Patent Publication Number: US-2009238627-A1

Title: Ribbon cassette and printer using the ribbon cassette

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims the benefit of priority from and is a Continuation of application Ser. No. 11/468,873 filed on Aug. 31, 2006, the entire contents of which are incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a ribbon cassette furnished with an ink replenishing function for an ink ribbon and a printer using the ribbon cassette. 
     2. Description of the Related Art 
     A wire dot method has been used widely as a method of printing arbitrary characters and figures on a medium subject to printing, such as a sheet of paper. According to the wire dot method, the medium subject to printing is disposed in a space between the print head and the platen. An ink ribbon impregnated with ink is also disposed in a space between the print head and the print medium. In performing the printing, a wire called a needle is activated to protrude from the print head while a carrier onto which is mounted the print head is moved along the platen, so that dot-shaped printing is performed on the print medium by causing the tip end of the needle to collide on the surface of the print medium via the ink ribbon. 
     The ink ribbon is of an endless shape and it forms a ribbon cassette by being accommodated in a case provided with an ink replenishing mechanism. The ribbon cassette is mounted on the carrier together with the print head, and disposed for part of the endless ink ribbon to oppose the print head. It is configured in such a manner that the endless ink ribbon is circulated to move in the length direction in association with the movements of the carrier for a new ink ribbon surface to oppose the print head. 
     The invention related to such a ribbon cassette is disclosed, for example, in JP-UM-A-6-42197, JP-A-5-16506, and so forth. 
       FIG. 1  shows the outward appearance of such a ribbon cassette  10 , and components thereof are, as is shown in  FIG. 2 , accommodated in a lower portion case  11  having an open top surface. The lower portion case  11  has a main body portion  11   a  and a pair of arm portions  11   b  and  11   c  that respectively extend substantially in the shape of a circular arc from the both ends of one side of the case main body  11   a . A space between the tip ends of this pair of arm portions  11   b  and  11   c  defines a print portion  10   a  (shown in  FIG. 1 ) opposing an unillustrated print head. The pair of arm portions  11   b  and  11   a  therefore functions as inbound and outbound paths for an endless ink ribbon  12  to be circulated to move with respect to the print portion  10   a . In addition, a driving mechanism  13  that feeds the endless ink ribbon  12  in the length direction to be circulated to move in association with movements of the carrier, and an ink replenishing mechanism  14  for the ink ribbon  12  are provided within the case main body  11   a . The ink replenishing mechanism  14  replenishes a post-printing portion of the ink ribbon  12  having returned from the print portion  10   a  by passing through the arm portion  11   c  (the outbound path in circulation movements) through circulation movements of the ink ribbon  12  by the feeding operation of the driving mechanism  13  with ink. 
     The driving mechanism  13  has a driving roller  13   a  and a driven roller  13   b  that together nip the ink ribbon  12 . The driving roller  13   a  rotates in a clockwise direction in the drawing in association with movements of the carrier to feed the ink ribbon  12  to the left in the drawing. The ink replenishing mechanism  14  has a roller-shaped ink tank  15 . The ink tank  15  is shaped like a cylindrical column made of a sponge material or the like impregnated with ink, and is configured to be rotatable about the center of axis. The outer circumferential surface of a transfer roller  16  comes into contact with the outer circumferential surface of the ink tank  15 , and this contact relation allows the ink tank  15  and the transfer roller to rotate in cooperation with each other. Further, a portion of the endless ink ribbon  12  having returned from the print portion  10   a  is stretched over the outer circumference of the transfer roller  16  to come into contact therewith. The transfer roller  16  therefore replenishes the contact portion (post-printing portion) of the ink ribbon  12  with ink by transferring the ink soaked through the ink tank  15 . In this manner, the ink ribbon  12  replenished with ink is temporarily accommodated within a ribbon accommodation portion  17 . Thereafter, the ink ribbon  12  is fed to the print portion  10   a  by passing through one arm portion  11   b  (the inbound path in circulation movements) as the driving roller  13   a  rotates in a clockwise direction in the drawing in association with the movements of the carrier. 
