Patent Publication Number: US-2011078712-A1

Title: Spindle motor and information storage device including the same

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a National Stage of PCT International Patent Application No. PCT/KR2009/007140, filed Dec. 2, 2009, and claims the benefit of Korean Patent Application No. 10-2009-0007411, filed Jan. 30, 2009 in the Korean Intellectual Property Office, the disclosures of which are incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     Aspects of the present invention relate to a spindle motor on which an information storage medium having a central opening portion can be easily installed or detached and a center of the information storage medium can be automatically aligned with a rotational center of the spindle motor, and to a rotational information storage device including the spindle motor. 
     2. Description of the Related Art 
     In recent years, an optical disc such as a CD or a DVD clearly tends to increase its rotational speed of the optical disc. As the rotation speed of such an optical disc is increased, the centrifugal force of the optical disc excessively increases for various reasons. Thus, when the optical disc is installed at a driving motor, a correction device that allows a rotational center of the spindle motor and a rotational center of the optical disc to be identical with each other has been developed. 
     In a rotational information storage device at which or from which an optical disc is installed or detached, such as an optical disc drive, a spindle motor rotates the optical disc to be used as an information storage medium. In an optical disc having a central opening portion, a bottom surface of the optical disc is mounted on a turntable disposed above the spindle motor, and the central opening portion thereof is inserted in a protrusion formed in the middle of the turntable and the optical disc is rotated along with the spindle motor. However, In mass production of optical discs made of a flexible material, such as plastic. It is difficult to keep the dimension of an inner hole of the optical disc uniform. Thus, when optical discs that are manufactured on a mass scale are installed at the spindle motor, a gap between an inner circumferential surface of the central opening portion of the optical disc and the protrusion of the turntable occurs. 
     When a gap between the inner hole of the optical disc and the protrusion of the turntable occurs, the rotational center of the optical disc is not identical with the rotational center of the spindle motor. As such, errors occur when data is written on the optical disc and/or read from the optical disc. 
     In order to solve the problem, a conventional spindle motor is shown in  FIG. 8 . 
     In the conventional spindle motor of  FIG. 8 , a plurality of hook-shaped claws  2   b  are formed at an outer circumferential surface of a protrusion  2   a  of a turntable  2  that comes in contact with an inner circumferential surface  1   a  of a central opening portion of an optical disc  1 . As indicated in  FIG. 8 , it is an elastic member that the hookshaped claws  2   b  formed at the outer circumferential surface of the protrusion  2   a  of the turntable  2 . The size of each of the claws  2   b  is greater than the size of an inner hole of the optical disc  1  and each of the claws  2   b  has the form of a hook. Thus, when the optical disc  1  is inserted in the protrusion  2   a  of the turntable  2 , the hook-shaped claws  2   b  are pressed to a center of a rotation shaft and come in contact with the inner circumferential surface  1   a  of the central opening portion of the optical disc  1 . In this case, due to an elastic force that the hook-shaped claws  2   b  are restored to their original shape, an outer circumferential surface of the central opening portion of the optical disc  1  is pushed from a rotational center of the optical disc  1  to the outside so as to retain the optical disc  1  while an equilibrium between the retaining force and the centrifugal force imposed on the optical disc  1  has been maintained. As such, the claws  2   b  allow the outer circumferential surface of the central opening portion of the optical disc  1  to be pushed out of a radial direction and as a result, the rotational center of the optical disc  1  may be identical with the rotational center of the spindle motor. 
     However, the optical disc  1  is generally formed of a flexible material such as plastics and thus damage, deformation or wear may occur when the optical disc  1  is manufactured, handled or kept. When damage, deformation or wear occurs in the optical disc  1 , a center of mass of the optical disc  1  deviates from the rotational center of the optical disc  1 . When the center of mass of the optical disc  1  deviates from the rotational center of the optical disc  1  and the spindle motor rotates at high speed, a centrifugal force is greatly increased, and the centrifugal force is greater than elasticity or a restoration force of the claws  2   b  formed at the outer circumferential surface of the protrusion  2   a  of the turntable  2 . Thus, the rotational center of the optical disc  1  deviates from the rotational center of the spindle motor. 
     When the center of the optical disc  1  deviates from the rotational center of the spindle motor, data written in the optical disc  1  may not be read, or data may not be written in a designated position of the optical disc  1 . In other words, when the centrifugal force of the optical disc  1  is weak, any special problem does not occur. However, when the centrifugal force of the optical disc  1  is excessive, the optical disc  1  does not operate normally. 
