JP2001100482A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming device making quality of the color image improved by preventing color slippage owing to unsteady driving of the image forming body. SOLUTION: In this image forming device, forming the color toner image with regard to a photoreceptor drum 10 by arranging plural scorotron electrifier 11, the image exposing device 12 and developing device 13, position aligning means, is made to perform position aligning control by forming the monochrome toner image consisting of a specified regist pattern, based on this positional deviation, in adopting the charging device 11 Y on the most upstream side, the developing device 13 K on the most downstream side, and plural image exposing devices 12 Y, M, C and K.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of arranging a plurality of charging means, image exposing means and developing means close to the peripheral surface of an image forming member, and rotating the image forming member corresponding to the length of one image. The present invention relates to an electrophotographic image forming apparatus that forms a color image by superimposing a toner image on the inside.

[0002]

2. Description of the Related Art As an apparatus for recording a multicolor image, the same number of charging means, image exposing means and developing means as the number of colors required for image formation are arranged around an image forming body. While the body rotates corresponding to the length of the image, charging, image exposure and development for each color are sequentially performed to superimpose the toner images to form a color toner image, which is collectively formed on a transfer material. 2. Related Art A transfer type color image forming apparatus is known.

In such an apparatus, since the formation of toner images of each color is started successively with a slight time difference, the speed of color image formation is high, and a color image larger than the length of the peripheral surface of the image forming body is formed. It also has the feature that it can be formed.

[0004] However, when the processing accuracy of the image forming body is deteriorated or the rotation is uneven, the quality of the obtained image is not always good.

[0005]

As described above, in the image forming apparatus, many image forming devices including image exposure and developing means are arranged at a high density on the peripheral surface of the drum-shaped image forming body. In order to ensure that the equipment operates stably and obtain high image quality, the drum-shaped image forming body is precision machined and assembled so that it is a cylinder of the correct dimensions. It is indispensable that the relative position with respect to is always kept constant.

[0006] However, it is difficult to completely satisfy such basic conditions, and if there is drive unevenness in the drive system, density unevenness and color misregistration particularly in the rotation direction (sub-scanning direction) occur, resulting in a color image. Image quality was significantly impaired.

SUMMARY OF THE INVENTION It is an object of the present invention to provide an image forming apparatus which prevents color misregistration due to the above-mentioned equipment installation position error and driving unevenness and improves the quality of a color image.

[0008]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a plurality of sets of charging means, image exposing means, and developing means on a drum-shaped image forming body to perform charging, image exposing, and developing. ,
In an image forming apparatus that forms a color toner image by superimposing a toner image on an image forming body, a positioning unit uses a most upstream charging unit and a most downstream developing unit, and a plurality of image exposure units therebetween. This is achieved by an image forming apparatus that forms a single-color toner image having a specific resist pattern, and performs alignment control of image exposure based on the displacement.

Further, a plurality of sets of charging means, image exposing means and developing means are arranged on the drum-shaped image forming body to perform charging, image exposure and development, and a toner image is superposed on the image forming body. In an image forming apparatus for forming a color toner image, two of the image exposure units are disposed so as to be opposed to each other by 180 °, and a monochromatic toner image including a specific resist pattern is formed by using the two image exposure units. The present invention is also achieved by an image forming apparatus characterized in that the image forming apparatus forms the image and controls the alignment of the image exposure based on the positional deviation.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The structure and function of an image forming apparatus according to the present invention will be described with reference to FIGS. The image forming apparatus shown in FIG. 1 is an image forming apparatus that has an image exposing unit inside a latent image forming body, forms a toner image on the image forming body, and collectively transfers and fixes the toner image. However, embodiments of the present invention are not limited to this.

The photosensitive drum 10, which is a latent image forming body (image forming body), has a cylindrical base formed of a transparent member of, for example, glass or transparent acrylic resin provided inside, and a transparent conductive layer, a- A photosensitive layer such as an Si layer or an organic photosensitive layer (OPC) is formed on the outer periphery of the substrate, and is rotated clockwise as indicated by an arrow in FIG. 1 with the transparent conductive layer grounded.

