Patent Publication Number: US-10787000-B2

Title: Thermal printhead having asymmetric recording elements

Description:
BACKGROUND 
     Thermal print heads are typically used to print images to substrates by heating portions of a thermal print ribbon having a transferable print consumable, such as colored dye, black resin, or other print consumable. The thermal print head includes a row of print elements. Each print element is configured to heat a pixel-sized portion of the print ribbon to transfer a corresponding image pixel of the print consumable to the substrate. 
     SUMMARY 
     Embodiments of the present disclosure are directed to an asymmetric thermal print head, a method of printing an image on a substrate using the asymmetric thermal print head, and a credential production device that includes the asymmetric thermal print head. Some embodiments of the asymmetric thermal print head include a print head body and a plurality of print elements supported on the print head body. The print elements are aligned along a first axis. Each print element includes a heater portion having a burn width measured along the first axis corresponding to a first print resolution, and a burn length measured along a second axis, which is perpendicular to the first axis, corresponding to a second print resolution. The second print resolution is higher than the first print resolution. One or more control circuits are configured to individually activate the print elements. 
     In some embodiments of the method, an image line is printed on a surface of the substrate by printing a plurality of pixels using the asymmetric print head. Each of the pixels has a pixel width measured along a first axis that is aligned with the image line, and a pixel length measured along a second axis that is perpendicular to the first axis. The print head is shifted relative to the substrate along the second axis a distance corresponding to the pixel length. These printing and shifting steps are repeated a limited number of times to complete the printing of the image on the substrate. 
     Some embodiments of the credential production device include a print ribbon, and the asymmetric thermal print head configured to print an image to a surface of a substrate using the print ribbon. The asymmetric thermal print head includes a print head body and a plurality of print elements supported on the print head body. The print elements are aligned along a first axis. Each print element includes a heater portion having a burn width measured along the first axis corresponding to a first print resolution, and a burn length measured along a second axis, which is perpendicular to the first axis, corresponding to a second print resolution. The second print resolution is higher than the first print resolution. One or more control circuits are configured to individually activate the print elements. 
     This Summary is provided to introduce a selection of concepts in a simplified form that are further described below in the Detailed Description. This Summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used as an aid in determining the scope of the claimed subject matter. The claimed subject matter is not limited to implementations that solve any or all disadvantages noted in the Background. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a simplified bottom view of an exemplary asymmetric thermal print head, in accordance with embodiments of the present disclosure. 
         FIG. 2  is a simplified cross-sectional view of the print head of  FIG. 1  taken generally along line  2 - 2 . 
         FIG. 3  is a simplified side view of an asymmetric thermal print head performing an exemplary print operation on a substrate using a print ribbon. 
         FIG. 4  is a simplified top view of the print operation of  FIG. 3 , but without the print ribbon. 
         FIG. 5  is a simplified top view of an exemplary pixel printed using a symmetric thermal print head in accordance with the prior art. 
         FIG. 6  is a simplified top view of an exemplary pixel printed using an asymmetric thermal print head, which is formed in accordance embodiments of the present disclosure. 
         FIG. 7  is a simplified top view of an exemplary image printed using the asymmetric thermal print head. 
         FIGS. 8 and 9  are simplified side views of exemplary credential production devices, in accordance with embodiments of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS 
       FIG. 1  is a simplified bottom view of an exemplary asymmetric thermal print head  100  in accordance with embodiments of the present disclosure.  FIG. 2  is a simplified cross-sectional view of the print head  100  taken generally along line  2 - 2 . The print head  100  includes a plurality of print elements  102 , which are supported on a print head body  104 . Each of the print elements  102  includes a heater portion  106  that is generally aligned with a burn axis  108  to form a row of the heater portions  106  across a width of the print head body  104 . In some embodiments, the heater portions  106  each include a resistive heating element that generates heat in response to an electric current. 
     The print head  100  also includes one or more control circuits  110 , each of which is configured to selectively activate print elements  102  within a group. This activation of a print element  102  involves delivering a current to the heater portion  106  of the print element  102  through corresponding electrodes  112 , in accordance with conventional thermal print head operations. The resistive heating element of the heater portions  106  generates heat in response to the current. A protective glaze  113  may be applied over the heater portions  106  to protect the heater portions  106 , and provide a smooth contact surface, as shown in  FIG. 2 . 
