Abstract:
An optical disk drive includes a motor base, a rotational shaft that is rotatably held on the motor base, a rotor that is fixed to the rotational shaft and is rotated when supplied with a magnetic field, a stator that is provided in a space between the rotor and the motor base and is capable of applying a magnetic field to the rotor, and a drive circuit that is provided on a region on the motor base, which is outside a region defined by projection of the rotor, and causes a magnetic field to be produced from the stator.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]     This application is based upon and claims the benefit of priority from prior Japanese Patent Application No. 2003-197399, filed Jul. 15, 2003, the entire contents of which are incorporated herein by reference.  
       BACKGROUND OF THE INVENTION  
       [0002]     1. Field of the Invention  
         [0003]     The present invention relates generally to an optical disk drive that reproduces information from an optical disk, which is an information recording medium, or records information on the optical disk, and to an information recording/reproducing apparatus that employs the optical disk drive.  
         [0004]     2. Description of the Related Art  
         [0005]     Optical disks, which have widely been used, fall into three categories: read-only type, typified by a CD and a DVD-ROM; write-once type, typified by a CD-R and a DVD-R; and rewritable type, typified by an external storage of a computer and recording/reproducing video media.  
         [0006]     An optical disk drive, which reproduces information from an optical disk or records information on the optical disk, is required to have a smaller thickness, less power consumption and a lighter weight. A demand for smaller thickness is particularly strong with respect to an optical disk drive that is so designed as to be built in a portable device.  
         [0007]     An optical disk rotating device (spindle motor) is one of factors that determine the thickness of the optical disk drive. A turntable that holds an optical disk and a chucking mechanism that fixes the optical disk to the turntable are integrally formed to the shaft of the spindle motor.  
         [0008]     Thus, in order to reduce the thickness of the optical disk drive, it is necessary to reduce the thickness of the spindle motor and the thickness of the turntable and chucking mechanism.  
         [0009]     The chucking mechanism, however, is required to chuck the optical disk set on the turntable so as to prevent undesirable removal of the optical disk. If the optical disk set on the turntable rotates idly, this would lead to an error in reading data recorded on the optical disk or an error in recording data on the optical disk. The chucking mechanism is thus required to hold the optical disk on the turntable.  
         [0010]     On the other hand, as is well known, if the force, with which the chucking mechanism holds the optical disk on the turntable, is too strong, the optical disk warps considerably in its radial direction due to a force of reaction from the turntable. This leads to an error in reading/recording.  
         [0011]     An optical disk clamp mechanism has already been proposed (e.g. Jpn. Pat. Appln. KOKAI Publication No. 10-124967 (see claims  1  and  2 ,  FIG. 1 , paragraph [0017]). This clamp mechanism includes a clamp member that clamps an optical disk on a turntable and a level difference part that corrects the curving of the optical disk.  
         [0012]     When the level difference part for correcting the curving of the disk, as disclosed in Jpn. Pat. Appln. KOKAI Publication No. 10-124967, is provided, the following problems will arise: 
        1) A reaction force against the pushing force by the claw occurs at the level difference part with a very small area. Consequently, a disk slip tends to easily occur when the motor is driven or when the rotation speed of the motor varies.     2) Since the level difference part is located at a radially inner position, the disk tends to incline due to non-uniformity in height of the level difference part or non-uniformity in thickness of the radially inner part of the disk.        
 
         [0015]     In the prior art, if the inside diameter of an annular rubber member, which is used for preventing slip of the disk, is made less than the radius of the disk, the following problem arises. That is, since precision in height of a chucking holder for slidably holding the chucking claw is not secured, the chucking force becomes non-uniform, which leads to wobbling or disengagement of the disk due to inadequate chucking force, or a curving of the disk due to excessive chucking force.  
         [0016]     Specifically, the height of the claw that produces the chucking force is determined by the height of the radially inside part of the chucking holder that slidably holds the claw. This requires some devices that are to be made to the chucking holder provided near the radially inside part of the disk and to the shape of the rubber member.  
         [0017]     One factor of the occurrence of curving of the optical disk that is set and chucked on the turntable is as follows. Since the thickness of the turntable and chucking mechanism is reduced, a bending moment occurs due to the direction of force (toward the turntable) that is exerted on the optical disk from the chucking mechanism and the direction of force (toward the chucking mechanism) that is exerted on the optical disk from the turntable.  
