Page 372 - Design for Six Sigma a Roadmap for Product Development

342 Chapter Nine

Axiomatic design TRIZ
Theorem 2: Decoupling of coupled design. Building substance-field models, class 1 of
When a design is coupled because of the “76 standard solutions,” shares the same
greater number of FRs than DPs (m n), idea with Theorem 2 in AD. This standard
it may be decoupled by the addition of the solution states that if a given object is
design new DPs so as to make the unreceptive (or barely receptive) to
number of FRs and DPs equal to each required changes and the problem
other, if a set of the design matrix description does not include any
containing n
n elements constitutes a restriction for introducing substances or
triangular matrix. fields, the problem can be solved by
completing the substance-field model to
introduce the missing element.
Theorem 5: Need for new design. When a Enhancing substance-field model, class 2
given set of FRs is changed by the of “76 standard solutions,” corresponds to
addition of a new FR, or substitution of Theorem 5. The addition of a new FR, or
one of the FRs by a new one, or by substitution of one of the FRs by a new
selection of a completely different set of one, means that the previous system is an
FRs, the design solution given by the inefficient substance-field model. In this
original DPs cannot satisfy the new set of case, enhancing substance-field model is
FRs. Consequently, a new design solution required to improve the system functions.
must be sought.

9.11.1 A case study: Using TRIZ separation
principles to resolve coupling
An independence axiom in AD implies that the design matrix be of a
special form. The consequences of applying axiom 1 to the design
matrix are as follows:
1. It is desirable to have a square matrix (i.e., n m).
2. The matrix should be either diagonal or triangular.

In real design situations, we need to search for DPs that yield a diag-
onal or triangular design matrix. The degree of independence can be
treated as the definition of tolerance. There are hierarchies in both the
functional domain and the physical domain, and a zigzagging process
between two domains in the design process. The domain process is
most straightforward when the solution consists of uncoupled design
at each level. When the design is uncoupled, we can deal with the indi-
vidual FRs of a hierarchical level without considering other FRs of the
same level and preceding hierarchical levels. When the design is cou-
pled, we must consider the effect of a decision on other FRs and DPs.
Therefore, the designer should try to find solutions by attempting to
uncouple or decouple design in every level of the design hierarchy.
The problem is how to decouple a coupled design. It is obvious to
modify a design matrix to be either diagonal or triangular. In practice,
many coupled designs undergo changes and become decoupled through
a trial-and-error process that is in opposition to TRIZ methodology. In