Abstract:
The present disclosure relates to a method for printing a secure image on media using an inkjet printing device. The method includes printing an underlayer using an inkjet printing device that penetrates into a front surface of media. The underlayer is configured to define identification indicia. Included in the method is printing a secure image on top of the underlayer using an inkjet printing device. Examination of a back surface opposite the front surface allows viewing of the identification indicia for authenticating the secure image.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to inkjet printing devices for printing secure images on media. 
     Inkjet printing systems frequently make use of an inkjet printhead mounted to a carriage which is moved back and forth across print media such as paper. As the printhead is moved across the print media, a control device selectively activates each of a plurality of drop generators within the printhead to eject or deposit ink droplets onto the print media to form images and text characters. An ink supply that is either carried with the printhead or remote from the printhead provides ink for replenishing the plurality of drop generators. 
     Individual drop generators are selectively activated by the use of an activation signal that is provided by the printing system to the printhead. In the case of thermal inkjet printing, each drop generator is activated by passing an electric current through a resistive element such as a resistor. In response to the electric current the resistor produces heat, that in turn, heats ink in a vaporization chamber adjacent the resistor. Once the ink reaches vaporization, a rapidly expanding vapor front forces ink within the vaporization chamber through an adjacent orifice or nozzle. Ink droplets ejected from the nozzles are deposited on print media to accomplish printing. 
     There is frequently a need to print documents that can be verified as original documents. Documents that can be verified as original documents are referred to herein as “secure” documents. Several examples of documents that require verification of their originality would be desirable include tickets, coupons, and various types of certificates, to name a few. For these printing applications it is necessary that the source of the document be verifiable by examination of the document. The technique used to identify the source of the document should be difficult to duplicate using readily available duplication systems such as copiers and scanners to prevent counterfeiting of the document. 
     There is an ever-present need for techniques for secure printing using ink-jet printing technology. These techniques should be capable of allowing the source of the printed media to be identifiable without adding significant costs to the printing system. These techniques should be suitable for use with standard media. Finally, these techniques for authenticating original inkjet printed documents should be reliable and easily accomplished. 
     SUMMARY OF THE INVENTION 
     One aspect of the present invention is a method for printing a secure image on media using an inkjet printing device. The method includes printing an underlayer using an inkjet printing device that penetrates into a front surface of media. The underlayer is configured to define identification indicia. Included in the method is printing a secure image on top of the underlayer using an inkjet printing device. Examination of a back surface opposite the front surface allows viewing of the identification indicia for authenticating the secure image. 
     Another aspect of the present invention is an inkjet printing device for secure printing. The inkjet printing device includes an input device for receiving image information for specifying images to be printed. Included is a storage device for storing identification indicia information. Also included is a control device for selecting between the input device and the storage device. The control device selects information from each of the first input device and the storage device for each image printed. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a top perspective view of an inkjet printing system of the present invention for accomplishing secure printing on print media. 
         FIG. 2  is block diagram of the inkjet printing system of  FIG. 1  shown connected to a host device. 
         FIGS. 3   a  and  3   b  represent exemplary text and graphic images for printing using the printing system of the present invention. 
         FIGS. 4   a  and  4   b  represent exemplary underlayers for printing using the printing system of the present invention. 
         FIGS. 5   a  and  5   b  is an exploded view representing the text and graphic images of  FIGS. 3   a  and  3   b  printed over the underlayer shown in  FIGS. 4   a  and  4   b , respectively, using the printing system of the present invention. 
         FIG. 6  is a flow diagram depicting the method of the present invention for printing a secure document. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       FIG. 1  is a perspective view of one exemplary embodiment of an inkjet printing system  10  of the present invention shown with its cover open. The inkjet printing system of the present invention, as will be discussed in more detail, allows secure documents to be printed. In one exemplary embodiment, the inkjet printing system  10  includes a printer portion  12  having at least one print cartridge  14  and  16  installed in a scanning carriage  18 . The printing portion  12  includes a media tray  20  for receiving media  22 . As the print media  22  is stepped through a print zone  24 , the scanning carriage  18  moves the print cartridges  14  and  16  across the print media  22 . The printer portion  12  selectively activates drop generators within a printhead portion (not shown) associated with each of the print cartridges  14  and  16  to deposit ink on the print media. 
