Image forming device

Abstract

To provide an image formation apparatus which can improve accuracy of an image formation position in additional printing.SOLUTION: An image formation apparatus comprises: a timing control unit which generates a writing timing reference signal (Mst_Index); and an image processing unit which processes image data, calculates a delay amount of detection timing from a relation between the writing timing reference signal (Mst_Index) and detection timing of a formation position of a first image, and performs processing of moving a formation position of a second image to the image data by the delay amount.SELECTED DRAWING: Figure 8

Description

[Technical Field]

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

[0002] In an image forming apparatus, after an image is formed on a continuous recording material (hereinafter referred to as a continuous recording material) such as a continuous recording material on which an image has already been formed by the image forming apparatus, a further image is formed on top of the image-formed surface, a process known as overprinting. In overprinting, in order to align the position of the overprinted image with the previously formed image, for example, a mark is formed on the continuous recording material to align with the leading edge of the image formation position in the previous image formation. An image forming apparatus has been proposed that detects the mark to determine the timing of image formation and forms the overprinted image at an appropriate position (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2019-77043 Summary of the Invention [Problem to be solved by the invention]

[0004] However, even in a configuration such as the image forming apparatus described in Patent Document 1 above, which detects marks formed on continuous recording material and adjusts the image forming position, variations in the image forming position occur during overprinting.

[0005] In order to solve the above-mentioned problems, the present invention provides an image forming apparatus capable of improving the accuracy of the image forming position in overprinting. [Means for solving the problem]

[0006] The image forming apparatus of the present invention is capable of overprinting, in which a first image is formed on a recording material and then a second image is formed on the first image, and includes a detection unit that detects the formation position of the first image and a control unit that controls the image formation operation of the image forming apparatus. The control unit also includes a timing control unit that generates a laser writing timing reference signal (Mst_Index) synchronized with the scanning of one surface of the polygon mirror, and an image processing unit that processes image data. The timing control unit calculates a delay amount of the detection timing relative to the writing timing reference signal (Mst_Index) based on the relationship between the writing timing reference signal (Mst_Index) and the detection timing of the formation position of the first image by the detection unit. The image processing unit performs processing to move the formation position of the second image relative to the image data by the delay amount. [Effects of the Invention]

[0007] According to the present invention, it is possible to provide an image forming apparatus capable of improving the accuracy of the image forming position in overprinting. [Brief explanation of the drawings]

[0008] [Figure 1] 1 is a schematic diagram illustrating the configuration of an image forming system including an image forming apparatus. [Figure 2] FIG. 2 is a diagram illustrating a configuration of an exposure device provided in the image forming apparatus. [Figure 3] FIG. 10 is a diagram showing an image formed by overprinting. [Figure 4] 10A and 10B are diagrams illustrating positional deviation of a formed image due to overprinting. [Figure 5] FIG. 10 is a timing diagram of overprinting in which image misalignment occurs. [Figure 6] FIG. 2 is a diagram showing the length of a conveying path for a recording material and a toner image in the image forming apparatus. [Figure 7] FIG. 2 is a diagram illustrating a configuration of a control unit of the image forming apparatus. [Figure 8] FIG. 4 is a timing chart of overprinting by the control unit of the image forming apparatus. DETAILED DESCRIPTION OF THE INVENTION

[0009] <Embodiment of Image Forming Apparatus> Hereinafter, examples of embodiments for carrying out the present invention will be described, but the present invention is not limited to the following examples. [Image formation system] Fig. 1 shows a schematic configuration diagram of an image forming system including an image forming apparatus according to this embodiment. As shown in Fig. 1, the image forming system 1 includes an image forming apparatus 7, a supply adjustment section 4 connected upstream of the image forming apparatus 7, and a recording material supply device 3 connected upstream of the supply adjustment section 4. A winding adjustment section 8 is connected to the recording material discharge side of the image forming apparatus 7, and a winding device 9 is connected to the recording material discharge side of the winding adjustment section 8.

