| 摘要 |
PURPOSE:To well detect the dangerous zone inrush point of a lens to a disc surface and prevent the occurrence of damages on the disc by relating and comparing one of the detection outputs differentially detecting the reproduction light signal and the other detection output. CONSTITUTION:The reproduction light signal which is read from a disc D via read lens 6, etc. is detected with photo detectors D1, D2 and the detection outputs of the detectors D1, D2 assume increasing and decreasing as well as decreasing and increasing states according to approaching o detaching of a lens 6 to or from the disc D. The differentially detected output by of the detectors D1, D2 by a differential amplifier DA and the detection output of the detector D1 are processed in comparators COMa, COMb respectively, by which the detection outputs of the detectors D1, D2 are mutually related. When the lens 6 protrudes in the dangerous zone in proximity to the disc D, a flip-flop MISFF is set by the comparison output of the comparator COMa as a set signal and the comparison output of the comparator COMb as a clock. Thereby, the inrush of the lens into the dangerous zone is well detected and the lens 6 is forcefully detached from the disc D by way of an upper limit circuit ULC, thus the occurrence of damages on the disc by the collision is prevented. |
