Abstract:
An optical pick-up device includes a lens that focuses light onto a recording medium, a lens holder that holds the lens, a suspension holder that supports the lens holder disposed opposite a distal end of the lens holder, a frame formed so as to be disposed opposite both lateral surfaces of the lens holder and the distal end of the lens holder, the frame supporting the suspension holder, a plurality of elastic supports that movably support the lens holder, a distal end of the elastic supports mounted on the suspension holder, and an actuator that drives the lens holder, wherein a plurality of projections is provided on at least one of the lens holder, the frame and the suspension holder, the projections acting as stoppers that restrict a rotation of the lens holder so as to prevent excessive deformation of the elastic supports.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The present invention relates generally to an optical pick-up device, and more particularly, to an improved optical pick-up device for reading and/or writing information to and from a recording medium, in which a lens holder that holds a lens that focuses light onto a recording surface of the recording medium is movably supported by cantilever springs.  
           [0003]    2. Description of the Related Art  
           [0004]    In for example CD-ROM or CD-RW disk drive units in which a rotating disk-like recording medium (hereinafter simply disk) is loaded, a laser beam is projected onto the disk and information is recorded (written) onto the disk or reproduced (read) from the disk. The optical pick-up device installed in such types of disk drive units includes, among other components, an object lens that directs a laser beam emitted from a laser diode onto the disk. The orientation of the object lens is adjusted so that the focus of the light directed onto the disk by the object lens coincides with a recording surface of the disk.  
           [0005]    In other words, an optical pick-up device performs focus control and tracking control so that the object lens follows changes in the track due to eccentricities in the rotation of the disk and/or wobble due to rotation of the disk. This type of control of the object lens is performed by an actuator using an electromagnetic force, the actuator being typically composed of a combination of a coil and a magnet.  
           [0006]    A lens holder that supports the object lens is made compact and lightweight in order to facilitate focus and tracking control, with four wire-like elastic supports (that is, cantilever springs) arranged in parallel forming a supporting structure that supports the lens holder and that moves minutely in either a focus direction or a tracking direction, as the case may be, by the driving force from the actuator.  
           [0007]    Further, the lens holder is placed so as to be contained within a frame formed into the shape of the letter U, the open portion being at a proximal end. Base portions of the four wire-like elastic supports are joined to a suspension fixedly mounted on a distal end of the frame, with tip portions joined to the lateral surfaces of the lens holder. As a result, the lens holder is supported by the four wire-like elastic supports in such a way as to be movable in a direction parallel to the frame.  
           [0008]    However, a drawback of the above-described conventional optical pick-up device is that, when installed in a laptop personal computer or other similar portable apparatus and such apparatus is dropped during handling, the movement of the lens holder caused by such an impact on the pick-up unit is greater than that which is normally imparted thereto, thus damaging the wire-like elastic supports.  
           [0009]    It is possible to provide the lens holder with lateral projections protruding therefrom, so that the projections contact the frame so as to restrict the range of movement of the lens holder and thus prevent the lens holder from being damaged by excessive movement. However, if the center of gravity of the lens holder and the center drive point of the actuator diverge from each other, an angular moment comes into play around the projection after the projection contacts the frame, thus twisting or rotating the lens holder around the tip of the projection and thereby deforming the wire-like elastic supports.  
           [0010]    With the disk drives installed in laptop personal computers in particular, in which a seek direction (that is, the tracking direction) of the optical pick-up is slanted at approximately a 45 degree angle with respect to a front panel of the disk holder (thus taking advantage of the additional length afforded by using a corner of the disk drive unit frame instead of a lateral side of the frame), the direction of the shock of impact upon dropping the laptop (assuming the laptop is dropped on the front panel of the disk holder) and the direction of drive of the actuator are at approximately a 45 degree angle with respect to each other. In short, the structure easily allows an angular moment to be generated about the tip of the projection of the lens holder, thereby deforming the wire-like elastic supports.  
           [0011]    If the wire-like elastic supports are thus deformed, then the positioning and angle of the lens can change and information can no longer be written to or read from the disk.  
