Abstract:
In order to simplify operation control and achieve smaller-sized apparatuses, the present invention provides an object lens drive apparatus having a fixed block, a movable block holding an objective lens, support springs connecting the fixed block and the movable block, a focusing coil, tracking coils, a tilt coil, first magnets constituting a first magnetic circuit, and a second magnet constituting a second magnetic circuit and arranged in a state being inserted in the tilt coil. The objective lens and the second magnet are positioned separately in a direction orthogonal to both a focusing and tracking directions. The second magnet is polarized to an N pole and an S pole parallely in the tracking direction. Portions of the tilt coil opposed to each other in the tracking direction with the second magnet put therebetween are formed to be tilt drive portions moving the movable block in a tilt direction.

Description:
CROSS REFERENCES TO RELATED APPLICATIONS  
       [0001]     The present document is based on Japanese Priority Document JP 2003-295058, filed in the Japanese Patent Office on Aug. 19, 2003, the entire contents of which being incorporated herein by reference.  
       BACKGROUND OF THE INVENTION  
       [0002]     1. Field of the Invention  
         [0003]     The present invention relates to an optical pickup and a disc drive apparatus. More minutely, the present invention relates to a technical field of an optical pickup including an objective lens driving apparatus in which a movable block is supported by a fixed block with a support spring put between them and the movable block is moved in three directions of a focusing direction, a tracking direction and a tilt direction, and a disc drive apparatus provided with the optical pickup.  
         [0004]     2. Description of Related Art  
         [0005]     There is a disc drive apparatus for performing the recording and the reproducing of an information signal into and from a disc-shaped recording medium such as an optical disc and a magneto-optical disc. Such a disc drive apparatus is provided with an optical pickup, which moves in a radial direction of the disc-shaped recording medium to radiate a laser beam to the disc-shaped recording medium.  
         [0006]     The optical pickup is provided with an objective lens driving apparatus. A focusing adjustment is carried out by the objective lens driving apparatus moving an objective lens held by the movable block thereof in a focusing direction, which is the direction in which the movable block approaches to or withdraws from the recording surface of the disc-shaped recording medium. Also a tracking adjustment is carried out by the objective lens driving apparatus by moving the objective lens in a tracking direction, which is substantially a radial direction of the disc-shaped recording medium, and thereby the optical pickup condenses the spot of a laser beam to be radiated onto the disc-shaped recording medium through the objective lens to a recording track of the disc-shaped recording medium.  
         [0007]     As described above, the optical pickup generally performs the focusing adjustment and the tracking adjustment by means of the objective lens driving apparatus. However, in recent years, for achieving the improvement of the traceability of a spot of a laser beam to a recording track, an objective lens driving apparatus called “three-axis actuator” has been developed. The three-axis actuator also enables the adjustment at the time of the occurrence of surface vibrations and the like of a rotating disc-shaped recording medium by enabling the movable block to tilt to the recording surface of the disc-shaped recording medium in addition to the two-axis direction adjustment of the focusing adjustment and the tracking adjustment.  
         [0008]     Such objective lens driving apparatuses called the three-axis actuators, for example, include one which moves a movable block in three directions of a focusing direction, a tracking direction and a tilt direction by means of a plurality of coil bodies each made by unifying a focusing coil, a tracking coil and a tilt coil (see, for example, Patent Document 1).  
         [0009]     Moreover, the objective lens driving apparatus called the three-axis actuators, for example, also include one which moves a movable block into a focusing direction and a tracking direction by means of a coil body made by unifying a focusing coil and a tracking coil, and which moves the movable block in a tilt direction by means of a plurality of tilt coils provided separately from the focusing coil and the tracking coil (see, for example, Patent Document 2).  
         [0010]     [Patent Document 1] Japanese Patent Application Publication No. Hei 10-261233  
         [0011]     [Patent Document 2] Japanese Patent Application Publication No. 2001-110075  
       SUMMARY OF THE INVENTION  
       [0012]     However, because three kinds of coils of the focusing coils, the tracking coils and the tilt coils, each having a different function from each other, are unified in the above-mentioned conventional objective lens driving apparatus of the optical pickup shown in Patent Document 1, the operation control of the objective lens driving apparatus is complicated. Also because the focusing coils are severally divided into a plurality of portions, there is a possibility that the decrease of sensitivity at a focusing operation occurs.  
