JP3420003B2 - Color shift correction method for image forming apparatus - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a dot line of one image carrier, which is formed by imaging the modulated beams of a plurality of LEDs on each corresponding image carrier and transferring the image onto the recording medium by the image carrier. On the other hand, the present invention relates to a color misregistration correction method for an image forming apparatus for correcting the inclination of the dot line of the other image carrier.

[0002]

2. Description of the Related Art Heretofore, various methods and apparatuses have been known for forming a multicolor image on a recording medium by transferring an image on a photoconductor exposed by a plurality of different LED light sources to a transfer body. Since these are multicolor images, first, the process of exposing and developing the photoconductor with the beam light whose data is modulated corresponding to a plurality of colors on the photoconductor, and then transferring it to the transfer body is performed plural times. , Images of each color are transferred to the same position on the transfer body. Therefore, unless these are transferred to the same position on the transfer body, the reproducibility of the image is deteriorated, and the contrast is poor and a blurred image is formed.

The reason why images from a plurality of different LED light sources are not transferred to the same position on the photoconductor is that the characteristics of the optical system change due to changes in the magnification of the optical system, tilts of the optical system, etc. due to manufacturing / assembling errors of each mechanical component. Changes, exposure timing deviation of the optical system that exposes the latent image on the surface of the photoconductor, tilt of the photoconductor with respect to the transfer body, and the emission positions of the plurality of LED light sources are different. The exposure position was misaligned.

Among the above causes, the change in the characteristics of the optical system due to the magnification and inclination of the optical system is influenced by the error of the optical housing and the like, and the change in the scanning direction of the image transferred onto the recording medium via the photoconductor is caused. LE in the main scanning direction as it causes misalignment
The D element is arranged with a margin, an electric time lag is provided at the exposure timing of the optical system that exposes the latent image on the surface of the photoconductor, and adjustment and setting are performed so that the image is transferred to the same position on the photoconductor.

Further, the inclination of the photosensitive member with respect to the transfer member is mechanically adjusted by adjusting the inclination of the photosensitive member axis with respect to the intermediate transfer member axis to correct the image misalignment or is finely adjusted by an optical system. The technology was known and adjusted by that technology.

[0006]

However, recent image forming apparatuses tend to require a narrow adjustment width as the resolution increases. For example, in a high resolution printer such as 600 dpi, the pitch between dots is about 4
The width is as narrow as 2.3 μm, and it is necessary to correct the adjustment width equal to or smaller than the pitch width by the above-mentioned conventional technique, which complicates the adjustment mechanism and requires high technology.

In view of such circumstances, the object of the present invention is to
An object of the present invention is to provide a color misregistration correction method for an image forming apparatus capable of adjusting color misregistration with a simple configuration. Another object of the present invention is to provide a color misregistration correction method for an image forming apparatus in which jaggies are suppressed as much as possible.

[0008]

SUMMARY OF THE INVENTION According to the present invention, a plurality of modulated beams are imaged on corresponding image carriers, and the formed dot lines are transferred to one transfer medium through the image carriers. In a color misregistration correction method of an image forming apparatus for forming a predetermined image, a large number of LED elements are arranged in the scanning direction on each of the image carriers, and one image carrier scans one dot line to the other image. While carrying out the dot line scanning of the carrier a plurality of times, the dot line of the other image carrier is divided into a plurality of dot groups in the line direction, and the divided dot groups are the dot lines of the one image carrier. The sub-scanning direction is shifted in the direction in which the relative inclination of the image is reduced to form an image.

Further, between the dot lines in the sub-scanning direction of the dot lines of the one image carrier, the dot lines of the other image carrier divided into a plurality of dot groups are additionally scanned by one dot line or more. It is also an effective means of the present invention.

Further, it is an effective means of the present invention that the plurality of dot groups are calculated by a Round function [x] that rounds x to an integer.

Further, at least before the image information transferred to the recording medium is carried on the image carrier, a test scan of a suitable pattern is performed on the image carrier, and the dot line of the one image carrier is tested. The relative inclination of the dot line of the other image carrier and the relative distance in the sub-scanning direction of the scanning start point are detected, and these data and the calculated value based on the data are stored, and the calculated value is used. It is also an effective means of the present invention to configure so as to correct the dot line of the other image carrier.

