Automatic Conversion And Repair Of IGES Files Models

In the process of developing the practical application of CAD/CAM technology,geometric kernels used by CAD/CAM systems differed,and there is a demand for data exchange of product model data between different systems,which led to the establishment of product data exchange specifications.In 1980,the U.S.National Bureau of Standards established the American Technical Standards Committee and formulated the American Basic Graphics Conversion Standard IGES.The IGES neutral file was created to resolve the complexity and tediousness of different CAD/CAM data exchange.With the development of the IGES standard,from the initial version 1.0 to the recent version 6.0,it has become more and more mature,covering more and more all CAD/CAM systems that require data exchange in more fields have become the most extensive data exchange standard.When data is exchanged between different CAD systems(especially heterogeneous systems),ensuring the accuracy and integrity of the transferred CAD models becomes an important issue.In this thesis,through the analysis of the IGES neutral file structure of the initial graphics exchange specification,the research is conducted from two aspects of data conversion and simple repair of geometric models in the process of data conversion.The main research contents are as follows:(1)The key design techniques of IGES post-processor and pre-processor are given.For the Open CASCADE geometry kernel(subsequently referred to as OCC),the design of the post-processor for converting IGES file models from bounded surfaces,trimmed surfaces,and manifold solid to OCC data models is realized;the design of the pre-processor for converting OCC data models from trimmed surfaces and manifold solids to IGES standard neutral files is realized.(2)For the case that the geometric continuity at the nodes appears in the 2D parameter space becomes C~0during the conversion of IGES geometric model to OCC geometric model,we use the method of inserting heavy nodes to partition the curved and surface from the 2D parameter space and the corresponding 3D space at the same nodes to avoid this situation.The above theories and methods,based on the geometry engine of OCC,designed the IGES pre-processor and post-processor,and repaired the geometric continuity of the geometric model during the conversion process.The related conversion and repair are realized by using the object-oriented language C++,and its effectiveness is verified by some examples.