Abstract:
Ribs serving as reinforcing members of the hub pawls provided to the inner peripheral surface of a cylindrical hub around which a tape is wound can be formed in a simple shape using an electric discharge electrode. A hub comprises plural hub pawls projected from the inner peripheral surface of a hub hole of a tape winding hub, and ribs each of which has a slant surface and is provided to the base portions at both the sides in the hub rotational direction of the hub pawl, wherein the slant surface of the rib is formed in a convex three-dimensional shape (arcuate shape) which is inclined with respect to the cylindrical hub pawl.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a tape cartridge, and more particularly to an enforcing rib provided to a hub pawl of a tape winding hub. 
     2. Description of the Related Art 
     As shown in FIG. 1, a tape cartridge in a prior art is constructed so that plastic (generally, high-impact polystyrene) hubs  12  around which a tape  11  is wound are freely rotatably located on respective driving shaft insertion holes  13  at the right and left sides in a main body case  10 . Each of both the ends of the tape  11  is hooked and coupled to a part of each outer periphery of the right and left hubs  12  by a cramping piece  14 , and the tape  11  is drawn from one hub  12  to the front face of the main body case  10  and wound by the other hub  12 . 
     The hub  12  has a hub hole  15  at the center thereof, and a plurality of hub pawls  16  are integrally projected from the inner peripheral surface of the hub hole  15  in the central direction so as to be spaced from one another at predetermined intervals. 
     The hub pawl  16  is designed in a substantially cylindrical shape of about 1.5 mm in diameter and about 1 mm in length, and it is extremely smaller as compared with the size, thickness, etc. of the overall hub  12 . Therefore, fast feeding or rewinding operation by a recent tape recorder imposes a large impact load on the hub pawls  16 , and excessive stress is applied to the bases of the hub pawl  16 , so that such a problem as damage or the like may occur. Particularly since there frequently occurs such a case that a user carries a tape cartridge on the road when the user goes outdoors, when a drop impact or the like is applied to a tape cartridge while the tape cartridge is accommodated in an accommodation case, a hub rotation stop member at the accommodation case side and the hub pawls  16  collide against each other, and the hub pawls  16  may be damaged at the base portions thereof. 
     JP-A-60-51685U previously proposed a device of a countermeasure of preventing the damage of the hub pawls  16  as described above. In this device, as shown in FIG. 2, the base portion of the hub pawl  16  in the rotational direction is provided with ribs  18  each comprising a rounded R-surface  17 . By forming the R-surface  17  as described above, the concentration of the excessive stress due to the impact load which is applied to the hub pawls  16  in the rotational direction can be avoided, and the strength can be enhanced, so that the damage preventing effect of the hub pawls  16  can be expected. 
     However, in case of the hub pawl  16  having the ribs  18  having the R-surface  17  as described above, when the hub  12  is manufactured, it is necessary to process the place of a die corresponding to the R-surface portion of the hub pawl in a minute and complicated three-dimensional shape, and it is difficult or impossible to perform the processing by using equipment such as an electric discharge machine or the like. Therefore, there is a problem that the cutting work must be manually carried out on the place. 
     In order to solve this problem, there is known JP-A-62-80280U. In this device, as shown in FIGS. 3 and 4, the rib  19  provided to the base of the hub pawl  16  is designed in a simple two-dimensional shape to have an R-surface  20 . That is, as shown in FIG. 4, the rib  19  has the R-surface  20  provided in the rotational direction of the hub  12 , and side surfaces  22  which are crossed to the R-surface  20  through the ridgelines at both the sides of the R-surface  20 , and the R-surface  20  is designed to have the same curvature in the pawl peripheral direction W. The rib  19  of the hub pawl  16  is designed in such a two-dimensional simple shape as described above, so that the electric discharge machining to form a die can be performed and the die processing can be facilitated. 
     However, even when the R-surface of the rib provided to the hub pawl in the prior art described above is designed in a simple two-dimensional shape, the shape of an electrode required for the electric discharge machining to form a die must be processed in conformity with the shape of the rib. Therefore, there is a problem that the shape of the electrode is complicated. 
     Accordingly, there is a problem that a rib must be designed in such a shape that an electrode for the electric discharge machining used to process a die for the rib provided to the hub pawl is simple. 
     SUMMARY OF THE INVENTION 
     In order to solve the above problem, a tape cartridge according to the present invention in which a hub for winding a tape therearound is accommodated, is characterized in that the hub comprises a hub hole penetrating through the center position, a plurality of cylindrical hub pawls projected from the inner peripheral surface of the hub hole, and ribs having slant surfaces which are provided to the base portions of the plural hub pawls in the hub rotational direction, the slant surfaces of the ribs are designed in a three-dimensional convex shape which is swollen from the cylindrical hub pawls, and further the ribs having the three-dimensional swollen convex shape are designed in an arcuate shape which is inclined with respect to the cylindrical hub pawls. 
     Further, each of the arcuate ribs inclined with respect to the cylindrical hub pawls has a slant angle of 30 degrees to 70 degrees, and the rib height dimension which comprises the cross point between the slant surface and the hub pawl, and the tangential line of the hub hole is set to 0.37 mm to 0.47 mm. 
     By adopting the above structure, the processing becomes possible merely by designing an electrode used when the electric discharge machining of a die is performed into a simple shape such as a cylindrical shape, a semi-cylindrical shape or the like, so that the power saving when forming the electrode for the electric discharge machining can be achieved and also the cost can be reduced. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a plan view showing a hub of a prior art which is mounted on a tape cartridge; 
     FIG. 2 is an explanatory view showing a state where ribs are provided to hub pawls as is shown in JP-A-60-51685U; 
     FIG.  3 . is a plan view showing a state where ribs are provided to hub pawls as shown in JP-A-62-80180U; 
     FIG. 4 is a perspective view showing ribs provided to hub pawls in FIG. 3; 
     FIG. 5 is a plan view showing a hub for winding a tape contained in a tape cartridge according to the present invention; 
