JP2001005245A - Color image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To realize a color image forming device which is low in price and capable of realizing an image of high print quality. SOLUTION: The result of the detection of a toner image based on a reference pattern generated by a regist pattern generating means 21 is transferred to an initial data setting means 31 from a pattern detecting means 14, and based on the comparison of the reference pattern and the toner image with each other, the value Py of an interspace between added pixels and the number Dy of added pixels are calculated. One value pixcnt of a pixel count by a pixel counting means 26 is added each time a clock signal clk rises. In a first comparison means 28, when the value pixcnt of the pixel count matches the value Py of the interspace between the added pixels, a pixel addition flag addenb becomes valid and pixels are added to an input video data Vy. A second comparison means 29 terminates the pixel addition when the number of the pixels added to the input video data Vy mataches the number Dy of the added pixels.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrophotographic color image forming apparatus having a plurality of photosensitive members, and more particularly to a color image forming apparatus having a function of correcting a difference in image width of each color in the main scanning direction. It is.

[0002]

2. Description of the Related Art Conventionally, in an image forming apparatus employing an electrophotographic system, a photoconductor as an image carrier is charged by a charger, and the charged photoconductor is irradiated with light in accordance with image information to form a latent image. An image is formed, the latent image is developed by a developing device, and the developed toner image is transferred to a sheet material or the like to form an image.

On the other hand, with the colorization of images, a plurality of image forming stations for performing the above-described image forming processes are provided, and each color image of a cyan image, a magenta image, a yellow image, and preferably a black image is formed. A tandem-type color image forming apparatus that forms a full-color image by superposing and transferring each color image onto a sheet material at a transfer position of each image carrier is also proposed. Such a tandem-type color image forming apparatus has an image forming unit for each color, which is advantageous for speeding up.

[0004] However, the tandem type color image forming apparatus has a problem in how to properly perform registration (registration) of each image formed in different image forming units. 4 transferred to sheet material
This is because a shift in the color image forming position eventually appears as a position shift or a change in color tone.

One of the causes of the displacement of the transferred image is as follows.
There is a difference in the image width of each color in the main scanning direction. This is because the optical path length from the scanning optical system to the photosensitive drum of the image forming station becomes different for each color due to replacement of the image forming station, a change in the installation state of the color image forming apparatus, and a change in the temperature or humidity in the color image forming apparatus. The main cause is the difference between them.

Therefore, in the direction perpendicular to the main scanning direction,
For example, a reference pattern (hereinafter, referred to as a resist pattern) such as a plurality of straight lines is drawn on a sheet material or the like for each color, a position where the resist pattern is drawn is detected by a sensor, and an expected position at which the resist pattern is drawn and an actual position are drawn. Calculate the amount of deviation from the position where the resist pattern was drawn,
It has been proposed to perform alignment of images of respective colors in accordance with the shift amount.

Next, a conventional method for keeping the image width of each color in the main scanning direction constant will be described.

FIG. 13 is a schematic diagram showing a means for detecting a displacement of a resist pattern.

As shown in FIG. 13, a pair of pattern detecting means is provided near both ends on a line perpendicular to the conveying direction A of the intermediate transfer belt 12 on which a toner image is transferred from an image carrier (not shown). 14 are arranged. The pair of pattern detection units 14 detect the position of the toner image formed on the intermediate transfer belt 12 in the main scanning direction.

In order to examine how the image width in the main scanning direction differs for each color, toner image expected positions 38a, 38b, 39a, 39, which are target positions where toner images are formed, are examined.
b, 40a, 40b, 41a, 41b are compared with actual toner image formation positions.

The expected toner image positions 38a and 38b are set at a black main scanning start position and a black main scanning end position, respectively, and are straight lines having a fixed length along the conveyance direction A of the intermediate transfer belt 12. Similarly, expected toner image position 3
9a and 39b are cyan and toner image expected positions 40a and 40, respectively.
b denotes magenta and expected toner image positions 41a and 41b
Is a straight line having a certain length along the conveyance direction A of the intermediate transfer belt 12, which is set at each of the main scanning start position and the main scanning end position of yellow.

FIGS. 14A to 14H show toner images formed on the intermediate transfer belt 12 and expected toner image positions 38a, 38b, 39a, 39b, 40a, 40b, 4 in FIG.
It is a figure showing a gap with 1a and 41b.

FIGS. 14A and 14B show the deviation of the black scanning start position and the deviation of the scanning end position, respectively. The toner image 42a of the resist pattern formed on the intermediate transfer belt 12 is shown in FIG. , 42b are scanning start deviations Xb with respect to the expected toner image positions 38a, 38b.
1 and a scanning end shift Xb2. Assuming that the positive directions of the scanning start deviation Xb1 and the scanning end deviation Xb2 are the directions of the arrows in the figure, Xb1-Xb2 is the difference between the target image width and the actual image width (hereinafter, referred to as main scanning magnification error). Becomes Further, based on the relationship between the resolution in the main scanning direction and the number of pixels in the main scanning direction, a pixel-converted main scanning magnification error Eb obtained by converting the black main scanning magnification error Xb1-Xb2 into the number of pixels is obtained.

