JP2005131961A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To precisely correct density irregularities in a horizontal scanning direction different by image densities, by means of an exposure amount correction of an exposure device. <P>SOLUTION: When carrying out density irregularities correction processing, a control circuit 210 makes an image forming part 100 output a pattern for density irregularities detection which is composed of a plurality of regions different in the image density Cin. The outputted pattern is read by an image reading device 280 and converted to density data by the control circuit 210. The control circuit 210 calculates an exposure correction amount curve for each image density Cin from this density data, and further develops the exposure correction amount curve to the whole tone region. In image forming, the exposure amount correction by the appropriate exposure correction amount curve is conducted to a pixel value of each pixel supplied from a printing control part 230. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an image forming apparatus having a function of correcting density unevenness of an output image by correcting light amount of an exposure apparatus.

  In an image forming apparatus such as a printer or a copier using an electrophotographic process, density unevenness may occur in an output image due to various factors, for example, photoreceptor sensitivity unevenness, exposure apparatus exposure unevenness, transfer unevenness, and the like. . This density unevenness usually varies depending on the color to be output, the type of screen pattern, or the type of image such as a photograph or character. Conventionally, this density unevenness has been corrected by correcting the exposure amount of the exposure apparatus according to each case (for example, see Patent Document 1). The technique described in Patent Document 1 will be referred to as “conventional technique”.

JP 2002-172817 A

  Some image forming apparatuses have a tandem configuration. In this method, image forming engines corresponding to each color of YMCK are arranged in the horizontal direction, and image formation of each color is sequentially performed. During this image forming process, the image on the photosensitive drum in each image forming engine is once transferred to the intermediate transfer member. This transfer to the intermediate transfer member is called primary transfer. During this primary transfer, density unevenness may also occur in the direction of the rotation axis of the photosensitive drum (hereinafter referred to as “main scanning direction”). In the prior art, the density unevenness generated in the main scanning direction is also corrected by the exposure amount of the exposure apparatus.

  It is known that the density unevenness in the main scanning direction has a different distribution depending on the image density of the output image (hereinafter, referred to as “Cin” as appropriate). FIG. 8 is a diagram illustrating the relationship between image density and density unevenness in the main scanning direction. When Cin is 20% and 60%, the density distribution in the main scanning direction is different as shown in FIG.

However, the exposure amount correction in the conventional technique is performed based on the density unevenness distribution of a certain image density. FIG. 9 illustrates this situation. As shown in the figure, in the conventional exposure amount correction, even if an appropriate exposure correction amount can be supplied at a certain image density, the exposure apparatus may be overcorrected at another image density, which is not preferable.
The present invention has been made in view of the above-described circumstances, and an object thereof is to provide an image forming apparatus capable of correcting density unevenness distribution in the main scanning direction in all density regions.

In order to solve the above problems, the present invention is a photoconductive image carrier and means for exposing the surface of the image carrier according to image data, and extends in the main scanning direction on the surface of the image carrier. An operation of exposing the exposure target area according to the image data is performed while moving the exposure target area along a sub-scanning direction orthogonal to the main scanning direction, thereby generating an electrostatic latent image corresponding to the image data. An exposure means for forming on the surface of the image carrier; a developing means for visualizing the electrostatic latent image on the surface of the image carrier; and an output for outputting the visible image on the surface of the image carrier to a recording medium. Generating exposure correction amount distribution data representing an exposure correction amount distribution depending on a combination of an image density represented by the image data and a position in the main scanning direction. When exposure correction amount distribution data is acquired in advance and image data to be output is given, exposure corresponding to each position in the main scanning direction and corresponding to the density of the image represented by the image data An exposure correction amount determination unit that determines a correction amount based on the exposure correction amount distribution data, and an exposure amount control that controls an exposure amount in the exposure unit based on the exposure correction amount determined by the exposure correction amount determination unit And an image forming apparatus.
According to such an image forming apparatus, the exposure unit uses the exposure correction amount corresponding to the density of the image represented by the image data to be output and corresponding to each position along the main scanning direction. The exposure amount is controlled by.

  The best mode for carrying out the present invention will be described below with reference to the drawings.

