Image reading device and image forming apparatus

Abstract

To improve the accuracy of skew correction.SOLUTION: An image reading device comprises: a conveying unit that conveys a document D; a skimming glass 21; a white sheet 51 that is arranged opposite to the skimming glass 21; and a reading unit having an illumination unit 40 that is arranged on the opposite side of the white sheet 51 with the skimming glass 21 therebetween and irradiates the document D and white sheet 51 with light, and a CCD that reads a shadow of the document D projected on the white sheet 51 as reflected light through the skimming glass 21. The illumination unit 40 is in a direction in which the light irradiation direction is inclined to the downstream side of a conveyance direction DF from a side of the reading unit 20 toward a side of the white sheet 51 when seen from a width direction of the document D orthogonal to the conveyance direction DF. The white sheet 51 has a planar shape inclined to approach the skimming glass 21 on the downstream side compared to an upstream side in the conveyance direction DF.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to an image reading device that reads an image on a sheet-like document, and an image forming apparatus to which the image reading device is applied. [Background technology]

[0002] Conventionally, image forming apparatuses such as copying machines and facsimiles are known that are equipped with an image reading device that optically reads an image of an original (sheet). This type of image reading device has an automatic document feeder that feeds originals one by one, and a scanner unit that reads the image of the fed original. As a method for correcting the skew of a scanned image of such an image reading device, a method called digital skew correction that corrects the scanned skewed image by image processing is widely used. This method detects the shadow of the leading edge of the original that appears in the background, and by setting the background color to white, it is possible to create a contrast with the black color of the shadow that appears in the background, and the leading edge of the original can be detected regardless of the color of the original. As an image reading device that applies this method, there is known an image reading device that detects the skew of the leading edge of the original when the leading edge of the original passes through a reading unit, and performs skew correction by tilting the read image by the amount of the skew of the shadow, assuming that the skew of the shadow and the skew of the original are approximately the same (see Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2018-157417 A Summary of the Invention [Problem to be solved by the invention]

[0004] However, in the image reading device described in the above-mentioned Patent Document 1, depending on the shape of the guide member that forms the background of the read image, there is a risk that the shadow of the leading edge of the document will not be generated sufficiently. For example, if there is not a sufficiently sharp contrast between the black of the shadow and the white of the background at the boundary between the scanned background and the shadow of the document, the position of the shadow cannot be accurately recognized, and the accuracy of the skew correction may decrease.

[0005] SUMMARY OF THE DISCLOSURE An object of the present invention is to provide an image reading device and an image forming device that can improve the accuracy of skew correction. [Means for solving the problem]

[0006] One aspect of the present invention is an image reading device comprising: a conveying section for conveying a sheet; a transparent member; a background section arranged opposite the transparent member; a reading unit having a light source arranged on the opposite side of the background section across the transparent member and irradiating light toward the sheet and the background section; and a reading section that reads the shadow of the sheet projected onto the background section as reflected light through the transparent member, wherein, when viewed from the width direction of the sheet which is perpendicular to the conveying direction of the sheet, the light source irradiates light in a direction that slopes from the reading unit side toward the background section downstream in the conveying direction, and the background section has a planar shape that is inclined so that the downstream side in the conveying direction is closer to the transparent member than the upstream side.

[0007] Another aspect of the present invention is an image forming apparatus comprising: an image reading device as described in claim 1 or 2 that reads an image of a sheet-like document; and an image forming unit that forms an image on a sheet based on image information read by the image reading device. Effect of the Invention

[0008] According to the present invention, the accuracy of skew correction can be improved. [Brief description of the drawings]

