| 摘要 |
PROBLEM TO BE SOLVED: To provide a tilt detecting method where a circuit scale is small and inexpensive and quick response is possible without requiring a tilt sensor in addition. SOLUTION: The center of a reproduction information track is irradiated with a main beam and a position deviated outward from the center of the reproduction information track by a fixed quantity is irradiated with two sub beams. The reflected light beams of the two sub beams are photodetected by quadripartite photodetective elements divided by dividing lines orthogonal respectively independently. In accordance with the two sub beams, the absolute value of a difference between two adding results obtained by mutually adding the outputs of the photodetective elements forming the diagonal of the quadripartite photodetective elements respectively independently is outputted. A tilt quantity is obtained based on the difference between two output signals corresponding to the two sub beams.
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