Research On Technology Of CAD Model Repair

In practical engineering, data exchange among different CAD system happens frequently. Due to the different interior description method and precision between different systems (especially heterogeneous systems), some errors are introduced in the process of model transformation between different file format, such as dangling surfaces, dangling edges, surface cracks and so on. Hence, the usage the CAD model repairing technology to ensure the completeness and accuracy of CAD model has significant effects on improving the design quality of products during the period of products'design. This paper focuses on the problems existing in CAD model transformation, makes the thorough research on the CAD model repairing technology.This paper researches on the formation mechanism of CAD model errors according to the feature of topological representation and geometric representation in CAD model, and points out the roots of topological error and geometric error in CAD model. The inspection method of topological error based on manifold principle is proposed, and the inspection method of geometric error based on judgment criteria for surface and curve approximation error is present too.This paper focuses on repairing of cracks between NURBS surfaces because of the universal usage of NURBS in CAD system. Aiming at these big cracks, the algorithm of surface cracks repair based on interpolation generating blending surface is proposed. B-Spline surface is constructed and interpolated on the data point in this algorithm. In the other hand, the repair approach based on extension of B-Spline surface aiming at the small cracks is present too, in which the extension of NURBS surface and curve is transformed into the extension of B-Spline surface to minimize computational complexity.Based on the above mentioned theory and method, the main errors in CAD model are analyzed based on the ACIS geometry engine platform. The error inspection and repair algorithm are realized using the object-oriented programming languages VC++, At last, the validity of these algorithms in this paper is verified through some examples of crack repair.