Measurement And Modeling Of Rotational Axis Geometric Error For CNC Machining Center

In the field of basic manufacturing equipment,five-axis CNC machine tool is becoming more and more important because of its superior machining performance.A five-axis CNC machine tool includes a moving shaft and a rotating shaft.There are relatively mature theories and methods for geometric errors measuring and modeling of moving axes,but there is a lack of systematic research scheme for rotating axes.For this reason,this subject is committed to the study of five axis machining center axis geometric error measurement and modeling,and error measurement experiments,to improve the accuracy of the machine tool to lay the foundation.This paper carried out the following research contents:(1)An experimental scheme for measuring geometric errors of single and double rotating axes of five-axis CNC machine tools is presented.One is to use the standard shaft to measure the three run-out errors of the center positioning hole of the workbench.The other is to use renishaw XL-80 laser interferometer to measure the rotation table angle positioning error,axial channeling error and radial runout error.It is converted into six basic geometric errors of rotation axis by geometric error identification algorithm.The standard axis measurement results can be used as a reference to correct the laser measurement errors,so as to obtain the error size introduced in the laser interferometer measurement scheme and provide a theoretical basis for improving the error measurement accuracy.The experimental scheme of measuring 12 basic geometrical errors,4 position errors and 4 vertical errors of two rotating axes simultaneously was designed by using renishaw XL-80 laser interferometer.It lays a theoretical foundation for the follow-up study on the error measurement scheme of other moving axes in the five-axis machining center and the geometric error compensation of the machine tool.(2)Based on the differential transformation method,the mathematical models of 41 geometric errors of nc machine tools and 20 geometric errors of BC rotation axis were established.Firstly,based on the theory of homogeneous coordinate transformation,the corresponding homogeneous coordinate transformation matrix of each axis is established according to the topological structure of the machine tool.Secondly,the differential transformation matrix is obtained accordin g to the homogeneous coordinate transformation theory between two coordinate systems.Then,the differential motion vector of each axis is expressed by its corresponding error term.Then add them together to get the motion vector of the cutter end in the cutter coordinate system.Finally,41 geometric error models of nc machine tools and 20 basic geometric error models of double rotation axes can be obtained by transforming them into the coordinate system of the workbench.(3)The error measurement experiment of rotation axis is carried out.In the experiment,the multi-tooth indexing table was taken as the measuring object,and the flat and side position of the multi-tooth indexing table was regarded as the C rotation axis and B rotation axis of the five-axis CNC machine tool.Using the micrometer with the designed parts,the radial run-out error along the X axis of axis C and axis B,the radial run-out error along the Y axis,and the axial motion error along the Z axis were measured in turn.Finally,three angular rotation errors of the multi-tooth dividing table are obtained by the corresponding identification method,which verifies the accuracy of the identification method.The spatial error model of rotation axis is obtained.At the same time,the installation error and measurement system error of the dividing table are analyzed,which lays a theoretical foundation for improving the measurement accuracy of geometric error.