Image forming apparatus and method for controlling the image forming apparatus

Abstract

To immediately correct an image to be printed even when there is a change in the shape of a sheet in the middle of printing.SOLUTION: An image formation apparatus 100 comprises: image formation units 102, 103 which print images on sheets; a correction unit which corrects a printing position of the image to the sheets; and a first sensor 110 which is arranged in a conveyance path on the upstream side with respect to the image formation units and detects the sheets to output detection data to the correction unit. The correction unit obtains a change amount of the shape of the first sheet with respect to the shape of the second sheet printed before the first sheet on the basis of the detection data, and corrects the printing position of the first image to the first sheet on the basis of the change amount.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present disclosure relates to image forming apparatuses, and more particularly to techniques for correcting printed images. [Background technology]

[0002] When performing double-sided printing, an image forming device prints on the front side of a sheet of paper, then inverts the sheet in a reversing path, prints on the back side of the inverted sheet, and discharges the sheet. When performing double-sided printing continuously, if the size of the sheet of paper changes, the position of the images printed on the front and back of the sheet of paper will shift accordingly. To address this issue, image forming devices have been developed that place an image sensor in the discharge path to read the image printed on the sheet of paper, and correct the printed image according to changes in the size of the sheet of paper.

[0003] Regarding a technique for correcting a printed image, for example, Japanese Patent Application Laid-Open No. 2014-238544 (Patent Document 1) discloses an image forming apparatus that has an image transfer unit, a fixing unit, and an inversion unit, and is capable of transferring an image to the front and back sides of paper, wherein the size measurement unit corrects the image based on the measured size of the paper and is positioned on the transport path so that the time from when the size measurement unit measures the size of the paper to when the paper reaches the transfer position is equal to or longer than the time it takes for the transfer belt to which the corrected image has been transferred to reach the transfer position, and the image correction is performed on at least one of the front and back sides of the paper" (see [Abstract]).

[0004] Further, other techniques relating to correction techniques for images to be printed are disclosed in, for example, Patent Documents 2 to 4. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2014-238544 A [Patent Document 2] JP 2009-42461 A [Patent Document 3] JP 2010-212745 A [Patent Document 4] JP 2017-209935 A Summary of the Invention [Problem to be solved by the invention]

[0006] According to the techniques disclosed in Patent Documents 1 to 4, it is possible to correct image position deviation when the size of the printing paper changes, but in order to correctly control the image position, it is necessary to correctly measure the size of the printing paper, and how to achieve this has been an issue. Therefore, when the shape of the paper changes suddenly during printing, it is not possible to correct the printed image, or even if it is possible, there is a delay in the correction because the correction is controlled after observing the print result. Therefore, there is a need for a technique that can immediately correct the printed image even if the shape of the paper changes during printing.

[0007] The present disclosure has been made in consideration of the above-described background, and an object of one aspect is to provide a technology for instantly correcting a printed image even if the shape of the paper changes during printing. [Means for solving the problem]

[0008] According to one embodiment, there is provided an image forming apparatus. The image forming apparatus includes an image forming unit that prints an image on paper, a correction unit that corrects the printing position of the image on the paper, and a first sensor that is disposed on a conveyance path upstream of the image forming unit and detects the paper and outputs detection data to the correction unit. The correction unit obtains an amount of change in the shape of the first paper relative to the shape of a second paper that was printed before the first paper based on the detection data, and corrects the printing position of the first image on the first paper based on the amount of change.

[0009] In one aspect, correcting the position of the first image formed on the first sheet of paper based on the amount of change includes aligning the size of the margins in the first direction of the second image formed on the second sheet of paper with the size of the margins in the first direction of the first image.

[0010] In one aspect, the margin in the first direction is a margin in the paper feed direction on the transport path of the first sheet and the second sheet, or a margin on the opposite side to the paper feed direction.

[0011] In one aspect, the correction unit corrects the print position of an image on the back side of the first sheet so as to overlap the image on the front side of the first sheet, based on double-sided printing being performed on the first sheet.

[0012] In one aspect, the image forming apparatus further includes a registration roller disposed in the transport path between the image forming unit and the first sensor. The correction unit switches an operation for determining the amount of change based on whether or not the leading edge of the paper strikes the registration roller before the trailing edge of the paper has completely passed the first sensor.

[0013] In one aspect, when the leading edge of the paper does not strike the resist roller before the trailing edge of the paper has completely passed the first sensor, the correction unit calculates the amount of change based on the time from when the first sensor detects the leading edge of the paper to when the trailing edge of the paper passes the first sensor.

[0014] In one aspect, when the leading edge of the paper hits the resist roller before the trailing edge of the paper has completely passed the first sensor, the correction unit calculates the amount of change based on the time from when the paper hits the resist roller, stops, and starts moving again until the trailing edge of the paper passes the first sensor.

[0015] In one aspect, the image forming apparatus further includes a second sensor that detects the paper at a position different from the first sensor on the transport path, and the correction unit ejects the first paper as waste paper based on the difference between the amount of change detected by the first sensor and the amount of change detected by the second sensor, and executes the printing process again.

[0016] In one aspect, the image forming apparatus further includes a third sensor downstream of the image forming unit on the transport path for detecting the paper after the printing process. The correction unit analyzes detection data of the paper after the printing process acquired from the third sensor, and if the image misalignment has occurred due to a change in the shape of the paper, discharges the paper as waste paper and corrects the image misalignment based on the change in the shape of the paper, and if the image misalignment has occurred due to an environmental change, corrects the print position of the image using the measurement result of the third sensor.

[0017] In one aspect, the image forming apparatus further includes an input unit for receiving input of attribute information of the paper or a fourth sensor for acquiring the attribute information. The correction unit acquires the attribute information from the input unit or the fourth sensor, estimates a size change due to a fixing process of the paper based on the attribute information, and adjusts a correction amount of the print position of the image based on the estimated size change.

[0018] In one aspect, the correction unit reduces the amount of correction of the print position of the image in response to determining, based on the attribute information, that the change in size of the paper due to the fixing process is equal to or greater than a predetermined amount.

[0019] In one aspect, the correction unit corrects the printing position of the image printed on the first sheet based on the operation timing of the registration roller or the transfer timing of the image when image misalignment has occurred due to the amount of change, and deforms the image printed on the first sheet when image misalignment has occurred due to the angle, edge shape or distortion of the first sheet.

[0020] According to another embodiment, there is provided a control method for an image forming apparatus, the control method including the steps of: acquiring detection data of a sheet from a first sensor disposed on a transport path upstream of an image forming unit, determining an amount of change in a shape of the first sheet of paper relative to a shape of a second sheet of paper printed before the first sheet of paper based on the detection data, and correcting a printing position of a first image on the first sheet of paper based on the amount of change.

[0021] In one aspect, the step of correcting the position of the first image formed on the first sheet of paper based on the amount of change includes a step of aligning the size of the margins in the first direction of the second image formed on the second sheet of paper with the size of the margins in the first direction of the first image.

