JPS60218671A - Electrophotographic copying device - Google Patents

Abstract

PURPOSE:To detect the variation of electrostatic charging characteristics of a photosensitive body to correct image forming conditions by measuring a current flowed to the photosensitive body at an electrostatic precharging time. CONSTITUTION:A photosensitive drum 1 is electrostatically precharged with an electrostatic charging voltage for the preceding copying by an electrifier 2, and the electrostatic charging current at this time is detected by a detector 5 and is compared with a reference value 7 by a comparator 6 to correct the voltage of a high voltage generator 4. The photosensitive drum 1 is electrostatically charged mainly with the corrected quantity, and an image is exposed by an optical system 8 and is developed by a developing device 11, and the toner image is transferred to a transfer paper by the transfer electrifier 2 used as a main electrifier. Not only the quantity of main electrostatic charging but also the exposure and the developing bias are changed on a basis of the detected current value to obtain copies having an optimum picture density.

Description

[Detailed Description of the Invention] Industrial Application Field The present invention corrects the surface potential of a photoreceptor, which is one of the imaging conditions for electrophotography used in electronic copying machines, etc., in accordance with the magnitude of the photoreceptor current. The present invention relates to an electrophotographic copying apparatus as described above.

Conventional Structure and Problems A method using a rotating photoreceptor such as a photoreceptor drum and completing a series of copying steps during two rotations of the photoreceptor is generally called a two-cycle method.

It is also known that this two-cycle method has advantages such as the ability to easily downsize the copying apparatus.

Furthermore, by using one corona charger for both main charging operation and transfer charging operation, power consumption and cost can be reduced.
It is also known that there are advantages such as miniaturization.

Generally, when an electrostatic latent image is formed on a photoreceptor in an electrophotographic copying device, the surface potential of the photoreceptor is 1.0 even when a constant voltage is applied to the corona charger. Residual potential of photoreceptor, environment (temperature, humidity).

atmospheric pressure), dirt on the corona charger, deterioration of the discharge electrode, etc.
It is not necessarily constant and will fluctuate depending on many other factors. Fluctuations in the surface potential of the photoreceptor have a large effect on the final image quality even if other image forming conditions (for example, exposure amount, development rate, etc.) are kept constant.

Therefore, even if the above-mentioned various factors exist, there is a method of making the high-voltage power supply that applies high voltage to the corona charger constant current so as to reduce fluctuations in the surface potential of the photoreceptor due to these factors. That is, this method attempts to supply a constant electric charge to the surface of the photoreceptor by always keeping the current output from the high voltage power supply constant. However, even if the high-voltage power supply that applies high voltage to the corona charger is made to have a constant current, it is not possible to eliminate all of the various factors mentioned above. The balance between the impedance between the shield plate and the impedance between the discharge electrode of the corona charger and the conductive substrate of the photoreceptor changes, and the amount of charge supplied to the photoreceptor surface changes, causing the surface potential of the photoreceptor to change. This has the drawback of having a large impact on image quality since the image quality fluctuates.

OBJECT OF THE INVENTION The present invention aims to eliminate the drawbacks of the above-mentioned conventional examples.
It is an object of the present invention to provide an electrophotographic copying apparatus that can easily detect and compensate for changes in the surface potential of a photoreceptor.

Structure of the Invention In order to achieve the above object, the present invention transfers the main charging, exposing, and developing operations during the first rotation of the photoreceptor to the second rotation of the photoreceptor. , static elimination.

A two-rotation, one-cycle type electrophotographic copying apparatus that performs each cleaning operation, which performs a pre-charging operation before a main charging operation, and is provided with current detection means for detecting a current flowing through the photoreceptor during the pre-charging operation. According to this structure, at least one of the amount of IW current applied to the photoreceptor, the amount of exposure, and the developing bias is changed based on the magnitude of the photoreceptor current, and the photoreceptor is This compensates for changes in surface potential.

DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments of the present invention will be described based on the drawings. 1st
The figure is a block diagram of the main parts of an electrophotographic copying apparatus according to the present invention. In the figure, reference numeral 1 denotes a photoreceptor having a photoconductor layer formed in the shape of a drum, and this photoreceptor 1 rotates twice in the counterclockwise direction (in the direction of arrow F) to complete one copying operation. A corona charger 2 that serves both the main charging operation and the transfer charging operation is disposed close to the surface of the photoreceptor 10, and a wire-shaped discharge electrode 3 of the corona charger 2 is provided with a high voltage generator 4. Power is supplied from. At this time, wire-like N is released due to corona discharge.
A corona discharge current flows from the pole 3 to the photoreceptor 1. This corona discharge current is detected by the detector 5. Comparator 6. It is fed back to the high voltage generator 4 via the reference source 7. Indeed, this corona charger 2 constitutes a part of the transfer device together with a transfer material supply device (not shown). First, an optical system 8 is provided on the side of the corona charger 2 in the direction in which photoreceptor 1 travels, and then a static elimination lamp 9 is provided. The static eliminating lamp 9 is supplied with power via a switch 10 so that light is irradiated every time the photoreceptor 1 rotates.

