Abstract:
A system for processing document to scan the documents to obtain optical image data representing the document is provided. The system ( 10 ) includes elements that reduce or eliminate the effects of debris that can create streaks in the scanned images. One element is a recess ( 174 ) in the lens ( 170 ) through which an imaging device ( 60 ) scans the document. Another element is a guide ( 80 ) having an opening ( 84 ) opposing the lens ( 70, 170 ) of the imaging device ( 60 ). The opening ( 84 ) reduces or eliminates light reflecting off the guide back to the imaging device so that the area around the document is scanned as black.

Description:
PRIORITY CLAIM 
       [0001]    The present invention claims priority to U.S. Provisional Application No. 61/694,385 filed Aug. 29, 2012 and U.S. Provisional Application No. 61/794,285 filed Mar. 15, 2013. The entire disclosure of each of the foregoing applications is hereby incorporated herein by reference. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention relates to the field of scanning systems and in particular to systems that scan and sort items such as documents and pieces of mail. 
       BACKGROUND 
       [0003]    Often scanned document images are analyzed and decisions are made based on the analysis of the image. Additionally, frequently the image is stored and referenced during further processing rather than using the actual item, particularly if the item is a document. 
         [0004]    If the scanned image is not acceptable the user must retrieve the original document and re-scan the image. This significantly reduces the efficiency of the system. Therefore, it is desirable to mitigate problems that can lead to poor images. 
         [0005]    A common problem that results in poor images is dust accumulation at the scanner. If the scanner uses a moveable head, the dust simply shows up as a small spot or speck on the image. In contrast, when the scanner incorporates a stationary head and the item travels past the head, the dust shows up as an elongated streak along the length of the document. 
         [0006]    Additionally, scanners commonly utilize a guide to guide the documents toward or against a glass plate and the scanner scans the image as the document passes across the plate. One commonly used guide is a black foam or rubber roller that urges the documents toward the plate. During use, such rollers accumulate dust and eventually become lighter, and therefore it becomes more difficult to distinguish the document image from the background. Eventually, the roller needs to be cleaned or replaced. 
         [0007]    Accordingly, although many attempts have been made to mitigate the impact of dust and debris adjacent the image, dust and debris remain problem. 
       SUMMARY OF THE INVENTION 
       [0008]    In light of the foregoing, an improved scanner is provided for a sorting system. 
         [0009]    According to one aspect, the present invention provides a system for processing documents to obtain optical image data. The system includes an imager for scanning a document to obtain image data, wherein the imager comprises a lens through which the imager scans the document. The imager has a depth a field that includes a surface of the lens, wherein elements within the depth of field are generally in focus and elements outside the depth of field are generally not in focus. A document transport conveys the document along a document path over the lens and the imager scans the document as the transport conveys the document over the lens. A guide opposing the lens guides the document toward the lens as the document transport conveys the document past the imager. The guide comprises an opening opposing the imager that is configured so that portions of the guide exposed to the imager are positioned outside the depth of field of the imager. 
         [0010]    According to another aspect, the present invention provides a system for processing documents to obtain optical image data that includes an imaging element, a lens having a recess and a document transport. The imaging element is operable to scan a document to obtain image data. The lens is positioned so that the recess overlies the imaging element. In this way, the imaging element scans the document through the recess and the recess has a bottom outside the focus of the imaging element. The document transport conveys the document over the lens and the imaging element scans the document as the document transport conveys the document over the lens. 
     
    
     
       DESCRIPTION OF THE DRAWINGS 
         [0011]    The foregoing summary and the following detailed description of the preferred embodiments of the present invention will be best understood when read in conjunction with the appended drawings, in which: 
           [0012]      FIG. 1  is a side elevation view of an imaging station 
           [0013]      FIG. 2  is an enlarged cross-section view of an imaging assembly of the imaging station illustrated in  FIG. 1 . 
           [0014]      FIG. 3  is a perspective view of a document guide of the imaging station illustrated in  FIG. 1 . 
           [0015]      FIG. 4  is an enlarged cross-sectional view of an alternate imaging assembly. 
           [0016]      FIG. 5  is an enlarged cross-sectional view of a second alternate imaging assembly. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0017]    Referring now to the drawings in general and to  FIGS. 1-2  specifically, a document imaging system is designated generally  10 . The system  10  includes a plurality of rollers  15  that drive documents  5  along a document path  22 , along with guides  20  that guide the document as it is conveyed along the document path. An imaging station  30  position along the document path  22  is operable to scan documents  5  to obtain image data for the documents. The image data can be processed and used by the system and/or exported and stored for subsequent use or viewing. For instance, the image data may be exported to a file server or other device for storing data. 
