Abstract:
In an objective lens driving device having a lens holder which is movable and holds an objective lens, coil devices are disposed around the objective lens and held by the lens holder. Around the objective lens, main magnets are disposed for applying driving forces to the coil devices according to energization to the coil devices. Furthermore, each of auxiliary magnets are disposed between adjacent ones of the coil devices. The auxiliary magnets apply forces to the coil devices according to the energization to the coil devices for supplementing the driving forces.

Description:
[0001]     This application claims priority to prior Japanese patent application JP 2003-396190, the disclosure of which is incorporated herein by reference.  
       BACKGROUND OF THE INVENTION  
       [0002]     This invention relates to an objective lens driving device suitable for use in an optical pickup of an optical disk drive or the like, and further relates to an optical pickup using it.  
         [0003]     An optical disk drive is a device for reading or writing information from or into an optical disk (CD, CD-ROM, CD-R, CD-RW, DVD-ROM, DVD+R, DVD-R, DVD-RAM, DVD+RW, DVD-RW, Blu-ray, AOD, or the like). In order to achieve reading or writing the information from or into the optical disk, the optical disk drive of this type comprises an optical pickup for irradiating a laser beam onto the optical disk and detecting its reflected light.  
         [0004]     In general, an optical pickup comprises a laser beam source for emitting a laser beam and an optical system for guiding the emitted laser beam to an optical disk and further guiding its reflected light to a photodetector. This optical system includes an objective lens disposed so as to confront the optical disk.  
         [0005]     It is necessary that the objective lens used in the optical pickup be accurately controlled in position with respect to a focus direction along an optical axis and a track direction along a radial direction of the optical disk to thereby accurately focus a laser beam on a track of a recording surface of the rotating optical disk. These controls are called a focusing control and a tracking control, respectively. Further, following improvement in recording density, there have recently been increasing demands for removing or suppressing the influence caused by warping of the optical disk. In view of this, it is also necessary that the objective lens be subjected to a so-called tilting control.  
         [0006]     In an objective lens driving device of this type, a lens holder holding the objective lens is elastically supported by a plurality of suspension wires for enabling the focusing control, the tracking control, and the tilting control. Further, focusing coils, tracking coils, and tilting coils are attached to the lens holder. These coils are partly located in gaps of a magnetic circuit. With this structure, the conventional objective lens driving device is capable of finely controlling a position and an inclination of the objective lens by controlling currents flowing through the respective coils.  
         [0007]     Recently, there has been available a super thin type optical disk drive called an ultra slim drive. In the super thin type optical disk drive of this type, an objective lens driving device is normally configured as a so-called asymmetry type. With this asymmetry type objective lens driving device, acceleration sensitivity can be enhanced, but it is quite difficult to prevent occurrence of undesired resonance such as rolling, pitching, or yawing of an objective lens.  
         [0008]     On the other hand, it has also been proposed to configure an objective lens driving device as a so-called symmetry type (e.g. see JP-A-2001-93177). With this symmetry type objective lens driving device, it is easy to prevent occurrence of undesired resonance of an objective lens, but acceleration sensitivity is lowered not only in the foregoing focus direction but in a so-called tilt direction. Therefore, it is difficult to achieve the speed-up of the optical disk drive.  
       SUMMARY OF THE INVENTION  
       [0009]     It is therefore an object of this invention to provide an objective lens driving device that can prevent occurrence of undesired resonance and increase acceleration sensitivity in focus and tilt directions, thereby enabling the speed-up of an optical disk drive.  
         [0010]     It is another object of this invention to provide an optical pickup comprising the foregoing objective lens driving device.  
         [0011]     Other objects of this invention will become clear as the description proceeds.  
         [0012]     According to an aspect of this invention, there is provided an objective lens driving device comprising a lens holder being movable and holding an objective lens, coil devices disposed around said objective lens and held by said lens holder, main magnets disposed around said objective lens and applying driving forces to said coil devices according to energization to said coil devices, and auxiliary magnets each disposed between adjacent ones of said coil devices and applying forces to said coil devices according to the energization to said coil devices for supplementing said driving forces.  
         [0013]     According to another aspect of this invention, there is provided an optical pickup for irradiating a beam onto an optical medium and detecting a reflected beam reflected from the optical medium, the optical pickup including an objective lens driving device which comprises a damper base, a suspension member elastically supporting the lens holder with respect to the damper base, and a damper member interposed between the damper base and the lens holder for separating, in terms of vibration, the lens holder from the damper base, the damper base being movably supported. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0014]      FIG. 1  is a perspective view of an objective lens driving device according to a preferred embodiment of this invention;  
         [0015]      FIG. 2  is an exploded perspective view, as seen obliquely from above, of the objective lens driving device shown in  FIG. 1 ;  
         [0016]      FIG. 3  is an exploded perspective view, as seen obliquely from below, of the objective lens driving device shown in  FIG. 1 ; and  
         [0017]      FIG. 4  is an exemplary diagram for describing the main part of the objective lens driving device shown in  FIG. 1 . 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0018]     Referring to  FIG. 1 , description will be made about the overall structure of an objective lens driving device according to a preferred embodiment of this invention.  
