Patent Publication Number: US-2004056135-A1

Title: Recording tape cartridge

Description:
CROSS-REFERENCE TO RELATED APPLICATION  
     [0001] This application claims priority under 35 USC 119 from Japanese Patent Application No. 2002-276805, the disclosure of which is incorporated by reference herein. 
    
    
     
       BACKGROUND OF THE INVENTION  
       [0002] 1. Field of the Invention  
       [0003] The present invention relates to a recording tape cartridge which rotatably accommodates a reel on which a recording tape, such as a magnetic tape or the like, is wound.  
       [0004] 2. Description of the Related Art  
       [0005] Recording tapes, such as magnetic tapes and the like, are used as external recording media of computers and the like. Little space is required for storage of the recording tape, and a large amount of information can be recorded thereon. A so-called single-reel recording tape cartridge is used which rotatably accommodates, within a case, a single reel on which such a recording tape is wound.  
       [0006] Such a recording tape cartridge has a braking mechanism so that the reel does not rotate within the case when the recording tape cartridge is not being used (see, for example, Japanese Patent No. 3187022). A recording tape cartridge equipped with this braking mechanism will be described hereinafter on the basis of FIGS. 11 and 12.  
       [0007] In a recording tape cartridge  200  shown in FIG. 11, a single reel  204  is accommodated within a case  202  which is formed by joining together peripheral walls of a lower case  202 A and an upper case  202 B. The case  202  has a gear opening  206  which is formed in the central portion of a floor plate of the lower case  202 A, and a rotation restricting rib  208  which projects downward from the ceiling plate of the upper case  202 B.  
       [0008] The reel  204  has a reel hub  210  which is formed in the shape of a cylinder having a floor, and on whose outer peripheral portion a recording tape is wound. A reel gear  214 , which can mesh with a driving gear  212 A formed at a rotating shaft  212  of a drive device, is formed in an annular form at the bottom surface of a floor portion  210 A of the reel hub  210 . Through holes  216 , which pass through the floor portion  210 A, are provided at a plurality of places which are evenly spaced on a circumference at the region where the reel gear  214  is formed. The diameter of each through hole  216  is greater than the gear pitch of the reel gear  214 . Teeth of the reel gear  214  are not provided around each through hole  216 .  
       [0009] On the other hand, anchor projections  218  stand erect at the top surface of the floor portion  210 A of the reel hub  210 , discretely at plural positions between the through holes  216  which are disposed along a predetermined circumference. A gear teeth  218 A is formed at the top end portion of each anchor projection  218 .  
       [0010] A disc-shaped braking member  220  is inserted in the reel hub  210 . A braking gear  220 A, which is annular and which can mesh with the gear teeth  218 A, is provided at the bottom surface of the braking member  220 . A projection  222  stands erect at the top surface of the braking member  220 . An insertion groove  222 A, in which the rotation restricting rib  208  of the case  202  is inserted, is provided at the projection  222 . Due to the rotation restricting rib  208  being inserted in the insertion groove  222 A, the braking member  220  cannot rotate with respect to the case  202 . The braking member  220  can move in the vertical directions while being guided by the rotation restricting rib  208 .  
       [0011] A compression coil spring  224  is disposed between the ceiling plate of the upper case  202 B and the braking member  220 . Usually, the braking member  220  is urged downward by the urging force of the compression coil spring  224 , such that the braking gear  220 A meshes with the gear teeth  218 A. In this way, there is usually a rotation locked state in which rotation of the reel  204  with respect to the case  202  is impeded. Further, the reel gear  214  is exposed from the gear opening  206  while the reel  204  is pushed against the floor plate of the lower case  202 A by this urging force.  
       [0012] Moreover, a releasing member  226  is disposed between the floor portion  210 A of the reel hub  210  and the braking member  220 , so as to abut both. The releasing member  226  has leg portions  226 A which are formed in the shape of plates which do not interfere with the anchor projections  218 , and which enter into the respective through holes  216 .  
       [0013] In this way, due to the braking gear  212 A meshing with the reel gear  214 , as shown in FIG. 12, the leg portions  226 A are pushed by the driving gear  212 A against the urging force of the compression coil spring  224 , and the releasing member  226  is pushed upward. When the braking member  220  is pushed upward while the releasing member  226  moves away from the floor portion  210 A, the meshing of the braking gear  220 A and the gear teeth  218 A is released. At this time, the reel  204  also floats up from the floor plate of the lower case  202 A, and the reel  204  becomes able to rotate within the case  202 .  
       [0014] Then, when the rotating shaft  212  rotates, the reel  204 , whose reel gear  214  is meshing with the driving gear  212 A of the rotating shaft  212 , rotates within the case  202 . At this time, the releasing member  226  rotates together with the reel  204 , and the axially central portion of the releasing member  226  slidingly contacts the axially central portion of the braking member  220 . Thus, the axially central portion of the braking member  220  is a convex portion  220 B which is formed in the shape of a substantially spherical surface, and substantially point-contacts the axially central portion of the releasing member  226 .  
       [0015] On the other hand, when the state in which the driving gear  212 A and the reel gear  214  mesh together is released, due to the urging force of the compression coil spring  224 , the braking member  220  moves downward, the braking gear  220 A and the gear teeth  218 A mesh together, and the reel  204  is pushed against the floor plate of the lower case  202 A. In this way, the reel  204  returns to the rotation locked state in which rotation of the reel  204  with respect to the case  202  is impeded.  
       [0016] At the time of assembling the recording tape cartridge  200 , the reel  204  is placed on the lower case  202  such that the bottom end portion of the reel hub  210  enters into the gear opening  206 . Thereafter, the releasing member  216  is placed on the floor portion  210 A of the reel hub  210  while the respective leg portions  226 A are inserted in the through holes  216 . Next, the braking member  220  is placed on the anchor projections  218  of the reel hub  210  such that the braking gear  220 A meshes with the gear teeth  218 A. In the state in which the compression coil spring  224  is placed on the braking member  220 , while the compression coil spring  224  is compressed and the rotation restricting rib  208  is inserted in the insertion groove  222 A of the braking member  220 , the upper case  202 B is made to approach the lower case  202 A, and the upper case  202 B and the lower case  202 A are joined together in a state in which the peripheral walls thereof abut one another. In this way, when the recording tape cartridge  200  is not being used (e.g. is being shipped), rotation of the reel  204  with respect to the case  202  is impeded.  
       [0017] Further, although not illustrated, a structure is known which does not have the releasing member  226 . In this structure, the convex portion  220 B of the braking member  220  is directly pressed by a releasing portion, which projects at the axially central portion of the rotating shaft  212  and enters in from a through hole which passes through the floor portion  210 A of the reel hub  210 , such that the braking member  220  is pushed upward and the rotation locked state of the reel  204  is released (see, for example, Japanese Patent Application Laid-Open (JP-A) No. 63-251983). A recording tape cartridge having such a structure does not have the anchor projections  218 , and the gear teeth are provided in an annular form at the floor portion of the reel hub. However, this structure is the same as the previously-described recording tape cartridge  200  in that rotation of the braking member is impeded by the rotation restricting rib of the case, and in that the braking member is guided by the rotation restricting rib in directions of approaching and moving away from the gear teeth. Thus, the processes of assembling the recording tape cartridge having this structure are basically the same as the processes of assembling the above-described recording tape cartridge  200 , except for the process of assembling the releasing member  226 .  
