Patent Publication Number: US-2022232137-A1

Title: Image reading apparatus and image forming system

Description:
BACKGROUND OF THE DISCLOSURE 
     Field of the Disclosure 
     The present disclosure relates to an image reading apparatus and an image forming system. 
     Description of the Related Art 
     Conventionally, in order to improve image quality, an inspection apparatus incorporating an image reading apparatus has been devised as a device configured to read an image output from an image forming apparatus such as a copying machine and to detect the presence or absence of a defect in the image. The inspection apparatus reads an image data printed on a sheet while conveying a recording material (hereinafter referred to as a sheet) such as a sheet of paper on a reading glass. Further, Japanese Patent Application Laid-Open No. H11-69043 discloses an image reading apparatus in which a guide configured to introduce a sheet is provided on the upstream side of the reading glass in the sheet conveyance direction in order to smoothly pass the sheet onto the reading glass. 
     However, if there is a gap between the reading glass and the image reading apparatus, a foreign substance such as paper dust and dirt may enter through the gap. When the foreign substance adheres to a back side of the reading glass or a sensor of the image reading apparatus, the foreign substance is included as noise in an image data read by the image reading apparatus. Therefore, good image data cannot be obtained. To this end, it is conceivable to arrange an elastic member such as a sponge made of a foamed material for preventing intrusion of foreign substance in the gap between the reading glass and the image reading apparatus. By disposing the sponge in a squeezed state between the reading glass and the image reading apparatus, the intrusion path of the foreign substance can be blocked. 
     However, the reaction force of the squeezed sponge deflects the reading glass toward an opposed member. When the reading glass is deflected, a gap between the reading glass and the opposed member becomes smaller than a set distance. Therefore, a focus position of the image reading apparatus is shifted, which causes an issue of not being able to obtain good reading data. 
     SUMMARY OF THE DISCLOSURE 
     This disclosure improves image reading performance by reducing deflection of the reading glass. 
     An image reading apparatus configured to read an image of a sheet conveyed from an image forming apparatus configured to form the image on the sheet, the image reading apparatus comprising: a conveyance portion configured to convey the sheet in a conveyance direction; a transparent member including a first surface disposed on a first side on which the sheet is conveyed by the conveyance portion and a second surface disposed on a second side opposite to the first side; an image reading portion disposed on the second side with respect to the transparent member and configured to read the image of the sheet through the transparent member; an elastic member disposed to abut against the second surface of the transparent member on the second side and configured to press the transparent member toward the first side; and a guide disposed upstream of a reading position where the image reading portion reads the image of the sheet with respect to the conveyance direction and configured to guide the sheet conveyed by the conveyance portion to the reading position, wherein the guide is provided so that a downstream end of the guide with respect to the conveyance direction contacts with the first surface of the transparent member and presses the transparent member toward the second side. 
     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 a view showing an image forming system. 
         FIG. 2  is a cross-sectional view of a first image reading apparatus and a second image reading apparatus. 
         FIG. 3  is an explanatory view of a first image reading process portion. 
         FIG. 4  is a cross-sectional view of the first image reading process portion taken along line IV-IV of  FIG. 3 . 
         FIG. 5  is an explanatory view of a focal position of a CIS. 
         FIG. 6  is an explanatory view of a gap between a reading glass and a backing roller. 
         FIG. 7  is an explanatory view of a deflecting of a sheet in a case in which an introduction guide of a reference example is used. 
         FIG. 8  is an explanatory view of a deflecting of a sheet in a case in which an introduction guide of the embodiment is used. 
         FIG. 9  is a view of an introduction guide fixed to a frame. 
         FIG. 10  is a perspective view of a first image reading apparatus. 
         FIG. 11  is a perspective view of a first image reading apparatus in which a frame, an introduction guide and a backing roller are assembled. 
     
    
    
     DESCRIPTION OF THE EMBODIMENTS 
     The embodiments will be described in exemplary detail with reference to the drawings below. However, the dimensions, materials and shapes of the components described in the embodiments should be appropriately changed according to the configuration of the apparatus to which the disclosure is applied and various conditions, and the scope of the disclosure is not limited to the following embodiments. 
