Image reading device and image forming system

Abstract

To reduce reading failure of an image of a sheet, in an image reading device for reading an image of a sheet on which an image has been formed by an image forming part.SOLUTION: An image reading device 102 includes: a first reading unit 113 and a second reading unit 116 for reading an image of a sheet; and outlet conveyance rollers 119, 120 for conveying the sheet. Furthermore, the image reading device 102 includes: a backing roller 115 opposing to a glass member 114; and a backing roller 118 opposing to a glass member 117. The peripheral velocity of the backing roller 115 is set to be faster than the peripheral velocity of the outlet conveyance rollers 119, 120.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to an image reading device that reads an image on a sheet and an image forming system that includes the same. [Background technology]

[0002] Conventionally, image forming systems equipped with image reading devices that read images on sheets on which an image has been formed by an image forming unit are known. Some image reading devices used in such image forming systems have a reading unit that reads images on the sheets through a transparent member that forms a transport path along which the sheets are transported. Patent Document 1 discloses an image reading device in which a reading unit that reads an image on the top surface of a sheet is disposed downstream of a reading unit that reads an image on the bottom surface of the sheet in order to read images on both sides of the sheet received from the image forming unit. Furthermore, the image reading device described in Patent Document 1 has backing rollers disposed on the opposite side of the transparent member with respect to the transport path to stabilize the distance between the sheet and the reading unit at the reading position. The backing rollers are disposed in positions facing the reading units on both sides and are rotatable by a drive mechanism. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent Publication No. 2021-125802 Summary of the Invention [Problem to be solved by the invention]

[0004] However, when the trailing edge of the sheet being conveyed passes through the backing roller facing the upstream reading unit, the speed of the sheet may temporarily fluctuate during conveyance. Such fluctuations in the sheet conveyance speed can cause partial enlargement or reduction of the image read by the downstream reading unit, resulting in reading errors.

[0005] SUMMARY OF THE INVENTION It is therefore an object of the present invention to reduce sheet image reading failures in an image reading device that reads an image on a sheet on which an image has been formed by an image forming unit. [Means for solving the problem]

[0006] In order to solve the above-mentioned problems, an image reading device according to the present invention includes a conveying means for conveying a sheet along a conveying path, a first transparent member provided on the conveying path and facing a first side of the sheet conveyed by the conveying means, a first reading unit at a first reading position for reading an image on the first side of the sheet through the first transparent member, a first backing roller provided rotatably and facing the first transparent member at the first reading position, a second transparent member provided on the conveying path and facing a second side of the sheet conveyed by the conveying means, the second transparent member being opposite to the first side, and a second reading position located downstream of the first reading position in the conveying direction of the conveying means. the sheet conveying device is characterized in that it comprises a second reading unit that reads an image on the second side of the sheet through the second transparent member, a second backing roller that is rotatably arranged and faces the second transparent member at the second reading position, and a driving means that drives the first backing roller, wherein the conveying means is a conveying roller that is arranged downstream of the first backing roller in the conveying direction, and includes a conveying roller whose rear end passes through the first reading position while the conveying roller is conveying the sheet, and the driving means drives the first backing roller so that the peripheral speed of the first backing roller is faster than the peripheral speed of the conveying roller. [Effects of the Invention]

[0007] According to the present invention, in an image reading device that reads an image on a sheet on which an image has been formed by an image forming unit, it is possible to reduce failures in reading the image on the sheet. [Brief explanation of the drawings]

[0008] [Figure 1] 1 is an overall view of an image forming system. [Figure 2] FIG. [Figure 3] FIG. [Figure 4] FIG. 3 is a side view of the image reading device at the reading position. [Figure 5] FIG. 3 is a side view of the image reading device at the reading position. [Figure 6] FIG. 10 is a diagram showing the gap between the backing roller and the glass. [Figure 7] FIG. 10 is a diagram showing the backing roller when conveying cardboard. [Figure 8] 10 is a diagram showing the force when cardboard passes through a backing roller. [Figure 9] FIG. 4 is a diagram showing an image enlargement / reduction ratio in the sub-scanning direction. [Figure 10] 4 is a flowchart showing control of the image forming system. DETAILED DESCRIPTION OF THE INVENTION

[0009] Hereinafter, embodiments of the present invention will be described by way of example with reference to the drawings. However, the dimensions, materials, shapes, and relative positions of the components described in the present embodiments may be changed as appropriate depending on the configuration of the device to which the present invention is applied and various conditions, and the scope of the present invention is not limited to the following embodiments.

