JP2001121745A - Method for correcting density and image-forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain high-quality images by reducing a density unevenness in output images. SOLUTION: A light-emitting element having a beam diameter in a vertical scanning direction different from a natural beam diameter (reference beam diameter) is turned on by a plurality of the number of times with an intensity (quantity of light) different from a natural intensity in response to one lighting signal. A position is changed in the vertical scanning direction at this time. A synthetic profile is thus agreed with a profile of the natural beam diameter. A density unevenness caused by a variation of the beam diameter in the vertical scanning direction by each light-emitting element is suppressed accordingly.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a density correction method and an image forming apparatus, and more particularly to a print head in which a plurality of light emitting elements are arranged in a line, and the print head and an image carrier are relatively moved. While lighting the light emitting element once for each predetermined area based on image data,
The present invention relates to a density correction method and an image forming apparatus that are used in an image forming apparatus that forms an image and that correct density unevenness of a formed image.

[0002]

2. Description of the Related Art At present, an image forming apparatus for copying an image on transfer paper by digital electrophotography has become widespread.
In such an image forming apparatus, generally, a photosensitive member having a uniformly charged surface is exposed based on image data to form an electrostatic latent image, and toner is supplied to the obtained electrostatic latent image. After development, transfer paper is superimposed on the developed toner image, and the toner image is transferred by electrostatically adsorbing the toner to the transfer paper surface,
Thereafter, heat or pressure is applied to the transfer paper to fix the transferred toner image, thereby forming an image.

Exposures based on image data can be broadly divided into those of a laser scanning type that scans with a laser beam and those of a laser scanning type.
There is an LED print head type combining an ED array and a lens array. Since the LED print head system can reduce the size of the device compared to the laser scanning system,
In recent years, the usage ratio has been rapidly increasing.

The LED print head includes an LED image bar on which a plurality of LED chips each including a large number of LED elements are arranged, a selfoc lens for forming a light beam emitted from the LED elements on the surface of a photoconductor, and the like. ing. That is, in the LED print head system, each LED element is driven based on image data to emit a light beam toward the photoconductor, and the emitted light beam is imaged on the photoconductor surface by a selfoc lens. Thus, exposure based on the image data of the photoconductor is performed.

At this time, the light beam imaged on the photoreceptor by the LED print head generally has a light amount distribution (profile) as shown in FIG. As can be seen from FIG. 42, the profile of this light beam is substantially similar to a Gaussian distribution, and as shown in FIG. 43, the shape is more strictly functionalized by adding Gaussian distribution functions having different diameters. be able to.

In FIG. 43, a light beam having a diameter of 55 μm is synthesized by combining a light beam having a Gaussian distribution having a diameter of 37 μm and a light beam having a Gaussian distribution having a diameter of 74 μm at a light intensity ratio of 1: 0.8. This shows an example in which a profile equivalent to the above is obtained. The diameter of the light beam is 1 / e ² (e: of the light intensity at the center of the light beam).
The diameter (so-called “beam diameter”) of a point serving as a base of a natural logarithm is shown.

On the other hand, in the LED print head, a profile of a light beam connected to a photoconductor is formed by an LED.
There is a problem that it varies from element to element. This is because the positional relationship between the LED element and the SELFOC lens shifts, and the beam diameter of the light beam connected on the photoconductor by the LED print head changes. Causes of the displacement between the LED element and the Selfoc lens include the following phenomena.

Incorrect mounting of the LED chip on the LED image bar. The position of the LED image bar and the SELFOC lens are not matched. Deformation of the SELFOC lens. Incorrect mounting of the LED element in the LED chip. When the LED image bar is improperly mounted, the beam diameter changes for each chip. Such a change in the beam diameter causes a change in the density of the output image when, for example, outputting a gradation image.

In FIG. 44, the beam diameter in the main scanning direction (direction in which the LED elements are arranged) is fixed to 55 μm, and the beam diameter in the sub-scanning direction (direction orthogonal to the main scanning direction) is 40 to 60 μm.
Density of output image when changed in width of m (calculation result)
Indicates fluctuation. Specifically, the gradation image of a matrix type digital screen where the number of exposure dots changes according to the density,
When the beam diameter in the sub-scanning direction was 40 μm, the optical density was 0.85. On the other hand, the degree of the density change was calculated with the setting in which the beam diameter changed uniformly in a wide area.

From this result (see FIG. 44), when the beam diameter is changed from 40 μm to 60 μm, the density becomes 0.1 μm.
07 fluctuates. Note that this beam diameter variation is the range variation that can actually occur in the LED print head.

On the other hand, it has been experimentally found that if there is a portion where a density variation of 0.03 occurs in a halftone image that is to be output at a uniform density, a person who evaluates the image feels annoying. know. In other words, when a range variation that can actually occur in the beam diameter in the sub-scanning direction occurs,
Density fluctuation more than twice the allowable density fluctuation amount occurs.

For this reason, an image forming apparatus of the LED print head type is required to correct the variation of the beam diameter for each LED element. As a technique for correcting the variation of the beam diameter, Japanese Patent Application Laid-Open No. 8-142406 discloses a technique of measuring a light emission intensity distribution (light beam profile) of each light emitting element of an LED print head, and slicing the distribution with a reference light emission intensity value. A technique is disclosed in which a light emission intensity range of the reference light emission intensity value is calculated for each light emitting element, and drive energy is corrected so that the light emission intensity widths become equal to cause each light emitting element to emit light. Specifically, as shown in FIG. 45, when the emission intensity width at the reference emission intensity value is smaller than the nominal value (the beam diameter is small), the light amount is increased (A), and the light intensity is larger than the nominal value (that is, the beam diameter is larger). In the case of (thick), the variation in beam diameter can be corrected by reducing the light amount (B).

[0013]

However, according to the above technique, when the light amount is reduced with respect to the case where the beam diameter is large, the emission intensity width at the reference emission intensity value becomes the same, but the emission intensity peak decreases. Therefore, although the area of the area where the toner is to be adhered is the same, the layer thickness of the adhered toner is reduced, and the density may be excessively lowered. On the other hand, when the light amount is increased when the beam diameter is small, the density may be excessively increased, which is not preferable.

