Image forming device

Abstract

To provide an image forming apparatus that can satisfactorily prevent front and back misregistration.SOLUTION: Since an image forming apparatus forms a first image on a first face of a recording medium until the apparatus forms a second image on a second face of the recording medium, the apparatus detects the formation position on the first face of the first image, and based on the detected formation position of the first image, calculates an adjustment value for adjusting the formation position on the second face of the second image. The image forming apparatus detects the formation position on the second face of the second image that is formed on the second face while the formation position is adjusted with the adjustment value, and based on the detected formation position of the second image, calculates a correction value for correcting the adjustment value.SELECTED DRAWING: Figure 12

Description

[Technical field]

[0001] The present invention relates to an image forming apparatus. [Background technology]

[0002] Patent Document 1 describes an image forming apparatus equipped with a second image adjustment value calculation means for calculating an adjustment value for adjusting the formation position of a second image on a recording medium during the period from when a first image is formed on a first surface of the recording medium to when a second image is formed on a second surface of the recording medium. The second image adjustment value calculation means detects the formation position of the first image formed on the first surface of the recording medium, and calculates an adjustment value for adjusting the formation position of the second image on the second surface based on the detected first image. Summary of the Invention [Problem to be solved by the invention]

[0003] However, there is room for improvement in the front-to-back misregistration, which is the relative positional deviation between the first image and the second image. [Means for solving the problem]

[0004] In order to solve the above-mentioned problems, the present invention provides an image forming apparatus equipped with a second image adjustment value calculation means that detects the formation position of the first image on the first surface of a recording medium between when a first image is formed on the first surface of the recording medium and when a second image is formed on the second surface of the recording medium, and calculates an adjustment value for adjusting the formation position of the second image on the second surface based on the detected formation position of the first image, and is characterized in that the image forming apparatus further comprises a correction value calculation means that detects the formation position on the second surface of the second image formed on the second surface by adjusting the formation position based on the adjustment value, and calculates a correction value for correcting the adjustment value based on the detected formation position of the second image. Effect of the Invention

[0005] According to the present invention, misregistration between the front and back can be effectively suppressed. [Brief description of the drawings]

[0006] [Figure 1] FIG. 1 is a schematic configuration diagram illustrating an example of an image forming apparatus according to an embodiment. [Diagram 2] FIG. 4 is a diagram for explaining reading of a first surface of a sheet by a reading device. [Diagram 3] 5A and 5B are diagrams for explaining reading of a second surface of a sheet by a reading device. [Figure 4] FIG. 4 is a control block diagram relating to alignment control. [Diagram 5] FIG. 4 is a diagram showing an example of a detection pattern formed on a sheet. [Figure 6] 6A to 6C are views for explaining correction of a first image and a second image in an adjustment mode. [Figure 7] 5A and 5B are diagrams for explaining writing start position correction. [Figure 8] 5A to 5C are diagrams illustrating magnification correction. [Figure 9] FIG. 4 is a diagram illustrating skew correction. [Figure 10] 6A to 6C are diagrams for explaining a procedure for calculating correction values ​​for front and back adjustment. [Figure 11] 6A and 6B are diagrams for explaining calculation of correction values ​​for front and back adjustment correction values; [Figure 12] FIG. 4 is a control flow diagram of image registration control in the present embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0007] Hereinafter, an embodiment in which the present invention is applied to an image forming apparatus that forms images by an electrophotographic method will be described. First, a basic configuration of the image forming apparatus according to the embodiment will be described. FIG. 1 is a schematic diagram showing an example of an image forming apparatus 100 according to an embodiment. This image forming apparatus 100 includes two exposure devices 1YM and 1CK, and four process units 2Y, 2M, 2C, and 2K for forming toner images of yellow (Y), magenta (M), cyan (C), and black (K).It also includes a paper feed path 30, a pre-transfer transport path 31, a manual paper feed path 32, a manual feed tray 33, a pair of registration rollers 34, a transport belt unit 35, a fixing device 40, a transport switching device 50, a paper discharge path 51, a pair of paper discharge rollers 52, a paper discharge tray 53, a paper feed device 7, a re-feed device, and the like.

[0008] The sheet feed device 7, which is a feeding means, includes a first sheet feed cassette 101 and a second sheet feed cassette 102, which are stacking units. The first sheet feed cassette 101 and the second sheet feed cassette 102 each store a stack of sheets P as recording materials therein. Then, the top sheet P in the stack is sent toward the sheet feed path 30 by the rotational drive of the sheet feed rollers 101a and 102a. The sheet feed path 30 is connected to a pre-transfer conveyance path 31 for conveying the sheet immediately before the secondary transfer nip, which will be described later. The sheet P sent from the sheet feed cassettes 101 and 102 enters the pre-transfer conveyance path 31 via the sheet feed path 30. The above-mentioned sheet includes paper, coated paper, label paper, OHP sheet, film, etc.

[0009] A manual feed tray 33 is disposed on the side of the device housing so as to be openable and closable relative to the housing, and a stack of sheets is manually fed onto the upper surface of the tray when it is open relative to the housing. The top sheet P of the manually fed stack of sheets is sent out toward the pre-transfer transport path 31 by a feed roller of the manual feed tray 33.

[0010] The two exposure devices 1YM and 1CK each have a laser diode, a polygon mirror, various lenses, and the like. Based on image information read by a scanner outside the device or image information sent from a personal computer, the laser diode is driven to optically scan the photoconductors 3Y, 3M, 3C, and 3K of the process units 2Y, 2M, 2C, and 2K. Specifically, the photoconductors 3Y, 3M, 3C, and 3K of the process units 2Y, 2M, 2C, and 2K are rotated counterclockwise in the figure by a driving means. The exposure device 1YM performs an optical scanning process by irradiating the driven photoconductors 3Y and 3M with a laser beam while deflecting it in the direction of the rotation axis. As a result, electrostatic latent images based on the Y image information and the M image information are formed on the photoconductors 3Y and 3M, respectively. The exposure device 1CK also performs an optical scanning process by irradiating the driven photoconductors 3C and 3K with a laser beam while deflecting it in the direction of the rotation axis. As a result, electrostatic latent images based on the C image information and the K image information are formed on the photoconductors 3C and 3K, respectively.

[0011] The process units 2Y, 2M, 2C, and 2K each have a drum-shaped photoconductor 3Y, 3M, 3C, and 3K as a latent image carrier. In addition, the process units 2Y, 2M, 2C, and 2K support various devices arranged around the photoconductor 3Y, 3M, 3C, and 3K as one unit on a common support, and these are detachable from the image forming unit main body. The process units 2Y, 2M, 2C, and 2K have the same configuration except that the colors of toner used are different. For example, the process unit 2Y for Y has a photoconductor 3Y and a developing device 4Y for developing the electrostatic latent image formed on the surface of the photoconductor 3Y into a Y toner image. It also has a charging device 5Y that performs a uniform charging process on the surface of the photoconductor 3Y that is rotated and a drum cleaning device 6Y that cleans the transfer residual toner adhering to the surface of the photoconductor 3Y after passing through the Y primary transfer nip described later.

