JP6354664B2 - Image reading apparatus and image forming apparatus - Google Patents

Description

  The present invention relates to an image reading apparatus and an image forming apparatus including the same.

  2. Description of the Related Art Conventionally, there is known an image reading apparatus that irradiates a document with light from a light source and receives reflected light by a light receiving element to read image data of the document. In such an image reading apparatus, the image data is read with a uniform density regardless of the sensitivity unevenness of the light receiving element and the light amount unevenness of the light source. Therefore, white reference data is acquired by reading the white reference member for each light receiving element. The

  There is also known an image reading apparatus that simultaneously reads image data on the front and back surfaces of a document when the document is conveyed. The image reading apparatus includes a reading unit for the front surface and a reading unit for the back surface. In Patent Document 1, the white reference member arranged corresponding to the reading unit for the back surface is composed of a belt member. By rotating the belt-shaped white reference member, the relative positions of the reading unit and the white reference member change, and a plurality of white reference data are acquired.

JP 2009-130890 A

  In the technique described in Patent Document 1, when shading correction of the two reading units for the front side and the back side is periodically executed, the reading productivity of the continuous reading operation of a plurality of document sheets decreases. there were.

  The present invention has been made in view of the above problems, and in an image reading apparatus capable of reading both-side original images with one sheet passing and an image forming apparatus provided with the image reading apparatus, the reading productivity at the time of continuous reading is achieved. It aims at suppressing that it falls.

  An image reading apparatus according to an aspect of the present invention includes a document placement unit on which a document sheet is placed, and the document sheet that extends from the document placement unit and passes through a predetermined document reading position. A sheet conveyance path, a document discharge section for discharging the document sheet that has passed through the document reading position, and an opposite side of the document reading position, and reading an image on the first surface of the document sheet. A first reading unit, a first white reference member disposed to face the first reading unit, and the sheet conveying path between the document reading position and the document placing unit, A second reading unit that reads an image on a second side opposite to the first side of the original sheet; a second white reference member that is disposed opposite the second reading unit; and the first reading unit. And a reading control unit for controlling the second reading unit, The reading control unit is configured to read the first reading unit before the original sheet is carried into the sheet conveyance path during double-sided reading in which images of the first surface and the second surface of the original sheet are read. And by causing the second reading unit to read the first white reference member and the second white reference member, shading correction of the first reading unit and the second reading unit is performed, and the first of the original sheets is At the time of single-sided reading in which only an image on one side is read, the first reading unit performs the first reading unit without performing shading correction of the second reading unit before the original sheet is carried into the sheet conveyance path. The shading correction of the first reading unit is executed by reading one white reference member.

  According to this configuration, since the shading correction of the first reading unit and the second reading unit is executed according to the type of image reading operation, it is possible to prevent the reading productivity of the continuous reading operation from being lowered.

  In the above configuration, the reading control unit performs the shading correction of the first reading unit by causing the first reading unit to read the first white reference member, and then the reading operation includes the double-side reading and the double-side reading. It is determined whether the one-side reading, and when the reading operation is the double-side reading, the second white reference member is further read by the second reading unit, thereby shading the second reading unit. After executing the correction, the original sheet is carried into the sheet conveyance path, and when the reading operation is the single-sided reading, the original sheet is moved to the sheet without executing the shading correction of the second reading unit. It may be carried into the conveyance path.

  According to this configuration, when an image reading operation request is made, the shading correction of the first reading unit is promptly executed. When it is determined that the image reading operation is double-sided reading, shading correction of the second reading unit is executed. As a result, it is further suppressed that the reading productivity of the continuous reading operation is lowered.

  In the above configuration, in the continuous double-sided reading in which the double-sided reading is performed while the plurality of document sheets placed on the document placing unit are continuously carried into the sheet conveyance path, the reading control unit Is necessary for shading correction of the first reading unit or the second reading unit between the image reading operation of the first document sheet and the image reading operation of the second document sheet following the previous first document sheet. A shading correction determination operation is performed to determine whether or not, and when it is determined that shading correction is necessary in the first reading unit or the second reading unit, the second original sheet is carried into the sheet conveyance path. In the interrupted state, after the shading correction of the first reading unit and the second reading unit is executed, the second original sheet may be carried into the sheet conveyance path.

  According to this configuration, when it is determined that shading correction is required in at least one of the first reading unit and the second reading unit, the first reading unit is used by using the time during which the second document sheet is interrupted. Then, shading correction of the second reading unit is executed. For this reason, the reading quality is stably maintained while preventing the reading productivity of the image reading apparatus from being lowered.

  In the above configuration, the reading control unit executes the shading correction determination operation of the first reading unit between the image reading operation of the first document sheet and the image reading operation of the second document sheet. You may do it.

  According to this configuration, the shading correction of the first reading unit and the second reading unit can be performed based on the shading correction determination operation of the first reading unit.

  In the above configuration, the reading control unit executes the shading correction determination operation of the second reading unit between the image reading operation of the first document sheet and the image reading operation of the second document sheet. You may do it.

  According to this configuration, the shading correction of the first reading unit and the second reading unit can be performed based on the shading correction determination operation of the second reading unit.

  In the above-described configuration, the reading control unit may perform the first reading unit and the second reading unit between the image reading operation of the first document sheet and the image reading operation of the second document sheet. A shading correction determination operation may be executed.

  According to this configuration, the shading correction of the first reading unit and the second reading unit can be performed based on the shading correction determination operation of the first reading unit and the second reading unit.

  In the above configuration, in order for the first reading unit to read the document image, a first light source that emits irradiation light applied to the document sheet, and for the second reading unit to read the document image, A second light source that emits irradiation light applied to the original sheet, and the reading control unit is configured to determine whether the first reading unit or the second reading unit is the first reading unit during the shading correction determination operation. A first output value output when reading one white reference member or the second white reference member, and the first reading unit or the second reading when the first light source or the second light source is turned off. Even when one of the second output values output by the unit exceeds a preset threshold, the shading correction is determined to be necessary in the first reading unit or the second reading unit. There.

  According to this configuration, it is determined whether or not shading correction is necessary based on a change in the white reading level or the black reading level.

  In the above configuration, the reading control unit performs the shading correction determination operation when the image reading operation of the original sheet is executed for a predetermined threshold number of sheets during the continuous double-sided reading. But you can.

  According to this configuration, the shading correction determination operation is executed when a predetermined threshold number of images are read. For this reason, it is prevented that the read image is defective due to the temperature characteristics of the first reading unit or the second reading unit.

  In the above configuration, the threshold number when a color image is read by the first reading unit or the second reading unit is the threshold value when a monochrome image is read by the first reading unit or the second reading unit. It is desirable to set it smaller than the number of sheets.

  According to this configuration, more stable shading correction is performed for a color image reading operation.

