CN101111807A - Control system with a plurality of spatially distributed stations and method for transmitting data in said control system - Google Patents

Abstract

The invention relates to a method for transmitting data in a control system, wherein a first station (14) generates a data frame (46) having a plurality of data fields. At least one data field to be filled with transmission data is explicitly assigned to each further station (16-20). The data frame (46) is transmitted as an output data frame (46' ) from one station to the next, wherein each station fills the respectively assigned data field with transmission data. The last station (20) returns the data frame to the group of stations as a return data frame (46'). According to an aspect of the invention, the stations (14-20) read the extraneous transmission data from data fields in the return data frame (46'), preferably the respective data fields being assigned to the stations (14-20) respectively.

Description

Control system with a plurality of spatially distributed stations and method of transferring data in said control system

technical field

The invention relates to a method for transferring data in a control system having a plurality of spatially distributed stations interconnected via a communication medium, said stations being logically arranged into a group defining a first station, at least one In the second and last station, the method comprises the steps of:

- said first station generates a data frame with a plurality of data fields, wherein each second and last station is explicitly allocated at least one data field for filling transmission data;

- said first station sends said data frame as an output data frame to a second station in said group following said first station;

- each second station receives said output data frame from its respective preceding station in said group, fills its assigned data field with transmission data, and sends an output data frame with said transmission data to said group the next stop in ; and

- the last station receives said output data frame from the previous station in said group, fills the data field assigned to it with the last transmitted data, and returns a data frame with all transmitted data to said station group.

The invention also relates to a control system for automatic control of installations or appliances, said control system comprising a plurality of spatially distributed stations interconnected via a communication medium, wherein said stations are logically arranged in a group, the group A first station, at least one second station and a last station are defined, and wherein said stations are designed to implement a method of the type described above.

Background technique

A system and method of the aforementioned type are known from DE19934514C1.

DE19934514 C1 defines a method for configuring stations connected to a fieldbus (called bus users in this document). In particular, this document relates to the fail-safe assignment of logical addresses to stations which are connected to other bus users/stations via the so-called Interbus. Interbus is a known and designated fieldbus system especially for industrial automation of plants and machines. Other known field bus systems are the so-called CAN bus and the so-called Profibus.

Known fieldbus systems are used to interconnect a plurality of spatially distributed stations/bus subscribers so that they can exchange information with one another. In this context, fieldbus systems are particularly suitable for the communication requirements for use as a communication medium in control systems for automatic controls and appliances. In addition to the simplest and most robust wiring possible, these include in particular a deterministic time response for data transmission, and also the ability to transfer smaller amounts of data from many stations. Typically, a fieldbus has one or several (intelligent) control units connected to it, and also a number of remote I/O units which obtain status signals from the device or instrument via sensors and will It reports to the control unit and/or receives control data from a superordinate control unit and operates the appropriate actuators according to it. As an example, the I/O unit can receive signals from, inter alia, position switches, visors, rotary position transducers and can send said signals via a fieldbus to a superordinated control unit. A control unit, usually a programmable logic controller (PLC), considers these process variables as the basis for determining control data for actuators, such as solenoid valves, contactors, drives, in particular. The I/O unit receives control data from a superior controller via the fieldbus, and operates the brakes.

The Interbus cited in the introduction operates in the manner of a large shift register whose individual memory locations are in the connected stations. A so-called bus master, usually physically arranged in a superordinate control unit, generates a data frame with several data fields corresponding to the number of memory locations in a "shift register". This data frame is sent from the bus master to the grouped stations, and in doing so is forwarded from one station to the next data field by data field. The last station in the group returns a data frame to the bus master so that a ring structure is finally obtained. The bus master signals all The connected stations must accept the data, which are then used in their respective shift registers for further processing. In addition, when the bus master initiates a new cycle of data, stations "empty" their shift registers filled with transmitted data by sending the data stored in their internal shift registers to the next station in the ring . A characteristic of Interbus is thus that the number of data fields in a cyclic data frame is equal to the number of memory locations in the connected stations. Additionally, communication actually occurs only between each individual station and the bus master. Since the sending station first sends its data to the bus master and the bus master forwards this data to the receiving station in the second data cycle, interconnect traffic between two stations without bus mastering capabilities may only be One transfer loops to the next. The advantage of the Interbus concept is the deterministic time response, i.e. the time required to send a piece of information can be predicted with a high degree of certainty. Also, no collisions will occur between competing messages.

In contrast, in the case of so-called message-oriented fieldbus systems such as the CAN bus, collisions are basically possible since the individual stations can generate and send data messages independently. In the case of the CAN bus, such conflicts are resolved by means of stations with different priorities, wherein the station with the higher priority maintains its authority in the event of a conflict. However, for a station with a lower priority, this means that it is at least temporarily prohibited from sending messages. In order to achieve a deterministic time response, it is necessary to limit the maximum utilization level of the fieldbus, since the probability of collisions increases with the bus utilization level. On the other hand, a control system based on the CAN bus offers a higher level of flexibility, since interconnection services are in principle possible without the interposition of a bus master. This means in particular that safety-relevant data such as emergency disconnection commands can be sent more quickly, if appropriate even as broadcast telegrams.

