Drive-controller interaction: not what we are used to....
13 November 2015
A small but very important change is happening in the world of drives, and it points the way ahead for a vast number of applications over the next twenty years, as Jonathan Smith reveals.
That ‘small’ change referred to in the introduction seems deceptively simple. Drives can now be instructed directly from the control system. That doesn’t even sound much like a change at all – control systems have for some time been able to provide a digital command whether via conventional I/O or a network to start, to stop or to reverse a drive. The latest evolution within drives is a little different though – and here’s how.
At the moment, drives are ‘parameter based’ and this means, for instance, that the controller sends a start command which the drive then processes. The drive then starts the motor at a speed and/or acceleration defined by its programming before sending a message back to the controller to tell it how it is working. They are, essentially, standalone devices that can either be networked or that operate with their local programming, without a controller.
Until now, drives have needed to have a certain amount of local control – their own ‘brains’ that turn the command from the controller into actions. However the next generation of drives do not have that disconnect from the control system.
The latest evolution changes this relationship in a small but important way. For instance, now it is possible for the controller to send an instruction for a drive to be told to start with a defined or even changing rate of acceleration rather than be limited by the fixed acceleration rate in a drive parameter setting. The drive will now do exactly what it is told and the controller knows (and can present real-time feedback about) exactly what the drive is doing.
In order to get to grips with why this small change will make a big difference, it helps to zoom out a bit and place the drive back in the context of the whole automation system. No drive is an island. The drive could be performing one of any number of functions – in fact, the possibilities are almost endless; if it needs to move and have control over speed and perhaps position as well, it generally needs a drive. This new functionality is based upon ‘instruction sets’ and provides the control system with the ability to define the performance of a drive – normally this is defined by the parameters that a user has to set-up as part of the commissioning process – so acceleration rates and shapes (camming, for instance), position moves, and synchronisation of real time instructions to multiple drives can now all be achieved within a standard programming environment.
At Rockwell Automation we talk a lot about the Connected Enterprise. That’s because the information revolution is the single biggest force of change in the automated environment – it has been for some time and will be for the foreseeable future. Concepts such as the Internet of Things, or the Internet of Everything, have led to initiatives such as Future Factories and Industry 4.0.
For specifiers, systems integrators, OEMs and factory managers, many of the advantages of this super connected, super integrated world of the future are exactly that – the future. Because very few are building brand new multi-million pound facilities from the ground up. Rather, as is always the case with such things, the revolution happens by evolution.
Our Connected Enterprise offerings are the basis for the future almost no matter what happens, since they place, front and centre, information enabled solutions that will allow for the levels of connectivity demanded by the plant of the future. Connected Enterprise is about bringing Operational Technology (OT) systems and Information Technology (IT) systems together. Put simply, it doesn’t matter what the next internet-enabled tool or system is – if your IT system and your OT system don’t work together, you won’t be able to get the benefit of it.
The ability, through modern, integrated systems, to know and control the state of the operation in real-time then, is vital. You might think of modern automation as an almost sentient organism… The drives would be the heartbeat. Information, and how it is conveyed throughout the enterprise, is like the central nervous system. Controllers are the brains. This idea might help explain the importance of that small change at the drive level.
The benefits are numerous and include the ability for Safety functions to be managed by the automation controllers via EtherNet/IP rather than locally. This approach can also provide the ability to change safety zone configurations without the need to alter hardware.
Common Industrial Protocol (CIP) based motion is another advantage to the new evolution of drives. As mentioned earlier, drives are able to move with a set acceleration or move to different positioning or do any other synchronised commands - commands linked to master clocks on the system. This is because CIP Motion coordinates devices a lot like we humans would coordinate a business meeting – or even a birthday party.
All invitees (devices) have clocks to compare time to an absolute base and scale – in our case, good old GMT. For the Automation system, it’s the master clock. A destination (position) is targeted for the event – the meeting room or pub for us, perhaps, but a precisely set operating position for the devices on the CIP Motion system. The time (timestamp) of the event is set and a message sent to each invitee (device) to meet at the given place at the pre-determined time. The potential applications of these advantages are numerous.
CIP Energy is also worth a mention as an advantage of the dawning era of drives. With the control based instruction sets energy monitoring software can offer a level of energy management hitherto impossible. Each device – such as a drive – in effect becomes a sophisticated energy measurement device which provides a great deal more gradual energy usage information. This is achieved by using a standard profile that means the energy monitoring software can address each device in the same way as a dedicated energy or power meter.
What this all adds up to is a paradigm shift. The new era is one of agility and capability and there's been an interesting debate in theoretical terms about how much intelligence should go into a field device and how much should be held separately. The drawback to local intelligence though – or intelligence at ‘the edge’- is that it can be difficult to get that intelligence into the control systems; it's less flexible. But if you have instruction sets in the controller, by simply giving instructions to the device it becomes part of the control system. The ethos of EtherNet/IP, the vendor neutral industry communication standard behind the Connected Enterprise which will enable Industry 4.0, is visibility across the whole system – in a sense, the number of controllers or functions becomes irrelevant; they are just IP addresses in a single entity: the Connected Enterprise.
It’s very hard to imagine what drives will be like 20 years from now, and it would be foolish to guess too much – but we’re certainly on the cusp of exciting technology developments, and if the advantages of Industry 4.0 are to be realised, it’s hard to imagine that the newest drives won’t be the beating heart of the solutions that deliver it. In the shorter term, it’s fair to say that these new drives are not what we are used to. They are a big step forward.
Jonathan Smith is business leader, Rockwell Automation Power Control business
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