Poka-yoke is a Japanese quality control technique developed by former Toyota engineer Shigeo Shingo. Translated as “mistake-proofing”, poka-yoke aims to prevent defects in the manufacturing process that are the result of human error. Poka-yoke is a lean manufacturing technique that ensures that the right conditions exist before a step in the process is executed. This makes it a preventative form of quality control since errors are detected and then rectified before they occur.
Fundamentally, poka-yoke is a lean manufacturing technique that ensures that the right conditions exist before a step in the process is executed.
This makes it a preventative form of quality control since errors are detected before they occur.
Of course, some process errors cannot be detected ahead of time. In this case, the poka-yoke technique seeks to eliminate errors as early on in the process as is feasible.
Although the poka-yoke technique became a key part of Toyota’s manufacturing process, it can be applied to any industry or indeed any situation where there is potential for human error.
One of the most well-known examples of poka-yoke in action is in the case of a manual automobile.
The driver must engage the clutch (a process step) before changing gears. This prevents unintended movement of the car and reduces wear on the engine and gearbox.
Another example can be found in washing machines, which do not operate if the door isn’t closed properly to prevent flooding.
In both cases, poka-yoke principles mean that automation is in place to prevent errors before they occur.
History of poka-yoke
How did poka-yoke come to be? Let’s take a brief look at its history in the final section.
As we touched on at the outset, poka-yoke was developed by Japanese industrial engineer Shigeo Shingo.
During the 1950s, Shingo was a leading advocate of statistical process control in Japanese manufacturing.
Eventually, however, he became disenfranchised with this approach after realizing it would never reduce the product defect rate to zero.
While visiting a Toyota plant in 1961, he observed that workers on occasion neglected to insert the springs in an on/off switch.
This was a small, simple, and seemingly harmless mistake, but it resulted in the manufacture and distribution of defective components.
This was an embarrassing and costly situation for Toyota with engineers often having to travel to the customer’s location and reassemble the switch.
Shingo concluded that two human mistakes served as the root cause of the problem. The first was that workers sometimes forgot to do things.
The second was that workers sometimes forgot that they had forgotten to do things.
Shingo then set about improving the process to make it idiot-proof (baka-yoke).
However, the name was changed after some employees believed the term to be offensive and dishonorable.
Poka-yoke was then born to shift the focus from human error to the process itself.
The process of assembling the on/off switch was redesigned such that the operation could not proceed until the worker had inserted the spring.
In essence, the worker would perform the task in two steps.
The first step required the worker to place the springs into a placeholder dish, with the second step involving the transfer of the springs from the placeholder to the switch.
When workers could see that the springs for the previous switch were still in the placeholder, they knew they had forgotten to insert them and could rectify the mistake with ease.
One critical distinction Shingo made was between human mistakes and defects.
Mistakes, he posited, were inevitable because humans were not machines and could not be expected to concentrate on their work or understand their instructions every time.
Defects, on the other hand, were simply mistakes that were allowed to reach the customer.
As a result, the overarching goal of poka-yoke is to engineer processes that facilitate the early detection and correction of mistakes.
Refinement of the idea and expansion
Over the next few decades, Shingo refined the mistake-proofing concept of poka-yoke, developing entire manufacturing systems with a core focus on achieving zero production defects.
His idea proliferated across Japanese factories with many implementing hundreds of thousands of individual fail-safe mechanisms based on poka-yoke principles.
The popularity of the system was due to several factors.
Aside from the obvious benefits to production efficiency, poka-yoke systems were simple and cost-effective to implement.
They were also placed in proximity to where the mistakes occurred which meant workers could provide rapid feedback on the process and correct mistakes easily.
The six principles of poka-yoke
To reduce the prevalence of process errors, poka-yoke is based on six principles in decreasing order of effectiveness.
These principles are otherwise known as methods of mistake proofing, but whatever the name, they ensure that the proper conditions exist before a process step is executed.
Note that the first four principles prevent the occurrence of human error, while the final two minimize the effect of human error after it has occurred.
The most preferable solution. It involves redesigning a product or process so that a particular step is no longer necessary.