In addition to specifying fieldbus technology, communication networks based on the so-called Ethernet standard are becoming widely used due to the networking of the Internet and personal computers. In Ethernet, each user (each station) has an individual address called a MAC address. In principle, any station can send a message at any time. Each sending station monitors the connection line to determine whether a sent message can be read in uncorrupted form, which would not be the case if there was a conflict with a station sending synchronously. In case of a collision, each station sends its transmission again after a randomly selected period of time. Due to its widespread use, Ethernet has the advantage that the associated hardware components are very inexpensive. However, they do not have a defined timing response and are more optimized for the acyclic transmission of relatively large amounts of data by several connection stations. By contrast, control systems primarily require cyclic data transmission. However, inexpensive hardware components also mean that efforts have been made over the years to use Ethernet technology for communication between stations in control systems for controlling technical installations or technical equipment. The principle and the supplier of the corresponding components are described as examples in the German publication "Industrial Ethernet", which is available from Vogel-Industrie Medien GmbH und Co.KG in 97064 Wurzburg via ISBN 3-8259-1925-0.

However, the previously proposed method of using Ethernet components in an automatic control system is not optimal. Difficulties arise in particular from the transmission of safety-relevant control data, such as the transmission of emergency disconnection signals or the transmission of shutdown commands which are subsequently generated by the drive's control unit. For example, the data transmission with short cycle times required for drive control is also difficult to implement based on Ethernet components.

Contents of the invention

Against this background, it is an object of the present invention to provide a method of the kind mentioned in the introduction which enables data to be transmitted with high real-time requirements in a control system for an automatic control device or appliance. Another object of the present invention is to provide a control system of the kind mentioned in the introduction, in which control and process data can be sent using commercial components, in particular Ethernet components, which system is however intended to be implemented with Transmission of safety-related control and process data.

According to one aspect of the invention, this object is achieved by the method mentioned in the introduction, in which a station reads incoming transmission data from a data field in a return data frame.

According to another aspect of the invention, a control system of the kind mentioned in the introduction is proposed, wherein the stations are designed to read the incoming transmission data from the data field in the return data frame, and wherein the stations are individually assigned output Data fields in data frames to fill their own transmit data, and data fields in return data frames to read incoming transmit data.

It is particularly preferred if the station comprises at least one control unit which is designed to process process data cyclically and to generate control data based thereon, and also comprises a plurality of control units which are designed to send process data to and receive control data from the control unit an I/O unit. In principle, however, the new method can also be used in other control systems and/or communication networks.

According to another aspect, the invention proposes a communication module for a station in the aforementioned control system, wherein said communication module is designed to implement the method of the invention in the station, in other words to implement the method according to the The communication protocol of the method described above.

The invention is therefore based on a concept known in principle from Interbus, namely the generation and transmission of data frames with a plurality of data fields, which are forwarded from one station to the next in a group of stations. However, the present invention differs from the known Interbus in that the individual stations read incoming transmission data directly from return data frames, whereas in the case of Interbus typically only read data from outgoing data frames. Preferably, stations only read incoming transmission data from return data frames, and they place their own transmission data only in the data field in outgoing data frames. Deviating from this, however, a more general subdivision of the invention also includes exceptions to the stated general principles.

In actual implementation, the invention differs fundamentally from Interbus which according to the specification is in the form of a large "shift register". In contrast, the present invention is independent of the physical realization of the communication medium. In a particularly preferred subdivision to be discussed further below, the communication medium is an Ethernet-compatible transmission link and the data frame is an Ethernet-compatible data frame, ie a data frame whose basic structure is adapted to the Ethernet specification.

Whereas the known Interbus implements a ring structure for sending data, where the last station returns a data frame directly to the first station in a logical item, the present invention creates a "double wire", where outgoing data frames and returning data frames Both go through all stations in the logical item. Only in this way, individual stations can fill their own transmission data into the data field of the output data frame and read the incoming transmission data from the return data frame. Due to this feature, each station receives a cyclic data frame twice in one transmission cycle. This enables any interconnection traffic between two or more arbitrary stations to be inferred in one transmission cycle. The invention thus enables data communication that meets high real-time requirements.

The invention also enables extremely flexible communication between arbitrary stations. The invention thus has the advantage of message-oriented transmission methods, such as those of CAN bus or Ethernet connections.

The invention enables very rapid and deterministic communication by means of cyclic data frames and the inventive opportunity for direct cross communication. It is therefore well suited for sending even safety-related control data in a manner that will be described in detail below.

