Automatic Generation of Tolerance Chains from Mating Relations Represented in Assembly Models

Abstract

This paper presents an algorithm for generating tolerance chains from the mating relations between components of assemblies. The algorithm is developed upon a feature-based assembly modeling strategy that represents each component in close relation to its mating features, dimensions, and tolerances. The mating relations within an assembly are described by a mating graph. Tolerance chains together with their dimensions and tolerances are generated automatically by searching through a mating graph for matching mating features. A prototype program package based on the presented algorithm has been developed, and several examples of various complexity have been tested with success.

A dimensional tolerancing knowledge management system using Nested Ripple Down Rules (NRDR)

“…The theoretical and methodological foundation of AI as applies to aspects of mechanical design in general is of great interest (Chapman, 1999). Specific to tolerancing, the idea of utilizing computer-based techniques (mainly computer-aided tolerancing, CAT) (Chiesi and Governi, 2003;Shen, 2003) for the purpose of automating tolerance generation and modelling to enhance the process of specifying proper tolerances is an area of active research (Wang and Ozsoy, 1993;King and de Sam Lazaro, 1994;Desrochers, 2003;Wu and Rao, 2004;Hu and Peng, 2007). The idea being is to develop rule-based expert systems to help the designer create complete and functional designs with appropriate dimensions and tolerances in the design stage.…”

A single representation to support assembly and process planning in feature-based design machined parts

“…Against and Fits are relationships originally defined by Lee and Gossard [29] and later used by Wang and Ozsoy [28], and Aligns is a useful composite relationship as described below. Against is a relationship between faces that in geometric terms ensures that the normal vectors to the two faces are in opposing directions.…”

“…Zeid [26] provides a comprehensive description of such information models and the uses to which they are put, but many representation schemes have been developed, the main differences being the way in which the locations and orientations of the parts and their hierarchical relationships are represented. Most use a hierarchical structure, and Wang and Ozsoy [28] are typical in using an assembly graph for hierarchical representation of the assembly, its subassemblies and components where the mating conditions of 'against', 'fit' and 'parallel' are stored as a set of mating links. Spatial information is typically represented either explicitly or implicitly.…”

Sequential Design of Optimum Sized and Geometric Tolerances

“…Optimal methods have also been presented to allocate B/P tolerances in product design using tolerance chart in process planning Swift et al, 1999) but the generation of dimensional and tolerance chains being one of the most important problems. In onedimensional (1D) cases, the apparent path tracing and tree approach were commonly used to tolerance chart for manual treatment (Ngoi & Ong, 1993;Ji, 1993a;Ji, 1993b;Wang & Ozsoy, 1993;Ngoi & Cheong, 1998b). Automatic generation of dimensional chains in assembly based on the data structure has been presented (Treacy et al, 1991;Wang & Ozsoy, 1993).…”

“…In onedimensional (1D) cases, the apparent path tracing and tree approach were commonly used to tolerance chart for manual treatment (Ngoi & Ong, 1993;Ji, 1993a;Ji, 1993b;Wang & Ozsoy, 1993;Ngoi & Cheong, 1998b). Automatic generation of dimensional chains in assembly based on the data structure has been presented (Treacy et al, 1991;Wang & Ozsoy, 1993). Using an Expert System, assembly tolerances analysis and allocation have been implemented by appropriate algorithm in CAD system (Ramani et al, 1998).…”