JPH04313824A - Lens driver in optical information reader - Google Patents

Abstract

PURPOSE:To perform the correct information reading by positioning the gravity center of a movable optical system in corresponding to approximately the central part of the length from the fixed edge of a supporting member to its free edge, and providing a driving force to the gravity center with a driving force providing means. CONSTITUTION:A gravity center G of a movable optical system composed of an objective lens 1 and a lens holder 2 supporting the lens 1 is set to position in corresponding to the central part of length L from a fixed edge 12a of each supporting member 12 up to a free edge 12b. A driving force providing means provides driving force to the gravity center G. In such a case, by supplying the current to a focusing coil 4, the movable optical system always performs the parallel movement in a focusing direction F without making inclination. In the same way, by supplying the current to a tracking coil 5, the parallel movement is performed in a tracking direction T without making inclination. Then, the correct signal reproduction from the optical disk can be performed.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a lens driving device for a pickup section in an optical information reading device.

0002

[Background Art] An optical information reading device focuses and irradiates a recording track formed on an information recording surface of a recording medium with a laser beam for reading information as a spot light, and detects changes in reflected light from the recording surface. It is used to read information. For this purpose, it is necessary to always focus the information reading laser beam onto the recording track despite surface runout caused by surface warping of the recording medium, so the objective lens for laser beam focusing must be placed on the information recording surface. The focus servo is used to move the lens minutely in the vertical direction (focus servo). Furthermore, since it is necessary for the laser beam to always accurately track the recording track despite the eccentricity of the recording track, it is also possible to move the objective lens minutely in a direction perpendicular to the recording track (tracking servo). ing.

[0003] For such movement of the objective lens, FIG.
Lens driving devices shown in FIGS. 1 to 16 have already been developed. As shown in FIGS. 14 and 15, objective lens 1
01 is attached to one end of the lens holder 102. A through hole 102a is formed in the lens holder 2, and the center axis of the coil is aligned with the objective lens 10 in the through hole.
Focusing coil 10 parallel to the optical axis of 1
3 is installed. As shown in FIG. 16, the center axis of the coil is located on the outside of the focusing coil 103.
Two tracking coils 104 are attached perpendicularly to the optical axis of 01. Note that the tracking coil 104 is shown only in FIG. 16. Each tracking coil 104 is formed by winding each coil into a rectangular ring shape and pasting it onto the focusing coil 103 in advance. The objective lens 101 and the lens holder 102 are spaced apart from each other in the optical axis direction of the objective lens 101, and extend parallel to each other in a first direction (arrow X direction) perpendicular to the optical axis direction. Book cantilever support member 1
It is carried on the free end of 05. Each support member 105 is attached to a base 107. Each support member 105
has flexibility, so that the movable optical system consisting of the objective lens 101 and the lens holder 102 can move in the optical axis direction of the objective lens (direction of arrow F) and in the first direction (direction of arrow
It is movable in two directions, a second direction (direction of arrow T) perpendicular to each of the two directions (direction) and the direction of the optical axis.

The above-mentioned focusing coil 103 and tracking coil 104 are located within a magnetic gap of a magnetic circuit consisting of a magnet 108 and a yoke 109. A parallel magnetic flux is generated in the magnetic gap that interlinks with each coil at right angles, and by supplying a predetermined current to each coil, the objective lens 1 is moved in each direction of arrows F and T.
01 can be driven.

As shown in FIG. 17, in this lens driving device, the objective lens 1 is driven by a driving force P generated by supplying a current to a focusing coil 103.
When 01 is driven in the direction of arrow F, a bending moment M is generated, and axial forces T in the stretching direction and the compression direction are applied to the two upper and lower support members, respectively. As a result, each support member 5 is distorted in its axial direction, and as a result, the objective lens 10
The movable optical system including 1 is tilted. When the movable optical system is tilted in this manner, aberrations occur, making it difficult to read information on the disc and increasing the error rate. If this is severe, the focus error signal and tracking error signal may not be accurately obtained, and normal reproduction may not be possible.

[0006]

[Object of the Invention] The present invention has been made in view of the above points, and its purpose is to provide a lens driving device that enables accurate information reading by accurately moving an objective lens in parallel. It is to be.

