Image forming device

Abstract

To reduce the conveyance speed of a sheet when reading images of a plurality of sheets to prevent extension of time of a step of reading the images of the plurality of sheets without impairing reading accuracy.SOLUTION: An image forming apparatus 100 comprises: a first reverse roller 171 that reverses and conveys a sheet 1 having been conveyed thereto; a pre-reverse conveyance path 133 that guides the sheet 1 to the first reverse roller 171; a post-reverse conveyance path 141 that guides the sheet 1 having been revered by the first reverse roller 171 to an ejection roller 139a; a color sensor 200 that reads an image of the sheet 1; and a printer controller that, when reading images of a plurality of sheets with the color sensor 200, controls the conveyance speed of the sheets in reading the images of the sheets to be a second conveyance speed slower than a first conveyance speed. The color sensor 200 is arranged to read the images of the sheets conveyed to the post-reverse conveyance path 141.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to an image forming apparatus including an image reading unit that reads an image on a sheet. [Background technology]

[0002] Conventionally, in image forming devices such as printers and multifunction devices that form images on sheets, devices have been proposed that read the image formed on a sheet and use the result for correction in the next image formation (see Patent Documents 1, 2, and 3). In the device of Patent Document 1, a reading unit that reads the position of the image formed on the sheet is provided in a double-sided conveying path for inverting a sheet with an image formed on one side and conveying it again to an image forming unit, and the image forming position of the next sheet is corrected. In addition, in the devices of Patent Documents 2 and 3, a color sensor is disposed in the conveying path between the image forming unit and an inverting unit that inverts the sheet, a patch image of the sheet is read by the color sensor to create a profile, and color adjustment is performed based on the profile. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2005-221582 A [Patent Document 2] JP 2013-54324 A [Patent Document 3] JP 2014-131205 A Summary of the Invention [Problem to be solved by the invention]

[0004] Incidentally, for example, when a patch image is read by a color sensor as a reading unit to create a profile, the number of color patches is determined by a chromaticity standard certification organization for certification, and it becomes necessary to read, for example, 1000 or more color patches. Furthermore, these color patches are formed across multiple sheets, and the sheets on which these color patches are formed are discarded. In order to reduce such discarded sheets, it is required to arrange as many color patches as possible on one sheet. However, when a large number of color patches are arranged condensed on one sheet in this way, it becomes necessary to slow down the reading speed (sheet conveying speed) when reading in order to read these color patches without losing accuracy.

[0005] For example, if the reading unit is located on the duplex conveying path as in Patent Document 1, the sheet to be discarded will be re-conveyed to the image forming unit and passed through, which lengthens the conveying time until the sheet is discharged, and the adjustment process takes a long time to begin with. Also, if the reading unit is located before the reversing unit as in Patent Documents 2 and 3, when consecutive sheets are read, it is necessary to widen the space between the sheets so that the next sheet does not interfere with the sheet being read, which also lengthens the adjustment process time.

[0006] Therefore, an object of the present invention is to provide an image forming apparatus that can slow down the sheet transport speed when reading images on multiple sheets without compromising reading accuracy, and can prevent the process of reading images on multiple sheets from taking too long. [Means for solving the problem]

[0007] According to one aspect of the present invention, there is provided a printing apparatus including an image forming unit for forming an image on a sheet, and an ejection unit for ejecting the sheet on which the image has been formed by the image forming unit to the outside. a discharge conveying path on which rollers are arranged and which extends from the image forming unit to the discharge rollers; a first conveying path branched downward from the discharge conveying path between the image forming unit and the discharge rollers on the discharge conveying path; a first switching unit that is switchable between a state in which a sheet is conveyed from the image forming unit to the discharge rollers through the discharge conveying path and a state in which the sheet is conveyed from the discharge conveying path to the first conveying path; a reversing conveying path that is formed continuously from the first conveying path and that reverses a conveying direction of the sheet conveyed from the image forming unit through the first conveying path and conveys the sheet;a second conveying path that guides the sheet inverted by the reversing conveying path from the reversing conveying path to the discharge conveying path, and is switchable between a state in which the sheet is conveyed from the first conveying path to the reversing conveying path and a state in which the sheet is conveyed from the reversing conveying path to the second conveying path. Second A switching unit and the Second a reading unit that reads, in the second transport path, an image on the sheet that has passed through a switching unit and been transported from the reversing transport path to the second transport path. Effect of the Invention