     The ribbon cassette  10  has an upper portion case  18  shown in  FIG. 1  corresponding to the lower potion case  11  to cover the components accommodated in the interior thereof. The upper portion case  18  also has a main body portion  18   a  and a pair of arm portions  18   b  and  18   c  to correspond to the lower portion case  11 . A tank cover portion  18   d  corresponding to the ink tank  15  accommodated inside and a shaft cover portion  18   e  corresponding to the driving roller  13   a  are formed on the top surface of the main body portion  18   a.    
     The driving roller  13   a  is used also to take up (wind up) the slack in the ink ribbon  12 . For example, in a case where the slack occurs in the ink ribbon  12  when the ribbon cassette  10  is attached to the carrier, the slack is taken up by feeding the ribbon  12  in the length direction through manual rotational operations. In short, the driving roller  13   a  serves also as the take-up shaft to take up the slack in the ink ribbon  12 . For this reason, as is shown in  FIG. 1 , an operation knob  19  is provided on the top of the shaft of the driving roller  13   a.    
     The ink tank  15  in the related has a large diameter to increase a capacity (volume) of soaked ink. As is shown in  FIG. 2 , the ink ribbon  12  is therefore disposed to go along the outer circumference of the ink tank  15 , which essentially requires the driving roller  13   a  to be provided near the outer circumference of the ink tank  15 . 
     As is shown in  FIG. 1 , the tank cover portion  18   d  and the shaft cover portion  18   e  provided on the top surface of the upper portion case  18  are in extremely close proximity to each other, and they are substantially made into one unit. This positional relation makes it impossible to operate the operation knob  19  provided on the top of the driving roller  13   a  unless it is provided to protrude above the top surface of tank cover  18   d.  It is thus necessary to secure a space comparable to the height of the operation knob  19  from the top surface above the tank cover  18   d.    
     Generally, many components, such as the printed circuit board, are packaged densely in the interior of the printer into which the ribbon cassette  10  is provided. Securing such a space above the ribbon cassette  10  that moves by being mounted on the carrier is therefore a considerable waste in terms of efficient use of a space. The height in the axial direction may be increased as a countermeasure to increase the capacity of the ink tank  15 . Increasing the height of the ink tank  15  in the axial direction, however, generates a considerable waste of the space for the reason described above, and is therefore almost infeasible in practice. In view of the foregoing, a need to increase the capacity of the ink tank  15  has not been addressed appropriately. 
     In addition, because the ink tank  15  has a large diameter, as is shown in  FIG. 2 , the transfer roller  16  and the driving roller  13   a  have to be spread out to be disposed, respectively, at the lower right and left in the drawing near the outer circumference of the ink tank  15  within a limited space. The ink ribbon  12  therefore passes by the transfer roller  16  from the arm portion  11   c  and is bent by nearly 90 degrees in this portion, after which it reaches the driving roller  13   a.  This configuration extends a distance until the ink ribbon  12  reaches the driving roller  13   a;  moreover, the ink ribbon  12  is bent considerably. When a distance to the driving roller  13   a  is long and the ink ribbon  12  is bent considerably, the slack readily occurs therein, and ribbon jamming resulting from the slack occurs frequently. In addition, the driving roller  13   a  needs a large driving force to move the ink ribbon  12 . Further, an assembling mistake occurs frequently during assembly. 
     Also, in a case where the case  11  is made smaller to reduce the ribbon cassette  10  in size, the position of the driving roller  13   a  in  FIG. 2  shifts upward in the drawing. This requires a reduction of the diameter of the ink tank  15  and an ink capacity is undesirably reduced. In this case, a reduction of an ink capacity (volume) may be prevented by increasing the height of the ink tank  15  in the axis line direction. However, it is infeasible to increase the height of the ink tank  15  due to the relation with the operation knob  19  described above. As a result, a capacity of the ink tank  15  is reduced, which shortens the life of the ribbon cassette  10 . 
     SUMMARY OF THE INVENTION 
     An object of the invention is therefore to provide a ribbon cassette that makes it difficult for the slack in the ink ribbon and ribbon jamming resulting from the slack to occur and makes a large driving quantity unnecessary to move the ink ribbon by making a travel distance of the ink ribbon to the driving roller shorter and linear, and a printer using the ribbon cassette. 