When the light beam profile is adjusted with the reference light emission intensity value, the distribution of the level lower than the reference light emission intensity value also changes accordingly. Since this low level distribution overlaps the adjacent light beam, the density of the adjacent pixel may be affected.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and has as its object to provide a density correction method and an image forming apparatus capable of reducing density unevenness of an output image and obtaining a high-quality image. And

[0016]

According to one aspect of the present invention, there is provided a print head in which a plurality of light emitting elements are arranged in a line, wherein the print head and the image carrier are arranged in a line. A density correction method used in an image forming apparatus for forming an image by turning on the light emitting element once for each predetermined area based on image data while relatively moving the image, and correcting density unevenness of the formed image The light emitting element that outputs a light beam whose beam diameter in the relative movement direction is a predetermined value or out of a predetermined range is replaced with the one-time lighting, instead of the original light amount or the original lighting. It is characterized in that the lighting is performed a plurality of times by shifting the time and by a predetermined distance in the relative movement direction for each of the predetermined areas.

According to the first aspect of the present invention, the light emitting element that outputs a light beam having a beam diameter other than the predetermined beam diameter is replaced with the original one.
Instead of lighting one time (actual light beam output for one lighting signal), by changing the position in the sub-scanning direction with a different intensity from the original or with a different lighting time from the original, the sub-lighting is performed. Density unevenness (density fluctuation) that occurs in an output image due to variation in beam diameter in the scanning direction is corrected. Hereinafter, the principle of this correction will be described in detail.

FIG. 1 shows profiles of two light beams having the same light amount and different beam diameters. Here, as an example, the profile P1 of a light beam having a beam diameter of 40 μm in the sub-scanning direction and the profile P of a light beam having a beam diameter of 60 μm
2 is shown. The beam diameter in the main scanning direction is 55 μm. In the following, unless otherwise specified,
The beam diameter in the sub-scanning direction will be described simply as “beam diameter”.

From FIG. 1, it can be seen that there is a difference in peak height (light amount) when the beam diameter is different even with the same light amount.
In order to clearly show this, FIG. 2 shows the profiles P1 of two light beams having different beam diameters shown in FIG.
The profile section of P2 in the sub-scanning direction is shown in an overlapping manner. From FIG. 2, the light beam having the beam diameter in the sub-scanning direction of 60 μm has a peak height slightly less than 0.7 times that of the light beam having the beam diameter in the sub-scanning direction of 40 μm, and the distribution width is also small. It can be seen that there is a difference. This difference in the profile appears as a difference in the layer thickness of the adhered toner and the toner adhered area during image formation. That is, even if the light amount is the same, exposure with a light beam having a different profile changes the density of an output image.

Next, FIG. 3 shows an example of exposure using two light beams having different beam diameters shown in FIGS. In FIG. 3, a solid line indicates an exposure distribution (exposure profile) when a light beam having a beam diameter of 60 μm is lit once. The dotted line represents a light beam having a beam diameter of 40 μm.
/ 3 different positions in the sub-scanning direction (here, 10.
This is an exposure amount distribution (synthesized exposure profile) obtained by lighting three times (at an interval of 4 μm) (see a chain line) and synthesizing them.

Since the two lines (the solid line and the dotted line) are almost the same, a light beam having a beam diameter of 40 μm is divided into a plurality of times and illuminated a plurality of times to perform a composite exposure, whereby the beam diameter becomes 60 μm.
It can be seen that an exposure profile substantially the same as that obtained when exposure was performed with a light beam of m was obtained, and the image density was substantially the same. That is, even if there is a variation in the beam diameter for each light emitting element, light emitting elements whose beam diameter is different from the original beam diameter (reference beam diameter) are output in the sub-scanning direction at a different intensity (light quantity) from the original. By changing the position and lighting a plurality of times, the combined exposure profile can be made to coincide with the exposure profile (reference exposure profile) by the light beam having the original beam diameter, and the density variation can be suppressed.

Next, a method for determining the following parameters will be described.

The intensity different from the original intensity ratio p is changed in the sub-scanning direction. The distance s is changed a plurality of times. The number of times is k. The number of times is k. (y, φ).
Here, y is the position in the sub-scanning direction (μm), and φ is the beam diameter (μm). Specifically, as described above, a function obtained by combining Gaussian distributions may be used. Or,
Substantially equivalent results can be obtained by using the Gaussian distribution function itself, where φ is the beam diameter of 1 / e ² . When the latter is used, the exposure profile equation is expressed as in equation (1).

[0024]

(Equation 1)

Next, a reference exposure profile is obtained. Assuming that the central beam diameter is a μm, the reference exposure profile is

[0026]

(Equation 2)

## EQU1 ##

The light beam is shifted by a predetermined distance s, and k times,
The combined exposure profile when the lighting is performed at the intensity ratio p is represented by Expression (3).

[0029]

(Equation 3)

Therefore, the parameters p, s, and k are set so that the error between Equations (2) and (3) is minimized, that is, the error between the reference exposure profile and the composite exposure profile is minimized. As a result, optimal parameters can be obtained. Equation (2) and Equation (3)
Is expressed by equation (4).

[0031]

(Equation 4)

It should be noted that if the light quantity is set to be p = 1 / k (times) with respect to the light quantity of the reference light beam, a substantially satisfactory correction can be made.

The parameters used in the description of FIG.
By substituting the following conditions into the equation (4) to obtain a function of the distance s, the value of s that gives the best result is calculated.

Reference beam diameter 60 μm, φ = 40 μm, p
= 1 / k times, k = 3 times FIG. 4 is a graph showing the result of substituting this condition. FIG.
It can be seen that the error is minimum when the distance S is 10.4 μm, and the error is minimum when the light beams are turned on at 10.4 μm intervals.

Further, the following conditions are substituted into FIG. 5, and in each case where the beam diameter φ to be corrected is 30, 35, 40, 45, and 50 μm, the number of times of lighting k and the minimum error (Error (φ, p,
The relationship of Error (φ, p, s, k) at s when s, k) is minimized is shown in a graph.

Reference beam diameter 55 μm, P = 1 / k times From FIG. 5, it can be seen that Error (φ, p, s, k) can be reduced as the value of the number of lighting times k increases, that is, as the lighting increases. It can be seen that good correction can be performed.

It should be noted that the number of lighting times k is determined by the beam diameter φ to be corrected.
Since the complicated control is required to change or to finely chop according to the lighting conditions, the lighting number k may be determined according to the range of the beam diameter to be corrected. According to the calculation by the inventor, for example, the range of 40 to 60 μm is corrected to 60 μm (or the range of 40 to 60 μm is corrected to a central value of 55 μm).
In the case of (correction to ± 5 μm), sufficiently good results were obtained by performing correction three times. This can be understood from the fact that the error value changes substantially horizontally in FIG. 5 when the correction target beam diameter φ is 40, 45, and 50 μm and the number of lighting times k is 3 or more.

