Abstract:
An object lens driving device comprises a movable unit which supports an object lens and is movably supported by a fixed unit, a first mechanism which has a first magnet affixed to a fixed unit and a first coil affixed to a movable unit, and drives the movable unit in a predetermined direction by supplying electricity to the first coil, and a second mechanism which has a second coil affixed to a fixed unit and a second magnet affixed to a movable unit, and drives the movable unit in a direction different from that of the first mechanism by supplying electricity to the second coil, wherein the first and second magnets are arranged so that their polarities have the same orientation.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
         [0001]    This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2002-135438, filed May 10, 2002, the entire contents of which are incorporated herein by reference.  
         BACKGROUND OF THE INVENTION  
         [0002]    1. Field of the Invention  
           [0003]    The present invention relates to an object lens driving device which drives an object lens for focusing a light beam on an optical disk and recording or reproducing information, and an optical head having the same.  
           [0004]    2. Description of the Related Art  
           [0005]    It is well known that a driving device for recording or reproducing information into/from an optical disk such as a CD (Compact Disk), CD-RW (Rewritable), DVD (Digital Versatile Disk)-ROM (Read Only Memory) and DVD-RAM (Random Access Memory) has spread in recent years.  
           [0006]    Such a driving device records or reproduces information into/from an optical disk by radiating a light beam from an optical head to the optical disk. In this case, an optical head uses an object lens to focus a light beam radiated from a light source on to a predetermined position on an optical disk.  
           [0007]    Thus, an optical head is provided with an object lens driving device which comprises a focusing mechanism to control an object lens in the focusing direction, a tracking mechanism to control the object lens in the tracking direction, and a tilting mechanism to control the tilt of the object lens.  
           [0008]    Each of the focusing mechanism, tracking mechanism and tilting mechanism of the object lens drive device adopts electromechanical conversion technology which moves the object lens by a predetermined distance in a predetermined direction by combining a coil and a magnet and controlling the electricity applied to the coil.  
           [0009]    However, in current object lens driving devices, all the magnets and coils constituting each mechanism are mounted close to one another, and this structure raises a problem that the magnetic flux around the magnets constituting a focusing mechanism or a tracking mechanism, for example, affects the operation of the tilting mechanism.  
         BRIEF SUMMARY OF THE INVENTION  
         [0010]    According to one aspect of the present invention, there is provided an object lens driving device comprising:  
           [0011]    a fixed unit;  
           [0012]    a movable unit configured to hold an object lens and to be movably supported by the fixed unit;  
           [0013]    a first mechanism having a first magnet affixed to the fixed unit and a first coil affixed to the movable unit, and configured to drive the movable unit in a predetermined direction by supplying electricity to the first coil; and  
           [0014]    a second mechanism having a second coil affixed to the fixed unit and a second magnet affixed to the movable unit, and configured to drive the movable unit in a direction different from that of the first mechanism by supplying electricity to the second coil; wherein  
           [0015]    the first and second magnets are arranged so that their polarities have the same orientation.  
           [0016]    According to another aspect of the present invention, there is provided an optical head comprising:  
           [0017]    a light source;  
           [0018]    an object lens configured to condense the light from the light source on a disk;  
           [0019]    a movable unit configured to hold the object lens and to be movably supported by a fixed unit;  
           [0020]    a first mechanism having a first magnet affixed to the movable unit and a first coil affixed to the fixed unit, and configured to drive the movable unit in a predetermined direction by supplying electricity to the first coil; and  
           [0021]    a second mechanism having a second coil affixed to the movable unit and a second magnet affixed to the fixed unit, and configured to drive the movable unit in a direction different from that of the first mechanism by supplying electricity to the second coil; wherein  
           [0022]    the first and second magnets are arranged so that their polarities have the same orientation. 
       
    
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING  
       [0023]    The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate presently preferred embodiments of the invention, and together with the general description given above and the detailed description of the embodiments given below, serve to explain the principles of the invention.  
         [0024]    [0024]FIG. 1 is a block diagram showing the optical head of an embodiment of the present invention;  
         [0025]    [0025]FIG. 2 is a perspective view of an object lens driving device of the same embodiment;  
         [0026]    [0026]FIG. 3 is a perspective view of the object lens driving device of the same embodiment from another angle;  
         [0027]    [0027]FIG. 4 is a plan view from above the object lens driving device of the same embodiment;  
         [0028]    [0028]FIG. 5 is a plan view of the object lens diving device of the same embodiment, with the lid removed; and  
         [0029]    [0029]FIG. 6 is a sectional view for explaining the relation between each magnet, yoke and lid of the object lens driving device in the same embodiment. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0030]    Hereinafter, one embodiment of the present invention will be explained in detail with reference to the accompanied drawings. FIG. 1 shows the optical head  11  explained in this embodiment. The optical head  11  is faced to the optical disk  12  and supported movably in the radial direction, i.e., in the directions of arrows A and B.  