[0007]

SUMMARY OF THE INVENTION A lens driving device according to the present invention includes a movable optical system including an objective lens for irradiating a recording surface of a recording medium with a spot light, and a movable optical system including a movable optical system that is substantially perpendicular to the optical axis direction of the objective lens. a second direction extending in one direction and substantially perpendicular to each of the optical axis direction and the first direction;
a cantilever-like support member that is flexible in both the optical axis direction and the optical axis direction and supports the movable optical system at its free end; and a driving force applying means for applying a driving force to the movable optical system, wherein the center of gravity of the movable optical system is located approximately at the center of the length from the fixed end to the free end of the support member. The driving force applying means is characterized in that it applies a driving force to the center of gravity.

[0008]

In the lens driving device having such a structure, the movable optical system including the objective lens always moves in parallel without being tilted by the driving force applied thereto.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A lens driving device as an embodiment of the present invention will be described below with reference to the accompanying drawings. As shown in FIGS. 1 and 2, an objective lens is used to focus light emitted from a light emitting means (not shown) and irradiate the recording surface of an optical information recording disk (not shown) as a recording medium as a spot light. 1 is attached to one end of a lens holder 2 formed into a substantially rectangular plate shape. Specifically, a circular through hole is formed at the one end, and the objective lens 1 is fitted into this through hole. The lens holder 2 also has a substantially rectangular through hole 2a formed in the rear of the objective lens 1, and a focusing coil 4 wound in a rectangular annular shape is inserted into the through hole 2a so that the center axis of the coil is is mounted so that it is parallel to the optical axis of the objective lens 1. As shown in FIG. 3, two tracking coils 5 are attached to the outer peripheral surface of the focusing coil 4 so that the center axis of the coils is perpendicular to the optical axis of the objective lens 1. Note that the tracking coil 5 is shown only in FIG. Each tracking coil 5 is wound in advance into a rectangular ring shape and pasted onto the focusing coil 4. The focusing coil 4 and the tracking coil 5 are located within a magnetic gap 8a of a magnetic circuit 8 made up of a magnet 6 and a yoke 7. The yoke 7 is formed in a U-shape and is fixed on the chassis 10 so as to open upward, and the magnet 6 is fixed to the inner wall surface of the rear piece of the yoke. In the magnetic gap 8a, parallel magnetic flux is generated to perpendicularly intersect the focusing coil 4 and the tracking coil 5. By these focusing coil 4, tracking coil 5 and magnetic circuit 8,
A driving force applying means is configured to apply driving force in two directions, which will be described later, to a movable optical system consisting of an objective lens 1 and a lens holder 2.

A movable optical system consisting of an objective lens 1 and a lens holder 2 moves in the optical axis direction of the objective lens 1 (direction of arrow F).
Two equal elongated linear support members 1 extending parallel to each other in a first direction (direction of arrow X) perpendicular to
It is attached to the end of 2. Both support members 12 have the same length, are located at the same distance S from the center of gravity of the movable part as will be described later, and are cantilevered at one end with respect to a base 13 fixed on the chassis 10. It is fixed. Therefore, the movable optical system is supported by the free ends of both support members. Both support members 12 can be freely deflected in any direction perpendicular to their axial centers. Thereby, the movable optical system including the objective lens 1 moves in the optical axis direction of the objective lens (direction of arrow F) and in the first direction.
It is movable in two directions: a second direction (direction of arrow T) perpendicular to each direction (direction of arrow X) and the direction of the optical axis. Note that this optical axis direction is a focusing direction set perpendicular to the information recording surface of the information recording disk, and the second direction is a tracking direction that crosses the recording track formed on the information recording surface at right angles. be. The driving force applying means described above applies driving forces in these two directions to the movable optical system. That is, by supplying predetermined currents to the focusing coil 4 and the tracking coil 5, respectively, the movable optical system is driven in the focusing direction and the tracking direction.

As is clear from FIGS. 1 and 2, the center of gravity G of the movable optical system consisting of the objective lens 1 and the lens holder 2 holding it is the length from the fixed end 12a to the free end 12b of each support member 12. It is set to be located corresponding to the center part of the length L. Moreover, this center of gravity G is between the respective axes of the two support members 12 that are provided parallel to each other along a plane, including the first direction (direction of arrow X) and the second direction (direction of arrow T). It is set to the middle position of the distance. The above-mentioned driving force applying means is configured to apply a driving force to this center of gravity G. Note that this driving force application center point is indicated by E in FIG.

