Abstract:
An objective lens drive apparatus configured to drive an objective lens that focuses a laser beam on an optical disk is disclosed, the apparatus including a holding member that holds the objective lens; at least one pair of drive magnets arranged to face each other at opposite sides of the holding member with respect a tangential direction that is parallel to a tangential line of the optical disk, the drive magnets having protruding end portions that protrude from each side of the holding member with respect to a tracking direction that is parallel to a radial direction of the optical disk; and plural drive coils configured to drive the holding member through interaction with the drive magnets, at least one of the drive coils being arranged on each side of the drive magnets with respect to the tangential direction.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an objective lens drive apparatus configured to drive an objective lens that focuses a laser beam, an optical pickup that includes such an objective lens drive apparatus, and an information read/write apparatus that includes such an optical pickup. 
     2. Description of the Related Art 
     With the development of data digitizing techniques and data compression techniques, large-capacity optical disks such as the DVD (digital versatile disk) and BD (Blu-ray disk) are becoming widely used as recording media. Upon reading and writing information on such large capacity disks, a laser beam has to be accurately focused on tracks of the optical disk, which is rotated at a high speed. Therefore, an objective lens onto which the laser beam is focused has to be driven at a high speed in accordance with the deflection of the optical disk and/or the eccentricity of the tracks, for example. 
     An apparatus for driving such an objective lens is preferably arranged to have a movable part that is reduced in weight to enable the objective lens to be moved at a high speed and be capable of controlling high degree resonance of the mobile part resulting from the drive operations. In this regard, for example, Japanese Laid-Open Patent Publication No. 2001-331956 discloses a drive apparatus implementing the so-called moving magnet method to achieve advantageous characteristics with respect to high degree resonance, the apparatus also being configured to drive the objective lens at a high speed. 
     The drive apparatus disclosed in Japanese Laid-Open Patent Publication No. 2001-331956 implements measures for improving drive sensitivity for the objective lens by arranging drive magnets each facing one side and the other side of a coil to double the effective area of the coil on which electromagnetic forces act. However, in this drive apparatus, parts of the magnetic fields acting on the coil that are generated by the opposing magnets may cancel each other out. Also, it is noted that in this apparatus, a small magnetic piece is arranged within the drive coil, and the line of magnetic force from a drive magnetic field enters this magnetic piece of the drive coil from the N pole, exists the drive coil from a given location, and reenters the magnetic piece from the S pole. With such a configuration, although effective forces may be generated by the magnetic fields in the tangential directions of the magnets and their surrounding areas, undesired forces may be generated at other parts of the drive coil to thereby cause degradation in drive performance. Further, it is noted that since four drive magnets are arranged at two sides of a movable part in this drive apparatus, degradation of high degree resonance characteristics resulting from elastic deformation of the movable part may occur. 
     SUMMARY OF THE INVENTION 
     An aspect of the present invention is directed to providing an objective lens drive apparatus that is capable of effectively using magnetic fields generated by drive magnets to improve drive sensitivity for driving an objective lens. 
     Another aspect of the present invention is directed to providing an optical pickup that is capable of accurately focusing a laser beam on a track of an optical disk. 
     Another aspect of the present invention is directed to providing an optical disk apparatus that is capable of accurately reading or writing information on an optical disk. 
     According to one embodiment of the present invention, an objective lens drive apparatus is provided that is configured to drive an objective lens that focuses a laser beam on an optical disk, the apparatus including: 
     a holding member that holds the objective lens; 
     at least one pair of drive magnets arranged to face each other at opposite sides of the holding member with respect a tangential direction that is parallel to a tangential line of the optical disk, the drive magnets having protruding end portions that protrude from each side of the holding member with respect to a tracking direction that is parallel to a radial direction of the optical disk; and 
     plural drive coils configured to drive the holding member through interaction with the drive magnets, at least one of the drive coils being arranged on each side of the drive magnets with respect to the tangential direction. 
     According to another embodiment of the present invention, an optical pickup is provided that irradiates a laser beam on an optical disk and receives reflected light from the optical disk, the optical pickup including 
     a light source that irradiates the laser beam; 
     an objective lens drive apparatus according to an embodiment of the present invention that focuses the laser beam irradiated from the light source on a recording surface of the optical disk; and 
     a light receiving system that receives the reflected light that is reflected by the recording surface of the optical disk. 
