JP2008112557A - Objective lens driving device, optical pickup device, and optical disk drive - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an objective lens driving device which destabilize the control on the objective lens driving device such as the rolling resonance or the pitching resonance caused by the destroyed weight balance of the objective lens driving device, at low cost without requiring additional components such as a balancing member or the like. <P>SOLUTION: The objective lens driving device used for an optical pickup device is provided. The objective lens driving device is provided with first and second objective lenses and a lens holder for supporting the first and second objective lenses. The lens holder has a first through-hole for passage of first laser beam and a second through-hole for passage of second laser beam. Where a plane defined by a central axis of the first objective lens and a central axis of the second objective lens is a central plane, a plane perpendicular to the central plane and including the central axis of the first objective lens is a first plane, and a plane perpendicular to the central plane and including the central axis of the second objective lens is a second plane, the first through-hole is asymmetrical with respect to the first plane and/or the second through-hole is asymmetrical with respect to the second plane. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an optical disc apparatus for writing and reading data to and from a plurality of types of optical discs having different recording densities, an optical pickup device used in the optical disc device, and an objective lens driving device used in the optical pickup device About. In particular, the present invention relates to an objective lens driving device used in an optical pickup device equipped with a plurality of objective lenses.

  Currently, CDs (Compact Discs) and DVDs (Digital Versatile Discs) are widely used as disc-shaped recording media (optical discs) for writing and / or reading data using light. In addition, in recent years, optical discs with high recording density such as BD (Blu-ray Disc) have been developed and proposed. The wavelength of the laser beam used is around 780 nm for CD, around 660 nm for DVD, and around 405 nm for BD.

  There is a demand for recording and reproducing a plurality of types of optical disks using laser beams of different wavelengths with a single optical pickup device. As an example for realizing this, there has been proposed an optical pickup device of a type in which different objective lenses are prepared for CD / DVD and BD, for example, and mounted on one objective lens driving device.

  FIG. 10A shows an example of an objective lens driving device of a conventional optical pickup device equipped with two types of objective lenses. For example, Patent Document 1 discloses such an objective lens driving device.

  The lens holder 300 is provided with a first objective lens installation port 301 and a second objective lens installation port 302, which are formed so that a first objective lens and a second objective lens (not shown) can be mounted, respectively. Yes.

  FIG. 10B shows a first through hole 303 and a second through hole 304 having a circular cross section penetrating the lens holder 300. The first objective lens installation port 301 and the second objective lens installation port 302 described above are open ends of the first through hole 303 and the second through hole 304, respectively. The diameter of the objective lens installation port and the diameter of the through hole do not need to match.

  The first through hole 303 and the second through hole 304 serve as an optical path for laser light incident from a light source (not shown) side provided below the focus direction. The laser light that has passed through the objective lens is focused on an optical disk (not shown) arranged on the upper side in the focus direction, and the reflected light returns in the opposite direction to the detector (not shown) provided on the light source side.

  The lens holder 300 is elastically supported by a spring (not shown) and includes a magnetic circuit for independently driving in a focus direction perpendicular to the recording surface of the optical disc and a tracking direction that is a radial direction of the optical disc.

In recent years, an increase in thrust has been demanded due to an increase in needs for an improvement in recording speed / reproduction speed, and high sensitivity has been demanded by reducing the weight of a movable part including the lens holder 300. At the same time, in order to cope with an increase in the gain of the control system, a high rigidity is required to increase the resonance frequency in the high range of the movable part. That is, the objective lens driving device is required to have contradictory characteristics such as light weight and high rigidity.
JP 2003-281758 A

  By the way, for example, in an optical pickup device equipped with two types of objective lenses, the weights of the two lenses are often different. From the viewpoint of cost and weight reduction, plastic is desirable as a lens material, but for laser light having a wavelength of 405 nm, glass may be selected from the viewpoint of light resistance of the material. On the other hand, for example, if plastic is selected as the lens material of an objective lens used for a DVD, the weight of the glass objective lens is, for example, three times or more than the weight of the plastic objective lens due to the difference in specific gravity between glass and plastic. It can be heavy.

  When such lenses having different weights are mounted on the lens holder 300, the weight balance is lost and the center of gravity is shifted from the center of the movable part. If the entire lens holder 300 is large and the arrangement of the individual lenses can be optimized, the center of gravity can be set at the center of the lens holder so as to coincide with the center of thrust generated by the magnetic circuit.

  However, it is desirable that the lens holder be as small as possible because of the demand for light weight and high rigidity accompanying the recent increase in speed. Furthermore, it is required that the two lenses be arranged as close as possible, and the degree of freedom of arrangement has become very small. Therefore, it is difficult to optimize the weight balance by lens arrangement.

  If the weight balance is lost and the center of gravity is shifted from the center of the movable part (thrust center), when a driving force is applied to the movable part by the magnetic circuit, the rotational moment is determined from the difference between the center of thrust and the position of the center of gravity. Has occurred, causing unnecessary resonance and unstable control.

  For example, in FIG. 10A, the objective lenses are arranged side by side in the tracking direction, and the weight balance in the tracking direction is lost. Therefore, when the entire movable part is driven in the focus direction, the movable part rotates around the tangential direction. To generate rolling resonance. Unlike the conventional example, when the objective lenses are arranged side by side in the tangential direction, when the entire movable part is driven in the focus direction, pitching resonance is generated in which the movable part rotates around the tracking direction. To do.

  The object of the present invention is to solve the control instabilities such as rolling resonance and pitching resonance caused by the unbalance of the weight of the objective lens driving device at low cost without adding parts such as a balancing member. Another object of the present invention is to provide an objective lens driving device capable of minimizing the influence on sensitivity reduction and rigidity reduction.