[0009] According to the present invention, by slowing down the sheet transport speed when reading images on multiple sheets, it is possible to prevent the process of reading images on multiple sheets from taking too long without compromising reading accuracy. [Brief description of the drawings]

[0010] [Figure 1] 1 is a schematic diagram of an image forming apparatus according to an embodiment of the present invention. [Diagram 2] FIG. 2 is a schematic diagram showing the structure of a color sensor. [Diagram 3] FIG. 2 is a block diagram showing a control configuration of the image forming apparatus. [Figure 4] A diagram explaining an ICC profile. [Diagram 5] Schematic diagram showing a color management environment. [Figure 6] 6 is a flowchart showing control of a color measurement job according to the present embodiment. [Figure 7] 5 is a diagram of sheet transport in a color measurement job according to the present embodiment. [Figure 8] FIG. 2 is a schematic diagram of an image forming apparatus according to a first comparative example. [Figure 9] 11 is a diagram of sheet transport in a color measurement job according to a first comparative example. [Figure 10] FIG. 11 is a schematic diagram of an image forming apparatus according to a second comparative example. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

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

[0012] [General configuration of image forming device] 1 is a schematic diagram showing an image forming apparatus 100 according to the present embodiment. Note that, in the present embodiment, the image forming apparatus 100 is an electrophotographic laser beam printer, but the image forming apparatus is not limited thereto, and may be an inkjet printer or a dye-sublimation printer.

[0013] An image forming engine 102 and a control board storage section (not shown) that houses a printer controller 103 (see FIG. 3) that is a control section that controls the operation of the image forming apparatus 100 are mounted on a housing 101 of the image forming apparatus 100. The image forming engine 102 as an 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 1 used as the recording material. As the recording material, sheets such as plain paper and cardboard, paper with a surface treatment such as coated paper and embossed paper, plastic film, cloth, etc. can be used.

[0014] The optical processing mechanism 10 includes stations 120, 121, 122, and 123 that form toner images of each color, yellow, magenta, cyan, and black, and an intermediate transfer belt 106. In 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 body. The laser scanner unit 107 performs exposure processing of the photosensitive drum 105 based on a command signal that is generated based on image data and transmitted to the laser scanner unit 107. The laser scanner unit 107 has a laser driver that drives a laser light emitted from a semiconductor laser (not shown) to be on and off. The laser scanner unit 107 guides the laser light from the semiconductor laser to the photosensitive drum 105 via a reflecting mirror 109 while distributing the laser light from the semiconductor laser in the main scanning direction (width direction of the sheet) using a rotating polygon mirror. 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 unit 112 contains a developer containing toner therein, and supplies charged toner particles to the photosensitive drum 105. The toner particles adhere to the drum surface in accordance with the surface potential distribution, and the electrostatic latent image carried on the photosensitive drum 105 is visualized as a toner image. 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 a color image is formed, the toner images formed by the four stations 120 to 123 are transferred in multiple layers onto the intermediate transfer belt 106 so as to be superimposed on each other, forming a full-color toner image on the belt.

[0016] On the other hand, the feeding process mechanism 30 feeds the sheets 1 one by one from a sheet storage 113 inserted retractably into the housing 101 of the image forming apparatus 100 toward a transfer roller 114. The toner image carried on the intermediate transfer belt 106, which is an intermediate transfer body, is transferred (secondary transfer) onto the sheet 1 by the transfer roller 114.

[0017] Around the intermediate transfer belt 106, there are arranged an image formation start position detection sensor 115 for determining a print start position when forming an image, a feed timing sensor 116 for timing the feeding of the sheet 1, and a density sensor 117. 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 setting of the charging target potential of the primary charger 111 and the bias voltage of the developer 112) based on the detection result of the density sensor 117.

[0018] The fixing process mechanism 20 of this embodiment is composed of a fixing device 150 and a cooling unit 160. The fixing device 150 includes a fixing roller 151 for applying heat to the sheet 1, a pressure belt 152 for pressing the sheet 1 against the fixing roller 151, and a post-fixing sensor 153 for detecting the completion of the fixing process by the fixing device 150. The fixing roller 151 is a hollow roller and has a heater inside. The fixing device 150 applies heat and pressure to the toner image on the sheet while sandwiching and conveying the sheet 1 between the fixing roller 151 and the pressure belt 152, which are a pair of rotating bodies. This melts the toner particles, which then become fixed, thereby fixing the image on the sheet 1.

