| 摘要 |
PURPOSE:To correct a focus dislocation due to an optical system by adding a signal to correct the focus dislocation due to the optical system in a focus position control loop after a desired delay time passes from the point of time when a servo loop is closed. CONSTITUTION:A focusing servo loop On signal C is turned on, a pull-in action is executed, a desired time is delayed by a delay circuit and a pull-in detecting signal D is outputted. Further, a waveform gets blunted through an integrating circuit shown in E, and a switch is turned gradually from OFF to ON. When a switch 26 is turned on, a DC voltage F set by a volume 25 is added to a servo loop by an adding amplifier 24. When the DC voltage F is added, for an output G of the adding amplifier 24, a bias voltage, an action point in which the section between a disk 1 recording surface and an objective lens 3 goes to be a true focusing position, is impressed. Here beforehand, the action point is obtained in which the best condition is obtained. Thus, a focus dislocation is corrected which occurs due to a variance of respective composite factors of a light pick-up. |