As shown in FIG. 1, an LED head (1A, 1B) having a plurality of LED elements arranged side by side in the main scanning direction.
Each modulated beam of a plurality of image carriers (photoconductors) 4A,
The dot lines (LAn, LBn) that are imaged on the image carrier 4B and transferred onto the recording medium by the image carrier are on the dot line LA1 of one image carrier 4A on the intermediate transfer member 5 as shown in FIG. On the other hand, the dot line LB of the other image carrier 4B
1 is transferred with a relative inclination of the angle θ.

On the other hand, as shown in FIG. 5B, the other dot line LBn is divided into a plurality of dot groups (LBn0, LBn1, LBn3, ...) In the line direction and in the sub-scanning direction. Pixel dot groups (LB1n0, LB1n1, LB1n) forming the dot groups, which are deviated in the direction in which the inclination of the dot line decreases.
Pixel dot groups (LB1n0 ′, LB) corresponding to
1n1 ', LB1n3', ... are driven to correct the color shift for each of the dot groups (LBn0, LBn1, LBn3, ...).

Then, as enlargedly shown in FIG. 5B, n0, n1 and n2 are calculated by the Round [x] function that rounds x to an integer, and each dot is 1 dot in the sub-scanning direction. Since it is divided into groups that increase and decrease by n, n0s to n0e have the same number of dots,
When the integer increases by 1 from n0, the number of dots increases by 1 and n1
Therefore, the number of dots is the same from n1s to n1e, and similarly, the toner image LBn of yellow color is corrected and transferred in the same manner as n2 and n3 to the toner image LAn.

As described above, n0, n1 and n2 are:
Since it is calculated by the Round [x] function and is divided into groups that increase / decrease by 1 dot in the sub-scanning direction and is stored, it is possible to shift the reading of the image bitmap data at that timing, It is possible to suppress the deviation from the reference line LA1 within one dot and correct the relative dot deviation between the dot lines LA1 and LB1 without providing the division reference of No. 1 and performing complicated calculation.

However, in this method, as shown in FIG. 7A, LBno and LBn are arranged at a pitch of R = 1 dot.
1, LBn2 is corrected stepwise, so that the jaggies are conspicuous. Therefore, the dot line of the other image carrier divided into a plurality of dot groups is configured to be additionally scanned once or more between the dot lines of the dot line of the one image carrier in the sub-scanning direction. Thereby, the resolution in the sub-scanning direction can be increased.

As shown in FIG. 7B, between the dot lines R in the sub-scanning direction of the dot lines of the one image carrier,
If the dot line of the other image carrier divided into a plurality of dot groups is configured to be scanned twice, the toner image LA1 of the second photoconductor 4B coincides with the toner image LA1 of the first photoconductor 4A. LB2 and LB3 are LBn
Since o, LBn1 and LBn2 and R / 3 pitch are formed and corrected in a stepwise manner, the jaggies are less noticeable.

With this configuration, as shown in FIG. 8, the dot line LB1 of the other image carrier is
A plurality of dot groups (LB1n0, LB1n1, LB1n2, ...) for each (n0, n1, n2, n3) dot.
LB1n3, ...), and moves in the sub-scanning direction in the direction in which the inclination of the dot line decreases,
0 ', LB1n1', LB1n2'LB1n3 ', ~)
Is corrected as follows. Also, the dot lines LB2 and LB
Also in No. 3, the color shift is corrected by performing the same correction as that of the dot line LB1 described above.

Then, between the dot lines in the sub-scanning direction of the dot lines of the one image carrier, two dot lines of the other image carrier divided into a plurality of dot groups are formed.
When the scanning is performed extra times, the other photoconductor requires three times as many dot lines as the one photoconductor, and the storage operation is performed based on the number of dots.

Therefore, n0, n1, n in FIG.
2 to Round [x] that rounds x to an integer
Calculated by a function and divided into groups that increase / decrease by 1 dot (1/3 dot for one photoconductor) in the sub-scanning direction, so n of LB1n0
When the integer is increased by 1 from 0, the number of dots is increased by 1 to become n1, and in the same manner (n2, n3, ...), the number of dots is increased.