       [0018] However, in the above-described conventional recording tape cartridge  200 , when the braking member  220  is placed on the anchor projections  218  of the reel hub  210 , if the axial center of the braking member is offset from the axial center of the reel  204 , there are cases in which the braking member  220  is placed on the anchor projections  218  in a state in which the addendum of the braking gear  220 A ride on the addendum of the gear teeth  218 A. Even in such cases, because there is a clearance between the insertion groove  222 A of the braking member and the rotation restricting rib  208  of the upper case  202 B, the rotation restricting rib  208  may be inserted in the insertion groove  222 A. Thus, there is the concern that when the subsequent processes are carried out and the recording tape cartridge  200  is assembled, the recording tape cartridge  200  in which rotation of the reel  204  is permitted will be shipped. In particular, it is easy for such problems to arise in processes for assembling the recording tape cartridge  200  which are carried out by manual work.  
       SUMMARY OF THE INVENTION  
       [0019] In view of the aforementioned, an object of the present invention is to provide a recording tape cartridge in which it is possible to appropriately assemble a braking member which impedes rotation of a reel at a time when the recording tape cartridge is not being used.  
       [0020] A first aspect of the present invention provides a recording tape cartridge comprising: a reel which is accommodated in a case, and gear teeth are provided, along a circumference which is substantially coaxial with a reel hub around which a recording tape is wound, at a floor portion of the reel hub; a braking member formed in a disc-shape, and a braking gear which can mesh with the gear teeth is provided at one surface of the braking member, and the braking member approaches and moves away from the floor portion in the reel hub so as to be positioned at a meshing position, at which the braking gear meshes with the gear teeth, and a released position at which a meshed state of the breaking gear and the gear teeth is released; and a taper wall standing erect at the floor portion along a circumference which has a greater diameter than an outer diameter of the braking member and which is substantially coaxial with the reel hub, wherein the braking member is supported at the case so as to be unable to rotate, and accompanying operation of inserting the braking member in the reel hub, the taper wall guides the braking member to the meshing position at which the braking gear meshes with the gear teeth.  
       [0021] In the above-described recording tape cartridge, when the braking member, which is supported so as to be unable to rotate with respect to the case, approaches the floor portion of the reel hub within the reel hub, the braking gear meshes with the gear teeth such that rotation of the reel is impeded. On the other hand, when the braking member moves away from the floor portion of the reel hub, the meshed state is released, and the reel can rotate within the case.  
       [0022] At the time of inserting the braking member into the reel hub, the braking member is moved toward the floor portion of the reel hub (substantially along the axial direction) and is placed on the region of the floor portion where the gear teeth are formed (which may be the floor portion itself), so that the braking gear meshes with the gear teeth of the floor portion of the reel hub.  
       [0023] Here, the taper wall stands erect at the floor portion of the reel hub, along a circumference which has a greater diameter than the outer diameter of the disc-shaped braking member and which is coaxial with the reel hub. Accompanying the above-described insertion operation (movement in a direction substantially along the axial direction), the taper wall guides the braking member in such that the braking gear meshes with the gear teeth. In other words, the taper wall guides the braking member in such that the axial center of the braking member coincides with the axial center of the reel hub. Thus, when the braking member is inserted in the reel hub, the braking gear reliably meshes with the gear teeth.  
       [0024] In the recording tape cartridge having the above-described structure, the braking member, which impedes rotation of the reel when the recording tape cartridge is not being used, can be assembled appropriately.  
       [0025] Further, the recording tape cartridge of the first aspect further comprises a plurality of projections at the floor portion of the reel hub, and the gear teeth are provided at distal ends of the plurality of projections.  
       [0026] Moreover, the taper wall is provided integrally with the plurality of projections at an inner peripheral surface side of the reel hub.  
       [0027] In the above-described recording tape cartridge, the gear teeth are provided at the distal ends of projections which project from the floor surface of the reel hub, in order to, for example, dispose, between the braking member and the floor portion of the reel hub, a releasing member for releasing the state in which rotation of the reel is impeded by the braking member. The taper surface is provided integrally at the reel hub inner peripheral surface side (the reel hub radial direction outer side) of the projections. Thus, the taper wall can function to reliably mesh the braking gear with the gear teeth at the time when the braking member is assembled in the reel, without increasing a thick portion at the floor portion of the reel hub.  
       [0028] A second aspect of the present invention provides a method of assembling a recording tape cartridge having: a case formed from an upper case and a lower case; a reel having a reel hub on which a recording tape is wound in the case, and gear teeth are provided along a circumference which is substantially coaxial with the reel hub, at an inner side of a floor portion of the reel hub; and a braking member formed in a disc-shape, and a braking gear which can mesh with the gear teeth is provided at one surface of the braking member, and the braking member impedes rotation of the reel, the method comprising the steps of: (a) disposing the reel at the lower case; (b) placing the braking member in the reel hub such that the gear teeth and the braking gear mesh together; and (c) joining the upper case and the lower case.  
       [0029] A third aspect of the present invention provides a method of manufacturing a recording tape cartridge having a braking member which impedes rotation of a reel which is accommodated in a case and on which a recording tape is wound, the method comprising the steps of: (a) forming gear teeth at an inner side of a floor portion of a reel hub of the reel; (b) forming a disc-shaped braking member which can approach and move away from the floor portion in the reel hub, and a braking gear, which can mesh with the gear teeth, is provided at one surface of the braking member; (c) forming a taper wall which stands erect at the floor portion of the reel hub along a circumference which is substantially coaxial with the reel hub; and (d) combining the braking member and the reel within the case by meshing together the braking gear of the braking member and the gear teeth of the reel hub. 
     
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
     [0030]FIG. 1 is a perspective view showing the overall structure of a recording tape cartridge relating to an embodiment of the present invention.  
     [0031]FIG. 2 is an exploded perspective view of the recording tape cartridge relating to the embodiment of the present invention.  
     [0032]FIG. 3 is a bottom view of an upper case structuring the recording tape cartridge relating to the embodiment of the present invention.  
     [0033]FIG. 4 is a plan view of a lower case structuring the recording tape cartridge relating to the embodiment of the present invention.  
     [0034]FIG. 5A is a view, as seen with the upper case removed, showing a process of opening an opening of the recording tape cartridge relating to the embodiment of the present invention, and is a plan view showing an initial state of engagement of an engaging projecting portion of a drive device with an operation projection of a door.  
     [0035]FIG. 5B is a plan view showing a state during the process of opening the opening of the recording tape cartridge of FIG. 5A.  
     [0036]FIG. 5C is a plan view showing a state in which opening of the opening of the recording tape cartridge of FIG. 5A has been completed.  
     [0037]FIG. 6 is an exploded perspective view, as seen from below, showing a braking mechanism and a reel structuring the recording tape cartridge relating to the embodiment of the present invention.  
     [0038]FIG. 7 is a cross-sectional view showing a rotation locked state of the reel in the recording tape cartridge relating to the embodiment of the present invention.  
     [0039]FIG. 8 is a cross-sectional view showing a rotatable state of the reel in the recording tape cartridge relating to the embodiment of the present invention.  
     [0040]FIG. 9 is a perspective view showing, in an enlarged manner, an interior of a reel hub structuring the recording tape cartridge relating to the embodiment of the present invention.  