[0019] The cooling unit 160 is disposed downstream of the fixing device 150 in the sheet conveying direction, and is disposed for the purpose of lowering the temperature of the sheet 1 fixed by the fixing device 150, thereby reducing the heat supply from the sheet 1 to the image forming portion and reducing the amount of curl in the finished product, particularly during double-sided printing. The cooling unit 160 includes rollers 161 and 162, and a post-cooling sensor 163 that detects the completion of the cooling process by the cooling unit 160. The cooling unit 160 transfers the heat of the sheet 1 to the rollers 161 and 162 by clamping the sheet 1 with a nip formed by the rollers 161 and 162. The heat transferred to the rollers 161 and 162 is dissipated by a cooling fan (not shown).

[0020] The sheet 1 that has passed through the cooling unit 160 is guided from the conveying path 131 to either the discharge conveying path 139 or the pre-reversal conveying path 133 as the first conveying path by the first switching flapper 132 via the pre-discharge conveying path 142 as the fourth conveying path. The sheet 1 conveyed to the pre-reversal conveying path 133 passes through the second switching flapper 134 and is guided to the reversal conveying path 135. The sheet 1 conveyed to the reversal conveying path 135 is guided toward the standby path 138 by the first reversal rollers 171 and / or the second reversal rollers 172 as a reversal conveying section while the position of the sheet 1 is detected by the reversal sensor 137.

[0021] In the case of double-sided printing, the sheet 1 with an image formed on its front side is conveyed into a waiting path 138 until its rear end passes through a third switching flapper 136 based on detection by a reversing sensor 137. Then, the downstream end (leading end) and the upstream end (rear end) in the sheet conveying direction are switched by a switchback operation performed by a second reversing roller 172. With the leading and rear ends switched by the second reversing roller 172, the sheet is guided again by the third switching flapper 136 toward the transfer roller 114 via a re-conveyance path 140 as a third conveyance path, and an image is formed on the rear side opposite to the front side.

[0022] Then, the sheet 1 on which image formation for single-sided printing has been completed or the sheet 1 on which image formation for the back side has been completed in double-sided printing is guided to the discharge conveying path 139 via the pre-discharge conveying path 142. The sheet 1 conveyed to the discharge conveying path 139 is discharged onto a discharge tray 700 provided outside the image forming apparatus 100 by discharge rollers 139a as a discharge section.

[0023] On the other hand, when the sheet 1 that has passed through the cooling unit 160 is reversed and discharged (when a color measurement job described later is executed), the sheet 1 on whose front surface an image is formed is guided to the pre-reversal conveying path 133. Thereafter, based on the detection of the reversal sensor 137, the sheet is conveyed to the reversal conveying path 135 and the waiting path 138 until its rear end passes the second switching flapper 134. Then, the downstream end (leading end) and the upstream end (rear end) in the sheet conveying direction are swapped by the switchback operation performed by the first reversal roller 171. The sheet 1 whose leading and rear ends have been swapped by the first reversal roller 171 is guided by the second switching flapper 134 to the post-reversal conveying path 141 as a second conveying path connecting the reversal conveying path 135 and the discharge conveying path 139, and is then guided toward the discharge conveying path 139. The sheet 1 thus inverted and then transported to the discharge transport path 139 is also discharged in an inverted state by discharge rollers 139a onto a discharge tray 700 provided outside the image forming apparatus 100. In other words, the post-reversal transport path 141 can be said to be a transport path dedicated to discharge when double-sided printing is not performed and the inverted sheet 1 is discharged.

[0024] [Color sensor configuration] Next, the arrangement and structure of the color sensor 200 in the color measurement unit 500 will be described with reference to Figs. 1 and 2. Fig. 2 is a schematic diagram showing the structure of the color sensor. A color measurement unit 500 that reads an image of the surface of the inverted sheet 1 transported along the post-reversal transport path 141 is arranged along the above-mentioned post-reversal transport path 141. The color measurement unit 500 is provided with the color sensor 200 as a reading unit that reads the image of the sheet 1.

