Patent Publication Number: US-2022219932-A1

Title: Image reading device and image forming apparatus incorporating the image reading device

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This patent application is based on and claims priority pursuant to 35 U.S.C. § 119(a) to Japanese Patent Application Nos. 2021-003114, filed on Jan. 12, 2021, and 2021-118759, filed on Jul. 19, 2021, in the Japan Patent Office, the entire disclosure of each of which is hereby incorporated by reference herein. 
     BACKGROUND 
     Technical Field 
     Embodiments of the present disclosure relate to an image reading device and an image forming apparatus incorporating the image reading device. 
     Background Art 
     Various image forming apparatuses are known to include an image reading device that reads a sheet material on which an image is formed, so as to use the reading result for detecting a defect image (abnormal image) and correcting the position and the color of the image to be formed. 
     A known image forming apparatus has a configuration in which a cleaning chart is conveyed while contacting a reading plate to remove foreign materials on the reading plate. Such a cleaning chart is known to form a convex cleaning image projected with toner on the cleaning chart. 
     SUMMARY 
     Embodiments of the present disclosure described herein provide a novel image reading device including a reader, a transparent member, an opposing member, a first conveyance rotator, a second conveyance rotator, and circuitry. The reader reads a sheet. The transparent member is disposed between the reader and the sheet facing the reader. The opposing member is disposed facing the reader via the transparent member. The first conveyance rotator is disposed upstream from the reader in a conveyance direction of the sheet. The second conveyance rotator is disposed downstream from the reader in the conveyance direction. The circuitry causes the first conveyance rotator and the second conveyance rotator to convey a cleaning sheet at respective conveying speeds different from each other and bring the cleaning sheet into contact with at least one of the transparent member or the opposing member. 
     Further, embodiments of the present disclosure described herein provide an image forming apparatus including an image forming device configured to form an image on a sheet, and the above-described image reading device to read the image on the sheet. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
       Exemplary embodiments of this disclosure will be described in detail based on the following figures, wherein: 
         FIG. 1  is a diagram illustrating an image reading device according to a first embodiment of the present disclosure and a conveyance passage through which a reading target object passes; 
         FIG. 2  is a side view of the image reading device of  FIG. 1 , when conveying a sheet; 
         FIG. 3  is a plan view of the image reading device of  FIG. 1 , when conveying the sheet; 
         FIGS. 4A and 4B  are side views, each illustrating the image reading device of  FIG. 1 , when conveying a cleaning sheet; 
         FIG. 5  is a plan view of the image reading device of  FIG. 1 , for explaining a foreign material on an exposure glass mounted on the image reading device and the reading result; 
         FIG. 6  is a plan view of the image reading device of  FIG. 1 , for explaining the reading result; 
         FIGS. 7A and 7B  are side views, each illustrating an image reading device according to a second embodiment of the present disclosure, in a cleaning operation performed on the image reading device; 
         FIGS. 8A and 8B  are diagrams, each illustrating a cleaning sheet used in the image reading device of  FIGS. 7A and 7B ; 
         FIGS. 9A and 9B  are side views, each illustrating an image reading device according to a third embodiment of the present disclosure, in a cleaning operation performed on the image reading device; 
         FIGS. 10A and 10B  are diagrams, each illustrating a cleaning sheet used in the image reading device of  FIGS. 9A and 9B ; 
         FIGS. 11A and 11B  are diagrams, each illustrating a cleaning sheet used in a cleaning operation performed on an image reading device according to a fourth embodiment of the present disclosure; 
         FIG. 12  is a side view of an image forming apparatus according to a fifth embodiment of the present disclosure; 
         FIG. 13  is a side view of an image forming apparatus according to a sixth embodiment of the present disclosure; 
         FIG. 14  is a side view of an image forming apparatus according to a seventh embodiment of the present disclosure; 
         FIG. 15  is a side view of an image reading device included in the image forming apparatus of  FIG. 14 ; 
         FIG. 16  is a flowchart of a control flow in a cleaning operation in continuous printing executed by a controller according to the seventh embodiment; 
         FIG. 17  is a side view of an image forming apparatus according to an eighth embodiment of the present disclosure; 
         FIG. 18  is a flowchart of a first control flow in a cleaning operation executed by a controller according to the eighth embodiment; 
         FIG. 19  is a flowchart of a second control flow in a cleaning operation executed by the controller according to the eighth embodiment; 
         FIG. 20  is a side view of an image reader included in an image forming apparatus according to a ninth embodiment of the present disclosure; 
         FIG. 21  is a flowchart of a control flow in a cleaning operation performed on upstream reader according to the ninth embodiment; 
         FIG. 22  is a flowchart of a control flow in a cleaning operation performed on a downstream reading unit according to the ninth embodiment; and 
         FIG. 23  is a diagram illustrating a black background roller of a background switching revolver according to a tenth embodiment of the present disclosure, for explaining a relation of the black background roller and each of the width of a sheet and the width of a cleaning sheet. 
     
    
    
     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 
     It will be understood that if an element or layer is referred to as being “on,” “against,” “connected to” or “coupled to” another element or layer, then it can be directly on, against, connected or coupled to the other element or layer, or intervening elements or layers may be present. In contrast, if an element is referred to as being “directly on,” “directly connected to” or “directly coupled to” another element or layer, then there are no intervening elements or layers present. Like numbers referred to like elements throughout. As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items. 
     Spatially relative terms, such as “beneath,” “below,” “lower,” “above,” “upper” and the like may be used herein for ease of description to describe one element or feature&#39;s relationship to another element(s) or feature(s) as illustrated in the figures. It will be understood that the spatially relative terms are intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. For example, if the device in the figures is turned over, elements describes as “below” or “beneath” other elements or features would then be oriented “above” the other elements or features. Thus, term such as “below” can encompass both an orientation of above and below. The device may be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors herein interpreted accordingly. 
     The terminology used herein is for describing particular embodiments and examples and is not intended to be limiting of exemplary embodiments of this 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. 
     Referring now to the drawings, embodiments of the present disclosure are described below. In the drawings for explaining the following embodiments, the same reference codes are allocated to elements (members or components) having the same function or shape and redundant descriptions thereof are omitted below. 
     Next, a description is given of a configuration and functions of an image reading device and an image forming apparatus, according to an embodiment of the present disclosure, with reference to drawings. Note that identical parts or equivalents are given identical reference numerals and redundant descriptions are summarized or omitted accordingly. 
     Embodiments of the present disclosure are described below with reference to the attached drawings. 
     A description is given of a first embodiment of the present disclosure, with reference to  FIGS. 1 to 4B . 
       FIG. 1  is a diagram illustrating an image reading device according to a first embodiment of the present disclosure and a conveyance passage through which a reading target passes. 
       FIG. 2  is a side view of the image reading device of  FIG. 1 , when conveying a sheet. 
       FIG. 3  is a plan view of the image reading device of  FIG. 1 , when conveying the sheet. 
       FIGS. 4A and 4B  are side views, each illustrating the image reading device of  FIG. 1 , when conveying a cleaning sheet. 
     The image reading device  1  includes a reading unit  11 , an exposure glass  12 , a background switching revolver  13 , an upstream conveyance roller pair  14 , and a downstream conveyance roller pair  15 . 
     The reading unit  11  reads a sheet S that is conveyed in the image reading device  1 . The process of reading the sheet S includes confirmation of the sheet S and reading of an image formed on the sheet S. In the present embodiment, the reading unit  11  uses a contact image sensor that includes a reading unit and an irradiation unit as a single unit. However, the structure of the reading unit  11  is not limited to this structure. 
