Patent Publication Number: US-2013234552-A1

Title: Rotating device

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a rotating device like a disk drive device, and more specifically, to a rotating device having a shaft fastened to a stationary body. 
     2. Description of the Related Art 
     Rotating devices like disk drive devices are becoming compact and increasing the capacity, and loaded in various electronic devices. In particular, loading of hard disk drives that are a kind of the disk drive devices in portable electronic devices, such as a laptop computer and a portable music player, is advancing. Rotating devices like disk drive devices loaded in such portable electronic device need improvement of shock resistance and vibration resistance in order to withstand a shock due to a falling and a vibration at the time of carrying in comparison with the rotating devices loaded in a stationary electronic device like a desktop computer. Conversely, such rotating devices need thinning and reduction in weight in comparison with the rotating devices loaded in the stationary electronic device like a desktop computer. In general, thinning and improvement of shock resistance are in a trade-off relationship. 
     The inventors of the present invention propose, in JP 2010-261580 A, for example, a rotating device having a shaft fastened to a base and employing a bearing unit that is a fluid dynamic bearing mechanism. According to the disk drive device disclosed in JP 2010-261580 A, a shaft of a fluid dynamic bearing unit has one end directly joined with a base member to form a joined part. A screw hole is formed in another end of the shaft, and a top cover is fixed thereto by a screw. Moreover, another end of the shaft is joined with a flange member to form a joined part. That is, the joined part of the base and the shaft and the joined part of the flange member and the shaft overlap in the axial direction, and thus a relationship is satisfied in which the length in the axial direction of another joined part becomes short when the length in the axial direction of the one joined part is increased under a condition in which the thickness of the rotating device in the axial direction is restricted. 
     In order to make the rotating device thinner, a technique of reducing the length in the axial direction of the joined part of the base and the shaft is possible. According to the conventional fastened-shaft type motor disclosed in, for example, JP 2010-261580 A, however, when the length in the axial direction of the joined part of the base and the shaft is reduced, since the diameter of that joined part is small, the joining strength decreases. Moreover, when a shock is applied to the rotating device, the joined part of the base and the shaft highly possibly breaks down. That is, in order to make the rotating device thinner, there is a task of enhancing the strength of the joined part of the base and the shaft, thereby suppressing the reduction of the shock-resistance strength. 
     Moreover, a technique of reducing the dimension in the rotation axis direction of a dynamic pressure generating part is also possible in order to make the rotating device thinner. However, when the dimension in the rotation axis direction of the dynamic pressure generating part is reduced, it results in the reduction of the rigidity of the bearing unit, which may negatively affects the shock resistance and vibration resistance of the motor. Alternatively, such a motor includes a stationary body and a rotating body, and the stationary body and the rotating body may have respective faces in the rotation axis direction contacting with each other when a shock like a falling is applied. When the stationary body and the rotating body contact with each other, it becomes a cause of a breakdown in the worst case. 
     Alternatively, according to the conventional fastened-shaft type motor disclosed in JP 2010-261580 A, a top cover is formed with a hole at the center part thereof, and a screw passing all the way through this hole is engaged and joined with the screw hole in the end of a shaft of a fluid dynamic bearing unit. Accordingly, since the screw hole is formed in another end of the shaft, the thickness of such an area where the screw hole is formed is reduced in the radial direction, and thus the strength may be reduced. In general, when such a rotating device is made thin, the dimension in the axial direction of the shaft is reduced. When the shaft becomes short with the dimension of the screw hole in the axial direction being constant, the ratio of the area of the shaft where the screw hole is formed in the axial direction increases. When a screw is engaged with the screw hole of the shaft having the ratio of the screw-hole formed area high, compression stress that compresses the shaft in the axial direction is applied to the shaft. This compression stress causes the shaft to expand from the outer circumferential surface thereof, and to be deformed non-uniformly. The caused deformation may negatively affect the fluid dynamic bearing unit provided around the outer circumferential surface of the shaft. For example, the gap of the fluid dynamic bearing unit may become uneven, and thus the stationary body and the rotating body may have circumferential surfaces contacting with each other. When the stationary body and the rotating body contact with each other, the contacting part is worn, which reduces the lifetime of the rotating device. Moreover, when the stationary body and the rotating body contact with each other, it becomes a cause of a breakdown of the rotating device in the worst case. Conversely, when the dimension in the axial direction of the screw hole is reduced, the engaged area between the screw and the screw hole becomes small, and thus the joining strength between the screw and the screw hole decreases. According to such a rotating device, when a shock like a falling is applied, the possibility that the joined part of the screw and the screw hole comes loose increases. When the joined part of the screw and the screw hole becomes loose, it becomes a cause of a breakdown in the worst case. Hence, there is also a task of joining the shaft with the top cover without providing a screw hole to be engaged with a screw in another end of the shaft. 
     The same is true of not only the rotating devices loaded in portable electronic devices, but also electronic devices of other types, in particular, rotating devices having a shaft fastened to a stationary body and employing a fluid dynamic bearing unit. 
     The present invention has been made in view of such circumstances, and it is an object of the present invention to provide a rotating device which is an improvement of conventional rotating devices and which enhances the shock resistance of a part forming a fluid dynamic bearing unit, thereby facilitating a thinning. 
     SUMMARY OF THE INVENTION 
     A first aspect of the present invention relates to a rotating device. This rotating device includes: a base including a peripheral wall provided at a peripheral edge of the base; a top cover fastened to the peripheral wall; an axial body having one end fixedly provided to the base, and having another end joined with the top cover; a bearing body which retains thereinside the axial body and which is supported in a freely rotatable manner relative to the base; a radial dynamic pressure generating groove provided in either one of surfaces of the axial body and the bearing body facing with each other in a radial direction; a lubricating medium present in a space between the axial body and the bearing body; a lower flange provided on a side face of the axial body at the one-end side, and extending outwardly of the radial direction; and an upper flange provided on a side face of the axial body at the another-end side, and extending outwardly of the radial direction. The bearing unit is placed in a space between the upper flange and the lower flange in an axial direction, and the axial body includes a lower rod to which the lower flange is fastened, and an upper rod which encircles the lower rod and to which the upper flange is fastened. 
     A second aspect of the present invention also relates to a rotating device. This rotating device includes: a base including a peripheral wall provided at a peripheral edge of the base; a top cover fastened to the peripheral wall; an axial body having one end fixedly provided to the base, and having another end joined with the top cover; a bearing body which retains thereinside the axial body and which is supported in a freely rotatable manner relative to the base; a radial dynamic pressure generating groove provided in either one of surfaces of the axial body and the bearing body facing with each other in a radial direction; a lubricating medium present in a space between the axial body and the bearing body; a lower flange provided on a side face of the axial body at the one-end side, and extending outwardly of the radial direction; and an upper flange provided on a side face of the axial body at the another-end side, and extending outwardly of the radial direction. The bearing unit is placed in a space between the upper flange and the lower flange in an axial direction, the axial body includes a lower rod to which the lower flange is fastened, and an upper rod which encircles the lower rod and to which the upper flange is fastened, and the axial body further includes an axial-body convexity engaged with an engagement hole provided in the top cover. 
