| 摘要 |
PURPOSE:To prevent dust from going into a fixed cylinder, and to prevent the deterioration of a servo-characteristic due to dust by providing circumferentially a doughnut- like plate between the lower end face of a cylinder provided circumferentially on the circumferential surface of a through-hole for making an optical beam pass through, and the outside circumferential surface of the upper part of a movable cylinder. CONSTITUTION:An emitted light from a laser 5 is made incident to a disk 10 through a mirror 9, and its reflected light is made incident to an optical sensor 11. A doughnut- shape plate 21 is provided circumferentially between the lower end face of a cylinder 20 provided circumferentially on the circumferential surface of a through-hole 2C for making an optical beam pass through, and the outside circumferential surface of the upper part of a movable cylinder 1. Also, since a cylinder 22 is provided on the outside circumferential part of the plate 21, even if the movable cylinder 1 moves, a path through which dust is introduced from the outside goes into the inside of a fixed cylinder 2 is elongated, therefore, it is not introduced beyond a tracking controlling coil 1A and a permanent magnet 2A. Accordingly, it is possible to prevent the deterioration of a servo-characteristic, which is caused by the fact that dust is piled on and the movable cylinder 1 is cuaght by the dust. |
