Abstract:
A ribbon cassette containing a supply core, a web located on the supply core, a storage core, a device for increasing the tension on the web as it passes from said supply core to said storage core to produce a tensioned web, a drive roller contiguous with the web, and a nip roller contiguous with the web. The said tensioned web is passed in a first rotary direction around a portion of the drive roller, and then it is passed in a second rotary direction around a portion of the nip roller, and then it is passed in a in rotary direction identical to the first rotary direction around a portion of the storage core. A nip is formed between the nip roller, the web, and the drive roller such that either the nip roller or the drive roller is compressed by at least about 0.001 percent.

Description:
CROSS-REFERENCE TO RELATED PATENT APPLICATIONS  
       [0001]     This application is a continuation-in-part of co-pending patent application U.S. Ser. No. 10/234,284, filed on Sep. 4, 2002. The entire content of this application is hereby incorporated by reference into this specification. 
     
    
     FIELD OF THE INVENTION  
       [0002]     A ribbon cassette capable of stabilizing the movement of an ink ribbon.  
       BACKGROUND OF THE INVENTION  
       [0003]     U.S. Pat. No. 6,290,408 discloses that, with conventional ribbon cassettes, it is difficult to stabilize the ink ribbons during use as printing conditions vary. At column 2 of this patent, and with regard to a conventional ribbon cassette used in thermal printing, it is disclosed that: “Since the tensile load is applied to the ink ribbon  3  by the agency of the tension shaft of the thermal transfer printer, the tensile load is kept constant for all types of ink ribbons regardless of type. Therefore, all types of ink ribbons are not necessarily able to move steadily. Different types of ink ribbons behave differently when used for printing on the thermal transfer printer. Therefore, printing conditions, such as pressure for pressing the thermal print head against the platen, mode of driving the heating elements of the thermal print head and printing speed are controlled to print images properly. However, it is impossible to stabilize the movement of all types of ink ribbons only through the control of the printing conditions for the thermal transfer printer and, consequently, images are printed in a poor print quality.” 
         [0004]     The solution to this problem that is disclosed and claimed in U.S. Pat. No. 6,290,408 is “A ribbon cassette comprising: a take-up reel and a feed reel supported for rotation in a housing, and an ink ribbon wound on the take-up reel and the feed reel; a print head receiving part formed in a section of a passage for the ink ribbon between the take-up reel and the feed reel to receive a thermal print head therein when the ribbon cassette is set in place on a thermal transfer printer; a take-up pinch roller and a feed pinch roller supported for rotation at a position between the print head receiving part and the take-up reel and at a position between the print head receiving part and the feed reel, respectively; and a friction mechanism for exerting a frictional force to the feed pinch roller to apply a tensile load to the ink ribbon, wherein the friction mechanism comprises an elastic friction member capable of exerting a frictional force on a core barrel included in the feed pinch roller by clasping the core barrel.” 
         [0005]     The system described in U.S. Pat. No. 6,290,408 does not allow one to readily vary the tension on the ink ribbon for different conditions. Furthermore, such prior art system does not provide good tension control for used ribbon taken up on the take up spool, which often tends to swell and thus precludes efficient gathering of all of the used ribbon. It is an object of this invention to provide an improved system which overcomes the problems presented by the system of such United States patent.  