  In the above configuration, when the first reading unit or the second reading unit reads an image at the first resolution, the threshold number of sheets is the first resolution in the first reading unit or the second reading unit. It is desirable that the threshold number is set to be smaller than that when an image is read at a second resolution smaller than that.

  According to this configuration, more stable shading correction is executed for a high-resolution reading operation.

  In the above-described configuration, the second white reference member is disposed to face the second reading unit with the sheet conveyance path interposed therebetween, and the second white reference member is arranged to be orthogonal to the document sheet conveyance direction. A moving mechanism for moving the second white reference member in the main scanning direction while the moving mechanism moves the second white reference member in the main scanning direction in the shading correction of the second reading unit; It is desirable to read two white reference members.

  According to this configuration, the second white reference member is moved in the main scanning direction, so that the shading correction of the second reading unit can be executed. For this reason, it is possible to employ a plate-like member as the second white reference member, and the image reading apparatus is configured at a lower cost compared to the case where the white reference member is composed of a roller or a belt member.

  An image forming apparatus according to another aspect of the present invention provides an image on a sheet based on any one of the image reading apparatuses described above and a document image read by the first reading unit or the second reading unit. And an image forming unit that forms the image.

  According to this structure, it can suppress that reading productivity at the time of continuous reading of an image reading apparatus falls. As a result, the productivity of the image forming apparatus that forms an image on the sheet is maintained high.

  ADVANTAGE OF THE INVENTION According to this invention, it can suppress that reading productivity at the time of continuous reading falls in the image reading apparatus which can read the document image of both sides | surfaces, and an image forming apparatus provided with the image reading apparatus once. .

1 is a cross-sectional view showing an internal structure of an image forming apparatus according to an embodiment of the present invention. 1 is a perspective view of an image reading apparatus according to an embodiment of the present invention. FIG. 3 is a top view of a document placement surface of the image reading apparatus according to the embodiment of the present invention. FIG. 3 is a cross-sectional view of a document conveying unit of the image reading apparatus according to the embodiment of the present invention. It is sectional drawing of the periphery of the 1st white reference member of the image reading apparatus which concerns on one Embodiment of this invention. It is a side view of the periphery of the 2nd white reference member of the image reading apparatus which concerns on one Embodiment of this invention. It is the schematic of the moving mechanism of the 2nd white reference member of the image reading apparatus which concerns on one Embodiment of this invention. 1 is a block diagram illustrating an electrical configuration of an image reading apparatus according to an embodiment of the present invention. 5 is a flowchart of a shading correction operation executed in the image reading apparatus according to an embodiment of the present invention.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

<Configuration of image forming apparatus>
First, the configuration of an image forming apparatus 1 according to an embodiment of the present disclosure will be described with reference to FIG. FIG. 1 is a cross-sectional view showing the internal structure of the image forming apparatus 1.

  Referring to FIG. 1, image forming apparatus 1 is a copying machine and includes a main body housing 10 having a housing structure. In the main body housing 10, the image reading device 2, the paper feeding unit 20, the image forming unit 30, the transfer unit 40, the supply unit 50, and the fixing unit 60 are arranged.

  The main body housing 10 includes an upper housing 11 and a lower housing 12 having a substantially rectangular parallelepiped housing structure, and a connection housing 13. The main body housing 10 is configured by connecting an upper casing 11 and a lower casing 12 disposed below the upper casing 11 by a connecting casing 13. An area surrounded by the upper casing 11, the lower casing 12, and the connecting casing 13 is configured as a sheet discharge space 10A in which a sheet after image forming processing is discharged.

  Referring to FIG. 1, a sheet feeding unit 20 is a part for storing a sheet on which an image forming process is performed and feeding the sheet. The sheet feeding unit 20 is disposed in the lower housing 12 and includes a sheet feeding cassette 21 for storing a sheet bundle, a pickup roller 22 and a sheet feeding roller pair 23 disposed in the vicinity of the sheet feeding cassette 21, Is provided.

  The paper feed cassette 21 is pulled out from the lower housing 12 in the front direction when sheets are supplied. The pickup roller 22 feeds the sheet bundle stored in the paper feed cassette 21 one by one from the top surface. The pair of paper feed rollers 23 sends out the sheet fed by the pickup roller 22 to the sheet conveyance path side.

  The image forming unit 30 forms a toner image to be transferred to the sheet based on the image data of the original document acquired by the later-described reading unit 3 and back surface reading unit 806 of the image reading device 2. The image forming unit 30 includes a yellow unit 30Y using a yellow (Y) developer and a magenta unit using a magenta (M) developer as a plurality of image forming units that form toner images of different colors. 30M, a cyan unit 30C that uses a cyan (C) developer, and a black unit 30Bk that uses a black (Bk) developer. The image forming units 30Y, 30M, 30C, and 30Bk are sequentially arranged from the upstream side in the rotation direction of the intermediate transfer belt 41 described later toward the downstream side.

  Each of the image forming units 30Y, 30M, 30C, and 30Bk includes a photosensitive drum 31, a charging device 32 disposed around the photosensitive drum 31, a developing device 34, a primary transfer roller 35, a cleaning device 36, Is provided. The image forming unit 30 further includes an exposure device 33 arranged below the image forming units 30Y, 30M, 30C, and 30Bk.

  The photosensitive drum 31 is made of an amorphous silicon (a-Si) material, and an electrostatic latent image and a toner image are formed on the peripheral surface thereof. The charging device 32 uniformly charges the surface of the photosensitive drum 31. The exposure device 33 includes various optical devices such as a light source and a mirror. The exposure device 33 irradiates the peripheral surface of the photosensitive drum 31 uniformly charged by the charging device 32 with light based on the image data of the document acquired by the image reading device 2, thereby forming an electrostatic latent image. Form.

  The developing device 34 develops the electrostatic latent image by supplying toner as a developer to the photosensitive drum 31 on which the electrostatic latent image is formed. The developing device 34 contains a developing housing 34A that contains toner, a developing roller 34B that carries the toner on the circumferential surface, supplies the toner to the photosensitive drum 31, a magnetic roller 34C, and the toner in the developing housing 34A. And a first conveying screw 34D and a second conveying screw 34E that are circulated and conveyed.

  The primary transfer roller 35 forms a primary transfer nip portion with the photosensitive drum 31 with an intermediate transfer belt 41 described later interposed therebetween, and the toner image formed on the peripheral surface of the photosensitive drum 31 is primary transferred onto the intermediate transfer belt 41. To do. The cleaning device 36 cleans the peripheral surface of the photosensitive drum 31 after the toner image is primarily transferred to the intermediate transfer belt 41.

