Abstract:
Disclosed is a spindle motor comprising: an integral turntable including: a table on which a rotating body to be installed, and an inner side wall and an outer side wall formed to be recessed upwards at a portion therebetween on a lower surface of the table so that a predetermined hollow is formed, a surface of thereof being formed slant; a ball cover for covering a ball inserted into the hollow and the hollow; a rotation shaft an upper portion of which is inserted into a center of the integral turntable; a bearing supporting a lower portion of the rotation shaft; a coil formed on an outside of the rotation shaft; and a magnet formed on an outside of the coil.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a continuation of pending U.S. application Ser. No. 11/832,313, which is a divisional of U.S. application Ser. No. 10/859,155 (now U.S. Pat. No. 7,461,391), which is a continuation of PCTKR2002002202, the entire contents of each of which are hereby incorporated by reference. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention relates to a spindle motor, and more particularly, to a spindle motor having a ball and a ball casing to reduce vibration and achieve optimal stable revolution. In particular, the invention is directed to a spindle motor in which a friction surface enabling the ball to be subject to a proper frictional force is achieved. 
       BACKGROUND 
       [0003]    In a general spindle motor, rotation shaft is forcedly inserted in T-bush, and the T-bush is coupled with clamp plate, turntable and ball case storing balls. In other words, the T-bush, the clamp plate, the turntable and the ball case are fabricated separately. As a result, the clamp plate is coupled with the upper surface of the T-bush. The turntable and the ball case are coupled with an outer cylindrical surface of the T-bush. The T-bush is forcedly inserted into the rotation shaft. So, the conventional spindle motor as described above is fabricated very complicatedly. Fabrication cost also rises due to the complicated fabrication. To overcome the problem as described above, there was proposed a spindle motor consisting of a T-bush, a clamp plate, a turntable and a ball casing. 
         [0004]      FIG. 1  is a cross sectional view of a spindle motor having an integral turntable. Referring to  FIG. 1 , a bearing housing  21  is installed on a plate  10  and a bearing  23  supporting a rotation shaft  30  is forcedly inserted in an inner cylindrical surface of the bearing housing  21 . A core  41  is coupled with an outer cylinder of the bearing housing  21 . A coil  43  is wound on the core  41 . A rotor yoke  51  surrounding the core  41  is installed at the almost center of the rotation shaft  30 . A magnet  53  opposed to the core  41  is installed on an inner cylindrical surface of the rotor yoke  51 . An integral turntable  60  is coupled with an upper portion of the rotation shaft  30 . A disk  70  is mounted on an upper surface of the integral turntable  60 . A ball  61  and a ball cover  63  are installed in the integral turntable  60  to reduce vibration caused by eccentricity of a rotating body. Balancing operation of the ball  61  will be described schematically. 
         [0005]    When a spindle motor is rotated, a rotating body is vibrated due to the integral turntable  60  as itself and the eccentricity of the disk  70  installed on the turntable  60 . Here, when the revolution per second of the motor exceeds the resonance frequency of a set, the ball  61  contacted to the inner cylindrical surface of an outer wall  60   a  of the turntable  60  moves to the opposite direction of eccentricity and stops at the location at which the eccentricity of the rotating body is compensated owing to centrifugal force caused by rotation of the rotating body and frictional force at a contact surface of the balls so that vibration is reduced. 
         [0006]    Since centrifugal force depends on the revolution of the rotating body, vibration reduction of the spindle motor is controlled according to the frictional force of the contacted frictional surface between the balls. In other words, if a frictional force is weak, vibration reduction is excellent and stabilization revolution of a spindle motor is achieved at a high revolution. On the contrary, if a frictional force is strong, vibration reduction is reduced and stabilization revolution of a spindle motor is achieved at a low revolution. 
         [0007]    On the other hand, it is not desired that the balls  61  move continuously even in normal operation state of the spindle motor since if a frictional force of the contact surface between the balls  61  is weak, the stabilization revolution gets high. For example, in the case of an audio compact disk, the spindle motor should operate at 3,700 rpm in a normal state. However, if a friction force is weak and a stabilization revolution approaches to or exceeds 3,700 rpm, the spindle motor does not operate stably since the balls fluctuate. 
