Darrell
MANN
Industrial
Fellow, Department Of Mechanical Engineering
University
Of Bath, Bath, BA2 7AY, UK
+44
(1225) 826465 FAX +44 (1225) 826928
D.L.Mann@bath.ac.uk
INTRODUCTION
We often hear talk about ‘design without compromise’ and ‘contradiction
elimination’ in papers about TRIZ. Both terms carry the implication that TRIZ
offers some kind of a panacea to the ills of the engineering and design worlds.
While this is clearly not the case in practice, the Contradictions tools and
methods contained in the TRIZ schema are nevertheless still very important
paradigm changing tools that offer much to help design better products,
processes and services.
This brief article examines some of the underlying truths behind the
Contradictions methods in order to perhaps begin to establish what we really
mean when we talk about ‘elimination’ of contradictions.
TWO
CONTRADICTION SCENARIOS
A technical contradiction can often be usefully drawn as a graph of the type
illustrated in Figure 1.
Figure 1:
Graphical Representation of a Technical Contradiction
On the graph, the red line may be seen as a ‘line of constant design
capability’, or as a representation of the current design paradigm. For
example, referring back to an earlier article concerned with the design of
flange joints (Reference 1), we might see Parameter A as ‘leakage performance’
of the flange, and Parameter B as the number of bolts around the flange joint.
Traditional flange design – where, incidentally, the designer may only be
sub-consciously aware of the Figure 1 graph characteristic – sees the designer
trying to find a balance between adequate leakage performance and minimum number
of bolts. This generally means the flange is designed such that it ‘just’
doesn’t leak (which, in turn probably explains why most flange joints leak).
Or, with reference to Figure 1, the designer finds the point on the red line
where the ‘best’ compromise is obtained.
When
we talk about design solutions in which we ‘eliminate’ contradictions we can
mean one of two things: Firstly we can mean that we have really
eliminated the contradiction, and
secondly we can mean that we have improved the
contradiction scenario. For arguments sake, we will call these two solution
types ‘discrete’ and ‘continuous’ respectively. The main difference
between the two types is best examined through a pair of examples:
Discrete
A good example of a ‘discrete’ contradiction solution scenario is the
bicycle seat case discussed in Reference 2. In this case, we could draw a figure
like Figure 1 above, in which the width of the current saddle is drawn along the
x-axis, and a parameter like ‘shape’ is drawn up the y-axis.
In the saddle case study, the contradiction was stated to be ‘eliminated’.
In ‘eliminating’ the width-shape contradiction, the Figure 1 graph is no
longer relevant – i.e. the axes of the figure no longer make sense because
width and shape are no longer in conflict. This is a discrete contradiction
solution scenario. It is discrete because the
particular technical contradiction
under consideration has literally
been eliminated; we had a contradiction, and then we didn’t.
Continuous
Continuous solution scenarios are generally more common. The above flange joint
example may be seen as a continuous contradiction in that while we managed to
halve the number of bolts around the joint, the contradiction between leakage
performance and number of bolts still exists.
Likewise, we might see the
well known contradiction between physical size and the fuel burn efficiency of
the internal combustion engine – Figure 2 – as another example of a
continuous solution scenario. The correlation between size and efficiency is
very well established for most if not all internal combustion engine types, and
in selecting a particular engine for a given application, when constrained to
work within a traditional design approach, the designer has little scope for
improving on the red-line characteristic. I.e. selecting engine size more or
less simultaneously fixes engine efficiency for a given engine configuration.
Figure 2: Typical Size versus Efficiency Contradiction for an Internal
Combustion Engine
The exception to this rule occurs when the designer is able to change the design
paradigm. Using the Contradictions tools in TRIZ is a good means of achieving
this design paradigm change. For example, the size-efficiency relationship is
changed – i.e. a new red-line is drawn – if the design paradigm shifts from,
say, a conventional eight-valve to a sixteen valve porting configuration.