In the present invention, a profile equivalent to a large beam diameter is obtained by combining and exposing a small beam diameter.
It is necessary to set the beam diameter on the thick side to the beam diameter to be corrected, that is, the reference beam diameter.

Here, when it is desired to converge the beam diameter variation to be 0 μm, the target having the largest beam diameter among the variations may be selected. 40-60 mentioned above
If the variation is in the range of μm, 60 μm is the beam diameter of the correction reference.

On the other hand, when it is desired to reduce the variation of the beam diameter to within a certain range, the combined exposure profile may be contained within a certain beam diameter range including the upper limit on the thick side. For example, if this range is determined from the relationship between the beam diameter in the sub-scanning direction and the density fluctuation shown in FIG. 44 and the value of 0.03 which is the target value of the density fluctuation, the beam diameter in the sub-scanning direction is 50 to 60 μm. If it is within the range, the goal will be met. Therefore, in this case, it is appropriate to set the beam diameter as the correction reference such that the center value is 55 μm and the tolerance width is within ± 5 μm.

The method of selecting the center value in the range to be set is as follows: center value: range lower eye tolerance width: plus tolerance center value: range center tolerance width: plus / minus tolerance center value: range upper limit tolerance width : Negative tolerance or an intermediate value may be selected.

When the light quantity is changed, it is preferable that the changed light quantity is one of the original light quantity that is a multiple of the original light quantity. Also,
In the case where the lighting time is changed, the changed lighting time may be set to one of the plurality of times of the original lighting time.

Further, as described in claim 4,
The plurality of combined exposure distributions in the relative movement direction obtained when the light emitting element is turned on a plurality of times and the image carrier is exposed, the beam diameter of the light beam to be output is the predetermined value. The predetermined distance may be set so as to substantially coincide with an exposure amount distribution in the relative movement direction obtained when the image carrier is exposed by turning on the light emitting element that coincides once.

Further, as described in claim 5,
It is preferable that the predetermined value is a dimension of the largest beam diameter of the light beams output from the plurality of light emitting elements. Alternatively, as described in claim 6, it is preferable that the predetermined range includes the largest beam diameter of the light beams output from the plurality of light emitting elements.

Further, the invention according to claim 7 includes a print head in which a plurality of light emitting elements are arranged in a line,
An image forming apparatus for forming an image by illuminating the light emitting element once for each predetermined region based on image data while relatively moving the print head and the image carrier, wherein the light emitting element outputs Determining means for determining whether the beam diameter of the light beam in the relative movement direction is within a predetermined value or a predetermined range set in advance; and The light emitting element whose beam diameter is determined to be outside the predetermined value or outside the predetermined range is replaced with the single lighting, and the original light amount or the original lighting time is changed to change the light emitting element for each of the predetermined regions. Lighting control means for turning on the light a plurality of times while being shifted by a predetermined distance in the relative movement direction.

According to the present invention, the judging means judges whether or not the beam diameter of the light beam output from each light emitting element is within a predetermined value or a predetermined range set in advance. You. A light emitting element whose beam diameter is determined to be out of the predetermined value or out of the predetermined range, that is, a light emitting element that outputs a light beam other than the predetermined beam diameter, is controlled by the lighting control means to perform a single lighting (one lighting signal). Instead of the actual light beam output), the light is illuminated a plurality of times by changing the position in the sub-scanning direction with an intensity different from the original or with an illuminating time different from the original. That is, since an image is formed by performing density correction for correcting density unevenness that occurs in an output image due to the beam diameter variation in the sub-scanning direction, a high-quality image can be obtained. .

[0047]

Next, an example of an embodiment according to the present invention will be described in detail with reference to the drawings.

(First Embodiment) FIG. 6 shows a schematic configuration of an LED print head type image forming apparatus to which the present invention is applied. As shown in FIG. 6, the image forming apparatus 10 has a cylindrical photosensitive drum 12 that rotates at a constant speed in the direction of arrow A, and image data (the image forming apparatus 10 in the present embodiment targets a monochrome image). Therefore, an LED print head 14 that irradiates a light beam based on grayscale image data) to the photosensitive drum 12
And

As shown in FIG. 7, the LED print head 14 includes an LED image bar 16, a selfoc lens 18, a heat radiating plate 20, and the like. As shown in FIG. 8, the LED image bar 16 has a plurality of LED chips 24 in which LED elements 22 as light emitting elements are densely arranged, with the light emitting surface facing up.

More specifically, each LED chip 24 has a large number of LED elements 22 arranged at predetermined intervals in the longitudinal direction. Each LED chip 24 has a longitudinal direction L.
The ED print heads 14 are arranged at predetermined intervals so as to coincide with the longitudinal direction. For example, an LED image bar that performs exposure in the short direction of A3 size at a resolution of 600 dpi has the following specifications.

LED chip: The chip width (length in the longitudinal direction) is 5 mm, and 118 LED elements 22 are arranged in a longitudinal direction at an interval of 42.3 μm in one chip.

LED image bar: 60 chips are arranged in a straight line.

That is, the LED image bar 16
The ED elements 22 are arranged in a line, and a plurality of light beams are emitted in a line. LED image bar 16
Are arranged so that their longitudinal direction (the arrangement direction of the LED elements 22) coincides with the axial direction of the photosensitive drum 12, and
The print head 14 emits light beams arranged in a line in a direction perpendicular to the paper surface of FIG.

The selfoc lens 18 includes the LED element 2
The light beams emitted from the respective LED elements 22 enter the Selfoc lens 18. As shown in FIG. 9, the selfoc lens 18 is a lens array in which a plurality of rod lenses 26 are arranged, and forms a light beam emitted from the LED element 22 on the photosensitive drum 12 into an erect equal-magnification image. Let it.

Further, as shown in FIG.
A charger 30 is disposed near the peripheral surface of No. 2 and upstream of the light irradiation position of the LED print head 14 in the rotation direction of the photosensitive drum. The charger 30 uniformly charges the photosensitive drum 12. The photoreceptor drum 12 uniformly charged by the charger 30 is rotated in the direction of arrow A shown in FIG. 1 to be irradiated with a light beam by the LED print head 14 and is subjected to sub-scanning. A latent image is formed on the drum 12.

