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