Patent Publication Number: US-2023164277-A1

Title: Image reading apparatus and image forming system

Description:
BACKGROUND 
     Field 
     The present disclosure relates to an image reading apparatus that reads an image on a sheet and an image forming system including the same. 
     Description of the Related Art 
     There are known image forming systems equipped with an image reading apparatus that reads an image on a sheet formed by the image forming unit. In some image reading apparatuses used in the above-described image forming systems, the reading unit reads an image on a sheet through a transparent member that forms a conveyance path along which the sheet is conveyed. Japanese Patent Application Laid-Open No. 2021-125802 discusses an image reading apparatus in which a reading unit that reads the image on the top side of a sheet is arranged downstream of another reading unit that reads the image on the back side of the sheet to read the images on both sides of the sheet received from the image forming unit. Further, the image reading apparatus discussed in Japanese Patent Application Laid-Open No. 2021-125802 includes an opposing roller for stabilizing the distance between a sheet and a reading unit at the reading position arranged opposed to the transparent member of the conveyance path. The opposing roller is arranged at a position opposed to the reading unit on either side and is rotatable by a driving mechanism. 
     However, when the trailing edge of a sheet exits from the opposing roller opposed to the reading unit upstream, the speed of the sheet sometimes temporarily varies. Such varying conveyance speed of a sheet can create partial expansion or reduction of the read image, resulting in a reading failure. 
     SUMMARY 
     The present disclosure is directed to reduction of reading failures of images on sheets in an image reading apparatus that reads images on the sheets formed by the image forming unit. 
     According to an aspect of the present disclosure, an image reading apparatus includes a first conveyance roller configured to convey a sheet along a conveyance path, a first transparent member configured to be arranged on the conveyance path and to be opposed to a first surface of the sheet conveyed by the first conveyance roller, a first reading unit configured to read an image on the first surface of the sheet through the first transparent member at a first reading position, a first opposing roller configured to be rotatable, to be opposed to the first transparent member at the first reading position, and to be opposed to a second surface opposite to the first surface of the sheet, a driving unit configured to drive the first opposing roller, a second transparent member configured to be arranged on the conveyance path and to be opposed to the second surface of the sheet conveyed by the first conveyance roller, a second reading unit configured to read an image on the second surface of the sheet through the second transparent member at a second reading position downstream of the first reading position in a conveyance direction of the first conveyance roller, a second opposing roller configured to be rotatable, to be opposed to the second transparent member at the second reading position, and to be opposed to the first surface of the sheet, and a second conveyance roller configured to convey the sheet when the second reading unit reads the image on the sheet, wherein the second conveyance roller is arranged at a position where a trailing edge of the sheet passes through the first reading position while the second conveyance roller is conveying the sheet, wherein the driving unit drives the first opposing roller so that a circumferential speed of the first opposing roller is faster than a circumferential speed of the second conveyance roller. 
     Further features of the present disclosure will become apparent from the following description of exemplary embodiments with reference to the attached drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is the overall view of an image forming system. 
         FIG.  2    is a cross-sectional view of an image reading apparatus. 
         FIG.  3    is a cross-sectional view of a stacking apparatus. 
         FIG.  4    is a side view of the image reading apparatus at a reading position. 
         FIG.  5    is a side view of the image reading apparatus at the reading position. 
         FIG.  6    illustrates a gap between a backing roller and a glass. 
         FIG.  7    illustrates the backing roller in conveying thick paper. 
         FIG.  8    illustrates a force when the thick paper passes through the backing roller. 
         FIGS.  9 A to  9 D  illustrate image scaling ratios in the sub scanning direction. 
         FIG.  10    is a flowchart illustrating control of the image forming system. 
     
    
    
     DESCRIPTION OF THE EMBODIMENTS 
     Exemplary embodiments for implementing the present disclosure will be described in detail below with reference to the attached drawings. However, components described in the following exemplary embodiments can be appropriately modified in dimension, material, shape, and relative position with configurations and various conditions of an apparatus to which the present disclosure is applied, and are not intended to limit the scope of the present disclosure. 
