JP5736803B2 - Magnet structure of objective lens drive unit - Google Patents

Description

  The present invention relates to a magnet structure of an objective lens driving device that constitutes an optical recording device that records an information signal by irradiating an optical disc with a laser beam and reproduces the recorded information signal.

  The objective lens driving device is one of the parts constituting the optical recording device. An optical recording device guides laser light generated from a light source to an objective lens through an optical element such as a collimator or a mirror, and converges the laser light with the objective lens to record on an optical disk such as a CD or DVD. Information is recorded by irradiating a laser beam on the laser beam, and information is reproduced by detecting the laser beam reflected by the recording surface with a photodetector.

  The role of the objective lens is to converge the incident laser beam and supply the laser beam with less aberration to the disc. The laser beam is focused on the recording surface and the laser beam is scanned accurately with respect to the recording surface. That is. Therefore, an objective lens driving device that drives the objective lens is required to have a response that instantaneously follows the objective lens with respect to the focus direction and the tracking direction in accordance with surface deflection accompanying high-speed rotation of the optical disk.

  The driving principle of this objective lens driving device is to generate a driving force by the interaction between magnetism and electricity in accordance with Fleming's left-hand rule. FIG. 1 shows an objective lens driving device of a system called a moving coil type. As shown in the drawing, driving coils 3 and 4 for driving the lens holder 2 in the tracking direction and the focusing direction are fixed to the four side surfaces of the lens holder 2 on which the objective lens 1 is mounted with an adhesive. Yes. A pair of drive coils are arranged so as to face the focus direction and the tracking direction, respectively. In other words, a pair of tracking direction driving coils 3 is disposed in a direction perpendicular to the tracking direction with the lens holder 2 interposed therebetween, and a pair of focus direction driving coils in the direction perpendicular to the focus direction with the lens holder 2 interposed therebetween. A coil 4 is arranged. The lens holder 2 provided with these driving coils 3 and 4 is cantilevered by a metal wire (not shown). On the other hand, on the outside of the lens holder 2, permanent magnets 5 and 6 for generating a magnetic field are arranged at positions facing the respective drive coils 3 and 4.

  Next, the principle that the objective lens 1 operates in the focus direction and the tracking direction will be described. The magnetic fields generated by the permanent magnets 5 and 6 act on the currents flowing in the tracking direction driving coil 3 and the focus direction driving coil 4, and as a result, the driving coils 3 and 4 are subjected to Fleming's left-hand rule. A driving force that moves in the tracking direction and the focus direction acts. Here, since the lens holder 2 is cantilever-supported in a suspended state by a metal wire, the lens holder 2 can freely move its position depending on the direction of the current flowing through each driving coil.

  By the way, the objective lens driving device can be classified into two types, that is, the moving coil type and the moving magnet type described above, depending on the driving method.

  The moving coil type is a system in which a lens unit having a driving coil attached to a lens holder moves, as described with reference to FIG. On the other hand, the moving magnet type is a system in which a lens unit in which a permanent magnet for generating a magnetic field is attached to a lens holder with an adhesive moves.

  FIG. 2 shows a typical moving magnet type objective lens driving device. As shown in the figure, permanent magnets 5 and 6 are fixed to the four side surfaces of the lens holder 2 on which the objective lens 1 is mounted with an adhesive. The lens holder 2 is cantilevered by a metal wire (not shown). On the other hand, a tracking direction drive coil 3 and a focus direction drive coil 4 are arranged outside the permanent magnets 5 and 6 fixed to the lens holder 2. The magnetic field generated by the permanent magnets 5 and 6 acts on the current flowing through the driving coils 3 and 4, and as a result, the driving coils 3 and 4 have a tracking direction and a focusing direction in accordance with Fleming's left-hand rule. A moving drive force is generated. Here, since each driving coil is fixed, the lens holder 2 that is cantilevered in a suspended state can be moved freely according to the law of action and reaction.

JP-A-10-27361

  When comparing the moving coil type and the moving magnet type as described above, the moving coil type can easily reduce the weight of the lens unit that is the target of operation including the driving coil itself, so that many objective lens drives have been driven so far. Has been adopted in the device.