           [0012]    It is possible to use relatively thick wire for the wire-like elastic supports so as to prevent the wire-like elastic supports from being deformed by the shock of impact. However, the thicker the wire the more rigid the wire-like elastic support, which makes it more difficult to move the primary resonance frequency (at which focus control and tracking control low-frequency sensitivity tends to deteriorate) to a desired frequency.  
           [0013]    In order to set the primary resonance frequency to a desired frequency and prevent focus control and tracking control low-frequency sensitivity from deteriorating, the longer the suspension the better. However, the conventional optical pick-up typically installed in an ordinary laptop computer, and particularly the recording pick-up, has a substantial number of mounted parts, thus limiting the space available to lengthen the suspension.  
           [0014]    More specifically, there is limited space in which to accommodate the optical pick-up devices of the disk drive units typically installed in laptop computers. Optical pick-up devices of optical disk drive units that can record are becoming more common, but these, too, have the disadvantage of a large number of component parts as compared to the read-only type of optical pick-up device, thus placing additional constraints on the already limited amount of space available for installation. For both these reasons, the wire-like elastic supports can be neither lengthened nor thickened. Additionally, thickening the wire-like elastic supports reduces their sensitivity, which is undesirable.  
         SUMMARY OF THE INVENTION  
         [0015]    Accordingly, it is an object of the present invention to provide an improved and useful optical pickup device, in which the above-described disadvantage is eliminated.  
           [0016]    The above-described object of the present invention is achieved by an optical pick-up device comprising a lens that focuses light onto a recording medium; a lens holder that holds the lens; a suspension that supports the lens holder disposed opposite a distal end of the lens holder; a frame formed so as to be disposed opposite both lateral surfaces of the lens holder and the distal end of the lens holder, the frame supporting the suspension; a plurality of elastic supports that movably support the lens holder, a distal end of the elastic supports mounted on the suspension and a proximal end retained by the lens holder; and an actuator that drives the lens holder, the actuator including a focus coil, a tracking coil and at least one magnet, the optical pick-up device having a plurality of projections provided on at least one of the lens holder, the frame and the suspension, the projections acting as stoppers that restrict a rotation of the lens holder so as to prevent excessive deformation of the elastic supports.  
           [0017]    According to this one aspect of the invention, excessive displacement of the lens holder due to impact can be prevented and a rotational moment prevented from acting on the lens holder, thus making it possible to prevent deformation of the cantilever springs and to prevent deterioration in the accuracy of the focus control and tracking control of the lens holder due to the impact of an external shock to the optical pick-up device. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0018]    These and other objects, features, aspects and advantages of the present invention will become better understood and more apparent from the following description, appended claims and accompanying drawings, in which:  
         [0019]    [0019]FIG. 1 is a perspective view of an optical pickup device according to one embodiment of the present invention;  
         [0020]    [0020]FIG. 2 is a plan view of an optical pick-up device according to one embodiment of the present invention;  
         [0021]    [0021]FIG. 3 is a lateral cross-sectional view of an optical pick-up device according to one embodiment of the present invention;  
         [0022]    [0022]FIG. 4 is a perspective exploded view of a movable part and a yoke base that supports the movable part;  
         [0023]    [0023]FIG. 5 is a plan view showing a case in which an impact acts in a direction B on an optical pick-up device according to the present invention;  
         [0024]    [0024]FIG. 6 is a perspective view of a disk drive unit;  
         [0025]    [0025]FIG. 7 is a plan view of a disk drive unit;  
         [0026]    [0026]FIG. 8 is a plan view of a disk drive unit with the tray extended;  
         [0027]    [0027]FIG. 9 is a plan view of a disk drive, a double-headed arrow showing a direction of movement of the optical pick-up device;  
         [0028]    [0028]FIG. 10 shows a load acting on an optical pickup device according to the present invention when the disk device has been dropped;  
         [0029]    [0029]FIG. 11 is a schematic diagram showing a direction of effect of a rotational moment in the event of an impact acting in directions H, I on a lens holder center of gravity G;  
         [0030]    [0030]FIG. 12 is a schematic diagram showing a direction of effect of a rotational moment in the event of an impact acting in directions J, K on a lens holder center of gravity G; and  
         [0031]    [0031]FIG. 13 is a plan view of an optical pick-up device according to one variation of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0032]    A detailed description will now be given of an improved optical pick-up device according to the present invention, with reference to the accompanying drawings. It should be noted that identical or corresponding elements are given identical or corresponding reference numbers in all drawings, with detailed descriptions thereof given once and thereafter omitted.  
