JPH04310652A - Objective lens actuator - Google Patents

Abstract

PURPOSE:To prevent the influence due to a leaking magnetic field without worsening the focusing follow-up characteristic even when the force to move an objective lens is changed. CONSTITUTION:The permanent magnetic of the magnetic circuit is arranged so that the magnetic direction can be the direction parallel to the optical axis of an objective lens 3 and the direction of each magnetic flux can be the opposite direction. the magnetic path material is fixed to both magnetic poles of permanent magnets 4 and 5, arranged parallel to the optical axis of the above- mentioned objective lens 3 and bear an objective lens holder 10, and the magnetic cavity of a pair of the magnetic circuits is formed on two planes parallel to the recording surface of an information recording support. Two coils 9 and 10 formed so as to surround objective lens holder 10 are respectively fitted into the magnetic cavity of the magnetic circuit out of the magnetic cavities formed like this and other magnetic cavity of the magnetic circuit having the magnetic flux direction of the direction opposite to the magnetic flux direction of the magnetic cavity.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an objective lens actuator for an optical disk drive.

0002

[Prior Art] In a magneto-optical optical pickup that records and reproduces information using an external magnetic field, an objective lens actuator (hereinafter referred to as an actuator)
It holds an objective lens that focuses the laser beam and irradiates the recording surface of the optical disk on which the magnetic coating is formed with the laser beam. This actuator also maintains the focus of the laser beam on the recording surface of the optical disc.
Move the objective lens in the optical axis direction.

However, since the objective lens is moved by this actuator using electromagnetic force, leakage magnetism from this actuator changes the magnitude of the magnetic field at the focal point of the laser beam, making it difficult to record and reproduce information on the optical disk. It may not be done properly.

[0004] In order to prevent the influence of this magnetic leakage, measures are taken, such as providing a magnetic shielding member between the optical disk and the optical pickup, or providing a correction magnet around the actuator. The increase in the number of parts, the complexity of the process, and the increase in the weight of the moving parts of the optical system have led to slower access speeds.

Next, FIG. 3 shows an actuator for a conventional opto-magnetic type optical pickup that prevents the influence of leakage magnetism without providing a new magnetic shielding member or the like.
, 4 will be used for explanation. Here, (a) in FIG. 3 is a front sectional view of a conventional actuator excluding the coil, and (a) in FIG.
FIG. 4(a) is a front sectional view of the conventional actuator, and FIG. 3(b) is a plan view thereof.

As shown in FIGS. 3 and 4, a conventional actuator is composed of yokes 1 and 2 and permanent magnets 4 and 5 magnetized in a direction perpendicular to the optical axis (hereinafter referred to as optical axis) A of an objective lens 3. Objective lens driving magnetic circuits (hereinafter referred to as magnetic circuits) 6 and 7 are arranged symmetrically with respect to the optical axis A.

When the permanent magnets 4 and 5 are arranged in this way,
Since the magnetization directions of the permanent magnets 4 and 5 are the same across the optical axis A, both magnetic circuits 6 and 7 are polarized as shown by arrows B and C.
The direction of magnetic leakage from is in the opposite direction. Therefore, on the optical axis A, the vertical components of the leakage magnetism have the same magnitude and opposite directions, so the magnetisms at the focal point F of the laser beam on the recording surface of the optical disk 8 cancel each other out, and the influence of the leakage magnetism disappears.

[0008]

However, in such a conventional actuator, since the permanent magnets 4 and 5 are arranged as described above, the force for moving the objective lens 3 in the direction of the optical axis A cannot be applied in the same direction. In order to generate this, it is necessary to fit separate coils 9a and 9b into the magnetic gaps S1 and S2 of the magnetic circuits 6 and 7, respectively, as shown in FIG.

For this reason, the coils 9a and 9b are not wound around and fixed around the objective lens holder (hereinafter referred to as holder) 10, but are glued to both sides of the objective lens holder 10 facing the magnetic circuits 6 and 7. and fix it. As a result, the holder 10 has coils 9a and 9b provided on both sides thereof.
and the magnetic circuits 6 and 7, thereby ensuring a degree of freedom in the direction of the optical axis A.

However, when the coils 9a and 9b are bonded and fixed to the side surface of the holder 10 in this way, the rigidity of the actuator movable part becomes weaker than in an actuator in which the coils are integrated and molded.

Furthermore, the distance L1 between the respective coils 9a and 9b fitted into the magnetic gaps S1 and S2 of the magnetic circuits 6 and 7 of the conventional actuator shown in FIG. 5(a) is as shown in FIG. 5(b). For example, compared to the distance L2 when the coil 11 is wound around the holder 10 as shown in FIG. .