<First Embodiment: Image Forming Apparatus>
<1-1: Image Forming Unit 100>
FIG. 1 is a schematic configuration diagram of an image forming apparatus 10 according to the present embodiment.
The image forming apparatus 10 is roughly composed of an image forming unit 100 and a control unit 200. In FIG. 1, each device constituting the image forming unit 100 is assigned a 100th symbol, and each device constituting the control unit 200 is given a 200th symbol.
The image forming unit 100 includes four image forming engines 110Y, 110M, 110C, and 110K corresponding to four colors of Y (yellow), M (magenta), C (cyan), and K (black), respectively. Since the basic configuration of each image forming engine is common, the image forming engine 110Y will be described here.

The image forming engine 110Y includes a charging device 130, an exposure device 140, a developing device 150, and the like arranged around a cylindrical photoconductive drum 120 having photoconductivity.
The charging device 130 is for charging the photosensitive drum 120 that is rotationally driven. In the present embodiment, a scorotron that uses corona discharge is used. By this charging device 130, the surface potential of the photosensitive drum 120 becomes a predetermined charging potential.
There are various charging modes, such as those using a direct current BCR, an alternating current BCR, or a charging brush, and those using corona discharge, but the effect according to the present embodiment can be obtained by using any charging means. be able to.

The exposure device 140 is a ROS (Raster Output Scanner) that irradiates the photosensitive drum 120 charged to a predetermined charging potential by the charging device 130 with an exposure beam based on the output image. . As a light source of ROS, LD (Laser Diode) is mainly used. The scanning direction of the LD is equal to the axial direction of the photosensitive drum 120, and in the present embodiment, this direction is called a main scanning direction (FS (Fast Scanning) direction). A direction perpendicular to the main scanning direction is referred to as a sub-scanning direction (SS (Slow Scanning) direction). Each LD constituting the exposure apparatus 140 corresponds to one pixel in an image output by the image forming apparatus 10.
The surface potential of the surface irradiated with the beam on the surface of the photosensitive drum 120 is reduced to a predetermined level due to the photoconductivity of the photosensitive drum 120. The potential on the surface of the photosensitive drum 120 is measured by the potential sensor 141. As the surface potential of the photosensitive drum 120 changes in this way, an electrostatic latent image based on the output image is formed on the surface of the photosensitive drum 120 exposed by the exposure device 140.

The developing device 150 is a device that visualizes the electrostatic latent image formed on the surface of the photosensitive drum 120. The developing device 150 visualizes the electrostatic latent image by adhering the developer (toner) conveyed on a developing sleeve (not shown) to the electrostatic latent image formed on the surface of the photosensitive drum 120. To do. The toner moves from the developing sleeve to the surface of the photosensitive drum 120 due to a potential difference between the potential generated on the developing sleeve by a predetermined developing bias and the surface potential of the photosensitive drum 120, and adheres. Therefore, the toner adheres only to the portion where the surface potential is reduced by exposure, and the electrostatic latent image becomes a visible image.
The above is the details of the image forming engine 110Y. The other image forming engines 110M, 110C, and 110K have the same configuration except that the toner corresponds to each color. The image forming unit 100 according to the present embodiment has a so-called 4-drum tandem arrangement configuration in which these four image forming engines are arranged in series.

  Below each image forming engine, an intermediate transfer member 160 is provided so that a part of the intermediate transfer member 160 comes into contact with the photosensitive drum 120. The intermediate transfer body 160 is an endless belt, and is wound around the drive roll 161 and the backup roll 162 driven by the drive roll 161 so as to maintain a constant tension. The photosensitive drums 120 of the image forming engines 110Y, 110M, 110C, and 110K described above are rotationally driven in the same direction with their respective surfaces in contact with the surface of the intermediate transfer member 160. The intermediate transfer member 160 is circulated and driven in the same direction as the moving direction of the surface of the photosensitive drum 120 by a driving device (not shown) that drives the driving roll 161. At each contact position between the intermediate transfer body 160 and the photosensitive drum 120 corresponding to each color, a primary transfer roll 163 corresponding to each color is disposed so as to sandwich the intermediate transfer body 160. The visible image on each photoconductor drum 120 is pressed against the intermediate transfer member 160 by the primary transfer roll and is multiplex-transferred to the intermediate transfer member 160.

