Abstract:
A portable viewer for viewing bar codes and other markings printed at least in part with invisible inks includes a light source for illuminating and exciting the ink of the bar code, a camera for detecting light emitted by the excited bar code and for outputting image data, a display for creating a visible image of the bar code from the image data output from the camera, and an optical system for projecting the visible image onto a viewing screen. The display may be a miniature, transmissive active matrix liquid crystal display with high resolution that produces a sharp, bright image. A backlight and lens project the image produced by the display to generate an enlarged virtual image that can be easily viewed by a user. The portable viewer is compact in size and can be accommodated in a small package and requires only a small amount of power.

Description:
FIELD OF THE INVENTION 
     The present invention relates generally to the field of bar code readers and viewers, and more particularly to a portable bar code viewer for viewing bar codes and other markings that are not visible to the unaided eye. 
     BACKGROUND OF THE INVENTION 
     Bar codes have been used in a wide variety of applications as a method for conveying information about products. For example, bar codes are frequently applied to products to identify the product and the price of the product. This information is used by point-of-sale terminals, quality control systems, and inventory control systems. Bar codes are also frequently used in personnel access systems and mailing systems. 
     Bar codes typically comprise a series of black lines. The width and spacing between the lines corresponds to a code. There are many different kinds of bar codes known in the art. In each bar code system, an alphanumeric character or other symbol is represented by a unique pattern of lines. The bar code is read by scanning the bar code with a beam of visible, infrared, or ultraviolet light. The lines of the bar code absorb a portion of the light and a portion of the light is reflected by the background of the bar code, or vice versa. The light reflected from the bar code is detected by the scanner, converted into an electrical signal and then decoded. 
     Most bar codes are printed with inks that are visible to the naked eye. One disadvantage of visible bar codes is that the visible bar code takes up space on products and labels, often detracting from their appearance. Inks that are not visible to the naked eye have also been used in the past to print bar codes. Bar codes printed in invisible inks can be printed over other information on labels, thereby saving space on the product, package, or label. Also, invisible bar codes can be used to authenticate products or documents and to prevent or hinder counterfeiting. For example, invisible bar codes can be printed on stock certificates, bonds, currency, and licenses. Unlike visible bar codes, invisible bar codes are difficult to forge because special inks are required that may not be generally available. 
     When bar codes are printed in invisible inks, there is a problem in locating the code so that it can be scanned. Viewers or scanners for reading invisible bar codes tend to be large and bulky and therefore not suitable for use as portable, hand-held scanners or viewers. Accordingly, there is a need for a portable scanner or viewer that is capable of reading invisible bar codes or other markings. 
     SUMMARY OF THE INVENTION 
     The present invention is a portable viewer for viewing bar codes and other markings printed in whole or in part with invisible inks. The viewer comprises a light source for illuminating and exciting the ink of the bar code, a camera for detecting light emitted by the excited bar code and for outputting image data, a display for creating a visible image of the bar code from the image data output from the camera, and an optical system for projecting the visible image onto a viewing screen. The display is preferably a miniature, transmissive active matrix liquid crystal display (AMLCD) with high resolution that produces a sharp, bright image. A backlight and lens project the image produced by the display to generate an enlarged virtual image that can be easily viewed on the viewing screen. 
     One benefit of a viewer using such a display and optical system is that it requires only a small amount of power. Therefore, a relatively small battery can be used to power the viewer. Also, the components are compact in size and can be accommodated in a small package. These factors are important in being able to meet the demand for a portable, hand-held viewer capable of reading invisible bar codes or other markings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view of the bar code viewer of the present invention including the optional sheath with the end flaps open showing the viewing end. 
     FIG. 2 is a perspective view of the bar code viewer of FIG. 1 showing the light source end. 
     FIG. 3 is a perspective view of the bar code viewer of FIG. 1 with the sheath end flaps closed. 
     FIG. 4 is a schematic block diagram of the bar code viewer. 
     FIG. 5 is a simplified diagram of the optical system of the bar code viewer. 
     FIG. 6 perspective view of the bar code viewer with the sheath main body moved to the deployed position so as form a shroud for the viewer. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     For purposes of illustration, the present invention will be described in the context of viewing an invisible bar code. However, the present invention is not so limited and also encompasses viewing other invisible markings, for example, certification marks and the like, and viewing markings having both visible and invisible portions. 
