Research On Piezoelectric Equivalent Circuit With Losses And Its Application On Ultrasonic Motor

Compared with the traditional electromagnetic motors,ultrasonic motors have practical advantages such as compact structure,high torque,and electromagnetic compatible,and are widely utilized in aeronautics and astronautics,medical devices and precision instruments,etc.Ultrasonic motors show the competitiveness particularly in miniaturization applications.Therefore,research on the improvement of power and efficiency of ultrasonic motors maintains considerable significance.In this dissertation,a six-terminal equivalent circuit model considering all three losses is established,and utilized for the research of a novel standing wave ultrasonic motor.According to the novel structure,three types of ultrasonic motors with specific functions are developed,respectively.In addition,aiming at minimizing the required energy and increasing the efficiency,an optimized driving frequency between the resonance and antiresonance frequencies is proposed for the piezo-transducer.In general,main contributions of this dissertation are listed as follows:1.There exist three fundamental losses in the piezoelectric materials,namely,dielectric,elastic and piezoelectric losses.Based on the widely used k₃₁ vibration mode,a new equivalent circuit is proposed considering three losses.In order to verify the feasibility of the new circuit,piezoelectrics with four different external load configurations are explored and simulated.The three losses are verified to play an important role in the energy dissipation mechanisms by simulation and experimental results.2.A new standing wave ultrasonic motor operating in radial vibration mode is studied.According to the operating mode,a new equivalent circuit with three loss characteristics is built for the stator.The resonance and antiresonance frequencies and their corresponding mechanical quality factors are derived and analyzed from the circuits.The experimental results of the motor show a stall torque of 0.27Nm,a no-load speed of 147r/min under an operating voltage of200V_pp.3.Piezoelectric transducers are commonly operated at their resonance frequency.However,this is not the ideal driving frequency from a power dissipation standpoint.In this study,an optimized driving frequency is proposed for the piezo-transducer.The optimum driving frequency in between the resonance and antiresonance frequencies of a Langevin transducer is characterized using a constant vibration velocity measurement method.Compared with the resonance drive,the optimized frequency drive reduces the required power by 1/2 which correlates to the mechanical quality factor?efficiency?increasing two-fold.4.A self-correcting standing wave ultrasonic stepping motor is designed using blades and grooves for positioning.The stepping motor is superior to those previously reported due to the positioning mechanism,which eliminates displacement cumulative error with an open-loop control system.The prototype with a diameter of 30mm,a height of 10mm is experimentally characterized.The results show that the rotor runs as the desired step angle of 45°without miss-step.Owing to the radial operating mode and metal-to-metal directly friction drive,the motor shows stall torque of 55mNm at a relatively low applied voltage of 100V_pp.The proposed motor has advantages of high torque density,simple drive and high scalability.5.A high torque standing wave ultrasonic motor and a bi-directional standing wave ultrasonic motor are proposed.The design of the specific performance contributes to the development and application of the radial vibration mode standing wave ultrasonic motor.