Abstract:
A disk drive including a disk rotatably mounted in a housing and having a plurality of tracks, a rotating mechanism for rotating the disk, a head slider having a transducer for reading/writing data on the disk, and an actuator for moving the head slider across the tracks. The actuator includes an actuator arm rotatably mounted in the housing, a suspension having a front end portion for supporting the head slider and a base end portion fixed to the actuator arm, and a pad mounted on a disk opposing surface of the actuator arm. The pad overlaps at least an outermost circumferential portion of the disk in a specific position of the actuator upon stoppage of driving of the disk drive.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The present invention relates generally to a disk drive, and more particularly to a disk drive designed to prevent a contact of a disk and an actuator arm due to an external shock.  
           [0003]    2. Description of the Related Art  
           [0004]    In a conventional magnetic disk drive, there is a case that an actuator arm or a spindle on which a magnetic disk is mounted may be tilted to some extent by an external shock exerted on the magnetic disk drive. In such a case, the front end of the actuator arm comes closest to the magnetic disk, because the actuator arm is usually flat in shape. Further, since the actuator arm is supported in a cantilever fashion, the amplitude of vertical vibration of the actuator arm due to the external shock is largest at the front end of the arm. Therefore, upon receipt of the external shock, the tilt of the actuator or the spindle is associated with the vertical displacement of the actuator arm, resulting in a structure such that the front end of the actuator arm tends to come into contact with a data region of the magnetic disk.  
           [0005]    In general, a magnetic disk drive sometimes receives an external shock in mounting it into a computer, carrying a portable computer in which the disk drive is built, etc. It is therefore required to improve the external shock resistance of a magnetic disk drive. However, due to a recent decrease in size of a magnetic head in response to a decrease in thickness and an increase in storage capacity in a magnetic disk drive, a magnetic head mounting height (the distance between an actuator arm and a magnetic disk) becomes smaller, with the result that the allowable amplitude of vertical vibration of the actuator arm upon receipt of an external shock is reduced. Accordingly, when the magnetic disk drive receives an external shock, the front end of the actuator arm tends to come into contact with the magnetic disk surface, causing a damage to the data region of the magnetic disk. Further, in many cases, a magnetic disk drive having a small number of magnetic disks adopts a single-supported spindle structure such that a spindle shaft is fixed to a base only, from a cost-reduction viewpoint. However, this structure is inferior to a double-supported spindle structure in that the spindle shaft is more tilted, causing a problem that the outermost circumferential portion of the magnetic disk tends to come into contact with the actuator arm facing thereto.  
         SUMMARY OF THE INVENTION  
         [0006]    It is therefore an object of the present invention to provide a disk drive which can minimize the vibrations of the actuator arms and the disks when the disk drive receiving an external shock, thereby preventing a damage to the disks.  
           [0007]    In accordance with an aspect of the present invention, there is provided a disk drive comprising a housing; a disk rotatably mounted in said housing and having a plurality of tracks; a rotating mechanism for rotating said disk; a head slider having a transducer for reading/writing data on said disk; and an actuator for moving said head slider across said tracks of said disk; said actuator comprising an actuator arm rotatably mounted in said housing; a suspension having a front end portion for supporting said head slider and a base end portion fixed to a front end portion of said actuator arm; and a pad mounted on a disk opposing surface of said actuator arm; said pad overlapping at least an outermost circumferential portion of said disk in a specific position of said actuator upon stoppage of driving of said disk drive.  
           [0008]    Preferably, the pad is formed of resin or rubber, and overlaps a non-data region formed in the outermost circumferential portion of the disk. The thickness of the pad is set preferably smaller than the thickness of the head slider. By mounting the pad on the actuator arm, a clearance between the actuator arm and the disk at the outermost circumferential portion of the disk in a direction perpendicular to the disk surface can be reduced. Accordingly, even when the disk drive receives an external shock, the pad mounted on the actuator arm comes into contact with the outermost circumferential portion (the non-data region) of the disk, thereby limiting a tilt of the actuator or the spindle to prevent a contact of the front end of the actuator arm with a data region of the disk.  
