Abstract:
Air guides provided in a dynamic-pressure-bearing motor on a rotor-surrounding wall of the motor casing. The air guides project radially from the casing wall and have an axially extending guide surface that concentrates air, made to flow by rotation of the rotor, radially inward toward a predetermined position along the rotor with respect to its cylindrical surface, to apply radially directed pressure against the rotor. If the motor is for a disk drive, the rotor may carry a number of storage disks and the air guides may be disposed proximate at least one of the axial upper/lower surfaces among those of all or a portion of the storage disks. The pressure developed by the air guides maintains the spinning rotor in an eccentric state, which works to resist the wobbling due to half-speed whirling and improve the motor&#39;s rotational precision.

Description:
BACKGROUND OF THE INVENTION 
     1. Technical Field 
     The present invention relates to rotary and storage devices provided with radial dynamic-pressure bearings. In particular it relates to radial-dynamic-pressure-bearing equipped rotary and storage devices having compensatory means to prevent unstable rotation such as wobbling from developing in the rotor. 
     2. Description of Related Art 
     Programs and data for personal computers generally are stored in storage-disk rotary-type storage devices such as hard-disk drives. Various storage media—the magnetic disks that are hard disks, CD-ROMs, or optical disks such as DVDs—are employed in the storage devices according to content of the programs or data stored, storage volume and preference conditions of how used. 
     In recent years, due to the increasing tendency towards complexity and sophistication in programs and data as noted above, storage device improvements in storage volume and performance, such as in running speed, have been striven for. This has placed demands that are becoming more and more stringent on the rotary devices (e.g. spindle motors) that spin recording disks for, in addition to higher speed, rotational precision improvements from wobbling. 
     Some such storage devices employ spindle motors that are provided with bearing means such as radial hydrodynamic-pressure bearing structures in which either the motor shaft or a sleeve element by which it is surrounded at a gap rotatively supports the other. Half-speed whirl occurring in the bearing region, which causes non-repetitive (non-repeatable) runout—also known as asynchronous error motion—may impede the rotational precision of these spindle motors. 
     Half-speed whirl is a phenomenon that arises in bearing means in which the shaft component and the sleeve component of radial dynamic-pressure bearings are rotatively supported mutually out of contact. To illustrate by the example of shaft-rotating type spindle motors in which the shaft component spins: Half-speed whirl is phenomenon of the shaft component in an unstable wobbling rotational state due to being shaken by the lubricating fluid, which revolves at half the speed of the rotational speed of the shaft component. 
     In order to prevent such wobble in radial dynamic-pressure bearings, the technique of making the sleeve component or the shaft component that constitute the radial dynamic-pressure bearing structure not a true circle in cross-sectional form has been proposed. For example, Japanese Laid-Open Pat. Pub. No. 10-205538 proposes a configuration wherein a slit is formed on the inner peripheral surface of the sleeve component. Nevertheless, this technique brings with it difficulties in production of the sleeve component or the shaft component. 
     A different technique is also known from Japanese Laid-Open Pat. Pub. No. 11-55918 for example, which sets forth a technique in which local magnetic imbalance is set up in the stator opposing the rotor magnet of a spindle motor that is provided with radial dynamic-pressure bearings. This technique prevents sleeve-component wobble by maintaining a constant off-center state in which the sleeve component, rotatively supported by the radial dynamic-pressure bearings, is magnetically attracted in a predetermined diametrical direction to displace the rotational center of the sleeve component from the rotational center of the shaft component. Nevertheless, insofar as this technique is concerned, not only are difficulties in production of the sleeve element involved, but the local magnetic imbalance in the stator risks furthering electromagnetic fluctuation during rotation. 
     Still another technique is known from Japanese Laid-Open Pat. Pub. No. 6-43382 for example, which sets forth a technique in which the rotary member, which may be the shaft or sleeve, rotates while being pushed in a predetermined diametrical direction by fluid pressure from a pressure distribution varying means, furnished in the sleeve component or base components to alter pressure distribution in the fluid surrounding the rotary member. Nevertheless, this technique involves difficulties in production of the pressure variable-distribution means, and otherwise brings with it difficulties in setting aside space in which the means is disposed. 
