Patent ID: 7061835

Claim:
A focus control apparatus which controls a focus of an objective lens for focusing light against an optical disk having a plurality of signal recorded layers, comprising: focus drive means for moving the objective lens in a direction orthogonal to the recorded layers of the optical disk; photodetection means for detecting reflected light from said optical disk; focus-error-signal generation means for generating a focus error signal which corresponds to defocusing of said objective lens relative to any of said recorded layers of said optical disk, on the basis of a detection signal of said photodetection means; recorded-layer movement control means for generating a signal which controls said focus drive means, on the basis of the error signal, in order to move said objective lens for changing the recorded layer which is an objective of the focus of said objective lens; and focus pull-in means for pulling in the focus of said objective lens onto said recorded layer on which said objective lens is to be focused, said pull-in means being permitted to switch on and off by said recorded-layer movement control means; wherein said recorded-layer movement control means calculates an intermediate value of said focus error signal from a maximum value and a minimum value of said focus error signal corresponding to said recorded layer; and in an automatic adjustment of a focus bias for each recording layer, said apparatus carries out processing of: a) measuring a focus error signal of the optical disk; b) calculating an intermediate value from a maximum value and a minimum value of the focus error signal in the recording layer which is a destination layer of the movement; c) pulling in the focus of said objective lens onto the recorded layer which is an origin layer of the movement to carry out automatic adjustment of a focus bias; d) moving the focus of said objective lens onto the destination layer and turning on the focus pull-in means when the focus error signal reaches to the intermediate value; and e) carrying out the automatic adjustment of the focus bias of the destination recording layer.