Patent Publication Number: US-8995027-B2

Title: Image reading apparatus and an image processing system including an image sensor and a reference plate on the conveyance path for detecting the thickness of a medium

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is based upon and claims the benefit of priority of prior Japanese Patent Application No. 2012-202900, filed on Sep. 14, 2012, the entire contents of which are incorporated herein by reference. 
     TECHNICAL FIELD 
     Embodiments illustrated herein relate to an image reading apparatus and an image processing system. Particularly, the embodiments relate to an image reading apparatus for reading an image of a sheet-shaped document on a conveyance path, and an image processing system. 
     BACKGROUND 
     An ultrasonic double-sheet detecting method is known to detect conveyance of a plurality of paper sheets in which the paper sheets overlap each other. In the ultrasonic double-sheet detecting method, a threshold common to all paper sheets is calculated in advance, the threshold is automatically set in a detected-wave high-level setting circuit of a controller at the time of the start of a paper feeding unit, and the threshold is used to determine whether the number of paper sheets from the paper feeding unit is two or not. 
     Further, a double feed detecting circuit including a white reference storage unit and a reference value correcting unit is known. The white reference storage unit stores paper-sheet-penetration light amount value information that is measured by a sensor in a state where there is no paper sheet, the sensor being provided on a conveyance path for conveying a paper sheet. The reference value correcting unit calculates a reference value used in an electric signal converting process at the time of conveying a paper sheet. The reference value correcting unit compares white reference information from the white reference storage unit, with the paper-sheet-penetration light amount value information depending on a paper sheet thickness of a document to perform calculation. Thereby, the reference value correcting unit obtains a calculation result as a white reference change amount to correct an analogue-to-digital (A/D) conversion reference value. On the basis of the corrected A/D conversion reference value, an A/D conversion unit converts a penetration light amount measured value of a conveyed document into an electrical signal to be output as paper sheet thickness value information. A conveyance controller compares the paper sheet thickness value information with the double feed value information stored in a paper sheet thickness storage unit to perform calculation. Thereby, the conveyance controller detects the double feed of documents. 
     Furthermore, it is known that a paper-type detection unit that detects a paper-type of a document, and a paper thickness detection unit that detects a paper thickness are arranged between a separation unit and a conveyance roller. Both of the units detect a reflected light amount and a penetrated amount of light. Information from two sensors is treated as reference data that is a penetrated light amount from the paper thickness detection unit corresponding to a reflected light amount from a paper-type detection unit. The double feed of documents is determined by the comparison of the information from the two sensors with the recorded reference data. 
     Related art is disclosed in Japanese Laid-open Patent Publications No. 05-193786, No. 06-9106 and No. 2003-137457. 
     SUMMARY 
     In an image reading apparatus including a device for conveying a document, it may be preferable to detect a thickness of a document in the process of conveyance. 
     For example, when an ultrasonic sensor is used to detect whether a single document is being conveyed or double feed is occurring, not only the number of documents but also a thickness of a document changes an output level of an ultrasonic sensor. For this reason, when a thick document such as a card is conveyed, it can be erroneously detected that a double feed of thin paper documents is occurring. In such a case, if a thickness of a document can be detected, a conveyance of a thick document can be distinguished from a double feed of thin documents. 
     An object of the an apparatus and a system illustrated herein is to provide an image reading apparatus that can detect a thickness of a document in the process of conveyance. 
     In accordance with an aspect of the embodiment, there is provided an image reading apparatus including a first unit fixed on one side of a conveyance path of a sheet medium, a second unit provided on the other side of the conveyance path and facing the first unit, a guide unit that is provided at the second unit and that contacts the medium inserted into a gap between the first unit and the second unit to move the second unit in a direction of separating from the conveyance path, an imaging unit provided at one of the first unit and the second unit, a reference plate provided at the other of the first unit and the second unit, and a thickness detection unit for detecting a thickness of the medium on the basis of an image signal output by the imaging unit that captures an image of the reference plate with the medium inserted into the gap between the first unit and the second unit. 
     In accordance with another aspect of the embodiment, there is provided an image processing system including an image reading apparatus, and an information processing apparatus that receives from the image reading apparatus an image read by the image reading apparatus. The image reading apparatus includes a first unit fixed on one side of a conveyance path of a sheet medium, a second unit provided on the other side of the conveyance path and facing the first unit, a guide unit that is provided at the second unit and that contacts the medium inserted into a gap between the first unit and the second unit to move the second unit in a direction of separating from the conveyance path, an imaging unit provided at one of the first unit and the second unit, a reference plate provided at the other of the first unit and the second unit, a thickness detection unit for detecting a thickness of the medium on the basis of an image signal output by the imaging unit that captures an image of the reference plate with the medium inserted into the gap between the first unit and the second unit, and a notifying unit for notifying the information processing apparatus of the thickness of the medium. The information processing apparatus includes a storage unit for storing a plurality of image processing application programs that can be executed, and a selecting unit for selecting, in accordance with the thickness of the medium, from the plurality of image processing application programs, an image processing application program being for processing a captured image of the medium. 
     The object and advantages of the invention will be realized and attained by means of the elements and combinations particularly pointed out in the claims. It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are not restrictive of the invention, as claimed. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  illustrates one example of a configuration of an image processing system. 
         FIG. 2  is a perspective view of an image reading apparatus  100  in a state where a document table  103  is set. 
         FIG. 3  illustrates a conveyance path inside the image reading apparatus  100 . 
         FIG. 4  illustrates a first imaging unit  130   a , a second imaging unit  130   b , and an imaging unit guide  120 . 
         FIG. 5  illustrates operation of the second imaging unit  130   b  at the time of conveying a document. 
         FIG. 6  illustrates candidates for an arrangement position of the second document detection unit  118 . 
         FIG. 7  illustrates one example of a hardware configuration of the image reading apparatus  100 . 
         FIG. 8  illustrates one example of a functional configuration of the image reading apparatus  100 . 
         FIG. 9A  illustrates detection of a first white reference level. 
         FIG. 9B  illustrates detection of a second white reference level. 
         FIG. 9C  illustrates detection of a second white reference level. 
         FIG. 10A  represents examples of respective output of an ultrasonic sensor  115  when documents that are different media are conveyed. 
         FIG. 10B  illustrates change in a white reference level due to a difference in a thickness of a medium. 
         FIG. 11  illustrates one example of conditions for determining a double feed occurrence and a document thickness. 
         FIG. 12  schematically illustrates waveforms of an electric current that flows in A-phase coils and B-phase coils of a two-phase stepping motor. 
         FIG. 13A  illustrates a distance between a document back surface and a second image sensor  133   b  when a document is not a thick medium. 
         FIG. 13B  illustrates a distance between a document back surface and the second image sensor  133   b  when a document is a thick medium. 
         FIG. 14A  illustrate a distances between the image sensor  133  and a white reference unit  134  when a document is not a thick medium. 
         FIG. 14B  illustrate a distances between the image sensor  133  and the white reference unit  134  when a document is a thick medium. 
         FIG. 15A  schematically illustrates image data of a document when a document is not a thick medium. 
         FIG. 15B  schematically illustrates image data of a document when a document is a thick medium. 
         FIG. 16A  illustrates a brightness change at an edge when a document is not a thick medium. 
         FIG. 16B  illustrates a brightness change at an edge when a document is a thick medium. 
         FIG. 17  is a flowchart of an operational example for the entire processing of the image reading apparatus  100 . 
