Modeling for Orientation Deviation of Workpiece and Analysis of Machining Accuracy Modeling for Orientation Deviation of Workpiece and Analysis of Machining Accuracy

Modeling for Orientation Deviation of Workpiece and Analysis of Machining Accuracy

  • 期刊名字:天津大学学报(英文版)
  • 文件大小:455kb
  • 论文作者:HE Gaiyun,YANG Baolong,ZHENG H
  • 作者单位:School of Mechanical Engineering
  • 更新时间:2020-12-06
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论文简介

Trans. Tianjin Univ. 2011, 17: 324-328DOI 10.1007/s12209-011-1 647-8Modeling for Orientation Deviation of Workpiece andAnalysis of Machining AccuracyHE Gaiyun (何改云),YANG Baolong (杨保龙),ZHENG Huiiang (郑慧江),JIA Hongyang(贾红洋)(School of Mechanical Engineering, Tianjin University, Tianjin 300072, China)◎Tianjin University and Springer-Verlag Berlin Heidelberg 2011Abstract: The machining accuracy of workpiece is influenced by its orientation deviation, which is caused by thefixture-workpiece error. Based on the spatial coordinate theory, the orientation deviation of workpiece is measured byusing an on-machine verification system, which can take into account the errors resulting from fixture manufacturing,installation and adjustment, location and clamping of workpiece. According to the least square method, the model oforientation deviation is built to determine the relationship between the theoretical and actual coordinate systems. Theinfluence of orientation deviation on machining accuracy is quantified, and it is shown that the orientation deviationonly affects the dimensional precision and position precision, rather than shape precision. In the experiment, the com-pensation processing of realtime errors was conducted, and the perpendicularity and inclination errors of the tetragonalpart were reduced by 38.46% and 47.06%, respectively.Keywords: orientation deviation; on-machine verification; least square method; machining accuracyWorkpiece orientation is an important factor in and thereby select the position of locating and supportingmany manufacturing processes. For example, in the nu- elements'. The influence of the position of wrap linemerical control (NC) milling, a particular workpiece was caused by workpiece, which was subjected to dintorientation may allow the machining of an entire part in and heat transformls. A mathematical representation us-one setup; while for other orientations, the portions of ing homogeneous transformation matrices was developedworkpiece may not be accessible by the milling tool, thus for the position, orientation and form characteristics asreorientation and refixturing are required. Based on thedefined in ANSI-Y4.59. The relationship between loca-geometry of part surface and machining surface of the tion source errors and position deviation of workpiecetool, and the degrees of freedom available for the multi-was determined quantitativelyl"-H2l. For the error com-axis NC machine, an optimal workpiece orientation could pensation, a realtime error compensation method for thebe computed. The workpiece's geometric error, loca-5-axis NC machine tool was investigatedl5!. Using thetor's geometric ertor, and clamping error influence the realtime error compensation, the orientation deviation ofworkpiece setup in workpiece fixturing. For the purpose workpiece can be compensated to improve the machiningof minimizing the machining error, a modification strat- accuracy.egy of the nominal tool path is to modify the cutter loca-The above researches focused on the mapping mod-tion source file from the computer-aided manufacturing els between locator errors and the position and orienta-system by means of the proposed modification model ontion deviations of workpiece. They mainly considered thethe basis of prediction deviation' . An algorithm was error source of the position and orientation deviations ofproposed for calculating the inverse kinematics of 5-axis workpiece. In this paper, the workpiece with the positionmachines close to singular configurations's. The position and orientation errors is analyzed, and an orientation de-of the steady determined the shape of roundness devia-viation model is built in actual processing, with the focustion and its valuelo. An attempt was to minimize the de- on the workpiece orientation deviation.viation in the machining zone due to the variation in size,中国煤化工Accepied date: 201 1-05-20.