[0022] In one aspect, the margin in the first direction is a margin in the paper feed direction on the transport path of the first sheet and the second sheet, or a margin on the opposite side to the paper feed direction.

[0023] In one aspect, the method further includes a step of correcting the printing position of an image on the back side of the first sheet so as to overlap the image on the front side of the first sheet, based on double-sided printing on the first sheet.

[0024] In one aspect, the method further includes a step of switching the operation for determining the amount of change based on whether or not the leading edge of the paper hits a registration roller arranged in the transport path between the image forming unit and the first sensor before the trailing edge of the paper has completely passed the first sensor.

[0025] In one aspect, the method further includes a step of determining the amount of change based on the time from when the first sensor detects the leading edge of the paper to when the trailing edge of the paper passes the first sensor, if the leading edge of the paper does not strike the resist roller before the trailing edge of the paper has completely passed the first sensor.

[0026] In one aspect, the method further includes a step of calculating the amount of change based on the time from when the leading edge of the paper hits the resist roller, stops, and starts moving again until the trailing edge of the paper passes the first sensor, if the leading edge of the paper hits the resist roller before the trailing edge of the paper has completely passed the first sensor.

[0027] In one aspect, the method further includes a step of discharging the first paper as waste paper and performing the printing process again based on a difference between the amount of change detected by the first sensor and the amount of change detected by a second sensor that detects the paper at a position on the transport path different from the first sensor.

[0028] In one aspect, the method further includes a step of analyzing detection data of the paper after printing process obtained from a third sensor that detects the paper after printing process downstream of the image forming unit on the transport path, and if image misalignment has occurred due to a change in the shape of the paper, discharging the paper as waste paper and correcting the image misalignment based on the change in the shape of the paper, and if image misalignment has occurred due to an environmental change, correcting the printing position of the image using the measurement results of the third sensor.

[0029] In one aspect, the method further includes a step of acquiring attribute information from an input unit for accepting input of attribute information of the paper or a fourth sensor for acquiring the attribute information, and a step of estimating a size change due to the fixing process of the paper based on the attribute information, and adjusting a correction amount of the printing position of the image based on the estimated size change.

[0030] In one aspect, the method further includes a step of reducing the amount of correction of the printing position of the image in response to determining, based on the attribute information, that the size change due to the fixing process of the paper is equal to or greater than a predetermined amount.

[0031] In one aspect, the method further includes a step of correcting the printing position of the image printed on the first sheet based on the operation timing of the registration roller or the transfer timing of the image if image misalignment has occurred due to the amount of change, and a step of deforming the image printed on the first sheet if image misalignment has occurred due to the angle, edge shape or distortion of the first sheet. Effect of the Invention

[0032] According to one embodiment, even if the shape of the paper changes during printing, the image to be printed can be instantly corrected.

[0033] The above and other objects, features, aspects and advantages of the present disclosure will become apparent from the following detailed description of the disclosure taken in conjunction with the accompanying drawings. [Brief description of the drawings]

[0034] [Figure 1] FIG. 1 illustrates an example of a hardware configuration of an image forming system 100 according to an embodiment. [Diagram 2] FIG. 2 is a diagram showing an example of a configuration of a main control circuit of an image forming system 100 according to an embodiment. [Diagram 3] FIG. 11 is a diagram showing an example of a first stage of a correction procedure for an image printed on paper. [Figure 4] FIG. 11 is a diagram showing an example of a second stage of the procedure for correcting an image printed on paper. [Diagram 5] FIG. 11 is a diagram showing an example of a third stage of the procedure for correcting an image printed on paper. [Figure 6] FIG. 11 is a diagram showing an example of a fourth stage of the procedure for correcting an image printed on paper. [Figure 7] 2 is a diagram showing an example of the timing of each process in the image forming system 100. FIG. [Figure 8] 4 is a flowchart showing a first example of internal processing in the image forming system 100. [Figure 9] 13 is a flowchart showing a second example of the internal processing in the image forming system 100. [Figure 10] FIG. 2 is a diagram illustrating a second example of a hardware configuration of an image forming system according to an embodiment. [Figure 11] FIG. 13 is a diagram illustrating a third example of a hardware configuration of an image forming system according to an embodiment. [Figure 12] 10A to 10C are diagrams illustrating an example of a correction result of an image position shift amount when the process shown in the flowchart in FIG. 9 is executed. [Figure 13] It is a diagram showing a first application example of image correction by an image forming system according to an embodiment. [Figure 14] It is a diagram showing a second application example of image correction by an image forming system according to an embodiment.

Embodiments for Carrying Out the Invention

[0035] Hereinafter, embodiments of the technical idea according to the present disclosure will be described with reference to the drawings. In the following description, the same parts are denoted by the same reference numerals. Their names and functions are also the same. Therefore, detailed descriptions thereof will not be repeated.

[0036] <A. Configuration of Image Forming System> First, with reference to FIGS. 1 and 2, an example of the hardware configuration and operation outline of the image forming system according to the present embodiment will be described. In a certain aspect, the image forming system according to the present embodiment may include any configuration other than the configurations shown in FIGS. 1 and 2. Further, in another aspect, the image forming system according to the present embodiment may not include a part of the configurations shown in FIGS. 1 and 2.

[0037] FIG. 1 is a diagram showing an example of the hardware configuration of an image forming system 100 according to the present embodiment.

[0038] The image forming system 100 mainly includes a first media detection unit 101, a paper feed sensor 111, an image transfer unit 102, a fixing unit 103, a relay unit 104, a second media detection unit 105, a paper reversing unit 106, and a paper feed tray 130.

[0039] The first media detection unit 101 includes a media sensor 110. The second media detection unit 105 includes media sensors 112 and 113. The image transfer unit 102 includes a photoconductor unit 121 for each color and an intermediate transfer belt 122. The fixing unit 103 includes a fixing roller 123. The image transfer unit 102 and the fixing unit 103 may be collectively referred to as an image forming unit.

[0040] The first media detection unit 101 detects paper conveyed from the paper feed tray 130 using the media sensor 110. The media sensor 110 is, for example, an image sensor. As an example, the image analysis unit 201 (see FIG. 2) can detect the shape of the paper, the type of the paper, or both, by analyzing the image acquired from the media sensor 110. The shape of the paper here can include the size, angle, distortion, etc., of the paper in the vertical and horizontal directions.

[0041] The paper passing sensor 111 may be disposed, for example, near the registration roller 206 (see FIG. 2). The paper passing sensor 111 detects the paper being conveyed. As an example, the image analysis unit 201 may detect that the leading edge of the paper has hit the registration roller 206 based on a signal obtained from the paper passing sensor 111.

[0042] The image transfer unit 102 transfers an image input as a print job onto paper via a photoconductor unit 121 and an intermediate transfer belt 122. The photoconductor unit 121 may include, for example, photoconductor units that form toner images of cyan, magenta, yellow, black (key plate), and special colors. The toner images formed on the photoconductor units 121 of each color are transferred to the intermediate transfer belt 122, and each transferred toner image forms a final color (including black and white) toner image. The toner images transferred to the intermediate transfer belt 122 are transferred onto the paper that is being transported.

