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ABB - System Programs Robot Work Cells |
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Industrial robots and work cells built around them have made great
strides in automating foundry operations, but with one big exception:
Cleaning castings, which remains the foundry's most labor-intensive
operations. In theory, robot-based automation is ideal for sawing off
gates and risers, deburring surfaces after those cuts, and removing
parting-line flash, especially in aluminum foundries.
However, other than for long runs—thousands or tens of thousands of
castings—programming the robot takes too long, often as long as two
weeks, during which the entire work cell is out of production. For long
runs, a two-week setup time is acceptable. But when runs are dozens or
hundreds of castings —increasingly the norm—the entire job may not take
two weeks.
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The problem in automating the cleaning of castings is the way robots
are set up for each new task. In this teach mode, the robot arm is
manually moved (or “jogged” with its controller) through each of
hundreds of points in 3D space, one point at a time. The robot’s
controller incorporates the point data into a task-specific program, a
sequence of arcs, distances, vectors, starts, accelerations,
decelerations and stops that mimic the way a human would do the job.
Because this must be done inside the work cell, i.e. “online,” it has a
big drawback. The robot must be taken out of production during the
programming. This is true whether the robot holds the casting or the
tool.
To solve this programming problem, ABB Automation Technologies /
Robotics in Sweden has developed an off-line programming system called
RobotStudio. RobotStudio makes it possible to do all the programming
off-line, to simulate workstations and to optimize programs without
interrupting the production.
ABB solved the problem with a breakthrough called TeachSaver that
automatically generates robot programs from strings of 3D coordinate
points. The points are gathered with a Stinger II™ portable coordinate
measuring machine (PCMM). After simulation and optimization in
TeachSaver the programs are downloaded to the robot in the work cell
when it’s available.
Equipped with a Renishaw touch probe, the Stinger II was developed to
gather 3D coordinate points for inspection, dimensional measurement and
reverse engineering. With a Stinger II incorporated into each
TeachSaver system by ABB, the time to program most casting-cleaning
jobs can be reduced to less than four hours.
This means that the time needed to program complex tasks off-line has
fallen by as much as 90 percent, and marketing managers at ABB Robotics
are delighted with the results. With a Stinger II interfaces to
TeachSaver, their customers now have a fast and robust way of gathering
reliable 3D point data for off-line programming systems.
When programming and performance tests and debugging are done in an
office, away from the work cell, production can continue uninterrupted.
TeachSaver programs can be cloned and shared whenever multiple cells
are being set up to do identical work; some recalibration will probably
be needed.
In turn, that opened a huge number of short- and medium-run foundry
production tasks to robotics, from dozens to several hundred castings.
Within weeks of the system’s final approval, ABB was quoting dozens of
applications in foundries around the world.
For ABB, the biggest opportunity lies with cleaning castings in sand
and permanent-mold aluminum foundries. With Stinger II and TeachSaver,
these hard, dirty, noisy and occasionally hazardous tasks can now be
economically robotized.
The business opportunity of this essentially untapped market is huge by
any measure. ABB estimates that 300,000 people work under unpleasant
conditions in foundry cleaning departments—200,000 in Europe and
100,000 more in North America.
ABB expects robotization of foundry cleaning operations will eventually pay off big for its foundry customers through:
• Fewer worker’s compensation and disability claims as these dirty and dangerous jobs are automated.
• Less difficulty recruiting good workers; like every other
manufacturer, foundries must deal with rising labor costs while
customers demand lower prices.
• More consistent part quality.
• Lower scrap and reclaim / rework rates.
About 80% of the work of cleaning castings is still done manually, ABB
calculates, despite high levels of automation and robotics nearly
everywhere else in foundries. To put this new market in perspective, in
its three decades in business, fewer than 11,000 ABB robots have been
installed in foundries.
To achieve true off-line programming, RobotStudio utilizes ABB’s
VirtualRobot Technology, a copy of the robot controller. The linked
technologies have long been instrumental in automating long production
runs of castings for the automakers, especially for the heaviest parts
such as engine blocks, heads and transmission housings. (ABB also
offers its own high-level programming language, RAPID, and an Internet
browser-based package called WebWare for local and remote monitoring
and control of production.)
