JPH07220294A - Objective lens driving device - Google Patents

Abstract

PURPOSE:To precisely perform the position control of an objective lens with a simple structure and to improve the reliability of the device specially when the device is made thin. CONSTITUTION:A magnetic circuit regulating part 91 composed of a recessed part or a hole is provided on a prescribed position of a fixed yoke member 18 and a distance between the fixed yoke member 18 and a magnetic piece 90 is kept at a certain extent or more by virtue of the existence of the magnetic circuit regulating part 91 even when the magnetic piece 90 is driven in the focusing direction and approaches close to the fixed yoke member 18. By preventing the generation of unwanted magnetic circuit between the fixed yoke member 18 and the magnetic piece 90, the linearity of magnetic attracting force is obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an objective lens driving device for driving a lens holder holding an objective lens in a focusing direction and a tracking direction.

[0002]

2. Description of the Related Art Generally, in an objective lens driving device (actuator) of an optical pickup used in an optical disk device or the like, a lens holder holding the objective lens is arranged facing a fixed yoke member. A drive coil is provided on one side of the yoke member and a magnet is provided on the other side. By energizing the drive coil, the lens holder is driven in the focusing direction and the tracking direction.

Among them, in the so-called magnetic levitation type objective lens driving device disclosed in Japanese Patent Laid-Open No. 1-317234, a magnetic piece is fixed to one side of the lens holder and the fixed yoke member. Due to the magnetic attraction of the magnet to the magnetic piece, the lens holder
It is configured to be held at a neutral point in the focusing direction and the tracking direction.

[0004]

However, in such a conventional magnetic levitation type objective lens driving device, if another magnetic substance exists near the movable range of the magnetic piece,
There is a problem that the magnetic field is distorted so that the linearity of the magnetic attraction force cannot be obtained, resulting in poor position control of the objective lens. Especially when the device is made thinner, when the lens holder is driven in the focusing direction, the magnetic piece comes very close to the bottom surface of the fixed yoke member, which causes an unnecessary magnetic circuit and deteriorates linearity. I often do it. In some cases, the magnetic pieces may be attracted to the fixed yoke member.

Therefore, it is an object of the present invention to provide an objective lens driving device capable of accurately controlling the position of an objective lens while maintaining a simple structure suitable for thinning.

[0006]

To achieve the above object, the present invention provides a drive coil on one side of a lens holder holding an objective lens and a fixed yoke member and a magnet on the other side, and drives these. A coil and a magnet are disposed so as to face each other, and the drive coil is energized to drive the lens holder in the focusing direction and the tracking direction, and a magnetism for holding the lens holder at a neutral point in the focusing direction and the tracking direction. In a magnetic levitation type objective lens driving device having a piece, a magnetic circuit straightening portion consisting of a recess or a hole is provided at a predetermined position of the fixed yoke member, and the magnetic circuit straightening portion is the magnetic piece. Is arranged at a position facing the fixed yoke member in the focusing direction. That.

[0007]

According to the objective lens driving device of the above invention, when the lens holder is driven in the focusing direction, the fixed yoke member and the magnetic piece are fixed by the magnetic circuit adjusting section provided on the bottom surface of the fixed yoke member. Are separated from each other by a predetermined distance or more, so that an unnecessary magnetic circuit is not generated between the fixed yoke member and the magnetic piece.

[0008]

Embodiments of the objective lens driving device according to the present invention will be described below with reference to the drawings. In FIGS. 1, 2 and 3, a fixed unit 1 having an outer yoke 18 and an inner yoke 20 is placed on a frame 10 formed by resin integral molding or the like. On the other hand, the movable unit 2 is mounted on the support shaft 26 integrally formed of resin so as to be movable in the axial direction, that is, the focusing direction and the axial rotation direction, that is, the tracking direction. The above-described frame 10 is attached so as to be able to reciprocate along a guide rail (not shown), and the frame 10 is configured to move integrally as a whole so that a so-called seek operation is performed. There is.

The outer yoke 18 and the inner yoke 20 of the fixed unit 1 are made of large and small cylindrical members with a bottom.
An inner yoke 20 is superposed on the outer yoke 18. Each of the yokes 18 and 20 is formed by cutting out a part of the peripheral wall and the bottom surface of the substantially bottomed cylindrical member, and at the symmetrical positions with the center holes 15 and 17 provided therebetween, respectively, A pair of peripheral wall plates each having a partially cylindrical shape are provided. The peripheral wall plate of the outer yoke 18 and the peripheral wall plate of the inner yoke 20 are arranged to face each other inside and outside at a predetermined interval in the radial direction.

