Image forming apparatus

Abstract

To make it possible to stably locate the position of a sheet at a reading position on a guide surface.SOLUTION: An image reading mechanism comprises: a driven roller 142a that has roller parts 142ra, 142rb; an image reading unit that reads an image of a sheet conveyed at reading positions 500A, 500B; a conveyance guide 600 that has a guide surface 600s for guiding the sheet; a conveyance guide 601 that is curved with respect to a direction orthogonal to an axial direction of a rotation axis 142x and a sheet conveyance direction and guides the sheet; and a pressure roller that conveys the sheet while pressing the sheet toward the guide surface 600s. The reading positions 500A, 500B are arranged between an end W1 at one side and an end W2 at the other side within a range W where the roller parts 142ra, 142rb are arranged in the axial direction when viewed from the sheet conveyance direction.SELECTED DRAWING: Figure 5

Description

Technical Field

[0001] The present invention relates to a sheet to form an image and an image forming apparatus.

Background Art

[0002] In recent years, an image forming system has been proposed in which, after an image is formed on a sheet by an image forming apparatus, the image information of the sheet is read by an image reading apparatus, and then adjustment of the image (particularly color adjustment) is performed when forming an image by the image forming apparatus (see Patent Documents 1 and 2). In these Patent Documents 1 and 2, a patch image formed on a sheet is detected by a color sensor to create a profile, and color adjustment is performed based on the profile.

[0003] In such color adjustment, it is necessary to satisfy a color matching accuracy standard (for example, ISO 12647-7, etc.). For this purpose, it is necessary to maintain the detection accuracy of the color sensor at a high level. And, in order to maintain the detection accuracy of the color sensor at a high level, it is important to reduce the variation in the distance (focus position) between the sheet on which the image is formed and the sensor. Therefore, a proposal has been made to set the focus position of the color sensor at a position along the surface of the conveyance guide and press the sheet against the guide surface of the conveyance guide by a conveyance roller to position it at the focus position (see Patent Document 3).

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0005] Incidentally, a color sensor disposed inside an image forming apparatus, for example, is not necessarily disposed in a conveyance path linearly formed as in Patent Document 3 above. For example, due to space constraints inside the image forming apparatus, there may be a case where it has to be disposed at a portion where the conveyance path is curved on the downstream side in the sheet conveyance direction. In such a case, if the stiffness of the sheet is high, the sheet tends to bend in a direction opposite to the pressing direction by the pressing roller as described above due to the curved conveyance path, and it is difficult to stably position the position of the sheet on the guide surface of the conveyance guide.

[0006] Therefore, an object of the present invention is to provide an image forming apparatus capable of stably positioning the position of a sheet at a reading position on a guide surface. such a painting Means for Solving the Problems

[0007] One aspect of the present invention includes an image forming unit that forms an image on a sheet, a reversing unit that reverses the direction in which the sheet on which the image has been formed by the image forming unit is conveyed, and a conveyance path that conveys the sheet reversed by the reversing unit to the image forming unit, the conveyance path including a curved portion curved upward, a plurality of rollers that convey the sheet in the conveyance path, and an image reading unit that reads an image of the sheet at a reading position in the conveyance path, wherein the plurality of rollers are arranged at the position closest to the curved portion on the upstream side of the curved portion in the sheet conveyance direction among the plurality of rollers, a first roller having a first rotation axis and a first roller portion that is disposed on the first rotation axis and contacts the sheet to convey the sheet, and a second roller disposed at the position closest to the first roller on the upstream side of the first roller in the sheet conveyance direction among the plurality of rollers, the second roller having a second rotation axis and a second roller portion that is disposed on the second rotation axis and contacts the sheet at the reading position and conveys the sheet while pressing the sheet toward the image reading unit, and the reading position is in the axial direction of the first rotation axis as viewed from the sheet conveyance direction. arranged side by side in multiple multiple ​​An image forming apparatus, characterized in that it is disposed between one end and the other end in a range where the first roller unit is disposed.

Advantages of the Invention

[0009] According to the present invention, the position of the sheet at the reading position can be stably positioned on the guide surface.

Brief Description of the Drawings

[0010]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Embodiments for Carrying Out the Invention

[0011] Hereinafter, an image reading apparatus or an image forming apparatus according to the present embodiment will be described with reference to the drawings. The dimensions, materials, shapes, relative arrangements, etc. of the components described in the following embodiments are not intended to limit the scope of application of the present technology only to those, unless otherwise specifically described.

[0012] [Schematic Configuration of Image Forming Apparatus] FIG. 1 is a schematic diagram showing an image forming apparatus 100 according to the present embodiment. In the present embodiment, as the image forming apparatus, an image forming apparatus 100 which is an electrophotographic laser beam printer will be described as an example, but the present invention is not limited thereto, and the image forming apparatus may be an inkjet printer or a sublimation printer. Further, a processing apparatus that performs various processes on a sheet on which an image is formed by the present image forming apparatus may be connected to the image forming apparatus 100 to constitute an image forming system together with these processing apparatuses. As the processing apparatus, any apparatus such as an inspection apparatus for inspecting a sheet, a perforating apparatus for perforating a sheet, a binding apparatus (so-called finisher) for stapling or sewing a sheet without needles, and a bookbinding apparatus for collating and binding a sheet may be used.