[0010] [Configuration of image forming device] 1 is an overall view of an image forming system 100 according to this embodiment. The image forming system 100 is a system in which a printer 101, an image reading device 102, and a loading device 103 are connected. The image forming system 100 also includes an operation unit 21 that allows a user to input various information to the image forming system.

[0011] The printer 101, which is an image forming apparatus, is a four-color full-color printer that uses an electrophotographic process. This printer 101 forms a toner image on a recording material based on an image signal input to a control unit 301 from an external device 300, such as an information terminal such as a personal computer or an image reader. The recording material is a recording medium (hereinafter referred to as sheet P) on which a toner image can be formed, and examples of the recording material include plain paper, thick paper, extra thick paper, overhead projector sheets, coated paper, and label paper.

[0012] The printer 101 has four image forming units 101a that form toner images of yellow (Y), magenta (M), cyan (C), and black (Bk). The image forming units 101a form toner images using a conventionally known electrophotographic process. These four image forming units 101a are arranged in parallel from left to right in FIG. 1. A laser scanner unit 3 serving as an exposure device is disposed above the image forming units 101a, and an intermediate transfer belt 50 is disposed below the image forming units 101a. The intermediate transfer belt 50 is stretched over a drive roller 51, a tension roller 52, and a secondary transfer inner roller 53, and is driven in the direction of the arrow in FIG. 1.

[0013] Each imaging mechanism 101a has the same electrophotographic process configuration, and differs only in the color of the toner (developer) used. The imaging mechanism 101a has a photosensitive drum 1 as an image carrier, a charger 2, a developing unit 4, a primary transfer roller 6, and a drum cleaner 7. Note that in FIG. 1, to avoid cluttering the drawing, reference numerals for imaging mechanism 101a other than the black (Bk) imaging mechanism 101a are omitted.

[0014] The toner images of each color are superimposed and primarily transferred from the photosensitive drums 1 of the image forming mechanisms 101a to the intermediate transfer belt 50. As a result, a full-color unfixed toner image of four superimposed colors Y, M, C, and Bk is formed on the intermediate transfer belt 50.

[0015] The printer 101 includes a cassette 24 that stores sheets P. The sheets P fed from the cassette 24 pass through a conveying path 13 and are introduced into a secondary transfer nip portion 15, which is a pressure contact portion between the intermediate transfer belt 50 and the secondary transfer roller 14, at a predetermined controlled timing. As a result, the four-color superimposed toner image on the intermediate transfer belt 50 is secondarily transferred onto the sheet P. Then, any residual toner remaining on the transfer belt 50 after the secondary transfer onto the sheet P is removed from the surface of the intermediate transfer belt 50 by a belt cleaner 19.

[0016] Thereafter, the sheet P onto which the toner image has been transferred is introduced into the fixing device 16, where it undergoes a fixing process that includes the application of heat and pressure. After passing through the fixing device 16, the sheet P is discharged from the printer 101 by a pair of discharge rollers 17 and conveyed to the image reading device 102. In the case of double-sided printing, the sheet P with the image formed on one side passes through the reverse conveying path 57 and is conveyed again to the secondary transfer nip portion 15.

[0017] The image forming unit of the printer 101 in this embodiment is configured to use an electrophotographic process, but the image forming unit may be configured to use another image forming method such as an inkjet system.

