JPH01300434A - Objective lens driving device - Google Patents

Abstract

PURPOSE:To prevent the adverse effect of leakage magnetic flux from being given on a disk recording plane by confronting the planes of different polarity of a pair of magnets with a prescribed gap, and directing the flow of the magnetic flux of a magnetic circuit consisting of the pair of magnets and a pair of a field member from the direction of the magnet on one side to that of the magnet on the other side. CONSTITUTION:On a disk 50, movable parts 42 and 68 having an objective lens 44 which converges a beam of light, and the pair of magnets 52a and 52b having the prescribed gap and in which the different polarity are confronted are provided. Furthermore, coils 38a and 38b constituted integrally with the pair of field members 54a and 54b arranged being brought into contact with the plane of a side opposite to the confronting plane and which drive the objective lens 44 in the gap in a prescribed direction for the plane of the disk 50 are provided. As a result, the magnetic flux from the magnet on one side flows in the direction of the magnet on the other side, and no flow of the magnetic flux in the direction of the objective lens or the disk is generated. In such a way, it is possible to dissolve the adverse effect due to the magnetic flux of the magnetic circuit on the recording plane of the disk.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to an objective lens driving device for an optical head that records/reproduces information on an optical disk.

Conventional technology Optical disk devices have been commercialized as large-capacity storage devices, applied to various file devices and digital audio discs. There is also a growing demand for compatibility. For this reason, the objective lens driving device of the optical head, which is an important component that makes up the device, is
There is also a need for thinner devices.

However, as the objective lens drive device became smaller and thinner,
A problem arises in that the magnetic circuit for driving the objective lens becomes saturated and leakage magnetic flux increases. This leakage magnetic flux may have an adverse effect on the recording surface of a magneto-optical disk, which is an erasable disk, in particular.

The conventional objective lens driving device is shown in Figures 6 to 8 below.
This will be explained with reference to the figures.

FIG. 6 is an exploded perspective view of the main parts of a conventional optical head. Coils 2a and 2b are wound around a bobbin 1, and these coils 2a and 2b are energized in the same direction as the arrow (A). are connected in a flowing manner. And this coil 2a
, 2b are bonded to the bobbin 1 with adhesive. After the coils 3a and 3b are wound into a flat shape, they are formed into a U-shape as shown, and are bonded onto the coils 21L and 2b with an adhesive. The coils 3a and 3b are connected so that current flows in the same direction as arrow (B). Also, a mounting plate 4゜5 having mounting holes 4a and 51 is provided.
are bonded onto the coils 3a and 3b with adhesive, and an objective lens 6 is bonded to the mounting plate 4.

As shown in FIG. 7, the coil assembly 7 thus formed is supported by an elastic support member 8 so as to be freely displaceable in the directions of arrows (A) and (B). A magnet 10 and a yoke 11 are attached to a back yoke 9 made of a magnetic material, and the back yoke 9, magnet 1o, and yoke 11 constitute a magnetic circuit. A coil assembly is incorporated into this magnetic circuit to form the coil 2a.

When current flows through coils 2b and coils 3a and 3b, a driving force is generated depending on the direction of the current. Note that the N poles of the two magnets 10 in this magnetic circuit face the yoke 11, and the direction of the magnetic flux is the direction shown by the arrow (C).

Now, when a current in the direction of arrow (B) flows through the coils 2a and 2b by a control circuit (not shown), according to Fleming's left hand rule, the current in the direction of arrow (A) flows through the coils 2a and 2b. A driving force in the direction is generated, and the coil assembly moves in the direction of arrow (A) while being elastically supported by the elastic support member 8.
displacement in the direction. Therefore, the objective lens 6 is also indicated by the arrow (A).
A control circuit (not shown) controls the focus of the objective lens 6 onto the recording surface of the disk 12.