[0012] The image forming apparatus 100 has a so-called tandem configuration in which four process units 2Y, 2M, 2C, and 2K are arranged along the endless movement direction of an intermediate transfer belt 61, which will be described later. The photoconductor 3Y is a drum-shaped one having a photosensitive layer formed by coating an organic photosensitive material having photosensitivity on a bare tube made of aluminum, etc. However, an endless belt-shaped one may also be used.

[0013] The developing device 4Y develops the latent image using a two-component developer (hereinafter simply referred to as "developer") containing a magnetic carrier and a non-magnetic Y toner. The developing device 4Y may be of a type that performs development using a one-component developer that does not contain a magnetic carrier, instead of the two-component developer. The developing device 4Y is appropriately replenished with Y toner from a Y toner bottle 103Y by a Y toner replenishing device.

[0014] The drum cleaning device 6Y uses a system in which a cleaning blade made of polyurethane rubber, which is a cleaning member, is pressed against the photoreceptor 3Y, but other systems may also be used. In order to improve cleaning performance, the image forming apparatus 100 uses a system in which a rotatable fur brush is brought into contact with the photoreceptor 3Y. This fur brush also serves to scrape off the lubricant from the solid lubricant, turn it into fine powder, and apply it to the surface of the photoreceptor 3Y.

[0015] A discharge lamp is disposed above the photoconductor 3Y, and this discharge lamp is also a part of the process unit 2Y. The discharge lamp discharges the surface of the photoconductor 3Y by irradiating it with light after it has passed through the drum cleaning device 6Y. The discharged surface of the photoconductor 3Y is uniformly charged by the charging device 5Y, and then optically scanned by the exposure device 1YM. The charging device 5Y is driven to rotate while receiving a charging bias from a power source. Instead of this system, a scorotron charger system may be used to charge the photoconductor 3Y without contact.

[0016] The process unit 2Y for Y has been described above, but the process units 2M, 2C, and 2K for M, C, and K have the same configuration as that for Y.

[0017] A transfer unit 60 is disposed below the four process units 2Y, 2M, 2C, and 2K. This transfer unit 60 moves an intermediate transfer belt 61, which is an endless belt stretched by a plurality of support rollers, in a clockwise direction in the drawing (endless movement) while contacting the photoconductors 3Y, 3M, 3C, and 3K by rotating one of the support rollers. As a result, primary transfer nips for Y, M, C, and K are formed where the intermediate transfer belt 61 contacts the photoconductors 3Y, 3M, 3C, and 3K.

[0018] Primary transfer rollers 62Y, 62M, 62C, and 62K are disposed as primary transfer members in a space surrounded by the inner peripheral surface of the intermediate transfer belt, i.e., in the belt loop. These primary transfer rollers 62Y, 62M, 62C, and 62K press the intermediate transfer belt 61 against the photoconductors 3Y, 3M, 3C, and 3K to form primary transfer nips. A primary transfer bias is applied to each of the primary transfer rollers 62Y, 62M, 62C, and 62K by a power source. As a result, a primary transfer electric field is formed in the primary transfer nips for Y, M, C, and K, which electrostatically moves the toner images on the photoconductors 3Y, 3M, 3C, and 3K toward the intermediate transfer belt 61.

[0019] As the intermediate transfer belt 61 moves endlessly in the clockwise direction in the figure, it passes through the primary transfer nips for Y, M, C, and K in sequence, and toner images are sequentially superimposed and primarily transferred to the outer peripheral surface of the intermediate transfer belt 61 at each primary transfer nip. By this superimposed primary transfer, a four-color superimposed toner image (hereinafter referred to as a "four-color toner image") is formed on the outer peripheral surface of the intermediate transfer belt 61.

[0020] A secondary transfer roller 72 serving as a secondary transfer member is disposed below the intermediate transfer belt 61 in the drawing. This secondary transfer roller 72 abuts against the outer circumferential surface of the intermediate transfer belt 61 at a position where the intermediate transfer belt 61 is wound around the secondary transfer backup roller 68, forming a secondary transfer nip. This forms a secondary transfer nip where the outer circumferential surface of the intermediate transfer belt 61 and the secondary transfer roller 72 abut against each other.

[0021] A secondary transfer bias is applied from a power source to the secondary transfer roller 72. Meanwhile, the secondary transfer backup roller 68 in the belt loop is grounded, so that a secondary transfer electric field is formed in the secondary transfer nip.

[0022] The above-mentioned registration roller pair 34 is disposed on the right side of the secondary transfer nip in the figure, and sends the sheet P sandwiched between the rollers to the secondary transfer nip at a timing that allows it to be synchronized with the four-color toner image on the intermediate transfer belt 61. In the secondary transfer nip, the four-color toner image on the intermediate transfer belt 61 is secondarily transferred all at once onto the sheet P due to the influence of the secondary transfer electric field and nip pressure, and is combined with the white color of the sheet P to form a full-color image.

[0023] Residual toner that was not transferred to the sheet P at the secondary transfer nip adheres to the outer peripheral surface of the intermediate transfer belt 61 that has passed through the secondary transfer nip. This residual toner is cleaned by a belt cleaning device 75 that comes into contact with the intermediate transfer belt 61.

[0024] Further, on the left side of the secondary transfer nip in the figure (downstream side in the sheet conveying direction), a fixing device 40, a cooling device 70, and a reading device 80 as a detection means are sequentially arranged. The sheet P that has passed through the secondary transfer nip is separated from the intermediate transfer belt 61 and is delivered to the conveyor belt unit 35. The conveyor belt unit 35 moves the endless belt-like conveyor belt 36 in the counterclockwise direction in the figure by rotating the drive roller 37 while tensioning the endless belt-like conveyor belt 36 between a drive roller 37 and a driven roller 38. The sheet P delivered from the secondary transfer nip is held on the tension surface of the outer circumferential surface of the conveyor belt, and is conveyed in accordance with the endless movement of the conveyor belt 36, and is delivered to a fixing device 40 as a fixing means.

[0025] The sheet P delivered to the fixing device 40 is pressurized and heated by a fixing roller and a pressure roller, so that the toner image is fixed onto the sheet. Then, the sheet P that has passed through the fixing device 40 is cooled by a cooling device 70.

[0026] In the image forming apparatus 100, the conveyance switching device 50, the re-sending path 54, the switchback path 55, the post-switchback conveyance path 56, and the like constitute a reverse conveyance means. Specifically, the conveyance switching device 50 switches the subsequent conveyance destination of the sheet P received from the fixing device 40 between the discharge path 51 and the re-sending path 54. When a print job in a single-sided mode in which an image is formed only on the first side of the sheet P is executed, the conveyance destination of the sheet P is set to the discharge path 51. As a result, the sheet P with the image formed only on the first side is sent to the discharge roller pair 52 via the discharge path 51 and discharged onto the discharge tray 53 outside the machine. Also, when a print job in a double-sided mode in which images are formed on both sides of the sheet P, respectively, is executed, when the sheet P with the images fixed on both sides is received from the fixing device 40, the conveyance destination of the sheet P is also set to the discharge path 51. As a result, the sheet P with the images formed on both sides is discharged onto the discharge tray 53 outside the machine. On the other hand, when a print job in the double-sided mode is executed, when a sheet P with an image fixed only on its first side is received from the fixing device 40, the conveying destination of the sheet P is set to the re-feed path .