[0013] The housing 101 of the image forming apparatus 100 is equipped with an image forming engine 102, a control board storage section (not shown) for housing a printer controller 103 (see FIG. 2) that controls the operation of the image forming apparatus 100, and an image reading mechanism 50. The image forming engine 102 as the image forming section includes an optical processing mechanism 10 and a fixing processing mechanism 20 that form an image on a recording material by an image forming process, and a feeding processing mechanism 30 and a conveying processing mechanism 40 that feed and convey a rectangular sheet S used as the recording material. As the recording material, paper such as plain paper and thick paper, paper with surface treatment such as coated paper and embossed paper, plastic film, cloth, and other sheets can be used.

[0014] The optical processing mechanism 10 includes stations 120, 121, 122, 123 that form toner images of each color of yellow, magenta, cyan, and black, and an intermediate transfer belt 106. At each of the stations 120 to 123, a primary charger 111 charges the surface of a photosensitive drum 105, which is a drum-shaped photosensitive member. The laser scanner unit 107 performs an exposure process on the photosensitive drum 105 based on a command signal generated based on image data and transmitted to the laser scanner unit 107. The laser scanner unit 107 has a laser driver that drives the laser light emitted from a semiconductor laser (not shown) to be turned on and off. The laser scanner unit 107 distributes the laser light from the semiconductor laser in the main scanning direction (the width direction of the sheet) by a rotating polygon mirror and guides it to the photosensitive drum 105 via a reflection mirror 109. As a result, an electrostatic latent image corresponding to the image data is formed on the surface of the photosensitive drum 105.

[0015] The developing device 112 houses a developer containing toner inside and supplies charged toner particles to the photosensitive drum 105. The electrostatic latent image carried on the photosensitive drum 105 is visualized as a toner image by the toner particles adhering to the drum surface according to the surface potential distribution. The toner image carried on the photosensitive drum 105 is transferred (primary transfer) to the intermediate transfer belt 106 to which a voltage of the opposite polarity to the normal charging polarity of the toner is applied. When forming a color image, the toner images formed by the four stations 120 to 123 are multiply transferred so as to overlap each other on the intermediate transfer belt 106, thereby forming a full-color toner image on the belt.

[0016] On the other hand, the sheet feeding processing mechanism 30 feeds the sheets S one by one from a sheet storage 113 that is inserted into the housing 101 of the image forming apparatus 100 so as to be pullable, toward a transfer roller 114. The toner image carried on the intermediate transfer belt 106, which is an intermediate transfer member, is transferred (secondary transfer) to the sheet S by the transfer roller 114.

[0017] Around the intermediate transfer belt 106, an image formation start position detection sensor 115 for determining the printing start position when performing image formation, a feeding timing sensor 116 for timing the feeding of the sheet S, and a density sensor 117 are arranged. The density sensor 117 measures the density of a test patch image carried on the intermediate transfer belt 106. The printer controller 103 adjusts the operating conditions of the optical processing mechanism 10 (for example, the charging target potential of the primary charger 111 and the setting of the bias voltage of the developing device 112) based on the detection result of the density sensor 117.

[0018] The fixing processing mechanism 20 of the present embodiment is composed of a first fixing device 150 and a second fixing device 160. The first fixing device 150 includes a fixing roller 151 for applying heat to the sheet S, a pressure belt 152 for pressing the sheet S against the fixing roller 151, and a first post-fixing sensor 153 for detecting the completion of the fixing process by the first fixing device 150. The fixing roller 151 is a hollow roller and has a heater inside. The first fixing device 150 sandwiches and conveys the sheet S by the fixing roller 151 and the pressure belt 152 which are a pair of rotating bodies, and applies heat and pressure to the toner image on the sheet. As a result, the toner particles melt and then adhere, so that the image is fixed on the sheet S.

[0019] The second fixing device 160 is arranged on the downstream side of the first fixing device 150 in the conveyance path of the sheet S. The second fixing device 160 has a function of enhancing the glossiness of the image subjected to the fixing process by the first fixing device 150 or ensuring the fixability of the image on the sheet S. Similar to the first fixing device 150, the second fixing device 160 has a fixing roller 161 and a pressure roller 162 which are a pair of rotating bodies for heating and pressing while conveying the sheet S, and a second post-fixing sensor 163 for detecting the completion of the fixing process by the second fixing device 160.

[0020] Note that depending on the type of the sheet S, it may not be necessary to pass through the second fixing device 160. In such a case, for the purpose of reducing the energy consumption, the image forming apparatus 100 has a bypass conveyance path 130 for discharging the sheet S without passing through the second fixing device 160. The sheet S sent out from the first fixing device 150 is guided to either the second fixing device 160 or the bypass conveyance path 130 by the first switching flapper 131.