     (Image Forming System) 
       FIG. 1  is a view showing an image forming system  100 . The image forming system  100  includes a printer  101 , an inspection apparatus (an image reading apparatus)  102 , and an output sheet sorting device (hereinafter referred to as a sorter)  103 . The printer  101  is an image forming apparatus configure to form an image on a sheet (recording material) P. The inspection apparatus  102  is connected to the printer  101  downstream of the printer  101  with respect to a conveyance direction CD of the sheet P. The sorter  103  is connected to the inspection apparatus  102  downstream of the inspection apparatus  102  with respect to the conveyance direction CD of the sheet P. 
     (Image Forming Apparatus) 
     The printer  101  is a four-color full-color printer using an electrophotographic process. The printer  101  forms an image on the sheet P based on an image signal inputted to a control unit (not shown) from an information terminal (not shown) such as a personal computer (not shown) or an external device (not shown) such as an image reader (not shown), and discharges the sheet P on which the image is formed. The sheet P is a recording material on which an image is formed with toner. The sheet P includes, for example, plain paper, cardboard, transparencies, coated paper, and label paper. An operator operates the printer  101  through an operation portion  21 . 
     The printer  101  has four image forming portions  11 Y,  11 M,  11 C and  11 K provided side by side. The image forming portion  11 Y forms a yellow (Y) toner image. The image forming portion  11 M forms a magenta (M) toner image. The image forming portion  11 C forms a cyan (C) toner image. The image forming portion  11 K forms a black (K) toner image. Laser scanner units  3 Y,  3 M,  3 C, and  3 K as exposure apparatuses are arranged in the upper portions of the image forming portions  11 Y,  11 M,  11 C, and  11 K, respectively. The image forming portions  11 Y,  11 M,  11 C and  11 K are provided with electrophotographic photosensitive drums  1 Y,  1 M,  1 C and  1 K as image bearing members, chargers  2 Y,  2 M,  2 C and  2 K, and developing units  4 Y,  4 M,  4 C and  4 K, respectively. The image forming portions  11 Y,  11 M,  11 C and  11 K further have drum cleaners  7 Y,  7 M,  7 C and  7 K, respectively. 
     An intermediate transfer belt  50  is disposed below the image forming portions  11 Y,  11 M,  11 C and  11 K. The intermediate transfer belt  50  is stretched over a drive roller  51 , a tension roller  52  and a secondary transfer inner roller  53 , and is rotated in a direction indicated by an arrow R. The primary transfer rollers  6 Y,  6 M,  6 C, and  6 K are disposed opposite to the electrophotographic photosensitive drums  1 Y,  1 M,  1 C, and  1 K, respectively, via the intermediate transfer belt  50 . The image forming portions  11 Y,  11 M,  11 C and  11 K have substantially the same structure except for the color of the toner contained in the developing units  4 Y,  4 M,  4 C and  4 K. 
     The chargers  2 Y,  2 M,  2 C, and  2 K uniformly charge surfaces of the electrophotographic photosensitive drums  1 Y,  1 M,  1 C, and  1 K, respectively. The laser scanner units  3 Y,  3 M,  3 C, and  3 K expose the uniformly charged surfaces of the electrophotographic photosensitive drums  1 Y,  1 M,  1 C, and  1 K according to image signals of respective colors to form electrostatic latent images. The developing units  4 Y,  4 M,  4 C, and  4 K develop the electrostatic latent images formed on the surfaces of the electrophotographic photosensitive drums  1 Y,  1 M,  1 C, and  1 K with toners of respective colors to form toner images of yellow, magenta, cyan, and black. The yellow, magenta, cyan and black toner images are transferred on the intermediate transfer belt  50  by the primary transfer rollers  6 Y,  6 M,  6 C and  6 K and superimposed on top of one another. 