         FIG. 18  is a flowchart of an operational example of a double feed determining processing. 
         FIG. 19A  is a flowchart representing a first example of an operation of a document conveyance processing. 
         FIG. 19B  is a flowchart representing a second example of an operation of the document conveyance processing. 
         FIG. 20  is a flowchart of an operational example of a motor torque adjusting processing. 
         FIG. 21  is a flowchart of an operational example of a shading processing. 
         FIG. 22  is a flowchart of an operational example of an image processing. 
         FIG. 23  illustrates one example of a hardware configuration of an information processing apparatus  10 . 
         FIG. 24  illustrates one example of a functional configuration of the information processing apparatus  10  executing a driver program  611 . 
         FIG. 25A  illustrates a first example of a dialog box that displays a candidate list. 
         FIG. 25B  illustrates a second example of the dialog box that displays a candidate list. 
         FIG. 26  is a flowchart of a processing example of the driver program. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     In the following, an image reading apparatus and an image processing system according to one aspect of the present invention will be described with reference to the attached drawings.  FIG. 1  illustrates one example of a configuration of the image processing system. It is to be noted, however, that, the technical scope of the present invention is not limited to the embodiments of implementation of the invention, but covers the invention described in the claims and the equivalent of the invention. 
     The image reading apparatus of a present embodied example is configured as an image reading apparatus  100  such as an image scanner. The image processing system  1  includes the image reading apparatus  100  and an information processing apparatus  10 . In  FIG. 1 , the image reading apparatus  100  is depicted by a perspective illustration. 
     The image reading apparatus  100  includes a lower housing  101 , an upper housing  102 , a document table  103 , a front surface cover  105   a , an opening/closing detection unit  107 , and the like. The image reading apparatus  100  is connected to the information processing apparatus  10 . The image processing apparatus  10  is a personal computer, or a personal digital assistant, for example. 
     Moreover,  FIG. 2  is a perspective view of the image reading apparatus  100  where the document table  103  is set. The image reading apparatus  100  includes an upper surface cover  105   b , an auxiliary cover  105   c , and operation button  106 . The document table  103  engages the lower casing  101  by hinges so as to be rotated in the direction indicated by the arrow A 1 . In a state of  FIG. 1 , the document table  103  is arranged at a position where the document table  103  covers the upper case  102 , the upper surface cover  105   b , and the auxiliary cover  105   c . Thus, the document table  103  functions as an exterior cover. 
     Meanwhile, in the state as depicted in  FIG. 2 , the document table  103  is arranged such that documents can be placed on the document table  103 . Provided in the document table  103  are side guides  104   a  and  104   b  that are movable in the right and left directions of the conveyance direction of a document. The side guides  104   a  and  104   b  are aligned with a width of a document to restrict the document in the width direction of the document. 
     The front surface cover  105   a  engages the lower housing  101  by hinges so as to be rotated in the direction indicated by the arrow A 2 . The upper surface cover  105   b  is connected at one end to the front surface cover  105   a , and is connected at the other end to the auxiliary cover  105   c . When it is necessary, the auxiliary cover  105   c  is let out from the upper surface cover  105   b  to hold a document. 
     The operation button  106  is arranged on the surface of the upper housing  102 , which button generates and outputs an operation detection signal by pressing down. The opening/closing detection unit  107  includes a contact detecting sensor arranged at a position that faces the document table  103  in a closed state, and detects an opened state and a closed state of the document table  103 . The opening/closing detection unit  107  generates and outputs an opening/closing detection signal of which signal value changes by the state of the document table  103  whether it is open or closed. 
       FIG. 3  illustrates a conveyance path inside the image reading apparatus  100 . The image reading apparatus  100  includes a first document detection unit  110 , a pick arm  111 , a flap  112 , a sheet feeding roller  113 , a retard roller  114 , an ultrasonic wave transmitter  115   a , an ultrasonic wave receiver  115   b , a first conveyance roller  116 , and a first driven roller  117 . The image reading apparatus  100  includes a second document detection unit  118 , an imaging unit guide  120 , a first imaging unit  130   a , a second imaging unit  130   b , a second conveyance roller  140 , a second driven roller  141 , and the like. 
     A lower surface of the upper housing  102  forms an upper guide  108   a  of the document conveyance path, and an upper surface of the lower housing  101  forms a lower guide  108   b  of the document conveyance path. In  FIG. 3 , the arrow A 3  indicates the conveyance direction of a document. In the following, the term “upstream” means “upstream in the conveyance direction A 3 ”, and the term “downstream” means “downstream in the conveyance direction A 3 . 
     The first document detection unit  110  includes a contact detecting sensor arranged in the upstream side of the pick arm  111 , and detects whether or not a document is placed on the document table  103 . The first document detection unit  110  generates and outputs a first document detection signal of which signal value changes by the state whether or not a document is placed on the document table  103 . 
     The sheet feeding roller  113  is supported by a main body unit of the image reading apparatus in a rotation-free manner. Provided in an outer circumferential surface of the sheet feeding roller  113  is a contact material  142  that contacts a document placed on the document table  103 . The contact material  142  is made of rubber, for example, of which coefficient of friction with a document is large. 
     The retard roller  114  is arranged to face the sheet feeding roller  113 , and restricts so that a document that does not contact the sheet feeding roller  113  is not conveyed in the conveyance direction A 3 . The retard roller  114  is supported by the main body unit of the image reading apparatus in a rotation-free manner. Provided in an outer circumferential surface of the retard roller  114  is a contact material  143  that contacts a document placed on the document table  103 . The contact material  143  is made of rubber, for example, of which coefficient of friction with a document is large. 
     The ultrasonic wave transmitter  115   a  and the ultrasonic wave receiver  115   b  are arranged near the document conveyance path so as to sandwich the conveyance path and face each other. The ultrasonic wave transmitter  115   a  transmits an ultrasonic wave. Meanwhile, the ultrasonic wave receiver  115   b  detects an ultrasonic wave that has been transmitted by the ultrasonic wave transmitter  115   a  and has penetrated a document, and generates and outputs an ultrasonic wave signal that is an electrical signal depending on the detected ultrasonic wave. In the following, the ultrasonic wave transmitter  115   a  and the ultrasonic wave receiver  115   b  may be collectively referred to as an ultrasonic sensor  115 . 
     The first conveyance roller  116  and the first driven roller  117  are respectively supported by the main body unit of the image reading apparatus in a rotation-free manner. The first conveyance roller  116  and the first driven roller  117  are arranged on the upstream side of the first imaging unit  130   a  and the second imaging unit  130   b . The first driven roller  117  is arranged above the first conveyance roller  116  to face the first conveyance roller  116 . The first conveyance roller  116  is fixed, and the first driven roller  117  is arranged so as to be movable upward (in the direction of the arrow A 4 ) relative to the first conveyance roller  116 . 
     The second conveyance roller  140  and the second driven roller  141  are respectively supported by the main body unit of the image reading apparatus in a rotation-free manner. The second conveyance roller  140  and the second driven roller  141  are arranged on the downstream side of an imaging unit  130 . The second driven roller  141  is arranged above the second conveyance roller  140  to face the second conveyance roller  140 . The second conveyance roller  140  is fixed, and the second driven roller  141  is arranged so as to be movable upward (in the direction of the arrow A 5 ) relative to the second conveyance roller  140 . 