         [0019]     The illustrated objective lens driving device  100  comprises a damper base  10 , a lens holder  20 , an objective lens  30  retained by the lens holder  20 , four first suspension wires  54  and two second suspension wires  8  swingably supporting the lens holder  20  relative to the damper base  10 , a yoke base  3  fixed to the damper base  10 , and four main or first permanent magnets  1  and two auxiliary or second permanent magnets  2  fixed to the yoke base  3 .  
         [0020]     The objective lens driving device  100  is mounted on an optical base (not illustrated) of an optical disk drive and forms part of an optical pickup. The optical base is attached to guide bars (not illustrated) so as to be movable in a radial direction of an optical disk (i.e. a tracking direction Tr) loaded into the optical disk drive. The objective lens  30  has an optical axis extending in a focusing direction F perpendicular to the optical disk loaded in the optical disk drive.  
         [0021]     The optical base is further mounted with a laser diode, a photodetector, and a predetermined optical system. A laser beam from the laser diode is irradiated onto the optical disk via the optical system, and its reflected light is guided to the photodetector via the optical system. In this case, the objective lens  30  is included in the optical system.  
         [0022]     On both lateral sides, with respect to a tangential direction Tg, of the damper base  10 , fixing portions  12  and  13  are respectively formed for fixing the first suspension wires  54  thereto. Specifically, the fixing portions  12  and  13  elastically support two spaced-apart portions of each first suspension wire  54  via damper members  12   a  and  13   a  made of rubber or the like, respectively.  
         [0023]     Further, at a center portion, in the tracking direction Tr, of the damper base  10 , fixing portions  17  are formed at a front end thereof on both sides with respect to the center of the front end of the center portion. In addition, fixing grooves  9  are formed in one-to-one correspondence with the fixing portions  17 . The fixing grooves  9  are each formed into an S-shape so as to be more spaced apart from each other as approaching a rear end, in the tangential direction Tg, of the damper base  10 . Each fixing groove  9  extends in the tangential direction Tg to open to the outside at the rear end of the damper base  10 . The second suspension wires  8  are elastically supported by the fixing portions  17  via damper members  17   a  made of rubber or the like, respectively.  
         [0024]     With the structure as described above, the lens holder  20  is elastically supported by the first suspension wires  54  and the second suspension wires  8  so as to be freely movable within a small range in various directions above the yoke base  3 . That is, the lens holder  20  is substantially separated, in terms of vibration, from the damper base  10  and the yoke base  3 .  
         [0025]     Referring to  FIGS. 2 and 3  along with  FIG. 1 , description will be made about a detailed structure of the objective lens driving device  100 .  
         [0026]     The lens holder  20  is in the shape of a rectangular thick plate and has a mounting hole  21  formed at its center for mounting the objective lens  30  therein, coil mounting holes  22  formed symmetrically at its four corners for mounting coil members  16  therein, respectively, and holes  23  formed for the second permanent magnets  2  to extend therethrough, respectively. The lens holder  20  further has fixing portions  11  for fixing the suspension wires  54  thereto, respectively. The fixing portions  11  are formed at both ends, in the tracking direction Tr, of the lens holder  20  with the two of them arranged vertically at each end. Moreover, the lens holder  20  has four pairs of bobbins (hook portions)  24  at both ends thereof in the tangential direction Tg, with the two pairs thereof projecting in the tangential direction Tg at each end. Each pair of bobbins are arranged vertically for a corresponding tracking coil  4  to be wound therearound.  
         [0027]     The yoke base  3  comprises four plate-shaped yokes  5  with the two of them provided at two portions on each of both sides of a center portion, in the tangential direction Tg, of the yoke base  3 , two plate-shaped yokes  3   a  provided at portions near one end, in the tangential direction Tg, of the yoke base  3 , and a bridge-shaped yoke  3   b  provided at the other end thereof in the tangential direction Tg. The plate-shaped yokes  5  are received in and extend through the corresponding coil members  16 , respectively.  
         [0028]     Referring further to  FIG. 4 , description will be made about arrangement and polarity of the first permanent magnets  1  and the second permanent magnets  2 .  
         [0029]     The first permanent magnets  1  are disposed in contact with the plate-shaped yokes  3   a  and  3   b , respectively, and have polarities in the tangential direction Tg, respectively. Of the first permanent magnets  1 , each pair of the two arranged in the tangential direction Tg are set to have the same polarities while each pair of the two arranged in the tracking direction Tr are set to have the opposite polarities. Each of the second permanent magnets  2  is disposed in the middle between the two first permanent magnets  1  arranged in the tangential direction Tg and has a polarity in the tangential direction Tg which, however, is set opposite to the polarities of those first permanent magnets  1 . Therefore, the polarities of the second permanent magnets  2  are set opposite to each other.  
