Abstract:
It is an exemplified object of the present invention is to provide an image reading device and method that would realize a high-resolution image reading. The present invention connects to a movable optical system in a double-sided image readable device at least one of black and white references that a fixed side should referred to.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates generally to image reading (or readable) devices and methods, and more particularly to a double-sided image readable device and method. A double-sided image readable device means a device that serves to read front and rear surfaces of a document simultaneously. The present invention is suitable for double-sided readable image scanners, copiers, facsimile machines, electrophotographic devices having flat bed unit and automatic document feed (“ADF”) unit (or a sheet feed unit). A flat bed unit means a type that uses an optical system to read a document statically placed on a glass board, while an ADF unit means a type that automatically and mechanically feeds a document paper so as to read it using a static optical system. 
     As recent demands for effective use of resource have increased opportunities to use documents having images on its both sides, high-speed and high-resolution double-sided readable image scanners that may read the images on both document sides have been sought. An image scanner converts data indicative of lightness and density for each pixel color that has been obtained by scanning, into digital data as a result of comparison with white and black reference data. A double-sided readable image scanner typically includes flat bed and ADF units, a first optical system at the flat bed unit side, a second optical system at the ADF unit side, first and second white reference boards, and first black reference board. These white and black reference boards are fixed onto a housing. The first optical system reads one document surface, whereas the second optical system reads the other surface of the document. Each optical system includes a fluorescent lamp and CCD sensor, and reads the document by emitting lamplight onto the document and converting the reflection light into an electronic signal using the CCD sensor. The first white and black reference boards are arranged apart from a document feed path, and used as white and black references, respectively, for the first optical system. The second white reference board is located below the document feed path and used as white and black references for the second optical system. 
     In general, an image scanner corrects white and black reference data at the beginning of reading and at an appropriate intermission during a reading of a large amount of pages (for instance, every 50-page reading) in order to correct a change in quantity of lamp&#39;s light and the sensitivity dispersion of photosensitive pixels in the CCD sensor. According to the conventional correction method of white and black reference data, the first optical system, which is movable, moves to the first white and black reference boards and reads them while the lamp turns on. The second optical system, which is not movable, reads the second white reference board just below the feed path while the lamp turns on and sets the resultant value as a white reference. In addition, the second optical system reads the second white reference board while the lamp turns off and sets the resultant value as a black reference. 
     White and black reference values are generated as one line pixel data from the read white and black reference data, and stored in a memory. In reading the document, these white and black reference values are used for correction of image data (which is referred to as “shading correction”). 
     However, external leakage light that reaches the second white reference board even when the fluorescent lamp turns off would cause the second white reference board to be incomplete or whitish black. Light black set as a black reference, or recognition of white as black would cause a read image to be more blackish than an actual image, disadvantageously preventing a high-resolution image reading. 
     BRIEF SUMMARY OF THE INVENTION 
     Therefore, it is an exemplified general object of the present invention to provide a novel and useful image reading device and method in which the above disadvantages are eliminated. 
     Another exemplified and more specific object of the present invention is to provide an image reading device and method that would realize a high-resolution image reading. 
     In order to achieve the above objects, an image reading device of one aspect according to the present invention comprises a first optical system which reads one surface of a document, a drive part which moves the first optical system, a second optical system which reads the other surface of a document, first white reference part and first black reference part readable by the first optical system moved by the first drive part, second white reference part and second black reference part readable by the second optical system, at least one of the second white and black reference parts being arranged to be movable, and a control part which controls the first optical system, drive part, and second optical system. This image reading device movably arranges at least one of the second white and black reference parts, and enables the second optical system to read the one reference part. Therefore, the second optical system may read both of the second white and black reference parts even when the other of the second white and black reference parts is fixed. 