In the present embodiment, the photoconductor layer of the photoconductor drum needs to have an exposure light amount having a wavelength capable of providing an appropriate contrast with respect to the light attenuation characteristic (photocarrier generation) of the photoconductor layer. I just need. Therefore, the light transmittance of the transparent substrate of the photoreceptor drum in the present embodiment does not need to be 100%, and may be such that a certain amount of light is absorbed when the exposure light is transmitted. As a material of the light-transmitting substrate, an acrylic resin, particularly one polymerized using a methyl methacrylate monomer, is preferably used because it is excellent in transparency, strength, precision, surface properties, and the like, but is used for other general optical members and the like. Used soda glass, pyrex glass, borosilicate glass and acrylic,
Various translucent resins such as fluorine, polyester, polycarbonate, and polyethylene terephthalate can be used. Further, as long as it has a light-transmitting property with respect to the exposure light, it may be colored. As the translucent conductive layer, indium
Tin / oxide (ITO), tin oxide, lead oxide, indium oxide, copper iodide, and a metal thin film of Au, Ag, Ni, Al, etc., which maintain light transmissivity, are used. A vacuum evaporation method, an active reaction evaporation method, various sputtering methods, various CVD methods, a dip coating method, a spray coating method, and the like are used. As the photoconductor layer, an amorphous silicon (a-Si) alloy photosensitive layer, an amorphous selenium alloy photosensitive layer, or various organic photosensitive layers (OPC) can be used.

The photosensitive drum 10 has a red component (700 n
m) and infrared light, especially far infrared light (2800 n).
m) is transparent and has no light sensitivity. It is preferable to use infrared light as the image exposure light of the present invention as described later.

The photosensitive drum 10 is rotated clockwise by its power with the transparent conductive layer being grounded.

Scorotron charger 11 as charging means
Is used in an image forming process of each color of yellow (Y), magenta (M), cyan (C) and black (K), and is exposed in a direction orthogonal to a moving direction of the photosensitive drum 10 as an image forming body. It is installed facing the body drum 10,
A charging operation is performed by a control grid maintained at a predetermined potential with respect to the above-described organic photoconductor layer of the photoconductor drum 10 and corona discharge by a discharge wire.
To give a uniform potential.

Image exposing device 12 as image exposing means for each color
Indicates that the exposure position on the photosensitive drum 10 is set between the discharge electrode 11 a of the scorotron charger 11 and the developing position of the developing device 13 with respect to the developing sleeve 130.
0 is provided on the upstream side in the rotation direction.

The image exposure device 12 is composed of an LED array having a light emission wavelength of 680 nm arranged in parallel (main scanning direction) to the axis of the photosensitive drum 10 and a selfoc lens as an equal magnification imaging element. With line-shaped image exposure means,
All of them are mounted on a common columnar support member 20 and each of the image exposure units 12 (Y), 12 (M), 12 (C), 12
(K) are arranged at equal intervals and housed inside the substrate of the photosensitive drum 10, and each of the exposure devices 12
Are accurately and linearly arranged in a direction orthogonal to the direction of movement of the moving object.

As the exposure element, a linear element in which a plurality of light-emitting elements such as FL (phosphor emission), EL (electroluminescence), PL (plasma discharge), and LED (light-emitting diode) are arranged in an array is used. Used.

In the present invention, as shown in FIG. 3, the most upstream image exposure unit 12 is provided so that the color matching control can be performed accurately.
The distance between (Y) and the most downstream image exposure device 12 (K) is
180 at an angle about the rotation center of the photosensitive drum 10
, And the angles among the image exposure units 12 (Y), 12 (M), 12 (C), and 12 (K) are arranged at equal intervals, each being 60 degrees. .

A developing unit 13 as a developing means provided on the rotating photosensitive drum 10 in accordance with the color order in which the image is formed and the rotating photosensitive drum 10 includes yellow (Y), magenta (M), cyan (C), Black (K) developers are accommodated in the photosensitive drum 10 at the developing position while maintaining a predetermined gap from the peripheral surface of the photosensitive drum 10.
Rotate in the same direction as the rotation direction of, for example, a thickness of 0.3 to
The developing sleeve 130 is formed of a nonmagnetic stainless steel or aluminum material having a cylindrical shape of 0.5 mm and an outer diameter of 10 to 20 mm.