[0043] The fixing unit 103 heats the conveyed paper with a fixing roller 123 equipped with a heater, and fixes the toner image on the paper. In the case of single-sided printing, the paper after the fixing process on the front side is conveyed to a relay unit 104. In the case of double-sided printing, the paper after the fixing process on the front side is conveyed to a paper inversion unit 106, and the paper after the fixing process on the back side is conveyed to the relay unit 104.

[0044] The paper inverting unit 106 inverts the paper and returns the inverted paper to the conveyance path upstream of the registration rollers 206. An image is printed on the back side of the paper inverted by the paper inverting unit 106 in the same procedure as on the front side.

[0045] The relay unit 104 transports the paper for which printing has been completed toward the discharge tray. The second media detection unit 105 acquires an image printed on a sheet of paper via the media sensors 112 and 113. The media sensors 112 and 113 are, for example, image sensors. As an example, the image analysis unit 201 may detect a misalignment of an image printed on a sheet of paper by analyzing the image acquired from the media sensors 112 and 113. The image misalignment here may include, for example, a misalignment between a position of an image printed on the front side of a first sheet of paper and a position of an image printed on the front side of a second sheet of paper. The image misalignment may also include a misalignment between a position of an image printed on the front side of a sheet of paper and a position of an image printed on the back side of the sheet of paper.

[0046] 2 is a diagram showing an example of the configuration of a main control circuit of image forming system 100 according to the present embodiment. Image forming system 100 includes, as an example, image forming apparatus 200 and paper tray device 220. In one aspect, image forming system 100 may be realized as a single image forming apparatus including image forming apparatus 200 and paper tray device 220.

[0047] The image forming apparatus 200 includes, as main control circuits, an image analysis unit 201, an image control unit 202, an information I / F (Interface) unit 203, an operation display unit 204, and an image formation control unit 205.

[0048] The image analysis section 201 acquires an image (detection data of the image) from the first media detection unit 101, a signal from the paper passing sensor 111, and an image (detection data of the image) from the second media detection unit 105. Note that the image analysis section may be in one place as shown in the figure, or an image analysis section may be provided for each of the first media detection unit 101 and the second media detection unit 105 to separately receive and analyze the images from each of them, and a third image analysis section may be provided in addition to the above, and the analysis results may be received from each of the image analysis sections, and various controls for image position correction may be performed.

[0049] Furthermore, the image analysis unit 201 analyzes these images and signals, detects changes in the shape of the paper, and corrects the image printed on the paper based on the changes in the shape of the paper. The image correction may include, for example, adjustment of the print position of the image and deformation of the image. Examples of image correction will be described later with reference to FIGS. 3 to 6, 13, and 14. The image analysis unit 201 outputs the amount of image correction to the image control unit 202. Since the image analysis unit 201 corrects the image, it can also be said to be an image correction unit. In a certain aspect, the image analysis unit 201 may obtain information about a print job from the image control unit 202. In this case, the image analysis unit 201 may generate the amount of image correction based on the information about the print job (print image), the image from the first media detection unit 101, the signal from the paper passage sensor 111, and part or all of the image from the second media detection unit 105.

[0050] The image control unit 202 executes the input job. The job may include, for example, a process of printing the image on paper and a process of saving the image as data. When the image control unit 202 acquires the amount of correction of the image, the image control unit 202 outputs a print command of the corrected image to the image formation control unit 205.

[0051] The information I / F unit 203 is an interface for communication with external devices. The information I / F unit 203 can receive a job from an external device and output the job to the image control unit 202. In one aspect, a wired LAN (Local Area Network) port may be used as the information I / F unit 203. In another aspect, a Wi-Fi (registered trademark) module may be used as the information I / F unit 203. The information I / F unit 203 can transmit and receive data using communication protocols such as TCP / IP (Transmission Control Protocol / Internet Protocol) and UDP (User Datagram Protocol).

[0052] The operation display unit 204 presents information to the user and receives input operations from the user. The input operation may include, for example, print settings. In one aspect, the operation display unit 204 may be an operation panel including a display and operation buttons. In this case, the display may include a liquid crystal monitor, an organic EL (Electro Luminescence) monitor, etc. The liquid crystal monitor, the organic EL monitor, etc. may include a touch sensor, display an operation menu, and receive input by touch from the user.

[0053] The image formation control unit 205 controls the image transfer unit 102 based on the print command acquired from the image control unit 202. In one aspect, the image formation control unit 205 may also control the fixing unit 103. In another aspect, the function of the image formation control unit 205 may be included in the image control unit 202.

[0054] <B. Correction of Printed Image> Next, with reference to FIGS. 3 to 6, it will be described how the image printed on the paper is corrected when the shape (length in the paper conveyance direction) of the paper changes (correction in the case where the shape of the paper is distorted will be described later with reference to FIGS. 13 and 14). Further, the image forming system 100 may perform different operations for each length in the paper conveyance direction of the conveyed paper, and the operation of the image forming system 100 will also be described.

[0055] (a. Image correction procedure) 3 is a diagram showing an example of a first stage of a correction procedure for an image printed on a sheet of paper. First, the image analysis unit 201 detects a reference length of the sheet of paper based on an image (image of the sheet of paper) acquired from the first media detection unit 101, and sets the length of the sheet of paper in the sheet feed direction as, for example, a reference length of "X mm". Next, the image control unit 202 performs double-sided printing on the sheet of paper. Assume that an image 310A is printed on the front side 300A of the sheet of paper, and an image 310B is printed on the back side 300B of the sheet of paper.

[0056] The paper may be created by the user by cutting a roll of paper, and is not necessarily the same length. For example, even if the image forming device 200 recognizes the paper being conveyed as A4 size, in reality, there is some error in the length of the paper in the paper feed direction, so the front and back margins of the paper are not uniform. In the example shown in FIG. 3, the leading margin in the paper feed direction on the front surface 300A of the paper is "A mm" and the trailing margin is "B mm", which are different lengths. In this case, when the image forming device 200 prints on both sides of the paper, the orientation of the image changes between the front surface 300A and the back surface 300B of the paper, and the printing position of the image is shifted between the front surface 300A and the back surface 300B of the paper.

[0057] Image analysis unit 201 stores the reference length of the paper "Xmm" (length in the paper feed direction), the leading margin "Amm", and the trailing margin "Bmm". In one aspect, image analysis unit 201 may be provided with a storage device (not shown) for storing the reference length of the paper "Xmm", the leading margin "Amm", and the trailing margin "Bmm", or may use a storage device located elsewhere.

[0058] Fig. 4 is a diagram showing an example of a second stage of the correction procedure for an image printed on a sheet of paper. After executing the process described with reference to Fig. 3, if the image analysis unit 201 detects a sheet of paper having a reference length of "X mm" in the paper feed direction based on the image acquired from the first media detection unit 101, the image analysis unit 201 corrects the image so that the positions of the images printed on both sides of the sheet of paper match.

