Image forming apparatus

Abstract

This prevents the user image area from becoming too narrow when aligning images that form images on both sides. [Solution] The image forming apparatus comprises an image forming unit that forms images on both sides of a recording medium, a transport unit that transports the recording medium, a detection unit that detects the edges of the recording medium, and a correction unit that, with respect to the recording medium whose edges have been detected by the detection unit, corrects the position of the first image formed on the first side of the two sides to the position of the second image formed on the second side of the two sides based on the detection result of the detection unit, wherein the detection unit is installed downstream of the image forming unit in the transport direction in which the transport unit transports the recording medium.

Description

Technical Field

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

Background Art

[0002] When an image forming apparatus forms images on both sides of a recording medium (hereinafter, one side of the both sides is referred to as "first side", and the side different from the first side is referred to as "second side"), a technique for correcting and aligning the images on both sides is known.

[0003] Specifically, the image forming apparatus forms images on the first side and the second side of the recording medium, respectively. Next, the image forming apparatus detects the positions of the images formed on each side. Then, the image forming apparatus performs image alignment and correction of magnification error based on the detection results. In this way, a technique for accurately aligning the image positions and the image sizes on both sides in duplex printing is known (for example, see Patent Document 1).

Summary of the Invention

Problems to be Solved by the Invention

[0004] In the conventional technique, an area for forming correction marks is secured on the recording medium. Therefore, the area where the user can form an image such as an image instructed by the user to form (hereinafter referred to as "user image area") becomes narrower by the amount of the area for forming correction marks. Thus, the conventional technique has a problem that the user image area becomes narrower in order to align the positions of the images formed on both sides.

[0005] An object of the present invention is to prevent the user image area from becoming narrower when aligning the positions of images formed on both sides.

Means for Solving the Problems

[0006] In order to solve the above problems, an image forming apparatus according to an aspect of the present invention includes an image forming unit that forms images on both sides of a recording medium, A transport unit for transporting the recording medium, A detection unit for detecting the edge of the recording medium, With respect to the recording medium whose edge has been detected by the detection unit, the recording medium includes a correction unit that, based on the detection result of the detection unit, corrects the position of the first image formed on the first surface of the two surfaces to correct the second image formed on the second surface of the two surfaces, In the transport direction in which the transport unit transports the recording medium, the detection unit is characterized in that it is installed downstream of the image forming unit. [Effects of the Invention]

[0007] According to the present invention, when aligning images formed on both sides, it is possible to prevent the user image area from becoming narrower. [Brief explanation of the drawing]

[0008] [Figure 1] This figure shows an example of the overall configuration of an image forming apparatus. [Figure 2] This is a diagram showing an example of the configuration of a reading device. [Figure 3] This figure shows an example of the overall processing in the first embodiment. [Figure 4] The figure shows an example of the paper. [Figure 5] This diagram shows an example of a mechanism for regulating posture. [Figure 6] This figure shows an example of posture regulation. [Figure 7] This figure shows an example of image formation on the first surface. [Figure 8] This figure shows an example of shape detection. [Figure 9] This figure shows an example where the paper is reversed. [Figure 10] This figure shows an example of how the orientation of the paper after inversion is regulated. [Figure 11] This figure shows an example of correction and image formation on the second surface using the second image. [Figure 12] This figure shows an example of the overall processing in the second embodiment. [Figure 13]It is a diagram showing an example of the overall process in the third embodiment. [Figure 14] It is a diagram showing an example of a functional configuration.

Modes for Carrying Out the Invention

[0009] Hereinafter, specific examples will be described with reference to the accompanying drawings. Note that the embodiments are not limited to the specific examples described below. Also, the following description will be given by taking a recording medium as an example of paper.

