Image forming apparatus, and image forming system

Abstract

To provide an image forming apparatus that performs calibration processing on an image reading sensor while preventing a reduction in productivity.SOLUTION: An image forming apparatus 101 comprises: a printing device 107 that prints an image on a sheet; and a sensing unit 108 that acquires the sheet on which the image is printed from the printing device 107 and reads the image on the sheet. The printing device 107 notifies the sensing unit 108 of the inter-sheet time indicating the ejection interval between a plurality of sheets to be continuously conveyed to the sensing unit 108. When the inter-sheet time is longer than the time required for calibration processing on the sensing unit 108, the sensing unit 108 determines the timing to perform the calibration processing.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to an image forming apparatus such as a printer, a copier, a facsimile, or a multifunction peripheral. [Background technology]

[0002] Stable print position accuracy is required for deliverables generated by commercial image forming devices. Patent Document 1 discloses an image forming device that aims to stabilize print position accuracy. To stabilize the print position accuracy, this image forming device creates an adjustment chart by printing an adjustment image that serves as a marker for the print position (image formation position) on a sheet. The adjustment image on the adjustment chart is read by an image reading sensor provided on the sheet transport path. The image forming device adjusts the print position by feeding back the reading result of the adjustment image to the image formation conditions.

[0003] Image forming devices need to perform maintenance operations, such as automatic registration, every time the number of printed sheets reaches a predetermined number. Automatic registration is a process that corrects, for example, color misregistration and geometric characteristics such as the position and shape of an image. When the number of sheets printed by a print job reaches a predetermined number, the maintenance operation is performed by extending the time indicating the sheet interval when conveying multiple sheets (hereinafter, referred to as the sheet interval time).

[0004] When adjusting the image position using an adjustment image, the temperature of an image reading sensor such as a CIS (Contact Image Sensor) that reads the adjustment image may rise. This causes fluctuations in the position of the image detected by reading the adjustment image. In Patent Document 2, when the image reading sensor continues to operate for a predetermined period of time or more, shading correction is performed to correct fluctuations in reading accuracy due to temperature fluctuations. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2006-11285 A [Patent Document 2] JP 2021-192077 A Summary of the Invention [Problem to be solved by the invention]

[0006] The disclosure of Patent Document 2 makes it possible to perform shading correction of multiple image reading sensors efficiently and with high accuracy. However, while shading correction is being performed, images cannot be read. As a result, printing by the image forming device is put on hold until the shading correction is completed, resulting in reduced productivity.

[0007] The present invention has been made in consideration of the above problems, and has an object to provide an image forming apparatus that performs calibration processing such as shading correction of an image reading sensor while suppressing a decrease in productivity. [Means for solving the problem]

[0008] The image forming apparatus of the present invention comprises a printing means for printing an image on a sheet, and a sheet processing means for acquiring the sheet on which the image has been printed from the printing means and processing the sheet, wherein the printing means notifies the sheet processing means of a paper interval indicating the interval between the discharge of multiple sheets which are continuously transported to the sheet processing means, and the sheet processing means determines the timing of performing the calibration processing when the paper interval is longer than the time required for the calibration processing of the sheet processing means. Effect of the Invention

[0009] According to the present invention, it is possible to perform the calibration process while suppressing a decrease in productivity. [Brief description of the drawings]

[0010] [Figure 1] FIG. 1 is a diagram showing the configuration of an image forming system. [Diagram 2] system configuration diagram. [Diagram 3]FIG. 1 is a diagram illustrating the configuration of an image forming apparatus. [Figure 4] Diagram of CIS. [Diagram 5] 4(a) to (c) are explanatory diagrams of the setting screen. [Figure 6] FIG. 4 is an explanatory diagram of a gain adjustment value. [Figure 7] 4A and 4B are diagrams illustrating shading correction values. [Figure 8] 6 is an explanatory diagram of a sheet discharge timing determination process. [Figure 9] 11 is a flowchart showing a process for determining the execution timing of shading correction. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] Hereinafter, the embodiments will be described in detail with reference to the drawings.

[0012] (Image forming system) 1 is a configuration diagram of an image forming system including an image forming apparatus according to this embodiment. The image forming system includes an image forming apparatus 101 and an external controller 102. The image forming apparatus 101 is realized by, for example, a multifunction peripheral (MFP), etc. The external controller 102 is, for example, an image processing controller, a digital front end (DFE), a print server, etc.

[0013] The image forming apparatus 101 and the external controller 102 are communicatively connected via an internal LAN (Local Area Network) 105 and a video cable 106. The external controller 102 is connected to a client PC (Personal Computer) 103, which is an external device, via an external LAN 104. The external controller 102 obtains a print instruction (print job) from the client PC 103.

[0014] A printer driver having a function of converting image data into a print description language that can be processed by the external controller 102 is installed in the client PC 103. A user can instruct printing via the printer driver using various applications. The printer driver transmits a print job including image data to the external controller 102 based on a print instruction from the user. The external controller 102 performs data analysis and rasterization processing on the image data included in the print job received from the client PC 103, and instructs the image forming apparatus 101 to print (form an image) based on the processed image data.

[0015] The image forming apparatus 101 is configured by connecting a plurality of devices having different functions, including a printing device 107, and is capable of complex printing processes such as bookbinding. The image forming apparatus 101 of this embodiment includes the printing device 107, and a sensing unit 108 and a finisher 109, which are sheet processing devices. The printing device 107 forms an image on a sheet fed from a paper feed unit provided at the bottom of the main body, using a developer (e.g., toner).

[0016] For example, the printing device 107 reflects a beam of light such as a laser beam modulated according to image data using a rotating polygon mirror, and irradiates the beam as scanning light onto a photoconductor having a uniformly charged photosensitive layer. An electrostatic latent image is formed on the photoconductor by the irradiation of the scanning light. The electrostatic latent image is developed into a toner image using toner. The toner image is transferred to a sheet. The printing device 107 sequentially executes this series of image formation processes using toners of each color, yellow (Y), magenta (M), cyan (C), and black (K), to form a full-color image on the sheet. The toner image is then fixed to the sheet to generate a finished product.

[0017] The sheet on which the image is formed is transported from the printing device 107 to the finisher 109 via the sensing unit 108. The sensing unit 108 reads an adjustment image from an adjustment chart, which is a sheet on which an adjustment image for adjusting image formation conditions is formed. To this end, the sensing unit 108 includes a CIS (described later) as an image reading sensor that reads the image on the sheet. The image formation conditions are corrected based on the result of reading the adjustment image by the sensing unit 108. The finisher 109 stacks the sheets on which the image is formed.