[0027] A switchback path 55 is connected to the re-sending path 54, and the sheet P sent to the re-sending path 54 enters the switchback path 55. When the entire area of ​​the sheet P in the conveying direction enters the switchback path 55, the conveying direction of the sheet P is reversed, and the sheet P switches back. In addition to the re-sending path 54, a post-switchback conveying path 56 is connected to the switchback path 55, and the switched-back sheet P enters the post-switchback conveying path 56. At this time, the sheet P is turned upside down. The upside-down inverted sheet P is re-sent to the secondary transfer nip via the post-switchback conveying path 56 and the paper feed path 30. The sheet P, whose second surface has also been transferred with a toner image at the secondary transfer nip, passes through the fixing device 40, where the toner image is fixed to the second surface, and is then discharged onto the paper discharge tray 53 via the conveying switching device 50, the paper discharge path 51, and the paper discharge roller pair 52.

[0028] In this embodiment, a purge tray 58 onto which unnecessary sheets are discharged is provided at the lower left side of the device in the drawing. For example, a sheet present in the device when the device is stopped due to a jam or the like is conveyed to the purge tray 58. Specifically, a tray conveying path 57 for conveying a sheet to the purge tray 58 is connected to the re-sending path 54, and when a sheet is conveyed to the purge tray 58, the conveying destination of the sheet P is set to the tray conveying path 57. As a result, the sheet conveyed to the re-sending path 54 is conveyed to the tray conveying path 57 just before the post-switchback conveying path 56 and discharged to the purge tray 58.

[0029] The image forming apparatus 100 also has an operation panel 8. Operation settings and the like of the image forming apparatus 100 are performed based on the user's operation of the operation panel 8. Also, the display unit of the operation panel 8 displays the operating status and the like.

[0030] FIG. 2 is a diagram for explaining reading of the first surface of a sheet by the reading device 80. As shown in FIG. A first image G1 (first toner image) is transferred to a first surface of a sheet P fed from a paper feed cassette at a secondary transfer nip. The sheet P with the first image G1 transferred to its first surface is transported to a fixing device 40, where the first image G1 on the first surface is fixed to the sheet. After passing through the fixing device 40, the sheet is cooled by a cooling device 70 and then transported to a reading device 80, where the first image G1 formed on the first surface of the sheet P and the sheet P (the shape of the sheet P) are read.

[0031] FIG. 3 is a diagram for explaining reading of the second surface of the sheet by the reading device 80. As shown in FIG. In the case of a print job in a double-sided mode in which an image is formed on both sides of a sheet, the sheet that has passed the reading device 80 is conveyed to the re-sending path 54. The sheet P conveyed to the re-sending path 54 enters the switchback path 55, where the conveying direction of the sheet P is reversed, and the trailing end of the sheet P in the conveying direction when an image is formed on the first side of the sheet becomes the leading end, and the sheet P enters the post-switchback conveying path 56. At this time, the sheet P is turned upside down. Then, the upside-down inverted sheet P is re-sent to the secondary transfer nip via the post-switchback conveying path 56 and the paper feed path 30. In the secondary transfer nip, the second image G2 rotated by 180° is transferred to the second side of the sheet, and the transferred sheet P passes through the fixing device 40 to have the toner image fixed to the second side. After that, the sheet P is cooled by the cooling device 70, and then conveyed to the reading device 80, where the second image G2 formed on the second side of the sheet P and the sheet P (the shape of the sheet P) are read. The sheet P that has passed through the reading device 80 passes through a paper discharge path 51 and a pair of paper discharge rollers 52 and is discharged onto a paper discharge tray 53 .

[0032] The sheet P when the second side is read by the reading device 80 has shrunk more than the sheet P (indicated by the dashed line in the figure) when the first side is read by the reading device 80. This is because the sheet passes through the fixing device 40 again after the first side is read, causing further moisture evaporation from the sheet and accelerating shrinkage.

[0033] In this image forming apparatus 100, a reading device 80 is disposed between the fixing device 40, the re-feed path 54, and the discharge path 51. This makes it possible to read images G1 and G2 formed on both sides of a sheet while the sheet is being transported within the image forming apparatus (without being discharged from the image forming apparatus).

[0034] In addition, the sheet transport path from the reading device 80 until the sheet is turned upside down and reaches the secondary transfer nip again is sufficiently long. Therefore, the image formation of the second image is started with a sufficient time after the rear end of the sheet passes the reading device 80 and the reading of the first image G1 is completed. As a result, as described later, before the image formation of the second image G2 is started, a correction value for correcting the image formation position of the second image, etc. is calculated based on the first image G1 read by the reading device 80. Therefore, the second image can be corrected with the correction value calculated before the image formation of the second image G2 is started, and the second image can be formed.

[0035] Due to a cutting error in the sheet stack, one end of the sheet that becomes the leading edge in the transport direction when an image is formed on the first side of the sheet, and the other end of the sheet that becomes the trailing edge in the transport direction when an image is formed on the first side of the sheet, may be inclined with respect to the transport direction. As described above, when an image is formed on the second side of the sheet, the sheet is switched back, then inverted, and transported to the secondary transfer nip again. Therefore, the other end of the recording paper that is the trailing edge in the recording paper transport direction when an image is formed on the first side becomes the leading edge in the paper transport direction when an image is formed on the second side.

[0036] Before the sheet is conveyed to the secondary transfer nip, the leading edge of the sheet in the conveying direction abuts against the pair of registration rollers 34. If there is a cutting error in the sheet, the posture when the leading edge of the sheet abuts against the pair of registration rollers 34 differs between when an image is transferred to the first surface of the sheet and when an image is transferred to the second surface of the sheet. This is because when an image is transferred to the first surface of the sheet, one end of the sheet in the conveying direction abuts against the registration rollers, whereas when an image is transferred to the first surface of the sheet, the other end of the sheet in the conveying direction abuts against the pair of registration rollers 34. If the posture when the leading edge of the sheet abuts against the pair of registration rollers 34 differs between when an image is transferred to the first surface of the sheet and when an image is transferred to the second surface of the sheet, the following problem occurs. That is, the conveying posture of the sheet when an image is transferred to the first surface of the sheet and the conveying posture of the sheet when an image is transferred to the back surface of the sheet differ from each other, and a problem occurs in which misregistration occurs between the front and back due to a cutting error in the sheet stack.

[0037] Therefore, in this image forming apparatus, alignment control is performed between a first image G1 formed on a first surface of a sheet and a second image formed on a second surface of the sheet, based on the image and the sheet read by the reading device 80. Note that the alignment here means that the first image and the second image match when viewed from the second surface side.