The aforementioned objectives are thus fully achieved.

In a preferred subdivision of the invention, said first station cyclically generates output data frames at predetermined time intervals and sends them to the next second station.

In a preferred exemplary embodiment, the cycle time is adjustable, ie the time between the transmission of two consecutive but mutually independent data frames. In a preferred exemplary embodiment, the cycle time can be adjusted between about 60 μs and about 6 ms in each intermediate step.

This subdivision is particularly suitable for control systems for automatically controlling technical installations or appliances, since information is usually generated cyclically in these control systems. In particular with a short cycle time of eg 62.5 μs, this subdivision enables the process and control data required to adjust the drives in the machine to be sent with the new method. In other words, the control system in this subdivision can be integrated into the control loop of the drive control of the machine, which in particular enables inexpensive and flexible automation of devices or appliances.

In another subdivision, said data frame contains at least a first and a second set of data fields, wherein data fields in said first set are fixedly assigned to respective stations for all data frames, and wherein said second set The data fields in are assigned to stations based on individual requests for the respective data frames.

This subdivision increases the flexibility of communication and allows the control system to be optimized in terms of data throughput and transmission speed. The first set of data fields may be used to send data without adding address information to them. This is because the fixed association of the individual data fields fixedly dictates the address structure. On the other hand, the second set of data fields enables additional transmission capacity to be reserved for individual stations on request. Said second set of data fields is particularly advantageous for sending acyclic data such as diagnostic data. In addition, the data fields in said second group can also be used very advantageously for sending data on a communication medium available outside the system, eg printer data sent from a PC to a printer connected to a communication network. In a particularly preferred embodiment, the data fields in said second group are assigned with flags which are reset to the state "data field empty" on each new data frame. Stations that want to fill data fields in the second set need thus only check the flag and set it to "occupied" if appropriate. Acyclic communication is preferably handled using a known addressing method, wherein an address is also sent in the data field of said second set.

In another subdivision, the return data frames pass through the station groups in the reverse order of the outgoing data frames.

Optionally, return data frames can in principle also be routed in a different order. Furthermore, it is also possible in principle to send return data frames simultaneously to several or all connected stations, which is quite possible in the case of eg a wireless link as transmission medium. On the contrary, this subdivision has the advantage that management complexity is simplified to ensure error-free communication. In particular, the first station in the preferred subdivision can very easily monitor whether return data frames have reached all connected stations. This is particularly important for the transmission of safety-relevant data such as emergency disconnection control commands.

In another subdivision, the first station monitors whether return data frames arrive within a pre-sequence period.

Monitoring of return data frames in the first station is particularly advantageous for the transmission of safety-relevant data, since this allows failures of the communication link to be quickly detected. Based on real-time requirements, the first station can thus either initiate a repeat frame or start an error handling routine.

In a particularly preferred subdivision, the communication medium is an Ethernet-compatible transmission link and the data frames are Ethernet-compatible data frames.

This subdivision is at least to some extent commercially available and therefore very cheap hardware components can be used. In addition, this subdivision makes it very easy to use data transmission links which are intended for control tasks also for other purposes, for example for transmitting TCP/IP-compatible data packets. Considerable cost savings can thus be achieved when networking components in a workshop or the like. A feature of this subdivision is, inter alia, that each station has its own MAC address, which in principle allows random communication between the various stations. In connection with the invention, however, each station sends at least an output data frame (and preferably also a return data frame) to exactly one precisely defined other station.

In another subdivision, each station sends outgoing data frames to the next station in the group using a so-called cut-through method.

The cut-through method is specific to Ethernet-compatible transmission links and involves the stations actually analyzing and forwarding incoming data frames before they have been fully received by the respective stations. This subdivision reduces the delay time between receipt and forwarding of outgoing data frames. This allows the cycle time of the system to be minimized very easily.

In another subdivision, each station sends output data frames to exactly one next station.

Deviating from this, branches can also be generated in principle, in particular when Ethernet components are used. However, the preferred subdivision prevents the formation of loops. In addition, collisions on the transmission link are excluded, which allows deterministic time responses to be generated with very short cycle times.

In another subdivision, the first station generates a plurality of data frames and sends them as output data frames to the immediately next next second station.

In this subdivision, which is itself an inventive development of known methods for transmitting data in control systems, the first station generates and transmits a plurality of data frames in one transmission cycle. In other words, the first outgoing data frame and the immediately following further data frames (subsequent frames) are transmitted within the cycle time. This subdivision is particularly advantageous if the amount of data to be sent cyclically is very large and secondly the length of an individual data frame cannot exceed a certain maximum value. This subdivision is thus particularly advantageous when a large amount of cyclic data has to be transmitted but the data frames used cannot exceed the length defined in the Ethernet specification of approximately 1500 bytes.

In another subdivision, each data field in a data frame is optionally filled by at least two stations to transmit data.

