JP2011118983A - Objective lens driving device and optical head device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce an uneven temperature distribution of an objective lens with an inexpensive and simple structure, in an objective lens driving device having two objective lenses mounted on a common lens holder, and an optical head device. <P>SOLUTION: A plurality of focus coils and a plurality of tracking coils are attached to a lens holder 3 for holding two objective lenses 4, 5. Each of the plurality of focus coils is disposed in the periphery of each objective lens at a position symmetrical with respect to a plane that passes through the center axis of the objective lens and is perpendicular to a track, and at a position symmetrical with respect to a plane that passes through the center axis of the objective lens and is parallel to the track. Each of the plurality of tracking coils is disposed in the periphery of each objective lens at a position symmetrical with respect to a plane that passes through the center axis of the objective lens and is perpendicular to a track, and at a position symmetrical with respect to a plane that passes through the center axis of the objective lens and is parallel to the track. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an optical head device used in an optical disc apparatus for optically recording information on an optical disc or reproducing information recorded on an optical disc by converging light on a recording surface of the optical disc via an objective lens, The present invention also relates to an objective lens driving device used in the optical head device.

  In order to focus the light beam emitted from the light source on the recording surface of the optical disk, the optical head device follows the light beam to the track of the optical disk and the focus actuator that moves the objective lens in the focus direction that is the optical axis direction. Therefore, an objective lens driving device having a tracking actuator for moving the objective lens in a tracking direction orthogonal to the optical axis is provided. Many actuators that use electromagnetic force generated by arranging a coil in a magnetic field generated by a magnet and energizing the coil are used.

  The objective lens driving device includes an objective lens and a lens holder that holds the objective lens. A focus coil for generating a driving force in the focus direction and a tracking coil for generating a driving force in the tracking direction are attached to the lens holder.

  In recent optical head devices, an objective lens made of plastic is often used. This is because it is easier to mold than a glass objective lens, and the cost can be kept low. In addition, the objective lens is often arranged close to the focus coil and the tracking coil, which are heat sources, as the optical head device is downsized. Furthermore, as the recording / reproducing speed is increased, the drive current supplied to the focus coil and the tracking coil tends to increase.

  For these reasons, in recent optical head devices, the temperature of the objective lens tends to increase due to the heat generated by each coil, and in particular, the temperature near the coil of the objective lens is higher than the temperature far from the coil. A temperature distribution may occur. Since a plastic objective lens is easily deformed due to a temperature change, if an asymmetric temperature distribution occurs with respect to the central axis (optical axis), there is a problem that aberration increases due to thermal deformation and the light condensing performance decreases. .

  Therefore, in order to reduce the aberration caused by the temperature distribution of the objective lens, Patent Document 1 discloses a material having high thermal conductivity so that the lens holder of the objective lens driving device contacts the lower side of the plastic objective lens. Disposing an annular member made of (beryllium copper alloy) is disclosed.

Japanese Patent Laid-Open No. 11-176209 (see paragraphs 0014 to 0018 and FIG. 3)

  However, in the objective lens driving device disclosed in Patent Document 1, since the heat generated by the coil is diffused by the annular member having high thermal conductivity, the temperature distribution of the objective lens can be reduced to some extent. The tendency that the temperature near the coil is slightly higher than the temperature far from the coil cannot be resolved.

  Moreover, since an annular member is mounted on the lens holder in addition to the objective lens and each coil, the weight of the movable part of the objective lens driving device increases. In order to obtain a driving force corresponding to the increase in the weight of the movable part, the driving current must be increased, resulting in a problem that the amount of heat generated by the coil increases. In addition, the cost of parts increases due to the addition of the annular member, and the number of assembling steps of the objective lens driving device increases.

  In particular, in the objective lens driving apparatus of the type in which two objective lenses are mounted on a common lens holder, the above problem appears remarkably because an annular member must be provided for each of the two objective lenses.

  The present invention has been made in order to solve the above-described problems. In an objective lens driving device and an optical head device in which two objective lenses are mounted on a common lens holder, the objective lens has a low-cost and simple configuration, and the objective lens is not defective. The object is to reduce the uniform temperature distribution.

  The objective lens driving device of the present invention supports a lens holder that holds two objective lenses so as to face an optical disc, a plurality of focus coils and a plurality of tracking coils attached to the lens holder, and a lens holder that is movable. Supporting means, a base supporting the supporting means, and a plurality of magnets disposed on the base so as to face the plurality of focus coils and the plurality of tracking coils. Further, a plurality of focus coils are symmetrical around a plane that passes through the central axis of the objective lens and is perpendicular to the track around each objective lens, and is symmetrical with respect to a plane that passes through the central axis of the objective lens and is parallel to the track. Place in position. Further, the plurality of tracking coils are symmetrical around a plane that passes through the central axis of the objective lens and is perpendicular to the track around each objective lens, and is symmetrical with respect to a plane that passes through the central axis of the objective lens and is parallel to the track. Place in position.

