Patent Publication Number: US-7900223-B2

Title: Motor with a chucking device for detachably holding a disk and disk drive apparatus equipped with the same

Description:
FIELD OF THE INVENTION 
     The present invention relates to a motor provided with a chucking device for removably holding a disk and a disk drive apparatus equipped with the motor; and, more particularly, to a technique of increasing a disk holding force of a chucking device and reducing a disk mounting force. 
     BACKGROUND OF THE INVENTION 
     A chucking device has heretofore been developed as a device for removably holding an optical disk such as a compact disk or the like (hereinafter simply referred to as a “disk”). In general, the chucking device is attached to a top portion of a motor and is rotated together with the motor to thereby rotate the disk. 
     In keeping with a recent demand for a low-profile disk drive apparatus, it becomes essential to reduce the thickness of a motor provided with a chucking device. In this type of motor, the thickness of the chucking device accounts for a large percentage of the overall thickness of the motor. Therefore, reduction in thickness of the chucking device is very effective in providing a low-profile disk drive apparatus. 
     A conventional chucking device that realizes thickness reduction is disclosed in Japanese Patent Laid-open Publication No. 2005-251298 (JP2005-251298A). The chucking device includes claw members for holding a disk. Each of the claw members has a disk holding surface that makes contact with the disk and a pair of downwardly extending guide surfaces formed on the opposite circumferential sides of the disk holding surface for guiding radial inward movement of each of the claw members. 
     Along with the increase in a quantity of information stored in a disk, it is a recent trend that a laminated disk, such as a DVD or the like, formed by bonding two disks together is frequently used in recent years. Since the laminated disk has an increased thickness, a low-profile chucking device is incapable of exerting a disk holding force (hereinafter referred to as a “holding force”) great enough to hold the laminated disk. Particularly, in case of the claw members disclosed in JP2005-251298A, it is difficult to increase a circumferential width of the disk holding surface because the downwardly extending guide surfaces are formed on the opposite sides of the disk holding surface. This means that the chucking device disclosed in JP2005-251298A is unable to exert a holding force great enough to hold a disk having an increased thickness. 
     It would be thinkable that the spring force of a coil spring is increased to obtain the holding force as required. If the spring force is increased, however, it becomes hard for the claw members to move in a radial inward direction when the disk is mounted to the chucking device. This poses a problem in that the disk mounting force is increased. 
     In keeping with the thickness reduction of a disk drive apparatus, the moving distance of a disk required in traversing a motor becomes small. This reduces the force by which the disk is mounted to a chucking device. Therefore, it is necessary for the chucking device to have a structure that allows the disk to be mounted with ease. 
     SUMMARY OF THE INVENTION 
     The present invention provides a motor provided with a chucking device that makes it possible to mount a disk with ease and can exert a holding force great enough to hold a disk with an increased thickness such as a laminated disk or the like, and a disk drive apparatus equipped with the motor. 
     In accordance with an aspect of the present invention, there is provided a motor including: a chucking device for detachably holding a disk having a central opening portion; a rotating body rotatable about a specified center axis, the rotating body including a rotor magnet and a rotor holder, the rotor holder having a cylindrical portion for holding the rotor magnet in place, a cover portion extending from the cylindrical portion to the center axis and a disk support portion formed on an upper surface of the cover portion for making contact with a lower surface of the disk; and a fixed body including a bearing member for rotatably supporting the rotating body and a stator arranged to face the rotor magnet, wherein the chucking device includes: a center case to which the central opening portion of the disk is inserted, the center case having a cylindrical portion coaxial with the center axis and a cover portion for covering an axial upper side of the cylindrical portion of the center case, at least a part of the cylindrical portion of the center case arranged axially above the rotating body; resilient members received within the center case; and claw members for holding the disk in place, the claw members remaining in contact with radial outer ends of the respective resilient member, wherein each of the claw members has a tip end portion, a disk holding surface positioned axially below the tip end portion for holding the disk in place, and a recessed sliding portion formed substantially at a circumferential center region of the disk holding surface, the sliding portion serving to guide movement of the claw member, wherein rest portions are formed in the center case in a facing relationship with the respective sliding portions, the rest portions serving to support the respective sliding portions by contacting therewith, and wherein the sliding portions are designed to make contact with the respective rest portions when the disk is mounted to the chucking device. 
     With such configuration, it is possible to reduce the axial height of the claw member by forming the sliding portion into a recess shape substantially at the circumferential center region of the disk holding surface. This makes it possible to reduce the axial height of the chucking device, thereby providing a low-profile motor. 
     Since there is no need to form sliding portions on the opposite sides of the disk holding surface, it is possible to reduce the circumferential width of the claw member, consequently providing a small-sized chucking device. If the circumferential width of the claw member is the same as that of a claw member having sliding portions on the opposite sides of the disk holding surface, it is possible to further increase the circumferential width of the disk holding surface, thereby further enhancing the disk holding force. 
     Furthermore, it is possible to allow the rest portion and the sliding portion to make contact with each other in an axially higher position by forming the sliding portion into a recess substantially at the circumferential center region of the disk holding surface. This makes it possible to prevent the claw member from moving axially downwardly to an excessive extent when mounting the disk to the chucking device. In other words, it is possible to keep the tip end portion of the claw member in an axially higher position. As a result, when a laminated disk such as a DVD or the like produced by bonding two disk substrates together is mounted to the chucking device, it is possible to avoid so-called half-chucking, which refers to a phenomenon that the tip end portion of the claw member is positioned in alignment with a bonding layer of the disk substrates, i.e., between the disk substrates. By allowing the rest portion and the sliding portion to make contact with each other in an axially higher position, it is possible to shorten the distance between the contact position and the tip end portion of the claw member. This makes it possible to have the tip end portion of the claw member move to a greater extent in an axial downward direction during the process of mounting the disk. This allows the claw member to be inclined axially downwardly to a greater extent, thereby making it possible to reduce the force required in mounting the disk. 
     The disk holding surface may continuously extend along a circumferential center region of the claw member radially lying between the tip end portion and the sliding portion of the claw member. 
     With such configurations, it is possible to hold a disk having an increased thickness with a greater holding force by making the disk holding surface continuously extend in a circumferential direction in its region near the tip end of the recess portion. In case of a disk with a reduced thickness, it is possible to hold the disk by a lower region of the disk holding surface. This allows the tip end portion of the claw member to be positioned more distantly from the inner edge of the central opening portion of the disk in a radial outward direction. In case of a disk with an increased thickness, however, the disk is held by an upper region of the disk holding surface. Therefore, as the thickness of the disk gets greater, it becomes difficult to position the tip end portion of the claw member distantly from the inner edge of the central opening portion of the disk in a radial outward direction. This reduces the disk holding force. In this regard, by forming the region of the disk holding surface near the tip end of the recess portion to continuously extend in a circumferential direction, it is possible to increase the circumferential area of the disk holding surface over which the disk with an increased thickness makes contact therewith. This increases the force acting against removal of the disk, consequently making it possible to keep the disk holding force high. 
     Each of the sliding portion and the rest portion may be formed of a planar contact surface having no gradient in a circumferential direction. 
     With such configurations, it is possible to prevent the disk from being held in a state that the claw member is tilted in a circumferential direction. This makes it possible to provide a chucking device and a motor that can prevent shaking of the claw member when mounting the disk to the chucking device. 
