Image forming apparatus

Abstract

To reduce deviation of an image position when sheets are seen spread.SOLUTION: An image forming apparatus comprises image forming means, inversion means, detection means that detects a leading end and a rear end of a sheet, and alignment means that performs alignment of an image to the leading end of the sheet. The image forming apparatus creates a product obtained by superimposing a second sheet on which a second image is formed on a first sheet on which a first image is formed, in which a surface of the first sheet on which the first image is formed and a surface of the second sheet on which the second image is formed face each other, and a rear end of the first sheet when the first image is formed and a leading end of the second sheet when the second image is formed face each other. The alignment means corrects the position of the second image with respect to the leading end of the second sheet when the second image is formed on the basis of a result of detection of the rear end of the first sheet performed by the detection means when the first image is formed.SELECTED DRAWING: Figure 8

Description

[Technical Field]

[0001] The present invention relates to an image forming apparatus that forms an image on a sheet. [Background technology]

[0002] In a printed product such as a booklet that is viewed in a spread, it is desirable that the image positions of two adjacent pages (spread pages) be aligned when viewed in a spread. Patent Document 1 describes that in a spread mode, image formation is performed on every other sheet by swapping the front and back sides of the image data, and then the sheet is discharged in an inverted state. According to this document, if one of the spread pages is an image (front side image) formed in the first image formation process in double-sided printing, for example, the other spread page will also be the front side image, so that the front and back side images are consistent between the spread pages. Therefore, when one of the spread pages is the front side image and the other is the back side image, misalignment of the image positions due to differences in the image writing reference position between the front side (leading edge of the paper) and the back side (trailing edge of the paper) is reduced. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2004-215188 Summary of the Invention [Problem to be solved by the invention]

[0004] An object of the present invention is to provide a new technique for reducing the misalignment of an image when viewed in a double-page spread. [Means for solving the problem]

[0005] One aspect of the present invention is an image forming device that includes an image forming means that forms an image on a sheet in an image forming section, an inversion means that inverts a sheet that has passed through the image forming section so that it can be transported again toward the image forming section, a detection means that detects the leading and trailing ends of the sheet in the sheet transport direction, and an alignment means that aligns the image formed on the sheet by the image forming means with the leading end of the sheet based on the detection result of the leading end of the sheet by the detection means, and that creates a product in which a first sheet on which a first image has been formed by the image forming means and a second sheet on which a second image has been formed by the image forming means are stacked, wherein the side of the first sheet on which the first image has been formed is opposite to the side of the second sheet on which the second image has been formed, and the trailing end of the first sheet when the first image is formed is opposite to the leading end of the second sheet when the second image is formed, and the alignment means corrects the position of the second image with respect to the leading end of the second sheet when the second image is formed, based on the detection result of the trailing end of the first sheet by the detection means when the first image is formed. [Effects of the Invention]

[0006] According to the present invention, a new technique can be provided for reducing the deviation of image position when viewed in a double-page spread. [Brief explanation of the drawings]

[0007] [Figure 1] 1 is a schematic diagram of an image forming apparatus according to a first embodiment. [Figure 2] 5A and 5B are diagrams for explaining a booklet production job according to the first embodiment. [Figure 3] 5A and 5B are diagrams for explaining a booklet production job according to the first embodiment. [Figure 4] 5A and 5B are diagrams for explaining a booklet production job according to the first embodiment. [Figure 5] 5A and 5B are schematic diagrams showing the positional relationship of sheets in a binding processing section according to the first embodiment. [Figure 6]5A and 5B are diagrams for explaining image positional deviation according to the first embodiment. [Figure 7] FIG. 4 is a diagram showing the procedure for executing a booklet production job according to the first embodiment. [Figure 8] 5A and 5B are diagrams for explaining the position of an image according to the first embodiment. [Figure 9] FIG. 2 is a diagram showing a control unit according to the first embodiment. [Figure 10] 8A and 8B are schematic diagrams of an image forming apparatus according to a second embodiment and a modified example thereof. [Figure 11] FIG. 11 is a diagram showing the procedure for executing a booklet production job according to the second embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0008] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings.

[0009] First Embodiment FIG. 1 is a schematic cross-sectional view showing an image forming apparatus 1 according to a first embodiment. The image forming apparatus 1 is an image forming system including an image forming apparatus main body (hereinafter referred to as apparatus main body 2) and a sheet processing apparatus 50 connected to the apparatus main body 2 via an intermediary conveyance unit 20. The image forming apparatus 1 forms an image on a sheet S, which is a recording material (recording medium), based on image information input from an external device, and discharges the sheet S as a finished product after processing it as necessary in the sheet processing apparatus 50. Note that the sheet S can be a variety of sheet materials of different sizes and materials, including paper such as plain paper and cardboard, surface-treated sheet materials such as plastic film, cloth, and coated paper, and sheet materials with special shapes such as envelopes and index paper.

[0010] (Device body) The apparatus main body 2 has a feeding cassette 3, a feeding roller 4, pairs of conveying rollers 5 and 6, an image forming unit 2A, a fixing device 10, a pair of conveying rollers 11, a pair of discharge rollers 12, a pair of reversing rollers 13, and pairs of conveying rollers 15 and 16. The apparatus main body 2 also has a control unit 85 and a sheet detection unit 81.

[0011] The feed cassette 3 is a storage unit in which sheets S are stacked and stored. The feed roller 4 is a feeding unit that feeds the sheets S one by one. The conveying roller pairs 5, 6, 11, 15, and 16, the discharge roller pair 12, and the reversing roller pair 13 are a conveying unit that conveys the sheet S along a conveying path within the apparatus main body 2. The conveying roller pair 6 is disposed immediately before the secondary transfer unit T2 in the sheet conveying direction. The conveying roller pair 6 is also called a registration roller pair that aligns (registers) the leading edge of the image in the sheet conveying direction (sub-scanning direction) with the leading edge of the sheet S. The conveying roller pair 6 also functions as a skew correction unit that corrects skew of the sheet S by having the leading edge of the sheet S abut against the nip portion of the conveying roller pair 6 when the conveying roller pair 6 is stopped.

[0012] The discharge roller pair 12 is a discharge means that discharges the sheet S from the apparatus main body 2. The reversing roller pair 13 is an example of a reversing means that reverses the sheet S that has passed through the image forming unit 2A so that the sheet S can be conveyed again toward the image forming unit 2A. Note that, in this embodiment, the reversing roller pair 13 is disposed separately from the discharge roller pair 12, but the discharge roller pair 12 may also be configured to reverse and convey the sheet S as a reversing means.

[0013] The image forming unit 2A is an example of an image forming means that forms an image on the sheet S. The image forming unit 2A of this embodiment is an electrophotographic unit using an intermediate transfer method. Specifically, the image forming unit 2A of this embodiment includes a photosensitive drum 7 as an image carrier, a laser scanner 8 as an exposure means, an intermediate transfer belt 9 as an intermediate transfer body, and a secondary transfer roller 92 as a transfer means. The photosensitive drum 7 is an electrophotographic photosensitive member having a photosensitive layer made of an organic photosensitive material or the like formed on the outer periphery of a cylindrical base. A charging device and a developing device (not shown) are arranged around the photosensitive drum 7. The laser scanner 8 includes an oscillator that emits laser light and an exposure optical system that guides the laser light toward the photosensitive drum 7 and scans the laser light in the direction of the rotation axis of the photosensitive drum 7 (the main scanning direction). The laser scanner 8 is an example of an exposure means; for example, an LED exposure device with light-emitting elements (LEDs) arranged in the main scanning direction may also be used. The intermediate transfer belt 9 is stretched over multiple rollers 93 and 94. A primary transfer roller 91 is disposed on the inner circumferential side of the intermediate transfer belt 9. A secondary transfer roller 92 is disposed so as to sandwich the intermediate transfer belt 9 together with a roller 93 (secondary transfer inner roller). A secondary transfer portion T2 is formed as a nip portion between the secondary transfer roller 92 and the intermediate transfer belt 9. The secondary transfer portion T2 is an example of an image forming portion where an image is formed on the sheet S.

[0014] The fixing device 10 has a heating element, a pressure element that forms a nip (fixing nip) together with the heating element, and a heating means for heating the heating element. The heating element is, for example, a rigid roller element or a flexible cylindrical film element. The heating means can be a halogen lamp that emits radiant heat or a heater substrate with a heating resistor.

[0015] The control unit 85 is a control means that controls the image forming apparatus 1. As shown in Fig. 9, the control unit 85 includes a CPU 86 that executes a program for controlling the image forming apparatus 1, and a storage device 87 that stores the program and data (such as condition settings for the image forming operation) necessary for controlling the image forming apparatus 1. The control unit 85 controls the operation of the image forming apparatus 1 by the CPU 86 reading and executing the program from the storage device 87 and controlling each part of the apparatus main body 2 and the sheet processing apparatus 50. The controlled objects include the laser scanner 8 and the conveying motor 6M that drives the conveying roller pair 6.

