Patent Publication Number: US-6989850-B2

Title: Thermal printer apparatus

Description:
REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of provisional application Ser. No. 60/436,278, filed Dec. 23, 2002. 
     This application is related to commonly assigned U.S. patent application Ser. No. 10/743,235, filed on even date herewith the entire disclosure of which is hereby incorporated by reference herein. 
    
    
     TECHNICAL FIELD 
     The present invention relates to thermal print head assemblies in which a platen roller is moveably mounted for pressuring print media against a fixedly mounted print head. 
     BACKGROUND OF THE INVENTION 
     Modern thermal print heads have achieved levels of resolution based upon integrated circuit construction techniques which can locate a great number of individual heating elements in close proximity to each other. This advantage of resolution creates a limitation on the total span of the print head due to the possibility of faults occurring in the semiconductor, both in the manufacturing process and later in the printing application. Larger print spans have been achieved by aligning two or more smaller print heads to achieve the wider span. Also, due to the resolution achieved, relatively small misalignment between such multiple print heads are easily noticed in the resulting printed product. Even misalignments of as little as one pixel can be visually determined. 
     The construction and accuracy of multiple thermal print head alignment is further challenged by the need to substantial squeeze the print media against the thermal print head to provide good thermal conductivity. 
     SUMMARY OF THE INVENTION 
     The present invention relates to a thermal printer apparatus, including one or more thermal print heads fixedly mounted with respect to a print media path, one or more platen roller assemblies each including a platen roller adapted to press print media in the print media path against at least one of the print heads and a frame adapted to support a respective platen roller, and a pivotally mounted support member adapted for mounting the platen roller assembly frames to extend from the support member and press its respective platen roller against the thermal print heads. 
     The support member may be adapted to pivot with respect to an imaginary plane defined by the platen rollers mounted to the support member. The platen rollers may include a rotational axis, and the support member may be adapted to pivot in an imaginary plane defined by all of the axes of the platen rollers. Alternatively, the support member may be adapted to pivot the platen rollers in an arc while the platen assembly frames remain tangential to the arc. 
     The apparatus may further include a plurality of parallel platen roller assemblies, wherein the platen rollers of the plurality of platen roller assemblies define an imaginary plane, and further wherein the frame is adapted to pivot with respect to the imaginary plane. The apparatus may also include one or more second thermal print heads fixedly mounted with respect to the print media path, wherein the second thermal print heads are located in close proximity to the first thermal print heads. 
     The apparatus may further include one or more second platen roller assemblies each including a platen roller adapted to press print media in the print media path against at least one of the second thermal print heads and a frame adapted to support a respective platen roller, and a pivotally mounted second support member adapted for mounting the second platen roller assembly frames to extend from the second support member and press its respective platen roller against the second thermal print heads. The first and second thermal print heads may be fixedly mounted with respect to the print media path by a unified structure. The first thermal print heads may be fixedly mounted to print from one side of the print media path, and the second thermal print heads may be fixedly mounted to print from an opposing side of the print media path. The first thermal print heads may be mounted on a first subframe section and the second thermal print heads may be mounted on a second subframe section, and the first platen roller assemblies may be adapted to extend through the second subframe section to contact the first thermal print heads and the second platen roller assemblies may be adapted to extend through the first subframe section to contact the second thermal print heads. 
     These variations better enable the use of fixed thermal print heads while providing a convenient and effective apparatus. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       For a better understanding of the invention as well as other objects and further features thereof, reference is made to the following detailed description of various preferred embodiments thereof taken in conjunction with the accompanying drawings wherein: 
         FIG. 1  is a perspective view of one side of a thermal print head assembly according to the invention; 
         FIG. 2  is a perspective view of the other side of the assembly of  FIG. 1 ; 
         FIG. 3  is a perspective view of a portion of the assembly of  FIGS. 1 and 2  in combination with an additional printer component; 
         FIG. 4  is a perspective view of a thermal printer apparatus which includes the components described in reference to  FIGS. 1–3 ; 
         FIG. 5  is another perspective view of the apparatus of  FIG. 4 ; and 
         FIG. 6  is a side view of some of the components of  FIG. 3 . 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       FIG. 1  shows a thermal print head assembly  10  generally including a plurality of elongated thermal print heads  12  and  14  and a frame  16 . Frame  16  mounts print heads  12  and  14  to print across a print media path  18  with print heads  12  and  14  being oriented in parallel and orthogonally to the direction of print media movement indicated by arrows  20 . 
     Frame  16  is provided in two complementary sections  16   a ,  16   b  with section  16   a  mounting print heads  12  and  14  and section  16   b  mounting an additional plurality of print heads  22  and  24 . For the purpose of this disclosure, print heads  12 ,  14 ,  22  and  24  necessarily include a semiconductor portion,  22   a  and  24   a  shown for print heads  22  and  24  and a holder portion,  12   b  and  14   b  shown for print heads  12  and  14 . The semiconductor portions are the printing side of the print heads and include hundreds of semiconductor heating elements formed per linear inch of the elongated semiconductor elements.  FIG. 2  shows the opposite side of assembly  10  and the respective opposite sides of print heads  12 ,  22 ,  14  and  24 . 
     By this arrangement frame  16   a  positions print heads  12  and  14  to print across substantially different lateral portions of print media path  18 . Each of the thermal print heads is positioned to print at a different sequential location along print media path  18  in the direction  20 . Print heads  12  and  14  and  22  and  24  are shown to be elongated with an identifiable print length and frame  16  positions print heads  12 ,  14 ,  22  and  24  across the width of print media path  18 , which width is substantially equal to the total of the printing lengths of either plurality of print heads  12  and  14  or  22  and  24 . 