As described above, n0, n1 and n2 are:
Since it is calculated by the Round [x] function and is divided and stored in groups that increase / decrease by 1 dot in the sub-scanning direction, the bit map data of the image is read at that timing so that a special Without setting a division criterion and performing complicated calculations, FIG.
As shown in (b), it is possible to provide an image forming apparatus in which the color misregistration is corrected with a step difference of (1/3) R with respect to the dot spacing R of the other photoconductor, and jaggies are not noticeable.

Further, according to the present invention, as shown in FIG. 1, the sensors 6A, 6A, 6A, 6A, 6A, 6C, 6A, 6C, 6C, 6D, 6E, 6E, 6C, 6D, 6E, 6C, 6D, 6E, 6C, 6E, and 6C are provided so that images at both ends in the axial direction of the circumferential region of the intermediate transfer member 5 formed into a cylinder are transferred.
6B is arranged, images 8a, 8b, 9a, 9b of appropriate test patterns are transferred from the image bearing members (photoconductors) 4A, 4B to the intermediate transfer member 5 by the test scan of the LED heads 1A, 1B, and the test patterns are transferred. Detects the relative inclination of both dot lines and the relative distance of the scanning start point in the sub-scanning direction, stores these data and the calculated value based on the data, and transfers the actual image transfer by the calculated value. At times, it is configured to correct the other dot line.

The data and the calculated value based on the data may be stored at least before the image information transferred to the recording medium is carried on the image carrier, and therefore, at the time of final assembly of the factory, Alternatively, the repair may be completed, or after the image forming apparatus is started, or when the recording medium is fed in the middle between the first screen and the second screen, or when the recording medium cut into individual sheets is used, The image may not be transferred to the recording medium between the previous page and the next page during non-transfer.

In particular, in the case where the surface of the photoconductor is polished by the toner to which the abrasive is added, it is desirable to update the data and the calculated value based on the data after transferring a predetermined number of sheets. It is desirable that the test scan be performed at the time of the above-mentioned non-transfer after the transfer of the predetermined number of sheets or at the time of starting the apparatus after the transfer of the predetermined number of sheets.

Further, among a plurality of color materials for developing the latent image on the image carrier, a dot line formed by a color material having a high lightness is configured to be corrected, or one dot line is formed. The latent image of one image carrier is developed with a color material having a low lightness among a plurality of color materials, and the latent image of the other image carrier forming the other dot line is developed with a color material having a high lightness. However, it is also an effective means of the present invention to configure so as to correct the other dot line.

Generally, an image is often transferred onto a recording medium having high brightness. For example, use a blank paper as the recording medium,
When yellow, cyan, magenta, and black pigments are used as toner color materials, the brightness generally decreases in the order of white paper, yellow, cyan, magenta, and black. When a black color material having a large difference in brightness is transferred to a white paper having a high brightness, the contrast between the two becomes large, and they are clearly visible.

Therefore, when a color material having a large difference in lightness is transferred discontinuously, that is, stepwise to a white paper, a stepped portion which is a discontinuous portion of the dot line is conspicuous and so-called jaggies are visually recognized. However, when a color material having a small difference in lightness such as white paper and yellow is transferred to the white paper, the contrast between the two is small and the jaggies are less noticeable.

Therefore, in the present invention, the photoconductor 4A is developed with black and magenta color materials, and the photoconductor 4B is developed with yellow and cyan color materials. That is, the photoconductor 4A
First, the latent image is developed with a black color material and transferred to the intermediate transfer member 5, and when the dot line of the transferred image comes to the contact position with the photosensitive member 4B, the photosensitive member 4B changes the yellow color. The developed toner dot line is divided into a plurality of dot groups in the line direction, and the pixel dot group corresponding to the pixel dot group forming the dot group, which is displaced in the direction in which the inclination of the dot line is reduced, is driven. , The color shift is corrected.

When the black and yellow dot lines of the intermediate transfer member 5 rotate counterclockwise in FIG. 1 to reach the contact position with the photosensitive member 4A, the magenta coloring material is applied to the photosensitive member 4A. The latent image is developed by and is transferred to the intermediate transfer member 5 in alignment with the black and yellow dot lines, and when the dot line of the transferred image comes to the contact position with the photosensitive member 4B, The toner dot line developed by cyan is divided into a plurality of dot groups in the line direction, and the pixel dot group corresponding to the pixel dot group forming the dot group is displaced in the direction in which the inclination of the dot line is reduced. Then, the color misregistration is corrected.