Further, the toner is supplied to the photosensitive drum 12 at a position downstream of the light beam irradiation position of the LED print head 14 in the rotation direction of the photosensitive drum 12 so as to face the peripheral surface of the photosensitive drum 12. A developing device 32 is provided. The toner supplied from the developing device 32 is electrostatically attracted to a portion where the latent image is formed. As a result, a toner image is formed on the photosensitive drum 12.

On the downstream side in the rotation direction of the photosensitive drum 12 from the position where the developing device 32 is disposed (position where the axis of the photosensitive drum 12 is suspended), the transfer charging is opposed to the peripheral surface of the photosensitive drum 12. A vessel 34 is provided. The transfer charger 34 transfers the toner image formed on the photosensitive drum 12 to a transfer medium 36 such as paper. Transfer medium 36 onto which the toner image has been transferred
Is subjected to a fixing process by a fixing device (not shown) and then discharged out of the apparatus.

A cleaner 38 is provided downstream of the transfer charger 34 in the rotational direction of the photosensitive drum 12 so as to face the photosensitive drum 12. The toner remaining on the surface of the photosensitive drum 12 after the transfer is removed by the cleaner 38.

The image forming apparatus 10 is provided with control means 40 such as a microcomputer. The control means 40 includes
An image signal sent from a computer or the like is input. The control means 40 controls each LED based on this image signal.
A lighting signal for the element 22 is generated, and the LED print head 1
Then, the generated lighting signal is transmitted to No. 4. At this time, for the LED element 22 that needs to be corrected, the lighting position information and the light amount value information are added and a lighting signal is transmitted (described later). The LED print head 14 turns on each LED element 22 based on the lighting signal to form a latent image on the photosensitive drum 12.

(Structural Example of Control Means) FIG.
An example of 0 is shown. In FIG. 10, the control means 40
Has a RAM 42, a ROM 44, a CPU 46, and an I / O port 48. In addition, these RAM42, ROM
The 44, the CPU 46, and the I / O port 48 are interconnected via a system bus 50.

A parameter (hereinafter, referred to as a parameter) for correcting variations in the beam diameter φ in the sub-scanning direction is stored in the ROM 44 in advance.
"Optimal parameters" are stored. This optimal parameter is the error Error shown in the above equation (4).
Of the parameters of (φ, p, s, k), the number of lightings k (times) and the intensity ratio p (times) do not cause any problem even if the conditions are almost fixed.
Is preferably fixed as a constant, and the error in equation (4) is preferably a function of the distance s (μm) of the interval at which the light beam is turned on, and a value solved for s so as to minimize the error. In the present embodiment, the case of the following correction conditions will be specifically described.

Range of variation in beam diameter φ in the sub-scanning direction: 40 ≦ φ ≦ 60 μm
Tolerance width within ± 5 μm ・ Lighting frequency 3 times (k = 3), intensity ratio 1/3 times (p = 1/3) Examples of parameters in this case are shown below. Table 1 shows that the beam diameter as a correction reference is 55 μm and the number of lighting times is 3 (k = 3).
FIG. 10 is a calculation result of an optimum distance s (μm) obtained by solving Expression (4) for each value of the beam diameter φ in each sub-scanning direction with the intensity ratio being 1/3 times (p = 1/3). .

[0063]

[Table 1]

The ROM 44 stores such parameter relationships.

The beam diameter φ in the sub-scanning direction is input to the control means 40 for each LED element 22. CPU
At 46, it is determined whether or not each LED element 22 needs to be corrected based on the input beam diameter φ in the sub-scanning direction, and the result is stored in the RAM 42.

The LED element 2 which is determined to need correction
For 2, the optimum distance s (obtained from Table 1) corresponding to the beam diameter φ of the LED element 22 in the sub-scanning direction is stored as correction pitch information.

When the control means 40 converts the image signal into a lighting signal and outputs the same, the correction pitch information stored in the RAM 42 and the ROM
The lighting number k (k = 3 in the present embodiment) and the intensity ratio p times (p = 1 / in the present embodiment) stored in advance in 44.
Based on 3), the lighting position information and the light amount value information are added and transmitted to the LED print head 14. The LED print head 14 determines whether the LED element 2 that needs to be corrected based on the lighting signal to which the lighting position information and the light amount value information are added.
By turning on 2, the fluctuation of the output image density due to the variation of the beam diameter in the sub-scanning direction is corrected.

(Operation) Next, the operation of the first embodiment will be described.

First, before the LED print head 14 is mounted on the image forming apparatus 10, an exposure profile is measured for each LED element 22. By this exposure profile measurement, the beam diameter of the light beam in the sub-scanning direction is obtained. That is, for example, “the beam diameter φμm in the sub-scanning direction of the light beam corresponding to the x-th LED element 22 from the reference”
Is obtained. The measuring means for measuring the exposure profile is a CCD equipped with an objective lens.
A camera is suitable.

The measured exposure profile is input to the control means 40. The control means 40 determines whether correction is necessary for each LED element 22 based on the beam diameter φ μm in the sub-scanning direction obtained from the measurement and the correction reference beam diameter.

In this embodiment, the variation range of the beam diameter φ in the sub-scanning direction is 40 ≦ φ ≦ 60 μm, and the beam diameter center value 55 μm in the sub-scanning direction as a correction reference.
m, the tolerance width is ± 5 μm or less. Therefore, if the measured beam diameter φ in the sub-scanning direction is 50 ≦ φ ≦ 60 μm, this light beam (the LED element 22 corresponding to this light beam) It is determined that the correction of the present invention is not necessary.

When the measured beam diameter φ in the sub-scanning direction is 40 ≦
If φ <50 μm, it is determined that the light beam (the LED element 22 corresponding to the light beam) needs the correction of the present invention. When the control unit 40 determines that correction is necessary, the control unit 40 sets a correction pitch based on the beam diameter φ in the sub-scanning direction. The determination result of the presence or absence of this correction and the set correction pitch are stored and held in the RAM 42.

When the LED print head 14 is mounted on the image forming apparatus 10 and an image signal is input to the control means 40, the control means 40 controls the LED element 2 based on the image signal.
Generated for every two lighting signals. At this time, the presence / absence of the correction and the lighting position information and light amount value information corresponding to the correction are added to the lighting signal. The generated lighting signal is transmitted to the LED print head 14, and the respective LED elements 22 are driven based on the lighting signal, and the photosensitive drum 1
2 is irradiated with a light beam based on the image signal.