         [0013]     On the other hand, because the tilt coils are separately arranged from the focusing coil and the tracking coil in the conventional objective lens driving apparatus of the optical pickup shown in Patent Document 2, the simplification of operation control can be achieved. However, the plurality of tilt coils and a plurality of tilt magnets positioned to be opposed to the tilt coils are needed, and then the objective lens driving apparatus has problems of the increase of the number of parts and of the growth in size.  
         [0014]     Accordingly, an optical pickup and a disc drive apparatus according to the present invention each have an object to overcome the above-mentioned problems to achieve the simplification of operation control, miniaturization and the like.  
         [0015]     For solving the above-mentioned problems, an objective lens driving apparatus and a disc drive apparatus according to the present invention are severally provided with as components of the objective lens driving apparatus a fixed block, a movable block, a support spring, a focusing coil, a tracking coil, a tilt coil, a first magnet, and a second magnet. The fixed block is fixed to a moving base. The movable block moves in a focusing direction being one in which the movable block approaches to or withdraws from a recording surface of the disc-shaped recording medium against the fixed block, a tracking direction being substantially a radial direction of the disc-shaped recording medium, and a tilt direction being a rotation direction around an axis perpendicular to both of the focusing direction and the tracking direction, and holds the objective lens. The support spring connects the fixed block and the movable block with each other. The focusing coil is energized at the time when the movable block operates into the focusing direction, the tracking coil is energized at the time when the movable block operates into the tracking direction, and the tilt coil is energized at the time when the movable block operates into the tilt direction. The first magnet constitutes a first magnetic circuit together with the focusing coil and the tracking coil, and the second magnet constitutes a second magnetic circuit together with the tilt coil and is arranged in a state in which the second magnet is inserted into the tilt coil. In the objective lens driving apparatus, the objective lens and the second magnet are positioned separately in a direction perpendicular to both of the focusing direction and the tracking direction, the second magnet has an N pole and an S pole, both polarized in juxtaposition in the tracking direction, and portions of the tilt coil opposed to each other in the tracking direction with the second magnet put therebetween are severally formed to be a tilt drive portion for moving the movable block in the tilt direction.  
         [0016]     Consequently, in the objective lens driving apparatus and the disc drive apparatus according to the present invention, the tilt coil is arranged independently from the focusing coil and the tracking coil, and the second magnet for a tilt drive is arranged inside of the tilt coil.  
         [0017]     An optical pickup according to the present invention is one provided with a moving base moving in a radial direction of a disc-shaped recording medium mounted on a disc table, and an objective lens driving apparatus arranged in the moving base. The objective lens driving apparatus includes: a fixed block, a movable block, a support spring, a focusing coil, a tracking coil, a tilt coil, a first magnet, and a second magnet. The fixed block is fixed to a moving base. The movable block moves in a focusing direction being one in which the movable block approaches to or withdraws from a recording surface of the disc-shaped recording medium against the fixed block, a tracking direction being substantially a radial direction of the disc-shaped recording medium, and a tilt direction being a rotation direction around an axis perpendicular to both of the focusing direction and the tracking direction, and holds the objective lens. The support spring connects the fixed block and the movable block with each other. The focusing coil is energized at the time when the movable block operates into the focusing direction, the tracking coil is energized at the time when the movable block operates into the tracking direction, and the tilt coil is energized at the time when the movable block operates into the tilt direction. The first magnet constitutes a first magnetic circuit together with the focusing coil and the tracking coil, and the second magnet constitutes a second magnetic circuit together with the tilt coil and is arranged in a state in which the second magnet is inserted into the tilt coil. In the objective lens driving apparatus, the objective lens and the second magnet are positioned separately in a direction perpendicular to both of the focusing direction and the tracking direction, the second magnet has an N pole and an S pole, both polarized in juxtaposition in the tracking direction, and portions of the tilt coil opposed to each other in the tracking direction with the second magnet put therebetween are severally formed to be a tilt drive portion for moving the movable block in the tilt direction.  
