Abstract:
A recording disk cartridge includes a plurality of flexible recording disk media integrally rotatably housed within a cartridge case. Each of the recording disk media is fixed to a center core which is stacked one on another through a spacer. The cartridge case includes: a lower plate for configuring a lower wall parallel to the plurality of the recording disk media; at least one inner plate that is stacked and fixed on the lower plate, and partitions the plurality of the recording disk media; and an upper plate that is stacked and fixed on the inner plate, and configures an upper wall of the cartridge case. Each spacer is provided with locking protrusions at upper and lower surfaces thereof, and each center core is provided with locking holes for engagement with the locking protrusions of adjacent spacers.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS  
       [0001]     This application claims the foreign priority benefit under Title 35, United States Code, §119(a)-(d) of Japanese Patent Application No. 2004-239628, filed on Aug. 19, 2004 in the Japan Patent Office, the disclosure of which is herein incorporated by reference in its entirety.  
       BACKGROUND OF THE INVENTION  
       [0002]     1. Field of the Invention  
         [0003]     The present invention relates to a recording disk cartridge comprising a plurality of flexible recording disk media.  
         [0004]     2. Description of the Related Art  
         [0005]     Conventionally, as a recording disk medium a flexible recording disk medium is known where a magnetic layer is formed on both faces of a disc-form support body consisting of a flexible material such as a polyester sheet. Although the magnetic disk medium has a merit of speedily accessing data in comparison with a magnetic tape, on the other hand, it has a demerit of a memory capacity being small because a recording area thereof is small.  
         [0006]     In order to solve the demerit of the flexible magnetic disk medium, it is conventionally disclosed a magnetic disk cartridge for housing a plurality of magnetic disk media in one cartridge case (for example, see JP 2004-22011A).  
         [0007]     In this connection, because a flexible magnetic disk medium is low in rigidity thereof, there is a problem that the medium tends to vibrate in a vertical direction for a recording face when rotated. Therefore, in an invention of JP 2004-22011A each magnetic disk medium is made a configuration of being pinched by shutters. Thus by arranging plate members of high rigidity such as the shutters in a vicinity of the magnetic disk medium, the recording face can be stabilized because the medium becomes along the plate members, accompanied with a rotation of the medium.  
         [0008]     However, because a magnetic disk cartridge of JP 2004-22011A is configured of movable shutters arranged by four for one magnetic disk medium, there is a problem that the cartridge is complicated in a structure thereof and is difficult to keep a parallelism to the medium. In addition, because the magnetic disk cartridge is mass produced goods, it is preferable to be excellent in assembling ability and productivity. It is also preferable that the magnetic disk cartridge excels in rotational stability. Furthermore, the magnetic disk cartridge is preferable to be high in a degree of freedom in a design change so as to easily set a plurality of kinds thereof where number of magnetic disk media is made three, five, and the like.  
         [0009]     In addition, because the magnetic disk cartridge has a possibility of generating an error in recording/reproducing data due to an invasion of dust, it is necessary to prevent the invasion of the dust.  
         [0010]     From such a background is strongly requested a recording disk cartridge having a simple structure, excellent in assembling ability, productivity, and rotational stability, and also easy in changing a number of recording disk media.  
       SUMMARY OF THE INVENTION  
       [0011]     It is an aspect of the present invention to provide a recording disk cartridge including a plurality of flexible recording disk media integrally rotatably housed within a cartridge case, wherein each of said recording disk media is fixed to a center core which is stacked one on another through a spacer. The cartridge case comprises: a lower plate for configuring a lower wall parallel to the plurality of the recording disk media; at least one inner plate that is stacked and fixed on the lower plate, and partitions the plurality of the recording disk media; and an upper plate that is stacked and fixed on said inner plate, and configures an upper wall of the cartridge case. Each spacer is provided with locking protrusions at upper and lower surfaces thereof, and each center core is provided with locking holes for engagement with the locking protrusions of adjacent spacers.  