[0038] FIG. 4 is a control block diagram relating to the alignment control. 4, the control unit 90, which is responsible for controlling the entire image forming apparatus, includes a read image acquisition unit 98 that acquires a read image from the reading device 80. The control unit 90 also includes a coordinate acquisition unit 97 that acquires, based on the read image acquired by the read image acquisition unit 98, the coordinates of the four corners of the sheet P in the read image and the coordinates of four detection marks formed near the four corners of the sheet, which will be described later.

[0039] The control unit 90 also includes a correction value acquisition unit 92 that acquires correction values ​​for correcting the image position from the operation panel 8. Specifically, when the user wants to fine-tune the image position after viewing the image on the output sheet, the user operates the operation panel 8 to display an image position adjustment screen. Based on this image position adjustment screen, the user inputs correction values ​​for correcting, for example, the width direction position and length direction (sheet conveyance direction) position of the first image formed on the first surface. The correction value acquisition unit 92 acquires the correction values ​​input by the user operating the operation panel 8.

[0040] As will be described later, the control unit 90 also has a correction value calculation unit 95 that calculates a correction value for correcting the correction value, and a correction value calculation unit 96. The correction value calculated by the correction value calculation unit 95 is stored in a correction value / correction value storage unit 94. Then, the correction value is read out when correcting the front and back adjustment correction value calculated by the correction value calculation unit 96, and after the calculated front and back adjustment correction value is corrected by the correction value, it is sent to the written image generation unit 93.

[0041] The correction value calculation unit 96 calculates a correction value as an adjustment value for positioning the first image at an ideal position, based on the coordinate information of the first image and the coordinate information of the sheet acquired by the coordinate acquisition unit 97. The correction value calculation unit 96 also calculates a correction value as an adjustment value for positioning the second image at an ideal position, based on the coordinate information of the second image and the coordinate information of the sheet.

[0042] The correction value calculation unit 96 also calculates a front / back adjustment correction value for matching the position of the second image to the position of the first image based on the coordinate information of the first image and the coordinate information of the sheet. The correction value calculation unit 96 also calculates a new correction value based on the correction value stored in the correction value / modification value storage unit 94 and the correction value input by the user acquired by the correction value acquisition unit 92. The correction value calculated by the correction value calculation unit 96 is stored in the correction value / modification value storage unit 94 after calculation, or is sent to the writing image generation unit 93 and used to generate a writing image.

[0043] The correction value / modification value storage unit 94 stores the correction values ​​calculated by the correction value calculation unit 96 and the modification values ​​calculated by the modification value calculation unit 95. The control unit 90 also includes a coordinate information storage unit 99 that temporarily stores coordinate information of the first image used for calculating the modification values ​​by the modification value calculation unit 95 and the sheet coordinates when the first image is read.

[0044] The control unit 90 includes an image data acquisition unit 91 that acquires image data to be formed on the sheet from an external device such as a personal computer. The control unit 90 also includes a writing image generation unit 93 that generates a writing image to be input to the exposure device 1. The writing image generation unit 93 generates a writing image to be input to the exposure device 1 from the image data acquired by the image data acquisition unit 91 based on a correction value calculated by a correction value calculation unit 96. The exposure device 1 is controlled based on the writing image corrected by this correction value, so that the position of the first image is formed to match the ideal position of the sheet, or the second image is formed so that the position of the second image on the sheet matches the position of the first image on the sheet when viewed from the second surface side.

[0045] FIG. 5 is a diagram showing an example of a detection pattern formed on a sheet P for grasping the position, shape, size, etc. of an image formed on the sheet. In this embodiment, as described below, the first image and the second image are always aligned during continuous printing in double-sided mode, and Figure 5 shows an example of a detection pattern formed on sheet P during continuous printing in this double-sided mode. 5, L-shaped detection marks a, b, c, and d are formed near the four corners of the sheet together with an image G formed based on image data acquired from an external device such as a personal computer. The sheet on which the detection marks have been formed is conveyed to a reading device 80 after passing through a fixing process by a fixing device 40 and a cooling process by a cooling device 70.

[0046] The reading device 80 reads the entire sheet P and the detection marks a, b, c, and d. The coordinate acquisition unit 97 of the control unit 90 acquires the coordinates of the four corners P1 to P4 of the sheet P and the coordinates a1, b1, c1, and d1 of the center positions of each detection mark. The coordinates of each detection mark and the sheet are acquired with one end P1 of the sheet as the origin of the coordinates.

[0047] A correction value calculation unit 96 of the control unit 90 grasps the shape of the sheet P based on the coordinates of the four corners P1 to P4 of the sheet P, and grasps the position and shape of the image to be formed on the sheet P based on the coordinates a1 to d1 of the center positions of the detection marks. Then, the correction value calculation unit 96 calculates a correction value for correcting the position and the like of the image to be formed on the sheet P based on the grasped shape of the sheet P, the position and the shape of the image.

[0048] This image forming apparatus also has an adjustment mode that is executed at a predetermined timing, such as when the power is turned on. In this adjustment mode, the image G is not formed, and only the detection pattern is formed on the sheet P.

[0049] FIG. 6 is a diagram for explaining the correction of the first image and the second image of the sheet in this adjustment mode. In the adjustment mode, detection marks a to d are formed on the first and second surfaces of the sheet, respectively, and coordinates a1 to d1 of the detection marks are obtained from the read image read by the reading device 80. FIG. 6(a) shows the coordinates a1 to d1 of the detection marks. Due to various factors such as an assembly error of the exposure device 1 to the device and an assembly error of the photosensitive body, the positions of the detection marks formed on the sheet are shifted from the original ideal positions R1 to R4, as shown in FIG. 6(b). The control unit 90 (correction value calculation unit 96) calculates the amount of deviation of each detection mark from the ideal positions R1 to R4, and calculates a correction value based on this deviation so that each detection mark is formed at the ideal positions R1 to R4, as shown in FIG. 6(c).

[0050] Examples of image correction include registration correction shown in FIG. 7, magnification correction shown in FIG. 8, and skew correction shown in FIG. 9. Registration correction shown in FIG. 7 corrects the write start timing of the exposure device 1. Specifically, a correction value calculation unit 96 of the control unit calculates a write start correction value for correcting the write start timing based on the amount of deviation of the coordinate a1 of the detection mark from the ideal position R1. The calculated write start correction value is stored in a correction value / modification value storage unit 94. When writing a latent image on the photoconductor based on the image data, the write start correction value is read from the correction value / modification value storage unit 94 to correct the write start timing. As a result, the start position of the image G formed on the sheet P is corrected to the ideal position R1 as shown in FIG. 7(b).

[0051] In the magnification correction shown in FIG. 8, the correction value calculation unit 96 obtains a magnification error between the size of the image to be formed on the sheet and the size of a target image based on the coordinates a1 to d1 of each detection mark, and calculates a magnification correction value based on the obtained magnification error. This magnification correction value is stored in the correction value / modification value storage unit 94. When forming an image based on image data, the write image generation unit 93 reads out the magnification correction value from the correction value / modification value storage unit 94, corrects the magnification of the image data using the magnification correction value, and generates a write image. As a result, as shown in FIG. 8(b), the size of the image G1 to be formed on the sheet P is corrected to the size of the target image. Note that a known method can be used for the magnification correction of the image data.

