Robotic Arms Lend a Hand in Manufacturing
Chrissy L.S. George, NEMA Communications
M
y interest in how machines work is largely due to my father. In his
working days, he was an engineer by day and inventor by night. Always
building things, he encouraged me to design useful inventions, one of which
was a fool-proof fishing lure. We even built a model of it together.
Fast-forward a few decades, and I’m still curious about how things
work, but on a much larger scale. For example, I’ve been known
to linger at construction sites and ask (too many) questions
about augers, shoring, and welding. In a factory setting, I’m
fascinated by robotic arms—the swiftness, the accuracy.
Robotic arms range in size, but the main components
remain the same: base/foot, frame, lower arm, upper arm,
and wrist. Between the arms are gearboxes—an essential,
and perhaps, most important element.
Repetition is the name of the game for these robots, as
they are designed to complete the same action repeatedly.
According to ABB Product Manager for Large Robots Ola
Svanström, precision is a result of several factors.
“Choosing the right gear boxes is a key strategic
question for all robot manufacturers. The gear
box’s stiffness and backlash sets, to a large
extent, the possible accuracy of a robot, both in
positions and paths,” he said. “This also means
that the gear box always needs to be a precision
component and, therefore, a major portion of the
robot’s system cost.”
used for electronic production are smaller with a 2–5 kilogram
[4–11 pounds] payload,” said Mr. Svanström.
ABB manufactures a large size range of robotic arms, from
the IRB 120 with an approximate payload of 3 kg [6.6 lbs.] and
an overall weight of 25 kg [55 lbs.] to the IRB 7600 with an
approximate payload of 500 kg [110 lbs.] and an overall weight of
2,450 kg [5,410 lbs.]. The smallest robots handle cell phones and
microchips; the larger ones
handle cars and trucks.
Mr. Svanström also
mentioned that in microchip
production, SCARA (Selective Compliance
Assembly Robot Arm) robots are often used since they
are both fast and stiff in vertical direction, ideal qualities
for assembling such small-scale products.
As with all manufacturing, industry standards are
followed and include:
• EN ISO 10218 Robots and robotic devices—
Safety requirements
• EN ISO 13732:2008 Ergonomics of the thermal
environment—Part 1: Hot surfaces
• EN 614-1:2009 Safety of machinery, ergonomic
design principles—Part 1: Terminology and
general principles
• EN 574+A1:2008 Safety of machinery. Two-hand
control devices. Functional aspects. Principles
for design
Precision is also the result of motor type. Many
robots use a stepper motor—a dc motor that
• EN 953+A1:2009 Safety of machinery. Guards.
operates in phases or steps. ABB robots use a
General requirements for the design and
servomotor, which is similar in functionality to a
The IRB 6700 is designed for spot welding,
construction of fixed and movable guards
stepper motor, but slightly different. A servomotor
material handling, and machine tending.
rests between held positions without consuming Photo courtesy of ABB
“There are three main directives for building robot
power; a stepper continues to draw power at rest.
arms,” said Mr. Svanström. “The machinery directive,
which
relates
to overall safety; the low voltage directive, which
How does the arm know which actions to perform? A
relates
to
electrical
safety; and the electromagnetic compatibility
programmer choreographs its movements with a handheld
directive,
which
makes
sure that the robot can withstand
controller, “teaching” the robot its actions until it “remembers”
electromagnetic
radiation
and does not emit too many
and can perform them on its own. Many robots have
electromagnetic
disturbances.”
interchangeable end effectors, such as a grasping tool or drill,
which allow them to perform different functions. In some
instances, this eliminates the need for additional robots only
able to complete one specific task.
When it comes to tasking, the main difference between a robotic
arm that assembles a car and one that assembles a microchip is
simple—size.
“Arms for auto applications are bigger, with payloads between
200–300 kilograms [440–661 pounds] for most robots. Those
24 NEMA electroindustry • October 2014
So think about it: How many things in your life were assembled
by robots? More than you considered?
Now that my father is enjoying retirement, perhaps our next
project is building a robot. It sure is a step up from a fishing lure. ei
Ms. George ([email protected]), is the editor of
eiXtra. She received a 2014 Hermes Creative Award (Honorable
Mention) for her writing.