Image forming device

Abstract

To provide an image forming device capable of simultaneously achieving correction accuracy of skew correction and miniaturization of a margin between images.SOLUTION: This image forming device comprises: a color shifting amount calculation unit that calculates a color shifting amount; and first and second skew correction control units that control skew correction of color shifting. The first skew correction control unit controls first skew correction carried out by a mechanical operation of an image forming unit on the basis of a preset first color shifting residual target value. The second skew correction control unit controls second skew correction carried out by image processing on the basis of a preset second color shifting residual target value for color shifting after the control by the first skew correction control unit.SELECTED DRAWING: Figure 12

Description

[Technical Field]

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

[0002] Image forming devices form color images by superimposing multiple color images. For example, when forming a color image using four color toners, a light beam modulated according to the image to be formed is scanned on a photosensitive member to form four electrostatic latent images. These electrostatic latent images are then developed with toners of different colors, for example, black (K), cyan (C), magenta (M), and yellow (Y), to form four monochromatic images. These four monochromatic images are then superimposed on one another and transferred to a recording material. This forms a color image.

[0003] If there is a deviation in the image formation position of the monochrome image, this will be visually recognized as a color deviation on the color image. In order to form high-quality color images without color shift, it is necessary to detect the amount of shift between a reference monochrome image and other monochrome images, and then precisely adjust the image formation position of each monochrome image according to the detected amount of shift. In image forming devices, this type of adjustment is called color shift correction.

[0004] Color misregistration correction in image forming devices generally involves correcting six components: main scanning, overall horizontal magnification, partial horizontal magnification, sub-scanning, skew, and bow. The configuration for achieving these corrections varies depending on the model of image forming device. For example, the control unit of an image forming device has the function of correcting color misregistration in main scanning, overall horizontal magnification, partial horizontal magnification, sub-scanning, and bow through image processing.

[0005] There are two methods that can be applied to correct color misregistration due to skew (skew correction): a configuration in which correction is performed by a mechanical mechanism of the image forming apparatus, and a configuration in which correction is performed by image processing in a control unit. In mechanical skew correction, for example, a motor is driven to tilt the laser unit, causing the laser to scan the photosensitive drum at an angle. In image processing skew correction, the image data is tilted by image processing in the control unit. This is how skew correction is performed in the image forming device. Furthermore, an image forming apparatus has been proposed that has a so-called hybrid correction configuration in which skew correction is performed using two methods: correction by a mechanical mechanism and correction by image processing (see, for example, Patent Document 1).

[0006] When the image forming apparatus determines that the amount of color misalignment due to skew exceeds the allowable range for correction by image processing, it performs correction using a mechanical mechanism to correct the amount of color misalignment to a value that falls within the allowable range for correction by image processing.The image forming apparatus then performs correction using image processing on the color misalignment that has been reduced by the mechanical mechanism. Furthermore, in the image forming apparatus described above, if it is determined that the amount of color misregistration due to skew is within the allowable range for correction by image processing, only correction by image processing is performed. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Laid-Open No. 2003-182146 Summary of the Invention [Problem to be solved by the invention]

[0008] Skew correction by image processing has a correction resolution in the μm range, allowing for highly accurate correction. For this reason, image forming apparatuses that perform the hybrid correction described above maximize the skew correction by image processing to achieve highly accurate skew correction. However, skew correction using image processing requires that the image data be tilted. In this case, the image size must be expanded in the conveyance direction (lengthwise direction) of the recording material to avoid image loss. Furthermore, because image data cannot be overlapped between pages, the expanded image size appears as a margin (image gap) between pages. In an image forming apparatus configured to continuously form images on a recording material such as roll paper, the margins between pages are discarded (waste paper), and therefore it is required to reduce the amount of margins in image formation. Furthermore, although correction using a mechanical mechanism does not leave any white space between pages, because the position of the mechanical mechanism is adjusted by a motor, it is difficult to achieve accurate correction resolution in the μm range, making it difficult to achieve highly accurate correction. Therefore, in an image forming apparatus that forms a color image by overlapping single-color images, it is required to ensure the accuracy of skew correction and minimize the margins between images.

[0009] In order to solve the above-mentioned problems, the present invention provides an image forming apparatus that can achieve both high accuracy in skew correction and minimization of blank spaces between images. [Means for solving the problem]

[0010] The image forming apparatus of the present invention forms images of multiple colors on a recording material and includes an image forming unit that forms images on the recording material and a control unit that controls image formation in the image forming unit and skew correction in the image formation. The control unit includes a color misregistration amount calculation unit that calculates the amount of color misregistration from the color misregistration of each color image in the image forming unit, a first skew correction control unit that controls skew correction of the color misregistration, and a second skew correction control unit. The first skew correction control unit controls first skew correction by mechanical operation of the image forming unit based on a preset first color misregistration residual target value. The second skew correction control unit controls second skew correction by image processing for the color misregistration after control by the first skew correction control unit based on a preset second color misregistration residual target value. [Effects of the Invention]

[0011] According to the present invention, it is possible to provide an image forming apparatus that can achieve both high accuracy in skew correction and minimization of blank spaces between images. [Brief explanation of the drawings]

[0012] [Figure 1] FIG. 1 is a diagram illustrating a schematic configuration of an image forming system. [Figure 2] FIG. 1 is a block diagram showing a configuration of an image forming apparatus. [Figure 3] FIG. 2 is a functional block diagram of a control unit of the image forming apparatus. [Figure 4] 10A and 10B are diagrams illustrating control of the first skew correction by a mechanical mechanism of the first skew correction control unit. [Figure 5] 10A and 10B are diagrams illustrating control of the first skew correction by a mechanical mechanism of the first skew correction control unit. [Figure 6] 10A and 10B are diagrams illustrating control of the first skew correction by a mechanical mechanism of the first skew correction control unit. [Figure 7] 10A and 10B are diagrams illustrating control of second skew correction by image processing by a second skew correction control unit. [Figure 8] 10A and 10B are diagrams illustrating control of second skew correction by image processing by a second skew correction control unit. [Figure 9] 10A and 10B are diagrams illustrating image data with different correction rates in the second skew correction. [Figure 10] 10A and 10B are diagrams illustrating image data with different correction rates in the second skew correction. [Figure 11] 10A and 10B are diagrams illustrating an example of image data in which the margin amount is set to a fixed value by a margin setting unit. [Figure 12] 10 is a flowchart of a first processing method for skew correction. [Figure 13] 10 is a flowchart of a second processing method for skew correction. [Figure 14] 10 is a flowchart of a third processing method for skew correction. [Figure 15] 10 is a flowchart of a fourth processing method for skew correction. [Figure 16] 10 is a flowchart of a fifth processing method for skew correction. [Figure 17] 10 is a flowchart of a sixth processing method for skew correction. [Figure 18] 10 is a flowchart of a seventh processing method for skew correction. DETAILED DESCRIPTION OF THE INVENTION

[0013] <Embodiment of Image Forming Apparatus> Hereinafter, an example of an embodiment of the image forming apparatus of the present invention will be described, but the present invention is not limited to the following example.

[0014] [Configuration of image forming device] Fig. 1 shows a schematic configuration of an image forming system including an image forming apparatus according to this embodiment. The image forming system 1 shown in Fig. 1 uses a roll-shaped recording material S, which is continuous paper, as the recording material, and forms an image on this recording material S. The image forming system 1 includes, from the upstream side in the conveyance direction of the recording material S, a paper feed unit 10, an image forming device 40, and a collection device 60. The image forming system 1 shown in Fig. 1 includes a supply adjustment unit 20 between the paper feed unit 10 and the image forming device 40, and a collection adjustment unit 50 between the image forming device 40 and the collection device 60.

[0015] The paper feed unit 10 has a support shaft 11 that rotatably holds the recording material S wound in a roll, and transports the recording material S wound around the support shaft 11 to the supply adjustment unit 20 by a plurality of rollers at a constant speed. The shape of the recording material S is not limited to a roll of continuous paper. The recording material S may be of any length that allows multiple pages of images to be continuously formed on the recording material S in the image forming device 40. For example, the recording material S may be in a foldable shape or in the shape of long paper. The paper feed unit 10 is an example of a recording material supply device that supplies the recording material to the image forming device 40.

[0016] The supply adjustment unit 20 conveys the recording material S conveyed from the paper feed unit 10 to the image forming unit 46 of the image forming apparatus 40. In order to absorb the speed difference between the feeding and conveying speed of the recording material S from the paper feed unit 10 and the conveying speed of the recording material S in the image forming unit 46, the supply adjustment unit 20 holds the recording material S with slack and adjusts the feeding of the recording material S to the image forming unit 46.