     The above-described problems in rotary devices provided with radial dynamic-pressure bearings also arise with regard to rotary devices provided with radial dynamic-pressure bearings, but other than storage-disk rotary-type storage devices. Polygonal scanner motors installed in laser printers are a case in point. A plurality of mirrored surfaces employed in laser beam scanning that is related to image information is provided on the rotor in polygonal scanner motors, and in some instances radial dynamic-pressure bearings are provided in the bearing means. The fact that radial dynamic-pressure bearings are provided in polygonal scanner motors leads to the possibility of unstable rotatory states such as wobbling in the rotor, likewise as in the storage devices described above, and the rotatory states as such will affect printing precision. For that reason, there likewise exist demands calling for improvements in rotational precision in polygonal scanner motors by preventing asynchronous runout and synchronous runout due to wobbling. 
     Japanese Laid-Open Pat. Pub. No. 6-294937 for example proposes to diminish non-repeating deflection errors in the rotation of a rotary polyhedral mirror spun by a motor in the base of cylindrical bracket that houses the mirror. The lateral spacing between the cylindrical bracket and the polyhedral mirror is made non-uniform either by establishing an offset between the centers of the bracket and the mirror, or by forming the inner circumferential wall of the bracket with diametrically opposed convex and concave conformations. Thus a maximum gap differential is set up along the line of maximum eccentricity between the two centers, or along the line where the convex and concave conformations are diametrically opposed. The gap differential generates a difference in air pressure surrounding the polyhedral mirror when it spins, such that lateral pressure acts on the mirror in the position along the inner circumferential wall of the bracket where the gap is narrowest. 
     Of course, in rotary devices provided with radial dynamic-pressure bearings the above-described problems arise not only in particular in spindle motors and polygon scanner motors for storage devices, but also occur in other rotary devices equipped with radial dynamic pressure bearings. Therein demands calling for improvements in rotational precision likewise exist. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is in providing rotary devices and storage devices, furnished with radial dynamic-pressure bearings, that are designed for improvement in rotational precision. 
     Another object of the present invention is to provide rotary devices and storage devices, furnished with radial dynamic-pressure bearings, that realize rotational precision without attendant manufacturing difficulties. 
     Another object of the present invention is to provide rotary devices and storage devices, furnished with radial dynamic-pressure bearings, that realize rotational precision without attendant promotion of electromagnetic fluctuations. 
     Yet another object of the present invention is to provide rotary devices and storage devices, furnished with radial dynamic-pressure bearings, that realize rotational precision without bringing on difficulties in component arrangement. 
     Still another object of the present invention is in providing rotary devices and storage devices, furnished with radial dynamic-pressure bearings, that prevent the harm of damage to the radial dynamic-pressure bearings owing to the rotational center of the rotor being overly de-centered. 
     Another object of the present invention is in providing storage devices that heighten read/write accuracy with respect to recording media. 
     Another object of the present invention is in providing storage devices that heighten read/write accuracy with respect to recording media without hindering the read/write operation of the read/write head. 
     According to a rotary device of the present invention, furnished with radial dynamic-pressure bearings, the rotor is rotatively supported against a stationary member via bearing means including a radial dynamic-pressure bearing. The rotor has a rotary main having an outer peripheral surface section, and one or more flat plate-shaped members projecting diametrically outward from the outer peripheral surface section, coaxially with the rotary main. The stationary member is provided with a fluid guide member proximate to at least one face of axially upper and lower surfaces respectively in all or a part of the flat plate-shaped members. 
     Fluid, such as air, present over the recording medium rotates with the rotation of the recording medium and is guided heading diametrically inward to a predetermined position on the outer peripheral surface section by the fluid guide member(s), and pressure is gained in a predetermined diametrical direction with respect to the rotor. Because this pressure maintains the rotor in an eccentrically urged state, the above-described rotary device suppresses wobbling action due to half-speed whirling, which works toward improving rotational precision. 
     Further, according to a storage device of the present invention, the rotor is rotatively supported against a stationary section via radial dynamic-pressure bearings. The rotor has a rotary main having an outer peripheral surface section and a flat plate-shaped recording medium installed on the rotary main, with the medium projecting diametrically outward from the outer peripheral surface section, coaxially with the rotary main. The stationary section has a fluid guide member proximate to all or a part of at least one of axially upper and lower surfaces of the recording medium, and a read/write head that performs reading/writing of data on the recording medium. Fluid, such as air, present over the recording medium rotates with the rotation of the recording medium and is guided heading diametrically inward to a predetermined position on the outer peripheral surface section by the fluid guide member, and pressure is gained in a predetermined diametrical direction with respect to the rotor. Because this pressure maintains the rotor in an eccentrically urged state, the foregoing storage device suppresses wobbling action due to half-speed whirling, which works toward improving rotational precision. The fluid guide member is located so as not to disturb the operation of the read/write head on the head mechanism, and desirably is disposed in a diametrically opposite position from the head with respect to the rotor body. Therefore, because the recording medium does not develop unstable rotation such as wobbling, rotational precision is heightened. 