  The transfer unit 40 transfers the toner image formed by the image forming unit 30 to a sheet sent out from the paper supply unit 20. The transfer unit 40 includes an intermediate transfer belt 41 formed of an endless belt-like rotating body, and a driving roller 43 and a driven roller 44 that are rotatably supported. The intermediate transfer belt 41 is sandwiched between the photosensitive drum 31 and the primary transfer roller 35, and is stretched around the driving roller 43 and the driven roller 44.

  The transfer unit 40 further includes a secondary transfer roller 44 disposed to face the drive roller 43. The secondary transfer roller 44 forms a secondary transfer nip portion with the driving roller 43 with the intermediate transfer belt 41 interposed therebetween. The toner image primarily transferred onto the intermediate transfer belt 41 is secondarily transferred to the sheet fed from the sheet feeding unit 20 at the secondary transfer nip portion.

  The replenishing unit 50 is a part that stores toner used in the image forming unit 30. The replenishing unit 50 includes a yellow toner container 50Y, a magenta toner container 50M, a cyan toner container 50C, and a black toner container 50Bk. Each toner container 50Y, 50M, 50C, 50Bk replenishes each color toner to the developing device 34 of each image forming unit 30Y, 30M, 30C, 30Bk.

  The fixing unit 60 performs a fixing process of the toner image secondarily transferred onto the sheet in the secondary transfer nip portion. The fixing unit 60 includes a fixing roller 61 having a heating source (not shown) therein, and a pressure roller 62 that forms a fixing nip portion between the fixing roller 61. By passing the sheet on which the toner image has been secondarily transferred through the fixing nip portion, the toner image is fixed on the sheet by heating by the fixing roller 61 and pressing by the pressure roller 62.

  FIG. 2 is a perspective view of the image reading apparatus 2 according to the present embodiment. FIG. 3 is a top view of the document placing surface (mounting surface 70A) of the image reading apparatus 2. FIG. FIG. 4 is a cross-sectional view of the document conveying unit 16 of the image reading apparatus 2.

  With reference to FIGS. 1 and 2, the image reading apparatus 2 includes an automatic document feeder 1 </ b> A and a reading unit 3 (first reading unit) disposed in the upper housing 11. As shown in FIG. 2, the automatic document feeder 1A has a substantially rectangular parallelepiped shape having a predetermined height in the vertical direction. The automatic document feeder 1 </ b> A is rotatable up and down with respect to the upper housing 11 around a fulcrum portion (not shown) disposed on the rear end side. The automatic document feeder 1A includes a document feed tray 14 (document placement unit), a document delivery tray 15 (document delivery unit), and a document delivery unit 16.

  The document feed tray 14 is a plate-like tray disposed in the upper part of the automatic document feeder 1A. A document sheet before the image reading operation is placed on the document feed tray 14. The document discharge tray 15 is a flat portion that is disposed below the document feed tray 14 at an interval. A document sheet that has passed through a later-described transported document reading glass 71 (document reading position) is discharged to the document discharge tray 15. The document conveyance unit 16 is disposed on the left side of the automatic document conveyance device 1A. The document transport unit 16 transports the document sheet placed on the document feed tray 14 to the document discharge tray 15.

  Referring to FIG. 3, the image reading apparatus 2 further includes a fixed document reading glass 70, a conveyed document reading glass 71, and a document discharge guide 72 arranged on the upper surface 11 </ b> A of the upper housing 11.

  The fixed original reading glass 70 has a rectangular shape having a longitudinal direction in the sub-scanning direction D2, and has a placement surface 70A (FIG. 3) on which the original is placed. The transported document reading glass 71 has a rectangular shape having a longitudinal direction in the main scanning direction D1 perpendicular to the sub-scanning direction D2, and is disposed adjacent to the left side of the fixed document reading glass 70. The document discharge guide 72 is disposed between the fixed document reading glass 70 and the transported document reading glass 71.

  When the document sheet (fixed document) is manually placed, the automatic document feeder 1A is opened upward, and the document sheet is placed on the placement surface 70A. The document sheet is pressed and fixed on the fixed document reading glass 70 by a platen mat (not shown) or the automatic document feeder 1A. Then, under the fixed original reading glass 70, the image data of the original sheet is read by scanning the reading unit 3 (FIG. 1) in the sub-scanning direction D2.

  On the other hand, when the document is automatically conveyed, as shown in FIGS. 1 and 2, the automatic document conveyance device 1 </ b> A is arranged on the upper surface 11 </ b> A of the upper housing 11 and the document sheet is placed on the document tray 15. . Further, the reading unit 3 is moved by a drive mechanism (not shown), and the reading unit 3 is disposed below the transported document reading glass 71 (FIG. 2) so as to face the transported document reading glass 71. Then, the document sheet placed on the document tray 15 is transported on the transported document reading glass 71 by the document transport unit 16, whereby the image of the document sheet is read. At this time, the reading unit 3 reads an image on the surface (first surface) of the document sheet. Then, the read original sheet is discharged to the original feed tray 14.

  Referring to FIG. 4, the document transport unit 16 includes a pickup roller 801, a paper feed roller 802, a retard roller 803, an upper white reference member 804 (second white reference member), a counter glass 805, and a back side reading. Unit 806 (second reading unit), first driven roller 807, transport roller 808, second driven roller 809, white guide member 810, upper discharge guide 811, lower discharge guide 812, and discharge roller pair 813. Further, the document transporting section 16 extends from the document feed tray 14 and passes through the transported document reading glass 71 to reach the document discharge tray 15 (FIG. 2). (Conveyance path) is arranged.

  The pickup roller 801 is a roller that is disposed above the left end portion of the document feed tray 14 and is driven to rotate. The pickup roller 801 sends out a document sheet placed on the document feed tray 14. The paper feed roller 802 is disposed downstream of the pickup roller 801 in the document sheet conveyance direction. The paper feed roller 802 is driven to rotate and further conveys the original sheet. The retard roller 803 forms a paper feed nip portion through which the original sheet passes with the paper feed roller 802. By the retard roller 803, the uppermost document sheet among the document sheets placed on the document feed tray 14 is carried into the document transport path SP.

  The upper white reference member 804 defines an upper portion of the document transport path SP on the downstream side in the transport direction from the paper feed roller 802. The upper white reference member 804 is made of a white resin material. The upper white reference member 804 has a plate shape extending in the main scanning direction (front-rear direction) and a flat portion facing the document transport path SP. The facing glass 805 is disposed below the upper white reference member 804 so as to face the upper white reference member 804. The counter glass 805 is a transparent glass plate. The counter glass 805 defines a lower portion of the document transport path SP.

  The back side reading unit 806 is a contact image sensor (CIS: Contact Image Sensor) arranged in a fixed manner. The back side reading unit 806 is arranged to face the document transport path SP through the counter glass 805. The back side reading unit 806 is disposed between the transported document reading glass 71 and the document feed tray 14 in the document transport path SP. A back side reading unit 806 reads an image on the back side (second side) of the document sheet. The upper white reference member 804 is disposed so as to face the back surface reading unit 806 through a transparent counter glass 805.