FIGS. 14 (c) and 14 (d) show the deviation of the scanning start position and the deviation of the scanning end position of cyan.
4 (e) and 14 (f) show the shift of the magenta scan start position and the scan end position, and FIGS. 14 (g) and 14 (h) show the shift of the yellow scan start position and the shift of the scan end position. Are respectively shown. Similar to the black main scanning magnification error Xb1-Xb2, Xc1-Xc2
Is a main scanning magnification error of cyan, Xm1-Xm2 is a main scanning magnification error of magenta, and Xy1-Xy2 is a main scanning magnification error of yellow. Pixel conversion main scanning is performed by converting each main scanning magnification error into the number of pixels. Magnification errors Ec, E
m and Ey are determined.

Table 1 shows pixel-converted main scanning magnification errors Eb,
An example of Ec, Em, and Ey is shown. In this case, the main scanning output resolution is 1200 dpi, and the main scanning image width is 9600 pixels.

[0016]

[Table 1]

As can be seen from Table 1, since the pixel-converted main scanning magnification errors Eb, Ec, Em, and Ey are different from each other, the image width of each color is different. In this case, each image width of black, cyan, magenta and yellow is 9598
Pixels, 9600 pixels, 9601 pixels, and 9603 pixels.

FIG. 15 is a block diagram of a conventional color shift correcting means, and FIG. 16 is a diagram showing clock waveforms generated by a plurality of clock generating means of the color shift correcting means of FIG. The main scanning magnification error is corrected by the color shift correcting unit.

As shown in FIG. 15, the conventional color misregistration correction means includes a CPU (Central Processing Unit) 50, a clock selection means 37, a plurality of clock generation means 38, and image data output means 32a, 32b, 32c for each color. , 32d.

The input video data of each color is applied to image data output means 32a, 32b, 32c, 32d of each color. The scanning start deviations Xb1, Xc1, and Xm of each color detected by the pair of pattern detection units 14 in FIG.
1, Xy1 and scan end shifts Xb2, Xc2, Xm
2 and Xy2 are given to the CPU 50. The CPU 50 converts the pixel-converted main scanning magnification errors Eb, Ec,
Em and Ey are calculated, and the pixel conversion main scanning magnification errors Eb, Ec, Em and Ey are given to the clock selecting means 37 in FIG. The clock selecting means 37 selects a clock cycle according to the plurality of image data output means 32a, 32b, 32c, 32d from the clock generating means 38 for generating a plurality of different clock cycles.

As shown in FIG. 16, the plurality of clock generating means 38 of this embodiment can generate seven data clocks. clk4 is a reference clock, which is +3 pixels, +2 pixels, +1 pixel, -1 pixel, -2
The clocks having an image width of pixel and -3 pixels are cl, respectively.
k1, clk2, clk3, clk5, clk6, cl
k7. In FIG. 16, each clock cycle T1, T
2, T3, T5, T6, and T7 are respectively T1 = T4 × 9603/9600 T2 = T4 × 9602/9600 T3 = T4 × 9601/9600 T5 = T4 × 9599/9600 T6 = T4 × 9598/9600 T7 = T4 × 9597/9600. The clock selecting means 37 in FIG. 15 sends cl to the black image data output means 32a based on the pixel conversion main scanning magnification errors Eb, Ec, Em and Ey shown in (Table 2).
k6, clk4, cyan image data output means 32b
The main scanning magnification error can be corrected by selecting clk3 for the magenta image data output unit 32c and clk1 for the yellow image data output unit 32d.

[0022]

[Table 2]

[0023]

However, in the above-mentioned conventional color image forming apparatus, when a main scanning magnification error occurs ± N pixels, a clock of 2 × N + 1 system is required. Therefore, this method has led to an increase in cost.

The present invention has been made to solve these problems, and an object of the present invention is to provide a color image forming apparatus capable of obtaining a low-cost image with high print quality.

[0025]

A color image forming apparatus according to the present invention comprises: a plurality of toner image forming means for forming a plurality of color toner images based on a plurality of image data divided for each color; A transfer unit that forms a composite image by sequentially superimposing a plurality of color toner images formed by the toner image forming unit on a transfer material; and detecting a shift amount of an image width of the plurality of color toner images transferred to the transfer material. A shift amount detecting unit, and a shift amount correcting unit that adds a pixel to each of the plurality of color image data based on the shift amount detected by the shift amount detecting unit so that the image widths of the plurality of color toner images match. It is provided.

In the color image forming apparatus according to the present invention, a plurality of color toner images are formed by a plurality of toner image forming means, and a shift amount of the image width of the plurality of color toner images is detected by a shift amount detecting means. . The shift amount correction unit adds a pixel to each of the plurality of color image data based on the shift amount of the image width of the plurality of color toner images so that the image widths of the plurality of color toner images match. As a result, even when the deviation amount of the image widths of the toner images of a plurality of colors becomes large due to aging or the like, the deviation amount can be corrected only by increasing the number of pixels to be added. Also, since the image widths of the toner images of a plurality of colors match,
An image with high print quality can be obtained. Therefore,
Even if the amount of deviation of the image width of the toner image of a plurality of colors becomes large due to aging or the like, an image with high print quality can be obtained without increasing the cost.

[0027]

According to a first aspect of the present invention, there is provided a color image forming apparatus, comprising: a plurality of toner image forming means for forming a plurality of color toner images based on a plurality of image data divided for each color; Transfer means for sequentially superimposing a plurality of color toner images formed by the toner image forming means on a transfer material to form a composite image, and detecting a shift amount of an image width of the plurality of color toner images transferred to the transfer material. A shift amount detecting unit, and a shift amount correcting unit that adds a pixel to each of the plurality of color image data so that the image widths of the plurality of color toner images match based on the shift amount detected by the shift amount detecting unit. It is provided with.