[0016] For example, based on the detection result of the sheet detection unit 81, the control unit 85 performs leading edge registration of an image transferred to the sheet S at the secondary transfer unit T2 relative to the leading edge of the sheet S in the sheet conveyance direction. That is, the control unit 85 functions as a registration unit that aligns an image formed on the sheet by the image forming unit relative to the leading edge of the sheet. The control unit 85 performs leading edge registration by, for example, adjusting the timing at which the laser scanner 8 starts writing an electrostatic latent image on the photosensitive drum 7 (hereinafter referred to as exposure write timing). Adjusting the exposure write timing changes the start point of the electrostatic latent image in the sub-scanning direction of the photosensitive drum 7, thereby controlling the image position relative to the sheet S. Alternatively, instead of or in addition to adjusting the exposure write timing, the control unit 85 may perform leading edge registration by adjusting the timing at which the leading edge of the sheet S reaches the secondary transfer unit T2 by adjusting the speed of the conveyance roller pair 6, for example.

[0017] In this embodiment, the control unit 85 is described as directly controlling the operation of the sheet processing apparatus 50, but the sheet processing apparatus 50 may have a second control unit. In this case, the second control unit controls the operation of the sheet processing apparatus 50 based on instructions from the control unit 85 of the apparatus main body 2.

[0018] The sheet detection unit 81 is an example of a detection means for detecting the leading and trailing ends of the sheet S in the sheet transport direction. Here, the leading end of the sheet S is the downstream end of the sheet S in the main sheet transport direction in the sheet transport path. The trailing end of the sheet S is the upstream end of the sheet S in the main sheet transport direction in the sheet transport path. The sheet detection unit 81 emits a detection signal corresponding to the presence or absence of the sheet S at a predetermined position (detection position) on the sheet transport path. The control unit 85 can detect that the leading or trailing end of the sheet S has passed the detection position based on a change in the detection signal emitted by the sheet detection unit 81.

[0019] The sheet detection unit 81 of this embodiment is disposed so as to detect the sheet S at a position between the secondary transfer unit T2 and a pair of conveying rollers 6 (upstream roller pair) disposed upstream of the secondary transfer unit T2 in the sheet conveying direction. The sheet detection unit 81 may be disposed so as to detect the sheet S at a position substantially the same as the nip portion of the pair of conveying rollers 6 in the sheet conveying direction. The sheet detection unit 81 may also be disposed so as to detect the sheet S at a position between the secondary transfer unit T2 and a pair of conveying rollers (downstream roller pair) disposed downstream of the secondary transfer unit T2 in the sheet conveying direction, or at a position substantially the same as the nip portion of the downstream roller pair.

[0020] The sheet detection unit 81 can use, for example, a reflective photoelectric sensor having a light emitting element that emits detection light toward the sheet transport path and a light emitting element that is arranged to receive the detection light reflected by the sheet and emits a detection signal according to the amount of received light.The sheet detection unit 81 can also use, for example, a flag-type sensor that combines a flag that protrudes into the sheet transport path and rotates when pressed by the sheet S, and a photoelectric sensor that detects the rotation of the flag.

[0021] (Image formation operation) The following describes a series of operations (image forming operations) by which the image forming apparatus 1 forms an image on a sheet S. The image forming apparatus 1 starts the image forming operation when the control unit 85 receives an instruction to perform the image forming operation (print command) and image information from an external device. When the image forming operation starts, the sheets S stacked in the feed cassette 3 are fed while being separated one by one by the feed roller 4, and are then conveyed to the secondary transfer unit T2 by the conveying roller pair 5 and 6.

[0022] Meanwhile, in the image forming unit 2A, the formation of a toner image by an electrophotographic process begins. First, the photosensitive drum 7 is rotated, and the charging device uniformly charges the surface of the photosensitive drum 7. The laser scanner 8 irradiates the photosensitive drum 7 with laser light based on a video signal generated from image information, exposing the photosensitive drum 7. As a result, the surface charge of the photosensitive drum 7 decays in the area irradiated with the laser light, and an electrostatic latent image is formed on the surface of the photosensitive drum 7. The developing device supplies toner as a developer to the photosensitive drum 7, developing the electrostatic latent image into a toner image. The toner image carried on the photosensitive drum 7 is primarily transferred to the intermediate transfer belt 9 by the primary transfer roller 91. The toner image carried on the intermediate transfer belt 9 is transported to the secondary transfer portion T2 by the rotation of the intermediate transfer belt 9. The toner image is then secondarily transferred to the first surface of the sheet S transported from the intermediate transfer belt 9 to the secondary transfer portion T2 by a bias electric field formed by the secondary transfer roller 92. That is, an image is formed on the first surface of the sheet S at the secondary transfer portion T2 serving as an image forming portion.

[0023] The sheet S that has passed through the secondary transfer portion T2 undergoes a fixing process of the toner image in the fixing device 10. The fixing device 10 applies heat and pressure to the image on the sheet S while nipping and conveying the sheet S in a fixing nip.

[0024] In the case of single-sided image formation (single-sided printing) in which an image is formed on only one side of the sheet S, the sheet S that has passed through the fixing device 10 is conveyed from the conveying roller pair 11 to the discharging roller pair 12, and is discharged to the relay conveying unit 20 by the discharging roller pair 12. The relay conveying unit 20 discharges the sheet S to the sheet processing device 50 by the conveying roller pairs 21 and 22.

[0025] In the case of double-sided image formation (double-sided printing), in which images are formed on both sides of a sheet S, the sheet S that has passed through the fixing device 10 is conveyed from the conveying roller pair 11 to the reversing roller pair 13. The reversing roller pair 13 performs reverse conveyance (switchback) of the sheet S and conveys the sheet S to a double-sided conveyance path 14. Reversing conveyance is an operation in which the reversing roller pair 13 conveys the sheet S in a first conveyance direction toward the outside of the apparatus body, and then switches the rotation direction before the trailing edge of the sheet in the first conveyance direction passes through the reversing roller pair 13, thereby conveying the sheet S in a second conveyance direction opposite to the first conveyance direction. The sheet S conveyed to the double-sided conveyance path 14 is conveyed again to the conveying roller pair 6 by the conveying roller pairs 15 and 16. Then, while the sheet S passes through the secondary transfer portion T2 again, a toner image is transferred to the second side of the sheet S, which is opposite to the first side. That is, an image is formed on the second side of the sheet S in the secondary transfer portion T2, which serves as an image forming portion.

[0026] The sheet S that has passed through the secondary transfer portion T2 undergoes a fixing process of the toner image by a fixing device 10. The sheet S that has passed through the fixing device 10 is conveyed from a conveying roller pair 11 to a discharging roller pair 12, and is discharged by the discharging roller pair 12 to an intermediary conveying unit 20. The intermediary conveying unit 20 discharges the sheet S to the sheet processing device 50 by conveying roller pairs 21 and 22.

[0027] When the sheet S inverted by the reversing roller pair 13 passes through the secondary transfer portion T2 for the second time, the second side of the sheet S faces the photosensitive drum 7. Furthermore, the leading edge of the sheet S when the sheet S inverted by the reversing roller pair 13 passes through the secondary transfer portion T2 for the second time is the trailing edge of the sheet S when the sheet S before being inverted by the reversing roller pair 13 passes through the secondary transfer portion T2 for the first time. In other words, the reversing roller pair 13 inverts and conveys the sheet S so that the first side and the second side of the sheet S that has passed through the secondary transfer portion T2 are switched and the leading edge and the trailing edge of the sheet S are switched, and the sheet S is conveyed again to the secondary transfer portion T2.

[0028] In this embodiment, the "first side" of the sheet S refers to the side that faces the photosensitive drum 7 when the sheet S fed from the feeding cassette 3 passes through the secondary transfer portion T2 for the first time. The "second side" of the sheet S refers to the side that faces the photosensitive drum 7 when the sheet S, which has passed through the secondary transfer portion T2 for the first time and then been inverted and conveyed by the reversing roller pair 13, passes through the secondary transfer portion T2 for the second time.

[0029] (sheet processing device) The sheet processing device 50 is a device (post-processing device, finisher) that processes sheets S on which images have been formed in the device main body 2. The sheet processing device 50 of this embodiment can bind multiple sheets S to create a sheet bundle and discharge the sheet bundle as an output of the image forming device 1.

[0030] The sheet processing device 50 includes an entrance roller pair 52, a conveying roller pair 53, a discharge roller pair 54, conveying roller pairs 57, 58, and 59, a binding processing unit 51, a bundle discharge roller pair 60, an upper discharge tray 55, and a lower discharge tray 61.

[0031] The entrance roller pair 52, the conveying roller pair 53, and the discharge roller pair 54 are arranged on a first conveying path that runs from an inlet where the sheet processing device 50 receives the sheet S toward the upper discharge tray 55. The conveying roller pairs 57, 58, and 59 are arranged on a second conveying path that branches off from the first conveying path and runs toward the binding processing unit 51. The bundle discharge roller pair 60 is arranged on a third conveying path that runs from the binding processing unit 51 toward the lower discharge tray 61.

