When industrial robotics were originally conceived, they were designed to use
hydraulic actuators and vacuum tubes. While functional, the applications for
these robots were limited. As technology progressed, the use of hydraulics
eventually gave way to faster and more precise electric servo motors.
Similarly, vacuum tubes were replaced by transistors and microcomputers. And
the various devices used to record the robot’s physical position have evolved
into resolvers and encoders.
As various robot manufacturers ramped up production, improvements to speed,
precision and reliability continued to ramp up as well. Lighter and more rigid
castings were used. These, along with higher precision gear boxes and servo
motors, have allowed robots to continue to shrink in size, handle larger
payloads and have a smaller footprint on the manufacturing floor. Applications
where hard automation used to be the only solution now have robotic solutions.
For instance, in the automotive industry, hard automation was used exclusively
to move parts of the vehicle or the entire vehicle from one line to another or
from one station to another. Now, robots can lift the entire vehicle and
reposition it as needed. This solution is considerably more cost effective
than hard automation and very easy to adapt to model changes or multiple
models on the same production line.
All of these robotic advancements help increase productivity, decrease cost of
ownership and reduce capital expense while also improving the useful life of
the machine. With these technological advancements, the industrial robot is
quickly becoming commonplace in manufacturing. These advancements are not
limited to the industrial environment. Manufacturers have developed humanoid
robots that can run, jump and even help in a variety of surgical settings.
Each of these diverse application areas are being absorbed as a whole across
the automation discipline. It’s these various advancements that have allowed
manufacturers to mount a laser to a robot and perform welding or cutting with
extreme precision and versatility.
Laser Advances
Lasers have also evolved in many ways from their early beginnings. The power
range of lasers started from less than 1 W back in the 1960s to being pushed
to 2 trillion W today. The newer fiber lasers have made a huge impact by
reducing cost and size while also improving beam quality, reliability and
efficiency.
By using beam splitters, a single laser generator can be used for both cutting
and welding. Beam splitters allow a single generator to use different fiber
delivery sizes to optimize the process for different materials or material
thicknesses. Previously, these processes may have required dedicated hardware
for each.
Also, advancements in optical heads and optical fibers have made it more
possible than ever to apply a robotic arm.
Along with the advancements in laser hardware are some equally impressive
features in software. For instance, greater control over the power output and
varying the available power across a larger range are now possible. The output
can also be pulsed and the power, duration and frequency of the pulses can be
varied. In welding applications, this allows better control of the penetration
depth and profile and minimizes the surrounding heat-affected zone, making for
a higher quality weld. All of these parameters cannot only be controlled by
the robot, but can also be monitored by the robot for process and quality
control.
The robot also has the ability to directly couple the output power of the
laser to the travel speed of the tool center 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.
There are also low-powered lasers that guide the robot along various seams or
patterns in the material so that the robot 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.