Martin Rostan speaks to SA Instrumentation and Control about the origin and advantages of EtherCAT fieldbus.
Executive director of the EtherCAT Technology Group, Martin Rostan, was recently in the country to present a series of breakfast seminars in conjunction with Technews Publishing and event co-sponsors SA Power and Beckhoff Automation. Hosted at select venues in Johannesburg, Cape Town, Port Elizabeth and Durban, Rostan – a world-renowned expert in fieldbus and Ethernet technologies – presented the origins and advantages of EtherCAT fieldbus to over 350 industry delegates.
The origins of EtherCAT
With the advent of the personal computer in the mid 1980s, visionary automation entrepreneur, Hans Beckhoff, immediately recognised the possibilities it offered to process and machine control applications. Thanks to the powerful processing technology, PC-based controllers could be made fast and feature rich, much more so than any of the traditional hardware controllers that existed at the time. However, there was a practicality: ‘How could one efficiently bring this processing power down to the level of the sensors and actuators at the plant one wanted to control?’
“Plug-in cards offered a solution,” explains Rostan during a discussion at the Suncoast Casino after the Durban event, “but the maximum number of I/O is then limited by the number of available slots.” What was needed was an appropriately fast serial fieldbus. Prompted by this, the Beckhoff team set about developing the Lightbus protocol that today forms the basis of the real-time Ethernet fieldbus: EtherCAT.
“The power of Lightbus came from its principle of telegram processing on the fly,” outlines Rostan. “But even though this was fast at the time, it is not fast enough to exploit the full power of today’s PC processors.”
So the ‘Fast Lightbus’ project was the next step and this took the fibre optic based technology from 2,5 Mbit/s to 50 Mbit/s. According to Rostan, this was still not fast enough: superfast control, after all, requires a super-fast bus technology. “The breakthrough came when we realised that we could get the performance we wanted by combining the Lightbus protocol with the Ethernet physical layer,” he says reflectively.
Today, on 100 Mbit/s Fast Ethernet, EtherCAT can communicate, for example, with 100 servo axes every 100 μs. This means that Beckhoff has essentially ‘future proofed’ the technology, since currently not even the fastest microprocessors can compute the control algorithms for all 100 axes in that time.
The power of processing on the fly
“Three primary factors limit the performance of standard Ethernet in real-time communication applications,” says Rostan. “Bandwidth utilisation, stack delays and switch delays.”
EtherCAT gets around these problems, as, instead of sending one frame to each node and then receiving a response back from every node in every cycle, it sends just one frame through all the nodes. Each node then extracts its data from that frame on the fly, and can insert data into the same frame as well.
EtherCAT is full duplex, and since all of the nodes share one frame, there is only one overhead (per cycle) and the need for stacks and switches in the network is entirely eliminated. The protocol is also topology independent versus the star only limitation of traditional Ethernet.
“Think of a train travelling through a series of stations where each individual carriage can be loaded and offloaded, but without the train itself ever needing to stop,” explains Rostan. “When the train (EtherCAT message), arrives at its destination (EtherCAT master), it can then be ascertained what was loaded at each station (EtherCAT slave). Processing on the fly is what gives EtherCAT its unique capabilities.”
Time synchronisation is also remarkably simple using the distributed clock protocol. The EtherCAT master controller selects one clock (which could reside on an EtherCAT slave) to be the master network clock. All other clocks on the network then adjust for any offset between themselves and the master. The resulting synchronisation allows real-time network determinism (with less than 100 ns! jitter) right down to the I/O level on any network that supports the distributed clock protocol.
EtherCAT is for slower applications too
Typically, EtherCAT, because of its fast bus speed, is associated with precision applications like multi-axis control in CNC machining and robotic applications.
“Many people think that because of EtherCAT’s superior performance, it must be more expensive to use in situations where bus speed is not a critical factor,” says Rostan. “But in fact this is not true as cost savings can be achieved in many areas right through from design to network operation.”
At the device hardware level, no dedicated plug-in card is required on the master as any standard Ethernet port will do just fine. On the slave devices, a chip with EtherCAT slave controller functionality is required, but according to Rostan, these are now lowcost and freely available from many different chip suppliers. Beckhohoff does not control the supply of chips in any way, but does act as a watchdog to ensure that all chip suppliers conform to the required specifications and standards.
