Abstract:
An image scanning device including: a conveyance path which conveys originals; a first scanning means and a second scanning means which are placed such that they sandwich the conveyance path; and a white reference member used for adjusting the white levels of the scanning means; wherein at least one of the first scanning means, the second scanning means and the white reference member is movable; the first scanning means and the second scanning means can scan the same surface of said white reference member since the first scanning means or the second scanning means is moved or the white reference member is moved.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates to image scanning devices capable of scanning images on the both surfaces of an original and, more particularly, to image scanning devices capable of reducing the white level difference between the surface and the back surface and correcting the density difference in order to prevent the occurrence of scanning density differences between the both sides. 
         [0003]    2. Description of the Related Art 
         [0004]    Conventionally, there have been suggested and provided various types of image scanning devices capable of concurrently scanning images on the both surfaces of an original while conveying the original. Among them, there have been suggested sheet-feeding type image scanning devices including scanning means fixedly provided at the both sides of an original conveyance path and also there have been suggested image scanning devices configured to include a flat-bed type original conveying device which enables scanning non-conveyable originals such as brochures and also include a back-surface scanning means placed within the original conveying device, as described in Japanese Patent Application Laid-open (JP-A) No. 5-83480. 
         [0005]    A conventional image scanning device capable of scanning the both surfaces of an original will be described using  FIG. 8  and  FIG. 9 .  FIG. 8  is a main part explanation view illustrating the scanning mechanism part of a conventional image scanning device and  FIG. 9  is a view illustrating an image-signal processing circuit. 
         [0006]    The image scanning device illustrated in  FIG. 8  is for scanning the both surfaces of originals  39  and includes optical scanning units  36  and  40  which are placed such that they sandwich an original conveyance path. In the figure, the lower surface of the original  36  is referred to as a surface and the upper surface thereof is referred to as the back surface. A feeding roller  38  for conveying originals  39  is used for successive scanning of originals  39  or double-surface scanning. 
         [0007]    The optical scanning unit  36  is a scanning means for scaring the surfaces of originals  39  and is movable within a flat bed part  35 . The optical scanning unit  36  can scan an original secured on a platen glass by moving and also can scan an original being conveyed at a standstill state. The optical scanning unit  36  includes a lamp  42  and a CCD  44 . Further, on the flat bed part  35 , there is provided a white reference plate  37  for the optical scanning unit  36 . 
         [0008]    The optical scanning unit  40  is a scanning means for scanning the back surface of an original  39  and is fixedly placed within the original conveying device. The optical scanning unit  40  includes a lamp  43  and a CCD  45 . At a position facing to the optical scanning unit  40 , there is placed a platen roller  41  for the optical scanning unit  40 , the platen roller  41  being also used as a white reference. 
         [0009]    During double-surface scanning operations, the optical scanning unit  36  for surface scanning moves to the white reference plate  37  and scans the white reference plate  37  for adjusting the white level thereof and then it is moved to a usual scanning position (the illustrated position) and stopped. The optical scanning unit  40  for back-surface scanning scans a white reference on the platen roller  41  for adjusting the white level thereof and then waits an original  39  being conveyed thereto. 
         [0010]    The originals  39  are successively fed to the original conveyance path through the feeding roller  38 . Then, in the respective optical scanning units  36  and  40 , the originals  39  are irradiated with the lamps  42  and  43  at their to-be-scanned regions on the surface and the back surface and are scanned by the CCDs  44  and  45 . 
         [0011]    As in the image-signal processing circuit illustrated in  FIG. 9 , the CCDs  44  and  45  are connected to amplifiers  46  and  47 , A/D conversion circuits  48  and  49 , white-level correction circuits  50  and  51 , and memories  52  and  53 , respectively. The white levels of the white references which are first scanned by the surface scanning CCD  44  and the back-surface scanning CCD  45  are respectively stored in the white-level correcting circuits  50  and  51  and are corrected according to the ground colors of originals which are subsequently scanned. The corrected white levels are output to the A/D conversion circuits  48  and  49 . The A/D conversion circuits  48  and  49  convert analog image signals (video signals) received from the CCDs  44  and  45  through the amplifiers  46  and  47  into image data with corresponding density levels, by setting the white levels supplied from the white level correcting circuits  50  and  51  to the density saturation values. Thus, images on the surface and the back surface of the original are scanned with a proper contrast and then stored in the memories  52  and  53 . 
