Fujitsu MHX2250BT, Product Manual

Page: 72 / 296

Theory of Device Operation
4.7.4 Actuator motor control
The voice coil motor (VCM) is controlled by feeding back the servo data recorded
on the data surface. The MPU fetches the position sense data on the servo frame
at a constant interval of sampling time, executes calculation, and updates the VCM
drive current.
The servo control of the actuator includes the operation to move the head to the
reference cylinder, the seek operation to move the head to the target cylinder to
read or write data, and the track-following operation to position the head onto the
target track.
(1) Operation to move the head to the reference cylinder
The MPU moves the head to the reference cylinder when the power is turned. The
reference cylinder is in the data area.
When power is applied the heads are moved from the outside of media to the
normal servo data zone in the following sequence:
a) Micro current is fed to the VCM to press the head against the outer direction.
b) The head is loaded on the disk.
c) When the servo mark is detected the head is moved slowly toward the inner
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/write 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.
4-18 C141-E254