       FIG. 3  shows frame section  16   b  of assembly  10  ( FIG. 1 ) in combination with a pair of platen roller assemblies  32  and  34  being mounted on a support member  36 . Each platen roller assembly  32  and  34  includes a platen roller  32   a ,  34   a  and a mounting frame  32   b ,  34   b , respectively. Platen rollers  32   a  and  34   a  are aligned with the semiconductor surfaces  22   a  and  24   a  of respective print heads  22  and  24  ( FIGS. 1 and 2 ) in a position for biasing print media located there between against the respective print heads  22  and  24 . Platen rollers  32   a  and  34   a  are approximately as long as, or only slightly longer than, the printing length of print heads  22  and  24 , and platen rollers  32   a  and  34   a  are further each spring biased from their respective mounting frames  32   b ,  34   b  for allowing rollers  32   a ,  34   a  to conform as necessary to their respective print heads  22 ,  24 . Frame section  16   a  is not present in  FIG. 3  for purposes of clarity in showing the interaction between print heads  22  and  24  and platen roller assemblies  32  and  34 . 
     Platen roller assemblies  32  and  34  can each be a platen roller assembly such as is disclosed and claimed in commonly assigned U.S. patent application Ser. No. 10/743,235, filed on even date herewith, the entire disclosure of which is hereby incorporated by reference herein. 
     Whereas, existing thermal printers mount multiple print heads along a single platen roller, the present application of individual platen rollers to each separate print head provides a better interface function between the platen roller and print head to control thermal contact between print media and the print heads. 
     This fixed attachment of print heads uses a unique apparatus for engaging the respective platen rollers with the print heads.  FIG. 4  shows a thermal printer apparatus  38  including frame  16 , support member  36  and platen roller assemblies  32  and  34 . Also shown is a separate support member  40  which mounts platen roller assemblies  42  and  44  to interface with print heads  12  and  14 , respectively, on frame section  16   a . Each of the separate support members  36  and  40  is pivotally mounted at respective locations  46  and  48  by a pair of orthogonal, or “L” shaped, support member extensions  47  and  49 , respectively. These orthogonal support member extensions  47  and  49  cause the their respective support members  36  and  40  to rotate around respective axes at pivot points  46  and  48 , which axes lie in the same imaginary planes as the axis of rotation the platen rollers mounted from the respective support member. 
     It can be seen that the pivotally mounted platen roller support allows for a simple loading mechanism when a plurality of platen rollers are loaded simultaneously and sequentially to prevent media “bagging” and/or “wrinkling”. It will be appreciated by those skilled in the art that the respective platen rollers contact the media sequentially because the respective platen rollers are located at different distances from the pivot point. 
     The platen rollers and the print heads can be arranged substantially in line with one another or in overlapping arrangement across the print media path. Further, the print heads can be located on one side or both sides of the media. 
       FIG. 5  shows a perspective view wherein support members  36  and  40  are pivoted into position to make contact between the respective print heads and platen rollers. It demonstrates how platen roller assembly  34  extends through frame section  16   a  to the thermal printer head  24  ( FIGS. 1–3 ) mounted on frame section  16   b . Platen rollers  42 ,  44 ,  32  and  34  are positioned on their respective support members  40 ,  36  interfacing with alignment with their respective print heads  12 ,  14 ,  22  and  24 . In order to adequately perform this alignment, support members  36 ,  40  rotate platen roller assemblies  32 ,  34 ,  42  and  44  to extend through opposite respective frame sections  16   a  and  16   b  and interface with the thermal print heads  22 ,  24 ,  12 ,  14 , respectively. 
       FIG. 6  shows a side view of support member  36  and roller assemblies  32  and  34 . The orthogonal extensions  47  and  49  cause their respective support members  36  and  40  to rotate about pivot points  46  and  48 , respectively, which are aligned in the imaginary plane  50  defined by respective platen rollers  32   a ,  34   a ,  42   a  and  44   a . In this manner, platen rollers  32   a ,  34   a ,  42   a  and  44   a  each defines a rotational arc ( 52  for platen roller  34   a ) and the respective platen roller frames ( 34   b ) are maintained at a tangent ( 54 ) to each arc. This enables platen roller assemblies  32 ,  34 ,  42  and  44  to pass through their respectively opposite frame sections  16   a  and  16   b  in alignment with the respective print heads  22 ,  24 ,  12  and  14 , without interfering with any portions of the respective opposite frame member  16   a ,  16   b.    
     The arrangement of pivot points  46  and  48  being substantially located in an imaginary plane defined by the axes of the respective platen rollers, has an added benefit of providing sequential loading of the print media as the platen rollers are moved into the printing position of  FIG. 5  by their respective support members  36  and  40 . Specifically, as support member  36  ( FIG. 6 ) is moved into the printing position of  FIG. 5 , platen roller  32   a  makes contact with the print media prior to platen roller  34   a . This sequential loading of the print media reduces print media tensioning problems which can occur. 
     Although  FIGS. 4 and 5  show different pivot points  46  and  48  for support members  36 ,  40 , the benefits of the present arrangement may be derived by using the same pivot point for both support members  36 ,  40 . In this refinement, the rotational axis of support members  36 ,  40  is very closely aligned with the imaginary plane  50  defined by the platen rollers and thus provides the benefits described above in a simplified structure. 
     Thus, platen roller assemblies  32 ,  34 ,  42  and  44  may be readily removed from frame  16  to allow the loading of print media  56  through the print media path of frame  16  and to further readily enable any maintenance and cleaning of the print heads. 
     Although the invention has been described in detail with respect to various preferred embodiments thereof, it will be recognized by those skilled in the art that the invention is not limited thereto but rather that variations and modifications can be made therein which are within the spirit of the invention and the scope of the amended claims.