JPH1069153A - Method for color slippage correction for image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide the method for color slippage correction for an image forming device capable of correcting the color slippage with the simple constitution. SOLUTION: In respect to the method for color slippage correction for the image forming device forming a specific image by allowing plural modulation beams to form image on severally corresponding image carrier and making the formed dot line transferred on one transfer body through the respective image carriers, the device is composed so as to divide at least one dot line LB1 among the image formed on several image carrier into plural dot groups (LB1n0 , Lb1n1 , ...) in the line direction, and to form the image as picture element group (LB1n0 ', Lb1n1 ', ...) by shifting the subscanning direction, in the direction by which the relative inclination of the divided dot group corresponding to the other side dot line LA1.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for deflecting each of a plurality of laser beams to form an image on a plurality of image carriers, and transferring the dot lines of one of the image carriers transferred onto a recording medium by the image carriers. The present invention relates to a color misregistration correction method of an image forming apparatus for correcting the inclination of a dot line of the other image carrier.

[0002]

2. Description of the Related Art Conventionally, various methods and apparatuses for forming a multicolor image on a recording medium by transferring an image of a photoreceptor exposed by a plurality of different light sources to a transfer member have been known. Since these are multicolor images, the process of exposing and developing the photoconductor with a light source of laser light that modulates data corresponding to a plurality of colors on the photoconductor and then transferring the photoconductor to the transfer body is performed a plurality of times. The image of each color is transferred to the same position on the transfer body. Therefore, if these are not transferred to the same position on the transfer body, the reproducibility of the image is reduced, and the contrast is poor and a blurred image is formed.

The reason that images from a plurality of different light sources are not transferred to the same position on the photoreceptor is a change in the magnification of the optical system, a change in the characteristics of the optical system due to a tilt of the optical system, etc. due to a manufacturing / assembly error of each mechanical component. The exposure timing of the optical system that exposes the latent image to the surface of the photosensitive member, the inclination of the photosensitive member with respect to the transfer member, etc. occur. Shifts.

Among the above causes, the change in the characteristics of the optical system due to the magnification and inclination of the optical system is caused by the f-θ lens
It is affected by the θ characteristic, the mirror angle on the optical path, the optical path length after the mirror and the polygon mirror, the error of the optical housing, etc., and causes a shift in the scanning direction of the image transferred to the recording medium via the photoconductor. Therefore, an electrical time lag is provided for the exposure timing of the optical system that exposes the latent image on the surface of the photoconductor, and adjustment is made so that the image is transferred to the same position on the photoconductor.

The inclination of the photosensitive member with respect to the transfer member is mechanically corrected by adjusting the inclination of the photosensitive member axis with respect to the intermediate transfer member axis to improve the image shift, and Japanese Patent Laid-Open No. 3-142412. As disclosed in the official gazette, a technique for adjusting the angle of the reflecting mirror on the optical path by finely adjusting the angle using a linear step actuator is known, and the technique has been used to adjust the angle.

[0006]

However, recent image forming apparatuses tend to require a narrow adjustment range as resolution increases. For example, in a printer having a high resolution such as 600 dpi, the pitch between dots is as fine as about 42.3 μm, and the inclination of the dot line by a plurality of image carriers on the transfer material conveying belt is determined by the above-described conventional technology. It is necessary to correct an adjustment width equal to or smaller than the pitch width by the adjustment, which complicates the adjustment mechanism and requires advanced technology.

In view of such circumstances, an 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 which minimizes the occurrence of jaggies.

[0008]

According to the present invention, a plurality of modulated beams are formed on a corresponding image carrier, and the formed dot lines are transferred to one transfer body via the image carriers. In the color misregistration correction method of an image forming apparatus that forms a predetermined image, at least one dot line formed on each of the image carriers is divided into a plurality of dot groups in a line direction, and the divided dot groups are An image is formed by shifting the sub-scanning direction in a direction in which the relative inclination with respect to the other dot line decreases.

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

At least before the image information transferred to the recording medium is carried on the image carrier, a test scan of an appropriate pattern is performed on the image carrier, and the other dot with respect to the one dot line is read. The relative slope of the line,
And detecting the relative distance of the scanning start point in the sub-scanning direction, storing these data and a calculated value based on the data, and correcting the other dot line based on the calculated value. This is an effective means of the present invention.

As shown in FIG. 1, a plurality of lasers (1A,
1B) is deflected by the polygon mirror 2 to form an image on a plurality of image carriers (photoconductors) 4A, 4B, and the dot lines (LAN, L) transferred onto a recording medium by the image carriers.
Bn), as shown in FIG. 2, the dot line LB1 of the other image carrier 4B is transferred onto the intermediate transfer member 5 with the inclination of the angle θ relative to the dot line LA1 of the other image carrier 4A. Is done.

