JPS58224355A - Method for correcting surface potential of photoreceptor of electrophotographic copying machine - Google Patents

Abstract

PURPOSE:To eliminate ground stains and to improve poor reproducibility, by detecting the surface potential of the latent image of a pattern having medium contrast and controlling and correcting the voltage to be applied on an exposing lamp. CONSTITUTION:The output of the latent image potential of a pattern from an electrometer 11 is inputted to a controller 18, by which said output is compared with a standard potential and the voltage to be applied on an exposing lamp 3 is controlled by the difference between the same. A sensor pattern 2, an eraser 12, and a P-sensor 14 are used for controlling the density of a picture image based on a P-sensor method, and the pattern 2 is exposed on a photoreceptor 9 by an image exposing device to form a latent image which is developed with a developing device 13 and the pattern image is formed. The reflectivity thereof is detected with a P-sensor 14 and the replenishing of a toner to the device 13 is controlled, whereby the density of the image is controlled.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for correcting changes in surface potential during image exposure based on changes in sensitivity of a photoreceptor in an electrophotographic copying machine.

When a photoreceptor used in an electrophotographic copying machine is continuously used to form an electrostatic latent image, the sensitivity of the photoreceptor gradually changes, and when it is left unused for a certain period of time. When used for the first time after the exposure, the sensitivity will change in the opposite direction to the above, and as a result, even if the original is exposed under the same exposure conditions and an electrostatic latent image is formed, the surface potential of the photoreceptor will change and background smear will occur. It is known that the reproducibility of images deteriorates.

In addition, photoreceptors vary in their characteristics during manufacture, and there are differences in sensitivity when the photoreceptor is replaced or between machines, so it is not always possible to obtain the same reproducibility even when copying is performed under the same conditions.

As a means of correcting this, a method has been proposed in which the latent image potential for the halftone image is detected and a developing bias voltage equal to this latent image potential is applied to the developing electrode. and the image a degree fluctuation is large,
This will cause deterioration of guar reproducibility.

The manner in which the sensitivity of the photoreceptor changes as described above varies depending on the type of photoreceptor and the copying system; in some cases, the surface potential gradually decreases with repeated use, while in others it increases.

The present invention provides a method for repeatedly carrying out copying or copying after being left unused, which eliminates the above-mentioned drawbacks of the conventional correction method for changes in surface potential due to changes in sensitivity due to repeated use or neglect of the photoreceptor; Or, the surface potential of the photoreceptor can compensate for changes in surface potential during exposure due to changes in the sensitivity of the photoreceptor due to mechanical changes, or when the photoreceptor is replaced, making it possible to obtain copies with good poor reproducibility without background smudges. The purpose is to provide a correction method.

The purpose of this is to form an electrostatic latent image of the pattern on the photoreceptor by exposing a pattern having an intermediate density on the photoreceptor under the same conditions as the original image exposure, and to detect the entire surface potential of the photoreceptor. This is achieved by controlling the voltage applied to the exposure lamp so that the surface potential of the patterned electrostatic latent image becomes a predetermined value.

Examples of experiments conducted to confirm the principle and effects of the present invention will be described in detail below.

Figure 1 shows the results of a standard machine, machine settings, repeated use, and the first copy after one week of storage when a certain photoreceptor is installed in a copying machine and exposed under certain conditions. FIG. 3 is a curve diagram showing how a surface potential curve changes with respect to the original reflectance.

The horizontal axis of the figure shows the original reflectance in %, and the vertical axis shows the photoreceptor surface potential 1V. The curve ■ is for standard machine settings, ■ is for repeated use, and ■ is for the first sheet after one week of storage. This is the copy-temporal curve.

As is clear from the figure, in this example, the curve for repeated use ■
Compared to the curve with standard machine settings, the potential is reduced over the entire range of the original reflectance, but the largest potential change is at the original reflectance of about 63, and the surface potential id: It has decreased by 90V K from 210V. Also, areas with high original reflectance (background areas, low density areas)
For example, at the 90th section, the surface potential decreases from 90V to 20V, and the rate of decrease is extremely large.

On the other hand, when comparing the curve for the first copy after one week of storage with all standard machine settings, the surface potential increases over the entire range of the original reflectance, for example, the reflectance 6 mentioned above.
In the 3rd ratio part, 210V becomes 300V, and in the 90th ratio part, fl 90V changes to 180V.The higher the ζ reflectance, the larger the amount of change in surface potential.

On the other hand, the r curve of image density versus surface potential of the photoreceptor is as shown in FIG. 2, for example. This curve shows that the photoreceptor has a dark potential (original density 2 (surface potential at 1) total of 700 V) and a light potential (
Surface potential at original reflectance coefficient of 90) 'i 9
This is a curve obtained when copying is performed under the conditions of setting 0V, developing bias voltage t2oov, developer toner concentration 3 weight ratio.

Therefore, if the sensitivity of the photoreceptor changes during repeated use or the first copy after being left unused, and the surface potential of the photoreceptor during exposure changes as shown in Figure 1, the curve of image density relative to the original density will naturally change. do.

