Quality

Lean Learning’s #5 Poka-yoke

The concept Poka-yoke was originally developed as part of the Toyota productions system by  Shigeo Shingo. it is a Japanese term that means “mistake-proofing”.  By interestingly it was originally named “baka-Yoke”, which has the meaning “Fool-proofing”, but this was quickly changed to the less offensive form.

The name is derived from two Japanese words, Poka meaning “Mistakes” and Yokeru meaning “avoid” and really is applied to any mechanism in a lean manufacturing process that helps an equipment operator avoid making mistakes.  Its purpose is to stop the process at the point where a defect occurs. This has two effects. Firstly and most obviously, it stops the defect from being passed on the other processes further down the
line. But also, secondly it allows an error to be investigated at the very point and time the defect originated. This makes problem solving much easier and allows ‘counter-measures’ to be put in place, thus improving quality.

There are 3 main types of Poka-yoke device:

  1. Contact type, which is designed to identify defects by testing the  product’s shape, size, color, or other physical attributes.
  2. Fixed-value type, which is designed to alert the operator if a certain number  of movements are not made.
  3. Motion-step (or sequence) type,  which tests if the prescribed steps of the process have been followed.

Poka-Yoke and its use is not reserved for business. Examples can be seen in everyday life. Here’s just a few:

Fill a car with Fuel. Look at the area around the Filler flap. There are at least 3 examples of Poka-yoke devices present.

  1. The size of the nozzle varies depending on the type of fuel to stop unleaded being put into a diesel. But you can make the error the other way around, so this is not a perfect example.
  2. When you take the fuel cap off, the cap is tethered to the main body, stopping the motorist driving off having left the cap on the roof!
  3. The Cap is fitted with a ratchet to prevent over tightening.

Circuit breakers in houses are designed to prevent electrical overloads . When the load becomes too great, the circuit is broken.

Computer Leads, Look at the back of any computer and you will see a plethora of leads. All of the leads have different type plugs on them to stop them being fitted into the wrong socket.

ATM Machines, return your card before your cash is dispensed to stop you forgetting it. This one works on the basis you are unlikely to forget your cash !!!

In the UK 240v/50Hz electricity is used. This can injure people so electrical plugs are designed so that live electrical pins are never exposed. Two forms of Poka-yoke are used here:

  1. The ‘3 pins’, Live, neutral and earth are positioned and orientated are such that the plug can only fit one way in the socket.
  2. The pins are insulated near the plug body so that electric shock is not possible when the plug is being  pushed in, this also means that if the plug is not fully inserted the current will still pass, but electric shock is not possible since only the insulated portion of the pins is exposed.

Of course there are many more, but I hope this gives you a few examples you can use in lean training courses, or just impress people at a party with your knowledge of Poka-yoke !