       FIG. 4  illustrates the first imaging unit  130   a , the second imaging unit  130   b , and the imaging unit guide  120 . The first imaging unit  130   a  captures an image of a front surface of a conveyed document, and the second imaging unit  130   b  captures an image of a back surface of the conveyed document. The second imaging unit  130   b  is arranged above the first imaging unit  130   a  to face the first imaging unit  130   a . The second imaging unit  130   b  includes the imaging unit guide  120  for guiding a document between the first imaging unit  130   a  and the second imaging unit  130   b . In the following, the first imaging unit  130   a  and the second imaging unit  130   b  may be collectively referred to as the imaging unit  130 . 
     The first imaging unit  130   a  is fixed to the lower housing  101 . Meanwhile, the second imaging unit  130   b  is supported by the upper housing  102  so as to be movable in the direction perpendicular to the conveyance path. The second imaging unit  130   b  includes a pushing spring  131  at an upper position thereof. The pushing spring  131  pushes the second imaging unit  130   b  toward the first imaging unit  130   a . When there is no document at the conveyance path, pushing force of the pushing spring  131  returns the second imaging unit  130   b  back to an initial position. 
     When the second imaging unit  130   b  is at the initial position, a width of a gap between the first imaging unit  130   a  and the second imaging unit  130   b  facing each other is larger than the thicknesses of a copy paper sheet, a print paper sheet, a photo paper sheet, and the like. For this reason, the second imaging unit  130   b  does not move from the initial position after any of these sheets are conveyed. 
     The first imaging unit  130   a  includes a first light source  132   a , a first image sensor  133   a , a first white reference unit  134   a , a first glass surface  135   a , and the like. The second imaging unit  130   b  includes a second light source  132   b , a second image sensor  133   b , a second white reference unit  134   b , a glass surface  135   b , and the like. In the following, the first image sensor  133   a  and the second image sensor  133   b  may be collectively referred to as an image sensor  133 . The first white reference unit  134   a  and the second white reference unit  134   b  may be collectively referred to as a white reference unit  134 . 
     The first light source  132   a  includes light emitting diodes (LEDs) of respective colors RGB and a light guiding material, and emits an illuminating light to a document surface. When there is no document at an illuminating position, the second white reference unit  134   b  of the second imaging unit  130   b  is irradiated with illuminating light. Similarly, the second light source  132   b  includes LEDs of respective colors RGB and a light guiding material, and emits an illuminating light to a document surface. When there is no document at an illuminating position, the first white reference unit  134   a  of the first imaging unit  130   a  is irradiated with illuminating light. 
     The image sensor  133  is a contact image sensor (CIS) that is a unit-magnification optical system that includes an imaging element constituted by charge coupled devices (CCDs) that are linearly arranged in a main scanning direction. The image sensor  133  reads a surface of a document to generate and output an image signal. Alternatively, instead of the CCDs, complementary metal oxide semiconductors (CMOSs) may be used. Further, alternatively, instead of the CIS, an image sensor that is an optical reduction system can be used. 
     The first white reference unit  134   a  is arranged at a position facing the second image sensor  133   b  of the second imaging unit  130   b . When a document is not conveyed to the imaging unit  130 , the second image sensor  133   b  captures an image of the first white reference unit  134   a  to generate an image signal. Similarly, the second white reference unit  134   b  is arranged at a position facing the first image sensor  133   a  of the first imaging unit  130   a . When a document is not conveyed to the imaging unit  130 , the first image sensor  133   a  captures an image of the second white reference unit  134   b  to generate an image signal. On the basis of the image signals generated by capturing the images of the first white reference unit  134   a  and the second white reference unit  134   b , the image reading apparatus can perform image correction such as shading, and the like. 
     Provided at the imaging unit guide  120  is a guide member  121  that guides a document to a position between the first imaging unit  130   a  and the second imaging unit  130   b . Provided above the guide member  121  is a contact detecting sensor included in the second document detection unit  118 . A lever unit  118   b  of the contact detecting sensor penetrates a penetration hole  122  provided in the guide member  121  to contact a document on the conveyance path. 
       FIG. 5  illustrates an operation of the second imaging unit  130   b  at the time of conveying a document. It is assumed that a thick medium such as a cardboard, a banking card, and a credit card is conveyed as a document  150 . A thickness of the medium is larger than thicknesses of a copy paper sheet, a print paper sheet, and a photo paper sheet. 
     In the following description, a relatively thick medium such as cardboard, a banking card, and a credit card is referred to as a thick medium. Meanwhile, a relatively thin medium such as a thin paper sheet is referred to as a thin medium. A medium that is thicker than a thin medium and thinner than a thick medium and that has a thickness of a copy paper sheet, a print paper sheet, a photo paper sheet, or the like is referred to as an intermediate-thickness medium. 
     When a document  150  that is a thick medium is conveyed to a position of the imaging unit guide  120 , the document  150  having a certain degree of strength contacts the guide member  121 , and the imaging unit guide  120  and the second imaging unit  130   b  move in the direction of the arrow A 10 , separating from the conveyance path. On the other hand, even when a document  150  that is a thin medium or an intermediate-thickness medium is conveyed to the imaging unit guide  120 , the second imaging unit  130   b  does not moved from the initial position. Thereby, in case that a document that is a thick medium is conveyed, a gap between the first imaging unit  130   a  and the second imaging unit  130   b  is widened, compared with a case of a document that is a thin medium or an intermediate-thickness medium being conveyed. 
     A fluctuation in a gap between the first imaging unit  130   a  and the second imaging unit  130   b  changes brightness of an image of the white reference unit  134  captured by the image sensor  133 . Accordingly, on the basis of a difference of a change of images of the white reference unit  134  before and after a document  150  moves the second imaging unit  130   b , a thickness of the document  150  can be detected. 
     A document  150  that contacted the guide member  121  then contacts the lever unit  118   b  of the second document detection unit  118  that penetrates the penetration hole  122  of the guide member  121 . Thereby, the second document detection unit  118  detects that the document  150  exists at a position of the lever unit  118   b . The second document detection unit  118  generates and outputs a second document detection signal that has a first value in a state where the lever unit  118   b  does not contact a document  150 , and that has a second value in a state where the lever unit  118   b  contacts a document  150 . 
     The lever unit  118   b  is provided at a position where the lever unit  118   b  detects a leading end of a document  150  when the document  150  that is a thick medium moves the second imaging unit  130   b  in the direction A 10  by a movement amount corresponding to a thickness of the document  150 . Moreover, for detecting a thickness of a document  150 , an image of the first white reference unit  134   a  or the second white reference unit  134   b  is used, such an image being captured after a leading end of the document  150  is detected. For this reason, the lever unit  118  is positioned such that a leading end of a document  150  is detected on the upstream side of at least one of image capturing positions of the first image sensor  133   a  and the second image sensor  133   b.    
       FIG. 6  illustrates candidates for an arrangement position of the second document detection unit  118 . As described above, the second document detection unit  118  is positioned such that a leading end of a document is detected on the upstream side of at least one of the image capturing position p 1  of the first image sensor  133   a  and the image capturing position p 2  of the second image sensor  133   b . Moreover, to detect a document after the second imaging unit  130   b  is moved, the second document detection unit  118  is positioned such that a leading end of a document is detected on the downstream side of a front end position p 3  of an upstream side of the imaging unit guide  120 . 