     Referring now to the drawings, the bar code viewer of the present invention is shown therein and indicated generally by the numeral  10 . The bar code viewer  10  includes a housing  20  containing a battery  42 , a power supply  44 , a light source  50 , a camera  60 , an electronic display  70 , and an optical system  80  for viewing the image on the display  70 . The battery  42 , which may be a single cell or multiple cells, supplies power to the rest of the viewer  10  via the power supply  44 . The power supply  44  conditions the power from the battery  42  to a type suitable for driving the rest of the electrical components of the viewer  10 . The light source  50  illuminates the invisible bar code. The camera  60  detects light reflected or emitted by the invisible bar code. The electronic display  70  produces a visible image from data output from the electronic camera  60 . 
     The power supply  44  should be highly power-efficient. One or more on/off switches  46 , 48  may be interposed between the battery  42  and the power supply  44  so as to enable the viewer  10  to be turned on and off. Preferably, one switch  46  is a slidable type and the other  48  is a momentary press type such that when the first switch  46  is enabled and the second switch  48  is pressed, the bar code viewer  10  is turned on; otherwise the viewer  10  is not powered. 
     The light source  50  comprises at least one, and preferably a plurality of light emitting diodes (LEDs)  50 , and is typically disposed on one end face of the housing  20 . The are preferably eight LEDs  50  arranged in a two row array on either side of the lens of the camera  60 . For this described embodiment, the LEDs  50  illuminate the invisible bar code with light having a wavelength of approximately 685 nm. When the bar code is illuminated at this wavelength, the phosphors in the ink emit light above 690 nm which is detected by the camera  60 . An example of LEDs  50  suitable for this embodiment are model CMD41101UR/E lamps from Chicago Miniature of Buffalo Grove, Ill. These LEDs  50  have a peak wavelength of 660 nm, but produce a significant amount of light at 685 nm when energized. The typical inks used for invisible bar codes are excited by light at 685 nm and emit light in the range of 700-1100 nm in response thereto. The LEDs  50  should also produce very little, if any, light above 700 nm, thereby minimizing interference with the detection of emitted light from the bar code. As described above, the activation of the light source  50  is controlled by switches  46 , 48  so that the power usage by the light source  50  can be limited to only when necessary for viewing. 
     The camera  60  is a commercially available CCD, CMOS, or the like type of camera. One embodiment uses a model VL5402-S-003 camera  60  manufactured by VLSI Vision Ltd. of Scotland. The VL5402 camera  60  incorporates a 388×295 pixel image sensor and a fixed aperture lens. The camera  60  produces a composite analog video signal. The video signal output from the camera  60  is directed by a display switch  74  to either an external monitor (not shown) or to a standard RS170/LCD driver circuit  66 . The driver circuit  66  converts the analog video signals to digital signals that are used to drive the display  70 . The driver circuit  66  also produces the proper voltage to drive the backlight  72 . If desired, display switch  74  may also control power to the driver circuit  66  so as depower the driver circuit  66  when the video signal output is directed to the external monitor, thereby further reducing unnecessary power usage. 
     The camera  60  preferably includes an infrared filter  62  attached to the lens of the camera  60 . The filter  62  reduces background light and light from the light source  50  sufficiently to allow the camera  60  to detect the bar code. For example, a model RT-380 filter from Edmund Scientific of Barrington, N.J. may be used. This filter  62  blocks most light below 700 nm (approximately 95%), but allows light to pass through that is between 700 nm and approximately 1200 nm. Thus, the filter  62  allows the light emitted by the invisible ink to pass through, but preferentially blocks any reflected light from the light source  50 . Further, the filter  62  should limit or completely prevent unwanted ambient light from reaching the camera  60 . 
     While a particular light source  50  and filter  62  combination has been used for illustrative purposes, other light sources  50  and filters  62  may be used. The particular light source  50  and filter  62  identified above are suitable for detecting the invisible ink known as CLIR Code ink available from Eastman Chemical Company of Kingsport, Tenn. In practice, the light source  50  and filter  62  used for a particular viewer  10  will depend upon the characteristics of the invisible ink to be detected. The light source  50  should be able to excite the ink, and the filter  62  should allow the ink-emitted light to pass through but preferentially block most of the visible spectrum and the light emitted by the light source  50 . 
     Also disposed on the housing  20  near the opening for the lens of the camera  60  may be an ambient infrared light sensor  54  which senses when the ambient infrared light levels are too high. High ambient infrared light levels have a tendency to drown out the light from the invisible ink, thereby making viewing very difficult. The ambient infrared light sensor  54  should cause an alarm to be activated, such as activating a warning indicator, when the ambient light levels are above a predetermined level, such as approximately 2 lux of sunlight or incandescent light. 
