JPH11188922A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To form a highly accurate electrostatic latent image by regulating an exposing means such that the shaft of interval of a plurality of light beams from a prescribed value and the shift of the quantity of light of each light beam from a mean quantity of light determined by dividing total quantity of light by the number of light beams fall within a range satisfying a specific equation. SOLUTION: An image exposing unit 3 comprises two semiconductor lasers 11a, 11b emitting laser light beam, a collimator lens 12, and a laser track circuit 15. When the difference of output between two lasers 11a, 11b is varied and the scanning line interval of laser is combined with the quantity of laser light, the shift x% of line interval and the shift y% of the quantity of laser light can be suppressed to an allowable level as a result of evaluation with eyes if a relationship x+y<10 is satisfied. Consequently, a pattern can be eliminated or can e rendered inconspicuous even for a solid image.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrophotographic image forming apparatus, and more particularly to a technique for forming a high-precision electrostatic latent image at the time of exposure with a light beam to improve image quality.

[0002]

2. Description of the Related Art A digital image forming apparatus using an electrophotographic technique, such as a copying machine or a printer, irradiates a light beam corresponding to an original to a photosensitive layer on the surface of a photoreceptor uniformly charged by a charging device. This forms an electrostatic latent image.

A light beam for exposing the surface of the photoreceptor is obtained by condensing (collimating) light generated by a laser diode, is reflected by a polygon mirror rotating at a high speed, and scans and exposes the surface of the photoreceptor. .

A typical latent image writing method is a binary recording method in which a light beam is applied to a photosensitive layer or not, and image processing such as an error diffusion method and a dither method is performed on an original image signal. Can reproduce halftones.

By attaching toner to the electrostatic latent image thus formed by a developing device, the latent image on the photoconductor is visualized, and the toner image is transferred to a sheet material by a transfer device. Then, the toner image transferred to the sheet material is heated and pressed and fixed by a fixing device.

In order to improve the durability of such an image forming apparatus, it has been proposed to use an amorphous silicon photoconductor applied to a high-speed analog copying machine instead of an organic compound photoconductor conventionally used. Have been.

Here, the potential distribution formed on the amorphous silicon photoreceptor by the light beam irradiation by the laser is more intense than the potential distribution formed on the organic compound photoreceptor. It is close.

Accordingly, the latent image formed on the amorphous silicon photoreceptor is sharper than the latent image formed on the organic compound photoreceptor. There is also an advantage that the reproducibility of fine lines in the scanning direction is excellent.

[0009] Further, with the speeding up of the digital image forming apparatus, a twin beam laser capable of simultaneously emitting two light beams or a laser array comprising two lasers is used to form a laser beam on the photosensitive member. A method of simultaneously writing a book line has been adopted.

[0010]

However, the prior art as described above has the following problems.

As described above, the amorphous silicon photoreceptor has a sharper latent image than the organic photoreceptor and therefore has excellent dot reproducibility that is faithful to minute pixels. When writing with a laser beam, when the interval between two light beams on the photoconductor surface to be scanned at a pixel pitch in the sub-scanning direction is shifted as shown in FIG. In addition, the distance from A to B is small, and the distance from B to A is wide), and a slight shift produces a latent image potential distribution as shown in FIG. 7C, which is easily reproduced faithfully.
It has been found that a problem occurs that a stripe pattern of a two-pixel pitch is generated after development in a solid image or the like.

[0012] Also, with respect to the respective laser light amounts of the two lasers, when there is a difference in the light amounts as schematically shown in FIG. 7B, a latent image as shown in FIG. Because of the potential distribution, the same problem as described above occurs.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to provide a high-precision static electricity when a plurality of light beams simultaneously expose a photosensitive member. By forming an electrostatic latent image, high image quality is achieved.
An object of the present invention is to provide an image forming apparatus capable of forming an image in which a stripe pattern is not generated even in a solid image, or in which a stripe pattern is very inconspicuous.