  However, in recent years, with the increase in the reproduction speed of the optical recording apparatus, higher speed has been required for driving the objective lens. Therefore, it has become necessary to increase the current flowing through the driving coil. However, if a large current is passed through the driving coil, the driving coil generates a large amount of heat, which causes distortion in the objective lens itself and causes a signal reading error. Furthermore, in the case of the moving coil type, the drive coil itself is an active part, so the signal wire connected to the drive coil is suspended in a suspended state, and the assembly work is very delicate and the assembly work There is a problem that becomes extremely difficult.

  On the other hand, such a problem does not occur in the moving magnet type structure. In other words, since the driving coil is separated from the lens holder, the heat generated by the driving coil does not affect the objective lens, and the signal line is also arranged on the fixed side, so that it is not suspended. For these reasons, a moving magnet type objective lens driving device has attracted attention.

  However, the moving magnet type is a system in which a permanent magnet is attached to the lens holder 2 with an adhesive as shown in FIG. That is, when the permanent magnets 5 and 6 are fixed to the lens holder 2 with an adhesive, the external dimensions of the entire lens unit are not stable depending on the manner of adhesion. Therefore, the design of the space gap with the drive coil must be made larger than desired. Since this space gap becomes large, driving efficiency is lowered. Further, based on common sense so far, it is common to use a sintered magnet made of NdFeB as a magnetic material as a permanent magnet. However, when a sintered magnet having a large specific gravity such as NdFeB is used as a permanent magnet, not only the driving efficiency is poor, but also integration with the lens holder is difficult.

  In order to solve such a problem, as shown in FIG. 4, the objective lens driving device disclosed in Patent Document 1 has a lens holder itself made of a magnet composed of a resin and a magnetic material, that is, a permanent magnet. It is a moving magnet type objective lens driving device that constitutes a magnet.

  In such an objective lens driving device, the lens holder itself is entirely made of a ferromagnetic material. In addition, the ferromagnet is magnetized so that it is parallel to the recording surface of the optical disk and perpendicular to the tracking direction, so that one has an N pole and the other has an S pole. Allows movement in the direction and tracking direction. That is, a current is passed through the driving coil, the yoke around which the driving coil is wound is magnetized, and the driving principle is attraction and repulsion with the magnetic pole of the lens holder. Thus, by configuring the lens holder with a ferromagnetic material, the gap between the driving coil and the magnetic field generating permanent magnet can be designed accurately. As a result, the space gap can be made smaller than in the prior art, and the driving efficiency can be increased. Further, by using a relatively light bonded magnet as compared with the sintered magnet, not only the driving efficiency is improved, but also the lens holder and the permanent magnet can be easily integrated.

  However, in this objective lens driving device, current is passed through a coil wound around the yoke to magnetize the yoke, and the attraction and repulsion of the magnetic force and the magnetic force of the permanent magnet are utilized. Therefore, the problem of so-called hysteresis loss when magnetizing the yoke must be taken into consideration. That is, responsiveness and driving efficiency are reduced as compared with an objective lens driving device that is directly driven by the interaction between magnetism and electricity in accordance with Fleming's left-hand rule.

  For example, consider a case where the material of the yoke is an inexpensive iron SS400. Iron is generally a material having anisotropy in the easy axis of magnetization. When this easy axis is aligned with the easy axis of the yoke in either the tracking direction or the focus direction, a delay occurs in the rise of the other magnetization. As a result, the hysteresis loss increases, and the responsiveness and drive efficiency decrease. Hysteresis loss can be reduced by selecting a material having a high magnetic permeability, such as a non-oriented silicon steel plate, and a magnetically isotropic material. However, even in this case, not only the hysteresis loss occurs but also the material cost becomes relatively high.

  In order to avoid such a problem of hysteresis loss, the lens holder is made of a ferromagnetic material as shown in FIG. 3, and the interaction between electricity and magnetism according to Fleming's left-hand rule is used as the driving principle. In this case, an objective lens driving device is conceivable. By forming the lens holder from a ferromagnetic material, it becomes easy to precisely design the gap between the driving coil and the permanent magnet for generating the magnetic field. In other words, the gap between the driving coil and the permanent magnet for generating the magnetic field can be made smaller than before, so that not only the driving efficiency can be increased, but also the responsiveness is achieved because the driving is performed directly by the interaction between magnetism and electricity. Excellent.