This subdivision, which is even itself an inventive development of known methods for sending data in control systems, enables a multiplexing mode in which individual data fields are filled by different stations from one cycle to the next. In this case, however, the individual data fields are also unambiguously assigned to the stations concerned. Said multiplexing mode is particularly advantageous when cyclic data with different repetition rates are present in the control system. In this case, slower stations can share the individual data fields in a multiplexed mode, so that the total available transmission capacity is utilized to an optimum degree.

In a further subdivision, the respective station fills at least one data field in the data frame with fieldbus telegram-compatible transmission data. It is particularly preferred if the transmission data are compatible with CAN-bus, Profibus and/or Devicenet-based telegrams.

In this subdivision, the fieldbus telegrams are sent "tunneled" using the new method. This subdivision enables existing fieldbus networks and their components to be integrated very easily. The tunneling of safety-relevant process and control data in this way is particularly preferred, since in this case tried-and-tested and certified or approved components can be used for safety-oriented automation.

In a further subdivision, the stations are individually allocated data fields in outgoing data frames for filling with their own transmission data and data fields in return data frames for reading incoming transmission data.

This subdivision enables a very flexible and fast information transfer between arbitrary stations over the communication medium. In particular, this subdivision makes it very easy for a station to receive information or data from multiple other stations in one transmission cycle. For this reason, the station only needs to individually fetch specific data from the returned data frame.

In another subdivision, even itself an inventive development of the known method for sending data in a control system, the station reads the incoming transmission from the return data frame (or from each different return data frame) data, and rearrange them to form a data word for a given station. Thus, each station contains a communication module of the above-mentioned type with a data sorter designed to rearrange incoming transmitted data from return data frames to form a data word for a given station.

As an alternative, it is also possible, for example, to actually compile the external transmission data with respect to the sender or with respect to the transmission in a manner suitable for the receiver. In contrast, the preferred subdivision has a higher level of flexibility, since each receiving station can compile the incoming transmission data associated with it on an individual basis so that subsequent data processing in this receiving station can be carried out in an optimal manner. In particular, transmission data may be compiled multiple times in different ways in different combinations of designated stations. A particular preference in this context is whether or not the data classification of a given receiver takes place in the communication module, i.e. at a very low level of the OSI reference model, since higher applications on the receiving station can very quickly and conveniently handle reordering. arrayed data. This enables a wide range of interoperability. In addition, this subdivision is particularly advantageous in conjunction with the use of subsequent frames and/or the use of the multiplexing mode described above, since the compilation of transmitted data based on multiple return data frames is greatly simplified.

In another subdivision, said first station generates each output data frame with a plurality of status fields, wherein each second station is assigned at least one status field, and wherein each second station outputs data each time A frame changes its status field as it passes.

This status field can be used to implement lifetime monitoring very easily. The fact that each station changes its status field based on the passage means that the first station can check whether the second station that was originally present is still present and active at the end of each cycle. This subdivision is particularly advantageous when the new method is intended to be used for sending safety-relevant process and control data, since a failure of a safety-relevant station is a safety-critical state and suitable error messages or The error handling routine needs to be started.

It goes without saying that the features which have been described above and which will be described below can be used not only in the respectively indicated combination but also in other combinations or on their own without departing from the scope of the present invention.

Description of drawings

Exemplary embodiments of the invention are shown in the drawings and described in detail in the following description. in:

Figure 1 schematically illustrates an exemplary embodiment of the novel control system;

Figure 2 schematically illustrates another exemplary embodiment of the novel control system;

Figure 3 shows a schematic diagram for illustrating the novel method;

Figure 4 shows a timing diagram illustrating various modes of operation of various exemplary embodiments of the novel control system or the novel method;

Figure 5 shows a plurality of Ethernet telegrams being sent in succession in an exemplary embodiment of the novel method;

Figure 6 shows a plurality of Ethernet telegrams being sent successively in another exemplary embodiment of the novel method;

Figure 7 schematically illustrates a station from the novel control system; and

Figure 8 schematically illustrates a preferred exemplary embodiment in which data is rearranged as it is read from the return data frame.

Detailed ways

An exemplary embodiment of the novel control system is generally designated 10 in FIG. 1 .

The control system 10 includes a control unit 12 in the form of, for example, a programmable logic controller referred to herein as a PLC. Optionally, it can also be a different control unit, such as an Industrial PC. At the application level, the control unit 12 takes over the control of technical installations (not shown in detail here), for example production or delivery installations. In this regard, it processes process or status data from the device captured with sensors and generates control data that is used to operate the brakes. To communicate with the sensors and actuators, the control unit 12 uses a communication network implementing an exemplary embodiment of the novel method in the manner described below.