[0025] 2, the color sensor 200 includes a white LED 201 that irradiates light onto a patch image 1P consisting of a number of color patches formed as a test image on the sheet 1, and a diffraction grating 202 that separates the light reflected from the patch image 1P into wavelengths. The color sensor 200 also includes a built-in lens 206 that focuses the light irradiated from the white LED 201 onto the patch image 1P on the sheet 1 and focuses the light reflected from the patch image 1P onto the diffraction grating. The color sensor 200 also includes a line sensor 203 (203-1 to 203-n) that is a CMOS sensor consisting of n pixels that detects the light separated into wavelengths by the diffraction grating 202. The color sensor 200 also includes a built-in calculation unit 204 that performs various calculations from the light intensity values ​​of each pixel detected by the line sensor 203, and a built-in memory 205 that stores various data. The color measurement unit 500 includes an A / D converter, and transmits the color measurement results to the printer controller 103 in FIG. 3 as digital signals.

[0026] The pixel information of 1 to n of the line sensor 203 has the same relationship as the spectral wavelength. In order to ultimately output a detection result having a resolution of 10 nm from 380 to 780 nm, it is desirable for n to be 41 or more. In order to align the relationship between the wavelength and the pixel number, 48 pixels or 64 pixels are appropriate, taking into consideration the adjustment range, etc. Alternatively, a simple configuration can be considered in which the number of pixels is reduced and the missing wavelengths are calculated by interpolation. Although such a simple configuration is acceptable, the detection accuracy will decrease.

[0027] [Control configuration of image forming device] Next, the control of the image forming apparatus 100 will be explained with reference to Fig. 3 to Fig. 5. Fig. 3 is a diagram showing the control configuration of the image forming apparatus, Fig. 4 is a diagram explaining the ICC profile, and Fig. 5 is a schematic diagram showing the color management environment. The host computer 300 and the image forming apparatus 100 are connected by a communication line such as USB 2.0 High-Speed ​​or LAN.

[0028] In the image forming apparatus 100, the printer controller 103 controls the operation of the entire printer. The printer controller 103 is also connected to an I / F unit 308 that handles input and output with the host computer 300, the operation unit 180, the color sensor 200, and an engine control unit 312. The printer controller 103 also has a ROM 320 that contains control programs and control data, together with a CPU and RAM (not shown). Each control program in the ROM 320 constitutes a RIP (Raster Image Processor) unit 314 that develops an image object into a bitmap image. Each control program in the ROM 320 also constitutes a color processing unit 315 that performs color conversion processing of multi-colors (to be described later), a gradation correction table generation unit 316 that performs gradation correction of a single color, a multi-color table generation unit 317 that reflects the correction results of multi-colors, and a maximum density condition determination unit 318.

[0029] The engine control unit 312 causes the image forming engine 102 to perform the above-mentioned image forming process to form an image on a sheet based on a command signal from the printer controller 103, etc. For example, the engine control unit 312 inputs detection signals from the post-fixing sensor 153, the post-cooling sensor 163, and the inversion sensor 137. Then, based on these detection signals, the engine control unit 312 controls the operations of the conveying motor 311 that drives the rollers that convey the sheet, the first switching flapper 132, the second switching flapper 134, and the third switching flapper 136.

[0030] The image forming apparatus 100 is provided with an operation unit 180 that serves as a user interface (see FIG. 1). The operation unit 180 has a display as a display means for displaying information to the user. The operation unit 180 also has 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 indicating sheet attributes such as the name, basis weight, and whether or not the sheet is surface-treated, of a sheet set in a certain sheet storage 113 (see FIG. 1), to the printer controller 103.

[0031] [Color adjustment for image formation] Next, color adjustment of image formation when the patch image 1P of the sheet 1 is measured by the color sensor 200 will be described in detail. That is, a control flow for creating a color profile in the image forming apparatus 100 in this embodiment and outputting an image using the color profile will be described. The color profile creation process is performed by the printer controller 103. First, an instruction for creating a profile is input to the profile creation unit 301 via the operation unit 180. The profile creation unit 301 transmits a CMYK (Cyan Magenta Yellow Black) color chart of the ISO12642 test form to the image forming engine 102 so that it is output without going through a profile. At the same time, a color measurement instruction is sent to the color sensor control unit 302.

