I.5 Taguchi’s PhilosophyI.5 Taguchi’s Philosophy Some Important AspectsSome Important Aspects Loss FunctionsLoss Functions Exploiting NonlinearitiesExploiting Nonlinearities ExamplesExamples Taguchi - Comments and Taguchi - Comments and

CriticismsCriticisms

Some Important AspectsSome Important Aspects Uses DOE to Make Rugged Products Uses DOE to Make Rugged Products

and Processesand Processes– DOE Is Used As a Tool “For Reducing the DOE Is Used As a Tool “For Reducing the

Effects of Variation”Effects of Variation”– Traditional DOE Had “Focused More on Traditional DOE Had “Focused More on

Optimizing Average Product Optimizing Average Product Performance Than on Considering the Performance Than on Considering the Effects of Variation”Effects of Variation”

Some Important AspectsSome Important AspectsLoss FunctionsLoss Functions

For Squared Error Loss,For Squared Error Loss,

Loss = Variance + (Bias)Loss = Variance + (Bias)22

Minimizing This Loss InvolvesMinimizing This Loss Involves– Reducing VariationReducing Variation– Targeting The ProcessTargeting The Process

Some Important AspectsSome Important AspectsLoss FunctionsLoss Functions

Minimizing This Loss Minimizing This Loss −May Involve Conflicting GoalsMay Involve Conflicting Goals

You may not be able to You may not be able to simultaneouslysimultaneously

– Optimally target the process and Optimally target the process and reduce variationreduce variation

Taguchi tries to resolve the conflict Taguchi tries to resolve the conflict through signal to noise through signal to noise performance measuresperformance measures

Some Important AspectsSome Important AspectsLoss FunctionsLoss Functions

Just Meeting SpecsJust Meeting Specsversusversus

Squared Error LossSquared Error Loss

Target

Squared Error Loss

LSL USL

Target

Just Meeting Specifications Loss Function

LSL USL

Some Important AspectsSome Important AspectsLoss FunctionsLoss Functions

Sony USA vs Sony JAPANSony USA vs Sony JAPAN

Sony Japan Sony USA

LSL USL

Distribution of The Color Density in Television Sets Target Value is

Some Important AspectsSome Important Aspects

The competitive race is never endingThe competitive race is never ending– Deming/Shewhart PDSA CycleDeming/Shewhart PDSA Cycle– Juran “Managerial Breakthrough”Juran “Managerial Breakthrough”– KaizenKaizen– Continual ImprovementContinual Improvement– Improvement Occurs When Variation Is Improvement Occurs When Variation Is

Reduced (Mostly Effected at The Product Reduced (Mostly Effected at The Product and Process Design Stage)and Process Design Stage)

Some Important AspectsSome Important AspectsReduce The Effects Of Variation!Reduce The Effects Of Variation!

How?How?

““By Exploiting The Nonlinear Effects of By Exploiting The Nonlinear Effects of Product Parameters On The Performance Product Parameters On The Performance Characteristics”Characteristics”

Use DOEUse DOE– To Search For Interactions Between Control To Search For Interactions Between Control

Factors and Noise Factors. If There Is An Factors and Noise Factors. If There Is An Interaction, It May Be Useful For Mitigating The Interaction, It May Be Useful For Mitigating The Effect Of The Noise FactorEffect Of The Noise Factor

– To Identify The Design Parameters That Have To Identify The Design Parameters That Have The Most Effect On Product Performance.The Most Effect On Product Performance.

1

2

Some Important AspectsSome Important AspectsExample 3: Improving a ProcessExample 3: Improving a Process

Which Factors AffectWhich Factors Affect– Accuracy?Accuracy?– Precision?Precision?

Some Important AspectsSome Important AspectsExploiting NonlinearitiesExploiting Nonlinearities

To Understand This Concept Let’s To Understand This Concept Let’s Consider an Example On Estimating Consider an Example On Estimating AnglesAngles

Some Important AspectsSome Important AspectsExploiting Nonlinearities - Other ExamplesExploiting Nonlinearities - Other Examples

INA TileINA Tile Plasticity of CaramelPlasticity of Caramel Electric CircuitElectric Circuit

Some Important AspectsSome Important AspectsExploiting NonlinearitiesExploiting Nonlinearities

To Fix This Idea Let’sTo Fix This Idea Let’s

See How To Keep a Hubcap From See How To Keep a Hubcap From Falling Off!Falling Off!