  According to the present invention, in an objective lens driving device in which two objective lenses are mounted on a common lens holder, the temperature distribution of the objective lens due to heat generated in the coil can be made uniform with an inexpensive and simple configuration. Thereby, characteristic deterioration (an increase in aberrations, etc.) due to an uneven temperature distribution of the objective lens can be suppressed, and good recording / reproducing performance can be obtained.

It is a perspective view which shows the objective lens drive device in Embodiment 1 of this invention. It is the top view (A) and side view (B) which show the objective lens drive device in Embodiment 1 of this invention. It is a disassembled perspective view which shows the objective lens drive device in Embodiment 1 of this invention separately in a movable part and a fixed part. It is a disassembled perspective view which shows the fixing | fixed part of the objective lens drive device in Embodiment 1 of this invention. It is a disassembled perspective view which shows the movable part of the objective lens drive device in Embodiment 1 of this invention. FIG. 4 is a plan view (A) showing the arrangement of tracking coils attached to the lens holder of the objective lens driving device according to Embodiment 1 of the present invention and a bottom view (B) showing the arrangement of focus coils. It is the top view (A) and sectional drawing (B) which show arrangement | positioning of the objective lens attached to the objective lens drive device in Embodiment 1 of this invention, an aperture, and an inner yoke. It is a perspective view which shows the principal part of the optical disk apparatus containing the optical head apparatus using the objective lens drive device in Embodiment 1 of this invention.

Embodiment 1 FIG.
FIG. 1 is a perspective view of an objective lens driving device according to Embodiment 1 of the present invention. FIG. 2 is a plan view (A) and a side view (B) of the objective lens driving device according to the first embodiment. FIG. 3 is an exploded perspective view showing the objective lens driving device according to Embodiment 1 divided into a movable part and a fixed part. FIG. 4 is an exploded perspective view showing a fixed portion of the objective lens driving device according to Embodiment 1 of the present invention. FIG. 5 is an exploded perspective view showing a movable part of the objective lens driving device according to Embodiment 1 of the present invention. FIG. 6 is a plan view (A) and a bottom view (B) showing the arrangement of the objective lens and the coil attached to the lens holder of the objective lens driving device according to Embodiment 1 of the present invention.

  In each figure, the direction parallel to the optical axis of the objective lens is defined as the Z direction (focus direction), and the radial direction (tracking direction, radial direction) of the optical disk in the plane orthogonal to the Z direction is defined as the Y direction. The tangential direction orthogonal to the Z direction and the Y direction, that is, the track direction of the optical disk is defined as the X direction. For convenience of explanation, in the Z direction, the direction from the objective lens toward the optical disk is “upward”, that is, + Z direction, and the opposite direction is “downward”, that is, −Z direction.

  As shown in FIGS. 1 and 2, the objective lens driving device according to Embodiment 1 is elastic to a base 1, a fixed holder 2 provided on the base 1, and a wire (described later) to the fixed holder 2. A substantially rectangular parallelepiped lens holder 3 to be supported and objective lenses 4 and 5 held by the lens holder 3 are provided.

  The objective lenses 4 and 5 focus the light beam emitted from a light source (not shown) on the optical disc, and correspond to different types of optical discs. For example, the objective lens 4 is used for condensing a light flux having a wavelength band of 400 to 410 nm on an optical disc, and the objective lens 5 is a light flux having a wavelength band of 650 to 660 nm and a light flux having a wavelength band of 760 to 800 nm. Used to collect light on an optical disk. These objective lenses 4 and 5 are positioned on the lens holder 3 side by side in the radial direction (Y direction) and fixed by bonding.

  As shown in FIG. 3, the lens holder 3 is a member made of a light and high-rigidity plastic such as a liquid crystal polymer, and the objective lenses 4 and 5 are disposed on the surface (upper surface 30) facing the optical disk. It has objective lens holding parts 40 and 50 which are protrusions that hold the outer peripheral part. The objective lenses 4 and 5 are held by the objective lens holding portions 40 and 50 so that their optical axes are orthogonal to the recording surface of the optical disc (recording medium).

  The lens holder 3 has a substantially rectangular parallelepiped shape, and includes thin side walls 31 and 32 forming two side surfaces parallel to the YZ plane, and thin side walls 33 and 34 forming two side surfaces parallel to the XZ plane. ing. The side walls 31 and 32 form both end faces in the X direction of the lens holder 3, and the side walls 33 and 34 form both end faces in the Y direction of the lens holder 3.

  Buffer members 12 a and 12 b made of silicon rubber are attached to the objective lens holding portion 40 on the upper surface 30 of the lens holder 3. The buffer members 12a and 12b are formed by applying a room temperature curable silicone rubber liquid having an appropriate viscosity to the two recesses formed in the objective lens holding portion 40 of the lens holder 3 (see FIG. 5) and curing the liquid. Is done. As shown in FIG. 2B, the upper ends of the buffer members 12a and 12b are at the same height, are higher than the top surfaces of the objective lenses 4 and 5, and are emitted from the objective lenses 4 and 5. Is at a lower position than the optical disk when focusing on the optical disk.

