Poka-yoke is Japanese for mistake-proofing: a device or method that makes an error impossible, or makes it obvious at once, so it does not become a defect. Common examples are a fixture a part only fits one way, a counter that checks every screw is in and a connector that only plugs in the right way.

What are the three types of poka-yoke?

They are grouped by how the device catches the error. Contact methods check a physical feature such as shape, size, position or colour. Fixed-value methods check that the right number of parts or moves has been done. Motion-step methods check that the steps were done in the right order. Each can prevent the error or detect it.

What is the difference between prevention and detection?

A prevention device stops the error being made at all, for example a part that cannot be loaded the wrong way. A detection device lets the error happen but catches it straight away, before the part moves on, for example a sensor that stops the line when a screw is missing. Prevention is stronger, so use detection where prevention is not practical.

Is poka-yoke the same as inspection?

No. Inspection at the end of a process finds defects after they are made, often on a sample. A poka-yoke device works at the step where the error happens, on every part, so the error is stopped or caught before it becomes a defect.

How does poka-yoke relate to jidoka?

Jidoka means stopping the process as soon as something goes wrong, so the problem is fixed instead of passed on. Many poka-yoke devices are how that happens at a station: they detect the error and stop the machine or hold the part.

Free template

Poka-yoke worksheet

Poka-yoke, Japanese for mistake-proofing, is a device or method that stops a mistake from being made, or makes it obvious the moment it is made, so it cannot turn into a defect. This worksheet takes one job step by step. For each step you write the errors that could happen and what they lead to, how they are caught today, whether the fix should prevent the error or detect it, and which method fits: contact, fixed value or motion step. Then you describe the device, give it an owner and a due date, and tick it as verified once someone has tried to make the error on purpose and the device stopped it.

Free to use: print it, copy it and edit it for your team. Enter your name and work email once to download.

The poka-yoke worksheet: header fields for process, area, team and date, a key to prevention and detection and the three methods, and a table with columns for step, possible error, effect, how it is caught today, type, method, device idea, owner and verified. — Steps and possible errorsEffect and today's controlPrevention or detectionContact, fixed-value or motion-step methodDevice idea, owner, dueVerified box

When to use it

When to use a poka-yoke worksheet

After a root cause analysis that ends at a human error training has not stopped, such as a part fitted the wrong way round or a step left out.
When a defect has reached a customer, to stop the error at the step where it is made. It fits the permanent corrective action of an 8D.
When a new product, fixture or station is set up, to go through each step for possible errors before production starts.
On steps where one slip becomes scrap, rework or an injury, such as choosing between two similar parts or setting a torque.
Not in place of finding the cause: if nobody knows why the error happens, start with a 5 Whys or a fishbone diagram.

How to fill it in

1
Fill in the header
Process or part, area or line, team and date. Take the sheet to the station and go through the job with the people who do it.
2
List the steps
Write each step of the job in order, in a few words. Start from the standard work or work instruction if there is one, and check it against what really happens.
3
Write what could go wrong
For each step, the errors that could happen: a step left out, the wrong part, the wrong way round, the wrong setting, too many or too few. Add the errors that have already happened, from defect records and complaints.
4
Note the effect and today's control
What the error leads to (scrap, rework, a complaint, an injury) and how it is caught today, if at all. Errors caught only at final inspection, or not at all, come first.
5
Choose prevention or detection
Prevention makes the error impossible, like a fixture a part only fits one way. Detection lets the error happen but catches it at once and stops or warns, like a sensor that counts the screws. Use detection only where prevention can't be done.
6
Choose the method and the device
Contact: the device checks shape, size, position or colour. Fixed value: it checks that a set number of parts or moves is done. Motion step: it checks the steps happen in order. Describe or sketch the simplest device that would work.
7
Test it and add it to the standard
Give each idea an owner and a due date. Once the device is fitted, try to make the error on purpose, tick verified if it is stopped or caught, and add the device and a regular check that it still works to the standard work.

A filled-in example

Illustrative, not a benchmark

A worksheet for a bracket assembly station where the left-hand and right-hand brackets look almost the same.

Step: fit the bracket. Error: a right-hand bracket fitted to a left-hand unit. Effect: the unit is rejected at the customer. Caught today: a visual check at final inspection.
Prevention, contact method: a locating pin on the fixture that only the correct bracket's hole fits over.
Step: fit four screws. Error: a screw left out. Effect: a loose bracket. Caught today: not caught.
Detection, fixed-value method: the screwdriver controller counts four tightenings, and the fixture clamp does not open until it has.
Step: label the unit, then fit the cover. Error: cover fitted first, so the label is missed. Detection, motion-step method: the cover bin opens only after the label has been scanned.

The sheet ends with three device ideas, one for each method, each with an owner and a date. The pin prevents the wrong bracket, and the screw count and the label scan catch the other two errors at the station. Each device is tested by trying to make the error before it goes into the standard work.

Common mistakes

Adding inspection instead
A check at the end finds defects after they are made. Put the device at the step where the error happens.
Blaming the operator
Mistake-proofing starts from the idea that anyone can make a mistake. Ask how the process lets the error happen, not who made it.
Settling for a warning when a stop is possible
A light or a buzzer can be missed or ignored. Where the error matters, prefer a device that stops the process or will not take the wrong part.
Starting with something complicated
Many good devices are a pin, a guide, a template or a counter. Try the simplest thing that makes the error impossible or obvious.
Never checking the device again
Sensors get bypassed and pins wear. Put a check that each device still works into a start-of-shift routine or the machine's CILR checklist.

Download the template

Free to use: print it, copy it and edit it for your team. Enter your name and work email once to download.

Run this template in LeanSuite

In LeanSuite quality issues are logged as tags, ranked in the QA Matrix and traced to their root cause, and digital instructions and checklists with number limits, required photos and signatures build quality into every task.

Poka-yoke worksheet

When to use a poka-yoke worksheet

How to fill it in

Fill in the header

List the steps

Write what could go wrong

Note the effect and today's control

Choose prevention or detection

Choose the method and the device

Test it and add it to the standard

A filled-in example

Common mistakes

Adding inspection instead

Blaming the operator

Settling for a warning when a stop is possible

Starting with something complicated

Never checking the device again

Download the template

Run this template in LeanSuite

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