     The heat generated by the heater portions  106  of an activated print element  102  may be used to print an image to a substrate, as generally illustrated in  FIGS. 3 and 4 .  FIG. 3  is a simplified side view of the print head  100  performing a print operation on a substrate  114  using a print ribbon  116 , and  FIG. 4  is a simplified top view of the print head  100  performing the print operation of  FIG. 3 , but with the print ribbon  116  removed. 
     The print ribbon  116  generally includes a print consumable attached to a carrier layer that may be transferred to the surface  118  of the substrate  114  from the carrier layer using the print head  100  during a print operation. The print consumable may take on any suitable form, such as a colored dye (e.g., yellow, cyan, or magenta), a black resin, or other print consumable, in accordance with conventional thermal print ribbons  116 . 
     An image  120  may be printed to the surface  118  of the substrate  114  through the printing of several image lines  122  using the print head  100  and the print ribbon  116 , as shown in  FIG. 4 . Each image line  122  of the image  120  is aligned with the burn axis  108 , and comprises one or more pixels  124 . Each pixel  124  is printed by activating a corresponding print element  102 , using the control circuit  110 . Heat generated by the heater portion  106  in response to the activation causes a print consumable to transfer from the print ribbon  116  to the surface  118  and form the pixel  124  of the image line  122 . The print head  100  may then be shifted relative to the substrate  114  in the direction indicated by arrow  126  along an axis  128  to position the burn axis  108  in the position of the next image line  122 , and the print elements  102  are selectively activated using the control circuits  110  to print the pixels  124  for the new image line  122 . This process is repeated until the image  120  or a layer of the image  120  is printed to the surface  118  of the substrate  114 . For some colored pixels  124  of the image  120 , this printing process may be repeated to overlay different colored print consumables from the print ribbon  116  to the pixels  124  to form the desired colored pixels  124  of the image  120 . 
     The heater portions  106  of the thermal print head  100  each have a burn width  130  measured along the burn axis  108 , and a burn length  132  measured along the axis  128  that is perpendicular to the burn axis  108 , as shown in  FIG. 1 . The burn width  130  corresponds to a width of the printed pixel  124 , and the burn length  132  corresponds to a length of the printed pixel  124 . Additionally, the burn width  130  corresponds to a print resolution along the burn axis  108 , and the burn length  132  corresponds to a print resolution along the axis  128 . 
     Conventional thermal print heads utilize print elements  102  having symmetric heater portions. That is, the burn width of the heater portions of conventional print heads substantially match their burn length. As a result, conventional symmetric thermal print heads are configured to produce symmetric pixels  124 ′ each having a width  134 ′ that substantially matches its length  136 ′, as generally shown in  FIG. 5 , which is a simplified top view of an exemplary pixel  124 ′ printed using a symmetric thermal print head in accordance with the prior art. Accordingly, a 300 dots-per-inch (dpi) conventional thermal print head generally has a 300 dpi resolution along both the burn axis  108  and the axis  128 , and produces pixels  124 ′ having a width  134 ′ of 3.33 mil and a length  136 ′ of 3.33 mil. 
     The asymmetric thermal print head  100  of the present disclosure includes print elements  102  each having a burn width  130  that is different from the burn length  132 . Thus, the print elements  102  of the asymmetric thermal print head  100  are configured to print asymmetric pixels  124 , an example of which is illustrated in the simplified top view of  FIG. 6 . In some embodiments, the thermal print head  100  has a higher resolution along the axis  128  than along the burn axis  108 . Thus, in some embodiments, the burn length  132  of the heater portions  106  is shorter than the burn width  130 . Additionally, the burn length  132  is shorter than the burn length  132 ′ of conventional heater portions  106 ′ that substantially match the burn length  130 , as indicated in phantom lines in  FIG. 2 . As a result, each pixel  124  printed using the asymmetric thermal print head  100  in accordance with embodiments of the present disclosure has a width  134  that is longer than its length  136 , as shown in  FIG. 6 . 