Since the present invention is constructed in this way,
It is corrected using a dot line made of a color material having a small difference in brightness from the recording medium. Therefore, the contrast with the surface of the recording medium is small, so that it is possible to form a good image with less noticeable jaggies.

[0031]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be exemplarily described in detail below with reference to the drawings. However, unless otherwise specified, the dimensions, materials, shapes, relative positions, etc. of the components described in this embodiment are not intended to limit the scope of the present invention thereto, but merely illustrative examples. Nothing more.

In the image forming apparatus according to the embodiment of the present invention, as shown in FIG.
LED heads (1 with A and 4B arranged facing the surface to be scanned)
Optical scanning is performed while the modulated beam is incident from A, 1B). Therefore, the light from the LED heads 1A and 1B causes the photosensitive drum (photosensitive member) 4A, which is an image carrier,
An electrostatic latent image is carried on 4B.

Although not shown, the photosensitive drums 4A and 4B include a charger for charging the drum, a developing device (for example, black color, magenta color, yellow color and cyan color) and cleaning for removing residual toner. A blade etc. is attached.

Color materials (black color, magenta color, yellow color and cyan color) supplied to the developing device and a white paper as a recording medium are set in a uniform color space (L *, U) defined by CIE (International Commission on Illumination). *, V * space) values are compared, the measured value of lightness (L *) is white paper (96.9),
Yellow (87.87), cyan (52.89), magenta (46.47), and black (20.32).

Therefore, black and magenta are attached to the photosensitive drum 4A, and yellow and cyan are attached to the photosensitive drum 4B. Therefore, light that forms dot lines of yellow and cyan, which are color materials having high lightness, is formed. At the time of scanning, the photosensitive drum 4B is optically scanned with the dot line corrected with respect to the dot line optically scanned on the photosensitive drum 4A serving as a reference by the correcting unit described later.

In general, an image is often transferred onto a recording medium (white paper) having high brightness. Use blank paper as the recording medium,
When yellow, cyan, magenta, and black pigments are used as toner color materials, the brightness generally decreases in the order of white paper, yellow, cyan, magenta, and black as described above. When a black color material having a large difference in brightness is transferred to a white paper having a high brightness, the contrast between the two becomes large, and they are clearly visible.

Therefore, a color material having a large difference in brightness is discontinuously formed,
That is, when transferred to a blank sheet in a stepwise manner, so-called jaggies are visually recognized because the stepped portion which is the discontinuous portion of the dot line is conspicuous. However, when a color material having a small difference in lightness such as white paper and yellow is transferred to the white paper, the contrast between the two is small and the jaggies are less noticeable.

Therefore, in this embodiment, the photoconductor 4A is developed with black and magenta color materials, and the photoconductor 4B is developed with yellow and cyan color materials.
That is, when the latent image is first developed on the photoconductor 4A with a color material of black or magenta and transferred to the intermediate transfer body 5, when the dot line of the transferred image comes to the contact position with the photoconductor 4B. The toner dot line developed by the photoconductor 4B with yellow or cyan is divided into a plurality of dot groups in the line direction, and the dot dot is shifted in a direction in which the inclination of the dot line is reduced, to form a pixel dot group forming the dot group. The corresponding pixel dot group is driven to correct the color shift.

Since the present embodiment is configured in this way, correction is performed using dot lines made of a color material having a small difference in brightness from the recording medium. Therefore, it is possible to form a good image with a small contrast with the surface of the recording medium and less noticeable jaggies.

The intermediate transfer sheet 17 on the outer surface of the intermediate transfer body 5 with which the surfaces of the photosensitive drums 4A and 4B are in contact is a resistor having a volume resistivity of 10 ¹⁰ to 10 ¹⁴ Ωcm in the medium resistance region, and has a thickness of It is molded of polycarbonate, polyimide, polyetheretherketone or the like having a thickness of about 150 μm.

