CONTROL NETWORKS

Control buses are specialized fast industrial digital networks with real time and deterministic features. They are particularly designed for fast control and automated applications requiring very short response delays. Typically, these applications concern motion control, multi-axes control, servo-drives control, robotics, fast counting, special machines requiring short response time in writing and reading the inputs and the outputs, or interactive devices requiring quick data exchanges in order to get an efficient synchronisation ( between a programmable controller and a robot controller for instance ).

Some of these control networks have been designed to be embedded in the system to be controlled. The control networks providing the highest performances can benefit of technologies like Fast-Ethernet, Gigabit Ethernet and Real Time Ethernet ( RTE ) by using the ISO 1588 standard or any other synchronisation technology. Some of these control buses implement the real time capabilities in the interfaces in a software manner, some other in a hardware manner, by using ASIC or FPGA components for instance.

« Controller Area Network » ( CAN ) is a digital communication network especially developed for embedded use in cars, and more generally for many embedded control usages. It is also often used for servo-drives networking systems in motion control applications such as axes control applications for example, although it does not provide any deterministic features natively. Then this technology is often mixed with more robust networking technologies in order to offer real-time, pre-emptive and / or deterministic capabilities when needed. The CANopen bus specifications can also be used as a complete or partial basis for other industrial communication networks such as DeviceNet, Ethernet open Powerlink, SafetyBus-P or SafetyNet-P for instance.

• CAN bus introduction.

  Short resume about the bus technologies and about the structure of the system, in relation with the OSI layers standard. By surfing this folder, you will also discover some informations about CAN-FD ( for « Flexible Data-rate » controller area network bus ), about the data link layer, about the physical layer, and about higher level protocols based on the CAN Open technology.

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• CAN Open introduction with an overview of the protocols it uses.

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• CAN Open specifications and technical documentation with public access for the most part, after registration.

CAN OPEN Association - www.canopen.org

• CAN Bus Interface Description.

  This page describes quickly the electronic interface, the structure of the message frames, the bus pin out and the signal names, and finally the hardware characteristics.

  www.interfacebus.com

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• Embedded Networking with CAN Open.

  First, this technical overview presents why the author think that CAN Open is the most suitable solution for embedded networking. Then you will get considerations about the object dictionary concept, how the data are processed, what are the Service Data Object ( SDO ) and the Process Data Object ( PDO ), and a short introduction to the device profiles and to the Electronic Data Sheets EDS.

  www.esacademy.com

« ControlNet » is a real time and deterministic control bus, part of the CIP network family based on the « Common Industrial Protocol » ( CIP ) and on a producer-consumer architecture. It can be installed by using several topologies ( linear, star, tree ) and it offers redundancy and safety options. Originally, CONTROLNET uses a time sliced algorithm ( Concurrent Time Domain Multiple Access - CTDMA ) to get real-time and deterministic capabilities in order to transmit time critical data.

This document begins with an interesting overview about this communication solution. It defines the use of ControlNet communication modules in a whole control system, it describes the potential capacity of the technique and lists the topologies and the architectures available for an installation. Then, it details how data are exchanged on the network, how they are synchronized and packeted, and how the network schedule is operating.

The other chapters are most software and hardware dependent, and detail how to configure network modules, how to configure control IO, how to produce and consume tags, how to operate messaging and more.

literature.rockwellautomation.com

This document of around 50 pages starts introducing the network and how it is specific.

Then it describes basic and common informations about data exchange on a ControlNet link, before presenting the producer / consumer model ( sending scheduled or unscheduled data, sending immediate data, mapping data … ).

Finally, it presents ControlNet media ( cables, connectors, repeaters and so on ) through proprietary products.

www.inf.uniroma3.it

DRIVECOM is a standardized digital communication interface designed for accessing drive data. Its actual version is called « DriveServer ». The DriveServer specifications are based on the OPC interface standard. Actually, DriveServer acts as an additional OPC layer, interfacing an application layer acting as an OPC client and a communication layer acting as an OPC server. Thus, DriveServer benefits of the advantages offered by the widespread OPC standard technologies and run in a very flexible way.