  The objective lens driving device according to the present invention is used in an optical pickup device. The objective lens driving device includes a first objective lens that condenses the first laser light, a second objective lens that condenses the second laser light, and a lens that supports the first objective lens and the second objective lens. A holder, and the lens holder is provided with a first through hole through which the first laser light passes and a second through hole through which the second laser light passes. A plane formed by a central axis and the central axis of the second objective lens is defined as a central plane, a plane perpendicular to the central plane and including the central axis of the first objective lens is defined as a first plane, and is perpendicular to the central plane. When the plane including the central axis of the second objective lens is the second plane, the first through hole is asymmetric with respect to the first plane, and / or the second through hole is the first plane. Asymmetric with respect to two planes It is.

  The first objective lens is heavier than the second objective lens, and the centroid of the cross section of the first through hole by a plane perpendicular to the central axis of the first objective lens is larger than the central axis of the first objective lens The lens holder may be located outside the lens holder.

  The second objective lens is lighter in weight than the first objective lens, and the centroid of the cross section of the second through-hole by a plane perpendicular to the central axis of the second objective lens is smaller than the central axis of the second objective lens The lens holder may be located inside the lens holder.

  A cross section of the first through hole by a plane perpendicular to the central axis of the first objective lens is substantially rectangular, and portions corresponding to the four corners of the substantially rectangular shape are each formed in an arc shape. The radius of two arc-shaped parts located outside the lens holder among the arc-shaped parts may be smaller than the radius of the other two arc-shaped parts located inside the lens holder.

  The cross section of the second through-hole by a plane perpendicular to the central axis of the second objective lens is substantially rectangular, and the portions corresponding to the four corners of the substantially rectangular shape are each formed in an arc shape. The radius of two arc-shaped parts located inside the lens holder among the arc-shaped parts may be smaller than the radius of the other two arc-shaped parts located outside the lens holder.

  The first objective lens is heavier than the second objective lens, and the centroid of the cross section of the first through hole by the central plane is located outside the lens holder with respect to the central axis of the first objective lens. It may be.

  The first through hole may increase the distance from the central axis of the first objective lens in at least one place according to the distance from the first objective lens.

  In the first through hole, the distance from the central axis of the first objective lens may change continuously or stepwise depending on the distance from the first objective lens.

  The weight of the first objective lens and the weight of the second objective lens may be different.

  One of the first objective lens and the second objective lens may be a glass lens, and the other may be a plastic lens.

  The first objective lens and the second objective lens may be formed of the same material.

  An optical pickup device according to the present invention includes the above-described objective lens driving device, a first laser light source that outputs the first laser light, and a second laser light source that outputs the second laser light, and the first laser. The light and the second laser light are condensed on information recording surfaces of different types of optical discs.

  An optical disc apparatus according to the present invention includes the above-described optical pickup device, a motor for rotationally driving the optical disc, and a control unit that controls the optical pickup device and the motor.

  According to the present invention, the cross-sectional shapes of the first through hole and the second through hole are asymmetric with respect to the first plane and the second plane that are perpendicular to the central plane and include the central axis of each objective lens. Therefore, the weight balance in the direction in which the objective lenses are arranged can be changed only by changing the hole shape, and the weight imbalance due to the difference in the diameter and weight of the objective lenses can be improved.

  According to the present invention, the cross-sectional shape of the first through hole provided under the heavy first objective lens is arranged such that its centroid is outside the lens holder with respect to the central axis of the first objective lens. Since the shape is positioned in the direction, the weight of the part near the outside of the lens holder away from the center of the movable part is further reduced, and a large center of gravity movement effect can be obtained with a small amount of reduction, so the weight balance While improving, the deterioration of the rigidity of the entire movable part can be minimized.

  Further, according to the present invention, the cross section of the first through hole has a substantially quadrangular shape having arc portions at four corners, and two of the arc portions in the outer direction of the lens holder have a smaller radius than two in the inner direction. Therefore, the weight balance can be improved only by the radius of the arc portion while keeping the cross-sectional shape substantially square, and the deterioration of the rigidity of the entire movable portion can be minimized.

  Hereinafter, an embodiment of an objective lens driving device according to the present invention will be described with reference to the accompanying drawings.

(Embodiment 1)
FIG. 1 is a perspective view of the objective lens driving device 100 according to the present embodiment. The objective lens driving device 100 includes a first objective lens 1, a second objective lens 2, a lens holder 3, a terminal plate 4, a wire 5, a suspension holder 6, a coil group 7, and a base 8. And a yoke 9 and a magnet 10.

  The 1st objective lens 1 and the 2nd objective lens 2 are arrange | positioned facing the optical disk (not shown) which is a disk shaped recording medium. Information is recorded and reproduced by irradiating the recording layer of the optical disc with laser light.

  The first objective lens 1 is an optical disk (for example, BD) objective lens that uses laser light having a wavelength of about 405 nm. The first objective lens 1 is manufactured using glass having excellent light resistance, and is configured to be able to form a very small spot with a high numerical aperture (NA).

  The second objective lens 2 is an objective lens used for both a CD using a laser beam having a wavelength of about 780 nm and a DVD having a wavelength of about 660 nm. The second objective lens 2 is manufactured using plastic and is available at a relatively low cost. The weight of the second objective lens 2 is, for example, about one third of that of the first objective lens made of glass.

  The lens holder 3 is a member that fixes and supports the first objective lens 1 and the second objective lens 2. The lens holder 3 is manufactured using a lightweight and highly rigid fiber-containing resin. A part of the structure of the lens holder 3 is removed in order to realize weight reduction, and a large number of ribs are provided in order to realize structural high rigidity. As a result, the shape of the lens holder 3 is optimized.

  The objective lens driving device 100 is configured to be movable in the tracking direction, which is the radial direction of the optical disc, as a whole by a transfer device (not shown).

  In the lens holder 3, the first objective lens 1 and the second objective lens 2 are arranged side by side in the tangential direction. The tangential direction is a direction orthogonal to both the tracking direction and the focus direction. The lens holder 3 has a structure that does not easily come into contact with other members such as a spindle motor 211 (FIG. 9) and an optical disk cartridge (not shown), which will be described later, when the objective lens driving device 100 is transferred to the inner or outer periphery of the optical disk. Is formed.

