I used to caution customers, actually I preferred to talk customers out of the idea of using control networks with motion control applications. But having been around motion control, now mechatronics, for 30 years, a lot of things have changed. In fact, the whole game has changed.
Motion control has always been challenging to control systems because it is the hardest of hard real time applications. But our notion of time has changed. The processors that manage electronically commutated motors operate at 50mHz with incredible code efficiency, requiring nonosecond precision oscilloscopes to measure events. Considering that we used to be thrilled at the prospect of controlling things in the microsecond world, I’d say that’s game-changing (another over-used catch phrase).
So corresponding changes in the communications realms shouldn’t be a surprise. Though I think that we hadn’t even invented Ethernet 30 years ago. But ignoring that detail, we’ve seen Ethernet technology bloom from a mere megabit per second to Gigabit Ethernet. Bandwidth is not a problem. And with universal adoption of the technology by business and telephone communications systems, the cost of the physical layer and connectors have dropped to incredibly low levels. As you would expect.
In fact, Ethernet is so cost effective, it’s starting to take over the industrial control landscape. To the point where Ethernet connectors are available for dust tight and wash down environments. That’s pretty extreme for a consumer grade communications platform. But that’s wasn’t my primary point.
The dilemma for applying a communications protocol to motion control is it’s ability to move data faster than the synchronous control of the motor. So industrial networks, even at a few megahertz, can’t keep up. Particularly when there are two axes of motion which must coordinate their relative motion at the update rate of their position feedback sensors. And in the case of linear motors with extremely high resolution tape scale encoders, you can end up in situations where the feedback is running 20 mHz. So good luck coordinating 2 or 3 linear motor axes.
But, of course, we do this kind of thing every day. With micro controllers. But not with networks. But what if you could? It’s coming soon. IEEE-1588 is a time synchronous version of Ethernet that permits precise coordination of data movement over Ethernet. And it’s compatible with existing Ethernet networks. Sounds like a pretty good deal. And that makes it a workable solution for coordinated axes of motion control. It’s been tested at a technical university in Zurich Switzerland. And like good solutions, may have many other applications. Look for it in new motor control products coming soon.