Poka-Yoke
Douglas M. Stewart, Ph.D.
Anderson Schools of Management
University of New Mexico
Zero Quality Control
• Started in the factory• Refined by Shingo at Toyota• Involves 100% Informative inspection• Uses simple devices and procedures
called poka-yoke– Photo sensors– Trip switches– Fixtures to orient parts– Checklists– Kitting of parts
When to Inspect
Additional Inspection Points
• Where raw material is received
• Prior to costly operations
• Prior to potential damage
• Prior to point of no return
• Prior to stocking
• Where quality responsibility changes hands
How are errors detected?
• Self monitoring• Checking by others• Environmental cues
– The primary objective of a poka-yoke
– Warning vs. Control
Doing the Poka-yoke
• Poka-yoke: (From the Japanese, yokeru – to prevent, and poka – inadvertent errors.) Simple, inexpensive, failsafe devices or systems which prevent mistakes from being made or from becoming defects.
What do you failsafe?
Poka-yoke Classification
• Classification based on what is fail-safed:
Server Poka-Yokes
Task
Treatment Tangibles
Customer Poka-Yokes
Preparation
Encounter
Resolution
• Classification based on fail-safing method– Physical detection and control (contact methods)
• Identify items by their physical characteristics
– Sequencing (motion-step methods)• Indicate, discourage or prevent deviation from
process steps
– Grouping and counting• Assure correct groupings, ordering, and the use of
all and only the correct components
– Information enhancement• Prevent failed or incomplete communications as well
as enhance existing communications
Provider Errors
• Task Errors– Doing the work incorrectly– Doing work not requested– Doing work in the wrong order– Doing work too slowly
• Treatment Errors– Not acknowledging the customer– Not listening to the customer– Not reacting appropriately to the customer
• Tangible Errors– Failure to clean facilities– Failure to control noise– Failure to proof documents for content and
presentation
Customer Errors
• Preparation Errors– Failure to bring necessary materials to the encounter– Failure to understand role in the service transaction– Failure to engage the correct service
• Encounter Errors– Failure to remember steps in the service process– Failure to follow system flow– Failure to specify desires sufficiently– Failure to follow instructions
• Resolution Errors– Failure to signal service failures– Failure to learn from experience– Failure to adjust expectations appropriately– Failure to execute appropriate post-encounter actions
Fail-safing the Customer
• Preparation for the encounter– DEC service flier
• During the encounter– Locks on airline doors activate lights
• Resolution of the encounter– Outlines for toys on floor of child care center
DEC Service Flier
Fail-safing the Server
• Task– Operating room trays with indentations for instruments
• Treatment– Smile checklist (greeting, taking order, informing of
desert special, and giving change)
• Tangibles– Mirrors for personal appearance inspection– Chairs with armrests to prevent sleeping
Physical Detection and Control Methods
• Orientation and placement
• Delimiting and controlling the physical space
• Lock-outs, and lock-ins
• Go / no-go gauging
• Dispensers
• Detecting presence or absence
• Improved visibility
• Unusual physical attributes
Examples
Labeling TemplateJig for Part Placement
Jig
Guide Pins and Cutouts (that limit orientation)
CutoutGuide Pins
Correctly Oriented Incorrectly Oriented
Examples (cont.)
Height Gauge at Amusement Park
You must be
at least this
tall to ride.
Examples (cont.)
Examples (cont.)
Switches
Proximity Sensor Detects Broken Bit
broken bit
proximity sensor
warning lamp
Limit Switches on Jig
Examples (cont.)
Lines on Wall Indicate Reorder Points
Sequencing Methods
• Baiting
• Task substitution
• Interlocks
Examples
Examples (cont.)
Grouping and Counting Methods
• Counting and ordering
• Arrangement
• Kits
• Layout mats
• Checklists
Examples
Information Enhancement Poka-Yokes
• Moving information through time– Storing it for later use– Consolidating it to get the big picture– Prediction
• Moving information across space
• Making information stand out
How do you Fail-safe?
• Educate the team about poka-yoke devices• Find the source of the errors
– Blueprint (flowchart)– Find defects– Trace to source
• Brainstorm– Inexpensive, clever devices– Only one device per error
• Toyota averages 12 per machine
– Type of Cue• Warning• Control
– The 50-50 rule
Fail-safing works best when…
• There is a fixed sequence of operation that are routinely followed
• Each operation has clearly identifiable goals and specifications
• The number and range of inputs you must control for each operation is small
• The customer “knows the drill” in general terms at least
• Task and tangibles rather than treatments are the core features of the service
• The process design must be fundamentally sound