(Case Study
Applications of TRIZ and the Theory of Constraints)
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
Roy STRATTON
Senior Lecturer, Department Of Mechanical and Manufacturing Engineering
Nottingham Trent University, Nottingham, NG14BU, UK
+44 (115) 848 2336 FAX +44 (115) 848 6166
roy.stratton@ntu.ac.uk
INTRODUCTION
An early TRIZ Journal article (1) hinted
at possible links between TRIZ and the Theory of Constraints (TOC). Subsequent
articles last May (2) and September (3) progressed the connection further by
examining how two particular TOC tools - the Current Reality Tree (CRT) and the
Conflict Resolution Diagram (CRD) – could help in the definition of the
inventive situation and identification of the core problem to be tackled with
TRIZ methods. This article picks up the connection between TRIZ and the Conflict
Resolution Diagram – or ‘Evaporating Cloud' – and demonstrates how the
two techniques are being integrated and used to mutual benefit in the solution
of both technical and non-technical problems.
The area of greatest common ground
between the Evaporating Cloud (EvC) and TRIZ lies in the way in which the Cloud
helps to define Physical Contradictions. Case studies are presented which
demonstrate how the Cloud not only helps to define the ‘right'
contradiction, but also subsequently offers new problem solution strategies to
complement and enhance a purely TRIZ-based approach. Similarly, the TRIZ
physical contradiction solution techniques are shown to offer valuable new
insights to the way in which those more familiar with TOC can approach and solve
problems.
A short final section of the article
examines the potential for further, more rigorous integration between the two
problem definition and solving methods on the road towards a truly generic
systematic innovation methodology.
Three case studies will be considered:-
1)
A TOC originated non-technical case concerning the production manufacture
logistics.
2)
A TRIZ originated case concerning the solving of a technical problem
associated with a piece of manufacture equipment.
3)
A TRIZ originated case examining use of a combined TRIZ/TOC approach to
help solve a human relations problem.
CASE STUDY 1 – Manufacture Logistics
This case comes from an article written
about the use of TOC to avoid ‘trade-off' solutions (Reference 4). The case
surrounds the commonly found manufacture issue of calculating batch sizes in a
production environment. The calculation of ‘optimum' batch size – usually
called Economic Batch Quantity (EBQ) – has developed into a sophisticated
science. The basis of the EBQ calculation process derives from an established
relationship with annual demand, machine set-up cost, and inventory carrying
cost per unit. The mathematical relationship is:-
In graphical terms, the EBQ emerges from
the addition of two conflicting characteristics to form a third ‘total cost'
characteristic possessing a parabolic shape in which the minimum cost point is
seen to occur at the EBQ ‘answer', x – Figure 1.
Figure 1: Traditional Trade-Off Between Batch Size and Cost
The parabolic shape of the total-cost
curve is characteristic of a physical contradiction. This mapping between a
parabolic curve and a physical contradiction is complementary to the previously
described (Reference 5) relationship between hyberbolic-shaped curves and
technical contradictions – Figure 2.
In this case the two conflicting cost
elements, linear and hyperbolic, are synonymous with the TRIZ concept of
technical contradictions combining to produce the parabolic curve characteristic
of a physical contradiction. The parabolic curve in this case helps to identify
that a physical contradiction exists in relation to the EBQ – in that there
are simultaneously conflicting desires to have an EBQ which is both LARGE and
SMALL.
This contradiction is expressed in the
TOC Evaporating Cloud
(EvC) as the pair of opposing problem 'prerequisites'. Construction
of the full EvC
is then intended to systematically identify the assumptions which relate the
conflict to the requirements and objectives of the business. A comprehensive
explanation of the EvC and its use may be found in Reference 6.
Figure 2: Graphical Characteristics of Physical and Technical Contradictions
The Evaporating Cloud for the EBQ
conflict may be drawn as shown in Figure 3.
Figure 3: Evaporating Cloud Diagram For EBQ Problem
In the diagram, the requirements B&C
are necessary(but
not sufficient) to achieve the objective A.
The prerequisites
at D are necessary (but not sufficient) to achieve the requirements at B and C.
The prerequisites at D define
the physical contradiction. It is normal with the
EvC to formulate the problem from the prerequisite conflict and to
then work from there, clarifying the thinking behind the causal links along the
way, back to B, C & A.
Each of the arrows in the diagram is
then used during a TOC analysis of the problem situation to examine the
assumptions contained in the problem definition. In TOC terms, the Cloud is
evaporated (i.e. the problem is solved) if one of the assumptions contained in
the arrows can in some way be invalidated.
By way of example, the Reference 4
article challenges the assumption contained in the arrow between B and D that
large batches are a prerequisite for reducing setup costs. If means are found to
break the perceived
relationship – for example if a setup is being performed by workers
who would be on the payroll whether a setup was being performed or not (and
saleable output is unaffected by the downtime) – then the problem is solved.
