FUJITSU MHZ2250BJ - Manual (Page 69)

4.7 Servo Control
(1) Microprocessor unit (MPU)
The MPU executes startup of the spindle motor, movement to the reference
cylinder, seek to the specified cylinder, and calibration operations.
The main internal operations of the MPU are shown below.
a. Spindle motor start
Starts the spindle motor and accelerates it to normal speed when power is
applied.
b. Move head to reference cylinder
Drives the VCM to position the head at the any cylinder in the data area. The
logical initial cylinder is at the outermost circumference (cylinder 0).
c. Seek to specified cylinder
Drives the VCM to position the head to the specified cylinder.
d. Calibration
Senses and stores the thermal offset between heads and the mechanical forces
on the actuator, and stores the calibration value.
(2) Servo burst capture circuit
The servo burst capture circuit reproduces signals (position signals) that indicate
the head position from the servo data on the data surface. From the servo area on
the data area surface, via the data head, the burst signals of EVEN1, ODD,
EVEN2 are output as shown in Figure 4.7 in subsequent to the servo mark, gray
code that indicates the cylinder position, and index information. The servo signals
do A/D-convert by Fourier-demodulator in the servo burst capture circuit. At that
time the AGC circuit is in hold mode. The A/D converted data is recognized by
the MPU as position information.
(3) D/A converter (DAC)
The control program calculates the specified data value (digital value) of the VCM
drive current, and the value is converted from digital-to-analog so that an analog
output voltage is sent to the power amplifier.
(4) Power amplifier
The power amplifier feeds currents, corresponding to the DAC output signal
voltage to the VCM.
(5) Spindle motor control circuit
The spindle motor control circuit controls the sensor-less spindle motor. A spindle
driver IC with a built-in PLL circuit that is on a hardware unit controls the sensor-
less spindle motor.
C141-E280 4-13