JPS6318189B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a charging device for charging a photoreceptor of, for example, an electrophotographic copying machine.

Corona chargers are currently used in most electrophotographic copying machines, but corona chargers use high voltage, are dangerous, pollute the atmosphere and equipment due to ozone generation, and are expensive. There was a problem in becoming something. On the other hand, charging devices using rollers or brushes, which have been tried in various ways for a long time, have had the problem of mechanically damaging the photoreceptor or electrically damaging it.

Therefore, in order to solve the above-mentioned problems, the present applicant has already filed an application as Japanese Patent Application No. 55-30093. Figure 1 shows the schematic structure of the above application, where a is a photoreceptor such as ZnO, b is an electrode with a moderate resistance, c is an electric resistor like a cloth with dense piles, and d is a A DC power source applies a DC voltage to the electrode b, e is an AC power source that applies an AC voltage to the electrode b via a capacitor f, and g is a capacitor for attenuating the AC electric field. When a DC voltage and an AC voltage are applied to the contact charging device configured in this way, as shown in FIG.
The AC voltage is highest at point B, and as it moves toward point B, the AC voltage attenuates, but the DC voltage is
There is an almost constant potential distribution between A and B, and very good results have been obtained in repeatedly charging the photoreceptor a.

However, when the circuit shown in FIG. 1 is used, for example, if we consider the minute portion of the object to be charged and consider how it is charged, the result will be as shown in FIG. 3. In other words, if we analyze the charged object by considering it as a capacitor, the current flowing into the charged object I(t)=V-V(t)/R The surface potential of the charged object V(t)=1/C∫ ^t _p I(t)dt V: AC power supply voltage R: Contact resistance (ignoring electrode resistance) C: Due to the capacitance of the charged object, the surface voltage when the contact first contacts the charged object is 0. Inserting a certain fact and solving, I(t)=V/Rex _p (-t/RC) V(t)=V{1-ex _p (-t/RC)}, and the current flowing into the charged object is at its maximum when it first contacts the contactor, and at this time electrical damage to the charged object becomes maximum, shortening the life of the charged object such as a photoreceptor.

This invention was made in view of the above circumstances, and its purpose is to increase the resistance value of the contact on the side where the contact first comes into contact with the charged object to prevent electrical damage to the charged object. It is an object of the present invention to provide a charging device that can reduce the amount of electrification and extend the life of the object to be charged.

The present invention will be explained below based on an embodiment shown in the drawings. FIG. 4 shows the basic configuration of an electronic copying machine, where 1 is the main body. A document mounting table 2 is provided on the upper surface of the main body 1, and is configured to reciprocate by a drive motor 3 provided within the main body 1. A drum-shaped zinc oxide-resin dispersion photoreceptor 4 serving as a charged member rotates at a circumferential speed of 80 mm/sec in synchronization with the above-mentioned mounting table 2 at approximately the center of the main body 1 . An exposure system 7 consisting of a lamp 5, a convergent light transmitter 6, etc. is provided between the photoreceptor 4 and the original platen 2, and illuminates the original on the original platen 2, and directs the reflected light to the photoreceptor. 4 to form an image of the document. A developing device 8, a transfer device 9, a cleaning device 10, and a charging device 11, which will be described later, are arranged in this order along the rotational direction of the photoreceptor 4 from this image forming position. The above developing device 8
The latent image of the document formed on the surface of the photoreceptor 4 by the exposure system 7 is visualized. The transfer device 9 transfers the original toner image formed on the photoreceptor 4 onto the copy paper P, and the cleaning device 1
0 removes toner remaining on the surface of the photoreceptor 4. Further, at the bottom of the main body 1, there is provided a paper feeding device 14 consisting of a removable cassette 12 for storing copy paper P and a paper feed roller 13 for feeding the copy paper P. Further, the transfer device 9 includes a transfer roller 15 and a plurality of guide rollers 16, 1.
6 and a transfer belt 17 having an insulating property such as Mylar (trade name). The transfer belt 17 is in contact with a part of the outer circumferential surface of the photoreceptor 4, and the transfer belt 17 includes a transfer charging device 18, which has basically the same structure as the charging device 11, and a cleaning blade 19. are in contact with. Furthermore, a fixing device 20 and a delivery roller 21 are provided on the delivery end side of the transfer belt 17 so that the copy paper P onto which the image has been transferred by the transfer device 9 is fixed, and then delivered to the tray 22. It's summery. Note that 23 is a control device.

