| With the rapid development of micro/nano precision drive technology,higher requirements are proposed on the performance indexes,such as output accuracy,structure size,working range,response speed and load of the micro/nano precision positioning system.The piezoelectric drive stage has the characteristics of compact structure,high resolution,fast response and low energy consumption compared with the traditional drive stage,which becomes a hot research topic in recent years.However,piezoelectric actuators have a nonlinear hysteresis problem,which seriously affects the overall micro/nano precision positioning performance.At the same time,due to the needs and occasions of different application fields,it is difficult for the actuators to consider multiple performance indexes such as miniaturization,output displacement,load,accuracy.In order to solve the above problems,this thesis designs a linear piezoelectric walking stage system with a dual-mode control strategy,aiming at reducing the nonlinear effect of hysteresis,increasing the output displacement and load,improving the accuracy and speed,and reducing the structure size.This thesis expounds on the motion principle of the linear piezoelectric walking stage system and introduces the system composition of the linear piezoelectric walking stage.The proposed precision positioning system based on piezoelectric stack actuators and shear piezoelectric actuators is summarized and analyzed,which has the characteristics of compact structure,large stroke,high load and self-locking ability,fast response and high controllability.According to the driving principle of the piezoelectric actuators,the static and dynamic theoretical models are established for the clamping mechanism and driving mechanism of the linear piezoelectric walking stage based on the pseudo-rigid body model and the e-type piezoelectric constitutive equation.The theoretical static and dynamic models of the linear piezoelectric walking stage were analyzed and verified by simulation.Aiming at the problem of inaccurate output caused by the hysteresis of the linear piezoelectric walking stage,this thesis analyzes the linear piezoelectric walking stage by separating it into two parts: the linear dynamic model and the hysteresis model,and establishes mathematical models.In order to make the linear piezoelectric walking stage produce accurate output displacement,a variable parameter Bouc-Wen hysteresis model is proposed,which considers the influence of load,driving frequency and ambient temperature on the hysteresis characteristics of the piezoelectric actuators.The parameters of the variable parameter Bouc-Wen hysteresis model are identified.Experiments verify that the proposed variable parameter Bouc-Wen hysteresis model can accurately describe the nonlinear hysteresis curves of the linear piezoelectric walking stage under any load,driving frequency and ambient temperature.Thereby the accuracy of the mathematical model of the linear piezoelectric walking stage is improved.A dual-mode motion control strategy for linear piezoelectric walking stage is proposed.In the coarse positioning mode,when the external load changes,the controller uses the coarse positioning control based on the optimal driving frequency to select the optimal driving frequency to drive,and realizes the fast positioning of the linear piezoelectric walking stage.In the precision positioning mode,when multiple external conditions(load,driving frequency and temperature)change,the controller based on the feedforward feedback control strategy of variable parameter Bouc-Wen hysteresis model analyze and calculate to output the appropriate control signal,and realize a stable and accurate output displacement of the linear piezoelectric walking stage.The linear piezoelectric walking stage is linearized by the variable parameter Bouc-Wen hysteresis inverse model,and the proposed feedback controller considers the linear dynamics part of the linear piezoelectric walking stage.The sensitivity analysis of the linear piezoelectric walking stage system is carried out to reduce the influence of modeling error and external interference on the output accuracy of the linear piezoelectric walking stage.Through the simulation of the precision positioning control system of the linear piezoelectric walking stage with or without noise or model modeling error,it is verified that the precision positioning control system has good trajectory tracking performance.In order to test the performance of the linear piezoelectric walking stage system,the thesis establishes the experiment test system of the coarse positioning mode,the precision positioning mode and the dual-mode positioning mode through the linear piezoelectric walking stage prototype.According to the experimental test results of the coarse positioning mode,the maximum output speed,the maximum output force and the resolution of the linear piezoelectric walking stage prototype system is obtained,which provide the basis for the coarse positioning control.This thesis tests the precision positioning mode control performance of the Bouc-Wen model based on variable parameters when multiple external conditions change,and tests the step response and trajectory tracking characteristics of the linear piezoelectric walking stage prototype.The performance of the dual-mode control mode is tested and analyzed to verify that the proposed linear piezoelectric walking stage prototype can achieve fast,stable and accurate output performance under external conditions,modelling errors and external disturbance. |
