| 摘要 |
PURPOSE:To apply focus control without offset by detecting the luminous quantity distribution in the tangential direction after the end of search state and switching an offset canceling means in the operating state, thereby enabling sure servo pull-in. CONSTITUTION:Outputs of light receiving elements 9A, 9B of a photodetector 9 are subject to differential processing and the result goes to a focus error signal to apply focus search. When the search state is finished, a focus servo pull-in signal is generated to close a switch S by the changeover operation comprising a switch, driving circuit 51 and a switch S, then servo pull-in is applied. Then the luminous quantity distribution in the tangential direction of an optical recording medium is detected by photoelements 33C, 33D of the photodetector 33 and a differential processing arithmetic circuit 34 and a focus error signal erased with an offset is outputted from an arithmetic circuit 35 of an offset erasure means to apply focus control. Through the constitution above, sure servo pull-in is applied to attain excellent servo control without offset.
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