[0032] In the image forming apparatus 100, an ISO 12642 test form is transferred and fixed as a patch image 1P on the sheet 1 through processes such as charging, exposure, development, transfer, and fixing, and the patch image 1P is measured by the color sensor 200 of the color measurement unit 500. The measured spectral reflectance data of the 928 patches is input to the printer controller 103 and converted to L*a*b* data via the Lab calculation unit 303. The L*a*b* data is then stored as a color setting table in the color sensor input ICC profile storage unit 304 and input to the profile creation unit 301. Note that instead of L*a*b*, the data may be converted to the CIE 1931 XYZ color system, which is a device-independent color space signal.

[0033] Furthermore, the profile creation unit 301 creates an output ICC profile based on the relationship between the output CMYK signals and the input L*a*b* data, and updates the ICC profile by replacing it with the output ICC profile stored in the ICC output profile storage unit 305.

[0034] The ISO12642 test form includes CMYK color signal patches that cover the color reproduction range that a typical copier can output, and creates a color conversion table based on the relationship between each color signal value and the measured L*a*b* value. In other words, a CMYK → Lab conversion table (A2Bx tag) is created. Based on this conversion table, a reverse conversion table (B2Ax tag) is created.

[0035] An ICC profile has a structure as shown in Figure 4, and consists of a header, tags, and their data. The tags include not only the color conversion table mentioned above, but also the white point (Wtpt) and a tag (gamt) that describes whether a certain color expressed by the L*a*b* values ​​defined within the profile is inside or outside the reproducible reproduction range of the hard copy.

[0036] If the profile creation command is input from an I / F 308 of an external device, the output ICC profile created by the external device that sent the command may be uploaded, and the user may perform color conversion using an application that supports the ICC profile.

[0037] In color conversion for normal color output, image signals input assuming RGB signal values ​​input via an external I / F 308 such as a scanner unit or standard printing CMYK signal values ​​such as JapanColor are sent to an input ICC profile storage unit 307. 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 I / F 308. The input ICC profile is composed of a one-dimensional LUT (lookup 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 tables, conversion is performed from a device-dependent color space to device-independent L*a*b* data.

[0038] The image signal converted into the L*a*b* chromaticity coordinates is input to a CMM (color management module) 306. Then, a GUMAT conversion is performed to map mismatches between the read color space of an external I / F 308 such as a scanner unit as an input device and the output color reproduction range of the image forming apparatus 100 as an output device. Furthermore, 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 a mismatch in color temperature setting) and black character determination are also performed. As a result, the L*a*b* data is converted into L*'a*'b*' data and input to an ICC output profile storage unit 305. The profile created as described above is stored in the ICC output profile storage unit 305, and the color is converted by the newly created ICC profile, converted into a CMYK signal dependent on the output device, and output.

[0039] In the above description, the block configuration is separated into the CMM 306, the input ICC profile storage unit 307, and the ICC output profile storage unit 305. However, as shown in Fig. 5, the CMM is a module that controls color management, and performs color conversion using an input profile and an output profile.

[0040] A maximum density condition determination unit 318, a gradation correction table generation unit 316, and a multi-color table generation unit 317 that reflects the multi-color correction results manage and update the ICC profile, γLUT, and Vcont information used during image formation. That is, by changing (reflecting) each table using the color processing unit 315, the multi-color table generation unit 317, etc., it is possible to output the desired color.

[0041] [Color measurement job operation] Next, the control of the color measurement job, which is an adjustment process for adjusting color in this embodiment, and the conveying state of multiple sheets in this color measurement job will be described with reference to Fig. 6 and Fig. 7. Fig. 6 is a flowchart showing the control of the color measurement job according to this embodiment, and Fig. 7 is a diagram of sheet conveyance in the color measurement job according to this embodiment. Note that Fig. 7 shows the position of each sheet 1 when, for example, three consecutive sheets 1 are conveyed when the color measurement job is executed.

[0042] For example, when a color measurement job such as color profile creation is specified from the operation unit 180 by a user operation, the printer controller 103 starts the main control shown in Fig. 6 (S1). As shown in Figs. 6 and 7, first, the feeding operation of the sheet 1 is started, and the sheet 1 is fed from the sheet storage 113 toward the transfer roller 114 (S2). Meanwhile, in the image forming engine 102, a toner image of a test form is formed on the intermediate transfer belt 106, and is transferred to the sheet 1 that has been expedited as a patch image 1P for color profile creation (S3). Then, after the patch image is fixed by the fixing device 150, the sheet is cooled by the cooling unit 160 (S4), and image formation is completed. At this time, the sheet 1 is conveyed through the transfer roller 114, the fixing device 150, and the cooling unit 160 at a conveying speed of 600 mm / sec as an image forming process speed.

