JPH09193454A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To determine a position for an edge part in a subscan direction without changing the shape of an image to be formed. SOLUTION: Data on a single pixel is read from among sets of image data stored in memory (100-102), and adjacent pixel data in a subscan direction is referred to decide whether it is an edge part in the subscan direction (104). If it is some part other than the edge part, a routine pulse width and a routine intensity of light are calculated in accordance with the gradation and color of such another part (110). If it is the edge part in the subscan direction, an optimal intensity of light for forming the edge part is calculated (106), and an optimal pulse width is calculated based on the calculated intensity of light (108). A laser beam source is driven by these optimal intensity of light and pulse width, and a photosynthesis distribution of the adjacent pixel is formed by a laser beam in accordance with the pixel data on the surface of a photosensor by repeating the drive of the laser beam source. Thus a latent image potential synthesis distribution almost free from a dispersion is formed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus, and more particularly to an image forming apparatus that forms an image by scanning a light beam.

[0002]

2. Description of the Related Art In an image forming apparatus such as a laser beam printer, a digital copying machine or a facsimile, a light beam such as a laser beam emitted from a gas laser or a semiconductor laser is predetermined by a rotating polygon mirror. Direction, main scanning is performed, and the light beam reflected by the rotating polygon mirror is moved in a direction orthogonal to a predetermined direction on the image forming surface of the photoconductor or the like, or an element such as a galvanomirror The light beam is deflected by the sub scanning. As an optical system for converging a light beam deflected by a polygon mirror in a state of constant velocity linear motion, an optical system including an fθ lens or the like is mainly used.

FIG. 12 shows a schematic structure of an optical scanning device of a general laser printer. In this optical scanning device, the laser beam emitted from the laser light source 12 is collimated by the collimator lens 14 and is rotated in a predetermined direction (rotation in the direction of arrow B in FIG. 12) by the rotating polygon mirror (polygon mirror) 16 (FIG. 12). Then, main scanning (deflection) is performed in the direction of arrow M). The laser beam main-scanned by the polygon mirror 16 has its scanning speed corrected by the fθ lens 18, and then exposes the cylindrical photoconductor 24 through the reflection mirror 26. In this case, the laser beam with which the photoconductor 24 is exposed forms a linear scanning line by the main scanning, and this scanning light is substantially orthogonal to the central axis of the photoconductor 24. A position detection sensor (pickup mirror 20 and sensor 22) is provided in the laser beam scanning region outside the photoconductor region in order to detect the image signal writing timing signal (SOS) in the main scanning direction on the photoconductor 24. There is. Further, the photoconductor 24 is formed in a cylindrical shape, and has a predetermined direction (FIG.
Step drive rotation or constant speed rotation in the direction of arrow A). Looking at the scanning of the laser beam on the photoconductor 24, the rotation of the photoconductor 24 causes the laser beam to scan in a direction substantially orthogonal to the direction in which the main scan is performed (the arrow M direction in FIG. 12, hereinafter, the main scanning direction). Photoconductor 24
Rotation corresponds to sub-scanning. By performing these main scanning and sub-scanning, the photoconductor 24 can be exposed two-dimensionally.

Therefore, when the laser beam is turned on / off in synchronization with the main scanning and the sub-scanning, an image is formed (exposed) on the photoconductor 24. By this exposure, the photoconductor 2
A latent image potential distribution is generated on the surface 4, and a two-dimensional image can be formed on a recording medium such as paper by attaching and fixing toner by a developing device (not shown). See Figure 1 for details.
8 and the sensitivity shown in FIG. 19 (relationship between light energy and latent image potential, hereinafter referred to as PIDC) is used on the surface of the photoconductor 24, a laser beam for each pixel corresponding to image data representing an image. The light energy is distributed by the exposure of, and a latent image potential distribution according to PIDC shown in FIG. 18 or 19 is formed.