     According to one aspect of the invention, a ribbon cassette includes: an endless ink ribbon; a driving mechanism having a driving roller and a driven roller that together nip the endless ink ribbon and configured to circulate the endless ink ribbon to move to and from a print portion opposing a print head through rotating operations of the rollers; a case having a main body portion accommodating the driving mechanism and a pair of arm portions forming an inbound path and an outbound path of a circulation movement of the ink ribbon with respect to the print portion; a roller-shaped ink tank impregnated with ink and provided inside the main body portion of the case on one of sides divided by a virtual straight line linking an inlet portion of the ink ribbon from the arm portion serving as the outbound path from the print portion and an outer circumferential surface of the driving roller over which the ink ribbon is stretched, and configured to be rotatable about a center of axis in a positional relation that an outer circumferential surface of a cylindrical column is in close proximity to the virtual straight line; and a transfer roller having a shape of a cylindrical column rotatable about a center of axis with an outer circumferential surface thereof coming into contact with an outer circumferential surface of the ink tank on a side closer to the virtual straight line while a portion of the ink ribbon from the arm portion serving as the outbound path to the driving roller being stretched over an outer circumferential surface thereof on an opposite side to a contact portion with the ink tank. 
     Further, according to another aspect of the invention, a printer includes: a ribbon cassette having a driving mechanism configured to nip an endless ink ribbon and circulate the endless ink ribbon to move to and from a print portion opposing a print head through rotating operations, a case having a main body portion accommodating the driving mechanism and a pair of arm portions forming an inbound path and an outbound path of a circulation movement of the ink ribbon with respect to the print portion, a roller-shaped ink tank impregnated with ink and provided inside the main body portion of the case on one of sides divided by a virtual straight line linking an inlet portion of the ink ribbon from the arm portion serving as the outbound path from the print portion and an outer circumferential surface of the driving roller over which the ink ribbon is stretched, and configured to be rotatable about a center of axis in a positional relation that an outer circumferential surface of a cylindrical column is in close proximity to the virtual straight line, and a transfer roller having a shape of a cylindrical column rotatable about a center of axis with an outer circumferential surface thereof coming into contact with an outer circumferential surface of the ink tank on a side closer to the virtual straight line while a portion of the ink ribbon from the arm portion serving as the outbound path to the driving roller being stretched over an outer circumferential surface thereof on an opposite side to a contact portion with the ink tank; a carrier on which the print head is mounted to oppose a platen fixedly disposed along a specific printing direction and to which the ribbon cassette is attached for the print portion thereof to be positioned in a space between the print head and the platen, and configured to enable a reciprocal movement along a length direction of the platen; and a medium feeding mechanism configured to supply a medium subject to printing to a space between the platen and the ink ribbon as well as the print head and move the medium in a direction orthogonal to a moving direction of the carrier in association with a movement of the carrier. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS  
         FIG. 1  is a perspective view used to describe a ribbon cassette in the related art; 
         FIG. 2  is a plan view showing part of the internal configuration of the ribbon cassette in the related art; 
         FIG. 3  is a perspective view showing the outward shape of a ribbon cassette according to a first embodiment of the invention; 
         FIG. 4  is a plan view showing the internal configuration of the ribbon cassette according to the first embodiment of the invention; 
         FIG. 5  is a perspective view showing the outward shape of a printer using the ribbon cassette according to the first embodiment of the invention; and 
         FIG. 6  is a perspective view showing the internal configuration of the printer using the ribbon cassette according to the first embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
     Hereinafter, one embodiment of the invention will be described in detail with reference to the accompanying drawings. 
       FIG. 3  shows the outward appearance of a ribbon cassette  20  according to a first embodiment of the invention, and  FIG. 4  shows the internal configuration thereof. As is shown in  FIG. 4 , the components forming the interior of the ribbon cassette  20  are formed to be disposed in the interior of a lower portion case  21  having an open top surface, and as is shown in  FIG. 3 , the top surface thereof is covered with an upper portion case  28 . These cases  21  and  28  respectively have main body portions  21   a  and  28   a  and a pair of arm portions  21   b  and  21   c  and a pair of arm portions  28   b  and  28   c  that extend substantially in the shape of a circular arc, respectively, from the both ends of the upper sides of the main body portions  21   a  and  28   a  in the drawing. Spaces between the tip ends of these pair of the arm portions  21   b  and  21   c  and pair of arm portions  28   b  and  28   c  define a print portion  20   a  that opposes the print head described below. 
