Reading device, image forming system

Abstract

To provide a reading device that can accurately read an image on a sheet conveyed in the vertical direction.SOLUTION: A reading device comprises a color measuring unit 500 that reads an image from a sheet S conveyed upward from below in the vertical direction through a conveyance path 432. The color measuring unit 500 has a color detection sensor 551 that is arranged between an upstream conveyance drive roller 581 and an upstream conveyance driven roller 582 and a downstream conveyance drive roller 583 and a downstream conveyance driven roller 584, and detects the image from the sheet S sandwiched by the upstream conveyance drive roller 581 and the upstream conveyance driven roller 582 and the downstream conveyance drive roller 583 and the downstream conveyance driven roller 584.SELECTED DRAWING: Figure 10

Description

[Technical field]

[0001] The present invention relates to a reading device that is provided in an image forming apparatus such as a copying machine, a multifunction machine, or a printer, and that reads an image formed on a sheet. [Background technology]

[0002] In recent years, the market for on-demand image forming devices has expanded. For example, electrophotographic image forming devices are becoming more widespread in the offset printing market. In addition, there are inkjet image forming devices that have succeeded in cultivating a wide range of markets due to their large format, low initial cost, and ultra-high speed. However, market expansion is not easy, and the image quality (hereinafter referred to as "image quality") of the previous image forming devices that have dominated that market must be maintained.

[0003] Image quality includes gradation, graininess, in-plane uniformity, character quality, color reproducibility (including color stability), etc. Among these, color reproducibility is said to be the most important. Humans have memories of colors they expect based on experience (especially human skin, sky, metal, etc.), and can feel discomfort when they see colors that are beyond the tolerance range of this memory. Such memorized colors are called "memory colors." The reproducibility of memory colors becomes important when outputting them as photographs, etc. In addition, office users who feel discomfort when they see differences in color between printed business documents and their monitors, and graphic arts users who handle computer graphics, etc., have high demands for color reproducibility, including stability, for on-demand image forming devices.

[0004] Color reproducibility is an issue not only between the same model, but also between different models, image forming devices of different types, and image display devices such as monitors. To perform color matching between these devices, there is software and color measurement devices that create multidimensional LUTs (Look Up Tables) called ICC (International Color Consortium) profiles. Professional users create an ICC profile for the printer and an ICC profile for the offset press to build a color management environment. This makes it possible to match the colors output by the printer to the colors printed by the offset press, so the printer can be used for color proofing of the offset press and printing small runs.

[0005] The contents of the offset press ICC profile and the printer ICC profile are calibrated to correspond to a color space that is independent of the press and printer, based on the color measurement results of patch images using a colorimeter. The color space is, for example, the CIE L*a*b* color space (CIE stands for Commission Internationale d'Eclairage). This allows the colors printed by the press to match the colors printed by the printer. The color management module (CMM) can create print data by performing color conversion using these ICC profiles.

[0006] As described above, color management environments including colorimeters, applications, and profile creation software are in place. However, offline colorimeters take time to measure colors. In addition, this environment has issues such as creating ICC profiles, uploading ICC profiles to printers, and making effective use of uploaded ICC profiles, and is not widespread among general users. In order to perform color measurements more quickly, create ICC profiles more easily, and automate the setting process, image forming devices are provided that are equipped with a reading device that has an inline colorimeter mounted near the printer's sheet discharge section.

[0007] Patent Documents 1 and 2 disclose an image forming apparatus that detects patch images formed on a sheet using a color sensor consisting of a light source, a diffraction grating, and a position detection sensor. The color sensor is configured as an in-line colorimeter that improves detection accuracy. The detection value by the color sensor can be converted into a spectral reflectance and converted into CIE L*a*b* taking into account tristimulus values, etc.

[0008] As an index of color matching accuracy and color stability, the color matching accuracy standard (IT8.7 / 4 (ISO 12642:1617 patches) [4.2.2]) described in ISO 12647-7 specifies an average ΔE of 4.0. In addition, the color stability standard, reproducibility [4.2.3], specifies that each patch image must have a ΔE of 1.5 or less. To satisfy these specifications, it is desirable for the detection accuracy of the color sensor to be ΔE of 1.0 or less. ΔE is a value expressed by the following three-dimensional distance formula between two points (L1, a1, b1) and (L2, a2, b2) in the L*a*b* color space defined by CIE. ΔE=((L1-L2)^2+(a1-a2)^2+(b1-b2)^2)^1 / 2 [Prior art documents] [Patent documents]

[0009] [Patent Document 1] JP 2013-54324 A [Patent Document 2] JP 2009-53346 A Summary of the Invention [Problem to be solved by the invention]

[0010] As described above, in-line color management has been conventionally performed by an image forming apparatus equipped with a reading device equipped with a color sensor (colorimeter) at the rear of a printer. However, in the case of a configuration such as that of Patent Document 1, for example, the color sensor is fixed, so that it can only read (measure the color of) patch images at the reading position of the color sensor in a direction perpendicular to the sheet conveyance direction (hereinafter referred to as the "main scanning direction"). Therefore, the number of patch images read from one sheet is reduced. In other words, the number of sheets required for color management increases. By arranging multiple color sensors in the main scanning direction, it is possible to read many patch images from one sheet. However, since color sensors are generally expensive, the product cost increases. In addition to the viewpoint of arranging many patch images, it is also necessary to check the color tone over the entire area in the main scanning direction in order to check the image uniformity and density uniformity in the main scanning direction.

[0011] By moving the color sensor in the main scanning direction, it is possible to scan the sheet in the main scanning direction. By repeatedly scanning in the main scanning direction and feeding / stopping the sheet, it becomes possible to detect patch images over the entire area of ​​the sheet. If patch images over the entire area of ​​the sheet can be detected, the number of patch images per sheet can be increased, thereby reducing the number of sheets required for color correction. In addition, in order to detect patch images over the entire area in the main scanning direction, it is also possible to correct the density uniformity in the main scanning direction.

[0012] The color sensor may be provided on a transport path that guides a sheet in the vertical direction. In this case, the sheet is read by the color sensor while being transported in the vertical direction. When reading a sheet transported in the vertical direction, if the stiffness of the sheet is low, the state of the sheet becomes unstable due to its own weight. As a result, the color sensor may be unable to move in the main scanning direction due to the sheet. Even if the color sensor is movable, the distance between the color sensor and the sheet may deviate from the required value, and color measurement performance may not be guaranteed.

