JP2019120767A - Color image forming apparatus - Google Patents

Abstract

To improve color shift adjustment resolution with an inexpensive configuration, in a multibeam type color image forming apparatus comprising a plurality of light sources each having a plurality of light-emitting points.SOLUTION: A pixel corresponding area corresponding to one pixel of image data on a surface of each image carrier is scanned with M light beams emitted from light sources. A writing control unit performs color shift correction by selectively executing first writing processing of performing writing of the image data, while equalizing the quantities of light from M light-emitting points so that the center of gravity of the light quantity of the pixel corresponding area in which the writing of image data is performed is located at the center in a sub-scanning direction of the pixel corresponding area (step S5), and second writing processing of performing writing of the image data, while making different the quantities of light of the M light beams so that the center of gravity of the light quantity of the pixel corresponding area in which the writing of image data is performed is offset by a predetermined amount from the center position in the sub-scanning direction of the pixel corresponding area (step S6).SELECTED DRAWING: Figure 11

Description

  The present invention relates to a color image forming apparatus.

  Generally, an electrophotographic color image forming apparatus includes a plurality of photosensitive drums and an optical scanning device that exposes the surface of each photosensitive drum to form an electrostatic latent image. The electrostatic latent image formed on the surface of each photosensitive drum is developed with toners of different colors by a developing device. The toner images of the respective colors developed on the surfaces of the respective photosensitive drums are superimposed and transferred onto the material to be transferred.

  Further, in recent years, while demands for higher speed and higher resolution have been increasing, multi-beam type optical scanning devices are widely spread. In this optical scanning device, a light source for emitting a light beam to each photosensitive drum has a plurality of light emitting points.

Japanese Patent Laid-Open No. 7-242019

  In the above-described color image forming apparatus, in recent years, the amount of toner development has decreased with the improvement of toner coloring performance. For this reason, positional deviation between the toner images (hereinafter referred to as "color deviation") which occurs when superposing toner images (dots or lines of a plurality of colors) on the material to be transferred easily causes a difference in tint. . The color change caused by the color shift leads to periodical density change (jitter), resulting in deterioration of the image quality. In order to prevent the deterioration of the image quality, it is necessary to adjust the color misregistration amount to a predetermined amount or less.

What becomes important in this color misregistration adjustment is the adjustment resolution in the sub scanning direction (transport direction). Even if the color shift amount can be detected by a sensor or the like, there are cases where the color shift amount can not be adjusted to a predetermined amount or less due to the restriction of the adjustment resolution.
One of the limitations of adjustment resolution is the increase in the number of light beams scanned in one pixel. For example, when the resolution of image data is 600 dpi, and the optical resolution is also 600 dpi, the number of light beams for scanning the pixel corresponding area (area corresponding to one pixel of image data) on the surface of the image carrier is one. Therefore, when the adjustment resolution is 1 pixel and the optical resolution is 1200 dpi, the adjustment resolution is 1/2 pixel because the number of light beams scanning the inside of the pixel corresponding area is two, and when the optical resolution is 2400 dpi, the inside of the pixel corresponding area The adjustment resolution is 1⁄4 pixel because there are four light beams for scanning the image.

  However, if the color shift adjustment resolution is improved by increasing the number of light beams (the number of light emitting points of each light source), the number of light emitting points of each light source increases, which causes a problem of cost increase.

  The present invention has been made in view of the above-mentioned point, and an object of the present invention is to provide a multi-beam type color image forming apparatus having a plurality of light sources each having a plurality of light emitting points. The purpose is to improve the shift adjustment resolution.

The image forming apparatus according to the present invention is exposed to a plurality of light sources each having M (M is 2 or more) light emitting points and M light beams emitted from each light source, and an electrostatic latent image is formed on the surface A plurality of image carriers on which the toner image is formed, a plurality of developing devices for developing electrostatic latent images formed on the surfaces of the plurality of image carriers with toners of different colors to form toner images, and each image carrier A transfer unit for overlapping and transferring toner images of respective colors formed on the surface of the body onto a material to be transferred; and a write control unit for writing image data on the surface of the image carrier by controlling the operation of each light source. Have.
The pixel corresponding region corresponding to one pixel of the image data on the surface of each image carrier is scanned in a plurality of lines by the M light beams emitted from each light source, and the write control unit The light amounts of the M light emitting points are made the same so that the light amounts of the M light emitting points are the same so that the light amount barycenter position of each pixel corresponding region corresponding to each pixel of the image data is positioned at the center of the pixel corresponding region The light quantity of the M light beams is made different so that the first writing process to write data and the light quantity barycentric position of each pixel corresponding area is offset by a predetermined amount from the center position in the sub scanning direction of each pixel corresponding area. The color misregistration correction is performed by selectively switching and executing the second writing process of writing the image data.