  The second objective lens 2 is bonded to the lens holder 3 via a swing holder 3a. The swing holder 3a and the lens holder 3 are in contact via a spherical sliding surface (not shown), and the relative inclination between the lens holder 3 and the second objective lens 2 can be freely set within a predetermined range. It is configured so that it can be set, and is fixed by adhesion or the like after adjustment.

  The terminal plate 4 is a small substrate that is fixed to both ends of the lens holder 3 in the tracking direction. The terminal plate 4 is fixed to the lens holder 3 using an adhesive or the like, and six wires 5 that are elastic support members are soldered. . The other end of the wire 5 is soldered to a substrate (not shown) provided on the suspension holder 6. Although only three wires 5 are shown in FIG. 1, the remaining three wires are provided at positions symmetrical to the lens center.

  The wire 5 also functions as a conductive member for the coil group 7 provided in the lens holder 3. The wire 5 is installed with its longitudinal direction along the tangential direction, and elastically supports the lens holder 3 including the first objective lens 1 and the second objective lens 2 so as to be movable in the focus direction and the tracking direction. FIG. 1 shows a movable part 101 sandwiched between magnets 10. Details of the movable unit 101 will be described later.

  The suspension holder 6 has a function of fixing and supporting one end of the wire 5 and a pocket for storing a gel-like vibration suppression member in the vicinity of the fixed support portion of the wire 5 and suppressing resonance of the wire 5. Yes.

  The base 8 is formed integrally with the yoke 9 and is used for fixing the suspension holder 6.

  The yoke 9 is a part for bonding and fixing a magnet, and is formed of a material having high magnetic permeability.

  The magnet 10 is bonded and fixed to the yoke 9 so as to sandwich both end surfaces of the lens holder 3 in the tangential direction. The magnet 10 is disposed opposite to the coil group 7 with a slight gap. The magnet 10 constitutes a part of a magnetic circuit, and thrust is generated by the electromagnetic force generated by energizing the coil group 7 and the magnet 10. Since the coil group 7 and the magnet 10 are arranged symmetrically, they have a thrust acting point at the center of the shape of the lens holder. Here, “symmetry” means that the two magnets 10 are symmetrical with respect to a plane existing between the two magnets 10 (the normal is the tangential direction), and that the two magnets 10 are divided in the tangential direction. This means that the two magnets 10 are symmetric with respect to the plane (the normal line is the tracking direction).

  FIG. 2A is a perspective view of the movable part 101 of the objective lens driving device according to the present embodiment, and FIG. 2B is a plan view of the movable part 101.

  2A and 2B, the movable part 101 includes a first objective lens 1, a second objective lens 2, a lens holder 3, a terminal plate 4, and a coil group 7. The movable portion 101 is elastically supported by the wire 5 (FIG. 1), and can be freely moved by thrust in the focus direction and tracking direction generated by the magnetic circuit.

  The coil group 7 includes four focus coils 7a and two tracking coils 7b. FIG. 2A shows two focus coils 7 a and one tracking coil 7 b provided on one side of the lens holder 3. The same applies to the other side.

  The tracking coil 7b is disposed near the center of the end face of the lens holder 3 in the tangential direction. Two focus coils 7a are arranged on both sides of the tracking coil 7b. The tracking coil 7b is longer in the focus direction than the focus coil 7a.

  When the two tracking coils 7b are energized in the magnetic field generated by the magnet 10 (FIG. 1), a thrust in the tracking direction is generated. Further, when energizing the four focus coils 7a, thrust in the focus direction is generated. The arrangement of the coil group 7 when viewed from the focus direction is such that the central plane 20 (tracking) formed by the central axis (optical axis) of the first objective lens 1 and the central axis (optical axis) of the second objective lens 2 is arranged. The second central plane 21 that is equidistant from the end face of the lens holder 3 in the tangential direction. Therefore, the point of action of thrust (thrust center 22) coincides with the shape center of the lens holder 3 where the center plane 20 and the second center plane 21 intersect in both the focus direction and the tracking direction. The central axis (optical axis) of the objective lens is a straight line connecting the centers of curvature of one surface on which light is incident and the other surface.

  On the other hand, the center of mass of the movable part 101, that is, the center of gravity may not coincide with the center of shape.

  Focusing on the weight, the movable portion 101 is configured substantially symmetrically with respect to the central plane 20. However, the movable part 101 is not symmetrical with respect to the second central plane 21. This is because the mass distribution is not uniform due to the difference in the shape and weight of the first objective lens 1 and the second objective lens 2. As a result, the center of gravity of the movable part 101 and the shape center of the movable part may deviate.

  For example, it is assumed that the first objective lens 1 is made of glass and the second objective lens 2 is made of plastic. Since the weight of the first objective lens 1 is larger than the weight of the second objective lens 2, the center of gravity of the entire movable portion 101 is shifted from the center of the shape in the tangential direction. As mentioned in the section of the background art, when the movable part 101 is driven in the focus direction while the deviation between the center of gravity and the thrust center 22 remains, pitching resonance in which the entire movable part 101 rotates around the axis extending in the tracking direction occurs. Occurs, resulting in control instability.

  The lens that eliminates the unnecessary resonance such as pitching resonance by eliminating the deviation between the center of gravity and the thrust center 22 when incorporated in the movable part 101 by adjusting the internal structure without changing the outer shape of the lens holder 3 below. The configuration of the holder 3 will be described.

  3A is a perspective view of the lens holder 3 according to the present embodiment, FIG. 3B is a plan view of the lens holder 3 according to the present embodiment, and FIG. 3C is a front view of the lens holder 3 according to the present embodiment.

  Reference is first made to FIG. 3A. The lens holder 3 is provided with a first objective lens installation port 25 and a second objective lens installation port 26. The first objective lens 1 is installed in the first objective lens installation port 25 and fixed with an adhesive or the like. The second objective lens 2 is installed in the second objective lens installation port 26. The second objective lens 2 is provided on the swing holder 3a and fixed with an adhesive or the like.

