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Poka-yoke (ポカヨケ ?) (IPA: [poka joke]) is a Japanese term that means "fail-safing" or "mistake-proofing". A poka-yoke is any mechanism in a Lean manufacturing process that helps an equipment operator avoid (yokeru) mistakes (poka). Its purpose is to eliminate product defects by preventing, correcting, or drawing attention to human errors as they occur.[1] The concept was formalised, and the term adopted, by Shigeo Shingo as part of the Toyota Production System.[2][3] It was originally described as baka-yoke, but as this means "fool-proofing" (or "idiot-proofing") the name was changed to the milder poka-yoke.

More broadly, the term can refer to any behavior-shaping constraint designed into a product to prevent incorrect operation by the user.

Contents

Implementation in products

Examples of poka-yoke in consumer products include:

  • Automatic transmissions: the inability to remove a car key from the ignition switch of an automobile if the automatic transmission is not first put in the "Park" position, so that the driver cannot leave the car in an unsafe parking condition where the wheels are not locked against movement. This is an example of trapped key interlocking.
  • 3.5" floppy disks: the top-right corner is shaped in a certain way so that the disk cannot be inserted upside-down.
  • High-security padlocks: it is impossible to remove the key from some high-security padlocks unless the shackle on the padlock is closed. Only by locking the padlock can the key be removed. Security mistakes/accidents are therefore much less likely to occur, particularly where the padlock key is kept on a chain attached to someone's belt. This is because the design ensures that a key cannot easily be left in an unlocked padlock, or a padlock left unlocked after opening it, or not fully closing the shackle of a padlock. Each of these three scenarios would be dangerous in high-security scenarios such as military installations, armories, prisons or bonded warehouses. In contrast, most standard-security padlocks do allow a key to be removed from a padlock, regardless of whether the shackle is closed or not.
  • UK 13 amp electric plugs: it is impossible to wrongly insert the plug into the socket, due to its arrangement of three rectangular pins.
  • Microwave ovens: a door switch automatically disconnects the activation button when the door of the oven is opened. As a result, it is impossible to cook anything in a microwave oven unless the door (which contains a Faraday cage to block microwaves) is fully closed. If it were possible to activate an oven with the door open, this would allow dangerous leakage of high intensity microwave radiation, which would be very harmful to any living creatures in the immediate area.

Implementation in manufacturing

Poka-yoke can be implemented at any step of a manufacturing process where something can go wrong or an error can be made.[4] For example, a jig that holds pieces for processing might be modified to only allow pieces to be held in the correct orientation,[5] or a digital counter might track the number of spot welds on each piece to ensure that the worker executes the correct number of welds.[6]

Shigeo Shingo recognized three types of poka-yoke for detecting and preventing errors in a mass production system:[4][2]

  1. The contact method identifies product defects by testing the product's shape, size, color, or other physical attributes.
  2. The fixed-value (or constant number) method alerts the operator if a certain number of movements are not made.
  3. The motion-step (or sequence) method determines whether the prescribed steps of the process have been followed.

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. In Shingo's lexicon, the former implementation would be called a warning poka-yoke, while the latter would be referred to as a control poka-yoke.[7]

Shingo argued that 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.[8]

See also

References

  1. ^ Robinson, Harry (1997). "Using Poka-Yoke Techniques for Early Defect Detection". http://facultyweb.berry.edu/jgrout/pokasoft.html. Retrieved May 4, 2009.  
  2. ^ a b Shingo, Shigeo; Andrew P. Dillon (1989). A study of the Toyota production system from an industrial engineering viewpoint. Portland, Oregon: Productivity Press. p. 22. ISBN 0-915299-17-8. OCLC 19740349.  
  3. ^ John R. Grout, Brian T. Downs. "A Brief Tutorial on Mistake-proofing, Poka-Yoke, and ZQC". MistakeProofing.com. http://www.mistakeproofing.com/tutorial.html. Retrieved May 4, 2009.  
  4. ^ a b "Poka Yoke or Mistake Proofing :: Overview". The Quality Portal. http://thequalityportal.com/pokayoke.htm. Retrieved May 5, 2009.  
  5. ^ Nikkan Kogyo Shimbun (1988). Poka-yoke: improving product quality by preventing defects. Productivity Press. p. 111.  
  6. ^ Nikkan Kogyo Shimbun (1988). Poka-yoke: improving product quality by preventing defects. Productivity Press. p. 209.  
  7. ^ Shingo, Shigeo; Andrew P. Dillon (1989). A study of the Toyota production system from an industrial engineering viewpoint. Portland, Oregon: Productivity Press. p. 21. ISBN 0-915299-17-8. OCLC 19740349.  
  8. ^ "Pokayoke". The Manufacturing Advisory Service in the South West (MAS-SW). http://www.swmas.co.uk/info/index.php/Pokayoke. Retrieved May 2, 2009.  