[0010] [First Embodiment]

[0011] [Overall Configuration Example] FIG. 1 is a diagram showing an example of the overall configuration of an image forming apparatus. Hereinafter, the conveyance direction of the recording medium is referred to as the "Y direction". Also, the direction orthogonal to the conveyance direction is referred to as the "X direction". Further, the direction perpendicular to the X-Y plane is referred to as the "Z direction".

[0012] The image forming apparatus 1 has a black photoreceptor 12K, a cyan photoreceptor 12C, a magenta photoreceptor 12M, and a yellow photoreceptor 12Y. Each photoreceptor applies toner to the conveyance belt 11.

[0013] The conveyance belt 11 transfers the intermediate transfer image to the paper M.

[0014] The paper feed tray 13 feeds the paper M to the printing device 310. Then, the paper M passes on the conveyance path R and is conveyed to the transfer roller 14. And the transfer roller 14 transfers the intermediate transfer image on the conveyance belt 11 to the paper M.

[0015] The fixing roller 15 fixes the image to the paper M.

[0016] The reading device 401 reads the image formed on the paper M. For example, the reading device 401 is an optical sensor or the like.

[0017] The reading device 401 optically reads an image such as a position detection mark formed on the paper M.

[0018] Figure 2 shows an example of the configuration of the reading device. Figure 2 also shows the main components of the mechanical configuration.

[0019] The reading device 401 includes an illumination light source 91, an opposing member 93, a contact glass 94, and a support member 95.

[0020] The illumination light source 91 is positioned on the side of the paper M where the image is formed. The illumination light source 91 then shines light on the reading position in the transport path R where the sensor reads the image formed on the paper M.

[0021] The reading device 401 has optical components such as an image sensor having a reflecting mirror, an imaging lens, and an image sensor. Alternatively, the reading device 401 may be a line sensor with an array of image sensors. The reading device 401 reads the image formed on the paper M using the image sensor.

[0022] The opposing member 93 has outer peripheral surfaces 931a, 932a, 933a, and 934a. The opposing member 93 is positioned on the back side of the paper M where the image is formed. In addition, the opposing member 93 is constructed by rotatably holding a roller by a roller bracket. The roller has outer peripheral surfaces 931a, 932a, 933a, and 934a that serve as convexly curved reference surfaces. The roller is a rotatable rotating body that rotates independently of the roller bracket. Furthermore, the outer peripheral surfaces 931a, 932a, 933a, and 934a are positioned opposite the contact glass 94.

[0023] The reading position is the position closest to the contact glass 94. The contact glass 94 is a light-transmitting member. The contact glass 94 is positioned on the side of the paper M where the image is formed.

[0024] The illumination light source 91 and the reading device 401 are fixed to the support member 95.

[0025] Upstream of the transport path R, the reading device 401 has a first transport roller 96. On the other hand, downstream of the transport path R, the reading device 401 has a second transport roller 97.

[0026] When the paper M is transported, the reader 401 reads the image from the side indicated by the arrow 940 through the contact glass 94. The roller also rotates in conjunction with the transport of the paper M.

[0027] The reading device 401 may have a configuration other than that described above.

[0028] In Figure 1, when image formation is performed on both sides, the direction in which the paper M is transported differs at branch 17. Specifically, once image formation on both sides is complete, the paper M is transported at branch 17 toward the discharge tray 500 (upward in the figure).

[0029] On the other hand, if image formation is to be performed on the second surface after image formation is completed on the first surface, the paper M is transported so that it proceeds along branch 17 to the inversion path 16 (downward in the figure). After that, the paper M is transported from the inversion path 16 to the printing device 310.

[0030] Furthermore, the image forming apparatus 1 includes a Central Processing Unit (hereinafter referred to as "CPU21") and a storage device 22.

[0031] CPU21 is an example of an arithmetic unit and control unit.

[0032] The storage device 22 may be Random Access Memory (RAM), Read Only Memory (ROM), auxiliary storage device, or a combination thereof.