     On the other hand, sheets P are fed one by one from a cassette  24  and conveyed through a conveyance path  13  to a secondary transfer nip portion  15  formed between the intermediate transfer belt  50  and a secondary transfer roller  14  at a predetermined control timing. The toner images of the four colors on the intermediate transfer belt  50  are collectively transferred to a sheet P by the secondary transfer nip portion  15 . A transfer residual toner remaining on the intermediate transfer belt  50  after the secondary transfer is removed from the surface of the intermediate transfer belt  50  by a belt cleaner  19 . The sheet P on which the toner image is transferred is conveyed to a fixing device  16 . The fixing device  16  heats and pressurizes the sheet P to fix the toner image on the sheet P. A sheet P on which a full color image is formed is discharged from the printer  101  by a pair of discharge rollers  17 . 
     (Inspection Apparatus) 
     The sheet P discharged from the printer  101  is delivered to the inspection apparatus  102  connected downstream of the printer  101 . The inspection apparatus  102  is a device configured to detect the presence/absence of abnormality of print information of the sheet P discharged from the printer  101 . The inspection apparatus  102  has a first image reading apparatus  202  configured to read an image formed on one side of the sheet P and a second image reading apparatus  204  configured to read an image formed on the other side of the sheet P. First, a sheet P on which reference images are formed is conveyed to the inspection apparatus  102 . The first image reading apparatus  202  and the second image reading apparatus  204  read the reference images formed on the sheet P, and register (save) the images as the reference images in a computer  210  connected to the inspection apparatus  102 . 
     Thereafter, the inspection apparatus  102  reads the images of the sheet P conveyed from the printer  101  by the first image reading apparatus  202  and the second image reading apparatus  204 . The computer (an inspection portion)  210  performs image inspection by comparing the read images with the reference images. The image information of the read sheet P is compared with the image information of the reference images registered in advance, and an existence of a difference between the images formed by the printer  101  and the reference images is determined. Based on the difference between the image information of the images formed by the printer  101  and the image information of the reference images, it is determined whether or not the image formed on the sheet P by the printer  101  is an abnormal image. 
     (Sorter) 
     The sheet P discharged from the inspection apparatus  102  is conveyed to the sorter  103 . In a case in which the inspection apparatus  102  determines that there is no abnormality in the image formed on the sheet P discharged from the printer  101 , the sorter  103  discharges the sheet P to a tray  501 . In a case in which the inspection apparatus  102  determines that there is an abnormality in the image formed on the sheet P discharged from the printer  101 , the sorter  103  discharges the sheet P to a tray  502 . As a result, a series of image forming, inspection processing and sorting processing by the image forming system  100  is completed. 
     (Image Reading Apparatus) 
       FIG. 2  is a cross-sectional view of the first image reading apparatus  202  and the second image reading apparatus  204 . A conveyance of the sheet P (not shown in  FIG. 2 ) in the first image reading apparatus  202  and the second image reading apparatus  204  disposed in the inspection apparatus  102  will be described with reference to  FIG. 2 . The printer  101  (not shown in  FIG. 2 ) is disposed on the right side of  FIG. 2 , and the sorter  103  (not shown in  FIG. 2 ) is disposed on the left side of  FIG. 2 . There is a floor (not shown in  FIG. 2 ) on the lower side of  FIG. 2  and a ceiling (not shown in  FIG. 2 ) on the upper side of  FIG. 2 . The sheet P is conveyed in the conveyance direction CD. 
     The inspection apparatus  102  has an inlet lower guide  221  and an inlet upper guide  222 . The inlet lower guide  221  and the inlet upper guide  222  suppress the fluttering of the sheet P caused by the conveyance of the sheet P entering the inspection apparatus  102 . The material of the inlet lower guide  221  and the inlet upper guide  222  is SUS 420 CP. A polishing process is applied to the contact surfaces of the inlet lower guide  221  and the inlet upper guide  222  with the sheet P to improve the surface properties of the contact surfaces so as not to damage the sheet P. An inlet sensor  223  detects the sheet P entering the inspection apparatus  102 . A reflection type photosensor is used as the inlet sensor  223 . 
     Based on a timing at which the inlet sensor  223  detects the sheet P entering the inspection apparatus  102 , a timing at which the first image reading apparatus  202  reads the image formed on the one side of the sheet P is controlled. Further, if it is determined based on the detection result of the inlet sensor  223  that there is an abnormality in the conveyance of the sheet P, a jam processing of the sheet P is executed. 
