Interoperable communication between components and machines, between machines themselves or between machines and IT systems such as a cloud forms the basis for numerous Industry 4.0 fields of application. Interoperable communication across manufacturers and industries and the associated data availability enable the rapid integration of machines and components into new and existing systems, cross-manufacturer and global condition monitoring, simplified process optimization and future applications such as cross-manufacturer machine learning.

The goal: cross-industry interoperability as the highest expansion stage of Industry 4.0.

© VDMA

In order to simplify and standardize this exchange of information between a wide variety of communication partners from different manufacturers and thus enable Plug&Work, a manufacturer-independent and industry-wide accepted semantic self-description of components, machines and systems is required. For industry-independent semantic interoperability, there should also be a superordinate semantics. This should uniformly define relevant elements for the entire mechanical and plant engineering industry. The aim is for elements with the same meaning to be defined by the same elements (structure, nomenclature and description), regardless of the industry and communication partner. The OPC UA communication standard plays a key role in implementing this scenario: OPC UA Companion Specifications define and standardize the semantic self-description of information models for machines and components within the OPC UA communication architecture recommended in the Industry 4.0 world. The VDMA has recognized the urgency of developing OPC UA Companion Specifications, the semantic self-description for them and the resulting semantic interoperability. The VDMA specialist associations are developing the OPC UA Companion Specifications together with their member companies, international associations and the OPC Foundation. These are to gain international acceptance through dissemination via the VDMA network, the international associations and the OPC Foundation.

Central coordination

The development of the OPC UA Companion Specifications in the working groups of the VDMA specialist associations is coordinated centrally. Best practices, networking between the working groups, corresponding templates and ultimately the expert knowledge provided accelerate and structure the development of the OPC UA Companion Specifications within the VDMA. Synergy effects are leveraged within the VDMA and attention is paid to a coherent orientation and objectives of the working groups across all working groups. The process for developing OPC UA Companion Specifications can be divided into three sections, which are supported by different roles within the VDMA. These sections are

• The start phase: Here, the project and target definition as well as the comparison with existing standards or standards under development are taken into account. Through central coordination, common and coherent objectives can be defined between the working groups for the various components, machines and systems (hereinafter machine type).
• The standardization phase: The industry expertise of the working group and the VDMA specialist association consultant is now used to identify, consolidate and finally standardize the relevant communication elements such as variables or states. This is based on the machine types defined in the start phase, the planned use cases of the OPC UA Companion Specification and the identified communication partners. As in the start phase, existing standards and other OPC UA Companion Specifications must be analyzed and communication elements with the same content must be adopted.
• Modeling OPC UA information models: In the final stage of the process, the standardized communication elements are transferred and detailed into an OPC UA information model using the modeling elements available in OPC UA, such as alarms, methods or objects. This is done with the help of OPC UA experts. These can be participants in the working group itself, the VDMA specialist association consultant or an external service provider. Within the modeling, communication elements with the same content are adopted or referenced from existing OPC UA Companion Specifications.

The VDMA's unique selling point lies particularly in the first and third sections. The central coordination by the VDMA is intended to promote cross-industry interoperability of the Companion Specifications. One of the aims is to differentiate the machine types from one another in such a way that there is no overlap and that the communication partners and use cases are aligned. This is only possible if several working groups from different sectors are coordinated and networked together in one organization in the early development phases. In the third section, it is important to use suitable means to standardize the industry-specific communication content in OPC UA in such a way that different working groups describe the same communication content identically and reference each other.

The process for developing OPC UA Companion Specifications is described in VDMA Standard Sheet 40 000. The OPC UA Companion Specifications are published as part of the VDMA Standard Sheet 40xxx series. It is available for download free of charge at opcua.vdma.org.

The working groups

There are now over 15 working groups within the VDMA for the development of OPC UA Companion Specifications. There are working groups for the mining, die casting, glass and wood industries, for electric drives, industrial image processing, integrated assembly solutions, plastics, rubber, food and packaging machines, surface technology, robotics, weighing technology and machine tools (VDW).

All working groups follow four principles equally:

1. Involvement of the steakholders of the deployment scenario of the respective OPC UA Companion Specification.
2. International cooperation during the development, dissemination, acceptance and application of the OPC UA Companion Specification.
3. Harmonization of the OPC UA Companion Specifications to enable cross-industry interoperability.
4. Test implementations of the OPC UA Companion Specification for quality assurance.