[0010] The image forming device 7 is provided with a detection unit 5 at a position where the continuous recording material S (hereinafter also simply referred to as recording material S) is transported from the supply adjustment unit 4. The detection unit 5 is configured with a sensor or the like that is capable of detecting the leading edge position of an image (first image) formed on the continuous recording material S transported by the transport unit 21. For example, the detection unit 5 detects the leading edge portion of the first image formed on the recording material S or the image position for detecting the leading edge position from the difference in contrast between an image (timing detection mark) for detecting the leading edge position of the first image and the background color, such as the color of the recording material S.

[0011] The recording material supply device 3 has a function of storing and holding the continuous recording material S and supplying it to the image forming device 7. The continuous recording material S is, for example, roll paper. The winding device 9 has a function of holding the continuous recording material S discharged from the image forming device 7. The supply adjustment unit 4 has a buffer function for absorbing slight speed differences and deviations between the recording material supply device 3 and the image forming device 7. The winding adjustment unit 8 has a buffer function for absorbing slight speed differences and deviations between the winding device 9 and the image forming device 7.

[0012] The image forming system 1 includes an image forming unit 23 that forms an image on a continuous recording material S inside an image forming device 7, and a setting unit 6 is provided above the image forming device 7. The setting unit 6 includes a display unit 61 and an operation unit 62, and accepts operations from an operator via the operation unit 62, displays information on the display unit 61, and enables various settings for, for example, printing operations to be made. The image forming device 7 is also provided with an automatic document recording material supply device that automatically reads documents and a document image scanning device. The document image scanning device is capable of reading images through a platen glass. The document image scanning device reads, for example, an image of a document, stores the image in an image memory (not shown), and uses it to form an image by the image forming unit 23.

[0013] The image forming unit 23 is provided downstream of the detection unit 5 and includes photosensitive drums 44 for each color such as cyan, magenta, yellow, black, etc., and a charging device 41, an exposure device 42, and a developing device 43 are provided around each photosensitive drum 44. The surface of the photosensitive drum 44, which has been charged by the charging device 41, is exposed to light by the exposure device 42 based on image information of the original document stored in an image memory or the like, forming an electrostatic latent image. The electrostatic latent image is developed by the developing device 43 into a toner image. The toner image is transferred to the intermediate transfer belt 46.

[0014] The toner image transferred to the intermediate transfer belt 46 is transferred to the continuous recording material S, which is conveyed by the conveying unit 21 along the conveying path 22, while being pressed by the secondary transfer roller 47. The conveying unit 21 includes various rollers such as a conveying roller 31 and a registration roller 32. The toner image transferred by the secondary transfer roller 47 is heated and pressed by the fixing unit 25 and fixed to the continuous recording material S. In other words, the image forming unit 23 transfers the image to the continuous recording material S by forming an image using an electrophotographic process. A drum cleaning device 45 is provided around the photosensitive drum 44. The drum cleaning device 45 removes residual toner remaining on the intermediate transfer belt 46. The conveying path 22 supplies and conveys the continuous recording material S. The continuous recording material S contained in the recording material supplying device 3 is supplied along the conveying path 22, and the continuous recording material S is conveyed to the image forming unit 23 via the conveying roller 31 and the registration roller 32.

[0015] [Exposure equipment] The exposure device 42 included in the image forming apparatus 7 will be described with reference to Fig. 2. Fig. 2 is a diagram showing the configuration of the exposure device 42. The exposure device 42 includes a light source 51, a collimator lens 52, a cylindrical lens 53, a polygon mirror 54, an fθ lens 55, a cylindrical lens 56, a mirror 57, and photodiodes 58 and 59. The photodiodes 58 and 59 are arranged in the main scanning direction.

