A variational geometric constraints network for a tolerance types specification

Abstract

A geometric tolerance specification includes specifying the tolerance types and values for nominal geometry parts. In current computer-aided tolerancing practices, designers have to specify manually both tolerance types and values in a CAD system, usually starting out from single components. The paper presents a framework and computer implementation that provides automated methods for the specification of geometric tolerance types. Based on the ISO/TC 213 geometric product specification, a new concept of a variational geometric constraints network is presented. The generation and application of the network to specify geometric tolerance types is studied. An example is analysed to show the scheme to be effective, and the model for a tolerance specification, including the types and values specification, is presented.

Enriching the semantics of variational geometric constraint data with ontology

“…These data describe the geometric variation information which is indispensable in tolerance analysis and synthesis. Hu et al [5] proposed an approach to use the data to generate the variational geometric constraint types to construct a tolerance chain for tolerance analysis and synthesis. This approach was implemented as a part of the FOCAT system [6] later.…”

“…It is not based on formal semantics so that it does not enable computers to automatically distinguish the different meanings of a terminology in different contexts [27]. The approach in [5] and the FOCAT system are thus insufficient to satisfy the requirements of exchanging the semantics of variational geometric constraint data. To overcome this limitation, This paper extends the implemented meta-model of tolerance type data [33] by adding the OWL 2 DL/SWRL description of variational geometric constraint data to achieve a semantically enriched ontology of the variational geometric constraint specification data in CAD systems.…”

“…Various product data exchange standards, including the standard for the exchange of product model data (STEP) [1], have been developed to meet this requirement during the last few decades. Although these standards constraint network theory [5] and the function oriented computer aided tolerancing (FOCAT) system [6]. Even though the variational geometric constraint network theory and the FOCAT system have provided and implemented an approach to use the variational geometric constraint data to generate the variational geometric constraint types to construct a tolerance chain to facilitate product tolerance design, the semantics of the data were not expressed and interpreted explicitly in this implemented approach.…”

“…The role of ontologies with rigorous semantics is highlighted in a comprehensive review on the knowledge representation techniques in product design systems [12]. With an ontology-based approach, variational geometric constraint specifications defined in the variational geometric constraint network theory [5] are formalized in OWL 2 DL [13] and SWRL [14], two ontology representation languages developed by the World Wide Web Consortium (W3C). Then the formalized specifications are instantiated by the variational geometric constraint data extracted from CAD systems.…”

A review of representation models of tolerance information

“…The polychromatic set model was presented by Zhang et al [45]. This model is based on the variational geometric constraint network theory [72] and is hierarchically organized. It consists of five layers of assembly layer, part layer, assembly feature surface layer, assembly tolerance specification layer, and assembly tolerance zone layer.…”