[0017] The image forming apparatus 40 includes a control unit 41, an operation display unit 42, a scanner unit 43, a conveying unit 44, a color misregistration detection sensor 45, an image forming unit 46, and a fixing unit 47. The image forming apparatus 40 may include the above-described paper feed unit 10 as a recording material supply unit within the image forming apparatus 40.

[0018] The scanner unit 43 exposes and scans the surface of a document placed on a document table using a light source, receives reflected light from the document surface, photoelectrically converts the received reflected light using a CCD (Charge Coupled Device), generates image data, and outputs it to the control unit 41.

[0019] The control unit 41 controls the image forming system 1 and each component of the image forming apparatus 40. The control unit 41 also performs image processing on image data input from the scanner unit 43 and the control unit 41, and outputs the processed image data to the image forming unit 46. The control unit 41 also detects the positional deviation (color deviation) of the toner images of each color from the positions of the toner images of each color detected by the color deviation detection sensor 45, and calculates the amount of color deviation of the toner of each color. The configuration of the control unit 41 will be described in detail later.

[0020] The operation display unit 42 is composed of a display unit configured with a display such as a liquid crystal display device, and an operation unit configured with a touch panel and multiple keys, etc., superimposed on this display. The display screen is covered with a pressure-sensitive (resistive film pressure) touch panel configured with transparent electrodes arranged in a grid pattern, which detects the X and Y coordinates of the point of force pressed with a finger, a touch pen, etc. as a voltage value, and outputs the detected position signal to the control unit 41 as an operation signal. The operation display unit 42 also has various operation buttons such as number buttons and a start button, and outputs operation signals to the control unit 41 in response to button operations.

[0021] The image forming unit 46 forms an image on the recording material S conveyed from the supply adjustment unit 20 by electrophotography, based on the image data of each page input from the control unit 41. The image forming unit 46 is provided with a recording material conveying path on which are arranged a conveying belt, conveying rollers such as registration rollers, and motors (not shown) that drive these, and forms an image on the recording material S while conveying it according to the control of the control unit 41.

[0022] The image forming unit 46 includes four sets of exposure units 461, photoconductors 462, developing units 463, and primary transfer rollers 464 corresponding to the color components Y, M, C, and K, an intermediate transfer belt 465, and a secondary transfer roller 466. The four sets of exposure units 461, photoconductors 462, developing units 463, and primary transfer rollers 464 corresponding to the color components are arranged in the order of Y, M, C, and K from the upstream side.

[0023] The exposure section 461 is composed of a laser writing unit, a tilt adjustment section for the laser writing unit, a polygon motor, a polygon mirror, and multiple lenses, etc. The exposure section 461 irradiates and exposes a charged photosensitive member 462 with laser light 460 using the laser writing unit and polygon mirror in accordance with the recording material conveyance speed, and forms an electrostatic latent image on the photosensitive member 462.

[0024] In the exposure section 461, the angle (tilt) of the path (laser path) of irradiation of the laser light 460 onto the photosensitive member 462 is adjusted by the tilt adjustment section 467 (FIGS. 2, 4, and 5). The tilt adjustment section changes the tilt of the laser writing unit and adjusts the tilt of the laser path onto the photosensitive member 462, thereby performing skew correction using a mechanical mechanism.

[0025] The developing unit 463 supplies toner of a predetermined color (Y, M, C, or K) onto the exposed photoconductor 462 to develop the electrostatic latent image formed on the photoconductor 462 . Primary transfer roller 464 is disposed opposite to photoreceptor 462. A primary transfer bias of opposite polarity to that of the toner is applied to primary transfer roller 464, and a predetermined position on intermediate transfer belt 465 is pressed against photoreceptor 462, thereby transferring (primary transfer) the toner image formed on photoreceptor 462 to intermediate transfer belt 465. Primary transfer rollers 464 for Y, M, C, and K sequentially press predetermined positions of intermediate transfer belt 465 against photoreceptor 462, thereby writing a color toner image in which layers of each color are superimposed on intermediate transfer belt 465.

[0026] Intermediate transfer belt 465 is a semiconductive endless belt suspended on a plurality of rollers and rotatably supported, and is driven to rotate in conjunction with the rotation of the rollers, conveying the written toner image to secondary transfer roller 466 . The secondary transfer roller 466 is applied with a bias of the opposite polarity to the toner, and transfers (secondary transfers) the color toner image written on the intermediate transfer belt 465 onto the recording material S by sandwiching and transporting the conveyed recording material S.

[0027] The color misregistration detection sensor 45 detects the position of the toner image of each color formed on the intermediate transfer belt 465 . Color misregistration detection sensor 45 is disposed on intermediate transfer belt 465 and is composed of a light source, an image sensor that detects a toner image, etc. Color misregistration detection sensor 45 has an image sensor that detects a toner image on intermediate transfer belt 465, and is disposed on a line perpendicular to the direction of movement of intermediate transfer belt 465. To detect misalignment of the toner images of each color, first, a toner image of each color, which is a pattern (registration pattern) of lines, figures, or the like predetermined by the image forming operation, is transferred to intermediate transfer belt 465. Then, color misalignment detection sensor 45 reads the toner image of each color and detects the transfer position of the toner image. Then, color misalignment detection sensor 45 sends the detected transfer position of the toner image to control unit 41, and control unit 41 detects the misalignment of the toner image of each color based on the position of the toner image.

[0028] The fixing unit 47 heats and pressurizes the toner image transferred onto the recording material S, thereby fixing the toner image to the recording material S. The fixing unit 47 includes a fixing roller 471 incorporating a halogen heater or the like, and a pressure roller 472 as a pressure member that presses the fixing roller 471, which is disposed opposite the fixing roller 471 across the recording material transport path. The fixing unit 47 also includes a temperature sensor for detecting the temperature of the fixing roller 471. The fixing unit 47 heats and pressurizes the toner image on the recording material S at a nip formed between the fixing roller 471 and the pressure roller 472, while sandwiching and transporting the recording material S onto which the toner image has been transferred. In addition, fixing unit 47 has a position change mechanism (not shown) that adjusts the position of fixing roller 471 in order to adjust the nip pressure of the nip portion between fixing roller 471 and pressure roller 472 and release the pressure contact.

[0029] The collection adjustment unit 50 is installed downstream of the image forming device 40 and upstream of the collection device 60 in the conveying direction of the recording material S. The collection adjustment unit 50 is a device that conveys the recording material S conveyed from the image forming device 40 to the collection device 60, and adjusts the discharge of the recording material S from the image forming device 40 by holding the recording material S with slack in order to absorb the speed difference between the conveying speed of the recording material S in the image forming device 40 and the conveying speed of the recording material S in the collection device 60. The recovery device 60 includes a paper discharge section that winds up the recording material S conveyed from the recovery adjustment section 50 around a support shaft 61 at a constant speed via a plurality of rollers.

[0030] [System block diagram of image forming device] Next, FIG. 2 shows a block diagram of an example of the configuration of the image forming apparatus 40. As shown in FIG. As shown in FIG. 2, the image forming device 40 includes a paper feed unit 10, a control unit 41, an operation display unit 42, a conveying unit 44, a color misregistration detection sensor 45, an image forming unit 46, an inclination adjustment unit 467, a fixing unit 47, and a non-volatile memory 48.

[0031] The control unit 41 of the image forming apparatus 40 is configured with, for example, a CPU (Central Processing Unit), RAM (Random Access Memory), ROM (Read Only Memory), etc. (not shown). The CPU of the control unit 41 reads various processing programs stored in the ROM and loads them into the RAM, and in accordance with the loaded programs, performs overall control of the operations of each unit of the image forming apparatus 40, such as the paper feed unit 10, operation display unit 42, conveyance unit 44, color misregistration detection sensor 45, image forming unit 46, fixing unit 47, and non-volatile memory 48, which are connected via the system bus of the image forming apparatus 40.

[0032] The nonvolatile memory 48 stores programs executed by the control unit 41 and is used as a work area for the control unit 41. The nonvolatile memory 48 also stores image forming conditions set in an image forming job, recording material information including the size and type of the recording material S, etc. The nonvolatile memory 48 also stores information such as the positions of the toner images of each color detected by the color shift detection sensor 45, and the amount of color shift calculated based on the positions of the toner images.

[0033] Furthermore, the control unit 41 acquires image data from the input job information and performs image processing. The control unit 41 performs image processing such as shading correction, image density adjustment, and image compression on the acquired image data as necessary. The image data processed by the control unit 41 is then sent to the image forming unit 46. Based on the control of the control unit 41, the conveying unit 44 conveys the recording material S fed from the paper feeding unit 10 to the image forming unit 46, the fixing unit 47, and the like. The image forming section 46 receives the image data that has been image-processed by the control section 41, and forms an image on the recording material S that has been conveyed to the image forming section 46 by the conveying section 44 based on this image data. Furthermore, in the image forming section 46, the tilt adjustment section 467 adjusts the angle of the laser writing unit in accordance with the amount of operation of the tilt adjustment section 467 calculated by the control section 41, and performs skew correction using a mechanical mechanism.