[0013] The present invention has been made in consideration of the above-mentioned problems, and has as its main object to provide a reading device capable of reading, with high accuracy, an image on a sheet transported in the vertical direction. [Means for solving the problem]

[0014] The reading device of the present invention is a reading device that reads an image of a sheet transported from an image forming device, and includes a first transport path for transporting a sheet from the image forming device to a post-processing device connected downstream of the reading device and performing post-processing on the sheet, a tray disposed vertically above the first transport path and onto which the sheet is discharged, a second transport path that branches off from the first transport path at a branching portion and transports the sheet to the tray, a first transport roller pair disposed vertically above the branching portion and on the second transport path, nipping and transporting the sheet, a second transport roller pair disposed vertically above both the branching portion and the first transport roller pair and between the first transport roller pair and the tray, nipping and transporting the sheet transported along the second transport path by the first transport roller pair, and a reading means that moves in a direction intersecting a sheet transport direction, and a sheet is sandwiched between the first transport roller pair and the second transport roller pair. a reading unit that reads an image on a sheet located in a region between the first conveying roller pair and the second conveying roller pair by moving in a direction intersecting a conveying direction of the sheet in a state where the sheet is conveyed in the conveying direction, a distance from a leading edge of the sheet in the conveying direction to a leading edge of an image formed on the sheet in the conveying direction is a first distance, a distance from a reading position where the image formed on the sheet is read by the reading unit to a nip of the second conveying roller pair in the conveying direction is a second distance, the first distance is longer than the second distance, a distance from a rear end of the sheet in the conveying direction to a rear end of the image formed on the sheet in the conveying direction is a third distance, a distance from a reading position where the image formed on the sheet is read by the reading unit to the nip of the first conveying roller pair in the conveying direction is a fourth distance, the third distance is longer than the fourth distance, and the reading unit is configured to read an image on the sheet located in a region between the first conveying roller pair and the second conveying roller pair when the sheet is conveyed in the conveying direction. Delivery The method is characterized in that, while the sheet is nipped and stopped by a pair of rollers, it moves in a direction intersecting the conveying direction, thereby reading an image formed on the rearmost end side of the sheet in the conveying direction. The image forming system of the present invention includes an image forming device that forms an image on a sheet, a reading device that reads the image on the sheet on which the image is formed by the image forming device and which is transported from the image forming device, and a post-processing device that is connected to the reading device and performs post-processing on the sheet that has passed the reading device, and controls the density of the image formed by the image forming device based on the reading result by the reading device, and the reading device includes a discharge tray to which the sheet is discharged, a first transport path for transporting the sheet from the image forming device to the post-processing device, and a second transport path that branches off from a first transport path at a branching portion and transports a sheet from the branching portion to the discharge tray; a first transport roller pair that is provided on the second transport path and nip and transports a sheet; a second transport roller pair that is provided on the second transport path between the first transport roller pair and the discharge tray and nip and transports a sheet transported on the second transport path by the first transport roller pair; and a reading means that moves in a direction intersecting a transport direction of the sheet, and when a sheet is sandwiched between the first transport roller pair and the second transport roller pair, the reading means reads the sheet from the first transport roller pair and the second transport roller pair. a reading unit that reads an image on a sheet located between the first conveying roller pair and the second conveying roller pair by moving in a direction intersecting a conveying direction of the sheet, wherein the discharge tray, the second conveying path, the first conveying roller pair, and the second conveying roller pair are disposed vertically above the branching portion, and the second conveying roller pair is disposed vertically above the first conveying roller pair, and in the conveying direction of the sheet, a distance from a leading edge of the sheet in the conveying direction to a leading edge of an image formed on the sheet in the conveying direction is a first distance, a distance from a reading position where an image formed on a sheet by the reading means is read to a nip of the second conveying roller pair is a second distance, the first distance is longer than the second distance, a distance in the conveying direction from a rear end of the sheet in the conveying direction to a rear end of the image formed on the sheet in the conveying direction is a third distance, a distance in the conveying direction from a reading position where an image formed on a sheet by the reading means is read to a nip of the first conveying roller pair is a fourth distance, the third distance is longer than the fourth distance, and the reading meansThe sheet is the first, Delivery The method is characterized in that, while the sheet is nipped and stopped by a pair of rollers, it moves in a direction intersecting the conveying direction, thereby reading an image formed on the rearmost end side of the sheet in the conveying direction. Effect of the Invention

[0015] According to the present invention, it is possible to read an image on a sheet transported in the vertical direction with high accuracy. [Brief description of the drawings]

[0016] [Figure 1] FIG. 1 is a diagram illustrating the configuration of an image forming apparatus. [Diagram 2] FIG. [Diagram 3] FIG. [Figure 4] FIG. [Diagram 5] An illustration of an ICC profile. [Figure 6] FIG. 1 is an explanatory diagram of color management. [Figure 7] FIG. [Figure 8] FIG. [Figure 9] FIG. [Figure 10] 6A to 6C are diagrams illustrating examples of the posture of a sheet transported through a reading path. [Figure 11] 4A to 4E are explanatory diagrams of the patch image reading process (colorimetry). [Figure 12] 4A and 4B are explanatory diagrams of the formation range of a patch image. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0017] Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

[0018] (Image forming device) 1 is a configuration diagram of an image forming apparatus according to the present embodiment. The image forming apparatus 1 according to the present embodiment is composed of a printer 100, an automatic reader 400, and a paper discharge device 600. The printer 100 forms an image on a sheet S by an electrophotographic method. The printer according to the present embodiment may be an inkjet printer or a dye-sublimation printer.

[0019] The printer 100 includes, within a housing 101, mechanisms that constitute an engine section for image formation, and a controller (described below) that controls the operation of each mechanism. An operation panel 180 is provided on the top of the housing 101. The operation panel 180 is a user interface, and includes an input device that accepts instructions from a user, and an output device that displays screens such as an operation screen. The input device is various key buttons, a touch panel, etc. The output device is a display and a speaker. The mechanisms that constitute the engine section include a mechanism that forms an image (image forming mechanism), a mechanism that transfers an image to a sheet S (transfer mechanism), a mechanism that feeds the sheet S (feed mechanism), and a mechanism that fixes the image on the sheet S (fixing mechanism).

[0020] The image forming mechanism includes four image forming units 120, 121, 122, and 123 corresponding to the colors of yellow (Y), magenta (M), cyan (C), and black (K). The image forming units 120, 121, 122, and 123 form images of the corresponding colors. The image forming units 120, 121, 122, and 123 have the same configuration, except that the colors of the images they form are different. Here, the configuration of the image forming unit 120 will be described, and descriptions of the configurations of the other image forming units 121, 122, and 123 will be omitted.

