Patent ID: 7164550

Claim:
A disk drive with a servo system for conducting position control of a head by use of the servo signal recorded on a recording disk, the servo system comprising: a head position signal generator configured to generate, from the servo signal read from the recording disk, a head position signal associated with a position of the head; a peak filter having a peak at each of a plurality of frequencies, the peak filter compensating for a repeatable run-out error; and a control signal output unit which, on the basis of the head position signal, a reference signal, and an output of the peak filter, outputs a control signal for a driving device for moving the head; wherein, in a Nyquist diagram based on an open-loop transfer function of the servo system, when: with regard to each of all peaks of “ωk”, except “ω=0”, of the peak filter where k is an integer greater than or equal to 1, Z 0 is a point (−1, 0), Z 01 is a point of the open-loop transfer function of the servo system at “ωk” in the case where the peak filter is not present, and Z k is a point of the open-loop transfer function of the servo system at “ωk” in the case where the peak filter is present, the angle formed by a straight line extending from the Z 0 point toward the Z 01 point and a straight line extending from the Z 01 point toward the Z k point is 90° or less.