Section 3
Principles
of
Operation
3.1.1
BASE CASTING ASSEMBLY
The base casting is a single-piece cast aluminum alloy which provides a mounting surface for the rest
of
the
drive mechanism.
It
has two machined holes for mounting the motor/spindle assembly and the positioner
assembly. A gasket is mounted on the outside top edge to ensure a seal with the metal cover. Surfaces are
provided for mounting the magnet plate assemblies for the rotary positioner assembly, and a read/write
preamplifier. Mounting holes are provided outside the cover area, for the PCB and shock mount bracket
assembly. .
3.1.2
DISK STACK ASSEMBLY
The disk stack assembly is secured to the
DC
spindle motor which is bolted to the base casting.
It
consists
of
disks, disk spacers and a disk clamp. The
DC
motor assembly consists
of
a DC motor, spindle bearing
assembly, disk mounting hub, and ferro-fluid magnetic seal. This seal prevents outside air from entering
the drive through the bearing bore
or
along the bearing shaft. In the ProDrive 80S, three disks and two
spacers are placed
on
the hub and clamped in place; the ProDrive 40S uses two disks and one spacer. The
disks are an aluminum alloy with a thin film magnetic metal coating which is lubricated using a carbon
overcoat. This overcoat prevents head and media wear when the heads are in contact with the disk surface,
which only occurs outside the data area.
3.1.3
ROTARY POSITIONER ASSEMBLY (ACTUATOR)
The positioner used
on
the ProDrive is a Quantum proprietary design. It consists
of
the upper and lower
magnet plates, a rotary single phase coil, a headstack mounting hub, and a bearing shaft. The magnets are
composed
of
two alternating poles bonded to the magnet plates which in tum, are bolted to the base
casting. The rotor and hub are molded together. The shaft is pressed into the base casting. Crash stops
mounted to the magnet plate assembly prevent the heads from being driven into the spindle
or
off
the disk
surface.
3.1.4 HEADSTACK ASSEMBLY
The headstack assembly consists
of
the read/write heads, head arms, spacers, flex circuit, an optical scale,
and the rotary positioner assembly. It is designed such that the mass center
of
the entire stack is at the
center
of
the mounting hub. This is accomplished without the need for external counterbalances through a
design in which the head arms, optical scale, and rotary positioner coil assembly balance each other. The
heads are mini-composite slider type heads. They are mounted to Whitney-style spring steel flexures which
are screwed to the head arms. The head conductors are flex cables routed through one flex circuit. A read
preamplifier/write driver is mounted to this flex circuit.
3.1.5
OPTICAL ENCODER
The optical encoder assembly consists
of
a housing, an infared light-emitting diode (LED), a mirror, an
optical reticle, a multi-cell photo diode matrix, and a flex circuit.
The infrared LED and the mirror are mounted in the upper portion
of
the housing. This allows the optical
scale mounted with the headstack to move between the mirror-reflected light from the infared LED and the
lower portion
of
the housing which contains the reticle and photo cells. The reticle masks the photo cells
so that each cell only
rece'ives light through a specific portion
of
the movable scale. Both the clearance and
angular position
of
the reticle and scale are precision adjustments made when the drive is manufactured.
3 - 2 Principles
of
Operation
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