Thermal Error Modeling And Compensation Of Three-axis Vertical Machining Center

Three-axis vertical machining center is the important equipment for finishing precision parts of small and medium batch.With the development of products in the electronic,automobile,ship and medical equipment industries towards precision,the requirements of high precision,high efficiency and intelligence for vertical machining center are also put forward.Thermal error is the biggest error which can directly affect the machining accuracy of vertical machining center.In actual machining,thermal error compensation technology can effectively reduce the influence of thermal error on the machining accuracy of machine tools.At present,scholars at home and abroad often only research part of the core technology of thermal error compensation technology,especially the thermal error modeling technology,but not fully research the thermal error compensation technology of machine tools.Which has great limitations in improving the machining accuracy and efficiency of machine tools.Therefore,this paper studies the optimization of temperature measurement points,thermal error modeling and thermal error compensation module development for the three-axis vertical machining center.It has a good theoretical guidance value for improving the machining accuracy,machining efficiency and intelligent ability of this kind machine tools.The main contents of this paper are as following:(1)The heat source distribution and temperature field of three-axis vertical machining center is studied,so as to design the thermal error measurement test and complete the thermal error data collection.Firstly,the structure of the three-axis vertical machining center,the causes of thermal deformation and the heat transfer are analyzed.Then,the finite element analysis of the thermal characteristics of the machine tool is carried out to obtain the steady-state temperature field nephogram and thermal deformation nephogram of the machine tool,so as to preliminarily understand the variation rule of the thermal error and determine the location of the temperature measuring points of the machine tool.Finally,the temperature and displacement measurement system of the machine tool is designed to collect the thermal error test data of the machine tool.(2)The temperature measurement points of the three-axis vertical machining center are optimized by the improved ordered clustering method.Firstly,the mutual information method is used to select the temperature variables.Secondly,the class diameter matrix is calculated,the error function is compared,and the initial classification of temperature measurement points is obtained by inductive method;Then,based on the statistical analysis of multiple linear regression,the best clustering number and the best temperature measuring point is determined by the correlation test and residual comparison.Finally,the thermal error models of the three optimization methods are compared to verify the effectiveness of the improved sequential clustering method in the temperature measurement points optimization of the three-axis vertical machining centers.(3)The thermal error model is established by support vector regression(SVR).Firstly,the parameters of machine tool SVR algorithm are optimized by using grid search method and particle swarm optimization algorithm,so as to obtain the optimal parameters of SVR algorithm.Then,the thermal error model of machine tool is established based on the SVR algorithm after parameter optimization.Compared with the MLR thermal error model,the results show that the SVR thermal error model has higher prediction accuracy and robustness.(4)Based on the secondary development platform of HNC-8 v2.0 numerical control system,the thermal error compensation module of the three-axis vertical machining center is developed.First,the temperature measuring point detection system is designed,and then the thermal error compensation setting interface and function are developed by QT software on the secondary development platform.Finally,the three compensation functions of the developed thermal error compensation module are tested and verified.