| 摘要 |
PURPOSE:To correct an off-center and to improve the quality and S/N of a tracking error signal by controlling the neutral position of an objective lens so that the output adjoining to right and left sides of a four-dividing light detector can be respectively equal. CONSTITUTION:Respective adding outputs A+C and B+D of the photodetecting signal of a four-dividing light detector 10 are sent to a detecting circuit 28 and detected by a tracking error. The photodetecting signals of the detector 10, which are at respective right and left adjoining positions, are added. For the outputs A+D and B+C, the difference between them is detected in a detecting circuit 32. When on/off switches 33 and 38 of the tracking and the field servo loop are on, a tracking servo loop is controlled so that the error signal can be zero and a feeding servo loop is controlled so that the adjoining sum output difference (A+D)-(B+C) can be zero. Consequently, even when the off-center occurs, a tracking actuator 22 and a feeding motor 26 are controlled and an optical spot is controlled to the center of the detector 10.
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