Process that helps an equipment operator avoid mistakes
Poka-yoke (ポカヨケ, [poka joke]) is
a Japanese term that means "mistake-proofing" or "error 🌧️ prevention". It is also
sometimes referred to as a forcing function or a behavior-shaping constraint.
A
poka-yoke is any mechanism in 🌧️ a process that helps an equipment operator avoid (yokeru)
mistakes (poka) and defects by preventing, correcting, or drawing attention to 🌧️ human
errors as they occur.[1] The concept was formalized, and the term adopted, by Shigeo
Shingo as part of the 🌧️ Toyota Production System.[2][3]
Etymology [ edit ]
Poka-yoke was
originally baka-yoke, but as this means "fool-proofing" (or "idiot-proofing") the name
was changed 🌧️ to the milder poka-yoke.[4] Poka-yoke is derived from poka o yokeru
(ポカを避ける), a term in shogi that means avoiding an 🌧️ unthinkably bad move.
Usage and
examples [ edit ]
More broadly, the term can refer to any behavior-shaping constraint
designed into a 🌧️ process to prevent incorrect operation by the user.
A simple poka-yoke
example is demonstrated when a driver of the car equipped 🌧️ with a manual gearbox must
press on the clutch pedal (a process step, therefore a poka-yoke) prior to starting an
🌧️ automobile.[5] The interlock serves to prevent unintended movement of the car. Another
example of poka-yoke would be the car equipped 🌧️ with an automatic transmission, which
has a switch that requires the car to be in "Park" or "Neutral" before the 🌧️ car can be
started (some automatic transmissions require the brake pedal to be depressed as well).
These serve as behavior-shaping 🌧️ constraints as the action of "car in Park (or Neutral)"
or "foot depressing the clutch/brake pedal" must be performed before 🌧️ the car is allowed
to start. The requirement of a depressed brake pedal to shift most of the cars with 🌧️ an
automatic transmission from "Park" to any other gear is yet another example of a
poka-yoke application. Over time, the 🌧️ driver's behavior is conformed with the
requirements by repetition and habit.
When automobiles first started shipping with
on-board GPS systems, it 🌧️ was not uncommon to use a forcing function which prevented the
user from interacting with the GPS (such as entering 🌧️ in a destination) while the car
was in motion. This ensures that the driver's attention is not distracted by the 🌧️ GPS.
However, many drivers found this feature irksome, and the forcing function has largely
been abandoned. This reinforces the idea 🌧️ that forcing functions are not always the best
approach to shaping behavior.
The microwave oven provides another example of a forcing
🌧️ function.[6] In all modern microwave ovens, it is impossible to start the microwave
while the door is still open. Likewise, 🌧️ the microwave will shut off automatically if
the door is opened by the user. By forcing the user to close 🌧️ the microwave door while
it is in use, it becomes impossible for the user to err by leaving the door 🌧️ open.
Forcing functions are very effective in safety critical situations such as this, but
can cause confusion in more complex 🌧️ systems that do not inform the user of the error
that has been made.
These forcing functions are being used in 🌧️ the service industry as
well. Call centers concerned with credit card fraud and friendly fraud are using
agent-assisted automation to 🌧️ prevent the agent from seeing or hearing the credit card
information so that it cannot be stolen. The customer punches 🌧️ the information into
their phone keypad, the tones are masked to the agent and are not visible in the
customer 🌧️ relationship management software.[7]
History [ edit ]
The term poka-yoke was
applied by Shigeo Shingo in the 1960s to industrial processes designed 🌧️ to prevent human
errors.[1] Shingo redesigned a process in which factory workers, while assembling a
small switch, would often forget 🌧️ to insert the required spring under one of the switch
buttons. In the redesigned process, the worker would perform the 🌧️ task in two steps,
first preparing the two required springs and placing them in a placeholder, then
inserting the springs 🌧️ from the placeholder into the switch. When a spring remained in
the placeholder, the workers knew that they had forgotten 🌧️ to insert it and could
correct the mistake effortlessly.[8]
Shingo distinguished between the concepts of
inevitable human mistakes and defects in 🌧️ the production. Defects occur when the
mistakes are allowed to reach the customer. The aim of poka-yoke is to design 🌧️ the
process so that mistakes can be detected and corrected immediately, eliminating defects
at the source.
Implementation in manufacturing [ edit 🌧️ ]
Poka-yoke can be implemented at
any step of a manufacturing process where something can go wrong or an error can 🌧️ be
made.[9] For example, a fixture that holds pieces for processing might be modified to
only allow pieces to be 🌧️ held in the correct orientation,[10] 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.[10]
Shingo recognized three types of poka-yoke for detecting
and preventing errors 🌧️ in a mass production system:[2][9]
The contact method identifies
product defects by testing the product's shape, size, color, or other physical
🌧️ attributes. The fixed-value (or constant number) method alerts the operator if a
certain number of movements are not made. 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.[2]
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.[citation
needed]
Benefits of poka-yoke implementation [ edit ]
A typical feature of poka-yoke
solutions is that they don't 🌧️ let an error in a process happen. Other advantages
include:[11]
Less time spent on training workers;
Elimination of many operations
related to 🌧️ quality control;
Unburdening of operators from repetitive
operations;
Promotion of the work improvement-oriented approach and actions;
A reduced
number of rejects;
Immediate action when 🌧️ a problem occurs;
100% built-in quality
control;
Preventing bad products from reaching customers;
Detecting mistakes as they
occur;
Eliminating defects before they occur.
See also 🌧️ [ edit ]
References [ edit ]
