Abstract:
The present invention provides an optical disk apparatus and an optical pickup which are of a thin type and capable of correcting spherical aberration, including: a semiconductor laser for emitting light; an objective lens for condensing the light from the semiconductor laser on a recording layer through a light transmission layer; at least two optical elements arranged between the semiconductor laser and the objective lend and having a predetermined refractive power; a spherical aberration correction element driving mechanism for moving at least one of the optical elements along an optical axis so as to cancel spherical aberration of imaging light on the recording layer; and a lens holder for holding at least one of the optical elements, a part of the lens folder being inserted into an opening of a cartridge and which.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The present invention relates to an optical disk apparatus and an optical pickup device for recording information on an optical disk or reproducing information therefrom, in particular, an optical disk apparatus and an optical pickup equipped with an optical element for correcting spherical aberration in a beam spot generated due to a thickness error in an optical disk protecting substrate.  
         [0003]     2. Related Background Art  
         [0004]     Recently, in the technical field in which the recording or reproduction of information signals is effected by using, for example, an optical disk as an information recording medium, the development of an optical disk apparatus having a small size and a large capacity is under way in order to handle high definition still images, moving pictures, etc. An optical disk apparatus is equipped with an optical pickup device for forming a beam spot on the information recording surface of an optical disk, and, as is known in the art, in this optical pickup device, there is generated spherical aberration when a light beam emitted from a light source passes through a transparent protective substrate layer for protecting the information recording layer. As a method of correcting spherical aberration, a method is known according to which an optical element for correction is moved in the optical axis direction.  
         [0005]     As a method using such an optical element for correction, for example, Japanese Patent Application Laid-Open No. 2002-312971 proposes use of a device in which there are provided a movable optical element for correcting spherical aberration and a stationary optical element, wherein a movable optical element holder is moved by a DC motor driving force through a driving mechanism, thereby correcting spherical aberration.  
         [0006]     Similarly, Japanese Patent Application Laid-Open No. 2003-091847 proposes a device for correcting spherical aberration which uses a concave lens and a convex lens for spherical aberration correction, wherein the concave lens is held by a lens holder, which is driven by a stepping motor, thereby effecting spherical aberration correction.  
         [0007]     In the above prior-art techniques, the optical disk is neither accommodated in a cartridge nor reduced in the size and thickness of the pickup device. If such a spherical aberration correcting device is applied to a small and thin optical pickup device which uses a cartridge, such as a portable MD drive, the following problems will be involved.  
         [0008]     In the technique as disclosed in Japanese Patent Application Laid-Open No. 2002-312971, the movable optical element holder holding the movable optical element is formed as a cylinder surrounding the periphery of the optical element, and is driven in the optical axis direction of the optical element by a DC motor while guided by a reference shaft. While the thickness of the movable optical element holder with respect to the driving mechanism including the DC motor is not explicitly given here, this holder has a problem that the thickness of the optical element holder in a direction perpendicular to the optical axis of the optical element is rather large with respect to the diameter of the optical element.  
         [0009]     Similarly, in the technique as disclosed in Japanese Patent Application Laid-Open No. 2003-091847, the lens holding member for holding the concave lens out of the expander lenses is formed so as to surround the entire periphery of the concave lens, and the outer diameter of the lens holding member is very large as compared with the lens diameter, so that the width of the optical pickup device in a direction perpendicular to the optical axis of the spherical aberration correction lens group is rather large, resulting in a rather large optical pickup device.  
       SUMMARY OF THE INVENTION  
       [0010]     It is an object of the present invention to provide an optical disk apparatus and an optical pickup device which are of a thin type and capable of spherical aberration correction.  
         [0011]     The optical disk apparatus of the present invention is an optical disk apparatus for recording information on an optical disk accommodated in a cartridge or reproducing recorded information from the optical disk includes:  
         [0012]     a light source;  
         [0013]     an objective lens for condensing light from the light source on the optical disk;  
         [0014]     at least two optical elements arranged between the light source and the objective lens and having a predetermined refractive power;  
         [0015]     a moving mechanism for moving at least one of the optical elements along an optical axis to cancel spherical aberration of imaging light on the recording surface of the optical disk; and  
         [0016]     a lens holder for holding at least one of the optical elements, a part of the lens holder being inserted into an opening of the cartridge.  
