Patent ID: 7864484

Claim:
A hard-disk drive comprising: a main control circuit for an actuator configured to move a magnetic-recording head relative to a magnetic-recording disk, the main control circuit comprising: a frequency-hunting peak filter comprising: a peak filter wherein a gain at a center frequency becomes finite and a reciprocal of the transfer function is represented by z/F D in z-transform space, where a denominator of the transfer function of the peak filter that is represented by F D , has a real part and an imaginary part, wherein the real part of the denominator of the transfer function becomes zero at the center frequency and the imaginary part of the denominator of the transfer function becomes a positive number at the center frequency; and a frequency updating unit that updates the center frequency to converge onto a frequency of a disturbance by obtaining a comparative relation between the center frequency and the frequency of the disturbance acting on the control system in accordance with a phase difference between an input and output of the transfer function represented by z/F D .