     Moreover, if a leading end of a document is at a downstream position of any of the rollers conveying a document provided at an upstream side of the imaging unit  130 , it is possible to determine how far the document is to be transferred from this position so that the second imaging unit  130   b  is moved by an amount corresponding to the thickness of the document that is a thick medium. Accordingly, the second document detection unit  118  may be positioned such that a leading end of a document is detected on the downstream side of at least one of a position p 4  on the downstream side of the first conveyance roller  116 , and a position p 5  on the downstream side of the sheet feeding roller  113 . 
     In the above-described embodied example, the second imaging unit  130   b  provided above the conveyance path is configured to move by a document  150  that is a thick medium. Alternatively, the first imaging unit  130   a  provided below the conveyance path may be configured to move by a document  150  that is a thick medium. 
       FIG. 7  illustrates one example of a hardware configuration of the image reading apparatus  100 . The image reading apparatus  100  includes a central processing unit (CPU)  300 , a memory  301 , a large scale integration (LSI)  302  for image processing, a buffer memory  303 , and a communication interface circuit  304  as well as the above-described configuration. In the attached drawings and the following description, an interface may be referred to as an IF. 
     Moreover, the image reading apparatus  100  includes a light source drive circuit  310 , an image sensor drive circuit  311 , an ultrasonic sensor drive circuit  312 , an ultrasonic sensor output reading circuit  313 , a motor  314 , a motor drive circuit  315 , and an input IF circuit  316 . The first imaging unit  130   a  and the second imaging unit  130   b  include a first analogue front-end processor (AFE)  320   a  and a second AFE  320   b , respectively. 
     The CPU  300  controls an operation of the image reading apparatus  100  in accordance with a computer program stored in the memory  301 . In some embodied example, the CPU  300  may perform a part of or all of image processing for an image read by the image reading apparatus  100 . Stored in the memory  301  are the computer program executed by the CPU  300 , and the data used in executing the computer program. The memory  301  may include a nonvolatile storage device for storing the program, and a volatile memory for temporarily storing the data. 
     The first AFE  320   a  and the second AFE  320   b  convert analogue image signals into digital signals to generate digital image data, the analogue image signals being output from the first image sensor  133   a  of the first imaging unit  130   a  and the second image sensor  133   b  of the second imaging unit  130   b . The first AFE  320   a  and the second AFE  320   b  output the image data to the LSI  320  for image processing. 
     The LSI  302  for image processing performs a shading process and predetermined image processing on the image data received from the imaging unit  130 . The LSI  302  for image processing stores such image data in the buffer memory  303  as the image processing is performed. 
     The communication IF circuit  304  is a wired or wireless communication interface between the image reading apparatus  100  and the information processing apparatus  10 . The CPU  300  reads the image date from the buffer memory  303  to transmit the image data to the information processing apparatus  10  via the communication IF circuit  304 . 
     The light source drive circuit  310  drives the first light source  132   a  of the first imaging unit  130   a  and the second light source  132   b  of the second imaging unit  130   b  in accordance with the control performed by the CPU  300 . The image sensor drive circuit  311  drives the first image sensor  133   a  of the first imaging unit  130   a  and the second image sensor  133   b  of the second imaging unit  130   b  in accordance with the control performed by the CPU  300 . 
     The ultrasonic sensor drive circuit  312  drives the ultrasonic wave transmitter  115   a  to cause the ultrasonic wave to be transmitted. The ultrasonic sensor output reading circuit  313  reads an output signal of the ultrasonic wave receiver  115   b  to transmit the output signal to the CPU  300  via a bus. 
     The motor  314  gives rotational driving force to the sheet feeding roller  113 , the retard roller  114 , the first conveyance roller  116 , and the second conveyance roller  140 . A plurality of the motors  314  may be provided. In accordance with the control performed by the CPU  300 , the motor drive circuit  315  generates a drive current that is supplied to the motor  314 . 
     The input IF circuit  316  receives an operation detection signal output by the operation button  106 , a first document detection signal output by the first document detection unit  110 , and a second document detection signal output by the second document detection unit  118  to transmit the signals to the CPU  300  via the bus. 
     The hardware configuration illustrated in  FIG. 7  is merely an example for explanation of the embodied example. The image reading apparatus  100  may include any other hardware configurations as long as the operation described in the following may be performed. 
       FIG. 8  illustrates one example of a functional configuration of the image reading apparatus  100 . The image reading apparatus  100  includes a control unit  400 . Moreover, the functional configuration diagram of  FIG. 8  mainly represents a configuration related to the function of the image reading apparatus  100  that are described in the present specification. The image reading apparatus  100  may include the configuration elements other than the configuration elements represented in the drawing. Moreover, an operation of the control unit  400  is performed by cooperation of the CPU  300  and the LSI  302  for image processing in  FIG. 7 . 
     The control unit  400  includes a conveyance control unit  401 , a white reference level detection unit  402 , a double feed determination unit  403 , a thickness detection unit  404 , a motor control unit  405 , a shading processing unit  406 , an image processing unit  407 , an image transmitting unit  408 , and a notifying unit  409 . 
     The conveyance control unit  401  controls a rotational operation of the motor  314  for conveying a document. The white reference level detection unit  402  detects a white reference level that indicates brightness of an image signal obtained by image capturing of the white reference unit  134 , the image capturing being performed by the image sensor  133 . 
       FIG. 9A  illustrates a detection of a first white reference level. The white reference level detection unit  402  detects a first white reference level L 1  before a document  150  reaches the position of the imaging unit guide  120  after a document conveyance is started. 
       FIG. 9B  and  FIG. 9C  illustrate a detection of a second white reference level. The conveyance control unit  401  stops the conveyance when a leading end of the document  150  to be conveyed is detected by the second document detection unit  118 , and the value of a second document detection signal changes from the first value to the second value. In this state, the white reference level detection unit  402  detects a white reference level L 2  for the second time. 
       FIG. 9B  illustrates a state of detecting a white reference level L 2  when a document  150  is a thin medium or an intermediate-thickness medium. In this case, a position of the second imaging unit  130   b  is maintained at the initial position.  FIG. 9C  illustrates a state of detecting a white reference level L 2  when a document  150  is a thick medium. When a document  150  is a thick medium, the second imaging unit  130   b  moves in the direction of separating from the conveyance path. For this reason, a gap between the image sensor  133  and the white reference unit  134  becomes wider than a gap when a document  150  is a thin medium or an intermediate-thickness medium. 
     The double feed determination unit  403  performs a double feed determining process of determining whether or not a double feed occurred, in which a plurality of documents overlapping each other are conveyed. As illustrated in  FIGS. 9A to 9C , while one or more documents exist between the ultrasonic wave transmitter  115   a  and the ultrasonic wave receiver  115   b , the double feed determination unit  403  reads output Lus of the ultrasonic wave receiver  115   b.    
       FIG. 10A  represents examples of respective output Lus of the ultrasonic sensor  115  when the documents of different media are conveyed. The horizontal axis indicates by which sampling a measured value is obtained, and the vertical axis indicates a digital value that is an index value of a document thickness converted from output Lus of the ultrasonic sensor  115 . When a document is a thin medium, and a double feed does not occur, an output value  500  is stabilized at a value larger than a threshold “224”. When output Lus of the ultrasonic sensor  115  is larger than this threshold, it can be determined that the double feed has not occurred. 
     Moreover, when a double feed of a document of an intermediate-thickness media occurs, output Lus is stabilized at a value equal to or smaller than a threshold “160”. Accordingly, when output Lus of the ultrasonic sensor  115  is equal to or smaller than this threshold, it can be determined that a double feed has occurred. 