     From the following detailed description in conjunction with the accompanying drawings, the foregoing and other objects, features, aspects and advantages of the present invention will become readily apparent to those skilled in the art. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a plan view showing a state in which the top plate has been taken off in a storage device illustrating an embodiment of the present invention; 
     FIG. 2 is a sectional view taken along the line II—II in FIG. 1; 
     FIG. 3 is a sectional view taken along the line III—III in FIG. 2; 
     FIG. 4 is an oblique view of an air-current guide plate removed from FIG. 1; and 
     FIG. 5 is a lateral elevational view of the storage device shown in FIG. 1, shown set on its side and again with the top plate taken away for the convenience of illustration. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     A hard disk drive device (“HDD” hereinafter) as an embodiment of the present invention will be explained with reference to the drawings. 
     In the HDD shown in FIG. 1 is a spindle motor  14  on which hard disks (“disks” hereinafter)  12  as a recording medium are installed. A head mechanism  15  is furnished with a magnetic head  16  as a read/write means for reading/writing data on the disk  12 . A control circuit (not shown) controls the spindle motor  14  and the head mechanism  15 . The spindle motor, disks, head mechanism and control circuit are arranged within a casing  10 , which is a rectangular parallelepiped in outer shape. 
     With reference to FIG. 2 as well, the casing  10  is made up of a boxy casing body  10   a  the upper end of which is open, and a top plate  20  that closes off the opening. The casing body  10   a  is made up of a rectangular bottom wall  10   a   1  and lateral side walls  10   a   2  consisting of four flanks. The inner surfaces of the lateral walls  10   a   2  of the casing body  10   a  are made up of cylindrical faces  10   b  formed to conform with the shape of the disks  12  loaded on the spindle motor  14  so as to encompass the circumference of the disks  12 ; and approximately rectangular faces  10   c  ranging to a portion of the cylindrical faces  10   b , for arranging the head mechanism  15  and the control circuit. The casing  10  interior is an airtight clean space in which air is present, but so that air pressure difference inside/outside the casing  10  will not occur, it is an airtight space, moreover, that is substantially sealed—that ventilates air to an extent that does not infringe its cleanliness. 
     In the spindle motor  14  a hub  24  on which the disks  12  are loaded is rotatively supported via a bearing means against a stationary shaft  22  the lower end of which is fixed into the bottom wall  10   a   1 . The stationary shaft  22  is made up of a round cylindrical portion mortised into the bottom wall  10   a   1 , and a disk-shaped thrust plate portion that widens diametrically on the upper end of the round cylindrical portion. The hub  24  is made up of: a cup-shaped cylindrical member  25  on the outer surface of which the disks  12  are loaded, and on the inner surface of which is a cylindrical permanent magnet (not illustrated); and, on the inner side of the cylindrical section  25 , a rotary sleeve member  26  opposing the stationary shaft via a micro-gap. 
     The bearing means is made up principally of: a radial dynamic-pressure bearing section  28  in which lubricating oil is sustained in a micro-gap formed between the rotary sleeve member  26  and the round cylindrical portion of the stationary shaft  22 , non-contactually supporting the diametrical load of the hub  24 ; and a thrust dynamic-pressure bearing section  29  via lubricating oil in a micro-gap formed between the rotary sleeve member  26  and the thrust plate portion, non-contactually supporting the axial load of the hub  24 . That is, the spindle motor  14  is a rotary device furnished with a radial dynamic-pressure bearing section  28 . 
     Further, a stator (not illustrated) having coils wound around an iron core, is arranged on the stationary shaft  22 , in a location opposing the permanent magnets on the hub  24 . Torque is generated in the stator when the magnetic field that arises from passing electricity into the coils acts magnetically on the permanent magnet, which rotates the hub  24  in the direction of arrow R in FIG.  3 . It should be understood that the lubricating fluid in the bearing means might be air instead of oil. The thrust bearing section  29  of the bearing means may be other bearing means such as magnetic bearings that employ magnetic repulsion in order to support axial load. 
