Study On Hybrid CAD Modeling Theory And Method In Reverse Engineering

Reverse Engineering (RE) is a discipline of transforming physical parts into engineering concepts and CAD model, covers a series of methods and techniques. It has been an important branch of modern design methodology. With the developing of computer and measurement technique, RE concentrates on no longer product copy but innovation. In order to operate the CAD model constructed by RE method, a hybrid CAD modeling method and some related key techniques are studied in this dissertation.Hybrid CAD modeling method is a kind of integration of RE and conventional design in which the product features, geometric constraints and design intent are addressed by inheriting and developing the initial design of a physical prototype. Fundamental theory included in this method, such as modeling strategy, feature and constraint definition, classification and representation, are researched in chapter two. Based on model analysis, modeling procedures are described by RE modeling tree, which is introduced from the graph theory. Main contents in relation to the hybrid modeling method are discussed, and some key techniques such as quadric surface feature extraction and blend surface feature extraction are addressed in details.Free form surface reconstruction plays a key role in RE. The reconstructed surface not only needs to meet approximating precision and looks smooth, but also needs to reach certain continuity with adjacent surfaces. Reconstruction region is defined by point cloud slicing method and should satisfy the given principle. When the curve network is ready, B-spline surface skinning based on point cloud slicing, optimization bicubic B-spline surface reconstruction method with or without boundary constraint is proposed. The objective function consists of least squares approximating term and simplified surface energy term, which affect the precision and fairing of the reconstructed surface respectively. It can be solved by iteration approaches.Surface fairing techniques, including energy based surface fairing, order elevation surface fairing and wavelet decomposition surface fairing, are introduced. Pros and cons of various fairing method are also described. In order to keep whole surface model G~1 continuous, an energy based fairing method with boundary constraint of curves or cross boundary derivatives is presented.In the process of RE modeling, it is always necessary to do some further surface...