     A third aspect of the present invention also relates to a rotating device. This rotating device includes: a base including a peripheral wall provided at a peripheral edge of the base; a top cover fastened to the peripheral wall; an axial body having one end fixedly provided to the base, and having another end joined with the top cover; a bearing body which retains thereinside the axial body and which is supported in a freely rotatable manner relative to the base; a radial dynamic pressure generating groove provided in either one of surfaces of the axial body and the bearing body facing with each other in a radial direction; and a lubricating medium present in a space between the axial body and the bearing body. The axial body includes an axial-body convexity engaged with an engagement hole provided in the top cover. 
     Any combination of the above-explained components and replacement of the component of the present invention and the expression thereof between a method, a device, and a system, etc., are also advantageous as an aspect of the present invention. 
     According to the present invention, it becomes possible to provide a rotating device which enhances the shock resistance of a part forming a fluid dynamic bearing unit, thereby facilitating a thinning. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an exploded perspective view illustrating a rotating device according to a first embodiment; 
         FIG. 2  is a cross-sectional view taken along a line A-A in  FIG. 1 ; 
         FIG. 3  is an enlarged exploded cross-sectional view illustrating a fluid dynamic bearing unit in  FIG. 2  exploded so as to illustrate the major components in an enlarged manner; 
         FIG. 4  is an enlarged cross-sectional view illustrating a periphery of an area where a lubricant in  FIG. 2  is present in an enlarged manner; 
         FIG. 5  is an enlarged cross-sectional view illustrating the rotating device in  FIG. 2  with a top cover attached thereto; 
         FIG. 6  is an enlarged cross-sectional view illustrating a joined part of the top cover in  FIG. 5  with an upper shaft member; 
         FIG. 7  is an enlarged cross-sectional view illustrating a joined part of a top cover of a rotating device and an upper shaft member thereof according to a first modified example; 
         FIG. 8  is an enlarged cross-sectional view illustrating a joined part of a top cover of a rotating device and an upper shaft member thereof according to a second modified example; 
         FIG. 9  is an enlarged cross-sectional view illustrating a joined part of a top cover of a rotating device and an upper shaft member thereof according to a third modified example; 
         FIG. 10  is an enlarged cross-sectional view illustrating a joined part of a top cover of a rotating device and an upper shaft member thereof according to a fourth modified example; 
         FIG. 11  is an enlarged cross-sectional view illustrating a joined part of a top cover of a rotating device and an upper shaft member thereof according to a fifth modified example; and 
         FIG. 12  is an enlarged cross-sectional view illustrating a joined part of a top cover of a rotating device and an upper shaft member thereof according to a sixth modified example; 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Preferred embodiments of the present invention will be explained below with reference to the accompanying drawings. The same or equivalent component illustrated in the respective figures will be denoted by the same reference numeral, and the duplicated explanation thereof will be omitted accordingly. The dimension of a component in each figure is indicated in an enlarged or scale-down manner as needed in order to facilitate understanding to the present invention. A part of a component not important to explain an embodiment of the present invention in each figure will be omitted. 
     The rotating device according to an embodiment is suitably used as a disk drive device like a hard disk drive as an example on which a magnetic recording disk magnetically recording data is to be mounted and which rotates and drives such a magnetic recording disk. In particular, it is suitably used as a fastened-shaft disk drive device which has a shaft fastened to a base and which has a hub rotating relative to the shaft. For example, this rotating device includes a rotating body that is attached to a stationary body in a freely rotatable manner through a bearing unit. For example, the rotating body includes a mount which can mount a drive-target medium like the magnetic recording disk. For example, the bearing unit includes a radial bearing unit formed in either one of the stationary body and the rotating body. For example, the bearing unit includes a thrust bearing unit formed in either one of the stationary body and the rotating body. For example, the thrust bearing unit is located outwardly of the radial bearing unit in the radial direction. For example, the radial bearing unit and the thrust bearing unit may produce dynamic pressure to a lubricating medium. For example, the radial bearing unit and the thrust bearing unit may include the lubricating medium. For example, the rotating device may include a rotating-driving unit that applies rotation torque to the rotating body. For example, the rotating-driving unit may be a brush-less spindle motor. For example, this rotating-driving unit may include coils and a magnet. 
     Embodiment 
       FIG. 1  is a perspective view illustrating a rotating device  100  according to an embodiment of the present invention.  FIG. 1  illustrates a condition in which a top cover  22  is detached in order to facilitate understanding to the present invention. The rotating device  100  includes a base  24 , an upper shaft member  110 , a hub  26 , a magnetic recording disk  62 , a data reader/writer  60 , the top cover  22 , and for example, six screws  104 . 
     In the following explanation it is defined that a side where the hub  26  is mounted on the base  24  is an upper side. Moreover, a direction along a rotation axis R of a rotating body, an arbitrary direction passing through the rotation axis R on a plane orthogonal to the rotation axis R, and an arbitrary direction on that plane are defined as an axial direction, a radial direction, and a planar direction, respectively. 
     The magnetic recording disk  62  is, for example, a 2.5-inch magnetic recording disk formed of glass and having a diameter of 65 mm. The magnetic recording disk  62  has a center hole with a diameter of, for example, 20 mm, and has a thickness of, for example, 0.65 mm. The hub  26  carries, for example, one magnetic recording disk  62 . The magnetic recording disk  62  is fastened to the hub  26  by, for example, unillustrated clamper. The magnetic recording disk  62  may be held between the clamper and the hub  26 . The clamper may be fastened by, for example, engaging the inner circumferential surface with a circumferential groove  26 G of the hub  26  to be discussed later. 
     The base  24  is formed by performing die-cast molding on an aluminum alloy. The base  24  includes a bottom plate  24 A that forms the bottom of the rotating device  100 , and an outer peripheral wall  24 B formed along the outer circumference of the bottom plate  24 A so as to surround an area where the magnetic recording disk  62  is to be mounted. The outer peripheral wall  24 B has, for example, six screw holes  24 C provided in the top face. 
     The data reader/writer  60  includes a recording/playing head (unillustrated), a swing arm  64 , a voice coil motor  66 , and a pivot assembly  68 . The recording/playing head is attached to the tip of the swing arm  64 , records data in the magnetic recording disk  62 , or reads the data therefrom. The pivot assembly  68  supports the swing arm  64  in a swingable manner to the base  24  around a head rotating shaft S. The voice coil motor  66  allows the swing arm  64  to swing around the head rotating shaft S to move the recording/playing head to a desired location over the top face of the magnetic recording disk  62 . The voice coil motor  66  and the pivot assembly  68  are configured by a conventionally well-known technology of controlling the position of a head. 