  According to the present invention, in a multi-beam type color image forming apparatus provided with a plurality of light sources each having a plurality of light emitting points, it is possible to improve color misregistration adjustment resolution with an inexpensive configuration.

FIG. 1 is a schematic view showing the entire configuration of the image forming apparatus in the embodiment. FIG. 2 is a perspective view showing a state in which the cover member is removed from the light scanning device. FIG. 3 is a plan view of the light source as viewed from the proximal side. FIG. 4 is a block diagram showing a configuration of a control system of the image forming apparatus. FIG. 5 is a schematic view showing a patch image for color misregistration correction transferred onto the intermediate transfer belt. FIG. 6 is a schematic view virtually showing each pixel corresponding area corresponding to each pixel of the image data on the surface of the photosensitive drum. FIG. 7 is a schematic view showing an example of the exposure state in one pixel corresponding area, in which the optical gravity center position is located at the center of the pixel area in the sub scanning direction. FIG. 8 is a schematic view showing an example of the exposure state in one pixel corresponding area, in which the optical gravity center position is offset in the sub scanning direction with respect to the center position in the sub scanning direction of the pixel area. FIG. 9 is a light quantity distribution data showing the light quantity distribution characteristic in the sub scanning direction in the pixel corresponding area when the light quantity ratio of the first light emitting point exposing the pixel corresponding area and the second light emitting point is changed in graph form It is. FIG. 10 is light amount barycentric data showing the change characteristics of the light amount barycentric position when the light amount ratio between the first and second light beams is changed, in the form of a graph. FIG. 11 is a flowchart showing the contents of color misregistration correction control executed by the control unit. FIG. 12 is a view corresponding to FIG. 7 showing the second embodiment. FIG. 13 is a view corresponding to FIG. 8 showing the second embodiment. FIG. 14 is a view corresponding to FIG. 9 showing the second embodiment. FIG. 15 is a view corresponding to FIG. 10 showing the second embodiment.

Hereinafter, embodiments of the present invention will be described in detail based on the drawings. The present invention is not limited to the following embodiments.
<< Embodiment >>

  FIG. 1 shows a schematic configuration diagram of an image forming apparatus 1 in the present embodiment. The image forming apparatus 1 is a tandem-type color printer, and includes an image forming unit 3 in a box-shaped case 2. The image forming unit 3 transfers and forms an image on a sheet P based on image data transmitted from an external device such as a computer connected to a network. Below the image forming unit 3, four light scanning devices 4 for emitting laser light are disposed, and above the image forming unit 3, an intermediate transfer belt (transfer material) 5 is disposed. Below the light scanning device 4, a sheet feeding unit 6 for storing the sheet P is disposed. Above the left side of the intermediate transfer belt 5, a fixing unit 8 for fixing the image transferred and formed on the sheet P is disposed. In the upper part of the housing 2, a paper discharge unit 9 for discharging the sheet P subjected to the fixing process by the fixing unit 8 is formed. In the image forming apparatus 1, a sheet conveyance path extending from the sheet feeding unit 6 to the sheet discharging unit 9 is provided.

  The image forming unit 3 includes four image forming units 10Bk, 10M, 10C, and 10Y arranged in a line along the intermediate transfer belt 5. The image forming units 10Bk, 10M, 10C and 10Y respectively form toner images of black, magenta, cyan and yellow. In the following description, when it is necessary to distinguish which of the four image forming units 10Bk, 10M, 10C, and 10Y the constituent element belongs to, the subscripts Bk, M, C, or Y are added to the reference numerals. .

  The light scanning devices 4Bk, 4M, 4C and 4Y are disposed below the image forming units 10Bk, 10M, 10C and 10Y, respectively. Each of the image forming units 10Bk, 10M, 10C, and 10Y has a photosensitive drum 11 as an image carrier. A charger 12 is disposed immediately below each photosensitive drum 11, a developing device 13 is disposed on the right of each photosensitive drum 11, and a primary transfer roller (transfer unit) is disposed immediately above each photosensitive drum 11. 14 is disposed, and on the left side of each photosensitive drum 11, a cleaning unit 15 for cleaning the circumferential surface of the photosensitive drum 11 is disposed.

