Poka yoke

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Poka yoke
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Poka yoke (ang. mistake proofing, error proofing) is an action or improvement to the process or product, which helps to significantly reduce the opportunity for error (human mistake) either by making it more difficult to produce a defected product during production process or by making mistake so obvious, that it will be eliminated before product leaves the factory and reaches customer.

Mistake proofing is very popular these days. It is not limited to production. There are special solutions for services, programming, car driving, etc.

Poka yoke is one of Lean manufacturing pillars, together with: Konnyaku stone, Jidoka, Hansei, Andon, Just in time, Heijunka, Kaizen, Genchi genbutsu, Nemawashi.

Who invented Poka yoke?

Poka yoke was used for the first time in 1961 in Japan. It's creator was Shingeo Shingo, engineer in Toyota. He suggested that workers, even the most involved, will make errors when they are tired or not concentrated. New solutions were intended to make errors impossible.

Poka yoke meaning for the company

Poka yoke brings many advantages to the organization:

  • shorter time required for training,
  • less inspection required,
  • often repeated operations are less involving,
  • promotion of continuous improvement
  • reduction of defects
  • detection direct on workplace, not later in process

Poka yoke solutions

Shingeo Shingo determined several solutions that can help workers to perform their work correctly:

  • Regulatory functions
    • Control methods - in case of defect, the machine is stopped. Worker has to manually remove product and start the machine.
    • Warning methods - in case of defect, aural or light signal turns on, but the machine still works. The worker has to stop it manually.
  • Setting functions
    • Contact methods - machine has detectors that are able to detect wrong installation of element by worker, wrong colour, weight, temperature, etc.
    • Fixed value methods - the defect is detected if worker didn't perform exact number of movements or didn't use exact number of elements, e.g. took too few screws from bin. This requires photocell or other utility.
    • Motion step methods - detection is based on time, e.g. the element won't leave the workplace if photocell didn't noticed taking a screw from bin.

Poka yoke examples in everyday life

Nowadays, the poka yoke is widespread. Everyone meets poka yoke solutions everyday, e.g.:

Computers

Poka yoke examples

  • colors of plugs correspond to colors of sockets in desktop computer
  • USB plug cannot be inserted inversely
  • Ethernet plug cannot be inserted into other socket
  • SATA disk plug cannot be inserted inversely

No poka yoke / not full poka yoke examples

  • USB plug can be inserted into ethernet socket, especially in laptops

Other examples

  • SIM card in your telephone cannot be inserted inversely
  • Frying pan can have temperature indicator (red dot) which signals correct working temperature
  • On many roads, before tunnels special gates are installed in order to stop too high trucks
  • Modern cars and modern gas stations have solutions that limit possibility of inserting wrong fuel nozzles into fuel fill
  • In modern car you cannot forget fastening your seatbelt. Unless you're deaf.
  • In car with automatic transmission you cannot take start engine until setting Park mode or Neutral.

No poka yoke example

  • Credit card can be inserted in 4 ways into ATM machine, while only one is proper. The ATM software detects it and returns the card.

References

Author: Slawomir Wawak