         [0018]    The system  10  may be configured for single-sided or double-sided scanning. The embodiment in  FIG. 1  is configured to provide double-sided scanning, so the imaging station comprises a front imaging assembly  40 A and a back imaging assembly  40 B. As a document  5  passes through the imaging station  30 , the document first passes the front imaging assembly  40 A, which scans the front side of the document to obtain image data for the front side of the document. After exiting the upper imaging assembly  40 A, the document is conveyed to the back imaging assembly  40 B, which scans the back side of the document to obtain image data for the back side of the document. The document then exits the imaging station  30 . From the imaging station, the document may be further processed, such as by sorting according to one or more characteristics. For instance, the documents may be sorted according to a document characteristic identified from the scanned image data. Alternatively, the document may be sorted according to a characteristic of other documents. For instance, documents from a packet or a transaction may be processed together and/or sorted together so that the documents remain associated with one another. It should be understood, that sorting is simply one example of how the document may be processed after being discharged from the imaging station. In other embodiments, the documents may simply be discharged into an output area or bin after leaving the imaging station. 
         [0019]    The frontside and backside imaging assemblies  40 A,B are configured substantially similarly, except that the backside imaging assembly  40 B is oriented oppositely of the frontside imaging assembly  40 A as can be seen in  FIG. 1 . Accordingly, in the following description, the details of the front imaging assembly  40 A are provided and it should be understood that the details of the back imaging assembly  40 B are substantially the same. 
         [0020]    The front imaging assembly  40 A comprises an imaging device  60  positioned in a housing  50 . The housing  50  is an elongated channel that extends across the width of the document path. In the present instance, the housing is formed of metal, such as aluminum. However, the housing can be formed of a variety of generally rigid materials. The housing  50  includes an elongated cavity  52  that extends the length of the housing. The imaging device  60  is positioned in the base of the cavity  52  and directed toward the paper path. In particular, as shown in  FIG. 2 , the imaging device is directed downwardly, whereas the imaging device in the backside imaging assembly  40 B is directed upwardly. 
         [0021]    The imaging device  60  may be any of a variety of digital imaging devices configured to scan documents at a high speed to obtain image data corresponding to the documents, including but not limited to line scan cameras, charge-coupled devices and contact image sensors (CIS). In the present instance, the imaging device  60  is a CIS array extending across the width of the document path, so that the CIS array extends across a width at least as wide as the widest document the system  10  is configured to process. 
         [0022]    The imaging assembly  40 A may also include an illumination source  65  for providing light to illuminate the documents  5 . In the present instance, the side walls  54  of the cavity are angled and a lighting element is mounted onto one or both of the side walls. In this way, the lighting element  65  provide a source of light directed toward the document path so that the lighting element illuminates the documents as the documents are conveyed along the document path. In the frontside imaging assembly  40 A, the lighting element is directed downwardly toward the document path. In the backside imaging assembly  40 B, the lighting element is directed downwardly toward the document path. 
         [0023]    A lens or cover  70  extends over the length of the housing to enclose the opening in the cavity  52  to impede entrance of debris into the housing  50 . The lens has a longitudinal length that extends across the width of the document path. The lens  70  has a width along the direction of the paper path, wherein the lens width is substantially smaller than the longitudinal length of the lens. The lens  70  may be formed as a platen from any of a variety of substantially transparent materials, including glass and plastic. Specifically, the lens may have a generally planar surface that engages or presses against the document to flatten the document as the document is conveyed along the document path. The documents are conveyed over the lens  70  as the documents are conveyed along the document path  22 , and the sensor array  60  scans the document through the lens  70  to obtain image data for the document. 
         [0024]    The lens  70  may be mounted directly onto the housing, however, in the present instance the lens is mounted onto a lens holder  72  that engages the edges of the lens  70 . The lens holder  72  includes flanges that project outwardly along the length of the lens holder so that the flanges project from the longitudinal sides of the lens. The flanges project into slots in the housing  50  to connect the lens and holder  70 / 72  to the housing. Additionally, the lens holder further includes a pair of detents or protrusions that project inwardly to engage the lens to hold the lens in place in the holder. Specifically, the lens  70  may include one or more recesses along the longitudinal edges of the lens and the detents engage the recesses in the lens to retain the lens in the holder. 