         [0018]     Consequently, because the first magnetic circuit for performing a focusing drive and a tracking drive and the second magnetic circuit for performing a tilt drive are formed separately from each other, the simplification of operation control can be achieved, and furthermore the improvement of sensitivity at a focusing operation can be achieved.  
         [0019]     Moreover, because the second magnet having the n pole and the s pole, both polarized in juxtaposition in the tracking direction, is arranged in a state in which the second magnet is inserted into the tilt coil, the space inside of the tilt coil can be effectively used as an arrangement space of the second magnet, and consequently miniaturization can be achieved by the degree of the space.  
         [0020]     In another aspect of the present invention, the focusing coil is arranged between the objective lens and the second magnet, and the movable block is configured to tilt into the tilt direction owing to a traverse of a leakage flux of the second magnet across the focusing coil when the focusing coil is energized, and further positions of the N pole and the S pole of the second magnet are set in order that a tilt of the movable block owing to the leakage flux of the second magnet when the focusing coil is energized may be in a same direction as a tilt direction of a recording surface owing to a warpage of the disc-shaped recording medium. Consequently, the drive quantity of the movable block by the second magnetic circuit at the time of the tilt drive can be decreased, and thereby it can be achieved to make operation control easier and to decrease electric power consumption.  
         [0021]     Moreover, because the direction in which the tilt drive is performed by the second magnetic circuit is the same as the direction in which the movable block is tilted owing to the influence of the leakage flux of the second magnet, the force generated by the second magnetic circuit and the force generated by the influence of the leakage flux of the second magnet are not to be any resistance to each other, and thereby the improvement of the reliability of the operation of the focusing drive and the tilt drive can be achieved.  
         [0022]     A disc drive apparatus according to the present invention is a disc drive apparatus equipped with a disc table, on which a disc-shaped recording medium is mounted, and an optical pickup radiating a laser beam to the disc-shaped recording medium mounted on the disc table through an objective lens. The optical pickup includes a moving base moving into a radial direction of the disc-shaped recording medium mounted on the disc table, and an objective lens driving apparatus arranged on the moving base. The objective lens driving apparatus includes: a fixed block, a movable block, a support spring, a focusing coil, a tracking coil, a tilt coil, a first magnet, and a second magnet. The fixed block is fixed to a moving base. The movable block moves in a focusing direction being one in which the movable block approaches to or withdraws from a recording surface of the disc-shaped recording medium against the fixed block, a tracking direction being substantially a radial direction of the disc-shaped recording medium, and a tilt direction being a rotation direction around an axis perpendicular to both of the focusing direction and the tracking direction, and holds the objective lens. The support spring connects the fixed block and the movable block with each other. The focusing coil is energized at the time when the movable block operates into the focusing direction, the tracking coil is energized at the time when the movable block operates into the tracking direction, and the tilt coil is energized at the time when the movable block operates into the tilt direction. The first magnet constitutes a first magnetic circuit together with the focusing coil and the tracking coil, and the second magnet constitutes a second magnetic circuit together with the tilt coil and is arranged in a state in which the second magnet is inserted into the tilt coil. In the objective lens driving apparatus, the objective lens and the second magnet are positioned separately in a direction perpendicular to both of the focusing direction and the tracking direction, the second magnet has an N-pole and an S-pole, both polarized in juxtaposition in the tracking direction, and portions of the tilt coil opposed to each other in the tracking direction with the second magnet put therebetween are severally formed to be a tilt drive portion for moving the movable block in the tilt direction.  
         [0023]     Consequently, because the first magnetic circuit for performing a focusing drive and a tracking drive and the second magnetic circuit for performing a tilt drive are formed separately from each other, the simplification of operation control can be achieved, and furthermore the improvement of sensitivity at a focusing operation can be achieved.  