[0021] The sheet S that has passed through the second fixing device 160 or the bypass conveyance path 130 is guided to either the discharge conveyance path 139 or the reverse conveyance path 135 by the second switching flapper 132. The position of the sheet S carried into the reverse conveyance path 135 is detected by the reverse sensor 137, and the downstream end (front end) and the upstream end (rear end) in the sub-scanning direction (the direction in which the sheet is conveyed) are interchanged by the switchback operation performed by the reverse unit 136. In the case of double-sided printing, the sheet S with an image formed on the front surface is conveyed again toward the transfer roller 114 via the re-conveyance path 138 in a state where the front and rear ends are interchanged by the reverse unit 136, and an image is formed on the back surface opposite to the front surface.

[0022] As described above, the sheet S for which the image formation for single-sided printing has been completed or the sheet S for which the image formation on the back surface in double-sided printing has been completed is discharged to the outside of the image forming apparatus 100 by the discharge roller 139a (discharge unit) provided in the discharge conveyance path 139. Note that between the reverse conveyance path 135 and the discharge conveyance path 139, a fourth switching flapper 134 is provided that can guide the sheet S that has been switchbacked by the reverse unit 136 toward the discharge conveyance path 139, and is configured to be able to select the front and back of the sheet S when discharging.

[0023] [Outline of Color Sensor] Next, an outline configuration of an image reading mechanism 50 that is an image reading apparatus of the present embodiment and reads a patch image (hereinafter simply referred to as "patch") formed on a sheet S by the image forming engine 102 will be described.

[0024] The image quality of an image forming apparatus (hereinafter referred to as image quality) includes granularity, in-plane uniformity, character quality, color reproducibility (including color stability), etc., but it is said that the most important is color reproducibility. Humans have memories of expected colors based on experience (especially human skin, blue sky, metal, etc.), and if it exceeds that allowable range, they will feel a sense of discomfort. These colors are called memory colors, and their reproducibility is often questioned when outputting photos, etc. Also, not limited to memory colors, in documents as well, the requirement for color reproducibility (including stability) of the image forming apparatus is increasing for office user layers that feel a sense of discomfort due to the color difference from the monitor, and graphic arts user layers that pursue the color reproducibility of CG images.

[0025] In the image forming apparatus 100 of the present embodiment, when forming an image on a sheet, color tone adjustment is performed based on a profile. Specifically, when performing color tone adjustment, the image forming apparatus 100 first forms a patch 220 (see FIG. 3) on the sheet S by the image forming engine 102. Thereafter, the color sensor 200 of the image reading mechanism 50 reads the patch 220 on the sheet S, performs colorimetry, and transmits (feeds back) the colorimetry result as image information to the printer controller 103 (see FIG. 2). The printer controller 103 creates a profile based on the colorimetry result received from the color sensor 200, and performs color tone adjustment when forming the job image on the sheet S based on it. The image forming apparatus 100 of the present embodiment can improve the image quality by performing such color tone adjustment. In the present embodiment, two color sensors 200A and 200B (see FIG. 4) are provided, but when it is not necessary to distinguish between these two color sensors 200A and 200B, one or both of them are referred to simply as the color sensor 200.

[0026] Also, as shown in FIG. 3, the color sensor 200 includes a white LED 201 that irradiates light onto a toner patch 220 as image information formed on the sheet S, and a diffraction grating 202 that disperses the light reflected from the patch 220 for each wavelength. Further, the color sensor 200 incorporates a lens 206 that condenses the light irradiated from the white LED 201 onto the patch 220 on the sheet S and also condenses the light reflected from the patch 220 onto the diffraction grating. The color sensor 200 is also provided with a line sensor 203 (203-1 to 203-n) composed of n pixels that detects the light decomposed for each wavelength by the diffraction grating 202. And the color sensor 200 incorporates an arithmetic unit 204 that performs various calculations from the light intensity values of the respective pixels detected by the line sensor 203, and a memory 205 that stores various data.

[0027] [Control Configuration of Image Forming System] As shown in FIG. 2, the image forming apparatus 100 includes a printer controller 103 as control means for overall control of operations, and an engine control unit 312 that controls the image forming engine 102 (see FIG. 1). The printer controller 103 is a control board on which at least one processor and a memory are mounted.

[0028] Based on a command signal or the like from the printer controller 103, the engine control unit 312 causes the image forming engine 102 to perform the above-described image forming process to form an image on the sheet. For example, the engine control unit 312 controls the operations of the conveyance motor 311 and the first to fourth switching flaps 131 to 134 based on the detection signals of the first post-fixing sensor 153, the second post-fixing sensor 163, and the inversion sensor 137. Note that the conveyance motor 311 is a motor that serves as a drive source for driving the rollers that convey the sheet.

[0029] The image forming apparatus 100 is provided with an operation unit 180 serving as a user interface (see FIG. 1). The operation unit 180 includes a display as display means for displaying information to the user. Further, the operation unit 180 includes physical keys such as a numeric keypad and a print execution button, and a touch panel function of the display, as input means by which the user can input commands and data to the image forming apparatus 100. By operating the operation unit 180, the user can input information representing sheet attributes such as the name, basis weight, and presence or absence of surface treatment of the sheet set in a certain sheet storage unit 113 (see FIG. 1) to the printer controller 103.

