What is Poka Yoke?

Poka-yoke, pronounced PO-ka-yo-KAY, is the use or design of a device or mechanism that assists an operator (or anyone else) in avoiding mistakes. Poka Yoke is a Japanese term that means “mistake-proofing” (or “inadvertent errors prevention”) and was previously called baka-yoke which meant “fool proofing”. Poka Yoke is a technique that eliminates product defects by correcting or preventing them from occurring. This means that manufacturing does not accept, create, or allow defects to move down the production line.

Poka Yoke devices are designed to prevent mistakes from happening. It plays a more detective role and tries to eliminate defects as soon as possible. A prevention based Poka Yoke system detects a defect and issues an alert. A detection based Poka Yoke system instantly alerts an operator when a mistake has been made. The system stops the process from continuing, which allows the operator to quickly correct the error.

Two approaches to Poka Yoke devices are available: the warning approach or the control approach.

  • Warning approach. Devices that use the warning approach detect and alert of deviations (or trends of deviations), through an escalating number of warning devices (buzzers lights, etc.). This approach differs from the control approach in that it does not automatically shut down the process when an error is detected.
  • Control approach. Devices that use the control approach detect a problem and stop it. This allows for immediate action to fix the problem.

Examples

Some examples in manufacturing include: magnets in food-processing plants to detect and remove metal parts before packaging; interlock switches that identify the location of a guard on a machine and turn off the machine when it is lifted; safety mats near dangerous machinery that trigger an automatic shutdown when someone steps on them; personal protective equipment such as gloves in eye-catching colors that are used in the food industry in the event that they fall into food and standardized containers at workstations that have exact amounts of material.

Implementation

Here are some things you should consider before starting to use the Poka Yoke methods and methodology. Management must be open to supporting the Poka Yoke methods and the devices before anything else can happen. You will need to train operators and provide the necessary tools and skills to perform their jobs.

  • Create a team: Building a team of cross-functional people to review the current processes is the first step towards implementing poka-yoke. The team should consist of operators, quality technicians and manufacturing and quality engineers as well as production supervisors. Each member of your team should have knowledge and training in Poka Yoke methods. It is also a good idea to be aware of any product defect history or process errors.
  • Select the process. Choose the process you wish to evaluate. It could be determined by the impact it has on key performance indicators (KPIs) of the company, the complexity of the process and the frequency of errors. You should choose a process with a high chance of improvement.
  • Review the process map: Discuss each step with your team and look for areas that have been affected in the past. Create a process flow diagram if you don’t already have one.
  • Identify Risk: Gather your team and brainstorm all possible errors in the process. Keep in mind when human mistakes are most likely to occur. A great tool to identify risk is Failure mode and Effect Analysis (FMEA).
  • Locate the source: Begin with the potential errors and then work your way through the process flow until you find the point of initiation. You can brainstorm ways to avoid the error by looking at the point of initiation.
  • Outline your options Once you have identified potential errors, think of ways to prevent them from happening. You can simplify the step to eliminate the error or make it easier to do the task.
  • Select the method: When you are implementing Poka Yoke (meaning that the step cannot be simplified or eliminated), it is time to select the most suitable Poka Yoke technique. This involves deciding collectively on the contact, fixed value or motion-step Poka Yoke method.
  • Validation and implementation: Select and develop the Poka Yoke method or device, and then implement it in the existing process. Make sure operators are informed about the changes and how they will affect them. You can monitor the efficiency of the changes, as well as rework and scrap, over time.

Where can you implement Poka-Yoke?

After deciding which process would benefit from a Poka Yoke device, there are some areas you should consider where the device or method should be placed within the workflow. It can have an impact on the effectiveness of the device’s location within the workflow.

The ideal location to place a Poka Yoke is before the operator or machine begins a task. It is best to avoid any mistakes by not allowing the process to begin until certain conditions are met.

The second-best location to place a Poka Yoke device during a specific step of a process is at the end. An operator or machine is notified if there is an error. This stops the process or part from moving.

The third best location to store a Poka Yoke is downstream after the process step has been completed, usually at an inspection station. You are now assuming that errors or defects might have occurred. This is why you need to rely on detection controls to locate the defects before proceeding with the process.

Benefits of Poka Yoke

Other than the obvious benefits, which aim to eliminate human and machine errors and prevent others from passing them along, there are other benefits.

  • safety increase is a benefit for workers who are exposed to dangerous materials or machinery, such as high-inertia machines and petrochemicals.
  • Operators will require less training, as processes that contain Poka Yokedevice automatically correct deviations from what is expected.
  • Operators are less likely to do repetitive work because they can go through the process error-free and avoid having to go back again.
  • Less quality checks via sampling and inspection are required thanks to the error-proofing features of poka-yoke. Inspections are still important, but Poka Yoke makes it possible to eliminate mistakes by predicting or detecting errors and defects.
  • Higher quality products are possible when processes are improved. Effective teams work together to ensure that errors are avoided and improve processes.