Patent Publication Number: US-2023156139-A1

Title: Image reading apparatus and image forming apparatus

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This patent application is based on and claims priority pursuant to 35 U.S.C. § 119(a) to Japanese Patent Application No. 2021-185911, filed on Nov. 15, 2021, in the Japan Patent Office, the entire disclosure of which is hereby incorporated by reference herein. 
     BACKGROUND 
     Technical Field 
     Embodiments of the present disclosure relate to an image reading apparatus and an image forming apparatus. 
     Background Art 
     In the related art, some technologies have been proposed that correct the shading on the scanned image based on the correction data obtained from the readout signal of a base in an image reading apparatus that outputs the scanned image of a document. The term shading used herein refers to the unevenness in brightness. 
     In the above technologies that correct the shading, the power consumption is controlled in order to reduce the error in correction according to the temperature characteristics of an image sensor, and the corrected data is obtained in a state where the temperature of the image sensor is increased. Then, the shading on the scanned image of a document, which is obtained by the image sensor, is corrected based on the correction data. 
     SUMMARY 
     Embodiments of the present disclosure described herein provide an image reading apparatus includes a light emitter to irradiate a document with light, a first light guide to guide the light reflected by the document, an output device to output a readout signal obtained from the light reflected and guided by the first light guide, a base to correct shading in the readout signal, and circuitry to output a scanned image in which the shading of the document in the readout signal is corrected, based on correction data obtained from the readout signal of the base output from the output device, control a timing at which the light emitter emits the light and a timing at which the output device outputs a signal, heat the first light guide with the light emitted from the light emitter before the output device outputs the readout signal of each of the document and the base, and correct the shading in the readout signal of the document output from the output device when the first light guide is heated, based on the correction data obtained when the first light guide is heated. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A more complete appreciation of embodiments and the many attendant advantages thereof will be readily obtained as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings. 
         FIG.  1    is a diagram illustrating a configuration of an image reading apparatus according to an embodiment of the present disclosure, and is a sectional view of the image reading apparatus. 
         FIG.  2    is a block diagram illustrating a configuration of an image reading apparatus according to the first embodiment of the present disclosure. 
         FIG.  3    is a diagram illustrating a configuration of a first reader according to the first embodiment of the present disclosure. 
         FIG.  4    is a diagram illustrating the shading correction using a first reading roller, according to an embodiment of the present disclosure. 
         FIG.  5    is a block diagram of a functional configuration of a controller according to the first embodiment of the present disclosure. 
         FIG.  6    is the first flowchart of the processes of an image reading apparatus according to the first embodiment of the present disclosure. 
         FIG.  7    is the second flowchart of the processes of an image reading apparatus according to the first embodiment of the present disclosure. 
         FIG.  8    is a block diagram of a functional configuration of a controller according to a second embodiment of the present disclosure. 
         FIG.  9    is a diagram illustrating a configuration of an image forming apparatus according to a third embodiment of the present disclosure. 
     
    
    
     The accompanying drawings are intended to depict embodiments of the present disclosure and should not be interpreted to limit the scope thereof. The accompanying drawings are not to be considered as drawn to scale unless explicitly noted. 
     DETAILED DESCRIPTION 
     The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the present disclosure. As used herein, the singular forms “a”, “an”, and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “includes” and/or “including”, when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. 
     In describing example embodiments illustrated in the drawings, specific terminology is employed for the sake of clarity. However, the present disclosure is not intended to be limited to the specific terminology so selected and it is to be understood that each specific element includes all technical equivalents that have the same structure, operate in a similar manner, and achieve a similar result. 
     An image reading apparatus and an image forming apparatus according to an embodiment of the present disclosure will be described below in detail with reference to the accompanying drawings. An image reading apparatus and an image forming apparatus according to embodiments of the present disclosure are described below to implement the technical ideas, and no limitation is indicated to the embodiments of the present disclosure given below. 
     For example, the size, material, and shape of components and the relative positions of the arranged components are given by way of example in the following description, and the scope of the present disclosure is not limited thereto unless particularly specified. For example, the size of these elements and the relative positions of these elements may be exaggerated for purposes of illustration in the drawings. In the description given below with reference to the drawings, like reference signs denote like elements, and overlapping description may be simplified or omitted as appropriate. 
     First Embodiment 
     A configuration of an image reading apparatus  100  according to a first embodiment of an embodiment of the present disclosure is described below with reference to  FIG.  1    and  FIG.  2   . 
       FIG.  1    is a diagram illustrating a configuration of the image reading apparatus  100  according to the present embodiment, and is a sectional view of the image reading apparatus  100  viewed in a direction parallel to the rotation axis of a conveyance roller used for the conveyance of a document  1 . 
       FIG.  2    is a block diagram illustrating a configuration of the image reading apparatus  100  according to the present embodiment. 
     The image reading apparatus  100  according to the present embodiment scans the document  1 , which is a to-be-scanned object, while conveying the document  1  in a conveyance direction m at a predetermined speed, and outputs a scanned image obtained as a result of the scanning performed on the document  1 . 
     In the present embodiment, the image reading apparatus  100  serves as an automatic document feeder (ADF). 
     As illustrated in  FIG.  1   , schematically, the image reading apparatus  100  mainly includes a document placement unit A, a sheet separating and feeding part B, a registration part C, a reversing unit D, a first reading and conveying part E, a second reading and conveying part F, a sheet ejection unit G, and a stacking unit H. 
     The document placement unit A is a portion on which a document  1  to be read is placed. The document  1  may be a single sheet of document or a bundle of documents in which a plurality of documents are stacked. The document placement unit A includes a document table  2 , a placement feeler  4 , a placement sensor  5 , a base-plate home position (HP) sensor  6 , a document length sensor  30 , and a document length sensor  31 . 
     The document table  2  according to the present embodiment includes a movable document table  3  that is movable such that the document  1  can be placed according to the size of the document  1 . 
     For example, the document  1  is placed on the document table  2  such that one document plane faces vertically upward. Both ends of the document  1  in a direction intersecting with the conveyance direction m are pressed by a pair of side guides, and the relative position of the document  1  is determined. The placement feeler  4  and the placement sensor  5  detect that the document  1  is placed on the document table  2  and output a placement detection signal. 
     The document length sensor  30  and the document length sensor  31  detect the length of the document  1  placed on the document table  2  in the conveyance direction m and output a length detection signal. The length detection signal is used to determine whether the document  1  placed on the document table  2  is vertically placed or horizontally placed. The document length sensor  30  and the document length sensor  31  are disposed such that these sensors can detect the length of the document  1 . 