         [0012]     In accordance with such the configuration, in the recording disk cartridge of the present invention the cartridge case is configured in a form of stacking up the lower plate, the inner plate, and the upper plate. Therefore, a pair of the inner plate and the recording disk medium is made one unit, all inner plates can be made a same part, and therefore, the recording disk cartridge is excellent in productivity. And because the recording disk medium in an assembling process can also be carried by making a lower plate and an inner plate as a substitute of a tray, the recording disk cartridge is excellent also in assembling ability without damaging and staining the medium. In addition, in a case that it is intended to make a specification of changing a number of recording disk media, it is easy to change the specification because it suffices to mainly change a number of inner plates. Furthermore, because an inner plate of a partition plate is fixed as part of the cartridge case, the recording disk cartridge is easy to realize accuracy such as a parallelism to the recording disk media and can heighten a rotational stability especially at a high speed such as 2000 to 8000 rpm.  
         [0013]     In addition, in a recording disk cartridge according to the present invention, each center core is engaged with the spacer with the locking protrusions of the spacer entered into the corresponding locking holes of the center core, so that a plurality of center cores can be integrally rotatable. Therefore, it is possible to improve rotational stability of the plurality of recording disk media. Furthermore, a plurality of center cores are readily assembled with each center core and the spacer being engaged each other, leading to excellent assembling ability.  
         [0014]     In the aforementioned recording disk cartridge, the locking protrusions may be arranged equidistantly along a circle of which center is a rotation axis of the spacer, so that the combination of the center cores can be strengthened during the rotation thereof.  
         [0015]     In the aforementioned recording disk cartridge, the locking protrusions may be arranged so as to protrude alternately at an upper side and a lower side of the spacer. This can strengthen the combination of the center cores at upper and lower layers.  
         [0016]     Further, in the aforementioned recording disk cartridge, the number of locking protrusions for engagement with the upper side and the lower side of the center core may be at least two each.  
         [0017]     In the aforementioned recording disk cartridge, the locking holes may be penetration holes formed in the center core, and a height of each locking protrusion may be greater than a thickness of the center core. Further, the spacer may be provided with recesses, a depth of each recess is greater than a protrusion amount of each locking protrusion that protrudes from the corresponding locking hole. Therefore, it is possible to provide a reliable engagement between the spacer and the center core.  
         [0018]     In the aforementioned recording disk cartridge, the center core may comprise a circular bottom plate, a cylindrical side wall rising from a peripheral rim of said bottom plate, and a flange widening in an outer diameter direction from an upper end of said side wall. And, a plurality of locking holes may be provided around a center hole located in center of said bottom plate to surround said center hole.  
         [0019]     In the aforementioned recording disk cartridge, the spacer may comprise a ring-shaped main body portion having a plurality of penetration holes. And, the locking protrusions may be pins pressed into said penetration holes.  
         [0020]     Further, in the aforementioned recording disk cartridge, the penetration holes may be formed in positions corresponding to said locking holes of said center core. And each of the penetration holes may be formed so that a small diameter hole portion into which said pin is pressed is coaxially adjacent to a large diameter hole portion whose diameter is larger than said small diameter hole portion.  
         [0021]     In the aforementioned recording disk cartridge, adjacent penetration holes of said spacer may be arranged such that the small diameter hole portion and the large diameter hole portion are located upside down.  
         [0022]     In the aforementioned recording disk cartridge, an end of said pin may be located on a boundary between said small diameter hole portion and said large diameter hole portion, and the other end of said pin may protrude outside said small diameter hole portion.  
         [0023]     Further, in the aforementioned recording disk cartridge, when said center core is stacked one on another through the spacer, each of said pins of the spacer may extend through the corresponding locking hole of said center core and position in said large diameter hole portion of another adjacent spacer.  
         [0024]     According to the present invention, the recording disk medium may be a magnetic disk medium. Also, the recording disk medium may be an optical disk medium. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0025]      FIG. 1  is an exploded perspective view of a magnetic disk cartridge according to one embodiment of the present invention.  