[0018] In this image forming system, an external controller 102 is connected to an image forming apparatus 101, but the external controller 102 is not necessarily required. For example, the image forming apparatus 101 may be configured to directly obtain a print job including image data from a client PC 103 via an external LAN 104. In this case, the image forming apparatus 101 performs the data analysis and rasterization processing that are performed by the external controller 102. In other words, the image forming apparatus 101 and the external controller 102 may be configured as one unit.

[0019] (System Configuration) 2 is a system configuration diagram that controls the operation of the image forming system. Here, controllers that control the operation of the image forming apparatus 101 (printing device 107, sensing unit 108, finisher 109), external controller 102, and client PC 103 will be described.

[0020] ·Printing device The printing device 107 includes a communication interface (I / F) 217, a LAN I / F 218, and a video I / F 220 for communicating with other devices. The printing device 107 includes a CPU (Central Processing Unit) 222, a memory 223, a storage 221, an image reading unit 231, and an image processing unit 232 for controlling the operation of the printing device 107. The printing device 107 includes an exposure unit 227, an image creating unit 228, a fixing unit 229, and a paper feeding unit 230 for forming an image. The printing device 107 includes an operation unit 224 and a display 225 as user interfaces. These components are connected to each other via a system bus 233 so as to be able to communicate with each other.

[0021] The communication I / F 217 is connected to the sensing unit 108 and the finisher 109 via a communication cable 249, and controls communication between the sensing unit 108 and the finisher 109. When the printing device 107 and the sensing unit 108 operate in cooperation with each other, information and data are transmitted and received via the communication I / F 217. When the printing device 107 and the finisher 109 operate in cooperation with each other, information and data are transmitted and received via the communication I / F 217. The LAN I / F 218 is connected to the external controller 102 via the internal LAN 105, and controls communication with the external controller 102. The printing device 107 acquires print settings and image data from the external controller 102 via the LAN I / F 218. The video I / F 220 is connected to the external controller 102 via a video cable 106, and controls communication with the external controller 102. The printing device 107 acquires image data representing an image to be formed from the external controller 102 via the video I / F 220.

[0022] The CPU 222 comprehensively controls image processing and printing by executing computer programs stored in the storage 221. A large-capacity storage device such as a hard disk drive (HDD) or a solid state drive (SSD) is used as the storage 221. The memory 223 provides a work area for the CPU 222 to execute various processes. When performing image formation processing, the CPU 222 controls an exposure unit 227, an image forming unit 228, a fixing unit 229, and a paper feed unit 230.

[0023] The exposure unit 227 includes a photoconductor, a charging wire for charging the photoconductor, and a light source for exposing the photoconductor charged by the charging wire to light in order to form an electrostatic latent image on the photoconductor. The photoconductor is, for example, a photosensitive belt having a photosensitive layer formed on the surface of a belt-shaped elastic member, or a photosensitive drum having a photosensitive layer formed on the surface of a cylinder. A charging roller may be used instead of the charging wire. The exposure unit 227 charges the surface of the photoconductor to a uniform negative potential by the charging wire. The exposure unit 227 outputs a laser beam from the light source based on image data. The laser beam scans the surface of the photoconductor that is uniformly charged. As a result, the potential of the photoconductor at the position where the laser beam is irradiated fluctuates, and an electrostatic latent image is formed on the surface. Four photoconductors are provided corresponding to four colors, yellow, magenta, cyan, and black. Electrostatic latent images corresponding to images of different colors are formed on the four photoconductors.

[0024] The image forming unit 228 transfers the toner image formed on the photoconductor to a sheet. The image forming unit 228 includes a developing unit, a transfer unit, and a toner supply unit. The developing unit forms a toner image by attaching negatively charged toner from a developing cylinder to an electrostatic latent image formed on the surface of the photoconductor. Four developing units are provided corresponding to the four colors of yellow, magenta, cyan, and black. The developing units visualize the electrostatic latent image on the photoconductor with toner of the corresponding color.

[0025] The transfer unit has an intermediate transfer belt and transfers a toner image from the photoconductor to the intermediate transfer belt. A primary transfer roller is provided at a position facing the photoconductor across the intermediate transfer belt. When a positive potential is applied to the primary transfer roller, the toner images from each of the four photoconductors are transferred to the intermediate transfer belt in a superimposed state. As a result, a full-color toner image is formed on the intermediate transfer belt. The toner image formed on the intermediate transfer belt is transferred to a sheet by a secondary transfer roller, which will be described later. When a positive potential is applied to the secondary transfer roller, the full-color toner image is transferred from the intermediate transfer belt to the sheet.

[0026] The fixing unit 229 fixes the transferred toner image onto the sheet. The fixing unit 229 has a heater and a pair of rollers. The fixing unit 229 melts and fixes the toner image on the sheet by heating and pressurizing the toner image on the sheet with the heater and the pair of rollers. This forms an image on the sheet. The paper feed unit 230 has a conveying roller and various sensors on the conveying path, and controls the sheet feeding operation.

[0027] The image reading unit 231 is a sensor that reads an adjustment image (auto-registration image) for performing auto-registration, which will be described later, based on an instruction from the CPU 222. The image reading unit 231 of this embodiment reads an auto-registration image formed on the intermediate transfer belt. The image processing unit 232 performs a process of converting image data acquired from the external controller 102 into image data that can be processed by the exposure unit 227, based on an instruction from the CPU 222. The operation unit 224 is an input device that accepts input of various settings and operation instructions from a user. The operation unit 224 is, for example, various input keys or a touch panel. The display 225 is an output device that displays setting information of the image forming apparatus 101 and the processing status (status information) of a print job.

[0028] Finisher The finisher 109 performs post-processing such as stapling on a product output from the printing device 107. The finisher 109 includes a communication I / F 241, a CPU 242, a memory 243, and a paper discharge control unit 244. These components are connected to each other via a system bus 245 so as to be able to communicate with each other.

[0029] The communication I / F 241 is connected to the printing device 107 and the sensing unit 108 via a communication cable 249, and controls communication between the printing device 107 and the sensing unit 108. When the finisher 109 and the printing device 107 work together, information and data are transmitted and received via the communication I / F 241. When the finisher 109 and the sensing unit 108 work together, information and data are transmitted and received via the communication I / F 241. The CPU 242 executes a control program stored in the memory 243, and performs various controls required for paper discharge. The memory 243 stores the control program. The memory 243 also provides a work area when the CPU 242 executes various processes. The paper discharge control unit 244 discharges the conveyed sheet to a stack tray 332 shown in FIG. 3 based on an instruction from the CPU 242.