The developing unit 13 is moved to a predetermined distance from the photosensitive drum 10 by an abutting roller (not shown), for example, 100 μm.
A developing bias voltage obtained by applying a DC or further AC voltage to the developing sleeve 131 is applied to the developing sleeve 131 during the developing operation of the developing device 13 for each color. Jumping development is performed by the developer contained in the developing unit 13 attached to the layer, and a developing bias voltage having the same polarity as that of the toner is applied to the negatively charged photosensitive drum 10 that grounds the transparent conductive layer, Reverse development is performed in a non-contact state where toner is attached to the exposed portion. The developing gap accuracy at this time needs to be about 20 μm to prevent image unevenness.

The developer used here is a spherical toner having a volume average particle diameter of 1 to 20 μm, preferably 4 to 10 μm, since the transfer of the toner can be effectively controlled by an oscillating electric field. Average particle size is 10
A two-component developer comprising a carrier having a size of from 60 to 60 μm, preferably from 20 to 50 μm is preferably used. When a toner having a volume average particle diameter of 10 μm or less is used, the resolving power is remarkably improved, and a clear high-quality image with faithful reproduction of the density difference is obtained, and the volume average particle diameter is 20 μm. Above, the image quality is reduced. When the volume average particle diameter of the toner is 4 μm or less, the cohesive force is large and triboelectricity is likely to be insufficient. When the volume average particle diameter is 1 μm or less, the toner is liable to be scattered, which is not preferable.

Next, a process of forming a color image in the present apparatus will be described.

Image information read from an original image by an image sensor by an image reading device separate from the present device;
Alternatively, image data for each color of Y, M, C, and K obtained by performing gamma correction and other image processing on image information of an image edited by a computer is temporarily stored in an image memory.

Printing (image recording) is started by pressing a start button on an operation panel (not shown). At the start of image recording, the photoconductor drum 10 is rotated clockwise by the start of the pulse motor 10M, which is the drive motor of the photoconductor drum 10, and at the same time, the electric potential is applied to the photoconductor drum 10 by the charging action of the scorotron charger 11 (Y). Is started.

After the photosensitive drum 10 is applied with a potential,
Exposure of the image exposing unit 12 (Y) by an electric signal corresponding to yellow (Y) image data, which is a first color signal read from the image memory, is started, and the photosensitive drum 10
Yellow (Y) on the photosensitive layer on the surface by the rotational scanning of
An electrostatic latent image corresponding to the image is formed.

The latent image is reversal-developed by the developing device 13 (Y) in a state where the developer on the developing sleeve 130 is not in contact, and a yellow (Y) toner image is formed according to the rotation of the photosensitive drum 10. .

Next, the photosensitive drum 10 is further provided with a scorotron charger 1 on the yellow (Y) toner image.
1 (M) is charged with a potential, and the image exposure device 1
Exposure is performed using the second (M) second color signal, that is, image data of magenta (M), and the magenta image is formed on the yellow (Y) toner image by non-contact reversal development by the developing device 13 (M). The toner images (M) are sequentially superimposed and formed.

By the same process, the scorotron charger 11 (C), the image exposure unit 12 (C) and the developing unit 13 (C)
And a cyan (C) toner image corresponding to the third color signal, and a fourth color signal corresponding to the scorotron charger 11 (K), the image exposure unit 12 (K), and the developing unit 13 (K). The black (K) toner images are sequentially superimposed, and a color toner image is formed on the peripheral surface within one rotation of the photosensitive drum 10 and sometimes over one rotation.

The exposure of the organic photosensitive layer of the photosensitive drum 10 by the Y, M, C, and K image exposure devices 12 is performed from the inside of the drum through the above-mentioned transparent substrate. Therefore, the exposure of the images corresponding to the second, third, and fourth color signals is performed without any influence from the previously formed toner image, and the same exposure as the image corresponding to the first color signal is performed. It is possible to form an electrostatic latent image. Developing device 1
3, the developing sleeve 1
A developing bias voltage in which an alternating current is superimposed on a direct current is applied to the photosensitive drum 30, a jumping development is performed by a one-component or two-component developer stored in the developing device 13, and the photosensitive drum 10 that grounds the transparent conductive layer is applied to the photosensitive drum 10. In this way, non-contact reversal development is performed.

Thus, the color toner image formed on the peripheral surface of the photosensitive drum 10 is transferred from the paper feed cassette 15 in the transfer unit 14A and is transferred onto the transfer paper fed synchronously by the driving of the timing roller 16. You.