  The circumferential surface of each photosensitive drum 11 is uniformly charged by the charger 12, and a laser corresponding to each color based on the image data input from the computer or the like is applied to the circumferential surface of the photosensitive drum 11 after the charging. Light is emitted from the light scanning devices 4Bk, 4M, 4C and 4Y. As a result, electrostatic latent images are formed on the circumferential surfaces of the respective photosensitive drums 11. A developer is supplied to the electrostatic latent image from the developing device 13, and a yellow, magenta, cyan or black toner image is formed on the circumferential surface of each photosensitive drum 11. The toner images are transferred onto the intermediate transfer belt 5 in a superimposed manner by the transfer bias applied to the primary transfer roller 14.

  A secondary transfer roller 16 is disposed on the left side of the intermediate transfer belt 5. The secondary transfer roller 16 is disposed in contact with the intermediate transfer belt 5. The secondary transfer roller 16 nips the sheet P conveyed from the sheet feeding unit 6 along the sheet conveyance path T with the secondary transfer roller 16 and the intermediate transfer belt 5. A transfer bias is applied to the secondary transfer roller 16, and the toner image on the intermediate transfer belt 5 is transferred to the sheet P by the applied transfer bias.

  The fixing unit 8 includes a heating roller 18 and a pressure roller 19, and the sheet P is held by the heating roller 18 and the pressure roller 19 and heated while being pressed. Then, the fixing unit 8 fixes the toner image transferred to the sheet P to the sheet P. The sheet P after the fixing process is discharged to the sheet discharge unit 9.

  Next, each of the optical scanning devices 4Bk, 4M, 4C and 4Y will be described in detail with reference to FIG. The configuration of each of the light scanning devices 4Bk, 4M, 4C, 4Y is the same.

  Each of the light scanning devices 4Bk, 4M, 4C, 4Y has a sealed housing 40. On the side wall portion 42 of the housing 40, light sources 43Bk, 43M, 43C, and 43Y made of, for example, a laser diode (LD) are provided. The light sources 43 </ b> Bk, 43 </ b> M, 43 </ b> C, and 43 </ b> Y are mounted on a substrate 44 attached to the outer surface of the side wall portion 42. The light sources 43Bk, 43M, 43C, and 43Y are multi-beam light sources that emit light beams in a plurality of lines (two lines in the present embodiment), and as shown in FIG. It has a point LD2.

  The first light emission point LD1 and the second light emission point LD2 obliquely intersect the rotation tangent direction (the left and right direction in FIG. 3) of the polygon mirror 46 when viewed from the base end side of each light source 43Bk, 43M, 43C, 43Y. They are spaced from one another in the direction. In the following description, the light beam emitted from the first light emitting point D1 is referred to as a first light beam B1, and the light beam emitted from the second light emitting point D2 is referred to as a second light beam B2.

  The light amounts of the first light emitting point LD1 and the second light emitting point LD2 (the light amounts of the first light beam B1 and the second light beam B2) are controlled by the control unit 100 described later. Inside the housing 40, a collimator lens (not shown), a cylindrical lens 45, and a polygon mirror (rotation polygon mirror) 46 are provided along the emission direction of the light beams emitted from the light sources 43Bk, 43M, 43C, 43Y. It is arranged on a straight line. The polygon mirror 46 is rotationally driven by a polygon motor M fixed to the bottom wall portion 41 of the housing 40. A first imaging lens 48 a and a second imaging lens 48 b are arranged at intervals in the radial direction on the side of the polygon mirror 46. The first imaging lens 48a and the second imaging lens 48b are, for example, fθ lenses. A folding mirror 47 is disposed on the side of the second imaging lens 48b.

  The polygon mirror 46 is a polygonal rotating mirror having a plurality of reflecting surfaces on its circumferential surface. The polygon mirror 46 reflects (deflects) each of the light beams B1 and B2 emitted from the first and second light emitting points LD1 and LD2 to scan in the main scanning direction. The first imaging lens 48 a and the second imaging lens 48 b convert the respective light beams B 1 and B 2 deflected and scanned by the polygon mirror 46 into constant velocity. The folding mirror 47 reflects the light beams B1 and B2 having passed through the second imaging lens 48b and guides the light beams B1 and B2 to the circumferential surface of the photosensitive drum 11.