     Due to the dimensions of the burn portions  106 , the print head  100  may perform a printing operation having a higher resolution along the axis  128  than along the burn axis  108 , as shown in  FIG. 7 , which is a simplified top view of an exemplary image  120  printed using the asymmetric thermal print head  100 . For instance, a first pixel  124 A may be printed using one of the print elements  102  of the print head  100 . The print head  100  may then be shifted along the axis  128  relative to the substrate a distance that is substantially equal to the burn length  132  of the heater portions  106 , and a pixel  124 B may then be printed. This may be followed by the printing of a pixel  124 C after shifting the print head  100  by the burn length  132  along the axis  128  to complete the image  120  shown in  FIG. 7 . Here, the pixels  124 A-C do not overlap and provide a higher printing resolution along the axis  128  relative to the print resolution along the burn axis  108 . 
     In some embodiments, the print resolution of the asymmetric thermal print head  100  along the axis  128  is approximately double (e.g., ±10%) the print resolution along the burn axis  108 , as generally shown in  FIG. 2 , where the asymmetric burn length  132  of the print head  100  is approximately one half (e.g., ±10%) of the corresponding symmetric burn length  132 ′ of the symmetrically sized heater portion  106 ′ (shown in phantom lines). In some embodiments, the thermal print head  100  is configured to have a 300 dpi print resolution along the burn axis  108 , and a 600 dpi resolution along the axis  128 . Thus, in some embodiments, the heater portions  106  of the thermal print head  100  generally have a burn width  130  of approximately 3.33 mil (e.g., ±10%), and a burn length  132  of approximately 1.67 mil (e.g., ±10%), and the pixels  124  printed by the print elements  102  have a width  134  of approximately 3.33 mil (e.g., ±10%), and a length  136  of approximately 1.67 mil (e.g., ±10%). 
     It should be noted that the thermal print head  100  provides a higher printing resolution along the axis  128  while using the same number of control circuits  110  required to provide the lower print resolution along the burn axis  108 . This provides advantages over symmetric print heads that are configured to print at the higher resolution. For example, the asymmetric print head  100  requires fewer control circuits  110  than are required by the symmetric version, while providing the higher print resolution along the axis  128 . This allows the asymmetric print head  100  to be produced at a significantly lower cost than the symmetric version. 
     Additional embodiments include methods of printing an image to a substrate using the asymmetric thermal print head  100 , which is formed in accordance with one or more embodiments of the present disclosure. In the method, an image line  122  is printed on a surface  118  of a substrate  114  by printing a plurality of pixels  124 , as discussed above and illustrated in  FIGS. 3 and 4 . Each of the pixels  124  has a width  134  ( FIG. 6 ) measured along the burn axis  108 , which is aligned with the image line  122 , and a length  136  measured along the axis  128 . The print head  100  is then shifted relative to the substrate  114  along the axis  128  in the direction  126  a distance corresponding to the pixel length  136  or burn length  132  of the heater portion  106 . These printing and shifting steps are then repeated a limited number of times to print the image  120  to the surface  118  of the substrate  114 . In some embodiments, the pixel width  134  corresponds to a first print resolution, and the pixel length  136  corresponds to a second print resolution that is higher than the first print resolution. In some embodiments, the pixel width  134  is approximately double (e.g., ±10%) the pixel length  136 , and the second resolution is approximately double (e.g., ±10%) the first resolution. In some embodiments, the first print resolution is approximately 300 dpi (e.g., ±10%), and the second print resolution is approximately 600 dpi (e.g., ±10%). In some embodiments, the pixel width  134  is approximately 3.33 mil (e.g., ±10%), and the pixel length  136  is approximately 1.67 mil (e.g., ±10%). 
     Some embodiments are directed to credential production devices that include the asymmetric thermal print head  100  formed in accordance with one or more embodiments of the present disclosure.  FIGS. 8 and 9  respectively show simplified side views of exemplary credential production devices  150 A and  150 B in accordance with embodiments of the present disclosure. 
