| 摘要 |
PURPOSE: To make possible generating a high precision tracking error signal with a sufficiently large size even when an angle between a locus of a scan unit and a track is changed considerably by combining a radiation sense detection system having plural detection elements with an electronic circuit. CONSTITUTION: The scan unit 10 consisting of a semiconductor laser, a beam separation element, art objective lens and the radiation sense detection system is supported by a turning arm 11 to move along circular track 20 around a support point 17. Thus, the angleαfor the direction of the track 7 is changed considerably. The radiation sense detection system for following the unit 10 up the track 7 consists of a first sub-circuit combining plural detection elements and their output signals and forming plural tracking error signals that respective signals answer to in the various directions of a boundary line and a second sub-circuit selecting the largest error signal among them, and can control the direction of the boundary line in the direction of the valid track.
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