Control node for a network of control nodes

0001The invention relates to a control node for a network of control nodes and a system with such control nodes.

0002Modern concepts for industrial automation are based on the idea of ​​decentralized control. The control task to be executed is geographically and functionally optimally distributed to the control nodes of the decentralized control. The control nodes communicate with each other and with the higher-level systems via local networks. Due to the decentralized control, the communication effort can be reduced since the individual control nodes themselves have to assume control tasks related to their areas and only have to communicate with the other control nodes or with the higher-level systems for coordination.

0003The decentralized control is based on the basic idea of ​​dividing the automation task into individual functional and logically completed modules, which can then be arranged close to the process, thereby reducing the cabling and installation effort. By dividing into modules, the complexity can be reduced, making it easier to implement functions.

0004The Ethernet concept is the most widely used communication standard in local area networks (LAN). The Ethernet is based on a LAN structure in which a plurality of control nodes, such as computers or machines, are interconnected via a common transmission medium, wherein the Ethernet protocol encapsulates the data to be transmitted in data packets, also referred to as a telegram, with a predetermined format.

0005Ethernet protocols are primarily used in office communication networks. Due to the advantages of the Ethernet concept in the use of standard hardware and standard software components as well as the ability to achieve high data transfer rates with simple networking technology, Ethernet network communication is increasingly being used in industrial manufacturing for data exchange between control nodes.

0006In the control of machines in industrial automation, it is necessary that a cyclic processing of the control task without temporal fluctuations, ie with only small deviations from the desired cycle time in the range of a few microseconds, with a predictable response time to the control request is responded. Real-time capability and fast response times, as required in industrial automation, are of minor importance in standard data processing applications where Ethernet communication is commonly used. In order to guarantee real-time capability and fast response time when using Ethernet communication in industrial automation, methods for prioritizing Ethernet telegrams for real-time applications have been developed.

0007Despite the increasing use of distributed open-loop controllers, where data transfer is based on the Ethernet protocol, and the consequent cost benefits, there is still a problem of return-of-investment in industrial automation, especially because of the ever-shortening ones product life cycles. Although new products are already being developed in such a way that they can be easily produced automatically. However, the automation systems for the production of the products are generally designed specifically for the product to be manufactured and can therefore only be adapted to product and process changes with great effort.

0008The state of the art is out of the <patcit id="pcit0001" dnum="WO9967690A"><text>WO99 / ​​67690A</text></patcit>. <nplcit id="ncit0001" npl-type="b"><text>LUDWIG WINKEL ED - ANONYMOUS: "Real-Time Ethernet in IEC 61784-2 and IEC 61158 series" INDUSTRIAL INFORMATICS, 2006 IEEE INTERNATIONAL CONFERENCE ON, IEEE, PI, August 1, 2006 (2006-08-01), pages 246-250</text></nplcit>. <nplcit id="ncit0002" npl-type="b"><text>FELSER M: "Real-Time Ethernet-Industry Prospective" PROCEEDINGS OF THE IEEE, IEEE. NEW YORK, US, Vol. 93, No. 6, 1 June 2005 (2005-06-01), pages 1118-1129</text></nplcit>, of the <patcit id="pcit0002" dnum="DE10309886A1"><text>DE10309886A1</text></patcit> and the <patcit id="pcit0003" dnum="WO2005047991A2"><text>WO2005 / 047991A2</text></patcit> known. The document<patcit id="pcit0004" dnum="WO2005066728A"><text>WO2005066728</text></patcit> describes a control node in the field of industrial automation, wherein the data transmission between the control nodes in the network takes place in the form of data packets, wherein the control node has a transmission module which is designed to manage the data to be sent in an output process image, the output process image into a data packet implement and output the data packet to the network at a given time.

0009The object of the invention is to provide a control node for a network of control nodes and a system with such a control node, which allow a flexible asset management.

0010This object is achieved by a control node according to claim 1 and a system according to claim 9. Preferred developments are specified in the dependent claims.

