Research On Framework And Method For Collaborative Top-down Product Design

There are two important characters for complex mechanical product design, one is that it is usually carried out in a top-down manner; the other is that it is generally accomplished collaboratively by several teams or designers. However, it is difficult for traditional CAD systems to support the collaborative top-down product design. Because of the complexity of the collaborative top-down product design, as the first step, our research now focuses on the collaborative product design that is right after the concept design which means that a group of designers collaboratively fulfill the product design from abstract to detail.The main works of the dissertation is presented as follows:1. A framework is proposed for the collaborative top-down product design. We divide the collaborative top-down product design into three phases including layout design, collaborative skeleton design and collaborative detail design. Based on its requirements six functions are proposed for the collaborative top-down product design which are symbol based layout design, calculation of coupled structural parameters, collaborative assembly modeling, collaborative feature modeling, agent based variation propagation and multimedia conference based negotiation.2. A hierarchical and distributed product assembly model is presented. The assembly model contains three levels which are layout assembly model, skeleton assembly model and detail assembly model. The assembly model is distributed on the clients and server in replication mode. The assembly model on the server is a complete assembly model including the whole assembly model information. The client assembly model is dynamically loaded according to the designer's design information requirement, which includes both the information of the subassemblies or parts undertaken by the designer and those having assembly relationships with the subassemblies or parts. A naming mechanism that contains global IDs and local IDs is proposed to ensure the object IDs of distributed assembly model to be consistent all over the distributed system.3. A method is proposed to support the collaborative calculation of the coupled structural parameters. The fuzzy design parameters are represented based on fuzzy theory. Utility function is used to represent the priority of the different values of a parameter which is determined by the designers according to their design knowledge and experiences. The designers collaboratively establish the optimization model taking the utility as the target. Genetic algorithm is adopted to solve the optimization model.4. An agent based approach is presented for addressing design variation propagation during collaborative top-down product design. The assembly model changes are automatically monitored through the interaction and cooperation of the agents located at the clients and the server. The changes and distributions of the related distributed assembly model are figured out by the agent located at the server through the reasoning of engineering constraint variations, feature variations, assembly constraint variations and hierarchical variations. Based on the reasoning result the distributed assembly model of the related clients and the server are updated in a command based mechanism, which ensures the consistency of the distributed assembly model.5. A prototype named CTDAD is implemented based on the proposed research. The system adopts replicated client-server architecture and contains the following kernel functional modules: layout design, collaboration calculation of coupled structural parameters, feature modeling, assembly modeling, variation propagation agent, ID management, negotiation management. Base on the CTDAD, the collaborative top-down product design of a manipulation is accomplished to verify the framework and method proposed in the paper.