JPH03107103A - Optical head - Google Patents

Abstract

PURPOSE:To eliminate the need for moving an objective lens in a focus direction and to execute stable focusing control by changing the surface curvature of an objective lens, thereby changing a focal length. CONSTITUTION:The objective lens 10 is constituted by coating a transparent silicon gel 11 with a transparent acrylic resin 12. A lens pressing member 12 presses the peripheral part 19 of the objective lens 10 to change the focal length of the objective lens 10. The lens pressing member 21 receives force in a focusing direction by the current impressed on a focusing coil 22 and the magnetic flux generated by a magnet 23 and a yoke 24 and stops in the position where the recovering force of the objective lens 10 balances. A lens supporting member 25 supports the lens pressing member 21 via an elastic member 26 to prevent the pressing member 21 from deviating. The elastic member 26 is constituted of a sponge-like member and is so elastically deformed as to permit the movement of the lens pressing member 21.

Description

[Detailed Description of the Invention] [Summary] The present invention relates to a focusing mechanism for an optical head used in an optical disk device, etc., and aims to provide a focusing mechanism that does not require moving a condensing lens in the focusing direction. A condensing lens whose surface curvature can change to condense light, and a focal length of the condensing lens by changing the surface curvature of the condensing lens so that the light on the object is in a predetermined condensed state. An optical head comprising a focusing means is constituted.

[Industrial application field]

The present invention relates to an optical head used in an optical disk device, and more particularly to a focusing mechanism of an optical head.

Optical disk devices record and reproduce data by irradiating a recording medium with laser light. An optical head used to irradiate a recording medium with a laser beam includes an optical system for irradiating the laser beam onto the recording medium, a tracking mechanism for focusing the laser beam on a desired recording position on the recording medium, and a tracking mechanism for focusing the laser beam on a desired recording position on the recording medium. It consists of a focusing mechanism, etc.

[Conventional technology]

Various types of optical heads are used in optical disk devices, and the optical head shown in FIG. 7 is one example.

As shown in FIG. 9B, the objective lens 90 is supported by a lens support member 92, and the lens support member 92 is movably supported by a frame 96 via a spiral leaf spring 91. Further, as shown in FIG. 2A, a magnet 94 and a yoke 95 are attached to the frame 96, and a focusing coil 93 is wound around the lens support member 92.

The beam irradiated onto an optical disc (not shown) through the objective lens 10 is tracked so that it forms a beam spot of a predetermined size on the optical disc, and is tracked onto a predetermined recording track on the optical disc. Focusing is controlled so that a beam spot is formed.

Focusing is performed by moving the objective lens 90 in a focusing direction 99. When a current is applied to the focusing coil 93, the focusing coil 93 receives a force in the focus jig direction 99 due to the magnetic flux generated by the magnet 94 and the yoke 95, and the lens support member 99
2 and the objective lens 90 move in the focusing direction.

On the other hand, tracking is performed by changing the angle of the galvanometer mirror 97 so that the beam spot moves in the tracking direction 98. It is also possible to perform tracking by moving the objective lens 90 in the tracking direction without using a galvanometer mirror.

The above is an explanation of one type of optical head.
For any type of optical head, focussig is
This is done by moving the objective lens in the focusing direction.

[Problem to be solved by the invention]

To perform focus jig, conventionally the objective lens is moved closer to or farther away from the recording medium. However, since the objective lens is moved in the focusing direction, it is necessary to consider residual vibrations at the end of the movement of the objective lens, inertia of the objective lens, etc. Furthermore, since the objective lens is supported so as to be movable in the focusing direction, there is a problem in that the objective lens vibrates due to external vibrations.

SUMMARY OF THE INVENTION In order to solve the above problems, it is an object of the present invention to provide an optical head that does not require moving the objective lens in the focusing direction. Another object of the present invention is to provide an optical head equipped with a new focusing mechanism that is different from conventional focusing mechanisms.

[Means to solve the problem]

In order to achieve the above purpose, the object 8 as shown in FIG.
A condensing lens 1 whose surface curvature can be changed to condense light onto the object 8, and a condensing lens 1 whose surface curvature can be changed so that the light on the object 8 is condensed in a predetermined state. An optical head comprising a focusing means 2 for changing the focal length is configured.

[Effect]

That is, in the present invention, the objective lens 1 changes its surface curvature by the focusing means 2 without moving in the focusing direction,
Focal length changes. As shown in FIGS. 1(a) and 1(b), when the distance between the condenser lens 1 and the object 8 is different from d+ and d2, the focus jig means 2 adjusts the surface curvature of the condenser lens 1 to rl and r2. so that the light is just focused on the object 8.