[0052] In the skew correction shown in FIG. 9, the amount of skew of an image relative to a target image is found based on the coordinates a1 to d1 of each detection mark, and a skew correction value is calculated based on the found amount of skew. This skew correction value is stored in a correction value / modification value storage unit 94. When forming an image based on image data, a write image generating unit 93 reads out the skew correction value from the correction value / modification value storage unit 94, skews (pixel shifts) the image data based on the skew correction value, and then generates a write image. As a result, the start position of an image G formed on a sheet P is corrected to an ideal position R1, as shown in FIG. 9(b). A known method can be used for the skew correction of image data.

[0053] By appropriately combining these corrections and other known corrections such as keystone correction to correct the image formed on the sheet, the image formed on the sheet can be formed in an ideal position, as shown in Figure 6(c). By forming the first image and the second image based on the correction values ​​for the first image and the second image obtained in this adjustment mode, both the first image and the second image can be formed in an ideal position.

[0054] Even if the first image and the second image can be formed in ideal positions based on the correction values ​​calculated by the above-mentioned adjustment modes, a so-called front-back misregistration may occur in which the positions of the first image and the second image do not match when viewed from one side of the sheet due to sheet cutting errors, etc. Therefore, the present image forming apparatus calculates a front-back adjustment correction value as an adjustment value for aligning the position of the second image formed on the second side with the position of the first image.

[0055] The front and back adjustment correction values ​​for aligning the second image with the first image are calculated for each sheet during continuous printing in double-sided mode, and the front and back adjustment correction values ​​are calculated by reading detection marks a to d on the first side of the sheet together with image G, as shown in Figure 5.

[0056] In addition, the calculation of the correction value for front and back adjustment is completed before the start of image formation of the second image formed on the second side of the sheet after the detection mark formed on the first side is read, so that the correction value for front and back adjustment can be used when forming the second image. In this way, in order to calculate the correction value for front and back adjustment before the start of image formation of the second image formed on the second side of the sheet after the detection mark formed on the first side is read, the image forming apparatus satisfies at least the following condition. That is, the condition is that the time from when the rear end of the sheet with the maximum length that the image forming apparatus can convey leaves the reading device 80 until the sheet reaches the secondary transfer nip again is longer than the shortest time from when the exposure device 1 starts writing until the imaged image reaches the secondary transfer nip. In the image forming apparatus, the time from when writing starts on the K-color photoconductor until the imaged K-color image reaches the secondary transfer nip is the shortest time.

[0057] When the sheet transport speed and the image transport speed are the same, a condition is required that the sheet transport distance from the leading edge of the sheet to the secondary transfer nip when the trailing edge of the maximum length sheet passes through the reading device 80 is longer than the image transport distance from the exposure position of K color to the secondary transfer nip. Therefore, the reading device 80 is disposed at a position that satisfies this condition. In addition, in the case of a device that can slow down the sheet transport speed after the trailing end of the sheet passes through the reading device 80, it may be placed downstream in the sheet transport direction as long as the above conditions are met, compared to a device in which the sheet transport speed is constant.

[0058] Next, calculation of the front and back adjustment correction values ​​will be described. Fig. 10 is a diagram for explaining the calculation procedure of the correction value for front and back adjustment. Fig. 10(a) shows a first image G1 based on the coordinates a1 to d1 of each detection mark formed on the first surface, and Fig. 10(b) shows an inverted image G1h obtained by inverting the first image shown in Fig. 10(a) in the sheet conveying direction (the up-down direction in the figure). Fig. 10(c) is a diagram showing a target image M and a second image at an ideal position, and Fig. 10(d) is a diagram showing a state in which the second image is corrected to match the target image.

[0059] As shown in Fig. 10(a), the first image actually formed on the first surface of the sheet may not be formed at the ideal position. Specifically, the first image may not be formed at the ideal position due to factors such as sheet cutting error, variation in the amount of expansion and contraction of the sheet, change in the amount of expansion and contraction of the sheet due to a change in the temperature environment of the device from when the adjustment mode is executed, and expansion and contraction of the image due to a change in the diameter of the transfer roller. Note that Fig. 10(a) is significantly shifted from the ideal position for ease of understanding, but the actual deviation from the ideal position due to cutting error, etc. is small.

[0060] The reading device 80 reads the first surface of the sheet, and the coordinates (a1 to d1) of each detection mark formed on the first surface are acquired by the coordinate acquisition unit 97, and the acquired coordinates (a1 to d1) of each detection mark are set as the target coordinates (target position) of the second image. However, when an image is transferred to the second surface of the sheet, the sheet is inverted, and the first image formed on the first surface of the sheet is also inverted. Therefore, the correction value calculation unit 96 performs coordinate conversion such as inversion processing on the acquired coordinates of each detection mark, and obtains an inverted image G1h of the first image as shown in FIG. 10(b). Then, the inverted image G1h based on each coordinate (a1h to d1h) after this coordinate conversion is set as the target image M of the second image G2 as shown in FIG. 10(c), and a correction value for front and back adjustment is calculated so that the second image formed on the second surface of the sheet matches this target image M.

[0061] The acquired coordinates (a1 to d1) of each detection mark and the coordinates of the sheet are temporarily stored in a coordinate information storage unit 99 for use in calculating correction values, which will be described later.

[0062] As described above, in the adjustment mode, the correction values ​​for adjusting the second image to the ideal position have already been calculated and are stored in the correction value / modification value storage unit 94. Therefore, the correction values ​​for front and back adjustment are correction values ​​for moving from the ideal position to the target image M (a2→b1h, b2→a1h, c2→d1h, d2→c1h). The correction values ​​for front and back adjustment include a writing correction value, a magnification correction value, and a skew correction value.

[0063] The correction value calculation unit 96 calculates new correction values ​​based on each correction value for positioning the second image at an ideal position stored in the correction value / modification value storage unit 94 and each calculated correction value for front and back adjustment. For example, for the write correction value for front and back adjustment, the magnification correction value for front and back adjustment, and the skew correction value for front and back adjustment, the correction value for front and back adjustment is calculated as a total correction value of the correction value for positioning the second image at an ideal position obtained in the adjustment mode and the correction value for front and back adjustment. This total correction value is sent to the write image generation unit 93.

[0064] The write image generating unit 93 generates a write image based on the total correction value and the image data acquired by the image data acquiring unit 91. For example, the total correction value is used to correct the image data (magnification correction and skew correction) and correct the write start position. As a result, as shown in Fig. 10(d), the formation position on the second surface is adjusted so that the position of the second image formed on the second surface of the sheet matches the position of the first image formed on the first surface, and an image is formed on the second surface.

