JPS58152267A - Electrophotographic copying device - Google Patents

Abstract

PURPOSE:To obtain sharp picture images irrespectively of humidity condition by detecting the high humidity condition or condensation condition at the inside and outside of a device body and controlling the high voltage current to be applied to an electrifier. CONSTITUTION:When the high humidity condition or condensation condition around an electrostatic drum 8 is detected with a switching element 22, the signal from a detecting part 23 is conducted to a control system 25. When the moisture responsive film 29 of the element 22 absorbs moisture in the high moisture condition, the resistance of the element 22 changes. Thereupon, an adequate detecting level is regulated with a variable resistor 34 connected to a terminal 33, by which the signal from the terminal 33 is inputted to the system 25. Thus the quantity of the electrostatic charge on the drum 8 is changed to increase or decrease the amt. of the toners to be stuck on the drum 8 by controlling the high voltage current to be applied to the electrifier in the above- mentioned way, whereby the sharp copies are obtained irrespectively of the humidity condition.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an electrophotographic copying apparatus, and more particularly to an electrophotographic copying apparatus that can provide clear copies regardless of high humidity spray conditions or dew condensation conditions.

First, an electrophotographic copying apparatus, which is the background of the present invention, will be explained.

FIG. 1 shows the main configuration of an electrophotographic copying apparatus based on plain paper electrostatic transfer (PPC), and will be described in accordance with the operation of copying an original onto copy paper.

Reference numeral 1 denotes a main body of an electrophotographic copying apparatus, and an original 2 is placed on an original glass at the top of the main body 1. The document 2 is illuminated by the illumination lamp 3 from below, and as the illumination lamp 3 moves, the document 2
surface is irradiated. The image is formed on the electrostatic drum 8 by optical elements including a reflecting mirror 4.5, an in-mirror lens 6, a mirror 7, and the like. The electrostatic drum 8 has a photoconductive layer of, for example, selenium formed on its surface, and rotates counterclockwise as shown. The charger 1 is supplied with a positive high voltage current h) from the high voltage power supply section 9.
At zero, the surface of the electrostatic drum 8 is charged with positive ions in advance, and when an image is formed on the electrostatic drum 8, the exposed area becomes conductive, so the positive ions disappear and the light is absorbed. Charges remain in areas that are not hit, that is, areas that correspond to the image area, forming a latent image.

Next, the toner, which has been triboelectrically charged and given a negative charge, is caused to flow from the toner supply mechanism 11 onto the electrostatic drum 8 and adheres to the latent image to form a visible image.

On the other hand, the copy paper 4 is removed from the cassette 12 storing the copy paper.
3 is supplied, and brought into close contact with the electrostatic drum 8 by the tenth rollers 14a and 14b, and the image on the electrostatic drum 8 is transferred to the copy paper 13 by a positive high voltage current from the high voltage power source 9 using the transfer charger 15.
transferred on top.

After the transfer, the transfer paper 13 is peeled off from the electrostatic drum 8 by the separation roller 16 and guided to the toner constant monitoring mechanism 19 by the 20th rollers 17a and 17b. In the toner constant W mechanism 19, toner is fixed onto the copy paper 13 by the heater 20 and recorded on the copy paper 13.

The toner remaining on the electrostatic drum 8 is removed by the cleaning roller 21, and the next copying operation is started again.

By the way, if the surrounding environment of such an electrophotographic copying apparatus becomes high humidity or dew condensation, for example, the electrostatic drum 8 will be exposed to moisture or dew, and leakage will occur when it is charged. Moreover, when such a state is realized, light guide′! ! This also causes deterioration of the i-layer, significantly shortening the life characteristics.

If this condition or dew condensation condition is realized, a good image cannot be formed on the electrostatic drum 8, and clear copies cannot be made.

Furthermore, in high humidity or dew condensation conditions, the toner absorbs moisture, making it difficult to direct the toner in a negative direction and making it difficult to attach the toner to the electrostatic drum 8, making it difficult to copy images. I won't be able to do it.

This invention aims to prevent the above-mentioned situations by detecting high humidity conditions and dew condensation conditions.

FIG. 2 is a schematic diagram of essential parts showing an example of an electrophotographic copying apparatus according to the present invention.

In the figure, 8 indicates the electrostatic drum shown in FIG. 1, and in this example, a switching element 22 for detecting a high humidity state or a dew condensation state around the electrostatic drum 8 is arranged.