         [0025]    A guide  80  opposing the imaging assembly  40 A guides documents against the cover  70  as the documents are conveyed along the document path  22 . The guide is an elongated element that extends across the width of the document path. In the present instance, the guide is coextensive with the width of the imaging assembly  40 A, so that the guide overlies substantially the entire width of the imaging assembly. More specifically, the guide  80  overlies substantially the entire width of the sensor array  60 . 
         [0026]    The guide urges the documents against the lens  70  as the documents are conveyed along the document path so that the documents are pressed generally or substantially flat against the lens. Since the guide may be wider than the width of some of the documents being scanned, the imaging device  60  may scan the image of the lateral edges of the guide that extend beyond the lateral edges of the documents. Accordingly, the guide  80  may be configured to substantially reduce light reflected back toward the imaging array. In this way, as a document passes between the guide  80  and the imaging assembly  40 A, the portions of the guide that are not covered by the document will scan as substantially black. Therefore, an image processor can process the image data to identify the edges of the document by using the dark black edges as an indicator of the document edge. Similarly, the leading and trailing edges of the document will appear as substantially black because the gap between successive documents will leave the guide uncovered. 
         [0027]    The guide  80  is preferably formed of a substantially light absorbing material. For instance, in the present instance, the guide is formed of plastic and has a flat black surface finish. The finish can either be a coating or the type of material used to form the guide. 
         [0028]    The guide  80  may also include a slot  84  that extends the width of the document path  22 . More specifically, in the present instance, the slot  84  extends the width of the sensor array  60 . The slot may extend through the entire thickness of the guide  80  or the slot may have a bottom so that the slot forms a cavity. In the present instance, the slot extends through the thickness of the guide along substantially the entire length of the guide. However, the slot includes cross ribs  86  that span the width of the slot to increase the rigidity of the guide. Preferably the ribs are also recessed having a bottom surface as shown in  FIG. 2 . In the present instance, the bottom of the rib  86  is tapered so that the bottom forms an acute angle with the axis of the sensor array (designated “a” in  FIG. 2 ). In this way, the tapered surface will tend to scatter the light against surfaces in the cavity rather directing the light back toward the sensor. In the present instance, the interior surface of the slot  84  and the ribs  86  are also substantially light absorbing surfaces, such as flat black. Additionally, the interior surface may be covered with a light absorbing finish, such as flocking. 
         [0029]    In the present instance, the depth of slot  84  is deeper than the depth of focus for the sensor array  60 . Specifically, the depth of focus of the sensor array is generally quite shallow, on the order of 0.010 inches or 0.3 mm, and the depth of the slot  84  is at least several millimeters. In this way, the portion of the guide  80  aligned with the imaging device is spaced apart from the focal plane of the imaging device. Further still, the portion of the guide aligned with the imaging device is sufficiently spaced from the focal plane of the imaging device that the guide  80  is substantially outside the depth of field of the imaging device, so that the guide is out of focus. In this way, the guide is both out of the focal plane and reflects little to no light so that the portion of the guide overlying the imaging device that is outside the lateral edges of a document being scanned appears substantially black. 
         [0030]    The guide may also be formed to direct the documents toward the lens  70  of the imaging assembly  40 A. For instance, in the present instance, the leading edge  82  of the guide  80  comprises an angled surface that tapers toward the imaging assembly  40 A forming a tip  87  having a flat contact surface as shown in  FIGS. 2-3 . In this way, the leading edge of the guide directs the leading edge of an incoming document toward the imaging assembly so that the face of the document is urged toward the lens  70 . The trailing edge  88  of the guide is also angled so that it tapers away from the imaging assembly. Further still, preferably the trailing edge is formed to reduce the likelihood that an edge of the document will catch on the trailing edge of the slot  84  as the document passes over the guide  80 . Specifically, in the present instance, the trailing edge of the slot  84  is rounded so that the trailing edge tapers away from the lens  70 , while the tip  87  of leading edge  82  projects toward the lens so that the gap between the lens and the leading edge of the guide  80  adjacent the slot is less than the gap between the lens and the trailing edge of the guide adjacent the slot. 
         [0031]    The guide  80  may also include contact elements for positioning the guide relative to the imaging assembly  40 A. For example, in the present instance, the guide  80  includes tabs or pads  89  that protrude outwardly. As shown in  FIG. 2 , the pads  89  protrude closer to the lens  70  of the imaging assembly  60  than the tip  87  leading edge  82 . Referring to  FIG. 3 , the tabs are positioned at the longitudinal ends of the guide, outside the document path. Specifically, the first pair of pads is positioned at the proximal end of the guide  80  and the second pair is positioned at the distal end of the guide, so that the documents pass between the pads as the documents pass over the imaging assembly. 