     According to another embodiment of the present invention, an optical disk apparatus is provided that is configured to read and/or write information on an optical disk, the optical disk apparatus including 
     a rotational drive system that rotates the optical disk; 
     an optical pickup according to an embodiment of the present invention that irradiates a laser beam on a recording surface of the optical disk that is rotated by the rotational drive system; and 
     a seek system that moves the optical pickup in the tracking direction of the optical disk. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of an objective lens drive apparatus according to a first embodiment of the present invention; 
         FIG. 2  is another perspective view of the objective lens drive apparatus according to the first embodiment with a coil unit being removed; 
         FIG. 3  is a perspective view of the coil unit of the objective lens drive apparatus according to the first embodiment; 
         FIG. 4  is a perspective view of a yoke member and a base of the objective lens drive apparatus according to the first embodiment; 
         FIG. 5  is a diagram showing a magnetic circuit formed in the objective lens drive apparatus according to the first embodiment; 
         FIG. 6  is a perspective view of an objective lens drive apparatus according to a second embodiment of the present invention; 
         FIG. 7  is a perspective view of a coil unit of the objective lens drive apparatus according to the second embodiment; 
         FIG. 8  is a diagram showing a magnetic circuit formed in the objective lens drive apparatus according to the second embodiment; 
         FIG. 9  is a perspective view of an objective lens drive apparatus according to a third embodiment of the present invention; 
         FIG. 10  is a perspective view of a base of the objective lens drive apparatus according to the third embodiment; 
         FIG. 11  is a diagram showing a magnetic circuit formed in the objective lens drive apparatus according to the third embodiment; 
         FIG. 12  is a diagram showing a first modified configuration of the objective lens drive apparatus according to the third embodiment; 
         FIG. 13  is a diagram showing a second modified configuration of the objective lens drive apparatus according to the third embodiment; 
         FIG. 14  is a diagram showing a first modified configuration of a pair of drive magnets; 
         FIG. 15  is a diagram showing a second modified configuration of the pair of drive magnets; 
         FIG. 16A  is a plan view of an optical disk apparatus according to an embodiment of the present invention; 
         FIG. 16B  is a side view of the optical disk apparatus shown in  FIG. 16A ; and 
         FIG. 17  is a diagram showing an optical pickup according to an embodiment of the present invention. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     In the following, preferred embodiments of the present invention are described with reference to the accompanying drawings. 
     First Embodiment 
     A first embodiment of the present invention is described below with reference to  FIG. 1 . 
       FIG. 1  is a perspective view of an objective lens drive apparatus  10 A according to the first embodiment of the present invention. As is shown in  FIG. 1 , the optical lens drive apparatus  10 A includes a base  12 , a support member  14  fixed to the base  12 , an objective lens holding member  16  that is supported by the support member  14  via support wires  18 , a coil unit  20  arranged to surround the peripheral face of the objective lens holding member  16 , and a pair of drive magnets  19  that are fixed to the objective lens holding member  16 , for example. 
     The base  12  is made up of a frame member having a long side extending in the Y axis direction of  FIG. 1  and an upper face on which the support member  14  is fixed at the −Y side end and the coil unit  20  is fixed at the +Y side end. 
     The support member  14  has a long side extending in the X axis direction of  FIG. 1  and is fixed on the upper face of the base  12 . The support member  14  is provided with some elasticity and is arranged to support the −Y side ends of four support wires  18  that extend in the Y axis direction. 
       FIG. 2  is a perspective view of the objective lens drive apparatus  10 A with the coil unit  20  being removed to show the objective lens holding member  16  that is supported by the support member  14  via the support wires  18 . As is shown in  FIG. 2 , the objective lens holding member  16  is a cubic member having a through hole (not shown) extending in the Z axis direction of  FIG. 2 . The objective lens  17  with its optical axis extending in the Z axis direction and having substantially the same diameter as this through hole is fixed to the upper face of the objective lens holding member  16 . The objective lens holding member  16  has four coupling parts  16   a  arranged at the −Y side corner portions of its +X side and −X side faces. The +Y side ends of the four support wires  18  are coupled to these coupling parts so that the objective lens  17  may be elastically supported by the four support wires  18  to be arranged at a substantially horizontal position. 
