A Lean Journey 
Generally the
most effective way to achieve quality is to avoid having defects in the first
place. It is much less costly to prevent a problem from ever happening than it
is to find and correct the problem after it has occurred. Focusing on
prevention activities whose purpose is to reduce the number of defects is
better. The idea is to have processes and procedures in place that reduce or
eliminate mistakes.
Mistake
Proofing is about adding controls to prevent defects, reduce their severity,
and detect them if they can occur. The concept was first put to widespread use
by Shigeo Shingo within the Toyota Production System (TPS).
Proofing is about adding controls to prevent defects, reduce their severity,
and detect them if they can occur. The concept was first put to widespread use
by Shigeo Shingo within the Toyota Production System (TPS).
The main aim of
mistake proofing is:
mistake proofing is:
PREVENT a
defect from occurring and when this is not possible, DETECT the defect every
time one occurs.
defect from occurring and when this is not possible, DETECT the defect every
time one occurs.
Defects found
in later operations or steps of a process have more costs associated with them.
There are more materials, labor, overhead, previously reworked product that are
at risk. Ultimately if the product gets to the customer as a defect, the
intangibles, such as reputation, can exceed the tangible cost.
in later operations or steps of a process have more costs associated with them.
There are more materials, labor, overhead, previously reworked product that are
at risk. Ultimately if the product gets to the customer as a defect, the
intangibles, such as reputation, can exceed the tangible cost.
Poka-yoke
devices could be characterized by effectiveness:
devices could be characterized by effectiveness:
GOOD: Detect
defect before proceeding to next step.
defect before proceeding to next step.
BETTER: Detects
defects while in process at an operation.
defects while in process at an operation.
BEST: Prevent
defects from occurring at all.
defects from occurring at all.
The 7 best
poka-yoke devices are:
poka-yoke devices are:
1. Guide Pins
Guide pins of
different sizes and/or shapes and placed in the proper locations ensure that
parts are being assembled correctly by providing the operator feedback when a
mistake has been made. Guide pins can also be used to ensure proper positioning
of the part.
different sizes and/or shapes and placed in the proper locations ensure that
parts are being assembled correctly by providing the operator feedback when a
mistake has been made. Guide pins can also be used to ensure proper positioning
of the part.
Applications
- Proper
alignment of a work piece - Proper
orientation of a work piece
Features
- Easy
to develop & implement - May
be the result of DFA and DFM activities
Human Error
Prevention
- Wrong
order, incorrect selection, incorrect positioning, incorrect orientation
2. Error
Detection & Alarms
Detection & Alarms
In general, an
error detection device can provide a visual alarm such as a flashing light or
an audible alarm such as a horn or siren.
error detection device can provide a visual alarm such as a flashing light or
an audible alarm such as a horn or siren.
These devices
signal that a problem is either about to occur or has just happened. With a
warning effect, the response is not automatic; someone has to take action.
signal that a problem is either about to occur or has just happened. With a
warning effect, the response is not automatic; someone has to take action.
Application
- The
signal must be triggered by something in the process, usually a sensor.
Features
- For
audible warnings, there are sirens, horns, bells, and even voice synthesizers. - For
visual alarms, there are lights that flash, rotate, strobe, or just light up.
Warning: If you
do use these warnings, the audible or visual signal must stand out from background
noise and lights. If audible alarms are used, be careful not to exceed noise
standards.
do use these warnings, the audible or visual signal must stand out from background
noise and lights. If audible alarms are used, be careful not to exceed noise
standards.
Be careful of
“alarm silence buttons.” It is easy to silence the alarm and then forget to
take action. Operators need thorough training on how to react to warnings.
“alarm silence buttons.” It is easy to silence the alarm and then forget to
take action. Operators need thorough training on how to react to warnings.
3. Limit
Switches
Switches
Limit switches
are electro-mechanical devices that are activated or deactivated when an object
comes in contact with them. They are used to detect the presence or absence of
an object.
are electro-mechanical devices that are activated or deactivated when an object
comes in contact with them. They are used to detect the presence or absence of
an object.