         [0033]    [0033]FIG. 1 is a perspective view of an optical pickup device according to one embodiment of the present invention. FIG. 2 is a plan view of an optical pick-up device according to one embodiment of the present invention. FIG. 3 is a lateral cross-sectional view of an optical pick-up device according to one embodiment of the present invention. FIG. 4 is a perspective exploded view of a movable part and a yoke base that supports the movable part.  
         [0034]    As shown in FIGS.  1 - 4 , an optical pick-up device  10  comprises an object lens  12 , a lens holder  14  that holds the object lens  12 , a yoke base  15  (hereinafter frame  15 ) that supports the lens holder  14 , a focus coil  16  mounted on the lens holder  14  and a tracking coil  18  mounted on the lens holder  14 , a pair of magnets  30 ,  32 , a yoke  22  integrally mounted on the frame  15  that supports the pair of magnets  30 ,  32 , a suspension holder  24  fixedly mounted on the frame  15  and that supports four wire-like elastic supports—in actuality cantilever springs— 26   a ,  26   b ,  26   c  and  26   d  positioned between the frame  15  and the lens holder  14 . The lens holder  14  is thus supported by the four cantilever springs  26   a - 26   d  so as to be movable in a horizontal tracking direction (that is, a direction indicated by arrow A-B) as well as in a vertical focusing direction (a direction indicated by arrow C-D), the four cantilever springs  26   a - 26   d  being arranged in parallel The focus coil  16  is an actuator for driving the object lens  12  in a vertical direction. The tracking coil  18  is an actuator for driving the object lens  12  in the horizontal direction. The yoke  22 , which has a pair of U-shaped arms  22   a ,  22   b  bent so as to extend vertically, is fixedly mounted on a floor plate  15   c  disposed between a pair of arms  15   a ,  15   b  extending horizontally from the frame  15 . The magnet  30  is mounted on one arm  22   a  of the yoke  22  so as to pass through an interior of the focus coil  16 . The magnet  32  is mounted on the other arm  22   b  of the yoke  22 , opposite the tracking coil  18 .  
         [0035]    A first set of projections  37   a ,  37   b  project laterally from lateral surfaces of a proximal end of the lens holder  14 . A second set of projections  38   a ,  38   b  project laterally from an intermediate position on the lateral surfaces of the lens holder  14 . Finally, a third set of projections  39   a ,  39   b  project from the suspension holder  24  toward a distal end  14   c  of the lens holder  14 .  
         [0036]    The first set of projections  37   a ,  37   b  are shorter than the second set of projections  38   a ,  38   b  by approximately 1 to 2 mm, so when the lens holder  14  swings the second set of projections  38   a ,  38   b  contacts an inner surfaces of the arms  15   a ,  15   b  of the frame  15  first, after which the first set of projections  37   a ,  37   b  then contacts the inner surfaces of the arms  15   a ,  15   b  so as to restrict a rotation of the lens holder.  
         [0037]    Additionally, as noted previously, the distal end  14   c  of the lens holder  14  opposes the third set of projections  39   a ,  39   b , thus restricting a rotation of the lens holder  14  in a direction opposite the direction or rotation restricted by the first set of projections  37   a ,  37   b  when the distal end  14   c  of the lens holder  14  contacts the third set of projections  39   a ,  39   b.    
         [0038]    Accordingly, the contacting of the first set of projections  37   a ,  37   b  and the second set of projections  38   a ,  38   b  against the inner surfaces of the arms  15   a ,  15   b  of the frame  15  prevents a rotational moment from acting on the cantilever springs  26   a - 26   d , thereby preventing the cantilever springs  26   a - 26   d  from being deformed by an excessive force and preventing a deterioration in accuracy in the focus control or tracking control of the lens holder due to the impact of an external shock.  
