Once a rare sight in manufacturing plants, PCs are becoming more commonplace in factories today as manufacturers are finding that they really can control applications from machining to material handling.
Case in point: At the Honda Engine Plant in Anna, OH, engineers recently upgraded three transfer machines with Allen-Bradley "SoftLogix" controllers. And there's no turning back, says Honda's engineering coordinator Nick Balster: the PC-based controllers measurably improve machine data integration and save maintenance time and support.
"We needed to upgrade because the control technology on the existing line was more than ten years old," he adds. "We managed individual PLCs on as many as 14 different machining stations, and loading and unloading stations on each of the three machines. A lack of spare parts made the system difficult to maintain and an outdated relay interlocking system made troubleshooting time-consuming."
The choice of PCs was no trifling matter: the 1.3 million square foot plant is the largest Honda site in the world, with a full casting and assembly operation that produces 900,000 engines each year. The recently upgraded PC-based transfer lines are responsible for the milling, drilling, tapping, boring and reaming of V6 cylinder heads. SoftLogix now handles the control and sequencing for all stations on each machine, with one PC replacing fourteen PLCs on the first line and two PCs replacing 23 PLCs on the linked second and third lines.
Honda likes the PC-based systems because they're easier to use and have better I/O and communications than PLCs. But most of all, the PCs offer superb information integration.
"The new system is really about passing information from station to station via software rather than hardware," said Balster. "We can access line management data and control information such as abnormal file alarms, output, and tooling data," he added. The PCs then download the collected data to a Microsoft Excel database where it is sorted and averaged for a better understanding of tool life or other trends, and machine or station abnormalities.
"There was some skepticism about the reliability of PC-based control mainly related to a general fear of system crashes," Balster said. "The other issue was that Honda had never used this type of control in a machining environment. We did several things to make everyone trust the system, from a hardware, software and training side."
Honda's concerns mirror those of many engineers who are skeptical of the reliability of PC-based control. As with any new control system, the risks can be minimized by making simple reliability choices. Honda installed three industrial-hardened PCs and the entire system, including the monitor, is enclosed in a cabinet accessible only to those familiar with the system. The computers are equipped with a level 1 RAID (redundant array of inexpensive disks) system to safeguard against disk failures and ensure continued operation by an identical system. A UPS (uninterruptible power source) guards against external power failure, in the case of a complete power failure, would perform a "soft landing" so that system shutdown operates normally without accident or loss of data.
"Moving from standard hardware-based to PC-based control can be intimidating, especially for those who haven't worked with Microsoft Windows," explained Steve Shark, equipment service team leader. "We built a simulated system that included everything a service technician would see on the floor. Equipment service technicians from each shift were trained on how to program the system, and how to do online editing."
While the vast majority of the lines at Honda's engine plant are still controlled by programmable logic controllers (PLCs), the PC based systems have delivered on the benefits the engineering team originally sought, and Honda will likely expand the usage of PC control into other areas.
Making a Difference
The most celebrated success story for control PCs is at General Motors' Powertrain plants in the Detroit area. There, over three thousand PCs in a dozen factories go to work every day machining and assembling engines and transmissions. Ladder logic PLCs have completely disappeared; OEMs supplying new machinery to Powertrain must conform to the PC control specification.
"For GM, the key advantage is the flowchart software used by the PCs," explains John Dunlap, director of marketing at Nematron Corp. (Ann Arbor, MI, www.nematron.com) First introduced in 1986 at the Hydra-matic plant in Warren as FloPro, the software astonished engineers for its transparency and ability to provide a high level of diagnostics. "Downtime reductions were so dramatic, the technology soon spread to other plants," says Dunlap. But actual downtime improvement figures are hard to come by, as Powertrain considers it a major competitive advantage and cloaks it in secrecy.
Software Only, on One CPU Please
Europe's most successful PC pioneer, Hans Beckhoff, has a simple two-part formula for success: Put everything in software, on one platform, and two, give the customer everything he needs so he doesn't have to buy anything else.