[0016] The light source 51 generates a plurality of laser beams. The light source 51 is composed of a plurality of laser diodes and configured to output a plurality of laser beams. The light source 51 may also be realized as a multi-beam laser array in which a plurality of laser diodes are integrally formed. The plurality of laser diodes are arranged in a row obliquely relative to the main scanning direction. A drive signal is input to the light source 51 from an image processing unit 104 (see FIG. 3), which will be described later, and the light source 51 drives the laser diodes in accordance with this drive signal.

[0017] The collimator lens 52 and the cylindrical lens 53 optically correct the laser beam. The polygon mirror 54 has a polygonal mirror surface that rotates at high speed (20,000 to 40,000 revolutions per minute) to scan the laser beam in the main scanning direction. The polygon mirror 54 shown in Figure 2 is an example formed with six mirror surfaces. The fθ lens 55 optically corrects the scanning angle. The cylindrical lens 56 corrects the light that has passed through the fθ lens 55. The mirror 57 reflects the horizontal synchronization signal that has passed through the cylindrical lens 56 toward the photodiodes 58 and 59. The photodiodes 58 and 59 detect the horizontal synchronization signal. The multiple laser beams output from the light source 51 are scanned by a polygon mirror 54 or the like in the main scanning direction on the photosensitive drum 44 serving as an image carrier, and the rotation of the photosensitive drum 44 scans in the sub-scanning direction, forming a latent image on the surface of the photosensitive drum 44 in accordance with the laser beams. Although FIG. 2 illustrates an example in which four lines of laser beams are generated, the number of laser beams is not limited to four lines.

[0018] [Additional printing] Next, we will explain overprinting using the above-mentioned image forming system 1 and image forming apparatus 7. As shown in Fig. 3, first, in the image forming apparatus 7, an image (hereinafter referred to as a first image) 71 is formed on the recording material S. Then, in the overprinting, an overprinting image (hereinafter referred to as a second image) 72 is further formed on the first image 71 previously formed on the recording material S by the overprinting.

[0019] 3, when performing overprinting, the image forming device 7 forms a timing detection mark 73 for detecting the leading edge position of the image forming area of ​​the first image 71 at the same time as forming the first image 71 on the recording material S. The timing detection mark 73 is formed outside the image forming area of ​​the first image 71 (in a margin) so that the image forming position on the leading edge side of the timing detection mark 73 coincides with the image forming position on the leading edge side of the first image 71 in the conveyance direction of the recording material S indicated by the arrow in FIG.

[0020] In overprinting, the detection unit 5 of the image forming device 7 detects a timing detection mark 73 formed on the recording material S, thereby obtaining the formation position of the first image 71 on the recording material S. The image forming device 7 detects the timing (overprinting timing) for the image forming unit 23 to start overprinting the second image 72 on the first image 71 from the timing when the detection unit 5 detects the timing detection mark 73. Then, the image forming device 7 drives the image forming unit 23 based on the detected overprinting timing, thereby forming the second image 72 at an appropriate position on the first image 71 shown in FIG. 3 .

[0021] Note that the detection unit 5 may detect something other than the timing detection mark 73 as long as it can detect the leading edge position of the first image 71. For example, if the formation area of ​​the first image 71 is large in the width direction of the recording material S and no margin is formed on the recording material S, and the timing detection mark 73 cannot be formed, the leading edge position of the first image 71 can be detected by detecting the leading edge portion of the first image 71.

[0022] 4, when overprinting is performed, even if the overprinting timing is detected from the detection timing of the timing detection mark 73 by the detection unit 5 and the image forming unit 23 is driven, the formation position of the second image 72 may be shifted (misaligned) from the appropriate position on the first image 71. This misalignment of the second image 72 occurs in the opposite direction (rearward) to the conveyance direction of the recording material S with respect to the target position 72A where the second image 72 is to be formed, which is based on the formation position of the first image 71. Furthermore, when misalignment of the second image 72 occurs during overprinting, the amount of shift A of the second image 72 from the target position 72A is not constant even on the same recording material S, but varies each time the second image 72 is formed on the first image 71.

