JPH0850727A - Objective lens driver - Google Patents

Abstract

PURPOSE:To correct the optical axis with respect to the inclination of the optical axis of an objective lens to an information recording medium in an objective lens driver for recording and reproducing information in the medium. CONSTITUTION:Magnet holding pieces 8a, 8b and opposed yokes 9a-9d are so provided inside the pieces 8a, 8b at a base 2 of a stationary base as to be opposed. Particularly, the yokes 9a-9d are divided in a tracking direction so that the magnetic flux density distribution of a magnetic circuit to a focusing drive coil 10 is double-humped. Thus, even if a movable element including the lens 3 is not displaced in the tracking direction and the focusing direction, the balance of rotary moment is held, and the optical axis of the lens 3 is not inclined. In this manner, the quality of the signal at the time of recording or reproducing can be improved, an optical recorder/reproducer can be easily reduced in size and cost.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an objective lens drive used in an optical recording / reproducing apparatus for recording / reproducing information by condensing a light beam emitted from a light source such as a semiconductor laser on a plate-shaped recording medium. It relates to the device.

[0002]

2. Description of the Related Art There is a conventional objective lens driving device of this type configured as shown in FIG. FIG.
In the figure, Z is an arrow indicating a focusing direction, X is a tracking direction, and Y is an arrow indicating a direction perpendicular to the focusing direction and the tracking direction. In the objective lens driving device 100 shown in this figure, a magnetic base 102 is provided between a light source section (not shown) and an optical disc (not shown) which is a plate-shaped recording medium.

The base 102 has a magnet holding piece 108 made of a magnetic material protruding from both ends thereof in a rectangular parallelepiped shape.
a and 108b are provided so as to face each other along the Y direction. These magnet holding pieces 108a, 108
The magnet 10 has a rectangular parallelepiped shape magnetized in the Y direction.
1a and 101b are attached respectively. Inside the magnet holding pieces 108a and 108b, rectangular parallelepiped opposed yokes 109a and 109b are provided at regular intervals.
It constitutes a magnetic circuit. Also, the magnet holding piece 108
A fixing member 107 is attached to the outside of b. One end of each of the four linear support members 106a, 106b, 106c and 106d is fixed to the left and right ends of the fixing member 107. At the other end of the supporting members 106a to 106d, for example, a substantially rectangular lens holder 1 made of a material such as polyphenylene sulfide resin or epoxy resin.
04 is attached.

An objective lens 103 is incorporated in the center of the lens holder 104 so as to have an optical axis in the Z direction.
On the other hand, a focusing drive coil 110 is wound around the lens holder 104, and the objective lens 103
Four connected ring-shaped tracking drive coils 105 are provided on the outer peripheral end surfaces facing each other with respect to the center. Of the four sides of the focusing drive coil 110, the two sides parallel to the X direction, the tracking drive coil 105, the magnets 101a and 101b, and the opposing yoke 109.
They are arranged in the magnetic gaps between a and 109b, respectively.

As described above, the objective lens 103, the lens holder 104, the focusing drive coil 110, and the tracking drive coil 105 constitute a movable body. Further, the focusing drive coil 110 and the magnet 101a,
Focusing drive means is constituted by 101b and opposed yokes 109a and 109b.

FIG. 9 and FIG. 10 are perspective views showing the relationship between the magnetic flux density distribution of the magnetic circuit and the movable body in the objective lens driving device 100 thus constructed. As shown in FIG. 9, at the neutral position where the movable body is not driven in the focusing direction (Z) and the tracking direction (X), the center of gravity G passing through the center of gravity of the movable body and the drive center line F of the movable body intersect.

In such a configuration, the focus deviation of the light beam with respect to the plate-shaped recording medium surface (optical disk) and the track deviation of the light beam with respect to the track groove are detected, and the focusing drive coil 110 and the tracking drive coil 105 are detected by the detection signals. Attitude control current must be applied to. That is, the magnets 101a, 101
By using the magnetic flux formed by b, the magnet holding pieces 108a and 108b, and the opposing yokes 109a and 109b, the movable body is moved up and down in the focusing direction and driven in parallel with the tracking direction.
The position of the objective lens 103 is controlled.