     A first conveyance roller pair  201  comprises a conveyance roller  211  having a steel shaft  211   a  attached with two pieces of silicone rubber  211   b  having an outer diameter of 20 mm, and a rotatable member  212  made of POM resin arranged at a position corresponding to each piece of the silicone rubber  211   b . The POM resin is a polyoxymethylene resin or a polyacetal resin. The conveyance roller  211  is rotated by a rotation drive transmitted from a driving motor (not shown) to the end of the conveyance roller  211  via a timing belt (not shown). 
     The rotatable member  212  is rotatably supported on an axis. The rotatable member  212  is urged against the conveyance roller  211  by an elastic member such as a spring (not shown) with a force of 1.2N. The rotatable member  212  is rotated in association with the rotation of the conveyance roller  211 . 
     The sheet P is conveyed by the conveyance roller  211  to a first image reading process portion  231  comprising the first image reading apparatus  202  and a first backing roller  203 . The sheet P is further conveyed by the conveyance roller  211  to a second image reading process portion  232  comprising the second image reading apparatus  204  and a second backing roller  205 . The first image reading apparatus  202  and the first backing roller  203  have the same structures as the second image reading apparatus  204  and the second backing roller  205 , respectively. The first image reading apparatus  202  is arranged below the conveyance path for the sheet P. The second image reading apparatus  204  is arranged above the conveyance path for the sheet P. The first image reading apparatus  202  and the second image reading apparatus  204  are arranged opposite to each other with respect to the conveyance path. The first image reading apparatus  202  and the second image reading apparatus  204  have different reading directions. Therefore, the first image reading apparatus  202  and the second image reading apparatus  204  can read image information of images formed on both sides (front side and back side) of the sheet P only by passing the sheet P through the conveyance path one time without reversing the sheet P in another conveyance path. 
     The sheet P passed through the second image reading apparatus  204  is guided by an outlet lower guide  224  and an outlet upper guide  225 , and is discharged from the inspection apparatus  102  by a second conveyance roller pair  206  and conveyed to the sorter  103 . The material of the outlet lower guide  224  and the outlet upper guide  225  is SUS 420 CP. The polishing process is applied to the contact surfaces of the outlet lower guide  224  and the outlet upper guide  225  with the sheet P to improve the surface properties of the contact surfaces so as not to damage the sheet P. Since the second conveyance roller pair  206  has the same structure as the first conveyance roller pair  201 , a description thereof will be omitted. An outlet sensor  226  detects the sheet P discharged from the inspection apparatus  102 . Since the outlet sensor  226  has the same structure as the inlet sensor  223 , a description thereof will be omitted. 
     A conveyance speed of the sheet P conveyed by the first pair of conveyance rollers (conveyance portion)  201  is the same as a conveyance speed of the sheet P discharged from the printer  101 . A line connecting a nip of the first conveyance roller pair  201  and a nip of the second conveyance roller pair  206  is arranged so as to substantially coincide with a sheet-passing surface through the first image reading apparatus  202  and a sheet-passing surface through the second image reading apparatus  204 . The reason is to keep the sheet P conveyed in the inspection apparatus  102  straight so as not to apply deflecting stress to the sheet P. 
     In a case in which the conveyance path of the sheet P is bent, the deformation stress to the sheet P increases at the bent point, so that an issue occurs in that the image formed on the sheet P is damaged or the paper dust is generated. In a case in which the image of the sheet P is damaged or the paper dust is generated, noise is mixed in the read image information of the sheet P so that good read image information cannot be obtained. Therefore, the conveyance path of the sheet P is configured so as not to cause the above-mentioned issue. 
       FIG. 3  is an explanatory view of the first image reading process portion  231 . The first image reading process portion  231  comprises the first image reading apparatus  202  and the first backing roller  203  provided in the inspection apparatus  102 . The printer  101  is disposed on the right side of  FIG. 3 . The sorter  103  is disposed on the left side of  FIG. 3 . The floor is below  FIG. 3  and the ceiling is above  FIG. 3 .  FIG. 4  is a cross-sectional view of the first image reading process portion  231  taken along line IV-IV of  FIG. 3 . 