The transfer paper to which the toner image has been transferred is separated from the peripheral surface of the photoreceptor drum 10 by the removal of the charge by the charge eliminator 14B, and is fixed by fusing the toner image in the fixing device 17. The paper is discharged onto a tray 200 at the top of the apparatus via the paper discharge roller 18.

On the other hand, the photosensitive drum 10 from which the transfer paper is separated
The cleaning device 19 removes and cleans the residual toner to continue the formation of the toner image, or temporarily stops and waits for the formation of a new next image.

The photosensitive drum 10 shown in the embodiment of FIG. 1 includes each scorotron charger 11 and developing device 1
3 together with a cleaning device 19, a toner storage container 40 for supplying toner to each of the developing devices 13 and a waste toner container 50 for storing waste toner collected by the cleaning device 19, in a process cartridge 30. The main body 1 is configured so that it can be pulled out, for example, in the horizontal direction, moved, and further taken out of the apparatus main body 1.

FIG. 2 shows a cross section taken along line AA of FIG.
The photosensitive drum 10 is fitted concentrically to a flange member 10A at the front end, and the flange member 10A is an intermediate part near the end of the fixed shaft member 21 of the support member 20 of the image exposure device 12 via a bearing B3. The portion is concentrically supported, and the end of the fixed shaft member 21 is fitted into a fixing hole in the wall surface of the process cartridge 30 so as to be directly fixed and supported. Further, the flange member 10B at the rear end portion concentrically supports an intermediate portion near the opposite end portion of the fixed shaft member 21 via the bearing B4. At the same time, the opposite end of the fixed shaft member 21 is fixed to and supported by a concentric fitting hole at the center of the disk member 30A detachable from the process cartridge 30.

A magnet MB, which is a ring-shaped driving body of the pulse motor 10M, is mounted on the flange member 10A concentrically with the photosensitive drum 10, and the flange member 1
A pulse motor 1 is mounted on the process cartridge 30 on the 0A side.
A 0M drive coil MA is mounted concentrically with the photosensitive drum 10. The magnet MB is a permanent magnet that is magnetized such that a number of magnetic poles are arranged in a ring at equal intervals, and the drive coil MA is a coil group provided in a ring corresponding to the number of magnetic poles of the magnet MB.

A rotary encoder 10S is mounted concentrically with the photosensitive drum 10 at an end of the flange member 10B, and an encoder reader 30S for the rotary encoder 10S is mounted on the disk member 30A. Thereby, the angular position, the rotation speed, and the like of the photosensitive drum 10 can be measured.

The control unit has a built-in clock for performing clocking using crystal oscillation or the like, and performs adjustment control for image formation and image alignment based on the clocking.

Since the photosensitive drum 10 is made of plastic except for glass and formed by centrifugal polymerization, the dimensional accuracy of the outer diameter is high. Therefore, fitting the flange members 10A and 10B on the basis of the outer diameter of the photoconductor drum 10 makes it possible to relatively easily perform high-precision coupling in which center runout is less likely to occur, and furthermore, driving by the pulse motor 10M directly connected to the photoconductor drum 10. Is driven at a very constant speed.

If a rotational drive is performed via a gear or the like, a speed irregularity occurs on the peripheral surface of the photosensitive drum 10 where a complicated high frequency and low frequency are synthesized due to pitch irregularity and eccentricity of the gear. In this embodiment, since the drive motor and the photosensitive drum 10 are directly connected, the speed unevenness on the peripheral surface of the photosensitive drum 10 is mainly caused by eccentricity, and is approximately indicated by a Sin curve. (FIG. 4).

[Adjustment of Alignment] Next, the adjustment of the alignment performed prior to the image formation will be described.

The image exposure means for yellow (Y), magenta (M), cyan (C) and black (K) are all provided at predetermined positions. The timing of image exposure is set so that image exposure is performed in a non-existent form. A program for alignment adjustment is set in advance and stored in ROM, and when the adjustment mode is set, the adjustment is performed in the following order. Is performed.