         [0008]    For this problem, the roughness is enhanced in the related art in order to enhance the frictional force. However, in case that a T-bush, a clamp plate, a turntable and a ball contacting surface are integrated as an integral turntable, an inner cylindrical surface of an outer wall  60   a  as a contacting surface of ball  61  is difficult to form to have a proper roughness in its manufacturing procedure. Even though it has a proper roughness, it is practically difficult to make a satisfactorily reliable roughness in its manufacturing procedure to obtain a proper stable revolution. Even if all products are produced in the same condition, the products are different from each other in their roughness. Accordingly, since their stabilization revolutions are possibly set to be differently, it is very difficult to adjust frictional force by making roughness in manufacturing spindle motors employing integral turntables. 
       SUMMARY 
       [0009]    Accordingly, the present invention is directed to a spindle motor that substantially obviates one or more of the problems due to limitations and disadvantages of the related art. 
         [0010]    An object of the present invention is to provide a spindle motor to obtain both of vibration reduction capability and stabilization revolution by forming the surface contacting balls slant with respect to centrifugal force in order to increase frictional force of a ball&#39;s frictional surface contacting another ball. 
         [0011]    Additional features and advantages of the invention will be set forth in the description which follows, and in part will be apparent from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and claims thereof as well as the appended drawings. 
         [0012]    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 including: a bearing housing having an inner cylindrical surface of which a bearing is forcedly inserted into; a rotation shaft having an upper portion of which is exposed to an upper portion of the bearing housing and a lower portion of which is supported by the bearing; a core installed on an outer side of the bearing housing and wound by a coil; a rotor yoke surrounding the core and coupled with a vertical center portion of the rotor axis; a magnet adhered to an inner cylindrical surface of the rotor yoke to be opposed to the core; and an integral turntable including: a forcibly inserting unit inserted forcibly into the upper portion of the rotation shaft, a table unit extending to the outer side of the forcibly inserting unit and allowing a rotating body to be installed thereon, an inner side wall and an outer side wall extending downwards perpendicular to a direction of a centrifugal force of the table unit at a lower surface of the table unit and spaced from each other to allow a ball to be inserted therebetween, and a ball cover coupled with the lower surface of the inner side wall and the outer side wall, an inner cylindrical surface of the outer side wall being slant as it travels downwards. 
         [0013]    In another aspect of the present invention, a spindle motor includes: an integral turntable including: a table on which a rotating body to be installed, and an inner side wall and an outer side wall formed to be recessed upwards at a portion therebetween on a lower surface of the table so that a predetermined hollow is formed, a surface of thereof being formed slant; a ball cover for covering a ball inserted into the hollow; a rotation shaft having an upper portion of which is inserted into a center of the integral turntable; a bearing supporting a lower portion of the rotation shaft; a coil formed on an outside of the rotation shaft; and a magnet formed on an outside of the coil. 
         [0014]    As the present invention, the frictional surface of a ball is formed so that the manufacturing steps are simplified and further the reliability of products is enhanced. It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0015]    The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the description serve to explain the principles of the invention. 
           [0016]      FIG. 1  is a cross sectional view of a spindle motor having one body turntable; 
           [0017]      FIG. 2  is a cross-sectional view of a spindle motor according to the first embodiment of the present invention; 
           [0018]      FIG. 3  is a magnified view of “A” of  FIG. 2 ; 
           [0019]      FIG. 4  is a cross-sectional view of main portion of a spindle motor according to the second embodiment of the present invention; 
           [0020]      FIG. 5  is a cross-sectional view of main portion of a spindle motor according to the third embodiment of the present invention; and 
           [0021]      FIG. 6  is a cross-sectional view of main portion of a spindle motor according to the fourth embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0022]    Reference will now be made in detail to the spindle motor according to the preferred embodiments of the present invention, examples of which are illustrated in the accompanying drawings. 