In the color image forming apparatus according to the present invention, a plurality of color toner images are formed by a plurality of toner image forming means, and a shift amount of the image width of the plurality of color toner images is detected by a shift amount detecting means. . The shift amount correction unit adds a pixel to each of the plurality of color image data based on the shift amount of the image width of the plurality of color toner images so that the image widths of the plurality of color toner images match. The toner images of a plurality of colors formed based on the image data with the added pixels are sequentially superimposed on a transfer material by a transfer unit to form a composite image.

Since the image widths of the toner images of a plurality of colors are matched by adding a pixel to each of the image data of a plurality of colors, when the amount of deviation of the image widths of the toner images of a plurality of colors becomes large due to aging or the like. However, the shift amount can be corrected only by increasing the number of pixels to be added. Further, since the image widths of the toner images of a plurality of colors match, an image with high print quality can be obtained. As a result, even when the deviation amount of the image width of the toner images of a plurality of colors becomes large due to aging or the like, an image with high print quality can be obtained without increasing the cost.

According to a second aspect of the present invention, in the color image forming apparatus according to the first aspect of the present invention, the shift amount detecting means separates each color corresponding to the image width in the main scanning direction. Reference pattern generating means for generating a plurality of reference patterns, and pattern detecting means for detecting a plurality of toner images transferred onto a transfer material by a transfer means based on the plurality of reference patterns generated by the reference pattern generating means. Based on a comparison between the plurality of toner images detected by the pattern detection means and the reference pattern generated by the reference pattern generation means, so that the image widths of the plurality of color toner images in the main scanning direction match. Pixel number calculation means for calculating the number of pixels to be added to the image data, wherein the shift amount correction means calculates the number of pixels based on the number of pixels calculated by the pixel number calculation means. In each of several colors image data is obtained comprising a plurality of pixels additional means for adding a pixel.

In this case, the toner images of a plurality of colors formed based on the plurality of reference patterns generated by the reference pattern generating means are transferred onto the transfer material by the transfer means. The plurality of toner images on the transfer material are detected by the pattern detecting means. The pixel number calculation unit compares the reference pattern generated by the reference pattern generation unit with the plurality of toner images detected by the pattern detection unit so that the image widths of the plurality of color toner images in the main scanning direction match. First, the number of pixels to be added to the image data of a plurality of colors is calculated. The plurality of pixel adding means adds a pixel to each of the plurality of color image data based on the number of pixels to be added.

As described above, by comparing the reference pattern generated for each color by the reference pattern generating means with the toner image based on the reference pattern, the number of pixels to be added to each of the plurality of color image data is obtained. be able to.

According to a third aspect of the present invention, in the color image forming apparatus according to the second aspect of the present invention, each of the plurality of pixel adding means should be added from a pixel number calculating means. A pixel interval calculating unit that calculates a pixel interval to be added based on the number of pixels, a first pixel counting unit that counts pixels of image data, and a pixel interval calculating unit based on a count value of the first pixel counting unit. Pixel insertion means for inserting pixels into the image data for each calculated pixel interval, second pixel counting means for counting the number of pixels inserted by the pixel insertion means,
Terminating means for terminating the pixel insertion by the pixel inserting means when the count value of the second pixel counting means coincides with the number of pixels calculated by the pixel number calculating means.

In this case, based on the number of pixels to be added provided by the number-of-pixels calculating means, the pixel interval calculating means calculates the pixel interval to be added. The pixel inserting unit inserts a pixel into the image data at each pixel interval calculated by the pixel interval calculating unit based on the count value of the first pixel counting unit. Further, the second pixel counting means counts the number of pixels inserted into the image data, and when the count value of the second pixel counting means coincides with the number of pixels calculated by the pixel number calculating means, the ending means displays the image. The insertion of the pixel into the data ends.

This makes it possible to insert pixels into the image data at the pixel interval calculated by the pixel interval calculating means and the number of pixels calculated by the pixel number calculating means.

According to a fourth aspect of the present invention, in the color image forming apparatus according to the third aspect of the present invention, each of the plurality of pixel adding means scans an offset value which varies depending on a scanning line. The apparatus further comprises an offset generating means to be applied to the first pixel counting means before starting.

In this case, the first pixel counting means is provided with an offset value which varies depending on the line to be scanned from the offset generating means before the start of scanning. This allows
Since the pixels inserted into the image data are shifted by the offset value for each line, no pixels are inserted adjacent to the image data, and the occurrence of an unnatural pattern is suppressed. Therefore, a color image with high print quality can be obtained.

According to a fifth aspect of the present invention, in the color image forming apparatus according to the third aspect, the pixel intervals calculated by the pixel interval calculating means are irregular. It is.

In this case, the intervals between the pixels inserted into the image data become irregular. As a result, pixels are irregularly inserted into the image data, so that unnatural patterns in all directions are eliminated, and a color image with higher print quality can be obtained.

According to a sixth aspect of the present invention, there is provided a color image forming apparatus according to any one of the second to fifth aspects of the present invention, wherein the pixel added by each of the plurality of pixel adding means. Is higher than the resolution of the image data of a plurality of colors given to the plurality of pixel adding means.

