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標題: 含NURBS曲線之車床刀具路徑產生
Tool Path Generation with NURBS Curves for Lathe
作者: 邱成豪
Chou, Cheng Hao
關鍵字: lathe
tool path generation
NURBS curve
Bezier curve
出版社: 機械工程學系
摘要: 本論文之主要目的在於研究發展一套車床專用CAD/CAM系統,藉由自行輸入的直線、圓弧和自由曲線(Bezier、B-Spline、NURBS)作車削工件外形的設計,進而針對設計的外形作偏置(offset),再將偏置後的外形進行粗、精切的刀具路徑規劃,產生快速、有效率的刀具路徑,使能在合乎精度且無過切的的狀況下車削出所設計的工件外形。 對於外形曲線的偏置部分,應用原本用於封閉曲線的干涉指數演繹法作為基礎,解決自由曲線偏置後自交迴圈干涉的問題。利用Bezier曲線的凸殼特性和及位置誤差累積的觀念,將自由曲線分解成片段Bezier曲線來求取偏置曲線。在取得正確的偏置曲線後,可以針對所設計的外形特性選擇合適的刀具路徑產生法,得到正確的刀具路徑。 一般商業CAD/CAM專用軟體對於車床粗切刀具路徑的產生方法,最常用的程序有:軸向粗切削複合循環(G71)、端面粗切削複合循環(G72)和成形加工複合循環(G73)三種。為了避免粗切削時,發生切削到需要保留之材料的過切現象,在路徑規劃時必須針對不同車削工件外形特性選擇合適的刀具路徑產生程序組合。本系統提供其中兩種(G71和G72)切削路徑程序來產生切削上的安全區域,藉以得到合乎精確、完整的車削工件。 關鍵字:車床,刀具路徑規劃,NURBS曲線,Bezier曲線,偏置
The purpose of this thesis is to develop a CAD/CAM system for lathe machining. Users can design the geometry of a workpiece by elements which include types of lines, arcs and freeform curves(Bezier, B-Spline and NURBS curves). After offsetting the designed contour, efficient tool paths for rough cut and finish cut can be generated to lathe machining, the designed workpiece contour satisfying the precision requirement without gauging. As to the contour offsetting, interference index method is applied to solve the self-intersecting loop interference problems for freeform curves. The convex hull property of Bezier curves and the idea of accumulative position errors are used to obtain offset curves by decomposing freeform curves into piecewise Bezier curves. After correct offset curves have being obtained, tool paths are generated by proper path generation methods according contour shape characteristics. In most commercial CAD/CAM softwares, three commonly used procedures are include in the path generation method: repetitive turning cycle(G71), repetitive facing cycle(G72) and pattern repetitive cycle(G73). In order to avoid undercutting in rough cut, proper combination of procedures for path generation are chosen according to the contour characteristics of the designed workpiece. This system provides two lathe machining cycle procedures(G71 and G72) to produce secure zone in machining, such that an accurate and intact designed workpiece can be lathe machined. Keyword: lathe, tool path generation, NURBS curve, Bezier curve, offset.
Appears in Collections:機械工程學系所



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