[0034] The operation display unit 42 displays various operation buttons, device status indication, operation status of each function, etc. on the display screen in accordance with instructions of a display signal input from the control unit 41. Furthermore, the operation display unit 42 accepts input of various instructions, characters, numbers, and other data by user operation, and outputs the input signal to the control unit 41.

[0035] [Controller function configuration] Next, the functional configuration of the control unit of the image forming apparatus will be described with reference to the functional block diagram of FIG. Next, a description will be given of the functional configuration of the control unit 41 of the image forming apparatus 40. Fig. 3 shows a functional block diagram of the control unit 41 of the image forming apparatus 40. The control unit 41 shown in Fig. 3 has a color misregistration amount calculation unit 411, a first skew correction control unit 412, a second skew correction control unit 413, an execution setting unit 414, and a margin setting unit 415.

[0036] (Color shift calculation section) The color misregistration amount calculation unit 411 calculates the amount of color misregistration of each color image in the image forming unit based on the position of the toner image of each color on the intermediate transfer belt 465 detected by the color misregistration detection sensor 45. Furthermore, the color misregistration amount calculation unit 411 compares the calculated amount of color misregistration with a color misregistration residual target value, which is a preset target value for the amount of color misregistration, and determines whether the calculated amount of color misregistration is larger or smaller than the color misregistration residual target value.

[0037] (Skew correction control section) The first skew correction control unit 412 and the second skew correction control unit 413 control skew color shift correction (skew correction) in the image forming apparatus 40. In the image forming apparatus 40, the first skew correction control unit 412 controls skew correction (first skew correction), and then the second skew correction control unit 413 controls skew correction (second skew correction). As a result, the image forming apparatus 40 performs the second skew correction on the amount of color shift (color shift residual) of the image corrected by the first skew correction. In this way, by performing the second skew correction after reducing the amount of color shift (color shift residual) by the first skew correction, the correction amount of the second skew correction can be reduced.

[0038] The first skew correction control unit 412 performs the first skew correction when the initial color misregistration amount calculated by the color misregistration amount calculation unit 411 is equal to or greater than the minimum unit (resolution) at which correction by the first skew correction is possible. Therefore, when the initial color misregistration amount is less than the minimum unit (resolution) at which correction by the first skew correction is possible, the first skew correction control unit 412 does not perform the first skew correction, and only the second skew correction control unit 413 performs the second skew correction, thereby completing the skew correction in the image forming apparatus 40.

[0039] Furthermore, the image forming apparatus 40 may be configured such that a user can arbitrarily set whether or not the second skew correction is to be performed by the second skew correction control unit. For example, by stopping the execution of the second skew correction, it is possible to complete the skew correction in the image forming apparatus 40 by performing only the first skew correction by the first skew correction control unit 412 without performing the second skew correction by the second skew correction control unit 413.

[0040] (First skew correction control unit) The first skew correction control unit 412 controls the driving of the tilt adjustment unit 467 and adjusts the tilt of the laser writing unit to perform skew correction (first skew correction). That is, the first skew correction control unit 412 controls skew correction by a mechanical mechanism in the image forming apparatus 40.

[0041] The first skew correction control unit 412 executes the first skew correction so that the color shift amount calculated by the color shift amount calculation unit 411 falls below a preset first color shift residual target value. This first color shift residual target value is the minimum unit (resolution) at which correction by the first skew correction is possible. By performing the first skew correction so that the color shift residual after the first skew correction is equal to or less than the first color shift residual target value, the correction by the first skew correction is maximized among the skew corrections. This makes it possible to minimize the margins between images.

[0042] Alternatively, the first skew correction control unit 412 may count the number of times the first skew correction has been performed and perform the first skew correction up to a predetermined number of times. If the first color misregistration residual target value is not set, the first skew correction control unit 412 repeatedly performs the first skew correction until the number of times the first skew correction has been performed reaches a predetermined first correction number. This allows the first skew correction to be performed more frequently among the skew corrections, thereby making it possible to reduce the margins between images.

[0043] (Skew correction by the first skew correction control unit) 4, 5, and 6 are diagrams for explaining the control of the first skew correction by the mechanical mechanism of the first skew correction control unit 412. FIG. 4 is a diagram showing the laser writing unit 468, the tilt adjustment unit 467 that adjusts the tilt of the laser writing unit 468, and the photoconductor 462 before the first skew correction is performed. Before the first skew correction, the laser writing unit 468 irradiates the surface of the photoconductor 462 with laser light 460 perpendicular to the surface. As a result, a laser trajectory 469 that is parallel to the direction (main scanning direction) perpendicular to the rotation direction is formed on the surface of the photoconductor 462. As a result, a parallel electrostatic latent image that has not been skew corrected is formed on the photoconductor 462.

[0044] FIG. 5 is a diagram showing the laser writing unit 468 after the first skew correction has been performed, the tilt adjustment unit 467 that adjusts the tilt of the laser writing unit 468, and the photosensitive member 462. As shown in FIG. The first skew correction control unit 412 drives the tilt adjustment unit 467, and the laser writing unit 468 is tilted obliquely with respect to the main scanning direction of the photoconductor 462. In this state, when the laser writing unit 468 irradiates the photoconductor 462 with laser light 460, a laser locus 469 is formed on the surface of the photoconductor 462, which is tilted from a line parallel to the main scanning direction. As a result, a tilted, skew-corrected electrostatic latent image is formed on the photoconductor 462. Then, toner is supplied from the developing unit 463 to this tilted electrostatic latent image, and the skew-corrected electrostatic latent image is developed on the photoconductor 462 and transferred (primary transfer) to the intermediate transfer belt 465. By the control of the first skew correction control unit 412 described above, the toner image that has been subjected to skew correction (first skew correction) by a mechanical mechanism can be transferred onto the intermediate transfer belt 465.

[0045] 6 shows toner image 101 and toner image 102 that have been corrected by the first skew correction and transferred onto intermediate transfer belt 465. In FIG. 6, toner image 101 is transferred onto intermediate transfer belt 465 first, and toner image 102 is transferred after toner image 101. As shown in FIG. 6, the first skew correction is performed by a mechanical mechanism through the first skew correction controlled by first skew correction control unit 412, and toner images 101 and 102, which are formed at an angle to the main scanning direction, are transferred continuously onto intermediate transfer belt 465 without forming any margins. In this way, by performing the first skew correction by a mechanical mechanism and transferring (secondary transfer) the toner image onto the recording material S, continuous image formation becomes possible without forming margins between pages or between images. Therefore, in the first skew correction performed under the control of the first skew correction control unit 412, no waste paper (waste paper) is discarded due to the margins between pages or between images.

[0046] (Second skew correction control section) The control unit 41 acquires image data from the input job information and performs image processing. For example, the control unit 41 performs image processing such as shading correction, image density adjustment, and image compression on the acquired image data as needed. Then, the image forming unit 46 forms an image on each page of the recording material S by electrophotography based on the image data that has been image processed by the control unit 41.

[0047] The second skew correction control unit 413 performs skew correction (second skew correction) during image processing of image data performed in the control unit 41. That is, the second skew correction control unit 413 controls skew correction by image processing in the image forming apparatus 40.

[0048] The second skew correction control unit 413 performs second skew correction on the color shift amount (color shift residual) of the image after the first skew correction control performed by the first skew correction control unit 412. The second skew correction control unit 413 performs second skew correction so that the color shift residual falls below a preset second color shift residual target value. This second color shift residual target value is preferably the smallest unit (resolution) that can be corrected by the second skew correction. By performing the second skew correction so that the color shift residual after the second skew correction falls below the second color shift residual target value, highly accurate skew correction can be performed.

[0049] Alternatively, the second skew correction control unit 413 may count the number of times the second skew correction has been performed and perform the second skew correction up to a predetermined number of times. If the second color misregistration residual target value is not set, the second skew correction control unit 413 repeatedly performs the second skew correction until the number of times the second skew correction has been performed reaches a predetermined number of times. This allows the second skew correction control unit 413 to perform skew correction with high accuracy.

[0050] The first skew correction described above is a correction using a mechanical mechanism, and since it follows the resolution of the operating amount of the motors and the like that make up tilt adjustment unit 467, the minimum unit of correction (resolution) is about 10 μm. On the other hand, the second skew correction is a correction using image processing, so correction is possible in image pixel units, and correction can be made in minimum units (resolution) of several μm or less. Therefore, by performing the second skew correction, highly accurate skew correction can be performed.

