Robot logic: slower line speed, higher output Essay

Engineers at Fisher Guide, Div of General Motors Corp, Columbus, OH,
automated a nine-press production line to manufacture door-frame
reinforcements for midsize cars. In retrofitting a fully automated
system for the nine presses, the firm installed 10 robots, eight
positioning fixtures, and a variety of sensors. As a result, line speed
had to be reduced from 290 to 275 pcs/hr. The slower rate, however, was
more than offset by extended uptime through breaks, lunch hours, shift
changes, and a third shift–thus producing a steadier and longer flow of
good parts.

There are already many secondary benefits. “We have reduced
scrap rates because there are fewer mishits,” says Ralph Smith,
superintendent of productivity engineering at the plant, “and our
production supervisor says that the need for die maintenance is reduced
considerably because of more precise die loading.”

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The Fisher Guide-Columbus press line is tended by GMF’s
cylindrical coordinate M-1A robots. One operator oversees the entire
140-ft press line, although the system doesn’t need 100-percent
surveillance. “At the end of the second shift,” Smith
explains, “we load the bank of blank pallets, and the line will run
untended until it faults, or all of the pallets have been emptied.”

Blanks are presented to the first robot by a nonsynchronous
indexing conveyor equipped with 12 pallets, each holding nearly 100
pieces. Each 9″ X 12″ blank weight 1-1/2 lb.

Electric choice for light parts

Size and weight of the part have a lot to do with the robot chosen
for an application. Smith remarks, “Our parts are light. Electric
robots are the only way to go as far as we’re concerned. The
electric robots are less costly, have greater accuracy, require less
preventive maintenance, and have higher uptime than hydraulic

The first robot, equipped with vacuum grippers, senses the top of
the stack with a limit switch. A fiber-optic sensor also detects
whether there are any remaining blanks on the pallet. If there are
none, another pallet indexes into position.

As this robot turns to load the forming press, it passes the blank
through the rollers of a sensing device mounted near the die opening.
This sensor verifies that there is only one blank. If more than one
blank is sensed, the robot discards the “batch” and goes back
to pick up another. Upon confirmation of a single blank, the robot
loads it into a draw die that creates the basic part form.

The second robot unloads the part and immediately turns to load a
gap press for restrike. It then removes the part and places it on the
first staging fixture. The third robot moves the workpiece from this
fixture to the next press, then to the next fixture. Robots 4 through 9
repeat this action, transferring the part through trim and pierce dies.

The operation at the ninth die is the slowest. To minimize its
effect on total line speed, the die was altered so the gripper can stay
in the die area during the press cycle. The press doesn’t have to
wait for it to retract. Instead, the arm merely relaxes its grip on the
workpiece during the press stroke. In some other stations, engineers
had to give the dies slightly more clearance so the end-of-arm tooling
would fit while inserting or removing the workpiece.

The last staging fixture collects four finished parts before a
signal is sent to the 10th robot for palletizing. Standard GMF palletizing software allowed several pattern alternatives. With
mechanical grippers, the 10th robot grasps the stack of four parts and
palletizes them in shipping containers. Tooled with vacuum grippers,
the robot separates layers of parts with cardboard sheets. When one
basket is full, a flashing red light alerts the operator, and the robot
immediately begins palletizing in the empty alternate container.

Orienting fixtures

Staging fixtures are integral elements in this automated press
line. Equipped with 90-degree or 180-degree rotating axes, they orient
workpieces for proper loading in the dies. Without this intermediate
orientation, each robot would need additional axes.

The last fixture incorporates a fiber-optic sensor to check the
quality of the first part placed on the stand. It senses if all five
holes are pierced, eliminating the need for visual part inspection and
minimizing the chances of running the line with a broken punch or
button. The system automatically shuts the line down if it detects a
missing hole.

A programmable logic controller (PLC), with elaborate interfacing,
coordinates all communication and most work within the line. The
controller displays location of a fault, whether it’s a press
fixture or robot that didn’t operate. This fault-diagnostics
system covers 128 possible errors. Its intelligent display scrolls
alphanumeric messages describing all 128 system errors to the operator.
Operators need troubleshoot only the origin of uncommon errors.

Move over for die changes

“Our production runs last about two weeks,” reports Gary
Hay, senior manufacturing engineer at the Columbus plant. “Eight
of the robots are mounted on a track. Before beginning a new run, we
can move the robots aside by removing four bolts and two locating pins.
One man can then easily push the robot aside to make room for die
changes.” This feature is also helpful for robot repair and

The entire 140-ft line is surrounded by an infrared light curtain.
When someone breaks a light beam by entering the work area, a signal to
the supervisory PLC instantaneously stops all equipment. Since there
are so many areas where a person could enter the work envelopes without
being seen, the light curtain consists of 15 zones. The operator must
reset the curtain where it was violated and return to the main
controller to restart the line. A loop chain keeps people from casually
entering the light-curtain area.

