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National Guard
Black Belt Training
Module 46
Mistake Proofing
(Poka Yoke)
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CPI Roadmap – Improve
8-STEP PROCESS
6. See
1.Validate 2. Identify 3. Set 4. Determine 5. Develop 7. Confirm 8. Standardize
Counter-
the Performance Improvement Root Counter- Results Successful
Measures
Problem Gaps Targets Cause Measures & Process Processes
Through
Define Measure Analyze Improve Control
TOOLS
ACTIVITIES
•Brainstorming
• Develop Potential Solutions
•Replenishment Pull/Kanban
• Develop Evaluation Criteria
•Stocking Strategy
• Select Best Solutions
•Process Flow Improvement
• Develop Future State Process Map(s)
•Process Balancing
• Develop Pilot Plan
•Standard Work
• Pilot Solution
•Quick Change Over
• Develop Full Scale Action/
•Design of Experiments (DOE)
Implementation Plan
•Solution Selection Matrix
• Complete Improve Gate
•‘To-Be’ Process Mapping
•Poka-Yoke
•6S Visual Mgt
•RIE
Note: Activities and tools vary by project. Lists provided here are not necessarily all-inclusive. UNCLASSIFIED / FOUO 2

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Learning Objective
 Use Lean techniques to improve the process
 Understand and apply Mistake Proofing tools and
techniques
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Class Exercise - Inspection
Purpose: To illustrate that inspection is not only Non-Value
Added but also an ineffective means to achieve quality.
Exercise: You have 60 seconds to count the letter “S” in the
paragraph below. Document your answer below.
Six Sigma Black Belts are assigned to Six Sigma projects. These
projects are solved by identifying, measuring, analyzing,
improving, and finally controlling the measure of interest. Six
Sigma Champions help stomp out barriers to ensure success. Ad
hoc teams lend their process and product skills. As the defect
levels fall, so does the associated cost of poor quality. Six Sigma
projects deliver measurable business results. The Black Belt
resource ensures the program’s success.
Answer: _________
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Mistake Proofing
 A poka-yoke device is any mechanism that either
prevents a mistake from being made or makes the
mistake obvious at a glance
 Simple example – applying brake to shift
transmission from “park”
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Old Process Assumptions
“Defects are inevitable, but can be caught before
leaving the organization or area (check points,
multitude of inspectors, sampling tables, SPC)”
“A disciplined, well-trained and highly motivated
employee will not make mistakes”
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Quality Goal - 99.9%
Is this Good
Enough?
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Quality Goal - 99.9%
 If the product were your heart, you would spend
almost 9 hours a year in cardiac arrest
 There would be 2 unsafe landings at Chicago a day
 One hour of unsafe drinking water every 8 weeks
 200,000 wrong prescriptions each year
 15,000 newborn babies dropped each year
 Nine missspelled words on evry page of every
magazzine
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New Assumption
It is impossible to eliminate all errors
from any task performed by humans.
Indeed, inadvertent errors are both
possible and inevitable
Errors will not turn into defects if
feedback and action takes place at the
Error Stage
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Poka Yoke: What Is It?
 Poka (inadvertent errors) Yokeru (avoid)
 Methods for preventing mistakes becoming defects
 “Quality at Source”
Can you think of an example of Poka Yoke?
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Mistake-Proofing: Conserve Electricity
Door key-card must be
inserted in holder to
activate electricity in room
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Mistake-Proofing the Ketchup lid?
Forget to shake the Ketchup?
H.J. Heinz did their best to keep the watery
liquid part of ketchup from soaking your bun.
Their redesigned bottle lid had a little
reservoir around the spout to catch the liquid.
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Carry-on Luggage Mistake-Proofing
Self-check to determine if the bag is going to fit
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Mistake-Proofing the ATM?
 New generation ATMs
perform transactions
without the card leaving
your hand.
 Chances of leaving your
card in the machine
remote or impossible
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Uses of Mistake-Proofing
 Enforce procedures or sequences
 Signal or stop a process if a defect is created
 Eliminate choices leading to incorrect actions
 Prevent product or process damage
 Prevent equipment damage
 Prevent personal injury
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Steps in Mistake-Proofing
 Describe the defect (or abnormality)
 Identify the location at which defect occurs
 Detail current standard procedures
 Identify mistakes or deviations from standards
 Identify conditions that provoke mistakes
 Identify root cause of defect condition
 Mistake proofing is significantly easier if true root
cause is known
 Identify type of Mistake-Proofing device required
 Create the device, test and standardize
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Why Use Mistake-Proofing?