[0009] [Figure 1] 1 is a cross-sectional view showing an image forming apparatus according to an embodiment. [Diagram 2] 1 is a cross-sectional view showing a main part of an automatic document reading device according to an embodiment. [Diagram 3] 2 is a schematic diagram showing an original document read by the automatic document reading apparatus according to the embodiment; FIG. [Figure 4] This figure shows how incident light is reflected: (a) is incident on a horizontal surface from the upstream side, (b) is incident on an inclined surface from the upstream side, and (c) is incident on an inclined surface from the downstream side. [Diagram 5] 1A and 1B are cross-sectional views showing how light is incident on a document being conveyed, in which (a) is state (A) and (b) is state (B). [Figure 6] 10A and 10B are cross-sectional views showing how light is incident on a document being conveyed, in which (a) is state (C) and (b) is state (D). [Figure 7] 10A and 10B are cross-sectional views showing how light is incident on a document being conveyed, in which (a) is state (E) and (b) is state (F). [Figure 8] 11 is a graph showing the combined amount of light received due to incident light from the upstream and downstream sides, where (a) is a case where the background part is a horizontal surface, and (b) is a case where the background part is an inclined surface. [Figure 9] 11 is a cross-sectional view showing the vertical movement of a background portion when a platen guide moves in a transport direction. FIG. [Figure 10] FIG. 11 is a cross-sectional view showing a main part of an automatic document reading device according to a modified example of the embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] Hereinafter, exemplary embodiments of the present invention will be described with reference to the drawings.

[0011] 1 is a schematic diagram of an image forming apparatus 1 including an automatic document reading device 10, which is an example of an image reading device according to an embodiment of the present disclosure. The image forming apparatus 1 includes an image forming unit 2 that forms an image on a sheet based on image information read by the automatic document reading device 10, and a control unit 3.

[0012] The image forming unit 2 may be, for example, an electrophotographic system in which a toner image formed on a photoreceptor is transferred to the sheet S via an intermediate transfer body, or a direct transfer system in which a toner image formed on a photoreceptor is directly transferred to the sheet S without an intermediate transfer body. In addition, the image forming unit 2 is not limited to the electrophotographic system, and may be, for example, an inkjet printing unit or an offset printing mechanism.

[0013] The control unit 3 has a CPU, RAM, and ROM, and controls each unit in the image forming apparatus 1. The CPU outputs an output signal to each electric component to operate the electric component at the desired timing and with the required amount of control based on the detection signals input from each sensor and the information stored in the ROM. Therefore, it is the CPU that actually controls the electric components. The ROM and RAM store information data required for controlling each unit, and the CPU reads the information data stored in the ROM and writes it to the RAM. Note that the control unit 3 also controls the automatic document reader 10.

[0014] [Automatic document reader] The configuration of an automatic document reading device 10 according to this embodiment will be described with reference to Fig. 1. Fig. 1 is a schematic diagram showing the cross-sectional configuration of the automatic document reading device 10 according to this embodiment.

[0015] The automatic document reading device 10 includes an ADF 11 (Auto Document Feeder) that transports documents, and a reader 12 that reads image information from a moving document transported by the ADF 11 and a stationary document placed on a document table glass 13. The ADF 11 is connected to the reader 12, which is fixed to the top of the device body 1a of the image forming device 1, via an opening / closing hinge provided on the rear side of the top surface of the reader 12 so as to be able to open and close freely.

[0016] The reader 12 has a glass platen 13, a reading unit 20 for the front side, and a reading movement guide (not shown). The reader 12 performs a fixed reading operation of scanning the front side of a document placed on the glass platen 13, which is a transparent member, through the glass platen 13 while moving the reading unit 20 along the reading movement guide using a motor. In this case, the reading unit 20 obtains a line image in the main scanning direction (alignment direction of the CCD 23) line by line, and integrates the line images in the movement direction of the reading unit 20, which is the sub-scanning direction, to obtain image data of the entire document.

[0017] The reader 12 is also provided with a front side flow reading glass 21, which is a transparent member separate from the document table glass 13. When the automatic document reader 10 performs a flow reading operation in which image data is read while the ADF 11 transports documents one by one, the reading unit 20 scans the front side (first surface) of the document through the flow reading glass 21 and reads the image data of the front side. The flow reading glass 21 is an example of a transparent member that forms part of the transport path. In this case as well, the reading unit 20 obtains line images in the main scanning direction line by line, and integrates the line images in the document transport direction DF, which is the sub-scanning direction, to obtain image data of the entire front side of the document.

[0018] The reading unit 20 is an integrated scanning optical unit of the CCD (Charge Coupled Devices) type. The reading unit 20 has an illumination unit 40, a plurality of mirrors 22, and a CCD 23. The reading unit 20 takes in the scattered reflected light of the light irradiated onto a sheet-like original D by the illumination unit 40, and obtains an image formed on the CCD 23 via the mirror 22 as a read image. The illumination unit 40 is attached to the upper part of the box frame of the reading unit 20. The illumination unit 40 has a first illumination section 41 and a second illumination section 42 (see FIG. 2). The CCD 23 is an example of a reading section that reads the shadow SH of the original D projected onto a white sheet 51 (described later) as reflected light through the flow reading glass 21.

