Printing forms, brochures, calendars and mailers with cut inserts is a high-speed job with tight precision requirements. When Jakob Graphic Services GmbH upgraded its operations, motion control and short set-up times were key criteria for its network selection.

These complex printing jobs have many steps, such as slitting, gluing, punching and folding. All of them are closely intertwined. Jakob, based in Pfungstadt, Germany, handles many jobs, so set-up has to be quick, and production can’t stop.

Cutting is also an important job. The separating cuts must be synchronized with the paper web speed to maximize productivity. The networks that link the presses and cutting tools must deliver messages at exactly the right time, or cuts will be at the wrong place, ruining the printed materials. The equipment works with paper rolls that have maximum roll diameter up to 50 inches, and roll widths ranging from four to 27 inches.

Jakob employed hardware and software from Kollmorgen to handle these high-precision jobs. The Radford, Va., equipment manufacturer uses EtherCat networking to meet real-time requirements. That choice is important to Kollmorgen, but most of its customers don’t really care which networking architecture is handling their critical deterministic commands.

“A lot of users don’t really think about determinism. They just know about their application, that they want to trim paper or cut 350 bags a minute with a specific accuracy,” says Carroll Wontrop, senior system engineer at Kollmorgen. Customers do want to know that Ethernet is being used for communications, but only the most focused engineers care which variant is being used for data packets that have extremely time-sensitive instructions.

That’s true with many of the industrial suppliers. There are many applications that require deterministic networks, and their numbers are growing as production equipment runs faster and customers expect extremely precise cuts, folds and seals. In the most demanding of these applications, packet delivery times must be measured in nanoseconds.

Timing is everything

The engineers who focus on network design spend a lot of time defining the level of determinism needed so that users can meet their design requirements without worrying about how bits are delivered. When these specialists look at networking architecture, they fret over miniscule fractions of seconds.

“EtherCat is able to achieve real-world jitter numbers of +/- 20 nanoseconds of the actual signal on the wire of the output devices,” says Joey Stubbs, North American Representative for the EtherCat Technology Group’s Austin, Texas, office.

Network developers are taking advantage of a standard promulgated by the Institute of Electrical and Electronics Engineers (IEEE) that’s seen solid acceptance in demanding technical environments. The wordy title of IEEE 1588 explains its basic concept: “Standard for a Precision Clock Synchronization Protocol for Networked Measurement and Control Systems.” It ensures that all actuations take place at a precise time.

“With EtherNet/IP and IEEE 1588 time synchronization, you can synchronize nodes to within 100 nanoseconds,” says Steve Zuponcic, application engineering manager for supplier Rockwell Automation Inc., in Mayfield Heights, Ohio. “When each node knows precisely what time it is, you can tell every drive and every motor to be at a certain point at a certain time. They’ll all be synchronized, giving you very tight control.”

Network developers need to embed these technologies into their equipment and software so that users don’t have to worry about programming steps that happen thousands of times in a second. Even though many control engineers haven’t worked with time-based systems until the past few years, they’ll be able to use well-known programming languages to set up their work nodes.

“Using absolute time is a new concept for coordinating motion control . It is transparent to programmers,” Zuponcic says. “People programming with SERCOS (serial real-time communications system) won’t see any difference, they can use the same instructions they’ve always used.”

When customers are setting up their systems, they generally have to resist the temptation to put the highest priority on all data. If all traffic on the network must be delivered at peak rates, networks will quickly reach a saturation point. “Not everything needs to be deterministic. If you make everything time-critical, you will run out of space,” Wontrop says. “Customers must know their performance needs, which information needs to get from point A to point B in a deterministic fashion.”

Timing is also important in EtherCat networks, where the master synchronizes and locks all the device clocks to a reference clock’s time. That effectively distributes the exact 64-bit time values to all the field slave devices. The master can then ...