[0023] (Image misalignment) The above-mentioned variation in the formation position of the second image 72 is thought to be caused in part by a mismatch between the timing of overprinting the second image 72 in the image forming unit 23 and the timing of starting exposure (write start timing signal) by the exposure device 42 in the image forming unit 23. The reasons for the mismatch and variation in the formation position of the second image 72 will be explained below. FIG. 5 shows the timing of overprinting when the above-mentioned deviation and variation in the formation position of the second image 72 occurs during overprinting, and a timing diagram of the write start timing signal.

[0024] When forming an electrostatic latent image on the photosensitive drum 44, the image forming unit 23 generates a write timing reference signal (Mst_Index) in synchronization with the scanning of the laser light from one surface of the polygon mirror 54 constituting the exposure device 42, and generates an exposure start timing (write timing signal) in synchronization with this write timing reference signal (Mst_Index). However, this write timing signal does not necessarily coincide with the overprinting timing of the second image 72 in the image forming unit 23, which is generated based on the detection of the timing detection mark 73 by the detection unit 5. For example, in Figure 5, there is a difference of delay B between the generation position of the overprinting timing and the write timing reference signal (Mst_Index).

[0025] As shown in FIG. 5, the write timing reference signal (Mst_Index) synchronized with the scanning of the polygon mirror 54 is generated at regular intervals. In contrast, the overprint timing is generated according to the intervals between the first images 71 formed on the recording material S. However, the first images 71 are not formed at regular intervals due to various factors in the image forming apparatus 7, such as the conveyance speed of the recording material S and thermal shrinkage of the recording material S. Therefore, the overprint timing generated from the detection timing of the timing detection mark 73 by the detection unit 5 is not generated at regular intervals. Because the overprint timing is not generated at regular intervals, a delay of B occurs between the overprint timing and the write timing reference signal (Mst_Index) generated at regular intervals. Specifically, as shown in FIG. 5, the generation timing T2 of the overprint timing, which is generated based on the detection of the timing detection mark 73 by the detection unit 5, is delayed by the delay B from the generation timing T1 of the write timing reference signal (Mst_Index).

[0026] The write start timing signal (Vtop) of the exposure device 42 must be generated in synchronization with the write start timing reference signal (Mst_Index). Specifically, in the image forming apparatus 7, as shown in Fig. 6, the difference between the path length L1 along which the recording material S is transported from the detection unit 5 to the secondary transfer unit and the path length L2 along which the toner image is transported from the electrostatic latent image formation position (exposure position) on the photosensitive drum 44 to the secondary transfer unit is set as a set distance Lw (Lx = L1 - L2). Also, as shown in Fig. 5, the time required to transport the recording material S by the set distance Lw is set as a predetermined time Tx. In such a setting of the image forming device 7, in order to form a second image 72 without misalignment by overprinting, as shown in Figure 5, it is necessary to generate a write start timing signal (Vtop) at timing T4, a predetermined time Tx after the generation timing T2 of the overprinting timing generated based on the detection of the timing detection mark 73 by the detection unit 5.

[0027] However, since the write timing signal (Vtop) is generated in synchronization with the write timing reference signal (Mst_Index), the write timing signal cannot be generated at timing T4, which is a predetermined time Tx after timing T2, when the additional printing timing is generated. Furthermore, the write timing signal cannot be generated at timing T4 because timing T4 is delayed by delay amount B from the write timing reference signal (Mst_Index) generated at timing T3. As a result, the write timing signal (Vtop) of the exposure device 42 is generated at timing T5, which is synchronized with the write timing reference signal (Mst_Index) immediately after timing T4.

[0028] Therefore, the write timing signal (Vtop) of the exposure device 42, which is generated in synchronization with the write timing reference signal (Mst_Index) at the timing T5 described above, is generated with a delay of the period C from the original write timing T4 for forming the second image 72 at a position without misalignment. This delay of the period C in the write timing signal results in a delay in the actual writing of the second image 72 in the exposure device 42 of the image forming unit 23. Due to this delay in the writing of the exposure device 42, the second image 72 is formed at a position shifted (delayed) by the conveyance distance of the recording material S over the period C, which corresponds to the amount of deviation A from the target position 72A based on the formation position of the first image 71, as shown in FIG.