         [0026]      FIG. 2A  is an external perspective view of the magnetic disk cartridge with a shutter closed;  FIG. 2B  is an external perspective view of the magnetic disk cartridge with the shutter opened.  
         [0027]      FIG. 3  is a perspective view showing an inner face of an upper plate.  
         [0028]      FIG. 4  is a section view taken along the line IV-IV of  FIG. 2B  with the magnetic disk cartridge loaded on a magnetic disk drive.  
         [0029]      FIG. 5  is a partially enlarged drawing of  FIG. 4 .  
         [0030]      FIG. 6  is an exploded perspective view showing a stack structure of magnetic disk media.  
         [0031]      FIG. 7  is an explanatory view showing a depth of a large diameter hole portion of the center core. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0032]     Here will be described an embodiment of the present invention in detail, referring to drawings as needed. In the embodiment will be described a case of adopting a magnetic disk medium as an example of a recording disk medium.  
         [0033]     Meanwhile, in a description below, with respect to up/down directions, making it a standard a typical use state of the magnetic disk cartridge, vertical directions for faces of magnetic disk media are called the up/down directions for convenience.  
         [0034]     As shown in  FIG. 1 , in a magnetic disk cartridge  1  of an example of a recording disk cartridge are stacked a lower plate  10  for configuring a lower wall thereof; a plurality of, for example, four inner plates  20 , and an upper plate  30  for configuring an upper wall thereof in this order; these are fastened and fixed with four screws  91 ; and thereby a cartridge case  2  (see  FIG. 2A ) is configured. Between the lower plate  10  and the lowermost inner plate  20 , between any adjacent two of the four inner plates  20 , and between the uppermost inner plate  20  and the upper plate  30  is arranged a magnetic disk medium  41 , respectively. Each magnetic disk medium  41  is a disc form having an opening  41   a  at center thereof, and a center core  42  made of metal is affixed at rim of the opening  41   a . It is designed that any adjacent two center cores  42  are engaged by spacers  43 ,  43 ′, and that five magnetic disk media  41  (the magnetic disk media  41  stacked and integrated are assumed to be a disk stack  40 ) are integrally rotated.  
         [0035]     In each of the inner plates  20  is formed a rib  22  for abutting with upper/lower plates at a peripheral rim of a flat main plate  21 . Part of a right near side of each of the inner plates  20  in  FIG. 1  forms a notch  23  so that magnetic heads  63  (see  FIG. 4 ) can easily move onto the magnetic disk media  41 . At the portion of the notch  23  is not formed the rib  22 , and therefore, when the inner plates  20  are stacked up, an opening  3  is formed on a side face of the cartridge case  2  as shown in  FIG. 2A .  
         [0036]     The opening  3  is opened/closed by a shutter  4  that coaxially rotates with the disk stack  40 . As shown in  FIG. 1 , the shutter  4  is configured by combining a lower rotor  51  and an upper rotor  52 .  
         [0037]     Next will be described each member in more detail.  
         [0038]     The lower plate  10  is designed at a peripheral rim of a main plate  11  of a substantially square to mainly form a side wall  13  and a rib  12  for abutting with a lower face of the rib  22  of the lowermost inner plate  20 . The side wall  13  is vertically provided in a predetermined range, for example, around one third range of one edge, from one corner of the main plate  11  (near side corner in  FIG. 1 ), and is formed approximately in height of the inner plates  20  stacked.  
         [0039]     A sector portion toward a center of the main plate  11  from one edge  11   a  (one edge of right near side in  FIG. 1 ) continuing into the side wall  13  of the main plate  11  is designed to form a depression  14   a  lowered by one step, not to form the rib  12  at the peripheral rim of the main plate  11 , and to become an opening  14 . Thus it becomes easy for the magnetic heads  63  to proceed into the cartridge case  2 .  