[0012] Here, the resonance frequency is the magnetic air gap S1, S2
The stiffness decreases as the distance between the coils 9a and 9b fitted in the coil becomes longer, and as the rigidity of the movable part becomes weaker. Therefore, in the conventional actuator, even if the force generated in the coils 9a, 9b in the magnetic circuits 6, 7 changes at a low frequency, resonance will occur.

When such resonance occurs, the movement of the coils 9a and 9b does not match the movement of the objective lens 3, resulting in a problem that focusing followability deteriorates.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide an objective lens actuator that can prevent the effects of leakage magnetic fields without deteriorating focusing followability even when the force for moving the objective lens changes at low frequencies. shall be.

[0015]

[Means for Solving the Problems] The present invention provides an objective lens that irradiates a light beam from a light source onto an information recording carrier, a holder that holds the objective lens and has a coil fixed to its side, and an optical axis of the objective lens. In an objective lens actuator, the objective lens actuator is provided with a pair of magnetic circuits composed of a permanent magnet and a magnetic path material, which form a magnetic gap into which a coil fixed to the holder is inserted. is parallel to the optical axis of the objective lens, and the magnetic flux directions are opposite to each other; the magnetic path material fixed to both magnetic poles of the permanent magnet; A pair of magnetic paths formed by a magnetic path material arranged parallel to the optical axis of the objective lens and near the objective lens so as to form air gaps in two planes parallel to the recording surface of the information recording carrier. and a magnetic air gap formed in the pair of magnetic circuits, each of which is fitted into the magnetic air gap of one of the magnetic circuits and the magnetic air gap of the other magnetic circuit having a magnetic flux direction opposite to the magnetic flux direction of this magnetic gap. and an objective lens holder in which two coils are fixed so as to surround the objective lens holder.

[0016]

[Operation] With this configuration, the directions of magnetic flux in the direction parallel to the optical axis of each magnetic circuit of the actuator can be made to be opposite directions, thereby suppressing the influence of leakage magnetic flux from the actuator. Also,
Since the coil is wound around the holder, the rigidity of the actuator movable part can be increased.

[0017]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1(a) is a plan view of an actuator according to an embodiment of the present invention, FIG. 1(b) is a front sectional view thereof, and FIG. FIG. 1 and 2, the same reference numerals as those in FIGS. 3 and 4 indicate the same or corresponding parts.

In FIGS. 1 and 2, the magnetization directions of the permanent magnets 4 and 5 are parallel to the optical axis A, and the direction of their magnetic flux is parallel to the optical axis A as shown by arrows B and C in FIG. They are arranged so that they are in opposite directions in parallel directions and in the same direction in two planes parallel to the recording surface of the disk. Further, each magnetic pole of the permanent magnets 4 and 5 is provided with outer upper yokes 1aa and 2.
aa and outer lower yokes 1ab and 2ab are arranged.

In contrast to the outer upper yokes 1aa, 2aa and the outer lower yokes 1ab, 2ab, inner yokes 1b, 2b are arranged parallel to the optical axis A near the holder 10, sandwiching a coil to be described later. Thereby, each magnetic circuit 4, 5 has two magnetic gaps, namely, magnetic gaps S1a, S2a formed by the outer upper yokes 1aa, 2aa and the inner yokes 1b, 2b, and the outer lower yokes 1ab,
2ab and the internal yokes 1b, 2b form magnetic gaps S1b, S2b.

The two coils 11a and 11b are attached to the holder 9.
and is wound so as to surround the internal yokes 1b and 2b of each magnetic circuit 4 and 5. One of the coils 11a is wound diagonally so that the direction of the force acting on the coil 11a is the same in each magnetic circuit 4, 5, and the outer upper yoke 1aa of one magnetic circuit 4 and the inner yoke 1b, and a magnetic gap S2b formed between the outer lower yoke 2ab and the inner yoke 2b of the other magnetic circuit 5.

[0021] Also, the other coil 11b is also connected to this coil 11.
The outer lower yoke 1ab and the inner yoke 1 of one magnetic circuit 4 are wound diagonally so that the direction of the force acting on b is the same.
b and the other magnetic circuit 5.
It is fitted into a magnetic gap S2a formed by the outer upper yoke 2aa and the inner yoke 2b.

[0022] These two coils 11a and 11b
is a holder 10 that is not affected by magnetism due to the magnetic circuits 4 and 5.
The side faces not facing the magnetic circuits 4 and 5 are wound so as to intersect with each other, and are also molded. Note that the number of turns of these two coils 11a and 11b is half the number of turns of coils 9a and 9b of the conventional actuator.

