Method and apparatus for composite tracking servo system with track offset correction and rotary optical disc having at least one correction mark for correcting track offset

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

• preparing a rotary recording medium having a first field and a second field alternately arranged along the direction of rotation of the recording medium to provide a sector, pregrooves being provided at least in 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;
• irraddiating 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 pregrooves on said recording medium:
• detecting a second tracking error signal from the reflection of said light spot traversing said wobbled track marks;
• correcting said first tracking error signal on the basis of said second tracking error signal;
• and
• using the corrected signal for the tracking control;
• wherein said wobbled track mark signal on the basis of said second tracking error signal;
• and
• using the corrected signal for the tracking control;
• wherein the gain of said second tracking error signal in a low frequency range is selected to be larger than that of said first tracking error signal, and said second tracking error signal whose high frequency components are removed by a band-limited low-pass filter is used to correct said first tracking error signal.

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

• preparing a rotary recording medium having a first field and a second field alternately arranged along the direction of rotation of the recording medium to provide a sector, pregrooves being provided at least in 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 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 pregrooves on said recording medium;
• detecting a second tracking error signal from the reflection of said light spot traversing said wobbled track marks;
• correcting said first tracking error signal on the basis of said second tracking error signal;
• and
• using the corrected signal for the tracking control;
• wherein said wobbled track mark is recognized by pattern recognition means, and, only when the result of pattern recognition shows that said wobbled track mark detection is normal, said second tracking error signal is delivered as an output signal of a sample and hold circuit.

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 of said recording medium to provide a sector, pregrooves being provided at least in 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 pregrooves on said recording medium;
• second detecting means for detecting a second tracking error signal from the reflection of said light spot traversing said wobbled track marks, said second detecting means having a detection sensitivity in a low frequency range which is higher than that of said first detecting means;
• means for correcting said first tracking error signal on the basis of said second tracking error signal, said correcting means including a low-pass filter for limiting the band of said second tracking error signal and adder means for adding an output signal of said low-pass filter to said first tracking error signal;
• and
• means for driving a tracking control means disposed in said irradiating means in response to the application of an output signal of said correcting means.

A tracking control apparatus comprising:

• a rotary recording medium having a first field and a second field alternately arranged along the direction of rotation of the recording medium to provide a sector, pregrooves being provided at least in said second field, said first field including at least one correction mark for correcting track offset due to said pregrooves;
• 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 pregrooves on said recording medium;
• second detecting means for detecting a second tracking error signal by sampling a signal due to the reflection of said light spot traversing said correction mark;
• removing means for removing high frequency components of said second tracking error signal;
• means for correcting said first tracking error signal on the basis of an output signal of said removing means;
• and
• means for driving a tracking control means disposed in said irradiating means in response to the application of an output signal of said correcting means;
• wherein said second detecting means has a detection sensitivity in a low frequency range which is higher than that of said first detecting means.

A tracking control apparatus comprising:

• a rotary recording medium having a first field and a second field alternately arranged along the direction of rotation of the recording medium to provide a sector, pregrooves being provided at least in said second field, said first field including at least one correction mark for correcting track offset due to said pregrooves;
• 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 pregrooves on said recording medium;
• second detecting means for detecting a second tracking error signal by sampling a signal due to the reflection of said light spot traversing said correction mark;
• removing means for removing high frequency components of said second tracking error signal;
• means for correcting said first tracking error signal on the basis of an output signal of said removing means;
• and
• means for driving a tracking control means disposed in said irradiating means in response to the application of an output signal of said correcting means;
• wherein said second detecting means further includes means for recognizing the pattern of said correction mark on the basis of the reflection of said light spot traversing said correction mark and for generating an output signal to control said sampling;
• and further comprising memory means for storing said corrected first tracking error signal, switching means for switching over between an output signal of said memory means and an output signal of said second detecting means;
• and means for generating a signal for controlling the switching operation of said switching means on the basis of the output signal from said recognizing means.

A tracking control method for an optical disc hagving at least one correction mark for correcting track offset, comprising the steps of:

• preparing said optical disc having a first field and a second field alternately arranged along the direction of rotation of said optical disc to provide a sector, pregrooves being provided at least on said second field, said first field including said at least one correction mark;
• irradiating the recording surface of said optical disc with a light spot;
• detecting a first tracking error signal from the reflection of said light spot diffracted by said pregrooves on said optical disc;
• detecting a second tracking error signal by sampling a signal due to the reflection of said light spot traversing said correction mark, the gain of said second tracking error signal in a low freqeuncy range being selected to be larger than that of said first tracking error signal;
• removing high frequency components of said second tracking signal by a band-limited low-pass filter:
• correcting said first tracking error signal on the basis of an output signal of said filter;
• and
• using the corrected signal for the tracking control.