Therefore, stable image quality cannot be obtained unless the surface potential of the photoreceptor is corrected depending on the usage state of the photoreceptor, ie, repeated use, first use after being left unused, and when the photoreceptor is replaced.

Since variations in the photoreceptor surface potential are caused by changes in the sensitivity of the photoreceptor, if the exposure amount is changed according to the sensitivity, the same surface potential can always be obtained over the entire original density range. The method is to detect variations in surface potential in areas where surface potential changes are more significant, particularly in areas that have a large effect on the image, for example, in the example in Figure 1, where the original reflectance is approximately 63. The most accurate correction can be achieved by controlling the amount of light from the exposure lamp using the difference between the detected amount and the standard surface potential (for example, 210 V).

This method was applied to an actual copying machine and an experiment was conducted to confirm its effectiveness, and an example will be described in detail below.

Example 1 As shown in FIG. 3, the copying machine used in the experiment was provided with a sensor pattern 2 continuous to the lower surface of the image leading edge position la of the contact glass l fixed to the machine frame. Below the contact glass 1, an exposure lamp 3, a first mirror 4,
A known slit exposure system consisting of a second mirror 5, an imaging lens 6, a third mirror 7, and a fourth mirror 8 is provided. The exposure pump 3 and the first mirror 4 integrally move parallel to the contact glass l at a speed of 1/mV, and the second mirror moves synchronously in the same direction at a speed of 5%. An image is formed around the photoreceptor drum 90, which rotates at a constant speed at certain positions, and exposure scanning is performed. In the order of rotation direction indicated by an arrow on the circumferential surface of the photoreceptor drum 90, the charger lO1, the exposure position, the electrometer 11 used in the method of the present invention, the eraser 12, the developing device 13, the P-sensor 14, Transfer art separation charger 15, cleaning device 1
6. A quenching device 17 is provided.

The output of the pattern a image potential based on the potential word -1ttK is input to the controller 18 and compared with a standard potential, and the voltage applied to the exposure rung 3 is controlled based on the difference therebetween.

Sensor pattern 2, eraser 12, P-sensor 1
4 is used for image density control by the P sensor method, and sensor pattern 2 is exposed on the photoreceptor 9 by a Vi image exposure device to form a latent image, which is developed by a developing device 13 to form a pattern image. be done. Its reflectance'
The toner is detected by the 4p sensor 14 and the toner supply to the developing device 13 is controlled to control the image density.

All other copying process equipment is commonly used to carry out the copying process.

In the replication system described above, each condition was set to the standard conditions described above. Sensor pattern 2 has a reflectance of 63 from FIG.
(density 0.2) was pasted.

The set value to be compared with the pattern latent image potential of the controller 18 is 2.
10VVC was set. Then, exposure is performed while changing the density of sensor pattern 2, and the pattern latent image potential is always 210V.
After confirming that the exposure lamp voltage changes so that
was not observed, there was no change in poor reproducibility, and stable image density was obtained. The surface potential at this time was a dark potential of 30 V, a light potential of 30 V, and a sensor pattern potential of 10 V, which were variations from the set values.

Example 0: Copy of Example I/Write potential set in stem is not fully set,
The controller was set to control the exposure lamp with a sensor pattern reflectance of 63% (density 0.2) and a surface potential of 210V. As in Example 1, I continuously copied 1000 normal images, and compared the first copy after leaving it for one night and the first copy after leaving it for a week, but no changes were observed and stable, good image quality was obtained. Ta. Regarding background stains and poor reproducibility with this machine,
Although the developing bias can be changed as an adjustment mechanism by the user, it has been confirmed that good copies can be obtained with the same notch without the need for any adjustment.

As described above, according to the present invention, variations in sensitivity of the photoconductor due to usage conditions such as continuous copying, first copying after being left unused, replacement of the photoconductor, and differences between machines can be avoided! It is possible to stably obtain image quality with good poor reproducibility without scratches, and to eliminate the need for adjustments during assembly or by the user during use, and other remarkable effects can be obtained.

[Brief explanation of the drawing]

Figure 1 is a curve diagram showing an example of sensitivity change depending on the usage conditions of the photoreceptor, Figure 2 is a curve diagram showing the relationship between the surface potential of the photoreceptor and image density, and Figure 3 is a curve diagram showing the relationship between the surface potential of the photoreceptor and image density. 1 is a sectional view showing a schematic configuration of an example of an electrophotographic copying machine. 2...Pattern 3...Exposure lamp 9...Photoreceptor 11...Potential 8-118...Controller

Claims (1)

[Claims] lf! based on the sensitivity change of the photoreceptor of the electrophotographic copying machine! 1
i(fJ 'tIn a method for correcting changes in surface potential during K light, a pattern having an intermediate density is exposed on a photoreceptor under the same conditions as the original image exposure, and an electrostatic latent image of the pattern is formed on the photoreceptor. A surface potential correction method comprising: forming a pattern electrostatic latent image, detecting the surface potential thereof, and controlling the application load of an exposure lamp so that the surface potential of the patterned electrostatic latent image becomes a predetermined value.