Image forming apparatus

Abstract

To provide an image forming apparatus that can perform shading compensation while suppressing reduction in productivity.SOLUTION: An image forming apparatus comprises: an image forming unit that forms an image on a sheet on the basis of an image forming condition; an image reading unit 231 that reads an image for adjustment of the image forming condition formed on the sheet; a memory 223 that stores a result of reading of the image for adjustment performed by the image reading unit 231; and a CPU 222 that performs shading compensation on the basis of, a result of reading of a white reference plate performed by the image reading unit 231. When the shading compensation and conveyance of the sheet on which the image for adjustment is formed to a reading position of the image reading unit 231 are performed in parallel, the CPU 222 does not update the reading result stored in the memory 223 with the result of reading of the image for adjustment.SELECTED DRAWING: Figure 2

Description

Technical Field

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

Background Art

[0002] Printed materials produced by commercial printing machines are required to have stable printing position accuracy. Patent Document 1 discloses an image forming apparatus for stabilizing printing position accuracy. In order to stabilize the printing position accuracy, this image forming apparatus prints an adjustment image serving as a mark of a printing position (image forming position) on a sheet to create an adjustment chart. The adjustment chart is read by an image reading sensor provided in the sheet conveyance path. The image forming apparatus feeds back the reading result of the adjustment image to the image forming conditions to adjust the printing position.

[0003] The image reading sensor is calibrated in order to maintain detection accuracy. Calibration of the image reading sensor is called shading correction. Shading correction is periodically executed, for example, when images are continuously formed on a plurality of sheets. Patent Document 2 discloses a technique for performing shading correction of a plurality of image reading sensors.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0005] During shading correction, the image reading sensor is unable to read images. Therefore, the image forming machine will have to wait to begin image formation for the print job until the shading correction is complete. This leads to a decrease in productivity. Furthermore, waiting can cause changes in the internal temperature of the image forming machine, potentially causing fluctuations in the print position.

[0006] The present invention has been made in view of the above problems, and aims to provide an image forming apparatus that can perform shading correction while suppressing a decrease in productivity. [Means for solving the problem]

[0007] The image forming apparatus of the present invention forms an image on a sheet based on image forming conditions. and adjustment images Image forming means for forming an image, Fixing means for fixing the image formed by the image forming means and the adjustment image to the sheet, a reference member, and reading means provided downstream of the fixing means in the transport direction in which the sheet is transported, wherein the image formed on the sheet is formed when the sheet is passing through the reading area. A reading means for reading the adjustment image, system Your means and, The control means generates the image formation conditions based on the reading result of the adjustment image by the reading means, performs shading correction of the reading means based on the reading result of the reference member by the reading means, and in the first mode in which both the image and the adjustment image are formed on each of the plurality of sheets, the control means causes the reference member to be read when the plurality of sheets on which both the image and the adjustment image are formed are passing through the reading area, and in the second mode in which either the image or the adjustment image is formed on each of the plurality of sheets, the control means causes the reference member to be read when the sheet on which the adjustment image is formed is not passing through the reading area. It is characterized by the following: [Effects of the Invention]

[0008] According to the present invention, shading correction can be performed while suppressing a decrease in productivity. [Brief explanation of the drawing]

[0009] [Figure 1] A diagram illustrating the configuration of an image processing system. [Figure 2] system configuration diagram. [Figure 3] Diagram showing the configuration of an image forming apparatus. [Figure 4] CIS explanatory diagram. [Figure 5] A schematic diagram illustrating sheet transport in real-time adjustment mode. [Figure 6] A schematic diagram illustrating sheet transport in interrupt adjustment mode. [Figure 7] A diagram illustrating the information stored in memory. [Figure 8] (a) to (d) are diagrams illustrating the settings screen. [Figure 9] Explanation diagram of gain adjustment. [Figure 10] (a) and (b) are explanation diagrams of shading correction values. [Figure 11] (a) and (b) are flowcharts representing the adjustment process of image formation conditions. [Figure 12] (a) and (b) are explanation diagrams of shading correction and the reading timing of the adjustment chart. [Figure 13] Flowchart representing the printing process in the image quality priority mode. [Figure 14] Exemplary diagram of the operation mode selection screen.

Mode for Carrying Out the Invention

[0010] Hereinafter, embodiments will be described in detail with reference to the drawings.

[0011] (First Embodiment) (Image Processing System) FIG. 1 is a configuration diagram of an image processing system including the image forming device of the present embodiment. The image processing system includes an image forming apparatus 101 and an external controller 102. The image forming apparatus 101 is, for example, a multifunction machine, a multi-function peripheral (MFP), or the like. The external controller 102 is, for example, an image processing controller, a digital front end (DFE), a print server, or the like.

[0012] The image forming apparatus 101 and the external controller 102 are communicably 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 via an external LAN 104. The external controller 102 acquires a print instruction (print job) from the client PC 103.

[0013] The client PC 103 has a printer driver installed that has the function of converting image data into a print description language that can be processed by the external controller 102. The user can instruct printing via the printer driver using various applications. The printer driver transmits image data to the external controller 102 based on the print job from the user. The external controller 102 receives a print job including image data from the client PC 103, performs data analysis and rasterization processing, and instructs the image forming apparatus 101 to perform printing (image formation) based on the image data.

[0014] The image forming apparatus 101 is configured by connecting a plurality of different function devices including the printing apparatus 107, and can perform complex printing processes such as bookbinding. The image forming apparatus 101 of the present embodiment includes a printing apparatus 107 and a finisher 109. The printing apparatus 107 forms an image on a sheet fed from a paper feeding unit provided at the lower part of the main body using a developer (for example, toner). The printing apparatus 107 forms images of yellow (Y), magenta (M), cyan (C), and black (K). A full-color image in which images of each color are superimposed is formed on the sheet. The sheet on which the image is formed is conveyed from the printing apparatus 107 to the finisher 109. The finisher 109 stacks the sheets on which the images are formed.

[0015] This image processing system has a configuration in which the external controller 102 is connected to the 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 acquire a print job including image data from the client PC 103 via the external LAN 104. In this case, the image forming apparatus 101 performs the data analysis and rasterization processing that was performed by the external controller 102. That is, the image forming apparatus 101 and the external controller 102 may be integrally configured.