By the way, as shown in FIG. 4, a free end 20b of a cantilever beam 20 of length L whose own weight is negligible and whose cross section is uniform
The free end 20 when downward P in the figure acts on
The inclination angle i1 at b is obtained by the following equation. i1=PL2/2EI However, E: Young's modulus of the cantilever beam 20 I: Moment of inertia of the beam cross section of the cantilever beam 20 with respect to the horizontal principal axis Also, as shown in FIG. Inclination angle i when a moment M in the direction is applied
2 is obtained by the following equation.

i2=-ML/EI Here, as shown in FIG. 6, the above force P is applied to the free end 20b.
Considering the case where , and moment M are applied at the same time, the magnitude of moment M is determined when the inclination angle i1 due to force P and the inclination angle i2 due to moment M cancel each other out, that is, the sum of both inclination angles becomes 0. That is, from equations 1 and 2, PL2/2E
I-ML/EI=0 Therefore, M=PL/2 is obtained. This means that a longitudinal rigid body 22 is attached to the free end 20b of the cantilever 20, as shown in FIG.
One end 22a is fixed so that the rigid body extends toward the fixed end 20a of the cantilever beam 20, and the rigid body 22 is fixed at a position corresponding to the central portion of the length of the cantilever beam 20 with respect to the rigid body 22. If a force P is applied from one end 22a to a position L/2, the moment M at the free end 20b becomes PL/2, making it possible to always make the inclination angle of the steel body 22 0 regardless of the size of P. It shows that there is.

Now, considering the weight W of the rigid body 22, its center of gravity G is set at a position where the above force P is applied. Then, the above-mentioned principle holds true just by adding the weight W to the force P, and the rigid body 22 can move in parallel. To be precise, this principle is based on the spring constant of the cantilever beam 20 being k,
The natural frequency f is determined by the following formula as the mass m of the rigid body 22
This only holds true in the vibration region lower than o, that is, in the elastic control region, and causes parallel movement.

[0015]

Note that in the inertia control region where the frequency is higher than this fo, the elasticity of the cantilever beam 20 can be ignored and the force acts on the center of gravity G of the rigid body 22, so the rigid body 22 still does not move in parallel. Eggplant. Therefore, by setting the center of gravity G of the rigid body 22 and the driving force application point at a position corresponding to the central portion of the length of the cantilever beam 20, the rigid body will move in parallel in all vibration bands. As mentioned above, the above principle is utilized in the lens driving device shown in FIGS. 1 and 2. That is, the movable optical system and support member 12 in the lens driving device correspond to the rigid body 22 and cantilever beam 20 shown in FIG. 7, respectively.

In this configuration, as shown in FIGS. 8 and 9, by supplying current to the focusing coil 4, the movable optical system always moves in parallel in the focusing direction F without tilting. Similarly, as shown in FIGS. 10 and 11, the tracking coil 5 (
By supplying a current to the position shown in FIG. 3), parallel movement is performed in the tracking direction T without tilting. Therefore, accurate signal reproduction from the optical disc becomes possible.

Note that in the above embodiment, the support member 1
Although two 2 are provided, the configuration is not limited to this, for example, as shown in FIGS. 12 and 13, along a plane including the first direction (direction of arrow A total of four supporting members 12 may be provided, each consisting of two sets of supporting members 12 extending parallel to each other and spaced apart in the optical axis direction (direction of arrow F). In this case, the center of gravity G is set at the intersection of two diagonal lines connecting each support member 12 in a plane including the optical axis direction and the second direction. Although not shown, the movable optical system is supported by only two support members 12 extending parallel to each other in the first direction (direction of arrow X) and separated from each other in the direction of the optical axis (direction of arrow F). It is also possible to do this. Furthermore, the above-mentioned principle is also applied to a configuration in which only one support member 12 is provided.

By the way, regarding the servo drive in the tracking direction T, since there is no major problem in performance even if the movable optical system is not necessarily moved in parallel, each support member 12 is arranged in parallel as shown in FIG. Instead, for example, the supporting members may be provided at an angle such that the spacing between the supporting members becomes gradually narrower in the tracking direction T toward the fixed end 12a.

