Patent ID: 6744709
Filing Date: 2004-06-01
Classification: G11B

Abstract:
A focus control apparatus for use in an optical disk playback apparatus, comprising:an object lens which condenses a light beam on an optical disk having a plurality of signal recording layers; focusing drive means for moving said object lens in a direction orthogonal to the recording layers of the optical disk; photodetection means for detecting light reflected from said optical disk; focus error signal generation means for generating a focus error signal which corresponds to defocusing of said object lens relative to a specified one of said recording layers of said optical disk, on the basis of a detection signal of said photodetection means; peak detection means for detecting peaks of the focus error signal; reference value calculation means for calculating reference values of said focus error signal in accordance with detection signals of said peak detection means; comparison signal generation means for comparing said focus error signal with its reference values, and generating comparison signals based on results of the comparisons; and control means for accepting a request for moving a focusing position of said object lens, and generating and outputting signals which control said focusing drive means, on the basis of the detection signals of said peak detection means and the comparison signals; wherein the signals which control said focusing drive means are a signal which moves said object lens, and a signal which brakes said object lens, wherein when the request for moving the focus of said object lens in accepted, the signal for moving said object lens is outputted, and wherein when it is sensed from the comparison signal that said focus error signal has exceeded its reference value, the output of said signal for moving said object lens is terminated; further comprising: means for measuring a 1st time period for which said signal for moving said object lens is outputted; and means for calculating a 2nd time period for which the signal for braking said object lens is outputted, on the basis of the measured time period; wherein, when it is sensed from the comparison signal that said focus error signal has exceeded its reference value, after the termination of said output of said signal for moving said object lens, said signal for braking said object lens is outputted; and after the second time period has lapsed, the output of said signal for braking said object lens is terminated.