Design Realization/Detailed Design - Medical Device Design: Innovation from Concept to Market - page 195

Figure 8.24
Comparison of two knobs: Which is better (a) or (b)?
The previous anecdote should reveal to you that considering the end-user means “ considering
the end-user”; there are two meanings of consider - to just think about something for a
decision, or to think about someone with consideration. These are, in effect, all of the
potential failure modes when in use. By now you should have seen that this is really an
extension of the FMEA we saw earlier. However, instead of just thinking of how the device
can fail operatively, we also consider how it can let the end-user down.
8.8.1 Ergonomics
Ergonomics is the science associated with the ability of things to fit with the human form.
There are two considerations: does it “it,” and do the forces required to perform the function
fall within normal human ranges. Consider your desk at the office. The chair can be designed
so that it feels comfortable to sit in (i.e., passes the “it fits” test), but are you sitting in such a
position that when you work at your desk it causes you to strain to reach things (i.e. it fails the
“within normal ranges” test)? Your biomechanics reference topic will come in handy again.
One of the main considerations is lifting. If your device needs carrying at any time can it be
lifted? If so how many people are required to lift it safely? Does it need handles? Virtually
every country has health and safety laws associated with lifting and carrying; your device
must be designed with due consideration of these.
Consider Figure 8.24 . Here we have two knobs to examine. Which is better? It all depends on
what they are to be used for. Certainly if the knob was for turning then the profile of (a) and
its indicator dot makes this more usable and ergonomically more suitable. Knob (b) on the
other hand is far more suitable for a “pulling” action. Hence you tend to see knobs of type (a)
on amplifiers, etc. where they need to be turned; you tend to see (b) on drawers and cupboards
(and old church organs) where they need to be pulled. What if the end-user was infirm - could
they activate the device now? Do they need anything special?