JPH03126051A - Electrophotographic device - Google Patents

Abstract

PURPOSE:To stably maintain a specified image density or gradation by providing traveling means capable of setting a screen gap arbitrarily in a screen filter. CONSTITUTION:The traveling means 40 to 42 capable of setting arbitrarily the screen gap in the screen filter 15 are provided. The photosensitive body 9 allows its image density and gradation to change with increase of the number of pieces to be copied, on the other hand, in the screen filter 15, the image density and the gradation can be set by the screen gap. The screen gap 15 can be arbitrarily set by the traveling means 40 to 42. Therefore, the screen gap 15 can be set responding to the change in the photosensitive body 9. Thus, the specified image density and the gradation can be stably maintained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an electrophotographic apparatus such as a copying machine or a laser printer that stabilizes an image using a screen filter of an exposure optical system.

[Conventional technology]

An electrophotographic device illuminates the original with light from a copy lamp,
It has an optical system section that guides reflected light from the original to the photoreceptor. In this optical system section, a screen filter is usually disposed close to the photoreceptor, and this screen filter consists of a transparent member such as polyethylene terephthalate, and a large number of fine stripes provided on the transparent member. It consists of

The above screen filter separates the reflected light into halftone dots and irradiates it onto the photoreceptor, and the image density can be adjusted by setting the screen gap, which is the distance between the screen filter and the photoreceptor. It has become. In other words, if the screen gap is set wide,
The density characteristics, which indicate the relationship between the image density and the original density, generally increase, leading to an increase in saturation density and deterioration of gradation. On the other hand, when the screen gap is set narrow, the density characteristics generally increase. This results in a decrease in saturation density and an improvement in gradation.

Conventional electrophotographic devices use the change in density characteristics caused by the screen filter described above to set a screen gap that corresponds to the density characteristics of the photoreceptor, thereby improving image density and gradation. It has become.

[Problem B to be Solved by the Invention] However, the conventional electrophotographic apparatus described above has a problem in that it is difficult to stably maintain the image density and gradation set at the initial stage of copying. .

In other words, the lifespan of the photoreceptor, which is a consumable item, has become longer in recent years, but as shown in Figure 4, the density characteristics change due to changes in Dev resistance and toner chargeability. As shown by the solid line A in the initial stage and the broken line B in the case of multiple copies, it is still difficult to maintain stability. Then, in the case of the broken line B of multiple copies, the saturation density decreases and the gradation property improves excessively.

On the other hand, in a screen filter, the screen gap is fixed at a certain distance in advance, so that it is possible to maintain stable density characteristics.

However, a preset constant density characteristic does not correspond to changes in the density characteristic of the photoreceptor. Therefore,
In conventional electrophotographic apparatuses, the edge effect increases as the number of copies increases. This increase in edge effect reproduces the stripes of the screen filter in low-density areas, causing blurring, and strongly reproduces the stripes of the screen filter in linear shapes in high-density areas, resulting in a decrease in image density. I will do it.

As described above, conventional electrophotographic equipment uses screen filters to improve image density and gradation at the initial stage of copying, but as the number of copies increases, the density characteristics of the photoreceptor change. This makes it difficult to stably maintain the image density and gradation described above. Therefore, in the present invention, it is possible to stably maintain predetermined image density and gradation by making it possible to set a screen gap that corresponds to changes in the density characteristics of the photoreceptor as the number of copies increases. The purpose is to provide an electrophotographic device that can.

[Means to solve the problem]

In order to solve the above problems, an electrophotographic apparatus according to the present invention includes an optical system section that guides reflected light from a document to a photoreceptor,
In an electrophotographic apparatus that is provided with a screen filter that is arranged with a screen gap on the optical path of the optical system section and whose image density and gradation can be set by the screen gap, the screen filter has , is characterized by being provided with a moving means that can arbitrarily set the screen gap.

[For production]

According to the above configuration, the image density and gradation of the photoreceptor change as the number of copies increases. On the other hand, in the screen filter, the image density and gradation can be set by the screen gap. The above-mentioned screen gap can be set arbitrarily by the moving means.

Therefore, if the screen gap is set in accordance with changes in the photoreceptor, stable image density and gradation can be maintained from the initial stage of copying to the copying of a large number of copies.