Therefore, the photosensitive drums 4A and 4B are sequentially developed one color by one from the developing device for each rotation of the drum and transferred to the intermediate transfer sheet 17 by Coulomb force. After the transfer of one color is completed, the photosensitive drum removes toner with a cleaning blade (not shown), and then another color is developed on the photosensitive drum. Specifically, the photosensitive drum 4
The black color is transferred from A to the intermediate transfer sheet 17 and then rotated to the position of the photosensitive drum 4B.
The yellow color 7 is transferred from the photosensitive drum 4B.

After transferring the black color to the intermediate transfer sheet 17, the photosensitive drum 4A removes the residual toner with a cleaner, develops the magenta color, and transfers the magenta color to the intermediate transfer sheet 17. Similarly, also on the photosensitive drum 4B, after transferring the yellow color, the residual toner is removed by a cleaner, the cyan color is developed, and the transfer is performed.

Further, in the present embodiment, as shown in FIG. 1, the sensor for visually recognizing the images of both ends in the axial direction of the circumferential region to which the image of the intermediate transfer member 5 formed in a cylindrical shape is transferred. 6A and 6B are arranged. Before the image information transferred to the recording medium is carried on the photoconductors 4A and 4B which are the image carriers, these sensors perform a test scan of an appropriate pattern on the image carriers to make dot lines LAn and LBn. And the relative distance of the scanning start point in the sub-scanning direction.

As shown in FIG. 3, before the image information transferred onto the recording medium is carried on the photoconductors 4A and 4B, the test patterns 8a and 8b are formed on the intermediate transfer body 5 under the control of the control circuit described later. To form a toner image on the photoconductor 4B, and a toner image on the photoconductor 4A to form the test patterns 9a and 9b on the intermediate transfer body 5. If the intermediate transfer member 5 and the photoconductors 4A and 4B are designed according to the designed values and are assembled according to the designed values, the dot lines LA1 and LB1 are transferred at the theoretical distance dc dots shown in FIG. It

However, both the dot line LA1 and the dot line LB1 are
The transfer is not always performed at right angles to the feeding direction of the recording medium. And normally, as shown in FIG.
The dot line LB1 is transferred onto the recording medium at an angle of θ with respect to the dot line LA1 serving as the reference line.

L1 from the inner left end of the drawing area of all N dots
Reflective reading sensors 6A and 6B having a light emitting source and a light receiving source are arranged at the dot and the (L1 + L2) dot, and the test patterns 8a and 8b on the intermediate transfer member 5 transferred from the photosensitive member 4B and the photosensitive The test patterns 9a and 9b transferred from the body 4A are detected.

Then, with the sensors 6A and 6B, the passage time t between the test patterns 8a and 9a on the intermediate transfer member 5 is passed.
a, and the passing time td between the test patterns 8b and 9b
Is measured, and the distance da between the test patterns 8a and 9a and the distance db between the test patterns 8b and 9b are calculated from the predetermined rotational speed v of the intermediate transfer member 5,
From the inter-dot pitch p, the number of dots dad between the distances da is calculated as (da / p), and the number of dots dbd between the distances db is calculated as (db / p).

The inclination m between the dot line LA1 and the dot line LB1 is expressed by m = tan θ = (dad−dbd) / L2 (1) where θ is the angle between the two lines.

Further, the shift amount y0 of the data of the i = 0th dot at the head in the sub-scanning direction is a function that rounds Round [X] to an integer by rounding X, and dcd is the number of dots between theoretical distances. , Y0 = Round [dad-dcd + mL1] = Round [{(L1 + L2) dad-L1dbd-L2dcd} / L2] (2)

The shift amount yi of the i-th dot from the beginning in the sub-scanning direction is: yi = Round [dad-dcd + mL1-mi] = Round [{(L1 + L2-i) dad- (i-L1) dbd- L2dcd} / L2] (3)

Therefore, when these calculations are performed from the 0th to the Nth dot, yi increases / decreases by 1 dot each time i increases to some extent, and the positions at which yi increases / decreases by 1 dot are sequentially n0, n1, and n1. Remember n2 (dots) ~,
By shifting the reading of the image bitmap data at that timing, the dot lines LA1 and LB are
The relative dot shift of 1 can be corrected.