[0008]

Consider a case in which the movable body is driven only in the focusing direction when the movable body is located at the neutral position of the magnetic circuit as shown in FIG.
Magnets 101a, 101b and magnet holding piece 10
Focusing drive coil 1 inserted in the magnetic gap is a gap of the magnetic circuit formed by 8a, 108b and opposing yokes 109a, 109b.
Assuming that the distribution of the magnetic flux density in the Y direction with respect to 10 is H, the magnetic flux density distribution H has line symmetry about the center of gravity G along the Y direction of the movable body as shown in FIG. When the driving center point of the focusing driving force is F _G , the center of gravity axis G passing through the center of gravity of the movable body intersects at the driving center point F _G. Therefore, no rotational moment about the center of gravity G is generated with respect to the movable body, and the inclination of the optical axis of the objective lens 103 is not generated.

However, as shown in FIG. 10, let us consider a case where the movable body simultaneously moves from the neutral position in the focusing direction Z and the tracking direction. In this case, the distribution H of the magnetic flux density in the Y direction with respect to the focusing drive coil 110 inserted in the magnetic gap is shifted from the center of gravity G of the movable body in the X direction. Therefore, the driving center point F _G of the focusing driving force and the center of gravity _G of the movable body shift,
The drive center line F and the center of gravity G are in a twisted state. Therefore, a rotation moment indicated by an arrow is generated around the center of gravity G with respect to the movable body, and the optical axis of the objective lens 103 is tilted.

As a result, the beam condensed by the objective lens 103 is tilted, causing optical aberration and defocusing, deteriorating the reproduction signal of the data recorded on the plate-shaped recording medium, and recording the data during recording. There were problems such as incorrect recording.

The present invention has been made in view of the above conventional problems, and improves the magnetic flux density distribution with respect to the focusing drive coil provided on the movable body.
It is an object of the present invention to realize an objective lens driving device that prevents the generation of a rotation moment when a movable body including an objective lens is displaced in the focusing direction or the tracking direction and can stably record and reproduce a signal.

[0012]

According to a first aspect of the present invention, there is provided a movable body including an objective lens and a lens holder for holding the objective lens, a movable body having a focusing direction substantially parallel to an optical axis of the objective lens, and substantially the same. Tracking drive means for driving the movable body in the tracking direction, including a support means for supporting the movable body in the vertical tracking direction, a fixed base for fixing one end of the support means, and a tracking drive coil attached to the movable body. And a focusing drive means that includes a focusing drive coil attached to the movable body, drives the movable body in the focusing direction, and suppresses a rotational moment with respect to the center of gravity axis of the movable body perpendicular to the focusing direction and the tracking direction. It is characterized by having.

[0013]

According to the present invention having such characteristics, the movable body including the objective lens is driven in the focusing direction and the tracking direction at the same time, and when the driving center point of focusing deviates from the center of gravity of the movable body, the movable body moves. The rotational moment generated in the body is made symmetrical about the center of gravity. Therefore, the rotational moment applied to the movable body is suppressed. In this case, the objective lens is not tilted and the quality of the reproduction signal and the quality of the recording signal are improved.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An objective lens driving device in a first embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a perspective view showing the configuration of an optical recording / reproducing apparatus according to the first embodiment of the present invention. 2 is a perspective view of a magnetic circuit portion in the objective lens driving device of the first embodiment. FIG.
FIG. 3A is a partial plan view of a magnetic circuit of the objective lens driving device of the present embodiment, and FIG. 3B is a distribution diagram of magnetic flux density penetrating the focusing driving coil.

1 to 3, the arrow Z indicates the focusing direction, X indicates the tracking direction, and Y indicates the focusing direction and the direction perpendicular to the tracking direction, as in the conventional example. In FIG. 1, the objective lens driving device includes
A magnetic base 2 is provided as a fixed base. At both ends of the base 2 along the Y direction, rectangular parallelepiped magnet holding pieces 8a and 8b are fixed so as to face each other. The magnet holding pieces 8a and 8b respectively hold the rectangular parallelepiped magnets 1a and 1b magnetized in the Y direction.