     When a document is a thick medium, and a double feed does not occur, an output value  501  possibly becomes a value close to an output value  502  when a double feed of documents that are thin media occurs. For this reason, in a double feed determination based on output Lus of the ultrasonic sensor  115 , when a document is a thick medium, and a double feed does not occur, it can be erroneously determined that a double feed occurs. Further, when a double feed of a document of a thin media occurs, it can be erroneously determined that a document is a thick medium, and a double feed does not occur. 
     For this reason, the thickness detection unit  404  detects a thickness of a conveyed document on the basis of a white reference level difference DL=(L 1 −L 2 ) that is a difference between a first white reference level L 1  and a second white reference level L 2 .  FIG. 10B  illustrates a change of a second white reference level L 2  due to a difference in a thickness of a medium. The horizontal axis indicates a pixel position in a main scanning direction when the image sensor  133  captures image of the white reference unit  134 . The vertical axis indicates a gradation value, i.e., a brightness difference value of a white reference level. 
     In the case of a thin medium or an intermediate-thickness medium, a position of the second imaging unit  130   b  is maintained at the initial position. Accordingly, a second white reference level  510  for a thin medium or an intermediate-thickness medium is the same as a first white reference level L 1 . The brightness of a second white reference level  511  for a thick medium becomes smaller by widening of a gap between the image sensor  133  and the white reference unit  134 . For this reason, a white reference level difference DL when a document is a thick medium becomes larger than a white reference level difference DL when a document is a thin medium or an intermediate-thickness medium. 
     In accordance with a result of a document thickness detection performed by the thickness detection unit  404 , the double feed determination unit  403  determines whether or not a double feed of documents is occurring, when output Lus of the ultrasonic sensor  115  stays within a range of a value that is output when a document is a thick medium, and a double feed does not occur. 
       FIG. 11  illustrates one example of the conditions for determining a double feed occurrence and a document thickness. When output Lus is equal to or smaller than a threshold Th 1 , the double feed determination unit  403  determines that a double feed has occurred. In the case of respective output examples of the ultrasonic sensor  115  of  FIG. 10A , the threshold Th 1  may be set at “160”. When output Lus is larger than a threshold Th 2 , the double feed determination unit  403  determines that a document is a thin medium, and a double feed is not occurring. In the case of respective output examples of the ultrasonic sensor  115  of  FIG. 10A , the threshold Th 2  may be set at “224”. 
     When output Lus is equal to or smaller than the threshold Th 2 , and is larger than the threshold Th 1 , the thickness detection unit  404  determines whether or not a document is a thick medium, on the basis of a white reference level difference DL being larger than a threshold Th 3  or not. When the document is a thick medium, the double feed determination unit  403  determines that double feed is not occurring. When the document is not a thick medium, the double feed determination unit  403  determines that a double feed has occurred. 
     Reference is made to  FIG. 8 . In accordance with a result of a detection made by the thickness detection unit  404 , the motor control unit  405  performs a motor torque adjusting process of changing a generating torque of the motor  314 . If a document that is a thick medium is conveyed by the same torque as for a document that is not a thick medium, the motor  314  possibly loses steps. When a document is a thick medium, the motor control unit  405  causes a generating torque of the motor  314  to be larger than the case when a document is not a thick medium. 
     For example, the motor control unit  405  increases the maximum value of an electric current applied to the motor  314  to increase a generating torque of the motor  314 . Alternatively, for example, the motor control unit  405  may change a method of exciting the motor  314  to increase a generating torque. 
     For example, the motor control unit  405  may change an exciting method from an one-phase exciting method to a two-phase exciting method to increase a drive electric current area of coils of the motor  314  per unit time without changing the maximum value of an electric current, and thereby, a generating torque may be increased. Also when the motor  314  is driven by a micro-step drive, the motor control unit  405  may change a drive electric current area of coils of the motor  314  per unit time without changing the maximum value of an electric current, and thereby, a generating torque of the motor  314  may be increased. 
       FIG. 12  schematically illustrates waveforms of an electric current that is made to flow in A-phase coils and B-phase coils when the motor  314  that is a two-phase stepping motor is driven by a micro-step drive. The waveforms of the solid lines are the waveforms of a drive electric current that is made to flow in the coils of the motor  314  when a document is not a thick medium, and the waveforms of the broken lines are waveforms of a drive electric current that is made to flow in the coils of the motor  314  when a document is a thick medium. As illustrated in  FIG. 12 , when a document is a thick medium, a generating torque of the motor  314  can be increased by increasing a drive electric current area per unit time to be larger than that when a document is not a thick medium. 
     Reference is made to  FIG. 8 . The shading processing unit  406  performs a shading processing of the data received from the imaging unit  130 . On the basis of a brightness distribution of an image data of the second white reference unit  134   b  obtained by detecting a second white reference level L 2 , the shading processing unit  406  generates a shading correction data for a shading correction of a front-surface image data of a document  150  shot by the first imaging unit  130   a . On the basis of a brightness distribution of an image data of the first white reference unit  134   a  obtained by detecting a second white reference level L 2 , the shading processing unit  406  generates a shading correction date for a shading correction of a back-surface image data of a document  150  shot by the second imaging unit  130   b.    
     When a document is a thick medium, an entire characteristic of an image possibly differs between a front-surface image data and a back-surface image data of the document  150 .  FIG. 13A  and  FIG. 13B  illustrate a distance between a document back surface and the second image sensor  133   b  when a document is not a thick medium and when a document is a thick medium. 
     When a document is not a thick medium, a thickness of the document  150  is smaller than a gap between the second imaging unit  130   b  at the initial position and the first imaging unit  130 , and accordingly, a gap d 1  between a back surface of the document  150  and the second imaging unit  130   b  is relatively large. On the other hand, when a document is a thick medium, the second imaging unit  130   b  moves, following a thickness of the document  150  rather than by a contact between the imaging unit guide  120  and the document  150 . Accordingly, a gap d 2  between a back surface of the document  150  and the second imaging unit  130   b  is relatively small. As a result, when a document is a thick medium, an image data of a back surface of the document  150  tends to have a higher brightness compared with the case in which the document is not a thick medium. 
     When a document is a thick medium, the shading processing unit  406  corrects a shading correction data for a back surface of a document  150 . For example, when a document is a thick medium, the shading processing unit  406  may correct the shading correction data by increasing a brightness of the a shading correction data such that the image data of a back surface of a document  150  is corrected to become darker. At this time, the shading processing unit  406  may determine a correcting amount of the shading correction data in accordance with a white reference level difference DL. 
     Moreover, when a document is a thick medium, a gap between a back surface of the document  150  and the second imaging unit  130   b  is narrowed, that makes a focus displaced. When a document is a thick medium, the image processing unit  407  may perform an unsharp mask process on image data of a back surface. 
     Moreover, the image processing unit  407  performs a predetermined image processing on image data received from the imaging unit  130 . For example, the image processing unit  407  performs, as the predetermined image process, a cropping processing of removing a background region in image data to cut out only a document region. 
     An edge that is a boundary between a background region and a document region is performed by comparing the brightness of each pixel in image data with a threshold to distinguish the document region and the background region having different a brightness. When a document is a thick medium, the brightness of a background region drops compared with the brightness of a background region when a document is a thin medium, and the brightness change at a boundary between a document region and a background region becomes gentle, possibly reducing the accuracy in detecting an edge. 