         [0024]     Moreover, because the second magnet having the n pole and the s pole, both polarized in juxtaposition in the tracking direction, is arranged in a state in which the second magnet is inserted into the tilt coil, the space inside of the tilt coil can be effectively used as an arrangement space of the second magnet, and consequently miniaturization can be achieved by the degree of the space.  
         [0025]     In still another aspect of the present invention, the focusing coil is arranged between the objective lens and the second magnet, and the movable block is configured to tilt in the tilt direction owing to a traverse of the focusing coil by a leakage flux of the second magnet when the focusing coil is energized, and further positions of the N pole and the S pole of the second magnet are set in order that a tilt of the movable block owing to the leakage flux of the second magnet when the focusing coil is energized may be in a same direction as a tilt direction of the recording surface owing to a warpage of the disc-shaped recording medium. Consequently, the drive quantity of the movable block by the second magnetic circuit at the tilt drive can be decreased, and thereby it can be achieved to make operation control easier and to decrease electric power consumption.  
         [0026]     Moreover, because the direction in which the tilt drive is performed by the second magnetic circuit is the same as the direction in which the movable block is tilted owing to the influence of the leakage flux of the second magnet, the force generated by the second magnetic circuit and the force generated by the influence of the leakage flux of the second magnet are not to be any resistance to each other, and thereby the improvement of the reliability of the operation of the focusing drive and the tilt drive can be achieved.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0027]      FIG. 1  shows an embodiment the present invention together with  FIGS. 2-5 , and  FIG. 1  is a schematic perspective view of a disc drive apparatus.  
         [0028]      FIG. 2  is an enlarged perspective view of an objective lens driving apparatus.  
         [0029]      FIG. 3  is an enlarged plan view of the objective lens driving apparatus.  
         [0030]      FIG. 4  is an enlarged rear view of the objective lens driving apparatus, in which a fixed block is omitted to be shown.  
         [0031]      FIG. 5  is a conceptual view for illustrating an operation state of a movable block of the objective lens driving apparatus. 
     
    
     DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0032]     In the following, preferred embodiments of an optical pickup and a disc drive apparatus according to the present invention will be described with reference to the attached drawings.  
         [0033]     A disc drive apparatus  1  is formed of each of required members and mechanisms, all arranged in an external housing  2  (see  FIG. 1 ), and a not shown disc insertion opening is formed in the external housing  2 .  
         [0034]     A not shown chassis is disposed in the external housing  2 , and a disc table  3  is fixed to a motor shaft of a spindle motor attached to the chassis.  
         [0035]     Parallel guide shafts  4  are attached to the chassis, and a lead screw  5  rotated by a not shown feed motor is supported on the chassis.  
         [0036]     An optical pickup  6  includes a moving base  7 , required optical parts provided on the moving base  7 , and an objective lens driving apparatus  8  disposed on the moving base  7 . Bearing portions  7   a  and  7   b  formed on both ends of the moving base  7  are severally supported by the guide shafts  4  slidably (see  FIG. 1 ). A not shown nut member provided on the moving base  7  is screwed with the lead screw  5 . When the lead screw  5  is rotated by the feed motor, the nut member is fed in the direction corresponding to the rotation direction of the lead screw  5 , and then the optical pickup  6  is moved to a radial direction of a disc-shaped recording medium  100  mounted on the disc table  3 .  
         [0037]     The objective lens driving apparatus  8  includes a base member  9 , a fixed block  10  and a movable block  11  moving to the fixed block  10  (see  FIGS. 2-4 ).  
         [0038]     Each part of the base member  9  is made of a magnetic metallic material in a single body. The base member  9  is composed of a base portion  9   a  attached to the moving base  7 , and yoke portions  9   b  bent to stand perpendicularly severally at both of a front end and a rear end of the base portion  9   a.    
         [0039]     First magnets  12  are severally attached to the surfaces, which are opposed to each other, of the yoke portions  9   b.    