The size-efficiency relationship may be seen as a continuous contradiction
solution because even if the designer is able to employ TRIZ to change the
design paradigm in this way – ‘to eliminate the contradiction’ to use the
incorrect terminology – the size-efficiency conflict still exists. The only
difference now is that it exists on a new (hopefully better) red-line – Figure
3.
Figure 3: Design Paradigm Change Shifts Contradiction Characteristic Position
CONTRADICTION
CHAINS
The continuous solution scenario may be seen as a chain of contradictions. A
chain in that successive paradigm shifts will gradually move the characteristic
line closer and closer to the optimum. Using Contradictions to assist in
creating these paradigm shifts is one of the great strengths of the TRIZ
methodology.
The difference between the TRIZ Contradiction design philosophy and the
traditional ‘design is a trade-off’ scenario may thus be illustrated by the
graph shown in Figure 4.
The term ‘contradiction chains’ is appropriate in the continuous solution
context because each paradigm shift serves to improve the relationship between
the two conflicting parameters in question, and thus increases the net value to
the customer, even though the conflict still exists to some extent.
But then, what about the discrete contradiction solution scenario? What about
those cases where we actually do
achieve an elimination of the contradiction?
Again the bicycle seat case study holds a number of clues. In this example we
see that a width-shape contradiction has literally been eliminated. However,
this is not the same thing as ‘design without compromise’. This is evident
because the new seat continues to contain other contradictions. More
specifically, it contains new contradictions that weren’t present in the
original scenario.
In this context, the term ‘contradiction
chains’ continues to be relevant. Elimination of one contradiction has created
others. If the designer has done a good job, there has been a net benefit to the
overall system – i.e. the overall design paradigm has been changed for the
better – but as with the continuous solutions scenario, there remain other
possibilities to improve the design.
Figure 4: – Comparison of TRIZ and Traditional Design
Strategies
Again, the idea is perhaps best seen through example. The split bicycle seat
that eliminated the width-shape contradiction (Figure 5), creates a new
contradiction resulting from the fact that the moving seat components create new
problems when the cyclist tries to turn a high speed corner. So whereas with the
original saddle design, the cyclist is able to press his or her leg against the
side of the saddle to help turn the corner, with the new seat design this is no
longer possible. A new harmful side-effect versus force (i.e. the
stiffness/resistance of the seat motion) contradiction has emerged. And so,
although there is a net benefit (to most users!) with the new design, there is
still much potential for improvement.
Figure 5: ABS Sports ‘Dual Action Seat’ (from Reference 2)
In most cases, the designer then has to make decisions on just how far to take
the contradiction chain. Is it appropriate to launch the product in its Figure 5
form, or would it be better to continue challenging the design paradigm by
attempting to eliminate further design contradictions. This can only be done on
a case by case basis, with due consideration of commercial and marketing issues.
In the specific case of the Figure 5 bicycle seat, it now appears that it would
perhaps have been more prudent to extend the contradiction chain to ‘eliminate’
more contradictions before product launch.
CONCLUSIONS
1)
The TRIZ ‘Contradictions’ tools and methods are
extremely potent design paradigm changers.
2)
Solutions to technical contradiction problems come
in both ‘discrete’ and ‘continuous’ types.
3)
‘Discrete’ solutions – where we literally
eliminate a contradiction – usually give rise to other –hopefully lesser –
contradictions.
4)
‘Continuous’ solutions do not literally ‘eliminate’
a contradiction (even though we often say that they do), but if successfully
deployed, do change the design paradigm for the better.
5)
Contradictions come in chains. How far along a given
chain a designer travels before a decision to launch a new product, process or
service is made can only be reliably made on a case-by-case basis, taking due
account of all time, cost, risk and specification issues surrounding the basic
technical design circumstances.
REFERENCES
1)
Mann, D.L., ‘Case Studies In TRIZ: Halving The
Number of Bolts Around A Flange Joint’, TRIZ Journal, November 1998.
2)
Mann, D.L., ‘Case Studies In TRIZ: A Comfortable
Bicycle Seat’, TRIZ Journal, December 1998.