[0051] (Skew correction by the second skew correction control unit) 7 and 8 are diagrams for explaining the control of the second skew correction by the image processing of the second skew correction control unit 413. FIG.

[0052] 7 is a diagram showing image data 103 before the second skew correction is performed and image data 104 after the second skew correction is performed. In the image data 103 and image data 104 shown in Fig. 7, the vertical direction of the drawing is the direction parallel to the conveyance direction of the recording material S during image formation (sub-scanning direction), and the horizontal direction is the direction perpendicular to the conveyance direction of the recording material S during image formation (main scanning direction).

[0053] In the image data 103 before the second skew correction is performed, a leading edge 103a and a trailing edge 103b of the image data 103 are formed in positions parallel to the main scanning direction. In contrast, after the second skew correction is performed, the image data 104 generates an image portion 104g that is tilted with respect to the main scanning direction according to the amount of color misregistration. Furthermore, the image data 104 generated by the second skew correction has its overall length in the sub-scanning direction enlarged. That is, in the image data 104, the leading edge 104a and trailing edge 104b of the tilted image portion 104g are formed at an angle with respect to the main scanning direction. A margin 104e is formed in the area between the leading edge 104a of the image portion 104g and the leading edge 104c of the image data 104. Furthermore, a margin 104f is formed in the area between the trailing edge 104b of the image portion 104g and the trailing edge 104d of the image data 104.

[0054] In this way, the image data 104 is enlarged in the sub-scanning direction by the amount that the image portion 104g is tilted with respect to the main scanning direction due to the second skew correction performed by the second skew correction control unit 413. Then, margins 104e and 104f, where the image portion 104g is not formed, are generated in the regions on the leading and trailing ends of the enlarged image data 104. Therefore, when the second skew correction is performed by the image processing of the second skew correction control unit 413, the area including the image portion 104g formed diagonally with respect to the main scanning direction and the margins 104e and 104f becomes one page of the image data 104.

[0055] 8 shows images 105 and 106 corrected by the second skew correction and formed on the recording material S. In FIG. 8, image 105 is formed on the recording material S first (secondary transfer and fixing), and image 106 is formed after image 105. As shown in Fig. 8, image 105, which has undergone second skew correction by image processing by second skew correction control unit 413, has margin 105a formed on its leading edge and margin 105b formed on its trailing edge. Similarly, image 106 has margin 106a formed on its leading edge and margin 106b formed on its trailing edge. Margins 105a and 106a correspond to margin 104e on the leading edge of image data 104 shown in Fig. 7 above. Margins 105b and 106b correspond to margin 104f on the trailing edge of image data 104 shown in Fig. 7 above.

[0056] In this way, when the second skew correction is performed, a margin 107 consisting of margins 105b and 106a is formed between the images 105 and 106. As a result, when the second skew correction is performed under the control of the second skew correction control unit 413 in the image forming apparatus 40, when images are continuously formed on the recording material S, a margin is formed between the formed images and between each page.

[0057] (Execution Settings Section) The execution setting unit 414 accepts a setting to enable or disable the execution of the second skew correction by the second skew correction control unit 413. For example, the execution setting unit 414 accepts a setting by a user or the like via the operation display unit 42 of the image forming apparatus 40, and sets whether the execution of the second skew correction is enabled or disabled. If the setting of the second skew correction in the execution setting unit 414 is enabled, the second skew correction control unit 413 executes the second skew correction by image processing. If the setting of the second skew correction in the execution setting unit 414 is disabled, the second skew correction control unit 413 does not execute the second skew correction by image processing.

[0058] Image processing using the second skew correction cannot be used to make the margins between successive images formed on the recording material S zero. For example, if the output product is something like masking tape, the margins between images must be zero, so image processing using the second skew correction must be disabled. For this reason, it is desirable to keep the first skew correction using a mechanical mechanism always enabled, but the second skew correction using image processing must be set to ON / OFF for each job.

[0059] The execution setting unit 414 can perform skew correction without generating margins between images by disabling the second skew correction performed by the second skew correction control unit 413. When the setting of the second skew correction is disabled by the execution setting unit 414, the control unit 41 performs only the first skew correction performed by the first skew correction control unit 412.

[0060] (Margin setting section) The margin setting unit 415 sets the amount of margin between the skew-corrected images to a fixed value. For example, the margin setting unit 415 sets the amount of margin between the images to one type of preset margin amount (fixed value), a value selected by the user from multiple preset margin amounts (selected value), or a value arbitrarily set by the user or the like as the amount of margin (arbitrary value).

[0061] If one type of margin amount is set in advance, for example, if image forming apparatus 40 has a fixed margin amount of 1 mm, margin setting unit 415 will have the preset fixed value of 1 mm as the margin amount. Therefore, margin setting unit 415 sets this preset fixed value as the margin amount. Furthermore, when the user selects a value from a plurality of preset margin amounts, the margin setting unit 415 presents to the user, for example, three selectable values ​​of "1 mm, 2 mm, or 3 mm" as settable margin amounts (on the operation display unit 42).The margin setting unit 415 then accepts the user's selection from the presented values ​​and sets the selected value (selected value) as the margin amount. Furthermore, when a user or the like arbitrarily sets the amount of margin, the margin setting unit 415 accepts an input of an arbitrary value (arbitrary value) of the amount of margin by the user or the like on the operation display unit 42. Then, the margin setting unit 415 sets the arbitrary value input by the user or the like as the amount of margin.

[0062] 8, in the second skew correction described above, a margin 107 (margins 105b, 106a) due to image processing occurs between images 105 and 106 formed consecutively on the recording material S. The amount of margin 107 (margins 105b, 106a) generated in the second skew correction differs depending on the correction rate in the image processing.

[0063] Image data with different correction rates for image processing in the second skew correction are shown in Figures 9 and 10. Figure 9 shows image data 108 when the correction rate for skew correction is small (small slope) in the second skew correction. Figure 10 shows image data 109 when the correction rate for skew correction is large (large slope) in the second skew correction.

[0064] 9, after the second skew correction is performed, the image data 108 generates an image portion 108g that is inclined with respect to the main scanning direction according to the amount of color misregistration. Furthermore, the image data 108 generated by the second skew correction has an overall length in the sub-scanning direction expanded according to the correction rate, and a margin 108e is formed on the leading edge side of the image portion 108g, and a margin 108f is formed on the trailing edge side. 10, image data 109 after the second skew correction is performed generates image portion 109g that is inclined with respect to the main scanning direction according to the amount of color misregistration. Furthermore, image data 109 generated by the second skew correction has its overall length in the sub-scanning direction expanded according to the correction rate, and margin 109e is formed on the leading edge side of image portion 109g, and margin 109f is formed on the trailing edge side.

[0065] Between the image data 108 and the image data 109, the correction rate of the second skew correction is greater in the image data 109, and the inclination of the image portion 109g is greater in the image data 109. Therefore, the areas of the margins 109e and 109f formed on the leading and trailing edges of the image portion 109g are larger in the sub-scanning direction than the areas of the margins 108e and 108f formed on the leading and trailing edges of the image portion 108g of the image data 108.

[0066] In image data that has undergone the second skew correction, such as the image data 108 and the image data 109, the interval between image portions that are successively formed on the recording material S is determined by the magnitude of the correction rate of the skew correction. However, the amount of color misregistration varies depending on the individual image forming apparatus 40 and the internal temperature. Therefore, if the margin between image portions is set to the minimum value corresponding to the correction rate of the second skew correction, the margin between images will vary not only depending on the image forming apparatus executing the job, but also each time the second skew correction is performed, even when the same image forming apparatus is used. Such fluctuations in the margin between images reduce user convenience. For example, in post-processing after image formation, it is necessary to set the processing position and cutting position depending on the margin between images. Therefore, if the margin amount changes each time a job is executed, post-processing settings must be configured for each job, which increases the user's workload.

[0067] Therefore, even when second skew correction is performed by the image processing of the second skew correction control unit 413, the margin setting unit 415 sets the amount of margin between images formed consecutively on the recording material S to a constant value regardless of the correction rate of the image processing. Fig. 11 shows an example of image data when the margin amount is set to a fixed value. Fig. 11 shows an example in which the image data 108 and image data 109 shown in Figs. 9 and 10 are continuously formed on the intermediate transfer belt 465 and the recording material S, respectively. In Fig. 11, image areas 108g and 109g are continuously arranged in the sub-scanning direction. The distance between the rearmost and leading ends of image areas 108g and 109g in the sub-scanning direction is shown as margin 110.