[0043] Thereafter, when the rear end of the sheet 1 passes through the cooling unit 160, the sheet 1 is transported toward the pre-reversal transport path 133, the reversal transport path 135, and the standby path 138 at an increased transport speed of 1500 mm / sec (first transport speed) as a reversal retraction speed. In addition, after the leading edge of the sheet 1 passes the reversal sensor 137, a timer count for the length of the sheet 1 is started (S5). Then, when the timer reaches 0, the rear end of the sheet 1 is in a position beyond the second switching flapper 134, so the transport of the sheet 1 is stopped, that is, the sheet 1 is transported to the reversal transport path 135 and the standby path 138 and made to wait (S6).

[0044] Next, the first reversing roller 171 reverses the conveying direction of the sheet 1 that was once stopped in the reversing conveying path 135 and the waiting path 138, and the second switching flapper 134 resumes conveying toward the post-reversal conveying path 141 (S7, see FIG. 7). At this time, the conveying speed is increased (S8), and the sheet 1 is conveyed to the position of the color sensor 200 of the color measurement unit 500 at a conveying speed of 1500 mm / sec as a post-reversal speed. Then, just before the leading edge of the sheet 1 reaches the reading position of the color sensor 200, the conveying speed is decelerated to a conveying speed of 300 mm / sec (second conveying speed) as a reading speed (S9), and the sheet 1 is conveyed to the color sensor 200 at that speed (S10).

[0045] At this time, a timer count that determines the start timing of conveying the succeeding sheet 1 is started (S11), and the timing is measured so that the distance between the leading edge of the succeeding sheet 1 and the trailing edge of the preceding sheet 1 becomes as small as possible at the reading position of the color sensor 200. Then, when the timer count ends, feeding of the succeeding sheet 1 is permitted (S12). Note that if there is no succeeding sheet 1 (Y in S17 described below), the flag permitting feeding is simply turned ON, and feeding is not actually performed.

[0046] On the other hand, when the sheet 1 is conveyed to the reading position of the color sensor 200, the color of the patch image 1P is detected (measured) by the reading operation of the color sensor 200 (S13). When the color sensor 200 completes reading the patch image 1P drawn on the sheet up to the rear end, the conveying speed is increased to 1500 mm / sec, which is the sheet discharge speed, in order to discharge the sheet 1 as soon as possible (S14). Then, the discharge roller 139a discharges the sheet 1 onto the discharge tray 700 (S15). In addition, the color measurement result of reading the patch image 1P is sent to the Lab calculation unit 303, converted into L*a*b* data, and stored as a color setting table in the color sensor input ICC profile storage unit 304, and input to the profile creation unit 301 (S16).

[0047] When the reading operation of the patch image 1P on the preceding sheet 1 is completed as described above, it is determined whether or not the colorimetry of the required number of sheets has been completed (S17), that is, whether or not the colorimetry of the 928 patches required for creating a color profile has been completed. If the colorimetry of the 928 patches required for creating a color profile has not been completed (N in S17), feeding of the subsequent sheet 1 is started. As a result, the continuation of the patches for which colorimetry has not been completed is formed on the subsequent sheet 1, and a similar reading operation is performed on the subsequent sheet 1. Then, if the colorimetry of the 928 patches required for creating a color profile has been completed (Y in S17), this control ends (S18), that is, the colorimetry job is completed.

[0048] [Summary of this embodiment] In this embodiment, as described above, the color sensor 200 is disposed along the post-reversal conveying path 141 that connects the standby path 138 to the discharge conveying path 139. Then, the timing of feeding the sheet 1 is controlled so that the leading edge of the succeeding sheet 1 is conveyed to the reading position of the color sensor 200 at the timing when the trailing edge of the preceding sheet 1 leaves the reading position of the color sensor 200. This makes it possible to bring the trailing edge of the preceding sheet 1 and the leading edge of the succeeding sheet 1 closer to each other at the reading position of the color sensor 200. Therefore, as shown in FIG. 7, the job time T1 from the start to the end of the job can be minimized, that is, it is possible to prevent the time of the color measurement job from becoming long.

