Mistake-Proofing (Poka-Yoke)

MISTAKE-PROOFING
(POKA-YOKE)
The Effective Approach to Zero Defects
© Operational Excellence Consulting. All rights reserved.

© Operational Excellence Consulting
LEARNING OBJECTIVES
2
Gain knowledge on
the key concepts and
principles of Zero
Quality Control
Identify the limitations
and best practices of
mistake-proofing
Learn the approaches,
methods and tools for
designing and
implementing poka-
yoke systems
NOTE: This is a PARTIAL PREVIEW.
To download the complete presentation, please
visit: https://www.oeconsulting.com.sg

CONTENTS
3
INTRODUCTION TO
ZERO QUALITY
CONTROL
BASIC ELEMENTS
OF THE ZQC
SYSTEM
USING POKA-YOKE
SYSTEMS
EXAMPLES OF
POKA-YOKE
APPLICATIONS
01 04
03
02
LIMITATIONS &
BEST PRACTICES
05

TRADITIONAL INSPECTION IS A POOR SUBSTITUTE FOR QUALITY
4
Traditional 100% inspection does not
provide 100% defect-free products.

WHAT IS ZERO QUALITY CONTROL (ZQC)?
5
The Goal is
Zero Defect
Defects Can Be
Prevented
Does Not Place
Blame on People
ZQC is an approach that
does not point fingers at
people. It recognizes that
machines and people
make mistakes
sometimes, and it finds
ways to keep those errors
from turning into defects.
Zero Quality Control
(ZQC) is an approach
for achieving zero
defects. “Zero” refers to
the goal of making
products with zero
defects.
ZQC is based on the
principle that defects are
prevented by controlling
the performance of a
process so that it cannot
produce defects – even
when a mistake is made
by a person or machine.

WHY FOCUS ON ZERO DEFECTS?
6
Improve company
image and reputation
Facilitate lean
production methods with
smaller inventories
Improve productivity and
competitiveness
Develop a culture of
continuous improvement
and innovation
Maintain customer
satisfaction and loyalty
High cost of poor quality
(e.g. rework, scrap,
warranty claims)

© Operational Excellence Consulting 7
WHAT CAUSES DEFECTS?
Damaged or
excessively variable
materials
Worn machine parts Simple human mistakes
Specification of
inappropriate
procedures or standards
Excessive variability in
the operations
Most defects happen in one of five situations:

THE ZQC APPROACH CONSISTS OF FOUR BASIC ELEMENTS
8
Source
inspection
100 percent
inspection
A short
Feedback loop
Mistake-proofing
(poka-yoke)
systems
FOUR
ELEMENTS OF
ZQC

● Source inspection is the key to the ZQC
control function
● Source inspection assures that the
conditions are in place beforehand to
perform a process properly
● Source inspection is different from other
types of inspection, such as judgement
inspection or informative inspection
SOURCE INSPECTION
© Operational Excellence Consulting. All rights reserved. 9

1. Judgment inspection:
Inspection that discovers
defects
2. Informative inspection:
Inspection that reduces defects
3. Source inspection:
Inspection that eliminates
defects
THREE APPROACHES TO PRODUCT INSPECTION AND THEIR RESULTS
10
Source
Inspection
Informative
Inspection
Judgment
Inspection
Discovers
defects but does
not reduce them
Reduces defects
by informing the
process after
they happen
Eliminates
defects by
catching and
fixing their
causes

SOURCE INSPECTIONS PREVENT DEFECTS
11
● Source inspection is different from
judgment inspection and
informative inspection
● Source inspection catches errors
– and gives feedback about them
– before processing
● This is the integration of the Check
and Do stages: something controls
the doing so that it cannot be done
wrong
A Process
with
Zero Defects
Discovery of mistakes
before processing
Feedback and
corrective action

SOURCE INSPECTION KEEPS ERRORS FROM TURNING INTO DEFECTS
12
The integration of Check and
Do stages keeps defects from
being passed down the line.

