Abstract:
A multi-lightguide document imaging device is proposed for scanning a document transported atop it. The device includes:
       a line image sensor module having a top sensing area and built-in circuitry for converting an incident line image into video signal output.   an intervening rod lens for focusing line image lights from the document onto the sensing area.   a number of lightguides lightguide-j (j=1, 2, . . . , N) disposed below the document where each lightguide-j has its own built-in light sources, a transverse cross section spaced at a distance SPC j  from the scan line and oriented angularly along a θ-coordinate so as to project a line-illumination aiming at the scan line.   an imager frame having a base for holding the line image sensor module, a multi-element support for holding the rod lens plus the lightguides and a scan line backing portion for backing the document.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates to electronic document imaging. More particularly, the present invention is directed to a linear electronic document imaging device as used in an image reading apparatus such as copying apparatus, facsimile apparatus, scanner and electronic blackboard. 
         [0003]    2. Related Background Art 
         [0004]    To facilitate explaining the background leading to the present invention, a typical traditional lightguide electronic document imager  10  is illustrated here in  FIG. 1A  and  FIG. 2A . The traditional lightguide electronic document imager  10  has an imager frame  30  whose top part has a scan line backing portion  33  with a transparent window  34  located therein. The top surface of the scan line backing portion  33  and the transparent window  34  are both flat for supporting an advancing document  2  with its image side down and along a transport direction as indicated by an arrow. The mechanism for advancing the document  2  is well known in the art, including for example stepper motor and drive rollers, and not shown here. To facilitate further description, a background X-Y-Z Cartesian coordinates are added wherein the X-Y plane is further alternatively expressed with an r-θ polar coordinates with the r-axis coincides with the X-axis and the θ-coordinate incrementing clockwise. Thus, as the document  2  is advanced atop the transparent window  34 , the image side of the document  2  gets scanned by the traditional lightguide electronic document imager  10  line-by-line with a scan line  4  lies parallel to the Z-axis and centered at X=Y=0. Below the scan line backing portion  33  and located inside the imager frame  30  are a lightguide  13 , a rod lens  20  and a line image sensor module  11 . Atop the line image sensor module  11  is a line image sensing area  12  and associated built-in signal conversion circuitry (not shown) for converting an incident line image light into a corresponding video signal output  14 . The lightguide  13  typically includes internal light sources such as red light source  151 R, blue light source  151 B and green light source  151 G. The lightguide  13  further converts emissions from the internal light sources into line-illumination  17  generally aiming at the scan line  4 . The line-illumination  17  then gets image-wise reflected by the image side of the document  2  along the scan line  4  and focused by the rod lens  20  into incident line image  5  ultimately focusing onto the line image sensing area  12  thus consequently converted into the video signal output  14 . For convenience of technical description to be presently described, an imaging parameter called imaging distance  15  (IMD) is shown that is defined as the distance between the scan line  4  and the focal point of the line image sensing area  12 . A highly important and well known performance parameter for an electronic document imager is its output signal-to-noise ratio (S/N) as measured from the video signal output  14 . Accordingly, it is a primary object of the present invention to provide an improved lightguide electronic document imager with a higher S/N. 
       SUMMARY OF THE INVENTION 
       [0005]    A multi-lightguide document imaging device is proposed for line-by-line scanning of a document transported atop it. This device includes:
       a line image sensor module having a top line image sensing area and built-in electronic circuitry for converting an incident line image into video signal output.   an intervening rod lens for focusing line image lights reflected from a scan line of the document onto the line image sensing area through an imaging distance.   a number of lightguides lightguide- 1 , lightguide- 2 , . . . , lightguide-j, . . . , lightguide-N (N&gt;=2) disposed below the document where each lightguide-j has one or more built-in light sources, a longitudinal body parallel to the scan line with a transverse cross section spaced at a distance SPC j  from the scan line and oriented angularly along a θ-coordinate so as to project a corresponding line-illumination aiming predominantly in an illuminating direction ILD j  and closely at the scan line.   an imager frame having an integrated base portion, a multi-element support portion and a scan line backing portion. Structurally, the base portion holds the line image sensor module, the multi-element support portion holds the rod lens plus the number of lightguides and shields various imaging lights, and the scan line backing portion backs the document being transported while allowing its line-illumination through a transparent window by the numerous lightguides.       