     Each one of the document length sensor  30  and the document length sensor  31  may be, for example, a reflection sensor that outputs an electrical signal that indicates the radiation intensity of the light reflected by the document  1  or an actuator sensor that can detect the length of the document  1  even if the document  1  is a single sheet. The base-plate HP sensor  6  detects the HP of the base-plate, that is, the initial position. 
     The movable document table  3  can be moved in a direction indicated by the arrow of a first movable direction  51  by a base-plate lift-up motor  105  (see  FIG.  2   ). As the base-plate lift-up motor  105  rotates in forward direction in response to, for example, a placement detection signal output from the placement feeler  4  and the placement sensor  5 , the movable document table  3  is lifted such that the uppermost surface of the document  1  contacts the picking-up roller  7 . 
     The separating and feeding unit B is an element that has a function to feed the document  1  placed on the document placement unit A. When the document  1  is a bundle of documents, the separating and feeding unit B separates and feeds the documents on a one-by-one basis from the bundle of documents. The separating and feeding portion B includes a picking-up roller  7 , a table sheet-feeding position sensor  8 , a sheet feeding belt  9 , and a reverse roller  10 . 
     The picking-up roller  7  is moved in a direction indicated by arrow of a second movable direction  52  by a picking-up motor  101  (see  FIG.  2   ) and a cam mechanism, and is pressed by the upper side of the document  1  moved by the movable document table  3 . The table sheet-feeding position sensor  8  outputs a position detection signal indicating the position of the picking-up roller  7 . 
     The sheet feeding belt  9  is driven by the rotation in forward direction of a sheet feeding motor  102  (see  FIG.  2   ). Accordingly, the reverse roller  10  is driven to rotate in a direction opposite to the conveyance direction m, i.e., a clockwise direction in  FIG.  1   , by the rotation in forward direction of the sheet feeding motor  102 . The separating and feeding portion B drives the sheet feeding belt  9  and the reverse roller  10  to separate the uppermost one of the documents  1  and the rest of the documents  1  placed below. By so doing, only the uppermost one of the documents  1  can be fed. 
     More specifically, the reverse roller  10  contacts the sheet feeding belt  9  at predetermined pressure, and the reverse roller  10  is driven to rotate in the counterclockwise direction in accordance with the rotation of the sheet feeding belt  9  when the reverse roller  10  directly contacts the sheet feeding belt  9  or when the reverse roller  10  directly contacts the sheet feeding belt  9  through one sheet of document  1 . The force of corotation is set in advance to be lower than the torque of the torque limiter, and if two or more sheets of documents  1  enter the nip between the sheet feeding belt  9  and the reverse roller  10 , the reverse roller  10  rotates in a clockwise direction, which is the original direction of rotation, and the excessive ones of the multiple documents  1  are pushed back. Due to such a configuration and function, multiple feeding can be prevented from occurring. The document  1  that is separated into one sheet by the sheet feeding belt  9  and the reverse roller  10  is conveyed by the sheet feeding belt  9  toward the registration part C in the conveying direction m. 
     The registration part C is an element that has a function to primarily contact the document  1  fed from the sheet separating and feeding part B and a function to draw out and convey the document  1  that has contacted a sensor. The registration part C includes a contact sensor  11 , a pull-out roller pair  12 , and a document-width sensor  13 . 
     The front end of the document  1  that is conveyed by the separating and feeding portion B is detected by the contact sensor  11 , and the document  1  is further conveyed and contacts the pull-out roller pair  12  that is not rotating. Subsequently, the document  1  is conveyed by a predetermined distance in accordance with the contact detection signal output from the contact sensor  11 . Subsequently, the document  1  is stopped in a state of being pressed against the pull-out roller pair  12  with a predetermined deflection. While the document  1  is stopped, the front end of the document  1  enters the nip formed by the rollers of the pull-out roller pair  12 , and skew adjustment is performed to align the front end of the document  1 . 
     The pull-out roller pair  12  is driven by the reverse rotation of the sheet feeding motor  102  (see  FIG.  2   ) to convey the skew-corrected document  1  to the position of the intermediate roller pair  14 . When the sheet feeding motor  102  rotates in the reverse direction, the pull-out roller pair  12  and the intermediate roller pair  14  are driven, but the picking-up roller  7  and the sheet feeding belt  9  are not driven. 
     A plurality of document-width sensors  13  are arranged in the width direction of the document  1  to detect the length of the document  1  conveyed by the pull-out roller pair  12  in the width direction. The length of the document  1  in the conveyance direction m is detected based on the result of the detection of the front end and trailing end of the document  1  performed by the contact sensor  11 . 
     The reversing unit D is an element that has a function to reverse the document  1  being conveyed and convey the document  1  such that the to-be-scanned side of the document will face the first reading and conveying part E side in  FIG.  1   . The reversing unit D includes an intermediate roller pair  14 . The intermediate roller pair  14  includes a pair of rollers, and the document  1  is nipped and conveyed by the pair of rollers. 
     The document  1  is conveyed from the registration portion C to the reversing unit D by driving of the pull-out roller pair  12  and the intermediate roller pair  14 . The conveyance speed in the registration section C is predetermined to be faster than the conveyance speed in the first reading conveyance section E. Thus, the processing time for feeding the document  1  to the first reading conveyance section E can be shortened. 
     The first reading and conveying part E is an element that has a function to scan one side of the being-conveyed document  1  from the other side of the document  1  across the contact glass. In the following description, this side of the document may be referred to as the front side of the document  1 . The first reading and conveying part E outputs the read image of the front side of the document  1 . 
     The first reading and conveying part E includes a first reading-entrance sensor  15 , a first reading-entrance roller pair  16 , a registration sensor  17 , a first reading roller  19 , a first reader  20 , and a first reading-exit roller pair  23 . When the front end of the document  1  in the conveyance direction m is detected by the first reading-entrance sensor  15 , the first reading and conveying part E starts deceleration to make the conveyance speed of the document  1  approximately equivalent to the scanning speed before the front end of the document  1  enters the nip between the pair of rollers of the first reading-entrance roller pair  16 . Together with that, the first reading and conveying part E drives the reading motor  103  (see  FIG.  2   ) to rotate in forward direction to drive the first reading-entrance roller pair  16  and the first reading-exit roller pair  23 . 
     When the registration sensor  17  detects the leading edge of the document  1  in the conveyance direction m, the first reading and conveying part E decelerates while the document  1  is conveyed by a predetermined distance, and temporarily stops before entering the first reader  20 . 