     In the exemplary embodiment, the cartridge  14  is a three-color cartridge containing cyan, magenta, and yellow inks. In this exemplary embodiment, a separate print cartridge  16  is provided for black ink. The present invention will herein be described with respect to this preferred embodiment by way of example only. There are numerous other configurations in which the method and apparatus of the present invention is also suitable. For example, the present invention is suited to configurations wherein the printing system contains separate print cartridges for each color of ink used in printing. Alternatively, the present invention is applicable to printing systems wherein more than four ink colors are used such as in high fidelity printing wherein six or more colors are used. Finally, the present invention is applicable to printing systems that make use of various types of print cartridges such as print cartridges which include a printhead portion and a separate ink container portion, spaced from the printhead, that used to either continuously or intermittently replenish the printhead portion with ink. 
     The ink cartridge  14  and  16  shown in  FIG. 1  includes a printhead portion (not shown) that is responsive to activation signals from the printing system  12  for selectively depositing ink on media  22 . In the exemplary embodiment, the print cartridges  14  and  16  each include a plurality of electrical contacts that are disposed and arranged on the print cartridge so that when properly inserted into the scanning carriage  18 , electrical contact is established between corresponding electrical contacts associated with the printer portion  12 . In this matter, activation signals from the printer portion  12  are provided to the ink-jet printhead for ejecting ink. 
       FIG. 2  depicts a simplified electrical block diagram of the printer portion  12  shown connected to an information source or host device  26 . The host  26  represents a source of the image to be printed. The host  26  is a computer, processor or any other device that provides an image to be printed to the printing system  10 . The image provided by the host  26  is in one of a number of types, such as, an image description using an image description language or a bit map images. Some examples of the host  26  are a personal computer (pc), a digital camera or an internet link for directly receiving image information from an internet source, to name a few. 
     The printer portion  12  includes an input device  28  for receiving information from the host  26  and a storage device  30  for storing image information. The printing device  12  further includes a printer controller  32  capable of selectively receiving image information from each of the input device  28  and the storage device  30 . The printer controller  32  provides image information to the print mechanism  34 . The print mechanism  34  provides control signals to a media transport device for transporting media  22  through the print zone  24 . In addition, the print mechanism  34  includes a carriage transport device for controlling movement of the carriage  18  through the print zone  24  as the printer controller  32  selectively activates the inkjet printhead on each of the cartridges  14  and  16  to selectively form images on print media  22 . 
     Although, the printing system  10  is described herein as having a printhead that is disposed in a scanning carriage  18 , there are other arrangements of achieving relative movement between the printhead and media  22 . For example, the printing system  10  can also be configured to have a fixed printhead portion and wherein the media  22  is moved past the fixed printhead or another example is where the media  22  is fixed and the printhead is moved past the fixed media  22 , to name a few. 
     The input device  28  receives the image information from the host  26  and converts this image information into a format suitable for the printer controller  32 . The input device  28  typically performs various process functions as well as buffering functions on image information prior to providing this information to the printer controller  32 . 
     The storage device  30  stores image information for identifying a source of the image to be printed. This identification information can be unique to the particular printing system  10  or can be unique to a particular or user or organization. This image information stored in the storage device  30  is used by the printer controller  32  and the print mechanism  34  for providing identification indicia on the print media  22  for identifying the particular printing system  10  responsible for printing the image on media  22 . The identification information stored in the storage device  30  is either loaded into the storage device  30  from a remote source or is loaded by the printer portion  10 . In the case where the printer portion  10  loads the identification information, this information is derived from the image to be printed or altered by the image to be printed. The image is stored in each of the input device  28  and the storage device  30  will now be discussed with respect to  FIGS. 3 ,  4 , and  5  by way of example in order to illustrate the technique of the present invention. 
