Contents I. Introduction
The so called assembly tolerance analysis is referred to the calculating process of dimensional distribution (assembly tolerance) for assembly parts by taking into account the accumulation and propagation of variation according to the dimensional distribution (tolerance) of the known parts, the aim of which is to judge whether the tolerance distribution of the parts meets the requirement of assembly function. Three-dimensional assembly tolerance analysis is a problem usually met in mechanical structure of complex product such as aircraft. The calculation of this problem is one of the challenges all the time in the field of traditional tolerance analysis. Digital technology provides powerful tool for the solving of this problem, and scholars have put forward different ways to solve computer aided tolerance analysis problem [1]–[7]. At present, products have been able to be specified in full three-dimensional accurate models, and the CAD system has powerful parameter and variation designing function, which creates conditions for exploring and establishing new methods of tolerance analysis and solving the problem of three-dimensional dimension chain calculation. In fact, the essential objective for introducing the concept of tolerance is to measure and define the variation ranges of key geometrical elements of parts and components (e.g. point, face) as well as their correlations (e.g. parallel, vertical, etc.). Therefore, we can achieve the objective of traditional dimension chain analysis by solving geometric relationship on the basis of product's three-dimensional digital model. Reference [8] puts forward a geometric method, i.e. dimensional element chain analysis (DECA), for the analysis of dimensional tolerance. This paper further demonstrates the geometric model (i.e. dimensional element model) and its analysis method of geometric tolerance in digital environment.