  The secondary transfer roll 172 faces the backup roll 162 with the intermediate transfer member 160 interposed therebetween. The sheet 171 held on the sheet tray 170 in the image forming unit 100 is sent to a position where the secondary transfer roll 172 and the backup roll 162 are opposed to each other, together with the intermediate transfer body 160 on which the visible images of each color are multiplex-transferred. It passes between the secondary transfer roll 172 and the backup roll 162. At that time, the sheet 171 is brought into pressure contact with the intermediate transfer member 160 by the secondary transfer roll 172, and the visible image that has been multiple-transferred onto the intermediate transfer member 160 is transferred to the sheet 171. The visible image transferred onto the paper 171 in this manner is finally subjected to fixing processing such as heating and pressing by the fixing device 180 and then discharged from the discharge unit 181. The details of the image forming unit 100 have been described above.

<1-2: Control unit 200>
The control unit 200 controls the operation of the image forming unit 100 and performs control for executing density unevenness correction processing according to the present embodiment.
FIG. 2 shows a portion related to density unevenness correction processing in the present embodiment among the devices constituting the control unit 200. Hereinafter, the control unit 200 will be described with reference to FIGS. 1 and 2.

  The control circuit 210 is a device that controls each part of the control unit 200 and controls various operations in the image forming unit 100, and includes a CPU (Central Processing Unit), a RAM (Random Access Memory), and a ROM (Read Only). Memory). Examples of the control performed by the control circuit 210 include exposure amount correction processing of the exposure device 140 in each image forming engine, processing of a potential detection signal supplied from the potential sensor 141, and density data supplied from an image reading device described later. Examples include processing, control of a pattern forming unit 220, a print control unit 230, and an image density control unit 240 described later.

  The pattern forming unit 220 generates a density unevenness detection pattern used for the density unevenness correction process and a control patch for controlling the toner supply amount in the image forming unit 100. When the control circuit 210 instructs the print control unit 230 to output an image, the print control unit 230 generates image data of the image. The image count unit 250 generates an image density target value that represents the average density of the image represented by the image data generated by the pattern forming unit 220 or the print control unit 230, and supplies the image density target value to the image density control unit 240. The image density control unit 240 controls a toner supply signal for controlling the amount of toner used in the developing device 150 based on the image density target value supplied from the image count unit 250.

On the other hand, the image data generated by the pattern forming unit 220 or the print control unit 230 is supplied to the image processing unit 260 via the image count unit 250. The image processing unit 260 generates density data corresponding to each color of YMCK from the supplied image data, and supplies the density data to the pulse width modulation circuit 261. In the pulse width modulation circuit 261, a PWM (Pulse Width Modulation) signal is generated based on the density data and supplied to the laser driver 262 that drives the exposure apparatus 140.
The laser driver 262 drives the exposure device 140 in each image forming engine based on the pulse width modulation signal supplied from the pulse width modulation circuit 261. When density unevenness correction processing described later is performed, the laser driver 262 is given an exposure correction amount for correcting the exposure amount of the exposure apparatus 140 from the control circuit 210.

  The image density detection signal processing unit 270 processes the density detection signal output from the density sensor 271 located slightly downstream of the primary transfer position of the image forming engine 110K in the traveling direction of the intermediate transfer body 160, and controls image density control. It is a circuit supplied to the unit 240. The density sensor 271 is a sensor that detects the density of a density control patch formed between images on the intermediate transfer body 160, that is, in a so-called inter-image portion. The image data of the density control patch is given from the pattern forming unit 220 described above. The image density control unit 240 compares the density information of the density control patch with the image density target value given from the image count unit 250 to correct the toner density used in the developing device 150. Such correction of toner density is called ADC (Auto Developability Control) control.

The image reading device 280 is installed in the image forming apparatus 10 and has a function equivalent to that of an externally connected image reading device such as a scanner. The image reading device 280 is controlled by the control circuit 210. When a density unevenness detection pattern is output to the paper 171 in a density unevenness correction process described later, the fixing process is performed by the fixing device 180, The density unevenness detection pattern on the paper 171 is read. The density data of the pattern obtained by this reading process is supplied to the control circuit 210. During the density unevenness correction process, the control circuit 210 calculates the density unevenness distribution in the main scanning direction based on the density data received from the image reading device 280, and calculates the exposure correction amount distribution. Further, the control circuit 210 creates this exposure correction amount distribution for each image density Cin. Therefore, the above-described laser driver 262 is given an exposure correction amount for each image density Cin.
In the present embodiment, the image reading device 280 is built in the image forming apparatus 10, but it is not always necessary to be in this mode. For example, instead of providing the image reading device 280 in the image forming device 10, image data or density data obtained when an image reading device such as a scanner is provided externally and a density unevenness detection pattern is read by the image reading device is used. A receiving device that receives the image data may be provided in the image forming apparatus 10. In this case, the same effect as that of the present embodiment can be obtained.