[0032] The sheet processing device 50 receives the sheet S from the relay conveyance unit 20 via the entrance roller pair 52 and conveys it to the discharge roller pair 54 via the conveyance roller pair 53. When the binding process is not performed, the sheet S is discharged to an upper discharge tray 55 by the discharge roller pair 54. When the binding process is performed, the discharge roller pair 54 reverses and conveys the sheet S. In this case, the sheet S is guided to a second conveyance path by a backflow prevention member 56 and conveyed to the binding processing unit 51 by conveyance roller pairs 57, 58, and 59. The sheets S stacked on the tray of the binding processing unit 51 are aligned in the X direction (the conveyance direction when the sheet bundle is conveyed toward the bundle discharge roller pair 60) and in the Y direction perpendicular to the X direction by an alignment member provided in the binding processing unit 51. When a predetermined number of sheets S to be processed are stacked and aligned, the binding processing unit 51 binds the predetermined number of sheets S using a stapler or the like. This creates a sheet bundle in which the predetermined number of sheets S are bound. After the binding process, the sheet bundle is pushed out of the tray in the X direction by a push-out member provided in the binding processing unit 51. Furthermore, the sheet bundle is discharged to the outside of the sheet processing device 50 by a pair of bundle discharge rollers 60, and is stacked on a lower discharge tray 61 serving as a stacking unit for the product.

[0033] (Booklet creation job) 2(a) to 5(b), a booklet production job will be described, which is a series of operations in which the image forming apparatus 1 successively forms images on a plurality of sheets S and produces a bound sheet bundle (hereinafter referred to as a booklet). When a print command is received, the control unit 85 of the image forming apparatus 1 analyzes whether the command contains information instructing the production of a booklet, and if such an command is contained, executes the booklet production job.

[0034] Here, an example of a booklet creation job will be described in which a booklet including two sheets S is created. Also, here, an example of a booklet creation job will be described in which the front and back covers of the booklet are blank, and images are formed on two pages (facing pages) facing each other inside the booklet.

[0035] In this booklet production job, the sheet S fed first from the feeding cassette 3 is called the "preceding sheet S1," and the sheet S fed from the feeding cassette 3 after the preceding sheet S1 is called the "subsequent sheet S2."

[0036] In order to make the inside of the booklet a double-page spread, it is necessary to perform binding processing in the sheet processing apparatus 50 while the preceding sheet S1 and the succeeding sheet S2 are stacked so that the image side of the preceding sheet S1 and the image side of the succeeding sheet S2 face each other. The image side is the side (printed side) of the first and second sides of the sheet S on which an image is formed in the booklet production job.

[0037] First, only the conveyance of the preceding sheet S1 will be described. As shown in FIG. 2(a), the preceding sheet S1 is fed from the feeding cassette 3, and a toner image is transferred to a first surface of the preceding sheet S1 at the secondary transfer portion T2. ​​That is, when the preceding sheet S1 passes through the image forming portion (secondary transfer portion T2) for the first time, an image is formed on the first surface of the preceding sheet S1. Then, the toner image on the first surface is fixed by the fixing device 10.

[0038] 2(b), the preceding sheet S1 with the image formed on its first side is conveyed to the pair of reversing rollers 13, and is reversed and conveyed by the pair of reversing rollers 13. The preceding sheet S1 is further guided to the pair of conveying rollers 6 via the double-sided conveying path 14, and is conveyed again to the secondary transfer portion T2. ​​By being reversed and conveyed by the pair of reversing rollers 13, the leading edge and trailing edge of the preceding sheet S1 are switched when passing through the secondary transfer portion T2.

[0039] When the preceding sheet S1 passes through the secondary transfer portion T2 again, the toner image is not transferred onto the preceding sheet S1. In other words, when the preceding sheet S1 passes through the image forming portion (secondary transfer portion T2) for the second time, no image is formed on the second side of the preceding sheet S1.

[0040] 3(a), the preceding sheet S1 is conveyed to the discharge roller pair 12 with an image formed on its first side and a blank second side. Then, as shown in FIG. 3(b), the preceding sheet S1 is conveyed to the sheet processing device 50 via the relay conveyance unit 20 with the first side, which is the image side, facing upward.

[0041] 2(a) to 4(b), the image side of the preceding sheet S1 is indicated by a dashed line. For example, in FIG. 3(b), the upward facing side of the preceding sheet S1 in the drawing is the first side, which is the image side, and the downward facing side in the drawing is the second side, which is the non-image side (blank state).

[0042] 4(a), in the sheet processing device 50, the preceding sheet S1 is reversed and conveyed by a pair of discharge rollers 54, and then stacked in the binding processing section 51. The preceding sheet S1 is stacked in the binding processing section 51 with the first side, which is the image side, facing upward.

[0043] Next, the conveyance of the subsequent sheet S2 will be described. As shown in FIG. 2(b), the subsequent sheet S2 is fed by the feed roller 4 following the preceding sheet S1. Unlike the preceding sheet S1, when the subsequent sheet S2 passes through the secondary transfer portion T2 for the first time, no toner image is transferred to the subsequent sheet S2, and the subsequent sheet S2 is conveyed in a blank state. In other words, when the subsequent sheet S2 passes through the image forming portion (secondary transfer portion T2) for the first time, no image is formed on the first side of the subsequent sheet S2.

[0044] Thereafter, the succeeding sheet S2 is conveyed to the reversing roller pair 13, conveyed to the reversing roller pair 13, and reversed and conveyed by the reversing roller pair 13. The succeeding sheet S2 is further guided to the conveying roller pair 6 via the double-sided conveying path 14, and conveyed again to the secondary transfer portion T2. ​​By being reversed and conveyed by the reversing roller pair 13, the leading edge and trailing edge of the succeeding sheet S2 are switched when passing through the secondary transfer portion T2.

[0045] When the succeeding sheet S2 passes through the secondary transfer portion T2 again, the toner image is transferred to the succeeding sheet S2. That is, when the succeeding sheet S2 passes through the image forming portion (secondary transfer portion T2) for the second time, an image is formed on the second side of the succeeding sheet S2. Then, the toner image on the second side is fixed by the fixing device 10.

[0046] 4(a), the succeeding sheet S2 is conveyed to the discharge roller pair 12 with an image formed on its second side and a blank first side. Then, the succeeding sheet S2 is conveyed to the sheet processing device 50 via the relay conveying unit 20 with the second side, which is the image side, facing downward.

[0047] As with the preceding sheet S1, the image side of the succeeding sheet S2 is indicated by a dashed line in each of Figures 2(a) to 4(b). For example, in Figure 4(a), the downward facing side of the succeeding sheet S2 in the figure is the second side, which is the image side, and the upward facing side in the figure is the first side, which is the non-image side (blank state).

[0048] 4(b), in the sheet processing device 50, the subsequent sheet S2 is reversed and conveyed by the discharge roller pair 54, and then stacked in the binding processing unit 51. The subsequent sheet S2 is stacked in the binding processing unit 51 with the second surface, which is the image surface, facing downward, i.e., with the image surface of the preceding sheet S1 and the image surface of the subsequent sheet S2 facing each other.

[0049] Then, the preceding sheet S1 and the succeeding sheet S2 are aligned in the X and Y directions by an alignment member of the binding processing section 51, and then the preceding sheet S1 and the succeeding sheet S2 are bound by a binding means to produce a booklet. The booklet is then discharged by a bundle discharge roller pair 60 and stacked on a lower discharge tray 61.

[0050] (Correspondence between the leading and trailing edges of the preceding and succeeding sheets) The behavior of the preceding sheet S1 and the succeeding sheet S2 in the binding processing section 51 will be described with reference to FIGS.

[0051] FIG. 5(a) is a schematic diagram showing a state in which the preceding sheet S1 is stacked on the processing tray 51a of the binding processing unit 51. The processing tray 51a is a stacking unit (intermediate stacking unit) on which sheets to be bound are stacked. An image Im1 of "A" is formed on the first side S1F, which is the image side, of the preceding sheet S1. The second side S1R of the preceding sheet S1 is blank. The preceding sheet S1 is stacked on the processing tray 51a with the first side S1F facing upward and the second side S1R facing downward, facing the processing tray 51a.

[0052] The leading edge of the preceding sheet S1 in the sheet conveyance direction when the preceding sheet S1 passes through the secondary transfer portion T2 for the first time is defined as leading edge S1T at the time of image transfer, and the trailing edge of the preceding sheet S1 in the sheet conveyance direction is defined as trailing edge S1B at the time of image transfer. In this embodiment, an image is formed on the preceding sheet S1 when it passes through the secondary transfer portion T2 for the first time, and then the preceding sheet S1 is reversed once by the reversing roller pair 13 and conveyed to the sheet processing device 50. Therefore, when the preceding sheet S1 is stacked in the binding processing portion 51, the leading edge of the preceding sheet S1 in the X direction (the conveyance direction to the bundle discharge roller pair 60) is the trailing edge S1B at the time of image transfer, and the trailing edge of the preceding sheet S1 in the X direction is the leading edge S1T at the time of image transfer.

[0053] FIG. 5(b) is a schematic diagram showing a state in which a subsequent sheet S2 is stacked in the binding processing section 51 following the preceding sheet S1. An image Im2 of "B" is formed on the second side S2F, which is the image side of the subsequent sheet S2. Note that the second side S2R is on the top side, which is the side facing the back of the paper in FIG. 5(b), so the image Im2 is represented by an outline in FIG. 5(b). The first side S2F of the subsequent sheet S2 is blank. The subsequent sheet S2 is stacked on the processing tray 51a with the second side S2R facing downward and facing the first side S1F of the preceding sheet S1, and the first side S2F facing upward.