       SUMMARY OF THE INVENTION  
       [0006]     In accordance with this invention, there is provided a ribbon cassette comprising a supply core, a web disposed on said supply core, a storage core, means for passing said web from said supply core to said storage core, means for increasing the tension on said web as it passes from said supply core to said storage core to produce a tensioned web, a drive roller contiguous with said web, and a nip roller contiguous with said web, wherein said tensioned web is passed in a first rotary direction around a portion of said drive roller, wherein said tensioned web is passed in a second rotary direction opposite to said first rotary direction around a portion of said nip roller, wherein said tensioned web is passed in a in rotary direction identical to said first rotary direction around a portion of said storage core, and wherein said ribbon cassette is comprised of means for compressing said drive roller or said nip roller by at least about 0.001 percent.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0007]     The invention will be described by reference to the following drawings, in which like numerals refer to like elements, and in which:  
         [0008]      FIG. 1  is a schematic view of one preferred embodiment of the ribbon cassette of this invention;  
         [0009]      FIG. 2  is a top view of the cartridge base of the ribbon cassette of  FIG. 1 ;  
         [0010]      FIG. 3  is a top view of the cartridge cover of the ribbon cassette of  FIG. 1 ;  
         [0011]      FIG. 4  is an exploded view of the ribbon cassette of  FIG. 1 ;  
         [0012]      FIGS. 5A, 5B , and  5 C are a sectional view, an end view, and a front view of the drive roller used in the ribbon cassette of  FIG. 1 ;  
         [0013]      FIG. 6A  is a partial sectional view of the roller used in the ribbon cassette of  FIG. 1 ;  
         [0014]      FIGS. 6B, 6C , and  6 D are each sectional views, a front view, and a back view of the roller depicted in  FIG. 6A ;  
         [0015]      FIGS. 7-21  each depicts a schematic view of another preferred ribbon cassette of the invention; and  
         [0016]      FIGS. 22A and 22B  are sectional and top views of the nip roller used in the ribbon cassette of  FIG. 1 . 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0017]      FIG. 1  is a schematic illustration of one preferred ribbon cassette  10 . In the embodiment depicted in  FIG. 1 , and for ease of description of the components of the ribbon cassette  10 , the top casing (not shown in  FIG. 1 ) has been removed from the cassette  10  depicted, showing the components of the cassette  10  disposed within bottom casing  12 .  
         [0018]     Referring to  FIG. 1 , it will be seen that, disposed within bottom casing  12  is supply core  14  from which ribbon  16  is unwound. The ribbon  16  can be wound around a variable tensioning assembly  18  in different configurations to impart differing degrees of tension to it.  
         [0019]     In the embodiment depicted in the  FIG. 1 , the variable tensioning assembly  18  is comprised of a guide roller  20 , a first stationary brake  22 , and a second stationary brake  24 .  
         [0020]     Each of brake  22  and brake  24  is a stationary structure which preferably has a cylindrical cross sectional shape. This cylindrical cross-sectional shape maximizes the amount of contact between the ribbon  16  and the brake. The manner is which the ribbon  16  is wound about the brake  22  and/or the brake  24  will affect the contact angle(s) between the ribbon  16  and such brake(s) and, consequently, affect the degree to which the tension of the ribbon is increased. In the embodiment depicted in the  FIG. 1 , a contact angle  26  between ribbon  16  and brake  24  is illustrated.  
         [0021]     As used in this specification, the term “contact angle” refers to the angular degree of wrap, i.e., the number of degrees that the ribbon contacts either brake  22  and/or brake  24 . By way of illustration, if the ribbon contacted one-half of the periphery of each of brake  22  and brake  24 , the contact angle would be 360 degrees.  
         [0022]     In one embodiment, the angular degree of wrap in the cassette  10  is from about 8 to about 600 degrees. In one aspect of this embodiment, the angular degree of wrap is from about 180 to about 360 degrees.  
         [0023]     In the embodiment depicted in  FIG. 1 , the brakes  22  and  24  have a circular cross-sectional shape. In other embodiments, not shown, such brakes  22  and  24  have non-circular arcuate shapes such as, e.g., an oval shape, an elliptical shape, an irregular arcuate shape, etc.  
         [0024]     In one preferred embodiment, each of brake  22  and brake  24  is substantially parallel to the ribbon  16  to insure the maximum amount of contact between the ribbon  16  and the brakes  22 / 24 . Furthermore, in this embodiment, each of the ribbon  16  and the brakes  22 / 24  are preferably substantially perpendicular to the bottom casing  12 .  
         [0025]     It is preferred that each of brake  22  and brake  24  have a coefficient of friction of from about 0.1 to about 0.8. It is more preferred that such coefficient of friction be from about 0.2 to about 0.6.  
         [0026]     Referring again to  FIG. 1 , it will be seen that the ribbon  16  can be wound around the guide roller  20  and the brake  22  and/or the brake  24  in different manners, each of which will impart a different angular degree of wrap and a different amount of tensioning to the ribbon  16 .  
         [0027]     In the manner depicted in  FIG. 7 , for ribbon cassette  10 , the ribbon  16  is first contacted in a counterclockwise direction with guide roller  20  and thereafter contacted in a counterclockwise direction with brake  24 . In the embodiment depicted, the angle of wrap of the ribbon  16  around brake  24  is 76 degrees (1.32 radians), and the coefficient of friction is 0.4. This tensioning method increases the tension of the ribbon  16  by about 170 percent.  
