Patent Publication Number: US-7908614-B2

Title: Chucking mechanism, brushless motor having the chucking mechanism, and disk driving apparatus having the brushless motor

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a chucking mechanism operable to detachably set thereon a discoid disk, and to a motor including the chucking mechanism, and a disk driving apparatus including the motor. 
     2. Description of Related Art 
     In recent years, a slot loading mechanism in which a disk is slid in and out of a disk driving apparatus is used in a personal computer (hereinafter, referred to as PC). This mechanism is particularly useful for a PC having a slim shape. 
     The slot loading mechanism requires no tray moving the disk to a spindle motor which rotates the disk, and therefore is allowed to be slim. However, there is an increased demand to further slim down the disk driving apparatus. In order to further slim down the disk driving apparatus, the spindle motor used therein also needs to be slimmer. It is, however, a difficult task to reduce a thickness of a chucking mechanism on which the disk is removably set and which is arranged in the spindle motor. 
     Also, the disk driving apparatus having applied thereon the slot loading mechanism usually retains the disk by itself without using a clamping member in order to achieve a thin chucking mechanism. 
       FIG. 14  is a diagram showing a cross sectional view, in an axial direction, of a conventional configuration of the chucking mechanism. 
     According to  FIG. 14 , a chucking mechanism  1  includes a turn table  2  having a disk setting surface  2   a  on which a disk (not shown in  FIG. 14 ) having a central opening portion, a center case  3 , a plurality of claw members  4 , and an elastic member  5  providing a radial force for each claw member  4 . The center case  3  includes a cylindrical portion  3   a  around which an inner circumferential surface of the central opening portion of the disk will be arranged, a top plate portion  3   b  arranged such as to cover a top end of the cylindrical portion  3   a , and a plurality of openings  3   c  allowing the claw members  4  to move therethrough. The claw member  4  includes a disk retaining surface  4   a  which makes contact with the central opening portion so as to retain the disk. Also, the center case  3  preferably includes an upward guiding surface  3   d  which makes contact with the claw member  4  so as to guide a sliding movement of the claw member  4 . 
     SUMMARY OF THE INVENTION 
     A chucking mechanism according to the present invention, a claw member includes a movement pivot portion and a movement support portion at a portion of the claw member radially further inward than the movement pivot portion in order to allow the claw member to move in a radial and an axial direction. When the movement support portion makes contact with the movement support receiving portion, the radial movement of the claw member is well supported, and therefore, a disk will be retained by the chucking mechanism effectively. 
     Other features, elements, steps, characteristics and advantages of the present invention will become more apparent from the following detailed description of preferred embodiments thereof with reference to the attached drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic cross sectional view in an axial direction showing a brushless motor according to a preferred embodiment of the present invention. 
         FIG. 2  is a plan view of a chucking mechanism of the present invention as seen from above. 
         FIG. 3   a  is a schematic cross sectional view of a center case of the present invention. 
         FIG. 3   b  is a plan view of the center case as seen from above. 
         FIG. 4   a  is a side view of a claw member of the present invention. 
         FIG. 4   b  is a front view of the claw member of the present invention. 
         FIG. 4   c  is a plan view of the claw member of the present invention. 
         FIG. 4   d  is a schematic cross sectional view of the claw member of the present invention. 
         FIG. 5  is a cross sectional view of the chucking mechanism before a disk makes contact therewith. 
         FIG. 6  is a cross sectional view of the chucking mechanism when the disk begins to make contact with a disk guiding surface. 
         FIG. 7  is a cross sectional view of the chucking mechanism according to the present invention in which a movement support portion is arranged at a position of a curved surface. 
         FIG. 8  is a cross sectional view of the chucking mechanism according to the present invention in which the movement support portion slides over an upper movement support surface. 
         FIG. 9  is a schematic cross sectional view of the chucking mechanism according to the present invention in which a tip portion thereof is at an axially lowest position. 
         FIG. 10  is a schematic cross sectional view of the chucking mechanism according to the present invention in which the claw member retains the disk. 
         FIG. 11  is a cross sectional view of the chucking mechanism according to the present invention in which an inner configuration of the claw portion according to  FIG. 9  is shown. 
         FIG. 12  is a graph indicating a correlation between a rate of occurrence of chucking failure and an axial height of a tip portion of the claw member of the chucking mechanism according to the present invention. 
         FIG. 13  is a cross sectional view of a disk driving apparatus according to a preferred embodiment of the present invention. 
         FIG. 14  is a cross sectional view of a conventional chucking mechanism before a disk makes contact therewith. 
         FIG. 15  is a cross sectional view of the conventional chucking mechanism when the disk begins to make contact with a claw member. 
         FIG. 16  is a cross sectional view of the conventional chucking mechanism in which a tip portion thereof is at an axially lowest position. 
         FIG. 17  is a cross sectional view showing a relationship between the claw portion and the elastic member. 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     Note that in the description of the preferred embodiments of the present invention herein, words such as upper, lower, left, right, upward, downward, top, and bottom for describing positional relationships between respective member and directions merely indicate positional relationships and directions in the drawings. Such words do not indicate positional relationships and directions of the member set in an actual device. Also note that a direction parallel to Z axis herein will be referred to as an axial direction. Also, note that the reference numerals, figure numbers and supplementary descriptions are shown below for assisting the reader in finding corresponding components in the description of the preferred embodiments below to facilitate the understanding of the present invention. It should be noted that these expressions in no way restrict the scope of the present invention. 
     Structure of Brushless Motor 
     Hereinafter a brushless motor according to a preferred embodiment of the present invention will be described with reference to  FIG. 1 .  FIG. 1  is a schematic cross sectional view in an axial direction of a brushless motor according to a preferred embodiment of the present invention. 
