Poka-Yoke

What is Poka-yoke?

Poka-Yoke is a Japanese term that means “mistake-proofing” or “error prevention“. A poka-yoke is any mechanism in a process that helps an equipment operator to avoid (yokeru) mistakes (poka) and defects by preventing, correcting, or drawing attention to human errors as they occurs.

History

The term poka-yoke was applied by Shigeo Shingo in the 1960s to industrial processes designed to prevent human errors. Shingo redesigned a process in which factory workers, while assembling a small switch, would often forget to insert the required spring under one of the switch buttons. In the redesigned process, the worker would perform the task in two steps, first preparing the two required springs and placing them in a placeholder, then inserting the springs from the placeholder into the switch. When a spring remained in the placeholder, the workers knew that they had forgotten to insert it and could correct the mistake effortlessly.

Shingo distinguished between the concepts of inevitable human mistakes and defects in the production. Defects occur when the mistakes are allowed to reach the customer. The aim of poka-yoke is to design the process so that mistakes can be detected and corrected immediately, eliminating defects at the source.

Principles of Mistake-proofing / Poka-Yoke

1. Elimination (“don’t do it anymore”) is to eliminate the possibility of error by redesigning the product or process so that the task or part is no longer necessary.

2. Prevention (“make sure it can never be done wrong”) is to design and engineer the product or process so that it is impossible to make a mistake at all.

3. Replacement (“use something better “) is to substitute a more reliable process to improve consistency.

4. Facilitation (“make tasks easier to perform”) is to employ. Techniques and to combine steps to make work easier to perform.

5. Detection (“notice what is going wrong and stop it”) is to identify an error before further processing occurs so that the user can quickly correct the problem.

6. Mitigation (“don’t let the situation get too bad”) is to seek to minimize the effects of errors.

Elimination, Prevention, Replacement and Facilitation are to avoid the occurrence of mistakes. Detection and Mitigation are to minimize the effects of mistakes once they occur.

Examples Of Poka-yoke:

Implementation in Manufacturing

Poka-yoke can be implemented at any step of a manufacturing process where something can go wrong, or an error can be made. 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.

Shingo recognized three types of poka-yoke for detecting and preventing errors in a mass production system:

1. The contact method identifies product defects by testing the product’s shape, size, color, or other physical attributes.

2. The fixed-value (or constant number) method alerts the operator if a certain number of movements are not made.

3. The motion-step (or sequence) method determines whether the prescribed steps of the process have been followed.

Either the operator is alerted when a mistake is about to be made, or the poka-yoke device prevents the mistake from being made. In Shingo’s lexicon, the former implementation would be called a warning poka-yoke, while the latter would be referred to as a control poka-yoke.

Shingo argued that errors are inevitable in any manufacturing process, but that if appropriate poka-yokes are implemented, then mistakes can be caught quickly and prevented from resulting in defects. By eliminating defects at the source, the cost of mistakes within a company is reduced.

A methodic approach to build up poka-yoke countermeasures has been proposed by the Applied Problem Solving (APS) methodology, which consists of a three-step analysis of the risks to be managed:

1. Identification of the need

2. Identification of possible mistakes

3. Management of mistakes before satisfying the need

This approach can be used to emphasize the technical aspect of finding effective solutions during brainstorming sessions.

3 Rules of Poka Yoke

1. Do not wait for the perfect POKA YOKE. Do it now!

2. If your Poka-Yoke idea has better than 50% chance to succeed…Do it!

3. Do it now…. improve later!

Benefits Of poka-yoke Implementation

A typical feature of poka-yoke solutions is that they don’t let an error in a process happen. Other advantages include:

1. Less time spent on training workers.

2. Elimination of many operations related to quality control;

3. Unburdening of operators from repetitive operations.

4. Promotion of the work improvement-oriented approach and actions.

5. A reduced number of rejects.

6. Immediate action when a problem occurs.

7. 100% built-in quality control.

8. Preventing bad products from reaching customers.

9. Detecting mistakes as they occur.

10. Eliminating defects before they occur.

References:

1. Robinson, Harry (1997). “Using Poka-Yoke Techniques for Early Defect Detection”. Berry College. Archived from the original on December 27, 2014. Retrieved May 4, 2009.

2. ^ Jump up to:^a ^b ^c Shingo, Shigeo; Dillon, Andrew (1989). A study of the Toyota production system from an industrial engineering viewpoint. Portland, OR: Productivity Press. ISBN 0-915299-17-8. OCLC 19740349.

3. ^ John R. Grout, Brian T. Downs. “A Brief Tutorial on Mistake-proofing, Poka-Yoke, and ZQC”. John Grout’s Mistake-Proofing Center. Archived from the original on Apr 14, 2009. Retrieved May 4, 2009.

4. ^ “The Sayings of Shigeo Shingo: Key Strategies for Plant Improvement”. QualityCoach.Net. ISBN 9781563273841. Archived from the original on January 28, 2014. Retrieved August 20, 2012.

5. ^ Jump up to:^a ^b “Poka Yoke or Mistake Proofing :: Overview”. The Quality Portal. Retrieved May 5, 2009.

6. ^ Jump up to:^a ^b Nikan (1988). Poka-yoke: improving product quality by preventing defects. Productivity Press. p. 111. ISBN 978-0-915299-31-7.