     The exposure glass  12  is a transparent member (reading plate) interposed between the reading unit  11  and the sheet S while being conveyed under the exposure glass  12 . 
     The background switching revolver  13  is an opposing member disposed facing the reading unit  11  across the exposure glass  12  (transparent member). The background switching revolver  13  has two black background rollers  13   a  and two white background rollers  13   b  around the circumferential surface. Each of the black background rollers  13   a  has a black peripheral surface. Each of the white background rollers  13   b  has a white peripheral surface. The background switching revolver  13  is rotated to switch a background color in accordance with white shading or a reading target that is an object to be read. 
     The upstream conveyance roller pair  14  includes a conveyance roller  14   a  and a driven roller  14   b . The conveyance roller  14   a  and the driven roller  14   b  are disposed upstream from the reading unit  11  in a conveyance direction in which the sheet S is conveyed. The conveyance roller  14   a  functions as a first conveyance rotator. The downstream conveyance roller pair  15  includes a conveyance roller  15   a  and a driven roller  15   b . The conveyance roller  15   a  and the driven roller  15   b  are disposed downstream from the reading unit  11  in the conveyance direction of the sheet S. The conveyance roller  15   a  functions as a second conveyance rotator. 
     A straight conveyance passage  16  and a reverse conveyance passage  17  extend toward downstream in the conveyance direction of the sheet S in the image reading device  1 . A conveyance roller pair  18  is disposed on the straight conveyance passage  16 . Conveyance roller pairs  19  including a conveyance roller pair  19 A and a conveyance roller pair  19 B are disposed on the reverse conveyance passage  17 . The conveyance roller pair  19 B is disposed downstream from the conveyance roller pair  19 A in the conveyance direction of the sheet S. 
     The sheet S is conveyed through the straight conveyance passage  16  to be ejected with the face up. By contrast, the sheet S is conveyed through the reverse conveyance passage  17  to be ejected with the face down. Alternatively, in duplex printing, the sheet S is conveyed through the reverse conveyance passage  17  after the first face of the sheet S is printed, and is then conveyed through the straight conveyance passage  16  after the second face of the sheet S. 
     The conveyance roller  14   a  of the upstream conveyance roller pair  14  is driven and rotated by a drive motor  24 . The conveyance roller  15   a  of the downstream conveyance roller pair  15  is driven and rotated by a drive motor  25 . The drive motors  24  and  25  are driven and rotated by a motor driver  21 . 
     A cleaning controller  20  controls each of driving of the first conveyance rotator (i.e., the conveyance roller  14   a ) and driving of the second conveyance rotator (i.e., the conveyance roller  15   a ) via the motor driver  21  when cleaning the exposure glass  12  or the background switching revolver  13 . 
     When a sheet-like cleaning member  46  is conveyed to clean the exposure glass  12  or the background switching revolver  13 , the cleaning controller  20  causes the conveyance roller  14   a  and the conveyance roller  15   a  to rotate at the conveying speeds different from each other. The sheet-like cleaning member  46  is hereinafter referred to as a cleaning sheet  46 . 
     In the present embodiment, by setting the number of rotations of the conveyance roller  14   a  and the number of rotations of the conveyance roller  15   a  different from each other, the cleaning controller  20  causes the cleaning sheet  46  to contact the exposure glass  12  (transparent member) or the background switching revolver  13  (opposing member). 
     Next, a description is given of operations of reading the sheet S by the image reading device  1 . 
     As illustrated in  FIGS. 2 and 3 , when the sheet S passes below the reading unit  11 , the image reading device  1  causes the reading unit  11  to sequentially read the state of the sheet S on a reading line  31 , so that the image reading device  1  acquires data of sheet S and data of the image formed on the sheet S. 
     At this time, the background switching revolver  13  switches the background roller in accordance with the sheet S. When the sheet S is white, either one of the black background rollers  13   a  is brought over the reading line  31 . When the sheet S is black or when show-through of an image is concerned, either one of white background rollers  13   b  is brought over the reading line  31 . 
     Next, a description is given of the image reading device with an example of a foreign material on the exposure glass and a reading result, with reference to  FIGS. 5 and 6 . 
       FIG. 5  is a plan view of the image reading device, for explaining a foreign material on the exposure glass mounted on the image reading device and the reading result. 
       FIG. 6  is a plan view of the image reading device, for explaining the reading result. 
     As illustrated in  FIG. 5 , it is assumed that a foreign material  32  is adhered on the exposure glass  12  on the reading line  31  on which the reading unit  11  reads the sheet S. When the reading unit  11  reads the sheet S with the foreign material  32  adhered on the reading line  31 , a read image as illustrated in  FIG. 6  is produced. 
     The read image that is read by the reading unit  11  includes not only a sheet reading image  33  and a read background  34  but also a longitudinal streak  35  generated due to the foreign material  32  along the conveyance direction of the sheet S. 
     As described above, when the foreign material  32  is adhered on the reading line  31 , the foreign material  32  blocks irradiation light from the reading unit  11 . For this reason, when the foreign material  32  is adhered in an area on the reading line  31 , the reading unit  11  cannot read information of the area of the sheet S. When the area of the sheet S cannot be read, even if a defect image is in the area, the reading unit  11  cannot read, resulting in the functional deterioration. Alternatively, even when there is no defect in the image, it is likely that the reading unit  11  reads the foreign material  32  to determine that the image is defected. 
     In order to avoid this situation, it is highly desirable that the reading result of a sheet by the reading unit  11  is not to be affected by foreign materials such as debris. However, in a case in which the sheet S is paper, it is difficult to avoid such an adverse effect on the sheet S due to various causes of occurrence of foreign materials such as paper dust or toner in an image forming apparatus. 
     In order to avoid this situation, in the present embodiment, the sheet-like cleaning member (cleaning sheet)  46  is brought to contact the exposure glass  12  or the background switching revolver  13 , so as to clean the exposure glass  12  or the background switching revolver  13 . Note that the cleaning sheet  46  may be a special sheet for cleaning or a sheet S for image formation. The cleaning sheet  46  may be, for example, a convex-concave paper or a Japanese paper. 
     Next, a description is given of a cleaning operation performed when cleaning an exposure glass or a background switching revolver, according to the present embodiment. 
     As described above, when cleaning the exposure glass  12  or the background switching revolver  13 , the cleaning controller  20  causes the number of rotations of the conveyance roller  14   a  of the upstream conveyance roller pair  14  and the number of rotations of the conveyance roller  15   a  of the downstream conveyance roller pair  15  to be different from each other. For convenience, the conveyance roller  14   a  of the upstream conveyance roller pair  14  is referred to as an upstream conveyance roller  14   a . Similarly, the conveyance roller  15   a  of the downstream conveyance roller pair  15  is referred to as a downstream conveyance roller  15   a . Note that, in the present embodiment, the upstream conveyance roller  14   a  and the downstream conveyance roller  15   a  have the same diameter and the different number of rotations from each other. According to this configuration, the upstream conveyance roller  14   a  and the downstream conveyance roller  15   a  have the different surface linear velocities from each other, and therefore also have the different conveying speeds from each other. 
