Research On Key Techniques For CSCW Based CAD System

Global economy has made manufacturing industry become more distributed than ever before. Product design requires more involvement from various technical disciplines at different location. With the development of Internet/Intranet and the wide spread of parallel, high performance computer and transaction, the concept of distributing, collaboration and virtual design are currently widely used in CAD. This dissertation mainly deals with a CSCW based CAD system and some related key technologies. Many techniques are reviewed and several new techniques are also proposed.Basing on the analysis of current collaborative CAD systems, a novel Web Service based distributed collaborative CAD system is proposed in this paper. The system uses XML to define feature operations and the communication protocol between the server and the client. To reduce network load and increase response ability of the system, the feature information is updated incrementally on the client. As it is constructed with Web Service, the system is able to support collaboratively designing on heterogeneous platforms. Its framework and communication protocols are analyzed in detail. The experimental results from the developed prototype system show that it can effectively support collaborative design under the distributed environment.Currently, feature is employed by most of the parametric solid modeling systems which are the kernel modeling system of the network-centric CAD systems. When modifying a feature, in order to maintain the original design intent, it is important to establish the correct correspondence between the previous and current topological entities of a feature model. This problem is known as persistent naming mechanism of topological entities. Based on the analysis of existing naming mechanism, a hybrid, simple and effective mechanism is proposed, which is based on both topological faces and design histories. It includes entity naming and entity retrieval. The necessary history information of faces is kept by the face's name. All topological entities are managed by the modeling system through three kinds of tables: face tables, edge tables and vertex tables. What's more, a two-level representation is provided to support model re-revaluation. It potential use in network centric CAD system is also discussed. Comparing to SolidWords, experimental result demonstrated that the proposed approach can handle most of the naming problems effectively.As the emergence of the need of transmission and sharing solid model on the network, how to transfer the solid model information effectively and reduce network delay is a hot issue in distributed CAD system research fields. The two commonly used techniques are the simplifying of B-rep of the model and the Cellular Topology technique. Nevertheless, these methods did not take into account of design history and dependencies among features. A new approach to transmission feature-centric model progressively and incrementally is proposed. It makes use of name mechanism of entities to update the solid model, and designer can selectively require the server to transmit the concerning portion of the feature model according to design histories and feature dependence net. It is showed that when the primary solid model is complex and contains many surfaces, employing this method may greatly reduce data transferred among the server and the client, making collaborative design effectively.It is well known that the nature of designing parallelly is a process of seeking a solution that satisfies various constrains imposed on the design product, or a process finding a solution for a constraint net. Besides used as a tool for assisting in locating geometric elements during sketching stage, constrains is also a useful tool for convey design intents and knowledge during conceptional design stage. Hence, a robust and efficient constraint solving system that supports under- /over- constrained condition is crucial to the network-centric CAD system. A new method for solving the constrain satisfaction problem is pr...