Unlike the conventional example, opposed yokes 9a and 9b are provided at a constant interval in the X direction so as to face the magnet 1a fixed to the magnet holding piece 8a. The lens holder 4 holding the objective lens 3 has two rectangular through holes formed in parallel with the central axis thereof.
9b is attached to the base 2. Also, so as to face the magnet 1b fixed to the magnet holding piece 8b,
Opposing yokes 9c and 9d are provided at a constant interval in the X direction. And these opposing yokes 9c and 9d
Is attached to the base 2 so as to be positioned in the other through hole of the lens holder 4.

The opposing yokes 9a and 9b, the magnet 1a, and a part of the base 2 constitute a first magnetic circuit having a constant distance in the Y direction. Similarly, the opposing yokes 9c and 9d
The magnet 1b and a part of the base 2 form a second magnetic circuit having a constant distance in the Y direction. A fixing member 7 having a U-shaped cross section is attached to the outside of the magnet holding piece 8b. And the fixing member 7
Four linear support members 6a, 6b, 6 at the left and right ends of the
One ends of c and 6d are fixed. Support members 6a to 6d
Is a supporting means having elasticity, and the other end is the lens holder 4
By being fixed to the side projection of the lens holder 4
The movable body including is held so that it can be finely moved in the X and Z directions.

The lens holder 4 is made of, for example, polyphenylene sulfide resin, epoxy resin or the like in a substantially rectangular shape, and the objective lens 3 is incorporated in the center thereof. The focusing drive coil 10 is wound around the four side surfaces of the lens holder 4. The focusing drive coil 10 receives an electromagnetic force by the magnetic flux of the magnetic gap portion where the facing yokes 9a to 9d and the magnets 1a and 1b face each other, and finely moves the objective lens 3 in the Z-axis direction to adjust the focus. On the other hand, Y of the lens holder 4
Tracking drive coils 5 are attached one by one to two side surfaces located in the direction. The tracking drive coil 5 is a coil wound in a ring shape and receives an electromagnetic force due to the magnetic flux of the magnetic gap portion to finely move the objective lens 3 in the X direction to cause the laser beam to follow the track of the recording medium. .

Here, the focusing drive coil 10, the magnets 1a and 1b, and the opposing yokes 9a to 9d constitute a laser beam focusing drive means and a moment suppressing means for preventing the optical axis of the objective lens 3 from moving. . Further, the objective lens 3, the lens holder 4,
Magnets 1a, 1b, focusing drive coil 1
0, the tracking drive coil 5 constitutes a movable body.

Now, as shown in FIGS. 2 and 3 (a), 1
The opposing yokes 9a and 9b are attached to the two magnets 1a by X.
By installing at two locations in the direction, magnet 1
By installing the opposed yokes 9c and 9d at two positions in the X direction with respect to b, the magnetic flux density distribution on the XY plane for the focusing drive coil 10 becomes as shown in FIG. 3 (b).

The operation of the objective lens driving device thus configured will be described. FIG. 4 is an explanatory diagram when the center of gravity G of the lens holder 4 is at the center of the magnetic flux density distribution H, and FIG. 5 is where the center of gravity G of the lens holder 4 is the magnetic flux density distribution H.
It is explanatory drawing in the case of being deviated to the + X direction from the center part. Here, in order to make the explanation easy to understand, the center of gravity G of the movable body is
A plane including the above and parallel to the focusing direction is defined as a plane ABCD, and the movable body is divided into an L section and an R section with this plane as a boundary.

[0022] Thus the movable body L unit, when divided into R unit, represents a driving force generated in the L unit vector, the sum of this vector as a driving force F _L, Working the driving force F _L Let the position be the driving point L _P of the L portion. Similarly, the driving force F _R and the driving point R _P are also set in the R section. Further, the distance between the center of gravity axis G and the driving point L _P is L _G , and the distance between the center of gravity axis G and the driving point R _P is R _G.

As shown in FIG. 4, the movable body has a magnetic flux density distribution H
When the movable body is driven only in the focusing direction in the case of being located in the neutral position, the magnetic flux density distribution H with respect to the focusing drive coil 10 inserted in the magnetic gap portion has two different average values as shown in the figure. The shape is such that a Gaussian distribution is superimposed. However, this distribution curve differs depending on the arrangement and shape of the members forming the magnetic circuit. The distribution of the focusing driving force generated in the focusing driving coil 10 in this case has the shape described on the front side surface of the lens holder 4.

