Abstract:
An imaging device preferably for use in a 2-D CCD or CMOS sensor is disclosed. The illumination means uses a plurality of illumination sources, some of which are coupled to lenses in an offset manner to promote far field illumination, and some of which are not so coupled and are arranged to provide near field illumination.

Description:
TECHNICAL FIELD 
     This invention relates to imaging devices, and more specifically, to an optimized illumination system having particular application in 2-D imaging systems. 
     BACKGROUND OF THE INVENTION 
     2-D imaging systems typically involve an illumination means and an imaging array, such as Complimentary Metal on Silicon (“CMOS”) or a Charge Coupled Device (“CCD”). Such systems use LEDs or other means to illuminate the object to be captured, and the light reflected from such object is then incident upon the imaging matrix. One problem associated with such devices is that the depth of field over which the illumination of the object can be kept constant is relatively narrow. For example,  FIG. 1  shows how the intensity of illumination falls off drastically as a function of distance from the source. 
     In the prior art, solutions to this problem typically involve installing an additional one or more LEDs or other illumination means, which is directed to the area close to the device. One such arrangement is disclosed in U.S. Published Application No. 2006-0219792. In the &#39;792 publication, two modes of operation are used, each of which has its own associated set of LEDs. Depending upon whether it is desired to capture images in the near field or far field, a different mode of operation is selected, which results in a different set of LEDs being illuminated. However, the position of the various LEDs, renders this arrangement somewhat less than optimal. 
     Another prior art arrangement with a separate set of LEDs to illuminate an area close to the imaging array is disclosed in U.S. Published Application No. 2006-0118627. As depicted in  FIGS. 2A and 2B  of the present application, which are taken from the referenced publication, showing a device having a housing  20 , folding mirror  44 , two illumination systems  42 A and  42 B, and imager  40 . Illumination system  42 A includes a plurality of LEDs exteriorly arranged on housing  20  around window  18 . Each exterior LED projects light over a conical volume, shown as region  56 A and  56 B. The second illumination system  42 B includes one or more LEDs disposed in housing  20  remote from window  18 . The LEDs of system  42 B project light over conical volume  58 . In this fashion, system  42 A illuminates a near range field-of-view and system  42 B illuminates a far-range field-of-view, a separate set of LEDs is disposed vertically to the remaining circuit board in the device, and light is directed from these LEDs to illuminate the close in field of view. 
     These and other prior art arrangements are all suboptimal in that they require arrangements that are either too large in size, too expensive to manufacture, or which are cumbersome to use. Many involve positioning the source of secondary illumination in a manner that increases the manufacturing cost of the device. 
     Some such prior art arrangements are also less than optimal because the illumination means are positioned in a manner that may shine into a user&#39;s eyes. Thus, there exists a need in the art for an improved device that can provide for uniform illumination over a wide range of distances from the imaging array. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows the intensity of light over field of view as distance from the imaging array varies, using a prior art system; 
         FIGS. 2A and 2B  show one exemplary prior art arrangement for attempting to uniformly illuminate objects at a close field of view; 
         FIG. 3  shows a side view from an exemplary embodiment of the present invention; 
         FIG. 4A  is a front view of an exemplary embodiment of the present invention and  FIG. 4B  depicts the manner in which the location of an LED is referenced with respect to the mask opening. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The above and other problems with the prior art are overcome in accordance with the present invention which relates to the technique of providing both near field and far field illumination while at the same time avoiding many of the drawbacks of the prior art. Specifically, a plurality of illumination sources such as LEDs are utilized, where each is positioned behind a lens in an offset manner. Because the LED is offset with respect to the lens in front thereof, the illumination can be directed to the far or near fields of view. 
       FIG. 3  depicts a conceptual side view of an imaging device utilizing the illumination technique of the present invention. The arrangement includes a masking device  306  which partially shields the illumination means  301  and  304  as shown, thereby avoiding the illumination being projected into a user&#39;s eyes. An inner portion of the mask is designated  307 . The mask is preferably continuous, as shown in  FIG. 4A , and includes an opening surrounding the LED to provide an output path for the light. 
     As shown best in  FIG. 3 , an illumination means  304  is placed behind a lens  305  in an offset manner so that the lens  305  acts to direct the illumination to a far field of view. A similar arrangement is employed and depicted as illumination means  301  with lens  310 . The illumination means  301  and  304  act in concert to provide illumination for the far field of view, also as depicted in  FIG. 3 . Further, the illumination means  302  acts to provide illumination for the near field of view. 
     Although the arrangement provides for a substantially uniform illumination from a near field of view to a far field of view, it is nonetheless still contemplated that a user can select between the near and far field of view, and activate the appropriate illumination means (e.g., LEDs). Or, both can simply be activated when the device is activated for capturing an image. 
     For example, and with reference to  FIG. 4A , a user may select, via a user selectable switch for example, LEDs  301  and  304  to be illuminated, which would illuminate a far field of view, or a user may select LEDs  302  to illuminate when an object is within the near field of view. It is also possible that such selection can occur automatically, and to illuminate the appropriate LEDs, such as by a laser based distance measuring apparatus known in the art. 
     The LEDs  301  and  304  may be mounted on a circuit board  340 , and other electronics may be on circuit board  350  as well. 
     Note exemplary LED  304  is aligned with a side of a lens  305  that itself is aligned with an outer mask portion  306 . By placing the LED  304  near to the outer side mask, the beam is directed correctly as shown, and the outer side mask shields the user from having to view the light being emitted by the illumination means  301  and  304 . 
       FIG. 4A  depicts a front view of the imaging device, showing the mask, having inner portion  307  and outer portion  306  (see  FIG. 3 ) as well as camera lens  6  and CCD or CMOS sensor  7  and indicating the field-of-view (FOV) of the imaging device. Within the mask are openings  407  through  410  that enable light from the upper LEDs  301  and lower LEDs  304  to properly illuminate the target. Note that each opening  407 - 410  is actually plural openings; that is, in the illustrative embodiment, there are paired openings  407  (i.e., the two upper-right openings in  FIG. 4A ), paired openings  408  (i.e., the two upper-left openings), etc. The LED within each opening is closest to a different portion thereof for each of the four sets  407 ,  408 ,  409 , and  410  of two openings. Specifically, the LED within each opening  409  is closest to a part of the opening that would form an angle of 315 degrees with respect to the horizontal, if the opening represented a Cartesian plane. This measurement scheme is illustrated in  FIG. 4B . Within opening  410 , that angle would be 215 degrees. Within opening  407 , that angle would be 135 degrees. And within opening  408 , that angle would be 45 degrees. 
     The foregoing positioning of the LEDs within the openings results in the illumination of the proper field of view for objects located relatively far from the device. For near field objects, the illuminations means  302  is used, as shown in  FIGS. 3 and 4A . These LEDs  302  are optionally not surrounded by mask portions  306  and  307 , but their light is nonetheless advantageously blocked from the user&#39;s view by mask portions  306  and  307 . Of course, the entire device may be disposed within a suitable housing, shown only conceptually as  380  for purposes of explanation. 
     While the foregoing describes the preferred embodiments of the present invention, other variations are possible as well. The imaging array may be comprised of any suitable technology other than CMOS or CCD. The lenses shown may be LED mask lenses, or other types of lenses, and the illumination may be derived from sources other than LEDs. These and other embodiments are intended to be within the scope of the appended claims.