[0049] In addition, when reading images of a plurality of sheets 1, the reading speed, which is the sheet conveying speed, is set slower than the reversal lead-in speed, the post-reversal speed, and the discharge speed, so that the reading accuracy is not impaired. Furthermore, for example, when the sheet 1 is conveyed to the re-conveying path 140 and a reading operation is performed in the re-conveying path 140, the sheet 1 is conveyed again through the transfer roller 114, the fixing unit 150, and the cooling unit 160 before being conveyed to the discharge conveying path 19, so that the conveying time becomes long. However, in this embodiment, the sheet 1 can be immediately conveyed from the post-reversal conveying path 141 to the discharge conveying path 139, so that the time for the color measurement job for reading images of a plurality of sheets 1 can be prevented from becoming long. Therefore, the time for the color measurement job as an adjustment process can be shortened, and the productivity can be improved. In other words, it is possible to provide an image forming apparatus with high color stability and high operating rate.

[0050] <First Comparative Example> Next, the present embodiment will be compared with the first comparative example to explain the shortening of the time for the color measurement job in the present embodiment. Fig. 8 is a schematic diagram of an image forming apparatus according to the first comparative example, and Fig. 9 is a diagram of sheet conveyance in the color measurement job according to the first comparative example.

[0051] 8, in the first comparative example, the color measurement unit 500 (color sensor 200) is disposed downstream of the third switching flapper 136 in the sheet conveying direction before inversion, that is, disposed near the entrance of the waiting path 138. Therefore, by conveying the sheet 1 to the waiting path 138, it becomes possible to read all of the patch images 1P on the sheet 1.

[0052] However, the expected length of the sheet 1 in the conveying direction is such that the leading edge of the sheet 1 reaches the reading position of the color sensor 200 before the trailing edge of the sheet 1 leaves the cooling unit 160. Therefore, as described above, the conveying speed cannot be increased to 1500 mm / sec, which is the reversing and retracting speed, after the trailing edge of the sheet 1 leaves the cooling unit 160. Furthermore, the timing at which the conveying speed is decelerated from 600 mm / sec, which is the image formation process speed, to 300 mm / sec, which is the reading speed, occurs immediately before the leading edge of the sheet 1 reaches the reading position of the color sensor 200 (S9).

[0053] Therefore, the timing at which the reading of the patch image 1P of the first sheet 1 is completed is earlier than in this embodiment. However, in order to transport the subsequent sheet 1 to the color sensor 200, it is necessary to do so after the rear end of the preceding sheet 1 has passed the second switching flapper 134 so as to prevent the sheets from colliding with each other. Therefore, the start of the reading operation of the subsequent sheet 1 is delayed by the time difference dT shown in FIG. 9. And for these reasons, the job time T2 (see FIG. 9) required until the color measurement job of the multiple sheets 1 in this first comparative example is completed is longer than the job time T1 (see FIG. 7) in this embodiment.

[0054] <Second Comparative Example> Next, a second comparative example will be described with reference to Fig. 10. Fig. 10 is a schematic diagram of an image forming apparatus according to the second comparative example.

[0055] As shown in FIG. 10, in the second comparative example, the color measurement unit 500 (color sensor 200) is disposed along the discharge conveying path 139 upstream of the discharge roller 139a in the sheet conveying direction. In this second comparative example, there is no need to pull the sheet 1 into the pre-reversal conveying path 133, the reversal conveying path 135, or the post-reversal conveying path 141 in the first place, and it is sufficient to convey the sheet 1 through the pre-reversal conveying path 142 and the discharge conveying path 139. However, until the rear end of the sheet 1 leaves the cooling unit 160, the sheet 1 needs to be conveyed at a conveying speed of 600 mm / sec, which is the image forming process speed. However, on the other hand, it is necessary to decelerate the conveying speed to 300 mm / sec, which is the reading speed, so as not to impair the reading accuracy of the patch image 1P. Therefore, it is necessary to lengthen the discharge conveying path 139 (or the pre-reversal conveying path 142) so that the leading end of the sheet 1 reaches the reading position of the color sensor 200 after the rear end of the sheet 1 leaves the cooling unit 160. For this reason, the width of image forming apparatus 100 increases as indicated by arrow W. Therefore, image forming apparatus 100 according to the present embodiment can be made smaller in size than the second comparative example.

