John Slupsky, Scott Peabody, Tim Kunze

Texas State University, San Marcos TX, 78666

Introduction

Place a quarter on a flat surface. Now, as best as you can,

place a dime concentrically overtop. It can be guaranteed,

to some degree of accuracy, that the two coins are not

perfectly concentric. This infuriating statement hinges on

the inaccuracy of visual alignment. So, how can

concentricity be achieved?

A poka-yoke (otherwise known as fool-proofing) is a

mechanical aid that can reliably take the guess-work

out of (coin) alignment.

The question is, how to design such a thing?

Caterpillar asked this very question, when faced with a

similar alignment problem on its production line. A pressing

operation relied on visual alignment, and was producing

out-of-spec assemblies. These assemblies were either

offset, or had an uneven/wrongly sized resulting gap.

Such assemblies were scrapped. A (poka-yoke) fixture

was desired to fix the problem.

Planning & Report

Find Best Design

GenerationSelectionBrainstormSketchCADH. of Quality

Build

DraftingCADPrototypeMaterials3D PrintMachine

Test

ProblemsSolutionsImprovement

Results

Mechanical stops

• Held in place by the fixture

• Prevent over-pressing

Alignment pins

• Nest inside mechanical stop

• Protrude through adapter plate

• Provide guidance for the mount

Plastic thread protectors

• Thread into the mount

• Protect mount threads

Pressing operation setup before modification

Conclusion

Although using a mechanical method is

slower and requires more operator

activity than a visual method, it is a sure-

fire way to achieve accurate alignment.

By controlling operation alignment and

final gap size via poka-yoke, we were

able to save Caterpillar money by

lowering the scrap rate at this particular

station.

Over-pressing

Mount guidance

Thread damage

Assembly purpose

Next StepsA new press-head was designed to

combine the prior operation with this one;

pressing dowel pins into the sides of the

adapter plate.

CAD drawings and manufacturing

procedures for this design will be

recommended. Cost is currently the main

prohibiting factor from manufacturing.Uneven gaps can be fixed with mechanical stops

Acknowledgements

Naveen Laxmaiahgari – Sponsor

Sagar Navle – 3D printing

Dr. Austin Talley – Advice / feedback

Roller Plunger Switch

• Bolted to the fixture

• Prevents over-pressing

• Prevents damage