     An image reading method of another aspect of the present invention comprises a first step of reading one surface of a document using a first optical system and the other surface of the document using a second optical system, a second step of moving the first optical system and first white reference part relative to each other, and reading the first white reference part using the first optical system, a third step of moving the first optical system and first black reference part relative to each other, and reading the first black reference part using the first optical system, a fourth step of moving one of second white reference part and second black reference part relative to each other, and reading the one of the second white and black reference parts using the second optical system, and a fifth step of reading the other of the second white and black reference parts using the second optical system. Such a reading method may realize the above operation. 
     Other objects and further features of the present invention will become readily apparent from the following description of the embodiments with reference to accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF DRAWINGS 
     FIG. 1 is a partially enlarged schematic section of a double-sided image scanner of one aspect the present invention. 
     FIG. 2 is a schematic sectional overview of the double-sided image scanner shown in FIG.  1 . 
     FIG. 3 is a schematic block diagram of a control system in the image scanner shown in FIG.  1 . 
     FIG. 4 is a flowchart for explaining an exemplified operation of the control part shown in FIG.  3 . 
    
    
     DETAILED DESCRIPTION OF INVENTION 
     A description will now be given of double-sided readable image scanner (hereafter “image scanner”)  100  of one embodiment according to the present invention, with reference to FIGS. 1 through 3. FIG. 1 is a partially enlarged schematic section of the double-sided image scanner  100  of the present invention. FIG. 2 is a schematic sectional overview of the double-sided image scanner shown in FIG.  1 . FIG. 3 is a block diagram of the image scanner  100  shown in FIG.  1 . As shown in FIG. 1, the image scanner  100  includes lower housing  1  that constitutes a flat bed unit, and upper housing  2  that constitutes an ADF unit. Needless to say, the lower housing  1  is not limited the flat bed unit, and the upper housing  2  is not limited to the ADF unit. 
     Exemplarily, the lower housing  1  is approximately cuboid and has document glass table  1   a  at the top thereof. Transparent glass is attached to the document glass table  1   a . The lower housing  1  includes first optical system  10 , white reference part  32 , black reference part  34 , and drive system  40  which moves first optical system  10  in a vertical scanning direction, optical sensor  52 , one roller  65   a  of feed rollers  65 , and eject tray  68  which stores ejected document D at front end  1   b . The eject tray  68  is typically attached detachably to the front end  1   b  of the lower housing  1 . 
     The first optical system  10  includes in housing  11 , lamp (light-emitting element)  12 , mirror  13  and  14 , lens  15 , and photoelectric converter (light-receiving element)  16 . The illustrated kind, arrangement, number of these elements are merely example, and various modifications may be made as far as the photoelectric converter  16  receives reflection light from the lamp  12  through a document surface. For example, any position and number of mirrors may be freely selected according to the necessary light path. A filter having a predetermined transmissivity (or a plurality of filters having different transmissivities) may be provided on the light path. The lamp  12  includes, for example, a halogen or fluorescent lamp, and serves as a light source what emits light onto document D via the slit  11   a  in the housing  11  and the document glass table  1   a . A reflector (not shown) that partially focuses light from the lamp  12  on the document D is provided around the lamp  12 . The mirrors  13  and  14  serve to reflect reflection light that is light emitted from the lamp  12  onto a document surface. The lens  15  focuses light reflected by mirror  14  onto a light-receiving surface on the photoelectric converter  16 . The photoelectric converter  16  is made of a CCD sensor which includes a photosensitive element having 600 pixels per inch, and may output as an analog signal a pixel for one line from the document D or the white and black reference parts  36  and  38  which will be described later. As the photoelectric converter  16  may handle binary and multi-gradation images, the image scanner  100  may be used as monochromatic, multi-gradation, and multi-color scanners. 
     The white and black reference parts  32  and  34  are provided at the top  11   b  of the housing  11  in the first optical system  10 . The white and black reference parts  32  and  34  are respectively made, for example, of white and black plastic labels. The illustrated number, size, position and the like of white and black reference parts  32  and  34  are a mere example. Although the instant embodiment arranges the white reference part  32  at the left side of the black reference part  34  as shown in FIG. 1, it may arrange the white reference part  32  at the right side of the black reference part  34 . The second optical system  20  refers to the white and black reference parts  32  and  34  when correcting a change in the light amount of the lamp  22  and the sensitivity dispersion of the photoelectric converter  26 . 