         [0023]      FIG. 2  is a cross-sectional view of a spindle motor according to the first embodiment of the present invention. 
         [0024]    Referring to  FIG. 2 , a spindle motor  100  comprises a bearing housing  110  which has an opening on an upper surface, a plate  80  coupled with a lower portion of the bearing housing  110 , and a bearing  115  forcibly inserted into a contracting surface of the bearing housing  110  and a rotation shaft  120 . A cogging unit  111  is installed on an outer cylindrical surface of the lower portion of the bearing housing  110  to fix the bearing housing  110  to the plate  80 . A bearing  115  supports the lower portion of the rotation shaft  120  and the upper portion of the rotation shaft  120  is exposed to the upper portion of the bearing housing  110 . A core  135  wound by a coil  130  is coupled with an outer cylindrical surface of the bearing housing  110 . A rotor yoke  140  having a lower surface of which is opened is coupled with a center portion of a rotation shaft  120 . The rotor yoke  140  is installed to surround the core  135 . A magnet  145  opposed to the core  135  is further installed on an inner cylindrical surface of the rotor yoke  140 . An integral turntable  150  is forcibly inserted into an upper portion of the rotation shaft  120 . 
         [0025]    In detail, an integral turntable includes a forcibly inserting unit  151  inserted forcibly into the rotation shaft  120  and in a plate shape, a table  153  extending to the outer side of the outer cylinder of the forcibly inserting unit  151  and in a plate shape, an outer side wall  155  and an inner side  157  wall recessed upward at a lower surface  153   a  of the table  153  and in a ring shape, and a ball cover  159  coupled with the lower surface of the outer side wall  155  and the inner side wall  157 . A clamp (not shown in  FIG. 2 ) is contacted going up and down on an upper surface of the forcibly inserting unit  151 . A disk  170  is further installed on an upper surface of the table  153 . The clamp is contacted with the upper surface  151   a  of the forcibly inserting unit  151  and the disk  170  to prevent the disk from shifting. The center portion of the forcibly inserting unit  151  is formed to be a hollow portion in order to minimize the weight of the integral turntable  150 . 
         [0026]    On the other hand, the outer side wall  155  extends from the lower surface of a peripheral side of the table  153  to an upper side of the table  153 . The inner side wall  157  is spaced from the outer side wall  155  with a predetermined distance and recessed upwards at the lower surface of the table  153 . Here, the inner side wall  157  is formed perpendicular to a direction of a centrifugal force. A ball cover  159  is coupled with the lower surface of the outer side wall  155  and the inner side wall  157  to form a predetermined space for a ball  160  between the outer side wall  155  and the inner side wall  157 . The ball  160  to reduce vibration is placed at the space formed by the outer side wall  155 , the inner side wall  157  and the ball cover  159 . The references  181 ,  183 ,  190  and  191  not described depict a support plate, a washer, a circuit board and a sensor, respectively. 
         [0027]    Specifically, in the spindle motor  100  according to the present invention, the inner cylindrical surface  155   a  of the outer side wall  155  is slant so as to increase a frictional force of the ball  160  and the integral turntable  150 . More detailed describing, the inner cylindrical surface  155   a  of the outer side wall  155  is slant outwards as it travels downwards. The inclination of the outer side wall  155  and the inner side wall  157  will be described separately and the description will be the same. 
         [0028]      FIG. 3  is a magnified view of “A” of  FIG. 2 . Referring to  FIG. 3 , when a current is applied to the coil  130 , the rotor yoke  140  is rotated by the interaction of the core  135  and the magnet  145 . Similarly, the rotation shaft coupled with the rotor yoke  140  and the integral turntable  150  are also rotated. Here, the ball  160  is moved in the direction to contact the inner cylindrical surface  155   a  of the outer side wall  155  by a centrifugal force as depicted by dotted line in  FIG. 3 . When the revolution of the spindle motor  100  exceeds a resonance frequency of a rotating body, the ball  160  contacted with the inner cylindrical surface  155   a  of the outer side wall  155  is moved in the direction opposite to that of the eccentricity of the rotating body and reduces a vibration of the rotating body so as to suppress vibration caused by the eccentricity of the integral turntable and the disk  170  mounted on the integral turntable. 