[0016] (System Configuration) Figure 2 is a system configuration diagram showing the control of the image processing system. Here, the controllers that control the operation of the image forming apparatus 101, the external controller 102, and the client PC 103 are described.

[0017] ·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 communication with other devices. The printing device 107 includes a CPU (Central Processing Unit) 222, memory 223, 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 making unit 228, a fixing unit 229, and a paper feeding unit 230 for forming images. The printing device 107 includes an operation unit 224 and a display 225 as a user interface. These components are connected to each other so as to be able to communicate with each other via a system bus 233.

[0018] The communication interface 217 is connected to the finisher 109 via the communication cable 249 and controls communication with the finisher 109. When the printer 107 and the finisher 109 operate in cooperation, information and data are sent and received via the communication interface 217. The LAN interface 218 is connected to the external controller 102 via the internal LAN 105 and controls communication with the external controller 102. The printer 107 receives print settings and image data from the external controller 102 via the LAN interface 218. The video interface 220 is connected to the external controller 102 via the video cable 106 and controls communication with the external controller 102. The printer 107 receives image data representing the image to be formed from the external controller 102 via the video interface 220.

[0019] The CPU 222 comprehensively controls image processing and printing by executing computer programs stored in the storage 221. The memory 223 provides a work area for the CPU 222 to perform various processes. When performing image forming processing, the CPU 222 controls the exposure unit 227, the image formation unit 228, the fixing unit 229, and the paper feeding unit 230.

[0020] The exposure unit 227 includes a photoreceptor, a charging wire for charging the photoreceptor, and a light source for exposing the photoreceptor, which has been charged by the charging wire, in order to form an electrostatic latent image on the photoreceptor. The photoreceptor is, for example, a photosensitive belt with a photosensitive layer formed on the surface of a belt-shaped elastic member, or a photosensitive drum with a photosensitive layer formed on the surface of a cylinder. Alternatively, a charging roller may be used instead of the charging wire. The exposure unit 227 charges the surface of the photoreceptor to a uniform negative potential using the charging wire. Based on the image data, the exposure unit 227 outputs laser light from the light source. The laser light scans the surface of the uniformly charged photoreceptor. As a result, the potential of the photoreceptor fluctuates at the position where the laser light is irradiated, and an electrostatic latent image is formed on the surface. Four photoreceptors are provided, corresponding to four colors: yellow (Y), magenta (M), cyan (C), and black (K). Electrostatic latent images corresponding to different colored images are formed on each of the four photoreceptors.

[0021] The image-forming unit 228 transfers the toner image formed on the photoreceptor to a sheet. The image-forming unit 228 includes a developer, a transfer unit, and a toner supply unit. The developer forms a toner image by attaching negatively charged toner from a developing cylinder to the electrostatic latent image formed on the surface of the photoreceptor. There are four developers, one for each of the four colors: yellow (Y), magenta (M), cyan (C), and black (K). The developer makes the electrostatic latent image on the photoreceptor visible using the corresponding color toner.

[0022] The transfer unit has an intermediate transfer belt, which transfers the toner image from the photoreceptor to the intermediate transfer belt. A primary transfer roller is provided at a position opposite the photoreceptor across the intermediate transfer belt. When a positive potential is applied to the primary transfer roller, toner images from each of the four photoreceptors are superimposed and transferred onto the intermediate transfer belt. This forms a full-color toner image on the intermediate transfer belt. The toner image formed on the intermediate transfer belt is then transferred to the sheet by a secondary transfer roller, which will be described later. When a positive potential is applied to the secondary transfer roller, it transfers the full-color toner image from the intermediate transfer belt to the sheet.

[0023] The fuser unit 229 fixes the transferred toner image onto the sheet. The fuser unit 229 has a heater and a pair of rollers. The fuser unit 229 heats and pressurizes the toner image on the sheet using the heater and the pair of rollers, melting and fixing the toner image to the sheet. This forms an image on the sheet. The paper feed unit 230 is equipped with transport rollers and various sensors in the transport path and controls the sheet feeding operation.

[0024] The image reading unit 231 reads the image formed on the conveyed sheet based on instructions from the CPU 222. When the CPU 222 adjusts the image formation conditions, for example, it reads the image for adjusting the image formation conditions formed on the sheet from the image reading unit 231. The operation unit 224 is an input device that receives various settings inputs and operation instructions from the user. The operation unit 224 consists of various input keys and 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 print jobs.

[0025] Finisher The finisher 109 performs stapling on the output from, for example, the printing device 107. The finisher 109 includes a communication interface 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 that they can communicate with one another. The communication interface 241 is connected to the printing device 107 via a communication cable 249 and controls communication between the finisher 109 and the printing device 107. When the finisher 109 and the printing device 107 work together, information and data are sent and received via the communication interface 241. The CPU 242 executes a control program stored in the memory 243 and performs various controls necessary for paper discharge. The memory 243 stores the control program. The memory 243 also provides a work area for the CPU 242 when it performs various processes. The paper discharge control unit 244 discharges the transported sheets into the stack tray 332 shown in Figure 3 based on instructions from the CPU 242.

[0026] • External controller The external controller 102 includes a LAN I / F 213, a LAN I / F 214, and a video I / F 215 for communication with other devices. The external controller 102 includes a CPU 208, memory 209, and storage 210 to control the operation of the external controller 102. The external controller 102 includes a keyboard 211 and a display 212 as a user interface. These components are connected to each other so as to be able to communicate with each other via a system bus 216.

[0027] 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 obtains print jobs from the client PC 103 via LAN I / F 213. LAN I / F 214 is connected to the printer 107 via the internal LAN 105 and controls communication with the printer 107. The external controller 102 sends print settings and image data to the printer 107 via LAN I / F 214. Video I / F 215 is connected to the printer 107 via video cable 106 and controls communication with the printer 107. The external controller 102 sends image data to the printer 107 via video I / F 215.

[0028] The CPU 208 comprehensively performs processing such as receiving image data transmitted from the client PC 103, RIP processing, and transmitting image data to the image forming apparatus 101 by executing computer programs stored in the storage 210. The memory 209 provides a work area for the CPU 208 to perform various processes. The keyboard 211 is an input device that accepts various settings inputs and operation instructions from the user. The display 212 is an output device that displays information of the application being executed by the external controller 102 as still images or videos.