  As described above, the first objective lens installation port 25 is located at the end of the first through hole 30. When entering the inside of the lens holder 3 from the first objective lens installation port 25, the diameter of the first through hole 30 is slightly reduced. This portion is referred to as a first aperture 27. The second objective lens installation port 26 is located at the end of the second through hole 31. When entering the inside of the lens holder 3 from the second objective lens installation port 26, the diameter of the second through hole 31 is slightly increased. This part is called a second aperture 28. The shapes of the first through hole 30 and the second through hole 31 will be described in detail with reference to FIGS. 4A and 4B.

  Next, in order to describe the cross-sectional shape of the lens holder 3, a plane is defined with reference to FIGS. 3B and 3C. First, a plane perpendicular to the central plane 20 and including the central axis of the first objective lens 1 is referred to as a first plane 32, and is a plane perpendicular to the central plane 20 and including the central axis of the second objective lens 2. Is referred to as a second plane 33. Further, a plane perpendicular to all of the central plane 20, the first plane 32, and the second plane 33 shown in FIG. 3C is referred to as a third plane 34.

  4A is a cross-sectional view of the lens holder 3 according to the present embodiment taken along the central plane 20, and FIG. 4B is a cross-sectional view of the lens holder 3 taken along the third plane 34.

  4A, the first through hole 30 penetrates to the lower end surface in the focus direction of the lens holder 3, and the second through hole 31 penetrates to the lower end surface in the focus direction of the lens holder 3.

  The shape of the holes of the first through hole 30 and the second through hole 31 is optimum with unnecessary portions being reduced and ribs for maintaining strength being provided so as to satisfy both weight reduction and high rigidity. It has become.

  If the hole diameter is made extremely large to reduce the thickness around the hole, or the first through hole 30 and the second through hole 31 are connected to form a single hole, the weight of the movable portion is reduced. Can increase the sensitivity. However, on the other hand, the rigidity of the lens holder 3 is lowered and the resonance frequency in the high range is lowered, the control becomes unstable, and the lens holder 3 cannot be used for an objective lens driving device that requires a high speed. On the other hand, if the hole diameter is too small, the rigidity of the lens holder 3 can be increased. However, since the thickness around the hole increases, the weight increases, and the sensitivity decreases, it is impossible to realize a sensitivity that can cope with higher speed. Usually, the range of design solutions that satisfy both the requirements of light weight and high rigidity is not wide, and pinpoints are often specified.

  4A, the cross-sectional shape of the first through hole 30 and the second through hole 31 by the central plane 20 is such that the cross section in the tangential direction is substantially parallel to the focus direction. Therefore, the cross-sectional shapes of the first through hole 30 and the second through hole 31 shown in FIG. 4B are substantially the same regardless of the position in the focus direction.

  The cross-sectional shapes of the first through hole 30 and the second through hole 31 by the third plane 34 shown in FIG. 4B are symmetric with respect to the center plane 20, but the cross-sectional shape of the first through hole 30 is The first plane 32 is asymmetric.

  As described above, when the cross-sectional shape of the first through hole 30 is asymmetric only in a specific direction (only in the first plane 32 in the present embodiment), the thickness of the lens holder 3 around the first through hole 30 is increased. Is changed to change the weight distribution. This means that it becomes possible to change the weight balance only in that direction. That is, it is possible to adjust the weight balance of the lens holder 3 only by changing the hole cross-sectional shape.

  As shown in FIG. 4B, in the present embodiment, the cross-sectional shape of the first through hole 30 provided under the heavy first objective lens 1 (not shown) is substantially rectangular. Portions 41 to 44 corresponding to the four corners of the quadrangle are shaped in an arc shape. The radius of the arcuate portions 43 and 44 is smaller than the radius of the inner arcuate portions 41 and 42. When the radius is adjusted in this way, the cross-sectional centroid 45 is positioned outside the lens holder 3 with respect to the central axis of the first objective lens 1. This means that the structure on the outside of the lens holder 3 is further reduced as viewed from the central axis of the first objective lens 1. By increasing the thickness reduction amount of the outer part of the lens holder 3 structure away from the center of the movable part 101, the thickness reduction amount can be reduced compared with the case where the thickness around the cross section is uniformly reduced. An equivalent center-of-gravity movement effect can be obtained.

  According to the lens holder 3 of the present embodiment, since only the outer portion of the lens holder 3 structure is reduced, the center of gravity position of the entire movable portion 101 is temporarily set to the first penetration without reducing the thickness of the rib 35. The temporary center of gravity 50 when the cross-sectional shape of the hole 30 is symmetric can be moved to the center of gravity 51 that coincides with the center of thrust. Accordingly, it is possible to provide an objective lens driving device capable of preventing occurrence of unnecessary resonance such as pitching resonance and performing stable control.

  The rib 35 between the first through hole 30 and the second through hole 31 shown in FIG. 4A is provided at the center of the lens holder 3 and is indispensable for maintaining the rigidity of the entire structure. However, since the first objective lens 1 and the second objective lens 2 are disposed at extremely close positions in order to realize a reduction in size and weight, the rib 35 cannot be made too thick. It is not desirable to further reduce the thickness of the rib 35 because of the need to maintain the rigidity of the entire structure. Therefore, the above-described method according to the present embodiment is suitable.

  In the above description, the cross-sectional shape of the first through hole 30 is substantially rectangular, and the portions corresponding to the four corners are arcuate, and the radii of the arcuate portions 43 and 44 are set to the inner arcuate portions 41 and 42. It was supposed to be smaller than the radius. This configuration is derived as a result of various experiments conducted by the inventors.

  The inventors of the present application have paid attention to the fact that the performance of the lens holder 3 is greatly influenced by changing the radius of the arc-shaped portions 41 to 44. Then, the lens holder obtained by changing the magnitude | size of the radius of an arc-shaped part variously was evaluated quantitatively. The criteria for evaluation are the weight of the lens holder, the shift amount of the center of gravity, and the resonance frequency.

