The Measuring And Modeling Of The Volumetric Accuracy For Large-scale 5-axis Machine Tool Based On Laser Tracker

In aerospace manufacturing,there are many different types of large size and complex parts.The large-scale five-axis CNC machine tool has obvious advantages in the processing of these parts because of its large working space and flexible structure compared with the small machine tools.However,the large-scale machine tool is often limited by the precision of its manufacturing and assembly,which can not meet the precision requirement in the ultra precision machining,and the research contents of volumetric accuracy is the comprehensive effect of each error in the machine tool system,which can reflect the precision of the machine in the whole working space and provide the basis for the error compensation.Therefore,in order to improve the accuracy of the five axis CNC machine tools,this paper studies the spatial accuracy detection and modeling.Specific contents are as follows:(1)The source analysis of volumetric error is carried out firstly,and the representation method of spatial accuracy is studied.Considering the characteristics of large workspace of five axis machine tool,choosing the API laser tracker as detection instrument,this paper has studied the correlation detection principle which include the principle of 3D coordinate measurement and the principle of transfer station measurement.Based on the features of the volumetric accuracy of five axis machine tools,the detection scheme of the volumetric accuracy is designed.The working space of the five-axis NC machine tool is analyzed by using Monte Carlo method.(2)Based on the principle of GPS,by using a laser tracker,a multi-station method is used for detecting five-axis CNC machine tool pose accuracy.Based on the analysis of the work space,the algorithm of generating spatial measuring points is studied,the measuring points of the machine tool workspace are generated.And the station of laser tracker in the process of measurement and measurement path was optimized by using a GA,which can ensure the accuracy of measurement and improve measurement efficiency.(3)Polynomial function is used to fit the error value of each single error at any position of each axis of the machine tool.The position and pose vector of the machine tool is calculated based on the kinematics model of the machine tool,which was compared with the position and pose data detected by laser tracker,the difference vector can be obtained.The LM algorithm is used to identify the polynomial coefficients of each single error,and the volumetric accuracy of the 5-axis machine tool in the whole workspace is predicted.The modeling of five-axis machine tool's volumetric accuracy is realized.(4)The software of modeling and prediction of large-scale 5-axis machine tool's volumetric accuracy is developed based on the MATLAB GUI,and the different function modules are designed.The software application of the algorithm is realized.