     In order to overcome the problem, the elasticity of the claws  2   b  may be sufficiently increased. In this case, the inner hole of the optical disc  1  is strongly fixed at the protrusion  2   a  of the turntable  2  so that the optical disc  1  may not be smoothly replaced with a new one. Due to the drawback, it is difficult to store and reproduce information according to an optical disc while replacing the optical disc with a new one. 
     SUMMARY OF THE INVENTION 
     Accordingly, An object of the present invention is to provide a spindle motor in which an operation of replacing an optical disc is smoothly performed and of which a center is automatically adjusted so that a slide cone may come in contact with a central opening portion of the optical disc, a rotational center of the optical disc may be substantially identical with a rotational center of the spindle motor even under a strong centrifugal force of the optical disc. 
     Another object of the present invention is to provide a spindle motor which starts rotating while an information storage medium is not slid. 
     Another object of the present invention is to provide a spindle motor that includes a small rotor portion and a turntable at which a relatively large optical disc is installed. 
     Another object of the present invention is to provide an information storage device which is not affected by an increase in the centrifugal force of an optical disc and uses a spindle motor that is easily installed or detached at or from the optical disc so that information may be stably written or reproduced in or from the optical disc. 
     To achieve these and other advantages and in accordance with the purpose of the present invention, as embodied and broadly described, there is provided a spindle motor at which or from which an information storage medium having a central opening portion is installed or detached, for rotating the information storage medium, the spindle motor including: a rotation shaft; a slide cone of a substantially cup-like shape comprising a cone cylindrical portion of a substantially cylindrical shape having an outer circumferential surface that may contact an inner circumferential portion of the central opening portion of the information storage medium, a cone bottom portion in which the rotation shaft is inserted so that the cone is movable in an axial direction with respect to the rotation shaft, and a hollow portion formed upwards by the cone cylindrical portion and the cone bottom portion; a turntable of a substantially hat-like shape comprising a turntable cylindrical portion of a substantially cylindrical shape having a top surface extended outward of the turntable cylindrical portion making contact with a bottom surface of the information storage medium, a turntable bottom portion in which the rotation shaft is inserted so that the spindle motor rotates along with the rotation shaft, and a hollow portion in which, when the slide cone goes down in an axial direction, the slide cone is accommodated by the turntable cylindrical portion and the turntable bottom portion; a yoke fixed at upper portions of the rotation shaft that protrudes from the slide cone within the hollow portion of the slide cone; a clamp magnet disposed on the yoke; and a cone yoke fixed at the cone bottom portion so that the cone yoke makes an axial motion in a direction below the yoke together with the slide cone and formed of a magnetic material. 
     Also, the cone yoke may be fixed at a top surface or a bottom surface of the cone bottom portion of the slide cone. Furthermore the cone yoke may be a permanent magnet. 
     Also, the spindle motor may further include a rubber plate that is substantially attached to the top surface of the cylindrical portion of the turntable so that, when the information storage medium is mounted on the spindle motor, the bottom surface of the information storage medium directly contacts the rubber plate. 
     Also, the spindle motor may further include a rotor magnet; and a rotor case rotating along with the rotation shaft and comprising a cylindrical portion at which the rotor magnet is installed, wherein an outer circumferential surface of the cylindrical portion of the rotor case is placed in an inner position than a position of a cylindrical outer circumferential surface of the top surface of the cylindrical portion of the turntable in a radial direction. 
     According to another aspect of the preset invention, there is provided an information storage device including: the spindle motor described above; a pickup unit comprising an information writing portion for writing information in an information storage medium and an information reading portion for sensing the information from the information storage medium; a controller controlling a motion of the pickup unit; and a signal converter converting a signal transmitted from the pickup unit into a predetermined signal. 
     As described above, in the spindle motor according to the present invention, the center of an optical disc does not deviate from the rotational center of the spindle motor even during high-speed rotation but is identical therewith so that, in an optical disc drive rotating at high speed, errors that may occur in writing or reading data in or from the optical disc can be reduced and the optical disc can be easily replaced with a new one. Furthermore, when the spindle motor starts rotating, a robust rotational force of a storage medium may be exerted by friction between a rubber plate and a storage medium so that sliding during rotation can be prevented. 