Further reading

External links

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Poka-yoke (ポカヨケ?) (IPA: [poka joke]) is a Japanese term that means "fail-safing" or "mistake-proofing". A poka-yoke is any mechanism in a lean manufacturing process that helps an equipment operator avoid (yokeru) mistakes (poka). Its purpose is to eliminate product defects by preventing, correcting, or drawing attention to human errors as they occur.[1] The concept was formalised, and the term adopted, by Shigeo Shingo as part of the Toyota Production System.[2][3] It was originally described as baka-yoke, but as this means "fool-proofing" (or "idiot-proofing") the name was changed to the milder poka-yoke.

More broadly, the term can refer to any behavior-shaping constraint designed into a product to prevent incorrect operation by the user.[citation needed]

Contents

Implementation in manufacturing

Poka-yoke can be implemented at any step of a manufacturing process where something can go wrong or an error can be made.[4] For example, a jig that holds pieces for processing might be modified to only allow pieces to be held in the correct orientation,[5] or a digital counter might track the number of spot welds on each piece to ensure that the worker executes the correct number of welds.[6]

Shigeo Shingo recognized three types of poka-yoke for detecting and preventing errors in a mass production system:[2][4]

  1. The contact method identifies product defects by testing the product's shape, size, color, or other physical attributes.
  2. The fixed-value (or constant number) method alerts the operator if a certain number of movements are not made.
  3. The motion-step (or sequence) method determines whether the prescribed steps of the process have been followed.

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. In Shingo's lexicon, the former implementation would be called a warning poka-yoke, while the latter would be referred to as a control poka-yoke.[7]

Shingo argued that 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.[8]

See also

References

  1. ^ Robinson, Harry (1997). "Using Poka-Yoke Techniques for Early Defect Detection". http://facultyweb.berry.edu/jgrout/pokasoft.html. Retrieved May 4, 2009. 
  2. ^ a b Shingo, Shigeo; Andrew P. Dillon (1989). A study of the Toyota production system from an industrial engineering viewpoint. Portland, Oregon: Productivity Press. p. 22. ISBN 0-915299-17-8. OCLC 19740349. 
  3. ^ John R. Grout, Brian T. Downs. "A Brief Tutorial on Mistake-proofing, Poka-Yoke, and ZQC". MistakeProofing.com. http://www.mistakeproofing.com/tutorial.html. Retrieved May 4, 2009. 
  4. ^ a b "Poka Yoke or Mistake Proofing :: Overview". The Quality Portal. http://thequalityportal.com/pokayoke.htm. Retrieved May 5, 2009. 
  5. ^ Shimbun, Nikkan Kogyo (1988). Poka-yoke: improving product quality by preventing defects. Productivity Press. p. 111. ISBN 978-0-915299-31-7. 
  6. ^ Shimbun, Nikkan Kogyo (1988). Poka-yoke: improving product quality by preventing defects. Productivity Press. p. 209. ISBN 978-0-915299-31-7. 
  7. ^ Shingo, Shigeo; Andrew P. Dillon (1989). A study of the Toyota production system from an industrial engineering viewpoint. Portland, Oregon: Productivity Press. p. 21. ISBN 0-915299-17-8. OCLC 19740349. 
  8. ^ "Pokayoke". The Manufacturing Advisory Service in the South West (MAS-SW). http://www.swmas.co.uk/info/index.php/Pokayoke. Retrieved May 2, 2009. 

Further reading

External links


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