[0030] Sensing unit The sensing unit 108 includes a communication I / F 341, a CPU 342, a memory 343, and a CIS control unit 344. These components are connected via a system bus 345 so as to be able to communicate with each other.

[0031] The communication I / F 341 is connected to the printing device 107 and the finisher 109 via a communication cable 249, and controls communication between the printing device 107 and the finisher 109. When the sensing unit 108 and the printing device 107 work together, information and data are transmitted and received via the communication I / F 341. When the sensing unit 108 and the finisher 109 work together, information and data are transmitted and received via the communication I / F 341. The CPU 342 executes a control program stored in the memory 343, and performs various controls required for reading the adjustment chart. The memory 343 stores the control program. The memory 343 also provides a work area when the CPU 342 executes various processes. The CIS control unit 344 controls a CIS, which is an image reading sensor and will be described later, based on an instruction from the CPU 342, and reads an adjustment image from the conveyed sheet (adjustment chart).

[0032] External Controller The external controller 102 includes a LAN I / F 213, a LAN I / F 214, and a video I / F 215 for communicating with other devices. The external controller 102 includes a CPU 208, a memory 209, and a storage 210 for controlling the operation of the external controller 102. The external controller 102 includes a keyboard 211 and a display 212 as user interfaces. These components are connected to each other via a system bus 216 so as to be able to communicate with each other.

[0033] The LAN I / F 213 is connected to the client PC 103 via the external LAN 104, and controls communication with the client PC 103. The external controller 102 acquires a print job from the client PC 103 via the LAN I / F 213. The LAN I / F 214 is connected to the printing device 107 via the internal LAN 105, and controls communication with the printing device 107. The external controller 102 transmits print settings and image data to the printing device 107 via the LAN I / F 214. The video I / F 215 is connected to the printing device 107 via the video cable 106, and controls communication with the printing device 107. The external controller 102 transmits image data to the printing device 107 via the video I / F 215.

[0034] The CPU 208 executes computer programs stored in the storage 210 to comprehensively perform processes such as receiving image data transmitted from the client PC 103, RIP processing, and transmitting image data to the image forming apparatus 101. A large-capacity storage device such as an HDD or SSD is used for the storage 210. The memory 209 provides a work area when the CPU 208 executes various processes. The keyboard 211 is an input device that accepts input of various settings and operation instructions from the user. The display 212 is an output device that displays information about applications executed by the external controller 102 using still images and moving images.

[0035] Client PC The client PC 103 includes a CPU 201, a memory 202, a storage 203, a keyboard 204, a display 205, and a LAN I / F 206. These components are connected via a system bus 207 so as to be able to communicate with each other.

[0036] The CPU 201 controls the operation of the client PC 103 by executing a computer program stored in the storage 203. A large-capacity storage device such as an HDD or SSD is used for the storage 203. In this embodiment, the CPU 201 creates image data and transmits print jobs. The memory 202 provides a work area for the CPU 201 to execute various processes. The CPU 201 also generates print jobs and print instructions using a printer driver based on an application such as a document processing program stored in the storage 203.

[0037] The keyboard 204 and the display 205 are user interfaces. The keyboard 204 is an input device that accepts instructions from a user. The display 205 is an output device that displays information of an application executed by the client PC 103 using still images and moving images. The LAN I / F 206 is connected to the external controller 102 via the external LAN 104, and controls communication with the external controller 102. The client PC 103 transmits a print job to the external controller 102 via the LAN I / F 206.

[0038] The external controller 102 and the image forming apparatus 101 are connected by an internal LAN 105 and a video cable 106, but any other configuration is acceptable as long as data necessary for printing can be transmitted and received, and for example, the connection may be made by only a video cable. The memory 202, memory 209, memory 223, memory 243, and memory 343 may each be a storage device for holding data and programs. For example, these memories may be volatile random access memory (RAM), non-volatile read only memory (ROM), storage, or universal serial bus (USB) memory.

[0039] (Configuration of Image Forming Apparatus) 3 is a configuration diagram of the image forming apparatus 101. A display 225 is provided on the top of the printing device 107. The display 225 displays information on the printing status and settings of the image forming apparatus 101. A sheet on which an image has been formed by the printing device 107 is transported to a finisher 109 via a sensing unit 108 provided downstream.

[0040] The printing device 107 includes a plurality of paper feed decks 301, 302 and a transport path 303 as the paper feed section 230. Each of the paper feed decks 301, 302 can accommodate different types of sheets. The top sheet of each of the paper feed decks 301, 302 is separated and fed to the transport path 303. The printing device 107 includes image forming units 304, 305, 306, and 307 as the exposure unit 227 for forming images. The printing device 107 forms a color image. To this end, the image forming unit 304 forms a black image (toner image). The image forming unit 305 forms a cyan image (toner image). The image forming unit 306 forms a magenta image (toner image). The image forming unit 307 forms a yellow image (toner image).

[0041] The printing device 107 includes, as the image creating unit 228, an intermediate transfer belt 308 and a secondary transfer roller 309 onto which toner images are transferred from the image forming units 304, 305, 306, and 307. The intermediate transfer belt 308 rotates clockwise in the figure, and is an image carrier onto which toner images are transferred in a superimposed manner from the image forming units 307, 306, 305, and 304 in this order. As a result, a full-color toner image is formed on the intermediate transfer belt 308. The intermediate transfer belt 308 conveys the toner image to the secondary transfer roller 309 by rotating. A sheet is conveyed to the secondary transfer roller 309 in accordance with the timing at which the toner image is conveyed to the secondary transfer roller 309. The secondary transfer roller 309 transfers the toner image on the intermediate transfer belt 308 to the conveyed sheet.

[0042] An image reading unit 231 is provided downstream of the image forming unit 304 in the rotation direction of the intermediate transfer belt 308. By providing the image reading unit 231 at this position, the image reading unit 231 can read the toner images of the adjustment images transferred to the intermediate transfer belt 308 from the image forming units 304, 305, 306, and 307.