     [0041]FIG. 10A is a plan view showing the relationship between taper walls and a braking member structuring the recording tape cartridge relating to the embodiment of the present invention.  
     [0042]FIG. 10B is a cross-sectional view taken along line  10 B- 10 B of FIG. 10A.  
     [0043]FIG. 11 is a cross-sectional view showing a rotation locked state of a reel in a conventional recording tape cartridge.  
     [0044]FIG. 12 is a cross-sectional view showing a rotatable state of the reel in the conventional recording tape cartridge. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
     [0045] Hereinafter, a recording tape cartridge  10  relating to an embodiment of the present invention will be described on the basis of FIGS. 1 through 10. First, the basic, overall structure of the recording tape cartridge  10 , and the structures of an opening and a door will be described. Then, a reel  14 , which is a main portion of the present invention, and a braking mechanism, which impedes rotation of the reel  14  at the time when the recording tape cartridge  10  is not in use, will be described. Note that, for convenience of explanation, the direction of loading the recording tape cartridge  10  into a drive device, which is denoted by arrow A, is the forward direction (front side) of the recording tape cartridge  10 . Further, the direction of arrow B, which is orthogonal to arrow A, is the rightward direction.  
     [0046] Overall Structure of Recording Tape Cartridge  
     [0047] The overall structure of the recording tape cartridge  10  is shown in perspective view in FIG. 1. A schematic exploded perspective view of the recording tape cartridge  10  is shown in FIG. 2.  
     [0048] As shown in FIGS. 1 and 2, the recording tape cartridge  10  is structured such that a single reel  14 , on which is wound a magnetic tape T serving as a recording tape which is an information recording/playback medium, is rotatably accommodated within a case  12  which is substantially rectangular as seen in plan view. The structure of the reel  14  will be described later.  
     [0049] The case  12  is formed by joining together an upper case  16  and a lower case  18  with peripheral walls  16 A,  18 A thereof opposing each other. The front right corner portion of each of the upper case  16  and the lower case  18 , which is one corner portion at the leading side in the direction of loading the recording tape cartridge  10  into a drive device, is cut away. A space for accommodating the reel  14 , on which the magnetic tape T is wound, is provided at the interior of the case  12 . The corner portion of the upper case  16  and the lower case  18 , at which corner portion the peripheral walls  16 A,  18 A have been cut away, forms an opening  20  which is for pulling-out of the magnetic tape T. The detailed structures of the opening  20  and a door  50 , which opens and closes the opening  20 , will be described later.  
     [0050] A leader pin  22 , which is pulled-out while being anchored (engaged) by a pull-out mechanism of a drive device, is connected to the free end of the magnetic tape T which is pulled out from the opening  20 . An annular groove  22 A is formed in each of the end portions of the leader pin  22  which project out further than the transverse direction end portions of the magnetic tape T. The annular grooves  22 A are anchored by hooks or the like of the pull-out mechanism. In this way, the hooks or the like do not contact and scratch the magnetic tape T at the time of pulling-out the magnetic tape T.  
     [0051] A pair of upper and lower pin stands  24 , which position and hold the leader pin  22  within the case  12 , are provided at the inner side of the opening  20  of the case  12 . The pin stands  24  are formed in semi-cylindrical shapes which open in the direction of arrow B. Both end portions of the leader pin  22 , which is in a state of standing upright, are held in concave portions  24 A of the pin stands  24 . The pin stands  24  are continuous with ribs  44  which will be described later.  
     [0052] A plate spring  25  is fixed in the vicinity of the pin stands  24 . The plate spring  25  engages the upper and lower end portions of the leader pin  22 , and holds the leader pin  22  at the pin stands  24 . When the leader pin  22  enters into and exits out from the pin stands  24 , arm portions  25 A of the plate spring  25  are appropriately elastically deformed, such that movement of the leader pin  22  is permitted.  
     [0053] Further, a gear opening  26 , which serves as an opening for exposing a reel gear  66  (which will be described later) of the reel  14  to the exterior, is formed in the central portion of the lower case  18 . The reel  14  is driven to rotate within the case  12  by the reel gear  66  meshing with a driving gear of a drive device. Further, the reel  14  is held so as to not joggle by play restricting walls  28  which project out at portions of the inner surfaces of the upper case  16  and the lower case  18 , and which serve as inner walls which are on a circular locus which is coaxial with the gear opening  26 . Moreover, an annular rib  26 A projects toward the inner side of the case  12  at the edge portion of the gear opening  26  at the lower case  18 . The annular rib  26 A is for positioning of the reel  14 .  
     [0054] A hollow portion  28 A, in which a hole for position regulation is formed, is continuous with the end portion of the play restricting wall  28  in a vicinity of the opening  20 . Further, a hollow portion  28 B, in which is formed a hole for position regulation which is a long hole, stands erect in the space sandwiched between the front left corner portion of the case  12  and the play restricting wall  28 . The hollow portions  28 A,  28 B are disposed on a single straight line which extends along the direction of arrow B. End portions of the play restricting walls  28 , except for the end portion thereof at which the hollow portion  28 A is continuous, are continuous with the peripheral wall  16 A or the peripheral wall  18 A of the case  12 , so as to partition the outer sides of the play restricting walls  28  and the space at which the reel  14  is set.  
     [0055] A memory board M, which stores various types of information, is set at the rear right portion of the lower case  18  for each recording tape cartridge  10 . A portion of an inclined rear wall  18 C forming the peripheral wall  18 A is inclined at a predetermined angle and the memory board M is disposed so as to be inclined at a predetermined angle such that sensing is possible at a drive device, which reads information recorded on the memory board M from the bottom surface side of the case  12 , and at a library device, which reads information recorded on the memory board M from the rear surface side of the case  12 .  
     [0056] Opening, and Structure of Case in Vicinity of Opening  
     [0057] As shown in FIG. 3 (which is a bottom view of the upper case  16 ) and in FIG. 4 (which is a plan view of the lower case  18 ), a pair of upper and lower screw bosses  32  and a pair of upper and lower screw bosses  36  are provided at the front and rear edge portions of the opening  20 , respectively. The screw bosses  32 ,  36 , as well as other screw bosses which are not illustrated, are for the screwing-in of screws for joining the upper case  16  and the lower case  18 .  
     [0058] The screw bosses  32 , which are positioned at the front edge portion of the opening  20 , are continuous with the right end portion of a front wall  12 A of the case  12  (the front wall  12 A is the portions of the peripheral walls  16 A,  18 A whose outer surfaces are directed in the direction of arrow A), and are continuous with a pair of upper and lower dustproofing walls  30  which are short and are bent along the plane of opening of the opening  20  from the right end portion of the front wall  12 A. Concave portions  30 A, into which the distal end portion of the door  50  which will be described later enters, are formed between the screw bosses  32  and the dustproofing walls  30 .  
     [0059] The screw bosses  36 , which are positioned at the rear edge portion of the opening  20 , are continuous with bent walls  38  and with the front end portions of a pair of upper and lower arc-shaped walls  34 . The bent walls  38  are formed such that the front end portion of a right wall  12 B of the case  12  (the right wall  12 B is the right side walls of the peripheral walls  16 A,  18 A which run along the direction of arrow A) is bent substantially along the plane of opening of the opening  20 . The arc-shaped walls  34  are provided at the inner side of the right wall  12 B. The upper and lower arc-shaped walls  34  are formed in an arc-shape which, in plan view, substantially corresponds to the outer peripheral surface of (i.e., the locus of movement of the outer peripheral surface of) the door  50  which will be described later. The upper and lower arc-shaped walls  34  extend rearward from the screw bosses  36  by a predetermined length, and are continuous with the right wall  12 B (the peripheral wall  16 A or the peripheral wall  18 A) via short connecting walls  34 A at the rear portions thereof.  
