What is Poka Yoke?
Poka Yoke is a Japanese term that translates to “mistake-proofing” or “error-proofing.” It is a technique used in manufacturing and service industries to prevent errors and defects from occurring during the production or service delivery process.
The primary goal of Poka Yoke is to eliminate mistakes or defects by making it impossible for them to happen in the first place. It involves designing processes or systems in a way that makes it difficult or impossible for mistakes to occur. This is achieved through the use of visual or physical cues that signal when an error is about to occur, preventing it from happening.
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While creating a password for your e-mail account in case the password is too petite, a warning shows up on the screen: “Password strength: too short”. When you try to locate an item in Google, it offers you the alternative of spell check to make sure that you get the spelling of the item correct.
In the case of an electronic door lock system, the lock of the car door does not open when the engine is running. These are all cases of Poka Yoke in our day-to-day life. Alternatively, Poka Yoke implies to a series of methods that supports error prevention.
These techniques recognize how things can go wrong and how mistakes can be prevented as the priority. Therefore, Poka Yoke can be defined as a series of quality management techniques that supports removing defects in products by choosing various kinds of mistakes at the design phase or the production phase.
Poka Yoke comprises various simple tools for mistake prevention. For instance, we set an alarm to wake up on time (this prevents the error of waking up late), and arrange a checklist to make sure all the necessary items have been packed before going for a vacation(preventing the mistake of not shipping valuable items such as passports or tickets or other passes), etc.
Same as personal lives, there are big numbers of simple mistake-prevention techniques followed in organizations that put off damage and enhance quality. For instance, we have color coding of the wires and the plugs in a computer CPU so that the right wires (like those of keypads and pointers) are linked to the right plugs.
The term PokaYoke is an amalgamation of two Japanese words ‘poka’ meaning unintentional error and ‘Yoke’ meaning stop. The main concept of Poka Yoke is to devise the organizational processes in such a manner that errors are avoided or found and corrected at an initial phase of production.
Formal Poka Yoke practices were launched by Shigeo Shingo, a Japanese industrial engineer. Shigeo Shingo was even one of the proponents of statistical tools in quality control in Japanese manufacturing in the 1950s. Thus, steadily he recognized that statistical process control tools are unable of lessening product errors to zero.
The cause, as per him, was that the statistical control method trusted on sampling method, due to which 100% of products are not inspected before they arrive at the customers. Due to the random sampling approach, the statistical methods examine only a small part of the products.
So, the statistical methods leave much scope for a rate of errors to get to the customers. That is exactly when he designed Poka Yoke to entirely eliminate defects in products. As described by Shingo, “Poka Yoke is a “100% inspection” technique and it concentrates on inspecting 100% products before they arrive at the customers.
While visiting the Yamada Electric Plant in 1961, Shingo was informed about specific errors in one of the products of the plant. In a portion of the product, there was a little switch including two push buttons held by two springs. On the other hand, on other occasions, workers would not remember to put a spring under a push button.
This mistake could not be recognized before the product reached the customers and the defects were recognized by them. In this condition, the company had to send engineers to the location of the customer, dismantle the product and position the spring under the button.
The management of the firm took many steps, consisting of warning the workers against many mistakes and expecting them to be more helpful. Thus, despite the efforts of the workers, the issue of misplacing of spring could not be totally eradicated.
In such a scenario, Shingo advised positioning a small dish in front of the part box. The workers were expected to take two springs from the toolbox and place those on the plate. After that, they were expected to put in the springs a switch. Thus, in case any spring was left on the plate, workers routinely knew that they did not put in a spring in the switch. The recognition of the error was simpler and exact and the issue of missing spring was entirely eradicated.
The idea of Poka Yoke started from this mistake-proofing concept of Shingo. For the subsequent thirty years, he kept on developing the concept. Poka Yoke is not a complicated approach to quality control. Instead, it is a method of applying different easier mistake-proofing concepts used in everyday life. Firms use various easy Poka Yoke methods to enhance efficiency, superiority, and competence. For instance, Toyota uses an average of 12 mistake-proofing devices at every workstation.
Objectives of Poke Yoke
The main idea or building blocks of Poka Yoke is also called the objectives of Poka Yoke. Below are the objectives of Poka Yoke:
- To build quality as an in-built nature into the production processes. This supports in enhancing quality at a limited cost and effort
- To remove all unintended errors and human errors
- To initiate to do it correctly from now onwards
- To ignore excuses and put positive efforts into the quality enhancement
- Removing errors and lessening defects to zero is possible only through mixed efforts of all the workers concerned in the process. So, optimistic inspiration and a sense of obligation toward quality development are relevant
- Executing a concept that has even a 51% chance of thriving is a good concept.
- To concern, workers are extremely relevant in enhancing quality.