     Preferably, the planar contact surface of the sliding portion that makes contact with the rest portion preferably has a circumferential width greater than that of the planar contact surface of the rest portion that makes contact with the sliding portion. 
     With such configurations, it is possible to prevent the rest portion and the disk holding surface from making contact with each other. 
     Preferably, the disk holding surface and the center axis make an acute angle smaller than an acute angle made by the sliding portion and the center axis. 
     With such configurations, it is possible for the claw member to be stably moved along the sliding portion. Therefore, even when the disk is repeatedly mounted to the chucking device, the chucking device is capable of holding the disk in a stable state. This makes it possible to provide a motor provided with a highly reliable chucking device. 
     The claw member is formed by injection molding, a slanting portion continuously extending from the disk holding surface in such a fashion as not to make contact with the disk is formed axially below the disk holding surface, and the slanting portion and the center axis make an acute angle substantially equal to the acute angle made by the sliding portion and the center axis. 
     With such configurations, since the slanting portion and the center axis make an acute angle substantially equal to an acute angle made by the sliding portion and the center axis, it is possible to easily release a mold in an injection molding process. Furthermore, it is possible to reduce mold production costs by simplifying the shape of the mold. 
     The disk holding surface may have a pair of regions lying circumferentially outwardly of the sliding portion and having a circumferential width getting greater toward the tip end portion. 
     With such configurations, it is possible to increase the pressing force applied to the disk by increasing the circumferential width of the disk holding surface. This makes it possible to prevent circumferential deflection of the disk relative to the disk support surface which would otherwise occur when the disk is rotated at a varying speed. 
     The tip end portion may be formed of a curved surface, the curved surface formed into an arcuate shape with a radius of about 0.25 mm to about 0.30 mm. 
     With such configurations, it is possible to avoid so-called half-chucking by which the tip end portion of the claw member is positioned between the disk substrates. By setting the size of the tip end portion within the above-noted range, it is possible to secure the size of the disk holding surface even when the axial size of the claw member is made small. Consequently, it is possible to provide a motor capable of securing the disk pressing force and avoiding the half-chucking. 
     In accordance with another aspect of the present invention, there is provided a disk drive apparatus equipped with the aforementioned motor, including: an optical pickup mechanism for optically recording and reproducing information on and from the disk; a moving mechanism for moving the optical pickup mechanism in a radial direction of the disk; and a chassis to which the motor is attached, the chassis having an opening, the optical pickup mechanism arranged inside the opening. 
     With such configurations, it is possible to provide a highly reliable low-profile disk drive apparatus. 
     In accordance with the present invention, it is possible to provide a motor provided with a chucking device that makes it possible to mount a disk with ease and can exert a holding force great enough to hold a disk with an increased thickness such as a laminated disk or the like, and a disk drive apparatus equipped with the motor. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The objects and features of the present invention will become apparent from the following description of embodiments given in conjunction with the accompanying drawings, in which: 
         FIG. 1  is an axially-cut schematic section view showing a motor in accordance with one embodiment of the present invention; 
         FIG. 2  is an enlarged view illustrating a chucking device of the motor shown in  FIG. 1  and its vicinities; 
         FIG. 3  is a top plan view showing the chucking device of the present invention; 
         FIG. 4  is an axially-cut schematic section view showing a center case employed in the chucking device of the present invention; 
         FIG. 5  is a top plan view of the center case employed in the chucking device of the present invention; 
         FIG. 6  is a bottom plan view of the center case employed in the chucking device of the present invention; 
         FIG. 7  is an enlarged view illustrating a rest portion of the center case shown in  FIG. 4  and its vicinities; 
         FIG. 8  is a radial view illustrating the rest portion of the center case employed in the chucking device of the present invention and its vicinities; 
         FIG. 9  is a perspective view showing a claw member employed in the chucking device of the present invention; 
         FIG. 10  is a front view of the claw member employed in the chucking device of the present invention; 
         FIG. 11  is a top plan view of the claw member employed in the chucking device of the present invention; 
         FIG. 12  is a bottom plan view of the claw member employed in the chucking device of the present invention; 
         FIG. 13  is a rear view of the claw member employed in the chucking device of the present invention; 
         FIG. 14  is an axially-cut schematic section view of the claw member employed in the chucking device of the present invention; 
         FIG. 15  is an axially-cut schematic half-section view illustrating the chucking device of the present invention kept in a standby state; 
         FIG. 16  is an axially-cut schematic half-section view illustrating a state that a disk is being mounted to the chucking device of the present invention; 
         FIG. 17  is another axially-cut schematic half-section view illustrating a state that the disk is being mounted to the chucking device of the present invention; 
         FIG. 18  is an axially-cut schematic half-section view illustrating a state that the disk is completely mounted to the chucking device of the present invention; 
         FIG. 19  is an axially-cut schematic half-section view illustrating a state that a disk with a reduced thickness is completely mounted to the chucking device of the present invention; and 
         FIG. 20  is an axially-cut schematic half-section view showing a disk drive apparatus in accordance with the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     &lt;Overall Structure of a Motor&gt; 
     One embodiment of a motor in accordance with an embodiment of the present invention will now be described with reference to  FIG. 1 , which shows an axially-cut schematic section view of a motor. 
     Referring to  FIG. 1 , a motor  10  of the present embodiment includes a rotating body  20  designed to rotate about a specified center axis J 1 , a fixed body  30  for rotatably supporting the rotating body  20  and a chucking device  40  arranged on an axial top side of the rotating body  20  for removably holding a disk (not shown). 
     First, description will be made regarding the rotating body  20 . 
     The rotating body  20  includes a generally columnar shaft  21  arranged in a coaxial relationship with the center axis J 1 , a rotor holder  22  fixed to an upper portion of the shaft  21  and an annular rotor magnet  23  fixedly secured to the rotor holder  22 . 
     The rotor holder  22  is produced by press-forming a thin magnetic metal plate. The rotor holder  22  includes a cylindrical shaft-fixed portion  221  having an inner circumferential surface fixed to an outer circumferential surface of the shaft  21 , a cover portion  222  extending radially outwardly from the shaft-fixed portion  221  and a cylindrical portion  223  extending axially downwardly from an outer circumferential edge of the cover portion  222 . The rotor magnet  23  is bonded to an inner circumferential surface of the cylindrical portion  223  by means of an adhesive agent. 
     An axially upwardly recessed central protrusion portion  2221  is formed in a center region of the cover portion  222  in a generally coaxial relationship with the center axis J 1 . A removal-proof member  24  having a plurality of radially inwardly extending lugs  241  (three lugs in the present embodiment) is fixed to the underside of the cover portion  222  that extends radially outwardly from the lower end of the central protrusion portion  2221 . 
     Next, description will be made regarding the fixed body  30 . 
     The fixed body  30  includes a sleeve  31  for rotatably supporting the shaft  21  radially, a bearing bush  32  with a bore for holding the sleeve  31  in place, a cover plate  33  for covering an axial lower end of the bore of the bearing bush  32 , a thrust plate  34  arranged on a top surface of the cover plate  33  for rotatably supporting the shaft  21  in an axial direction by making contact with a lower end surface of the shaft  21 , a stator  35  fixed to the outside of the bearing bush  32 , a circuit board  36  arranged below the stator  35  and an attachment plate  37  fixed to the bearing bush  32 , the attachment plate  37  having an upper surface kept in contact with a lower surface of the circuit board  36 . 