  FIG. 5A shows the relationship between the weight of each lens holder and the amount of deviation of the center of gravity when the lens holders A to D are created by changing the radii of the arcuate portions 41 to 44 in four ways. The weight indicates a difference when the weight W of the lens holder D is used as a reference. The left side of the horizontal axis represents that the weight is less than the weight W. On the other hand, the center-of-gravity shift indicates a shift amount from the center of thrust. The lower side of the vertical axis indicates that the amount of deviation from the center of thrust is small.

  The weight of the lens holder is preferably light, and the smaller the deviation of the center of gravity, the better. That is, in FIG. 5A, a lens holder that is plotted in the more left direction and in the lower direction is preferable. The most preferable lens holder is the lens holder A located at the lower left. The lens holder A has a small radius (R) on both the outside and the inside. Then, the lens holder B having a small radius only on the outside, the lens holder C having a small radius only on the inside, and the lens holder D are continued. In the lens holder D, the arc-shaped portions 41 to 44 are substantially absent, and the first objective lens installation port 25 is formed in a substantially circular shape.

  On the other hand, FIG. 5B shows the relationship between the resonance frequency of each lens holder and the center-of-gravity deviation when lens holders A to D in which the radii of arcuate portions 41 to 44 are changed in four ways are shown.

  In FIG. 5B, a lens holder that is plotted more rightward and more downwardly is preferred. First, considering the lens holder A that showed the best performance in FIG. 5A, the resonance frequency characteristic of the lens holder A is very low, showing the most unfavorable value. On the other hand, when examining the lens holder B, the resonance frequency is relatively high and the center of gravity deviation is relatively small. The performance of the lens holder C is clearly inferior in relation to the performance of the lens holder B. For the lens holder D, the resonance frequency characteristic is suitable, but on the other hand, the center-of-gravity shift amount is very large, indicating the most undesirable value.

  5A and 5B, it is understood that the lens holder B exhibits the most balanced performance in all of the weight of the lens holder, the shift amount of the center of gravity, and the resonance frequency. In response to this result, the present inventors have adopted the lens holder B described above as the lens holder 3 in which the radius (R) of the arc-shaped portion is small only on the outside.

  According to the present embodiment, the cross-sectional shape of the first through-hole 30 of the heavy first objective lens 1 is asymmetric only with respect to the first plane 32 and is close to the outside of the lens holder 3 from the center of the movable portion 101. By reducing the thickness of the part, a large center-of-gravity movement effect can be obtained with a small amount of thickness reduction. Therefore, it is possible to prevent the occurrence of unnecessary resonance by minimizing the decrease in rigidity of the movable portion 101 without reducing the thickness of the rib 35.

  Note that which configuration of the lens holder is preferable depends on the performance required of the lens holder. Therefore, any of the lens holders A to D described above can be employed depending on the required performance. For example, the position of the center of gravity 51 may be optimized by reducing the radius of only the arc-shaped portion located inside the lens holder, such as the lens holder C.

  If there is no significant difference in weight between the first objective lens 1 and the second objective lens 2, the position of the temporary center of gravity 50 is not necessarily in the direction of the first objective lens 1 when viewed from the second central plane 21. There may not be. In such a case, the through hole in the direction in which the temporary center of gravity 50 is located when viewed from the second center plane 21 may be asymmetrical, and the same effect can be obtained.

  Further, in the present embodiment, it is assumed that the temporary center of gravity 50 is located on the center plane 20 and that there is almost no weight imbalance in the tracking direction. However, when the temporary center of gravity 50 is not located on the central plane 20, the shape of the first through hole 30 and the shape of the second through hole 31 are asymmetric in the direction in which the temporary center of gravity 50 is located when viewed from the central plane 20. It is also good.

  For example, in FIG. 4B, when the temporary center of gravity 50 deviates from the thrust center 22 (not shown) not only in the tangential direction but also in the positive direction of the tracking direction (upward in the figure), the arc portion 41 is the arc portion 42. The radius may be made larger and the radius of the arc portion 43 may be made larger than that of the arc portion 44 so that all four arc portions have different radii. Accordingly, it is possible to provide an objective lens driving device that can prevent rolling resonance due to weight imbalance not only in the tangential direction but also in the tracking direction and that can be stably controlled.

  In the present embodiment, the first objective lens 1 and the second objective lens 2 are made of different materials (glass and plastic), but may be made of the same material. For example, when the first objective lens 1 for BD is also made of plastic, the manufacturing cost of the lens can be reduced and the weight can be reduced. However, the case where the weights of the objective lenses 1 and 2 are different due to the difference in the specifications of the objective lenses is sufficiently conceivable. Therefore, the configuration described in this embodiment can be suitable.

(Embodiment 2)
6A is a cross-sectional view of the lens holder 103 according to the present embodiment taken along the center plane 20, and FIG. 6B is a cross-sectional view taken along the third plane 34 of the lens holder 103 according to the present embodiment. Other components including the outer shape of the lens holder 103 are the same as those in the first embodiment, and a description thereof will be omitted. The lens holder 103 is incorporated in the objective lens driving device 100 instead of the lens holder 3 according to the first embodiment.

  A cross section taken along the central plane 20 (FIG. 6B) shown in FIG. 6A is a plane stretched by the tangential direction and the focus direction. Therefore, the cross-sectional shapes of the first through hole 30 and the second through hole 31 shown in FIG. 6B are substantially the same regardless of the position in the focus direction.

  Further, the cross-sectional shapes of the first through hole 30 and the second through hole 31 shown in FIG. 6B are symmetric with respect to the central plane 20. However, the first through hole 30 is asymmetric with respect to the first plane 32, and the cross-sectional shape of the second through hole 31 is also asymmetric with respect to the second plane 33. Thereby, even when the weight difference between the first objective lens 1 and the second objective lens 2 is larger than that in the example of the first embodiment and the degree of unbalance is larger, the center of gravity coincides with the center of thrust. Can be made.

