This paper introduces an approach for modeling and representation of geometric tolerances on any 3D solid model using the Objected Oriented Programming (OOP) paradigm. The modeling scheme is supported by a comprehensive validation engine, which certifies the tolerance type against the 3D geometry context both syntactically and semantically. The major objective of this work is to develop a methodology for interfacing tolerance modeling with boundary representation (B-Rep) based 3D solid model geometry. We will demonstrate that the OOP paradigm is very efficient and flexible for tolerance model representation, which is required within the interactive design process. Six categories of tolerance classes have been developed for size, form, orientation, position, runout and profile, which extend a general tolerance class through inheritance. An instance of the general tolerance class will be initialized when picking a feature or a group of features to tolerance, depending upon feature(s’) characteristics and attributes. To apply a tolerance object the system obtains the 3D geometric data from the solid model using the feature extraction paradigm. When the required tolerance type is selected for modeling, an instance from the specified tolerance type class will be initialized through inheritance from the general feature tolerance class and gathers the necessary information / tolerance data. An intelligent validation engine that supports the modeler is introduced. The engine validates any selected tolerancing activity in two stages. First, it ensures that the selected feature or group of features is suitable for the selected tolerance type. Second, it ensures that the data specified does not lead to over/under-dimensioning. The paper also discusses a prototype system implemented to test the modeler and the validation engine. The results have been very encouraging while testing the system on a number of engineering models.

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