Method and apparatus for composite wobbled and push-pull tracking servo system

A tracking control method for a composite wobbled tracking servo system, comprising the steps of:

• preparing a rotary recording medium rotating at a frequency fd and having a first field and a second field alternately arranged along the direction of rotation to provide a total of N first fields in one complete revolution, guide grooves (pregrooves) being provided in at least said second field, each of said first fields including at least one pair of wobbled track marks disposed in a relation wobbled relative to the center of a track;
• irradiating the recording surface of said recording medium with a light spot;
• detecting a first tracking error signal from the reflection of said light spot diffracted by said pregroove on said recording medium;
• detecting a second tracking error signal from the reflection of said light spot passing said wobbled track marks;
• holding said second tracking error signal in holding means while said light spot passes said second field;
• attenuating the gain of said second tracking error signal held in and appearing from said holding means by low-pass filter means so that the gain of said second tracking error signal having been held in said holding means and passed through said low-pass filter means becomes equal to that of said first tracking error signal at a frequency fe satisfying the relation
• 1/50.multidot.N.multidot.fd<fe<1/5.multidot.N.multidot.fd ;
• combining said second tracking error signal having been passed through said low-pass filter means with said first tracking error signal to provide a composite tracking error signal;
• and
• using said composite tracking error signal for the tracking control.

A tracking control apparatus for a composite wobbled tracking system, comprising:

• a rotary recording medium having a first field and a second field alternately arranged along the direction of rotation, guide grooves (pregrooves) being provided in at least said second field, said first field including at least one pair of wobbled track marks disposed in a relation wobbled relative to the center of a track;
• irradiating means for irradiating the recording surface of said recording medium with a light spot;
• first detecting means for detecting a first tracking error signal from the reflection of said light spot diffracted by said pregroove on said recording medium
• second detecting means having a gain higher than that of said first detecting means and detecting a second tracking error signal from the reflection of said light spot passing said wobbled track marks;
• low-pass filter means for attenuating the gain of said second tracking error signal so that the gain of said second tracking error signal having been passed through said low-pass filter means becomes equal to that of said first tracking error signal at a frequency fe satisfying the relation
• 1/50.multidot.N.multidot.fd<fe<1/5.multidot.N.multidot.fd
• where N is the number of said first fields included in one complete revolution of said recording medium, and fd is the frequency of rotation of said recording medium;
• signal combining means for combining the output signal of said low-pass filter means with said first tracking error signal to generate a composite tracking error signal;
• and
• driving means for driving tracking means provided in said irradiating means in response to the output signal of said signal combining means.

A tracking control apparatus for a composite wobbled tracking servo system, comprising:

• a rotary recording medium having a first field and a second field alternately arranged along the direction of rotation, guide grooves (pregrooves) being provided in at least said second field, said first field including at least one pair of wobbled track marks disposed in a relation wobbled relative to the center of a track;
• irradiating means for irradiating the recording surface of said recording medium with a light spot;
• first detecting means for detecting a first tracking error signal from the reflection of said light spot diffracted by said pregroove on said recording medium;
• second detecting means having a gain higher than that of said first detecting means and detecting a second tracking error signal from the reflection of said light spot passing said wobbled track marks;
• low-pass filter means coupled to said second detecting means for attenuating the gain of said second tracking error signal;
• signal combining means for combining the output signal of said low-pass filter means with said first tracking error signal to generate a composite tracking error signal;
• and
• driving means for driving tracking means provided in said irradiating means in response to the output signal of said signal combining means;
• said low-pass filter means attenuating the gain of said second tracking error signal so that the gain of said second tracking error signal after having been passed through said low-pass filter means becomes equal to that of said first tracking error signal at a frequency fe satisfying the relation
• 1/50.multidot.N.multidot.fd<fe<1/5.multidot.N.multidot.fd
• where N is the number of said first fields included in one complete revolution of said recording medium, and fd is the frequency of rotation of said recording medium.