FIG. 9 is a block diagram of a control circuit used in the image forming apparatus according to this embodiment. The main memory 20 for storing the image information data is connected to the MPU 21 so as to be able to send the data, and the MPU 21 has a reading detection means 22 shown by the sensors 6A and 6B in FIG. 1, detection data from the reading detection means 22, and A storage unit 23 for storing a calculation result calculated based on the data, other device data, a calculation program, and the like is connected.

Further, the MPU 21 is provided with a CPU 24 which controls a calculation unit 26 which calculates an input data group, and a correction means 25 which corrects the formation of dot lines based on the calculation result. The MPU 21 is connected to a VRAM 27 for storing modulation data for the first photoconductor (4A) and a VRAM 28 for storing modulation data for the second photoconductor (4B) via the correction means 25. V
The RAM 27 includes an LED drive circuit 29 that drives the first photoconductor 4A by scanning according to the modulation data, and the VR.
An LED drive circuit 30 that is driven according to the modulation data to scan the second photoconductor 4B is connected to the AM 28.

Next, the operation of the image forming apparatus configured as described above will be described. As shown in FIG. 1, optical scanning is performed while a beam is incident from the LED heads (1A, 1B). As shown in FIG. 3, before the image information transferred to the recording medium is carried on the image carrier, the VRA of FIG.
LED drive circuit 29 via M27 and VRAM 28
And 30 are driven to expose the test patterns on the photoconductors 4 and 4B. The photoconductor 4A is developed with black toner, the photoconductor 4B is developed with yellow toner, and the test patterns 8a, 8 are formed on the surface of the intermediate transfer body 5.
b, 9a, 9b are transcribed.

Then, as shown in FIG. 4, the dot line LB1 is transferred onto the recording medium at an angle θ relative to the dot line LA1 which is the reference line. In the sensors 6A and 6B, the passage time ta between the test patterns 8a and 9a on the intermediate transfer member 5 and the test patterns 8b and 9a are measured.
The passing time td between b is measured, and the test patterns 8a and 9 are obtained from the predetermined rotational speed v of the intermediate transfer member 5.
The distance da between the a and the distance db between the test patterns 8b and 9b are calculated. From the dot pitch p, the dot number dad between the distances da is (da / p), and the dot number dbd between the distances db. Is calculated as (db / p).

From these data, the dot line L
The inclination m between A1 and the dot line LB1, the shift amount y0 of the head i = 0th dot data in the sub-scanning direction, the shift amount yi of the first i-th dot data in the sub-scanning direction, and the like are M.
The calculation is performed in the PU 21 and these calculations are performed from the 0th to the Nth dot, yi is increased / decreased by 1 dot each time i increases to some extent, and the positions at which this yi is increased / decreased by 1 dot are sequentially n0, n1, n2 (dots) to are stored in the storage unit 23.

In a normal print operation of the image forming apparatus, the VRAM 27 and the VRAM 28 shown in FIG.
The LED drive circuits 29 and 30 are driven to scan and expose the photoconductors 4A and 4B with the modulated beam. Photoconductor 4A is V
The data stored in the RAM 27 is exposed and developed with black toner, and the black toner image LAn (FIG. 1) is transferred to the surface of the intermediate transfer body 5.

On the other hand, according to the data of the shift amounts y0 and yi stored in the storage unit 23, the photoconductor 4B is exposed through the correction unit 25 and the VRAM 28, developed with yellow toner, and the intermediate transfer member 5 is developed. A black toner image LBn (FIG. 1) is transferred to the surface of the. At that time, as shown enlarged in FIG. 5B, n0, n1, n
2 to 2 are calculated by the Round [x] function that rounds x to an integer by rounding x according to the equation (3), and each is divided into groups that increase or decrease by 1 dot in the sub-scanning direction. n0e is the same number of dots, and when the integer is increased by 1 from n0, the number of dots is increased by 1 to become n1, and the same number of dots is obtained from n1s to n1e. LA
The yellow toner image LBn is corrected and transferred in conformity with n.