  As shown in FIG. 4, the base 1 is, for example, a plate-like member formed of a magnetic material (for example, a metal having magnetism). The base 1 is formed with a through hole 1a through which light incident on the objective lenses 4 and 5 passes.

  Inner yokes 1b, 1c, 1d, and 1e extending in the + Z direction are provided around the through hole 1a of the base 1. The inner yokes 1b, 1c, 1d, and 1e are arranged such that the inner yokes 1b and 1d face each other in the X direction, and the inner yokes 1c and 1e face each other in the X direction. Magnet yokes 1f and 1g extending in the + Z direction are provided outside the inner yokes 1b, 1c, 1d, and 1e so as to face each other in the X direction. The inner yokes 1b to 1e and the magnet yokes 1f and 1g are formed by bending a part of the base 1 in the Z direction by a method such as pressing.

  Magnets 11a and 11b are fixed to the mutually opposing surfaces of the magnet yokes 1f and 1g, respectively. Each of the magnets 11a and 11b is two-pole magnetized so that different magnetic poles are adjacent to each other across a division line at the center in the Y direction. Further, the magnets 11a and 11b are arranged so that their S poles and N poles face each other. Further, when the movable part including the lens holder 3 is at the reference position in the tracking direction, the magnets 11a and 11b are arranged such that the Y-direction positions of the respective dividing lines coincide with the midpoints of both the centers of the objective lenses 4 and 5. Is arranged.

  The fixed holder 2 is formed of a light and high rigidity plastic such as polyphenylene sulfide. The fixed holder 2 is provided on the upper surface of the base 1 and on one end side in the X direction, and faces the side wall 32 of the side walls 31 and 32 of the lens holder 3. The fixed holder 2 elastically supports the lens holder 3 through a wire described below.

  As shown in FIG. 5, on the side walls 33 and 34 (both end surfaces in the Y direction) of the lens holder 3, there are three conductive wires (elastic supports) 6a, 6b, 6c, 6d, 6e, and 6f. A book is attached one by one. The wires 6a, 6b, and 6c are arranged side by side in the Z direction, and each tip is fixed to a protrusion formed on the side wall 33 of the lens holder 3 by solder 7a, 7b, and 7c. Each end portion of the wires 6a, 6b, 6c is fixed to the substrate 8 attached to the fixing holder 2. Similarly, the wires 6d, 6e, 6f are arranged side by side in the Z direction, and each tip is fixed to a protrusion formed on the side wall 34 of the lens holder 3 by solder 7d, 7e, 7f. Each end portion of the wires 6d, 6e, 6f is fixed to the substrate 8.

  The above-described fixed holder 2 (FIG. 4) is filled with a gel-like damper agent (not shown) so as to surround each terminal portion of the wires 6a to 6f. These wires (elastic supports) 6 a to 6 f, the fixed holder 2, and the substrate 8 constitute support means for supporting the lens holder 3.

  Next, the arrangement of the focus coils 9a and 9b and the tracking coils 10a to 10f in the present embodiment will be described.

  As shown in FIGS. 5 and 6B, focus coils 9 a and 9 b are attached to the inside of the lens holder 3. The focus coils 9a and 9b are fixed inside the side walls so as to be surrounded by the side walls 31 and 32 parallel to the YZ plane and the side walls 33 and 34 parallel to the XZ plane. The focus coils 9a and 9b are wound in a substantially rectangular shape so that the winding axis direction is in the Z direction, the same wire diameter and the same number of turns, and current flows in the Y direction and the X direction.

  As shown in FIG. 6B, the winding axis of the focus coil 9a substantially coincides with the central axis (optical axis) of the objective lens 4, and the winding axis of the focus coil 9b is the central axis (optical axis) of the objective lens 5. It arrange | positions so that it may correspond substantially. That is, the focus coil 9a is symmetrical with respect to a plane (AA plane parallel to the YZ plane) that passes through the central axis of the objective lens 4 and is perpendicular to the track (X direction), and is parallel to the track through the central axis of the objective lens 4. Are arranged in symmetrical positions with respect to a flat plane (CC plane parallel to the XZ plane).

  Similarly, the focus coil 9b is symmetrical with respect to a plane (AA plane parallel to the YZ plane) that passes through the central axis of the objective lens 5 and is perpendicular to the track, and a plane that passes through the central axis of the objective lens 5 and is parallel to the track ( (DD plane parallel to the XZ plane).

