The main objective of poke yoke is to achieve zero defects. In fact, it is just one of the many components of Shingo's Zero Quality Control (ZQC) system, the goal of which is to eliminate defective products. Poka Yoke is a quality management concept developed by a Matsushita manufacturing engineer named Shigeo Shingo to prevent human errors from occurring in the production line. Poka yoke (pronounced "poh-kah yoh-kay") comes from two Japanese words - "yokeru" which means, "to avoid", and "poka" which means "inadvertent errors." Thus, poka yoke more or less translates to "avoiding inadvertent errors".
Some people as "fool-proofing" sometimes refer to Poka yoke in English. However, this doesn't sound politically correct if applied to employees, so the English equivalent used by Shingo was "error avoidance." Other variants like "mistake proofing" or "fail-safe operation" have likewise become popular.
Poka Yoke is more of a concept than a procedure. Thus, its implementation is governed by what people think they can do to prevent errors in their workplace, and not by a set of step-by-step instructions on how they should do their job.
Poka yoke is implemented by using simple objects like fixtures, jigs, gadgets, warning devices, paper systems, and the like to prevent people from committing mistakes, even if they try to! These objects, known as poka yoke devices, are usually used to stop the machine and alert the operator if something is about to go wrong.
Categories of poka-yoke devices
Poka-yoke devices fall into two major categories: prevention and detection.
A prevention device engineers the process so that it is impossible to make a mistake at all. A classic example of a prevention device is the design of a 3.5 inch computer diskette.The diskette is carefully engineered to be slightly asymmetrical so that it will not fit into the disk drive in any orientation other than the correct one. Prevention devices remove the need to correct a mistake, since the user cannot make the mistake in the first place.
A detection device signals the user when a mistake has been made, so that the user can quickly correct the problem. The small dish used at the Yamada Electric plant was a detection device; it alerted the worker when a spring had been forgotten. Detection devices typically warn the user of a problem, but they do not enforce the correction.
Why is it important?
Poka-yoke helps people and processes work right the first time. Poka-yoke refers to techniques that make it impossible to make mistakes. These techniques can drive defects out of products and processes and substantially improve quality and reliability.
It can be thought of as an extension of FMEA. It can also be used to fine tune improvements and process designs from six-sigma Define - Measure - Analyze - Improve - Control (DMAIC) projects.
The use of simple poka-yoke ideas and methods in product and process design can eliminate both human and mechanical errors.
Poka-yoke does not need to be costly. For instance, Toyota has an average of 12 mistake- proofing devices at each workstation and a goal of implementing each mistake-proofing device for under $150.
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 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.