Research Of A Process-based CAD Model And Prototype System

The Project is "A Process-based CAD Model and Prototype System" which is supported by National Natural Science Foundation(Grant No. 50075058 ).In order to remain competitive of products, new approaches in the field of mechanical engineering are needed to improve the effectiveness and efficiency of the design process. The design process of a kind of new product is a process that involves much complex reasoning and determination. Any design always starts out from requirement but not from geometries. The geometries are the result of design but not start point. However, CAD systems in existence have a big weakness, which is that they regard geometries as main body of design. They start from drawing and only can describe final results of design process, i.e. geometric detail design stage, but not whole design process. Designers just can know product data from a CAD files but cannot get design process data.Based on research of modern design technology and CAD technology, this paper presents a process-based CAD model and approach which can support whole product design process, i.e. requirement description, conceptual design, structural design, detail design and production plan. The model and approach is able to support generation, evaluation and selection of designer's concept, to capture and structure the design data and domain knowledge, to support coordinating and distributed design based on Internet.At present, CAD systems cannot entirely support product design process. This paper presents a process-based CAD model, PCAD model, which focus on activityand tasks of design process and logical relationship between them. The model does not tell designers how to design but aid them designing and help them manage and optimize design process, to the effect that improving product quality, reducing product development cost, shortening development cycle and raising product competitive. PCAD model covers whole product design process, and it is developed by using the blackboard-based technology to combine the design matrix, function-means tree, product tree, IDEF3 model and third-party software tools. It is helpful to handle complex problems and build distributed application that is platform independent.According to PCAD theory model, the author develops a software prototype system using Java and XML. The core of the prototype system is to apply computer to support whole design process and achieve reuse of design data. Meanwhile, the system is platform independent and data is independent, so that coordinating and distributed design platform can be built. The PCAD system adopts object-orient programming method to design each function module. Its emphasis lies in supporting product design process, achieving Design Data Model and data exchange between system and XML files. XML files are used to store product design data. It has good universal property and expansibility and is easy to communication online. The paper defines CellData.dtd, the template of XML files, to standard the structure of XML files.PCAD software prototype system has been built in the main and verified the practicability of the theory model. The system manage design process of a product with project mode, and can establish and manage function-means tree, product tree and design matrixes to store structurized design data. In the cells of design matrixes, designers can use sketch, text, picture, and the third party software tools and so on to describe product design process.At present, the prototype system is just completed in the main, so there is still lots of work to be do in the further development.