The motor 3 is a motor equipped with an exhaust fan, and is designed to exhaust heat generated in the exposure system 7 as the motor rotates to the outside of the main body 1. The photoreceptor 4 is formed by coating a thin aluminum drum with a thickness of 0.8 mm and a diameter of about 80 mm with a binder type photoreceptor of zinc oxide-resin dispersant sensitized with a dye such as rose bengal. It is something. Further, the cleaning blade 19 described above scrapes off toner adhering to the transfer belt 17 to clean the transfer belt 17.

Next, the charging device 11 will be explained based on FIGS. 5 to 7. 24 is a charger base which is a base body. The charger base 24 is made of a resin material such as acrylic or ABS and is formed into a prismatic shape.
A mounting member 26 having a diameter of 5 is fixed. The engagement groove 25 of the attachment member 26 is slidably engaged and supported by a guide frame 27 provided on the main body 1. Further, a contactor 28 and an electrode 29 are attached to the front portion of the charger base 24 in order from the front surface thereof, that is, the side in contact with the photoreceptor 4. The contactor 28 is made of velveteen-like cloth, and the base cloth 30 is made of carbon-dispersed rayon fiber, and the bristles 31 are flocked with a length of 3 mm, a thickness of 5 denier, and a density of about 16,000 strands/cm ^{2 .} It is something that has been done.

The contactor 28 is divided into a front stage 28a and a rear stage 28b in the rotation direction of the photoreceptor 4, and the resistance value of the front stage ^28a is controlled depending on the amount of carbon dispersed in the fibers. ^8Ω
cm, and the rear stage 28b is set to 10 ⁵ to 10 ⁶ Ωcm. Further, the width of the front stage 28a is 10 cm, and the width of the rear stage 28b is 15 cm. The electrode 29 is made of conductive rubber made of carbon (VULCAN Voltage and DC voltage are applied.

Therefore, when copying the original on the original platen 2, by pressing the copy start button, each device can eject the copy paper P on which the original copy image has been obtained to the tray 22 by a known operation. can. At this time, in the charging device 11, when an AC voltage and a DC voltage are applied from the electrode 29 as the photoreceptor 4 rotates, the front stage 28 of the contactor 28
Since a has a larger contact resistance R than the rear stage 28b,
The charging characteristics when considering a small portion of the photoreceptor 4 are as follows.
It will look like the figure. In other words, in the former stage 28a, the current is more limited than in the conventional example because the contact resistance R is large, and in the latter stage 28b, even though the contact resistance is the same as in the conventional example, the photoreceptor 4 already has a potential. Therefore, the peak of the current is smaller than in the conventional case, and electrical damage to the photoreceptor 4 is reduced. As a result, the charging efficiency is the same as that of the conventional method, and the life of the photoreceptor 4 used as the charged object can be extended.

In addition, in the above embodiment, the contactor 28 is
It is divided into two stages: a front stage 28a and a rear stage 28b, and the resistance value is 10 ⁷ to 10 ⁸ Ωcm for the front stage 28a and 10 ⁵ for the rear stage 28b.
~ ¹⁰⁶ , but if the resistance value decreases from the part A where it first contacts the photoreceptor 4 to the part B where the photoreceptor 4 moves away from the contact 28, it can be changed in multiple stages or continuously. By doing so, electrical damage to the photoreceptor 4 is reduced.

As explained above, in this invention, in a device that charges an object by bringing a contact into contact with the object, the resistance value of the contact is large on the side where it first contacts the object to be charged, and small on the opposite side. Therefore, the peak of the current flowing into the object to be charged is reduced, electrical damage to the photoreceptor as the object to be charged can be reduced, and the life of the photoreceptor can be extended.

[Brief explanation of the drawing]

Fig. 1 is a schematic illustration showing the principle of the contact charging device, Fig. 2 is an illustration showing the voltage distribution applied to the photoreceptor, Fig. 3 is a graph showing the charging characteristics, and Fig. 4 is the invention. 5 is a sectional view of the charging device, FIG. 6 is an enlarged sectional view of the main parts, and FIG. 7 is a graph showing the charging characteristics. It is. 4...Photoreceptor (charged body), 28...Contactor,
29...electrode.

Claims (1)

[Claims] 1. A charging device that has a flexible contact and means for applying a voltage to the contact, and charges the object by bringing the contact into contact with a charged object that moves in one direction relative to the contact. A charging device characterized in that the resistance value of the contact is large on the side where the contact first contacts the object to be charged, and small on the opposite side.