| 摘要 |
PURPOSE:To set a shift in the position of a light spot by fitting an optical pickup so that the phase difference between a tack signal and a track crossing direction detection signal is equal between the innermost and outermost peripheries of an optical recording medium. CONSTITUTION:The reflected light of a main beam strikes a photodetection surface 13 of a photodetector 12 and the reflected light of a subordinate beam strikes a photodetection surface 14 respectively, so that the track crossing direction detection signal 30 indicating the crossing direction of the main beam on an information recording track is obtained. Further, the tack signal 32 is obtained from an LED, a phototransistor 31, and a reflecting plate so as to obtain the rotation period signal of an optical recording medium. This tack signal 32 and track crossing direction detection signal 30 are phase-compared by a comparator 33 to obtain a phase information signal 34. Then, the optical pickup is so fitted that the phase difference signal 34 is equal between the outermost periphery and inner most periphery of the medium, and consequently the pickup is set at the optimum position where there is no position pickup is set at the optimum position where there is no position shift of a light spot from the radial feed shaft penetrating the center of the rotating shaft of the medium.
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