[0033] The image forming apparatus 1 performs processing by having the CPU 21 and the storage device 22 work together. The image forming apparatus 1 may also have auxiliary devices, input devices, and output devices. Furthermore, there may be more than one arithmetic unit, control device, storage device, input device, and output device.

[0034] [Overall processing example] Figure 3 shows an example of the overall processing in the first embodiment.

[0035] In step S0301, the image forming apparatus 1 feeds paper M.

[0036] Figure 4 shows an example of paper. Hereafter, we will assume that the paper M has the shape shown in the figure (hereinafter sometimes simply referred to as "shape") and that it is transported in the orientation shown in the figure.

[0037] In Figure 4, the reference point is indicated by the "reference line 40". The reference line 40 is a virtual line parallel to the axis in the X direction (X-axis) that has already been explained. The state shown in Figure 4, that is, the state before the orientation of the paper M is restricted, is a state in which the leading edge of the paper M (the first edge 41 in Figure 4) has an inclination θ with respect to the reference line 40. In other words, the state shown in Figure 4 is a state in which the inclination θ is not "0°", and the first edge 41 is inclined with respect to the reference line 40.

[0038] In step S0302, it is desirable for the image forming apparatus 1 to regulate the orientation of the paper M. Specifically, the image forming apparatus 1 regulates the orientation of the paper M using the following mechanism.

[0039] Figure 5 shows an example of the configuration of a mechanism for regulating posture. Figure 5(a) is a plan view, and Figure 5(b) is a side view. Hereinafter, a device having a mechanism for regulating posture will be referred to as a "conveying device 30".

[0040] The position of paper M is detected by multiple contact image sensors (CIS).

[0041] A CIS is a device that uses a Light Emitting Diode (LED) as its light source. Furthermore, a CIS is a linear sensor that receives light through a lens and reads an image formed on a sheet of paper (M).

[0042] Hereinafter, the four CISs of the conveying device 30, starting from the upstream side (right side in Figure 5) in the conveying path R, will be referred to as "1st CIS100", "2nd CIS101", "3rd CIS102", and "4th CIS103".

[0043] The first CIS100 and the second CIS101 are located upstream of the gripping roller pair 31. On the other hand, the first CIS100 and the second CIS101 are located downstream of the conveying roller pair 35.

[0044] The third CIS102 and the fourth CIS103 are located downstream of the clamping roller pair 31. On the other hand, the third CIS102 and the fourth CIS103 are located upstream of the timing roller pair 32.

[0045] The first CIS100, second CIS101, third CIS102, and fourth CIS103 are installed parallel to the width direction of the paper M, i.e., the X-axis. In addition, the relative positions and positional relationships with the clamping roller pair 31 of the first CIS100, second CIS101, third CIS102, and fourth CIS103 are set in advance in the transport direction, i.e., the Y-axis.

[0046] The first CIS100, second CIS101, third CIS102, and fourth CIS103 detect edges such as the first side 41 or the second side 42.

[0047] Note that the sensor is not limited to CIS; any other type that can detect the shape or the edge of the paper (M) is acceptable.

[0048] The clamping roller pair 31 regulates the orientation of the paper M. Specifically, the clamping roller pair 31 regulates the displacement of the paper M in the width direction. In the example shown in Figure 5, the displacement of the paper M in the width direction is "displacement amount α".

[0049] Furthermore, the gripping roller pair 31 restricts the oblique angle of the paper M with respect to the transport direction. In the example shown in Figure 5, the oblique angle of the paper M with respect to the transport direction is "angle β".

[0050] To control the angle β, the clamping roller pair 31 rotates in the YX plane around axis 104a. In the example shown in Figure 5, the clamping roller pair 31 rotates in the rotation direction W. In Figure 5, the axis of rotation is located midway along the length of the clamping roller pair 31 in the X direction, but it can be at any other position as long as the orientation of the paper M is controlled. Furthermore, to control the amount of displacement α, the clamping roller pair 31 moves in the width direction. In the example shown in Figure 5, the clamping roller pair 31 moves in the movement direction S.

