Page 374 - Design for Six Sigma a Roadmap for Product Development

344 Chapter Nine

μ > μ 2 μ 1
1

μ 2

Figure 9.8 Basic concept of the paper isolation
mechanism.
A 12 and A 21 represent the friction between two bills, so A 12 is equal to
A 21 . Compared to A 11 and A 22 , A 12 and A 21 can be disregarded; thus two
requirements can be satisfied independently.
The remaining questions are:
■ What happens if three or more bills are inserted between the two
rollers at the same time?
■ What happens after the first bill is sent forward if the roller contin-
ues to rotate?
■ What happens when the quality of the bill changes?

To answer these questions, the following four FRs must be defined:
FR 3 slant the cross section of the piled bills to make isolation easy
FR 4 pull out the isolate bill
FR 5 adjust the friction force
FR 6 decrease the forward force after one bill is gone

In AD theory, these six FRs are the minimum set of independent require-
ments that completely characterize the design objectives for the specific
needs of the paper-handling mechanism. Six DPs in the physical domain
are selected as follows, and the mechanism is illustrated in Fig. 9.8.

DP 1 upper rollers
DP 2 lower roller
DP 3 wedge-shaped floor guide
DP 4 carriage pinch rollers
DP 5 press plate
DP 6 cam
The function of the cam (DP 6 ) is to reduce the forward force after one
bill is gone. However, when the cam turns, it also affects FR 1 ,FR 2 ,FR 3 ,
and FR 5 because it changes the pressure and slope of the floor guide.