A feature-based approach for detecting global symmetries in CAD models with free-form surfaces

Detecting global symmetries in CAD models with free-form surfaces (FFS CAD models) is of great importance in the research of CAD/CAE/CAM integration. A feature-based approach is proposed to rapidly detect global symmetries in FFS CAD models. The key problem is how to detect global symmetries of surface (or curve) models by using feature information. First, our previous basic theories on detecting solid models´ symmetries are expanded to handle surface (or curve) models. Then, the feature tuples are used to uniquely describe the surface (or curve) models´ non-unique design histories. Based on these studies, the feature reference tree and the parent-child relationships of topological elements are built to construct feature tuples. Finally, the symmetries of the surface (or curve) models are robustly and rapidly detected by using feature information in feature tuples and using the symmetries that have already been detected in solid, surface and curve layers. Experiments show that the FFS CAD models´ symmetries can be robustly and rapidly detected by using our approach.