     [Configuration of Image Forming Apparatus] 
       FIG.  1    is the overall view of an image forming system  100  according to the present exemplary embodiment. The image forming system  100  is a system in which a printer  101 , an image reading apparatus  102 , and a stacking apparatus  103  are connected. The image forming system  100  includes an operation unit  21  for users to perform various inputs to the image forming system  100 . 
     The printer  101 , which is an image forming apparatus, is a full color printer using an electrophotographic process with four colors. The printer  101  forms a toner image on a recording material based on an image signal input to a control unit  301  from an information terminal such as a personal computer (PC) or an external apparatus  300  such as an image reader. The recording material is a recording medium (hereinafter, referred to as a sheet P) on which a toner image can be formed, and plain paper, thick paper, super-thick paper, an overhead projector (OHP) sheet, coated paper, label paper, and other types of paper can be used as the recording material. 
     The printer  101  includes four image forming mechanism units  101   a  as image forming units that each form a toner image in the corresponding color among yellow (Y), magenta (M), cyan (C), and black (Bk). The image forming mechanism units  101   a  form toner images using the conventionally known electrophotographic process. These four image forming mechanism units  101   a  are arranged in parallel from left to right in  FIG.  1   . 
     A laser scanner unit  3 , which is an exposure apparatus, is arranged above each image forming mechanism unit  101   a , and an intermediate transfer belt  50  is arranged below the image forming mechanism units  101   a . The intermediate transfer belt  50  is stretched around a driving roller  51 , a tension roller  52 , and an inner secondary transfer roller  53 , and is driven in the direction of an arrow in  FIG.  1   . 
     Each of the image forming mechanism units  101   a  has a similar electrophotographic process configuration and differs only in the color of toner (developer) to be used. Each image forming mechanism unit  101   a  includes a photosensitive drum  1  as an image bearing member, a charger  2 , a development unit  4 , a primary transfer roller  6 , and a drum cleaner  7 . In  FIG.  1   , the reference numerals of the image forming mechanism units  101   a  other than the image forming mechanism unit  101 a for black (Bk) are omitted to avoid complication of the drawing. 
     The toner image in each color is primarily transferred from the photosensitive drum  1  of the image forming mechanism unit  101   a  to the intermediate transfer belt  50  to be superimposed one by one. This process forms an unfixed full-color toner image with the four color toners of Y, M, C, and Bk superimposed on the intermediate transfer belt  50 . 
     The printer  101  includes a cassette  24  in which the sheet P is stored. The sheet P fed from the cassette  24  passes through a conveyance path  13  and is conveyed into a secondary transfer nip portion  15 , which is a pressure contact portion between the intermediate transfer belt  50  and a secondary transfer roller  14 , at a predetermined control timing. Then, the superimposed four-color toner image on the intermediate transfer belt  50  is secondarily transferred onto the sheet P. Then, the residual toner remaining on the intermediate transfer belt  50  after the secondary transfer to the sheet P is removed from the surface of the intermediate transfer belt  50  by a belt cleaner  19 . 
     Then, the sheet P with the toner image transferred thereon is conveyed into a fixing device  16  and is subjected to fixing processing of heating and pressing. After passing through the fixing device  16 , the sheet P is discharged from the printer  101  by a discharging roller pair  17  and is conveyed to the image reading apparatus  102 . In duplex printing, the sheet P with an image formed on one surface passes through a reverse conveyance path  57  and is conveyed again to the secondary transfer nip portion  15 . 
     Each image forming unit of the printer  101  according to the present exemplary embodiment has a configuration using the electrophotographic process, but may have a configuration using another image forming system such as an ink-jet system. 