[0068] As shown in FIG. 11, when image areas 108g are formed consecutively and when image areas 109g are formed consecutively, the distance in the sub-scanning direction of the margin 110 between image areas 108g and between image areas 109g is set to the same value. In this way, by setting the margin amount of the margin 110 between image areas 108g and 109g to a constant value, the margin amount of the output can be kept constant regardless of changes in the margin amount that occur in the second skew correction for each job. Therefore, in image forming apparatus 40, since control unit 41 has margin setting unit 415, it is possible to suppress deterioration in user convenience due to fluctuations in the margin amount during post-processing, etc.

[0069] The value of the margin amount of the output product set by the margin setting unit 415 is reflected in the control of image processing in the second skew correction by the second skew correction control unit 413. The second skew correction control unit 413 sets the amount of margin between images of image data generated in the second skew correction to a fixed value set by the margin setting unit 415. For example, in the second skew correction, if the amount of margin generated at a correction rate according to the amount of color misalignment is less than the fixed value set by the margin setting unit 415, the second skew correction control unit 413 inserts a margin amount according to the difference from the set margin amount value between the images, and generates image data so that the amount of margin becomes the fixed value. 11, margin 110 between image portions 108g is formed by inserting margin 110a between margin 108e and margin 108f. Also, margin 110 between image portions 109g is formed by inserting margin 110b between margin 109e and margin 109f. In this way, image data is generated by inserting further margins 110a and 110b between margins 108e and 108f and margins 109e and 109f generated by image processing so that the amount of margin between images becomes a set fixed value.

[0070] Furthermore, the second skew correction control unit 413 limits the skew correction rate of the image processing of the second skew correction control unit 413 so as not to exceed the value set in the margin setting unit 415. In the second skew correction, if the correction rate is set according to the amount of color misregistration, there is a possibility that the amount of margin generated in the image data will exceed the certain value set in the margin setting unit 415. For this reason, the second skew correction control unit 413 generates image data by limiting the correction rate in the second skew correction to a correction rate that makes the amount of margin generated in the image data equal to or less than the certain value set in the margin setting unit 415.

[0071] It is preferable that the upper limit of the margin amount set by the margin setting unit 415, which can be arbitrarily set by a user or the like, be equal to or less than the first color shift residual target value (T1) of the first skew correction. When the first skew correction is performed to the maximum, the maximum value of the margin amount generated by the image processing of the second skew correction will be equal to or less than the first color shift residual target value (T1). Therefore, by setting the margin amount equal to or less than the first color shift residual target value (T1), it is possible to suppress the amount of margin generated in the color shift correction.

[0072] [Color misregistration correction (skew correction) processing method 1] Next, a specific processing method for correcting color misregistration (skew correction) by the image forming apparatus described above will be described. Fig. 12 shows a flowchart of a first processing method for skew correction performed by the image forming apparatus.

[0073] First, test image formation for color misregistration correction is started in image forming apparatus 40. Then, color misregistration amount calculation unit 411 calculates the amount of color misregistration based on the position of the toner image transferred to intermediate transfer belt 465 detected by color misregistration detection sensor 45 (step S101).

[0074] Next, the first skew correction control unit 412 performs the first skew correction based on the amount of color shift calculated by the color shift amount calculation unit 411 (step S102). The first skew correction control unit 412 performs the skew correction by the mechanical mechanism of the image forming apparatus 40 as described above.

[0075] After the first skew correction, the color shift amount calculation unit 411 calculates the color shift amount (color shift residual) after the first skew correction and determines whether the color shift residual is less than the first color shift residual target value (T1) (step S103). In this determination, first, a test image is formed again in the image forming apparatus 40, and the color shift detection sensor 45 detects the position of the toner image. Then, based on the position of the toner image after the first skew correction detected by the color shift detection sensor 45, the color shift amount calculation unit 411 calculates the color shift amount (color shift residual) after the first skew correction. Furthermore, the color shift amount calculation unit 411 determines whether the color shift residual after the first skew correction is less than the first color shift residual target value (T1), which is the minimum unit (resolution) at which correction by the first skew correction is possible.

[0076] If the color shift residual is not less than the first color shift residual target value (T1) (No in step S103), the control unit 41 repeats the processing of steps S101 and S102, and repeats the first skew correction until the color shift residual after the first skew correction falls below the first color shift residual target value (T1).

[0077] If the color misregistration residual is less than the first color misregistration residual target value (T1) (Yes in step S103), the color misregistration amount calculation unit 411 calculates the color misregistration amount after the first skew correction (step S104).

[0078] Next, the second skew correction control unit 413 performs the second skew correction based on the amount of color shift after the first skew correction calculated by the color shift amount calculation unit 411 (step S105). The second skew correction control unit 413 performs the skew correction by image processing.

[0079] After the second skew correction, the color shift amount calculation unit 411 calculates the color shift amount after the second skew correction (color shift residual) and determines whether the color shift residual is less than the second color shift residual target value (T2) (step S106). In this determination, first, a test image is formed again in the image forming apparatus 40, and the position of the toner image is detected by the color shift detection sensor 45. Then, based on the position of the toner image after the second skew correction detected by the color shift detection sensor 45, the color shift amount calculation unit 411 calculates the color shift amount after the second skew correction (color shift residual). Furthermore, the color shift amount calculation unit 411 determines whether the color shift residual after the second skew correction is less than the second color shift residual target value (T2), which is the minimum unit (resolution) at which correction by the second skew correction is possible.

[0080] If the color shift residual is not less than the second color shift residual target value (T2) (No in step S106), the control unit 41 repeats the processing of steps S104 and S105, and repeats the second skew correction until the color shift residual after the second skew correction falls below the second color shift residual target value (T2).

[0081] If the color misregistration residual is less than the second color misregistration residual target value (T2) (Yes in step S106), the process according to this flowchart ends. In the above process, the first skew correction is repeated until the color shift residual after the first skew correction becomes less than the first color shift residual target value, thereby maximizing the correction by the first skew correction that does not create white space between images. Then, the second skew correction with higher resolution is performed. This minimizes the amount of second skew correction that creates white space, thereby reducing the occurrence of white space. Furthermore, by performing the first skew correction with lower resolution followed by the second skew correction with higher resolution, color shift correction can be performed with high accuracy.

[0082] [Color misregistration correction (skew correction) processing method 2] Next, a second processing method for color misregistration correction (skew correction) by the image forming apparatus described above will be described. In the first processing method described above, the color misregistration residual is compared with a color misregistration residual target value to determine whether skew correction is complete, but in the second processing method described below, the first skew correction and the second skew correction are repeated a preset number of times to complete skew correction.

[0083] FIG. 13 is a flowchart showing a second processing method for skew correction performed by the image forming apparatus. First, the first skew correction control unit 412 sets the count of the number of times the first skew correction has been performed to 0 (step S201).

[0084] Next, in the image forming device 40, test image formation is started for color shift correction, and the color shift amount calculation unit 411 calculates the amount of color shift based on the position of the toner image transferred to the intermediate transfer belt 465 detected by the color shift detection sensor 45 (step S202).

[0085] Next, the first skew correction control unit 412 performs the first skew correction based on the color shift amount calculated by the color shift amount calculation unit 411 (step S203). Then, the first skew correction control unit 412 adds 1 to the count of the current number of corrections of the first skew correction (step S204).

[0086] Next, the first skew correction control unit 412 determines whether the current number of corrections matches a preset first number of corrections S1 (step S205). If the current number of corrections does not match the preset first number of corrections S1 (No in step S205), the control unit 41 repeats the processing from step S202 to step S204, and repeats the first skew correction until the current number of corrections of the first skew correction matches the preset first number of corrections S1. If the current number of corrections matches the preset first number of corrections S1 (Yes in step S205), the second skew correction control unit 413 sets the count of the number of corrections of the second skew correction to 0 (step S206).

[0087] Next, the color misregistration amount calculation unit 411 calculates the color misregistration amount after the first skew correction (step S207). The second skew correction control unit 413 performs the second skew correction based on the amount of color shift after the first skew correction calculated by the color shift amount calculation unit 411 (step S208). Then, the second skew correction control unit 413 adds 1 to the count of the current number of corrections of the second skew correction (step S209).

[0088] Next, the second skew correction control unit 413 determines whether the current number of corrections matches a preset second number of corrections S2 (step S210). If the current number of corrections does not match the preset second number of corrections S2 (No in step S210), the control unit 41 repeats the processing from step S207 to step S209, and repeats the second skew correction until the current number of corrections of the second skew correction matches the preset second number of corrections S2.

