JPH11203697A - Actuator device for optical pickup - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make an normal tracking servo achievable by preventing rotation when a moving part is driven in a tracking direction. SOLUTION: A yoke 3 is mounted on a lens holder 1 holding an objective lens 2, and a permanent magnet 5 is fixed on one inner wall 3a of opposing inner walls 3a, 3b, and an auxiliary yoke 12 is formed so as to cover both end faces of the magnet. A focus coil 9 wound in the direction perpendicular to an optical axis of an objective lens is mounted on a base, and a pair of tracking coils 10, 11 wound in a reverse direction to each other is bonded to a part of the focus coil 9, and both tracking coils 10, 11 are arranged in the direction perpendicular to the focus coil 9. The joining part of these coils is inserted in the gap between the permanent magnet 5 and the inner wall face 3b of the yoke 3 opposed thereto, and when the lens holder 1 is driven by the current made to flow through both of the tracking coils 10, 11 in the tracking direction of the objective lens 2, a magnetic flux density both on the right and left sides holding both tracking coils 10, 11 is made uniform by the auxiliary yoke 12.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an actuator device for an optical pickup for recording or reproducing information on a medium such as a compact disk or a mini disk.

[0002]

2. Description of the Related Art FIG. 6 is a perspective view showing an actuator device of a conventional optical pickup, FIG. 7 is a plan sectional view showing a magnetic circuit of the actuator device, and FIG. 8 is an explanatory view of a tracking coil provided in the actuator device. In these figures, reference numeral 1 indicates a lens holder,
The objective lens 2 and the yoke 3 are attached to the lens holder 1. The yoke 3 is a U-shaped magnetic body having an open upper end, and a top yoke 4 is joined to the open end to form a closed magnetic path. Opposing inner wall surfaces 3 of the yoke 3
The permanent magnet 5 is attached to one of the inner wall surfaces 3a of the first and second a and b, and the yoke 3 and the permanent magnet 5 form a magnetic circuit. The components on the lens holder 1 side including this magnetic circuit constitute a movable part, and the lens holder 1
Is attached to the upright portion 7a of the base 7 via the four wires 6, so that the movable portion is elastically supported by the upright portion 7a of the base 7 serving as a fixed portion.

A focus coil 9 is mounted on a base 7 via a bobbin 8, and the focus coil 9 is wound in a frame shape in a direction orthogonal to the optical axis of the objective lens 2. A pair of tracking coils 10 and 11 are adhered to a part of the focus coil 9, and both tracking coils 10 and 11 are arranged side by side in a direction orthogonal to the focus coil 9. As shown in FIG. 8, both tracking coils 10 and 11 are wound in opposite directions to each other.
When current is supplied in the direction shown by the solid line or the broken line in FIG. 3, the wires are connected so that current flows in the same direction to the adjacent effective portions 10a and 11a. As shown in FIG. 7, the joint between the focus coil 9 and the tracking coils 10 and 11 is inserted into the gap between the permanent magnet 5 and the inner wall surface 3b of the yoke 3 opposed thereto. , That is, the magnetic flux in the Y direction of the coordinate axis shown in FIG. 6 intersects with the current flowing through each of the coils 9, 10, 11. Therefore, the focus coil 9
, The force in the Z direction of the coordinate axis acts, and the lens holder 1 moves in the focus direction of the objective lens 2, that is, in the Z direction. Similarly, both tracking coils 1
The current in the effective portions 10a and 11a adjacent to 0 and 11 also exerts a force in the X direction of the coordinate axis, and the lens holder 1 is moved in the tracking direction of the objective lens 2.

[0004]

By the way, in the above-mentioned conventional actuator device for an optical pickup, as shown in FIG. 7, in addition to the magnetic flux from the permanent magnet 5 toward the inner wall surface 3b of the yoke 3, the permanent magnet 5, there is a magnetic flux directed obliquely to the tracking coils 10, 11 from both side surfaces of the tracking coils 10, 11,
Are in an unbalanced state in which the permanent magnet 5 side is dense and the inner wall surface 3b side is sparse. If the two tracking coils 10 and 11 are regarded as small magnets, the winding directions of the two tracking coils 10 and 11 are opposite.
When a current flows in the direction indicated by the solid line in FIG. 8 in FIG. 1, the permanent magnet 5 side of one of the tracking coils 10 becomes an N pole,
The permanent magnet 5 side of the other tracking coil 11 is an S pole. Therefore, as shown by the black arrows in FIG.
Due to the unbalance of the distribution state of the magnetic flux density, a force for attracting to one of the tracking coils 10 toward the permanent magnet 5 acts, and the other of the tracking coils 11 to the permanent magnet 5 side. Are applied, and these forces generate a rotational moment. As a result, there is a problem that undesired rotational motion is induced in the movable portion including the lens holder 1, and dynamic characteristics in a high frequency region are disturbed (see FIG. 9).

