JP6142981B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus.

  Japanese Patent Application Laid-Open No. 2004-228561 controls the timing of laser scanning by two exposure units for color shift caused by positional deviation of toner images when a plurality of toner images respectively corresponding to a plurality of colors are superimposed on an intermediate transfer member. An image forming apparatus for color electrophotography which is suppressed by this is shown.

JP 2000-168135 A

  An object of the present invention is to provide an image forming apparatus that suppresses the occurrence of color misregistration in which a color on an image deviates from a target color.

Claim 1
A plurality of photoreceptors on which electrostatic latent images are formed by repeatedly scanning with exposure light in the main scanning direction;
An image holding member that moves in the sub-scanning direction intersecting the main scanning direction along the plurality of photosensitive members to hold a toner image on the surface;
The surface of each of the plurality of photoconductors is repeatedly scanned with exposure light in the main scanning direction to form an electrostatic latent image on the surface of each of the plurality of photoconductors, and the electrostatic latent image has a different color for each photoconductor. Developing with toner to form a plurality of single color toner images of different colors on the surface of the plurality of photoconductors, and sequentially superimposing the plurality of single color toner images on the surface of the image carrier moving in the sub-scanning direction. , an image forming unit for holding a plurality toner image by single-color toner of a plurality of colors on the image holding member,
A transfer unit for transferring a multi-color toner image held on the image carrier onto a sheet;
A fixing unit that fixes the multi-color toner images transferred onto the paper by the transfer unit on the paper;
The image forming unit has a predetermined threshold value on the image carrier, in which a total value of the amounts of single color toners over the plurality of single color toner images among the corresponding pixels straddling the plurality of single color toner images is predetermined. The monochromatic toners of different colors are arranged in different regions when the pixel is divided into a plurality of regions only in the main scanning direction of the main scanning direction and the sub-scanning direction, For pixels whose total amount does not exceed the threshold value, a single color toner image in which the arrangement area of the single color toner in each pixel is adjusted so that the plurality of single color toner images sequentially overlap each other is formed. The image forming apparatus.

Claim 2 is the method of claim 1,
The image forming unit includes pixels in the pixels corresponding to each other across the plurality of single color toner images, the total amount of the single color toners over the plurality of single color toner images exceeding a predetermined threshold. The present invention is characterized in that a monochromatic toner image is formed in which the arrangement area of the monochromatic toner in the pixel is adjusted so as to avoid the overlapping of the monochromatic toners.

  According to the image forming apparatus of the first aspect, it is difficult to cause color misregistration in which toner of a specific color is lost during transfer onto a sheet and the color of the image on the sheet is shifted from the target color.

According to the image forming apparatus according to claim 1, the data processing time is shortened.

1 is an overall configuration diagram of an image forming apparatus according to an exemplary embodiment. It is a flowchart of the image data generation for electrostatic latent image formation. FIG. 3 is a schematic diagram illustrating a toner arrangement area for pixels formed based on a pulse signal for each color of YMCK generated in step S3 of FIG. 2 in each color toner image on each photoconductor. FIG. 6 is a diagram illustrating toner arrangement in one pixel in a multicolor toner image on an intermediate transfer belt together with toner arrangement according to a conventional method. FIG. 6 is a diagram illustrating a state of toner arrangement in each pixel on the intermediate transfer belt for six pixels arranged in the width direction on the intermediate transfer belt.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 is an overall configuration diagram of an image forming apparatus 100 according to the present embodiment.

  The image forming apparatus 100 shown in FIG. 1 is a color printer that forms toner images using yellow (Y), magenta (M), cyan (C), and black (K) toners. is there. This image forming apparatus 100 is a so-called tandem type printer in which four image forming engines 20Y, 20M, 20C, and 20K that respectively form toner images of toners of YMCK colors are arranged along the paper transport direction. .