     The pair of drive magnets  19  corresponds to a pair of rectangular plate-shaped permanent magnets having long sides extending in the X axis direction. The drive magnets  19  may be fixed to the +Y side and −Y side faces of the objective lens holding member  16  with their N poles (i.e., colored portions in  FIG. 2 ) facing each other, for example. It is noted that the length of the drive magnets  19  in the X axis direction is arranged to be substantially greater than the width of the objective lens holding member  16 , and the +X side and −X side end portions of the drive magnets  19  are arranged to protrude from the +X side and −X side faces of the objective lens holding member  16 . In the following descriptions, such protruding portions of the drive magnets  19  may simply be referred to as ‘protruding portions’. 
       FIG. 3  is a perspective view of the coil unit  20  of the objective lens drive apparatus  10 A. As is shown in  FIG. 3 , the coil unit  20  includes a yoke member  21  that is fixed to the base  12 , a pair of focusing drive coils  22 A and  22 B, and a pair of tracking drive coils  23 A and  23 B. 
     The yoke member  21  is made of a magnetic material such as iron. As is shown in  FIG. 4 , the yoke member  21  includes a rectangular frame portion  21   a  that is fixed to the upper face of the base  12 , a pair of first yoke portions  21   c  having long sides extending in the X axis direction that are arranged at the +Y side and −Y side portions of the frame portion  21   a , and a pair of L-shaped second yoke portions  21   b  that are arranged at +X side and −X side portions of the frame portion  21   a . As is shown in  FIG. 3 , focusing-drive coils  22 A and  22 B having wires wound around shafts that are parallel to the Z axis are arranged on the first yoke portions  21   c , and tracking drive coils  23 A and  23 B having wires wound around shafts that are parallel to the X axis are arranged on the second yoke portions  21   b.    
     As is shown in  FIG. 1 , the coil unit  20  is arranged in the objective lens drive unit  10 A with the focusing drive coils  22 A and  22 B being positioned at the −Y side and +Y side of the objective lens holding member  16  via the drive magnets  19  and the tracking drive coils  23 A and  23 B being positioned within the space provided between the drive magnets  19  at the −X side and +X side of the objective lens holding member  16 . In this way, a magnetic circuit as is shown in  FIG. 5  may be formed in the objective lens drive apparatus  10 A so that the lines of magnetic force from the N poles of the drive magnets  19  may penetrate through the second yoke portion  21   b , the frame portion  21   a , and the first yoke portion  21   c  of the yoke member  21  to reenter the drive magnets  19  via their S poles as is illustrated by the arrows shown in  FIG. 5 . 
     In the above-described objective lens drive apparatus  10 A according to the first embodiment of the present invention, the X axis direction is arranged to correspond to the tracking direction, the Y axis direction, to the tangential direction, and the Z axis direction, to the focusing direction with respect to the optical disk so that a laser beam emitted in the Z axis direction and incident on the objective lens  17  may be focused on the recording layer of the optical disk. By exciting the focusing drive coils  22 A and  22 B, the objective lens  17  may be driven in the focusing direction (Z axis direction) by the interaction of the focusing coils  22 A and  22 B with the drive magnets  19 , and by exciting the tracking drive coils  23 A and  23 B, the objective lens  17  may be driven in the tracking direction (X axis direction) by the interaction of the tracking drive coils  23 A and  23 B with the drive magnets  19 . Also, by exciting the focusing drive coils  22 A and  22 B in opposite directions, the objective lens  17  may be moved around a shaft that is parallel to the X axis. 
     As can be appreciated from the above descriptions, in the objective lens drive apparatus  10 A according to the first embodiment of the present invention, the tracking direction end portions of the drive magnets  19  fixed to the objective lens holding member  16  are arranged to protrude from the −X side and +X side faces of the objective lens holding member  16 , the tracking drive coils  23 A and  23 B are arranged at the N pole side of the drive magnets  19 , and the focusing drive coils  22 A and  22 B are arranged at the S pole side of the drive magnets  19  (see  FIG. 1 ). In this way, both the magnetic field of the N pole side and the magnetic field of the S pole side of the drive magnets  19  may be used so that drive sensitivity for the objective lens  17  may be improved. 