[0029] Furthermore, the delay amount B by which the generation of the overprinting timing is delayed relative to the write timing reference signal (Mst_Index) is equal to or less than the period of the write timing reference signal (Mst_Index). Therefore, the period C by which the write timing signal is delayed relative to the overprinting timing is also equal to or less than the period of the write timing reference signal (Mst_Index). Furthermore, because the delay amount B for the generation of the overprinting timing relative to the write timing reference signal (Mst_Index) is non-uniform according to the interval between the first images 71, variation in the formation position of the second image 72 occurs within the distance that the recording material S is transported during the period equal to or less than the write timing reference signal (Mst_Index). If the above-described misalignment or variation in the formation position of the second image 72 occurs, problems such as misalignment of the printing position, printing defects due to overlapping of the first image 71 and the second image 72, and image loss due to cutting of the recording material S will occur.

[0030] Therefore, in order to form a second image 72 without misalignment in overprinting printing, the image forming device 7 controls each timing to adjust the respective deviations of the timing T3 at which a write timing reference signal (Mst_Index) synchronized with the scanning of one surface of the polygon mirror 54 is generated, the timing T4 at which a second image 72 without misalignment can be formed in overprinting printing, and the timing T5 at which a write timing signal (Vtop) of the exposure device 42 is generated.

[0031] Specifically, the image forming device 7 generates a write timing signal (Vtop) for the exposure device 42 at timing T3 of the write timing reference signal (Mst_Index), which is generated just before timing T4, a predetermined time Tx has elapsed since timing T2, when the overprint timing is generated. Furthermore, in this state, the timing T3 at which the write start timing signal (Vtop) is generated is earlier than the original write start timing T4 for forming the second image 72 at a position without misalignment. As a result, the second image 72 is shifted in the opposite direction to the shift amount A shown in Fig. 4, and is generated at a position shifted toward the conveying direction (forward) from the target position 72A by the distance the recording material S is conveyed by the delay amount B. For this reason, the image forming apparatus 7 corrects the image data by image processing so that the formation position of the second image 72 is shifted backward in the transport direction by the distance by which the recording material S is transported for the delay amount B. In other words, the image forming apparatus 7 corrects the image so that the formation position of the second image 72 is moved backward in the image data by the delay amount B. By performing the above control (processing), the image forming apparatus 7 can suppress deviations and variations in the formation position of the second image 72 in overprinting printing with the first image 71 as the reference.

[0032] [Control Unit: System Configuration] 7 shows the configuration of the control unit 100 of the image forming apparatus 7. As shown in FIG.

[0033] Printer control unit 101 includes engine control unit 102 and timing control unit 103. In this example, printer control unit 101 is described as including two control units, engine control unit 102 and timing control unit 103, but printer control unit 101 is not limited to this and may be configured as a single control unit.

[0034] The engine control unit 102 includes, for example, an engine central processing unit (CPU), a read-only memory (ROM), a random access memory (RAM), etc. The ROM stores a control program for controlling the operation of the engine unit of the image forming apparatus 7. The engine CPU reads out the control program stored in the ROM and loads the control program into the RAM to control the engine unit.

[0035] The engine CPU controls each part of the image forming device 7 based on various information stored in the ROM for forming images in the image forming device 7. For example, by adjusting the timing at which the exposure device 42 starts forming an electrostatic latent image, a color toner image is formed without misalignment on the intermediate transfer belt 46. In addition, by controlling the formation of a toner image by the image forming unit 23 and the drive unit of the conveyance unit 21 for the recording material S, the engine CPU controls the timing of transfer of these images by the secondary transfer roller 47 to match. The engine CPU also rotates a drum motor (not shown), causing the photosensitive drum 44 to rotate and the charging device 41 to charge the photosensitive drum 44. The engine CPU also causes the developing device 43 to develop the electrostatic latent image on the photosensitive drum 44 with toner.