     For application to a printer, as is shown in  FIG. 6 , the ribbon cassette  20  is attached to a carrier  32  on which a print head  31  of the wire dot method is mounted. To be more specific, the ribbon cassette  20  is attached to the carrier  32  in such a manner that the pair of arm portions  21   b  and  21   c  and the pair of arm portions  28   b  and  28   c  surround the print head  31 , and that the print portion  20   a  defined by the space between the tip ends of these pair of arm portions  21   b  and  21   c  and pair of the arm portions  28   b  and  28   c  opposes the portion of the print head  31  from which a wire called a needle protrudes. In the ribbon cassette  20 , an endless ink ribbon  22  accommodated inside and described below is circulated to move to the print portion  20   a.    
     As is shown in  FIG. 6 , the carrier  32  is supported on a guiding rod  34  disposed in the lateral direction in the drawing to be allowed to reciprocate within a lower portion case  33  of the printer. The carrier  32  is driven along the guiding rod  34  by a driving mechanism comprising a pair of pulleys  35  and  36  disposed on the left and right and a timing belt  37  stretched across these pulleys in association with the printing operation described below. In addition, a platen  39  is provided fixedly inside the lower portion case  33  at the position opposing the print head  31  mounted onto the carrier  32 . The platen  39  is formed horizontally long in order to cover the print range of the print head  31  in association with the movements of the carrier  32 . 
     Although it is not shown in the drawing, a roller that supplies a medium subject to printing (a sheet of paper or the like) into a space between the platen  39  and the print head  31  is provided below the platen  39 . This supply roller forms a medium feeding mechanism together with a discharging roller  40  disposed above the platen  39 . 
     As has been described, the print head  31  is mounted on the carrier  32  and opposes the platen  39  fixedly disposed along a specific printing direction. Also, the ribbon cassette  20  is attached to the carrier  32  in such a manner that part of the ink ribbon  22  (portion positioned at the print portion  20   a ) is positioned in a space between the print head  31  and the platen  39 . Further, the medium feeding mechanism having the discharge roller  40  supplies a medium subject to printing in a space between the platen  39  and the ink ribbon  22  as well as the print head  31 , and moves the medium in a direction orthogonal to the moving direction of the carrier in association with the movements of the carrier  32 . 
     As is shown in  FIG. 5 , an upper portion case  42  is provided in an openable and closable manner to correspond to the lower portion case  33  of the printer. Various control components, such as the printed circuit board, used to control the respective portions of the printer are provided inside the upper portion case  42 . In addition, an operation portion  43  is disposed on the top surface of the upper portion case  42  on the front side in the drawing, and it is provided with plural switches  44  used to input various control instructions. Further, an insert portion  46  of a medium subject to printing and a discharge portion  45  of a printed medium are provided on the top surface portion of the upper portion case  42 . 
     A medium, such as a sheet of paper, is fed into a space between the print head  31  and the platen  39  by the medium feeding mechanism. Also, the print portion  20   a  of the ribbon cassette  20  is positioned in a space between the print head  31  and the print medium. A portion of the ink ribbon  22  impregnated with ink is supplied to the print portion  20   a.  In performing the printing, the print head  31  is activated, so that a wire called a needle is activated to protrude. The tip end of the wire activated to protrude collides on the surface of the medium via the ink ribbon  22 . Dot-shaped printing is thus performed on the medium. Arbitrary characters and figures are drawn on the medium by moving the carrier  32  along the platen  39  in association with the operations of the print head  31 . 
     The detailed configuration of the ribbon cassette  20  described above will now be described. Referring to  FIG. 4 , the pair of arm portions  21   b  and  21   c  of the lower portion case  21  functions as inbound and outbound paths for the endless ink ribbon  22  to be circulated to move with respect to the print portion  20   a.  A driving mechanism  23  that feeds the endless ink ribbon  22  in the length direction for circulation movements in association with the movements of the carrier  32  and an ink replenishing mechanism  24  for the ink ribbon  22  are provided inside the main body portion  21   a  of the lower portion case  21 . The ink replenishing mechanism  24  replenishes the post-printing portion of the ink ribbon  22  having returned from the print portion  20   a  by passing through the arm portion  21   c  (the outbound path) through the feeding operation of the driving mechanism  23  with ink. 
