JPH0980874A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prolong the life by applying a cleaning voltage which electrifies an image carrier to a specific potential to a first contact electrification means, and by applying a cleaning voltage wherein its potential has a specific difference between the electrification potential of an image carrier and is opposite that used in image electrification to a second contact electrification means. SOLUTION: In first cleaning mode, a voltage which is applied to the second electrification roll 2b is a cleaning voltage of -600V-400V, and every time the cleaning voltage is applied, a cleaning test is performed. As a result, in the case where the cleaning voltage higher than -460V is applied to the second electrification roll 2b in the first cleaning mode, that is, in the case where the cleaning voltage having a potential difference of 200V or higher than the electrification potential (-660V)of the photoreceptor 1 and having potential opposite that used in image electrification is applied to the roll, soil on the second electrification roll 2b can be suppressed. Further, in any cleaning tests, soil on a transfer roll 5a is suppressed to the degree of practical use.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrophotographic type or electrostatic recording type image forming apparatus such as a copying machine or a laser beam printer, and more specifically, to charge an image carrier such as a photoconductor to form an image. The present invention relates to an image forming apparatus to be formed.

Conventionally, in this type of image forming apparatus, a corona discharger such as a corotron is widely used as a means for charging an image carrier. The corona discharger is arranged so as to face the image carrier with a gap therebetween, and is excellent in the ability to uniformly charge the image carrier (high charging ability). However, the corona discharger needs to apply a large charging power of several kV and several hundreds to several thousands of μA to charge the image carrier, and thus a large high voltage power source must be used. However, since the discharge is performed in a wide range, there is a problem that a large amount of ozone is generated and the ozone deteriorates the surrounding rubber parts and the image carrier and causes environmental pollution.

Therefore, conventionally, a contact charging means having a roll shape or a brush shape is arranged in contact with the image carrier, and a charging voltage consisting of only a DC voltage is applied to the contact charging means to form the image carrier. Image forming apparatuses that are charged have been proposed. However, in the image forming apparatus described above, when the charging condition changes due to a change in environmental conditions or a decrease in the thickness of the image carrier, fogging occurs in the image or a change in density occurs. In particular, when a discharge is generated between the contact charging means and the image carrier, and the image carrier is charged by the discharge, the discharge start voltage may be changed due to changes in environmental conditions or the thickness of the image carrier becoming thin. Fluctuates, so the problems of fog and density change occur remarkably.

Therefore, conventionally, an image forming apparatus has been proposed which uses a voltage obtained by superposing an AC voltage and a DC voltage as a charging voltage. However, in the above-described image forming apparatus, since the potential relationship between the charging potential and the charging voltage of the image carrier before charging is switched, electrostatic attraction force or electrostatic repulsion acts between the image carrier and the contact charging means. Since force is applied, the image carrier and the contact charging means vibrate, and noise is generated. Further, in the above image forming apparatus, since the image carrier is discharged while the contact charging means faces each other, the amount of current flowing through the image carrier during each discharge is large, and the image carrier can be carried out early. The body surface becomes brittle. The surface of the fragile image carrier is scraped off by a cleaning blade or the like. In the image forming apparatus, the voltage (current) of the AC voltage is applied so that the above problems do not occur.
When the or frequency is lowered, uneven charging occurs remarkably, and uneven density or black streaks occur in the image.

Therefore, as shown in FIG.
The two charging rolls 10a and 10b are connected to the organic photosensitive drum 1
While disposed is brought into contact with the rotating direction upstream side of the charging roller 10a of the drum 1 (hereinafter, the first charging roll hereinafter) to 1500V _pp, AC voltage 500H _Z and -660
An image forming apparatus was constructed by applying a charging voltage superimposed with a DC voltage of V and applying only a DC voltage of -1350V to the downstream charging roll 10b (hereinafter referred to as a second charging roll). In this image forming apparatus, after the photoconductor 1 is charged to about -660V by the first charging roll 10a, discharge is performed between the second charging roll 10b and the photoconductor 1,
The surface of the photoconductor 1 is configured to be charged to -770V.