     Also, in the present embodiment, the focusing drive coils  22 A,  22 B, and the tracking drive coils  23 A,  23 B are arranged around the first and second yoke portions  21   b  and  21   c  of the yoke member  21  that is made of magnetic material, and the lines of magnetic force from the N poles of the drive magnets  19  are guided through a magnetic circuit including the yoke member  21  to be directed toward the S poles of the drive magnets  19  (see  FIG. 5 ). In this way, the lines of magnetic force from the N poles of the drive magnets  19  opposing each other may pass through the focusing drive coils  22 A,  22 B, and the tracking drive coils  23 A,  23 B in an efficient manner without reacting to each other so that the magnetic fields generated by the drive magnets  19  may be efficiently used and drive sensitivity for the objective lens  17  may be improved as a result. 
     Second Embodiment 
     A second embodiment of the present invention is described below with reference to  FIGS. 6-8 . It is noted that in these drawings, elements that are substantially identical to those shown in  FIGS. 1-5  of the first embodiment are given the same reference numerals and their descriptions are omitted or simplified. 
       FIG. 6  is a perspective view of an objective lens drive apparatus  10 B according to the second embodiment of the present invention. The illustrated objective lens drive apparatus  10 B of the second embodiment may be distinguished from the objective lens drive apparatus  10 A of the first embodiment in that the yoke member  21  of the coil unit  20  is arranged into a different shape and the drive coils  22 A,  22 B,  23 A, and  23 B are arranged in different positions. 
       FIG. 7  is a perspective view of the coil unit  20  of the objective lens drive apparatus  10 B according to the second embodiment. As is shown in  FIG. 7 , the yoke member  21  of the coil unit  20  according to the present embodiment includes a first yoke portion  21   d  that is arranged into a rectangular frame and L-shaped second yoke portions  21   e  that are connected to the +X side and −X side of the first yoke portion  21   d . Focusing drive coils  22 A and  22 B having wires wound around shafts that are parallel to the Z axis are arranged on the second yoke portions  21   e , and tracking coils  23 A and  23 B having wires wound around shafts that are parallel to the X axis are arranged on the −Y side and the +Y side of the first yoke portion  21   d.    
     As is shown in  FIG. 6 , the coil unit  20  of the present embodiment is arranged in the objective lens drive apparatus  10 B with the tracking drive coils  23 A and  23 B being arranged at the −Y side and +Y side of the objective lens holding member  16  via the drive magnets  19  and the focusing drive coils  22 A and  22 B being arranged within the spaces provided between the drive magnets  19  at the −X side and +X side of the objective lens holding member  16 . In this way, a magnetic circuit as is shown in  FIG. 8  may be formed in the objective lens drive apparatus  10 B so that the lines of magnetic force from the N poles of the drive magnets  19  penetrate through the second yoke portions  21   e  and the first yoke portion  21   d  of the yoke member  21  to be directed back to the S poles of the drive magnets  19  as is illustrated by the arrows shown in  FIG. 8 . 
     In the objective lens drive apparatus  10 B according to the second embodiment of the present invention, by exciting the focusing drive coils  22 A and  22 B, the objective lens  17  may be driven in the focusing direction (Z axis direction) by the interaction of the focusing coils  22 A and  22 B with the drive magnets  19 , and by exciting the tracking drive coils  23 A and  23 B, the objective lens  17  may be driven in the tracking direction (X axis direction) by the interaction of the tracking drive coils  23 A and  23 B with the drive magnets  19 . Also, by exciting the focusing drive coils  22 A and  22 B in opposite directions, the objective lens  17  may be moved around a shaft that is parallel to the Y axis. 
     As can be appreciated from the above descriptions, in the objective lens drive apparatus  10 B according to the second embodiment of the present invention, the tracking direction end portions of the drive magnets  19  fixed to the objective lens holding member  16  are arranged to protrude from the −X side and +X side faces of the objective lens holding member  16 , the focusing drive coils  22 A and  22 B are arranged at the N pole side of the drive magnets  19 , and the tracking drive coils  23 A and  23 B are arranged at the S pole side of the drive magnets  19  (see  FIG. 6 ). In this way, both the magnetic field of the N pole side and the magnetic field of the S pole side of the drive magnets  19  may be used so that drive sensitivity for the objective lens  17  may be improved. 