           [0009]    In accordance with another aspect of the present invention, there is provided a disk drive comprising a housing having a base and a cover fixed to said base; a disk rotatably mounted in said housing and having a plurality of tracks; a rotating mechanism for rotating said disk; a head slider having a transducer for reading/writing data on said disk; an actuator for moving said head slider across said tracks of said disk; and a stopper fixed to said base, said stopper having a groove for receiving an outermost circumferential portion of said disk with a given vertical clearance.  
           [0010]    In a disk drive wherein the actuator takes a rest position in the outermost circumferential portion of the disk upon stoppage of driving of the disk drive, a stopper for suppressing the vertical vibration of the actuator arm at the rest position of the actuator may be fixed to the base.  
           [0011]    In accordance with a further aspect of the present invention, there is provided a disk drive comprising a housing; a disk rotatably mounted in said housing and having a plurality of tracks; a rotating mechanism for rotating said disk; a head slider having a transducer for reading/writing data on said disk; and an actuator for moving said head slider across said tracks of said disk; said actuator comprising an actuator arm rotatably mounted in said housing; a spacer fixed to a front end portion of said actuator arm; a suspension having a front end portion for supporting said head slider and a base end portion fixed to said spacer; and a pad provided on a disk opposing surface of said actuator arm at a position near said spacer.  
           [0012]    Preferably, the pad is formed of resin or rubber, and the thickness of the pad is set smaller than the thickness of the head slider.  
           [0013]    In accordance with a still further aspect of the present invention, there is provided a disk drive comprising a housing having a base and a cover fixed to said base; a spindle assembly having a shaft fixed to said base, a spindle hub rotatably mounted on said shaft, and a motor for rotating said spindle hub; a disk mounted on said spindle hub and having a plurality of tracks; a head slider having a transducer for reading/writing data on said disk; and an actuator for moving said head slider across said tracks of said disk; said spindle hub being integrally formed at its upper end with an annular projection; said cover having a circular recess for receiving said annular projection with a given horizontal clearance. 
       
    
    
       [0014]    The above and other objects, features and advantages of the present invention and the manner of realizing them will become more apparent, and the invention itself will best be understood from a study of the following description and appended claims with reference to the attached drawings showing some preferred embodiments of the invention.  
       BRIEF DESCRIPTION OF THE DRAWINGS  
       [0015]    [0015]FIG. 1 is a plan view of a magnetic disk drive according to a first preferred embodiment of the present invention;  
         [0016]    [0016]FIG. 2 is a cross section taken along the line  2 A- 2 A in FIG. 1;  
         [0017]    [0017]FIG. 3 is a plan view of a magnetic disk drive according to a second preferred embodiment of the present invention;  
         [0018]    [0018]FIG. 4 is a cross section taken along the line  4 A- 4 A in FIG. 3;  
         [0019]    [0019]FIG. 5 is a plan view of a magnetic disk drive according to a third preferred embodiment of the present invention;.  