[0029] Client PC The client PC 103 includes a CPU 201, memory 202, storage 203, keyboard 204, display 205, and LAN I / F 206. These components are interconnected and can communicate with each other via a system bus 207.

[0030] The CPU 201 controls the operation of the client PC 103 by executing computer programs stored in the storage 203. In this embodiment, the CPU 201 performs image data creation and print job transmission processing. The memory 202 provides a work area for the CPU 201 to perform various processes. The keyboard 204 and display 205 are the user interface. The keyboard 204 is an input device that receives instructions from the user. The display 205 is an output device that displays information about the application being executed on the client PC 103 as still images or videos. 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 sends print jobs to the external controller 102 via the LAN I / F 206.

[0031] The external controller 102 and the image forming apparatus 101 are connected by an internal LAN 105 and a video cable 106, but any configuration that allows for the transmission and reception of data necessary for printing is acceptable, and for example, they may be connected by a video cable alone. Memories 202, 209, 223, and 243 can each be storage devices for holding data or programs. These memories can be, for example, volatile RAM (Random Access Memory), non-volatile ROM (Read Only Memory), storage, or USB (Universal Serial Bus) memory.

[0032] (Configuration of an image forming apparatus) Figure 3 is a diagram showing the configuration of the image forming apparatus 101. A display 225 is provided above the printing device 107. The display 225 displays information for the printing status and settings of the image forming apparatus 101. The sheet on which the image has been formed in the printing device 107 is transported to the finisher 109 located downstream.

[0033] The printing device 107 includes a paper feeding section 230 comprising multiple paper feeding decks 301, 302 and a transport path 303. Each paper feeding deck 301, 302 is capable of accommodating different types of sheets. The top sheet of each paper feeding deck 301, 302 is separated and fed to the transport path 303. The printing device 107 includes an exposure section 227 comprising image forming sections 304, 305, 306, 307 for forming images. The printing device 107 forms a color image. To this end, the image forming section 304 forms a black (K) image (toner image). The image forming section 305 forms a cyan (C) image (toner image). The image forming section 306 forms a magenta (M) image (toner image). The image forming section 307 forms a yellow (Y) image (toner image).

[0034] The printing apparatus 107 includes an image-forming unit 228, an intermediate transfer belt 308 and a secondary transfer roller 309, to which toner images are transferred from each of the image-forming units 304, 305, 306, and 307. The intermediate transfer belt 308 rotates clockwise in the figure, and toner images are superimposed and transferred in the order of image-forming unit 307, image-forming unit 306, image-forming unit 305, and image-forming unit 304. As a result, a full-color toner image is formed on the intermediate transfer belt 308. The intermediate transfer belt 308 transports the toner image to the secondary transfer roller 309 as it rotates. The sheet is transported to the secondary transfer roller 309 at the same time that the toner image is transported to the secondary transfer roller 309. The secondary transfer roller 309 transfers the toner image on the intermediate transfer belt 308 to the transported sheet.

[0035] The printing apparatus 107 includes a first fuser 311 and a second fuser 318 as a fixing unit 229. The first fuser 311 and the second fuser 318 have the same configuration and fix the toner image to the sheet. For this purpose, the first fuser 311 and the second fuser 318 are each equipped with a pressure roller and a heating roller. The sheet is heated and pressurized as it passes between the pressure roller and the heating roller, and the toner image is melted and pressed onto the sheet. The sheet that has passed through the second fuser 318 is transported to the transport path 314. The second fuser 318 is located downstream of the first fuser 311 in the sheet transport direction and is used to add gloss to the image on the sheet that has been fixed by the first fuser 311 and to ensure fixation. For this reason, the second fuser 318 may not be used depending on the type of sheet and the content of the image forming process. A transport path 312 is provided to transport the sheet that has been fixed in the first fuser 311 without going through the second fuser 318.

[0036] After the transport path 314 and transport path 312 merge, a transport path 315 and a reversal path 316 are provided. When double-sided printing is instructed, the sheet is transported to the reversal path 316. The sheet transported to the reversal path 316 has its transport direction reversed and is transported to the double-sided transport path 317. The sheet is reversed by the reversal path 316 and the double-sided transport path 317, with the side on which the image is formed (the first side) being reversed. The sheet is then transported to the transport path 303 by the double-sided transport path 317, and as it passes through the secondary transfer roller 309 and the fixing unit 229, an image is formed on the second side.

[0037] In the case of single-sided printing, or when an image is formed on both sides in double-sided printing, the sheet is transported to the transport path 315. A transport path 323 is located downstream of the transport path 315 in the direction of sheet transport.

[0038] In the transport path 323, two Contact Image Sensors (CIS) 321 and 322 are arranged opposite each other on either side of the transport path 323 as image reading units 231. Figure 4 is an explanatory diagram of the CIS 321 and 322. CIS 321 is an optical sensor that reads the image of the upper surface of the sheet being transported along the transport path 323. CIS 322 is an optical sensor that reads the image of the lower surface of the sheet being transported along the transport path 323.

[0039] The CIS321 comprises 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 illuminates the upper surface of a sheet when the sheet being transported along the transport path 323 reaches the reading position. The reading sensor 351 has multiple light receiving elements (photoelectric conversion elements) oriented perpendicular to the sheet transport direction. Therefore, the direction perpendicular to the sheet transport direction becomes the main scanning direction of the CIS321. The reading sensor 351 receives reflected light from the sheet. The multiple 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 values ​​(electrical signals) output from the multiple light receiving elements are transmitted to the CPU 222. In this way, the image formed on the sheet is read. The white reference plate 352 is a calibration member (reference member) used when correcting the shading of the CIS321. During shading correction, the LED 350 and reading sensor 351 move to a position where they can read the white reference plate 352. Alternatively, during shading correction, the white reference plate 352 moves to the reading position of the LED 350 and reading sensor 351. Shading correction of the CIS 321 is performed based on the reading result of the white reference plate 352. For this reason, the CIS 321 cannot read the image formed on the sheet during shading correction.

