Abstract:
An aligning device for a disk recording medium capable of reducing eccentricity using a simple structure, without an increase in cost, is provided. An aligning member has a tapered portion that contacts with a center hole of a disk, and fits with a guide portion that is fixed to a turntable with a sliding gap therebetween. The sliding gap between the aligning member and the guide portion is formed such that a leading end side sliding gap of the turntable in the sliding direction of the aligning member differs from a trailing end side sliding gap of the disk side in the sliding direction. The leading end side sliding gap is formed smaller than the trailing end side sliding gap. The amount of eccentricity of the disk becomes smaller according to this structure.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The present invention relates to an aligning device for a disk recording medium such as a Mini Disc (MD), CD, or DVD, and to an information recording/reproducing apparatus in which this type of aligning device is mounted.  
         [0003]     2. Related Background Art  
         [0004]     Alignment of an optical disk and a rotation shaft of an information recording/reproducing apparatus is conventionally performed by using an aligning member that is provided to a spindle motor that rotationally drives the optical disk.  FIG. 10  shows a specific spindle motor that is mounted in a disk drive such as a recordable MD. It should be noted that the disk aligning structure shown in  FIG. 10  is disclosed, for example, in Japanese Patent Application Laid-open No. 2003-036585, which was proposed by the applicants of the present invention.  
         [0005]     A spindle motor  30  includes a rotor portion  32  that is rotatably supported with respect to a stator portion  31  that is fixedly disposed. The stator portion  31  comprises a stator substrate  33 ; a housing  34  that is attached to the stator substrate  33 ; coils  35  that is fixedly disposed surrounding the housing  34  from an outer circumference of the housing  34 ; and a sliding bearing  36  that is press-inserted and held within the housing  34 .  
         [0006]     On the other hand, the rotor portion  32  comprises a rotation shaft  37  that is rotatably supported by the sliding bearing  36 ; a turntable  38  that is attached to the rotation shaft  37 ; a cylindrical rotor yoke  39  that is attached to the turntable  38  and surrounds the coils  35  from an outer circumference of the coils  35 , with a lower end of the cylindrical rotor yoke  39  not connected; a rotor magnet  40  that is provided on an inner side of the rotor yoke  39 ; an attraction magnet  41  that is provided to an upper surface of the turntable  38 ; an adjusting member  42  that fits into a turntable cylindrical portion  38   a ; a regulating member  43  that regulates an upward range of movement for the adjusting member  42 ; and an urging member  44  that urges the adjusting member  42  upward with respect to the turntable  38 .  
         [0007]     In addition, a disk  45  is set onto the turntable  38 . A fixing disk  46  is mounted from above the disk  45 , and a magnetic attraction force of the attraction magnet  41  of the rotor portion  32  pulls the fixing disk  46 . The disk  45  is thus mounted onto the turntable  38 . A center hole lower edge  45   a  of the disk  45  contacts with a tapered surface  42   a  of the aligning member  42  at this point. The aligning member  42  is pressed down in a downward direction against a force of the urging member  44 , and the disk  45  is mounted onto the turntable  38  while aligned substantially coaxially with the rotation shaft  37 . It should be noted that the urging member  44  is provided in order to respond to tolerance fluctuation of the center hole diameter of the disk  45 .  
         [0008]     Problems develop if the aligning member  42  is fixed. Fluctuation of the center hole diameter of the disk  45  cannot be tracked. The disk  45  cannot be mounted to the turntable  38  for cases where the center hole diameter is a minimum, and the disk is not aligned when lash with respect to the aligning member  42  becomes large for cases in which the center hole diameter is a maximum. It should be noted that a compression coil spring having a circular cross section is employed for the urging member  44  in the conventional example in order to prevent collapse of the coil when compressed.  
         [0009]     The conventional spindle motor  30  is thus configured. A magnetic field that develops in the coils  35  due to suitable electrification of the coils  35  acts in concert with a magnetic field due to the rotor magnet  40  and the rotor yoke  39  of the rotor portion  32 . The rotor portion  32  is thus rotationally driven. It thus becomes possible for the disk  45  mounted on the turntable  38  to rotate in synchronism with the rotation of the rotor portion  32  without sliding owing to the attractive force of the attraction magnet  41 .  