[0056] <Possibilities for other embodiments> In this embodiment, a spectral color sensor is used as the color sensor. However, a compact image sensor such as a CIS (contact image sensor) may be used as the reading unit. Even in this case, the need to slow down the conveying speed during image reading to ensure reading accuracy remains the same, so the same control is applied to color measurement jobs that read multiple sheets.

[0057] In addition, in this embodiment, an image forming apparatus that includes the re-conveying path 140 has been described, but an image forming apparatus that exclusively performs single-sided printing may not include the re-conveying path 140. Furthermore, in this embodiment, an image forming apparatus that includes the pre-discharge conveying path 142 has been described, but an image forming apparatus that always reverses and discharges a sheet may not include the pre-discharge conveying path 142.

[0058] Furthermore, in this embodiment, the patch image is configured from a large number of color patches. However, it is also possible to perform calibration by reading black and white patch images.

[0059] In addition, in this embodiment, the reading speed is described as being slower than the image formation process speed, but the relationship between these speeds may be any speed as long as the image can be formed with high accuracy and reading accuracy is maintained.

[0060] Further, in the present embodiment, the sheet 1 is inverted by the first inversion roller 171 in the color measurement job. However, the present invention is not limited to this, and the sheet 1 may be inverted by the second inversion roller 172. [Explanation of symbols]

[0061] 1...sheet / 1P...patch image (test image) / 100...image forming apparatus / 102...image forming engine (image forming section) / 103...printer controller (control section) / 133...pre-reversal conveying path (first conveying path) / 139a...discharge roller (discharge section) / 140...re-conveying path (third conveying path) / 141...post-reversal conveying path (second conveying path) / 142...pre-discharge conveying path (fourth conveying path) / 171...first reversing roller (reversing conveying section) / 200...color sensor (reading section)

Claims

1. an image forming unit that forms an image on a sheet; a discharge conveyance path including a discharge roller for discharging the sheet on which the image is formed by the image forming unit to the outside, the discharge conveyance path extending from the image forming unit to the discharge roller; a first conveying path that branches downward from the discharge conveying path between the image forming unit and the discharge rollers in the discharge conveying path; a first switching unit that can switch between a state in which the sheet is transported from the image forming unit to the discharge rollers through the discharge transport path and a state in which the sheet is transported from the discharge transport path to the first transport path; a reversing conveying path that is formed continuously from the first conveying path and that reverses a conveying direction of the sheet conveyed from the image forming unit via the first conveying path and conveys the sheet; a second conveying path that is connected from the reversing conveying path to the discharge conveying path between the first switching unit and the discharge rollers in the discharge conveying path and that guides the sheet that has been reversed by the reversing conveying path from the reversing conveying path to the discharge conveying path; a second switching unit that is switchable between a state in which the sheet is transported from the first transport path to the reverse transport path and a state in which the sheet is transported from the reverse transport path to the second transport path; a reading unit configured to read, in the second conveying path, an image of the sheet that has passed through the second switching unit and been conveyed from the inversion conveying path to the second conveying path, 1. An image forming apparatus comprising:

2. a third conveying path that guides the sheet inverted by the inverting conveying path to the image forming unit; 2. The image forming apparatus according to claim 1,

3. a control unit that controls a sheet conveying speed to be a second conveying speed slower than a first conveying speed in the first conveying path when the image of the sheet is read by the reading unit in a case where the image of the sheet is read by the reading unit and the image of the sheet is read by the reading unit, 3. The image forming apparatus according to claim 1, wherein the first and second electrodes are arranged in a first direction.

4. The control unit is forming test images on a plurality of sheets that are continuously conveyed in the image forming unit; reading test images on the plurality of sheets conveyed continuously in the reading unit; correcting an image to be formed on a sheet by the image forming unit based on the read test image; 4. The image forming apparatus according to claim 3.

5. the image forming unit forms the test image in color; The reading unit is a color sensor that reads the color of the test image.

5. The image forming apparatus according to claim 4.

6. the control unit controls the second conveying speed to be slower than an image forming process speed at which an image is formed on a sheet in the image forming unit.

6. The image forming apparatus according to claim 3, wherein the image forming apparatus further comprises a first fixing unit.

7. While a first sheet is being read by the reading unit, a second sheet to be read by the reading unit after the first sheet arrives at the reverse conveying path.

7. The image forming apparatus according to claim 1, wherein the image forming apparatus comprises: a first fixing member;

Images