Abstract:
An easy-to-manufacture spindle motor has an aligning mechanism whose precision is equal to that of cutting of metallic materials without entailing an extra cost. The aligning mechanism is in contact with the center hole of a disk-shaped recording medium and comprises a turntable and an aligning member that has a sliding portion which can be slidably fitted into a guide portion disposed on the turntable. At least one of respective sliding faces of the guide portion disposed on the turntable and the aligning member is configured of a metallic component, and parts other than the metallic component or components of the turntable and/or aligning member are configured of resin materials.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to a spindle motor having an aligning mechanism for disk-shaped recording media including, for instance, minidisks (MDs), CDs and DVDs, and an information recording/reproducing apparatus mounted with such a spindle motor. 
   2. Related Background Art 
   Conventionally, alignment of an optical disk-shaped recording medium with the rotation shaft of an information recording/reproducing apparatus is accomplished with an aligning member provided on a spindle motor for turning the optical disk-shaped recording medium. To illustrate it in more specific terms, a spindle motor mounted on a disk drive for MDs or the like is shown in  FIG. 5 . Incidentally, this example of conventional aligning structure is substantially the same as an aligning structure of the invention disclosed in the Japanese Patent Application Laid-Open No. 2003-36585. 
   A spindle motor  30  is configured of a stator unit  31  disposed stationarily and a rotor unit  32  supported to be turnable relative to the stator unit  31 . 
   The stator unit  31  comprises a stator board  33 , a housing  34  fitted to the stator board  33 , wound coils  35  stationarily disposed to surround the housing  34  from outside, and a plain bearing  36  held within the housing  34  by pressure fitting or otherwise. On the other hand, the rotor unit  32  comprises a rotation shaft  8  turnably held by the plain bearing  36 , a turntable  5  fitted to this rotation shaft  8 , a cylindrical rotor yoke  9  with an open lower end fitted to this turntable  5  and surrounding the wound coils  35  from outside, a rotor magnet  10  provided within this rotor yoke  9 , an attracting magnet  41  disposed on the upper face of the turntable  5 , an aligning member  3  slidably fitted into a turntable cylinder portion  6 , a restrictive member  43  for restricting the upward movement of the aligning member  3 , and a force-applying member  44  for applying an upward force to the aligning member  3  relative to the turntable  5 . 
   Further a disk  1  having an attractable plate  46  over the center hole is mounted on the turntable  5  and, by attracting the attractable plate  46  with the magnetic attraction of the attracting magnet  41  of the rotor unit  32 , the disk  1  is mounted on the turntable  5 . In this mounting process, the center hole lower end  2  of the disk  1  comes into contact with a tapered face  4 , which is the contact portion of the aligning member  3 , the aligning member  3  is pressed downward against the force of the force-applying member  44 , and the disk  1 , aligned to be substantially coaxial with the rotation shaft  8 , is mounted on the turntable  5 . Incidentally, the force-applying member  44  is disposed to compensate for any tolerance fluctuation of the center hole bore of the disk  1 . In other words, the fixation of the aligning member  3  makes impossible compliance with tolerance fluctuations of the center hole bore of the disk  1 . When the center hole bore is at its minimum, the disk  1  cannot be mounted on the turntable  5 , or when the center hole bore is at its maximum, the backlash from the aligning member  3  increases, making alignment impossible. Additional in this conventional arrangement, the force-applying member  44  uses a compressive coils spring having a round section to prevent the coils from being deformed by compression. 
   The conventional spindle motor  30  is configured as described above, wherein the rotor unit  32  is rotationally driven by a magnetic field generated on the wound coils  35  by appropriately supplying electricity to the wound coils  35 , and the rotor magnet  10  of the rotor unit  32  and the magnetic field derived from the rotor yoke  9  act on each other. In synchronism with the rotation of the rotor unit  32 , the disk  1  mounted on the turntable  5  is enabled to turn without slipping by the attractive force of the attracting magnet  41 . 
   When information is to be recorded onto or reproduced out of the disk-shaped recording medium (hereinafter referred to as simply “disk”), it is necessary to accurately align the track position on the disk and the position of the pickup for recording/reproducing information. Especially if the disk becomes eccentric, the track position will vary in the radial direction of the disk in each turn of the disk correspondingly to the extent of eccentricity. For instance where a CD is played back, pit signals of 1.6 μm in pitch are accurately traced to detect the recorded signals. To accurately align this pickup position, alignment in the radial direction of the disk is accomplished according to the prior art by tracking servo, for instance. 