         [0040]     A second magnet  13  is attached to the rear end of the base portion  9   a . The second magnet  13  is formed in a shape of a square bar elongated in the vertical direction, and is polarized into an N pole and an S pole in a right and left direction, or the tracking direction.  
         [0041]     The fixed block  10  is fixed on the moving base  7 , and includes four spring attachment portions  10   a  separately in upper, lower, right and left positions at the rear end of the fixed block  10 . A circuit board  14  is attached to the rear surface of the fixed block  10 , and the circuit board  14  is connected to a not shown power supply circuit.  
         [0042]     One end of each of support springs  15  is attached to the spring attachment portions  10   a  of the fixed block  10 , and the end of each of the support springs  15  is connected to the circuit board  14  attached to the fixed block  10 . A drive current for a focusing drive or a tracking drive is supplied from the power supply circuit to the support springs  15  through the circuit board  14 .  
         [0043]     The movable block  11  is composed of a lens attachment portion  16  positioned on the front side and a magnetic circuit portion  17  positioned on the rear side, both formed in a single body.  
         [0044]     Two spring attachment projection portions  16   a  are severally provided on the right side and on the left side of the lens attachment portion  16 . The two spring attachment projection portions  16   a  are severally separated into an upper one and a lower one. The other end of each of the support springs  15  is attached to each of the spring attachment projection portions  16   a . Consequently, the movable block  11  is connected with the fixed block  10  to be held in the air with the support springs  15 .  
         [0045]     An arrangement hole  17   a  penetrating the magnetic circuit portion  17  from the upper side to the lower side is formed in the magnetic circuit portion  17 . A coil attachment portion  17   b  is formed at the central part in the right and left direction at the rear end of the magnetic circuit portion  17 .  
         [0046]     An objective lens  18  is attached to the top surface of the lens attachment portion  16  to be held thereat.  
         [0047]     A coil body  19  is attached to the magnetic circuit portion  17 . The coil body  19  is formed of a focusing coil  20  and tracking coils  21 , which are connected to the focusing coil  20 .  
         [0048]     The focusing coil  20  is formed to be substantially a square pillar long from side to side the axial direction of which coincides with the upper and lower direction. The tracking coils  21  are severally formed to be a thin ring the axial direction of which coincides with the front and rear direction, and are attached to the front surface of the focusing coil  20  in parallel to each other on the right and the left sides. The coil body  19  is attached to the inner peripheral surface of the magnetic circuit portion  17  with being disposed in the arrangement hole  17   a . In the state in which the coil body  19  is attached to the magnetic circuit portion  17 , a space is formed on the front side of the coil body  19 .  
         [0049]     The yoke portions  9   b  of the base member  9 , and the first magnets  12  attached to the yoke portions  9   b  are inserted into the arrangement hole  17   a  of the magnetic circuit portion  17  to be arranged therein. The first magnets  12  are positioned to be opposed to each other with a portion positioned on the front side of the focusing coil  20  and the tracking coils  21  put between them.  
         [0050]     The base portion  9   a  and the yoke portions  9   b  of the base member  9 , the first magnets  12 , the focusing coil  20  and the tracking coils  21  constitute a first magnetic circuit  22  for moving the movable block  11  in the focusing direction or the tracking direction.  
         [0051]     A drive current is supplied from the power supply circuit to each of the focusing coil  20  and the tracking coils  21  through the circuit board  14  and the support springs  15 , which are attached to the fixed block  10 .  
         [0052]     When the drive current flows through the focusing coil  20 , a thrust force is generated into a predetermined direction according to the direction of the drive current flowing through the focusing coil  20 , and the movable block  11  is moved against the fixed block  10  in an F-F direction shown in  FIGS. 2 and 4 , i.e. in the focusing direction being one in which the movable block  11  approaches to or withdraws from the recording surface of the disc-shaped recording medium  100  mounted on the disc table  3 .  
         [0053]     When the drive current is supplied to the tracking coils  21 , a thrust force is generated into a predetermined direction according to the direction of the drive current flowing through the tracking coils  21 , the movable block  11  is moved against the fixed block  10  in a T-T direction shown in  FIGS. 2-4 , i.e. in the tracking direction being substantially a radial direction of the disc-shaped recording medium  100  mounted on the disc table  3 .  