  Further, the focus coils 9a and 9b are symmetrical with respect to a plane (AA plane parallel to the YZ plane) that passes through the central axes of the objective lenses 4 and 5 and is perpendicular to the track, and an intermediate point between both centers of the objective lenses 4 and 5 And a symmetric positional relationship with respect to a plane parallel to the track (BB plane parallel to the XZ plane).

  Both ends of the focus coil 9a are fixed to the protrusions formed on the side wall 33 parallel to the XZ plane of the lens holder 3 by solders 7b and 7c (FIG. 5), and are electrically connected to the wires 6b and 6c. As a result, a current is supplied to the focus coil 9a through the wires 6b and 6c and the substrate 8. Similarly, both ends of the focus coil 9b are fixed to the protrusions formed on the side wall 34 parallel to the XZ plane of the lens holder 3 by solders 7e and 7f (FIG. 5), and are electrically connected to the wires 6e and 6f. ing. Thereby, a current is supplied to the focus coil 9b via the wires 6e and 6f and the substrate 8.

  The focus coil 9a is arranged so that two sides extending in the Y direction face one magnetic pole of each of the magnets 11a and 11b shown in FIG. 4 (here, each N pole of the magnets 11a and 11b). ing. Further, the focus coil 9b is arranged so that two sides extending in the Y direction face the other magnetic poles of the magnets 11a and 11b (here, the S poles of the magnets 11a and 11b).

  As shown in FIG. 6A, tracking coils 10a, 10b, and 10c are fixed to one side wall 31 parallel to the YZ plane of the lens holder 3. The tracking coils 10d, 10e, and 10f are fixed to the other side wall 32 parallel to the YZ plane of the lens holder 3. Each of the tracking coils 10a to 10f has a winding axis in the X direction, is wound in a substantially rectangular shape so that current flows in the Y direction and the Z direction, and has the same wire diameter and the same It is wound with the same number of turns so as to have a direct current resistance.

  Of the six tracking coils 10a to 10f, the tracking coils 10a and 10d face each other in the X direction, the tracking coils 10b and 10e face each other in the X direction, and the tracking coils 10c and 10f face each other in the X direction. Further, in the Y direction, the tracking coils 10a and 10d are located on one side of the lens holder 3, the tracking coils 10c and 10f are located on the other side of the lens holder 3, and the tracking coils 10b and 10e are the objective lens 4, 5 in the middle.

  As shown in FIG. 6A, the tracking coils 10a, 10b, 10d, and 10e are symmetrical with respect to a plane (AA plane parallel to the YZ plane) that passes through the central axis of the objective lens 4 and is perpendicular to the track, and is objective. The lens 4 is disposed at a symmetrical position with respect to a plane passing through the central axis of the lens 4 and parallel to the track (CC plane parallel to the XZ plane). Similarly, the tracking coils 10b, 10c, 10e, and 10f pass through the central axis of the objective lens 5 and are symmetrical with respect to a plane perpendicular to the track (AA plane parallel to the YZ plane), and pass through the central axis of the objective lens 5. They are arranged at symmetrical positions with respect to a plane parallel to the track (DD plane parallel to the XZ plane).

  The winding axes of the tracking coils 10b and 10e are on a plane parallel to the track (BB plane parallel to the XZ plane) passing through the midpoint between the centers of the objective lenses 4 and 5. The tracking coils 10a, 10b, and 10c and the tracking coils 10d, 10e, and 10f are in a symmetric positional relationship with respect to a plane (AA plane parallel to the YZ plane) passing through both central axes of the objective lenses 4 and 5 and perpendicular to the track. Further, the tracking coils 10a and 10d have a symmetric positional relationship with the tracking coils 10c and 10f with respect to a plane (BB plane parallel to the XZ plane) that passes through the middle point between the centers of the objective lenses 4 and 5 and is parallel to the track. .

  The tracking coils 10a to 10f are connected in series so that current flows in the same direction through the tracking coils 10a, 10c, and 10e, and current flows through the tracking coils 10b, 10d, and 10f in the opposite direction to the tracking coils 10a, 10c, and 10e. It is connected to the. Both ends of the tracking coils 10a to 10f connected in series are electrically connected to the wires 6a and 6d via the solders 7a and 7d (FIG. 5) at the protrusions formed on the side walls 33 and 34 of the lens holder 3. ing. As a result, current is supplied to the tracking coils 10a to 10f via the wires 6a and 6d and the substrate 8.

  In the tracking coils 10a, 10c, 10d, and 10f, one side extending in the Z direction faces one magnetic pole of the magnets 11a and 11b, and the other side extending in the Z direction is the magnet 11a, 11b (see FIG. 2). The tracking coils 10b and 10e are arranged so that two sides extending in the Z direction face opposite magnetic poles (two poles) of the magnets 11a and 11b.