     The first image reading apparatus  202  includes a contact image sensor (hereinafter referred to as CIS)  301  serving as an image reading portion. A reading glass (transparent member)  302  is disposed at a predetermined distance L from an upper surface T of the CIS  301 . In the present embodiment, the predetermined distance L is 13.1 mm, but the present disclosure is not limited thereto. In the present embodiment, the thickness of the reading glass  302  is 3.9 mm, but the present disclosure is not limited thereto. The reading glass  302  has a length of 38 mm in the conveyance direction CD of the sheet P and a length of 366 mm in a main scanning direction MS orthogonal to the conveyance direction CD. The first image reading apparatus  202  is arranged opposite to the reading glass  302  on a side (second side) opposite to a side (first side) on which the sheet P is conveyed with respect to the reading glass  302 , and reads an image of the sheet P conveyed on the reading glass  302 . 
     A surface treatment is applied to the sheet-passing surface (passing surface)  302   a  of the reading glass  302  on which the sheet P passes in order to eliminate elements that obstruct the conveyance property of the sheet P such as sticking of the sheet P to the sheet-passing surface  302   a . As described above, the sheet-passing surface  302   a  of the reading glass  302  has the same level as the line connecting the nip of the first conveyance roller pair  201  and the nip of the second conveyance roller pair  206 . 
     A dustproof plate  303  configured to prevent intrusion of foreign substance is arranged between the CIS  301  and the reading glass  302 . The dustproof plate  303  includes a steel plate  303   a  of ZINKOTE (trademark) having a thickness of 1 mm, and foamed urethane sponges (elastic members)  303   b  and  303   c  fixed to the steel plate  303   a  by double-sided adhesive tape. The sponge  303   b  is disposed between the steel plate  303   a  and a non-sheet-passing surface  302   b  of the reading glass  302 . The sponge  303   c  is disposed between the steel plate  303   a  and an upper surface T of the CIS  301 . The dustproof plate  303  including sponges  303   a  and  303   b  extends in the main scanning direction along the reading glass  302 . 
     In order to smoothly deliver the sheet P conveyed from the first conveyance roller pair  201  to the sheet-passing surface  302   a  of the reading glass  302 , an introduction guide  305  is provided on the upstream side of the reading glass  302  in the conveyance direction CD. The introduction guide  305  is made of a spring material (elastic material) made of SUS 304 CSP-1/2H having a thickness of 0.1 mm. One end of the introduction guide  305  is fixed to a frame  306  by screws  307 , and the other end (free end) of the introduction guide  305  is disposed so as to be in close contact with the upper surface of the reading glass  302 . A portion of the frame  306  is a supporting member of the introduction guide  305  and also serves as a sheet guide configured to guide the sheet P. 
     CIS holders  401  and  402  made of aluminum as holding members configured to hold the CIS  301  are fixed to both ends of the CIS  301  with respect to the main scanning direction MS by screws. The CIS holders  401  and  402  also hold the reading glass  302  at a predetermined distance (predetermined value) L from the upper surface T of the CIS  301 . Positioning portions (butting portions)  401   a  and  402   a  having protrusions projecting toward the reading glass  302  are provided on the upper portions of the CIS holders  401  and  402 , respectively. The sheet-passing surface  302   a  of the reading glass  302  is butted against the positioning portions  401   a  and  402   a . As shown in  FIG. 4 , the non-sheet-passing surface  302   b  of the reading glass  302  is butted against a pressing member  403 . The pressing member  403  includes a steel plate  403   a  of ZINKOTE (trademark) and a hard rubber (elastic member)  403   b . The hard rubber  403   b  is disposed between the steel plate  403   a  and the non-sheet-passing surface  302   b  of the reading glass  302 . The pressing member  403  presses the reading glass  302  against the positioning portions  401   a  and  402   a  to fix the reading glass  302 . 