[0059] More specifically, the image analysis unit 201 generates a correction amount (print setting correction amount) based on the reference length "Xmm", the leading margin "Amm", and the trailing margin "Bmm" (or based on the amount of image position shift between the front and back) so that the leading margin and the trailing margin in the paper feed direction are the same, and outputs the correction amount to the image control unit 202.

[0060] In the example shown in Fig. 4, image analysis unit 201 generates a correction amount so that the leading and trailing margins of image 410A printed on front surface 400A of the paper are "Cmm". In this case, since the leading and trailing margins are equal, when image forming apparatus 200 prints on both sides of the paper, the position of image 410A printed on front surface 400A of the paper matches the position of image 410B printed on back surface 400B of the paper. In this way, when image forming system 100 detects a paper whose length in the paper feed direction is the reference length "Xmm", it can correct the positional deviation of the image by correcting the image as described above.

[0061] 5 is a diagram showing an example of a third stage of the procedure for correcting an image printed on paper. Next, image correction when image forming apparatus 200 prints an image on paper having a length different from the reference length "X mm" will be described.

[0062] After executing the process described with reference to FIG. 3, when the image analysis unit 201 detects a sheet whose length in the paper feed direction is not the reference length "X mm" based on the image acquired from the first media detection unit 101 (when detecting the change in the shape of the sheet), the image analysis unit 201 generates a correction amount so that the leading margin of the image 510A on the front surface 500A of the sheet is always constant (for example, "Cmm"). Next, when printing the image 510B on the back surface 500B of the sheet, the image analysis unit 201 generates a correction amount so that the trailing margin of the image 510B on the back surface 500B of the sheet always matches the leading margin of the image 510A on the front surface 500A of the sheet (in this case, "Cmm"). In this way, the image forming system 100 can always keep one margin of the sheet constant. In the example shown in FIG. 5, the image forming system 100 can always keep one margin of the sheet at "Cmm".

[0063] In one aspect, image analysis unit 201 may generate a correction amount so that the end margin of image 510A on front side 500A of the paper is always constant. In this case, image analysis unit 201 generates a correction amount so that the leading margin of image 510B on back side 500B of the paper always matches the end margin of image 510A on front side 500A of the paper.

[0064] Fig. 6 is a diagram showing an example of a fourth stage of the procedure for correcting an image printed on paper. As described with reference to Figs. 3 to 5, when printing on paper of different lengths, the image forming system 100 always prints an image on the paper so that the margin on one side of the paper is a length "Cmm" calculated based on the reference length "Xmm" of the paper. This allows the user to easily align the shape of the paper and center the print position of the image on the paper by cutting one margin of the printed paper (the uneven margin) to "Cmm".

[0065] (b. Overview of operation of image forming device for each paper) As described with reference to Figures 3 to 6, image forming system 100 can print an image while always keeping one margin of the paper constant. In order to always keep one margin of the paper constant even when the shape of the paper (length in the paper feed direction) changes suddenly, image forming system 100 selectively uses a first operating procedure and a second operating procedure described below.

[0066] First, the first operation procedure will be described with reference to Fig. 2. When the image forming system 100 detects a short sheet of paper, it executes the first operation procedure. Here, a short sheet of paper means a sheet of paper whose leading edge does not strike the registration roller 206 between the time when the leading edge of the sheet passes the media sensor 110 and the time when the trailing edge of the sheet passes the media sensor 110. In other words, a short sheet of paper is a sheet of paper whose length in the paper feed direction is shorter than the transport path between the media sensor 110 and the registration roller 206.

[0067] When a short sheet of paper is transported from the paper feed tray 130, the image analysis unit 201 detects the shape of the image (the length in the paper feed direction) before the printing process based on changes in the image obtained from the media sensor 110 (the image changes significantly when the beginning and end of the paper pass the media sensor 110).

[0068] Next, image control unit 202 executes printing processing on the front side of the paper so that the leading margin on the front side of the paper is constant (for example, so that the leading margin is always "Cmm"). In one aspect, when printing an image on the front side of the paper, image control unit 202 may always use a correction value generated based on a reference length "Xmm" that is the length in the paper feed direction of the first sheet of paper (for example, a test printing sheet).

[0069] Next, image control unit 202 executes printing processing on the back side of the paper so that the rear margin on the back side of the paper is constant (for example, so that the rear margin is always "Cmm") based on the correction value acquired from image analysis unit 201. In other words, image control unit 202 adjusts the front margin on the back side of the paper.

[0070] As described above, when performing printing processing on short paper, the image forming system 100 can detect the change in the length of the paper in the paper feed direction from the image obtained from the media sensor 110 before the printing processing, and correct the image to be printed on the paper based on the change in the length of the paper in the paper feed direction.

[0071] Next, the second operation procedure will be described. When the image forming system 100 detects a long sheet of paper, it executes the second operation procedure. Here, the long sheet of paper means a sheet of paper whose leading edge abuts against the registration roller 206 between the time when the leading edge of the sheet passes the media sensor 110 and the time when the trailing edge of the sheet passes the media sensor 110. In other words, the long sheet of paper is a sheet of paper whose length in the paper feed direction is equal to or longer than the conveyance path between the media sensor 110 and the registration roller 206.

[0072] When a long sheet of paper is conveyed from the paper feed tray 130, the image analysis unit 201 measures the time from the timing when the leading edge of the sheet hits the registration roller 206, pauses, and conveyance is restarted, to the timing when the trailing edge of the sheet passes the media sensor 110. By measuring the time from the timing when the leading edge of the sheet hits the registration roller 206, pauses, and conveyance is restarted, to the timing when the trailing edge of the sheet passes the media sensor 110, the image analysis unit 201 can detect how much the shape of the current sheet (length in the paper feed direction) has changed from the shape of the previous sheet (length in the paper feed direction) without measuring the exact shape of the sheet (length in the paper feed direction). The image analysis unit 201 generates a correction value based on the change in the shape of the current sheet (length in the paper feed direction) from the shape of the previous sheet (length in the paper feed direction), and outputs the correction value to the image control unit 202.

[0073] Next, image control unit 202 executes printing processing on the front side of the paper so that the leading margin on the front side of the paper is constant (for example, so that the leading margin is always "Cmm"). In one aspect, when printing an image on the front side of the paper, image control unit 202 may always use a correction value generated based on a reference length "Xmm" that is the length in the paper feed direction of the first sheet of paper (for example, a test printing sheet).

[0074] Next, image control unit 202 executes printing processing on the back side of the paper so that the end margin on the front side of the paper is constant (for example, so that the end margin is always "Cmm") based on the correction value acquired from image analysis unit 201. In other words, image control unit 202 adjusts the start margin on the back side of the paper.

[0075] As described above, when performing printing processing on long paper, the image forming system 100 can detect the change in the length of the paper in the paper feed direction from the image obtained from the media sensor 110 after the paper hits the registration roller 206 before the printing processing, and correct the image to be printed on the paper based on the change in the length of the paper in the paper feed direction.