Elimination may also require that a product be made more simple. If there is a part defect or assembly error, it should be consolidated.
One example of elimination is the use of sensors that detect movement and ambient light in a loading bay.
To reduce waste related to energy consumption, illumination will only switch on in the presence of a moving object (usually a person) or after dark when ambient light drops below a certain level.
Or engineering a product or service so that it is virtually impossible for an individual to make a mistake.
The most obvious example of prevention is the use of a limit switch to ensure that a part is correctly located or fixtured before a process step is performed. Prevention can also be facilitated by the nature of the part itself. Some parts can only be assembled in one orientation, while others may feature unique connectors or symmetry to avoid incorrect assembly.
Also consider the example of a television company that has received complaints from consumers that the instruction manual was missing from the box.
To ensure no TV is sent to retailers without a manual, the company stacks them in sets of 50 to match a production run of 50 televisions.
If there are still manuals left at the end of a production run, the company knows that not all televisions have instructions.
Can a more reliable process be substituted to lessen the chances of an error occurring?
Replacement is most often associated with robotics and automation because of its ability to improve repeatability and consistency.
One example of replacement is an automatic dispenser that measures the exact amount of adhesive for a part.
Another is a probe that tells a soft drink company worker when the correct amount of liquid has been dispensed into a bottle.
Or the adoption of techniques to make a task easier to perform. This may involve combining certain steps.
Facilitation tends to involve visual controls such as color coding, checklists that detail the tasks to be performed, labeled parts to facilitate correct assembly, and exaggerated asymmetry to ensure parts are correctly oriented.
When gas stations first introduced unleaded fuel in the 1970s, the nozzles were made smaller than those for leaded fuel so consumers would not fill their tanks with the incorrect type.
Or identifying an error before further process steps are undertaken. This allows the error to be rectified without further damage to equipment or personnel.
The most obvious example of detection is the Andon system, which alerts workers in various areas if there is a problem on their part of the assembly line.
In some cases, the line or process may be shut down until the error is resolved to prevent equipment damage or avoid safety risks to personnel.
The least preferable solution. Here, the aim is to minimize the effects of errors without necessarily solving them.
Examples of mitigation include fuses that break the circuit if there is too much current flowing through an appliance.
Another example is the deliberate design of products that have simple, low-cost rework procedures in the event an error is discovered.
When should poka-yoke be used?
Here are some common situations where the poka-yoke approach should be used:
- During a hand-off step in a process when output is transferred to another employee.
- For any seemingly minor error that has the potential to cause major problems later on.
- Whenever the consequences of an error are costly or unsafe.
- Any service process where customers are liable to make an effort that impacts output.
- Any process step where human error has been identified as a driver of defects or mistakes. This is particularly important for processes that rely on an employee’s experience, skill, and undivided attention.
Poka-yoke error detection methods
To detect and prevent errors or mistakes, there are three different methods:
Fixed value method
Ideal for operations where the same process is repeated many times over.
The fixed value method utilizes automatic counters and sensory devices to control the number of moves, the length of movement, and other crucial manufacturing parameters.
Motion step method
The motion step method is used for any process requiring a single worker to carry out different activities in one process.
Primarily, the motion step method ensures the worker does not omit an important step or add a step that is not a part of the standard procedure.
A broad set of methods that detect errors in shape, dimension, position, or any other physical trait via direct contact with the product itself.
The contact method is useful in manufacturing characterized by intense repetition or in facilities where production is infrequent.
For example, a winery that operates a bottling production line for only a few weeks each year.
On that note, the method can also be used to detect errors resulting from dust, temperature, noise, and improper lighting.
A simple poka-yoke procedure
Poka-yoke is simple to implement because it is a rational approach that can be applied in almost any situation.
Consider the following step-by-step process:
Start by identifying the operation or process
Consult a flowchart if possible and review process steps where errors are likely to occur.
For each of the errors identified, work backward to discover its source in the process.
Some use the 5 Whys method to assist in this step.
Then, the team must brainstorm ideas that will make it impossible for the error to occur
Return to the six principles of poka-yoke and remember that elimination, prevention, and replacement are the most desirable courses of action.