  Further, in the housing 40, a synchronization detection mirror 49 and a synchronization detection sensor 50 are provided. The synchronization detection mirror 49 directs each light beam B1 or B2 deflected by the polygon mirror 46 to the synchronization detection sensor 50 along an optical path out of the effective scanning area (the image forming area where the image data is actually written). reflect.

  The synchronization detection sensor 50 is configured of, for example, a photodiode, a phototransistor, a photo IC, and the like. The synchronization detection sensor 50 outputs a detection signal when each of the light beams B1 and B2 is detected. The detection signal output from the synchronization detection sensor 50 is transmitted to the control unit 100 described later.

  As shown in FIG. 4, the control unit (write control unit) 100 comprises a microcomputer having a CPU, a ROM and a RAM. The control unit 100 is connected to the synchronization detection sensor 50, the operation setting unit 53, and the light sources 43Bk, 43M, 43C, and 43Y so as to be able to transmit and receive signals.

  The control unit 100 controls the operation of each of the light scanning devices 4Bk, 4C, 4M and 4Y. The control unit 100 controls the write start timing of the image data by the light sources 43Bk, 43M, 43C and 43Y based on the signals from the synchronous detection sensor 50 provided in the respective light scanning devices 4Bk, 4C, 4M and 4Y. The controller 100 controls the light emission points LD1 and LD2 of the light sources 43Bk, 43M, 43C and 43Y to write image data on the surface of the photosensitive drum 11 at a predetermined optical resolution (for example, 1200 dpi in this embodiment). Do.

  The operation setting unit 53 is configured of, for example, a touch-type liquid crystal panel or the like. The user can switch between the print mode and the test mode by operating the operation setting unit 53. In the test mode, the amount of positional deviation (hereinafter referred to as the amount of color misregistration) of the toner image of each color transferred onto the intermediate transfer belt 5 from each photosensitive drum 11 is detected. In the color misregistration detection process, color misregistration amounts of the other three colors with respect to a predetermined reference color are calculated. The reference color may be any of black, magenta, yellow and cyan, but is preferably magenta or yellow. In the print mode, printing of image data is performed with color shift correction processing for reducing the amount of color shift detected in the test mode.

  Here, an example of the color misregistration detection process performed in the test mode will be described. In this color misregistration detection process, four color patch images g1 to g4 (see FIG. 5) are formed on the intermediate transfer belt 5 by controlling the image forming units 10Bk, 10M, 10C, and 10Y by the control unit 100. The characters Bk, M, C, and Y in FIG. 5 represent the colors of the patch images, and these characters are not actually formed. The control unit 100 calculates the separation distance in the sub-scanning direction of the patch images g1 to g4 of the four colors based on a detection signal from a density detection sensor (for example, a photo sensor) 101 provided opposite to the intermediate transfer belt. Do. Then, the control unit 100 calculates the difference between the calculated separation distance and the separation distance in the sub scanning direction of each photosensitive drum 11 to calculate the amount of color misregistration of the other three colors with respect to the reference color. Then, the control unit 100 configures a color shift amount detection unit.

  Next, with reference to FIG. 6, the process of writing image data performed in the print mode will be described. FIG. 6 is a schematic view virtually showing pixel corresponding regions R arranged in a lattice on the surface of each photosensitive drum 11. Here, each pixel correspondence area R corresponds to one pixel of image data to be printed.

FIG. 7 virtually shows an example of the exposure state of one pixel corresponding region R. The example of the figure shows the case where the resolution of the image data is 600 dpi. In this case, the vertical size and the horizontal size of each pixel corresponding area R are 42.3 μm. Each pixel corresponding region R is virtually equally divided into a first line region r1 scanned by the first light beam B1 and a second line region r2 scanned by the second light beam B2. The change of the exposure region in the main scanning direction is dealt with by a technique of modulating the pulse width of the light emission signal in order to suppress the increase in the frequency of the clock. The division number n in the main scanning direction is determined from the bit number m of the image data, and has a relationship of n = 2 ^m −1. In the example of FIG. 6, the case of m = 4 and n = 15 is shown.

  In FIG. 7, the higher the density is, the higher the exposure amount is, and the white is a non-exposed area. In the example of this figure, five sections are exposed from the left end in the first line area r1 and the second line area r2, and the light amount of the first light emitting point LD1 which exposes the first line area r1 (the first light beam B1 The light amount) and the light amount of the second light emitting point LD2 (the light amount of the second light beam B2) for exposing the second line area r2 are equal. Therefore, in this example, the light amount gravity center position G is located at the center of the image corresponding region R in the sub scanning direction.