[0030] The printer controller 103 is connected to an external wired or wireless communication network via an external interface (I / F) 308 and can communicate with an external computer (not shown). Further, the printer controller 103 is also connected to a control circuit of a device (not shown) that is connected to the image forming apparatus 100 to form an image forming system. The printer controller 103 communicates with these devices to coordinate the operations of the image forming apparatus 100 and each device.

[0031] [Regarding Color Adjustment of Image Formation] Here, the color adjustment (configuration for feedback) of image formation when the patch 220 of the sheet S is color-measured by the color sensor 200 will be described in detail. That is, the control flow for creating a profile and outputting an image using the profile in the image forming apparatus 100 in the present embodiment will be described. As a profile for realizing excellent color reproducibility, here, an ICC (International Color Consortium) profile that has been accepted in the market in recent years will be used. Note that in the present embodiment, the use of an ICC profile will be described, but the present invention is not limited thereto. In addition to the ICC profile, a CRD (Color Rendering Dictionary) adopted from PostScript level 2 proposed by Adobe or a color separation table in Photoshop can also be used. Further, CMYK simulation in ColorWise of EFI that maintains ink plate information can also be used.

[0032] The image reading mechanism 50 according to the present embodiment incorporates a color sensor 200 that can measure the spectral reflectance as the above-described reading means. It can measure the spectral reflectance, convert it into chromaticity, and create its own color conversion profile. Then, the internal conversion color process is performed using the created color conversion profile.

[0033] (Measurement by Color Sensor, Calculation of Chromaticity) Here, the calculation of chromaticity will be described. The signal measured and generated by the color sensor 200 is the spectral reflectance detected on the CMOS sensor arranged in each wavelength region from 380 nm to 720 nm, where the light irradiated from the white LED hits the measurement object and the reflected light is dispersed by the diffraction grating. In the Lab calculation unit 303 shown in FIG. 2 in the present embodiment, in order to improve the detection calculation accuracy, it is converted into L*a*b* through an isochromatic function or the like from the spectral reflectance as defined by the CIE. Then, the relationship between the patch information converted into L*a*b* and the signal value of the patch is obtained, and an ICC profile, which is a color conversion profile, is created as follows.

[0034] (Profile Creation Process) When a custom engineer replaces parts, before a JOB that requires color matching accuracy, or when the user wants to know the color tone of the final output during the design concept stage, etc., the user operates the operation unit 180 to perform the color profile creation process.

[0035] The profile creation process is performed in the printer controller 103 shown in the control block diagram of FIG. 2. First, an instruction to create a profile is input to the profile creation unit 301 via the operation unit 180. The profile creation unit 301 sends a signal to the engine control unit 312 to output the CMYK (Cyan Magenta Yellow Black) color chart of the ISO12642 test form without going through the profile.

[0036] In the image forming apparatus 100, an ISO12642 test form (patch 220) is transferred and fixed onto the sheet S by processes such as charging, exposure, development, transfer, and fixing. The sheet S is conveyed to the recirculation path 138 and colorimetry is performed by the color sensor 200. The spectral reflectance data of the colorimetric patch 220 is input to the printer controller 103, converted into L*a*b* data by the Lab calculation unit 303, stored in the input ICC profile storage unit 304 for the color sensor, and input to the profile creation unit 301. Note that it may be converted to the CIE1931XYZ color system, which is a device-independent color space signal that is not L*a*b*.

[0037] Furthermore, the profile creation unit 301 creates an output ICC profile based on the relationship between the output CMYK signal and the input L*a*b* data, and replaces it with the output ICC profile stored in the output ICC profile storage unit 305. The ISO12642 test form includes CMYK color signal patches that cover the color reproduction range that a general copier can output, and a color conversion table is created from the relationship between each color signal value and the measured L*a*b* value. That is, a CMYK→Lab conversion table (A2Bx tag) is created. Based on this conversion table, an inverse conversion table (B2Ax tag) is created.

[0038] The ICC profile consists of a header, tags, and their data. The tags include not only the above color conversion table, but also tags such as the white point (Wtpt) and the gamt tag that describes whether the color represented by the Lab values defined within the profile is inside or outside the reproducible range of its hard copy.

[0039] Note that the profile creation command may be input from an external interface 308 such as an external connected device like a PC. In this case, the user may be allowed to upload the output ICC profile created by the transmitting external device so that color conversion can be performed with an application corresponding to the ICC profile.

[0040] (Color conversion process) The color conversion in normal color output will be described. The image signal assumed to be input via the external interface 308 such as the scanner unit, such as the RGB signal value or the standard print CMYK signal value like JapanColor, is sent to the input ICC profile storage unit 307 for external input. In the input ICC profile storage unit 307, RGB→L*a*b* or CMYK→L*a*b* conversion is performed according to the image signal input from the external interface 308. The input ICC profile is composed of a one-dimensional LUT (look-up table) that controls the gamma of the input signal, a multi-color LUT called direct mapping, and a one-dimensional LUT that controls the gamma of the generated conversion data. Using these look-up tables, the conversion is made from a device-dependent color space to device-independent L*a*b* data.