For communication with local sensors and actuators, the control unit 12 in this case has a so-called bus manager 14 , which is the first station in the context of the present invention. In other exemplary embodiments of the present invention, the bus manager may be realized separately from the control unit 12 . The control unit 12 can in this case contain a communication module which, in the context of the invention, connects it to the communication network as a second station.

The control system 10 also includes a plurality of stations 16, 18, 20, 22, 24, wherein stations 16-22 are the second station for the purposes of the present invention, and station 24 in this exemplary embodiment is the last station for the purposes of the present invention one stop. In the illustrated embodiment, stations 1624 are each I/O units designed to obtain input signals from sensors and output control signals to actuators.

The bus manager 14 (and thus the control unit 12 ) is connected to the stations 16 to 24 by means of a communication medium 26 . In this case, the communication medium 26 includes a switch 28 shown here as an example of one possible implementation. In particular, the bus manager 14 is connected in this case to one connection of the switch 28 by means of an Ethernet cable. The second connection of the switch 28 is connected to the first connection of the station 16 by means of another Ethernet cable. The second connection of station 16 is connected to the first connection of station 18 by means of another Ethernet cable. Finally, station 18 is connected to station 20 by means of a second connection and another Ethernet cable. The bus manager 14, the switch 28 and the stations 16-20 are thus physically arranged in a group, where each station is connected to its neighbor in the group by means of a point-to-point connection.

In this exemplary embodiment, switch 28 is also connected to station 22 by means of a third connection and a further Ethernet cable, and to station 24 by means of a fourth connection and a further Ethernet cable. The communication network in the control system 10 in this exemplary embodiment thus has a hybrid form including a serial topology and a star topology. Logically, however, all stations 16-24 and bus manager 14 are arranged into a group as described in more detail below.

In this simplified exemplary embodiment, station 16 has a protective door 30 attached thereto. This involves sensors that can be used to monitor the open and closed state of the protective door. Similarly, station 18 has an emergency disconnect switch 32 connected thereto, and station 22 has a light barrier 34 connected thereto. The above three sensors 30, 32, 34 are typical examples of sensors used to protect the automatic running device. It goes without saying that the invention is not limited to the use of such safety sensors, ie the stations 16 - 20 could also have sensors connected thereto for standard control tasks.

In this case, the stations 22 and 24 have, by way of example, solenoid valves 36 , 38 and drives 40 connected thereto. These are typical brakes used in automatic controls, although the invention is not limited to these brakes.

In this exemplary embodiment, the connections between the individual stations and the bus manager and the switch are realized by means of CAT5 Ethernet cables. Accordingly, the respective connections 42 of the station, bus manager and switch are in the form of RJ45 connections 42 . However, in other exemplary embodiments of the invention, other lines such as glass fiber optic cables or wireless links (eg WLAN) may also be used.

According to the novel method, the bus manager 14 generates at regular time intervals bus telegrams 44 which contain data frames 46 with a plurality of data fields (not shown separately in this case). In the exemplary embodiment of FIG. 1 , the bus telegram 44 is an Ethernet compatible telegram with an Ethernet header at the beginning and a checksum at the end. The data field provided by the Ethernet telegram is the data frame 46 .

The bus manager 14 sends a bus telegram 44 to the following station 16 in the logical group. In this case it addresses the station 16 using its MAC address in a manner known from Ethernet. Station 16 receives this bus telegram 44, fills the data fields assigned to it with transmission data in the manner described below, and sends a data frame 46 with a new Ethernet-compatible bus telegram (not shown here) to the next Station 18. In this context, station 16 also addresses station 18 using its MAC address. In the same manner, station 18 sends a data frame to station 20. Next, station 20 sends the data frame to station 22. From there, the data frame is forwarded to station 24 and then data frame 46 passes through stations 22 to 16 in reverse order and finally reaches bus master 14 . In this context, data frames 46 are forwarded from one station to the next using the respective MAC addresses of the destination stations. The switch 28 is transparent, ie although it physically appears to route the data frame 46 only from the respective sending station to the addressed receiving station without requiring the data frame 46 to be changed in the process.

Figure 2 shows the forwarding of a data frame 46 from one station to the next and vice versa in a simplified embodiment in which the physical topology of the communication network also corresponds to said logical grouping. In this case, the same reference numerals designate the same elements as before.

The data frame 46 is first sent to the station 16 by the bus manager 14, which addresses the station 16 using its MAC address. Station 16 fills its assigned data field in data frame 46 with transmission data and sends data frame 46' to station 18 containing the new transmission data. Station 18 places its transmission data in its assigned data field and sends a data frame 46" containing the transmission data from stations 16 and 18 to station 20. Station 20 fills its assigned data with its transmission data field, and returns a data frame 46''' containing all transmitted data to the station 18. On the return path, the data frame 46'' passes through all the stations until it reaches the bus manager 14. Each station comprising the bus manager can thus Reads incoming transmissions from other stations if it is properly configured.