  FIG. 8 is different from the example of FIG. 7 in the light amount ratio of the first light emitting point LD1 and the second light emitting point LD2. The position, range, and total light amount of the exposure region are the same as in the example of FIG. In the example of FIG. 8, the light amount of the first light emitting point LD1 exposing the first line region r1 is set larger than the light amount of the second light emitting point LD2 exposing the second line region r1. Therefore, in this case, the light amount gravity center position G is offset to the first line region r1 side with respect to the central position of the pixel corresponding region R in the sub scanning direction.

  The light amount barycentric position G of each pixel corresponding area R is a position where toner adheres, that is, a dot formation position. The control unit 100 executes color misregistration correction control by adjusting the light amount barycentric position G of each pixel corresponding region R by adjusting the light amount ratio between the light amount of the first light emitting point LD1 and the light amount ratio of the second light emitting point LD2. Details of this color misregistration correction control will be described later.

  FIG. 9 shows the light quantity distribution characteristic in the sub-scanning direction when the light quantity ratio between the first light emitting point LD1 for exposing the first line area r1 and the second light emitting point LD2 for exposing the second line area r2 is changed. It is graphed data (hereinafter referred to as light amount distribution data). Although this light quantity distribution data is based on theoretical calculation, it may be actual experimental data or the like. 0 on the horizontal axis of the graph means the center position in the sub scanning direction, the plus side means the first line area r1 side, and the minus side means the second line area r2 side. The light amount distribution data is stored in advance in a data storage unit (second data storage unit) 102 connected to the control unit 100. From FIG. 9, it can be read that when the light amount ratio of the first light emitting point LD1 and the second light emitting point LD2 is 10:10, the light amount barycentric position G (the light amount peak position) is located at the center in the sub scanning direction. The light amount barycentric position G is offset toward the first line region r1 as the light amount of the first light emitting point LD1 is increased while keeping the total of the light amounts of the first light emitting point LD1 and the second light emitting point LD2 constant. When the light quantity ratio between the light quantity of the first light emission point LD1 and the light quantity ratio of the second light emission point LD2 becomes 20: 0, the distance between the light quantity gravity center position G and the central position in the subscanning direction of the pixel correspondence area R becomes maximum (= 10 μm )become. Further, according to the light quantity distribution data, it is understood that the light quantity peak value is increased as the offset amount of the light quantity barycenter position G is increased. This amount of increase (the amount of increase based on the light intensity peak value when the light intensity ratio of the first light emission point LD1 and the second light emission point LD2 is 10:10) is used for the purpose of correcting the light amount in color misregistration correction (Step S7 described later). Note that δ in the drawing indicates, as an example, the amount of increase of the light amount peak value when the light amount ratio is 20: 0.

  FIG. 10 is light amount barycentric data in which the change characteristic of the light amount barycentric position G when the light amount ratio between the light amount of the first light emitting point LD1 and the second light emitting point LD2 is changed is graphed. The horizontal axis indicates the light quantity ratio between the first light emitting point LD1 and the second light emitting point LD2, and the vertical axis indicates the offset amount to the first line area r1 side from the center position of the light quantity barycentric position G in the sub scanning direction. Meaning, 0 on the vertical axis means the center position in the sub scanning direction. The light amount gravity center data is stored in advance in the data storage unit (first data storage unit) 102 connected to the control unit 100. Although this light quantity distribution data is based on theoretical calculation, it may be actual experimental data or the like. Although the example of FIG. 10 shows only the case where the light quantity of the first light emitting point LD1 is larger than the light quantity of the second light emitting point LD2, the light quantity of the first light emitting point LD2 is actually the light quantity of the second light emitting point LD2. The following data is also stored. The control unit 100 executes the color misregistration correction control based on the light amount gravity center data stored in the data storage unit 102. The light amount barycenter data is not limited to graph data, and may be table data, for example.

  FIG. 11 is a flowchart showing details of the color misregistration correction processing executed by the control unit 100. This process is performed on the light scanning devices 4 other than the reference color.

  In step S1, the color shift amount X of each color (other three colors) detected in the test mode is read.

  In step S2, a quotient A and a remainder B are calculated by dividing the read color misregistration amount X by the width W in the sub scanning direction of each of the line areas r1 and r2. In the example of the present embodiment, W is 21.1 μm (= 25.4 / 600/2 × 1000: truncation to the second decimal place).