TaguchiTaguchiCommentsComments

Developed A Comprehensive Developed A Comprehensive Model of Quality Engineering Model of Quality Engineering

Quality Engineering Philosophy Quality Engineering Philosophy Is Fundamentally SoundIs Fundamentally Sound– Exploiting Nonlinearities To Exploiting Nonlinearities To

Mitigate Noise Factors Is NovelMitigate Noise Factors Is Novel– Loss FunctionsLoss Functions

TaguchiTaguchiCriticismsCriticisms

There Is Room For Improvement In His There Is Room For Improvement In His Methodology By The Use Of More Methodology By The Use Of More Sound Statistical IdeasSound Statistical Ideas– Better Designs May Be AvailableBetter Designs May Be Available– S/N Ratio Application May Be Better S/N Ratio Application May Be Better

Analyzed If Viewed As A Bivariate Analyzed If Viewed As A Bivariate Response (S,N) ProblemResponse (S,N) Problem S/N Can Mask Factor EffectsS/N Can Mask Factor Effects

– Ignores Sequential ExperimentationIgnores Sequential Experimentation– EVOP and Response Surface TechniquesEVOP and Response Surface Techniques– Adaptive designAdaptive design

TaguchiTaguchiCriticismsCriticisms

Traditional DOE Terminology and Traditional DOE Terminology and Methodology Is Modified Which Methodology Is Modified Which Leads To Unnecessarily Leads To Unnecessarily ComplicationsComplications– Linear Graphs rather than Alias Linear Graphs rather than Alias

Structure for Choosing DesignsStructure for Choosing Designs

TaguchiTaguchiCriticismsCriticisms

The Term “Taguchi The Term “Taguchi Methodology”*Methodology”*– Is ObjectionableIs Objectionable– Ignores the Major Contribution of Ignores the Major Contribution of

Others to This EndeavorOthers to This Endeavor

TaguchiTaguchiCriticismsCriticisms

The Term “Taguchi Methodology”*The Term “Taguchi Methodology”*– ””Taguchi himself has said that he Taguchi himself has said that he

does not like the use of that term, does not like the use of that term, which to his embarrassment has which to his embarrassment has been used by others, ignorant of been used by others, ignorant of statistical history, to include such statistical history, to include such tools as analysis of variance, tools as analysis of variance, fractional factorials, orthogonal fractional factorials, orthogonal arrays, and so forth.” Box et al arrays, and so forth.” Box et al (1988)(1988)

Part I ReferencesPart I References G.E.P. Box, W.G. Hunter and J.S.Hunter (1978). G.E.P. Box, W.G. Hunter and J.S.Hunter (1978).

Statistics for Experimenters, John Wiley & Sons, N.Y.Statistics for Experimenters, John Wiley & Sons, N.Y. G.E.P. Box, S. Bisgaard and C. Fung (1988). “An G.E.P. Box, S. Bisgaard and C. Fung (1988). “An

Explanation and Critique of Taguchi's Contributions to Explanation and Critique of Taguchi's Contributions to Quality Engineering,”University of Wisconsin Center Quality Engineering,”University of Wisconsin Center for Quality and Productivity Improvement, Report #28.for Quality and Productivity Improvement, Report #28.

C. Daniel (1976). Applications of Statistics to C. Daniel (1976). Applications of Statistics to Industrial Experimentation, John Wiley & Sons, N.Y.Industrial Experimentation, John Wiley & Sons, N.Y.

H. Karatsu (1988). TQC Wisdom of Japan, Productivity H. Karatsu (1988). TQC Wisdom of Japan, Productivity Press, Cambridge, MA.Press, Cambridge, MA.

R. Snee (1990). Statistical Thinking and Its R. Snee (1990). Statistical Thinking and Its Contribution to Total Quality, The American Contribution to Total Quality, The American Statistician, 44, 116-121.Statistician, 44, 116-121.