JPH0968874A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent damage to an image carrier caused by a transfer and electrification and to obtain an image of high quality, without blurring the rear end part of the image, at the time of transferring it by changing the sizes of the non-image areas of the end parts of a recording material. SOLUTION: In this image forming device for developing an electrostatic latent image formed on the image carrier (photoreceptor drum) and transferring a visual image onto the recording material, for preventing the damage to the photoreceptor drum at the rear end of the recording material, a first test pattern (the image hardly having the non-image area in the rear end part of the recording material, that is, a rear end margin) is outputted to confirm that the image is blurred in the rear end part of the recording material. When the image is not blurred, the timing of turning off a transfer current is adjusted until the image is blurred and in this state, a second test pattern (the image having the same rear end margin as that at the time of normally outputting the image is outputted to confirm that the rear end of the image is blurred or not. Only when the image is blurred, the rear end margin is repeatedly adjusted until the image is not blurred.

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 such as a copying machine or a printer.

[0002]

2. Description of the Related Art An example of a conventional color image forming apparatus for forming a full color image will be described with reference to FIG.

In the color image forming apparatus shown in FIG. 1, a photosensitive drum 1, which is an image carrier, is rotatably supported in the direction of an arrow, and a corona charger 2, an optical system 3, and a photosensitive drum 1 are provided around the photosensitive drum 1.
A developing device 4, a transfer device 5, and a cleaning device 6 are arranged.

The optical system 3 is, for example, a laser beam exposure device which irradiates the photosensitive drum 1 with a color-separated optical image or an optical image E corresponding to the color-separated image which is composed of a document scanning section and a color separation filter.

The photosensitive drum 1 uniformly charged by the corona charger 2 is irradiated with a light image E for each color separation color to form a latent image. The developing device 4 is a rotary developing device, and the central shaft 4
4 developing devices around b, namely black developing device 4K,
A cyan developing device 4C, a magenta developing device 4M, and a yellow developing device 4Y are arranged, and a predetermined developing device is rotated to a developing position facing the photosensitive drum 1 to develop the latent image on the photosensitive drum 1, and An image is formed with a toner whose base is a resin.

Further, the toner image on the photosensitive drum 1 is
The recording material is transferred onto the recording material supplied from the recording material cassette 7 through the conveying system and the transfer device 5 at a position facing the photosensitive drum 1 according to the paper path indicated by the dotted line in the figure.

The transfer device 5 includes a transfer drum 5a, a transfer corona charger 5b, an adsorption charger 5c for electrostatically adsorbing a recording material, an adsorption roller 5g, and an inner corona charger 5.
d, a recording material carrying sheet 5f made of a dielectric material is integrally stretched in a cylindrical shape in the peripheral opening area of the transfer drum 5a which is rotatably supported and has an outer corona charger 5e. Has been done.

As the transfer drum 5a rotates, the toner image on the photosensitive drum 1 is transferred onto the recording material carried on the recording material carrying sheet 5f by the transfer charger 5b.

A desired number of color images are transferred to the recording material adsorbed on the recording material carrying sheet 5f to form a full-color image.

When the transfer of the desired number of toner images is completed in this way, the recording material is discharged from the transfer drum 5a by the separating means 8 after being discharged by the separation charging device 5h, and is transferred to the tray via the heat roller fixing device 9. The paper is discharged to 10.

On the other hand, the post-transfer photosensitive drum 1 is cleaned of residual toner on the surface by the cleaning device 6, and the pre-exposure lamp 1
After the charge is removed in step 1, the image forming step is performed again.

[0012]

In the conventional color image forming apparatus, as shown in FIG. 3, when the transfer current is output to the trailing edge of the recording material during transfer (see FIGS. 3C and 3D), The potential of the photosensitive drum after the transfer is positively charged (hereinafter referred to as damage) at the position corresponding to the trailing edge of the recording material (see FIG. 3B).

Therefore, the damage D after transfer shown in FIG. 4 (a) remains as it is because the static charge removal of the photosensitive drum potential by the pre-exposure lamp acts only to minus (see FIG. 4 (b)). ), The history of damage remains even after being charged (see FIG. 4C), and this damage D appears as a sharp horizontal stripe in the image, particularly in the halftone image in the highlight part. was there.

