The robot also has the ability to directly
couple the output power of the laser
to the travel speed of the tool centre
point. This allows for a higher quality
weld or cut when processing across
curved surfaces or across multiple
planes of surfaces with a continuous and
consistent-looking end result.
In an application such as laser cladding,
the laser output can be used to dictate
the rate at which the cladding material
is deposited. Similarly, if performing laser
brazing, the laser output can be tied
to a wire feeder, and the speed of the
wire being fed into the process can be
regulated.
HEAD MOVEMENT
Recent advancements within the laser
processing head have now made it
possible for the robot to control the
trepanning motion in some heads. Similar
to a scanner welding head that directs
the laser beam using galvanometric
rotating mirrors controlled by a
microcomputer, the robot controls the
mirrors or lenses using auxiliary servo
motors and it is, therefore, programmable
using standard teach pendant robot
programming.
This allows the robot to go to a fixed
position and create unique patterns for
different weld designs. These types of
welding processes are quickly replacing
traditional spot-welding applications
due to their speed, control and ability
to be used on various materials beyond
standard steel.
As the capabilities of the robots and
their controllers advanced so did the
availability and implementation of
peripheral devices. For instance, laser
height sensors have been adapted into
robotics as a means of locating parts
instead of traditional touch sensing. The
benefits being it is faster than locating a
part with the weld wire and has a higher
resolution and better repeatability than
the weld wire. Furthermore, it does not
require physical contact with the part
allowing for searches in tighter areas and
areas further away from the tooling.
A laser weld head with a wire delivery
device. Advancements in software allow
laser power and tool centre point speed
to regulate the speed of the wire being
fed into the laser process.
There are also low-powered lasers that
guide the robot along various seams or
patterns in the material so that the robot
38
can adjust its path in real time to ensure
it is still performing quality welding and
cutting even if the base material contains
a significant amount of variation.
Machine vision is another area that
has grown tremendously in robotic
automation. Industrial hardened camera
systems have been used on robots to
identify parts, read bar codes, perform
inspections, pick objects from moving
conveyor systems or out of bins, and
locate objects in 3-D space and guide the
robot to them.
FREEDOM OF MOVEMENT
In a market that has been traditionally
dominated by CNC controlled heads,
robotically positioned laser welding
and cutting is starting to gain market
share as a result of the above-mentioned
advancements and, not surprisingly, by
the flexibility of having a robot-carried
processing head.
This means six degrees of freedom are
possible, which allows the user to break
away from the flat plate limitations of
an X-Y table and explore processing 3-D
parts in 3-D space. This could be circular
or square tubing or it could be part of an
assembly like the inside of a truck frame.
Additionally, if auxiliary motors or
another robot are used to manipulate the
part, access within complex geometries is
made easier by positioning the part and
the robot into an optimum location. This
also promotes the ability of coordinating
the motion between the part and the
robot so that the process can continue
uninterrupted.
Another benefit of using a robot-carried
head is the ability to change out the
end-of-arm tooling between a welding
head and a cutting head or change from
a welding head to a pressure-driven
grinding or polishing device for post-
weld processing. This minimizes the real
estate required on the expensive factory
floor by not having individually dedicated
processes.
With a simple tool changer, one robotic
cell can perform multiple functions,
increasing the quality and optimizing
the cycle time per part. This solution
also minimizes the amount of expensive,
dedicated floor space required for
performing multiple processes.