  In step S3, the writing position of the image data is shifted by the A line to the color misregistration reduction side in the sub-scanning direction (the side where the color misregistration amount decreases). For example, when shifting by one line, the image data sent to the first light emitting point LD1 is sent to the second light emitting point LD2, and the image data of the second light emitting point LD2 is sent to the first light emitting point LD1 of the next scan. Once transmitted, color misregistration correction for one line (21.1 μm) becomes possible. For example, if the image data of the first light emission point LD1 is moved to the first light emission point LD1 of the next scan and the image data of the second light emission point LD2 is moved to the second light emission point LD2 of the next scan, two lines (42.3 μm) Color shift correction is possible. Similarly, if the image data of the first light emission point LD1 is moved to the second light emission point LD2 of the pre-scan and the image data of the second light emission point LD2 is moved to the first light emission point LD1 of the same scan, -1 line (-21 Color shift correction is possible. Here, the side from the line area r1 to the second line area r2 is defined as +.

  In step S4, it is determined whether the remainder B calculated in step S2 is less than a predetermined threshold value. If the determination is NO, the process proceeds to step S6, and if YES, the process proceeds to step S5. This predetermined threshold is the maximum value of the amount of color misregistration permitted in the product specification.

  In step S5, the light amount of the first light emitting point LD1 and the light amount of the second light emitting point LD2 are equalized to write the image data to each pixel corresponding region R, and then the process returns. The total of the light amounts of the light emitting points LD1 and LD2 is calculated according to the density value of the pixel data which is the basis of the pixel corresponding area R to be written.

  In step S6, the light amount ratio of both light emitting points LD1 and LD2 for shifting the light amount barycentric position G by the remainder B toward the color shift reduction side is calculated. In this calculation, the light amount ratio corresponding to the necessary shift amount is determined using the light amount barycenter data (see FIG. 10) stored in the data storage unit 102. The total of the light amounts of the light emitting points LD1 and LD2 is calculated according to the density value of the pixel data which is the basis of the pixel corresponding area R to be written.

  In step S7, with reference to the light quantity distribution data (see FIG. 9) stored in the data storage unit 102, an increase in light quantity peak value when the light quantity ratio determined in step S6 is adopted is calculated. Then, each light emitting point LD1, DL2 is set such that the calculated light amount peak value becomes a predetermined reference light amount (in the present embodiment, the light amount peak value when the light amount ratio of both light emitting points LD1, DL2 is 10:10). Correct the amount of light at the same magnification.

  In step S8, writing of image data is executed, and then, the process returns.

  In the image forming apparatus 1 configured as described above, the control unit 100 causes the light amount barycentric position G of the pixel corresponding area R in which the image data is written to be positioned at the center of the pixel corresponding area R in the sub scanning direction. The first writing process (step S5) for writing the image data with the same light quantity of the two light emitting points LD1 and LD2 and the light quantity gravity center position G of the pixel corresponding area R for writing the image data corresponds to the pixel The second writing process (step S6) for writing the image data while making the light amounts of the two light emitting points LD1 and LD2 different so as to offset the center position of the region R in the sub scanning direction by a predetermined amount selectively It is configured to perform color misregistration correction by executing.

  According to this configuration, the color misregistration resolution in the sub-scanning direction of the writing position of the image data can be remarkably improved as compared with the case where the control unit 100 executes only the first writing process.

  The control unit 100 sets the color shift amount of the toner image of the other color (color other than the reference color) detected in the color shift amount detection process to X in the sub-scanning direction, and the width of each line region r1 and r2 in the sub-scanning direction. The quotient A and remainder B are obtained by dividing the color misregistration amount X by the width W with W as W, and the writing position of the image data is shifted by the A line to the color misregistration reduction side in the subscanning direction It is determined whether or not it is less than the threshold, and when it is determined that it is less than the predetermined threshold, the first writing process is executed, while when it is determined that it is more than the predetermined threshold, the second writing process is executed. By doing this, the light amount barycentric position G of the pixel corresponding area R in which the image data is written is offset by an amount equivalent to the remainder B on the color misregistration reduction side in the sub scanning direction with respect to the center position in the sub scanning direction. Color shift correction processing (step S To perform the processing)

  According to this configuration, the light amount barycentric position is corrected in the range of 10 μm or less by changing the light amount ratio and changing the light amount ratio (rough processing in step S3) that corrects the light amount barycentric position G in line units (21.1 μm units). By combining the fine correction (the processes of steps S6 and S7 and refer to FIG. 9 and FIG. 10), the color misregistration amount in the sub-scanning direction of each toner image can be accurately corrected over a wide range.

