Research On Point-Based Geometric Model And Its CAD/CAM Applications

The development of CAD/CAM technology has greatly improved the products' design and manufacture process and has proved to be the ultimate solution to innovate the manufacturing industry. Geometric model is the kernel and base of CAD/CAM application. The conventional geometric models, such as wireframe model, surface model and solid model, suit most products and have been applied to practice widely. But there are still some products with complex shape that can hardly be represented by these three conventional models or if can, the subsequent CAD and CAM operations can be hardly realized.With the development of 3D scanning technology, obtaining the objects' surface points effectively and precisely has been possible, so that the reverse engineering technology based on the surface data points can developed greatly. As the fundamental geometric primitive, point is the base of curve and surface representing and application. Point has also experienced a major renaissance in Computer Graphics and point-based model has attracted great research attention. Point-based geometric model, abbreviated as PBGM, which uses surface data points to represent product geometry and realizes CAD/CAM through manipulating these points, has the good characteristics that the conventional geometric models do not possess and can be applied to CAD/CAM to realize some products' effective design and manufacture.Shoe last is the mold to make shoes. The traditional last making methods are hard to satisfy increasing demands. CAD/CAM technology is the vital solution to improve shoe last industry. To realize shoe last CAD/CAM, the key is how to describe the shoe last geometry and how to develop appropriate design and NC programming functions.From the point of view of CAD/CAM application, this paper uses point-based geometric model as research subject and makes systematic research on its correlative theory, technology and application. The innovative achievements of this paper are listed as below:1. According to the current status and future trends of CAD/CAM and scanning technology and combined with the research status of Point-Based Computer Graphics, Point-Based Geometric Model applied to CAD/CAM is put forward for the first time. The definition of PBGM and its CAD/CAM application process are presented. PBGM is divided to regular PBGM and non-regular PBGM according to the structure and application feature. Each model's intrinsic attributes are researched separately.2. CAD methods of PBGM are researched. Geometric transformation operations such as translation, rotation, scaling and offset are presented. Local modification function isrealized by deformation domain and deformation function. The CSG function is realized by constructing octree and making cell inside-outside judgment. The combination design function is realized by transition region.3. CAM methods of PBGM are researched. PBGM has no consecutive form, so the tool path can be obtained only by discrete point information. After reviewed the conventional CAD model based CAM methods and point-based CAM methods, a parametric machining method suited to regular PBGM and a general tool path generation method are proposed. And the corresponding machining simulation and NC machinery are also discussed.4. To apply PBGM to concrete products, CAD/CAM system is necessary. Point-based CAD/CAM system development should follow the methods of software engineering, but its graphic functions are more important. Four development methods: from base, based on CAD/CAM platform, based on conventional CAD/CAM system and based on reverse engineering software, are discussed. According to the situation of China, the development and application of point-based CAD/CAM system for special products are analyzed.5. Apply PBGM and its correlated CAD/CAM technology to shoe last practically and successfully. First, point-based geometric model for shoe last is defined. According to the characteristics of CAD and the shoe last geometry, the CAD methods of shoe last are presented and the detailed processes of three design functions, such as constructing shoe last model from sample last, combination design and local modification, are discussed. Second, shoe last CAM is realized and the detailed process is presented. Finally, shoe last CAD/CAM system is developed and applied to practice successfully.The contribution of this paper is to put forward PBGM and make systematic research on its correlated theory and application. This brings a new idea to CAD/CAM. With the research going deeper, Point-Based Geometric Model must be a kernel model of CAD/CAM system and play a very important role in products' design and manufacture process in the future.