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Mistake Proofing

 

Mistake Proofing or Poka Yoke - is a technique for eliminating errors by making it impossible to make mistakes in the process. It is often considered the best approach to process control.

It works on the principle - "It is good to do it right the first time. It is even better to make it impossible to do it wrong the first time".

Mistake Proofing can be preventive (prevent the error from occurring) or detective (detect the error if it happens) in nature and is usually implemented in one of the following ways.

1. Warning: audio and/or visual warning either before the error occurs or after it has occurred.
2. Control: errors are not possible or even if an error occurs, it is not allowed to move to the next step.
3. Shutdown: machine or process shutdown when an error is about to happen or as soon as an error occurs.

 

 

An application oriented question on the topic along with responses can be seen below. The best answer was provided by Arunesh Ramalingam on 21st Septemer 2017. 

 

 

Question

Q11. While it is understood that mistake proofing is immensely effective, there is some confusion about what it means or intends to achieve. Let us look at the following interpretations of Poka Yoke - 

 

  1. The human error will not happen at all.  
  2. Human error may continue to happen but the defect will not happen. 
  3. Human error may happen, the defect is less likely to happen.
  4. Human error may happen, the defect will also happen but will be detected and corrected automatically.  

 

Which of the above interpretations are correct? Please explain with valid examples. 

 

Note for website visitors - Two questions are asked every week on this platform. One on Tuesday and the other on Friday.

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Poka -yoke or Mistake Proofing is about using a process or design feature and control mechanisms to

  • prevent defects,
  • detect them if there are not preventable.
  • reduce the severity of the defects.

The main motive is to: PREVENT a defect from occurring and if that is not possible, DETECT the defect every time it occurs.

 

It is critical to prevent and detect errors/ defects as early as possible in the process because the later they are found the more expensive they become i.e. costs associated with them increases - more materials, labour, overhead, time. While implementing poka-yoke designs, care should also be taken that the implementation does not enhance any other issues or open new issues that may cause defects.

 

Poka -yoke or Mistake Proofing has varying degrees of effectiveness. - Control Vs Warning Poka yoke. One must balance getting the most effective poka-yoke while keeping in mind the practical and economic feasibility of the solution.

 

I feel all the interpretations provided in the question are all correct and validate the varying degrees of effectiveness.

 

1.       The human error will not happen at all. 

Example:

  • Rectangular design of 3.5” floppy disc so that the wrong side cannot be inserted.
  • SIM card slot in cell phones is designed in such a way that user can insert SIM card in correct way only.

There is no chance for user to make a mistake while putting SIM card in a cell phone or floppy in the drive.

 

2.       Human error may continue to happen but the defect will not happen.

Example:

  • Validation check when creating new password to contain the required combination of Upper, lower case, numeric and special characters to ensure a strong password. The system does not accept a password unless it fulfils the criterion.
  • Double Entry Box: Most websites & software where one needs to enter a critical bank account number, or a password create option, users are asked to enter the same value twice (with paste option disabled). This is to ensure people haven't made a mistake while entering the value, and that both boxes hold the same value

 

3.       Human error may happen, the defect is less likely to happen.

Example:

  • Some of the email software pop up an error message like “there is no attachment, do you want to send it anyway?”, if they find the key words “Find attached” (or other variants of the same) and do not see an attachment when the user tries to send the email.
  • Some Email software pop up a message if the subject is missing when the user tries to send the message.
  • Car Seat belt Warning indicator beeps to warn that the user has forgotten to put on the seat belt, if he drives without putting on the belt.

 

4.       Human error may happen, the defect will also happen but will be detected and corrected automatically. 

Example:

  • Microsoft word, Google search automatically corrects typographical spelling error.
  • Auto logout functionality in websites (especially Banks). When user forgets to logout before closing the website and reopens, then he has to provide the credentials and log back in.

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Inarguably all the above 4 statements holds true for Poka Yoke, as the intention of Poka Yoke is to either prevent the mistakes or detect the defects. Prevention prevents errors from occurring or prevents those errors from causing defects. Detection identifies a defect and immediately initiates a corrective action to prevent multiple defects from leaving the workstation.

Detection devices are usually used to deal with the errors that is difficult to eliminate or is under review and the main idea of prevention techniques is to keep an error from producing multiple defects.

