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