In this case, since pixels are added at a resolution higher than the resolution of the image data of a plurality of colors given to each of the plurality of pixel adding means, the image width in the main scanning direction can be corrected with high accuracy. .

(Embodiment 1) Hereinafter, Embodiment 1 of the present invention will be described. FIG. 1 is a configuration diagram of a color image forming apparatus according to Embodiment 1 of the present invention.

First, a process for obtaining a color image will be described with reference to FIG.
This will be described with reference to FIG.

In FIG. 1, the color image forming apparatus
One image station 1a, 1b, c, 1d is arranged, and each image station 1a, 1b, 1c, 1d has a photoreceptor 2a, 2b, 2c, 2d as an image carrier. Charging means 3a, 3b, 3
c, 3d, developing means 4a, 4b, 4c, 4d, cleaning means 5a, 5b, 5c, 5d, and exposure means 6a, 6b of a scanning optical system for irradiating each photosensitive drum with light corresponding to image information. , 6c, 6d and transfer portions 8a, 8b, 8c, 8d in the transfer means 7 are arranged respectively.

Here, the exposure means 6a, 6b, 6c, 6d
Outputs light 9a, 9b, 9c, 9d corresponding to a yellow image, a magenta image, a cyan image, and a black image, and the image stations 1a, 1b, 1c, 1d output a yellow image, a magenta image, a cyan image, and a black image, respectively. To form Each image station 1a, 1
b, 1c, 1d, the photosensitive members 2a, 2b,
An unsupported belt-shaped intermediate transfer belt 12 supported by support rollers 10 and 11 is disposed below 2c and 2d.
Move in the direction of arrow A. These operations are controlled by control means (not shown).

Further, the color image forming apparatus corrects the image width of each color in the main scanning direction by using a straight line (hereinafter referred to as a resist pattern) as a reference of the image width in the main scanning direction on both sides of the intermediate transfer belt 12. The unit has a resist pattern generating means 21 for generating a signal for forming each color. Above the intermediate transfer belt 12, the intermediate transfer belt 1
A pair of pattern detection means 14 for detecting a resist pattern formed on both sides of the upper surface 2 is provided (see FIG. 13). Based on the detection results obtained by the pair of pattern detection means 14, input video data Vy, Vm,
In order to correct Vc and Vb, color shift correction means 13a, 1
3b, 13c and 13d are input video data Vy, Vm,
It is provided corresponding to each of Vc and Vb.

The sheet material 17 stored in the sheet cassette 16 is fed by a sheet feeding roller 18 and is discharged to a sheet discharge tray (not shown) via a sheet material transfer roller 18 and a fixing unit 20. You.

With the above arrangement, first, the intermediate transfer belt 12 is controlled based on the resist pattern data Ry, Rm, Rc, Rb generated by the resist pattern generating means 21.
A resist pattern is formed thereon. The pair of pattern detecting means 14 sequentially detects the resist pattern corresponding to each color, and outputs the detection result to the color shift correcting means 13a, 13b, 1
3c and 13d. Color shift correction means 13
In a, 13b, 13c, and 13d, input video data Vy, Vm, V
Correction is performed for c and Vb, respectively, and output video data Qy, Qm, Qc, and Qb are output.

On the basis of the output video data Qb output from the black color misregistration correcting means 13d, the black of image information is recorded on the photosensitive member 2d by a known electrophotographic process means such as a charging means 3d and an exposing means 6d of the image station 1d. After the latent image of the component color is formed, the latent image is visualized as a black toner image by a developing material having black toner by the developing unit 4d, and the black toner image is transferred to the intermediate transfer belt 12 by the transfer unit 8d. Is done.

On the other hand, while the black toner image is being transferred to the intermediate transfer belt 12, a latent image of a cyan component color is formed in the image station 1c, and a cyan toner image of cyan toner is obtained by the developing means 4c. At 8c, the toner image is transferred to the intermediate transfer belt and is superimposed on the black toner image previously transferred onto the intermediate transfer belt 12.

Thereafter, the magenta toner image and the yellow toner image are formed in the same manner, and when the superposition of the four color toner images on the intermediate transfer belt 12 is completed, the paper feed cassette Sheet transfer roller 1 on a sheet material 17 such as paper fed from
9, the toner images of four colors are collectively transferred and conveyed,
The sheet is heated and fixed by the fixing unit 20, and a full-color image is obtained on the sheet material 17.

Each of the photosensitive members 2 whose transfer has been completed
a, 2b, 2c, 2d to cleaning means 5a, 5
The remaining toner is removed at b, 5c and 5d, and the printing operation is completed in preparation for the next image formation to be performed subsequently.

Next, a method for making the image width of each color constant will be described.

In the prior art, the pixel-converted main scanning magnification errors Eb, Ec, Em, and Ey in (Table 1) were obtained based on the concept shown in FIGS. Also in the present embodiment, pixel conversion main scanning magnification errors Eb, Eb
Find c, Em, and Ey. The results obtained are shown in (Table 2). In this case, the main scanning output resolution is 1200 dpi, and the main scanning image width is 9600 pixels.