[0021] The image forming unit 120 includes a photosensitive drum 105, a charger 111, a laser scanner 107, and a developing unit 112. The photosensitive drum 105 is a drum-shaped photosensitive body having a photosensitive layer on its surface, and rotates around a drum axis. The charger 111 uniformly charges the photosensitive layer on the surface of the rotating photosensitive drum 105. The laser scanner 107 scans the surface of the photosensitive drum 105 with a laser beam modulated based on image data representing an image to be formed. The laser scanner 107 includes a light emitting unit 108 that scans the laser beam emitted from a semiconductor laser in one direction, and a reflecting mirror 109 that reflects the laser beam from the light emitting unit 108 toward the photosensitive drum 105. The direction in which the laser scanner 107 scans the photosensitive drum 105 (the depth direction in the figure) is the main scanning direction.

[0022] The photosensitive drum 105 is charged and then scanned with a laser beam, so that an electrostatic latent image corresponding to the image data is formed on the surface. The developing unit 112 develops the electrostatic latent image formed on the photosensitive drum 105 with a developer of a corresponding color. As a result, an image in which the electrostatic latent image is visualized is formed on the surface of the photosensitive drum 105. A yellow image is formed on the photosensitive drum 105 of the image forming unit 120. A magenta image is formed on the photosensitive drum 105 of the image forming unit 121. A cyan image is formed on the photosensitive drum 105 of the image forming unit 122. A black image is formed on the photosensitive drum 105 of the image forming unit 123. The photosensitive drum 105 and the developing unit 112 are detachable from the housing 101.

[0023] The transfer mechanism includes an intermediate transfer body 106 and a transfer roller 114. Images are transferred from the photosensitive drums 105 of the image forming units 120, 121, 122, and 123 in a sequentially superimposed manner onto the intermediate transfer body 106. In this embodiment, the intermediate transfer body 106 rotates clockwise in the figure, and images are transferred in the order of the image forming unit 120 (yellow), the image forming unit 121 (magenta), the image forming unit 122 (cyan), and the image forming unit 123 (black). An image density detection sensor 117 is provided downstream of the image forming unit 123 in the rotation direction of the intermediate transfer body 106 for detecting image density from an image for image density detection formed on the intermediate transfer body 106.

[0024] The image transferred to the intermediate transfer body 106 is transported to a transfer roller 114 as the intermediate transfer body 106 rotates. An image formation start position detection sensor 115 for determining the transfer position onto the sheet S is provided upstream of the transfer roller 114 in the rotation direction of the intermediate transfer body 106. The transfer roller 114 presses the sheet S against the intermediate transfer body 106 and at the same time applies a bias having reverse characteristics to the image on the intermediate transfer body 106, thereby transferring the image from the intermediate transfer body 106 to the sheet S.

[0025] The feeding mechanism includes a paper feed cassette 113 that stores sheets S, a conveying path along which the sheets S are fed, and various rollers for conveying the sheets S to the conveying path. The sheets S are fed from the paper feed cassette 113, and while being conveyed along the conveying path, an image is transferred and fixed onto the sheets S to form an image thereon. The sheets S are then discharged to the outside of the housing 101.

[0026] For this purpose, the sheet S is first fed from a paper feed cassette 113 and conveyed along a conveying path to the transfer roller 114. A paper feed timing sensor 116 for adjusting the conveying timing of the sheet S is provided along the conveying path from the paper feed cassette 113 to the transfer roller 114. The timing at which the sheet S is conveyed to the transfer roller 114 is adjusted based on the timing at which the image formation start position detection sensor 115 detects the image on the intermediate transfer body 106 and the timing at which the paper feed timing sensor 116 detects the sheet S. As a result, the image is transferred from the intermediate transfer body 106 to a predetermined position on the sheet S.

[0027] The sheet S onto which the image has been transferred is transported to a fixing mechanism. The fixing mechanism of this embodiment includes a first fixing unit 150 and a second fixing unit 160. The first fixing unit 150 includes a fixing roller 151 for heating the sheet S in order to thermally pressurize the image onto the sheet S, a pressure belt 152 for pressing the sheet S against the fixing roller 151, and a post-fixing sensor 153 for detecting the completion of fixing. The fixing roller 151 is a hollow roller having an internal heater 1510 and configured to transport the sheet S by rotating. The pressure belt 152 presses the sheet S against the fixing roller 151. The post-fixing sensor 153 detects the sheet S after the image has been fixed.

[0028] The second fixing device 160 is disposed downstream of the first fixing device 150 in the conveying direction of the sheet S, and is used to add gloss to the image on the sheet S fixed by the first fixing device 150 and to ensure fixability. The second fixing device 160 has a fixing roller 161, a pressure roller 162, and a post-fixing sensor 163. The fixing roller 161 has a configuration similar to that of the fixing roller 151, and functions similarly. The pressure roller 162 functions similarly to the pressure belt 152. The post-fixing sensor 163 functions similarly to the post-fixing sensor 153. The second fixing device 160 performs a fixing process on the sheet S in the same manner as the first fixing device 150.

[0029] The second fixing device 160 may not be used depending on the type of sheet S and the contents of the image forming process. The conveying path 130 is provided to convey the sheet S that has been subjected to the fixing process by the first fixing device 150 without passing through the second fixing device 160. For that purpose, a flapper 131 for guiding the sheet S to either the second fixing device 160 or the conveying path 130 is provided downstream of the first fixing device 150 in the conveying direction of the sheet S.

[0030] The sheet S that has passed through either the second fixing device 160 or the conveying path 130 may be discharged as is or may be conveyed to the conveying path 135. For this reason, a flapper 132 is provided after the conveying path after the second fixing device 160 and the conveying path 130 join together. The flapper 132 guides the sheet S to either the conveying path 135 or a discharge path for the sheet S. The sheet S guided to the discharge path is discharged to the outside of the housing 101 with the surface on which the image has been formed facing up.

[0031] The conveying path 135 is a path for conveying the sheet S to an inversion path 136 used for inverting the front and back sides of the sheet S. The inversion path 136 is provided with an inversion sensor 137 for detecting the sheet S. When the inversion sensor 137 detects the rear end of the sheet S, the conveying direction of the sheet S is inverted in the inversion path 136. The sheet S whose conveying direction has been inverted is conveyed to either the conveying path 135 or the inversion path 138. For this purpose, a flapper 133 is provided at the branch point between the conveying path 135 and the inversion path 138. When conveyed to the conveying path 135, the sheet S is guided to the conveying path 135 by the flapper 133, and is discharged to the outside of the housing 101 with the front and back sides inverted (with the side on which the image is formed facing downward). When conveyed to the inversion path 138, the sheet S is guided to the inversion path 138 by the flapper 133. The sheet S guided to the inversion path 138 is inverted with the front and back sides inverted, and conveyed to the transfer roller 114 again. As a result, an image is formed on the back side of the sheet S.