     As illustrated in  FIG. 4A , when the cleaning sheet  46  is conveyed to clean the exposure glass  12  (transparent member), the number of rotations of the downstream conveyance roller  15   a  is smaller than the number of rotations of the upstream conveyance roller  14   a . At this time, the linear velocity of the downstream conveyance roller  15   a  is slower than the linear velocity of the upstream conveyance roller  14   a.    
     As a result, the cleaning sheet  46  may be bent between the upstream conveyance roller pair  14  and the downstream conveyance roller pair  15  so as to be convex (outward) toward the exposure glass  12 . With such a configuration, the cleaning sheet  46  is conveyed while the cleaning sheet  46  is pressed against the exposure glass  12  with an appropriate pressure, so that the surface of the exposure glass  12  is cleaned. 
     As illustrated in  FIG. 4B , when the cleaning sheet  46  is conveyed to clean the background switching revolver  13  (opposing member), the number of rotations of the downstream conveyance roller  15   a  is greater than the number of rotations of the upstream conveyance roller  14   a . At this time, the linear velocity of the downstream conveyance roller  15   a  is faster than the linear velocity of the upstream conveyance roller  14   a.    
     As a result, as illustrated in  FIG. 4B , the cleaning sheet  46  is conveyed while being stretched taut between the upstream conveyance roller pair  14  and the downstream conveyance roller pair  15  so as to be reliably contact the circumferential surface of the background switching revolver  13 . With such a configuration, the background switching revolver  13  is rotated to bring the black background roller  13   a  or the white background roller  13   b  to the position at which the black background roller  13   a  or the white background roller  13   b  contacts the cleaning sheet  46 . By so doing, the (circumferential) surface of the black background roller  13   a  or the (circumferential) surface of the white background roller  13   b  is cleaned. The white shading surface is cleaned similarly. 
     As described above, the exposure glass  12  or the background face of the background switching revolver  13  is cleaned while the cleaning sheet  46  is in contact with the exposure glass  12  or the background switching revolver  13 , thereby enhancing the cleanability in the image reading device  1 . 
     Next, a description is given of the image reading device according to a second embodiment of the present disclosure, with reference to  FIGS. 7A to 8B . 
       FIGS. 7A and 7B  are side views, each illustrating the image reading device according to the second embodiment of the present disclosure, in the cleaning operation performed on the image reading device. 
       FIGS. 8A and 8B  are diagrams, each illustrating the cleaning sheet used in the image reading device of  FIGS. 7A and 7B . 
     As illustrated in  FIGS. 8A and 8B , the cleaning sheet  46  used in the present embodiment includes a base  46   a  and brushes  46   b  for cleaning disposed partly on one side of the base  46   a , along the conveyance direction of the cleaning sheet  46 . The brushes  46   b  are aligned in a belt-like shape along a direction that intersects with the conveyance direction of the cleaning sheet  46 . The brushes  46   b  in  FIGS. 8A and 8B  are aligned in a direction orthogonal to the conveyance direction of the cleaning sheet  46 . However, the brushes  46   b  may be aligned in an oblique direction to the conveyance direction of the cleaning sheet  46 . 
     Further, in order to prevent instant impact between the brushes  46   b  of the cleaning sheet  46  and each of the exposure glass  12  and the background switching revolver  13 , it is preferable to sufficiently obtain a distance X from the leading end of the base  46   a  in the conveyance direction of the cleaning sheet  46 , to the first brush  46   b  of the brushes  46   b.    
     When cleaning the exposure glass  12  by the cleaning sheet  46 , the cleaning sheet  46  is conveyed with the brushes  46   b  facing the exposure glass  12 , as illustrated in  FIG. 7A . At this time, as in the first embodiment, the number of rotations of the downstream conveyance roller  15   a  is smaller than the number of rotations of the upstream conveyance roller  14   a.    
     As a result, the cleaning sheet  46  is bent to be convex (outward) toward the exposure glass  12 , so that the brushes  46   b  of the cleaning sheet  46  may be brought to contact the exposure glass  12 . With such a configuration, the cleaning sheet  46  is conveyed to wipe and clean the exposure glass  12  by the brushes  46   b.    
     When cleaning the background switching revolver  13  with the cleaning sheet  46 , the cleaning sheet  46  is conveyed with the brushes  46   b  facing the background switching revolver  13 , as illustrated in  FIG. 7B . At this time, as in the first embodiment, the number of rotations of the downstream conveyance roller  15   a  is greater than the number of rotations of the upstream conveyance roller  14   a.    
     As a result, the cleaning sheet  46  is stretched taut, so that the brushes  46   b  of the cleaning sheet  46  may be brought to contact the black background roller  13   a  or the white background roller  13   b  of the background switching revolver  13 . With such a configuration, the cleaning sheet  46  is conveyed to wipe and clean the circumferential surface of the black background roller  13   a  or the circumferential surface of the white background roller  13   b  by the brushes  46   b.    
     As described above, the cleaning sheet  46  includes the brushes  46   b  for cleaning, thereby further enhancing the cleanability in the image reading device  1 . 
     Note that, instead of disposing the brushes  46   b  partly on the cleaning sheet  46 , the cleaning sheet  46  may dispose the brushes  46   b  covering the whole surface of the base  46   a . Further, in order to prevent instant impact between the brushes  46   b  of the cleaning sheet  46  and each of the exposure glass  12  and the background switching revolver  13 , the distance X from the leading end of the base  46   a  in the conveyance direction of the cleaning sheet  46  to the first brush  46   b  of the brushes  46   b  may be sufficiently obtained. 
     Next, a description is given of the image reading device according to a third embodiment of the present disclosure, with reference to  FIGS. 9A to 10B . 
       FIGS. 9A and 9B  are side views, each illustrating the image reading device according to the third embodiment of the present disclosure, in a cleaning operation performed on the image reading device. 
       FIGS. 10A and 10B  are diagrams, each illustrating the cleaning sheet used in the image reading device of  FIGS. 9A and 9B . 
     As illustrated in  FIGS. 10A and 10B , the cleaning sheet  46  used in the present embodiment includes the base  46   a  and the brushes  46   b  for cleaning (upper brushes  46   b   1  and lower brushes  46   b   2 ) on both sides, which are front and back sides, of the base  46   a , along the conveyance direction of the cleaning sheet  46 . Specifically, the upper brushes  46   b   1  are on the front side of the base  46   a  and the lower brushes  46   b   2  are on the back side of the base  46   a . The upper brushes  46   b   1  and the lower brushes  46   b   2  are aligned in a belt-like shape in the direction that intersects with the conveyance direction of the cleaning sheet  46 . The upper brushes  46   b   1  and the lower brushes  46   b   2  in  FIGS. 10A and 10B  are aligned in the direction orthogonal to the conveyance direction of the cleaning sheet  46 . However, the upper brushes  46   b   1  and the lower brushes  46   b   2  may be aligned in the oblique direction to the conveyance direction of the cleaning sheet  46 . 
     Further, in order to prevent instant impact between the upper brushes  46   b   1  of the cleaning sheet  46  and each of the exposure glass  12  and the background switching revolver  13 , it is preferable to sufficiently obtain the distance X from the leading end of the base  46   a  in the conveyance direction of the cleaning sheet  46  to the first upper brush  46   b   1  of the upper brushes  46   b   1 . 
     When cleaning the exposure glass  12  and the background switching revolver  13  by the cleaning sheet  46  illustrated in  FIGS. 10A and 10B , as in the first embodiment, the number of rotations of the downstream conveyance roller  15   a  is smaller than the number of rotations of the upstream conveyance roller  14   a.    