     Four disks  12  are fit over the hub  24 , and are each fixedly maintained coaxial with the hub  24 ; the number of disks is not limited to this however. The lowermost disk  12  is loaded onto a brim-shaped portion  24   a  projecting from the lower end outer periphery of the round cylindrical portion of the hub  24 , and disks  12  are layered above this disk  12 , one after the other by turns via annular spacers  30 . An annular damper  31  that is fixed to the hub  24  presses vertically on the uppermost disk  12 , fixedly retaining all of the disks  12 . 
     The head mechanism  15  is made up of an access arm  18 , the tip of which is furnished with the magnetic head  16 , and a support  19  that through a bearing means pivotally supports the access arm  18 . Because magnetic heads  16  are required for each of the disks  12  respectively, four of the access arms  18  are arranged. 
     In response to read/write operation, the magnetic heads  16  are arbitrarily shifted along an arc, centered on the pivotal axis of the support  19 , and covering the read/write area that can be read from/written into from the inner periphery of the disks  12  to the outer periphery thereof, and to a retraction area where the magnetic heads  16  are not facing the disks  12 . 
     In the foregoing the casing  10  and the stationary shaft  22  chiefly constitute the stationary sections, and the hub  24 , the spacers  30 , and the damper  31  chiefly constitute the rotary main members. The disks  12  constitute the flat plate-shaped members, while further the rotor is constituted from these rotary main members and the flat plate-shaped members. 
     Furthermore, five air-current guide plates  32  as fluid guide members are arranged on the cylindrical faces  10   b  of the casing  10 , facing the disks  12 . Since the air-current guide plates  32  are all of like form, particulars of the shape will be explained focussing on the uppermost one set forth in FIG.  1 . This air-current guide plate  32  flanks the hub  24  in roughly the opposite side against the magnetic head  16  supported on the access arm  18 , and with a predetermined circumferential position A that is proximate the external peripheral surfaces of the clamper  31  as a tip, widens across a certain range rearward (upstream-ward) in the rotational direction of the disks  12  (arrow R). 
     That is, the air-current guide plate  32  is plate-shaped, substantially parallel with the axially upper and lower faces of the disks  12 . Its lateral faces are made up of a rearward face  32   a  facing rearward with respect to the rotational direction of the disks  12 , and a frontward face  32   b  facing forward. The two lateral faces  32   a ,  32   b  are connected in the predetermined position A. The two lateral faces  32   a ,  32   b  are planes parallel to the rotational axis of the hub  24  et al., forming planes perpendicular with respect to a plane orthogonal to the rotational axis (for example, the axially upper/lower faces of the disks  12 ). 
     As FIG. 4 illustrates, the rearward lateral face  32   a  extends from the predetermined position A to a predetermined position B on cylindrical face  10   b  of the casing  10  that is rearward in the rotational direction of the disks  12 , so as to describe an arcuate line that extends forward in the rotational direction of the disks  12 , and assume a form that approaches gradually heading from the predetermined position B to the predetermined position A. (The rearward lateral face  32   a  is equivalent to a guide surface.) Further, the frontward lateral face  32   b  extends from the predetermined position A to a predetermined position C on cylindrical face  10   b  of the casing  10  that is rearward in the rotational direction of the disks  12  to some extent from predetermined position A, so as to describe an arcuate line that extends rearward in the rotational direction of the disks  12 , and assume a form that approaches gradually heading from the predetermined position C to the predetermined position A. 
     As far as the other air-current guide plates  32  are concerned, they are of like form as the uppermost air-current guide plate  32 ; and the lowermost air-current guide plate  32  is proximate the brim-shaped portion  24   a  of the hub  24 , and the intermediate air-current guides  32  are respectively proximate the spacers  30 . Also, the predetermined position A as noted above is defined by the magnetic head  16  and the hub  24 . The predetermined position B as noted above is defined by the predetermined position A, and is located on the casing  10  rearward in the rotational direction of the disks  12  to a certain extent from the predetermined position A. The predetermined position C is defined by the predetermined position B, and is located on the casing  10  forward in the rotational direction of the disks  12 . Therein, the predetermined position C is rearward of the predetermined position A with respect to the rotational direction of the disks  12 , but may be forward thereof. 
     The upper face of the air-current guide plate  32  for the lowermost disk  12  is proximate or adjacent to the lower face of the lowermost disk  12 ; and its lower face is proximate or adjacent to the upper face of the bottom wall  10   a   1  of the casing  10 . The upper/lower faces of the air-current guide plates  32  between the disks  12  are proximate respectively to the lower face of the disk  12  above, and to the upper face of the disk  12  below. The lower face of the air-current guide plate  32  for the uppermost disk  12  is proximate to the upper face of the uppermost disk  12 ; and its upper face is proximate to the lower face of the top plate  20 . Being that the air-current guide plates  32  all coincide in form and distributional position, only the uppermost air-current guide plate  32  is shown in FIG.  1 . 