         [0028]     As is known to those skilled in the art, the capstan equation may be used to calculate the ratio of the tension out to the tension in (To/Ti). This ratio is equal to e ub , wherein e is the base of the natural logarithm and is equal to about 2.71828, u is the coefficient of friction of the brake material, and b is the wrap angle of the web around the brake (in radians). For a discussion of the capstan equation, reference may be had, e.g., to U.S. Pat. Nos. 4,610,060; 3,840,972; 3,778,878; 6,123,990; 5,912,078; 5,648,010; 5,523,243; 4,995,884; 4,124,156; 6,207,088; 6,120,695; 6,117,353; 6,077,468; 6,068,805; 4,624,793; 3,955,737; and the like. The entire disclosure of each of these United States patents is hereby incorporated by reference into this specification.  
         [0029]     The configuration  11  depicted in  FIG. 8  is similar to the configuration  10  depicted in  FIG. 7 , with the exception that the ribbon  16  is first contacted in a clockwise direction with guide roller  20 . In configuration  11 , the angle of wrap is 145 degrees (2.539 radians) and the coefficient of friction is 0.4. This configuration  11  will create a larger contact angle between the ribbon  16  and the brake  24  than is created in the configuration  10 . Thus, this tensioning method  11  increases the tension of ribbon  16  by about 280 percent.  
         [0030]     In the configuration  13  depicted in  FIG. 9 , the ribbon  16  is first contacted in a clockwise direction with brake  22 , then it is contacted in a counterclockwise direction with guide roller  20 , and then it is contacted in a counterclockwise direction with brake  24 . In this configuration  13  the angle of wrap is 292 degrees (5.094 radians) and the coefficient of friction is 0.4. This configuration creates tension with both brake  22  and brake  24 ; and it increases the tension of ribbon  16  by about 770 percent.  
         [0031]     In the configuration  15  depicted in  FIG. 10 , the ribbon  16  is first contacted in a clockwise direction with brake  22  and then contacted in a counterclockwise direction with brake  24 . In this configuration  15 , the wrap angle is 350 degrees (6.113 radians) and the coefficient of friction is 0.4. In the configuration  15 , there is a substantial amount of contact between ribbon  16  and both brake  22  and brake  24 ; and the use of this configuration increases the tension of ribbon  16  by about 1,150 percent.  
         [0032]     In the configuration  17  depicted in  FIG. 11 , the ribbon  16  is first contacted in a counterclockwise direction with guide roller  20 , and then in a clockwise direction with brake  22 , and then in a clockwise direction with brake  24 . In this configuration  17 , the angle of wrap is 434 degrees (7.571 radians) and the coefficient of friction is 0.4. The use of this configuration  17  increases the tensioning of ribbon  16  by about 2,070 percent.  
         [0033]     In  FIGS. 12 through 16 , the configurations depicted are similar to the configurations depicted in  FIGS. 7 through 11  with the exception that the guide roller  20  used in  FIGS. 7 through 11  is replaced with a fixed arcuate surface (brake)  21  in the configurations depicted in  FIGS. 12 through 16 .  
         [0034]     Referring to  FIGS. 12 through 16 , the wrap angles for configurations  19 ,  21 ,  23 ,  25 , and  27  are 93 degrees (1.623 radians), 212 degrees (3.707 radians), 462 degrees (8.067 radians), 350 degrees (6.114 radians), and 558 degrees (9.734 radians), respectively; and the coefficients of friction for configurations  19 ,  21 ,  23 ,  25 , and  27  are each 0.4. The ratio of Tout/Tin for configurations  19 ,  21 ,  23 ,  25 , and  27 , is 1.9, 4.4, 25.2, 11.5, and 49.1, respectively.  
         [0035]     The configurations depicted in  FIGS. 17, 18 ,  19 ,  20 , and  21  are similar to the configurations depicted in  FIGS. 12 through 16 . Referring to  FIGS. 17, 18 ,  19 ,  20 , and  21 , the wrap angles for configurations  29 ,  31 ,  33 ,  35 , and  37  are 8 degrees (0.140 radians), 77 degrees (1.335 radians), 377 degrees (6.585 radians), 162 degrees (2.824 radians), and 360 degrees (6.287 radians), respectively; and the coefficients of friction for these configurations are 0.4. The ratio of Tout/Tin for configurations  29 ,  31 ,  33 ,  35 , and  37  are 1.1, 1.7, 13.9, 3.1, and 12.4, respectively.  