  The first driven roller 807 is a roller that is disposed on the downstream side in the transport direction with respect to the upper white reference member 804 and faces the document transport path SP. The transport roller 808 is a roller disposed below the first driven roller 807. The second driven roller 809 is a roller that is disposed below and to the left of the transport roller 808. As shown in FIG. 4, the transport roller 808 has a larger diameter than the first driven roller 807 and the second driven roller 809. The transport roller 808 is rotationally driven by a drive mechanism (not shown). The first driven roller 807 and the second driven roller 809 are rotated following the conveyance roller 808. A peripheral surface of the transport roller 808 defines a part of the document transport path SP. The document sheet reaches the transported document reading glass 71 while being transported along the peripheral surface of the transport roller 808.

  The white guide member 810 is disposed to face the conveyed document reading glass 71. The white guide member 810 defines the upper part of the document transport path SP. On the other hand, the transported document reading glass 71 defines a part of the lower portion of the document transport path SP. As the document sheet passes between the white guide member 810 and the transported document reading glass 71, the image on the surface of the document sheet is read by the reading unit 3. The document discharge guide 72 described above defines a part of the lower portion of the document transport path SP at a position spaced downstream of the transport document reading glass 71 in the transport direction. In order to convey the document sheet toward the document discharge tray 15, the document discharge guide 72 has an inclined surface that rises toward the right.

  The document discharge guide 72 includes a lower white reference member 72A (first white reference member) inside. The lower white reference member 72A is a white plate-like member. FIG. 5 is an enlarged cross-sectional view of the periphery of the lower white reference member 72A of the document conveying unit 16 in FIG. When the reading unit 3 is moved slightly to the right as shown in FIG. 5 from the state shown in FIG. 4 (see the arrow in FIG. 5), the lower white reference member 72A moves the fixed original reading glass 70 over. It is arranged so as to face the reading unit 3 with being sandwiched. Then, the reading optical axis L of the reading unit 3 moves while passing through the lower white reference member 72A, so that the white portion of the lower white reference member 72A is read by the reading unit 3. The reading unit 3 includes a reading unit slider 3S. The reading unit slider 3 </ b> S is a protrusion that protrudes upward from the reading unit 3. The reading unit 3 is smoothly moved by moving the reading unit slider 3 </ b> S while being in contact with the transported document reading glass 71 and the fixed document reading glass 70. Further, the distance between the reading unit 3 and the fixed original reading glass 70 and the conveyed original reading glass 71 is kept constant by the reading unit slider 3S.

  The upper discharge guide 811 and the lower discharge guide 812 are guide members that define an upper portion and a lower portion of the document transport path SP on the downstream side in the transport direction from the document discharge guide 72. The discharge roller pair 813 is a roller pair disposed near the exit of the document transport path SP. A document sheet is discharged to the document discharge tray 15 by the discharge roller pair 813.

  FIG. 6 is a side view of the periphery of the upper white reference member 804 of the document conveying unit 16. FIG. 6 corresponds to a view of the periphery of the upper white reference member 804 as viewed from the document feed tray 14 side along the document sheet conveyance direction. As described above, the document transport path SP is formed between the upper white reference member 804 and the counter glass 805. In the present embodiment, as indicated by the arrows in FIG. 6, the upper white reference member 804 is movable in the front-rear direction. The upper white reference member 804 includes a reference member slider 804S. The reference member slider 804 </ b> S is a protrusion that protrudes downward from both ends of the upper white reference member 804 in the front-rear direction. When the reference member slider 804S abuts against the counter glass 805, the upper white reference member 804 can be moved smoothly, and the document transport path SP formed between the upper white reference member 804 and the counter glass 805 can be realized. The height is kept constant.

  Further, the back surface reading unit 806 includes a CIS positioning protrusion 806S. The CIS positioning protrusion 806 </ b> S is a protrusion that protrudes upward from both ends in the front-rear direction of the back surface reading unit 806. When the CIS positioning protrusion 806 </ b> S comes into contact with the counter glass 805, the distance between the back surface reading unit 806 and the counter glass 805 is maintained constant.

  FIG. 7 is a schematic diagram of a moving mechanism of the upper white reference member 804 of the document conveying unit 16 of the image reading apparatus 2. FIG. 8 is a block diagram showing an electrical configuration of the image reading apparatus 2. The image reading apparatus 2 further includes a control unit 91 (reading control unit), a drive motor 814, a first clutch 815, a cam 816, a biasing spring 817, a second clutch 818, and a standing wall 16H. .

  The control unit 91 electrically controls each member in the image reading apparatus 2 including the reading unit 3 and the back surface reading unit 806. The driving motor 814 generates a driving force that moves the upper white reference member 804. In the present embodiment, the drive motor 814 generates a driving force for rotating the pickup roller 801, the paper feed roller 802, and the retard roller 803. For this reason, the drive motor 814 can rotate forward and backward. The first clutch 815 is a clutch disposed between the drive motor 814 and the cam 816. In the present embodiment, the first clutch 815 is a one-way clutch. In another embodiment, the first clutch 815 may be an electromagnetic clutch controlled by the control unit 91.

  The cam 816 is rotatably supported in the document conveying unit 16. The cam 816 is rotated by the rotational driving force generated by the drive motor 814. The circumferential surface of the cam 816 contacts the rear side wall (the pressed portion 804H) of the upper white reference member 804. The urging spring 817 is a spring member that is compressed between the front side wall of the upper white reference member 804 and the standing wall 16 </ b> H disposed inside the document conveying unit 16. The biasing spring 817 biases the upper white reference member 804 rearward. The second clutch 818 is a clutch disposed between the drive motor 814 and the pickup roller 801, the paper feed roller 802, and the retard roller 803. In the present embodiment, the second clutch 818 is a one-way clutch. In another embodiment, the second clutch 818 may be an electromagnetic clutch controlled by the control unit 91. The drive motor 814, the first clutch 815, the cam 816, and the biasing spring 817 function as a moving mechanism of this embodiment. The moving mechanism moves the back surface reading unit 806 in the main scanning direction orthogonal to the document sheet conveyance direction.

  Referring to FIG. 7, when drive motor 814 is rotated forward by control unit 91, the rotational drive force of drive motor 814 is transmitted to pickup roller 801, paper feed roller 802 and retard roller 803, and these rollers are It is rotated. As a result, the document sheet placed on the document feed tray 14 is carried into the document transport path SP. At this time, the rotational driving force of the drive motor 814 is not transmitted to the cam 816 due to the action of the first clutch 815. Therefore, when the drive motor 814 is rotated forward, the upper white reference member 804 does not move. Therefore, the original sheet is stably conveyed between the upper white reference member 804 and the counter glass 805. Since the upper white reference member 804 is fixed, the back side reading unit 806 (FIG. 4) stably reads the back side image of the original sheet.