Furthermore, in the conventional configuration shown in FIG.
Although it is possible to generate a force that overcomes the bending moment generated in the movable optical system by setting the interval C between the upper and lower support members 105 large, and to bring the movable optical system close to a parallel movement state, as described above, the present invention In the lens drive device, the movable optical system does not inherently tilt, so
As shown in FIG. 13, this C can be made as small as possible. Therefore, it contributes to making the lens driving device thinner.

[0021]

As described in detail above, in the lens driving device according to the present invention, the lens drive device extends in the first direction substantially perpendicular to the optical axis direction of the objective lens, and
At the free end of a cantilever-shaped support member that is flexible in two directions, a second direction substantially perpendicular to each direction and the optical axis direction,
A movable optical system including the objective lens is attached, and the center of gravity of the movable optical system is positioned corresponding to approximately the center of the length from the fixed end to the free end of the support member, and the movable optical system is driven to the center of gravity. power is given.

Because of this configuration, the movable optical system always moves in parallel without being tilted by the driving force applied thereto. Therefore, an error signal for servo driving can be obtained accurately, and information can be read smoothly.

[Brief explanation of drawings]

FIG. 1 is a plan view including a partial cross section of a lens driving device as a first embodiment of the present invention.

FIG. 2 is a side view of the lens driving device shown in FIG. 1.

FIG. 3 is a perspective view of a driving coil included in the lens driving device shown in FIGS. 1 and 2. FIG.

FIG. 4 is a diagram showing the operating principle of the lens driving device according to the present invention.

FIG. 5 is a diagram showing the operating principle of the lens driving device according to the present invention.

FIG. 6 is a diagram showing the operating principle of the lens driving device according to the present invention.

FIG. 7 is a diagram showing the operating principle of the lens driving device according to the present invention.

8 is an explanatory diagram of the operation of the lens driving device shown in FIGS. 1 and 2. FIG.

9 is an explanatory diagram of the operation of the lens driving device shown in FIGS. 1 and 2. FIG.

10 is an explanatory diagram of the operation of the lens driving device shown in FIGS. 1 and 2. FIG.

11 is an explanatory diagram of the operation of the lens driving device shown in FIGS. 1 and 2. FIG.

FIG. 12 is a plan view including a partial cross section of a lens driving device as a second embodiment of the present invention.

13 is a side view of the lens driving device shown in FIG. 12. FIG.

FIG. 14 is a plan view including a partial cross section of a conventional lens driving device.

15 is a side view of the lens driving device shown in FIG. 14. FIG.

16 is a perspective view of a driving coil included in the lens driving device shown in FIGS. 14 and 15. FIG.

17 is an explanatory diagram of the operation of the lens driving device shown in FIGS. 14 and 15. FIG.

[Explanation of symbols of main parts]

1...Objective lens 2...Lens holder 3...Focusing coil 4...Tracking coil 6...Magnet 7...York 8...Magnetic circuit 12...Supporting member 13...Base

Claims (3)

[Claims] 1. A movable optical system including an objective lens for irradiating a recording surface of a recording medium with a spot light; a cantilever-like support member that is flexible in both the axial direction, a second direction substantially perpendicular to the first direction, and the optical axis direction, and supports the movable optical system at its free end; , a lens drive device including a driving force applying means for applying a driving force in the optical axis direction and the second direction to the movable optical system, wherein the center of gravity of the movable optical system is fixed to the support member. A lens driving device, characterized in that the driving force applying means is positioned approximately at the center of the length from the end to the free end, and the driving force applying means applies a driving force to the center of gravity. 2. Two supporting members are provided substantially parallel to each other along a plane including the first and second directions, and the center of gravity is set at an intermediate position between the axial centers of each of the supporting members. The lens driving device according to claim 1, characterized in that: 3. Two sets of the support members are provided, each extending substantially parallel to each other along a plane including the first and second directions, and spaced apart in the optical axis direction; 2. The lens driving device according to claim 1, wherein the center of gravity is set at an intersection of two diagonal lines connecting each of the support members in a plane including the optical axis direction and the second direction.