Holes that penetrate the outer yoke 18 and the inner yoke 20 are formed in the bottom surface portion where the outer yoke 18 and the inner yoke 20 directly overlap with each other, and rivets made of a resin material are passed through these holes. By molding the portion 38, the outer yoke 18 and the inner yoke 20 are integrally connected. Simultaneously with the integral molding, the central hole 15 of the outer yoke 18 is filled with resin to form the base portion 28, and the support shaft 26 is integrally molded with the resin. The support shaft 26 extends from the base portion 28 through the center hole 17 of the inner yoke 20. The bottom surface of the base portion 28 is curved so as to form a part of a spherical surface, and the adjustment surface 3 for adjusting the tilt angle of the support shaft 26, which will be described later, is formed.
It is done in 2.

Simultaneously with the integral molding, a jetty 44 for positioning a drive magnet, which will be described later, is integrally molded on the bottom surface of the outer yoke 18. The jetty 44 is formed by the peripheral wall plate of the outer yoke 18 and the inner yoke 20.
The projection 66 is integrally formed on the jetty 44. The jetty 44 positions the drive magnet in the axial direction, and the protrusion 66 positions the drive magnet in the circumferential direction.

As described above, when the outer yoke 18 and the inner yoke 20 are molded from resin and integrally connected, the outer yoke 18 and the inner yoke 20 are integrally molded in a state of being positioned in the molding die. Therefore,
The relative positional relationship between the outer yoke 18, the inner yoke 20, and the support shaft 26, particularly the support shaft 2 for the respective yokes 18, 20.
The verticality of 6 depends on the precision of the mold, and the relative positional relationship and the support shaft 26 can be obtained by accurately preparing the mold.
Is made with necessary and sufficient accuracy.

On the other hand, a focusing drive magnet 22 and a tracking drive magnet 24 are fixed by adhesion or the like to the inner surface side of the partially cylindrical peripheral wall plates forming a pair of the outer yokes 18. The drive magnets 22 and 24 are positioned in the direction of the support shaft 26 by being brought into contact with the upper surface of the jetty 44, and are positioned by the protrusions 66 in the circumferential direction. Thus, the fixed unit 1 is configured.

At this time, in the fixing unit 1, the adjusting surface 32, which is a spherical surface of the base portion 28 of the fixing unit 1, has the frame 1
It is dropped in the concave portion 30 formed of a spherical surface of 0. The tilt angle adjusting screws 34 and 36 are inserted from the frame 10 side, and the tilt angle adjusting screws 34 and 36 are attached to the outer yoke 18
Is screwed into the screw hole. In addition, the frame 10
The base end portion of the leaf spring 40 is fixed by means of a mounting screw 42, and the tip end portion of the leaf spring 40 presses the farthest position from the screw hole of the outer yoke 18 with the support shaft 26 interposed therebetween. ing. Therefore, the tilt angle adjusting screw 3
By tightening or loosening 4, 36, the adjusting surface 32 is slidably in contact with the recess 30 and is rotated around the spherical center of the adjusting surface 32 against the elastic force of the leaf spring 40 or the elastic force thereof. The tilt angle of the unit 1 (see the reference symbol θ _{r in} FIG. 1 and the reference symbol θ j in FIG. 3) changes.

Further, the movable unit 2 includes a support shaft 26.
It has a substantially cylindrical lens holder 12 mounted so as to be rotatable and slidable with respect to. The objective lens 16 is provided near the circumference of the upper end surface of the lens holder 12 in the drawing.
The holding frame of is attached. The objective lens 16
Is mounted so that its optical axis is parallel to the support shaft 26. Further, the drive coils 14 are fixed to the cylindrical outer peripheral surface of the lens holder 12 so as to be paired at symmetrical positions with the support shaft 26 interposed therebetween.