[Embodiment] An embodiment of the present invention will be described below with reference to FIGS. 1 to 3.

As shown in FIG. 1, a full-color copying machine (hereinafter referred to as a copying machine) as an electrophotographic apparatus according to this embodiment
A transparent document table 3 on which a document 2 is placed is provided at the top of the machine frame 1. An optical system section 4 is provided below the document table 3 to scan the document 2 and form an electrostatic latent image on a photoreceptor 9, which will be described later. This optical system section 4 is connected to the document 2 on the document table 3.
A copying lamp 5 that irradiates light onto the original 2, a plurality of mirrors 6 that guide the reflected light from the original 2 onto the photoreceptor 9 as shown by the dashed line, and an imaging lens 7 disposed on the optical path. and,
A color separation filter 8 having color filters for three primary colors of red, green, and blue is provided.

A belt-shaped photoreceptor 9 is provided below the optical system section 4, and this photoreceptor 9 is connected to a first photoreceptor roller lO and a second photoreceptor roller 11 that are arranged at a predetermined interval. It is being constructed. A cleaning device 12 is disposed below the photoconductor 9 on the second photoconductor roller 11 side, facing the photoconductor 9.
Toner remaining on the surface of the photoreceptor 9 is removed.

In addition, a static elimination lamp 13 is provided at a portion facing the photoconductor 9 in the moving direction of the photoconductor 9 from the cleaning device 12.
A charger 14, a screen filter 15, and a blank lamp 16 are provided. A screen filter 15 disposed between the charger 14 and the blank lamp 16 is provided on the optical path of the reflected light from the document 2 that is guided by the optical system section 4 and reaches the photoconductor 9, and is arranged on the optical path of the reflected light from the original 2 that is guided by the optical system section 4 and reaches the photoreceptor 9. It is designed to separate halftone dots.

The above-mentioned screen filter 15 is made up of a transparent member such as polyethylene terephthalate, and a large number of fine stripes provided on this transparent member. It is supported by a member 42.

The screen support member 42 is provided with a moving means that can move the screen filter 15 vertically with respect to the photoreceptor 9 and set the screen gap as desired. This moving means includes cams 40 provided at each end of the screen support member 42, and these cams 40...
The shaft member 41 is provided off-axis, and a stepping motor (not shown), for example, is provided on each shaft member 41. And screen filter 15
The above-mentioned stepping motor eccentrically rotates the cams 40 through the shaft members 41, so that the photoconductor 9 is moved in the vertical direction.

Further, as shown in FIG. 1, developing devices 17, 18, and 19 are disposed near the center above the photoreceptor 9 without contacting the photoreceptor 9. These developing devices 17, 18, and 19 individually accommodate yellow, magenta, and cyan color developers. Further, below the second photoreceptor roller 11, transfer paper 2o...
Paper feed cassettes 21 and 22 for each paper size are arranged at the upper limit. Paper feed rollers 23 and 24 are provided at the paper output portion of each paper feed cassette 21 and 22, and a timing roller 25 is further provided in the paper output direction of the paper feed cassettes 21 and 22.

On the other hand, an intermediate transfer device 26 is provided on the first photoreceptor roller 10 side.
is provided. This intermediate transfer device 26 includes a belt-shaped intermediate transfer body 27, first to thirtieth rollers 28, 29, and 30 that rotationally drive this intermediate transfer body 27, and a first transfer roller 3.
1, second transfer roller 32, and cleaning device 33
It is composed of etc.

The intermediate transfer member 27 is pressed against the first photoreceptor roller 10 via the photoreceptor 9, and the back surface of the intermediate transfer member 27 at this portion is pressed against the surface of the photoreceptor 9. A first transfer roller 31 is provided. Further, the second transfer roller 32 forms a pair with the 30th roller 30 and is pressed against the 30th roller 30 via the intermediate transfer body 27.

In the paper output direction of the second transfer roller 32, a conveyor belt 35, a fixing device 36, and a paper discharge section 37 are provided in this order.

An outline of the full-color copying operation of this copying machine in the above configuration will be explained below.

First, the copy lamp 5 of the optical system unit 4 irradiates light onto the original 2 placed on the original platen 3 to perform scanning several times. As shown by the dashed line, the reflected light from the original 2 reaches the screen filter 15 via a plurality of mirrors 6 . After that, it reaches the surface of the photoreceptor 9.