Pixel-converted main scanning magnification errors Eb, Ec, E
With magenta having the largest image width among m and Ey as a reference image width, the number of additional pixels Db, Dc, and Dy for black, cyan, and yellow are obtained. In this case, the reference magenta pixel addition number Dm is zero. The results are shown in (Table 2). By adding pixels in the main scanning direction by the number of added pixels Db, Dc, and Dy without adding pixels to magenta, it is possible to equalize the image widths of the four colors in the main scanning direction. Can be corrected.

Next, the main-scanning image width of 9600 pixels is divided by the pixel addition numbers Db, Dc and Dy to obtain black, cyan and yellow pixel addition interval values Pb, Pc and Py. The results are shown in (Table 2). In this case, pixels are added at different intervals for each color. As mentioned above,
Since no pixel is added to magenta, the pixel addition interval value Pm of magenta is 0.

FIGS. 2A to 2D are diagrams for explaining rules for determining the level of a pixel to be added.

FIGS. 2 (a), 2 (b) and 2 (c)
As shown in (2), when at least one of the pixels before and after the point where the pixel is added is on, the pixel level of the pixel to be added is turned on. As shown in FIG. 2D, when both the pixels before and after the point to add a pixel are off, the pixel level of the pixel to be added is turned off.

Next, the color misregistration correction means 13a, 13 shown in FIG.
b, 13c, 13d input video data V
y, Vm, Vc, and Vb will be described. Here, the input video data Vy given to the color shift correcting means 13a will be described, but the color shift correcting means 13b, 13c, 13d.
The same processing is performed on the input video data Vm, Vc, and Vb provided to.

FIG. 3 is a diagram for explaining the relationship between the input video data Vy of FIG. 1 and the gradation modulation input data.

As shown in FIG. 3, in synchronism with the dot clock of the image processing section, the gradation is 8 bits and the main scanning data resolution is 6 bits.
00 dpi gradation modulation input data Ay is provided to a gradation processing unit (not shown). In the gradation processing unit, the gradation modulation input data Ay is converted into 2 bits by, for example, an organized dither method.
And outputs the gradation-modulated output data By to PS (parallel-serial) conversion means (not shown). The PS conversion means converts the gradation modulation output data By from parallel to serial, and in synchronization with the clock signal clk generated by the clock generation means 22 shown in FIG. 1, the gradation is 1 bit and the main scanning data resolution is 1200 dpi.
Is input to the color misregistration correction means 13a.

Next, the color misregistration correction means 13a, 13b, 1
The configuration and operation of 3c and 13d will be described. Each of the color misregistration correction means 13a, 13b, 13c, 13d
Since they have the same configuration, the color misregistration correction unit 13a will be representatively described here. In Table 2, the operation of the magenta color misregistration correction means 13b that does not require the addition of pixels is different from the operation of the other color misregistration correction means 13a, 13c, and 13d.

FIG. 4 is a block diagram of the color shift correcting means 13a of FIG. 1, and FIG. 5 is a timing chart showing the operation of the color shift correcting means 13a of FIG.

As shown in FIG. 4, the color shift correcting means 13a
Are initial data setting means 31 and image data output means 3
0, storage means 23, pixel addition interval setting means 27, pixel counting means 26, pixel addition number setting means 25, pixel addition number counting means 24, first comparing means 28 and second
Of comparison means 29.

The detection result of the yellow resist pattern detected by the pattern detecting means 14 is given to the initial data setting means 31. The initial data setting means 31
Pixel addition interval value Py and pixel addition number D shown in Table 2
Before the vertical print area becomes valid, the pixel addition interval value Py is given to the pixel addition interval setting means 27, and the pixel addition number Dy is given to the pixel addition number setting means 25 before the vertical printing area becomes effective. further,
The initial data setting means 31 gives 0 to the pixel counting means 26 and the pixel addition number counting means 24 before the horizontal printing area becomes effective.

In the magenta color misregistration correction means 13b, the initial data setting means 31
Is given to the pixel counting means 26, and 1 is given to the pixel addition number counting means 24. This allows
The color shift correction unit 13b recognizes that it is not necessary to add a pixel.

The pixel addition interval Py is given from the pixel addition interval setting means 27 to the first comparison means 28, and the pixel addition number D
y is given from the pixel addition number setting means 25 to the second comparison means 29, respectively. The first comparing means 28 outputs a pixel addition flag addenb based on the pixel addition interval value Py and the pixel count value. The pixel addition flag “addenb” is given to the image data output unit 30 and the pixel addition number counting unit 24.

As shown in FIG. 5, when the horizontal printing area HSZ is in the valid state (“1”), the pixel count value pixcnt in the pixel counting means 26 is changed every time the clock signal clk generated by the clock generating means 22 rises. Is incremented by one. Pixel count value p
The ixcnt is provided from the pixel counting unit 26 to the first comparing unit 28, and the first comparing unit 28 compares the pixel count value pixcnt with the pixel addition interval value Py.

If the pixel count value pixcnt is smaller than the pixel addition interval value Py, the pixel addition flag adde
nb becomes invalid (low level). When the pixel count value pixcnt becomes equal to the pixel addition interval value Py, the pixel addition flag addenb becomes valid (high level). Then, the pixel count value pixcnt
Is reset, and the addition starts from 1 again.

On the other hand, the input video data Vy applied to the image data output means 30 is applied to the storage means 23 as the write data WD when the write control signal WCT is in the valid state ("1"). The storage unit 23 stores, for example, a FIFO (First In First Out).
It is of the system. Thereby, the image data output means 3
0 to the read control signal RC applied to the storage means 23
When T is in a valid state (high level), read data RD is supplied from the storage unit 23 to the image data output unit 30 in the order of writing of the write data WD supplied from the image data output unit 30 to the storage unit 23.

