Six Sigma Master Black Belt – Chapter 11 BHH STATISTICS FOR

Six Sigma – Master Black Belt
Advanced Design of Experiments
Six Sigma Master Black Belt – Chapter 11 BHH
STATISTICS FOR EXPERIMENTERS
Box, Hunter and Hunter II
Chapter 11
Response Surface Designs
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Six Sigma Master Black Belt – Chapter 11 BHH
THERE HAS NEVER BEEN A SIGNAL
IN THE ABSENCE OF NOISE
THE GODS LOVE THE NOISE
AS MUCH AS THEY LOVE THE SIGNAL
LEARN TO MODEL THE SIGNAL
LEARN TO MODEL THE NOISE
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Advanced Design of Experiments
Six Sigma Master Black Belt – Chapter 11 BHH
THE TWO MODEL PROBLEM
Every observation y has two components
y =  + 
(eta + epsilon)
 = the actual (true) response function being observed
Examples:    0  1 x1 a straight line
   0 (1  e  x ) a differential equation solution
1 1
 = the “noise”,
“ i ” the “disturbance”,
“ i
” the “error”
“
”
Example:  is a random event from a Normal distribution
with expectation zero and variance 2
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 is thought to be a smooth function of the factor x1
2, the variance of the observations, the measure of noise, is unknown
An experimental design:
Take several equally spaced values of x1
Plan to take repeated observations at chosen settings of x1
Randomly run ALL experiments
The design and observations
x1 1
1
1
2
2
3
y 6.4 5.6 6.0 7.5 6.5 8.3
3
4
4
7.7 11.7 10.3
5
17.6
5
18.0
5
18.4
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Advanced Design of Experiments
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Advanced Design of Experiments
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Advanced Design of Experiments
Six Sigma Master Black Belt – Chapter 11 BHH
Fitted Second Order Model
yˆ  8.42  3.15 x1  1.00 x12
SSq
df
Crude Sum of
Squares  y 2
1550.3000 12
Sum of Squares of
Predicted Values  yˆ 2
1544.5714
Residual Sum of
Squares  y 2   yˆ 2
5.7286
9
Lack of Fit Sum
of Squares
3.4206
estimates 2
3
2 = 1.7142 = s2
if model is OK
Error Sum of
Squares
2.3000
Lack of fit F test: F2,7 =
7 = 0.3286 = s2 estimates 2
1.7142
0.3286
= 5.21, F2,7,0.05 = 4.79
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Advanced Design of Experiments
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Advanced Design of Experiments
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Advanced Design of Experiments
Six Sigma Master Black Belt – Chapter 11 BHH
Figure 11.7 (BBH, Fig 15.6, p525)
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Six Sigma Master Black Belt – Chapter 11 BHH
50
40
60
70
temperature
a)
temperature
temperature
b)
c)
Fig 11.2: a) Contours surfaces; b) 23 factorial design; c) Fitted contour surfaces.
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Advanced Design of Experiments
Six Sigma Master Black Belt – Chapter 11 BHH
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Advanced Design of Experiments
Six Sigma Master Black Belt – Chapter 11 BHH
The model for the observations yu
yu     u
   0   1 x1   2 x 2
 u  NID (0,  2 )
The fitted (1st order) model
yˆ  b0  b1 x1  b2 x2
ˆy  61.7  2.4 x1  3.6 x2
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yˆ  6 1 .7  2 .4 x 1  3 .6 x 2
Least squares insures that
 y u2