         [0020]    [0020]FIG. 6 is a cross section taken along the line  6 A- 6 A in FIG. 5;  
         [0021]    [0021]FIG. 7 is a plan view of a magnetic disk drive according to a fourth preferred embodiment of the present invention;  
         [0022]    [0022]FIG. 8 is a cross section taken along the line  8 A- 8 A in FIG. 7;  
         [0023]    [0023]FIG. 9 is a plan view of a magnetic disk drive according to a fifth preferred embodiment of the present invention;  
         [0024]    [0024]FIG. 10 is a cross section taken along the line  10 A- 10 A in FIG. 9;  
         [0025]    [0025]FIGS. 11A and 11B are schematic perspective views showing preferred embodiments of a pad mounting method;  
         [0026]    [0026]FIGS. 12A and 12B are schematic perspective views showing other preferred embodiments of the pad mounting method;  
         [0027]    [0027]FIG. 13 is a schematic perspective view showing a still another preferred embodiment of the pad mounting method;  
         [0028]    [0028]FIG. 14 is a schematic perspective view showing a further preferred embodiment of the pad mounting method;  
         [0029]    [0029]FIG. 15 is a plan view of a magnetic disk drive according to a sixth preferred embodiment of the present invention;  
         [0030]    [0030]FIG. 16 is a cross section taken along the line  16 A- 16 A in FIG. 15;  
         [0031]    [0031]FIG. 17 is a plan view of a magnetic disk drive according to a seventh preferred embodiment of the present invention;  
         [0032]    [0032]FIG. 18 is a cross section taken along the line  18 A- 18 A in FIG. 17;  
         [0033]    [0033]FIG. 19 is a plan view of a magnetic disk drive according to an eighth preferred embodiment of the present invention;  
         [0034]    [0034]FIG. 20A is a cross section taken along the line  20 A- 20 A in FIG. 19;  
         [0035]    [0035]FIG. 20B is a cross section taken along the line  20 B- 20 B in FIG. 19;  
         [0036]    [0036]FIG. 21 is a plan view of a magnetic disk drive according to a ninth preferred embodiment of the present invention;  
         [0037]    [0037]FIG. 22 is a cross section taken along the line  22 A- 22 A in FIG. 21;  
         [0038]    [0038]FIG. 23 is a schematic sectional view of a front end portion of an actuator arm in a magnetic disk drive according to a tenth preferred embodiment of the present invention; and  
         [0039]    [0039]FIG. 24 is a sectional view of a spindle assembly in a magnetic disk drive according to an eleventh preferred embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0040]    Various preferred embodiments of the present invention will now be described in detail with reference to the drawings. In the following description of the preferred embodiments, substantially the same parts will be denoted by the same reference numerals.  
         [0041]    Referring to FIG. 1, there is shown a plan view of a magnetic disk drive according to a first preferred embodiment of the present invention in the condition where a cover has been removed. A spindle hub (not shown) rotatably driven by a motor  16  is provided on a base  12 . A plurality of magnetic disks  14  and spacers (not shown) are mounted on the spindle hub in such a manner as to be alternately stacked. That is, the plural magnetic disks  14  are fixedly mounted on the spindle hub by securing a disk clamp  18  to the spindle hub by screws, and are equally spaced a given distance by the spacers.  
         [0042]    Reference numeral  20  denotes a rotary actuator consisting of an actuator assembly  22  and a magnetic circuit  24 . The actuator assembly  22  is rotatably mounted on a shaft  26  fixed to the base  12 . The actuator assembly  22  includes an actuator block  30  rotatably mounted on the shaft  26  through a bearing  28 , a plurality of actuator arms  32  integral with the actuator block  30  and extending radially therefrom in one direction, and a coil supporting member  34  integral with the actuator block  30  and extending radially therefrom in a direction opposite to the direction of extension of the actuator arms  32 .  
         [0043]    A head assembly  36  is fixed to a front end portion of each actuator arm  32 , and a head slider  40  is mounted on a front end portion of the suspension  38 . The suspension  38  and the head slider  40  constitute a head assembly  36 . The head slider  40  has a transducer for reading/writing data on the corresponding magnetic disk  14 . A coil  42  is supported by the coil supporting member  34 . The magnetic circuit  24  and the coil  42  inserted in a gap of the magnetic circuit  24  constitute a voice coil motor (VCM)  44 .  
         [0044]    Reference numeral  46  denotes a main flexible printed circuit board (main FPC) for taking a read signal from the transducer mounted on the head slider  40  and supplying a write signal to the transducer. The read/write FPC  46  has a read/write amplifier, passive electronic components, etc. The main FPC  46  is fixed at its one end portion to the side surface of the actuator block  30 . An intermediate portion of the main FPC  46  is vertically fixed to the base  12  by a fixing member  48 , and the other end portion of the main FPC  46  is horizontally mounted on the base  12 .  