     [Configuration of Image Reading Apparatus] 
       FIG.  2    is a cross-sectional view of the image reading apparatus  102 . The image reading apparatus  102  reads an image on a sheet formed by the printer  101 . The image reading apparatus  102  includes a conveyance path  123  along which the sheet conveyed from the printer  101  is conveyed. The conveyance path  123  is a nearly horizontal conveyance path formed by an upper conveyance guide  121  and a lower conveyance guide  122 . Inlet conveyance rollers  111  and  112  as first conveyance rollers and outlet conveyance rollers  119  and  120  as second conveyance rollers are arranged on the conveyance path  123 . The inlet conveyance rollers  111  and  112  are rollers that receive the sheet discharged from the printer  101  upstream of the image reading apparatus  102 . The outlet conveyance rollers  119  and  120  are rollers that discharge the sheet to the stacking apparatus  103  downstream of the image reading apparatus  102 . 
     A first reading unit  113  and a second reading unit  116  are arranged in an image reading unit  147  of the image reading apparatus  102 . The first reading unit  113  reads an image on the lower surface (a first surface) of the sheet, and the second reading unit  116  reads an image on the upper surface (a second surface) of the sheet. This configuration allows the image reading apparatus  102  to read the images on both surfaces of the sheet. The second reading unit  116  is at a position downstream of the first reading unit  113  in the conveyance direction of the conveyance path  123 , and the reading position (a second reading position) of the second reading unit  116  is downstream of the reading position (a first reading position) of the first reading unit  113 . The first reading unit  113  and the second reading unit  116  are, for example, contact image sensors (CIS) or charge coupled device (CCD) cameras. 
     The images read by the first reading unit  113  and the second reading unit  116  are transmitted as signals to an external PC  305 . The external PC  305  compares the images read by the first reading unit  113  and the second reading unit  116  with the corresponding image data registered in advance and detects an image defect such as dirt on the sheet. This manner allows the external PC  305 , which is a determination unit, to determine whether the sheet on which the image is formed by the printer  101  is normal. 
     According to the present exemplary embodiment, the external PC  305  is provided outside the image reading apparatus  102 , but may be provided integrally with the image reading apparatus  102  or the printer  101 . 
     A glass  114 , which is a first transparent member and forms a part of the conveyance path  123 , is incorporated in the lower conveyance guide  122 . The glass  114  faces the lower surface of the sheet being conveyed. The image on the lower surface of the sheet conveyed along the conveyance path  123  is read by the first reading unit  113  through the glass  114 . 
     A backing roller  115  is arranged at a position opposed to the glass  114  of the conveyance path  123 . The backing roller  115  is an example of a first opposing roller according to the present exemplary embodiment. The backing roller  115  is arranged at the reading position of the first reading unit  113  in the conveyance direction. The backing roller  115  is supported by the upper conveyance guide  121 . The backing roller  115  can be rotationally driven by a driving gear  351  connected to a driving motor  350 , which is a first motor (refer to  FIG.  4    described below). The driving gear  351  transmits driving force from the driving motor  350  to the backing roller  115 . The pair of driving motor  350  and the driving gear  351  are an example of a driving unit according to the present exemplary embodiment. 
     A glass  117 , which is a second transparent member and forms a part of the conveyance path  123 , is incorporated in the upper conveyance guide  121 . The glass  117  faces the upper surface of the sheet being conveyed. The image on the upper surface of the sheet conveyed along the conveyance path  123  is read by the second reading unit  116  through the glass  117 . 
     A backing roller  118  is arranged at a position opposed to the glass  117  of the conveyance path  123 . The backing roller  118  is an example of a second opposing roller according to the present exemplary embodiment. The backing roller  118  is arranged at the reading position of the second reading unit  116  in the conveyance direction. The backing roller  118  is supported by the lower conveyance guide  122 . The backing roller  118  can be rotationally driven by a second motor, which is not illustrated, in the same manner as the backing roller  115 . The pressure with which the backing rollers  115  and  118  press the sheet is smaller than the nip pressure between the outlet conveyance rollers  119  and  120 . 
     The sheet of which the images are read by the first reading unit  113  and the second reading unit  116  is conveyed from the image reading apparatus  102  to the stacking apparatus  103  by the outlet conveyance rollers  119  and  120 . A control apparatus  302 , which is a control unit, controls the driving of each roller in the image reading apparatus  102 , and controls the first reading unit  113 , and the second reading unit  116 . Each roller, the first reading unit  113 , the second reading unit  116 , and the control apparatus  302  described above are housed inside a housing  136  of the image reading apparatus  102 . 