     Subsequently, the first reading and conveying part E start conveying the stopped document  1  in response to the reading start signal while accelerating the conveyance speed of the document  1  to a predetermined conveyance speed until the front end of the document  1  reaches the first reader  20  in the conveyance direction m. 
     The first reading and conveying part E reads the front side of the document  1  and outputs a signal indicating the scanned image during a period from when the front end of the document  1  in the conveyance direction m enters the position of the first reader  20  to when the trailing end of the document  1  in the conveyance direction m exits the position of the first reader  20 . 
     The first reading roller  19  serves as a base that prevents floating of the document  1  at the time of reading by the first reader  20  and obtains correction data  306  (see  FIG.  5   ) used to correct the shading of an image scanned by the first reader  20 . 
     When only one side of the document  1  is to be read, the first reading and conveying part E conveys the document  1  that has passed through to the sheet ejection unit G through the second reading and conveying part F. In so doing, when the sheet ejection sensor  24  detects the front end of the document  1  in the conveyance direction m, the first reading and conveying part E drives the sheet ejection motor  104  (see  FIG.  2   ) to rotate in forward direction to rotate the output roller pair  28  in a counterclockwise direction. 
     The first reading and conveying part E counts the driving pulses of the sheet ejection motor  104  from the time when the sheet ejection sensor  24  detects the front end of the document  1  in the conveyance direction m. The first reading and conveying part E reduces the conveyance speed by the sheet ejection motor  104  immediately before the trailing end of the document  1  in the conveyance direction m exits from the nip of the roller pair included in the output roller pair  28 . By so doing, the first reading and conveying part E performs control such that the document  1  ejected to the output tray  29  does not jump out of the output tray  29 . 
     The second reading and conveying part F has a function to scan the other side of the document  1 . In the following description, the other side of the document may be referred to as the rear side of the document  1 . The second reading and conveying part F outputs the scanned image of the rear side of the document  1 . The second reading and conveying part F includes a sheet ejection sensor  24 , a second reader  25 , a second reading roller  26 , a second reading exit roller pair  27 , and a output roller pair  28 . 
     Basically, the configuration or structure of the second reader  25  is equivalent to that of the first reader  20 , but only the installation position of the second reader  25  is different from that of the first reader  20  in order to scan the rear side of the document  1 . Basically, the configuration or functionality of the second reading roller  26  is equivalent to that of the first roller  19 , but only the installation position of the second reading roller  26  is different from that of the first roller  19  in order to scan the rear side of the document  1 . The configuration of the second reader  25  may be different from the configuration of the first reader  20 , and the configuration of the second reading roller  26  may be different from the configuration of the first reading roller  19 . 
     When reading the rear side of the document  1 , the second reading and conveying part F counts the driving pulse of the reading motor  103  (see  FIG.  2   ) after the front end of the document  1  in the conveyance direction m is detected by the sheet ejection sensor  24 . 
     The second reading and conveying part F reads the rear side of the document  1  and outputs a read image signal during a period from when the front end of the document  1  in the conveyance direction m enters the position of the second reader  25  to when the trailing end of the document  1  in the conveyance direction m exits the position of the second reader  25 . 
     The sheet discharge portion G is a portion of the apparatus for ejecting the document  1  whose front and rear sides have been scanned to the outside of the apparatus. 
     The stacking unit H is a portion of the apparatus for stacking and holding the document  1  that has already been scanned. 
     As illustrated in  FIG.  2   , the image reading apparatus  100  according to the present embodiment includes a controller  300  and an operation panel  106 . The controller  300  and the operation panel  106  are electrically connected to each other through an interface  107 . The controller  300  controls the operation of the image reading apparatus  100 . 
     The controller  300  according to the present embodiment is electrically connected to, for example, a registration sensor  17 , a placement sensor  5 , a sheet ejection sensor  24 , the contact sensor  11 , a document-width sensor  13 , a first reading-entrance sensor  15 , a table sheet-feeding position sensor  8 , and a base-plate home position (HP) sensor  6  receives a detection signal sent from each sensor. 
     Moreover, the controller  300  according to the present embodiment is electrically connected to, for example, a first reader  20 , a second reader  25 , the picking-up motor  101 , a sheet feeding motor  102 , a reading motor  103 , a sheet ejection motor  104 , and a base-plate lift-up motor  105 . 
     The controller  300  controls the operations of the first reader  20  and the second reader  25 , and receives a signal indicating the scanned image from each one of the first reader  20  and the second reader  25 . 
     Further, the controller  300  controls the operation of each one of the picking-up motor  101 , the sheet feeding motor  102 , the reading motor  103 , the sheet ejection motor  104 , and the base-plate lift-up motor  105 . 
       FIG.  3    is a diagram illustrating a configuration of the first reader  20  according to the present embodiment. 
     The first reader  20  according to the present embodiment includes a light emitter  201 , a light guide  202 , a rod lens array  203 , and a light receiver  204 . The first reader  20  is, for example, a contact image sensor (CIS). However, no limitation is intended thereby, and the first reader  20  may be provided with a reduction optical system. 
     The light emitter  201  according to the present embodiment serves as a light emitter. Light emitter  201  includes a first light emitter  201   a  and a second light emitter  201   b . The first light emitter  201   a  is disposed at one end of the light guide  202  in the width direction n approximately orthogonal to the conveyance direction m, and emits the light toward the one end. The second light emitter  201   b  is disposed at the other end of the light guide  202  in the width direction n, and emits the light toward the other end. 
     For example, each one of the first light emitter  201   a  and the second light emitter  201   b  is a light-emitting diode (LED). However, the light emitter  201  is not limited to a pair of LEDs as long as it can emit light, and the number of the LEDs or the like of the light emitter  201  is not limited to two. 
     d denotes the distance between the first light emitter  201   a  and one end of the light guide  202  in the width direction n. 
     d also denotes the distance between the second light emitter  201   b  and the other end of the light guide  202  in the width direction n. The distance d is not limited to any particular range or value, and the distance d in the image reading apparatus  100  can be set to any desired range or value depending on, for example, the application or specification of the image reading apparatus  100 . 
     The light guide  202  according to the present embodiment serves as a second light guide that guides the light emitted from the light emitter  201  to the document  1 . The light guide  202  has a cylindrical shape whose longer-side direction is parallel to the width direction n, and is a translucent member through which the light can be guided. 
     The light that is emitted from each one of the first light emitter  201   a  and the second light emitter  201   b  and enters from both ends of the light guide  202  in the width direction n is guided in the width direction n while repeating total internal reflection inside the light guide  202 . In the process of guiding the light, the light incident on the principal plane of the light guide  202  in the longer-side direction is emitted from the inside to the outside of the light guide  202  at an incident angle smaller than the critical angle. 