         [0010]     Further, for cases where information is recorded onto or reproduced from the disk  45 , it is necessary to accurately align tract positions of the disk  45  with pickup positions that record and reproduce information. In particular, the track positions vary in a radial direction of the disk according to the amount of eccentricity within one disk rotation for cases where eccentricity occurs with the disk  45 . For example, a 1.6 μm pitch bit signal is accurately traced and detected for CD reproduction. Positioning is conventionally performed in the radial direction of the disk by using a tracking servo, for example, in order to accurately adjust the pickup positions.  
         [0011]     The narrowing of track pitch accompanying higher information density, and the increase in disk rotational velocity accompanying higher transfer rates have been advancing in recent disk recording/reproducing apparatuses. Accordingly, the positioning accuracy of the tracking servo described above demands higher precision and higher speed. However, it is obvious that control at higher precision and higher speed is difficult with the current conventional tracking servo operating range. The operating range of the tracking servo is also tending to become smaller, and therefore it has to be accomplished to reduce the amount of eccentricity.  
         [0012]     With publicly disclosed apparatuses, the tolerance fluctuation of the center hole of the disk is made negligible, and high precision alignment is performed, by using a configuration as described above. That is, it is possible for an aligning member that fits into a guide portion of a turntable on which a disk is mounted, the aligning member having a tapered surface contacting with a center hole of the-disk, to slide in a rotation shaft direction of the turntable. However, it is necessary to have a 5 to 20 μm pp sliding gap for a sliding portion because of ambient temperatures, differences in material properties, finishing accuracy, and the like. Accordingly, there is a problem in that the angle of the tapered surfaces changes because the aligning member inclines due to the sliding gap, and eccentricity develops during disk mounting.  
         [0013]     In addition, when considering hole fitting of the sliding portion and the guide portion shapes, it is necessary to impart a tolerance fluctuation on the order of 5 to 10 μm to each of the diameter dimensions due to fabrication problems. Accordingly, even with identical designs, the sliding gap described above will have a lash range between the maximum value and the minimum value due to the tolerances of the sliding portion and the guide portion. For example, the sliding gap becomes from 5 to 20 μm when the tolerance of the guide portion is from −10 to 0 μm, and the tolerance of the sliding portion is from +5 to +10 μm.  
         [0014]     Further, with these high precision dimensional tolerances, not only is there fluctuation between each component, but the dimensions also change, for example, within the tolerance fluctuation described above for the sliding portion of one individual component. Accordingly, the eccentricity that develops from the incline of the aligning member changes greatly because there is a range in the sliding gap. However, in order to maintain a constant sliding gap, work for further reducing the tolerance fluctuation of the components, selecting each component by inspecting its dimensions, and the like becomes necessary, and there is a problem in that this work leads to higher costs.  
       SUMMARY OF THE INVENTION  
       [0015]     The present invention has been made in order to resolve problems like those described above. An object of the present invention is to provide an aligning device for a disk recording medium and an information recording/reproducing apparatus which makes it possible to reduce the amount of eccentricity of the disk recording medium by using a simple configuration, without an increase in cost.  
         [0016]     According to the present invention, there is provided an aligning device for a disk recording medium, the aligning device including: a turntable on which the disk recording medium is placed; a rotation shaft that rotates the turntable; and an aligning member that contacts with a center hole of the recording medium and aligns the center of the rotation shaft and the center of the recording medium; wherein the aligning member fits with a guide portion that is fixed to the turntable with a sliding gap therebetween; wherein the sliding gap is formed such that a leading end side sliding gap on a turntable side in a sliding direction of the aligning member differs from a trailing end side sliding gap on a disk recording medium side in the sliding direction; and wherein the leading end side sliding gap is formed smaller than the trailing end side sliding gap.  