Now let us take a look at the 4 statements and how poka yoke is applied to each

The human error will not happen at all

This is a kind of Prevention Poka Yoke and is generally associated with design. Some examples could be Kettle cut off switch, USB ports plug in, Plug points etc.

Human error may continue to happen but the defect will not happen.

This is a detection Poka Yoke, in such cases the mistake proofing technique is implemented such that even if the operator makes a mistake the defect will not happen e.g a machine will not start if all the components are not put in its place, a  printer will wait for the paper feed if there is no paper in the tray etc

Human error may happen, the defect is less likely to happen

This is also a detection poka yoke, wherein the chances of defect happening is reduced but not completely eliminated. Examples of such scenario is the auto cut feature while filling petrol, Alerts on printer ink being low, machines shutting down when the sensor detects some abnormality so that operator can take corrective action and restart the machine etc

Human error may happen, the defect will also happen but will be detected and corrected automatically.

Another detection poka yoke scenario, one example of such scenario is Spell check feature in Microsoft office products like word, excel, email etc. wherein even if we make mistake it will be autocorrected.

 

Thanks

Jisha Nair

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I suppose the 4th option i.e. 'Human error may happen, the defect will also happen but will be detected and corrected automatically. ' is most appropriate interpretation for poka-yoke.

 

Whenever and whichever process humans are involved, error can't be elimitated in totality. If error happens, defect will happen. Most important is to ensure that the defect is rectified and not allowed to pass to next stage, else this would lead to output being defective.

 

There are several examples of poka-yoke. Would like to site one such example from my field-

Circuit breakers - they trip in case of overload current and the current  flow stops 

The breaker don't stop the overload current from reaching the circuit but doesn't allow it to flow through remaining circuit. Thus saving the remaining elements which are mostly high value items. 

Conclusion- though the defect occurred i.e. circuit breaker tripped,   it has saved the remaining elements i.e. defective circuit creation   has been avoided.

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Mistake proofing is intended in building up a system/process which eliminates, replaces, prevents, facilitates, detects and mitigates errors leading to failures. One can deploy few or all of these characteristics to make the setup error free. Since 94% of the time the problems are system driven rather than human misses, it becomes imperative to have an acknowledgement of the common causes, prevention of special causes in the systems and promotion of continuous improvement onto people and processes.

 

Let us discuss the cases below

 

The human error will not happen at all – Never is really harsh to use. If we measure from six sigma stand point, then it is possible provided the environment is controlled and standardized. Bomb squad, Pit stop for F1 cars and critical surgeries are a few examples.

 

Human error may continue to happen but the defect will not happen - This is possible when the specification limits and control limits are way too accommodating. The voices are not heard and corresponding measurements are not fixed. Neither designing issues are worked upon nor the customer is expecting any change with the status quo.

 

Human error may happen, the defect is less likely to happen - Possible again. User making a  wrong entry and the systems identifying, prompting and ensuring correction. Defect is alerted and failure is averted.

 

Human error may happen, the defect will also happen but will be detected and corrected automatically - Human and system interface at its best. Human error while flying a plane is detected and the change is mitigated by the system correcting the deviation and confirming back to the standard.

 

Below are the common human mistakes been mapped to the mistake proofing principles. The matrix is subjected to severity, occurrence and detection specific to the environment and objectives.

 

HUMAN MISTAKES and PROOFING

 

Elimination (remove to improve)

Replacement (deploy a reliable substitute )

Prevention ( modify to avoid)

Facilitation ( Visuals and tools )

Detection (identify & rectify)

Mitigation ( cushioning the impact)

Forgetfulness                    

X

X

X

X

 

 

Misunderstanding

X

 

X

X

 

 

Wrong identification

X

 

 

X

X

 

Lack of experience

 

 

X

X

X

X

Willful (ignoring rules or procedure)

X

X

 

X

 

X

Inadvertent or sloppiness

X

 

 

 

X

X

Slowness

X

X

 

 

X

 

Lack of standardization

X

 

 

X

X

X

Surprise (unexpected machine operation, etc.)

