以特徵為基礎之工作構建方法論

Abstract

本論文在研究以特微為基礎之工件構建方法論，並以所提出之方法論實做一操作簡便的範例系統。本文中視特徵為物件，並於實做系統中應用了物件導向的觀念。此範例系統由三個子系統組成：(1)特徵為基工件設計子系統；(2)特徵基工件編輯系統；(3)特徵為基組裝件設計子系統。 (1)特徽為基工件設計子系統：本研究著眼於探討具凹特徵之方形工件設計，其中透過預先定義之三維凹特徽做設計及修改之基本元件。所提供的兩組功能可使設計人員方便地構建及修改工件。特徵為基之工件設計結果，則同時以構建式實體幾何資料及零件邊界資料表達方式存檔。而此構建式實體幾何資料之特微使本子系統不需透過繁複的特徵辨認及抽取過程，即可輕易地與電腦輔助製程規劃╱電腦輔助製造系統整合。 (2)特徵為基工件編輯子系統：本研究針對工件編輯時，特徵交互作用情形（尤其是特徵交集和特徵包含）所產生的影響及對應解決方案的深入探討；並以系統化的分析方式，推導出一套更新工件零邊界資料及構式實體幾何資料之法則，得以迅速有效地完成工件編輯後之資料更新動作，並保有最精簡的工件特徵資料。 (3)特徵為基組裝件設計子系統：此子系統具備了完整之零件╱組裝件設計、編輯功能；在易學易用的操作界面上，設計人員可透過本系統充分表達其設計理念。本計畫利用「裝配特徵」的描述，可減化設計人員在零件定位之資料輸入工作，及協助編輯工作之進行。所設計的組裝件，分別以組裝樹及組裝關係圖來表達，除了易於構建外，也使得工件資料之編輯、更新更易達成。 本論文在工件構建理論，及在使設計人員簡便修改工件理伭上均有相當貢獻。所構建完成的工件特徵資料更可成為電腦輔助設計及電腦輔助製造系統極佳的溝通界面。不謹單一工作可方便地由本研究所提出的方法論進行構建外，單一工作間更可透過彼此共有的特徵資訊，以本文所提之電腦輔助定位方法快速地進行組裝件之裝配。

This dissertation is to study a feature-based design methodology for part modelling. A prototype system of the proposed methodology with user-friendly design environment is implemented. A feature is treated as an object in part modelling. The object-oriented concept is used in implementing the proposed system, including a feature-based part design subssytem, a feature-based part editing substem, and a feature-based assembly desin subsystem. In the feature-based part design subsystem, this research focuses on the design of prismatic parts in which predefined 3D depression features, instead of low-level 2D lines and points are used as entities for representation and manipulation. Two special sets of functions are devised which enable designers to freely construct and modify the parts. The feature-based parts are saved in both CSG form and B-rep form. The feature-based CSG form allows the propos d 3D part design subsystem to be easily integrated into CAPP/CAM systems without complex feature-recognition and-extraction processes. In the feature-based part editing subsystem, this research aims to address the issue about the problem of feature interaction, especially for enclosure and intersectionk among the modified feature and the other existing features. An efficient new approach to solving the feature interaction problem encountered in part-editing is thus proposed. A set of rules that facilitate updating the B-rep data and the feature-based representation of the part are devised. Such that, the B-rep data of the modified part can be updated efficiently and its feature list can be stored compactly. Moreover, the resulting part will be consistent with the designer's internt. Finally, in the prototype feature-based assembly design subsystem, this research tries to propose full design and edit functions for individual parts and assemblies. Through the userfriendly interface, designers can easily implement their design intent. A new convenient method for computer-aided positioning parts in an assembly is presented. High-level entities of mating features and mating relations are used to describe the composed state of parts in an assembly. Both the tree model and the relational graph model are used to represent the assembly in the developed subsystem. An effecient algorithum of transforming the tree model of an assembly into its relational graph model is also presented. With this hybrid representation scheme and the computer-aided part positioning approach, the assembly can be modelled more easily with less input data; meanwhile, the related data for mating parts can be modified consistently and quickly. This dissertation contributes to not only the construction aspects, but also the issue of enabling designers to modify feature models of existing parts conveniently. The created part feature models can be a well communication medium in CAD/CAM applications. Moreover, individual parts with feature information can be easily mated into an assembly model through the proposed computer-aided part positioning approach.