[0065] In addition, it is preferable that the shape of the sheet is taken into consideration when calculating the skew correction value for front and back adjustment. Specifically, the inclination of one end of the sheet in the sheet conveying direction is calculated from the coordinates of two corners P1 and P2 on one end of the sheet conveying direction, and the inclination of the other end of the sheet in the sheet conveying direction is calculated from the coordinates of two corners P3 and P4 on the other end of the sheet conveying direction. Then, the difference between the inclination of one end of the sheet conveying direction and the inclination of the other end of the sheet conveying direction is calculated. This difference value becomes the sheet skew difference between when the image on the first side is formed and when the image on the second side is formed when the sheet is conveyed to the secondary transfer nip, which leads to misregistration of the first image and the second image. Therefore, by calculating the skew correction value for front and back adjustment while taking this difference value into consideration, the second image formed on the second side of the sheet can be accurately aligned with the position of the first image formed on the first side.

[0066] By adjusting the formation position of the second image using the correction value for front and back adjustment, misregistration between front and back can be suppressed. Furthermore, the second image formed on the second side of the sheet after reading the detection mark formed on the first side of the sheet is corrected by the correction value for front and back adjustment. This makes it possible to adjust the formation position of the second image to match the position of the first image in response to the position fluctuation of the first image that occurs for each sheet, such as the variation in the amount of expansion and contraction of the sheet and the expansion and contraction of the image due to the diameter fluctuation of the secondary transfer roller, and to effectively suppress misregistration between front and back.

[0067] As shown in Fig. 10(a), the first image is slightly shifted from the target position due to sheet cutting errors, variations in the amount of expansion and contraction of the sheet, changes in the amount of expansion and contraction of the sheet due to changes in the temperature environment of the device from when the adjustment mode was executed, image expansion and contraction due to changes in the diameter of the transfer roller, etc. When the user confirms such a positional deviation from the target position on the printed sheet, this image forming apparatus allows the user to correct the deviation from the target position by operating the operation panel 8.

[0068] Specifically, as described above, the user operates the operation panel 8 as a reception means to display the image position adjustment screen. Based on this image position adjustment screen, the user inputs, for example, correction values ​​for correcting the width direction position and length direction (sheet conveying direction) position of the first image. The correction value acquisition unit 92 acquires the correction values ​​input by the user operating the operation panel 8. Based on the input correction values, the correction value calculation unit 96 appropriately corrects each correction value (write correction value, magnification correction value, skew correction value, etc.) for positioning the first image at an ideal position stored in the correction value / modification value storage unit 94, and stores the corrected new correction values ​​in the correction value / modification value storage unit 94. As a result, after the correction values ​​are input, writing is performed in the exposure device 1 based on the new correction values, and slight deviations from the target position are corrected by the user. The position of the second image is corrected so that it matches the position of the first image corrected by the user, so that the second image is also formed at the target position.

[0069] However, even if the above-mentioned calculation of the front and back adjustment correction values ​​is performed and alignment control of the first image and the second image during double-sided printing is performed, there are cases where slight misregistration between the front and back of the printed matter remains in the actual printed matter.

[0070] Therefore, in this image forming apparatus, the position of the actual second image formed on the second side of the sheet is read by the reading device 80, and it is monitored whether the positions of the actual first image and the second image match. If the positions of the first image and the second image do not match, the correction value for front and back adjustment is modified.

[0071] FIG. 11 is a diagram for explaining calculation of the modified value for the front and back adjustment correction value. The calculation of the modification value is almost the same as the calculation procedure of the front and back adjustment correction values ​​described with reference to FIG. The correction value calculation unit 95 performs coordinate conversion such as inversion processing on the coordinates (a1 to d1) of each detection mark formed on the first surface that was used when calculating the correction values ​​for front and back adjustment temporarily stored in the coordinate information memory unit 99, to obtain an inverted image G1h of the first image (Figures 11(a) to 11(b1)). Note that the inverted image G1h of the first image obtained when the front and back adjustment correction values ​​are calculated may be temporarily stored, and this temporarily stored inverted image G1h of the first image may be used when calculating the correction values.

[0072] This inverted image G1h is an inverted image of the coordinates at the time of reading the first side of the sheet P, and at the time of reading the second side, the sheet passes through the fixing device again and shrinks, causing the image formed on the first side to shrink as well. Therefore, for the inverted image for calculating the correction value, a shrinkage rate is calculated as a change in the shape of the sheet based on the sheet shape at the time of reading the first side and the sheet shape at the time of reading the second side. Then, the inverted image is corrected based on the calculated shrinkage rate.

[0073] Specifically, the sheet shrinkage ratio is calculated by performing a coordinate conversion such as a reversal process on the sheet coordinates when the first side is read to obtain an inverted sheet shape, and then comparing the inverted sheet shape with the sheet shape obtained based on the sheet coordinates when the second side is read to obtain the sheet shrinkage ratio. Note that the sheet coordinates when the second side is read may also be subjected to a coordinate conversion such as a reversal process on the sheet coordinates when the second side is read to obtain an inverted sheet shape, and then comparing the inverted sheet shape with the sheet coordinates when the first side is read to obtain the sheet shrinkage ratio.

[0074] The coordinate acquisition unit 97 acquires the coordinates (a2-d2) of each detection mark formed on the second surface read by the reading device 80 (FIG. 11(b2)). The correction value calculation unit 95 then compares the inverted image G1h corrected based on the sheet shape with the second image obtained from the coordinates (a2-d2) of each detection mark formed on the second surface, and determines the amount of deviation of the actual second image G2 from the inverted image G1h (FIG. 11(c)). The correction value calculation unit 95 then calculates a correction value for aligning the second image with the inverted image G1h based on the determined amount of deviation.

[0075] The calculated correction value is stored in the correction value / correction value storage unit 94, and is applied to the subsequent second image for which image formation has not yet begun. The subsequent second image is corrected with the corrected front and back adjustment correction value. Specifically, when calculating the front and back adjustment correction value to be applied to the subsequent second image, the correction value calculation unit 96 reads out the correction value from the correction value / correction value storage unit 94, corrects the calculated front and back adjustment correction value with the correction value, and the corrected front and back adjustment correction value is used to correct the second image.

[0076] The correction values ​​are a correction value for correcting the write correction value for front and back adjustment, a correction value for correcting the magnification correction value for front and back adjustment, a correction value for correcting the skew correction value for front and back adjustment, etc. Based on the deviation of the actual second image G2 with respect to the inverted image G1h, the correction values ​​for correcting the write correction value for front and back adjustment, the magnification correction value for front and back adjustment, and the skew correction value for front and back adjustment are calculated as appropriate.

[0077] Since this correction value is applied to the subsequent second image, it is necessary to eliminate accidental positional deviations that occur only on that sheet, such as positional deviations caused by variations in the amount of expansion and contraction for each sheet, etc. Therefore, it is preferable to calculate an average of the correction values ​​for multiple sheets or calculate a correction value based on the average amount of positional deviations for multiple sheets, and reflect the correction value from which accidental positional deviations have been eliminated in the front and back adjustment correction value.

[0078] In the above description, the inverted image G1h is corrected based on the calculated shrinkage rate of the sheet, but the second image G2 may be corrected (enlarged) based on the shrinkage rate of the sheet. Also, the first image may be corrected based on the calculated shrinkage rate of the sheet, and the corrected first image may be inverted to obtain the inverted image G1h.