[0043] The printing device 107 includes a first fixer 311 and a second fixer 313 as the fixing section 229. The first fixer 311 and the second fixer 313 have the same configuration and fix the toner image to the sheet. To this end, the first fixer 311 and the second fixer 313 each include a pressure roller and a heating roller. The sheet is heated and pressurized by passing between the pressure roller and the heating roller, and the toner image is melted and pressed onto the sheet. The sheet that has passed the second fixer 313 is transported to a transport path 314. The second fixer 313 performs a fixing process similar to that of the first fixer 311.

[0044] The second fixing device 313 is disposed downstream of the first fixing device 311 in the sheet conveying direction, and is used to add gloss to the image on the sheet fixed by the first fixing device 311 and to ensure fixation. Therefore, the second fixing device 313 may not be used depending on the type of sheet and the contents of the image forming process. A conveying path 312 is provided to convey the sheet fixed by the first fixing device 311 without passing through the second fixing device 313.

[0045] After the conveying path 314 and the conveying path 312 join, a conveying path 315 and an inversion path 316 are provided. When double-sided printing is instructed, the sheet is conveyed to the inversion path 316. The conveying direction of the sheet conveyed to the inversion path 316 is inverted by the inversion path 316 and the sheet is conveyed to a double-sided conveying path 317. The inversion path 316 and the double-sided conveying path 317 invert the side on which the image is formed (first side). The sheet is conveyed to the conveying path 303 by the double-sided conveying path 317, and passes through a secondary transfer roller 309 and a fixing unit 229, whereby an image is formed on the second side, which is the side opposite to the first side.

[0046] In the case of single-sided printing, or in the case of double-sided printing in which images are formed on both sides, the sheet is transported to a transport path 315. A sensing unit 108 is provided downstream of the transport path 315 in the sheet transport direction. In the sensing unit 108, a CIS 321 and a CIS 322 are disposed at positions facing each other across a transport path 323. FIG. 4 is an explanatory diagram of the CISs 321 and 322. The CIS 321 is an optical sensor that reads an image of the upper surface of the sheet transported on the transport path 323. The CIS 322 is an optical sensor that reads an image of the lower surface of the sheet transported on the transport path 323.

[0047] The CIS 321 includes an LED (Light Emitting Diode) 350 as a light source, a reading sensor 351 as a light receiving unit, and a white reference plate 352. The LED 350 irradiates light onto the upper surface of the sheet when the sheet conveyed along the conveying path 323 reaches the reading position. The reading sensor 351 includes a plurality of light receiving elements (photoelectric conversion elements) in a direction perpendicular to the sheet conveying direction. Therefore, the direction perpendicular to the sheet conveying direction is the main scanning direction of the CIS 321. The reading sensor 351 receives light reflected by the sheet. The plurality of light receiving elements of the reading sensor 351 output an output value (electrical signal) based on the intensity of the received reflected light. The output value (electrical signal) output from the plurality of light receiving elements is transmitted to the CPU 342. The CPU 342 transmits the acquired output value (electrical signal) as a read image to the CPU 222 of the printing device 107 via the communication cable 249. In this manner, the image formed on the sheet is read.

[0048] The white reference plate 352 is a calibration member (reference member) used during a calibration process of the CIS 321, for example, during shading correction. The LED 350 and the reading sensor 351 move to a position where the white reference plate 352 can be read during shading correction. Alternatively, the white reference plate 352 moves to a reading position of the LED 350 and the reading sensor 351 during shading correction. Therefore, the CIS 321 cannot read an image formed on a sheet during shading correction. The shading correction of the CIS 321 is performed based on the reading result of the white reference plate 352.

[0049] Similarly to the CIS 321, the CIS 322 includes an LED 353, a reading sensor 354, and a white reference plate 355. The CIS 322 operates similarly to the CIS 321, and reads an image formed on the lower surface of the sheet when the sheet conveyed along the conveying path 323 reaches the reading position. Note that, in addition to the CISs 321 and 322, a CCD or CMOS sensor may be used.

[0050] The printing device 107 of this embodiment can form an adjustment image for adjusting image formation conditions on both sides of a sheet. A sheet on which an adjustment image is formed is called an adjustment chart. The printing device 107 prints the adjustment image on a sheet to create an adjustment chart. The sensing unit 108 reads the adjustment image from the adjustment chart by the CIS 321 and CIS 322. The reading results (read images) of the adjustment chart by the CIS 321 and CIS 322 are transmitted to the printing device 107 via the communication cable 249 and stored in the memory 223. The CPU 222 refers to the memory 223, analyzes the read images by the CIS 321 and CIS 322, and feeds back the results to the image formation conditions to adjust the image formation conditions.

[0051] For example, when the temperature inside the printing device 107 rises, the geometric characteristics of the image formed on the sheet change compared to when the temperature inside the printing device 107 is low. Here, the geometric characteristics of the image include, for example, perpendicularity and the print position of the image on the sheet. The printing device 107 creates an adjustment chart. The sensing unit 108 reads the adjustment image on the adjustment sheet using the CIS 321 and 322, and transmits the read result (read image) to the printing device 107. The printing device 107 detects the geometric characteristics based on the acquired read result (read image) using the CPU 222. The CPU 222 acquires the amount of variation of the detected geometric characteristics relative to the ideal geometric characteristics. The printing device 107 adjusts the image data based on the acquired amount of variation using the CPU 222, and forms an image on the sheet using the adjusted image data, thereby controlling the geometric characteristics of the image formed on the sheet. This allows the printing device 107 to suppress fluctuations in the geometric characteristics of an image caused by fluctuations in temperature inside the device, and stabilize the accuracy of the geometric characteristics.

[0052] The adjustment image formed on the adjustment chart may be an image for detecting image density or an image for detecting color shift, in addition to an image for detecting geometric characteristics. When the adjustment image for detecting image density is formed, the CPU 222 generates image forming conditions for suppressing fluctuations in image density based on the reading result of the CIS 321 (or CIS 322). The CPU 222 controls the intensity of the light source of the exposure unit 227 based on the image forming conditions, thereby adjusting the image density of the printing device 107 to an ideal image density. Alternatively, the CPU 222 generates a one-dimensional gradation correction table for suppressing fluctuations in image density based on the reading result of the CIS 321 (or CIS 322). The CPU 222 converts image data based on the gradation correction table. The printing device 107 forms an image on a sheet based on the image data converted by the CPU 222, thereby adjusting the image density of the printing device 107 to an ideal image density.

[0053] Furthermore, when an adjustment image for detecting color misregistration is formed, the CPU 222 detects the color misregistration based on the reading result of the CIS 321 (or CIS 322). The CPU 222 corrects the color misregistration by controlling the position of the image formed on the photoconductor by the exposure unit 227 based on the detected color misregistration.