         [0017]     Further, the optical pickup device of the present invention is an optical pickup device for use in an optical disk apparatus which records information on an optical disk accommodated in a cartridge or reproduces recorded information from the optical disk includes:  
         [0018]     a light source;  
         [0019]     an objective lens for condensing light from the light source on the optical disk;  
         [0020]     at least two optical elements arranged between the light source and the objective lens and having a predetermined refractive power;  
         [0021]     a moving mechanism for moving at least one of the optical elements along an optical axis to cancel spherical aberration of imaging light on the recording surface of the optical disk; and  
         [0022]     a lens holder for holding at least one of the optical elements, a part of the lens holder being inserted into an opening of the cartridge. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0023]      FIG. 1  is a perspective plan view of an optical disk apparatus according to an embodiment of the present invention;  
         [0024]      FIG. 2  is a sectional view taken in the line  2 - 2  of  FIG. 1 ;  
         [0025]      FIG. 3  is a plan view showing an initial position of a spherical aberration correction element driving mechanism;  
         [0026]      FIG. 4  is a side view of  FIG. 3 ;  
         [0027]      FIG. 5  is a plan view showing the position of the spherical aberration correction element driving mechanism after the supply of a predetermined pulse;  
         [0028]      FIG. 6  is an exploded perspective view of an optical pickup device; and  
         [0029]      FIG. 7  is a perspective view of a lens holder as seen from two directions. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0030]     Next, a best mode for carrying out the present invention will be described in detail with reference to the drawings.  FIG. 1  is a perspective plan view of an optical disk apparatus according to an embodiment of the present invention. In  FIG. 1 , reference numeral  1  indicates an optical disk serving as an information recording medium, reference numeral  2  indicates a cartridge accommodating the optical disk, reference numeral  3  indicates an opening provided in the cartridge, and reference numeral  4  indicates a turntable on which the optical disk  1  is to be placed. The turntable  4  is provided at the distal end of a spindle motor  6  installed on a chassis  5  constituting the substrate for the mechanism portion of the apparatus.  
         [0031]     Reference numeral  7  indicates an optical pickup device in which a light beam is emitted to the optical disk  1  to record on the disk or read an information signal from the disk. The optical pickup device  7  moves along the recording surface of the optical disk  1  in a disk radial direction (in the direction shown by the arrow X of  FIG. 1 ) by using as guide means a guide shaft  9  supported by guide shaft support members  8   a  and  8   b  provided on the chassis  5  and a lead screw  11  rotatably supported by lead screw support members  10   a  and  10   b.    
         [0032]     In this regard, there is adopted a mechanism in which a rack gear  12  mounted to the back surface of the optical pickup device  7  so as to extend in a direction perpendicular to the disk radial direction is engaged with the lead screw  11  and in which the driving force of a traverse motor  13  is transmitted to the lead screw  11  through reduction gears  14   a  through  14   d ; the lead screw  11  is rotated by the driving of the traverse motor  13 , thereby moving the optical pickup device  7  in the radial direction of the optical disk  1 . Further, at one end of the optical pickup device  7 , there is provided a U-shaped protrusion, which is engaged with the guide shaft  9  as shown in  FIG. 4 , thereby enabling the optical pickup  7  to slide.  
         [0033]      FIG. 2  is a sectional view of the optical pickup device  7  taken in the line  2 - 2  of  FIG. 1 . FIG.  3  is a plan view showing an initial position of a spherical aberration correction element driving mechanism;  FIG. 4  is a side view of  FIG. 3 ;  FIG. 5  is a plan view showing the position of the spherical aberration correction element driving mechanism after movement thereof;  FIG. 6  is an exploded perspective view of a spherical aberration correction element driving mechanism  16 ; and  FIG. 7  is a perspective view of a lens holder as seen from two directions.  