If it is deemed impossible or economically unviable to prevent the error from occurring, the team should think of ways to minimize its effects
There are two options here. The first is setting functions, which are methods used to inspect process parameters or product attributes for errors.
The second option is regulatory functions, which are alerts such as bells, buzzers, or lights that let workers know an error has occurred.
With the above in mind, it is time to choose, test, and implement the most suitable prevention method for each error
Most businesses can collect rapid feedback by three different inspection methods.
The first is a simple inspection that is performed at the next step in the process by another worker.
Feedback may also be gathered via self-inspection, where the worker verifies their own work immediately after it has been performed.
The third and final inspection method involves source inspection checks.
These are carried out before the step takes place to ensure conditions are correct.
Benefits of poka-yoke principles for businesses
Error prevention is an obvious advantage to poka-yoke, but what positive ramifications does error prevention have for a business?
Errors on production lines decrease profitability – whether that be through line shutdowns or expensive worker injuries.
But poka-yoke principles improve a company’s bottom line in other ways.
For example, hotels now require that guests insert their key-card into a slot to activate electricity in their room.
Since many guests do not bother to turn the lights off after they leave, the hotel can save money on wasted electricity consumption.
Preventing errors before they occur increases productivity. Online forms require that every field be filled out before submission.
This reduces errors in forms resulting from incomplete or missing information, saving the company time and money in having to chase up consumers for the extra details.
ATMs also chime or flash to remind the customer to retrieve their debit card and cash.
This greatly reduces the once common error of customers leaving their cards in the machine.
It also saves the bank money in loss prevention, giving customer support the resources to deal with other problems.
Simplification of smaller, error-prone tasks
Small tasks with a high probability of error are particularly prevalent in some industries such as the service and hospitality industries.
Cashier errors in counting change, for example, are relatively inconsequential errors in isolation that have the potential to lose a business a lot of money over the long term.
To this end, poka-yoke principles have automated the change counting process and where automation is not possible, digital interfaces verify that the cashier has given the correct amount of change.
Similar systems are now in place to prevent errors in order fulfillment and delivery of orders to a table.
Poka-yoke types can be classified according to whether they detect or prevent errors.
In the following sections, we will take a look at both categories and provide examples for some of the five core poka-yoke types.
The fixed value method
The fixed value method defines a set number of steps in processes where tasks must be repeated several times.
It is often associated with relatively basic techniques that enable the individual to track the frequency of performed tasks and ensure standards are met or exceeded.
Consider a factory worker who is required to insert ten screws in a product before it moves to the next station on the production line.
The activity of screw insertion is performed to a fixed value – which in this example is ten times.
To ensure that the task is completed successfully, poka-yoke principles may dictate that the screws be placed in a container that has a capacity of exactly ten screws.
The motion-step method
In the motion-step method, poka-yoke clarifies whether the prescribed steps in a process are completed in the correct order.
Similar to the fixed value method, this method is ideal in situations where multiple different (or repeated) activities are carried out by the same operator.
However, the main defining feature of motion-step is that it should only be used for tasks that are completed in a specific sequence.
Specialized devices detect when tasks have been performed out of order or if a step has been skipped. Alerts then enable employees to correct the mistake.
The contact method
In this case, process defects are identified via sensory devices that analyze the physical properties of a product such as size, color, weight, or shape.
Again, the device will alert the nearest employee that an abnormality has been detected.
Defects tend to be caused by incorrect worker assembly or products that are not positioned properly before assembly commences.
The contact method is best suited to fast-moving production lines where errors are hard to detect with the naked eye.
But it can also be used for infrequent production or any environment affected by dust, noise, or a lack of proper illumination.
The control method
The control method strives to prevent mistakes by making their occurrence technically impossible.
In a factory environment, the machine, process, or production line is shut down so that measures can be taken before a defect has a chance to materialize.
Automatic doors, such as those installed in elevators, use the control method to ensure they do not close on an individual and cause injury.
The warning method
As the name suggests, the warning method uses alerts to prevent additional errors from occurring. These alerts may take the form of sounds, colors, lights, or messages.