[0054] The leading edge of the subsequent sheet S2 in the sheet conveyance direction when the subsequent sheet S2 passes through the secondary transfer portion T2 for the second time is defined as leading edge S2T at the time of image transfer, and the trailing edge of the subsequent sheet S2 in the sheet conveyance direction is defined as trailing edge S2B at the time of image transfer. In this embodiment, after an image is formed on the subsequent sheet S2 when it passes through the secondary transfer portion T2 for the second time, the subsequent sheet S2 is conveyed to the sheet processing device 50 without being reversed by the reversing roller pair 13. Therefore, when the subsequent sheet S2 is stacked in the binding processing portion 51, the leading edge of the subsequent sheet S2 in the X direction (the conveyance direction toward the bundle discharge roller pair 60) is defined as leading edge S2T at the time of image transfer, and the trailing edge of the subsequent sheet S2 in the X direction is defined as trailing edge S2B at the time of image transfer.

[0055] 5(b), when the preceding sheet S1 and the succeeding sheet S2 are stacked in the binding processing section 51, the leading edge S1T of the preceding sheet S1 faces the trailing edge S2B of the succeeding sheet S2 when the image is transferred. Also, in the above state, the trailing edge S1B of the preceding sheet S1 faces the leading edge S2T of the succeeding sheet S2 when the image is transferred. In other words, when the preceding sheet S1 and the succeeding sheet S2 are stacked so that their image sides face each other to form a double-page spread, the positional relationship between the leading and trailing edges of the sheets when images are formed on their image sides is reversed between the two sheets.

[0056] In the binding processing unit 51, the preceding sheet S1 and the following sheet S2 are bound along the ends S1L and S2L of the preceding sheet S1 and the following sheet S2 in the Y direction perpendicular to the sheet conveyance direction in the image forming apparatus 1. For this reason, the leading edge S1T of the preceding sheet S1 at the time of image transfer becomes the bottom edge (bottom) of the booklet, whereas the trailing edge S2B of the following sheet S2 at the time of image transfer becomes the top edge (head) of the booklet. In other words, between two-page spreads, the correspondence between the leading edge / trailing edge at the time of image transfer and the top edge / bottom edge when viewed in a two-page spread is reversed.

[0057] In other words, in this embodiment, after the image forming unit forms the first image on the first sheet, the image forming device inverts and conveys the first sheet using the inverting device, and then stacks the first sheet on the stacking unit. Also, after the image forming unit forms the second image on the second sheet, the image forming device inverts and conveys the second sheet using the inverting device, and then stacks the second sheet on the stacking unit. Therefore, when the first sheet and the second sheet are stacked, the positional relationship between the leading edge and the trailing edge during image formation is reversed between the first sheet and the second sheet.

[0058] The image Im1 is formed on the preceding sheet S1 with the upper side of the image (the apex of "A") facing the trailing edge S1B when the image is transferred. On the other hand, the image Im2 is formed on the succeeding sheet S2 with the upper side of the image facing the leading edge S2T when the image is transferred.

[0059] That is, the orientation of image Im2 relative to the succeeding sheet S2 is opposite to the orientation of image Im1 relative to the preceding sheet S1 in terms of the sheet conveyance direction (the sub-scanning direction of the photosensitive drum 7). This allows the top and bottom of image Im1 and image Im2 to be aligned when the preceding sheet S1 and the succeeding sheet S2 are viewed as a double-page spread.

[0060] In addition, in this embodiment, as shown in Figure 5(b), an image is formed on the sheet S using long edge feed (the long edge is parallel to the sheet transport direction), and long edge binding can be performed in the binding processing unit 51, in which multiple sheets S are bound along the long edge.

[0061] (Image position misalignment) Next, using Figures 6(a) and (b), we will explain why image position misalignment occurs on a double-page spread and how to reduce the image position misalignment. Figure 6(a) is a schematic diagram showing effective print areas A1 and A2 on the image surfaces of the preceding sheet S1 and the succeeding sheet S2 in a reference example in which the processing of this embodiment is not applied. Figure 6(b) is a schematic diagram showing effective print areas A1 and A2 on the image surfaces of the preceding sheet S1 and the succeeding sheet S2 in the case in which the processing of this embodiment is applied. The effective print areas A1 and A2 are the maximum areas in which the image forming unit 2A can form an image on the sheet.

[0062] Hereinafter, for the preceding sheet S1, the edge of the effective print area A1 closest to the leading edge S1T during image transfer will be referred to as the print area leading edge A1T, and the edge closest to the trailing edge S1B during image transfer will be referred to as the print area trailing edge A1B. The distance from the leading edge S1T of the preceding sheet S1 during image transfer to the print area leading edge A1T will be referred to as the leading edge margin L1T. The distance from the trailing edge S1B of the preceding sheet S1 during image transfer to the print area trailing edge A1B will be referred to as the trailing edge margin L1B. Of the effective print area A2 of the succeeding sheet S2, the edge closest to the leading edge S2T during image transfer will be referred to as the print area leading edge A2T, and the edge closest to the trailing edge S2B during image transfer will be referred to as the print area trailing edge A2B. The distance from the leading edge S2T to the print area leading edge A2T during image transfer of the succeeding sheet S2 will be referred to as the leading edge margin L2T. The distance from the trailing edge S2B of the succeeding sheet S2 during image transfer to the print area trailing edge A2B will be referred to as the trailing edge margin L2B.

[0063] For simplicity, a case will be described in which a booklet is produced with the leading edge margins L1T, L2T and the trailing edge margins L1B, L2B all set to a preset target value L0.

[0064] 6(a), when the images Im1 and Im2 are formed, it is preferable that the trailing margin L1B of the preceding sheet S1 and the leading margin L2T of the following sheet S2 coincide when the image surfaces of the preceding sheet S1 and the following sheet S2 are viewed as a double-page spread. It is also preferable that the leading margin L1T of the preceding sheet S1 and the trailing margin L2B of the following sheet S2 coincide. In this case, a high-quality booklet is produced in which the vertical positions of the images Im1 and Im2 are aligned when viewed as a double-page spread.

[0065] However, for the following reasons, the trailing margin L1B of the preceding sheet S1 and the leading margin L2T of the succeeding sheet S2 may not match, and the trailing margin L1B of the preceding sheet S1 and the leading margin L2T of the succeeding sheet S2 may not match.

[0066] First, when considering the sheet transport direction when images Im1 and Im2 are formed, the trailing edge margin L1B of the preceding sheet S1 is the margin on the trailing edge S1B side when the image is transferred, whereas the leading edge margin L2T of the succeeding sheet S2 is the margin on the leading edge S2T side when the image is transferred.

[0067] 6(a), the leading edge of each sheet is registered based on the target value L0, and the leading edge margins L1T, L2T of the preceding sheet S1 and the succeeding sheet S2 are both adjusted to the target value L0. In other words, the control unit 85 determines the exposure and writing timing based on the timing at which the sheet detection unit 81 detects the leading edge of the sheet so that the leading edge margins L1T, L2T become the target value L0.

[0068] By appropriately setting the magnification in the sub-scanning direction of the electrostatic latent image formed on the photosensitive drum 7 by the laser scanner 8, ideally, the trailing edge margin L2B of the succeeding sheet S2, which corresponds to the leading edge margin L1T of the preceding sheet S1, can also be set to the target value L0.

[0069] However, in reality, the trailing edge margin L1B of the preceding sheet S1 becomes a value that deviates from L0 for various reasons. For example, the timing at which the detection signal of the sheet detection unit 81 changes in response to the passage of the leading edge of the preceding sheet S1 may vary with respect to the timing at which the leading edge of the preceding sheet S1 actually passes the detection position of the sheet detection unit 81. Also, fluctuations in the conveying speed of the preceding sheet S1 may cause variation in the time from when the leading edge of the preceding sheet S1 passes the sheet detection unit 81 until when the trailing edge of the preceding sheet S1 passes the sheet detection unit 81.

[0070] For these reasons, if the trailing margin L1B of the preceding sheet S1 deviates from L0, the trailing margin L1B of the preceding sheet S1 and the leading margin L2T of the following sheet S2 will not match, which may result in a deterioration in the quality of the booklet.Furthermore, for the same reasons, if the trailing margin L2B of the following sheet S2 deviates from L0, the leading margin L1T of the preceding sheet S1 and the trailing margin L2B of the following sheet S2 will not match, which may result in a deterioration in the quality of the booklet.

[0071] Variations in the trailing edge margins L1B and L2B are caused by the cumulative effects of various factors, such as variations in the leading edges A1T and A2T of the printing area, wear on the conveying roller pair 6, and component and assembly tolerances of the sheet detection unit 81 and the conveying roller pair 6. For this reason, it is difficult to accurately match the trailing edge margins L1B and L2B with the target value L0 of the leading edge margins L1T and L2T.

[0072] Therefore, in this embodiment, the position of the leading edge A2T of the print area of ​​the subsequent sheet S2 is corrected based on the detection result of the trailing edge S1B of the preceding sheet S1 by the sheet detection unit 81 when the image is transferred. In other words, the control unit 85, which serves as the alignment unit in this embodiment, corrects the position of the second image relative to the leading edge of the second sheet when the second image is formed, based on the detection result of the trailing edge of the first sheet by the detection unit when the first image is formed. This reduces the misalignment between the leading edge margin of the first sheet and the trailing edge margin of the second sheet, improving the quality of the booklet.