     Hereinafter, a stator portion of the brushless motor will be described. 
     A housing  10  preferably having a substantially cylindrical shape concentric with a central axis J 1  is preferably made by a deformation process such as cutting performed on a copper base material. A sleeve  20  is affixed to an inner circumferential surface of a cylindrical portion  11  of the housing  10 . The sleeve  20  preferably having a substantially cylindrical shape is a sintered member impregnated with oil. 
     The housing  10  preferably includes at a portion axially below the cylindrical portion  11  a stator base portion  12  preferably having a substantially cylindrical shape extending radially outward, wherein the cylindrical portion  11  and the stator base portion  12  are preferably formed integrally. The stator base portion  12  preferably includes at a bottom surface thereof a protrusion extending radially inward and a protrusion extending radially outward (hereinafter, referred to as inner circumferential protrusion  12   a  and outer circumferential protrusion  12   b , respectively). A plate  30  is arranged extending inwardly from the inner circumferential protrusion  12   a . The plate  30  and the inner circumferential protrusion  12   a  are affixed to one another by calking. A thrust plate  40  preferably having a substantially disk shape preferably made of a material excellent in abrasion resistance quality is arranged axially above the plate  30 . 
     The housing  10  preferably includes at an outer circumferential portion of the stator base portion  12  a stator setting portion  12   c  for setting thereon a stator  50  (described below). The stator  50  preferably includes a stator core  51  having a core back portion  51   a , a plurality of tooth portions  51   b  each extending radially outward of the core back portion  51   a , and a plurality of coils  52  each formed by winding a plurality of times a conductive wire around each tooth portion  51   b.    
     The housing  10  preferably includes at a portion radially inward of the stator  50  of the stator base portion  12  a pressuring magnet  60  preferably having a substantially annular shape. The pressuring magnet  60  is arranged such as to axially oppose a bottom surface of a lid portion  101  of a rotor holder  100  (described below). 
     An attachment board  70  is affixed by calking to the housing  10  at an outer circumferential surface of the outer circumferential protrusion  12   b . A circuit board  80  for controlling a rotation of the brushless motor is arranged on a top surface of the attachment board  70 . An axially lower portion of the stator  50  is preferably covered by the circuit board  80  and the attachment board  70 . 
     Hereinafter, a rotor portion of the brushless motor will be described. 
     A shaft  90  is inserted in an inner circumferential surface of the sleeve  20  in a concentric manner with the central axis J 1 . The shaft  90  is rotatably supported in a radial direction by the inner circumferential surface of the sleeve  20  while the same is supported in the axial direction by the thrust plate  40 . 
     A rotor holder  100  preferably having an operculated and substantially cylindrical shape is affixed at an upper portion of the shaft  90  so as to cover the stator  50 . The rotor holder  100  is preferably formed by pressing a magnetic steel plate. Also, the rotor holder  100  preferably includes the lid portion  101  and a cylindrical portion  102 . The lid portion  101  preferably includes at a portion axially corresponding to the sleeve  20  and the cylindrical portion  11  a leveled portion  101   a . By virtue of such configuration, the sleeve  20  can be extended in the axial direction. At a bottom surface of the leveled portion  101   a  a stopper member  120  for preventing the rotor holder  100  from being removed in the axial direction is arranged. 
     A rotor magnet  110  is arranged at an inner circumferential surface of the cylindrical portion  102 . An inner circumferential surface of the rotor magnet  110  is opposed, via a gap in the radial direction, to an outer circumferential surface of the tooth portions  51   b  of the stator  50 . 
     A center case  210  of a chucking mechanism  200  for detachably setting thereon a disk (not shown in  FIG. 1 ) is arranged on a top surface of the lid portion  101 . A disk setting portion  101   b  for setting thereon the disk is arranged at an outer end of the lid portion  101 . According to the present preferred embodiment of the present invention the rotor holder  100  functions as a turn table. 
     Chucking Mechanism 
     Hereinafter, the chucking mechanism  200  according to a preferred embodiment of the present invention will be described with reference to  FIGS. 2 through 5 .  FIG. 2  is a plan view of the chucking mechanism  200  according to the present preferred embodiment of the present invention.  FIG. 3   a  is a schematic cross sectional view in the axial direction of the center case  210  according to the present preferred embodiment of the present invention.  FIG. 3   b  is a plan view of the center case  210  according to the present preferred embodiment of the present invention.  FIG. 4   a  is a schematic side view of a claw member  220  according to a preferred embodiment of the present invention.  FIG. 4   b  is a schematic front view of the claw member  220  according to the present preferred embodiment of the present invention.  FIG. 4   c  is a plan view of the claw member  220  according to the preferred embodiment of the present invention.  FIG. 5  is an enlarged schematic cross sectional view of the chucking mechanism  200  according to a preferred embodiment of the present invention. 
     According to  FIG. 2   r  the chucking mechanism  200  preferably includes the center case  210  preferably having a substantially cylindrical shape concentric with the central axis J 1 , and the rotor holder  100  (i.e., turn table) having the disk setting portion  101   b . The disk setting portion  101   b  set on the rotor holder  100  is preferably made of a material excellent in coefficient of friction. 
     The center case  210  preferably includes at an outer circumference thereof a plurality of aligning claws  211  for aligning a central opening portion of the disk with the central axis J 1 , a plurality of claw members  220  arranged so as to contact with the inner circumferential surface of the central opening of the disk. To be more specific, according to the preferred embodiment of the present invention, the chucking mechanism  200  preferably includes three aligning claws  211  and claw members  220  each are alternately arranged in the circumferential direction evenly apart from one another. Also, the center case  210  preferably includes an elastic member  230  which provides radial force for each claw member  220 . 
