The Design Process - Medical Device Design: Innovation from Concept to Market - page 40

Specification
Embodiment
Detailed design
Manufacture
Figure 3.13
The waterfall design model.
typical Gantt chart for a design project. It is by no means a model Gantt chart and should only
be considered as an example.
The example Gantt chart illustrates how one task follows another - and this is the essential
problem with a serial model. One only identifies an issue once a task has started. In the chart,
“testing” take over the baton from design when they have finished. Suppose testing determine
something is wrong; this information goes back to design, who change their ideas, and then
testing take over the baton again. This backward and forward cycle is common in poorly
managed design systems. Also, as has happened in the past, the whole design may have to be
scrapped; as you can imagine this wastes a lot of time and money. An example of how project
management can speed up the process is by running fully independent tasks simultaneously
(develop test regime, detail design (1), and detail design (2)). Even so this is still, essentially,
nose to tail. In essence it is hard to “look backward,” or to enforce feedback control in
serial design. Some people demonstrate this by using a waterfall model ( Figure 3.13 ). The
project flows like water from one task to the next by flowing over the edge after said task is
complete - and, as everyone knows, water does not flow uphill.
3.3.1.2 Ad Hoc 9 Feedback
To try and overcome the issues discussed in the previous section people have tried to insert
feedback into the system. However this feedback tends to be “reactive” and only happens
when a problem has been identified.
An example of this form of ad hoc feedback would be when final packaging is selected.
Often, at this stage the packagers will say, “If only your device was 12 mm (½ inch) shorter it
would have fit in one of our standard boxes.” This is clearly true, but unhelpful.
While ad hoc feedback is better than none at all, it is inefficient. It leads to long lead times,
often leads to severe frustration, and is a major source of internal tension: the classic example
being between the manufacturing office and the design office. It is often the case that the
manufacturing office accuse the design office of designing things that cannot be made and the
9 Ad hoc is a Latin word. It generally signifies a solution designed for a specific problem or task. It is not general,
and not intended to be able to be adapted to other purposes. It is often a reaction to an event.