Against this problem, as shown in FIG.
Although the transfer current is controlled to be cut off at the same time as the end of the image area (see FIGS. 5C and 5D), the transfer current supplied from the high-voltage power supply is not immediately cut off, so that a sufficient effect can be obtained. Not (see FIG. 5 (b)).

When the transfer current is cut off in the image area in order to obtain a more sufficient effect (see FIGS. 6C and 6D),
As shown in FIG. 6A, the image S from the portion where the transfer current is cut off to the non-image area at the trailing edge of the recording material (hereinafter referred to as the trailing edge margin) is not completely transferred and is blurred.
The rear end margin is generally set to 2.5 mm.

Therefore, a first object of the present invention is to provide an image forming apparatus capable of preventing the image carrier from being damaged by transfer charging.

A second object of the present invention is to provide an image forming apparatus capable of obtaining a high quality image without causing the trailing edge of the image to be particularly blurred during image transfer.

[0018]

The above object is achieved by an image forming apparatus according to the present invention. In summary, the present invention provides:
An image carrier, a latent image forming unit for forming an electrostatic latent image on the image carrier, a developing unit for converting the electrostatic latent image into a visible image, and a visible image on the recording material. An image forming apparatus having a transfer means for transferring, wherein the size of the non-image area at the edge of the recording material is changed.

The non-image area at the edge of the recording material is preferably the trailing edge of the recording material. It is preferable that the size of the non-image area at the edge of the recording material can be arbitrarily changed. According to another aspect, the size of the non-image area at the edge of the recording material preferably changes automatically depending on the environment. The environment is preferably the water content of the recording material. The transfer means is preferably controlled according to the size of the non-image area at the edge of the recording material.

The first non-image area at the edge of the recording material is small.
After outputting the test pattern of No. 1 to obtain a blurred image, output a second test pattern having a normal non-image area, and adjust the off timing of the transfer current by the transfer unit until the blurred image disappears. It is preferable to change the size of the non-image area.

[0021]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An image forming apparatus according to the present invention will be described below in more detail with reference to the drawings. In the embodiment described below, the image forming apparatus of the present invention is embodied in the color image forming apparatus shown in FIG. Therefore, a detailed description of the overall configuration and function of the color image forming apparatus will be omitted, and the features of the present invention will be described.

Example 1 Example 1 according to the present invention will be described mainly with reference to the flowchart of FIG. 1 and FIGS.

In the flowchart of FIG. 1, a test pattern (an image with almost no trailing edge margin as shown in FIG. 7) is output in order to remove damage to the photosensitive drum which is the image carrier at the trailing edge of the recording material. (S1), it is confirmed that the image is blurred at the trailing edge of the recording material (S2). If it is not blurred, the OFF timing of the transfer current is adjusted until it is blurred (S3).

Next, in a state where the image is blurred at the trailing edge of the recording material, a test pattern (an image having the same trailing edge margin as the normal image output as shown in FIG. 8) is output (S
4) It is confirmed whether the trailing edge of the image is not blurred, and it is determined whether the trailing edge margin adjustment is performed (S5). If it is not blurred, the trailing edge margin is not adjusted, and if it is blurred, the trailing edge margin is adjusted (S6). This trailing edge margin adjustment is repeated until the blur does not disappear.

When the present invention is applied to a conventional image forming apparatus, as shown in FIG. 9, there is almost no damage to the photosensitive drum, that is, there is no positive charge, and no sharp horizontal streak is observed on the image. It was The test pattern used here is a solid image because blurring can be easily confirmed.

Second Embodiment In general, the transfer current OFF timing is adjusted in order to guarantee the variation in the output of the high-voltage power supply that supplies the transfer current, and the same applies to the first embodiment.

However, the setting for absorbing the variation of the high-voltage power supply and guaranteeing that the transfer current is completely off at the trailing edge of the recording material makes it unnecessary to adjust the transfer current OFF timing.

