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“Pinball Wizards” Bank on
Motion/Stress
Analysis
Software to Redesign
Game
Stern Pinball of Melrose Park, IL, is
the only manufacturer of coin-operated
pinball machines in the world.
Today, Stern’s pinball games are designed
using sophisticated computer simulation
software.
Using 3D modeling tools to create
many of the typical game parts, Stern
employs four mechanical engineers and
numerous designers to create state-ofthe-
art pinball machines. Each new
game takes about a year to design. Stern
employs 63 core staff members augmented
by up to 200 temporary employees
who produce up to 55 new games 
per day. Stern recently used finite element
analysis software from ALGOR,
Inc. (Pittsburgh, PA) to analyze a mechanical
assembly that was failing during
use in one of its games.
Stern designers ran into problems
with a part called the “drop-target assembly,” a mechanical assembly on the
pinball playfield. The assembly consists
of a plastic target that retracts beneath
the playfield when struck by the solid
metal pinball. The idea of the game element
is to strike the target and then
redirect the ball up the ramp to score
points. In the new game, the drop target
was placed, without backing, in front of
the ramp. When struck by the ball at
near-maximum speeds, the testers
found a high incidence of breakage in
the target.
John Rotharmel, Stern project engineer,
evaluated the drop-target design
using ALGOR’s Mechanical Event Simulation
(MES) software, which combines
large-scale motion and stress analysis,
and includes linear and nonlinear material
models. The combination of motion
and stress analysis considering full inertial
effects allows engineers to see motion
and its results, such as impact, buckling,
and permanent deformation.
Stern also purchased a high-speed
video camera and Rotharmel recorded
the action of the ball as it struck the
drop target. Engineers then compared
the high-speed video with the analysis results.
After several iterations, Rotharmel
successfully modeled the event quite
closely, and was able to confirm that the
drop target needed to be strengthened
before use in one of its recent games.
Results 
Using the results of the analysis, the
part was redesigned entirely, and the
new target assembly barely resembles
the previous part. The hardware was
changed, and while made of the same
material, the target itself was flattened
and simplified. Stern engineers also cut
the cost of designing and engineering
the part.
More Information
For more information on finite element
analysis and Mechanical Event Simulation
software from ALGOR, visit
http://info.ims.ca/5657-325.
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