[0054] The adjustment chart is removed so that a user image corresponding to the print job is not mixed into the printed product. For this purpose, the sensing unit 108 includes a flapper 324, a discharge path 326, a transport sensor 327, and a discharge tray 328. The adjustment chart, whose image (adjustment image) has been read by the CISs 321 and 322, is transported to the discharge path 326 by the flapper 324. The sheet transported to the discharge path 326 is discharged to the discharge tray 328.

[0055] If the sheet is not an adjustment chart, the sheet is transported from the transport path 323 to the downstream transport path 325 by a flapper 324. The sheet transported to the downstream transport path 325 is transported to the finisher 109. When the sensing unit 108 receives a notification of the occurrence of a transport jam from the finisher 109, it discharges all sheets (residual sheets) in the printing device 107 and the sensing unit 108 to the discharge tray 328, regardless of whether the sheets are adjustment charts or not. Discharging the residual sheets to the discharge tray 328 reduces the burden on the user of clearing the jam.

[0056] The finisher 109 can stack sheets delivered from the printing device 107. The finisher 109 includes a transport path 331 and a stack tray 332 for stacking sheets. The transport path 331 is provided with transport sensors 333, 334, 335, and 336. Sheets transported from the printing device 107 are stacked on the stack tray 332 via the transport path 331. The transport sensors 333, 334, 335, and 336 detect the passage of a sheet transported along the transport path 331. If the transport sensors 333, 334, 335, and 336 do not detect the leading or trailing end of the sheet in the transport direction even after a predetermined time has elapsed since the start of sheet transport, the CPU 242 determines that a transport jam (transport abnormality) has occurred in the finisher 109. In this case, the CPU 242 notifies the printing device 107 and the sensing unit 108 that a transport jam has occurred.

[0057] The adjustment image may be printed on the same sheet as the user image. For example, the adjustment image may be printed outside the area where the user image is printed. In this case, the sensing unit 108 reads the adjustment image and then conveys the sheet to the finisher 109. The finisher 109 cuts the area where the adjustment image is printed as a post-processing step to generate a deliverable.

[0058] (Automatic cash register) One of the automatic registration processes is a process of detecting the expansion / contraction of intermediate transfer belt 308 and correcting the position of each color image based on the detected amount of expansion / contraction. In this process, a detection image for the expansion / contraction of intermediate transfer belt 308 is formed on intermediate transfer belt 308, and this detection image is read by image reading unit 231. Image reading unit 231 performs a reading process while intermediate transfer belt 308 rotates one revolution or more. A detection interval of the detection image is obtained from the reading result of one revolution or more of intermediate transfer belt 308. The amount of expansion / contraction of intermediate transfer belt 308 is obtained from the detection interval of the detection image when there is no expansion / contraction of intermediate transfer belt 308 and the measured detection interval.

[0059] If the amount of expansion is longer than a reference value, for example, it is known that intermediate transfer belt 308 has expanded. At the time of the next image formation, CPU 222 performs control so as to delay the image formation timing of other image forming units 304 to 306 relative to the image formation timing of image forming unit 307 according to the amount of expansion of intermediate transfer belt 308. This maintains the overlay accuracy of the four color toner images.

[0060] In this way, automatic registration requires intermediate transfer belt 308 to rotate at least once, during which the job is suspended. Automatic registration is performed between sheets (between sheets) after a predetermined number of sheets have been printed. Therefore, the time between sheets at this time is longer by the time it takes for automatic registration to be performed.

[0061] (Adjustment mode setting) The image forming apparatus 101 can operate in a "real-time adjustment mode" in which an adjustment image is printed on the same sheet as the user image, and an "interrupt adjustment mode" in which an adjustment chart is printed for every predetermined number of sheets. In the real-time adjustment mode of this embodiment, an adjustment image is printed for every page. In the interrupt adjustment mode of this embodiment, an adjustment chart is inserted every time a predetermined number of user images are formed. For example, an adjustment chart is inserted between the sheet on which the Nth page of user images is formed and the sheet on which the N+1th page of user images is formed. FIG. 5 is an example view of a setting screen for setting the adjustment mode.

[0062] The setting screen is displayed on the display 225 by the CPU 222. Fig. 5(a) is the initial screen. When the user selects the softkey "Advanced Mode" from the initial screen, the CPU 222 displays the advanced mode selection screen of Fig. 5(b) on the display 225. When the user selects the softkey "Adjustment" from the advanced mode selection screen, the CPU 222 displays the adjustment mode selection screen of Fig. 5(c) on the display 225. When the user selects the softkey "Close" from the advanced mode selection screen, the CPU 222 displays the initial screen on the display 225.

[0063] The real-time adjustment mode is set when the user selects the soft key "real time" from the adjustment mode selection screen. This completes the setting for printing an adjustment image in the margin area of ​​all sheets on which a user image is printed. The interrupt adjustment mode is set when the user selects the soft key "interrupt" from the adjustment mode selection screen. The CPU 222 notifies the external controller 102 of the setting contents. The external controller 102 notifies the printing of an adjustment image in the margin area when instructing the printing device 107 to form an image according to a print job. The interrupt adjustment mode can also be set from the adjustment mode selection screen, but a description thereof will be omitted here.

[0064] (Shading correction) Initial adjustment including shading correction is performed as a calibration process on the CISs 321 and 322. Here, the initial adjustment of the CIS 321 will be described, but the initial adjustment of the CIS 322 is performed in the same manner.

[0065] When the CPU 342 starts the initial adjustment, it moves the LED 350 and the reading sensor 351 to directly above the white reference plate 352 by a CIS drive motor (not shown). Here, the position directly above the white reference plate 352 is set as the shading reading position. When the movement is completed, the CPU 342 turns on the LED 350 to read the image of the white reference plate 352, and calculates a gain adjustment value for the CIS 321 according to the reading result. After the CPU 342 reads the white reference plate 352 at the shading reading position, it moves the LED 350 and the reading sensor 351 to the chart reading position shown in FIG. 4 by a CIS drive motor (not shown). By moving the LED 350 and the reading sensor 351 to the chart reading position, the CIS 321 becomes able to read the adjustment image from the sheet transported on the transport path 323.

