What Is Poka-Yoke in Manufacturing? 

October 17, 2022

Poka-yoke is a Lean methodology stemming from the Japanese term for “mistake-proofing.” Poka-yoke translates to avoid (“yokeru”) mistakes (“poka”). Applying this concept to your manufacturing processes can help eliminate errors and improve efficiency. 

Poka-yoke is based on the understanding that human error is unavoidable. So, rather than expecting workers to perform a task perfectly every time, the process or the product should be designed to make errors impossible

The essence of poka-yoke: an approach in which potential errors are engineered out of a task before they happen. 

The poka-yoke concept can be applied to your internal manufacturing process and to how the end product functions, delivering benefits for both employees and customers.

When errors are successfully prevented in the manufacturing stage, defective products can’t reach the customer. Time-consuming reworks are avoided, and customer satisfaction remains high.

And, designing a product so that the end user can only operate the product in one way ensures that human error is removed from the picture. The result: the product can only be used as intended. 

Poka-Yoke Examples in Everyday Life

An everyday example of poka-yoke is how washing machines won’t work with the door open or USB cables fit into a port in only one direction. 

By designing the product so the user can’t operate it incorrectly in the first place, the manufacturer is assured that its product will function as designed. Using clever design, the company has effectively fool-proofed its product and can deliver a better customer experience

By applying the same type of “one way only” idiot-proofing approach in a manufacturing environment, –where productivity and efficiency are under the microscope–you can potentially save serious time and money. 

The Birth of Poka-Yoke

The term “poka-yoke” was originally coined by Shigeo Shingo, an industrial engineer at Toyota. The Toyota Production System is widely accepted as the benchmark for incredible efficiency and quality. Shingo was a fundamental contributor to concepts like just-in-time manufacturing and the “pull” production system, documenting many concepts that we now think of as Lean manufacturing. 

In the 1960s, Shingo created the poka-yoke system, eliminating defects as they occurred and allowing quick correction on the factory floor. (Originally known as “baka-yoke” or “fool-proofing,” the term was later changed to “poka-yoke” to avoid the negative connotations of foolishness, instead focusing on “avoiding mistakes.”)

Shingo eventually expanded his methods, combining poka-yoke techniques called Zero Quality Control. This method of inspecting errors at the source allowed workers to correct possible defects in a low-cost way quickly.  

Highlighting errors as they occurred through “source inspection”–rather than inspecting products later in final QA checks–allowed corrections to be made on the go instead of reworking or scrapping a near-complete product.

How Does the Poka-Yoke Technique Work? 

Several poka-yoke techniques contribute to a robust error-proofing process. Managers can implement these controls individually or as a whole system, depending on the type of process or task performed. 

However, the first step is to take a step back and understand how and why errors occur using process improvement methodologies such as Lean Six Sigma. This starts by defining the acceptable quality for customer value and prioritizes continuous improvement. Over time, it results in fewer errors and mistakes by looking to address the root cause of a problem instead of just treating the symptoms. 

Therefore, the first thing to do is analyze your workflow to uncover why an error occurred. Then you can get to work preventing the error from recurring. 

The 3 Types of Poka-Yoke Techniques 

Contact Method

This approach checks for physical attributes that are out of place, such as scales to detect incorrect weight or a laser scanner placed on a production line to detect inconsistencies in dimensions. If the sensor device finds an abnormality, it alerts a machine or a worker to rectify the issue.

The contact method of poka-yoke is ideal for fast-moving production situations where employees can easily become distracted and make mistakes or assembly-line situations where product failure can occur if parts are incorrectly assembled. 

Employing poka-yoke for error prevention means using measures like proximity switches, dies, templates, and locator pins that position items in the exact position required.

Fixed-Value Method

Companies use fixed-value methods of poka-yoke when a process must be performed a specific number of times or when a constant number of parts are required to complete a task. 

For example, say eight bolts are required to fix a plate to a product. Package the bolts in sets of eight, indicating to workers visually to use all eight bolts. Once all eight bolts are used, the product is ready for the next stage of assembly. 

This also helps prevent inadvertent errors like missing bolts or screws on a product–by placing the bolts in sets of eight. The employee can ensure the process is completed correctly by simply using up all the bolts in the pack.

The Motion-Step Method

This method uses poka-yoke devices like buzzers, lights, sensors, or limit switches as tools to indicate problems. Motion-step methods rely on these devices to ensure that the right actions occur in the correct order. 

This method prevents process errors and detects issues stemming from a series of steps performed out of sequence. A buzzer, light, or other alarm alerts workers to the incorrect or skipped step, allowing them to fix the error on the spot.

Benefits of Poka-Yoke

  • Because poka-yoke aims to achieve zero defects, employee and customer safety increases.
  • When errors are detected and rectified early in the manufacturing process, you save time and money on reworks and returns.
  • Operational errors are reduced when you use processes, templates, and devices to ensure processes are performed correctly every time.
  • Greater production efficiency can be achieved through a reduction in machine errors, setup time, and assembly problems. 

Ultimately, the different types of poka-yoke all deliver a more efficient, productive, high-quality, and error-free flow to your production process. 

When quality control and customer satisfaction really matter to your business, it’s worth investigating how you can integrate poka-yoke techniques into your organization.

Poka-Yoke in Manufacturing

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Caroline Eisner
Caroline Eisner
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