Smith notes that GMF was responsible for all automation, but robot
application involved joint cooperation between vendor and user.
“When we first istalled the robots and fixtures, order volumes
didn’t allow us to debug the line, so we made gripper, die,
electrical, and part-positioner revisions between manufacturing runs.
Ideally, as engineers, we wanted to debug the system before producing
parts. Instead, our system evolved with many changes after

For robot and automation information from GMF Robotcs Corp, Troy,
MI, circle E2.

Six-axis robot welding work cell

Foundation of a new work cell is the six-axis Cyro 1000 articulated
arm robot made by Advanced Robotics Corp, Columbus, OH. The sixth axis
eliminates the need for special torches or brackets which were
previously required to achieve the proper welding angle in many
applications. With the sixth axis, the proper torch attitude can be
maintained even while welding complex joint profiles.

Also, the robot reduces or eliminates the need for an indexing
table or multiple-axis positioner by providing more robot dexterity.
This reduces the work cell cost while providing maximum joint

The new unit features a weight carrying capacity of 22 lb at the
torch-mounting face plate, harmonic drive and ballscrews for smooth
motion, and demonstrated reliability (99 percent uptime with
approximately 4000 hr mean-time-between-failure). Working envelope
radius is 1400 mm, and the robot’s six-axis offset wrist design
provides a larger range of movement within that radius.

The work cell utilizes the recently introduced Cyro C-30 controller
with program shift and translation features designed to reduce
programming time. A CRT screen built into the C-30 control cabinet
displays English diagnostic messages and useful production data. The
C-30’s expanded teach pendant includes all programming and control
commands and controls the robot, the weld process equipment, and
associated positioning equipment.

Other key features include weld path weave capability, torch-angle
compensation, and the capability to manually fine-tune weld speed,
current, and voltage during program execution. Its offset wrist design
eliminates interference of the torch body with the arm, thereby
providing improved range in the tilt axis. The work cell can be
equipped with an X-axis rail system to greatly expand the work envelope.
Standard configurations come in 2.5-, 5.0-, and 7.0-meter lengths.

For more information, circle E34.

End effector combines welding and material handling

Retooling a single function robot to perform a dual-function task
can maximize efficiency of an application. The DeVilbiss Co, Toledo,
OH, accomplished this for JI Case by designing an exclusive gripper
assembly for the EPR-1000 arc-welding robot (see photo and sketch). The
retooled assembly houses two welding torches and a pneumatic gripper.

When Case approached DeVilbiss, as well as several other robot
builders, the concept of an integrated robot system that could both
pick-and-place and weld hadn’t yet been developed. John Treuschel,
manager of process automation at DeVilbiss, explains that the small part
size made it possible to combine both functions. “Our primary goal
was to design a gripper that could be integrated with an arc-welding
robot and perform both functions with accuracy and repeatability. The
entire system would have to locate, clamp and transfer parts, then weld
with two torches.”

The EPR-1000 is installed at Case’s Bettendorf, IA, facility.
Its assignment is to pick-and-place and weld encased nuts to steel
angles that will later be assembled into the Series 450, 850, 1150, and
1450 crawler bulldozers and loaders.

Case has three sizes of encased nuts (3/8″, 1/2″,
5/8″), and cages that are welded to more than 60 parts ranging from
12″ to 12 ft. The multiple combinations are a challenge for
repeatability, but by carefully programming the gripper to adjust to
each size, the robot successfully places each nut within 0.005″.

The process begins as the nuts and cages are manually loaded into a
gravity feed track that leads to the pickup station. Using a magnetic
fixture, the operator aligns and secures the angles on the welding
table. Once set, the operator presses the control button to rotate the
tabletop 180 degrees, positoning the angle in front of the robot.
Simultaneously, the robot’s articulated arm picks up the proper
nut, transfers it to the table, and places it over one of several holds.
The EPR-1000 then welds the encased nut to the angle with its two
torches, which are positioned on either side of the gripper.

To maximize efficiency, the table is equipped with two sets of
fixtures, allowing the operator to align and secure a second angle while
the robot is welding nuts to the first. When the robot finishes
welding, the operator again rotates the tabletop and replaces the
assembly with a new angle, while the robot welds on the other side of
the table.

Before the robot was installed, a single operator manually welded
each encased nut to the angles. Bill DeVenny, welding engineer at Case,
cites the advantage of automating, “Production rates are up 30
percent and reject rates are down 10 percent.”

As a result, Case is looking at additional applications. “Arc
welding is our primary interest,” says DeVenny. “In relation
to this need, we will be examining the potential of machine vision as a
means to automate even further. Robots are definitely a part of our
future plans.”

For more information about welding with robots, circle E61.


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