  The image forming engines 20Y, 20M, 20C, and 20K include electrophotographic laminated photoconductors 21Y, 21M, and 21B that rotate in the directions of the arrows By, Bm, Bc, and Bk in FIG. 21C and 21K are provided. In addition, the image forming engines 20Y, 20M, 20C, and 20K include charging units 22Y, 22M, 22C, and 22K, exposure units 23Y, 23M, 23C, and 23K, and developing units around the photoreceptors 21Y, 21M, 21C, and 21K. 24Y, 24M, 24C, 24K, primary transfer rolls 25Y, 25M, 25C, 25K, and photoconductor cleaning devices 26Y, 26M, 26C, 26K are provided, respectively. The photoreceptor in each image forming engine is charged by a charger in each image forming engine so that the surface potential reaches a predetermined potential. Then, the exposure unit in each image forming engine performs a raster scan on the charged photoconductor in the direction along the rotation axis of each photoconductor to be expressed as a potential distribution. An electrostatic latent image is formed on each photoconductor. The electrostatic latent image is developed by electrostatically attaching the toner in the developer containing the charged toner to the electrostatic latent image by a developing unit in each image forming engine. At this time, the amount of toner adhering to each portion of the electrostatic latent image changes according to the intensity of the laser beam, and the more the toner is adhered, the stronger the intensity of the laser beam.

  Further, an intermediate transfer belt 30 that is in contact with the photosensitive member in each image forming engine is provided below each image forming engine in FIG. The intermediate transfer belt 30 circulates and moves in the direction of arrow A in FIG. 1 while receiving a driving force from the driving roll 31 while being stretched by the stretching roll 32 and a plurality of other rolls. Primary transfer rolls 25Y, 25M, 25C, and 25K are provided at positions facing the photoconductors 21Y, 21M, 21C, and 21K with the intermediate transfer belt 30 interposed therebetween. This intermediate transfer belt 30 receives the transfer (primary transfer) of the developed image formed on each photoconductor and conveys the primary transfer image. Note that toner remaining on the photoreceptors 21Y, 21M, 21C, and 21K without being transferred to the intermediate transfer belt 30 is removed by the photoreceptor cleaning devices 26Y, 26M, 26C, and 26K, respectively. Here, the intermediate transfer belt 30 corresponds to an example of the image carrier referred to in the present invention.

  Further, a backup roll 33 and a secondary transfer roll 40 are provided downstream of the four primary transfer rolls 25Y, 25M, 25C, and 25K in the moving direction of the intermediate transfer belt 30, and the intermediate transfer belt is provided. 30 is pressed against the secondary transfer roll 40 by the backup roll 33. Further, the image forming apparatus 100 is provided with a tray 60 for storing paper. The primary transfer image conveyed to the position of the secondary transfer roll 40 by the intermediate transfer belt 30 is the secondary transfer roll 40. As a result, the image is secondarily transferred onto the sheet taken out from the tray 60. Further, the image forming apparatus 100 is provided with a fixing device 50 and an intermediate transfer belt cleaning device 70. The fixing device 50 performs a process of fixing the unfixed secondary transfer image secondarily transferred onto the paper onto the paper, and the intermediate transfer belt cleaning device 70 does not perform the secondary transfer onto the paper. The toner remaining on the intermediate transfer belt 30 is removed. The image forming apparatus 100 is also provided with a control unit 600 that controls each unit in the image forming apparatus 100. Here, the combination of the control unit 600 and the above-described image forming engines 20Y, 20M, 20C, and 20K corresponds to an example of the image forming unit referred to in the present invention. The secondary transfer roll 40 corresponds to an example of a transfer portion referred to in the present invention, and the fixing device 50 corresponds to an example of a fixing portion referred to in the present invention.

  Next, a series of image forming operations in the image forming apparatus 100 will be described.

  First, the controller 600 controls the chargers 22Y, 22M, 22C, and 22K to charge the photoreceptors 21Y, 21M, 21C, and 21K, respectively. Next, the controller 600 controls the exposure units 23Y, 23M, 23C, and 23K to form electrostatic latent images on the charged photoconductors 21Y, 21M, 21C, and 21K, respectively. At this time, the electrostatic latent images formed on the YMCK toners 21Y, 21M, 21C, and 21K for the respective colors are displayed as image data representing an image to be formed on the sheet, as shown in FIG. This is based on image data for forming an electrostatic latent image generated by a method described later based on image data input to 100.

  The electrostatic latent images formed on the photoreceptors 21Y, 21M, 21C, and 21K are toners in the developer including toners of colors corresponding to the respective image forming engines by the developing devices 24Y, 24M, 24C, and 24K. Each toner image is developed to form a YMCK toner image of each color. The toner images formed for the respective image forming engines in this way are the primary transfer rolls 25Y, 25M, and 25C, so that the pixels corresponding to each other in these toner images overlap each other on the intermediate transfer belt 30. The images are sequentially transferred (primary transfer) onto the intermediate transfer belt 30 at 25C and 25K.