     Also, in the present embodiment, the focusing drive coils  22 A,  22 B, and the tracking drive coils  23 A,  23 B are arranged around the first and second yoke portions  21   d  and  21   e  of the yoke member  21  that is made of magnetic material, and the lines of magnetic force from the N poles of the drive magnets  19  are guided through a magnetic circuit including the yoke member  21  to be directed toward the S poles of the drive magnets  19  (see  FIG. 8 ). In this way, the lines of magnetic force from the N poles of the drive magnets  19  opposing each other may pass through the focusing drive coils  22 A,  22 B, and the tracking drive coils  23 A,  23 B in an efficient manner without reacting to each other so that the magnetic fields generated by the drive magnets  19  may be efficiently used and drive sensitivity for the objective lens  17  may be improved as a result. 
     It is noted that a conventional optical disk uses a relatively thick substrate (e.g., having a thickness of approximately 1 mm); however, an optical disk system for the so-called flexible optical disk that uses a relatively thin substrate (e.g., having a thickness of approximately 0.1 mm) is presently being developed. The flexible optical disk is provided with flexibility so that it may be prevented from being damaged even when it is rotated at a high speed at which a conventional optical disk may be broken. Thus, by using such a flexible optical disk to realize high speed rotation, data transmission speed may be increased, for example. Also, air stabilizing techniques using a stabilizer may be implemented to prevent vertical deviation even during high speed rotation of the flexible optical disk. However, it is noted that since tracking direction eccentricity characteristics of the flexible optical disk may be substantially the same as those of the conventional disk, performance of the flexible optical system may be restricted more by its tracking direction characteristics rather than its focusing direction characteristics. In this respect, the objective lens drive apparatus  10 B according to the second embodiment is capable of securing a longer effective length for the tracking coils compared to the objective lens drive apparatus  10 A according to the first embodiment so that it may be better adapted for improving acceleration characteristics in the tracking direction than the acceleration characteristics in the focusing direction (Z axis direction). In other words, the objective lens drive apparatus  10 B according to the second embodiment is designed to meet the acceleration sensitivity characteristic requirements of a flexible optical disk system. 
     Third Embodiment 
     A third embodiment of the present invention is described below with reference to  FIGS. 9-11 . It is noted that in these drawings, elements that are substantially identical to those of the first embodiment and the second embodiment are given the same reference numerals and their descriptions are omitted or simplified. 
       FIG. 9  is a perspective view of an objective lens drive apparatus  10 C according to the third embodiment of the present invention. The illustrated objective lens drive apparatus  10 C of the third embodiment may be distinguished from the objective lens drive apparatuses  10 A and  10 B of the first and second embodiment in that the opposing faces of the drive magnets  19  are arranged to have different magnetic polarities. Also, as a consequence of such an arrangement, the base  12  is arranged to function as a yoke member in the present embodiment. 
       FIG. 10  is a perspective view of the base  12  according to the present embodiment. In  FIG. 10 , the base  12  is a rectangular frame-shaped member having a long side extending in the Y axis direction that is made of a magnetic material such as iron. The illustrated base  12  has a circular opening  12   c  formed at a position slightly toward the +Y side of its center for enabling passage of a laser beam transmitted through the objective lens  17 , first yoke portions  12   b  arranged at the +X side and −X side of the circular opening  12   c , and second yoke portions  12   a  arranged at the +Y side and −Y side of the circular opening  12   c . As is shown in  FIG. 9 , four tracking drive coils  23   1 ,  23   2 ,  23   3 , and  23   4  having wires wound around shafts that are parallel to the Y axis are fixed to the +Y side and −Y side faces of the first yoke portions  12   b , and focusing drive coils  22 A and  22 B having wires wound around shafts parallel to the Z axis are fixed to the second yoke portions  12   a . Thus, the focusing coils  22 A and  22 B are arranged at the −Y side and +Y side of the objective lens holding member  16  via the drive magnets  19 , and +X side portions of the tracking drive coils  23   1  and  23   2  where currents flow in the focusing direction (Z axis direction) and −X side portions of the tracking drive coils  23   3  and  23   4  where currents flow in the focusing direction (Z axis direction) are arranged within the spaces provided between the drive magnets  19 . 
