Towards Intelligent Design Of Tolerance Specifications:an Ontology-Based Methodology

In most of today's product development,designing tolerance specification schemes is still manually carried out by designers according to product functional and assembly requirements and specific tolerancing standards.Different designers may design different tolerance specification schemes for the same geometric feature under the same circumstance.This may increase the uncertainty in product development and will eventually have a certain impact on the performance of the developed product.In addition,the EXPRESS language is widely used to represent tolerance information in industry.Even though using this language is capable to establish a syntactically correct representation model of tolerance information,it cannot represent the semantics of tolerance information explicitly.For this reason,using EXPRESS only is unable to satisfy the requirements of the representation and exchange of tolerance information semantics.To meet such requirements and to reduce the uncertainty in product development,the ontology theory and technology in the area of artificial intelligence are introduced to the study of computer-aided tolerance specification design and an intelligent design methodology of tolerance specifications based on ontology is proposed in this dissertation.The main research works of the dissertation are summarized as follows:A hierarchical representation model of tolerance specification information is established.Based on the spatial relation model,a representation model of tolerance specification information,which consists of five layers of part layer,feature layer,variational geometric constraint layer,tolerance specification scheme layer and tolerance zone layer,is established to meet the demand of the representation of the semantics of tolerance specification information.Each layer of the established representation model is described by one or more adjacency matrices respectively.A generation method of variational geometric constraints based on ontology is presented.On the basis of the variational geometric constraint theory,different types of variational geometric constraints are formally represented using description logic terminologi-cal axioms.The assembly information is formally represented leveraging description logic assertional axioms based on the part layer,the feature layer and the variational geometric constraint layer.On the basis of the description logic representations of variational geometric constraints and assembly information,the specific steps of the generation of variational geometric constraints are then given.The effectiveness of the generation method is verified via an example.A generation method of tolerance specification schemes based on ontology-driven case-based reasoning is presented.According to the general processes of tolerance specification and case-based reasoning,the framework of the generation method is designed.The generation steps of the datum and toleranced features of an arbitrary part are given on the basis of some existing research findings.Based on the tolerance specification scheme layer,the source and target tolerance specification cases are formally represented by leveraging description logic terminological and assertional axioms.The computation and highly accurate linear combination of the similarity between the toleranced features of a source case and a target case,the similarity between the part features of a source case and a target case and the similarity between the topological relations of a source case and a target case are studied.Then a retrieval algorithm of similar source cases is designed.The effectiveness of the generation method is verified by an example.A generation method of tolerance zone based on ontology is presented.On the basis of the tolerance zone layer,the tolerance zones of thirty-eight different types of geometric tolerances are formally represented by leveraging description logic terminological axioms.The tolerance specification scheme information of parts is formally represented by using description logic assertional axioms based on the tolerance specification scheme layer.On the basis of the description logic representations of tolerance zones and tolerance specification scheme information,the specific steps of the generation of tolerance zones are then given.The effectiveness of the generation method is verified via an example.An intelligent design prototype system of tolerance specifications based on ontology is developed.On the basis of the established representation model and presented genera-tion methods above,a tolerance specification ontology is constructed using the seven-step ontology construction method.The constructed ontology is then developed in Protégé 5.Based on the developed tolerance specification ontology,the implementation processes of the main function modules of the prototype system are explained.The effectiveness of the prototype system is verified by two application examples.