[0032] (Automatic reading device) FIG. 2 is a configuration diagram of the automatic reading device 400. The automatic reading device 400 is provided at the rear of the printer 100, and receives the sheet S after image formation discharged from the printer 100. The automatic reading device 400 has two conveying paths, a through path 431 and a reading path 432. The through path 431 is provided to convey the sheet S in the horizontal direction. The reading path 432 is provided to convey the sheet S in the vertical direction. The through path 431 is provided with conveying rollers 401, 402, 403, and a discharge roller 404. The reading path 432 is provided with conveying rollers 405, 406, 407, and a discharge roller 408. In the reading path 432, a sheet sensor 421 is provided between the conveying roller 405 and the conveying roller 406, and a color measurement unit 500 is provided between the conveying roller 406 and the conveying roller 407. A sheet S sent from the printer 100 is conveyed by conveyance rollers 401, 402, and 403 to a branch point of a through path 431 and a reading path 432. At the branch point, the sheet S is conveyed to either the through path 431 or the reading path 432. For this purpose, a flapper 422 is provided at the branch point of the through path 431 and the reading path 432.

[0033] When the sheet S is conveyed directly through the through path 431, the sheet S is guided by the flapper 422 to the discharge roller 404 side and discharged to the outside (sheet discharge device 600) of the automatic reading device 400. The sheet discharge device 600 discharges the sheet S to the outside. The sheet discharge device 600 may be a post-processing device that performs post-processing such as binding or bookbinding on the sheet S.

[0034] When the sheet S is transported to the reading path 432, the sheet S is guided to the reading path 432 by a flapper 422. The sheet S guided to the reading path 432 has a patch image read by a colorimetric unit 500, and then is discharged to a discharge tray 423 by a discharge roller 408. The colorimetric unit 500 is an in-line sensor that reads an image from the sheet S transported along the reading path 432.

[0035] (Color measurement unit) 3 is a diagram illustrating the configuration of the color measurement unit 500. The color measurement unit 500 includes a color detection sensor 551. The color detection sensor 551 is a color sensor for detecting the spectral reflectance of a patch image P formed on a sheet S to perform color measurement. The color detection sensor 551 includes a white LED (Light Emitting Diode) 501, a diffraction grating 502, a line sensor 503, a calculation unit 504, a memory 505, and a lens 506. The color detection sensor 551 reads an image formed on the sheet S while moving in a main scanning direction (depth direction in FIG. 2) perpendicular to the conveying direction of the sheet S. A movement mechanism for moving the color detection sensor 551 in the main scanning direction will be described later.

[0036] The white LED 501 is a light emitting unit that irradiates white light onto the sheet S transported through the reading path 432. The diffraction grating 502 separates the light reflected by the patch image P into separate wavelengths. The lens 506 focuses the white light irradiated from the white LED 501 onto the patch image P, and also focuses the light reflected by the patch image P onto the diffraction grating 502.

[0037] The line sensor 503 is a light receiving unit having n light receiving elements 503-1 to 503-n. Each of the light receiving elements 503-1 to 503-n of the line sensor 503 receives reflected light separated by wavelength by the diffraction grating 502. Each of the light receiving elements 503-1 to 503-n outputs, as a detection result, for example, a light intensity value representing the intensity of the received reflected light. The calculation unit 504 performs a predetermined calculation on the light intensity values ​​output from each of the light receiving elements 503-1 to 503-n. For example, the calculation unit 504 calculates a spectroscopic calculation or Lab value on the light intensity value. The memory 505 stores various data such as the calculation results.

[0038] (controller) 4 is an explanatory diagram of a controller that controls the operation of the image forming apparatus 1 configured as above. The printer 100 is provided with a printer controller 103 that controls the operation of the printer 100 and an engine control unit 312 that controls the operation of an engine unit for image formation, as controllers. The automatic reading device 400 is provided with a control unit 451 that controls the operation of the automatic reading device 400 and a communication unit 450 that communicates with the printer controller 103.

[0039] The engine control unit 312 is connected to the post-fixing sensors 153 and 163, the reversing sensor 137, a drive motor 311 that drives each roller that transports the sheet S, and the flappers 131 and 132. The engine control unit 312 controls the drive motor 311 and the flappers 131 and 132 based on the detection results of each sensor, thereby causing the engine unit to transport the sheet S. Although not shown in the figure, the engine control unit 312 also controls the operations of an image forming mechanism, a transfer mechanism, a feeding mechanism, and a fixing mechanism to form an image on the sheet S. The operation of the engine control unit 312 is controlled by the printer controller 103.

[0040] An operation panel 180 and an external I / F 308 are connected to the printer controller 103. The external I / F 308 is a communication interface that communicates with an external device via a predetermined network. The printer controller 103 can receive jobs and the like from an external device via the external I / F 308. The operation of the printer controller 103 will be described in detail later.

[0041] A control unit 451 of the automatic reading device 400 is connected to a conveying motor 452, a sheet sensor 421, a flapper 422, and a color measurement unit 500. The control unit 451 communicates with the printer controller 103 via a communication unit 450, and performs processing in cooperation with the printer controller 103. The control unit 451 controls the operation of the conveying rollers 401, 402, and 403, the discharge roller 404, the conveying rollers 405, 406, and 407, and the discharge roller 408 in the automatic reading device 400 by the conveying motor 452, to convey the sheet S. The control unit 451 controls the operation of the flapper 422. The control unit 451 controls the operation of the color measurement unit 500 in accordance with the timing when the sheet sensor 421 detects the sheet S, and detects a patch image P on the sheet S.

[0042] (Basic adjustment process) In the image forming apparatus 1 of this embodiment, a patch image P for maintaining image quality is formed on a sheet S by the printer 100. The printer 100 conveys the sheet S on which the patch image P has been formed to the automatic reading device 400. The automatic reading device 400 reads the patch image P formed on the sheet S by a color measurement unit 500 (color detection sensor 551). The printer controller 103 performs feedback control based on the detection result (reading result) by the color detection sensor 551 to maintain image quality such as color reproducibility. To this end, the printer controller 103 corrects the image forming conditions by the printer 100 based on the color measurement result by the color measurement unit 500 in order to maintain image quality such as color reproducibility.

[0043] The image forming apparatus 1 of this embodiment creates a profile as an image forming condition, and forms an image using the created profile. In this embodiment, an ICC profile is used as a profile that realizes excellent color reproducibility. Note that the profile may also use a CRD (Color Rendering Dictionary), a color separation table, or a CMYK simulation in ColorWise.

