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More about Analogies

| On 08, May 1998

By Kalevi Rantanen
Brahenk. 9 E 18
phone/fax +358 2 251 1623

Different analogies are widely used as problem solving tools. The engineer can compare analogical systems consisting of object, tool, energy source, energy transmission and control. This like analogy is described in the paper of E. Domb. Using Analogies to Develop Breakthrough Concepts (TRIZ Journal April 98). I would like add another analogy that can be called a feature transfer analogy, or a bisystem analogy.

Feature transfer means that the “pluses” of several systems are accumulated into the new product, and the “minuses” are removed. Competing systems are compared pairwise. “Pluses” are combined and drawbacks “neutralized”. Innovative principles, effects, standard solutions etc. are used for realizing the feature transfer.

An example: mechanical and quartz watches are alternative systems for measuring time. The mechanical watch do not need any battery (+), but is complex (-). The quartz watch is simple (+), but requires a battery. There are already watches that combine the pluses of mechanical and electronic timepieces. Seiko Kinetic converts the kinetic energy of moving hand to electrical one. Citizen´s Eco-Drive uses light as energy source. We can describe the solution by a simple table or matrix:

Mechanical Watch + No battery – Complex
Quartz Watch – Battery needed + Simple
Quartz watch without batteries + Simple + Easy

Now we can use this known solution to solve new problems. For example: how to improve a clinical thermometer (fever thermometer). There are at least two competing systems:

  • Traditional mercury thermometer: Simple (+), but uncomfortable to use (-)
  • Digital thermometer: Comfortable (+), but requires a battery

The matrix or table:

Mercury thermometer + Simple – Uncomfortable
Digital thermometer – Battery needed + Comfortable
Ideal thermometer + +

A watch analogy gives nearly ready answer. A mercury thermometer should, anyway, be “tuned” by shaking. We can use “shaking power” to charge a thermometer. Or the user can press the device, and the energy of pressing can be converted to electrical one. Or the energy of light can be used.

To solve the same problem we can use the system analogy (Figure 3 in Domb´s paper). The worksheet seems as follows:

Object Time Time Temperature Temperature
Tool Quartz watch with battery “No battery quartz watch” Thermometer with battery “No battery thermometer”
Energy Source Battery Person´s hand/Light Battery Muscular power/Light
Energy Transmission Wires Mechanical/electric Wires Mechanical/electric
Guidance & Control Human Human Human Human

Let´s compare the two models:

The “two pluses matrix”:

  • Contradictions (pluses coupled with minuses) are displayed
  • The inner structure of the system is consciously ignored

The system model:

  • The main elements of the system are identified
  • Features and contradictions remain outside the model

We see that the models complement each other.