Poka-Yoke or Mistake Proofing

Poka -yoke is a Japanese improvement strategy for mistake proofing to prevent defects from arising during production processes.

It’s aim is to achieve ‘zero defect’

WHAT IS POKA-YOKE ?

Developed by Shigeo Shingo in 1961

Poka means mistakes yokeru means avoid

Poka-yoke refers to techniques that make it

impossible to make mistakes.

Poka-yoke techniques can drive defects out

of products and processes and substantially

improve quality and reliability.

Characteristics

Errors can be of any type-i. Processing Error: Process operation missed or not

performed per the SOP.ii. Setup Error: Using the wrong tooling or setting

machine adjustments incorrectly. iii. Missing Part: Not all parts included in the assembly,

welding, or other processes.iv. Improper part/item: Wrong part used in the process.v. Operations Error: Carrying out an operation

incorrectly; having the incorrect version of the specification.

vi. Measurement Error: Errors in machine adjustment, test measurement or dimensions of a part coming in from a supplier.  

ERRORS

PREVENTION BASED

Prevents the defects from occurring

DETECTION BASED Detects the defects and prevent its

progress

TYPES OF APPROACHES

CONTROL METHOD

This method senses a problem and stops a

line or process, so that corrective action can

take place immediately

EXAMPLE: Assembly operation in which one

component is missing before actual

assembly whole operation is stopped

PREVENTION BASED

This method signals the occurrence of a deviation or trend of deviations through an escalating series of buzzers, lights or other warning devices

This method does not shut down the process on every occurrence

WARNING METHOD

CONTACT METHOD This method detects any deviation in shape,

dimensional characteristics or other specific defects, through mechanisms that are kept in direct contact with the part

Fixed Value Method: This method is used in operations, where a set of steps is sequentially performed.

A sensor counts the number of times a part is used or a process is completed and releases the part only when the right count is reached.

DETECTION BASED

Motion Step Method: This method ensures that a process or

operator does not mistakenly perform a step that is not part of the normal process.

An example of this is colour coding of electronic components on drawings and totes to prevent using mixed or incorrect parts.

Remove defect from root cause or source Faster detection and correction Lesser attention from workers/operators Improve safety of workers Improves equipment effectiveness and

assures higher reliability

Advantages

Requires special expertise on instrumentation knoweledge

Implementation cost is high Training of workers is a must which adds the

cost

Limitations

CASE STUDY