         [0030]     Referring back to FIGS.  1  to  3 , each of the coil members  16  comprises a tilting coil  6  and a focusing coil  7  wound therearound. Four coil devices each formed by a combination of the coil member  16  and the tracking coil  4  are disposed symmetrically with respect to the lens holder  20 . The tilting coil  6  and the focusing coil  7  may be wound around a non-illustrated bobbin or formed as air-core coils. As described above, the tracking coils  4  are wound around the bobbins  24  of the lens holder  20 . In this manner, the three kinds of the coils are provided on the lens holder  20 . Thereafter, the objective lens  30  is attached to the lens holder  20 .  
         [0031]     The focusing coils  7  and the tracking coils  4  have end portions respectively connected to the fixing portions  11 , serving as connection terminals, of the lens holder  20 . As described above, the first suspension wires  54  are also connected at their ends to the fixing portions  11 , respectively.  
         [0032]     On the other hand, each tilting coil  6  has one end connected to one end of the second suspension wire  8  extending with a stepped portion formed on the way to its other end. Specifically, such one end of the tilting coil  6  is drawn out into a space of the lens holder  20  and fixed by soldering to an L-shaped bent end portion formed at the one end of the second suspension wire  8 . In the state where the second suspension wire  8  passes through the fixing portion  17  and the S-shaped bent fixing groove  9  of the damper base  10  so as to be fixed, the other end of the second suspension wire  8  projects reward of the damper base  10 .  
         [0033]     A positional relationship among the tilting coils  6 , the focusing coils  7 , the tracking coils  4 , the main magnets  1 , the auxiliary magnets  2 , and the yokes  3   a ,  3   b , and  5  can be readily understood from  FIG. 4 . Specifically, the coil devices are disposed symmetrically at both sides of a plane which includes the optical axis and extends in the tangential direction Tg. The main magnets  1  are also disposed symmetrically at both sides of the plane. Simultaneously, the auxiliary magnets  2  are disposed symmetrically at both sides of the plane. In addition, the tilting coils  6 , the focusing coils  7 , and the tracking coils  4  are partly disposed in magnetic gaps of a magnetic circuit formed by a combination of the yokes  3   a ,  3   b , and  5 , the main magnets  1 , and the auxiliary magnets  2 .  
         [0034]     By properly controlling currents that flow through the coils  6 ,  7 , and  4 , the lens holder  20  makes one or more of a tilting motion in the tracking direction Tr (i.e. a turning motion with respect to an axis extending in the tangential direction Tg), a movement in the tracking direction Tr, and a movement in the focusing direction F on the basis of a relationship among magnetic fields produced by the main magnets  1 , the auxiliary magnets  2 , and the yokes  3   a ,  3   b , and  5 . In this event, the main magnets  1  serve to apply driving forces to the focusing coils  7  and the tracking coils  4 . The auxiliary magnets  2  serve to supplement driving forces to the focusing coils  7  and the tilting coils  6 . Note that the focusing direction F, the tangential direction Tg, and the tracking direction Tr may also be called a first direction, a second direction, and a third direction, respectively.  
         [0035]     When the coils  6 ,  7 , and  4  are energized, the focusing coils  7  on both lateral, i.e. right and left, sides with respect to the tangential direction Tg receive driving forces in the same direction with respect to the focusing direction F. Likewise, the tracking coils  4  on both right and left sides with respect to the tangential direction Tg receive driving forces in the same direction with respect to the tracking direction Tr.  
         [0036]     On the other hand, the tilting coils  6  on the right and left sides with respect to the tangential direction Tg receive driving forces in mutually opposite directions. In this event, since the magnetic force lines are bent by the auxiliary magnets  2  so as to be directed toward the outside and the inside of the yokes in the tracking direction Tr, driving forces in the same direction are applied to the coils on the outside and the inside in the tracking direction Tr to thereby increase electromagnetic forces.  
         [0037]     Further, since the second suspension wires  8  are supported on the inside in the tracking direction Tr, the acceleration sensitivity in the tilt direction can be increased and the undesired resonance caused by the tilting coils  6  can be prevented. Likewise, the acceleration sensitivity can also be increased with respect to the focusing coils  7  by the arrangement of the auxiliary magnets  2 . Therefore, it is possible to obtain the objective lens driving device that can prevent occurrence of the undesired resonance and achieve the speed-up of the ultra slim drive, i.e. the super thin type optical disk drive.  
         [0038]     While this invention has thus far been described in connection with the preferred embodiments thereof, it will be readily possible for those skilled in the art to put this invention into practice in various other manners without departing from the scope of this invention.