     The sleeve  31  is made of an oil-containing sintered metal and is formed into a generally cylindrical shape so that it can have an inner circumferential surface which serves as a shaft rest surface for supporting an outer circumferential surface of the shaft  21 . The sleeve  31  has an outer circumferential surface fixed to an inner circumferential surface of the bearing bush  32 . 
     The bearing bush  32  has a cylindrical portion  321  for holding the sleeve  31  in place and a stator-fixing portion  322  extending radially outwardly from the cylindrical portion  321  to hold the stator  35  in place. On a lower surface of the bearing bush  32 , there are formed an inner protrusion portion  323  for fixing the cover plate  33  by caulking and an outer protrusion portion  324  arranged radially outwardly of the inner protrusion portion  323  for fixing the attachment plate  37  by caulking. A radially outwardly extending hook portion  3211  is formed in a top end of the cylindrical portion  321 . In this regard, the lugs  241  of the removal-proof member  24  are positioned on an axial lower side of the hook portion  3211 . Each of the lugs  241  has an inner circumferential edge positioned radially inwardly of an outer circumferential edge of the hook portion  3211 . This ensures that, even when the rotating body  20  is urged to move axially upwardly, an upper surface of each of the lugs  241  makes contact with a lower surface of the hook portion  3211  to thereby restrict axial upward movement of the rotating body  20 . 
     An annular attracting magnet  25  for axially downwardly attracting the rotor holder  22  is arranged on an upper surface of the bearing bush  32  that remains in an axially facing relationship with the removal-proof member  24 . 
     The stator  35  is fixed to the stator-fixing portion  322  of the bearing bush  32  by means of an adhesive agent. The stator  35  includes a stator core  351  formed of a plurality of axially layered thin magnetic steel plates and a coil  352  formed of a conductive wire wound around the stator core  351 . The stator core  351  is constructed from an annular core-back portion  3511  and a plurality of tooth portions  3512  radially outwardly extending from the core-back portion  3511 . The coil  352  is formed by winding the conductive wire around the tooth portions  3512  in plural turns. 
     If an electric current is supplied to the coil  352  from an external power source (not shown), rotating magnetic fields are formed between the coil  352  and the rotor magnet  23 . Thus, the rotating body  20  is rotated in a specified circumferential direction by a rotational torque that acts about the center axis J 1 . 
     &lt;Structure of the Chucking Device&gt; 
     Next, the chucking device  40  of the present invention will be described with reference to  FIGS. 2 to 14 .  FIG. 2  is an enlarged view illustrating the chucking device and its vicinities.  FIG. 3  is a top plan view of the chucking device  40 . 
       FIGS. 4 to 8  show a center case  41  employed in the chucking device  40 . Specifically,  FIG. 4  is an axially-cut schematic section view of the center case  41 ,  FIG. 5  being a top plan view of the center case  41  and  FIG. 6  being a bottom plan view of the center case  41 .  FIGS. 7 and 8  are enlarged views showing the rest portion  4141  of the chucking device  40  and its vicinities. Specifically,  FIG. 7  is an enlarged view illustrating the rest portion  4141  and its vicinities.  FIG. 8  is a front view of the rest portion  4141 . 
       FIGS. 9 to 14  show a claw member  42  of the chucking device  40 . Specifically,  FIG. 9  is a perspective view of the claw member  42 ,  FIG. 10  being a front view of the claw member  42 ,  FIG. 11  being a top plan view of the claw member  42 ,  FIG. 12  being a bottom plan view of the claw member  42 ,  FIG. 13  being a rear view of the claw member  42 , and  FIG. 14  being an axially-cut schematic section view of the claw member  42 . 
     Referring to  FIGS. 2 and 3 , the chucking device  40  includes a generally disk-like center case  41  arranged in a coaxial relationship with the center axis J 1 , radially movable claw members  42  (three claw members in the present embodiment) protruding from the center case  41 , resilient members  43  (coil springs in the present embodiment) received within the center case  41  for radially outwardly biasing the respective claw members  42 , and a disk support portion  44  arranged radially outwardly of the center case  41  and adapted to make contact with a lower surface of a disk (not shown). 
     Referring to  FIG. 2 , the central protrusion portion  2221  of the rotor holder  22  includes an inner cylindrical portion  2221   a  and an inner cover portion  2221   b  for interconnecting the inner cylindrical portion  2221   a  and the shaft-fixed portion  221 . The inner cover portion  2221   b  is joined to the shaft-fixed portion  221  at its inner circumferential edge. 
     The center case  41  includes a below-mentioned base portion  411  whose inner circumferential surface is brought into contact with and fixedly secured to the outer circumferential surface of the shaft-fixed portion  221 . The base portion  411  has a lower surface that does not make contact with an upper surface of the inner cover portion  2221   b . In other words, a minute axial gap is left between the lower surface of the base portion  411  and the upper surface of the inner cover portion  2221   b . The center case  41  includes a below-mentioned cylindrical portion  414  whose lower surface does not make contact with an upper surface of the cover portion  222 . In other words, a minute axial gap is left between the lower surface of the cylindrical portion  414  and the upper surface of the cover portion  222 . These structures make it possible to highly accurately attach the center case  41  to the rotor holder  22  without affecting the parallelism of the lower surface of the base portion  411  and the parallelism of the lower surface of the cylindrical portion  414 . Therefore, it becomes possible to accurately set the axial and radial positions of rest portions  4141  formed in the center case  41 , which prevent deviation in the movement of the respective claw members  42 . 
     Referring to  FIGS. 4 to 9 , the center case  41  is integrally formed by injection-molding a resin material such as polycarbonate or the like. The center case  41  includes a base portion  411  having an inner circumferential surface that makes contact with the outer circumferential surface of the shaft-fixed portion  221 , a cover portion  412  formed on an axial upper side of the base portion  411  in such a fashion as to extend radially outwardly from the outer circumferential surface of the base portion  411 , an axially downwardly inclined guide portion  413  extending radially outwardly from an outer circumferential edge of the cover portion  412 , a cylindrical portion  414  extending axially downwardly from an outer circumferential edge of the guide portion  413  and an aligning claw  415  (three aligning claws in the present embodiment) circumferentially spaced apart 180 degrees from the claw member  42 . 
     The lower surface of the base portion  411  is formed axially above the lower surface of the cylindrical portion  414 , and axially below the upper end of the cylindrical portion  414 . A plurality of contact portions  4111  is formed on the outer circumferential surface of the base portion  411  at an interval of about 120 degrees in a circumferential direction. Each of the contact portions  4111  makes contact with a radial inner end of the resilient member  43 . Each of the contact portions  4111  has a lower surface extending axially downwardly, which is located below the lower surface of the base portion  411  and above the lower surface of the cylindrical portion  414 . This allows the radial inner end of the resilient member  43  to make contact with only a below-mentioned contact surface  4111   a , which means that the positioning accuracy of the radial inner end of the resilient member  43  depends on the surface accuracy of the contact surface  4111   a  alone. Therefore, it is possible to increase the positioning accuracy of the radial inner end of the resilient member  43 . Moreover, by forming the lower surface of each of the contact portions  4111  axially above the lower surface of the cylindrical portion  414 , it is possible to prevent the lower surface of each of the contact portions  4111  from making contact with the upper surface of the cover portion  222  of the rotor holder  22 . Consequently, it is possible to accurately arrange the center case  41  relative to the rotor holder  22 . 