[0019] The ADF 11 includes a document tray 121, a pickup roller 101, a pair of separation rollers 102, a pair of pull-out rollers 103, a pair of upstream lead rollers 104, a pair of intermediate lead rollers 105, a pair of discharge rollers 106, and a discharge tray 122. The document tray 121 is a loading section capable of loading a plurality of documents D, which are sheets to be read. The pickup roller 101 contacts the upper surface of a stack of documents loaded on the document tray 121, and sends the topmost document toward the pair of separation rollers 102. The pair of separation rollers 102 has a conveying roller and a separation roller that form a separation nip, and conveys the documents sent by the pickup roller 101 while separating them one by one. The separation roller that separates the documents D is connected to a shaft fixed to the frame of the ADF 11, for example, via a torque limiter, and separates the documents D by applying a frictional force to the documents D in the separation nip.

[0020] The pull-out roller pair 103, the lead upstream roller pair 104, the lead intermediate roller pair 105, and the discharge roller pair 106 are arranged along a conveying path curved in a U-shape from the document tray 121 toward the discharge tray 122 arranged below it. These roller pairs constitute a conveying section 14 that conveys the document D along the conveying path through a reading position. The pull-out roller pair 103 holds the document that has passed through the separation nip and conveys it toward the lead upstream roller pair 104. The lead upstream roller pair 104 conveys the document D through a position where the reading unit 20 scans the surface of the document D through a flow reading glass 21. The reading unit 20 and the flow reading glass 21 are arranged between the lead upstream roller pair 104 and the lead intermediate roller pair 105 with respect to the conveying direction DF of the document D on the conveying path inside the ADF 11. In addition, a platen guide 50 is provided facing the flow reading glass 21. The platen guide 50 will be described later.

[0021] Here, the ADF 11 of the present embodiment includes a back-side reading unit 30 that reads image data from the back side (second surface) of the document D, and a back-side flow-reading glass 31 that is a transparent member. The reading unit 30 has a built-in CIS 32. The reading unit 30 and the flow-reading glass 31 are disposed between the lead intermediate roller pair 105 and the discharge roller pair 106 in the transport direction DF in the transport path inside the ADF 11. In the flow-reading operation, the document D is transported through a position where the reading unit 30 scans the back side of the document D through the flow-reading glass 31. The flow-reading glass 31 is an example of a transparent member that forms a part of the transport path. In this case, the reading unit 30 obtains line images in the main scanning direction line by line, and the line images are integrated in the transport direction DF of the document D, which is the sub-scanning direction, to obtain image data of the entire back side of the document D. That is, the reading unit 30 can scan the back side of the document D at the back side reading position and read the image data on the back side in parallel with the reading unit 20 reading the image data on the front side.

[0022] The document D that has passed the back-surface reading position is discharged to a discharge tray 122 by a pair of discharge rollers 106. When a plurality of documents D are stacked on the document tray 121, the automatic document reading device 10 repeats a series of operations including feeding, separating, transporting, reading image data from the front and / or back surface, and discharging the documents D until the operation of skimming the final document is completed.

[0023] [Platen Guide] Next, the platen guide 50 provided opposite the flow reading glass 21 and the configuration of the periphery thereof will be described with reference to FIG. 2. FIG. 2 is a cross-sectional view showing the reading unit 20 and the periphery of the platen guide 50 in FIG. 1 cut at an arbitrary main scanning position. The platen guide 50 is an example of an opposing member disposed opposite the flow reading glass 21 and forming a transport path for the document D together with the flow reading glass 21. The platen guide 50 is urged to the flow reading glass 21 at a predetermined distance by a spring member 52, which is an example of a second urging section connected to the frame 11a of the ADF 11. That is, the platen guide 50 is urged toward the flow reading glass 21 by the spring member 52, and is abutted against the flow reading glass 21 at a position other than the transport path for the document D to maintain the distance. For example, a compression coil spring is used as the spring member 52, but the present invention is not limited thereto, and other shapes of springs, rubber, sponge, or other elastic bodies may be used.

