JPS6245302Y2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a focus control device for an optical recording medium such as a video disk, and particularly to protection of an objective lens for focusing a light beam from a light source onto a disc-shaped recording medium.

FIG. 1 shows a conventional focus control device, in which A is a magnetic circuit, which is composed of a magnet B, a plate C, and a yoke D. E is an objective lens arranged to be movable up and down inside a hole provided in the center of the yoke D, F is a movable bobbin fixed to the objective lens E, and a coil G is wound around the bobbin F. This coil G is located in the magnetic gap of the magnetic circuit A. Reference numeral H denotes a stopper fixed on the plate C. The stopper H prevents the objective lens E from slipping out from above. A lens cap I is detachably attached to the center hole of the stopper H. .

Therefore, a magnetic flux that crosses the coil G is generated in the magnetic gap of the magnetic circuit A, and when a current is passed through the coil G, the objective lens E is displaced in the vertical direction.
Further, during storage, a lens cap I is attached to a stopper H to protect the objective lens E.

However, the conventional structure described above requires a stopper H for mounting the lens cap I, which increases the thickness of the entire focus control device. Further, due to the dimensional relationship with the stopper H, there was a risk that it would take time to attach and detach the lens cap I.

Therefore, in order to solve the above-mentioned drawbacks, the present invention forms at least a part of the lens cap of the objective lens with a magnetic material or a permanent magnet, and uses the attraction force with the magnetic flux generated near the magnetic gap to attract the objective lens. To provide a focus control device for an optical recording medium, which is configured to be attached to a lens, has a small number of parts, can reduce the overall thickness, and facilitates attachment and detachment of a lens cap.

Hereinafter, the present invention will be explained based on the embodiments shown in the drawings. Fig. 2 is a longitudinal sectional view of a focus control device according to the present invention. In the figure, 1 is a magnetic circuit, and the magnetic circuit 1 is connected to a magnet 2. , plate 3 and yoke 4
It is made up of. Reference numeral 5 denotes an objective lens housed in a lens barrel, and the objective lens 5 is arranged to be vertically movable inside a hole provided in the center of the yoke 4. A movable bobbin 6 is fixed to the objective lens 5, and a coil 7 is wound around the bobbin 6.
This coil 7 is located within the magnetic gap 1a of the magnetic circuit 1. 8 is a damper, and this damper 8 also serves as a stopper to prevent the objective lens 5 from slipping out from above. Reference numeral 9 designates a lens cap of the objective lens 5, and a link-shaped magnetic material or permanent magnet 10 is embedded around the lens cap 9 at a position corresponding to the inner peripheral portion 8a of the damper 8.

Next, as for the effect of the above embodiment, when a current is passed through the coil 7, the objective lens 5 is vertically displaced as in the conventional example described above. When the lens cap 9 is not in use such as during storage, the lens cap 9 is attached to the inner peripheral part 8 of the damper 8.
a, the magnetic body or permanent magnet 10 in the lens cap 9 receives an attractive force from the magnetic flux generated near the magnetic gap 1a, and the lens cap 9
is attached to the inner peripheral portion 8a of the damper 8 to protect the objective lens 5.

FIG. 3 shows another embodiment of the present invention, in which a stopper 11 of the objective lens 5 is provided on the lens barrel of the objective lens 5 that protrudes downward from the yoke 4 on the side opposite to the movable bobbin 6 side. Therefore, the entire structure can be made thinner. In the drawings, the same reference numbers as in the above-mentioned embodiments indicate the same parts and have the same functions.

In another embodiment shown in FIG. 4, the entire lens cap 9 is made of a magnetic material or a permanent magnet 10, and a pad 12 made of rubber or the like is pasted on the surface of the cap 9 that comes into contact with the movable bobbin 6, so that it can be moved when attached. This prevents the bobbin 6 from being damaged.

As described above, the present invention consists of an objective lens 5 for focusing a light beam from a light source on a recording track of a disk recording medium, and a magnetic circuit for vertically displacing the objective lens so that the light beam can follow the recording track. 1 and a coil 7, and a lens cap 9 that protects the objective lens 5, and at least a part of the lens cap 9 includes a magnetic material or a permanent magnet 10 that generates an attractive force with the leakage magnetic flux of the magnetic circuit 1. Since the lens cap 9 is provided, there is no need for any special parts for attaching the lens cap 9, and the number of parts can be reduced and the overall thickness can be made thinner. or,
Since the suction force is used, the lens cap 9 can be easily attached and detached.

[Brief explanation of drawings]

FIG. 1 is a longitudinal sectional view showing a conventional focus control device, FIG. 2 is a longitudinal sectional view showing an embodiment of the focus control device according to the present invention, and FIG. 3 is a longitudinal sectional view showing another embodiment of the same device. FIG. 4 is a longitudinal sectional view of a main part showing still another embodiment of the same device. 1...Magnetic circuit, 1a...Magnetic gap, 5...
...Objective lens, 7...Coil, 9...Lens cap, 10...Magnetic material or permanent magnet.

Claims (1)

[Scope of utility model registration request] An objective lens for focusing a light beam from a light source on a recording track of a disc-shaped recording medium, a magnetic circuit and a coil for vertically displacing the objective lens so that the light beam follows the recording track, and protecting the objective lens. A focus control device for an optical recording medium, comprising a lens cap, and at least a part of the lens cap is provided with a magnetic material or a permanent magnet that generates an attractive force with the leakage magnetic flux of a magnetic circuit. .