Patent ID: 7869157

Claim:
A magnetic disk drive comprising: a magnetic disk, a magnetic head adapted to read out information recorded on the magnetic disk, an arm adapted to support the magnetic head, a coarse actuator adapted to drive the arm to move the magnetic head on the magnetic disk in response to a coarse actuator control signal, a fine actuator adapted to adjust a position of the magnetic head with respect to the arm, the fine actuator having a gain, a fine actuator model adapted to estimate a displacement amount of the fine actuator, the fine actuator model having a gain, a feedback path for feeding back a position error signal representing a positional error between a target position and a present position of the magnetic head, to a controller of the fine actuator and to a controller of the coarse actuator, a decoupling path adapted to add the displacement amount of the fine actuator, estimated by the fine actuator model, to the coarse actuator control signal, a switch adapted to open and close the feedback path to the controller of the fine actuator; and an excitation signal generator for adding the excitation signal to the coarse actuator control signal, wherein the magnetic disk drive is suitably programmed to: (a) cause the generation of the excitation signal and add the excitation signal to the coarse actuator control signal; (b) open the feedback path to the controller of the fine actuator using the switch and obtain a first gain value of an open-loop transfer function of a feedback loop of the coarse actuator, for the excitation signal generated; (c) close the feedback path to the controller of the fine actuator using the switch and obtain a second gain value of the open-loop transfer function of the feedback loop of the coarse actuator, for the excitation signal generated; (d) obtain a deviation of the fine actuator model gain from the fine actuator gain when the feedback path to the controller of the fine actuator is closed, by comparing the first and the second gain values of the open-loop transfer functions of the feedback loop of the coarse actuator; and (e) calibrate the fine actuator model gain based on the deviation obtained.