       FIGS. 3   a  and  3   b  are exemplary images  36   a  and  36   b  to be printed by the printing system  12 . These images are typically images that are received by the input device  28  from the host or source of image information  26 .  FIG. 3   a  represents a text image  36   a  and  FIG. 3   b  represents a graphic image  36   b . Both of the exemplary images are formed using black ink. The images to be printed can alternatively be other colors as well. Alternatively, the image  36   a  and  36   b  that are sent by the host  26  could also be a gray scale image such as a binary representation of a continuous tone image. One example of a continuous tone image is a photograph that is then digitized to produce a binary representation of the photograph. 
       FIGS. 4   a  and  4   b  represent identification information or an indicia  38   a ,  38   b ,  40   a ,  40   b  that can be stored in the storage device  30 . The identification indicia in  FIG. 4   a  includes a first indicia  38   a  and a second indicia  40   a . The identification indicia  38   a ,  38   b ,  40   a ,  40   b  are shown as cross-hatched regions that represent areas of ink coverage. These regions are formed using small drops of ink to deposit a pattern or shape. These patterns are formed so that they are visible from either the back of the media or front side of the media as will be discussed latter. The indicia  38   a  and  40   a  are selected to be an ink color that is different from the ink color of the image to be printed  36   a . In this exemplary embodiment, the first indicia  38   a  is formed using cyan ink and the second indicia  40   a  is formed using magenta ink. The first and second indicia  38   a  and  40   a  colors are selected to be different from the black ink used to print the image to be printed  36   a . The first and second indicia  38   a  and  40   a  can be formed using other ink colors as well. 
     In this exemplary embodiment, each indicia is formed using small well-spaced droplets of ink. The media  22  is selected to be a media that allows ink to penetrate into the media  22 . Various types of media manufactured by media manufacturers such as Union Camp and Jamestown allow ink to penetrate into the media  22 . The ink droplet spacing is selected based on drop volume as well as media penetration so that the indicia  38   a  and  40   a  are not visible when viewed under normal lighting conditions. 
       FIG. 4   b  shows alternative indicia  38   b  and  40   b  that are stored in the storage device  30  in the printing system  10 . The indicia  38   b  and  40   b  in  FIG. 4   b , in contrast to the indicia in  FIG. 4   a , are selected to be related to the image  36   b  to be printed shown in  FIG. 3   b . In this exemplary embodiment, the indicia  38   b  and  40   b  includes a portion  38   b  formed using cyan ink and a portion  40   b  formed using magenta ink. Each of the cyan portion  38   b  and the magenta portion  40   b  are selected based on the image to be printed  36   b  shown in  FIG. 3   b . The identification indicia  38   b  and  40   b  in  FIG. 4   b  has portions that are configured to correspond to a shape of the image to be printed  36   b  in  FIG. 3   b . The identification indicia  38   b  and  40   b  in  FIG. 4   b  are formed using cyan and magenta inks instead of black ink shown in  FIG. 3   b . As will be discussed with respect to  FIG. 5   b  it is important that the identification indicia  38   b  and  40   b  in  FIG. 4   b  be formed to be completely covered by the image to be printed  36   b  in  FIG. 3   b  when this image  36   b  is overprinted on the identification indicia  38   b  and  40   b.    
       FIGS. 5   a  and  5   b  illustrates the technique of the present invention whereby the identification indicia  38   a ,  38   b ,  40   a ,  40   b  are printed prior to the image to be printed  36   a ,  36   b . The image to be printed  36   a  and  36   b  is printed over the respective identification indicia. The backside of the media  22  can then be examined for the identification indicia  38   a ,  38   b ,  40   a ,  40   b  to identify the printing system  10  to authenticate the image. 