As a result, in the above-mentioned image forming apparatus, the photosensitive drum 1 can be charged to a stable potential regardless of environmental conditions and the thickness of the photosensitive member 1 (image bearing member), and noise or noise of the photosensitive member 1 can be prevented. The brittleness could be suppressed to a level without problems, and furthermore, the photosensitive drum 1 could be uniformly charged.
Further, in the image forming apparatus, the amount of ozone generated due to the discharge is about 1/100 of that of the corona discharger.

The image forming apparatus discharges between the second charging roll 10b and the photoconductor 1 and the charging ability of the second charging roll 10b is high. Image forming apparatus for reducing uneven charging potential of the image bearing member 1 due to charge injection, mainly by charge injection (JP-A-4-30).
(See Japanese Patent No. 1861 and Japanese Patent Laid-Open No. 6-95478)
Compared with the above, the photosensitive drum 1 can be charged uniformly. In addition, the image forming apparatus includes the second charging roll 10
Since the second charging roller 10b has a high charging ability by discharging between b and the photoconductor 1, the rotation speed (process speed) of the image carrier 1 is increased unlike the image forming apparatus of the above publication. However, the image carrier 1 formed by the previous image formation can eliminate the charging potential difference, and the image carrier 1 can be uniformly charged, and even in a halftone image, density unevenness due to the charging history is generated. Does not occur. By the way, in the above-mentioned JP-A-6-95478, it is claimed that the second contact charging means discharges the image carrier, but the DC voltage component of the first contact charging means and the second contact charging means Since the same voltage is used as the DC voltage of the contact charging means, the potential of the second contact charging means and the charging potential of the image carrier at the position opposite thereto are only a dozen V, so that discharge cannot occur. .

[0008]

However, in the above image forming apparatus, a large amount of adhered substances such as toner, external additives, and paper dust adhere to the surface of the second charging roll 10b during the repeated image formation. However, since the electric resistance value of the charging roll 10b increases, discharge does not occur properly, uneven charging occurs, and black streaks or white spots occur in the image.

Further, in the image forming apparatus, if a large amount of the adhering matter adheres to the surface of the second charging roll 10b, the adhering matter cannot be removed from the surface of the second charging roll 10b. , The second charging roll 10b
Had to replace. The period until the second charging roll 10b is replaced due to the adhered matter is one of the replacement times due to the deterioration of the characteristics of the second charging roll 10b itself.
It was / 10 or less.

Therefore, as a result of detailed examination of the deposits attached to the surface of the second charging roll 10b, the inventors have found that the deposits are charged to the same polarity as shown in FIG. At first, it adheres to the surface of the second charging roll 10b by electrostatic attraction, but during repeated image formation, it is crushed between the second charging roll 10b and the image carrier 1, It was found that the second charging roll 10b and the image carrier 1 are physically fixed on the second charging roll 10b by being heated by heat generated by discharge or friction between the second charging roll 10b and the image carrier 1, and thus the present invention is completed. Came to do.

At least in the charging roll to which the AC voltage is applied, the deposits on the charging roll return to the image carrier side every time the potential relationship between the charging potential and the charging voltage of the image carrier before charging changes. Therefore, the charging roll does not become dirty until the image is affected.

Therefore, an object of the present invention is to provide an image forming apparatus which can remove deposits from the second charging roll and can use the charging roll for a long period of time.

