Posts tagged “Poka-Yoke

If it’s worth doing, it’s worth doing right

I’ve been doing some thinking about “Continuous Improvement” lately and was lucky enough to find a Dope Sheet with an example of Poka-Yoke, a technique that makes it impossible to make mistakes. More accurately, the image above shows Joe getting ready to use a headspace gauge to adjust the distance between the face of the bolt and the base of the cartridge case on a caliber .50 HB machine gun, M2. You didn’t know that by looking at it? Well, I might as well admit that I had to look up a few things on the internet. According to an online manual I happened to find, “Firing a weapon that has improperly set headspace and timing could result in damage to the machine gun, or injury to the gunner”. By reading the limerick, you can guess that some soldiers were adjusting the headspace by “ear” or “pre-arranged marks” and mistakes were likely made that could have led to failures and/or injuries.

A Poka-Yoke can be as simple as the go/no-go gauge shown above (a two-sided tool for checking tolerances of a part or assembly) or as complex as a set of limit switches that prevent a drill press operator from drilling a hole too shallow or deep. One of my favorite examples of a Poka-Yoke is a gas cap. In this one item are two separate ways to prevent you from making a mistake. One, is the lanyard that keeps you from driving off without your gas cap and the second is the ratchet mechanism that keeps you from over-tightening the gas cap and damaging something or keeping you from getting it off the next time you fill up. If you count the entry to the gas tank in this example, you can add the different diameters of gas pump fill nozzles that prevent you from filling up your unleaded gas car with diesel fuel.

Here are some steps you can take to implement a Poka-Yoke in your area:

  1. Look for a process or operation that is a leading cause of production loss, waste or equipment downtime. Use a Pareto chart or other tool to identify one that has lots of room for improvement.
  2. Apply Fault Tree Analysis or some other fault finding tool to identify all of the ways the process or operation can fail.
  3. Decide on a Poka-Yoke technique to use. Here are some approaches:
  4. Shut Out – Does not allow an error to occur
    Attention Type – Alerts that an error has been made
    More comprehensive – A combination or an alert to keep an error from happening

  5. Test it in the field to see if it works or if some adjustments need to be made.
  6. Train the users, review the performance, measure the results and publicize the success.

I recently has reviewing an adjustment procedure on a vehicle that described ensuring a gap of .25″ – .38″ between a door and a jam. I was made aware of the adjustment procedure after reports of the doors not closing properly and causing increased dwell time at the stations and decreased carrying capacity. There happened to be 24 doors on each vehicle and 12 vehicles in the fleet. Using a tape-measure or scale would have taken the craftworker forever and it still wouldn’t have eliminated the possibility of missing the dimension. I felt this was a great opportunity to create a go/no-go gauge for the craftworkers to use. Now, a quick check at a few points around the door with both sides of the gauge ensures that the doors are adjusted properly.

Does anyone have any good examples of a Poka-Yoke in their area? How about one that maybe didn’t work? What happened and what did you do afterwards?

[added 6/11 – After publishing the above post, I continued to do some research into continuous improvement and was slightly dismayed to learn that a go/no-go gauge is, technically, not a Poka-Yoke. Since it relies on the operator to remember to use it, it will not guarantee a mistake cannot be made. My apologies.]