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FDD412A/B
2.5.6
Operations
Related
to
Spindle
Motor
Drive
Mechanism
(1)
Interface
signal
None
(automatic
control
initiated
upon
power
application)
(2)
Outline
of operation
Applying
power
immediately
rotates
the
spindle
motor.
The
mechanism
automatically
keeps
the
rotational
speed
constant
(360
rpm)
through
a feedback
loop.
(3)
Block
diagram
of spindle
motor
drive
mechanism
MTR
SPD
OK
Phase
com-
Power
pensator
amplifier
t
t
'
!
Position
detection
(HALL
IC)
|
1
'
amplifier
Frequency
oe
S
generator
'
(FG)
:
CP
ri
Ro
aes
prec
|
a
oe
es
Motor
coil |
Fig.
2.28
Block
Diagram of Spindle
Motor
Drive Mechanism
(4)
Operating
principles of spindle
motor
drive
mechanism
(a)
Drive
section
The
S pole
of the
rotary
magnet
is detected
by a position
detecting
element
(HALL
IC).
In the
setup
of Fig.
2.29,
Hy
detects
the
S pole.
This
'drives
amplifier
Vw,
allows
current
Ip to
flow,
and
rotates
the
rotor.
With
the
rotor
rotating
H,,
Hy and
Hy detects
the
S pole
in
turn
to generate
drive
voltages
(Fig.
2.30)
for motor
drive.
(b)
Feedback
section
The
frequency
generator
generates
frequencies
proportionate
to
the
rotor
revolutions.
The
generator
output
and
crystal
oscillator
output
are
compared
in phase
shift
and
frequency
to
calculate
rotation
correction
values.
— 28—
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