         [0017]     According to the present invention, there is provided an information recording/reproducing apparatus comprising: a spindle motor for rotating a disk recording medium; the aligning device described above that is installed on the spindle motor; and an optical pickup for irradiating the rotating recording medium with an optical beam. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0018]      FIGS. 1A and 1B  are schematic cross sectional views that show an aligning device according to a first embodiment of the present invention;  
         [0019]      FIGS. 2A, 2B  and  2 C are schematic cross sectional views for explaining meshing between an upper base portion and a lower base portion of the first embodiment of the present invention;  
         [0020]      FIGS. 3A and 3B  are schematic cross sectional views for explaining meshing according to a diagonal line of the first embodiment of the present invention;  
         [0021]      FIGS. 4A and 4B  are schematic cross sectional views that show translation motion from among operations leading to meshing according to the diagonal line of  FIGS. 3A and 3B ;  
         [0022]      FIG. 5  is a schematic cross sectional view for explaining a difference in eccentricity amount by cross sectional shape of the meshing according to the diagonal line of  FIGS. 3A and 3B ;  
         [0023]      FIGS. 6A and 6B  are schematic cross sectional views for explaining dimensional values for specific analysis of the first embodiment;  
         [0024]      FIG. 7  is a diagram that shows results of analyzing the first embodiment;  
         [0025]      FIG. 8  is a schematic cross sectional view that shows a variation of the first embodiment;  
         [0026]      FIG. 9  is a schematic cross sectional view that shows an aligning device according to a second embodiment of the present invention;  
         [0027]      FIG. 10  is a schematic cross sectional view that shows a conventional aligning device; and  
         [0028]      FIG. 11  is a schematic diagram that shows an information recording/reproducing apparatus of the present invention. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0029]     Preferred embodiments for implementing the present invention, with specific dimensional values, are explained in detail next. It should be noted that only important points of the present invention are extracted and shown in the embodiments described below. Specific structures of other elements not shown are identical to those of the conventional example of  FIG. 10 . That is, the present invention is especially characterized by an alignment structure according to an aligning member, and the basic configuration except such structure is similar to that of  FIG. 10 .  
       Embodiment 1  
       [0030]      FIGS. 1A and 1B  are schematic cross sectional views that show a first embodiment of the present invention.  FIGS. 1A and 1B  show significant forms of sliding gaps that can be formed due to tolerance fluctuation as described above. It should be noted that  FIG. 1A  is a cross sectional view that shows a case of a cross sectional shape K 1  of an aligning member  3  according to this embodiment (where the diameter of an upper end surface thereof is greater than the diameter of a lower end surface thereof in a portion that slides along a guide portion  6 ). Further, for comparison,  FIG. 1B  shows a case of a cross sectional shape K 2  of the aligning member  3  (where the diameter of the lower end surface thereof is greater than the diameter of the upper end surface thereof in the portion that slides along the guide portion  6 ).  
         [0031]     An alignment object disk, such as a Mini Disc (MD), CD, or DVD is shown in  FIGS. 1A and 1B . Reference numerals  2   a  and  2   b  denote center holes of respective disks  1  for the cross sectional shapes K 1  and K 2 , reference numeral  3  denotes aligning members, and reference numerals  4   a  and  4   b  denote tapered portions that respectively contact with the center holes  2   a  and  2   b  of the disks  1  of the aligning members  3 . Reference numeral  5  denotes a turntable, and reference numeral  6  denotes a guide portion that is formed integrally with the turntable  5 . Reference numerals  7   a  and  7   b  denote a sliding portion of the fitting aligning member  3  that fits with the guide portion  6  of each of the cross sectional shapes K 1  and K 2 . The sliding portions  7   a  and  7   b  each have a minimum sliding gap S 1  and a maximum sliding gap S 2 . Reference numeral  8  denotes a rotation shaft that is integrally fastened to the turntable  5 . The aligning member  3  urges the disk  1  side by using an urging member, similar to the case of  FIG. 10 .  
         [0032]     It should be noted that, for simplicity in this embodiment, the sliding gap between the aligning member  3  and the guide portion  6  is made into a trapezoidal cross sectional shape with respect to the rotation shaft, while the specific structure except such gap and alignment method conform to conventional examples. Further, the aligning member  3  slides in a downward direction in the drawings when aligning in this embodiment. Accordingly, the term “leading end side sliding gap” as used herein means a sliding gap between the diameter of the lower end surface and the guide portion  6 , and the term “trailing end side sliding gap” as used herein means a sliding gap between the diameter of the upper end surface and the guide portion  6 .  