     As a result, as illustrated in  FIG. 9A , the cleaning sheet  46  is bent to be convex (outward) toward the exposure glass  12 , so that the upper brushes  46   b   1  on the upper surface of the cleaning sheet  46  may be brought to contact the exposure glass  12 . In addition, as illustrated in  FIG. 9B , since the lower brushes  46   b   2  on the lower surface of the cleaning sheet  46  is projected downwardly from the base  46   a , the lower brushes  46   b   2  may be brought to contact the circumferential surface of the background switching revolver  13  (i.e., the circumferential surface of the black background roller  13   a  or the circumferential surface of the white background roller  13   b ). 
     The cleaning sheet  46  is conveyed with such a configuration, so that the upper brushes  46   b   1  wipe and clean the surface of the exposure glass  12  and the lower brushes  46   b   2  wipe and clean the circumferential surface of the background switching revolver  13 , in other words, the circumferential surface of the black background roller  13   a  or the circumferential surface of the white background roller  13   b.    
     As described above, since the cleaning sheet  46  includes the upper brushes  46   b   1  and the lower brushes  46   b   2 , the exposure glass  12  (transparent member) and the background switching revolver  13  (opposing member) are cleaned at one time in one conveyance. 
     Further, in the present embodiment, the upper brushes  46   b   1  on one side (i.e., upper surface) of the base  46   a  of the cleaning sheet  46  are disposed at respective positions different from respective positions of the lower brushes  46   b   2  on the other side (i.e., lower surface) of the base  46   a  of the cleaning sheet  46  in a zigzag (staggered) pattern as viewed in  FIG. 10B . 
     As a result, in cleaning with the cleaning sheet  46 , the thickness of the cleaning sheet  46  equals the sum of the thickness of the base  46   a , the height of the upper brushes  46   b   1 , and the height of the lower brushes  46   b   2 . This structure restrains a decrease in conveyance of the cleaning sheet  46 . 
     Next, a description is given of the image reading device according to a fourth embodiment of the present disclosure, with reference to  FIGS. 11A and 11B . 
       FIGS. 11A and 11B  are diagrams, each illustrating the cleaning sheet used in the cleaning operation performed on the image reading device according to the fourth embodiment of the present disclosure. 
     As illustrated in  FIGS. 11A and 11B , as in the third embodiment, the cleaning sheet  46  used in the present embodiment includes the base  46   a  and the brushes  46   b  (i.e., the upper brushes  46   b   1  and the lower brushes  46   b   2 ) on both sides, which are front and back sides, of the base  46   a  of the cleaning sheet  46 , along the conveyance direction of the cleaning sheet  46 . Specifically, the upper brushes  46   b   1  are on one side (i.e., upper surface) of the base  46   a  and the lower brushes  46   b   2  are on the other side (i.e., lower surface) of the base  46   a . The upper brushes  46   b   1  and the lower brushes  46   b   2  are aligned in a belt-like shape in the direction that intersects with the conveyance direction of the cleaning sheet  46 . The upper brushes  46   b   1  and the lower brushes  46   b   2  in  FIGS. 10A and 10B  are aligned in the direction orthogonal to the conveyance direction of the cleaning sheet  46 . However, the upper brushes  46   b   1  and the lower brushes  46   b   2  may be aligned in the oblique direction to the conveyance direction of the cleaning sheet  46 . 
     The upper brushes  46   b   1  on the upper surface that contacts the exposure glass  12  and the lower brushes  46   b   2  on the lower surface that contacts the circumferential surface of the background switching revolver  13  have different heights (length) from each other. Specifically, the height (length) h 2  of the lower brushes  46   b   2  on the lower surface of the cleaning sheet  46  is higher (longer) than the height (length) h 1  of the upper brushes  46   b   1  on the upper surface of the cleaning sheet  46 . 
     As a result, as in the third embodiment, when the cleaning sheet  46  is conveyed while the cleaning sheet  46  is bent so as to be convex (outward) toward the exposure glass  12 , the lower brushes  46   b   2  reliably contact the circumferential surface of the background switching revolver  13 , thereby restraining defect cleaning of the exposure glass  12  and the background switching revolver  13  included in the image reading device  1 . 
     Note that a flame-retardant material such as nylon may be preferably used for the brushes  46   b  including the upper brushes  46   b   1  and the lower brushes  46   b   2  of the cleaning sheet  46 . This structure of the brushes  46   b  (upper brushes  46   b   1 , lower brushes  46   b   2 ) prevents thermal deformation on the cleaning sheet  46  when, for example, the cleaning sheet  46  is conveyed through a fixing device of an image forming apparatus. In this case, the cleaning sheet  46  may be conveyed through the fixing device under control that the fixing temperature in the fixing device is set to be relatively low. At this time, in order to prevent contamination on the background of sheet S in a secondary transfer portion, a primary transfer portion may be fully separated from sheet S or the transfer bias of the secondary transfer portion and the transfer bias of the primary transfer portion are highly reduced. 
     Next, a description is given of an image forming apparatus according to a fifth embodiment of the present disclosure, with reference to  FIG. 12 . 
       FIG. 12  is a side view of an image forming apparatus according to the fifth embodiment of the present disclosure. 
     An image forming apparatus  100 A according to the present embodiment includes an image reading device  1 AA, a fixing unit  60 , and a cooling unit  70 . In the image forming apparatus  100 A according to the present embodiment, after an image is fixed to a sheet in the fixing unit  60 , the sheet is cooled by the cooling unit  70 , then the image on the sheet is read by the image reading device  1 AA. 
     The image reading device  1 AA includes an inline sensor  52  of a reduction optical system. 
     Next, a description is given of an image forming apparatus according to a sixth embodiment of the present disclosure, with reference to  FIG. 13 . 
       FIG. 13  is a side view of an image forming apparatus according to the sixth embodiment of the present disclosure. 
     An image forming apparatus  100 B according to the present embodiment includes an image reading device  1 BB, the fixing unit  60 , and the cooling unit  70 . In the image forming apparatus  100 B according to the present embodiment, after an image is fixed to a sheet in the fixing unit  60 , the sheet is cooled by the cooling unit  70 , then the image on the sheet is read by the image reading device  1 BB. 
     The image reading device  1 BB includes an inline sensor  55  of an equal magnification optical system. 
     Next, a description is given of an image forming apparatus according to a seventh embodiment of the present disclosure, with reference to  FIGS. 14 and 15 . 
       FIG. 14  is a side view of an image forming apparatus according to the seventh embodiment of the present disclosure. 
       FIG. 15  is a side view of an image reading device included in the image forming apparatus according to the seventh embodiment of the present disclosure. 
     An image forming apparatus  100  includes an image forming device  110 , a sheet conveyor  120 , an image reader  130 , and a controller  150 . The controller  150  controls an overall operation of the image forming apparatus  100  and a series of processes for forming an image on a sheet S to be used for image formation. The controller  150  includes the cleaning controller  20  described in the above-described embodiments. 
     The image forming device  110  includes photoconductor drums  112  (namely, photoconductor drums  112 Y,  112 M,  112 C, and  112 K) to form latent images corresponding to different single color images. In the image forming device  110  according to the present embodiment, the photoconductor drums  112 Y,  112 M,  112 C, and  112 K for forming latent images corresponding to images of respective colors are disposed so as to correspond to image forming processes using image forming materials of respective colors such as toners of yellow (Y), magenta (M), cyan (C), and black (K). 
