Tracking servo apparatus for an optical information reproducing system

Claim 1

A tracking control apparatus for an optical information reproducing system in which a light beam for reading the information is incident on a signal record surface of a recording carrier on which a substantially circular record track is formed, comprising: photo-detector means including first and second portions for detecting said light beam from said recording carrier and generating respective first and second outputs, and means for generating from said first and second outputs an information signal and a first tracking error signal indicative of deviations of beam position relative to the center of said record track, said information signal being the sum of said first and second outputs and said first tracking error signal being the difference between said first and second outputs; tracking control means receiving said first tracking error signal for controlling the transverse position of said light beam with respect to said center of said record track; measuring means for generating a digital second tracking error signal indicative of any eccentricity of said recording carrier during at least one revolution of said recording carrier, said measuring means including delayed flip-flop means with a delayed input terminal, a clock input terminal and an output terminal and providing an output signal at said output terminal, a preset up/down counter having a clock input terminal, an up/down switching control terminal and an output terminal and providing an output signal at said output terminal, said information signal from said photo-detector means being supplied to said delayed input terminal of said delayed flip-flop means, said first tracking error signal from said photo-detector means being supplied to said clock input terminals of said delayed flip-flop means and said up/down counter, said output signal of said delayed flip-flop means being supplied to said up/down switching control terminal of said counter; memory means receiving said output of said counter for storing said digital second tracking error signal; means for converting said digital second tracking error signal from said memory means to an analog signal; and means for supplying said analog signal from said means for converting to said tracking control means to adjust said beam position in response thereto.