         [0012]    As described above, in a conventional double-surface image scanning device, a surface-scanning optical scanning unit and a back-surface-scanning optical scanning unit create white levels using specific white references such as a white reference plate and a platen roller. 
         [0013]    However, (1) in the case where the respective white references are made of different materials, there is a reflectivity difference there between. (2) Even when the respective white references are made of the same material, the individual components cause density variations. (3) Along with the conveyance of originals, the difference in the degree of contaminations between the white references is advanced. In this case, the surface white reference plate  37  is not contaminated while the platen roller  41  which is the back-surface white reference is contaminated at its surface along with conveyance of originals. 
         [0014]    For these reasons, the white reference levels of the optical scanning units  36  and  40  may not be in agreement with each other, thereby causing density differences among scanned image data. Consequently, there has been a need for performing burdensome level adjustments. Particularly, in the case of color scanning, the reflectivity differences on the respective color constituent basis (RGB) will cause color differences in scanned images and, therefore, it has been necessary to perform, for the respective white reference members, complicated controls, such as measuring the reflectivities of the respective RGB constituents and setting the white reference levels based on the reflectivities, for the respective components. 
         [0015]    Further, JP-A No. 4-371072 discloses a configuration which scans images on the surface and the back surface of a prepared white reference test chart and adjusts the levels such that the scanned values obtained from the surface and the back surface are in agreement with each other. However, this configuration can overcome the aforementioned problems (1) and (2), but can not address the problem (3). Further, there is a need for preparing a sheet for adjustment, thereby causing the problems of cost increases and the necessity of adjusting operations. 
         [0016]    Further, JP-A No. 2002-290685 and JP-A No. 2002-335380 disclose configurations in which a surface-scanning optical scanning unit and a back-surface-scanning optical scanning unit scan a single white reference member to perform white level correction. However, even though a single white reference member is used for white level correction, the surface-scanning optical scanning unit and the back-surface scanning optical scanning unit scan different regions, thereby causing the problem of impossibility of proper white level correction. 
       SUMMARY OF THE INVENTION 
       [0017]    Therefore, it is an object of the present invention to provide an image scanning device capable of preventing the occurrence of density differences due to deviations of white-level adjustment during scanning the both sides of an original, with a simple structure without involving an increase of the cost. 
         [0018]    In order to overcome the aforementioned problem, a representative structure of an image scanning device according to the present invention includes: a conveyance path which conveys originals; a first scanning means and a second scanning means which are placed such that they sandwich the conveyance path; and a white reference member used for adjusting the white levels of the scanning means; wherein at least one of the first scanning means, the second scanning means and the white reference member is movable, and the first scanning means and the second scanning means can scan the same surface of said white reference member since the first scanning means or the second scanning means is moved or the white reference member is moved. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0019]      FIG. 1  is a general structural view of an image scanning device. 
           [0020]      FIG. 2  is a main part enlarged view of the scanning part. 
           [0021]      FIG. 3  is a view illustrating the structure of an image-signal processing circuit. 
           [0022]      FIG. 4A  is a view illustrating the detailed structures of a white-level correcting circuit and a level-variable circuit 
           [0023]      FIG. 4B  is a view illustrating the detailed structures of a white-level correcting circuit and a level-variable circuit. 
           [0024]      FIG. 5  is a flow chart explaining a process for creating white-level controlling data. 
           [0025]      FIG. 6  is a main part enlarged view of a scanning part for explaining another embodiment 
           [0026]      FIG. 7  is a main part enlarged view of a scanning part for explaining a further embodiment. 
           [0027]      FIG. 8  is a main part explanation view illustrating the scanning mechanism part of a conventional image scanning device. 
