Patent Publication Number: US-6910656-B2

Title: Ink ribbon cartridge with leaf spring and method of assembling the same

Description:
FIELD OF THE INVENTION 
   The invention relates generally to an ink ribbon cartridge such as may be used in a thermal printer and to a method of assembling the same, and in particular to an ink ribbon cartridge that has a leaf spring for biasing an ink ribbon spool axially to deter accidental rotation of the spool in the cartridge. 
   BACKGROUND OF THE INVENTION 
   Ink ribbon cartridges for a thermal printer are well known. Typically, the ink ribbon cartridge includes an ink ribbon supply spool and an ink ribbon take-up spool that are rotationally supported parallel to one another in a cartridge housing. The ink ribbon has a repeating series of three different color sections or patches such as a yellow color patch, a magenta color patch, and a cyan color patch. Also, there may be a transparent colorless laminating section or patch immediately after each cyan color patch. 
   Often, a compression-type spring is interposed between an inner wall at one side of the cartridge housing and one hub end of each spool. The spring urges a spool in one direction along the rotation axis of the spool, to force the opposite hub end of the spool against an inner wall at another side of the cartridge housing. This is done to prevent the spool from being rotated accidentally, such as might occur when the cartridge is jarred, which could cause the ink ribbon to partially unwind from the spool and slacken. 
   During cartridge assembly in prior art U.S. Pat. No. 4,883,234 issued Nov. 28, 1989 a u-shaped leaf spring is rotationally engaged with one hub end of a spool. The spool, engaged with the leaf spring, is inserted laterally into a housing-half to position the leaf spring against an inner wall at one side of the housing-half. The leaf spring then urges the opposite hub end of the spool against an inner wall at another side of the housing-half. 
   During cartridge assembly in prior art U.S. Pat. No. 5,110,228 issued May 5, 1992 a spool is inserted laterally into a housing-half to position one hub end of the spool against a resilient member projecting integrally from an inner wall at one side of the housing-half. The resilient member urges an opposite end of the spool against a rotation stopper on an inner wall at another side of the housing-half. 
   SUMMARY OF THE INVENTION 
   According to one aspect of the invention, an ink ribbon cartridge comprising an ink ribbon spool having opposite hub ends and a rotation axis, a housing-half into which the spool is inserted laterally relative to the rotation axis during cartridge assembly, and a leaf spring that presses against one of the hub ends of said spool to urge the spool in one direction along the rotation axis in the housing-half, is characterized in that: 
   the leaf spring has a mounting frame and a flat spring finger that longitudinally extends from the mounting frame, beginning at an opening in the mounting frame, and at an acute angle from the opening, in order to be depressed at least partially into the opening by the one hub end when the spool is laterally inserted into the housing-half, whereby the spring finger will urge the spool in one direction along the rotation axis. 
   According to another aspect of the invention, a method of assembling an ink ribbon cartridge comprises: 
   inserting a leaf spring having a mounting frame and a flat spring finger that longitudinally extends from the mounting frame, beginning at an opening in the mounting frame, and at an acute angle from the opening, into a housing-half to position the spring finger pointing at the acute angle into the housing-half; and 
   inserting an ink ribbon spool having opposite hub ends and a rotation axis into the housing-half, laterally relative to the rotation axis, to cause one of the hub ends to depress the spring finger at least partially into the opening, whereby the spring finger will urge the spool in one direction along the rotation axis. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is an exploded perspective view of an ink ribbon cartridge with a leaf spring according to a preferred embodiment of the invention; and 
       FIG. 2  is an enlarged perspective view of the leaf spring. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   Because the features of an ink ribbon cartridge such as may be used in a thermal printer are generally known, the description which follows is directed in particular only to those elements forming part of or cooperating with the invention. It is to be understood, however, that other elements not disclosed may take various forms known to persons of ordinary skill in the art. 