     [Configuration of Stacking Apparatus] 
       FIG.  3    is a cross-sectional view of the stacking apparatus  103 . Sheets conveyed from the image reading apparatus  102  to the stacking apparatus  103  are stacked in a first stacking unit  158  or a second stacking unit  165 . A flapper  155  switches between conveyance paths  153  and  154  to and along which the sheet is to be conveyed. 
     If the sheet is discharged to the first stacking unit  158 , the sheet is conveyed along the conveyance path  153  by conveyance rollers  151  and  152  and conveyance rollers  156  and  157 . If the sheet is discharged to the second stacking unit  165 , the sheet is guided to the conveyance path  154  by the flapper  155  and is conveyed by conveyance rollers  159  and  160 , conveyance rollers  161  and  162 , and conveyance rollers  163  and  164 . A control unit  303  controls the driving of each conveyance roller and the flapper  155 . 
     As described above, the image forming system  100  can inspect the image read by the image reading apparatus  102 . The control unit  303  controls each conveyance roller and the flapper  155  to discharge the sheet determined to be normal by the external PC  305  to the first stacking unit  158  and to discharge the sheet determined to be abnormal by the external PC  305  to the second stacking unit  165 . 
     [Description of Image Reading Unit] 
       FIG.  4    is a side view of the first reading unit  113  and the backing roller  115  with a sheet  201  having a thickness t of less than 0.4 millimeter [mm] conveyed therein. An example of the sheet  201  having a thickness t of less than 0.4 [mm] is plain paper generally used for printing. 
     As illustrated in  FIG.  4   , abutting units  131  that abut on the glass  114  are arranged at both ends of the backing roller  115  in the width direction of the backing roller  115  (perpendicular to the conveyance direction). The backing roller  115  is movable in a direction separating from the glass  114  (upward in  FIG.  4   ) and is urged toward the glass  114  by springs  135 , which are an urging member. At this time, the abutting units  131 , which are a gap forming unit, abut on the glass  114 , forming a gap  133  between the glass  114  and the backing roller  115 . 
     According to the present exemplary embodiment, the gap  133  is approximately 0.4 [mm], and the backing roller  115  prevents the sheet  201  being conveyed from floating above the glass  114  by 0.4 [mm] or more. Since the thickness of the sheet  201  is less than 0.4 [mm], the sheet  201  does not lift the backing roller  115 . Thus, when the sheet  201  is being conveyed, the abutting unit  131  remains abutting on the glass  114 . The second reading unit  116  downstream is also configured with a mechanism similar to the first reading unit  113  and the backing roller  115 , except that it is disposed upside down. 
       FIG.  5    is a side view of the first reading unit  113  and the backing roller  115  with a sheet (super-thick paper)  202  having a thickness t of 0.4 [mm] or more conveyed therein. 
     As illustrated in  FIG.  5   , the thickness of the sheet  202  is greater than the original gap  133 , so that the sheet  202  lifts the backing roller  115  against the urging force of the springs  135 , and the abutting units  131  are lifted up from the glass  114 . At this time, the lower surface of the sheet  202  is in close contact with the glass  114 , so that the first reading unit  113  can correctly read the image on the sheet  202 . 
     If the gap  133  is set wider, it is not possible to regulate floating of the sheet  201  having a thickness t of less than 0.4 [mm] in the depth direction (a direction perpendicular to the surface of the glass  114 ), which may result in a reading failure. According to the present exemplary embodiment, the gap  133  is set at 0.4 [mm], which is a range in which the first reading unit  113  and the second reading unit  116  can read the image correctly. If the sheet  202  having a thickness t of 0.4 [mm] or more, the backing roller  115  is pushed and lifted by the sheet being conveyed, causing the gap  133  to be changed. Thus, the image reading apparatus  102  can read images on sheets of various thicknesses. According to the present exemplary embodiment, the gap  133  is 0.4 [mm], but the gap between the glass  114  and the backing roller  115  is not limited to this value and is desirable to be set appropriately based on the performance of the reading units. 