[0040] Like the CIS321, the CIS322 includes an LED 353, a reading sensor 354, and a white reference plate 355. The CIS322 operates similarly to the CIS321, reading the image formed on the underside of the sheet when the sheet being transported along the transport path 323 reaches the reading position. In addition to the CIS321 and 322, the image reading unit 231 can also be implemented using a CCD or CMOS sensor.

[0041] The printing apparatus 107 of this embodiment is capable of forming adjustment images on both sides of a sheet to adjust image formation conditions. The sheet on which the adjustment images are formed is called an adjustment chart. The printing apparatus 107 prints the adjustment images onto the sheet to create an adjustment chart, and reads the adjustment images using CIS321 and CIS322. The images of the adjustment chart read by CIS321 and CIS322 are stored in memory 223. The CPU 222 refers to memory 223, analyzes the images read by CIS321 and CIS322, and feeds this back into the image formation conditions to adjust them.

[0042] For example, when the internal temperature of the printing device 107 rises, the geometric characteristics of the image formed on the sheet change compared to when the internal temperature of the printing device 107 is low. Here, the geometric characteristics of the image include, for example, perpendicularity and the printing position of the image on the sheet. The printing device 107 creates an adjustment chart and detects the geometric characteristics based on the readings of CIS 321 and 322. The CPU 222 performs an affine transformation on the image data so that the detected geometric characteristics become ideal geometric characteristics. The printing device 107 can control the geometric characteristics of the image formed on the sheet by forming an image on the sheet based on the image data transformed by the CPU 222. In this way, the printing device 107 can suppress fluctuations in the geometric characteristics of the image caused by fluctuations in the internal temperature.

[0043] The adjustment image formed on the adjustment chart may be an image for detecting geometric characteristics, an image for detecting image density, or an image for detecting color shift. If an adjustment image for detecting image density is formed, the CPU 222 generates image formation conditions to suppress fluctuations in image density based on the reading results 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 formation 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 to suppress fluctuations in image density based on the reading results of the CIS 321 (or CIS 322). The CPU 222 converts the 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.

[0044] Furthermore, if an adjustment image for detecting color misalignment is formed, the CPU 222 detects the color misalignment based on the reading result of the CIS 321 (or CIS 322). Based on the detected color misalignment, the CPU 222 corrects the color misalignment by controlling the position of the image formed on the photoreceptor by the exposure unit 227.

[0045] The adjustment image may be printed as an adjustment chart on a different sheet from the user image, or on the same sheet as the user image. When printed as an adjustment chart, the CPU 222 creates image data from the received image data in which the adjustment chart is inserted between the user image on page N and the user image on page N+1 each time the number of printed pages reaches a predetermined number N. When the adjustment image is formed on the same sheet as the user image, it is preferable that the adjustment image is formed in the cutting area of ​​the sheet. This is because the adjustment image is removed from the output when the cutting process is performed. Here, the user image is an image included in the image data transferred from the client PC 103.

[0046] The image forming apparatus 101 of this embodiment is controlled based on 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 at predetermined intervals. The image forming apparatus 101 of this embodiment will now be described in the case where an adjustment image is formed to detect geometric characteristics. The user can set whether or not to perform geometric characteristic correction using the operation unit 224 of the printing apparatus 107. Furthermore, if geometric characteristic correction is to be performed, the user selects an adjustment mode from the real-time adjustment mode and the interrupt adjustment mode. Note that the selection of the adjustment mode is not limited to the operation unit 224; for example, the user may select the adjustment mode using a client PC 103.

[0047] In the real-time adjustment mode of this embodiment, an adjustment image is printed on each page. Figure 5 is a schematic diagram showing the sheet transport in real-time adjustment mode, illustrating how an adjustment image is printed on each page in real-time adjustment mode. Sheets with the adjustment image printed on them pass through a transport path 323, which is provided with CIS 321 and 322, in order from the leftmost sheet to the rightmost sheet in the figure. As shown in Figure 5, the adjustment image has V-shaped adjustment patches formed at the four corners of the sheet. A user image is also formed on the sheet with the adjustment image printed on it. Sheets with both the adjustment image and the user image are discharged to the stack tray 332.

[0048] In the interrupt adjustment mode of this embodiment, an adjustment chart is inserted each 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. Figure 6 is a schematic diagram showing the sheet transport in the interrupt adjustment mode, and shows how an adjustment chart is printed every predetermined number of sheets in the interrupt adjustment mode. The schematic diagram in Figure 6, like the schematic diagram in Figure 5, shows the sheets passing through a transport path 323 in which CIS 321 and 32 are provided in order from the leftmost sheet to the rightmost sheet in the diagram. As shown in Figure 6, the adjustment chart has V-shaped adjustment patches formed at the four corners of the sheet. Here, no user images are formed on the adjustment chart. In the interrupt adjustment mode, the adjustment chart is discharged to a different tray from the sheets on which user images are formed. The sheets on which user images are formed are discharged to the stack tray 332, and the adjustment chart is discharged to the discharge tray 328.

[0049] As mentioned above, the adjustment chart is excluded so as not to be mixed with the printed materials corresponding to the print job. For this purpose, the printing device 107 is equipped with a flapper 324, an discharge path 326, a transport sensor 327, and an discharge tray 328. The adjustment chart, whose image (adjustment image) has been read by CIS 321 and 322, is transported to the discharge path 326 by the flapper 324. The sheet transported to the discharge path 326 is discharged into the discharge tray 328.

[0050] If the sheet is not an adjustment chart, it is transported by the flapper 324 from the transport path 323 to the downstream transport path 325. The sheet transported to the downstream transport path 325 is handed over to the finisher 109. When the printing device 107 receives notification of a transport jam from the finisher 109, it switches the flapper 324 to the discharge path 326, regardless of whether it is an adjustment chart or not, and discharges all sheets (residual paper) in the machine to the discharge tray 328. Discharging the residual paper to the discharge tray 328 reduces the burden on the user in handling jams.