     The photoconductor drums  112  are disposed along an intermediate transfer belt  111  that is an endless belt included in a movement assembly. The intermediate transfer belt  111  is wound around at least one drive roller and a plurality of driven rollers and moves between a primary transfer position and a secondary transfer position. The first transfer position is a position where an image (toner image) developed on the photoconductor drum  112  is transferred and the secondary transfer position is a position where the image (toner image) is transferred to the sheet S. 
     A transfer unit  113  is disposed at the secondary transfer position. The transfer unit  113  includes a transfer roller  113   a  and a counter roller  113   b  disposed opposite the transfer roller  113   a . In the transfer unit  113 , the toner image is transferred from the intermediate transfer belt  111  to the sheet S to form an image at a predetermined position (i.e., image forming position) on the sheet S. A gap is provided between the transfer roller  113   a  and the counter roller  113   b , so that the intermediate transfer belt  111  and the sheet S pass through the gap while being nipped between the transfer roller  113   a  and the counter roller  113   b . An image is transferred onto the sheet S while the sheet S is nipped in the gap between the transfer roller  113   a  and the counter roller  113   b  and conveyed in the conveyance direction of the sheet S (sub-scanning direction). 
     The sheet conveyor  120  includes a sheet feed tray  121 A and a sheet feed tray  121 B that functions as a sheet feeder. The sheet feed tray  121 A loads sheets to be used for image formation. The sheet feed tray  121 B loads cleaning sheets  46 . In other words, the cleaning sheet  46  is fed from a sheet feeder different from a sheet feeder loading the sheet S on which an image is formed. 
     The sheet conveyor  120  further includes a conveyance passage  122 , a fixing roller pair  123 , a conveyance passage switcher  124 , and a reversal passage  125 . The conveyance passage  122  is defined by multiple roller pairs to convey the cleaning sheet  46 . The fixing roller pair  123  is disposed downstream from the transfer unit  113  in the conveyance direction of the sheet S. 
     When the image forming process is performed, under the predetermined control processing by the controller  150 , the sheet S loaded in the sheet feed tray  121 A is separated by a pickup roller and conveyed along the conveyance passage  122 . Then, the sheet S reaches the transfer unit  113 . 
     As the sheet S reaches the transfer unit  113 , the transfer process is performed. That is, the sheet S is conveyed in the predetermined conveyance direction while being nipped between the surface of the intermediate transfer belt  111  and the counter roller  113   b . The transfer roller  113   a  biases (presses) the intermediate transfer belt  111  toward the counter roller  113   b . When the sheet S passes between the intermediate transfer belt  111  and the counter roller  113   b , an image forming material on the surface of the intermediate transfer belt  111  is transferred onto the sheet S. In this transfer process, an image is formed on one side (first face) of the sheet S. 
     The sheet S having the image on the first face is further conveyed, so that the image is fixed to the sheet S by the fixing roller pair  123 . Then, the sheet S is conveyed to the conveyance passage switcher  124  disposed downstream from fixing roller pair  123  in the conveyance direction of the sheet S. The conveyance passage switcher  124  reverses the travel direction of the sheet S and conveys the reversed sheet S to the reversal passage  125 . Thereafter, the sheet S is conveyed again to the transfer position of the transfer roller  113   a  so that the image formed on the intermediate transfer belt  111  is transferred onto the second face of the sheet S. 
     The sheet S having the image on the second face is further conveyed, so that the image on the second face of the sheet S is fixed to the sheet S by the fixing roller pair  123 . Then, the sheet S is conveyed to the image reader  130  disposed downstream from the fixing roller pair  123  in the conveyance direction of the sheet S. 
     The image reader  130  includes a reader  130   a  and a reader  130   b . The reader  130   a  is constructed by an image reading device that reads the first face of the sheet S. The reader  130   b  is constructed by an image reading device that reads the second face of the sheet S. 
     The sheet S for image formation that has passed through the image reader  130  is ejected to a sheet ejection tray  126 A that functions as a sheet stacker. The cleaning sheet  46  that has passed through the image reader  130  is ejected to a sheet ejection tray  126 B that functions as a sheet stacker. 
     As described above, the sheet S for image formation and cleaning sheet  46  are ejected to different sheet ejection trays. By so doing, even when a cleaning operation is performed in continuous printing, the cleaning sheet  46  is prevented from being mixed into the sheets S for image formation. 
     Each of the readers  130   a  and  130   b  of the image reader  130  includes the image reading device  1 . The image reading device  1  (readers  130   a  and  130   b ) includes the reading unit  11  provided with an irradiation unit  11   b  and a line image sensor. The irradiation unit  11   b  irradiates a sheet S with light when the sheet S passes through a reading position. The line image sensor includes imaging elements  11   a  that perform photoelectric conversion for each pixel. The imaging elements  11   a  are disposed in a one-dimensional shape along a direction orthogonal to the conveyance direction of the sheet S. 
     The image reading device  1  repeatedly performs a reading operation of an image for one line extending in the conveyance direction of the sheet S in accordance with a passing operation of the sheet S that passes the reading position, so as to read the image printed on the sheet S as a two-dimensional image. 
     The background switching revolver  13  is disposed at a position facing the reading unit  11  across the conveyance passage and reflects irradiation light with which the sheet S is irradiated when reading an image. 
     The exposure glass  12  that functions as a transparent member is disposed on the front face of the reading unit  11  and is disposed facing the background switching revolver  13 . The exposure glass  12  penetrates light emitted from the reading unit  11  and reflected light returning after the emitted light is reflected by the background switching revolver  13  and the sheet S. 
     Next, a description is given of control of a cleaning operation in continuous printing by a controller  150  according to the present embodiment, with reference to a flowchart in  FIG. 16 . 
       FIG. 16  is a flowchart of a control flow in a cleaning operation in continuous printing executed by a controller according to the seventh embodiment. 
     The controller  150  executes continuous printing while detecting a defect image (abnormal image) and correcting a position at which an image is formed or a color tone, based on the reading result of the sheet S by the image reading device  1  (reading device) (step S 1 , hereinafter referred to as “S 1 ”). 
     At this time, the cleaning sheet  46  is conveyed and the controller  150  determines whether an automatic cleaning mode is ON or OFF (S 2 ). In the automatic cleaning mode, the cleaning sheet  46  cleans the surface of the exposure glass  12  of the image reading device  1  or the surface of the background switching revolver  13  of the image reading device  1 . 
     When the automatic cleaning mode is ON (YES in S 2 ), the controller  150  then determines whether the number of output sheets (number of printed sheets) is equal to or greater than the predetermined number of sheets for entering the automatic cleaning mode (S 3 ). 
     At this time, when the number of output sheets is equal to or greater than the predetermined number of sheets for entering the automatic cleaning mode (YES in S 3 ), the image output is stopped and, for example, the cleaning sheet  46  with the brushes  46   b  is fed and conveyed from the sheet feed tray  121 B, and then the surface of the exposure glass  12  or the surface of the background switching revolver  13  is cleaned by the cleaning sheet  46  (S 4 ). 
     Thereafter, the controller  150  determines whether no more cleaning operation is to be performed in the image reading device  1  (reading device) (S 5 ). When another cleaning operation is to be performed in the image reading device  1  (NO in S 5 ), the process goes back to S 4  to repeat the operation in S 4  until it is determined that no more cleaning operation is to be performed. 