       FIG.  6    is an enlarged view of the backing roller  115  with the sheet  201  (a second sheet) having a thickness t of less than 0.4 [mm] conveyed therein. The sheet  201  is conveyed at a movement speed (a conveyance speed) Vs. The outlet conveyance rollers  119  and  120  are provided at positions at which the outlet conveyance rollers  119  and  120  are in contact with the sheet while the second reading unit  116  reads the image on the sheet. Thus, the conveyance speed Vs is almost the same as the circumferential speed of the outlet conveyance rollers  119  and  120  located downstream of the first reading unit  113 . Then, while the outlet conveyance rollers  119  and  120  convey the sheet, the trailing edge of the sheet passes over the reading position of the first reading unit  113  (between the glass  114  and the backing roller  115 ). According to the present exemplary embodiment, a circumferential speed is the speed of the outer surface of a roller in rotation. 
     The backing roller  115  rotates at a circumferential speed Vb. According to the present exemplary embodiment, the control apparatus  302  controls the driving motor  350  in such a manner that the circumferential speed Vb of the backing roller  115  is faster than the conveyance speed Vs. In other words, the circumferential speed Vb of the backing roller  115  is set to a value faster than the circumferential speed of the outlet conveyance rollers  119  and  120 . When the sheet  201  is conveyed, the backing roller  115  does not move in the direction separating from the glass  114 . 
     As illustrated in  FIG.  6   , the backing roller  115  is driven to rotate at the circumferential speed Vb, and when the sheet  201  having a thickness t of less than 0.4 [mm] is conveyed, there is a gap between the backing roller  115  and the sheet  201 . Thus, the sheet conveyance force applied to the sheet  201  by the backing roller  115  is extremely small. Thus, the speed difference between the conveyance speed Vs and the circumferential speed Vb of the backing roller  115  has almost no effect on the image reading of the sheet  201 . 
       FIG.  7    is an enlarged view of the backing roller  115  with the sheet  202  (a first sheet) having a thickness t of 0.4 [mm] or more conveyed therein. As illustrated in  FIG.  7   , when the sheet  202  is conveyed, the backing roller  115  is pushed by the sheet  202  and is moved in the direction separating from the glass  114 . At this time, the backing roller  115  is in contact with the sheet  202 . However, the pressure with which the backing roller  115  presses the sheet is set smaller than the nip pressure between the outlet conveyance rollers  119  and  120 , so that the speed difference between the conveyance speed Vs and the circumferential speed Vb of the backing roller  115  has almost no effect on the image reading of the sheet  202 . The sheet  202  having a thickness t of 0.4 [mm] or more has higher rigidity than the sheet  201  having a thickness t of less than 0.4 [mm] and is hard to deform, and the backing roller  115  slips on the sheet  202 . This reduces the effect on the image reading of the sheet  202  due to the speed difference between the conveyance speed Vs and the circumferential speed Vb of the backing roller  115 . The pressure with which the backing roller  115  presses the sheet is determined by the springs  135 . 
       FIG.  8    is an enlarged view of the backing roller  115  when the trailing edge of the sheet  202  having a thickness t of 0.4 [mm] or more exits the backing roller  115 . As illustrated in  FIG.  8   , when the trailing edge of the sheet  202  exits the backing roller  115 , the trailing edge of the sheet  202  is advancing by an angle θ from immediately under the rotation center of the backing roller  115  in the conveyance direction. At this time, the component in the conveyance direction of the circumferential speed Vb of the backing roller  115  at a point where the sheet  202  is in contact with the backing roller  115  is expressed as Vb×cos(θ). 
     Supposing the circumferential speed Vb of the backing roller  115  is set to the same speed as the conveyance speed Vs (Vb=Vs), the component Vb×cos(θ) is smaller than the conveyance speed Vs (Vb×cos(θ)&lt;Vs). As a result, the sheet is pulled by the outlet conveyance rollers  119  and  120  and the backing roller  115 , so that a shock that occurs when the sheet  202  is released from the pull out of contact with the backing roller  115  could lead to an image defect in the second reading unit  116 . 