<1-3: Density unevenness correction processing>
FIG. 3 is a flowchart showing a processing procedure of density unevenness correction processing according to the present embodiment.
In a preferred embodiment, the density unevenness correction process is performed when the photosensitive drum 120 is replaced in each image forming engine. In another preferred embodiment, the density unevenness correction processing is performed every time a predetermined number of prints (for example, 50,000) are printed. Furthermore, in another preferable aspect, the density unevenness correction process is executed when the user performs a predetermined operation at an arbitrary timing. In still another preferred embodiment, the density unevenness correction process is automatically executed at a predetermined timing.

  When the density unevenness correction processing is started, the control circuit 210 instructs the pattern forming unit 220 to output image data of the density unevenness detection pattern, and controls each part of the image forming unit 100 and the control unit 200. A density unevenness detection pattern is output on the paper 171 (step S301). The output of the density unevenness detection pattern is performed for the image forming engine that is a correction target of the density unevenness. Here, it is assumed that density unevenness correction processing is performed on a single color, for example, the image forming engine 110Y.

FIG. 4 is a schematic diagram of a density unevenness detection pattern according to this embodiment.
The density unevenness detection pattern in the present embodiment is a pattern having a certain width in the sub-scanning direction and stripe-like uniform density regions extending in the main scanning direction arranged in the sub-scanning direction. . Here, the image density Cin of each stripe-shaped uniform density region changes stepwise by 10% from 10% to 100%. Generally, the gradation expression method expresses the density of each pixel by density data of a plurality of bits, and gives a density gradation method for each pixel, and a plurality of pixels having a density of 1 bit. Thus, there is an area gray scale method in which a gray scale unit matrix is formed and the gray scale is expressed as a single pixel, and the former is used in this embodiment. When this method is used, a high-definition image can be obtained as compared with the latter area gradation method.

  In the present embodiment, the image data for one pixel output from each of the print control unit 230 and the pattern forming unit 220 is composed of 8 bits, and 256 gradations from “0” to “255” are displayed. Is done.

When the output of the density unevenness detection pattern is finished, the image of the density unevenness detection pattern output to the paper 171 is read by the image reading device 280, and the density of the image of each part of the read pattern is detected (step S302). In the present embodiment, density unevenness correction processing for the image forming engine 110Y is described. In this case, the image reading device 280 detects “Y”, that is, the density of a single yellow color.
Note that the image forming apparatus 10 according to the present embodiment uses, as a density unevenness detection pattern, in addition to YMCK single color, RGB or YMC which is a secondary color expressed by a combination of two of these YMCK colors. Gray or the like, which is a tertiary color that is configured, can be output.

  Next, density data for each color of YMCK (here, only Y) is calculated from the detected density (step S303) and supplied to the control circuit 210. In the case of YMCK single color, step S303 is executed. For example, if the density unevenness detection pattern is formed with a tertiary color, in step S302, each of the RGB colors obtained by reading the density unevenness detection pattern is processed. The image data is output from the image reading device 280, and the RGB color data is once converted into L * a * b * data by the control circuit 210 (step S304). Further, the L * a * b * data is converted into YMC density data (step S305).

  When the density data of each pixel constituting the density unevenness detection pattern is obtained in this way, the control circuit 210 calculates the density distribution of each pixel along the main scanning direction for each image density Cin (step S306). Further details are as follows. As already described, the density unevenness detection pattern has a plurality of stripe-like uniform density regions with different image densities Cin. The control circuit 210 uses the density data corresponding to each stripe-shaped uniform density area (that is, for each image density Cin) for each of these stripe-shaped uniform density areas on the paper 171 in the main scanning direction. Is demanded. Next, the control circuit 210 calculates an exposure correction amount based on the density distribution for each image density Cin (step S307). In calculating the exposure correction amount, first, the density values of all the pixels arranged in the main scanning direction on the paper 171 are averaged for each image density Cin. Then, for each pixel, a difference from the average value of their densities is calculated. This is the density error. Further, the density at the writing position (region) in the main scanning direction may be used as a reference instead of the average value.