     The contact surface  4111   a  is formed on an outer surface of each of the contact portions  4111  in a generally perpendicular relationship with the extension direction of the resilient member  43 . A radially outwardly extending protrusion portion  4111   b  having a generally columnar shape is formed at the center of the contact surface  4111   a . The radial inner surface of each of the contact portions  4111  is extended circumferentially along the outer circumferential surface of the inner cylindrical portion  2221   a  of the central protrusion portion  2221  of the rotor holder  22  in order to avoid contact between the radial inner surface of each of the contact portions  4111  and the outer circumferential surface of the inner cylindrical portion  2221   a . The radial inner surface of each of the contact portions  4111  is formed of a slanting portion  4111   c  inclined radially inwardly and axially upwardly (toward the cover portion  412 ). The slanting portion  4111   c  serves to increase the thickness of each of the contact portions  4111 , thereby improving the strength of the contact portions  4111 . This makes it possible to have the radial position of the contact surface  4111   a  come closer to the outer circumferential surface of the inner cylindrical portion  2221   a  of the central protrusion portion  2221  of the rotor holder  22 . Therefore, it is possible to increase the radial distance between the contact surface  4111   a  and the cylindrical portion  414  of the center case  41 . As a result, it becomes possible to increase the space in which the claw member  42  and the resilient member  43  are installed. This makes it possible to improve the design flexibility in respect of the radial inward movement of the claw member  42 . It is also possible to improve the design flexibility in respect of the radial inward movement of the resilient member  43 . 
     Connection portions  416  extend radially outwardly from the outer surface of the base portion  411 . The connection portions  416  are joined to the inner circumferential surface of the cylindrical portion  414  (or the guide portion  413 ) and also to the lower surface of the cover portion  412 . The connection portions  416  are formed on the opposite circumferential sides of each of the contact portions  4111  in a mutually parallel relationship. Each of the connection portions  416  has a lower surface positioned axially above the lower surface of the cylindrical portion  414 . 
     A pair of circumferential gaps exists between the individual contact portion  4111  and the connection portions  416 . The gaps are formed to extend radially inwardly from the contact surface  4111   a . In other words, a pair of radially inwardly recessed groove portions  4161  (contact-proof portions) is formed. 
     The cover portion  412  has openings  4121  formed in such positions as to retractably receive the respective claw members  42  and openings  4122  formed in alignment with the respective aligning claws  415 . 
     The openings  4121  are formed in the guide portion  413  to extend to an axial upper portion of the cylindrical portion  414 . The opening  4121  is provided with a wide opening portion  4121   a  having an increased circumferential width, the wide opening portion  4121   a  being formed between an upper end of the guide portion  413  and an axially lower side thereof, and a slant portion  4121   b  having an axially upwardly decreasing circumferential width, the slant portion  4121   b  being formed in the guide portion  413  to extend axially upwardly from the wide opening portion  4121   a . The slant portion  4121   b  helps avoid generation of burrs which would otherwise be generated when a mold is released during an injection molding process. In case of a low-profile disk drive apparatus, an axial gap having a size of no greater than about 0.1 mm exists between the upper surface of the cover portion  412  of the chucking device  40  and the lower surface of a moving disk. Therefore, if axially upwardly protruding burrs are generated, damage may possibly be caused to the lower surface of the disk. This leaves a possibility that errors may occur in the course of recording and reproducing the disk. In accordance with the present embodiment, generation of axially upwardly protruding burrs is prevented by forming the slant portion  4121   b , so that it becomes possible to avoid damage of the lower surface of the disk. As a result, it is possible to provide a motor provided with a highly reliable chucking device that helps keep a disk free from damage when the disk is moved to the chucking device. 
     The opening  4122  is formed on the opposite circumferential sides of the aligning claw  415 . The opening  4122  is opened in both the guide portion  413  and the cylindrical portion  414  with the same width. 
     The cover portion  412  has three gate portions  4123  formed in the positions in which a resin material is injected during an injection molding process. Each of the gate portions  4123  is formed into a cylindrical groove shape. A cylindrical protrusion  4123   a  is arranged in each of the gate portions  4123 . The protrusion  4123   a  is formed to extend axially upwardly below the upper surface of the cover portion  412 . Each of the gate portions  4123  is formed radially outwardly of the inner cylindrical portion  2221   a  of the central protrusion portion  2221  of the rotor holder  22 . Each of the gate portions  4123  has a lower surface is formed axially downwardly below the lower surface of the base portion  411 . This helps improve the flexibility in designing the depth of each of the cylindrically recessed gate portions  4123 . Therefore, it is possible to easily design a mold by which the protrusion  4123   a  can be formed not to protrude axially upwardly beyond the upper surface of the cover portion  412 . In this connection, a part of the upper surface of each gate portion  4123  may be overlapped with the base portion  411  in a radial direction. 
     An aperture  4124  for exposing the protrusion  4111   b  of the contact surface  4111   a  to the outside is formed in the cover portion  412  in alignment with the protrusion  4111   b.  This makes it possible to release a mold in an axial direction, thereby allowing the protrusion  4111   b  to be formed with ease. 
     The aligning claw  415  includes a first arm portion  4151  extending radially outwardly from the opening  4122  of the cover portion  412 , a second arm portion  4152  extending in conformity with the inclination of the guide portion  413  and a third arm portion  4153  arranged radially outwardly of the cylindrical portion  414  to make contact with a central opening portion (not shown) of a disk. By making contact with the central opening portion of the disk, the third arm portion  4153  serves to bring the center of the central opening portion of the disk into alignment with the center of the chucking device  40 . 
     The rest portions  4141  for guiding movement of the respective claw members  42  are formed in the cylindrical portion  414  in alignment with the respective openings  4121 . On an inner circumference side of the rest portion  4141 , there is formed a slanting surface  4141   a  inclined radially inwardly and axially downwardly. The slanting surface  4141   a  is a planar surface having no gradient in a circumferential direction. A curved surface portion  4141   b  is formed so that it can be joined to an outer edge of the slanting surface  4141   a  (namely, an upper end of the slanting surface  4141   a ). The curved surface portion  4141   b  includes an apex portion of the rest portion  4141 . The curved surface portion  4141   b  is joined to the outer circumference of the rest portion  4141 , i.e., the outer circumferential surface of the cylindrical portion  414 . The slanting surface  4141   a  and the curved surface portion  4141   b  are mirror-machined. The surface roughness of the slanting surface  4141   a  and the curved surface portion  4141   b  is about 0.8 μm in terms of Ry. This makes it possible to smoothly guide radial inward movement of the claw member  42 . Therefore, it is possible to reduce the force required in mounting a disk (the disk mounting force). 
     A straight portion  4141   c  is formed in the circumferential center of the rest portion  4141 . Circumferential curved portions  4141   d  that extend away from the straight portion  4141   c  are formed on the opposite circumferential sides of the straight portion  4141   c.    