     When it is determined that no more cleaning operation is to be performed in the image reading device  1  (YES in S 5 ), continuous printing is continued (S 6 ). When the automatic cleaning mode is not ON (NO in S 2 ) or when the number of output sheets is not equal to or greater than the predetermined number of sheets for entering the automatic cleaning mode (NO in S 3 ), continuous printing is continued (S 6 ). 
     As described above, since the image reading device  1  has a configuration that automatically enters the automatic cleaning mode and performs the cleaning operation with the cleaning sheet, a preferable image is formed reliably. Note that entering the automatic cleaning mode may be performed, for example, manually or at the end of the job. 
     Next, a description is given of an image forming apparatus according to an eighth embodiment of the present disclosure, with reference to  FIG. 17 . 
       FIG. 17  is a side view of an image forming apparatus according to the eighth embodiment of the present disclosure. 
     An image forming apparatus  100 C includes the image forming device  110 , the sheet conveyor  120 , an image reader  130 C, and the controller  150 . The controller  150  controls an overall operation of the image forming apparatus  100 C and a series of processes for forming an image on a sheet S to be used for image formation. The controller  150  includes the cleaning controller  20  described in the above-described embodiments. 
     The image forming device  110  includes photoconductor drums  112  (namely, photoconductor drums  112 Y,  112 M,  112 C, and  112 K) to form latent images corresponding to different single color images. In the image forming device  110  according to the present embodiment, the photoconductor drums  112 Y,  112 M,  112 C, and  112 K for forming latent images corresponding to images of respective colors are disposed so as to correspond to image forming processes using image forming materials of respective colors such as toners of yellow (Y), magenta (M), cyan (C), and black (K). 
     The photoconductor drums  112 Y,  112 M,  112 C, and  112  are disposed along the intermediate transfer belt  111  that is an endless belt included in the movement assembly. The intermediate transfer belt  111  is wound around at least one drive roller and a plurality of driven rollers and moves between a primary transfer position and a secondary transfer position. The first transfer position is a position where an image (toner image) developed on the photoconductor drum  112  is transferred and the secondary transfer position is a position where the image (toner image) is transferred to the sheet S. 
     The transfer unit  113  is disposed at the secondary transfer position. The transfer unit  113  includes the transfer roller  113   a  and the counter roller  113   b  disposed facing the transfer roller  113   a . In the transfer unit  113 , the toner image is transferred from the intermediate transfer belt  111  to the sheet S to form an image at a predetermined position (i.e., image forming position) on the sheet S. A gap is provided between the transfer roller  113   a  and the counter roller  113   b , so that the intermediate transfer belt  111  and the sheet S pass through the gap while being nipped between the transfer roller  113   a  and the counter roller  113   b . An image is transferred onto the sheet S while the sheet S is nipped in the gap between the transfer roller  113   a  and the counter roller  113   b  and conveyed in the conveyance direction of the sheet S (sub-scanning direction). 
     The sheet conveyor  120  includes the sheet feed tray  121 A that functions as a first sheet feeder and the sheet feed tray  121 B that functions as a second sheet feeder. The sheet feed tray  121 A loads sheets to be used for image formation. The sheet feed tray  121 B loads cleaning sheets  46 . In other words, the cleaning sheet  46  is fed from a sheet feeder different from a sheet feeder loading the sheet S on which an image is formed. 
     The sheet conveyor  120  receives sheets from the sheet feed tray  121 A and includes a conveyance passage  122 A, the fixing roller pair  123 , the conveyance passage switcher  124 , and the reversal passage  125 . The conveyance passage  122 A is defined by multiple roller pairs to convey the sheet S. The fixing roller pair  123  is disposed downstream from the transfer unit  113  in the conveyance direction of the sheet S. The sheet conveyor  120  also receives sheets from the sheet feed tray  121 B and includes a conveyance passage  122 B along which the cleaning sheet  46  is conveyed. 
     When the image forming process is performed, under the predetermined control processing by the controller  150 , the sheet S loaded in the sheet feed tray  121 A is separated by the pickup roller and then conveyed along the conveyance passage  122 A. Then, the sheet S reaches the transfer unit  113 . 
     As the sheet S reaches the transfer unit  113 , the transfer process is performed. That is, the sheet S is conveyed in the predetermined conveyance direction while being nipped between the surface of the intermediate transfer belt  111  and the counter roller  113   b . The transfer roller  113   a  biases (presses) the intermediate transfer belt  111  toward the counter roller  113   b . When the sheet S passes between the intermediate transfer belt  111  and the counter roller  113   b , an image forming material on the surface of the intermediate transfer belt  111  is transferred onto the sheet S. In this transfer process, an image is formed on one side (first face) of the sheet S. 
     The sheet S having the image on the first face is further conveyed, so that the image is fixed to the sheet S by the fixing roller pair  123 . Then, the sheet S is conveyed to the conveyance passage switcher  124  disposed downstream from fixing roller pair  123  in the conveyance direction of the sheet S. The conveyance passage switcher  124  reverses the travel direction of the sheet S and conveys the reversed sheet S to the reversal passage  125 . Thereafter, the sheet S is conveyed again to the transfer position of the transfer roller  113   a  so that the image formed on the intermediate transfer belt  111  is transferred onto the second face of the sheet S. 
     The sheet S having the image on the second face is further conveyed, and the image on the second face of the sheet S is fixed to the sheet S by the fixing roller pair  123 . Then, the sheet S is conveyed to the image reading device  1  described in the above-described embodiments including the first embodiment. 
     The sheet S for image formation passes through the image reading device  1  where the first face of the sheet S is read. Then, the sheet S for image formation is reversed with the first face down by the reverse conveyance passage  17  and then is conveyed to the reversal passage  125 . Then, the sheet S for image formation is conveyed by a conveyance roller pair  19 C, to the image reading device  1  again. After the second face of the sheet S is read by the image reading device  1 , the sheet S is ejected to the sheet ejection tray  126 A. 
     The cleaning sheet  46  that is conveyed from the sheet feed tray  121 B is conveyed through the conveyance passage  122 B to the image reading device  1 . The cleaning sheet  46  that has passed through the image reading device  1  is ejected to the sheet ejection tray  126 B. 
     As described above, the sheet S for image formation and cleaning sheet  46  are ejected to different sheet ejection trays. By so doing, even when a cleaning operation is performed in continuous printing, the cleaning sheet  46  is prevented from being mixed into the sheets S for image formation. 
     The cleaning sheet  46  that is conveyed from the sheet feed tray  121 B does not pass the transfer unit  113  and the fixing roller pair  123 , thereby restraining damage on the cleaning sheet  46  due to toner contamination and heat. 
     Next, a description is given of control of a cleaning operation in continuous printing by a controller according to the present embodiment, with reference to a flowchart in  FIG. 18 . 
       FIG. 18  is a flowchart of a first control flow in a cleaning operation executed by a controller according to the present embodiment. 
     The first example is same as the examples illustrated in  FIGS. 4A, 4B, 7A, and 7B  of the first embodiment, in which one of the exposure glass  12  and the background switching revolver  13  (one of the cleaning targets) is wiped and cleaned in one conveyance of the cleaning sheet  46 . 
     First, the cleaning sheet  46  that is conveyed from the sheet feed tray  121 B is conveyed as illustrated in  FIGS. 4A and 7A  to wipe and clean the exposure glass  12  (S 11 ). At this time, the controller  150  controls so that the number of rotations of the downstream conveyance roller  14   a  is greater than the number of rotations of the upstream conveyance roller  15   a . In other words, the controller  150  controls to satisfy the following relation: the number of rotations of the downstream conveyance roller  14   a &gt;the number of rotations of the upstream conveyance roller  15   a.    
