Research On The Theory, Method And Application Of Process-and-history-oriented Assembly Modeling In Virtual Environment

This dissertation presents a new theory and method of process-and-history-oriented assembly modeling in virtual environment to make the most of the potential advantages of virtual reality in product design. Great progress has been made in the research of the key techniques of virtual assembly, which includes the assembly model representation, assembly relationship recognition, assembly motion navigation, physical constraint modeling, and assembly history reusing. On the basis of the theoretical research, a virtual assembly system is developed, which can support the designer in performing assembly modeling in virtual environment intuitively and freely. The research of process-and-history-oriented virtual assembly modeling has promoted the assembly modeling from constraint based modeling to semantics based modeling, from geometrically based modeling to physically based modeling, from result-oriented modeling to process-oriented modeling in virtual environment. And the successful applications in several research projects have proved the utility, flexibility, and power of the theory, methods and software system proposed in the dissertation.The dissertation is organized as follows:Chapter 1 (the introduction) gives a review of the development situation in virtual design and virtual assembly research and application, while the open questions are also analyzed. And the background, significance and contents of process-and-history-oriented virtual assembly modeling are proposed particularly.Chapter 2 presents a process-and-history-oriented virtual assembly model, which includes the representation of part attributes, assembly relationships, and assembly process information. A multi-hierarchical part model is used to represent the part attribute information, the assembly semantics are adopted to describe the assembly relationships between the assembled parts, and an assembly history model is devised to store the assembly process and history information. This virtual assembly model not only supports the designer to express the assembly relationships via semantics that are more abstract and precise than constraints, but also records the assembly operations, assembly tasks, assembly trajectory, assembly sequence constraints and the generation history of the assembly hierarchy and constraint relationships. Further more, the designer's assembly experience and knowledge are also contained in the virtual assembly model.Chapter 3 puts forward the theory and approaches of assembly relationship recognition based on assembly semantics. The expression method of assembly relationship through virtual reality interaction is researched. The semantics recognition is implemented according to the matching of the spatial positions, assembly orientations, types and parameters of the semantics entity. A new geometry constraint recognition method based on assembly semantics is proposed to capture the user's intention, which improves the efficiency and veracity of assembly relationship recognition. Assembly relationship recognition based on assembly semantics promotes the interaction ofassembly modeling from lower-level geometry constraints operation to assembly task-level operation, and the assembly relationships can be recognized automatically rather than be specified explicitly by the designer.Chapter 4 presents a motion navigation method for virtual assembly based on the analysis of degree of freedom. The allowable motion space is obtained through the analysis of degree of freedom. Then, the assembly position solving, motion adjustment and semantics navigation tools are devised to achieve the motion navigation in the virtual assembly. Thus, the designer can assemble or disassemble the parts in the virtual environment freely and precisely.Chapter 5 puts forward a virtual assembly modeling method based on physical models. The physical constraint generation method is presented, in which the pair constraint is created through the constraint mapping method. A variable-stiffness spring, which can map the geometrical displacemen...