  FIG. 7A is a plan view showing the positional relationship among the objective lenses 4 and 5, the aperture 3 a, the base 1, and the inner yokes 1 b to 1 e of the objective lens driving device in Embodiment 1, and the lens holder 3 is omitted. ing. FIG. 7B is a cross-sectional view taken along line EE in FIG. As shown in FIG. 7B, the lens holder 3 is provided with an aperture 3a that is an opening for restricting the light beam incident on the objective lens 4. Here, the inner dimension 1bd of the inner yoke 1b and the inner yoke 1d in the X direction is wider than the diameter 3ad of the aperture 3a of the lens holder 3 and smaller than the outer diameter 4ad of the objective lens 4. Similarly, although not shown, the inner dimensions of the inner yoke 1 c and the inner yoke 1 e are wider than the diameter of the aperture that restricts the light beam incident on the objective lens 5 and smaller than the outer diameter of the objective lens 5.

  Next, the operation of the objective lens driving device according to Embodiment 1 of the present invention will be described. First, focus control will be described.

  In the focus control, first, a known astigmatism method or the like provided in the optical head device is used for the focal direction deviation amount (focus deviation amount) of the focused spot formed on the optical disk by the objective lens 4 or the objective lens 5. Detect with focus sensor. A current corresponding to the detected focus deviation amount is supplied to the focus coils 9a and 9b via the wires 6b and 6c and the wires 6e and 6f. Due to the mutual electromagnetic action between the current flowing through the focus coils 9a and 9b and the magnetic field of the magnets 11a and 11b, a driving force in the optical axis direction (Z direction) is generated in the focus coils 9a and 9b. , 5 in the direction of the optical axis, and focus control is performed.

  The position of the center of gravity of the movable part including the lens holder 3 is on the line where the AA plane and the BB plane intersect in FIG. When focus control is performed, the same current flows through the focus coils 9a and 9b, so that the driving forces generated in the focus coils 9a and 9b are the same, and the focus coils 9a and 9b are symmetrical with respect to the AA plane and the BB plane. Since it is arranged at the position, the resultant force of the driving force acts on the position of the center of gravity. Therefore, the lens holder 3 moves in the optical axis direction (Z direction) without tilting.

  The focus coil 9 a is wound so that its winding axis coincides with the central axis of the objective lens 4, and is arranged symmetrically with respect to the central axis, so that the heat generated by the focus coil 9 a is the central axis of the objective lens 4. And a uniform (symmetric) temperature distribution with respect to the central axis of the objective lens 4 is obtained. Therefore, characteristic deterioration (an increase in aberration, etc.) of the objective lens 4 due to the non-uniform temperature distribution is suppressed. Similarly, the focus coil 9b is wound so that its winding axis coincides with the central axis of the objective lens 5, and is arranged symmetrically with respect to the central axis. Therefore, the heat generated in the focus coil 9b is It is transmitted symmetrically with respect to the central axis of the objective lens 5, and a uniform (symmetric) temperature distribution is obtained with respect to the central axis of the objective lens 5. Therefore, characteristic deterioration (an increase in aberration, etc.) of the objective lens 5 due to the non-uniform temperature distribution is suppressed.

  As described above, the inner dimension 1bd (FIG. 7B) of the inner yoke 1b and the inner yoke 1d in the X direction is wider than the diameter 3ad of the aperture 3a that regulates the light beam incident on the objective lens 4. The light beam incident on the objective lens 4 is not hindered. Further, since the inner dimension 1bd is narrower than the outer diameter 4ad of the objective lens 4, the length of the side along the X direction of the focus coils 9a and 9b arranged outside the inner yokes 1b and 1d is shortened. Therefore, the focus coils 9a and 9b can be downsized, and the movable portion can be downsized and lightened. As a result, the focus driving force and the tracking driving force can be improved. In addition, since the length of the side (side along the X direction) that does not contribute to driving of the focus coils 9a and 9b is shortened, the utilization efficiency of the focus coils 9a and 9b can be improved.

  Here, the objective lens is used when information is recorded or reproduced on an optical disc having a large amount of surface deflection, when the optical disc is held in an incorrect state, or when a large impact is applied to the objective lens driving device. The focus control of 4 and 5 may not operate normally, and the lens holder 3 may approach a position very close to the optical disc.

  Even in such a case, in the present embodiment, as shown in FIG. 2B, the uppermost surfaces of the buffer members 12a and 12b are located higher than the uppermost surfaces of the objective lenses 4 and 5, so 5 does not contact the optical disc, and the objective lens is not damaged. The buffer members 12a and 12b are made of silicon rubber, and it has been experimentally found that the optical disk is not damaged even after 5000 collisions. Further, it has been experimentally clarified that the amount of wear of the buffer members 12a and 12b itself due to the collision is several tens of μm or less after 5000 collisions. Therefore, for example, if the uppermost surfaces of the buffer members 12a and 12b are made about 100 μm higher than the uppermost surfaces of the objective lenses 4 and 5, the objective lenses 4 and 5 can be prevented from directly colliding with the optical disk due to wear of the buffer material. Can do.

