The industry associations behind Industrie 4.0 (I4.0) published numerous documents in April of this year, some of which provide a detailed insight into the current state of discussion of the standardization work surrounding this topic. One of these documents is the VDMA guideline Industry 4.0 Communication with OPC UA. This guideline claims to support machine and plant manufacturers and operators in the introduction of Industry 4.0 communication based on OPC UA by describing three migration steps. This takes into account the discrepancy that arises due to the sometimes very abstract - but still incomplete - I4.0 concepts and specifications of the various standardization working groups and the increasing competitive pressure caused by the ever faster pace of digitalization. In other words, the VDMA guideline can be classified as a pragmatic solution approach. Overall, the VDMA document can be seen as a concrete recommendation for action to create value-added services for existing products, machines and systems.

Three steps to the goal

In this respect, it is first of all made clear that 'I4.0 communication' is not about another method for the time-critical transport of process and control data, but about fundamentally new concepts such as service-oriented architectures (SOA) and information models. This allows individual components, machines and systems to offer their services within an IP network in order to be orchestrated into more abstract machine and system services based on SOA. However, "simple and relatively down-to-earth applications" such as condition monitoring or energy efficiency optimization can also be implemented as value-added services via I4.0 communication. To encourage machine and plant manufacturers and operators to subsequently integrate and use OPC UA, the guide outlines a migration path consisting of three steps.

First migration step:
First of all, from the VDMA's point of view, users must implement an IP-based network for OPC UA use that extends beyond the local area of a machine or plant and also includes IT systems such as MES and ERP. According to the guidelines, 'Ethernet, WLAN and 5G mobile communications' are suitable for this, although we will probably have to wait a few more years for 5G and 4G should be sufficient in the meantime. After appropriate configuration, a suitable OPC UA server is inserted into this extended IP network, which has a connection to at least one PLC. With the help of the server, the OPC UA client of an MES system can then access the PLC data in order to implement condition monitoring or energy efficiency monitoring. When describing the first migration step, the guide also refers to IT security and describes that users must configure access rights and create and manage certificates for OPC UA communication between the server and client.

Second migration step:
In automation technology, OPC UA is the only established standard with broad support that is based on information models and, in addition to protocol-based data access, comprehensively specifies how such models are documented, implemented and referenced. An OPC UA information model forms a superset of different data objects, i.e. a more or less abstract representation of individual nodes with their properties, relationships and operations that can be executed with them. As other standards focus primarily on the actual communication rules for protocols, information models are exactly what M2M communication has been lacking until now. For this reason, as a second migration step on the way to I4.0 communication, the VDMA guideline recommends that manufacturers come together within an industry and develop a standardized OPC UA companion specification. As an example, the association presents EUROMAP 77 for injection molding machines in relative detail.

Third migration step:
OPC UA differentiates between three different categories for information models: Firstly, information models for devices as a basis. Building on this are the aforementioned companion specifications and, thirdly, higher-level extended information models.

Several of these models can be used simultaneously in a single OPC UA application. In this respect, the third step in the VDMA guideline is primarily aimed at component manufacturers and machine builders. It is made clear to them that, despite a standardized industry companion specification, there may still be clear distinguishing features between functionally identical products in the future. The authors of the guidelines believe that the extended OPC UA information models are suitable for this purpose. They enable a manufacturer to implement proprietary knowledge in order to stand out from the competition.

The practical implementation of the first two migration steps from the VDMA guidelines in particular promises interesting added value. However, it also requires a great deal of detailed work, the complexity and costs of which should not be underestimated, especially by system operators. It should be borne in mind that an OPC UA server interface cannot easily be added to most existing machines and systems in order to access the data available in the controllers.

Do not underestimate details

Even if access to PLC data has been enabled by a subsequently installed OPC UA gateway, there is still no guarantee that the available data really offers added value or results in a useful information model. It may be necessary to intervene in the PLC program to enable the gateway to access suitable data. In many cases, special sensors even have to be added subsequently in order to obtain data for condition monitoring or predictive maintenance.

Overall, the VDMA guideline is a step in the right direction. By adding OPC UA-based communication, suitable value-added services can be created in many machines and systems that increase overall efficiency and thus quickly amortize an investment. However, due to a lack of detailed specifications, the required OPC UA information models often have to be defined according to individual requirements and, if necessary, adapted to existing I4.0 standards at a later date. However, these problems are justifiable, especially as they only involve configuration changes. Furthermore, the OPC UA communication described by the VDMA can also be supplemented by an I4.0-compliant administration shell via additional software components, so that the step towards Industry 4.0 is even clearer and the ZVEI guideline with the requirements for I4.0 products is implemented at the same time.

Author:
Klaus-Dieter Walter is a member of the management board at SSV Software Systems.

Optional I4.0 expertise

The intensive Internet of Things (IoT) seminar, which is being held as 'Training for Professionals' on July 19 and 20 in Haar near Munich, is expanding its program. In addition to the questions

• What do typical IoT architectures and reference solutions look like?
• Which protocols, data formats and logical interfaces (APIs) are required?
• Which physical interfaces and sensors need to be dealt with?
• Which wireless technologies are relevant for the IoT?
• What do example applications look like and what are their practical benefits?
• How does 'big data' work and what possible uses are conceivable?
• How can the necessary security be created?
• Are there actually internationally recognized standards for the IoT?

- Industrial Internet of Things (IIoT) and Industry 4.0 topics are also integrated into the program as optional points.
This means that participants can also receive answers to the questions:

• What possibilities does Node-RED offer and how can I use them?
• How do I get Modbus sensor data into a cloud?
• How can I integrate OPC UA into an existing product?
• What possibilities do new (I) IoT wireless standards such as LoRa and NB-IoT offer?

Exercise examples are provided for these questions. For example, a complete OPC UA server will be implemented and equipped with an information model for sensors in order to provide other applications with I4.0-compliant status data. Registration for the intensive seminar is now open.