     The light emitter  201  and the light guide  202  constitute an irradiation unit that makes up the document  1  with the irradiation light Ls. The light emitter  201  and the light guide  202  can irradiate the document  1  with light emitted toward the document  1  among light emitted from the inside to the outside of the light guide  202  as irradiation light Ls. The irradiation light Ls is linear light extending in the width direction n. 
     The rod lens array  203  according to the present embodiment serves as a first light guide that guides the reflected light Lr of the irradiation light Ls emitted from the light emitter  201  and the light guide  202  and reflected by the document  1 . The rod lens array  203  includes a plurality of rod lenses  203   a  aligned in the width direction n. 
     Each one of the multiple rod lenses  203   a  is a rod-like unity-magnification imaging optical device through which the light can be guided. For example, each one of the multiple rod lenses  203   a  is a gradient index lens. Alternatively, each one of the multiple rod lens  203   a  may be a refractive lens or a diffractive lens. 
     The reflection light Lr incident on each of the multiple rod lenses  203   a  from the document  1  side is guided inside the rod lenses  203   a  and is emitted to the side opposite to the document  1  in the rod lens array  203 . The light that is emitted from the rod lens array  203  is incident on the light receiver  204  arranged on the other side of the document  1  with the rod lens array  203  interposed therebetween, and is received by the light receiver  204 . 
     The light receiver  204  according to the present embodiment serves as an output device that outputs a readout signal Is obtained from the reflected light Lr guided by the rod lens array  203 . The light receiver  204  is, for example, a line image sensor in which a plurality of light-receiving elements such as a charge-coupled device (CCD) and a complementary metal-oxide semiconductor (CMOS) are aligned as a plurality of pixels in the width direction n, and such a line image sensor outputs a one-dimensional readout signal Is to be used to form a one-dimensional read image. 
     The light receiver  204  may output a monochrome readout signal Is to be used to form a monochrome read image, or may output a color readout signal Is to be used to form a color read image. The light receiver  204  is not limited to a line image sensor, and may be an area image sensor that outputs a two-dimensional readout signal Is to be used to form a two-dimensional read image. 
     The multiple light-receiving elements included in the light receiver  204  output an electrical signal corresponding to the light intensity of the received light as a readout signal Is. Analog-to-digital (A/D) conversion is performed on the readout signals (Is, Ic) output from the multiple light-receiving elements to a plurality of digital signals, and the light receiver  204  pieces together the digital signals in the width direction. As a result, a digital line image whose longer-side direction is parallel to the width direction can be captured. 
     Only the configuration or structure of the first reader  20  is described in the above description, but the configuration or structure and the function of the second reader  25  is equivalent to those of the first reader  20 . When the second reader  25  is used for scanning, the second reading roller  26  is used as a base. The first reader  20  will be described below, but the following description of the first reader  20  can be applied to the second reader  25  in a similar manner. 
     In the present embodiment, there are some cases in which unevenness in brightness called shading is included in the readout signal Is output from the light receiver  204 . As the shading is unevenness in brightness that has nothing to do with the document plane of the document  1  to be scanned by the image reading apparatus  100 , such shading indicates the error in scanning of the document  1  performed by the image reading apparatus  100 . 
     There are various kinds of factors that cause shading. For example, the unevenness in brightness in the width direction n of the irradiation light Ls emitted from the light emitter  201  and the light guide  202  to the document  1 , the unevenness in brightness in the width direction n of the light guided by the rod lens array  203  and incident on the light receiver  204 , and the differences in characteristics between a plurality of light-receiving elements provided for the light receiver  204  may cause shading. Factors of the shading based on the rod lens array  203  include, for example, a characteristic difference between the multiple rod lenses  203   a , or unevenness in the amount of guided light based on a joint between adjacent rod lenses  203   a.    
     The image reading apparatus  100  corrects the above shading using the first reading roller  19 . The first reading roller  19  according to the present embodiment serves as a base for correcting the shading in the readout signal Is output from the light receiver  204 . The first reading roller  19  is a rotor configured to have a predetermined distribution of density in the width direction n. The predetermined distribution of density is, for example, a white distribution of density which is substantially uniform in the width direction n, or a black distribution of density which is substantially uniform in the width direction n. However, no limitation is intended thereby, and any distribution of density may be adopted as long as such a distribution of density is determined in advance. In the image reading apparatus  100 , a plurality of distributions of density that are different from each other may be arranged on the first reading roller  19 , and the shading may be corrected based on the correction data obtained using those multiple distributions of density. 
       FIG.  4    is a diagram illustrating the shading correction using the first reading roller  19 , according to the present embodiment. 
     As illustrated in  FIG.  4   , when the shading correction is to be performed, the image reading apparatus  100  arranges the first reading roller  19  instead of the document  1  at a position irradiated with the irradiation light Ls from the light emitter  201  and the light guide  202 . 
     As the first reading roller  19  also serves as a member having a function to prevent, for example, the floating of the document  1  when the document  1  is being scanned. For this reason, it can be said that the state of the image reading apparatus  100  when the shading correction is performed is equivalent to a state in which the document  1  is removed from the nip between the first reader  20  and the first reading roller  19 . 
     In the configuration or structure as illustrated in  FIG.  4   , the first reader  20  scans the predetermined distribution of density of the first reading roller  19 , and outputs a reading signal Ic of the first reading roller  19  from the light receiver  204 . By subtracting a predetermined distribution of density of the first reading roller  19  from the readout signal Ic, correction data for correcting the shading can be obtained. 
     The image reading apparatus  100  stores the obtained correction data in a storage unit  304  (see  FIG.  5   ) at an earlier stage, and subtracts the correction data from the line image obtained from the readout signal Is of the document  1 . As a result, the shading can appropriately be corrected. The image reading apparatus  100  can output a one-dimensional read image in which shading in the readout signal Is is corrected. In the image reading apparatus  100 , the multiple line images that are obtained by capturing the document  1  being conveyed in the conveyance direction m may be pieced together in the conveyance direction m. By so doing, a two-dimensional scanned image can be output. 
       FIG.  5    is a block diagram illustrating a functional configuration of the controller  300  according to the present embodiment. 
     The controller  300  according to the present embodiment serves as a controller that controls the timing at which the light receiver  204  outputs a signal and the timing at which light is emitted from the light emitter  201  and the light guide  202 . 
     As illustrated in  FIG.  5   , the controller  300  according to the present embodiment includes a light-emission timing controller  301 , a readout timing controller  302 , a correction unit  303 , a storage unit  304 , an input and output device  305 , and a power supply controller  307 . 