Next, tilt control will be described.
In the tilt control, the relative tilt of the objective lens 4 or the objective lens 5 with respect to the optical disk is detected by means (not shown) provided in the optical head device. Different currents are supplied to the focus coils 9a and 9b through the wires 6b and 6c and the wires 6e and 6f according to the detected inclination amount. Due to the mutual electromagnetic action between the current flowing through the focus coils 9a and 9b and the magnetic field generated by the magnets 11a and 11b, a driving force in the optical axis direction (Z direction) is generated in the focus coils 9a and 9b. The magnitude of the generated driving force is different, and therefore the amount of movement in the optical axis direction (Z direction) is different. In accordance with the difference in the amount of movement, the tilt of the lens holder 3 about the X-direction axis changes, and tilt control is performed. Note that the focus control and the tilt control may be performed simultaneously. In this case, the focus coils 9a and 9b are energized by adding a current necessary for the focus control and a current necessary for the tilt control.

  Also in the tilt control described above, the focus coils 9a and 9b are arranged symmetrically with respect to the central axes of the objective lenses 4 and 5, respectively. Degradation of the characteristics of the lenses 4 and 5 (increased aberration, etc.) is suppressed.

Next, tracking control will be described.
In tracking control, a tracking direction deviation (tracking deviation amount) of a focused spot on an optical disc with respect to a desired track is detected by a tracking sensor using a known differential push-pull method provided in the optical head device. A current corresponding to the detected tracking deviation amount is passed through the tracking coils 10a to 10f via the wires 6a and 6d. Due to the mutual electromagnetic action between the current flowing through the tracking coils 10a to 10f and the magnetic fields of the magnets 11a and 11b, a driving force in the Y direction is generated in the tracking coils 10a to 10f. Thereby, the lens holder 3 moves in the tracking direction orthogonal to the optical axis of the objective lens 4 or the objective lens 5, and tracking control is performed.

  In the tracking coils 10a to 10f, current flows through the tracking coils 10a, 10c, and 10e in the same direction, and current flows through the tracking coils 10b, 10d, and 10f in the opposite direction to the coils 10a, 10c, and 10e. Since they are connected in series, a driving force in the same direction is generated in all the tracking coils 10a to 10f.

  In the objective lens driving device according to Embodiment 1 of the present invention, since the tracking coils 10a to 10f are connected in series, the same current flows through each coil when energized. Furthermore, since the tracking coils 10a to 10f are wound so as to have the same resistance value, the amount of heat generated in each coil is the same. Furthermore, the tracking coils 10a, 10b, 10d, and 10e provided close to the objective lens 4 are symmetrical with respect to a plane (AA plane parallel to the YZ plane) that passes through the central axis of the objective lens 4 and is perpendicular to the track. In addition, the heat generated in these tracking coils 10a, 10b, 10d, and 10e is arranged at a symmetrical position with respect to a plane passing through the central axis of the objective lens 4 and parallel to the track (CC plane parallel to the XZ plane). Are transmitted symmetrically with respect to the central axis of the objective lens 4. On the other hand, since the distance from the objective lens 4 to the tracking coils 10c, 10f is long, the amount of heat transferred from the tracking coils 10c, 10f to the objective lens 4 is the amount of heat transferred from the tracking coils 10a, 10b, 10d, 10e. Small enough compared to Therefore, nonuniformity of the temperature distribution of the objective lens 4 due to the heat generated by the tracking coils 10a to 10f hardly occurs, and characteristic deterioration such as an increase in aberrations is suppressed.

  Similarly, tracking coils 10b, 10c, 10e, and 10f provided close to the objective lens 5 are symmetrical with respect to a plane (AA plane parallel to the YZ plane) passing through the central axis of the objective lens 5 and perpendicular to the track. In addition, since they are arranged symmetrically with respect to a plane passing through the central axis of the objective lens 5 and parallel to the track (DD plane parallel to the XZ plane), the heat generated by these tracking coils 10b, 10c, 10e, 10f Is transmitted symmetrically with respect to the central axis of the objective lens 5. On the other hand, since the distance from the objective lens 5 to the tracking coils 10a, 10d is long, the amount of heat transferred from the tracking coils 10a, 10d to the objective lens 5 is the amount of heat transferred from the tracking coils 10b, 10c, 10e, 10f. Small enough compared to Therefore, nonuniformity of the temperature distribution of the objective lens 5 due to the current flowing through the tracking coils 10a to 10f hardly occurs, and characteristic deterioration such as an increase in aberrations is suppressed.

  The position of the center of gravity of the movable part including the lens holder 3 is on the line where the AA plane and the BB plane intersect in FIG. In the tracking control, the resultant force of the driving force of the tracking coils 10a, 10c, 10d, and 10f acts on the position of the center of gravity. In addition, the resultant force of the driving force of the tracking coils 10b and 10e also acts on the position of the center of gravity. Accordingly, the lens holder 3 moves in the tracking direction without tilting.