[0051] The finisher 109 can load sheets received from the printing device 107. The finisher 109 includes a transport path 331 and a stack tray 332 for loading sheets. Transport sensors 333, 334, 335, and 336 are provided in the transport path 331. Sheets transported from the printing device 107 are loaded onto the stack tray 332 via the transport path 331. Transport sensors 333, 334, 335, and 336 detect the passage of sheets being transported along the transport path 331. If the CPU 242 determines that a transport jam (transport abnormality) has occurred in the finisher 109 if the leading or trailing end of the sheet in the transport direction is not detected by the transport sensors 333, 334, 335, or 336 even after a predetermined time has elapsed since the start of sheet transport. In this case, the CPU 242 notifies the printing device 107 that a transport jam has occurred.

[0052] Figure 7 is an explanatory diagram of the information stored in the memory 223 of the printing device 107. The memory 223 stores information used for shading correction and geometric characteristic correction. The information used for shading correction is the correction coefficient (shading correction value) obtained from the reading results of the white reference plates 352 and 355. The information used for image position adjustment is the adjustment patch position for the front surface (front) and the adjustment patch position for the back surface (back) obtained from the reading results of the adjustment chart. In addition, the memory 223 stores correction values ​​for adjusting geometric characteristics. The correction values ​​for adjusting geometric characteristics include tip position correction, left edge position correction, main scanning direction magnification, etc. The correction values ​​for adjusting geometric characteristics are used when the printing device 107 forms an image.

[0053] Furthermore, memory 223 stores the interval at which adjustment charts are created in interrupt adjustment mode (adjustment chart insertion interval). An adjustment chart is created each time a predetermined number of sheets are printed. In other words, the correction values ​​for adjusting geometric characteristics in interrupt adjustment mode are updated each time a predetermined number of sheets are printed. The predetermined number can be changed based on the number of sheets indicated by the user. The number of sheets indicated is, for example, an integer greater than 0. The adjustment interval for the print position is set based on the number of sheets indicated.

[0054] Figure 8 is an explanatory diagram of the setting screen for setting the interval for creating adjustment charts in interrupt adjustment mode. The setting screen is displayed on the display 225 by the CPU 222. Adjustment charts are created in adjustment mode, and the adjustment mode is set by the user using the operation unit 224.

[0055] Figure 8(a) shows the initial screen. When the user selects the "Advanced Mode" soft key from the initial screen, the CPU 222 displays the Advanced Mode selection screen shown in Figure 8(b) on the display 225. When the user selects the "Adjust" soft key from the Advanced Mode selection screen, the CPU 222 displays the Adjustment Mode selection screen shown in Figure 8(c) on the display 225. Selecting "Adjust" puts the printer 107 into adjustment mode. When the user selects the "Close" soft key from the Advanced Mode selection screen, the CPU 222 displays the initial screen on the display 225.

[0056] The real-time adjustment mode is selected by the user by selecting the "Real-time" soft key from the adjustment mode selection screen. The CPU 222 notifies the external controller 102 of the settings. When the external controller 102 instructs the printing device 107 to form an image according to the print job, it notifies the printing of an adjustment image in the margin area.

[0057] When the user selects the "predetermined interval" soft key from the adjustment mode selection screen, the CPU 222 displays the insertion interval setting screen shown in Figure 8(d) on the display 225. When the user selects the "back" soft key from the adjustment mode selection screen, the CPU 222 displays the application mode selection screen on the display 225.

[0058] When the user enters the number of insertion intervals using the numeric keypad on the insertion interval setting screen and selects the soft key "OK", the CPU 222 sets the number of insertion intervals for the adjustment chart. The CPU 222 stores the number of insertion intervals entered on the insertion interval setting screen in memory 223 when "OK" is selected. When the user selects the soft key "Back" from the insertion interval setting screen, the CPU 222 displays the adjustment mode selection screen on the display 225.

[0059] The CPU 222 notifies the external controller 102 of the number of insertion intervals stored in the memory 223. The external controller 102 stores the notified number of insertion intervals in the memory 209. When the number of insertion intervals is printed on a sheet, the external controller 102 instructs the printer 107 to create an adjustment chart. For example, if "200" is entered and "OK" is selected on the insertion interval setting screen, the printer 107 will be instructed by the external controller 102 to print an adjustment chart every 200 pages. If the print job instructs printing 1000 pages, the printer 107 will create adjustment charts between pages 200 and 201, between pages 400 and 401, between pages 600 and 601, and between pages 800 and 801.

[0060] As described above, a predetermined number of pages (insertion interval pages) is set at the timing when the adjustment chart is created. Here, an example has been described in which the insertion interval pages are set by the printing device 107, but the insertion interval pages may also be set by the external controller 102 or the client PC 103. When the external controller 102 is used, each screen in Figure 8 is displayed on the display 212. When the client PC 103 is used, each screen in Figure 8 is displayed on the display 205. The set insertion interval pages are notified from the client PC 103 to the external controller 102.

[0061] (Shading correction) Initial adjustments, including shading correction, are performed on the CIS321 and 322. This section describes the initial adjustments for the CIS321, but the initial adjustments for the CIS322 are performed similarly.

[0062] When the CPU 222 starts the initial adjustment, it uses a CIS drive motor (not shown) to move the LED 350 and the reading sensor 351 to directly above the white reference plate 352. Here, the position directly above the white reference plate 352 is designated as the shading reading position. Once the movement is complete, the CPU 222 lights up the LED 350 to read the image on the white reference plate 352 and calculates the gain adjustment value for the CIS 321 according to the reading result. After reading the white reference plate 352 at the shading reading position, the CPU 222 uses a CIS drive motor (not shown) to move the LED 350 and the reading sensor 351 to the chart reading position shown in Figure 4.

[0063] Figure 9 is an explanatory diagram of gain adjustment. The horizontal axis shows the position of each pixel when reading one line of the image on the white reference plate 352 in the main scanning direction. The vertical axis shows the reading result (luminance value) for each pixel position. The dotted line A shows the luminance value characteristics when reading the white reference plate 352 with the initial settings at startup. The maximum luminance value for "white" is shown as "Tgt0".

[0064] Due to the light distribution characteristics of the LED 350 and the reading sensor 351, the maximum value of the reading result (luminance value) of the white reference plate 352 in the initial settings does not match the expected "white" luminance value Tgt0. The reading result is uniformly amplified by the amplification circuit in the image processing unit 232 so that the maximum value of the reading result luminance value matches Tgt0. This amplification rate is the gain adjustment value. The characteristic of the luminance value for one line after adjustment by the gain adjustment value is shown by the solid line B. The CPU 222 calculates the gain adjustment value, sets the calculated gain adjustment value in the image processing unit 232, and reflects it in subsequent readings.