     The controller  300  may implement the multiple functions of the light-emission timing controller  301 , the readout timing controller  302 , the correction unit  303 , the input and output device  305 , and the power supply controller  307  as a central processing unit (CPU) launches a program stored in a memory such as a read-only memory (ROM) into a work area such as a random access memory (RAM) and executes the developed program. Alternatively, the controller  300  may implement at least some of the multiple functions of the above-described elements by an electric circuit, or may implement it using a plurality of programs or a plurality of electric circuits. Alternatively, the controller  300  may implement the function of the storage unit  304  by a storage device such as a hard disk drive (HDD). 
     At least some of the functions of the controller  300  may be implemented by other elements such as the first reader  20 . 
     The light-emission timing controller  301  controls the timing at which each one of the light emitter  201  and the light guide  202  emits the light. For example, the light-emission timing controller  301  outputs an irradiation control signal St to the first reader through the input-and-output device  305 . As a result, the timing at which the light emitter  201  and the light guide  202  emit the irradiation light Ls can appropriately be controlled. 
     More specifically, the light-emission timing controller  301  outputs the irradiation control signal St upon switching the logic in response to the register access from the CPU to the light emitter  201 , and control whether the light emitter  201  is to emit light or is not to emit the light. By so doing, the timing at which the irradiation light Ls is emitted can appropriately be controlled. 
     The readout timing controller  302  controls the timing at which the light receiver  204  outputs a signal. For example, when reading the document  1 , the readout timing controller  302  outputs the scanning control signal Sr to the first reader  20  through the input-and-output device  305 . By so doing, the timing at which the light receiver  204  outputs the reading signal Is can be controlled. Moreover, when obtaining the correction data, the readout timing controller  302  outputs the scanning control signal Sr to the first reader  20  through the input-and-output device  305 . By so doing, the timing at which the light receiver  204  outputs the reading signal Ic can be controlled. 
     More specifically, the readout timing controller  302  uses a clock signal or a line synchronizing signal supplied to the light receiver  204  as a scanning control signal Sr, and controls the reading timing by controlling the clock signal or the line synchronizing signal by accessing a register from the CPU. 
     The correction unit  303  according to the present embodiment serves as a corrector that corrects the shading using the correction data  306 . The correction data  306  is obtained based on the readout signal Ic of the first reading roller  19  output from the light receiver  204 , and is stored in the storage unit  304  in advance. When the readout signal Is of the document  1  is output from the light receiver  204 , the correction unit  303  can acquire the correction data  306  with reference to the storage unit  304 , and output the readout signal Ic obtained by correcting the readout signal Is using the correction data  306  as a one-dimensional read image through the input-and-output device  305 . 
     In the present embodiment, the correction data  306  is obtained before the readout signal Is of the document  1  is output from the light receiver  204 , and is stored in the storage unit  304 . However, when the reading signal Is of the document  1  is output by the light receiver  204 , the rod lens array  203  and the light guide  202  may be heated by the light emitted by the light emitter  201 , and the amount of thermal deformation thereof may change over time. In other words, the amount of thermal deformation of the rod lens array  203  and the light guide  202  may change over time due to the change in temperature over time of the image reading apparatus  100 . 
     For example, when the rod lens array  203  is deformed to expand and contract in the width direction n due to heating and the amount of deformation changes with time, the shading at the time of acquiring the correction data  306  and the shading at the time of reading the document  1  become different. Due to such a difference, the image reading apparatus  100  cannot appropriately correct shading when reading the document  1 . 
     In a similar manner to the above, when the light guide  202  is deformed to expand and contract in the width direction n due to heating and the amount of deformation changes with time, the shading at the time of acquiring the correction data  306  and the shading at the time of reading the document  1  become different. Due to such a difference, the image reading apparatus  100  cannot appropriately correct shading when reading the document  1 . 
     In the present embodiment, the controller  300  heats the rod lens array  203  with the irradiation light Ls emitted from the light emitter  201  and the light guide  202  before the light receiver  204  outputs each of the readout signal Is of the document  1  and the readout signal Ic of the first reading roller  19 . 
     More specifically, when acquiring the correction data  306 , the controller  300  controls the first reader  20  so as to irradiate the rod lens array  203  with the irradiation light Ls from the light emitter  201  and the light guide  202  before the light receiver  204  outputs the reading signal Ic of the first reading roller  19 . The rod lens array  203  is heated as irradiated with the irradiation light Ls. As a result, the rod lens array  203  expands or contracts, and may be deformed. The light guide  202  is heated as irradiated with the light emitted from the light emitter  201 . As a result, the light guide  202  expands or contracts, and may be deformed. 
     The light receiver  204  outputs the reading signal Ic of the first reading roller  19  in a state in which each of the rod lens array  203  and the light guide  202  is deformed to expand and contract. As described above, the correction data  306  is obtained from the output readout signal Ic and then is stored in the storage unit  304 . 
     When the scanned image of the document  1  is to be obtained, the controller  300  controls the first reader  20  such that the rod lens array  203  will be irradiated with the irradiation light Ls emitted from the light emitter  201  and the light guide  202  before the light receiver  204  outputs the readout signal Is of the document  1 . The rod lens array  203  is heated as irradiated with the irradiation light Ls. As a result, the rod lens array  203  expands or contracts, and may be deformed. The light guide  202  is heated as irradiated with the light emitted from the light emitter  201 . As a result, the light guide  202  expands or contracts, and may be deformed. 
     The light receiver  204  outputs a readout signal Is of the document  1  in a state in which each one of the rod lens array  203  and the light guide  202  is deformed to expand and contract. 
     The correction unit  303  uses the correction data  306  obtained in the state where the rod lens array  203  and the light guide  202  are heated to correct the readout signal Is of the document  1  output in the state where the rod lens array  203  and the light guide  202  are heated. The correction unit  303  outputs the corrected readout signal Ic. 
     The power supply controller  307  controls the supply of the power Pw to the first reader  20 . 
     The image reading apparatus  100  can obtain the correction data  306  in a state in which each of the rod lens array  203  and the light guide  202  is deformed to expand and contract due to heating, and can correct the readout signal Is of the document  1 . Accordingly, in the image reading apparatus  100  according to the present embodiment, the state of deformation of the rod lens array  203  can be made close to the state of deformation of the light guide  202  between the time of acquisition of the correction data  306  and the time of scanning the document  1 . As a result, the difference between the amount of deformation of the rod lens array  203  and the amount of deformation of the light guide  202  can be reduced, and the error in the shading correction can sufficiently be reduced. 