     Thereafter, the cleaning sheet  46  is conveyed to the reverse conveyance passage  17  (S 12 ), where the cleaning sheet  46  is reversed with the first face down and is conveyed to the image reading device  1  again. At this time, the cleaning sheet  46  is conveyed as illustrated in  FIGS. 4B and 7B  to wipe and clean the circumferential surface of the background switching revolver  13 , that is, the circumferential surface of the black background roller  13   a  or the circumferential surface of the white background roller  13   b  (S 13 ). At this time, the controller  150  controls so that the number of rotations of the downstream conveyance roller  14   a  is smaller than the number of rotations of the upstream conveyance roller  15   a . In other words, the controller  150  controls to satisfy the following relation: the number of rotations of the downstream conveyance roller  14   a &lt;the number of rotations of the upstream conveyance roller  15   a.    
     Thereafter, the cleaning sheet  46  is ejected to the sheet ejection tray  126 B (S 14 ). 
     Next, a description is given of control of a cleaning operation in continuous printing by a controller according to the present embodiment, with reference to a flowchart in  FIG. 19 . 
       FIG. 19  is a flowchart of a second control flow in a cleaning operation executed by the controller according to the present embodiment. 
     The second example is same as the examples illustrated in  FIGS. 9A, 9B, 10A, and 10B  of the third embodiment, in which the exposure glass  12  and the background switching revolver  13  (both cleaning targets) are wiped and cleaned in one conveyance of the cleaning sheet  46 . 
     First, the cleaning sheet  46  that is conveyed from the sheet feed tray  121 B, as illustrated in  FIGS. 10A and 10B , is conveyed as illustrated in  FIGS. 9A and 9B , so as to wipe and clean the exposure glass  12  and the circumferential surface of the background switching revolver  13 , that is, the circumferential surface of the black background roller  13   a  or the circumferential surface of the white background roller  13   b  (S 21 ). At this time, the controller  150  controls so that the number of rotations of the downstream conveyance roller  14   a  is greater than the number of rotations of the upstream conveyance roller  15   a . In other words, the controller  150  controls to satisfy the following relation: the number of rotations of the downstream conveyance roller  14   a &gt;the number of rotations of the upstream conveyance roller  15   a.    
     Then, the controller  150  determines whether or not another cleaning is to be performed (S 22 ). 
     When another cleaning is not to be performed (NO in S 22 ), the cleaning sheet  46  is ejected to the sheet ejection tray  126 B (S 25 ), and the process ends. 
     As described above, since the exposure glass  12  and the circumferential surface of the background switching revolver  13  (both cleaning targets) are wiped and cleaned in one conveyance of the cleaning sheet  46 , the cleaning sheet  46  is not conveyed in the reverse conveyance passage  17  to be further conveyed to the image reading device  1  again. 
     On the other hand, when another cleaning is to be performed, in other words, multiple cleanings are to be performed (YES in S 22 ), the cleaning sheet  46  is conveyed to the reverse conveyance passage  17  (S 23 ). Then, the cleaning sheet  46  is conveyed as illustrated in  FIGS. 9A and 9B , so as to wipe and clean the exposure glass  12  and the circumferential surface of the background switching revolver  13 , that is, the circumferential surface of the black background roller  13   a  or the circumferential surface of the white background roller  13   b  (S 24 ). At this time, the controller  150  controls so that the number of rotations of the downstream conveyance roller  14   a  is greater than the number of rotations of the upstream conveyance roller  15   a . In other words, the controller  150  controls to satisfy the following relation: the number of rotations of the downstream conveyance roller  14   a &gt;the number of rotations of the upstream conveyance roller  15   a.    
     Thereafter, the cleaning sheet  46  is ejected to the sheet ejection tray  126 B (S 25 ), and the process ends. 
     Note that the process of cleaning is completed after performing the cleaning operation twice. However, after completion of the cleaning in step S 24 , the process may return to step S 22  in which the controller  150  determines whether further cleaning is to be performed or not. By so doing, the cleaning may be performed for three or more times. 
     Next, a description is given of an image reader included in an image forming apparatus according to a ninth embodiment of the present disclosure, with reference to  FIG. 20 . 
       FIG. 20  is a side view of an image reader included in an image forming apparatus according to the ninth embodiment of the present disclosure. 
     The configuration of the image forming apparatus according to the present embodiment is similar to the configuration of the image forming apparatus according to the seventh embodiment, except that the image forming apparatus according to the present embodiment includes an image reader  130  including two readers. The image reader  130  includes a downstream reader  130   a  and an upstream reader  130   b . The upstream reader  130   b  is constructed by an image reading device  1 B and the downstream reader  130   a  is constructed by an image reading device  1 A. 
     The image reading device  1 B includes an irradiation unit  11   bb  and a line image sensor. The irradiation unit  11   bb  irradiates a sheet S with light when the sheet S passes through a reading position. The line image sensor includes imaging elements  11   ab  that perform photoelectric conversion for each pixel. The imaging elements  11   ab  are disposed in a one-dimensional shape along a direction orthogonal to the conveyance direction of the sheet S. 
     The image reading device  1 B repeatedly performs a reading operation of an image for one line extending in the conveyance direction of the sheet S in accordance with a passing operation of the sheet S that passes the reading position, so as to read the image printed on the sheet S as a two-dimensional image. 
     The background switching revolver  13 B is disposed at a position facing the reading unit  11 B across the conveyance passage and reflects irradiation light with which the sheet S is irradiated when reading an image. 
     An exposure glass  12   b  that functions as a transparent member is disposed on the front face of the reading unit  11 B and is disposed facing the background switching revolver  13 B. The exposure glass  12   b  penetrates light emitted from the reading unit  11 B and reflected light returning after the emitted light is reflected by the background switching revolver  13 B and the sheet S. 
     An upstream conveyance roller pair  14 B including an upstream conveyance roller  14   ab  is disposed upstream from the reading unit  11 B in the conveyance direction of the sheet S. A downstream conveyance roller pair  15 B including a downstream conveyance roller  15   ab  is disposed downstream from the reading unit  11 B in the conveyance direction of the sheet S. 
     The image reading device  1 A includes an irradiation unit  11   ba  and a line image sensor. The irradiation unit  11   ba  irradiates a sheet S with light when the sheet S passes through a reading position. The line image sensor includes imaging elements  11   aa  that perform photoelectric conversion for each pixel. The imaging elements  11   aa  are disposed in a one-dimensional shape along a direction orthogonal to the conveyance direction of the sheet S. 
     The image reading device  1 A repeatedly performs a reading operation of an image for one line extending in the conveyance direction of the sheet S in accordance with a passing operation of the sheet S that passes the reading position, so as to read the image printed on the sheet S as a two-dimensional image. 
     The background switching revolver  13 A is disposed at a position facing the reading unit  11 A across the conveyance passage and reflects irradiation light with which the sheet S is irradiated when reading an image. 
     An upstream conveyance roller pair  14 A including an upstream conveyance roller  14   aa  is disposed upstream from the reading unit  11 A in the conveyance direction of the sheet S. A downstream conveyance roller pair  15 A including a downstream conveyance roller  15   aa  is disposed downstream from the reading unit  11 A in the conveyance direction of the sheet S. 
