Research On Automatic Recognition Of Features From Freeform Surface In Semantic Feature Modeling

Feature modeling is one of important techniques in integrated system of CAD or CAM, which is a key to modeling. Building product modeling can solve fundamentally the problems of data exchanging and sharing which exist among designing, producing, quality-control, organizing management , and implement maintenance and editing of models. Semantic feature modelling is a declarative feature modelling approach that not only provides a welldefined specification of feature semantics,but also effectively maintains this semantics during the modeling process. In fact ,one of the basic ideas of feature–based modeling is the ability to associate functional information to shape information in a feature model,that form the semantic of the feature together.The current technology of feature modeling is based on the features of regular shape, but with its development more and more application is involving irregular surface, which is an imperative problem to be solved.Feature recognition(FR) is an effective manner of finding producing features from solid models. And FR is an ideal interface of CAD and CAPP. It is the focus that many scientists are researching in CAD and CAPP field. And it is paid much attention, with effort the scientists proposed several kinds of methods of FR.Aaiming at feature recognition domain limits to the prismatic and cylindrical shapes in most feature modeling systems,This paper mainly discusses feature recognition of freeform surface in Standard Triangulation Language. After the errors on STL files were classified, using an errors descriptive graph represent the topology of checked error elements, then STL files were repaired. On the basis of it, a novle hybrid region segmentation algorithm based on edges and region is proposed. By detecting and filtering unwanted feature edges of STL models, the models were segmented into regions in different density, then using geometric characteristics of vertices and edges dentify type of the region, finally recognize the freefrom surface .After tested in HUST-CAID system, it can recognize accurately some freeform surface features.Introducing the technology of freeform surface feaures recognition not only make HUST-CAID more perfect, but also have pracicality,which effectively meet the demand of users.