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Aggiornamento: 8 nov 2021

How to get opposite requirements – quick simple solutions to difficult problems.

Understanding Physical Contradictions gives us great clarity of thought which is immensely powerful because they help us ask the right questions, such as: ‘ under what circumstances (including where and when) do we need these contradictory requirements? ’ The way we solve these opposite requirements is by understanding how we can separate what we want, in order to get opposite benefits at different times or in different places or under certain conditions. The guide to achieving these opposite benefits/ solutions is the TRIZ Separation Principles to show which of the 40 Principles to use.

Separation Principles – separate opposite requirements

Separate in Time

We want opposite benefits at different times.

We want a plastic bag to be large and small (large when full of groceries but small before and after use). We want something there when we want to use it but not there when not in use.

Board Pointers need to be long to point and short enough to fit in a briefcase. These opposite benefits are achieved by applying Principle No 7 – Nested Doll . We are surrounded by systems which give us opposite benefits at different times such umbrellas (Principle No 15 – Dynamics) and aircraft wings (long for takeoff, and then pivot back to short for high - speed flight).

Separating in time – seeing that we want opposite needs at different times – helps us solve many simple but ingenious problems. In sandblasting, we have a problem that dirty sand accumulates and must be cleared after the cleaning is completed. How do we get the abrasive quality when we want it and get it to disappear by itself after it has been useful? One effective solution is to use dry ice chips as the abrasive – there when you need them then not there afterwards. There are lots of examples of using ice when you want a system – there and later not there (ice pigeons for shooting at are there when being shot at but then not there afterwards as they disappear by melting). Or if we want to lower something heavy to the ground slowly, we can place it on an ice stand: if ambient temperature is above freezing then the stand just melts away.

Physical Contradictions are Everywhere in the Real World

Opposite benefits or solutions – in the following example we can separate in time as we want a pile that is sharp and not - sharp.

The feature sharp makes it easier to drive it into the ground; the opposite feature blunt is good for load bearing. Therefore we want our pile sharp and blunt at different times.

A simple solution for separate in time. The pile changes from sharp to blunt – pile is easy to drive in and can carry great load.

Another solution to this pile problem using separate in time – an explosive charge is lowered into a hollowed out pile, set into the ground. The resulting explosion forms a cavity into which concrete is poured. Thus the conrete pile is easy to drive into the ground and very good at bearing a load.

Physical contradictions help us understand how to solve problems by using both time and space to see clever solutions. The Separation Principles are very simple guides to solving problems. In some ways Physical Contradictions help us visualize the problem by separating out the conflicts between different times and different places. Simple mapping of a system in time or space steps (and visualizing its use at different times and places) gives us great clarity of understanding and helps us see obvious solutions. Simply by seeing how to separate in time can help with all engineering problems. At a recent in-house TRIZ course a simple fire - alarm control panel was described as having to be large and small. For fifteen years it had been made large. Why and when does it have to be large was asked? It had to be large when installed to allow the detector wires to be connected easily on site by someone unfamiliar with the device – but it would be better to be small when in use. They had always designed it for installation rather than use. They realized they had a Physical Contradiction: they wanted the device to be large for installation but small when in use so they could separate in time. When they identified the relevant Inventive Principles this took them straight to a very simple (but to them innovative) solution of using hinged layers so it could be made large and therefore easy to install – but then be folded down to become small. They said the simple solution had saved them at least £ 300,000 and had been eluding them for many months.

Separate in Space

Present in one place; absent in another. We need to ask is there somewhere in space where the benefit is not needed? We want a cup for hot drinks to be hot and cold: cold where we hold it; hot where it contains tea or coffee. For separate in space we need to ask is there somewhere in space where hotness is not needed? Or where coldness is not needed?

What solutions do the relevant principles suggest?

Suggested Inventive Principles for Separate in Space

1 Segmentation

2 Taking Out

3 Local Quality

4 Asymmetry

7 Nested Doll

13 The Other Way Round

14 Spheroidality/Curvature

17 Another Dimension

24 Intermediary

26 Copying

30 Flexible Membranes and Thin Films

40 Composite Materials

1 Segmentation : Relevant layers? 40 Composite Materials : The right material for the cup? 4 Asymmetry : A handle? 7 Nested Doll : For thin plastic cups – another holder?

Similar questions can be asked when using a plate for hot food – does the rim ever need to be hot? It is a classic separate in space example – as we only need heat in the middle of the plate ( No 3 Local Quality ).

Another separate in space challenge is solved when submarines separate sonar detectors from their own noise by pulling sonar detectors at the end of several thousand feet of cable.

A very simple everyday example – a knife illustrates successful use of separate in space – sharp in one place and blunt in another.

