Research On Error Model Of Encoder Measuring System

As an important method in the field of precision measurement,encoder displacement measurement technology has some advantages,such as low environmental impact,high measurement accuracy,and high speed.Based on the encoder displacement measurement system,this work derives the measurement model of the system in connection with the grating and reading head layout by studying the principle and system layout of the encoder displacement measurement,and calculates the error of the measurement model on the simulation software.In order to investigate the influence of different grating read head combinations on the measurement model,four measurement models of different read head combinations are deduced respectively,and the solution errors of different read head combination measurement models are analyzed,and the grating read head combination with six degrees of freedom was optimized.At the same time,this work analyzes the installation error of the encoder displacement measurement system,which provides a reference for actual engineering applications.The main research contents are divided into the following parts:Firstly,this paper defines the motion coordinate system,reference coordinate system and reading head coordinate system used in the displacement measurement model,and then derive the system displacement model,position model and measurement model,the four measurement models corresponding to the four grating read head combinations are deduced respectively.Secondly,according to the model error index,the expression of the established measurement model is simplified.The 6 DOF measurement method is analyzed,and the grating-read head combination scheme for solving 6 DOF is given.Besides,the error source of the displacement measurement system model is analyzed,and the corresponding error compensation scheme is given.Furthermore,Set the motion trajectory and simulation method of the wafer stage,simulate the measurement model on the simulation software,and verify the correctness of the measurement model derivation and the feasibility of the simulation method.In addition,the error of 6 DOF model is solved.The model solution errors of the X and Y-direction degrees of freedom are both less than 0.1nm,the Rx and Ry-direction degrees of freedom are less than 10 nrad,and the Rz and Z-direction degrees of freedom are less than 5nrad and0.2nm respectively,these results meet the requirements of measurement system indicators.Besides,the 6 DOF model errors calculated by the four read head combinations in the full range of travel is compared,and it provides an optimization plan for the read head combination of the wafer stage under each movement trajectory.Finally,Based on the assembly condition of the grating and the reading head of the encoder displacement measurement system,the influence of the installation error of the grating and the reading head on the encoder displacement measurement system is analyzed,and the motion trajectory of the motion table is planned on this basis,and the error terms are compared in pairs.The method dynamically introduces the installation error into the measurement system,and then simulates the solution of the four measurement models to verify the accuracy of the measurement model.When all the error terms are combined in pairs,the measurement model meets the measurement system index requirements.Besides,analyze the solution of the 6 DOF model error of each grating read head combination in the full range of travel,compare the model error calculations of each grating read head combination,and select a combination of grating reading heads with smaller model solution errors of the wafer stage under each movement trajectory,which can provide a theoretical basis for subsequent large-range measurement and reading head switching.