Integrated CAD frameworks: Tolerance representation scheme in a solid model

The major objective of this paper is to develop a representational scheme for geometric tolerances that are to be interfaced with a solid model. This includes the development of (i) an efficient user interface system for input of tolerance information, (ii) a suitable tolerancing data module (to be attached to the solid model), and (iii) an information retrieval system from the stored database for future tolerance analysis. This user interactive environment which enables the user to input the tolerance information in both the unevaluated (CSG) and the evaluated (B-Rep) databases, requires an effective linking mechanism between the CSG and the B-Rep data models at each stage of the object development. This has been achieved through the development of a reference face list. Tolerance information has been attached with this face list as "constraint nodes", which are formed and updated after each "set operation." Several functions have also been developed to retrieve essential information from the data structure in order to answer various queries. The prototype system has been implemented on a polyhedral solid modeler based on this representational scheme.