[0076] Whether short paper or long paper is detected, image forming system 100 does not need to measure the absolute value of the length of the paper in the paper feed direction, but only needs to find the amount of change in the shape of the current paper relative to the shape of the paper used in the previous printing (or the reference paper used in test printing). Since image forming system 100 detects the change in the shape of the paper (length in the paper feed direction) before printing, it can immediately correct the image printed on the paper even if the shape of the paper (length in the paper feed direction) changes suddenly.

[0077] Further, the image forming system 100 may print while always keeping the leading margin on the front surface of the paper constant, and only adjust the leading margin on the back surface of the paper (match the trailing margin on the back surface of the paper to the leading margin on the back surface of the paper). By doing so, even when the time from when the media sensor 110 measures the shape (length in the paper feed direction) of the paper until the front surface of the paper reaches the transfer position is short (even when there is no time to correct the image on the front surface of the paper), the image forming system 100 can always make the position of the image on the front surface of the paper coincide with the position of the image on the back surface.

[0078] In a certain situation, when the time or distance from when the media sensor 110 measures the shape (length in the paper feed direction) of the paper until the front surface of the paper reaches the transfer position is sufficiently ensured, the image forming system 100 may also correct the position of the image printed on the front surface of the paper each time. The situation where the time or distance from when the media sensor 110 measures the shape (length in the paper feed direction) of the paper until the front surface of the paper reaches the transfer position is sufficiently ensured means that the image control unit 202 can complete the printing settings including the correction value from when the media sensor 110 measures the shape (length in the paper feed direction) of the paper until the front surface of the paper reaches the transfer position.

[0079] <C. Processing Procedure of Image Forming System> Next, with reference to FIGS. 7 to 9, the internal processing of the image forming system 100 will be described. FIG. 7 is a diagram showing an example of the timing of each process in the image forming system 100.

[0080] In step S705, the image control unit 202 starts the printing operation and starts transporting the paper from the paper feed tray 130.

[0081] In step S710, the first media detection unit 101 detects the paper. A period 701 is a period during which the paper passes through the first media detection unit 101 (media sensor 110). The image analysis unit 201 generates a correction value for the image based on an image 750 acquired from the first media detection unit 101. The correction value for the image may include both or one of a correction value for an image printed on the front side of the paper and a correction value for an image printed on the back side of the paper.

[0082] When the time or distance from when the shape of the paper (length in the paper feed direction) is measured until the front side of the paper arrives at the transfer position is sufficiently secured, image analysis unit 201 outputs correction value 760 of the image to be printed on the front side of the paper to image control unit 202. If not, image control unit 202 may always print an image on the front side of the paper using the same correction value (for example, the setting of the top margin "Cmm" shown in FIG. 4). Image control unit 202 generates print settings using the acquired correction value 760 and outputs the print settings to image formation control unit 205.

[0083] In step S715, the image transfer unit 102 transfers the toner image onto the front surface of the paper. The transfer position of the toner image can be corrected based on the correction value 760. For example, the position of the image can be corrected so that the top margin on the front surface of the paper is always "Cmm". Furthermore, the fixing unit 103 fixes the toner image onto the front surface of the paper.

[0084] In step S720, paper inverting unit 106 inverts the paper and returns the inverted paper to the transport path upstream of registration rollers 206. Image analysis unit 201 outputs correction values ​​765 of the image to be printed on the back side of the paper to image control unit 202. Image control unit 202 generates print settings using the acquired correction values ​​765 and outputs the print settings to image formation control unit 205. In one aspect, image analysis unit 201 may output correction values ​​765 of the image to be printed on the back side of the paper to image control unit 202 at a timing prior to step S715.

[0085] In step S725, the image transfer unit 102 transfers the toner image onto the back surface of the paper. The transfer position of the toner image can be corrected based on the correction value 765. For example, the position of the image can be corrected so that the end margin on the back surface of the paper is always "Cmm". Furthermore, the fixing unit 103 fixes the toner image onto the back surface of the paper.

[0086] In step S730, the second media detection unit 105 outputs an image 770 of the printed paper to the image analysis unit 201. The image analysis unit 201 may output correction values ​​780 and 785 obtained by further adjusting the correction values ​​760 and 765 based on the image 770 acquired from the second media detection unit 105 to the image control unit 202. For example, there may be a case where the paper is deformed due to heat and humidity inside the image forming apparatus 200. Therefore, the image analysis unit 201 may detect a shift in the print result of the image acquired from the second media detection unit 105, and generate correction values ​​780 and 785 obtained by further adjusting the correction values ​​760 and 765 based on the detected shift.

[0087] In step S735, the relay unit 104 or the like ejects the printed paper. Fig. 8 is a flowchart showing a first example of internal processing in image forming system 100. The flowchart shown in Fig. 8 shows processing for performing image correction without using second media detection unit 105 during printing. In one aspect, image analysis unit 201 or image control unit 202 may load a program for performing the processing of Fig. 8 from a non-volatile storage medium (not shown) into a main storage device (not shown) and execute the program. In another aspect, a part or all of the processing may be realized as a combination of circuit elements configured to execute the processing.

[0088] In step S805, image forming system 100 detects that paper has been set in paper feed tray 130. Image forming system 100 may also detect an operation input for test printing of paper. Test printing here refers to printing for determining the length of a margin by using the length of the test printed paper in the paper feed direction as a reference length (corresponding to the processing described with reference to FIGS. 3 and 4).

[0089] In step S810, image forming system 100 measures the shape of the paper (length in the paper feed direction) using first media detection unit 101. In one aspect, when a long paper sheet is transported from paper feed tray 130, image forming system 100 may measure the time from when the leading edge of the paper hits registration roller 206, causing it to temporarily stop, and when transport is restarted, until when the trailing edge of the paper passes media sensor 110.

[0090] In step S815, image forming system 100 obtains an image of the printed paper using second media detection unit 105, and adjusts the print settings for the front and back sides. More specifically, image forming system 100 can adjust subtle deviations, distortions, and the like between the position of the image on the front side of the paper and the position of the image on the back side of the paper in the actual print result.

[0091] In step S820, the image forming system 100 stores the paper shape and image position (for example, the length in the paper feed direction "X mm" and the margin "C mm") as a set in the main memory device or a non-volatile memory medium. Through the processing from steps S805 to S820, the image forming system 100 can determine the initial print settings (for example, determining the length in the paper feed direction to be "X mm" and the margin to be "C mm").

[0092] In step S825, the image forming system 100 starts a print job using paper from the same paper feed tray 130.

[0093] In step S830, the image forming system 100 repeatedly executes the processes from step S835 onwards until the print job is completed.

[0094] In step S835, image forming system 100 measures the shape of the paper (the amount of change in length in the paper feed direction) using first media detection unit 101. In one aspect, when a long paper sheet is transported from paper feed tray 130, image forming system 100 may measure the time from when the leading edge of the paper hits registration roller 206, pauses, and then transport is restarted, until the trailing edge of the paper passes media sensor 110. Image forming system 100 does not need to measure the absolute value of the length of the paper in the paper feed direction, and only needs to find the amount of change in the shape of the current paper sheet relative to the shape of the paper sheet used in the previous printing (or the reference paper sheet used in test printing).

