Theory And Application Research Of CAD Model Reconstruction Based On Vision Measurement

3D CAD technology has been widely used in the manufacturing industry with the development of computer graphics, computer aided geometric design, high performance computing and other related technologies. The CAD model is the basis of product development, manufacturing, re-design and maintenance. Therefore, it is necessary to acquire the CAD model by reverse engineering. Reverse engineering of physical objects refers to the process of creating engineering design data(including the CAD model)from existing parts by using many digitized technologies and CAD technology. The thesis addresses the reconstruction theory and methods of CAD models based on the vision measurement system.The paper introduces the meaning, main application fields and development trends of reverse engineering. The author also analyzes and compares few traditional data acquiring methods, and introduces the measuring theory and methods of the COMET system.The original point clouds acquired by light scaning are highly dense and scated, which include large number of redundancies and noises. Thus it is necessary to delete those redundancies and noises to reduce the compute cost of the downstream process. Data preprocessing refers to the process of polygonization, smoothing, decimation and registration. The flow and main steps of data preprocessing are described here. Several specific cases, for example the sampling method based on grid, the smoothing method based on gaussian, averaging and median, are discussed.The paper discusses the thoery and method of curves and surfaces reconstruction. Reconstruction srufaces methods based on clouds and curves being constructed before is proposed, discussed. Several methods to evaluate the surface smoothness, such high line and reflection line, etc. are also investigated and discussed. At last, the theory and methods discussed above were applied in the project"The Reconstruction of cover of varial pole in a Car". The CAD model of the cover is reconstructed successfully by those methods.