Patent Document

FIELD OF THE INVENTION 
       [0001]    The present invention relates to an illumination system for an imaging-based reader and, more particularly, to an illumination system for an imaging-based bar code reader including an illumination guide that provides uniform illumination having an increased area from which illumination exits the imaging based bar-code reader and directs the exiting light in a predetermined direction toward a target object for imaging. 
       BACKGROUND ART 
       [0002]    Various electro-optical systems have been developed for reading optical indicia, such as bar codes. A bar code is a coded pattern of graphical indicia comprised of a series of bars and spaces of varying widths, the bars and spaces having differing light reflecting characteristics. Some of the more popular bar code symbologies include: Uniform Product Code (UPC), typically used in retail stores sales; Code 39, primarily used in inventory tracking; and Postnet, which is used for encoding zip codes for U.S. mail. Systems that read and decode bar codes employing charged coupled device (CCD) or complementary metal oxide semiconductor (CMOS) based imaging systems are typically referred to hereinafter as imagining systems, imaging-based bar code readers or bar code scanners. 
         [0003]    Imaging-based bar code reader systems electro-optically transform the graphic indicia into electrical signals, which are decoded into alphanumerical characters that are intended to be descriptive of the article or some characteristic thereof. The characters are then typically represented in digital form and utilized as an input to a data processing system for various end-user applications such as point-of-sale processing, inventory control and the like. 
         [0004]    Imaging-based bar code reader systems that include CCD, CMOS, or other imaging configurations comprise a plurality of photosensitive elements (photosensors) or pixels typically aligned in an array pattern that could include a number of arrays. The imaging-based bar code reader systems employ light emitting diodes (LEDs) or other light sources for illuminating a target object, e.g., a target bar code. Light reflected from the target bar code is focused through a lens of the imaging system onto the pixel array. As a result, the focusing lens generates an image from its field of view (FOV) that is projected onto the pixel array. Periodically, the pixels of the array are sequentially read out creating an analog signal representative of a captured image frame. The analog signal is amplified by a gain factor, by for example an operational amplifier or microprocessor. The amplified analog signal is digitized by an analog-to-digital converter. Decoding circuitry of the imaging system processes the digitized signals representative of the captured image frame and attempts to decode the imaged bar code. 
         [0005]    As mentioned above, imaging-based bar code readers typically employ an illumination system to flood a target object with illumination from a light source such as an LED in the reader. Light from the light source or LED is reflected from the target object. The reflected light is then focused through a lens of the imaging system onto the pixel array, the target object being within a field of view of the lens. It is not uncommon for a single reader to employ multiple LED sources or a bank or cluster of LEDs in order to achieve the amount of illumination necessary for a successful reflection from the target object. Such configurations are often costly to manufacture, and also undesirably, demand increased power requirements, thus reducing battery life on portable readers. In addition, multiple LED sources may create non-uniform illumination with hot spots in the image, i.e. local areas of bright light 
         [0006]    What is needed is a cost effective imaging-based bar code reader system capable of generating an illumination pattern having a sufficient lighting to produce a successful image from the target object, while minimizing power requirements, maximizing the systems efficiency. 
       SUMMARY 
       [0007]    In accordance with one example embodiment of the present invention, an illumination assembly for emitting illumination for imaging a target object, the imaging assembly comprises an illumination source that emits at least one light beam upon activation toward an illumination guide. The illumination guide has a first and a second side, the light beam from the illumination source being diffused between the first and second sides. A textured surface is located substantially along the first side of the illumination guide. The diffused light exits the illumination guide from the textured surface to form a prescribed illumination pattern for imaging a target object. 
         [0008]    In accordance with another example of the present invention, a method for imaging a target object comprises the steps of energizing an illumination source to form a light beam and positioning the illumination source in contact or close proximity to an illumination guide having first and second side, one of the sides has a textured surface while the other of the sides has a smooth surface. The method further comprises diffusing the light beam through the illumination guide and influencing the diffused light beam to exit from the illumination guide through the textured surface forming a controlled illumination pattern for imaging a target object. 
