Configurable Communication OPC UA FX

Artifact - Configurable Communication with OPC UA FX

Artifact Factsheet

Fact Sheet



Name
Configurable Communication with OPC UA Field eXchange (FX)

Artifact Type
Design Pattern

Target Users
Software Architects, PLC Programmers

Objective
This design pattern defines, in accordance with the OPC UA FX specification, the necessary information models and corresponding mirror data types for integration into control programs. OPC UA FX already describes a standard mechanism for direct information exchange between controllers. The pattern defines necessary components and describes their application.

Relevant Publications

Content partially published in [SBB+23] and based on OPC UA Specification 10000-8X [OPC10000-80].

Artifact Description

The design pattern Configurable Communication with OPC UA FX defines the necessary components for applying OPC UA FX in Controller-to-Controller (C2C) execution. The uniqueness of this design pattern lies in the fact that OPC UA FX C2C is already specified for the use case pursued with the concrete design patterns of configurable communication.

The OPC UA FX specification describes how connections between two endpoints are to be configured. The information must be described in a defined form, requiring data types for the control program and associated OPC UA models to be defined.

This design pattern enables Communication Pattern Variant 2, as currently only OPC UA Publish/Subscribe is specified for OPC UA FX. In the future, application for OPC UA Client/Server is also expected, which would also support variants 3 and 4.

Artifact Technological Conditions

Unlike OPC UA Publish/Subscribe and OPC UA Client/Server, OPC UA FX does not require explicit logic for communication in the user program. It is implemented as a firmware function in the controller. The FunctionalEntityTypes and the necessary AutomationComponentType for configuration are created via the information model provided by the OPC UA Server.

Corresponding preparations are required for linking between the control program and information model, which are described in this design pattern. The components themselves create the data types that correspond to the FunctionalEntityTypes and make them available. The standardization of these constructs is crucial for the vendor neutrality of automation service choreographies and enables integration into the Connection Manager.

Artifact Building Blocks

The design pattern comprises nine definitions that enable equipping an active choreography participant with communication functions according to the OPC UA FX standard.

Pattern Components and Data Types Figure: Components and data types of the OPC UA Field Exchange specific design pattern for configurable communication

Figure: Pattern-specific information models for using OPC UA FX in automation service choreographies

OpcUaFxManager

The core component that links the proxy data types for FunctionalEntityTypes with the input elements of the configurable logic.

FxInputEntityType

Contains the associated information element for incoming OPC UA FX information on the control program side. The Index specifies which input element the associated FxInput element is transferred to.

FxOutputEntityType

Contains the associated information element for outgoing OPC UA FX information on the control program side. The Index specifies from which output element the value for the associated FxOutput element should be taken.

ParticipantComponentType

A subtype of AutomationComponentType that represents the root element of a choreography participant relevant in an OPC UA FX relation.

ParticipantFunctionalEntityType

A subtype of FunctionalEntityType that represents the top functional element of a choreography participant.

UnionInputFunctionalEntityType

A subtype of FunctionalEntityType that represents the functional element of an input element. It has a folder object with Organizes relations to variables of the FxInput data type originating from the control program.

UnionOutputFunctionalEntityType

A subtype of FunctionalEntityType that represents the functional element of an output element. It has a folder object with Organizes relations to variables of the FxOutput data type originating from the control program.

Artifact Decisions

Mirror Data Types for OPC UA FX Models

The linking of OPC UA information models and controller application programs is implemented through mapping. To make this mapping as simple as possible, mirror data types are specified for the application program that correspond to the information models defined in OPC UA FX. This makes future mapping easier for both developers and tool-supported mapping.

Artifact Implementation Details

The central aspect of the design pattern is the division of components in the control program and the definitions of the OPC UA FX information model. In the control program, the data types FxInputEntityType and FxOutputEntityType represent mirror definitions to the OPC UA FX definitions FxInputEntityData and FxOutputEntityData.

Communication execution occurs via the system functions of the OPC UA FX firmware. Each FxInputEntityType and FxOutputEntityType has index information that addresses the corresponding element of the input or output list.

Artifact Application

Application Example Figure: Application of the OPC UA FX-specific design pattern for implementing incoming and outgoing information following the active choreography participant design pattern

The design pattern serves to connect incoming and outgoing information between active choreography participants based on OPC UA FX. When OPC UA FX functionality is integrated into the control system firmware, an active choreography participant can be equipped with OPC UA FX mechanisms using the extensions of basic models and mirror definitions described here.

Artifact Pros/Cons

Advantages:

Enables extensive integration of C2C communication in industrial control systems
Significantly reduces effort in the application program
Standardized mechanism for direct controller-to-controller communication

Disadvantages:

Novelty risks: No commercial applications currently exist, and the specification is relatively new
Specification changes and limitations in productive use are likely
Connection preparation is necessary for OPC UA FX connections
Not suitable for integrating existing systems due to preparation requirements
Actual benefits can only be definitively evaluated with available commercial implementations

Fact Sheet
Name	Configurable Communication with OPC UA Field eXchange (FX)
Artifact Type	Design Pattern
Target Users	Software Architects, PLC Programmers
Objective	This design pattern defines, in accordance with the OPC UA FX specification, the necessary information models and corresponding mirror data types for integration into control programs. OPC UA FX already describes a standard mechanism for direct information exchange between controllers. The pattern defines necessary components and describes their application.