     According to  FIGS. 3   a  and  3   b , the center case  210  preferably includes a cylindrical portion  212 , a guiding portion  213  arranged axially above the cylindrical portion  212  for guiding the disk to the cylindrical portion  212 , a base portion  214  for connecting the center case  210  with the rotor holder  100 , and a top plate portion  215  connecting the guiding portion  213  and the base portion  214 . Also, the center case  210  preferably includes at a portion between the cylindrical portion  212  and an outer edge of the top plate portion  215  an opening  216  for each claw member  220 . Note that the center case  210  is made by an injection molding and made of a resin material and as a single component. 
     The opening  216  preferably includes a side opening portion  216   a  opening toward the cylindrical portion  212  and the guiding portion  213 , and an upper side opening portion  216   b  opening continuously upwardly from the side opening portion  216   a . It is to be appreciated that a circumferential width of the side opening portion  216   a  is greater than that of a claw portion  221  (described later) of the claw member  220 , and is smaller than that of the claw member  220  including a pair of movement support portions  222  (described later). Also, the side opening portion  216   a  penetrates to a bottom surface of the cylindrical portion  212 . Also, a circumferential width of the upper side opening portion  216   b  is greater than that of the claw portion  221 , and is smaller than that of the claw member  220  including a pair of movement pivot portions  222   a  (described later) of the movement support portions  222 . Also the upper side opening portion  216   b  includes a widened portion  216   b   1  whose circumferential width is equal to or greater than that of a pair of movement pivot receiving portions  217  (described later) circumferentially binding the claw portion  221 . Also, the circumferential width of the widened portion  216   b   1  is smaller than that of a pair of upper side contact surfaces  222   a   2  (described later) of the movement support portion  222 . Also, the radial width of the widened portion  216   b   1  is equal to or greater than that of movement pivot receiving portion  217 . 
     The top plate portion  215  preferably includes at a position corresponding to both sides in the circumferential ends of the widened portion  216   b   1  a lower side receiving surface  215   a  which restricts a radial movement of the claw member  220  by making contact with the upper side contact surface  222   a   2 . 
     The cylindrical portion  212  preferably includes at both sides in the circumferential direction of the side opening portion  216   a  the movement pivot receiving portion  217  which preferably includes a plane surface extending substantially perpendicularly to the central axis J 1 , and makes contact with the movement pivot portion  222   a . The movement pivot receiving portion  217  extends further radially inwardly than a radial position of the movement pivot portion  222   a  when the claw member  220  is at a radially innermost position. Also, the movement pivot receiving portion  217  is connected to the cylindrical portion  212 . Also, at a portion connecting the movement pivot receiving portion  217  and the cylindrical portion  212  a curved surface  217   a  having an indent surface is arranged. It is to be appreciated that the forming of the widened portion  216   b   1  allows a configuration of a mold used to form the center case  210  to be simple. In particular, the mold used to form the center case  210 , which is a single component, includes an upper mold, which slides, and a lower mold, which is fixed, wherein the upper mold is removed from the lower mold in a simple manner. 
     The base portion  214  includes a plane surface which is perpendicular to a direction in which the elastic member  230  extends and which makes contact with the elastic member  230 . The plane surface includes a movement restricting indent portion  214   a  which is equal to or slightly greater than a diameter of the elastic member  230  which is a spring. The movement restricting indent portion  214   a  restricts a movement of the elastic member  230  in the circumferential direction. By virtue of such configuration, when a radial force acting toward the central axis is applied (i.e., when the disk is placed on the chucking mechanism  200 ) to the claw member  220 , the force is not dispersed in the circumferential direction, and therefore, the chucking mechanism  200  allows the disk to be set thereon smoothly. 
     Also, the base portion  214  preferably includes at a portion connecting the movement restricting indent portion  214   a  and the top plate portion  215  a lower contact surface  214   b  which restricts, by making contact with the elastic member  230 , an axial movement of the elastic member  230 . By virtue of such configuration, when the radial force acting toward the central axis is applied to the claw member  220 , the force is not dispersed in the axial direction, and therefore, the chucking mechanism  200  allows the disk to be set thereon smoothly. 
     A movement support receiving portion  218  having two surfaces each having an inclination different from one another is formed radially inward of the movement pivot receiving portion  217 . The movement support receiving portion  218  includes an upper movement support surface  218   a  which is connected to the top plate portion  215  and which is inclined such that the further radially outward a portion thereof is the axially lower the portion is, and a lower movement support surface  218   b  which is arranged radially outwardly and axially lower and which is inclined such that the further radially outward a portion thereof is the axially lower the portion is. A curved surface  218   c  is arranged protrudingly in the substantially radially outward direction at a portion connecting the upper movement support surface  218   a  and the lower movement support surface  218   b . Also, the curved surface  218   c  is formed such that an angle θ 2  defined by the upper movement support surface  218   a  and the central axis J 1  is greater than an angle θ 1  defined by the lower movement support surface  218   b  and the central axis J 1 . The angle θ 1  may be designed such that the movement assist portion  222   b  will be restricted from moving in the radially inward direction. By virtue of such configuration, the disk guiding surface  221   a  is allowed to remain inclined radially outwardly and axially downwardly while moving on to the upper movement support surface  218   a . Also, at the upper movement support surface  218   a  on which the claw member  220  moves in the radial direction, an axial movement of the tip portion  221   b  will be supported. Also, at the upper movement support surface  218   a , the radial movement of the claw member  220  will be supported effectively. Therefore, the disk will be set on the chucking mechanism  200  effectively. 