[0036] The engine control unit 102 and the timing control unit 103 receive information (hardware settings) on the system configuration of the image forming device 7, and retain information such as the path length L1 along which the recording material S is transported from the detection unit 5 to the secondary transfer unit, the path length L2 along which the toner image is transported from the electrostatic latent image formation position (exposure position) on the photosensitive drum 44 to the secondary transfer unit, and the set distance Lw (Lx = L1 - L2), as shown in Figure 6 above.

[0037] The timing control section 103 is configured by, for example, an FPGA (Field Programmable Gate Array) or the like. The timing control unit 103 receives a detection signal of the formation position of the first image 71 from the detection unit 5, for example, a detection signal of the timing detection mark 73 or the leading edge portion of the first image 71, and generates the overprint timing. Furthermore, the timing control unit 103 generates a write timing reference signal (Mst_Index) for one surface of the polygon mirror 54 in synchronization with the polygon mirror 54 .

[0038] Furthermore, the timing control unit 103 generates a write start timing signal (Vtop) for the exposure device 42 based on the detection timing of the formation position (the timing detection mark 73 or the leading edge portion) of the first image 71 by the detection unit 5. This write start timing signal (Vtop) is generated based on the write start timing reference signal (Mst_Index). Specifically, the timing control unit 103 generates the write start timing signal (Vtop) for the exposure device 42 in synchronization with the write start timing reference signal (Mst_Index) that is generated immediately before the predetermined time Tx during which the recording material S is transported the above-mentioned set distance Lw (Lx = L1 - L2) is reached, based on the generation of the overprinting timing based on the detection of the timing detection mark by the detection unit 5. Then, the timing control unit 103 notifies the image processing unit 104 of the generated overprinting timing signal (Vtop).

[0039] Furthermore, the timing control unit 103 measures the delay in the generation time of the overprint timing (Vtop) relative to the writing timing reference signal (Mstindex) using an internal clock and calculates it as a delay amount B. Then, the timing control unit 103 notifies the image processing unit 104 of the calculated delay amount B.

[0040] The image processing unit 104 is configured by, for example, an ASIC (application specific integrated circuit), etc. The image processing unit 104 may also be configured to include the above-mentioned CPU, ROM, and RAM. The image processing unit 104 performs various image processes on image data (first image data) used for an overprinting print job input by a user or the like. In this image processing, the image processing unit 104 adjusts the image formation position of the second image 72 included in the first image data based on the delay amount B calculated by the timing control unit 103. For example, the image processing unit 104 calculates the distance the recording material S is transported during the period of the delay amount B. Then, the image processing unit 104 performs image processing to move the image formation position of the second image 72 included in the first image data in the opposite direction (rearward) to the transport direction of the recording material S. As a result, the image processing unit 104 generates image data (second image data) in which the formation position of the second image 72 has moved rearward in the transport direction by the distance the recording material S is transported during the period of delay amount B.

[0041] Then, image processing unit 104 causes exposure device 42 to expose photosensitive drum 44 based on the generated second image data. For example, when light source 51 (FIG. 2) having a plurality of light-emitting elements performs parallel exposure, image processing unit 104 is configured to output image data for each line in parallel corresponding to the plurality of light sources 51. Image processing unit 104 may also be configured to output image data for one line at a time, hold image data for multiple lines on the exposure device 42 side, and drive light source 51 for multiple lines in parallel.