The Just in Time approach to this
problem was to challenge the assumption that set-up times were cast in stone.
Radically reducing the set-up time eliminates the conflict at source, often with
little expense.
As may be seen, the TOC cloud is
addressing an organisational paradigm that includes assumptions that may no
longer be valid due to changing circumstances.
This particular cloud can also be broken
at the D conflict arrow as the definition of ‘batch' was traditionally
ambiguously defined and the distinction now exists, acknowledging that one
prerequisite relates to a process batch and the other to a transfer batch.
TOC is rarely used to challenge the
assumptions relating to the arrow at D, i.e. to challenge the physical
contradiction. Consequently the TOC method does not contain any systematic means
through which such challenges may be identified and invalidated.
And here, then, is the point where TRIZ
is able to potentially offer tangible benefit to the EC, through use of the
Physical Contradiction solving strategies. These strategies traditionally
involve use of separation in time or space, satisfying the contradiction or use
of alternative ways. Each of these may likewise be related in turn to the 40
Inventive Principles of TRIZ as illustrated in Figure 4. (Data here based on
Invention Machine TechOptimizer plus University of Bath research findings.)
Figure 4: Relationship Between Physical Contradiction Solution Strategies and
Inventive Principles
Several of these
contradiction-eliminating strategies appear to have something of value to offer
in the solution of the EBQ problem:-
Separate in Space – Segmentation (Principle 1) – splitting of batches into
different sizes in different parts of the manufacture operation – for example
segmentation into ‘process' and ‘transfer' batches. This is the obvious
one that challenges what is a ‘physical' contradiction. Back in the early
1980s manufacturing development resulted in the loose definition of the term ‘batch'
being widely challenged, indicating that transfer batches were feasible if
production was arranged in cells where the machines were adjacent to each
other.)
Separation in Time – Dynamics/Preliminary Action – active calculation and
re-calculation of EBQ according to prevailing market conditions, time of week,
or even time of day.
Satisfying the Contradiction – Strong Oxidants (Principle 38) (‘Boosted
interactions' in a non-technical sense – Reference 7) – elimination of ‘batches'
altogether in favour of a much more active manufacture setup in which successive
parts of the line communicate effectively with each other – in many senses,
much in common with the TOC-founder, Eli Goldratt's ‘Critical Chain
(Reference 8) recommendation.
Alternative Ways – Transition to Sub-system – Segmentation – operation of
split-batches.
Alternative Ways – Transition to Super-system – Merging (Principle 5) –
elimination of batches through use of ‘manufacture cells' – i.e. bringing
together all of the machines required to manufacture a particular type of
component to form a coherent unit through which components pass as singles
rather than batches.
Thus TRIZ may be seen to offer several
(systematic) triggers through which the Cloud can be challenged at the physical
contradiction stage.
In many senses, solving the problem at
this stage rather that at any of the other arrows in the EC model, offers the
potential for the most potent solution (in the D®B challenge above, one might
ask if, in the long term, it is appropriate to employ workers irrespective of
whether they perform set-ups or not). That is not to say, however, that the
other assumptions shouldn't be challenged – why solve a contradiction which
has no relevance? – but that TOC offers TRIZ a systematic causal chain
structure through which the basis of the Contradiction validity may be
rigorously explored.
Meanwhile, the Physical Contradiction
solution tools within TRIZ clearly have much to offer TOC in terms of providing
systematic solution triggers to help evaporate the Cloud in certain situations.
CASE STUDY 2 – A Furnace Cooling Problem
This case originates from an
illustrative example used by John Terninko et al. (Reference 9, pp 49-58). A
more recent development in TRIZ is a solution system based on the modeling of
the useful and harmful functions and the development of problem statements.
These problem statements then work as operators to challenge the underlying
assumptions. The example will be viewed using TRIZ functional modeling and then
the TOC tools of Effect-Cause-Effect (ECE) analysis and EvC.
The case involves the need to design a
furnace and the desire to avoid a particular problem associated with the cooling
system. The simplified TRIZ functional model is shown in Figure 5.
Figure 5 TRIZ functional model of the furnace problem
The design focus is initially on the problem of explosions occurring when a
traditional pressurised cooling system and the incident of a burst pipe results
in a water leak. Functional modeling is normally used early in the TRIZ process
to map the system's useful functions, but also the harmful effects and their
remedy. For example the cooling system is there to counter the harmful effect of
the heat on the furnace walls. The model also effectively identifies
contradictions. This diagram shows two physical contradictions, one associated
with ‘heat furnace' and the other with ‘pressurised system'. The problem
formulation operators are then used to challenge the assumptions behind each
arrow. The application of these operators has been incorporated into the
Ideation IWB software (10) and has been used to generate the following
statements, which have been restricted to the ‘pressurised system' function
block links. The problem formulation for the whole diagram amounts to over 30
statements.