© Operational Excellence Consulting. All rights reserved.
100 PERCENT INSPECTION CATCHES
ALL ERRORS
● The second unique element of the
ZQC system is that it does a
source inspection on every
single product
● An SQC system, however, only
inspects a sampling of the product
and does not prevent defects from
occurring
● ZQC uses methods that check
100% of the products
13

“
Humans are animals that
make mistakes.”
SHIGEO SHINGO
14

WHAT IS POKA-YOKE?
15
Poka-yoke means implementing simple low-cost devices that
either detect abnormal situations before they occur, or once
they occur, stop the line to prevent defects.
POKA
Mistakes
YOKE
Prevention
Source: Based on Pascal Dennis, 2015

Poka-yoke should not be implemented
for the sake of trying to look Lean!
POKA-YOKE IS WORTH PURSUING ONLY WHEN HUMAN ERROR IS THE
MAIN CAUSE OF QUALITY DEFECTS
16

TWO APPROACHES TO POKA-YOKE
17
CONTROL SYSTEM
● Controls the process so that when a
defect occurs, the process stops until
correction takes place
● High capability of achieving zero
defects
● For example, an ATM machine
withholds your cash until you have
removed your card so that you cannot
forget the card
● Signals operators when a defect
occurs so that operators take
corrective action
● Sometimes an automatic shutdown is
not an option
● For example, when word-processing
software highlights a misspelled word
so that you can go back and fix it
WARNING SYSTEM

● People and machines do make
mistakes or errors
● A portion of mistakes turn into
defects
● Poka-yoke systems can be applied
to prevent mistakes from
happening, as well as detect
mistakes after they have happened
THE DUAL FOCUS OF POKA-YOKE SYSTEMS – MISTAKE PREVENTION &
MISTAKE DETECTION
Defects
Mistakes
Process
PREVENTION
Poka-yoke that focuses here
works on mistake prevention
or making mistakes
impossible.
DETECTION
Poka-yoke that focuses here
works on mistake detection,
or making sure mistakes do
not turn into defects.
18

● An example of a positive stop based
on the contact method is on
equipment that requires operators to
perform a safety task before starting
the machinery. To activate the power
to the equipment, the operator must
first close the cover. Other examples
include blenders, washers and
microwaves that stop when their door
is opened to prevent operator injury or
damage to the equipment.
SAFETY COVER
19

● When fast-food restaurant employees
are filling a bag of fries, customers will
be unhappy if the bag is too little, but if
it is too much, the company loses
money. With a dispenser such as the
french-fry scooper, the amount of fries
can be controlled. Based on the fixed-
value method, this tool ensures that
bags of fries are slightly overflowing
without being too generous.
DISPENSING EQUIPMENT
20

● A common poka-yoke system in
assembly processes is light-guided
picking, also known as pick-to-light. Pick-
to-light devices use colored LEDs to
visually guide assemblers to pick the
correct parts, in the right quantities, and
in the proper sequence. This motion-
step method reduces the risk of human
errors and speeds up build times to
ensure high quality while maximizing
productivity.
PICK-TO-LIGHT
21

● Mistakes can be prevented by
separating contradictory or opposing
feature requirements in time. The
light indicates the allowed flow of
traffic separating the flow by specific
periods of time. Based on the
motion-step method, many
stoplights are timed with a three-
second delay to allow previous cars
to exit the intersection before cross
traffic is permitted to enter.
TIME SEPARATION
22

● At the pharmacy, the more
complicated your routine
medications are, the harder they
can be to administer properly. In
this case, having a visual indicator
of whether you’ve taken your pills
for Wednesday can do a great deal
to make sure that you’re getting the
medicine that you need at the right
time.
PHARMACY
23

BEST PRACTICES
24
● Poka-yoke is a means to achieve
the goal of zero defects, not the
end in itself
● Do not react to human errors by
blaming them for being sloppy
● Line process capability issues
should be addressed first before
implementing poka-yoke
● Poka-yoke should make the job of
the operator easier, not add more
work
● Involve team members in the
design and implementation of
poka-yoke systems
● Provide knowledge such as used
cases to the team members in
implementing poke-yoke
● Do not make poka-yoke devices
extremely sophisticated and
complicated – go for the simplest
and most effective method!

Operational Excellence Consulting is a management
training and consulting firm that assists organizations
in improving business performance and effectiveness.
Based in Singapore, the firm’s mission is to create
business value for organizations through innovative
design and operational excellence management
training and consulting solutions. For more
information, please visit www.oeconsulting.com.sg
END OF PARTIAL PREVIEW

Mistake-Proofing (Poka-Yoke)

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