These advances have allowed programming to be done in the engineering
office for many years while production continues rather than in the
work cell. But until TeachSaver and the Stinger II PCMMs were joined,
there was no quick and easy way to generate process points and there
were no foolproof methods for calibrating the locations and
orientations of tools and workpieces.
Teaching a robot to do a single complex task like cleaning castings
takes up to 100 hours, during which the robot produces nothing and the
work cell’s output is zero. “Until now, that was why only long
production runs were economically feasible for robotic cleaning,” said
Per Astrom, TeachSaver specialist at ABB Robotics headquarters in
Vasteras, Sweden.
“By using TeachSaver, the robot and work cell can be kept in
production,” he added, noting that off-line programming, by itself,
typically boosts uptime in foundry cleaning cells to 80 percent from
60, a one-third increase in output. Even optimizing programs for cycle
time can be done with TeachSaver, along with calculating tradeoffs
between robot reach and part weight.
“The economic order quantity (EOQ) of castings for cleaning has now
been sharply lowered,” Astrom added. “That accounts for the
multiplication of the potential size of the market.
“The biggest part of the savings comes from not having to go back and
forth to the fixed-in-place coordinate measuring machine (CMM) to
fine-tune the robot's program,” he pointed out. “Tuning just one robot
program can take several days,” not counting queue time if the CMM is
overloaded. This is why ABB insisted on a PCMM to go with TeachSaver,
The interface between the Stinger II controls and RobotStudio was
developed in mid-2003 at ABB’s Northeastern U.S. regional application
center in Windsor, Connecticut. The Stinger II interface was developed
with the ActiveX applications programming interface (API) in
TeachSaver. ActiveX makes it very easy to write code modules for
external devices, ABB said, and any necessary interpolation or
translation of the 3D coordinate points gathered by the PCMM is done in
TeachSaver.
Among the reasons why the Stinger II was chosen:
• Accuracy. “Basically the portable CMM arm needs to be just a little
bit more accurate than the robot’s repeatability, which is between 0.1
and 0.2 millimeter,” Astrom said. “The Stinger II gives us that and a
lot more.”
• Price. “Other arms that could do the job were as much as three times
more expensive than the Stinger II and still were not as accurate,”
Astrom said.
• Ease of use. Another firm’s coordinate point data was in a hard-to-handle format, ABB engineers said
Automating those some of those 300,000 jobs is already getting under way. For example:
Cleaning turbine blade and vane castings for a large U.S. jet engine
manufacturer, an application developed at ABB’s application center in
Windsor. This low-pressure, permanent-mold operation was the initial
application of the Stinger II and TeachSaver.
Cleaning die castings, a turnkey-systems approach built by Rimrock
Corp., Columbus, Ohio, and its Rimrock Automation Inc. unit in New
Berlin, Wisconsin. As ABB’s largest systems integrator in North
America, Rimrock focuses exclusively on high-pressure die-casting.
A sand-cast cylinder head was programmed for cleaning with over 1,000
points located and entered in four hours. The job was done by long-time
ABB systems integrator Laempe GmbH in Germany.
The technical skill required for TeachSaver users is not trivial,
Astrom pointed out. Programmers need to know how to work with robots
manually or off-line, including the key task of gathering coordinate
points with a PCMM.
Programmers must also have experience with speeds, RPMs and traverse
rates appropriate to the sizes and types of robots used in foundries.
Skill with foundry cleaning tools is also needed to optimize operations
for tool life and cleaning quality. “If cleaning is not done correctly,
the tools can be destroyed,” said Astrom. “Part of the casting might
even be melted.”
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CIMCORE
a brand of ROMER Inc.
a Hexagon Metrology Company
51170 Grand River Ave.
Wixom, MI 48393
Toll Free Phone: 800.218.7125
Phone: 248.449.9519
Fax: 248.449.9445
sales@cimcore.com
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