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 Pixel dot groups (LB1n0, LB1n1, LB1n) forming the dot group, which are shifted in the direction in which the inclination of the dot line decreases.
3,... Corresponding to the pixel dot group (LB1n0 ′, LB
1n1 ', LB1n3',... Are driven, and the color shift is corrected for each of the dot groups (LBn0, LBn1, LBn3,...).

As shown in the enlarged view of FIG. 5B, n0, n1, and n2 are calculated by a Round [x] function that rounds x to an integer, and each dot is one dot in the sub-scanning direction. N0s to n0e are the same number of dots because they are divided into groups that increase or decrease by
If the integer increases by one from n0, the number of dots increases by one and n1
The dot numbers are the same for n1s to n1e, and similarly, n2, n3 and so on, and the yellow toner image LBn is corrected and transferred in agreement with the toner image LAn.

As described above, n0, n1, n2 are:
It is calculated by the Round [x] function and stored in groups each of which increases or decreases by one dot in the sub-scanning direction. , The deviation from the reference line LA1 can be suppressed to within one dot, and the relative dot deviation between the dot lines LA1 and LB1 can be corrected.

Further, as shown in FIG. 1, according to the present invention, the sensors 6A, 6B are provided so that the images at both ends in the axial direction of the circumferential area on which the image of the intermediate transfer body 5 formed in a cylindrical shape is transferred.
6B, the images 8a, 8b, 9a, 9b of appropriate test patterns are transferred from the image carriers (photosensitive members) 4A, 4B to the intermediate transfer member 5 by test scanning of the polygon mirror 2,
The relative inclination of the two dot lines and the relative distance of the scanning start point in the sub-scanning direction are detected by the test pattern, and these data and a calculated value based on the data are stored. When the image is transferred, the other dot line is corrected.

The data and the calculated values based on the data need to be stored at least before the image information transferred to the recording medium is carried on the image carrier. Alternatively, it may be at the end of repair, or after starting the image forming apparatus, at the time of feeding a recording medium between the first screen and the second screen, or when using a recording medium cut one by one, It may be a non-transfer time when the image is not transferred to the recording medium between the previous page and the next page.

In particular, when the surface of the photoreceptor is polished with a toner to which an abrasive has been 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 preferable that the test scanning is 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.

[0018] In addition, of the plurality of color materials for developing the latent image on the image carrier, a dot line formed by a color material having high lightness may be corrected, or one of the dot lines may be formed. The latent image on one image carrier is developed with a low-brightness color material among a plurality of color materials, and the latent image on the other image carrier forming the other dot line is developed with a high-brightness color material. The above-described configuration is also an effective means of the present invention, in which the other dot line is corrected.

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

Therefore, a color material having a large difference in brightness is converted into a discontinuous color material.
In other words, when the image is transferred stepwise onto white paper, a stepped portion that is a discontinuous portion of the dot line is conspicuous, and a so-called jaggy is visually recognized. However, when a color material having a small difference in brightness between the two, such as white paper and yellow, is transferred to white paper, the contrast between the two is small, and the jaggies are less noticeable.

Therefore, in the present invention, the photoreceptor 4A is developed with black and magenta color materials, and the photoreceptor 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 latent image is changed to yellow by the photosensitive member 4B. The developed toner dot line is divided into a plurality of dot groups in the line direction and shifted in a direction in which the inclination of the dot line decreases, and the pixel dot group corresponding to the pixel dot group forming the dot group 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 come into contact with the photosensitive member 4A, the magenta color material The latent image is developed and transferred to the intermediate transfer member 5 in accordance with the black and yellow dot lines. When the dot line of the transferred image comes to a contact position with the photosensitive member 4B, The toner dot lines developed by cyan are divided into a plurality of dot groups in the line direction, and the pixel dot groups corresponding to the pixel dot groups forming the dot groups, which are shifted in a direction in which the inclination of the dot lines decreases, are driven. Then, the color misregistration is corrected.

Since the present invention is configured as described above,
The correction is performed using a dot line 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 low contrast with the surface of the recording medium and, therefore, with less noticeable jaggies.

[0024]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be illustratively described in detail below with reference to the drawings. However, unless otherwise specified, the dimensions, materials, shapes, relative arrangements, and the like of the components described in this embodiment are not intended to limit the scope of the present invention thereto, but are merely illustrative examples. It's just

As shown in FIG. 1, the image forming apparatus according to the embodiment of the present invention is provided on both sides of a single polygon mirror 2 via condensing lenses (3A, 3B) for scanning. Photoreceptors 4A and 4B forming a scanning surface are arranged, and the polygon mirror 2 is rotated while applying a beam from a laser light source (1A, 1B) to a deflection surface of the polygon mirror 2 facing the surface to be scanned. Optical scanning is performed.

