Poka-yoke is a mistake proofing in Japanese terms. It is a device involved in lean manufacturing used to minimize errors on equipment operators. Its purpose is to identify mistakes and incorrect parts in a product being assembled. It helps in the elimination of defective products by correcting, preventing and detecting the occurrence of human errors. Dr. Shigeo Shingo, a well-known authority in efficiency and quality control in Japan, adopted Poka-yoke as a formalized mistake-proofing concept and later on, it became a part of Toyota’s system of production.
Japan manufacturing is very particular with the quality of their products. They have a Zero Defect Quality Control and Poka-yoke is one of its components. Most Japanese companies perform the Poka-yoke scheme. Dr. Shigeo Shingo knows the value of efficient quality control and regarded this system to be sorting defective items as well as improving the manufacturing process. Poka-yoke is an agile mistake-proof mechanism that is very beneficial to lean manufacturing. It differentiates defects from mistakes and it provides fast feedback on defects and workers can check the quality of their work.
Dr. Shigeo Shingo classified Poka-yoke into 3 types:
1. Contact Method
Contact Method is the type that identifies product defects through testing its physical attributes like shape, color, or size. This method is very useful on situations like infrequent production, rapid repetition or environmental problems.
Examples: Fixed Diameter Holes, Limit switches, Toggle switches UTP cables with RJ45, Screw, fueling area of cars, Ethernet cable plug, analog and discrete sensors, etc.
2. Fixed-Value Method
This method has the ability to alert operators whenever certain movements are not done on the repetitive processes in lean manufacturing. This method has a fixed design wherein there is a fixed number of parts.
Examples: Egg tray, airport luggage cart, shoe-size gauges, etc.
3. Motion-Step Method
This method is responsible for determining if the prescribed steps in the manufacturing process were followed. There must be correct sequence.
Example: The operator needs to step on a pedal every cycle of the assembly; sewing machine, wheelchair, etc.
The Poka-yoke device alerts operators if there will be a mistake happening or if it actually prevented the mistake from happening. Dr. Shingo stated that errors are unavoidable in manufacturing processes. The solution for this is the appropriate implementation of Poka-yokes which would have positive benefits like error elimination and quality improvement, improvement in the capacity of production, simplified housekeeping, safety, lower costs, increased production and flexibility and operators will have improved attitudes.
Poka-yoke is a very important aspect of lean manufacturing in terms of incurring zero defects because defects results to higher cost of production and the need to reworking or eliminating the manufactured product. Using Poka-yoke devices to mistake-proof is necessary so that defects may be reduced and prevent it from happening. With the elimination and reduction of defects, satisfaction levels of customers will increase. There will be quality processes and higher production, workers will be more effective, problems are solved immediately, waste elimination and continuous innovations which equals to first-time product quality.
— Slimane Zouggari