[0073] More specifically, the control unit 85 calculates the trailing edge margin L1B of the preceding sheet S1 based on the detection result of the trailing edge S1B of the preceding sheet S1 by the sheet detection unit 81 during image transfer. The control unit 85 calculates the difference (trailing edge deviation amount) between the calculated trailing edge margin L1B and the target value (here, L0) of the trailing edge margin L1B. Then, when performing leading edge registration of the subsequent sheet S2, the control unit 85 shifts the position of the leading edge A2T of the printing area of ​​the subsequent sheet S2 by the trailing edge deviation amount of the preceding sheet S1. In other words, the control unit 85 corrects the target value L0 of the leading edge margin based on the trailing edge deviation amount of the preceding sheet S1, and sets the result as the target value of the leading edge margin L2T of the subsequent sheet S2.

[0074] As a result, as shown in FIG. 6B, the leading edge margin L2T of the succeeding sheet S2 and the trailing edge margin L1B of the preceding sheet S1 can be aligned, improving the quality of the double-page spread.

[0075] (Booklet Creation Job Execution Procedure) An example of the execution procedure for a booklet production job according to this embodiment will be described using Fig. 7 and Figs. 8(a) and (b). Fig. 7 shows a chronological order of processing for the preceding sheet S1 and the succeeding sheet S2 in the booklet production job described above, and also shows a flowchart of the processing in the booklet production job. Each step (S101 to S107) in the flowchart is achieved by the control unit 85 of the image forming apparatus 1. Figs. 8(a) and (b) are schematic diagrams showing the effective print areas A1 and A2 of the preceding sheet S1 and the succeeding sheet S2.

[0076] When a booklet production job is started, feeding of the preceding sheet S1 begins. In S101, an image Im1 is formed on the first side of the preceding sheet S1 (FIG. 2(a)). At this time, the leading edge of the preceding sheet S1 is registered so that the leading edge margin L1T of the preceding sheet S1 becomes a preset target value L1T'. The target value L1T' is preset based on the setting information of the booklet production job.

[0077] Thereafter, the preceding sheet S1 is reversed and conveyed by the pair of reversing rollers 13 (FIG. 2(b)), and then discharged from the apparatus main body 2 toward the sheet processing device 50 (FIG. 3(b)), and is stacked in the binding processing section 51 (FIG. 4(a)). However, FIG. 7 does not specify the time sequence between each process of the conveying operation after forming an image on the first side of the preceding sheet S1 and the processes of S103 to S105.

[0078] In S102, the sheet detection unit 81 detects the trailing edge of the preceding sheet S1 when the image Im1 is formed on the first side thereof (i.e., the trailing edge S1B when the image is transferred). In S103, the trailing edge margin L1B of the preceding sheet S1 is calculated based on the timing of detection of the trailing edge S1B of the preceding sheet S1 when the image is transferred by the sheet detection unit 81 and the nominal timing of the end of image writing on the first side of the preceding sheet S1. FIG. 8(a) is a schematic diagram showing the parameter (trailing edge margin L1B) calculated in S103.

[0079] The nominal image writing end timing for the first side of the preceding sheet S1 is the timing (exposure end timing) when the laser scanner 8 completes exposure of the area on the photosensitive drum 7 corresponding to the trailing edge A1B of the print area. To calculate the trailing edge margin L1B based on the detection timing of the trailing edge S1B by the sheet detection unit 81 and the nominal image writing end timing, specifically, for example, the following procedure is performed. First, a first timing at which the exposure end position on the photosensitive drum 7 reaches the secondary transfer unit T2 is determined based on the nominal image writing end timing and the rotation speed of the photosensitive drum 7. Next, a second timing at which the trailing edge S1B reaches the secondary transfer unit T2 is determined based on the detection timing of the trailing edge S1B by the sheet detection unit 81 and the nominal sheet conveyance speed (process speed) at the secondary transfer unit T2. The trailing edge margin L1B of the preceding sheet S1 can be calculated by multiplying the difference between the first and second timings by the process speed. In practice, a calculation formula that produces the same results as the above calculation procedure may be determined in advance, and the detection timing and the image writing end timing may be substituted into the calculation formula to perform the calculation.

[0080] The left side of Figure 8(a) shows the leading edge margin L2T when no leading edge registration correction is performed on the subsequent sheet S2. In this case, the leading edge A2T of the print area of ​​the subsequent sheet S2 is aligned to a position where the leading edge margin L2T is the target value L2T'. The target value L2T' is set in advance based on the setting information of the booklet production job.

[0081] In S104, the difference (trailing edge deviation ΔL) between the calculated trailing edge margin L1B and the target value L1B' of the trailing edge margin L1B is calculated. That is, ΔL = L1B - L1B'. In other words, the control unit 85 as a positioning unit calculates the difference between the trailing edge margin of the first sheet and the target value based on the timing when the detection unit detects the trailing edge of the first sheet and the timing when the exposure unit finishes forming the electrostatic latent image. The target value L1B' is set in advance based on the setting information of the booklet production job.

[0082] The subsequent sheet S2 is fed following the preceding sheet S1, passes through the secondary transfer portion T2 without an image being transferred (FIG. 2(b)), and is then reversed and conveyed by the pair of reversing rollers 13 (FIG. 3(a)). However, FIG. 7 does not specify the time sequence between each process of the conveying operation before forming an image on the second side of the subsequent sheet S2 and the processes of S101 to S104.

[0083] In S105, an image Im2 is formed on the second surface of the succeeding sheet S2. At this time, the target value of the leading edge margin L2T of the succeeding sheet S2 is corrected using the trailing edge shift amount ΔL calculated in S104. In other words, the control unit 85 as a position alignment unit corrects the leading edge margin of the second sheet from the target value by the amount of the difference between the trailing edge margin of the first sheet and the target value.

[0084] 8B is a schematic diagram showing the parameter (trailing edge deviation ΔL) calculated in S104 and the correction amount for the leading edge registration of the subsequent sheet S2. As shown in the figure, the position of the leading edge A2T of the print area, which is the reference position on the leading edge side of the image Im2 formed on the subsequent sheet S2, is corrected by the same amount as the trailing edge deviation ΔL that occurred in the preceding sheet S1. As a result of this correction, the target value for the leading edge margin L2T in the leading edge registration of the subsequent sheet S2 becomes L2T' + ΔL.

[0085] Thereafter, the subsequent sheet S2 is discharged from the apparatus main body 2 toward the sheet processing device 50 (FIG. 4(a)), and is stacked in the binding processing unit 51 (FIG. 4(b)). In S106, the preceding sheet S1 and the subsequent sheet S2 are aligned in the X and Y directions in the binding processing unit 51. In S107, the preceding sheet S1 and the subsequent sheet S2 are bound. Then, the completed booklet is discharged by the bundle discharge roller pair 60, and the booklet production job is completed.

[0086] (Advantages of this embodiment) As described above, according to this embodiment, a product is created in which the preceding sheet S1 and the succeeding sheet S2 are stacked so that the surfaces on which the images Im1 and Im2, which form the facing pages, face each other. In this product, the trailing edge S1B of the preceding sheet S1 during image transfer faces the leading edge S2T of the succeeding sheet S2 during image transfer. Then, based on the detection result of the sheet detection unit 81 of the trailing edge S1B of the preceding sheet S1 during image transfer, the control unit 85 corrects the position of the leading edge A2T of the print area of ​​the succeeding sheet S2 relative to the leading edge S2T during image transfer.

[0087] In other words, the image forming apparatus creates a product in which a first sheet on which a first image is formed by the image forming means and a second sheet on which a second image is formed by the image forming means are superimposed. In this product, the side of the first sheet on which the first image is formed faces the side of the second sheet on which the second image is formed, and the rear end of the first sheet when the first image is formed faces the front end of the second sheet when the second image is formed. The alignment means corrects the position of the second image with respect to the front end of the second sheet when the second image is formed, based on the detection result of the rear end of the first sheet by the detection means when the first image is formed.

[0088] This allows the positions of the first and second images to be aligned when the finished product in which the first and second sheets are superimposed is viewed as a double-page spread, thereby improving the quality of the finished product.

[0089] Furthermore, the leading edge margin L1T of the preceding sheet S1 is set to a preset target value, while the leading edge registration of the succeeding sheet S2 is performed so that the trailing edge margin L2B of the succeeding sheet S2 is equal to the trailing edge margin L1B of the preceding sheet S1. In other words, the first image is aligned with the leading edge of the first sheet so that the leading edge margin of the first sheet is equal to the preset target value. Furthermore, the second image is aligned with the leading edge of the second sheet so that the leading edge margin of the second sheet is equal to the trailing edge margin of the first sheet. This allows the trailing edge margin L1B of the preceding sheet S1 and the leading edge margin L2T of the succeeding sheet S2 to be aligned when viewed in a double-page spread.

[0090] In this embodiment, an example has been described in which the trailing margin L2B of the subsequent sheet S2 is set equal to the trailing margin L1B of the preceding sheet S1, but depending on the purpose of the finished product, the trailing margin L2B of the subsequent sheet S2 may be set to a value different from the trailing margin L1B of the preceding sheet S1.

[0091] 6A, the preceding sheet S1 and the succeeding sheet S2 are bound together. In other words, a binding processing unit is further provided that binds the first sheet and the second sheet so that the side of the first sheet on which the first image is formed and the side of the second sheet on which the second image is formed form a two-page spread. This makes it possible to create a booklet in which the trailing edge margin L1B of the preceding sheet S1 and the leading edge margin L2T of the succeeding sheet S2 are aligned when viewed in a two-page spread. In other words, it is possible to provide an image forming apparatus 1 that can create a product in which the image positions between the two-page spread pages are aligned and bound together.

