EN 
DE Merging of Information Technology (IT) and Operational Technology (OT) in Industry 4.0 systems
Author: Dr. René Graf, Siemens AG
Contribution – Embedded Software Engineering Congress 2017
This article describes the combination of IT and OT for the realization of dynamically configurable manufacturing facilities. The OT world retains its determinism, necessary for controlling physical processes, while overlying IT mechanisms realize the dynamics of the production process.
Introduction
Traditional factory automation is referred to as Operational Technology (OT) and relies largely on completely different mechanisms and protocols than the Information Technology (IT) used in data centers. At first glance, the respective paradigms seem rather incompatible, but the trend toward comprehensive networking of industrial plants affects both worlds.
In modern, flexible manufacturing, however, these differences diminish because both technologies merge, while retaining the advantages of each.
Differences between IT and OT
IT in data centers (see. PDF, Figure 1) is characterized by many computing nodes (19″ racks) in a small space, all of which are interconnected, so that tasks can be distributed almost arbitrarily across the available instances.
The networks are highly dynamically organized because, with such a large number of computers, an average of one fails and needs to be replaced every week. Accordingly, the software architecture is also highly dynamic, so that a hardware failure does not immediately lead to a software failure.
The OT, on the other hand, is found in small control cabinets distributed throughout a large plant. Besides computing units, these cabinets also contain electrical components, as shown in Figure 2 (see...). PDF) can be seen. The computing units, in turn, are usually not standard computers with common operating systems, but special automation computers called PLCs (Programmable Logic Controllers).
The network within a control cabinet is completely static and usually configured manually. If several control cabinets are present in a large system, the network and communication connections between them, or between the devices within them, are also completely statically defined.
Common IT protocols are only slowly finding their way into control cabinets. Web access (http or https) has been available in controllers for several years. The current trend is towards the OPC UA protocol, which, in addition to pure data transport, also offers the possibility of information modeling. Nevertheless, OPC UA does not force any changes to the static network topology.
Flexible production facilities
This requirement is becoming increasingly important with the trend towards flexible and modular production facilities, whereby there are two use cases to distinguish, which in turn bring different aspects with them:
- Various productsOn one production line, various products are to be manufactured, so the different processing modules are rearranged depending on the product. The system's setup is therefore quasi-static, as the system is not constantly being reconfigured.
- Flexible productA product, such as a car, can be configured very flexibly by the customer, theoretically resulting in 100,000 or more different combinations. The initial production planning may be flawed, creating a bottleneck for a specific configuration option that slows down the entire production process. In this case, the plant configuration must be modified during operation.
In both cases, the modules must react because their communication relationships change. Conventional OT mechanisms lack this dynamism, while conventional IT mechanisms lack the coupling to the physical world of the production process, as they are designed for the pure manipulation of data.
Plant and network concept
Therefore, a sensible combination of mechanisms from both worlds is the right way to meet these challenges. To this end, the system is divided into two essential parts: the central transport and infrastructure system (TIS) and the manufacturing modules (FM), which manipulate the objects transported there.
The TIS is responsible both for transporting the products between the stations and for supplying the connected FM with energy, compressed air and network.
The FMs, on the other hand, depend on a connection to the TIS and its network. However, this is separated from the FM's internal network, which fully meets the OT mechanisms, by a network component.
The Siemens product names used below are solely for the purpose of easier identification of the devices in the illustrations. The functionality and task described in each case can also be achieved without limitations using equivalent devices from other manufacturers.
Structure of the central system
Figure 3 (see. PDFFigure 1 shows the schematic structure of the network of the central system with a PLC (S7-1500) and corresponding peripherals (ET200) for controlling the transport system (e.g., conveyor belt) as well as RFID readers (RF180C) for identifying the carts. Local operation is via a panel (IPC277E), while the production process is controlled by a MES (Manufacturing Execution System), which is not part of this description.
The green network is completely static and uses Profinet as its protocol.
The red network is partly static and partly dynamic. The typical automation components (PLC and panel) have static IP addresses, as do the plant server (IPC427D) and the plant switch (XM416-4C), while the FMs on the other switch ports receive dynamic IP addresses.
The central instance for this is the plant server, on which both the IT-typical network services DHCP and DNS run, as well as an OPC UA server that provides the current plant configuration.
Structure of the manufacturing modules
The FM has inside both a Profinet (green) for peripherals and a modular network (purple) for all other components, both of which are completely static.
These networks are hidden from the outside via the security switch (S615), which only allows specific services to pass through and forwards requests to the internal devices. Specifically, these are OPC UA to the PLC and VNC as a remote desktop connection to the panel.
This highlights the major advantage of this structure, as the FM (Factory Management System) can be built completely differently internally and with components from other manufacturers, as long as the interface to TIS (Technical Information System) is correctly operated with all the necessary services. (see...). PDF, Figure 4)
Topology detection
Besides the fact that a specific manufacturing module is in principle available in the plant, its position in the plant must be determined so that the carts with the products to be processed can find their way to the correct station.
This is done via the system switch (XM416-4C). After the FM is connected to the TIS, it sends a DHCP request and receives a dynamic IP address. The switch is then queried to determine which port, and therefore which position on the TIS, the new module is connected to. After the FM has been queried via OPC UA to identify itself and its capabilities, all this information is displayed in the OPC UA server of the system server. Conversely, when an FM is disconnected, the corresponding entry is removed.
In Figure 5 (see. PDFTwo FMs are connected to the TIS and are entered by name into the OPC UA information model of the plant server at the position corresponding to the topology. For each FM, the additional data that complies with the OPC UA Companion Standard Device Integration is stored there.
Example research facility
The new research facility of the Digital Factory division's pre-development department in Nuremberg is set up exactly as described above, with a TIS and several FMs that can be connected at any point or not.
Figure 6 (see. PDF) shows the structure of the plant with the central transport system, which has a siding at each possible module connection position so that wagons with products for the module can park there without blocking the transport overall.
When a product is to be manufactured, the MES first queries the TIS plant server to check whether all necessary FMs are available in the current configuration. The cart carrying the growing product is then moved to the positions determined by the topology, and the respective FM performs its step in the production process.
Conclusion
Using a suitably configured network component, OT-compliant manufacturing modules can be dynamically connected to a central system built according to IT standards and also topologically tracked. Furthermore, this method simplifies the heterogeneous design of a system, as the internal components of the modules remain hidden and can originate from different manufacturers.
author
Dr.-Ing. René Graf studied physics at the University of Karlsruhe and received his doctorate in 2000 from the Institute of Robotics at the Faculty of Computer Science. He then spent eight years at Siemens developing various generations of the Simatic S7 PLC. As Principal Key Expert in the advanced development phase of the DF (Digital Factory) division, he focuses on the architecture of industrial control systems and their integration into modern plant and network structures. In 2013, Dr. René Graf was awarded "Siemens Inventor of the Year.".
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