Optical disk apparatus

An optical disk apparatus comprising:

• an optical head having focusing means for focusing a light beam along a light axis of said focusing means and onto an optical recording medium having tracks, and having detecting means for detecting a light beam reflected from the optical recording medium and for outputting a detection signal;
• mode setting means for selectively setting one of a coarse track accessing mode, for making said optical head coarsely access a target track through a plurality of tracks, and a fine track accessing mode, for making said optical head finely access the target track;
• means, coupled to the mode setting means, for producing a first drive signal;
• first drive means, coupled to the first drive signal means, for moving said optical head in a radial direction of the optical recording medium through the plurality of tracks, in response to the first drive signal, when the coarse track accessing mode is set;
• second drive means, coupled to the focusing means, for moving said focusing means in a direction perpendicular to the light axis of said focusing means in response to a second drive signal;
• first signal-generating means, coupled to the detecting means, for generating a tracking-error signal, with a frequency, in response to the detection signal output from said detecting means;
• tracking means, coupled to the second drive means, for causing said second drive means to adjust a relative position between said focusing means and the target track of said optical recording medium in the fine track accessing mode after the first drive means has moved said optical head in the coarse track accessing mode, and to move said focusing means to the target track in response to the tracking-error signal generated by said first signal-generating means;
• second signal-generating means, coupled to the tracking means, for generating the second drive signal and for operating said second drive means;
• positioning means, coupled to the second drive means, for causing said second drive means to position said focusing means at a predetermined position within said optical head when said coarse track accessing mode is set and a predetermined time has elapsed, or in response to the tracking-error signal;
• judging means, coupled to said focusing means, for determining that a rate of change in position between said focusing means and said optical recording medium becomes lower than a predetermined value in response to a detection that the frequency of the tracking-error signal becomes lower than a predetermined frequency when said coarse track accessing mode is set;
• and
• control means, coupled to said tracking means, for controlling said tracking means such that said tracking means causes said second drive means to position said focusing means at the predetermined position, and to cause said mode setting means to set the fine track access mode after said optical head is moved to the target track in response to the first drive signal, and to position said focusing means at the target track when said judging means determines a decrease in the rate of change in position between the optical recording medium and said focusing means below the predetermined value.