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Machine builders debate PC vs PLC control

Part two of our report on PC vs PLC control for packaging machinery, from the perspective of design engineers at leading packaging machinery builders.

Joe Kimbrell, Rovema
Joe Kimbrell, Rovema

As PC-based control continues to evolve, many packagers are beginning to wonder: Should they make the switch from PLCs? To answer that question, Packaging World took the unusual step of interviewing engineers at leading packaging machinery builders, vs end-users. Normally PW restricts its feature article coverage to news that's made by other readers.

But in this case, many end-users defer the choice of control to the engineering judgement of the machine builders who specify them. For this reason, we asked the machinery builders to put aside commercial concerns and speak out candidly on the topic. This report is the second of a two-part series. (For the first part, see PW, Sept. '99, p. 118 or packworld.com/go/pcctrl.)

PC 'standard' isn't

One of the challenges facing PC controllers is ironically the same problem that PLC manufacturers have faced for years: a lack of generally agreed-upon standards for the programming language and operating system. While Microsoft is famous for its iron grip on the PC operating system market for the consumer and office computer market, its footing in PC controls for packaging equipment is far less sure.

Few if any packaging machinery builders use PC controllers with a Microsoft Windows(TM) operating system for machine control. Instead, they are using either a DOS-based operating system or operating systems that are known as Real-Time Operating Systems (RTOS), from a variety of suppliers. This lack of standardization is holding many machinery builders back.

"There isn't a standard on how you perform real-time control on a PC," says Joe Kimbrell. He's the electrical engineering manager at Rovema (Lawrenceville, GA), which makes form/fill/seal equipment and typically uses PLCs to control them. "Everyone says Windows NT, but almost everybody that uses Windows NT modifies that to some extent, so it's not an off-the-shelf Windows NT package anymore."

For others, such as Krones (Franklin, WI)--which uses PLCs and PCs, sometimes on the same machine--there are questions surrounding the performance of a Windows-based OS for high-end control.

"What we see with the PC control," says Mark Oldenburg, electrical R&D supervisor, "is the software solutions that [PC controls vendors] are attempting to implement are typically commercial or consumer systems being contorted into industrial systems."

Windows NT, agrees Oldenburg, is "too large and bulky for embedded applications," says Oldenburg. ("Embedded" refers to a controller that is embedded as a component of the machine, vs a stand-alone PC in its own separate enclosure.)

Even Microsoft has acknowledged that NT isn't appropriate for embedded control applications. Its solution is the forthcoming version CE 3.0, due out April 2000. Windows CE is a smaller, scaled-down OS that debuted on hand-held and palm-size computing devices. However, Microsoft has visions of using the OS for embedded applications everywhere, from TV set-top cable boxes to automobiles to packaging machinery. And that, according to Oldenburg, is precisely the problem.

"We used to say 'Windows for Washing Machines,'" jokes Oldenburg. The problem boils down to what is referred to as "deterministic" or hard real-time control. That's the ability of the controller to keep up with, or actually outpace, the speed and accuracy requirements of the physical machine, no matter how fast the machine runs.

"If you're a snail crossing the highway, real time is pretty slow," says Oldenburg. "If you're talking in the tens or hundreds of microseconds, hard real time is very, very fast.

"In some cases CE might work," acknowledges Oldenburg. But he questions whether "Microsoft [will] pump the needed dollars into Windows CE to achieve" the performance required for high-end packaging applications.

What does work are DOS-based or real-time operating systems. In packaging, it's currently the overwhelming choice for PC control. But no one RTOS dominates as a standard.

"It's a difficult question," admits Ed Young, project manager with Ilapak (Newton, PA). Ilapak makes horizontal overwrappers and vertical f/f/s machines that are typically PC-controlled.

"But for our application we feel that speed and price" outweigh any questions over standards, according to Young.

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