         [0045]    As best shown in FIG. 2 which is a cross section taken along the line  2 A- 2 A in FIG. 1, pads  50  are mounted on the side surface of the actuator block  30  so as to extend along disk opposing surfaces  32   a  of the actuator arms  32  which face the recording surfaces of the magnetic disks  14 . Each magnetic disk  14  has a non-data region  14   a  circularly extending along the outer circumference of the disk  14  on each side and having a width of about 2 mm. In a contact start and stop (CSS) position of the actuator  20  shown in FIG. 1 where the magnetic disk drive is not driven, that is, the magnetic disks  14  are not rotated, the pads  50  overlap the non-data regions  14   a  of the magnetic disks  14 .  
         [0046]    As shown in FIG. 2, a very small clearance (0.1 to 0.2 mm) is defined between each pad  50  and the corresponding magnetic disk  14 . Preferably, each pad  50  is formed of resin or rubber. Further, the thickness of each pad  50  is set preferably smaller than the thickness of the head slider  40  mounted on each suspension  38 . While each pad  50  has a length along the corresponding actuator arm  32  enough to overlap the non-data region  14   a  of the corresponding magnetic disk  14  in the CSS position of the actuator  20  as shown in FIG. 1, each pad  50  may extend from the actuator block  30  over a distance up to the half or less of the entire length of the corresponding actuator arm  32 . As a modification, each pad  50  may be mounted on the disk opposing surface  32   a  of the corresponding actuator arm  32 .  
         [0047]    In this preferred embodiment, each pad  50  is mounted on the actuator block  30  or the disk opposing surface  32   a  of the corresponding actuator arm  32 . Accordingly, a vertical clearance between each actuator arm  32  and the disk surface opposed thereto at the outermost circumferential portion of each magnetic disk  14  is reduced in the CSS position of the actuator  20 . As a result, even when the magnetic disk drive receives an external shock, each pad  50  comes into contact with the non-data region  14   a  of the corresponding magnetic disk  14 , thereby limiting a tilt of the actuator  20  or the spindle. Therefore, it is possible to prevent that the front end of each actuator arm  32  may come into contact with the disk surface (data region) of the corresponding magnetic disk  14 .  
         [0048]    [0048]FIG. 3 is a plan view of a magnetic disk drive according to a second preferred embodiment of the present invention, and FIG. 4 is a cross section taken along the line  4 A- 4 A in FIG. 3. This preferred embodiment employs pads  52  different in shape from the pads  50  used in the first preferred embodiment. Each pad  52  is mounted on the disk opposing surface  32   a  of the corresponding actuator arm  32 . The operation of this preferred embodiment is similar to that of the first preferred embodiment.  
         [0049]    [0049]FIG. 5 is a plan view of a magnetic disk drive according to a third preferred embodiment of the present invention, and FIG. 6 is a cross section taken along the line  6 A- 6 A in FIG. 5. This preferred embodiment employs pads  54  larger in area than the pads  52  used in the second preferred embodiment. That is, each pad  54  is mounted on the disk opposing surface  32   a  of the corresponding actuator arm  32  so as to project from one side surface thereof. The operation of this preferred embodiment is similar to that of the first preferred embodiment.  
         [0050]    [0050]FIG. 7 is a plan view of a magnetic disk drive according to a fourth preferred embodiment of the present invention, and FIG. 8 is a cross section taken along the line  8 A- 8 A in FIG. 7. This preferred embodiment employs pads  56  each having a plurality of projections  56   a  adapted to come into contact with the non-data region  14   a . Each pad  56  is mounted on the disk opposing surface  32   a  of the corresponding actuator arm  32  so as to project from one side surface thereof. Also in this preferred embodiment, a similar effect can be obtained.  
         [0051]    [0051]FIG. 9 is a plan view of a magnetic disk drive according to a fifth preferred embodiment of the present invention, and FIG. 10 is a cross section taken along the line  10 A- 10 A in FIG. 9. In this preferred embodiment, each actuator arm  32  is integrally formed at its base end portion with a thick-walled portion  58 . Each thick-walled portion  58  has a length along the corresponding actuator arm  32  enough to overlap the non-data region  14   a  of the corresponding magnetic disk  14  in the CSS position of the actuator  20 . The thick-walled portions  58  are formed by aluminum die casting, for example, in manufacturing the actuator arms  32 . The difference in thickness between the thick-walled portion  58  of each actuator arm  32  and the other portion thereof is set preferably smaller than the thickness of the head slider  40  mounted on each suspension  38 . Each thick-walled portion  58  in this preferred embodiment functions like each pad used in the previous preferred embodiments.  