       BRIEF SUMMARY OF THE INVENTION  
       [0018]     According to an aspect of the present invention, there is provided a disk support mechanism comprising: a turntable having a surface extending perpendicular to a rotational shaft thereof, the turntable supporting a to-be-supported object; a claw member that applies an urging force in a direction parallel to the rotational shaft, with the object interposed between the turntable and the claw member; and an elastic member that is formed on the turntable concentrically with the rotational shaft and produces a force of reaction capable of relaxing a bending moment that is caused by a reaction to the urging force in the direction parallel to the rotational shaft.  
         [0019]     According to another aspect of the present invention, there is provided an optical disk drive comprising: a disk motor including (i) a motor base that rotatably holds a rotational shaft, (ii) a rotor fixed to the rotational shaft, (iii) a medium holding mechanism that is able to apply an urging force to the rotor in a direction parallel to an axis of the rotational shaft, at a predetermined radial position from a center of the rotational shaft, and positions a recording medium so as to be rotatable along with the rotor, and (iv) an elastic member that is formed on the rotor concentrically with the rotational shaft and applies to the medium holding mechanism a force of reaction capable of relaxing a bending moment that is caused by a reaction to the urging force from the medium holding mechanism, in a state in which the recording medium is interposed between the medium holding mechanism and the elastic member, the elastic member having a sheet-like shape and including an outside diameter portion defined by a first radius from the rotational shaft, an inner peripheral portion defined by a second radius that is less than the first radius of the outside diameter portion, and an reaction portion defined by a third radius that is less than the second radius of the inner peripheral portion; an optical head that emits light to the recording medium and reproduces information recorded on the recording medium on the basis of the light reflected by the recording medium; and a motor control unit that rotates the disk motor at a predetermined speed.  
         [0020]     According to further another aspect of the present invention, there is provided a disk support mechanism comprising: a turntable having a surface extending perpendicular to a rotational shaft thereof, the turntable supporting a to-be-supported object; a claw member that applies an urging force in a direction parallel to the rotational shaft to the to-be-supported object that is loaded on the turntable; a claw height restricting member that keeps at a predetermined value a distance between the claw member and the turntable; and an elastic member that is formed on the turntable concentrically with the rotational shaft and produces a force of reaction capable of relaxing a bending moment that is caused by a reaction to the urging force in the direction parallel to the rotational shaft.  
         [0021]     According to another aspect of the present invention, there is provided a disk support mechanism comprising: a turntable having a surface extending perpendicular to a rotational shaft thereof, the turntable supporting a to-be-supported object; a support member that is disposed on the turntable concentrically with the rotational shaft and applies, when the to-be-supported object is loaded, a force to the to-be-supported object at least at three locations, the force acting in an axial direction of the rotational shaft away from the surface of the turntable; and a disk chucking member that receives the force from the support member and produces a force of reaction capable of putting the to-be-supported object in close contact with the support member.  
         [0022]     According to further another aspect of the present invention, there is provided a motor unit comprising: a motor base; a rotational shaft that is rotatably held by the motor base; a rotor fixed to the rotational shaft; a medium holding mechanism that is able to apply an urging force to the rotor in a direction parallel to an axis of the rotational shaft, at a predetermined radial position from a center of the rotational shaft, and positions a recording medium so as to be rotatable along with the rotor; and an elastic member that is formed on the rotor concentrically with the rotational shaft and applies to the medium holding mechanism a force of reaction capable of relaxing a bending moment that is caused by a reaction to the urging force from the medium holding mechanism, in a state in which the recording medium is interposed between the medium holding mechanism and the elastic member, the elastic member having a sheet-like shape and including an outside diameter portion defined by a first radius from the rotational shaft, an inner peripheral portion defined by a second radius that is less than the first radius of the outside diameter portion, and an reaction portion defined by a third radius that is less than the second radius of the inner peripheral portion. 
     
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING  
       [0023]     The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate presently preferred embodiments of the invention, and together with the general description given above and the detailed description of the preferred embodiments given below, serve to explain the principles of the invention.  