On the other hand, when current flows in the direction of the arrow (A) through the coils 3a and 3b by a control circuit (not shown), the current in the direction of the arrow (B) flows through the coils sa and 3b according to Fleming's left hand rule.
A driving force in the direction is generated, and the coil assembly 7 is displaced in the direction of arrow (B) while being elastically supported by the elastic support member 8. Therefore, the objective lens 6 is also displaced in the direction of arrow (B), and a control circuit (not shown) controls tracking of the objective lens 6 to the recording surface of the disk 12.

Problems to be Solved by the Invention However, in the above-mentioned conventional configuration, as a result of being made smaller and thinner, the magnetic flux leaking from the magnetic circuit is caused by the same polarity of the two magnets 1o (
Since the N pole (N pole) faces the yoke 11, they repel each other and wrap around each other up and down as shown in FIG. As a result, information is recorded and reproduced by the objective lens 6 on the disc 1.
Leakage magnetic flux always exists on the recording surface on the objective lens 6 of No. 2, and especially when the disk is a magneto-optical disk, this leakage magnetic flux may have an adverse effect on the recording surface of the disk. That is, when the bias magnetic field for erasing of the magneto-optical disk has the same polarity as the leakage magnetic flux, Id causes erroneous erasure. Furthermore, if the recording bias magnetic field has the same polarity as the leakage magnetic flux, it may cause erroneous recording.

SUMMARY OF THE INVENTION In view of the above-mentioned problems, it is an object of the present invention to provide an objective lens driving device suitable for downsizing and thinning.

Means for Solving the Problems In order to solve the above problems, the objective lens drive device of the present invention includes a movable part having an objective lens that converges a light beam onto a disk, and a movable part having a predetermined gap between the two parts. 7 A pair of magnets with opposing polarities, a pair of field members disposed in contact with the opposite side of the opposing surfaces of the pair of magnets, and a magnetic field member that is integrally formed with this movable part and that is located in the air gap. and a coil for driving the objective lens in a predetermined direction with respect to the disk surface.

Function As described above, the present invention allows the different polarity surfaces of a pair of magnets to face each other with a predetermined gap, and directs the flow of magnetic flux in a magnetic circuit constituted by a pair of magnets and a pair of field members from one magnet to another. direction of the magnet. By doing this, the magnetic flux will not flow in the direction of the disk surface above the objective lens, eliminating the cause of erroneous erasure or recording.

EXAMPLE Hereinafter, an objective lens driving device of the present invention will be explained with reference to the drawings.

1 to 5 show an objective lens driving device in one embodiment of the present invention, FIG. 1 is a plan view, and FIG. 2 is a Y
-Y sectional view, FIG. 3 is a XX sectional view, FIG. 4 is a plan view of the main part, and FIG. 5 is an exploded perspective view of the main part.

1 to 5, tracking coils 34&, 34b are located on the outer periphery of the bobbins 30a, 30b at arrows A in FIG.
It is wound in the direction shown. Also, the focus coils 36a, 36 are wound into a flat shape and then formed into an L-shape.
b is fixed onto the tracking coils 34a and 34b by adhesive, and in this way the pair of coil assemblies 3
8a and 38b are configured.

The coil assemblies 38a and 38b are attached to the holding member 4 shown in FIG.
C) & 40b are sandwiched from above and below and bonded together with the holding members 40a and 40b. In this way, the movable part A42 shown in No. 2N is constructed, but since the objective lens 44 is integrally attached to the holding member 40a, the movable part A42 is composed of the coil assemblies 38a, 38.
b. Holding member 40a.

40b, and an objective lens 44.

One end of the pair of upper and lower leaf springs 46a, 46b is fixed to the frames 48a, 48b, and the other end is fixed to the objective lens 44 and the holding member 40b, respectively. the frame 4
8a and 48b, the disk 5o is elastically supported in the surface direction and radial direction. Frames 48a, 48b
is the support column 62a.

62b, and a mirror 64 is provided on the support column 62b. Also, the frame 48a.

A bearing 66 is rotatably supported on 48b. And these leaf springs 461.46b.

7 frames 48a, 48b, struts 52 &, 62b.

The mirror 64 and the bearing 66 form a movable part 868. The tab, the movable part A42, and the movable part B68 are connected by a pair of leaf springs 46a and 46b.

