Page 318 - Design for Six Sigma a Roadmap for Product Development

288 Chapter Nine

Normal useful action

Insufficient useful action

Excessive useful action Figure 9.1 Legends for various
actions in functional analysis
diagrams.
Harmful action

However, if we use the toothbrush too gently and do not brush long enough,
or we use a worn toothbrush, then our teeth will not get enough cleaning. In
this case, we call it an “insufficient useful action” and we can express this by
using the following functional analysis diagram:

Brush
Toothbrush Teeth
Mech.
If we use a very strong toothbrush, and brush our teeth with large force and
strong strokes, then our gums will get hurt, and so will our teeth. We can
use the following functional analysis diagram to describe this situation:
Brush
Toothbrush Teeth
Wear

Tear
Gums

That is, the toothbrush delivers excessive brush action to teeth, and exces-
sive brushing will deliver a harmful action, “tearing the gums,” making
them bleed; and the teeth also may deliver a harmful action, “wearing the
toothbrush.”

Functional modeling and analysis example. Figure 9.2 is a schematic view
of an overhead projector. Figure 9.3 is the functional modeling and
analysis diagram for the whole system. In this example, there are many
“chain actions”; that is, an “object” can be other object’s subject. Then we
have a sequence of “subject-action-object-action-” chains. Each chain
describes a complete function. We can identify the following functions:

1. From “electricity to image in screen,” that is, the function of “to pro-
ject image in the film to screen,” we can think that is the main basic
function.
2. From “hand” to “focusing device” to “mirror,” that is, the function of
“to focus the image,” which is a secondary basic function.