In a positioning control device for a two-stage actuator having a coarse-movement
actuator and a fine-movement actuator, a notch filter having a cutoff frequency
fn is provided to a coarse-movement control loop, and the fine-movement actuator
is driven by a sine wave of the frequency fn. At the frequency fn, a head position
signal becomes identical with an output signal of the fine-movement actuator, by
which the gain of the fine-movement actuator can be estimated by an adaptive identification
unit with high accuracy based on the control input to the fine-movement actuator
and the head position signal.
