I.5 Taguchi

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I.5 Taguchis Philosophy

• Some Important Aspects
• Loss Functions
• Exploiting Nonlinearities
• Examples
• Taguchi - Comments and Criticisms

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Some Important Aspects

• Uses DOE to Make Rugged Products and Processes
• DOE Is Used As a Tool For Reducing the Effects
  of Variation
• Traditional DOE Had Focused More on Optimizing
  Average Product Performance Than on Considering
  the Effects of Variation

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Some Important AspectsLoss Functions

• For Squared Error Loss, Loss Variance
  (Bias)2
• Minimizing This Loss Involves
• Reducing Variation
• Targeting The Process

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Some Important AspectsLoss Functions

• Minimizing This Loss
• May Involve Conflicting Goals
• You may not be able to simultaneously
• Optimally target the process and reduce variation
• Taguchi tries to resolve the conflict through
  signal to noise performance measures

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Some Important AspectsLoss Functions

• Just Meeting SpecsversusSquared Error Loss

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Some Important AspectsLoss FunctionsSony USA vs
Sony JAPAN
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Some Important Aspects

• The competitive race is never ending
• Deming/Shewhart PDSA Cycle
• Juran Managerial Breakthrough
• Kaizen
• Continual Improvement
• Improvement Occurs When Variation Is Reduced
  (Mostly Effected at The Product and Process
  Design Stage)

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Some Important AspectsReduce The Effects Of
Variation!How?

• By Exploiting The Nonlinear Effects of Product
  Parameters On The Performance Characteristics
• Use DOE
• To Search For Interactions Between Control
  Factors and Noise Factors. If There Is An
  Interaction, It May Be Useful For Mitigating The
  Effect Of The Noise Factor
• To Identify The Design Parameters That Have The
  Most Effect On Product Performance.

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Some Important AspectsExample 3 Improving a
Process

• Which Factors Affect
• Accuracy?
• Precision?

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Some Important AspectsExploiting Nonlinearities

• To Understand This Concept Lets Consider an
  Example On Estimating Angles

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Some Important AspectsExploiting Nonlinearities
- Other Examples

• INA Tile
• Plasticity of Caramel
• Electric Circuit

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Some Important AspectsExploiting
NonlinearitiesTo Fix This Idea Lets

• See How To Keep a Hubcap From Falling Off!

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TaguchiComments

• Developed A Comprehensive Model of Quality
  Engineering
• Quality Engineering Philosophy Is Fundamentally
  Sound
• Exploiting Nonlinearities To Mitigate Noise
  Factors Is Novel
• Loss Functions

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TaguchiCriticisms

• There Is Room For Improvement In His Methodology
  By The Use Of More Sound Statistical Ideas
• Better Designs May Be Available
• S/N Ratio Application May Be Better Analyzed If
  Viewed As A Bivariate Response (S,N) Problem
• S/N Can Mask Factor Effects
• Ignores Sequential Experimentation
• EVOP and Response Surface Techniques
• Adaptive design

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TaguchiCriticisms

• Traditional DOE Terminology and Methodology Is
  Modified Which Leads To Unnecessarily
  Complications
• Linear Graphs rather than Alias Structure for
  Choosing Designs

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TaguchiCriticisms

• The Term Taguchi Methodology
• Is Objectionable
• Ignores the Major Contribution of Others to This
  Endeavor

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TaguchiCriticisms

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

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Part I References

• G.E.P. Box, W.G. Hunter and J.S.Hunter (1978).
  Statistics for Experimenters, John Wiley Sons,
  N.Y.
• G.E.P. Box, S. Bisgaard and C. Fung (1988). An
  Explanation and Critique of Taguchi's
  Contributions to Quality Engineering,University
  of Wisconsin Center for Quality and Productivity
  Improvement, Report 28.
• C. Daniel (1976). Applications of Statistics to
  Industrial Experimentation, John Wiley Sons,
  N.Y.
• H. Karatsu (1988). TQC Wisdom of Japan,
  Productivity Press, Cambridge, MA.
• R. Snee (1990). Statistical Thinking and Its
  Contribution to Total Quality, The American
  Statistician, 44, 116-121.