Patent ID: 8804266

Claim:
A magnetic disc apparatus comprising: a magnetic head which reads information stored in a magnetic disc; an arm which supports the magnetic head; and a feedback controller which comprises: a coarse controller configured to control a coarse actuator to move the magnetic head above the magnetic disc by driving the arm, a fine controller configured to hold a position of the magnetic head, and a feedback path which feeds back a displacement of a fine actuator to a target value of the coarse actuator, wherein the feedback controller controls decoupling due to the feedback path of a double actuator system which adds up the coarse actuator and the fine actuator, wherein the coarse controller comprises a first amplifier which amplifies a signal input to the coarse controller and a first notch filter which notches an output of the first amplifier, and wherein the coarse controller does not comprise a phase compensator, and wherein the fine controller comprises a second amplifier which amplifies a signal input to the fine controller, an integrator which integrates an output of the second amplifier, and a second notch filter which notches an output of the integrator.