     Also, since the movement pivot receiving portion  217  is arranged radially inside of the cylindrical portion  212 , when the movement pivot portion  222   a  makes contact with an inner circumferential surface of the cylindrical portion  212 , a mechanism to restrict the claw member  220  from moving exceedingly in the radial direction is formed. Therefore, a separate mechanism for restricting the radial movement of the claw member  220  will not be necessary. Further, the radial length of the movement pivot receiving portion  217  is freely determined within a distance between the inner circumferential surface of the cylindrical portion  212  and the base portion  214  in accordance with the radial movement of the claw member  220 . 
     Also, the radial length of the movement support receiving portion  218  is freely determined within the distance between the inner circumferential surface of the cylindrical portion  212  and the base portion  214  in accordance with the radial movement of the claw member  220 . Also, since the movement support receiving portion  218  and the movement pivot receiving portion  217  are arranged such as not to overlap in the radial direction with one another, the movement of the movement pivot receiving portion  217  will not be in the way of the movement support receiving portion  218  or vice-versa. Therefore the movement pivot receiving portion  217  and the movement support receiving portion  218  each will be designed in accordance with their movement. 
     Also, the lower side receiving surface  215   a  is arranged between the movement pivot receiving portion  217  and the movement support receiving portion  218  in the circumferential direction. 
     The aligning claw  211  includes an aligning surface  211   a  which makes contact with the central opening portion of the disk (shown in  FIGS. 3   a  and  3   b ) so as to align the disk, and a guiding inclined surface  211   b  which guides the disk to the aligning surface  211   a . The guiding inclined surface  211   b  includes a portion thereof which is arranged axially below the guiding portion  213 . That is a portion radially inward of the cylindrical portion  212  of the guiding inclined surface  211   b  makes no contact with the disk. That is, a portion radially outward of the cylindrical portion  212  guides the disk to the aligning surface  211 . 
     According to  FIGS. 4   a  to  4   d , the claw member  220  includes the claw portion  221  and the pair of movement support portions  222  arranged on circumferentially both sides of the claw portion  221 . The movement support portion  222  supports the axial movement of the claw member  220 . 
     The claw portion  221  includes the disk guiding surface  221   a  which makes an initial contact with the disk when the disk is set on the chucking mechanism  200 , a tip portion  221   b  which is formed continuously toward the axially lower direction from the disk guiding surface  221   a  and radially outwardly, and a disk retaining surface  221   c  which is formed continuously toward the axially lower direction from the tip portion  221   b  and retains the disk. 
     The disk guiding surface  221   a  guides the disk to the disk retaining surface  221   c . Also, the disk guiding surface  221   a  is a plane surface having no inclination. The disk retaining surface  221   c  includes an inclined surface which is inclined such that the further radially outward a portion thereof is the axially upper the portion is, and which makes contact with an upper end of the central opening portion of the disk when the disk is set on the disk setting surface  101   b . Here, the disk guiding surface  221   a  is arranged axially above a bottom surface of the top plate portion  215  before the disk is set on the chucking mechanism  200 . Since the disk guiding surface  221   a  is a plane surface having no inclination, an axial length of the claw portion  221  is minimized. Consequently, the chucking mechanism  200  can be designed having a reduced axial thickness. 
     Also, mirror polishing which allows the disk to travel smoothly to the disk retaining surface  221   c  is applied on the disk guiding surface  221   a  and the disk retaining surface  221   c . By virtue of such configuration, the disk can be attached to and detached from the chucking mechanism  200 . 
     According to  FIG. 4   d , the claw portion  221  includes at the inner circumferential surface a protrusion  221   d  protruding radially inwardly so as to make contact with the elastic member  230 . The protrusion  221   d  includes at an upper portion thereof a protrusion inclined surface  221   d   1  which is inclined such that the further radially inward a portion thereof is the axially lower the portion is. Also, the claw portion  221  includes at a radially inner surface and a bottom portion thereof an inner circumferential surface side inclined surface  221   d   2  which is inclined such that the further radially outward a portion thereof is the axially lower the portion is. 
     The pair of movement support portions  222  attached to the claw portion  221  are extending radially inwardly from a radially inner circumferential side of the claw portion  221 . Also, the movement support portion  222  includes the movement pivot portion  222   a  which is a pivotal portion of the movement of the claw member  220 , and the movement assist portion  222   b  which is arranged radially inward of the movement pivot portion  222   a  and guides the claw member  220  in the radial direction. Also, the movement support portion  222  includes at a surface thereof which is connected to the upper side contact surface  222   a   2  and which is inclined such that the further radially a portion thereof is the axially lower the portion is. By virtue of such inclined surface, when the tip portion  221   b  of the claw member  220  moves axially downwardly, the movement support portion  222  makes no contact with the top plate portion  215 . 
     The movement pivot portion  222   a  preferably includes a movement pivot side curved surface  222   a   1  which slides with a top surface of the movement pivot receiving portion  217 . The movement pivot side curved surface  222   a   1  needs at least enough curve to allow the tip portion  221   b  to move in the axial direction. In particular, the movement pivot side curved surface  222   a   1  of the movement pivot portion  222   a  has preferably an even curvature radius. By virtue of such configuration, only the tip portion  221   b  of the claw member  220  is allowed to move in the axial direction. 
     Also, the movement pivot portion  222   a  preferably includes at a portion extending radially inwardly from a bottom end surface of the movement pivot side curved surface  222   a   1  an extending plane surface  222   c . The extending plane surface  222   c  is a plane surface which is substantially parallel with the top surface of the movement pivot receiving portion  217  when the claw member  220  is contained within the center case  210 . 
     Also, the pair of movement support portions  222  are arranged substantially on circumferential sides of the claw member  220  preferably including the pair of movement assist portions  222   b . Also, a surface of the movement assist portion  222   b  opposed to the movement support receiving portion  218  preferably includes a movement support portion side curved surface  222   b   1  which protrudes toward the movement support receiving portion  218 . The movement support portion side curved surface  222   b   1  is a curved surface which allows the claw member  220  to slide with the upper movement support surface  218   a  and the lower movement support surface  218   b.    