     The ink ribbon  22  is of an endless shape, and the length thereof is sufficiently longer than the length of the circulation path of the ribbon comprising the case main body portion  21   a  and the pair of arm portions  21   b  and  21   c . Most of the ink ribbon  22  is therefore accommodated in a folded state within a ribbon accommodation chamber  27  defined by a partition wall  21   d  inside the case main body  21   a  as is shown in the drawing. 
     The ink replenishing mechanism  24  has a roller-shaped ink tank  25 . The ink tank  25  is shaped like a cylindrical column made of a sponge material or the like impregnated with ink, and it is formed to be rotatable in the shape of a roller. It is preferable for the ink tank  25  to have a larger ink capacity, and there has been a need to increase the volume thereof. To address this need, the ink capacity is increased in this embodiment not by increasing the diameter of the cylindrical column as in the related art, but by increasing the height in the axial direction to increase the volume. 
     The ink tank  25  is provided in a rotatable manner inside the lower portion case  21  in an upper right portion of  FIG. 4 , that is, in a portion in close proximity to the outbound path of the ink ribbon  22  from the print portion  20   a  near the root of the arm portion  21   c.  A transfer roller  26  is provided in a rotatable manner on the right side of the ink tank  25  in the drawing. The outer circumferential surface thereof comes into contact with the outer circumferential surface of the ink tank  25 . In the outer circumferential portion of the transfer roller  26  on the right in the drawing, the ink ribbon  22  is guided by guiding members  47  and  48  disposed above and below the ink ribbon  22  to come into contact with the transfer roller  26 . The contact portion (post-printing portion) of the ink ribbon  22  is thus replenished with ink soaked through the ink tank  25  by being transferred by the transfer roller  26 . The inner circumference  26   a  of the axial core portion of the transfer roller  26  is loosely fit in a supporting shaft  21   e  on the case side. The center of rotation of the transfer roller  26  is therefore allowed to undergo displacement in the horizontal direction in the drawing, and it is configured in such a manner so as to change a contact pressure against the ink tank  25 . 
     The driving mechanism  23  has a driving roller  23   a  and a driven roller  23   b  that together nip the ink ribbon  22 . The driving roller  23   a  is configured to rotate in a clockwise direction in the drawing in association with the movements of the carrier  32 , and feeds the ink ribbon  22  into the ribbon accommodation chamber  27  on the left in the drawing through these clockwise rotations. 
     The driving roller  23   a  is disposed below the ink tank  25  and the portion of the ink ribbon  22  coming into contact with the transfer roller  26  is stretched over the driving roller  23   a,  and thereby feeds the ink ribbon  22  replenished with ink into the ribbon accommodation chamber  27  through the clockwise rotations in the drawing together with the driven roller  23   b.  Also, the driving roller  23   a  is disposed with a sufficient distance from the outer circumferential surface of the ink tank  25 . 
     As is shown in  FIG. 3 , the upper portion case  28  is provided to correspond to the lower portion case  21  that accommodates the respective components to cover these components accommodated inside. As has been described, the upper portion case  28  also has the main body portion  28   a  and the pair of arm portions  28   b  and  28   c  to correspond to the lower portion case  21 . A tank cover portion  28   d  corresponding to the ink tank  25  packaged inside is formed on the top surface of the main body portion  28   a.    
     The driving roller  23   a  is used also as a take-up shaft that takes up the slack occurred in the ink ribbon  22 . For this reason, as is shown in  FIG. 3 , an operation knob  29  is provided on the top of the shaft of the driving roller  23   a.  The operation knob  29  is provided to stand upright on the top surface of the main body portion  28   a  of the upper portion case  28  to enable rotational operations. 
     As has been described, because the driving roller  23   a  is disposed with a sufficient distance from the outer circumferential surface of the ink tank  25 , the operation knob  29  is naturally positioned with a sufficient distance from the outer circumferential surface of the tank cover portion  28   d.  Hence, unlike the related art, there is no need to provide the operation knob  29  to be higher than the top surface of the tank cover portion  28   d,  and even when it is provided to stand upright on the top surface of the case main body  28   a  as is shown in  FIG. 3 , it is possible to hold and operates the operation knob  29  by rotation. 
     The positional relation among the ink ribbon  22 , the driving roller  23   a,  the ink tank  25 , and the transfer roller  26  inside the case main body portion  21   a  will now be described in detail. 