     The top cover  22  is a thin plate formed in a substantially rectangular shape, and has, for example, six screw through-holes  22 C provided at the periphery of the top cover  22 , a cover recess  22 E, and an engagement hole  22 D provided at the center of the cover recess  22 E. The top cover  22  is formed by, for example, pressing an aluminum plate or an iron-steel plate into a predetermined shape. A surface processing like plating may be applied on the top cover  22  in order to suppress corrosion. The top cover  22  is fastened to the top face of the outer peripheral wall  24 B of the base  24  by, for example, the six screws  104 . The six screws  104  correspond to the six screw holes  24 C, respectively. In particular, the top cover  22  and the top face of the outer peripheral wall  24 B are fastened with each other so as to suppress a leak into the interior of the rotating device  100  from the joined portion of the top cover  22  and the top face of the outer peripheral wall  24 B. The interior of the rotating device  100  is, more specifically, a clean space  70  surrounded by the bottom plate  24 A of the base  24 , the outer peripheral wall  24 B of the base  24 , and the top cover  22 . This clean space  70  is designed so as to be fully sealed, i.e., so as not to have a leak-in from the exterior and a leak-out to the exterior. The clean space  70  is filled with clean air having particles eliminated. Hence, foreign materials like the particles are prevented from sticking to the magnetic recording disk  62 , thereby improving the reliability of the operation of the rotating device  100 . The engagement hole  22 D of the top cover  22  is engaged and joined with a cylindrical convexity  110 F of the upper shaft member  110 . 
       FIG. 2  is a cross-sectional view taken along a line A-A in  FIG. 1 .  FIG. 3  is an enlarged exploded cross-sectional view illustrating the major components of a fluid dynamic bearing unit in an enlarged manner by exploding the fluid dynamic bearing unit illustrated in  FIG. 2 .  FIGS. 2 and 3  are symmetrical along the rotation axis R, and either right or left reference numeral for the same component will be omitted in some cases in the figures. 
     With reference to  FIG. 2 , a stationary body  2  includes the upper shaft member  110 , a lower shaft member  112 , a stator core  32 , coils  30 , and a magnetic ring  34 . The upper shaft member  110  includes an upper rod  10  and an upper flange  12 . The lower shaft member  112  includes a lower rod  14 , a lower flange  16 , and a flange encircling member  18 . 
     A rotating body  4  includes a shaft encircling member  40 , a cap  48 , and a cylindrical magnet  28 . A lubricant  20  is continuously present in several portions between the rotating body  4  and the stationary body  2 . The shaft encircling member  40  includes a sleeve  42 , a cylindrical member  44 , and a ring member  46 . 
     The base  24  is formed with an opening  24 D around the rotation axis R of the rotating body  4 , and includes an annular protrusion  24 E encircling the opening  24 D. The protrusion  24 E protrudes toward the hub  26  from the upper face of the base  24 . 
     The stator core  32  includes an annular part and, for example, 12 salient poles running outwardly of the radial direction from the annular part, and is fastened to, for example, an outer circumferential surface of the protrusion  24 E at the upper-surface side of the base  24 . The stator core  32  can be joined with the base  24  by press-fitting, bonding or a combination thereof. The stator core  32  is formed by, for example, laminating five electromagnetic steel sheets each with a thickness of 0.2 mm and joining those sheets together by caulking. A skin layer is provided on the surface of the stator core  32 . Insulation painting, such as electrodeposition coating or a power coating, is applied on the surface of the stator core  32 . The coil  30  is wound around each salient pole of the stator core  32 . When, for example, a three-phase substantially sinusoidal waveform drive current is caused to flow through the coils  30 , field magnetic field is produced along the respective salient poles. 
     The magnetic ring  34  is coaxial with the magnet  28  along the rotation axis R, and is firmly fastened to the upper face of the base  24  by, for example, bonding, caulking or a combination thereof. The magnetic ring  34  is in a hollow ring shape that is thin in the axial direction, and is formed by pressing, for example, a ferrous sheet with soft magnetism. The magnetic ring  34  has an area facing with a bottom face  28 D of the magnet  28  in a non-contact manner therewith in the axial direction, and applies downward suction force to the magnet  28 . This structure suppresses a floating of the rotating body  4  in the axial direction when the rotating body  4  is rotating. 
     The hub  26  includes a hollow first annular part  26 A, a disk part  26 D extending outwardly of the radial direction from an outer circumferential surface  26 C of the first annular part  26 A, a second annular part  26 E extending downwardly of the axial direction from the outer circumference of the disk part  26 D, and a mount part  26 J extending outwardly of the radial direction from a lower outer circumferential surface  26 F of the second annular part  26 E. The hub  26  is formed in a substantially cup shape. The first annular part  26 A, the disk part  26 D, the second annular part  26 E, and the mount part  26 J are formed coaxially with each other along the rotation axis R. The first annular part  26 A, the disk part  26   d , the second annular part  26 E, and the mount part  26 J are formed together as a single piece. Any part may be formed separately and joined with the other parts. The hub  26  is formed of a ferrous material with soft magnetism like SUS 430F. The outer circumferential surface  26 F of the second annular part  26 E of the hub  26  is engaged with the inner circumferential surface of the magnetic recording disk  62  in a doughnut shape. The magnetic recording disk  62  is to be mounted on the top of the mount part  26 J of the hub  26 . The circumferential groove  26 G recessed inwardly of the radial direction is formed annularly in the outer circumferential surface  26 F of the second annular part  26 E. The circumferential groove  26 G is located above the top face of the magnetic recording disk  62  in the axial direction when the magnetic recording disk  62  is mounted on the hub  26 . For example, an inner circumference of the clamper may be fitted and fastened to the circumferential groove  26 G. A protrusion  26 M protruding downwardly of the axial direction is provided on the lower face of the disk part  26 D at the outer circumferential side. A recess  261  recessed outwardly of the radial direction is provided annularly at the upper part of an inner circumferential surface  26 B of the first annular part  26 A. 
     The magnet  28  is in a hollow ring shape, and has an outer circumferential surface fastened to an inner circumferential surface  26 H of the hub  26  by, for example, bonding. An upper face  28 C contacts the protrusion  26 M of the hub  26 . 16 drive magnetic poles are provided at an inner circumferential surface  28 B in the circumferential direction by magnetization. The magnet  28  is formed of a material containing, for example, neodymium, iron, or boron. The magnet  28  may contain a resin at a predetermined percentage. The magnet  28  may be formed of a material containing a ferrite magnetic material, or may be formed by laminating a layer containing a ferrite magnetic material and a layer containing a rare-earth material like neodymium. A skin layer is provided on the surface of the magnetic layer of the magnet  28 . For example, electrodeposition coating or spray painting is applied on the surface of the magnet  28 . The provided skin layer suppresses an oxidization of the magnet, or suppresses a peeling of the surface of the magnet. 