[0018] [Image reader configuration] 2 is a cross-sectional view of the image reading device 102. The image reading device 102 is a device that reads an image on a sheet on which an image has been formed by the printer 101. The image reading device 102 has a conveying path 123 along which the sheet conveyed from the printer 101 is conveyed. The conveying path 123 is a substantially horizontal conveying path formed by an upper conveying guide 121 and a lower conveying guide 122. In the conveying path 123, entrance conveying rollers 111 and 112 and exit conveying rollers 119 and 120, which are conveying means, are arranged.

[0019] The image reading section 147 of the image reading device 102 is provided with a first reading unit 113 and a second reading unit 116. The first reading unit 113 reads an image on the bottom surface (first surface) of a sheet, and the second reading unit 116 reads an image on the top surface (second surface) of the sheet. This allows the image reading device 102 to read images on both sides of a sheet. The second reading unit 116 is disposed downstream of the first reading unit 113 in the conveying direction of the conveying path 123, and the reading position (second reading position) of the second reading unit 116 is downstream of the reading position (first reading position) of the first reading unit 113. The first reading unit 113 and the second reading unit 116 are, for example, CIS or CCD cameras.

[0020] The images read by the first reading unit 113 and the second reading unit 116 are sent as signals to the external PC 305. The external PC 305 compares the images read by the first reading unit 113 and the second reading unit 116 with pre-registered image data and detects image defects such as stains on the sheet. In this way, the external PC 305, which serves as a determination means, can determine whether the sheet on which the image is formed by the printer 101 is normal.

[0021] In this embodiment, the external PC 305 is provided outside the image reading device 102, but the external PC 305 may be provided integrally with the image reading device 102 or the printer 101.

[0022] A glass 114, which is a first transparent member, is incorporated into the lower conveying guide 122, and the glass 114 forms part of the conveying path 123. The glass 114 faces the lower surface of the sheet being conveyed. An image on the lower surface of the sheet being conveyed on the conveying path 123 is read by the first reading unit 113 through the glass 114.

[0023] A backing roller 115 is disposed at a position facing the glass 114 on the conveying path 123. The backing roller 115 is an example of a first backing roller in this embodiment. The backing roller 115 is disposed at a reading position of the first reading unit 113 in the conveying direction. The backing roller 115 is supported by the upper conveying guide 121. The backing roller 115 can be rotated by a drive gear 351 connected to a drive motor 350, which is a first motor (see FIG. 4, described later). The drive gear 351 transmits the driving force from the drive motor 350 to the backing roller 115. The drive motor 350 and the drive gear 351 are an example of a drive means in this embodiment.

[0024] A second transparent member, glass 117, is incorporated into the upper conveying guide 121, and the glass 117 forms part of the conveying path 123. The glass 117 faces the upper surface of the sheet being conveyed. An image on the upper surface of the sheet being conveyed along the conveying path 123 is read by the second reading unit 116 through the glass 117.

[0025] A backing roller 118 is disposed at a position facing the glass 117 on the conveying path 123. The backing roller 118 is an example of a second backing roller in this embodiment. The backing roller 118 is disposed at a reading position of the second reading unit 116 in the conveying direction. The backing roller 118 is supported by a lower conveying guide 122. The backing roller 118 can be rotated by a second motor (not shown) in the same way as the backing roller 115. The pressure with which the backing rollers 115 and 118 press the sheet is smaller than the nip pressure of the exit conveying rollers 119 and 120.

[0026] The sheet on which the image has been read by the first reading unit 113 and the second reading unit 116 is transported from the image reading device 102 to the stacking device 103 by exit transport rollers 119 and 120. A control device 302, which is a control means, controls the driving of each roller of the image reading device 102 and the first reading unit 113 and second reading unit 116. The rollers, first reading unit 113, second reading unit 116, and control device 302 described above are housed inside a housing 136 of the image reading device 102.