From the network point of view, no switches or hubs are required and standard Ethernet cabling and connectors are all that is needed in most cases. Network setup and configuration are quick and easy, since addresses are distributed automatically.
From an operating perspective, PLCs significantly reduce their reaction times due to the efficient bus cycle management, which accelerates any application with sequential control tasks. Therefore, even ‘slow’ applications benefit from the network performance.
Furthermore, what should be considered is the built-in redundancy capability of EtherCAT’s self-terminating properties in ring topologies. Any node that does not detect a next node in the ring automatically terminates the network at that point and terminating nodes then copy messages from the master’s transmit to the master’s receive path. “If a node fails or a cable fault occurs, the nodes immediately before and after simply act as terminators,” explains Rostan. “This means the network will split into two self contained loops and everything else continues as normal.”
Where is the technology headed?
“We have recently introduced EtherCAT P,” says Rostan. “This is a significant milestone as it greatly reduces cabling complexity for machine builders and end users. Wiring an EtherCAT network has always been simpler than standard Ethernet because the user is not restricted to a star topology, or a line topology limited due to cascaded switches. Now, with EtherCAT P, there is no need to run separate power cables either.”
EtherCAT P is something equivalent to PoE (Power over Ethernet) in the standard technology. It combines communication and power supply (2 x 24 VDC/3 A) in a standard 4-wire Ethernet cable, which enables direct power for both EtherCAT slaves and any connected sensors and actuators, eliminating the need for separate power cables.
“The power supplies are daisy chained through the EtherCAT devices,” explains Rostan. “Installation costs are therefore saved through reduced wiring time, to which can be added the extra savings achieved by eliminating unnecessary cables and connectors.” Beckhoff has developed a special coded M8 connector for EtherCAT P to avoid confusion with standard EtherCAT cables, making the technology even easier to use.
Industry 4.0 in sight
At its most basic, Industry 4.0 is the term for gathering masses of raw data from the machines on the factory floor and then transmitting these to the giant server farms in the cloud for processing by the applications that reside there. Next, the actionable information that results must be communicated back to the company’s IT network for executives to use as a decision-making aid in the quest for ultimate efficiency. Secure open systems are an obvious prerequisite.
“With EtherCAT, we have very strong experience in communication at the process control level,” says Rostan, “but even though we could, we decided not to develop our own cloud technology. It made much more sense for us to collaborate with the OPC Foundation, which already has an open standards-based system platform at that level. With our experience in process automation, coupled with theirs in cloud technology, we feel confident that we can create the required scalable data bridges between the machines running on the factory floor and the IT networks connecting people in the head offices.”
According to Rostan, the agreement reached in mid-2015 is a win-win for both parties. The ETG would like to reach the cloud through the OPC Foundation’s existing technology, and vice versa, the OPC Foundation would like to reach the shop floor through the ETG’s existing platforms. “It was a good move,” he says.
The function and makeup of the EtherCAT Technology Group (ETG)
With over 3900 members from 63 countries, the EtherCAT Technology Group has become the world’s largest fieldbus organisation since it was founded in 2003. Beckhoff, as the inventor of the EtherCAT technology, is a core member and Rostan is both executive director of the ETG, as well as head of technology marketing at Beckhoff.
“The core function of the ETG is to promote the technology through the development of the open EtherCAT standard, and to oversee conformance through interoperability testing and certification,” he explains.
The ETG manages the future direction of the technology through its various working groups and technical committees. “About two-thirds of our ETG members are automation vendors,” says Rostan.
“So we have a situation where the technology is advancing not just through the ideas of Beckhoff, but by incorporating the thinking of many of our leading competitors as well. This is good because it keeps us on our toes and forces us to be at the forefront of all new developments. By opening up the technology to everyone, Beckhoff has essentially given up its control in the interests of creating a larger market for EtherCAT products and services.”
An open high-performance fieldbus technology that incorporates power over the communication cable, safety integrated systems, built-in redundancy and all the benefits of standard Ethernet diagnostic technology. Supported by multiple vendors and suppliers it is as suitable for low-speed monitoring as it is for high-speed multiaxis control applications, it is standards-based under the guidance of the ETG and its 3900 members, and it is Industry 4.0 ready. Martin Rostan’s closing remark resonates with me long after everyone else has left the venue: “Why would you want to use anything slower just because it is more expensive?”
For more information contact EtherCAT Technology Group, +49 911 540 5620, [email protected], www.ethercat.org
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