On the other hand, the pair of magnets 1-52&, 52b are connected to the pair of field members 54 with different polarities facing each other through the air gap 58.
A and 54b are busy. and these magneso) 52a.

9.

52b, field members 54ia, and 54b constitute a single magnetic circuit 8Q, and serve to make the magnetic circuit 80 of the side yokes 60a, 60b a closed magnetic circuit. The movable part B68 and the magnetic circuit 80 have the magnet 52a and the field member 54& in the opening 3Qa' of the bobbin 30a, and
The magnet 52b and the field member 54b are inserted into the opening 30b' of the bobbin 30b to complete the assembly.

The movable portion A42 and the movable portion Be8 are movable in the radial direction of the disk 5o as the bearing 66 rotates on the rail 70. Moreover, the movable part A42 is a plate spring 4.
It is supported by 52L and 46b and is movable in the surface direction of the disk 5o.

The length of the magnetic circuit 80 is set to be sufficient for the objective lens 44 to move over the entire recording width in the radial direction of the disk 5o.
b and focus coil 36a.

Common to 36b. The light beam 74 from the fixed optical system 72, which remains in a fixed position regardless of the movement of the objective lens 44, is reflected by the mirror 64 and enters the objective lens 10/, -7. converge on the recording surface.

The operation of the objective lens driving device of the present invention configured as described above will be explained. Tracking coil 34a, 3
4b and focus carp/1z35a.

The effective flow of magnetic flux for causing each coil of 36b to perform its respective action is in the direction of the arrow shown in FIGS. 2 and 4, and the tracking coil 34a generates a driving force by interlinking with this magnetic flux. 34b and focus coil 36a
, 36b are interlinkage planes shown in FIG. First, the focus coil 36a.

The action of 36b will be explained. The pair of focus coils 361L and 36b are connected to the magnetic circuit 80 when current is applied.
are connected so that the driving force generated by electromagnetic action in response to the magnetic flux of is directed in the same direction as the focusing direction. That is, as shown in FIG. 5, when a current flows in the direction of arrow B in the focus coil 36a at the interlinkage plane with the magnetic flux, the current flows in the focus coil 36b in the direction of arrow B as well. By doing this, 11
,.

The driving force in the focus direction is provided by focus coils 36a and 3.
The force generated at 6b is added.

In the focus direction, the movable part A42 is attached to a plate spring 46.
a, 46b, and the objective lens 44 moves while being elastically supported by the disk 5 by a control circuit (not shown).
Focus is controlled to 0.

Next, the action of the tracking coil 34 will be explained. A pair of tracking coils 34a.

34b is connected so that when current is applied, the driving force generated by electromagnetic action upon receiving the magnetic flux of the magnetic circuit 8o is in the same direction as the tracking direction. In other words, as shown in FIG. 5, the tracking coil 34? When a current in the direction of arrow C flows through L, the tracking coil 34b is connected so that the current also flows in the direction of arrow C.

By doing this, the driving force in the tracking direction is
The driving force generated in the tracking coils 34a and 34b is calculated by multiplying the force.

The operation in the tracking direction differs depending on the frequency band of the current applied to the coil. In other words, if the frequency of the applied current is lower than the resonance frequency of the leaf springs 46a and 46b in the tracking direction, it is possible! , 7[5A42 and the movable portion B68 are connected by leaf springs 46a and 48a and move in the radial direction of the disk 50 as a unit.

This is the operation at the time of access or when the objective lens 44 follows the eccentricity of the disk 5o at a low frequency.

Furthermore, when the frequency of the current applied to the tracking coils 34a and 34b is higher than the resonance frequency of the leaf springs 46a and 46b in the tracking direction, the leaf spring 46a
, 46b are essentially the same as those without, and the movable part A
Only 42 moves slightly in the tracking direction. This is the normal tracking servo operation.

The resonant frequency of the leaf spring in the tracking direction is set from several hundred Hz to several KHz VC. The operation and characteristics in this tracking direction are described in detail in Japanese Patent Application No. Sho 59-G6880.