     An explanation will be given of the fluid dynamic bearing unit with reference to  FIG. 4 .  FIG. 4  is an enlarged cross-sectional view illustrating the periphery of an area where the lubricant  20  is present in  FIG. 2  in an enlarged manner.  FIG. 4  illustrates only the left part relative to the rotation axis R. 
     The lower shaft member  112  includes a lower rod  14  in a rod shape having a through-hole  14 B formed in the center thereof, a lower flange  16  in a disk shape extending outwardly of the radial direction from the lower end of an outer circumferential surface  14 A of the lower rod  14 , and a flange encircling member  18  in a cylindrical shape protruding upwardly of the axial direction from the outer peripheral edge of the lower flange  16 . For example, the lower shaft member  112  has the lower rod  14 , the lower flange  16 , and the flange encircling member  18  formed together as a single piece. In this case, the production error of the lower shaft member  112  can be reduced, and the labor work for joining those members can be eliminated. Alternatively, the lower shaft member  112  can be prevented from being deformed by a shock and a load. For example, the lower shaft member  112  is formed by cutting and machining a metallic material like SUS 303. The lower shaft member  112  may be formed of other materials like a resin, and may be formed by other techniques, such as pressing and molding. The lower shaft member  112  has an outer circumferential surface  18 B of the flange encircling member  18  and an outer circumferential surface  16 B of the lower flange  16  bonded to the inner circumferential surface of the opening  24 D, thereby being fastened to the base  24 . The lower rod  14  has a passage cover  120  that covers the lower end of the through-hole  14 B. For example, the passage cover  120  is formed by applying a sealant around the lower end of the through-hole  14 B and the edge thereof, and letting such a sealant to be cured. The passage cover  120  may be formed by bonding and fastening a sheet formed of, for example, a metallic material or a resin material. For example, an upper end  18 C of the flange encircling member  18  is located at or above an area where a first dynamic pressure generating groove  50  to be discussed later is provided in the axial direction. This structure increases the volume of a space between an inner circumferential surface  18 A of the flange encircling member  18  and an outer circumferential surface of the shaft encircling member  40  to be discussed later, thereby increasing the volume of the retainable lubricant  20 . The increase of the retained lubricant  20  reduces the possibility that a failure occurs due to the lack of the lubricant  20 . 
     The upper shaft member  110  includes an upper rod  10  in a rod shape having a retainer hole  10 A formed in the center thereof and retaining the lower rod  14 , and an upper flange  12  in a substantially disk shape extending outwardly of the radial direction from the upper end of an outer circumferential surface  10 C of the upper rod  10 . The upper shaft member  110  includes the cylindrical convexity  110 F at an upper end of the upper rod  10  and protruding in a cylindrical shape upwardly of the axial direction. For example, the upper shaft member  110  has the upper rod  10 , the upper flange  12 , and the cylindrical convexity  110 F formed together as a single piece. For example, the upper shaft member  110  may have the upper rod  10  and the cylindrical convexity  110 F formed together and have the upper flange  12  formed separately but joined together. For example, the upper shaft member  110  is formed by cutting and machining a ferrous material like SUS 420 J2. For example, the upper shaft member  110  may be quenched in order to increase the hardness. For example, the upper shaft member  110  may have an outer circumferential surface  10 C of the upper rod  10  and a lower face  12 C of the upper flange  12  polished in order to enhance the dimensional precision. The upper shaft member  110  may be formed of other materials like a resin, and may be formed by other techniques, such as pressing and molding. The upper shaft member  110  has an upper end fastened to the top cover  22  through a method to be discussed later. The lower rod  14  is encircled by and fastened to the upper rod  10 . For example, the lower rod  14  has the outer circumferential surface  14 A fastened to the retainer hole  10 A by a combination technique of bonding and press-fitting. In  FIG. 4 , a lower part of the outer circumferential surface  14 A is defined as a press-fit surface  14 AA, while a bonding surface  14 AB having a smaller diameter than the press-fit surface  14 AA is provided above the press-fit surface  14 AA. A bond of, for example, anaerobic is present between the retainer hole  10 A and the bonding surface  14 AB. 
     As will be discussed later, the cylindrical convexity  110 F is fitted in and bonded to the engagement hole  22 D of the top cover  22 , and thus the upper shaft member  110  is fastened to the top cover  22 . Moreover, the top cover  22  is fastened to the base  24 . According to the rotating device of this type having both ends of the shaft fastened to a chassis including the base  24  and the top cover  22 , among the fastened-shaft rotating devices, the shock resistance of the rotating device and the vibration resistance thereof can be enhanced. 
     The upper end of the upper shaft member  110  may be fastened to the top cover  22  by other techniques than bonding, such as caulking and welding. Since no threaded screw hole to which a screw is fastened is formed in the upper end of the upper shaft member  110 , a deformation of the outer circumferential surface of the upper rod  10  that occurs in the case of a structure in which a screw is engaged with a screw hole can be suppressed. 
     The upper rod  10  has a gas reservoir  10 B provided at an upper end area of the retainer hole  10 A and reserving a gas. The gas reservoir  10 B is formed as a space in a substantially conical or cylindrical shape. The gas reservoir  10 B is in communication with the through-hole  14 B of the lower rod  14 . When an uncured bond is present between the retainer hole  10 A and the outer circumferential surface  14 A, this bond is let cured while producing a gas of contained volatile components. However, by providing the gas reservoir  10 B, the volatile component gas of the bond is efficiently discharged to the exterior through the gas reservoir  10 B and the through-hole  14 B. This results in a reduction of a curing time of the bond, and a reduction of a labor hour. Moreover, the passage cover  120  is provided so as to block off the through-hole  14 B after a predetermined time has elapsed since such a work completes. This reduces the possibility of a leak-in of foreign materials from the through-hole  14 B, the gas reservoir  10 B, and the space between the upper rod  10  and the lower rod  14  to the region where the lubricant  20  is present. Moreover, in a labor work of fitting the lower rod  14  into the retainer hole  10 A, air in the retainer hole  10 A is discharged to the exterior through the gas reservoir  10 B and the through-hole  14 B, the efficiency of the fitting work improves. 
     The upper flange  12  includes an inclined surface  12 AA provided at an outer circumferential surface  12 A and having a distance in the radial direction from the rotation axis R becoming large as becoming close to the base  24 . The upper flange  12  has the lower face  12 C facing with an upper face  42 C of the sleeve  42  of the shaft encircling member  40  to be discussed later with a gap in the axial direction. The upper flange  12  includes a terrace  12 D extending inwardly of the radial direction from the upper end of the outer circumferential surface  12 A, and an uplift  12 E raised upwardly of the axial direction in a substantially cylindrical shape from the internal end of the terrace  12 D. The cylindrical convexity  110 F protrudes upwardly of the axial direction from the middle part of the uplift  12 E. The cylindrical convexity  110 F includes a circumferential recess  110 G provided around the outer circumferential surface of the cylindrical convexity  110 F. A seat  110 H with which a lower surface of the top cover  22  contacts and which extends outwardly of the radial direction is provided around the cylindrical convexity  110 F. 
