Automatic generation of min/max tolerance charts for tolerance analysis from CAD models

Abstract

The so-called min/max tolerance charts are popular for analysing tolerance accumulation in parts and assemblies, despite the fact that this method is limited to one-dimensional worst-case analysis. Since different chart construction rules apply to different tolerance classes, the user has to remember all the different rules to construct a valid tolerance chart. Constructing the charts manually, as is common practice in industry today, is time-consuming and error-prone. This paper presents procedures for automating tolerance charting. It requires a computer aided design (CAD) model with GD&T specifications as input. The automation is based on a data model called the constraint-feature-tolerance (CTF) graph and machine interpretable representation of charting rules specific to each tolerance class. This paper also presents procedures for automatically extracting dimension and tolerance stacks for any user defined analysis dimension, and automatic part arrangement in assemblies corresponding to worst case analyses. Important implementation issues are also discussed and several case studies are presented, the results of which have been verified by manual chart construction.

A review of two models for tolerance analysis of an assembly: Jacobian and torsor

“…The foremost works are found in Requicha that introduced the mathematical definition of the tolerance's semantic (Requicha 1983, Requicha 1993) and proposed a solid offset approach for this purpose. Since then, a lot of models are (Chase et al 1995, Chase et al 1996, Gao et al 1998; the variational uses homogeneous transformation matrix to represent the variability of an assembly due to tolerances and assembly constraints (Martino et al 1989, Boyer et al 1991, Gupta et al 1993; the matrix uses displacement matrix to describe any roto-translational variation a feature may be subjected to (Salomons et al 1996, Desrochers et al 1997; the tolerance-map uses hypothetical solid including points in n-dimensions which represent all possible variations of a feature or an assembly (Davidson et al 2002, Mujezinovic et al 2004, Ameta et al 2007, Shen et al 2008, Singh et al 2009; the jacobian uses an approach derived from the description of kinematic chains in robotics to formulated the displacement matrices; and the torsor uses screw parameters to model three dimensional tolerance zones. In the literature, some studies compare these models for tolerance analysis by dealing with their general features (Hong et al 2002, Shen et al 2005.…”

A tolerance analysis and optimization methodology. The combined use of 3D CAT, a dimensional hierarchization matrix and an optimization algorithm

“…The average value and the tolerance of 'J' was obtained by three different tolerance analysis methods in 1D: arithmetic (WC), quadratic (RSS) and probabilistic (uniform distribution). Ngoi [19] and Shen [20] used this method, but only to analyze tolerances in the WC method.…”

Development of a function oriented computer aided tolerancing (FOCAT) system

“…Wu et al [2] proposed the geometric dimensioning and tolerancing (GD&T) global model to satisfy four basic requirements: completeness, compatibility, computability, and validity. Shen et al [3,4] presented the procedures for automating tolerance charting based on a data model called the constraint-feature-tolerance graph and machine interpretable representation of charting rules specific to each tolerance class. Shah et al [5] presented the method of dimension model for design specification and for automatic dimensioning of volumes produced by volume decomposition in feature recognition or mapping.…”