           [0028]      FIG. 9  is a view illustrating an image-signal processing circuit. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     First Embodiment 
       [0029]    There will be described an image scanning device according to a first embodiment of the present invention.  FIG. 1  is a general structural view of the image scanning device.  FIG. 2  is a main part enlarged view of the scanning part.  FIG. 3  is a view illustrating the structure of an image-signal processing circuit  FIG. 4A  is a view illustrating the detailed structures of a white-level correcting circuit and a level-variable circuit.  FIG. 5  is a flow chart explaining a process for creating white-level controlling data. In the present embodiment in the drawings, the lower surface of an original during image scanning is referred to as an original surface while the upper surface thereof is referred to as an original back surface. 
         [0030]    The image scanning device illustrated in  FIG. 1  is constituted by an automated original feeding device (hereinafter, referred to as an ADF  100 ) and a scanning device main body  200 . The scanning device main body  200  has a first scanning mode for scanning an image by moving a surface scanner  201  (first scanning means) while placing an original on a platen glass  202  of the scanning device main body  200 . Further, the scanning device main body  200  has a second scanning mode for scanning an image on an original being transferred by the ADF  100  while maintaining the surface scanner  201  standstill at a predetermined position. In the second scanning mode, it is possible to scan the surface of an original by the surface scanner  201  while scanning the original back surface by a back-surface scanner (second scanning means)  301  fixedly placed in the ADF  100 . 
         [0031]    The scanning device main body  200  includes, at the upper surface thereof, a platen glass  202  for mounting an original thereon in the first scanning mode and a platen glass  203  for scanning an image on an original being conveyed in the second scanning mode. The scanning device main body  200  includes, inside thereof, the surface scanner  201  including a lamp  204 , a reflection capping  205  and a minor  206 , a two-mirror unit  209  having mirrors  207  and  208 , a lens unit  210  and a CCD  16 . Inage information optically scanned by the CCD  16  is photoelectrically converted into image data and then the image data is input. In the first scanning mode, the surface scanner  201  scans an image while moving along the platen glass  202  and, in the second scanning mode, it scans an image while being maintained standstill at a position facing to the platen glass  203 . 
         [0032]    At a position which can be scanned by the surface scanner  201  through the platen glass  202 , there is provided a white reference member  402  (standard white reference member) used for adjusting the white level of the surface scanner  201 . 
         [0033]    The ADF  100  includes a sheet tray  111  as an original mounting table, and originals on the sheet tray  111  are fed therefrom in order from an uppermost original through a feeding roller  112  as a feeding means. Then, the originals fed therefrom are separated into individual originals through a separation feeding roller  113  and a separation pad  114  which constitute a separating means. The separated originals are conveyed to the platen glass  203  of the scanning device main body  200  through a pair of conveyance rollers  117  and a pair of upstream lead rollers  103 . 
         [0034]    Before entering the platen glass  203 , the originals are butted against the nip portions of the pair of upstream lead rollers  103  at their tip ends to form a loop, thereby correcting the skew feeding and adjusting the timing. Thereafter, the originals are passed by a back-surface scanner  301  and then discharged onto a discharge tray  116  through a pair of downstream lead rollers and a pair of discharge rollers  115 . 
         [0035]    As illustrated in  FIG. 2 , the back-surface scanner  301  is placed at the opposite side to the surface scanner  201  as a first scanning means with respect to the conveyance path and is configured to scan images on the back surfaces of originals. The back-surface scanner  301  includes a lamp  304 , mirrors  306 ,  307  and  308 , a lens unit  310 , and a CCD  17 . The back-surface scanner  301  optically scans image information recorded on to-be-scanned originals, photoelectrically converts it into image data and then inputs the image data. 
         [0036]    As illustrated in  FIG. 2 , the position of the platen glass  203  at which images can be scanned by the surface scanner  201  is referred to as a surface scanning position  102  and the position at which images can be scanned by the back-surface scanner  301  is referred to as a back-surface scanning position  302 . These are scanning positions in the aforementioned second scanning mode. 
         [0037]    At the surface scanning position  102 , there is provided a surface scanning roller  120  for pressing an original being conveyed there through against the platen glass  203 , at a position facing to the surface scanner  201  through the platen glass  203  and the original conveyance path. The surface scanning roller  120  has a white color, in order not to exert influences on to-be-scanned images. However, in the present embodiment, the surface scanning roller  120  is not utilized as a white reference. 