  Specifically, the cross-sectional shape of the second through-hole 31 provided with the light second objective lens 2 is substantially rectangular, and portions 61 to 64 corresponding to the four corners are formed in an arc shape. In the arc-shaped portions 61 to 64, the radius of the arc portions 63 and 64) located outside is larger than the radius of the arc portions 61 and 62 located inside the lens holder 103.

  As a result, the second centroid 65 having a cross-sectional shape moves to the inside of the lens holder 103 from the center of the second objective lens 2, and a large thickness remains outside the lens holder as viewed from the center of the second objective lens 2. Will be. Compared with the case where the thickness around the cross section is uniformly increased by leaving a large thickness of the outer portion of the lens holder 103 that is away from the center of the movable portion 101, the center of gravity shift is equivalent with a small increase in thickness. An effect can be obtained.

  That is, the position of the center of gravity of the entire movable part 101 is changed from the temporary center of gravity 50 when the cross-sectional shape of the second through hole 31 is symmetric to the center of gravity 51 that coincides with the thrust center 22 by increasing the thickness. It can be moved with minimal degradation. Accordingly, it is possible to provide an objective lens driving device capable of preventing occurrence of unnecessary resonance such as pitching resonance and performing stable control.

  In addition, since only the radius of the arc portion of the corner is changed in the cross-sectional shape of the second through hole 31 that is substantially square, the position of the center of gravity 51 is optimized by changing the thickness only inside the substantially square. Is possible.

  According to the present embodiment, the cross-sectional shape of the second through-hole 31 of the light second objective lens 2 is asymmetric only with respect to the second plane 33, and is close to the outside of the lens holder 103 from the center of the movable portion 101. By increasing the thickness of the portion, a large center-of-gravity movement effect can be obtained with a small amount of increase in thickness, and the occurrence of unnecessary resonance can be prevented while minimizing thrust reduction.

(Embodiment 3)
7A is a cross-sectional view of the lens holder 113 according to the present embodiment taken along the center plane 20, and FIG. 7B is a cross-sectional view taken along the third plane 34 of the lens holder 113 according to the present embodiment. Other components including the outer shape of the lens holder 113 are the same as those in the first embodiment, and a description thereof will be omitted. The lens holder 113 is incorporated in the objective lens driving device 100 instead of the lens holder 3 according to the first embodiment.

  As shown in FIG. 7A, the cross section of the first through hole 30 by the central plane 20 (FIG. 7B) is not parallel to the focus direction but is tapered. The distance between the peripheral wall of the first through hole 30 and the central axis of the first objective lens 1 changes so as to increase as the distance from the first objective lens installation port 25 increases. In other words, the thickness of the structure portion of the lens holder 113 sandwiched between the first through hole 30 and the outer peripheral surface of the lens holder 113 changes so as to decrease as the distance from the first objective lens installation port 25 increases. ing. Further, since the first through hole 30 is formed in a tapered shape, the first through hole 30 is asymmetric with respect to the first plane 32.

  In the lens holder 113, the third centroid 66, which is the centroid of the cross-sectional shape of the first through-hole 30 by the center plane 20, is outside the lens holder 113 from the center axis of the heavy first objective lens 1. As a result, the thickness on the outside of the lens holder is greatly reduced as viewed from the central axis of the first objective lens 1. By increasing the thickness reduction amount of the outer portion of the lens holder 113 that is away from the center of the movable portion 101, the thickness reduction amount is equal to that of a case where the thickness around the cross section is uniformly reduced. The center of gravity movement effect can be obtained.

  That is, the position of the center of gravity of the entire movable part 101 is changed from the temporary center of gravity 50 when the cross-sectional shape of the first through hole 30 is symmetric to the first plane 32 to the center of gravity 51 that coincides with the thrust center 22. It can be moved while minimizing the decrease in rigidity due to the decrease in thickness. Accordingly, it is possible to provide an objective lens driving device capable of preventing occurrence of unnecessary resonance such as pitching resonance and performing stable control.

  As shown in FIG. 7B, in the present embodiment, the first through hole 30 and the second through hole 31 have substantially the same cross-sectional shape of the third plane 34 with respect to the first plane 32 and the second plane 33. Although these are symmetrical shapes, these may also be asymmetrical shapes, and the temporary center of gravity 50 may coincide with the thrust center 22 together.

(Embodiment 4)
8A is a cross-sectional view of the lens holder 123 according to the present embodiment taken along the center plane 20, and FIG. 8B is a cross-sectional view taken along the third plane 34 of the lens holder 123 according to the present embodiment. Other components including the outer shape of the lens holder 123 are the same as those in the first embodiment, and a description thereof will be omitted. The lens holder 123 is incorporated in the objective lens driving device 100 in place of the lens holder 3 according to the first embodiment.

  As shown in FIG. 8A, the cross section of the first through hole 30 by the central plane 20 (FIG. 8B) is formed so that the cross section in the tangential direction is stepped in the focus direction. As a result, the distance from the central axis of the first objective lens 1 to the outside of the peripheral wall of the first through hole 30 changes. In other words, the thickness of the structure portion of the lens holder 123 sandwiched between the first through hole 30 and the outer peripheral surface of the lens holder 123 decreases stepwise as the distance from the first objective lens installation port 25 increases. It has changed. Since the structure portion is formed in a step shape, the shape of the first through hole 30 is asymmetric with respect to the first plane 32.

  In the lens holder 123, the fourth centroid 67, which is the centroid of the cross-sectional shape of the first through-hole 30 by the center plane 20, is outside the lens holder 123 from the center axis of the heavy first objective lens 1. As a result, the thickness on the outside of the lens holder is greatly reduced as viewed from the central axis of the first objective lens 1. By increasing the thickness reduction amount of the outer portion of the lens holder 123 far from the center of the movable part 101, the thickness reduction amount is the same with a small thickness reduction amount compared with the case of uniformly reducing the thickness around the cross section. The center of gravity movement effect can be obtained.

