What is Poka-Yoke?

What Is Poka-Yoke

In Japanese, Poka Yoke (pronounced poh-kah-yoh-keh) - ポカヨケ - means to mistake-proof or to prevent errors. It’s a Lean practice that will prevent mistakes from occurring by error-proofing an operation or activity, hence building a well defined standardization into the process.

Lean project management teaches that to cut expenses, you should not inspect for quality of work, but rather build quality in - how? By creating an environment that has all the elements required for a process step to be done right, as well as building in mechanisms that will call out a mistake exactly at the time when it’s occurring, not several process steps later.

Implementing Poka-Yoke in these 2 forms will not only smooth out the mechanics of a process, it will also help to reshape workers’ behavior patterns, teaching them to stop what they are doing the moment they notice a mistake. In the long term, this can change how people focus on quality above all else, becoming their second nature. A lot like having your text automatically spell-checked everywhere online, can create a habit of spell-checking any text you’ve been writing offline.

Don’t inspect for quality, build it in!

The Toyota Production System, later renamed “Lean” by the researchers at MIT, based heavily on the teaching of W.Edwards Deming. He had travelled to Japan and impacted the country’s industries profoundly.

Deming explained how when someone is watching a production line and inspecting items for quality, by the time they have found the cause of a defect, the damage has already been done and a cost was incurred. In line with the Rule of Ten, every time an erroneous part gets through a quality assurance step undetected, the cost of fixing it increases tenfold. It is therefore far better to make sure that defects don’t make it to production in the first place, by preventing, fixing, and drawing attention to errors as they happen in real-time.

The Toyota Production System was truly blessed with some of the best minds of that century. Shigeo Shingo was one of their engineers, who not only documented the TPS for the West but was intricately involved with quality on their manufacturing line. It was him who created the concept of Poka-Yoke, which is still alive and well today, in fact, present in each of our everyday lives.

What does Poka-Yoke look like in real life?

We have grown so accustomed to many error-proofing practices that we don’t even notice them. But think back to a few years ago - it was not uncommon to fill out an entire form, hit submit, and be told that you had filled it out incorrectly, and had to start from scratch. Now, built-in mechanisms follow our edits in real-time, to tell us whether each field is filled correctly or not. Better still, sometimes the field is presented in such a way, for example as a date format, that you have no choice but to fill it out correctly the first time!

Other examples include having to put a car’s automatic transmission into “park” before starting the engine, to avoid uncontrolled movements of the car, elevator doors not closing, when an obstacle is detected in the doorway, overflow outlets in sinks and bathtubs preventing flooding and so on.

The simplicity of Poka-Yoke solutions for process management can sometimes put them at risk of being disregarded by management, but a good process manager will recognize that the simplest solutions are often the best.

The necessary traits of good Poka-Yoke applications are:

  • Simplicity - which is typically followed by low implementation cost
  • Safety - necessary for them to be relevant
  • Automation - a Poka-Yoke mechanism must be fully or partially automated, so as not to create additional work, furthering error opportunities
  • Interconnection - error-proofing tools must have feedback loops built-in, so that information of error recognition, along with its nature, location and specifics, is automatically passed on to the controller

Kanban boards for project management also have the Poka-Yoke concept built-in: once you have stipulated your Work In Progress limit for a particular work stage, the board will keep you in check, letting you know you’ve added too many items to be processed than was allowed.

Poka-Yoke should also work in tandem with Kaizen and Gemba in your Kanban practice. Not only will they improve your quality, and keep the improvement continuous, but they will educate and grow your employee’s skills and safety at work.

Furthermore, on top of improvements in productivity due to fewer errors, this will also reduce stress among the team, which in and of itself boosts efficiency, not to mention job satisfaction.

How to use Poka-Yoke?

In short, Poka-Yoke is an easy technique of improving a process by proactive elimination of mistakes. Using it will decrease the time you have to spend on finding and removing errors, and the time you need to spend controlling and training team members. It also actively promotes the continuous improvement mindset across all levels of an organization. It can increase your process efficiency and ensure that faulty products don’t make their way to the customer!

To apply it to your process, follow these steps:

Step 1: Determine the process step to error-proof

Not sure where to start? Either begin at the most error-prone station or process stage, or use value stream mapping to identify which process step, and hence which kind of errors, have the biggest impact on how customers view and can use your product. In principle, however, your Poka-Yoke measure should be implemented at exactly the work step that causes the error that is to be avoided.

Step 2: Identify potential errors

Use historical data on your process, do a 5 Whys session, or take a Gemba walk to get the worker’s insight into what can and what typically goes wrong at their station.

Step 3: Determine which approach to use for each defined failure point

You should:

  • prevent the mistake from occurring, and
  • implement a mechanism that will fix it immediately whenever it occurs. And, if error prevention is not possible, then you should
  • apply a detection mechanism (i.e. an Andon) which will highlight the issue to the controller as soon as it presents.

Step 4: Plan, implement and test the solution

How you implement this depends on the nature of your process. You can use digital Andons, signaling lights, automatic switches, information cards, Kanban board automation, emails, calls, custom hardware, and software programming.. the possibilities are endless. But sometimes the best theory won’t work in practice, so, in the spirit of continuous improvements, make sure to test each Poka-Yoke solution and to make it possible for team members to give you their thoughts on its operation at any time.

Step 5: Review the systems regularly

As with anything Kanban, no improvement is recognized without having been measured. For that reason, you need to compare process efficiency before and post error-proofing. This will be easy to do on a basic Lead & Cycle Time diagram. Whenever you see an opportunity to make things even a little bit better - go for it and apply it, but make sure the team is up to date with any changes you make. Communication is key to every process’ health, and necessary to improve it too.