 
         [0010]    As a refinement, the imaging distance and each of the distance SPC j  are further adjusted to minimize, for each lightguide-j, a corresponding imaging conjugate distance ICD j  defined as the total distance a light travels between the lightguide-j and the line image sensing area, so as to maximize the corresponding portion, as contributed by the lightguide-j, of light power of the incident line image. 
         [0011]    As another refinement, the θ-coordinate of each lightguide-j is further adjusted so as to maximize the corresponding portion, as contributed by the lightguide-j, of light power of the incident line image. 
         [0012]    As another refinement, all surfaces of the imager frame potentially exposable to stray lights along all the imaging conjugate distances ICD j  (j=1, . . . , N) are further made highly non light reflective to reduce the S/N. 
         [0013]    As a more specific embodiment for the case of a dual-lightguide document imaging device where N=2, the transverse cross sections of the two lightguides are oriented angularly along the θ-coordinate respectively at θ=45+/−25° and 0=135+/−25° and each of the two lightguides is provided with three built-in light sources of red, green and blue. This makes the dual-lightguide document imaging device a full color imaging device having a per-color document illumination intensity that is about double that of an otherwise traditional, single lightguide imaging device. 
         [0014]    These aspects of the present invention and their numerous embodiments are further made apparent, in the remainder of the present description, to those of ordinary skill in the art. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0015]    In order to more fully describe numerous embodiments of the present invention, reference is made to the accompanying drawings. However, these drawings are not to be considered limitations in the scope of the invention, but are merely illustrative: 
           [0016]      FIG. 1A  and  FIG. 2A  depict a typical traditional electronic document imager in cross sectional and combination cross sectional/perspective views and were already described before; 
           [0017]      FIG. 1B  and  FIG. 2B  depict a dual-lightguide electronic document imager in cross sectional and combination cross sectional/perspective views according to an embodiment of the present invention; 
           [0018]      FIG. 3A  and  FIG. 3B  further illustrate, for the dual-lightguide electronic document imager, some key linear dimensional parameters affecting the light power of the incident line image at the line image sensing area; 
           [0019]      FIG. 4A  and  FIG. 4B  further illustrate, for the dual-lightguide electronic document imager, some key angular dimensional parameters affecting the light power of the incident line image at the line image sensing area; 
           [0020]      FIG. 5A  depicts a triple-lightguide electronic document imager in cross sectional view according to another embodiment of the present invention; and 
           [0021]      FIG. 5B  depicts a quadruple-lightguide electronic document imager in cross sectional view according to yet another embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0022]    The description above and below plus the drawings contained herein merely focus on one or more currently preferred embodiments of the present invention and also describe some exemplary optional features and/or alternative embodiments. The description and drawings are presented for the purpose of illustration and, as such, are not limitations of the present invention. Thus, those of ordinary skill in the art would readily recognize variations, modifications, and alternatives. Such variations, modifications and alternatives should be understood to be also within the scope of the present invention. 