[0079] FIG. 12 is a control flow diagram of image alignment control in this embodiment. When continuous printing in double-sided mode is started, the control unit 90 prints an image based on image data acquired from an external device such as a personal computer and detection marks a to d on the first surface of the sheet, as shown in FIG. 5 (S1).

[0080] Next, the first side of the sheet is read by the reading device 80, and the coordinates (a1 to d1) of the detection marks formed on the first side and the coordinates of the four corners P1 to P4 of the sheet are measured (obtained) (S2). Next, the coordinates (a1 to d1) of the detection marks are inverted to obtain a target image M (S3). Then, a second image located at a target position is compared with the target image M to calculate the amount of deviation between the second image and the target image M, and a correction value for front and back adjustment is calculated based on the amount of deviation (S4).

[0081] Next, an image based on the image data and a detection mark are printed on the second side of the sheet reflecting the calculated front and back adjustment correction value (S5). Next, the second side of the sheet is read by the reading device 80, and the coordinates (a2 to d2) of the detection mark formed on the second side and the coordinates of the four corners P1 to P4 of the sheet are measured (obtained) (S7).

[0082] Next, as described with reference to FIG. 11, the sheet shrinkage ratio is calculated as a change in the shape of the sheet from the coordinates of the four corners of the sheet when the first side is read and the coordinates of the four corners of the sheet when the second side is read. Then, based on the calculated sheet shrinkage ratio, the inverted image obtained by inverting the coordinates (a1 to d1) of the detection mark formed on the first side is corrected. Then, the amount of deviation of the actual second image obtained from the coordinates (a2 to d2) of the detection mark formed on the second side relative to the corrected inverted image is calculated. Then, a correction value is calculated based on the amount of deviation (S8).

[0083] The calculated correction value is reflected when forming the second image on the second side of the next sheet (S9). As described above, the correction value to be reflected is the average value of the correction values ​​of multiple sheets or a correction value calculated based on the average amount of positional deviation of multiple sheets, in order to eliminate accidental positional deviation that occurs only on that sheet.

[0084] The operations of S1 to S10 are repeated until continuous printing in the double-sided mode is completed (No in S10).

[0085] The above description is merely an example, and each of the following aspects provides unique effects. (Aspect 1) In an image forming apparatus equipped with a second image adjustment value calculation means such as a control unit 90 that detects the formation position of the first image on the first surface of a recording medium such as a sheet P and calculates an adjustment value such as a front / back adjustment correction value for adjusting the formation position of the second image on the second surface based on the detected formation position of the first image, the apparatus further comprises a correction value calculation means such as a control unit 90 that detects the formation position on the second surface of the second image formed on the second surface by adjusting the formation position using the adjustment value and calculates a correction value for correcting the adjustment value based on the detected formation position of the second image. According to this, the second image can be formed by adjusting the formation position using an adjustment value such as a front-back adjustment correction value on the second side of the same recording medium on which the first image was detected. This makes it possible to effectively suppress front-back misregistration, which is the relative positional deviation between the first image and the second image of a printed matter caused by cutting errors of the recording medium, the shrinkage rate of the recording medium after passing through the fixing device, etc. Furthermore, by calculating the adjustment value for each recording medium, it is also possible to effectively suppress front-back misregistration caused by the characteristics of each recording medium, such as the variation in the shrinkage rate of each recording medium. However, for example, due to temperature conditions in the device during continuous image formation, the recording medium may expand or contract during the time from when the first image is detected until when the second image is transferred to the second surface of the recording medium, causing the shape of the recording medium to change. As a result, the formation position of the second image actually formed on the recording medium may shift from the target position of the recording medium (in this embodiment, the inverted image G1h of the first image), and misregistration between the front and back may remain. Therefore, in the first aspect, by detecting the formation position of the second image actually formed on the second surface of the recording medium, it is possible to grasp the deviation between the actual formation position of the second image on the recording medium and the target position on the recording medium. As a result, by forming the second image by adjusting the formation position using the adjustment value corrected by the correction value calculation means, it is possible to form the second image satisfactorily at the target position on the recording medium, and obtain a printed matter in which misregistration between the front and back is further suppressed.

[0086] (Aspect 2) In aspect 1, the calculation of the adjustment value by a second image adjustment value calculation means such as the control unit 90 and the calculation of the correction value by a correction value calculation means such as the control unit 90 are performed during double-sided continuous image printing, and the correction value calculated by the correction value calculation means is reflected in the formation of a second image in the continuous image printing for which image formation has not yet begun. According to this, during continuous image printing, the position of the second image can be adjusted so that the position of the second image matches the position of the first image as viewed from the second surface side.

[0087] (Aspect 3) In aspect 1 or 2, a detection means such as a reading device 80 that detects an image formed on a recording medium such as a sheet P is provided, and a second image adjustment value calculation means such as a control unit 90 calculates an adjustment value such as a correction value for front and back adjustment based on the first image detected by the detection means, and a correction value calculation means calculates a correction value based on the first image detected by the detection means and the second image. According to this, as described in the embodiment, it is possible to calculate adjustment values ​​such as the front and back adjustment correction values ​​so as to match the first image actually formed on a recording medium such as a sheet P. Also, it is possible to correct the adjustment values ​​based on the actual second image formed on the sheet. This makes it possible to accurately match the position of the second image to the position of the first image.

[0088] (Aspect 4) In the third embodiment, a detection means such as the reading device 80 is disposed at a position where detection of the first image is completed before the start of image formation of the second image to be formed on the second side of the recording medium. According to this, as described in the embodiment, a correction value such as a back adjustment correction value is calculated during the period from when a first image is formed on a first surface of a recording medium such as a sheet P until when a second image is formed on a second surface of the recording medium, and the correction value can be reflected in the second image formed on the second surface of the sheet on which the detection unit detects the first image. This makes it possible to suppress misalignment of the second image with respect to the first image caused by factors that differ for each sheet, such as variations in the amount of expansion and contraction of the sheet.

[0089] (Aspect 5) In any of the first to fourth aspects, the detection of the first and second images is performed based on position detection marks such as the detection marks a to d formed on the recording medium. According to this, the position of the image to be formed on the sheet and the shape of the image can be grasped satisfactorily from the position of the position detection mark on the sheet.

[0090] (Aspect 5-1) In the fifth aspect, the position detection marks such as the detection marks a to d are formed near the four corners of a recording medium such as a sheet. This allows the position detection marks such as the detection marks a to d to be separated as far as possible, and enables changes in the shape of the image due to cutting errors of the recording medium to be detected with high sensitivity, making it possible to calculate a correction value with high accuracy. Also, it is possible to prevent the detection marks from overlapping with an image based on image data formed together with the detection marks.

[0091] (Aspect 6) In any one of the aspects 1 to 5, a second image adjustment value calculation means such as the control unit 90 calculates an adjustment value for adjusting the image formation start position of the second image, such as the writing start position. This allows the writing start position of the second image to coincide with one end of the first image as viewed from the second surface side.

[0092] (Aspect 6-1) In any one of aspects 1 to 6, a second image adjustment value calculation means such as the control unit 90 calculates an adjustment value for adjusting the magnification of the second image. This allows the second image to be adjusted to the size of the first image.