0011According to the invention, the control node for exchanging data with other control nodes in the network in the form of data packets on a transmission module which is designed to manage the data to be sent in an output process image to convert the output process image into a data packet and the data packet at a predetermined time to spend on the network. Furthermore, the control node has a reception module which is designed to log on to the data packets of one or more transmission modules from further control nodes and to convert a received data packet into an input process image.

0012The inventive design of the control node allows a decentralized control in the form of an open system with a high compatibility and flexibility with respect to the function of the control nodes. In fact, all control nodes have simple, uniform communication services that can be easily adapted to desired production and manufacturing processes. The transmit-receive communication model according to the invention makes it possible to present the data traffic between the control nodes to the outside in relation to the operator of the plant in the form of a simple process image. The possibility that a control node can register with the aid of its receiving module to the data packets of several control nodes, the communication relationships between the control nodes can be flexibly set,

0013According to a preferred embodiment, the receiving module of the control node is designed to associate the data packet received with a quality date indicating the age of the data packet. From the time offset between the sending and the arrival of the data, the control node can determine the quality of the data communication. The application program in the control node can then respond to this quality value.

0014According to a further preferred embodiment, the transmission module can directly address the data packet to one or more further control nodes, in which way preferably non-real-time data is sent acyclically. Alternatively, however, the transmission module can also forward the data packet to all control nodes present on the network, in which case real-time data is preferably transmitted cyclically. With this design, a parallel data transmission of real-time data and non-real-time data can be performed. The real-time data is cyclically distributed to all control nodes, while non-real-time data is sent acyclically as needed. The communication relationships between the control nodes can thus be optimally adapted to the production and production conditions.

0015According to a further preferred embodiment, the data transmission between subscribers in the control node is performed in the form of data mapping operations, wherein each subscriber in the control node is designed to directly access the control node process image transmitted between the subscribers. This direct access in the internal data transfer in the control node allows a very fast data exchange with little protocol effort.

0016According to a further preferred embodiment, each participant in the control node is subdivided into an organization unit for executing a state machine, which determines the mode and operating state, and a functional unit for executing the application program assigned to the respective state machine. This design makes it possible to design the individual nodes in the control node as self-sufficient modules with a minimum number of interfaces to the outside world, whereby an improved decentralization of the control can be realized while reducing the complexity of the modules. Distributing the participants into an organizational unit containing the state machine and a functional unit executing the application programs makes it possible to

0017According to a further preferred embodiment, each subscriber comprises an event detection unit which is designed to classify and buffer events, and a data acquisition unit which is designed to buffer data. This refinement makes it possible to reduce the interfaces to the outside world per subscriber to two universal interfaces, namely one for event logging and one for data logging.

0018According to a further preferred embodiment, the input / output unit of the subscribers is made variable, the input / output ports being defined as local variables with a wildcard address that are freely configurable. This approach makes it possible, without having to make complicated hardware and software changes, to adapt process flows in the control node to desired production and production processes.

0019According to the invention, the system with a network of control nodes has a network configurator which is designed to establish the communication relationship between the control nodes or the subscribers in the control node. With this configuration can be easily responded to production expansion and production change. The network configurator makes it possible by simple reprogramming to make appropriate adjustments to the communication relationships between the individual control nodes or the participants in the control node.

0020The invention will be explained in more detail with reference to the accompanying drawing. Show it:<ul><li><figref idref="f0001">Fig.1</figref> schematically a network with control node and network configurator;</li><li><figref idref="f0002">Fig.2</figref> an initialization phase in a network;</li><li><figref idref="f0003">Figure 3</figref> a control node architecture;</li><li><figref idref="f0004">Figure 4</figref> a detailed representation of in <figref idref="f0003">Fig. 3</figref> shown control node architecture; and</li><li><figref idref="f0005">Figure 5</figref> a data exchange between two control nodes with two participants.</li></ul>