Assignment of which data fields each station 16 to 22 is allowed to fill with its own transmission data, and which data fields containing incoming transmission data the stations 16 to 20 and the bus manager 14 are allowed to read, before the control mode is started It is set individually in configuration mode, which is schematically indicated by the box arrow 48 .

FIG. 3 shows the circulation of data frames 46 and the filling and reading of the individual data fields in the diagram. The data frame 46 is shown in this case as a ring segment with eight data fields 50 of different sizes. Each of these eight stations has in this case been assigned a data field 50 dedicated to filling for transmission of data. As an example, station 18 fills data field 2 with transmission data, station 20 fills data field 3, and station 22 fills data field 4. FIG. The data field 50 is filled to transmit data when the station has received the data frame 46 from a previous station, and before or when the station forwards the data frame 46 to the next station, respectively. The described reception and forwarding of the data frame 46 is shown by arrow 52 .

When the data frame 46 filled with all transmitted data is returned from the last station 24 in the opposite direction (arrow 54), each station can read the incoming transmitted data from the other data fields. As an example, FIG. 3 shows station 18 reading transmission data from data field 1 , ie transmission data from station 16 . In this case, station 20 reads transmission data from data fields 2 and 5 and station 22 reads transmission data from data field 7 . When a data frame 46 has been sent once from the bus manager 14 to the last station 24 and back again, all relevant stations have the opportunity to send their own transmission data and to read incoming transmission data.

FIG. 4 illustrates timing for sending data frames 46 in various exemplary embodiments of the invention. Reference numeral 60 shows the length of the data frame 46 (more precisely the length of the bus telegram 44 containing the data frame 46). Reference numeral 62 denotes the cycle time, ie the time between the generation of two successive but mutually independent data frames 46 .

FIG. 4A shows a timing diagram in which exactly one data frame 46 is generated and transmitted in each cycle time 62 . In the preferred exemplary embodiment of the invention, the data frame 46 must be returned to the bus manager 14 within the cycle time 62 so that the bus manager 14 can send a repeat frame in the next cycle time 62 if appropriate. This preferred embodiment has the advantage that the links between the individual stations always carry only one bus telegram 44, which avoids the typical collisions of Ethernet. Alternatively, however, the second data frame 46 b can basically be transmitted even before the first data frame 46 a reaches the bus manager 14 again.

FIG. 4B shows an exemplary embodiment in which in each cycle time 62 the bus manager 14 generates and transmits two directly consecutive data frames 46 , 64 . The respective second data frame 64 is designated as a subsequent frame, which is sent with a separate bus telegram. Logically, however, the two data frames 46, 64 belong to one whole, i.e. split into two separate frames 46, 64. In this case only to observe the telegram width of the Ethernet specification, even if the data word provided in the Ethernet telegram This amount (typically 1500 bytes) is not sufficient to provide the required data fields for all connected stations.

Figure 4C shows an exemplary embodiment in which the various data fields 50 are used in a multiplexed mode. In a first transmission cycle, the data field 50a is filled, for example, by the station 18 to transmit data. In the next transmission cycle, the same data field (now denoted 50b) is filled by station 20 to transmit data. In a third transmission cycle, station 18 again fills data field 50a and so on. Meanwhile, other data fields in the data frame 46 may be assigned to other stations individually. As already mentioned, a multiplexing mode can be used to enable individual stations to have transmission cycles with shorter continuous times than other stations.

Figure 4D illustrates an exemplary embodiment utilizing both the subsequent frame shown in 4B and the multiplexing pattern shown in 4C. Preferably, the data field in the multiplex mode is only sent in subsequent frames 64 in this case.

FIG. 5 shows an exemplary embodiment of the novel method in which the individual Ethernet bus telegrams 44 a , 44 b and 44 e are sent using the communication medium 26 . Each Ethernet bus telegram has an Ethernet header 70 and a checksum 72 as known. The Ethernet header 70 contains in particular the sender's and receiver's MAC addresses specific to the Ethernet-compatible communication medium. The data field of the Ethernet telegram includes data fields 50 which are respectively assigned to the individual stations. The data field 50 is not shown separately in FIG. 5 but is denoted by the term "cyclic", since the respectively assigned data field is preferably used for the cyclic transmission of data in every nth bus telegram, where n=1, 2 , 3... Furthermore, the bus telegram 44 in this case contains an acyclic data area 74 in its data area. Each station can fill the acyclic data area with transmission data when requested. If the acyclic data area 74 has been filled by stations to transmit data, this is signaled by means of an occupancy flag (not shown), which can be provided, for example, at the beginning of the acyclic area. A station wishing to send data in the acyclic data area 74 can thus only do so if the acyclic data area 74 has not been filled by a previous station. This can be easily identified from occupancy markings (not shown).