     Furthermore, an additional elastic member that pushes a slide cone is not even used, but, the slide cone is moved upwards due to an attractive force between a yoke and a cone yoke that is a magnet or an attractive force between the cone yoke that is formed of a magnetic material and a clamp magnet so that the storage medium be retained on the turntable and a slim spindle motor can be provided and the productivity and assembling characteristics of the spindle motor can be improved. 
     Furthermore, the spindle motor including a smaller rotor portion can be employed in the optical disc drive. 
     Additional aspects and/or advantages of the invention will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       These and/or other aspects and advantages of the invention will become apparent and more readily appreciated from the following description of the embodiments, taken in conjunction with the accompanying drawings of which: 
         FIG. 1  is a partial cross-sectional view of a spindle motor before an optical disc is mounted on the spindle motor, according to an embodiment of the present invention; 
         FIG. 2  is a partial cross-sectional view of the spindle motor of  FIG. 1  after the optical disc is mounted on the spindle motor of  FIG. 1 ; 
         FIG. 3  is a partial cross-sectional view of a spindle motor before an optical disc is mounted on the spindle motor, according to another embodiment of the present invention; 
         FIG. 4  is a partial cross-sectional view of the spindle motor of  FIG. 3  after the optical disc is mounted on the spindle motor of  FIG. 3 ; 
         FIG. 5  is a partial cross-sectional view of a spindle motor before an optical disc is mounted on the spindle motor, according to another embodiment of the present invention; 
         FIG. 6  is a partial cross-sectional view of the spindle motor of  FIG. 5  after the optical disc is mounted on the spindle motor of  FIG. 5 ; 
         FIG. 7  is a cross-sectional view of an optical disc drive in which the optical disc of  FIG. 1 ,  3  or  5  is used; and 
         FIG. 8  is a partial cross-sectional view of a conventional spindle motor. 
     
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     Reference will now be made in detail to the present embodiments of the present invention, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to the like elements throughout. The embodiments are described below in order to explain the present invention by referring to the figures. 
     The above and other aspects of the present invention will become more apparent by describing in detail exemplary embodiments thereof with reference to the attached drawings. 
     The terminology or term used in the present specification and the claims should not be construed as limited to general or dictionary&#39;s definitions. The terminology or term used herein should be construed to meet the technical spirit of the invention on the basis of the concept of the terminology appropriately defined in order to describe the inventor(s)&#39; invention in the best manner. 
     Detailed illustrative example embodiments are disclosed herein. However, specific structural and functional details disclosed herein are merely representative for purposes of describing example embodiments. This invention may, however, may be embodied in many alternate forms and should not be construed as limited to only the example embodiments set forth herein. 
     It will be understood that the terms “above”, “below”, “under”, “on”, “left”, “right”, “inner”, and “outer” may be used herein to describe the relative position or direction between various elements or parts and the relative position or direction in the drawings. 
     Hereinafter, the present invention will be described in detail by explaining exemplary embodiments of the invention with reference to the attached drawings. 
       FIG. 1  is a partial cross-sectional view of a spindle motor before an optical disc is mounted on the spindle motor, according to an embodiment of the present invention, and  FIG. 2  is a partial cross-sectional view of the spindle motor of  FIG. 1  after the optical disc is mounted on the spindle motor of  FIG. 1 . In the present embodiment, a cone yoke that will be described later is a magnet fixed at a top surface of a bottom portion of a slide cone. 
     As illustrated in  FIGS. 1 and 2 , the spindle motor includes a stator portion  100  that is fixed at an optical disc drive and a rotor portion  200  that rotates along with a rotation shaft  150 . 