0021In industrial automation, ie the control and monitoring of technical processes by means of software, increasingly decentralized control systems are used. In decentralized control, the control task is distributed to control nodes. The control nodes communicate with each other and, if necessary, with higher-level systems via an industrial local network.<figref idref="f0001">Fig.1</figref> shows such a decentralized control with three control nodes 1A, 1B, 1C and a network configurator 2 for configuring and monitoring the network. The control nodes 1 and the network configurator 2 form a local communication network, a so-called Local Area Network (LAN). LANs are local communication networks that are limited to a geographical area and are composed on one or more servers or workstations, the control nodes, which are interconnected via a communication line 3, eg, a twisted pair cable or a fiber optic cable. Different network designs are possible with the LANs, the best known being the bus, ring, star and tree structures.<figref idref="f0001">Fig. 1</figref> shows the formation of the LAN with a bus structure.

0022The essential requirement for the LAN when used in industrial automation as a so-called fieldbus system is its real-time capability. The fieldbus system must ensure that every data packet sent arrives at the receiver within a limited guaranteed time. LANs operate with a network operating system and a single network protocol. The preferred communication standard is the Ethernet concept. The Ethernet concept offers the possibility of using standard hardware and software components. Furthermore, the Ethernet concept is characterized by a simple networking technology with a simultaneously high data transmission rate.

0023In the OSI layer model, the international reference model for data transmission in networks, which is built on a seven-layer layer stack, each layer defining a set of protocols, each providing its services to the next higher layer, is the Internet Protocol of FIG. Layer, the so-called line layer assigned. In this line layer, data to be transmitted is bundled into packets to which specific information for the respective communication protocol is added. The line layer is responsible in the network for the transport of the data packets from control node to control node and for error detection. In the Ethernet concept, the routing layer is divided into two levels, with the first level adding a first header to the data containing information, which are required for a correct data transmission from the receiver protocol. In the 2nd level, the data packet to be sent is then encapsulated with a further header section and an end section for the transport of the data packets from control node to control node. With such Ethernet packets, also known as Ethernet telegrams, data with a length of up to 1500 bytes can be transmitted.

0024To be able to use the Ethernet concept also in industrial automation, where real-time capability is required, each control node 1 has an extended network connection 11 for real-time operation. The network interface 11 can be realized both hardware and software technology in the control node. The network interface 11 in the control node 1 enables the parallel use of the bus system 3 for the detection of data for real-time applications and for non-real-time applications. The data for real-time applications are thereby treated prioritized by the network interface 11 so that real-time data is transmitted first and then the data for non-real-time applications in the remaining time until the next real-time applications are transmitted.

0025For the data transmission via the bus system 3, the network connection 11 of the control node 1 is subdivided into a transmission module 12 and a reception module 13. The transmission module 12 manages the data to be sent in an output process image. The data packets are sent eg in the form of Ethernet telegrams. The transmission module 12 of the transmitter control node 1 converts the output process image according to the network protocol into a data packet and then outputs the data packet to the network at a predetermined time. The receive module 13 of the receiver control node 1 - the receive module 13 can be registered for the reception of data packets which are output by one or more transmit modules 12 from further control nodes 1 - then sets the received data packet in an input process image around,

0026With this design, it is possible, the communication relationships between the control nodes in the network flexible and also during the system runtime, ie dynamically set and thus in a simple way to achieve a decentralized control with high compatibility with respect to the equipment and devices used. Changes in the production and manufacturing process, such as production expansion or change of production can be easily by changing the communication relationships, ie redefine the send-receive module relations that specify which control node to which other control nodes must transmit data run.