     For example, the controller  300  controls the rod lens array  203  and the light guide  202  to be heated until the deformation of each of the rod lens array  203  and the light guide  202  due to heating is saturated. A state in which the deformation is saturated in the present embodiment refers to a state in which each of the rod lens array  203  and the light guide  202  is sufficiently deformed and the amount of deformation has decreased to a predetermined small value. Due to such a configuration, in the image reading apparatus  100  according to the present embodiment, the state of deformation of the rod lens array  203  can be made close to the state of deformation of the light guide  202  between the time of acquisition of the correction data  306  and the time of scanning the document  1 , and the error in the shading correction can preferably be reduced. 
     The operation of the image reading apparatus  100  is described below with reference to  FIG.  6    and  FIG.  7   . 
       FIG.  6    is a first flowchart of the operation of the image reading apparatus  100 , according to the present embodiment. 
       FIG.  7    is a second flowchart of the operation of the image reading apparatus  100 , according to the present embodiment. 
     In the image reading apparatus  100  according to the present embodiment, it is assumed that the first reader  20  is disabled drive power is not supplied to the first reader except when instructions to start scanning are given. The image reading apparatus  100  starts the operation of  FIG.  5    upon receipt of the instructions to start scanning. The instructions to start scanning may be an operation or input made through an operation panel of the image reading apparatus  100  or may be a control signal input from an external device. 
     Firstly, in a step S 61 , the image reading apparatus  100  causes the power supply controller  307  to supply the power Pw to the first reader  20  in response to the received instructions to start scanning. 
     Subsequently, in a step S 62 , the image reading apparatus  100  causes the light-emission timing controller  301  to output the irradiation control signal St to the first reader  20  through the input-and-output device  305 . The light emitter  201  and the light guide  202  irradiate the first reading roller  19  with the irradiation light Ls in response to the irradiation control signal St. 
     Subsequently, in a step S 63 , the image reading apparatus  100  goes on standby until the rod lens array  203  and the light guide  202  are heated by the irradiation light Ls and the temperature rises. The waiting time is a predetermined length of time until the deformation of each of the rod lens array  203  and the light guide  202  is saturated. 
     Subsequently, in a step S 64 , the image reading apparatus  100  uses the readout timing controller  302  to output the scanning control signal Sr to the first reader  20  through the input-and-output device  305  after the rod lens array  203  and the light guide  202  rise have risen in temperature sufficient to saturate the deformation of each of the rod lens array  203  and the light guide  202 . The light receiver  204  outputs a reading signal Ic of the first reading roller  19  in response to the scanning control signal Sr. The image reading apparatus  100  uses the storage unit  304  to store the correction data  306  obtained from the readout signal Ic. 
     Subsequently, in a step S 65 , the image reading apparatus  100  causes the readout timing controller  302  to output the scanning control signal Sr to the first reader through the input-and-output device  305 . The light receiver  204  outputs a readout signal Is of the document  1  according to the read control signal Sr. The image reading apparatus  100  refers to the storage unit  304  to obtain the correction data  306 , and corrects the readout signal Is based on the obtained correction data  306 . As a result, the scanned image of the document  1  can be obtained from the corrected readout signal Ic. 
     Subsequently, in a step S 66 , the controller  300  of the image reading apparatus  100  determines whether or not there is a next document  1 . 
     When it is determined that there is such a next document  1  in the step S 66  (“YES” in the step S 66 ), the image reading apparatus  100  performs the processes in the step S 65  and the subsequent steps again. By contrast, when it is determined that there is no such next document  1  (“NO” in the step S 66 ), in a step S 67 , the image reading apparatus  100  uses the power supply controller  307  to terminate the supply of the power Pw to the first reader  20 . Subsequently, the image reading apparatus  100  ends the operation. 
     As described above, the image reading apparatus  100  can correct the shading of the read image and output the read image obtained from the corrected readout signal Ic. 
     In the second flowchart according to the first embodiment of the present disclosure as illustrated in  FIG.  7   , the image reading apparatus  100  starts the processes depicted in  FIG.  7    upon receipt of the placement detection signal output from the placement sensor  5 . 
     Firstly, in a step S 71 , the image reading apparatus  100  causes the power supply controller  307  to supply the power Pw to the first reader  20  in response to the placement detection signal output from the placement sensor  5 . 
     Subsequently, in a step S 72 , the image reading apparatus  100  causes the light-emission timing controller  301  to output the irradiation control signal St to the first reader  20  through the input-and-output device  305 . The light emitter  201  and the light guide  202  irradiate the first reading roller  19  with the irradiation light Ls in response to the irradiation control signal St. 
     Subsequently, in a step S 73 , the controller  300  of the image reading apparatus  100  receives instructions to start reading the document  1 . 
     Subsequently, in a step S 74 , the image reading apparatus  100  goes on standby until the rod lens array  203  and the light guide  202  are heated by the irradiation light Ls and the temperature rises. 
     The processes in the step S 75  and the subsequent steps in  FIG.  7    are equivalent to the processes in the step S 64  and the subsequent steps in  FIG.  6   . Thus, the overlapping description of those equivalent processes in  FIG.  7    are omitted. 
     As described above, the image reading apparatus  100  can correct the shading of the read image and output the read image obtained from the corrected readout signal Ic. In the second flowchart according to the first embodiment of the present disclosure as illustrated in  FIG.  7   , the timing at which the document  1  is placed on the document placement unit A is used as a trigger to start heating the light emitter  201  and the light guide  202 . Accordingly, the standby time until the rod lens array  203  and the light guide  202  rise in temperature can be shortened. As a result, the error in the shading correction can sufficiently be reduced while the productivity in scanning the document  1  can also be increased. 
     Some advantageous effects of the image reading apparatus  100  are described below. 
     In the related art, image reading apparatuses that correct the shading on a scanned image are known. As the brightness of irradiation light that is emitted by the light emitter provided for the image reading apparatus may change over time, it is desired that the shading correction be performed each time a document is scanned. 
     However, if the shading correction is performed every time a document is scanned, the frequency of obtaining the correction data that is used to correct the shading increases in, for example, a clearance period where no document is to be scanned. As a result, the productivity of the document scanning may deteriorate. 
     In particular, when the scanning position of a base and the scanning position of a document, which are used for the shading correction in the image reading apparatus, are different from each other in the conveyance direction of the document, it is necessary to reciprocate a carriage on which a reader is mounted between the scanning position of the base and the scanning position of the document repeatedly. In such cases, the productivity decreases significantly. 