- Locating the sole reason for the defects supports getting permanent remedies for preventing the errors instead of taking a short-term and makeshift method.
Poka Yoke Techniques
Various Poka Yoke methods can be applied at various levels of a process. For instance, certain methods support preventing occurrences of mistakes in the first place; while other techniques since the mistakes once they have happened.
Poka Yoke techniques are chiefly applied in the below three levels:
- Preventing a Mistake From Being Committed
- Detecting Mistakes Incurred Unintentionally
- Mitigating the Risk
Preventing a Mistake From Being Committed
This is the first stage of Poka Yoke. Although Poka Yoke identifies that because of human mistakes, errors are expected. But, the method expects at lessening the errors from happening primarily. For instance, consider an automobile manufacturer who expects to put definite particular heat-resistant bolts in the engine assembly.
To stop mistakes of putting the bolts in other assemblies, the bolts can be made of certain physical dimensions that would only fit the engine assembly. This way, the workers cannot erroneously use the special bolts in other assemblies except the engine assembly.
Detecting Mistakes Incurred Unintentionally
The technique expects detecting mistakes before they become the main problems and considerable cost to the company. For instance, a car seatbelt warning indicator beeps when a person overlooks putting on the seat belt while driving. This informs the customer about the incidence of the error that is, forgetting to put on the seat belt.
Mitigating the Risk
At this stage, Poka Yoke methods alleviate threats by detecting mistakes that have previously happened. For instance, indicators are used in industrial complexes to find out occurrences of unwanted incidences, like the release of harmful gases.
Poka Yoke Systems
Poka Yoke devices are the different sensing devices used to find errors and stop failures. There are chiefly two kinds of sensing devices used in Poka Yoke:
Physical Contact Devices
As the name denotes, these devices function by actually touching a product or a part of a machine. Usually, the physical contact devices are programmed in which the instruments propel an electronic signal when contact happens. Below are a few of the physical contact equipment of Poka Yoke:
Limit Switches
These devices sense the place of any object contacting a small lever on the switch. Limit switches are the most ordinary and profitable kind of contact device.
Touch Switches
These switches work in the same manner as limit switches except that these switches find out light touch on a thin antenna.
Energy Sensing Devices
These devices use energy, like electricity rather than physical contact to find errors. Below are various kinds of energy-sensing devices:
Proximity Switches
These use beams of light to detect the right color and size of objects, the passage of objects on conveyor belts, and the appropriate flow of parts.
Beam Sensors
These use electron beams to find items. An instance of the use of beam sensors is at the entrance of retail stores which stops any customer from taking goods without making payment. In situations of unauthorized taking of items through these gates, the beeper in the gates intimates the store staff about it.
In addition to these two kinds of Poka Yoke sensing devices, there is one more kind of instrument that sense alterations in different situations, like temperature and pressure. A few examples of these instruments comprise thermostats, meter relays, and pressure gauges.
Quality at Source
Quality at the Source (QatS) is a division of lean manufacturing concepts. The standard explains that the quality is not just measured at the end of the production, but it should be evaluated and managed at each step of the production process. Regrettably, it is one of the most misinterpreted and ignored of the 14 building blocks.
Quality at Source is made of five aspects:
- Consistent work
- Self-examination
- Successive examination
- Visual management and
- Error proofing and incessant upgrading
The representation of Quality at the Source is the Andon light. This light shows the quality standard at the workstation, the light will turn on when the quality drops to a certain measure. Throughout this situation, the Work stops and a team of workers and engineers start resolving the issue to get rid of the source of the dreadful production.
Jidoka Concepts
Jidoka implies the capacity of humans or machines to mark an irregularity or variance condition in materials, machines, or approach, and to make sure that the irregularity does not go by or move on to the ensuing process. This is known as In Station Process Control (ISPC).
The aim of ISPC is to:
- Create quality by preventing the mass production of faulty products
- Prevent harming employees or injury to any part, or damage of device, or equipment upon the occurrence of an unusual condition
- Disconnect human work from machine work
As per Toyota’s website, the term ‘jidoka’ automation with a human touch. Typically, completed parts and products are examined by an inspector before making the final delivery to the end user. Regardless of examination, a variety of finished goods does not make sure error-free parts.
The figure demonstrates that TPS is sturdily dedicated to “build the quality into the process”, in which all team members have the accountability to examine quality carefully at each phase of his/her work so that errors are not passed downstream.
Every team member is familiar with such thinking and is conscious that “the downstream process is a customer” and must never be held with a faulty product. In case there is a flaw in the device, or it is not performing normally, either the machine itself should be competent to reveal the concern in a manner, for instance, making noise, variation in speed, churning out faulty products, etc.;
Or some system should be capable to identify the concern and discontinue function. Mistake-proofing instruments are frequently used as straightforward measures for this reason. This even enables maintaining the quality.