         [0023]      FIG. 1B  and  FIG. 2B  depict a dual lightguide electronic document imager  50  in cross sectional and combination cross sectional/perspective views according to an embodiment of the present invention. Comparing with the traditional lightguide electronic document imager  10  depicted in  FIG. 1A  and  FIG. 2A , the structural portion of the dual lightguide electronic document imager  50  dealing with document transport and imaging light path from the scan line  4  down to the rod lens  20  and the line image sensing area  12  is the same as the traditional case. However, instead of a single lightguide, two lightguides, lightguide- 1   151  and lightguide- 2   152 , are now disposed below the scan line  4 . The lightguide- 1   151  has three built-in light sources red light source  151 R, blue light source  151 B and green light source  151 G. The lightguide- 2   152  also has three built-in light sources red light source  152 R, blue light source  152 B and green light source  152 G. The longitudinal body of both lightguides  151  and  152  lie parallel to the Z-axis while their transverse cross sections are oriented angularly along the θ-coordinate so as to respectively project a first corresponding line-illumination- 1   161  and a second corresponding line-illumination- 2   162  aiming predominantly in a first illuminating direction ILD 1  and a second illuminating direction ILD 2  closely at the scan line  4  with essentially no spatial interference between the bodies of lightguides  151  and  152  and the numerous focusing lights, labeled as incident line image  5 , between the scan line  4  and the line image sensing area  12 . For structural support, the imager frame  30  is now provided with an integrated base portion  31 , a multi-element support portion  32  and a scan line backing portion  33 . Like before, the base portion  31  holds the line image sensor module  11 . However, the scan line backing portion  33  backs the document  2  being transported while allowing its line-illumination by the lightguides  151  and  152  and the multi-element support portion  32  holds the rod lens  20  plus the lightguides  151  and  152  and shields the numerous lights of the incident line image  5 . As the total light power from the lights of the incident line image  5  is now contributed by two lightguides  151  and  152  instead of only one lightguide  13  before, a corresponding increase of S/N of the dual lightguide electronic document imager  50  can be expected. As an example, for the case where light power from each of the lightguides  151  and  152  is the same as that from the lightguide  13  the S/N is doubled. As a second example, for the case where light power from each of the lightguides  151  and  152  is only 70% of that from the lightguide  13  the S/N is still increased by 40%. In another embodiment, while not shown here to avoid obscuring details, the video signal output  14  can be made digital by incorporating an Analog-to-Digital Converter (ADC) in the built-in electronic circuitry of the line image sensor module  11 . Furthermore, while the illustrated composition of the built-in light sources of lightguides  151  and  152  are the same, red, green and blue for full color imaging, the composition does not have to be the same under other embodiments and this will be presently described. 
         [0024]      FIG. 3A  and  FIG. 3B  further illustrate, for the dual lightguide electronic document imager  50 , some key linear dimensional parameters affecting the light power of the incident line image  5  at the line image sensing area  12 . For simplicity of description, define LPWR 1  to be the light power of the incident line image  5  at the line image sensing area  12  as contributed by lightguide- 1   151 . Similarly, define LPWR 2  to be the light power of the incident line image  5  at the line image sensing area  12  as contributed by lightguide- 2   152 . As described before, the first key linear dimensional parameter of imaging distance  15  (IMD) is the distance between the scan line  4  and the focal point of the line image sensing area  12 . A second key linear dimensional parameter is the distance SPC 1  between the apex of the transverse cross section (X-Y plane) of the lightguide- 1   151  and the scan line  4 . Likewise, a third key linear dimensional parameter is the distance SPC 2  between the apex of the transverse cross section (X-Y plane) of the lightguide- 2   152  and the scan line  4 . As a result, a first derived key linear dimensional parameter called imaging conjugate distance ICD 1  is defined as: 
         [0000]    
       
      
       ICD 
       1 
       =IMD+SPC 
       1  
      
     
         [0000]    and the LPWR 1  is a nonlinear, highly decreasing function of ICD 1 . It can be seen that the ICD 1  is the total distance a light travels between the lightguide- 1   151  and the focal point of the line image sensing area  12 . Similarly, a second derived key linear dimensional parameter called imaging conjugate distance ICD 2  is defined as: 
         [0000]    
       
      
       ICD 
       2 
       =IMD+SPC 
       2  
      
     
         [0000]    and the LPWR 2  is a nonlinear, highly decreasing function of ICD 2 . The ICD 2  is the total distance a light travels between the lightguide- 2   152  and the focal point of the line image sensing area  12 . As each of the various components lightguide- 1   151 , lightguide- 2   152  and rod lens  20  needs to be of certain minimum physical size to insure their individual functionality and the physical separation amongst them must also be large enough to insure that there is essentially no spatial interference between the bodies of lightguides  151  and  152  and the numerous focusing lights of the incident line image  5 , the allowable range of both IMD and SPC 1  are constrained. This results in a correspondingly constrained functional value  171  of LPWR 1  as depicted in  FIG. 3B  with a local maximum light power 1 . Hence, under this embodiment both IMD and distance SPC 1  are selected to minimize a corresponding imaging conjugate distance ICD 1  so as to produce the desired local maximum light power 1 . Likewise, as also depicted in  FIG. 3B , both IMD and distance SPC 2  are selected with reference to another constrained functional value  172  to minimize a corresponding imaging conjugate distance ICD 2  so as to produce a desired local maximum light power 2 . 