 

 

 

 

X

X

Intentional (sabotage)

 

 

X

 

X

X

 

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Primarily Poka Yoke is about setting of system where human error will not happen at all. Example is in case of Car, driver will be able to shift gears only by pressing the clutch pedal, this ensures that there is no uneven movements as the gear is shifted. Also in many cases car can be started only if brake pedal is pressed which ensures that there is no sudden movement of car.

In case of human error may continue to happen but defects will not happen, where the fixture of machine would be equipped with the sensor, it will make sure that fixture does not operate unless the part is appropriately inserted in fixture.

In case of error may happen, defect also may happen but will be detected and corrected, example would be auto correction feature on computers and mobiles.

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The statement Human error may happen, the defect will also happen but will be detected and corrected automatically seems to be correct because Poka - Yoke helps us to detect and preventing errors while doing some work whether it is manufacturing industry or service industry. Either the operator is alerted when a mistake is about to be made, or the poka-yoke device actually prevents the mistake from being made. The former implementation would be called a warning poka-yoke, while the latter would be referred to as a control Poka- Yoke. For example in manufacturing industry a digital counter attached on spot welding machine which indicates to an operator to have an exactly required number of spots to parts for welding. Another example also A fixture is redesigned or modified so that a part can fit into it in a particular orientation, so it will prevent to produce wrong part while welding.

 

if we see mobile phones, sim slot is called as Poka- Yoke in which sim goes only in one direction, every time we used to do mistake while putting sim inside mobile but it does allow us because of the design of sim slot.

 

If we see automatic transmission cars, cars will not start unless we don't press the brake pedal, on the other hand, some have a switch that requires being a car in the park of neutral before the car to start.

 

Let me discuss one case of my company, two different cars using two different Door Panel of different number of holes into it but of same size & orientation but the problem is that both door panel can be fixed in the  fixture at the time of spot welding and operator was not able to identify that which model door panel is going to process every time. There was a chance of door panel mixing of both models at back end due to same size & same orientation. So Some Poka- Yoke done in the fixture to differentiate in both model door panel by identifying some holes which are not common in both panels. A PU Pad Pressing Pin connected with a sensor which is connected with alarm. PU Pad used so that it will not generate dent to the panel.Whenever door panel of another car fix into the fixture it presses the pin and gives alarm because this pin is in the same direction where hole location is there in the door panel of one car but not in another car door panel. 

 

So by doing this it prevents wrong door panel to be processed and gives warning also to the operator that there is the wrong panel in the fixture.

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Poka Yoke refers to mistake proofing and its aim is to "prevent" mistakes, by implementing thoughtful precautions upstream in the process.

 

The ideal state is to have a design in the process in such a way that the mistake cannot be caused at all. One popular example is to have a bridge built across the railway track when a road has to cross the track. It is often referred to as Level-3 Poka Yoke, that prevents or eliminates the possibility  a defect (collision) occurrence. This type of Poka Yoke is possible only by pre-planned design of the process and investments, and will be highly effective. Another example would be a car seat belt that automatically fastens upon the driver, when the ignition is turned on.

 

It may not be possible to get a preventive Poka Yoke implemented in all situations immediately. There we resort to a Poka Yoke at a control level, often refers to as Level-2 Poka Yoke. In the rail-track example, where the bridge is not an immediate possibility, we can have a gate that will stop the road traffic. The gates may be designed to close whenever the signal is green for an approaching train to cross. While this level of Poka Yoke is possible with lower cost, effort and time, it will have some risks and inconveniences. There is a possibility of malfunctioning of the gate closing sensors, or a motorist crashing onto the gate. In this example, it also causes inconvenience to the road users, who will have to wait until the train crosses. As for the seat belt example, in this case, it could be that, unless you fasten the seat-belt, the car engine would not start. The Level 2 Poka Yoke would not be as effective and advantageous compared to Level-3, however, Level-2 Poka Yoke's are quite popular and widely made use of.

 

In situations where even a Level-2 poka yoke is not possible, the rail-track example can still have a control based on warning alarm, signals flashing, or a manually governed gate. These are often refereed to as Level-1 Poka Yoke. In such cases there is dependency on the alertness and action by a human to respond appropriately to the warnings to prevent the mistake from happening. For car seat belt example, if not worn,  may result in an alarm beeping with a red light flashing, but will not prevent you from starting the engine. Obviously the reliability of such controls are the least compared to the other levels and human dependency is higher.