         [0033]     The aligning member  3  is pressed in the direction of an arrow B and rotates, inclining until engaging with the guide portion  6 , when the center holes  2   a  and  2   b  of the disks  1  contact with the tapered portions  4   a  and  4   b  of the aligning members  3 , respectively, at points A in  FIGS. 1A and 1B . Engagement occurs in two ways. For case (1), engagement occurs at reference symbols m in the figures, that is, at the lower base of the shape K 1  of  FIGS. 1A , and at the upper base of the shape K 2  of  FIG. 1B . For case (2), engagement occurs with respect to a diagonal line n.  
         [0034]     First, the case (1) of engagement with respect to the line segments m (the lower bases with the cross sectional shape K 1 , and the upper base with the cross sectional shape K 2 ) is discussed.  
         [0035]      FIG. 2A  shows the cross sectional shape K 1 , and  FIG. 2B  shows the cross sectional shape K 2  for this case. Points Ca and Cb in  FIGS. 2A and 2B  are rotation centers for the cross sectional shapes K 1  and K 2 , respectively. From  FIGS. 2A and 2B , it can be understood that an amount of eccentricity R 1  for the cross sectional shape K 1  is less than an amount of eccentricity R 2  for the cross sectional shape K 2 . Reasons for this result are explained using  FIG. 2C .  FIG. 2C  is a diagram that schematically shows the rotation centers Ca and Cb of  FIGS. 2A and 2B , respectively, and a point D that is described hereinafter. As shown in  FIG. 2B , the x-axis and the y-axis are set by taking the rotation center Cb as an origin when the cross sectional shape K 2  contacts with the guide portion  6 .  
         [0036]     Further, the rotation center Ca when the cross sectional shape K 1  contacts with the guide portion  6  is on the y-axis. Accordingly, an upper surface portion and a lower surface portion (not shown) of the aligning members  3  of the cross sectional shapes K 1  and K 2  are moved in parallel along the y-axis and disposed so that they coincide after inclining. It should be noted that, in  FIG. 2C , the tapered portions  4   a  and  4   b  before inclination that contact with the guide portion  6  when the rotation centers of the cross sectional shapes K 1  and K 2  move in parallel are shown by a double dotted line, the cross sectional shape K 1  after inclination is shown by a solid line, and the cross sectional shape K 2  after inclination is shown by a broken line.  
         [0037]     A state where a center line (not shown) of the aligning member  3  before inclination and a center line (not shown) of the guide portion  6  coincide with each other is taken as an initial state. The amounts of movement from the initial state along the x-axis until the rotation centers Ca and Cb contact with the guide portions  6  are identical at a minimum gap S 1 . Accordingly, the tapered portion before inclination, shown by the double dotted line, is disposed in the same position for both the cross sectional shapes K 1  and K 2 .  
         [0038]     Further, the line segments m have identical lengths in the cross sectional shapes K 1  and K 2 , and the line segments m before inclination are parallel to the x-axis. Accordingly, rotational angles θ until engagement occurs after contact with the guide portions  6  are identical, without being limited to the cases of the cross sectional shapes K 1  and K 2 . Accordingly, points of contact between the tapered portions  4   a  and  4   b , and the center holes  2   a  and  2   b  of the disks  1  during alignment after inclination become points on the same coordinates with a relative coordinate system of the aligning members  3  of the cross sectional shapes K 1  and K 2  (for example, coordinate systems in which the lower end of the tapered portions  4   a  and  4   b  are taken as origins).  
         [0039]     In  FIG. 2C , a point where a straight line formed between the tapered portions  4   a  and  4   b  of the aligning members  3  before inclination, shown by the double dotted line in  FIG. 2C , intersects the x-axis is taken as a point D. The point D after inclination in the cross sectional shape K 1  is taken as a point Da′, and the point D after inclination in the cross sectional shape K 2  is taken as a point Db′. It then becomes possible to compute an alignment performance difference R 2 −R 1  between the cross sectional shape K 1  and the cross sectional shape K 2  by computing the x-axis distance between the point Da′ and the point Db′.  
         [0040]     The distance between the rotation centers Ca and Cb is taken as h, and the distance between a line segment Cb and the point D is taken as XD. From  FIG. 2C , an x-coordinate distance XDa′ of the point Da′ and an x-coordinate distance XDb′ of the point Db′ are computed from the following equations. 