  However, in this objective lens driving device, as shown in FIG. 3, two types of driving coils, that is, a focus direction driving coil 4 and a tracking direction driving coil 3 are arranged side by side in order from the lens holder 7 side. Arrangement. Therefore, the tracking direction driving coil 3 must be arranged at a position farther from the lens holder 7 (driving permanent magnet) than the focusing direction driving coil 4. Since the magnetic force decreases in inverse proportion to the square of the distance from the surface of the permanent magnet, driving in the tracking direction has a problem that driving efficiency is greatly reduced compared to driving in the focusing direction. Occur.

  The present invention has been made in view of the background as described above, that is, a lens holder for driving an objective lens that can be used for an optical recording apparatus, dramatically increases driving sensitivity, and is excellent in productivity. The purpose is to provide.

  In order to achieve the above object, a magnet structure according to the present invention includes a lens holder for holding an objective lens, and a plurality of driving coils arranged outside the lens holder. A magnet structure in an objective lens driving device that drives the lens holder in a focus direction and a tracking direction by an interaction between a magnetic pole provided and a magnetic field generated by energization of the driving coil. The entirety is composed of a substantially cubic bonded magnet, and at least two different magnetic poles are formed on one side surface excluding the surface on which the objective lens is mounted. An objective lens drive comprising the drive coils arranged so as to face the magnetic poles. A magnet structure of the device.

  The lens holder is preferably molded by injection molding. The lens holder is preferably made of an anisotropic rare earth-iron-nitrogen bonded magnet composition.

  By adopting the magnet structure of the present invention, the entire lens holder is formed of a bonded magnet, so that the lens unit is compared with a moving magnet type objective lens driving device in which a conventional sintered magnet is bonded and fixed to the lens holder. The weight can be reduced.

  The entire lens holder is formed of a bonded magnet. Thereby, since the dimensional accuracy of the bond magnet depends on the dimensional accuracy of the mold for molding the bonded magnet, a lens holder with excellent dimensional accuracy can be obtained as a molded product. Since such a lens holder of the present invention has excellent dimensional accuracy, the distance between the driving coil and the permanent magnet can be reduced to the limit, and an optimum design for improving the driving efficiency can be performed. Further, according to the present invention, two or more magnetic poles are provided on all four side surfaces of the substantially cube-shaped lens holder, and driving coils corresponding to the magnetic pole surfaces are arranged on the outer sides. Thereby, compared with the magnet structure of the objective lens drive device described in FIG. 3, the distance between the drive coil and the permanent magnet can be reduced, so that the drive efficiency can be improved.

  Further, in the present invention, a molded product having a desired orientation pattern and a high surface magnetic flux density can be obtained by using an anisotropic rare earth-iron-nitrogen bonded magnet composition as a raw material for the bond magnet constituting the lens holder. .

FIG. 1 is a perspective view showing a magnet structure of a conventional objective lens driving device. FIG. 2 is a perspective view showing a magnet structure of a conventional objective lens driving device. FIG. 3 is a perspective view showing a magnet structure of a conventional objective lens driving device. FIG. 4 is a perspective view showing a magnet structure of a conventional objective lens driving device. FIG. 5 is a perspective view showing a magnet structure of the objective lens driving device according to the embodiment of the present invention. FIG. 6 is a front view for explaining driving in the tracking direction in the magnet structure of the objective lens driving device according to the embodiment of the present invention. FIG. 7 is a front view for explaining driving in the focus direction in the magnet structure of the objective lens driving device according to the embodiment of the present invention. FIG. 8 is a perspective view showing a mold for injection molding a lens holder in the magnet structure of the objective lens driving device according to the embodiment of the present invention.

  The best mode for carrying out the present invention will be described below with reference to the drawings. However, the form shown below illustrates the magnet structure of the objective lens driving device for embodying the technical idea of the present invention, and the present invention limits the magnet structure of the objective lens driving device to the following. It is not a thing.