         [0024]      FIG. 1  is a schematic view illustrating an example of an optical disk drive according to an embodiment of the present invention;  
         [0025]      FIG. 2A  and  FIG. 2B  are a schematic view illustrating an example of a chucking mechanism that is built in the optical disk drive shown in  FIG. 1 ;  
         [0026]      FIG. 3  is a schematic view illustrating another example of the chucking mechanism shown in  FIG. 2A  and  FIG. 2B ;  
         [0027]      FIG. 4A  and  FIG. 4B  are a schematic cross-sectional view illustrating the structure of the chucking mechanism shown in  FIG. 3 ; and  
         [0028]      FIG. 5  is a schematic block diagram illustrating an example of the operation of the optical disk drive shown in  FIG. 1 . 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0029]     An embodiment of the present invention will now be described with reference to the accompanying drawings.  
         [0030]      FIG. 1  is a schematic view illustrating an example of an optical disk drive to which an embodiment of the present invention is applicable.  
         [0031]     As is shown in  FIG. 1 , an optical disk drive  101  includes a housing  11  and a drawer unit  112  that is configured to be able to perform an eject operation (movement in the direction of an arrow A) and a loading operation (movement in the direction of an arrow A′), relative to the housing  11 .  
         [0032]     A turntable  113  for rotating an optical disk (information recording medium) D with a predetermined number of revolutions is provided at a predetermined position on the drawer unit  112 .  
         [0033]     The drawer unit  112  includes a pickup drive mechanism that moves an optical pickup including an objective lens in a direction of the radius of the optical disk D (details being omitted) and a motor unit including a spindle motor that rotates the optical disk D set on the turntable  113  at a predetermined number of revolutions, as will be described in greater detail referring to  FIG. 2A  and  FIG. 2B .  
         [0034]      FIG. 2A  and  FIG. 2B  is a schematic view illustrating an example of the motor unit that is built in the drawer unit  112  shown in  FIG. 1 .  FIG. 2A  is a plan view showing a region including the motor unit and spindle motor.  FIG. 2B  is a cross-sectional view of the region including the spindle motor, taken along the axis of the shaft of the motor.  
         [0035]     As is shown in  FIG. 2A  and  FIG. 2B , a motor unit  131  including the turntable  113  includes a spindle motor  141  and a chucking mechanism  151 . The spindle motor  141  is supported on a motor base  132 . The chucking mechanism  151  is provided on a table surface  113   a  of the turntable  113  that is fixed to a shaft  142  of the spindle motor  141 . The turntable  113  doubles as a rotor  143  that is secured to the shaft  142  of the spindle motor  141 .  
         [0036]     The chucking mechanism  151  includes a boss portion  152 , springs  153  and chucking claws  154 . The boss portion  152  is put in contact with, and rotated along with, the turntable  113  and the shaft  142 . The springs  153  are disposed at predetermined positions of the boss portion  152  so as to be able to exert forces of reaction in predetermined directions relative to the axis of the boss portion  152 . Each of the chucking claws  154  is configured to be movable in a predetermined direction relative to the axis of the boss portion  152  by a force of reaction exerted by the associated spring  153 , thereby holding the optical disk (to-be-held object) D on the turntable  113 . In this example, three springs  153  and three chucking claws  154  are disposed concentrically with the shaft  142  or boss portion  152  at three equidistant positions on a circumference that is defined by a predetermined radius.  
         [0037]     An elastic member  155  that holds the optical disk D is provided on the rotor  143 , that is, the turntable  113 . The elastic member  155  is formed concentrically with the shaft  142  and boss portion  152  at a predetermined radial position relative to the outer circumference of the turntable  113 .  
         [0038]     The elastic member  155  is formed of, e.g. a rubber sheet or a resin sheet with a predetermined thickness. The elastic member  155  has an annular shape, as shown in  FIG. 2A . The elastic member  155  includes smooth-out stress portions  155   a  that are formed at predetermined intervals along the inside diameter of the elastic member  155 , with the area of each smooth-out stress portion  155   a  being increased toward the inside in the direction of the radius. The smooth-out stress portions  155   a  can smooth out an error in thickness of the optical disk D, an error in shape of the chucking claws, or a variation in spring force of the springs  153 .  