Plastic and rubber machines

Two OPC UA Companion Specifications for plastics and rubber machinery are already available as a release - Euromap 83 and Euromap 77. Euromap is the European umbrella organization for plastics and rubber machinery manufacturers. Euromap 83 defines an OPC UA Companion Specification for general information related to plastics and rubber machinery. The aim is to ensure that object types that are relevant for different machines and applications are only defined once. Euromap 83 defines information blocks and functionalities that can potentially be used for numerous machine types in the plastics and rubber machinery family. Euromap 83 is a growing library of reusable type definitions. It is the basis for all other Euromap OPC UA Companion Specifications. For specific applications - such as connecting injection molding machines to Manufacturing Execution Systems (MES) - specific OPC UA Companion Specifications (here: Euromap 77) are used.

Euromap 77 is the first OPC UA-based standard for digital interfaces in the plastics and rubber machinery sector. Euromap 77 describes the interface for data exchange between injection molding machines and MES. Euromap 77 enables the exchange of general information about the injection molding machine - manufacturer, model, serial number ... -, the current configuration and the status of the machine including the molds, injection units and drives. The standard describes a logbook for relevant changes to the machine and includes order management with information on current orders, process parameters of the production cycles, methods and is used to transfer orders from the MES to the machine and release production. In addition, setting data record management is standardized, in which injection moulding machines save their configuration in so-called setting data records. These contain information on process target values (times, temperatures, pressures, etc.) in relation to the injection molding machine, but also for installed handling systems.

Industrial image processing

In the field of machine vision, an OPC UA Companion Specification is in the draft stage as a release candidate. This standard was developed together with the G3 initiative. The international G3 initiative coordinates the development of globally recognized image processing standards. Cooperation takes place between the industry associations of America (AIA), China (CMVU), Europe (VDMA and EMVA) and Japan (JIIA). The standard enables the management of recipes, configurations and results in a standardized way, while the respective contents are treated as a manufacturer-specific black box. The abstracted behavior of an industrial image processing system is described via a status machine concept described in the standard.

Robotics

Structure of a motion device system.

© VDMA

There is also an OPC UA Companion Specification for robotics in draft status as a release candidate. The OPC UA Companion Specification describes a complete motion device system that contains a list of motion devices (kinematics). Motion devices can be any existing robot type or even a fictitious future robot type. These include, for example, industrial robots (stationary), mobile robots (also with multiple robot arms), robots with multiple controllers, robot peripherals without their own OPC UA server and service robots.

The self-description of a motion device system is based on a component-oriented information modeling approach. The information objects are modeled based on the physical structure of a motion device system in a granularity adapted to the use case. All common types of motion device systems can be described using OPC Robotics.

The OPC UA Companion Specification Robotics is divided into several parts, with Part 1 representing the basic specification. Part 1 describes an abstraction of the generic motion device system, i.e. the representation of the so-called digital twin of the system. The OPC UA Companion Specification includes the use cases of asset management, condition monitoring, predictive maintenance and vertical integration into production IT systems (PLC, MES, SCADA, cloud). Future parts will extend the basic description of a motion device system and include use cases such as configuring and controlling a motion device system or the motion devices it contains, initiating actions on the robot system using methods and a status machine, reporting statuses, alarms and events and storing customer-specific information on the server (e.g. ERP data, cost center).

The Industry 4.0 asset administration shell and OPC UA

The joint working group 'I4AAS OPC UA' of the OPC Foundation, the VDMA and the ZVEI will develop an OPC UA information model for the Industrie 4.0 Asset Administration Shell (I4AAS).

The I4AAS concept, which has so far been defined independently of technology, is to be transferred to OPC UA. The I4AAS concept is a result of the Plattform Industrie 4.0 working group 1 'Norms, Standards and Reference Architecture', the ZVEI mirror group 'SG Standards and Models' and the ZVEI sub-working group 'Administration Shell in Detail'. Within this working group, the VDMA aims to ensure the interoperability of the I4AAS with the OPC UA Companion Specifications developed by the VDMA. Many groups are currently working solely on the prototype implementation of the I4AAS based on OPC UA. The working group should harmonize all these activities, but also coordinate with other stakeholders such as the VDMA in order to synchronize the I4AAS with the process and central coordination and thus all working groups within the VDMA.

Author:
Andreas Faath heads the strategic orientation of the VDMA in the area of interoperability with OPC UA.

The Umati interface of the VDW

With the Umati brand, the VDW is developing a standard for an open interface for connecting machine tools to higher-level IT systems. And here, too, the OPC UA Companion Specs are the focus, as Dr. Alexander Broos, Head of Research and Technology at the VDW, explains in an interview.