     Connecting portions  4142  are formed to extend from the rest portion  4141  in a circumferential direction. The connecting portions  4142  are joined to the cylindrical portion  414 . Each of the connecting portions  4142  has an upper slanting surface inclined radially inwardly and axially downwardly (as indicated by a broken line in  FIGS. 7 and 8 ). The inclination angle of each of the connecting portions  4142  is preferably set as small as possible within an extent that it does not make contact with a below-mentioned claw-side slanting surface  4215  of the claw member  42  in a standby state. In this regard, the inclination angle refers to an acute angle that the slanting surface of each of the connecting portions  4142  makes relative to a plane perpendicular to the center axis J 1 . By reducing the inclination angle, it becomes possible to make high the axial position of an inner circumferential surface of each of the connecting portions  4142 . In other words, it becomes possible to increase the axial width of the inner circumferential surface of each of the connecting portions  4142 . As a consequence, it is possible to improve the strength of the connecting portions  4142 . This makes it possible to provide a motor provided with a highly reliably chucking device that can keep the rest portion  4141  and the connecting portions  4142  free from plastic deformation even when a claw-side stopper  4216  of the claw member  42  makes contact with a below-mentioned planar portion  4143   a  of the rest portion  4141  in a repeated manner. 
     On the inner circumferential surface of the cylindrical portion  414  corresponding to the circumferential position of each of the openings  4121 , there are formed a first recess portion  4143  that forms the inner circumferential surfaces of the rest portion  4141  and the connecting portions  4142  and second recess portions  4144  lying on the opposite circumferential sides of the first recess portion  4143 . 
     The planar portion  4143   a  perpendicular to a radial direction is formed in the circumferential center of the first recess portion  4143 . Curved surface portions  4143   b  having the same radius of curvature as that of the inner circumferential surface of the cylindrical portion  414  are formed on the opposite circumferential sides of the planar portion  4143   a  of the first recess portion  4143 . The below-mentioned claw-side stopper  4216  of the claw member  42  makes contact with the planar portion  4143   a . The planar portion  4143   a  has substantially the same circumferential width as that of the rest portion  4141 . 
     Furthermore, the first recess portion  4143  has substantially the same circumferential width as that of a below-mentioned claw portion  421  of the claw member  42 . This makes it possible to restrict circumferential movement of the claw member  42 . The radial moving distance of the claw member  42  can be increased by forming the first recess portion  4143  radially outwardly of the inner circumferential surface of the cylindrical portion  414 . Therefore, it is possible to improve the flexibility in designing the radial movement of the claw member  42 . 
     The second recess portions  4144  are formed radially inwardly of the first recess portion  4143  and also radially outwardly of the inner circumferential surface of the cylindrical portion  414 . Each of the second recess portions  4144  has substantially the same circumferential width as that of a lateral extension portion  4222  of a wing portion  422  of the claw member  42  which will be described below. This makes it possible to improve the flexibility in designing the radial movement of the claw member  42  so that the lateral extension portion  4222  can move radially outwardly of the inner circumferential surface of the cylindrical portion  414 . It is also possible to increase the radial thickness of the cylindrical portion  414 , thereby enhancing the strength of the cylindrical portion  414 . This is particularly desirable in a chucking device that needs to be fabricated into a low profile. 
     A reduced diameter portion  4145  whose outer diameter is reduced in a radial direction is formed in a lower portion of the outer circumferential surface of the cylindrical portion  414  including the bottom end thereof. The reduced diameter portion  4145  helps prevent generation of axially downwardly protruding burrs which would otherwise be generated when a mold is released in an axial direction during the process of injection-molding the center case  41 . Therefore, it is possible to reliably prevent the lower surface of the cylindrical portion  414  from making contact with the upper surface of the cover portion  222 . This makes it possible to accurately attach the center case  41  with respect to the rotor holder  22 . 
     Referring to  FIGS. 9 to 14 , the claw member  42  is integrally formed by injection-molding a resin material such as polyacetal or the like. The claw member  42  includes a claw portion  421  having a disk holding surface  4213  for holding a disk in place and a pair of wing portions  422  extending radially inwardly from the claw portion  421 . 
     The claw portion  421  includes a guide portion  4211  with which a disk makes contact for the first time among other portions of the claw member  42  when mounting the disk to the chucking device  40 , a tip end portion  4212  of curved surface shape bulged radially outwardly from an outer circumferential edge of the guide portion  4211 , the disk holding surface  4213  joined to the tip end portion  4212  and inclined radially inwardly and axially downwardly, a sliding portion  4214  formed into a recessed shape on a circumferential center region of the disk holding surface  4213  and claw-side slanting portions  4215  joined to the disk holding surface  4213  and formed below the disk holding surface  4213 . 
     The guide portion  4211  is formed into a planar surface substantially parallel to the upper surface of the cover portion  412  of the center case  41 . The guide portion  4211  has a circumferential width smaller than that of the disk holding surface  4213 . On the opposite circumferential sides of the guide portion  4211 , there is formed a pair of upper contact surfaces  4211   a  that makes contact with the lower surface of the cover portion  412  of the center case  41 . The guide portion  4211  protrudes axially upwardly from the upper contact surfaces  4211   a  (and therefore may be called an upper protrusion portion). The guide portion  4211  is arranged substantially in the same axial position as that of the upper surface of the cover portion  412  of the center case  41 . It may be possible to lower the axial height of the guide portion  4211  within the extent of thickness of the cover portion  412 . If the guide portion  4211  is arranged axially above the cover portion  412 , there is a possibility that the disk (not shown) may make contact with the guide portion  4211  when it is moved near the upper surface of the center case  41 . In the present embodiment, however, the guide portion  4211  is arranged substantially in the same axial position as that of the upper surface of the cover portion  412  or the axial height of the guide portion  4211  is lowered within the extent of thickness of the cover portion  412 . This makes it possible to provide a highly reliable motor that can keep the disk out of contact with the guide portion  4211  during its radial movement across the upper surface of the center case  41  and a disk drive apparatus incorporating the motor. It is particularly desirable to apply the motor to a low-profile disk drive apparatus. Each of the upper contact surfaces  4211   a  has substantially the same radial length as that of the guide portion  4211 . In an outer circumferential edge of each of the upper contact surfaces  4211   a , there is formed a tip end side portion  4212   a  which is a curved surface having a radius of curvature smaller than that of the tip end portion  4212 . The tip end side portion  4212   a  and the tip end portion  4212  are formed to have the same circumferential curvature when the claw member  42  is seen in a top plan view. 
     The tip end portion  4212  is formed to have substantially the same circumferential width as that of the guide portion  4211 . It is preferred that the tip end portion  4212  be formed into the shape of an arc having a radius of 0.25 mm to 0.30 mm when the claw member  42  is seen in an axially-cut section view. 
     The disk holding surface  4213  serves to hold a disk in place by pressing the upper edge of the center opening portion of the disk in a state that the disk is mounted on the disk support portion  44 . The disk holding surface  4213  has an upper portion formed over the entire circumference of the claw portion  421 . On the lower side of the upper portion, there is formed a recess portion  4213   a  of generally curved surface shape having a straight portion  4213   b  at its center region. The disk holding surface  4213  is formed in such a fashion that the recess portion  4213   a  is centrally positioned in a circumferential direction. Therefore, the disk holding surface  4213  has an inverted U-like shape when seen in a front view. The disk holding surface  4213  has a pair of side surface regions formed on opposite circumferential sides of the recess portion  4213   a . Each of the side surface regions is gradually widened as it comes closer to the tip end portion  4212 . Thus, the recess portion  4213   a  has a gradually reducing circumferential width, consequently increasing the area of the disk holding surface  4213 . This makes it possible to increase the area over which the disk holding surface  4213  makes contact with the center opening portion of the disk. Therefore, it is possible to prevent deformation of the disk by reducing the pressure applied to the center opening portion of the disk. As a result, it becomes possible to align the disk with increased accuracy. Furthermore, if the contact area between the disk holding surface  4213  and the center opening portion of the disk is increased as mentioned above, the resistant force against the upwardly moving force of the disk becomes greater. Owing to the fact that the disk holding surface  4213  of the claw member  42  exerts an increased resistant force against movement of the disk, it is possible to reliably hold the disk even when the disk is tilted by an external shock during its rotation. 