  Here, the exposure correction amount based on this density error may be calculated for all pixels. For example, in an exposure apparatus in which the LD writes at a resolution of 1200 dpi (dot per inch), the total number of LD write pixels is a number. In such a case, if the exposure correction amount is calculated for each writing pixel, the processing load of the control circuit 210 may increase. Therefore, in the present embodiment, the exposure correction amount is calculated as follows.

The control circuit 210 handles write pixels constituting the exposure apparatus 140 by dividing them into hundreds of element groups. Here, it is assumed that this element group is formed every 256 elements, and all 50 element groups are arranged in the main scanning direction. The control circuit 210 extracts several elements at appropriate intervals in each element group, and acquires density errors of pixels on the density distribution corresponding to these elements. For example, if this density error is acquired at intervals of 16 pixels, a density error of 16 pixels per element group and a total of 800 pixels can be obtained. The control circuit 210 performs the calculation shown in the following formula (1) based on the acquired density error.
Δexp = 1 / Sensitivity · ΔD (1)
Here, Δexp is an exposure correction amount, and ΔD is a density error. “Sensitivity” is a sensitivity coefficient, and varies depending on the image density Cin and each color of CMYK. This sensitivity coefficient is calculated by the following equation (2) when the image density Cin is “X” (unit:%).
Sensitivity = b ₀ + b ₁ • X + b ₂ • X ² +... + B ₆ • X ⁶ (2)
Here, b _{0 to} b ₆ are constants different for each color, and are given by regression calculation.

As a result of these calculations, 16 exposure correction amounts Δexp for correcting the density error are obtained for each element group. The control circuit 210 interpolates these 16 data by linear interpolation for each element group. The interpolation mode is not limited to this, and spline interpolation or the like may be performed. As a result of this interpolation processing, an exposure correction amount correction curve is obtained for each element group. When this interpolation is performed, for example, if the control circuit 210 performs control so as to interpolate the 256th pixel of a certain element group and the 16th pixel of an adjacent element group, the continuous 1 in the main scanning direction. A book exposure correction amount curve is obtained. This exposure amount calculation process is performed for each image density Cin. As a result, in step S307, 10 types of exposure amount correction curves with an image density Cin ranging from 10% to 100% are obtained.
Here, the image forming engine 110Y is described as an object, but it is a matter of course that an exposure correction amount curve corresponding to each color can be obtained by targeting each color of YMCK at the time of actual correction processing execution. .

  When the exposure correction amount curve is calculated for each color and each Cin, the control circuit 210 expands the exposure correction amount curve to 8 bits, that is, 256 gradations (step S308). The density unevenness detection pattern may be output in 256 gradations, but this is also not preferable in consideration of the processing load of the control circuit 210 as described above. Here, the intermediate gradation is interpolated based on the exposure correction amount curve for 10 gradations to obtain an exposure correction amount curve for 256 gradations. As an interpolation method, linear interpolation is used as in step S307. That is, the exposure correction amount for the above-described 800 pixels is connected to the actually measured image density Cin. In this connection, the exposure correction amount when Cin is 0% is zero. As a result of this connection processing, an exposure correction amount curve is obtained in all gradation regions where Cin is 0% to 100%. Finally, by dividing this region into 256 equal parts, an exposure correction amount curve corresponding to the image density of 256 gradations is obtained (step S309). The exposure correction amount curve thus obtained is stored in a RAM (not shown) by the control circuit 210.

  FIG. 5 is a relationship diagram between the image density Cin and the exposure correction amount in a certain pixel. It can be seen that the exposure correction amount increases as the image density increases. In the figure, the exposure correction amount is shown as a ratio to the exposure amount before correction. Further, the exposure correction amount curve in the entire density region in the main scanning direction obtained in step S308 is obtained by superimposing the curves shown in FIG. 5 in the directions orthogonal to the vertical axis and the horizontal axis, respectively.

  When the exposure correction amount curve for all pixels in the main scanning direction and all image densities is obtained as described above, the control circuit 210 thereafter outputs input image data obtained from the print control unit 230 to the paper 171. Further, an exposure correction amount is calculated for each pixel from the pixel value represented by the input image data and the exposure correction amount curve stored in the RAM, and the exposure correction based on the exposure correction amount is corrected by the laser driver 262. To instruct.