When the pixel addition flag addenb given from the first comparing means 28 to the image data output means 30 becomes valid (high level), the image data output means 30
Read control signal RCT applied to storage means 23 from
Becomes invalid (low level). Thus, the image data output unit 30 stops reading from the storage unit 23. In this case, the read signal RD given to the image data output means 30 holds the previous data.

The read data latch included in the image data output means 30 stores the read data RD from the storage means 23 when the pixel addition flag addenb is in an invalid state.
Is written, but when the pixel addition flag addenb becomes valid, the previous data written in the read data latch is retained without writing the read data RD from the storage unit 23.

Next, when the pixel addition flag addenb is in an invalid state, the image data output means 30 outputs the value held in the read data latch to the output video data Q.
Output as y. Also, the pixel addition flag addenb
Is valid, the image data output means 30 sets the value of the read data latch in accordance with the rule described with reference to FIG. 2 and outputs it as output video data Qy.

In the pixel addition number counting means 24,
When the pixel addition flag addenb becomes valid, the pixel addition count value addcnt is incremented by one. The pixel addition count value addcnt is provided from the pixel addition number counting unit 24 to the second comparison unit 29, and the second comparison unit 29 compares the pixel addition count value addcnt with the pixel addition number Dy. Pixel additional count value a
When ddcnt becomes equal to the pixel addition number Dy, an end signal indicating that the pixel addition has been completed is given from the second comparing means 29 to the image data output means 30. Thus, the addition of the pixel for yellow is completed, and the remaining data held in the read data latch is output as output video data Qy as it is.

FIG. 6 is a diagram showing the relationship between the horizontal print area and the output video data horizontal print area.

As shown in FIG. 6, the write control signal WC
T is always in the valid state while the horizontal print area HSZ is in the valid state. Therefore, the horizontal print area HS
While Z is in the valid state, the input video data Vy is written to the storage means 23.

On the other hand, the read control signal RCT is in the valid state when the write control signal WCT is in the valid state, but when the pixel addition flag addenb is in the valid state, the read control signal RCT has the same period and the same period as the valid state of the pixel addition flag addenb. It becomes invalid at the timing and is added to the write control signal WCT in the valid state. Since the number of times that the pixel addition flag addenb becomes valid is the same as the number of pixel additions Dy, the read control signal RCT remains in the valid state for a period corresponding to the number of pixel additions Dy even when the valid state of the horizontal print area HSZ ends. Is extended. As a result, the output video data horizontal printing area HSZOUT, which indicates the area where the output video data Qy is output, is also extended by a period corresponding to the number of added pixels Dy, so that the image width of the yellow in the main scanning direction can be corrected. .

As described above, according to the color image forming apparatus of the present embodiment, even when the main scanning magnification error becomes large due to aging or the like, the image width of each color in the main scanning direction can be changed without changing the circuit. Can be corrected. This allows
An image with high printing quality can be obtained without increasing the cost.

In the color image forming apparatus of the present embodiment, pixels are added at the same resolution as that of the input video data to enable highly accurate correction of the image width in the main scanning direction. By adding pixels with a resolution equal to or higher than the resolution of, the image width in the main scanning direction can be corrected with higher accuracy.

(Embodiment 2) Next, Embodiment 2 of the present invention will be described. The color image forming apparatus according to the second embodiment differs from the color image forming apparatus according to the first embodiment in the configuration of the color misregistration correction unit. FIG. 7 is a block diagram of the color misregistration correction unit 13a according to the second embodiment of the present invention.

The configuration of the color shift correcting means 13a in the second embodiment shown in FIG. 7 is different from the structure of the color shift correcting means 13a in the first embodiment shown in FIG. Is merely added. The offset value OFS is generated by the offset generating means 35 and is supplied to the adder 36. In the adder 36, the offset value OFS is added to 0 given from the initial data setting means 31, and the offset value OFS is provided from the adder 36 to the pixel counting means 26 before the horizontal print area HSZ becomes valid.

For example, the offset value OFS may be a value obtained by the following equation: OFS = (N−4 × Int (N / 4)) × 7 (1) based on the line number N of the line currently being scanned. Good. Here, Int (N /
4) shows an integer part of N / 4. According to the above equation, the offset generating means 35 sets 0, 7, 1 according to the line number.
4, 21 occur repeatedly in this order.

FIG. 8A shows the color shift correcting means 13a shown in FIG.
8 is a timing chart at the start of the horizontal print area, FIG.
7B is a timing chart in the horizontal printing area of the color misregistration correction unit 13a in FIG.

As shown in FIG. 8A, the horizontal print area H
If the horizontal synchronizing signal HSYNC becomes valid (high level) before SZ becomes valid, the offset value OFS is given to the pixel counting means 26. As a result, the initial value of the pixel count value pixcnt becomes the offset value OFS. Then, when the horizontal print area HSZ is enabled, the pixel count value pixcnt is incremented by one at every rising edge of the clock signal clk.

As shown in FIG. 8B, when the pixel count value pixcnt becomes equal to the pixel addition interval value Py, the pixel addition flag addenb becomes valid. Thereafter, the pixel count value is reset and the addition is started from 1. Subsequent processing is the same as in the first embodiment.