Since the resolution in the sub-scanning direction is limited by the amount of movement of the sub-scanning and the number of rotations of the polygon mirror, in order to improve the resolution in the sub-scanning direction, an image in the sub-scanning direction when forming an image is formed. There is proposed an image forming apparatus that controls the edge position in the sub-scanning direction by changing the light intensity at the end portion (hereinafter referred to as the edge portion) (see Japanese Patent Laid-Open No. 6-91930).

For example, when writing a vertical line having a predetermined length in the sub-scanning direction on the surface of the photoconductor 24, the photoconductor 24 is exposed by the light spots 28 ₁ , 28 ₂ , 28 ₃ , 28 ₄ , 28 ₅ of the laser beam. (FIG. 12). At this time, FIG.
As shown in (1), a light spot 28 is formed on the photoconductor 24.
Optical energy corresponding to _{1-28 5} are distributed. On a straight line 30 in the sub-scanning direction passing through the approximate center of each spot,
As shown in 3 (2), the light intensities of the adjacent laser beams that overlap each other are combined to exceed the latent image potential L ₀ (hereinafter referred to as the development level L ₀ ) that should be made apparent during development.
It becomes the predetermined potential level La.

Of these light spots 28 _{1 to} 28 ₅ , the light intensity of the light spot 28 _{5 at} the edge portion is 100%,
When sequentially modulated at 75%, 50%, 25%, 0%, the light energy distribution at the edge portion becomes smaller (FIG. 13).
(See (2)). The light energy composite distribution at this time fluctuates in the sub-scanning direction according to the magnitude of modulation, as shown in FIG. Therefore, in this case, toner adheres to the development level L ₀ (hatched area according to the modulation degree in FIG. 14), and the edge portion of the toner adhesion is controlled in the sub-scanning direction according to the modulation of the light intensity. can do.

[0008]

However, in the conventional image forming apparatus, as shown in FIG. 16, the edge position is in the direction in which the formed line segment becomes shorter as the light intensity becomes smaller. The area of the non-toner-attached portion becomes larger as the light intensity decreases. By this, although the position in the sub-scanning direction can be controlled, it also affects the main scanning direction according to the control amount (the magnitude of the light intensity).

That is, as shown in FIGS. 15 (1) to 15 (5), the toner adhering portion can correct the edge position in the sub-scanning direction by controlling the light intensity of the edge portion in the sub-scanning direction. However, the shape of the toner adhesion portion at the edge portion changes. Especially, the light intensity is low (see FIG. 15 (2)).
Sometimes the shape of the toner adhesion part at the edge part changes greatly,
Originally, the light intensity of 100% (the shape of the tip portion, which should be substantially the same shape as that of FIG. 15 (5) or rectangular shape) is a convex shape, and the edge portion is jagged.

[0012] This edge portion is notably appearing at the edge portion (corner portion) in the main scanning direction and the sub scanning direction.
In a conventional image forming apparatus, for example, when an attempt is made to correct the edge position of the sub-scanning by controlling the light intensity of the edge portion in the sub-scanning direction with respect to the character, the corner portion is changed due to the continuous shape change of the toner adhering portion. A chipping phenomenon occurs (see FIG. 17).

In view of the above facts, an object of the present invention is to obtain an image forming apparatus capable of positioning the position of the edge portion in the sub-scanning direction without changing the shape of the image to be formed.

[0012]

In order to achieve the above object, an image forming apparatus of the present invention comprises a light beam emitting means for emitting a light beam, and scanning exposure of the light beam in a predetermined main scanning direction. While performing scanning exposure in a sub-direction intersecting with the main scanning direction, a light beam having a predetermined beam diameter larger than a scanning interval when scanning in the sub-scanning direction is made to overlap a part of adjacent light beams in the sub-scanning direction. When a boundary between the exposed portion and the unexposed portion is formed at a predetermined position in the sub-scanning direction on the photosensitive member and a scanning light collecting means for collecting light on the photosensitive member, a boundary is formed at the predetermined position. A control hand that controls the intensity of the light beam corresponding to the boundary and controls the emission time of the light beam based on the intensity of the light beam corresponding to the boundary so that the energy density on the photoconductor becomes constant. It has a, and.

