Poka-yoke (pronounced PO-kah yo-KAY) is a Japanese cartoon, itâs actually a Japanese term that means to avoid (yokeru) mistakes (poka).Â
Poka-yoke is one of several Lean manufacturing tools designed to help organizations eliminate waste, streamline processes, and increase efficiency. Specifically, poka-yoke tries to achieve zero defects by preventing and eliminating errors.
Often referred to as âerror-proofingâ or âmistake-proofing,â the idea of poka-yoke was developed in the 1960s by Shigeo Shingo, a Japanese industrial engineer whose production innovations are still important in Lean and Six Sigma methodologies today.
In this article, we will:
- Define poka-yoke and briefly explore its history.
- Discuss how poka-yoke fits into Lean manufacturing.
- Present some poka-yoke examples.
- Show you how to implement the poka-yoke system in your organization.
What is poka-yoke?
While visiting a plant in the early 1960s, Shingo noticed that workers were forgetting to insert springs in a simple on/off switch. This one small mistake resulted in defective parts being manufactured and shipped. From his observations, Shingo learned two things:
- Sometimes people forget to do things.
- Sometimes people forget that they have forgotten to do things.
Knowing that these simple human errors were the root cause of the problem, Shingo started working on ways to improve the process and to make it âidiot-proofâ (baka-yoke). After a worker complained that the term was insulting, he changed it to poka-yoke, which shifts the focus from the worker to the process.
By redesigning the process so that the operation could not proceed until the worker had inserted the spring into the switch, fewer human errors were made and higher quality products were shipped.Â
You encounter poka-yoke every day. For example, you canât start the microwave until the door is closed, and it will stop immediately if you open the door before the timer has stopped. In addition, you often create your own poke-yoke by doing something as simple as taping your car keys to an item that you need to take to work.
How does poka-yoke fit into Lean manufacturing?
The main purpose of Lean is to eliminate waste, continually improve processes, increase product value, and solve customer problems all while reducing your costs. Lean concepts and tools are generally simple and easy to implement. For any Lean implementation to be truly successful, you must have total buy-in of all employees from the top down.
As with the Lean concept of the Theory of Constraints (TOC), poka-yoke recognizes that there will be constraining factors that can slow down manufacturing and result in defective products. Your job is to find the root causes of the constraints.
After identifying the root cause, TOC aims to exploit the constraint using existing resources to reduce the impact of the constraint. For example, if the constraint is an overworked employee, redistributing assignments to balance the workload can lead to increased efficiency and higher productivity.
Poka-yoke complements TOC by implementing processes or fixes that make it impossible for constraints to exist in the system. For example, itâs impossible to start an automatic car if the selection lever is not set on Park. This makes it impossible for the car to accidentally move when you turn the key, eliminating the possibility of making a mistake.
Types of poka-yoke
There are two types of poka-yoke: control and warning.
- Control: The goal is to make it mechanically impossible to make mistakes. For example, there is only one way you can plug a three-prong electric cord into a power outlet.
- Warning: Color or sound is used to alert operators that they are about to make a mistake. For example, a message pops up on your screen to remind you to save your documents before closing an application.
The goal of any poka-yoke system should be zero defects. Letâs say that you only have one defect out of every 10,000 units produced. Thatâs a very good ratio. However, that one defect represents a 100% defective product to the person who buys it.
Benefits of using poka-yoke
Implementing poka-yoke in your organization will benefit your organization in many ways:Â
- Error prevention (control) and error avoidance (warning) means that you spend less time and money training your employees.
- Fewer errors means more safety for workers and consumers.
- Less time and money is wasted on quality checks and inspection because the system is designed to be mistake-proof.
- Employees adopt a culture of continuous improvement as a way of life.
- Zero defects, or as close to zero as possible, reduces waste and costs.
- Higher quality products lead to increased customer satisfaction and stakeholder confidence.
Using poka-yoke prevents or greatly reduces errors and this builds confidence in employees, management, and stakeholders. Increased confidence that comes from getting work done right the first time can result in superior products, better customer satisfaction, enhanced brand loyalty, and increased profits.
How to implement poka-yoke
Implementing poka-yoke should be easy, inexpensive, and aligned with current processes. You should see immediate benefits and measurable improvements in quality and production. You can implement poka-yoke by using the steps described below.
Step 1: Identify the problem
Remember that humans make mistakes. One or two mistakes are to be expected. A series or pattern of mistakes indicates that there is a problem that needs to be addressed. That problem may be with the employee or with a flaw in a machine.
Youâll need to observe the process to identify where the problem is occurring. Enlist the help of others to determine whether the error is human or mechanical. Consider using a flowchart to visualize your current process and design the future state you want to see.