[0065] As shown in Figure 9, even when the CIS321 reads the white reference plate 352, which has a uniform color across its entire surface, variations occur in the characteristics of the brightness values ​​obtained from the reading, depending on the pixel position in the main scanning direction. To compensate for these variations, shading correction is performed. After the CPU222 sets the gain adjustment value in the image processing unit 232, it reads the image of the white reference plate 352 again using the CIS321 and generates a shading correction value based on the reading result.

[0066] Figure 10 is an explanatory diagram of the shading correction value. The solid line in Figure 10(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 the uniform density white reference plate 352 be a uniform "white" luminance value. The luminance value that indicates "white" is the target value Tgt. The value of the target value Tgt is greater than the maximum luminance value Tgt0 and is predetermined according to the content of the job to be executed.

[0067] As shown by the arrows in Figure 10(a), the CPU 222 calculates a shading correction value for each pixel in the main scanning direction so that the brightness value of one line at each pixel position becomes the target value Tgt. The size of the arrow at each pixel position corresponds to the shading correction value. The calculated shading correction values ​​are stored in the memory 223 for each pixel position in the main scanning direction via the image processing unit 232. Figure 10(b) shows the shading correction values ​​for each pixel in the main scanning direction. When reading the image with the CIS 321, the shading correction value for the corresponding pixel position is reflected in the reading result of each pixel (shading correction is performed). This allows the CPU 222 to suppress variations between pixels (photodetectors) of the LED 350 and reading sensor 351 and obtain a uniform reading result. After shading correction, the CPU 222 can store the reading result of the shading-corrected image in the memory 223.

[0068] Shading correction must be performed each time a predetermined number of sheets pass the reading positions of CIS321 and 322. Here, we will describe a case where shading correction is performed every 100 sheets, but the predetermined number can be any number. The predetermined number is the number of sheets that pass the reading positions of CIS321 and 322, and is irrelevant whether CIS321 and 322 read the image of the sheet or not. When 100 sheets have been transported, CPU222 performs shading correction on CIS321 and 322. Alternatively, shading correction may be performed each time the cumulative illumination time of LED350 reaches a predetermined time. Or, a temperature sensor may be provided on CIS321, and shading correction may be performed when the temperature detected by the temperature sensor changes by a predetermined temperature or more. Shading correction on CIS321 can be performed even while sheets are being transported because LED350 and reading sensor351 move directly above the white reference plate352. Similarly, shading correction for the CIS322 can also be performed during sheet transport.

[0069] (Adjustment of image formation conditions during shading correction) Figure 11 is a flowchart illustrating the adjustment process for image formation conditions using an adjustment chart during shading correction.

[0070] Figure 11(a) is a flowchart of the image formation process for one page. The CPU 222 calculates adjustment values ​​for image formation conditions from the reading results of the adjustment chart stored in memory 223 and stores them in memory 223. The adjustment values ​​for image formation conditions are, for example, the difference between the detected geometric characteristics and the ideal geometric characteristics. The CPU 222 calculates adjustment values ​​from the reading results of the adjustment chart and stores them in memory 223 (S1001). The CPU 222 performs an affine transformation on the image data based on the adjustment values ​​stored in memory 223 and prints the image on the sheet based on the transformed image data (S1002). In real-time adjustment mode, the CPU 222 forms a user image and an adjustment image on each page. In interrupt adjustment mode, the CPU 222 prints a user image according to the print job on a sheet, and when it has printed user images on a predetermined number of sheets according to the adjustment chart insertion interval, it prints an adjustment image on the sheet. An adjustment chart is created by printing the adjustment image on the sheet.

[0071] Figure 11(b) is a flowchart showing the reading process of the adjustment chart. In this embodiment, shading correction is performed every time 100 pages of images are formed. The CPU 222 reads the adjustment image using the image reading unit 231 (CIS 321, 322) (S2001). The CPU 222 increments the correction counter cnt, which represents the number of sheets that have passed through the reading positions of CIS 321, 322, by 1 (S2002).

[0072] CPU222 determines whether or not shading correction was performed while reading the adjustment image (S2003). If shading correction was not performed (S2003:N), CPU222 updates the reading result of the adjustment image stored in memory 223 with the reading result from processing in S2001 (S2004). The reading result of the adjustment image stored in memory 223 is used to calculate the adjustment value. If shading correction was performed (S2003:Y), CPU222 does not update the reading result of the adjustment image stored in memory 223. Since the adjustment image cannot be read while shading correction is being performed, CPU222 cannot update the reading result.

[0073] Subsequently, the CPU 222 determines whether or not to perform shading correction based on the correction counter cnt. The CPU 222 determines whether or not to perform shading correction based on whether or not the correction counter cnt is greater than a predetermined threshold cnt_th (S2005). As described above, shading correction is performed each time a predetermined number of sheets pass through the reading positions of CIS 321 and 322. The threshold cnt_th is this predetermined number, which in this embodiment is 100 sheets.

[0074] If the correction counter cnt is less than or equal to the threshold cnt_th, i.e., 100 frames or less (S2005:N), CPU222 terminates processing without performing shading correction. If the correction counter cnt is greater than the threshold cnt_th, i.e., more than 100 frames (S2005:Y), CPU222 starts shading correction (S2006). After shading correction, CPU222 terminates processing.

[0075] As described above, in this embodiment, the periodic execution of shading correction in CIS321 and 322 and the reading process of the adjustment image are performed in parallel. Therefore, the decrease in productivity due to shading correction can be suppressed. In this case, the adjustment image used during shading correction is not read and is therefore not applied to the adjustment values ​​during printing.

[0076] (Second Embodiment) In the first embodiment, the image forming apparatus 101 prioritizes reading the white reference plate 352 even if the adjustment image has passed the reading position, regardless of the adjustment mode, when the timing for shading correction arrives. Therefore, in interrupt adjustment mode, even if an adjustment chart is printed, shading correction may take priority, potentially causing the reading of the adjustment chart to be skipped. If the reading of the adjustment chart is skipped, it becomes impossible to correct the geometric characteristics of the image with high precision until the next adjustment value is updated.