     FIG. 6 is an enlarged perspective view of the main part of a hub pawl of the hub; 
     FIG. 7 is a plan view showing a part of the hub pawl; 
     FIG. 8 is a side view showing the dimensional relationship between the hub pawl and the hub; 
     FIG. 9 shows a die and an electrode therefor viewed from the rib rotational direction of the die rib portion provided to the base of the die hub pawl portion, wherein (A) is an explanatory view showing a cylindrical electrode, and (B) is an explanatory view showing a semi-cylindrical electrode; 
     FIG. 10 shows a die and an electrode therefor viewed from a direction perpendicular to the rib rotational direction of the die rib portion provided to the base of the die hub pawl portion, wherein (A) is an explanatory view showing an electrode for forming one die rib portion, (B) is an explanatory view showing an electrode for forming the other die rib portion, and (C) is an explanatory view showing the die rib portion provided to both the ends of the rib rotational direction of the die hub pawl portion; 
     FIG. 11 is an explanatory view showing a test method of hub drop strength by the plastic case; 
     FIG. 12 is a plan view showing a state where a rotation stopper is provided to the hub in the plastic case in the drop method of FIG. 11; and 
     FIG. 13 is a plan view showing points for measuring the rupture strength of the hub pawls. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Next, a tape cartridge according to the present invention will be described with reference to the drawings. Incidentally, a main body case constituting the tape cartridge is similar to the main body case  10  shown in FIG. 1 described in the prior art, and thus the same elements are represented by the same reference numerals. 
     As shown in FIG. 5 to FIG. 8, the tape cartridge according to the present invention is designed so that ribs  25  are provided to the base portions of plural hub pawls  16  in the hub rotational direction so as to enforce the hub pawls  16 . 
     The rib  25  is designed in a three-dimensional swollen convex shape having a slant surface  26  which is inclined at a slant surface angle X=45 degrees at the base portion of the cylindrical hub pawl  16  and in the rotational direction of the hub  12  and integrally formed with the base portion of the hub pawl  16 , that is, in a convex arcuate shape inclined with respect to the cylindrical hub pawl  16 . 
     Although the slant surface  26  is shaped along the rotational direction of the base portion of the hub pawl  16 , damage to the hub pawl  16  typically occurs at the end thereon extending into the hub hole  15 . Therefore, it is necessary and sufficient to provide the slant surface  26  on opposed sides of the bad portion in the hub rotational direction of the hub pawl  16 . 
     The addition range of the slant surface  26  in this case is preferably set as follows: 
     Slant surface angle X=30 degrees to 70 degrees. The hub height dimension from the tangential line  27  of the hub hole  15  to the cross point Z between the hub pawl  16  and the slant surface  26  is preferably set as follows: 
     Hub height dimension Y=0.37 mm to 0.47 mm. 
     If the slant surface angle X is less than 30 degrees or the hub height dimension Y=0.37 mm or less, the damage preventing effect is extremely lowered. If the slant surface angle X=70 degrees or more or the hub height dimension Y=0.47 mm or more, there is a risk that the rib interferes with the driving shaft at the tape recorder side. 
     Therefore, the addition range of the rib  25  having the slant surface  26  described above is set to such a range that the damage strength can be ensured and the rib does not come into contact with the driving shaft at the tape recorder side. 
     Next, a die for forming the rib  25  having the slant surface  26  inclined at 45 degrees for example and provided to the hub pawl  16  in a three-dimensional cylindrical shape will be described with reference to FIGS. 9 and 10. 
     A die  30  is constructed by providing an arcuate die rib portion  32  to a die hub pawl portion  31  bored in a cylindrical form so as to be linked to the die hub pawl portion  31 . The die rib portion  32  is formed by a semi-cylindrical electrode  33 A having an U-shaped surface which is brought into contact with the rib portion  32  (see FIG.  9 (B)), or by an cylindrical electrode  33 B (see FIG.  9 (A)). 
     The electrode  33 A,  33 B shown in FIG.  9 (A), (B) may be an electrode having a simple shape in which the contact surface thereof for forming the die rib portion  32  is R-shaped, and it is not limited to the semi-cylindrical or cylindrical electrode  33 A,  33 B. The processing surface of the electrode may be inclined at 45 degrees for example, and abutted against the die (hub pawl base portion). 
     That is, as shown in FIG.  10 (A), the electrode  33 A,  33 B is brought into contact with one side of the die hub pawl portion  31  in the rotational direction of the die hub pawl portion  31  with being inclined at 45 degrees to perform electric discharge machining. Subsequently, as shown in FIG.  10 (B), the electrode  33 A,  33 B is brought into contact with the other side of the die hub pawl portion  31  in the rotational direction thereof with being inclined at  45  degrees to perform electric discharge machining. When the electric discharge machining is performed as described above, as shown in FIG.  10 (C), arcuate die rib portions  32 ,  32  which are inclined to both the sides of the die hub pawl portion  31  in the rotational direction thereof can be formed. 
     By the above processing method, the rib  25  having the slant surface in the hub pawl  16  is shaped into the arcuate three-dimensional form, whereby power saving in the electrode forming process based on the electric discharge machining can be achieved and the cost can be reduced. 
     Next, the strength of the rib  25  formed by the die  30  which was actually formed by the electric discharge machining (see FIGS. 9,  10 ) will be described with reference to the sample data of Table 1. 
     The following Table 1 shows data of the strength of prototype samples formed by the above processing method. The test articles used in this test were formed by the same resin and the same die. A sample 1 has a rib height dimension of 0.25 mm (0.24 to 0.26 mm), and it is set to a value so that the precision, etc. thereof are varied in accordance with the kind of resin, etc. A sample 2 has a rib height dimension of 0.42 mm (0.37 to 0.47 m), and it is set to a range in which the precision, etc. thereof are not varied in accordance with the kind of the resin, etc. 
     As shown in FIGS. 11 and 12, in a drop test method, a tape cassette  10 A in which 90-minute tape  11  is wound is dropped from a position P above a tile  35  (in this embodiment, P=75 cm) under a state that the hub pawls  16  are put on a rotation stopper  34  of a plastic case  33 . 
     As shown in FIG. 13, in a pawl rupture strength measuring method, measuring places of the hub pawls  16  of the hub  12  (in this embodiment, points A to F) are pushed by tension gauge of 5 kgf to read the value when rupture occurs. 
     