  On the other hand, when the drive motor 814 is reversely rotated by the controller 91, the rotational driving force of the drive motor 814 is transmitted to the cam 816, and the upper white reference member 804 is reciprocated in the front-rear direction. As a result, as described later, shading correction of the back surface reading unit 806 can be performed. At this time, the rotational driving force of the drive motor 814 is not transmitted to the pickup roller 801 or the like due to the action of the second clutch 818. Accordingly, it is possible to prevent the original sheet from being erroneously carried into the original transport path SP during the shading correction of the back surface reading unit 806.

  In the present embodiment, since the upper white reference member 804 corresponding to the back surface reading unit 806 is made of a white plate, the upper white reference member 804 is configured at a lower cost than the white reference member made of a rotatable roller or belt member. Is done. Further, the upper white reference member 804 is moved in the main scanning direction by a driving motor 814 that generates a rotational driving force such as a pickup roller 801. For this reason, it is not necessary to provide a dedicated drive motor for moving the upper white reference member 804, and the movement of the upper white reference member 804 can be realized at low cost.

  Referring to FIG. 8, the reading unit 3 is a contact image sensor (CIS) similar to the back surface reading unit 806. The reading unit 3 includes a light source 4 (first light source) that emits light irradiated on the document sheet, a lens (not shown) that collects reflected light from the document sheet, and a light receiving unit 5 that receives the reflected light. And a drive unit 9 that moves the reading unit 3 in the sub-scanning direction D2 (FIG. 3). The reading unit 3 is disposed below the fixed document reading glass 70 and the conveyed document reading glass 71 in the upper housing 11 (FIG. 1), and is movable in the sub-scanning direction D2.

  The light source 4 emits irradiation light that irradiates the document sheet so that the reading unit 3 reads the document image. The light source 4 is a light source including a plurality of LEDs (Light Emitting Diodes), and emits light of three colors of red (R), green (G), and blue (B). The light source 4 is controlled by the control unit 91 to selectively emit any one of red, green, and blue. Note that the light source 4 is not limited to an LED light source, and may use another light emitting method. The light receiving unit 5 is a one-line sensor in which a plurality of (for example, 5000) light receiving elements (pixels) are arranged one-dimensionally in the main scanning direction D1 (FIG. 2). The light receiving unit 5 is controlled by the control unit 91 to receive reflected light from the original sheet at the light receiving element, and photoelectrically converts the reflected light to form image data.

  The reading unit 3 is controlled by the control unit 91 to irradiate the original sheet placed on the fixed original reading glass 70 with light of red, green, and blue while moving in the sub-scanning direction D2. The original sheet is scanned by receiving the reflected light. The reading unit 3 is controlled by the control unit 91 to irradiate light of each color onto the original sheet automatically conveyed by the original conveying unit 16 on the conveyed original reading glass 71 (original reading position) and reflect the light. The original sheet is scanned by receiving light.

  In the image reading device 2, since the original image is read at a uniform density regardless of the sensitivity unevenness of the light receiving element of the light receiving unit 5 and the light amount unevenness of the light source 4, the white reference data is periodically read by the lower white reference member 72A (FIG. 5). Is acquired (shading correction).

  At the time of shading correction, the reading unit 3 irradiates the lower white reference member 72A with light of each color of red, green, and blue while moving in the sub-scanning direction D2, and receives the reflected light, thereby receiving the lower white reference member 72A. Scan (read). Then, the white reference data is acquired by averaging the plurality of data obtained by the scan.

  Specifically, when the lower white reference member 72A is scanned, the reading unit 3 switches the light emission color (R, G, B) every time 1/3 pixel moves in the sub-scanning direction D2. Then, the reflected light from the lower white reference member 72A is received by each light receiving element of the light receiving unit 5 constituting one line sensor. When foreign matter of different colors adheres to the lower white reference member 72A, appropriate white reference data is acquired by removing the abnormal white reference data output under the influence of the foreign matter.

  Referring to FIG. 8, the image reading apparatus 2 includes a control unit 91 that controls the operation of the reading unit 3, a memory unit 92 that stores document image data and white reference data, and data stored in the memory unit 92. And a processing unit 93 for processing.

  The control unit 91 is connected to each of the light source 4, the light receiving unit 5, and the driving unit 9 of the reading unit 3 and controls the reading unit 3. The driving unit 9 includes a motor that generates a driving force for moving the reading unit 3. The driving force of the motor is transmitted to the reading unit 3 through a power transmission mechanism such as a gear or a pulley. The control unit 91 controls the drive unit 9 so that the reading unit 3 moves relative to the lower white reference member 72A in the sub-scanning direction D2. Further, the control unit 91 controls the light source 4 so that light emitted to the lower white reference member 72A is switched to light of three colors of red, green, and blue at each of a plurality of reading positions on the lower white reference member 72A. To do. In addition, the control unit 91 controls the light receiving unit 5 so that the reflected light of red, green, and blue light irradiated on the lower white reference member 72A is received by each of the plurality of light receiving elements.

  The memory unit 92 is connected to the light receiving unit 5 and the processing unit 93. The memory unit 92 has a memory area for storing white reference data in addition to a memory area for storing image data of an original sheet.

  The processing unit 93 is electrically connected to the memory unit 92. The processing unit 93 performs a process of rearranging the white reference data in the memory area of the memory unit 92 and specifying abnormal data included in the white reference data stored in the memory unit 92. The processing unit 93 calculates white reference data averaged for each pixel of the light receiving unit 5 from the white reference data in the memory area, excluding the abnormal data, and stores the white reference data in the memory unit 92 after associating it with the pixel address. To do.

  Note that the back side reading unit 806 described above also includes the light source 4 (second light source) (FIG. 8) and the light receiving unit 5, similarly to the reading unit 3. The light source 4 of the back side reading unit 806 emits irradiation light that is applied to the original sheet so that the back side reading unit 806 reads the original image. Further, the back surface reading unit 806 is electrically connected to the control unit 91 and the memory unit 92 described above. The control unit 91 electrically controls the back side reading unit 806. The control unit 91 controls the back side reading unit 806 to read an image on the back side of the document sheet. The functions of the control unit 91, the memory unit 92, and the processing unit 93 during the image operation of the back side reading unit 806 are the same as those of the reading unit 3. In addition, the control unit 91 controls the back surface reading unit 806 and the above-described moving mechanism to periodically acquire white reference data of the upper white reference member 804 (shading correction). In the shading correction of the back surface reading unit 806, the back surface reading unit 806 scans the upper white reference member 804 while the moving mechanism moves the upper white reference member 804 in the main scanning direction. As in the case of the reading unit 3, when foreign matter of a different color adheres to the upper white reference member 804, the abnormal white reference data output under the influence of the foreign matter is removed, so that an appropriate white color is obtained. Reference data is acquired.