[0092] (Variation) While the present embodiment illustrates the creation of a booklet including two sheets, a booklet including three or more sheets may be created in a booklet creation job. Even in this case, the processing of this embodiment can be applied between a sheet (first sheet) on which an image (first image) is formed first in the booklet and a sheet (second sheet) on which an image (second image) is formed after the first image and which, together with the first sheet, forms a two-page spread. In other words, for each pair of two sheets that form a two-page spread among the three or more sheets, the alignment unit corrects the position of the image relative to the leading edge of one sheet when the image forming unit forms the other image of the two-page spread on the other sheet based on the detection result of the trailing edge of the one sheet by the detection unit when the image forming unit forms one image of the two-page spread on the other sheet. This allows a booklet to be created in which the image positions are aligned on each of the two-page spread pages included in the booklet.

[0093] In addition, although the present embodiment has been described as an example in which no image is formed on the front and back covers of the booklet, it is also possible to produce a booklet with images formed on the front and back covers. For example, in the procedure of the booklet production job shown in Fig. 7, an image may be formed on the second side of the preceding sheet S1, and an image may be formed on the first side of the succeeding sheet S2.

[0094] In the present embodiment, the following sheet S2 passes through the secondary transfer portion T2 without an image being transferred to its first side, and is then inverted and conveyed, after which an image is transferred to its second side. However, the first side of the following sheet S2 may be the image side. For example, in the procedure of the booklet production job shown in FIG. 7, the following sheet S2 may have an image transferred to its first side when it passes through the secondary transfer portion T2 for the first time ("image transferred to first side" instead of "image transferred to second side"). In this case, the following sheet S2, whose image has been transferred to its first side, is discharged from the apparatus main body 2 toward the sheet processing device 50 (FIG. 4A) and stacked in the binding processing portion 51 (FIG. 4B) without being inverted and conveyed by the reversing roller pair 13. This modification also provides the same advantages as the present embodiment by correcting the target value of the leading edge registration when forming an image on the first side of the following sheet S2 based on the trailing edge deviation amount ΔL of the preceding sheet S1. The advantage of this modified example is that the number of steps in the transport operation of the subsequent sheet S2 is reduced (it becomes a single-sided printing sequence), which reduces the time that the preceding sheet S1 waits in the state shown in Figure 2(b), for example, thereby improving the productivity of the booklet production job.

[0095] Furthermore, in this embodiment, the first side of the preceding sheet S1 (the side on which the image is transferred when it passes through the secondary transfer portion T2 for the first time after feeding) is the image side of the double-page spread, but the second side of the preceding sheet S1 may also be the image side of the double-page spread. That is, although productivity will be reduced, the number of inversions within the apparatus main body 2 may be increased so that the preceding sheet S1 passes through the secondary transfer portion T2 without an image being transferred to its first side, and then the image may be transferred to the second side of the preceding sheet S1 after it is inverted and conveyed. In this modified example, the same advantages as in this embodiment can be obtained by correcting the target value of the leading edge registration when forming an image on the subsequent sheet S2 based on the trailing edge deviation amount ΔL when forming an image on the second side of the preceding sheet S1.

[0096] In this embodiment, "preceding sheet S1" and "subsequent sheet S2" do not represent the order of pages in the created booklet. For example, in the spread state shown in FIG. 6(b), the page on which image Im2 of subsequent sheet S2 is formed may be the page that is read before the page on which image Im1 of preceding sheet S1 is formed. Similarly, "first sheet" and "second sheet" do not specify the order of pages in the created deliverable.

[0097] For example, in Fig. 5, binding may be performed along the edges of the preceding sheet S1 and the succeeding sheet S2 opposite to the edges S1L and S2L in the X direction. In this case, a booklet is created in which the left and right sides of the images Im1 and Im2 are reversed when viewed in a double-page spread, compared to the example in Fig. 6(a).

[0098] Second Embodiment An image forming apparatus according to a second embodiment, which has a different layout of the apparatus main body 2' from that of the first embodiment, will be described with reference to Fig. 10(a). Below, elements with the same reference numerals as those in the first embodiment have substantially the same configurations and functions as those described in the first embodiment, and differences from the first embodiment will be mainly described.

[0099] Hereinafter, the term "through discharge" refers to the state in which the sheet S, onto which an image has been transferred at the secondary transfer portion T2, is discharged from the apparatus main body 2 without being reversed and conveyed by the reversing roller pair 13. In the first embodiment shown in FIG. 1, when the sheet S, onto which an image has been transferred at the secondary transfer portion T2, is discharged through and stacked in the binding processing portion 51, the image side becomes the sheet side facing downward in the binding processing portion 51.

[0100] In contrast, in the image forming apparatus of the second embodiment shown in FIG. 10(a), the layout of the apparatus main body 2′ is different from that of the first embodiment. Specifically, in the first embodiment, when a sheet S having an image transferred to one side (image side) is discharged through the apparatus main body 2, the image side is discharged with the image side facing downward (face down). In contrast, in the second embodiment, when a sheet S having an image transferred to one side (image side) is discharged through the apparatus main body 2, the image side is discharged with the image side facing upward (face up). Therefore, in the second embodiment, when a sheet S having an image transferred to one side (image side) at the secondary transfer unit T2 is discharged through the apparatus main body 2 and stacked in the binding processing unit 51, the image side becomes the sheet side facing upward in the binding processing unit 51.

[0101] In the case of such a layout, the following can be done to make the image sides of the first sheet and the second sheet face each other in the binding processing section 51 to form a double-page spread. That is, after an image is transferred to the first side of the first sheet, the first sheet is discharged through the binding processing section 51 and stacked in the binding processing section 51. After an image is transferred to the second side of the second sheet, the second sheet is reversed and conveyed within the device main body 2, and then discharged, and stacked on top of the first sheet in the binding processing section 51.

[0102] (Booklet Creation Job Execution Procedure) An example of the execution procedure of a booklet production job according to this embodiment will be described with reference to Fig. 11. Fig. 11 shows the processing for the preceding sheet S1 and the succeeding sheet S2 in the booklet production job in chronological order, and also shows the processing in the booklet production job in the form of a flowchart. Each step (S201 to S207) in the flowchart is realized by the control unit 85 of the image forming apparatus 1.

[0103] When a booklet production job is started, feeding of the preceding sheet S1 begins. In S201, an image is formed on the first side of the preceding sheet S1. At this time, the leading edge of the preceding sheet S1 is registered so that the leading edge margin L1T of the preceding sheet S1 becomes a preset target value L1T'. The target value L1T' is preset based on the setting information of the booklet production job. Thereafter, the preceding sheet S1 is reversed and conveyed by the reversing roller pair 13, and then discharged from the device main body 2 toward the sheet processing device 50 and stacked in the binding processing unit 51.

[0104] In S202, the sheet detection unit 81 detects the trailing edge of the preceding sheet S1 when an image is formed on the first side thereof (i.e., the trailing edge S1B when the image is transferred). In S203, the trailing edge margin L1B of the preceding sheet S1 is calculated based on the timing at which the sheet detection unit 81 detects the trailing edge S1B of the preceding sheet S1 when the image is transferred and the nominal timing at which image formation on the preceding sheet S1 is completed. In S204, the difference between the calculated trailing edge margin L1B and the target value L1B' of the trailing edge margin L1B (trailing edge deviation amount ΔL) is calculated. That is, ΔL = L1B - L1B'.

[0105] The subsequent sheet S2 is fed following the preceding sheet S1. In S205, an image is formed on the first side of the subsequent sheet S2. At this time, the target value of the leading edge margin L2T of the subsequent sheet S2 is corrected using the trailing edge deviation ΔL calculated in S204. In other words, the position of the leading edge A2T of the print area, which is the reference position on the leading edge side of the image to be formed on the subsequent sheet S2, is corrected by the same amount as the trailing edge deviation ΔL that occurred in the preceding sheet S1. As a result of this correction, the target value of the leading edge margin L2T in the leading edge registration of the subsequent sheet S2 becomes L2T' + ΔL.

[0106] Thereafter, the subsequent sheet S2 is discharged from the apparatus main body 2 toward the sheet processing apparatus 50 and is stacked in the binding processing section 51. At this time, the first side, which is the image side of the subsequent sheet S2, faces upward in the binding processing section 51.

[0107] The inverted and conveyed preceding sheet S1 is discharged from the device main body 2 toward the sheet processing device 50 following the succeeding sheet S2, and is stacked in the binding processing section 51. At this time, the first side, which is the image side of the preceding sheet S1, faces downward in the binding processing section 51 and faces the image side of the succeeding sheet S2.

[0108] In S206, the preceding sheet S1 and the succeeding sheet S2 are aligned in the X and Y directions in the binding processing unit 51. In S207, the preceding sheet S1 and the succeeding sheet S2 are bound. Then, the completed booklet is discharged by the bundle discharge roller pair 60, and the booklet production job is completed.

