Bidirectional control of the integrated product-process digital twin

The fourth industrial revolution has greatly influenced and redefined the manufacturing industry.
Modern manufacturing is driven towards high value-added, technological-based manufacturing.
Business-wise, it is to maximise or maintain competitiveness in an emerging digital era. This
technological transformation has been triggered by tremendous growth and innovative breakthroughs
in the digital world. It has led to the increasing integration of information and communication
technologies (ICT) with industrial operational technologies (OT). To support the positioning of the
manufacturing industry to effectively play its role in the fourth industrial revolution, this research makes
its contribution by exploring and applying the digital twin (DT) concept in the digitisation of
manufacturing processes. This is intended to digitise and control manufacturing processes to achieve
real-time cyber-physical interaction and integration, involving both product and process digital twins.
This is geared towards achieving dynamic production systems as part of the expectations of the fourth
industrial revolution.

The methodology adopted in this study involved a systematic literature review, system identification,
modelling and simulations. This enabled the definition of entities, functions, quantities, performance
metrics and propositions analysed through experimentation. A case study on a Festo CP smart factory
was presented as evidence of the feasibility and effectiveness of the propositions made in this research.

The contributions made by this research included:
• A proposed digital twin framework that supports the integration of the product and process
digital twins for applications in manufacturing
• Proposed techniques to support real-time synchronised interaction between the asset-twin.
These include a dependency rule that logically defines a bidirectional relationship between the
product DT and its processes DTs; and a real-time synchronisation mechanism that supports a
synchronised real-time interactive environment
• A proposed cyber-physical control structure for a Cyber-physical production system (CPPS)
DT and an implementation strategy of the Cyber-physical control structure. This framework
integrates the digital twin virtual control structure with the physical asset’s control system over
a real-time bidirectional communication link
• A proposed CPPS DT decision support system (CPPS_DTDSS) that positions the integrated
product-process DT to access/share resources across the Hierarchy levels of the RAMI4.0
automation architecture. This is an automation reference architecture for Industry 4.0 that
includes the product and connected world in its Hierarchy levels. This extends the concept of
integration across the Hierarchy levels of the RAMI4.0 architecture

The real-time collaborative interaction between the asset-twin extends the numerous digital capabilities
of the DT to the operational phase of the CPPS. This positions the DT as a decision-support mechanism
for the CPPS. The CPPS supports its DT simulations, analyses and visualisation with operational data
and control. The DT, with a Cyber-physical control structure, can execute real-time control, production
management and product customisation.