由形狀特徵建立組件關聯模型之機械工件重建及可切削單元推導

Abstract

本論文提出一套新方法，能夠自動地由一機械工件的二維電腦輔助設計資 料中辨認出該工件的形狀特徵，重建該三維實體，並進而擷取出該工件的 可切削單元資料。本論文分為兩個階段。首先，由一工件的二維工程圖中 自動地辨認出該工件的形狀特徵，將之記錄於形狀特徵相鄰關係圖中，用 來重建該三維實體；其次再由此相鄰關係圖中自動擷取出該工件的可切削 單元的特徵資料。此兩階段可以單獨應用，亦可結合成一個系統使用。三 維實體的重建包含三個主要步驟：（１）利用圖形分解方式來擷取二維電 輔助設計資料之工程圖的點與邊，（２）根據許多已發展的生產規則來辨 認形狀特徵，（３）利用平移掃掠及體積交集的操作決定相鄰關係中的基 底，（４）將形狀特徵之間相互空間關係建成一相鄰關係圖，並且據此重 建三維實體。 可切削單元的自動地擷取過程則是利用前階段之工件形 狀特徵相關係圖作為輸入，然後進行下列步驟：（１）先將方形素材與各 三視圖輪廓掃掠子塊進行體積交集的操作，擷取出可去除單元，（２）再 利用各突出形狀特徵外圍體積轉換其互補體積方式擷取此局部的可去除單 元，（３）辨認前述兩步驟中可去除單元間體積包含關係，擷取出實際工 件可去除單元組成，（４）利用可切削單元擷取演算法，擷取前述結果中 各類可切削單元。擷取所得的輸出資料有工件之可切削單元的順序與相關 幾何資料，及加工時可能的進刀方向。 本文利用許多例子來闡述主要 的程序，並對所提的方法進行模擬分析俾以驗證其應用於ＣＡＤ╱ＣＡＭ 整合的可行性，論文中列有詳細模擬結果。 This dissertation is to develop a new method to automate the form feature recognition, part reconstruction and machinable form feature (MFF) extraction from a 2D CAD data. To be more specific, the dissertation is organized as two phases. First, a method is developed to recognize 3D form features from 2D CAD data and to build form feature adjacency graph(FFAG) for 3D part reconstruction. Second, a method for automatic extraction of machinable form features from an FFAG model. These two phases are designed in such a way that they can work individually or jointly. The 3D part reconstruction process consists of four main stages: (1) to use the divide-and-conquer strategy to extract the vertex-edge data from each 2D engineering drawing in the IGES format, (2) to develop a set of production rules to facilitate form feature extraction, and (3) to use a sweeping operation and a volumetric intersection operation to get 3D part base, (4) to construct the form feature adjacency graph from the recognized form features and the part base; then reconstruct the 3D part according to the spatial relations given in the FFAG model. The process of machinable form features extraction uses the FFAG representation as the input and involves the following steps: (1) extract the removable volumes by the volumetric intersection of a cuboid stock and the swept subparts of a set of 3-view drawing contours, (2) substitute the local protrusion by their bounding envelop volume minus complemented volumes, (3) check the inclusion relationship to obtain the resultant removable volume, and (4) classify the removable volumes into varoous types of MFF using MFF extraction algorithm. The attributes of extracted MFFs include related geometric datum, sequences and possible tooling entrance directions, etc. Detailed examples are included to illustrate the feasibility of the proposed system. And the simulation results and discussions are also reported.