JPH0689448A - Driving device for objective lens - Google Patents

Abstract

PURPOSE:To suppress the generation of the unwanted angular moment of a coil located outside a magnetic gap due to leaked magnetic flux and to make the device small in size by thickening only the thickness of a yoke facing a focusing coil outside a magnetic gap thicker than other parts by sticking an outside plate. CONSTITUTION:A lens holder 3 for holding an objective lens 2 is supported by an elestic body 5 so as to be movable in two directions and a focusing coil 6 and a tracking coil 7 are fixed into a hole at the central section of the holder 3. Some portions of the coils 6, 7 are arranged within the magnetic gap 9 of a magnetic circuit 8 extended from a fixing part 4 and the circuit 8 is composed of parmanent magnets 10a, 10b and a U-shaped yoke composed of yoke feet 11a, 11b mounted inside the magnets. The coil 6 is wound so as to surround the magnet 10a, the foot 11a and a outside plate of yoke 11c provided only on the foot 11a and a coil 6a which is a part unnecessary for generating driving force is located outside the gap 9. Consequently, angular moment caused by the action of the coil 6a is suppressed, the resonant peak is improved to be small and the miniaturization of the device is attained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an objective provided in an optical information recording / reproducing apparatus capable of optically recording, reproducing, or erasing information by irradiating a recording medium with a light beam. The present invention relates to a lens driving device.

[0002]

2. Description of the Related Art Conventionally, an objective lens is biaxially driven in order to control a focusing position of a light beam applied to an information recording medium such as a magneto-optical disk through the objective lens in a focusing direction and a tracking direction. Objective lens drive devices are known.

FIG. 4 is a perspective view of an example of such an objective lens driving device. The objective lens driving device 51 is provided with a lens holder 53 that holds the objective lens 52. The lens holder 53 is provided on both sides of the lens holder 53.
Elastic body 5 for movably supporting the fixed portion 54 in two directions
5 are attached to the top and bottom respectively, and the lens holder 5
The focusing coil 56 and the tracking coil 57 are fixed to the hole at the center of the No. 3. The focusing coil 56 moves the lens holder 53 in the vertical arrow A direction with respect to the fixed portion in the drawing, and the tracking coil 5 is moved.
7 moves the lens holder 53 in the horizontal arrow B direction with respect to the fixed portion in the figure.

A part of the focusing coil 56 and the tracking coil 57 is arranged in the magnetic gap 59 of the magnetic circuit 58 extending from the fixed portion 54, and the magnetic circuit 5 is provided.
Reference numeral 8 is composed of permanent magnets 60a and 60b and a U-shaped yoke 61 having them attached inside. 61a and 61b are legs of the yoke 61. The focusing coil 56 includes a permanent magnet 60 located farther from the objective lens 52.
It is wound so as to surround a and the yoke leg 61a on the outside thereof, and an unnecessary portion 56a for generating a driving force is located outside the magnetic gap 59.

[0005]

However, in the above-mentioned conventional structure, the magnetic flux leaking from the back surface of the yoke leg 61a acts on the portion 56a of the focusing coil 56 located outside the magnetic gap 59, and the lens holder 53 is covered. On the other hand, the rotation moment acts as shown by the arrow in FIG.
A resonance peak appears on the frequency characteristic as shown in (b). FIG. 6A is a graph relating to frequency and gain, and FIG. 6B is a graph relating to frequency and phase.

In order to reduce the leakage of the magnetic flux from the rear surface of the yoke leg 61a, the thickness of the yoke 61 is increased or the yoke legs 61a and 61b are bridged by a ferromagnetic material having a sufficient thickness. It is effective to prevent the saturation by making it into a box shape, but if the whole yoke 61 is made thicker or the ferromagnetic material having a large thickness is made into a box shape and the yoke 61 is made higher, the device becomes smaller. ， It becomes difficult to reduce the thickness.

[0007]

An objective lens driving device according to the present invention comprises a focusing means for focusing a light beam and irradiating the recording medium, a holding means for holding the focusing means, and a recording of the light beam. In order to control the irradiation position with respect to the medium at least in the focusing direction, a focusing driving means having a magnetic circuit composed of a coil, a yoke, a permanent magnet and the like for displacing the holding means in the focusing direction is provided, and the coil has a part thereof. The thickness of the yoke that is arranged in the magnetic gap of the magnetic circuit and is partially wound outside the magnetic gap so as to surround the yoke, and faces the portion of the coil that is located outside the magnetic gap. Thicker than the rest of the yoke.

[0008]

By the above, the amount of leakage magnetic flux acting on the portion of the focusing coil located outside the magnetic gap can be reduced, and at the same time,
Since the entire yoke is not made thick or large, the device can be made smaller and thinner.

