Feature-based Geometric Dimension and Tolerance Modeling System

This paper reports a complete system for modeling, representation, and validation of geometric tolerances, using feature-based approach from boundary representation (B-Rep) based solid models. The utility of feature based representation scheme for representing Geometric Dimensioning and Tolerancing (GDT) information in geometric models is highlighted. Explicit information from B-Rep is culled using feature extraction and recognition algorithms such as graph matching and form/design feature rules. The major objective is to develop a scheme necessary for interfacing the tolerance module with the solid model. This includes the development of a point-and-click graphic user interface that allows a user to select geometric or functional entities (face, axis, surface, datum, etc.). It validates the entity selection based on the context of the type of tolerance being defined, collects the controlled and controlling feature and numerical value(s) for the tolerance in question. This work also proposes, an apposite tolerancing model representation as part of the feature based geometric model that can be easily used by the downline manufacturing activities. The proposed schema provides built-in checking of validity of tolerances defined during modeling. Also, a scheme for over-toleranced and over/under dimensioning validity checking is introduced.