         [0039]    The suspension holder  24  is fixedly mounted on a mounting part  15   d  of the frame  15  together with a printed circuit board  34  by a screw  36 . A base portion of the cantilever springs  26   a - 26   d , which are positioned so as to extend in a horizontal direction, penetrates the printed circuit board  34 . A proximal tip (that is, a free end) of the cantilever springs  26   a - 26   d  passes above and below the second set of projections  38   a ,  38   b . Additionally, silicon gel adhesives  40  for elastically mounting the cantilever springs  26   a - 26   d  are adhered to a proximal surface of the suspension holder  24 . The adhesive  40  is gelled by ultraviolet radiation so as to provide the cantilever springs  26   a - 26   d  with a viscous damping effect with respect to movement of the lens holder  14  in a focus direction and movement of the lens holder  14  in a tracking direction.  
         [0040]    Additionally, ends of the focus coil  16  and the tracking coil  18  are connected to relay substrates  42 ,  44  through which the free ends of the cantilever springs  26   a - 26   d  pass, with an electrical current being supplied to the focus coil  16  and the tracking coil  18  via the cantilever springs  26   a - 26   d.    
         [0041]    It should be noted that a movable part  46  subject to focus control and tracking control comprises the above-described object lens  12 , lens holder  14 , focus coil  16 , tracking coil  18 , and coil relay substrates  42 ,  44 .  
         [0042]    The object lens  12  supported by the lens holder  14  is adjusted to a position at which an electromagnetic force generated by the passing of current through the focus coil  16  and the tracking coil  18  is balanced with a magnetic force arising between the pair of magnets  30 ,  32 .  
         [0043]    A more detailed description will now be given of the structure of the lens holder  14 .  
         [0044]    The lens holder  14  has a lens holder part  14   a  and a coil holder part  14   b  that extends distally toward the suspension holder  24  from the lens holder part  14   a  and supports the focus coil  16  and the tracking coil  18 .  
         [0045]    As shown in FIG. 3, a laser beam (indicated by an arrow) emitted from a laser diode  28  is reflected by a reflecting mirror  50  toward the object lens  12 , where it is focused onto a disk  12  disposed opposite to and above the object lens  12 . The pair of magnets  30 ,  32  are disposed opposite the U-shaped mounting arms  22   a ,  22   b  of the yoke  22 , and opposite the focus coil  16  and tracking coil  18  provided on the lens holder  14 . As noted previously, the lens holder  14  is movably supported by the four cantilever springs  26   a - 26   d  that extend horizontally.  
         [0046]    [0046]FIG. 5 is a plan view showing a case in which an impact acts in a direction B on an optical pick-up device according to the present invention.  
         [0047]    As shown in FIG. 5, in a case in which the optical pick-up  10  is subjected to an impact force F acting in the direction indicated as B in the drawing, the lens holder  14  supported by the four cantilever springs  26   a - 26   d  moves in the B direction and the second projection  38   a  projecting from the lateral surface of the lens holder  14  contacts the inner surface of the arm  15   a  of the frame  15 , after which the first projection  37   a  projecting from the lateral surface of the lens holder  14  contacts the inner surface of the arm  15   a  of the frame  15 . As a result, a counter-clockwise rotation of the lens holder  14  is stopped by the first projection  37   a  and the second projection  38   a  coming into contact with the inner surface of the arm  15   a . Additionally, after the second projection  38   a  contacts the inner surface of the arm  15   a , the third projection  39   a  extending proximally from the suspension holder  24  toward a distal end  14   c  of the lens holder  14  keeps the lens holder  14  from rotating in a clockwise direction.  
         [0048]    Thus, damage to the cantilever springs  26   a - 26   d  can be prevented even in the event of an external shock to the unit because the first set of projections  37   a ,  37   b , the second set of projections  38   a ,  38   b  and the third set of projections  39   a ,  39   b  function as stoppers that restrict the rotation of the lens holder  14 .  
         [0049]    A description will now be given of the above-described optical pick-up device  10  installed in a typical CD-ROM drive unit.  
