Integration of Distributed Control Systems in Virtual Automation Networks Matthias Riedl, Frank Naumann Institut f. Automation und Kommunikation e.V. Magdeburg Steinfeldstr. 3, 39179 Barleben, Germany {matthias.riedl|frank.naumann}@ifak.eu http://www.ifak.eu/
Christian Diedrich Institute of Control Systems Otto-von-Guericke-University Magdeburg Universitaetsplatz 2, 39106 Magdeburg, Germany
[email protected] http://www.uni-magdeburg.de/
Abstract— This paper presents an adaptation of the concept for the engineering of Distributed Control Systems (DCSs) based on heterogeneous communication systems as defined in the European Integrated Project Virtual Automation Networks. The adapted approach offers the possibility to configure an object-oriented distributed automation system DOME. The details of the engineering are derived from the VAN protocol specifications which are based on the OSI Reference ASE model. The paper presents also the mapping of the engineering concept to FDT/TCI technologies in general which is used to evaluate the information model and the usefulness of the VAN information model and the interaction of the tools with the VAN devices.
components to provide the bridge between the industrial segments. Todays engineering process can basically be subdivided into the phases modelling, planning, configuration, commissioning, production and maintenance. Existing tools are well advanced with respect to the phases configuration, commissioning, production and maintenance. However there is a lack of methods to derive a formal model of the automation system from customer requirements systematically and refine this model for the planning of the automation system continuously. B. Ideas of DOME
I. Introduction A. Ideas of VAN Distributed control systems force the engineering and its workflow to adapt their methods and tools. Within the European funded research project VAN (Virtual Automation Networks [Ne2008], [VA2007a]) solutions for the usage of LANs and WANs public and private, wired and wireless forming Virtual Automation Networks (VANs), for application in industrial domains as mentioned above will be investigated and developed. The resulting engineering has to meet all existing engineering steps and tools which are faced with new functionalities and features. Based on the definitions of the ISO OSI Reference model and the harmonised specification format of industrial communication standards in the IEC 61158 series and the IEC 61784 series, VAN specifies the top layer access point using so called Application Service Elements (ASEs) [ISO1994]. ASEs are the model describing the service object of the communication protocols of layer 7. VAN focuses on heterogeneous networking of production and manufacturing processes. This heterogeneous characteristic has to be faced by the engineering concepts and tools. The main focus is on a balance between well established technologies and tools and new necessary system
978-1-4244-1666-0/08/$25.00 '2008 IEEE
DOME is the abbreviation for Distributed Object Model Environment. It is designed as a middleware, offering a range of capabilities for an automation specific object-oriented application [Ri2005]. In DOME, an application consists of objects, which can be predefined or developed by the user. The objects itself are defined in the form of classes, in which features like abstract classes, inheritance or polymorphism are offered. For the clear reference of an object, each of them gets a unique name in the automation system. Therefore it is possible for the engineering of an application, to define all object instances and a network of links between the objects. The links itself are also objects, called Link Objects, so all features of the mentioned class concept can be used for the definition of different link types. Therefore all objects, both Automation Objects (with algorithms) or Link Objects, can be treated in the same way (see Figure 1). The flexible usage of the Automation Objects is guaranteed by the late binding of the information/data flow between the Automation Objects. Therefore the Ports (with their special roles as service and requires interface) are aggregated in each Automation Object. The Ports decouple the connection of Automation Objects at run time from the design of the algorithm inside the Automation Object
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Fig. 2. Components and objects of the distributed application Fig. 1. Automation- and Link Objects
completely. So it is possible to handle the very complex interaction unchained from the Automation Object design. In order to manage all these objects, an efficient object management is necessary. The requirements are e.g. memory allocation, life time control or persistence. This object management is a central component of the approach. Each device of the automation system has to have such an object management instance. Its usage will be discussed in later sections. C. Combination of ideas In order to demonstrate the powerful solutions of VAN, we have adapted the VAN solutions for configuring [Ho2007] also the application based of DOME. VAN defines a set of infrastructure components, e.g. for the registration of ASEs or a Web Service server, publishing the ASE functionality [VA2006]. These components are located in each VAN enabled automation device. This paper discusses the usage of VAN technologies for an existing factory automation application. It explains the integration of DOME in VAN technology using the central VAN components. The DOME application itself controls the robot via different levels. The remainder of this paper is organised as follows: The second chapter gives an overview about the considered distributed application, the third chapter discusses the integration of VAN ideas in the DOME approach and the fourth chapter explains the provided functionality from the point of view of VAN. The fifth chapter demonstrates user interaction examples. The sixth chapter discusses the engineering approach of VAN in relationship to the found solution of the DOME integration. Finally the last chapter concludes the found experiences and gives an outlook of further applications. II. Technical Details of Distributed Application The complete automation system consists of three controllers (e.g. industrial PCs), see Figure 2. On each of them the DOME runtime is installed. Inside this