[0093] (Aspect 6-2) In any one of aspects 1 to 6, a second image adjustment value calculation means such as the control unit 90 calculates an adjustment value for adjusting the inclination of the second image. This allows the inclination of the second image to match the inclination of the first image.

[0094] (Aspect 7) In any of aspects 1 to 6, a first image adjustment value calculation means such as a control unit 90 is provided that detects a first image formed on a first surface of a recording medium such as a sheet, and calculates an adjustment value for adjusting the position of the first image based on the detected first image so that it is located at a target position on the recording medium. According to this, the amount of deviation from the target position is measured based on the actual first image formed on the first surface of the recording medium, and the formation position of the first image on the recording medium can be adjusted so that the first image is positioned at the target position on the sheet. This makes it possible to satisfactorily form the first image at the target position on the sheet.

[0095] (Aspect 8) In the seventh aspect, a first image adjustment value calculation means such as the control unit 90 calculates an adjustment value such as a writing start correction value for adjusting the image formation start position of the first image, such as the writing start position. According to this, the image formation start position of the first image, such as the writing start position of the first image, can be aligned with the target position.

[0096] (Aspect 8-1) In the seventh or eighth aspect, a first image adjustment value calculation means such as the control unit 90 calculates an adjustment value such as a magnification correction value for adjusting the magnification of the first image. This allows the size of the first image to be adjusted to the target size.

[0097] (Aspect 8-2) In the seventh or eighth aspect, a first image adjustment value calculation means such as the control unit 90 calculates an adjustment value such as a skew correction value for adjusting the inclination of the first image. This allows the inclination of the first image to be the target inclination.

[0098] (Aspect 9) In any of aspects 1 to 8, a correction value calculation means such as the control unit 90 calculates a shape change, such as the shrinkage rate, of the recording medium based on the shape of the recording medium when the first image is detected and the shape of the recording medium when the second image is detected, and corrects either the first image or the second image (in this embodiment, an inverted image of the first image) based on the calculated shape change to calculate a correction value. According to this, as described in the embodiment, the correction value can be calculated taking into account the change in shape of the image on the recording medium that accompanies a change in the shape of the recording medium, such as shrinkage of the recording medium, and the correction value can be calculated with high accuracy.

[0099] (Aspect 10) In any one of the first to ninth aspects, a receiving unit such as an operation panel 8 that receives an adjustment operation for at least one of the first image and the second image is provided. According to this, as explained in the embodiment, when the user looks at the printed image and finds a positional deviation or the like, the image can be adjusted by a reception means such as the operation panel 8.

[0100] (Aspect 11) In the tenth aspect, a receiving unit such as the operation panel 8 receives an adjustment operation for the image forming position. This allows the user to correct the image formation start position, such as the writing start position.

[0101] (Aspect 11-1) In the tenth and eleventh aspects, a receiving means such as the operation panel 8 receives an adjustment operation for the image magnification. This allows a user to correct large differences in an image formed on a recording medium such as a sheet.

[0102] (Aspect 11-2) In the tenth and eleventh aspects, a receiving means such as the operation panel 8 receives an operation for adjusting the tilt of an image. This allows the user to correct the inclination of an image formed on a recording medium such as a sheet. [Explanation of symbols]

[0103] 1: Exposure equipment 2: Process unit 3: Photoreceptor 8: Operation panel 34: Registration roller pair 40: Fixing device 50: Transport switching device 51: Paper ejection path 52: Paper discharge roller pair 53: Paper output tray 54:Resend route 55: Switchback Road 56: After switchback 61: Intermediate transfer belt 70: Cooling device 80: Reading device 90: Control section 91: Image data acquisition unit 92: Correction value acquisition unit 93: Write image generation unit 94: Correction value / modification value memory section 95: Correction value calculation section 96: Correction value calculation section 97: Coordinate acquisition section 98: Image acquisition unit 99: Coordinate information storage unit 100: Image forming apparatus G1: First image G1h : Inverted image G2: Second image M: Target image P: Seat P1~P4: Sheet corners a~d: Detection mark [Prior art documents] [Patent documents]

[0104] [Patent Document 1] JP 2019-101326 A

Claims

1. an image forming apparatus including a second image adjustment value calculation means for detecting a formation position of a first image on a first surface of a recording medium during a period from when a first image is formed on the first surface of the recording medium to when a second image is formed on the second surface of the recording medium, and calculating an adjustment value for adjusting a formation position of the second image on the second surface based on the detected formation position of the first image, an image forming apparatus comprising: a correction value calculation means for detecting a formation position on the second surface of the second image formed on the second surface by adjusting the formation position using the adjustment value; and calculating a correction value for correcting the adjustment value based on the detected formation position of the second image.

2. 2. The image forming apparatus according to claim 1, the calculation of the adjustment value by the second image adjustment value calculation means and the calculation of the correction value by the correction value calculation means are performed during double-sided continuous image printing, The image forming apparatus according to claim 1, wherein the correction value calculated by the correction value calculation means is reflected in formation of the second image in continuous image printing, where image formation has not yet started.

3. 3. The image forming apparatus according to claim 1, a detection means for detecting an image formed on the recording medium, The second image adjustment value calculation means calculates the adjustment value based on the first image detected by the detection means, The image forming apparatus according to claim 1, wherein the correction value calculation means calculates the correction value based on the first image and the second image detected by the detection means.

4. 4. The image forming apparatus according to claim 3, The image forming apparatus according to claim 1, wherein the detection means is disposed at a position where detection of the first image is completed before formation of the second image on the second surface of the recording medium is started.

5. 5. The image forming apparatus according to claim 1, The image forming apparatus according to claim 1, wherein the detection of the first image and the second image is performed based on a position detection mark formed on the recording medium.

6. 6. The image forming apparatus according to claim 1, The image forming apparatus according to claim 1, wherein the second image adjustment value calculation unit calculates an adjustment value for adjusting an image formation start position of the second image.

7. 7. The image forming apparatus according to claim 1, An image forming apparatus characterized by comprising a first image adjustment value calculation means for detecting the first image formed on the first surface, and calculating an adjustment value for adjusting the position of the first image so that it is located at a target position on the recording medium based on the detected first image.

8. 8. The image forming apparatus according to claim 7, The image forming apparatus according to claim 1, wherein the first image adjustment value calculation unit calculates an adjustment value for adjusting an image formation start position of the first image.

9. 9. The image forming apparatus according to claim 1, The image forming apparatus is characterized in that the correction value calculation means calculates a change in shape of the recording medium based on the shape of the recording medium when the first image is detected and the shape of the recording medium when the second image is detected, and corrects either the first image or the second image based on the calculated shape change to calculate the correction value.

10. 10. The image forming apparatus according to claim 1, The image forming apparatus further comprises a reception unit that receives an adjustment operation for at least one of the first image and the second image.

11. 11. The image forming apparatus according to claim 10, The image forming apparatus according to claim 1, wherein the accepting unit accepts an adjustment operation for an image forming position.

Images