0027The determination of the communication relationships of the transmitting and receiving modules is preferably carried out in the context of an initialization phase with the aid of the network configurator 2. The network configurator 2 has a detection module 21 for detecting the control nodes connected to the network. The detection module 21 is connected in the network configurator 2 with a configuration module 22, which determines the communication relationships of the transmitting and receiving modules 12, 13 of the determining control node 1, ie which control node with its receiving module at which other control node for receiving data from whose send module should register. The configuration module 22 is in turn connected to a programming module 23,

0028However, the network configurator 2 can dynamically adjust the communication relationship between the control nodes and the nodes in the control node even after the initialization phase. With this configuration can be easily responded to production expansion and production change. The network configurator 2 then makes it possible, by simple reprogramming, to make appropriate adjustments to the communication relationships between the individual control nodes or the subscribers in the control node.

0029The initialization phase of in <figref idref="f0001">Fig. 1</figref> shown decentralized control is in <figref idref="f0002">Fig. 2</figref> shown in detail. The arrows in the figure indicate the data exchange carried out. In a first step of the initialization phase, the network configurator 2 acquires the control node 1 connected to the network. For this purpose, the control nodes have an unambiguous address assigned to the respective control node, via which the control node can be addressed. The control node can obtain this address, for example when booting on the bus system via the Dynamic Configuration Protocol (DHCP) or via Automatic IP. However, the address can also be pre-stored in the control node.

0030For automatic detection of the control nodes 1 of the network configurator 2 different mechanisms use. The detection module of the network configurator 2 can send a so-called broadcast telegram to all control nodes 1 which are connected to the network 3. The control nodes 1 then respond to this broadcast telegram with a response message and thereby announce their valid address. Alternatively, there is also the possibility that each control node automatically sends an identification telegram with its address to the detection module of the network configurator 2 during startup.

0031Parallel to the address acquisition, the detection module of the network configurator 2 can also query a device description that characterizes the network properties and the function of the control node from the control node, or the control node can automatically transmit the device description to the acquisition module of the network configurator at startup.

0032On the basis of the number of detected control nodes and their device properties then sets the configuration module of the network configurator 2, the communication relationships between the control nodes on the network, ie which control node register with its receiving module at which other control node to receive data from the transmission module should. The configuration module preferably contains a plant object model that contains a standardized plant representation and process description, which are combined with the device properties of the determined control nodes in order to define the communication relationships. As an alternative to entering the device description via the control nodes, the device description can also be read in via an external database or also entered directly into the network configurator 2 via a man-machine interface. The system display and the process description can be obtained by the network configurator, for example, from an engineering system.

0033The communication relationships established by the network configurator 2 between the control nodes 1 respectively indicate the transmission module transmitting the data and the reception module receiving the data, as well as the data transmission type and the data type. The data to be transferred are divided into event data, device data and process data. Event data serve, for example, to specify or monitor the operating mode and operating state of the control nodes or to transmit device data, which is not subject to any real-time requirements, between nodes. Such event data may be the occurrence of an error, the message of the operating state, the change of a process signal, etc. Device data may be calibration data, process and product parameters, or other data. The event data and the device data are usually exchanged acyclically between the control nodes. Process data, on the other hand, is usually function data that is necessary for the process and production process. Process data necessary for the real-time application are exchanged cyclically between the control nodes in order to guarantee a defined data transmission. Data not required for real-time transmission, such as process and product parameters, ie device data is instead transferred acyclically between the control nodes.

0034The data records with the communication relationships are written by the programming module of the network configurator 2 via the bus system 3 into the control nodes 1. In addition, the network configurator 2 may transfer to the product and process parameters for performing the desired production and manufacturing process on the control nodes. Upon completion of the initialization process, the remote controller is then switched to machine operation to perform the desired production and manufacturing process. In this mode of operation the network configurator 2 is no longer needed. The network configurator 2 can then either be switched off or assume an observational function in the production and manufacturing process, for example, carry out an error monitoring and diagnosis.

0035The control nodes exchange process and event data during the production and manufacturing process in accordance with the communication relationships established by the network configurator. The Sender Mödul the transmitter control node can send data in a point-to-point connection directly to the receiving module of the receiver control node. Alternatively, however, the transmit module of the sender control node may also send the data to the receive modules of multiple receiver control nodes. Further, there is the possibility of sending the data through the transmitting module of the transmitter control node to the receiving modules of all connected to the networka control node. Non-real-time data is usually exchanged acyclically via point-to-point connections. Such non-real-time data is event data or product and process parameters. On the other hand, process data required to execute real-time applications are sent cyclically to all control nodes. For real-time data, point to multipoint connections or broadcast transmission can be performed.