     [0060] A slit  40 , which is of a predetermined length and serves as a window portion which communicates the interior and the exterior of the case  12 , is formed in the right wall  12 B of the case  12 . The slit  40  is for exposing an operation projection  52  of the door  50  which will be described later. The slit  40  is formed by cutting out the lower portion of the peripheral wall  16 A which forms the right wall  12 B. The slit  40  opens toward the front as well by also cutting out the lower portion of the bent wall  38  of the upper case  16 .  
     [0061] A guide groove  42  which guides the door  50  is provided in each of the upper case  16  and the lower case  18  forming the case  12 . The groove walls of the guide grooves  42  are structured by the ribs  44  standing erect at a ceiling plate  16 B of the upper case  16  or a floor plate  18 B of the lower case  18 , the right wall  12 B (either the peripheral wall  16 A or the peripheral wall  18 A), and the play restricting walls  28 . In this way, the guide grooves  42  are formed without making the ceiling plate  16 B or the floor plate  18 B thinner. The ribs  44  are continuous with the pin stands  24 .  
     [0062] Each guide groove  42  is formed in an arc-shape which runs along a predetermined circumference whose proximal end is the concave portion  30 A and which reaches the right rear corner portion of the case  12 . This predetermined circumference is determined so as to pass (thread its way through) at the outer side of the screw bosses  32 , the inner side of the screw bosses  36 , and between the right wall  12 B and the play restricting walls  28 . In the present embodiment, the central position of this predetermined circumference (i.e., the center of rotation of the door  50  which will be described later) is set such that the left-right direction position (coordinate) thereof substantially coincides with a position further toward the outer side than the left end of the case  12 , and the front-back direction position (coordinate) thereof substantially coincides with the center of rotation of the reel  14  (the axial center of the play restricting walls  28 ).  
     [0063] Further, the portion of the guide groove  42  positioned at the opening  20  is continuous with the concave portion  24 A due to the rib  44  being cut-out at the right side of the pin stand  24 , and is also continuous with a spring groove  45  in which the arm portion  25 A of the plate spring  25  is disposed. Moreover, at the cut-out portion of the guide groove  42 , a taper opening  20 A, which guides the leader pin  22  into the case  12 , is continuous with the concave portion  24 A of the pin stand  24 . In addition, a rib  46 , which is formed along the rear edge of the taper opening  20 A, the front edge of the screw boss  36 , and the plane of opening of the opening  20 , respectively, is continuous with the rib  44 . In this way, the strength around the opening  20  of the case  12  can be ensured or improved.  
     [0064] Moreover, at the rear end of the rib  44 , which forms the rear half portion of each guide groove  42 , the rib  44  bends back in a substantial U shape and is closed. Moreover, the rib  44  of the upper case  16  is formed to be longer toward the rear than the rib  44  of the lower case  18 . This is in order for the memory board M, which is disposed at the right wall  12 B side, to not interfere with the door  50 , because the inclined rear wall  18 C (peripheral wall  18 A) of the lower case  18  is formed as an inclined surface of a predetermined angle.  
     [0065] A pair of top and bottom spring catching pins  55  are provided at the longitudinally central portion of the inner side portion of the rear half portion of the rib  44 . The spring catching pins  55  are continuous with the play restricting walls  28 . The spring catching pin  55  at the lower case  18  side is formed to be longer. One end side annular portion  56 A of a coil spring  56  which will be described later catches on the portion of this spring catching pin  55  which projects higher than the play restricting wall  28 . The coil spring  56  is prevented from falling out due to the short spring catching pin  55  at the upper case  16  side abutting the spring catching pin  55  at the lower case  18  side.  
     [0066] The case  12  is formed by the upper case  16  and the lower case  18 , which were described above, being fixed or joined together by unillustrated screws being screwed, from beneath, into the screw bosses  32 ,  36  as well as other screw bosses (not illustrated), in a state in which the peripheral walls  16 A,  18 A abut one another. Further, by forming the opening  20  by cutting away the front right corner portion, the plane of opening of the opening  20  faces in the direction of arrow A and in the direction of arrow B. Thus, the pull-out mechanism of a drive device can access and engage the leader pin  22  from the direction of arrow A, or from the direction of arrow B, or from between the direction of arrow A and the direction of arrow B. In this way, the area over which the pin stands  24  which hold the leader pin  22  can be set is broadened, and the region at which the pull-out mechanism of the drive device can engage the leader pin  22  is broadened. Thus, the positions where the pin stands  24  are disposed can be set in accordance with the specifications of the drive device which engages the leader pin  22  from the direction of arrow A or from the direction of arrow B. Therefore, the degrees of freedom in designing the drive device are increased.  
     [0067] Structure of Door  
     [0068] The above-described opening  20  is opened and closed by the door  50  which serves as a shielding member. The door  50  is formed in an arc-shape which curves along the direction of plate thickness thereof, and whose curvature as seen in plan view coincides with the curvature of the guide grooves  42  (the predetermined circumference). Further, the portion of the door  50  at the front portion thereof (at least the portion thereof which closes the opening  20 ) where the plate width (height) is formed to be substantially the same as the opening height of the opening  20 , is a closing portion  50 A. The portion of the door  50  which is at the rear side of the closing portion  50 A and whose plate width is slightly smaller than that of the closing portion  50 A, is a driving portion  50 B.  
     [0069] The plate length of the door  50  (the curved longitudinal dimension thereof) is determined such that, in the state in which the door  50  closes the opening  20 , the rear end portion of the driving portion  50 B is positioned in the right rear corner portion of the case  12  (see FIG. 5A). Note that the bottom rear portion of the driving portion  50 B is cut obliquely in order to avoid the memory board M which is disposed at the inclined surface of the inclined rear wall  18 C of the lower case  18 .  
     [0070] The door  50  closes the opening  20  (see FIG. 5A) in a state in which the distal end portion of the closing portion  50 A enters into the concave portions  30 A which are positioned at the outer sides of the screw bosses  32 . When the door  50  moves or rotates substantially rearward along the guide grooves  42  so as to open the opening  20  (see FIG. 5B) and the outer peripheral surface of a vicinity of the distal end of the closing portion  50 A reaches a vicinity of the inner sides of the screw bosses  36 , the opening  20  is completely opened (see FIG. 5C). Further, the door  50  closes the opening  20  by rotating in the direction substantially opposite to the direction at the time of opening the opening  20 .  
     [0071] In this way, the door  50  is curved so as to open and close the opening  20  by rotating without jutting out from the predetermined circumference which is the locus of movement of the door  50 . It suffices for the center of rotation and the radius of the door  50  (the configuration of the guide grooves  42 ) to be appropriately determined in accordance with the positions of the front and rear edge portions of the opening  20  (the screw bosses  32 ,  36 ) which are determined by the requirements of the drive device, or in accordance with the angle of the plane of opening of the opening  20  which is determined by the requirements of the library device, or the like.  
     [0072] Further, a plurality of convex portions  51 , which enter into the upper and lower guide grooves  42 , project at the upper and lower ends of the door  50 . The projecting heights of the convex portions  51  differ at the closing portion  50 A and the driving portion  50 B. However, the distance from the central line running along the longitudinal direction of the door  50  to the peak portion of each convex portion  51  is constant. In this way, the top and bottom convex portions  51  slide along the ceiling plate  16 B or the floor plate  18 B which are the floor portions of the guide grooves  42 .  
     [0073] Projections  51 A (see FIGS. 5A through 5C), whose peak portions run along the end surfaces in the direction of the plate thickness of the door  50 , project at the both sides, in the direction of plate thickness of the door  50 , of each convex portion  51 . The projections  51 A slide along the groove walls (the ribs  44  and the like) of the guide grooves  42 . Note that the convex portion  51  which is positioned furthest toward the front is disposed such that, when the opening  20  is being opened or closed, it does not enter into the taper opening  20 A which is continuous with the guide groove  42 .  
     [0074] At the time when the door  50  is opening and closing the opening  20 , the door  50  is guided in the guide grooves  42  by the convex portions  51  and the projections  51 A, and does not jut out from the aforementioned locus of movement. The door  50  twists its way through at the outer sides of the screw bosses  32  and the inner sides of the screw bosses  36  and between the right wall  12 B and the play restricting walls  28 , and reliably opens the opening  20 .  
     [0075] The operation projection  52 , which serves as an operation portion, projects along the radial direction of the door  50  at the outer peripheral portion in a vicinity of the front end (the closing portion  50 A side) of the driving portion  50 B of the door  50 . The operation projection  52  is exposed to the exterior of the case  12  from the slit  40 . Accompanying the loading (relative movement) of the recording tape cartridge  10  into a drive device, the operation projection  52  engages with an engaging projecting portion  104  which enters in from the portion of the slit  40  which opens toward the front. The operation projection  52  thereby moves the door  50  in the direction of opening the opening  20 .  
     [0076] A substantially L-shaped spring catching portion  54  projects toward the inner surface side of the door  50  at the rear end portion of the driving portion  50 B of the door  50 . The upper side of the spring catching portion  54  is the free end thereof. The spring catching portion  54  is for anchoring and holding the coil spring  56  serving as an urging mechanism. Specifically, the annular portions  56 A,  56 B for anchoring are provided at the end portions of the coil spring  56 . The spring catching pins  55  of the case  12  are inserted through the annular portion  56 A such that the annular portion  56 A is anchored and held at the case  12 . The spring catching portion  54  is inserted through the annular portion  56 B such that the annular portion  56 B is anchored and held at the door  50 .  
     [0077] In this way, the door  50  is urged in the direction of closing the opening  20  by the urging force of the coil spring  56 , and usually closes the opening  20 . The coil spring  56  has a length which reaches the rear right corner portion of the case  12  in the state in which the door  50  closes the opening  20  as described above. Therefore, the space between the play restricting walls  28  and the peripheral walls  16 A,  18 A (the inclined rear wall  18 C) at this rear right corner portion can be utilized effectively.  
     [0078] Stoppers  58 , which abut the upper end portion side surface and the lower end portion side surface of the leader pin  22  when the opening  20  is closed, project at the inner surface of the closing portion  50 A of the door  50 . The stoppers  58  can reliably prevent the leader pin  22  from falling out from the pin stands  24  due to the impact of a drop or the like.  
     [0079] Due to the operation of the recording tape cartridge  10  being loaded into a drive device, the operation projection  52  engages with the engaging projecting portion  104  of the drive device (see FIGS. 5A through 5C). The above-described door  50  thereby moves with respect to the case  12  against the urging force of the coil spring  56 , and opens the opening  20 . When the recording tape cartridge  10  is to be ejected from the drive device, the door  50  closes the opening  20  due to the urging force of the coil spring  56 .  
     [0080] Moreover, the door  50 , which is curved in an arc-shape, opens and closes the opening  20  (which is inclined with respect to the direction of arrow A) by rotating so as to circle around the outer sides of the reel  14  and the pin stands  24  (the leader pin  22 ), without jutting out from the locus of movement which runs along the curved configuration of the door  50 . In this way, the door  50  does not jut out from the region of the outer shape of the case  12  at the time of opening and closing the opening  20 .  
     [0081] Structures of Reel and Braking Mechanism  
     [0082] As shown in FIGS. 2 and 6, the reel  14  has a reel hub  60  which is shaped as a substantial hollow cylinder having a bottom. The reel hub  60  has a tubular portion  60 A, on whose outer peripheral surface the magnetic tape T is wound, and a floor portion  60 B which closes the bottom portion of the tubular portion  60 A. A lower flange  62  extends integrally, substantially coaxially, and outwardly in the radial direction, from a vicinity of the floor portion  60 B side end portion (the bottom end portion) of the reel hub  60 . On the other hand, an upper flange  64  is joined by ultrasonic welding or the like substantially coaxially to the upper end portion of the reel hub  60 . The inner diameter of the upper flange  64  is substantially the same as the inner diameter of the tubular portion  60 A, and the outer diameter of the upper flange  64  is the same as the outer diameter of the lower flange  62 .  
     [0083] In this way, between the opposing surfaces of the lower flange  62  and the upper flange  64  at the reel  14 , the magnetic tape T is wound around the outer peripheral surface of the tubular portion  60 A of the reel hub  60 , and the tubular portion  60 A is open upwardly. The outer diameters of the lower flange  62  and the upper flange  64  are slightly smaller than the inner diameters of the play restricting walls  28  of the case  12 , such that the reel  14  can rotate within the case  12 .  
     [0084] Further, as shown in FIG. 7, the bottom end portion of the floor portion  60 B of the reel hub  60  projects slightly more than the bottom surface of the lower flange  62 . A reel gear  66 , which is formed in an annular form, is provided in a vicinity of the outer periphery of this bottom end portion. The reel gear  66  can mesh with a driving gear  102  which is provided at the distal end of a rotating shaft  100  of a drive device.  
     [0085] Through holes  68 , which pass through the floor portion  60 B (the reel gear  66 ) are provided at three places which are spaced apart uniformly on a circumference at the region where the reel gear  66  is set. The diameter of each through hole  68  is larger than the gear pitch of the reel gear  66 . The teeth of the reel gear  66  are not provided around each through hole  68 .  
     [0086] Moreover, a reel plate  70 , which is an annular plate formed of a magnetic material which can be attracted by a magnet, is provided integrally by insert molding at the inner side of the reel gear  66  at the bottom end surface of the floor portion  60 B of the reel hub  60 .  
     [0087] The bottom end portion of the floor portion  60 B of the reel hub  60 , which bottom end portion projects further than the lower flange  62 , enters into (is fit with play in) the gear opening  26  of the case  12  in a state in which the radial direction inner end portion of the lower flange  62  abuts the top end portion of the annular rib  26 A. In this way, the reel gear  66  and the reel plate  70  are exposed to the exterior of the case  12 .  
     [0088] On the other hand, pairs of anchor projections  72  stand erect so as to be spaced evenly apart on a circumference at three places, between the respective insert holes  68 , at the top surface of the floor portion  60 B of the reel hub  60  (see FIG. 2). (Namely, there are a total of six anchor projections  72 .) A gear tooth  72 A is formed at the distal end portion (the top end portion) of each anchor projection  72  (see FIG. 8). The gear teeth  72 A can mesh with a braking gear  74 A of a braking member  74  which will be described later. The anchor projection  72  corresponds to the projection in the present invention.  
     [0089] Taper walls  96  stand erect at the floor portion  60 B of the reel hub  60 . Details of the taper walls  96  will be described later.  
     [0090] The recording tape cartridge  10  is equipped with a braking mechanism for impeding rotation of the reel  14  when the recording tape cartridge  10  is not in use. This braking mechanism has the braking member  74  serving as a braking member. The braking member  74  is formed in a substantial disc shape. The braking gear  74 A, which can mesh with the gear teeth  72 A of the reel  14 , is formed in an annular form in a vicinity of the outer periphery of the lower end surface of this disc portion.  
     [0091] A sliding-contact projecting portion  76 , which abuts a release pad  90  which will be described later, projects at the axially central portion of the bottom surface of the braking member  74 . The sliding-contact projecting portion  76  is shaped as a substantially spherical surface, and substantially point-contacts the release pad  90 .  
     [0092] On the other hand, as shown in FIG. 2, a cross-shaped projection  78  serving as a groove wall portion stands erect at the top surface of the braking member  74 . An insertion groove  78 A, which is substantially cross-shaped in plan view, is formed at the inside of the cross-shaped projection  78 . Further, a spring receiving recess  80 , which is surrounded by a wall portion which is annular as seen in plan view, is formed at the outer side of the cross-shaped projection  78  at the top surface of the braking member  74 .  
     [0093] Through holes  82  are provided in the plate thickness portion (i.e., the disc portion) of the braking member  74 . Four of the through holes  82  are formed so as to communicate with the braking member  74  radial direction outer side portions of the insertion groove  78 A (which is formed in a cross shape in plan view), except for the intersection portion which is the axially central portion of the insertion groove  78 A. The through holes  82  are formed in rectangular shapes corresponding to these portions. The respective through holes  82  are positioned at the radial direction outer side of the sliding-contact projecting portion  76 , and pass through the braking member  74  in the direction of plate thickness thereof.  
     [0094] The braking member  74 , which is structured as described above, is inserted into the tubular portion  60 A of the reel hub  60  so as to be substantially coaxial with the reel  14  and so as to be movable in the vertical directions (i.e., the axial direction of the reel  14 ). Namely, due to the braking member  74  moving in the vertical directions, the braking gear  74 A can move between a position of meshing with the gear teeth  72 A of the anchor projections  72  which are provided at the reel hub  60  (i.e., a rotation locked position which is a meshing position), and a position at which the aforementioned meshing is released (i.e., a released position).  
     [0095] Further, a cross-shaped rib  84  (see FIGS. 3 and 6), which serves as an engaging projection and projects downward from the ceiling plate  16 B of the case  12 , enters into the insertion groove  78 A of the cross-shaped projection  78  of the braking member  74 . The cross-shaped rib  84  is shaped as a detent which is formed as if two thin plate pieces intersect one another perpendicularly. Due to the cross-shaped rib  84  engaging with the cross-shaped projection  78  (the groove walls of the insertion groove  78 A), rotation of the braking member  74  with respect to the case  12  is impeded.  
     [0096] In this way, in the state in which the braking gear  74 A of the braking member  74  meshes with the gear teeth  72 A of the reel hub  60 , the braking member  74  impedes rotation of the reel  14 . Note that the cross-shaped rib  84  is maintained in a state of being inserted in the insertion groove  78 A along the entire vertical direction stroke of movement of the braking member  74 , and also functions to guide the direction of movement of the braking member  74  in the vertical directions.  
     [0097] Projecting pieces  84 A extend downward from four places at the bottom end portion of the cross-shaped rib  84 , other than the aforementioned intersection portion. Each projecting piece  84 A enters into the through hole  82  of the braking member  74  (passes through and projects toward the braking gear  74 A side) when the braking member  74  is positioned at the released position. In this way, the amount of engagement (the depth of insertion) of the cross-shaped rib  84 , which has the projecting pieces  84 A, with the braking member  74  is greatly increased, and tilting of the braking member  74  with respect to the case  12  is suppressed. In the present embodiment, the amount of engagement, in the axial direction, of the cross-shaped rib  84  (including the projecting pieces  84 A) with the braking member  74  which is positioned at the rotation locked position, is set to be sufficiently larger than the entire stroke of movement of the braking member  74  (see FIGS. 7 and 8).  
     [0098] Further, a compression coil spring  86  serving as an urging mechanism is disposed between the ceiling plate  16 B and the spring receiving recess  80  of the braking member  74 . One end portion of the compression coil spring  86  enters into the spring receiving recess  80 , whereas the other end portion of the compression coil spring  86  enters in at the inner side of an annular wall portion  88  which projects from the outer side of the cross-shaped rib  84  at the ceiling plate  16 B. The position of the compression coil spring  86  does not become offset in the radial direction.  
     [0099] Due to the urging force of the compression coil spring  86 , the braking member  74  is urged downward, and usually, the braking gear  74 A meshes with the gear teeth  72 A such that inadvertent rotation of the reel  14  is reliably prevented (i.e., the braking member  74  is positioned at the rotation locked position). Further, due to this urging force, the reel  14 , which meshes with the braking member  74  at the anchor projections  72 , also is urged downward, and, as described above, the lower flange  62  abuts the annular rib  26 A such that the reel  14  does not joggle within the case  12 .  
     [0100] The release pad  90 , which serves as a releasing member, is disposed between the braking member  74  and the floor portion  60 B within the reel hub  60  (the tubular portion  60 A) of the reel  14 . The release pad  90  is formed in the shape of a flat plate which substantially is an equilateral triangle as seen in plan view. Three leg portions  92 , which are solid cylindrical and correspond to the through holes  68  of the floor portion  60 B, project from the bottom surface of the release pad  90  in vicinities of the respective vertices. A sliding-contact projecting portion  94 , which abuts the sliding-contact projecting portion  76  of the braking member  74 , projects from the central portion of the top surface of the release pad  90 .  
     [0101] In the state in which the respective leg portions  92  are inserted through the through holes  68  so as to be movable in the vertical directions, the release pad  90  is placed on the floor portion  60 B of the reel hub  60  so as to not interfere with the anchor projections  72  (i.e., the bottom surface of the release pad  90  abuts the top surface of the floor portion  60 B). In this state, the leg portions  92  project further than the bottom end portions of the through holes  68 , such that the distal ends of the leg portions  92  and the addendum of the reel gear  66  are substantially the same level. Due to the sliding-contact projecting portion  94  of the release pad  90  abutting the sliding-contact projecting portion  76  of the braking member  74 , the release pad  90  maintains the above-described projected state of the leg portions  92  due to the urging force of the compression coil spring  86 .  
     [0102] On the other hand, when the leg portions  92  are pushed upward against the urging force of the compression coil spring  86 , the release pad  90  pushes up the braking member  74  which the release pad  90  is abutting at the sliding-contact projecting portion  94  thereof. The meshing of the braking gear  74 A and the gear teeth  72 A of the anchor projections  72  is released (the braking member  74  is moved to the released position).  
     [0103] Specifically, when the driving gear  102  meshes with the reel gear  66  of the reel  14 , due to the rotating shaft  100  moving upward relative to the case  12 , the leg portions  92  of the release pad  90  are pushed by the addendum of the driving gear  102 . In this way, accompanying the meshing of the driving gear  102  with the reel gear  66 , the reel  14  floats up within the case  12  against the urging force of the compression coil spring  86  (the lower flange  62  is moved away from the annular rib  26 A). Simultaneously, the state in which rotation is impeded by the braking member  74  is released, such that the reel  14  becomes able to rotate within the case  12 .  
     [0104] Note that, in this state, the leg portions  92  of the release pad  90  are positioned within the through holes  68  of the reel hub  60 , and when the rotating shaft  100  rotates, the release pad  90  rotates together with the reel  14 . Thus, the braking member  74  and the release pad  90  rotate relative to one another at the time when the reel  14  is rotating, and the sliding-contact projecting portions  76 ,  94  thereof (which are the regions thereof which abut one another) slidingly contact one another.  
     [0105] The taper walls  96  of the reel  14  will now be described. As shown in FIG. 9, the taper walls  96  are provided at the inner peripheral surface side of the tubular portion  60 A (the outer side in the radial direction of the reel hub  60 ) at the respective anchor projections  72 . The taper wall  96  stands erect at the floor portion  60 B, integrally with the anchor projection  72 . Namely, pairs of the taper walls  96  are disposed at three places which are spaced apart uniformly on a circumference which is substantially coaxial with the floor portion  60 B (i.e., there are a total of six taper walls  96 ).  
     [0106] As shown in FIG. 10A, the respective taper walls  96  are formed in arc-shapes which are substantially coaxial with the reel hub  60  as seen in plan view. Further, as shown in FIG. 10B, in side view, the taper wall  96  is formed in a tapered shape which is inclined continuously such that the upper side thereof is further away from the axis of the reel hub  60  than the lower side thereof (the taper wall  96  becomes thinner toward the upper side thereof). The dimensions and the like of the taper wall  96  will be described later.  
     [0107] The diameter of an unillustrated imaginary circle, which connects the inner edge portions of the taper walls  96  (which are formed in arc-shapes in plan view) at the top end portions (root portions) of the anchor projections  72  (i.e., an imaginary circle connecting the radial direction outer edges of the gear teeth  72 A, which circle is coaxial with the reel hub  60 ), is slightly larger than the outer diameter of the braking member  74 . Thus, the diameter of the imaginary circle connecting the inner edge portions of the upper ends of the taper walls  96  is sufficiently larger than the outer diameter of the braking member  74  (see FIGS. 10A and 10B).  
     [0108] In this way, the respective taper walls  96  guide the braking member  74 , which is inserted (assembled) in the tubular portion  60 A, such that the braking member  74  is centered with respect to the axis of the tubular portion  60 A. Namely, the taper walls  96  guide the braking member  74 , which is moved toward the floor portion  60 B and is inserted in the tubular-portion  60 A, such that the braking gear  74 A appropriately meshes with the gear teeth  72 A.  
     [0109] The heights of the taper walls  96  are determined such that the top end portions of the taper walls  96  are positioned further upward than the addendum of the braking gear  74 A of the braking member  74  which is positioned at the released position. In this way, when the braking member  74  returns to the rotation locked position due to the urging force of the compression coil spring  86 , even if, for example, the position of the braking member  74  is offset (the center of the braking member  74  is offset or the braking member  74  is tilted), the braking member  74  is guided (guided in) by the taper walls  96 , and the braking gear  74 A appropriately meshes with the gear teeth  72 A.  
     [0110] Next, operation of the present embodiment will be described.  
     [0111] When the recording tape cartridge  10  having the above-described structure is not being used (e.g., is being stored or transported or the like), the door  50 , whose distal end portion has entered into the concave portions  30 A due to the urging force of the coil spring  56 , closes the opening  20 .  
     [0112] Further, as shown in FIG. 7, at the reel  14 , the reel gear  66  is exposed from the gear opening  26  while the lower flange  62  is being pushed against or is being made to abut the annular rib  26 A due to the urging force of the compression coil spring  86  which is transmitted via (the release pad  90  and) the braking member  74  which meshes with the anchor projections  72 .  
     [0113] Due to the urging force of the compression coil spring  86 , the braking gear  74 A of the braking member  74  meshes with the gear teeth  72 A of the anchor projections  72 , and rotation of the reel  14  with respect to the case  12  is impeded. Namely, the braking member  74  is positioned at the rotation locked position.  
     [0114] On the other hand, when the magnetic tape T is to be used, the recording tape cartridge  10  is loaded into a bucket (not illustrated) of a drive device along the direction of arrow A. Accompanying this loading, the engaging projecting portion  104  (see FIGS. 5A through 5C), which is fixed to the bucket, engages with the operation projection  52  of the door  50 . The door  50  thereby rotates substantially rearward and opens the opening  20 .  
     [0115] Then, when the recording tape cartridge  10  is loaded to a predetermined depth in the bucket, the bucket is lowered. The rotating shaft  100  of the drive device relatively approaches the gear opening  26  of the case  12  (i.e., relatively moves upward), and holds the reel  14 . Specifically, the driving gear  102  meshes with the reel gear  66  while the reel plate  70  is attracted and held by the magnet (not illustrated) disposed at the distal end portion of the rotating shaft  100 .  
     [0116] Accompanying this meshing of the reel gear  66  and the driving gear  102 , the addendum of the driving gear  102  abut the distal ends (lower end surfaces) of the leg portions  92  of the release pad  90 , and push the release pad  90  upward against the urging force of the compression coil spring  86 . In this way, the braking member  74 , which is abutting the release pad  90  at the sliding-contact projecting portion  76 , is also moved upward. The meshing of the braking gear  74 A of the braking member  74  and the gear teeth  72 A of the anchor projections  72  is released.  
     [0117] When the rotating shaft  100  moves further upward, the reel  14  is, against the urging force of the compression coil spring  86 , raised upward together with the release pad  90  and the braking member  74  (with the relative positions thereof remaining unchanged), and the lower flange  62  moves apart from the annular rib  26 A. In this way, the reel  14  floats up within the case  12 , and becomes able to rotate in a state in which it does not contact the inner surfaces of the case  12 .  
     [0118] Further, due to the bucket being lowered, the recording tape cartridge  10  is positioned within the drive device. In this state, the pull-out mechanism of the drive device pulls the leader pin  22  out from the opening  20  which has been opened, and accommodates the leader pin  22  at a take-up reel of the drive device. When the drive device drives and rotates the take-up reel and the reel  14  (the rotating shaft  100 ) synchronously, the magnetic tape T is successively pulled-out from the case  12  while being taken-up onto the take-up reel. Information is recorded or played-back by a recording/playback head or the like disposed along a predetermined tape path.  
     [0119] At this time, the sliding-contact projecting portion  76  of the braking member  74 , which cannot rotate with respect to the case  12 , slidingly contacts the sliding-contact projecting portion  94  of the release pad  90  which, together with the reel  14 , rotates with respect to the case  12 .  
     [0120] On the other hand, when the magnetic tape T is rewound onto the reel  14  and the leader pin  22  is held at the pin stands  24 , the magnetic force of the magnet is cancelled, and the attraction between the rotating shaft  100  and the reel plate  70  is cancelled simultaneously, the bucket, in which the recording tape cartridge  10  is loaded, is raised.  
     [0121] In this way, the meshing of the reel gear  66  and the driving gear  102  is cancelled, and the abutment of the driving gear  102  and the leg portions  92  of the release pad  90  is cancelled. Due to the urging force of the compression coil spring  86 , the release pad  90  moves downward together with the braking member  74  (while the state in which the release pad  90  and the braking member  74  abut one another is maintained).  