[0027] [Loading device configuration] 3 is a cross-sectional view of the stacking device 103. A sheet transported from the image reading device 102 to the stacking device 103 is stacked on a first stacking unit 158 ​​or a second stacking unit 165. A flapper 155 switches the transport path along which the sheet is transported between a transport path 153 and a transport path 154. When a sheet is discharged to the first stacking unit 158, the sheet is transported along the transport path 153 by transport rollers 151 and 152 and transport rollers 156 and 157. When a sheet is discharged to the second stacking unit 165, the sheet is guided to the transport path 154 by the flapper 155 and transported by transport rollers 159 and 160, transport rollers 161 and 162, and transport rollers 163 and 164. A control unit 303 controls the driving of each transport roller and the flapper 155.

[0028] As described above, the image forming system 100 can inspect the image read by the image reading device 102. The control unit 303 controls each conveyance roller and the flapper 155 so that a sheet determined to be normal by the external PC 305 is discharged to the first stacking unit 158, and a sheet determined to be abnormal by the external PC 305 is discharged to the second stacking unit 165.

[0029] [Explanation of the image reading unit] 4 is a side view of the first reading unit 113 and the backing roller 115 when a sheet 201 having a thickness t of less than 0.4 mm is being conveyed. An example of the sheet 201 having a thickness t of less than 0.4 mm is plain paper that is generally used for printing.

[0030] As shown in Figure 4, abutment portions 131 that abut against the glass 114 are disposed on both ends of the backing roller 115 in the width direction (the direction perpendicular to the conveying direction). The backing roller 115 is configured to be movable in a direction away from the glass 114 (upward in Figure 4), and is biased toward the glass 114 by a spring 135, which serves as a biasing means. At this time, the abutment portions 131, which serve as gap forming portions, abut against the glass 114, forming a gap 133 between the glass 114 and the backing roller 115.

[0031] In this embodiment, the gap 133 is approximately 0.4 mm, and the backing roller 115 prevents the sheet 201 from floating more than 0.4 mm above the glass 114 during transport. Because the thickness of the sheet 201 is less than 0.4 mm, the sheet 201 does not push up against the backing roller 115. Therefore, while the sheet 201 is being transported, the abutment portion 131 remains in contact with the glass 114. The second reading unit 116 on the downstream side is also configured with a mechanism similar to that of the first reading unit 113 and the backing roller 115, except that the orientation is reversed.

[0032] FIG. 5 is a side view of the first reading unit 113 and the backing roller 115 in a state where a sheet (ultra-thick paper) 202 having a thickness t of 0.4 mm or more is being conveyed.

[0033] 5, the thickness of the sheet 202 is greater than the original gap 133, so the sheet 202 lifts the backing roller 115 against the biasing force of the spring 135, and the abutment portion 131 rises from the glass 114. At this time, the lower surface of the sheet 202 is in close contact with the glass 114, so the first reading unit 113 can correctly read the image on the sheet 202.

[0034] If the gap 133 were set too large, it would be impossible to prevent the sheet 201 with a thickness t of less than 0.4 mm from lifting in the depth direction (the direction perpendicular to the surface of the glass 114), which could result in poor reading. In this embodiment, the gap 133 is set to 0.4 mm, which is within the range in which the first reading unit 113 and the second reading unit 116 can correctly read the image. For a sheet 202 with a thickness t of 0.4 mm or more, the backing roller 115 is pushed up by the sheet being conveyed, causing the gap 133 to fluctuate. This allows the image reading device 102 to read images on sheets of various thicknesses. Note that while the gap 133 in this embodiment is 0.4 mm, the size of the gap between the glass 114 and the backing roller 115 is not limited to this, and it is preferable to set it appropriately according to the performance of the reading unit.