According to the present invention, the adjacent light beams in the sub-scanning direction are condensed on the photosensitive member so that they partially overlap with each other,
The combined energy of the light beam is provided to the photoreceptor. When a boundary between the exposed portion and the unexposed portion is formed at a predetermined position on the photosensitive member in the sub-scanning direction so that an edge portion is formed on this photosensitive member, the intensity of the light beam corresponding to the boundary is controlled, The scanning is performed so that the exposure portion is formed up to a predetermined position. At this time, only by controlling the intensity of the light beam, the boundary between the exposed portion and the unexposed portion in the main scanning direction changes. In the present invention, the emission time of the light beam is made constant based on the intensity of the light beam to be controlled so that the energy density on the photoconductor becomes constant. Therefore, the energy density on the photoconductor by the light beam corresponding to the boundary becomes constant, and the boundary between the exposed portion and the unexposed portion in the main scanning direction does not change.

Further, as described in claim 2, the control means can prolong the emission time as the intensity of the light beam is reduced. By doing so, the emission time becomes longer as the intensity of the light beam becomes smaller, and the energy density on the photoconductor by the light beam corresponding to the boundary can be made constant.

Further, as described in claim 3, the control means can make the emission time of the light beam corresponding to the boundary longer than the emission time of light beams other than the light beam corresponding to the boundary. . By doing so, the light energy in the vicinity of the boundary can be made larger than that in the exposed portion up to the boundary, and even if the intensity of the light beam corresponding to the boundary is reduced, the photoconductor in the vicinity of the boundary can be reduced. The upper energy density can be constant.

Further, as described in claim 4, the control means determines the emission time of the light beam other than the light beam corresponding to the boundary from the emission time for forming one pixel in the main scanning direction. Can be shortened. By doing so, the adjacent light beams in the sub-scanning direction are converged so as to overlap with each other on the photoconductor, so that the combined light intensity of the light beams other than the light beam corresponding to the boundary is collected. The energy can be stably determined in consideration of the energy, and the intensity of the light beam corresponding to the boundary can be determined so that the energy density on the photoconductor in the vicinity corresponding to the boundary is constant.

Further, the light beam emitting means is characterized in that
As described above, it is possible to emit a light beam having a stepwise intensity change in the sub-scanning direction. On the photoconductor, the light beams adjacent to each other in the sub-scanning direction are condensed so that they partially overlap each other. Therefore, even if the intensity of the light beams corresponding to the boundary is reduced, the light energy near the boundary changes rapidly. However, the boundary and the intensity of the light beam corresponding to the boundary can be easily associated with each other.

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings.

FIG. 1 shows a schematic configuration of an optical scanning device 40 of a laser printer according to this embodiment. The optical scanning device 40 of the present embodiment includes a laser light source 42,
A collimator lens 44 and a polygon mirror 46 are sequentially arranged on the emission side of the laser light source 42. The laser light source 42 is a control device 58 (details will be described later) including a light intensity / pulse width calculator configured by a microcomputer.
It is connected to the. The polygon mirror 46 is rotated by a control device 58 at a constant speed in a predetermined direction (direction of arrow B in FIG. 1). Therefore, the laser beam emitted from the laser light source 42 is collimated by the collimator lens 44, and is main-scanned (deflected) in a predetermined direction (arrow M direction in FIG. 1) on the photoconductor by the rotation of the polygon mirror 46.

An fθ lens 48 is provided on the reflection side of the polygon mirror 46 to correct the incident laser beam to a constant scanning speed, and a reflection mirror 56 is provided downstream of the fθ lens 48. There is. This reflection mirror 5
A cylindrical photoconductor 54 is provided on the reflection side of 6.
Therefore, the scanning speed of the laser beam scanned by the polygon mirror 46 is corrected by the fθ lens 48, and then the photoconductor 54 is exposed through the reflection mirror 56. A linear scanning line is formed on the photoconductor 54 by the main scanning of the laser beam.
4 is substantially orthogonal to the central axis.