[0005] Such a problem is not limited to a moving magnet (MM) type actuator device having a magnetic circuit attached to the movable portion side, but a moving coil (MC) having a focus coil and a tracking coil attached to the movable portion side. The same applies to the actuator device of the type.

[0006]

According to the present invention, there is provided an auxiliary yoke for reducing a magnetic flux on a side of a magnet, and the magnetic flux is obliquely directed to a pair of tracking coils arranged in parallel with the winding direction reversed. I did not go to. When such an auxiliary yoke is provided, the imbalance of the magnetic flux density on both sides of the tracking coil is eliminated, so that it is possible to prevent undesired rotational motion from being induced in the movable portion.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In an actuator device for an optical pickup according to the present invention, a lens holder for holding an objective lens, a focus coil wound in a direction orthogonal to the optical axis of the objective lens, A pair of tracking coils which are arranged side by side in a direction orthogonal to each other and have winding directions opposite to each other, and have opposing surfaces opposing each other with the focus coil and the tracking coil interposed therebetween, from one opposing surface to the other opposing surface A magnet and a yoke for generating a heading magnetic flux, and auxiliary yokes provided on both end faces of the magnet along the direction in which the tracking coils are arranged. Interaction with magnetic flux causes the lens holder to move in the focus direction and tracking direction. It was configured to drive.

With this configuration, since the magnetic flux from both end surfaces of the magnet is reduced by the auxiliary yoke, the magnetic flux oblique to the pair of tracking coils from the both end surfaces of the magnet is reduced, and both sides of the tracking coil are reduced. Can be made uniform in the state of density of the magnetic flux density. As a result, undesired rotational movement is not induced in the movable portion including the lens holder, and normal dynamic characteristics in a high-frequency region can be maintained (see FIG. 5).

Although the above-described configuration can be applied to a moving coil type actuator device, it is particularly effective when applied to a moving magnet type in which components of a magnetic circuit are attached to a movable portion side.

[0010] The magnet is arranged in such a manner that the opposite pole faces the opposing surface of the yoke opposing the tracking coil.
However, if the magnet is arranged on one of the opposing surfaces of the yoke to reduce the weight of the movable part, the imbalance of the magnetic flux density on both sides of the tracking coil becomes remarkable. It is effective to apply it to an actuator device of a system.

The auxiliary yoke may have another component attached to the yoke. However, if the auxiliary yoke is integrally bent and formed on the side of the yoke, the number of components can be reduced and the assembling operation can be simplified. can do.

[0012]

Embodiments will be described with reference to the drawings.
FIG. 1 is a perspective view showing an actuator device of an optical pickup, FIG. 2 is a plan sectional view showing a main part of the actuator device, FIG. 3 is a perspective view showing components of a magnetic circuit, and FIG. FIG. 9 is a cross-sectional view, in which parts corresponding to FIG. 6 to FIG.

The difference between the actuator device of the optical pickup according to the present embodiment and the above-described prior art is that auxiliary yokes 12 are provided on both end surfaces of the permanent magnet 5 along the direction in which the tracking coils 10 and 11 are juxtaposed. The other configuration is basically the same. That is,
On both sides of the U-shaped yoke 3 having an open upper end, auxiliary yokes 12 bent substantially at right angles to one inner wall surface 3a are integrally formed, and these auxiliary yokes 12 are attached to one inner wall surface 3a. The permanent magnet 5 extends toward the other inner wall surface 3a so as to cover both end surfaces. Since the auxiliary yoke 12 reduces the magnetic flux from the permanent magnet 5 obliquely to the two tracking coils 10 and 11, the magnetic flux from the permanent magnet 5 to the inner wall surface 3b of the yoke 3 is reduced as shown in FIG. Only the magnetic flux density distribution on the left and right sides of FIG.

