Micro Friction And Wear Analysis And Experimental Investigation Of Linear Ultrasonic Motor

Linear ultrasonic motor(LUSM)uses the converse piezoelectric effect of piezoelectric materials to excite the micro vibration of stator in ultrasonic frequency,then the rotor driven by frictional effect between stator and rotor moves in a straight line.The frictional contact between stator and rotor is the key point of LUSM,which affects the output performance and efficiency of the motor.The contact state of LUSM is related to the surface profile,wear and so on.The actual contact surfaces are composed of many rough peaks,the height and distribution of peaks not only affect the output characteristics of motor,but also influence the stability and reliability.The research on micro friction and wear of LUSM involves many aspects,which is worthwhile to make further study.For these reasons,this manuscript focuses on the micro contact of LUSM,both theoretical and experimental researches are carried out.The main contributions of the dissertation are summarized as follows:(1)The contact surfaces of LUSM can be regarded as a series of rough asperities with different sizes and heights.The rough peaks will occur not only elastic deformation but also plastic deformation during the contact.Based on the contact theory,an elasto-plastic contact model is proposed,where the surface roughness is considered.The whole dynamic model of LUSM based on the in-plane longitudinal and bending modes is established by using the developed contact model.The influence of roughness parameters on the relative contact time and output performance of motor is investigated,the behavior of the force transmission between the stator and rotor is analyzed.Furthermore,a comparison between the proposed model and the spring model is conducted.The results indicated that the developed model can reflect the contact state between the stator and rotor and evaluate the output performance of the motor.(2)Based on the dynamic model of LUSM,a detailed thermodynamic analyses for LUSM is introduced by ANSYS.The temperature distribution of motor is analyzed,and the influence of surface roughness on temperature is investigated.Due to the assumptions that the material parameters,output characteristics and energy loss of the motor are not affected by temperature in the finite element analysis,the relationships between the temperature of motor and material properties and output performance can not be reflected.To solve these problems,a thermal-mechanical-electric coupling dynamic model is estabilished on the basis of the motor dynamic model and the thermodynamic characteristic of stator materials,where the interaction between the temperature rise and material parameters is considered.The experimental results show that the proposed model can be applied to predict the temperature changes during long time running and estimate the effects of surface roughness and thermo-mechanical-electric coupling on the output performance of the motor.(3)An experimental system is designed to study the friction and wear of LUSM based on the working principle of LUSM,which provides an experimental platform for research.The influences of friction material,preload and driving frequency on the velocity and wear rate of LUSM are studied by using the friction and wear test platform.Based on the experimental results,the morphology and wear mechanism of the contact surfaces are analyzed,which provide theoretical and experimental support for the life prediction of LUSM.(4)Based on the elasto-plastic contact model and Archard wear equation,a wear prediction model of LUSM is established by considering the effect of ultrasonic vibration.In the developed model,both the changes of roughness parameters with wear and the relationship between wear height and preload are considered.The wear prediction curve and velocity curve of the motor are obtained by simulation,and the validity of the prediction model is verified by comparing with the experimental results.The results show that the developed model can be used to predict the dynamic changes of wear volume and velocity of motor under operation.