     Next, a description is given of cleaning operations with respect to the upstream reader according to the present embodiment, with reference to a flowchart in  FIG. 21 . 
       FIG. 21  is a flowchart of a control flow in a cleaning operation performed on upstream reader according to the ninth embodiment of the present disclosure. 
     First, the cleaning sheet  46  that is conveyed from the sheet feed tray  121 B is conveyed to wipe and clean the exposure glass  12   b  of the image reading device  1 B that is disposed upstream in the conveyance direction of the cleaning sheet  46  in the image reader  130  in  FIG. 20  (S 41 ). At this time, the controller  150  controls so that the number of rotations of the downstream conveyance roller  14   ab  is greater than the number of rotations of the upstream conveyance roller  15   ab . In other words, the controller  150  controls to satisfy the following relation: the number of rotations of the downstream conveyance roller  14   ab &gt;the number of rotations of the upstream conveyance roller  15   ab.    
     Thereafter, the controller  150  determines whether the trailing end of the cleaning sheet  46  has passed the downstream conveyance roller  15   ab  (S 42 ). 
     When the trailing end of the cleaning sheet  46  has not passed the downstream conveyance roller  15   ab  (NO in S 42 ), step S 42  is repeated until the trailing end of the cleaning sheet  46  passes the downstream conveyance roller  15   ab . When the trailing end of the cleaning sheet  46  has passed the downstream conveyance roller  15   ab  (YES in S 42 ), the cleaning sheet  46  that is reversed with the first face down is conveyed (S 43 ). 
     The reversed cleaning sheet  46  wipes and cleans the circumferential surface of the background switching revolver  13 B of the image reading device  1 B disposed upstream in the image reader  130  in the conveyance direction of the cleaning sheet  46  (S 44 ). At this time, the controller  150  controls so that the number of rotations of the downstream conveyance roller  14   ab  is smaller than the number of rotations of the upstream conveyance roller  15   ab . In other words, the controller  150  controls to satisfy the following relation: the number of rotations of the downstream conveyance roller  14   ab &lt;the number of rotations of the upstream conveyance roller  15   ab.    
     Thereafter, the controller  150  determines whether the trailing end of the cleaning sheet  46  has passed the downstream conveyance roller  15   ab  (S 45 ). When the trailing end of the cleaning sheet  46  has not passed the downstream conveyance roller  15   ab  (NO in S 45 ), step S 45  is repeated until the trailing end of the cleaning sheet  46  passes the downstream conveyance roller  15   ab . When the trailing end of the cleaning sheet  46  has passed the downstream conveyance roller  15   ab  (YES in S 45 ), the process ends. 
     Next, a description is given of cleaning operations with respect to the downstream reading device according to the present embodiment, with reference to a flowchart in  FIG. 22 . 
       FIG. 22  is a flowchart of a control flow in a cleaning operation performed on a downstream reading unit according to the ninth embodiment of the present disclosure. 
     First, the cleaning sheet  46  that has passed the image reading device  1 B disposed upstream in the image reader  130  in the conveyance direction of the cleaning sheet  46  or another cleaning sheet  46  that is newly conveyed from the sheet feed tray  121 B is conveyed to wipe and clean the circumferential surface of the background switching revolver  13 A of the image reading device  1 A disposed downstream in the image reader  130  in the conveyance direction of the cleaning sheet  46  in  FIG. 20  (S 51 ). At this time, the controller  150  controls so that the number of rotations of the downstream conveyance roller  14   aa  is greater than the number of rotations of the upstream conveyance roller  15   aa . In other words, the controller  150  controls to satisfy the following relation: the number of rotations of the downstream conveyance roller  14   aa &gt;the number of rotations of the upstream conveyance roller  15   aa.    
     Thereafter, the controller  150  determines whether the trailing end of the cleaning sheet  46  has passed the downstream conveyance roller  15   aa  (S 52 ). 
     When the trailing end of the cleaning sheet  46  has not passed the downstream conveyance roller  15   aa  (NO in S 52 ), step S 52  is repeated until the trailing end of the cleaning sheet  46  passes the downstream conveyance roller  15   aa . When the trailing end of the cleaning sheet  46  has passed the downstream conveyance roller  15   aa  (YES in S 52 ), the cleaning sheet  46  is conveyed to the image reading device  1 A disposed downstream in the image reader  130  in the conveyance direction of the cleaning sheet  46  and is reversed with the first face down, so that the cleaning sheet  46  wipes and cleans the exposure glass  12   a  (S 53 ). At this time, the controller  150  controls so that the number of rotations of the downstream conveyance roller  14   aa  is smaller than the number of rotations of the upstream conveyance roller  15   aa . In other words, the controller  150  controls to satisfy the following relation: the number of rotations of the downstream conveyance roller  14   aa &lt;the number of rotations of the upstream conveyance roller  15   aa.    
     Thereafter, the controller  150  determines whether the trailing end of the cleaning sheet  46  has passed the downstream conveyance roller  15   aa  (S 54 ). When the trailing end of the cleaning sheet  46  has not passed the downstream conveyance roller  15   aa  (NO in S 54 ), step S 54  is repeated until the trailing end of the cleaning sheet  46  passes the downstream conveyance roller  15   aa . When the trailing end of the cleaning sheet  46  has passed the downstream conveyance roller  15   aa  (YES in S 54 ), the process ends. 
     Next, a description is given of a black background roller of a background switching revolver according to a tenth embodiment of the present disclosure, with reference to  FIG. 23 . 
       FIG. 23  is a diagram illustrating a black background roller of a background switching revolver according to the tenth embodiment of the present disclosure, for explaining a relation of the black background roller and each of the width of a sheet and the width of a cleaning sheet. 
     In the present embodiment, cleaning is performed with a cleaning sheet that has a width wider than the width of a sheet S to be read by the image reading device  1 . In other words, cleaning is performed with a cleaning sheet that has a width wider than the width of the sheet S in a direction orthogonal to the conveyance direction of the sheet S. 
     When reading a white sheet S, the background roller of the background switching revolver  13  is switched to the black background roller  13   a . By so doing, the reading unit  11  reads the end boundary of the white sheet S. 
     A width L 2  of the cleaning sheet  46  is preferably greater than the maximum width L 1  of sheet S to be conveyed. As a result, the cleaning sheet  46  wipes and cleans dirt on the black background roller  13   a  near the maximum width of sheet S. Due to this configuration, degradation in reading of the end boundary of the sheet S having the maximum width is restrained. 
     The present disclosure is not limited to specific embodiments described above, and numerous additional modifications and variations are possible in light of the teachings within the technical scope of the appended claims. It is therefore to be understood that, the disclosure of this patent specification may be practiced otherwise by those skilled in the art than as specifically described herein, and such, modifications, alternatives are within the technical scope of the appended claims. Such embodiments and variations thereof are included in the scope and gist of the embodiments of the present disclosure and are included in the embodiments described in claims and the equivalent scope thereof. 
     The effects described in the embodiments of this disclosure are listed as the examples of preferable effects derived from this disclosure, and therefore are not intended to limit to the embodiments of this disclosure. 
     The embodiments described above are presented as an example to implement this disclosure. The embodiments described above are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other forms, and various omissions, replacements, or changes can be made without departing from the gist of the invention. These embodiments and their variations are included in the scope and gist of this disclosure and are included in the scope of the invention recited in the claims and its equivalent. 
     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.