 

Considering the understanding of PokaYoke and the levels of implementation possible, let us examine the 4 definitions one by one.

 

1. Human error will not happen at all..... This is certainly not right, since the very purpose of going for Poka Yoke is to reduce the dependency on human to prevent error occurrence. However,  as we tend towards level-3 Poka Yoke, the effort is made to reduce the circumstance(s) in which a human can falter.

 

2. Human error may continue to happen but the defect will not happen... This is an ideal objective for Poka Yoke, however depending upon the level of Poka yoke, the elimination of defect occurrence may not be guaranteed, though the closest to this expectation is achieved by the level-3 Poka yoke.

 

3. Human error may happen, the defect is less likely to happen......Even when a human lapse occurs, it should not get translated to a defect; this is the premise upon which the Poka Yoke is evolved. However, we still maintain that the likelihood of defect occurrence is greatly reduced though may not be eliminated. 

 

4. Human error may happen, the defect will also happen but will be detected and corrected automatically..... This may not be in line with a Poka Yoke definition, since the defect has been allowed to occur, but we resort to a containment and rework action. By Poka Yoke, we certainly expect more than this scenario.

 

With these deliberations and examples, the 3rd definition appears most appropriate that "Human errors may happen, but the defect is less likely to happen".

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Mistake proofing, or its Japanese equivalent "Poka-Yoke", is the use of any automatic device or method that either makes it impossible for an error to occur or makes the error immediately obvious once it has occurred.

 

For each error, think of potential ways to make it impossible for the error to occur. Consider:

  1. Elimination—eliminating the step that causes the error - Expensive and requires huge investement of time cost and efforts
  2. Replacement—replacing the step with an error-proof one - Less expensive than Elimination
  3. Facilitation—making the correct action far easier than the error - Inexpensive and has further scope to move up

 

Considering the above definition, it will be best to rate the 4 interpretations.

  • The human error will not happen at all - Ranks 3rd - practically only possible with huge investment of efforts and full automation
  • Human error may continue to happen but the defect will not happen - Ranks 1st - Humans will continue to make mistakes, hence Poka-Yoke can help mitigate the risk and prompt/feedback about the error/mistake
  • Human error may happen, the defect is less likely to happen - Ranks 2nd - partial mistake proofing
  • Human error may happen, the defect will also happen but will be detected and corrected automatically - Ranks 4th - This is not mistake proofing at all - If it can be detected and corrected automatically then there is a scope of full automation.

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As per me 4th interpretation is correct. It is natural that human errors are tend to happen. There are even chances of errors getting converted to defect. But as per poka yoke, it ensures that the defects are identified at detection stage and corrected so that it does not get converted to defective.

Example. In a customer service industry, there are chances that a staff gives wrong information to client and makes an error, but further on confirmation it is obvious that the system will identify the defect and correct automatically.

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Let us have the 4 interpretations as each case. Before that let us see the definition of Poka-yoke

Poka-Yoke means mistake-proofing.  It basically tries to eliminate the error that can be induced by an operator (user)

 

Case 1 : The human error will not happen at all

Eg: Take the case of 3-pin plug. It cannot fit into any other socket other than a 3-pin hole. This serves as a best poka-yoke mechanism

 

Case 2 : Human error may continue to happen but the defect will not happen

There cannot be any process or system in the world which can be defect free irrespective of whether human error happens or not.  In this case, if human error happens, then defect is bound to come. So this case is not valid when dealing with Poka-yoke

 

Case 3: Human error may happen, the defect is less likely to happen

 Consider a measuring jar – say for instance, a feeding bottle of a child. Here, the feeding bottle serves as the Poka-Yoke tool.  Person using it, might by mistake put more milk occasionally due to lapse of concentration or by oversight, but in general, because of the measuring unit, the chance for that mistake is very limited.

