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A Poka Yoké (ポカヨケ), Poka for ” error of inattention ” and Yokeru for “avoid ” (translated as: anti-error or even misleading) is a simple and reliable device to make a defect impossible.

Historical

Originally, the term was Baka Yoké1 for ” Anti-Idiot ” (Baka 馬鹿 means ” Idiot ” in Japanese, Baka-Yoké resulting in “preventing errors in the standard is above the person’s skills“). Considered a bit strong (it was in 1963 that a worker of Arakawa Body Company refused to use a Baka-Yoké in his work, finding this term dishonorable and with negative connotation), he was replaced by Poka-Yoké (“Prevent Errors caused by an absence, a normal error“). This term and technique is attributed to Shigeo Shingo in the years 1960, also the custodian of the SMED, eminent Japanese quality specialist of the last century who worked on behalf of Toyota.

While visiting the Yamada Electric site in 1961, Shingo is called to discuss a problem that company has with one of its products2. Part of this product is a small switch with 2 buttons supported by 2 springs. From time to time, the operator forgot to insert the springs under each of the buttons. Sometimes the error was discovered only when the customer arrived and the company had to detach an engineer for the customer site to repair the button. The problem was both economical and embarrassing. The management of the company wanted to warn employees to pay more attention to their work, but despite the best attentions, the problem reappeared.

Shingo suggested a solution that will become the first Poka Yoké3 :

  • In the old method, an operator began by taking two springs in a large box and then assembly them in the switch.
  • In the new approach, a small disk is placed in front of the large box and the first task of the operator is to take 2 springs from the box and place them on the disc. Then the operator assembles the switch. If a spring remains on the disk, the operator knows that he has forgotten one.

The new procedure allowed the whole problem to be eliminated.

Examples

In a ticket distributor, you must first remove your credit card before you can withdraw the tickets. This prevents the card from being forgotten in the dispenser.

The scart socket does not allow to put this plug otherwise than in a specific sense

Issue

Behind the Poka-Yoké is the search for the 0 defect by ” producing quality and not controlling it” starting from the observation that it is better to avoid producing faults than to improve the detection and control processes.

This notion comes from the observation that:

  • A human cannot maintain permanent attention. This is due to fatigue, weariness or even the mood of the day…
  • Freedoms are left and are not always used wisely.
  • Operating procedures and other instructions are not properly understood.

The Poka-Yoké will have 2 functions4 :

  • prevent: makes the error impossible and makes the correction unnecessary. This avoids the costs of non-quality.
  • detections: Alert when an error has been made and thus limiting the number of control.

Design of a Poka Yoké

Design process

The design of a Poka-Yoké must be carried out very upstream, as soon as the product/process design phase. We follow the following process:

  1. To identify the operation, function or process according to its importance and its criticality: Use for example the FMEA or the Pareto. In general, whenever a problem arises, consider how to set up a Poka-Yoké to avoid recurrence.
  2. Made an analysis 5 Why To identify the causes of a problem.
  3. Determine what type of Poka-Yoké is most appropriate to the situation.
  4. Test the method and check how it works.
  5. Train staff and measure earnings

Specifications

On the other hand, a Poka-Yoké is5:

  • Simple, sturdy and does not require too much maintenance.
  • Little expensive.
  • Set up as close to the origin of the errors as to allow no defect to pass through.

Anti-ergonomics Concept6

Let’s take the example of a square Part . It can be placed in four different ways, a triangle in three different ways. The idea is to use anti-ergonomic forms, like a round with a half-moon inside. This can only be inserted in one way. This concept makes it possible to avoid at all times the problem.

Type of keyed7

The Contact keyed

The presence of the latter during the operation obliges the operator not to make an error. The example of the unbuckled safety belt that prevents the car from starting is part of this category of anti-error tool.

The reporting keyed

The reporting deceiving that indicates in a procedure if one of the operations was not performed. It is the permanent beep that is put in place when an operation is missing in a procedure and will only stop when the operation is performed.

Different forms of reporting are distinguished:

  • meters: It is the use of measuring devices to count objects and to ensure that the quantities are reached or respected.
  • Audible and luminous signals: use of a beep or light to signal a failure. Example: Dashboard indicator light that signals when a vehicle door is open.
  • marking, labelling: use of a graphic to indicate for example the direction of handling. For example, avoid flipping the contents of a crate.
  • Color codes: For example, in a refinery, pipeline lines have a different color depending on the product being transported.

The sequential or chronological keyed

The chronological deceiving which is a sequence of obligatory operations to be carried out chronologically to start a machine: This is the verification carried out by an airplane pilot when taking orders.

Deployment of Poka Yoké

The first step in the deployment of the Poka-Yoké comes from the management which must stimulate a state of mind and the tools of quality:

  • Setting up of problem solving tools (5 Why, PDCA…).
  • Set up a culture of Jidoka.
  • Allocate time and resources.
  • Welcome problems Positively

Next, the Poka-Yoké should be included in the ” Top start ” standards of production to ensure their presence and proper functioning.

 

Who

Code

Line

Ok

Nok

What if NOK?

Comment

Operator

9113-2c

9113

Prevent First Line Leader and start in gradient mode.

99121-7d

9121

9123-4a

9123

9125-87Z

9125

9131-34D

9131

9133-11pm

9133

 

2 cases may be presented:

  • The Poka Yoké is not in operation: one puts a red card directly on the machine and this indicates that there must be a 100% control of the elements pending repair of the system
  • The Poka Yoké is in operation, can be produced in the right conditions.

 

Source

1 – J. P. Womack, D. T. Jones (2009) – Lean system: Thinking about the company at the fairest

2 – D. Rogers (2011) – The Future of Lean Six Sigma Thinking in a changing business environment

3-S. Shingo (1986) – Zero Quality control: Source Inspection and the Poka-yoke system

4-R. Chalice (2005) – Stop Rising healthcare costs using Toyota Lean production methods

5 – G. Beauvallet, M. Ballee (2013) – The Lean management

6 – B. Piller, G. Stern (2009) – Poka-Yoke

7 – M. Miliani and B. Behrad (2013) – Introduction to Quality

A. P. Dillon (1989). A Study of the Toyota production system from an industrial engineering viewpoint

S. Shingo (1987)-The yinges of Shigeo Shingo: Key Strategies for Plant improvement

N. Kogyo (1988) – Poka Yoke: Improving product quality by preventing defects

 

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