Patent ID: 7394609

Claim:
A magnetic disk drive comprising: a magnetic disk that records information; a magnetic head that records information on said magnetic disk or plays back the information on said magnetic disk; an actuator that drives said magnetic head; and a control portion that creates a control signal for controlling said magnetic head such that the magnetic head assumes a target position, based on a given target position signal and on a position signal played back by said magnetic head, the control portion controlling an object to be controlled including said magnetic head and said actuator; wherein said control portion is configured such that (i) a resonant characteristic is present in open-loop transfer characteristics when said control portion and said controlled object are connected, at a frequency other than a mechanical resonant frequency of the controlled object, (ii) a frequency of said resonant characteristic is higher than a frequency at which a gain characteristic of said open-loop transfer characteristics becomes 0 dB, and (iii) a phase of said open-loop transfer characteristics at the frequency of said resonant characteristic becomes arctangent ((Rop+1)/lop) when coordinates of a vector locus of said open-loop transfer characteristics are (Rop, lop) at the frequency of said resonant characteristic.