     First, the stator portion  100  includes a core  110 , a coil  115 , a circuit board  120 , a bracket  130 , a bearing housing  140 , a cap  145 , the rotation shaft  150 , a washer  160 , a sliding bearing  170 , and a thrust plate  180 , which are sequentially assembled. In detail, the rotation shaft  150  is inserted in the sliding bearing  170  and rotates therein, and the sliding bearing  170  is disposed in the bearing housing  140  and is fixed therein. The bearing housing  140  is cylindrical, and a stator is disposed at an outer circumferential surface of the bearing housing  140 . The stator generally includes a plurality of cores  110  and the coil  115  that surrounds the cores  110 . The cap  145  is inserted from a top of the cylindrical bearing housing  140  into an opening formed in lower portions of the cylindrical bearing housing  140 , or the bearing housing  140  is formed as one body in a cup shape (not shown) and the sliding bearing  170  in which the rotation shaft  150  is inserted may be placed in the bearing housing  140 . In case of using the cap  145 , the washer  160  is disposed above a top surface of a cylindrical wall of the cap  145 . In case of using the cup shape bearing housing  140 , a cylindrical wall surface of the lower portions of the bearing housing  140  is formed as stepped surfaces so that the washer  160  may be disposed on the stepped surfaces. The washer  160  may be inserted in a small diameter portion of the rotation shaft  150 . The sliding bearing  170  is a porous metal-containing bearing. Lowest bottom ends of the cylindrical sliding bearing  170  contact the top surface of the washer  160 , and the cylindrical sliding bearing  170  is inserted in the bearing housing  140  so that an outer circumferential surface of the cylindrical sliding bearing  170  may contact an inner circumferential surface of the bearing housing  140 . The thrust plate  180  is disposed on the cap  145  or on the bottom surface of the cup shape bearing housing  140  so that the thrust plate  180  may contact the lowest bottom ends of the rotation shaft  150 . The bearing housing  140  is inserted in a cylindrical protrusion of the bracket  130  and is fixed therein. An outer circumferential surface of a top end of the protrusion is disposed to support the cores  110 , and the circuit board  120  is disposed on the top surface of the bracket  130  below the cores  110 . 
     Secondly, the rotor portion  200  includes a rotor case  210 , a rotor magnet  220 , a turntable  230 , a rubber plate  240 , a clamp magnet  250 , a slide cone  260 , a thrust magnet  270 , a washer  275 , and a rotation shaft  150 , which are sequentially assembled. In detail, the rotor case  210  is substantially cylindrical, and the rotor magnet  220  of a cylindrical shape that faces the stator  190  is attached to an inner circumferential surface of the cylindrical rotor case  210 . The rotation shaft  150  is inserted in a cylindrical portion of a center of the rotor case  210  above upper portions of the sliding bearing  170  and the rotation shaft  150  is fixed at an inner circumferential surface of the cylindrical portion of the center of the rotor case  210  so that the rotor case  210  and the rotor magnet  220  may rotate along with the rotation shaft  150 . The thrust magnet  270  is disposed at an outer circumferential surface of the cylindrical portion of the center of the rotor case  210  fixed at the rotation shaft  150 , and the washer  275  is disposed in an opening formed in a bottom end of the cylindrical portion of the center of rotor case  210 . 
     The turntable  230  having a substantially hat-like shape is disposed on the rotor case  210  so that the turntable  230  may rotate along with the rotation shaft  150 , and an optical disc  1  that is an information storage medium is disposed on the top surface of a cylindrical portion  230   a  of the turntable  230 . A bottom portion  230   b  in which the rotation shaft  150  is perforated and is fixed is formed in the cylindrical portion  230   a  of the turntable  230 , and a hollow portion in which the slide cone  260  may be placed is formed by the cylindrical portion  230   a  and the bottom portion  230   b . In this case, in order to use a variety of small motors, the outer circumferential surface of the cylindrical portion of the rotor case  210  may be placed in an inner position than the position of a cylindrical outer circumferential surface of an optical disc mounting portion  230   b  in a radial direction. 
     The slide cone  260  is substantially cup-shaped. When the optical disc  1  is installed at the spindle motor, an outer circumferential surface of a cylindrical portion  260   a  of the slide cone  260  closely contacts the inner circumferential portion  1   a  of the opening portion of the optical disc  1 , and the rotation shaft  150  is perforated in a bottom portion  260   b  of the slide cone  260  so that the slide cone  260  may slide along the rotation shaft  150  in an axial direction. 
     In the present embodiment, a hollow cone yoke  280  is fixed at the hollow portion of the slide cone  260  and on the top surface of the bottom portion  260   b  of the slide cone  260 , and the rotation shaft  150  is perforated in a hollow surface of the cone yoke  280  so that the rotation shaft  150  may be vertically slid. Thus, the cone yoke  280  may be vertically slid in an axial direction together with the slide cone  260 . In the present embodiment, the rotation shaft  150  is disposed on a top end of a yoke  255  in which the clamp magnet  250  is inserted in the rotation shaft  150 , and the cone yoke  280  is placed below the yoke  255 . 
     Also, the rubber plate  240  is substantially attached to the top surface of the optical disc mounting portion  230   b  so that the bottom surface of the optical disc  1  may directly contact the rubber plate  240  and the optical disc  1  may rotate without sliding when a motor is rotated. 
