| The machining accuracy of NC machine tool is one of the important performance indexes of machine tool.The error sources that affect the machining accuracy mainly include geometric error,thermal error,force error and machine control system error,among which geometric error is the most important one.in this pap,based on that kinematic model of NC machine tool,the geometric error measurement method and error identification model are studied.taking XYFZ NC machine tool as the experimental object,the laser interferometer is use,the nine-line identification model is combined,the ridge estimation algorithm is used to optimize the identification model,and 21 geometric errors of the NC machine tool are identified,Based on the mathematical model of geometric errors,the mapping model of 21 geometric errors of three-axis CNC machine tool to the change of tool position and orientation was established,and then the mapping model of geometric errors to workpiece surface was calculated.The identification results were visualized by MATLAB software.(1)In this paper,the mathematical modeling of geometric error of NC machine tools is carried out by using the multi-body system kinematics as the core theory and the homogeneous coordinate transformation as the mathematical tool.The kinematic transformation matrix of the machine tool under ideal and practical conditions is derived.The topological structure of the machine tool is described by the method of low-order body array.(2)After the error model is established,the geometric error is measured and identified.The identification process of "nine-line method" is analyzed in detail,and the solving method of its identification model is analyzed.Ridge estimation algorithm is proposed to identify the errors,so as to obtain more reliable 21 geometric errors of three-axis CNC machine tools.In the identification experiment,the YCM-65 A CNC machine tool of Taiwan Yongjin is taken as the test object,the Renishaw laser interferometer is used,a reasonable test scheme is designed,and based on the theory of "nine-line method," the reasonable measurement space is selected to measure the error,and the measurement process is repeated for many times to improve the accuracy of the measurement results.According to the identification model,the measurement results are solved by the least square method and ridge estimation respectively to verify the reliability of the identification model based on ridge estimation.(3)A method of geometric error visualization is proposed in this paper.According to the geometric error,the mathematical model of tool pose affected by geometric error is solved.Based on the motion of tool relative to workpiece,the mathematical model of workpiece surface affected by geometric error is calculated according to the motion mode of tool cutting workpiece surface along the machining path with geometric error.take that ball-end cutter as an example,simulate the surface of the workpiece with complex curved surface,comparing the ideal surface of the workpiece with the actual surface of the workpiece by MATLAB software,visualizing the geometric error,show the effect of the geometric error of the three-axis CNC machine tool on the surface of the workpiece according to the single axis error and the overall error of the machine tool,and observe the influence of the machine tool error on the surface of the workpiece in the visual diagram.(4)The related contents of machine tool error compensation are discussed in detail,including the principle and process of error compensation.By exploring the influence of NC machine tool error on the workpiece surface,the workpiece surface parameter equation expression with machine tool geometric error is subtracted from the original workpiece surface to obtain the position coordinate deviation of machine tool geometric error on the workpiece surface in x,y and z directions.According to the position coordinate deviation,the machining instruction is corrected to achieve the purpose of error compensation. |
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