         [0040]     An approximately central one third range of the other edge  11   b  (one edge of left near side in  FIG. 1 ) continuing into the side wall  13  of the main plate  11  is designed not to form the rib  12  but to become an opening  15  so that a gear  51   f  of the lower rotor  51  described later can be exposed. In addition, outside the side wall  13  of the other edge  11   b  is formed a groove  13   a  along a periphery of the lower plate  10 , continuing into the opening  15 . The groove  13   a  is designed to be a passage where a shutter open gear  67  (see  FIG. 2A ) of a magnetic disk drive proceeds in a direction shown in an arrow Ar of  FIG. 2A  and enters in the opening  15  in order to engage in the gear  51   f.    
         [0041]     The rib  12  is formed so as to protrude upward across all periphery except the side wall  13  and the openings  14 , 15  out of a peripheral rim of the main plate  11 . At center of the main plate  11  is formed a circular opening  16  for exposing the center core  42  provided inside the lowermost magnetic disk medium  41 . At upper rim of the opening  16 , across all periphery thereof is formed a rib  17  outside which a central opening  51   c  formed at center of the lower rotor  51  fits. The rib  17  rotationally freely supports the lower rotor  51 .  
         [0042]     In addition, on an upper face (inner face) of the main plate  11  is formed a circular lower rotor support groove  18  at a position corresponding to peripheral rim of the lower rotor  51 . The lower rotor support groove  18  rotationally freely supports the lower rotor  51  coaxially with the magnetic disk media  41  by engaging in a rib  51   d  (see  FIG. 4 ) formed downward at a peripheral rim of the lower rotor  51 .  
         [0043]     In addition, at four corners of the main plate  11  are formed screw holes  19  where female threads are formed, respectively, with penetrating through the up/down directions.  
         [0044]     The main plate  21  of each of the inner plates  20  is substantially a square, and a portion corresponding to one of four corners of the square is designed to be an arc (arc portion  24 ) one size larger than the magnetic disk medium  41 . At one edge (right near side in  FIG. 1 ) continuing into the arc portion  24  is formed the notch  23  into a sector. The rib  22  protrudes the up/down directions and is formed across all periphery except the arc portion  24  and the notch  23  out of periphery rim of the main plate  21 . At center of the main plate  21  is formed a central opening  21   c  for enabling the upper center core  42  to be exposed and to be coupled with the lower center core  42 .  
         [0045]     In addition, at three corners of the main plate  21 , with penetrating through the three corners in the up/down directions, are formed holes  29  through which screw shaft portions  91   a  of the screws  91  are inserted, respectively.  
         [0046]     The upper plate  30  is formed substantially symmetric to the lower plate  10 . As shown in  FIG. 3 , in the upper plate  30 , on a substantially square main plate  31  are formed a depression  34  corresponding to the depression  14   a , a rib  37  corresponding to the rib  17 , and an upper rotor support groove  38  corresponding to the lower rotor support groove  18 . Meanwhile, at center of the main plate  31  are not formed an opening and a side wall corresponding to the side wall  13 .  
         [0047]     In addition, at a peripheral rim of the main plate  31 , across all periphery except the depression  34  is formed a rib  32  protruding downward.  
         [0048]     In addition, at four corners of the main plate  31  are respectively formed holes  39  that enables the screw shaft portions  91   a  of the screws  91  to be penetrated therethrough.  
         [0049]     The lower rotor  51  is designed so that: a central opening  51   c , a notch  51   e , a rib  51   d , and the gear  51   f  are formed on a ring-form lower rotor plate  51   a  substantially same as the magnetic disk media  41 ; and a shutter plate  51   b  is vertically provided at the peripheral rim of the lower rotor plate  51   a . The central opening  51   c  is formed as a circle fitting outside the rib  17 , the notch  51   e  is formed as a sector corresponding to the depression  14   a . In addition, the rib  51   d  is provided downward at a peripheral rim of a lower face of the lower rotor plate  51   a , corresponding to the lower rotor support groove  18 .  
