Poka Yoke | Mistake Proofing | Error Proofing | Lean Tool

What is Poka-yoke?

→ Poka-yoke means "error proofing" or "mistake-proofing". It came from the word "Poka" which means "mistake" and "Yokeru" which means "to avoid" and it is a Japanese term.
→  It is any mechanism in any process that helps for "mistake-proofing" or "error proofing".
→ We can eliminate product defects by preventing it, correcting it or detecting is as they occur.
→ It is one of the Lean Manufacturing Tools
→ This concept was adopted, by Shigeo Shingo as part of the Toyota Production System.
→ Shigeo Shingo used the word "Poka-yoke" in the 1960s for the prevention of human error during industrial processes design.

Examples of Poka-yoke

→ A simple example is when we start a car having a manual gearbox, we must have to press on the clutch pedal before starting.
→ This prevents us against the unintended movement or jerk of the car during the starting
→ Seat Belt wearing Indicator.
→ Auto-locking of the door at the certain speed of the car.
→ Bar code for correct product identification

Poka Yoke Examples



Implementation in manufacturing:

→ It can be implemented at any step of the manufacturing process.
→ We should implement this tool, where the possibility of something can go wrong or an error can be made.
→ It is a part of Lean Manufacturing

Steps of Poka-yoke Implementation:

  1. Identification Problems
  2. Prioritize
  3. Seek root cause
  4. Find and Implement solutions
  5. Measure the results


Types of Poka-Yoke:

→ Shigeo Shingo recognized three types for detecting and preventing errors in a process as mentioned below.

[1] The contact method:

→ The contact method identifies defects using a part’s shape, color, size, other physical attributes.
→ It can also include limit switches and proximity sensors.

[2] The constant number (or fixed-value) method:

→ When certain movements are not made then this error-proofing or mistake-proofing tool informs the operator this method is known as the constant number (or fixed-value) method.
→ Counters can be used for this at each step of the process as necessary.

[3] The sequence (or motion step) method:

→ This method ensures the sequence fo the process step before moving to the next step.
→ This is known as the sequence (or motion step) method.
→ The sequence method is not allowing the mistake to be made in the first place.
→ Example of sequence method is color coding and tagging and this parameter are checked at each step before moving forward.



Guidelines for Poka-Yoke:

  1. Quality Processes
  2. Utilize a Team Environment
  3. Elimination of Errors
  4. Eliminate the Root Cause
  5. Do It Right The First Time
  6. Eliminate Non-Value Added Decisions and Activity
  7. Implement a Continual Improvement Approach
[1] Quality Processes:
→ Make a robust process design for zero defect manufacturing.

[2] Utilize a Team Environment:
→ For any improvement, brainstorm with the teams so we can use their knowledge and experience to implement our improvement.

[3] Elimination of Errors:
→ Use various problem-solving methodologies or techniques for reducing defects and decrease defect to zero.

[4] Eliminate the Root Cause:
→ Eliminate the root cause of any problem by implementing this tool.

[5] Do It Right The First Time:
→ Make the process very effective to perform functions correctly for the first time.

[6] Eliminate Non-Value Added Decisions and Activity:
→ Identify all non-value added decisions and activities and eliminate them.

[7] Implement a Continual Improvement Approach:
→ We can not get 100% result in a single try.
→ So, implement improvement actions immediately and focus on continual improvements so we can get a 100% result.



Six Poka-Yoke Techniques for Error Proofing

  1. Elimination
  2. Replacement
  3. Prevention
  4. Facilitation
  5. Detection
  6. Mitigation
Six Poka-Yoke Techniques for Error Proofing

[1] Elimination:

→ Primarily focus on elimination
→ In Elimination, we have to eliminate the step that is responsible for the mistake
→ Remove Non-Value Added activities
→ Redesign the product and modification of the process (as applicable)
→ Examples: Replace manual data entry with barcode scanning

[2] Replacement:

→ If elimination is not possible the second option is Replacement.
→ In Replacement, we have to replace the step with a more reliable mistake-proof one
→ Automation of repetitive motion activities
→ Examples: Welding Robotics for an automotive manufacturer

[3] Prevention:

→ If the above two methods are not possible then the 3rd option is prevention.
→ Change product or process (as applicable) so that mistake is prevented.
→ Prevention is a physical barrier to prevent undesired action.
→ Examples: Safety guards on rides, Plugs for 110V & 220V, Printer cartridges and Go/No Go Gauges, etc...



[4] Facilitation:

→ If the above three methods are not possible then the 4th option is facilitation.
→ Facilitation is to help someone to take the right decision.
→ We can facilitate any process or product by visual controls like color coding, labels, lines, and signs, etc...
→ Examples: Warning signs, Checklists, Traffic lane markings, Color-coded parts or tools, etc...

[5] Detection:

→ If the above four methods are not possible then the 5th option is facilitation.
→ Detection is to identify or detect the wrong product or process immediately after it happens
→ We can provide detection by Sensors, limit switches, or light sensors
→ Examples: Safety guard limit switches to prevent machine running in an open condition, Computer warning if all information is not filled in

[6] Mitigation:

→ If the above five methods are not possible then the 6th option is mitigation.
→ Mitigation is to minimize the effects of mistakes or failures.
→ This method is used when the mistake cannot be eliminated
→ Examples: Personal protective equipment, Airbags in cars, Electrical Fuses, and An eraser on a pencil, etc...


Benefits of poka-yoke implementation:

→ Elimination of many operations related to quality control
→ Increase the motivation of an employee
→ Reduce the overburden of operators from repetitive operations
→ A reduced number of rejects
→ Immediate action when a problem occurs
→ 100% built-in quality control.
→ Less time spent on training workers
→ Promotion of the work improvement-oriented approach


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