       FIG. 14A  and  FIG. 14B  illustrate a distance between the image sensor  133  and the white reference unit  134  when a document is not a thick medium and when a document is a thick medium.  FIG. 15A  and  FIG. 15B  schematically illustrate the image data of a document respectively when a document is not a thick medium and when a document is a thick medium. The reference code  520  indicates an image data before a cropping processing, the reference code  521  indicates a document region, and the reference code  522  indicates a background region. 
     A distance d 2  between the image sensor  133  and the white reference unit  134  when a document is a thick medium is larger than a distance d 1  between the image sensor  133  and the white reference unit  134  when a document is not a thick medium. For this reason, when a document is a thick medium, the brightness of a background region  522  drops, compared with the brightness of a background region  522  when a document is not a thick medium. 
       FIG. 16A  and  FIG. 16B  illustrate the brightness change at the edges respectively when a document is not a thick medium and when a document is a thick medium. The horizontal axis indicates a pixel position in a main scanning direction, and the vertical axis indicates the brightness of each pixel. When a document is a thick medium, a distance between the image sensor  133  and the white reference unit  134  becomes longer, that makes a position of the white reference unit  134  shifted out of the depth of field of the image sensor  133 . For this reason, the brightness change at a boundary between a document region and a background region becomes gentle. 
     As a result, when the same threshold Th 6  is used for a document that is not a thick medium and for a document that is a thick medium, the edge position p 2  detected for a document that is a thick medium is displaced by an error amount e from the edge position p 1  detected for a document that is not a thick medium. For this reason, when a document is a thick medium, the image processing unit  407  corrects a detection threshold used in an edge detection in the cropping processing. For example, when a document is a thick medium, the image processing unit  407  corrects a detection threshold to be a value for detecting an edge at a pixel having a higher brightness. 
     Reference is made to  FIG. 8 . The image transmitting unit  408  transmits an image data to the information processing apparatus  10 . The notifying unit  409  notifies the information processing apparatus  10  of a result of a document thickness detection performed by the thickness detection unit  404  as a thickness information. 
       FIG. 17  is a flowchart of an operational example for the entire processing of the image reading apparatus  100 . At the step S 100 , the image reading apparatus  100  detects that the operation button  106  is pressed down by a user. The step S 101  corresponds to the processing of the conveyance control unit  401 . 
     At the step S 101 , on the basis of a first document detection signal received from the first document detection unit  110 , the image reading apparatus  100  determines whether or not a document is placed on the document table  103 . The step S 102  corresponds to a process of the conveyance control unit  401 . When a document is placed (yes at the step S 101 ), the processing proceeds to the step S 103 . When a document is not placed (no at the step S 101 ), the processing proceeds to the step S 102 . At the step S 102 , the image reading apparatus  100  performs a predetermined error process, and then returns the processing to the step S 100 . 
     At the step S 103 , the image reading apparatus  100  drives the motor  314  to rotate the sheet feeding roller  113 , the retard roller  114 , the first conveyance roller  116 , and the second conveyance roller  140 , thereby starting a conveyance of a document. The step S 103  corresponds to a processing of the conveyance control unit  401 . At the step S 104 , the image reading apparatus  100  detects a first white reference level L 1 . The step  104  corresponds to a processing of the white reference level detection unit  402 . 
     At the step S 105 , the image reading apparatus  100  performs a double feed determining process and detection of a thickness of a document, and stops the conveyance of the document. The step S 105  corresponds to a processing of the conveyance control unit  401 , the white reference level detection unit  402 , the double feed determination unit  403 , and the thickness detection unit  404 . 
     At the step S 106 , the image reading apparatus  100  determines whether or not a double feed is occurring. The step S 106  corresponds to a processing of the double feed determination unit  403 . When a double feed occurs (yes at the step S 106 ), the processing proceeds to the S 107 . When double feed does not occur (no at the step S 106 ), the processing proceeds to the S 108 . At the step S 107 , the image reading apparatus  100  performs a predetermined error processing, and then terminates the processing. 
     At the step S 108 , the image reading apparatus  100  performs a calibration for generating a shading correction data. The image reading apparatus  100  detects a second white reference level L 2 , and generates the shading correction data on the basis of a brightness distribution of the image data of the white reference unit  134 . The step S 108  corresponds to a processing of the white reference level detection unit  402  and the shading processing unit  406 . When a second white reference level L 2  was detected for detecting a thickness of a document in the double feed determining process of the step S 105 , a calibration may be performed on the basis of a brightness distribution of the image data of the white reference unit  134  detected at the step S 105 . 
     At the step S 109 , the image reading apparatus  100  performs a motor torque adjusting process. The step S 109  corresponds to a processing of the motor control unit  405 . At the step S 110 , the image reading apparatus  100  restarts a conveyance of a document. The step S 110  corresponds to a processing of the conveyance control unit  401 . 
     At the step S 111 , the image reading apparatus  100  reads the image data output from the imaging unit  130 . The step S 111  corresponds to a processing of the shading processing unit  406 . At the step S 112 , the image reading apparatus  100  performs a shading processing on the read image. The step S 112  corresponds to a processing of the shading processing unit  406 . 
     At the step S 113 , the image reading apparatus  100  performs a predetermined image processing on the image on which a shading processing is performed. The step S 113  corresponds to a processing of the image processing unit  407 . At the step S 114 , the image reading apparatus  100  transmits the image data after the image processing to the information processing apparatus  10 . The step S 114  corresponds to a processing of the image transmitting unit  408 . At the step S 115 , the image reading apparatus  100  informs a thickness information to the information processing apparatus  10 . The step S 115  corresponds to a processing of the notifying unit  409 . 
     At the step S 116 , the image reading apparatus  100  determines whether or not a document is placed on the document table  103 . The step S 116  corresponds to a processing of the conveyance control unit  401 . When a document is placed (yes at the step S 116 ), the processing returns to the step S 103 . When a document is not placed (no at the step S 116 ), the processing is terminated. 
       FIG. 18  is a flowchart of an operational example of the double feed determining process. At the step S 200 , the double feed determination unit  403  reads output Lus of the ultrasonic sensor  115 . At the step S 201 , the double feed determination unit  403  determines whether or not the output Lus of the ultrasonic sensor  115  is larger than the threshold Th 1 . When the output Lus is larger than the threshold Th 1  (yes at the step S 201 ), the processing proceeds to the step S 204 . When the output Lus is equal to or smaller than the threshold Th 1  (no at the step S 201 ), the processing proceeds to the step S 202 . 
     At the step S 202 , the double feed determination unit  403  determines that a double feed has occurred. At the step S 203 , the conveyance control unit  401  stops the conveyance of a document when the second document detection unit  118  detects a leading end of the document. Then, the double feed determining process is terminated. 
     At the step S 204 , the double feed determination unit  403  determines whether or not the output Lus of the ultrasonic sensor  115  is larger than the threshold Th 2 . When the output Lus is larger than the threshold Th 2  (yes at the step S 204 ), the processing proceeds to the step S 205 . When the output Lus is equal to or smaller than the threshold Th 2  (no at the step S 204 ), the processing proceeds to the step S 207 . 
     At the step S 205 , the double feed determination unit  403  determines that the document is not a thick medium, and a double feed is not occurring. At the step S 206 , the conveyance control unit  401  temporarily stops the conveyance of the document when the second document detection unit  118  detects a leading end of the document. Then, the double feed determining process is terminated. 