   However, in recent information recording/reproducing apparatuses, the disk is turned increasingly faster along with the narrowing of the track pitch and the rise of the transfer rate to meet the need of increased density of information. As a result, the alignment of tracking servo is required to be more accurate and faster. However, it is evidently difficult to achieve more accurate and faster control while maintaining the operating range of tracking servo as it is, and the range tends to be narrowed, making it indispensable to reduce eccentricity. 
   For this reason, the currently used method is, as described above, to configure an aligning member having a tapered face, which fits with the guide portion of a turntable to be mounted with a disk and comes into contact with the center hole of the disk to be slidable in the direction of the rotation axis of the turntable, and thereby to absorb any tolerance fluctuation of the center hole of the disk to achieve highly precise alignment. However, this involves a problem that the play needed for this sliding causes the aligning member to incline and accordingly to vary the angle of the taper face, inviting eccentricity at the time of mounting the disk. This problem is usually addressed by fabricating the turntable and the aligning member together constituting the play for sliding from metallic materials which permit precision machining so as to minimize the play for sliding. However, by reason of the limitation of machining accuracy, it is also necessary to allow for a tolerance fluctuation of 5 to 10 μm to the diameter of the guide portion disposed on the turntable and the sliding portion of the aligning member, which together constitute the play for sliding. Therefore, even if the tolerance fluctuation due to the combination of the guide portion and the sliding portion is minimized to 0 μm (though sliding is virtually impossible with a play of 0 μm between the sliding portions), the play can be as large as 20 μm at the maximum depending on the combination, which would cause the aligning member to substantially incline, resulting in increased eccentricity. For this reason, by the conventional process, even if the aligning member and the turntable are cut from metallic materials permitting precision machining, the constituent parts should go through screening by dimensional inspection to reduce the tolerance fluctuation of combinations, and this pushes up the production cost. 
   Furthermore, where the aligning member and the turntable are configured solely of metallic materials as in the conventional process, the usual shapes of the aligning member and the turntable do not permit fabrication by machining in only one direction, and the chucking directions of the aligning member and turntable under machining should be altered on the way, which would undeniably invite an increase in the number of machining steps. Moreover, the change in chucking direction makes it difficult to achieve coaxiality and therefore necessitates adjustment. Furthermore, in the small spindle motor for MD use which the prior art refers to, since both the aligning member  3  and the turntable  5  are very small and thin, their parts may be deformed by the heat in the cutting-off or lathing process, not only the machining time becomes a matter of concern but also dimensional measurement is required after completion. The aforementioned possibility of deformation reduces the yield. Obviously, steps of fastening the rotor yoke  9  and pressing the rotation shaft  8  in are necessitated. 
   Or if injection molding is used to reduce the production cost, it will be difficult to keep the precision of component parts equal to that of cutting of metallic materials, and this would adversely affect the alignment performance. Problems will also arise in the lubrication and durability of sliding portions. 
   SUMMARY OF THE INVENTION 
   An object of the present invention is to provide an easy-to-manufacture spindle motor having an aligning mechanism whose precision is equal to that of cutting of metallic materials without entailing an extra cost, and an information recording/reproducing apparatus mounted with such a spindle motor. 
   A spindle motor according to the invention has the following configuration. 
   It comprises a stator unit at least comprising a stationarily disposed stator board, a bearing fitted over the stator board, and wound coils arranged around the bearing; and a rotor unit at least comprising a rotation shaft turnably supported by the bearing, a turntable integrally fastened to the rotation shaft and to be mounted with the disk-shaped recording medium, a rotor magnet fastened to the turntable to be opposite the wound coils, and an aligning member which has a contact portion to be in contact with the center hole of the disk-shaped recording medium and can slide against a guide portion of the turntable, wherein at least one of the respective sliding faces of the guide portion of the turntable and the aligning member is configured of a metallic component, and other parts than the metallic component or components of the turntable and/or aligning member are configured of resin materials. 