And consequently, it is hardware independent and quite universal since it works with any OPC client and any OPC server applications. For instance, it is implemented into Profibus devices and is compatible with Profidrive and Profibus DP, by interfacing the Profibus OPC servers. To work fine with any drive controller, DriveServer uses a drive description called « Drivecom Device Description » which is based on the XML ( eXtended Markup Language ) standards. This device description structures the informations related to the functionalities and to the parameters of the drive to control.

The DRIVECOM User Group promotes the DriveServer technologies and provides all the specifications in the download section, with technical guides related to the Interbus and to the Profibus interfaces, plus the specifications of the Drivecom Device Description.

• Drive server overview.
• Specifications and technical guides.
• Software download.

www.esacademy.com

The « EtherCAT » ( Ethernet for control automation technology ) networking system has been originally developed by the « Beckhoff Automation company » and has been standardized later under the « IEC 61158 » reference. This very fast digital communication technique is based on the Ethernet standards, which have been adapted to deliver a fast and deterministic control networking technology at low cost with real time capabilities. It offers a flexible architecture, can be installed using various topologies and complies with some other industrial networking protocols.

In order to implement real time and deterministic characteristics over Ethernet, the designers have chosen both hardware and software solutions based on shared reference time distributed clock technique compatible with the SERCOS protocol.

• Field devices - programmable controllers, inputs and outputs interfaces and so on - need than real-time features have to be managed through hardware.
• As the higher level devices - say at workshop level, at factory level and up, they do not need any specific hardware to dialogue with a field station or between them. They can access the network with standard Ethernet interfaces, and consequently with standard connections. Nevertheless, when highest performances are required, theses devices will benefit to be associated with Ethercat compliant hard real time devices such as Ethernet switches, hubs, routers and so on.

Main features

• Supports standard Ethernet frames ( EOE ), CANOpen frames ( COE ), file access ( FOE ), servo-drive profiles ( SOE ) and vendor specific profiles ( VOE ).

• Ethernet TCP and UDP protocols implementation.
• Master/slave and client/server architecture.
• Star topology, line topology, several daisy-chain topologies, tree topology are all possible.
• The network processing cycle duration is less than 100 µs.

• Distributed clock with shared reference time.
• None switch needed within a pure Ethercat network installation.
• XFC ( extremely fast control ) module optional.

The Ethercat consortium proposes some interesting resources.

• Introduction to the technology.
• EtherCAT detailed technical overview. ( )
• Ethercat automation protocol ( EAP ). ( )

EtherCAT consortium - www.ethercat.org

This document explains all you want to know about the 1.08 system version.

• A technical overview with a presentation of the specifications.
• How installing and connecting Ethercat ? Including the description of the Ethercat interface and wire specifications.
• What about CanOpen over Ethercat ? ( the model, the slave informations, the state machine,the PDO mapping and the emergency messages ).
• What about the synchronisation of the network based on distributed clocks ?.
• Description of the object dictionary.

www.estuneurope.eu

« MACRO » is a digital communication interface - developed by « Delta Tau Data Systems » - which has been designed to connect multi-axes motion controllers, amplifiers and I/O. It consists in an Ethernet based protocol that uses a multi-mode fiber optic ( FDDI - Fibre Distributed Data Interface ) or twisted pair copper ( CAT 5 ) which is called 100 BASE x, implemented by using a ring topology.

• About the MACRO protocol.

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• Technical notes.

  [ Archives ]

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• MACRO technical overview.

  http://machinedesign.com

MECHATROLINK is a field network positioned as a motion control bus. Only one communication line is required to connect 30 stations on a network. This can reduce costs for wiring. Since the Mechatrolink system is all digital and communicate directly with the devices, there is no need to connect any analogical signal, consequently speed or torque references are transmitted directly without using any digital-analogical converter ( DAC ).

• Generalities about Mechatrolink III control bus ( 100 Mbps, Fast Ethernet based ).
• Mechatrolink II control bus main features ( 10 Mbps ).
• Specifications of the communication.

www.mechatrolink.org/en/

« Ethernet Powerlink » is a fast, hard real time and deterministic Ethernet control bus, based both on the Ethernet standard and on the CanOpen standard, leading in a « Can Open » real time and deterministic network. This networking standard focuses on the transport layer resulting in a cycle time of typically 100 µs while the network jitter is below 1 microsecond. This system does not need any specific hardware : it is absolutely and completely independent from hardware.