       FIG. 1  illustrates the spindle motor before the optical disc  1  is mounted on the turntable  230 , according to an embodiment of the present invention. Referring to  FIG. 1 , a component that allows the optical disc  1  to be mounted on the turntable  230  and to be retained therein is the slide cone  260 , the turntable  230 , the clamp magnet  250 , and a disc clamp (not shown). An outside of the cylindrical portion  260   a  of the slide cone  260  is usually formed in a cone shape and closely contacts the inner circumferential surface  1   a  of the opening portion of the optical disc  1 , and the clamp magnet  250  and the yoke  255  formed of metal are disposed in the opening portion of the optical disc  1 , and the cone yoke  280  is fixed at the top surface of the bottom portion  260   b  of the slide cone  260  so that the cone yoke  280  may make a vertical motion with respect to the rotation shaft  150  together with the slide cone  260 . In the present embodiment, the cone yoke  280  is formed using a magnet. Thus, an attractive force occurs between the cone yoke  280  formed of magnet movable in an axial direction with respect to the rotation shaft and the yoke  255  formed of metal that is disposed in upper portions of the spindle motor and is fixed at the rotation shaft  150  so that the attractive force may exert to push the slide cone  260  upwards. As such, the inner circumferential surface  1   a  of the opening portion of the optical disc  1  and a conic outer circumferential surface of the slide cone  260  may be kept in a closely contact state. 
       FIG. 2  illustrates the spindle motor after the optical disc  1  is mounted on the turntable  230 , according to an embodiment of the present invention. When a disc clamp (not shown) operates, metal is formed in the center of the disc clamp installed in an optical device, and due to a magnetic force of the clamp magnet  250 , the disc clamp is fixed on the clamp magnet, and the disc clamp pushes the optical disc  1  and the slide cone  260  which the optical disc  1  closely contacts downward in the axial direction, and the bottom surface of the optical disc  1  is placed on the top surface of the rubber plate  240  disposed above the turntable  230 . When the spindle motor starts rotating, the optical disc  1  rotates due to a frictional force between the spindle motor and the rubber plate  240 . Even when a center of mass of the optical disc  1  is not identical with the rotational center of the spindle motor, the inner hole of the optical disc  1  closely contacts the conic outer circumferential surface of the slide cone  260  so that the center of the optical disc  1  may not deviate from the rotational center of the spindle motor and may be identical therewith. 
       FIG. 3  is a partial cross-sectional view of a spindle motor before an optical disc is mounted on the spindle motor, according to another embodiment of the present invention, and  FIG. 4  is a partial cross-sectional view of the spindle motor of  FIG. 3  after the optical disc is mounted on the spindle motor of  FIG. 3 . The only difference between  FIGS. 3 and 4  and  FIGS. 1 and 2  is that the cone yoke  280  that is a magnet is fixedly installed at a bottom surface of the bottom portion  260   b  of the slide cone  260 , and the other configuration of the spindle motor of  FIGS. 3 and 4  is the same as that of the spindle motor illustrated in  FIGS. 1 and 2 . Thus, the cone yoke  280  is fixed at the bottom surface of the bottom portion  260   b  of the slide cone  260 , and the cone yoke  280  makes a vertical motion with respect to the rotation shaft  150  together with the slide cone  260 . Thus, as in  FIGS. 1 and 2 , due to a magnetic force of the cone yoke  280 , an attractive force occurs between the cone yoke  280  formed of magnet movable in an axial direction with respect to the rotation shaft and the yoke  255  that is disposed in upper portions of the spindle motor and is fixed at the rotation shaft  150  and is formed of metal so that a force may exert to push the slide cone  260  upwards. As such, the inner circumferential surface  1   a  of the opening portion of the optical disc  1  and the conic outer circumferential surface of the slide cone  260  may be kept in a closely contact state. 
       FIG. 5  is a partial cross-sectional view of a spindle motor before an optical disc is mounted on the spindle motor, according to another embodiment of the present invention, and  FIG. 6  is a partial cross-sectional view of the spindle motor of  FIG. 5  after the optical disc is mounted on the spindle motor of  FIG. 5 . The only difference between  FIGS. 5 and 6  and  FIGS. 3 and 4  is that the cone yoke  280  is not a magnet but is formed of a magnetic material as like ferromagnetic substances, and the other configuration of the spindle motor of  FIGS. 5 and 6  is the same as that of the spindle motor illustrated in  FIGS. 3 and 4 . 
