Networks and Control

Network technology has changed dramatically. Speeds that would have seemed unimaginable ten years ago are off-the-shelf these days. And with the speed a lot of bottlenecks have disappeared. With the possible exception of motion control applications.

Networks for motion are still a in category by themselves. Sercos has gone through major evolution to its current level, Sercos III, to continue to hold its position as the top performing motion network. Other implementations of Ethernet, EtherCat, Powerlink and others bring the high bandwidth available in Ethernet and add features to the network to insure its performance for motion control applications.

But the network technology momentum continues. There is a specification from IEEE, 1588 Protocol, which adds hard real time to Ethernet by clocking to make sure that messages get where they are supposed to be WHEN they are supposed to be there. This feature creates a level of determinism that has long been a stumbling block to more broad acceptance of Ethernet in the industrial community, possibly eliminating any serious impediment to using Ethernet for motion.

The controversy is usually around the question of “What is Real Time?” How fast is fast? Well, its usually whatever is fast enough for your specific application. But that doesn’t really help control system manufacturers when developing solutions for a broad audience. So its nice to find that the technology migration is starting to resolve some of the basic issues with respect to motion control, with something more broad than a vendor specific solution.

Even the Open DeviceNet Vendors Association seems to be exploring the potential of IEEE 1588 as their Common Industrial Protocol as a platform for bringing the legacy networks of manufacturers together as an overall solution. This is a very significant effort, one that has been difficult to achieve, that many users need help with. Operating a manufacturing or process plant is hard enough without having 3 or 4 different networks to maintain, and worse still, exchange information across different platforms.

My guess is the cost pressure of inexpensive Ethernet components will continue to push manufacturers toward finding similar solutions. But is sure would bring everyone along more quickly if the competition among control system providers were balanced with an option that everyone can find acceptable. IEEE 1588 is certainly a possibility worth considering.

Motion and Communication

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. Read more

Got Control? Part 2

So when is a PC (personal computer) a PAC (programmable automation controller) or a PLC (programmable logic controller)? They are all the same. They all have microprocessors. They are all programmable. They are all available with hardware that is rated for industrial environments, shock, vibration, temperature extremes and various other requirements. They are all connected to real world devices such as sensors, switches, etc. They all execute control based on a programmed binary model of a real world manufacturing process.

They have differing abilities in terms of data storage and throughput. In previous generations of PLC and CNC, the memory for those systems was very expensive and early memories were hand wound wire and discrete magnet memory. With the advent of mass manufactured memory for the PC, the industrial platforms have had to engineer hardware with different components to take advantage of competitive costs. A hard disk drive module was available for some PLC systems where extensive process information was needed.

In today’s market one vendor offers an industrial computer platform that replaces the PLC, the HMI (human to machine interface) and uses a touch screen interface, using the PC platform to reduce control system costs in many applications by doing several functions with the same hardware. Sounds like a Tablet PC engineered for the plant floor. Nothing unreasonable about that. Read more

Got Control?

The modern era of manufacturing is largely an outgrowth of controls. And that migration has had a long history since the relay logic and Computer Numerical Control systems of the 1950’s. (CNC for any younger readers that might not know what some of these crazy acronyms actually stand for). Would high speed automation of manufacturing be possible without control systems?

Probably not. And since all business is ultimately governed by return on investment, what are the implications on manufacturing processes when control systems cost in the tens of thousands of dollars as they did in the Seventies? Or over time, as the cost of control has decreased, are we justified in putting a controller on everything?

Is the alphabet soup of industrial control the basis of real distinctions in functionality? Or is it a matter of keeping the domain of a particular field of application in the hands of a few suppliers of proprietary solutions? In the early days, I think a lot of new control frontiers were driven by the demands of particular industries, Military and Aerospace applications of CNC’s where speed and precision were required, and high costs were acceptable. This stimulated the creation of a whole universe of equipment which, as with all things electronic, have become more affordable over time. Read more