[0035] FIG. 6 is an enlarged view of the backing roller 115 when a sheet 201 with a thickness t of less than 0.4 mm is being conveyed. Vs indicates the movement speed (conveyance speed) of the sheet 201. The exit conveyance rollers 119 and 120 are positioned so as to contact the sheet while the second reading unit 116 is reading the image on the sheet. Therefore, the conveyance speed Vs is almost the same as the peripheral speed of the exit conveyance rollers 119 and 120, which are disposed downstream of the first reading unit 113. While the exit conveyance rollers 119 and 120 are conveying the sheet, the trailing edge of the sheet passes through the reading position of the first reading unit 113 (between the glass 114 and the backing roller 115). In this embodiment, the peripheral speed refers to the speed of the outer surface of the rotating roller.

[0036] Vb indicates the peripheral speed of the backing roller 115. In this embodiment, the control device 302 controls the drive motor 350 so that the peripheral speed Vb of the backing roller 115 is faster than the conveying speed Vs. In other words, the peripheral speed Vb of the backing roller 115 is set to a value faster than the peripheral speeds of the exit conveying rollers 119 and 120.

[0037] 6, the backing roller 115 is driven to rotate at a peripheral speed Vb, but when a sheet 201 with a thickness t of less than 0.4 mm is being conveyed, there is a gap between the backing roller 115 and the sheet 201. Therefore, the sheet conveying force applied to the sheet by the backing roller 115 is extremely small. Therefore, the speed difference between the conveying speed Vs and the peripheral speed Vb of the backing roller 115 has almost no effect on the image reading of the sheet 201.

[0038] FIG. 7 is an enlarged view of the backing roller 115 while a sheet 202 having a thickness t of 0.4 mm or more is being conveyed. As shown in FIG. 7, when the sheet 202 is being conveyed, the backing roller 115 is pushed by the sheet 202 and moves in a direction away from the glass 114. At this time, the backing roller 115 is in contact with the sheet 202. However, because the pressure with which the backing roller 115 presses the sheet is smaller than the nip pressure of the exit conveyance rollers 119 and 120, the speed difference between the conveyance speed Vs and the peripheral speed Vb of the backing roller 115 has almost no effect on image reading of the sheet 202. Furthermore, since the sheet 202 having a thickness t of 0.4 mm or more has higher rigidity than the sheet 201 having a thickness t of less than 0.4 mm, the sheet 202 is less likely to deform, and the backing roller 115 and the sheet 202 slip. Therefore, the influence of the speed difference between the conveying speed Vs and the peripheral speed Vb of the backing roller 115 on the image reading of the sheet 202 is reduced.

[0039] Fig. 8 is an enlarged view of backing roller 115 when the trailing end of sheet 202, whose thickness t is 0.4 mm or more, leaves backing roller 115. As shown in Fig. 8, when the trailing end of sheet 202 leaves backing roller 115, the trailing end of sheet 202 has advanced in the conveying direction from directly below the center of rotation of backing roller 115 by an angle θ. At this time, the component of the peripheral speed Vb of backing roller 115 along the conveying direction at the point where sheet 202 and backing roller 115 are in contact is Vb × COS(θ).

[0040] If the peripheral speed Vb of the backing roller 115 is set to the same speed as the conveyance speed Vs (Vb = Vs), then Vb × COS(θ) becomes smaller than the conveyance speed Vs (Vb × COS(θ) < Vs). As a result, a tug-of-war of the sheet occurs between the outlet conveyance rollers 119 and 120 and the backing roller 115, and when the sheet is released from the tug-of-war, a roller dropout shock occurs, which may lead to image defects in the second reading unit 116.

[0041] On the other hand, in the present embodiment, the peripheral speed Vb of the backing roller 115 is set to a value higher than the conveyance speed Vs. More specifically, the peripheral speed Vb of the backing roller 115 is set to a value that satisfies Vs < Vb × COS(θ). Therefore, no tug-of-war of the sheet occurs between the outlet conveyance rollers 119 and 120 and the backing roller 115. That is, since the roller dropout shock when the sheet is released from the tug-of-war can be suppressed, it is possible to suppress image defects in the downstream second reading unit 116.