The photoconductor 54 is step-driven or rotated at a constant speed in a predetermined direction (direction of arrow A in FIG. 1) by the controller 58. Therefore, on the photoconductor 54, the laser beam is scanned by the rotation of the photoconductor 54 in a direction substantially orthogonal to the main scanning direction at the time of main scanning, and is sub-scanned.

In order to detect the image signal writing timing signal (SOS) in the main scanning direction on the photoconductor 54, a position formed by the pickup mirror 50 and the sensor 52 is located in the laser beam scanning region outside the photoconductor region. A detection sensor is provided.

As shown in FIG. 2, the control device 58 includes a light intensity / pulse width calculator 60 composed of a microcomputer. The light intensity / pulse width calculator 60 is connected to a memory 68 for storing image data (all pixel data for one image). In this memory 68,
All pixel data (image data) for one image supplied from an image data output device such as a host computer (not shown) is stored.

The light intensity / pulse width calculator 60 is connected to the driver 66 via a pulse width modulator 62 for generating a pulse width signal based on the pixel data, and also the light intensity signal based on the pixel data. Is connected to a driver 66 via a light intensity modulator 64 for generating The driver 66 is connected to the laser light source 42, and drives the laser light source with a pulse width and a light intensity according to the signals output from the pulse width modulator 62 and the light intensity modulator 64.

Further, the light intensity / pulse width calculator 60 includes
The sensor 52 is connected via the synchronization detector 70.
The timing of the light intensity / pulse width calculator 60 main scanning and sub-scanning can be detected by the synchronization signal output from the synchronization detector 70. Further, the synchronization detector 70 is
The sync signal output from the sync detector 70 is a main scan driver 72 for driving the polygon mirror 46 and the photoconductor 5.
4 are connected to each other so as to be output to the sub-scan driver 74 for rotating 4. The sub-scan driver 74 rotates the photoconductor 54 at a constant speed. In the main scanning driver 72, the polygon mirror 46 can be rotated at a constant speed by driving the polygon mirror 46 so that the cycle of the synchronization signal becomes constant, and the laser beam from the fθ lens 48 is kept constant. It is possible to scan at a constant speed. Further, in the sub-scanning driver 74, the speed in the sub-scanning direction can be made constant by changing the rotational speed of the photoconductor in accordance with the cycle of the synchronization signal. Further, the position in the sub-scanning direction can be specified by counting the synchronization signal.

Next, the operation of the optical scanning device 40 of this embodiment will be described with reference to the flow chart of FIG.

In the present embodiment, the relationship between the beam diameter of the laser beam and the relationship between the adjacent laser beams is set so that a part of the adjacent laser beams overlaps because a photosynthetic distribution is formed on the photoconductor. Has been done. The laser light source controls the exposure amount by performing pulse width modulation and light intensity modulation. Further, in the following description, the resolution of the optical scanning device is 800 DPI (dots / inch), the beam diameter of the laser beam (on the photoconductor) is 65 μm × 65 μm, and the latent image potential composite distribution by PIDC of FIG. 19 is formed. The case will be described as an example.

When the power of the optical scanning device 40 is turned on, the laser light source 42 is initially stabilized (process control such as setting the light intensity and pulse width of the laser beam to a predetermined value). The polygon mirror 46 is rotated at a constant speed while the photosensitive member 54 is rotatable. When the initial setting is completed, the light intensity / pulse width calculator 60 of the control device 58 causes the step 1 of FIG.
00 is executed to read the image data, which is all pixel data of one image, from the memory 68. In the next step 102, one pixel data to be scanned is read, and it is determined whether the pixel data read in the next step 104 is the pixel data of the edge portion. This determination can be performed by determining whether any one of the pixels adjacent to the read pixel data in the sub-scanning direction is unexposed pixel data. It is also possible to determine the position data in the sub-scanning direction from the image data and determine whether or not it is the end portion.