     In order to prevent the productivity of document scanning from decreasing, technologies have been proposed that correct the intermittent shading. In such technologies, correction data is obtained at prescribed time intervals. However, the above conventional technologies to correct the intermittent shading cannot correct the influence of the thermal deformation of a light guiding member such as a rod lens array or a light guide due to change in temperature over time. 
     For example, in the case of rod lens arrays, as the rod lens array is deformed to expand and contract in the width direction intersecting the conveyance direction of the document, the positions of the multiple rod lenses provided for the rod lens array and the positions of the multiple light-receiving elements provided for the light receiver may be shifted from each other in the width direction. As a result, the peak positions of the light intensity may be shifted from each other in the width direction in the shading between the correction data and the readout signal output from the light receiver, and streak-like abnormal image such as a black streak or a white streak extending in the conveyance direction may appear on the scanned image. 
     By contrast, in the case of light guides, as the load is applied due to the deformation of the light guide on the connecting part between the light guide and a fixation member that fixes the light guide, the direction in which the light is emitted from the light guide may change over time. As a result, the shading in the width direction changes over time. Accordingly, the shading differs between the correction data and the readout signal output from the light receiver, and an error in the correction of shading occurs. 
     The image reading apparatus  100  according to the present embodiment includes the light emitter  201  and the light guide  202  that serve as an irradiation unit, and irradiate the document  1  with irradiation light Ls, and the rod lens array  203  that serves as a first light guide and guides the reflected light Lr of the irradiation light Ls emitted from the light emitter  201  and the light guide  202  and reflected by the document  1 . Moreover, the image reading apparatus  100  according to the present embodiment includes the light receiver  204  that serves as an output device and outputs the readout signal Is obtained from the reflected light Lr guided by the rod lens array  203 , and the first reading roller  19  that serves as a base for correcting the shading in the readout signal Is output from the light receiver  204 . Further, the image reading apparatus  100  according to the present embodiment includes the correction unit  303  that outputs the readout signal Ic of the scanned image in which the shading of the document  1  in the readout signal Is is corrected using the correction data  306  obtained based on the readout signal Is of the first reading roller  19  output from the light receiver  204 , and the controller  300  that serves as a controller and controls the timing at which the light receiver  204  outputs a signal and the timing at which light is emitted from the light emitter  201  and the light guide  202 . 
     The controller  300  according to the present embodiment heats the rod lens array  203  with the irradiation light Ls emitted from the light emitter  201  and the light guide  202  before the light receiver  204  outputs the readout signal Is of each of the document  1  and the first reading roller  19 . The correction unit  303  uses the correction data  306  obtained in the state where the rod lens array  203  is heated to correct the shading in the readout signal Is of the document  1  output from the light receiver  204  in the state where the rod lens array  203  is heated. 
     The image reading apparatus  100  can obtain the correction data  306  in a state in which each of the rod lens array  203  and the light guide  202  is deformed to expand and contract due to heating, and can correct the readout signal Is of the document  1  based on the obtained correction data  306 . Accordingly, in the image reading apparatus  100  according to the present embodiment, the state of deformation of the rod lens array  203  can be made close to the state of deformation of the light guide  202  between the time of acquisition of the correction data  306  and the time of scanning the document  1 . As a result, the difference in the amount of deformation of each of the rod lens array  203  and the light guide  202  between the time of acquisition of the correction data  306  and the time of scanning the document  1  can be reduced, and the error in the shading correction due to the changes in the temperature of the image reading apparatus  100  can be reduced. 
     For example, it is desired that the controller  300  control the rod lens array  203  and the light guide  202  to be heated until the deformation of each of the rod lens array  203  and the light guide  202  due to heating is saturated. Due to such a configuration, in the image reading apparatus  100  according to the present embodiment, the state of deformation of the rod lens array  203  can be made close to the state of deformation of the light guide  202  between the time of acquisition of the correction data  306  and the time of scanning the document  1 , and the error in the shading correction due to the changes in the temperature of the image reading apparatus  100  can further be reduced. 
     When the image reading apparatus  100  reads a plurality of documents  1 , that is, when the light receiver  204  outputs the readout signal Is of each of the multiple documents  1 , the controller  300  preferably heats the rod lens array  203  and the light guide  202  with the irradiation light Ls irradiated from the light emitter  201  and the light guide  202  only once before the first readout signal Is among the readout signals Is of each of the multiple documents  1  is output from the light receiver  204 . It is desired that the correction unit  303  use the correction data  306  obtained in the state where each of the rod lens array  203  and the light guide  202  is heated to correct the shading in the readout signal Is of the document  1  output from the light receiver  204  in the state where the rod lens array  203  and the light guide  202  are heated. Due to such a configuration, it is no longer necessary for the image reading apparatus  100  to obtain the correction data  306  every time a plurality of documents  1  are scanned, and the length of time it takes to obtain the correction data  306  can be shortened. As a result, the image reading apparatus  100  can prevent the error in the shading correction due to the change in temperature of the image reading apparatus  100  while increasing the productivity of scanning the multiple documents  1 . 
     In order to output the readout signal Is of the being-conveyed document  1  from the light receiver  204 , it is desired that the controller  300  start the irradiation of the irradiation light Ls by the light emitter  201  and the light guide  202  when the document  1  is placed at, for example, the position of the document placement unit A where the conveyance of the document  1  starts. Thus, since the heating of the rod lens array  203  and the light guide  202  can be started immediately after the document  1  is placed on the document placement unit A, the standby time until the rod lens array  203  and the light guide  202  are deformed by heating can be shortened. As a result, the image reading apparatus  100  according to the present embodiment can reduce the error in the shading correction due to the changes in the temperature of the image reading apparatus  100  while increasing the productivity of scanning the multiple documents  1 . 
     The controller  300  according to the present embodiment may change the timing at which the light emitter  201  starts light emission depending on the distance d between the light emitter  201  and the light guide  202 . The time during which the light guide  202  is deformed by heating varies depending on the distance d. For example, when the distance d is short, the heating efficiency increases. As a result, the light guide  202  can be deformed in a timely manner. By contrast, when the distance d is long, the heating efficiency decreases. As a result, the deformation of the light guide  202  tends to be delayed. The distance d is determined in accordance with the arrangement of components of the image reading apparatus  100 . 
     For example, when the distance d is 3 millimeters (mm), the length of time since the emission of the irradiation light Ls to the output of the readout signal Is by the light receiver  204  is set to 3 seconds in the image reading apparatus  100 . 