 
 XDa ′=( XD−h ·sin θ)·cos θ  (1-1) 
 
 XDb′=XD ·cos θ  (1-2) 
 
 Accordingly, the difference between XDa′ and XDb′ becomes the difference in the amount of eccentricity R 2 −R 1  between the cross sectional shape K 1  and the cross sectional shape K 2 . 
 
 R   2 − R   1 = XDb′−XDa′=h ·sin θ·cos θ  (1-3) 
 
         [0042]     In Eq. (1-3), h is greater than zero. When taking a clockwise direction in  FIG. 2C  as a positive direction, the rotational angle θ is greater than zero because the rotation direction does not reverse. Further, rotation of the aligning member does not equal or exceed 90° in practice due to the structure used, and the rotation angle θ therefore lies in a range of 0&lt;θ&lt;90°. Accordingly, sin θ&gt;0, and cos θ&gt;0 (0&lt;θ&lt;90°), and Eq. (1-3) becomes positive.  
         [0043]     It becomes clear from the above explanation that the case of the cross sectional shape K 1  according to this embodiment, where the diameter of the upper end surface is greater than the diameter of the lower end surface, has a smaller amount of eccentricity than the case of the cross sectional shape K 2 , where the diameter of the lower end surface is greater than the diameter of the upper end surface.  
         [0044]     The case (2) of engagement with respect to the diagonal line n is explained.  
         [0045]     Engagement with respect to the diagonal line n is explained in detail below using  FIGS. 3A, 3B ,  4 A,  4 B, and  5 . First, a state where engagement takes place at both ends at the diagonal line n is shown in  FIGS. 3A and 3B .  FIG. 3A  shows the state of the cross sectional shape K 1 , and  FIG. 3B  shows the state of the cross sectional shape K 2 . In  FIGS. 3A and 3B , points Ea and Eb are rotation centers of the cross sectional shape K 1  and the cross sectional shape K 2  respectively. Points Ta and Tb are contact portions between the center holes  2   a  and  2   b  of the disks  1  and the tapered portions  4   a  and  4   b  for the cross sectional shapes K 1  and K 2 , respectively, during alignment (only left side cross sectional views of the rotation shaft are shown in the figures).  
         [0046]     It should be noted that the length of the diagonal lines n are equal for the cross sectional shape K 1  and the cross sectional shape K 2 , and that angles θn, which indicate angles formed by the diagonal lines n and a direction orthogonal to the rotation shaft (angles formed by the diagonal lines n and a horizontal direction in the figures), are also equal. Accordingly, the rotation angles θ (noted in  FIG. 5 ) until the cross sectional shapes K 1  and K 2  becomes in engagement are also identical. The contact positions are therefore also identical in relative coordinate systems that take the aligning member  3  as a reference when aligning the center holes  2   a  and  2   b  of the disks  1  in the cross sectional shapes K 1  and K 2  (for example, coordinate systems for cases of using lower end points U of the tapered portions  4   a  and  4   b  as origins).  
         [0047]     Processes until engagement occurs with respect to the diagonal lines n are considered next for the trapezoidal cross sectional shapes K 1  and K 2  described above. The processes are separated into two movements: (i) translation motion of the aligning member  3  in a direction that is orthogonal to the rotation shaft, and (ii) rotation.  
         [0048]      FIGS. 4A and 4B  show the case of (i) translation motion of the aligning member  3  in a direction that is orthogonal to the rotation shaft. In  FIGS. 4A and 4B , the disk  1  is omitted.  FIG. 4A  shows the case of the cross sectional shape K 1 , while  FIG. 4B  shows that of the cross sectional shape K 2 . States before translation motion are shown by double dotted lines. States where the aligning members  3  translate in the direction orthogonal to the rotation shaft (the x-axis direction) until rotation centers Ea and Eb of  FIGS. 3A and 3B , respectively, contact with the guide portions  6  are shown by solid lines.  
         [0049]     It should be noted that each symbol, including the rotation centers Ea and Eb, are given for states after translation motion (shown by the solid lines). Taking the rotation centers Ea and Eb as origins, the x-axis is set in the direction that is orthogonal to the rotation shaft, and the y-axis is set in the direction parallel to the rotation shaft.  