     The shaft encircling member  40  encircles the upper rod  10  with a gap, and is rotatable relative to the upper rod  10 . The shaft encircling member  40  is present between the upper flange  12  and the lower flange  16  with respective gaps. The shaft encircling member  40  is encircled by and fastened to the hub  26 . The shaft encircling member  40  is encircled by the flange encircling member  18  of the lower shaft member  112  with a gap. According to such a structure, the hub  26  is supported in a rotatable manner relative to the base  24 . 
     The shaft encircling member  40  includes the substantially cylindrical sleeve  42  that encircles the upper rod  10 , a cylindrical member  44  in a substantially cylindrical shape that encircles and is joined with the sleeve  42 , and a ring member  46  in a ring shape that is joined with an upper end part of the cylindrical member  44 . The sleeve  42  and the cylindrical member  44  are each formed by, for example, cutting and machining a metallic material like brass, and applying electroless nickel plating on the surface thereof. The sleeve  42  and the cylindrical member  44  may be formed of other materials like stainless steel. For example, the sleeve  42  is joined with the cylindrical member  44  by interference fitting like press-fitting or bonding. The sleeve  42  and the cylindrical member  44  may be formed together as a single piece. 
     The sleeve  42  is in a substantially hollow cylindrical shape, and includes an inner circumferential surface  42 A, an outer circumferential surface  42 B, the upper face  42 C, and a lower face  42 D. The sleeve  42  has the inner circumferential surface  42 A encircling the upper rod  10  with a gap. The sleeve  42  has the first dynamic pressure generating groove  50  and a second dynamic pressure generating groove  52  for generating radial dynamic pressure and provided in areas of the inner circumferential surface  42   a  facing with the outer circumferential surface  10 C of the upper rod  10  in the radial direction. The second dynamic pressure generating groove  52  is provided above the first dynamic pressure generating groove  50  so as to be distant therefrom. The first and second dynamic pressure generating grooves  50  and  52  may be provided in the outer circumferential surface  10 C of the upper rod  10  instead of the sleeve  42 . 
     A third dynamic pressure generating groove  54  for generating thrust dynamic pressure is provided in an area of the upper face  42 C of the sleeve  42  facing with the upper flange  12  in the axial direction. The third dynamic pressure generating groove  54  may be provided in an area of the lower face  12 C of the upper flange  12  facing with the sleeve  42  in the axial direction instead of the sleeve  42 . A fourth dynamic pressure generating groove  56  for generating thrust dynamic pressure is provided in an area of the lower face  42 D of the sleeve  42  facing with the lower flange  16  in the axial direction. The fourth dynamic pressure generating groove  56  may be provided in an area of an upper face  16 A of the lower flange  16  facing with the sleeve  42  in the axial direction instead of the sleeve  42 . 
     For example, the first and second dynamic pressure generating grooves  50  and  52  are each formed in a herringbone shape. The first and second dynamic pressure generating grooves  50  and  52  may be in other shapes like a spiral shape. For example, the third and fourth dynamic pressure generating grooves  54  and  56  are each formed in a herringbone shape. The third and fourth dynamic pressure generating grooves  54  and  56  may be formed in other shapes like a spiral shape. The first, second, third and fourth dynamic pressure generating grooves  50 ,  52 ,  54 , and  56  are formed by, for example, pressing, ball-rolling, etching, and cutting and machining. Those dynamic pressure generating grooves may be formed by different techniques from each other. 
     The cylindrical member  44  is in a substantially hollow cylindrical shape, and includes an inner circumferential surface  44 A, an outer circumferential surface  44 B, an upper face  44 C, a lower face  44 D, and a recess  44 E provided annularly at the upper end side of the inner circumferential surface  44 A so as to be concaved outwardly of the radial direction. The inner circumferential surface  44 A is joined with the sleeve  42 . An upper part of the outer circumferential surface  44 B is joined with an inner circumferential surface  26 B of the first annular part  26 A of the hub  26 . A part of the outer circumferential surface  44 B below the area joined with the hub  26  is encircled by the flange encircling member  18  with a gap. The outer circumferential surface  44 B includes an inclined surface  44 BA provided at an area facing with the inner circumferential surface  18 A of the flange encircling member  18  in the radial direction and having a radius becoming small as coming close to the upper end of the outer circumferential surface  44 B. A gap between the inclined surface  44 BA and the inner circumferential surface  18 A gradually becomes widespread toward the upper space in the axial direction. The inclined surface  44 BA and the inner circumferential surface  18 A contact a first air-liquid interface  122  of the lubricant  20  to be discussed later, and form a capillary seal that prevents the lubricant  20  from being splashed by capillary force. For example, the first air-liquid interface  122  is located at or above the area where the first dynamic pressure generating groove  50  is disposed in the axial direction. This structure enables the rotating device  1  to retain a larger amount of lubricant  20 , thereby reducing the possibility of a breakdown due to the lack of the lubricant  20 . For example, the first air-liquid interface  122  is provided outwardly of the third and fourth dynamic pressure generating grooves  54  and  56  in the radial direction. 
     The ring member  46  is in a hollow ring shape, and includes an inner circumferential surface  46 A, an outer circumferential surface  46 B, an upper face  46 C, and a lower face  46 D. The ring member  46  is formed by, for example, cutting and machining a stainless-steel material like SUS 303 or SUS 430. The ring member  46  has the outer circumferential surface  46 B and the lower face  46 D fitted in the recess  44 E of the cylindrical member  44 , and bonded and fastened thereto. The ring member  46  includes an inclined surface  46 AA provided at the inner circumferential surface  46 A and having a diameter that becomes small as coming close to the upper end of the inner circumferential surface  46 A. The inclined surface  46 AA of the ring member  46  and the inclined surface  12 AA of the upper flange  12  contact a second air-liquid interface  124  of the lubricant  20  to be discussed later, and form a capillary seal that prevents the lubricant  20  from being splashed by capillary force. 
     The cap  48  is a hollow ring shape thin in the axial direction, and includes an inner circumferential surface  48 A, an outer circumferential surface  48 B, an upper face and a lower face  48 D. For example, the cap  48  is formed by cutting and machining a stainless-steel material like SUS 303 or SUS 430. The cap  48  may be formed of other metallic materials or resin materials or may be formed through other techniques, such as pressing and molding. The cap  48  has the outer circumferential surface  48 B fitted in the recess  261  of the inner circumferential surface  26 B of the first annular part  26 A of the hub  26 , and bonded and joined thereto. The cap  48  has the lower face  48 D covering the second air-liquid interface  124 . The cap  48  has the inner circumferential surface  48 A encircling the side face of the uplift  12 E of the upper flange  12  in a non-contact manner. The inner circumferential side of the lower face  48 D of the cap  48  faces the terrace  12 D of the upper flange  12  in a non-contact manner in the axial direction. This structure causes the cap  48  and the upper flange  12  to form a labyrinth to the lubricant  20 , thereby preventing the lubricant  20  from being splashed. 