[Embodiment] FIG. 3 shows a configuration diagram of an embodiment of the present invention. In the figure, 10 is an objective lens that is elastically deformed, 21 is a lens pressing member 22 that presses the objective lens 10 to elastically deform it, is a focusing coil wound around the lens pressing part, 23 is a magnet,
24 is a yoke.

These members are assembled as shown in Figure (a).

The objective lens 10 is, for example, a transparent silicone gel 11 coated with a transparent acrylic resin 12, as shown in FIG.

The lens pressing member 21 changes the focal length of the objective lens 10 by pressing the peripheral portion 19 of the objective lens 10. The lens pressing member 21 is the focusing coil 2
2 and the magnetic flux generated by the magnet 23 and the yoke 24, which receives a force in the focusing jig direction,
It stops at a position balanced with the restoring force of the objective lens 10.

Further, the lens support member 25 supports the lens pressing member 21 via an elastic member 26, and prevents the lens pressing member 21 from coming off. Further, the elastic member 26 is made of a sponge-like member, and is elastically deformed to allow movement of the lens pressing member 21.

FIG. 4 is an explanatory diagram of the principle of elastic deformation of the objective lens. The objective lens 10 is elastically deformed by having its peripheral edge sandwiched between an annular member 201 provided to protrude from a lens pressing member 21 and an end surface of a cylindrical member 202 extending upward from a yoke 24. do. Figures (a) and (b) illustrate a case where the distance between members 201 and 202 that sandwich the objective lens changes. When the distance between members 201 and 202 is d+ as shown in FIG.
Silicone gel 1 in the area sandwiched between members 201 and 202
The volume of 2 is ■, and the length of the surface of the objective lens 10 is! , is.

In this state, the lens pressing member 21 is driven by passing a current through the focusing coil 22.
When the distance between the members 201 and 202 is reduced to d2 as shown in , the silicon gel 12 in the part sandwiched between the members 201 and 202 flows out to the center side of the objective lens 10, and the part sandwiched between the members 201 and 202 flows out to the center side of the objective lens 10. The volume becomes smaller than ■. At the same time, since the volume of the silicon gel 12 on the center side of the objective lens 10 increases, the acrylic resin 11 stretches, and the length of the surface of the objective lens 10 increases to 2 squares. Therefore, the surface curvature of the objective lens becomes thicker (as compared to the state shown in FIG. 12A), and the focal length of the objective lens 10 becomes shorter.

On the other hand, when changing from the state shown in FIG. 2B to the state shown in FIG. The silicon gel 12 of the objective lens 10
, and the length of the surface of the objective lens 10 becomes smaller. Therefore, the surface curvature of the objective lens 10 becomes smaller, and the focal length of the objective lens becomes longer.

In this manner, in this embodiment, focusing can be performed without moving the objective lens 10 in the focusing direction. Therefore, the mass of the movable part including the focusing coil 22 can be reduced, the inertia can also be reduced, and the response characteristics can be improved.

FIG. 5 is a graph showing the relationship between the force for deforming the objective lens and the focal length. When the force F that elastically deforms the objective lens is increased, the focal length R of the objective lens becomes shorter. As the force that elastically deforms the objective lens increases, the focal length of the objective lens decreases accordingly. However, when increasing the focal length, if the restoring force of the objective lens is small, the time for the surface curvature of the objective lens to change becomes long (this results in poor response characteristics of the focal length of the objective lens).

The restoring force of the objective lens increases as the force that elastically deforms the objective lens increases. Therefore, the objective lens is elastically deformed with a certain force f2 so that the restoring force of the objective lens becomes a predetermined value, and the objective lens 10 at this time is The focal length r2 of is used as a reference. Then, a force r1 deforms the objective lens 10 so that the focal length changes between r and r with r2 as the center.
~f3 should be added.

Further, instead of the lens support member 25 and the elastic member 26, the lens pressing member 21 may be configured to support the upper and lower ends of the lens pressing member 21 with spiral leaf springs as shown in FIG. 7, respectively. However, in this case, the temporary spring's vibration suppression ability is small, so the response is slightly lower.

FIG. 6 is a configuration diagram of an optical disk device to which the present invention is applied. In the figure, a beam output from a semiconductor laser 15 is irradiated onto an optical disk 80 via a beam splitter I6 and a quarter-wavelength filter 17, and further via a galvanomirror 61 for tracking and an objective lens 10 that is elastically deformed. The reflected light from the optical disk is returned to the objective lens 10,
The reflected beam from the optical disk 80 is input to the beam splitter 16 via the galvanometer mirror 61 and the quarter-wavelength filter 17, but the reflected beam from the optical disk 80 is output in the direction of the photodetector 30 because it has a different polarization angle from the incident beam from the semiconductor laser 15. be done.