Specifically, the LED element 22 that does not need to be corrected emits a light beam at a predetermined position on the photosensitive drum 12 (hereinafter referred to as a “reference lighting position”) with a reference light amount. Is turned on for a predetermined time with the drive current of On the other hand, the LED element 22 that needs to be corrected changes the drive current value so as to be １ ／ times the reference light amount, and sets a predetermined lighting position and a position separated by an optimum distance sμm in the sub-scanning direction (hereinafter, referred to as “sm”). Lighting is performed three times so as to irradiate a light beam to a total of three positions on the photosensitive drum 12 (referred to as "auxiliary lighting positions"). In this case, one lighting is the same lighting time as when no correction is performed.

For example, when the image signals shown in FIG. 11 are input, if the LED elements 22 whose lighting is controlled based on the image signals in the second and fourth columns from the left require correction, the control means 40 Then, as shown in FIG.
Is driven so that the lighting signal is driven.

Here, for the sake of simplicity, the image signal is a binary signal indicating the presence or absence of an image for each pixel, that is, whether the image is black or white.
Pixels with an image are distinguished by drawing “●” in the grid. Further, the beam diameter φ in the sub-scanning direction of the LED element 22 whose lighting is controlled based on the image signal in the second column from the left is 40 μm, and the LED element 22 whose lighting is controlled based on the image signal in the fourth column from the left. The beam diameter φ in the sub-scanning direction is 48 μm.

As shown in FIG. 12, the LED elements 22 which need not be corrected and whose lighting is controlled based on the image signals in the first and third columns from the left are determined in accordance with the resolution of the image. At the lighting position, the light is lit at a reference light amount for a predetermined time. The reference lighting position is, for example, a resolution of 600 dp.
In the case of i, it is set at intervals of 42.3 μm in the sub-scanning direction.

The LED element 22 whose lighting is controlled based on the image signal in the second column from the left has a reference lighting position and 10.4 μm in the sub-scanning direction with respect to the reference lighting position.
At an auxiliary lighting position separated by (see Table 1), the light is lit for a predetermined time at a light amount of 1/3 of the reference light amount.

The LED element 22 whose lighting is controlled based on the image signal in the fourth column from the left has a reference lighting position and 7.9 μm before and after the reference lighting position in the sub-scanning direction (see Table 1). At an auxiliary lighting position that is only
The light is turned on for a predetermined time at a light amount of 3.

The latent image formed on the photosensitive member by being irradiated with the light beam by the LED print head 14 is
And transferred to the transfer medium 36 by the transfer charger 34. The transfer medium 36 is discharged out of the apparatus after the fixing process is performed. As a result, an image can be obtained in which the variation in the beam diameter in the sub-scanning direction is corrected based on the image signal.

FIGS. 13 to 13 show examples in which a light beam having a beam diameter φ in the sub-scanning direction of 40 to 49 μm is corrected using the light beam having a beam diameter in the sub-scanning direction of 55 μm as a correction reference. As shown in FIG. In each figure, the vertical axis indicates the exposure amount, and the horizontal axis indicates the position in the sub-scanning direction. Further, the exposure profile of a light beam having a beam diameter of 55 μm in the sub-scanning direction as a correction reference is indicated by a solid line, and the combined exposure profile obtained by lighting the light beam of the beam diameter to be corrected three times (see a dashed line) is indicated by a dotted line.

In each of FIGS. 13 to 22, the combined exposure profile (dotted line) is an exposure profile (solid line) of a light beam having a beam diameter of 55 μm in the sub-scanning direction as a correction reference.
And it can be seen that the correction according to the present invention is satisfactorily performed.

Instead of the light quantity, the light quantity of the LED is fixed to the reference, and the lighting time of the LED is set to one of the predetermined lighting time.
The same correction effect can be obtained with.

The first embodiment has been described on the assumption that the correction light beam can be applied to an arbitrary position on the LED element 22 that needs correction. However, irradiating a light beam to an arbitrary position may involve complicated control and increase the cost. For easier control, the correction light beam may be turned on according to the resolution in the sub-scanning direction. An example of this case will be described below as a second embodiment.

(Second Embodiment) First, the resolution of an image input from a computer is set to 600 dpi, and the resolution in the sub-scanning direction which can be developed on the image forming apparatus 10 is 240.
The case of 0 dpi will be described. In this case, 2400
The light beam can be turned on at a pitch corresponding to dpi, that is, at an interval of 10.6 μm. The correction condition is
As shown below, it is the same as the first embodiment.

Range of variation in beam diameter φ in the sub-scanning direction: 40 ≦ φ ≦ 60 μm
The tolerance width is within ± 5 μm. The number of times of lighting is three times (k = 3), the intensity ratio is 1/3 times (p = 1/3). Here, as an example, the image signal shown in FIG. The case where the LED element 22 whose lighting is controlled based on the image signal in the second column from the left in the drawing needs to be corrected will be described.

When the image signal shown in FIG. 23 is input, the control means 40 generates a lighting signal so that each LED element 22 is driven as shown in FIG. That is, even if the output resolution is 2400 dpi, the LED element 22 that does not need to be corrected is lit only once in four lines,
Lighting is performed once based on one image signal.

On the other hand, the LED element 22 which needs to be corrected
Is illuminated by an original lighting line (a line where the LED element 22 that does not need to be corrected is lit: a reference lighting position) and one line before and after it (an auxiliary lighting position) Lighting is performed three times based on one image signal. That is, the original one lighting operation reduces the amount of emitted light by one.
/ 3, the original lighting line and the three lines before and after it
It is lit in different times. Note that the auxiliary lighting position may not be a line adjacent to the reference lighting position.

As described above, if correction is performed in accordance with the resolution in the sub-scanning direction that can be developed on the image forming apparatus 10, each LE
When viewed from the D element 22 unit, the same amount of light is always maintained and used, so that the present invention can be implemented by a normal LED print head driving method. Note that the amount of emitted light is 1
Instead of / 3, the lighting time may be １ ／.

Next, a case where the resolution in the sub-scanning direction that can be developed on the image forming apparatus 10 is 4800 dpi will be described. In this case, the light beam can be turned on at a pitch corresponding to 4800 dpi, that is, at an interval of 5.3 μm. On the other hand, the optimum distance s obtained based on the correction conditions is 7.4 μm to 10.4 μm as shown in Table 1.
It is.