[0024] The document D passes through this conveying path at a predetermined constant speed by the conveying unit 14. At this time, when the document is read from the leading edge to the trailing edge by the front side reading unit 20, an image as shown in FIG. 3 is obtained. At the leading edge of the document in the read image, a shadow SH is projected onto the background (white sheet 51), and the outline of the shadow SH is a gradation from black to white to a greater or lesser extent. The control unit 3 recognizes this boundary, regards it as a line at the leading edge of the document, and performs digital skew correction by performing rotation correction. In this embodiment, the control of the skew correction is performed by the control unit 3 provided in the image forming device 1, but this is not limited thereto, and the automatic document reading device 10 or an external device may have a control unit and perform the correction by this control unit. That is, the control unit 3 can perform skew correction based on the image of the document D read by the CCD 23, and the control unit 3 may be installed anywhere.

[0025] Here, in order to detect a shadow SH, a predetermined interval is determined within the gradation of the shadow SH, and the change in luminance during that interval is calculated. When the value of this luminance change is higher than a predetermined threshold, it is possible to detect the presence of a shadow SH boundary at that point. By lowering this threshold, it becomes possible to detect a shadow SH boundary that is not sharp, but since there is a high possibility that a shadow SH will be erroneously detected as a shadow SH when there is actually no shadow SH when, for example, S / N noise occurs in the image, it is desirable to set the threshold as high as possible. For that reason, it is preferable for the gradation of the boundary to have a sharp transition between black and white, and this embodiment is intended to achieve this.

[0026] 1 and 2, the reading unit 20 is disposed below the flow reading glass 21, that is, on the opposite side of the platen guide 50 with the flow reading glass 21 in between. The lighting unit 40 is an example of a light source that irradiates light toward the original D and the platen guide 50. The first lighting section 41 of the lighting unit 40 irradiates light toward the original D from the upstream side of the transport direction DF, and the second lighting section 42 irradiates light from the downstream side of the transport direction DF. That is, the first lighting section 41 has a light irradiation direction that is inclined toward the downstream side of the transport direction DF from the reading unit 20 side (reading unit side) toward the platen guide 50 side (background side) when viewed from the width direction of the original D that is perpendicular to the transport direction DF of the original D. The light irradiated from the first lighting section 41 and the second lighting section 42 reaches an intermediate surface 43 located halfway between them in the conveying direction DF, and the light reflected by the white sheet 51 or the original D is read by the reading unit 20 with the intermediate surface 43 as the reading position.

[0027] In this embodiment, a white sheet 51 is attached to a reading position (position where the intermediate surface 43 overlaps) that is disposed on the platen guide 50 facing the flow reading glass 21 and serves as a background portion. When the platen guide 50 is mass-produced, it is desirable to avoid the risk that the whiteness of the surface when read will be non-uniform due to molding defects such as sink marks. Therefore, in this embodiment, a sheet material with more stable productivity is attached to the platen guide 50 as the white sheet 51 and used as the background portion. However, it is not limited to using the white sheet 51 that is a sheet material, and the surface of the platen guide 50 may be used as the background portion. In addition, it is not limited to being white, and other light colors may be used.

[0028] The image read by the reading unit 20 is produced by scattered light when the light emitted from the illumination unit 40 hits an object on the intermediate surface 43. In particular, when the document D has not yet reached the reading position (intermediate surface 43), the scattered light at position 51a on the white sheet 51 becomes the read image. Here, in this embodiment, the white sheet 51, which serves as the background during reading, is disposed on the side directly facing the first illumination unit 41 from the horizontal angle, i.e., so that the angle θ1 is positive. In other words, the white sheet 51 has a planar shape that is inclined so that the downstream side is closer to the running reading glass 21 than the upstream side in the conveying direction DF.

[0029] In general, when light hits an object (e.g., horizontal sheet 151), the distribution of reflected light is as shown in FIG. 4(a). The specular reflection component light Lr, which has a reflection angle θr equal to the incidence angle θi of the incident light Li, has the strongest intensity as reflected light, and the intensity of scattered light decreases as the angle increases from the specular reflection component light Lr, with the specular reflection component light Lr being approximately the center. The vector distribution VD of the intensity and direction of the scattered light is such that the end points of the reflected light vectors are arranged on a substantially ellipse. Among the scattered light distributed in this way, in this embodiment, only the vertically downward component scattered light Lp of the incident light irradiated at position 51a in FIG. 2 is input to the reading unit 20, and the brightness as an image is obtained.