[0044] (Spectral reflectance measurement, chromaticity calculation) The automatic reader 400 measures the spectral reflectance of the patch image P using the color detection sensor 551, converts the measurement result into chromaticity, and creates an ICC profile as a color conversion profile. The internal conversion color processing is performed using the created ICC profile.

[0045] The calculation formula for chromaticity will be described. The color detection sensor 551 splits the white light irradiated from the white LED 501 and reflected by the measurement object using the diffraction grating 502, and detects it using light receiving elements 503-1 to 503-n arranged in each wavelength range of 380 [nm] to 720 [nm]. The calculation unit 504 of the color detection sensor 551 calculates the spectral reflectance from the detection results of the light receiving elements 503-1 to 503-n. In this embodiment, the calculation unit 504 converts the spectral reflectance into a chromaticity value (L*a*b*) using a color matching function or the like as specified by the CIE in order to improve the detection and calculation accuracy. An ICC profile, which is a color conversion profile, is created based on the relationship between L*a*b* and the signal value (image data) of the patch image P.

[0046] (L*a*b* operation) The following is the method for calculating chromaticity values ​​(L*a*b*) from spectral reflectance (specified in ISO13655). a. Calculate the spectral reflectance R(λ) of the sample (380[nm]~780[nm]) b. Color matching functions x(λ), y(λ), z(λ) and standard light spectral distribution SD50(λ) are provided. The color matching functions are specified in JIS Z8701, and SD50(λ) is specified in JIS Z8720; they are also called auxiliary standard illuminant D50. cR(λ)×SD50(λ)×x(λ), R(λ)×SD50(λ)×y(λ), R(λ)×SD50(λ)×z(λ) d.Each wavelength integration Σ{R(λ)×SD50(λ)×x(λ)} Σ{R(λ)×SD50(λ)×y(λ)} Σ{R(λ)×SD50(λ)×z(λ)} e. Calculate the product of the color matching function y(λ) and the standard light spectral distribution SD50(λ) for each wavelength. Σ{SD50(λ)×y(λ)} f.XYZ calculation X=100×Σ{SD50(λ)×y(λ)} / Σ{R(λ)×SD50(λ)×x(λ)} Y=100×Σ{SD50(λ)×y(λ)} / Σ{R(λ)×SD50(λ)×y(λ)} Z=100×Σ{SD50(λ)×y(λ)} / Σ{R(λ)×SD50(λ)×z(λ)} gL*a*b* calculation L*=116×(Y / Yn)^(1 / 3)-16 a*=500{(X / Xn)^(1 / 3)-(Y / Yn)^(1 / 3)} b*=200{(Y / Yn)^(1 / 3)-(Z / Zn)^(1 / 3)} When Y / Yn>0.008856 When Y / Yn>0.008856: Xn, Yn, and Zn are standard tristimulus values. (X / Xn)^(1 / 3)=7.78(X / Xn)^(1 / 3)+16 / 116 (Y / Yn)^(1 / 3)=7.78(Y / Yn)^(1 / 3)+16 / 116 (Z / Zn)^(1 / 3)=7.78(Z / Zn)^(1 / 3)+16 / 116

[0047] (Create a profile) When a customer engineer replaces a part, before a job that requires color matching accuracy is started, or when the user wants to know the color of the final output at the design concept stage, the user instructs the profile creation process through the operation panel 180. The printer controller 103 creates a profile in response to the instruction from the operation panel 180.

[0048] As shown in FIG. 4, the printer controller 103 includes a profile creation unit 301 , a Lab calculation unit 303 , an output ICC profile storage unit 305 , a CMM 306 , and an input ICC profile storage unit 307 .

[0049] An instruction to create a profile is input to the profile creation unit 301 from the operation panel 180. In response to the instruction, the profile creation unit 301 sends a signal to the engine control unit 312 to form CMYK (cyan, magenta, yellow, black) color signals (patch images) of the ISO12642 test form without using a profile. At the same time, the printer controller 103 sends a color measurement instruction to the color detection sensor 551. The engine control unit 312 controls the operation of the printer 100 to print the ISO12642 test form (patch images) on the sheet S. The sheet S on which the test form (patch images) is printed is subjected to color measurement by the color detection sensor 551. The spectral reflectance of the measured 928 patch images is input to the printer controller 103. The spectral reflectance is converted to L*a*b* data via the Lab calculation unit 303 and input to the profile creation unit 301. The spectral reflectance may be converted into the CIE1931XYZ color system, which is a device-independent color space signal, rather than L*a*b*.

[0050] The profile creation unit 301 creates an output ICC profile based on the relationship between the CMYK color signals of the test form and the input L*a*b* data. The profile creation unit 301 replaces the output ICC profile already stored in the output ICC profile storage unit 305 with the created output ICC profile.

[0051] The ISO12642 test form includes patch images of CMYK color signals that cover the color reproduction range that a general copier can output. The profile creation unit 301 creates a color conversion table based on the relationship between each color signal value and the measured L*a*b* data. In other words, a conversion table (A2Bx tag) from CMYK to Lab is created. Based on this conversion table, a reverse conversion table (B2Ax tag) is created.

[0052] Figure 5 is an explanatory diagram of an ICC profile. An ICC profile consists of a header, tags, and data. The tags include not only a color conversion table, but also a tag (gamt) that describes whether the color expressed by the white point (Wtpt) and the Lab values ​​defined in the profile is inside or outside the reproducible reproduction range of a hard copy.

[0053] The printer controller 103 may also receive an instruction to create a profile from an external device via the external I / F 308. In this case, the printer controller 103 obtains the output ICC profile created by the external device, and performs color conversion using an application compatible with the ICC profile.

[0054] (Color conversion processing) In color conversion in normal color image formation, image data inputted assuming RGB signal values ​​inputted via an external I / F 308 or standard printing CMYK signal values ​​such as JapanColor is stored in an input ICC profile storage unit 307 for external input. In this case, a scanner or the like is connected to the external I / F 308 as an external device. The image data stored in the input ICC profile storage unit 307 is converted from RGB to L*a*b* or CMYK to L*a*b*. The input ICC profile is composed of a one-dimensional LUT that controls the gamma value of the input signal, a multi-color LUT called direct mapping, and a one-dimensional LUT that controls the gamma value of the generated conversion data. Using these tables, the image data stored in the input ICC profile storage unit 307 is converted from a device-dependent color space to device-independent L*a*b* data.

