Research On Error Measurementand Modeling For Multi-Axis Precision CNC Machine Tools

Multi-axis precision CNC machine tools play an increasingly important role in the development of the manufacturing industry.However,the complex structure and the cumbersomeness of the control system affect the machining accuracy of multi-axis precision CNC machine tools.In order to improve the machining accuracy and work efficiency of CNC machine tools,this paper takes the independently developed four-axis and five-axis precision CNC machine tools as the research object.Through measuring and analyzing the errors of multi-axis CNC machine tools,an error model was established.The main contents and research results are as follows:(1)Explains the description method of the low sequence array.Alignment sub-coordinate transformation theory and its derivation process are introduced in detail.Based on the multi-body system theory,a geometric comprehensive error model for five-axis precision CNC machine tools was established.(2)The geometric error of the moving axis of five axis precision CNC machine tools was measured and analyzed by laser interferometer.It was found that positioning error is the main influence factor of machine tool geometry error.According to the Chebyshev polynomial,the basic geometric error term model is established.It is found that the basic geometric error model has a high degree of approximation by comparing the measured curve.The basic geometric error model is substituted into the geometric error model to obtain the integrated geometric error model.Obtain the comprehension error variation rules of axes movement along axis X,Y,or Z and angle error in the case of two-axis linkage.The modeling process is simple and easy to program,improving effectively the accuracy and efficiency of an optical free-form surface Precision CNC Machine Tools.(3)The positioning error of the moving axis of the four-axis precision CNC machine tools is measured by the laser interferometer.It is found that the position error of the moving axis of the experimental table increased with the increase of the temperature of the platform until the experimental stage reached the thermal state and the positioning error fluctuated in a small range.According to the fuzzy C-means clustering and correlation analysis,the temperature measurement point is selected as the thermal error modeling variable.The comprehensive model of four-axis precision CNC machine tool positioning error was established by polynomial theory and minimization of squares.The model has high fitting accuracy and good robustness.(4)The thermal error prediction model for the axes of the four-axis precision CNC machine tool was established by a least squares support vector machine(LS-SVM).According to least square support vector machine thermal error model to calculate the prediction data comparing curves of the linear axes positioning error in the thermal equilibrium state.It was found that LS-SVM thermal error model has higher prediction accuracy.By comparing the polynomial error model with the LS-SVM error model,it is found that the LS-SVM thermal error model performs well,the fitting deviation bandwidth is narrow,and the mean square error is small.