     The magnetic material is material that is attached to a magnet and includes a magnet. However, in the present embodiment, the cone yoke  280  is formed of a general magnetic material such as iron that is not a slightly high-priced magnet so that costs may be reduced. Also, an interference with other element that may unexpectedly occur due to the force of a magnet may be prevented. 
     In the present embodiment, the cone yoke  280  is fixed at the bottom surface of the bottom portion  260   b  of the slide cone  260 , and the cone yoke  280  makes a vertical motion with respect to the rotation shaft  150  together with the slide cone  260 . However, the cone yoke  280  may be fixedly installed at the top surface of the bottom the conic outer circumferential surface of the slide cone  260  so that the center of the optical disc  1  may not deviate from the rotational center of the spindle motor and may be identical therewith. 
       FIG. 3  is a partial cross-sectional view of a spindle motor before an optical disc is mounted on the spindle motor, according to another embodiment of the present invention, and  FIG. 4  is a partial cross-sectional view of the spindle motor of  FIG. 3  after the optical disc is mounted on the spindle motor of  FIG. 3 . The only difference between  FIGS. 3 and 4  and  FIGS. 1 and 2  is that the cone yoke  280  that is a magnet is fixedly installed at a bottom surface of the bottom portion  260   b  of the slide cone  260 , and the other configuration of the spindle motor of  FIGS. 3 and 4  is the same as that of the spindle motor illustrated in  FIGS. 1 and 2 . Thus, the cone yoke  280  is fixed at the bottom surface of the bottom portion  260   b  of the slide cone  260 , and the cone yoke  280  makes a vertical motion with respect to the rotation shaft  150  together with the slide cone  260 . Thus, as in  FIGS. 1 and 2 , due to a magnetic force of the cone yoke  280 , an attractive force occurs between the cone yoke  280  formed of magnet movable in an axial direction with respect to the rotation shaft and the yoke  255  that is disposed in upper portions of the spindle motor and is fixed at the rotation shaft  150  and is formed of metal so that a force may exert to push the slide cone  260  upwards. As such, the inner circumferential surface  1   a  of the opening portion of the optical disc  1  and the conic outer circumferential surface of the slide cone  260  may be kept in a closely contact state. 
       FIG. 5  is a partial cross-sectional view of a spindle motor before an optical disc is mounted on the spindle motor, according to another embodiment of the present invention, and  FIG. 6  is a partial cross-sectional view of the spindle motor of  FIG. 5  after the optical disc is mounted on the spindle motor of  FIG. 5 . The only difference between  FIGS. 5 and 6  and  FIGS. 3 and 4  is that the cone yoke  280  is not a magnet but is formed of a magnetic material as like ferromagnetic substances, and the other configuration of the spindle motor of  FIGS. 5 and 6  is the same as that of the spindle motor illustrated in  FIGS. 3 and 4 . 
     The magnetic material is material that is attached to a magnet and includes a magnet. However, in the present embodiment, the cone yoke  280  is formed of a general magnetic material such as iron that is not a slightly high-priced magnet so that costs may be reduced. Also, an interference with other element that may unexpectedly occur due to the force of a magnet may be prevented. 
     In the present embodiment, the cone yoke  280  is fixed at the bottom surface of the bottom portion  260   b  of the slide cone  260 , and the cone yoke  280  makes a vertical motion with respect to the rotation shaft  150  together with the slide cone  260 . However, the cone yoke  280  may be fixedly installed at the top surface of the bottom portion  260   b  of the slide cone  260 . In this case, the cone yoke  280  is formed of material that may be attached to a magnet, such as iron, i.e., a magnetic material so that, due to the magnetic force of the clamp magnet  250  disposed in upper portions of the spindle motor and fixed at the rotation shaft  150 , a force may exert to push the slide cone  260  upwards. As such, the inner circumferential surface  1   a  of the opening portion of the optical disc  1  and the conic outer circumferential surface of the slide cone  260  may be kept in a closely contact state. 
       FIG. 7  is a cross-sectional view of an optical disc drive in which the optical disc of  FIG. 1 ,  3  or  5  is used. Referring to  FIG. 7 , the optical disc drive according to the present embodiment includes a spindle motor  300  illustrated in  FIGS. 1 through 6 , a tray  400  that carries out the optical disc  1  into the optical disc drive, a driving unit  500  that pulls the spindle motor  300  upwards, an optical pickup unit  600  that writes information in the optical disc  1  or reads the information from the optical disc  1 , a controller  700  that controls the motion of the optical pickup unit  600 , and a signal converter  800  that converts a signal transmitted from the optical pickup unit  600  into a predetermined signal. 