  That is, the position of the center of gravity of the entire movable part 101 is changed from the temporary center of gravity 50 when the cross-sectional shape of the first through hole 30 is symmetric to the first plane 32 to the center of gravity 51 that coincides with the thrust center 22. It can be moved while minimizing the decrease in rigidity due to the decrease in thickness. Accordingly, it is possible to provide an objective lens driving device capable of preventing occurrence of unnecessary resonance such as pitching resonance and performing stable control.

  As shown in FIG. 8B, in the present embodiment, the first through hole 30 and the second through hole 31 have substantially the same cross-sectional shape of the third plane 34 with respect to the first plane 32 and the second plane 33. Although these are symmetrical shapes, these may also be asymmetrical shapes, and the temporary center of gravity 50 may coincide with the thrust center 22 together. In the present embodiment, the cross-sectional shape of the first through hole 30 by the central plane 20 is a stepped outer cross section in the tangential direction of the peripheral wall, but is not limited to this and is formed in a plurality of steps. However, the same effect can be obtained.

(Embodiment 5)
FIG. 9 shows a functional block configuration of the optical pickup device 213 according to the present embodiment and the optical disc device 214 including the optical pickup device 213.

  The optical disk device 214 includes an optical pickup device 213, a signal processing circuit 209, a servo control circuit 210, a spindle motor 211, and a traverse motor 212. Although FIG. 9 shows an optical disc 200, this is for convenience of explanation and is not a component of the optical disc device 214.

  Hereinafter, the operation of the optical disk device 214 will be described. The optical pickup device 213 emits a light beam to the optical disc 200 to detect the reflected light from the optical disc 200, and outputs a light amount signal corresponding to the detection position of the reflected light and the detected light amount. The signal processing circuit 209 performs a focus error (FE) signal indicating the focused state of the light beam on the optical disc 200 in accordance with the light amount signal output from the optical pickup device 213, the focal position of the light beam, and the track of the optical disc 200. A tracking error (TE) signal or the like indicating the positional relationship is generated and output.

  The servo control circuit 210 generates a plurality of types of drive signals based on these signals. The type of drive signal differs depending on the output destination. Output destinations are the spindle motor 211, the traverse motor 212, and the objective lens driving device 100 of the optical pickup device 213.

  The spindle motor 211 rotates the optical disc 200 at a rotation speed corresponding to the recording speed / reproduction speed based on the drive signal. The traverse motor 212 moves the optical pickup device 213 in the radial direction of the optical disc 200 to the target recording position or reproduction position based on the drive signal.

  The objective lens driving device 100 adjusts the position of the first objective lens 1 or the second objective lens 2 based on the drive signal. Thus, the focus of the light beam emitted to the optical disc 200 is controlled so as not to be out of the recording layer.

  In a state where the focal point of the light beam is controlled so as not to deviate from the recording layer, the signal processing circuit 209 outputs a reproduction signal based on the light amount signal. The reproduction signal indicates data written on the optical disc 200. Thereby, reading of data from the optical disc 200 is realized. In addition, data can be written to the optical disc 200 by making the optical power of the light beam larger than that during reproduction.

  Hereinafter, the configuration of the optical pickup device 213 will be described. The optical pickup device 213 includes an objective lens driving device 100 having a first objective lens 1 and a second objective lens 2, light sources 201a and 201b, a beam splitter 202, collimating lenses 203a and 203b, and mirrors 204a and 204b. And a cylindrical lens 207 and a photodiode 208.

  The light source 201a is a semiconductor laser light source that emits blue laser light having a wavelength of 405 nm. The light source 201b is a semiconductor laser light source that emits red laser light having a wavelength of 660 nm. Both light sources emit coherent light for reading and writing data to the recording layer of the optical disc 100.

  The beam splitter 202 reflects the light beam emitted from the light source 201b in the direction of the collimating lens 203b.

  The collimating lens 203a converts the light beam emitted from the light source 201a into parallel light. The collimator lens 203b converts the light beam emitted from the light source 201b into parallel light.

  The mirror 204 a transmits the incident light beam toward the optical disc 200. The mirror 204 b reflects the incident light beam and directs the reflected light beam to the optical disc 200.

  The first objective lens 1 and the second objective lens 2 of the objective lens driving device 100 each collect the light beam on the recording layer of the optical disc.

  Now, it is assumed that the optical disc 200 is a DVD, and red laser light is output from the laser light source 201b. The red laser light is reflected by the beam splitter 202 and condensed on the optical disc 200 through the collimator lens 203b, the mirror 204b, and the second objective lens 2.

  The objective lens driving device 100 changes the position of the second objective lens 2 in a direction perpendicular to the optical disc 200 and / or a direction parallel to the optical disc 200 in accordance with the level of the applied drive signal. The light beam is focused on the recording layer.

  The reflected light from the optical disk 200 passes through the same optical path as the forward path, passes through the beam splitter 202, and enters the cylindrical lens 207. The cylindrical lens 207 focuses the light beam on the photodiode 208. The photodiode 208 receives the light beam reflected by the recording layer of the optical disc 200 and converts it into an electrical signal (light amount signal) according to the light amount. Note that the photodiode 208 may include a plurality of light receiving elements. The signal processing circuit 209 that receives the light amount signal generates an FE signal and a TE signal using information about which light receiving element the light amount signal is output from.

  The objective lens driving device according to the present invention changes the outside of the lens holder out of the cross-sectional shapes of the first through hole 30 and the second through hole 31 provided in the lens holder so that the center of gravity of the movable part matches the thrust center 22. Therefore, the amount of change can be suppressed to a small level, and unnecessary resonance can be suppressed by minimizing a decrease in rigidity and sensitivity deterioration, which is useful as an objective lens driving device having excellent stability.