         [0025]      FIG. 4A  and  FIG. 4B  further illustrate, for the dual lightguide electronic document imager  50 , some key angular dimensional parameters affecting the light power of the incident line image  5  at the line image sensing area  12 . In this case, the first key angular dimensional parameter θ 1  is the angular orientation, with reference to the first illuminating direction ILD 1 , along the θ-coordinate of the lightguide- 1   151 . The second key angular dimensional parameter θ 2  is the angular orientation, with reference to the second illuminating direction ILD 1 , along the θ-coordinate of the lightguide- 2   152 . Due to an unavoidable angular, along the θ-coordinate, output light power distribution from the lightguide- 1   151 , the LPWR 1  is also a constrained functional value  181  of θ 1  within its constrained range and this is illustrated in  FIG. 4B . Hence, under this embodiment the first key angular dimensional parameter θ 1  is selected to be θ 0  so as to produce a desired local maximum light power 1 . Due to an unavoidable angular, along the θ-coordinate, output light power distribution from the lightguide- 2   152 , the LPWR 2  is also a constrained functional value  182  of θ 2  within its constrained range and this is also illustrated in  FIG. 4B . Hence, under this embodiment the second key angular dimensional parameter θ 2  is selected to be θ 0  so as to produce a desired local maximum light power 2 . A specific embodiment under this practice is θ 1 =45+/−25° and θ 2 =135+/−25°.” 
         [0026]    To those skilled in the art, by now it should become clear that, within the physical limit imposed by the minimum practical sizes of the lightguides and rod lens, the present invention is not limited to the case of two lightguides. Thus,  FIG. 5A  illustrates a triple lightguide electronic document imager  100  in cross sectional view according to another embodiment of the present invention. A first lightguide- 1   151  produces a line-illumination- 1   161 . A second lightguide- 2   152  produces a line-illumination- 2   162 . A third lightguide- 3   153  produces a line-illumination- 3   163 . Furthermore, the composition of built-in light sources amongst the lightguides are not the same. Specifically, the lightguide- 2   152  is provided with two white light sources  152 W. The variation of light source composition, in combination with a corresponding consistent adjustment of the built-in electronic circuitry of the line image sensor module  11  then allows numerous other applications such as custom color image scanning. 
         [0027]      FIG. 5B  depicts a quadruple lightguide electronic document imager  150  in cross sectional view according to yet another embodiment of the present invention. A first lightguide- 1   151  produces a line-illumination- 1   161 . A second lightguide- 2   152  produces a line-illumination- 2   162 . A third lightguide- 3   153  produces a line-illumination- 3   163 . A fourth lightguide- 4   154  produces a line-illumination- 4   164 . In addition to having the four lightguides  151 ,  152 ,  153  and  154 , each of the two lightguides  151 ,  154  has a built-in custom light source C, for example “orange” in color. Furthermore, all imager frame interior surfaces  35  of the imager frame  30  potentially exposable to stray lights along the imaging conjugate distances ICD 1 , ICD 2 , ICD 3  and ICD 4 , are further made highly none light reflective to reduce the S/N of the quadruple lightguide electronic document imager  150 . The imager frame interior surfaces  35  can be treated with, for example, surface coating using a matt black paint. 
         [0028]    Throughout the description and drawings, numerous exemplary embodiments were given with reference to specific configurations. It will be appreciated by those of ordinary skill in the art that the present invention can be embodied in numerous other specific forms and those of ordinary skill in the art would be able to practice such other embodiments without undue experimentation. The scope of the present invention, for the purpose of the present patent document, is hence not limited merely to the specific exemplary embodiments of the foregoing description, but rather is indicated by the following claims. Any and all modifications that come within the meaning and range of equivalents within the claims are intended to be considered as being embraced within the spirit and scope of the present invention.