[0014]

In order to achieve the above object, according to the present invention, as one component of an electrophotographic image forming means, a photosensitive member is exposed to a plurality of lines simultaneously by a plurality of light beams. An image forming apparatus provided with an exposing means for forming an electrostatic latent image by using an image forming apparatus, wherein a deviation of a distance between the plurality of light beams from a predetermined value is x% (absolute value), and a total light amount of the plurality of light beams When the deviation of the light amount of each light beam alone from the average light amount obtained by dividing the light amount by the number of light beams is set to y% (absolute value), the exposure means is set in a range where the numerical values of x and y satisfy 2x + y <10. It is characterized by having been adjusted so that

It is also preferred that the photoconductor is an amorphous silicon photoconductor.

The photosensitive layer of the photosensitive member has a thickness of 20 μm.
It is also preferable that the thickness be from m to 40 μm.

It is also preferable that the photoreceptor is an organic photoreceptor, and the carrier transport layer has a thickness of 10 μm or less.

Further, it is preferable that the electrostatic latent image formed on the photosensitive member is a binary latent image.

It is also preferable that the adjustment items of the exposure means are an interval between a plurality of light beams and a light amount of each light beam.

The image forming means includes a charging means for uniformly charging the photosensitive member to a predetermined potential, a signal generating means for generating a signal corresponding to an image to be formed, and a signal of the signal generating means. The exposure means for simultaneously exposing a plurality of lines of the photoconductor to form an electrostatic latent image by scanning a plurality of condensed laser beams with scanning optical means; It is also preferable that the image forming apparatus further comprises a developing unit that obtains a visible image by attaching toner to the image.

Therefore, the intervals between the plurality of light beams and the light amounts of the respective light beams, which are the adjustment items, are not independent of each other, but are correlated with each other, and the two are defined within a certain range, so that the photosensitive member can be controlled. When exposure is performed, a high-precision electrostatic latent image is formed to achieve high image quality, and a solid image can be formed without a stripe pattern or an image in which the stripe pattern is very inconspicuous.

[0022]

(Embodiment 1) Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

FIG. 1 shows a configuration of a main part of an image forming apparatus according to a first embodiment of the present invention. In FIG. 1, reference numeral 1 denotes a photosensitive member mainly made of drum-shaped amorphous silicon which is driven to rotate clockwise in the drawing, and reference numeral 2 denotes a primary charger as charging means.

Reference numeral 3 denotes an image exposure device as exposure means for irradiating image light corresponding to an image binarized by an error diffusion process or the like by an image processing unit (not shown) from two semiconductor lasers. 4 is a developing device, 5 is a transfer / separation device,
Reference numeral 6 denotes a cleaning device, 7 denotes a pre-exposure device, and 8 denotes a fixing device.

The present embodiment is a reversal developing system, in which a latent image is visualized by attaching toner to a portion exposed by an image exposing device 3 by a developing device 4, and the toner is transferred by a transfer / separation device 5. The image is transferred to the sheet material. The toner image transferred to the sheet material is heated and pressed and fixed by the fixing device 8.

As shown in FIG. 2, the image exposure device 3 includes two semiconductor lasers 11a and 11b for irradiating a laser beam as a light beam, a collimator lens 12, a polygon mirror 13, an f-θ lens 14, a signal generating means. And a laser drive circuit 15 functioning as a laser drive circuit.

The laser driving circuit 15 operates based on a print signal from an image processing unit (not shown) based on the semiconductor lasers 11a and 1a.
1b is turned on / off. In this embodiment, the photosensitive layer 1 has a total thickness of the amorphous silicon photosensitive layer of about 30 μm.
Something was used.

Hereinafter, the electrostatic latent image method of the present invention having the above configuration will be described. The potential of the photoreceptor surface after charging by the primary charger 2 is set to about 400 V in the image forming apparatus having the above configuration.
And the voltage of the DC component of the developing bias in the developing device 4 was set to 250V.

Since the resolution in both the main scanning direction and the sub-scanning direction is set to 600 DPI, the pixel pitch in both scanning directions is about 42.3 μm, and the length of the diagonal line of four sides of one pixel is about 60 μm. Therefore, the normal spot diameter is 6
Since it is about 0 μm, here 60 μm (1 /
It was in what was defined in e ^2).