  On the other hand, the paper in the tray 60 is taken out in response to the formation of the primary transfer image with the YMCK color toners. The taken-out sheet is positioned at the position of the secondary transfer roll 40 in time for the multi-color toner image made up of the toner images of the primary transfer to reach the position of the secondary transfer roll 40 by the intermediate transfer belt 30. The multi-color toner image is transferred (secondary transfer) onto the sheet by the secondary transfer roll 40. Then, a fixing process is performed on the secondary transfer image on the sheet by the fixing device 50 and the sheet is discharged onto a paper discharge tray (not shown). In FIG. 1, a sheet conveyance path from the tray 60 until it is discharged onto a paper discharge tray (not shown) is indicated by a path indicated by a right-pointing dotted arrow in FIG. 1. The toner remaining on the intermediate transfer belt 30 after the secondary transfer onto the paper is removed by the intermediate transfer belt cleaning device 70.

  The above is a description of a series of image forming operations in the image forming apparatus 100.

  Generally, a type in which a plurality of toner images of a plurality of colors are transferred onto an intermediate transfer belt so that the toners of the respective colors overlap to form a multicolor toner image, and the multicolor toner image is secondarily transferred to a sheet. In the image forming apparatus, the toner of the layer farthest from the intermediate transfer belt among the multiple layers of toner constituting the multicolor toner image is more easily transferred from the intermediate transfer belt to the paper, and the layer closer to the intermediate transfer belt. The toner tends to be less easily transferred from the intermediate transfer belt to the paper.

  For this reason, in such a type of image forming apparatus, when a secondary transfer failure occurs, the color toner constituting the layer on the side close to the intermediate transfer belt is lost in the secondary transfer image on the paper, and finally, There arises a so-called color misregistration problem that the color of the fixed image fixed on the paper is different from the originally intended color.

  In addition, when performing secondary transfer on a sheet, a part of the color toner constituting the layer far from the intermediate transfer belt may be buried between the fibers of the sheet. This phenomenon is particularly remarkable when a rough sheet is used. In this way, when a part of the color toner constituting the layer far from the intermediate transfer belt is buried between the fibers of the paper, the layer far from the intermediate transfer belt is formed in the secondary transfer image on the paper. This is substantially the same as a case where a part of the color toner is lost. Also at this time, there arises a problem of color misregistration in which the color of the fixed image is different from the originally intended color.

  In the image forming apparatus 100 of FIG. 1, in order to suppress the occurrence of such color misregistration, in the YMCK multicolor toner image of YMCK on the intermediate transfer belt 30, each color of YMCK in each pixel constituting the multicolor toner image is changed. The toner is devised so that the toner images are arranged separately in regions determined for each color of YMCK in each pixel without overlapping each other in each pixel. Below, this device is demonstrated.

  As described above, when forming an image, image data representing an image to be formed on a sheet is input to the image forming apparatus 100 in FIG. Here, the image represented by this image data is composed of pixels arranged in the horizontal direction and the vertical direction of the image, and this image data has a format in which the halftone value of the toner of each color of YMCK is expressed for each pixel. This is image data representing an image. Based on this image data, the control unit 600 generates image data for forming an electrostatic latent image for each color of YMCK in the following procedure.

  FIG. 2 is a flowchart for generating image data for forming an electrostatic latent image.

  The control unit 600 in FIG. 1 analyzes the image data and determines whether or not the sum of the halftone values of the YMCK toners that determine the color of each pixel exceeds 100% for each pixel in the image ( Step S1).

  For pixels whose sum of halftone values does not exceed 100% (Step S1; No), each YMCK color has a pulse width corresponding to the halftone value of each YMCK color independently, and its peak value is determined in advance. A pulse signal is generated for each color of YMCK having the reference peak value (step S2). The generated pulse signals for each color of YMCK are sent to the exposure units 23Y, 23M, 23C, and 23K in accordance with the exposure timing of the exposure units 23Y, 23M, 23C, and 23K (step S4). Here, the peak value corresponds to the intensity of the laser beam in the exposure device, and the pulse width corresponds to the width of the irradiation region of the laser beam along the rotation axis direction of each photoconductor. Therefore, in each pulse signal, the adhesion amount of toner of each color in the pixel is determined by the pulse width and the peak value. The pulse signal generated by the method of step S2 is the same as that generated by the conventional method (for example, Patent Document 1).