         [0029]    On the other hand, in the moving of the ball  160 , since the inner cylindrical surface  155   a  of the outer side wall  155  is slant outwards as it travels downwards, the ball  160  is contacted with the ball cover  159  as well as the inner cylindrical surface  155   a  of the outer side wall  155  due to the force of the ball  160  going down along with the inner cylindrical surface  155   a  of the outer side wall  155  so that two strong frictional forces are generated. Therefore, since the frictional force increases more properly compared to the case of an outer side  155  of vertical shape in the related art, the vibration reduction capability may be decreased but the stabilization revolution can be reduced. As a result, a proper frictional force can be generated according to a rotation state and concrete application conditions of a rotating body. 
         [0030]    It is desired that the angle A between the inner cylindrical surface  155   a  of the outer side wall and a lower surface of the table  153  according to the first embodiment of the present invention is made to be 93 to 110 degrees when a general optical disk is employed. In other words, the inner cylindrical surface  155   a  of the outer side wall  155  is slant from a virtual vertical line perpendicular to the lower surface of the table by 3 to 20 degrees A′. This value is suggested by a number of experiments and the choice of this value is not the simple choice of a value. However, in case that the application of the spindle motors is changed or the weight of the ball of the spindle motor is changed, different value can be suggested. Due to such a way mentioned above, even when an integral turntable is employed, the stabilization revolution of the spindle motor is can be controlled conveniently. In addition, the reliability of products is further enhanced in comparison with the way of controlling the roughness of the frictional surface contacting a ball in the related art, by applying a proper frictional force in two directions such as a frictional force on the ball and the number of a frictional surface contacting the ball. According to the experiments, in comparison with the way of enhancing the roughness in the related art, a process capability index Cpk is enhanced from 0.71 to 1.57 in vibration and from 2.86 to 3.74 in revolution. 
       Second Embodiment 
       [0031]      FIG. 4  is a cross-sectional view of main portion of a spindle motor according to the second embodiment of the present invention. Simply the difference from the first embodiment will be described. The spindle motor according to the second embodiment has an inner cylindrical surface  255   a  of the outer side wall  255  of the integral turntable  250  that is slant inwards as it travels downwards. In this case, when a spindle motor  200  is operated, a frictional force is increased since a ball  160  is contacted with the inner cylindrical surface  255   a  of the outer side wall  255  and an inner cylindrical surface  253   a  of the table  253 . In other words, due to the operation of the spindle motor  200 , the position of the ball  160  depicted by a solid line is shifted to the position depicted by a dotted line. Due to such a moving of the ball  160 , the ball is moved upwards along with the inner cylindrical surface  255   a  of the outer side wall  255  and contacted with the lower surface  253   a  of the table  253  as well as the inner cylindrical surface  255   a  of the outer side wall  255  with a strong force. The angle B between the inner cylindrical surface  255   a  of the outer side wall  255  according to the second embodiment of the present invention and a ball cover  259  is made to be 93 to 110 degrees. In other words, the angle B′ between the inner cylindrical surface  255   a  of the outer side wall  255  and a virtual vertical line perpendicular to the upper surface of the ball cover  259  is made to be 3 to 20 degrees. 