[0009]

FIG. 1 is a perspective view of an embodiment according to the present invention, and the overall structure is almost the same as that of the conventional example of FIG. Figure 1
The reference numerals in FIG. 4 are obtained by subtracting 50 from the reference numerals in FIG.

A lens holder 3 for holding the objective lens 2 is provided, and elastic bodies 5 for movably supporting the lens holder 3 in two directions with respect to a fixed portion 4 are provided on both side surfaces of the lens holder 3.
Are attached to the upper and lower sides, respectively, and the focusing coil 6 and the tracking coil 7 are fixed to the central hole of the lens holder 3. A part of the focusing coil 6 and the tracking coil 7 is arranged in the magnetic gap 9 of the magnetic circuit 8 extending from the fixed portion 4, and the magnetic circuit 8 has permanent magnets 10a and 10b and a U-shape in which these are attached. It is composed of a yoke 11. The yoke 11 includes yoke legs 11a and 11b.
The focusing coil 6 is wound so as to surround one permanent magnet 10a, the yoke leg 11a, and the yoke outer plate 11c, and the unnecessary portion 6a for generating a driving force is located outside the magnetic gap 9. ing.

The difference from the conventional example of FIG. 4 is that the thickness of the yoke on the side surrounded by the focusing coil 6 is such that the yoke leg 11a and the yoke outer plate 11c on the outer side of the yoke leg 11a make the thickness of the yoke 11 smaller.
It is thicker than other parts.

As an example of the structure in which the outer side of the yoke 11 is surrounded by the focusing coil, the thickness is increased as shown in FIG.
The yoke 11 is machined into a shape such that the yoke leg 11a is thickened, or is formed by sintering, or
When the yoke 11 is formed by bending a metal plate as shown in FIG. 2B, it is conceivable to attach a thin yoke outer plate 11c made of another ferromagnetic material to the back surface of the yoke leg 11a. . FIG. 1 shows this case.

As described above, the force acting on the focusing coil 6a located outside the magnetic gap 9 is reduced to suppress the rotation moment, so that the frequency characteristics in the focusing direction are shown in FIGS. 3 (a) and 3 (b). ), The resonance peak can be improved to be small. Figure 3
6 (a) and 6 (b) are shown in FIGS. 6 (a) and 6 (b), respectively.
It corresponds to.

Although the permanent magnets 10a and 10b are fixed to the yoke legs 11a and 11b, respectively, in the above embodiment, the same effect can be obtained even if the permanent magnets are not fixed to the yoke legs 11a. .

[0015]

Since the objective lens driving device according to the present invention has the above-described structure, the amount of leakage magnetic flux acting on the portion of the focusing coil located outside the magnetic gap is reduced, and the lens holder is reduced. It is possible to suppress the generation of a rotational moment with respect to the above, and since the yoke as a whole is not made thick or large, it is possible to supply a small and thin device.

[Brief description of drawings]

FIG. 1 is a perspective view of an embodiment of the present invention.

2 (a) and 2 (b) are side sectional views of an embodiment of the present invention.

3A and 3B are graphs of frequency versus gain and frequency versus phase, respectively.

FIG. 4 is a perspective view of a conventional example.

5 is a side cross-sectional view of the magnetic circuit of FIG.

6A and 6B are graphs of frequency vs. gain and frequency vs. phase in the focusing direction in a conventional device, respectively.

[Explanation of symbols]

 1 Objective Lens Driving Device 2 Objective Lens 3 Lens Holder 4 Fixed Part 5 Elastic Body 6 Focusing Coil 7 Tracking Coil 8 Magnetic Circuit 10 Permanent Magnet 11 Yoke

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Nobuo Ogata 22-22 Nagaike-cho, Abeno-ku, Osaka-shi, Osaka Within Sharp Corporation (72) Hidero Sato 22-22 Nagaike-cho, Abeno-ku, Osaka, Osaka Within the corporation

Claims (1)

[Claims] 1. A light condensing means for converging a light beam to irradiate a recording medium, a holding means for holding the light condensing means, and an irradiation position of the light beam on the recording medium for controlling at least a focusing direction. A coil for displacing the holding means in the focusing direction, a focusing drive means having a magnetic circuit composed of a yoke, a permanent magnet and the like, and a part of the coil is arranged in a magnetic gap of the magnetic circuit, and Part of the coil is wound outside the magnetic gap so as to surround at least the yoke, and the thickness of the yoke facing the part of the coil located outside the magnetic gap is made thicker than the other parts of the yoke. An objective lens driving device characterized by: