Patent Publication Number: US-6988686-B2

Title: Recording tape cartridge

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a recording tape cartridge which rotatably accommodates in a case a single reel onto which a recording tape such as a magnetic tape or the like is wound, and is principally utilized as a recording/replaying medium for computers and the like. 
     2. Description of the Related Art 
     Magnetic tape cartridges which accommodate in a case a single reel onto which a magnetic tape is wound, and which are principally utilized as a recording/replaying medium for computers and the like, have been known in the prior art. A leader member, which is to say a leader pin, a leader tape, a leader block or the like, is provided at a distal end of such a magnetic tape. The leader member is drawn out through an opening aperture of the magnetic tape cartridge by drawing-out means provided at a drive device side. Thence, the magnetic tape to which the leader member is fixed is wound around a drive device side winding reel. 
     A reel gear is formed in an annular shape at the middle of a lower face of the reel, and is exposed through an opening hole formed in a lower face of the magnetic tape cartridge. A driving gear provided at a drive device side rotation shaft meshes with the reel gear. Thus, in this structure, the reel is driven to rotate. Consequently, the reel of the magnetic tape cartridge and the winding reel of the drive device are rotated contemporaneously. Hence, data can be recorded to the magnetic tape, and data recorded at the magnetic tape can be replayed. 
     Such magnetic tape cartridges can be kept in a small accommodation space at a time of storage, and can record large volumes of information. As shown in  FIGS. 10  to  12 , the position of the opening aperture, and the type of a door that opens and closes the opening aperture is different for each of the different types of leader member. Specifically, in the case of a leader pin  110 , as shown in  FIG. 10 , an opening  118  is formed in a side wall  114  of a case  112 . The side wall  114  is parallel with a loading direction into a drive device (the direction of an arrow P). The opening  118  is opened and closed by a door  116 , which slides to move in the same direction as the loading direction. 
     However, if the opening  118  is provided in the side wall  114  of the case  112  in this manner, the drive device side drawing-out means must turn the leader pin  110  around from a left-right transverse direction of the case  112  to draw out the leader pin  110 . Therefore, a space for the drawing-out means to turn around must be reserved at the drive device side, and a mechanism for turning around of the drawing-out means is complicated. Thus, the drive device will become larger, which is disadvantageous. Moreover, there is a further problem in that a drawing-out path of a magnetic tape  111  becomes longer. 
     Alternatively, in the case of a leader tape  120 , as shown in  FIG. 11 , an opening  128  is formed in a front wall  124  of a case  122 . The front wall  124  intersects the direction of loading into the drive device (the direction of arrow P). A door  126  opens and closes the opening  128 . The door  126  is a rotating-type door which rotates forward about a support shaft  125  which supports the door  126  at a corner portion vicinity of the case  122 . However, when the opening  128  is provided in the front wall  124  of the case  122  in this manner, although there is no need for drive device side drawing-out means to turn around, the door opens forward by a large amount. Therefore, it is necessary to reserve space at the drive device side, such that no part of the drive device impedes the door  126  when the opening  128  is opened. Thus, the drive device becomes larger, and this is disadvantageous. 
     Furthermore, in the case of a leader block  130 , as shown in  FIG. 12 , an opening  138  is formed by diagonally cutting away a corner portion  134  at a front side in the direction of loading into the drive device. The opening  138  is directly opened and closed by the leader block  130 . However, when the leader block  130  opens and closes the opening  138  in this manner, there is a problem in that the leader block  130  will tend to become damaged or soiled. That is, the leader block  130  fits into a drive device side reel hub  136 , and structures a portion of the reel hub  136 . Therefore, damage and soiling that would not be a problem for usual use as a door make it difficult to fit the leader block  130  with the reel hub  136 , and there is a risk that running of the magnetic tape  111  may be disadvantaged. 
     Moreover, the leader block  130  is anchored only at peripheral portions of the opening  138 . Therefore, it is easy for the leader block  130  to come out if the magnetic tape cartridge is dropped, which is disadvantageous. In addition, the size of the leader block  130  is large in comparison to the leader pin  110 . Therefore, there is a problem in that constraints on the form of the case are numerous. Thus, the leader pin  110 , from which the function of the door is separated, is superior to the leader block  130 , which is combinedly used as the door. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to provide a recording tape cartridge which is provided with an opening aperture which minimizes length of a drawing out path of a recording tape and a door which can open and close the aperture opening in little space, in which tape cartridge the door which closes the aperture and a leader member for drawing out the recording tape are provided as separate members, and which can provide for a reduction in size of a drive device. 
     In order to achieve the object described above, according to a first aspect of the present invention, a tape cartridge which is insertable at a tape drive, the tape drive being provided with an opening member which is operably engageable with the tape cartridge at a time of insertion of the tape cartridge and carrying out at least one of reading and writing of data, includes: a case which includes a front wall portion facing in a direction of insertion of the cartridge, a side wall portion substantially parallel to the cartridge insertion direction, and an angled wall portion connecting the front wall portion and the side wall portion, and angled relative to the cartridge insertion direction; a tape access opening provided at the angled wall portion of the case; a covering member which is reciprocally moveable along a circular arc-form movement path between a closed position for closing the tape access opening and an open position for opening the tape access opening; and an operation portion provided at the covering member, the operation portion being capable of moving the covering member in an open position direction when engaged with the opening member of the tape drive by an operation of insertion of the tape cartridge, wherein a position in the cartridge insertion direction of a point at which the circular arc-form movement path is closest to the side wall portion of the case is outside a range, in the cartridge insertion direction, of movement of a point of engagement of the opening member of the tape drive with the operation portion. 
     According to another aspect of the present invention, in a tape drive for carrying out at least one of reading and writing of data at a tape cartridge that includes: a case which includes a front wall portion facing in a direction of insertion of the cartridge, a side wall portion substantially parallel to the cartridge insertion direction, and an angled wall portion connecting the front wall portion and the side wall portion and angled relative to the cartridge insertion direction; a tape access opening provided at the angled wall portion of the case; a covering member which is reciprocally moveable along a circular arc-form movement path between a closed position for closing the tape access opening and an open position for opening the tape access opening; and an operation portion provided at the covering member, the operation portion being capable of moving the covering member in an open position direction when engaged with the tape drive by an operation of insertion of the tape cartridge, a position in the cartridge insertion direction of a point at which the circular arc-form movement path is closest to the side wall portion of the case being outside a range, in the cartridge insertion direction, of movement of a point of engagement of the opening member of the tape drive with the operation portion, the tape drive includes an opening member which is capable of engaging with the operating portion of the covering member and moving the covering member in the open position direction at the time of insertion of the tape cartridge. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic perspective view of a recording tape cartridge. 
         FIG. 2  is a schematic exploded perspective view of the recording tape cartridge. 
         FIG. 3  is a schematic plan view of a lower case. 
         FIG. 4  is a schematic perspective view, viewed from above, showing a door in a closed state of an opening. 
         FIG. 5  is a schematic perspective view, viewed from above, showing the door in an open state of the opening. 
         FIG. 6A  is a schematic plan view showing a state during a transition of the door from the closed state of the opening to the open state. 
         FIG. 6B  is a schematic plan view showing another state during a transition of the door from the closed state of the opening to the open state. 
         FIG. 6C  is a schematic plan view showing yet another state during a transition of the door from the closed state of the opening to the open state. 
         FIG. 7  is a schematic plan view of the lower case showing the door in the closed state of the opening. 
         FIG. 8  is a schematic plan view of the lower case showing the door in the open state of the opening. 
         FIG. 9  is an explanatory diagram showing a process of movement of an operation projection of the door. 
         FIG. 10  is a schematic perspective view of a conventional recording tape cartridge equipped with a leader pin. 
         FIG. 11  is a schematic perspective view of a conventional recording tape cartridge equipped with a leader tape. 
         FIG. 12  is a schematic plan view of a conventional recording tape cartridge equipped with a leader block. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     A recording tape cartridge  10  according to an embodiment of the present invention will be explained based on  FIGS. 1 through 6 . Firstly, general overall structure of the recording tape cartridge  10  will be explained. Then, principal elements of the present invention, an opening  20  and a door  50  which serves as a covering member for opening and closing the opening  20 , will be explained. For the sake of convenience of explanation, a loading direction of the recording tape cartridge  10  into a drive device, which is shown as arrow A, is referred to as a forward direction (front side) of the recording tape cartridge  10 , and the direction of an arrow B intersecting arrow A is a rightward direction. 
     [Overall Structure of Recording Tape Cartridge] 
       FIG. 1  shows a perspective view of overall structure of the recording tape cartridge  10 .  FIG. 2  shows a schematic exploded perspective view of the recording tape cartridge  10 . As shown in these drawings, the recording tape cartridge  10  is structured to rotatably accommodate a single reel  14  in a case  12 . The case  12  is substantially rectangular in plan view. A magnetic tape T is wound onto the reel  14 . The magnetic tape T serves as a recording tape which is an information recording/replaying (reading/writing) medium. 
     The case  12  is structured by matching up and joining two peripheral walls  16 A and  18 A of an upper case  16  and a lower case  18  to one another. A front-right corner portion of each of the upper case  16  and the lower case  18 , which is a single corner portion at a front end side in the direction of loading into the drive device, is cut away. An accommodation space for the reel  14 , onto which the magnetic tape T is wound, is provided inside the case  12 . Hence, the cut away corner portions of the peripheral walls  16 A and  18 A of the upper case  16  and the lower case  18  serve as the opening  20  for drawing out the magnetic tape T. 
     A leader pin  22  is connected at a free end of the magnetic tape T that is drawn out through the opening  20 . The leader pin  22  is caught up (engaged) by drawing-out means of the drive device, and subjected to a drawing-out operation. At each of two end portions of the leader pin  22 , which protrude beyond width direction end portions of the magnetic tape T, an annular groove  22 A is formed. These annular grooves  22 A are caught on to by hooks or the like of the drawing-out means. Consequently, in this structure, the hooks or the like do not contact and damage the magnetic tape T when the magnetic tape T is drawn out. 
     At an inner side of the opening  20  of the case  12 , a pair of upper and lower pin stands  24  are provided for positioning and retaining the leader pin  22  in the case  12 . The pin stands  24  have semi-tubular forms, and both the end portions of the leader pin  22  are held at recess portions  24 A of the pin stands  24  in a state in which the leader pin  22  is standing thereat. Outer peripheral walls of the pin stands  24  are open at a magnetic tape T drawing-out side thereof, to form exit/entry apertures through which the leader pin  22  is removed and inserted. 
     A leaf spring  25  is fixedly disposed in a vicinity of the pin stands  24 . The leaf spring  25  engages with upper and lower end portions of the leader pin  22 , and holds the leader pin  22  at the pin stands  24 . The leaf spring  25  is structured to resiliently deform appropriately when the leader pin  22  is removed or inserted at the pin stands  24 , and to allow movements of the leader pin  22 . 
     A gear aperture  26  is formed at a central portion of the lower case  18 . The gear aperture  26  is for exposing an unillustrated reel gear of the reel  14  to the outside. The reel gear meshes with a driving gear of the drive device, and the reel  14  is driven to rotate inside the case  12 . Further, the reel  14  is held by free play-restricting walls  28  so as not to rattle about. The free play-restricting walls  28  are provided projecting at interior surfaces of the upper case  16  and the lower case  18 , to serve as interior walls partially disposed along a circular path which is coaxial with the gear aperture  26 . 
     A hollow portion  28 A is provided continuously with an end portion of the free play-restricting walls  28  in a vicinity of the opening  20 . A hole for regulation of position at an interior is formed in the hollow portion  28 A. In addition, a hollow portion  28 B is formed continuously with the free play-restricting walls  28  at an inner side of a front-left corner portion of the case  12 . Another hole for regulation of position, which is a long hole, is formed in the hollow portion  28 B. The hollow portion  28 A and the hollow portion  28 B are disposed co-linearly along the direction of arrow B. Except for the end portion at which the hollow portion  28 A is continuously provided, each of the free play-restricting walls  28  is provided continuously with the peripheral wall  16 A or the peripheral wall  18 A of the case  12 . Thus, outer sides of the free play-restricting walls  28  and the space for disposing the reel  14  are set apart. 
     [Structure of Opening and of Case at Opening Vicinity] 
     As described above, the opening  20  is formed by cutting away the front-right corner portion. Therefore, an opening face thereof (an angled wall portion) faces in the direction of arrow A and in the direction of arrow B. Consequently, the drawing-out means of the drive device can access and chuck the leader pin  22  from the direction of arrow A, from the direction of arrow B, or from a direction between the directions of arrow A and arrow B. As a result, an area in which the pin stands  24  that hold the leader pin  22  can be disposed is large, and a range from which the drawing-out means of the drive device can chuck the leader pin  22  is wide. Accordingly, a disposition position of the pin stands  24  can be specified to meet specifications of drive devices that carry out chucking from direction A and drive devices that carry out chucking from direction B. Thus, a degree of freedom of design of the drive device is broadened. 
     As is also shown in  FIG. 3 , which is a plan view of the lower case  18 , a pair of short upper and lower diagonal wall portions  30  is provided at a right corner portion of a front wall  12 A of the case  12  (a portion of the peripheral walls  16 A and  18 A whose outer surface faces in the direction of arrow A). The diagonal wall portions  30  define a front edge portion of the opening  20 . The diagonal wall portions  30  curve to run along the opening face of the opening  20 , and a wall thickness of the diagonal wall portions  30  is thicker than the front wall  12 A. A recess portion  30 A is formed at a thickness direction central portion of the diagonal wall portions  30 . A distal end of the door  50 , which is described later, enters into the recess portion  30 A. Further, a pair of upper and lower screw bosses  32  are provided continuously with an inner side of the front wall  12 A in a vicinity of a left end of the diagonal wall portions  30 . 
     A pair of upper and lower offset wall portions  34  is provided at a front end portion of a right wall  12 B of the case  12  (a right side wall of the peripheral walls  16 A and  18 A along the direction of arrow A). The offset wall portions  34  are slightly offset to the inside of the case  12  (leftward). Front ends of the offset wall portions  34  define a rear edge of the opening  20 . A pair of upper and lower screw bosses  36  is provided continuously with an inner side of front end portions of the offset wall portions  34 . Outer peripheral portions of the screw bosses  36  function as a guide for the door  50  which is slidable against the door  50  (to prevent rattling). Further, a pair of upper and lower step portions  38  is integrally formed between rear end portions of the offset wall portions  34  and the right wall  12 B. 
     A slit  40  having a predetermined length, which serves as a window portion communicating between the interior and exterior of the case  12 , is formed in the right wall  12 B rearward of the offset wall portions  34 . The slit  40  is for exposing an operation projection  52  of the below-described door  50 . The slit  40  is formed by cutting away a lower portion of the peripheral wall  16 A and an upper portion of the peripheral wall  18 A, which structure the right wall  12 B. By also cutting away a lower portion and an upper portion, respectively, of the upper and lower step portions  38 , the slit  40  is opened frontward. 
     The slit  40  may instead be defined from above and below simply by a ceiling plate and a floor plate of the case  12 . However, in view of strength when dropped, it is preferable if portions of the peripheral walls  16 A and  18 A are left above and below the slit  40  as described above, to function as ribs such that rigidity of the case  12  is maintained. In particular, the peripheral walls  16 A and  18 A, which join the upper and lower walls that define the slit  40  to one another at both ends thereof, are formed integrally (continuously) with the offset wall portions  34  (the step portions  38 ), which is even more preferable. 
     The protrusion portion  42  protrudes from rear end portions of the upper and lower offset wall portions  34 , at a side thereof which is opposite to a side thereof at which the step portions  38  are disposed (that is, inward of the case  12 ) and is provided to span the whole height of the offset wall portions  34 . A distal surface of the protrusion portion  42  is curved to correspond to an outer surface of the later-described door  50 . In addition, a protrusion portion  44  spanning the whole height is provided at a location of the free play-restricting walls  28  which corresponds to the protrusion portion  42 . The protrusion portion  44  is curved to correspond with an inner face of the door  50 , and opposes the protrusion portion  42 . 
     When the door  50  opens or closes the opening  20 , the protrusion portion  42  and the protrusion portion  44  are slidable against the door  50  while sandwiching the door  50 . Thus, the protrusion portion  42  and the protrusion portion  44  are for preventing the ingression of dust into the case  12 , and are for guiding the door  50  (preventing looseness). A further protrusion portion  46  protrudes inward of the case  12  at a portion of the right wall  12 B (the peripheral walls  16 A and  18 A) that defines a rear end of the slit  40 . The protrusion portion  46  is also for preventing the ingression of dust into the case  12  and guiding the door  50  (preventing rattling). 
     A recess portion  48  is formed rearward of the protrusion portion  46  of the lower case  18 . The recess portion  48  is recessed toward the inside of the case  12  at a portion of the peripheral wall  18 A, which does not include an upper end of the peripheral wall  18 A, and upward from a lower face of the case  12 , and substantially has a three-sided box shape in sectional view. The recess portion  48  is also formed in a left wall of the case  12 . These recess portions  48  serve as, for example, engaging portions for engaging with the drawing-out means of the drive device, with bottom surfaces of the recess portions  48  (surfaces that face downward) serving as reference surfaces for positioning in the drive device. Furthermore, twisting strength of the case  12  is improved by provision of the recess portions  48 . A portion of the right wall  12 B (the peripheral wall  18 A) that defines the recess portion  48  is curved to correspond to the outer surface of the door  50 . This guide surface  48 A serves as a guide for the door  50 , and is slideable against the outer surface of the door  50  when the opening  20  is opening or closing (to prevent looseness). 
     The upper case  16  and the lower case  18  described above are fixed (joined) by unillustrated screws which are screwed from the lower side into each of the screw bosses  32  and  36  (joining portions), which are located in the vicinities of edge portions of the opening  20 . Accordingly, corner portions at both ends of the opening  20 , which are defined by free ends of the diagonal wall portions  30  (the front wall  12 A) and the offset wall portions  34  (the right wall  12 B) and which tend to be severely affected when impacted against a floor or the like by a fall, are securely fixed. Thus, even if the case  12  is dropped, this structure will not be deformed or buckled by the overall weight of the recording tape cartridge  10 , so as to cause mispositioning. 
     A major diameter across the threads of the screws may be, for example, 2.0 mm. Thus, an external diameter of the screw bosses  32  and the screw bosses  36  may be 4.0 mm. In place of this fixing with screws, projections may project from the upper case  16  at positions corresponding to the screw bosses  32  and  36 , while fitting holes which fit with these projections are formed in the lower case  18 , and the projections and fitting holes may be fitted with one another. However, in such a case, it is desirable that the upper case  16  and the lower case  18  be fixed with screws at locations within radii of 30 mm of these fitting locations. Further, matching surfaces of the peripheral wall  16 A and the peripheral wall  18 A (at both side corner portions of the opening  20 ) may be fixed by welding. However, fixing with screws is more preferable in consideration of dismantling and recycling. 
     Plate thicknesses of both the upper case  16  and the lower case  18  are set to 2 mm at the area in which the pin stands  24  are disposed (the vicinity of the opening  20 ), which is thicker than thicknesses at other areas thereof. The case  12  (the upper case  16  and the lower case  18 ) is formed of a polycarbonate (PC) material. The case  12  may be formed of acrilonitrile butadiene styrene (ABS) or a metal instead of PC. The purpose of this is to raise the strength of the vicinity of the pin stands  24 , which is the location at which the leader pin  22  is held (positioned). Therefore, mispositioning of the leader pin  22 , which is the most important component for functioning of the recording tape cartridge  10  (and which must be accurately engaged by the drawing-out means when the recording tape is to be drawn out), subsequent to impacts due to dropping of the case  12  (the recording tape cartridge  10 ) or the like does not occur. 
     Positions at which the pin stands  24  are disposed may be determined such that an axial center of the leader pin  22  held thereat is positioned on a first imaginary line which joins the front and rear edge portions of the opening  20 , or further inside the case  12  than the first imaginary line. More preferably, the positions at which the pin stands  24  are disposed may be determined such that the axial center of the leader pin  22  is positioned on a second imaginary line which joins axial centers of the screw bosses  32  and the screw bosses  36 , or further inside the case  12  than the second imaginary line. In the present embodiment, the pin stands  24  are positioned at a position closer to the screw bosses  32  than to the screw bosses  36 . Consequently, with this structure, mispositioning of the leader pin  22  due to vibrations of the ceiling plate and the floor plate that accompany dropping of the case  12  or the like are prevented. In this case  12 , the peripheral wall  16 A of the upper case  16  and the peripheral wall  18 A of the lower case  18  are set to equal heights. Thus, machining accuracies of portions thereof that match up with one another (accuracies of resin-forming in molds) are at about the same level. Thus, assembly characteristics and dropping impact resistance are made favorable. 
     A diagonal angle of the opening face of the opening  20  with respect to the direction of arrow A (a diagonal angle of the ceiling plate and floor plate of the case  12  that define the top and bottom of the opening  20 ) is determined in accordance with requirements for distinguishing (identifying) the recording tape cartridge  10  at a library apparatus. That is, the library apparatus accommodates a plurality of the recording tape cartridge  10  and automatically (i.e., without human intermediation) mounts and removes the recording tape cartridge  10  at the drive device. In a case where there is a plurality of types of the recording tape cartridge  10  to be handled and a plurality of types of drive device, it is necessary to identify a generation, recording capacity or the like of the recording tape cartridge  10 . The diagonal angle of the opening face of the opening  20  may be utilized for this identification. 
     Accordingly, the opening  20  for drawing out of the magnetic tape T, which has been implemented in consideration of strength as described above, can also function as an identification portion in a library apparatus, based on the diagonal angle of the opening face of the opening  20  (to be specific, the diagonal angle of the ceiling plate and floor plate that define the top and bottom of the opening  20 ). Therefore, insufficient strength of the case  12 , a deterioration of dustproofing and complicated mold construction, which are concerns in a situation in which the opening  20  and the identification portion are provided separately (for example, a case in which one or a plurality of through-holes formed in the case  12  serve as an identification portion), can be prevented. 
     [Door Structure] 
     As shown in  FIGS. 4 and 5 , which are viewed with the reel  14 , the upper case  16  and the like removed, the opening  20  is opened and closed by the door  50 , which serves as a covering member. The door  50  is formed in a circular arc form in plan view, which is curved in a plate thickness direction along a predetermined circular circumference, with a plate width (height) of the door  50  set to be substantially the same as an opening height of the opening  20 , and a plate length thereof being significantly greater than an opening width of the opening  20 . 
     Specifically, in this structure, in a state in which the door  50  has entered into the recess portion  30 A of the diagonal wall portions  30  (a closed position), the door  50  closes the opening  20  (see FIG.  6 A). The door  50  opens the opening  20  by moving (rotating) substantially rearward along the aforementioned circular circumference, (see FIG.  6 B). When an outer peripheral surface of a distal end vicinity of the door  50  reaches a vicinity of the screw bosses  36 , the opening  20  is completely opened (an open position; see FIG.  6 C). When the opening  20  is open, the door  50  closes the opening  20  by rotating substantially in the opposite direction. In the closed state of the opening  20 , the door  50  abuts against at least one of the screw bosses  36 , the protrusion portion  42  and the protrusion portion  44 . 
     That is, the door  50  is formed to be curved in an arc shape corresponding to the predetermined circular circumference, which is a movement path of the door  50 . In the present embodiment, a position of a center of rotation of the door  50  in a left-right direction is specified to be at a left end vicinity of the case  12 , and a position thereof in a front-rear direction is specified to be at a vicinity of the rear end of the slit  40 . Consequently, the movement path of the door  50  is closest to the right wall  12 B of the case  12  in the vicinity of the rear end of the slit  40 . The rotation center and a turning radius of the door  50  may be suitably determined in accordance with the positions of the front and rear edge portions of the opening  20  (the diagonal wall portions  30  and the screw bosses  36 ). These positions are determined by requirements of the drive device, in accordance with the angle of the facing surface of the opening  20 , which is determined by requirements of a library apparatus, and the like. 
     A rear end portion of a length dimension along the curve of the door  50  is determined so as to be located at a rear-right corner portion, which is rearward of the recess portion  48  of the case  12 , in the state in which the opening  20  is closed. Accordingly, all through the process of opening and closing the opening  20 , the door  50  is guided (looseness thereof is restrained) by the screw bosses  36 , the protrusion portions  42 ,  44  and  46 , and the guide surface  48 A (and the free play-restricting walls  28 ) of the case  12 . 
     At an outer peripheral surface of the door  50 , slightly forward from a length direction central portion thereof, the operation projection  52  projects along a diametric direction of the door  50 , to serve as an operation portion. The operation projection  52  is exposed to the outside of the case  12  through the slit  40 . When the opening  20  is in the closed state, the operation projection  52  is positioned to be slightly separated from the protrusion portion  42  at the rear end of the offset wall portions  34 , and is operable through the portion of the slit  40  that opens frontward at the step portions  38 . 
     When the opening  20  is in the opened state, the operation projection  52  is positioned to be slightly separated from the protrusion portion  46  at the rear edge of the slit  40 . The dimensions of each portion are determined such that a length direction of the operation projection  52  is substantially perpendicular to the right wall  12 B of the case  12  (the direction of arrow A) in this state. 
     Thus, although this operation projection  52  communicates between the interior and exterior of the case  12  via the slit for exposure, the slit  40  is always substantially closed by the door  50 , which spans substantially the whole height of the interior of the case  12 , and by the protrusion portion  42  and protrusion portion  46  which guide the door  50 . In addition, a labyrinthine structure is formed between the slit  40  and the accommodation space for the reel  14  by the free play-restricting walls  28  which serve as inner walls and the protrusion portion  44  which guides the door  50 . Accordingly, adherence of dust and the like to the magnetic tape T wound onto the reel  14  is prevented. 
     A spring-holding portion  54  protrudes along the diametric direction of the door  50  from an interior peripheral portion at a rear end vicinity of the door  50 . One end portion of a coil spring  56 , which serves as urging means (an urging element), is engaged with a spring-engaging portion  55 , which is provided inside the case  12  at a vicinity of the recess portion  48 . Another end portion of the coil spring  56  is engaged and held at the spring-holding portion  54 . Accordingly, in this structure, the door  50  is urged in a direction to close the opening  20  by urging force of the coil spring  56 , and the door  50  continuously closes the opening  20 . The coil spring  56  has a length that reaches as far as the rear-right corner portion of the case  12  in the state in which the door  50  opens the opening  20  as described above. Thus, the coil spring  56  is disposed so as to effectively use a space between the free play-restricting walls  28  and the peripheral walls  16 A and  18 A at the rear-right corner portion. 
     The door  50  described hereabove is formed of, for example, a polyoxymethylene (POM) resin, which has a low coefficient of friction and has excellent abrasion resistance with respect to the case  12  constituted of PC. The operation projection  52 , the spring-holding portion  54  and the like may be structured as separate bodies (of different materials). Thus, because operation of the door  50  can be carried out smoothly, it is preferable if clearances between end surfaces at the top and bottom of the door  50  and the ceiling plate and floor plate of the  12  are set to the order of 0.05 mm to 0.2 mm each. 
     Next, operation of the recording tape cartridge  10  having the structure described above will be described. The opening  20  of the recording tape cartridge  10  is closed by the door  50  when the recording tape cartridge  10  is not in use (during storage, during transportation, and the like). Specifically, a distal end portion (front end portion) of the door  50  is entered into the recess portion  30 A of the diagonal wall portions  30  by the urging force of the coil spring  56 . At the same time, an intermediate portion outer peripheral surface of the door  50  abuts against the outer peripheral surface of the screw bosses  36  to close the opening  20 . 
     In contrast, when the magnetic tape T is to be used, the recording tape cartridge  10  is loaded into the bucket  60  of the drive device along the direction of arrow A. In accordance with this loading, as shown in  FIG. 6A , the engaging protrusion  60 , which serves as the opening member structuring opening means of the drive device, advances into the slit  40  which opens frontward at the step portions  38 , and engages with the operation projection  52  of the door  50 . 
     As the recording tape cartridge  10  (the case  12 ) is pushed in further, the urging force of the coil spring  56  is opposed by a force of pushing in and, as shown in  FIG. 6B , the engaging protrusion  60  moves the operation projection  52  rearward (that is, relatively rearward with respect to the case  12  which is being loaded in the direction of arrow A). Thus, the door  50  from which the operation projection  52  protrudes is guided by the screw bosses  36 , the protrusion portions  42 ,  44  and  46 , and the guide surface  48 A. At the same time, the door  50  rotates clockwise, in plan view, along the direction of curvature thereof. 
     That is, the door  50  moves substantially rearward so as to swing at the outer side of the reel  14  and the pin stands  24  without significantly deviating from the movement path along the shape of the curvature, and the door  50  opens the opening  20 . Thus, when the case  12  (the recording tape cartridge  10 ) is loaded to a predetermined depth in the drive device, the opening  20  is completely opened, as shown in FIG.  6 C. In this state, the recording tape cartridge  10  is positioned in the drive device, and further rotation of the door  50  (substantially rearward movement thereof) is restricted. 
     In this state, the recording tape cartridge  10  is positioned within the drive device. Then, the drawing-out means of the drive device advances into the case  12  through the opened opening  20 , and the drawing-out means takes out the leader pin  22 , which has been positioned and accommodated at the pin stands  24 , and accommodates the leader pin  22  at the winding reel. Then, the winding reel and the reel  14  are driven to rotate at the same time, and the magnetic tape T is wound around the winding reel while being sequentially drawn out from the case  12 . Information recording/replaying is carried out on the magnetic tape T by the recording/replaying head or the like which is disposed along the predetermined tape path. 
