Research On Error Modeling And Error Detection For Heavy Duty Vertical Machining Center

With the rapid development of technology, people’s requirement to the precision ofthe product is improved, and the accuracy of machine tool is concerned widely. Errorcompensation with good economy and practicality has become an effective way toimprove the accuracy of CNC machine tool. Through the actual test, the error model ofmachine tool is established. Then the original error can be compensated by the artificialerror. At present, the technology of error compensation for medium-sized CNC machinetool has been widely studied. In this paper, it will focus on the theory and application oferror modeling and error detection for heavy-duty vertical machining center.Error modeling is an important process of error compensation of CNC machine tool.Based on the analysis of structure characteristics and combined with the deviation of thetool’s theory and actual running track, the geometric error model of heavy-duty verticalmachining center is established. Error detection is a key factor to guarantee the accuracyof the model. Based on the characteristics of indirect-detection and direct-detectiontechnology, tested for heavy-duty machine tool through two method of error detection byusing laser tracker is more appropriate. Then all geometric errors are identified in everyposition along each axis.From the results of experiment, all angle errors are close to zero and could beignored when the heavy-duty machine tool moving along three axes. At the same time,the condition of “small angle assumption” which suitable for geometric error modeling ofheavy-duty machine tool is verified. Through analyzing the geometric errors of machinetool, it can be observed that the tilt of beam is the major reason which influenced theaccuracy. In machining simulation environment, changing the NC code through thetheory of polynomial least squares fitting of geometric error element. And showing thevalidity of error compensation through observes the surface of work-piece before andafter compensation.The worktable of heavy-duty machine tool is overloaded all the time and it isanother major factor which affecting the accuracy of machine tool. Through finiteelement analysis, the relationship between the main source of the thermal errors and thetable’s floating deviation can be determined. Based on the grey relational analysis of graysystem theory, the major reason which affecting the accuracy of worktable can beanalyzed. Then through the methods of multiple linear regression and BP neural networkrespectively to establish the thermal error model of heavy-duty vertical lathe. The resultshows that the precision of the thermal error model based on BP neural network is more accurate. And it provides good conditions for error modeling and error compensation aswell. Finally, the comprehensive error model between geometric error and thermal errorof this machine tool is established.