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
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
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
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
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
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
Motion cards from Motion Engineering Inc: Product
Viscous fan drives from Eaton Corp.'s Fluid Power
Div.: Product Code 4381
Electric cylinders from Parker Hannifin: Product
Pneumatic products from Festo Corp.: Product
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