     As mentioned above, the display  70  is preferably a transmissive type active matrix display. In the disclosed embodiment, the display  70  is a monochrome display that produces sharp, bright images. An example of a suitable display  70  has a resolution of 320×240 pixels and an active area measuring 0.24 inches diagonally. The display  70  includes a low power backlight  72  with high optical efficiency. The backlight  72  preferably provides approximately twenty foot-Lamberts of light. The display  70  and backlight  72  together have a low power consumption less than 20 mW. A display  70  and backlight  72  assembly suitable for use with the present invention is the Cyberdisplay monochrome display/backlight module (part no. KCD-QM01-AA) sold by Kopin Corporation of Taunton, Mass. 
     The optical system  80  enlarges and projects the image produced by the display  70 , which is too small for practical viewing. The optical system  80  includes a magnifying lens  82  and a kinoform  84 . The lens has a 16° field of view, allowing the bar code viewer  10  to be held at a comfortable distance from the viewer&#39;s eye. The kinoform  84  provides color correction depending on the color of the backlight  72 . Both the lens  82  and the kinoform  84  have an anti-reflective coating to reduce glare. A hard coating may also be applied to prevent abrasion of the lens  82  and kinoform  84 . As an alternative to hard-coating, a cover glass may be used to protect the kinoform  84  and lens  82 . In order to eliminate distortion, the central axis of the lens  82  should be substantially coplanar with the axis of the display  70  to within 1° (+/−0.5°). The kinoform  84  should also be aligned with the lens  82  for best viewing. For best results, the placement of the center of the kinoform  84  with respect to the optic axis of the lens  82  should be tightly controlled. Deviation from the optic axis should be within approximately 0.005 to 0.01 mm. Tilt of approximately 1° should not substantially degrade color correction of the kinoform  84 . The optical system  80  may be built from discrete components or may be purchased as an assembly. Kopin Corporation makes optical assemblies suitable for practicing the present invention under the model name Cyberlens. 
     A focusing mechanism (not shown) may be included to accommodate the average range of vision. If a focusing mechanism is employed, the lens  82  and kinoform  84  should preferably be moved together, maintaining a constant separation distance. 
     The display  70  and backlight  72  are designed to conserve space and to fit into a compact package suitable for use as a portable viewer  10 . Further, the components have an extremely low power consumption rate so that smaller batteries  42  can be used. Although the display  70  itself is miniature in size, when viewed through the magnifying lens  82  of one preferred embodiment the image is equivalent to viewing a twenty inch display from a distance of five feet. Using the components identified above, the effective focal length of the optical system  80  should be approximately 0.84 inches with a back focal length of approximately 0.68 inches, and a f number of 1.18. The miniature display  70  with its low power consumption, in combination with the optical system  80 , enables the building of a highly compact, portable viewer  10 . 
     Preferably, the housing  20  is surrounded by a sheath  30 , preferably made from a semi-rigid material such as leather, vinyl, or the like. See FIGS.  1 - 3 . The sheath  30  includes a main body  32  and preferably two opposed flexible end flaps  34 . The main body  32  generally conforms to the shape of the viewer housing  20 . In the embodiment shown, the housing  20  has a generally rectangular cross section so the sheath main body  32  likewise has a generally rectangular cross section. The end flaps  34  hinge about an edge of the openings at each respective end of the main body  32  and may be wrapped across the respective ends and snapped closed so as to enclose the viewer housing  20  within the sheath  30 . See FIG.  3 . One advantage of such a sheath  30  is that the main body  32  may be used as a shroud to shield the camera  60  from ambient infrared light. For instance, with the end flaps  34  open, the viewer housing  20  may be slid partially out of the sheath  30  so that the end of the viewer housing  20  having the camera  60  is displaced towards the middle of the sheath  30 . In this manner, the sheath main body  32  forms what can be loosely described as a telescoping shroud that extends out from the viewer  10 . See FIG.  6 . In conditions where the ambient infrared light is too bright, as may be indicated by the ambient infrared light sensor  54 , the sheath  30  may be deployed as described and placed close to or against the object having the bar code so as to better allow viewing thereof. 
     The present invention may, of course, be carried out in other specific ways than those herein set forth without departing from the spirit and essential characteristics of the invention. The present embodiments are, therefore, to be considered in all respects as illustrative and not restrictive, and all changes coming within the meaning and equivalency range of the appended claims are intended to be embraced therein.