If a negative determination is made in step 104, the data is data other than the edge portion in the sub-scanning direction, so the process proceeds to step 110, in which the pixel data is normally used according to the gradation, color, etc. of the pixel. Pulse width and laser beam light intensity are determined (calculated) and output.

On the other hand, if the determination in step 104 is affirmative, it means that the pixel is at the edge portion in the sub-scanning direction, so the process proceeds to step 106 and the pixel at the edge portion is detected by the exposure of the laser beam emitted from the laser light source 42. The optimum light intensity for forming is calculated, and the optimum pulse width is calculated in the next step 108 based on the calculated light intensity.

Here, the inventor has found that the resolution is 800 DP.
I, the beam diameter of the laser beam is 65 μm × 65 μm, and an experiment for forming a latent image potential composite distribution is performed by the PIDC of FIG. 19, and the light intensity / pulse calculator 6 of this embodiment is used.
The following equation (1) for obtaining the light intensity and the following (2) for obtaining the pulse width were derived as arithmetic expressions for generalizing the optimal light intensity and pulse width at 0.

Y = 0.0722X ² + 0.6893X (1) Z = −0.0002Y ³ + 0.024Y ² −1.5143Y + 200 (2) where X: edge position, Y: light intensity , Z: pulse width

In FIG. 4, the light intensity of the sub-scanning edge portion is 25
The image states formed when performed with different pulse width modulations in% are shown. FIG. 4 (1) shows the case where only the conventional light intensity described above is modulated, and FIG. 4 (2) shows the case where the pulse width of the edge part is extended to 150% of the pulse other than the edge part and modulated. 4 (3) shows each image state when the pulse width of the edge part is extended to 200% of the pulse width other than the edge part and modulated. In this way, as the pulse width of the edge portion is extended with respect to the pulse width other than the edge portion, the tip shape of the formed image (line in the example of FIG. 4) becomes better.

Therefore, the present inventor conducted a number of experiments in which the pulse width was changed at the light intensity of 50% and 75% at the edge portion in the sub-scanning direction, respectively, and as a result, it was confirmed that the toner adhesion area did not change. That is, the tip shape of the formed image (line in the example of FIG. 4) becomes good (substantially coincides with the time when the light intensity is 100%), and the solid line in FIG. 5 shows the relationship between the light intensity, the edge position and the pulse width. A characteristic 32 showing the relationship between the light intensity and the edge position and a flat characteristic 34 showing the relationship between the light intensity and the toner non-adhered area were obtained. From the characteristic 32 shown in FIG. 5, the characteristic 36 shown in FIG. 6 is obtained as the relationship between the light intensity and the edge position. The above equation (1) is approximately derived from the characteristic 36 shown in FIG. As another characteristic for obtaining the characteristic 36, the characteristic 38 shown in FIG. 7 was obtained as the relationship between the light intensity and the pulse width. From the characteristic 38, the above equation (2) is approximately derived.

Therefore, in each of the steps 106 and 108, the optimum light intensity Y and the optimum pulse width Z are calculated and output using the above equations (1) and (2).

The light intensity modulator 64 uses the laser light source 42 and the output light intensity and the optimum pulse width values.
The pulse width modulator 62 outputs the time (pulse width) for turning on the laser light source 42 to the driver 66 while outputting the current value supplied to the driver 66. The driver drives the laser light source 42 by the optimum light intensity and pulse width of the input laser beam. When the exposure of the photoconductor by the pixel data is started, the photoconductor is rotated in synchronization with the main scan and the sub-scan is started.

As a result, the laser beam emitted from the laser light source 42 is collimated by the collimator lens 44, scanned by the Bolgon mirror 46, the scanning speed is corrected by the fθ lens 48, and the surface of the photoconductor 54 is scanned. In accordance with the pixel data, a photosynthesis distribution by a laser beam of an adjacent pixel is formed to form a latent image potential synthesis distribution.

The above process is repeated for all pixels of the image data (step 112).