         [0054]     A tilt coil  23  is attached to the coil attachment portion  17   b  of the magnetic circuit portion  17 . The tilt coil  23  is formed to be substantially a square pillar having an axial direction in the upper and lower direction. Portions of the tilt coil  23  positioned separately on the left side and the right side of the tilt coil  23  are formed to be tilt drive portions  23   a  and  23   b , respectively, for performing a tilt drive.  
         [0055]     The second magnet  13  attached to the base portion  9   a  of the base member  9  is inserted into the inside of the tilt coil  23  to be disposed therein. Consequently, the tilt coil  23  and the second magnet  13  constitute a second magnetic circuit  24  for moving the movable block  11  in the tilt direction.  
         [0056]     A drive current is supplied to the tilt coil  23  from the power supply circuit through, for example, a flexible printed wiring board, a Litz wire or the like, which is not shown.  
         [0057]     When the drive current is supplied to the tilt coil  23 , a thrust force is generated in a predetermined direction according to the direction of the drive current flowing through the tilt coil  23 , and the movable block  11  is moved against the fixed block  10  in an R-R direction shown in  FIGS. 2 and 4 , i.e. the tilt direction being a rotation direction around the axis orthogonal to both of the focusing direction and the tracking direction.  
         [0058]     When the movable block  11  is moved in the focusing direction, the tracking direction or the tilt direction, the support springs  15  are elastically deformed.  
         [0059]     When the disc table  3  is rotated owing to the rotation of the spindle motor in the disc drive apparatus  1  configured as above, the disc-shaped recording medium  100  mounted on the disc table  3  is rotated, and at the same time the optical pickup  6  is moved into a radial direction of the disc-shaped recording medium  100 . Thereby, a recording operation or a reproducing operation of the disc-shaped recording medium  100  is performed.  
         [0060]     When a drive current is supplied to the focusing coil  20  in the recording operation or the reproducing operation, the movable block  11  of the objective lens driving apparatus  8  is moved against the fixed block  10  in the focusing direction F-F shown in  FIGS. 2 and 4  as described above, and a focusing adjustment is performed in order that a spot of a laser beam exited from a not shown semiconductor laser provided on the moving base  7  to be radiated through the objective lens  18  may be condensed on a recording track on the disc-shaped recording medium  100 . Moreover, when a drive current is supplied to the tracking coils  21 , the movable block  11  of the objective lens driving apparatus  8  is moved against the fixed block  10  in the tracking direction T-T shown in  FIGS. 2-4  as described above, and a tracking adjustment is performed in order that the spot of a laser beam exited from the semiconductor laser to be radiated through the objective lens  18  may be condensed on a recording track of the disc-shaped recording medium  100 .  
         [0061]     In the recording operation and the reproducing operation of the disc-shaped recording medium  100 , a tilt adjustment is also performed at the same time in addition to the focusing adjustment and the tracking adjustment, both mentioned above. The tilt adjustment is performed by moving the movable block  11 , while rotating, in the tilt direction R-R shown in  FIGS. 2 and 4  in order to make the movable block  11  follow the disc-shaped recording medium  100  by means of a force generated according to a current flowing through the tilt drive portions  23   a  and  23   b  of the tilt coil  23  and a magnetic flux of the second magnet  13  when, for example, a tilt of the recording surface owing to a warpage of the disc-shaped recording medium  100 , surface vibrations of the disc-shaped recording medium  100  during rotation, or the like is produced.  