         [0050]     Taking points where straight lines formed by the tapered portions  4   a  and  4   b  intersect with the x-axis as points Fa and Fb, respectively, and taking the x-axis coordinates at the points Fa and Fb as XFa and XFb, the following equation results. 
 
 XFb−XFa=S   2 − S   1   (2-1) 
 
         [0051]     Next,  FIG. 5  shows the rotation case.  FIG. 5  is a diagram that shows a state where the rotation centers Ea and Eb of the cross sectional shapes K 1  and K 2 , respectively, are made to coincide with each other as an origin point, and rotated until engagement occurs at both ends of the diagonal lines n. When points Fa and Fb after inclination are taken as Fa′ and Fb′, respectively, and the distances in the x-axis direction of the points Fa′ and Fb′ are taken as XFa′ and XFb′, respectively, a line segment TaTb and a line segment Fa′Fb′ become parallel. Accordingly, XFb′−XFa′ becomes the difference in the amount of eccentricity between the cross sectional shapes K 1  and K 2 , similar to the case (1) described above. The following equation thus results.  
                               XFb   ′     -     XFa   ′       =         XFb   ·   cos     ⁢           ⁢   θ     -       XFa   ·   cos     ⁢           ⁢   θ                   =         (     S2   -   S1     )     ·   cos     ⁢           ⁢   θ                   (2-2)           ⁢                                 
 
         [0052]     S 2 −S 1 &gt;0 here, the rotation angle θ lies within the range 0&lt;θ&lt;90° for reasons similar to those of the case (1). Accordingly, cos θ&gt;0, and Eq. (2-2) becomes positive.  
         [0053]     From the above descriptions, the cross sectional shape K 1  case (where the diameter of the upper end surface is greater than the diameter of the lower end surface) has a smaller amount of eccentricity than the cross sectional shape K 2  case (where the diameter of the lower end surface is greater than the diameter of the upper end surface).  
         [0054]     Specific analytical results are explained next using  FIGS. 6A and 6B .  FIGS. 6A and 6B  are diagrams in which the tapered portions  4   a  and  4   b  are disposed in three different positions, &lt;1&gt; above, &lt;2&gt; at the same height of, and &lt;3&gt; below the sliding portions  7   a  and  7   b , respectively, in the cross sectional shapes K 1  and K 2 . It should be noted that engagement of the aligning members  3  by inclination is in the case (2) of engagement with respect to the diagonal lines n.  
         [0055]     Dimensional parameters are taken as follows. The diameter d 6  of the guide portion  6  is 6.5 mm, the minimum sliding gap S 1  is 2.5 μm, the maximum sliding gap S 2  is 7.5 μm, the height of the sliding portion h is 1 mm, a taper angle φ is 60°, a taper portion reference diameter (diameter of a center portion of the taper) d 4  is 11 mm, and a disk center hole diameter d 2  is 11 mm. Taking the case &lt;2&gt; where the height of the tapered portions are the same as the height of the sliding portions, as a reference, an offset O 1  for the case &lt;1&gt; is 1.5 mm above, and an offset O 2  for the case &lt;3&gt; is 1.5 mm below.  
         [0056]      FIG. 7  shows analytical results. As can be understood from  FIG. 7 , it has been confirmed that the amount of eccentricity for the cross sectional shape K 1  of the sliding portion (where the diameter of the upper end surface is greater than the diameter of the lower end surface) is less than that for the cross sectional shape K 2  (where the diameter of the lower end surface is greater than the diameter of the upper end surface) for identical placements of the tapered portion. Further, the difference in the eccentricity amounts for each offset state all becomes 5 μm. With the above dimensional values, the rotation angle θ of the aligning member  3  is approximately 0.42°. Accordingly, substituting this into Eq. (2-2), the difference in the amount of eccentricity between the cross sectional shapes K 1  and K 2  becomes approximately 5 μm, matching with the analytical results. described above.  
         [0057]     It should be noted that the present invention is not limited to the shapes of this embodiment. For example, in practice chamfering is normally performed on both end portions of the upper surface side and the lower surface side of the sliding portion, and the cross sectional shapes are not strictly trapezoidal, that is, are not strictly tapered shapes. However, it becomes possible to obtain the effects of the present invention by setting the sliding gaps in portions to which chamfering is not implemented.  