Fig. 3. VAN components and objects inside a device
runtime DOME -objects can be instantiated, parameterised, connected and performed [Ri2006a]. On node called robot controller the DOME -object Roboter is running, controlling the positions of the robot. On the second node appl controller the proper application DOME -object Hanoi is running, controlling the movements of the tower. The aim of the application is to move of a tower of slices according to the rules of the game ”Towers of Hanoi”. The third node client controller provides the DOME -object Client, which is responsible for the setpoints of the tower, number of slices in it etc. This object can also pass controller commands such as START / STOP / PAUSE / RESUME etc. to the Hanoi object. The DOME middleware performs these commands in a dependable fashion [Ri2006b]. III. Integration in VAN VAN defines the following component and object structure as shown in Figure 3 for a device. Inside VAN, each object shown in Figure 3 has to register itself by the local Registry expressing its ASE type and some connection information. In order to integrate DOME into VAN, a central component of DOME must
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Fig. 4. ASE aggregates one or several DOME ObjectManagers
Fig. 6. Relationship between VAN ASEs and DOME Configuration
Figure 4. Each node offers its own separate ASEs for the specific DOME processes. Fig. 5. ASE inherits from DOME ObjectManager
C. ASE DOME Configuration
be addressable. This central DOME component is the so called ObjectManager, which is responsible for all objects inside one process and its connections to other DOME objects. For implementation, two alternatives are possible to propagate the VAN instructions from the web service interface to DOME. • VAN object aggregates an ObjectManager, see Figure 4 • VAN object inherits from ObjectManager, see Figure 5 Furthermore, one of the objects could be responsible for several ObjectManager objects, so the complete application could be configured and controlled by only one VAN device.
The ASE DOME Configuration inherits directly from the predefined ASE DeviceConfig, see Figure 8. It has the following attributes: • Process (string) – Name of the DOME process • Configuration (string) – DOME specific configuration file for the DOME process The DOME process running on the node offering the VAN functionality, has to instantiate for each DOME process one ASE representation. The ASE offers two services set and get for the manipulation of the configuration of the appropriated DOME process. The ID of the class ASE DOME Configuration is outside the predefined values and is defined with 0x0100. C.1 ASE DOME Operate
IV. Provided VAN functionality A. General In contrast to the ideas of the ASE, DOME configuration is an application relevant engineering task. Normally, ASE shall only explain the communication facilities of a VAN device. Nevertheless, ASE shall be used in order to do application specific tasks also by means of VAN engineering tools. From DOME point of view, the configuration of each component and the operator instructions must be performed. The configuration of a distributed DOME application will be done by means of specific configuration files for each node → such configuration files could be transferred by means of the content of XML messages. B. Found Solution At the moment, only the predefined ASE DeviceConfig shall be used. In contrast to the provided parameters, our implementation of this ASE provides only one attribute of type string, containing the DOME process name. All other parameters are added inside the central registry component. The implementation is following the approach from
The ASE DOME Operate inherits directly from the predefined ASE ASE, see Figure 8. It has the following attributes: • Command (string) – Allowed values: START, STOP, PAUSE, RESUME – If START is sent to the ASE, the whole DOME application will be moved into the DOME state ’running’, STOP moves to ’halt’ The ASE also offers two services set and get for the manipulation of the status of the appropriated DOME process. The ID of the class ASE DOME Operate is 0x0101. D. ASE DOME Operate Hanoi The ASE DOME Operate Hanoi inherits directly from the specific ASE DOME Operate, see Figure 8. It has the following attributes: • Command (string) – Modification of running state of the application from user / application point of view (START, STOP, PAUSE, RESUME) • Infinite (bool)
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Fig. 7. Relationship between VAN ASEs and DOME application operation mode
Fig. 9. Client for setting the DOME configuration
A. Requirements for ASE DOME Configuration The data to transmit to the device shall be load from a DOME specific configuration file. Therefore the configuration files shall be load by browsing and the file content has to be sent to the ASE via the set(). The content received via get() service has to be printed on the screen, see Figure 9. Fig. 8. Relationship between VAN ASEs and DOME application setpoints
B. Requirements for ASE DOME Operate The client should offer e.g. a dialog, providing buttons or flags (START, STOP, PAUSE, CONT) in order to define the content to transmit. The string of the selected operation shall be sent via set() and the received state via get() shall activate/highlight the appropriate user control. Nevertheless the client shown in Figure 9 can also be used for the DOME Operate ASE. Thus it is possible to select the Web Service to use and only the content of the data has to be modified.
