Poka Yoke
ポカヨケ - pronounced "POH-kah YOH-keh"

Poka-yoke is Japanese for mistake-proofing. These mechanisms are used either to prevent the special causes that result in defects, or to inexpensively inspect each item that is produced to determine whether it is acceptable or defective. Poka-yoke can be used wherever something can go wrong or an error can be made.

Shigeo Shingo was one of the industrial engineers at Toyota who has been credited with creating and formalizing Zero Quality Control (ZQC), an approach to quality management that relies heavily on the use of poka-yoke (pronounced POH-kah YOH-kay) devices.

When to use it?

Poka-yoke can be used wherever something can go wrong or an error can be made. It is a technique, a tool that can be applied to any type of process be it in manufacturing or the service industry. Errors are of many types -

1 Processing error
Process operation missed or not performed per the standard operating procedure.

2 Setup error
Using the wrong tooling or setting machine adjustments incorrectly.

3 Missing part
Not all parts included in the assembly, welding, or other processes.

4 Improper part/item
Wrong part used in the process.

5 Operations error
Carrying out an operation incorrectly; having the incorrect version of the specification.

6 Measurement error
Errors in machine adjustment, test measurement or dimensions of a part coming in from a supplier.

Implementation

Shigeo Shingo recognises three types of Poka-Yoke:

  1. The contact method identifies defects by whether or not contact is established between the device and the product. Colour detection and other product property techniques are considered extensions of this.
  2. The fixed-value method determines whether a given number of movements have been made.
  3. The motion-step method determines whether the prescribed steps or motions of the process have been followed.

Poka-yoke either give warnings or can prevent, or control, the wrong action. It is suggested that the choice between these two should be made based on the behaviours in the process, occasional errors may warrant warnings whereas frequent errors, or those impossible to correct, may warrant a control poka-yoke.