         [0031]    The optical head  11  can record information in the optical disk  12  by focusing a laser beam, which is radiated from a light source or a semiconductor laser  13  and modulated according to the information to be recorded, on the optical disk  12 , through an optical system  14  and an object lens  15 .  
         [0032]    The optical head  11  also focuses a laser beam of a certain level radiated from the semiconductor laser  13  on the optical disk  12  through the optical system  14  and object lens  15 , and causes the laser beam reflected from the optical disk  12  to return through the object lens  15  and to be refracted by the optical system  14  and received by an opto-electric converter  16 , thereby reproducing the information from the optical disk  12 .  
         [0033]    Here, the object lens  15  is supported by an object lens driving device  17  so that the focus, track and tilt can be controlled. Each coil described later to control the focus, track and tilt of the object lens  15  is connected to a printed circuit board  19  through a flexible printed circuit board  18 .  
         [0034]    The semiconductor laser  13  is also connected to the printed circuit board  19  through a flexible printed circuit board  20 . Further, the opto-electric converter  16  is electrically and mechanically connected to the printed circuit board  19 .  
         [0035]    The optical head  11  is electrically externally connected through the printed circuit board  19 , and controls the semiconductor laser  13  and object lens driving device  17 , and extracts the signal generated by the opto-electric converter  16 .  
         [0036]    [0036]FIG. 2 shows an external view of the object lens driving device  17 . FIG. 3 shows an external view of the object lens driving device  17  viewed from a different angle from FIG. 2. FIG. 4 shows the top view of the object lens driving device  17 .  
         [0037]    In FIG. 2 to FIG. 4, a reference numeral  21  indicates a base, which is a fixed unit. A wire holder  22  is fixed to one end of the base  21 . To the wire holder  22 , four wires  23  made of an elastic conductive material and formed like a bar are supported so that they are arranged substantially square against a tangent of the optical disk  12 .  
         [0038]    Fixed also to one end of the base  21  is one end  18   a  of the flexible printed circuit board  18 . One end of each wire  23  is electrically connected to the one end  18   a  of the flexible printed circuit board  18 , penetrating through the wire holder  22 . The other end  18   b  of the flexible printed circuit board  18  is connected to the printed circuit board  19 .  
         [0039]    Here, each wire  23  supports at the other end a lens holder  24  which is a movable unit. The lens holder  24  supports the object lens  15 . With this structure, the object lens  15  is supported against the base  21  by the elastic force of the wire  23 , so that the focusing direction, tracking direction and tilt can be controlled.  
         [0040]    Supported on the base  21  is a pair of magnets (not shown in FIG. 2 to FIG. 4) shared by a focusing mechanism to drive the object lens  15  in the focusing direction, and a tracking mechanism to drive the object lens  15  in the tracking direction.  
         [0041]    The pair of magnets is surrounded by the yoke fixed to the base  21  (not shown in FIG. 2 to FIG. 4), forming a magnetic field parallel to each other. The yoke is opened at one end, and the opening is covered by a lid  25 .  
         [0042]    The lens holder  24  supports a focus coil  26  constituting the focusing mechanism and a tracking coil constituting the tracking mechanism (not shown in FIG. 2 to FIG. 4).  
         [0043]    The focus coil  26  and tracking coil are partially exposed in the above-mentioned parallel magnetic field. The focus coil  26  and tracking coil can generate a driving force in the focusing and tracking directions with respect to the lens holder  24 , by controlling the amount and direction of current.  
         [0044]    On the other hand, two magnets  27  which constitute the tilting mechanism to control the tilt of the object lens  15  are affixed to the lens holder  24 . These magnets  27  are provided symmetrically side by side on both sides of the tangent C of the optical disk  12  passing through the center of the object lens  15  (see FIG. 4).  
         [0045]    These magnets  27  forms a parallel magnetic field through the above-mentioned yoke between the pair of magnets shared by the focusing mechanism and the tracking mechanism.  
         [0046]    Further, tilt coils  28  constituting the tilting mechanism are supported on the base  21  just like surrounding the two magnets  27 . These tilt coils  28  surround the magnets  27  so that the winding axes coincide with the focusing direction.  
         [0047]    By controlling the amount and direction of the current to flow the tilt coils  28 , the tilt coils  28  control the tilt of the object lens  15  with respect to the magnets  27  of the lens holder  24 . Namely, the tilt coils  28  can generate a driving force to turn the object lens  15  around the tangent C.  
         [0048]    [0048]FIG. 5 shows the state with the lid  25  removed. That is, in FIG. 5, a pair of magnets  29  and  30  shared by the focusing mechanism and the tracking mechanism are separated by a certain space and oppositely provided on the base  21 , along the tangent of the optical disk  12 .  