[0030] Next, the state of the image when the leading edge of the document enters the reading position (intermediate surface 43), that is, the shadow SH of the leading edge of the document used for digital skew correction, will be described. The process in which the leading edge of the document is transported to the right (downstream side) from the state shown in Fig. 2 until it reaches the reading position (intermediate surface 43) is illustrated in chronological order from state (A) to state (F) in Fig. 5(a) to Fig. 7(b).

[0031] 5(a) shows the state (A) at the moment when the document D approaches the reading position (intermediate surface 43) and enters the boundary of the illumination ray to position 51a by the first illumination unit 41. At this point in time, the vertically downward component of scattered light Lp read by the reading unit 20 is not yet affected by the shadow SH, and the reading unit 20 receives all of the reflected light from position 51a of the white sheet 51, resulting in a pure white image.

[0032] As the state transitions from state (B) to state (C) and state (D), the luminance of the first illumination unit 41 is gradually lost. For example, in state (C) shown in Fig. 6(a), about half of the light emitted from the first illumination unit 41 is blocked, and the luminance value is about half of the initial luminance value of the first illumination unit 41. In other words, the input luminance of the reading unit 20 is lower than the initial value, which is the shadow SH to be detected.

[0033] 7(a), all light emitted from the first illumination unit 41 to the position 51a is blocked, and the luminance input by the first illumination unit 41 becomes 0. Finally, in state (F), the leading edge of the document reaches the intermediate surface 43, and thereafter, vertically scattered light from the document surface is input to the reading unit 20.

[0034] Regarding the state of the luminance input as the read image at this time, FIG. 8(a) shows the background plane as a horizontal sheet 151 (see FIG. 4(a)), and FIG. 8(b) shows the background plane as an inclined surface (white sheet 51 in the embodiment) facing the first illumination unit 41. The horizontal axis in FIG. 8(a) and (b) is the sub-scanning position of the leading edge of the document, and when the leading edge of the document is on the reading position, it is set to 0, when the leading edge is downstream from the reading position, it is set to positive, and when the leading edge is upstream, it is set to negative. The lines in the graph show three types of luminance values: luminance values ​​by only the first illumination unit 41, luminance values ​​by only the second illumination unit 42, and luminance values ​​when both are combined. The positions of the vertical lines (A) to (F) in FIG. 8(a) and (b) correspond to the states (A) to (F) in FIG. 5(a) to FIG. 7(b).

[0035] The section for shadow detection is set from (B) to (D), and if the luminance change in the combined amount of received light at that time is equal to or greater than a certain level, it can be detected as a shadow. In other words, the larger the angle θ shown in Figures 8(a) and (b), the clearer the boundary between the background and the shadow, and the better the shadow detection performance will be. However, in the configuration of this embodiment, θ is large with respect to the horizontal plane, and it can be seen that the detection performance is good.

[0036] Next, the mechanism by which the luminance change increases due to the inclination of the background surface will be described with reference to Figs. 4(a) and (b). Fig. 4(a) is a diagram showing the distribution of scattered light in the horizontal sheet 151, and only Lp, which is vertically downward, is directed toward the reading unit 20. On the other hand, Fig. 4(b) shows the distribution of scattered light in the inclined surface (51). As in this embodiment, only Lp is directed toward the reading unit 20 among the light incident from the upstream side as in Fig. 4(a), but it can be seen that the vector length is long and more light enters than the horizontal sheet 151. Note that Fig. 4(c) shows the scattered light of the light by the second illumination unit 42 incident from the downstream side with respect to the same inclined surface (51), and it can be seen that the vector length is shorter than Lp in the case of the horizontal sheet 151, and less light enters the reading unit 20, contrary to Fig. 4(b).

[0037] That is, when the first illumination unit 41 and the second illumination unit 42 have the same illumination intensity, the maximum values ​​of the upstream light amount and the downstream light amount are the same in the horizontal sheet 151 as shown in FIG. 8(a) (here, each is set to 100). In contrast, by using the inclined surface (51) as in this embodiment, the amount of light from the first illumination unit 41 increases and the amount of light from the second illumination unit 42 decreases (here, the upstream maximum value is 150 and the downstream maximum value is 50), so that the reading is performed in the same way. The combined value of the first illumination unit 41 and the second illumination unit 42, that is, the reading brightness, is as shown by the solid lines in FIG. 8(a) and (b), and the inclined surface (51) of this embodiment has a larger θ, so that the boundary between the background and the shadow is clear and the shadow detection performance can be improved.