         [0052]    Referring to FIGS. 11A and 11B, there are shown schematic perspective views illustrating preferred embodiments of a pad mounting method. The preferred embodiment shown in FIG. 11A employs an actuator arm  32 A having a recess  60  and a pad  62  having a projection  64  adapted to be closely fitted with the recess  60 . Accordingly, by engaging the projection  64  into the recess  60 , the pad  62  is mounted on the actuator arm  32 A. FIG. 11B shows a modification of the method shown in FIG. 11A. This modification shown in FIG. 11B employs an actuator arm  32 B having a projection  66  and a pad  68  having a recess  70  adapted to be closely fitted with the projection  66 . Accordingly, by engaging the recess  70  with the projection  66 , the pad  68  is mounted on the actuator arm  32 B.  
         [0053]    [0053]FIGS. 12A and 12B show other preferred embodiments of the pad mounting method. The preferred embodiment shown in FIG. 12A employs an actuator arm  32 C having a groove  72  extending from an end surface of the actuator arm  32 C in its longitudinal direction and a pad  74  having a dovetail-like rib  76  adapted to tightly fit into the groove  72 . Accordingly, by inserting the rib  76  into the groove  72 , the pad  74  is mounted on the actuator arm  32 C. The preferred embodiment shown in FIG. 12B as a modification employs an actuator arm  32 D having a dovetail-like rib  78  and a pad  80  having a groove  82  adapted to be tightly fitted with the rib  78 . Accordingly, by fitting the groove  82  with sliding the rib  78 , the pad  80  is mounted on the actuator arm  32 D.  
         [0054]    [0054]FIG. 13 shows another preferred embodiment of the pad mounting method. This preferred embodiment employs an actuator block  30 A having a recess  83  and a pad  84  having a projection  86  adapted to be closely fitted with the recess  83 . Accordingly, by engaging the projection  86  into the recess  83 , the pad  84  is mounted on the actuator block  30 A. Although not shown, the pads to be mounted on the upper and lower surfaces of the adjacent actuator arms  32  may be integrated together to provide a U-shaped pad to be mounted on actuator block  30 .  
         [0055]    [0055]FIG. 14 shows a still another preferred embodiment of the pad mounting method. This preferred embodiment employs an actuator arm  32 E having a pair of notches  88  on the opposite side surfaces and a ringlike pad  90  adapted to be fitted with the notches  88 . Accordingly, by engaging the pad  90  with the notches  88 , the pad  90  is mounted on the actuator arm  32 E. The number of pads to be mounted on the actuator arms is arbitrary. For example, the pads may be mounted on the disk opposing surfaces of all the actuator arms. Alternatively, a single pad may be mounted on the disk opposing surface of only one actuator arm. Further, a plurality of pads may be mounted on the disk opposing surface of only one actuator arm.  
         [0056]    [0056]FIG. 15 is a plan view of a magnetic disk drive according to a sixth preferred embodiment of the present invention, and FIG. 16 is a cross section taken along the line  16 A- 16 A in FIG. 15. As shown in FIG. 16, a stopper  92  having a plurality of grooves  94  is fixed to the base  12  by a screw  96 , and the outermost circumferential portions of the plural magnetic disks  14  are inserted in the grooves  94  with a vertical clearance of about 0.1 to 0.2 mm. Preferably, the stopper  92  is formed of resin or rubber. According to this preferred embodiment, deformation of the magnetic disks  14  due to an external shock received can be prevented.  
