Research On The Reuse Technologies Of Mechanical Components Based On IGES Representation

For manufacturing industry, the effcient management and effective reuse of existingdata and knowledge become a key factor in reducing the design cost, shortening the prod-uct development cycle, and staying ahead in the competition. Based on China’s nationalstandard of digital representation for communication of product defnition data, calledInitial Graphics Exchange Specifcation (IGES), this dissertation focuses on the improve-ment of mechanical components reuse technologies, and expands the studies through dataexchange technologies and model retrieval algorithms, respectively. The main contentsand contributions are summarized as follows.First of all, some key technologies in IGES part data exchange based on Boundary-representation (B-rep) are provided. For the case that CAD systems based on Parasolidkernal do not support the closed revolution surfaces, a subdivision algorithm based on2D parameter domain is proposed; To solve the problem that B-rep models may lackparameter domain, an algorithm for reconstructing and amending the parameter domainfrom3D curves to2D parameter domain curves is designed. Additionally, to deal withthe different defnitions of topology data between IGES standard and CAD kernels, a“hypothesis–testing” based topology data exchange algorithm is presented. Based onthese algorithms, the pre-and-post processors of IGES part based on B-rep have beenimplemented.Secondly, some IGES data analysis and exchange technologies of assemblies basedon directed acyclic graph (DAG) and production rules are introduced. For the reasonthat current CAD systems cannot transfer mating conditions via IGES assembly data, theIGES semantic patterns have been extended by introducing the Associativity DefnitionEntity (ADE) and the Associativity Instance Entity (AIE). To handle the compatibilityproblems caused by the heterogeneous structures of IGES assembly fles, an approachbased on DAG is proposed to abstract the relationships between entities, and accordingto this approach, a production rule based method is presented to design the pre-and-post processers of assemblies. This method has good generality and scalability, and itscorrectness can be formally verifed.Besides, a functionality similarity based IGES part retrieval method is proposed. An algorithm to generate the canonical views of CAD models is designed frst, and a newfunctionality-based benchmark is constructed as well. Based on this preparatory work, atypical face based matching method for IGES part retrieval is introduced. This methodfrst gets the typical faces that are good at distinguishing the functionalities between CADmodels through training, then sorts these faces by their importance in descending order,and fnally computes the similarities between parts using a greedy strategy. Compared toexisting methods, the proposed method is more powerful in obtaining parts with similarfunctionalities, and hence could better support the reuse of assembling and design.Finally, an IGES assembly retrieval approach based on vector space model (VSM)is presented. By introducing the classical VSM in information retrieval feld into theassembly retrieval issue, the partial matching and quantitative ranking problems havebeen well solved. The scale-sensitive similarity measurement is further introduced in thecalculation of matching value, such that the original problem can be transformed into thebest complete bipartite graph matching problem. Moreover, two approximate methodsincluding typical parts based matching process and greed strategy based relaxed matchingalgorithm are presented and integrated in the framework for acceleration, and this makesthe prototype system could achieve interactive performance. A mass of experiments havedemonstrated the effectiveness of the proposed approach.