[0077] Therefore, in the interrupt adjustment mode, the image forming apparatus 101 of this embodiment controls the timing at which the adjustment chart passes the reading position so that the reading of the adjustment chart is not skipped by performing shading correction. For example, the CPU 222 determines whether or not the reading of the adjustment chart is skipped, and if the reading is skipped, it delays the formation of the adjustment chart and the transport of the sheet on which the adjustment chart is printed.

[0078] Figure 5, a schematic diagram showing the sheet transport in real-time adjustment mode, indicates whether the CIS321 reading operation is ON or OFF, and the type of reading data acquired during the reading operation. In Figure 5, even after the timing for executing shading correction (execution request) arrives, there is no delay in the formation timing of the adjustment image and the user image. As shown in Figure 5, reading data for the adjustment image is acquired for the first three pages from the left, and no reading data for the adjustment image is acquired while the sheets on pages 4 and 5 are passing the reading position. While the sheets on pages 4 and 5 are passing the reading position, reading data for the white reference plate 352 is acquired. Then, from the moment the sheet on page 6 passes the reading position, the acquisition of reading data for the adjustment image resumes.

[0079] Figure 6, a schematic diagram showing the sheet transport in interrupt adjustment mode, indicates whether the CIS321's reading operation is ON or OFF, and the type of reading data acquired during the reading operation. In Figure 6, after the shading correction execution timing (execution request) arrives, the adjustment chart does not reach the reading position. This is because the formation timing of the adjustment image is delayed. At this time, the formation of the adjustment patch on the photoreceptor has not yet begun. Subsequently, the CPU222 controls the timing of the formation of the adjustment patch on the photoreceptor so that the adjustment chart reaches the reading position after the reading of the white reference plate 352 is completed. As shown in Figure 6, the reading data of the white reference plate 352 is acquired during the period from when the third page from the left edge passes the reading position until the adjustment chart passes the reading position, and the adjustment chart passes the reading position after the CIS321 has entered a state where it can read the chart. Because the reading of the white reference plate 352 and the reading of the adjustment chart are performed sequentially, the reading of the adjustment chart is never skipped.

[0080] According to the image forming apparatus 101 of this embodiment, in real-time adjustment mode, a decrease in productivity can be suppressed even when shading correction is performed, and in interrupt adjustment mode, the skipping of the detection of geometric characteristics of the image can be suppressed. In real-time adjustment mode, the time from when the reading of the white reference plate 352 is completed until the adjustment image is read again is short. Therefore, even if the update of the adjustment value is delayed due to the reading of the white reference plate 352, the impact on the deviation of geometric characteristics is minimal. In interrupt adjustment mode, by prioritizing the reading of the white reference plate 352, the time until the adjustment image is read again becomes longer. If the adjustment value is not updated due to the reading of the white reference plate 352, the deviation of geometric characteristics is not suppressed. Therefore, in interrupt adjustment mode, the image forming apparatus 101 of this embodiment delays the formation of the adjustment chart and suppresses the decrease in image quality that occurs when the reading of the adjustment chart is skipped.

[0081] (modified version) This section describes a process that maintains a certain level of accuracy in image position based on the reading results of the adjustment chart by CIS321 and 322 while suppressing a decrease in productivity. In this embodiment, the image forming apparatus 101 operates in two operating modes: an image quality priority mode that prioritizes maintaining image quality, and a productivity priority mode that prioritizes productivity. In the image quality priority mode, the reading of the adjustment chart by CIS321 and 322 is prioritized, and the creation and reading of the adjustment chart are waited for until shading correction is completed. In the productivity priority mode, as shown in Figure 11(b), shading correction is performed while the adjustment chart is being read. The image quality priority mode and the productivity priority mode are switched depending on the frequency of creating and reading the adjustment chart. The productivity priority mode is the process shown in Figure 11(b), so its explanation is omitted.

[0082] (Switching operating modes) If the number of adjustment charts inserted at intervals exceeds a predetermined threshold (e.g., 50 charts), the frequency of reading the adjustment charts will decrease. In this case, the operating mode is set to an image quality priority mode, which delays reading the adjustment charts until shading correction is complete, ensuring that the adjustment charts are read.

[0083] If the insertion interval of the adjustment chart is smaller than the threshold, the frequency of reading the adjustment chart increases. This further suppresses variations in the print position of the image formed by the printing device 107. In this case, the operating mode is set to a productivity-priority mode in which the reading of the adjustment chart and shading correction are performed in parallel.

[0084] (Timing of reading shading correction and adjustment images) Figure 12 is an explanatory diagram of the shading correction and adjustment chart reading timing for each operating mode. Figure 12(a) shows the shading correction and adjustment chart reading timing in productivity priority mode. Figure 12(a) exemplifies the timing of when the 1st to 6th sheets pass the reading position of the CIS321, when images are formed on the 10th to 16th sheets, and when the adjustment chart reading results are updated. Figure 12(b) shows the shading correction and adjustment chart reading timing in image quality priority mode. Figure 12(b) exemplifies the timing of when the 1st to 6th sheets pass the reading position of the CIS321, when images are formed on the 10th to 15th sheets, and when the adjustment chart reading results are updated.

[0085] In the case of Figure 12(a), shading correction starts immediately after the trailing edge of the second sheet (adjustment chart) has finished reading. In parallel with the shading correction, the adjustment chart passes through the reading positions of CIS321 and 322. The CPU 222 of the printing device 107 does not use the reading results of the adjustment chart during shading correction to adjust the image formation conditions. Specifically, the image formation positions of the 13th to 15th sheets, where image formation starts after the trailing edge of the third sheet (adjustment chart) that passes through the reading position during shading correction, are not adjusted. This is because the reading results stored in memory 223 have not been updated by the reading results of the 3rd to 5th sheets (adjustment charts).

[0086] When reading is complete for sheets that are not affected by shading correction, such as the sixth sheet (adjustment chart), the reading results in memory 223 are updated. As a result, the image formation positions of the 16th sheet and subsequent sheets are adjusted based on the reading results.

