Precision Positioning System Design Based On The Piezoelectric Actuator

The piezoelectric actuator has the advantage of small size,large torque,low noise,high resolution of displacement and low requirement of the external electromagnetic environment.So it has been widely used in precision positioning.However,the piezoelectric actuator itself hysteresis,creep and other non-linear characteristics and driver requirements,seriously affecting its wider application.Hysteresis of piezoelectric actuator make it driving by voltage has error reaching 15%-20%,while the creep characteristics also increase its displacement error.Therefore,we need to design more precise control and drive system for the piezoelectric actuator.Firstly,this artical analyzes the nonlinear characteristics of piezoelectric actuator,from the conventional drive modes of piezoelectric actuator select the PWM switch mode to drive it;discussing common models for hysteresis nonlinearity of piezoelectric actuator,select the Bouc-wen hysteresis model to modelling the piezoelectric actuator;demonstrating the control plan to piezoelectric actuator,confirms the control scheme is the hybrid control combining feed forward compensation based on the Bouc-Wen model and PI feedback.the drive of piezoelectric actuator designed in this article consists of the ECU major control module,DC power module,charge-discharge control module,sampling feedback module and so on.DC power module achieve a high voltage DC source of 120 V,with the output current up to 1A,and the static ripple is around 0.05 V.Charge-discharge control module uses energy conservation model to drive piezoelectric actuator achieving the voltage output of 0-100 V.Testing the linearity of drive power,step response,frequency response characteristics and so on,the driving module has achieved the adjustable 0-100 V power,accuracy of about 0.2%,and has a good dynamic characteristics,low nonlinearity error about 0.25%,output current up to 1A.I use Bouc-wen model to make model for the piezoelectric actuator using in the article,and complete its identification,complete feed forward control Bouc-wen model through its inverse model.This article designs PI feedback control and the hybrid control combining feed forward compensation based on the Bouc-Wen model and PI feedback.Through the assay domain transfer function and the transfer function by using trial and error to get the corresponding control simulation parameter,by the time domain test method obtain the transfer function of piezoelectric actuator and by the transfer function using the trying method determines the parameter of PI controller.Finally,by experiment tests the whole control system.Through testing,in aspect of static,the drive control system has error of 0.3% or less in the displacement output.In aspect of dynamic,when the expectation is a sin of a frequency of 1Hz,the error is about 2%,compared to a sine of a frequency of 5Hz,10 Hz when 20 Hz,the error of displacement increases while the frequency increases.Finally,the reason generating the error of displacement has been analyzed and the improve proposals has put forward in the aspects of the driving power,modelling,the selecting of the parameter of PI controller and environmental factors.