[0038] In this embodiment, the white sheet 51 is inclined and the peripheral part is made a straight plane. This is because the reading position varies to some extent, and if the inclination angle is not stabilized as a plane, θ varies depending on the individual difference of the machine and the usage situation, making it difficult to stably detect good shadows. In addition, the background inclination angle that can obtain good detection accuracy in this embodiment is in the range of 8 degrees to 20 degrees, and 12 degrees is particularly good. That is, the white sheet 51 is inclined in the range of 98 degrees or more and 110 degrees or less with respect to the direction perpendicular to the conveying direction DF and the width direction when viewed from the width direction of the document D, and 102 degrees is optimal.

[0039] As described above, according to the automatic document reading device 10 of this embodiment, the white sheet 51 of the platen guide 50 has a planar shape that is inclined so that the downstream side in the transport direction DF is closer to the flow reading glass 21 than the upstream side. Also, the first illumination section 41 has a light irradiation direction that is inclined toward the downstream side in the transport direction DF from the reading unit 20 side toward the white sheet 51 side. This allows a sufficient shadow of the leading edge of the document to be generated, making it possible to accurately recognize the position of the shadow SH and improve the accuracy of skew correction.

[0040] That is, the upstream lighting has the effect of casting a shadow on the reading position in the background when irradiated on the leading edge of the document, whereas the downstream lighting only has the effect of erasing the shadow since it does not cast a shadow on the reading position in the background. As in this embodiment, the platen guide 50 is inclined in a direction facing the first lighting unit 41, so that the illumination effect on the read image by the first lighting unit 41 can be strengthened, and the effect on the read image by the second lighting unit 42 can be weakened. This strengthens the contrast of the shadow on the leading edge of the document, thereby improving the detection accuracy of the shadow. In addition, by making the background flat, the angle of the background, which has high sensitivity to the way the shadow is formed, can be kept constant even when the reading position is mechanically varied, so that a stable shadow contrast can be obtained.

[0041] In the above-described embodiment, as shown in FIG. 2, the platen guide 50 has a degree of freedom of play in the vertical direction so as to abut against the flow reading glass 21. That is, the platen guide 50 is movable in a direction intersecting the transport direction DF and the width direction of the document D (here, the vertical direction). For this reason, the platen guide 50 is configured to have some play in the transport direction DF relative to the frame 11a of the ADF 11 so as not to impede the vertical movement. However, if the play is provided in the transport direction DF, as shown in FIG. 9, the inclined white sheet 51 moves in the transport direction DF, and the intersection position with the intermediate surface 43 moves up and down, so that the position 51a moves in the vertical direction. The vertical movement of the position 51a is not preferable in terms of improving the detection accuracy because it is sensitive to changes in the brightness of the shadow.

[0042] 10, the pressing portion 11b may be arranged so as to be pressed from the upstream side to the downstream side by the spring member 53, and the platen guide 50 may be pressed against the regulating wall 11c. That is, the spring member 53 is an example of a first urging portion that urges the platen guide 50 to one side (here, the downstream side) in the conveying direction DF against the regulating wall 11c connected to the frame 11a, which is an example of a guide portion that guides the movement of the platen guide 50. This eliminates the play of the platen guide 50 in the conveying direction DF, and can obtain more stable detection accuracy. In addition, since the platen guide 50 collides against the downstream regulating wall 11c, the platen guide 50 will not be moved regardless of the urging force of the spring member 53, even if the document D comes into contact with the platen guide 50 and presses it downstream.