[0051] Furthermore, the mechanism for regulating the orientation of the paper M is not limited to the configuration and degrees of freedom shown in Figure 5. In other words, the mechanism can be any configuration that can move and rotate the paper M to regulate its orientation. For example, the mechanism could be one that maintains the paper M parallel to the transport direction.

[0052] Figure 6 shows an example of orientation regulation. Compared to Figure 4, Figure 6 differs in that the orientation of the paper M is regulated so that its first side 41 coincides with the reference line 40.

[0053] Furthermore, the method of regulating posture is set in advance.

[0054] In step S0303, the image forming apparatus 1 performs image formation on the first surface. For example, the image forming apparatus 1 forms an image (hereinafter, the image formed on the first surface will be referred to as "first image IMG1") on the paper M as follows.

[0055] Figure 7 shows an example of image formation on the first surface. Hereafter, as shown in Figure 7, the first image IMG1 will be described in an example where one side is formed parallel to the reference line 40. Specifically, of the four sides of the first image IMG1, the side at the tip (hereinafter referred to as "second side 42") is parallel to the reference line 40.

[0056] Hereafter, the image formed on the second surface will be referred to as "second image IMG2".

[0057] The user image area is an area on paper M where the user can instruct the formation of the first image IMG1 and the second image IMG2. First, the images that the user instructs to be formed, namely the first image IMG1 and the second image IMG2, are input into the image forming apparatus 1 in advance in the form of image data or the like.

[0058] For example, the user image area is determined by subtracting the areas used for mark formation and post-processing (such as the area used for punching) from the entire area of ​​the paper M. Therefore, if a large user image area can be secured, a larger image can be formed on the paper M.

[0059] In step S0304, the image forming apparatus 1 detects the shape.

[0060] Figure 8 shows an example of shape detection. The shape is determined by detecting the positions of the four corners (in Figure 8, the four corners are indicated by "point 43").

[0061] Note that the shape may be detected at locations other than the four corners. For example, the shape may be detected by identifying the four sides that make up the paper M.

[0062] Furthermore, shape detection is preferable after the first image IMG1 has been fixed to the paper M. Fixing involves applying heat to the paper M. Therefore, the heat generated during fixing often causes the paper M to shrink in size due to a decrease in moisture content.

[0063] In step S0305, the image forming apparatus 1 inverts the paper M and feeds it on the second side. When the paper M in the state shown in Figure 8, that is, the paper M on which an image has been formed on the first side, is inverted, the paper M will be in the following state.

[0064] Therefore, it is desirable to perform shape detection after fixing, i.e., after the shape has changed. As shown in Figure 1, when the reading device 401 is installed downstream of the fixing roller 15, the image forming apparatus 1 can detect the shape after fixing. Performing shape detection at a timing after the change due to fixing allows for accurate alignment.

[0065] Figure 9 shows an example of a paper that has been inverted. Compared to Figure 8, the difference is that the paper M is inverted around the X-axis (i.e., horizontally flipped). Therefore, in Figure 6, the edge of the paper M corresponding to the rear end in the transport direction (the third edge 44 in Figure 9) becomes the edge corresponding to the front end in the transport direction when the paper is fed. Also, the first image IMG1 is formed on the reverse side due to the inversion.

[0066] In step S0306, it is desirable for the image forming apparatus 1 to regulate the orientation of the inverted paper M.

[0067] Figure 10 shows an example of restricting the orientation of the paper after inversion. Compared to Figure 6, the difference is that after inversion, the orientation is restricted so that the third side 44 aligns with the reference line 40.

[0068] In step S0307, ​​the image forming apparatus 1 calculates the shape of the second surface, that is, the shape when the paper M is inverted from the first surface to the second surface.

[0069] In step S0308, the image forming apparatus 1 calculates the position on the second surface where the image will be formed.