  On the other hand, for pixels where the sum of the halftone values exceeds 100% (step S1; Yes), as described below, the peak value corresponding to the halftone value of each color of YMCK and a pulse width of 1/4 pixel width or less. Are generated for each color of YMCK (step S3), and a pulse signal having a rising edge shifted by 1/4 pixel width between the YMCK4 color pulse signals. Here, when the halftone value is 25% or less, the pulse width is a pulse width corresponding to the halftone value as in step S2, and the peak value is also the reference peak value as in step S2. On the other hand, when the halftone value exceeds 25%, the pulse width is ¼ pixel width. Further, the peak value in this case is realized when the pulse width corresponding to the halftone value and the reference peak value are adopted as in step S2 under the condition that the pulse width is 1/4 pixel width. It is determined to be a peak value necessary to realize the same toner adhesion amount as the toner adhesion amount. The pulse signals for each color of YMCK generated in this way are sent to the exposure units 23Y, 23M, 23C, and 23K in accordance with the exposure timing.

  Note that, as described in steps S2 and S3 above, the form of the pulse signal generated between a pixel whose sum of halftone values exceeds 100% and a pixel whose sum of halftone values does not exceed 100% The reason for changing will be described later.

  Even while the exposure timing is adjusted in step S4, the process proceeds to step S5 without waiting in step S4.

  When the generation of the pulse signal as described in the above steps S2 and S3 has not been completed for all the pixels in the image (step S5; No), the next generation of the pulse signal that has not yet been performed. A pulse signal is generated for the pixel. When the generation of such a pulse signal is completed for all the pixels in the image (step S5; Yes), the generation processing of image data for forming an electrostatic latent image composed of the pulse signal for each pixel is completed.

  Each of the exposure units 23Y, 23M, 23C, and 23K in FIG. 1 performs writing by laser light on each photoconductor with the intensity corresponding to the peak value of each pulse signal based on the pulse signal of each pixel for each color of YMCK. . Thereby, an electrostatic latent image is formed on each photoconductor. Each formed electrostatic latent image is developed with each color toner as described with reference to FIG. 1, and each color toner image is formed on each photoconductor.

  FIG. 3 is a schematic diagram showing toner arrangement areas for pixels formed on the basis of the pulse signals for each color of YMCK generated in step S3 of FIG. 2 in each color toner image on each photoconductor.

  In the four pixels corresponding to each other on the photoconductors 21Y, 21M, 21C, 21, the four colors YMCK toner are not overlapped with each other and are shifted by 1/4 pixel in the rotation axis direction of each photoconductor. , 210M, 210C, and 210K. Here, the width of each toner arrangement area along the rotation axis direction of each photoconductor is ¼ pixel, and the width of each toner arrangement area along the rotation direction of each photoconductor is one pixel. . In these pixels, the place where each color toner is arranged is limited in each toner arrangement area, and is not arranged in an area other than the toner arrangement area in the pixel. However, even if the area where the toner is arranged is limited to ¼ in this way, the amount of toner attached to each color changes in the entire pixel by adjusting the peak value of the pulse signal in step S3 in FIG. It is supposed not to.

  The toner images of the respective colors formed on the respective photoreceptors are sequentially transferred (primary transfer) onto the intermediate transfer belt 30 such that the mutually corresponding pixels straddling each other overlap each other on the intermediate transfer belt 30, and are multicolored. The toner image is formed.

  FIG. 4 is a diagram illustrating the arrangement of toner in one pixel in a multicolor toner image on the intermediate transfer belt, together with the arrangement of toner according to the conventional method.

  FIG. 4 shows the state of toner arrangement at this pixel on the intermediate transfer belt, taking as an example a pixel in which the dot area ratio of each color of YMCK is 100%. Here, for comparison, part (a) in FIG. 4 shows the toner arrangement based on the pulse signal of the conventional method (see step S2 in FIG. 2), and part (b) in FIG. ) Shows how toner is arranged based on the pulse signal generated in step S3 of FIG. Here, in both the part (a) in FIG. 4 and the part (b) in FIG. 4, the horizontal direction in the figure corresponds to the width direction of the intermediate transfer belt 30.

  As shown in part (a) of FIG. 4, the conventional toner arrangement has a configuration in which Y color toner, M color toner, C color toner, and K color toner are stacked in this order on the intermediate transfer belt 30. Have. As described above, in this stacked configuration, if a secondary transfer failure occurs during the secondary transfer to the paper, the Y color toner closest to the intermediate transfer belt 30 is easily lost, and the K color toner farthest from the intermediate transfer belt 30 is lost. Tends to be buried between paper fibers. For this reason, there is a high possibility that a color misregistration problem that the color of the fixed image on the paper differs from the originally intended color will occur.