     The recess portion  4213   a  is formed of a first curved portion  4213   c  continuously extending as a curved surface in a circumferential direction from the disk holding surface  4213 , a slanting portion  4213   d  inclined toward the straight portion  4123   b  and a second curved portion  4213   e  continuously extending as a curved surface in a circumferential direction from the slanting portion  4213   d  and the straight portion  4213   b . In the straight portion  4213   b , there is formed a slanting surface inclined radially inwardly and axially downwardly with no gradient in a circumferential direction. The straight portion  4213   b  has a circumferential width greater than that of the straight portion  4141   c  of the rest portion  4141 . The second curved portion  4213   e  and the slanting portion  4123   d  of the recess portion  4213   a  are formed more gently than the curved surface portion  4141   d  of the rest portion  4141 . This makes it possible to prevent the straight portion  4141   c  or other portions of the rest portion  4141  from making contact with the straight portion  4213   b  or other portions of the recess portion  4213   a  of the claw member  42 . If other portions make contact with one other during radial inward movement of the claw member  42 , such contact would hinder the movement of the claw member  42 , thereby increasing the disk mounting force. In the present embodiment, however, it is possible to make the claw member  42  smoothly move in a radial inward direction by preventing any portions of the claw member  42  and the rest portion  4141  from making contact with one another. This makes it possible to reduce the disk mounting force. 
     A claw-side stopper  4216  is provided radially inwardly of the recess portion  4213   a . The claw-side stopper  4216  restricts radial outward movement of the claw member  42  by making contact with the inner circumferential surface of the cylindrical portion  414  of the center case  41 . The claw-side stopper  4216  is formed of a planar surface extending along a radial direction and also extending perpendicularly to an axial direction. The claw-side stopper  4216  is formed circumferentially within the recess portion  4213   a . The claw-side stopper  4216  has a circumferential width greater than that of the straight portion  4213   b  of the recess portion  4213   a . This ensures that the claw member  42  is stably kept in position without deviating in a circumferential direction. On the opposite circumferential sides of the claw-side stopper  4216 , there are formed circumferential slanting portions  4216   a  inclined radially inwardly as they go away from the claw-side stopper  4216  in the circumferential direction. This eliminates the possibility that other portions of the claw member  42  than the claw-side stopper  4216  make contact with the inner circumferential surface of the cylindrical portion  414  of the center case  41 . Therefore, it is possible to prevent the claw member  42  from tilting in the circumferential direction, which would otherwise occur when other portions of the claw member  42  than the claw-side stopper  4216  come into contact with the cylindrical portion  414  of the center case  41 . This makes it possible to stably keep the claw member  42  in position. 
     The claw-side stopper  4216  is formed in such a manner that the circumferential width thereof becomes smaller than that of the planar portion  4143   a  formed on the inner circumferential surface of the cylindrical portion  414  of the center case  41 . This construction ensures that the claw-side stopper  4216  makes contact with only the planar portion  4143   a , thereby more stably keeping the claw member  42  in position. 
     On the rear surface of the claw portion  421 , there is formed a claw-side contact surface  4217  that makes contact with the radial outer end of the resilient member  43 . A generally conical protrusion portion  4217   a  that extends radially inwardly for engagement with the resilient member  43  is formed on the claw-side contact surface  4217 . The resilient member  43  engages with the protrusion portion  4217   a . In other words, the protrusion portion  4217   a  is inserted into a coil spring that constitutes the resilient member  43 . The connecting portion between the protrusion portion  4217   a  and the contact surface  4217 , i.e., the base surface of the protrusion portion  4217   a , is formed of an annular slanting surface  4217   b  whose diameter is increased radially outwardly. The resilient member  43  comes into contact with the annular slanting surface  4217   b . The annular slanting surface  4217   b  is arranged radially outwardly of an inner surface portion  4211   b  of the guide portion  4211 . That is to say, when seen in a section view, a recess portion  4217   c  is formed in an axial gap between the inner surface portion  4211   b  of the guide portion  4211  and the protrusion portion  4217   a . The axial gap between the resilient member  43  arranged in the recess portion  4217   c  and the inner surface portion  4211   b  of the guide portion  4211  is formed to have a size smaller than that of the axial gap between the resilient member  43  and the protrusion portion  4217   a . This makes it possible to restrict axial movement of the resilient member  43  which would otherwise occur when the resilient member  43  is loosely engaged with the protrusion portion  4217   a . Therefore, the resilient member  43  is able to impart a force to the claw member  42  in a specified direction, consequently assuring stable movement of the claw member  42 . The lower surface of the inner surface portion  4211   b  (namely, the surface axially facing the resilient member  43 ) is formed of a slanting portion  4211   c  which is inclined so that the axial width of the recess portion  4217   c  can be increased in a radial inward direction. This allows the resilient member  43  to be easily inserted into the recess portion  4217   c  even when the axial gap between the resilient member  43  and the slanting portion  4211   c  is set small. This means that the resilient member  43  is capable of making good contact with the claw-side contact surface  4217  even when the axial width of the recess portion  4217   c  is set small. As a result, it becomes possible to assure stable movement of the claw member  42 . 
     Each of the wing portions  422  includes a base portion  4221  formed on each of the opposite circumferential sides of the claw-side contact surface  4217  and a lateral extension portion  4222  formed radially inwardly and circumferentially outwardly of the base portion  4221 . 
     The base portion  4221  is formed to have substantially the same circumferential width as that of the upper contact surface  4211   a . The base portion  4221  has a slanting upper surface  4223  which is inclined radially inwardly and axially downwardly. The slanting upper surface  4223  has substantially the same inclination angle as that of the claw-side slanting surface  4215  of the claw portion  421 . This allows a mold to be released with ease in an injection molding process. 
     The base portions  4221  of the respective wing portions  422  have inner surfaces  4224  circumferentially facing the resilient member  43 . The inner surfaces  4224  of the base portions  4221  are inclined in such directions as to radially inwardly increase the circumferential width between the inner surfaces  4224 . In the present embodiment, the inclination angle θ is equal to 5 degrees, where the inclination angle θ refers to an acute angle that each of the inner surfaces  4224  makes with respect to a radial plane. By doing so, the circumferential width between the narrowest portions of the mutually facing inner surfaces  4224  (namely, the portions making contact with the claw-side contact surfaces  4217 ) is made nearly equal to the outer diameter of the resilient member  43 . As a result, it becomes possible to reduce circumferential free movement of the resilient member  43 , consequently assuring stable movement of the claw member  42 . Inasmuch as the inner surfaces  4224  are inclined as noted above, the circumferential gap between the mutually facing inner surfaces  4224  becomes greater than the outer diameter of the resilient member  43  in the radially inward side of the base portion  4221 . This makes it easy to insert the resilient member  43  between the inner surfaces  4224  of the respective base portions  4221 . As a consequence, it becomes possible to produce the chucking device with ease. The inner surfaces  4224  formed with an inclination angle make it easy to release a mold in an injection molding process. 