         [0036]     Referring again to  FIG. 1 , and in the preferred embodiment depicted therein, the brakes  22  and  24  preferably have a smooth exterior surface with no protuberances or irregularities that might damage the ribbon  16 . In one aspect of this embodiment, the brakes  22  and  24  are made of polystyrene.  
         [0037]     It is preferred that each of brakes  22  and  24  be substantially the same size and have a diameter of at least about 0.25 inches.  
         [0038]     Referring again to  FIG. 1 , and in the preferred embodiment depicted therein, the guide roller  20  is preferably rotatably disposed on a stationary shaft  9 .  
         [0039]     Referring again to  FIG. 1 , and in the embodiment depicted, the ribbon  16  is passed under idler roller  28  and then over stationary shaft  30 , and then over stationary shaft  32 .  
         [0040]     The ribbon  16  is then passed from stationary shaft  32  over drive roller  34  (in a counterclockwise direction, over nip roller  36  (in a clockwise direction), and back onto the storage core  38 . This arrangement is but one aspect of a general embodiment in which the ribbon  16  is passed over the drive roller  34  in a first rotary direction, and then passed over nip roller  36  in a second rotary direction that is opposite to the first rotary direction, and then passed over the storage core  38  in the first rotary direction.  
         [0041]     Drive roller  34  may be any drive roller conventionally used in ink ribbon cassettes. Reference may be had, e.g., to U.S. Pat. Nos. 5,122,003; 4,655,623 (ink ribbon cassette); U.S. Pat. No. 5,762,430 (ribbon cassette); U.S. Pat. No. 5,472,286 (ink ribbon cassette); U.S. Pat. No. 4,676,681 (ink ribbon cassette); U.S. Pat. No. 4,732,500 (drive mechanism including floating pressure ring for ink ribbon cassette); U.S. Pat. No. 5,915,859 (pivotable ink ribbon cassette); U.S. Pat. No. 4,449,838 (ink ribbon cassette); U.S. Pat. No. 4,747,713 (ink ribbon cassette including geared teeth); U.S. Pat. No. 5,531,528 (cartridge for printers); U.S. Pat. Nos. 5,618,118; 4,948,283; 5,226,740; 5,156,474; 5,902,059; 5,320,437; 5,052,832; 5,020,928; 5,071,272 (ribbon cassette and protector); and the like; the disclosure of each of these United States patents is hereby incorporated by reference into this specification.  
         [0042]     The nip roller  36  also may be similar to nip rollers known to those skilled in the art. Reference may be had, e.g., to U.S. Pat. Nos. 6,033,508; 5,875,034; 5,606,420; 5,493,409; 4,493,573 (see nip rollers  22  and  24 ); 5,713,504); and the like. The entire disclosure of each of these United States patents is hereby incorporated by reference into this specification.  
         [0043]     In one embodiment, the drive roller  34  preferably is made from an elastomeric material and has a Shore hardness reading of from about 30 to about 60. In another embodiment, the nip roller  36  is made from an elastomeric material and has a Shore hardness reading of from about 30 to about 60. In yet another embodiment, both the drive roller  34  and the nip roller  36  are made from elastomeric material. In yet another embodiment, one of the drive roller  34  and the nip roller  36  is made from elastomeric material, and the other such roller is made from a non-elastomeric, relatively hard material with a Shore hardness of from 30 to 60.  
         [0044]     In one embodiment, the drive roller  34  and the nip roller  36  are each contiguous with ribbon  16 , and the nip roller  36  compresses the diameter of the drive roller by at least about 0.001 percent. In another embodiment, the drive roller  34  and the nip roller  36  are each contiguous with ribbon  16 , and the drive roller  34  compresses the diameter of the nip roller  36  by at least about 0.001 percent. In both of these embodiments, a nip is formed between the driver roller  34 , the ribbon  16 , and the nip roller  36 , i.e., one of the nip roller  36  and the drive roller  34  is compressed by at least about 0.001 percent by this assembly.  
         [0045]     In one aspect of this embodiment, the diameter of the drive roller  34  or the nip roller  36  is compressed from about 0.001 to about 0.01 percent. In another aspect of this embodiment, the diameter of both the drive roller  34  and the nip roller  36  is compressed from about 0.001 to about 0.01 percent.  
         [0046]     It is preferred that the nip roller be free rolling, i.e., that the nip roller have a low moment of inertia. Reference may be had, e.g., to element  29  depicted in U.S. Pat. No. 4,201,002, the entire disclosure of which is hereby incorporated by reference into this specification.  
