But not Kevin Zeinemann, electrical engineering manager at Curt G. Joa Inc., in Sheboygan Falls, Wis. Instead, he ranks flexibility as the most important attribute of this generation of open networks that can accommodate signals from safety devices, in addition to the other data flowing within them.

His reason for ranking the benefits differently is that his employer is a privately held builder of custom machines that produce diapers and other kinds of disposable, absorbent pads made from laminated webs. These complex, 150-foot-long machines laminate together as many as nine webs of material.

Because many of Joa’s customers operate in fiercely competitive consumer markets, they are eager to incorporate the latest cost-saving technology, and to produce the latest features that are currently popular with consumers. Consequently, it is not unusual for their requirements for machines to change three and four times in the design phase alone. “It’s hard for us to lock down a design because our machines and processes are changing up to the minute they leave the building,” explains Zeinemann.

And the changes don’t stop at delivery. Customers continually update their machines in the field to cater to evolving consumer tastes or to introduce new cost-saving technologies as they become available. A diaper manufacturer, for example, may need to change graphics frequently, perhaps from Elmo to Bugs Bunny to another on a weekly basis. “It may be as simple as changing the materials,” says Zeinemann. “Or it may be as complex as pulling 40 feet out of the machine and putting in another 40 feet.”

To generate the necessary flexibility, Joa has adopted a modular approach. It builds its machines from a toolbox of predesigned and proven hardware and software components. Each machine, moreover, is made in 10-foot modular sections that are bolted and plugged together. Because each section has its own communications and control scheme, the sections can be unplugged for shipping and for retrofits in a few days. Until recently, the safety network had been a big obstacle to this strategy. The machine had to be hard-wired with numerous relays interlocked with drives, input/output (I/O) points and guard switches to protect operators and the machine at start-up and shutdown. “It is hard to modularize a hard-wired design,” says Zeinemann. “So installing the wiring, troubleshooting problems and making modifications was a nightmare.”

Nightmare begone

Things changed when he and his colleagues began using the GuardLogix integrated safety system from Milwaukee-based controls vendor Rockwell Automation Inc. They were able to integrate the safety system with the Allen-Bradley ControlLogix programmable automation controllers that they were already using. Although they had to put the safety devices on a separate DeviceNet network initially, they switched the safety devices to Ethernet as soon as EtherNet/IP became available.

Now, the designers tie the safety devices to local I/O blocks attached to the same EtherNet/IP-based network that runs throughout each machine. Besides streamlining disassembly for shipping, the modularity makes it much easier to accommodate dramatic design changes in a matter of hours, and to incorporate new drives and other technologies as they become available. “Having flexibility just makes it so much easier to deliver a highly engineered product without a lot of extra redesign work,” says Zeinemann.

The same holds true for retrofits in the field. If a customer wants to change a feature on its product, having only one network makes it much easier to replace a 30- to 40-foot section in the middle of the machine. “Instead of having to splice into that hard-wired circuit, we can drop a new modular machine section in and just plug it into the Ethernet,” Zeinemann explains.

He reports that achieving this new flexibility was not without a few challenges. First was the additional load that the safety functions put on the main processor. As a result, the processing speed was too slow to control the complex motion of the entire line. Because a machine typically has six to eight controllers on it, “we decided to put the motion component on one of the other secondary processors,” says Zeinemann. The other major challenge was learning to lock programs with signatures to prevent unauthorized people from opening and modifying the programs.

Packaging safety data

Clever ways of packaging data are the technical breakthroughs that allow users such as Joa to send safety signals over the same network as other kinds of data. For Rockwell Automation’s networks, the key is the safety extensions that the Open DeviceNet Vendors Association (ODVA), of Ann Arbor, Mich., added to its common ...