What network works for you?

Deciding on a machine control network isn't about all the marketing hype. It's about solving the problem.

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By Joe Feeley, Editor in Chief

Joe FeeleyMachine buyers are moving slowly but relentlessly away from mechanically-centric control to the expanding world of electronic and electromechanical solutions. And they’re demanding that their OEMs go with them. “OEMs are steeped in a culture where innovative mechanical solutions are regarded as a strategic advantage,” says Sal Spada, automation analyst, ARC Advisory Group, Dedham, Mass. “Innovation is the lifeblood to many motion control suppliers, but it’s been the nemesis of many users and OEMs.” Spada shares the thoughts of many OEMs, who see standards as the only way to make the crossing to electronic solutions without having to support multiple, cost-prohibitive proprietary solutions. Machine networks are a big part of this issue.

While the future may hold some promise for standardization, machine network choices remain as much a political investigation as a technical one for OEMs and end users. Motion control protocols seem to be gravitating to SERCOS and FireWire, while the more I/O-intensive machine network decisions involve choosing among the usual suspects.

OEM Customers Want a Standard
Since there is no dominant networking protocol for motion control, suppliers try to influence users as to which of the existing protocols is the best candidate to be a standard. Though some end users have standardized on Ethernet for controller- to-controller communications, few have a motion control networking standard, and those who do tend to specify SERCOS. SERCOS is seen by many as a sound technology, but it’s adoption may be limited by its level of vendor support.

For an OEM customer, that’s no help. “From my perspective, vendor support is a marketing question and not a technical question,” responds Keith Campbell, director of automation and integration for Hershey Foods, a company that has standardized on SERCOS. “It does what we need and we don’t have any enhancements in mind. It’s up to the supplier community to respond.”

But it is still a problem. “We don’t go to an automation vendor and say we want SERCOS,” says Nabisco’s Don Boyle, senior director, process control systems. “We’ll listen to their presentation, but we would want to know why all the motion vendors haven’t adopted it as a primary communications protocol.”

Has Ethernet been considered as an alternative to SERCOS? “No, but FireWire has sparked my interest,” responds Procter & Gamble’s Rob Aleksa, corporate controls section head. FireWire, a fast network protocol, was originally created by Apple Computer. It is now an open standard under IEEE-1394, but, so far, only a few motion vendors support it.

What OEMs Are Saying
The important thing, of course, is what OEMs have learned from their experiences with the various networks available to them. And there are ample opinions, ably summarized by some OEMs who’ve worked with a number of the networks.

“For assembly automation, InterBus is not the fastest kid on the block, but I believe it’s the best because of its synchronicity, determinism, and safety, and it has standard interfacing specifications for a lot of applications,” says control engineer Rick Ahnen, Gilman Engineering, Janesville, Wis. “It also has easy setup and maintenance, good throughput for its baud rate, and seamless data transfer through fiberoptic, shielded, and inexpensive two-wire mediums. I just wish there were some more U.S. vendors to aid in competition and interest.”

Ahren rates DeviceNet second. “I’m a long-time DeviceNet user and have a love/hate relationship with it,” he says. “I love it because I know it well enough to comfortably employ it and there are a lot of U.S. vendors that interface to it.” That’s the good news. “I hate it for its cumbersome setup, EDS files, noncommittal interfacing specs that result in inconsistent I/O vendor products, and its management software,” he states.

Fogg Filler Co., Holland, Mich., is an OEM of rotary filling machines for flowable, non-carbonated liquids. “We use DeviceNet for our machine control, which involves motors and variable-frequency drives, along with some basic discrete I/O,” says Dan Winebrenner, electrical engineer. “We chose DeviceNet mainly for the wiring savings and because of the readily available component base provided by Allen-Bradley.” Winebrenner says Fogg started with DeviceNet and they understand it better than any other at the moment.

Winebrenner doesn’t feel any pressure from his customers to choose among the networks. “Probably 90% of our customers don’t care what control system decisions we make,” he says. “The cause of advancing new control ideas is more of a push from the OEMs rather than a pull from the customer base.”

Next comes Profibus for Ahnen because he finds it fast, with a significant number of I/O vendors, and it has large following in Europe. “However, it’s expensive and can be as big a pain as DeviceNet for setup,” he says.

Winebrenner is now working with Profibus for a special trade-show prototype. “We were forced to try Profibus because of certain specific component choices we wanted to make,” he says. “But I’m impressed by its straightforward configuration and implementation.” He found better support available this time compared to his initial experiences about two years ago.

Advanced real-time control of particles in his company’s semiconductor process equipment is the mission for Bill Shade, vice president, vacuum products, Pacific Scientific Instruments, Grants Pass, Ore. “Fieldbus use by OEMs in this industry is still pretty new, but Modbus TCP/IP over Ethernet is our choice,” he says. “It is already common in semiconductor manufacturing, and this makes is easy for customers to install and maintain.”

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