[0070] In step S0309, the image forming apparatus 1 corrects the second image IMG2.

[0071] In step S0310, the image forming apparatus 1 forms the corrected second image IMG2 on the second surface. The processing results of steps S0309 and S0310 are as follows.

[0072] Figure 11 shows an example of correction and image formation of the second image on the second surface. As shown in the figure, the second image IMG2 is corrected and formed so that it is located on the back side of the first image IMG1.

[0073] The example shown in Figure 11 is a correction that tilts the second image IMG2 so that it aligns with the back surface of the first image IMG1.

[0074] Note that the correction is not limited to the process shown in Figure 11. The correction can be any process that modifies the second image so that the positions where the first and second images are formed coincide on both sides. Specifically, the correction may be a transformation of the image (or a part of the image), a change in magnification, a rotation, a translation, or a combination thereof.

[0075] Once the shape is detected, the image forming apparatus 1 can accurately align the second image IMG2 to the back surface of the first image IMG1. Specifically, once the shape is detected, the image forming apparatus 1 can determine that the paper M has a shape in which the third side 44 has an inclination γ with respect to the reference line 40. If the shape is as shown in Figure 9, then restricting the orientation of the paper M as shown in Figure 10 will cause the paper M to rotate by the inclination γ.

[0076] Such rotation can be calculated based on the tilt γ (step S0308). Therefore, the image forming apparatus 1 can correct the second image IMG2 in accordance with the tilt γ.

[0077] Note that Figure 3 shows an example where steps S0305 and S0306 and steps S0307 through S0309 are processed in parallel, but these processes do not necessarily have to be processed in parallel. In other words, steps S0305 and S0306 and steps S0307 through S0309 may be performed one after the other and then sequentially.

[0078] [Second Embodiment] The second embodiment differs from the first embodiment in its overall processing, as follows. The following explanation will focus on the differences from the first embodiment, omitting redundant explanations.

[0079] Figure 12 shows an example of the overall process in the second embodiment. Compared to the first embodiment, the difference is the addition of step S1201.

[0080] In step S1201, the image forming apparatus 1 receives a correction amount. The correction amount is the position for forming the image as instructed by the user. For example, the correction amount is set in advance by the user. Therefore, the correction amount is input by the user through an input device.

[0081] Note that step S1201 may occur at a timing other than that shown in Figure 12. For example, step S1201 may be performed at a timing that is in parallel with other processes.

[0082] The correction is performed based on the correction amount and the shape detection result. Specifically, if the paper M contains a large amount of moisture, or in special modes such as low-speed operation, the shape may deform severely, which may reduce the accuracy of the alignment. In addition, the user may want to set the second image IMG2 to be formed at a location other than the back surface of the first image IMG1, depending on the user's preference. In this way, the user inputs the position where they want the second image IMG2 to be formed as a correction amount to the image forming apparatus 1 (step S1201).

[0083] Then, the image forming apparatus 1 corrects the second image IMG2 so that it forms the second image IMG2 at the position indicated by the correction amount (step S0309). In this way, once the correction amount is input, the image forming apparatus 1 can form the second image IMG2 according to the user's preferences, etc.

[0084] [Third Embodiment] The third embodiment differs from the first embodiment in its overall processing, as follows. The following explanation will focus on the differences from the first embodiment, omitting redundant explanations.

[0085] Figure 13 shows an example of the overall process in the third embodiment. Compared to the first embodiment, the difference is the addition of step S1301.

[0086] In step S1301, the image forming apparatus 1 detects a mark.

[0087] The marks are formed on the paper M in advance. Therefore, the image forming apparatus 1 knows the shape of the marks, and can detect the position of the marks once they have been formed.

[0088] Then, the image forming apparatus 1 corrects the second image IMG2, taking into account the detection results of the marks (step S0309). In this way, by using the marks, the image forming apparatus 1 can align the images formed on both sides with greater precision.