     The first backing roller  203  is hereinafter simply referred to as a backing roller  203 . The backing roller  203  is disposed so that an outer periphery of the backing roller  203  is separated by a predetermined distance from the sheet-passing surface  302   a  of the reading glass  302 , thereby forming a gap δ between the outer periphery of the backing roller  203  and the sheet-passing surface  302   a  of the reading glass  302  ( FIG. 8 ). In the embodiment, the predetermined distance is 0.4 mm. However, the predetermined distance is not limited to 0.4 mm, and is appropriately set in accordance with the specifications of the inspection apparatus  102 . The backing roller  203  is disposed opposite to the reading glass  302  on the side (the first side) on which the sheet P is conveyed with respect to the reading glass  302 . The backing roller  203  functions as a regulating portion (an opposed member) configured to regulate the conveyance of the sheet P so as to properly maintain the distance between the reading glass  302  and the sheet P within a predetermined range. The backing roller  203  has an aluminum pipe material  203   a  and shafts  203   b  pressed into both ends of the pipe material  203   a . A black urethane coat is applied to an outer peripheral surface of the pipe material  203   a . The backing roller  203  has an outer diameter of 20 mm. 
     At each of both ends of the backing roller  203  with respect to the main scanning direction MS, a butt roller  404  having an outer diameter of 20.8 mm are arranged coaxially with the backing roller  203 . The backing roller  203  is supported by an arm  405  and is urged by springs  406  at a pressure of 5.9N. As a result, as shown in  FIG. 4 , the butt rollers  404  are butted against the sheet-passing surface  302   a  of the reading glass  302 , so that the gap δ ( FIG. 8 ) between the reading glass  302  and the backing roller  203  is held at 0.4 mm. 
     A rotational force is transmitted from a drive motor (not shown) to the end of the backing roller  203  on the right side (rear side) of  FIG. 4  through a timing belt (not shown). The backing roller  203  rotates at the same conveyance speed as the first conveyance roller pair  201  and the second conveyance roller pair  206 . This is to prevent the backing roller  203  from becoming a conveyance resistance of the sheet P when the sheet P passes through the gap δ ( FIG. 8 ) between the reading glass  302  and the backing roller  203 . Thus, paper dust generated when the sheet P passes through the backing roller  203  can be reduced. 
       FIG. 5  is an explanatory view of a focal position Q of the CIS  301 . The focal position Q of the CIS  301  is 0.2 mm±0.2 mm from the reading glass  302 . By setting the gap δ ( FIG. 8 ) between the reading glass  302  and the outer periphery of the backing roller  203  to 0.4 mm, no matter where the sheet P passes through the gap δ ( FIG. 8 ), the sheet P passes through a focal region of the CIS  301 , thereby ensuring good image reading. A light emitting portion  351  of the CIS  301  irradiates light M toward the focal position Q. A light receiving portion  352  of the CIS  301  receives light J. 
     A predetermined distance L between the upper surface T of the CIS  301  and the reading glass  302  shown in  FIG. 3  is held by the CIS holders  401  and  402  shown in  FIG. 4 . The dustproof plate  303  is disposed between the CIS  301  and the reading glass  302 . The sponge  303   b  is squeezed between the steel plate  303   a  and the reading glass  302 . An original thickness of the sponge  303   b  before mounting is 3 mm. A thickness D of the sponge  303   b  squeezed after mounting is 2 mm. The sponge  303   c  is squeezed between the steel plate  303   a  and the CIS  301 . An original width of the sponge  303   c  before mounting is 7 mm. A width E of the sponge  303   c  squeezed after mounting is 5.8 mm. Squeezing amounts of the sponges  303   b  and  303   c  are set to 1 mm and 1.2 mm, respectively. 
     In this way, the sponges  303   b  and  303   c  are arranged in a state in which the sponges  303   b  and  303   c  are squeezed between the reading glass  302  and the CIS  301 , thereby blocking the path through which foreign substances such as dirt and paper dust enter between the reading glass  302  and the CIS  301 . However, the squeezed sponge  303   b  presses the reading glass  302  toward the backing roller  203  on the side (first side) on which the sheet P is conveyed.  FIG. 6  is an explanatory view of the gap δ between the reading glass  302  and the backing roller  203 . Due to a reaction force W generated when the sponge  303   b  is squeezed, the reading glass  302  deflects toward the backing roller  203  as indicated by the two-dot chain line in  FIG. 6 . If the reading glass  302  deflects toward the backing roller  203 , the gap δ between the reading glass  302  and the backing roller  203  becomes smaller than the set value. In a case in which the gap δ becomes smaller than the set value, resistance may be generated in the conveyance of the sheet P in the gap δ between the reading glass  302  and the backing roller  203 , or paper dust may be generated. Therefore, in the embodiment, the deflection of the reading glass  302  is suppressed by the introduction guide  305 . Hereinafter, a mechanism configured to suppress the deflection of the reading glass  302  toward the backing roller  203  caused by the reaction force W generated when the sponge  303   b  is squeezed will be described. 