  As described above, in the present embodiment, the document images on the front and back surfaces of the document sheet can be read by the reading unit 3 and the back surface reading unit 806 while the document sheet is passed once through the document transport path SP. it can. When a plurality of document sheets are set on the document feed tray 14 (FIG. 2), it takes a certain amount of time until images of all document sheets are read. During this time, the read image density may vary depending on the temperature characteristics of the reading unit 3 and the back side reading unit 806. In particular, in the CIS such as the reading unit 3 and the back side reading unit 806, a plurality of light receiving elements (sensors) are arranged in parallel in the main scanning direction. For this reason, the temperature characteristics are different for each sensor, the density fluctuation amount is partially different in the document image, and uneven density tends to appear. For this reason, it is desirable that the white reference data of the reading unit 3 and the back side reading unit 806 is re-acquired during the continuous reading operation of a plurality of document sheets.

  In the present embodiment, the document image reading position (conveyed document reading glass 71) of the reading unit 3 and the white reference acquisition position (lower white reference member 72A) are different in the sub-scanning direction. For this reason, when it is not possible to secure a time for re-acquiring the white reference data between successive original sheets (so-called paper interval), it is necessary to temporarily stop the supply of the original sheets. If the white reference data of the back surface reading unit 806 is to be acquired between the sheets of the original sheet, the upper white reference member 804 is swung during the conveyance of the original sheet, and the original sheet image is distorted and read. For this reason, even when the white reference data is reacquired by the back surface reading unit 806, it is necessary to temporarily interrupt the feeding of the original sheet. However, when the document sheet is read while the document sheet feeding is frequently interrupted, the reading productivity of the image reading apparatus 2 is greatly reduced. In the present embodiment, in order to solve such a problem, the control unit 91 executes shading correction including acquisition of white reference data of the reading unit 3 and the back surface reading unit 806 at a suitable timing. FIG. 9 is a flowchart of the shading correction operation executed in the image reading apparatus 2 according to the present embodiment.

  Referring to FIG. 9, when an image sheet reading operation is requested in image reading apparatus 2 (step S <b> 1), control unit 91 executes shading correction of reading unit 3 (step S <b> 2). At this time, as described above, after the reading unit 3 is disposed below the document discharge guide 72, the lower white reference member 72A is read by the reading unit 3 while the reading unit 3 is moved in the sub-scanning direction. Thereafter, the control unit 91 determines whether the requested reading operation is double-sided reading or single-sided reading (step S3). If the reading operation is double-sided reading (YES in step S3), the control unit 91 causes the back surface reading unit 806 to read the upper white reference member 804 while moving the upper white reference member 804 in the main scanning direction. Thus, the shading correction of the back surface reading unit 806 is executed (step S4). Thereafter, the control unit 91 rotates the pickup roller 801 and the like to carry the first document sheet (first document sheet) into the document transport path SP (step S5), and the back surface reading unit 806 and the reading unit. Then, double-sided image reading of the original sheet is executed in step 3 (step S6). On the other hand, when the reading operation is single-sided reading (NO in step S3), the control unit 91 carries the original sheet into the original conveying path SP without executing the shading correction of the back side reading unit 806 (step S5). .

  When the reading operation for the first document sheet is completed, the control unit 91 determines whether all the requested document sheet reading operations have been completed, that is, whether the reading job has been completed (step S7). When all the original sheet reading operations have been completed (YES in step S7), the control unit 91 ends the series of image reading operations (step S8). On the other hand, when the document sheet that still needs the reading operation remains on the document feeding tray 14, that is, when the reading job has not ended (NO in step S7), the control unit 91 performs the shading correction determination operation. Execute (Step S9). The shading correction determination operation refers to the image reading operation of the first document sheet and the image reading of the second document sheet following the first document sheet at the time of continuous reading in which reading is performed on a plurality of document sheets. Between the operations, the control unit 91 determines whether or not the shading correction of the reading unit 3 or the back surface reading unit 806 is necessary. At this time, the control unit 91 may determine whether shading correction is required for one of the reading unit 3 and the back surface reading unit 806, or whether shading correction is required for both the reading unit 3 and the back surface reading unit 806. May be.

  In the shading correction necessity determination (step S9), the first output value (white reading level) that is output when the reading unit 3 or the back side reading unit 806 reads the white guide member 810 or the upper white reference member 804 between the sheets is used. When the preset threshold value is exceeded, it is determined that the shading correction of the reading unit 3 or the back side reading unit 806 is necessary. In another embodiment, when the light source 4 (first light source or second light source) corresponding to the reading unit 3 or the back side reading unit 806 is turned off between sheets, the reading unit 3 or the back side reading unit 806 outputs. When the second output value (black reading level) exceeds a preset threshold value, it may be determined that shading correction of the reading unit 3 or the back surface reading unit 806 is necessary.

  Note that it is desirable that the acquisition timing of the white reference data between sheets referred to in determining whether shading correction is necessary or not is set according to the image reading mode of the image reading apparatus 2. When the image reading operation of the original sheet is executed for a predetermined threshold number of sheets, white reference data between sheets is acquired. As a result, a stable read image can be acquired even when the temperature of the image reading apparatus 2 changes. In particular, the threshold number when a color image is read by the reading unit 3 or the back side reading unit 806 is set smaller than the threshold number when a monochrome image is read. As a result, in the case of a color image, the frequency of obtaining white reference data increases, and more stable shading correction is executed. Further, the threshold number of sheets when the image is read at the first resolution (600 dpi) in the reading unit 3 or the back surface reading unit 806 is the case where the image is read at the second resolution (300 dpi) smaller than the first resolution. It is set smaller than the threshold number. As a result, in the case of high resolution, the frequency of obtaining the white reference data increases, and more stable shading correction is executed. Thus, in this embodiment, the necessity of shading correction is determined based on the fluctuation of the white reading level or the black reading level.

  Referring to FIG. 9, when it is determined by reading unit 3 or back surface reading unit 806 that another shading correction is necessary (YES in step S <b> 9), control unit 91 executes two sheets following the first document sheet. The feeding of the original document sheet (second original sheet) is temporarily interrupted (step S10). And the control part 91 performs the shading correction of the reading part 3 again (step S2). When the double-sided reading operation is performed on a plurality of document sheets (YES in step S3), the control unit 91 executes the shading correction of the back surface reading unit 806 again (step S4). In this case, in practice, the shading correction of the reading unit 3 and the back side reading unit 806 is executed substantially in parallel. Thereafter, the controller 91 starts conveying the second original sheet (step S5), and the reading operation is executed (step S6). Similar control is executed for the subsequent original sheets.