1 is a perspective view of an objective lens driving device 100 according to Embodiment 1. FIG. 3 is a perspective view of a movable unit 101 according to Embodiment 1. FIG. 3 is a plan view of a movable unit 101 according to Embodiment 1. FIG. 2 is a perspective view of a lens holder 3 according to Embodiment 1. FIG. 2 is a plan view of a lens holder 3 according to Embodiment 1. FIG. 2 is a front view of a lens holder 3 according to Embodiment 1. FIG. FIG. 3 is a cross-sectional view of the lens holder 3 according to Embodiment 1 taken along a central plane 20. FIG. 4 is a cross-sectional view of the lens holder 3 according to Embodiment 1 taken along a third plane 34. It is a figure which shows the relationship between the weight of each lens holder, and the gravity center deviation | shift amount when changing the radius of the arc-shaped parts 41-44 into 4 types and producing lens holder AD. It is a figure which shows the relationship between the resonance frequency of each lens holder and the gravity center deviation | shift amount when producing the lens holders AD which changed the radius of the arc-shaped parts 41-44 into four kinds. FIG. 6 is a cross-sectional view of the lens holder 103 according to the second embodiment, taken along a central plane 20. FIG. 6 is a cross-sectional view of a lens holder 103 according to Embodiment 2 taken along a third plane. It is sectional drawing by the center plane 20 of the lens holder 113 by Embodiment 3. FIG. FIG. 10 is a cross-sectional view of a lens holder 113 according to a third embodiment, taken along a third plane. It is sectional drawing by the center plane 20 of the lens holder 123 by Embodiment 4. 6 is a cross-sectional view of a lens holder 123 according to a fourth embodiment, taken along a third plane. FIG. FIG. 10 is a diagram illustrating a functional block configuration of an optical pickup device 213 according to a fifth embodiment and an optical disc device 214 including the optical pickup device 213. It is a figure which shows an example of the objective lens drive device of the conventional optical pick-up apparatus which mounts two types of objective lenses. It is a figure which shows the 1st through-hole 303 and the 2nd through-hole 304 of the circular cross section which penetrate the lens holder 300. FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 1st objective lens 2 2nd objective lens 3 Lens holder 3a Swing holder 3a
4 Terminal Board 5 Wire 6 Suspension Holder 7 Coil Group 7a Focus Coil 7b Tracking Coil 8 Base 9 Yoke 10 Magnet 25 First Objective Lens Installation Port 26 Second Objective Lens Installation Port 27 First Aperture 28 Second Aperture 30 First through hole 31 Second through hole 45 Centroid of cross-sectional shape 50 Temporary center of gravity when cross-sectional shape of first through hole 30 is symmetric 51 Center of gravity (thrust center)
100 Objective lens driving device 101 Movable part

Claims (13)

An objective lens driving device used in an optical pickup device,
A first objective lens for condensing the first laser beam;
A second objective lens for condensing the second laser light;
A lens holder that supports the first objective lens and the second objective lens, wherein the lens holder has a first through hole through which the first laser light passes and a second through hole through which the second laser light passes. 2 through holes are provided,
A plane formed by the central axis of the first objective lens and the central axis of the second objective lens is defined as a central plane, and a plane perpendicular to the central plane and including the central axis of the first objective lens is defined as a first plane. When a plane perpendicular to the central plane and including the central axis of the second objective lens is a second plane,
The objective lens driving device, wherein the first through hole has an asymmetric shape with respect to the first plane, and / or the second through hole has an asymmetric shape with respect to the second plane.   The first objective lens is heavier than the second objective lens, and the centroid of the cross section of the first through hole by a plane perpendicular to the central axis of the first objective lens is larger than the central axis of the first objective lens The objective lens driving device according to claim 1, wherein the objective lens driving device is located outside the lens holder.   The second objective lens is lighter in weight than the first objective lens, and the centroid of the cross section of the second through-hole by a plane perpendicular to the central axis of the second objective lens is smaller than the central axis of the second objective lens The objective lens driving device according to claim 1, wherein the objective lens driving device is located inside the lens holder.   A cross section of the first through hole by a plane perpendicular to the central axis of the first objective lens is substantially rectangular, and portions corresponding to the four corners of the substantially rectangular shape are each formed in an arc shape. The objective lens according to claim 2, wherein a radius of two arc-shaped portions located outside the lens holder among the arc-shaped portions is smaller than a radius of two other arc-shaped portions located inside the lens holder. Drive device.   The cross section of the second through-hole by a plane perpendicular to the central axis of the second objective lens is substantially rectangular, and the portions corresponding to the four corners of the substantially rectangular shape are each formed in an arc shape. 4. The objective lens according to claim 3, wherein a radius of two arc-shaped portions positioned inside the lens holder among the arc-shaped portions is smaller than a radius of two other arc-shaped portions positioned outside the lens holder. 5. Drive device.   The first objective lens is heavier than the second objective lens, and the centroid of the cross section of the first through hole by the central plane is located outside the lens holder with respect to the central axis of the first objective lens. The objective lens driving device according to claim 1.   The objective lens driving device according to claim 6, wherein the distance between the first through hole and the central axis of the first objective lens is increased at least at one location according to the distance from the first objective lens.   The objective lens driving device according to claim 7, wherein the distance from the central axis of the first objective lens changes continuously or stepwise according to the distance from the first objective lens. .   The objective lens driving device according to claim 1, wherein a weight of the first objective lens and a weight of the second objective lens are different.   The objective lens driving device according to claim 9, wherein one of the first objective lens and the second objective lens is a glass lens, and the other is a plastic lens.   The objective lens driving device according to claim 9, wherein the first objective lens and the second objective lens are formed of the same material. The objective lens driving device according to claim 1;
A first laser light source for outputting the first laser light;
An optical pickup device comprising: a second laser light source that outputs the second laser light; and condensing the first laser light and the second laser light on information recording surfaces of different types of optical disks. An optical pickup device according to claim 12,
A motor for rotationally driving the optical disc;
An optical disc apparatus comprising: a control unit that controls the optical pickup device and the motor.