Abstract:
An apparatus for manufacturing a disc drive comprises an adjusting element, put in contact with a disc table engaged with a rotational shaft of a drive motor via an engaging portion, for varying an inclination of the disc table which is swingable with a point of support at the engaging portion, a non-contact displacement measuring unit for detecting, the inclination of the disc table varied by the adjusting element, control unit for receiving a detection signal from the non-contact displacement measuring unit and stopping rotation of the drive motor when the inclination of the disc table has decreased to a predetermined value or less, and an adhesive supply unit for fixing the disc table to the rotational shaft of the drive motor which has been stopped by the control unit.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
         [0001]    This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 11-353171, filed Dec. 13, 1999, the entire contents of which are incorporated herein by reference.  
         BACKGROUND OF THE INVENTION  
         [0002]    The present invention relates to a method of manufacturing a disc drive such as a DVD drive, to an apparatus for manufacturing the optical disc drive, and to the optical disc drive.  
           [0003]    [0003]FIG. 5 shows a conventional optical disc drive such as a DVD drive. A disc table  2  is fitted on a rotational shaft  1   a  of a spindle motor  1  serving as a drive motor. An optical disc  3  such as a DVD disc is supported on the disc table  2  and rotated.  
           [0004]    An important requirement for the optical disc drive is the “surface precision” of a disc mounting surface  2   a  of the disc table  2  relative to an axis S of the spindle motor rotational shaft  1   a  (i.e. the precision of the level of the disc mounting surface relative to the rotational shaft while the surface is being rotated). If there occurs even a slight surface run-out of the disc table  2  (i.e. “wobbling” of the table  2 ) while the rotational shaft  1   a  is being rotated, the surface of the optical disc  3  will similarly wobble, resulting in defective information reproduction or recording.  
           [0005]    In particular, in a DVD drive which requires high rotational precision, a brushless motor is used as the spindle motor  1 . In order to enhance the surface precision of the disc table  2 , the run-out of the disc mounting surface  2   a  of the disc table  2  is detected after the DVD drive is assembled as shown in FIG. 5. Then, the disc table  2  is removed from the rotational shaft  1   a  of the spindle motor  1 , and the disc mounting surface  2   a  of the disc table  2  is machined to reduce the run-out.  
           [0006]    Specifically, half-blanking is carried out to form three projecting portions from the back side of the disc mounting surface  2   a  of disc table  2 . The three projections are disposed equidistantly in a circle defined at the same radial distance on the back surface of the disc mounting surface  2   a.  A plane defined by the three points of these projecting portions is adjusted so as to become perpendicular to the axis S of the rotational shaft  1   a.    
           [0007]    [0007]FIG. 6 shows a CD drive which requires less mechanical rotational precision than the DVD drive. Thus, a general-purpose brushed motor (a motor with a brush), etc. can be used as a spindle motor  1 A and the manufacturing cost can be reduced accordingly.  
           [0008]    That surface of the spindle motor  1 A, from which a rotational shaft  1   a  projects, is placed on a chassis  4  and fixed by attachment screws  5 . A disc table  2   a  is fitted on the rotational shaft  1   a  by means of press-fitting, etc.  
           [0009]    In this CD drive, as shown in FIG. 7, in order to eliminate the surface run-out, a cutting process is performed to make a disc mounting surface  2   a  of disc table  2 A perpendicular to the axis S of the rotational shaft  1   a  in the state in which the disc table  2 A is fitted on the rotational shaft  1   a  that has been removed from the spindle motor  1 A. Thereafter, the rotational shaft  1   a  with the disc table  2 A is assembled into the spindle motor  1 A.  
           [0010]    In the case of the DVD drive shown in FIG. 5, however, the manufacturing cost increases because the run-out of the disc mounting surface  2   a  is measured once the DVD drive has been assembled, following which the DVD drive is disassembled, the disc table  2  is machined and the drive is assembled once again. Furthermore, since the expensive brushless motor is used as spindle motor  1 , the manufacturing cost increases.  
           [0011]    On the other hand, in the case of the CD drive shown in FIG. 6, when a commercially available optical disc with low precision of the center of gravity is mounted and rotated, even if a high-prevision brushed motor is used, the rotational shaft  1   a  is rotated with an elastic deformation caused by centrifugal force due to mass eccentricity of the optical disc. As a result, the precision in rotation deteriorates and satisfactory reproduction/recording cannot be performed.  
         BRIEF SUMMARY OF THE INVENTION  
         [0012]    A first object of the present invention is to provide a disc drive, such as a DVD drive requiring high rotational precision, which is realized with a simple, inexpensive structure like a CD drive.  
           [0013]    According to an aspect of the invention, there is provided an apparatus for manufacturing a disc drive, the apparatus comprising: urging means, put in contact with a disc table engaged with a rotational shaft of a drive motor via an engaging portion, for varying an inclination of the disc table which is swingable with a point of support at the engaging portion; detection means for detecting, in a non-contact state, the inclination of the disc table varied by the urging means; control means for receiving a detection signal from the detection means and stopping rotation of the drive motor when the inclination of the disc table has decreased to a predetermined value or less; and fixing means for fixing the disc table to the rotational shaft of the drive motor which has been stopped by the control means.  