         [0049]    Between these pair of magnets  29  and  30 , a pair of the above-mentioned tracking coils  31  supported by the lens holder  24  are interposed in such a manner that they are arranged side by side in the tracking direction. Further, the focus coil  26  supported by the lens holder  24  surrounds the magnet  30 .  
         [0050]    The tilt coil  28  is directly connected to one end  18   a  of the flexible printed circuit board  18 , and is energized. The focus coil  26  and tracking coil  31  are connected to one end  18   a  of the flexible printed circuit board  18  through a wire  23 , and are energized.  
         [0051]    [0051]FIG. 6 shows the relation between the magnets  27 ,  29 ,  30 , yoke  32  and lid  25  in the object lens driving device  17 . That is, the magnets  27 ,  29 ,  30  are arranged in the order of  29 ,  30 ,  27  from the nearest to the object lens  15  along the tangent of the optical disk  12 , so that their polarities have the same orientation.  
         [0052]    The yoke  32  is made of a magnetic material and is formed in one body with a yoke wall  32   a  located in the side of the magnet  29  opposite to the magnet  30  or the S-pole side of the magnet  29 , a yoke wall  32 b located in the side of the magnet  30  opposite to the magnet  29  or the N-pole side of the magnet  30 , a yoke wall  32   c  located in the side of the magnet  28  opposite to the magnet  30  or the N-pole side of the magnet  27 , and a yoke magnetic path  32   d  connecting the yoke walls  32   a,    32   b  and  32   c.    
         [0053]    The open end opposite to the side where the yoke magnetic path  32   d  is formed by the yoke walls  32   a  and  32   b,  is covered by the lid  25  forming a closed magnetic path.  
         [0054]    The yoke magnetic path  32   d  of the yoke  32  is fixed to the base  21 . As indicated by dashed line D in FIG. 6, the magnets  29 ,  30 ,  27  are arranged so that their centers in the height direction from the base  21  are substantially aligned.  
         [0055]    In the above-mentioned embodiment, the pair of magnets  29 ,  30  shared by the focusing mechanism and tracking mechanism are supported by the base  21  which is the fixed unit, and the magnet  27  constituting the tilting mechanism is supported by the lens holder  24  which is the movable unit, and the magnets  29 ,  30 ,  27  are arranged along the tangent of the optical disk  12  so that their polarities have the same orientation.  
         [0056]    Thus, it is possible to continuously form a stable parallel magnetic flux space between the magnets  29 ,  30  and  27 . This prevents the operation of the tilting mechanism from being affected by the magnetic flux around the magnets  29  and  30  constituting the focusing mechanism and tracking mechanism, for example.  
         [0057]    Further, since a magnetic circuit with a closed magnetic path is formed by surrounding the magnets  29  and  30  which is the fixed unit by the yoke walls  32   a,    32   b  of the yoke  32 , the yoke magnetic path  32   d  and the lid  25 , it is possible to form a stable parallel magnetic field between the magnets  29  and  30  without being influenced by the fluctuation in the magnetic field due to movement of the magnet  27 , which is the movable unit.  
         [0058]    Contrarily, by making a closed magnetic path, an extra magnetic field generated by the magnets  29  and  30  does not leak to the outside. This prevents movable unit influencing the magnet  27 , and minimizes the effect on the tilting mechanism.  
         [0059]    Since the centers of the magnets  29 ,  30  and  27  in the height direction as measured from the base  21  are substantially aligned, the height of the lens holder  24  can be held constant by the pulling force of both magnets.  
         [0060]    In the above-mentioned embodiment, the pair of magnets  29  and  30  constituting the focusing mechanism and tracking mechanism are supported by the base  21 , which is the fixed unit, and the magnet  27  constituting the tilting mechanism is supported by the lens holder  24 , which is the movable unit. Contrarily, it is also possible to support the pair of magnets  29  and  30  constituting the focusing mechanism and tracking mechanism by the lens holder  24 , which is the movable unit, and to support the magnet  27  constituting the tilting mechanism by the base  21 , which is the fixed unit.  
         [0061]    In this case, the focus coil  26  and tracking coil  31  are supported by the base  21 , which is the fixed unit, and the tilt coil  28  is supported by the lens holder  24 , which is the movable unit.  
         [0062]    Further, the tilt coils  28  can surround the magnet  27  so that their winding axes become orthogonal to the focusing direction.  
         [0063]    Additional advantages and modifications will readily occur to those skilled in the art. Therefore, the invention in its broader aspects is not limited to the specific details and representative embodiments shown and described herein. Accordingly, various modifications may be made without departing from the spirit or scope of the general inventive concept as defined by the appended claims and their equivalents.