Both the peripheral wall plates of the inner yoke 20 described above penetrate through the window holes formed in the lens holder 12 with a spatial margin, and face the drive magnets 22 and 24 with the drive coil 14 interposed therebetween. It is arranged to. As described above, the inner yoke 2 is arranged in order from the inner side.
0, the drive coil 14, the drive magnets 22 and 24, and the outer yoke 18 are arranged along an arc centered on the support shaft 26, and a substantially closed magnetic path passing through these is formed.

On the other hand, the above-mentioned drive coil 14 is composed of a sheet-shaped coil in which a spiral pattern coil is sandwiched by insulating materials, and is composed of a focusing drive coil and a tracking drive coil. The focusing drive coil is arranged to face the focusing drive magnet 22 described above, and the tracking drive coil is arranged to face the tracking drive magnet 24 described above. And drive coil 1
By controlling the energization of the focusing drive coil of No. 4, the movable unit 2 including the objective lens 16 reciprocates along the support shaft 26 by the thrust generated between the focusing drive magnet 22 and predetermined focusing control. By performing energization control of the tracking drive coil of the drive coil 14, the movable unit 2 including the objective lens 16 reciprocally rotates around the support shaft 26 by the thrust generated between the drive coil 14 and the tracking drive magnet 24. However, predetermined tracking control is performed.

Here, the focusing drive magnet 22 is polarized and magnetized so that the N pole and the S pole are aligned in the axial direction, and the tracking drive magnet 24 is used.
Are polarized and magnetized in a direction orthogonal to the magnetizing direction of the focusing drive magnet 22, whereby N and S poles are formed in the circumferential direction. The drive magnets 22 and 24 are arranged on a continuous common surface.

On the other hand, the focusing drive coil in the drive coil 14 is formed in a horizontally long rectangle, and its long side is arranged so as to face each magnetic pole of the focusing drive magnet 22. The tracking drive coil is formed in a vertically long rectangle, and its long side is arranged so as to face each magnetic pole of the tracking drive magnet 24.

Further, a magnetic piece 90 is fixed to the arcuate outer peripheral surface of the lens holder 12 described above so as to face the magnetic pole center of the focusing drive magnet 22. The magnetic piece 90 is narrow in the circumferential direction and long in the direction of the support shaft 26. That is, the width dimension in the circumferential direction about the support shaft 26 is formed to be considerably smaller than the circumferential dimension of the focusing drive magnet 22, and the length dimension in the support shaft 26 direction is for focusing. It is formed to be slightly shorter than the axial dimension of the drive magnet 22.

As described above, the focusing driving magnet 22 is polarized and magnetized in the axial direction.
In the plane orthogonal to 6, the magnetic flux has a maximum in the circumferential center of the air gap and decreases toward the ends of the air gap. Then, the magnetic piece 90 arranged in the space
A magnetic attraction force by the focusing drive magnet 22 acts on the magnetic field, and a restoring force equivalent to the elastic restoring force that tends to be stably held at the maximum point of the magnetic flux acts on the. By this restoring force, the lens holder 12 is held at the neutral point in the circumferential direction, and thus the objective lens 16 is held at the neutral point in the tracking direction. The restoring force at this time is proportional to the gradient of the magnetic flux distribution and the area of the magnetic piece 90, but in the normal movable range of the objective lens 16 in the tracking direction, the magnetic flux gradient changes approximately linearly. The restoring force can be obtained substantially uniformly in the normal movable range of the objective lens 16.

On the other hand, in the cross section of the focusing drive magnet 22 in the direction of the support shaft 26, the drive magnet 22 is polarized and magnetized in the direction of the support shaft 26. The gradient of the magnetic flux reverses in the middle part in the vertical direction. Here, the magnetic piece 90 acts as a part of the magnetic path, and the magnetic piece 90 is magnetically attracted to the central portion of the polarized magnetization. Then, this suction force acts as a restoring force, the lens holder 12 is held at a predetermined position in the direction of the support shaft 26, and thus the objective lens 16
Is held at the neutral point in the focusing direction. Further, as described above, the magnetic piece 90 acts as a magnetic path of the magnetic flux emitted from the driving magnet 22, so that the magnetic flux density is improved, which contributes to the improvement of the sensitivity of the objective lens driving device and the magnetic restoring force is increased. Stable over a wide range.