[0042] In the present embodiment, as an example, the conveyance speed Vs is 100 [mm / S], the peripheral speed Vb of the backing roller 115 is 103 [mm / S], and the outer diameter of the backing roller 115 is 20 [mm]. When the thickness t of the sheet 202 is 0.5 [mm], the angle θ is approximately 8.1°, and Vb × COS(θ) = 101.97 [mm / S]. That is, the peripheral speed Vb of the backing roller 115 is a value that satisfies Vs < Vb × COS(θ).

[0043] [Explanation of the disturbance of the image magnification ratio] FIG. 9 is a graph showing the image enlargement / reduction ratio in the sub-scanning direction of a read image when the downstream second reading unit 116 reads an image of a sheet (ultra-thick paper) with a thickness t of approximately 0.5 mm. The vertical axis of the graph in FIG. 9 represents the image enlargement / reduction ratio, and the horizontal axis represents the sheet transport distance. The image enlargement / reduction ratio is the rate at which the read image is enlarged or reduced at a predetermined pitch in the transport direction. It is desirable that the image enlargement / reduction ratio be stable at close to 0%. FIGS. 9(a) to 9(d) each show a different ratio of the circumferential speed Vb of the backing roller 115 to the transport speed Vs. FIG. 9(a) is a graph when the circumferential speed Vb of the backing roller 115 is 97% (3% slower) of the transport speed Vs. FIG. 9(b) is a graph when the circumferential speed Vb of the backing roller 115 is 100% (constant speed) of the transport speed Vs. 9(c) is a graph when the peripheral speed Vb of the backing roller 115 is 103% (3% faster) of the conveying speed Vs. FIG. 9(d) is a graph when the peripheral speed Vb of the backing roller 115 is 106% (6% faster) of the conveying speed Vs. That is, FIGS. 9(a) and 9(b) are graphs when the peripheral speed Vb of the backing roller 115 is set to be equal to or lower than the peripheral speeds of the exit conveying rollers 119 and 120. On the other hand, FIGS. 9(c) and 9(d) are graphs when the peripheral speed Vb of the backing roller 115 is set to be greater than the peripheral speeds of the exit conveying rollers 119 and 120.

[0044] 9(a) to 9(d), the timing when the trailing edge of the sheet leaves the backing roller 115 is when the value on the horizontal axis is near 400. At the timing when the trailing edge of the sheet leaves the backing roller 115, a temporary fluctuation in the sheet speed occurs, which may cause a disturbance in the image enlargement / reduction ratio of the image read by the second reading unit 116.

[0045] As shown in Figure 9(a), when the peripheral speed Vb of the backing roller 115 is 97% (3% slower) than the conveying speed Vs, the image enlargement / reduction ratio is significantly distorted, resulting in reading errors. As shown in Figure 9(b), even when the peripheral speed Vb of the backing roller 115 is 100% (constant speed) of the conveying speed Vs, the image enlargement / reduction ratio is slightly distorted. As shown in Figure 9(c), when the peripheral speed Vb of the backing roller 115 is 103% (3% faster) than the conveying speed Vs, the image enlargement / reduction ratio is only slightly distorted, and the positive and negative signals cancel each other out. As shown in Figure 9(d), when the peripheral speed Vb of the backing roller 115 is 106% (6% faster) than the conveying speed Vs, the image enlargement / reduction ratio is slightly distorted.

[0046] As described above, by setting the peripheral speed Vb of the backing roller 115 to a value greater than the peripheral speeds of the exit conveying rollers 119 and 120, the image enlargement / reduction ratio is stabilized and reading defects can be reduced. Furthermore, if the peripheral speed Vb of the backing roller 115 is set too fast, there is a risk that the image enlargement / reduction ratio will be disturbed. Therefore, it is preferable that the peripheral speed Vb of the backing roller 115 be 101% or more and 104% or less of the peripheral speed of the exit conveying rollers 119 and 120.