     In the image reading apparatus  100  according to the present embodiment, the timing at which the light emitter  201  starts light emission is changed depending on the distance d, and the length of time since the emission of the irradiation light Ls to the output of the readout signal Is by the light receiver  204  is changed. As a result, the heating of the light guide  202  can be started at an appropriate timing according to the arrangement of the components in the image reading apparatus  100 . As a result, the image reading apparatus  100  can reduce the error in the shading correction due to the changes in the temperature of the image reading apparatus  100 . 
     Second Embodiment 
     An image reading apparatus  100   a  according to a second embodiment is described below. In view of the first embodiment of the present disclosure as described above, like reference signs denote like elements, and redundant description may be omitted where appropriate. 
       FIG.  8    is a block diagram illustrating a functional configuration of a controller  300   a  provided for an image reading apparatus  100   a  according to a second embodiment of the present disclosure. 
     The image reading apparatus  100   a  according to the present embodiment includes a temperature sensor  400 . 
     The temperature sensor  400  according to the present embodiment serves as a temperature sensor that detects at least one of the temperature of the rod lens array  203  and the ambient temperature of the rod lens array  203 . The temperature sensor  400  is not limited to any particular sensor as long as it can output a detected temperature, and various kinds of temperature sensors such as a resistance thermometer or a radiation thermometer may be used. 
     The temperature sensors  400  may be disposed at any positions in the  100   a  of the image reading apparatus as long as at least one of the temperature of the rod lens array  203  and the ambient temperature of the rod lens array  203  can be detected. 
     The controller  300   a  includes a temperature acquisition unit  308  that receives a temperature detection signal Dt output from the temperature sensors  400  to obtain the degree of temperature. The controller  300   a  controls the light emitter  201  and the light guide  202  to start emitting the irradiation light Ls when the temperature detected by the temperature sensors  400  becomes equal to or higher than a predetermined temperature before the readout signals Is of each one of the document  1  and the first reading roller  19  is output from the light receiver  204 . 
     In the image reading apparatus  100  according to the first embodiment, when the timing at which the irradiation light Ls is emitted from the light emitter  201  and the light guide  202  is determined based on the elapsed time, there are some cases in which the error in the correction of shading cannot sufficiently be reduced. For example, when the ambient temperature of the image reading apparatus  100  is lower than the temperature at which the irradiation timing is determined, there are some cases in which the temperatures of the light emitter  201  and the light guide  202  do not sufficiently increase at the predetermined timing of light emission. As a result, the deformation of each of the rod lens array  203  and the light guide  202  differs between the time of acquisition of the correction data  306  and the time of scanning the document  1 , and an error in the correction of shading occurs. 
     In the present embodiment, the image reading apparatus  100   a  starts the emission of the irradiation light Ls based on the temperature detected by the temperature sensor  400 . Accordingly, regardless of the ambient temperature of the image reading apparatus  100 , for example, the irradiation light Ls can be emitted when the deformation of each of the rod lens array  203  and the light guide  202  is saturated. As a result, the image reading apparatus  100   a  can reduce the error in the shading correction due to the changes in the temperature of the image reading apparatus  100   a . The other aspects of the present embodiment are similar to those of the first embodiment of the present disclosure as described above. 
     Third Embodiment 
     An image forming apparatus  500  according to a third embodiment of the present disclosure is described below. The image forming apparatus  500  according to the present embodiment is provided with the image reading apparatus  100  according to the above embodiments of the present disclosure, and forms an image on a recording sheet, which serves as a recording medium, based on the image read by the image reading apparatus  100 . 
       FIG.  9    is a diagram illustrating a configuration or structure of an image forming apparatus  500  according to a third embodiment of the present disclosure. 
     More specifically,  FIG.  9    is a perspective front view of the image forming apparatus  500 . 
     As illustrated in  FIG.  9   , the image forming apparatus  500  includes the image reading apparatus  100 , an automatic document feeder (ADF)  510  that serves as an image reading apparatus, a sheet feeder  502 , and an image forming device  503 . The image forming apparatus  500  may include the image reading apparatus  100   a  according to the second embodiment of the present disclosure instead of the image reading apparatus  100 . 
     The sheet feeder  502  includes a sheet tray  521  and a sheet tray  522  that store a plurality of recording sheets with different sizes, and a sheet feed unit  523  that is composed of various kinds of rollers and conveys the recording sheets stored in the sheet tray  521  and the sheet tray  522  to the position at which an image is to be formed by the image forming device  503 . 
     The image forming device  503  includes an exposure device  531 , a photoconductor drum  532 , a developing device  533 , a transfer belt  534 , and a fixing device  535 . 
     In the image forming device  503  according to the present embodiment, the exposure device  531  is used to expose the photoconductor drum  532  based on the scanned image of a document obtained by an image reading unit provided inside the ADF  510 . As a result, a latent image can be formed on the photoconductor drum  532 . 
     Further, the image forming device  503  supplies toner of different colors to the photoconductor drum  532  by the developing device  533  to perform development of an image. Then, the image forming device  503  uses the transfer belt  534  to transfer the image developed on the photoconductor drum  532  to the recording sheet supplied from the sheet feeder  502 , and fuses or melts the toner on the toner image transferred to the recording sheet by the fixing device  535  to fix the color image on the recording sheet. 
     As the image forming apparatus  500  is provided with the image reading apparatus  100 , a high-quality image can be formed on a recording sheet based on the scanned image in which an error in the shading correction due to change in temperature of the image reading apparatus  100  is reduced. The other aspects of the present embodiment are similar to those of the image reading apparatus  100  and the image reading apparatus  100   a  according to the first and second embodiments of the present disclosure. 
     Numerous additional modifications and variations are possible in light of the above teachings. It is therefore to be understood that within the scope of the appended claims, the disclosure of the present disclosure may be practiced otherwise than as specifically described herein. For example, elements and/or features of different illustrative embodiments may be combined with each other and/or substituted for each other within the scope of this disclosure and appended claims. 
     The multiple functions according to the above embodiments of the present disclosure can be implemented by one or a plurality of processing circuits. The processing circuit herein includes, for example, devices such as a processor that is programmed to execute software to implement functions, like a processor with electronic circuits, an application specific integrated circuit (ASIC) that is designed to execute the above functions, a digital signal processor (DSP), a field-programmable gate array (FPGA), and a circuit module known in the art. 
     Any one of the above-described operations may be performed in various other ways, for example, in an order different from the one described above. 
     Each of the functions of the described embodiments may be implemented by one or more processing circuits or circuitry. Processing circuitry includes a programmed processor, as a processor includes circuitry. A processing circuit also includes devices such as an application-specific integrated circuit (ASIC), digital signal processor (DSP), field-programmable gate array (FPGA), and conventional circuit components arranged to perform the recited functions.