 Why use mistake-proofing?
 It works where other techniques don’t
 There is lots of evidence of its effectiveness
 The Poka Yoke devices tend to be inexpensive and very
effective
 Why is it important to CPI?
 Defects are caused by errors in processes
 Defects are waste and cause wasteful activities to deal with
them
 In a CPI operation, a defect disrupts the balance of work and
the flow.
 Immediate corrective action is taken to resolve the situation
but, it is better to avoid this type of downtime by finding and
eliminating the root cause.
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To Err Is Human
Have you ever done the following?
 Driven to work and not remembered it?
 Driven from work to home when you meant to stop at
a store?
It happens to workers too.
 Workers finish the day and don’t remember what they
have done
 After building “green widgets” all morning, the workers
put “green parts” on the “red widgets” in the afternoon
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Sources of Defects
10 Types of Human Error 10 Sources of Defects
1. Forgetfulness 1. Omitted process step
2. Misunderstanding 2. Processing errors
3. Misidentification 3. Errors in set up of parts
4. Lack of experience 4. Missing parts
5. Ignoring rules 5. Wrong parts
6. Inadvertent errors 6. Processed wrong part
7. Slowness 7. Mis-operation
8. Lack of standards 8. Adjustment error
9. Surprises 9. Errors in set up of equipment
10. Intentional errors 10. Design or preparation errors
in tools, jigs and fixtures
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Judgment Inspection
 Involves sorting the defects out of the acceptable product,
sometimes referred to as “inspecting in quality.”
 The consensus in modern quality control is that “inspecting in
quality” is not an effective quality management approach.
 Judgment inspection does not improve process and should be
used only in the short term.
Inspection
Description
Techniques
Assesses quality of production outputs or sorts out defects
Judgment inspection
from good product. (e.g. inspectors)
Assesses process by inspecting outputs and using information
Informative inspection
gained to control the process (a feedback loop) (e.g. SPC).
Assesses beforehand whether the conditions necessary for
Source inspection
high quality production to exist (e.g. Poka Yoke).
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Source Inspection
 Exists at Source of Defect (Root Cause):
 Checks for factors that cause errors, not the resulting defect
 100% Inspection:
 Uses inexpensive mistake proofing (poka-yoke) devices to inspect
automatically for errors or defective operating conditions
 Immediate Action:
 Operations are stopped instantly when a mistake is made and not
resumed until it is rectified
Never pass on a defect!
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Blame the Process Not the Person
 “The old way of dealing with human error was to scold people,
retrain them, and tell them to be more careful … My view is that
you can’t do much to change human nature, and people are
going to make mistakes. If you can’t tolerate them ... you should
remove the opportunities for error.”
 “Training and motivation work best when the physical part of the
system is well-designed. If you train people to use poorly
designed systems, they’ll be OK for awhile. Eventually, they’ll go
back to what they’re used to or what’s easy, instead of what’s
safe.”
 “You’re not going to become world class through just training,
you have to improve the system so that the easy way to do a job
is also the safe, right way. The potential for human error can be
dramatically reduced.”
Chappell, L. 1996. The Pokayoke Solution. Automotive News Insights, (August 5): 24i.
LaBar, G. 1996. Can Ergonomics Cure ‘Human Error’? Occupational Hazards 58(4): 48-51.
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Setting Functions
The real question you need to ask:
 How are you going to detect an error?
 automatic, not dependent on human attention
 fail in “detect” mode
 simple & low cost if possible
Setting function Description
Physical Checks to insure the physical attributes of the product or
(Shingo’s contact), process are correct and error-free (e.g. round hole).
Sequencing Checks the precedence relationship of the process to insure
(Shingo’s motion step), steps are conducted in the correct order (e.g. check list).
Grouping or Counting Facilitate checking that matched sets of resources are
available when needed or that the correct number of
(Shingo’s fixed value methods), repetitions has occurred (e.g. egg tray).