– Infinite loop of sorting the towers Hanoi Object Address (string) – Address of the Hanoi application object controlling the roboter • Slices (unsigned int) – Defines the number of slices in the tower • Source Pos (unsigned int, unsigned int, unsigned int) – This tuple of three values (x, y, z coordinates) defines C. Requirements for ASE DOME Operate Hanoi the starting position of the tower • Dest Pos (unsigned int, unsigned int, unsigned int) In order to enter and represent the properties of the Ha– This tuple of three values (x, y, z coordinates) defines noi towers, a user control as shown in Figure 10 could be the final position of the tower provided. Secondary to the unique attributes, informati• Intermediate Pos (unsigned int, unsigned int, unsigned on about the IP address of the roboter and the address of int) the node on which the DOME -application runs have to be – This tuple of three values (x, y, z coordinates) defines entered. the intermediate position of the tower The command for controlling the running state are the The values of the coordinates are conform to the coordi- same as the possibilities of DOME Operate and simplify the nate system of the robot. handling for the user. So the user has to interact only with The ASE offers two services set and get for the manipu- one ASE. The kind of implementation of the control enlation of the setpoints of the appropriated DOME process. hances the usability for the user. Depending on the reThe ID of the class ASE Operate Hanoi is 0x0102. cent state of the DOME -application, the control activates/deactivates the allowed buttons, so maloperations can be avoided. V. User Interactions
•
Unique for all client applications is the possibility to enter the URL of the Web Service for the selection of the subjected device and the object reference in order to communicate with the requested ASE instance. Further on, the user has to select a specially provided Web Service, in order to operate with the supported ASEs. The implemented clients achieve the following defined tasks.
VI. Engineering approach of VAN The engineering in VAN is based on a common Information Model, providing information about the whole virtual automation network. Besides the commissioning and maintenance of the devices of the network, also the configuration of the network form a vital interest. In general the same tasks have to be done also inside the DOME environment.
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Fig. 11. Generic tool for viewing DOME -processes
Fig. 10. Client for setting the application setpoints
A. Configuration The configuration phase of VAN is responsible for the network settings. The engineering tools can be used for configuration in offline mode based on the information provided by a device description. For parameterisation and download of configurations and programs, a connection to the devices is established via a direct link or through the network. Inside DOME the adresses of the devices also have to be planned at first. In the case of Ethernet IP based communication, the IP adresses have to be determined. Because the DOME device offers a generic functionality, no predefined device description is available, however DOME provides a mechanism called reflection in order to provide all information about the device. Therefore a special component is running on each device - the DOME Manager. The DOME Manager informs the user about all established DOME -processes on the device. After connecting with a DOME -process, the user can by means of introspection view all information about the objects, links between the objects and state information about the DOME -process. The generic tool in order to do this is called reperio, see Figure 11. B. Commissioning and Maintenance In context of VAN, the engineering tools are used in online mode, i.e. they are connected to the automation system for commissioning and maintenance tasks. For each composition, the adjustment of the configuration parameters may be necessary. The diagnostic features of the engineering tools are used to identify and solve problems. The engineering tools are connected to the devices through the systems network or via a direct link. In context of DOME, commissioning is defined as the phase of configuring a DOME -process as explained in chapter IV-C. Thus the introduced ASE types will be applied.