  As described above, in the present embodiment, the control unit 91 performs the reading unit 3 and the rear surface reading before the original sheet is carried into the original document conveyance path SP at the time of double-sided reading in which the images on the front and rear surfaces of the original sheet are read. By causing the lower white reference member 72A and the upper white reference member 804 to be read by the unit 806, shading correction of the reading unit 3 and the back surface reading unit 806 is executed. On the other hand, at the time of single-sided reading in which only the image on the front side of the original sheet is read, the reading unit 3 does not perform shading correction of the back side reading unit 806 before the original sheet is carried into the original transport path SP, and the lower white reference The shading correction of the reading unit 3 is executed by reading the member 72A. As described above, since the shading correction of the reading unit 3 and the back surface reading unit 806 is executed according to the image reading operation, it is possible to prevent the reading productivity of the continuous reading operation from being lowered. In particular, when a reading operation request is made, the shading correction of the reading unit 3 that is used for image reading on the front surface is executed promptly. When it is determined whether the reading operation is double-sided or single-sided, shading correction of the back side reading unit 806 is executed as necessary. As a result, it is further suppressed that the reading productivity of the continuous reading operation is lowered.

  In the present embodiment, when it is determined that shading correction is necessary in any one of the reading unit 3 and the back side reading unit 806, the time when the second original sheet is interrupted is used. Then, shading correction of both the reading unit 3 and the back side reading unit 806 is executed. For this reason, the reading quality is stably maintained while preventing the reading productivity of the image reading apparatus from being lowered.

  In the present embodiment, the control unit 91 performs a shading correction determination operation when an image reading operation of an original sheet is executed for a predetermined threshold number of sheets during continuous double-sided reading. For this reason, it is prevented that the read image is defective due to the temperature characteristics of the reading unit 3 or the back surface reading unit 806. As a result, the reading productivity of the image reading device 2 and the quality of the read image can be stably maintained.

DESCRIPTION OF SYMBOLS 1 Image forming apparatus 10 Main housing | casing 11 Upper housing | casing 11A Upper surface 12 Lower housing | casing 13 Connection housing | casing 14 Document feed tray (document placement part)
15 Document output tray (document output section)
16 Document conveying section 16H Standing wall 1A Automatic document conveying apparatus 2 Image reading apparatus 3 Reading section (first reading section)
4 Light sources (first light source, second light source)
5 Light Receiving Unit 70 Fixed Document Reading Glass 71 Conveyed Document Reading Glass 72 Document Discharge Guide 72A Lower White Reference Member (First White Reference Member)
804 Upper white reference member (second white reference member)
804H Pressed portion 805 Opposing glass 806 Back side reading unit (second reading unit)
810 White guide member 814 Drive motor 815 First clutch 816 Cam 817 Energizing spring 818 Second clutch 9 Drive unit 91 Control unit (reading control unit)
92 Memory unit 93 Processing unit L Reading optical axis SP Document conveyance path (sheet conveyance path)

Claims (11)