[0095] In step S840, image forming system 100 updates the correction values ​​and print settings based on the shape of the paper (length in the paper feed direction).

[0096] In step S845, image forming system 100 executes printing based on the updated correction values ​​and print settings. In one aspect, if there is sufficient time or distance between when media sensor 110 measures the shape of the paper (length in the paper feed direction) and when the front side of the paper reaches the transfer position, image forming system 100 may also correct the position of the image printed on the front side of the paper every time. In another aspect, image forming system 100 may print so that the leading margin of the front side of the paper is always kept constant, and adjust only the leading margin of the back side of the paper.

[0097] In step S850, if the print job is completed, the image forming system 100 ends the process. If not, the image forming system 100 repeatedly executes the processes from step S835 onward. In one aspect, the image forming system 100 may determine whether the print job is completed at the timing of step S830.

[0098] FIG. 9 is a flowchart showing a second example of the internal processing in the image forming system 100. The flowchart shown in FIG. 9 shows a process of performing image correction using the second media detection unit 105 during printing. In one aspect, the image analysis unit 201 or the image control unit 202 may load a program for performing the processing of FIG. 9 from a non-volatile storage medium into a main storage device and execute the program. In another aspect, a part or all of the processing may be realized as a combination of circuit elements configured to perform the processing. Among the processes shown in FIG. 9, the same processes as those in FIG. 8 are assigned the same step numbers. Therefore, the description of the same processes will not be repeated.

[0099] In step S950, image forming system 100 measures the print result with second media detection unit 105. In one aspect, image forming system 100 may analyze the image (paper detection data) acquired from second media detection unit 105 and determine whether the image misalignment has occurred due to a change in the shape of the paper or due to an environmental change.

[0100] When image misalignment occurs due to a change in the shape of the paper, the image forming system 100 may discharge the paper as waste paper and correct the image misalignment based on the change in the shape of the paper. Also, when image misalignment occurs due to an environmental change, the image forming system 100 may correct the print position of the image using the image acquired from the second media detection unit 105.

[0101] In step S955, image forming system 100 calculates the amount of front-back misalignment of the image (the amount of misalignment between the position of the image on the front side of the paper in the print result and the position of the image on the back side of the paper).

[0102] In step S960, the image forming system 100 calculates an additional correction value in order to correct the change in the front-back misalignment amount. At this time, in order to avoid a sudden change, the image forming system 100 sets an upper limit on the change in the correction amount for each printed sheet.

[0103] In step S965, the image forming system 100 then updates the correction value for the page on which image formation is to be performed next. More specifically, the image forming system 100 can update the final correction value and the printing settings based on the additional correction value obtained in step S960 and the shape of the paper (length in the paper feeding direction) obtained in steps S835 and S840 in the next loop.

[0104] <D. Application Example> Next, with reference to FIGS. 10 to 14, an application example of the image forming system 100 will be described. In a certain aspect, the disclosure contents shown in FIGS. 1 to 14 can be used in appropriate combination.

[0105] FIG. 10 is a diagram showing a second example of the hardware configuration of the image forming system according to the present embodiment. The image forming system 1000 further includes sensors 1001, 1002, and 1003 in addition to the configuration of the image forming system 100.

[0106] Sensors 1001 and 1002 are sensors for detecting the type or attributes of the paper. In a certain aspect, sensors 1001 and 1002 may be paper thickness sensors or tub amount sensors. The paper thickness sensor and the tub amount sensor can measure the thickness or weight of the paper. As an example, sensors 1001 and 1002 may be contact sensors or non-contact sensors that directly measure the thickness, or may measure the surface shape of the paper, the glossiness of the paper, the stiffness of the paper, the strength against bending of the paper, the light transmission amount of the paper, etc. The image analysis unit 201 can estimate the thickness of the paper based on this information.

[0107] The behavior of the paper when it is transported by the transport rollers may change depending on the hardness and thickness of the paper. For example, if the paper hits the transport rollers at an angle, the way the paper bends and the way it is bitten by the next transport roller may change, which may affect the image drawing position. Therefore, the image analysis unit 201 may predict the change in the position of the image to be printed from the change in the shape of the paper, and adjust the correction value of the image to be printed on the paper based on the prediction.

[0108] The image analysis unit 201 may also use a prediction formula for predicting changes in image position from changes in the shape of each sheet of paper having representative paper characteristics. The image analysis unit 201 may select a representative sheet of paper whose physical properties are close to those measured by the paper thickness and ink amount sensor, and correct the front-to-back misalignment using the prediction formula for the selected representative sheet of paper.

[0109] In another aspect, the sensors 1001 and 1002 may be gloss sensors and smoothness sensors. The gloss sensors and smoothness sensors measure the gloss and smoothness of the paper surface. Differences in the gloss and smoothness of the paper surface affect, for example, the amount of slippage when the paper is transported by a transport roller.

[0110] In still another aspect, the sensors 1001 and 1002 may be moisture content sensors. The characteristics of paper change significantly depending on the moisture content of the paper. For example, if the paper is dry, the paper shrinks less due to fixing, and the amount of charge increases during paper transport, making the paper more likely to be attracted to a transport roller. The moisture content can be determined, for example, by measuring the electrical conductivity of the paper.

[0111] Image analysis unit 201 may further adjust the correction value of the image printed on the paper based on the type or attribute information of the paper obtained from sensors 1001 and 1002. In one aspect, image analysis unit 201 may receive input of attribute information from operation display unit 204. Also, image analysis unit 201 may estimate a size change due to a fixing process of the paper based on the attribute information, and adjust the correction amount of the print position of the image based on the estimated size change. Also, in another aspect, image analysis unit 201 may reduce the correction amount of the print position of the image based on determining that a size change due to a fixing process of the paper is equal to or greater than a predetermined amount based on the attribute information, so as not to change the image position suddenly.

[0112] The sensor 1003 is a paper passing sensor and can be used to determine abnormality of the paper. It is assumed that the length of the next paper is 1% longer than that of the previous paper. In this case, it is predicted that the time required for the paper to pass each image sensor or paper passing sensor will also be 1% longer. If the amount of change in the paper passing time does not match between the respective sensors, it is considered that some change has occurred in the paper while the paper is passing through the transport path. For example, if the time (or the amount of change) at which the paper passes through the sensor 1003 does not match the time (or the amount of change) at which the paper passes through the media sensor 110, some change may have occurred in the paper and the change in the length of the paper in the paper passing direction may not be measured correctly. In this case, the image forming system 100 may discharge the paper as waste paper to the abnormal paper discharge path and execute the print process again. In addition, the image forming system 100 may display a message on the operation display unit 204 to notify the user that an abnormality has occurred, or may transmit the message to the user's computer. Note that the position of the sensor 1003 used here is not limited to that shown in the figure. For example, in a case where multiple paper trays are connected in series to the printer body, the sensor can be placed at a location farther away from the printer body, and this can function effectively when printing on longer paper.