         [0009]    In accordance with yet another example of the present invention, an imaging system for directing an illumination pattern at a target object when the system is actuated comprises a pixel array and a focusing lens to focus an image of the target object onto the pixel array. The system further comprises an illumination source emitting at least one light beam upon activation toward an illumination guide, the illumination source is in contact with the illumination guide. The illumination guide has a first and a second side, the light beam from the illumination source being diffused by the illumination guide between the first and second sides. A textured surface is located substantially along one of the sides and the other of the sides has a relatively smooth surface. The diffused light exits the illumination guide from the textured surface to form a prescribed illumination pattern at a target object. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
         [0010]    The foregoing and other features and advantages of the present invention will become apparent to one skilled in the art to which the present invention relates upon consideration of the following description of the invention with reference to the accompanying drawings, in which: 
           [0011]      FIG. 1  is an elevated view of an imaging-based bar code reader reading a series of bar codes from a “pick list”; 
           [0012]      FIG. 2  is a function block diagram of an imaging reader system constructed in accordance with one embodiment of the present invention; 
           [0013]      FIG. 3A  is perspective view of an imaging-based bar code reader constructed in accordance with one embodiment of the claimed invention; 
           [0014]      FIG. 3B  is a perspective view of an imaging-based bar code reader constructed in accordance with one embodiment of the claimed invention; 
           [0015]      FIG. 4  is a sectional view of an illumination guide as depicted along line  4 - 4  in  FIG. 3A ; 
           [0016]      FIG. 5  is a sectional view of an illumination guide as depicted along line  5 - 5  in  FIG. 3B ; and 
           [0017]      FIG. 6  is a sectional view of an illumination guide in accordance with one embodiment of the claimed invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0018]    An elevated side-view of an imaging-based reader  10  is depicted in  FIG. 1 . A typical profile of the portable bar code reader  10  is physically shown that uses an internal power source such as a battery, but could be a reader having a wire connection from which power is supplied, or remotely powered through an induction system without departing from the spirit and scope of the claimed invention. In addition to imaging and decoding 1D and 2D bar codes, including postal codes, and Code 39 bar codes, the reader  10  is also capable of capturing images and signatures. In one example embodiment, the bar code reader  10  is a hand held portable reader that can be carried and used by a user walking or riding through a store, warehouse, or plant, while reading bar codes for stocking and inventory control purposes. However, it should be recognized that the imaging-based bar code reader  10  of the present invention, to be explained below, may be advantageously used in connection with any type of imaging-based automatic identification system including, but not limited to, bar code scanners, signature imaging acquisition and identification systems, optical character recognition systems, fingerprint identification systems and the like. It is the intent of the present invention to encompass all such imaging-based automatic identification systems. 
         [0019]    Returning to  FIG. 1 , the imaging-based bar code reader  10  includes a handle  12 , which is located between an upper end  14  and lower end  16  of the reader  10 . The reader further includes a reading portion or head  18  situated between a first and second ends  20  and  22 , respectively. 
         [0020]    Typically located about the upper end  14  of the handle  12  is a trigger  24  that when engaged by an operator initiates the reading of a target object or in this example embodiment, a bar code  26 . The trigger  24  is coupled to the reader&#39;s circuitry for initiating the reading of the target bar code  26 , which is often positioned on an article such as a package, or at times on a pick list  28 , as shown in  FIG. 1 . The pick list  28  includes an array of bar codes with spaces or voids therebetween. 
         [0021]    If the reading process is to be manually performed by an operator, the process is typically activated by engaging the trigger  24 . However, other reading systems may be automated reading system initiated by an instruction internal to the reading system&#39;s software or circuitry. Alternatively, the initiation of the automatic reading system may be continuous once power is supplied to the reader. For either the manual or automatic reading system, an illumination source is energized projecting a first illumination pattern  30  from the first end  20  of the reader  10  through a window  32 , as depicted in  FIG. 1 . 
         [0022]    Referring now to  FIG. 2  is a functional block diagram of an imaging reader system  34  capturing a target object, this example being a two-dimensional image  36 . The system  34  includes several components typically located within the reader  10 , but could be remotely located without departing from the spirit and scope of the claimed invention. 
         [0023]    Functioning as a part of the system  34  is a scan engine  38  that is connected to reading components that perform functions such as imaging, control, and decoding. In this example embodiment, the system  34 , including the scan engine  38  is positioned within the head  18  and handle  12  of the reader  10 . The engagement of the trigger  14  initiates an illumination source  40  that results in the emission of a light beam  42 . In an automatic reader, the trigger  14  could be omitted since the light beam is typically enabled once power is supplied to an imaging-based reader  10 . The illumination source  40  may be any device capable of producing a light beam  42 , for example an LED or cold cathode lamp (CFL) would be suitable devices. 