         [0062]     For example, when a current flowing in a clockwise direction as seen in a plane (S1 direction in  FIG. 3 ) is supplied to the tilt coil  23  in a case where the second magnet  13  is polarized into an N pole and an S pole as shown in  FIG. 4 , an upwardly oriented moving force is generated in the tilt drive portion  23   a  on one side, and a downwardly oriented moving force is generated in the tilt drive portion  23   b  on the other side. Consequently, the movable block  11  is moved in an R1 direction. Conversely, when a current flowing in a counter-clockwise direction as seen in a plane (S2 direction shown in  FIG. 3 ) is supplied to the tilt coil  23 , an downwardly oriented moving force is generated in the tilt drive portion  23   a  on one side, and an upwardly oriented moving force is generated in the tilt drive portion  23   b  on the other side. Consequently, the movable block  11  is moved in an R2 direction.  
         [0063]     As described above, because the first magnetic circuit  22  for performing the focusing drive and the tracking drive and the second magnetic circuit  24  for performing the tilt drive are provided separately from each other in the objective lens driving apparatus  8 , the simplification of operation control can be achieved. Moreover, because the focusing coil  20  is configured to be only one, the improvement of sensitivity at the focusing operation can be achieved.  
         [0064]     Moreover, because the second magnet  13  polarize into the N pole and the S pole in parallel in the tracking direction is inserted into the tilt coil  23  to be disposed therein in the objective lens driving apparatus  8 , the space inside the tilt coil  23  can be effectively utilized as the arrangement space of the second magnet  13 , and thereby the miniaturization of the objective lens driving apparatus  8  can be achieved by an extent of the space.  
         [0065]     Because the second magnet  13  is disposed near to the focusing coil  20  in the objective lens driving apparatus  8 , the movable block  11  is influenced by a leakage flux from the second magnet  13  when the movable block  11  is moved in the focusing direction. That is, when a current flows through the focusing coil  20 , the movable block  11  is moved in the focusing direction, and the current oriented to the right side or the left side flows through a portion  20   a  positioned on the rear side of the focusing coil  20 . At this time, an upwardly or downwardly oriented moving force is generated at the portion  20   a  owing to a leakage flux P (see  FIG. 3 ) of the second magnet  13 , which operates in the way of traversing the portion  20   a.    
         [0066]     For example, when a current flows through the focusing coil  20  into a clockwise direction as seen in a plane, the movable block  11  is upwardly moved in accordance with the focusing drive, and a current flows through the portion  20   a  of the focusing coil  20  in the rightward direction (Q2 direction shown in  FIG. 3 ). At this time, the disc-shaped recording medium  100  is made to be in the state of a warpage in which the outer peripheral portion of the disc-shaped recording medium  100  is upwardly displaced owing to surface vibrations or the like (the state shown by a chain double-dashed line in  FIG. 5 ). Consequently, the movable block  11  is tilt-wise driven by the second magnetic circuit  24  into the direction (R2 direction shown in  FIG. 4 ) in which the portion positioned on the outer circumference side of the disc-shaped recording medium  100  is upwardly displaced and the portion positioned on the inner circumference side of the disc-shaped recording medium  100  is downwardly displaced in order to follow the warped direction of the disc-shaped recording medium  100 .  
         [0067]     When a current flows through the portion  20   a  of the focusing coil  20 , the moving force is generated at the portion  20   a  owing to the leakage flux of the second magnet  13  as described above. At this time, in the objective lens driving apparatus  8 , the polarized state of the second magnet  13  is set so that the influence of the leakage flux is oriented to the direction by which the movable block  11  is moved in the R2 direction. That is, the second magnet  13  is configured so that the N pole thereof resides on the left side and the S pole thereof resides on the right side. The downwardly oriented moving force is generated at the left side portion of the portion  20   a  (the portion positioned on the inner circumference side of the disc-shaped recording medium  100 ), and the upwardly oriented moving force is generated at the portion on the right side of the portion  20   a  (the portion positioned on the outer circumference side of the disc-shaped recording medium  100 ). The movable block  11  is tilted in the R2 direction shown in  FIGS. 4 and 5  (indicated by a chain double-dashed line in  FIG. 5 ) in order to follow the warped direction of the disc-shaped recording medium  100 .  