[0066] 6 is an explanatory diagram of gain adjustment values. The horizontal axis indicates each pixel position in the main scanning direction when one line of the image of the white reference plate 352 is read in the main scanning direction. The vertical axis indicates the read result (brightness value) of each pixel position. The dotted line A indicates the brightness value characteristics when the white reference plate 352 is read with the initial settings at startup. The maximum brightness value of "white" is indicated by "Tgt0".

[0067] Due to the light distribution characteristics of the LED 350 and the reading sensor 351, the maximum value of the reading result (brightness value) of the white reference plate 352 in the initial setting does not match the expected brightness value Tgt0 of "white". The reading result of the CIS 321 is uniformly amplified by the amplifier circuit in the CIS control unit 344 so that the maximum value of the brightness value of the reading result matches Tgt0. This amplification factor is the gain adjustment value. The characteristic of the brightness value for one line after adjustment by the gain adjustment value is indicated by the solid line B. The CPU 342 calculates the gain adjustment value and sets the calculated gain adjustment value in the CIS control unit 344 to be reflected in subsequent readings.

[0068] As shown in Fig. 6, even if the CIS 321 reads the white reference plate 352, which has a uniform color over its entire surface, the brightness value characteristics of the read result vary depending on the pixel position in the main scanning direction. In order to correct this variation, shading correction is performed. After setting a gain adjustment value in the CIS control unit 344, the CPU 342 reads the image of the white reference plate 352 again using the CIS 321, and generates a shading correction value based on the read result.

[0069] FIG. 7 is an explanatory diagram of shading correction values. The solid line in FIG. 7(a) shows the characteristics of the luminance value for one line after gain adjustment. The horizontal axis shows the pixel position in the main scanning direction. The vertical axis shows the luminance value at each pixel position. It is preferable that the reading result (luminance value) of a white reference plate 352 with a uniform image density is a uniform luminance value of "white." The luminance indicating "white" is the target value Tgt. The value of the target value Tgt is greater than the maximum luminance value Tgt0, and is determined in advance depending on the contents of the job to be executed.

[0070] As shown by the arrows in FIG. 7(a), the CPU 342 calculates a shading correction value for each pixel in the main scanning direction so that the luminance value of one line becomes the target value Tgt at each pixel position. The size of the arrow at each pixel position corresponds to the shading correction value. The calculated shading correction value is stored in the memory 343 in correspondence with each pixel position in the main scanning direction through the CIS control unit 344. FIG. 7(b) shows the shading correction value for each pixel in the main scanning direction. When the image is read by the CIS 321, the shading correction value at the corresponding pixel position is reflected in the read result of each pixel (shading correction is performed). This allows the CPU 342 to suppress variations between the pixels (light receiving elements) of the LED 350 and the read sensor 351 and obtain a uniform read result. After the shading correction, the CPU 342 stores the acquired shading correction value in the memory 343. Similarly, the shading correction value of the CIS 322 is also stored in the memory 343.

[0071] (Timing information notification processing) Fig. 8 is an explanatory diagram of a process for determining the timing of sheet discharge. Fig. 8 illustrates an example of timing information transmitted and received between devices when the finisher 109 is a sheet processing device that stacks sheets. That is, Fig. 8 illustrates timing information when a sheet discharged from the printing device 107 passes through the sensing unit 108 and is stacked on the finisher 109.

[0072] The capital letter "T" included in the timing information indicates a time interval. The part of the fix before the comma is used to identify each time. The part after the comma indicates the device that sent the timing information and the device that received it. In this embodiment, "i" represents the printing device 107, "s" represents the sensing unit 108, and "f" represents the finisher 109. For example, "s→f" indicates that the information is sent from the sensing unit 108 to the finisher 109. In the following explanation, the lowercase t in t send, i, etc. represents time.

[0073] The timing information 601 is information transmitted from the printing apparatus 107 to the sensing unit 108, which is the first sheet processing apparatus. The timing information 601 includes, for example, the following information: Sheet ID (SID(n)) Previous seat ID (SID(n-1)) Inter-page time (Tss,i→s) Post-processing information proc Loading device information TID

[0074] "n" is a natural number. The arrow "→" indicates the data transmission direction or the sheet transport direction. For example, "i→s" means that the sheet is transported from the printing device 107 to the sensing unit 108.

[0075] The sheet ID (SID(n)) is unique identification information given to a sheet (hereinafter referred to as the "current sheet") for which the timing of ejection from the printing device 107 is to be determined. The previous sheet ID (SID(n-1)) is identification information of a sheet that is ejected or is scheduled to be ejected from the printing device 107 to the sensing unit 108 prior to the current sheet. If there is no sheet (hereinafter referred to as the "current sheet") represented by the previous sheet ID, the previous sheet ID (SID(n-1)) is "0". The sheet interval is a time indicating the ejection interval between multiple sheets that are ejected consecutively. The time when the sheet interval has elapsed from the ejection time of the previous sheet is the ejection timing of the next sheet. The sheet interval (Tss, i→s) indicates the time interval from the time ti(n-1) when the previous sheet is scheduled to be ejected from the printing device 107 to the time ti(n) when the current sheet is scheduled to be ejected from the printing device 107. The inter-paper time (Tss, i→s) is an initial value of a time that is preset in the printing device 107.

[0076] When auto-registration is performed between the previous sheet and the current sheet, the paper interval (Tss, i→s) is longer than the normal paper interval Tss by the time it takes to perform auto-registration. In other words, if the execution time of auto-registration between sheets is Ta, the paper interval when auto-registration is performed (Tss, i→s) is expressed by the following formula. Tss,i→s = Tss + Ta …(1)

[0077] The post-processing information proc indicates information on what kind of post-processing is performed on the target sheet indicated by the sheet ID. The post-processing includes processing according to an adjustment mode set from the operation unit 224, stapling processing, cutting processing, etc. performed by the finisher 109. The stacking device information TID is identification information for specifying the sheet processing device (sensing unit 108, finisher 109) on which the target sheet is stacked.

[0078] The timing information 602 is information transmitted from the sensing unit 108 to the finisher 109. The timing information 602 is generated by the CPU 342 of the sensing unit 108 based on the timing information 601. The timing information 602 includes, for example, the following information: Sheet ID (SID(n)) Previous seat ID (SID(n-1)) Inter-paper time (Tss, s→f) Delay time (Tdly,s) Post-processing information proc Loading device information TID

[0079] The sheet interval time (Tss,s→f) indicates the time interval from the time ts(n-1) when the previous sheet is discharged from the sensing unit 108 to the time ts(n) when the current sheet is discharged from the sensing unit 108. If there is no previous sheet, the sheet interval time (Tss,s→f) is "0". The delay time (Tdly,s) indicates the time for delaying the arrival of the sheet when the sensing unit 108 cannot process the current sheet during the sheet interval time (Tss,i→s). The sensing unit 108 calculates the delay time (Tdly,s) based on the sheet interval time (Tss,i→s) and the processing time (Tprc,s) required for shading correction of the CIS.