         [0050]     The shutter plate  51   b  is a blocking member for blocking the opening  3  (see  FIG. 2A ) and the disk stack  40  and is vertically provided along the peripheral rim of the lower rotor plate  51   a  with neighboring the notch  51   e . The gear  51   f  is an engaged portion for opening/closing the shutter  4  (see  FIG. 2A ) from outside of the magnetic disk cartridge  1 , and is formed at a peripheral rim of the lower rotor plate  51   a  within a predetermined range with neighboring the shutter plate  51   b.    
         [0051]     The upper rotor  52  is designed to be substantially symmetric to the lower rotor  51 : the upper rotor  52  comprises an upper rotor plate  52   a  similar to the lower rotor plate  51   a ; on the upper rotor plate  52   a  are formed a central opening  52   c  fitting outside the rib  37  of the upper plate  30 , a notch  52   e  corresponding to the depression  34 , and a rib  52   d  corresponding to the upper rotor support groove  38 . In addition, at a portion adjacent to the notch  52   e  of a peripheral rim of the upper rotor plate  52   a  is formed a shutter groove  52   b , corresponding to the shutter plate  51   b  of the lower rotor  51 . The lower rotor  51  and the upper rotor  52  are designed to integrally rotate by the shutter groove  52   b  and upper end rim of the shutter plate  51   b  engaging.  
         [0052]     The upper rotor  52  is rotationally freely supported by the upper plate  30  by the central opening  52   c  fitting outside the rib  37  of the upper plate  30 , and the rib  52   d  engaging in the upper rotor support groove  38 . Meanwhile, the upper rotor  52  is prevented from dropping from the upper plate  30  by a stop member  53 . The stop member  53  comprises a cylindrical portion  53   a  inserted in the rib  37  (see  FIG. 3 ) and a flange  53   b  formed at one end of the cylindrical portion  53   a ; the cylindrical portion  53   a  is inserted in the central opening  52   c  from a lower side of the upper rotor  52  and is fixed at the rib  37  by ultrasonic welding, adhesion, and the like.  
         [0053]     As an enlarged section drawing shown in  FIG. 5 , an upper face of the lower rotor  51 , upper and lower faces of the inner plates  20 , and a lower face of the upper rotor  52  are faces opposing the magnetic disk media  41 , where liners  49  are affixed across portions opposing the media  41 , respectively.  
         [0054]     The liners  49  consist of, for example, a non-woven cloth such as a polyester fiber and a blended fabric fiber of rayon and polyester  
         [0055]     Next will be described a stack structure of the lower plate  10 , the inner plates  20 , and the upper plate  30 .  
         [0056]     In the rib  12  of the lower plate  10 , as shown in  FIG. 5 , an inside thereof is formed higher by one step than an outside thereof, and thereby a male type step portion  12   a  is formed; each rib  22  of the inner plates  20  forms a female type step portion  22   a  protruding downward at outermost periphery, and thus a periphery of the male type step portion  12   a  and an inner perimeter of the female type step portion  22   a  become able to be fitted. In addition, when the lower plate  10 , the inner plates  20 , and the upper plate  30  are fastened by the screws  91  (see  FIG. 1 ), an upper face of the male type step portion  12   a  and a corresponding portion of a lower face of the lowermost inner plate  20  are designed to be contacted. Thus, because the rib  12  of the lower plate  10  and the rib  22  of the inner plate  20  are sealingly abutted and fitted each other, an invasion of dust into the cartridge case  2  from outside is prevented.  