  Further, the present specification by no means specifies the members shown in the claims to the members of the embodiments. The dimensions, materials, shapes, relative arrangements, and the like of the components described in the embodiments are not intended to limit the scope of the present invention only to the description unless otherwise specified. It is just an example. Note that the size, positional relationship, and the like of the members shown in each drawing may be exaggerated for clarity of explanation. Further, in the following description, the same name and reference sign indicate the same or the same members, and detailed description will be omitted as appropriate. Furthermore, each element constituting the present invention may be configured such that a plurality of elements are constituted by the same member and the plurality of elements are shared by one member, and conversely, the function of one member is constituted by a plurality of members. It can also be realized by sharing.

  In order to achieve the above-mentioned object, the present inventors have intensively studied and as a result, the present invention has been completed.

  That is, according to the present invention, in a so-called moving magnet type objective lens driving device, when the entire lens holder having a substantially cubic shape is composed of a bonded magnet and the lens mounting surface is an upper surface, the four side surfaces excluding the upper surface and the lower surface are arranged. Magnetic poles are formed on all of the lens holders, and two different magnetic poles are formed on one of the four side surfaces, and the outer side of the lens holder corresponds to the magnetic pole on the side surface of each lens holder. A driving coil is arranged in the above.

  In addition, the lens holder for driving the objective lens is preferably molded by injection molding. In addition, the lens holder for the objective lens driving device is preferably made of an anisotropic rare earth-iron-nitrogen bonded magnet composition.

  Hereinafter, each structure of this form is explained in full detail. FIG. 5 is a perspective view of an objective lens driving device according to an embodiment of the present invention. The lens holder 9 is a support member for holding the objective lens 1 and also serves as a tracking direction driving permanent magnet and a focus direction driving permanent magnet. Further, the lens holder 9 includes an objective lens 1 at the center of the upper end thereof as shown in the drawing. The objective lens 1 plays a role of converging the laser light emitted from the light source. The lens holder 9 is entirely composed of a bonded magnet except for the through-hole for placing the objective lens 1. When the lens mounting surface is the upper surface as shown in the drawing, the upper and lower surfaces are excluded 4. Magnetic poles are formed on one side. Of these four side surfaces, two of the side surfaces with the objective lens 1 as the axis of symmetry have N poles and S poles formed in half in the vertical direction (that is, in the focus direction), and the remaining two side surfaces. Has a magnetic pole configuration in which N poles and S poles per side are formed in half in the lateral direction (that is, in the tracking direction). In FIG. 5, since the lens holder 9 is viewed from an oblique direction, the magnetic pole has two side surfaces on the near side, that is, one side surface in which the N pole and the S pole are formed in half in the vertical direction, and N A state in which the pole and the S pole are formed on one side surface formed in half in the horizontal direction is depicted.

  The lens holder 9 is cantilevered by a metal wire (not shown). As shown in FIG. 5, the tracking direction driving coil 3 and the focus direction driving coil 4 are arranged on the outer side of the lens holder 9 at intervals so as not to contact the lens holder. ing. FIG. 6 is a front view of the perspective view of FIG. 5 viewed from the tracking direction driving coil 3 side. As shown in FIG. 6, the tracking direction driving coil 3 is arranged so as to go around the N pole and the S pole formed on the side surface of the lens holder 9. FIG. 7 is a front view of the perspective view of FIG. 5 viewed from the focus direction driving coil 4 side. Further, as shown in FIG. 7, the focus direction driving coil 4 is arranged so as to go around the N pole and the S pole formed on the side surface of the lens holder 9.

  Next, the driving principle of the objective lens driving device will be described. As shown in FIG. 6, when a clockwise current flows in the tracking direction driving coil 3, the left hand of Fleming is between the current flowing in the tracking direction driving coil 3 and the magnetic field generated from the magnetic pole of the lens holder. In accordance with the law, the tracking direction driving coil 3 is driven by a driving force in the tracking direction, and the tracking direction driving coil 3 tends to move to the left in FIG. Here, since the tracking direction driving coil 3 is fixed, the lens holder 9 cantilevered in a suspended state moves to the right in FIG. 6 according to the law of action and reaction. Become. On the other hand, when a current is passed in the direction opposite to the direction shown in FIG. 6 (counterclockwise), the lens holder 9 moves leftward toward the plane of FIG.