A signal detected by the switching element 22 and detected by the detection section 23 is amplified by the amplifier 24 and introduced into the control system 25. An example of the switching element 22 will be explained in detail based on FIG. A pair of electrodes 27 and 28 are formed on the substrate 26, and these electrodes 2
Moisture Sensitive 1I29 was formed to cover 7.28. This switching element 22 has one electrode 28
A predetermined voltage is applied from the power supply terminal 30 to. With,
The other electrode 27 is connected via a resistor 31 to, for example, the gate of a FET 32 having high input impedance characteristics, and an output signal terminal 33 is led out from the source or drain. FET32 constitutes the detection circuit 23,
Terminal 33 is connected to the amplifier 250 input side.

Therefore, when the surface of the electrostatic drum 8 becomes high humidity or dew condensation, the moisture sensitive film 29 of the switching element 22
As a result, the resistance of the switching element 22 changes and the resistance between the electrodes 27 and 28 decreases, resulting in a low resistance.
A voltage almost equal to 0 is applied, and FET3
An output signal is obtained at the terminal 33 where 2 is turned on, and the control system 25 is driven by this signal.

At this time, a variable resistor 34 is connected in series to the terminal 33 to adjust the detection level, and the control system 25 is driven only when the detection level exceeds an appropriate detection level. Specifically, this υj-system 25 is for controlling the high voltage current applied to the charger 10 from the high voltage power supply section 9, and controls the high voltage current applied to the charger 10 only when a detection signal is obtained. The amount of charge on the electrostatic drum 8 is changed. Therefore, the amount of toner adhering to the electrostatic drum 8 can be increased or decreased depending on the high humidity state or dew condensation state, and clear copies can be provided regardless of the humidity state.

In this invention, a switching element having the following characteristics is used.

For example, an example of Ill III at a relative humidity of 80% will be described.

Figure 4 shows the relative humidity-resistance characteristics of the switching element, and Figure 6. The element shown in numeral 2 corresponds to a switching element, and has a characteristic that the resistance value is constant up to a certain relative humidity, in this example 60%, and the resistance value suddenly changes and decreases above that point.

Therefore, since the resistance value tends to decrease when the relative Milli exceeds 60%, the control system can be operated by matching the resistance value at higher relative humidity with the resistance value at the switching level.

It can be said that the use of a switching element having such relative humidity-resistance value characteristics has the following advantages.

In other words, if the characteristic values change due to changes over time or deterioration, for example at a rate of 50%, then the failure occurs! !
1, but the change in relative humidity is only a small value as shown by width A, and there is no significant change in the switching level due to the change in relative humidity.
This is convenient as a switching element.

On the other hand, as shown in FIG. 4, a humidity sensing element (solid line 2) has a relative humidity-resistance value characteristic different from that of the above-mentioned switching element.
When using , the following disadvantages occur. In other words,
When 50% characteristic deterioration occurs, as shown by solid line 2 and broken line 2 in a certain figure, the change in relative humidity is as shown by line B.
This is larger than when the above-mentioned switching element is used. Therefore, the switching action cannot be performed at the characteristic relative humidity, and stable operation cannot be expected.

In the above-described embodiments, an electrophotographic copying apparatus based on a plain paper electrostatic transfer method has been described, but the present invention can also be applied to an electrophotographic copying apparatus based on an electrostatic copying method using photosensitive paper. Therefore, sharp copies can be obtained by turning on the high voltage current applied to the charger from the high voltage power supply only when the switching element detects a high humidity state or a dew condensation state.

Further, the same effect can be achieved by arranging the switching element not only within the apparatus main body but also outside the apparatus main body.

As is clear from the above description, according to the present invention, a switching element for detecting a humid state or a dew condensation state inside or outside the main body is arranged in the apparatus main body, and this switching element detects a high humidity state or a dew condensation state. This electrophotographic copying apparatus is characterized in that the high-voltage current applied to the charger from the high-voltage power source is controlled only when

Therefore, even in high humidity or dew condensation conditions, by controlling the high voltage current applied to the charger to increase or decrease the amount of charge, it is possible to provide copies that are as clear as in low humidity conditions. .

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram showing the main parts of an electrophotographic copying device based on plain paper electrostatic transfer (PPC), FIG. 2 is a schematic diagram of the main parts showing an example of the electrophotographic copying device according to the present invention,
FIG. 3 is a partial circuit diagram thereof, and FIG. 4 is a relative humidity-resistance value characteristic diagram of the switching element. 1... Body of electrophotographic copying device, 8...
・Electrostatic drum, 22...Switching element, 2
3...Detection section, 24...Amplification section, 25
・・・・・・Control system. Patent applicant: Murata Manufacturing Co., Ltd.

Claims (1)

[Claims] A switching element is placed in the main body of the device to detect leakage or condensation inside or outside the main body, and only when this switching element detects high humidity or condensation, high voltage is applied from the voltage power source to the charger. An electrophotographic copying device characterized by controlling electric current.