Therefore, the light beams from the laser light sources 1A and 1B are transmitted to the photosensitive drum (image bearing member) by an optical scanning system including the polygon mirror 2, the scanning condenser lenses 3A and 3B, and the reflection mirrors 7A and 7B. An electrostatic latent image is carried on the photosensitive members 4A and 4B.

Although not shown, a charger for charging the photosensitive drums 4A and 4B, a developing device (for example, black, magenta, yellow and cyan) and a cleaning for removing residual toner are provided on the photosensitive drums 4A and 4B. A blade or the like is attached.

The color materials (black, magenta, yellow, and cyan) supplied to the developing device and blank paper as a recording medium are converted into uniform color spaces (L *, U) determined by the CIE (International Commission on Illumination). *, V * space), the measured value of lightness (L *) is blank (96.9),
Yellow (87.87), cyan (52.89), magenta (46.47), and black (20.32).

Accordingly, black and magenta are attached to the photosensitive drum 4A, and yellow and cyan are attached to the photosensitive drum 4B. Therefore, light for forming dot lines of yellow and cyan, which are color materials having high brightness, is provided. At the time of scanning, the photosensitive drum 4B is optically scanned by a dot line corrected by a later-described correction means with respect to a dot line optically scanned on the photosensitive drum 4A as a reference.

Generally, an image is often transferred onto a recording medium (blank paper) having high brightness. Using blank paper as the recording medium,
When yellow, cyan, magenta, and black pigments are used for the color material of the toner, white paper, yellow,
Lightness decreases in the order of cyan, magenta, and black. And
When the image is transferred to a high-brightness white paper using a black color material having a large difference in lightness, the contrast between the two becomes large and the two are clearly recognized.

Therefore, a color material having a large difference in lightness is converted into a discontinuous color material.
In other words, when the image is transferred stepwise onto white paper, a stepped portion that is a discontinuous portion of the dot line is conspicuous, and a so-called jaggy is visually recognized. However, when a color material having a small difference in brightness between the two, such as white paper and yellow, is transferred to 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, in the photoconductor 4A, first, a latent image is developed with a black or magenta color material and transferred to the intermediate transfer body 5, and when the dot line of the transferred image comes to a contact position with the photoconductor 4B. The toner dot lines developed with yellow or cyan by the photoreceptor 4B are divided into a plurality of dot groups in the line direction, and are shifted in a direction in which the inclination of the dot lines decreases. Driving the corresponding pixel dot group corrects the color shift.

Since the present embodiment is configured as described above, the correction is performed by using a dot line of a color material having a small difference in brightness from the recording medium. Therefore, it is possible to form a good image with low contrast with the surface of the recording medium and with 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
This is a resistor having a volume resistivity in a medium resistance region of 10 ¹⁰ to 10 ¹⁴ Ωcm, and is formed of polycarbonate, polyimide, polyetheretherketone or the like having a thickness of about 150 μm.

Accordingly, the photosensitive drums 4A and 4B are developed one by one from the developing device for each rotation of the drum, and are transferred to the intermediate transfer sheet 17 by Coulomb force. When the transfer of one color is completed, the toner is removed from the photosensitive drum by a cleaning blade (not shown), and then the other color is developed on the photosensitive drum. Specifically, the black color is transferred from the photosensitive drum 4A to the intermediate transfer sheet 17, and then the intermediate transfer sheet 17 rotated to the position of the photosensitive drum 4B transfers the yellow color from the photosensitive drum 4B.

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

In this embodiment, as shown in FIG. 1, the sensor 6 makes it possible to visually recognize the images at both ends in the axial direction of the circumferential area where the image of the intermediate transfer body 5 formed in a cylindrical shape is transferred.
A and 6B are arranged. These sensors are provided so that the image information transferred to the recording medium is a photosensitive member 4 serving as the image carrier.
A test scan of a pattern is appropriately performed on the image carrier before the image carrier is carried on A and 4B, and a relative inclination of dot lines Lan and LBn and a relative distance of a scanning start point in a sub-scanning direction are detected. It is.