     On the other hand, according to the present exemplary embodiment, the circumferential speed Vb of the backing roller  115  is set to the value faster than the conveyance speed Vs. More specifically, the circumferential speed Vb of the backing roller  115  is set to a value satisfying Vs&lt;Vb×cos(θ). Thus, the sheet is not pulled by the outlet conveyance rollers  119  and  120  and the backing roller  115 . In other words, the shock is prevented, which prevents the image defect in the second reading unit  116  downstream from occurring. 
     According to the present exemplary embodiment, as an example, the conveyance speed Vs is 100 [mm/S], the circumferential speed Vb of the backing roller  115  is 103 [mm/S], and the outer diameter of the backing roller  115  is 20 [mm]. If the thickness t of the sheet  202  is 0.5 [mm], the angle θ is about 8.1°, and the component Vb×cos(θ)=101.97 [mm/S]. In other words, the circumferential speed Vb of the backing roller  115  has a value satisfying Vs&lt;Vb×cos(θ). 
     [Description of Disturbance in Image Scaling Ratio] 
       FIGS.  9 A to  9 D  are graphs indicating image scaling ratios in the sub scanning direction of image reading when the second reading unit  116  downstream reads an image on a sheet (super-thick paper) having a thickness t of about 0.5 [mm]. In  FIGS.  9 A to  9 D , the vertical axes and the horizontal axes of the graphs respectively indicate image scaling ratios and sheet conveyance distances, respectively. The image scaling ratios are ratios of enlargement and reduction of a read image at a predetermined pitch in the conveyance direction. It is desirable that the image scaling ratio is stable near 0%. In  FIGS.  9 A to  9 D , ratios of the circumferential speed Vb of the backing roller  115  to the conveyance speed Vs are respectively different.  FIG.  9 A  is a graph when the circumferential speed Vb of the backing roller  115  is 97% of (3% slower than) the conveyance speed Vs.  FIG.  9 B  is a graph when the circumferential speed Vb of the backing roller  115  is 100% of (the same speed as) the conveyance speed Vs.  FIG.  9 C  is a graph when the circumferential speed Vb of the backing roller  115  is 103% of (3% faster than) the conveyance speed Vs. 
       FIG.  9 D  is a graph when the circumferential speed Vb of the backing roller  115  is 106% of (6% faster than) the conveyance speed Vs. In other words,  FIGS.  9 A and  9 B  are the graphs when the circumferential speed Vb of the backing roller  115  is set to the circumferential speed of the outlet conveyance rollers  119  and  120  or less. Meanwhile,  FIGS.  9 C and  9 D  are the graphs when the circumferential speed Vb of the backing roller  115  is set to values greater than the circumferential speed of the outlet conveyance rollers  119  and  120 . 
     In  FIGS.  9 A to  9 D , the timing when the trailing edge of the sheet exits from the backing roller  115  corresponds to a value near  400  on the horizontal axis. At the timing when the trailing edge of the sheet exits from the backing roller  115 , the image scaling ratio of the read image of the second reading unit  116  can be disturbed as the speed of the sheet temporarily changes. 
     As illustrated in  FIG.  9 A , when the circumferential speed Vb of the backing roller  115  is 97% of (3% slower than) the conveyance speed Vs, the image scaling ratio is greatly disturbed, causing a reading failure to occur. As illustrated in  FIG.  9 B , even when the circumferential speed Vb of the backing roller  115  is 100% of (the same speed as) the conveyance speed Vs, the image scaling ratio is slightly disturbed. As illustrated in  FIG.  9 C , when the circumferential speed Vb of the backing roller  115  is 103% of (3% faster than) the conveyance speed Vs, the disturbance on the image scaling ratio is small, and positive and negative waveforms cancel each other out. As illustrated in  FIG.  9 D , when the circumferential speed Vb of the backing roller  115  is 106% of (6% faster than) the conveyance speed Vs, the image scaling ratio is slightly disturbed. 