  On the other hand, as shown in FIG. 7, when a clockwise current flows through the focus direction driving coil 4, between the current flowing through the focus direction driving coil 4 and the magnetic field generated from the magnetic pole of the lens holder 9, In accordance with Fleming's left-hand rule, the focus direction driving coil 4 has a driving force in the focus direction, and the focus direction driving coil 4 tends to move downward toward the paper surface in FIG. Here, since the focus direction driving coil 4 is fixed, the lens holder 9 that is cantilevered in a suspended state is moved upward toward the paper surface of FIG. 7 according to the law of action and reaction. Become. On the other hand, when a current is passed in the direction opposite to the direction shown in FIG. 7 (counterclockwise), the lens holder 9 moves downward toward the plane of FIG.

  As described above, the lens holder 9 can be freely controlled in the focus direction or the tracking direction by supplying current to the tracking direction driving coil 3 and the focus direction driving coil 4 and controlling the direction of current flow. It becomes possible to do.

  In the objective lens driving device of the present invention, the entire lens holder 9 for arranging the objective lens is composed of bonded magnets, and has magnetic poles on all four side surfaces, and has different polarities on one side surface. At least two magnetic poles are formed.

  By forming the lens holder integrally with the objective lens with a bonded magnet in this way, it is superior in productivity and dimensional accuracy compared to the conventional configuration in which the permanent magnet is attached to the lens holder with an adhesive. Also gets higher. Therefore, there is an advantage that the layout design of the drive coil can be easily performed.

  As a conventional example, as shown in FIG. 3, a moving magnet type objective lens driving device in which a lens holder main body is formed of a molded magnet has been reported. However, the molded magnet is magnetized in a uniaxial direction so as to be parallel to the recording surface of the optical disk and perpendicular to the tracking direction, and the magnetic pole is used only on two side surfaces. .

  On the other hand, in the present invention, by having the magnetic poles on all four side surfaces, one drive coil can be allocated and arranged per one side surface. Therefore, as shown in FIG. 3, compared with the conventional configuration in which two driving coils are arranged per one side, the present invention has a lens holder magnetic pole and driving for all the driving coils. It is possible to reduce the distance from the coil for use by the same amount, which leads to a significant improvement in driving efficiency. Furthermore, as shown in FIG. 6 and FIG. 7, by arranging two poles of N pole and S pole per side surface, it is possible to arrange a coil with less waste.

  An anisotropic material is preferably used for the magnetic material used in the present invention. An anisotropic material is a material from which high magnetic properties can be obtained by anisotropy. An anisotropic material has magnetic anisotropy in each of its grains, and therefore it is necessary to align the crystal orientation in the direction of anisotropicity, that is, in the direction of magnetism. Anisotropic materials include rare earth-iron-nitrogen, ie, anisotropic SmFeN, and rare earth-iron-boron, ie, anisotropic NdFeB. Among these, anisotropic SmFeN is excellent in fluidity and is a material suitable for injection molding, and is therefore optimal for the present invention.

  On the other hand, the isotropic material has a simpler magnet manufacturing process, and the merit of obtaining a final product by adjusting the magnetization is well known without going through an anisotropic process. As the isotropic material, rare earth-iron-boron isotropic NdFeB is well known and used in a wide range of fields.

  However, the situation is different in the present invention. Consider a case where two or more magnetic poles are formed on all four side surfaces of a substantially cubic lens holder according to the present invention using an isotropic material. In this case, after the lens holder molding process is completed, a magnetizing process of sequentially magnetizing the four side surfaces is performed. However, after magnetizing the N and S poles on the first side, if the N and S poles on the second side adjacent to the first side are subsequently magnetized, the second side is magnetized. In this case, the magnetic pole orientation pattern on the first side surface magnetized first is disturbed by the influence of the magnetic field of magnetization.