     The lubricant  20  is present between the rotating body  4  and the stationary body  2  continuously from the first air-liquid interface  122  to the second air-liquid interface  124 . The lubricant  20  is present, for example, a space between the inclined surface  44 BA and the inner circumferential surface  18 A in the radial direction, a space between the cylindrical member  44  and the lower flange  16  in the axial direction, a space between the sleeve  42  and the lower flange  16  in the axial direction, a space between the sleeve  42  and the upper rod  10  in the radial direction, a space between the upper flange  12  and the sleeve  42  in the axial direction, a space between the upper flange  12  and the cylindrical member  44  in the radial direction, and a space between the inclined surface  12 AA and the inclined surface  46 AA in the radial direction. When the rotating body  4  rotates relative to the stationary body  2 , the first, second, third, and fourth dynamic pressure generating grooves  50 ,  52 ,  54 , and  56  cause the lubricant  20  to produce dynamic pressure. Such dynamic pressure supports the rotating body  4  in the radial direction and in the axial direction in a non-contact manner with the stationary body  2 . 
     The shaft encircling member  40  includes, separately from the gap between the sleeve  42  and the upper rod  10  in the radial direction, a communication passage BP of the lubricant  20  that causes the space between the upper flange  12  and the sleeve  42  in the axial direction and the space between the sleeve  42  and the lower flange  16  in the axial direction to be in communication with each other. For example, the communication passage BP includes a passage provided in the sleeve  42  in the axial direction. The communication passage BP may be provided in the cylindrical member  44  instead of the sleeve  42 . The communication passage BP reduces a pressure difference between the space between the upper flange  12  and the sleeve  42  in the axial direction and the space between the sleeve  42  and the lower flange  16  in the axial direction. As a result, a possibility that the lubricant  20  leaks out can be reduced. 
     An explanation will now be given of a structure in which the top cover  22  is joined with the upper shaft member  110  with reference to  FIGS. 5 and 6 .  FIG. 5  is an enlarged cross-sectional view illustrating how the top cover  22  is attached to the rotating device in  FIG. 2 .  FIG. 6  is an enlarged cross-sectional view illustrating a joined part between the top cover  22  and the upper shaft member  110  in  FIG. 5 .  FIGS. 5 and 6  are symmetrical along the rotation axis R, and the reference numeral for the same component at the right or left will be omitted in some cases. 
     The upper shaft member  110  has the cylindrical convexity  110 F fitted in the engagement hole  22 D of the top cover  22 , and the tip of the cylindrical convexity  110 F including the circumferential recess  110 G protrudes from the top face of the top cover  22 . A fastener  36  with a larger diameter than the engagement hole  22 D is fitted to the circumferential recess  110 G. For example, a U-shaped or C-shaped snap ring (circlip) as the fastener  36  is fitted to the circumferential recess  110 G. The seat  110 H and the fastener  36  hold therebetween the peripheral edge of the engagement hole  22 D, thereby joining the upper shaft member  110  to the top cover  22 . A sealant  38  covers across the peripheral edge of the engagement hole  22 D, the fastener  36 , and the cylindrical convexity  110 F. For example, the sealant  38  is formed by applying a curable resin with an ultraviolet curable characteristic to a predetermined area, and emitting ultraviolet rays of a predetermined integrated light quantity to such a resin. The sealant  38  is formed so as not to protrude from the top face of the top cover  22 . The top cover  22  has a cover film  58  applied thereto so as to cover the cylindrical convexity  110 F. The sealant  38  or the cover film  58  suppresses a leak-in of unclean ambient air from the exterior of the rotating device  100  to the clean space  70 . In particular, when the sealant  38  is attached to the side of the engagement hole  22 D and a space between the bottom face of the top cover  22  and the seat  110 H of the upper shaft member  110 , a leak-in of unclean ambient air can be further suppressed. 
     Next, with reference to  FIG. 5  and  FIGS. 3 ,  4  and  6  for the detail, an explanation will be given of an example method of manufacturing the rotating device  100 . 
     (1) The outer circumferential surface  42 D of the sleeve  42  is, for example, fitted in and fastened to the inner circumferential surface  44 A of the cylindrical member  44 . Bonding or press-fit bonding may be applied instead of press-fitting (see  FIG. 4 ). 
     (2) The first and second dynamic pressure generating grooves  50  and  52  are provided in the inner circumferential surface  42 A of the sleeve  42 . The third dynamic pressure generating groove  54  and the fourth dynamic pressure generating groove  56  are provided in the upper face  42 C of the sleeve  42  and the lower face  42 D thereof, respectively. 
     (3) The upper shaft member  110  having the upper rod  10  and the upper flange  12  already joined together is fitted in the inner circumferential surface  42 A of the sleeve  42 , and retained therein (see  FIG. 4 ). 
     (4) The lower shaft member  112  having the lower flange  16 , the flange encircling member  18  and the lower rod  14  already joined together is fitted in the retainer hole  10 A of the upper rod  10 , and is joined therewith. The lower rod  14  is joined with the retainer hole  10 A of the upper rod  10  by a combination of press-fitting and bonding. For example, the lower rod  14  is fitted in and fastened to the retainer hole  10 A at an area near the lower flange  16 , and is bonded and fastened to the retainer hole  10 A at an area near the upper flange  12 . That is, the bonding area of the lower rod  14  and the retainer hole  10 A is located above the press-fit area of those lower rod  14  and retainer hole  10 A. 
     Upon joining the upper rod  10  with the lower rod  14 , the sleeve  42  is present in a space where the upper flange  12  and the lower flange  16  face with each other in the axial direction (see  FIG. 4 ). 
     (5) The ring member  46  is, for example, press-fitted in and fastened to the cylindrical member  44 . Bonding or press-fit bonding may be applied instead of press-fitting (see  FIG. 4 ). 
     (6) The lubricant  20  is filled in the predetermined space between the rotating body  4  and the stationary body  2 . The fluid dynamic bearing unit is thus produced (see  FIG. 4 ). 
     (7) The magnet  28  is fastened to the inner circumferential surface  26 H of the second annular part  26 E of the hub  26  by, for example, bonding (see  FIG. 5 ). 
     (8) The outer circumferential surface  44 B of the cylindrical member  44  is fastened to the inner circumferential surface  26 B of the first annular part  26 A of the hub  26  by, for example, press-fitting. Bonding or press-fit bonding may be applied instead of press-fitting (see  FIG. 4 ). 
     (9) The cap  48  is fastened to the recess  261  of the first annular part  26 A by, for example, press-fitting. Bonding or press-fit bonding may be applied instead of press-fitting (see  FIG. 4 ). 