[0041] The image signal converted to L*a*b* color coordinates is input to the CMM (Color Management Module) 306. Then, GUMAT conversion is performed to map the mismatch between the reading color space of the external interface 308 by a scanner unit or the like as an input device and the output color reproduction range of the image forming apparatus 100 as an output device. Also, color conversion for adjusting the light source type mismatch at the time of input and the light source type mismatch when observing the output (also referred to as the color temperature setting mismatch) and black character determination are performed. As a result, the L*a*b* data is converted to L*’a*’b*’ data and input to the profile storage unit 305. The profile created as described above is stored in the profile storage unit 305, color-converted by the newly created ICC profile, converted to a CMYK signal dependent on the output device, and output to the engine control unit 312.

[0042] As described above, based on the image information measured (read) by the color sensor 200, an ICC profile is created, and based on this, the image formed on the sheet S by the image forming engine 102 of the image forming apparatus 100 is corrected. As a result, it is possible to execute color tone adjustment that performs feedback based on the patch 220 of the sheet S.

[0043] [Detailed Structure of Image Reading Mechanism 50] Next, the details of the image reading mechanism 50 as a color measurement unit that performs color measurement in order to perform color tone adjustment as described above in the image forming apparatus 100 of the present embodiment will be described with reference to FIGS. 4 to 9 while referring to FIG. 1. Note that FIG. 4 shows a state in which a color sensor unit 400 including two color sensors 200A and 200B and a sensor substrate 401 is attached in the image reading mechanism 50. Conversely, FIG. 5 shows a state in which the color sensor unit 400 is removed in the image reading mechanism 50. Note that FIG. 6 is a cross-sectional view taken along the arrow A in FIG. 4, and FIG. 7 is a cross-sectional view taken along the arrow B in FIG. 4.

[0044] As shown in FIG. 1, the image reading mechanism 50 includes a part of the re-conveying path 138 and conveying roller pairs 141, 142, 143, 144, and is configured to convey the sheet S by them. Further, a curved conveying path 145 from the downstream side in the sheet conveying direction of the conveying roller pair 142 to the conveying roller pair 141, which is a part of the re-conveying path 138, is curved so that the sheet S faces the transfer roller 114. Furthermore, the image reading mechanism 50 is provided with a color sensor 200 as an image reading unit that reads an image (patch 220) of the conveyed sheet S on the upstream side in the sheet conveying direction of the conveying roller pair 142. And the image reading mechanism 50 is provided with a pressing roller 140 that presses the sheet S toward the color sensor 200.

[0045] Specifically, as shown in FIG. 6, the conveying roller pair 141 has a driving roller 141b driven by the driving force of the conveying motor 311 and a driven roller 141a that is driven to rotate passively by the driving of the driving roller 141b. The driven roller 141a of the conveying roller pair 141 has a rotating shaft 141x rotatably supported and a plurality of roller portions 141ra, 141rb disposed on the rotating shaft 141x, as shown in FIG. 7. These roller portions 141ra, 141rb are in contact with the sheet S and sandwich and convey the sheet S together with the driving roller 141b.

[0046] Similarly, as shown in FIG. 6, the conveying roller pair 142 has a driving roller 142b driven by the driving force of the conveying motor 311 and a driven roller 142a as a first roller that is driven to rotate passively by the driving of the driving roller 142b. The driven roller 142a of the conveying roller pair 142 has a rotating shaft 142x as a first rotating shaft rotatably supported and a plurality of roller portions 142ra, 142rb as a plurality of first roller portions arranged in parallel on the rotating shaft 142x, as shown in FIGS. 4, 5, and 7. These roller portions 142ra, 142rb are in contact with the sheet S and sandwich and convey the sheet S together with the driving roller 142b.

[0047] Similarly, as shown in FIG. 6, the conveying roller pair 143 has a driving roller 143b driven by the driving force of the conveying motor 311 and a driven roller 143a that is driven to rotate passively by the driving of the driving roller 143b. As shown in FIGS. 4 and 5, the driven roller 143a of the conveying roller pair 143 has a rotatable support shaft 143x and a plurality of roller portions 143ra, 143rb disposed on the rotation shaft 143x. These roller portions 143ra, 143rb are in contact with the sheet S and sandwich and convey the sheet S together with the driving roller 143b.

[0048] Similarly, as shown in FIG. 6, the conveying roller pair 144 has a driving roller 144b driven by the driving force of the conveying motor 311 and a driven roller 144a that is driven to rotate passively by the driving of the driving roller 144b. As shown in FIGS. 4 and 5, the driven roller 144a of the conveying roller pair 144 has a rotatable support shaft 144x and a plurality of roller portions 144ra, 144rb disposed on the rotation shaft 144x. These roller portions 144ra, 144rb are in contact with the sheet S and sandwich and convey the sheet S together with the driving roller 144b.

