Research On Volumetric Error Modeling And Compensation Of Five-axis CNC Machine Tools

Volumetric error is an important factor that affects the machining accuracy of five-axis CNC machine tools,and a low-cost,flexible,and efficient methods to implement error compensation is required.Accurate,efficient and comprehensive geometric error identification and volumetric error modeling are the prerequisite and basis for error compensation,but the existing research results still cannot fully meet this demand.On the one hand,the geometric error identification process is complicated and difficult to operate,which is not conducive to quickly obtaining machine tool error elements.On the other hand,there are many types of five-axis machine tool structures,and the modeling efficiency of a certain type of volumetric error model is low and the versatility is poor.At the same time,the common off-line G code modification error compensation method is not suitable for flexible application scenarios and the machining requirements of complex structural parts.Therefore,based on efficient geometric error identification and generalized volumetric error modeling,this thesis uses offline and real-time methods to achieve machine tool volumetric error compensation.The main research work of this paper is as follows:(1)The translational axis error identification method based on the improved 9-line method and the geometric error identification method of the rotary axis based on the ball-bar multi-position measurement are studied.Use "single-line measurement of single error" instead of 9-line method of "single-line measurement of multiple errors" to realize simpler and more efficient translational axis error identification.Based on the HTM,the function relationship between the telescopic amount of the ball-bar and the error elements was derived,and then the multi-position error identification model of the rotary axis was established,and the test process was optimized.(2)A generalized volumetric error model based on screw theory is established.Based on the analysis of the difference between left and right multiplication of the error transformation matrix and the characteristics of the five-axis machine tool structure,a generalized volumetric error model suitable for any five-axis structure based on the screw theory is established.In addition,the modeling process and advantages and disadvantages of the above model and the HTM error model are compared through examples.(3)Improved the inverse kinematics solution method and developed a software system for volumetric error compensation.Aiming at the situation that the two rotary axes do not intersect,the inverse kinematics solution method based on the Paden-Kahan sub-problem is improved,and the existence of the multi-solution relationship and the solution of the inverse kinematics is analyzed.In the error compensation research,on the one hand,a general-purpose volumetric error modeling and compensation software was developed to realize the compensation in an offline manner;on the other hand,the HTM error model was integrated into the RTCP function of the CNC system to study the real-time error compensation.The two superiority complementation methods meet the needs of machine tools in mass production and flexible small batch production application scenarios.(4)Based on the above geometric error identification method,generalized volumetric error model and error compensation method,a verification test was carried out on a five-axis horizontal boring-milling-turning complex machining center.The results show that the research work of the thesis can effectively improve the volumetric geometric accuracy of the five-axis machine tool.