NURBS and Plex grammar based syntactic solid modeling and feature-based product design and recognition.

摘要

This dissertation describes (1) a new NURBS-based Syntactic Solid Modeling (NSSM) method, (2) a folding technique to generate entities using canonical NURBS surface patches, (3) an extension of Plex grammar to include containment topology and its application in solid modeling, (4) a syntactic product design process, and (5) a prototype of feature-based design and recognition scheme using NSSM. The NSSM is a hybrid method which combines characteristics of both conventional B-rep and CSG methods by including constructive history and boundary representation as NURBS surface. Extended Plex grammar is used as structural relationship descriptor to facilitate modeling and product design, and explicitly define the product structure and topological relations completely and unambiguously. A folding technique is developed to generate different types of entities using canonical representation of NURBS surface patch and the modeling domain of this method is large, versatile. The interconnections between the connected entities are specified by trim curves of the related entities and are described by Plex grammar. The concept of grammar driven object description combined with NURBS entities reveals the great potential applications in design automation. The syntactic product design process combines the conceptual design, syntactic grammar generation, and syntactic solid modeling processes and translates the design sketch into a meaningful product. The hierarchical structure of an object is obtained by analyzing conceptual sketches and subsequently translated into Plex grammar production rules to form an interconnection matrix that expresses the topological information among entities of an object. Validity and segment checking of design product and product modeling are implemented. A prototype feature-based design and recognition technique is proposed based on the above approaches which provide a high-level modeling tool of the generic design for manufacturing. Features are used as basic building entities. Hierarchical structure, group classification, and parameters are maintained to enhance the feature-based design efficiency. Features are extracted and recognized from the designed model for downstream applications. Compared to conventional solid modeling techniques and feature-based design and recognition schemes, this approach provides systematic object generation, manipulation and modification, and more control over congruity.