Modelling And Compensating For The Comprehensive Geometric Errors Of NC Machine Tools

There have two types of methods to improve the geometric precision of machine tool: Error Avoidence and Error Compensation. Using software technology, Error Compensation can enhance the precision not only for the new machine tool but also the used machine tool, and can be realized easily using low cost. In recent years, many researchers have devoted a great deal of effort to this work, and progress has been maken in certain aspect. However, some problems, such as modeling of spatial geometric errors between cutter and workpiece, fast measurement and identification of original errors, compensation of spatial geometric errors, have not been solved well. This thesis has carried out an in-depth study aiming at these problems and acquired the follow main achievements.Using multi-body kinematic theory, the modeling method of geometric error has been developed in this thesis. The mapping relationship between cutter-workpiece's spatial geometric errors and the original errors is studied, and the calculating formula for Vertical Machine center is deduced in detail. Aiming at five-axis CNC machine tool with rotary and swing table, the original errors of five-axis CNC machine tool are discussed, and the mapping relationship between cutter-workpiece's spatial geometric errors and the original errors is built. The transform matrix of spatial geometric errors for arbitrary structure CNC machine is also discussed.Two fast and low cost methods to measure and identify the original errors of CNC machine tool are presented in this thesis: nine threads measurement and T gauge measurement of 1-D hole arrays. Using laser interferometer to measure single axis movement in nine different positions, the first method deduces the mapping relationship between the single axis moving coordinate errors, linearity errors and the original errors. The second method deduces measurement and calculation of original errors using upright one another 1-D hole arrays of T gauge. The test equipment and data processing system are developed based on the two methods. Using the spatial error models of CNC machine tool, the calculating methods of spatial error compensation about localization motion, line interpolation motion and spiral interpolation motion, are built. And the dynamic compensation methods of geometric errors are integrated in Huazhong CNC.The experiment system of spatial geometric errors compensation for CNC machine tool is built. In this system, experiment validation of localization motion errors is realized. Spatial error compensations of one axis and two axes are also validated by experiment.Experiment results show that the model of spatial geometric errors, measurement methods of machine tool original errors and the compensation scheme of spatial geometric built by this paper are effective.