[0055] The image data converted into the L*a*b* chromaticity coordinates is input to the CMM 306. FIG. 6 is an explanatory diagram of color management by the CMM 306. The CMM 306 performs GUMAT conversion to map mismatches between the read color space of an external device such as a scanner and the output color reproduction range of the printer 100 as an output device. The CMM 306 also performs color conversion to adjust the mismatch between the light source type at the time of input and the light source type when observing the output (also called the mismatch of the color temperature setting), and performs black character determination, etc. As a result, the L*a*b* data is converted into L*'a*'b*' data and stored in the output ICC profile storage unit 305. As described above, the created profile is stored in the output ICC profile storage unit 305, and the data is color converted by the newly created ICC profile, converted into a CMYK signal dependent on the output device, and output. As shown in FIG. 6, the CMM 306 is a module that performs color management. The CMM 306 is a module that performs color conversion using an input profile and an output profile.

[0056] (Color measurement unit) 7, 8, and 9 are explanatory diagrams of a moving mechanism that moves the color detection sensor 551 in the main scanning direction. The color measurement unit 500 includes a moving mechanism in addition to the color detection sensor 551. The moving mechanism includes a moving unit 530 for moving the color detection sensor 551 in the main scanning direction, a moving drive motor 570 that drives the moving unit 530, and a position detection sensor 545. Although not shown, the color detection sensor 551 is attached to the moving unit 530. As peripheral components of the moving mechanism, a conveying roller unit 580 that conveys the sheet S in the a direction, and a conveying drive unit 590 that drives the conveying roller unit 580 are arranged. Drive control of the moving drive motor 570 and the conveying drive unit 590 is performed by the control unit 451.

[0057] When the sheet S is conveyed by the conveying roller unit 580 to the reading position 551S of the color detection sensor 551, the moving unit 530 starts moving the color detection sensor 551 in the main scanning direction (direction b). The timing at which the sheet S is conveyed to the reading position of the color detection sensor 551 is determined based on the timing at which the sheet sensor 421 detects the sheet S, the position at which the sheet sensor 421 detects the sheet S, and the conveying speed of the sheet S. The color detection sensor 551 reads (measures the color of) the image on the sheet S while moving in the main scanning direction.

[0058] The moving unit 530 has a moving support plate 531 to which a moving bearing 532 is attached. The moving bearing 532 is engaged with a moving belt 533 via a tooth surface, and is also engaged with a moving shaft 534. The moving belt 533 is connected to a moving drive motor 570 via a moving pulley 572. In this configuration, when the moving drive motor 570 is driven, the moving pulley 572 rotates, and the rotation of the moving pulley 572 rotates the moving belt 533. The rotation of the moving belt 533 moves the moving unit 530 in the b direction. A flag portion 531f is formed on the moving support plate 531. The moving position of the moving unit 530 is controlled by the number of pulses of a pulse signal supplied to the moving drive motor 570, with the timing when the position detection sensor 545 detects the flag portion 531f as the base point.

[0059] The transport roller unit 580 has an upstream transport drive roller 581 and an upstream transport driven roller 582 on the upstream side of the color detection sensor 551 in the transport direction (direction a) of the sheet S. The transport roller unit 580 also has a downstream transport drive roller 583 and a downstream transport driven roller 584 on the downstream side of the color detection sensor 551 in the transport direction of the sheet S. The transport roller unit 580 transports the sheet S transported from the transport roller 406 to the transport roller 407 via a reading position 551S (detection position).

[0060] The upstream transport drive roller 581 is an aluminum pipe with a urethane coating of 30 μm thick on its outer circumference, and has an outer diameter of 20 mm. Both ends of the upstream transport drive roller 581 are rotatably supported by bearings (not shown). The upstream transport driven roller 582 is configured by wrapping silicone rubber around a roller surface made of aluminum, and has an outer diameter of 20 mm. Both ends of the upstream transport driven roller 582 are also rotatably supported by bearings (not shown). The upstream transport drive roller 581 rotates in the R1 direction by being driven by the transport drive unit 590. The upstream transport driven roller 582 is biased toward the upstream transport drive roller 581 by a spring (not shown) and is pressed against the upstream transport drive roller 581. The upstream transport driven roller 582 rotates following the rotation of the upstream transport drive roller 581. A nip is formed by the upstream transport drive roller 581 and the upstream transport driven roller 582.

[0061] The downstream transport drive roller 583 has a similar configuration to the upstream transport drive roller 581, and is rotated in the R1 direction by the transport drive unit 590. The downstream transport driven roller 584 has a similar configuration to the upstream transport driven roller 582, and rotates following the rotation of the downstream transport drive roller 583. The downstream transport driven roller 584 is biased toward the downstream transport drive roller 583 by a spring (not shown), and is pressed against the downstream transport drive roller 583. A nip is formed by the downstream transport drive roller 583 and the downstream transport driven roller 584.

[0062] In this embodiment, the upstream transport drive roller 581 and the downstream transport drive roller 583 are driven by one transport drive unit 590. Alternatively, the upstream transport drive roller 581 and the downstream transport drive roller 583 may each be provided with a transport drive unit, and the upstream transport drive roller 581 and the downstream transport drive roller 583 may be individually driven and controlled.

[0063] (Color measurement operation) 10 illustrates an example of the posture of the color detection sensor 551 at the reading position 551S of the sheet S transported through the reading path 432. The reading path 432 is provided so that the sheet S is transported vertically from bottom to top. The color measurement unit 500 reads (measures) a patch image from the sheet S transported vertically. If the distance between the sheet S and the color detection sensor 551 of the color measurement unit 500 is not kept constant, the color detection sensor 551 may not be able to accurately read the patch image from the sheet S.

[0064] 10A illustrates a state in which the leading edge of the sheet S in the conveying direction reaches the nip between the downstream conveying drive roller 583 and the downstream conveying driven roller 584. The sheet S is sandwiched between the downstream conveying drive roller 583 and the downstream conveying driven roller 584, and is also sandwiched between the upstream conveying drive roller 581 and the upstream conveying driven roller 582. The conveying drive unit 590 is configured to make the conveying speed of the sheet S by the downstream conveying drive roller 583 and the downstream conveying driven roller 584 faster by a predetermined amount, for example, 10%, than the conveying speed of the sheet S by the upstream conveying drive roller 581 and the upstream conveying driven roller 582. This makes the sheet S in a state of being stretched with a predetermined tension. Therefore, in a state in which the distance A1 between the sheet S and the color detection sensor 551 is stable, the color detection sensor 551 can read the patch image while moving in the main scanning direction.