[0113] It should be noted that the sensors 1001, 1002, and 1003 shown in FIG. 10 are merely examples, and the type, number, and arrangement of the sensors 1001, 1002, and 1003 can be determined arbitrarily.

[0114] 11 is a diagram showing a third example of the hardware configuration of an image forming system according to the present embodiment. Image forming system 1000 includes a media sensor 1110 in addition to the components of image forming system 100.

[0115] The length of the paper A to be printed next is the length of whether or not the tail of the paper passes the media sensor 110 when the leading edge of the paper A hits the registration roller 206 and stops temporarily. A sudden change occurs in the paper conveying speed or the paper path before and after the paper A hits the registration roller 206 and stops temporarily. Therefore, the image analysis unit 201 may not be able to stably measure the change in the length of the paper A using only the media sensor 110. Therefore, the image forming system 1100 includes a media sensor 1110, for example, slightly upstream of the media sensor 110. The paper A passes through the media sensor 1110 before the leading edge of the paper A hits the registration roller 206. Therefore, the media sensor 1110 can stably measure the change in the length of the paper A in the paper feed direction (first operation procedure).

[0116] Furthermore, it is assumed that the length of the paper B to be printed next is the length at which the tail of the paper passes the media sensor 1110 when the leading edge of the paper B hits the registration roller 206 and stops temporarily. In this case, the paper B has not yet passed the media sensor 110 when the leading edge of the paper B hits the registration roller 206 and stops. Therefore, the media sensor 110 can stably measure the change in the length of the paper B in the paper feed direction (second operation procedure).

[0117] In this way, by providing the two media sensors 110, 1100, the image forming system 1000 can measure the change in length in the paper feed direction of paper of any shape, including paper of an odd length.

[0118] Fig. 12 is a diagram showing an example of the result of correcting the amount of image misalignment when the process shown in the flowchart of Fig. 9 is executed. The amount of image misalignment can include, for example, the amount of deviation of the image from the center of the paper, the amount of misalignment between the image position on the front side and the image position on the back side of the paper, etc.

[0119] Graphs 1210 and 1220 show the change in the amount of image positional deviation of an image printed on paper when the image forming system 100 does not perform image correction. Graphs 1260 and 1270 show the measurement results of the amount of change in the shape of the paper. Graph 1250 shows the correct position (correct amount of correction).

[0120] According to graphs 1210 and 1220, when image forming system 100 does not perform image correction, the image misalignment amount gradually increases. In addition, the image misalignment amount changes significantly at timing 1230. From this, it is presumed that the shape of the paper placed on paper feed tray 130 changed at timing 1230.

[0121] Each image forming system according to the present embodiment can correct the image misalignment amount of the paper by using the measurement result obtained from the second media detection unit 105, and can suppress a gradual increase in the image misalignment amount caused by environmental changes, etc., as shown in graphs 1210 and 1220. Also, each image forming system according to the present embodiment can suppress a sudden increase in the image misalignment amount caused by changes in the shape of the paper, etc., as shown at timing 1230, by using the measurement result obtained from the first media detection unit 101. Graph 1280 shows a change in the image misalignment amount when each image forming system according to the present embodiment corrects the image using the measurement results of the first media detection unit 101 and the second media detection unit 105. Graph 1280 can take a value close to graph 1250 of the correct position.

[0122] 13 is a diagram showing a first application example of image correction by the image forming system according to the present embodiment. The image forming system (image forming systems 100, 1000, 1100) further includes a paper bias detection sensor 1300. The paper bias detection sensor 1300 may be provided, for example, upstream of the registration rollers 206 in the conveyance path.

[0123] First, the image analysis unit 201 detects a distance 1320A from the paper bias detection sensor 1300 to the surface 1310A of the paper based on a signal from the paper bias detection sensor 1300.

[0124] Next, based on a signal from the paper bias detection sensor 1300, the image analysis unit 201 detects a distance 1320B from the paper bias detection sensor 1300 to the back surface 1310B of the paper.

[0125] Next, the image analysis unit 201 calculates the amount of deviation between the position of the image 1330A printed on the front side 1310A of the paper and the position of the image 1330B printed on the back side 1310B of the paper, based on the difference between the distances 1320A and 1320B.

[0126] Finally, image analysis unit 201 calculates the amount of correction for the image based on the amount of misalignment, and outputs the amount of correction to image control unit 202. Image control unit 202 aligns the position of image 1330A printed on front surface 1310A of the paper with the position of image 1330B printed on back surface 1310B of the paper based on the amount of correction.

[0127] In one aspect, image control unit 202 may align the position of image 1330B printed on back surface 1310B of the paper with the position of image 1330A printed on front surface 1310A of the paper based on the amount of correction. In another aspect, if a sufficient time or distance is ensured between when media sensor 110 measures the shape of the paper (length in the paper feed direction) and when the front surface of the paper arrives at the transfer position, image control unit 202 may also correct the position of image 1330A printed on front surface 1310A of the paper based on the amount of correction. In another aspect, image control unit 202 may detect paper bias, etc. using media sensor 110 instead of paper bias detection sensor 1300, or may detect paper bias, etc. using both media sensor 110 and paper bias detection sensor 1300.

[0128] As described above, the image forming system can also correct image position deviation in the direction perpendicular to the paper feed direction by detecting bias of the paper or the like.

[0129] 14 is a diagram showing a second application example of image correction by the image forming system according to the present embodiment. The image analysis unit 201 can detect a change in the shape of the paper (distortion such as a change from a rectangle to a trapezoid) by using the media sensor 110, the paper deviation detection sensor 1300, or both.

[0130] When the image analysis unit 201 detects a change in the shape of the paper (such as the angle of the paper, the shape or distortion of the edge), it may generate a correction value to change the shape of the image to match the change in the shape of the paper, and output the correction value to the image control unit 202.

[0131] In one aspect, image analysis unit 201 may generate a correction value to change the shape of the image in accordance with the shape of an edge in the paper feed direction. In another aspect, image analysis unit 201 may generate a correction value to change the shape of the image in accordance with the shape of an edge on the opposite side to the paper feed direction. In yet another aspect, image analysis unit 201 may generate a correction value to change the shape of the image in accordance with the shape of any edge of the paper. In yet another aspect, image analysis unit 201 may generate a correction value so that an image printed on the front side of the paper and an image printed on the back side of the paper overlap with each other.

[0132] The image forming system can detect all or some of the changes in the length of the paper in the paper feed direction, the changes in the paper skew, and the changes in the edges of the paper, and generate correction values ​​for the image in accordance with these changes.

[0133] In one aspect, when image misalignment occurs due to a change in the length of the paper, image analysis unit 201 may correct the print position of the image based on the operation timing of registration roller 206 or the transfer timing of the image. In another aspect, when image misalignment occurs due to the angle, edge shape, or distortion of the paper, image analysis unit 201 may deform the image printed on the paper (may correct the shape of the image).

[0134] As described above, the image forming system according to the present embodiment can correct the image printed on the paper based on the change in the shape of the paper. This allows the image forming system to appropriately adjust the print position of the image even if the shape of the paper changes suddenly during printing.