     Subsequently, when the magnetic tape T has been wound back to the reel  14  again, the recording tape cartridge  10  is ejected from the drive device. At this time, the state of positioning of the recording tape cartridge  10  is released, and the recording tape cartridge  10  is moved in a direction opposite to the direction of arrow A by the urging force of the coil spring  56  and/or by an unillustrated ejection mechanism. Thus, the door  50  is guided by the screw bosses  36 , the protrusion portions  42 ,  44  and  46 , and the guide surface  48 A, while being rotated in the closing direction of the opening  20  by the urging force of the coil spring  56 . The distal end portion of the door  50  enters into the recess portion  30 A of the diagonal wall portions  30 , and the door  50  returns to the initial state in which the opening  20  is completely closed. 
     Here, because the opening  20  is formed by cutting away the loading side corner portion of the rectangular case  12 , the opening face of the opening  20  faces in the direction of arrow A and in the direction of arrow B (the facing angle is diagonal with respect to the direction of arrow A). This means that the drawing-out means of the drive device can gain access to the leader pin  22  from a front face side which faces the case  12  in the direction of arrow A, and it is not required that the drawing-out means gain access from a side that is outside of the arrow B side peripheral walls (side walls)  16 A and  18 A (i.e., from an arrow B side). Consequently, in this drive device, a path for drawing out the magnetic tape T can be made as short as possible, and the drawing-out means does not require a drive mechanism for turning the magnetic tape T around from the arrow B side of the case  12 . Thus, a reduction in size and cost reductions can be expected. 
     Further, the door  50 , which is curvedly formed in the circular arc shape, is rotated to open and close the opening  20  by swinging around an outer side of the reel  14  and the pin stands  24  (and the leader pin  22 ) without deviating from the movement path along the shape of the curvature. Therefore, the door  50  will not protrude beyond an external profile region of the case  12  during opening and closing of the opening  20 . Consequently, a space for accommodation of the recording tape cartridge  10  in the drive device is small, and the movement path of the door  50  does not interfere with the pin stands  24  (the leader pin  22 ), the reel  14  and the like in the case  12 . 
     Further yet, it is sufficient that the engaging protrusion  60  of the drive device be fixedly disposed to be engageable with the operation projection  52  of the door  50  simply by advancing into the slit  40  from the front side thereof. Thus, construction is simple. Further again, because the door  50  closes the opening  20  due to the urging force of the coil spring  56 , a drive device side mechanism for driving the door  50  in the direction of closing the opening  20  is not required. Thus, construction of the opening means (opening member) of the drive device is made more simple. 
     Accordingly, with the recording tape cartridge  10  according to the present embodiment, the door  50 , which can make a space for accommodating the recording tape cartridge  10  at the drive device smaller, can open and close the opening  20 , whose structure can minimize length of the drawing-out path of the magnetic tape T, without the door  50  interfering with the reel  14  and the leader pin  22 . Moreover, the engaging protrusion  60 , which serves as the opening means (opening member) for operating the door  50  to open and close the opening  20 , can be given a simple structure. 
     Because the movement path of the door  50  as described above is a circular circumference (a curvilinear shape), the corner portion of the case  12  can be greatly cut away, and the opening  20  can be formed to be large. That is, in a case in which, for example, a flat plate-form covering member is inclined relative to the direction of arrow A, this covering member will be accommodated in an exterior profile region of the case  12 . In this situation, an operation area that is required for changing the attitude of the covering member by linear displacement or rotary displacement to open and close the opening  20  will be greater, and the opening  20  will have to be made smaller (the cutaway portion of the corner portion of the case  12  that forms the opening  20  will have to be made smaller) such that the operation of the covering member does not interfere with the leader pin  22 , the reel  14  and the like. However, with the recording tape cartridge  10  relating to the present embodiment, because the door  50  which opens and closes the opening  20  by turning on the predetermined circular arc without deviating therefrom as described above is provided, an increase in size of the opening  20  can be enabled. 
     In particular, a center of rotation of the door  50  for opening and closing the opening  20 , whose opening face is diagonal with respect to the direction of arrow A, can be determined independently of the position of an axial center of the reel  14 . Therefore, the angle of inclination of the opening face of the opening  20  relative to the direction of arrow A, the size of the opening  20  (a separation between front and rear edge portions thereof, and the like can be freely specified. Thus, the door  50  can be provided for opening and closing the opening  20 , with the opening  20  having dimensions and shape freely selected in accordance with requirements of the drive device and the like. That is, with the structure in which the door  50  is provided, a degree of freedom of design of the opening  20  (and thus the recording tape cartridge  10 ) is improved. 
     Further, when the length of the path for drawing out the magnetic tape T is minimized as described above, a running path of the magnetic tape T will inevitably be shortened too. As a result, contact friction of the magnetic tape T with tape guides (for example, rotatably supported rollers and the like) can be reduced. Furthermore, the opening  20  is formed by cutting away the corner portion of the case  12 , and faces in the direction of arrow A and in the direction of arrow B. Thus, a range of directions of access to the leader pin  22  by the drawing-out means (by hooks thereof or the like) is widened. Therefore, positions at which the leader pin  22  can be disposed in the case  12  are broadened. Therefore, given that the operation path of the door  50  as described above must not interfere with positions at which the leader pin  22  can be disposed in practice, a degree of freedom of design of the drive device is improved. 