         [0038]    At the back-surface scanning position  302 , there is provided a back-surface scanning roller  220  for pressing an original being transferred there through against the back-surface scanner  301 , at a position facing to the back-surface scanner  301  through the original conveyance path. The back-surface scanning roller  120  has a white color and is utilized as a white reference, in the present embodiment. 
         [0039]    The structure of the image-signal processing circuit will be described based on  FIG. 3 . In  FIG. 3 , the upper circuit part including the CCD  116  is used for scanning surfaces while the lower circuit part including the CCD  117  is used for scanning the back surfaces. 
         [0040]    Video signals output from the CCDs  116  and  117  are amplified by amplifiers  18  and  19  and then input to the white-level correction circuits  22  and  23  and A/D conversion circuits  20  and  21 . The white-level correction circuits  22  and  23  detect the ground-color levels of input video signals, correct the current white levels with a predetermined ratio and then supply them to the A/D conversion circuits  20  and  21  through level-variable circuits  22   a  and  23   a . The A/D conversion circuits  20  and  21  convert the input video signals into image data of digital signals by setting the white level values to the density saturation values (dynamic range values). The image data is stored in sequential addresses in RAMs  24  and  25 . The addresses are designated as AD 0  to ADn having n+1 bits. 
         [0041]    Latches  26  and  27  are state latches, which are interrupted during writing of image data into the RAMs  24  and  25 . A CPU  28  executes a controlling program stored in an EEPROM  28   a  to control the image scanning operation, white-level variation adjusting processes and the like. Controlling data resulted from the calculations is stored in the EEPROM  28   a . Further, the CPU  28  controls the respective level-variable circuits  22   a  and  23   a  through an I/O port  29  to adjust the white levels. 
         [0042]      FIG. 4A  is a view illustrating the detailed structures of the white-level correction circuit  22  and the level variable circuit  22   a  of  FIG. 3  which are enclosed in a dot line. The white-level correction circuit  23  and the level variable circuit  23   a  operate basically similarly to the circuits of  FIG. 4A . 
         [0043]    As illustrated in  FIG. 4A , the white-level correction circuit  23  includes a white-level memory  30  for holding a white level value. The white-level memory  30  holds a white level pattern (for a single line) as illustrated by dot-line waveforms in  FIG. 4B , wherein the white level pattern is updated for each line. The white level value is converted into an analog signal by a D/A conversion circuit  31 . 
         [0044]    A voltage dividing circuit  34  is a circuit which enables controlling the voltage division ratio thereof through analog switches  34   a  The analog switches  34   a  are operated according to the value of controlling data output from the I/O port  29  of  FIG. 3 . A comparator  33  makes comparison between the magnitudes of two inputs having positive and negative values and outputs the result as a binary value of I/O. The white level value which is adjusted by the D/A conversion circuit  31  through the voltage dividing circuit  34  is input to the positive input terminal of the comparator  33 . To the negative input terminal thereof, a video signal from the amplifier  18  of  FIG. 3  is input. 
         [0045]    A white-level algorism memory  32  includes a function table having address inputs which are the white-level value output from the white level memory  30  and the value I/O resulted from the comparison of the comparator  33  so that an updated value of the white level is read out therefrom as data based on a predetermined algorism. The data read from the white level algorism memory  32  is written into the white level memory  30  and is used as the white level for the next line. 
         [0046]    Next there will be described the white-level adjusting operations for the CCD  16  and the CCD  17 , using a flow chart of  FIG. 5 . 
         [0047]    First, the output of the level variable circuit  22   a  for the surface scanner  201  is maximized (the analog switches  34   a  in  FIG. 4A  are all turned on) to maximize the white level output (S 1 ). 
         [0048]    Then, the surface scanner  201  is moved to a position P 1  illustrated in  FIG. 2 , then the white reference member  402  as an exemplary standard white reference member is scanned by the CCD  16  (S 2 ) and then the read data (image data) of the white reference member  402  is taken in the RAM  24  through the latch  26 . As the white reference member  402 , for example, a member having a known reflectivity of 80% is employed. 