     As described above, the circumferential speed Vb of the backing roller  115  is set to a value greater than the circumferential speed of the outlet conveyance rollers  119  and  120 , so that the image scaling ratio is stabilized, reducing reading failures. Further, it is desirable that the circumferential speed Vb of the backing roller  115  is 101% or more and 104% or less of the circumferential speed of the outlet conveyance rollers  119  and  120 . 
     [Description of Flowchart] 
     As illustrated in  FIG.  8   , when the thickness t of the sheet is greater than the gap  133 , the backing roller  115  is pushed and lifted up by the sheet. Thus, when the thickness t of a sheet is a predetermined thickness or more, the circumferential speed Vb of the backing roller  115  may be set to a value greater than the circumferential speed of the outlet conveyance rollers  119  and  120 . 
       FIG.  10    is a flowchart illustrating a reading operation corresponding to a paper type performed by the control apparatus  302 . In the image reading apparatus  102 , the circumferential speed Vb of the backing roller  115  can be set to a value greater than the circumferential speed of the outlet conveyance rollers  119  and  120  regardless of the paper type, but when the frequency of opportunities of conveying super-thick paper is small, the circumferential speed Vb of the backing roller  115  can be changed based on the paper type. 
     The control apparatus  302  starts processing in the flowchart illustrated in  FIG.  10    when a sheet is conveyed from the printer  101  to the image reading apparatus  102 . As illustrated in  FIG.  10   , in step S 101 , the control apparatus  302  acquires information about the sheet to be conveyed. At this time, the control apparatus  302  functions as an acquisition unit and refers to the information about the sheet input by a user using the operation unit  21 . The information about the sheet input by the user using the operation unit  21  is stored in the control unit  301 . 
     Next, in step S 102 , the control apparatus  302  determines whether the thickness t of the sheet is a predetermined thickness or greater based on the information about the sheet acquired in step S 101 . According to the present exemplary embodiment, the predetermined thickness is set to 0.4 [mm], but may be appropriately changed based on the width of the gap  133 . 
     If the thickness t of the sheet is the predetermined thickness or greater (YES in step S 102 ), in step S 103 , the control apparatus  302  performs a high-speed backing roller mode. The high-speed backing roller mode is a mode for controlling the driving motor  350  so that the circumferential speed Vb of the backing roller  115  is greater than the circumferential speed of the outlet conveyance rollers  119  and  120 . More specifically, in the high-speed backing roller mode, the control apparatus  302  sets the circumferential speed Vb of the backing roller  115  between 101% and 104%, inclusive, of the circumferential speed of the outlet conveyance rollers  119  and  120 . The circumferential speed Vb of the backing roller  115  at this time is defined as a first circumferential speed. 
     On the other hand, if the thickness t of the sheet is not the predetermined thickness or more (NO in step S 102 ), in step S 104 , the control apparatus  302  performs a normal-speed backing roller mode. The normal-speed backing roller mode is a mode for controlling the driving motor  350  so that the circumferential speed Vb of the backing roller  115  is equivalent to the circumferential speed of the outlet conveyance rollers  119  and  120 . The circumferential speed Vb of the backing roller  115  at this time is defined as a second circumferential speed. The second circumferential speed is slower than the first circumferential speed. 
     Then, in step S 105 , the control apparatus  302  performs image reading with the first reading unit  113  and the second reading unit  116  while conveying the sheet in the high-speed backing roller mode or the normal-speed backing roller mode. After the image reading is completed, the control apparatus  302  terminates the processing in the flowchart. 
     By the above-described processing in the flowchart, the control apparatus  302  performs the high-speed backing roller mode if the thickness of the sheet is a first thickness greater than or equal to the predetermined thickness, and performs the normal-speed backing roller mode if the thickness of the sheet is a second thickness less than the predetermined thickness. 
