poka-yoke

What Is Poka-yoke And Why It Matters In Business

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. 

Understanding poka-yoke

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. 

Process improvements

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.

  1. Elimination – the most preferable solution. It involves redesigning a product or process so that a particular step is no longer necessary.
  2. Prevention – or engineering a product or service so that it is virtually impossible for an individual to make a mistake.
  3. Replacement – can a more reliable process be substituted in to lessen the chances of an error occurring?
  4. Facilitation – or the adoption of techniques to make a task easier to perform. This may involve combining certain steps.
  5. Detection – or identifying an error before further process steps are undertaken. This allows the error to be rectified without further damage to equipment or personnel.
  6. Mitigation – the least preferable solution. Here, the aim is to minimize the effects of errors without necessarily solving them.

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.

Contact method

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.

5-whys-method
The 5 Whys method is an interrogative problem-solving technique that seeks to understand cause-and-effect relationships. At its core, the technique is used to identify the root cause of a problem by asking the question of why five times. This might unlock new ways to think about a problem and therefore devise a creative solution to solve it.

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?

Improved profitability

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.

Improved productivity

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

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.

Error detection

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.

Error prevention

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.

Spell checkers

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.

Hotel rooms

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.

Lawn mowers

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.

Safety mats

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

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.

Grain processing

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.

Key takeaways:

  • 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.

Other Lean Manufacturing Frameworks

Toyota Production System

toyota-production-system
The Toyota Production System (TPS) is an early form of lean manufacturing created by auto-manufacturer Toyota. Created by the Toyota Motor Corporation in the 1940s and 50s, the Toyota Production System seeks to manufacture vehicles ordered by customers most quickly and efficiently possible.

Gemba Walk

gemba-walk
A Gemba Walk is a fundamental component of lean management. It describes the personal observation of work to learn more about it. Gemba is a Japanese word that loosely translates as “the real place”, or in business, “the place where value is created”. The Gemba Walk as a concept was created by Taiichi Ohno, the father of the Toyota Production System of lean manufacturing. Ohno wanted to encourage management executives to leave their offices and see where the real work happened. This, he hoped, would build relationships between employees with vastly different skillsets and build trust.

Kaizen Approach

kaizen-approach
Kaizen is a process developed by the auto industry. Its roots are found in the Toyota Production System, which was heavily influenced by Henry Ford’s assembly line system. The word Kaizen is a hybridization of two Japanese words, “kai” meaning “change” and “zen” meaning “good.” Two of the basic tenets of Kaizen involve making small incremental changes – or 1% improvement every day – and the full participation of everyone. 

Poka-yoke

poka-yoke
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.

Scrum

what-is-scrum
Scrum is a methodology co-created by Ken Schwaber and Jeff Sutherland for effective team collaboration on complex products. Scrum was primarily thought for software development projects to deliver new software capability every 2-4 weeks. It is a sub-group of agile also used in project management to improve startups’ productivity.

Six Sigma

six-sigma
Six Sigma is a data-driven approach and methodology for eliminating errors or defects in a product, service, or process. Six Sigma was developed by Motorola as a management approach based on quality fundamentals in the early 1980s. A decade later, it was popularized by General Electric who estimated that the methodology saved them $12 billion in the first five years of operation.

Assemble-To-Order

assemble-to-order
Assemble-to-order (ATO) is a manufacturing workflow where products are produced from scratch when an order is made by a customer. Assemble-to-order, therefore, is a production strategy where a product is assembled only after a consumer had ordered it. The strategy necessitates that the individual components of the product have already been assembled based on Make-to-stock (finished products manufactured in advance, stored, and supplied on demand). Or Make-to-order (goods are manufactured once the order has been received).

Jidoka

jidoka
Jidoka was first used in 1896 by Sakichi Toyoda, who invented a textile loom that would stop automatically when it encountered a defective thread. Jidoka is a Japanese term used in lean manufacturing. The term describes a scenario where machines cease operating without human intervention when a problem or defect is discovered.

5s System

5s-system
The 5S System is a lean manufacturing tool that improves efficiency and eliminates waste. First used in the Toyota Production System (TPS). The 5S System seeks to mitigate the factors contributing to process inefficiencies with six areas of concern: sort, set in order, shine, standardize, sustain, and safety.

Supply Chain

supply-chain
The supply chain is the set of steps between the sourcing, manufacturing, distribution of a product up to the steps it takes to reach the final customer. It’s the set of step it takes to bring a product from raw material (for physical products) to final customers and how companies manage those processes.

Value Stream Mapping

value-stream-mapping
Value stream mapping uses flowcharts to analyze and then improve on the delivery of products and services. Value stream mapping (VSM) is based on the concept of value streams – which are a series of sequential steps that explain how a product or service is delivered to consumers.

Kanban Framework

kanban
Kanban is a lean manufacturing framework first developed by Toyota in the late 1940s. The Kanban framework is a means of visualizing work as it moves through identifying potential bottlenecks. It does that through a process called just-in-time (JIT) manufacturing to optimize engineering processes, speed up manufacturing products, and improve the go-to-market strategy.

SMART Goals

smart-goals
A SMART goal is any goal with a carefully planned, concise, and trackable objective. To be such a goal needs to be specific, measurable, achievable, relevant, and time-based. Bringing structure and trackability to goal setting increases the chances goals will be achieved, and it helps align the organization around those goals.

TQM Framework

total-quality-management
The Total Quality Management (TQM) framework is a technique based on the premise that employees continuously work on their ability to provide value to customers. Importantly, the word “total” means that all employees are involved in the process – regardless of whether they work in development, production, or fulfillment.

Kepner-Tregoe Matrix

kepner-tregoe-matrix

Other strategy frameworks:

Additional resources:

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