0036<figref idref="f0003">Figure 3</figref> schematically shows the possible structure of a control node. Each control node has a device description representing the functional and communication characteristics of the control node in addition to the network interface 11 containing the transmission module 12 and the reception module 13. The form of this device description is preferably standardized for all control nodes and stored as a file in a memory area 14 of the control node. The device description can be retrieved from higher-level systems or also, as explained above, from the network configurator. The device description can also be changed externally, in turn, by the network configurator or a higher-level system or else via a human-machine interface,

0037The device description of the control node, which represents the hardware of the control node and its functions or the interfaces to the outside world, is assigned a machine model 15 in the control node. The machine model 15 simulates the device properties in the form of functionalities and thus decouples the device functionalities from the real hardware control. With the aid of the machine model, the plant or functionalities lying within the control nodes can be modularized in a simple and effective manner, thus establishing a decentralized control system. The machine model encapsulates the device functionality and thus provides autonomous module units which, for all device, communication and functional units, each follow a uniform, abstracted operating sequence for themselves,

0038The machine model 15 is subdivided into an organizational unit 151 and a functional unit 152. The organizational unit 151 determines the state of the control node. The state of the control node indicates the operating mode, ie whether the machine is operated manually, semi-automatically or automatically, whether the machine is in the initialization mode or in the machine operating mode. Furthermore, the operating state of the control node is defined in the organizational unit. Operating states can be eg start-up, stop or error operation. The operating states are clearly defined and executed by the organizational unit 151 of the machine model 15 in the control node 1. Furthermore, the organizational unit 151 of the machine model 15 in the control node 1 ensures that that the transitions between the operating states are clear. The organizational unit 151 thus provides a state machine which ensures that the desired state is reached by the control node without the aid of external events.

0039The functional unit 152 of the machine model 15 in the control node 1 contains the application programs assigned to the respective operating states, which are then triggered by the functional unit 152 depending on the operating state set by the organizational unit. The application programs in the functional units of the control nodes are called via individual identifiers. The organizational unit 151 contains the identifier and the function parameters of the functional unit 152 to be called up and executes the call. A functional unit provides an elementary function that can be parameterized from the outside. The overall functionality then results from the arrangement of the elementary functions.

0040The control nodes are preferably subdivided into subscribers 16A, 16B, 16C, which individually define addressable functionalities of the control node. The subdivision of the control nodes in subscribers is freely configurable and independent of the real hardware control. The participants are in turn subdivided analogously to the machine model into an organizational unit 161 for executing the state machine, which defines the operating mode and operating state, and a functional unit 162 for executing the application program assigned to the respective operating mode and the respective operating state. The participants of the control node can be made equivalent in terms of their functions or organized hierarchically. In particular, there is the possibility that the functionality of a subscriber is in turn subdivided into a plurality of sub-functionalities with a plurality of sub-subscribers, which are constructed analogously to the higher-level subscribers. The division of the control nodes into subscribers further simplifies the modularization, in particular with regard to the required definition of the communication relationships. The participants or the functional units 162 contained therein represent functionally autonomous units which can be configured and addressed independently.

0041With the subdivision of the control nodes into participants, the speed of the data communication can also be optimized. In a data transfer between the control nodes, the data transmission takes place in accordance with the network protocol, ie in particular the Ethernet protocol, the transmitting control node with its transmission module, the output process image to be sent in a network data packet, eg an Ethernet telegram, converts and then to the data packet at a given time on the network. The control nodes, which are registered with their receiving modules on this transmission module, then put the received data packet back into an input image process. In contrast, if the data communication is to be performed internally in the control nodes between the participants in the control node, the data exchange is preferably carried out transparently by data mapping operations with a direct data access of the subscribers to the control node process image transmitted between the subscribers. These direct data mapping operations of the participants in the control node ensure fast data exchange without complicated conversion processes or transfer processes via the send or receive modules.

