Biomedical Engineering Reference
Quality in Design
You are probably bored of me quoting ISO 13485, MDD, and the FDA. Unfortunately they
are very important to us. One of the main reasons for having our own ISO for medical devices
companies was that the totality of the ISO 9000 family did not sit comfortably with our
discipline. However it is, effectively, a sibling of the ISO 9000 family and as such is concerned
with ensuring quality. While we have formulated procedures to meet the ISO requirements,
they do not themselves ensure that a quality item has been designed. We can produce a brilliant
paper trail showing that we have met ISO 13485 - however it is the detail in the paper trail
that actually determines the quality of the device. In this chapter we will look at design tools
specifically developed to makes sure your design is an optimum design .
I am sorry but this chapter has some mathematical analyses. It was inevitable that you had to
get your calculator out at some point. However most of the tools I describe can be undertaken
in a spreadsheet, so maybe it's time to invest in a personal laptop and a copy of a spreadsheet
program. It may even be time to seek out the dedicated software that is available or to team
up with someone (such as a university) who has a copy. In this chapter we shall be examining
specific tools for design activities that promote quality. Specifically we shall examine
optimization, design of experiments (2 k factorial), House of Quality, FMEA, D4X, and 6 σ .
One of the main uses for optimization is to minimize mass. If you consider the aircraft
industry then it is pointless having a cargo plane that can only carry its own body weight.
To be optimal the body weight must be a minimum so that its payload is a maximum.
This is the point of optimization - you need to have an “objective” to achieve; this could be
maximum power, it could be minimum weight, it could be maximum volume. You then have
to manipulate your design to see if you can achieve the optimum. This often involves the
manipulation of numerous mathematical models - they need not be complex but there will
always be more than one.
Optimization is not new - it is the basis of evolution. Our human bodies have the most
wonderful optimization system built-in; it is called bone . Your bones remodel all of the
time based on the load they carry; in fact your skeleton is renewed every two years.