[0013]

That is, according to the present invention, there is provided a movable image carrier and a movable image carrier which is disposed in contact with the image carrier.
Two contact charging means are provided, and a charging voltage in which an AC voltage and a DC voltage are superposed is applied to the contact charging means provided on the upstream side in the moving direction of the image carrier, and the charging voltage is applied on the downstream side in the moving direction of the image carrier. In the image forming apparatus for forming an image by applying only a DC voltage to the contact charging means provided in the image charging unit to charge the image bearing member to a predetermined potential, it is arranged on the downstream side in the moving direction of the image bearing member. A cleaning mode for cleaning the provided contact charging means is provided, and in the cleaning mode, the contact charging means arranged on the upstream side in the moving direction of the image carrier charges the image carrier to a predetermined potential. A cleaning voltage is applied, and the contact charging means arranged on the downstream side in the moving direction of the image bearing member is charged with the charging potential of the image bearing member and 200
The image forming apparatus applies a cleaning voltage having a potential difference of V or more and having a potential relationship opposite to that at the time of image charging.

In the following description, the contact charging means arranged on the upstream side in the moving direction of the image carrier is referred to as a first contact charging means, and it is arranged on the downstream side in the moving direction of the image carrier. The contact charging means is called the second contact charging means. Further, in the following description, the operation of the image forming apparatus charging the image carrier to a predetermined potential for forming an image is called an image forming mode, and the contact charging unit operates the image carrier to form an image. The period of being charged to a predetermined potential is called the image charging time.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION In the present invention, the contact charging means may be arranged so as to be in contact with the image carrier to charge the image carrier, and examples thereof include a charging roll and a charging pad (web). , Charging blade, charging brush, etc.
Further, the two contact charging means may be combined in any manner.

As the above charging roll, for example, there is one in which a base rubber layer and a resistance layer are sequentially laminated on a conductive support member. Iron, stainless steel, aluminum, etc. can be used for the conductive support member, and E is used for the base rubber layer.
PDM rubber or polyurethane rubber having conductive particles or ion conductive agent dispersed therein can be used, and further, resin having conductive particles or ion conductive agent dispersed therein can be used for the resistance layer. . The conductive particles include carbon black, aluminum, etc., the ion conductive agent includes LiClO _4, etc., and the resins include polyamide resin, polyethylene resin, polyurethane resin, acrylic resin and the like. Furthermore, to prevent pinhole leakage,
A pressure resistant layer obtained by adding BaSO ₄ or the like to a cyano resin or a byron resin may be set between the surface layer (resistive layer) and the base rubber layer.

In the image forming mode, the image forming apparatus applies a charging voltage in which an AC voltage and a DC voltage are superimposed to the first contact charging means, and applies a charging voltage consisting of only the DC voltage to the second contact charging. Apply to the means. The charging voltage may be a value at which electric charge is injected from each contact charging means to the image carrier or a value at which electric discharge is performed between each contact charging means and the image carrier.

In the cleaning mode, the image forming apparatus applies a cleaning voltage for charging the image carrier to a predetermined potential to the first contact charging means, and has a potential difference of 200V or more from the charging potential of the image carrier. A cleaning voltage having a potential relationship opposite to that at the time of image charging is applied to the second contact charging means. Each of the above cleaning voltages may have a value such that electric charges are injected from the contact charging means to the image carrier, or a value that causes discharge between the contact charging means and the image carrier. Further, the voltage having a potential relationship opposite to that at the time of charging for image means, for example, that the image carrier charged to about -660V in the image forming mode is charged at a voltage of -1300V, and
The charge potential of the image carrier in the cleaning mode is -660.
In the case of V, it is smaller than -660V, for example, -400
This means setting to a potential such as V.

The cleaning mode may be executed at the time of non-image charging. The above-mentioned non-image charging means a period in which the contact charging means does not charge the image bearing member to a predetermined potential for forming an image, for example, immediately before the image charging and during the image charging. Immediately after the power supply of the image forming apparatus is turned on, after removing the jammed paper, the inter-image portion may be charged when a plurality of images are continuously formed.

In the image forming apparatus of the present invention, a cleaning mode for cleaning the second contact charging means is provided,
In the cleaning mode, a cleaning voltage for charging the image carrier to a predetermined potential is applied to the first contact charging means, and a potential difference of 200 V or more from the charging potential of the image carrier is applied to the second contact charging means. In addition, since a cleaning voltage having a potential relationship opposite to that at the time of image charging is applied,
The adhered matter that has adhered to the surface of the second contact charging means during image charging is transferred onto the image carrier.