         [0057]     Similarly, any adjacent two of the inner plates  20 , and the uppermost inner plate  20  and the upper plate  30  are stacked by being sealingly abutted and fitted each other. In other words, on an upper face of each of the inner plates  20  is formed a male type step portion  22   b  where an inside of the upper face is formed higher by one step; at a rib  32  of the upper plate  30  is formed a female type step portion  32   a  of which outermost periphery protrudes downward by one step. And the male type step portion  22   b  of one inner plate  20  and the female type step portion  22   a  of an upper adjacent inner plate  20  are sealingly abutted and fitted each other; the male type step portion  22   b  of the uppermost inner plate  20  and the female type step portion  32   a  of the upper plate  30  are sealingly abutted and fitted, and stacked. Thus any adjacent two of the ribs  12 ,  22 ,  32  are sealingly abutted and fitted each other, and dust from outside is prevented from invading into the cartridge case  2 . In addition, as soon as the lower plate  10 , the inner plates  20 , and the upper plate  30  are stacked, the side wall  13  of the cartridge case  2  is configured. Furthermore, because the lower plate  10 , the inner plates  20 , and the upper plate  30  are accurately positioned each other, and respective relative movements go away by being sealingly abutted and fitted each other, a rigidity of the cartridge case  2  improves.  
         [0058]     In addition, both of the female type step portion  22   a  and the male type step portion  22   b  protrude from the main plate  21  beyond a thickness of the liner  49 . Therefore, after affixing the liners  49  on the inner plates  20  and making an assembly, then even if placing it on a work bench, the liners  49  do not contact the work bench, and accordingly, are not contaminated with dust and the like.  
         [0059]     Such the configuration of the cartridge case  2  by stacking the inner plates  20  facilitates a change of a number of the magnetic disk media  41 ; although a height change of the side wall  13  and that of the shutter plate  51   b  are requested, a number of housing units of the magnetic disk media  41  formed within the cartridge case  2  can be changed only by mainly changing a number of the inner plates  20 .  
         [0060]     Next will be described the magnetic disk media  41  and a stack structure thereof. The magnetic disk media  41  are ones where magnetic paint is coated on both faces of a resin sheet, for example, such as polyester.  
         [0061]     As shown in  FIG. 6 , each of the center cores  42  is one substantially made a hat form with draw forming a metal plate by press: the center core  42  is mainly configured of a circular bottom plate  42   a , a low cylindrical side wall  42   b  rising from peripheral rim of the bottom plate  42   a , and a flange  42   c  widening in an outer diameter direction from an upper end of the side wall  42   b . At center of the bottom plate  42   a  is formed a center hole  42   d , and at rim of the plate  42   a  are formed six small holes (locking holes)  42   e  at a distance of 60 degrees, making the center hole  42   d  a center thereof. In other words, the small holes  42   e  are arranged equidistantly along a circle of which center is a rotation axis of a spacer  43  to be described later.  
         [0062]     A spacer  43  is provided between adjacent center cores  42 , keeps a distance of each of the center cores  42 , stops a rotation between each of the center cores  42 , and functions so that the stacked magnetic disk media  41  integrally rotate. The spacer  43  is mainly configured of a main body portion  43   a  shaped like a ring from a resin and metallic pins (locking protrusions)  43   b  pressed into the main body portion  43   a . In the main body portion  43   a  are formed six penetration holes h at positions corresponding to the small holes  42   e  of the center core  42 , wherein each of the penetration holes h consists of a small diameter hole portion  43   c , where the pin  43   b  is pressed, and a large diameter hole portion  43   d  that is coaxial with and slightly larger in diameter than the small diameter hole portion  43   c . The six penetration holes h are designed to be upside down in any two adjacent ones. In other words, penetration holes h 2  of both adjacent penetration holes h 1 , where each the large diameter hole portion  43   d  is positioned at an upper side thereof, are arranged so that the large diameter hole portion  43   d  is positioned at a lower side thereof.  
         [0063]     Into each of the small diameter portions  43   c  is pressed each one pin  43   b  from upper/lower sides thereof, one end of the pin  43   b  is positioned at a boundary of the large diameter hole portion  43   d  and the small diameter hole portion  43   c , and the other end thereof protrudes outside the small diameter portion  43   c . The large diameter hole portion  43   d  serves a function of a clearance at ends of pins  43   b  of adjacent spacers  43 .  