Modern cars use the warning method extensively.
Some will chime when the driver leaves the keys in the vehicle unattended, while others will warn the driver when the vehicle is about to leave its lane and potentially cause a collision.
Poka-yoke additional examples
Here are some additional poka-yoke examples in some obvious and not-so-obvious situations.
Computers and smartphones are equipped with tools that alert us to the presence of spelling or grammatical errors.
This is one poka-yoke example that does not immediately come to mind – but it is one almost all of us will encounter multiple times in a day.
Some hotel chains require key cards to be placed in a special holder inside the room to activate lights and electronics.
This saves the company money on electricity since the guest cannot vacate the room and leave appliances running.
The holder may also be foolproof in the sense that its visible location near the door reminds guests not to leave their keycard in the room and inadvertently lock themselves out.
When used incorrectly, lawn mowers can cause serious injury or even death.
In the United States and indeed many other countries, these machines must possess a “deadman control” or similar mechanism that must be engaged before the blades will spin.
The most common of these mechanisms on a walk-behind lawn mower is a lever attached to the handle.
For the motor to continue to run, the lever must be held down at all times. Since it is spring-loaded, the lever automatically reverts to the “off” position when the user needs to empty the catch, for example.
In a manufacturing context, pressure-sensitive safety mats are installed near potentially dangerous machines.
When a worker steps on the mat, the machine shuts off automatically to prevent injury or death.
These mats also prevent damage to the machine itself and tend to be equipped with either a diamond top or ribbed non-skid top surface.
Personal protective equipment
In the food industry, businesses use color-coded personal protective equipment (PPE) to reduce the risk of cross-contamination and product recalls.
Food handling gloves, for example, tend to be blue or black to make them easier to see in the event they contaminate a mix like bread dough.
Since these colors are also rarely found in unprocessed foods, they tend to attract more attention from workers.
Treadmills possess safety keys that stop the machine in an emergency.
The key is attached to the front panel of a treadmill with the other end connected to the user and works in a similar way to the keycard in a hotel room.
In other words, the treadmill will only function if the key is in the correct position.
If the user falls or otherwise dislodges the key from the front panel, the treadmill stops immediately to prevent injury from the rapidly spinning belt.
In the agriculture industry, magnets are used to reduce metal contamination in processed grain.
This contamination can cause extensive damage to machinery resulting in downtime and product recalls.
Facilities are equipped with magnetic separation equipment that attracts metal fragments of various sizes from fasteners, contract-friction surfaces, and screen material.
Poka-yoke examples in business
The pharmaceutical industry
Pharmaceutical manufacturing is a heavily regulated industry where even the smallest mistake can have serious consequences.
To prevent errors and ensure product quality, pharmaceutical companies use poka-yoke techniques to improve their manufacturing processes.
One application is in the labeling and packaging of medications, with labeling errors potentially causing illness or even death to the consumer.
By implementing poka-yoke techniques such as color-coding, barcode scanning, or automated label printing, manufacturers can reduce the risk of these errors and improve quality.
Poka-yoke is also present in the design of equipment and processes.
For example, machine sensors can be used to detect when a tablet is not properly formed or when a liquid is not at the correct temperature or viscosity.
This enables immediate corrective action to be taken before the product is packaged and shipped.
One specific example of how poka-yoke is used can be seen with Pfizer.
The Pfizer-BioNTech COVID-19 vaccine, for instance, requires a very specific temperature range for storage and transportation to maintain its efficacy.
To prevent errors in the handling of the vaccine, Pfizer uses a poka-yoke system that includes specialized packaging, labeling, and temperature monitoring devices.
For instance, the vials that contain the vaccine are color-coded to help healthcare practitioners avoid errors when doses are administered. Vaccines for children under 4 feature a maroon cap, while those for kids between 5 and 11 feature an orange cap.
For those who are at least 12 years old, the cap is grey. Each age group also features a prominent “B” on the booster dose to ensure it is not confused with the primary doses.
In the mid-2000s, GSK Bio (GlaxoSmithKline’s Belgium-based vaccine division) discovered that rival Merck was two years ahead of it in the race to develop an HPV vaccine.
