Standards drive production-line design; 8-17-98

August 17, 1998 Design News

INDUSTRIAL CONTROL/COVER STORY

Standards drive production-line design

Fieldbus and PC technology Deliver agile manufacturing

John Lewis, Northeast Technical Editor

As manufacturers travel down the road toward mass customization, they are using more open control architectures and fieldbus technology to improve agility. A recent example is Eaton Corp.'s Fluid Power Div. in Fletcher, NC. When Eaton-Fletcher engineers John Penton and Dan Young got the nod to design and build a new fan drive production cell from the ground up, they started looking into open control, fieldbus, and motion-control technologies that could increase output and quality, cut changeover time, and meet future needs.

The Fletcher plant met these goals in their new "Cell 7'' using two D720 Series Open Automation Computers from Eaton Corp.'s Cutler-Hammer Automation Div. An Interbus-S device-level network connects some 300 I/O points, while MEI Inc. (Santa Barbara, CA) supplies the integrated motion control. Cutler-Hammer's NetSolver and Netpoint software tie it all together in one easy-to-use platform.

Cell 7 machines and assembles four different series of medium-duty viscous-fan drives used in automotive cooling systems. Startup began just after the first of the year, according to Young, and currently the cell operates two to three shifts per day, seven days a week. Two lines actually make up the cell. One line produces bodies, the other makes covers. Together, they put out between 2,000 and 2,500 complete fan drive units per shift, depending on the number of changeovers.

Penton believes that for larger systems with more than 200 I/O points distributed across several different machines in an assembly line, PC and fieldbus technology is definitely the way to go. "Reducing 17 miles of wire to less than 1,000 ft with the device network allows easier line modifications and speeds up troubleshooting," says Young. "There is so much less wiring. It is much easier to track down problems. You have fewer connection points; therefore you have fewer failure points. So it really decreases installation time, and decreases downtime."

Because Eaton Fletcher's automotive customers demand fan-drive shipments to be frequent, on-time, and to have zero defects, the cell must produce high-quality products in small lot sizes. All this requires access to up-to-the-minute information.

"We wanted to give operators more time to produce parts, and to let engineers exchange information electronically to improve manufacturing agility and continuously enhance the line to meet future needs," explains Penton. "The solution was to network the production line control system with engineering department PCs, add programmable motion control and HMI (Human Machine Interface) to the control system, and use a device-level network in place of hardwired I/O."

Nodes on the EtherNet. This is the first application of PC-based controls at Fletcher. The existing PLC-based fan-drive manufacturing cells required manual production-data retrieval, and manual transfer of procedures, process data, and documents between engineering and the shop floor. "Now both lines in Cell 7 are just nodes on the EtherNet, clients on the NT server like the desktop PCs in our offices," explains Penton. "I can copy program files running on the factory floor, and dial up through a modem to check out a machine's status."

Networking the engineering computers and Oracle database with operator stations on the production line enables real-time, two-way exchange of drawings, procedures, and production data. And MEI's programmable motion control coupled with Cutler-Hammer's NetPoint HMI software greatly simplifies change-overs and production runs, adds Young.

The software handles the whole scheme including motion control, process control, and communications. "If you can integrate everything into one package, you don't have to manage different controllers for each axis on the floor with different programming languages, and different interfaces," explains Young.

To reduce changeover times, Penton and Young specified Parker Hannifin Corp.'s (Wadsworth, OH) electric cylinders with encoder feedback instead of traditional pneumatic cylinders. "Rather than change manual hard stops, operators simply select the new set point right in the control program," says Young. In addition, Cell 7 uses Cutler-Hammer motor starters, limit switches, breakers, and sensors. Penton and Young daisy-chained pneumatic-valve manifolds supplied by Festo Corp. (Hauppauge, NY) throughout the cell. Each manifold is a node on the Interbus-S network, so that trend and analysis of device-level data can provide pre-emptive diagnostics.

Combining the logic, programmable motion control, HMI, and network connections on one NT-based iPC platform was simpler, more flexible, and more cost-effective than using a proprietary PLC system, according to Penton. "Once the decisions leading to PC-based motion control, HMI, and NT connectivity were made, the decision to use a common iPC platform to combine all functions was an easy one," says Young, "saving time and thousands of dollars." Equally important, says Penton, is that future connections and modifications to hardware and software will be easier than with a PLC platform.

The results at Cell 7 are impressive. At least that's the contention of Cutler-Hammer's Automation Industry Manager Jim Ramming. He oversees every application of Cutler-Hammer technology in any Eaton automation project. "Going from 900 wires to essentially one cable," explains Ramming, "really simplifies configuration and setup." The new line was commissioned in about one-third the time of the old PLC-based lines.

"The iPC/device-level network enabled the system to be built off-site," explains Ramming, "and installed in the plant in six weeks instead of 18." With old systems, only the mechanics were modular. But since the control system is now modular as well, each station is complete and independently functional. This speeds up integration because each station arrives at the plant fully validated for production.

"Field bus technology let us debug each station one at a time. Plug in the fieldbus to a particular station, debug the program, set the limits and prox switches etc., and prove it out," explains Young. "After disconnecting the station, and moving it from the build site in the warehouse location to our plant, we hook up the fieldbus, daisy-chain our nodes back together, and we are up and running." Penton points out that you could do the same thing with a PLC-based system, although a large wiring team would be required.

Save time and money. According to Ramming, engineering and wiring savings of $42,000 more than off-set the extra $25,000 cost associated with the open controls and software. "We avoided 120 hours of up-front engineering and debug time, and 600 hours on machine-wiring alone."

As with any new technology, there is a learning curve associated with its implementation. "It's a different control scheme for us," explains Young, "so it has taken a little time for the operators to become accustomed to it. Particularly supervisors on the floor that have to make changes on the computer during changeovers. After six months, we are definitely on the vertical part of the learning curve."

Based on performance so far, says Ramming, faster changeovers are expected to save about 300 hours of production time per year, equaling well over $3 million of additional revenue per year.

"The system has done everything that Cutler-Hammer said it would," says Penton. "It's excellent real-time control, and I've never seen the line crash because of a computer problem." 

Beat the heat, conserve energy

The viscous fan drive, heart of Eaton's fan systems, increases or decreases fan speed at temperatures and rates specified by the OEM. By operating only when required--rather than continually at engine speed--the fan minimizes drain on horsepower and fuel economy. The engine also runs more quietly.

The design is simple, durable, and reliable. Two facing circular components rotate over each other through complementary lands and grooves. One turns with the engine's crankshaft, the other--with fan attached--is free to spin.

A thermostatic coil on the face of the drive reacts to the temperature of air flowing through the radiator to open or close a valve in the drive. A shroud ensures that the fan draws its air from the radiator.

When the valve is open, a viscous fluid flows between the lands and grooves, transmitting torque and increasing fan speed. When the valve is closed, the fluid drains out of the grooves, reducing friction and freeing the fan.

For more information

To speak with a company representative, call 1-800-828-6344 x 011 and key in the specific Product Code below:

• Industrial controls from Cutler-Hammer Automation: Product Code 4382

• Interbus-S from Phoenix Contact Inc.: Product Code 4379

• Motion cards from Motion Engineering Inc: Product Code 4380

• Viscous fan drives from Eaton Corp.'s Fluid Power Div.: Product Code 4381

• Electric cylinders from Parker Hannifin: Product Code 4383

• Pneumatic products from Festo Corp.: Product Code 4384