Abstract:
A variable reflectance cover for a scanning system. The cover comprises a backing moveable through a plurality of positions. Moving the backing through the plurality of positions varies the reflectance of the cover. In one embodiment, the backing is an endless rotatable belt. In a second embodiment, the backing is a removable panel having a first side with a first reflectance and a second side with a second reflectance. In yet a third embodiment, the backing includes polarizers placed adjacent to a reflective panel. Rotating one polarizer relative to another varies the reflectance of the cover.

Description:
FIELD OF THE INVENTION 
     The present invention relates to a cover for a scanning system, and more particularly to a cover with a variable reflective backing. 
     BACKGROUND 
     An optical scanner is used to generate an electronic file, a bitmap file for example, which is representative of a scanned object such as a document or photograph. This is typically accomplished by passing a controlled light source across the surface of the object. Light reflects off the surface of the object and back onto an array of photosensitive devices such as a charge coupled device, or CCD, array. As the light source passes over the object, the CCD array converts the reflected light intensity into an electronic signal that is ultimately digitized into an electronic file once the entire object is scanned. 
     In a conventional flatbed scanner, the light source and CCD array are located in a base covered by a plane of transparent glass. The object being scanned is placed, or sandwiched, between the glass plane and a cover. The inside surfaces of some covers are constructed of a high reflectance white material. The high reflectance white surface enables the conventional scanner to reduce or eliminate dark borders around the document, black circles where punch holes exist, and dark borders around multiple images such as multiple receipts on a single scan. Moreover, the high reflectance white surface enables the conventional document scanner to improve the contrast of the document&#39;s image by reflecting the light that is transmitted through the object back to the CCD array. For example, when scanning a transparency, the light passing through the transparency reflects off the white cover and is detected by the CCD array. 
     Although a high reflectance white surface will allow a conventional scanner to eliminate unwanted dark areas, this white surface limits the ability of the conventional scanner. More specifically, scanners have the ability to detect the location of the object being scanned. This detection enables the scanner to provide electronic registration and electronic skew correction. Moreover, the detection of the location of the object&#39;s edges enables the scanner to provide automatic magnification selection. However, this edge detection depends upon the ability of the scanner to sense the difference in the reflectance between the object and the cover. Thus, some objects would better be scanned with a black rather than white background on the cover. 
     A scanner with this low reflectance background cover allows for reliable edge detection, but the same background fails to suppress the black borders or punch holes. Moreover, the low reflectance background provides very low contrast when attempting to scan objects such as transparencies or semi opaque objects. 
     Since there are problems with using just a high or a low reflectance background with a scanner, a scanner with at least two modes of reflectance is ideal. Liquid crystal display technology has been used for scanning systems to provide a set of reflectance options. These scanning systems offer a good solution to the problem, but they are expensive. Also, if a problem arises with the liquid crystals it is not easy or inexpensive to repair. In many cases it is less expensive to purchase a new scanner rather than attempting to repair a liquid crystal cover. 
     SUMMARY 
     The present invention is directed to a variable reflectance cover for a scanning system. The cover comprises a backing moveable through a plurality of positions. Moving the backing through the plurality of positions varies the reflectance of the cover. In one embodiment, the backing is an endless rotatable belt. In a second embodiment, the backing is a removable panel having a first side with a first reflectance and a second side with a second reflectance. In yet a third embodiment, the backing includes polarizers placed adjacent to a reflective panel. Rotating one polarizer relative to another varies the reflectance of the cover. 
    
    
     
       DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of a flat bed optical scanner with a conventional cover. 
         FIG. 2  is a side view of the scanner of  FIG. 1  having a cover with a high reflectance backing. 
         FIG. 3  is a side view of the scanner of  FIG. 1  having a cover with a low reflectance backing. 
         FIGS. 4 and 5  are side views of a cover having a rotatable endless belt with high and low reflectance sections. In  FIG. 4 , a high reflectance section is positioned adjacent to a scanning surface. In  FIG. 5 , a low reflectance section is positioned adjacent to a scanning surface. 
         FIG. 6  is a side view of the cover of  FIGS. 4 and 5  wherein the endless belt is rotated by a motor. 
         FIG. 7  is a side view of an endless belt with an increased circumference. 
         FIG. 8  is an isometric view of a cover having a removable panel. 
         FIG. 9  is a top plan view of a cover having adjacent rotatable polarizers. 
         FIG. 10  is a section view taken along the line  10 - 10  in  FIG. 9  wherein the adjacent polarizers allow light to pass through and reflect off the backing. 
         FIG. 11  is a section view taken along the line  11 - 11  in  FIG. 9  wherein the adjacent polarizers are rotated to absorb light before reaching the backing. 
         FIG. 12  is a section view of the cover of  FIG. 9  including a motor for rotating one of the polarizers. 
     
    
    