     As shown in  FIGS. 5   a  and  5   b  the combined image resulting from printing the identification indicia  38   a ,  38   b ,  40   a ,  40   b  that is printed as an underlayer and the image to be printed  36   a  and  36   b  that is printed as an overlayer. As is shown in  FIG. 5   a , the image to be printed  36   a  only partially covers the underlayer or identification indicia  38   a  and  40   a . However, as discussed previously, the underlayer or identification indicia  38   a  and  40   a  are printed sufficiently light so as to not be visible when viewing the media  22  under normal light.  FIG. 5   b , in contrast, the underlayer or identification indicia  38   b  and  40   b  are completely hidden by the overlayer or image to be printed  36   b . Because the underlayers or identification indicia  38   b  and  40   b  are completely covered by the overlayer or image to be printed  36   b , the underlayer can be formed using a larger amount of ink than the case when the underlayer  38   a  and  40   a  is not hidden shown in  FIG. 5   a.    
     Once both the underlayer  38   a ,  38   b ,  40   a , and  40   b  is printed and the overlayer  36   a , and  36   b  are printed, the image is complete. The complete image is formed so that the underlayer  38   a ,  38   b ,  40   a , and  40   b  is not sufficiently visible to be duplicated using a copier or scanner thereby preventing counterfeiting of the complete image. The printed image can then be viewed from the backside opposite the printed side to view the underlayer  38   a ,  38   b ,  40   a , and  40   b  to identify this source of the image. Alternatively, for the case where the underlayer  38   a ,  40   a  is not completely covered by the overlayer  36   a  as shown in  FIG. 5   a  then the underlayer can be partially viewed from the from front side of the completed image to identify this source of the image. The underlayer in  FIG. 5   a  is viewed under special light or using an instrument to detect the identification indicia  38   a  and  40   a  from the backside or front side of media  22 . The underlayer in  FIG. 5   b  can be viewed without special light or instrument to view identification indicia  38   b  and  40   b . Because the underlayer  38   a ,  38   b ,  40   a , and  40   b  are characteristic to the particular printer, then the viewing of the underlayer can be used to identify the particular printer. In this manner, an inkjet printed image can be authenticated and in this regard, this technique allows secure printing. 
     While the underlayers  38   a ,  38   b ,  40   a , and  40   b  as shown as simple rows or bars of color as shown in  FIG. 4   a  for graphic images as shown in  FIG. 4   b , these images can be a variety of shapes and patterns to uniquely identify the particular printer that printed the image. In addition, the underlayer can be related to the image that is to be printed as shown in  FIG. 4   b . This is useful when a large number of images are to be printed such as a large number of certificates to be printed, the pattern for the underlayer can then be stored in the storage device  30  for use in printing each of the certificates. In this manner, the underlayer is configured to be hidden by the overlayer while still producing a unique indicia for identifying the printing system that printed the image. 
     In operation, an image to be printed is provided to the printing system  12  as represented by step  42  in  FIG. 6 . The printer controller  32  within the printing system  10  recalls an image description from the storage device  30  as represented in step  44 . The printing system  10  then prints the underlayer based on the image description recalled from the storage device  30 . An overlayer is then printed based on the image description provided by the input device  28  as represented by step  48 . The secure document, having both an underlayer and overlayer, is then complete as represented by step  50 . The present invention provides an economical way of printing secure documents. This technique allows the backside of the document to be reviewed either visually or using a special scanning device to read the underlayer from the backside for reading the characteristic image of the printing system  10 . The image can then be matched with the characteristic image of the printer  10  to authenticate the document as to the source or origination of the document. 
     The present invention has been described herein with respect to thermal ink-jet printing, however, there are other ink droplet ejection devices that are also suitable. The technique of the present invention is suitable for drop ejection devices that allow for ink droplets to be accurately deposited on media. Examples of these drop ejection devices, other than thermal inkjet, include piezo ejection devices and flex tensional ejection devices, to name a couple.