As shown in FIG. 3, before the image information transferred to the recording medium is carried on the photosensitive members 4A and 4B, the test patterns 6A and 6B are formed on the intermediate transfer member 5 by the control of a control circuit described later. Is formed on the photoreceptor 4B such that is transferred, and a toner image is formed on the photoreceptor 4A such that the test patterns 6A and 6B are transferred onto the intermediate transfer body 5. If the intermediate transfer member 5 and the photoconductors 4A and 4B are made according to the design values and are assembled according to the design values, the dot lines LA1 and LB1 are transferred at a theoretical distance of dc dots shown in FIG. .

However, due to manufacturing errors, assembly errors, etc., both the dot lines LA1 and LB1
The image is not always transferred at right angles to the feed direction of the recording medium. Normally, 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 serving as the reference line.

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

Then, the passing time t between the test patterns 8a and 9a on the intermediate transfer body 5 is detected by the sensors 6A and 6B.
a, and the transit 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 rotation speed v of the intermediate transfer body 5,
From the 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).

Further, the inclination m between the dot line LA1 and the dot line LB1 is represented by the following equation, assuming that the angle between both lines is θ: m = tan θ = (dad−dbd) / L2 (1)

Also, the shift amount y0 in the sub-scanning direction of the data at the leading i = 0th dot in the sub-scanning direction is a function of Round [X] being an integer obtained by rounding X, and the case where 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 data of the i-th dot from the head in the sub-scanning direction is as follows: yi = Round [dad-dcd + mL1-mi] = Round [{(L1 + L2-i) dad- (i-L1) dbd- L2dcd / L2] (3)

Therefore, when these calculations are performed for the 0th to Nth dots, yi increases or decreases by one dot every time i increases to some extent, and the positions at which yi increases or decreases by one dot are n0, n1, n1 in order from the left end. and memorize n2 (dot) ~
By shifting the reading of the bitmap data of the image at that timing, the dot lines LA1 and LB are shifted.
One relative dot shift can be corrected.

FIG. 6 is a configuration diagram of a control circuit used in the image forming apparatus according to the present embodiment. A main memory 20 for storing image information data is connected to the MPU 21 so as to be able to send the data, and the MPU 21 is connected to the sensor 6 in FIG.
A reading detection means 22 indicated by A and 6B, and storage means 23 for storing detection data from the reading detection means 22, a calculation result calculated based on the data, other device data, a calculation program, and the like are connected. .

The MPU 21 includes a CPU 24 for controlling a computing unit 26 for computing a group of input data, and a correcting means 25 for correcting the formation of dot lines based on the result of the computation. 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 correcting means 25. V
The RAM 27 includes a laser driving circuit 29 that scans the first photosensitive member 4A by driving according to the modulation data,
The AM 28 is connected to a laser driving circuit 30 that drives the second photoconductor 4B according to the modulation data to scan the second photoconductor 4B.

Next, the operation of the image forming apparatus configured as described above will be described. As shown in FIG. 1, scanning condensing lenses (3
A, 3B), a laser light source (1A, 1B) is provided on the deflection surface of the polygon mirror 2 facing the photoconductors 4A and 4B.
The light is scanned by rotating the polygon mirror 2 while the beam is incident from B).

As shown in FIG. 3, before the image information transferred to the recording medium is carried on the image carrier, the V
The laser drive circuits 29 and 30 are driven via the RAM 27 and the VRAM 28 to expose the photoconductors 4 and 4B with a test pattern. The photoconductor 4A is developed with black toner, the photoconductor 4B is developed with yellow toner, and the test patterns 8a, 8b, 9a, 9b are transferred to the surface of the intermediate transfer body 5 shown in FIG.

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 serving as the reference line. With the sensors 6A and 6B, the passing time ta between the test patterns 8a and 9a on the intermediate transfer body 5 and the test patterns 8b and 9
b, the transit time td between the test patterns 8a and 9d is determined from the predetermined rotational speed v of the intermediate transfer member 5.
The distance da between the test patterns 8a and 9b and the distance db between the test patterns 8b and 9b are calculated. From the pitch p between the dots, the number of dots dad between the distances da is set to (da / p), and the number of dots dbd between the distances db is calculated. 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 in the sub-scanning direction of the data at the leading i = 0th dot, and the shift amount yi in the sub-scanning direction of the data at the i-th dot from the head are M.
The calculation is performed in the PU 21 and these calculations are performed from the 0th to the Nth dot. The yi increases or decreases by one dot every time i increases to some extent, and the positions at which the yi increases or decreases by 1 dot are n0, n1, n1 in order from the left end. n2 (dot) 〜 and stored in the storage means 23.

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

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

After transferring the black color to the intermediate transfer sheet 17, the photosensitive drum 4 A removes the residual toner with a cleaner, develops the magenta color, and transfers the magenta color to the intermediate transfer sheet 17. Similarly, after transferring the yellow color also on the photosensitive drum 4B, the residual toner is removed with a cleaner, the cyan color is developed, the correction is performed in the same manner as described above, and the correction is made to the same position as the previous three colors. Transfer is performed.