[0089] If the current number of corrections matches the preset second number of corrections S2 (Yes in step S210), the process according to this flowchart ends. In the above process, the first skew correction, which does not create white space between images, is repeated a first number of times S1, and then the second skew correction, which has higher resolution, is repeated a second number of times S2. This reduces the occurrence of white space and enables highly accurate color misregistration correction.

[0090] [Color misregistration correction (skew correction) processing method 3] Next, a third processing method for color misregistration correction (skew correction) by the image forming apparatus described above will be described. In the first and second processing methods described above, the first skew correction and the second skew correction are repeated to complete the skew correction, but in the third processing method described below, the execution setting unit 414 checks whether the second skew correction control unit 413 has enabled or disabled the execution of the second skew correction before forming an image.

[0091] FIG. 14 is a flowchart showing a third processing method for skew correction performed by the image forming apparatus. First, the first skew correction control unit 412 executes the processes of steps S101 to S103 shown in FIG. 12 or steps S201 to S205 shown in FIG. 13 to perform the first skew correction (step S301).

[0092] Next, the execution setting unit 414 determines whether the execution of the second skew correction by the operation of the user or the like is valid (step S302). If the execution of the second skew correction is enabled (Yes in step S302), the second skew correction control unit 413 executes the processing of steps S104 to S106 shown in FIG. 12 or steps S206 to S210 shown in FIG. 13, and executes the second skew correction (step S303).

[0093] If the execution of the second skew correction is not enabled (No in step S302), or after the execution of the second skew correction in step S303, the image forming device 40 executes image formation in the image forming unit 46 (step S304) and ends the processing according to this flowchart.

[0094] [Color misregistration correction (skew correction) processing method 4] Next, a fourth processing method for color misregistration correction (skew correction) by the image forming apparatus described above will be described. The fourth processing method described below performs skew correction again on a job for which skew correction has already been performed by the first and second processing methods described above.

[0095] Inside the image forming device 40, the amount of color misregistration constantly fluctuates due to temperature changes and the like, so color misregistration correction is not a one-time process, but must be performed again in response to changes in the temperature inside the device, etc. Normally, from the second time onwards, the amount of color misregistration is calculated and the color misregistration correction is performed using the previous correction value as the initial value, thereby shortening the correction time.

[0096] A specific example of such a second color misregistration correction will be described below. In this example, in the color misregistration correction of the image forming apparatus 40, the resolution of the first skew correction by a mechanical mechanism is set to 10 μm, and the resolution of the second skew correction by image processing is set to 1 μm.

[0097] First, if the amount of color misregistration is calculated to be 25 μm in the first color misregistration correction, the amount of color misregistration to be subjected to the first skew correction is the total amount of color misregistration calculated, 25 μm. Since the resolution of the first skew correction is 10 μm, the amount of color misregistration that can be corrected by the first skew correction is 20 μm out of the total amount of color misregistration, 25 μm. The amount of color misregistration to be subjected to the second skew correction is 5 μm, which is the color misregistration residual in the first skew correction.

[0098] Next, a case will be described in which the processing method according to the flowchart shown in FIG. 12 or 3 is executed when the second color misregistration correction is performed in response to a change in the temperature inside the apparatus or the like. Assume that in the second color shift correction, a color shift of 5 μm has occurred compared to the first correction. In this state, the actual color shift amount is 30 μm. However, since a total of 25 μm of correction has been performed in the first and second skew corrections in the first color shift correction described above, the color shift amount calculated by color shift amount calculation unit 411 is 5 μm [30 μm (actual color shift amount) - 25 μm (25 μm corrected in the first correction) = 5 μm]. In this case, the amount of color misregistration that is the target of the first skew correction becomes 5 μm, which is less than the 10 μm resolution of the first skew correction, so the amount of color misregistration that can be corrected by the first skew correction is not changed (increased). As a result, the value of the first correction is continued, and the amount of color misregistration that can be corrected by the first skew correction is determined to be 20 μm. Then, in the second skew correction, the color shift residual of 5 μm from the first skew correction in the second color shift correction is added to the value of 5 μm from the first correction, and the color shift amount subject to the second skew correction becomes 10 μm [5 μm (first correction amount) + 5 μm (second color shift residual) = 10 μm]. Thus, in the processing method according to the flowchart shown in Figure 12 or 13 described above, the first skew correction control unit 412 does not perform the first skew correction if the calculated color shift amount is below the first color shift residual target value (resolution).

[0099] However, in order to minimize the margins between images on the output of the image forming apparatus 40, it is desirable to maximize the first skew correction using a mechanical mechanism and minimize the execution of image processing by the second skew correction, which generates margins. Therefore, in the above example, if the actual color misregistration amount in the second processing is 30 μm, it is desirable to perform a correction of 30 μm in the first skew correction, thereby correcting the color misregistration without generating margins due to image processing by the second skew correction.

[0100] The following describes a processing method for performing the first skew correction using a mechanical mechanism to the maximum extent possible in the second and subsequent color misregistration corrections. Fig. 15 shows a flowchart of the skew correction processing method performed by the image forming apparatus. Note that the flowchart shown in Fig. 15 is a process that is executed subsequently to the color misregistration correction method performed according to the flowchart shown in Fig. 12, Fig. 13, or Fig. 14.

[0101] First, the second skew correction control unit 413 erases (clears) the correction value of the second skew correction performed before this step (step S401). Next, the color shift amount calculation unit 411 calculates the color shift amount (step S402). The first skew correction control unit 412 performs the first skew correction based on the color shift amount calculated by the color shift amount calculation unit 411 (step S403). After the first skew correction, the color shift amount calculation unit 411 calculates the color shift amount (color shift residual) after the first skew correction, and determines whether the color shift residual is less than the first color shift residual target value (T1) (step S404). If the color shift residual is not less than the first color shift residual target value (T1) (No in step S404), the control unit 41 repeats the processing of steps S402 and S403, and repeats the first skew correction until the color shift residual after the first skew correction falls below the first color shift residual target value (T1). If the color misregistration residual is less than the first color misregistration residual target value (T1) (Yes in step S404), the color misregistration amount calculation unit 411 calculates the color misregistration amount after the first skew correction (step S405).

[0102] Next, the second skew correction control unit 413 performs the second skew correction based on the color shift amount after the first skew correction calculated by the color shift amount calculation unit 411 (step S406). After the second skew correction, the color shift amount calculation unit 411 calculates the color shift amount (color shift residual) after the second skew correction, and determines whether the color shift residual is less than a second color shift residual target value (T2) (step S407). If the color shift residual is not less than the second color shift residual target value (T2) (No in step S407), the control unit 41 repeats the processing of steps S405 and S406, and repeats the second skew correction until the color shift residual after the second skew correction falls below the second color shift residual target value (T2). If the color misregistration residual is less than the second color misregistration residual target value (T2) (Yes in step S407), the process according to this flowchart ends. The processes from step S402 to step S407 described above are the same as those from step S101 to step S106 shown in Fig. 12. Furthermore, the processes from step S402 to step S407 described above may be replaced by those from step S201 to step S210 shown in Fig. 13 or those from step S302 to step S304 shown in Fig. 14.

[0103] A specific example of the second color misregistration correction described above will be explained below, where the correction is performed in accordance with the process of the flowchart shown in Fig. 15. The resolution of the first skew correction, the resolution of the second skew correction, the process of the first color misregistration correction, and the amount of color misregistration in the second correction are as described above. That is, it is assumed that in the second color misregistration correction, an additional 5 µm of color misregistration occurs compared to the first correction, and the actual amount of color misregistration is 30 µm.

[0104] First, in step S401, the correction amount of the second skew correction executed in the first color misregistration correction is cleared, thereby setting the correction amount of 5 μm of the second skew correction executed in the first color misregistration correction to 0 μm. Next, in step S402, the color misregistration amount calculation unit 411 calculates the amount of color misregistration to be 10 μm. Here, the first color misregistration correction (first skew correction and second skew correction) has been performed to a total of 25 μm, but since the correction amount of the second skew correction was cleared in step S401, the calculated value of the color misregistration amount calculation unit 411 is 10 μm [30 μm (actual color misregistration amount) - 25 μm (25 μm corrected in the first correction) + 5 μm (cleared second skew correction amount) = 10 μm].

[0105] Next, in step S403, the first skew correction control unit 412 performs the first skew correction on the color misregistration amount of 10 μm calculated by the color misregistration amount calculation unit 411. Here, because the resolution of the first skew correction is 10 μm, the second color misregistration amount of 10 μm is added to the value of the first correction, 20 μm, and the color misregistration amount to be subjected to the first skew correction becomes a total of 30 μm.

