PATENT ABSTRACT
An apparatus and method for calibrating a scanner connected to a document feeder are provided. In one embodiment, the apparatus includes a calibration strip attached to a rotatable wheel assembly disposed within the document feeder. A cam is provided to rotate the wheel assembly and expose the calibration strip to the field of view of a head assembly of the scanner for calibration. The cam is configured to then rotate the wheel assembly in the opposite direction, so that the calibration strip is no longer exposed to the head assembly. A cleaning blade may be provided to wipe the calibration strip as it is moved to its non-exposed position.

PATENT DESCRIPTION
BACKGROUND OF THE INVENTION 
     The present invention generally relates to an improved apparatus and method for calibrating an image-capturing device that is connected to a document feeder. More particularly, it relates to an apparatus and method for calibrating a scanner which positions a calibration strip within the document feeder into an optical path of a scanner head assembly while the assembly is ready to scan a document fed by the document feeder. 
     Image-capturing peripherals such as scanners have become increasingly useful, affordable and common devices for homes and businesses. These devices are useful for capturing and storing images such as text, graphic or pictorial images contained on documents. Various types of scanners include flatbed, drum and handheld scanners. With a flatbed scanner, one of the most common types of scanners, a document to be scanned is typically placed onto a transparent glass platen of the scanner, where a scanner head assembly (also referred to as a carriage assembly) moves underneath the document to capture the image contained on the document. The image in digital form is often transmitted to a connected computer, though it may instead be stored within the scanner, or transmitted directly to another peripheral such as a printer or facsimile (fax) machine. 
     To scan a quantity of documents, a document feeder (such as an automatic document feeder or ADF) may be attached to the scanner to feed documents over the scanner head assembly, where the images on the documents are captured as they pass over the scanner head assembly. Often, a scanner and document feeder are integrated with a printer or fax machine to form a multi-function printer. Alternatively, the scanner may digitally send image information to the printer. 
       FIG. 1  is a cross-sectional view of a typical flatbed scanner combined with a document feeder. A scanner, indicated generally at  10 , includes a head assembly  12  having a scanning lamp for producing a light for illuminating a document through a glass platen  14 , and may also contain mirrors and a lens to direct and focus the reflected light. The head assembly  12  includes a photodetector, such as a charge-coupled device (CCD) containing an array of pixels, each of which are configured to detect the reflected light and convert it into a signal for processing by another peripheral or by a connected computer (not shown). The head assembly  12  travels longitudinally along one or more rails  16  of the scanner  10 , and is driven by a pulley and one or more rollers (not shown). 
     A document feeder  20 , which may be attached to the scanner  10  via hinges (not shown), feeds the paper into a scanning position along a generally U-shaped paper path  22  (more clearly shown in FIGS.  2  and  3 ), substantially surrounding a guiding mechanism such as a typically hollow cylindrical guide  50 . The document feeder  20  uses a feeding mechanism having a series of rollers, including a pick-up roller  24 , pairs of feed rollers  26 ,  28 ,  30 , and a pair of delivery rollers  34  to feed the paper through the paper path  22 . A transparent guide strip  36  of polyester, such as MYLAR, guides the paper along a bottom portion of the paper path  22 . A section  38  of the guide strip  36  allows the head assembly  12 , when in a scan position  40  (as shown in  FIGS. 1 and 2 ) to capture images on paper, because the paper is within an optical path (field of view) of the head assembly. 
     Before scanning one or more documents, a scanner is typically calibrated for photo response non-uniformity (PRNU) calibration, among other things.  FIG. 3  shows a simplified representation of a typical scanner/document feeder with the head assembly  12  in a predetermined “home” (calibration) position  42 . To calibrate the scanner  10 , a stationary calibration strip  44  is attached to the scanner over the home position  42  of the head assembly  12 . The strip is positioned away from the paper path  22  and is thereby protected from dust from the paper being scanned. The head assembly  12  scans the stationary, preferably white calibration strip  40  to calibrate the scanner  10  in a manner known in the art. 
     When scanning a document fed by the document feeder  20 , and referring to  FIG. 2 , the head assembly  12  has to move from the home position  42  to the scan position  40  so that a portion of the paper being scanned is in the optical path or field of view of the head assembly  12  through the portion  38  of the guide strip  36 . The distance between the home position  42  and the scan position  40  is typically about 13 mm, but of course this distance may vary. 
     To produce a high quality scan, calibration ideally should be done for every scan page. However, for high speed document feeding, it is almost impossible to calibrate every scan page because of the mass and inertia of the head assembly  12 . Because additional time and power are required to activate the head assembly  12  for every ADF-fed scan job, the scan performance is gradually degraded, due to wear on the head assembly  12 , and its mechanism for movement. The redundant quick and short jacking motion of the head assembly  12  can detrimentally impact the scan quality of the scanner  10 . 
     Because about 80% of overall scan jobs are fed from the document feeder for a typical MFP, a significant improvement in reliability and scan quality of the scanner, as well as the print quality of connected printers, would result if the head assembly remained stationary during ADF-fed scanning jobs. 
     BRIEF SUMMARY OF THE INVENTION 
     The present invention provides an inventive apparatus for calibrating an image-capturing apparatus, such as a scanner, of the type which has a document feeder. The apparatus includes a calibration member that is disposed within the document feeder and is movable to a position within the optical path of the scanner head assembly when it is ready for scanning. Before a scan job, or before an individual document is scanned by the scanner head assembly, the head assembly scans the calibration member for the purpose of calibrating the scanner. In this way, it is possible to calibrate the scanner head assembly without moving the scanner from its scan position. 
     In one embodiment, a wheel assembly is provided for rotating the calibration member into and out of the optical path of the scanner head assembly. A cam, together with a biasing member, moves the wheel assembly between two positions, so that the calibration member is either exposed to the scanner head assembly or not. 
     In a preferred embodiment, the calibration apparatus includes a wheel assembly contained within a cylindrical guide of the document feeder, having a calibration strip attached to an outer circumferential surface. The cylindrical wheel rotates about an axis parallel to the length of the head assembly, across the width of the document feeder. A cam is provided for driving rotation of the wheel assembly by contacting a first flat surface of the wheel assembly. A biasing member is attached to a second flat surface of the wheel assembly, to bias the wheel assembly against the cam. The wheel assembly is rotated into either of two positions to position the calibration strip either into an exposed position (into the optical path of the head assembly) or non-exposed position (out of the optical path) while the head assembly is in a position ready for scanning. In a further preferred embodiment, a cleaning blade is also provided to remove contaminants from the calibration strip. 
    