As described above, in the present embodiment, n0,
n1, n2 are calculated by the Round [x] function that rounds x to an integer according to the above equation (3), and is divided into groups each of which increases or decreases by one dot in the sub-scanning direction, and is stored. Therefore, by shifting the reading of the bitmap data of the image at that timing, the deviation from the reference line LA1 can be suppressed within one dot, and the relative dot deviation between the dot lines LA1 and LB1 can be corrected. it can.

In this embodiment, an image of an appropriate test pattern is transferred from an image carrier (photoconductor) exposed by a test scan of a polygon mirror to an intermediate transfer body, and the test pattern is subjected to different photosensitivity by a sensor. The relative inclination of the dot line between the bodies and the relative distance of the scanning start point in the sub-scanning direction are detected, and these data and a calculated value based on the data are stored, and the calculated value is used in actual image transfer. In the above, since the other dot line with respect to the reference dot line is configured to be corrected, the storage of these data and the operation value based on the data is at least:
It is sufficient that the image information transferred to the recording medium is not carried on the photoconductors 4A and 4B. Therefore, it may be at the time of final assembly in a factory or at the time of completion of repair. When the recording medium is fed between the first screen and the second screen, or when a recording medium cut one by one is used, non-transfer is performed without transferring an image to the recording medium between the previous page and the next page. Of course, it may be time.

In particular, when the surface of the photoreceptor is polished with a toner to which an abrasive has been 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 preferable that the test scanning is 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.

In general, an image is often transferred onto white paper having high lightness. When the image is transferred to white paper having high lightness using a black color material having a large difference in lightness, the contrast between the two becomes large and the two are clearly visible. Is done. Therefore, when a color material having a large difference in brightness is transferred to a blank sheet in a discontinuous manner, that is, in a stepwise manner, a so-called jaggy is visually recognized in a stepped portion which is a discontinuous portion of the dot line.
Since the correction is performed using a dot line made of a color material having a small brightness difference between the two, such as white paper and yellow, the contrast with the recording medium surface is small, so that a good image with little jaggies can be formed. is there.

Although a laser has been described as a modulation light source as described above, the present embodiment is not limited to a laser alone, and it is a matter of course that an LED light source may be used.

[0060]

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

[Brief description of the drawings]

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

FIG. 2 is an explanatory diagram illustrating a deviation of a dot line 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 deviation angle and a position of a test pattern image.

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

FIG. 6 is a configuration diagram showing one embodiment of a control circuit used in the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Laser light source (1A, 1B) 2 Polygon mirror 3 Condensing lens (3A, 3B) 4 Photoconductor (4A, 4B) 5 Intermediate transfer body 6 Sensor 7 Reflection mirror (7A, 7B) 8, 9 Test pattern 20 Main memory Reference Signs List 21 MPU 22 Reading detection means 23 Storage means 24 CPU 25 Correction means 26 Calculation means 27, 28 VRAM 29, 30 Laser drive circuit

Claims (5)

[Claims] An image forming apparatus that forms a predetermined image by forming a plurality of modulated beams on corresponding image carriers and transferring formed dot lines to one transfer body via the image carriers. In the color misregistration correction method, at least one dot line formed on each of the image carriers is divided into a plurality of dot groups in a line direction, and the divided dot groups are relative to other dot lines. A color shift correcting method for an image forming apparatus, wherein an image is formed by shifting a sub-scanning direction in a direction in which a tilt decreases. 2. The method according to claim 1, wherein the plurality of dot groups are calculated by a Round function [x] that rounds x to an integer. 3. At least before the image information transferred to a recording medium is carried on the image carrier, a test scan of a pattern is appropriately performed on the image carrier, and the other dot with respect to the one dot line is In addition to detecting the relative inclination of the line and the relative distance of the scanning start point in the sub-scanning direction, these data and a calculated value based on the data are stored, and the other dot line is corrected by the calculated value. 2. The method according to claim 1, wherein the color misregistration of the image forming apparatus is corrected. 4. The image forming apparatus according to claim 1, wherein a dot line formed by a color material having high brightness among a plurality of color materials for developing the latent image on the image carrier is corrected. A method for correcting a color shift of a device. 5. A latent image of one image carrier forming one dot line is developed by a color material having a low brightness among a plurality of color materials, and a latent image of the other image carrier forming the other dot line is formed. 5. The method according to claim 4, wherein the latent image is developed with a color material having a high brightness, and the other dot line is corrected.