I used advise people working on motion control never to make a communications layer part of the application. There were too many things that could adversely impact the motion. But communications have gotten a lot faster, and there is a tendency to think of speed as the issue. Not really.
Motion Networks are a breed apart, Sercos, Firewire, USB and many proprietary solutions are offered in today’s marketplace. Claims are made about, not surprisingly, speed. And determinism. That’s the tricky part. Guarantee the message got there when it was supposed to.
And its kind of the same problem for PLC’s doing motion control. Yes, its true that most applications do not require tight coordination between two or more axes. So its perfectly reasonable to put the motion in the PLC and let it referee when independent motion axes start. It leads to the assumption that everything is fine no matter how many axes and if any are coordinated, synchronized or registered to a moving target.
Also, not really. Position register information about where the axis is at any given time is a data request that must be sent and received before it can be acted on. That means at least two cycles of the system must be executed before the value is updated and read by the program. Very confusing problem to diagnose based on the behavior of the machine, because at low speeds everything may work fine. But when you crank it up, the process doesn’t work.
So it is with networks. Speed and determinism bandwidths must be fast enough to guarantee that the position information for any axis is where it is supposed to be when it is supposed to be there.
So the network communications wars have gone the same way. Ethernet was a big deal at 1 Megabit. Did we think we would ever need more bandwidth? Now we have 100 Megabit as the common platform with 1Gig on the horizon, inexpensive connectors and wire, wireless if you like, and things are great. Except the “legacy” networks haven’t exceeded their useful life expectancy and don’t convert to Ethernet easily.
So what will the future bring? More network solutions. More attempts at building the perfect network. Perfect for what? Every application requirement has to be considered. For the motion world, where the most demanding performance is required, a different breed of network. Give us something with clock based synchronism to make all that bandwidth useful.
To be continued