Therefore, when the expandable sub-scanning direction resolution is 2400 dpi, the line as the auxiliary lighting position cannot be selected, and the interval between the reference lighting position and the auxiliary lighting position is uniform. Resolution in the sub-scanning direction is 4
In the case of 800 dpi, a line to be an auxiliary lighting position can be selected according to the beam diameter φ in the sub-scanning direction of the LED element 22 that needs to be corrected.

In other words, judging from the optimum distance sμm, it is better to make corrections on adjacent lines (corrected 5.3 μm away from the reference lighting position) depending on the beam diameter φ in the sub-scanning direction. (Corrected at a distance of 10.5 μm from the reference lighting position). Actually, 5.3 μm and 10.5 μm are set for s in the above-mentioned equation (4).
What is necessary is just to select the one with the smaller value obtained by substituting m with each other.

Table 2 shows auxiliary lighting positions (suitable number of lines) selected according to the beam diameter φ in the sub-scanning direction. FIGS. 25 to 34 show composite exposure profiles when the auxiliary lighting position is actually selected and corrected. In each figure, the vertical axis indicates the exposure amount, and the horizontal axis indicates the position in the sub-scanning direction. Further, the exposure profile of a light beam having a beam diameter of 55 μm in the sub-scanning direction as a correction reference is shown by a solid line, and the combined exposure profile obtained by lighting the light beam of the beam diameter to be corrected three times (see a dashed line) is shown by a dotted line.

Further, Table 2 lists how many μm of the combined exposure profile corresponds to the exposure profile of the beam diameter in the sub-scanning direction (the corrected beam diameter).

[0095]

[Table 2]

In Table 2, when the suitable number of lines is "1", the correction is performed on the adjacent line (corrected by a distance of 5.3 μm from the reference lighting position), and when the number is "2", two lines are separated. This indicates that it is appropriate to perform correction (correction at a distance of 10.5 μm from the reference lighting position).

The composite exposure profiles shown in FIGS. 25 to 34 are more accurate than the composite exposure profiles shown in FIGS. 13 to 22. Although it does not match the profile, it has a close profile shape. That is, in the correction of the second embodiment, although it is not possible to realize a correction as accurate as the correction described in the first embodiment, it is corrected to a value close to the beam diameter (55 μm) of the correction reference. I understand. From the beam diameter results after the correction shown in Table 2, the expected correction width of 50 to
It can be seen that each light beam is corrected within the range of 60 μm.

Naturally, if the resolution in the sub-scanning direction is increased on the image forming apparatus 10, the corrected combined exposure profile can be more accurately adjusted to the beam diameter of the correction reference, and the correction can be performed with higher accuracy. Becomes possible. However, on the other hand, since the number of data to be handled increases, there arises a problem that the processing speed of the image forming apparatus 10 must be increased. Therefore, it is necessary to select a device with just the right accuracy based on the requirements of the system (image quality, processing speed, cost, etc.).

In the second embodiment, an example has been described in which the resolution in the sub-scanning direction is increased only to correct the beam diameter in the sub-scanning direction. Increasing the resolution in the sub-scanning direction is a useful means for increasing the tone reproduction width or improving the character quality by performing edge smoothing processing.

Therefore, the actual image data writing density in the sub-scanning direction is made equal to the resolution for correcting the beam diameter in the sub-scanning direction, so that the gradation reproduction width can be increased or the edge scanning can be performed in the sub-scanning direction. It is preferable to correct the beam diameter. An example of this case will be described below as a third embodiment.

(Third Embodiment) In the third embodiment, the resolution of an image input from a computer is set to 600.
The case where the resolution is 2400 dpi in the sub-scanning direction that can be developed on the image forming apparatus 10 will be described as an example. Note that the correction conditions are the same as in the second embodiment.

Here, as an example, the image signal shown in FIG. 35 is input to the control means 40, and the LED element 22 whose lighting is controlled based on the image signal in the second column from the left in FIG.
Will be described.

When the image signal shown in FIG. 35 is input, the control means 40 first performs a smoothing process on the image constituted by the input image signal. By the smoothing process, as shown in FIG. 36, an image signal having a resolution four times in the sub-scanning direction, that is, 2400 dpi is generated. When the resolution of the input image signal in the sub-scanning direction is set to 2400 dpi in advance, this processing is omitted.

The control means 40 generates a lighting signal based on the image signal subjected to the smoothing process.
At this time, for the LED element 22 that needs to be corrected, the second
A lighting signal is generated by applying the correction method described in the embodiment. Here, the adjacent line is set as an auxiliary lighting position.

As a result, as shown in FIG. 37, the LED element 22 which does not need to be corrected is turned on with a reference light amount in accordance with the image signal subjected to the smoothing processing. On the other hand, in the LED element 22 that needs to be corrected, the original one-time lighting (lighting based on one image signal) reduces the amount of emitted light to １ ／, and the original lighting line and the lines before and after the original lighting line. Since the lights are allocated to three lines (see the ellipse in FIG. 37B), the light amount of 光 量, ／, and ／ (= 1) of the reference light amount can be selectively selected depending on the lighting state of the front and rear lines. Is set as the amount of emitted light and is turned on. Instead of changing the amount of emitted light, the lighting time is reduced to 1/3, 2/3,
It may be selectively changed to 1.

Hereinafter, the selection of the amount of lighting in the LED element 22 that needs to be corrected will be described in detail.

First, the case where correction is performed on adjacent lines will be described. When correction is performed on the adjacent line, the line of interest is also turned on to correct the original lighting (lighting based on the image signal) on the adjacent line.

Therefore, when correction is performed on the adjacent line, the lighting light amount of the target element (the LED element 22 requiring correction) on the target line is, as shown in FIG. The presence / absence of three lines of lighting signals (lighting signals indicated by oblique lines), that is, the lighting state is determined by being superimposed. In other words, the original lighting amount of the line of interest and the lighting amount of the adjacent line to be corrected by the line of interest are added to determine the lighting amount of light of the line of interest.

That is, when the total number of lighting signals for instructing lighting of the line of interest and the lines before and after the target line is 0, 1, 2, 3, 0, 1/3, 2 /
A light amount of 3 or 1 (light amount ratio with respect to the reference lighting amount) is selected as the lighting amount.