[0109] In this embodiment, the preceding sheet S1 is inverted and conveyed after image transfer and then stacked in the binding processing section 51, while the succeeding sheet S2 is stacked in the binding processing section 51 without being inverted and conveyed after image transfer. In other words, the image forming apparatus forms the first image on the first sheet by the image forming unit, and then stacks the first sheet on the stacking section without inverting and conveying the first sheet by the reversing unit. Also, the image forming apparatus forms the second image on the second sheet by the image forming unit, and then inverts and conveys the second sheet by the reversing unit, and then stacks the second sheet on the stacking section.

[0110] 5B in the first embodiment, the trailing edge of the preceding sheet S1 when the image is transferred faces the leading edge of the subsequent sheet S2 when the image is transferred in the binding processing section 51. Therefore, if no correction is made when performing leading edge registration of the subsequent sheet S2, the leading edge margin L1T of the preceding sheet S1 and the trailing edge margin L2B of the subsequent sheet S2 will not match, which may result in a decrease in the quality of the booklet (see FIG. 6B).

[0111] According to this embodiment, the control unit 85 corrects the position of the leading edge A2T of the printing area relative to the leading edge S2T when the image is transferred on the subsequent sheet S2, based on the detection result of the trailing edge S1B of the preceding sheet S1 when the image is transferred on the subsequent sheet S2 by the sheet detection unit 81. In other words, the alignment unit corrects the position of the second image relative to the leading edge of the second sheet when the second image is formed, based on the detection result of the trailing edge of the first sheet by the detection unit when the first image is formed.

[0112] As a result, even in an image forming apparatus having a different layout of the apparatus main body 2' from that of the first embodiment, it is possible to obtain the same advantages as those of the first embodiment.

[0113] In this embodiment, the first image to be formed on the image surface of the double-page spread is

[0114] (Variation) In the second embodiment, a configuration in which the layout of the apparatus main body 2' is different from that of the first embodiment has been exemplified, but the layout of the sheet processing device 50' may also be different from that of the first embodiment. In the image forming apparatus of the modified example shown in FIG. 10(b), the layout of the sheet processing device 50' is different from that of the first embodiment, and the sheet surface that faces upward when discharged from the apparatus main body 2 becomes the sheet surface that faces downward when stacked in the binding processing unit 51. Therefore, in this modified example, as in the second embodiment, when a sheet S with an image transferred to one side (image surface) at the secondary transfer unit T2 is discharged through and stacked in the binding processing unit 51, the image surface becomes the sheet surface that faces upward in the binding processing unit 51.

[0115] In this modified example, a booklet production job can be executed using the same execution procedure as in Fig. 11. In this case, the control unit 85 corrects the position of the leading edge A2T of the print area relative to the leading edge S2T of the subsequent sheet S2 when the image is transferred, based on the detection result of the trailing edge S1B of the preceding sheet S1 by the sheet detection unit 81 when the image is transferred. This makes it possible to obtain the same advantages as in the first embodiment even in an image forming apparatus having a sheet processing device 50' with a different layout from that of the first embodiment.

[0116] (Other variations) In the above-described embodiments, a stapler has been described as an example of the binding mechanism in the binding processing unit 51, but the binding mechanism is not limited to this. The binding mechanism may, for example, be a mechanism that bonds a stack of sheets coated with a powder adhesive by heating and pressurizing the stack with a heating plate equipped with a heater to melt the powder adhesive and thereby bond the sheets together. The powder adhesive may be the same as the toner (printing toner, color toner) used to form the image. The stapler may also be a mechanism that binds using a staple or a mechanism that performs stapleless binding. The stapleless binding method may be a method that fastens the sheets together by cutting out a portion of the sheet stack and folding it back to form a folded portion, or a method that clamps the sheet stack with uneven teeth to intertwine the fibers of the sheets and press them together.

[0117] In addition, in the above-described embodiment, a configuration in which binding processing is performed within the sheet processing device 50 connected to the device main body 2 is exemplified, but a loading section (buffer) for loading sheets may be provided within the device main body 2, and binding processing may be performed in the loading section.

[0118] In the above-described embodiment, the image forming apparatus 1 performs a one-stop process from image formation to binding. However, the binding process may be performed by a user. That is, the image forming apparatus may create a product in which a first sheet on which a first image is formed by the image forming unit and a second sheet on which a second image is formed by the image forming unit are stacked, but the first sheet and the second sheet are not bound. In the product, the side of the first sheet on which the first image is formed faces the side of the second sheet on which the second image is formed, and the trailing edge of the first sheet when the first image is formed faces the leading edge of the second sheet when the second image is formed. Even in this case, the same advantages as those of the respective embodiments can be obtained by correcting the position of the second image relative to the leading edge of the second sheet when the second image is formed based on the detection result of the trailing edge of the first sheet by the detection unit when the first image is formed.

[0119] In the above-described embodiment, a sensor that determines the presence or absence of a sheet at a detection position on the sheet transport path has been exemplified as the sheet detection unit 81. However, the sheet detection unit 81 may be, for example, a line sensor having a detection area that extends in a direction (main scanning direction, sheet width direction) perpendicular to the sheet transport direction. This line sensor may also serve as a lateral registration detection means that detects the position of the sheet in order to align the image in the sheet width direction (lateral registration).

[0120] The number and location of the sheet detection units 81 may also be changed. For example, two or more sheet detection units may be arranged at different locations in the sheet transport direction, and the sheet transport speed may be calculated based on the time difference between the detection timings of the leading and trailing edges of the same sheet. In this case, the calculation accuracy can be improved when calculating the trailing edge margin L1B of the preceding sheet S1 based on the detection result of the trailing edge S1B of the preceding sheet S1 during image transfer by the sheet detection unit 81. That is, in the above calculation example, the sheet transport speed calculated using multiple sheet detection units can be used instead of the nominal sheet transport speed at the secondary transfer unit T2. This allows the trailing edge margin L1B of the preceding sheet S1 to be calculated with higher accuracy, even when the sheet transport speed varies due to conditions such as differences in transport resistance due to the sheet material or wear on the transport rollers.

[0121] Furthermore, in the above-described embodiment, an intermediate transfer type image forming unit 2A was given as an example of the image forming means, but a direct transfer type image forming unit that transfers a toner image directly from the photosensitive drum 7 (image carrier) to the sheet S may also be used. Furthermore, the image forming means is not limited to the electrophotographic type, and may be an inkjet type that forms an image on the sheet S by ejecting ink from a nozzle, for example. In this case, the image forming unit refers to the portion on the sheet transport path where the sheet S faces the nozzle.

[0122] (Other embodiments) The present invention can also be realized by supplying a program that realizes one or more functions of the above-described embodiments to a system or device via a network or a storage medium, and having one or more processors in the computer of the system or device read and execute the program.The present invention can also be realized by a circuit (e.g., ASIC) that realizes one or more functions.

[0123] Summary of the Disclosure The present disclosure includes at least the following configurations or methods.

[0124] (Configuration 1) an image forming unit for forming an image on a sheet in an image forming section; a reversing unit that reverses the sheet that has passed through the image forming unit so that the sheet can be conveyed again toward the image forming unit; a detection unit for detecting the leading and trailing ends of the sheet in the sheet conveying direction; a positioning unit that aligns an image formed on a sheet by the image forming unit with respect to the leading edge of the sheet based on the detection result of the leading edge of the sheet by the detection unit; Equipped with An image forming apparatus for producing a product in which a first sheet on which a first image is formed by the image forming means and a second sheet on which a second image is formed by the image forming means are stacked together, wherein the surface of the first sheet on which the first image is formed faces the surface of the second sheet on which the second image is formed, and the rear end of the first sheet when the first image is formed faces the front end of the second sheet when the second image is formed, the alignment means corrects the position of the second image relative to the leading edge of the second sheet when the second image is formed, based on the detection result of the trailing edge of the first sheet by the detection means when the first image is formed. An image forming apparatus characterized by:

[0125] (Configuration 2) When the maximum area in which the image forming means can form an image on a sheet is defined as an effective printing area, the distance from the leading edge of the sheet in the sheet transport direction to the leading edge of the effective printing area in the sheet transport direction is defined as a leading edge margin, and the distance from the trailing edge of the sheet in the sheet transport direction to the trailing edge of the effective printing area in the sheet transport direction is defined as a trailing edge margin, The alignment means is aligning the first image with respect to the leading edge of the first sheet so that the leading edge margin of the first sheet is a preset target value; aligning the second image with respect to the leading edge of the second sheet so that the leading edge margin of the second sheet is equal to the trailing edge margin of the first sheet; 2. The image forming apparatus according to claim 1,

[0126] (Configuration 3) the image forming unit includes an image carrier and an exposure unit that exposes the image carrier to light to form an electrostatic latent image on the image carrier; The alignment means is calculating a difference between the trailing edge margin of the first sheet and the target value based on a timing when the detection unit detects the trailing edge of the first sheet and a timing when the exposure unit completes forming the electrostatic latent image; correcting the leading edge margin of the second sheet from the target value by the difference; 3. The image forming apparatus according to configuration 2.

[0127] (Configuration 4) the image forming unit includes an image carrier and an exposure unit that exposes the image carrier to light to form an electrostatic latent image on the image carrier; the alignment means adjusts the timing at which the exposure means starts forming the electrostatic latent image; 4. The image forming apparatus according to any one of configurations 1 to 3.

[0128] (Configuration 5) the image forming unit includes an image carrier and a transfer unit that transfers a toner image formed on the image carrier to a sheet in the image forming unit; the positioning means adjusts the timing at which the leading edge of the sheet reaches the image forming unit; 4. The image forming apparatus according to any one of configurations 1 to 3.