         [0039]     Each smooth-out stress portion  155   a , as shown in  FIG. 2B , extends toward the inside diameter part of the elastic member  155  up to a point substantially just below the chucking claw  154 , with the optical disk D interposed between the chucking claw  154  and the smooth-out stress portion  155   a . Thus, each smooth-out stress portion  155   a  smoothes out the above-mentioned errors in thickness and shape and variation in spring force, and also absorbs, by its own elastic deformation, the force exerted by the chucking claw  154  to the elastic member  155  via the optical disk D, that is, the urging force (stress) of the chucking claw  154 , or the stress from the chucking claw  154  thereby to prevent occurrence of bending moment in the optical disk D. To be more specific, the elastic member  155  includes an outside diameter portion defined by a first radius from the shaft  142 , an inside diameter portion defined by a second radius that is less than the first radius of the outside diameter portion, and the reaction portion defined by a third radius that is less than the second radius of the inside diameter portion. Preferably, the radius of the innermost part of the smooth-out stress portion  155   a  should be set to be slightly less than the radius of the inner part of the optical disk D.  
         [0040]     This structure prevents the optical disk D, which is set on the elastic member  155  on the turntable  113 , from curving due to the force exerted by the chucking claws  154 .  
         [0041]     Preferably, the smooth-out stress portions  155   a  of the elastic member  155  should be provided on only those plan-view areas (in  FIG. 2A ) that are in phase with (i.e. overlapping with) the associated chucking claws  154 . By virtue of this configuration, the work efficiency for attaching the boss portion  154  of the chucking mechanism  151  to the turntable  113  is improved, and the possibility of occurrence of bending moment in the optical disk D is minimized.  
         [0042]     As has been described above, according to the present invention, it is possible to prevent the optical disk D, which is set on the turntable (chucking mechanism), from curving in its radial direction by the urging force exerted by the chucking claws of the chucking mechanism and by the force of reaction from the elastic member on the turntable (i.e. the force of reaction that is exerted from the elastic member  155  provided on the turntable  113  and can relax a bending moment caused by a reaction to the force acting in the axial direction of the shaft  142 ). This feature also contributes to minimizing the clearance that is required between the housing (details being omitted) and drawer unit  112  of the optical disk drive  101 .  
         [0043]      FIG. 3  and  FIG. 4A  and  FIG. 4B  are schematic views illustrating another example of the structure of the motor unit shown in  FIG. 2A  and  FIG. 2B .  FIG. 3  shows, in enlarged scale, the region of the turntable of the motor unit that is similar to the motor unit shown in  FIG. 2A  and  FIG. 2B .  FIG. 4A  and  FIG. 4B  includes schematic cross-sectional views showing a region of a chucking claw and another region of the turntable shown in  FIG. 3 . In  FIGS. 3, 4A  and  4 B, the parts common to those in  FIG. 2A  and  FIG. 2B  are denoted by like reference numerals, and a detailed description is omitted.  
         [0044]     As is shown in  FIG. 3 , a motor unit  231  includes a turntable  213  that is rotated as one body with the shaft  142 .  
         [0045]     The turntable  213  is provided with a chucking mechanism  252  that is formed concentrically with the shaft  142 .  
         [0046]     The chucking mechanism  252  includes chucking claws  154 , springs  153 , and a claw height restricting member  256  (details shown in  FIG. 4B ). The chucking claws  154  are provided at predetermined positions on a boss portion  252  that is fixed to the shaft  142 . The springs  153  urges the chucking claws  154  toward the outside diameter from the center of the shaft  142 . The claw height restricting member  256  restricts the height of each chucking claw  154  from the turntable  131 .  
         [0047]     The claw height restricting member  256  defines spaces (recesses)  257  (shown in  FIG. 4A  in detail) that accommodate the springs  153 , which are formed integral to the boss portion  252 , and the chucking claws  154 . When the chucking claws  154  are mounted on the boss portion  252 , the claw height restricting member  256  prevents the height of each chucking claw  154  (height in the axial direction of boss portion  252 ) from being undesirably varied. The claw height restricting member  256  is provided in association with the elastic member  155  so as not to contact the smooth-out stress section  155   a  of the elastic member  155  that is disposed on the turntable  131  concentrically with the shaft  142 .  