[0047] [Flowchart explanation] 8, when the thickness t of the sheet is larger than the gap 133, the backing roller 115 is pushed up by the sheet. Therefore, the peripheral speed Vb of the backing roller 115 may be set to a value larger than the peripheral speeds of the exit conveying rollers 119 and 120 only when the thickness t of the sheet is equal to or larger than a predetermined thickness.

[0048] 10 shows a flowchart of the reading operation according to the paper type, executed by the control device 302. The image reading device 102 may set the peripheral speed Vb of the backing roller 115 to a value greater than the peripheral speeds of the exit conveying rollers 119 and 120 regardless of the paper type, but if ultra-thick paper is not frequently conveyed, the peripheral speed Vb of the backing roller 115 may be changed according to the paper type.

[0049] When a sheet is transported from the printer 101 to the image reading device 102, the control device 302 starts the process shown in the flowchart in Fig. 10. As shown in Fig. 10, the control device 302 acquires information about the sheet to be transported (S101). At this time, the control device 302 functions as an acquisition unit, and refers to the sheet information input by the user via the operation unit 21. The sheet information input by the user via the operation unit 21 is saved in the control unit 301.

[0050] Next, the control device 302 determines whether the sheet thickness t is equal to or greater than a predetermined thickness based on the paper information acquired in S101 (S102). In this embodiment, the predetermined thickness is set to 0.4 mm, but the predetermined thickness may be changed as appropriate depending on the size of the gap 133.

[0051] If the sheet thickness t is equal to or greater than a predetermined thickness (Yes in S102), the control device 302 executes the backing roller high-speed mode (S103). The backing roller high-speed mode is a mode in which the drive motor 350 is controlled so that the peripheral speed Vb of the backing roller 115 is greater than the peripheral speeds of the exit conveying rollers 119 and 120. More specifically, in the backing roller high-speed mode, the control device 302 sets the peripheral speed Vb of the backing roller 115 to be equal to or greater than 101% and equal to or less than 104% of the peripheral speeds of the exit conveying rollers 119 and 120. The peripheral speed Vb of the backing roller 115 at this time is defined as a first peripheral speed.

[0052] On the other hand, if the sheet thickness t is less than the predetermined thickness (No in S102), the control device 302 executes the backing roller normal speed mode (S104). The backing roller normal speed mode is a mode in which the drive motor 350 is controlled so that the peripheral speed Vb of the backing roller 115 is equal to the peripheral speed of the exit conveying rollers 119, 120. The peripheral speed Vb of the backing roller 115 at this time is defined as a second peripheral speed. The second peripheral speed is slower than the first peripheral speed.

[0053] Thereafter, the control device 302 executes image reading by the first reading unit 113 and the second reading unit 116 while conveying the sheet in the backing roller high speed mode or the backing roller normal speed mode (S105). After the image reading is completed, the control device 302 ends the processing of the flowchart.

[0054] By processing the above flowchart, the control device 302 executes the backing roller high speed mode when the sheet thickness is a first thickness that is greater than a predetermined thickness, and executes the backing roller normal speed mode when the sheet thickness is a second thickness that is less than the predetermined thickness.

[0055] 10, the control device 302 switches between the backing roller high-speed mode and the backing roller normal-speed mode based on the sheet thickness t. However, the control device 302 may also switch between the backing roller high-speed mode and the backing roller normal-speed mode based on the sheet basis weight. In this case, the control device 302 executes the backing roller high-speed mode when the sheet basis weight is a first basis weight that is equal to or greater than a predetermined basis weight, and executes the backing roller normal-speed mode when the sheet basis weight is a second basis weight that is smaller than the predetermined basis weight.

[0056] By such control, the control device 302 can set the peripheral speed Vb of the backing roller 115 to an appropriate value depending on the type of sheet being conveyed.

