Abstract:
A document printing and verification system and method. The system includes a printing apparatus for printing an image on a print medium, and an inkjet printer apparatus for printing an invisible identification pattern such as a barcode on the print medium which is invisible to the naked eye under normal ambient illumination. A scanner apparatus is positioned for producing an image of the identification image for verification use. The scanner apparatus includes a light source for illuminating an imaging zone with light including nonvisible energy components and a camera sensitive to nonvisible light from the print medium to form an image of the nonvisible identification image. The inkjet printhead is a high resolution printhead adapted to provide inkjet barcode printing resolution at least as high as 600 dots per inch, improving edge acuity of the pattern, and permits very high density information to be imprinted on the document page. The inkjet ink includes a UV dye and an FR/IR dye. The UV dye when illuminated with UV light provides an image of the barcode which is visible to the naked eye. The FR/IR dye is imaged using an FR/IR camera to capture electronically an image of the barcode.

Description:
TECHNICAL FIELD OF THE INVENTION 
     This invention relates to printing systems that imprint documents with a barcode and utilize downstream processes to track that the current number of pages in the document are present, and more particularly to such printing and tracking systems which utilize invisible ink for the barcoding. 
     BACKGROUND OF THE INVENTION 
     Electrophotographic printing systems are known that print black barcodes during the printing of documents, and use barcode scanners in downstream processing to verify information and to check that the proper number of pages are present in the document. These systems are typically used for the printing and tracking of insurance documents, checks, manuals and other print-on-demand documents. Some customers find objectionable the appearance of visible barcodes on their documents. 
     Conventional industrial inkjet barcode printers typically use printheads having a dot per inch spacing of 150 dots per inch (dpi) to 240 dpi, and have traditionally been continuous inkjet printers. These low dpi printheads produce drops that are large and consequently produce spot sizes on the print media that are relatively large. Ink formulation is also important in determining the spot size. It is this spot size that fundamentally determines the minimum barcode sizes that a printhead can print. 
     Accordingly, it would represent an advance in the art to provide a technique for imprinting barcodes on documents and subsequently scanning the documents for verification purposes which did not rely on visible barcode features. 
     It would further represent an advance in the art to provide a technique for producing smaller, denser barcodes on documents, and thereby increase the amount of data to be stored in a given area, increase the edge acuity of the printed barcodes and resulting scan reliability of the system. 
     SUMMARY OF THE INVENTION 
     A document printing and verification system is described. The system includes a printing apparatus for printing an image on a print medium, and an inkjet printer apparatus for printing an invisible identification pattern on the print medium which is invisible to the unaided eye under natural illumination. A scanner apparatus is positioned for producing an image of the identification image for verification use. The scanner apparatus includes a light source for illuminating an imaging zone with light including nonvisible energy components and a camera sensitive to nonvisible light from the print medium to form an image of the nonvisible identification image. 
     In accordance with another aspect of the invention, the inkjet printhead is a high resolution printhead adapted to provide inkjet barcode printing resolution at least as high as 600 dots per inch. This improves the edge acuity of the barcodes, and permits very high density barcode information to be imprinted on the document page. 
     In accordance with another aspect, the ink used to form the invisible barcode includes a UV dye and an FR/IR dye. The UV dye when illuminated with UV light provides an image of the barcode which is visible to the unaided eye, providing a visual check on the system operability. The FR/IR dye is imaged using an FR/IR camera to capture electronically an image of the barcode. The captured image is then used by the controller for verification purposes. 
     Yet another aspect of the invention includes backlighting the document page with FR/IR energy, and capturing an image of the barcode with an FR/IR sensitive camera. The FR/IR energy penetrates the page sufficiently to excite the FR/IR dye in the barcode ink. 
     Another aspect of the invention is a method for document printing and verification, comprising the following steps: 
     printing a page of a document; 
     printing an identification pattern on the document page using an inkjet printer, the pattern printed with ink which is invisible to the unaided eye under natural light illumination; 
     illuminating the document page with light energy including energy components in a non-visible band; 
     electronically capturing an image of the identification pattern at the imaging zone; and 
     performing a verification procedure using the electronically captured image. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     These and other features and advantages of the present invention will become more apparent from the following detailed description of an exemplary embodiment thereof, as illustrated in the accompanying drawings, in which: 
     FIG. 1 is a schematic block diagram of a document printing and verification system employing the invention. 