     A configuration of the chucking mechanism  200  prior to when the disk (not shown in  FIG. 5 ) is set thereon will be described with reference to  FIG. 1  and  FIG. 5 .  FIG. 5  is a cross sectional view of the chucking mechanism  200  before the disk makes contact therewith. 
     According to  FIG. 5 , the claw portion  221  protrudes radially outwardly from the opening  216  of the center case  210 . Also, the elastic member  230  is compressed and contained within the center case  210 . The elastic member  230  is arranged between an outer circumferential surface of the base portion  214  and an inner circumferential surface of the claw portion  221 . Also, the elastic member  230  makes contact with the protrusion  221   d  arranged at the inner circumferential surface of the claw portion  221 . The compressed elastic member  230  provides a radial force to the claw portion  221  in the radially outward direction. 
     Next, according to  FIG. 5 , the movement pivot portion  222   a  of the movement support portion  222  makes contact with the inner circumferential surface of the cylindrical portion  212  so as to prevent the claw member  220  from moving excessively in the radially outward direction. Also, the movement pivot portion  222   a  makes contact with the top surface of the movement pivot receiving portion  217 . 
     The movement pivot portion  222   a  preferably includes at the top surface thereof the upper side contact surface  222   a   2  operable to make contact with the bottom surface of the top plate portion  215 . Prior to when the disk makes contact with the chucking mechanism  200 , the upper side contact surface  222   a   2  is substantially opposed to the bottom surface of the top plate portion  215  via a minute gap in the axial direction. That is, since the upper side contact surface  222   a   2  is not in contact with the bottom surface of the top plate portion  215  prior to when the disk is set on the chucking mechanism  200 , an area in which the claw member  220  and the center case  210  make contact with one another will be reduced. Also, when the tip portion  221   b  moves in the axially downward direction, the upper side contact surface  222   a   2  is not in contact with the top plate portion  215 , the area in which the claw member  220  and the center case  210  make contact with one another will be reduced allowing the claw member  220  to move in the radially inward direction smoothly. By virtue of such configuration, the disk will be set on the chucking mechanism  200  smoothly. 
     Also, the movement assist portion  222   b  is arranged above the lid portion  101  via an axial gap. That is, an axial position of the claw member  220  is determined by the movement pivot portion  222   a  and the top surface of the movement pivot receiving portion  217 . If the axial position of the claw member  220  is determined by the contact between the lid portion  101  and the movement assist portion  222   b , an assembly error of the rotor holder  100  and the center case  210  will affect the axial position of the claw member  220 . According to the present invention, however, the axial position of the claw member  220  is determined by the movement pivot portion  222   a  and the top surface of the movement pivot receiving portion  217 , and therefore, is less likely to be affected by the assembly error. Therefore, the chucking mechanism  200  according to the present preferred embodiment of the present invention offers a reliable quality. Also note that the movement assist portion  222   b  is substantially opposed to the lower movement support surface  218   b  of the movement support receiving portion  218  via a minute gap. 
     It is to be noted that there is no extra component between the bottom surface of the disk retaining surface  221   c  and the top surface of the lid portion  101 . That is, the side opening portion  216   a  extends to a bottom end portion of the cylindrical portion  212 , and therefore, a space S 1  which defines an axial space between the bottom surface of the disk retaining surface  221   c  and the top surface of the lid portion  101  is minimized while the claw portion  221  makes no contact with the top surface of the lid portion  101  when the claw portion  221  is at the lowest position in the axial direction. According to the present invention, the excessive movement of the claw member  220  in the axial direction is prevented by the movement pivot portion  222   a  and the movement pivot receiving portion  217 , and therefore, it becomes possible to design the space S 1  having a minimum space and a preferable accuracy. By virtue of such configuration, it becomes possible to design the chucking mechanism  200  having a preferable thinness. 
     According to  FIG. 1 , it is preferable that the base portion  214  of the center case  210  is arranged to reach in the axial direction a central portion in the axial direction of the elastic member  230 , or more preferably below in the axial direction of the elastic member  230 . By virtue of such configuration, the center case  210  is operable to contain and affix to the rotor portion (e.g., rotor holder  100 , rotor magnet  110  and shaft  90 ) the claw member  220  and the elastic member  230 . Therefore, the chucking mechanism  200  will be assembled with facility and a productivity of the brushless motor will be improved. 
     Movement of Claw Member 
     Hereinafter, movement of the claw member  220  when a disk D is set on the chucking mechanism  200  will be described with reference to  FIG. 6  through  FIG. 11 .  FIG. 6  is a cross sectional view of the chucking mechanism  200  when the disk D begins to make contact with the disk guiding surface  221   a .  FIG. 7  is a cross sectional view of the chucking mechanism  200  according to the present invention in which the movement assist portion  222   b  is arranged at a position of a curved surface  218   c .  FIG. 8  is a cross sectional view of the chucking mechanism  200  according to the present invention in which the movement assist portion  222   b  slides over the upper movement support surface  218   a .  FIG. 9  is a schematic cross sectional view of the chucking mechanism  200  according to the present invention in which the tip portion  221   b  thereof is at the axially lowest position.  FIG. 10  is a schematic cross sectional view of the chucking mechanism  200  according to the present invention in which the claw member  220  retains the disk D.  FIG. 11  is a cross sectional view of the chucking mechanism  200  according to the present invention in which an inner configuration of the claw portion  221  according to  FIG. 9  is shown. Hereinafter, the disk D is a multi-layered disk including an upper disk Da and a lower disk Db wherein the disk Da is pasted to the disk Db via an adhesive. Note that the elastic member  230  is omitted from  FIGS. 6 through 10  in order to better show a relationship between the claw member  220  and the center case  210 . 
