Feature-based Design Methodology for Part Modelling
|關鍵字:||電腦輔助設計;特徵為基礎設計;組裝樹模式;關係圖模式;CAD;Feture-based Design;Tree Model;Relational Graph Model|
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.
|Appears in Collections:||Thesis|