What is Poka-yoke?

Quality Guru Shigeo Shingo advocated the concept of zero quality control by arguing that inspection processes or the use of statistical control should be eliminated. He believes that quality should be controlled at the source of the problem and not after it has manifested itself.

Poka-yoke (pronounced poh-kah yoh-kay) comes from two Japanese words

• yokeru means to avoid
• poka means inadvertent errors.

Thus, poka-yoke more or less translates to avoiding inadvertent errors.

Three types of systems

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

• The contact method identifies product defects by testing the product’s shape, size, colour, or other physical attributes.
• The fixed-value (or constant number) method alerts the operator if a certain number of movements are not made.
• The motion-step (or sequence) method determines whether the prescribed steps of the process have been followed.

Three levels

• Level 3: Eliminating/preventing the defect opportunity at design level (or at the source), e.g. One-way assembly (Electrical three-pin top only put in one way, A USB drive can be inserted one way only).
• Level 2: Put the control system to detect the defect as it is being made & remove or quarantine it. e.g. alarms sound (Spell checks in MS office)
• Level 1: Stop the defect from reaching the next operation (e.g. Inspection, checklist, colour coding)

Advantages:

• It prevents bad products from getting passed to customers.
• It detects mistakes as they occur.
• It eliminates defects before they occur.