     Referring to  FIG. 7 , the tray  400  that may protrude from the optical disc drive carries out the optical disc  1  into the optical disc drive. When the optical disc  1  is put on the tray  400  and power is supplied to the optical disc drive, the tray  400  is slid into the optical disc drive and is entered into a designated position of the optical disc drive. 
     When the tray  400  is entered into the designated position of the optical disc drive, the spindle motor  300  moves upwards, and the conic outer circumferential surface of the slide cone  260  of the spindle motor  300  closely contacts the inner hole of the optical disc  1 , and the optical disc  1  is pulled upwards by the tray  400  and is separated from the tray  400 . After the optical disc  1  is separated from the tray  400 , the disc clamp (not shown) installed in the optical disc drive closely contacts the clamp magnet  250  of the spindle motor  300  due to a magnetic force of the clamp magnet  250 . In this case, the disc clamp is pushed downwards, and the bottom surface of the optical disc  1  closely contacts the top surface of the annular rubber plate  240  attached to the turntable  230 . In other words, the top surface of the optical disc  1  closely contacts the disc clamp, and the disc clamp closely contacts the clamp magnet  250  and is fixed at the spindle motor  300 . 
     As the disc clamp operates, the optical disc  1  closely contacts the top surface of the annular rubber plate  240  disposed on the turntable  230 , and the optical disc  1  and the slide cone  260  are pushed downwards and go down. In this case, due to an attractive force between a yoke and a cone yoke that is a magnet or an attractive force between the cone yoke that is formed of a magnetic material and the clamp magnet  250 , the slide cone  260  is moved upwards. As such, the inner hole of the optical disc  1  is kept to closely contact the conic outer circumferential surface of the slide cone  260 . When power is supplied to the spindle motor  300 , the spindle motor  300  starts rotating. In this case, the optical disc  1  mounted on the turntable  230  of the spindle motor  300  closely contacts the slide cone  260  and the disc clamp and rotates together with the spindle motor  300 . When the center of mass of the optical disc  1  is not identical with the rotational center of the spindle motor  300 , the rotation speed of the spindle motor  300  is increased, and the centrifugal force of the optical disc  1  is rapidly increased. In this case, the centrifugal force of the optical disc  1  is rapidly increased, and even when the optical disc  1  is moved in a direction perpendicular to the rotation shaft  150  of the spindle motor  300 , the conic inner circumferential surface of the slide cone  260  closely contacts a cylindrical outer circumferential surface that forms a shaft support of the turntable  230  so that the optical disc  1  may be prevented from being moved in the direction perpendicular to the rotation shaft  150  of the spindle motor  300 . 
     The present invention includes a spindle motor that uses an optical disc drive using a circular optical disc as an information storage medium and an information storage medium having various shapes including a hollow portion, and a rotational information storage device at which or from which the information storage medium is installed or detached. 
     While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it will be understood by those of ordinary skill in the art that various changes in form and details may be made therein without departing from the spirit and scope of the present invention as defined by the following claims. 
     As described above, in the spindle motor according to the present invention, the center of an optical disc does not deviate from the rotational center of the spindle motor even during high-speed rotation but is identical therewith so that, in an optical disc drive rotating at high speed, errors that may occur in writing or reading data in or from the optical disc can be reduced and the optical disc can be easily replaced with a new one. 
     Furthermore, when the spindle motor starts rotating, a robust rotational force may exert by using friction between a rubber plate and a storage medium so that sliding during rotation can be prevented. 
     Furthermore, an additional elastic member that pushes a slide cone is not disposed, and due to an attractive force between a yoke and a cone yoke that is a magnet or an attractive force between the cone yoke that is formed of a magnetic material and a clamp magnet, the slide cone is moved upwards so that a thinner and smaller spindle motor can be provided and productivity and assembling characteristics of the spindle motor can be improved. 
     Furthermore, the spindle motor including a smaller rotor portion can be employed in the optical disc drive. 
     Although a few embodiments of the present invention have been shown and described, it would be appreciated by those skilled in the art that changes may be made in this embodiment without departing from the principles and spirit of the invention, the scope of which is defined in the claims and their equivalents.