 

Case 4 : Human error may happen, the defect will also happen but will be detected and corrected automatically

Eg: In Mobile packing, this situation (case 4) can occur.  There can be set of accessories that may come as part of a box and weighing 300 grams cumulative.  Each of this box would be weighed at the as part of the mobile packing process. There is a chance that few accessories might not be placed in the box and hence the weight (in grams) might be less than 300 grams.  There may also be chances where extra accessories might be accidentally placed on the box resulting in more weight (in grams) added to the box. Both these errors can be corrected with the weighing machine in place at final stage of the production process.  So the missing item or extra items can be detected and corrected.  

 

Conclusion:  Case 1, Case 3, Case 4 are correct interpretations.  Case 2 is not a valid interpretation.

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The human error does happen but it can be corrected before creating defects. The effectiveness is judged after observing the performance.

  1. The rating of "Occurrence" and/or "Detection" have increased thereby increasing the RPN for the process. Poka Yoke techniques of mistake proofing are applied to these processes in order to lower the ratings of Occurrence and / or detection.

    Analysis of Customer complaints also reveals activities which are in need of mistake proofing, in order to achieve 'Zero Defect' level of working. Undertake application of Poka Yoke techniques to these processes.
  2. The selected mistake proofing technique should qualify the following criteria:
    • Inexpensive.
    • Based upon common sense, preferably of the operator or the 1st line employee.
    • It MUST eliminate Occurrence / Detection of the problem at the source itself.
  3. Occurrence oriented Poka Yoke should follow the procedure as below:
    A) First classify the source of 'Occurrence' as follows:
    B) After having classified the source, apply one of the following techniques, as appropriate, to prevent the occurrence:
    1. Required action is NOT performed or is performed incorrectly.
    2. Undesired action is exercised.
    3. Information essential for performing the action is mis-interpreted.
    4. Mistake occurs due to complexity.
    • Use of 100% prevention devices such as Fouling Pins, Contoured locators or templates, Proximity or Photo-electric sensors, Limit or Micro switches, Warning lights or Buzzers, Pressure transducers.
    • Design to modify to ensure that in assembly the parts shall not join if aligned wrongly.Machine will not run if operators' hands or feet are not outside or if the job & tooling are not in right position.
    • These techniques should be integral part of the process.The devices are placed sufficiently close to where the mistakes occur, providing fast feedback to the operator, of mistakes occurring.
  4. Detection oriented Poka Yoke should use one of the following techniques for ensuring 100% detection of the mistake:
    • It should be autonomous inspection occurring without intervention.
    • It should be 100% inspection which occurs without intervention.
    • It should determine 'before the fact' whether the conditions for 100% quality exist or not.
    • It should make the error visible to the operator.
    • Consider supply of exactly made kits of components to the assembler, so that any balance part will signal error in assembly.
    • Consider use of electronic sensors to activate warning lights or buzzers.
    • Use color coded parts or graphics.
    • Make use of contact devices e.g. Fixtures, Limit switches, probes or Non-contact devices e.g. LEDs, Pressure transducers etc.

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POKAYOKE – It is mistake proofing technique, in which opportunities of blocking the possibilities of errors/faults/mistakes/defects/ill-impact are found out, counter measures are designed & implemented in such a way that system does not allow such faults to occur & becomes immune to it. Unquestionably it is a very useful & effective concept in industry to prevent errors and protect customers from undesirable effects. Poka means mistake and Yoke means prevention – these are Japanese words. Japanese manufacturing industry institutionalized the concept of Pokayoke and automobile industry world wide accepted and improvised by bringing more and more sensors, logical machine programming, feedback techniques, measurements and real time reaction system in automation. Further to add in its maturity many lean practitioners worked on autonomation (intelligent Automation) to prevent errors or if cannot prevent then at least correct it or if at all cannot prevent or correct then detect as soon as possible and give alert to process operator for acting upon it.

Which of the given interpretations are correct? Explanation with valid examples. 

  1. The human error will not happen at all.  – It is very difficult for a human to not to make any mistake; since human are live person with a mind and emotions inbuild, we are bound to make some mistakes. Its because we humans are curious, and we learn continuously. We humans learn by trial and error. Hence errors are part and parcel of our behaviours and human life. Interpreting POKAYOKE as “human error will not happen at all” is thus incorrect. POKAYOKE mechanism will immediately identify errors made by human and prevent defect to happen or either correct it or alert the human to protect the customer (customer may be next process or next human in lean chain). Human error may be intentional or unintentional. Nobody decide to do mistake but it happens unintentionally. Mood of human is never constant and there is always a chance of deviation or abnormal behaviour by any human at work. No POKAYOKE in the word can “prevent” 100% human errors. Also % errors can be reduced by continuous training, high skill, Best workplace management and high motivation for perfection.