         [0068]     Conversely, when a current flows through the focusing coil  20  in the counter-clockwise direction as seen in a plane, the movable block  11  is downwardly moved in accordance with the focusing drive, and the current flows through the portion  20   a  of the focusing coil  20  toward the left side (Q1 direction shown in  FIG. 3 ). At this time, the disc-shaped recording medium  100  is made to be warped in which the outer peripheral portion of the disc-shaped recording medium  100  is downwardly displaced owing to surface vibrations or the like (the state shown by a dotted line in  FIG. 5 ). Consequently, the movable block  11  is tilt-wise driven by the second magnetic circuit  24  in the direction (R1 direction shown in  FIG. 4 ) in which the portion positioned on the outer circumference side of the disc-shaped recording medium  100  is downwardly displaced and the portion positioned on the inner circumference side of the disc-shaped recording medium  100  is upwardly displaced in order to follow the warped direction of the disc-shaped recording medium  100 .  
         [0069]     At this time, because the second magnet  13  is configured so that the N pole thereof resides on the left side and the S pole thereof resides on the right side, the upwardly oriented moving force is generated at the left side portion of the portion  20   a  (the portion positioned on the inner circumference side of the disc-shaped recording medium  100 ), and the downwardly oriented moving force is generated at the portion on the right side of the portion  20   a  (the portion positioned on the outer circumference side of the disc-shaped recording medium  100 ). The movable block  11  is consequently tilted in the R1 direction shown in  FIGS. 4 and 5  (indicated by a dotted line in  FIG. 5 ) in order to follow the warped direction of the disc-shaped recording medium  100 .  
         [0070]     Incidentally, if the objective lens driving apparatus  8  is set in order that the movable block  11  may be downwardly moved in accordance with the focusing drive when a current flows through the focusing coil  20  in the clockwise direction as seen in a plane, and that the movable block  11  may be upwardly moved in accordance with the focusing drive when a current flows through the focusing coil  20  in the counter-clockwise direction as seen in a plane, then the second magnet  13  is arranged to have the S pole on the left side and the N pole on the right side. Consequently, also in this case, the influence of the leakage flux of the second magnet  13  is exerted on the movable block  11  so as to tilt the movable block  11  in the warped direction of the disc-shaped recording medium  100  similarly to the above-described case.  
         [0071]     In the objective lens driving apparatus  8 , as described above, when a current flows through the focusing coil  20 , the influence of the leakage flux of the second magnet  13  is exerted on the movable block  11  so as to tilt the movable block  11  in the warped direction of the disc-shaped recording medium  100 .  
         [0072]     Consequently, the drive quantity of the movable block  11  by the second magnetic circuit  24  at the time of a tilt drive can be decreased, and it can be achieved to make the operation control easier and to decrease electric power consumption.  
         [0073]     Moreover, because the direction of a tilt drive by the second magnetic circuit  24  is the same as the direction of a tilt of the movable block  11  owing to the influence of the leakage flux of the second magnet  13 , the force generated by the second magnetic circuit  24  and the force generated by the influence of the leakage flux of the second magnet  13  are not any resistance to each other, the improvement of the reliability of the operation of the focusing drive and the tilt drive can be achieved.  
         [0074]     Incidentally, in the above, the so-called moving coil type objective lens driving apparatus  8 , in which the movable block  11  is provided with the focusing coil  20 , the tracking coils  21  and the tilt coil  23 , is exemplified to be described. However, the scope to which the present invention is applied is not limited to the moving coil type objective lens driving apparatus  8 , and the present invention can be also applied to the so-called moving magnet type objective lens driving apparatus, in which a fixed block is provided with a focusing coil, a tracking coil or a tilt coil and a movable block is provided with magnets corresponding to those coils.  
         [0075]     Moreover, in the above, the description is given to the case where the focusing direction is supposed to be the upper and lower direction and the tracking direction is supposed to be the right and left direction. However, these directions are shown as examples for the sake of the convenience of description, and the directions are not especially limited to those directions.  
         [0076]     The detailed forms and the configurations of the respective parts shown as the best mode for implementing the above-mentioned invention are all only examples of the actualization for implementing the present invention, and the scope of the present invention should not be interpreted to be limited to those forms and configurations.