<Second Embodiment: Image Forming Apparatus>
In the above-described embodiment, the image data is handled as a multi-value image having a density gradation of 8 bits for each pixel. As already described, gradation expression includes area gradation method in addition to density gradation method. In this area gradation method, one pixel has a density of 1 bit, that is, 0% or 100%. Instead, gradation expression is performed with a plurality of pixels as a unit. In such a case, the image density cannot be determined only by obtaining the density data of one pixel, and the density unevenness cannot be corrected in the above-described form. Here, a second embodiment in which such a problem is solved will be described.

  FIG. 6 is a block diagram of the control unit 400 in the image forming apparatus 20 according to the second embodiment of the present invention. The image forming unit is equivalent to the image forming unit 100 according to the first embodiment described above. Also, in the same figure, portions that are the same as those in FIG.

  The control unit 400 according to the present embodiment is different from the first embodiment in that the control circuit 210 includes an L line buffer 401. The L line buffer 401 is a buffer that holds the binarized image data supplied from the image processing unit 260 for L lines in the sub-scanning direction. Based on the image data for L lines held in the L line buffer 401, the control circuit 210 calculates the image density for each pixel.

FIG. 7 is a conceptual diagram showing a method for calculating the image density Cin in the present embodiment.
The control circuit 210 forms on the density unevenness detection pattern 402 a matrix of N rows and M columns composed of M pixels in the main scanning direction and N (N ≦ L) lines in the sub scanning direction. This matrix is a unit representing density gradation in the present embodiment. For example, when the matrix is composed of 16 pixels × 16 lines, it is possible to express density of 256 gradations.

  First, the control circuit 210 averages pixel values (pixel density data) for each pixel included in the matrix. The averaged pixel value is the density of the first pixel of this matrix. For example, when the pixels are lit in a staggered manner on this matrix, the ratio of the lit pixels is 50%, so the density of the first pixel in this matrix is determined to be 50%. When the density of the first pixel is calculated, the control circuit 210 moves this matrix one pixel at a time in the FS direction. Similarly, the average value is calculated to obtain the image density of the first pixel of the matrix. When this matrix is sequentially moved in the FS direction and the moving average is calculated in the same manner, the density Cin is obtained for each pixel in the main scanning direction.

  The density for each pixel calculated as the average of the M × N pixel values also has density unevenness in the main scanning direction. Therefore, when the density Cin of each pixel is calculated, the control circuit 210 calculates the exposure correction amount. However, in this case, even if an attempt is made to correct the density of each pixel, it is not possible to correct a pixel that is not lit (the actual pixel value is zero). Therefore, the control circuit 210 refers to the density distribution of each pixel obtained in the main scanning direction (the average density distribution obtained by the moving average process), and for the region including the low density pixel, Density control is performed so as to increase the number of lit pixels in the included matrix. Similarly, in a region including pixels with high density, the number of lighting pixels in the matrix is reduced, and the density unevenness distribution in the main scanning direction is made uniform. Even if such density unevenness correction processing is performed, a change that changes the number of lines of the screen pattern as a whole (the number of lines per inch diagonal of the matrix) does not appear, and the image quality is not affected. Although the processing for correcting the density unevenness by increasing / decreasing the lit pixel has been described here, of course, the density unevenness correction is performed by performing the exposure amount correction for each of the lit pixels (100% density). Also good.

  The density unevenness correction processing in this embodiment needs to be performed for each type of screen pattern, but since the density is calculated as the average of the matrix, any screen pattern can be handled. In addition, by appropriately determining the size of this matrix, for example, by setting the matrix small when the number of screen lines is large and by setting the matrix large when the number of screen lines is small, the density calculation accuracy for each pixel can be improved. it can.

1 is a diagram illustrating a configuration of an image forming apparatus 10 according to a first embodiment of the present invention. It is a block diagram which shows the structure of the part relevant to the light quantity correction process in the embodiment. It is a figure which shows the density nonuniformity detection pattern used in the same process. It is a flowchart of the process. It is a figure explaining the exposure correction amount interpolation process which concerns on the same process. It is a block diagram which shows the structure of the part relevant to the light quantity correction process in 2nd Embodiment of this invention. It is a figure explaining the image density calculation process which concerns on the same embodiment. It is a figure which illustrates the main scanning direction density nonuniformity distribution before correction | amendment which concerns on the background art of this invention. It is a figure which illustrates the main scanning direction density nonuniformity distribution after the correction | amendment in the same technique.