Next, the difference between the points where a pixel is added in the first embodiment and the second embodiment will be described using a specific example.

FIG. 9A is an enlarged view of an image before correction.
FIG. 9B is an enlarged view of the image after correction according to the first embodiment of the present invention, and FIG. 9C is an enlarged view of the image after correction according to the second embodiment of the present invention. The pixel addition point in FIG. 9B is determined based on the offset value OFS obtained from Expression (1).

Pixels added by the method of the first embodiment shown in FIG. 9A are arranged in a line in a direction perpendicular to the main scanning direction. On the other hand, the second embodiment shown in FIG.
The pixel added by the above method is added at a different point depending on the line number. That is, pixels are added while being shifted by the offset value OFS for each line, thereby achieving correction of the image width in the main scanning direction.

As described above, according to the color image forming apparatus of this embodiment, since the pixel addition point changes for each line, it is possible to suppress the occurrence of a pattern in the direction perpendicular to the scanning direction, and to achieve high print quality. A color image can be obtained.

(Embodiment 3) Next, Embodiment 3 of the present invention will be described. The color image forming apparatus according to the third embodiment differs from the color image forming apparatus according to the first embodiment in the configuration of the color misregistration correction unit. FIG. 10 is a block diagram of the color shift correcting means 13a according to the third embodiment of the present invention, and FIG. 11 is a timing chart showing the operation of the color shift correcting means 13a of FIG.

The structure of the color shift correcting means 13a in the third embodiment shown in FIG. 10 is different from the structure of the color shift correcting means 13a in the first embodiment shown in FIG. , Random data generating means 3
9 means that the pixel addition interval value Py which is a random value is given to the pixel addition interval setting means 27.

As shown in FIG. 11, when the pixel addition interval value Py given to the pixel addition interval setting means 27 becomes equal to the pixel count value pixcnt, the pixel addition flag addenb becomes valid. Then, the first embodiment
After the processing described in is performed, pixels are added to the output video data Qy.

When the pixel addition flag addenb becomes valid, the next pixel addition interval value Py is given from the random data generation means 39 to the pixel addition interval setting means 27, and the pixel count value pixcnt is reset and added from one. Start. Subsequent processing is the same as in the first embodiment.

Since the pixel addition interval value Py generated by the random data generation means 39 is a random value, a different pixel addition interval value Py is supplied to the pixel addition interval setting means 27 almost every time the pixel addition flag addenb rises. . Therefore, the interval between the added pixels becomes irregular.

FIG. 12A is a diagram showing pixel addition interval values Py, Pm, Pc, and Pd of each color on the first line.
(B) is a pixel addition interval value Py, P of each color of the second line.
It is a figure which shows m, Pc, Pd.

As shown in FIGS. 12 (a) and 12 (b), before the horizontal print area HSZ becomes effective, the random data generating means 39 of each of the color misregistration correcting means 13a, 13c, 13d First pixel addition interval value Py,
Pc and Pb are set. Then, each time a pixel is added, a new pixel addition interval value Py, Pc, Pb is set.
As described above, the random data generating unit 39 sets different pixel addition interval values Py, Pc, and Pb each time a pixel is added in the horizontal print area HSZ. Similarly, the pixel addition interval value P which is a random value in different lines
b, Pm, and Py are set.

The pixel addition interval value Pm of magenta which does not require the addition of a pixel is kept at 0.

As described above, according to the color image forming apparatus of the present embodiment, since the intervals at which the pixels are added are random, the occurrence of patterns in all directions is eliminated, and a color image with higher print quality is obtained. be able to.

[0099]

As described above, according to the present invention, it is possible to correct the image width of each color in the main scanning direction without changing the circuit even when the main scanning magnification error becomes large due to aging or the like. Become. Thereby, a color image with high print quality can be obtained without increasing the cost.

Furthermore, by regularly changing the pixel addition points for each line, it is possible to suppress the occurrence of a pattern in the direction perpendicular to the main scanning direction, so that a color image with high print quality can be obtained. Furthermore, by making the pixel addition intervals random, generation of patterns in all directions is eliminated, and a color image with higher print quality can be obtained.

Further, by adding pixels with a resolution higher than the resolution of the input video data, the image width in the main scanning direction can be corrected with high accuracy.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of a color image forming apparatus according to a first embodiment of the present invention.

FIGS. 2A to 2D are diagrams for explaining rules for determining the level of a pixel to be added;

FIG. 3 is a diagram for explaining a relationship between input video data and gradation modulation input data in FIG. 1;

FIG. 4 is a block diagram of a color misregistration correction unit in FIG. 1;

FIG. 5 is a timing chart showing the operation of the color misregistration correction unit of FIG. 4;

FIG. 6 is a diagram showing a relationship between a horizontal print area and an output video data horizontal print area.

FIG. 7 is a block diagram of a color misregistration correction unit according to the second embodiment of the present invention.

8A is a timing chart at the start of a horizontal printing area of the color misregistration correcting means of FIG. 7; FIG. 8B is a timing chart of the color misregistration correcting means of FIG.

9A is an enlarged view of an image before correction. FIG. 9B is an enlarged view of an image after correction according to the first embodiment of the present invention. FIG. 9C is an enlarged view of an image after correction according to the second embodiment of the present invention.

