FUJITSU MHA2032AT - Manual (Page 47)

4.5 Self-calibration
C141-E042-01EN 4-7
Figure 4.3 Power-on operation sequence
4.5 Self-calibration
The disk drive occasionally performs self-calibration in order to sense and
calibrate mechanical external forces on the actuator, and VCM tarque. This
enables precise seek and read/write operations.
4.5.1 Self-calibration contents
(1) Sensing and compensating for external forces
The actuator suffers from torque due to the FPC forces and winds accompanying
disk revolution. The torque vary with the disk drive and the cylinder where the
head is positioned. To execute stable fast seek operations, external forces are
occasionally sensed.
The firmware of the drive measures and stores the force (value of the actuator
motor drive current) that balances the torque for stopping head stably. This
includes the current offset in the power amplifier circuit and DAC system.