         [0057]    [0057]FIG. 17 is a plan view of a magnetic disk drive according to a seventh preferred embodiment of the present invention, and FIG. 18 is a cross section taken along the line  18 A- 18 A in FIG. 17. FIG. 17 shows a CSS position of the actuator  20  where the actuator arms  32  are opposed to the outermost circumferential portions of the magnetic disks  14 . As shown in FIG. 18, a stopper  98  having a plurality of grooves  100  is fixed to the base  12  by a screw  102 , and the side edge portions of intermediate ones of the actuator arms  32  are inserted in the grooves  100  with a vertical clearance of about 0.1 to 0.2 mm.  
         [0058]    When the actuator  20  is stopped in the CSS position as shown in FIG. 17, the side edge portions of the intermediate actuator arms  32  are inserted into the grooves  100  of the stopper  98 . Accordingly, deformation of the actuator arms  32  due to an external shock received can be prevented to thereby prevent a contact of the front ends of the actuator arms  32  with the magnetic disks  14 .  
         [0059]    [0059]FIG. 19 is a plan view of a magnetic disk drive according to an eighth preferred embodiment of the present invention, FIG. 20A is a cross section taken along the line  20 A- 20 A in FIG. 19, and FIG. 20B is a cross section taken along the line  20 B- 20 B in FIG. 19. FIG. 19 shows a CSS position of the actuator  20  where the actuator arms  32  are opposed to the outermost circumferential portions of the magnetic disks  14 . This preferred embodiment employs a stopper  104  consisting of a first stopper member  106  and a second stopper member  108  connected together.  
         [0060]    As shown in FIG. 20A, the first stopper member  106  having a plurality of grooves  110  respectively receiving the outermost circumferential portions of the magnetic disks  14  is fixed to the base  12  by a screw  112 . Similarly, as shown in FIG. 20B, the second stopper member  108  having a plurality of grooves  114  respectively receiving the side edge portions of the intermediate actuator arms  32  is fixed to the base  12  by a screw  116 .  
         [0061]    The outermost circumferential portions of the magnetic disks  14  are inserted in the grooves  110  of the first stopper member  106  with a vertical clearance of about 0.1 to 0.2 mm, and the side edge portions of the intermediate actuator arms  32  are inserted in the grooves  114  of the second stopper member  108  with a vertical clearance of about 0.1 to 0.2 mm. Preferably, the stopper  104  is formed of resin or rubber. According to this preferred embodiment, deformation of the magnetic disks  14  and the actuator arms  32  due to an external shock received can be prevented.  
         [0062]    [0062]FIG. 21 is a plan view of a magnetic disk drive according to a ninth preferred embodiment of the present invention, and FIG. 22 is a cross section taken along the line  22 A- 22 A in FIG. 21. In FIG. 22, reference numerals  118  denote spacers for use in crimping the suspensions  38  to the actuator arms  32 . In this preferred embodiment, each actuator arm  32  is integrally formed at its one side edge with a vertical projection or projections  120  higher (thicker) than the spacers  118 . Each projection  120  is located adjacent to one side edge of the corresponding spacer  118 . While the projection or projections  120  are integral with the corresponding actuator arm  32  in this preferred embodiment, a separate projection or projections  120  may be mounted on the corresponding actuator arm  32 .  
         [0063]    In this preferred embodiment, the projections  120  move together with the actuator arms  32  above the disk surfaces of the magnetic disks  14  at a small height in reading/writing data, so that control of the height of each projection  120  is very important. Specifically, the height of each projection  120  must be set smaller than the thickness of at least the head slider  40  mounted on the corresponding suspension  38 . A damage to the magnetic disks  14  due to an external shock received in the inoperative condition of the magnetic disk drive occurs primarily at a position opposed to the substantially front end portions of the actuator arms  32  to which the spacers  118  are fixed. This is considered to be caused by the fact that the magnetic disks  14  and the actuator arms  32  are vibrated upon receipt of an external shock, wherein the lightweight head assemblies  36  less damage the magnetic disks  14  and it is accordingly considered that the front end portions of the actuator arms  32  most damage the magnetic disks  14 .  
