Is EtherCAT the future of fieldbus?
The move to digitalization in the factory automation sectorcontinues to accelerate, driven by both technological innovationand advances, and importantly, by the industries’ increasingawareness and acceptance of the benefits it brings.
One of the important trends within this transformation is theincreasing role of edge computing. Moving intelligence closer to theprocesses being monitored and controlled has obvious benefits thathave been well documented. As the cost of processing power hasreduced, and the availability of rugged high performance hardwarehas increased, these benefits are being realized in more and moreuse cases. The trend is accelerated by concepts such asvirtualization. Here, the use of hypervisors to flexibly isolate andallocate portions of a multicore edge computer’s resources todifferent, often unrelated tasks further increases the flexibility andcost-effectiveness of edge devices.
The relentless push of edge computing deeper into the processbrings some challenges however.
The need for speed
Put simply, as the intelligence pushes further and further into thefactory processes, so the need for determinism and speed ofreaction at the physical interfaces to sensors and actuatorsincreases. Historically, this has been difficult to achieve using PCbased technologies, and so the use of specialist devices and ‘hard’PLCs has continued into the age of Industry 4.0. However, asprocessing power has increased and real-time operating systemshave become more mainstream, many of the justifications for usingthese specialist niche devices have disappeared, leaving only thequestion of how to interface the processing engine to physicalsensors and actuators in an open, robust, fast and deterministicway. This is the problem that EtherCAT solves, paving the way fordigitalization projects to reach even deeper into the automationprocesses.
Of course, there are many options available to users looking for anI/O fieldbus solution. So what are the characteristics of EtherCATthat make it an ideal choice for this part of an architecture?
First, EtherCAT is extremely fast. By embedding information for allattached devices within a single transmission frame, which ismodified ‘on the fly’ by the attached devices, it is able to achievedeterministic communications with a cycle time of 276 μS, and withclock synchronization across nodes of 1μS, making it the fastestopen industrial fieldbus currently available.
As implied above, EtherCAT is open, and is widely supported bymany vendors. This avoids the vendor lock-in associated with anumber of other common fieldbus systems, freeing users to adoptthe best-of-breed solutions for each application in their overallarchitecture.
EtherCAT is able to support many different connection topologies –daisy chain, star and ring to name but three. This means that it canbe deployed in almost any installation environment with a minimumof disruption.
Depending upon the connection topology implemented, EtherCAT isable to automatically compensate for breaks in the transmissionpath, providing a level of fault tolerance not possible with someother fieldbus solutions.
As compelling as each of these individual features can be in anygiven situation, it is when they are considered together that itbecomes clear that there is a compelling case to seriously considerEtherCAT as the fieldbus of choice for any given project.
There are essentially two different ways EtherCAT is used inconjunction with modern edge computing devices to implementdigitalization projects:
Perhaps the most obvious and familiar application is in theincreasing adoption of soft PLC technology. This is where, unlikethe dedicated PLC devices of the past, the PLC environmentbecomes an application running on an open edge computer.EtherCAT provides the I/O bus for the soft PLC, providing levels ofperformance that match those of the most powerful PLCs, but withthe added advantage that communications are much more flexible,and that the PLC functionality can be augmented by the addition offurther applications. This is especially relevant given the advancesmade in virtualization at the edge, where the performance of thePLC application can be protected and guaranteed in situationswhere other applications may allow more open access or have noawareness of time-critical operations.
Of course, not all applications can be addressed using soft PLCs, butinstead need to be coded using languages such as C or C+, and runon real time operating systems which don’t have native support forindustrial fieldbuses. Here, solutions are available in the form ofprotocol stacks that implement the EtherCAT interface and exposethis to the coded application using simple API calls. In this way,highly complex niche solutions can be developed for applicationssuch as semiconductor tool operation, robotic control and, ofcourse, to develop the soft PLC application which is then deployedand programmed by end users.
The automation industry is in the middle of a significanttransformation due to the adoption of the Industrial Internet ofThings, and the digitalization projects it has spawned. Crucial to thefuture success of these initiatives is the ability to extend the reachof the systems ever deeper into the processes being monitored andcontrolled. The deeper the reach of these systems, the more criticalit becomes that the edge is able to interface to real world sensorsand actuators in a robust, fast and deterministic way. EtherCAToffers a number of features, and a flexibility of implementation thatmake it an ideal solution in a large proportion of cases, and itshould therefore be amongst the first options considered by anyuser looking to implement an I/O fieldbus.