         [0064]     As shown in  FIG. 5 , such the spacers  43  are provided between adjacent center cores  42 , respectively. One pin  43   b  protruding toward a lower side of each of the spacers  43  enters in a small hole  42   e  of one center core  42  at the lower side of the spacer  43 , and stops a rotation relative to the center core  42  at the lower side. If there is another spacer  43  at a still lower side than the center core  42  at the lower side, a floating-up of the spacer  43  for the center core  42  is prevented by the distal end of the pin  43   b  entering the large diameter hole portion  43   d  in the spacer  43  at the lower side. The other pin  43   b  protruding toward an upper side of the spacer  43  enters in a small hole  42   e  of the other center core  42  at the upper side of the spacer  43 , and stops a rotation relative to the center core  42  at the upper side. If there is another spacer  43  at a still upper side than the center core  42  at the upper side, the top end of the pin  43   b  enters in the large diameter hole portion  43   d  in the spacer  43  at the upper side.  
         [0065]     Meanwhile, because at an upper side the uppermost center core  42  has no center core  42  to stop a rotation thereof, at the upper side is arranged a thin top spacer  43 ′ in thickness where the pin  43   b  is protruded only downward.  
         [0066]     As described above, the pins  43   b  of the spacer  43 ,  43 ′ are fitted into the small holes  42   e  of the center core  42  and the spacer  43 ,  43 ′ is fixed to the center core  42 , thereby engaging the spacer  43 ,  43 ′ with the center core  42 . Therefore, a plurality of center cores  42  are assembled integrally ( FIG. 5 ), so that the rotational stability of the center core  42  can be improved.  
         [0067]     Further, in this instance, the distal end of the pin  43   b  of the spacer  43 ,  43 ′ protrudes from the center core  42  as illustrated in  FIG. 5 . Considering the pins  43   b  protruding upwardly from the spacer  43 , as shown in  FIG. 7 , the protrusion amount B of each pin  43   b  that protrudes from the corresponding small hole  42   e  becomes smaller than the depth A of the recess of each large diameter hole portion  43   d . This can also be said to the pins  43   b  protruding downwardly from the spacer  43 . Therefore, the engagement can be improved between the pins  43   b  of the spacer  43 ,  43 ′ and the center core  42 , so that the rotational stability of the center core  42  will be enhanced further.  
         [0068]     The center core  42  excels in workability because it can be processed as a single part. In this instance, a metal mold can be used for manufacturing the center core  42  as a single part, which is advantageous in the cost.  
         [0069]     Further, the center core  42  can be inspected as a single part, thereby improving handleability. In this instance, if the center cores  42  that have been passed the inspection are selected and assembled, it is possible to improve the probability to pass the product inspection.  
         [0070]     The center plate  47  is a slide member affixed at the center of an inner face of the upper plate  30 , that is, on a flat face of an inside of the rib  37 . The center plate  47  can be composed of, for example, a material excellent in sliding ability and abrasion resistance such as polyoxymethylene and ultra high molecular weight polyethylene.  
         [0071]     Although the bearing ball  45  consists of a sphere made of, for example, steel used for a ball bearing, it may also be composed of a material excellent in sliding ability and abrasion resistance, for example, such as polytetrafluoroethylene and polyoxymethylene. The bearing ball  45  is arranged within the ball holding portion  44   b  of the coupling shaft  44 , abuts with the bottom face of the ball holding portion  44   b ; and a center of an inner face of the upper plate  30 , that is, the center plate  47  by a point contact, and rotationally supports the disk stack  40 .  
         [0072]     In the compression coil spring  46  one end (upper end) is held by the spring holding portion  44   c  of the coupling shaft  44 ; the other end (lower end) abuts with an upper face of the uppermost center core  42 , and energizes the stacked center cores  42  to the side of the lower plate  10 , that is, to the side of the spindle  65  of the magnetic disk drive. Thus the center cores  42  do not jounce within the cartridge case  2 , and the fluctuation of the magnetic disk media  41  is prevented in rotation thereof.  
