Patent ID: 7525883

Claim:
An optical disk apparatus comprising: an optical head that focuses a light beam to form a beam spot on a recording surface of an optical disk, and detects light that is reflected therefrom; an aberration adjuster provided in the optical head; an aberration adjuster drive portion that drives the aberration adjuster; a movement portion that moves the beam spot in a direction that is perpendicular to the recording surface or in a radial direction of the optical disk; a position control portion that controls a position of the movement portion based on an output signal of the optical head such that the beam spot is in a predetermined state with respect to the recording surface; an observer processing portion that estimates a state relating to the movement portion; and a summing portion that takes a sum of an output of the position control portion and an output of the observer processing portion; the optical disk apparatus driving the movement portion based on an output of the summing portion; wherein the optical disk apparatus further comprises: an ON/OFF control portion that controls whether the observer processing portion is on or off; a low-pass filter that attenuates high-frequency components of the output of the observer processing portion and holds a final value of the observer processing portion when the observer processing portion is turned off; a switching portion that switches its output between the output of the observer processing portion and an output of the low-pass filter according to whether the observer processing portion is on or off; and a state management portion that manages a transition to a state m which a loop gain of the position control by the position control portion fluctuates, the fluctuation of the loop gain being caused when the aberration adjuster is driven by the aberration adjuster drive portion so that spherical aberration does not occur; wherein the ON/OFF control portion controls whether the observer processing portion is on or off based on an output of the state management portion; wherein the state management portion sets the observer processing portion to off prior to transition to the state in which the loop gain of the position control fluctuates, and sets the observer processing portion to on after transition to a state in which the loop gain is stable; and wherein when the observer processing portion is in the on state, its output is supplied to the summing portion, and when the observer processing portion is in the off state, the output of the low-pass filter is supplied to the summing portion.