Flipping pallet loads has evolved to high art for Dave Loar. The equipment
engineer for pharmaceuticals giant Glaxo Wellcome, Inc., Research Triangle
Park, N.C., is responsible for spearheading an automatic pallet inversion
system. The system, just completed in June, allows the company's Zebulon,
N.C., plant to swap out clean, in-plant plastic pallets for standard wood
ones --automatically-- on palletized product headed out the door.
What's that you say? Why not just palletize on wood pallets to begin with?
"Since we have little control over the pallets as they come in, we
didn't want to take a chance on introducing anything into the production
area that we do not have full one-hundred percent control over," explains
Loar. While he says the production area is not technically a cleanroom environment,
steps are taken to try to control as much of the manufacturing environment
as possible. One thing the company can't verify (and hence control) is the
history of each wood pallet that comes in supporting its raw materials.
As a result, wood pallets are restricted from the production area, where
a variety of products are case-packed and hand-stacked upside-down on existing,
in-plant plastic pallets. The Zebulon facility produces a wide range of
prescription drugs in bottle, blister, aerosol and tube form.
In the past, material handlers would forklift each load over to the warehousing
area --too far for direct conveyance from the production area-- and place
an upside-down wood pallet atop each load, and deposit it into a semi-automatic
inverter. That unit would invert the load 180 degrees, putting the wood
pallet on the bottom and the plastic pallet on top. The load was then removed
from the inverter, the plastic pallet recovered and the load was stretch
wrapped.
However, running such a pallet swapping system was labor-intensive. "We
had bottlenecks --usually at the inverter-- that would require several people
to come in and help out," recalls Loar. The company selected Dillard
Packaging Systems to design and install a fully automatic pallet swapping
and stretch wrap line. Since the turnkey line is operatorless, it freed
up two existing operators and reduced the need for material handlers from
four to two. Total labor savings eclipse $100,000 a year. Plus, the system
can handle up to 50 pallets an hour up from the previous limit of 30, accommodating
expected future volume.
Which way is up?
At the line's infeed, fork lift drivers can place their upside-down cargo
from either the front or the side. The line starts conveying automatically:
"We have ultrasonic sensors so the system doesn't start until the forklift
backs away," says Loar. The live roller conveyor from W.L. Stevenson positions
the load directly beneath a Whallon robotic pallet placer. By the time the
load arrives under the placer's robotic arm, it has already swung 90 deg
to pick up an upside-down wood pallet from an accumulation bin and returned
over the line, holding the empty wood pallet on two sides with a pneumatically
clamping head. The head lowers until a limit switch encounters sufficient
resistance from the top of the load, stopping the downward motion. The wood
pallet is then released onto the load. Loar says the placer works well with
all types of incoming pallets, many of which arrive skewed.
Before the load can enter the inverter, supplied by Cherry's Industrial
Equipment, it must be centered from forward to back and from left to right.
For the former, a stop bar emerges from between the rollers to stop the
load while the rollers continue to push forward. For left-to-right centering,
two 6-in.-W hydraulic rails come in to center the sides. Both centering
mechanisms are part of the Cherry inverter.
The load then conveys into the inverter, which resembles a chamber with
a metal wail on the back and right side. The top and bottom are independent
conveyor roller sections. Viewed from the line's side, the load enters the
inverter from the left. Once the load is inside, the top comes down to compress
and hold the palletized cases; the entire chamber then rotates in a simple
clockwise motion until the pallet has been flipped 180 degrees. The load
is discharged to the right, continuing in the direction of the line.
A second Whallon pallet placer removes the plastic pallet and deposits it
in its own accumulation bin dispenser, which is emptied about twice an hour;
plastic pallets are cleaned and sterilized before they are reintroduced
into the production area. The wood pallet dispenser at the beginning of
the line is also replenished at the same frequency.
With the load firmly seated on the wood pallet, the unit is ready for stretch
wrapping. The load enters a Lan-Wrapper V-Series™ turntable stretch
wrapping system from Lantech. "It's fully automated and it's a nice, simple
unit to use," says Loar. The wrapper's turntable is made up of rollers that
integrate neatly into the rest of the conveyor line. One benefit of the
new wrapper is that it prestretches film 200 percent compared to 150 percent
previously. In fact, Glaxo's previous film wasn't designed to take such
a prestretch, so it switched to Mobilrap® Pro 70 linear low-density polyethylene
stretch film from Mobil. Wrapped loads emerge from the Lantech unit and
convey down a long stretch of conveyor where they can accumulate if necessary
before being put away in the warehouse.
No changeover
The beauty of the system is that it will work with any size pallet and any
height load. "There is no changeover," Loar says definitively. "We put them
in one end regardless of the height and configuration of the load, and it
discharges them out the other, stretch wrapped and ready to go."
How so? The Whallon pallet placers simply drop down until they detect the
pallet load, at heights ranging from 24 to 60 in. Similarly, the load centering
mechanisms and compression chamber on the Cherry inverter simply adapt to
the dimensions of the load. Glaxo uses mostly U.S. pallets, although Loar
says an occasional U.K. pallet will come through, which is thicker and has
a slightly different top deck configuration. The placers did need a slight
modification to work with such pallets.
Everything on the line has its own Allen-Bradley PLC: each of the two pallet
placers, the inverter, the stretch wrapper and one for the conveyor. "I
used fully motorized sections of conveyor at every location along the line.
It just gives me more control," says Loar. "All sections of the conveyor
are divided up into PLC-controlled zones so we have full zero-pressure accumulations
All PLCs are tied into a master PLC that's connected to an Allen-Bradley
Panelview operator interface. This setup permits ease of troubleshooting
as well as much greater flexibility in creating programs and controlling
the line, according to Loar.
The line not only saves Glaxo in labor costs and frees up operators, but
it obviated the need to replace two aging fork trucks, a purchase Loar values
at about $150,000. Plus the line's high capacity will continue to meet Glaxo's
material handling needs well into the future.
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