     FIG. 2A is a diagrammatic representation of respective barcode patterns printed with a 300 dpi resolution and a 600 dpi resolution; 
     FIG. 2B shows an exemplary two-dimensional barcode. 
     FIG. 3 is a schematic block diagram of a first alternate embodiment of a document printing and verification system in accordance with the invention. 
     FIG. 4 is a schematic block diagram of a second alternate embodiment of a document printing system and verification system in accordance with the invention. 
     FIG. 5 is a flow diagram illustrating steps of a document printing and verification method using this invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     An exemplary document printing and verification system  50  in accordance with the invention is shown in schematic form in FIG.  1 . This system includes a printer apparatus  52  positioned along the paper path  54  for printing desired text and/or graphical indicia onto the surface of a print medium  40 . The printer apparatus  52  can be, for example an electrophotographic printer, e.g. a laser printer, an LED printer, an inkjet printer, or any other type of printing system. The printer apparatus  52  in an exemplary embodiment is a laser printer, under control of a system controller  100 , which coordinates the printing of documents by the printer  52  and the verification processes performed by the barcode printer  60  and scanner  70  downstream of the electrophotographic printer  60 . 
     Positioned downstream of the printer apparatus  52  along the paper path  54  is an inkjet printing apparatus  60  for printing a barcode on the print medium  40 . In accordance with an aspect of the invention, the inkjet printer  60  includes a high resolution, 600 dpi printhead  62  which ejects droplets  64  of invisible ink to print the barcode. The printer  60  includes a carriage  66  for holding the printhead  62 . The printhead is connected via a fluid path to an ink reservoir, preferably a reservoir capable of holding a large ink volume, say on the order of 350 cc or greater. 
     As used in this description of the invention, “invisible” inks involve a broad class of ink formulations which cannot be seen by the unaided eye when applied to a substrate and viewed with “natural” light (e.g. light from the sun) or light from conventional incandescent lamps and the like. Both of these light forms (as well as other forms which are normally used for general illumination purposes in home, businesses and like) are collectively characterized as “white” light which involves a combination of all the various colored light components which fall within a wavelength range of about 300-700 nm. Under these illumination conditions, the invisible ink compositions are essentially colorless. Only after illumination with other, more narrow light wavelengths do the printed images become visible or otherwise detectable (either with or without auxiliary observation equipment). 
     The printhead  62  with 600 dpi resolution is used with small spot size inks to produce smaller, denser one or two dimensional barcodes than are possible with conventional, low resolution barcode inkjet printers. These barcodes allow more data to be stored in a given printed area. By reducing the spot size, the edge acuity of the printed barcodes is increased, thereby increasing the scan reliability of the system. FIG. 2A diagrammatically depicts a one-dimensional bar code  10  printed with a 300 dpi printhead, and the same one-dimensional barcode  20  but printed with a 600 dpi printhead using small spot size ink. As illustrated in FIG. 2A, the 600 dpi barcode  20  requires much less area than does the 300 dpi barcode  10 . The printhead  62  can also be used to print two-dimensional barcode patterns; an exemplary two-dimensional pattern is illustrated in FIG.  2 B. 
     A scanner  70  is disposed along the paper path  54  downstream of the inkjet printer  60 . The scanner  70  includes a camera  72  for capturing an image of the barcodes on the paper passing by the camera at an imaging zone  76 . The imaging zone is illuminated by a first lamp  80  emitting a light beam  80 A, through filter  84  and incident on the imaging zone. The imaging zone is further illuminated by a second lamp  82  emitting a light beam  82 A, through filter  88  and incident on the imaging zone. Light reflected from the paper is then passed through the filter  86  and to the camera  72 . 
     Two illumination sources are provided in this exemplary embodiment because a single side light source tends to produce non-uniform illumination of the media being imaged by the camera. Two sources positioned on opposite sides of the media produce a more uniform illumination of the sample. Of course, for some implementations, a single side illumination source can produce acceptable results, thereby simplifying the system. 