[0089] [Example of Functional Configuration] Figure 14 shows an example of a functional configuration. The image forming apparatus 1 comprises an image forming unit 1F1, a detection unit 1F2, and a correction unit 1F3. It is also desirable that the image forming apparatus 1 further comprises a fixing unit 1F4, a correction amount input unit 1F5, a transport unit 1F6, a regulation unit 1F7, and an inversion unit 1F8.

[0090] The image forming unit 1F1 performs an image forming procedure to form an image on both sides of the paper M. For example, the image forming unit 1F1 is implemented by a printing device 310 or the like.

[0091] The detection unit 1F2 performs a detection procedure to detect the shape of the paper M. For example, the detection unit 1F2 is implemented by a reader 401 or the like.

[0092] The correction unit 1F3 performs a correction procedure to correct the second image IMG2 in relation to the first image IMG1 based on its shape. For example, the correction unit 1F3 is implemented by a CPU 21 or the like.

[0093] The fixing unit 1F4 performs a fixing procedure to fix the first image IMG1 onto the paper M. For example, the fixing unit 1F4 is implemented by a fixing roller 15 or the like.

[0094] The correction amount input unit 1F5 performs a correction amount input procedure for inputting the correction amount. For example, the correction amount input unit 1F5 can be implemented using an input device or the like.

[0095] The transport unit 1F6 performs the transport procedure for transporting the paper M. For example, the transport unit 1F6 can be implemented using transport rollers or the like.

[0096] The regulating unit 1F7 performs a regulating procedure to control the orientation of the paper M. For example, the regulating unit 1F7 is implemented by a pair of clamping rollers 31, etc.

[0097] The inversion unit 1F8 performs an inversion procedure to invert the first and second faces. For example, the inversion unit 1F8 is implemented by an inversion path 16, etc.

[0098] When image forming is performed on both sides, the image forming apparatus 1 first detects the shape using the detection unit 1F2. Once the shape is detected, the image forming apparatus 1 can correct the second image IMG2 to match the first image IMG1 based on the shape detection result. In other words, the image forming apparatus 1 can align images formed on both sides without using detection marks or the like as in the conventional technology. Therefore, it is possible to eliminate the need for an area to form detection marks or the like, and prevent the user image area from becoming narrower.

[0099] [Other embodiments] The image forming apparatus is not limited to the configuration described above. For example, the image forming apparatus may have devices other than those shown above. Furthermore, the arrangement of each device may be different from that described above.

[0100] The recording medium may be something other than paper (also called "plain paper," etc.). For example, the recording medium may be coated paper, label paper, overhead projector sheets, film, or flexible thin sheets. In other words, the material of the recording medium may be a material to which toner or ink droplets can adhere, to which they can temporarily adhere, to which they can adhere and solidify, or to which they can adhere and penetrate. Specifically, the recording medium may be a recording medium such as paper, film, or cloth, an electronic circuit board, an electronic component such as a piezoelectric element (also called a "piezoelectric component," etc.), a powder layer (also called a "powder layer," etc.), an organ model, or a test cell, etc. Thus, the material of the recording medium may be paper, thread, fiber, fabric, leather, metal, plastic, glass, wood, ceramics, or a combination thereof, to which liquids can adhere.

[0101] The device may consist of multiple devices. That is, each device may be configured to perform processing in a distributed, redundant, or parallel manner with other devices. On the other hand, each device may be a single unit. That is, the multiple devices described above may be implemented in a single device.

[0102] The image formation method described above may be implemented by an image formation program. That is, the image formation program implements the image formation method by having the computing unit, control unit, and memory device of a computer work together. The image formation program may also be distributed via a computer-readable recording medium or via a telecommunications line.

