Dimensioning and tolerancing (D&T) are inter-related tasks; the validity of the tolerance representation model is dependent on the dimension model. Geometric tolerances are used to refine dimension tolerances and control some aspects of form, orientation and position of part features. This paper presents a computable model for the representation of dimensions and tolerances, compatible with D&T practice. The model is implemented as a dimension and tolerance graph (DTG). Constrained entities are combined into progressively expanding clusters which can be used to represent datum references/ frames, features, patterns, or the entire part. Validation of all D&T relations is performed in a uniform way using the concept of degrees of freedom and Control Frames. The tolerance specification method proposed here supports all tolerance classes defined in the ANSI standard, as well as datum reference frames and special pattern clusters.
展开▼