In the Beckhoff philosophy, hardware add-ons are anathema. "If you want to take advantage of advancing technology and declining prices, then you must stay with the standard PC and put as little additional hardware as possible into the system," insists Beckhoff. "If you have an intelligent motion control board, then your price and performance are related to the motion card and not to the PC."
Beckhoff's TwinCAT software combines everything in one package: the logic and motion control, the operator interface, and all the special functions needed to control a machine, such as electronic gears, cam control, etc. TwinCAT has time on its side: with each new generation of PC, it runs better and faster.
Beckhoff also bundles the software with an industrial PC and everything needed for a control system: the fieldbus, the cabling, the terminal blocks, and the I/O system. No other PC controls company provides such a complete package.
There is no better illustration of the power of PC control than what Husky Injection Molding Systems (Bolton, Ontario, www.husky.ca) has done with Beckhoff's system. Husky's machines, which cover an area the size of a tennis court, require clusters of specialized controllers: a PLC to govern the machine process, an injection controller, a clamp controller, a robot controller, and a temperature controller. Electrical injection molding machines require servo control.
With Beckhoff's TwinCAT system, all of this was replaced with one PC, which also provides the operator interface. The separate cabinet for the servo motor power components has been eliminated, since these parts can be installed in the free space in the central control cabinet.
In Europe, Siemens has quietly gone into the auto industry with some successful and innovative PC-based control systems of its own. These combine Siemens' WinAC software with the company's new line of highly distributed, and highly intelligent control modules.
At the Audi plant in Neckarsulm a Simatic industrial PC is the host of a paint shop control system that is unlike anything seen in the U.S. The PC hosts a Profibus-based network of specially hardened ET200X modules that are located, not inside cabinets, but directly on the functional units they control. To protect operating personnel, the same PC, on the same Profibus network, hosts a series of ET200S "safety integrated" modules. Motor power for the remote modules is distributed via a 400V power bus. Siemens' motto is: "Throw away the control panel!"
After a year's experience with the new system, Eberhard Vogler, who is responsible for the control technology in the Audi paint shop, says he's pleased with the results. "PC-based control is being talked about all the time and it is important for us to test the potential of technical trends for us," he says.
"Audi imposes very strict test conditions for new systems. Before a system is integrated into production, test operation of 24 consecutive shifts is generally prescribed. During this trial operation, an availability of 99% must be attained."
Mr. Vogler says the PC-based controller proved to be "every bit as reliable" as a PLC, and that it passed an even more important hurdle: acceptance by the operating and maintenance personnel.
The Future: Convergence
The future of machine control will probably lie somewhere between the PC and the PLC. There are already signs of a convergence taking place.
In the U.S., the main driver for PC control has been the search for a control language more powerful and transparent than ladder logic. For several decades, European engineers have used languages such as function block and sequential function chart and some of these are now available in the U.S. on mainstream PLCs.
Another driver in favor of the PC is its ability to integrate large amounts of data, and pass it along to higher level computers. Recognizing this, PLC makers have supplied low cost Ethernet ports on their products, and have beefed up memory and processing power to bring their PLCs into the new era of data integration. In fact Craig Resnick of Automation Research Corp. (Dedham, MA) has suggested that the new age PLC change its name to "Programmable Automation Controller" to reflect its emerging status as a multi-domain, multi-discipline, open and modular information platform on the factory floor.
But this is precisely where the PC software companies have had, for many years, a big technology advantage over the PLCs: data integration and communication. It remains to be seen whether they can maintain this lead, and leverage it to their benefit.
Enterprise-wide data integration is the next big frontier for automation companies. They have been aggressively partnering and even buying manufacturing execution systems (MES) software companies to position themselves in the coming market.
Here is where PC control companies could shine. "It stuns us at how slow the industry has been in migrating data into the enterprise," says Nematron's John Dunlap. "There's very solid market growth in this area, and we are in a position to do it from either the HMI side or the PC control side."
And, the PC people have one more trick up their sleeves: Windows CE. Transporting downsized versions of their software to WinCE-platforms will make cost effective competitors for microPLCs. Early WinCE based products have had lacklustre performance, but look for companies like Phoenix Contract to beef up tiny CE panels with coprocessors and attack mid-range microPLCs that sell in the range of $2,000 to $3,000.