         [0024]    The light beam  42  is scattered by an illumination guide  44  that projects the illumination pattern  30  through the window  32  toward the barcode. It is desirable to have the illumination pattern  30  match or fill the field of view (FOV) of an imaging camera  43  located within the reader  10 . The illumination pattern  30 , illuminates the target object  26 . The target object  26  scatters the light forming an image  46  that is captured by the imaging camera  43 . The scattered light from the target object  26  is redirected back toward the reader  10  through the window  32  and illumination guide  44 , and is altered by a lens  48  connected to the imaging camera  43 . The image  46  is then formed or focused by the lens  48  and is directed onto a multi-dimensional pixel array  50 , filling the pixel array sensors with data. The lens  48  focuses or forms the image  46  onto the pixel array  50 , which is tied and captured to an imager  52 . The pixel array  50  and imager  52  are additional components that construct the imaging camera  43  that is located inside the reader  10 . The multi-dimensional pixel array  50  produces a data grid corresponding to the image  46  from the target object  36 . It should be appreciated by those skilled in the art that the pixel array  50  and imager  52  could be either a charged coupled device (CCD) or complementary metal oxide semiconductor (CMOS) based imaging type both having multi-dimensional array of sensors that sense the image  46  and form pixel data corresponding to the image of the target object  36 . 
         [0025]    An analog to digital (“A/D”) converter  54  located in the scan engine  30 , receives the stored analog image from the imager  52 . The A/D converter  54  then sends a digital signal to a decoder  56  where the signal becomes synthesized by the decoder&#39;s internal circuitry. An example of such a sensor is Micron Technology Inc. CMOS image sensor part number MT9M001. However, the A/D converter  54  and decoder  56  do not have to be incorporated into the scan engine, and may be housed in separate scanner components. The scan engine  30  is associated to a microprocessor  60  that is connected to the imaging reader  10 . The microprocessor  60  assists in processing and decoding the image into a data stream through firmware  62 . The firmware  62  is embedded within the microprocessor  60  or scan engine  30  onto for example, flash Read Only Memory (ROMs) or as a binary image file that can be programmed by a user. Alternatively, the scan engine could employ an application specific integrated circuit (ASIC). 
         [0026]    If the decode process executed within the decoder  56  is successful, the decode session may be terminated with the decoded information being transmitted to an output  64 , which could be tied to a number of reader peripherals. These could include for example, visual display devices such as a monitor or LED, a speaker, or the like. 
         [0027]      FIG. 3A  illustrates a perspective view of an imaging-based bar code reader  10  constructed in accordance with one embodiment of the claimed invention. The first end  20  of the head  18  is in view showing a circular-shaped window  32 . Located internally and behind the window  32  is a circular-shaped illumination guide  44  having a textured or crenulated surface  70 . While a circular shaped window  32  and illumination guide  44  are shown, the structures could be any geometrical shape without departing from the spirit and scope of the claimed invention. For example, the illumination guide could be circular, elliptical, or square. In addition, the scattering of the light by the illumination guide  44  could also be achieved by the geometrical shape of the guide. For example, a prism or wedge shaped illumination guide  44  could also be used to produce the scattered light effect. 
         [0028]      FIG. 3B  illustrates a perspective view of an imaging-based bar code reader  10  constructed in accordance with one embodiment of the claimed invention. Similarly oriented with the reader of  FIG. 3A , the reader  10  of  FIG. 3B  provides a view of the window  32 . However, the example embodiment of  FIG. 3B  further provides an area of discontinuity  72  located substantially about the center of the circular-shaped illumination guide  44 . The area of discontinuity  72  could however be positioned and assume any geometrical shape within the illumination guide  44  without departing from the spirit and scope of the claimed invention. 
         [0029]    The area of discontinuity  72  could be a through aperture in the illumination guide  44  or a section of material (optical transmission material) differing in composition from the type of material used for the illumination guide that would allow for uninhibited transmission of the image  46 . Alternately, the area of discontinuity could be from the same material as the illumination guide  44 , but the surface would lack texturing. An example of a suitable transmission material includes clear glass, plastic, or any optically translucent/transparent media. The illumination guide  44  further provides a dust seal, protecting the scan engine components from debris typically produced from external environments. 
         [0030]    Referring now to  FIG. 4  is a section view of the illumination guide  44  along line  4 - 4  as shown in  FIG. 3A . A single illumination source  40  is shown as being coupled to the illumination guide  44 . More specifically, the illumination source can be attached to, or in close proximity to the illumination guide  44  such that light passes through the guide and exiting through the textured, rough, or crenulating surface  70  in a scattered and predetermined direction toward the target object  26 . The illumination guide  44  is a plate-like structure, typically having a thickness or width that is much smaller relative to its height. The illumination guide  44  is made from optically translucent material and the typical thickness or width is very small ranging up to a few millimeters. The illumination guide&#39;s width is defined by two sides, where the sides could be parallel to each other or one side could include a small wedge. 