     (10) The stator core  32  having the coils  30  wound therearound is fastened to the base  24  by, for example, press-fitting. Bonding or Press-fit bonding may be applied instead of press-fitting (see  FIG. 5 ). 
     (11) The flange encircling member  18  is fitted in the opening  24 D of the base  24 , and is bonded and fastened thereto (see  FIG. 4 ). 
     (12) The magnetic recording disk  62  is mounted on the hub  26  (see  FIG. 5 ). 
     (13) The reader/writer  60  and other components are attached to the base  24 . 
     (14) The cylindrical convexity  110 F is fitted in the engagement hole  22 D of the top cover  22 , and the fastener  36  is attached. The sealant  38  is applied across the peripheral edge of the engagement hole  22 D, the fastener  36 , and the cylindrical convexity  110 F, and the cover film  58  is applied thereabove (see  FIG. 6 ). 
     (15) The top cover  22  is joined with the base  24 . The rotating device  100  is completely manufactured through other processes like a predetermined inspection. 
     The above-explained manufacturing method of the rotating device  100  and the procedures thereof are merely examples, and the rotating device  100  can be manufactured by other methods and procedures. 
     An explanation will now be given of an operation of the rotating device  100  employing the above-explained structure. Three-phase drive currents are supplied to the coils  30  in order to rotate the magnetic recording disk  62 . The drive currents flowing through the coils  30  produce field magnetic fluxes along the salient poles of the stator core  32 . Torque is applied to the magnet  28  by the mutual action of the field magnetic fluxes and the magnetic fluxes of the drive magnetic poles of the magnet  28 , and thus the hub  26  and the magnetic recording disk  62  engaged therewith are rotated. At the same time, the voice coil motor  66  causes the swing arm  64  to swing, thereby causing the recording/playing head to move back and forth within the swingable range over the magnetic recording disk  62 . The recording/playing head converts magnetic data recorded in the magnetic recording disk  62  into electric signals, and transmits such electric signals to a non-illustrated control substrate, or writes data transmitted from the control substrate in the form of electric signals into the magnetic recording disk  62  as magnetic data. 
     The rotating device  100  employing the above-explained structure according to the embodiment accomplishes the following advantages. 
     The shaft and the lower flange  16  are formed together, and the outer circumference of the lower flange  16  having a larger diameter than that of the shaft is joined with the base  24 , and thus the joining strength can be increased in comparison with a case in which the shaft is directly joined with the base  24 . This results in a decrease of the possibility that the joined part between the base  24  and the shaft breaks down when shock is applied to the rotating device. 
     Moreover, the lower rod  14 , the lower flange  16  and the flange encircling member  18  are formed together, and thus the labor work for assembling can be reduced in comparison with a case in which those members are separately formed and joined together later, thereby improving the work efficiency. Such integral formation suppresses a dimensional error of the lower rod  14 , the lower flange  16 , and the flange encircling member  18 , and thus it is advantageous for downsizing and thinning of the rotating device. 
     Moreover, the upper rod  10  and the upper flange  12  are formed together, and thus the labor work for assembling can be reduced in comparison with a case in which those members are formed separately and joined together later, thereby improving the work efficiency. Such integral formation suppresses a dimensional error of the upper rod  10  and the upper flange  12 , and thus it is advantageous for downsizing and thinning of the rotating device. 
     The rotating device employs a structure in which the lower flange  16  and the base  24  do not overlap with each other in the axial direction around the peripheral area of the shaft. This facilitates thinning by what corresponds to such non-overlap. Alternatively, when the thickness of the rotating device in the axial direction is restricted, the dimension of a dynamic pressure generating part can be increased in the rotation axis direction. 
     Since the lower rod  14  is retained in the retainer hole  10 A of the upper rod  10 , the engaging length thereof can be relatively elongated, and thus the lower rod  14  and the upper rod  10  can be easily aligned coaxially, thereby suppressing an inclination of the lower rod  14  and the upper rod  10 . Therefore, an inclination of the lower flange  16  fastened to the lower rod  14  and the upper flange  12  fastened to the upper rod  10  can be suppressed, thereby suppressing an increase of the dimensional error. 
     The cylindrical convexity  110 F of the upper shaft member  110  is engaged and joined with the engagement hole  22 D of the top cover  22 , and thus it becomes unnecessary to provide a screw hole where a screw is engaged in the end of the shaft. Accordingly, the shaft can have its end formed relatively solid. Hence, a deformation of the upper shaft member  110  when the top cover  22  and the upper shaft member  110  are joined together can be suppressed in comparison with a case in which the end of the shaft is relatively hollow, thereby suppressing the disadvantages inherent to such a deformation. 
     Moreover, the top cover  22  is provided with the engagement hole  22 D, a convexity is provided at the upper end of the upper shaft member  110 , and those are engaged with each other. Accordingly, the positioning of the top cover  22  is facilitated, which reduces the labor hours. Alternatively, the bond can be applied to the upper end of the upper shaft member  110  through the engagement hole which has no obstacle and is relatively easy to reach, and thus the bond applying work can be made easy. 
     MODIFIED EXAMPLES 
     An explanation will now be given of modified examples with reference to  FIGS. 7 to 12 . 
       FIG. 7  is an enlarged cross-sectional view illustrating a joined part of the top cover  22  of a rotating device  200  according to a first modified example and an upper shaft member  210  thereof.  FIG. 7  corresponds to  FIG. 6 . The upper shaft member  210  has a cylindrical convexity  210 F joined with the top cover  22  by interference fitting to an annular member. The upper shaft member  210  differs from the upper shaft member  110  of the above-explained embodiment only that the cylindrical convexity  210 F has a different shape. According to the first modified example, for example, a hollow cylindrical fastener  236  is subjected to interference fitting to and is joined with the side face of the tip of the cylindrical convexity  210 F. A fastener in a polygonal shape or in a wave shape in the circumferential direction may be used instead of the hollow cylindrical fastener  236 . The fastener  236  is formed of a stainless-steel material like SUS 430 or other metallic materials and formed by cutting and machining, pressing or other processes. The fastener  236  may be placed so as to cover the cylindrical convexity  210 F and may have the side face crimped inwardly of the radial direction against the cylindrical convexity  210 F by a tool instead of interference-fitting. The cylindrical convexity  210 F may have a circumferential recess provided in the side face thereof. Alternatively, threads (screw threads) may be provided on the outer circumferential surface of the cylindrical convexity  210 F and the inner circumferential surface of the fastener  236 , and those may be engaged with each other. The same is true of the above-explained embodiment that the sealant  38  and the cover film  58  are provided. 
       FIG. 8  is an enlarged cross-sectional view illustrating a joined part of the top cover  22  of a rotating device  300  according to a second modified example and an upper shaft member  310  thereof.  FIG. 8  corresponds to  FIG. 6 . A cylindrical convexity  310 F of the upper shaft member  310  has an end face crushed, thereby being fastened to the top cover  22 . The upper shaft member  310  differs from the upper shaft member  110  of the above-explained embodiment only that the cylindrical convexity  310 F has a different shape. According to the second modified example, for example, a recess  310 K is provided in the end face of the cylindrical convexity  310 F, and the edge of the recess  310 K is crushed outwardly of the radial direction, and thus the cylindrical convexity  310 F is crimped and joined with the top cover  22 . The same is true of the above-explained embodiment that the sealant  38  and the cover film  58  are provided. 
