Management Operations Process Improvement

Poka Yoke What? A Methodology for Quality Assurance to Prevent Costly Errors



Welcome to FAT FINGER’s blog. In this article, we’ll be discussing poka yoke. 

Poka yoke what?

Exactly, we’re not speaking English. Unless you know Japanese, this term will have you scratching your head. Poka yoke is Japanese meaning mistake-proofing. The poka yoke methodology is used to prevent costly errors from business operations, assure quality and deploy continuous improvement. It’s a methodology born from Toyota’s manufacturing processes to drive high-quality design and unyielding innovation. 

Learning from the Toyota powerhouse, you can implement the poka yoke methodology to build better business operations, and in this article, we’ll explain how. You’ll find out what poka yoke is, the three types of poka yoke approach (with real-life examples), and how to implement poka yoke in five stages. Ready?

  • What is poka yoke?
  • The three types of poka yoke 
  • Poka yoke examples (mistake prevention in the real world)
  • How to implement poka yoke in 5 steps (for business process improvement)
  • The benefits of implementing the poka yoke methodology
  • Process improvement: How to use documentation software to implement poka yoke

Tebanasu (let’s go)!

What is poka yoke?

Poka yoke (English translation of mistake-proofing) is a method that prevents errors in a system or process. 

The methodology was developed in the 1960s by Toyota engineer Shigeo Shingo. Shingo worked on the production line and developed the poka yoke methodology to prevent operational errors. The methodology is still used by Toyota today and is key to Toyota’s legendary quality control. The manufacturing process is streamlined to maintain high standards, quality, and process efficiency.

The idea behind the poka yoke methodology is to develop process steps that reduce error, or prevent mistakes from happening in the first place. Over time, and with repetition, the process operator is conditioned to this new way of getting work done.

To explain further, let’s go back to where it all started. While working on the engineering side, Shingo realized factory workers often forgot to insert one spring (out of the two needed) under one of the switch buttons. Shingo decided to re-design the process, making workers perform this task in two steps.

Step one was to prepare the two springs and place them in a placeholder.

Step two was to insert the springs from the placeholder into the switch.

When the one (often forgotten) spring remained in the placeholder, the workers knew they’d forgotten to insert the spring into the switch, and quickly corrected the error. This is poka yoke.

You can see how the poka yoke methodology designs error out of a system. If the mistakes can’t be designed out, then controls are added to prevent errors.

The three types of poka yoke 

There are three effective approaches to poka yoke that ensure the detection and prevention of mistakes:

  1. The contact method 
  2. The fixed value method 
  3. The motion step method 

The contact method 

The contact method is used to identify deviations in shapes, dimensions, forms, positions, or other physical characteristics of a product. Detection is possible through direct contact with the product. This method is used in rapid repetitive processes, infrequent production processes, and processes running in sub-par environments (e.g. poor lighting, dust, noise, etc). 

An example of this contact method would be an individual standing at a production line, checking products as they come through for defects.

The fixed value method 

The fixed value method is used in operations where the same activities are repeated several times. This method employs automatic counters or optical devices to control the number of moves, the rate of an operation, as well as other critical operating parameters. 

That is, if a certain number of steps are needed to complete a given operation, the fixed value method ensures the required number of steps have been completed. If they’re not, the operator is alerted of this fact to review what steps did or didn’t make it.

The motion step method 

This method ensures that the correct sequence of steps in a process is followed, and that these steps are completed within a certain period. It’s a useful method for processes requiring several different activities performed in a sequence by a single operator. The method also controls error by preventing steps from another – unrelated process – to creep in and affect a given process. This method is otherwise known as the sequence method.

Poka yoke examples (mistake prevention in the real world)

Poka yoke alters human behaviour to prevent mistakes. You’ll apply the poka yoke methodology in your everyday life without even realizing it. For instance:

  • When driving a car. In newer vehicles you’ll have to push the clutch pedal down before starting the engine. This process prevents unintended car movement. The step alters human behaviour to prevent error. This is an example of the fixed value method. A certain number of steps have to be completed for the car to move. 
  • Spell-check functions are a common example of poka yoke error proofing. Our phones, software, and other applications are equipped with spell-checking functionality. This is an example of the contact method. We, as operators, are alerted to deviances in the output from what we require. 
  • Process documentation software, such as FAT FINGER, are common poka yoke tools deployed by businesses. They ensure the correct sequence of steps is performed, in the right order and at the right time. This is an example of the motion step method. If you follow a documented procedure in your job, then you’re using the poka yoke methodology. 

Poka yoke forces costly errors out from operations creating lean processes. With this in mind, it’s easy to understand why this is a popular lean business methodology.

