Browsing by Author "Redelinghuys, Anro Johannes Hermanus"

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    An architecture for the digital twin of a manufacturing cell
    (Stellenbosch : Stellenbosch University., 2020-03) Redelinghuys, Anro Johannes Hermanus; Kruger, Karel; Basson, A. H.; Stellenbosch University. Faculty of Engineering. Dept. of Mechanical and Mechatronic Engineering.
    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.