     The white and black reference parts  32  and  34  are moved with the first optical system  10  by the drive system  40  as described later, but they may be moved independent of the first optical system  10  or driven by another drive source different from the drive system  40 . A moving direction of each of the white and black reference parts  32  and  34  is not limited to the vertical scanning direction as described later. The instant embodiment includes the black reference part  34  that has not been provided in conventional double-sided readable scanners. 
     The drive system  40  includes drive belt  42 , and pulley  44  that drives the drive belt  42 . The lower housing  1  is connected to the eject tray  68 . The drive system  40  reciprocates the first optical system  10  in the vertical scanning direction of the document D (i.e., an arrow direction in FIG.  2 ). The drive belt  42  is connected to the first optical system  10 , and rotatably driven by the pulley  44 . The drive system  40  moves the first optical system  10  between right edge position (“REP”) and left edge position (“LEP”) as indicated by broken lines in FIG.  2 . Read position (“RP”) and home position (“HP”) which is an initial position for the flat bed reading are placed between the REP and LEP. The real lines in FIGS. 1 and 2 indicate that the first optical system  10  is located at the RP. 
     The HP is a position to which the first optical system returns automatically during a predetermined flat bed reading operation of the image scanner  100 , and the HP is also used as a reference position for various operations. When the first optical system  10  is located at the HP, the control part  30  controls the motor  44  so that the first optical system  10  moves from this position by a predetermined clock. The RP is a read position for the first and second optical systems  10  and  20  to read the document D, and is also used for them to read the white reference parts  32  and  36  in the instant embodiment. When the white and black reference parts  32  and  34  are arranged conversely, it would be understood that the first and second optical systems  10  and  20  do not necessary read the white reference parts  32  and  36  at the RP. The LEP is a reference position to which the first optical system  10  is initially moved in an initial operation after the image scanner  100  turns on. The LEP is also used for subsequent various operations. When the first optical system  10  is located at the LEP, the control part  30  may control the motor  44  so that the first optical system  10  moves from this position by a predetermined clock. 
     Those skilled in the art would easily conceive the way of detecting a position of the first optical system  10  in view of the disclosure of the instant application, for example, using a reflection-type photo-interrupter, such as optical sensor  52  which will be described later, and a detailed description thereof will be omitted. The optical sensor  52  includes a light-receiving element, such as a pin photodiode, and may receive light from a light-emitting element (not shown) fixed onto the lower housing  1 . The optical sensor  52  is so arranged that it cannot receive light from the light-emitting element when the first optical system  10  is located at the LEP. 
     The upper housing  2  includes the second optical system  20  and feed system  60 . The second optical system  20  includes in housing  21 , lamp (light-emitting element)  22 , mirrors  23  and  24 , lens  25 , and photoelectric converter (light-receiving element)  26 . These elements correspond to lamp (light-emitting element)  12 , mirrors  13  and  14 , lens  15 , and photoelectric converter (light-receiving element)  16 , and a description thereof will be omitted. The second optical system  20  is fixed onto the upper housing  2  and thus it is not movable. 
     The feed system  60  defines the feed path FP, and includes paper-supply tray  61 , separation roller  62 , separation gate  63 , feed rollers  64  and  65  ( 65   b ), top plates  66  and  67 . The paper-supply tray  61  supplies documents D one by one to the upper housing  2 . The separation roller  62  introduces the lowest document D to the feed path FP by compressing a plurality of documents D mounted on the paper-supply tray  61  against the rubber separation gate  63 . The separation roller  62  rotates counterclockwise in FIGS. 1 and 2. The feed rollers  64  and  65  are driven by the same drive source as that of the separation roller  62  or a different drive source from that of the separation roller  62 , and move the document D along the feed path FP. The top plates  66  and  67  compress the document D from the top so as to prevent jamming caused by the crumpled or slacked document D. The ejected document D is mounted onto the eject tray  68  attached at the front end  1   b  of the lower housing  1 . 