     As is shown in  FIG. 11  a magnetic circuit is formed in the objective lens drive apparatus  10 C according to the present embodiment so that the lines of magnetic force from the N pole of the drive magnet  19  arranged at the −Y side of the objective lens holding member  16  penetrate through the portions of the tracking drive coils  23   1 - 23   4  where currents flow in the focusing direction to enter the S pole of the opposing drive magnet  19  arranged at the +Y side of the objective lens holding member  16 . Then, the lines of magnetic force exit the drive magnet  19  arranged at the +Y side from its N pole to successively penetrate through the focusing drive coil  22 B, the second yoke portion  12   a  on which the focusing drive coil  22 B is arranged, the base  12 , the focusing drive coil  22 A, and the second yoke portion  12   a  on which the focusing drive coil  22 A is arranged in this order after which the lines of magnetic force reenter the drive magnet  19  arranged at the −Y side from its S pole. According to the present embodiment, magnetic fields from the drive magnets  19  may be prevented from cancelling each other without having to create a magnetic circuit using a dedicated yoke member such as the yoke member  21  of the objective lens drive apparatuses  10 A and  10 B according to the first and second embodiments. Therefore, more lines of magnetic force may be arranged to penetrate through the portions of the tracking drive coils  23   1 - 23   4  where currents flow in the focusing direction so that drive sensitivity for the objective lens  17  may be improved. 
     It is noted that in the objective lens drive apparatus  10 C according to the third embodiment of the present invention, four tracking drive coils  23   1 - 23   4  are used. With such a configuration, the distance between the tracking drive coils  23   1 - 23   4  and the drive magnets  19  may be adjusted by adjusting the thickness of the first yoke portions  12   b  of the base  12 . Accordingly, even when general purpose coils are used as the tracking drive coils  23   1 - 23   4 , for example, adequate gaps may be secured between the tracking drive coils  23   1 - 23   4  and the drive magnets  19 . Also, the present embodiment may be modified to have the tracking drive coils  23   1  and  23   2  integrated into a single tracking coil  23 A and the tracking drive coils  23   3  and  23   4  integrated into a single tracking coil  23 B as is shown in  FIG. 12 . 
     Further, the present embodiment may be modified to have a configuration as is shown in  FIG. 13  where the protruding portions of the drive magnets  19  are each divided into regions A and B having differing magnetic pole orientations, region A facing one X direction side portion of a tracking drive coil  23  and region B facing the other X direction portion of the tracking drive coil  23 , and regions of the drive magnets  19  opposing each other are arranged to have differing magnetic polarities. In this way, the lines of magnetic force from the drive magnets may be arranged in the directions illustrated by the arrows shown in  FIG. 13 . Specifically, electric fields in opposite directions may be applied to the +X side and the −X side of the drive coils  23  so that the electromagnetic force generated by interaction of the drive coils  23  with the drive magnets  19  may be increased by approximately two times, for example. Also, by arranging the lines of magnetic force from region A to reenter the drive magnet  19  from region B, the lines of magnetic force may penetrate through the drive coils  23  in an efficient manner so that the drive sensitivity for the objective lens  17  may be improved as a result. 
     It is noted that although the drive magnets  19  are arranged into rectangular plates in the above-described embodiments of the present invention, other embodiments of the present invention may use drive magnets  19  having different configurations as is shown in  FIG. 14 , for example. In  FIG. 14 , the portions of the drive magnets  19  protruding from the objective lens holding member  16  are arranged to be thicker in the tangential direction (Y axis direction). By arranging the protruding portions at the sides to be thicker than the portions of the drive magnets  19  at the center, weight increase of the drive magnets  19  may be controlled to a minimum while increasing the magnetic field intensity of regions surrounding the drive coils, for example. 
       FIG. 15  illustrates another embodiment in which the portions of the drive magnets  19  protruding from the objective lens holding member  16  are arranged to be wider than the center portions. Specifically, dimensions of the protruding portions are increased in the focusing direction (Z axis direction). By arranging the protruding portions of the drive magnets  19  at the sides to be wider than the center portions, weight increase of the drive magnets  19  may be controlled to a minimum while increasing the effective areas of the opposing faces of the drive coils. 
     Also, it is noted that print coils formed on a printed circuit board may be used as the drive coils of the above-described embodiments, for example. In this way, unevenness of the drive coil surfaces may be reduced so that gaps formed between the drive magnets and the drive coils may be narrowed and the lines of magnetic force penetrating through the drive coils may be increased to thereby improve the drive sensitivity for the objective lens. 