  The movable part including the lens holder 3 is elastically supported by six wires 6a to 6f so as to be movable in the rotation direction with the Z direction, the Y direction, and the X direction as rotation axes. For this reason, when the energization to the focus coils 9a and 9b is released, the movement reference positions in the focus direction and the tilt direction are restored by the elastic force (restoring force) of the wires 6a to 6f. When the energization of the tracking coils 10a to 10f is released, the movement reference position in the tracking direction is restored by the elastic force of the wires 6a to 6f. Furthermore, since the vicinity of the base of the wires 6a to 6f is held by a gel-like damper agent, good focus control characteristics, tracking control characteristics, and tilt control characteristics can be obtained by the vibration damping effect on the movable part including the lens holder 3. In addition, vibration transmission from the outside to the movable part including the lens holder 3 is reduced.

  In the first embodiment, the configuration in which the tilt control is performed by causing the currents of different magnitudes to flow through the focus coils 9a and 9b has been described. However, the focus coil 9a and 9b may be located below (−Z side) or above the focus coils 9a and 9b. Even if two tilt coils having a winding axis coaxial with the central axes of the objective lenses 4 and 5 are further provided on the (+ Z side), and the tilt control is performed by supplying a current corresponding to the tilt amount to each tilt coil. Well, the same effect can be obtained. In this case, both the focus coil and the tilt coil are connected in series, and both ends are electrically connected to the wire and fixed.

  In the first embodiment, the focus coils 9a and 9b are configured in a rectangular shape having a winding axis in the Z direction, but may be configured in a circular shape having a winding axis in the Z direction. With this configuration, the amount of heat generated during energization is axially symmetric with respect to the central axes of the objective lenses 4 and 5, so that the temperature distribution of the objective lenses 4 and 5 can be made uniform and characteristics such as an increase in aberrations can be obtained. Deterioration can be further suppressed.

  Further, if a resin having high thermal conductivity is used as the material of the lens holder 3, the heat conduction amount is likely to be uniform regardless of the direction, so that the temperature distribution of the objective lenses 4 and 5 can be made more uniform.

  In the first embodiment, the focus coil 9a, 9b, the tracking coils 10a to 10f and the six wires 6a to 6f are used to perform the focus control, tracking control, and tilt control. Alternatively, the focus control and tracking control may be performed using a focus coil, a tracking coil, and four wires.

  As described above, according to the objective lens driving device in Embodiment 1 of the present invention, the focus coils 9a and 9b and the tracking coils 10a to 10f are arranged as described above (FIG. 6A, ( B)), heat generated in the focus coils 9a and 9b and the tracking coils 10a to 10f can be transmitted symmetrically with respect to the central axes of the objective lenses 4 and 5 with an inexpensive and simple configuration. Thereby, the temperature distribution of the objective lenses 4 and 5 can be made uniform, and characteristic deterioration such as an increase in aberration can be suppressed.

  In addition, since the driving force can be applied to the position of the center of gravity of the movable portion composed of the lens holder 3 and each component mounted thereon, the focus control and tracking control can be performed in a stable state.

  Since the tracking coils 10a to 10f are connected in series, the same current flows through the tracking coils 10a to 10f when energized. Furthermore, since the resistance values of the tracking coils 10a to 10f are wound to be the same, the amount of heat generated in each of the tracking coils 10a to 10f is the same, and heat is transmitted to the objective lenses 4 and 5 at substantially the same rate. Is done. Therefore, nonuniformity of the temperature distribution of the objective lens due to the heat generated in each tracking coil hardly occurs, and an increase in aberrations in the objective lenses 4 and 5 is suppressed.

  Further, the tracking coils 10a to 10e have currents flowing in the same direction, and the tracking coils 10b, 10d, and 10f have currents flowing in directions opposite to the tracking coils 10a, 10c, and 10e. Since 10f is connected, an electromagnetic force in the same direction is generated in all the tracking coils 10a to 10f, and a tracking driving force can be obtained efficiently. Therefore, the movable part which consists of the lens holder 3 and each component mounted in it can be driven to a tracking direction with little power consumption.

  Further, since the inner dimension 1bd between the inner yoke 1b and the inner yoke 1d is wider than the diameter 3ad of the aperture 3a of the lens holder 3 and narrower than the outer diameter 4ad of the objective lens 4, the incident light beam to the objective lens 4 is not blocked. And the length of the side along the X direction of focus coil 9a, 9b arrange | positioned on the outer side of inner yoke 1b, 1d can be shortened. Therefore, the focus coils 9a and 9b can be reduced in size, the movable part can be reduced in size and weight, and the movable part can be driven in the focus direction and the tracking direction with less power consumption. In addition, since the use efficiency of the focus coils 9a and 9b is improved by shortening the length of the side (side along the X direction) that does not contribute to the drive of the focus coils 9a and 9b, the power consumption can be reduced. It is possible to drive the movable part and contribute to further miniaturization and weight reduction of the objective lens driving device.