Separate in space can also work for management problems:

1. Have a calmer team working in a different place from the problem (Houston/Apollo).

2. Experienced charity crisis teams at home – advising those on the ground at disaster situations.

3. Sales - people on road or at client don’ t need all the detailed information with them (just access).

All these simple management examples of separate in space look obvious but numbers 2 and 3 above were both devised by TRIZ teams – working on problems that seemed insurmountable at the beginning of the session but easily solvable at the end – an example of simple but clever solutions being found systematically by TRIZ. Separate in time and space is used for bridges when we want them there for land traffic but not there when there is water traffic. Sometimes the permanent solutions are very simple but expensive such as two bridges at different heights (separate in space) but the separate in time bridges which change and move are rightly famous and appealing.

Separate on Condition

When we can ’ t separate in time or space then we need to see how we can separate on condition when we need to separate opposite solutions in the same place and at the same time. The opposite solutions are achieved according to some condition of the component or some feature. The solution works on some elements but not others – one solution for one element; the opposite for another. For example a kitchen sieve is there for (collects) spa-

ghetti but is not there for water (allows it to flow through). The ‘ hit and miss ’ fence is there for privacy but not there for the wind ( 31 Porous Materials ). Another example, ideal windows are see - through for the people inside (give us a good view outside) but not see - through for people outside – they can ’ t see in.

Suggested Inventive Principles Separate on Condition

28 Replace Mechanical System

29 Pneumatics and Hydraulics

31 Porous Materials

32 Colour Changes

35 Parameter Change

36 Phase Transition

38 Accelerated Oxidation

39 Inert Atmosphere

A bogus ‘ beware of the bull ’ sign alarms strangers passing a remote house, but is understood and ignored by those living in the area who are familiar with the property.

Polar bears are black and white at the same time and in the same place. A polar bear is black for warmth and the same colour as its environment (white in snow) for camoufl age.

Present/absent – water is soft if entered at a low speed. However, if one jumps into the same water from a height of 10 meters, the water feels considerably harder. Thus, the speed of the body ’ s interaction with the water is the condition to be considered when applying this principle. Frothing up the water at the surface makes diving safer. A teabag also solves many contradictions and demonstrates separate on condition in that it has to allow water to flow in and out for the tea leaves to flavour the water but contain the tealeaves keeping them separate from the water. Also it must contain the leaves when the teabag is thrown away. One contradiction a teabag design has not yet solved is how to allow water in and out when in the cup, but keep the water completely contained when out of the cup to be thrown in the bin.

Separate by System

(also known as ‘ Alternative Ways ’ ) If none of the above are appropriate to our problem then we need to find alternative ways of separating by system. This includes:

■ Separate in Scale

■ Transition to Inverse System

■ Transition to Alternative System – try a different system.

Separate in Scale

a) Transition to the Super-system – to achieve a particular benefit at the super-system even when we have the opposite benefit at the system level. In areas at risk of earthquake, buildings have different natural oscillating frequencies. By connecting them with cables ( 5 Merging ) they become one system and damp the vibrations between them. (In a complex dynamic system an approximately tuned damper may reduce the vibration intensity of a component not directly connected to the damper or even remotely located.)

b) Transition to the Sub-system – one value at the system level and the opposite value at the sub-system/component level . Bicycle chain is rigid at the subsystem but flexible at the system level. Putting fires out transition to subsystem – use a spray of water droplets rather than a large amount of water. What we want is water evaporation to take heat out of the fire. Water droplets give us a large surface area exposed to the heat, whereas water in bulk has lower surface area and can cause extensive water damage.

Suggested Inventive Principles for Separate in Scale

a) Super - system

5 Merging

6 Universality

12 Equipotentiality

22 Blessing in Disguise

33 Homogeneity

40 Composite Materials

b) Sub - system

1 Segmentation

3 Local Quality

24 Intermediary

27 Cheap Short Living Objects

Transition to Inverse System

Try the opposite or anti-system. Try turning something ‘ the other way round ’ to solve the Physical Contradiction (Inventive Principle No 13 ). Achieving all benefits by an inverse system applies to systems like wind tunnels or very small swimming pools with an artificial current for swimming. We stay still; the water moves. We can swim a long distance in a small pool.

Suggested Inventive Principles Inverse System

13 Other Way Around Alternative System

6 Universality

8 Anti - Weight

22 Blessing in Disguise

27 Cheap Short Living Objects

25 Self - service

40 Composite Materials


I want to move (by running – good exercise). I don ’ t want to move (I ’ d rather be at home). Solution: exercise machine.

Arranging a meeting

I want to meet with people in New York – I don ’ t want to go to New York. Solution: get the others to travel.

Transition to Alternative System – try a different system Solve the Physical Contradiction by switching to a different system. I ’ m a General. I want to visit troops at war to raise morale but I don ’ t want to go to a war zone (too busy).

Solution: send a ‘ double ’ instead.


TRIZ for Engineers: Enabling Inventive Problem Solving, First Edition. Karen Gadd.

© 2011 John Wiley & Sons, Ltd. Published 2011 by John Wiley & Sons, Ltd. ISBN: 978-0-470-74188-7

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