         [0049]    The CPU  28  obtained an average density value over a certain region of the image data of the white reference member  402  which is stored in the RAM  24  (S 3 ). A certain region is utilized for the calculation because if there are dusts adhered thereto, this will extemporaneously cause bright portions or dark portions. Namely, such bright portions and dark portions out of the scanned density values are cut by a predetermined amount (band-pass filter) and sampling is performed over the certain region, which enables calculations less prone to being affected by the condition. 
         [0050]    Based on the average value, the controlling data is calculated for white level adjustment in the level-variable circuit  22   a  of the white level correction circuit  22  (S 4 ). For example, the white level adjusting value is determined to be 255×0.8-204, in the case where the average density value is the reflectivity (80%) of the white reference member  402  and the level variable circuit  22   a  has 256 tones (0 to 255). More specifically, the white level adjusting value is ON/OFF controlling data for the analog switches  34   a  to provide a proper voltage division ratio to the voltage dividing circuit  34  of  FIG. 4A . 
         [0051]    Then, the CPU  28  writes the determined white-level adjusting value into the EEPROM  28   a  and also performs white-level adjustment for the CCD  16  (S 5 ). 
         [0052]    Next, the surface scanner  201  is moved to the position P 2  illustrated in  FIG. 2  and the back-surface scanning roller  220  is scanned by the CCD  16  (S 6 ). It is preferable that the back-surface scanning roller  220  is kept rotating at this time. The CPU  28  determines the average density value over a certain region, based on the image data of the back-surface scanning roller  220  which is stored in the RAM  24  (S 7 ). Since the correction of the CCD  16  has been already performed using the white reference member  402 , the average density obtained at this time is the density value of the back-surface scanning roller  220  and, thus, this average density is utilized as a target value α. 
         [0053]    Next the output of the level variable circuit  23   a  for the back-surface scanner  301  is maximized (S 8 ). Then, the back-surface scanning roller  220  is scanned by the CCD  17  on the back-surface scanner  301  (S 9 ) and the read data (image data) of the back-surface scanning roller  220  is taken in the RAM  25  through the latch  27 . It is preferable that the back-surface scanning roller  220  is kept rotating at this time. 
         [0054]    The CPU  28  determines the average density value over a certain region based on the image data of the back-surface scanning roller  220  which is stored in the RAM  25  (S 10 ). The average density is used as a target value β. 
         [0055]    Then, from the target values α and β, an optimal white level adjusting value for the back-surface scanner  301  (S 11 ) is obtained. More specifically, controlling data required for white level adjustment for the level variable circuit  23   a  is calculated such that the target value β is in agreement with the target value α. 
         [0056]    Then, the CPU  28  writes the obtained white level adjusting value in the EEPROM  28   a  and performs white level adjustment for the CCD  17  (S 12 ). 
         [0057]    By scanning the back-surface scanning roller  220  as a single white reference member through the CCD  16  on the surface scanner  201  and the CCD  17  on the back-surface scanner  301  and adjusting the white levels as described above, it is possible to prevent the occurrence of density differences due to deviations of white-level adjustment during scanning the both sides of an original, with a simple structure without involving an increase of the cost. 
         [0058]    Further, by adjusting, in advance, the white level of the CCD  16  of the surface scanner  201  using the standard white member (white reference member  402 ) which is less prone to receive contaminations from originals, it is possible to indirectly perform white level adjustment for the CCD  17  of the back-surface scanner  301  based on the standard white member, thereby enabling maintaining the accuracy of the white level for utilization across the years. 
       Other Embodiments 
       [0059]    There will be described image scanning devices according to other embodiments of the present invention. The same portions as those of the aforementioned first embodiment will be designated by the same reference characters and description thereof will not be shown. 
         [0060]    In the aforementioned first embodiment, the back-surface scanning roller  220  which is a white reference member has been described as a roller. On the contrary, as illustrated in  FIG. 6 , a back-surface belt member  223  as a white reference member is placed such that it is faced to the back-surface scanner  301 . The back-surface belt member  223  is a belt having a white-colored surface which is tightly stretched between a driving roller  222  and a stretching roller  221 . With the aforementioned structure, it is possible to improve the capability for conveying originals at the back-surface scanning position  302 , thereby reducing image deflections due to impacts during conveyance. 
