Research On Rotary Piezoelectric Motor Using In-plane Vibrations

Piezoelectric motors have been widely used in precision drive platform,aerospace,intelligent robot and optical instrument because of their quick response,high positioning accuracy and no electromagnetic interference,compared with electromagnetic motors.Nowadays,with the development of intelligent instruments,the demand for micro motors,which are the key actuating components,is getting greater and greater.But some piezoelectric motors are difficult to miniaturize due to limitations of the structure and principle.Because of the compact structure and simple mode excitation,piezoelectric motors using in-plane vibrations can be easily miniaturized.The most typical in-plane vibration motors are those using longitudinal and bending modes developed by Nanomotion Company.However,most of these motors are linear motors with rectangular plate structure.Therefore,the motors can not meet the application requirements on certain occasions because of their plate configuration and linear drive pattern.Furthermore,there are relatively few rotary motors using in-plane vibrations and their theoretical research is still not completed well.Consequently,theoretical researches on in-plane vibration motors,including their structure design and performance optimization are still need to be explored.This paper studies the constructing method and driving principle of micro motors using in-plane vibrations,which have good application prospects.In addition,new design ideas of in-plane vibration piezoelectric motors are also discussed.Based on the analyses,two methods of constructing hollow rotary micro motors using in-plane vibrations are presented.The methods provide new technological approaches for the miniaturization of piezoelectric motors.1.Research on piezoelectric motor using circumferential plane vibrationsTo expand configuration method of the hollow micro motor,constructing the circumferential surface vibration of the resonance stator by using multiple local resonance vibrators is first proposed.The transition mechanism between the bending mode of the vibrators and the torsional mode of the stator is also studied.The superposed modes of the stator are different because of diverse working modes of the vibrators.The number of vibrators can be chosen according to the application requirement,so that the motor designed by this method has strong extensibility.In the design,the dimensions of slots are optimized.According to the sensitivity analysis of the two mode frequencies to the slot parameters,how to realize frequency consistency of the two modes is proposed.To analyze the performance of the motor,the displacement response characteristic of the driving point is calculated by the finite element software.Based on theoretical analysis results,a prototype motor using circumferential surface vibrations is realized,and the feasibility of the design method is verified.Due to the vibrations of the stator concentrated in circumferential plane,the stator designed by this method can be a thin cylinder.The radial thickness of fabricated stator wall is 3.5 mm.The method overcomes the machining difficulty of conventional torsional piezoelectric plate.Meanwhile,the hollow structure of the motor is beneficial to reduce the occupied space and makes it possible to be applied to compact optical system with intermediate channel.2.Research on piezoelectric motor using vibrations in axis cutting planeTo meet the application requirements of in-vivo diagnostic instruments for piezoelectric micro motors,the single phase excitation theory of in-plane travelling wave and the resonance frequency adjusting method of the stator using magnetic field are presented.In addition,to meet the needs of energy wireless transmission and external control,the realization method of micro motor driven by external magnetic field is proposed on the basis of the single-phase drive piezoelectric motor.According to the incentive theory of two in-plane bending modes with the same order,the influence of additional mass on two mode frequencies and vibration directions of the hollow eight prism stator is analyzed as an example.Motor performances in two excitation ways are simulated to validate the feasibility of excitation mechanism theoretically.Finally,a prototype motor is fabricated to test the theory experimentally.As the stator vibrates in the axis cutting plane,the stator can be made into thin slice and then the occupied space is greatly reduced.The inner diameter of the prototype motor is 9 mm.Resonance frequencies of two in-plane bending modes are lower than that of out-of-plane bending modes used to construct shaking-head-type motors.Therefore,the output displacement of the proposed motor is larger than that of shaking-head-type motors under the same excitation voltage.The research of this project developes the in-plane vibration drive concept of piezoelectric motors and is helpful to broaden their application fields.