[0065] FIG. 10B illustrates a state in which the leading edge of the sheet S is out of the nip between the downstream transport driving roller 583 and the downstream transport driven roller 584. In this case, when the color detection sensor 551 attempts to read a patch image while moving in the main scanning direction, it may be pinched by the sheet S and unable to move. FIG. 10C illustrates a state in which the leading edge of the sheet S reaches the nip between the downstream transport driving roller 583 and the downstream transport driven roller 584, but the sheet S is not tensioned with a predetermined tension. In this case, the distance A2 between the sheet S and the color detection sensor 551 becomes unstable. If the color detection sensor 551 reads a patch image while moving in the main scanning direction in this state, the color measurement accuracy may decrease.

[0066] 11 is an explanatory diagram of the patch image reading process (colorimetry) by the colorimetry unit 500. A predetermined number of patch images are formed on the sheet S in both the row and column directions. In this embodiment, m rows of patch images P for colorimetry, P1 to Pm, are formed on the sheet S. In each row, n patch images, P1-1, P1-2, P1-3, . . . P1-n, are formed in the column direction. In other words, m×n patch images are arranged on one sheet S.

[0067] As described above, the color detection sensor 551 is moved in the main scanning direction perpendicular to the conveying direction of the sheet S by the moving unit 530. When the patch image is read by the color detection sensor 551, the conveying / stopping of the sheet S is controlled by the conveying roller unit 580, and the sheet S can be conveyed a predetermined amount. The conveying drive unit 590 repeats the operation of conveying the sheet S by a predetermined amount and pausing it by the conveying roller unit 580. The position of the sheet S is detected by a sheet position detection sensor (not shown). While the sheet S is temporarily stopped, the color detection sensor 551 moves in the main scanning direction and reads one line of the patch image.

[0068] 11(a), when sheet S is transported to reading position 551S of color detection sensor 551, color detection sensor 551 retreats to outside the area of ​​sheet S in the main scanning direction and waits. Sheet S is transported and stopped until reading position 551S of color detection sensor 551 and the position of patch image P1 of the first row are aligned in the transport direction. When transport of sheet S is stopped, color detection sensor 551 reads patch images P1-1 to P1-n of n rows of P1 while moving in the main scanning direction as shown in FIG. 11(b).

[0069] At this time, as shown in Fig. 10(a), the leading edge of the sheet S reaches the downstream transport driving roller 583 and the downstream transport driven roller 584. Therefore, the sheet S is sandwiched between the upstream transport driving roller 581 and the upstream transport driven roller 582, and the downstream transport driving roller 583 and the downstream transport driven roller 584. The color detection sensor 551 can read the patch image P1 while moving in the main scanning direction with the distance A1 to the sheet S being stable. If the sheet S is in the state of Fig. 10(b), the color detection sensor 551 cannot move in the main scanning direction due to the sheet S. If the sheet S is in the state of Fig. 10(c), the color detection sensor 551 reads the patch image P1 while moving in the main scanning direction with the distance A2 to the sheet S being unstable, and therefore the color measurement accuracy may decrease.

[0070] 12 is a diagram illustrating a formation range of a patch image on a sheet S. In this embodiment, the sheet S has a leading edge margin B1 on the leading edge side in the transport direction, and a trailing edge margin C1 on the trailing edge side in the transport direction. The leading edge margin B1 and the trailing edge margin C1 are areas where no patch image is formed.

[0071] The leading edge margin B1 is provided so as to be longer in the transport direction than a distance B2 in the transport direction between the reading position 551S of the color detection sensor 551 and a nip (center) formed by the downstream transport driving roller 583 and the downstream transport driven roller 584. For example, the leading edge margin B1 is 60 [mm] and the distance B2 is 50 [mm]. Therefore, the patch image P1 of the first row is formed at a position away from the leading edge of the sheet S in the transport direction by the distance B2.

[0072] The trailing edge margin C1 is provided so as to be longer in the transport direction than a distance C2 in the transport direction between the reading position 551S of the color detection sensor 551 and a nip (center) formed by the upstream transport drive roller 581 and the upstream transport driven roller 582. For example, the trailing edge margin C1 is 60 [mm] and the distance C2 is 50 [mm]. Therefore, the patch image Pm of the last line is formed at a position farther away from the trailing edge of the sheet S in the transport direction than the distance C2.

[0073] Therefore, the formation range of the patch image on the sheet S in this embodiment is within the range obtained by excluding the distance B2 from the leading edge and the distance C2 from the trailing edge from the length of the sheet S in the transport direction. It is not necessary to provide a margin in the direction perpendicular to the transport direction of the sheet S (main scanning direction). The margin in the main scanning direction is determined mainly by the performance of the image forming apparatus 1, and is, for example, 5 mm.

[0074] The color detection sensor 551 that reads the patch image P1 of the first row waits outside the area of ​​the sheet S in the main scanning direction as shown in FIG. 11(c). In this state, the sheet S is transported until the patch image P2 reaches the same position in the transport direction as the reading position 551S. When the patch image P2 reaches the same position in the transport direction as the reading position 551S, the color detection sensor 551 reads the n patch images P2 of the second row while moving in the direction of the patch image P2 as shown in FIG. 11(d). The color detection sensor 551 reads all m×n patch images P on the sheet S while moving back and forth m / 2 times in the main scanning direction. In this way, the color detection sensor 551 reads the patch images P one row at a time while moving back and forth in the main scanning direction.

[0075] 11(e), the color detection sensor 551 may detect the patch image of the same row twice, once on the forward path and once on the return path. In this case, the patch image of the same row is read twice, improving the reading accuracy.

[0076] In the present embodiment described above, the color detection sensor 551 of the color measurement unit 500 reads a patch image of the sheet S from the sheet S transported in the vertical direction. The color measurement unit 500 has roller pairs for pinching the sheet S on both the upstream side and the downstream side of the transport direction of the sheet S at positions sandwiching the reading position 551S. The sheet S is held between the two roller pairs (upstream transport drive roller 581 and upstream transport driven roller 582, downstream transport drive roller 583 and downstream transport driven roller 584) so ​​that the sheet S is stretched with a predetermined tension. The color detection sensor 551 reads the patch image from the sheet S in this state while moving in the main scanning direction. This reduces the possibility that the color detection sensor 551 will be unable to move due to the sheet S, and enables accurate detection of the patch image.

[0077] In the above description, an example in which the color measurement unit 500 is provided in the automatic reader 400 has been described, but the automatic reader 400 may be provided inside the printer 100. For example, a reading path 432 in which the color measurement unit 500 is disposed may be provided after the second fixing device 160 and the conveying path 130 join together.