     DETAILED DESCRIPTION 
       FIGS. 1-3  illustrate a conventional scanner  10  used in conjunction with a computer system (not shown) for acquiring an electronic image of an object  12  (shown in  FIGS. 2 and 3 ) such as a photograph or text document. Scanner  10  generally includes housing  14  containing guide  16  allowing linear movement of scanner carriage  18 . Carriage  18  is mounted below a transparent scanning surface  20  that supports object  12 . To illuminate object  12  carriage  18  includes lamp  22  and reflector  24 . Lamp  22  and reflector  24  are mounted in carriage  18  to focus light up through scanning surface  20  onto object  12 . Scanner  10  also includes cover  26  having backing  28 . 
     Referring to  FIGS. 2 and 3 , an object  12  to be scanned is placed on scanning surface  20  and cover  26  is closed sandwiching object  12  between scanning surface  20  and backing  28 . With lamp  22  illuminated, carriage  18  passes linearly underneath object  12 . Light from lamp  22  reflects off object  12  back onto an array of photosensitive devices such as a charge coupled device (CCD) array  30  in carriage  18 . Discerning the intensity of the reflected light, CCD array  30  generates an electrical signal allowing the computer system to produce a digitized representation of object  12 . 
     Some light also reaches backing  28 . This occurs in areas outside the edges or within punch holes of object  12 . Where object  12  is transparent or opaque, some light passes directly through object  12  reaching backing  28 . The backing  28  illustrated in  FIG. 2  is constructed a high reflectance and generally light colored or white material. Consequently, much of the light reaching backing  28 , either directly or through object  12  is reflected back to CCD array  30 . The backing  28 ′ illustrated in  FIG. 3  is constructed from a low reflectance and generally dark or black material. Consequently, much if not all of the light reaching backing  28 ′ is absorbed rather than reflected. 
     Referring now to  FIGS. 4-12 , the present invention lies in the construction of cover  40 . In the embodiment illustrated in  FIGS. 4-7 , backing  42  is an endless belt  44  rotatable around tension rollers  46  and  48  and partially enclosed within shell  50 . Endless belt  44  has a first high reflectance section  52  and a second low reflectance section  54 . For example, first section  52  may be white, while second section  54  may be black. In  FIGS. 4 and 5 , crank  56  coupled to tension roller  48  allows endless belt  44  to be manually rotated into a desired position. Referring to  FIG. 6 , endless belt  44  may instead be automatically rotated by motor  58  engaging tension roller  48 . It is envisioned that motor  58  will be a stepper motor accurately directed by a series of electrical pulses generated by controller  60 . Advantageously, endless belt  44  can be easily removed and replaced when damaged or interchanged with another belt having sections with different levels of reflectance. 
     With first section  52  rotated into place adjacent to object  12 , as shown in  FIG. 4 , light reaching first section  52  is reflected back to CCD array  30 . With cover  40  closed and second section  54  rotated into place adjacent to object  12 , light reaching backing  42  is absorbed rather than reflected. Alternatively, endless belt  44  may have more than two sections each having a specified reflectance. For example, in addition to including high and low reflectance sections, endless belt  44  can include additional sections having varying levels of reflectance. The possible combinations are infinite. The increased area needed for additional sections can be obtained by increasing the circumference of endless belt  44 . This increased circumference can be managed with additional tension rollers  62 ,  63 , and  64  as illustrated in  FIG. 7 . 
     In the embodiment of cover  40  illustrated in  FIG. 8 , backing  42  is a removable panel  66  held in a slot created by grips  68  and  70 . Panel  66  has a first side  72  having a first reflectance and a second side  74  having a second reflectance. With cover  40  open, panel  66  can be manually removed and replaced so as to expose either the first or the second side  72  or  74 . For example, first side  72  may be white and second side  74  may be black. Where a backing with a high reflectance is desired, panel  66  is placed between grips  68  and  70  such that first side  72  is exposed. When cover  40  is then closed, first side  72  will be immediately adjacent to the object being scanned. When a backing with a low reflectance is desired, panel  66  is removed and replaced such that second side  74  is exposed. Panel  66  can be easily replaced if damaged or can be interchanged with another panel when other reflectance levels are desired. 
     In the embodiment of cover illustrated in  FIGS. 9-12 , backing  42  includes a first polarizer  76 , second rotatable polarizer  78  affixed to reflective panel  80 . Polarizers  76  and  78  are rotatable relative to one another in order to vary the amount light from lamp  22  that reaches reflective panel  68 . Light can be represented as a transverse electromagnetic wave. Imagine, for example, a length of rope held by two children at opposite ends, the children begin to displace the ends of the rope in such a way that the rope moves in a plane either up and down, left and right, or any angle in between. Ordinary white light is made up of such waves that fluctuate at all possible angles. 
     Light is considered to be linearly polarized when it contains waves that only fluctuate in one specific plane. It is as if the rope in the example is strung through a picket fence. The wave can only move up and down in a vertical plane. A polarizer is a material that only allows only light with a specific angle of vibration to pass through while it absorbs the rest. The direction of fluctuation passed by the polarizer is referred to as the polarizer&#39;s optical axis. If two polarizers are set up in series so that their optical axes are parallel, light passes through both. However, if the polarizers are rotated relative to one another until their optical axes are perpendicular, the polarized light passing through the first will be absorbed by the second. As the polarizers are rotated in relation to one another and the angle between their optical axes varies from zero to ninety degrees, the amount of light passing through both polarizers decreases proportionally. 
     In  FIG. 10 , the optical axes of the first and second polarizers  76  and  78  are parallel. In  FIG. 11 , polarizer  78  is rotated until those axes are perpendicular to one another.  FIG. 10  illustrates the configuration generating a maximum effective reflectance with the greatest amount of light reaching reflective panel  80  and reflecting back to CCD array  30 .  FIG. 11 , on the other hand, illustrates the configuration producing a minimum effective reflectance with polarizers  76  and  78  absorbing all light before it reaches reflective panel  80 . The effective reflectance can be tuned to any desired level between the minimum and maximum levels by adjusting the angle between the optical axes of polarizers  76  and  78 . 
     In the embodiment illustrated in  FIGS. 9-11 , second polarizer  78  and attached reflective panel  80  are manually rotated using dial  82 . Dial  82  includes knob  84  coupled to shaft  86  passing through shell  50 . Shaft  86  is then coupled to reflective panel  80 . Turning knob  84  rotates reflective panel  80  and the attached second polarizer  78 . In one version, dial  82  may also include lever  88  and gauge  90 . Lever  88  extends radially outward from knob  84  across the surface of shell  50  allowing for a more accurate rotation and placement of second polarizer  78 . Lever  88  is placed such that when it points to one end of gauge  90 , the optical axes of polarizers  76  and  78  are parallel. When lever  88  is rotated so that it points to the other end of gauge  90 , the optical axes of polarizers  76  and  78  are perpendicular. Cover  40  may include stops  92  for holding dial  82  and joined second polarizer  78  stationary in one of many predetermined positions. Alternatively, second polarizer  78  can be automatically rotated by motor  94  as illustrated in  FIG. 12 . It is envisioned that motor  94  will be a stepper motor accurately directed by a series of electrical pulses generated by controller  96 . 
     Although the invention has been shown and described with reference to the foregoing exemplary embodiments, it is to be understood that other embodiments are possible, and variations of and modifications to the embodiments shown and described may be made, without departing from the spirit and scope of the invention as defined in following claims.