     When the disks  12  rotate in the direction of the arrow R by the spinning of the spindle motor  14 , air present on the upper/lower faces of each of the disks  12  accompanies the rotation of the disks  12  and travels in the same direction (arrow R). 
     Most of the travelling air collides with the rearward lateral faces  32   a  on the air-current guide plates  32  provided proximate the upper/lower faces of the disks  12 , is guided diametrically inward as indicated by the arrow S, and gathers in a predetermined position neighboring the outer peripheral surfaces of the damper  31 , spacers  30  and brim-shaped or flange portion  24   a  (on a line that passes through the above-noted predetermined position A, parallel with the rotational axis of the hub  24 ). In other words, the rearward lateral faces  32   a  act as guide surfaces that guide air on a line that passes through the above-noted predetermined position A, parallel with the rotational axis of the hub  24  (the rearward lateral faces are called guide faces hereinafter). When air thus guided passes the gap formed by the air-current guide plates  32 , and the brim-shaped or flange portion  24   a , spacers  30  and damper  31 , in the vicinity of that line, the air pressure becomes maximum, gaining pressure in the direction of the arrow P indicated in FIGS. 1 and 3. 
     For that reason, during rotation of the spindle motor  14 , because pressure against the hub  24  is constantly gained in the direction of the arrow P, as shown in FIG. 3 the bearing gap region where the arrow P crosses the radial dynamic-pressure bearing section  28  becomes smaller than the bearing gap in the remaining situation. Namely, an eccentricity is sustained in which the rotational axis of the rotary sleeve member  26  is offset in a constant direction (same direction as indicated by the arrow P) from the center axis of the stationary shaft  22 . In a radial dynamic-pressure bearing section  28  thus, pressure that resists shaking action caused by wobble in the rotatively supported rotary sleeve member  26  during rotation is constantly gained in the direction of the arrow P, which therefore prevents asynchronous wobble and synchronous wobble due to half-spaced whirling and heightens rotational precision. Accordingly, lessening discrepancies in position of the magnetic heads  16  with respect to the disks  12  heightens read/write accuracy. It should be understood that the direction of eccentricity of the rotary sleeve member  26 , because it is defined by the pressure gained by the air-current guide plates  32  in the orientation of the arrow P, may be freely established by how the predetermined position A on the air-current guide plates  32  is arranged. 
     Further the position at which the air-current guide plates  32  apply pressure to the hub  24  et al, (position at which the hub  24  et al. are proximate the line parallel with the rotational axis of the hub  24  that passes through the predetermined position A), and the position of the magnetic heads  16  are provided astride the hub  24  so as to be contrariwise, so that air after passing the gap near the predetermined circumferential position A formed by the air-current guide plates  32  does not stream directly into the magnetic heads. Therefore, the read/write operation of the magnetic head  16  is not disturbed or hindered. Of course the air-current guide plates  32  are sufficiently separated from the area through which the access arm  18  containing the magnetic head  16  travels, not to collide with it during the pivoting movement of the access arm  18  and hinder of the read/write operation. 
     Again, as noted above the form of the guide faces (rearward lateral faces)  32   a  in the air-current guide plates  32  describes an arcuate line, which lessens air resistance so that air is guided efficiently. Since the frontward lateral faces  32   b  are, as noted above, of form describing an arcuate line, turbulence due to swirling in of air after passing the gap in the vicinity of the predetermined position A is suppressed. It should be understood that in cases in which the influence of air resistance on the guide faces  32   a  is slight, the form may describe straight lines instead of the arcuate line. And likewise, in instances wherein the effects of turbulence on the frontward lateral faces  32   b  are slight, instead of the arcuate line, the form may describe straight lines. Furthermore, the two sets of faces  32   a ,  32   b  are surfaces parallel with respect to the rotational axis of the hub  24  et al. and in order to guide air efficiently with little air resistance, they may be surfaces that slant with respect to the rotational axis. The air-current guide plates  32  may be made in any form that guides air to the predetermined position A in the circumferential direction, proximate to the outer peripheral surfaces of the damper  31  et al. 
