Figure 4.46: Key components of underslung spindle motor.
Figure 4.47: The spindle motor with disks installed inside the drive enclosure.
For this type of motor, one end of the shaft is fi xedonthemotorbase
which itself is fi xed on the base-plate of HDD. The other end of the shaft can
be screwed onto the HDD cover through a hole on the shaft (Figure 4.47). This
ensures high stiffness for the entire spindle system.
Leakage of lubrication oil from the bearing can contribute to the conta-
mination inside the drive enclosure which is not good for the long life of the
HDD. Contamination from lubrication oil of the bearing is prevented in some
motors using ferro- fl uid sealing as shown in Figure 4.48. The ferro- fl uid is a
special kind of liquid whose distribution can be changed by applying a mag-
netic fi eld. In this type of sealing, the airgap between the rotating parts and
the stationary parts is fi lled with ferro-liquid, and a permanent magnet is used
to produce the magnetic fi eld to increase viscosity of the fl uid. This sealing
prevents leakage of lubrication oil without affecting the spinning of rotor.