     According to  FIG. 6 , a central opening portion D 1  of the disk D makes contact with the disk guiding surface  221   a . Then, the tip portion  221   b  of the claw member  220  moves in the axially downward direction. The movement of the claw member  220  is supported via a movable support point RC which is a point at which the movement pivot portion  222   a  makes contact with the movement pivot receiving portion  217 . Here, a moving radius R 1  of the claw member  220  in the axially downward direction equals a distance between the movable support point RC and the tip portion  221   b , and therefore, when the movable support point RC is arranged far from the tip portion  221   b , the moving radius R 1  can be increased. Consequently, a rotational force applied to the claw member  220  in the axially downward direction is reduced, which also reduces the force required to set the disk D on the chucking mechanism  200 . That is, the chucking mechanism  200  allows the disk D to be set thereon smoothly. 
     The movement assist portion  222   b  moves axially upward when the tip portion  221   b  moves axially downward. Also, when the movement assist portion  222   b  moves upward in the axial direction slightly, the movement assist portion  222   b  makes contact with and slides on the lower movement support surface  218   b . At this point, the claw member  220  moves radially inwardly along the lower movement support surface  21   b . Also, when the tip portion  221   b  of the claw member  220  moves in the axially downward direction, the axial gap between the movement support portion  222  and the lid portion  101  is gradually increased. 
     Next, according to  FIG. 7 , the movement assist portion  222   b  moves to the position of the curved surface  218   c . At this point, the movement assist portion  222   b  makes contact with both the lower movement support surface  218   b  and the upper movement support surface  218   a . At the position of the curved surface  218   c , the claw member  220  begins to move substantially in the radial direction. Here, since the tip portion  221   b  is already moving in the axially downward direction, the claw member  220  is allowed to move in the radial direction while an angle defined by the top surface of the disk guiding surface  221   a  and the central axis J 1  remains large. Therefore, when the disk D is being set on the chucking mechanism  200 , a great amount of force pushing the claw member  220  in the axially downward direction will not be required. 
     Next, according to  FIG. 8 , when the disk D moves further downward in the axial direction, the movement assist portion  222   b  makes contact with the upper movement support surface  218   a  since the claw member  220  moves radially inwardly. The force applied to the disk D to set the disk D on the chucking mechanism  200  is, because of the inclined surface of the upper movement support surface  218   a , shifted to the radially inward direction. Also, the tip portion  221   b  moves axially in the downward direction along the inclination of the upper movement support surface  218   a.    
     The movement pivot portion  222   a  moves radially inward by sliding on the surface of the movement pivot receiving portion  217 . Here, since the top surface of the movement pivot receiving portion  217  is arranged perpendicularly to the central axis J 1 , the claw member  220  will not be forced to move axially downwardly due to the force to set the disk Don the chucking mechanism  200 . The claw member  220  is allowed to move radially inwardly. 
     Next, according to  FIG. 9 , when the claw member  220  is at the radially innermost point (i.e., when the tip portion  221   b  makes contact with the inner circumferential surface of the central opening portion D 1  of the disk D), the tip portion  221   b  is at the axially lowest point. The point at which the tip portion  221   b  is determined by the way in which the movement assist portion  222   b  and the upper movement support surface  218   a  make contact with one another. Also, when the tip portion  221   b  is at the lowest point in the axial direction as shown in  FIG. 9 , an axial height (L 1 ) of the tip portion  221   b  from the disk setting surface  101   b  is greater than an axial height (L 2 ) which is an axial length between the disk setting surface  101   b  having set thereon the disk D and a line (BL) bordering the disk Da and the disk Db. Since the L 1  is axially above the BL from the disk setting surface  101   b , a chucking failure in which the tip portion  221   b  interferes with the BL. 
     The movement pivot portion  222   a  slides over the top surface of the movement pivot receiving portion  217 . Note that the top surface of the movement pivot receiving portion  217  extends radially inwardly further than an innermost point to which the movement pivot portion  222   a  reaches. Therefore, an entire sequence of radial movement of the claw member  220  will be conducted over the movement pivot portion  222   a  and the movement pivot receiving portion  217 . Since the claw member  220  is allowed to move substantially only in the radial direction, the elastic member  230  will not be deformed which may happen when the claw member  220  moves in the axial direction. By virtue of such configuration, the disk D will be set on the chucking mechanism  200  smoothly. 
     Also, when the tip portion  221   b  is at the axially lowest point as shown in  FIG. 9 , the protrusion inclined surface  221   d   1  which is arranged at the upper portion of the protrusion  221   d  and is a mechanism to prevent the elastic member  230  from being deformed in the axial direction becomes substantially perpendicular to the central axis J 1  (see  FIG. 11 ). The inner circumferential surface side inclined surface  221   d   2  which is arranged at the radially inner surface and the bottom portion of the claw portion  221  becomes substantially parallel to the central axis J 1 . By this, when the claw member  220  is at the axially lowest point, the protrusion inclined surface  221   d   1  is operable to substantially prevent the protrusion  221   d  from interfering with the elastic member  230 . Also, when the claw member  220  is at the axially lowest point, the inner circumferential surface side inclined surface  221   d   2  is operable to prevent the elastic member  230  from moving upward in the axial direction, substantially preventing deformation thereof. Consequently, the elastic member  230  is allowed to provide the radial force to the claw portion  221  without being interfered by the top plate portion  215 . 