     At the step S 207 , the conveyance control unit  401  performs a document conveyance processing for conveying the document to a position of the imaging unit guide  120 .  FIG. 19A  and  FIG. 19B  are flowcharts representing a first example and a second example of an operation of the document conveyance processing. The difference between  FIG. 19A  and  FIG. 19B  arises from an installed position of the second document detection unit  118 . 
       FIG. 19A  is the flowchart when the second imaging unit  130   b  has moved as much as a thickness of a thick medium when the second document detection unit  118  detects a leading end of the document.  FIG. 19B  is the flowchart when the second imaging unit  130   b  has moved as much as a thickness of a thick medium when the document is conveyed by a predetermined movement amount after the second document detection unit  118  detected a leading end of the document. 
     At the step S 300  in  FIG. 19A , the conveyance control unit  401  rotates the motor  314  to convey a document. At the step S 301 , the conveyance control unit  401  determines whether or not a value of a second document detection signal changed from the first value to the second value. When a value of the second document detection signal changed to the second value (yes at the step S 301 ), the processing proceeds to the step S 302 . When a value of the second document detection signal does not change to the second value (no at the step S 301 ), the processing returns to the step S 300 . At the step S 302 , the conveyance control unit  401  stops the motor  314  to stop the conveyance of the document, and terminates the document conveyance processing. 
     At the step S 310  in  FIG. 19B , the conveyance control unit  401  rotates the motor  314  to convey a document. At the step S 311 , the conveyance control unit  401  determines whether or not a value of a second document detection signal changed from the first value to the second value. When a value of the second document detection signal changed to the second value (yes at the step S 311 ), the processing proceeds to the step S 312 . When a value of the second document detection signal does not change to the second value (no at the step S 311 ), the processing returns to the step S 310 . 
     At the step S 312 , the conveyance control unit  401  rotates the motor by a predetermined rotational amount to conveyance the document by the predetermined movement amount. At the step S 313 , the conveyance control unit  401  stops the motor  314  to stop a conveyance of the document, and terminates the document conveyance processing. 
     Reference is made to  FIG. 18 . At the step S 208 , the white reference level detection unit  402  detects a second white reference level L 2 . At the step S 209 , the thickness detection unit  404  calculates a white reference level difference DL=(L 1 −L 2 ). The thickness detection unit  404  determines whether or not the white reference level difference DL is larger than the threshold Th 3 . When the DL is larger than the threshold Th 3  (yes at the step S 209 ), the processing proceeds to the step S 210 . When the DL is equal to or smaller than the threshold Th 3  (no at the step S 209 ), the processing proceeds to the step S 211 . 
     At the step S 210 , the thickness detection unit  404  determines that the document is a thick medium. Further, the double feed determination unit  403  determines that a double feed is not occurring, and the conveyance processing is terminated. 
       FIG. 20  is a flowchart of an operational example of the motor torque adjusting process. At the step S 400 , the motor control unit  405  determines whether or not the document is a thick medium. When the document is a thick medium (yes at the step S 400 ), the processing proceeds to the step S 401 . When the document is not a thick medium (no at the step S 400 ), the processing proceeds to the step S 402 . 
     At the step S 401 , the motor control unit  405  sets a control amount for rotating the motor  314 , to be a first control amount that causes the motor  314  to generate relatively large torque. For example, a control amount to be set may be the maximum electric current value applied to the motor  314 , or an exciting method. Then, the motor torque adjusting processing is terminated. At the step S 402 , the motor control unit  405  sets a control amount for rotating the motor  314 , to be a second control amount that causes the motor  314  to generate relatively small torque. Then, the motor torque adjusting processing is terminated. 
       FIG. 21  is a flowchart of an operational example of the shading process. At the step S 500 , the shading processing unit  406  determines whether or not the document is a thick medium. When the document is a thick medium (yes at the step S 500 ), the processing proceeds to the step S 501 . When the document is not a thick medium (no at the step S 500 ), the processing proceeds to the step S 502 . 
     At the step S 501 , the shading processing unit  406  corrects a shading correction data for a back surface of a document out of the shading correction data generated in the calibration at the step S 108 . Then, the processing proceeds to the step S 502 . At the step S 502 , the shading processing unit  406  performs the shading processing on the image data of the document. Then, the shading processing is terminated. 
       FIG. 22  is a flowchart of an operational example of the image processing. In this example, the image processing unit  407  performs, as the predetermined image processing, a cropping processing of cutting out a document region from the image data. 
     At the step S 600 , the image processing unit  407  determines whether or not the document is a thick medium. When the document is a thick medium (yes at the step S 600 ), the processing proceeds to the step S 601 . When the document is not a thick medium (no at the step S 600 ), the processing proceeds to the step S 602 . 
     At the step S 601 , the image processing unit  407  corrects an edge detection threshold for detecting an edge at a boundary between a background region and a document region. Then, the processing proceeds to the step S 602 . At the step S 602 , the image processing unit  407  performs an edge detection. At the step S 603 , the image processing unit  407  recognizes the boundary between the background region and the document region by the detected edge, and cuts out the document region from the image data. Then, the image processing is terminated. 
       FIG. 23  illustrates one example of a hardware configuration of the information processing apparatus  10 . The information processing apparatus  10  includes a CPU  600 , a memory  601 , an auxiliary storage device  602 , a communication IF circuit  603 , an operation unit  604 , a displaying unit  605 , and a medium reading unit  606 . 
     The auxiliary storage device  602  stores an operating system (OS), a driver program  611 , an application programs  612   a  to  612   n  that are executed by the CPU  600 . The driver program  611  is a computer program for causing the information processing apparatus  10  to control the image reading apparatus  100 , and to receive the image data read by the image reading apparatus  100 . Moreover, the application programs  612   a  to  612   n  are image processing application programs for processing the image data received from the image reading apparatus  100 . The auxiliary storage device  602  may include a nonvolatile storage device, a read only memory (ROM), a hard disk, and the like for storing the OS and the programs. 
     The memory  601  may include a program that is currently executed by the CPU  600 , and a volatile memory which stores the data that is temporarily used by this program. The communication IF circuit  603  is an interface for wired and/or wireless communication between the image reading apparatus  100  and the information processing apparatus  10 . 
     The operation unit  604  is an input device that receives an input operation executed by a user. The operation unit  604  may be a keypad, a keyboard, a pointing device, or a touch panel, for example. The displaying unit  605  is a displaying device that visually displays to a user the information that was processed by the information processing apparatus  10 . The displaying unit  605  may be a displaying device such as a liquid crystal display, a cathode ray tube (CRT) display, an organic electroluminescence display. 
     The medium reading unit  606  is an input device that reads the data stored in a computer-readable portable recording medium. For example, the medium reading unit  606  may be a CD-ROM drive device, a DVD-ROM drive device, a flexible disk drive device, a CD-R drive device, a DVD-R drive device, an MO drive device, or a device that can access a flash memory device. The driver program  611  and the application programs  612   a  to  612   n  may be, for example, recorded in the above-mentioned portable recording medium, and may be provided to be installed in the auxiliary storage device  602  by a known setup program, or the like. 
     Moreover, a hardware configuration illustrated in  FIG. 23  is merely one example for the explanation of an embodied example. As long as the hardware configuration can perform an operation described in the following, the information processing device  10  may include any of other configurations. 
       FIG. 24  illustrates one example of a functional configuration of the information processing apparatus  10  that is executing the driver program  611 . The information processing apparatus  10  includes a thickness information obtaining unit  700 , an image obtaining unit  701 , a selecting unit  702 , a candidate list outputting unit  703 , an activating unit  704 , and an image transferring unit  705 . Moreover, a functional configuration diagram of  FIG. 24  mainly represents a configuration related to processing of the driver program  611  described in the present specification. The information processing apparatus  10  may include configuration elements other than the configuration elements illustrated in the drawing. 