  On the other hand, as shown in part (b) of FIG. 4, in the toner arrangement based on the pulse signal generated in step S <b> 3 of FIG. 2, the Y toner, M toner, and C toner are placed on the intermediate transfer belt 30. , K color toners are arranged in a direction along the surface of the intermediate transfer belt 30, and even if a secondary transfer failure occurs during the secondary transfer to the paper, only a specific color toner is lost, The situation of being buried between fibers is avoided. In this way, when an image is formed using the pulse signal generated in step S3 in FIG. 2, the occurrence of color misregistration that the color of the fixed image on the paper is different from the originally intended color is suppressed. Will be.

  Here, such a color misregistration problem occurs when the toners of the respective colors overlap with each other. Therefore, when the total of the dot area ratios of the respective colors is small, a multicolor toner image can be formed by the above-described conventional method. In the multicolor toner image, the degree of overlapping of the toners of the respective colors is small, and the problem of color misregistration is not so serious.

  Here, as described above, in the image forming apparatus 100 in FIG. 1, as described in FIG. 2, the pulse having the form described in step S <b> 3 only when the sum of the halftone values exceeds 100%. Signal generation is performed. Since the generation of the pulse signal in the form described in step S3 takes a little time compared to the generation of the pulse signal in the form described in step S2, branching of processing according to the sum of the halftone values is performed. Thus, in the image forming apparatus 100, the time required to generate image data for forming an electrostatic latent image is shortened. Furthermore, since the number of times of irradiating each photoconductor with a strong laser beam by the pulse wave having a high peak value described in step S3 is reduced by such a branch of processing, it is possible to suppress deterioration of each photoconductor. .

  FIG. 5 is a diagram illustrating a state of toner arrangement at each pixel on the intermediate transfer belt for six pixels arranged in the width direction on the intermediate transfer belt.

  Part (a) of FIG. 5 shows the state of toner arrangement for each pixel based on the pulse signal of the conventional method (see step S2 of FIG. 2) for comparison. Part (a) of FIG. In FIG. 2b, the state of toner arrangement for each pixel based on the pulse signal generated in step S3 of FIG. 2 is shown. Here, in both part (a) in FIG. 5 and part (b) in FIG. 5, the horizontal direction in the figure corresponds to the width direction of the intermediate transfer belt 30. Each pixel is a pixel whose dot area ratio for YMCK4 colors is 0% or 100%. In the drawing, each of the area 91, the area 92, the area 93, the area 94, the area 95, and the area 96 For the pixels in each region, the arrangement of the color toner having a dot area ratio of 100% is shown.

  As shown in part (a) of FIG. 5, in the conventional toner arrangement, for example, the pixels in the region 91 have a configuration in which Y color toner and C color toner are stacked in this order on the intermediate transfer belt 30. doing. Similarly, the pixels in the area 93 have a configuration in which Y color toner and M color toner are stacked in this order on the intermediate transfer belt 30, and the pixels in the area 95 have M color toner and C color toner. It has the structure laminated | stacked in this order. The pixels in the region 94 have a configuration in which Y color toner, M color toner, and C color toner are stacked in this order on the intermediate transfer belt 30. On the other hand, the pixels in the region 92 and the pixels in the region 96 have a single-layer configuration made of Y toner or C toner.

  On the other hand, as shown in part (b) of FIG. 5, in the toner arrangement according to the method of step S2 of FIG. 2 and the method of FIG. 3, for example, the pixels in the region 91 are Y-color toner and C-color toner. As shown in (b), the Y-color toner area and the C-color toner area are separately arranged. Here, with regard to the M color toner and the K color toner, since the halftone value of these colors is zero in the pixels in the area 91, the M color toner is included in the M color toner area and the K color toner area. And there is no K color toner. Similarly, the pixel in the region 93 has a configuration in which the Y color toner and the M color toner are divided into the Y color toner region and the M color toner region, and the pixels in the region 95 are The M color toner and the C color toner have a configuration in which the toner is divided into a toner area for the M color toner and a toner area for the C color toner. Further, the pixels in the region 94 include a Y-color toner, an M-color toner, and a C-color toner on the intermediate transfer belt 30, respectively, a Y-color toner toner region, an M-color toner toner region, and a C-color toner. It has a configuration in which it is divided into toner areas for toner. On the other hand, the pixels in the region 92 and the pixels in the region 96 have a single-layer configuration made of Y color toner or C color toner, as in part (a) of FIG.