     The credential production device  150 A is generally configured to directly print an image to a surface  152  of a substrate  154  using the asymmetric thermal print head  100  and a thermal print ribbon  116 , as shown in  FIG. 8 . Here, the substrate  154  may form the final printed product. In some embodiments, the substrate  154  is a credential substrate. As used herein, the term “credential substrate” includes substrates used to form credentials, such as identification cards, membership cards, proximity cards, driver&#39;s licenses, passports, credit and debit cards, and other credentials or similar products. Exemplary credential substrates include paper substrates other than traditional paper sheets used in copiers or paper sheet printers, plastic substrates, rigid and semi-rigid card substrates and other similar substrates. 
     The substrate  154  is supported by a platen roller  156  or other suitable support, and the print ribbon  116 , which may be supported between a supply spool  158  and a take-up spool  160 , is positioned between the surface  152  and the print head  100 , as shown in  FIG. 8 . The print elements  102  of the print head  100  are selectively activated to transfer pixels of a print consumable from the print ribbon to the surface  152  to print a series of image lines  122  and form the image  120  on the surface  118 , such as shown in  FIGS. 3 and 4  with regard to the substrate  114 . 
     The credential production device  150 B is generally configured to perform a reverse-image transfer printing process to print an image to the surface  152  of a substrate  154 , such as a credential substrate, to form a final printed product. The print head  100  is configured to print the image to a transfer ribbon  162 , which may be supported between a supply spool  164  and a take-up spool  166 . The transfer ribbon  162  may be formed in accordance with conventional transfer ribbons and include a fracturable thin film laminate or overlaminate patches that may be transferred to a substrate  154 . The print head  100  prints the image to the transfer ribbon  162 , which is supported by a platen roller  168 , by thermally transferring a print consumable from the thermal print ribbon  116  to a transferrable surface  170  of the transfer ribbon  162 , such as shown in  FIGS. 3 and 4  where the substrate  114  is the transfer ribbon  162 . The imaged portion of the transfer ribbon  162  is then fed to a laminating unit  172 , which transfers the printed image to the surface of the substrate  154 , which may be supported by a platen roller  173 , using a heated transfer roller  174  or other suitable laminating device, in accordance with conventional techniques. 
     The credential production devices  150 A and  150 B may each include additional components to facilitate the production of a credential product. For example, the devices  150 A and  150 B may include a controller  176  that is configured to control components of the devices  150 A and  150 B to perform one or more functions described herein, such as printing operations using the asymmetric thermal print head  100 , for example. The controller  176  may represent one or more processors and memory (e.g., local or remote memory). The one or more processors are configured to control operations of the devices  150 A or  150 B in response to the execution of instructions contained in the memory. 
     In some embodiments, the devices  150 A and  150 B include a transport mechanism  178  configured to feed individual substrates  154  along a processing path  180 . In some embodiments, the transport mechanism includes motorized feed rollers and/or pinch roller pairs  182  for driving the individual substrates  154  along the processing path  180  to the print head  100  ( FIG. 8 ) for a printing operation, or to the laminating unit  172  ( FIG. 9 ) for a transfer or lamination operation. 
     In some embodiments, the devices  150 A and  150 B include a substrate supply  184  containing a plurality of the substrates  154 . The transport mechanism  178  may be configured to feed the individual substrates  154  from the supply  184  along the processing path  180 , as shown in  FIGS. 8 and 9 , for example. 
     In some embodiments, the devices  150 A and  150 B include a head lift mechanism  186  that is configured to move the asymmetric thermal print head  100  either relative to the processing path  180  or platen roller  156  ( FIG. 8 ), or the transfer ribbon  162  or platen roller  168  ( FIG. 9 ). 
     The credential production devices  150 A and  150 B may also include other processing devices  190  that are configured to perform one or more processes on the substrate  154 . These processing devices may include, for example, a substrate rotator  190 A configured to rotate the substrate  154 , a laminating unit  190 B for the device  150 A configured to apply an overlaminate to the surface  152  of the substrate  154 , a data encoder  190 C configured to read and/or write data to a memory chip of the substrate  152 , a magnetic stripe reader and/or writer  190 D configured to read and/or write data to a magnetic stripe of the substrate  154 , and/or other suitable substrate processing devices. 
     Although the embodiments of the present disclosure have been described with reference to preferred embodiments, workers skilled in the art will recognize that changes may be made in form and detail without departing from the spirit and scope of the present disclosure.