         [0050]    [0050]FIG. 6 is a perspective view of a disk drive unit. FIG. 7 is a plan view of a disk drive unit. FIG. 8 is a plan view of a disk drive unit with the tray extended.  
         [0051]    As shown in FIG. 6, a disk drive unit  61  is for example a CD-ROM drive unit installed in a laptop-type personal computer, and includes a top cover (for ease of description not shown in the diagram), a bottom cover  66 , with a turntable  68  rotatably supported by a tray  70  in a space created between the top cover and the bottom cover  66 . At a center of the turntable  68  there is a clamp mechanism  73  for engaging a disk  52  at an inner periphery of the disk  52  so as to clamp the disk  52  firmly onto the turntable  68 . A disk container  74  having a diameter larger than that of the disk  52  is disposed around an outer periphery of the turntable  68 .  
         [0052]    The optical pick-up device  10  for reading information recorded on the disk  52  clamped to the turntable by the clamping mechanism  73  of the turntable  68  is mounted below the disk container  74  so as to be movable in a direction of a radius of the disk  52  (hereinafter radial direction of the disk). The optical pick-up device  10  is contained in a concavity  74   a  of the disk container  74 . A pick-up cover  78  having an opening  78   a  that is as large as the range of movement of the object lens  12  of the optical pick-up device  10  covers the concavity  74   a.    
         [0053]    The opening  78   a  in the pick-up cover  78  extends in a direction that is at a diagonal, that is, an angle of approximately 45 degrees with respect to the tray  70 , that is, the direction indicated by an arrow Xa-Xb. The optical pick-up device  10  is also movable along the opening  78   a  in the pick-up cover  78  in the same diagonal direction.  
         [0054]    An eject button  82  is provided on a center of a front bezel  80  joined to a proximal edge the tray  70 .  
         [0055]    When a disk motor  69  provided beneath the turntable  68  is activated, thus rotating the turntable  68  and the disk  52  clamped onto the turntable  68  by the clamping mechanism  73 , the air at the center of the rotation is moved to the outer periphery of the disk by the centrifugal force of rotation.  
         [0056]    As shown in FIG. 8, the tray  70  is supported by guide rails  90 ,  92  along both sides thereof so that the tray  70  is slidable in the proximal and distal directions. When the eject button  82  provided on the front bezel  80  is pressed, the tray  70  lock is released and the released tray  70  is slid manually in the direction shown as Xa in FIGS. 7 and 8 to a point at which the disk may be replaced. After the disk  52  has been clamped onto the turntable  68  of the tray  70 , the tray  70  is then pushed manually back in the direction shown as Xb in FIGS. 7 and 8 until locked in a disk loaded position shown in FIG. 7.  
         [0057]    A description will now be given of a pick-up drive mechanism  84  that moves the optical pick-up device  10  in a radial direction of the disk.  
         [0058]    As shown in FIGS. 7 and 8, the pick-up drive mechanism  84  comprises a pair of guide shafts  85 ,  86  that guide the optical pick-up device  10  in a diagonal direction indicated by the dashed lines in FIG. 7, a drive motor  87  that drives the optical pick-up device  10 , and a transmission mechanism  88  that transmits the rotational drive force of the drive motor  87  to the optical pick-up device  10 . Bearings  76   a ,  76   b  and  76   c  project from both lateral surfaces of the optical pick-up device  10  and are fitted to the guide shafts  85 ,  86 , such that the optical pick-up device is guided by the guide shafts  85 ,  86 . The transmission mechanism  88  comprises a gear assembly  88   a  that reduces the rotation of the drive motor  87  and a lead screw  88   b  that is rotatably driven via the gear assembly  88   a . The optical pick-up device  10  has an engaging part  76   d  that engages the threads of the lead screw  88   b.    
         [0059]    A description will now be given of a movement operation of the optical pick-up device.  
         [0060]    [0060]FIG. 9 is a plan view of a disk drive, a double-headed arrow showing a direction of movement of the optical pick-up device.  