     The ink droplets  64  emitted by the printhead  62  in this exemplary embodiment have two dyes invisible under natural light illumination. One dye is a UV dye which, when illuminated by UV light of appropriate intensity, gives off a visible emission, permitting quick visual checking on the printing line to ensure the printing and verification system is working properly. The second dye is a far red (“FR)/infrared (“IR”) dye which when illuminated by FR/IR energy of appropriate intensity gives off an emission which is detectable by the camera  72  to provide an image of the barcode. Far red light normally involves a wavelength range of about 650 nm to 700 nm, with infrared light involving a wavelength range which exceeds about 700 nm up to about 1000 nm. The FR/IR dye provides media independence and system robustness, since papers are less efficient at absorbing FR/IR wavelength energy than UV wavelength energy, resulting in stronger emissions at FR/IR. 
     Inks suitable for the purpose is described in co-pending application entitled INVISIBLE IR/UV SENSITIVE INK COMPOSITIONS AND METHODS FOR USING THE SAME, Attorney Docket Number 10980234-1, the entire contents of which are incorporated herein by this reference. 
     The illumination sources produce light beams having significant energy in the UV and FR/IR wavelength bands. In an exemplary embodiment, the illumination sources  80 ,  82  are metal halide lamps to produce UV and RF/IR light components. In another embodiment, standard halogen light fixtures can be used as the illumination sources  80 ,  82 , to produce light with FR/IR components. Because halogen lamps will not produce light energy in the UV band to excite the UV dye, a hand-held black light can be employed in this alternate embodiment to verify that the barcode printer is printing properly. 
     Ideally, the lamp filters  84 ,  88  have a passband which matches the excitation frequency range of the FR/IR dye, and allow the use of more general lamps and cameras, i.e. lamps whose emission spectra are not limited to the specific excitation wavelengths of the FR/IR dye, and cameras having broader sensitivity than to just the FR/IR dye emission spectra. One ink suitable for the purpose has an FR dye with a peak excitation frequency of  675  nanometers (nm), and an emission peak at 690 nm. Ideally, the camera filter  86  has a different passband from that of the lamp filters  84 ,  88 , to keep the light energy from the illumination sources from entering the camera  72  and creating noise. Suitable filters for filters  84 ,  86  and  88  are commercially available. For example, an LS-650-F model filter from Corion, 73 Jeffery Avenue, Holliston, Mass. 01746, can be employed as the lamp filters  84 ,  88 . This filter has a 650 nm cutoff, and passes energy with wavelengths below 650 nm. An S10-700-F model filter from Corion can be employed as filter  86 . This filter is a bandpass filter with its passband centered at 700 nm and with a 10 nm passband. It is found that the LS-650-F filter passes sufficient IR energy at 675 nm to excite the FR dye in the ink, and the S10-700-F filter passes sufficient FR energy emitted by the dye at about 690 nm to produce good results. The use of off-the-shelf filter components provides a significant cost advantage in implementing the system. 
     The camera  72  comprising the scanner  70  is sensitive to the FR/IR band of interest, and particularly in this exemplary embodiment to the FR emission band of the FR dye in the ink used to print the barcode, and so will provide an FR image of the invisible ink barcode. The camera can be a CCD camera, but any camera having sensitivity in the spectral range of the FR emission from the dye can be employed. In an alternate embodiment, the camera  72  has sensitivity to the UV emissions from the UV dye in the ink forming the identification pattern, and captures an electronic image of the identification pattern in response to the emissions from the UV dye. 
     The exemplary embodiment illustrated in FIG. 1 is particularly suited to reading two-dimensional barcodes. The camera provides an image which is processed by the scanner to determine the barcode pattern. Data representing the sensed barcode image is provided to the system controller  100 , which determines whether the document passed under the scanner has an expected barcode. For a multi-page document, the controller verifies whether all pages are accounted for. The controller can generate a warning if all pages are not accounted for. Thus, the final document produced by the system is verified to have all expected printed pages. The barcode used in the verification procedure is invisible under natural illumination, and so does not provide a visible image which is objectionable in appearance. 
     The printer  52 , printer  60  and scanner  70  can all constitute one integrated machine. Alternatively, a document conveying system can be employed to convey documents or pages of documents as they are printed by machine  52 , to the barcode printing station, and subsequently to the scanning station along the paper path. It is also contemplated that documents can be printed by one machine  52 , manually carried or delivered to another printer machine  62  and subsequently manually carried to another scanner machine  70 . 
