One widely used solution to the problem is to “float” sheets by blowing compressed air between them. The tricky
part is getting the sheets to separate
so the air can do its work. New multi-bellow friction cups aid separation by
slightly bending the sheets’ outer edges
so less air is needed to float the sheets
(see Figure 2). This makes the picking
more reliable, again helping to minimize
downtime and increase SPM.
Other problems occur when automation equipment comes down too hard
on stacks of parts. This tends to wear or
damage vacuum cups and causes blanks
to stick together. The best approach is
to adjust the speed and distance of the
equipment to the parts and let the cups
do the work. When the cups engage a
sheet, they create a peeling effect by curling and separating it from other sheets.
As the robot or automation equipment
lifts the sheet, a shot of air can be used
as an “air knife” to complete the separation. On larger sheets, brushes also can
be used to assist the separation.
Also, blowoff can be used to release
parts quickly. Vacuum and compressed
air tend to take the path of least resistance, so it is important that the circuit
is designed and plumbed in such a way
that flow paths are equalized. This will
allow for speedy picking and
releasing of parts.
2. Use a Flexible Design
Flexibility will help customize your
production so you can match automation components to your specific needs.
Decentralized vacuum systems, such as
one cup per one vacuum generator (see
lead photo), generally are more flexible than centralized vacuum systems
with multiple cups per one vacuum generator.
Both centralized and decentralized
systems have their own set of advantages and challenges, depending on the
Quicker response and release times
are the main benefits of a decentralized system. Also, each vacuum cup is
independent, which means that if one
cup doesn’t make full contact with the
part, the other cups will be unaffected.
This ensures good, reliable,
and consistent parts picking.
Tubing lines can be smaller
and more flexible. On the rare occasion
that the vacuum and blowoff release at
the same time, fewer problems occur
in a decentralized system. This is very
important for accurately releasing parts
so that they are in the proper location
for the next die.
A challenge of decentralized systems
is that having several ejectors on each
gripper arm typically makes them more
expensive. Also, traditional ejectors are
built into the cup tooling, which means
that if there are any problems with the
ejector, the operator has to replace it
and also reset the cup’s position. Newer
technology provides lightweight, flexible decentralized ejectors that allow
for lighter cup tooling and easy ejector replacement without the downtime
associated with resetting cup positions.
Centralized systems, or all-in-one
ejectors, usually are located on the
robot, upstream of the end-of-arm tooling (EOAT), and they typically are set
up as multiple vacuum zones. Usually
there are two pumps per EOAT. Each
centralized ejector controls a set of vacuum cups. These ejectors have control
valves for turning on the vacuum and
blowoff. They also incorporate a vacuum switch, giving a go/no-go signal to
the robot. This signals that the desired
vacuum level has been achieved and that
the robot or automation can move the
part. The main advantages of this type of
system are lower cost and weight.
The challenges of the centralized
approach are related to the distance
from the vacuum source to the cups.
The vacuum flow determines the speed
Automation has been key in helping stamping manufacturers achieve productivity goals.
An increase of just 1 SPM can raise output by 1,440 more parts a day in a 24-hour-a-day
operation. However, challenges can occur at high speeds.
Bellows cups on edges facilitate a peeling effect.