In the above setting, the deviation amount of the laser scanning line interval was changed to 1, 2, 3, 4, 5 μm. These have a regular pixel pitch (42.3μ).
m) about 2.3, 4.7, 7.1, 9.5, 1 respectively
It corresponds to 1.8%. Here, the laser power was adjusted so that the outputs of the two semiconductor lasers 11a and 11b were equal.

When the charged surface of the photoreceptor is exposed while the semiconductor lasers 11a and 11b are always turned on, the potential on the surface of the photoreceptor becomes about 50 V. Was measured using a potentiometer capable of measuring.

The measured characteristics are shown by the minute potential irregularities of the solid exposed portion as shown in FIG. 3 and the maximum value V1max and the minimum value V1mi.
n, and it is considered that these differences (ΔVL = V1max−V1min) cause a stripe pattern every two lines.

In this manner, the visual evaluation of the stripe pattern every two lines when the scanning line interval was changed was performed. A list of ΔVL and evaluation results is shown in the table of FIG.

From the results, the difference Δ between V1max and V1min
It was found that the amorphous silicon photoreceptor can be tolerated up to a VL of about 10 V (this is a deviation of about 5% or less).

When the thickness of the photosensitive layer of the amorphous silicon photosensitive member is changed in the range of about 20 μm to about 40 μm, the result is almost the same, and when ΔVL is set to about 10 V or less, stripes having a pitch of two pixels are obtained. It was found that high image quality with less noticeable patterns could be obtained.

On the other hand, the difference between the laser scanning line intervals is set to 0 μm, and the output difference between the two semiconductor lasers 11 a and 11 b (total of the two divided by 2 is taken as the average value of the laser light amount. About), about 2,
FIG. 5 shows a similar table when the values are changed to 5, 8, 11, and 14%.

In the table of FIG. 5, unlike FIG.
It was found that there was almost no problem if L was about 20 V or less (this was about 10% or less in light amount difference).

That is, it is considered that the difference between the laser scanning line intervals has a greater effect on the stripe pattern every two lines than the laser light intensity difference. 7C, the profile of the latent image of one line is more disturbed than that of FIG. 7D when the laser light amount is shifted, and is emphasized by the edge enhancement of the development. Originally, two independent lines should have been developed, but it would be easier to develop as one line.

On the other hand, when the amount of laser light is shifted, an image is obtained in which each line has shading. Of course, development is concentrated on a stronger latent image by edge emphasis and developed as one line. Although it is the direction, it is considered that the influence is not as large as the deviation of the scanning line.

Here, when the worst of the respective threshold values (scan line deviation 5%, light amount deviation 10%) is combined, the evaluation is x level, and if adjusted alone, the stripe pattern every two lines may be conspicuous. Considering the combination of the scanning line interval and the amount of laser light, the results shown in the table of FIG. 6 were obtained. The format of the table is different from those shown in FIGS. 4 and 5, and only the visual evaluation is described by taking the deviation amount of the scanning line interval in the column direction and the deviation amount of the laser light amount in the row direction.

From this, the deviation of the line interval (x%)
Considering both light amount shifts (assumed to be y%): If there is no laser light amount difference, the line spacing shift amount x is 5%
When there is no deviation of the line interval, when the deviation amount y of the laser light amount is within 10%. When both are deviated, x, y such that 2x + y <10.
In the case of the relation of 評 価, the result of the visual evaluation, ○ (no problem) or ○ △
It turned out that it can be suppressed at the (very slight) level.

As described above, it is possible to provide an image forming apparatus in which a stripe pattern every two lines is hardly generated by correlating a scanning line shift amount and a laser light amount shift amount with each other and adjusting them. It became.

(Embodiment 2) In the first embodiment, an amorphous silicon photoreceptor is used. Here, an organic photoreceptor whose carrier transport layer has a thickness of 10 μm or less is used. .

An amorphous silicon photoreceptor can develop a latent image faithfully because of the sharpness of the latent image. However, in order to form a latent image sharply even with an organic photoreceptor (OPC), a carrier transport layer on the surface thereof is required. It is preferable to prevent light from being scattered in the carrier transport layer before reaching the carrier generation layer.

