Automobile Part Model Reconstruction Based On Geometric Constraints In Reverse Engineering

Reverse engineering is the process of creating a computer-aided model from the sensor data of an existing physical part. Currently reverse engineering has been one of the four main supporting technologies of rapid product development. Based on the review of its current condition and development home and abroad, the thesis expounds some achievements in the technology and methodology of geometric modeling in reverse engineering.In 3D shape measurement and model reconstruction of complicated products, extracting the constraint relationship between features of parts is necessary for integrating reverse engineering with CAD process, and it is an important condition for setting the exact assembly relation between mated parts. Constrains based 3D model reconstruction is one of the most important problem to be solved in reverse engineering.In this thesis, fundamental theories of feature technology in reverse engineering, such as feature definition, feature classification and feature representation and the freedom of feature are discussed, which are the theoretic base of extracting surface feature. Then constraint definition, constraint classification and constraint representation are also studied. For sententiously presenting constraint, constraint is translated into the form of basic constraint, which then is given the numbers of limitation to the freedom of feature.Constraints are sorted by priority and the importance of feature. Then a digraph-based geometric constraint network is proposed, considering degrees of freedom to obtain a consistent constraint system.According to geometric constraint network, the sequence of resolution is obtained and the complicated constraint problem is decomposed into sub-problems to be solved. Parameters retrieval in reverse engineering is also concerned. Integrated with the requirement of redesign and constraints-based method of reconstruction, the quality of the model reconstruction is improved.The approaches above are demonstrated with the practice"measured points of parts from an automobile transmission system and automobile engine". The underlying design intents of features are taken into account in reconstruction process, and the obtained geometric models are conformed to original design intents in geometric features and ensure assembly precision.