         [0032]    Referring to  FIG. 3 , the guide  80  is mounted on a bracket that provides rigidity to prevent the slot from expanding. The guide  80  may also include a plurality of cross-ribs to provide lateral strength. However, as shown in  FIG. 2 , any cross element in the cavity is recessed and configured to scatter light into the cavity rather than back toward the sensor array  60 . 
         [0033]    A biasing element biases the guide  80  toward the imaging assembly so that the guide directs documents toward the imaging assembly. However, the biasing element allows the guide to move away from the imaging assembly to provide a larger gap for thicker documents. In the present instance, the guide  80  is mounted on a pair of pivotable arms  91  that are biased by springs  92 . 
         [0034]    The system may also include one or more air movement elements for providing a flow of air over the imaging assembly  40 A. For example, in the present instance, a plurality of fans  100  are positioned below the guide and are configured to blow a stream of air through the slot  84  toward the imaging assembly. Although the slot in  FIG. 2  appears to be a closed cavity, the cross-section is open to the lower side of the guide (i.e. the slot includes openings through the bottom wall  86 ). The fans  100  may be mounted on the support bracket  90  and spaced along the length of the bracket as shown in  FIG. 3 . In this way, the fans  100  provide a stream of air along the width of the document path. 
         [0035]    An element may be provided to limit the build-up of static charge that could be created from the documents passing over the guide  80 . For instance, a corona wire or points can be integrated into the slot  84 , so the fans drive a flow of ionized air through the slot  84 . The fans are positioned to blow debris away from the lens  70  before the debris can settle on the cover and thereby impair the image quality. Specifically, the fans may be configured to provide an air-knife, and use the Coanda-effect to entrain air around the lead side of the guide to drive debris along the direction of flow for the documents, rather than settling on the lens  70 . Alternatively, the fans or other air-moving element(s) can be positioned remotely from guide and hose or ducting can provide the flow of air to drive debris away from the cover. 
         [0036]    Referring now to  FIG. 4 , an optional wiper for the imaging assembly  40 A is illustrated. The imaging assembly  40 A is substantially similar to the imaging assembly discussed above, except that the imaging assembly includes a wiper  83  attached to the leading edge of the guide  80 . The wiper  83  may be a thin plastic sheet (e.g. 0.002″ polyester) or fine bristles. By providing a wiper, the gap between the guide  80  and the cover  70  imaging assembly can be increased without creating a separation between the document and the cover that would reduce the quality of the image. Specifically, the wiper  83  is a resiliently flexible element that fills the gap between the guide  80  and the lens  70  of the imaging assembly  40 A. As the document transport  15  conveys the document along the document path, the leading edge of the document engages the wiper so that the wiper deforms to provide clearance for the document to pass through the gap between the guide  80  and the imaging assembly  40 A. As the wiper deforms, the resiliency of the wiper causes the wiper to urge the document toward the imaging assembly  40 A. 
         [0037]    Referring to  FIG. 5 , an alternate imaging assembly  40 C is illustrated. The alternate imaging assembly is substantially the same as the imaging assembly  40 A described above, except for the lens. The lens  170  includes a recess  174  aligned with the sensor array  60 . The recess  174  has a depth that is greater than the depth of focus of the sensor array  60 . In this way, debris on the lens will tend to settle in the bottom of the recess  174 . Since the recess is outside the focal area of the sensor array, the debris will not normally degrade the quality of the image. In the present instance, the leading edge of the lens  172  tapers away from the leading edge of the guide and the trailing edge  176  of the lens also tapers away from the leading edge of the guide. Therefore, the gap between the leading edge  172  of the lens  170  and the tip  87  of the leading edge of the guide  80  is greater than the gap between the trailing edge  176  of the lens  170  and the trailing edge of the guide  88 . In this way, document will have less of a tendency to catch on the recess as the documents are conveyed across the cover. 
         [0038]    It will be recognized by those skilled in the art that changes or modifications may be made to the above-described embodiments without departing from the broad inventive concepts of the invention. For instance, the lens of the imaging assembly may be modified to have a different shape than the recess  174  described above, while still having a surface that is spaced apart from the focal plane of the imager so that debris will tend to settle on the surface out of the depth of field for the imaging assembly. It should therefore be understood that this invention is not limited to the particular embodiments described herein, but is intended to include all changes and modifications that are within the scope and spirit of the invention as set forth in the claims.