[0080] When the paper interval time (Tss,i→s) is equal to or longer than the processing time (Tprc,s) required for shading correction, the delay time (Tdly,s) is calculated by the following formula: In this case, the delay time (Tdly,s) is 0 seconds. Tdly,s = 0 …(2)

[0081] When the paper interval time (Tss,i→s) is shorter than the processing time (Tprc,s) required for shading correction, the delay time (Tdly,s) is calculated by the following formula: In this case, the delay time (Tdly,s) is the difference between the processing time (Tprc,s) and the paper interval time (Tss,i→s). Tdly,s = Tprc,s - Tss,i→s …(3)

[0082] The timing information 603 is information transmitted from the finisher 109, which is a sheet processing apparatus, to the printing apparatus 107. The timing information 603 is generated by the CPU 242 of the finisher 109 based on the timing information 602. The timing information 603 includes, for example, information such as a sheet ID and a delay time (Tdly, f).

[0083] The delay time (Tdly,f) indicates the time by which the finisher 109 delays the arrival of a sheet when the finisher 109 cannot finish processing the previous sheet within the paper interval (Tss,s→f). The finisher 109 calculates the delay time (Tdly,f) based on the paper interval (Tss,s→f), the delay time (Tdly,s), and the processing time (Tprc,f) of the finisher 109. The processing time (Tprc,f) of the finisher 109 is, for example, the time required for stapling the previous sheet or the time required to move the stack tray 332 to stack the previous sheet.

[0084] When the inter-sheet time (Tss,s→f) is equal to or longer than the processing time (Tprc,f) of the finisher 109, the delay time (Tdly,f) is calculated by the following formula: In this case, the delay time (Tdly,f) is the delay time (Tdly,s). Tdly,f = Tdly,s …(4)

[0085] When the paper interval time (Tss,s→f) is shorter than the processing time (Tprc,f) of the finisher 109, the delay time (Tdly,f) is calculated by the following formula: In this case, the delay time (Tdly,f) is the difference between the paper interval time (Tss,s→f) and the sum of the processing time (Tprc,s) and the processing time (Tprc,f). Tdly,f = Tdly,s + Tprc,f - Tss,s→f …(5)

[0086] (Timing of shading correction) 9 is a flowchart showing a process for determining the execution timing of shading correction of the sensing unit 108. Here, the execution timing of shading correction of the CIS 321 will be described, but the execution timing of shading correction of the CIS 322 is also determined by a similar process.

[0087] The sensing unit 108 needs to perform shading correction when a predetermined time has elapsed after the LED 350 of the CIS 321 is turned on. In this embodiment, the predetermined time is 120 seconds, but the predetermined time is not limited to this. For example, in the case of real-time adjustment mode, the LED 350 is continuously turned on because the adjustment image is printed on all sheets. When the LED 350 is continuously turned on for a predetermined time (120 seconds), a calibration process such as shading correction of the CIS 321 is performed.

[0088] The CPU 342 of the sensing unit 108 confirms the start of a print job by the image forming apparatus 101 through a notification from the CPU 222 of the printing apparatus 107 (S1000). When the print job is started, the CPU 342 waits until it acquires timing information 601 including the paper interval time (Tss, i→s) from the printing apparatus 107 (S1001:N). When it acquires the timing information 601 (S1001:Y), the CPU 342 adds the paper interval time (Tss, i→s) to the cumulative time X managed in the memory 343 (S1002). The cumulative time X indicates the time during which the LED 350 is continuously lit. Thereafter, the CPU 342 refers to the post-processing information proc of the acquired timing information 601 to confirm whether the real-time adjustment mode is set or not (S1003).

[0089] If the real-time adjustment mode is not set in the post-processing information proc (S1003: N), the CPU 342 sets the delay time (Tdly, s) to "0" (S1004). If the real-time adjustment mode is set in the post-processing information proc (S1003: Y), the CPU 342 determines whether the CIS 321 is in an operating state, i.e., whether the LED 350 is turned on (S1005).

[0090] If the CIS 321 is not driven and the LED 350 is off (S1005: N), the CPU 342 drives the CIS 321 to turn on the LED 350 (S1006). The CPU 342 clears the accumulated time X managed in the memory 343 to "0" (S1007). The CPU 342 sets the delay time (Tdly, s) to "0" (S1008).

[0091] When the CIS 321 is driven and the LED 350 is turned on (S1005: Y), the CPU 342 determines whether or not to perform shading correction (S1009). The CPU 342 determines whether or not to perform shading correction based on whether or not the accumulated time X managed in the memory 343 exceeds 120 seconds. The CPU 342 determines that shading correction does not need to be performed if the accumulated time X does not exceed 120 seconds, and determines that shading correction needs to be performed if the accumulated time X exceeds 120 seconds.

[0092] If shading correction is not necessary (S1009: N), the CPU 342 compares the paper interval time (ss, i → s) with the shading operation time (S1010). If the paper interval time (Tss, i → s) is greater (S1010: Y), the CPU 342 determines that shading correction can be performed within the paper interval time. If the paper interval time (Tss, i → s) is smaller (S1010: N), the CPU 342 determines that shading correction cannot be performed within the paper interval time and sets the delay time (Tdly, s) to "0" (S1011).

[0093] If shading correction is necessary (S1009: Y), the CPU 342 stores in the memory 343 information that shading correction will be performed after the sheet having the sheet ID in the timing information 601 is conveyed (S1012). Even if the CPU 342 determines in the process of S1010 that shading correction can be performed within the paper interval time, the CPU 342 stores in the memory 343 information that shading correction will be performed after the sheet having the sheet ID in the timing information 601 is conveyed (S1012). Thereafter, the CPU 342 sets the shading operation time to the processing time (Tprc, s) required for the shading correction of the CIS 321 (S1013).