     In is to be noted that when the protrusion inclined surface  221   d   1  is as shown in  FIG. 9 , the protrusion inclined surface  221   d   1  is not limited to being substantially perpendicular to the central axis J 1 . The protrusion inclined surface  221   d   1  can be designed such that the further radially inward a portion thereof is the axially lower the portion is when the tip portion  221   b  is at the axially lowest point as shown in  FIG. 9 . 
     Next, according to  FIG. 10 , the tip portion  221   b  slides along the inner circumferential surface of the central opening portion D 1  of the disk D in the axial upward direction and reaches the top end of the central opening portion D 1 . Then the disk D is retained by the claw member  220 . 
     Also, while the disk D is retained by the claw member  220 , the extending plane surface  222   c  makes contact with the top surface of the movement pivot receiving portion  217 . A point (hereinafter, referred to as a support point NC) at which the extending plane surface  222   c  makes contact with the top surface of the movement pivot receiving portion  217  will function as a fulcrum via which the claw member  220  moves in the axially upward direction. Then, at a contact point TC, the upper side contact surface  222   a   2  of the movement support portion  222  makes contact with the bottom surface of the top plate portion  215 . At the contact point TC, the claw member  220  is prevented from moving excessively upward in the axial direction when the disk D is removed from the chucking mechanism  200 . By virtue of such configuration, an angle defined by the disk retaining surface  221   c  and a surface perpendicular to the central axis J 1  will be kept at an optimal degree so as to securely retain the disk D. Also, since the extending plane surface  222   c  and the movement pivot receiving portion  222   a  make contact with one another, and the upper side contact surface  222   a   2  and the bottom surface of the top plate portion  215  make contact with one another, the tip portion  221   b  of the claw member  220  is substantially prevented from moving in the axially upward direction, while the axial movement of the claw member  220  is executed within an axial space between the movement pivot receiving portion  217  and the top plate portion  215 . By virtue of such configuration, the movement of the claw member  220  will be controlled within an allowable error of assembling the center case  210 , and therefore, a reliable chucking mechanism will be provided. 
     Also, the movement pivot receiving portion  217  includes a plane surface extending radially inwardly. Also, the extending plane surface  222   c  of the claw member  220  is substantially parallel with the movement pivot receiving portion  217 , and therefore, substantially prevents the tip portion  221   b  of the claw member  220  from moving in the axially upward direction when the claw member  220  moves radially inwardly. 
     Axial Distance between Tip Portion and Disk Setting Surface 
     Hereinafter, an axial distance between the tip portion  221   b  of the claw portion  221  and the disk setting surface  101   b  will be described with reference to  FIG. 12 .  FIG. 12  is a graph indicating a correlation between a rate of occurrence of chucking failure and axial height (hereafter, referred to as L 1  shown in  FIG. 9 ) of the tip portion  221   b  measured from the disk setting surface  101   b  when, for example, a Dual Disc which includes a CD and a DVD pasted to one another via adhesive is placed on the disk setting surface  101   b  with the CD side of the dual disc on the bottom. Note that the adhesive is not applied to an entire surface connecting the CD and the DVD. Also note that the vertical axis (Y) of the graph indicates the frequency (%) of the occurrence of the malfunction of the chucking mechanism  200  and the horizontal axis (X) indicates the value (mm) of L 1 . 
     According to  FIG. 12 , the greater the value of L 1  is, the smaller the frequency of the occurrence of the malfunction of the chucking mechanism  200  becomes. When such relationship is numerically denoted, it is approximately: Y=−614.64X+667.63. That is, when Y is 0, no malfunction of the chucking mechanism occurs (i.e., when X equals approximately 1.08). Therefore, the value of L 1  at which Y becomes 0 is the preferable value for L 1 . It is to be appreciated that the value X may change in accordance with the amount of adhesive used in the Dual Disc. 
     Hereafter, an axially downward movement of the claw member  4  when setting a disk  6  on a conventional chucking mechanism  1  will be described with reference to  FIGS. 15 and 16 .  FIG. 15  is a cross sectional view of the conventional chucking mechanism  1  when the claw member  4  makes contact with a central opening portion  6   a  of the disk  6 .  FIG. 16  is a cross sectional view of the conventional chucking mechanism  1  in which the tip portion  4   b  thereof is at an axially lowest position. Note that the disk  6  is a multi-layered disk including an upper disk base  6   b  and a lower disk base  6   c  pasted to one another. 
     According to  FIG. 15 , the tip portion  4   b  of the claw member  4  moves axially downwardly when the claw member  4  makes, at a top surface thereof, contact with a bottom end of the central opening portion  6   a , then the claw member  4  moves radially inwardly. 
     However, according to the conventional chucking mechanism  1 , the axial position of the claw member  4  is lowered when the disk  6  makes contact therewith and the claw member  4  is at a radially innermost position inside a center case  3  (see  FIGS. 15 and 16 ). That is, the tip portion  4   b  is also moved axially downward causing the tip portion  4   b  to be substantially at a line bordering between two disk bases  6   b  and  6   c . By this, the chucking failure in which the tip portion  4   b  gets struck between the two disk bases  6   b  and  6   c  may occur. 
     Also, since the disk retaining surface  4   a  includes an upward guiding surface  3   d  is arranged at a portion corresponding to a lower side surface thereof, the claw member  4  needs to be arranged axially above the upward guiding surface  3   d . Therefore, such configuration made it difficult to design a thin chucking mechanism  1 . Also, the radially inward movement and the axially downward movement of the tip portion  4   b  are conducted via the sliding movement of the lower side surface of the disk retaining surface  4   a  and the upward guiding surface  3   d , and therefore, the claw member  4  was extended in the axial direction. By such configuration, it became difficult to design the claw member having a preferable axial thickness while achieving a preferable movement of the claw member  4  in the axially downward direction and in the radially inward direction. 
