Hardware Reference
In-Depth Information
Figure 4.58: Spectrum of acoustic noise for spindle motor with
fi
xed shaft
FDB.
The NRRO and acoustics performances of the FDB spindles are much bet-
ter than those of the ball bearing motors. The spectrum of the acoustic noise
in an FDB spindle motor is shown in Figure 4.58. Improvement is clearly evi-
dent when this spectrum is compared with the spectrum of the acoustic noise
for a ball-bearing spindle shown in Figure 4.54. The data for these spectra
are collected experimentally from two spindles of same geometry, one with a
ball-bearing motor while the other with a FDB motor.
It is easily concluded from these results that the acoustic noise of the spindle
motor is reduced signi
fi
cantly if FDB spindle is used. The NRRO is also
reduced signi
fi
cantly. These two are the major bene
fi
ts of using FDB spindle.
The friction between the oil
fi
lm and metal parts can still induce certain level
of acoustic noise and oil whirl when the motor is in motion, and irregular whirl
can induce NRRO. However, the amplitudes of such noise and NRRO are much
smaller than those caused by the rolling contacts in ball-bearing.
In an FDB spindle, the airgap between the sleeve and the shaft, and the
depth of the groove are only several micro meters. The tolerance of the geomet-
rical dimensions must be controlled very strictly during the poduction of these
FDB spindles. This requirement makes production of FDB components and
assembling of bearing difficult which, in effect, increases cost. Effective sealing
of the lubricant oil is another issue to be addressed while selecting FDB motors
for any application. Nevertheless, the developments in FDB design, precision
machining and precision assembling have successfully enabled the application
of FDB in increasing number of spindle motors.
For the FDB spindle motor, as there is more conforming surface through
the lubricant to the ball bearings, these spindles have better shock resistance.
However, if the motor operates at very high speed, the centrifugal force and
high temperature caused by the friction make the sealing of oil difficult. There-
fore, FDB spindle motor is not a good choice for HDDs with rotational speed
higher than 20,000 RPM.