[0106] Next, in step S404, it is determined that the color misregistration residual 0 μm due to the first skew correction [30 μm (calculated color misregistration amount)−30 μm (correction value of the first skew correction)=0 μm] is less than the first color misregistration residual target value (T1). Then, in step S405, the color misregistration amount calculation unit 411 calculates the color misregistration amount to be subjected to the second skew correction as 0 μm because the color misregistration residual of the first skew correction is 0 μm. As a result, in step S406, the correction amount by the second skew correction becomes 0, and further, in step S407, it becomes less than the second color misregistration residual target value (T2), and the processing according to the flowchart shown in FIG. 15 ends.

[0107] 15, if the actual color misregistration amount in the second process is 30 μm, by performing a 30 μm correction in the first skew correction, it is possible to correct the color misregistration without generating margins due to the image processing of the second skew correction. Therefore, it is possible to minimize the execution of image processing by the second skew correction, which generates margins, and to maximize the first skew correction using a mechanical mechanism, thereby minimizing the margins between images in the output.

[0108] [Color misregistration correction (skew correction) processing method 5] Next, a fifth processing method for color misregistration correction (skew correction) by the image forming apparatus described above will be described. In the first and second processing methods described above, the first skew correction is performed after calculating the amount of color misregistration. However, if the calculated amount of color misregistration is less than the first color misregistration residual target value, there is no need to perform the first skew correction. Therefore, in the fifth processing method described below, the first skew correction is performed only when the amount of color misregistration is equal to or greater than the first color misregistration residual target value, and if the amount of color misregistration is less than the first color misregistration residual target value, the first skew correction is omitted, thereby shortening the correction processing time in the image forming apparatus 40.

[0109] FIG. 16 is a flowchart showing a fifth processing method for skew correction performed by the image forming apparatus. First, in the image forming device 40, test image formation is started for color shift correction, and the color shift amount calculation unit 411 calculates the amount of color shift based on the position of the toner image transferred to the intermediate transfer belt 465 detected by the color shift detection sensor 45 (step S501).

[0110] Next, the color shift amount calculation unit 411 determines whether the calculated color shift amount is less than a first color shift residual target value (T1) (step S502). If the amount of color shift is not less than the first color shift residual target value (T1) (No in step S502), the first skew correction control unit 412 performs the first skew correction (step S503) based on the amount of color shift calculated by the color shift amount calculation unit 411. Then, after the first skew correction, the color shift amount calculation unit 411 repeats the processes of steps S501 to S503 described above until the amount of color shift (color shift residual) after the first skew correction becomes less than the first color shift residual target value (T1).

[0111] If the color shift amount is less than the first color shift residual target value (T1) (Yes in step S502), the color shift amount calculation unit 411 calculates the color shift amount after the first skew correction (step S504).

[0112] Next, the second skew correction control unit 413 performs the second skew correction based on the color shift amount after the first skew correction calculated by the color shift amount calculation unit 411 (step S505). After the second skew correction, the color shift amount calculation unit 411 calculates the color shift amount (color shift residual) after the second skew correction, and determines whether the color shift residual is less than a second color shift residual target value (T2) (step S506). If the color shift residual is not less than the second color shift residual target value (T2) (No in step S506), the control unit 41 repeats the processing of steps S504 and S505, and repeats the second skew correction until the color shift residual after the second skew correction falls below the second color shift residual target value (T2). If the color misregistration residual is less than the second color misregistration residual target value (T2) (Yes in step S506), the process according to this flowchart ends.

[0113] 16, before performing the first skew correction, the amount of color shift is compared with one color shift residual target value (T1), and if the amount of color shift is less than one color shift residual target value (T1), the first skew correction process is omitted. This enables the image forming apparatus 40 to perform color shift correction in a short time. In the above-described process, the same processes as steps S101 to S106 shown in FIG. 12 are performed, but the processes of steps S201 to S210 shown in FIG. 13 or steps S302 to S304 shown in FIG. 14 may also be performed.

[0114] [Color misregistration correction (skew correction) processing method 6] Next, a sixth processing method for color misregistration correction (skew correction) by the image forming apparatus described above will be described. In the first and second processing methods described above, when image processing is performed using the second skew correction, the amount of white space between images varies depending on the amount of color misregistration. For this reason, in the sixth processing method described below, the second skew correction is performed so that the amount of white space between images remains constant and is set to a preset amount.

[0115] FIG. 17 is a flowchart showing a sixth processing method for skew correction performed by the image forming apparatus. First, in the image forming device 40, test image formation is started for color shift correction, and the color shift amount calculation unit 411 calculates the amount of color shift based on the position of the toner image transferred to the intermediate transfer belt 465 detected by the color shift detection sensor 45 (step S601). Next, the first skew correction control unit 412 performs the first skew correction based on the color shift amount calculated by the color shift amount calculation unit 411 (step S602). After the first skew correction, the color shift amount calculation unit 411 calculates the color shift amount (color shift residual) after the first skew correction, and determines whether the color shift residual is less than the first color shift residual target value (T1) (step S603).

[0116] If the color shift residual is not less than the first color shift residual target value (T1) (No in step S603), the control unit 41 repeats the processing of steps S601 and S602, and repeats the first skew correction until the color shift residual after the first skew correction falls below the first color shift residual target value (T1). If the color misregistration residual is less than the first color misregistration residual target value (T1) (Yes in step S603), the color misregistration amount calculation unit 411 calculates the color misregistration amount after the first skew correction (step S604).

[0117] Next, the second skew correction control unit 413 determines whether the amount of margin generated by the second skew correction is less than the set margin amount set in the margin setting unit 415 based on the amount of color shift after the first skew correction calculated by the color shift amount calculation unit 411 (step S605). If the amount of margin generated in the second skew correction is less than the amount of margin set by the margin setting unit 415 (Yes in step S605), the second skew correction control unit 413 performs the second skew correction based on the amount of color shift after the first skew correction calculated by the color shift amount calculation unit 411 (step S606). After the second skew correction, the color shift amount calculation unit 411 calculates the color shift amount (color shift residual) after the second skew correction, and determines whether the color shift residual is less than a second color shift residual target value (T2) (step S607). If the color shift residual is not less than the second color shift residual target value (T2) (No in step S607), the control unit 41 repeats the processing from step S604 to step S606, and repeats the second skew correction until the color shift residual after the second skew correction falls below the second color shift residual target value (T2).

[0118] If the color shift residual is less than the second color shift residual target value (T2) (Yes in step S607), the second skew correction control unit 413 inserts margins between the images generated by the image processing of the second skew correction so that the margin amount is the amount set in the margin setting unit 415 (step S608).

[0119] If the amount of margin generated in the second skew correction is not less than the amount of margin set by the margin setting unit 415 (No in step S605), the second skew correction control unit 413 sets the amount of margin set by the margin setting unit 415 as the upper limit of the correction rate of the image correction in the second skew correction, and performs the second skew correction in accordance with this upper limit of the correction rate (step S609).

[0120] After the processing of step S608 or step S609, the processing according to this flowchart ends. The processes of steps S601 to S603, S604, S606, and S607 described above are the same as steps S101 to S106 shown in Fig. 12. Furthermore, the processes of steps S402 to S407 described above may be the processes of steps S201 to S210 shown in Fig. 13 or steps S302 to S304 shown in Fig. 14.

[0121] In the process of the flowchart shown in Fig. 17, when the second skew correction is performed, image processing and margin insertion are performed to achieve the set margin amount. This makes it possible to suppress fluctuations in the amount of margin between images even if the amount of color misregistration varies due to individual differences in image forming apparatus 40 or the temperature inside the apparatus. This reduces the effort required to change the settings of the processing position and cutting position depending on the amount of margin between images during post-processing after image formation, improving user convenience.

[0122] [Color misregistration correction (skew correction) processing method 7] In the first skew correction, a laser writing unit 468 is tilted by a tilt adjustment unit 467 made up of a motor, gears, etc., to correct color misalignment caused by a mechanical mechanism. Color misregistration is a relative relationship between colors, and is achieved by using one color as a reference and correcting the remaining colors. However, in image forming section 46 of image forming device 40, laser writing units 468 are arranged for each color, and there are motors and gears for each color, so when color misregistration correction is performed, it is possible that the motors or gears may be out of order. Therefore, in the seventh processing method described below, the first skew correction using a mechanical mechanism is not performed on the faulty color, but the first skew correction is performed to correct the color misalignment by correcting the non-faulty colors to match the faulty color, thereby achieving more accurate color misalignment correction.For example, generally, black (K) is used as the reference color for color misalignment when performing color misalignment correction, but if color misalignment residuals occur even after a certain number of corrections using black (K) as the reference, it is determined that the color other than black that generates the residuals, such as cyan (C), magenta (M), or yellow (Y), is faulty, and the reference color is changed to the color (C, M, or Y) that generates the residuals, and the first skew correction is performed.