As described above, by performing pulse modulation control on the edge portion in the sub-scanning direction for optimum light intensity, even when the edge portion is positioned in any of the sub-scanning directions,
It is possible to form a latent image potential composite distribution in which a change in the shape of the toner-attached portion at the edge portion (edge jaggedness) is suppressed and variation is small.

Next, another embodiment of the present invention will be described. Since the present embodiment has substantially the same configuration as the above-mentioned embodiment, the same reference numerals are given to the same portions and detailed description thereof will be omitted.

As shown in FIG. 8, in the optical scanning device of this embodiment, a slit 80 is provided on the downstream side of the collimator lens 44 in the traveling direction of the laser beam. The slit 80 is for forming diffracted light by forming a gap having a predetermined width in the sub-scanning direction.

By providing this slit 80,
On the photoconductor 54, as shown in FIG. 9A, the 0th order light and the 1st order light are mainly exposed in the sub-scanning direction. The beam profile of the laser beam including the diffracted light has a Gaussian distribution shape in the main scanning direction as shown in FIG. 9 (2), but is substantially in the sub-scanning direction as shown in FIG. 9 (3). On both sides of the 0th-order light having a Gaussian distribution shape, a substantially Gaussian distribution shape of the 1st-order light having a light intensity lower than that of the 0th-order light peculiar to diffracted light is provided.

As described above, when the photosensitive member is exposed to the diffracted light, the dots to be formed by one pixel are scattered in the sub-scanning direction. Therefore, in the present embodiment, the image forming position of the laser beam is changed. By displacing the laser beam from the surface of the photosensitive member by a predetermined distance (moving closer or farther from the focus), the beam shape is deformed in the sub-scanning direction on the surface of the photosensitive member as shown in FIG. The beam is continuous. In this case, the beam profile has a Gaussian distribution shape in the main scanning direction as shown in FIG. 10 (2), and a substantially Gaussian distribution shape in the sub-scanning direction as shown in FIG. 10 (3). The shape is such that the beam width is widened from the antinode portion (shape having side lobes).

Therefore, when the light intensity of the laser beam at the edge portion is changed without providing the slit 80, the combined light with the adjacent laser beam is combined by the light intensity at the skirt portion of the Gaussian distribution shape, and the edge portion is changed. However, when the slit 80 is provided and the light intensity of the laser beam having the side lobe portion is changed as in the present embodiment, the laser beam at the edge portion is also modulated. The light intensity is interpolated by the combined light of the laser beams in the side lobe portions, and the linearity between the edge position and the light intensity of the laser beam is increased.

The present inventor conducted an experiment using an optical scanning device provided with a slit for producing diffracted light and an optical scanning device not provided with a slit, and as shown by a dotted line in FIG. As a result, the linearity between the edge position and the light intensity of the laser beam was increased as compared with that not provided (the characteristic shown by the solid line in FIG. 11).

As described above, in this embodiment, since the linearity between the edge position and the light intensity of the laser beam is increased by providing the slit for generating the diffracted light, the edge portion is positioned at a predetermined position. Control becomes easier.

[0047]

As described above, according to the present invention, the boundary between the exposed portion and the unexposed portion is formed at a predetermined position in the sub-scanning direction on the photosensitive member so that the edge portion is formed on the photosensitive member. At this time, the intensity of the light beam corresponding to the boundary is controlled, and the emission time of the light beam is controlled based on the intensity of the light beam corresponding to the boundary so that the energy density on the photoconductor becomes constant. It is said that the energy density on the photoconductor by the emission time of the light beam based on the intensity becomes constant, the energy density on the photoconductor by the light beam corresponding to the boundary becomes constant, and no corners such as letters are missing. effective.

If a light beam having a stepwise intensity change in the sub-scanning direction is emitted, the light energy on the photoconductor does not change abruptly and becomes stepwise. There is an effect that the correspondence with the intensity of the corresponding light beam can be easily related and the control becomes easy.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a schematic configuration of an optical scanning device according to an embodiment of the present invention.

FIG. 2 is a block diagram showing a schematic configuration of a control device.

FIG. 3 is a flowchart showing a flow of a processing routine executed by a light intensity / pulse width calculator of the control device.