  On the other hand, when an anisotropic material is used, the direction of the magnetic material particles inside the molded product is already fixed in a predetermined direction at the stage of forming the bonded magnet. In other words, the desired magnetic pole orientation pattern has wrinkles, and the magnetic poles are not disturbed even if the first side surface to the fourth side surface are magnetized in order.

  Furthermore, BHmax of isotropic injection-molded permanent magnets that are industrially available at present is 6-9 MGOe, and BHmax of isotropic compression-molded permanent magnets is 8-11 MGOe. Since it is lower than BHmax (12 to 16 MGe) of an anisotropic injection molded permanent magnet typified by isotropic NdFeB, the surface magnetic flux density of the obtained molded product is also lowered.

  FIG. 8 is a diagram schematically showing the inside of the mold of the injection molding machine for molding the lens holder of the present invention, particularly the cavity portion. The cavity 12 is a space for molding the lens holder, and the shape thereof corresponds to the shape of the lens holder. Around the cavity 12, a partition 12 made of a non-magnetic material is provided so that a desired magnetic pole orientation pattern is formed on the side surface of the lens holder, and permanent magnets for orientation corresponding to the four side surfaces of the lens holder. 11 is arranged.

  The material of the magnet used for the permanent magnet 11 for orientation is preferably one having a residual magnetic flux density: Br of 1T or more. For example, a NdFeB sintered magnet can be used. When a material having a large magnetic force is used, the magnetic force generated in the cavity 12 is increased, and the magnetic force of the obtained bonded magnet molded product is also increased.

  Moreover, it is preferable that the bonded magnet molded product obtained by the above-mentioned injection mold is then magnetized together with the magnetic pole orientation pattern. By magnetizing, the magnetic force of the bonded magnet molded product can be made stronger.

Hereinafter, examples and comparative examples according to the present invention will be described in detail. Needless to say, the present invention is not limited to the following examples.
<Example>

  FIG. 8 is a perspective view showing a mold for injection molding a lens holder in the magnet structure of the objective lens driving device according to the present embodiment. First, an injection mold 14 having a shape as shown in FIG. 8 was prepared. The cavity 12 for molding the lens holder has a structure in which a core protrudes at the center portion thereof in order to provide a hole for accommodating the objective lens in the lens holder. The cavity 12 is a cube whose length × width × height is 6 mm × 6 mm × 6 mm. The diameter of the hole for arranging the objective lens was 3 mm. On the outer periphery of the cavity 12, orientation permanent magnets 11 are arranged on four side surfaces with a partition wall 13 therebetween. On the two sides with the objective lens as the axis of symmetry, N poles and S poles per side are formed in half in the vertical direction, and the remaining two sides have N poles and S poles per side. The orientation magnets were arranged so as to have a magnetic pole configuration formed in half in the horizontal direction.

  “A12 material” (product model number) manufactured by Nichia Corporation was used as a compound that is a material for injection molding. The A12 material is a bonded magnet composition made of anisotropic SmFeN and 12 nylon. The BHmax of the A12 material is 12.5 MGOe. The barrel temperature during injection molding was 275 ° C., and the mold temperature was 90 ° C. The dimension of the obtained molded product is 6 mm × 6 mm × 6 mm in length × width × height. A substantially cylindrical hole with a diameter of 3 mm for accommodating the objective lens is formed in the center of the molded product. In the magnetic pole pattern, the N-pole and the S-pole are formed in half in the vertical direction on each of the two side surfaces with the hole for accommodating the objective lens as an axis of symmetry, and on the remaining two side surfaces, It has a magnetic pole configuration in which N poles and S poles are formed in half in the lateral direction per side.