     Further, air-current guide plates  32  are provided between the upper/lower surfaces of all of the disks  12 , and besides, since all the air-current guide plates  32  coincide in form and distributional position, pressure gathering at the hub  24  et al. is gained nearly uniformly in all axial directions: vibrations in the disks  12  or totter of the rotational axis of the hub  24  due to the action of this pressure during rotation does not occur. 
     Still further, when the HDD is set on one of its sides, i.e. on one of the lateral walls  10   a   2  that compose the four flanks in the casing body  10   a , the direction of the rotational axis of the spindle motor becomes horizontal. The rotational center of the hub  24  is made eccentric in this orientation by the action of gravity. If the directions of gravity and of the pressure by the air-current guide plates  32  coincide, the eccentricity of the hub  24  is exaggerated, resulting in damage due to abnormal contact between the shaft and sleeve in the radial dynamic-pressure bearing section. When the HDD housing is set on the lateral wall  10   a   2 ′ as shown in FIG. 5, the direction of the pressure exerted on the hub  24  by means of the air-current guide plates  32  (arrow P) deviates by about 135 degrees with respect to the gravitational direction, by which extreme biasing (displacement) of the hub is avoided. Accordingly, the air-current guide plates  32  should be located in a position where such extreme biasing is avoided when the HDD casing is set on its side wall in its normal posture. If the casing is set on its shorter side wall  10   a   2 ″, the angle between the direction of biasing pressure by the air current guide and the gravitational direction is about 45 degrees, such that the combined biasing and gravitational forces result in a large force that may exaggerate the eccentricity. Such being the case, some measure to prevent the HDD housing or casing from being put in this posture may be provided on the wall  10   a   2 ″, such as a marking or projection. 
     The foregoing embodiment in the present invention has been explained taking the example of an HDD with four storage disks, but the number of disks and the configuration of the spindle motor are not limited to the described embodiments. Further, the present invention is likewise applicable to storage devices such as optical disk CD-ROMs furnished with radial dynamic-pressure bearings, and other than in storage devices to rotary devices such as polygon scanner motors furnished with radial dynamic-pressure bearings. The fluid guide members may be arranged to fit along the flat plate-shaped members in any storage device or recording device, but wherein there are a plurality of flat plate-shaped members, there do not necessarily have to be fluid guide members adjacent all of them. The fluid guide members may be arranged, for example, at only the axially uppermost and axially lowermost flat plate-shaped members, arranged according to size of the radial load in the radial dynamic-pressure bearing, or arranged on only one flank of the flat plate-shaped members. Thus various ways of establishing the presence/absence of the fluid guide members, or their form and distributional position are possible. 
     Again, as to distributional positions for the fluid guide members, in instances such as with CD-ROMs as removably installable type recording media the fluid guide members should be in a position such that they do not to interfere with the disk installing/removing operation. Or they may be made so as to be movable-type fluid guide members such that they retract momentarily from the recording medium insertion path. 
     Further, in the case of the above-described HDD the outer peripheral surface of the hub  24  is shaped as a constant-diameter cylinder, but the rotary main is not thus limited: in some instances the outer peripheral surface is beveled to be a locating guide when fitting on the recording medium, as in the case of removably installable type recording media such as CD-ROMs. 
     Further, the foregoing spindle motor is furnished with fixed-shaft type bearing means in which the shaft element (stationary shaft  22 ) is fixed, but the motor may be such that rotary-shaft type bearing means that are of the opposite configuration are provided. In other words, “rotary-shaft type bearing means” is a configuration in which a sleeve member that forms a part of a stationary section supports a shaft that forms a part of the rotor. 
     The laterals walls  10   a   2  of the casing body  10   a  are cylindrical faces shaped to encompass and match the form of the disks  12 , but it makes no difference if they are plane faces. The bottom wall  10   a   1  or the ceiling plate  20  are flat surfaces, but the air-current guide plates  32  adjoining them may be unitized therewith, and these regions only may be made in protruding or recessed shapes. 
     It should be understood that the top/bottom positional relationships in the foregoing description of the embodiments are established tentatively for the convenience of explanation, but do not limit the conditions of actual use. 
     While only selected embodiments have been chosen to illustrate the present invention, to those skilled in the art it will be apparent from this disclosure that various changes and modifications can be made herein without departing from the scope of the invention as defined in the appended claims. Furthermore, the foregoing description of the embodiments according to the present invention is provided for illustration only, and not for the purpose of limiting the invention as defined by the appended claims and their equivalents.