Industry analysts said manufacturing engineers are now taking a second look at PC technology and are shaking off long-held beliefs that PCs aren't up to the task of controlling factory floor operations. Driven by rising cost concerns, many engineers are finding ways to leverage the commodity nature of PCs and skim dollars off manufacturing's bottom line, experts say.

The result is that U.S. sales of PC control software have climbed to about $75 million annually, up from about $40 million two years ago. If the trend continues at its current pace, experts say it could signal a start to the long-expected change in the shape of the $1.4 billion U.S. market for programmable logic controllers (PLCs).

"The change is finally starting to take place," said Dick Slansky, senior analyst for the ARC Advisory Group (Dedham, Mass.). "We're seeing manufacturers making a major architectural shift toward PC-based controls."

Indeed, General Motors Corp., the world's biggest manufacturing enterprise, said last week that it has embarked on a program to adopt a hybrid-type control technology that mixes the characteristics of PCs and programmable logic controllers. The automotive giant said that it plans to use the technology across its entire North American manufacturing operation. GM has already adopted it in three manufacturing plants in Moraine, Ohio, and Oklahoma City, where it builds the GMC Envoy and Chevrolet Trailblazer; and in Lansing Grand River, Mich., where it makes the Cadillac CTS sedan.

"We're using it for all new programs going forward," said Phil Disch, engineering director for controls, robotics and welding at General Motors. "If we put an all-new body shop or assembly operation in North America, we're going with this technology."

GM's move mirrors similar decisions by other major manufacturers. At National Manufacturing Week in Chicago last month, Microsoft Corp. teamed with 30 industrial partners in its show booth, including such giants as Siemens, Rockwell Automation and Dell Computer, all of which are involved with Windows-based manufacturing solutions. Industry analysts say that such partnerships reflect a growing acceptance of PCs not just for the storage of information, but also as a tool that can be used to control automation equipment.

"There's no doubt now that industry is finally heading more toward PC-based systems," noted Tom Bullock, president of Industrial Controls Consulting (Fond du Lac, Wis.). "And we're going to see a lot more of this as Ethernet use grows on the factory floor."

Blurring lines

Experts say that the shift toward such controls is taking several forms, ranging from traditional "white-box" PCs with Windows-based control software to solutions that mix the characteristics of programmable logic controllers and PCs.

As a result, industry analysts say that the industrial-controls market is changing in a way that makes the phenomenon difficult to quantify. Most of the big industrial-controls vendors, such as Rockwell Automation (Mayfield Heights, Ohio) and Siemens Energy & Automation Inc. (Alpharetta, Ga.), now offer software packages that enable PC-like industrial controllers to emulate the behavior of PLCs. As the lines between the two technologies blur, experts say that customers are often unaware that their "PLC" may actually be a PC in disguise.

Whatever forms the solutions take, analysts say they are a reflection of a sometimes-grudging form of acceptance of the PC by industrial-controls engineers.

"It's less of a religious issue for them now," said industry consultant Nat Frampton of Real Time Development Corp. (Pearl River, La.). "It's becoming more of a functional matter. OEMs are saying, 'I need this capability. Supply it to me.' "

Such attitudes represent a sharp departure from the old status quo in the manufacturing world, where engineers long held that PCs simply weren't cut out for the rigors of factory floor control. PCs, they said, reached obsolescence too fast; they weren't robust enough; they lacked the ability to stand up to dust and vibration; and, worst of all, they lacked so-called "determinism."

Determinism — the ability of a machine to focus on a critical task — was key to the automation community. Engineers said they didn't want a PC to be polling its hard drive while a factory floor operator was frantically pressing an emergency stop on the assembly line. For that reason, many engineers dug in their heels and maintained their loyalty to the PLC, which has dominated the factory floor for nearly 30 years.