     The thickness information obtaining unit  700  obtains a thickness information of a document given by the image reading apparatus  100 . The image obtaining unit  701  obtains image data of a document transmitted by the image reading apparatus  100 . 
     In accordance with the obtained thickness information, the selecting unit  702  selects, from the application programs  612   a  to  612   n , an image processing application for processing the obtained image data. When a plurality of the application programs are selected, the candidate list outputting unit  703  outputs, to the displaying unit  605 , a list of a plurality of the selected application programs as a candidate list of applications for processing the image data. 
     For example, the candidate list outputting unit  703  may output a dialog box that urges a user to activate any of a plurality of the selected application programs.  FIG. 25A  illustrates a first example of the dialog box that displays the candidate list. The dialog box  800  includes a candidate list  801 , a setting button  802 , and a cancel button  803 . The reference code  804  indicates a cursor that can be moved by the operation of the operation unit  604 . 
     The candidate list  801  of  FIG. 25A  is displayed when it is informed by the thickness information that the document is not a thick medium. The candidate list  801  includes an optical character reader (OCR) software, a filing software, and an image processing software are image application programs for processing an image data of a document that is not a thick medium. 
       FIG. 25B  illustrates a second example of the dialog box that displays the candidate list. The candidate list  801  of  FIG. 25B  is displayed when it is informed by the thickness information that the document is a thick medium. The candidate list  801  includes a business card managing software and a license OCR software are image application programs for processing an image data of a document that is a thick medium. 
     After a user selects the desired application in the candidate list  801  by the cursor  804 , a user performs an operation of the operation unit  604  corresponding to pressing-down of the setting button  802  to select the image processing application to be activated for processing an image data. 
     Reference is made to  FIG. 24 . When the number of the application programs selected by the selecting unit  702  is one, the activating unit  704  activates the application program selected by the selecting unit  702 . When the number of the application program selected by the selecting unit  702  is plural, the activating unit  704  activates the application program that is selected by a user from the candidate list output from the candidate list outputting unit  703 . The image transferring unit  705  transfers the image data obtained by the image obtaining unit  701  to the image processing application program activated by the activating unit  704 . 
       FIG. 26  is a flowchart of a processing example of the driver program. At the step S 700 , the image obtaining unit  701  obtains the image data of a document transmitted from the image reading unit  100 . At the step S 701 , the thickness information obtaining unit  700  obtains a thickness information of a document given by the image reading unit  100 . 
     At the step S 702 , the selecting unit  702  selects either one of the application programs  612   a  to  612   n  in accordance with the thickness information. When the selecting unit  702  selects a plurality of the application programs (yes at the step S 703 ), the processing proceeds to the step S 705 . When the selecting unit  702  selects one of the application programs (no at the step S 703 ), the processing proceeds to the step S 704 . At the step S 704 , the activating unit  704  activates the application program selected by the selecting unit  702 . Then, the processing proceeds to the step S 708 . 
     At the step S 705 , the candidate list outputting unit  703  outputs, as a candidate list, a list of a plurality of the selected application programs to the displaying unit  605 . At the step S 706 , the activating unit  704  determines whether or not the operation unit  604  received a selecting operation made by a user for selecting either one of the programs in the candidate list. When the selecting operation was received (yes at the step S 706 ), the processing proceeds to the step S 707 . When the selecting operation is not received (no at the step S 706 ), the processing returns to the step S 706 . 
     At the step S 707 , the activating unit  704  activates the application program selected at the step  706 . At the step S 708 , the image transferring unit  705  transfers the image data obtained by the image obtaining unit  701 , to the image processing application activated by the activating unit  704 . 
     According to the present embodied example, in the image reading apparatus  100 , a thickness information of a document being conveyed can be obtained. Obtaining the thickness information facilitates distinguishing between a conveyance of a thick document and a double feed of thin documents in the double feed determination for a document. 
     According to the present embodied example, by changing a generating torque of the motor that provides a driving force for conveying a document in accordance with a thickness of a document, it is possible to suppress step-out of the motor at the time of conveying a document of a thick document. 
     Moreover, according to the present embodied example, an image data of one surface of a both-sided document is processed in accordance with a thickness of a document. Thereby, it becomes possible to reduce a difference in an entire characteristic between the image data of a front surface and the image data of a back surface, which difference is generated when a document is a thick medium. 
     According to the present embodied example, in the cropping process of removing a background region in the image data to cut out a document region, an edge detection threshold is corrected in accordance with a thickness of a document. Thereby, the degradation of the edge detecting accuracy which occurs when a document is a thick document is suppressed. 
     According to the present embodied example, in the information processing apparatus  10  that receives an image data, an image processing application program for processing image data, or candidates thereof is automatically selected. Thereby, it is possible to simplify an operation of selecting an application program by a user. 
     Moreover, according to the present embodied example, the second document detection unit  118  is provided such that at an upstream position of an image capturing position of the image sensor  133 , the second document detection unit  118  detects a leading end of a document. Moreover, when the second document detection unit  118  detects a leading end of a document, a conveyance of the document is stopped to detect a second white reference level L 2  used for detecting a thickness of the document. For this reason, the document is stopped at an appropriate position where an image capturing of the white reference unit  134  by the image sensor  133  is not interfered. As a result, the accuracy in detection of a thickness of a document using a second white reference level L 2  improved. 
     According to the present embodied example, a thickness of a document is detected on the basis of a fluctuation of a second white reference level L 2  due to a movement of the second imaging unit  130   b . For this reason, after the second imaging unit  130   b  is moved by a movement amount in accordance with a thickness of a document that is a thick medium, a second white reference level L 2  is detected. For this purpose, a second document detection unit  118  detects a leading end of a document when the second imaging unit  130   b  is moved by a movement amount in accordance with a thickness of the document that is a thick document. The second document detection unit  118  can detect that the second imaging unit  130   b  has been moved by a movement amount depending on a thickness of the document that is a thick document. Thereby, it is possible to obtain a white reference level L 2  having an intensity in accordance with a medium thickness, so that a detection accuracy of a document thickness can be improved. 
     According to a modified example of the present embodied example, the second document detection unit  118  detects a leading end of a document before the second imaging unit  130   b  is moved by a movement amount in accordance with a thickness of the document that is a thick document. Then, the document is conveyed by a predetermined conveyance amount so that the second imaging unit  130   b  is moved by the movement amount in accordance with the thickness of the document that is a thick document. As a result, it is possible to set a delayed time until a white reference level L 2  is appropriately detected after a leading end of a document is detected. Accordingly, for example, during the delayed time, by completing the preparation for the detection of a second white reference level L 2 , a throughput of a conveyance can be improved. 
     According to embodiments illustrated herein, an image reading apparatus that can detect a thickness of a document in the process of conveyance can be provided. 
     All examples and conditional language recited herein are intended for pedagogical purposes to aid the reader in understanding the invention and the concepts contributed by the inventor to furthering the art, and are to be construed as being without limitation to such specifically recited examples and conditions, nor does the organization of such examples in the specification relate to a showing of the superiority and inferiority of the invention. Although the embodiment(s) of the present inventions have been described in detail, it should be understood that the various changes, substitutions, and alterations could be made hereto without departing from the spirit and scope of the invention.