DISK DRIVE
Disk
Drive Mechanism
The
disk drive
mechanism
is a brushless direct drive
motor,
which
employs a velocity servo control
circuit
to
ensure
that
the
disk
rotates
at
a
constant
speed of 600 rpm.
The
drive is configured so
that
the
motor
rotates
only
when
a disk is
within
the
unit.
Removal of
the
disk from
the
drive
causes
the
motor
to stop.
The
time
taken
for
the
motor
to
reach
the
normal
operating speed, following
the
insertion
of
a disk, is
the
order of
one
second.
The
servo
control
circuit
also generates
the
index pulse
once per
revolution
of
the
disk.
Read/Write Head
The
head
consists
of a
read/write
element
and
a pair of
tunnel
erase heads
which
provide guard bands for adjacent
tracks.
Current
is
supplied
to
the
read/write
element
on
receipt of
an
active
Write
Gate
signal from
the
disk
controller,
which
also
activates
the
tunnel
erase section.
Head Positioning Mechanism
The
head
positioning
mechanism
uses a stepping
motor
and
a guide
arm
controlled
by a needle screw
to
precisely
position
t~e
read/write
head
over
the
tracks
on
the
disk_. _
Control
of
the
movement
of
the
head
is
supplied by
the
Step
and
Direction
inputs
from
the
disk controller.
On
application of
the
power
supplies,
the
drive
automatically
generates
control
signals to
position
the
head over
Track
o.
Head Load Mechanism
Head loading
is
controlled
by
the
Head Load signal from
the
System Board.
When
the
signal is active, a plunger
causes a pressure pad
to
press
the
disk against
the
head.
The
activity
indicator
on
the
front
panel
of
the
unit
remains
illuminated, as long as
the
head
remains
loaded.
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