[0123] FIG. 18 is a flowchart showing a seventh processing method for skew correction performed by the image forming apparatus. First, the first skew correction control unit 412 sets a reference color that serves as a reference for color misalignment when performing the first skew correction (step S701). Here, as an example, the first skew correction control unit 412 sets the reference color to black. Next, the first skew correction control unit 412 resets the count of the number of times the first skew correction has been performed for the reference color black to 0 (step S702).

[0124] Next, in the image forming device 40, test image formation is started for color shift correction, and the color shift amount calculation unit 411 calculates the color shift amount of toner images other than black, such as cyan, magenta, and yellow, based on the position of the black toner image transferred to the intermediate transfer belt 465 detected by the color shift detection sensor 45 (step S703).

[0125] Next, the first skew correction control unit 412 performs first skew correction on the cyan, magenta, and yellow laser writing units 468 based on the color shift amount calculated by the color shift amount calculation unit 411 (step S704). Then, the first skew correction control unit 412 adds 1 to the count of the current number of corrections of the first skew correction for the reference color black (step S705).

[0126] Next, the color shift amount calculation unit 411 calculates the color shift amount (color shift residual) of the cyan, magenta, and yellow toner images after the first skew correction, and determines for each color whether the color shift residual is less than the first color shift residual target value (T1) (step S706).

[0127] If the color misregistration residual for any color is not less than the first color misregistration residual target value (T1) (No in step S706), the first skew correction control unit 412 determines whether the current number of corrections for the reference color black matches a predetermined number of corrections C1 (step S707). Here, the predetermined number of corrections C1 is the number of times for determining that a malfunction has occurred in a mechanical mechanism other than the reference color, and is a value preset by the user, etc.

[0128] If the current number of corrections does not match the predetermined number of corrections C1 (No in step S707), the control unit 41 repeats the processing from step S703 to step S706, and repeats the first skew correction until the color shift residual after the first skew correction for each color falls below the first color shift residual target value (T1).

[0129] If the current number of corrections matches the preset number of corrections C1 (Yes in step S707), the reference color for the first skew correction is changed from the reference color (black) set in step S701 to a color (cyan, magenta, or yellow) for which the color shift residual after the first skew correction does not fall below the first color shift residual target value (T1) (step S708). After changing the reference color, the control unit 41 repeats the processes of steps S702 to S706, and repeats the first skew correction until the color shift residual after the first skew correction for each color falls below the first color shift residual target value (T1).

[0130] If the color shift residual of each color is less than the first color shift residual target value (T1) (Yes in step S706), the color shift amount calculation unit 411 calculates the color shift amount of each color after the first skew correction (step S709). Next, the second skew correction control unit 413 performs the second skew correction based on the amount of color shift for each color after the first skew correction calculated by the color shift amount calculation unit 411 (step S710). After the second skew correction, the color shift amount calculation unit 411 calculates the color shift amount (color shift residual) of each color after the second skew correction, and determines whether the color shift residual of each color is less than the second color shift residual target value (T2) (step S711). If the color shift residual of any color is not less than the second color shift residual target value (T2) (No in step S711), the control unit 41 repeats the processing of steps S709 and S710, and repeats the second skew correction until the color shift residual of each color after the second skew correction falls below the second color shift residual target value (T2). If the color shift residual of each color is less than the second color shift residual target value (T2) (Yes in step S711), the process according to this flowchart ends.

[0131] In the process of the flowchart shown in Figure 18, the color that is difficult to correct due to a malfunction in the first skew correction is set as the reference color for correction, and color shift correction is performed on other colors without performing color shift correction on this color.This saves time spent performing color shift correction on the color that has malfunctioned, and allows color shift correction to be performed efficiently.In addition, by performing the first skew correction based on the color that has malfunctioned in the mechanical mechanism, highly accurate color shift correction is possible.

[0132] 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]

[0133] 1 image forming system, 10 paper feed unit, 11,61 support shaft, 20 supply adjustment unit, 40 image forming device, 41 control unit, 42 operation display unit, 43 scanner unit, 44 conveyance unit, 45 detection sensor, 46 image forming unit, 47 fixing unit, 48 non-volatile memory, 50 collection adjustment unit, 60 collection device, 101,102 toner image, 103,104,108,109 image data, 103a,103b,104a,104b,104c,104d edge portion, 104e,104f,105a,105b,106a,106b,107,108e,108f,109e,109f,110,110,110b Margins, 104g, 108g, 109g Image section, 105, 106 Images, 411 Color misregistration amount calculation section, 412 First skew correction control section, 413 Second skew correction control section, 414 Execution setting section, 415 Margin setting section, 460 Laser light, 461 Exposure section, 462 Photosensitive body, 463 Development section, 464 Primary transfer roller, 465 Intermediate transfer belt, 466 Secondary transfer roller, 467 Inclination adjustment section, 468 Laser writing unit, 469 Laser trajectory, 471 Fixing roller, 472 Pressure roller

Claims

1. An image forming apparatus that forms a multi-color image on a recording material, an image forming section for forming an image on the recording material; a control unit that controls the image formation in the image forming unit and skew correction in the image formation, The control unit a color misregistration amount calculation unit that calculates a color misregistration amount from the color misregistration of each color image in the image forming unit; a first skew correction control unit and a second skew correction control unit that control skew correction of the color misregistration; the first skew correction control unit sets a first reference color that serves as a reference for color misregistration when performing the skew correction, and controls the first skew correction by mechanical operation of the image forming unit based on a preset first color misregistration residual target value; the second skew correction control unit controls second skew correction by image processing for the color misregistration after control by the first skew correction control unit based on a second color misregistration residual target value that is set in advance; After the first skew correction control unit performs the first skew correction for the first reference color a predetermined number of times, the color shift amount calculation unit calculates the color shift amount, and if the color shift amount after the first skew correction exceeds the first color shift residual target value, the first skew correction control unit sets a second reference color and performs the first skew correction. Image forming device.

2. The control unit repeats the calculation of the color misregistration amount by the color misregistration amount calculation unit and the control of the first skew correction by the first skew correction control unit until the color misregistration amount falls below the first color misregistration residual target value. The image forming apparatus according to claim 1 .

3. The control unit repeats the calculation of the color misregistration amount by the color misregistration amount calculation unit and the control of the second skew correction by the second skew correction control unit until the color misregistration amount falls below the second color misregistration residual target value.

3. The image forming apparatus according to claim 1.

4. The first skew correction control unit repeats the first skew correction a preset first number of times. The image forming apparatus according to claim 1 .

5. The second skew correction control unit repeats the second skew correction a preset second number of times.

5. The image forming apparatus according to claim 1.

6. the control unit has an execution setting unit that accepts a setting of whether execution of the second skew correction by the second skew correction control unit is enabled or disabled, performing the second skew correction by the second skew correction control unit when the setting by the execution setting unit is valid; When the setting of the execution setting unit is invalid, the second skew correction control unit does not execute the second skew correction.

6. The image forming apparatus according to claim 1.

7. The first skew correction control unit executes the first skew correction when the color misregistration amount is equal to or greater than the first color misregistration residual target value.

7. The image forming apparatus according to claim 1.

8. When the skew correction is performed again after the second skew correction, the color misregistration amount calculation unit calculates the color misregistration amount after the second skew correction by calculating the color misregistration amount after the second skew correction and initializing a correction value by controlling the second skew correction; the first skew correction control unit controls the first skew correction based on the color misregistration amount after the skew correction; The second skew correction control unit controls the second skew correction based on the amount of color misregistration after the first skew correction.

8. The image forming apparatus according to claim 1.

9. the control unit has a margin setting unit that sets the amount of margin between the images that are successively formed on the recording material to a constant value, The second skew correction control unit sets the amount of blank space of the image generated by the second skew correction to the constant value set in the blank space setting unit.

9. The image forming apparatus according to claim 1.

10. the margin setting unit accepts a user's setting of an arbitrary value for the fixed value of the margin amount, The second skew correction control unit sets the amount of margin between the images generated by the second skew correction to a value received by the margin setting unit. The image forming apparatus according to claim 9 .

11. the margin setting unit has a preset value as the margin amount, The second skew correction control unit sets the amount of margin between the images generated by the second skew correction to a value set by the margin setting unit. The image forming apparatus according to claim 9 .

12. the image forming unit has a laser writing unit for each color and an inclination adjustment unit that adjusts the inclination of the laser writing unit, The first skew correction control unit adjusts the tilt of the laser writing unit by controlling the amount of operation of the tilt adjustment unit, and performs the first skew correction.

12. The image forming apparatus according to claim 1.

Images