    
     
       DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a side sectional view of a typical prior art scanner combined with a document feeder; 
         FIG. 2  is a side illustration of a typical prior art scanner and document feeder with a scanner head assembly in a scan position; 
         FIG. 3  is a side illustration of the scanner and document feeder of  FIG. 2 , with the scanner head assembly in a home position; 
         FIG. 4  is a simplified side illustration, partially in cross-section, of a scanner combined with a document feeder fitted with one embodiment of the calibration apparatus of the present invention, with the head assembly in a scan position, and the wheel assembly rotated so that the calibration strip is in the optical path of the head assembly; 
         FIG. 5  is a perspective view of a wheel assembly used in one embodiment of the calibration apparatus and method of the present invention; and, 
         FIG. 6  is a side illustration of the scanner and document feeder of  FIG. 4 , with the head assembly in a scan position, with the wheel assembly rotated so that the calibration strip is retracted out of the optical path of the head assembly. 
     
    
    
     DETAILED DESCRIPTION 
     While the apparatus is described and pictured herein for a flatbed scanner having a document feeder, it is important to understand that the principles of the inventive calibration apparatus can be applied for any image-capturing apparatus that is combined or equipped with a document feeder. The descriptions that follow are in no way intended to limit the scope of the inventive calibration apparatus to an MFP or similar device. Where appropriate, the same reference characters are used to designate like parts. 
     Turning now to  FIGS. 4-6 , a calibration apparatus  46  having a wheel assembly  52  is shown contained within the cylindrical guide  50 . A calibration strip  48  is attached to a lower portion of an outer circumference  53  of the wheel assembly  52 , and runs along the length of the wheel assembly, parallel to the length of the head assembly  12 . The wheel assembly  52 , preferably made of lightweight material such as plastic, contains an inner cylindrical portion  54 , which rotates about an axle  56 . The outer circumference  53  of the wheel assembly  52  is concentric with the inner cylindrical portion  54 , extending approximately 240° around the cylindrical guide  50 , as shown in section in  FIGS. 4 and 6 . Preferably, the wheel assembly  52  contains a series of structural members  58  extending around the wheel assembly, located at approximately 60° intervals. First and second exposed flat surfaces  60 ,  62  are thus formed, which extend longitudinally along the wheel assembly  52 , as shown in FIG.  5 . 
     The calibration strip  48  is preferably made of lightweight material such as MYLAR, and may be attached to the wheel assembly  52  via adhesive, although other methods of attachment are possible. A space or recess  49  in the outer circumference  53  of the wheel assembly may be provided for accommodating the calibration strip  48 . The calibration strip  48  is typically a white strip employed for photo response non-uniformity (PRNU) calibration. The calibration strip  48  preferably has a length sufficient to be viewed by all of the pixel devices in the head assembly  12  while the head assembly is in its scan position  40 . 
     A cam  64  is disposed within the cylindrical guide  50 , abutting the first flat surface  60  of the wheel assembly  52 . Substantially semicircular in section, the cam  64  extends along a longitudinal portion of the wheel assembly  52 , as shown in FIG.  5 . The cam  64  is stationed on a pivot  66 , which is coupled to a pick-up mechanism (not shown) for the document feeder  20 , or other such mechanism for actuating rotation of the pivot. The cam  64  abuttingly contacts the first flat surface  60  of the wheel assembly either with a flat surface  68  of the cam or (tangentially) with its curved surface  70 . When the cam  64  rotates so that its point of contact with the wheel assembly  52  is changed from the cam&#39;s flat surface  68  to its curved surface  70 , the cam rotationally urges the wheel assembly in the counterclockwise direction, to the position shown in FIG.  4 . The wheel assembly  52  thus positions the calibration strip  48  in the optical path of the head assembly  12 , over the portion  38  of the guide strip  36 . Thus, while the head assembly  12  is ready to scan in position  40 , it can also scan the calibration strip  48  to calibrate the scanner  10 . 