The obtained molded product was magnetized in order of one side surface (N pole, S pole) on four side surfaces using a magnetizing yoke. The magnetization conditions were 500 μF and applied voltage 1500 V. The maximum surface magnetic flux density of the magnetic pole part of the magnetized product was 3000 gauss. In addition to this portion, the surface magnetic flux density was 3000 gauss in all the magnetic pole portions on the four side surfaces.
<Comparative Example 1>

A commercially available isotropic NdFeB compression-molded product (10 MGOe) was formed in the same shape as in the examples (cubes having a length × width × height of 6 mm × 6 mm × 6 mm). In addition, a cylindrical hole (diameter 3 mm) for accommodating the objective lens was opened at the center by cutting. Only one side (N pole, S pole) was magnetized using a magnetizing yoke. The magnetization conditions were 500 μF and applied voltage 1500 V. The maximum surface magnetic flux density of the magnetic pole part of the magnetized product was 2600 gauss. Subsequently, the second side surface adjacent to the first side surface magnetized earlier (N pole, S pole) was magnetized. The maximum surface magnetic flux density of the magnetic pole portion of the second side surface was 2600 gauss, but the maximum surface magnetic flux density of the magnetic pole portion of the first side surface was reduced to 1300 gauss.
<Comparative Example 2>

A commercially available isotropic NdFeB compression-molded product (10 MGOe) was formed in the same shape as the example (cube having a length × width × height of 6 mm × 6 mm × 6 mm). In addition, a cylindrical hole (diameter 3 mm) for accommodating the objective lens was formed in the center by cutting. An air-core coil was used to magnetize in one axial direction perpendicular to the axis of the objective lens. The magnetization conditions were 1000 μF and 2500 V. The maximum surface magnetic flux density of the magnetic pole portion was 2400 gauss.
<Comparative Example 3>

  Using a commercially available isotropic NdFeB compound for injection molding (7MGOe) as a raw material, a molded product having the same shape as that of Examples and Comparative Examples 1 and 2 was obtained by injection molding. About this molded product, only one side (N pole, S pole) was magnetized. The magnetization conditions were 500 μF and applied voltage 1500 V. The maximum surface magnetic flux density of the magnetic pole part of the magnetized product was 2000 gauss. Subsequently, the second side surface (N pole, S pole) adjacent to the first side surface magnetized earlier was magnetized. The maximum surface magnetic flux density of the magnetic pole portion on the second side surface was 2000 gauss, but the maximum surface magnetic flux density of the magnetic pole portion on the first side surface was reduced to 1000 gauss.

  As described above, according to the present invention, the material of the lens holder constituting the objective lens driving device is adopted as the anisotropic bonded magnet, and the N pole and the S pole are given to all four side surfaces. It was found that a permanent magnet for driving in the tracking direction and in the focus direction, which also serves as a lens holder, for an objective lens driving device having a sufficient magnetic force can be realized.

  INDUSTRIAL APPLICABILITY The present invention can be used as an objective lens driving device that constitutes an optical recording apparatus that records an information signal by irradiating a laser beam on an optical disk and reproduces the recorded information signal.

  DESCRIPTION OF SYMBOLS 1 ... Objective lens, 2 ... Lens holder, 3 ... Coil for tracking direction drive, 4 ... Coil for drive in focus direction, 5 ... Permanent magnet for drive in tracking direction, 6 ... Focus Permanent magnet for direction driving, 7 ... Lens holder / permanent magnet, 8 ... Yoke, 9 ... Lens holder / permanent magnet of the present invention, 10 ... Direction of driving current, 11 ... For orientation Permanent magnet, 12 ... cavity, 13 ... partition, 14 ... mold.

Claims (2)

A magnetic field generated by energizing the magnetic pole provided on the lens holder and the driving coil, and a lens holder for holding the objective lens, and a plurality of driving coils arranged outside the lens holder A magnet structure of an objective lens driving device that drives the lens holder in a focus direction and a tracking direction by interaction with
The lens holder is composed of a substantially cubic bonded magnet as a whole, and at least two different magnetic poles per side are formed on the four side surfaces excluding the surface on which the objective lens is mounted,
The driving coil, Ri Na is disposed so as to face the magnetic poles of each of the four sides,
The lens holder is formed from an anisotropic rare earth-iron-nitrogen bond magnet composition,
In the molding process of the lens holder, the magnetic particles are oriented in a predetermined direction,
The magnet structure of the objective lens driving device, wherein the magnetic pole is formed by sequentially magnetizing the four side surfaces after the molding step . The magnet structure of the objective lens driving device according to claim 1, wherein the lens holder is molded by injection molding.

Images