Industry 4.0 , the next industrial revolution has arrived – launching Internet technologies into production environments and introducing the spirit and mindset of apps, software driven value creation and the network economy. A flood of new terms has arisen together with this new spirit, e.g. Digital Twin, Asset Administration Shell or I4.0 component. Interestingly, some of these new terms already existed before Industry 4.0 and are being silently redefined, causing misunderstandings and confusion. However, non-harmonized terms hinder innovation, e.g. the term “digital twin” has currently three different interpretations, highlighting the fact that the meaning of this term hasevolved and, indeed, is still evolving.
The digital twin (in German: digitaler Zwilling) was first defined by NASA in 2010  as a simulation of a vehicle or system that uses the best available physical models to mirror the life of its flying twin. Its meaning is all about a highly-detailed simulation model of spacecraft or aircraft which tries to reproduce its physical behavior as close as possible in the virtual world.
Over time, “digital twin” became a hot marketing term, applied to a variety of simulation tools for machine or plant simulation. A powerful marketing campaign conducted by Siemens gave the term a second interpretation: it came to mean a dynamic 3D model, e.g. of a production unit, machine, or car, including simulation. The new focus was on the simulated and visible 3D model. This interpretation is currently state-of-theartand shared by a broad industrial audience from vendors to users. But in fact, looking into the technical implementation, this is still Industry 3.0 technology, useful for many use cases, but it is not Industry 4.0.
Fig. 1: The future digital twin/administration shell: a software layer on top of a physical asset including data and interfaces.
The evolution is ongoing. The term “digital twin” is slowly changing its meaning yet again. In a digital future, we will need digital twins as comprehensive physical and functional models for every physical asset , e.g. a component, product or system. Step-by-step, the digital twin will cover all the useful information which is relevant across the lifetime of the related asset, from the idea to the engineering, logistics, operation, maintenance, reuse and destruction. A future digital twin may contain a simulation model, but also a 3D model, hundreds of properties, historical data, handbooks, installation guidelines, proprietary function blocks, interlockings, state models, alarm and event definitions etc. Friends of the first or second interpretation may be surprised to hear that it might even have no simulation model at all, e.g. for static assets. It will be stored in a future Industry 4.0 infrastructure, be searchable, explorable, associated with and sometimes connected to its real counterpart. It will not be hidden in proprietary simulation tools. Sales tools, simulation tools, engineering tools, certification tools, maintenance tools etc. may connect to digital twins for sales, engineering, certification, maintenance, simulation or optimization purposes, sometimes long before the related real assets are ordered. It will be possible to associate delivered real devices with their individual digital twin whenever necessary at a later date.
Hence, the digital twin will become a powerful electronic data object with interfaces: it will hold or reference all useful data (see Fig. 1), some data will be semantically standardized (e.g. properties, geometry, topology), other data will be of a proprietary nature (e.g. ABB function blocks). Internally, the digital twin will communicate with its physical asset, e.g. via proprietary interfaces. However, externally, it will communicate via well-defined Industry 4.0 interfaces.
The future digital twin will incorporate both data and interfaces and be similar to a software driver – but far more. It will be a multifacetted digital counterpart of the real asset, embedded in the Industry 4.0 ecosystem, access point for a new generation of apps and algorithms, mediator between future Industry 4.0 services and the real world. Fig. 2 shows the digital twin in the middle of the tree layer concept of a cyber-physical system  in an Industry 4.0 environment.
Fig. 2: Three-level concept of a cyber-physical system .
And what is the Asset Administration Shell (AAS) ? According to , it contains the information and I4.0 interfaces for an asset. Sounds similar to the digital twin, doesn’t it? This is exactly what  proposes: the AAS will become synonymous with the digital twin in its future, fully enhanced version. As soon as the meaning of the digital twin finally morphs into the third interpretation, the differences between it and the AAS will disappear.
And what is an Industry 4.0 component? It is the physical asset together with its Asset Administration Shell/digital twin. It is an Industry 4.0 enabled device, that can register itself in the I4.0 network and be identified, explored and processed via Industry 4.0 interfaces.
Finally, the evolution of the term “digital twin” offers a powerful illustration of the upcoming revolution. The future digital twin, in combination with cloud technology, apps and algorithms, has the potential to revolutionize every aspect of industry because it touches every aspect. The possibilities are endless, the digital twin is only the beginning.
This article was written by our guest author, Rainer Drath. Read more articles on Industrial IoT – Digital Twin.
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