  Finally, a configuration example of an optical head device equipped with the objective lens driving device according to Embodiment 1 of the present invention will be described with reference to FIG. As shown in FIG. 8, the optical disc apparatus has a turntable 22 on which the optical disc 21 is placed, a spindle motor 23 that rotates the turntable 22, and an optical base 24. The optical base 24 includes the above-described objective lens driving device (indicated here by reference numeral 20) for driving the two objective lenses 4 and 5, a plurality of light sources (not shown) such as a semiconductor laser, and reflection from the optical disk. A light receiving element for receiving light is mounted. The optical base 24 is guided in the radial direction of the optical disc 21 by guide shafts 26a and 26b, and moves in the radial direction of the optical disc 21 by a mechanism (not shown). An optical head device is configured by the objective lenses 4 and 5, the objective lens driving device 20, the light source, the light receiving element, and the like mounted on the optical base 24.

  By mounting the above-described objective lens driving device in the present embodiment on the optical head device, the temperature distribution of the objective lenses 4 and 5 is made uniform (that is, symmetrical with respect to the central axis of the lens), and aberrations are deteriorated. Therefore, good recording / reproducing performance in the optical head device can be obtained with an inexpensive and simple configuration.

  1 Base, 1b, 1c, 1d, 1e Inner yoke, 1f, 1g Magnet yoke, 2 Fixed holder, 3 Lens holder, 3a Aperture, 31, 32, 33, 34 Side wall, 4 Objective lens, 5 Objective lens, 6a, 6b , 6c, 6d, 6e, 6f wire, 8 substrate, 9a, 9b focus coil, 10a, 10b, 10c, 10d, 10e, 10f tracking coil, 11a, 11b magnet, 12a, 12b buffer member.

Claims (11)

A lens holder for holding two objective lenses so as to face the optical disc;
A plurality of focus coils and a plurality of tracking coils attached to the lens holder;
Support means for movably supporting the lens holder;
A base for supporting the support means;
A plurality of magnets disposed on the base so as to face the plurality of focus coils and the plurality of tracking coils;
A plurality of focus coils are positioned around each objective lens and symmetrical with respect to a plane passing through the central axis of the objective lens and perpendicular to the track, and symmetrical with respect to a plane passing through the central axis of the objective lens and parallel to the track Placed in
A plurality of tracking coils are positioned around each objective lens and symmetrical with respect to a plane passing through the central axis of the objective lens and perpendicular to the track, and symmetrical with respect to a plane passing through the central axis of the objective lens and parallel to the track An objective lens driving device characterized by being arranged in   2. The objective lens driving device according to claim 1, wherein the plurality of focus coils are two focus coils wound so as to have a winding axis substantially coaxial with a central axis of each objective lens.   3. The plurality of tracking coils are arranged in a set of three locations respectively in the middle and on both sides of the two objective lenses in the arrangement direction of the two objective lenses. The objective-lens drive device of description. Each of the plurality of magnets is magnetized so that different magnetic poles are adjacent to each other in a direction perpendicular to both the optical axis direction and the track,
The plurality of tracking coils include
A set of tracking coils each having two sides extending in the direction of the optical axis, the two sides being arranged to face different magnetic poles of each magnet;
2. Two sets of tracking coils each having two sides extending in the optical axis direction, and having only one side opposed to one of the different magnetic poles of each magnet. 4. The objective lens driving device according to any one of items 1 to 3.   Each of the plurality of focus coils has two sides extending in a direction perpendicular to both the optical axis direction and the track, and the two sides face one of the different magnetic poles of each magnet. The objective lens driving device according to claim 4.   6. The objective lens driving apparatus according to claim 1, wherein the plurality of tracking coils have the same resistance value and are connected in series.   The plurality of tracking coils are connected so that currents flow in different directions to the tracking coils facing the track direction, and currents flow in different directions to the tracking coils arranged in a direction perpendicular to the track. The objective lens driving device according to claim 1, wherein the objective lens driving device is provided. The base includes an inner yoke extending in the optical axis direction of the two objective lenses,
The objective lens driving device according to claim 1, wherein an inner dimension of the inner yoke is narrower than an outer diameter dimension of the objective lens.   9. The shock absorber according to claim 1, wherein a buffer member that protrudes further toward the optical disc than the two objective lenses is provided on a surface of the lens holder facing the optical disc. The objective-lens drive device of description.   The supporting means includes a plurality of wires each having one end attached to the lens holder, a substrate having each other end attached to the plurality of wires, and a fixed holder attached to the base and holding the substrate. The objective lens driving device according to claim 1, wherein the objective lens driving device is provided. An optical head device for recording or reproducing information on an optical disc,
An optical head device comprising the objective lens driving device according to claim 1.

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