Poka-Yoke

A Japanese manufacturing term that means “mistake-proofing”, a poka-yoke is a device that uses constraints to eliminate the possibility of operator error. It is a fundamental element of standardized work.

Key Takeaways

  • Behavior-based constraints end up reducing operator error

  • Popularized by Toyota Production System in Japan

  • Poka-yoke means "fool-proofing" or "mistake-proofing"

A poka-yoke doesn’t need to be fancy or computational in order to work. It can be as simple as a child-lock on a cabinet, for example. Another great example of a poka-yoke is the gear shift in automatic cars: shifting gears from Neutral to Drive (or Reverse) requires a physical manipulation of the stick in order to cause a result. Other common poka-yoke examples include microwaves and washing machines, which can’t be turned on while the door is still open as a safety measure.

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Shigeo Shingo coined the term “poka-yoke” in the 1960s when he advocated for TPS (Toyota Production System). It was inspired by a common error he caught: assembly workers would occasionally forget to place a small spring underneath a button, and the product would fail to operate as intended. Shingo corrected this problem by adding an extra step — a poka-yoke — where the worker would have to first place the springs in a special holder before assembling. With one quick glance at the special holder, a worker can instantly double-check that they had installed the finicky screws.

Benefits and Results of Poka-Yoke

Since a poka-yoke is an adaptable tool rather than a strict methodology, it can be adopted almost anywhere in manufacturing settings for quick and long-lasting results. The top benefits include:

  • More efficient training time, and less time training overall
  • Better, built-in quality control
  • Less laborious tasks for assembly workers mean more interaction and stimulation on the job
  • Immediate response time to errors
  • Lower chance of defects in finished products
  • Increased safety while operating equipment
  • Behavioral angle means good habits become "muscle memory" over time

3 Types of Poka-Yoke

Since a poka–yoke can be as simple as a doorstop or as complicated as an automatic braking system, it is helpful to classify any poka-yoke into one of three categories:

1. Contact method

The contact method identifies defects by quantifying physical qualities of the product. Qualities can be assessed by shape, size, color, weight, or any other exact physical measurement. These data points can be captured manually or with the help of smart IoT scanners.

2. Fixed-value (constant number)

The fixed-value method, also known as the constant number method, requires the operator to perform a certain number of steps or movements. An example of this would be rules engines in digital work instructions, which require the operator to input data or perform certain actions to prompt the next consecutive step in the process.

3. Motion-step (sequence)

Also known as the sequence method, the motion-step method proactively corrects defects by requiring the operator to perform actions in a set permutation, or specific order. A great example of a motion-step method is a combination lock, where you can know the correct set of numbers, but you must also input them in the correct sequence in order to open the lock.

A Human Solution to Natural Mistakes

A poka-yoke is a unique tool in the manufacturing manager’s tool belt because it addresses behavioral habits and awareness of employees in the workplace. Even the most diligent and dedicated employees make innocent mistakes, and other management strategies like quotas or regular productivity rankings can be damaging to team morale. Also, these solutions fail to address the actual problems at hand, which are accidental mistakes due to human nature and adopted out of habit or necessity — perfect for a poka-yoke.

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