The Design Process - Medical Device Design: Innovation from Concept to Market - page 27

CHAPTER 3
The Design Process
3.1 Design Process versus Design Control
There are two fundamental reasons why we need to control our design processes. The first is
regulatory. In all medical devices regulations (for example FDA, 1997 ; FDA 21 CFR 820.30;
ISO 13485; and ISO 9001) you will find the term design control - hence we have to control
our design process in order to fulfill our obligations to the medical device authorities. The
second reason is for the life of the company. It is very easy to spend (sorry, waste) lots of
money undertaking uncontrolled design leading to outputs that are not fit for purpose. This is
futile. We should, as medical device designers, work to right first time every time . Using the
6 σ 1 model, if your first three designs are rubbish, then your next 999,997 have to be spot on.
Controlling the process also saves time. This not only saves money (saving staffing costs, etc.)
but also leads to shorter time-to-market , bringing obvious advantages.
People often wrongly assume that there is a conflict between a process and that which
controls it. Any control engineer will tell you this is false. Before you can control anything
you need to understand the process - you need to understand how the process changes the
input to an output . You need to measure the input and you need to measure the output. It is the
relationship between the two that is the process. Figure 3.1 illustrates a design activity as a
typical control block diagram.
The design process illustrated in Figure 3.1 is “open loop”: there is no feedback; the output
has no influence; and, worst of all, there is no measurement of whether the output is right or
wrong. Control engineers correct this by “closing the loop” - by introducing feedback. This is
illustrated in Figure 3.2 .
Closed loop systems are known to be more efficient ( Schrwazenbach & Gill, 1992 ), but we
are not designing a control system for a machine tool - we are trying to examine design as a
process. What is the lesson ?
It is something that the Six Sigma 2 fraternity picked up on very quickly. The term DMAIC
(Define, Measure, Analyze, Improve, Control) is a fundamental tenet of 6 σ ( Bicheno and
1 6 σ : stands for Six Sigma, a popular design/manufacturing management tool.
2 Six Sigma (6 σ ) was started by Motorola and spread to worldwide fame with General Electric's adoption: its aim
is to minimize defective components to a maximum of 3.4 in 1,000,000. There is a plethora of texts available.