In this case, the distribution of the driving force of the L portion and the distribution of the driving force of the R portion are symmetrical with respect to the plane ABCD. Therefore F
_R and F _L are equal in magnitude, the distance from the central axis G of the driving point R _P and L _P R _G and L _G are also equal. Therefore, the movable body can translate in the focusing direction without tilting along the Y axis.

Next, let us consider a case where the movable body simultaneously moves from the neutral position of the magnetic flux density distribution H in the focusing direction and the tracking direction as shown in FIG. The magnetic flux density distribution H for the focusing drive coil 10 inserted in the magnetic gap is the same as in the case of FIG. 4, but has a distribution shifted in the −X direction when viewed from the movable body. In this case, the driving force F _L of the L portion of the movable body decreases as the movable body is moved in the tracking direction. Further, the driving point L _P moves away from the center of gravity G in the −X direction, and the distance L _P between the driving point L _P and the center of gravity G increases.

On the other hand, in the R part of the movable body, the driving force F _R increases contrary to the L part, and the distance R _G between the driving point R _P and the center of gravity axis G decreases. Therefore, the moment M _R about the center of gravity G due to the driving force F _R, which is the product of the driving force F _R and the distance R _G ,
Driving force and F _L and the distance L around the moment M _L of the central axis G by the driving force F _L is the product of _G are equal, the movable body is translatable in the X direction or Z direction without tilting along the Y axis .

In such an objective lens driving device,
The focus drive coil 1 detects the focus shift of the light beam with respect to the surface of the plate-shaped recording medium and the track shift of the light beam with respect to the track groove of the recording medium.
0, a current is applied to the tracking drive coil 5. The magnets 1a and 1b and the magnet holding pieces 8a and 8
b, the position of the objective lens 3 can be stably controlled by using the magnetic flux formed by the opposing yokes 9a to 9d to move the movable body up and down in the focusing direction and drive it parallel to the tracking direction. it can.

In the first embodiment described above, as the moment suppressing means for preventing the inclination of the optical axis of the objective lens 3,
The facing yokes 9a to 9d are arranged in a divided form in the tracking direction as shown in FIG. By making the magnetic flux density distribution penetrating the focusing drive coil 10 as shown in FIG. 3, the rotational moment generated in the movable body could be suppressed.

On the other hand, as the objective lens driving device of the second embodiment, magnets 11a to 11 as shown in FIG.
d, opposing yokes 19a and 19b, magnet holding piece 18
It may be provided with a and 18b. Opposing yokes 19a and 19b shown in FIG. 6 have the same shape as the conventional objective lens driving device. On the other hand, the magnet holding pieces 18a and 18b have a T-shaped cross section, and two magnets are provided in the left and right concave portions of the lens holder 4.
It is fixed so as to be bilaterally symmetric with respect to the axis G of gravity.

By doing so, two pairs of magnets 11a to 11d are arranged in the tracking direction, so that the magnetic flux density distribution for the focusing drive coil 10 is shown in FIG.
It has the same shape as. In this case, the distribution of focusing driving force is similar to that shown in the first embodiment.

As the objective lens driving device of the third embodiment, magnets 11a to 11d, opposing yokes 29a to 29d, magnet holding pieces 18a, 1 as shown in FIG.
8b may be provided. The structure shown in FIG. 7 is a combination of the above-described two methods (the first embodiment and the second embodiment). That is, by arranging the opposed yokes 29a to 29d in a divided form in the tracking direction, and by sandwiching the magnets 11a to 11d between the magnet holding pieces 18a and 18b made of a magnetic material and disposing two pairs in the tracking direction, The same effect as the first embodiment can be obtained.

[0032]

As described above, according to the present invention, by dividing the yoke in the tracking direction, even if the movable body is driven in the focusing direction and the tracking direction at the same time, the generation of the rotational moment of the movable body is suppressed. can do. Therefore, the objective lens held by the movable body can be moved to a predetermined position without tilting. Therefore, the optical aberration and defocus of the recording medium are suppressed, and the quality of the reproduction signal and the quality of the recording signal can be improved. Therefore, the optical recording / reproducing apparatus can reduce errors in recording / reproducing data. Further, it is possible to further reduce the size and cost of the objective lens driving device.