  When executing the second writing process when executing the color misregistration correction process, the control unit 100 determines the light amount ratio of the two light emitting points LD1 and LD2 based on the graph data stored in the data storage unit 102. It is comprised so that it may determine (step S6).

  According to this configuration, it is possible to quickly calculate the shift amount of the light amount barycentric position G necessary for the color misregistration correction by a simple calculation using the graph data.

  Further, when the control unit 100 executes the second writing process when executing the color misregistration correction process, the light quantity associated with the offset of the light quantity barycentric position G based on the light quantity distribution data stored in the data storage unit 102. The total light quantity of the two light emitting points LD1 and LD2 is corrected to cancel the increase of the peak value (step S7).

According to this configuration, it is possible to prevent the occurrence of color unevenness due to the increase of the light amount peak value accompanying the offset of the light amount gravity center position G.
<< Embodiment 2 >>

  12 to 15 show the second embodiment. In this embodiment, as shown in FIG. 12, each light source 43Bk, 43M, 43C, 43Y has four light emitting points LD1 to LD4, and each pixel corresponding region R is scanned by four light beams B1 to B4. Is different from the above embodiment in the following points.

  As shown in FIGS. 12 and 13, each pixel correspondence area R is virtually equally divided into first to fourth line areas r1 to r4 scanned by the first to fourth light beams B1 to B4.

  FIG. 12 shows the case where the exposure amounts of the first to fourth line areas r1 to r4 are equal (that is, the light amounts of the four light emitting points LD1 to LD4 are equal). In this case, the light amount barycentric position G is located at the center in the sub scanning direction.

  FIG. 13 shows an example in which the light amount gravity center position G is offset to the first line region r1 side than the center position in the sub scanning direction. In this example, the light quantity of the first light emitting point LD1 for exposing the first line area r1 is set larger than the light quantity of the second light emitting point LD2 for exposing the second line area r2. The light quantity of the third light emitting point LD3 for exposing the third line area r3 is equal to the light quantity of the first light emitting point LD1, and the light quantity of the fourth light emitting point LD4 for exposing the fourth line area r4 is equal to that of the second light emitting point LD2. It is equal to the amount of light.

  FIG. 14 shows light amount distribution data in the present embodiment, and FIG. 15 shows light amount gravity center data in the present embodiment. In the light amount distribution data, only two lines of the case where the light amount ratio of the first light emitting point LD1 and the second light emitting point is 10:10 and 20: 0 are shown in consideration of easy viewing. According to these data, the light amount barycentric position G is sub-scanned by changing the light amount ratio of the first light emitting point LD1 and the second light emitting point LD2 (= the light amount ratio of the third light emitting point LD3 and the fourth light emitting point LD4). It can be seen that adjustment can be made within 5 μm from the central position in the direction. Therefore, in the present modification, by combining the 10.6 μm rough correction and the fine correction of 5 μm or less corresponding to the interval between the four light emitting points LD1 to LD4, a wide range of colors with high accuracy as compared with the above embodiment. Deviation correction can be performed.

  Other Embodiments

  In each of the above embodiments and modifications, the case where the number M of light emitting points of each light source is 2 or 4 has been described, but the present invention is not limited to this. That is, the number of light emitting points may be three, or five or more.

  In the above embodiment, an example in which the image forming apparatus 1 is a printer has been described, but the present invention is not limited to this. That is, the image forming apparatus 1 may be a copier, a multifunction peripheral (MFP), a facsimile, or the like.

  The present invention includes any combination of the above embodiments and variations.

  As described above, the present invention is useful for a color image forming apparatus, and particularly useful for a printer, a facsimile, a copying machine, and a multifunction peripheral (MFP).