   An information recording/reproducing apparatus according to the invention has a configuration containing the spindle motor described above. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  shows a schematic section of a spindle motor, which is a first preferred embodiment of the present invention; 
       FIGS. 2A and 2B  schematically show the fabrication process of the aligning member shown in  FIG. 1 ; 
       FIGS. 3A and 3B  schematically show the fabrication process of the turntable shown in  FIG. 1 ; 
       FIG. 4  shows a schematic section of a spindle motor, which is a second preferred embodiment of the invention; 
       FIG. 5  shows a schematic section of a spindle motor according to the prior art; and 
       FIG. 6  schematically shows an information recording/reproducing apparatus according to the invention. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Preferred embodiments of the present invention will be described in detail below. Only essential parts of the invention are extracted and referred to by signs, of which all are not marked in the drawings. Other specific aspects of the structure are the same as in the structure according to the prior art. 
   Embodiment 1 
     FIG. 1  schematically shows a section of the structure of a first preferred embodiment of the invention. In the drawing, reference numeral  1  denotes a disk;  2 , the center hole of the disk  1 ;  3 , an aligning member;  4 , the contact portion of the aligning member  3  in contact with the center hole  2  of the disk  1 ;  5 , a turntable;  6 , a guide portion provided on the turntable  5 ;  7 , the sliding portion of the aligning member  3  fitted into the guide portion  6 ;  8 , a rotation shaft integrally fastened to the turntable  5 ;  9 , a rotor yoke integrally fastened to the turntable  5 ; and  10 , a rotor magnet provided on the rotor yoke. 
   In this embodiment, the sliding faces of both the guide portion  6  and the sliding portion  7  are formed of cylindrical metallic (e.g. stainless steel) parts of thin walls. For this reason, the lubrication and durability of sliding portions can be improved over the conventional aligning member and turntable made of resin materials alone. The tendency of resin materials to be generally greater than metallic materials in the coefficient of expansion and the resultant susceptibility to the influence of temperature changes can also be solved by the invention. Even if only either, not both, of the guide portion  6  and the sliding portion  7  is made of a metallic material, improvement over the conventional configuration can be achieved. 
   Or by forming the aligning member  3  and the turntable  5  almost wholly of resin materials, the whole device can be reduced in weight as compared with using only metal materials. This would contribute not only to reducing the weight of the device but also to alleviating the load required for turning the spindle motor, which in turn would help realize a saving in power consumption in driving the spindle motor. 
   Next, the fabrication process of the aligning member  3  is shown in  FIGS. 2A and 2B . Of the two drawings,  FIG. 2A  illustrates a first step and  FIG. 2B , a second step. The two steps will be described in detail below. First, as shown in  FIG. 2A , a cylindrical stainless steel pipe which will be fabricated into the sliding portion  7  is arranged in a mold (not shown). After that, the pipe is filled with liquid crystal polymer as a molding resin material to form the aligning member as shown in  FIG. 2B . 
   Next, the fabrication process of the turntable  5  is shown in  FIGS. 3A and 3B . Of the two drawings,  FIG. 3A  illustrates a first step and  FIG. 3B , a second step. The two steps will be described in detail below. First, as shown in  FIG. 3A , a cylindrical stainless steel pipe which will be fabricated into the guide portion  6 , the rotation shaft  8 , and the rotor yoke  9  provided with the rotor magnet  10  is arranged in a mold (not shown). After that, the pipe is filled with liquid crystal polymer as a molding resin material to form the turntable  5  as shown in  FIG. 3B . 
   As described above with reference to  FIGS. 2A ,  2 B,  3 A and  3 B, the fabrication method according to the invention uses only a very few steps for producing the components of the spindle motor. Since the guide portion  6  and the sliding portion  7  which demand a high level of precision are composed of metal pipes, it is possible to fabricate them by injection molding after grinding the surface of the pipes and machining them with high precision. In particular, the pipe shape facilitates grinding. Moreover, if the guide portion  6  and the sliding portion  7  were formed by injection molding alone, it would be difficult to control the accuracy of dimensions of the metal molds for forming the guide portion  6  and the sliding portion  7 , including their surface accuracy and circularity, and there would also arise a problem of necessity for draft. Furthermore, as stated above, sliding between resin materials leaves problems in durability and lubrication unsolved. By contrast in the structure according to the invention, as it uses metal pipes, it is easy to control the accuracy of dimensions of the guide portion  6  and the sliding portion  7  including their surface precision and circularity, and for other parts the accuracy of dimensions that the conventional injection molding can provide is sufficient. This structure is also effective for controlling with high precision the coaxiality with the rotation shaft  8  and the degree of deviation of the turntable face  5   a  where the disk  1  and the turntable  5  come into contact with each other from the rotation shaft  8 . Thus, the invention enables the accuracy of components, even though formed by injection molding, to be equal to that of cutting of metallic materials, thereby making it possible to achieve comparable alignment performance to what is attained by cutting of metallic materials. It also makes possible overcoming the problems in lubrication and durability of sliding portions which injection molding entails. 