         [0034]     As shown in  FIG. 2 , in the optical pickup device  7 , a semiconductor laser  17  serving as a light source is mounted in an optical base  16  constituting a base. The optical axis of the semiconductor laser  17  is parallel to the disk surface, and, after passing a predetermined optical system  18 , a laser beam therefrom passes through a collimator lens  21 , and sequentially passed through a movable optical element  19  for correcting spherical aberration and a stationary optical element  20 , and is, further, reflected by a mirror  22  in a direction perpendicular to the optical disk  1 . Thereafter, it passes through an objective lens  23  to be condensed on the recording surface of the optical disk  1 . The beam reflected by the mirror  22  is a parallel beam, and the distance between the objective lens  23  and the optical disk  1  is determined to a predetermined working distance.  
         [0035]     Thus, to achieve the optical disk apparatus of a thin type, it is desirable for the distance between the objective lens  23  and the mirror  22  to be as small as possible, thereby making it possible to reduce the distance between the cartridge  2  and the optical pickup device  7 . Further, the optical pickup device  7  has a spherical aberration correction element driving mechanism  15  mounted thereon for driving the movable optical element  19  for spherical aberration correction. Further, although not shown in the drawings, the objective lens  23  is provided with a two-axis actuator for driving it in the focusing direction and the tracking direction.  
         [0036]     As shown in  FIG. 4 , the movable optical element  19  is held by a lens holder  31 , and the upper portion of a radial direction lens holding portion  24  of the lens holder  31  extends into the interior of the opening  3  of the cartridge. The portion of the radial direction lens holding portion  24  on a side opposite to the side of the upper portion is accommodated within the thickness of the optical base  16  without protruding beyond a bottom surface  25  of the optical base  16 .  
         [0037]     As shown in  FIG. 6 , the spherical aberration correction element driving mechanism  15  has a driving motor  26  on the optical base  16  and a spherical aberration correction element driving member  27  on a side surface of the optical base  16 . At the forward end of the driving motor  26 , there is provided a worm gear  29 , which is in mesh with a helical gear  28   a  provided on the spherical aberration correction element driving member  27 . The spherical aberration correction element driving member  27  is rotatably supported by a bearing portion  30  provided on the optical base  16 .  
         [0038]     The lens holder  31  is guided by two guide shafts  32  provided on the optical base  16 , and can move in the optical axis direction of the movable optical element  19  (the direction shown by the arrow Y of  FIG. 4 ). Further, the movable optical element holder  31  is equipped with a rack portion  33 , which is in mesh with a worm gear  28   b  provided on the spherical aberration correction element driving member  27 . Further, provided on the optical base  16  is a photo-interrupter  34  serving as a position sensor, detecting the position of the lens holder  31  (that is, the position of the movable optical element  19  in the optical axis direction) through insertion/detachment of a shielding plate  35  provided on the lens holder  31 .  
         [0039]     Further, as shown in  FIG. 7 , the lens holder  31  has a movable optical element mounting opening (recess portion)  36 , which is equipped with a radial-direction positioning portion  37  and an optical-axis-direction positioning portion  38  for the movable optical element  19 , with the movable optical element mounting opening  36  being formed so as to extend continuously toward the bottom surface of the optical base  16  down to the contour of the lens holder  31 . The lens holder  31  is equipped with a lens holder opening  40  allowing passage of light emitted from the semiconductor laser  18 .  
         [0040]     The lens holder opening  40  is formed in an ellipsoidal configuration elongated in the radial direction of the optical disk  1 . The lens holder  31  is formed, for example, of a resin allowing high precision molding like liquid crystal polymer, and cannot maintain the requisite strength if not endowed with a certain degree of wall thickness; in this embodiment, however, the lens holder opening  40  is formed in an ellipsoidal configuration, and the opening side of the movable optical element mounting opening  36  is reinforced, so that it is possible to maintain the requisite strength.  
         [0041]     Further, in this embodiment, the lens holder  31  is protruded with respect to the optical base  16  only on the side of the cartridge  2 . And, with the optical disk apparatus being loaded with a cartridge, the protruding portion (the forward end portion of the lens holder  31 ) is accommodated in the cartridge opening  3 . Thus, the movable range of the movable optical element  19  on the optical base  16  is set. Further, the protruding portion does not protrude on the opposite side, i.e., the bottom surface side of the optical base  16 . As a result, it is possible to bring the optical pickup device  7  close to the optical disk  1  and the cartridge  2 .  
