Appeal No. 2002-1240
Application 09/247,550
speed of the disc has been gradually increased. Appellants have
recognized that an increase in rotational speed has caused
increased disc oscillation due to a fluid force caused by
rotation so as to raise a new problem that the degree of
positioning accuracy is lowered. See page 1 of the Appellants’
specification.
Figure 1b is a top view illustrating the disc unit. See
page 4 of Appellants’ specification. Figure 1b shows a gap
between the outer peripheries of the disc 1 and the inner wall of
shroud 20 which is maintained at a predetermined distance. This
predetermined distance is referred to as the disc-shroud gap.
See page 5 of Appellants’ specification. Figures 4a to 4d show
contour lines of air pressure differentials between the outer and
rear surfaces of a rotating disc, which were obtained from
results of flow analysis in such a condition that the disc-shroud
gap is narrowed. Figures 4a to 4d show those with a disc-shroud
gap of 2 mm, 1 mm, 0.5 mm and 0.2 mm respectively. The figures
show that in the case of a disc-shroud gap of 2 mm or 1 mm, there
is pressure differential which causes the disc to flutter.
Meanwhile, in the case of a small disc-shroud gap of 0.5 mm or
0.2 mm, there is no pressure differential and thereby no flutter
is caused. Thus, it has also been understood from the results of
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