Servo Circuit - Fujitsu M2361A Customer Engineering Manual

4.6.3 Servo circuit
(1) Seek control operation
The seek control operation is classified roughly into the coarse control
operation and fine control operation.
a~
Coarse control operation
The coarse control operation is performed to move the head to the
desired cylinder position. That is, the head is moved with a speed
feedback loop at a high speed by comparing the target speed, derived
from the position difference between the desired position sent from
the logic circuit and the actual position, with the actual speed
derived from the position signal read from the servo surface with the
servo head.
The speed is decreased as the position difference is reduced and,
when the head approaches the desired cylinder, the speed becomes very
slow.
b. Fine control operation
4 - 68
When the head nears the desired cylinder and the difference between
the desired position and the current position is within the specified
range (on track), the coarse control operation is switched to the
fine control operation. During the fine control operation, the
position signal is fed back to ensure that the head is always on the
desired cylinder notwithstanding mechanical vibration and temperature
change.
The speed signal is used as the damping factor. The signal generated
by integrating the position signal is also used to increase
stiffness.
B03P-482S-0002A ••• 01