 yˆ u2 
 ( y u  yˆ u ) 2
3 8 2 2 9 .3 4  3 8 2 1 8 .6 6 
1 0 .6 8
Given the fitted model is appropriate s2
s2 =  ( y u  yˆ u ) 2 /( n  p ) = 10.68/(10 - 3) = 1.54
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Advanced Design of Experiments
Six Sigma Master Black Belt – Chapter 11 BHH
ANALYSIS OF VARIANCE TABLE: THE LACK OF FIT TEST
SSq
q
df
Sum of Squares y2
38229.34 10
SSq for b0 (CF)
38068.90
1
Corrected SSq ( y  y )2
160.44
9
SSq for b1
46.08 1
SSq for b2
103.68 1
Regression SSq
149.76
2
Residual SSq ( y  yˆ )2
10.68
7
Lack of Fit SSq
9.00
5
1.80 = s2 ? 2
2
Error SSq
1.68
2
0.85 = s ? 2 / if model is OK
F2,5 = 0.85/1.80 < 1.00, non sig, Model is OK
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Advanced Design of Experiments
Six Sigma Master Black Belt – Chapter 11 BHH
Mapping the 1st order (planar) surface
yˆ  61.7
61 7  22.4
4 x1  33.6
6 x2
The contour for yˆ = 60 is given by
the straight line in the space of x1 and x2
60  61.7  2.4 x1  3.6 x2
Substituting yˆ = 58, 60, 62, 64, 66 gives
the parallel contour lines shown in the figure
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Advanced Design of Experiments
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The Path of Steepest Ascent (descent)
yˆ  b0  b1 x1  b2 x2
yˆ  61.7  2.4 x1  3.6 x2
Move at right angles to the contour lines
For every b1 = +2.4 steps in x1 direction
simultaneously take
b2 = + 3.6
3 6 steps
t
in
i the
th x2 direction
di ti
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Advanced Design of Experiments
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Advanced Design of Experiments
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SECOND ORDER MODEL
   0  1 x1   2 x2  11 x12   22 x22  12 x1 x2
y  
  NID (0,  2 )
SECOND ORDER DESIGN
x1
x2
1
1
1
1
0
1
1
1
1
0
78.8
84.5
91.2
77.4
88.0
y
0
0
86.8
 2
0
83.3
 2
0
81.2
0  2
81.2
0  2
0
0
0
0
79.5
89.7
85.0
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Advanced Design of Experiments
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Advanced Design of Experiments
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Mapping the 2nd order (non-planar) surface
yˆ  87.38  1.38 x1  0.36 x2  2.14 x12  3.09 x22  4.88 x1 x2
The contour for yˆ = 85 is given by
the curved line in the space of x1 and x2
85 0  82.38
85.0
82 38  1.38
1 38 x1  00.36
36 x2  2.14
2 14 x12  3.09
3 09 x22  4.88
4 88 x1 x2
Substituting yˆ = 80, 82.5, 85.0, 87.5 gives
the curved contour lines shown in the figure
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Advanced Design of Experiments
Six Sigma Master Black Belt – Chapter 11 BHH
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Running experimental designs in blocks
Suppose all the yields in Block II are 10 units less
Q: What is the consequence on the response surface map?
A: Almost none. The fitted model is:
yˆ = 8 2 .33 8 - 1 .33 8 x 1 + 0 .33 6 x 2 - 2 .11 4 x 12 - 3 .00 9 x 22 - 4 .88 8 x 1 x 2
Only the constant term is changed
In this octagon design the blocks are “Orthogonal”
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Advanced Design of Experiments
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Advanced Design of Experiments
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k = 3 factor polynomial models
1st order model    0  1 x1   2 x2   3 x3
2nd order model    0  1 x1   2 x2   3 x3
 11 x12   22 x22   33 x32
 12 x1 x2  13 x1 x3   23 x2 x3
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Advanced Design of Experiments
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The Central Composite design
Sequentially assembled k = 3
   0  1 x1   2 x2  3 x3  11 x12   22 x22   33 x32  12 x1 x2  13 x1 x3   23 x2 x3
x1

+

+
0
0
x2


+
+
0
0
x3
+


+
0
0
Block I

+

+
0
0


+
+
0
0

+
+

0
0
Block II



0
0
0
0
0
0
0



0
0
0
0
0
0
0



0
The central composite design
can be made rotatable by
choosing  , the distance
along the coordinate axes,
equal to nc1/ 4 = 1.68. To place
all points on a sphere set
 = 3 = 1.73.
To all practical purposes either
value gives orthogonal blocking.
Block III
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Advanced Design of Experiments
Six Sigma Master Black Belt – Chapter 11 BHH
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Advanced Design of Experiments
Six Sigma Master Black Belt – Chapter 11 BHH
Characteristics of a good experimental design
Not too many levels
Enough levels to capture the full order of the
approximating polynomial model
Enough points to provide for a lack of fit test
Replication, or partial replication, to provide
an independent
p
estimate of  2
Easy to block, and assemble sequentially
Possess good information gathering over the
experimental region (rotatability).
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Advanced Design of Experiments
Six Sigma Master Black Belt – Chapter 11 BHH
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b)
Figure 11.13b
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Advanced Design of Experiments
Six Sigma Master Black Belt – Chapter 11 BHH
a)
Figure 11.13a
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a)
b)
+
=
+
=
c)
Figure 11.11: 23 with center points + Star = Central composite
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Advanced Design of Experiments
Six Sigma Master Black Belt – Chapter 11 BHH
Figure 11.22
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X1
X3
X1
X3
X2
X2
X1
X1
X3
X3
X2
X2
X1
X1
X3
X3
X2
X2
X1
X3
X2
Figure 11.19 Various three dimensional contour systems
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Advanced Design of Experiments
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a)
b)
Figure 11.14
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