Here, O having a carrier transport layer of 5 μm
When the present invention was applied to a PC photoreceptor, the same effects as in the first embodiment were obtained.

However, since the ordinary OPC photosensitive member is easily scraped, the film thickness is increased to improve the durability. Therefore, if the thickness is reduced, the durability is naturally inferior, but the use is limited (LBP
Etc.), the reproducibility of the minute latent image is excellent, and an image without a stripe pattern every two lines can be obtained.

Alternatively, it is possible to increase the hardness by dispersing Teflon or the like in the carrier generation layer. However, the image is slightly inferior due to light scattering. Alternatively, a thin hard coat layer can be provided on the carrier transport layer.

[0048]

As described in the embodiment of the present invention, the interval between a plurality of light beams and the light amount of each light beam, which are adjustment items in the exposure means, are not independent of each other, but are correlated with each other. By defining both in a certain range, a high-precision electrostatic latent image is formed when exposing the photoreceptor to achieve high image quality. It is possible to form an image in which the pattern is very inconspicuous.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating a configuration of a main part of an image forming apparatus according to a first embodiment of the present invention.

FIG. 2 is a diagram showing a configuration of an exposure unit according to the embodiment of the present invention.

FIG. 3 is a diagram showing measurement items of a latent image potential characteristic.

FIG. 4 is a diagram showing a visual evaluation result of a stripe pattern every two lines when a scanning line interval is changed.

FIG. 5 is a diagram showing a visual evaluation result of a stripe pattern when a laser output difference is changed.

FIG. 6 is a diagram showing a visual evaluation result of a stripe pattern with respect to a combination of a scanning line interval and a laser light amount.

FIG. 7 is a graph showing a distance between two light beams in a conventional example.
FIG. 4 is a diagram illustrating a latent image potential distribution when the light amount shifts.

[Description of Signs] 1 Photoconductor 2 Primary charger 3 Image exposure device (exposure means) 4 Developing device 5 Transfer / separation device 6 Cleaning device 7 Pre-exposure device 8 Fixing device 11a, 11b Semiconductor laser 12 Collimator lens 13 Polygon mirror 14 f-θ lens 15 Laser drive circuit (signal generation means)

Claims (7)

[Claims] 1. An image forming apparatus comprising: an exposure unit configured to simultaneously expose a photosensitive body with a plurality of light beams by a plurality of lines to form an electrostatic latent image, as one component of an image forming unit based on an electrophotographic method. The deviation of the interval between the plurality of light beams from a predetermined value is x%
(Absolute value) and the deviation of the light amount of each light beam alone from the average light amount obtained by dividing the total light amount of the plurality of light beams by the number of light beams is y% (absolute value). An image forming apparatus, wherein the means is adjusted so that the numerical values of x and y fall within a range satisfying 2x + y <10. 2. The image forming apparatus according to claim 1, wherein said photosensitive member is an amorphous silicon photosensitive member. 3. The photosensitive layer of the photosensitive member has a thickness of 20 μm or less.
The image forming apparatus according to claim 1, wherein the thickness is 40 μm. 4. The image forming apparatus according to claim 1, wherein the photoconductor is an organic photoconductor, and the carrier transport layer has a thickness of 10 μm or less. 5. An electrostatic latent image formed on the photoreceptor, wherein:
The image forming apparatus according to claim 1, wherein the image forming apparatus is a value latent image. 6. The image forming apparatus according to claim 1, wherein the adjustment items of the exposure unit are an interval between a plurality of light beams and a light amount of each light beam. 7. The image forming unit includes: a charging unit that uniformly charges the photoconductor to a predetermined potential; a signal generating unit that generates a signal corresponding to an image to be formed; and a signal of the signal generating unit. According to, by scanning the plurality of laser beams focused by the scanning optical means,
The image forming apparatus according to claim 1, further comprising: an exposing unit configured to simultaneously expose a plurality of lines of the photoconductor to form an electrostatic latent image; and a developing unit configured to attach a toner to the formed electrostatic latent image to obtain a visible image. Any one of items 1 to 6
Item 10. The image forming apparatus according to item 1.