[0087] In the case of Figure 12(b), shading correction begins immediately after the trailing edge of the second sheet (adjustment chart) has finished reading. The printer 107 does not read the adjustment chart or print the image using a print job at the time shading correction is performed. Because the adjustment chart is not read during shading correction, the reading results stored in memory 223 are not updated. When the adjustment chart (third sheet) is read after shading correction, the reading results stored in memory 223 are updated. As a result, the twelfth sheet has an image formed with the image formation position adjusted according to the latest adjustment chart reading results. In this way, even when the timing of shading correction and the timing of reading the adjustment chart occur simultaneously, image quality is maintained by delaying the timing of reading the adjustment chart.

[0088] Figure 13 is a flowchart illustrating the printing process in image quality priority mode. As mentioned above, in image quality priority mode, the system waits for the adjustment chart to be read and the image to be printed by the print job until the shading correction is complete.

[0089] CPU222 determines whether or not shading correction has been performed immediately before printing (S3001). If shading correction has been performed immediately before (S3001:Y), CPU222 determines whether or not the time required for shading correction has elapsed since the completion of image formation on the previous sheet (S3002). If the time required for shading correction has not elapsed (S3002:N), CPU222 waits until the time required for shading correction has elapsed. In other words, CPU222 waits until shading correction is completed.

[0090] If the time required for shading correction has elapsed (S3002:Y), the CPU 222 calculates the image position adjustment value based on the reading result of the adjustment chart stored in memory 223 (S3003). This reading result is the result read from the adjustment chart after shading correction. If shading correction has not been performed immediately beforehand (S3001:N), the CPU 222 calculates the image position adjustment value based on the reading result of the adjustment chart stored in memory 223 without waiting for the completion of shading correction (S3003). The CPU 222 then prints according to the calculated image position adjustment value (S3004). This completes the printing process in image quality priority mode.

[0091] In addition to the number of sheets inserted at intervals and thresholds, the operating mode may also be switched by user selection. Figure 14 is an example of an operating mode selection screen. The CPU 222 displays such a selection screen on the display 225. The user selects the operating mode using the operation unit 224 according to the selection screen on the display 225. The operating mode is switched according to the user's selection.

[0092] As explained above, by switching between productivity priority mode and image quality priority mode, it is possible to maintain a certain level of accuracy in adjusting the image position based on the reading results of CIS321 and 322 while suppressing a decrease in productivity.

Claims

1. Image forming means for forming an image and an adjustment image on a sheet based on image forming conditions, Fixing means for fixing the image formed by the image forming means and the adjustment image onto the sheet, Reference member and A reading means provided downstream of the fixing means in the transport direction in which the sheet is transported, the reading means reads the adjustment image formed on the sheet while the sheet is passing through the reading area, Equipped with control means, The control means generates the image formation conditions based on the reading result of the adjustment image by the reading means, and performs shading correction of the reading means based on the reading result of the reference member by the reading means. The control means is characterized in that, in a first mode in which both the image and the adjustment image are formed on each of a plurality of sheets, the reference member is read while the plurality of sheets on which both the image and the adjustment image are formed are passing through the reading area, and in a second mode in which either the image or the adjustment image is formed on each of the plurality of sheets, the reference member is read while the sheet on which the adjustment image is formed is not passing through the reading area. Image forming apparatus.

2. The control means is capable of switching the positional relationship between the reading means and the reference member between a first positional relationship for the reading means to read the adjustment image on the sheet in the reading area and a second positional relationship for the reading means to read the reference member. The control means is characterized in that, when the execution conditions for performing the reading of the reference member by the reading means are met, the positional relationship between the reading means and the reference member is set to the second positional relationship. The image forming apparatus according to claim 1.

3. The reading means is characterized in that, when reading the adjustment image, it moves to a first position for reading the adjustment image on the sheet passing through the reading area, and when reading the reference member, it moves to a second position for reading the reference member. The image forming apparatus according to claim 1.

4. The reading means is characterized in that, in the first positional relationship, it moves to a first position for reading the adjustment image on the sheet passing through the reading area, and in the second positional relationship, it moves to a second position for reading the reference member. The image forming apparatus according to claim 2.

5. The image forming conditions are characterized by being used to adjust the geometric characteristics of the image formed on the sheet by the image forming means. The image forming apparatus according to claim 1.

6. The geometric characteristics include the position on the sheet where the image is formed. The image forming apparatus according to claim 5.

7. The aforementioned geometric properties include the perpendicularity of the image on the sheet. The image forming apparatus according to claim 5.

8. The execution conditions for performing the reading of the reference member by the reading means are characterized in that they include conditions relating to the number of sheets passing through the reading area. The image forming apparatus according to claim 1.

9. The reading means includes a light source, The execution conditions for performing the reading of the reference member by the reading means are characterized in that they include the cumulative light emission time of the light source. The image forming apparatus according to claim 1.

10. The execution conditions for performing the reading of the reference member by the reading means are characterized in that they include conditions relating to the temperature of the reading means. The image forming apparatus according to claim 1.

11. The aforementioned reference member is characterized by being white in color. The image forming apparatus according to claim 1.

12. The reference member is characterized in that it is located between the reading means and the reading area in a direction perpendicular to both the length direction of the sheet as the conveying direction and the width direction of the sheet which is perpendicular to the length direction of the sheet. The image forming apparatus according to claim 1.

13. The reading means is characterized by being a CIS that receives reflected light from the sheet without folding it back. The image forming apparatus according to claim 1.

14. The reading means comprises a plurality of light-receiving elements in a direction perpendicular to the transport direction, The reading means is positioned upstream of the reference member in the transport direction, The control means is characterized by moving the reading means downstream in the transport direction to bring the reading means and the reference member into contact and perform reading of the reference member, or moving the reference member upstream in the transport direction to bring the reading means and the reference member into contact and perform reading of the reference member. The image forming apparatus according to claim 1.

15. The reading means comprises a plurality of light-receiving elements in a direction perpendicular to the transport direction, The reading means is positioned downstream of the reference member in the transport direction, The control means is characterized by moving the reading means upstream in the transport direction to bring the reading means and the reference member into contact and perform reading of the reference member, or moving the reference member downstream in the transport direction to bring the reading means and the reference member into contact and perform reading of the reference member. The image forming apparatus according to claim 1.

Images