OPC UA NodeSet Ontologies as a Pillar of Representing Semantic Digital Twins of Manufacturing Resources

Abstract

The effectiveness of cognitive manufacturing systems in agile production environments heavily depends on the automatic assessment of various levels of interoperability between manufacturing resources. For taking informed decisions, a semantically rich representation of all resources in a workcell or production line is required. OPC UA provides means for communication and information exchange in such distributed settings. This paper proposes a semantic representation of a resource's properties, in which we use OWL ontologies to encode the information models that can be found in OPC UA NodeSet specifications. We further combine these models with an OWLbased description of the resource's geometry and-if applicable-its kinematic model. This leads to a comprehensive semantic representation of hardware and software features of a manufacturing resource, which we call semantic digital twin. Among other things, it reduces costs through virtual prototyping and enables the automatic deployment of manufacturing tasks in production lines. As a result, small-batch assemblies become financially viable. In order to minimize the effort of creating OWL-based UA NodeSet descriptions, we provide a software tool for the automatic transformation of XML-based NodeSet specifications that adhere to the OPC Foundation's NodeSet2 XML schema.

The ontology-based modeling and evolution of digital twin for assembly workshop

“…Ontology modeling methods and the applications of ontology-based technologies have been widely studied in information virtualization, knowledge representation and expert system. Manufacturing resource virtualization has been one of the primary application methods of ontology technology [25] [35]. Focus on the field of assembly, the modeling methods aiming at product, process, resource [8][9] and system [6][37] in the assembly scenarios have been proposed in succession, enriching the description approaches of multifarious information in assembly.…”

A Generic Plug & Produce System Composed of Semantic OPC UA Skills

“…In [44], we show how NodeSet2 descriptions can be automatically transformed to an ontology-based representation, that allows to link the encoded information to other semantically represented models regarding, e.g., geometry, workcell layout, device topology, and process and product models. This approach includes the development of a core OPC UA ontology using the Web Ontology Language (OWL2) [45].…”

Toward a Knowledge-Based Data Backbone for Seamless Digital Engineering in Smart Factories

“…In recent years, there has been active research in knowledge representation for industrial automation and robotics. Many approaches follow the product-processresources paradigm (PPR) [6], in which products [7] and product designs [8], production processes [9], and manufacturing resources [10] are modeled. The combination of skills and explicit knowledge representation is often used to reduce the complexity of programming production systems [9], [11], [12].…”

“…In OPC UA, components describe their functionalities and internal states with so-called node sets, which can be remotely browsed by other components. OPC UA node sets are defined based on XML schemas and can be automatically transformed to OWL representations [10].…”