     A biasing member  72 , such as a spring, is connected at one end to the second flat surface  62  of the wheel assembly  52  and at its other end to a fixed stop  74  within the document feeder  20 . The fixed stop  74  runs parallel to the axle  56  of the wheel assembly  52 . The biasing member  72  constantly exerts a compressive, clockwise biasing force on the wheel assembly  52 , rotationally urging the wheel assembly toward the cam  64 . Therefore, when the cam pivot  66  rotates so that the flat surface  68  of the cam  64  contacts the wheel assembly  52 , the wheel assembly rotates clockwise against the cam. The wheel assembly  52  is rotated to the position shown in  FIG. 6 , and thus retracts the calibration strip  48  out of the optical path of the head assembly  12 . The wheel assembly  52  is constantly subjected to opposing rotational forces from the cam  64  and the biasing member  72 . The balance of these forces holds the wheel assembly  52  in the positions shown in  FIGS. 4 and 6 , respectively. 
     When the calibration strip  48  is exposed to the optical path of the head assembly  12 , it is simultaneously exposed to paper dust. To help prevent dust from the paper from contaminating the calibration strip  48 , a preferably stationary cleaning blade  76  is provided. The cleaning blade  76  is situated within and runs along the length of the cylindrical guide  50 , parallel to the length of the calibration strip  48 . The cleaning blade  76  is preferably manufactured of rubber and attached to the inner surface of the cylindrical guide  50  by known means. When the wheel assembly  52  rotates clockwise, and the calibration strip  48  is thus moved away from the optical path of the head assembly  12 , the cleaning blade  76  wipes the calibration strip  48 , cleaning the calibration strip. 
     With regard to the scanner calibration operation, at the beginning of a scan job, or as an individual page is scanned, the cam pivot  66  is configured to rotate. This in turn rotates the cam  64  so that its curved surface  70  tangentially contacts the first flat surface  60  of the wheel assembly  52 . The wheel assembly rotates counterclockwise so that the calibration strip  48  is exposed to the optical path of the head assembly  12  of the scanner  10 . The biasing member  72  biases the wheel assembly  52  clockwise against the cam  64  to hold the wheel assembly in this position. The head assembly  12  then scans the calibration strip  48  to calibrate the scanner  10 . 
     After the scanner  10  has been calibrated, the cam pivot  66  again rotates, rotating the cam  64  until the flat surface  68  of the cam contacts the flat surface  60  of the wheel assembly  52 . The biasing member  72  rotates the wheel assembly  52  clockwise, moving the calibration strip  48  out of the optical path of the head assembly  12 , and against the cleaning blade  76  so that the calibration strip  48  is wiped clean for the next calibration. 
     This calibration operation, or a similar one, can be configured to occur at the beginning of an ADF-fed scan job, or before individual pages are fed by the ADF. Such configuration will be apparent to those skilled in the art. 
     By employing a lightweight, low inertial calibration strip on the document feeder, additional motion of the head assembly is eliminated for ADF-fed scan jobs. A minimum of additional parts is necessary because the cam can be configured to be coupled to the existing pickup mechanism. As an additional benefit, since the calibration strip is in the document feeder behind the MYLAR guide strip (as shown in FIG.  4 ), the calibration strip has an identical optical path as that of a portion of an image scanned by an ADF-fed scan. Thus, imperfections, scratches, and smears present in the transparent portion of the guide strip are calibrated out, which is not possible for conventional scanner head assembly movement calibration. 
     From the foregoing description, it should be understood that an improved apparatus and method for calibrating an image-capturing device with a document feeder has been shown and described, which has many desirable attributes and advantages. With this inventive calibration apparatus, approximately 80% of scan jobs do not require movement of the scanner head assembly. As a result, the acoustic level of the scanner is reduced, and the reliability of the scanner mechanism is improved. The scan quality is improved due to identical optical path calibration. Impairment of print quality due to vibration of the scanner is reduced, and cost savings are derived due to an increased life cycle of the scanner. 
     While various embodiments of the present invention have been shown and described, it should be understood that other modifications, substitutions and alternatives can be made without departing from the spirit and scope of the invention, which should be determined from the appended claims.