Information enhancement Determines and ensures that information required in the
process is available at the correct time and place, and that it
(Chase and Stewart) stands out against a noisy background.
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Regulatory Function
The real questions you need to ask:
 How are you going to stop the process?
 the worker needs to get the message?
 By audible or visual warning
 By prohibiting further processing
 How are you going to eliminate the possibility of error?
 The Contrapositive of Murphy’s Law
 Simplicity
 Symmetry
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Regulatory Function
Regulatory
Description
Function
Warnings Signals mistake but allows process to continue.
System shuts down.
Gagging
Some resetting action required to correct the mistake.
Control Methods
Action leads to no response.
Non-response
The process does not crash nor does it proceed.
Process stops.
Self-correct
System proposes correction to mistake.
Process seeks information about what was really
Let’s talk about it
intended.
Process associates correct outcomes with incorrect
Teach me
actions.
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Poka Yoke: Preventing Errors
 “Hard” mistake-proofing: Designing
processes and tasks to ensure error-free
execution
 Anticipating errors to make processes
“fail-safe”
 Allows for preventive actions to be part
of process design
 Initiating individual accountability to
ensure quality work before handing off
to another step in the process
 “Soft” mistake-proofing: Creating alarm
signals to catch defects as they occur and
warn people
 Andon: processes and tools to STOP the
process when a problem or defect is
encountered
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Fail Safe
 Level 0 (No Control): Acceptance, Inspection
 Level 1 (Mitigation): Minimize Damage
Feedback should
 Build into Inspection: for example be immediate!
 Double signals (sound and visual)
 Cross footing in financial forms
 Level 2 (Detection): Feedback and Control
 Build into Process
 Checks etc.
 Posting Sequence
 Level 3 (Avoidance):
– Build into Design
 Wrong part or orientation, No fit
 Forms design
 Level 4 (Replacement):
– Automation or Elimination
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Fail Safe (Cont.)
 Fail Safing means embedding a device or procedure in a process so
that the process will never allow a nonconformity (error) to occur.
 The idea of Fail Safing is to prevent inevitable mistakes from turning
into a defect.
 Fail Safing requires the ability to discriminate the good from the bad.
Simple Fail Safing methods are the low cost way to parts per million
error rate.
Precise outcomes without precise knowledge or action?
=> provide clues about what to do:
 Natural Mappings
 Affordances
 Visibility
 Feedback
 Constraints
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Natural Mappings
Which dial turns on
the burner?
Stove A
Stove B
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Affordance
How would you operate these doors?
Push or pull? Left side or right? How do you know?
A B C
Visibility and feedback
 Visibility means making relevant parts visible, and effectively displaying system status
 Feedback means providing an immediate and obvious effect for each action taken.
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Is Box Full or Empty?
Compressed
Air
Before Improvement After Improvement
• Some boxes were unfilled • Empty boxes blown off
• Not found since box was conveyor
opaque • Pinwheel indicates
airstream functioning
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Mistake-Proofing Examples
Mistake-Proofing Illustrated
 Redesign the process to
eliminate or reduce the Fixture
possibility of a particular failure Workpiece
mode Chuck
 A way to avoid mistakes
Correct Position Wrong Position
(can be loaded) (cannot be loaded)
 Make the error impossible
 If you cannot prevent the
error, modify the process to
make the error obvious
(detection)
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Everyday Mistake-Proofing Examples
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Exercise: GGA Budgeting Recap
 The Generic Government Agency (GGA) represents a
government agency that is focused on obligating their
budgeted dollars
 GGA obligates funds by processing Budget Documents
(BDs)
 GGA’s ability to obtain all necessary products and services
is directly related to the efficiency and effectiveness with
which it processes Budget Documents
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Exercise: GGA Budget Mistake-Proofing
 As a CPI Belt you have been assigned the task of Mistake
Proofing the GGA Budget Document.
 Brainstorm ideas on how to Mistake-Proof the document
for the Generic Government Agency (IT solutions are
permitted)
 Put the ideas into 2 categories:
 Prevention
 Control/Warning
 Write the ideas on flip charts and be prepared to present
back to the group
20 Minutes
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Takeaways
Source Inspection
+
Mistake-Proofing
=
Zero Defects
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What other comments or questions
do you have?
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