     (Introduction Guide) 
     In order to smoothly deliver the sheet P conveyed by the first conveyance roller pair  201  onto the reading glass  302 , the introduction guide  305  is disposed upstream of the reading glass  302  in the conveyance direction CD. The introduction guide  305  is arranged on the side of the reading glass  302  with respect to a conveyance path in which the sheet P is conveyed. The introduction guide  305  can prevent the sheet P from being scratched by being caught on the end of the reading glass  302 , the sheet P from being broken, or the sheet P from being jammed. 
     As described above, a line connecting the nip of the first conveyance roller pair  201  and the nip of the second conveyance roller pair  206  is arranged so as to substantially coincide with the sheet-passing surface  302   a  of the reading glass  302 , thereby the sheet P is conveyed linearly during image reading. This is to reduce damage to an image of the sheet P and generation of paper dust by preventing deflecting stress from being applied to the sheet P during image reading. Therefore, a material requiring a thickness as a material for forming the introduction guide  305  is unsuitable. This is because a large deflecting stress is applied to the sheet P by a step (level difference) formed between the sheet-passing surface  302   a  of the reading glass  302  and the introduction guide  305 , and image damage and paper dust are generated. 
     Hereinafter, a mechanism will be described in which a step formed by the sheet-passing surface  302   a  of the reading glass  302  and an introduction guide  1305  causes paper dust and image damage in a case in which the introduction guide  1305  having a large thickness is used in place of the introduction guide  305  according to the present embodiment.  FIG. 7  is an explanatory view of the deflecting of the sheet P in a case in which the introduction guide  1305  of the reference example is used. The gap δ between the sheet-passing surface  302   a  of the reading glass  302  and the outer periphery of the backing roller  203  is set to 0.4 mm as described above. The introduction guide  1305  of the reference example is made of a steel plate having a thickness of 1 mm. The sheet P conveyed in the conveyance direction CD passes through the gap δ of 0.4 mm from a position having a height of 1 mm starting from the sheet-passing surface  302   a  of the reading glass  302 . At this time, as shown in  FIG. 7 , the sheet P is slightly bent. Therefore, the sheet P and the introduction guide  1305  of the reference example are more rubbed, and paper dust is generated. 
     Next, a case in which the introduction guide  305  according to the present embodiment is used will be described with reference to  FIG. 8 .  FIG. 8  is an explanatory view of the bending of the sheet P in a case in which the introduction guide  305  of the embodiment is used. The introduction guide  305  is made of a spring material having a thickness of 0.1 mm. The introduction guide  305  is provided with a bent portion  305   d . The radius of curvature of the bent portion  305   d  is preferably 0.5 mm or more. The sheet P conveyed in the conveyance direction CD passes through the gap δ having a height of 0.1 mm from a position having a height of 0.4 mm starting from the sheet-passing surface  302   a  of the reading glass  302 . Since the height of the step formed by the sheet-passing surface  302   a  of the reading glass  302  and the introduction guide  305  is 0.1 mm, the bending of the sheet P is suppressed. Thus, sliding resistance when the sheet P passes on the introduction guide  305  is reduced, and generation of paper dust is suppressed. 
     It is desirable that the height of the introduction guide  305  from the reading glass  302  is smaller than the gap δ between the reading glass  302  and the backing roller  203  and as low as possible. The introduction guide  305  of the embodiment is made of the spring material of SUS 304 CSP-1/2H having a thickness of 0.1 mm. By using the material having the thickness of 0.1 mm, the step caused by the reading glass  302  and the introduction guide  305  is reduced, and the generation of image damage and paper dust caused when the sheet P passes on the introduction guide  305  is reduced. The introduction guide  305  of the embodiment is preferably made of a thin spring material having the thickness of 0.1 mm. The spring material includes, for example, spring steel such as high carbon steel, alloy steel, and stainless steel. 