     The lateral extension portion  4222  extends radially inwardly from the base portion  4221 . The lateral extension portion  4222  has a radial outer slating surface inclined radially inwardly as it goes away from the base portion  4221  in a circumferential direction. The slanting surface of the lateral extension portion  4222  radially faces the inner circumferential surface of the second recess portion  4144  of the center case  41 . By forming the slanting surface in the lateral extension portion  4222 , it is possible to prevent the slanting surface from making contact with the inner circumferential surface of the second recess portion  4144 . Therefore, the claw member  42  does not make contact with the center case  41  in other portions than the claw-side stopper  4216  which makes contact with the planar portion  4143   a  of the first recess portion  4143  of the center case  41  since radial outward movement of the claw member  42  is restricted. As a result, it is possible to stably keep the circumferential position of the claw member  42  in a standby state. 
     The lateral extension portion  4222  circumferentially faces the groove portion  4161  formed between the individual contact portion  4111  and the connection portions  416  of the center case  41 . This means that the lateral extension portion  4222  is allowed to move radially inwardly beyond the contact surface  4111   a . As a result, it becomes possible to increase the distance by which the claw member  42  can move radially inwardly and also to improve the flexibility in designing radial inward movement of the claw member  42 . It is also possible improve the flexibility in designing the radial length of each of the wing portions  422 . 
     Seeing that the groove portion  4161  circumferentially faces the lateral extension portion  4222 , it is possible to increase the circumferential width of each of the contact portions  4111 . As set forth above, the inner circumferential surface of each of the contact portions  4111  is formed into a curved surface extending along the outer circumferential surface of the inner cylindrical portion  2221   a  of the rotor holder  22 . Furthermore, the contact surface  4111   a  is a surface perpendicular to the radial direction. Therefore, each of the contact portions  4111  is formed to have a radial thickness gradually increasing toward the circumferential ends thereof. In this regard, the radial thickness of each of the contact portions  4111  is increased in the opposite circumferential ends thereof as the circumferential width of the individual contact portion  4111  becomes greater. This makes it possible to increase the strength of the contact portions  4111 . It is preferred that each of the contact portions  4111  exhibits high strength, particularly because the resilient member  43  imparts a radially inwardly acting force to the individual contact portion  4111  and because the biasing force of the resilient member  43  shows a change in response to the radial movement of the claw member  42 . Therefore, it is desirable to employ a structure having an increased circumferential width, just like the contact portions  4111  of the present embodiment. 
     The lateral extension portions  4222  have inner surfaces  4222   a  circumferentially facing the resilient member  43 . The inner surfaces  4222   a  are formed of slanting surfaces inclined to get away from each other in a radial inward direction (at an inclination angle θ of about 5 degrees in the present embodiment, where the inclination angle θ refers to an acute angle that each of the inner surfaces  4222   a  makes with respect to a radial plane). 
     The upper surface of the lateral extension portion  4222  has the same inclination angle as that of the upper surface  4223  of the base portion  4221 . 
     The lower surfaces of the base portion  4221  and the lateral extension portion  4222  are formed into a generally spherical shape. Therefore, the claw member  42  makes contact with the upper surface of the cover portion  222  of the rotor holder  22  at two points. In a standby state, each of the lower surfaces of the base portion  4221  and the lateral extension portion  4222  has a first contact portion  4225  (see  FIG. 15 ) whose circumferential position lies on the center of each of the wing portions  422 . Each of the lower surfaces is curved axially upwardly (namely, becomes distant from the cover portion  222 ) as it gets away from the first contact portion  4225 . The radial position of the first contact portion  4225  is set radially inwardly of the claw portion  421 . 
     &lt;Standby State&gt; 
     Next, the standby state of the chucking device  40  will be described with reference to  FIG. 15 , which shows an axially-cut schematic half-section view of the chucking device  40  kept in the standby state. The resilient member  43  is omitted in  FIG. 15 . 
     Referring to  FIG. 15 , the claw member  42  remains motionless in a state that the sliding portion  4214  of the claw portion  421  stays in contact with the rest portion  4141 , the upper contact portions  4211   a  staying in contact with the lower surface of the cover portion  222 , the first contact portion  4225  of each of the wing portions  422  staying in contact with the upper surface of the cover portion  222 , and the claw-side stopper  4216  staying in contact with the planar portion  4143   a  of the rest portion  4141 . Such contact keeps the claw member  42  in a given posture. 
     In the standby state, the claw-side slanting surface  4215  of the claw member  42  is kept closest to the connecting portion  4142  (indicated by a dot line in  FIG. 15 ) that interconnects the rest portion  4141  and the cylindrical portion  414 . The inner and outer circumferential edges of the upper slanting surface of the connecting portion  4142  may be located axially upwardly as long as the slanting surface does not make contact with the claw-side slanting surface  4215  in the standby state. This makes it possible to increase the axial height of the connection portion  416 , consequently improving the strength of the connecting portion  4142 . 
     In the standby state, the axial height of the guide portion  4211  is substantially the same as, or axially lower than, that of the upper surface of the cover portion  412  of the center case  41 . This structure makes it possible to prevent the guide portion  4211  of the claw member  42  from making contact with the lower surface of a disk when the disk is moved in close proximity to the upper surface of the cover portion  412  of the chucking device  40 . 
     &lt;Operation of the Claw Member  42  During a Disk Mounting Process&gt; 
     Next, the operation of the claw member  42  when mounting the disk D 1  to the chucking device  40  will be described with reference to  FIGS. 16 to 18 .  FIG. 16  is a schematic half-section view illustrating a state that the disk D 1  begins to make contact with the chucking device  40 .  FIG. 17  is a schematic half-section view illustrating a state that the claw member  42  is moved radially inwardly to the greatest possible extent.  FIG. 18  is a schematic half-section view illustrating a state that the disk D 1  is held in place by means of the claw member  42 . In this connection, the disk D 1  is a laminated disk produced by bonding two disk substrates together. 
     Referring to  FIG. 16 , the lower end of the central opening portion D 1   a  of the disk D 1  makes contact with the upper surface of the guide portion  4211  of the claw member  42 . This causes the disk D 1  to impart an axially downwardly acting force to the claw member  42 . In response, the tip end portion  4212  of the claw member  42  is rotated axially downwardly about the contact point of the radial inner edges of the upper contact surface  4211   a  with the lower surface of the cover portion  412 . Simultaneously with this rotation, the claw member  42  is moved radially inwardly, at which time the sliding portion  4214  is slid along the upper surface of the rest portion  4141 . 
     Referring to  FIG. 17 , if the disk D 1  is further moved axially downwardly in the state illustrated in  FIG. 16 , the inner circumferential surface of the central opening portion D 1   a  of the disk D 1  comes into contact with the tip end portion  4212  of the claw member  42 . In this state, the tip end portion  4212  of the claw member  42  is kept moved axially downwardly to the greatest possible extent. Furthermore, the lateral extension portions  4222  of the claw member  42  are kept moved radially inwardly to the greatest possible extent. Moreover, the radial position of the lateral extension portions  4222  lies radially inwardly of the radial position of the contact surface  4111   a  of the center case  41 . In other words, a part of each of the lateral extension portions  4222  is received within the groove portion  4161 . 