     An alternate embodiment of a printing and verification system in accordance with the invention is shown in FIG.  3 . This system  50 ′ has the same printer  52 , inkjet printer  60  and printhead  62 . The ink need not have the UV dye in this embodiment. The illumination source  90  for the scanner  70  is placed beneath the imaging zone  76  to backlight the print media being scanned. Particularly, the print media has two opposed surfaces. The barcode printer  60  prints the barcode on the first surface facing the printhead. The illumination source  90  directs an illumination beam with FR/IR energy onto the second surface. The longer wavelength (FR/IR) energy passes through the paper print medium well enough to excite the FR/IR dye in the ink forming the barcode printed on the top (first) side of the print medium, so that the barcode can still be imaged by the camera  72 . 
     The backlighting provided by the embodiment of FIG. 3 provides several advantages. A single light source  90  can be employed, and its light beam  92  can provide a more uniform illumination than a side lighting from a single light source on the same side of the print media as the camera. The light source can be a laser, an LED, or the output from an optical fiber coupling a remotely located light source. Of course, a standard halogen light source could alternatively be employed. Another advantage is that the camera  72  will have a view of the sample being imaged which is unobstructed by the light source. Further, the light source can be positioned very close to the back surface of the print media, effectively reducing the required output intensity of the light source. Another advantage of the backlighting embodiment is that noise effects caused by glare, which can be a problem in the embodiment of FIG. 1., are eliminated. 
     FIG. 4 is a generalized schematic diagram of a further alternate embodiment of a document printing and verification system in accordance with the invention. This system  50 ″ has the same printer  52 , inkjet printer  60  and printhead  62  as described with respect to the system of FIG. 1, but uses a one-dimensional barcode scanner  70 ′ at the scanning station. The printer  60  can be simplified in this system, since it is only required to print a one-dimensional image. The scanner  70 ′ can be implemented by use of an off-the-shelf one dimensional scanner system, which includes a scanning light source  70 A′ and a photoreceptor  70 B′. One exemplary device suitable for the purpose is the Accusort model  22  uniform product code (UPC) scanner, marketed by Accusort Systems, Telford, Pa. 18969. The scanning light source of this commercial device is believed to be a laser source which emits FR energy at the excitation wavelength range of the FR/IR dye in the ink used by the printer  60 , and the receptor sensitive to the FR/IR emission spectra of the dye. The device  70 ′ performs the processing of the signals from the photoreceptor to provide an output signal to the controller  100  identifying the recognized barcode. 
     In each of the described embodiments, the pattern printed by the printer  60  has been described as a barcode. However, instead of a barcode, the invisible pattern can be other security or tracking indicia. For example, the image could be a document number, or provide the title of the document and/or pagination information. The pattern will be referred to in a general sense as an “identification pattern.” 
     FIG. 5 is a general flow diagram illustrating steps of a document printing and verification method in accordance with the invention. At step  202 , the document is printed by a document printer. Next, at step  204 , an invisible identification image is placed on each page of the document. This is done in an exemplary embodiment by an inkjet printer using an ink with an FR/IR dye. The identification pattern printed on the document is preferably different for each page, to provide a unique identifier for each page. At step  206 , the verification step includes verifying the presence of each page in the document. This is done in the exemplary embodiment by illuminating the document with FR/IR energy, capturing an electronic image of the identification pattern with an FR/IR camera, and using the electronic image in the verification process. 
     In an exemplary printing/verification process, the document printer sequentially prints each page of the document, and the pages are sequentially sent along the paper path to the printer  60  and scanner  70 . Alternatively, the document printer can operate in a “batch” fashion wherein complete documents are printed, and the complete documents are then passed page by page through the printer  60 . The barcoded documents can then be assembled before the pages are scanned for verification, or alternatively sent page by page along the paper path between the printer  60  and scanner  70 . 
     It is understood that the above-described embodiments are merely illustrative of the possible specific embodiments which may represent principles of the present invention. Other arrangements may readily be devised in accordance with these principles by those skilled in the art without departing from the scope and spirit of the invention.