Claims

1. A reading device that reads an image on a sheet conveyed from an image forming device, a first transport path for transporting a sheet from the image forming apparatus to a post-processing apparatus connected downstream of the reading apparatus for performing post-processing on the sheet; a tray provided vertically above the first transport path and onto which sheets are discharged; a second transport path that branches off from the first transport path at a branching portion and transports the sheet to the tray; a first conveying roller pair that is provided on the second conveying path and above the branching portion in the vertical direction and that nip and convey a sheet; a second conveying roller pair that is provided in the second conveying path between the first conveying roller pair and the tray and vertically above both the branching portion and the first conveying roller pair, and that nips and conveys the sheet conveyed on the second conveying path by the first conveying roller pair; a reading unit that moves in a direction intersecting a sheet conveying direction, and that reads an image on a sheet located in a region between the first conveying roller pair and the second conveying roller pair by moving in a direction intersecting the sheet conveying direction while the sheet is sandwiched between the first conveying roller pair and the second conveying roller pair, a distance in a conveying direction of the sheet from a leading edge of the sheet in the conveying direction to a leading edge of the image formed on the sheet in the conveying direction is a first distance; a distance from a reading position where the image formed on the sheet is read by the reading unit to a nip of the second conveying roller pair in the conveying direction is a second distance; the first distance is greater than the second distance; a distance in the transport direction from a trailing end of the sheet in the transport direction to a trailing end of the image formed on the sheet in the transport direction is a third distance; a distance from a reading position where the image formed on the sheet is read by the reading unit to a nip of the first conveying roller pair in the conveying direction is a fourth distance; the third distance is greater than the fourth distance; the reading means reads an image formed on the rear end side of the sheet in the conveying direction by moving in a direction intersecting the conveying direction while the sheet is nipped and stopped by the first conveying roller pair. Reading device.

2. The sheet conveying device further includes a guide member that is disposed at the branching portion and is switchable between a first state in which the sheet is guided to the first transport path and a second state in which the sheet is guided to the second transport path.

2. The reading device according to claim 1.

3. The sheet conveying device further includes a pair of discharge rollers that are provided downstream of the second conveying roller pair in the conveying direction on the second conveying path and that discharge the sheet onto the tray.

2. The reading device according to claim 1.

4. the second conveying path has a curved part and a straight part between the first conveying roller pair and the second conveying roller pair, 2. The reading device according to claim 1.

5. the second conveying path has a curved part and a straight part extending in a gravity direction between the first conveying roller pair and the second conveying roller pair, 2. The reading device according to claim 1.

6. the reading means is disposed in one of the areas sandwiching the second transport path, and the one area is an area on the side where the image forming apparatus to which the reading device is connected is disposed.

2. The reading device according to claim 1.

7. the reading means reads a part of the image on the sheet while moving in a first direction among directions intersecting the conveying direction, and reads another part of the image on the sheet while moving in a second direction opposite to the first direction, 2. The reading device according to claim 1.

8. the first conveying roller pair and the second conveying roller pair each convey the sheet intermittently, the reading unit reads the image on the sheet while moving in the direction intersecting the conveying direction each time the conveyance of the sheet is stopped.

2. The reading device according to claim 1.

9. a speed at which the second conveying roller pair conveys the sheet is faster than a speed at which the first conveying roller pair conveys the sheet, 2. The reading device according to claim 1.

10. an image forming apparatus for forming an image on a sheet; a reading device that reads an image on a sheet on which an image is formed by the image forming device and which is conveyed from the image forming device; a post-processing device connected to the reading device and performing post-processing on the sheet that has passed through the reading device; An image forming system that controls a density of an image formed by the image forming apparatus based on a reading result by the reading apparatus, The reading device is an output tray onto which the sheet is output; a first transport path for transporting a sheet from the image forming apparatus to the post-processing apparatus; a second transport path that branches off from the first transport path at a branching portion and transports the sheet from the branching portion to the discharge tray; a first conveying roller pair provided in the second conveying path for nipping and conveying a sheet; a second conveying roller pair that is provided in the second conveying path between the first conveying roller pair and the discharge tray and that nips and conveys the sheet being conveyed on the second conveying path by the first conveying roller pair; a reading unit that moves in a direction intersecting a sheet conveying direction, and that reads an image on a sheet located between the first conveying roller pair and the second conveying roller pair by moving in a direction intersecting the sheet conveying direction while the sheet is sandwiched between the first conveying roller pair and the second conveying roller pair; the discharge tray, the second transport path, the first transport roller pair, and the second transport roller pair are disposed vertically above the branching portion, the second conveying roller pair is disposed vertically above the first conveying roller pair, a distance in a conveying direction of the sheet from a leading edge of the sheet in the conveying direction to a leading edge of the image formed on the sheet in the conveying direction is a first distance; a distance from a reading position where the image formed on the sheet is read by the reading unit to a nip of the second conveying roller pair in the conveying direction is a second distance; the first distance is greater than the second distance; a distance in the transport direction from a trailing end of the sheet in the transport direction to a trailing end of the image formed on the sheet in the transport direction is a third distance; a distance from a reading position where the image formed on the sheet is read by the reading unit to a nip of the first conveying roller pair in the conveying direction is a fourth distance; the third distance is greater than the fourth distance; the reading means reads an image formed on the rear end side of the sheet in the conveying direction by moving in a direction intersecting the conveying direction while the sheet is nipped and stopped by the first conveying roller pair. Image forming system.

11. The reading device further includes a guide member disposed at the branching portion and switchable between a first state in which the sheet is guided to the first transport path and a second state in which the sheet is guided to the second transport path. The image forming system according to claim 10.

12. the reading device further includes a pair of discharge rollers that are provided downstream of the second conveying roller pair in the conveying direction on the second conveying path and that discharge the sheet onto the discharge tray. The image forming system according to claim 10.

13. the second conveying path has a curved part and a straight part between the first conveying roller pair and the second conveying roller pair, The image forming system according to claim 10.

14. the second conveying path has a curved part and a straight part extending in a gravity direction between the first conveying roller pair and the second conveying roller pair, The image forming system according to claim 10.

15. the reading means is disposed in one of the areas sandwiching the second transport path, and the one area is an area on the side where the image forming apparatus to which the reading device is connected is disposed. The image forming system according to claim 10.

16. the reading means reads a part of the image on the sheet while moving in a first direction among directions intersecting the conveying direction, and reads another part of the image on the sheet while moving in a second direction opposite to the first direction, The image forming system according to claim 10.

17. the first conveying roller pair and the second conveying roller pair each convey the sheet intermittently, the reading unit reads the image on the sheet while moving in the direction intersecting the conveying direction each time the conveyance of the sheet is stopped. The image forming system according to claim 10.

18. a speed at which the second conveying roller pair conveys the sheet is faster than a speed at which the first conveying roller pair conveys the sheet, The image forming system according to claim 10.

Images