Spindle Motor Control - Fujitsu MPG3xxxAT Product Manual

b) A current is fed to the VCM to move the head toward the outer circumference.
c) When the servo mark is detected the head is moved slowly toward the outer circumference at
a constant speed.
d) If the head is stopped at the reference cylinder from there. Track following control starts.
(2) Seek operation
Upon a data read/write request from the host, the MPU confirms the necessity of access to the
disk. If a read or instruction is issued, the MPU seeks the desired track.
The MPU feeds the VCM current via the D/A converter and power amplifier to move the head. The
MPU calculates the difference (speed error) between the specified target position and the current
position for each sampling timing during head moving. The MPU then feeds the VCM drive current
by setting the calculated result into the D/A converter. The calculation is digitally executed by the
firmware. When the head arrives at the target cylinder, the track is followed.
(3) Track following operation
Except during head movement to the reference cylinder and seek operation under the spindle
rotates in steady speed, the MPU does track following control. To position the head at the center
of a track, the DSP drives the VCM by feeding micro current. For each sampling time, the VCM
drive current is determined by filtering the position difference between the target position and the
position clarified by the detected position sense data. The filtering includes servo compensation.
These are digitally controlled by the firmware.
4.7.5

Spindle motor control

Hall-less three-phase eight-pole motor is used for the spindle motor, and the 3-phase full/half-
wave analog current control circuit is used as the spindle motor driver (called SVC hereafter).
The firmware operates on the MPU manufactured by Fujitsu. The spindle motor is controlled by
sending several signals from the MPU to the SVC. There are three modes for the spindle control;
start mode, acceleration mode, and stable rotation mode.
(1) Start mode
When power is supplied, the spindle motor is started in the following sequence:
a) After the power is turned on, the MPU sends a signal to the SVC to charge the change pump
capacitor of the SVC. The charged amount defines the current that flows in the spindle motor.
b) When the charge pump capacitor is charged enough, the MPU sets the SVC to the motor start
mode. Then, a current (approx. 1.6 A) flows into the spindle motor.
c) The SVC generates a phase switching signal by itself, and changes the phase of the current
flowed in the motor in the order of (V-phase to U-phase), (W-phase to U-phase), (W-phase to
V-phase), (U-phase to V-phase), (U-phase to W-phase), and (V-phase to W-phase) (after that,
repeating this order).
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