In the actuator configured in this manner, the vertical components of the leakage magnetism are equal in magnitude and opposite in direction on the optical axis A of the objective lens 3, so that the magnetism at the focal point of the laser beam cancels each other out. The influence of leakage magnetism disappears.

Furthermore, the directions of the magnetic fields in the two magnetic gaps S1a, S1b, S2a, and S2b formed in the respective magnetic circuits 4 and 5 are vertically opposite directions, as shown by arrows B and C in FIG. ing.

Therefore, the holder 10 is wound around the holder 10, and among the two magnetic gaps S1a, S1b, S2a, and S2b formed in the magnetic circuits 4 and 5, the magnetic flux passes through the magnetic gap in the same direction. It is held by the two coils 11a, 11b and the magnetic circuits 6, 7, which are wound in such a manner that the degree of freedom in the direction of the optical axis A is ensured.

[0026] Since the coils 11a and 11b wound around the holder 10 in this manner are integrated and molded, the rigidity of the movable part of the actuator is stronger than that of a conventional actuator.

Furthermore, the coils 11a and 11b are connected to the holder 1.
Since it is wound around 0, the magnetic gaps S1 and S2
The distance L2 between the coils 11a and 11b inserted into the actuator is shorter by the thickness T of the coils, as shown in FIG. 5(b), compared to the conventional actuator shown in FIG. 5(a) described above. .

[0028] Here, since the shorter the distance L2 and the stronger the rigidity of the movable part, the higher the resonance frequency becomes.
Even if the force generated in the coils 11a, 11b in the magnetic circuits 6, 7 to move the objective lens 3 changes at a low frequency, the holder 10 will not resonate.

In this way, the direction in which the permanent magnet is magnetized is in the optical axis direction, and the direction of each magnetic flux is opposite to the optical axis direction.
By arranging them in the same direction parallel to the recording surface of the disk, it is possible to prevent the influence of magnetic leakage and also to prevent the occurrence of resonance.

[0030]

As described above, according to the present invention, the direction of magnetic flux in the direction parallel to the optical axis of each magnetic circuit of the actuator can be made to be in the opposite direction, thereby reducing leakage magnetic flux from the actuator. The impact of this can be suppressed. Additionally, since the coil is wound around the holder, the rigidity of the actuator's moving part can be increased.
Focusing tracking performance can be improved. Furthermore, since the influence of leakage magnetic flux can be suppressed without newly providing a magnetic shield or the like, an increase in the number of parts and a complication of the process can be prevented.

[Brief explanation of drawings]

FIG. 1 is a plan view and a front sectional view of an objective lens actuator according to an embodiment of the present invention.

FIG. 2 is a sectional view taken along line XX of a plan view of an objective lens actuator according to an embodiment of the present invention.

FIG. 3 is a front sectional view and a plan view of a conventional objective lens actuator with the coil removed.

FIG. 4 is a front sectional view and a plan view of a conventional objective lens actuator.

FIG. 5 is a diagram showing the distance between a coil fitted into a magnetic gap and an optical axis.

[Explanation of symbols]

1, 2 York 3 Objective lens 4,5 Permanent magnet 6,7 Magnetic circuit 8. Optical disc 9,11 Coil 10 Objective lens holder

Claims (1)

[Claims] Claim 1: An objective lens that irradiates a light beam from a light source onto an information recording carrier; an objective lens holder that holds the objective lens and has a coil fixed to its side; and an objective lens holder that is provided symmetrically with respect to the optical axis of the objective lens. In the objective lens actuator, the objective lens actuator is provided with a pair of magnetic circuits constituted by a permanent magnet and a magnetic path material forming a magnetic gap into which a coil fixed to the objective lens holder is inserted, the magnetization direction being aligned with the objective lens. Information is recorded on the above-mentioned permanent magnets arranged parallel to the optical axis and with their respective magnetic flux directions in opposite directions, the magnetic path material fixed to both magnetic poles of this permanent magnet, and the magnetic gap. a pair of magnetic circuits formed by a magnetic path material disposed parallel to the optical axis of the objective lens and near the objective lens so as to form two planes parallel to the recording surface of the carrier; 2 which are respectively fitted into the magnetic air gap of one of the magnetic air gaps formed in a pair of magnetic circuits and the magnetic air gap of the other magnetic circuit having a magnetic flux direction opposite to the magnetic flux direction of this magnetic air gap.
and an objective lens holder in which two coils are fixed so as to surround the objective lens holder.