   Further, as shown in  FIGS. 3A and 3B , the rotor yoke  9  provided with the rotor magnet  10  can also be integrally fastened. Since the part of the rotor yoke  9  where the rotor magnet  10  is disposed is also cylindrically shaped, this structure is effective for controlling the accuracy of dimensions, including surface precision and circularity, and coaxiality with the rotation shaft  8  as is the case with the guide portion  6  and the sliding portion  7  mentioned earlier. In particular, since the deviation of the rotor yoke  9  and the rotation shaft  8  from mutual coaxiality would invite fluctuations of the rotation of the rotor unit in each turn of it and thereby seriously affect the signal grade of information obtained from the disk, it has to be kept to the practicable minimum. 
   Embodiment 2 
     FIG. 4  shows a schematic section of the structure of a second preferred embodiment of the invention. This embodiment is similar to Embodiment 1 in basic structure, and therefore the description of the same parts is dispensed with. 
   This embodiment differs from Embodiment 1 in that the guide portion  6  (in  FIG. 4 , the face of the sliding portion is shown as the guide portion) and the rotation shaft  8  are integrally formed. This integration facilitates a reduction in the number of parts and formation of the guide portion  6  and the rotation shaft  8  in highly precise coaxiality. Further, as the guide portion  6  is formed on the outer circumferential part of the rotation shaft  8 , it contributes to the ease of grinding and other modes of machining as does the pipe shape in Embodiment 1. 
   Obviously, the invention is not limited to the shape shown in connection with this embodiment, but it is possible not to taper toward the turntable  5  the rotor yoke  9  illustrated in the drawing and instead configure it in a cylindrical metallic pipe shape for instance. Another conceivable way of attracting the disk to the turntable, other than the use of an attracting magnet in this embodiment, is, for example, to use meca-clamping, by which the disk is pressed from above toward the turntable with some other force-applying member. 
   Embodiment 3 
     FIG. 6  schematically illustrates the structure of an information recording/reproducing apparatus according to the invention. An information recording/reproducing apparatus  21  is configured of a chassis  22  which constitutes the structural base, a spindle motor  23  disposed on the chassis  22  to turn a disk (not shown) that is mounted like its counterpart in Embodiment 1 or Embodiment 2, an optical pickup  24 , an objective lens  25  arranged on the optical pickup  24  to radiate a light beam, a feed motor  26  which is arranged on the chassis  22  and has a lead screw  28  to move the optical pickup  24  in the radial direction of the disk, and a guide shaft  27  for supporting the optical pickup  24 . 
   The disk  1  turned by the spindle motor  23  is irradiated with a light beam from the objective lens  25  of the optical pickup  24 . The lead screw  28  formed integrally with the rotation shaft of the feed motor  26  and the optical pickup  24  are meshed with each other through racks (not shown). By converting the rotational motion of the lead screw  28  into a parallel motion, the optical pickup  24  moves in the radial direction of the disk  1 , guided by the guide shaft  27 . In this way, the information recording/reproducing apparatus  21  records or reproduces information onto or out of the disk  1 . 
   This configuration makes it possible to provide an information recording/reproducing apparatus mounted with a spindle motor having an aligning mechanism as precise as one formed by cutting metallic materials without inviting an extra cost. Also, as resin is generally less in mass than metal, the information recording/reproducing apparatus thereby provided can be lighter in weight. 
   This application claims priority from Japanese Patent Application No. 2003-350344 filed on Oct. 9, 2003, which is hereby incorporated by reference herein.