A tracking error signal generator 31 and a focusing error signal generator 32 generate respective signals from the output of the photodetector 30. The tracking error signal is a signal indicating the amount of deviation from the desired track center, and the focusing error signal is a signal indicating the amount of deviation of the optical disc from the just focus position. These signals are generated using well-known methods and circuits. It is composed of

Focusing error signal is from focusing control circuit 4
0, and the far force control circuit 40 applies a current to the focusing coil 22 so that the beam is just focused on the optical disk. The focusing control circuit 40 is composed of a phase compensation circuit 41, a gain amplifier 42, a power amplifier 43, etc., similar to well-known focusing control, and the power amplifier 43 applies a current to the focusing coil 22 to press the lens pressing member 21. Drive in the focusing direction.

On the other hand, the tracking error signal is also input to the tracking control circuit 50, and like the focusing control circuit 40, the tracking control circuit 45, which is composed of a phase compensation circuit 51, a gain amplifier 52, a power amplifier 53, etc., controls the galvanometer mirror 61. A current is applied to the tracking coil 62 in the actuator 60 to drive the galvanometer mirror 61. Tracking is not limited to using a galvanometer mirror, and may be performed by driving the objective lens 10 in the tracking direction.

Further, in this embodiment, the surface curvature of the lens is changed by pressing the lens periphery, but the surface curvature of the lens may be changed by pulling the lens periphery outward or contracting it inward.

In order to expand and contract the peripheral portion of the lens in this way, the peripheral portion of the lens shown in Figure 2 is adhesively supported by a ring-shaped holder made of a piezoelectric element, and the expansion and contraction force of the piezoelectric element in the radial direction is utilized. You can do it like this.

Furthermore, in this embodiment, the distance between the objective lens and the optical disk was measured using the output of the 4-split photodetector 30, but the present invention is not limited to this, and other measurement means and measurement methods ( It goes without saying that the method (measurement of the distance between the focal point and the optical disk) may also be used.

Although the focusing mechanism of an optical disk device has been described above, the present invention can also be applied to focusing mechanisms of cameras, video cameras, and the like. For example, focusing can be performed by equipping the camera with a distance measuring device that measures the distance to the object and elastically deforming the objective lens according to the measured distance.

Furthermore, in this example, a transparent St gel 12 coated with an acrylic resin 11 was used as a lens whose curvature can be changed. , the curvature may be changed.

(Effects) The present invention can provide a focusing mechanism that is completely different from conventional focusing mechanisms, and the newly provided focusing mechanism changes the focal length by changing the surface curvature of the objective lens. There is no need to move the objective lens in the focusing direction, vibration of the objective lens in the focusing direction does not occur, and stable focusing control can be performed.

[Brief explanation of drawings]

Fig. 1 is a diagram explaining the principle of the present invention, Fig. 2 is an example of a condensing lens used in the present invention, Fig. 3 is a configuration diagram of an embodiment of the optical head of the present invention, and Fig. 4 is an elasticity of the objective lens. FIG. 5 is a diagram illustrating the principle of deformation, FIG. 5 is a configuration diagram of an embodiment of a force and countermeasure device for changing an objective lens, and FIG. 6 is a configuration diagram of a conventional optical head. In the figure, 1...Objective lens, 2...Focusing means 21...Lens pressing part 22...Focusing coil 23...Magnet 24...Yoke 56000...Lens support member ...Elastic member...Photodetector...Tracking control circuit...Focusing control circuit/object Example door 2 (α) (t)) Part of the door 3 of the wide part of the bridge of the present invention Figure 6 of Σ

Claims (1)

[Scope of Claims] [1] A condensing lens (1) whose surface curvature can be changed to condense light onto an object (8), and a condensing lens (1) whose surface curvature can be changed so that the light on the object (8) is condensed in a predetermined state. An optical head comprising a focusing means (2) for changing the focal length of the condensing lens (1) by changing the surface curvature of the condensing lens (1) so that the focal length of the condensing lens (1) is changed. [2] The focusing means (2) focuses on the object (
8) A detection means for detecting the condensing state of the light above, and a deforming means (2) for changing the surface curvature of the condensing lens (1) so that the detected condensing state becomes a predetermined condensing state. The optical head according to claim 1, characterized in that it comprises: [3] The focusing means (2) focuses on the object (
8) and a condenser lens (1); and a deforming means for changing the surface curvature of the condenser lens (1) according to the detected distance. Item 1. The optical head according to item 1.