Fig. 12. Integrated engineering concept of VAN
These ASEs can play the role for commissioning and maintenance. Setting the configuration can be treated as commissioning, reading the data is a kind of maintenance or disgnosis. The architecture of the VAN engineering tool defines two different concepts [VA2007b]. The first concept targets the development of a stand-alone VAN Engineering Tool, which is independent of the existing engineering tools present on the market. The focus of the second concept is to facilitate the enhancement of existing engineering tools. This integrated concept is elaborated to allow the use of standardised technologies and interfaces as FDT/DTM [IEC2007] and TCI [PI2006], see Figure 12. In the scope of the VAN project, the role and a specification of a VAN Device Description (VAN-DD) is worked which covers the new features of VAN devices and build a bridge to the existing device descriptions. Because of the limited numbers of pages this paper contains no explanations about the FDT and TCI technologies. Only their specific use is mentioned. The Tool Calling Interface (TCI) permits to call one soft-
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ware tool from another tool and to pass parameters between these tools. In the integrated concept TCI is used to couple a PLC programming environment with a communication configuration system of two different manufacturers. FDT is extended by a VAN Device DTM and VAN Communication DTM. In order to use the DOME enhanced ASEs also by means of the VAN engineering tools, a device description according to the VAN concept has to be provided for each DOME -device. The device description instance file constitutes the available ASEs. It is then possible to use the established engineering tools also for commissoning / maintenance of DOME.
[PI2006] [Ri2005]
[Ri2006a] [Ri2006b] [VA2006]
[VA2007a]
VII. Conclusions The access points to the devices are defined in the form of ASEs inside VAN. This approach was adapted for DOME in order to integrate this forward-looking concept also into VAN. The defined addional DOME -specific ASEs could be demonstrated in line with an organised demonstration session of the VAN consortia for the European Community technical officers. The integration of VAN specific configuration technologies by means of Web Services enhances the scope of VAN also to the application level. The scope of the VAN project is among others the development of a prototype and demonstrator which uses existing tools and shows the interaction between different tools. The presented integration concept of an existing distributed control system DOME offers the possibility to enlarge the end user benefit of VAN as well as the usage of real distributed systems beyound the existing technologies for decentral approaches. Especially the interesting use case of tele-control applications can also be considered from the point of view of a homogeneous concept, independent of vendor specifc, proprietary solutions.
[VA2007b]
VIII. Acknowlegdement The paper has been supported by the Virtual Automation Networks project (FP6/2004/IST/NMP/2 016696 VAN) funded by the European Community under the Information Society Technology Programme (http://www.van-eu.eu). The authors want to thank the whole VAN project team. References [Ne2008]
[IEC2007] [ISO1994] [Ho2007]
Neumann P.; Messerschmidt, R.; Poeschmann, A.: Horizontal and vertical integration for automation systems: virtual automation networks, IFAC World Congress 2008, Seoul International Electrotechnical Commission: IEC 62453 series CD2: Field Device Tool Specification, Geneva July 2007 International Standard Organisation: ISO/IEC 7498: Open Systems Interconnection Reference Model, 1994 Hoffmann, M.; Muehlhause, M.; Chiari, M.; Schwaab, C.: Uniform Engineering of Distributed Control Systems - The VAN Approach, ETFA Congress 2007
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PROFIBUS PROFINET Specification: Tool Calling Interface, Version 1.0 , PROFIBUS International, October 2006, Order No: 2.602 Riedl, M.: Distributed Object Model Environment - Ein objektorientiertes Softwaremodell f¨ ur verteilte Automatisierungssysteme, Dissertation, Ottovon-Guericke-Universit¨ at Magdeburg, Shaker Verlag, Magdeburger Schriften zum Empirischen Software Engineering, 2005, ISBN: 3-8322-4644-4 Riedl, M.; Diedrich, Ch.; Naumann, F.: Event Driven Applications for Automation Area, IFAC INCOM 2006, Mai 2006, St. Etienne Riedl, M.; Diedrich, Ch.; Naumann, F.: Dependable Distributed Start and Stop, IEEE INIDIN 06, August 2006, Singapure VAN Consortium: Deliverable D02.2-2 of the VAN project: Specification of the Open Platform for Automation Infrastructure, The VAN Consortium, November 2006 VAN Consortium: VAN project page, http://www.van-eu.eu, The VAN Consortium, March 2007 VAN Consortium: Deliverable D08.4-1 of the VAN project Engineering Tool Integration Concept and Tool Interfaces, The VAN Consortium, September 2007q