After transferring the black color to the intermediate transfer sheet 17, the photosensitive drum 4A removes the residual toner with a cleaner, develops the magenta color, and transfers the magenta color to the intermediate transfer sheet 17. Similarly, on the photosensitive drum 4B, after transferring the yellow color, the residual toner is removed with a cleaner, the cyan color is developed, and the correction is performed in the same manner as described above to the same position as the previous three colors. Transfer is performed. Then, as shown in FIG. 7A, which is an enlarged view of the A portion of FIG. 6, the dot line groups LBn0, LBn1, and LBn2 are corrected with a step for each dot interval R.

As described above, in the first embodiment, n
0, n1, and n2 are calculated by the Round [x] function that rounds x to an integer according to the equation (3), and is divided into groups that increase / decrease by 1 dot in the sub-scanning direction and are stored. Since the reading of the bitmap data of the image is shifted at that timing, the deviation from the reference line LA1 is suppressed to within 1 dot, and the relative dot deviation between the dot lines LA1 and LB1 is corrected. You can

Next, the operation of the second embodiment will be described.
In the second embodiment, the dot lines of the second photoconductor 4B divided into a plurality of dot groups are additionally scanned twice between the dot lines of the first photoconductor 4A in the sub-scanning direction. I am configuring. Therefore, one photoconductor needs three times the number of dot lines for the other photoconductor, and the storage operation is performed based on the number of dots.

Therefore, n0, n1, n in FIG.
2 to Round [x] that rounds x to an integer
Calculated by a function and divided into groups that increase / decrease by 1 dot (1/3 dot for one photoconductor) in the sub-scanning direction, so n of LB1n0
When the integer is increased by 1 from 0, the number of dots is increased by 1 to become n1, and in the same manner, the number of dots is increased from n2 to n3. By configuring in this way,
As shown in FIG. 8, the toner image LA by the first photoconductor 4A is
1 and the toner images LB1, L by the second photoconductor 4B
B2 and LB3 are formed and corrected.

As shown in FIG. 8, the dot line LB1 of the other image carrier is (n0, n1, n2, n3)
Multiple dot groups for each dot (LB1n0, LB1
n1, LB1n2, LB1n3, ...), and moved in the sub-scanning direction in the direction in which the inclination of the dot line is reduced, and then (LB1n0 ', LB1n1', LB1n2'LB
1n3 ', ~) is corrected. Further, also in the dot lines LB2 and LB3, the above-mentioned dot line L
The color misregistration is corrected by performing the same correction as B1.

As described above, n0, n1 and n2 are:
Since it is calculated by the Round [x] function and is divided into groups that increase / decrease by 1 dot in the sub-scanning direction and is stored, it is possible to shift the reading of the image bitmap data at that timing, It is possible to suppress the deviation from the reference line LA1 within one dot and correct the relative dot deviation between the dot lines LA1 and LB1 without performing complicated calculation by providing the division reference of FIG. As shown in b), the color misregistration is corrected with a step difference of (1/3) R with respect to the dot spacing R of one of the photoconductors, so that it is possible to provide an image forming apparatus in which jaggies are significantly less noticeable.

In both the first and second embodiments, the present embodiment transfers an image of an appropriate test pattern from the image carrier (photoreceptor) exposed by the test scan of the LED head to the intermediate transfer member. Then, the test pattern is used to detect the relative inclination of the dot line between the different photoconductors by the sensor and the relative distance of the scanning start point in the sub-scanning direction, and these data and the calculated value based on the data are stored. , The other dot line with respect to the reference dot line is corrected at the time of actual image transfer by the calculated value, so that these data and the calculated value based on the data are stored in the recording medium at least. It is sufficient before the transferred image information is carried on the photoconductors 4A and 4B, and therefore, it may be at the time of final assembly in the factory or at the end of repair. After the start of the forming device, also when the recording medium feed in the middle between the first screen and the second screen, also 1
When a recording medium cut into individual sheets is used, it goes without saying that the image may not be transferred to the recording medium between the previous page and the next page during non-transfer.

In particular, in the case where the surface of the photosensitive member is polished by the toner to which the abrasive is added, it is desirable to update the data and the calculated value based on the data after transferring a predetermined number of sheets. It is desirable that the test scan be performed at the time of the above-mentioned non-transfer after the transfer of the predetermined number of sheets or at the time of starting the apparatus after the transfer of the predetermined number of sheets.