     Initially, a virtual straight line (indicated by a broken line in the drawing) that links an inlet portion (in  FIG. 4 , the outer circumferential surface of the guiding member  47  on the left in the drawing) of the ink ribbon  22  from the arm portion  21   c  (the outbound path) and the outer circumferential surface of the driving roller  23   a  on the right in the drawing over which the ink ribbon  22  is stretched is drawn inside the case main body portion  21   a.  The roller-shaped ink tank  25  impregnated with ink is provided on one of the sides (left in the drawing) divided to the left and the right by the virtual straight line, and the outer circumferential surface of the cylindrical column is disposed in a positional relation in proximity to the virtual straight line as is shown in the drawing. Also, the ink tank  25  is configured to be rotatable about the center of axis. 
     The transfer roller  26  is also configured in the shape of a cylindrical column rotatable about the center of axis. The outer circumferential surface thereof comes into contact with the outer circumferential surface of the ink tank  25  on the side in close proximity to the virtual straight line. Also, a portion of the ink ribbon  22  from the arm portion  21   c  to the driving roller  23   a  is stretched over the outer circumferential surface of the transfer roller  26  on the side (on the right in the drawing) opposite to the contact portion with the ink tank  25 . 
     When configured in this manner, the length of the ink ribbon  22  from the inlet portion  47  to the driving roller  23   a  becomes shorter markedly than the one in the related art that is routed to go along the outer circumference of the ink tank. In addition, the ink ribbon  22  in this portion is almost linear, and is never bent considerably by nearly 90 degrees in the transfer roller portion as was the case in the related art. Because a distance to the driving roller  23   a  is short and the ink ribbon  22  is almost linear as described above, the slack hardly occurs therein, which in turn makes it possible to prevent the occurrence of ribbon jamming resulting from the slack effectively. The driving roller  23   a  is able to move the ink ribbon  22  with a relatively small driving force. Further, an assembling mistake during the assembly hardly occurs. Because the tank cover portion  28   d  of the ink tank  25  is disposed spaced apart from the operation knob  29 , it is possible to secure a sufficient height of the ink tank  25  in the axis line direction without being affected by the presence of the knob as was the case in the related art. Even when the diameter of the ink tank  25  is made smaller to make the ribbon cassette  20  more compact, a sufficient volume can be secured. An ink capacity of the ink tank  25  therefore will never be reduced as was the case in the related art. 
     In the configuration described above, as is shown in  FIG. 6 , the ribbon cassette  20  shown in  FIG. 3  is attached onto the carrier  32  on which the print head  31  is mounted. Print information is inputted into the printer shown in  FIG. 5  and  FIG. 6  from an unillustrated outside information device. Upon input of the print information, the printer activates the medium feeding mechanism, the carrier driving mechanism, and the print head described above by the control portion, such as the printed circuit board, to print desired characters and figures on a medium subject to printing. 
     More specifically, the medium, such as a sheet of paper, is fed into a space between the print head  31  and the platen  39  by the medium feeding mechanism provided with the discharge roller  40  for a portion subject to printing to oppose the print head  31 . The print head  31  activates the wire called the needle to protrude toward the platen  39  according to the print information, and causes the tip end thereof to collide on the medium via the ink ribbon  22  of the ribbon cassette  20  positioned at the print portion  20   a.  Dot-shaped printing is thus performed on the medium. Also, characters and figures according to the print information are printed on the medium as the carrier  32  moves in association with the operations of the print head  31 . 
     During the printing operation, because the driving roller  23   a  rotates in a clockwise direction in the drawing in association with the movements of the carrier  32  in the ribbon cassette  20 , the endless ink ribbon  22  is circulated to move in a clockwise direction in the drawing along the length direction. A portion of the ink ribbon  22  used for printing in the print portion  20   a  (a portion from which ink has been transferred onto the medium) is fed to the ink replenishing mechanism  24  by passing through the arm portion  21   c  (the outbound path) shown in  FIG. 4 . Also, a portion of the ink ribbon  22  that has not been used for printing is fed to the print portion  20   a  by passing through the arm portion  21   b  (the inbound path) to prepare for the following printing. 
