Composite tracking servo system for optical disc apparatus with track offset correction

A tracking servo system, comprising:

• a recording medium provided with pregrooves having a plurality of discontinued regions;
• an optical system for forming a light spot on said recording medium;
• photoelectric transducer means having at least two light receiving portions;
• first means coupled to said photoelectric transducer means to produce a first track error signal on the basis of a first track deviation signal derived by processing differently the outputs of said light receiving portions;
• second means coupled to said photoelectric transducer means for detecting intermittingly the outputs of said transducer means obtained during a period in which said light spot is positioned on said discontinued region to thereby output a second track error signal on the basis of a second track deviation signal obtained intermittingly through said intermittent detection;
• third means coupled to either one of said first or second means for outputting an offset correcting signal on the basis of said first or second track deviation signal;
• composite means coupled to said first, second and third means for combining compositely said first track error signal, said second error signal and said offset correcting signal;
• and
• tracking means coupled to said composite means for controlling the position irradiated by said light spot in accordance with the output of said composite means;
• wherein each of said discontinued regions is provided with at least a mirror surface area of a diameter greater than that of said light spot, said third means being coupled to said first means for outputting said offset correcting signal on the basis of said first track deviation signal obtained during a period in which said light spot is positioned on said mirror surface area;
• and
• wherein said third means include a sample and hold circuit for sampling said first track deviation signal during a period in which said light spot is positioned on said mirror surface area and holding the sampled signal, and a calibration circuit for multiplying the output of said sample and hold circuit with a predetermined factor.

An optical disc apparatus for recording and/or reproducing information on an optical disc by means of a light spot, comprising:

• an optical disc provided previously with pregrooves having a plurality of discontinued regions in the rotating direction of said disc;
• an optical system for forming a light spot on said optical disc;
• photoelectric transducer means having at least two light receiving portions for detecting light reflected from said disc;
• first means coupled to said transducer means for outputting a first track error signal on the basis of a first track deviated by processing differently the outputs of said light receiving portions;
• second means coupled to said transducer means for detecting intermittingly the output of said transducer means produced during a period in which said light spot is positioned on said discontinued region and outputting a second track error signal on the basis of a second track deviation signal obtained intermittingly;
• third means coupled to either one of said first or second means for outputting an offset correcting signal on the basis of said first or second track deviation signal;
• composite means directly coupled to said first, second and third means for compositely combining said first track error signal, said second error signal and said offset correcting signal;
• and
• tracking means coupled to said composite means for controlling the position irradiated by said light spot in accordance with the output of said composite means.