[0042] [Timing control for overprinting] Next, the timing control of overprinting by the control unit 100 of the image forming apparatus 7 described above will be described. FIG. 8 shows a timing diagram when overprinting is performed in the image forming apparatus 7. Note that FIG. 8 is a timing diagram in which a writing start timing signal (Vtop) whose timing is controlled by the control unit 100 is added to the timing diagram shown in FIG. 5 described above. For this reason, the same conditions as those in the timing diagram shown in FIG. 5 described above are applied to the overprinting shown in the timing diagram shown in FIG. 8. Furthermore, the writing start timing signal (Vtop) whose timing is controlled by the control unit 100 is shown as (after timing control), and the writing start timing signal (Vtop) whose timing is not controlled by the control unit 100 and which causes misalignment of the second image 72 during overprinting is shown as (before timing control).

[0043] When the detection unit 5 detects the timing detection mark 73 formed on the recording material S, it notifies the control unit 100 of the detection of the timing detection mark 73. In the control unit 100, the timing control unit 103 receives the detection notification of the timing detection mark 73 from the detection unit 5, and generates an overprint timing at timing T2 that coincides with the detection of the timing detection mark 73 by the detection unit 5. Furthermore, the timing control unit 103 generates a write timing reference signal (Mst_Index) at regular intervals in synchronization with the polygon mirror 54 of the exposure device 42 . At this time, the timing control unit 103 acquires the delay amount B as the amount of deviation between the timing T1 at which the writing timing reference signal (Mst_Index) is generated and the timing T2 at which the additional printing timing is generated.

[0044] As described above, in the image forming apparatus 7, a set distance Lw (Lx=L1-L2) is set as the difference between the path length L1 along which the recording material S is transported from the detection unit 5 to the secondary transfer unit and the path length L2 along which the toner image is transported from the electrostatic latent image formation position (exposure position) on the photosensitive drum 44 to the secondary transfer unit. Then, the timing control unit 103 sets a predetermined time Tx during which the recording material S is transported by the set distance Lw through drive control of the transport unit 21 by the engine control unit 102.

[0045] Next, the timing control unit 103 sets timing T4, which is the time when the predetermined time Tx has elapsed since the timing T2 for generating the additional printing timing. This timing T4 is the original writing start timing required to form the second image 72 in a position without misalignment when image processing is not performed, as in the case of FIG. 5 described above. The timing control unit 103 also detects timing T3 at which a write timing reference signal (Mst_Index) immediately prior to the generated timing T4 is generated. The timing control unit 103 then generates a timing-controlled write timing signal (Vtop) at this timing T3. The timing T3 at which the timing control unit 103 generates the write timing signal (Vtop) is the write timing reference signal (Mst_Index) immediately prior to the predetermined time Tx having elapsed since the generation timing T2 of the additional printing timing. In other words, in the timing diagram shown in FIG. 5 above, this is the write timing reference signal (Mst_Index) generated immediately prior to timing T5 at which the write timing signal (Vtop) before timing control is generated.

[0046] Next, in the control unit 100, the timing control unit 103 notifies the image processing unit 104 of the generated writing start timing signal (Vtop). Furthermore, the timing control unit 103 notifies the image processing unit 104 of the delay amount B, which is the amount of deviation between the timing T4 at which a predetermined time Tx arrives from the timing T2 at which the overprinting timing is generated and the timing T3 at which the writing start timing signal (Vtop) is generated. As described above, this delay amount B is the amount of deviation in time from the writing start timing reference signal (Mst_Index) to the generation of the overprinting timing, and is the same as the difference between the timing T1 at which the writing start timing reference signal (Mst_Index) is generated and the timing T2 at which the overprinting timing is generated.

[0047] Next, the image processing unit 104 performs image processing to move the formation position of the second image 72 in the opposite direction (rearward) to the conveying direction of the recording material S in the image data (first image data) for overprinting input by the user or the like. The amount by which the second image 72 is moved in the first image data is the distance by which the recording material S is conveyed by the delay amount B due to drive control of the conveying unit 21 by the engine control unit 102. Therefore, the image processing unit 104 newly generates image data (second image data) in which the formation position of the second image 72 is moved rearward in the conveying direction of the recording material S by a distance equivalent to the delay amount B. Then, the image processing unit 104 causes the exposure device 42 to expose the photosensitive drum 44 based on the generated second image data.