         [0073]     A magnetic disk drive for recoding/reproducing data for the magnetic disk cartridge  1  rotates, as shown in  FIG. 4 , the disk stack  40  by the spindle  65 . The spindle  65  attracts the lowermost center core  42  by magnetic force, enters in the center hole  42   d  of the center core  42 , and thereby matches an axis thereof with that of the disk stack  40 . At this time, because the spindle  65  slightly lifts up the center cores  42  with resisting an energizing force of the compression coil spring  46 , as shown in  FIGS. 4 and 5 , each of the magnetic disk media  41  is positioned at center of a space formed between the lower rotor  51  and the lowermost inner plate  20 , between upper and lower inner plates  20 , and between the uppermost inner plate  20  and the upper rotor  52 . The magnetic heads  63  are provided at top ends of swing arms  62 . Each of the magnetic heads  63  is arranged on both faces of each of the magnetic disk media  41 .  
         [0074]     The magnetic disk cartridge  1  thus described can prevent, in no use thereof as shown in  FIG. 2A , an invasion of dust thereto by closing the opening  3  with rotating the shutter  4  in a counterclockwise direction of the drawing; in use thereof as shown in  FIG. 2B , when loaded on the magnetic disk drive, the shutter open gear  67  fits in the groove  13   a , is guided thereby, engages in the gear  51   f , and rotates the shutter  4  in a clockwise direction of the drawing.  
         [0075]     In addition, the disk stack  40  rotates by the spindle  65  rotating. After then, the swing arms  62  rotate by being driven with an actuator  61 , and each of the magnetic heads  63  are moved onto each face of the magnetic disk media  41 .  
         [0076]     When recording data on the magnetic disk media  41  with the magnetic heads  63 , the data is recorded thereon by sending a signal to the magnetic heads  63  by a control circuit not shown; when reproducing data from the magnetic disk medium  41 , a signal is output by detecting a change of a magnetic field on the medium  41  with the magnetic heads  63   a.    
         [0077]     At this time, dust on the magnetic disk media  41  is removed by the liners  49  appropriately touching respective media  41 .  
         [0078]     After the use of the magnetic disk cartridge  1 , the magnetic heads  63  are retracted from the cartridge case  2 , thereafter ejects the magnetic disk cartridge  1 ; thereby the gear  51   f  is driven by the shutter open gear  67 , and the shutter  4  closes the opening  3 .  
         [0079]     Thus because the magnetic disk cartridge  1  has a plurality of the magnetic disk media  41 , data transfer can be performed at a higher speed by simultaneously accessing data with a plurality of magnetic heads  63 .  
         [0080]     In addition, because the cartridge case  2  is configured by stacking up the inner plates  20 , it is easy to perform a specification change of making a number of magnetic disk media  41  a different one. Then, in assembling the magnetic disk cartridge  1 , because the magnetic disk media  41  can be handled with being placed on the inner plates  20  and the lower rotor  51  built in the lower plate  10 , an occasion of touching the magnetic disk media  41  can be reduced and a quality of the cartridge  1  can be further stablized.  
         [0081]     In addition, because each of the inner plates  20  is stacked on the lower plate  10  or another inner plate  20  and is fixed, the magnetic disk cartridge  1  can make it higher a parallelism to the magnetic disk media  41 , can stabilize a rotation of the media  41 , and enable a higher speed rotation of the media  41 , furthermore a higher speed of a data transfer.  
         [0082]     Thus, although the embodiment of the present invention is described, the invention is not limited thereto and can be embodied with being changed as needed. For example, although in the embodiment the magnetic disk medium  41  is applied to a recording disk medium, an optical recording medium where data is recorded by light can also be applied thereto.  
         [0083]     In addition, although in the embodiment the lower plate  10 , the inner plates  20 , and the upper plate  30  are fastened and fixed by the screws  91 , they can also be integrally fixed by any of adhesion and welding.  
         [0084]     Furthermore, three pins  43   b  are provided on the spacer  43  at the upper side and the lower side, respectively. However, the number of pins  43   b  may be one, two or more than four.