     &lt;Optical Disk Apparatus&gt; 
     In the following, an optical disk apparatus including an objective lens drive apparatus according to an embodiment of the present invention is described. 
       FIG. 16A  is a plan view and  FIG. 16B  is a side view of an optical disk apparatus  50  that includes the above-described objective lens drive apparatus  10 A. As is shown in these drawings, the optical disk apparatus  50  includes a housing  51 , a rubber vibration isolator  52  that is arranged on the upper face of the housing  51 , an optical pickup module base  53  that is supported by the rubber vibration isolator  52  to be substantially horizontal, a spindle motor  54  that supports an optical disk  70  and enables the optical disk  70  to rotate around a shaft that is parallel to the Z axis, a pair of seek rails  55  extending in the X axis direction and arranged at the +Y side and −Y side of the upper face of the pickup module base  53 , and an optical pickup  42  that is guided by the pair of seek rails  55  and moves the objective lens drive apparatus  10 A in the X axis direction. 
       FIG. 17  is a diagram showing a configuration of the optical pickup  42  of the optical disk apparatus  50 . As is shown in this drawing, the optical pickup  42  includes a light source  43 , a collimator lens  44 , a beam splitter  45 , a mirror  46 , a condenser lens  47 , a cylindrical lens  48 , an optical receiver  49 , and the objective lens drive apparatus  10 A. In the illustrated optical pickup  42 , a laser beam emitted from the light source  43  is made substantially parallel by the collimator lens  44  after which the collimated laser beam passes through the beam splitter  45  to be incident on and reflected by the mirror  46 . The reflected laser beam is directed upward to be incident on the objective lens  17  of the objective lens drive apparatus  10 A so that a laser spot may be formed on the optical disk  70 . Also, a laser beam reflected by the optical disk  70  passes through the objective lens  17  and is refracted in a downward direction by the beam splitter  45  to be incident to the optical receiver  49  via the condenser lens  47  and the cylindrical lens  48 . 
     In the optical disk apparatus  50 , the optical pickup  42  is arranged to carry out seek operations with respect to the optical disk  70  that is driven by the spindle motor  54  to rotate at a predetermined rotational speed so that an opto-electric conversion signal may be output from the optical receiver  49 , and the focusing drive coils  22 A,  22 B and the tracking drive coils  23 A,  23 B of the objective lens drive apparatus  10 A are driven based on this opt-electric conversion signal. In this way, the objective lens  17  may be controlled to follow the positional change of the track formed on the optical disk  70  to read information recorded on the optical disk  70  and record information on the optical disk  70 . 
     As can be appreciated from the above descriptions, by including the objective lens drive apparatus  10 A, the optical pickup  42  may be able to accurately drive the objective lens  17  to thereby accurately focus a laser beam on a track of an optical disk. Also, since the objective lens drive apparatus  10 A has good acceleration sensitivity characteristics and high degree resonance characteristics, read/write operations may be accurately performed even when the optical disk is rotated at high speed. It is noted that although the above-described optical pickup  42  according to an embodiment of the present invention uses the objective lens drive apparatus  10 A, in other embodiments, the objective lens drive apparatus  10 B or  10 C may be used, for example. 
     Also, by including the optical pickup  42 , the optical disk apparatus may be able to accurately focus a laser beam on a track of the optical disk  70  so that it may accurately read/write information from/on the optical disk  70 . 
     As can be appreciated from the above descriptions, an objective lens drive apparatus according to an embodiment of the present invention may be used to accurately drive an objective lens upon reading/writing information from/on an optical disk. An optical pickup according to an embodiment of the present invention may be used to accurately focus a laser beam on a track of an optical disk. An optical disk apparatus according to an embodiment of the present invention may be used to accurately read/write information from/on an optical disk. 
     Although the present invention is shown and described with respect to certain preferred embodiments, it is obvious that equivalents and modifications may occur to others skilled in the art upon reading and understanding the specification. The present invention includes all such equivalents and modifications, and is limited only by the scope of the claims. 
     The present application is based on and claims the benefit of the earlier filing date of Japanese Patent Application No. 2006-343713 filed on Dec. 21, 2006, the entire contents of which are hereby incorporated by reference.