  As shown in part (b) of FIG. 5, since the toner arrangement area to be arranged for each color toner is determined in advance, the toner arrangement area in which each color toner does not exist is in a blank state. However, when the multi-color toner image having pixels having such a configuration is transferred (secondary transfer) from the intermediate transfer belt 30 to a sheet, and the fixing process is performed by the fixing device 50 of FIG. Each toner in each pixel is mixed by the heat and pressure in the image, and even if there is a blank toner arrangement area where each color toner does not exist before the secondary transfer, in terms of the image quality of the fixed image on the paper, There is no impact.

  The above is the description of the present embodiment.

  In the above description, the placement positions of the toners of the respective colors are limited within the predetermined toner placement areas of the respective colors in the pixel. However, in the present invention, the positions where the overlapping of the toners of the respective colors are avoided. It is sufficient that the toners of the respective colors are arranged on the screen, and the toner is not necessarily limited to a predetermined toner arrangement area of the respective colors. For example, the following pulse signal may be generated in step S3 of FIG. When the sum of the pulse widths corresponding to the halftone values of each color of YMCK is less than or equal to the pixel width, the pulse signals do not overlap each other in the pixel area, and the pulse signals are spaced from each other. Thus, each pulse signal whose peak value is the reference peak value is generated. On the other hand, when the total of each pulse width corresponding to the halftone value of each color of YMCK exceeds the pixel width, the total of each pulse width is reduced so as to coincide with the pixel width while maintaining the ratio of the halftone value. Each pulse signal having each pulse width and having a space between the pulse signals so as not to overlap each other, and each peak value is assumed to be a reference wave under each pulse width before reduction. Each pulse signal having each peak value necessary for realizing the same toner adhesion amount as that achieved when the high value is adopted is generated.

  In the above description, a tandem color single-sided output printer has been described as an example. However, the image forming apparatus of the present invention may be applied to a tandem color double-sided output printer. The image forming apparatus of the present invention may be applied to a rotary color printer, for example, as a color printer other than a tandem type color printer. In addition to a printer, the present invention may be applied to a copier or a fax machine.

100 Image forming apparatus 20Y, 20M, 20C, 20K Image forming engine 21Y, 21M, 21C, 21K Photoconductor 210Y, 210M, 210C, 210K Toner region 22Y, 22M, 22C, 22K Charger 23Y, 23M, 23C, 23K Exposure unit 24Y, 24M, 24C, 24K Developers 25Y, 25M, 25C, 25K Primary transfer rolls 26Y, 26M, 26C, 26K Photoconductor cleaning device 30 Intermediate transfer belt 31 Drive roll 32 Stretch roll 33 Backup roll 40 Secondary transfer Roll 50 Fixing device 60 Tray 600 Control unit 70 Intermediate transfer belt cleaning device 91, 92, 93, 94, 95, 96

Claims (1)

A plurality of photoreceptors on which electrostatic latent images are formed by repeatedly scanning with exposure light in the main scanning direction;
An image holding member that moves in the sub-scanning direction intersecting the main scanning direction along the plurality of photosensitive members to hold a toner image on the surface;
The surface of each of the plurality of photoconductors is repeatedly scanned with exposure light in the main scanning direction to form an electrostatic latent image on the surface of each of the plurality of photoconductors, and the electrostatic latent image has a different color for each photoconductor. Developing with toner to form a plurality of single color toner images of different colors on the surface of the plurality of photoconductors, and sequentially superimposing the plurality of single color toner images on the surface of the image carrier moving in the sub-scanning direction. , an image forming unit for holding a plurality toner image by single-color toner of a plurality of colors on the image holding member,
A transfer unit for transferring a multi-color toner image held on the image carrier onto a sheet;
A fixing unit that fixes the multi-color toner images transferred onto the paper by the transfer unit on the paper;
The image forming unit has a predetermined threshold value on the image carrier, in which a total value of the amounts of single color toners over the plurality of single color toner images among the corresponding pixels straddling the plurality of single color toner images is predetermined. The monochromatic toners of different colors are arranged in different regions when the pixel is divided into a plurality of regions only in the main scanning direction of the main scanning direction and the sub-scanning direction, For pixels whose total amount does not exceed the threshold value, a single color toner image in which the arrangement area of the single color toner in each pixel is adjusted so that the plurality of single color toner images sequentially overlap each other is formed. Image forming apparatus.

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