0042The data transfer operations, ie the direct data mapping between the subscribers and the network protocol conversions between the control nodes, are preferably predefined by the network configurator in the context of the previously described initialization process. The communication relationships between the participants in the control node are divided into event, parameter and process data streams analogously to the communication relationships between the control nodes. At the same time, the type of data transmission between the participants, ie whether the data transmission is to be performed cyclically or acyclically, is determined.

0043<figref idref="f0004">FIG. 4</figref> shows possible data streams in the <figref idref="f0003">Fig. 3</figref> shown control node 1 with the machine model 15, the three participants 16, each of which encapsulate a device function, wherein the organizational unit is the interface to the event data streams and the functional unit is the interface to the process data streams. The event data streams convey information about the operating mode and are preferably exchanged acyclically. On the one hand, the process data streams contain process data that are cyclically exchanged, but also product and process parameters or other statistical data, ie device data that is transmitted acyclically. The event, parameter and process data streams between the participants in the control node can be carried out from one participant to the next participant or in parallel to several or all participants.

0044For processing the event, parameter and process data streams, the control nodes each receive an event detection module 17 and a data acquisition module 18, which, like <figref idref="f0003">Fig. 3</figref> shows, with the network interface 11, the transmitting module 12 and receiving module 13 includes connected. Events, ie notes, messages, errors in the current machine operation, etc. are classified by the event detection module 17 and cached. Further, in particular higher-level control nodes have the ability to retrieve these cached events. The events are subdivided into acknowledgeable and non-acknowledgeable events. Acknowledgments must be acknowledged by an authorized authority before they can be removed from the event capture module 17. The data acquisition module 18 stores the process data and makes it possible for further, in particular higher-level subscribers or control nodes to pick up this process data.

0045<figref idref="f0005">FIG. 5</figref> shows a section of a decentralized control with two control nodes 101, 102, the machine model in each case divided into four participants 111, 121, 122, 123 with separate functionalities. Each subscriber in turn comprises two sub-subscribers 111A, 111B, 121A, 121B, 122A, 122B, 123A 123B, which represent autonomous device functions. In<figref idref="f0005">FIG. 5</figref> the data transmission paths between the control nodes or in the control nodes between the participants or subscribers are located. The data transmission in each control node takes place in the form of data mapping operations, which can be an effective faster data exchange can be achieved. The data transmission between the control nodes is carried out in the form of network telegrams into which the process images are converted.

0046The data transmission path starts at the control node 101, namely in the subscriber 111 and here in the sub-subscriber 111A, and from there proceeds to the sub-subscriber 111B. From the sub-subscriber 111B of the subscriber 111, the data transmission path then leads to the subscribers 121A of the subscriber 121 and from there to the sub-subscribers 121B in the subscriber 121. Further data exchange then takes place via control node boundaries from the sub-subscriber 121B in the subscriber 121 of the control node 101 to the sub-subscriber 122A of the subscriber 122 and the sub-subscriber 123A of the subscriber 123 of the control node 2. This data exchange takes place in accordance with the network protocol via the transmit-receive modules of the control nodes, the transmit module converting the output process image of the sub-participant 121B into data packets and to the receive module of the control node 2 sends, which in turn converts the data packets into an input process image and transfers them to the subparticipant 122A in the subscriber 122 and to the subparticipant 123A in the subscriber 123. The data transmission in the control node 102 then takes place from the sub-participant 122A to the sub-participant 122B of the participant 122 and from there to the sub-participant 123B of the participant 123 and further to the sub-participant 123A of the participant 123. At the same time, data transmission also starts from the sub-participant 123A of the participant 123 the sub-subscriber 123B of the subscriber 123.