         [0058]     Further, as shown in  FIG. 8 , taking a portion  7   m  (gap Sm) that is sandwiched by a leading end side sliding portion  7   t  (sliding gap St with respect to the guide portion  6 =minimum sliding gap S 1 ) and a trailing end side sliding portion  7   r  (sliding gap Sr with respect to the guide portion  6 =maximum sliding gap S 2 ) with respect to the sliding direction when aligning the aligning member  3 , it is also possible to form the gap Sm of the portion  7   m  larger than the sliding gap Sr of the trailing end side. It should be noted that, in this case, the sliding portion  7   t  of the leading end side and the sliding portion  7   r  of the trailing end side are tied together as shown by a double dotted line in  FIG. 8 . It is thus possible to also consider tapered shapes similar to the cross sectional shapes discussed above. Further, the contact surface area with the guide portion  6  of the sliding portion is reduced in this case, and it therefore becomes possible to reduce the sliding load.  
       Embodiment 2  
       [0059]      FIG. 9  is a cross sectional view that shows a second embodiment of the present invention. It should be noted that reference symbols identical to those of the first embodiment and those of  FIG. 10 . are used in  FIG. 9 . In this embodiment, the aligning member  3  comprises a tapered member  9 , an upper side sliding member  10  (a portion that forms trailing end side sliding gap), and a lower side sliding member  11  (a portion that forms a leading end side sliding gap). An inner diameter portion  12  of the tapered member  9  is larger than the sliding gaps, and also larger than the tolerance range. An upper side sliding portion  13  of the upper side sliding member  10  and a lower side sliding portion  14  of the lower side sliding member  11  are configured such that the inner diameter of the upper side sliding portion  13  is greater than the inner diameter of the lower side sliding portion  14 . The leading end side sliding gap is thus smaller than the trailing end side sliding gap in the direction toward which the aligning member  3 l slides.  
         [0060]     By making the aligning member  3  into a separate unit, the structure thus becomes complex compared to that of the first embodiment. However, it is possible to reduce difficulty of component fabrication of the alignment member, although the dimensional precision and surface properties of both the tapered portion and the sliding portion are required to be satisfied in the first embodiment. In particular, the shape of the aligning member  3  demands high precision for outer diameter fabrication and inner diameter fabrication in the first embodiment. According to this embodiment, however, it becomes possible to distribute high fabrication precision portions according to components. The dimensional precision and the surface properties of the tapered portion of the tapered member  9  are determined by the outer diameter fabrication, and the dimensional precision and the surface properties of the upper side sliding member  10  and the lower side sliding member  11  are determined by the inner diameter fabrication. Further, it becomes possible to reduce the contact surface area with the guide portion  6  of the sliding portion. Accordingly, it becomes possible to reduce the sliding load due to frictional forces. It should be noted that it is also effective to configure the tapered member  9  and the upper side sliding member  10  by using the same member, and combine this with the lower side sliding member  11 .  
       Embodiment 3  
       [0061]      FIG. 11  is a schematic view that shows the structure of an information recording/reproducing apparatus of the present invention. An information recording/reproducing apparatus  21  comprises a chassis  22  that becomes a structural base, a spindle motor  23  that mounts and rotates a disk (not shown) disposed on the chassis  22 , in which the aligning device shown in the first embodiment or the second embodiment is installed, an optical pickup  24 , an objective lens  25  that radiates an optical beam and is disposed in the optical pickup  24 , a feed motor  26  having a lead screw  28  that conveys the optical pickup  24  in a radial direction of the disk that is disposed on the chassis  22 , and a guide shaft  27  that supports the optical pickup  24 .  
         [0062]     A light beam is radiated from the objective lens  25  of the optical pickup  24  to the disk  1  that is rotated by the spindle motor  23 . Further, a lead screw  28  that is formed integrally with a rotation shaft of the feed motor  26  is engaged with the optical pickup  24  by a rack (not shown). By converting rotational motion of the lead screw  28  into translation motion, the optical pickup  24  moves in the radial direction of the disk  1  with the guide shaft  27  as a guide. The information recording/reproducing apparatus  21  thus performs information recording/reproducing to and from the disk  1 .  
         [0063]     This application claims priority from Japanese Patent Application No. 2003-353985 filed Oct. 14, 2003, which is hereby incorporated by reference herein.