FIG. 4 is an image diagram showing a latent image potential distribution on a photosensitive member when the laser beam forming a boundary (edge) in the sub-scanning direction is intensity-modulated in the optical scanning device of the present embodiment.

FIG. 5 is a diagram showing the relationship between the edge position in the sub-scanning direction and the light intensity and the relationship between the toner non-adhesion area and the light intensity in the optical scanning device according to the present embodiment.

FIG. 6 is a diagram showing a relationship between a boundary (edge) position in the sub-scanning direction and light intensity in the optical scanning device according to the present embodiment.

FIG. 7 is a diagram showing the relationship between light intensity and pulse width in the optical scanning device of the present embodiment.

FIG. 8 is a block diagram showing a schematic configuration of an optical scanning device according to another embodiment of the present invention.

FIG. 9 is a diagram showing a beam shape of a laser beam according to another embodiment of the present invention.

FIG. 10 is a diagram showing a beam shape of a laser beam in which an image forming position is shifted according to another embodiment of the present invention.

FIG. 11 is a diagram showing the relationship between the light intensity rate and the position of an edge portion depending on the presence or absence of a slit that produces diffracted light.

FIG. 12 is a block diagram showing a schematic configuration of an optical scanning device of a conventional image forming apparatus.

FIG. 13 is a diagram showing a position of a laser beam sub-scanned on a photosensitive member in a conventional optical scanning device and a laser beam corresponding to the position;
It is a diagram which shows the energy distribution of a beam.

FIG. 14 is a diagram showing the relationship between the position in the sub-scanning direction and the latent image potential when the intensity of a laser beam forming a boundary (edge) in the sub-scanning direction is modulated.

FIG. 15 is an image diagram showing a latent image potential distribution on a photosensitive member when the intensity of a laser beam forming a boundary in the sub-scanning direction is modulated.

FIG. 16 is a diagram showing a conventional relationship between a boundary (edge) position in the sub-scanning direction and light intensity, and a relationship between a toner non-adhered area and light intensity.

FIG. 17 is an image diagram showing a document and a result of forming characters by a conventional optical scanning device.

FIG. 18 is a diagram showing a relationship (PIDC) between exposure energy and a latent image potential of a certain photosensitive material.

FIG. 19 is a diagram showing a relationship (PIDC) between the exposure energy of another photosensitive material and the latent image potential.

[Explanation of symbols]

 40 Optical Scanning Device 42 Laser Light Source 46 Polygon Mirror 54 Photoreceptor 58 Control Device 60 Light Intensity / Pulse Width Calculator

Claims (5)

[Claims] 1. A light beam emitting means for emitting a light beam, and scanning exposure of the light beam in a predetermined main scanning direction and scanning exposure in a sub-direction intersecting the main scanning direction, and in the sub-scanning direction. Scanning converging means for condensing on the photoconductor a light beam having a predetermined beam diameter larger than the scanning interval for scanning so that adjacent light beams in the sub-scanning direction partially overlap each other; When a boundary between the exposed portion and the unexposed portion is formed at a predetermined position in the scanning direction, the intensity of the light beam corresponding to the boundary is controlled so that the boundary is formed at the predetermined position, and the boundary is responded to. An image forming apparatus comprising: a control unit that controls an emission time of the light beam based on the intensity of the light beam so that the energy density on the photoconductor becomes constant. 2. The image forming apparatus according to claim 1, wherein the control unit lengthens the emission time as the intensity of the light beam is reduced. 3. The image according to claim 1, wherein the control unit makes the emission time of the light beam corresponding to the boundary longer than the emission time of light beams other than the light beam corresponding to the boundary. Forming equipment. 4. The control means sets an emission time of a light beam other than the light beam corresponding to the boundary to be shorter than an emission time for forming one pixel in the main scanning direction. 1. The image forming apparatus according to 1. 5. The image forming apparatus according to claim 1, wherein the light beam emitting unit emits a light beam having a stepwise intensity change in the sub-scanning direction.