The Open-loop Compensation Research Of Arrayed Two-dimensional Piezoelectric Scanning Mirror Based On FPGA

Laser scanning mirror is a kind of precise beam control device,which can control the beam deflecting precisely or scanning fast,mainly used in space optical communication,laser radar and other fields.The laser scanning mirror driven by piezoelectric ceramic is suitable for high-frequency and small-angle scanning.However,the micro-displacement structure driven by piezoelectric ceramics is a nonlinear dynamical system,which contains hysteresis and creep.The existing mathematical model is difficult to describe this complex dynamic characteristic accurately,which has brought great challenges to the correction of nonlinear effect of piezoelectric ceramics.In order to compensate the nonlinear effect of piezoelectric ceramics,this article analyzes and measures the hysteresis and creep characteristics of piezoelectric ceramics which operates at frequency below 50 Hz.According to the empirical model of piezoelectric ceramics,a suitable open-loop compensation algorithm is summarized and proposed.This article builds a model based on the Madelung rule and the theory of Ru Changhai,which compensate hysteresis effect by the method of accurately calculating the output voltage corresponding to the target position after deflection,and compensate creep effect with outputting the reverse creep voltage.In order to meet the control and communication requirements of arrayed two-dimensional piezoelectric scanning mirror,on the basis of its mechanical structure and voltage amplifying circuit,the Field-Programmable Gate Array(FPGA)is selected as the control core,and Controller Area Network(CAN)communication is used as the main communication module.The host computer sends the deflection command through the CAN transmitter,while controlling the precise deflection of four two-dimensional piezoelectric scanning mirrors.Firstly,we need to measure the voltage-position curve of main hysteresis loop and the curve of the time-creep factor,stores it in the Flash memory to construct the corresponding table of hysteresis and creep.Then by taking the advantage of strong timing and high-speed computing power of FPGA,to compensate the piezoelectric hysteresis effect and creep effect.Finally,through the Digital to Analog conversion(DA)module output and coordinated with the external voltage amplifier circuit,the host computer can precisely control the deflection of the scanning mirror.All the control procedures are achieved by Verilog HDL language.The test platform is mainly composed by He-Ne laser,scanning mirror,Position Sensitive Detector(PSD)and NI data acquisition card.The LabVIEW program can be used in the test platform to obtain the angle deflection information through the displacement of the reflected spot on the PSD indirectly.The maximum error of the piezoelectric scanning mirror before correction is 2.414 mrad while it is less than 0.262 mrad after calibration,the error is reduced by an order of magnitude,and the hysteresis and creep effect correction of piezoelectric scanning mirror has achieved the desired effect.Due to the Inherent limitations of the open-loop algorithm,if it is necessary to further improve the deflection accuracy and operating frequency of the piezoelectric scanning mirror,the closed-loop control must be more appropriate,such as synovial control to compensate its nonlinear effect.