[0049] As shown in FIG. 4, the color sensor unit 400 according to the present embodiment has two color sensors 200A, 200B and a sensor substrate 401. As shown in FIG. 5, below the color sensor unit 400, a conveying guide 600 as a first guide portion (guide portion) is disposed between the driven roller 142a and the driven roller 143a in the sheet conveying direction. This conveying guide 600 is configured to cover the color sensor unit 400. The conveying guide 600 has a guide surface 600s on its surface that constitutes one surface of the re-conveying path 138, that is, the conveying guide 600 forms the re-conveying path 138.

[0050] On the transport guide 600, through holes 600a and 600b corresponding to reading positions 500A and 500B are formed, where the two color sensors 200A and 200B irradiate light, which is reflected by the sheet S and condensed for reading. The color sensors 200A and 200B have the opening portions of the guide surface 600s in these through holes 600a and 600b as the focal positions. That is, when the sheet S slides in contact with the guide surface 600s, the image reading accuracy is configured to be optimal. Also, in the present embodiment, the reading positions 500A and 500B mean the sheet transport direction and the axial direction (sheet width direction) of the rotation axis 142x, that is, the position of the plane coordinates on the guide surface 600s. Therefore, at these reading positions 500A and 500B, in the direction perpendicular to the guide surface 600s, the position of the three-dimensional coordinates that coincides with the guide surface 600s means the focal position.

[0051] And at a position facing the guide surface 600s of the transport guide 600, a pressing roller 140 as a second roller (pressing portion) is arranged. As shown in FIGS. 6 and 7, the pressing roller 140 has a rotation axis 140x as a second rotation axis rotatably supported, and a plurality of roller portions 140ra and 140rb as a second roller portion arranged in parallel on the rotation axis 140x. Each of these roller portions 140ra and 140rb is arranged at a position overlapping the reading positions 500A and 500B in the direction perpendicular to the guide surface 600s, that is, facing the reading positions 500A and 500B. The rotation axis 140x is pressed toward the guide surface 600s by a pressing means such as a spring (not shown), and these roller portions 140ra and 140rb rotate while contacting the sheet S and pressing and sandwiching the sheet S between them and the guide surface 600s. In the present embodiment, the rotation axis 140x is described as being pressed against the guide surface 600s by a pressing means (not shown), but the roller portions 140ra and 140rb may be made of a member that is easily elastically deformed such as a sponge, and the sheet S may be pressed against the guide surface 600s.

[0052] In the present embodiment, two roller portions of each of the driven rollers 141a, 142a, 143a, 144a and two roller portions of the pressing roller 140 are arranged in parallel in the same number on their rotation axes. And each of these roller portions is arranged at a position overlapping in the axial direction when viewed from the sheet conveyance direction.

[0053] On the other hand, on the downstream side of the conveyance roller pair 142 in the sheet conveyance direction, as shown in FIG. 6, conveyance guides 601, 602, 603 as the second guide portions are arranged. These conveyance guides 601, 602, 603 form a curved conveyance path 145 as a second conveyance path that curves with respect to the axial direction of the rotation shaft 142x (see FIG. 4) and the direction orthogonal to the sheet conveyance direction, that is, the vertical direction when viewed from the width direction of the sheet, and guide the sheet S. Note that this curved conveyance path 145 is a part of the re-conveyance path 138.

[0054] Next, the posture of the sheet S during image reading in the image reading mechanism 50 configured as described above will be described. As shown in FIGS. 6 and 7, when reading the patch 220 (see FIG. 3) of the sheet S by the image reading mechanism 50, the sheet S is conveyed by the conveyance roller pairs 141, 142, 143, 144. At that time, the sheet S is pressed against the guide surface 600s of the conveyance guide 600 by the pressing roller 140 so that the patch 220 of the sheet S passes through the reading positions 500A, 500B of the color sensors 200A, 200B.

[0055] When the central portion S1 of the sheet S passes through the reading positions 500A, 500B, it is pressed against the guide surface 600s by the pressing roller 140, and the end portion S2 of the sheet S hangs down due to its own weight and separates from the guide surface 600s. Further, when the leading end of the sheet S advances to the downstream side in the sheet conveyance direction from the conveyance roller pair 142 and advances through the curved conveyance path 145, the leading end of the sheet S advances upward (the pressing direction of the pressing roller 140). Then, the portion in the width direction near the reading positions 500A, 500B on the sheet S is pressed downward by the rigidity of the sheet S.

[0056] However, the roller portions 142ra and 142rb of the driven roller 142a of the conveying roller pair 142 and the roller portion (not shown) of the driving roller 142b sandwich the sheet S between the curved conveying path 145 and the reading positions 500A and 500B in the sheet conveying direction. Therefore, as shown in FIGS. 5 and 7, in the range W where the roller portions 142ra and 142rb are arranged in the axial direction (width direction) of the rotation axis 142x as viewed from the sheet conveying direction, the central portion S1 of the sheet S is easily pressed against the guide surface 600s by the pressing roller 140.