     [0122] In this way, the respective leg portions  92  of the release pad  90  project from the through holes  68  to the region where the reel gear  66  is formed, and the braking gear  74 A of the braking member  74  meshes with the gear teeth  72 A of the anchor projections  72 . Namely, the braking member  74  returns to the rotation locked position at which the braking member  74  impedes rotation of the reel  14 .  
     [0123] Moreover, accompanying the movement of the braking member  74  and the release pad  90  due to the urging force of the compression coil spring  86 , the reel  14  also moves downward. The reel  14  returns to the initial state in which the reel gear  66  is exposed from the gear opening  26  while the lower flange  62  of the reel  14  abuts the annular rib  26 A.  
     [0124] Further, when the recording tape cartridge  10  is to be ejected from the bucket, the recording tape cartridge  10  is moved in the direction opposite to the direction of arrow A by the urging force of the coil spring  56  or by an unillustrated ejecting mechanism. Accompanying this movement, the door  50  closes the opening  20  due to the urging force of the coil spring  56 . In this way, the recording tape cartridge  10  is ejected from the drive device and returned to its initial state.  
     [0125] In the recording tape cartridge  10 , when the reel  14  and the braking mechanism are assembled in, first, the reel  14  is accommodated at the inner side of the play restricting wall  28  of the lower case  18  such that the bottom end portion of the reel hub  60  enters in at the inner side of the annular rib  26 A and the reel gear  66  is exposed from the gear opening  26 . Next, the release pad  90  is placed on the floor portion  60 B of the reel hub  60 , while the leg portions  92  are inserted in the through holes  68 .  
     [0126] From this state, the braking member  74 , with the braking gear  74 A thereof facing downward, is moved downward substantially along the axial direction so as to enter in at the inner sides of the taper walls  96 , and the braking member  74  is set on the anchor projections  72  which project out further than the top surface of the release pad  90 . Due to this operation, the gear teeth  72 A and the braking gear  74 A mesh with one another due to the configurations of the teeth thereof. Further, the sliding-contact projecting portion  76  abuts the sliding-contact projecting portion  94 . In this state, the braking member  74  is disposed such that the cross-shaped rib  84  (the projecting pieces  84 A) can enter into the insertion groove  78 A when the upper case  16  and the lower case  18  are joined together.  
     [0127] Further, the compression coil spring  86  is placed in the spring receiving recess  80  of the braking member  74 . From this state, the upper case  16  is made to approach the lower case  18  while the cross-shaped rib  84  (the projecting pieces  84 A) enter into the insertion groove  78 A of the braking member  74  and the compression coil spring  86  is compressed (i.e., against the urging force of the compression coil spring  86 ). When the peripheral wall  16 A and the peripheral wall  18 A abut one another, the upper case  16  and the lower case  18  are joined together at the upper and lower screw bosses  32 ,  36  and the other screw bosses.  
     [0128] In this way, at the recording tape cartridge  10 , the reel  14  is accommodated in the case  12 , and the braking mechanism is structured. At the time when the recording tape cartridge  10  is shipped, which is a time when the recording tape cartridge  10  is not being used, rotation of the reel  14  with respect to the case  12  is impeded.  
     [0129] Here, the taper walls  96  stand erect along a circumference having a larger diameter than the outer diameter of the braking member  74 , at the floor portion  60 B of the reel hub  60  into which the braking member  74  has been moved and inserted substantially along the axial direction. The diameter of the imaginary circle, which connects the radial direction outer edges of the gear teeth  72 A at the root portions of the taper walls  96 , is slightly larger than the outer diameter of the braking member  74 . Thus, by the above-described insertion operation, the braking member  74  is guided to the position at which the braking gear  74 A appropriately meshes with the gear teeth  72 A. In other words, accompanying the above-described insertion operation, the braking member  74  is guided by the taper walls  96  in a direction in which the axial center of the braking member  74  coincides with the axial center of the reel hub  60 . In this way, when the braking member  74  is inserted in the reel hub  60 , the addendum of the braking gear  74 A are prevented from riding on the addendum of the gear teeth  72 A.  
     [0130] In this way, at the recording tape cartridge relating to the present embodiment, the braking member  74 , which impedes rotation of the reel  14  when the recording tape cartridge is not in use, can be assembled appropriately.  
     [0131] Moreover, by providing the taper walls  96 , when the braking member  74  is inserted in the reel hub  60 , there is no need for the careful operation of aligning the axial center of the braking member  74  and the axial center of the reel hub  60 , and the assembly workability is improved.  
     [0132] In addition, because the taper walls  96  stand erect at the floor portion  60 B integrally with the anchor projections  72 , the taper walls  96  can function to cause the braking gear  74 A to reliably mesh with the gear teeth  72 A at the time when the braking member  74  is inserted into the reel hub  60 , without increasing a thick portion at the floor portion  60 B of the reel hub  60  (i.e., without causing a deterioration in the moldability of the reel hub  60  which is generally formed by resin molding).  
     [0133] Note that, in the above-described embodiment, a plurality of the taper walls  96  are provided discretely along a circumference of a larger diameter than the outer diameter of the braking member  74 . However, the present invention is not limited to the same. The taper wall  96  may be formed in, for example, an annular form, provided that the taper wall  96  has a diameter larger than the outer diameter of the braking member  74  and that the taper wall  96  is provided along a circumference which is substantially coaxial with the reel hub  60 . Further, the taper walls  96  may be provided independently of the anchor projections  72 . In this case, the circumferential direction positions of the taper walls  96  may be offset from the anchor projections  72 .  
     [0134] In addition, the above-described embodiment is provided with the release pad  90  for releasing the state in which rotation of the reel  14  is locked by the braking member  74 . However, the present invention is not limited to the same. For example, a structure is possible in which the braking member  74  moves to the released position by the sliding-contact projecting portion  76  of the braking member  74  being directly pushed by a releasing projection of the rotating shaft  100  which enters in from a through hole formed in the axially central portion of the floor portion  60 B of the reel hub  60 . In this case, the anchor projections  72  for providing the gear teeth  72 A at positions which do not interfere with the release pad  90  are not provided, and the gear teeth can be provided in an annular form at the floor portion  60 B of the reel gear  60 .  
     [0135] Moreover, in the above-described embodiment, the recording tape cartridge  10  is a so-called one-reel recording tape cartridge in which the single reel  14  is accommodated within the case  12 . However, the present invention is not limited to the same. The recording tape cartridge  10  may be, for example, a so-called two-reel recording tape cartridge which accommodates two reels  14  which are for drawing-out and for taking-up. Accordingly, the present invention is not limited by the preferable structures of the opening  20  and the door  50  and the like.  
     [0136] In the above-described embodiment, the magnetic tape T is used as the recording tape. However, the present invention is not limited to the same. It suffices for the recording tape to be interpreted as an information recording/playback medium which is shaped as an elongated tape and on which information can be recorded and from which recorded information can be played back. It goes without saying that the recording tape cartridge relating to the present invention can be applied to recording tapes of any recording/playback systems.  
     [0137] As described above, the recording tape cartridge relating to the present invention has the excellent effect that it is possible to appropriately assemble a braking member which impedes rotation of a reel when the recording tape cartridge is not in use.