     Referring to  FIGS. 16 and 17 , the lower surface of each of the wing portions  422  makes contact with the upper surface of the cover portion  222  in a radially outward position from the first contact portion  4225 . Since the lower surface of each of the wing portions  422  is of a generally spherical shape, it makes point-to-point contact with the upper surface of the cover portion  222 . This reduces the contact area between the wing portions  422  and the cover portion  222 , thereby reducing the frictional force that acts between the claw member  42  and the cover portion  222 . As a result, the claw member  42  is able to move radially inwardly in a smooth manner. Therefore, it is possible to reduce the force required to mount the disk D 1  to the chucking device  40 . 
     When the claw member  42  is moved radially inwardly, the sliding portion  4214  of the claw member  42  is slid along the curved surface portion  4141   b  of the rest portion  4141 . This means that the sliding portion  4214  makes line-to-line contact with the rest portion  4141  during its sliding movement. This helps reduce the frictional force that acts between the sliding portion  4214  and the rest portion  4141 . As a result, the claw member  42  is able to move radially inwardly in a smoother manner. Therefore, it is possible to further reduce the force required to mount the disk D 1  to the chucking device  40 . 
     Referring to  FIG. 18 , once the lower surface of the disk D 1  is supported on the upper surface of the disk support portion  44 , the tip end portion  4212  of the claw member  42  is moved axially upwardly from the state illustrated in  FIG. 17 . Furthermore, the claw member  42  is caused to move radially outwardly. The disk holding surface  4213  of the claw member  42  comes into contact with the upper edge of the central opening portion D 1   a  of the disk D 1 , whereby the claw member  42  holds the disk D 1  in place. 
     In the state illustrated in  FIG. 18 , the region of the disk holding surface  4213  lying on the tip end side above the recess portion  4213   a  makes contact with the upper edge of the central opening portion D 1   a  of the disk D 1 . In other words, the continuously extending circumferential region of the disk holding surface  4213  makes contact with the upper edge of the central opening portion D 1   a  of the disk D 1 . This helps increase the area over which the disk holding surface  4213  makes contact with the central opening portion D 1   a . Therefore, it becomes possible to reduce the pressure applied to the central opening portion D 1   a  by the disk holding surface  4213 . As a result, it is possible to prevent deformation of the disk D 1  which would otherwise be caused by the disk holding surface  4213 . This makes it possible to highly accurately align the disk D 1  with the chucking device  40 . 
     Since the disk D 1  makes contact with the disk holding surface  4213  over a broad area, the disk D 1  is hardly separated from the chucking device  40  even if a disk-tilting force is imparted to the disk D 1  by an external shock or the like during rotation of the disk D 1 . This is because the increased contact area between the disk D 1  and the disk holding surface  4213  serves to increase the frictional force acting when the central opening portion D 1   a  is urged to move axially upwardly against the disk holding surface  4213 . Therefore, it is possible to provide a motor provided with a highly reliable chucking device that can keep a disk from being removed during its rotation. 
     &lt;Operation of the Claw Member in Case of Mounting a Thin Disk&gt; 
     Next, the operation of the claw member  42  when a disk D 2  having an axial thickness smaller than that of the disk D 1  is mounted to the chucking device  40  will be described with reference to  FIG. 19 .  FIG. 19  is an axially-cut schematic half-section view illustrating a state that the disk D 2  is mounted to the disk mounting portion  44 . 
     Referring to  FIG. 19 , when the disk D 2  is mounted in place, the claw member  42  is moved more radially outwardly than when the disk D 1  is mounted in place. This is because the upper edge of the central opening portion D 2   a  of the disk D 2  is positioned axially below that of the disk D 1 , thereby lowering the contact position between the disk holding surface  4213  and the upper edge of the central opening portion D 2   a  of the disk D 2 . Since the disk holding surface  4213  is formed of a slanting surface inclined axially downwardly and radially inwardly, the contact point between the disk holding surface  4213  and the disk D 2  having a reduced axial thickness lies more radially inwardly than the contact point between the disk holding surface  4213  and the disk D 1 . Therefore, the disk D 2  remains in contact with the regions of the disk holding surface  4213  lying circumferentially outwardly of the recess portion  4213   a.    
     When the disk D 2  is mounted in place, the tip end portion  4212  of the claw member  42  lies more radially outwardly from the central opening portion D 2   a  of the disk D 2  than when the disk D 1  is mounted in place. This means that the claw member  42  needs to be moved longer distance in a radial direction when removing the disk D 2  from the chucking device  40  than when removing the disk D 1 . Therefore, the disk D 2  is hard to remove from the chucking device  40  as compared to the disk D 1 . 
     &lt;Disk Drive Apparatus&gt; 
     Next, one embodiment of a disk drive apparatus equipped with the present motor will be described with reference to  FIG. 20 , which is an axially-cut schematic section view of the disk drive apparatus. 
     Referring to  FIG. 20 , the disk drive apparatus  50  includes a spindle motor  51  for rotating a disk  60  having an opening  61  at its center, the motor  51  being inserted into the opening  61  of the disk  60  to bring the center of the opening  61  into coaxial alignment with the rotational axis of the disk  60 , an optical pickup mechanism  52  for recording and reproducing information on and from the disk  60  by irradiating a laser beam toward the disk  60 , a gear mechanism  53  for moving the optical pickup mechanism  52  in a radial direction of the disk  60 , and a housing  54  for receiving the spindle motor  51 , the optical pickup mechanism  52  and the gear mechanism  53 . 
     The spindle motor  51  and the optical pickup mechanism  52  are held in place by means of a chassis  55 . As the chassis  55  is caused to move at least in an axial direction, the disk  60  is mounted at the opening  61  to the chucking device of the spindle motor  51 . The chassis  55  is provided with an aperture and the optical pickup mechanism  52  is arranged inside the aperture. 
     The gear mechanism  53  includes a motor  531 , which has an output shaft and a driving gear attached to the output shaft, and a driven gear  532  for receiving a torque of the motor  531 . 
     A thin partition plate  541  for isolating the disk  60  from the gear mechanism  53  is formed within the housing  54 . Furthermore, the housing  54  has an access opening  542  through which the disk  60  is inserted and taken out. 
     The optical pickup mechanism  521  includes a recording and reproducing unit  521  for irradiating a laser beam and a moving unit  522  for moving the recording and reproducing unit  521 , the moving unit  522  provided at a right angle relative to the moving direction of the recording and reproducing unit  521  that moves along the radial direction of the disk  60 . The moving unit  522  has a meshing portion  522   a  that comes into meshing engagement with the driven gear  532 . The recording and reproducing unit  521  is meshed with the moving unit  522  and consequently moved in the radial direction. 
     The driven gear  532  is rotated by coming into meshing engagement with a gear portion  531   a  attached to the motor  531 . The moving unit  522  is moved in the radial direction because the driven gear  532  remains meshed with the meshing portion  522   a  of the moving unit  522 . Upon movement of the moving unit  522 , the recording and reproducing unit  521  is moved in the radial direction. 
     Application of the present motor  10  to the spindle motor  51  of the disk drive apparatus  50  makes it possible to provide a highly reliable disk drive apparatus that can prevent the disk  60  from being removed from the chucking device  40  during its rotation. 
     Accordingly, it becomes possible to provide a highly reliable disk drive apparatus capable of preventing recording and reproducing errors which would otherwise be generated when the disk  60  is mounted to the spindle motor  51 . 
     While one embodiment of the present invention has been described hereinabove, the present invention is not limited thereto. Many changes or modifications may be made without departing from the scope of the claims.