[0057] On the other hand, in the range V which is outside the range W in the axial direction, the influence of the clamping force of the conveying roller pair 142 becomes weaker toward the end portion S2 of the sheet S, and the downward pressing received by the rigidity of the sheet S by the curved conveying path 145 is strengthened. Therefore, as shown in FIGS. 6 and 7, the end portion S2 of the sheet S will be greatly separated from the guide surface 600s.

[0058] Therefore, in the present embodiment, the reading positions 500A and 500B are arranged between one end portion W1 and the other end portion W2 in this range W. Specifically, the reading position 500A is arranged at a position overlapping the roller portion 142ra in the axial direction as viewed from the sheet conveying direction, and the reading position 500B is arranged at a position overlapping the roller portion 142rb in the axial direction as viewed from the sheet conveying direction. Thereby, even when the leading end of the sheet S is being conveyed along the curved conveying path 145, the sheet S can be stably positioned at the focal positions of the reading positions 500A and 500B by the pressing of the roller portions 140ra and 140rb of the pressing roller 140. Therefore, the accuracy of image reading can be improved.

[0059] [Description of Comparative Example] Incidentally, by increasing the pressing force of the pressing roller 140, it might be considered to bring the end portion S2 of the sheet S located axially outside the range W closer to the guide surface 600s. However, it is difficult to accommodate sheets S with different rigidities. That is, as shown in FIG. 8, assume that the pressing force of the roller portion 140rx of the pressing roller 140 is stronger than that in the present embodiment (see FIG. 6), and the rigidity of the sheet S is low. In this case, for example, at the reading position 500A, a part S1a of the sheet S enters the through hole 600a (see FIG. 5) and bulges. Therefore, when the rigidity of the sheet S is low, the sheet S is not at the focal position, and the accuracy of image reading cannot be improved.

[0060] Also, in order not to cause such bulging, as shown in FIG. 9, it might be considered to increase the pressing force of the pressing roller 140 and configure the roller portion 140ry with a member that is easily elastically deformed such as a sponge. However, as shown in FIG. 9, when the rigidity of the sheet S is high, the pressing force received from the curved conveyance path 145 based on the rigidity of the sheet S becomes large, so the roller portion 140ry is greatly deformed, and it is difficult to bring the end portion S2 of the sheet S closer to the guide surface 600s. Therefore, even if the pressing force of the pressing roller 140 is increased to bring the end portion S2 of the sheet S closer to the guide surface 600s and the reading position of the color sensor 200 is arranged within the range V, it is impossible to accommodate sheets with different rigidities, and the accuracy of image reading deteriorates.

[0061] [Possibilities of Other Embodiments] In the present embodiment described above, two color sensors are arranged, but it is not limited to this. For example, when reading the number of patches of the standard required for color adjustment, in order to reduce the number of sheets forming the patches, it might be considered to arrange more color sensors or arrange the color sensors so as to be movable in the axial direction, for example. In this case, in accordance with the range where the color sensors are arranged and the moving range of the color sensors, it might also be considered to widen the range W where the roller portions 142ra and 142rb of the conveyance roller pair 142 are arranged, increase the width of the roller portions, or increase the number of the roller portions.

[0062] In addition, in the present embodiment, the description has been made assuming that there are two roller portions 142ra and 142rb of the conveying roller pair 142. However, the present invention is not limited to this, and for example, it may be configured with one roller portion having the width of the range W, or a configuration in which three or more roller portions are arranged within the range W.

[0063] In addition, in the present embodiment, the description has been made assuming that there are two color sensors 200A and 200B as color sensors. However, the present invention is not limited to this, and the number of color sensors may be one or three or more.

[0064] In addition, in the present embodiment, the description has been made assuming that the reading position of the color sensor is arranged at a position overlapping either of the roller portions 142ra and 142rb of the conveying roller pair 142 when viewed from the sheet conveying direction. However, the present invention is not limited to this, and the reading position of the color sensor may be arranged between the roller portions 142ra and 142rb in the axial direction when viewed from the sheet conveying direction. Also in this case, the central portion S1 of the sheet S is difficult to separate from the guide surface 600s, and the sheet S can be stably positioned at the focal position of the reading position.

[0065] In addition, in the present embodiment, the description has been made assuming that the curved conveying path 145 is curved in the same direction as the pressing direction of the pressing roller 140 on the downstream side in the sheet conveying direction of the conveying roller pair 142. However, the present invention is not limited to this, and the shape of the curved conveying path 145 may be any shape, that is, any shape in which a force in a direction away from the focal position is generated at the reading position of the color sensor as the leading end of the sheet S is conveyed and guided.

[0066] In addition, in this embodiment, the curved conveyance path 145 as the external force applying portion has been described as applying a force in a direction away from the focal position (guide surface 600s) at the reading position of the color sensor as the tip of the sheet S is conveyed and guided. However, the present invention is not limited to this. For example, the tangent when viewed from the axial direction of the nip of the conveyance roller pair 142 may be inclined with respect to the guide surface 600s and away from the focal position at the reading position. In this case, as the sheet is nipped by the nip of the conveyance roller pair 142 as the external force applying portion, a force in a direction away from the focal position is applied at the reading position of the color sensor.