FIG. 10 is a block diagram of a color misregistration correction unit according to a third embodiment of the present invention.

FIG. 11 is a timing chart showing the operation of the color misregistration correction unit of FIG.

12A is a diagram illustrating a pixel addition interval value of each color on a first line. FIG. 12B is a diagram illustrating a pixel addition interval value of each color on a second line.

FIG. 13 is a schematic diagram showing a unit for detecting a displacement of a resist pattern.

14A is a diagram illustrating a deviation between a black toner image at a scanning start position and an expected toner image position. FIG. 14B is a diagram illustrating a deviation between a black toner image and a toner image expected position at a scanning end position. (D) A diagram showing the deviation between the cyan toner image and the expected toner image position at the scanning start position. (D) A diagram showing the deviation between the cyan toner image and the expected toner image position at the scanning end position. (E) Magenta at the scanning start position. (F) A diagram showing a deviation between the magenta toner image and the expected toner image position at the scanning end position. (G) A yellow toner image and a toner image at the scanning start position. (H) A diagram showing the deviation between the yellow toner image and the expected toner image position at the scanning end position.

FIG. 15 is a block diagram of a conventional color shift correction unit.

FIG. 16 is a diagram showing a clock waveform generated by a plurality of clock generating means in FIG.

[Explanation of symbols]

 1a, 1b, 1c, 1d Image station 2a, 2b, 2c, 2d Photoconductor 3a, 3b, 3c, 3d Charging means 4a, 4b, 4c, 4d Developing means 5a, 5b, 5c, 5d Cleaning means 6a, 6b, 6c , 6d Exposure unit 7 Transfer unit 8a, 8b, 8c, 8d Transfer unit 9a, 9b, 9c, 9d Light 10, 11 Support roller 12 Intermediate transfer belt 13a, 13b, 13c, 13d Color misregistration correction unit 14 Pattern detection unit 16 Paper cassette 17 Sheet material 18 Paper feed roller 19 Sheet material transfer roller 20 Fixing means 21 Pattern generation means 22 Clock generation means 23 Storage means 24 Pixel addition number counting means 25 Pixel addition number setting means 26 Pixel counting means 27 Pixel addition interval setting means 28 first comparing means 29 second comparing means 30 image data Data output means 31 initial data setting means 35 offset generating means 36 adder 39 random data generating means

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Kazuhiko Soeda, Inventor Kazuma 1006 Kadoma, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. Terms (reference) 2H027 DA38 DA50 EB04 EC03 EC06 EC20 ED06 ED24 EE02 EE07 EF09 2H030 AA01 AB02 AD12 AD17 BB02 BB16 BB23 BB42 BB56 5C074 AA10 BB03 CC22 DD15 DD24 EE04 FF15 GG01 HH02

Claims (6)

[Claims] A plurality of toner image forming means for forming a plurality of color toner images based on a plurality of image data divided for each color; and a plurality of color toner images formed by the plurality of toner image forming means. Transferring means for sequentially superimposing a plurality of toner images on a transfer material to form a composite image, a shift amount detecting means for detecting a shift amount of an image width of the plurality of color toner images transferred to the transfer material, and a shift amount detecting means And a shift amount correcting unit that adds a pixel to each of the image data of the plurality of colors so that the image widths of the toner images of the plurality of colors match based on the amount of shift detected by the method. Forming equipment. 2. The apparatus according to claim 1, wherein said shift amount detecting means generates a plurality of reference patterns divided for each color corresponding to an image width in the main scanning direction, and a plurality of reference patterns generated by said reference pattern generating means. Pattern detecting means for detecting a plurality of toner images transferred onto the transfer material by the transfer means based on the reference pattern, and a plurality of toner images detected by the pattern detecting means and generated by the reference pattern generating means. Pixel number calculating means for calculating the number of pixels to be added to the image data of the plurality of colors so that the image widths of the toner images of the plurality of colors in the main scanning direction match based on the comparison with the reference pattern. The shift amount correcting unit includes a plurality of pixel adding units that add a pixel to each of the plurality of color image data based on the number of pixels calculated by the number of pixel calculating unit. The color image forming apparatus according to claim 1, wherein the was e. 3. A method according to claim 1, wherein each of said plurality of pixel adding means calculates a pixel interval to be added based on the number of pixels to be added provided from said pixel number calculating means, and counts pixels of image data. A first pixel counting unit that performs the operation, a pixel inserting unit that inserts a pixel into image data at each pixel interval calculated by the pixel interval calculating unit based on a count value of the first pixel counting unit; Second pixel counting means for counting the number of pixels inserted by the means, and the pixel insertion means when a count value of the second pixel counting means matches the number of pixels calculated by the pixel number calculation means. 3. A color image forming apparatus according to claim 2, further comprising a termination unit for terminating the insertion of the pixel according to the image data. 4. The apparatus according to claim 1, wherein each of said plurality of pixel adding means further comprises an offset generating means for giving an offset value which varies according to the line to be scanned to said first pixel counting means before the start of scanning. Item 4. A color image forming apparatus according to Item 3. 5. The color image forming apparatus according to claim 3, wherein pixel intervals calculated by said pixel interval calculating means are irregular. 6. The resolution of a pixel added by each of said plurality of pixel addition means is equal to or higher than the resolution of said plurality of color image data provided to said plurality of pixel addition means. 6. The color image forming apparatus according to any one of claims 1 to 5,