[0043] 10, the platen guide 50 is pressed against the downstream restriction wall 11c by the spring member 53, but the present invention is not limited to this. For example, the platen guide 50 may be pressed from the downstream side to the upstream side by the spring member, so that the platen guide 50 abuts against the upstream restriction wall. In this case, when the document D comes into contact with the platen guide 50 and presses it downstream, if the spring member has a biasing force larger than the pressing force, it is possible to suppress the movement of the platen guide 50 in the transport direction DF. [Explanation of symbols]

[0044] 1...image forming apparatus, 2...image forming section, 10...automatic document reader (image reading device), 14...conveying section, 20...reading unit, 21...flow reading glass (transparent member), 23...CCD (reading section), 40...illumination unit (light source), 51...white sheet (background section), 52...spring member (second urging section), 53...spring member (first urging section), D...document (sheet), DF...conveying direction

Claims

1. a conveying unit that conveys a sheet; A transparent member; a background portion disposed opposite the transparent member; a reading unit that is disposed on the opposite side of the background section across the transparent member, and includes a light source that irradiates light toward the sheet and has a first irradiation section and a second irradiation section, and a reading section that reads the shadow of the sheet and the image of the sheet projected onto the background section through the transparent member, When viewed from a width direction of the sheet perpendicular to the conveying direction of the sheet, the irradiation direction of the light irradiated from the first irradiation unit is a direction inclined toward the downstream side of the conveying direction, and the irradiation direction of the light irradiated from the second irradiation unit is a direction inclined toward the upstream side of the conveying direction, the background portion has a planar shape that is inclined so that the downstream side is closer to the transparent member than the upstream side in the transport direction. An image reading device characterized by:

2. When viewed from the width direction, the inclination angle of the light irradiated from the first irradiation unit toward the background portion is different from the inclination angle of the light irradiated from the second irradiation unit toward the background portion.

2. The image reading device according to claim 1, wherein:

3. When the first irradiation unit and the second irradiation unit have equivalent illuminance, and when the first irradiation unit and the second irradiation unit irradiate light onto the background part so that the light irradiated from each of the first irradiation unit and the second irradiation unit is reflected by the background part and incident on the reading unit, the amount of light irradiated from the second irradiation unit, reflected by the background part and incident on the reading unit is less than the amount of light irradiated from the first irradiation unit, reflected by the background part and incident on the reading unit, 2. The image reading device according to claim 1, wherein:

4. the background portion is movable in a direction perpendicular to both the transport direction and the width direction while facing the transparent member, a first biasing portion that biases the background portion in the transport direction against a guide portion that guides the movement of the background portion, 2. The image reading device according to claim 1, wherein:

5. the first biasing portion biases the background portion downstream in the transport direction; 5. The image reading device according to claim 4, wherein:

6. The background portion is movable in a direction perpendicular to both the conveying direction and the width direction while facing the transparent member, a second biasing portion that biases the background portion toward the transparent member; 2. The image reading device according to claim 1, wherein:

7. When viewed from the width direction, the angle of the background portion with respect to a direction perpendicular to both the conveying direction and the width direction is 98 degrees or more and 110 degrees or less.

2. The image reading device according to claim 1, wherein:

8. When viewed from the width direction, the angle of the background portion with respect to the upper surface of the transparent member facing the background portion is 8 degrees or more and 20 degrees or less.

2. The image reading device according to claim 1, wherein:

9. an opposing member disposed opposite the transparent member and forming a sheet transport path together with the transparent member; The background portion is formed on the opposing member.

2. The image reading device according to claim 1, wherein:

10. the background portion is a sheet attached to the opposing member, 10. The image reading device according to claim 9, wherein:

11. The background is white.

2. The image reading device according to claim 1, wherein:

12. The image reading device further includes a control unit that corrects the tilt of the image of the sheet read by the reading unit based on the shadow of the sheet detected by the reading unit.

2. The image reading device according to claim 1, wherein:

13. A conveying section for conveying a sheet; A transparent member; a background portion disposed opposite the transparent member; a reading unit that is disposed on the opposite side of the background section across the transparent member, the reading unit including a light source that irradiates light toward the sheet and has a first irradiation section and a second irradiation section, and a reading section that reads the shadow of the sheet and the image of the sheet projected onto the background section through the transparent member; an image forming unit that forms an image on a sheet based on the image information read by the reading unit, When viewed from a width direction of the sheet perpendicular to the conveying direction of the sheet, the irradiation direction of the light irradiated from the first irradiation unit is a direction inclined toward the downstream side of the conveying direction, and the irradiation direction of the light irradiated from the second irradiation unit is a direction inclined toward the upstream side of the conveying direction, the background portion has a planar shape that is inclined so that the downstream side is closer to the transparent member than the upstream side in the transport direction. An image forming apparatus characterized by:

Images