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86 The PCB Magazine • June 2015 as close as you can come to bullet-proofing a process. These solutions truly design out the potential for producing an error or defect. A common example that everyone can relate to is the polarized plug on electrical devices. One blade is wider than the other, which matches up with a corresponding polarized outlet. This effectively makes it impossible, short of damaging the outlet, to place the plug into the outlet incorrectly. Figure 1 shows an example specific to the printed circuit manu- facturing industry: the four-slot offset tooling system which makes it impossible for an opera- tor to place a panel onto a machine incorrectly. As a side note, it is interesting to once again observe the generational impact that technology has had on us all. In my university classes, I often use the 5-¼ inch floppy disk as an example of a product that has been poka- yoked. With the proliferation of CD/DVD burning and jump drives, I am still surprised at the number of deer-in-the- headlight looks from traditional students (students right out of high school) when I mention a floppy disk. (By the way, the clipped upper right corner as - sures that the disk can only be inserted one way.) Warning System: Sometimes an automatic shutoff is not a viable option, so warning sys- tems are implemented. Lights, buzzers, beeps, messages, etc., can be utilized to alert the oper- ator of a potentially undesirable condition. As you might imagine, the warning system is not as bullet-proof as the control system; it requires the operator to take some action in response to the warning. A perfect example would be your vehicle, which is loaded with bells and whistles to alert the driver when some action is needed. Remember that a good poka-yoke removes the human element. The flaw in this system is, for example, that when the oil light goes off, there is nothing forcing the driver to get the oil changed. Though not as robust as the control system, it certainly is the next best option in cases like this where shutting down the process is not feasible (you wouldn't want your vehicle to shut down every time a warn - ing light goes off). The following are some common error- proofing devices within these systems that can be used to poka-yoke your process. Check lists, dowel and locating pins, error & alarm detec- tors, limit or touch switches, detectors/readers/ meters/and counters, non-symmetrical tool- ing/fixturing. When to Use Poka-yoke can be used wherever some- thing can go wrong (basically anywhere a human is involved). It is a a tool that can be applied to any type of process be it in manu- facturing or the service industry. Numerous error types are perfect for a poka-yoke solu- tion, including: • Processing error: Operations or tasks missed or not performed • Setup error: Using the wrong tooling or improper machine settings • Missing part(s): Not all parts included in the lamination, plating or other processes • Improper part/item: Wrong part or revision used in the process • Operations error: Carrying out an operation incorrectly • Measurement error: Errors in inspection, test or dimensions of a part, either internally or from a supplier The Three Rules of Poka-Yoke 1. Don't wait for the perfect poka-yoke. Do it now! 2. If your poka-yoke idea has better than a 50% chance to succeed…Do it! 3. Do it now…improve it later! Following these three rules will give you an excellent chance of success as you look to poka-yoke your process. PCB BEST PRACTICES 101, PART 8: POKA-YOKE continues Point oF View Steve williams is the president of Steve williams consulting llc and the former strategic sourc- ing manager for Plexus corp. He is the author of the books, Quality 101 Handbook and Sur- vival Is not Mandatory: 10 Things Every cEO Should Know about lean. To read past col- umns, or to contact williams, click here.