Fujitsu MAN3367FC - Enterprise 36.7 GB Hard Drive, Product/Maintenance Manual

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8.7 Servo Control
C141-E133-02EN 8-13
2) In the next timing phase of 1) above, the DSP creates a rotating magnetic field. The motor
rotates from a low rotational frequency up to about 100 min
-1
(100rpm). This is called
synchronization control.
3) When the motor reaches a high rotational frequency, a counter-electromotive voltage (back EMF)
is generated. This voltage tells the DSP the rotational frequency and angular position of the
motor. Using the rotation position detection data, the spindle controller supplies current to the
correct phase to rotate the motor. The MPU then detects the rotational frequency, and the spindle
controller accelerates the motor up to the steady-state angular frequency.
(2) Rotational speed control mode
When the activation mode terminates, the rotational speed control mode starts. The MPU controls
the controller to maintain the detected rotational speed.
8.7.5 Voice coil motor control
The voice coil motor is controlled by moving the head-mounted carriage according to the servo data
recorded on the specific data side. This control is done by firmware by digital servo control using the
DSP. This control provides return-to-zero (RTZ) operation, seek operation, and track following
operation.
(1) RTZ operation
When the power is turned on, or when a REZERO UNIT COMMAND is issued from the host
computer, the DSP moves the head to the reference cylinder (cylinder 0) by an internal command
from the MPU.
(2) Seek operation
When the host issues a data read/write request, the MPU issues a seek command to the DSP to move the
head to a target cylinder. When the DSP receives this command, the DSP drives the voice coil motor,
via the digital-to-analog converter and power amplifier, to move the head to the target cylinder. A
predetermined target speed is used depending on the distance to move. The head is accelerated or
decelerated to move to the target cylinder. Track following operation then begins.
(3) Track following operation
To read or write data from or to a disk, the head must be correctly centered over the target cylinder.
The DSP receives a position signal from the servo head, converts it to a digital signal using an
analog-to-digital converter, then decodes the signal. The digital servo control circuit controls the
voice coil motor so that the position signal is constant. This centers the head over the target cylinder.