How to implement poka yoke in 5 steps (for business process improvement)

To help you use poka yoke, we’ve split the implementation of this methodology into five steps. 

Step #1: Define

During the define stage, the problem causing a defect is described and defined. This should happen on the shop (factory) floor, which in Japanese terms is called Gemba. That is, you’d need to perform a Gemba Walk. A Gemba Walk is the action of going to see an actual process to understand the work performed.

Operation managers need to see the actual process occurring, ask questions and learn from the operating teams. It’s on the “shop floor” where the operational processes happen and where the cause of a problem might be hiding. Problems need to be identified and documented objectively from the perspective of the “shop floor”.

Step #2: Measure 

The measuring stage is applied for complex problems in production processes. A test is used to discover how often the problem occurs, and a percentage is then calculated based on the results. Problems with a higher percentage occurrence are prioritized.

Next, deploy a test group to use the product over a certain period to determine how the problem could be dealt with and solved. 

Step #3: Analyze

During the analysis phase, it becomes clear how poka yoke can be used to design error out from the system. Through thorough process analysis, the cause of the problem is pinned down meaning a solution can now be found. 

Step #4: Improve 

This is when the poka yoke improvement is applied. In many cases, the solution seems simple but has a significant positive impact. The aim is to alter process behaviour to prevent the same mistake from happening again.

The contact, fixed value, or motion step approaches to poka yoke can be applied here, to create lean, error-proof operations. 

Step #5: Control 

During this stage, the effectiveness of the poka yoka solution is measured. If the solution works well, then the chance of the same future error is negligible. The aim is to achieve zero quality control and zero defect. That is, defects are prevented by controlling process performance. The defect cannot occur even when a mistake is made by a machine or human. 

The benefits of implementing the poka yoke methodology 

Not allowing error to creep into operations comes with obvious benefits. Process errors can be costly both in terms of money and time. But there are also some less obvious and indirect benefits to the poka yoke methodology, as detailed in the book Standardized Work with TWI

  1. Less time is spent to train workers, as systems are designed to guide users to follow the correct procedures.
  2. Less time and money is spent on quality control, and operations are designed in a way that ensures quality. 
  3. Operators are unburdened by repetitive process checks.
  4. Less error means services and products meet the desired quality standards avoiding rejection.
  5. Immediate action is taken when a problem occurs.
  6. Quality control systems are built into operations meaning they are effective 100% of the time.
  7. Bad services and products are prevented from reaching customers, boosting customer satisfaction. 
  8.  Mistakes and defects are detected before they occur, preventing wasted time, money, and resources.

Process improvement: How to use process documentation software to implement poka yoke 

Process documentation software, such as FAT FINGER, is a tool that effectively complements the poka yoke methodology to create optimized business processes. And in this section, we’ll explain how.

Process documentation software has been specifically designed to detail, with full transparency, every step that makes up a business operation. This transparency aids poka yoke and the three approaches of this methodology, as we’ll explain:

  • The contact method: With full process transparency, every step that makes up a business operation can be scrutinized. This means if a product has a defect, the source of this defect can be found relatively quickly and easily. By resolving the issue from the source (the identified process step), product defects are eliminated. 
  • Fixed value: Workers following a documented process are guided through each step until the process is complete. With each step written down, there’s less chance of workers missing steps and the correct number of process steps are executed.
  • Motion step: Documented processes can be followed sequentially, step-by-step. This means the correct step series is followed within the period allocated.

By giving full process transparency, business process documentation aids the define stage of poka yoke implementation, because documenting processes makes it easy to see why errors are occurring.

Use FAT FINGER for business process documentation and poka yoke implementation

With FAT FINGER you can easily document your business operations using a checklist format. Use FAT FINGER’s features such as our Conditional Logic, Due Date, and Approval features to detail the complexities of your documented process. 

These features also act as error prevention checks. For instance:

  1. Due dates ensure process steps are executed on time. 
  2. Approval features act as a contact method check. The process is unable to come to completion until each step has been checked and approved. 
  3. Conditional logic features embed if-that-then-this rules into your processes, meaning the correct process sequence is followed for different scenarios.

FAT FINGER also provides real-time management dashboards to track operational performance. Performance can be compared to benchmarks expanding FAT FINGER’s use-case. That is, FAT FINGER can also aid the measure stage of poka yoke.

For more information about the FAT FINGER platform and how you can get started, watch the below video.

Sign up for your free trial at FAT FINGER to start documenting your business processes today. Use your documented processes to implement the poka yoke methodology, to design better business operations and prevent costly errors.