     As described above, the dustproof plate  303  configured to prevent foreign substance such as paper dust and dirt from entering is disposed between the CIS  301  and the reading glass  302  in the state in which the sponge  303   b  is squeezed. If the introduction guide  305  of the present embodiment is not provided on the reading glass  302 , as shown in  FIG. 6 , the reading glass  302  deflects toward the backing roller  203  and deforms so that the gap δ between the reading glass  302  and the backing roller  203  becomes small. However, in the embodiment, the introduction guide  305  made of the spring material is disposed on the reading glass  302 . 
       FIG. 9  is a view of the introduction guide  305  fixed to the frame  306 . The introduction guide  305  extends in the main scanning direction MS. An end portion (hereinafter referred to as one end portion)  305   a  on an upstream side of the introduction guide  305  with respect to the conveyance direction (sub-scanning direction) CD of the sheet P is fixed to the frame  306  as a fixed end portion by a plurality of screws  307 . The frame  306  is fixed to a casing  102   a  of the inspection apparatus  102  via another frame  411  ( FIG. 4 ). Since the one end portion  305   a  as the fixed end of the introduction guide  305  is fixed to the frame  306  by the screws  307 , the introduction guide  305  is surely grounded, and generation of static electricity can be prevented. 
     An end portion (hereinafter referred to as the other end portion)  305   b  on the downstream side of the introduction guide  305  with respect to the conveyance direction CD of the sheet P is a free end portion. When the frame  306  is attached to the another frame  411  by screws  410  ( FIG. 4 ), the other end portion  305   b , which is the free end portion of the introduction guide  305 , is disposed so as to be in close contact with the upper surface of the reading glass  302 . At this time, the other end portion  305   b , which is the free end portion of the introduction guide  305 , is attached so as to be in close contact with the reading glass  302  while being deformed by about 2.6 mm in the height direction. The other end portion  305   b , which is the free end portion of the introduction guide  305  formed of the spring material (leaf spring), generates a spring force toward the reading glass  302 . The other end portion  305   b , which is the free end portion of the introduction guide  305 , presses the reading glass  302  toward the side (second side) on which the first image reading apparatus  202  is disposed. The spring force of the introduction guide  305  can cancel the force of deflecting the reading glass  302  toward the backing roller  203  by the reaction force W generated when the sponge  303   b  is squeezed. That is, the other end portion  305   b  of the introduction guide  305  presses the reading glass  302  with a pressing force that suppresses deformation of the reading glass  302  by the sponge  303   b  and flattens the reading glass  302 . Therefore, the sheet-passing surface  302   a  of the reading glass  302  is held in a substantially horizontal state by the introduction guide  305 . The sheet P is conveyed without giving bending stress to the sheet P by the introduction guide  305 . 
       FIG. 10  is a perspective view of the first image reading apparatus  202 .  FIG. 11  is a perspective view of the first image reading apparatus  202  in which the frame  306 , the introduction guide  305  and the backing roller  203  are assembled. The other end portion  305   b , which is the free end portion of the introduction guide  305 , is in close contact with the reading glass  302  to prevent the deflection of the reading glass. Further, since the step between the reading glass  302  and the introduction guide  305  is small, image damage and paper dust are suppressed when the sheet P passes on the reading glass  302 , and image data with less noise can be read. 
     The first image reading apparatus  202  has been described above. The second image reading apparatus  204  is arranged in the direction opposite to that of the first image reading apparatus  202  with respect to the conveyance path of the sheet P. Since the configuration, functions and effects of the second image reading apparatus  204  are the same as those of the first image reading apparatus  202 , a description of the second image reading apparatus  204  is omitted. 
     According to the embodiment, the deflection of the reading glass  302  can be reduced to improve the image reading performance. 
     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. 2021-007005, filed Jan. 20, 2021, which is hereby incorporated by reference herein in its entirety.