[0057] As described above, in the image reading device 102 of this embodiment, the peripheral speed Vb of the backing roller 115 is set to be greater than the peripheral speeds of the exit conveying rollers 119 and 120. This makes it possible to suppress the roller disengagement shock when the sheet is released from the mutual pulling, and to suppress image defects in the downstream second reading unit 116. [Explanation of symbols]

[0058] 100 Image forming system 101 Printer 102 Image reader 103 Loading device 113 First reading unit 115 Backing Roller 116 Second reading unit 118 Backing Roller 111, 112 Entrance conveying rollers 119, 120 Exit conveying roller

Claims

1. a conveying means for conveying the sheet along a conveying path; a first transparent member provided in the conveying path and facing a first surface of the sheet conveyed by the conveying means; a first reading unit that reads an image on the first surface of the sheet through the first transparent member at a first reading position; a first backing roller that is rotatably provided and faces the first transparent member at the first reading position; a second transparent member provided in the conveying path and facing a second surface of the sheet conveyed by the conveying means, the second surface being opposite to the first surface; a second reading unit that reads an image on the second surface of the sheet through the second transparent member at a second reading position located downstream of the first reading position in the conveying direction of the conveying means; a second backing roller that is rotatably provided and faces the second transparent member at the second reading position; a driving means for driving the first backing roller; Equipped with the conveying means is a conveying roller provided downstream of the first backing roller in the conveying direction, and includes a conveying roller through which a rear end of the sheet passes the first reading position while the conveying roller is conveying the sheet; the driving means drives the first backing roller so that the peripheral speed of the first backing roller is faster than the peripheral speed of the conveying roller; An image reading device characterized by:

2. the conveying roller is provided at a position where it contacts the sheet while the second reading unit is reading an image on the sheet; 2. The image reading device according to claim 1, wherein:

3. the peripheral speed of the first backing roller is 101% or more of the peripheral speed of the conveying roller and 104% or less of the peripheral speed of the conveying roller; 3. The image reading device according to claim 1, wherein the image reading device is a scanning device.

4. the first backing roller is movable in a direction away from the first transparent member; 4. The image reading device according to claim 1, wherein the image reading device is a scanning device.

5. a gap forming portion that forms a gap between the first backing roller and the first transparent member; and a biasing means for biasing the first backing roller toward the first transparent member.

5. The image reading device according to claim 4, wherein:

6. the driving means includes a motor and a gear that transmits driving force from the motor to the first backing roller; 6. The image reading device according to claim 1, wherein the image reading device is a scanning device.

7. an acquisition unit for acquiring the thickness of the sheet conveyed by the conveying unit; a control means for controlling the driving means so that the peripheral speed of the first backing roller becomes a first peripheral speed that is faster than the peripheral speed of the conveying roller when the sheet thickness acquired by the acquisition means is a first thickness, and for controlling the driving means so that the peripheral speed of the first backing roller becomes a second peripheral speed that is slower than the first peripheral speed when the sheet thickness acquired by the acquisition means is a second thickness that is thinner than the first thickness.

7. The image reading device according to claim 1, wherein the image reading device is a scanning device.

8. an acquisition unit for acquiring the basis weight of the sheet conveyed by the conveying unit; a control means for controlling the driving means so that the peripheral speed of the first backing roller becomes a first peripheral speed that is faster than the peripheral speed of the conveying roller when the basis weight of the sheet acquired by the acquiring means is a first basis weight, and for controlling the driving means so that the peripheral speed of the first backing roller becomes a second peripheral speed that is slower than the first peripheral speed when the basis weight of the sheet acquired by the acquiring means is a second basis weight that is smaller than the first basis weight.

7. The image reading device according to claim 1, wherein the image reading device is a scanning device.

9. the second peripheral speed is equal to the peripheral speed of the conveying roller; 9. The image reading device according to claim 7, wherein the image reading device is a scanning device.

10. An image reading device according to any one of claims 1 to 9; an image forming unit that forms an image on a sheet; An image forming system comprising: The image reading device includes a determination unit that determines whether the image on the sheet is normal by comparing image data obtained by reading the image on the sheet on which the image is formed by the image forming unit with pre-registered image data. An image forming system comprising:

Images