         [0031]    The textured surface  70  is a microstructure that enhances the illumination pattern  30  by scattering the light toward the target object  26 . Such configuration eliminates the need for LED banks and clusters that are both costly and power consuming. In addition, the illumination guide  44  provides uniform illumination background and scatters the light over a larger area. In applications where the target object  26  is located on a shiny reflective surface such as surgical instruments or displays of cell phones, it is constructive to have a large illumination system, which the illumination guide  44  provides. The imaging camera  43  of the reader  10  captures the image of the target object  26  with the illumination system reflected on the background from the shiny surface of the object on which the target object appears. The light from the target object itself is scattered or absorbed and appears as dark features in the image  46 . The image  46  is further enhanced due to the reflection of the target object&#39;s supporting surface. 
         [0032]    The textured surface  70  includes a plurality of ridges  76  each having a microstructure height x and a pitch distance y. The illumination guide  44  is made from any material capable of scattering the light beam  42  into the desired illumination pattern  30 . Examples of suitable materials include any optically translucent materials, isotropic materials, translucent plastic, and etched glass. 
         [0033]    The textured surface  70  is a microstructure surface providing a desirable degree of light scattering at the target object  26 . The textured surface could be integrated into the illumination guide  44  or added to the surface of the guide as a separate substrate. An example of a suitable microstructure surface would include a surface having a pitch distance and microstructure height ranging from a few microns up to a half of a millimeter. The illumination guide  44  material and construction can be such that allows the reflected image  46  (the image of the target or scattered light from the target  26 )  46  to pass unaffected through the guide into the lens  48  without degradation to the reflected image as shown in  FIG. 2 . 
         [0034]    Alternatively, the example embodiment depicted in  FIGS. 3B and 5  include an area of discontinuity  72  for receiving the reflected image  46 .  FIG. 5  shows the alternative embodiment of the imaging-based bar code reader  10  such that objects previously discussed operating in a similar fashion are denoted with the addition of a prime next to the reference character. The illumination guide  44 ′ includes a first and a second section  44   a  and  44   b , respectively. The sections  44   a ,  44   b  may be continuous, if for example the illumination guide  44 ′ is circular-shaped as shown in  FIG. 3B . Alternatively, depending on the illumination guide  44 ′ geometry, the sections  44   a ,  44   b , may be separate, as the case for a rectangular shaped guide. 
         [0035]    In the illustrated embodiment the area of discontinuity  72  is centrally located about the illumination guide  44 ′, but could be located at any location along the illumination guide. The area of discontinuity  72  could be any material differing from the illumination guide  44 ′ that provides enhanced transmission of the reflected image  46  through the illumination guide, for example clear glass. Alternatively, the area of discontinuity could be an aperture or void in the illumination guide  44 ′ creating a passage for the reflected image  46  or be made from the same material as the illumination guide but without a textured surface. When a material is used in the area of discontinuity  72  it provides a secondary function, acting as a protective shield by preventing debris and other foreign objects from entering the imaging-based reader  10  that pass beyond the window  32 . Both the first and second sections  44   a ,  44   b  may have a respective illumination source  40   a ,  40   b , or be illuminated by a single illumination source similarly attached to, or in close proximity to one of the first or second sections. Alternatively, any number of illumination sources could be used around the perimeter of the illumination guide depending on the amount of illumination required for the desired application. 
         [0036]      FIG. 6  illustrates an example embodiment constructed in accordance with the claimed invention in which the illumination guide  44  includes a diffused screen  78  in contact or connected to the illumination guide along the interior side of the reader  10 . The diffuse screen  78  enhances the light uniformity and efficiency of the guide  44 . The diffuse screen may further enhance the scattering of light achieved by the illumination guide  44  by making the diffuse screen  78  from optically non-transparent material accomplished by the addition of color, such as white or a color consentient with the color of the LED(s) for producing the light. For example, if a red LED is used, the diffuse screen  78  may be similarly colored red. 
         [0037]    While the present invention has been described with a degree of particularity, it is the intent that the invention includes all modifications and alterations from the disclosed design falling with the spirit or scope of the appended claims.

Technology Category: 3