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What is a poka-yoke?
A poka-yoke is a mechanism that is put in place to prevent human error. The purpose of a poka-yoke is to inhibit, correct, or highlight an error as it occurs. Poka-yoke roughly means “avoid unexpected surprises” or “avoid mistakes” in Japanese. In English, a poka-yoke is sometimes called “mistake-proof” or “fool-proof”.
A poka-yoke checks that the proper conditions are met before a process moves on to the next step. Poka-yokes can be warning mechanisms or control mechanisms.
Warnings provide an alert designed to prevent additional errors or defects from occurring. Control mechanisms prevent the next step in a process from occurring.
Cars often have a series of poka-yokes to help drivers avoid making mistakes. If a driver gets out of the vehicle but doesn’t remove the key from the ignition, for example, many cars are designed with a poka-yoke that will warn the driver with an audible alert that they have forgotten their key.
To prevent the driver from accidentally locking out, some cars also have a control poka-yoke that prevents the vehicle door from locking when the key is still in the ignition in the off position.
Poka-yokes have their roots in lean manufacturing and are closely aligned with Six Sigma methodologies, continuous improvement (kaizen), and the Toyota Way production system.
Dr. Shigeo Shingo
The concept of designing process steps to be foolproof was developed by Dr. Shigeo Shingo, an industrial engineer who was a consultant to Toyota and the author of “Zero Quality Control: Source Inspection and the Poka-Yoke System.”
The concept was originally called baka-yoke, but Dr. Shingo changed the name to poka-yoke after realizing that the “foolproof” label was humiliating to workers.
Like kanban and many other lean manufacturing concepts, the concept of poka-yokes has been adopted by many other industries, including software development and health care.
Meaning of Poka-Yoke
The term Poka-Yoke (poh-kah yoh-keh) was coined in Japan during the 1960s by Shigeo Shingo, an industrial engineer at Toyota.
Shingo also created and formalized zero quality control, a combination of Poka-Yoke techniques to correct possible defects and source inspection to avoid defects.
Actually, the initial term was baka-yoke, which means “fool-proof”, but was later changed due to the dishonorable and offensive connotation of the term. Poka-Yoke means “mistake-proof” or, more literally, to prevent (yokeru) unintentional mistakes (poka).
It ensures that the proper conditions exist before a process step is executed, thereby preventing defects from occurring in the first place. When this is not possible, Poka-Yoke performs a detection function, removing defects from the process as quickly as possible.
Poka-Yoke is any mechanism in a lean manufacturing process that helps prevent errors.
Its purpose is to eliminate product defects by preventing, correcting, or calling attention to human errors as they occur.
Why is Poka-Yoke important?
The value of using Poka-Yoke is that they help people and processes work right the first time, making mistakes impossible to happen.
These techniques can significantly improve the quality and reliability of products and processes by eliminating defects.
This production approach fits perfectly with the culture of continuous improvement, which is also part of the Lean management arsenal.
It can also be used to fine-tune improvements and design Six Sigma Define, Measure, Analyze, Improve and Control (DMAIC) project layouts. The application of simple Poka-Yoke ideas and methods in product and process design can eliminate human and mechanical errors.
Poka-Yoke’s flexibility allows it to be inexpensive. For example, Toyota’s goal is to implement each failsafe device for less than $150. Depending on the size of the business, it can be an extremely profitable endeavor.
What is Error Test/Mistake Proofing?
Error proofing, or its Japanese equivalent poka-yoke (pronounced PO-ka yo-KAY), is the use of any automatic device or method that makes it impossible for an error to occur or makes the error immediately obvious once what has happened It is a common process analysis tool.
When to Use Mistake Proofing
When a process step has been identified where human error can cause errors or defects, especially in processes that rely on worker attention, skill, or experience.
In a service process, where the client can make a mistake that affects the output
In a transfer step in a process, when the output (or for service processes, the customer) is transferred to another worker
When a minor mistake early in the process causes major problems later in the process
When the consequences of a mistake are costly or dangerous
Examples of Poka-Yoke
Car safety features
Cars are equipped with many “mistake proof” features to keep us safe on the road. Many cars will beep or start if the doors are open while the engine is running, or if someone is in the passenger seat and their seat belt is not fastened.
Microwaves, washing machines, dishwashers and other household appliances
Many appliances such as microwaves, washers and dryers, and dishwashers have mechanisms that prevent them from working when the door is open. These are examples of control functions that prevent the process from running until the required conditions are met (ie the gate is closed).
Elevators and garage doors
Most elevators are equipped with sensors that prevent the doors from closing if someone or something is in the way. Garage doors, subway doors and other automatic doors are also equipped with this feature. Many elevators also beep and refuse to work if you exceed the weight limit.
A metal roller is used to laminate two surfaces joined with hot melt glue. The glue tended to stick to the roller and cause defects in the laminate surface. An investigation showed that if the roller was wet, the glue would not stick. Added a secondary roller to dampen the steel roller during the process, preventing the glue from sticking.
A production step at Motorola involves placing alphabetic characters on a keyboard and then verifying that each key is placed correctly. A group of workers designed a clear template with the letters placed slightly off center. By holding the template over the keyboard, assemblers can quickly spot errors.
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