As a specific example, the output of the high voltage power supply is turned off.
Since 1.5mm is required until the transfer current is actually cut off, and the variation tolerance of the high-voltage power supply is ± 1.5mm, the rear end margin is 4.5mm and the output of the high-voltage power supply is cut off. By setting the distance from the end to 3.0 mm, the transfer current OFF timing adjustment can be eliminated.

Even in this case, by applying the present invention, a defect-free image was obtained.

Third Embodiment Next, a third embodiment according to the present invention will be described. The position where the image starts to blur in the trailing edge margin of the recording material changes depending on the environment (water content) surrounding the recording material.

The graph of FIG. 10 shows the transfer current OF described in the first embodiment from a certain position on the recording material with respect to the water content.
This is a result of measuring the length until the image actually starts to be blurred by performing F control. It can be seen that the water content and the measurement length are substantially proportional.

In this embodiment, after the process described in Embodiment 1 is carried out, the trailing edge margin is set according to the amount of water detected by the temperature / humidity sensor (not shown) according to the table shown in FIG. It was possible to further enhance the effect by controlling the transfer current and changing the transfer current OFF timing in the same manner as the amount of change in the trailing edge margin.

[0033]

As is apparent from the above description, the image forming apparatus according to the present invention prevents the image carrier from being damaged by transfer charging by changing the size of the non-image area at the edge of the recording material. It is possible to obtain a high quality image by eliminating the occurrence of horizontal stripes on the image and preventing the occurrence of blurring at the trailing edge of the image.

[Brief description of drawings]

FIG. 1 is a flowchart for adjusting a trailing edge margin according to a first exemplary embodiment.

FIG. 2 is a configuration diagram showing an example of a conventional image forming apparatus.

FIG. 3 is an explanatory diagram showing transfer current control and damage to a photosensitive drum in the image forming apparatus of FIG.

FIG. 4 is an explanatory diagram showing a mechanism of horizontal stripes in the image forming apparatus of FIG.

5 is an explanatory diagram showing transfer current control and damage to a photosensitive drum in the image forming apparatus of FIG.

FIG. 6 is an explanatory diagram showing transfer current control when a blur occurs at a trailing edge of an image in the image forming apparatus of FIG.

FIG. 7 is an explanatory diagram illustrating a trailing edge margin when a test pattern is output according to the first exemplary embodiment.

FIG. 8 is an explanatory diagram illustrating a trailing edge margin when a test pattern is output according to the first exemplary embodiment.

FIG. 9 is an explanatory diagram showing effects of the first embodiment.

FIG. 10 is a graph showing the relationship between the amount of water and the amount of blur in Example 3.

11 is a graph showing a table showing the relationship between the water content and the trailing edge margin in Example 3. FIG.

[Explanation of symbols]

 1 photosensitive drum (image carrier) 2 primary charger 4 developing means 5 transfer means

Claims (7)

[Claims] 1. An image carrier, a latent image forming means for forming an electrostatic latent image on the image carrier, a developing means for converting the electrostatic latent image into a visible image, and a visible image. An image forming apparatus having a transfer unit for transferring the image onto a recording material, wherein the size of the non-image area at the edge of the recording material is changed. 2. The image forming apparatus according to claim 1, wherein the non-image area at the end of the recording material is the rear end of the recording material. 3. The image forming apparatus according to claim 1, wherein the size of the non-image area at the edge of the recording material can be changed arbitrarily. 4. The size of the non-image area at the edge of the recording material automatically changes according to the environment.
Image forming apparatus. 5. The image forming apparatus according to claim 4, wherein the environment is the water content of the recording material. 6. The image forming apparatus according to claim 1, wherein the transfer unit is controlled according to the size of the non-image area at the edge of the recording material. 7. A transfer method comprising outputting a first test pattern having a small non-image area at the end of the recording material to obtain a blurred image, and then outputting a second test pattern having a normal non-image area to transfer the transfer image. 8. The image forming apparatus according to claim 1, wherein the size of the non-image area is changed until the blurred image disappears by adjusting the off timing of the transfer current by the means.