       FIG. 9  is an enlarged cross-sectional view illustrating a joined part of the top cover  22  of a rotating device  400  according to a third modified example and an upper shaft member  410  thereof.  FIG. 9  corresponds to  FIG. 6 . The upper shaft member  410  differs from the upper shaft member  110  of the above-explained embodiment only that a cylindrical convexity  410 F has a different shape. A recess  410 K is provided in the end face of the cylindrical convexity  410 F, and a fastener  436  is press-fitted to the recess  410 K, thereby being joined with the top cover  22 . For example, the fastener  436  includes a flange  436 A in a disc shape and a cylindrical protrusion  436 B running downwardly from the lower end of the flange  436 A and press-fitted in the recess  410 K. The flange  436 A of the fastener  436  has a larger outer diameter than the internal diameter of the engagement hole  22 D of the top cover  22 . A peripheral edge of the engagement hole  22 D of the top cover  22  is held between the flange  436 A and a seat  410 H in the axial direction. The fastener  436  is formed of a ferrous material like SUS 430, and formed by cutting and machining, and pressing, etc. The same is true of the above-explained embodiment that the sealant  38  and the cover film  58  are provided. 
       FIG. 10  is an enlarged cross-sectional view illustrating a joined part of the top cover  22  of a rotating device  500  according to a fourth modified example and an upper shaft member  510  thereof.  FIG. 10  corresponds to  FIG. 6 . The upper shaft member  510  has a cylindrical convexity  510 F joined with the top cover  22  by bonding thereto. The upper shaft member  510  differs from the upper shaft member  110  of the above-explained embodiment only that the cylindrical convexity  510 F has a different shape. A circumferential recess  510 G is provided in the side face of the cylindrical convexity  510 F, and a UV-curable resin  538  is applied across the cylindrical convexity  510 F including the peripheral edge of the engagement hole  22 D and the circumferential recess  510 G. By applying the UV-curable resin  538  to the circumferential recess  510 G, the bonding strength can be enhanced. The labor work is facilitated since no fastener is used. The same is true of the above-explained embodiment that the cover film  58  is provided. 
       FIG. 11  is an enlarged cross-sectional view illustrating a joined part of a top cover  622  of a rotating device  600  according to a fifth modified example and an upper shaft member  610  thereof.  FIG. 11  corresponds to  FIG. 6 . The upper shaft member  610  has a cylindrical convexity  610 F joined with the top cover  622  by causing the edge of the top cover  622  to be fitted in a recess provided in the cylindrical convexity  610 F. The upper shaft member  610  differs from the upper shaft member  110  of the above-explained embodiment only that the cylindrical convexity  610 F has a different shape. The top cover  622  differs from the top cover  22  of the above-explained embodiment only that an engagement hole  622 D has a different shape. A circumferential recess  610 G is provided in the side face of the cylindrical convexity  610 F. The circumferential recess  610 G has a slightly larger aperture dimension in the axial direction than the thickness dimension of the top cover  622  in the axial direction. The engagement hole  622 D has a small-diameter opening in a substantially circular shape and slightly larger than the diameter of the circumferential recess  610 G and a large-diameter opening in a substantially circular shape and slightly larger than the diameter of the cylindrical convexity  610 F partially overlapping with each other. The tip of the cylindrical convexity  610 F passes all the way through the large-diameter opening, and protrudes from the top face of the top cover  622 . The top cover  622  is moved to the right in  FIG. 11 , and the edge of the small-diameter opening is fitted into the circumferential recess  610 G, thereby joining the upper shaft member  610  with the top cover  622 . The dimension of the cylindrical convexity  610 F in the axial direction can be reduced by what corresponds to the lack of a fastener, and thus the dimension of the rotating device  600  in the axial direction can be reduced. Alternatively, the labor work is facilitated since no fastener is attached. The same is true of the above-explained embodiment that the sealant  38  and the cover seat  58  are provided. 
       FIG. 12  is an enlarged cross-sectional view illustrating a joined part of the top cover  22  of a rotating device  700  according to a sixth modified example and an upper shaft member  710  thereof.  FIG. 12  corresponds to  FIG. 6 . The upper shaft member  710  has a cylindrical convexity  710 F joined with the top cover  22  by welding. The upper shaft member  710  differs from the upper shaft member  110  of the above-explained embodiment only that the cylindrical convexity  710 F has a different shape. Provided in the side face of the cylindrical convexity  710 F are a large-diameter part  710 FA protruding upwardly of the axial direction from a seat  710 H, and a small-diameter part  710 FB protruding upwardly of the axial direction from the upper face of the large-diameter part  710 FA. The small-diameter part  710 FB has an outer diameter smaller than the outer diameter of the large-diameter part  710 FA. The large-diameter part  710 FA has an upper end located below the peripheral edge of the engagement hole  22 D of the top cover  22 . For example, laser beam like YAG laser is emitted across the edge of the engagement hole  22 D, the large-diameter part  710 FA, and the small-diameter part  710 FB while moving in the circumferential direction, thereby forming a fused joined part  710 J (hatched area). That is, the fused joined part  710 J includes the inner circumferential side face of the peripheral edge of the engagement hole  22 D, the upper face thereof, the upper end face of the large-diameter part  710 FA, and the outer circumferential side face of the small-diameter part  710 FB. Since the fused joined part includes the side faces of the joining-target members and the end faces thereof, the variability of the joining strength can be reduced. The same is true of the above-explained embodiment that the sealant  38  and the cover film  58  are provided. 
     The explanation was given of the structures of the rotating devices according to the embodiment and the modified examples thereof, and the operations thereof. Those embodiment and the modified examples are merely examples, and it should be understood for those skilled in the art that the combination of the respective components permits various modifications, and such modifications are within the scope and spirit of the present invention. 
     In the above-explained embodiment, the explanation was given of the example case in which the lower shaft member is directly attached to the base, but the present invention is not limited to this case. For example, a brushless motor including a rotating body and a stationary body may be formed separately, and such a brushless motor may be attached to a chassis. 
     In the above-explained embodiment, the explanation was given of the example case (a so-called outer rotor structure) in which the stator core is encircled by the magnet, but the present invention is not limited to this case. For example, a structure (a so-called inner rotor structure) in which the magnet is encircled by the stator core may be employed. 
     In the above-explained embodiment, although a part of the cylindrical convexity of the upper shaft member protrudes from the top face of the top cover, the present invention is not limited to this case. For example, a structure may be employed in which the upper end face of the cylindrical convexity is bonded and fastened to the bottom face of the top cover.