| 摘要 |
PURPOSE:To prevent dust from adhering to a disk, by detecting a detecting laser output, and stopping the driving of the whole focus control means automatically by use of an up-and-down moving mechanism, when said output is below a prescribed output. CONSTITUTION:When the whole focus control mechanism containing a linear motor 17 descends through a motor 25 and an up-and-down driving mechanism 18 by an output of a controlling circuit 24, and approaches the vicinity of a focus, an optical beam B is reflected by the surface of a resist 2 of a disk 1, passes through an objective lens 9, a mirror 8, a lambda/4 plate 13, a polarized beam splitter 12 and is made incident to a 2-split detector 14. Its output is inputted to comparators 19, 20, and when its voltage exceeds prescribed voltage, the driving mechanism 18 is stopped through a gate circuit 21 and the controlling circuit 24 by outputs E, F. On the other hand, the optical beam B from a laser 10 is made incident to a detector 27 through a half mirror 26, and when its output becomes below the prescribed voltage through a discriminator 28, a pulse H is impressed to the circuit 24, and the focus control device stops. Since it is unnecessary that a man approaches, no dust adheres. |