[Brief description of drawings]

FIG. 1 is a perspective view showing the configuration of an objective lens driving device according to a first embodiment of the present invention.

FIG. 2 is a perspective view of a magnetic circuit portion in the objective lens driving device of the first embodiment.

FIG. 3A is a plan view of a magnetic circuit in the objective lens driving device of the first embodiment, and FIG. 3B is a distribution diagram of magnetic flux density penetrating the focusing driving coil.

FIG. 4 is a perspective view of relevant parts showing an operation (No. 1) of the objective lens driving device of the first example.

FIG. 5 is a perspective view of relevant parts showing an operation (No. 2) of the objective lens driving device of the first example.

FIG. 6 is a perspective view of a magnetic circuit portion of an objective lens driving device according to a second embodiment of the present invention.

FIG. 7 is a perspective view of a magnetic circuit portion of an objective lens driving device according to a third embodiment of the present invention.

FIG. 8 is a perspective view showing a configuration example of a conventional objective lens driving device.

FIG. 9 is a main part perspective view showing an operation (first) of the conventional objective lens driving device.

FIG. 10: Operation of conventional objective lens driving device (No. 2)
It is a principal part perspective view which shows.

[Explanation of symbols]

1a-1d, 11a-11d, 29a-29d Magnet 2 Base 3 Objective lens 4 Lens holder 5 Tracking drive coil 6a-6d Support member 7 Fixing member 8a, 8b, 18a, 18b Magnet holding piece 9a-9d, 19a, 19b Opposite. yoke 10 focusing drive coil X tracking direction Y direction perpendicular to the focusing direction and the fine tracking direction Z focusing direction F _R, F _L focusing drive force M _R, M _L rotation moment G gravity line H flux density distribution L _P, R _P drive point

Claims (4)

[Claims] 1. A movable body that includes an objective lens and a lens holder that holds the objective lens, and the movable body is finely supported in a focusing direction substantially parallel to an optical axis of the objective lens and a tracking direction substantially vertical to the optical axis. Supporting means, a fixed base for fixing one end of the supporting means, a tracking drive coil attached to the movable body, and a tracking drive means for driving the movable body in the tracking direction, and an attachment to the movable body. Focusing driving means for driving the movable body in the focusing direction and suppressing a rotational moment of the movable body perpendicular to the focusing direction and the tracking direction with respect to the center of gravity of the movable body. Characteristic objective lens drive device. 2. The focusing driving means includes at least one pair of magnets magnetized in a direction substantially perpendicular to the focusing direction and the tracking direction, and a winding shaft facing the magnet and in a direction substantially parallel to the focusing direction. A focusing drive coil, and a yoke made of a magnetic material that is disposed in a position facing the magnet via a part of the focusing drive coil and is divided into two in the tracking direction. The objective lens driving device according to claim 1, wherein a rotational moment generated by a magnetic flux formed by the is suppressed. 3. The focusing driving means is magnetized in a direction substantially perpendicular to the focusing direction and the tracking direction, and is provided at a position symmetrical with respect to the center of gravity of the movable body at a constant interval in the tracking direction. Two pairs of magnets, a focusing drive coil that faces each of the pair of magnets, and has a winding axis in a direction substantially perpendicular to the focusing direction, and a yoke made of a magnetic material that is disposed at a position that faces the magnets. 2. The objective lens drive device according to claim 1, further comprising: and a rotational moment generated by a magnetic flux formed by the magnet and the yoke. 4. The focusing driving means is magnetized in a direction substantially perpendicular to the focusing direction and the tracking direction, and is provided at a position symmetrical with respect to the center of gravity of the movable body at a constant interval in the tracking direction. Two pairs of magnets, a focusing drive coil that faces the pair of magnets, and has a winding axis in a direction substantially perpendicular to the focusing direction, and the pair of magnets via a part of the focusing drive coil. A yoke made of a magnetic material which is disposed at a position facing each other and is divided into two in the tracking direction, and suppresses a rotational moment generated by a magnetic flux formed by the magnet and the yoke. The objective lens driving device according to claim 1.