Further, as shown in FIG. 4, a hole 91 as a magnetic circuit adjusting portion is formed through the bottom surface portion 18a of the outer yoke 18 so as to penetrate therethrough. The hole 91 forming the magnetic circuit straightening portion is formed in a long hole shape and faces the magnetic piece 90 in the focusing direction (axial direction).
It is located at the location. The hole 91 is arranged within the range in which the magnetic piece 90 moves in the tracking direction.

In the embodiment having such a structure, when the lens holder 12 is driven in the focusing direction, the magnetic circuit is favorably maintained by the hole 91 provided in the bottom surface portion 18a of the outer yoke 18. . That is, the magnetic piece 90 moves the bottom portion 18 of the outer yoke 18 by the control operation of the lens holder 12 in the focusing direction.
Even when approaching a, the distance between the outer yoke 18 and the magnetic piece 90 is separated by a certain amount or more due to the presence of the hole 91 as the magnetic circuit adjusting portion. Therefore, also in this case, the outer yoke 18 is also separated. An unnecessary magnetic circuit does not occur between the magnetic piece 90 and the magnetic piece 90. As a result, the magnetic field is always well distributed without being distorted, and the linearity of the magnetic attractive force is obtained. This is particularly noticeable when the device is made thin.

Although the invention made by the present inventor has been specifically described based on the embodiments, the present invention is not limited to the above embodiments, and various modifications can be made without departing from the scope of the invention. Needless to say. For example, the magnetic circuit adjusting portion in the present invention is not limited to the hole as in the above-mentioned embodiment, but the outer yoke 18 and the magnetic piece 9 can be used.
It is also possible to form a concave portion such that the distance from 0 is a certain distance or more.

As the magnet, the focusing drive magnet and the tracking drive magnet may be provided separately from each other as in the illustrated embodiment, or one focusing magnet portion and one tracking magnet portion may be formed by molding. It can also be summarized in.

Further, the magnetic piece in the illustrated embodiment is arranged so as to be surrounded by the drive coil on the outer peripheral surface of the lens holder, but it may be embedded in the lens holder side. Alternatively, magnetic pieces may be arranged at positions facing both the focusing magnet portion and the tracking magnet portion.

Further, as the resin used for the above-mentioned integral molding, it is preferable to use a resin containing a filler such as carbon fiber or Teflon (trade name) for improving slidability. In this way, the movement of the movable unit 2 in the axial direction and the rotation around the axis can be smoothed without coating the surface of the support shaft 26.

[0030]

As described above, in the objective lens driving device according to the present invention, the magnetic circuit adjusting portion formed of the concave portion or the hole is provided at the predetermined position of the fixed yoke member, and the magnetic piece is driven in the focusing direction. Even if the fixed yoke member is close to the fixed yoke member, the fixed yoke member is separated from the magnetic piece by a certain distance due to the presence of the magnetic circuit straightening portion. An unnecessary magnetic circuit does not occur between them, and the linearity of the magnetic attraction force is obtained. Therefore, the position control of the objective lens can be performed accurately with a simple structure, and the reliability when the device is made thin is achieved. Can be improved.

[Brief description of drawings]

FIG. 1 is a side sectional view showing an objective lens driving device according to an embodiment of the present invention.

FIG. 2 is a plan view of the objective lens driving device shown in FIG.

FIG. 3 is a front sectional view of the objective lens driving device shown in FIG.

FIG. 4 is an external perspective view showing a fixed yoke member used in the objective lens driving device shown in FIG.

[Explanation of symbols]

 12 Lens Holder 18 Outer Yoke 18a Bottom Part 90 Magnetic Piece 91 Hole (Magnetic Circuit Alignment Part)

Claims (2)

[Claims] 1. A drive coil is provided on one side of a lens holder holding an objective lens and a fixed yoke member, and a magnet is provided on the other side, and the drive coil and the magnet are opposed to each other. A magnetic levitation type objective lens driving device for controlling movement of a lens holder in a focusing direction and a tracking direction, comprising a magnetic piece for holding the lens holder at a neutral point in the focusing direction and the tracking direction. A magnetic circuit straightening portion consisting of a recess or a hole is provided at a predetermined position of the member, and the magnetic circuit straightening portion is arranged at a position where the magnetic piece faces the fixed yoke member in the focusing direction. The objective lens drive device is characterized in that 2. The magnetic piece is attached to the lens holder side, and the magnetic circuit straightening portion is provided within a range in which the magnetic piece moves in the tracking direction. The described objective lens drive device.