Image exposure unit 12 for yellow (Y) and black (K)
As shown in FIG. 3, (Y) and 12 (K) are 180 ° apart and are axially symmetric. Accordingly, assuming that the time required for one rotation of the photosensitive drum 10 is T ₀ , the image exposure of K is performed when T _0/2 elapses after the image exposure of Y, and then the image is developed by the developing unit 13 (K) to develop a monochrome image. When the resist pattern is formed, the yellow (Y) and black (K) resist patterns match when the rotation speed of the photosensitive drum 10 does not change, and when there is a speed change, the resist pattern between the Y and K resist patterns changes. Causes a shift. Since the development is performed only by the developing device 13 (K), the direction of the shift cannot be determined for each resist pattern in the same color. Therefore, for example, the pattern of K is made longer than the other patterns so that the direction of the shift can be determined. If resist patterns are formed at equal intervals, for example, at intervals of 1 ° over one rotation, the two patterns are overlapped to form a single pattern having a large width because the amount of deviation is actually small. FIG. 5 shows an enlarged view.

The sensor S1 detects the resist pattern of (Y), (M), and (C), and the sensor S2 is a sensor for detecting a portion longer than the other resist pattern of (K) and is the same as the sensor S1. Position. Sensor S
Reference numerals 1 and S2 each include a photocoupler using infrared rays and are located between the developing unit 13 (K) and the transfer unit 14B so as to detect a resist pattern.

With such a configuration, the direction of deviation of the other resist pattern with respect to the K resist pattern is (+).
Or (-).

In the sensors S1 and S2, the light emitting portion of the photocoupler irradiates from inside the photosensitive drum 10 and detects the resist pattern by the reflected light.
It is also possible to provide a light-emitting unit outside the zero at a position facing the light-receiving unit of the photocoupler, and detect the resist pattern using transmitted light. It is preferable that the detection light has a transmittance of 70% or more to the photosensitive drum 10. It is preferable that the photoreceptor of the photoreceptor drum 10 has no light sensitivity to the detection light in order to prevent the toner image from being disturbed and the photoreceptor from being lightly fatigued. In order to increase the detection accuracy,
It is necessary that the light emitting elements of the sensors S1 and S2 are adjusted so that the focused light is irradiated on the line of the resist pattern.

First, the formation and measurement of the resist pattern
And K, and then M and K, and then C and K. This order may be performed in any combination.

The deviation of the resist pattern represents a color deviation, which is a direct current component (DC component) and an alternating current component (AC component).
In the resist pattern shown in FIG. 5, the portion where the interval is narrowest is a DC component generated mainly due to an installation error of the installation position. FIG. 5 is an enlarged view. Actually, by increasing the precision of parts and the mounting accuracy of the equipment, the lines become thicker even at the most distant places, and are not two lines.

This DC component is detected by the clock of the control unit during the time when the sensor S2 detects the resist pattern formed over one circumference, and only one resist pattern is detected from the shortest resist pattern detection time. Is subtracted from the time during which is detected.

(A) Detection of speed unevenness Measurement (1): First, Y exposure after Y charging, K exposure after T _0/2 hours, K exposure, and K development so that yellow (Y) and black (K) images match. The sensor S1 and the sensor S2 determine the narrowest space between the Y and K resist patterns, measure the amount of displacement of the resist pattern and the direction of the displacement, and obtain the DC component to be corrected (between YK). , And this is t _YK .

Measurement (2): Next, M exposure after charging M, T ₀ / M so that the magenta (M) and black (K) images match.
After 3 hours, K exposure and K development are performed, and the sensor S1 and the sensor S2 determine the narrowest interval between the M and K resist patterns, and measure and correct the positional shift amount and the direction of the resist pattern shift. A power DC component (between MKs) is obtained, which is referred to as t _MK .

Measurement (3): C exposure after C charging, T ₀ / T so that the images of magenta (C) and black (K) match.
Six hours later, K exposure and K development are performed, the position of the narrowest interval between the resist patterns is obtained by the sensors S1 and S2, and the positional deviation amounts and the directions of the C and K resist patterns are measured and corrected. To obtain the power DC component (between CK)
This is _defined as t _CK . Since the values of t _YK , t _MK and t _CK may be (+) and (−), these values are taken into account in the next correction.

(B) Timing Correction of Write Position The above-described correction of the DC component is mainly due to an attachment error with respect to the set position of the image exposure unit 12, but the AC component described below is mainly the eccentricity of the photosensitive drum 10. The deviation due to the speed unevenness is approximately the same as the amplitude a of one cycle of one rotation of the drum.
This is an n-curve.