[0067] In addition, in this embodiment, it has been described that the conveyance roller pairs 141, 142, 143, 144, etc. are such that the color sensor 200 is arranged on the re-conveyance path 138 and the one on the side where the color sensor 200 is arranged is the driven roller. However, conversely, the one on the side where the color sensor 200 is arranged with respect to the re-conveyance path 138 may be the driving roller.

[0068] In addition, in this embodiment, the pressing roller 140 has been described as a driven roller not connected to the drive source. However, the present invention is not limited to this, and it may be a driving roller connected to a drive source such as a conveyance motor. Furthermore, in this embodiment, it has been described that the sheet is pressed against the guide surface 600s by the pressing roller 140. However, for example, it may be constituted by a pressing portion such as a pressing plate made of fluororesin processed to be easily slidable and biased by a spring or the like.

[0069] In addition, in this embodiment, the color sensor 200 has been used as the image reading unit to perform color adjustment in the image forming apparatus. However, the present invention is not limited to this, and it may perform position adjustment, density adjustment, etc. of image formation. Furthermore, the image reading unit may be a monochrome sensor, and in that case, position adjustment, density adjustment, etc. of image formation can be performed.

Explanation of Reference Numerals

[0070] 50…Image reading mechanism (image reading device) / 100…Image forming device / 102…Image forming engine (image forming unit) / 140…Second roller / 140ra, 140rb…Roller part (second roller part) / 140x…Rotation axis (second rotation axis) / 142a…Driven roller (first roller, conveying roller) / 142b…Drive roller / 142ra, 142rb…Roller part (first roller part) / 142x…Rotation axis (first rotation axis) / 145…Curved conveying path (second conveying path) / 200A, 200B…Color sensor (image reading part) / 311…Conveying motor (drive source) / 500A, 500B…Reading position / 600…Conveying guide (first guide part, guide part) / 600s…Guide surface / 601, 602, 603…Conveying guide (second guide part) / S…Sheet / W…Range / W1…One side end / W2…The other side end

Claims

1. An image forming unit that forms an image on a sheet; A reversing unit that reverses the direction in which the sheet on which the image is formed by the image forming unit is conveyed; A conveyance path that conveys the sheet reversed by the reversing unit to the image forming unit and includes a curved portion curved upward; A plurality of rollers that convey the sheet in the conveyance path; An image reading unit that reads an image of the sheet at a reading position in the conveyance path, and comprising: The plurality of rollers include: A first roller disposed at the position closest to the curved portion on the upstream side of the curved portion in the sheet conveyance direction among the plurality of rollers, having a first rotation axis, and a first roller portion that is arranged in parallel with the first rotation axis and that contacts the sheet and conveys the sheet; A second roller disposed at the position closest to the first roller on the upstream side of the first roller in the sheet conveyance direction among the plurality of rollers, having a second rotation axis, and a second roller portion that is disposed on the second rotation axis, contacts the sheet at the reading position, and conveys the sheet while pressing the sheet toward the image reading unit; The reading position is disposed between one end and the other end in a range in which a plurality of the first roller portions are arranged in the axial direction of the first rotation axis as viewed from the sheet conveyance direction; An image forming apparatus, characterized in that.

2. The reading position is disposed at a position overlapping the first roller portion in the axial direction as viewed from the sheet conveyance direction; The image forming apparatus according to claim 1, characterized in that.

3. There are a plurality of the image reading units; Each reading position in the plurality of image reading units is disposed at a position overlapping any one of the plurality of first roller portions in the axial direction as viewed from the sheet conveyance direction; The image forming apparatus according to claim 1 or 2, characterized in that.

4. The second roller portion is arranged in parallel with the first roller portion in the same number on the second rotation axis, and is disposed at a position overlapping each of the plurality of first roller portions in the axial direction as viewed from the sheet conveyance direction; The image forming apparatus according to claim 3, characterized in that.

5. The curved portion is curved in the same direction as the pressing direction of the second roller; The image forming apparatus according to any one of claims 1 to 4, characterized in that.

6. A drive source that outputs a driving force; A driving roller that is driven by the driving force of the drive source, and comprising: The first roller is a driven roller that is driven to rotate passively by the driving of the driving roller. The image forming apparatus according to any one of claims 1 to 5, characterized in that...

7. The image reading unit is a color sensor that reads the color of the image information of the sheet. The image forming apparatus according to any one of claims 1 to 6, characterized in that...

8. The image reading unit includes a plurality of color sensors that read the color of the image information of the sheet. The reading positions of the plurality of color sensors are arranged in a region between one end and the other end in a range where the plurality of first roller units are arranged in the axial direction, and are not arranged outside the region in the axial direction. The image forming apparatus according to any one of claims 1 to 6, characterized in that...

9. The image forming unit corrects the image to be formed on the sheet based on the image information read by the image reading unit. The image forming apparatus according to any one of claims 1 to 8, characterized in that...

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