Research On Ontology-based Design Reuse Techniques With Its Applications In CAFD

With the development of global economic and information techneques, the considerable competitions among enterprises have been bloomed, and product innovation has become the main subject of manufacturing industry. The competitiveness of enterprises lies in its capability of product design, the focus of which is to quickly introduce new technologies and develop new products with highest quality and at lowest costs. Generally, knowledge is the basis of modern product design. Information is the carrier of knowledge, therefore, the design activities can be regarded as the flowing processes of the knowledge and information, i.e., relevant information can be materialized into a solution by information collection, processing and synthesizing. After the several decades'development, enterprises have accumulated a large number of design resources and design knowledge. Therefore, how to effectively reuse these design knowledge has been the important means of achieving rapid product design, improving product quality and reducing product costs, in which knowledge acquisition and retrieval are playing the core roles. Based on the state-of-the-art design reuse theory and relevant technical achievements, this dissertation conducted deep and detailed researches upon ontology-based key technologies of design reuse, providing a valuable solution for intelligent product design. In addition, the outcomes of this disseatation have also been applied in CAFD in terms of its characteristics and practical requirements. The main contributions of this dissertation are:The CAFD framework based on design reuse is proposed by combining the theory of design reuse with the characteristics of fixture design, so that existing fixture knowledge can be made good use of to achieve the rapid design of fixtures. This framework is based on fixture design ontology produced from domain corpus, which facilitates the commutations between different modules of this system. It encompasses ontology-based fixture design knowledge retrieval and ontology-based fixture model retrieval. The similarity between fixture model and fixture design requirements is assessed by the weighted average of the similarity of workpiece structural information and workpiece processing plan. Finally, a new fixture that meets the design requirements can be obtained by adapting the retrieved fixture model.On knowledge acquisition in design reuse, a graph-based approach for automatic construction of domain ontology from domain corpus, including concept extraction and relation extraction, has been proposed for knowledge and information management. First, each document in the collection is represented by a document graph. Then random walk term weighting is employed to estimate the relevance of the term information to the corpus from both local and global perspectives. Next, graph clustering algorithm is used to disambiguate terms with different meanings and group similar terms to produce concepts. Next, an improved frequent subgraph mining algorithm constrained by both vertices and informativeness is exploited to find arbitrary latent relations among these concepts. For ontology evaluation purposes, a method for adaptive adjustment of concepts and relations with respect to its practical effectiveness is conceived. Finally the domain ontology is formed by describing domain concepts and relations using OWL-DL, which is the basis of this dissertation.On the knowledge representation and retrieval, an ontology-based production information retrieval approach has been proposed. The semantics of the queries are first analyzed, and then converted into domain ontology concepts. The corresponding semantic features with regards to query semantics are expanded by ontology-based query expansion so that the retrieval system can understand the query intention of the users more clearly. The clustering between expanded queries and domain ontology concepts is performed during query process to find the proper ontology concepts closest to the queries, and then through the domain corpus labeled with domain ontology, the corresponding domain documents related to the query semantics are obtained. Finally, the relevant results are feedback to users by semantic matching.On the 3D shape descriptor and retrieval of product models for design reuse, a novel shape retrieval algorithm independent of CAD systems based on mesh salient critical points has been proposed. According to the Morse theory, the discrete mean curvature at vertices of the model mesh is used as the smooth real function to calculate salient critical points of the mesh, which reduces the impacts of insufficient sample points on algorithm performance. Then the approximate geodesic distance between two critical points and the corresponding cosine value of the intersection angle of the two vertex-normals are employed as the united shape function (USF) to describe the variation of global shape and local surfaces. Shape distributions are generated by computing the USF within each class of critical points, i.e. maximum, minimum, and saddle, respectively. The 3D shape is represented by the weighted average of these three sub-descriptors. Thus the matching of models is transformed into the comparison of corresponding shape distribution matrixes. This algorithm can assess the similarity of product models from the model itself without the requirements of other further information. In addition, a novel approach of retrieving fixture models by workpiece model is also addressed. In this method, a mapping from workpiece to its fixtures is established to achieve the retrieval of fixture models.The outcomes of this dissertation have been applied to computer-aided fixture design system, and the design-reuse based computer-aided modular fixture design (DR-CAMFD) system has been developed. In DR-CAMFD system, existing modular fixture design results, including fixture models and design knowledge and experiences, has been considered for a new fixture design. An evolutionary searching algorithm is used to find feasible solutions to the new design requirements in the design space. The fixture retrieved can be directly employed as the new solution if it meets the new design demands, or can be adapted to meet the new design requirements. We also took a modular fixture design as an example to verify the key techniques addressed in this dissertation.