| Ultrasonic motor is a new type of motor based on piezoelectric effect.Compared with the traditional electromagnetic motor,the ultrasonic motor has some unique advantages in its structure and driving characteristics,such as compact structure,fast response speed,and free from external magnetic field interference.It has a broad application prospect in precision equipment manufacturing.After long time stationary storage,the friction materials of ultrasonic motors are prone to aging and creep wear,which makes the operation stability of the ultrasonic motor worse,even the phenomenon that the ultrasonic motor cannot start normally,which seriously restricts the promotion of the ultrasonic motor use.Therefore,it is very important to develop a kind of friction material with excellent comprehensive performance and storage resistance.In this paper,the special driving method of the rotating travelling wave ultrasonic motor has been analyzed,and the effects of the elastic modulus,contact angle and friction coefficient of the friction material on the driving performance of the ultrasonic motor has been studied.According to the motion equation of the stator surface,the rotor motion equation and the principle of energy conservation,an ultrasonic motor contact interface driving model has been established.Based on the established model of the drive model,the effects of friction material aging and creep wear on the performance of ultrasonic motor has been analyzed,which provided a theoretical basis for composition selection and formula design of ultrasonic motor friction materials.In order to prepare the friction material of ultrasonic motor to meet the requirements of the subject,the accelerated aging and creep test of the original friction material in the laboratory has been carried out.The main reason for the degradation of the contact interface of the ultrasonic motor is that the friction material aging leads to the decline of the mechanical properties of the friction material and the friction coefficient of the contact interface between the stator and the rotor is reduced.Moreover,the material creep makes the surface of the friction material uneven,which increases the energy loss during the operation of the ultrasonic motor.On the basis of the established driving model of ultrasonic motor,and the friction material aging and creep on the performance of the ultrasonic motor.PTFE and polyimide was selected as the friction material matrix,the uniform test design method was used to study the influence of the content of each filler component on the performance of the friction material,and the range of reasonable amount was obtained.By using the regression analysis method,the designed friction material formula was further optimized,and an ultrasonic motor friction material with excellent comprehensive performance and long-term storage was developed. |