In the Y and K resist patterns shown in FIG. 4, a value obtained by subtracting the interval (DC component) at the narrowest portion from the interval at the widest portion corresponds to twice the amplitude a. . Therefore, the amplitude a is obtained from the resist pattern, but when the amplitude a is sufficiently small, it is not necessary to correct the AC component. It is compared with a threshold a ₀ is set sought amplitude a determined, determines whether to correct the AC component. The correction of the AC component is performed as follows.

In order to set the write start position (time) to (+), a reference position is provided upstream of the K image exposure position (time) by T _S as shown in FIG. The write start position of K is the position on the photosensitive drum 10 where the speed fluctuation = 0 from the curve in the previous speed unevenness detection, and the rotary encoder 1
This position is determined by 0S.

[0056] Correction (1): write start position of Y (time) is, T _S - and _{{(T 0/2) -t} YK}, color shift (speed variation) of the Y correction a {sin (-π + t ) / 2π-s
in (t / 2π).

[0057] Correction (2): write start position of the M (time) is, T _S - and _{{(T 0/3) -t} MK}, color shift (speed variation) of M correction a {sin (- [pi] / 3 + t) / 2π
−sin (t / 2π).

[0058] Correction (3): write start position of the C (point) is, T _S - and _{{(T 0/6) -t} CK}, color shift (speed variation) of C corrected a {sin (- [pi] / 6 + t) / 2π
−sin (t / 2π).

The write start position (time) of K is T _S , K
Color shift (speed unevenness) correction is zero.

As described above, it is possible to correct the color shift caused by the installation position error of the equipment of each color and the color shift caused by the fluctuation of the rotation of the photosensitive drum 10.

[0061]

As described above, according to the present invention, it is possible to prevent the occurrence of the color shift caused by the error in the installation position of the equipment and the color shift caused by the fluctuation of the rotation of the image forming body in a simple manner with a simple structure. Thus, it has become possible to provide an image forming apparatus capable of obtaining an image of extremely excellent image quality at low cost.

[Brief description of the drawings]

FIG. 1 is a cross-sectional configuration diagram of an embodiment of an image forming apparatus according to the present invention.

FIG. 2 is a sectional view showing a built-in structure of a photosensitive drum and an image exposure device.

FIG. 3 is an explanatory diagram showing an arrangement of the image exposure device of FIG. 2;

FIG. 4 is a graph showing a speed variation due to a rotation variation of an image forming body and a deviation between respective colors.

FIG. 5 is an enlarged view showing an example of a resist pattern.

[Explanation of symbols]

 Reference Signs List 10 photoconductor drum (image forming body) 10M pulse motor 10S rotary encoder 11 scorotron charger 12 image exposure unit 13 developing unit 20 support member 21 fixed shaft member 30 process cartridge 30A disk member 30S encoder reader S1 sensor S2 sensor

 ────────────────────────────────────────────────── ─── Continuing from the front page (72) Inventor ▲ Hama ▼ Sh 太 ta 2970, Ishikawacho, Hachioji-shi, Tokyo Konica Corporation F-term (reference) 2H027 DA38 DA50 EB04 EC03 EC06 EC20 ED06 ED16 ED24 EE02 EE07 EF09 2H030 AA01 AA06 AD12 AD17 BB02 BB16 BB23 BB44 BB56 BB71

Claims (3)

[Claims] 1. A plurality of sets of charging means, image exposing means, and developing means are arranged on a drum-shaped image forming body to perform charging, image exposure and development, and a toner image is superimposed on the image forming body. In an image forming apparatus for forming a color toner image, a positioning unit uses a most upstream charging unit, a most downstream developing unit, and a plurality of image exposure units therebetween to form a single color toner image including a specific resist pattern. An image forming apparatus, comprising: forming an image; and performing image exposure alignment control based on the positional deviation. 2. A plurality of sets of charging means, image exposing means and developing means are arranged on a drum-shaped image forming body to perform charging, image exposure and development, and a toner image is superposed on the image forming body. In the image forming apparatus for forming a color toner image, two of the image exposure units are disposed so as to be opposed to each other by 180 °, and the two image exposure units are used to form a single color toner image having a specific resist pattern. An image forming apparatus, comprising: forming an image; and performing image exposure alignment control based on the positional deviation. 3. The image forming apparatus according to claim 1, wherein the alignment control controls writing timing of the image exposure unit.