The proposed solution to this problem
emerges from challenging the need to have a pressurised system. The use of a
vacuum pump is identified (Reference 9) as a way of breaking the contradiction
centred on the need to pressurise the cooling system.
Having set the scene with this TRIZ tool
the question is, how does the TOC approach relate to this example?
TOC has been developed to deal with
organisational improvement and would not normally be applied in this way to a
technical problem, but it does raise some interesting perspectives on the
integration of these two approaches.
There are obvious similarities between
the TRIZ functional model with the associated problem statements and what TOC
users call a Current Reality Tree (CRT). A CRT for this example is given below
in Figure 6.
Figure 6 The Current Reality Tree
(effect-cause-effect diagram) Applied to the Furnace Case.
Traditional functional models will
normally describe the system as a whole, comprising the intended ‘useful'
functions. TRIZ modeling includes both useful functions and harmful
effects. A CRT attempts to define the core problem and in so doing map the often
more complex relationship between the harmful effects in a human activity
system. To achieve this it is necessary to provide sufficient explanation as to
why the harmful effects occur and therefore will naturally include relevant
detail on the related useful functions.
Whereas the TRIZ modeling, at first sight, looks similar to
traditional functional modeling the TOC CRT is more detailed incorporating
otherwise unstated assumptions.
The incorporation of the ‘and'
ellipse in these diagrams was introduced in about 1991 and made them so much
more useful when dealing with mapping human activity systems, where there are
often many hidden assumptions and lack of clarity over cause and effect.
Hence, the Tree's construction enables participation in
comprehensively defining the causes of the harmful effects and provides
opportunity to challenge these assumptions. If any entry into an ellipse is
invalidated then the resulting effect will fall also. So in the above, the
highlighted statements are obvious candidates for challenge that if invalidated
would impact on the problem.
The formulation of such diagrams can be
time consuming, but the improved understanding that results often helps to
identify false assumptions and a way forward.
The TRIZ functional modeling raises
questions about possible underlying assumptions through the generalised ‘operator'
of the problem statements and in some cases covers similar ground, but is not as
focused as the Current Reality Tree.
With both TRIZ and TOC, the use of these
maps provides a holistic view of the problem environment and both approaches at
this stage in the analysis will tend to focus in on the contradictions. In TOC,
the contradiction to be tackled normally appears towards the bottom of the CRT,
as it is commonly responsible for most of the harmful effects. This is where the
EvC is used to more directly challenge the thinking around a conflict or
contradiction. Whereas the CRT is used to define the necessary and sufficient
logic, the EvC maps only the necessary logic to highlight the conflict.
The formulation of the cloud can simply be the opposite of
the problem and then the requirements and finally the objective needs to be
verbalised. In the above case the problem is being tackled at the subsystem
level, but addressing the problem at the lower level would have additional
benefits, in that there would be no need for the cooling system at all.
If you recall, these diagrams are read
from the tip to the tail of the arrow:
'In
order to [tip of arrow] I must [tail of arrow], because
[assumptions].
Again, in a more focused way, it is
similar to the TRIZ functional modeling problem formulation, and naturally links
into the TRIZ work on contradiction theory covered in the first case.
In the above cloud the BD and CD arrows
raise assumptions that if broken would potentially provide much stronger
solutions. For example, the problem solver might challenge the assumptions that
melting ore requires a hot furnace, or that a hot furnace
necessitates hot furnace walls - e.g. picking up on the
basic functional requirements of ‘melt ore' or ‘cool surface', a TRIZ
Effects database might prompt use of corona discharge cooling, magnetic cooling
fluid, heat-pipes, etc to alleviate the current system problems.
The TRIZ functional modeling looks
beyond the contradictions for possible solution areas and clarifies the
relationship between the useful and harmful functions. This can be used to
identify the contradictions for further study.
The Current Reality Tree differs in that
it defines the logic between multiple harmful effects more thoroughly,
identifying the common denominator or core problem from a system wide
perspective. Whereas the CRT is designed to clarify and subsequently challenge
the specific assumptions in the diagram, TRIZ functional modeling uses a generic
operator to initiate lateral thought, but as a consequence is not as focused.
CASE STUDY 3 – A Human Relations
Problem
This case originates from an article by
Jim Kowalick on the use of TRIZ in the solution of human relations problems
(Reference 11). The case – slightly restructured here to overcome some
simplifications made in the original case, relates to John. John is a successful
line-manager, but his brash nature is adversely impacting the performance of
areas of the organisation other than his own. The problem scenario is
illustrated in Figure 7.
The conflict is defined as – “John
channels all resources under his control towards meeting the group's goals but
he does this in a style that demoralises and renders ineffective other
organisational goals”.