           [0014]    According to the present invention, even in a case of a disc drive requiring high rotational precision, a disc table can be fixed to a rotational shaft of a spindle motor while the position of the disc table is being adjusted. Therefore, a mechanism with a simple, inexpensive structure can be obtained.  
           [0015]    A second object of the invention is to provide an optical disc drive wherein, even when an optical disc such as a disc with mass eccentricity, which may deteriorate precision in rotation, is to be driven, run-out of the disc table can be exactly limited and high rotational precision is maintained, and therefore the reliability in information reproduction/recording can be enhanced.  
           [0016]    According to another aspect of the invention, there is provided an optical disc drive comprising: a drive motor; a disc table for mounting of an optical disc, the disc table being fixed to a rotational shaft of the drive motor; reproducing/recording means for effecting information reproduction/recording by radiating a laser beam to the optical disc; a chassis fixed to a rotational shaft projection surface of the drive motor; and a bearing member, provided on the chassis, for supporting the rotational shaft of the drive motor, which is located near the disc table.  
           [0017]    According to the invention, the rotational shaft is supported at two points within the motor body and it is also supported at a third point by the bearing member. Therefore, the occurrence of centrifugal force due to mass eccentricity of the disc can be prevented.  
           [0018]    Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.  
       
    
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING  
       [0019]    The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate presently preferred embodiments of the invention, and together with the general description given above and the detailed description of the preferred embodiments given below, serve to explain the principles of the invention.  
         [0020]    [0020]FIG. 1 shows a schematic structure of a disc table attachment/adjustment apparatus according to an embodiment of the present invention;  
         [0021]    [0021]FIG. 2 illustrates an engaging portion of a disc table in the embodiment;  
         [0022]    [0022]FIG. 3 is a cross-sectional view of a main part of a disc drive according to the embodiment;  
         [0023]    [0023]FIG. 4 is an exploded, perspective view showing the main part of the disc drive according to the embodiment;  
         [0024]    [0024]FIG. 5 is a cross-sectional view of a main part of a conventional disc drive;  
         [0025]    [0025]FIG. 6 is a cross-sectional view of a main part of another conventional disc drive; and  
         [0026]    [0026]FIG. 7 illustrates a step of increasing the surface precision of the disc table.  
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0027]    [0027]FIG. 1 shows a schematic structure of a disc table attachment/adjustment apparatus according to an embodiment of the present invention. This apparatus operates to attach a disc table  11  constituting a part of a disc drive to a rotational shaft  10   a  of a drive motor  10 , and to keep high surface precision of a disc mounting surface  11   a  of the disc table  11  relative to an axis S of the motor rotational shaft  10   a.    
         [0028]    A spindle motor constituting the drive motor  10  of the disc drive is a general-purpose brushed motor. The disc table  11  is fixed to the rotational shaft  10   a,  as will be described later.  
         [0029]    As is shown in FIG. 2, the disc table  11  has an engaging portion  12 . The engaging portion  12  is engaged with the rotational shaft  10   a  of spindle motor  10 . The engaging portion  12  comprises a hole portion formed at a center area of the disc table  11 . The engaging portion  12  is fitted on the rotational shaft  10   a  in a “light press-fitting state.” In the “light press-fitting state” in this context, the position of the engaging portion  12  relative to the rotational shaft  10   a  is varied only when an external force of a predetermined level or more is applied. In other words, this position of the engaging portion  12  is maintained in normal cases, while the angle of the disc mounting surface  11   a  to the axis S of the rotational shaft  10   a  is variable.  
         [0030]    The spindle motor  10  is connected to a circuit  14  including a power supply unit  13  for supplying power to the spindle motor  10 . The circuit  14  also includes a variable resistor  15  for controlling the number of revolutions of the spindle motor  10 .  
         [0031]    An adjusting element  16  holding a roller such as a cam follower is disposed in contact with an outer peripheral portion of the disc table  11 , which is fitted on the rotational shaft  10   a  of spindle motor  10  by means of light press-fitting. The adjusting element  16  is supported by a bracket  17 . The adjusting element  16  constitutes urging means which is slightly moved by a moving mechanism  30  in a thrust direction (indicated by a double-headed arrow T).  
         [0032]    On the other hand, a non-contact displacement measuring unit  18  is disposed near the disc table  11 . The non-contact displacement measuring unit  18  constitutes detection means for emitting a laser beam onto the disc mounting surface  11   a  of disc table  11  and receiving the reflection beam therefrom, thereby measuring the precision relating to run-out of the disc mounting surface  11   a  in a non-contact state.  
         [0033]    In addition, an adhesive supply unit  19  constituting fixing means is disposed near the disc table  11 . The adhesive supply unit  19  has a dispenser  19   a  for applying a proper amount of adhesive. The dispenser  19   a  has a supply port directed to a point between the engaging portion  12  of disc table  11  and the motor rotational shaft  10   a.    