Explanation of symbols

    DESCRIPTION OF SYMBOLS 10 ... Image forming apparatus (1st Embodiment), 20 ... Image forming apparatus (2nd Embodiment), 100 ... Image forming part, 110Y, 110M, 110C, 110K ... Image forming engine, 120 ... Photoconductor drum, 130 ... Charging device, 140 ... exposure device, 141 ... potential sensor, 150 ... developing device, 160 ... intermediate transfer member, 161 ... drive roll, 162 ... backup roll, 163 ... primary transfer roll, 170 ... paper tray, 171 ... paper, 172 ... Secondary transfer roll, 180 ... Fixing device, 181 ... Ejection unit, 200 ... Control unit (first embodiment), 210 ... Control unit, 220 ... Pattern forming unit, 230 ... Print control unit, 240 ... Image density control , 250: Image count unit, 260: Image processing unit, 261: Pulse width modulation circuit, 262: Laser driver, 270 ... Image density detection Output signal processing unit, 271 ... density sensor, 280 ... image reading device, 400 ... control unit (second embodiment), 401 ... L line buffer, 402 ... pattern for density unevenness detection.

Claims (6)

An image carrier having photoconductivity and a means for exposing the surface of the image carrier according to image data, wherein an exposure target area extending in the main scanning direction on the surface of the image carrier is exposed according to the image data. Exposure means for forming an electrostatic latent image corresponding to the image data on the surface of the image carrier by performing an operation while moving the exposure target area along a sub-scanning direction orthogonal to the main scanning direction; An image forming unit comprising: a developing unit that visualizes the electrostatic latent image on a surface of the image carrier; and an output unit that outputs a visible image of the surface of the image carrier to a recording medium;
When the exposure correction amount distribution data representing the distribution of the exposure correction amount depending on the combination of the density of the image represented by the image data and the position in the main scanning direction is acquired in advance, and image data to be output is given, Exposure correction amount determination means for determining an exposure correction amount corresponding to each position in the main scanning direction and corresponding to the density of the image represented by the image data based on the exposure correction amount distribution data;
An image forming apparatus comprising: an exposure amount control unit that controls an exposure amount in the exposure unit based on the exposure correction amount determined by the exposure correction amount determination unit. A pattern forming unit that gives image data of a density unevenness detection pattern whose density changes along the sub-scanning direction to the exposure unit;
An image reading device that reads the output pattern output from the output unit to the recording medium when image data of the density unevenness detection pattern is given to the exposure unit, and outputs the image data of the output pattern;
Conversion means for converting image data output from the image reading device into density data representing the density of each part of the output pattern on the recording medium;
Exposure correction amount distribution data is generated based on the target density of each part of the density unevenness detection pattern represented by the image data of the density unevenness detection pattern and the density of each part of the output pattern represented by the density data. The image forming apparatus according to claim 1, further comprising: an exposure correction amount distribution data generation unit. A pattern forming unit that gives image data of a density unevenness detection pattern whose density changes along the sub-scanning direction to the exposure unit;
Receiving means for receiving image data from an external image reading device;
Conversion means for converting the image data received by the receiving means into density data;
An exposure correction amount based on the target density of each part of the density unevenness detection pattern represented by the image data of the density unevenness detection pattern and the density of each part of the image represented by the density data obtained by the conversion means The image forming apparatus according to claim 1, further comprising: an exposure correction amount distribution data generation unit that generates distribution data. The image data is data representing the color of a pixel at each pixel position arranged in the main scanning direction and the sub-scanning direction,
2. The exposure correction amount is determined by the exposure correction amount distribution data generation unit and the exposure amount is controlled by the exposure control unit for each pixel color represented by the image data. Image forming apparatus. The image data is multi-value data representing pixel density at each pixel position arranged in the main scanning direction and the sub-scanning direction,
The image forming apparatus according to claim 1, wherein the exposure correction amount determining unit determines the exposure correction amount based on a density of each pixel represented by the image data. The image data is binary data representing on / off of pixels at each pixel position arranged in the main scanning direction and the sub-scanning direction,
The exposure correction amount determining means assumes, for each pixel position, a block for M pixels in the main scanning direction and N lines in the sub-scanning direction including the pixel position, and for the binary data in the ON state included in the block. The image forming apparatus according to claim 1, wherein the density of the pixel at the pixel position is estimated based on the number, and the exposure correction amount is determined based on the estimated density of each pixel.

Images