In a particularly preferred embodiment, two such Ethernet bus telegrams 44a, 44c can have a further Ethernet bus telegram 44b transmitted between them, which observes, for example, a protocol structure based on TCP/IP . In this way, in addition to control data for controlling the system 10, other data can also be transmitted. As an example, a PC connected to the communication medium 26 can thus send printer data to a printer also connected to the communication medium, these data being able to be completely independent of the control data.

FIG. 6 shows another exemplary embodiment for how control data and other data are sent together via the communication medium 26 . In contrast to the exemplary embodiment shown in FIG. 5 , TCP/IP-compatible data are transmitted in this case in the acyclic data area 74 of each bus telegram 44 a , 44 b , 44 c. This option is particularly preferred if the cycle time of the system does not allow the separate transmission of conventional Ethernet telegrams or only allows it with an increased risk of collisions. In a preferred embodiment of the invention, however, the data fields 50 for the cyclic transmission of control data are always reserved for the individual stations to which the data fields 50 are respectively assigned.

According to a further exemplary embodiment, the bus telegram 44 shown in FIGS. 5 and 6 also contains a further data area 76 which is used for sending telegram data compatible with conventional fieldbus telegrams. In a particularly preferred embodiment, the data area 76 is used to send transport data based on a specification called SafetyBUS p. This is a specific bus system based on the CAN bus (compatible with CAN), where additional protocol layers allow safety-related control data to be sent. In a particularly preferred embodiment, the data field 50 is used for sending control data for standard control tasks and the data field 74 is used for sending safety-related control data compatible with Safety BUS p, e.g. from safety sensors 30, 32 , 34 status information and stop commands for the brakes 36 to 40, as well as the data area 74 is used to transmit diagnostic data that the individual stations send separately only in relation to individual requests.

FIG. 7 is a simplified block diagram illustrating the structural design of various stations, such as station 16 . Reference numeral 80 denotes a microcontroller representing the application layer of the station 16 . This microcontroller implements the functions of the stations 16 in the control system 10 , namely in this case the functions of the I/O units. Instead of a microcontroller, it is also possible to use another component of the application-specific task, eg a PC or an application-specific IC (ASIC).

The application 80 communicates with a communication module 82 designed to implement a communication protocol based on the method of the invention. In the preferred embodiment, where the communication medium 26 is an Ethernet compatible transmission link, the communication module 82 is connected to the respective protocol block 88, 90 by means of two connections 84, 86. The protocol blocks 88, 90 are routed to the RJ45 connection 42 and generate an Ethernet compatible bus telegram 44 into which the data frame 46 according to the invention is embedded. The data frame 46 and data fields 74 , 76 (if used) are generated by the communication module 82 . In addition, each station 16 contains a memory 92 in particular storing configuration data which is used to assign to each station a data field 50 for writing or reading its own or foreign transmission data. Oscillator 94 generates a reference clock.

In the exemplary embodiment shown in FIG. 7 , the communication module 82 is in the form of an ASIC, which is particularly preferred for shorter cycle times, eg 62.5 μs or 125 μs. Optionally, the communication module 82 may also be in the form of a software block, which is executed on a suitable hardware platform. The latter is particularly preferred for longer cycle times, eg 1 ms or 5 ms.

FIG. 8 is a schematic diagram of a preferred embodiment in which transmitted data from two successive return data frames 46 , 64 are rearranged or recompiled as they are read so that they can be processed in a manner that is optimal for the application 100 . The read transmission data is compiled in the data sorter 102 to form new data words or data frames 104 which are accessed by the application 100 . For this purpose, the data classifier uses a classification table 106 which is assigned to the data classifier by the bus manager 14 when the system is initialized. As shown by the respective different patterns, the data sorter 102 can read each transmitted data from the successive return data frames 46, 64 and can compile it into a new data word 104 which implements the particularly advantageous operation. In addition, the data classifier 102 can also correctly associate data fields that are optionally populated in multiplexed mode in each case. For this it uses a frame counter (FC) and a cycle counter (not shown here). The former counts or identifies successive subsequent frames within a transmission cycle, while the latter distinguishes data frames from different transmission cycles.

The preferred embodiments of the present invention have been described with reference to an Ethernet compatible communication medium. This is particularly preferred since Ethernet is a widely used communication platform and the required hardware and software components are thus commercially available at low cost. However, as the above optional option, the present invention can also be implemented based on other communication media in principle.