     In the processing in the flowchart in  FIG.  10   , the control apparatus  302  switches between the high-speed backing roller mode and the normal-speed backing roller mode based on the thickness t of the sheet. However, the control apparatus  302  can switch between the high-speed backing roller mode and the normal-speed backing roller mode based on the basis weight of the sheet. Specifically, the control apparatus  302  performs the high-speed backing roller mode if the basis weight of the sheet is a first basis weight greater than or equal to a predetermined basis weight, and performs the normal-speed backing roller mode if the basis weight of the sheet is a second basis weight less than the predetermined basis weight. 
     The control apparatus  302  can switch between the high-speed backing roller mode and the normal-speed backing roller mode based on whether the print job specifies duplex printing. Specifically, the control apparatus  302  performs the high-speed backing roller mode if the print job specifies duplex printing, and performs the normal-speed backing roller mode if the print job specifies simplex printing. 
     The above-described control enables the control apparatus  302  to set the circumferential speed Vb of the backing roller  115  to an appropriate value corresponding to the type of the sheet to be conveyed. 
     The image reading apparatus  102  may include another conveyance roller pair between the first reading position and the second reading position in the conveyance direction. In this case, it is desirable that the circumferential speed Vb of the backing roller  115  is faster than the circumferential speed of the other conveyance roller pair. 
     The image forming system  100  according to the present exemplary embodiment is a system in which the printer  101 , the image reading apparatus  102 , and the stacking apparatus  103  are connected, but the configuration of the image forming system  100  is not limited to this one. The image forming system  100  may include another apparatus not illustrated. For example, an inserter for inserting sheets may be arranged between the printer  101  and the image reading apparatus  102 . In this case, all apparatuses including the printer  101  arranged upstream of the image reading apparatus  102  are collectively referred to as an image forming apparatus. Further, for example, a cutting apparatus for cutting sheets may be arranged between the image reading apparatus  102  and the stacking apparatus  103 . In this case, all apparatuses including the stacking apparatus  103  arranged downstream of the image reading apparatus  102  are collectively referred to as a discharge apparatus. 
     According to the present exemplary embodiment, the circumferential speed of the backing roller  118  can be the same as the conveyance speed. In other words, when the circumferential speeds of the backing roller  115  and the backing roller  118  are compared, the circumferential speed of the backing roller  115  may be set faster than the circumferential speed of the backing roller  118 . In this case, the power consumption can be reduced as compared with a case where the backing roller  118  is rotated at high speed. 
     As described above, the image reading apparatus  102  according to the present exemplary embodiment sets the circumferential speed Vb of the backing roller  115  to be greater than the circumferential speed of the outlet conveyance rollers  119  and  120 . This reduces a shock that will occur when a sheet is released from the pull between rollers, reducing an image defect in the second reading unit  116  downstream. 
     Embodiments of the present disclosure can also be realized by a computer of a system or apparatus that reads out and executes computer executable instructions (e.g., one or more programs) recorded on a storage medium (which may also be referred to more fully as a ‘non-transitory computer-readable storage medium’) to perform the functions of one or more of the above-described Embodiments and/or that includes one or more circuits (e.g., application specific integrated circuit (ASIC)) for performing the functions of one or more of the above-described Embodiments, and by a method performed by the computer of the system or apparatus by, for example, reading out and executing the computer executable instructions from the storage medium to perform the functions of one or more of the above-described Embodiments and/or controlling the one or more circuits to perform the functions of one or more of the above-described Embodiments. The computer may include one or more processors (e.g., central processing unit (CPU), micro processing unit (MPU)) and may include a network of separate computers or separate processors to read out and execute the computer executable instructions. The computer executable instructions may be provided to the computer, for example, from a network or the storage medium. The storage medium may include, for example, one or more of a hard disk, a random-access memory (RAM), a read-only memory (ROM), a storage of distributed computing systems, an optical disk (such as a compact disc (CD), digital versatile disc (DVD), or Blu-ray Disc™ (BD)), a flash memory device, a memory card, and the like. 
     While the present disclosure has been described with reference to exemplary embodiments, it is to be understood that the disclosure is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions. 
     This application claims the benefit of Japanese Patent Application No. 2021-190495, filed Nov. 24, 2021, which is hereby incorporated by reference herein in its entirety.