A developing device 1 is provided between the static elimination lamp 9 and the corona charger 2.
1 is provided. The developing device 11 is equipped with a magnetic plate.
7tj h l+ ----The same effect as the knob effect is performed. 12 is a heat fixing device.

The operation of the electrophotographic copying apparatus of this embodiment configured as described above will be described below. Figure 2 (a), (
b) , (C) , (d) , (el) , (
f) is a timing chart showing the process of the present invention. Characteristic curve A in Figure 3 shows the relationship between the current flowing through the photoreceptor (horizontal axis) and the surface potential (vertical axis), and characteristic curve B shows the relationship between the voltage applied to the corona charger (horizontal axis) and the surface potential. It shows the relationship with the electric potential (vertical axis), and the present invention utilizes these relationships. That is, the current flowing through the photoreceptor due to corona discharge from the corona charger is proportional to the surface potential of the photoreceptor, and the surface potential is proportional to the voltage applied to the corona charger. Therefore, by detecting the current flowing through the photoreceptor, it is possible to control the voltage applied to the corona charger and compensate for changes in surface potential.

Now, in the configuration diagram of FIG. 1, the print switch (not shown) is pressed to start the copying operation.
First, before the main charging by the corona charger 2, the voltage applied during the main charging of the previous copy is applied to the corona charger 2. At this time, the current flowing through the photoreceptor 1 is detected by a detector 5 made up of elements such as resistors. The output of this detector 5 and the output of a reference source 7 corresponding to a preset magnitude of the surface potential of the photoreceptor are compared and amplified, and fed back to the high voltage generator 4. Then, the feedback-controlled output of the high voltage generator 4 is applied to the corona charger 2 during the main charging operation. In other words, during pre-charging, the surface potential is lower than the predetermined surface potential.
In this case, the current flowing through the photoreceptor 1 also decreases, and the output of the detector 5 becomes smaller than the output of the reference source 7.The output of the high voltage generator 4 is increased through the comparator 6, and the output of the high voltage generator 4 is increased during the main charging operation. Correct the surface potential to a predetermined value. Furthermore, even if the surface potential is higher than a predetermined value during pre-charging, it can be similarly corrected.

In this way, the current flowing through the photoreceptor is
Since the surface potential is constantly monitored and corrected, stable and appropriate images can be obtained continuously from beginning to end.

In the above description, only the case where control is performed to obtain an appropriate image based on the relationship between the current flowing through the photoreceptor and the amount of charge on the photoreceptor is described, but the present invention is limited to these relationships. Of course, it is also possible to obtain an appropriate image by controlling, for example, based on the relationship between the current flowing through the photoreceptor and the exposure fk or the developing bias.

Effects of the Invention As detailed above, according to the electrophotographic copying apparatus of the present invention, the current flowing through the photoreceptor is constantly monitored by a small and inexpensive current detector such as a fixed resistor to determine the surface potential prior to main charging. Since this correction is performed, excellent effects can be obtained in that the quality of the copied image is improved and a stable and appropriate image can be obtained continuously from beginning to end.

[Brief explanation of drawings]

FIG. 1 is a block diagram of essential parts of an embodiment of the electrophotographic copying apparatus of the present invention, FIG. 2 is a timing chart thereof, and FIG. 3 is a characteristic diagram of the current flowing in the photoreceptor and the surface potential, and a corona charger. FIG. 3 is a characteristic diagram of applied voltage to and surface potential. 1. 8 photoreceptor, 2... corona charger, 4...
...High voltage generator, 5..Detector, 6.. Comparator, 7.-Reference source. Name of agent: Patent attorney Toshio Nakao and 1 other person No. 1
figure

Claims (1)

[Claims] A two-rotation, one-cycle system in which main charging, exposure, and development operations are performed during the first rotation of the photoreceptor, and transfer, charge removal, and cleaning operations are performed during the second rotation of the photoreceptor. The electrophotographic copying apparatus performs a pre-charging operation before a main charging operation, and includes a current detecting means for detecting a current flowing through the photoreceptor during the pre-charging operation, and the current detecting means detects the current flowing through the photoreceptor during the pre-charging operation. A change in the surface potential of the photoreceptor is compensated for by changing at least one of the amount of charge on the photoreceptor, the amount of exposure, and the developing bias based on the magnitude of the photoreceptor current. An electrophotographic copying device.