Page 35 - Plastics News July 2019

FeAtures

Payload controllers, blenders,
Cartesian and articulated-arm robots can both handle granulators and
substantial payloads. The main consideration with six- o per ato r wo r k
axis robots is that the payload rating can vary, based stations all competing
on the axis positions, or where the robot is within its for space around a
work envelope. Speed is also impacted by the payload. molding cell, most
Cartesian robots on the other hand, keep their rated man ufact ure rs
payload capacity throughout their full range of motions, want to minimize
and they can maintain their maximum payload capacity any additio nal
at all speeds. Collaborative robots typically have a much equipment’s impact
lower payload capability than both Cartesian and standard on the area. A floor-mounted six-axis robot will require
articulated-arm robots. In molding, payload plays such an an immense amount of room around the machine, and the
important factor in choosing robots. Because most molders press may have to be modified to allow the safety guarding
never know what job may be coming down the line, it is to remain open during robot operation. This adds to safety
important to choose a robot with enough payload capacity concerns, as well as costs to modify the equipment. The
not only for today, but for the future as well. I always say counterpoint to this is a top-entry gantry robot, which
it is better to have the payload capacity and not need it, frees up valuable floor space. If a six-axis robot were
then need it and not have it. mounted on top of the machine, it would typically have to
be oversized to allow the reach required to pick the part
When considering and move it all the way outside the machine to deposit it
payload, note that on a conveyor or pallet.
the part and runner
weights may be a Makers of collaborative robots promote that they don’t
very small portion require guarding. This may be true for the robot itself,
of the total load. but this may not reflect the entire picture. What if the
End-of-arm tooling robot was entering the injection machine from the back
(EOAT) can have side of the press (rear gate opened)? What if degating of
docking features, the parts was required? What if you were running a high-
shuttle cylinders, temperature material, and the parts need to be cooled
rotatory units, prior to an operator handling them? In these scenarios,
multiple grippers, even though the robot itself is “collaborative,” other parts
sensors, quick change mechanisms, etc. The weight of of the process may not be, so guarding would be required.
these can add up very quickly. And when you consider If you considered mounting the cobot on the operator
high-cavitation molds, even very small-tonnage molding side of the machine, that indeed might be a layout where
applications can require extremely high robot payloads. guarding would be unnecessary. But think about what that
Flexibility would do to the molding cycle time. The robot would have
to open the front gate, extract the parts, close the gate
There is no disputing that six-axis robots provide a wide and the press would start the next cycle. Although you
range of motion flexibility. That being said, Cartesian would have more
robots can be equipped with servo rotational axes at their consistency than
wrists. These additional axes can provide up to six axes of with an operator
total motion on the linear or gantry robot. Although this performing the
still doesn’t compare to the total motion flexibility of an same functions,
articulated arm, these features can provide linear robots this incr eas e
with much more flexibility than many commonly assume.
in cycle time
Floorspace would be very
The floor space around a molding machine is a scarce and detrimental to
valuable commodity. With equipment such as temperature overall production

35 July 2019 Plastics News