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Inconsistent Embodiments

Not every combination of embodiments make sense for a design intervention. You have to remove the combinations that you can demonstrate will not work before you generate design concepts.

During ideation, you were not interested in how different embodiments might interact. To generate design concepts, you will be combining different embodiments. We already know that using ideation can lead to a huge number of potential concepts, and that this arises from combining embodiments.

Consider the following example (taken from the ideation page).

Example problem Design problem: You have to design a joint for a detachable robotic arm. It's basic systems are:

  1. Structural system (to resist physical forces during operation)
  2. Connection system (to attach and disconnect automatically)
  3. Power system (to transmit power)
  4. Data system (to transmit data)

Here are some ways to embody these systems. (This can be thought of as a textual version of a morphological chart.)

A. Structural system

  1. Bolt and lug
  2. Concentric rods/shafts
  3. Cup and socket (like, say, your shoulder joint)
  4. Meshed teeth in compression (as in the Canadarm; see image.)
  5. Motorized hooks
  6. Magnetics

B. Connection/disconnection system

  1. Mechanical gearing
  2. Solenoid/electrical actuators
  3. Hydraulics

C. Power system

  1. Space-rated electrical wire with mechanical connector
  2. Space-rated electrical wire with magnetic connector
  3. Induction transmission

D. Data system

  1. Space-rated electrical wire
  2. RF transmission (as in radio)
  3. IR transmission (as is a TV remote)
  4. Microwave transmission
  5. Laser (optical fibre) transmission

If a design concept includes one embodiment for each system, then the list above represents 270 different concepts.

One way to proceed would be by “brute force” - just check every one of the 270 different concepts, looking for the best one. While this may be tractable for this kind of problem, it isn't in the general case, where one can identify tens of thousands of different concepts through ideation.

There are two relatively easy ways to prune the number of concepts your morphological chart describes. Both have to do with finding inconsistent embodiments.

The first way is to look for embodiments that are inconsistent with your product strategy. For instance, if you have determined in your strategy that you're looking for “low innovation” solutions, then you should look through all your embodiments for those that suggest high innovation and eliminate them. Similarly, you may have embodiments that run against some specific requirement. Take the time to review your embodiments with respect to both your strategy and requirements. Document embodiments that you removed from consideration because they are inconsistent in this way.

The second relatively easy way to prune the number of concepts that a morphological chart describes involves finding pairs of embodiments that you can demonstrate will not work together, and exclude any concept that includes that pair.

For instance, for our robot connector above, magnetics (embodiment A6) will likely not work with RF data transmission (embodiment D2), because the magnetic fields needed to carry structural loads will likely result in sufficient RF noise to disrupt communication.

How many concepts include embodiments A6 and D2? 1 x 3 x 3 x 1 = 9 concepts. So nine of the 270 concepts are eliminated if we exclude the combination of A6 and D2.

Another combination that will probably not work is C3 and D2, again because of RF noise that can be generated by induction transmission systems over short distances. In this case, there are 6 x 3 x 1 x 1 = 18 concepts that we can eliminate.

Embodiments may conflict for any number of reasons, including cost, mass, size, volume, usability, electrical properties, mechanical properties, manufacturability, assemblability, aesthetics, etc.

So by finding only two pairs of embodiments that do not work well together, we have already eliminated 10% of all concepts.

It is usually possible to dramatically cut the number of potential design concepts implied by a morphological chart in this way. Every concept you eliminate this way is an unfit concept; so the more such concepts you can eliminate early in the process, the faster and better your design process will be.

Go through your morphological chart, and consider every pair of embodiments. Note every pair of embodiments that (you believe) will not work together - for whatever reason. Make sure you document the reasons for adding any pair to this list.

A good way to capture in compact form all the inconsistent embodiments is to use a chart like that shown below.

In this chart, we've marked with an X any pair of embodiments that are (probably) inconsistent. Of course, providing just this chart is not enough; you would be expected to justify each X with a short, precise explanation.

In the example, finding 8 inconsistent embodiments eliminated 110 out of 270 possible concepts. (It's left as an exercise to the reader to understand how we calculated 110 concepts to exclude from the chart.) That means we've eliminated nearly half the design space with only 8 inconsistent embodiments. That's a pretty good use of your time and resources.

The deliverable of this activity is:

  • a chart like the one shown above;
  • calculations showing how many concepts are eliminated by each inconsistent embodiment pair, as well as the total number of inconsistent embodiments; and
  • justifications for excluding each inconsistent embodiment pair (i.e., why each pair is in fact inconsistent).
design/inconsistent_embodiment.txt · Last modified: 2020.03.12 13:30 (external edit)