The Structure of ARO

The ARO consists of different levels of specializations of reference concepts starting from the most generic concepts to most specialized concepts as shown

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in figure 3.5. Earlier, levels of specialization have been developed for single piece part manufacturing by Usman (2012) however they are not applicable to the assembly domain and hence they have been modified for the assembly domain. The specialization levels defined in the ARO provide an understanding of the varying levels of depth of the semantics of assembly concepts and consist of the following layers of reference concepts as shown in figure 3.5.

Generic Reference Concepts

Product Lifecycle Reference Concepts

Design and Manufacturing Reference Concepts Assembly Specific Reference Concepts

Assembly Design Reference Concepts

Assembly Process Planning Reference Concepts

The concepts within these specialization levels (shown in figure 3.5) have been identified by analysing the existing literature and the examples of product assembly scenarios explored in this thesis. In this research at first the key concepts have been identified and then they have been specialized and/or generalized. For example the concept assembly feature was identified from the existing sources (more detail can be found in section 4.3.12) however its generalized concepts e.g. product feature and feature has been adapted from Usman (2012). He used the concept part feature at Product Lifecycle Reference level and feature at Generic Reference level. The concept part feature has been adapted as product feature in this research.

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Figure 3.5: Structure of Assembly Reference Ontology

Similarly Usman (2012) used the Product Lifecycle Reference Concept part family which has been adapted as product family because the latter is applicable to assembly. The AyD and APP Reference Concepts “design product family” and “manufacturing product family” have also been adapted from Usman (2012)’s design part family and production part family respectively. Likewise the Product Lifecycle Reference Concept product version has also been adapted from part version which was used for part machining by Usman (2012). The

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concept design function has also been taken from (Usman, 2012) to represent the function of assembly components and features.

The reference concepts: BOM, component, auxiliary material, tolerance, dimension, assembly component, tolerance type, assembly process, assembly resource and manufacturing facility have been identified by exploring the examples of butterfly valve assembly and journal bearing assembly for assembly knowledge sharing. These reference concepts have been further explained in section 4.3.

The Generic Reference Concept shape attribute has been identified by exploring the examples of journal bearing assembly to capture the fits related knowledge. The Generic Reference Concept spatial location has been identified during the exploration of the case study to represent the location of features on product and assembly resource. The other Generic Reference Concepts such as family, process, resource, material, operation and facility are the generalized classes of product family, assembly process, assembly resource, auxiliary material, assembly operation and manufacturing facility.

From the analysis of case study (described in section 6.4) the concepts:

product, assembly operation and assembly resource feature were identified. A detail description of these concepts can be found in section 4.3.1, 4.3.14 and 4.3.19.

The different levels of reference concepts shown in figure 3.5 are explained in the following sections.

3.5.1 Generic Reference Concepts

The generic reference concepts are the first layer of concepts which are more specialized than the foundation concepts and are more generic as compared to the product lifecycle concepts. This implies that the generic reference concepts can be used to support interoperability across the product lifecycle domains e.g.

design, manufacture, assembly, operations, services, quality, and disposal, as

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well as other domains like finance, human resource, marketing etc. However this research work focuses on manufacturing assembly only which comes under the umbrella of product lifecycle domain, hence other domains are not part of the scope right now. The examples of generic reference concepts include concepts like family, feature, process, resource, material, operation, spatial location, shape attribute, and facility.

3.5.2 Product Lifecycle Reference Concepts

The product lifecycle reference concepts capture the semantics of concepts which are applicable to the product lifecycle domain only. The purpose of introducing these reference concepts is to support interoperability within the product lifecycle domain and to provide reference concepts for its sub-domains.

Examples of product lifecycle generic concepts include product, product version, product family, product feature, BOM, component, and auxiliary material. These reference concepts interlink the generic reference concepts with more specialized concepts like design and manufacturing reference concepts, assembly specific reference concepts etc. The knowledge captured through these concepts can be used across the product lifecycle domain. For example, knowledge related to the BOM can be used during the design, assembly, disassembly and service of the product.

3.5.3 Design and Manufacturing Reference Concepts

In general, design and manufacturing domain covers single piece part design, assembly design, single piece part manufacturing and assembly process planning domains. Hence the design and manufacturing reference concepts can support interoperability across the above mentioned domains by providing reference concepts which are applicable to all these domains. The examples of design reference concepts include design function, tolerance and dimension, and examples of manufacturing reference concepts include manufacturing facility, manufacturing resource, manufacturing operation, and manufacturing process.

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3.5.4 Assembly Specific Reference Concepts

Conceptually manufacturing assembly is significantly different from single piece part manufacturing as the former deals with relationships of parts rather than focussing on a single part. Hence it may require some concepts which are applicable to the assembly only. This would also support interoperability across the assembly design and assembly process planning domains. However not all of the assembly design and assembly process planning knowledge can be routed through assembly specific reference concepts. For example, in some cases, assembly specific reference concepts can be bypassed if appropriate reference concepts are not available to support interoperability across these domains. In those cases, higher level reference concepts e.g. product lifecycle reference concepts may be used to bridge the assembly design and assembly process planning domains. Examples of assembly specific reference concepts are assembly component, and assembly feature.

3.5.5 Assembly Design Reference Concepts

The assembly design reference concept layer is one of the most specialized layers in the ARO. The assembly design reference concepts have been added in the ARO to support the creation of new assembly design domain ontologies and/or to support interoperability across these domain ontologies. Examples of assembly design reference concepts are design product family, EBOM and tolerance type. These concepts capture the assembly design knowledge and can be further specialized to support specific applications.

3.5.6 Assembly Process Planning Reference Concepts

The assembly process planning reference concept layer is also one of the most specialized layers of ARO. Like the assembly design reference concepts, assembly process planning reference concepts also support the creation of new assembly process planning domain ontologies and facilitate interoperability across these domain specific ontologies. This kind of interoperability is termed

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as intra-domain interoperability as shown in figure 3.2. Examples of assembly process planning reference concepts are MBOM, manufacturing product family, assembly resource feature, assembly operation, assembly process and assembly resource.

3.6 Summary

This chapter has highlighted some of the assembly knowledge sharing issues which provide a base to develop a set of requirements and the research idea to deal with these requirements. It is argued in the chapter that the Assembly Reference Ontology (ARO) can support assembly knowledge sharing across assembly design and assembly process planning domains by providing a set of reference concepts. The chapter also put emphasis on the use of a heavyweight ontological based approach to represent and share assembly domain knowledge. It is also claimed that the ARO can support intra-domain knowledge sharing and the development of new application based ontologies.

Various levels of concept specialization have also been explored at the end of the chapter.

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CHAPTER 4

4 THE DEFINITION OF ASSEMBLY REFERENCE