     Referring to FIG. 1, the white and black reference parts  36  and  38  are attached to the bottom  66   a  of the top plate  66 . The white and black reference part  36  and  38  are made of white and black plastic labels, similar to the white and black reference parts  32  and  34 . The illustrated number, size, position of the white and black reference parts  36  and  38  are mere examples. As shown in FIG. 1, the instant embodiment arranges the white reference part  36  at the right side of the black reference part  38 , but may arrange the white reference part  36  at the left side of the black reference part  38 . The optical system  10  refers to the white and black reference parts  36  and  38  when correcting the light amount of the lamp  12  and the sensitivity dispersion of the photoelectric converter  16 . 
     In this way, the white and black reference parts  36  and  38  are fixed onto the upper housing  2 , but may be arranged to be movable relative to each other in the upper housing  2 . Although the white and black reference parts  36  and  38  have been fixed even in the conventional image scanners, they have typically been fixed in place so that the first optical system  10  near the HP in the lower housing  1  may read them. In contrast, the present embodiment arranges the white reference part  36  so that the optical system  10  at the RP may read it, and arranges the black reference part  38  so that the optical system  10  at the HP may read it. 
     The instant embodiment arranges the white and black reference parts  32 ,  34 ,  36 , and  38  so that when the first optical system  10  reads the white reference part  36 , the second optical system  20  reads the white reference part  32 , and when the first optical system  10  reads the black reference part  38 , the second optical system  20  reads the white reference part  34 . 
     FIG. 3 is a schematic block diagram of a control system in the image scanner  100 . As shown in FIG. 3, the control part  30  is connected to motors  44  and  62 , A/D converters  72  and  76 , shading correction circuits  74  and  78 , line memory  80 , ROM  82 , and RAM  84 . Those elements which are connected to the control part  30  are not limited to the above components, and FIG. 3 only illustrates a portion relevant to the instant embodiment. The A/D converter  72  and  76  optionally include an amplifier (not shown) at its previous stage, and the photoelectric converters  16  and  26  each convert an analog signal to a digital signal. The shading correction circuits  74  and  78  each perform a shading correction with respect to a digital signal. The line memory  80  includes a white line memory part that stores a white reference value (white reference data) and a black line memory part that stores a black reference value (black reference data). 
     With reference to FIG. 4, a description will be given of an operation of the image scanner  100 . FIG. 4 is a flowchart of an image scanning operation of the image scanner  100 . 
     When the image scanner  100  is powered on, the control part  30  drives the motor  44  so that the first optical system  10  moves to the LEP (step  1002 ). The sensor  52  thereby detects the first optical system  10 , and enables a positional control over the first optical system  10 . The first and second optical systems  10  and  20  then read the white and black reference parts  32  through  38 : The first and second optical systems  10  and  20  should read the white and black reference parts  32  through  38  at the beginning of ADF reading and whenever they continuously read predetermined pages (for example, 50 pages) of documents D, in order to correct changes in the light amount of the lamps  12  and  22  and the sensitivity dispersions of the photosensitive pixels in the CCD sensors  16  and  26 . In this case, the first optical system  10  is located at the HP, and the step  1002  is omitted and need not be repeated. 
     Next, the control part  30  drives the motor  44  so as to move the first optical system  10  to a read position of the black reference part  38  and make the first optical system  10  read the black reference part  38 . The control part  30  stores resultant black reference data in the line memory  80  (step  1004 ). The first optical system  10  is moved to the right by a predetermined clock from the LEP using the feed belt  42  and motor  44 . The instant embodiment simultaneously makes the second optical system  20  read the black reference part  34  and stores the resultant black reference data in the line memory  80  (step  1006 ). 