But while determinism was an issue three years ago, experts say that it's not anymore. Operating systems such as Windows CE now offer scan times of less than 5 milliseconds, well within the "hard-real-time" definition set by the Open Modular Architecture Users Group. Such Windows systems also have cycle variations, or latency, of less than 100 microseconds, also within the OMAC standards.

As a result, some industry consultants now believe that PCs are more deterministic than PLCs. "By the current definition of real-time, you could easily make the case that PCs are deterministic and PLCs aren't," Frampton of Real Time Development said.

"Almost everyone agrees that determinism is no longer an issue for PCs," added Bullock of Industrial Controls Consulting. "PCs are so fast that it really doesn't matter anymore."

Economic impetus

Still, PLCs clearly dominate the industrial-controls market, amassing about $18 in sales for every dollar spent on PC-control software. "Even though people have touted soft control, PLCs have stood their ground," noted Ron Bliss, Logix Netlinx software marketing manager for Rockwell Automation. "There's already an enormous installed base, and the attitude is, 'If it ain't broke, don't fix it.' "

Suppliers such as Rockwell Automation are developing an insurance policy against PC encroachment, however, by offering so-called "soft-PLC" products. Such software programs behave like PLCs, even allowing developers to code them using ladder logic, but are built on PC-type architectures and use Windows operating systems.

Rockwell's RSLogix 5000, which allows engineers to create a PLC-type controller but employs PC programming techniques, serves as the cornerstone for GM's recent industrial-controls decision. GM uses the software in general-assembly operations and even in more complex systems, such as stamping presses. The company's engineers say that it provides them with a common platform for all automation, and supplies them with an open architecture, which wasn't the norm during the heyday of the PLC. As a result, the automotive giant expects to save on manufacturing expenditures.

"Now, all our panels and all our equipment is identical from plant to plant," said Disch of GM. "All of our programming is the same, too. Because we write all the code in templates, we can autogenerate that code and use it over again in new plants."

Disch said that RSLogix's PC-type programming techniques provide an advantage that wasn't available from old-style PLCs. "If we write logic for a 'clamp-open' procedure in a simple assembly machine, then we can use the same logic again in a 'clamp-open' for a more complex machine, such as a stamping press," he said.

Like many new control products, RSLogix falls into the gray area between the PC and PLC, therefore allowing GM to continue in a PLC environment, despite the fact that RSLogix can be Windows-based. GM is running the software on a ControlLogix 5550 industrial controller, which Rockwell stresses is neither a PC nor a PLC.

Ultimately, makers of pure PC-control solutions hope to capture customers who are hovering in that fluid area between PLCs and PCs. Companies such as Entivity Inc. (Ann Arbor, Mich.), which makes soft-PLC controllers that are Windows-based and can run on white-box PCs, believe their products will serve as the next logical step for such customers. Pure PC products, they believe, can be more easily integrated with the front office, as well as with customers' and vendors' computers.

"We tell people that we replace PLCs that are trying to be PCs," said Ken Spenser, chief executive officer of Entivity.

The ultimate force

Analysts believe that the economy may ultimately be the driving force that pushes the automation community toward the PC. "When the economy was moving along at full tilt two years ago, the order of the day was for engineers to go to their regular suppliers and use their traditional solutions," said Slansky of ARC Advisory Group. "But since the economy has gone down, they've had time to analyze their technical requirements, and they've found that PC-based control can help them."

Like GM, many manufacturers are finding that PCs can offer economies of scale that can translate to lower engineering costs and lower initial system costs, Slansky said. For that reason, PCs are displacing PLCs at the high end of the market.

The PLC's stronghold, however, remains the low end of the market, where PCs can't compete with the $300 to $500 costs of so-called "shoe box" PLCs. By some estimates, such products now account for more than half of the existing PLC market.

During the next five years, however, engineers expect PC and PLC hardware to continue to merge, in the same way that PC and PLC software is merging today. "At some point, we are looking to build a hardened version of a PC that would run inside our hardware and provide a PLC life cycle," said Bliss of Rockwell. "Eventually, we see the market migrating that way."