3 basic Techniques of Poka-yoke

Poka-yoke is a Japanese word which means mistake proofing and it is explained in this article with examples. In this technique the system eliminates errors or make it impossible for errors to happen. We can see many examples of poka-yoke in our daily life like specific design of SIM card, they are explained in the later part of this article.

Background

Concept of poka-yoke is widely associated with Japanese quality leader Shigeo Shingo. Mr. Shingo recognized that human error does not necessarily create resulting defects. The success of poka-yoke is to provide some intervention device or procedure to catch the mistake before it is translated into nonconforming product.


Poka-yoke approach

There are numerous approaches(some are shown in Fig – 1). There are devises which can stop machines from working if a part or operation sequence is missed by the operator. A specialized tray can be used prior to assembly to assure that all parts are present, it acts as a visual checklist. Sensors are being used to ensure that machines work without any error and it detects any issue it will stop the operations. This will ensure that no defective part is manufactured.

Errors can occur in many ways:

  • Skipping an operation
  • Excessive variation in the process
  • Excessive variation in the inputs
  • Inaccurate measuring devices
  • Positioning parts in the wrong direction
  • Using wrong parts
  • Loose bolts


Mistake proofing can be accomplished through method by preventing human errors or by using a warning mechanism to indicate an error. Many mechanical screening devices can be used based on length, width, height and weight. Devices can stop machines from working if a part or operation sequence has been missed by an operator.

Some of the controls used to prevent human errors are:

  • Designing a part so it cannot be exchanged
  • Using tool and fixtures that will not load a miss-positioned part
  • Having a work procedure controlled by a sensor

A buzzer or light will signal that an error has occurred and immediate action is required. Team needs to do root cause analysis and corrective action before work resumes. Other than eliminating errors, mistake proofing is relatively inexpensive but needs to be carefully planned.

Examples of Poka-yoke used in our daily life:

  • Computer spell checker
  • Drop down box in a database
  • Gas cap attached to a car
  • Bar code for correct product identification
  • Seatbelt buzzer to warn drivers


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