The surface of the photoreceptor 9 is charged to a predetermined potential by a charger 14, and an electrostatic latent image is formed on the photoreceptor 9 by light from the optical system section 4. At this time, the above color separation filter 8 inserts three color filters into the optical path one by one during each scan, and separates the optical image into color components. Therefore, electrostatic latent images of three colors are sequentially formed on the photoreceptor 9.

The electrostatic latent image formed on the photoreceptor 9 is transferred to the developing device I7/18.
19, the image is sequentially developed with yellow, magenta, and cyan developers, which are complementary colors of each color filter in the color separation filter 8, to form a toner image. Next, these toner images of each color are sequentially transferred by the first transfer roller 31 from the surface of the photoreceptor 9 to the same position of the intermediate transfer member 27 in an overlapping manner to form one completed full-color toner image. It is formed.

On the other hand, the transfer paper 20 housed in the paper feed cassette 21 or 22 is supplied to the timing roller 25 by the paper feed roller 23 or 24. The timing roller 25 is
The transfer paper 20 is transferred to the intermediate transfer body 2 in synchronization with the intermediate transfer body 27.
7 and the second transfer roller 32. Then, the toner image on the intermediate transfer member 27 is transferred onto the transfer paper 2° by the second transfer roller 32. Thereafter, the transfer paper 20 on which the toner image has been transferred is sent to the fixing device 36 by the conveyance heald 35, and after the toner image is fixed, the paper ejection section 3
7 and is ejected from the aircraft.

On the thus obtained transfer paper 20, a good quality image with excellent gradation is copied by the screen filter 15, but if the number of copies increases and the photoreceptor 9 deteriorates, , the density characteristics of the photoreceptor 9 change, and this change in density characteristics results in a decrease in saturation density and an excessive improvement in gradation. On the other hand, the screen filter 15 is
A moving means including a stamping motor and a cam 40 is provided so as to be movable in the vertical direction with respect to the photoreceptor 9. When the screen gap of this screen filter 15 is moved to be wider than the screen gap set at the initial stage of copying, by changing the thickness of the stripes imagewise exposed to the photoreceptor 9, As shown in FIG. 3, by changing the density characteristic from the solid line C to the broken line, it is possible to increase the saturation density and reduce the gradation.

Therefore, if the screen gap is set by moving the screen filter 15 to correspond to changes in the density characteristics of the photoreceptor 9, stable image density and gradation can be maintained from the initial stage of copying to the copying of many copies. It becomes possible to maintain.

〔Effect of the invention〕

As described above, the electrophotographic apparatus according to the present invention has an optical system section that guides reflected light from an original to a photoreceptor, and is arranged with a screen gap on the optical path of this optical system section,
In the electrophotographic apparatus provided with a screen filter capable of setting image density and gradation by the screen gap, the screen filter is provided with a moving means capable of arbitrarily setting the screen gap. It is.

This makes it possible to set a screen gap that corresponds to changes in the image density and gradation of the photoreceptor as the number of copies increases, thereby stably maintaining a predetermined image density and gradation from the initial stage of copying to multiple copies. It has the effect of being able to

[Brief explanation of the drawing]

1 to 3 show one embodiment of the present invention. FIG. 1 is an overall configuration diagram of a full-color copying machine. FIG. 2 is a configuration diagram of the moving means. FIG. 3 is a graph showing how the density characteristics of the screen filter change depending on the screen gap. FIG. 4 shows a conventional example, and is a graph showing how the density characteristics of the photoreceptor change between the initial stage of copying and the copying of a large number of sheets. 2 is a document, 4 is an optical system section, 9 is a photoreceptor, 15 is a screen filter, 40 is a cam (transfer means), and 41 is a shaft member (moving means). 2nd factor diagram diagram talent density

Claims (1)

[Claims] 1. An optical system unit that guides reflected light from a document to a photoreceptor;
In an electrophotographic apparatus, a screen filter is provided with a screen gap on the optical path of the optical system section, and the image density and gradation can be set by the screen gap. An electrophotographic apparatus characterized in that it is provided with a moving means that can arbitrarily set a screen gap.