1. 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.
2. 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.
3. 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.
4. 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.
5. 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.
6. 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
1. 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.
2. 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.
3. 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.
4. 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
1. 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.
2. 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.
3. 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.
4. 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.
5. 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
1. 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.
2. 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
1. 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.
ELIMINATION
1. 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.
2. 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.
PREVENTION
1. Or engineering a product or service so that it is virtually impossible for an individual to make a mistake.
2. 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.
3. Also consider the example of a television company that has received complaints from consumers that the instruction manual was missing from the box.
4. 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.
5. If there are still manuals left at the end of a production run, the company knows that not all televisions have instructions.
REPLACEMENT
1. Can a more reliable process be substituted to lessen the chances of an error occurring?
2. Replacement is most often associated with robotics and automation because of its ability to improve repeatability and consistency.
3. One example of replacement is an automatic dispenser that measures the exact amount of adhesive for a part.
4. Another is a probe that tells a soft drink company worker when the correct amount of liquid has been dispensed into a bottle.
FACILITATION
1. Or the adoption of techniques to make a task easier to perform. This may involve combining certain steps.
2. 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.
3. 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.
DETECTION
1. Or identifying an error before further process steps are undertaken. This allows the error to be rectified without further damage to equipment or personnel.
2. 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.
3. 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.
MITIGATION
1. The least preferable solution. Here, the aim is to minimize the effects of errors without necessarily solving them.
2. Examples of mitigation include fuses that break the circuit if there is too much current flowing through an appliance.
3. Another example is the deliberate design of products that have simple, low-cost rework procedures in the event an error is discovered.
POKA-YOKE ERROR DETECTION METHODS
1. Fixed value method - Ideal for operations where the same process is repeated many times over.
2. 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.
3. Motion step method - The motion step method is used for any process requiring a single worker to carry out different activities in one process.
4. 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.
5. 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.
6. The contact method is useful in manufacturing characterized by intense repetition or in facilities where production is infrequent.
7. For example, a winery that operates a bottling production line for only a few weeks each year.
8. On that note, the method can also be used to detect errors resulting from dust, temperature, noise, and improper lighting.
Source:
https://fourweekmba.com/poka-yoke/