[0129] (Configuration 6) the image forming unit includes an image carrier, an exposure unit that exposes the image carrier to light to form an electrostatic latent image on the image carrier, and a transfer unit that transfers the toner image formed on the image carrier to a sheet in the image forming unit; the positioning unit adjusts the timing when the exposure unit starts forming the electrostatic latent image and the timing when the leading edge of the sheet reaches the image forming unit. 4. The image forming apparatus according to any one of configurations 1 to 3.

[0130] (Configuration 7) further comprising an upstream roller pair disposed upstream of the image forming means in the sheet conveying direction; the detection unit detects the sheet at a position of a nip portion of the upstream roller pair in the sheet conveying direction, or at a position between the nip portion and the image forming unit; 7. The image forming apparatus according to any one of configurations 1 to 6.

[0131] (Configuration 8) a downstream roller pair disposed downstream of the image forming means in the sheet conveying direction, the detection unit detects the sheet at a position of a nip portion of the downstream roller pair in the sheet conveying direction, or at a position between the nip portion and the image forming unit; 7. The image forming apparatus according to any one of configurations 1 to 6.

[0132] (Configuration 9) a binding processing unit that binds the first sheet and the second sheet so that the side of the first sheet on which the first image is formed and the side of the second sheet on which the second image is formed form a double-page spread; 9. The image forming apparatus according to any one of configurations 1 to 8.

[0133] (Configuration 10) the binding processing unit binds edges of the first sheet and the second sheet in a direction perpendicular to the sheet conveying direction, 10. The image forming apparatus according to configuration 9,

[0134] (Configuration 11) the binding processing unit is capable of binding three or more sheets including the first sheet and the second sheet, the positioning means, for each set of two sheets that form a double-page spread among the three or more sheets, corrects the position of the image relative to the leading edge of one sheet when the other image of the double-page spread is formed on the other sheet by the image forming means, based on the detection result of the trailing edge of the one sheet by the detection means when the one image of the double-page spread is formed on the other sheet by the image forming means; 11. The image forming apparatus according to configuration 9 or 10.

[0135] (Configuration 12) the binding processing section has a stacking section on which sheets to be bound are stacked, the image forming apparatus forms the first image on the first sheet by the image forming means, then reverses and conveys the first sheet by the reversing means, and then stacks the first sheet on the stacking section; and forms the second image on the second sheet by the image forming means, then stacks the second sheet on the stacking section without reversely conveying the second sheet by the reversing means. 12. The image forming apparatus according to any one of configurations 9 to 11.

[0136] (Configuration 13) the binding processing section has a stacking section on which sheets to be bound are stacked, the image forming apparatus forms the first image on the first sheet by the image forming means, and then stacks the first sheet on the stacking section without inverting and conveying the first sheet by the reversing means, and forms the second image on the second sheet by the image forming means, and then inverts and conveys the second sheet by the reversing means, and then stacks the second sheet on the stacking section. 12. The image forming apparatus according to any one of configurations 9 to 11.

[0137] (Configuration 14) a storage section in which the seat is stored; a feeding unit that feeds sheets one by one from the storage unit toward the image forming unit; Furthermore, the first sheet is a sheet that is fed first from the storage unit, and the second sheet is a sheet that is fed from the storage unit after the first sheet. 14. The image forming apparatus according to any one of configurations 1 to 13. [Explanation of symbols]

[0138] 2A... image forming means (image forming unit) / 13... reversing means (reversing roller pair) / 81... detection means (sheet detection section) / 85... alignment means (control section) / S1... first sheet (preceding sheet) / S2... second sheet (subsequent sheet) / T2... image forming section (transfer section)

Claims

1. an image forming unit for forming an image on a sheet in an image forming section; a reversing unit that reverses the sheet that has passed through the image forming unit so that the sheet is conveyed toward the image forming unit again; A detection unit for detecting the leading edge and the trailing edge of the sheet in the sheet conveying direction; a positioning unit that aligns an image formed on a sheet by the image forming unit with respect to the leading edge of the sheet based on a detection result of the leading edge of the sheet by the detection unit; Equipped with An image forming apparatus for producing a product in which a first sheet on which a first image is formed by the image forming means and a second sheet on which a second image is formed by the image forming means are stacked together, in which a surface of the first sheet on which the first image is formed faces a surface of the second sheet on which the second image is formed, and a rear end of the first sheet when the first image is formed faces a front end of the second sheet when the second image is formed, the position adjustment means corrects a position of the second image relative to the leading edge of the second sheet when the second image is formed, based on a detection result of the trailing edge of the first sheet by the detection means when the first image is formed.

1. An image forming apparatus comprising:

2. When the maximum area in which the image forming means can form an image on a sheet is defined as an effective printing area, the distance from the leading edge of the sheet in the sheet transport direction to the leading edge of the effective printing area in the sheet transport direction is defined as a leading edge margin, and the distance from the trailing edge of the sheet in the sheet transport direction to the trailing edge of the effective printing area in the sheet transport direction is defined as a trailing edge margin, The positioning means includes: aligning the first image with respect to the leading edge of the first sheet so that the leading edge margin of the first sheet is a preset target value; aligning the second image with respect to the leading edge of the second sheet such that the leading edge margin of the second sheet is equal to the trailing edge margin of the first sheet; 2. The image forming apparatus according to claim 1,

3. the image forming unit includes an image carrier and an exposure unit that exposes the image carrier to light to form an electrostatic latent image on the image carrier; The positioning means includes: calculating a difference between the trailing end margin of the first sheet and the target value based on a timing when the detection means detects the trailing end of the first sheet and a timing when the exposure means finishes forming the electrostatic latent image; The leading edge margin of the second sheet is corrected from the target value by the amount of the difference.

3. The image forming apparatus according to claim 2,

4. the image forming unit includes an image carrier and an exposure unit that exposes the image carrier to light to form an electrostatic latent image on the image carrier; the alignment means adjusts a timing at which the exposure means starts forming the electrostatic latent image; 2. The image forming apparatus according to claim 1,

5. the image forming unit includes an image carrier and a transfer unit that transfers a toner image formed on the image carrier to a sheet in the image forming section; the position adjustment unit adjusts the timing at which the leading edge of the sheet reaches the image forming unit; 2. The image forming apparatus according to claim 1,

6. the image forming unit includes an image carrier, an exposure unit that exposes the image carrier to light to form an electrostatic latent image on the image carrier, and a transfer unit that transfers the toner image formed on the image carrier to a sheet in the image forming section; the positioning unit adjusts the timing when the exposure unit starts forming the electrostatic latent image and the timing when the leading edge of the sheet reaches the image forming unit.

2. The image forming apparatus according to claim 1,

7. a pair of upstream rollers arranged upstream of the image forming means in the sheet conveying direction, the detection unit detects the sheet at a position of a nip portion of the upstream roller pair in the sheet conveying direction, or at a position between the nip portion and the image forming unit; 2. The image forming apparatus according to claim 1,

8. a downstream roller pair disposed downstream of the image forming means in the sheet conveying direction, the detection unit detects the sheet at a position of a nip portion of the downstream roller pair in the sheet conveying direction, or at a position between the nip portion and the image forming unit; 2. The image forming apparatus according to claim 1,

9. a binding processing unit that binds the first sheet and the second sheet such that a surface of the first sheet on which the first image is formed and a surface of the second sheet on which the second image is formed form a two-page spread.

9. The image forming apparatus according to claim 1, wherein the first and second electrodes are arranged in a first direction.

10. the binding processing unit binds ends of the first sheet and the second sheet in a direction perpendicular to the sheet conveying direction.

10. The image forming apparatus according to claim 9,

11. The binding processing unit is capable of binding three or more sheets including the first sheet and the second sheet, the positioning means, for each pair of two sheets that form a double-page spread among the three or more sheets, corrects a position of an image relative to a leading edge of the other sheet when the other image of the double-page spread is formed on the other sheet by the image forming means, based on a detection result of a trailing edge of the one sheet by the detection means when the one image of the double-page spread is formed on the one sheet by the image forming means; 10. The image forming apparatus according to claim 9,

12. The binding processing section has a stacking section on which sheets to be bound are stacked, the image forming apparatus forms the first image on the first sheet by the image forming means, then inverts and conveys the first sheet by the inverting means, and then stacks the first sheet on the stacking section, and forms the second image on the second sheet by the image forming means, then stacks the second sheet on the stacking section without inverting and conveying the second sheet by the inverting means.

10. The image forming apparatus according to claim 9,

13. The binding processing section has a stacking section on which sheets to be bound are stacked, the image forming apparatus forms the first image on the first sheet by the image forming means, stacks the first sheet on the stacking section without inverting and conveying the first sheet by the inverting means, and forms the second image on the second sheet by the image forming means, inverts and conveys the second sheet by the inverting means, and then stacks the second sheet on the stacking section.

10. The image forming apparatus according to claim 9,

14. A storage section in which the seat is stored; a feeding unit that feeds sheets one by one from the storage unit toward the image forming unit; Further equipped with the first sheet is a sheet that is fed first from the storage unit, and the second sheet is a sheet that is fed from the storage unit after the first sheet.

9. The image forming apparatus according to claim 1, wherein the first and second electrodes are arranged in a first direction.

Images