13. Next, the configuration of the magnetic circuit will be explained. In this embodiment, a pair of magnetrons 52a and 52b are connected to each other via a gap 58.
The pole and the south pole are arranged to face each other. Therefore, as shown in FIG. 2, the magnetic flux from one magnet flows toward the other magnet, and does not flow toward the force of the objective lens 44 or the disk 50. Furthermore, in general, it is desirable to narrow the air gap 58 of the magnetic circuit 8o in order to generate a large driving force in the tracking coil 32 and the focus coil 34, but in this configuration, the following experimental results were obtained. In other words, the gap 58 is 10 m.
Even with a relatively wide setting of around m, sufficient driving force will be generated in the focus coil 54 and tracking coil 52 if the thickness of the field member 54 is approximately 1.5 times or more the thickness of the magnet 52. The result is as follows.

Effects of the Invention As described above, the objective lens driving device of the present invention has a magnetic circuit that supplies magnetic flux to a coil that drives an objective lens, and a pair of 14, -7 opposite polarities having a predetermined gap. The structure consists of a magnet and a pair of field members placed in contact with the opposite surface of the pair of magnets, so that the magnetic flux from one magnet flows in the direction of the other magnet. Therefore, there is no magnetic flux flow fl in the direction of the objective lens or disk.

Therefore, it is possible to eliminate the adverse effect on the disk recording surface due to the magnetic flux of the magnetic circuit for driving the coil, which was a problem in the conventional example.

Further, since the magnetic circuit of the present invention is simply constructed of a pair of magnets and a pair of field members, it is effective in reducing the size and cost of the device.

[Brief explanation of the drawing]

FIG. 1 is a plan view of an objective lens driving device according to an embodiment of the present invention, FIG. 2 is a Y-Y sectional view thereof, and FIG.
-X sectional view, FIG. 4 is a plan view of the main part, and FIG. 5 is an exploded perspective view of the main part. 302L, 3ob--bobbin, 34a, 34b--
Tracking coil, 36a, 36b...Focusing coil, 38a, 38b Coil assembly, 1
5. 40a, 40b...holding member, 42...
・Movable part A, 44...Objective lens, 46a, 4eb
...Plate spring, 48a, 48b...Frame,
50...Disk, 52&, 52b-magnet, 54a, 54b...Field member, 58...
・Gap, 60a, 6ob...Side yoke, 68・
...Movable part B574...Light flux, 80...
...Magnetic circuit. Name of agent Patent attorney Toshio Nakao and 1 other person Q) Castle 2ct, 2b, 3ct, 3b-m-coil 4.5
---Mountain (I don't have k, ni 1 objective lens 10- magnet, stone lf --- yoke Fig. 6 44α 11 mo?73α, 3b - coil 6- objective lens lθ- magnet lf- 11 yoke t2 - Tisuf Figure 8 Otsu I2 Procedural Amendment (Regulations September 7, 1985 2 Name of Invention Objective Lens Drive Device 3 Relationship with the Case of Person Who Makes Amendments Patent Application
Address: 1006 Kadoma, Kadoma City, Osaka Prefecture
Name (582) Matsushita Electric Industrial Co., Ltd. Representative Akio Tanii 4 Agent 571 Address 7, Matsushita Electric Industrial Co., Ltd., 1006 Kadoma, Kadoma City, Osaka Prefecture, page 14, line 17 of the statement of contents of the amendment ``It is.'' Next to ``It is.''
FIG. 6 is an exploded perspective view of a main part of an optical head of a conventional objective lens driving device, FIG. 7 is an exploded perspective view of the same device, and FIG. 8 is a side view of the same device. ”.

Claims (1)

[Claims] a movable part having an objective lens that converges a light beam onto a disk; a pair of magnets having different polarities facing each other with a predetermined gap; an objective lens comprising: a pair of field members; and a coil that is integrally formed with the movable part and is located within the gap and drives the objective lens in a predetermined direction with respect to the disk. Drive device.