     In steps  1004  and  1006 , the first and second optical systems  10  and  20  turn on, but more preferably turn off, lamps  12  and  22 , read a plurality of lines of black reference parts  34  and  38 , add them to each other for each bit unit, calculate an average for each line from the addition result, and store the average in the line memory  80 . Then, the first optical system  10  may return to the HP or stay at a position after reading the black reference part, although the first optical system  10  returns to the HP in the instant embodiment. Thus, the second optical system  20  in the instant embodiment reads the complete black-color reference part  34 , not a white reference part under a turn-off condition, improving the reading reliance and providing a high quality image reading in comparison with the conventional way. A reading of black reference part  34  under a turn-off condition would use a more blackish image for a black reference and improve the reference data quality. 
     The control part  30  then drives the motor  44 , and moves the first optical system  10  to a read position for the white reference part  36 , makes it read the white reference part  36 , and stores the resultant white reference data in the line memory  80  (step  1008 ). The first optical system  10  is moved to the left by a predetermined clock from the HP by the feed belt  42  and motor  44 . This embodiment simultaneously makes the second optical system  20  read the white reference part  32 , and stores it as white reference data in the line memory  80  (step  1010 ). In the steps  1008  and  1010 , the first and second optical systems  10  and  20  turn on the lamps  12  and  22 , read the white reference parts  32  and  36  for a plurality of lines, add them to each other for each bit unit, calculate an average for each line from the addition result, and store the average in the line memory  80 . The steps  1008  and  1010  may be conducted prior to the steps  1004  and  1006 . Optionally, prior to the average operation, the control part  30  may calculate a difference between every line value and a reference value, and display a sign that prompts a user to remove a possible dust or dewfall on the white reference part  32  and/or  34  when judging that the difference exceeds a permissible value. 
     The control part  30  then judges whether a user of the image scanner  100  has selected an image reading with a white-color background (step  1012 ). The control part  30  moves the first optical system  10  to a read position for the white reference part  36  from the HP when judging that a user has selected the white-color background, and makes the first and second optical systems  10  and  20  read the document D using the white reference parts  32  and  36  as a background (step  1014 ). The white reference parts  32  and  36  are more whitish than a universal regular paper. In the reading operation, the photoelectric converters  16  and  26  integrally compare image data of the read document D with the line memory  80  for each line, and generates a trigger signal which indicates that the photoelectric converters  16  and  26  detect the edge of the document D when an output of image data is smaller than the data recorded in the line memory  80  and the document edge passes the read position. The control part  30  determines the read start time in response to the trigger signal. 
     In contrast, when the control part  30  judges that the user has selected an image reading with a black-color background (step  1012 ), it moves the first optical system  10  to the read position for the black reference part  38  from the HP, and makes the first and second optical parts  10  and  20  read the document D using the black reference parts  34  and  38  as a background (step  1016 ). 
     The steps  1014  and  1016  perform a shading correction. Generally, the corrected image data G′ is calculated using image data G prior to the correction, constant k, black reference value B, white reference value W as follows: 
     
       
         G′=k×{(G−B)/(W−B)} 
       
     
     This equation may be calculated by hardware such as a divider and a subtracter, or by software. As a result, changes in the light amount of the lamps  12  and  22  and sensitivity dispersions of photosensitive pixels in the CCD sensors  16  and  26  may be properly corrected. 
     Further, the present invention is not limited to these preferred embodiments, but various variations and modifications may be made without departing from the scope of the present invention. For example, the white and black reference parts  32  and  34  are both movable in the instant embodiment, but only one of them is made movable. For example, as seen in the conventional art, the white reference part  32  is fixed onto the lower housing  1  and the black reference part  34  is made movable so that the black reference part  34  interrupts a path between the second optical system  20  and the white reference part  32 . Conversely, the black reference part  34  is fixed onto the lower housing  1 , and the white reference part  32  is made movable so that the white reference part  32  interrupts a path between the second optical system  20  and the black reference part  34 . The white and black reference parts  32  and  34  are bonded together and made rotatable relative to the second optical system  20 . 
     According to the image reading device and method of one aspect of the present invention, the second optical system may read both of the second white and black reference parts, thus providing a higher quality image reading than the conventional image reading device that uses one white reference for both white and black references.