       Third Embodiment 
       [0032]      FIG. 5  is a cross-sectional view of main portion of a spindle motor according to the third embodiment of the present invention. Simply the difference from the first embodiment will be described. The spindle motor  300  according to the third embodiment has an inner cylindrical surface  355   a  of the outer side wall  355  of the integral turntable  350  that is slant outwards as it travels downwards and an inner cylindrical surface  355   a  of the outer side wall  355  and an inner cylindrical surface  357   a  of the inner side wall  357  that is slant inwards as it travels downwards. On the other hand, this embodiment of the present invention can be applied desirably when a spindle motor is made vertically and operated. The operation of this embodiment will be described. When the spindle motor  300  is operated, the force is generated to fell the ball  160  to the inner side wall  357  due to attraction of gravity because of a forming direction of the spindle motor  300  as well as the force that pushes the ball  160  to the outer side wall  355  caused by centrifugal force. Here, as depicted by a dotted line in  FIG. 5 , the ball  160  can be contacted with the ball cover  359  on the side of the inner cylindrical surface  357   a  of the inner side wall  357  due to attraction of gravity as well as with the inner cylindrical surface  355   a  of the outer side wall  355 . Here, the inner side wall  357  is formed to be slant and the ball is contacted with inner cylindrical surface  357   a  of the inner side wall and also the ball cover  359  so that the stabilization revolution can be controlled by increasing the frictional force. The angle C between the inner cylindrical surface of the inner side wall  357  according to the third embodiment of the present invention and a lower surface of the table  353  is made to be 93 to 110 degrees. In other words, the angle C′ between the inner cylindrical surface  357   a  of the inner side wall  357  and a virtual vertical line perpendicular to the lower surface of the turntable is made to be 3 to 20 degrees. 
       Fourth Embodiment 
       [0033]      FIG. 6  is a cross-sectional view of main portion of a spindle motor according to the fourth embodiment of the present invention. Simply the difference from the first embodiment will be described since many portions are similar to those of the first embodiment. In the present embodiment, the spindle motor is formed vertically so that this embodiment is applied when attraction of gravity affects on the ball  160  moving. The spindle motor  400  has an inner cylindrical surface  457   a  of the inner side wall  457  of the integral turntable  450  that is slant outwards as it travels downwards. In the present embodiment, when a ball  160  is moved downwards by attraction of gravity, the ball  160  is contacted with the inner cylindrical surface  457   a  of the outer side wall  457  and the lower surface  453   a  of the table  453 . In other words, the ball  160  is moved upwards along with the inner cylindrical surface  457   a  of the outer side wall  457 . Owing to such a structure, the contacting surfaces of the ball  160  or two frictional surfaces are formed so that the frictional force of the contacting surfaces of balls can be controlled. The angle D between the inner cylindrical surface  457   a  of the inner side wall  457  according to the fourth embodiment of the present invention and a upper surface of the ball cover  459  is made to be 93 to 110 degrees. In other words, the angle D′ between the inner cylindrical surface  457   a  of the inner side wall  457  and a virtual vertical line perpendicular to the upper surface of the ball cover  459  is made to be 3 to 20 degrees. 
         [0034]    The inner cylindrical surfaces  355   a  and  455   a  of the outer side walls  355  and  455  of the integral turntables  350  and  450  according to the third and fourth embodiment is formed to be slant inwards as they travel downwards as those of the first embodiment so that the frictional force is increased. 
         [0035]    The embodiment as described above provides the method of controlling a frictional force by forming racer surface contacted with one side and/or both sides of a ball to be slant. The people skilled in the art can easily suggest the other embodiments besides the embodiment suggested above. 
       INDUSTRIAL APPLICABILITY 
       [0036]    As described above, the spindle motor according to the present invention has increased frictional force since a ball is strongly contacted with many portions of the integral turntable, especially, contacting surface with which balls are contacted with each other. Therefore, the spindle motor of the present invention satisfies properly both of the desired vibration reduction capability and the desired stabilization revolution in comparison with the spindle motors in the related art. 
         [0037]    Specifically, it can more easily generate the frictional force to stop a ball even at the revolution proper to rotation of an optical disk. And also, the spindle motor of the present invention employs an integral turntable and can easily control the frictional force of the balls. Specifically, in the present invention, the reliability of revolution reduction and stabilization revolution is further improved in comparison with the conventional method of controlling the roughness so that all the products produced by one manufacturing procedure have the same performance reliably. 
         [0038]    While the present invention has been described and illustrated herein with reference to the preferred embodiments thereof, it will be apparent to those skilled in the art that various modifications and variations can be made therein without departing from the spirit and scope of the invention. Thus, it is intended that the present invention covers the modifications and variations of this invention that come within the scope of the appended claims and their equivalents.