[0135] The embodiments disclosed herein should be considered to be illustrative and not restrictive in all respects. The scope of the present disclosure is indicated by the claims, not by the above description, and is intended to include all modifications within the meaning and scope of the claims. In addition, the disclosure contents described in the embodiments and each modified example are intended to be implemented, as far as possible, either alone or in combination. [Explanation of symbols]

[0136] 100,1000,1100 Image forming system, 101 First media detection unit, 102 Image transfer unit, 103 Fixing unit, 104 Relay unit, 105 Second media detection unit, 106 Paper reversing unit, 110,112,113,1110 Media sensor, 111 Paper passing sensor, 121 Photoconductor unit, 122 Intermediate transfer belt, 123 Fixing roller, 130 Paper feed tray, 200 Image forming device, 201 Image analysis unit, 202 Image control unit, 203 Information I / F unit, 204 Operation display unit, 205 Image formation control unit, 206 Registration roller, 220 Paper tray device, 300A,400A,500A,1310A Surface, 300B,400B,500B,1310B Back side, 310A, 310B, 410A, 410B, 510A, 510B, 750, 770, 1330A, 1330B Image, 701 Period, 760, 765, 780, 785 Correction value, 1001, 1002, 1003 Sensor, 1210, 1220, 1250, 1260, 1270, 1280 Graph, 1230 Timing, 1300 Paper bias detection sensor, 1320A, 1320B Distance.

Claims

1. An image forming unit that forms an image on a recording medium; a first sensor provided upstream of the image forming unit in a conveyance path of the recording medium, the first sensor acquiring information regarding a size of the recording medium; a second sensor provided downstream of the image forming unit in a conveyance path of the recording medium, the second sensor reading the recording medium and generating a read image; a control unit for controlling a position where an image is formed on the recording medium, The control unit is correcting a formation position of an image on the second recording medium based on information regarding a size of the first recording medium acquired by the first sensor and information regarding a size of a second recording medium, different from the first recording medium, on which an image is formed later than the first recording medium, acquired by the first sensor; an image forming apparatus that adjusts a forming position of an image on the second recording medium based on the read image generated by the second sensor;

2. 2. The image forming apparatus according to claim 1, wherein the control unit corrects the image formation position on the second recording medium based on the amount of change between the information regarding the size of the first recording medium acquired by the first sensor and the information regarding the size of the second recording medium.

3. The image forming apparatus according to claim 1 , wherein the control unit sets a margin area on the recording medium based on information about a size of the recording medium acquired by the first sensor.

4. The image forming apparatus according to claim 3 , wherein the blank area is an area to be cut.

5. 5. An image forming apparatus as described in claim 3, wherein when forming an image on a second side of the recording medium, which is different from the first side of the recording medium having an image formed on the first side, a margin area on the recording medium is set based on information regarding the size of the recording medium obtained by the first sensor.

6. 6. The image forming apparatus according to claim 5, further comprising: a margin area set at an end portion on a leading edge side in a transport direction of the second surface of the recording medium based on information regarding a size of the recording medium acquired by the first sensor.

7. 7. The image forming apparatus according to claim 5, wherein a margin area at an end portion on a leading end side in a conveying direction of the first surface of the recording medium is a preset area.

8. 8. The image forming apparatus according to claim 1, wherein the control unit controls a storage unit to store information regarding the size of the first recording medium.

9. 9. The image forming apparatus according to claim 1, wherein the first sensor includes a reading unit that reads the recording medium.

10. 10. The image forming apparatus according to claim 1, wherein the first sensor further includes a sensor for detecting a type of the recording medium.

11. 11. The image forming apparatus according to claim 1, wherein the first sensor further includes a sensor for detecting an attribute of the recording medium.

12. 12. The image forming apparatus according to claim 10, wherein the first sensor is at least one of a paper thickness sensor, a pore volume sensor, a glossiness sensor, a smoothness sensor, and a moisture content sensor.

13. An image forming apparatus as described in any one of claims 1 to 12, further comprising an analysis unit that detects a positional misalignment between an image formed on a first surface of the recording medium and an image formed on a second surface different from the first surface of the recording medium based on the read image generated by the second sensor.

14. The image forming apparatus according to any one of claims 10 to 12, wherein the control unit corrects a position at which an image is formed on the recording medium based on the detection result of the first sensor and the read image generated by the second sensor.

15. A method for controlling an image forming apparatus, comprising: acquiring information about the size of the recording medium by a first sensor provided upstream of the image forming unit in a conveyance path of the recording medium; a step of reading the recording medium with a second sensor provided downstream of the image forming unit in a conveyance path of the recording medium to generate a read image; controlling a position where an image is formed on a recording medium; The step of controlling the image formation position includes: correcting a formation position of an image on the second recording medium based on information on a size of the first recording medium acquired by the first sensor and information on a size of a second recording medium, different from the first recording medium, on which an image is formed later than the first recording medium, acquired by the first sensor; adjusting a forming position of an image on the second recording medium based on the read image generated by the second sensor; A control method comprising:

16. The control method according to claim 15, wherein the control step corrects the image formation position on the recording medium based on the amount of change between the information regarding the size of the first recording medium acquired by the first sensor and the information regarding the size of the second recording medium.

17. 17. The control method according to claim 15, further comprising the step of setting a margin area on the recording medium based on information about a size of the recording medium obtained by the first sensor.

18. The control method according to claim 17 , wherein the blank area is an area to be cut.

19. The control method according to claim 17 or 18, wherein the step of setting the margin area sets a margin area on the recording medium based on information regarding the size of the recording medium acquired by the first sensor when an image is formed on a second side, which is different from the first side, of the recording medium on which an image has been formed on the first side.

20. The control method according to claim 19, wherein the step of setting the margin area sets a margin area at an end portion on the leading edge side in the transport direction of the second surface of the recording medium based on information regarding the size of the recording medium acquired by the first sensor.

21. 21. The control method according to claim 19, wherein the margin area at the end portion on the leading edge side in the transport direction of the first surface of the recording medium is a preset area.

22. A control method according to any one of claims 15 to 21, further comprising a step of storing information regarding the size of the first recording medium in a memory unit.

23. A control method described in any one of claims 15 to 22, wherein the first sensor further includes a sensor that detects the type of the recording medium.

24. A control method described in any one of claims 15 to 23, wherein the first sensor further includes a sensor that detects an attribute of the recording medium.

25. A control method as described in claim 23 or 24, wherein the first sensor is at least one of a paper thickness sensor, a pore volume sensor, a gloss sensor, a smoothness sensor, and a moisture content sensor.

26. A control method described in any of claims 15 to 25, further comprising a step of detecting a positional misalignment between an image formed on a first surface of the recording medium and an image formed on a second surface different from the first surface of the recording medium based on the read image generated by the second sensor.

27. ​​A control method described in any of claims 23 to 25, further comprising a step of correcting a position at which an image is formed on the recording medium based on the detection result of the first sensor and the read image generated by the second sensor.

Images