Research On Geometric Error Measurement And Modeling For Three-axis Machine Tools

With Chinese manufacturing industries continue to upgrade,high-end manufacturing industries such as medical equipment and aerospace are increasingly demanding the machining accuracy of CNC machine tools.Geometric error as the main part of CNC machine tool error sources has great influence on the machining accuracy of machine tool,so it is very important for the upgrading of Chinese manufacturing industry and the development of high-end manufacturing to accurately measure the machine tool geometric error and improve machining accuracy of CNC machine tools through the effective compensation way.In order to effectively improve the compensation efficiency,a method to compensate the geometric errors of machine tools by using multi-DOF measuring instruments and geometric error compensation model is presented in this dissertation.Firstly,the Homogeneous Transformation Matrix(HTM)compensation model suitable for XYFZ three-axis CNC machine tools is derived based on the theory of multi-body system,and the prerequisites for the application of this compensation model and the problems in compensating geometric errors of the machine tools with multi-DOF measuring instruments are analyzed.Secondly,this dissertation analyzes the geometric error transfer mechanism of XYFZ three-axis CNC machine tools based on Abbe principle,and gives the calculation formula of the influence of the positioning error of the machine tool's motion axis on the machining accuracy.Thirdly,the HTM error compensation model conforming to Abbe principle and Bryan principle is derived,and the problem of its adaptation to multi-DOF measuring instrument is solved.At the same time,the error compensation model conforming to the geometric error transfer mechanism is given,and the calculation software of spatial error is written based on the C++ language.Finally,the correctness of the geometric error transfer mechanism analysis based on abbe principle is verified on the X-axis of the machine tool through experiments,and the compensation accuracy of the error model is verified by comparing the fitting diagonal positioning error and measuring diagonal positioning error of the machine tools.The comparison results show that: the HTM compensation model can compensate the spatial positioning error of CNC machine tools from 41.15?m to 16.37?m with a compensation rate of 60.22%.The HTM compensation model optimized based on Abbe and Bryan principles can compensate the spatial positioning error of CNC machine tools from 41.15?m to 5.32?m with a compensation rate of 87.07%.The compensation rate of the optimized compensation model is effectively improved by 26.85%.On the basis of verifying the effectiveness of the compensation model,an economical and high-precision linear axis five-DOF geometric error measurement system is developed in this paper in order to further reduce the compensation cost of the geometric error,which is used to replace the expensive commercial multi-DOF measurement instrument.Firstly,the optical path of the measurement system is designed based on the measurement principle of double collimation beam.Then,the serial communication module of upper and lower computer and the measurement software of the measurement system are programmed based on the C++ language,and the functions of data acquisition and filtering,data display,chart drawing and data storage are realized.Finally,sensitivity calibration experiment,stability experiment,static and dynamic precision comparison experiment and repeatability experiment were carried out in order to test the performance indexes of the five-DOF geometric error measurement system.The experimental results show that the linear drift of the measurement system is less than 0.9?m and the angular drift is less than 0.73 " within 60 min.The alignment error of straightness is within ±1?m,the alignment error of yaw and pitch is within ±1.5 ",and the alignment error of roll is within ±2.1 ".The standard deviations of straightness,yaw,pitch and roll error obtained by the measuring instrument after five measurements are 0.71?m,0.62?m,1.92 ",1.59 "and 2.31",respectively.