[0103] The embodiments described above are preferred examples, but those skilled in the art can realize various modifications from the disclosed information. Such modifications are also included within the technical scope described in the claims. [Explanation of symbols]

[0104] 1: Image forming apparatus 1F1: Image forming section 1F2: Detection unit 1F3: Correction section 1F4: Fixing section 1F5: Correction amount input section 1F6: Conveyor Unit 1F7:Regulation Department 1F8: Reversal section 31: Clamping roller vs. 35: Conveyor roller pair 310 :Printing device 401: Reader IMG1: First image IMG2: Second image M:Paper [Prior art documents] [Patent Documents]

[0105] [Patent Document 1] Japanese Patent Publication No. 2017-090911

Claims

1. An image forming unit that forms images on both sides of the recording medium, A transport unit for transporting the recording medium, A detection unit for detecting the edge of the recording medium, With respect to the recording medium whose edge has been detected by the detection unit, the recording medium includes a correction unit that, based on the detection result of the detection unit, corrects the position of the first image formed on the first surface of the two surfaces to correct the second image formed on the second surface of the two surfaces, In the transport direction in which the transport unit transports the recording medium, the detection unit is installed downstream of the image forming unit. Image forming apparatus.

2. An image forming unit that forms images on both sides of the recording medium, A transport unit for transporting the recording medium, A detection unit for detecting the corner of the recording medium, With respect to the recording medium in which the detection unit has detected the corner, the recording medium is further equipped with a correction unit that, based on the detection result of the detection unit, corrects the position of the first image formed on the first surface of the two surfaces to correct the second image formed on the second surface of the two surfaces, In the transport direction in which the transport unit transports the recording medium, the detection unit is installed downstream of the image forming unit. Image forming apparatus.

3. The system further includes a fixing unit for fixing the first image onto the recording medium, The detection unit is After the fixing unit fixes the first image onto the recording medium, the edge is detected. The image forming apparatus according to claim 1.

4. The system further includes a fixing unit for fixing the first image onto the recording medium, The detection unit is After the fixing unit fixes the first image onto the recording medium, the corner is detected. The image forming apparatus according to claim 2.

5. It further includes a correction amount input section for inputting the correction amount, The correction unit, The second image is corrected based on the correction amount and the edges. The image forming apparatus according to claim 1 or 3.

6. It further includes a correction amount input section for inputting the correction amount, The correction unit, The second image is corrected based on the correction amount and the corner. The image forming apparatus according to claim 2 or 4.

7. A restricting unit that restricts the orientation of the recording medium when the image forming unit performs image formation on the recording medium, A reversal unit that reverses the first surface and the second surface Furthermore, The detection unit is The positions of the four sides of the recording medium are detected, The correction unit, Based on the detection results of the detection unit, the second surface shape, which is the shape when the recording medium is inverted from the first surface to the second surface, is calculated. The position for forming the second image and the magnification for forming the second image are corrected so that the second image is formed on the back of the first image, in accordance with the second surface shape. The image forming apparatus according to any one of claims 1, 3, or 5.

8. A restricting unit that restricts the orientation of the recording medium when the image forming unit performs image formation on the recording medium, A reversal unit that reverses the first surface and the second surface Furthermore, The detection unit is The positions of the four corners of the recording medium are detected, The correction unit, Based on the detection results of the detection unit, the second surface shape, which is the shape when the recording medium is inverted from the first surface to the second surface, is calculated. The position for forming the second image and the magnification for forming the second image are corrected so that the second image is formed on the back of the first image, in accordance with the second surface shape. The image forming apparatus according to any one of claims 2, 4, or 6.

9. The image forming unit further includes a restricting unit that restricts the orientation of the recording medium when the image forming unit performs image formation on the recording medium, The regulating unit rotates the recording medium such that the edge of the recording medium that becomes the leading edge in the transport direction is parallel to the direction perpendicular to the transport direction. The image forming apparatus according to any one of claims 1 to 8.

10. The detection unit is a Contact Image Sensor or) The image forming apparatus according to any one of claims 1 to 9.

Images