[0094] After that, the CPU 342 performs a process to determine the delay time (Tdly,s) by the sensing unit 108. First, the CPU 342 judges whether the paper interval time (Tss,i→s) is longer than the processing time (Tprc,s) required for shading correction (S1014). If the paper interval time (Tss,i→s) is longer than the processing time (Tprc,s) required for shading correction (S1014:Y), the shading operation time is not the rate limiting factor for the paper interval. In other words, since no delay time is required, the CPU 342 sets the delay time (Tdly,s) to "0" (S1015). If the paper interval time (Tss,i→s) is shorter than the processing time (Tprc,s) required for shading correction (S1014:N), the CPU 342 sets the delay time (Tdly,s) by the following formula since the shading operation time is the rate limiting factor for the paper interval (S1016). The delay time (Tdly, s) is the processing time (Tprc, s) required for shading correction minus the paper interval time (Tss, i→s). Tdly,s = Tprc,s - Tss,i→s …(6)

[0095] After setting the delay time (Tdly, s) through the process of S1015 or S1016, the CPU 342 clears the accumulated time X for determining whether or not to perform shading correction to "0" (S1017).

[0096] After clearing the accumulated time X or setting the delay time (Tdly, s) in S1004, S1008, or S1011, the CPU 342 transmits timing information 602 to the finisher 109, which is a downstream device (S1018). The CPU 342 determines whether or not timing information for all sheets in the print job has been acquired from the printing apparatus 107 (S1019). If timing information for all sheets in the print job has not been acquired (S1019: N), the CPU 342 repeats the processes from S1001 onwards. If timing information for all sheets in the print job has been acquired (S1019: Y), the CPU 342 ends the process of determining the execution timing of shading correction.

[0097] The delay time (Tdly,s) determined in the process of determining the execution timing of shading correction is included in the delay time (Tdly,f) of the timing information transmitted from the finisher 109 to the printing device 107 and is notified to the printing device 107. This allows the printing device 107 to set an inter-sheet time (Tss,i→s) reflecting the delay time (Tdly,s). For example, the delay time (Tdly,s) determined in the process of S1016 is reflected in the inter-sheet time (Tss,i→s) of the timing information transmitted from the printing device 107 to the sensing unit 108 when the next sheet is conveyed. The inter-sheet time (Tss,i→s) is lengthened by, for example, the delay time (Tdly,s). This allows the sensing unit 108 to perform shading correction after processing the next sheet.

[0098] In this embodiment, the sheet interval information (Tss, i→s) included in the timing information sent from the printing device 107 becomes longer when auto-registration is performed than when auto-registration is not performed. Shading correction is performed at the timing when this sheet interval time (Tss, i→s) becomes longer than the shading operation time. Note that the cause of the sheet interval time (Tss, i→s) being longer is not limited to the above-mentioned auto-registration. The sheet interval time (Tss, i→s) may also be longer due to maintenance processing of the printing device 107 other than auto-registration.

[0099] As described above, the image forming apparatus 101 of this embodiment is configured by connecting the sensing unit 108 and the finisher 109 in series as multiple sheet processing devices to the printing device 107. The sensing unit 108 performs processing to read an adjustment image printed on a sheet by the printing device 107. The finisher 109 performs predetermined post-processing on the sheet on which the image is printed by the printing device 107. A device that requires calibration at predetermined time intervals, such as the sensing unit 108, needs to perform calibration processing at an appropriate timing.

[0100] The timing of the calibration process is the timing when the inter-sheet time between sheets, which is determined by the image formation process in which the printing device 107 prints on the sheets and the maintenance process such as auto-registration, becomes longer than the time required for the calibration process. In other words, when the printing device 107 performs a time-consuming maintenance process such as auto-registration, the sensing unit 108 performs the calibration process. When the inter-sheet time is shorter than the time required for the calibration process, the sensing unit 108 notifies the printing device 107 of a delay time so that the inter-sheet time is longer. By the printing device 107 lengthening the inter-sheet time by the delay time, the sensing unit 108 can perform the calibration process when the next sheet is transported.

[0101] In this way, the image forming apparatus 101 performs a calibration process such as shading correction of the sensing unit 108 at a timing when the inter-paper time is longer than during normal image formation processing, such as the timing of maintenance of the printing device 107. Therefore, it is possible to suppress a decrease in the productivity of the entire image forming apparatus 101 due to the calibration process.

Claims

1. A printing means for printing an image on a sheet; a sheet processing means for acquiring the sheet on which the image is printed from the printing means and processing the sheet, the printing means notifies the sheet processing means of an inter-sheet time indicating an interval between discharges of a plurality of sheets to be continuously conveyed to the sheet processing means; the sheet processing means determines the timing to perform the calibration process when the sheet interval is longer than the time required for the calibration process of the sheet processing means, Image forming device.

2. The printing unit determines the paper interval time based on a time for printing an image on the sheet and a time for performing a maintenance process.

2. The image forming apparatus according to claim 1.

3. the printing means can notify the sheet processing means of a first sheet interval time, which is a time for printing an image on the sheet, and a second sheet interval time, which includes a time for printing the image on the sheet and a time for performing the maintenance processing; the sheet processing unit does not perform the calibration process when acquiring the first sheet interval time, and determines a timing to perform the calibration process when acquiring the second sheet interval time.

3. The image forming apparatus according to claim 2.

4. When the sheet processing unit acquires the first inter-sheet time, the sheet processing unit calculates a delay time from a time required for the calibration process and the first inter-sheet time, and notifies the printing unit of the delay time; The printing means reflects the delay time in a paper interval between sheets to be conveyed next.

4. The image forming apparatus according to claim 3.

5. the printing means includes an image forming means for forming the image, an image carrier for carrying the image formed by the image forming means, a transfer means for transferring the image from the image carrier to the sheet, a fixing means for fixing the image transferred to the sheet, and an image reading means for reading the image carried by the image carrier; The maintenance process is performed based on a result of reading an image carried by the image carrier by the image reading means.

3. The image forming apparatus according to claim 2.

6. The sheet processing means includes a reading means for reading the image printed on the sheet, and the reading means is calibrated by the calibration process.

2. The image forming apparatus according to claim 1.

7. The sheet processing means performs shading correction of the reading means by the calibration process.

7. The image forming apparatus according to claim 6.

8. A printing device that prints an image on a sheet; a sheet processing device that acquires the sheet on which the image is printed from the printing device and processes the sheet, the printing device notifies the sheet processing device of an inter-sheet time indicating an interval between discharges of a plurality of sheets that are continuously conveyed to the sheet processing device; the sheet processing apparatus determines a timing to perform the calibration process when the paper interval is longer than a time required for the calibration process of the sheet processing apparatus, Image forming system.

Images