     FIG. 1  shows an ink ribbon cartridge  10  having a (plastic) cartridge shell or housing  12  that comprises a housing-half  14 , which includes parallel semi-cylindrical chambers  16  and  18 , and also respective semi-cylindrical covers  20  and  22  for the two chambers. An ink ribbon supply (plastic) spool  24  having opposite hub ends  26  and  28  and an axis of rotation  30  resides in the chamber  16 , and an ink ribbon take-up (plastic) spool  32  having opposite hub ends  34  and  36  and an axis of rotation  38  resides in the chamber  18 . The ink ribbon supply and take-up spool  24  and  32  are essentially identical, and are intended to be unwindingly and windingingly rotated in the same direction, i.e. clockwise in  FIG. 1 , to advance an ink ribbon (not shown) from one spool to the other spool and over an intermediate ribbon tensioning (stainless steel) shaft  40  proximate the chamber  18 . The ink ribbon has a repeating series of three different color sections or patches such as a yellow color patch, a magenta color patch, and a cyan color patch. Also, there may be a transparent colorless laminating section or patch immediately after each cyan color patch. 
   As shown in  FIGS. 1 and 2 , two leaf springs  42  and  44  are identical and each one comprises a rectangular-shape thin mounting frame  46  that has a similar shape opening  48  and a flat spring finger  50 . Each one of the mounting frames  46 ,  46  of the leaf springs  42  and  44  is divided into a major-size portion  52  and a minor-size portion  54  which is slightly bent from the major portion at creases  56  and  58 . The spring fingers  50 ,  50  longitudinally extend from the minor portions  54 ,  54 , beginning at the openings  48 ,  48 , and at acute angles  60 ,  60  from the openings, and they taper away from the minor portions. The acute angles  60 ,  60  are less than 45°, and preferably are 12.4°. 
   The mounting frames  46 ,  46  of the leaf springs  42  and  44  are intended to be supported erect in the housing-half  14  as shown in  FIG. 1 , with the spring fingers  50 ,  50  pointing at the acute angles  60 ,  60  into the housing-half. Two hooks  62 ,  62  on the housing-half  14 , proximate the chambers  16  and  18 , project into the openings  48 ,  48  of the mounting frames  46 ,  46  to engage the major portions  52 ,  52  of the mounting frames in order to secure the mounting frames in the housing-half. See FIG.  2 . 
   The hub ends  26  and  34  of the ink ribbon supply and take-up spools  24  and  32  depress the spring fingers  50 ,  50  at least partially into the openings  48 ,  48  of the frames  46 ,  46  when the spools are in the chambers  16  and  18 . As a result, the spools  24  and  32  are urged by the spring fingers  50 ,  50  in one direction along their axes of rotation  30  and  38 , i.e. generally to the right in FIG.  1 . Respective ribs (not shown) on the housing-half  14 , project into the chambers  16  and  18  to engage toothed flanges  64  and  66  of the spools  24  and  32  to prevent accidental rotation of the spools. To rotate the spools  24  and  32 , they must first be slightly pushed to the left in  FIG. 1  at their hub ends  28  and  36  to disengage the flanges  58  and  60  from the ribs. 
   Assembly Method 
   The leaf springs  42  and  44  and the ink ribbon supply and take-up spools  24  and  32  are assembled in the housing-half  14  as follows. 
   The leaf springs  42  and  44  are manually inserted into the housing-half  14  as shown in  FIG. 1  by being manually pushed down at push tabs  68 ,  68  on the minor portions  54 ,  54  of the mounting frames  46 ,  46 . See FIG.  2 . The mounting frames  46 ,  46  are flexed over ramp-like surfaces  70 ,  70  of the hooks  62 ,  62  on the housing-half  14  and come to rest with the hooks projecting into the openings  48 ,  48  of the mounting frames. The major portions  52 ,  52  of the mounting frames  46 ,  46  have notches  72 ,  72  that receive projections  74 ,  74  on the housing-half  14  to ensure one-way insertion of the leaf springs  42  and  44  into the housing-half. See  FIGS. 1 and 2 . 
   The ink supply and take-up spools  24  and  32  are inserted laterally relative to their axes of rotation  30  and  38  into the chambers  16  and  18  as shown in  FIG. 1 , which causes their hub ends  26  and  34  to depress the spring fingers  50 ,  50  at least partially into the openings  48 ,  48  of the mounting frames  46 ,  46 . 
   The invention has been described in detail with particular reference to certain preferred embodiments thereof, but it will be understood that variations and modifications can be effected within the spirit and scope of the invention.