An architecture for the digital twin of a manufacturing cell

Redelinghuys, Anro Johannes Hermanus (2020-03)

Thesis (PhD)--Stellenbosch University, 2020.

Thesis

ENGLISH ABSTRACT: The ongoing development of modern manufacturing technology contributes to the rise of the fourth industrial revolution, or Industry 4.0. The digital twin is considered to be key for interaction between the virtual and physical worlds. An important step towards the success of Industry 4.0 is the establishment of practical reference architectures. The dissertation presents the development, implementation and evaluation of the Six-Layer Architecture for Digital Twins with Aggregation (SLADTA). The development starts with the SLADT (excluding aggregation) for a single manufacturing system element, with an industry related case study. The SLADT provides the communication between the physical and digital twin, as well as between the digital twin and the outside world. The architecture is aimed at situations where the products of various vendors are used in the physical and digital twins, and for developing digital twins for newly designed and legacy manufacturing systems. Layers 1 and 2 of the SLADT form part of the smart connection level or physical twin. An Open Platform Communications Unified Architecture (OPC UA) server in Layer 3 provides a vendor-neutral communication interface between the physical twin and the other layers. The data-to-information conversion level, or IoT Gateway, is added as Layer 4 to add context to the data received from Layer 3 before passing the information to Layer 5. When information flows from higher levels to the physical twin, Layer 4 also converts the information to data that can be used by the physical twin. Layers 5 and 6 are the cognition level of the architecture. Layer 5 consists of cloud services that host historical information received from Layer 4. Layer 6 consists of simulation and emulation tools. This dissertation also extends the SLADT, by also providing for Aggregation (SLADTA) and evaluates it for a laboratory scale manufacturing cell that consists of a variety of physical twins. A hierarchical approach is considered for aggregating information from lower- to higher-level digital twins. This approach can also be considered as a digital twin of twins that reduces complexity by breaking a larger digital twin into smaller digital twins of encapsulated functionality. The OPC UA server (Layer 3) supports and simplifies the secure information flow between digital twins, while the IoT Gateway (Layer 4) supervises the information flow. The evaluation of the SLADTA considered its ability to acquire the physical twin state (Layers 1, 2, 3 and 4), maintain an information repository (Layer 5), and simulate and emulate operation (Layer 6). The evaluation further considered the data and information flow, configuration, and decision-making capabilities. Latencies between the OPC UA server (Layer 3) and the IoT Gateway (Layer 4) were identified during the SLADT case study evaluation and had a significant impact on the real-time communication. The latency considerations, between Layers 3 and 4, are evaluated in this dissertation. This dissertation concludes that the SLADTA provides a functional mechanism to implement digital twins. The layers in the SLADTA are not platform dependent and thus allow flexibility for integration into newly designed and legacy manufacturing systems.

AFRIKAANSE OPSOMMING: Die deurlopende ontwikkeling van moderne vervaardigingstegnologie dra by tot die opkoms van die vierde industriële revolusie, of Industrie 4.0. Die digitale tweeling word beskou as 'n belangrike oorweging vir interaksie tussen die virtuele en fisiese wêrelde. 'n Sleutel tot die sukses van Industrie 4.0 is die vestiging van praktiese verwysingsargitekture. Die proefskrif beskryf die ontwikkeling, implementering en evaluering van 'n Ses-Laag Argitektuur vir Digitale Tweelinge met Samevoeging (SLADTA). Die ontwikkeling begin met die SLADT (uitsluitend die samevoeging) vir 'n enkele element van die vervaardigingstelsel, met 'n industrie-verwante gevallestudie. Die SLADT fasiliteer die kommunikasie tussen die fisiese en digitale tweeling, sowel as tussen die digitale tweeling en die buitewêreld. Die argitektuur is gerig op situasies waar die produkte van verskillende verskaffers gebruik word in die fisiese en digitale tweelinge, en vir die ontwikkeling van digitale tweelinge vir toekomstige en bestaande vervaardigingstelsels. Lae 1 en 2 van die SLADT vorm deel van die slim verbindingsvlak of fisiese tweeling. ‘n Open Platform Communications Unified Architecture (OPC UA) bediener in Laag 3 bied 'n verskaffer-neutrale kommunikasie koppelvlak tussen die fisiese tweeling en die ander lae. Die data-tot-inligting omskakelingvlak, of IoT Gateway, is bygevoeg as Laag 4 om konteks by te voeg tot die data wat vanaf Laag 3 ontvang is voordat die inligting oorgedra word aan Laag 5. Wanneer inligting van hoër vlakke na die fisiese tweeling vloei, kan laag 4 ook die inligting omskakel na data wat deur die fisiese tweeling gebruik kan word. Lae 5 en 6 is die kognisie vlak van die argitektuur. Laag 5 bestaan uit wolkdienste wat historiese inligting ontvang vanaf Laag 4 en behou. Laag 6 bestaan uit simulasie- en emulasie-instrumente. Hierdie proefskrif brei ook die SLADT uit deur voorsiening te maak vir Samevoeging (SLADTA) en evalueer dit vir 'n laboratoriumskaal vervaardigingsel wat bestaan uit 'n verskeidenheid fisiese tweelinge. 'n Hiërargiese benadering word oorweeg vir die versameling van inligting van laer- tot hoër vlak digitale tweeling. Hierdie benadering kan ook beskou word as 'n digitale tweeling van tweelinge, wat die kompleksiteit verminder deur 'n groter digitale tweeling in kleiner digitale tweelinge van ingekapselde funksionaliteit te verdeel. Die OPC UA bediener (Laag 3) ondersteun en vereenvoudig die veilige inligtingvloei tussen digitale tweelinge, terwyl die IoT Gateway (Laag 4) toesig hou oor die inligtingvloei. Met die evaluering van die SLADTA is die vermoë daarvan oorweeg om die fisiese tweelingstoestand te verkry (Lae 1, 2, 3 en 4), die handhawing van 'n inligting pakhuis (Laag 5), en simulasie en emulasie van prosesse (Laag 6). In die evaluering is die vloei van data en inligting, opstelling, en besluitnemingsvermoë verder oorweeg. Latentheid tussen die OPC UA bediener (Laag 3) en die IoT Gateway (Laag 4) is tydens die gevallestudie-evaluering geïdentifiseer en het ‘n beduidende impak gehad op die intydse kommunikasie. Die latentheid-oorwegings, tussen Laag 3 en 4, is in hierdie proefskrif geëvalueer. Hierdie proefskrif kom tot die gevolgtrekking dat die SLADTA 'n funksionele meganisme bied om digitale tweelinge te implementeer. Die lae in die SLADTA is nie platform-afhanklik nie en bied dus buigsaamheid vir integrasie in toekomstige en bestaande vervaardigingstelsels.

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