1. MISTAKE-PROOFING
(POKA-YOKE)
BY
CH JAYATEJA
DEPARTMENT OF MECHANICAL ENGINEERING
GUDLAVALLERU ENGINEERING COLLEGE
GUDLAVALLERU - 521356

2. Mistake/error-proofing
Avoiding simple human errors that occur in
manufacturing process by taking preventive action
early in the product design process.
The process of Zero Defects is also known as
“Mistake Proofing”.

3. Importance of poka-yoke
‘Poka’ means ‘Mistakes’ & ‘Yoke’ means ‘Avoid’. It’s objective is to
achieve Zero Defects.
Poka-Yoke was developed by Shigeo Shingo from Toyota Motor in
1961 as a tool to achieve Zero Defects.
Discipline should be concerned with anticipating human error.
 By taking over repetitive tasks or actions that depend on vigilance or
memory, Poka-Yoke can free workers time and mind to pursue more
value added activities.
Lean practice does not allow extra inventory to compensate for
scrap.
 Lean ideology focuses on speed ...
... speed cannot exist when defects and rework prevail.
 Cost pressures don’t tolerate continued mistakes: scrap, rework,
lateness.

4. Common mistakes in manufacturing are:
o Mistakes in work pieces and tools in machines or in fixtures
o Incorrect or missing parts in assemblies
o Processing the wrong work piece
o Improper operations or adjustment of machines

5. Inspection to find mistake
• Judgment Inspection: Separating good from bad after
processing.
• Informative Inspection: Inspect then take action to eliminate
future occurrence.
• 100% or Sampling inspection based on SPC (Statistical
process Control) methodologies.
• Inspection:
• assumes defects are inevitable.
• believes the process of inspection will reduce defects.
• can reinforce ‘quality’ is responsibility of the quality
department.
• is not 100% effective.

6. • “Self-Check” Inspection
A self-check occurs when the person performing the work
checks the work before the work moves to the next process
step.
• Successive-Check” Inspection
A successive-check occurs when the previous work is
completed and that work is checked by the next person in
the process.

7. Attributes of Zero Defect quality system
• source inspection - Checks conditions at the source
• 100% Inspection - Simple Poka-Yoke devices in place to
check every time the process occurs
• immediate Action - Operations stop and corrective action
is taken when a defect occurs
• teams brainstorm and implement new devices wherever
there is an opportunity for error

8. oThree basic poka-yoke functions to use
against defects:
1. shut down a machine or operation
2. control a process or operation
3. warn that a defect has occurred
oA defect exists in one of two states:
1. it is about to occur
2. it has already occurred

9. NEGATIVE APPROACH
Mistakes are Inevitable
• people make mistakes
• place blame
• detect at final inspection
• sampling inspection
• errors are inevitable
• no time, no money
• no support
POSITIVE APPROACH
Mistakes Can Be Eliminated
• create the ‘right’ environment
• focus on the process
deficiency
• ask “why?”, then “how?”
• learn from the opportunity
• apply mistake-proofing
methods
• train everyone to challenge
errors. show them it’s
possible; share
examples

10. Design mistakes
• Failure to properly use dimensions and tolerances.
• Incorrect information
Defective material
• Poor choosing of material
• Not up to quality standards
• Poorly designed dies or molds

11. Manufacturing mistakes
• Omitted operations, parts
• Wrong orientation of part
• Misaligned part
• Wrong location of part
• Selection of wrong parts
• Misadjustments
• Commit a prohibited action
• added material or parts
• Misread, mismeasure, or misinterpret

12. Human Mistakes Safeguard
• Inattentiveness Discipline; work standardization; work
instructions
• Forgetfulness Checking at regular intervals
Inexperience Skill enhancement; work
standardization
• Misunderstanding Training; checking in advance;
standard work practices
• Poor identification Training; attentiveness; vigilance

13. Mistake Proofing-process & solutions
• process
• Identify the problem
• Prioritize
• Use cause finding methods
• Identify and implement solutions
• Evaluate
• Solutions
• Control of variability
• Control of complexity
• Control of mistakes

14. Mistake-proofing devices
• Checklists
• Guide pins, guide ways, and slots
• Specialized fixtures and jigs
• Limit switches
• Counters

15. Methods for Using Poka-yoke
Poka-yoke systems consist of three primary methods:
• 1. Contact
• 2. Counting

16. PHYSICAL CONTACT DEVICES
Limit Switches Toggle Switches

17. Energy Contact Devices
Photoelectric switches
can be used with
objects that are
translucent or
transparent depending
upon the need
An example of a contact device using a limit
switch. In this case the switch makes contact
with a metal barb sensing it’s presence. If no
contact is made the process will shut down

18. Warning Sensors
• Warning sensors
signal the operator
that there is a
problem. These
sensors use colors,
alarms, lights to get
the workers attention
!
• These sensors may
be used in
conjunction with a
contact or energy
sensor to get the
operators attention

19. Examples of poka-yoke

20. Thank you