     Further again, because the door  50  is a separate member from the leader pin  22  that is drawn out from the case  12 , in this structure the door  50  cannot be taken out from the case  12  in an assembled state. Thus, the door  50  will not be removed from the case  12  by an impact when the recording tape cartridge  10  is dropped or the like. Moreover, the leader pin  22  is accommodated in the case  12  in a firmly shut state when the opening  20  has been closed by the door  50  at a time of non-use. Thus, the leader pin  22  is less likely to become damaged or soiled. Consequently, drawing out and running the magnetic tape T at the drive device will not affect the drive device, and the magnetic tape T itself will not suffer from damage. 
     Next, opening and closing operations of the door  50  of the recording tape cartridge described above will be described in further detail. The operation projection  52  of the door  50  is exposed through the slit  40  as shown in  FIGS. 7 and 8 . The engaging protrusion  60 , which is provided at the drive device as an opening member, moves the door  50  a certain distance substantially in the front-rear direction. At this time, the engaging protrusion  60  pushes the operation projection  52  relatively in a rearward direction parallel to the direction of loading into the drive device. However, because the door  50  is formed in the substantially circular arc form in plan view, a resultant pushing force F can be analyzed into two directions as shown in FIG.  9 . 
     That is, if a contact angle of the engaging protrusion  60  with the operation projection  52  is α, the pushing force is analysed into a force F cos α (below referred to as Fx), which acts in a tangential direction of the door  50 , and a force F sin α (below referred to as Fy), which acts in a direction normal to the door  50 . Of these, the force Fx acting in the tangential direction of the door  50  is a force that acts to move the door  50  in the opening direction. However, the force Fy acting in the normal direction of the door  50  (which at a front side is a direction into the case) is a resisting force which hinders movement of the door  50  in the opening direction. 
     The direction of operation of this resisting force Fy reverses between a front side and a rear side of a boundary point at a position S, at which the movement path of the door  50  is closest to the right wall  12 B (excluding the offset wall portions  34 , the protrusion portions  42  and  46 , and the guide surface  48 A) in plan view. That is, when the door  50  is moved in the opening direction and the operation projection  52  passes this position S, the resisting force Fy acting on the operation projection  52  changes from a direction into the case to a direction out of the case at the position S. Consequently, movement of the door  50  in the opening direction is inconsistent, resistance to movement during the opening operation is large, and the door  50  is difficult to open. 
     Accordingly, in the present embodiment, the operation projection  52  is moved at either one of a front side including the position S and a rear side including the position S (at which the movement path of the door  50  is closest to the right wall  12 B (excluding the offset wall portions  34 , the protrusion portions  42  and  46 , and the guide surface  48 A) in plan view), such that the resisting force Fy that acts in the normal direction of the door  50  works in one of the direction into the case and the direction out of the case. The position S is a position at which the engaging protrusion  60  and the operation projection  52  abut (engage) in a parallel state (α=0), and the resisting force Fy is at a zero point. Thus, the position S is a position at which the pushing force F from the engaging protrusion  60  is only the operating force Fx that acts in the tangential direction of the door  50  (F=Fx). 
     Consequently, by moving the operation projection  52  at the front side or rear side including (or, if desired, not including) the position S, the movement of the door  50  in the opening direction can be made consistent, and the door  50  can be made to move comparatively smoothly. The position that is closest to the right wall  12 B may also be defined as the position of a point of contact between the movement path of the door  50  and a tangent L of the movement path in a case in which the tangent L is drawn parallel to the direction of loading into the drive device. Further, the operation projection  52  may be provided at an outer peripheral portion of the door  50  with, for example, an unillustrated resilient member such as a leaf spring or the like interposed therebetween, such that the attitude of the operation projection  52  is deformable to follow the engaging protrusion  60 , so as to constantly contact the engaging protrusion  60  in a state of being parallel to the engaging protrusion  60  (α=0). 
     According to the present invention described above, an opening aperture is formed by cutting away a corner portion at a side of loading a case into a drive device. Therefore, an opening face of the opening aperture can be faced toward the drive device, and drawing-out means at the drive device side can be advanced into the opening aperture from a forward side thereof. Thus, a drawing-out path of a recording tape can be made as short as possible. Accordingly, a complicated mechanism for turning and guiding the recording tape at the drive device is not required, and the drive device can be designed to be compact, with low production costs. 
     Further, a covering member is formed in a substantially circular arc shape in plan view to move on a predetermined circular circumference. Thus, the opening aperture can be made larger, construction is simple, and a space-saving structure can be obtained. Therefore, efficient use of space in the case and in the drive device is provided for. Consequently, a cartridge area in the drive device can be made small, and a reduction in size of the drive device can be expected. 
     Furthermore, a range through which an operation member of the covering member moves is at one side of a position at which the movement path of the covering member is closest to a side wall, which is parallel to the direction of loading into the drive device, in plan view, and is bounded by that position. Therefore, a resisting force that a drive device side opening member applies to the operation portion acts in only one of a direction into the case and a direction out of the case. Consequently, compared to a situation in which the resisting force works in both directions, movement of the covering member in an opening direction can be made more consistent, and the covering member can be moved relatively smoothly.