         [0061]    As shown in FIG. 9, the optical pick-up device  10  is moved along the diagonal of the tray  70  by the transmission of the rotation of the drive motor  87  to the lead screw  88   b  via the gear assembly  88   a.    
         [0062]    [0062]FIG. 10 shows a load acting on an optical pickup device according to the present invention when the disk device has been dropped.  
         [0063]    As shown in FIG. 10, when the disk drive unit  61  is dropped on the front bezel  80 , a force F acts in a direction E on the optical pick-up device because the optical pick-up device  10  is designed to move along the diagonal of the tray  70 . In such a case, the force of impact F acts on the optical pick-up device  10  at an angle of approximately 45 degrees with respect to the direction in which the four cantilever springs  26   a - 26   d  extend. Additionally, because the force of impact F acts downward with respect to the center of gravity G of the lens holder  14 , a rotational moment M is generated about the center of gravity G.  
         [0064]    As a result, the lens holder  14 , supported as it is by the four cantilever springs  26   a - 26   d , moves in the direction E in which the force of impact F acts. Initially the second projection  38   a  contacts the inner surface of the arm  15   a  of the frame  15 , and then the third projection  39   a  contacts the distal end  14   c  of the lens holder  14  so that the lens holder  14  does not rotate in the clockwise direction (see FIG. 5).  
         [0065]    Accordingly, even when the disk drive unit  61  is dropped a rotational moment due to the force of impact F does not affect the lens holder  14  and thus damage to the four cantilever springs  26   a - 26   d  can be prevented.  
         [0066]    [0066]FIG. 11 is a schematic diagram showing a direction of effect of a rotational moment in the event of a force of impact acting in directions H, I on a lens holder center of gravity G.  
         [0067]    As shown in FIG. 11, in the case of a force of impact operating in directions H, I on the lens holder  14  center of gravity G, the rotational moment M acts in the H′, I′ directions. However, a rotation of the lens holder  14  is prevented by the first set of projections  37   a ,  37   b  projected from the proximal end of the lens holder  14  and the second set of projections  38   a ,  38   b  contacting the inner surfaces of the arms  15   a ,  15   b  of the frame  15 . Accordingly, a rotation moment M in the H′, I′ directions is prevented by the first set of projections  37   a ,  37   b  and the second set of projections  38   a ,  38   b.    
         [0068]    [0068]FIG. 12 is a schematic diagram showing a direction of effect of a rotational moment in the event of a force of impact acting in directions J, K on a lens holder center of gravity G.  
         [0069]    As shown in FIG. 12, in the case of a force of impact operating in directions J, K on the lens holder  14  center of gravity G, the rotational moment M acts in the J′, K′ directions. However, a rotation of the lens holder  14  is prevented by the second set of projections  38   a ,  38   b  projected from the lateral surfaces of the lens holder  14  contacting the inner surfaces of the arms  15   a ,  15   b  of the frame  15  and by the third set of projections  39   a ,  39   b  provided on the suspension holder  24  contacting the distal end  14   c  of the lens holder  14 . Accordingly, a rotation moment M in the J′, K′ directions is prevented by the second set of projections  38   a ,  38   b  and the third set of projections  39   a ,  39   b.    
         [0070]    As can be appreciated by those of ordinary skill in the art, although the present invention has been described with reference to embodiments in which projections functioning as stoppers are provided on the lateral surfaces of the lens holder  14  and on the suspension holder  24 , the present invention is not limited to such embodiments but includes also configurations in which, for example, projections that prevent a rotation of the lens holder  14  are provided on the lateral surfaces of the frame  15 , as shown in FIG. 13. FIG. 13 is a plan view of an optical pick-up device according to one variation of the present invention.  
         [0071]    The above description is provided in order to enable any person skilled in the art to make and use the invention and sets forth the best mode contemplated by the inventors of carrying out the invention.  
         [0072]    The present invention is not limited to the specifically disclosed embodiments, and variations and modifications may be made without departing from the scope and spirit of the present invention.  
         [0073]    The present application is based on Japanese Priority Application No. 2000-377692 filed on Dec. 12, 2000, the entire contents of which are hereby incorporated by reference.