Further, in general, an image is often transferred onto a white paper having a high lightness. When a black color material having a large lightness difference is transferred onto a white paper having a high lightness, the contrast between the two becomes large and the image is clearly visible. To be done. Therefore, when a color material having a large difference in lightness is discontinuously transferred, that is, when transferred to a white paper in a stepwise manner, a so-called jaggy is visually recognized as a stepped portion which is a discontinuous portion of the dot line, but in the present embodiment, Since correction is performed using dot lines made of color materials that have a small difference in brightness between white paper and yellow, the contrast with the surface of the recording medium is low, and therefore a good image with less noticeable jaggies can be formed. is there.

[0068]

As described in detail above, the present invention can provide a color misregistration correction method for an image forming apparatus capable of adjusting color misregistration with a simple structure.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing an embodiment of an image forming apparatus used in the present invention.

FIG. 2 is an explanatory diagram illustrating a deviation of dot lines transferred by two photoconductors.

FIG. 3 is an explanatory diagram showing an ideal state of a test pattern image.

FIG. 4 is an explanatory diagram illustrating an arithmetic expression for calculating a relative displacement angle and a position of a test pattern image.

FIG. 5 is an explanatory diagram illustrating a basic method of correcting color misregistration.

FIG. 6 is a diagram illustrating main scanning of an LED head.

FIG. 7 is an enlarged view of part A in FIG.

FIG. 8 is an explanatory diagram illustrating a color misregistration correction method according to the embodiment of the present invention.

FIG. 9 is a configuration diagram showing an embodiment of a control circuit used in the present invention.

[Explanation of symbols]

1 LED head (1A, 1B) 4 photoconductors (4A, 4B) 5 Intermediate transfer body 6 sensors (6A, 6B) 8, 9 test pattern 20 main memory 21 MPU 22 Read detection means 23 storage means 24 CPU 25 Correction means 26 Computing means 27, 28 VRAM 29, 30 LED drive circuit

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ identification code FI G03G 15/04 H04N 1/23 103 (58) Fields investigated (Int.Cl. ⁷ , DB name) G03G 15/01-15 / 01 117 G03G 15/04-15/04 120 B41J 2/447

Claims (6)

(57) [Claims] 1. An image forming apparatus for forming a predetermined image by forming an image of a plurality of modulated beams on respective corresponding image carriers and transferring the formed dot lines to one transfer member via the image carriers. In the color misregistration correction method described above, a large number of LED elements are arranged in the scanning direction on each of the image carriers, and one dot line of one image carrier is scanned for a plurality of dot line scans of the other image carrier. The direction in which the relative inclination of the dot line of the other image carrier is divided into a plurality of dot groups in the line direction, and the divided dot groups are reduced relative to the dot line of the one image carrier. In addition, a method for correcting color misregistration in an image forming apparatus, characterized in that the image is formed by shifting the sub-scanning direction. 2. The dot line of the other image carrier divided into a plurality of dot groups is additionally scanned by 1 dot line or more between the dot lines of the dot line of the one image carrier in the sub-scanning direction. Claim 1 characterized by the above.
A method for correcting color misregistration of the image forming apparatus described in claim 1. 3. The color misregistration correction method for an image forming apparatus according to claim 1, wherein the plurality of dot groups are calculated by a Round function [x] that rounds x to an integer. 4. At least a test scan of a pattern is appropriately performed on the image carrier before the image information transferred to a recording medium is carried on the image carrier, and the dot line of one of the image carriers is scanned. The relative inclination of the dot line of the other image carrier and the relative distance in the sub-scanning direction of the scanning start point are detected, and these data and the calculated value based on the data are stored, and the calculated value is used. 2. The color misregistration correction method for an image forming apparatus according to claim 1, wherein the dot line of the other image carrier is corrected. 5. The image forming apparatus according to claim 1, wherein a dot line formed by a color material having a high lightness among a plurality of color materials for developing the latent image on the image carrier is corrected. Color misregistration correction method. 6. A latent image of one image carrier that forms one dot line is developed with a color material having a low lightness among a plurality of color materials, and the other image carrier that forms the other dot line is formed. 6. The color misregistration correction method for an image forming apparatus according to claim 5, wherein the latent image is developed with a color material having a high lightness, and the other dot line is corrected.