       
         
               
               
               
             
               
               
               
               
             
           
               
                 TABLE 1 
               
             
             
               
                   
               
               
                 Prototype samples(see 
                 Drop strength test (75 cm above 
                   
               
               
                 FIG. 8) 
                 tile P) 
               
             
          
           
               
                 X:slant surface angle 
                 Occurrence 
                 Occurrence 
                 Pawl rupture 
               
               
                 Y:rib-height dimension 
                 number 
                 rate 
                 strength 
               
               
                   
               
               
                 Sample 1 
                   
                   
                   
               
               
                 X:45 degrees 
                 4turns/ 
                 20% 
                 3.47 kg 
               
               
                 Y:0.25 mm 
                 20turns 
               
               
                 Sample 2 
               
               
                 X:45 degrees 
                 2turns/ 
                 10% 
                 3.95 kg 
               
               
                 Y:0.37 mm 
                 20turns 
               
               
                   
               
             
          
         
       
     
     The Table 1 means that as the results of the drop test and the measurement of pawl rupture strength for the hubs  12  of the samples 1 and 2 (having the set dimensions of the present invention) made on an experimental basis, the sample 2 is reduced to be less in drop strength occurrence rate than the sample 1 by 10%, and increased to be more in pawl rupture strength than the sample 1 by about 10%. With these results, by providing the rib  25  of the set dimension of the present invention to the base portion of the hub pawl  16 , the damage preventing effect can be surely enhanced. 
     As described above, in the tape cartridge of the present invention, in order to enhance the damage preventing effect of the hub pawls, the rib having the slant surface is provided to the base portions of the hub pawl in the rotational direction, and the rib is designed in a convex three-dimensional shape which is inclined with respect to the cylindrical hub pawl, whereby the processing becomes possible merely by designing the electrode used when the electric discharge machining of the die is performed into a simple shape such as a cylindrical shape, a semi-cylindrical shape or the like, so that the power saving when forming the electrode for the electric discharge machining can be achieved and also the cost can be reduced.