In the actuator device of the optical pickup thus configured, the movable portion including the lens holder 1 is driven in the focusing direction of the objective lens 2 by the current flowing through the focus coil 9 and flows through the tracking coils 10 and 11. Lens holder 1 by electric current
Is movable in the tracking direction of the objective lens 2 in the same manner as in the conventional example, but when the movable part is driven in the tracking direction, the two tracking coils 10 and 1 are driven.
The magnetic flux density on both the left and right sides of
Therefore, the generation of the rotational moment is suppressed. Therefore, the lens holder 1
Undesirable rotational motion is not induced in the movable portion including the above, and normal dynamic characteristics in a high frequency region can be maintained.

In the above embodiment, the case where the auxiliary yoke 12 is integrally bent on both sides of the yoke 3 has been described.
2 may be integrated later. The auxiliary yoke 12
It is not always necessary to cover the entire side end surface of the permanent magnet 5. If the magnetic flux that causes the imbalance of the magnetic flux density distribution on both sides of the tracking coils 10 and 11 can be reduced, the side of the permanent magnet 5 can be reduced. The auxiliary yoke 12 may be arranged so as to cover a part of the end face.

[0016]

The present invention is embodied in the form described above and has the following effects.

A lens holder for holding the objective lens, a focus coil wound in a direction orthogonal to the optical axis of the objective lens, and a winding coil arranged in a direction orthogonal to the focus coil and having winding directions opposite to each other A pair of tracking coils, a magnet and a yoke, which have opposing surfaces that face each other with the focus coil and the tracking coil interposed therebetween, and generate a magnetic flux from one opposing surface to the other opposing surface; and the tracking in the magnet. Auxiliary yokes disposed on both end faces along the direction in which the coils are arranged, and an interaction between a current flowing through the focus coil and the tracking coil and a magnetic flux from the magnet,
When the lens holder is configured to be driven in the focus direction and the tracking direction, the magnetic flux from both end faces of the magnet is reduced by the auxiliary yoke, so that the magnetic flux traveling obliquely to the pair of tracking coils from both end faces of the magnet. And the density of the magnetic flux density on both sides of the tracking coil can be made uniform,
As a result, undesired rotational movement is not induced in the movable portion including the lens holder, and normal dynamic characteristics in a high-frequency region can be maintained.

[Brief description of the drawings]

FIG. 1 is a perspective view showing an actuator device of an optical pickup according to an embodiment.

FIG. 2 is a plan sectional view showing a main part of the actuator device.

FIG. 3 is a perspective view showing components of a magnetic circuit.

FIG. 4 is a plan sectional view of the magnetic circuit.

FIG. 5 is an explanatory diagram showing frequency characteristics of the actuator device.

FIG. 6 is a perspective view showing a conventional actuator device for an optical pickup.

FIG. 7 is a plan sectional view showing a magnetic circuit of the actuator device.

FIG. 8 is an explanatory diagram of a tracking coil provided in the actuator device.

FIG. 9 is an explanatory diagram showing frequency characteristics of a conventional actuator device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Lens holder 2 Objective lens 3 Yoke 3a, 3b Inner wall surface 5 Permanent magnet 6 Wire 7 Base 9 Focus coil 10, 11 Tracking coil 12 Auxiliary yoke

Claims (3)

[Claims] A lens holder for holding an objective lens;
A focus coil wound in a direction orthogonal to the optical axis of the objective lens, a pair of tracking coils arranged in parallel in a direction orthogonal to the focus coil and having winding directions opposite to each other, and the focus coil and A magnet and a yoke having facing surfaces facing each other with the tracking coil interposed therebetween, and generating a magnetic flux from one facing surface to the other facing surface; and a magnet and a yoke disposed on both sides of the magnet along the direction in which the tracking coils are juxtaposed. An actuator device for an optical pickup, comprising an auxiliary yoke provided. 2. The actuator device for an optical pickup according to claim 1, wherein components of the magnetic circuit including the magnet, the yoke, and the auxiliary yoke are attached to the lens holder. 3. The actuator device for an optical pickup according to claim 1, wherein the auxiliary yoke is formed by bending integrally with a side portion of the yoke.