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.

Figure 1. As the target is being struck by the pinball, the stresses on the arm during impact are shown. High-speed video and analysis results confirmed that the drop target needed to be strengthened.
Using 3D modeling tools to create many of the typical game parts, Stern employs four mechanical engineers and numerous designers to create state-of-the-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.

Figure 2. After modeling the event, the part was redesigned. The hardware was changed, and while made of the same material, the target itself was flattened and simplified.
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.


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.

Motion Control Technology Magazine

This article first appeared in the April, 2006 issue of Motion Control Technology Magazine.

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