         [0047]      FIG. 2  is a top view of the casing  12  of ribbon cassette  10 . Referring to  FIG. 2 , and in the preferred embodiment depicted therein, it will be seen that casing  12  is comprised of a multiplicity of orifices  50 ,  52 ,  54 ,  56 ,  58 ,  60 ,  62 ,  64 ,  66 ,  68 ,  70 ,  72 , and  74 . These orifices are adapted to receive a multiplicity of corresponding pins (pins  51 ,  53 ,  55 ,  57 ,  59 ,  61 ,  63 ,  65 ,  67 ,  69 ,  71 ,  73 , and  75 , respectively) that are preferably engageably disposed in such orifices and that extend upwardly from the base  77  of cartridge cover  79  (see  FIG. 3 ).  
         [0048]     Referring to  FIG. 3 , and in the embodiment depicted, it will be seen that there are 13 of such pins  51  et seq. In general, it is preferred to at least about 8 of such pins. In another embodiment, not shown, at least about 16 of such pins are used.  
         [0049]     In one embodiment, the pins  51  et seq. are preferably friction fit in the corresponding orifices  50  et seq. to removably connect the casing  12  to the cover  79 ; in another embodiment, the pins  51  et seq. are permanently disposed within the corresponding orifices so that, if one attempts to remove the cover from the casing, the pins will break. Each of these pins preferably has a length of at least about 0.125 inches. In one embodiment, each of these pins preferably has a length of at least about 0.25 inches.  
         [0050]      FIG. 4  is an exploded view of ink ribbon cassette  10  illustrating how cartridge cover  79  is preferably connected to casing  12  and, when so connected, encloses ribbon  16  with its supply core  14  and its take up core  38 .  
         [0051]      FIG. 5A  is a sectional view of drive roller  34 . In the preferred embodiment depicted therein, it will be seen that drive roller  34  is comprised of elastomeric surface  90  bonded to cylindrical wall  92 . The cylindrical wall  92  preferably is made out of a plastic material, such as polystyrene. In one embodiment, the cylindrical wall  92  has a Shore hardness of at least about 60.  
         [0052]     In the embodiment depicted in  FIG. 5A , the drive roller  34  preferably is comprised of reduced diameter sections  94  and  96  to facilitate the location of the drive roller  34  within the casing  12 .  
         [0053]     A multiplicity of drive splines  98 ,  100 , and  102  are disposed on the inside surface of cylindrical wall  92  to engage a typical printer drive shaft (not shown). In the preferred embodiment depicted in  FIGS. 5A and 5B , each of splines  98 ,  100 , and  102  preferably contains angled ends  104  and  106  to facilitate the engagement of such splines with the printer drive shaft (not shown).  
         [0054]      FIG. 6A  is a partial sectional view of one preferred embodiment of guide roller  28 .  FIGS. 6B, 6C , and  6 D are sectional, top, and bottom views of such guide roller  28 .  
         [0055]     It is preferred that the guide roller  28  be made out of a material with a Shore hardness of at least about 60 such, as, e.g., hard polystyrene.  
         [0056]      FIG. 22A  is a sectional view of nip roller  36  (see  FIG. 1 ). In one embodiment, the nip roller  36  may also be used as guide roller  20 .  
         [0057]     Referring to  FIG. 22A , and in the preferred embodiment depicted therein, it will be seen that nip roller  36  is comprised of an outer annular wall and an inner annular wall  122 . In one embodiment, not shown, there are no orifices or no spaces between the outer annular wall  120  and the inner annular wall  122 . In the embodiment depicted in  FIG. 22A , cutout portions  124  and  126  have been removed from the roller  36 .  
         [0058]     In the preferred embodiment depicted, nip roller  36  is comprised of outer wall  120  that is relatively hard, with a Shore hardness of at least 60. With this embodiment, it is preferred that the drive roller  34  have an elastomeric outer surface  90  that is compressible and preferably has a hardness of less than 60. It is preferred that the Shore hardness of outer wall  120  be at least 30 Shore hardness units greater than the Shore hardness of elastomeric outer surface  90 .  
         [0059]      FIG. 22B  is an end view of the preferred nip roller  36 .  
         [0060]     It is to be understood that the aforementioned description is illustrative only and that changes can be made in the apparatus, in the ingredients and their proportions, and in the sequence of combinations and process steps, as well as in other aspects of the invention discussed herein, without departing from the scope of the invention as defined in the following claims.