| 摘要 |
PURPOSE:To facilitate high-accuracy detecting by moving an optical disk substrate in an X-axial and a Y-axial direction while placing an optical pickup in a focus servo state on the optical disk substrate, detecting the innermost peripheral groove from the difference between a focus RF signal and a flat part level, and detecting the rotational center position of the innermost peripheral groove. CONSTITUTION:The optical disk substrate 18 with grooves are mounted on a table 2 and the position of the optical disk substrate is set to the just focus point of the optical pickup by a motor M1 for Z-axial driving and a focus servo circuit 12. The table 2 is moved in the X-axial and Y-axis directions in said state. At this time, when the focus RF signal of the optical pickup 10 is considered, there is a difference in signal level generated between the flat part and groove part of the optical disk substrate. This is utilized to detect the innermost peripheral groove part by a groove detecting circuit 14.
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