B1: first light beam B2: second light beam D1: first light emission point D2: second light emission point G: light gravity center position LD1: first light emission point LD2: second light emission point LD3: light emission point LD4: fourth light emission Point R: pixel corresponding area X: color shift amount n: division number r1: first line area r2: second line area r3: third line area r4: fourth line area 1: image forming apparatus 4: light scanning apparatus 4Bk : Optical scanning device 4C: Optical scanning device 4M: Optical scanning device 4Y: Optical scanning device 5: Intermediate transfer belt (transfer material)
11: Photosensitive drum (image carrier)
13: Developing device 14: Primary transfer roller (transfer section)
43Bk: light source 43C: light source 43M: light source 43Y: light source 100: control unit (color shift detection unit, writing control unit)
102: Data storage unit (first data storage unit, second data storage unit)

Claims (6)

A plurality of light sources each having M (M is 2 or more) light emitting points, and a plurality of image carriers exposed to M light beams emitted from the respective light sources to form electrostatic latent images on the surface A plurality of developing devices for developing electrostatic latent images formed on the surfaces of the plurality of image carriers with toners of different colors to form toner images, and colors of each color formed on the surfaces of the respective image carriers. A color image forming apparatus comprising: a transfer section for transferring a toner image on a transfer material in an overlapping manner; and a writing control section for writing image data on the surface of an image carrier by controlling the operation of each light source. ,
A pixel corresponding region corresponding to one pixel of the image data on the surface of each image carrier is scanned in a plurality of lines by the M light beams emitted from each light source,
The write control unit
Write the image data with the same light intensity of the M light emitting points so that the light intensity barycentric position of each pixel corresponding region corresponding to each pixel of the image data is positioned at the center of the pixel corresponding region in the sub scanning direction. The first writing process to
Writing the image data while varying the light amounts of the M light beams such that the light amount barycentric position of each of the pixel corresponding regions is offset by a predetermined amount from the center position in the sub scanning direction of each pixel corresponding region; (2) An image forming apparatus configured to perform color misregistration correction by selectively switching and executing two writing processes. In the image forming apparatus according to claim 1,
The apparatus further includes a color shift amount detection unit that detects a color shift amount of a toner image of another color with respect to a toner image of a predetermined reference color in the sub-scanning direction.
The writing control unit sets a color shift amount of the toner image of the other color detected by the color shift amount detection unit to X in the sub-scanning direction, and equally divides the pixel corresponding region into M in the sub-scanning direction. Assuming that the width of the line area in the sub scanning direction is W, the quotient A and remainder B are obtained by dividing the color misregistration amount X by the width W, and the writing position of the image data is reduced in color misregistration in the sub scanning direction. Shift by A line, and it is determined whether the remainder B is less than a predetermined threshold, and if it is determined that the remainder is less than the predetermined threshold, the first writing process is performed, while the predetermined threshold or more If it is determined that the second writing process is performed, the barycentric position of the light quantity of the pixel corresponding area in which the data is written is on the color misregistration reduction side in the sub scanning direction than the central position in the sub scanning direction. The amount corresponding to the above remainder B is offset It is configured to perform the color shift correction by causing bets, the image forming apparatus. In the image forming apparatus according to claim 2,
First, light intensity barycenter data indicating the change characteristic of the offset amount from the center position in the sub scanning direction of the light intensity barycentric position of the pixel corresponding region when the light amount ratio of the M light emitting points is changed is stored first Equipped with a data storage unit,
The writing control unit, when executing the second writing process at the time of execution of the color misregistration correction, calculates the light intensity of the M light emitting points based on the light intensity barycenter data stored in the first data storage unit. An image forming apparatus configured to set a ratio. In the image forming apparatus according to claim 3,
A second data storage unit for storing in advance light quantity distribution data indicating the light quantity distribution characteristic in the sub scanning direction in the pixel corresponding area when the light quantity ratio of the M light emitting points is changed;
When the second writing process is performed when the color misregistration correction is performed, the writing control unit uses the light intensity distribution data stored in the second data storage unit to offset the light intensity barycentric position. An image forming apparatus configured to correct a total light amount of the M light emitting points so as to cancel an accompanying increase in light amount peak value. The image forming apparatus according to any one of claims 1 to 4.
An image forming apparatus in which M = 2. The image forming apparatus according to any one of claims 1 to 5.
M = 4,
The four light emitting points are first to fourth light emitting points,
Each pixel corresponding region is a first line region exposed to the first light emitting point, a second line region exposed to the second light emitting point, a third line region exposed to the third light emitting point, A fourth line area exposed to the fourth light emitting point is arranged in this order in the sub scanning direction;
When executing the second writing process, the write control unit sets the light amount of the first light emitting point equal to the light amount of the third light emitting point, and the light amount of the second light emitting point and the fourth light An image forming apparatus that sets the light amount of the light emitting point equal.

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