[0048] In the above process, the exposure start timing of the exposure device 42 under the control of the image processing unit 104 is the generation timing T3 of the writing start timing signal (Vtop) synchronized with the writing start timing reference signal (Mst_Index). This means that the generation timing T3 of the writing start timing signal (Vtop) is earlier than the original writing start timing T4 for forming the second image 72 in a position without misalignment. However, the image processing unit 104 generates second image data in which the formation position of the second image 72 is moved backward in the transport direction of the recording material S, and based on this second image data, the exposure device 42 draws an electrostatic latent image on the photosensitive drum 44. Therefore, the timing at which the second image 72 is actually drawn on the photosensitive drum 44 from the exposure device 42 in the image forming device 7 coincides with the original write start timing T4 for forming the second image 72 in a position without misalignment.

[0049] Therefore, according to the control of the control unit 100 of the image forming device 7 described above, even if there is a time difference between the write timing reference signal (Mst_Index) (timing T1) and the overprint timing (timing T2) generated based on the detection of the timing detection mark 73 by the detection unit 5, the second image 72 can be formed without deviation at the target position 72A based on the formation position of the first image 71.

[0050] The present invention is not limited to the configurations described in the above-described embodiments, and various modifications and changes are possible without departing from the scope of the present invention. [Explanation of symbols]

[0051] 1 image forming system, 3 recording material supply device, 4 supply adjustment section, 5 detection section, 6 setting section, 7 image forming device, 8 take-up adjustment section, 9 take-up device, 21 transport section, 22 transport path, 23 image forming section, 25 fixing section, 31 transport roller, 32 registration roller, 41 charging device, 42 exposure device, 43 developing device, 44 photosensitive drum, 45 drum cleaning device, 46 intermediate transfer belt, 47 secondary transfer roller, 51 light source, 52 collimator lens, 53, 56 cylindrical lens, 54 polygon mirror, 55 fθ lens, 57 mirror, 58 photodiode, 61 display section, 62 operation section, 71 first image, 72 second image, 72A target position, 73 timing detection mark, 100 control section, 101 printer control section, 102 engine control section, 103 Timing control section, 104 image processing section, L1, L2 path length

Claims

1. An image forming apparatus capable of overprinting in which a first image is formed on a recording material and then a second image is formed on the first image, a detection unit that detects a formation position of the first image; a control unit that controls an image forming operation in the image forming apparatus, The control unit a timing control unit that generates a laser writing timing reference signal (Mst_Index) that is synchronized with the scanning of one surface of the polygon mirror; an image processing unit that processes image data, the timing control unit calculates a delay amount of the detection timing with respect to the writing timing reference signal (Mst_Index) based on a relationship between the writing timing reference signal (Mst_Index) and a detection timing of the formation position of the first image by the detection unit; The image processing unit performs processing to move the formation position of the second image with respect to the image data by the amount of the delay. Image forming device.

2. the timing control unit generates a writing start timing signal (Vtop) that starts exposure of the second image in synchronization with the writing start timing reference signal (Mst_Index); The image processing unit performs processing to move the formation position of the second image by the amount of the delay with respect to the image data, based on the writing start timing signal (Vtop). The image forming apparatus according to claim 1 .

3. The timing control unit generates the writing timing signal (Vtop) in response to the writing timing reference signal (Mst_Index) generated immediately before a predetermined time period from the detection of the formation position of the first image by the detection unit until the recording material is transported from the detection unit to a toner transfer position. The image forming apparatus according to claim 2 .

4. The detection unit detects a timing detection mark formed in a margin of the recording material corresponding to the first image as the detection of the formation position of the first image.

4. The image forming apparatus according to claim 1.

5. The detection unit detects a leading edge of the first image as the detection of the formation position of the first image.

4. The image forming apparatus according to claim 1.

6. The detection unit detects the formation position of the first image based on a difference in contrast.

6. The image forming apparatus according to claim 1.

Images