         [0064]    According to this preferred embodiment, each spacer  120  is located adjacent to one side edge of the corresponding spacer  118 . Accordingly, in the CSS position of the actuator  20  shown in FIG. 21, each projection  120  faces a non-data region  14   b  circularly formed along the inner circumference of the corresponding magnetic disk  14 . As a result, even when the magnetic disk drive receives an external shock in the inoperative condition, each projection  120  comes into contact with the non-data region  14   b  of the corresponding magnetic disk  14 . Thus, a damage to a data region of each magnetic disk  14  can be prevented.  
         [0065]    Referring to FIG. 23, there is shown a schematic longitudinal section of the front end portion of an actuator arm according to a tenth preferred embodiment of the present invention. In this preferred embodiment, a pad  122  formed of resin or rubber is mounted on the disk opposing surface  32   a  of the actuator arm  32  at a position adjacent to the base end of a spacer  118 . The pad  122  has a thickness smaller than the thickness of the head slider  40  mounted on the front end portion of the suspension  38 . According to this preferred embodiment, the pad  122  formed of a material softer than that of the spacer  118  is mounted on the disk opposing surface  32   a  of the actuator arm  32  near the spacer  118 . Accordingly, even when the magnetic disk drive receives an external shock, the pad  122  comes into contact with the magnetic disk  14  to thereby prevent a damage to the magnetic disk  14 .  
         [0066]    Referring to FIG. 24, there is shown a sectional view of a spindle assembly  124  in a magnetic disk drive according to an eleventh preferred embodiment of the present invention. A flange  126  is fixed to the base  12  by a plurality of screws  128  (one of which being shown). A shaft  130  is press-fitted with the flange  126 . Coils  138  are mounted on the flange  126 . A spindle hub  136  is rotatably mounted on the shaft  130  through a pair of bearings  132  and  134 . Permanent magnets  140  are mounted on the spindle hub  136  so as to be opposed to the coils  138  through a yoke  139 .  
         [0067]    Magnetic disks  14  and spacers  142  are mounted on the spindle hub  136  in such a manner as to be alternately stacked, and a clamp  144  is fixed to the spindle hub  136  by screws  146 , thereby mounting the magnetic disks  14  on the spindle hub  136  in equally spaced relationship with each other. The spindle hub  136  is integrally formed at its upper end with an annular projection  148 . Reference numeral  13  denotes a cover of the magnetic disk drive. The cover  13  is formed with a circular recess  150  for receiving the annular projection  148  of the spindle hub  136 . Preferably, there is defined an annular clearance of about 2 mm between the outer circumferential surface of the annular projection  148  and the inner wall surface of the circular recess  150 .  
         [0068]    The magnetic disk drive of this preferred embodiment has a single-supported spindle structure such that the shaft  130  is supported to the base  12  only. In general, such a single-supported spindle structure is inferior in shock resistance to a double-supported spindle structure. However, this preferred embodiment includes the annular projection  148  formed at the upper end of the spindle hub  136  and the circular recess  150  formed on the cover  13  for receiving the annular projection  148 , thereby preventing a tilt of the spindle assembly  124  due to an external shock received.  
         [0069]    According to one aspect of the present invention, a pad is provided on the disk opposing surface of an actuator arm. Accordingly, even when the magnetic disk drive receives an external shock, the pad provided on the actuator arm comes into contact with the outermost circumferential portion of a magnetic disk, thereby limiting a tilt of the actuator arm or a spindle to prevent a contact of the front end of the actuator arm with a data region on the disk surface.  
         [0070]    According to another aspect of the present invention, a stopper for limiting a vertical displacement of the magnetic disk and/or the actuator arm is fixed to the base, thereby preventing a deformation of the disk and the actuator arm.  
         [0071]    According to a further aspect of the present invention, there is provided a magnetic disk drive having a single-supported spindle structure wherein an annular projection is formed integrally at the upper end of a spindle hub, and a circular recess for receiving the annular projection is formed on a cover. With this configuration, a tilt of the spindle due to an external shock received can be prevented.