Automated manufacturing and the PLC: control on the edge
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Fifty years after the birth of the game-changing programmable logic controller (PLC), is industrial automation now at another turning point?
At a time when all the talk is of automation, Industrial Internet of Things, robotics et al, it is perhaps a fitting time to raise a toast to one of the building blocks of modern manufacturing, the PLC, which turns 50 this year.
Talk these days is of pushing control to the edge, where remote nodes can communicate with each other, while machine and system flexibility is largely taken for granted. All of which would have been inconceivable in the 60s when control came by virtue of banks of relays. Any change of function would require shutting down the machine, rewiring and adding to the relay matrix, debugging and then hoping the next change wasn’t imminent.
GM Motors needed more flexibility than this offered for its Hydra-matic manufacturing operation – the first mass-produced automatic transmission. The company that won the contract to supply this was Richard Morley’s Bedford Associates, and its Modicon (Modular Digital Control) technology was adopted as the company name. The design brief for the machine controller was that it had to have the flexibility to be reprogrammed, be a cheaper option than using relays and be modular. It also had to survive the rigours of the industrial environment. Sound familiar? The PLC was born, although it would be another three years until competitor Allen-Bradley would give it that name.
Even though the controller could now be reprogrammed by software, the process still involved burning the code into the chip – an E2PROM (electrical erasable, programmable read-only memory) – and reinserting that chip in the PLC. But gradually the process became smoother and it gained traction, initially in the automotive industry, but from the 1980s onwards throughout manufacturing as a whole.
Martin Walder, Schneider Electric’s VP Industry, UK & Ireland, comments: “The PLC has been a huge vehicle for accelerating the shift from manual labour to automation and what’s happened over the years is the cost of delivering PLCs to the market has come down dramatically.”
While the PLC of the 1970s may have cost the equivalent of £20,000, they are now available for little over £100. Consequently what used to be only justifiable for big automated lines can now be employed from everything from a parking barrier upwards. Relatively simple operations like this would previously have used dedicated electronics, but, as Walder points out: “If you can buy something off the shelf for that sort of money – it’s robust, industrial and can be connected – why would you create your own?”
Through mergers and acquisitions, Modicon has become part of Schneider Electric, a company with a broad perspective of industrial automation. Walder sees a constant evolution in the components that offer these automation solutions. Drives, for example, can contain simple logic themselves as can other parts of a system. “I think you’re seeing pieces of your control system are fragmented in different components on a network and all working together,” says Walder. “Whereas in the olden days the PLCs were big, centralised systems with every wire back to that central point. Now your control system can be fragmented across drives, remote IO blocks, motion, all doing a bit of the control, all talking to one another by a very solid network solution.”
The cost of networking now is minimal. Adding an Ethernet connection costs pennies and is now the default. This connectivity along with the protocols used and the ability to work in real-time is allowing this communication and distributed control.
Far from being the end of the road for the PLC, it is just the next stage in the evolution – driven by the demands of robotics yet building on its generic capabilities. Walder says: “The PLC is generic in its make-up, but over the last 20 years they have been tailored with software and by taking a traditional PLC and putting some motion cards in you can control a robot. But where those applications are getting more demanding and speeds are going faster, that traditional generic PLC approach has probably reached the limit and that’s where you’ve got more tailored applications. They’ve got some PLC functionality at their heart but they’ve also got some dedicated specialist functionality.”
There are plenty of generic PLCs on the market, some of which are modular systems that can be built up with motion cards. But such systems have their limitations. While it may seem counter-intuitive to customise a PLC, which has always had the appeal of being generic, at the top end is where Walder sees this new breed of dedicated PLCs come into their own. “I’m talking about five robots all in one line with various conveyors and axes on there and a sequence in,” he says, “that modular PLC just cannot cope with it anymore. That’s where we go to the dedicated, which is an all in one specialist box, so that all of the axes can communicate in microseconds, not milliseconds.”
The very nature of industrial equipment means that while inertia is not exactly welcome, rapid change is certainly not what the manufacturers want. “PLCs don’t change that fast. Most end-users don’t want them to change too fast because once they put them in, they want to live with that for 15 years maybe or 20 years,” Walder comments. Sometimes technology forces change and specifically at the moment the needs of real-time operation requires much faster bus systems than old hardware can cope with.
Also is the ever present cybersecurity threat, which requires a constant battle with the latest technology. Walder says: “How can a manufacturer stay ahead of the curve in terms of productivity, in terms of competitiveness, if they don’t use the technologies available? If they don’t, they’re only going to go out of business in time, but if they use it, they’ve got to make sure to protect it or their plants come down for weeks on end because they are bombarded with cyber attacks. So you can’t avoid it.
“People don’t want things to change too fast,” he concludes, “but I think we’re at a time in history when they have to.”