     Herein, because a tensile force is applied onto the endless ink ribbon  22  by the rotations of the driving roller  23   a,  the center of rotation of the transfer roller  26  is shifted to the left in the drawing by this tensile force, and the transfer roller  26  is pressed against the outer circumferential surface of the ink tank  25 . Ink soaked through the ink tank  25  thus adheres onto the ink ribbon  22  that comes into contact with the outer circumferential surface of the transfer roller  26  to replenish the printed portion with ink via the transfer roller  26 . In other words, in a normal state, the transfer roller  26  merely comes into contact with the outer circumference of the ink tank  25 , and does not replenish the ink ribbon  22  with ink. On the contrary, when the ink ribbon  22  is fed, the transfer roller  26  is pressed against the outer circumferential surface of the ink tank  25  by the tensile force of the ink ribbon  22  and replenishes the ink ribbon  22  with ink. 
     In short, the ink ribbon  22  is replenished with ink only when the ink ribbon  22  is circulated to move in association with the printing operation, and it is not replenished with ink in any other time. It is thus possible to prevent the ink ribbon  22  from being replenished with ink excessively. In addition, because a time for being pressed against the ink tank  25  is shorter than a case where it is kept pressed against the ink tank  25  constantly, it is possible to extend a time until the ink tank  25  undergoes deformation. A satisfactory printing state can be therefore maintained. 
     As has been described, during the printing operation, the endless ink ribbon  22  is circulated to move by rotations of the driving roller  23   a,  so that the portion of the ink ribbon  22  impregnated with ink is circulated to be supplied to the print portion  20   a  by passing through the inbound path. Also, the post-printing portion is fed back to the ink replenishing mechanism  24  by passing through the outbound path, and is fed into the ribbon accommodation portion  27  after it is replenished with ink. In this case, as has been described, a distance from the outbound path from the print portion  20   a  of the ink ribbon  22  to the driving roller  23   a  is short and this portion is almost linear, the slack hardly occurs in the ink ribbon  22 , which can in turn prevent ribbon jamming resulting from the slack. Also, a driving force of the driving roller  23   a  can be relatively small. Further, a reduction of the ribbon cassette  20  in size can be addressed without reducing a capacity of the ink tank  25 . 
     While the ink ribbon  22  is used over a long period, the texture is raveled. When it is used continuously in this condition, the texture is frayed, which gives rise to jamming. This may possibly impair the pin in the print head  31 . In this embodiment, however, it is possible to forestall the occurrence of such jamming. 
     More specifically, in this embodiment, a tensile force is conferred to the ink ribbon  22  by rotations of the driving roller  23   a  during the printing operation to allow the center of rotation of the transfer roller  26  to undergo displacement, so that the transfer roller  26  is pressed against the outer circumferential surface of the ink tank  25  for the ink soaked through the ink tank  25  to be transferred. However, in general, the tension of the texture becomes weak when the texture of the ink ribbon  22  starts raveling. In this case, a force induced by the tensile force of the ink ribbon  22  to press the transfer roller  26  against the outer circumferential surface of the ink tank  25  decreases, and a quantity of ink replenished to the ink ribbon  22  becomes smaller. Hence, the user is notified that printing is becoming lighter and the ink ribbon  22  has started raveling, and is requested to replace the ribbon. In other words, because the user is requested to replace the ribbon at the stage when the texture of the ink ribbon  22  starts raveling before it is frayed, it is possible to prevent the occurrence of jamming and damages to the pin in the print head  31  caused by the jamming. 
     The ink tank  25  is formed in the shape of a cylindrical column made of a sponge material or the like impregnated with ink. As has been described, the transfer roller  26  is pressed against the outer circumferential surface in association with the movements of the carrier  32 . Hence, the outer circumferential surface of the ink tank  25  undergoes concave deformation at the portion against which the transfer roller  26  is pressed. When the printing is not performed, the driving roller  23   a  is not rotating, and a tensile force to the ink ribbon  22  is released. The ink tank  25  thus pushes back the transfer roller  26  with its elasticity, and restores to its original shape. However, with the use over a long period, it does not restore to the original shape even when a tensile force to the ink ribbon  22  is released, and the concave deformation is fixed on the outer circumferential surface of the ink tank  25 . When the concave is fixed as has been described, a trouble may possibly occur in the following ink replenishing function. 
     Hence, the ink tank  25  is replaced with a new one when a concave occurs to always use the one in which deformation taking place on the outer circumferential surface at the contact portion with the transfer roller will not be fixed, so that the ink tank  25  is able to restore elastically to the original shape when released from a pressing force.