         [0048]     In short, the claw height restricting member  256  can exactly maintain the distance (height) between the chucking claw  154  and the turntable  131  (elastic member  155 ).  
         [0049]      FIG. 5  is a schematic block diagram illustrating an example of the operation of the optical disk drive according to the embodiment shown in  FIG. 1 .  
         [0050]     As is shown in  FIG. 5 , the optical disk drive has an optical pickup  121  that includes: a light source (laser)  50  including a semiconductor laser capable of emitting a light beam with a predetermined wavelength; an optical member (diffraction element)  70  that imparts predetermined optical characteristics to the beam emitted from the laser  50 ; a collimator lens  2 ; a polarizing beam splitter  3 ; a ¼ wavelength plate  4 ; an objective lens  7 ; an astigmatism detection system  90 ; and a photodetector  11 . A description is given mainly of the reproduction of a signal obtained from the photodetector  11  of the optical pickup  121 .  
         [0051]     The photodetector  11  includes first to fourth region photodiodes  11 A,  11 B,  11 C and  11 D. Outputs A, B, C and D from these photodiodes are amplified to a predetermined level by first to fourth amplifiers  21   a ,  21   b ,  21   c  and  21   d.    
         [0052]     Outputs A and B from the first and second amplifiers  21   a  and  21   b  are added by a first adder  22   a , and outputs C and D from the third and fourth amplifiers  21   c  and  21   d  are added by a second adder  22   b . Outputs from the adders  22   a  and  22   b  are added by a third adder  23 , that is, (C+D) is subtracted from (A+B). An output from the third adder  23  is delivered to a focus control circuit  31  as a focus error signal. The focus error signal makes the position of the objective lens  7  agree with a focal distance, with which the light beam that is converged by the objective lens  7  is focused at a position with a predetermined depth in a track (not shown) or a pit sequence (not shown) formed on the recording surface of the optical disk D.  
         [0053]     On the other hand, an adder  24  produces an output of (A+C), and an adder  25  produces an output of (B+D). A phase difference detector  32  receives (A+C) and (B+D). The phase difference detector  32  is advantageous since it exactly outputs a tracking error signal, even where the objective lens  7  is shifted.  
         [0054]     An adder  26  produces a sum of (A+B) and (C+D) and delivers it to a tracking control circuit  33  as a tracking error signal.  
         [0055]     An adder  27  adds (A+C) and (B+D) and outputs an added signal (A+B+C+D), that is, a reproduction signal. The reproduction signal is stored in a buffer memory  34 .  
         [0056]     An APC circuit  39  receives the intensity of return light from the laser  50 . Based on record data stored in a record data memory  36 , the APC circuit  39  controls the intensity of the light beam emitted from the laser  50  at a predetermined level.  
         [0057]     In the optical disk drive  101  having the above-described signal detection system, the optical disk D is set on the turntable  113  and a CPU  38  effects a control to execute a predetermined routine. Then, a motor drive circuit  35  rotates the spindle motor  141  with a predetermined speed, and a laser drive circuit  37  controls the laser  50  to emit a laser beam for reproduction to the recording surface of the optical disk D.  
         [0058]     Subsequently, the laser  50  continuously emits the laser beam for reproduction, and a signal reproduction operation begins, although details are omitted here.  
         [0059]     The present invention is not limited to the above-described embodiments. Various modifications can be made in practice without departing from the spirit of the invention. The embodiments, when practiced, may be combined as much as possible, and advantageous effects can be obtained from such combinations.  
         [0060]     As has been described above in detail, in the optical disk drive of the present invention, the chucking mechanism provided on the turntable can hold the optical disk by the urging force for urging the optical disk toward the turntable and by the elastic member that produces a force of reaction to the urging force so as not to cause a bending moment. Thereby, the optical disk is prevented from curving in its radial direction.  
         [0061]     Accordingly, the clearance that is required between the housing and drawer unit of the optical disk drive can be minimized, and the thickness of the drive can be reduced.  
         [0062]     Furthermore, neither the number of parts nor the number of assembly steps of the chucking mechanism increases. Besides, the manufacturing cost does not increase.