Claims (18)

1. A method for communicating data in a control system (10) comprising a plurality of spatially distributed stations (14-24) interconnected via a communication medium (26), said stations (14-24) being logically Arranged in a group, said group defining a first station (14), at least one second station (16-22) and a last station (24), said method comprising the steps of: - said first station (14) generates a data frame (46) having a plurality of data fields (50) for each second station (16-22; 16-18) and said last station (24; 20) explicitly allocating at least one data field (50) for padding to transmit data, - said first station (14) sends said data frame (46) as an output data frame (46', 46") to a second station following said first station (14) in said group (16), - each second station (16-22; 16-18) receives said output data frame (46', 46") from the respective preceding station in said group, fills the data field assigned to it with transmission data ( 50), and sending an output data frame (46', 46") with said transmission data to the next station in said group, and - said last station (24; 20) receives said outgoing data frame (46") from the previous station in said group, fills its assigned data field (50) with the last transmitted data, and will have The data frames of all transmitted data are returned to the station group as a return data frame (46), It is characterized in that the station (14-24) reads the incoming transmission data from the data field (50) of the return data frame (46''). 2. The method according to claim 1, characterized in that said first station (14) cyclically generates said output data frame (46) at predetermined time intervals (62) and sends it to the next first station (14) Two stops (16). 3. The method according to claim 1 or 2, characterized in that said data frame (46) comprises at least a first and a second data field set (50, 74), wherein for all said data frames (46) The data fields (50) in said first set are fixedly allocated to the respective stations (14-24), and wherein the data fields (74) in said second set are defined with respect to individual requests for respective data frames (46) are assigned to the stations (14-24). 4. The method according to one of claims 1 to 3, characterized in that the return data frame (46') passes through the group of stations in the reverse order to the outgoing data frame (46', 46") (14-24). 5. The method according to one of claims 1 to 4, characterized in that the first station (14) monitors whether the return data frame (46'') arrives within a defined period. 6. The method according to one of claims 1 to 5, characterized in that the communication medium (26) is an Ethernet-compatible transmission link, and the data frame (46) is Ethernet-compatible Data Frame. 7. The method according to one of the claims 1 to 6, characterized in that at least each second station (16-22) sends the outgoing data frame (46) to the next station in the group using a cut-through method one stop. 8. The method according to one of claims 1 to 7, characterized in that each station (14-24) sends the output data frame (46) to exactly one next station. 9. The method according to one of claims 1 to 8, characterized in that the first station (14) generates a plurality of data frames (46, 64) and sends them as output data frames to directly successive Next second stop (16). 10. Method according to one of claims 1 to 9, characterized in that each data field (50a, 50b) is optionally filled by at least two stations for the transmission of data. 11. The method as claimed in one of claims 1 to 10, characterized in that the respective station (14-24) fills at least one data field (76) in the data frame with transmission data compatible with fieldbus telegrams. 12. The method according to one of claims 1 to 11, characterized in that the stations (14-24) are allocated (48) respectively for the data fields in the output data frames (46', 46") are filled with their own transmission data, and the data field in the return data frame (46'') is used to read external transmission data. 13. The method according to one of claims 1 to 12, characterized in that the station (14-24) reads the incoming transmission data from the return data frame (46'') and rearranges them to form Data word for the specified station. 14. The method according to one of claims 1 to 13, characterized in that the first station (14) generates each output data frame (46) with a plurality of status fields, wherein for each second A station (16-22) is assigned at least one status field, and wherein each second station (16-22) changes its status field as said outgoing data frame (46) passes. 15. A control system for an automatic control device or apparatus comprising a plurality of spatially distributed stations (14-24) interconnected via a communication medium (26), wherein said stations (14-24) are logically arranged in a group defining a first station (14), at least one second station (16-22) and a last station (24), Wherein said first station (14) is designed to generate a data frame (46) having a plurality of data fields (50), wherein for each second station (16-22; 16-18) and said last A station (24; 20) explicitly allocates at least one data field (50) for padding to transmit data, Wherein said first station (14) is further designed to send said data frame (46) to said group following said first station (14) as output data frame (46', 46") After the second stop (16), Therein, each second station (16-22; 16-18) is designed to receive said output data frame (46', 46") from the respective preceding station in said group, fill the frame allocated to it with transmission data data field (50), and sending an output data frame (46', 46") with said transmission data to the next station in said group, and wherein said last station (24; 20) is designed to receive said output data frame (46', 46") from the previous station in said group, filling the data field assigned to it with the last transmitted data , and returning a data frame with all of said transmitted data to said station group as a return data frame (46'), It is characterized in that said station (14-24) is designed to read the incoming transmission data from the data field (50) in said return data frame (46'). 16. Control system according to claim 15, characterized in that the station comprises at least one control unit (12) designed to cyclically process process data and generate control data based thereon, and further comprises Data is sent to the control unit (12) and a plurality of I/O units (14-24) receive control data from the control unit (12). 17. A communication module (82) for a station in a control system according to claim 15 or 16, wherein the communication module (82) is designed to receive output data frames (46', 46") And fill it with the transmission data, and read the transmission data from the return data frame (46'') and forward the return data frame (46''). 18. A communication module (82) for a station in a control system according to claim 15 or 16, wherein the communication module (82) is designed to generate output data frames (46', 46") and send it to the next station (16).

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