Next, when the correction is performed by separating two lines, the lighting amount of the target element (the LED element 22 requiring correction) in the target line is, as shown in FIG. The presence / absence of lighting signals (lighting signals indicated by oblique lines) of a total of three lines, two lines separated from each other, is superimposed and determined. Depending on the total number of lighting signals instructing lighting of these lines, 0, 1/3, 2 /
Similarly, the lighting light amount is selected from the light amounts of 3 and 1 (light amount ratio with respect to the reference lighting light amount).

By the way, the LED element 22 that needs to be corrected
In the case where a plurality of auxiliary lighting positions coexist, such as a case where correction is performed on adjacent lines and a case where correction is performed by separating two lines as in the second embodiment, up to the farthest correction line , The lighting amount in each line can be determined by the lighting state in the preceding and succeeding n lines.

That is, after detecting the LED lighting signal within the range satisfying the following equation, the lighting light amount is determined.

The number of lines to be considered = 2 × n−1 (lines) Specifically, in this case, the control unit 40 converts the lighting signal generated based on the image signal subjected to the smoothing processing into the focused lighting. The number of lines shown in equation (5) is stored around the signal line. The control means 40:-How many lines apart the light beam of each LED element 22 is corrected? -For the lighting signal of the line of interest of each LED element 22,
Is there a lighting signal instructing lighting to be superimposed? Is determined, and the light emission intensity of the line of interest is determined.

FIG. 40 shows an example of a lighting signal stored when the farthest correction line is two lines ahead. In the example of FIG. 40, the LED element 22 that corrects in the adjacent line, the LED element 22 that corrects in the next line, the LE that does not need to be corrected
There are three patterns of the D element 22. Note that the lines corrected by the line of interest are shown in black and white reversed.

On the other hand, the control means 40
Using the matching pattern 60 shown in FIG. 41, each lighting state is detected, and the lighting light amount is determined. In the matching pattern 60 of FIG. 41, the line for detecting the lighting state is indicated by an arrow according to the pattern (three patterns) of the LED element 22 described above.

The control means 40 determines the light emission intensity of the line of interest in this way, changes the value of the LED drive current, and turns on the LED element 22 so as to output a light beam with the light emission intensity. The lower part of FIG. 40 shows the light amount (light amount ratio to the reference lighting amount) determined (selected) as the light emission intensity of the line of interest.

In this way, the lighting light amount of each LED element is determined for each line, and the LED element 22 is turned on with the determined light amount to form an image, whereby the beam diameter of the light beam in the sub-scanning direction varies. Is corrected, and an image on which a smoothing process is performed can be obtained. That is, instead of increasing the resolution in the sub-scanning direction only for the correction of the beam diameter in the sub-scanning direction, it can be performed together with the smoothing processing or the like.

In the first to third embodiments,
The number of lighting times is 3 (k = 3), and the intensity ratio is 1/3 times (p = 1
Although the case of (/ 3) has been described, the present invention is of course not limited to this.

In the first to third embodiments,
Although the example in which the present invention is applied to an image forming apparatus that forms a single color (black and white) image has been described, the present invention may be applied to an image forming apparatus that forms a color image of two or more colors.

[0120]

As described above, the present invention has an excellent effect that density unevenness of an output image can be reduced and a high-quality image can be obtained.

[Brief description of the drawings]

FIG. 1 shows the same light amount but different beam diameters in the sub-scanning direction.
Light beams (beam diameter in the sub-scanning direction: 40 μm, 60
FIG. 3 is a diagram showing a profile of μm and a beam diameter of 55 μm in the main scanning direction.

FIG. 2 is a diagram showing a cross section of the profiles of the two light beams shown in FIG. 1 in the sub-scanning direction.

FIG. 3 is a diagram for explaining the principle of the present invention, and shows an exposure profile when a photoconductor is exposed with a light beam having a beam diameter in the sub-scanning direction of 60 μm and light having a beam diameter in the sub-scanning direction of 40 μm. FIG. 9 shows a composite exposure profile in the case where exposure is performed three times by shifting the position in the sub-scanning direction with a beam.

FIG. 4 is a diagram showing a relationship between a distance at which a light beam to be corrected is shifted and turned on, and an error.

FIG. 5 is a diagram showing a relationship between the number of times of lighting of a light beam to be corrected and an error.

FIG. 6 is a schematic configuration diagram of an image forming apparatus according to an embodiment of the present invention.

FIG. 7 is a detailed configuration diagram of the LED print head according to the embodiment of the present invention.

FIG. 8 is a perspective view (A) of an LED image bar and a perspective view (B) of an LED chip according to an embodiment of the present invention.

FIG. 9 is a perspective view of a selfoc lens according to the embodiment of the present invention.

FIG. 10 is a block diagram illustrating an example of a configuration of a control unit according to the embodiment of the present invention.

FIG. 11 is a conceptual diagram of an image signal used as an example for describing correction performed in the first embodiment of the present invention.

FIG. 12 is a conceptual diagram of a lighting signal corresponding to FIG.

FIG. 13 is a diagram illustrating a correction result of a light beam having a beam diameter in the sub-scanning direction of 40 μm according to the first embodiment of the present invention.

FIG. 14 is a diagram illustrating a correction result of a light beam having a beam diameter in the sub-scanning direction of 41 μm according to the first embodiment of the present invention.

FIG. 15 is a diagram illustrating a correction result of a light beam having a beam diameter of 42 μm in the sub-scanning direction according to the first embodiment of the present invention.

FIG. 16 is a diagram illustrating a correction result of a light beam having a beam diameter of 43 μm in the sub-scanning direction according to the first embodiment of the present invention.

FIG. 17 is a diagram illustrating a correction result of a light beam having a beam diameter of 44 μm in the sub-scanning direction according to the first embodiment of the present invention.

FIG. 18 is a diagram illustrating a correction result of a light beam having a beam diameter of 45 μm in the sub-scanning direction according to the first embodiment of the present invention.

FIG. 19 is a diagram showing a correction result of a light beam having a beam diameter in the sub-scanning direction of 46 μm in the first embodiment of the present invention.

FIG. 20 is a diagram showing a correction result of a light beam having a beam diameter of 47 μm in the sub-scanning direction according to the first embodiment of the present invention.

FIG. 21 is a diagram showing a correction result of a light beam having a beam diameter of 48 μm in the sub-scanning direction according to the first embodiment of the present invention.

