Research On Error Modeling And Real Time Compensation Of Key Error On CNC Machine Tools Guideway System

The premise and foundation of error correction for CNC machine tools is to establish a precise comprehensive error compensation model. There exists lack of fully considering the influence of error correlation and offset for the error modeling and correction method. The Abbe error of guideway system for stack table can not be ignored because the influence of guide rail system error in one direction is two dimensional. Because the zero position of CNC machine tool measuring system can be moved with the bed thermal deformation, it need to establish a stable modeling reference point for the error compensation model. The zero point of measurement system is considered as the rotation center of Abbe error in the traditional analysis method. But the rotation center of working table and Abbe error are time-varying due to the existence of the guide way system error. So it is necessary to do further research to solve the problems existing in above aspects.Based on the thermal deformation theory, the critical point theory of thermal deformation was presented. The critical point was applied to improve the grating fixed way, which could eliminate machine thermal deformation of grating ruler of additional effects and ensure that the grating on the measured direction could expand freely according to the thermal expansion and contraction law. By using the critical point coordinate value of thermal deformation, the temperature variable and the thermal expansion coefficient of the grating ruler, the error of zero thermal drift error and the indication error prediction model of the grating system were established.A three axis CNC machine tool BV75 was selected as an example to study the principle and correlation of guide system Abbe error. The axial Abbe error calculation method and its model were analyzed and built which indicated that guideway system error in Y axis could be transferred to that o X axis and the additional Abbe error could produced. In addition, the Abbe arm calculated by using the traditional method that the center of Abbe error rotation is fixed did not agree with the actual size. So a rail system instantaneous motion center theory was proposed in this paper to do the accurate calculation of Abbe arm. Based on the theory of multi body system dynamics, the CNC machine error compensation model under the actual working condition was built by considering grating measurement error, Abbe error of guide way system, error correlation and offsetting.In this paper, the linear displacement location error, yaw angle error and pitch angle error was measured by using the dual frequency laser interferometer and the Abbe error compensation experiments of guideway system were done. The experiment results show that the positioning error of the linear displacement can be reduced from 450μm to-10 μm and the positioning accuracy can increase 45 times. The thermal deformation of grating ruler uder two different fixation methods was analyzed by using ANSYS software, whose results show that the CNC bed thermal deformation has no effect on the zero erro and the indication error of the grating system under the thermal deformation error critical fixed point method and provides a theoretical basis to build the the accurate CNC machine error compensation model.