| 摘要 |
PURPOSE:To prevent an erroneous measurement due to eccentricity, by detecting the crossing direction of a guide track with a low speed when a light spot corsses the guide track and adding/subtracting the crossing frequency of the guide track. CONSTITUTION:The outputs of photodetectors 13a and 13b in the inner and outer diameters of an optical disk respectively are amplified by peramplifiers 19, 26 and 28 and then pass through an LPF40 to undergo waveform shaping 41. A difference signal (d) is obtained between detectors 13a and 13b, and a signal (g) indicates the center of a guide track. A speed detector 101 detects the speed of a linear motor 25 which drives an optical pickup and then decides whether a reversible counter 46 is counted up or down by the crossing direction of the guide track as long as the spped of the motor 25 is within a prescribed value. |
