two bending vibration modeswith different frequencies are excited and superposed in this exciting method. Both thenormal vibration and the tangential vibration of contact point are superposition of twovibration modes, so the vibrator can obtain larger vibration intensity and the vibrator can domore work to the rotor subsequently. By selecting different electrode segments to excite thetwo vibration modes separately, each vibration mode could obtain the largest vibrationamplitude at the same time. According to theoretical analysis, an ultrasonic motor usingdual-frequency modal superposition exciting is successfully fabricated, and the motorperformances are experimentally measured to justify the effectiveness of this exciting method.2. A regulation method by combing genetic algorithm, neural network and finite elementanalysis is proposed to regulate the accordance of two frequencies of two vibration modes forultrasonic motors with rectangular shaped vibrator. This regulation method investigates thevibration of metal-piezoelectric composite vibrator, and modeling the mechanical-electriccoupling for metal-piezoelectric composite vibrator utilizing the finite element method. Theelectromechanical coupling of piezoelectric vibrator is accurately described. The backpropagation neural network is used to identify the objective mode from the output data offinite element analysis. This can automatically regulate the accordance of the frequencies oftwo different vibration modes, thus can save a lot of calculating time. The calculation results show that, using this regulation method, the frequency difference between two vibrationmodes can decrease to1.146Hz.3. An optimization method by combining artificial immune algorithm and finite elementanalysis is proposed for the exciting position optimization of a piezoceramic plate typeultrasonic motor. This method uses the artificial immune algorithm as optimizer. The artificialimmune algorithm has the merit of high efficiency which quick convergence. This can save alot of calculation time. This optimization method use the work that vibrator does to rotor asthe evaluation criterion, instead of only taking the vibration amplitude in one direction as theevaluation criterion of the possible solutions, which makes the calculating results closely tothe actual working condition. Calculating results show that, using this method to calculate theoptimal exciting electrode, the algorithm can quickly converge to global optimum. The motorperformances of two vibrators which include five exciting cases are experimentally measured.Experimental results show that, using the calculated optimal exciting electrode, the rotor canobtain the largest no-load rotational speed of five different exciting cases. These show goodagreement with the calculating results, which can justify the effectiveness of the objectivefunction. This proved that using this method, both the optimal exciting position and size ofexciting electrode can be quickly and accurately determined.