Poka-Yoke is a Japanese strategy for mistake-proofing that aims to prevent defects during production. It focuses on identifying and eliminating sources of variation that can lead to defects. Examples include fixtures that only allow correct part orientation or counters that check the number of spot welds to ensure quality. Implementing Poka-Yoke can help reduce costly defects and failures, especially for safety critical products. Common approaches use contact, fixed values, or motion steps to detect and prevent mistakes from occurring.

1. Poka-Yoke
• Poka-Yoke is a Japanese improvement strategy for mistake-proofing to
prevent defects (or nonconformities) from arising during production
processes.
• Poka-Yoke is a preventive action that focuses on identifying and
eliminating the special causes of variation in production processes,
which inevitably lead to product nonconformities or defects.
For example, a fixture that holds pieces for processing might be modified to only allow pieces to
be held in the correct orientation, or a digital counter might track the number of spot welds on
each piece to ensure that the worker executes the correct number of welds.

2. Why Poka-Yoke?
• Manufacturing defective products can be very costly. Some customers
will return a whole batch of parts if they find just one of them to be
defective. And some products are manufactured for safety critical
applications in motor vehicles, aerospace and oil exploration etc.
• A failure in these areas can have very serious consequences and
potentially cause loss of life.

3. Relationship of defects and human errors

5. Benefits of Poka-Yoke

6. Principles of Mistake-proofing/Poka-Yoke

7. Prevention vs Detection
A Prevention-based Poka Yoke system acts before a defect occurs. The Poka Yoke mechanisms sense an
abnormality that is about to happen and then signal the occurrence.
A Detection-based Poka Yoke signals the user when a mistake has been made. The system does not allow
continuation of the process so that the user can quickly correct the problem.

8. Approaches for Poka Yoke devices
• Control Approach: This approach senses a problem and stops a line
or process so that corrective action can take place immediately, thus
avoiding serial defect generation.
• Warning Approach: This approach signals the occurrence of a
deviation or trend of deviations through an escalating series of
buzzers, lights or other warning devices. However, unlike the control
method, the warning method does not shut down the process on
every occurrence.

9. • Poka-Yoke devices consist of three effective methods to ensure detection
and prevention of mistakes: 1.Contact method 2. Fixed-Value method 3.
Motion-step method; Each method can be used in Control approach or
Warning approach.
1. Contact method detects any deviation in shapes, dimensions, forms,
position or other physical characteristics through mechanisms that are kept
in direct contact with the part. Contact method can be used in situations of
rapid repetition, infrequent production or environmental problems such as
poor lighting, critical temperature, dust, noise and so on.
2. Fixed value method is used in operations, where the same activities is
repeated several times. The method employs automatic counters or optical
devices and controls the number of moves, rate and length of movement as
well as other critical operating parameters.
3. Motion step method is useful for processes requiring several different
activities performed in sequence by a single operator. The method ensures
that the operator dose not mistakenly perform a step that is not part of the
normal process.

11. Examples of Poka Yoke Used in
Manufacturing/Assembly Process

13. How to Implement?