*Supported by National Natural Science Foundation of China (No. 50975200).MHCNMHGHE Gaiyun, born in 1965. female. Dr, Prof.Correspondence 10 HE Gaiyun, E -mail: hegaiyun@4ju.edu.cn.HE Gaiyun et al: Modeling for Orientation Deviation of Workpiece and Analysis of Machining Accuracy1 Problem formulationvith cardan angle 8@w =[8aw ,8Bw ,8w]" 14. Further-more, the orientation deviation of workpiece can be de-The orientation deviation of workpiece is the differ- termined by error matrix T(8@w) as follows:ence between the theoretical and actual orientations, asshown in Fig.l. 0-XYZ is the machine coordinate systemLoeator坐(MCS). O"-XWY"ZW and O"-XWYWZW are the theo-orientation .retical and actual workpiece coordinate system (WCS),respectively. Assuming that O"-XγY ZY is a moving8B.coordinate system consolidated on the workpiece, and theposition of workpiece can be determined by vector w.Due to the locator errors, the workpiece will deviate fromthe theoretical orientation. After the rotation of angle电8cw around axis XW ,8Bw around axisYw,and 89wAclual orientationaround axis zW , the workpiece reaches the actual orienta-Fig.1 Diagram of workpiece locationtion. Therefore, the orientation error can be representedT(δθw)= T(8Yw )T(8Bw )T(aw)=「cos(Bw )cos(8rw) -cos(8axw )sin(S/w)+ sin(8aw )sin(SBw )cos(SrW) sin(Saw )sin(&(w)+ cos(8Cwv )sin(&Bw )cos(8rw) |cos(8B。)in(&yw) cos(8aw )cos(8yw)+ sin(8cw )sin(&Be )sin(8yw) - sin(SCw )cos(8YW)+ cos(Sav )sin(&Bw )sin(SYw)[- sin(8Bw)sin(&aw )cos(8Bw)cos(8Cw )cos(δβw)(1「0tic fixture. Through the on-machine verification, the ori-where T(8y.)=|0 cos(8aw)- -sin(Saw) |entation deviation of workpiece can be determined as[0 sin(8aw) cos(8w)shown in Fig.3 according to the least square method andcoordinate transform theory.「cos(8Bw) 0 sin(&yw)]T(SB.)=(- sin(8yw) 0 cos(6Bw)]Theoretiral position「cos(8yw) - sin(8jYw) 0ATT(8a.)=| sin(&Yw) cos(Syw) 0|Holel●少22 Determination of orientation deviation ofSide face 2workpieceActual positionFig.2 Orientation deviation of tetragonal partTool stting is a major step to guarantee the qualityof NC processing. Only with the knowledge of the rela-(1) By using the on-machine verification, enoughtionship between wCS and MCS, the moving path of points are measured on the two side faces to acquire thecutting tool can be described precisely. However, due to coordinates in MCS.the orientation error of workpiece, it is difficult to ensure(II) With the least square method, two planes arethe identical orientation between the theoretical and ac- ftted with the above points, whose unit normnal vectorstual coordinates even with reasonable workpiece coordi- are coordinate axes of theoretial wcS. Another axis cannate, which will lead to processing error. Therefore, the be confirmed by using the vector cross product. Then theorientation deviation must be determined to guarantee the actual WCS (O" -xWY% ZW ) can be determined.machining accuracy by taking compensation measures.(II) According to G54/G92['s, the theoretical WCS2.1 Analysis of orientation deviation of workpiece (o" XWY* Z$中国煤化工.Taking the tetragonal part in Fig.2 for example, the(IV) ByuHCN MH Grm theory, theworkpiece is located and clamped by a 3-2-1 determinis- orientation devianon OT Workplece 0w is determined一-325-Transactions of Tianjin University Vol.17 No.5 2011based on the relationship between the two coordinate ing is conducted by using the error compensation soft-systems.ware. And if it cannot be compensated, locators or ma-(V) If II 8@w |Iz

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