FIG. 22 is a diagram illustrating a correction result of a light beam having a beam diameter in the sub-scanning direction of 49 μm according to the first embodiment of the present invention.

FIG. 23 is a conceptual diagram of an image signal used as an example for describing correction performed in the second embodiment of the present invention.

24 is a conceptual diagram of a lighting signal corresponding to FIG.

FIG. 25 is a diagram illustrating a correction result of a light beam having a beam diameter in the sub-scanning direction of 40 μm according to the second embodiment of the present invention.

FIG. 26 is a diagram illustrating a correction result of a light beam having a beam diameter in the sub-scanning direction of 41 μm in the second embodiment of the present invention.

FIG. 27 is a diagram illustrating a correction result of a light beam having a beam diameter of 42 μm in the sub-scanning direction according to the second embodiment of the present invention.

FIG. 28 is a diagram illustrating a correction result of a light beam having a beam diameter of 43 μm in the sub-scanning direction according to the second embodiment of the present invention.

FIG. 29 is a diagram illustrating a correction result of a light beam having a beam diameter in the sub-scanning direction of 44 μm according to the second embodiment of the present invention.

FIG. 30 is a diagram showing a correction result of a light beam having a beam diameter of 45 μm in the sub-scanning direction according to the second embodiment of the present invention.

FIG. 31 is a diagram illustrating a correction result of a light beam having a beam diameter of 46 μm in the sub-scanning direction according to the second embodiment of the present invention.

FIG. 32 is a diagram illustrating a correction result of a light beam having a beam diameter of 47 μm in the sub-scanning direction according to the second embodiment of the present invention.

FIG. 33 is a diagram illustrating a correction result of a light beam having a beam diameter of 48 μm in the sub-scanning direction according to the second embodiment of the present invention.

FIG. 34 is a diagram illustrating a correction result of a light beam having a beam diameter in the sub-scanning direction of 49 μm according to the second embodiment of the present invention.

FIG. 35 is a conceptual diagram of an image signal used as an example for describing correction performed in the third embodiment of the present invention.

36 is a conceptual diagram of an image signal obtained by performing a smoothing process on an image formed by the image signals of FIG. 35.

FIG. 37A is a conceptual diagram of a lighting signal corresponding to the image signal of FIG. 36, and FIG. 37B is a diagram showing an LED element requiring correction, in which one-time lighting is performed by reducing the amount of emitted light to 1/3. It is a conceptual diagram for explaining that a lighting signal of (A) is obtained by lighting by allocating to three lines.

FIG. 38 is a conceptual diagram for explaining a method of determining the light emission intensity of an LED element when correction is performed on an adjacent line in the third embodiment of the present invention.

FIG. 39 is a conceptual diagram for describing a method of determining the light emission intensity of an LED element in a case where correction is performed by separating two lines in the third embodiment of the present invention.

FIG. 40 is a diagram illustrating an example of a lighting signal in the case where correction is performed with a maximum of two lines separated in the third embodiment of the present invention.

FIG. 41 is an example of a matching pattern used to determine light emission intensity in the third embodiment of the present invention.

FIG. 42 is a diagram showing a profile of a general light beam applied to a photoconductor in an image forming apparatus of an LED print head system.

FIG. 43 is a diagram for more strictly describing the shape of the profile of a light beam applied to a photoconductor in an image forming apparatus of the LED print head system.

FIG. 44 is a diagram showing the relationship between the beam diameter in the sub-scanning direction and the optical density.

FIG. 45 is a conceptual diagram showing a technique for correcting a variation in beam diameter in a conventional LED print head type image forming apparatus, where (A) shows a case where the beam diameter is small, and (B) shows a case where the beam diameter is small.
Indicates correction when the beam diameter is large.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Image forming apparatus 12 Photoreceptor drum (image carrier) 14 Print head 16 LED image bar 18 Selfoc lens 20 Heat sink 22 LED element (light emitting element) 24 LED chip 26 Rod lens 30 Charger 32 Developing device 34 Transfer charging Device 36 Transfer medium 38 Cleaner 40 Control means (judgment means, lighting control means)

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) G03G 15/04 H04N 1/23 103

Claims (7)

[Claims] A print head in which a plurality of light emitting elements are arranged in a line, and while the print head and an image carrier are relatively moved, the light emitting elements are set to one for each predetermined area based on image data. A density correction method used in an image forming apparatus that forms an image by illuminating the beam once and correcting density unevenness of the formed image, wherein the beam diameter in the relative movement direction is a predetermined value or a predetermined range. For the light-emitting element that outputs an external light beam, instead of the one-time lighting, the original light amount or the original lighting time is changed, and for each of the predetermined regions, a predetermined distance in the relative movement direction. A density correction method characterized by turning on a plurality of times while shifting. 2. The density correction method according to claim 1, wherein the light amount after the change is a light amount of one of the plurality of times of the original light amount. 3. The density correction method according to claim 1, wherein a lighting time after the change is a time of the multiple times of the original lighting time. 4. The multiple exposure distribution in the relative movement direction obtained when the image bearing member is exposed by turning on the light emitting element a plurality of times is a beam diameter of an output light beam. Setting the predetermined distance such that the light-emitting element corresponding to the predetermined value is lighted once and the image carrier is exposed, and the light-emitting element substantially matches the exposure amount distribution in the relative movement direction obtained when the image carrier is exposed. The density correction method according to any one of claims 1 to 3, wherein: 5. The light emitting device according to claim 1, wherein the predetermined value is a dimension of a largest beam diameter of the light beams output from the plurality of light emitting elements. Density correction method described in 1. 6. The light emitting device according to claim 1, wherein the predetermined range includes a diameter of a beam having a largest diameter among light beams output from the plurality of light emitting elements. The density correction method described in the section. 7. A print head in which a plurality of light emitting elements are arranged in a line, and while the print head and the image carrier are relatively moved, the light emitting elements are moved for each predetermined area based on image data. It is an image forming apparatus that forms an image by turning on the light once, and determines whether a beam diameter of the light beam output from the light emitting element in the relative movement direction is within a predetermined value or a predetermined range set in advance. The light emitting element whose beam diameter in the relative movement direction of the light beam to be output is determined to be outside a predetermined value or outside a predetermined range by the determination means for determining, Alternatively, lighting control means for changing the original light amount or the original lighting time, shifting the predetermined distance in the relative movement direction by a predetermined distance for each of the predetermined regions, and lighting a plurality of times. Image forming apparatus.