         [0061]    Further, while, in the aforementioned first embodiment, the surface scanning roller  120  is not utilized as a white reference member, it is also possible to eliminate the white reference member  402  and utilize the surface scanning roller  120  as a standard white member. This enables cost reduction due to the elimination of the white reference member  402 . 
         [0062]    Further, in the aforementioned first embodiment, there has been described that the surface scanner  201  as a first scanning means is moved to scan the back-surface scanning roller  220  which is a single white reference member by both the surface scanner  201  and the back-surface scanner  301 . However, it is also possible to configure the device such that the white reference member is moved for scanning the single white reference member by both the first and second scanning means. For example, as illustrated in  FIG. 7 , the white reference member  403  faced to the back-surface scanner  301  may be moved by being rotated and the surface thereof to be scanned by the back-surface scanner  301  can be also scanned by the surface scanner  201 . This enables preventing the occurrence of density differences, similarly to in the first embodiment. 
         [0063]    Further, in the structure according to the aforementioned first embodiment, the back-surface scanning roller  220  may be integrated and united with the back-surface scanner  301  (the lamp  304 , the mirrors  306 ,  307  and  308 , the lens unit  310  and the CCD  17 ), and the position of the back-surface scanning roller  220  with respect to the back-surface scanning position (the synchronizing position and the light path length from the CCD  17  to the back-surface roller  220 ) may be assembly-adjustable (the position is adjustable during assembling and securing). Further, the back-surface scanner  301  (including the back-surface scanning roller  220 ) is mounted in the ADF  100  such that it is swingable in such a direction that it recedes and approaches from and to the scanning device main body  200  and the back-surface scanning unit is positioned through biasing means and abutting means which are not shown such that the back-surface scanning roller  220  is at a predetermined distance from the platen glass  203 . Further, the position at which the back-surface scanning roller  220  is scanned by the surface scanner  201  (the direction of movement of the surface scanner  201 ) is also made assembly-adjustable. This can cause the back-surface scanning roller  220  to be scanned at a proper light-path position and a proper synchronizing position with respect to the surface scanner  201  and the back-surface scanner  301 , thereby further reducing the density difference between the surface and the back surface of an original. 
         [0064]    Also, during scanning the back-surface scanning roller  220  by the surface scanner  201  and the back-surface scanner  301 , the edges of the back-surface scanning roller  220  at its end portions in the axial direction may be detected and may be utilized for normalization of the scanning position in the direction perpendicular to the original conveyance direction. This enables scanning the same portion of the back-surface scanning roller  220  in the direction perpendicular to the original conveyance direction, thereby further reducing the density difference between the surface and the back surface of an original. 
         [0065]    Further, while, in the aforementioned first embodiment, there has been described that the white level of the second scanning means is adjusted using a white-level adjusting value of the first scanning means, this is not always necessary. For example, the white-level adjustment for the second scanning means may be performed based on scanned values of the white reference member obtained from the second scanning means. In this case, similarly the white level adjustment for the first scanning means may be performed based on scanned values of the white reference member obtained from the first scanning means. Namely, in the case where the white reference member is scanned by one of them for adjusting the white level, the other one may be adjusted using the adjusted white level as a reference. Further, in the case where the first and second scanning means are individually subjected to white level adjustment it is possible to concurrently perform processing thereof, thereby providing advantages of speeding up of processing and simplification of the control. Accordingly, for example, the image scanning device may be configured such that the white reference member is usually scanned by the first and second scanning means for adjusting the respective white levels and, only when a particular mode (for example, “a high accuracy mode” and the like) is specified, the adjusting process according to the aforementioned first embodiment is performed. 
         [0066]    With the aforementioned embodiments, it is possible to significantly reduce the difference in white-level adjustment between the first and second scanning means placed across the original conveyance path, thereby preventing the occurrence of density differences, with a simple structure without involving an increase of the cost. 
       CROSS REFERENCE TO RELATED APPLICATION 
       [0067]    This application claims the benefit of priority from the prior Japanese Patent Application No. 2004374573 filed on Dec. 24, 2004 the entire contents of which are incorporated by reference herein.