| Optical coherence tomography(OCT)endoscopy is an optical contrast method that combines OCT and medical electronic endoscopy.The OCT endoscopy with micron-level resolution has become the focus of scientific research,and it is applied to the examination of multi-site scanning angiography.At present,most control systems of the OCT endoscopes use electromagnetic actuators,which have complex structure and poor driving and control accuracy.Therefore,this dissertation focuses on the analysis of a new type of piezoelectric motor with integrated stator system.As a new type of material in the information age,piezoelectric ceramics can convert mechanical energy into electric energy and meet the needs of the MEMS.The micro piezoelectric motor is composed of stator and rotor,is a new type of micro special motor,using the inverse piezoelectric effect of piezoelectric ceramics,by applying a fixed frequency voltage to stimulate the specific mode of the stator,the stator generates high-frequency micro-amplitude vibration,and contact with the rotor generates friction to obtain kinetic energy,drive its rotation,meet the design requirements.The further miniaturization and industrialization of micro piezoelectric motors are the two major challenges facing us.The micro-driven piezoelectric motor studied in this dissertation works in the gastrointestinal tract of the human body,and the internal space is narrow and curved,which is difficult to control.Moreover,in today’s society,the number of gastroscopy is large,so solving the problem of miniaturization and industrialization is more urgent.The integrated stator design method is proposed to solve the above two problems to a certain extent.The main content of this dissertation is as follows:(1)To solve the problem of further miniaturization and industrialization of micro piezoelectric motors,a new type of stator structure,the integrated stator,is designed,which is composed of solid metal cylinder,two piezoelectric ceramics,metal cap,output shaft and magnetic metal.The metal cylinder has a diameter of 1 mm and a length of 5 mm.Two orthogonal sections are cut on the side during machining,which are used to paste the piezoelectric ceramic sheet.The metal cap is connected with the output shaft to the rotor,and the magnetic metal fixes one end of the stator.The integrated stator integrates a variety of components,the structure is simple and compact,easy to miniaturize,and the production and assembly is relatively simple,effectively solve the miniaturization and industrialization of the micro piezoelectric motor.(2)In order to study the feasibility of the integrated stator design,the finite element simulation software ANSYS is used to establish the integrated stator model.Considering the influence of different materials on the stator parameters,the metal steel is selected as the stator material.Firstly,the modal analysis method is used to optimize the modal vibration frequency of the integrated stator structure,and then the sweep frequency analysis method is combined with the harmonic response analysis method to study its vibration in the frequency range.Finally,the transient analysis method is used to verify the motion of the integrated stator in different time periods and verify the rationality of integrated stator design.The effects of the material characteristics of the stator with different length-diameter ratio,piezoelectric ceramic sheet with different thickness and adhesive on the stator vibration characteristics and modal frequency were studied.The simulation results show that the first-order modal vibration frequency will decrease with the increase of the length-diameter ratio of the stator.The modal frequency increases with the increase of the thickness of the piezoelectric ceramic sheet.The material properties and thickness of the adhesive have little influence on the modal frequency of the stator,but have great influence on the vibration characteristics of the stator.When the diameter and length of the integrated stator are determined to be 1 mm and 5 mm respectively,the first order bending vibration frequency is21.3k Hz.(3)In order to further study the motion mechanism of the micro piezoelectric motor,the stator is regarded as a beam with one end fixed and one end free.The dynamic response of the stator under the excitation of external voltage is obtained by using the Timoshenko beam model and the mode summation method.The modal vibration displacement of particle on the stator surface is obtained by combining Hamilton’s energy variational principle,and the formation of elliptical trajectory is analyzed.The whole electromechanical coupling dynamics model of the micro piezoelectric motor was established by using the constant rotor contact model and the torque balance principle.The effects of different excitation parameters on torque-speed,torque-efficiency and load characteristics of the motor were simulated and analyzed.The simulation results show that,under the action of alternating voltage,the stator which is perpendicular to each other synthesizes a one-line wave on its end face,and the motion path is elliptical.When the pre-pressure of piezoelectric motor increases within a certain range,the rotational speed decreases with the increase of the pre-pressure,and the lock-in torque increases with the increase of the pre-pressure.(4)The experimental study was carried out.Firstly,the piezoelectric ceramic plate was pasted on the micro piezoelectric motor and the motor integrated stator and rotor were assembled.Secondly,the capacitance check and impedance matching test are carried out on the piezoelectric motor.The capacitance is basically unchanged before and after pasting,and the impedance frequency is around 21 k Hz.The maximum no-load speed and torque of the piezoelectric motor are 400 rpm and 2.5 m N·m,respectively.The maximum output efficiency reaches 33%,which meets the requirements of OCT endoscope drive control application. |
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