Examples – Highly skilled workers, doctors, pilots, sports person and professionals make mistakes in their respective area, its evident from history of great people. Nothing can really prevent human errors to happen. It does happen but right POKAYOKE does not allow its consequences further.

  1. Human error may continue to happen but the defect will not happen. – Yes; this is appropriate interpretation of POKAYOKE. Having known that human errors will happen (because of human’s nature); sufficient process knowledge, training and skill is imparted into humans who are responsible for processes, to stick to standard operating conditions and errors are minimized. Nevertheless, it is essential for lean practitioner to design the mechanism (POKAYOKE) to not let human error result into defect. This can be achieved by sensors (by sensing the error/abnormality created by human) and building on the logic to change the course of process or stop the process (only if correction is not possible) to prevent defect to get created. Sensor’s signal is taken as input in POKAYOKE logic. This kind of POKAYOKE are best to have.

Examples – (a) When operator loads the part in machine in wrong orientation, then a shape based sensors (e.g proximity sensor) can sense its wrong orientation and activates the correction mechanism and prevents process to develop defect because of this reason. (b) Even if you forget to switch off the lights while leaving the room unoccupied, Movement sensor senses the ‘No Movement’ in the room and then lights are automatically puts on OFF condition after a while; preventing the wastage of energy further. (c) When wrong coloured part is loaded in the machine for processing; then colour sensor stops the process, till correct coloured part is loaded, when colour is a CTQ; and defect is prevented.

  1. Human error may happen, the defect is less likely to happen. – Yes; this is also an appropriate interpretation of POKAYOKE. In this human errors are detected and appropriate actions are inbuilt into process steps to prevent defect creation. However, is not possible to capture all the errors or not possible to build logic for all the type of corrections. These type of POKAYOKE will be good to have but will result in some % of wastages; though considerably less than not having any POKAYOKE. Pokayoke logic is same as explained in case-2 above; however, most of the industrial level sensing/technology may not be 100% perfect all the time, moreover regular wear/tear, aging, environmental factors come in effect and degrades the sensing efficiency and reduces the probability of 100 % defect prevention. Regular TPM practices is the key to restore POKAYOKE to its optimum performance.

Example – (a) Vision based sensors present in sheet metal press may not detect minor abnormality due to dust on sensor; and result into slightly less efficiency of POKAYOKE. But in most of the cases sensor will prevent defect to happen. (b) Even if a driver bangs the car on to a pole, airbags will immediately blow up and prevent injury to driver; there is less likely that driver will hit the head against the steering wheel and get injured.

  1. Human error may happen, the defect will also happen but will be detected and corrected automatically.  -  Yes; this is interpretation of substandard POKAYOKE than case 2 and 3 above. In this case human errors are not detected but defects are detected and appropriate actions are inbuilt into process steps which leads to correction or stoppage of the process, to restrict the defective part reach to next process/immediate customer. This is really a inferior Poka-yoke, but in some cases it is not possible to prevent defect to happen and we have to be dependent on correction only.

Example – (a) In an automatic packing line, if box is not filled up to required weight and goes ahead (abnormality), then at next station position (before final packing lock) weight is checked, if found abnormal then this unit is not packed but send back to previous station through a dedicated route and again filled up to right weight. (b) In a laminator machine, edge of laminate is continuously detected and if found shifted then correction unit shifts in inverse direction with same amount, shift is the defect but it is corrected in next station automatically.

Written by – Vivek Dahake Based on Auto-industry and FMCG industry experience.

 

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Poka-yoke is a Japanese term that means "mistake-proofing" or “inadvertent error prevention”. 

poka-yoke is any mechanism in a lean manufacturing process that helps an equipment operator avoid mistakes. 

 

Poka-yoke can be implemented at any step of a manufacturing process where something can go wrong or an error can be made. 

 

Errors are inevitable in any manufacturing process, but that if appropriate poka-yokes are implemented, then mistakes can be caught quickly and prevented from resulting in defects. By eliminating defects at the source, the cost of mistakes within a company is reduced.

