Page 288 - Design for Six Sigma a Roadmap for Product Development

258 Chapter Eight

{ } [ ] { } ➔ { } [ ]{ }
y 1

0
y 1

0
0
x 1
x
1
y 2
y 2

0
x 2

x
2

y 3
x 3

y 3
Figure 8.13 Decoupling by adding extra design parameters.
parameters so that the number of FRs equals the number of design
parameters, if a subset of the design matrix containing m
m
elements constitutes a triangular matrix (Fig. 8.13*).
2. Perform decoupling by utilizing the system’s sensitivity. In this
case, the designer is seeking parameters that have a minimal effect
on FRs other than the targeted FR. This can be done by analyzing
the magnitude of the off-diagonal elements in the design matrix by
varying the x values over an extreme design range.
Methods 1 and 2 seek decoupling or uncoupling by adding, replacing,
or changing the sensitivity of design parameters. These methods may
greatly benefit from other axiomatic design theorems and corollaries
(Suh 1990). In addition, a great solution synergy can be gained using
TRIZ contradiction elimination principles (Chap. 9) to reduce or elim-
inate coupling vulnerability:
Functional requirement (y 1 ) A 11 A 12 design parameter (DP 1 )
}
{Functional requirement (y 2 ) ]{design parameter (DP 2 )
} [A 21 A 22
Assume the coupled design matrix above. The DFSS team can use
TRIZ to make the sensitivities A 12 , A 21 , or both negligibly small by the
right choice of the DPs using TRIZ Altschuller’s contradiction matrix
(Sec. 9.8).
TRIZ is based on principles extracted from international patents
showing how people have invented solutions for different categories
of technical problems in the past. The principles are organized in prob-
lem categories for selective retrieval, and the methods include proce-
dural algorithms. Because the principles are associated with similar
problems successfully solved in the past the likelihood of success is
enhanced. A simplified TRIZ process description is given in the follow-
ing steps:
a. Convert the design problem statement into one of a conflict
between two FRs considerations

*The entry
in the Fig. 8.13 design matrices is a shorthand notation for nonzero
sensitivities (∂y i /∂x i A ji ).