Applications
- Proper
positioning of safety devices - Detection
presence or absence of an object - Positioning
of a work piece
Features
- Requires
physical contact
Human Error
Prevention
Prevention
- Omission,
excessive/insufficient repetition, incorrect selection, incorrect counting,
incorrect positioning, incorrect orientation
4. Sensors
A. Proximity
Sensors
Sensors
Proximity
sensors emit a high-frequency magnetic field and detect an upset in the field
when an object enters it. They can be used to detect the presence or absence of
an object.
sensors emit a high-frequency magnetic field and detect an upset in the field
when an object enters it. They can be used to detect the presence or absence of
an object.
Applications
- Sensing
of tank or bin level - Confirmation
of part or object passes by - Detection
presence or absence of object - Positioning
of work piece
Features
- Non-contact
- Work
in harsh environments - Small
sensors are available for installation in tight areas - Fast
response speed
Human Error Prevention
- Omission,
excessive/insufficient repetition, incorrect selection, incorrect counting,
incorrect positioning, incorrect orientation
B. Laser
Displacement Sensors
Displacement Sensors
Laser
displacement sensors focus a semiconductor laser beam on a target and use the reflectance
of the beam off the target to determine the presence of a target and distance
to it.
displacement sensors focus a semiconductor laser beam on a target and use the reflectance
of the beam off the target to determine the presence of a target and distance
to it.
Applications
- Measuring
distance - Detection
of presence or absence of a feature - Confirmation
of part or object passes by - Positioning
of work piece
Features
- Non-contact
- Works
in harsh environments - Some
devices can achieve measurement precision down to 0.004 mils (0.1 um)
Human Error
Prevention
Prevention
- Omission,
incorrect selection, incorrect counting, failing to sense danger.
5. Vision
Systems
Systems
Vision systems
use cameras to look at a surface and then compare the surface viewed to a
“standard” or reference surface stored in the computer. They can be used to
detect the presence or absence of an object, the presence of defects, or to
make distance measurements.
use cameras to look at a surface and then compare the surface viewed to a
“standard” or reference surface stored in the computer. They can be used to
detect the presence or absence of an object, the presence of defects, or to
make distance measurements.
Applications
- Missing
of incorrect parts in an automated assembly line - Poor
quality surfaces or components - Correct
orientation of parts or labels - Ensure
correct relative position - Color
detection
Features
- Non-contact
- Need
to have sufficient light - Flexible
(can be reprogrammed for a variety of applications) - Compact
systems are now available
Human Error
Prevention
Prevention
- Omission,
incorrect selection, incorrect positioning, incorrect orientation,
misrecognition
6. Counters
& Timers
& Timers
Counters
(optical or electro-mechanical) look at the occurrence of events. They are
usually triggered by some type of sensor. Counters can be programmed to shut
down the process if a set number of events do not occur or if too many events
occur. Timers can shut down the process if processing time or activity time
does not meet or exceeds a preset level.
(optical or electro-mechanical) look at the occurrence of events. They are
usually triggered by some type of sensor. Counters can be programmed to shut
down the process if a set number of events do not occur or if too many events
occur. Timers can shut down the process if processing time or activity time
does not meet or exceeds a preset level.
Applications
- Ensuring
the proper number of events occurred - Preventing
failure of equipment or a component usage
Features
- Flexible
- Easy
to use - Easy
for people to understand
Human Error
Prevention
Prevention
- Excessive/insufficient
repetition, incorrect counting, incorrect positioning, incorrect orientation
7. Checklists
A checklist is
a type of informational job aid used to reduce failure by compensating or
potential limits of human memory and attention. It helps to ensure consistency
and completeness in carrying out a task.
a type of informational job aid used to reduce failure by compensating or
potential limits of human memory and attention. It helps to ensure consistency
and completeness in carrying out a task.
Applications
- Shift
Start-up - Product
Changeover - Equipment
Set-up
Features
- Easy
to develop - Easy
to use - Easy
for people to understand
Human Error
Prevention
Prevention
- Omission,
early/late execution, wrong order, misrecognition
Ideally, poka-yoke ensures that proper conditions exist before actually executing a process step, preventing defects from occurring in the first place. Where this is not possible, poka-yoke performs a detective function, eliminating defects in the process as early as possible.
Don’t allow defects to occur in your processes by neglecting to prevent mistakes in your work. Use poka-yoke to make the work easier and mistake proof your process.
Post Courtesy of QualityTrainingPortal.com
Leave a Comment
Your email address will not be published. Required fields are marked with *