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Mistake proofing, or its Japanese equivalent poka-yoke, is the use of any automatic device or method that either,

makes it impossible for an error to occur OR

makes the error immediately obvious once it has occurred.

 

Given by the above second scenario, it is obvious that there is a scope for the error to occur , but an it is made obvious immediately. Hence, the 2nd point is an apt interpretation – Human Error may continue to happen , but the defect will not happen.

 

Given that most of the business activities can be considered to be a process. All processes have the potential for defects-  Poka Yoke works on a thought that Operators and Machines will sometimes make mistakes(errors) in the flow of the process- Find ways to keeps errors from becoming defects.

 

When it comes to human intervention in a process, we must recognize that it is natural for people to make mistakes.

Ten Types of Human Mistakes

1)      Forgetfulness

2)      Misunderstanding

3)      Wrong Identification

4)      Lack of Experience

5)      Willful (Ignoring Procedure/ Rule)

6)      Inadvertent or sloppiness

7)      Slowness

8)      Lack of Standardisation

9)      Surprise (Unexpected Machine Operation etc.)

10)   Intentional (On purpose/ Sabotage)

 

To curb all the above scope for human errors, Poka Yoke is a mistake proofing method that does not depend on operators catching mistakes and provides immediate feedback 100% times. The best way to eradicate the scope for defects is own the proactive approach and identifying the defect immediately (Point of origin inspection)

Two Poka Yoke system approaches are utilized in production/ Manufacturing which lead to successful Zero Defect Quality (ZDQ):

1)      Control Approach- Shuts down the process when error occurs

Example:. Automatic Shutdown of the heater, with the help of multiple temperature sensors,  when the temperature of the Heating/ Holding cabinet reaches the highest allowed  temperature, thus ensuring that the products that are kept in the cabinet do not get overheated/ Overcooked , which is a defect

2)      Warning Approach- Signals the operator to stop the process and correct the problem.

Example: There is a red light alert and a sound of siren that reaches the main production area if the temperature of the storage freezer goes above a defined danger temperature zone. Thus a very obvious and "unmissable" warning is provided to a section where maximum number of people are present at all times , to check and correct the temperature of the freezer

 

Thus as mentioned above, the 2nd point is an apt interpretation – Human Error may continue to happen , but the defect will not happen.

 

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I put forward the first point...the human error is not possible at all

As in our forging industry we have implemented poka yoke for underheat and overheat billets as per die specification...as the induction billet heater will over heat or under heat billet...it can prove to be very fatal for the person working on forging as well as die...the temp of billets is also important in view of rejection since the pressure and the impact of vertical die on component is also a deciding factor for the life of die as well as providing first pass yield. So the forher will always get a right temp billet to work on in its desired time..

Have a nice day 

Regards

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Mistake Proofing is a Japanese technique that makes it impossible to make an error or makes the error obvious once it has occurred. 

Here all the interpretations are correct. 

1) there are some prevention techniques  like shutdown prevention and control prevention through which error may not happen at all. Ex. These days furniture parts which has to be assembled are easy to do since there is only one way to assemble as per fitting and shape of joints.

 

4) some techniques are also such that error might happen but defect will  happen and get corrected. Ex. Autocorrect option in text messages . We may write incorrect spelling but it will get corrected automatically. 

 

3) human error may happen but defect is less likely. Ex. Warning prevention techniques like red light in traffic signal. Though when it's red light, it means one had to stop but still some people might commit mistake if they were absent minded but chances are less of this case.

 

2) human error may continue to happen but error won't happen in cases of shutdown detection. Example.: When washing machine gets overheated there is auto cut takes place which doesn't let washing machine to fail.

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Thanks everyone for providing your answers. As many of you mentioned, Poke Yoke is not only meant for preventing
errors but also for detecting errors thereby reducing defects or lowering its severity. The trick lies in maintaining a balance between acceptable limit of the defect , cost needed to deploy mistake proofing and practical feasibility of the solution(sometimes most challenging).

 

All the given statements are hence true in some way and Arunesh Ramalingam did the best job of explaining the same. Congratulations and thanks everyone for the participation.

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