     On the other hand, the chucking mechanism  200  according to the present invention, since the movement pivot receiving portion  217  is a plane surface which is substantially perpendicular to the central axis J 1 , the tip portion  221   b  of the claw member  220  moves in the axially downward direction and in the radially inward direction preventing the entire portion of the claw member  220  from moving in the axially downward direction. Therefore, the chucking mechanism  200  according to the present invention minimizes the occurrence of the chucking failure. 
     Also, the movement of the tip portion  221   b  is determined by the movement pivot receiving portion  217  and the movement support receiving portion  218 . Here, since the movement pivot receiving portion  217  is a plane surface perpendicular to the central axis J 1 , the axial position of the tip portion  221   b  with respect to the disk setting surface  101   b  will be determined with facility. By virtue of such configuration, a configuration of the movement support receiving portion  218  will be simplified, and the chucking failure will be substantially prevented. Also, since the movement pivot receiving portion  222   a  is arranged on the side of the claw portion  221 , and the movement assist portion  222   b  is arranged radially inwardly of the claw portion  221 , the movement pivot receiving portion  222   a  and the movement assist portion  222   b  are designed with greater degree of freedom. Also, since the movement pivot receiving portion  217  and the movement support receiving portion  218  are designed with greater degree of freedom, the claw member  220  can be designed to have a preferable thickness while achieving a preferable movement of the tip portion  221   b  of the claw member  4  in the axially downward direction and in the radially inward direction. 
     Disk Driving Apparatus 
     Hereinafter, a disk driving apparatus according to a preferred embodiment of the present invention will be described with reference to  FIG. 13 .  FIG. 13  is a cross sectional view seen in the axial direction of the disk driving apparatus according to the present preferred embodiment of the present invention. 
     According to  FIG. 13 , a disk driving apparatus  300  preferably includes a brushless motor  320  which fits an opening  311  arranged at a center of a disk shaped disk  310  and rotates the disk  310  in a concentric manner, an optical unit  330  which emits an optical light at the disk  310  in order to store data on the disk  310  and to reproduce data from the disk  310 , a gear mechanism  340  which moves the optical unit  330  in the radial direction with respect to the  310 , and a housing  350  for accommodating therein the brushless motor  320 , the optical unit  330  and the gear mechanism  340 . 
     The gear mechanism  340  includes a motor  341 , and a torque receiving gear  342  which receives a rotary torque generated by the motor  341 . 
     The housing  350  preferably includes a bordering plate  351  preferably made of a thin plate so as to divide the disk  310  and the gear mechanism  340 . Also the housing  350  preferably includes an opening  352  through which the disk  310  will be inserted and rejected. 
     The optical unit  330  preferably includes a storing/reproducing portion  331  which emits an optical light, and a moving portion  332  which is arranged vertically with respect to the moves the storing/reproducing portion  331 . The moving portion  332  preferably includes an engaging portion  332   a  which engages with the torque receiving gear  342 . The storing/reproducing portion  331  is engages with the moving portion  332  and is thereby allowed to move in the radial direction. 
     The torque receiving gear  342  rotates due to the engagement with a gear portion  341   a  which is attached to the motor  341 . The moving portion  332  moves in the radial direction due to the engagement of the torque receiving gear  342  with the engaging portion  332   a . Then, due to the moves of the moving portion  332 , the storing/reproducing portion  331  moves in the radial direction. 
     Since the disk driving apparatus  300  includes the brushless motor  320  according to the present invention, the disk driving apparatus  300  is allowed to be thin while the disk  310  is set thereon smoothly, and retained thereby securely. 
     While the present invention has been described in detail, the foregoing description is in all aspects illustrative and not restrictive. It is understood that numerous other modifications and variations can be devised without departing from the scope of the invention. 
     For example, although the present preferred embodiment assumes that the movement support receiving portion  218  includes the upper movement support surface  218   a  and the lower movement support surface  218   b , the present invention is not limited thereto; the movement support receiving portion  218  may only include the upper movement support surface  218   a . When the movement support receiving portion  218  only includes the upper movement support surface  218   a , the upper movement support surface  218   a  is preferably configured such as to allow the movement assist portion  222   b  to make a stable contact therewith. 
     For example, although the present preferred embodiment assumes that the disk D is a multi-layered disk, the present invention is compatible with a single layered disk. 
     For example, although the present preferred embodiment assumes that the protrusion  221   d  of the claw member  220  includes the protrusion inclined surface  221   d   1  in order to minimize the deformation occurring to the elastic member  230 , the present invention is not limited thereto; a step portion  221   d   3  may be arranged at a radially inner surface of the protrusion  221   d , via a radial gap therebetween, which may be included at the surface of the elastic member  230  making contact with the elastic member  230  in order to minimize the deformation of the elastic member  230  in the axial direction. As shown in  FIG. 17 , due to the gap between the elastic member  230  and the step portion  221   d   3 , even when the claw member  220  moves in the axially downward direction, the deformation in the axially upward direction occurring to the elastic member  230  due to the protrusion  221   d  will be minimized. 
     For example, the elastic member  230  of the present invention may make contact with the base portion  214  of the center case  210 , or the elastic member  230  may make contact with the base portion  214  and also with the leveled portion  101   a.    
     For example, although the present preferred embodiment of the present invention assumes that the opening  216  includes the widened portion  216   b   1 , the present invention is not limited thereto. A through hole may be arranged penetrating between the top surface and the bottom surface of the top plate portion  215  which is circumferentially apart from the opening  216 . In such case, the movement pivot receiving portion  217  is arranged at a position corresponding to the through hole. A circumferential width of the through hole is equal to or greater than that of the movement pivot receiving portion  217 .