Research On Thin-Plate Type In-Plane Longitudinal-Bending Linear Ultrasonic Motor

The thin-plate type in-plane longitudinal-bending composite linear ultrasonic motor has the characteristics of simple structure and miniaturization,which make it have significant advantages in applications such as micro-mechanical,aerospace,precision positioning,and low-power drive.However,its output performance has not met the requirements of engineering applications.In this paper,a thin-plate in-plane linear ultrasonic motor using composite transducer was studied to find a stator structure with large thrust-to-weight ratio,better output performance and miniaturization.Based on this motor,the research works and achievements are as follows:(1)An in-plane linear ultrasonic motor using composite transducer was designed and developed.This motor stator is made of 8 pieces of piezoelectric ceramics and rectangular metal plate.The metal plate has fully symmetrical structural slots and the bottom of the driving foot has a flexible design.The research shows that the slotted design of the stator metal plate can reduce the frequency difference between the firstorder longitudinal vibration and the second-order bending vibration(the frequency difference is 80Hz),satisfy the frequency degeneracy condition,and realize the longitudinal-bending composite modal work.Based on the harmonic response analysis and transient dynamics analysis,the surface of driving-foot can produce the effective elliptical locus.Under the longitudinal-bending composite vibration,the amplitude of the driving-foot in the X and Y directions increased by 66.67% and 28.53% respectively,which verified the optimization results of the stator structure of the motor.(2)According to the characteristics of the intermittent contact between the stator and the slider,comparing and analyzing the two situations of single-driving motor and double-driving motor,the contact dynamic model about standing wave type linear ultrasonic motor based on Coulomb Friction Model was established.Based on this mathematical model,the stator-slider contact time,the normal dynamic contact force and the contact interface friction of the linear ultrasonic motor were systematically studied.The research shows that the larger the pre-pressure,the longer the contact time of the stator and slider.Both the contact stiffness and the normal amplitude of stator affect the speed about the contact time varying with the pre-pressure.The normal dynamic contact force and the dynamic friction force change periodically.The larger the peak of the normal dynamic contact force,the larger the peak value of the dynamic friction of the contact interface.Simply increasing the pre-pressure does not improve the output performance of the motor.The increase of stator normal / tangential amplitude both can effectively improve the output performance of the motor.Reasonable selection of friction materials can improve the output performance of the motor.Under certain conditions,compared with the single-driving foot motor,the peak value of the frictional force of the double-driving foot motor becomes smaller,but the frequency of frictional work is doubled.(3)The experimental study on the in-plane longitudinal-bending linear ultrasonic motor was developed,including stator driving foot vibration performance and motor output performance.Comparing the two cases of the stator metal plate with or without slotted design,the rationality and feasibility of the new linear ultrasonic motor were verified.The results show that the amplitude of X and Y directions of the stator driving foot which had slotted design are increased by 1.60μm and 0.92μm,respectively.Under the conditions of excitation voltage 200 Vpp,pre-pressure 20 N,excitation frequency 45.7kHz,phase difference 90°,the maximum no-load speed of the motor is 0.25m/s,the maximum thrust is 3.4N,and the thrust-to-weight ratio is 47(the stator weighs 7.36g).The motor no-load speed increased by 51.5% and the maximum thrust increased by 36%.The optimized motor has the better output performance,simpler structure,lighter stator weight,and is more conducive to miniaturization.In this paper,the idea of slotted stator metal plate can be used to amplify the vibration displacement,and it was applied to a thin-plate type in-plane longitudinalbending composite linear ultrasonic motor.The results show that the motor stator weight is reduced and the motor performance is improved.On the other hand,the contact dynamics model of standing wave type linear ultrasonic motor was established,and the contact dynamic characteristics of single/double driving foot motor were compared and analyzed.