Figure 7: John Is A Brash Individual Problem Description
The scenario is highly amenable to the
construction of an Evaporating Cloud model. The model centres around the
contradiction that we both want and not want John as shown in Figure 8.
Figure 8: Evaporating Cloud Diagram for ‘John' Problem
Again, construction of the EvC diagram
assists in understanding the problem, and, through the process of challenging
the assumptions inherent in the arrows, offers a number of solution triggers
above and beyond those which would emerge from a purely TRIZ-based solution
approach.
For example, challenging the assumptions
underlying the B®D link might make us think more rigorously about whether it is
correct that only John can achieve
effective performance of the production line; what factors are responsible for
John's success; and then, do they exist in any other parts of the organisation
(for example in some of the people in the case study description that John has
‘trained').
This, along with similar challenges to
the C®D causal link suggest that there is a strong possibility that this
problem is solvable by means other than solving the identified contradiction.
For example, regarding the C®D link, there is an implicit assumption that John
is unaware of the effect he has on other areas – or rather that he is unaware
of the effect that other areas have on the overall performance of the factory.
It is thus difficult to see that if John were
made aware of what he is doing that he would continue to do it.
The major point from this (admittedly
over-simplified) example is that TOC offers problem solvers a number of
effective solution triggers which TRIZ alone would not generate. In this case it
appears likely that the TOC triggers provide more potent solutions than the
physical contradiction elimination originated ones described in the Reference 11
article.
TRIZ/TOC INTEGRATION
The three case studies just described
appear to firmly suggest that there is significant benefit to be obtained
through a problem definition and solving approach,
which combines the TRIZ and TOC methodologies.
With respect to the Evaporating Cloud
– Physical Contradiction link, it seems clear that the Cloud offers a simple
yet highly effective means of defining and understanding a problem. It then
provides a number of solution location points (each arrow in the diagram) from
which to challenge the assumptions built in to the problem definition. Four of
the five solution location points do not exist in TRIZ. For the fifth – the D
arrow – it appears clear that the systematic Physical Contradiction
elimination triggers offered by TRIZ are a potential addition to the EC method,
as illustrated in the first case study example.
There are clear parallels in the use of
TRIZ functional modeling and CRT and the relationship to defining conflicts or
core problems. Although the approaches have been developed for distinct areas of
application there is much potential to deepen our understanding and determining
more generic approaches.
The Evaporating Cloud – Physical
Contradiction link is but one of a host of beneficial links between TRIZ and
TOC. Links between other TRIZ and other TOC tools and strategies will be
explored in future articles.
CONCLUSIONS
1)
The Evaporating Cloud model in TOC offers much to help TRIZ problem
solvers in first identifying, and then systematically challenging the
assumptions underlying a Contradiction.
2)
The Physical Contradiction solution strategies contained within TRIZ
offer much to help Evaporate Clouds - at least where the conflict is physical in
nature.
3)
The respective system mapping tools complement each other and provide
opportunity for further development.
4)
There is considerable scope for further integration between TRIZ and TOC.
REFERENCES
1)
Rizzo, A.R., ‘Tools from the Theory of Constraints', TRIZ Journal,
May 1997.
2)
Domb, E., Dettmer, H. W., ‘Breakthrough Innovation in Conflict
Resolution', TRIZ Journal, May 1999.
3)
Moura, Eduardo C. ‘TOC Trees Help TRIZ', TRIZ Journal, September
1999.
4)
Jackson, G.C., Stoltman, J.L., Taylor, A., ‘Moving Beyond Trade-Offs',
International Journal of Physical Distribution and Logistics Management, Vol.
24, No. 1, 1994.
5)
Mann, D.L., ‘Contradiction Chains', TRIZ Journal, January 2000.
6)
Scheinkopf, L., ‘Thinking for a Change', St Lucie Press,
January 1999.
7)
Mann, D.L., Domb, E., '40 Inventive Management Principles With Examples',
TRIZ Journal, September 1999.
8)
Goldratt, E., ‘Critical Chain', North River Press, 1997.
9)
Terninko, J., Zusman, A., Zlotin, B., ‘Systematic Innovation',
St. Lucie Press, USA, 1998.
10) www.ideationtriz.com
11)Kowalick,
J., ‘The TRIZ Approach: Case Study – Creative Solutions to a Human Relations
Problem', TRIZ Journal, November 1997.
ABOUT THE AUTHORS
Roy Stratton is senior lecturer at Nottingham Trent
University, teaching researching and consulting in the area of strategic
operations management with a particular interest in the application of
Constraints Management.
Darrell Mann has been solving problems using TRIZ for the
last 8 years. He has been teaching, researching and consulting using TRIZ and
other systematic innovation methods at the University of Bath for the last three
years.