         [0034]    A control unit  40  constituting control means is connected to the power supply unit  13 , the variable resistor  15 , the moving mechanism  30  supporting adjustment element  16 , the non-contact displacement measuring unit  18  and the adhesive supply unit  19 . The control unit  40  provides necessary controls to these elements. Specifically, the control unit  40  is an adjusting unit functioning when the disc table  11  is to be attached to the rotational shaft  10   a.  The control unit  40  performs adjustments not only for fixing the disc table  11  to the rotational shaft  10   a  but also for maintaining the precision in run-out of the disc mounting surface  11   a  of the disc table  11  relative to the axis S of the rotational shaft  10   a.    
         [0035]    More specifically, the spindle motor  10  is rotated at very low speed and the adjusting element  16  is moved in the direction T and brought into contact with the outer periphery of the disc table  11 . Then, the adjusting element  16  is further moved by a slight amount.  
         [0036]    The non-contact displacement measuring unit  19  always detects the precision in run-out, or displacement, of the disc mounting surface  11   a  of disc table  11  and feeds the displacement data to the control unit  40 . The control unit  40  controls the movement of the adjusting element  16  so that the displacement represented by the displacement data may decrease to a minimum.  
         [0037]    When the displacement, or run-out, of the disc table  11  has decreased to a minimum, the control unit  40  stops the rotation of the spindle motor  10 . In fact, the adjusting element  16  is unable to effect positioning with a predetermined resolution or less. Thus, a specific displacement value may be set in advance, and if the measured value decreases below the specific displacement value, the spindle motor  10  may be stopped even if the measured value is not a minimum value.  
         [0038]    After the rotation of the spindle motor  10  has completely stopped, the adhesive supply unit  19  is driven to apply adhesive through the dispenser  19   a.  Thus, the disc table  11  is fixed to the rotational shaft  10   a.  Where the adhesive is of ultraviolet-setting type, ultraviolet is radiated for fixation.  
         [0039]    In this way, the disc table  11  is inclinably fitted on the spindle motor rotational shaft  10   a.  Then, the spindle motor  10  is driven to rotate the disc table  11 , while the disc table  11  is being slightly urged. When the displacement data has indicated a minimum value, the spindle motor  10  is stopped and the disc table  11  is fixed to the rotational shaft  10   a.  Thus, time-consuming, complex machining is not needed for the disc table  11 , and high rotational precision is obtained by a relatively simple structure and work.  
         [0040]    In this type of brushed motor, a distance between a rotational shaft projection surface  10   b  of the motor and the disc mounting surface  11   a  of disc table  11  is standardized. The axial length of the rotational shaft  10   a  is greater than that of the spindle motor  10  itself. The disc table  11  is attached to a distal end portion of the rotational shaft  10   a.    
         [0041]    At a glance, the rotational shaft  10   a  has a considerably “long neck” shape. Even where a high-precision brushed motor is used, if a commercially available disc with low precision of the center of gravity is mounted and rotated, the rotational shaft  10   a  is rotated with an elastic deformation caused by centrifugal force due to mass eccentricity of the disc.  
         [0042]    In other words, even if the disc table  11  is precisely fixed to the rotational shaft  10   a  using the above-described disc table attachment/adjustment apparatus, if the rotational shaft  10   a  rotates with an elastic deformation in actual use, run-out will occur with respect to the disc mounting surface  11   a  of disc table  11 .  
         [0043]    To solve this problem, as shown in FIG. 3, the rotational shaft projection surface  10   b  of spindle motor  10  is fixed to a chassis  20 , and the chassis  20  is provided with a bearing member  21  to support the rotational shaft  10   a.    
         [0044]    The bearing member  21  has such a length as to span the distance between the upper surface of the chassis  20  and the lower surface of the disc table  11 . An actual bearing portion  21   a  for the rotational shaft  10   a  is provided at a distal end portion of the bearing member  21 , which is located near the disc table  11 . In FIG. 3, reference numeral  50  denotes a light pickup unit  50  for radiating a laser beam L to the disc  3  to effect information reproduction/recording.  
         [0045]    [0045]FIG. 4 shows structural elements of a centering mechanism for centering when the disc  3  is to be mounted on the disc table  11 . The centering mechanism comprises a centering spring  22 , a center ring  23  and a clamp magnet  24 .  
         [0046]    In ordinary drive motors including the above-described spindle motor  10 , the rotational shaft is supported at two points within the motor body. A third support point, however, is provided by the above-described bearing member  21 . Accordingly, even where the commercially available disc with low precision of the center of gravity is mounted on the disc table  11  and rotated, it is possible to prevent the occurrence of centrifugal force due to mass eccentricity of the disc. Therefore, no elastic deformation of the rotational shaft  10   a  occurs, run-out of the disc table  11  is prevented, and high rotational precision is maintained.  
         [0047]    Needless to say, the present invention is not limited to the above-described embodiment, and various modifications can be made without departing from the spirit of the invention.  
         [0048]    Additional advantages and modifications will readily occur to those skilled in the art. Therefore, the invention in its broader aspects is not limited to the specific details and representative embodiments shown and described herein. Accordingly, various modifications may be made without departing from the spirit or scope of the general inventive concept as defined by the appended claims and their equivalents.