A document placement section on which a document sheet is placed;
A sheet conveyance path that extends from the document placement section and conveys the document sheet so as to pass a predetermined document reading position;
A document discharge section for discharging the document sheet that has passed through the document reading position;
A first reading unit that is disposed to face the document reading position and reads an image on a first surface of the document sheet;
A first white reference member disposed to face the first reading unit;
A second reading unit that is disposed between the document reading position and the document placing unit so as to face the sheet conveyance path and reads an image on a second surface opposite to the first surface of the document sheet. When,
A second white reference member disposed to face the second reading unit;
A reading control unit for controlling the first reading unit and the second reading unit;
Have
The reading control unit may perform the first reading before the original sheet is carried into the sheet conveyance path during double-sided reading in which images of the first surface and the second surface of the original sheet are read. And the second reading unit read the first white reference member and the second white reference member, thereby performing shading correction of the first reading unit and the second reading unit, and At the time of single-sided reading in which only the image on the first side is read, the first reading unit performs the shading correction of the second reading unit before the original sheet is carried into the sheet conveyance path. By causing the first white reference member to be read, the shading correction of the first reading unit is performed ,
The reading control unit causes the first reading unit to read the first white reference member, thereby performing shading correction of the first reading unit, and then reading operation on the document sheet includes the double-sided reading and the single-sided reading. When the reading operation is the double-sided reading, the second reading unit is further caused to read the second white reference member, thereby correcting the shading correction of the second reading unit. After the execution, the original sheet is carried into the sheet conveyance path, and when the reading operation is the single-sided reading, the original sheet is moved to the sheet conveyance path without performing shading correction of the second reading unit. An image reading apparatus which is carried into the apparatus. In the continuous double-sided reading in which the double-sided reading is performed while the plurality of original sheets placed on the original placing unit are continuously carried into the sheet conveyance path, the reading control unit includes Shading for determining whether shading correction of the first reading unit or the second reading unit is necessary between the image reading operation of the document sheet and the image reading operation of the second document sheet following the first document sheet When a correction determination operation is performed, and when it is determined that shading correction is necessary in the first reading unit or the second reading unit, the loading of the second original sheet into the sheet conveyance path is interrupted, after performing the first reading section and the shading correction of the second reading unit, the image reading according to claim 1, characterized in that to carry the second document sheet to the sheet conveying path Apparatus. The reading control unit executes the shading correction determination operation of the first reading unit between an image reading operation of the first document sheet and an image reading operation of the second document sheet. The image reading apparatus according to claim 2 . The reading control unit executes the shading correction determination operation of the second reading unit between an image reading operation of the first document sheet and an image reading operation of the second document sheet. The image reading apparatus according to claim 2 . In the continuous double-sided reading in which the double-sided reading is performed while the plurality of original sheets placed on the original placing unit are continuously carried into the sheet conveyance path, the reading control unit includes Shading for determining whether shading correction of the first reading unit and the second reading unit is necessary between the image reading operation of the document sheet and the image reading operation of the second document sheet following the first document sheet When a correction determination operation is performed, and when it is determined that shading correction is necessary in the first reading unit or the second reading unit, the loading of the second original sheet into the sheet conveyance path is interrupted, after performing the first reading section and the shading correction of the second reading unit, the image reading according to claim 1, characterized in that to carry the second document sheet to the sheet conveying path Apparatus. A document placement section on which a document sheet is placed;
A sheet conveyance path that extends from the document placement section and conveys the document sheet so as to pass a predetermined document reading position;
A document discharge section for discharging the document sheet that has passed through the document reading position;
A first reading unit that is disposed to face the document reading position and reads an image on a first surface of the document sheet;
A first white reference member disposed to face the first reading unit;
A second reading unit that is disposed between the document reading position and the document placing unit so as to face the sheet conveyance path and reads an image on a second surface opposite to the first surface of the document sheet. When,
A second white reference member disposed to face the second reading unit;
A reading control unit for controlling the first reading unit and the second reading unit;
Have
The reading control unit may perform the first reading before the original sheet is carried into the sheet conveyance path during double-sided reading in which images of the first surface and the second surface of the original sheet are read. And the second reading unit read the first white reference member and the second white reference member, thereby performing shading correction of the first reading unit and the second reading unit, and At the time of single-sided reading in which only the image on the first side is read, the first reading unit performs the shading correction of the second reading unit before the original sheet is carried into the sheet conveyance path. By causing the first white reference member to be read, the shading correction of the first reading unit is performed,
In the continuous double-sided reading in which the double-sided reading is performed while the plurality of original sheets placed on the original placing unit are continuously carried into the sheet conveyance path, the reading control unit includes Shading for determining whether shading correction of the first reading unit or the second reading unit is necessary between the image reading operation of the document sheet and the image reading operation of the second document sheet following the first document sheet When a correction determination operation is performed, and when it is determined that shading correction is necessary in the first reading unit or the second reading unit, the loading of the second original sheet into the sheet conveyance path is interrupted, After performing shading correction of the first reading unit and the second reading unit, the second original sheet is carried into the sheet conveyance path,
A first light source that emits irradiation light applied to the original sheet so that the first reading unit reads an image of the first surface of the original sheet;
A second light source that emits irradiation light applied to the document sheet so that the second reading unit reads an image of the second surface of the document sheet;
Further comprising
The reading control unit, the at the time of shading correction determination operation, the first light source when the first reading unit is emitted has read the first white reference member or the second light source is emitting the second scanning unit Outputs the first output value when reading the second white reference member , and the first reading unit or the second reading unit outputs when the first light source or the second light source is turned off. An image characterized by determining that the shading correction is necessary in the first reading unit or the second reading unit when any of the second output values exceeds a preset threshold value. Reader. The reading control unit executes the shading correction determination operation when an image reading operation of the original sheet is executed for a predetermined threshold number of sheets during the continuous double-sided reading. Item 7. The image reading apparatus according to any one of Items 2 to 6 . A document placement section on which a document sheet is placed;
A sheet conveyance path that extends from the document placement section and conveys the document sheet so as to pass a predetermined document reading position;
A document discharge section for discharging the document sheet that has passed through the document reading position;
A first reading unit that is disposed to face the document reading position and reads an image on a first surface of the document sheet;
A first white reference member disposed to face the first reading unit;
A second reading unit that is disposed between the document reading position and the document placing unit so as to face the sheet conveyance path and reads an image on a second surface opposite to the first surface of the document sheet. When,
A second white reference member disposed to face the second reading unit;
A reading control unit for controlling the first reading unit and the second reading unit;
Have
The reading control unit may perform the first reading before the original sheet is carried into the sheet conveyance path during double-sided reading in which images of the first surface and the second surface of the original sheet are read. And the second reading unit read the first white reference member and the second white reference member, thereby performing shading correction of the first reading unit and the second reading unit, and At the time of single-sided reading in which only the image on the first side is read, the first reading unit performs the shading correction of the second reading unit before the original sheet is carried into the sheet conveyance path. By causing the first white reference member to be read, the shading correction of the first reading unit is performed,
In the continuous double-sided reading in which the double-sided reading is performed while the plurality of original sheets placed on the original placing unit are continuously carried into the sheet conveyance path, the reading control unit includes Shading for determining whether shading correction of the first reading unit or the second reading unit is necessary between the image reading operation of the document sheet and the image reading operation of the second document sheet following the first document sheet When a correction determination operation is performed, and when it is determined that shading correction is necessary in the first reading unit or the second reading unit, the loading of the second original sheet into the sheet conveyance path is interrupted, After performing shading correction of the first reading unit and the second reading unit, the second original sheet is carried into the sheet conveyance path,
The reading control unit executes the shading correction determination operation when the image reading operation of the document sheet is executed for a predetermined threshold number of sheets during the continuous double-sided reading,
The threshold number when a color image is read by the first reading unit or the second reading unit is set smaller than the threshold number when a monochrome image is read by the first reading unit or the second reading unit. An image reading apparatus. A document placement section on which a document sheet is placed;
A sheet conveyance path that extends from the document placement section and conveys the document sheet so as to pass a predetermined document reading position;
A document discharge section for discharging the document sheet that has passed through the document reading position;
A first reading unit that is disposed to face the document reading position and reads an image on a first surface of the document sheet;
A first white reference member disposed to face the first reading unit;
A second reading unit that is disposed between the document reading position and the document placing unit so as to face the sheet conveyance path and reads an image on a second surface opposite to the first surface of the document sheet. When,
A second white reference member disposed to face the second reading unit;
A reading control unit for controlling the first reading unit and the second reading unit;
Have
The reading control unit may perform the first reading before the original sheet is carried into the sheet conveyance path during double-sided reading in which images of the first surface and the second surface of the original sheet are read. And the second reading unit read the first white reference member and the second white reference member, thereby performing shading correction of the first reading unit and the second reading unit, and At the time of single-sided reading in which only the image on the first side is read, the first reading unit performs the shading correction of the second reading unit before the original sheet is carried into the sheet conveyance path. By causing the first white reference member to be read, the shading correction of the first reading unit is performed,
In the continuous double-sided reading in which the double-sided reading is performed while the plurality of original sheets placed on the original placing unit are continuously carried into the sheet conveyance path, the reading control unit includes Shading for determining whether shading correction of the first reading unit or the second reading unit is necessary between the image reading operation of the document sheet and the image reading operation of the second document sheet following the first document sheet When a correction determination operation is performed, and when it is determined that shading correction is necessary in the first reading unit or the second reading unit, the loading of the second original sheet into the sheet conveyance path is interrupted, After performing shading correction of the first reading unit and the second reading unit, the second original sheet is carried into the sheet conveyance path,
The reading control unit executes the shading correction determination operation when the image reading operation of the document sheet is executed for a predetermined threshold number of sheets during the continuous double-sided reading,
The threshold number of sheets when the first reading unit or the second reading unit reads an image at the first resolution is a second smaller than the first resolution in the first reading unit or the second reading unit. An image reading apparatus, wherein the image reading apparatus is set to be smaller than the threshold number when an image is read at a resolution of. The second white reference member is disposed to face the second reading unit across the sheet conveyance path,
A moving mechanism for moving the second white reference member in a main scanning direction perpendicular to the conveying direction of the document sheet;
The shading correction of the second reading unit is characterized in that the second reading unit reads the second white reference member while the moving mechanism moves the second white reference member in the main scanning direction. Item 10. The image reading apparatus according to any one of Items 1 to 9 . An image reading apparatus according to any one of claims 1 to 10 ,
An image forming unit that forms an image on a sheet based on a document image read by the first reading unit or the second reading unit;
An image forming apparatus comprising:

Images