         [0042]     Next, the operation of the spherical aberration correction element driving mechanism  15  of this embodiment will be described. First, the spherical aberration correction element driving mechanism  15  is used in order to correct spherical aberration generated due to a thickness error in the cover layer of the optical disk  1 . That is, the movable optical element  19  is made movable in the optical axis direction, and correction is effected on a beam incident on the objective lens  23  such that the focus of the beam is formed on the recording layer of the optical disk irrespective of the thickness error of the cover layer. In performing this control, the movable optical element  19  is moved from a reference position by a predetermined distance, and the amplitude of an information reproduction signal is detected during the movement, the point where the reproduction signal amplitude is maximum being regarded as the correction position for the movable optical element  19 .  
         [0043]     More specifically,  FIG. 3  shows a state of the lens holder  31  at a reference position in which the shielding plate  35  has been inserted into the photo-interrupter  34 . When, in this state, the driving motor  26  constituting the drive source is rotated, the torque thereof is transmitted to the spherical aberration correction element driving member  27 . The rotation of the spherical aberration correction element driving member  27  is transmitted to the rack portion  33  of the movable optical element holder  31 , and the lens holder  31  moves in the optical axis direction of the movable optical element  19  while guided by the guide shaft  32 . At this time, the lens holder  31  is fit-engaged with the guide shaft  32  by means of a hole portion  31   a  and an engagement portion  31   b , and there is no fear of the optical axis of the movable optical element  19  being inclined or the center position thereof being deviated due to the movement of the lens holder  31 .  
         [0044]     As the driving motor  26 , a stepping motor is used; based on control by a control circuit (not shown), a motor drive circuit (not shown) supplies predetermined pulses to the driving motor  26  while counting the pulses from a reference position.  FIG. 5  shows a state after the supply of the predetermined pulses. During the movement, predetermined information of the optical disk  1  is reproduced by a reproducing circuit (not shown), and the amplitude of an information reproduction signal is detected by a detection circuit (not shown). The above-mentioned control circuit monitors the amplitude of the reproduction signal, and causes the driving motor  26  to make reverse rotation until a position is reached where the reproduction signal amplitude becomes maximum. In this way, the movable optical element  19  is moved to an optimum position where the reproduction signal amplitude becomes maximum, whereby any spherical aberration due to a thickness error in the optical disk  1  is corrected. There are no particular limitations regarding the information reproduced from the optical disk  1 .  
         [0045]     Here, when detecting the reference position by using the photo-interrupter  34 , shielding is effected between a light-emitting element and a light-receiving element contained in the photo-interrupter  34  when the shielding plate  35  provided on the lens holder  31  enters a detection groove of the photo-interrupter  34 . When the photo-interrupter  34  is shielded, pulse signals cease to be output to the driving motor  26  from the motor drive circuit (not shown), therefore the reference position detection is completed at this point in time, and position adjustment is performed on the above-described lens holder  31  using that position as the reference position. Thus, there is no need to apply any surplus load to the driving motor  26 , and the reference position detection is possible in a short time while achieving power saving. Such correction of spherical aberration by the spherical aberration correction element driving mechanism  15  is effected when turning on the power, when replacing the optical disk  1 , etc.  
         [0046]     Further, the rack portion  33  of the lens holder  31  is in mesh with the worm gear  28   b  of the spherical aberration correction element driving member  27 . The rack portion  33  is formed of resin and has elasticity, and is in contact with the worm gear  28   b  with no gap therebetween. Further, as shown in  FIGS. 3 through 5 , the spherical aberration correction element driving member  27  has a spherical shaft end  28   c  urged in the direction shown by the arrow Y of  FIG. 4  by a plate spring  39 . Thus, the lens holder  31  does not rattle in the optical axis direction, and can maintain the position of the movable optical element  19  with high accuracy. Further, since a small diameter stepping motor is used as the driving motor  26 , a step angle becomes large. However, since two worm gears are used and the pitch thereof can become small, the reduction ratio can be made large, so that it is possible to control the movable optical element position with high accuracy, whereby it is possible to correct spherical aberration with high accuracy.  
         [0047]     The present invention is not restricted to the above-described embodiment but allows various modifications without departing from the spirit of the present invention.  
         [0048]     This application claims priority from Japanese Patent Application No. 2003-013006 filed Jan. 21, 2004, which is hereby incorporated by reference herein.