When the Industrie 4.0 Working Group (I4.0 WG) started at PI, five focus topics were determined to be dealt with in separate sub working groups. One of these topics is OPC UA and the goal was to specify the mapping of PROFINET to OPC UA. At a minimum, OPC UA as a middleware is positioned to be one of the core components of the I4.0 architecture. Also today, OPC UA has become the de-facto standard for interoperable information exchange from the shop floor to the top floor. With its robust object-oriented information model and platform independence, OPC UA is proving to be the most efficient way to move semantic information around a plant. This fits perfectly to PROFINET as real-time switched Ethernet with its ability to run different protocols independent on the same cable. Therefore, OPC UA is a perfect aid to boost vertical integration in PROFINET systems and to bring added value to end-customers.

Companion Specification Approach

The mapping of PROFINET will be defined in an OPC UA Companion Specification. For this, a joint Working Group between PI and the OPC Foundation was convened in 2017. To have a comprehensive solution, the Working Group started with a detailed analysis based on use-cases. The first targets are Diagnostics and Asset Management, to create added value for vertical integration. Further evaluation showed that today, OPC UA modeling technologies typically based on device integration (DI) are not capable of covering all aspects of the required use-cases and therefore limit the potential data mapping. To overcome these restrictions, the PROFINET@OPC UA Working Group developed a new modeling technique called “Facet Modeling”.

New Modeling Technique for Added Value

Facet Modeling is based on independent partial models called facets, describing different aspects or views of an automation entity. The principle feature is the unique semantics for the modeling of facets and the use of typified references between these facets. Using this new technique it’s possible to model all aspects of an automation system, to aggregate sub-models to a complete system model, and to add additional semantic information for added value use-cases. The main facets defined are:

  • The PROFINET facet for the communication aspects
  • The physical facet for the asset related aspects
  • The functional facet for the logical and functional aspects like application models defines in PI Application Profiles

The next milestone will be the release of the first version of the PROFINET@OPC UA Companion Specification scheduled for Hannover Fair 2019. Work on proof of concept implementations has started and first demonstrations will be shown at the SPS/IPC/Drives fair this year and at the upcoming PI-Konferenz next year.

–Andreas Uhl
Industrie 4.0 Working Group
PROFIBUS/PROFINET International