This folder presents the technology and its main characteristics.

• You will learn how the system works, and how Powerlink looks like CanOpen over Ethernet.
• In the « technology in deep » section, you will get informations about the main powerlink features, such as its topology, addressing, hot plugging, multiplexing, asynchronous data, redundancy, diagnostic and more.

www.br-automation.com

This industrial networking standard is an open source solution which provides a library with all the required functions and services to implement master stations and slaves stations according to the POWERLINK protocol. The library is implemented in C language and respects all the specifications of the ANSI standard - The American National Standard Institute.

This system operates with Ethernet standard control cards with time cycle down to 400 microseconds ensuring a very good synchronization. Using co-processors, this digital communication system can even ensure time cycles down to 0.1 millisecond ( that is 100 microseconds ).

You can download the source code and the full documentation from the official web site. An Open Powerlink configuration open source software is available too.

This network is well known for its communication capabilities to do axis and fast control. Nevertheless, it can be used as a simple field bus transporting data or accessing a whole of sensors.

http://openpowerlink.sourceforge.net/

• Technical basics overview.

  This is a short overview about the Profidrive basics, standardization, communication and applications.

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• System description ( ).

  This document is a good summary about the profidrive technology and its applications.

  • At first, it presents a short overview about the Profidrive standardization, structure and safety.
  • Then, it presents the profidrive base model ( the devices classes, the profidrive and communication services ), the profidrive parameter model and the profidrive application model.
  • Next, you can learn about the Profidrive diagnostic capabilities and about additional profiles such as ProfiSafe or ProfiEnergy.
  • At last, you are learning how Profidrive is mapped to Profibus-DP and Profinet-IO, the well known standardized industrial networks.

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• Profibus and Profinet, the industrial networks adapted to motion control and drives.

www.profibus.com

« SERCOS » ( Serial real-time communication system ) defines a real time and deterministic protocol. In its first versions ( « Sercos I » and « Sercos II » ), it has been especially designed to interface drives. Nowadays ( « Sercos III » ) it is more universal and Sercos is developed to be used as a motion control bus.

The « SERCOS III » version is an Ethernet and Ethernet IP standards based network embedding the SERCOS interface, the whole implemented in a linear topology whether redundancy is not needed, or in a ring topology to benefit of redundancy features. The Sercos III interface groups more than 500 standardized parameters, quite universal to be used by all control devices.

Transmissions use a time sliced process, running cyclically in a master-slave architectures in order to transmit telegrams. Actually, one of the technologies used to manage real time communications is the basic token communication technique.

To manage efficiently the data, the protocol operates two channels through Ethernet.

• The « Real Time Channel » ( RTC ) is used to transmit the time critical data.
• The « Unified Communication Channel » ( UCC ) is used to transmit « conventional » Ethernet data ( that is not time critical ).

For safety applications, SERCOS embeds the « CIP safety » standard protocol.

• The Technologies operated in the basic versions and in the version Nr III. The official user association provides a technical overview about the technology. Here, you will find informations about the common features and how differs the last SERCOS III version, what are its specificities, particularly what are its real time characteristics, what about the protocol, the topology, the synchronisation, the redundancy and many more. Finally, it is reminded what are the based of the original versions Sercos I and Sercos II.

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• SERCOS II technical overview. ( )

  This is a detailed introduction to the protocol version II, with the presentation of the architecture, the topology, the different frames, the message structure, the standardized data and more.

Once you have been registered, you can get technical papers related to all the versions of Sercos plus the Sercos standard specifications in the « download » section.

www.sercos.org

« Synqnet » was a 100 base T industrial Fast Ethernet control interface particularly intended to OEM products. Its main characteristics were its high speed, its diagnostic and hot plugging capabilities, and its low cost. The open data layer has been implemented by Motion Engineering Inc, and 350 000 Synqnet nodes have been sold. Apparently, « Synqnet » has been discontinued since 2008, but the « Synqnet » organization still delivers a short introduction to the Synqnet technology ( ).

www.synqnet.org