To catch up to competitor Merck, GSK took inspiration from Renault and its “one-roof” management concept where operations were centralized at one location.
The company assembled various experts from different fields to develop the vaccine, which caused less waste and a faster cycle time for decision-making.
But since GSK Bio’s facility accommodates multiple production lines and disciplines, the potential for manufacturing and communication errors was elevated.
Some of the poka-yoke initiatives mentioned above are now a vital component of the company’s efficient and streamlined processes.
In terms of the HPV vaccine, GSK was able to cut its application timeline in Europe by two years and its FDA schedule in the USA by 18 months. The company hoped that its efforts would deliver up to 33% of its revenue over the next five years.
Crayola LLC, formerly known as Binney & Smith Company, is an American manufacturer of art supplies.
The company is most famous for its Crayola brand of crayons which have been manufactured in Pennsylvania for over a century.
Crayola has implemented quality control measures to ensure that its products meet safety standards and are free from defects.
For example, the company uses automated inspection systems to check for defects in its crayons, markers, and other products.
Since a standard box of crayons can have as many as 120 colors, the company also uses light sensors to ensure that each box contains exactly 120 crayons.
If the system detects that there are duplicates of a color or if a crayon is missing, the line shuts down.
Crayola’s poka-yoke initiatives also extend to its markers. These are designed with a unique shape and size to avoid a potential choking hazard if a child inhales the cap.
The caps also feature small holes to allow air to pass, which reduces the risk of suffocation if a cap is swallowed.
Poka Yoke vs. Jidoka
Similar to Poka Yoke, Jidoka is a technique within the larger lean manufacturing toolbox, that tries to not only minimize but also fix, for good, errors within the production process.
This goes through four main stages:
- Discover an abnormality (automated)
- Stop (automated)
- Fix the immediate problem (human)
- Investigate and correct the root cause by installing a countermeasure (human)
Poka Yoke vs. Kaizen
Whereas Poka Yoke focuses in error reduction, Kaizen focuses on the improvement of production, through five key phases:
- 1. Small incremental changes
- 2. Employees are active participants and provide ideas and solutions
- 3. Accountability and ownership of new processes/changes
- 4. Feedback, dialogue, open communication
- 5. Active monitoring and measuring of changes – positive or negative impact
Poka Yoke vs. Six Sigma
Poka Yoke is a method within a wider Six Sigma methodology for eliminating errors in a production environment through five phases:
And five implementation roles:
Poka-Yoke vs. Andon
Both Poja-Yoke and Andon are quality control techniques to minimize (or ideally remove) errors in the production system.
Indeed, similarly to Poka-Yoke, Andon tries to minimize production defects through a system of color-labeling, which enables identity and solving errors while stopping production if these errors are not solved/identified.
Andon is a narrower approach to solving production errors. Whereas Poka-Yoka is a broader method that comprises a set of principles to resolve production bottlenecks.
- Poka-yoke is a Japanese quality control technique that aims to make processes error-proof.
- Although having origins in the manufacturing industry, poka-yoke principles are useful in any scenario where there is potential for human error.
- Poka-yoke error prevention is guided by six principles, with elimination the most desirable and mitigation the least desirable. All six principles can nevertheless improve productivity, profitability, and simplify smaller, error-prone manual tasks.
What does Poka Yoke mean?
Translated as “mistake-proofing,” poka-yoke aims to prevent defects in the manufacturing process resulting from human error, thus minimizing the error rates in manufacturing processes by streamlining them thourhg a lean manufacturing technique that pervades the whole supply chain process through three main methods:
What is poka yoke with example?
Poka-Yoke is a lean methodology that minimizes mistakes within a process and task. A great example of Poka-Yoke is spellcheckers in computers and smartphones, which help users to prevent many grammar mistakes and make communication clearer.
Is Poka yoke a Six Sigma tool?
Six Sigma is a data-driven approach and methodology for eliminating errors or defects in a product, service, or process. Poka-Yoke is a method used within Six Sigma’s toolbox to enable a process to be freed from mistakes or reduce errors within a process and task.
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