Further, in the image forming apparatus of the present invention, since the image carrier is charged by the first charging means to execute the cleaning mode, it is necessary to newly provide a charging means for charging the image carrier for cleaning. In addition, the second contact charging unit can be cleaned easily and at low cost without complicating the configuration and structure of the image forming apparatus.

[0022]

Embodiments of the present invention will be described below with reference to the accompanying drawings.

First Embodiment FIG. 1 shows a copying machine according to the first embodiment to which the present invention is applied.
This copying machine includes an organic photoconductor drum 1 rotatable at 300 mm / s, a charging unit 2 arranged around the photoconductor drum 1 for charging the photoconductor 1 to a predetermined potential, and a photoconductor 1 according to image information.
A laser exposure unit 3 that exposes the latent image to form a latent image, a developing unit 4 that develops the latent image to form a toner image, a transfer unit 5 that transfers the toner image onto a recording sheet P, and a photoconductor. Cleaning means 6 for removing the residual toner from 1;
A charging means power supply 7 for applying a voltage to the charging means 2;
It has a transfer means power supply 8 for applying a voltage to the transfer means 5. The copying machine has an image forming mode M _P for forming an image and a standby mode M _{S in} a standby state.

The charging means 2 is in contact with the photoconductor 1 and is rotatably arranged on the first charging roll 2a.
It has a second charging roll 2b arranged in contact with the photoconductor 1 and rotatably arranged on the downstream side of the first charging roll 2a in the rotation direction of the photoconductor 1. Each of the charging rolls 2a and 2b has a rotary shaft made of a conductive material, a base rubber layer formed around the rotary shaft and provided with a conductive agent such as carbon black on EPDM rubber, and a polyamide resin. A resistance value of 10 ^2.5 to 10 ^3.3 Ω with a conductive agent of BaSO ₄ added around tin oxide and a thickness of 50 μm
m resistance layer, and is formed in a substantially cylindrical shape.

The power source 7 for the charging means applies an independent voltage to each of the first charging roll 2a and the second charging roll 2b, and each voltage is a standby mode M _S and an image forming mode M _P. Switch with and. In particular,
In the standby mode M _S , a voltage of 0V is applied to the first charging roll 2a and the second charging roll 2b. In the image forming mode M _P, 1500V _pp, the charging voltage obtained by superimposing a DC voltage of the AC voltage and -660V of 500H _Z and applies to the first charging roller 2a, a second charging roller a DC voltage of -1350V Apply to 2b. Therefore, in the image forming mode M _P , the photoconductor 1 is charged to about −660V by the first charging roll 2a (see FIG. 2).
(A)), -780 by discharge of the second charging roll 2b
It is uniformly charged to a V potential (FIG. 2B). Further, the charging potential is difficult and stable depending on environmental conditions and the thickness of the photoconductor 1, and there is no problem of noise due to charging or brittleness of the photoconductor 1,
The amount of ozone is about 1/100 of that of a corona discharger.

The exposing means 3 is for exposing the photoconductor 1 in the image forming mode M _P in accordance with image information to form a latent image, and is set so as to expose the image portion.

The developing means 4 develops the latent image in the image forming mode M _P to form a toner image, and includes a developing roll 4a which is rotatably arranged facing the photoconductor 1. The developing roll 4a has a developing voltage applied thereto to perform development. Specifically, the developing voltage is 0 V in the standby mode M _S and is switched to −600 V in the image forming mode M _P.

The transfer means 5 has a rotatable transfer roll 5a which is arranged in contact with the photosensitive member 1. The transfer means power source 8 applies a voltage to the transfer roll 5a, and the voltage is switched between the standby mode M _S and the image forming mode M _P. Specifically, in the standby mode M _S , a voltage is applied so that a current of 0 μA flows from the transfer roll 4a toward the photoconductor 1, and in the image forming mode M _P , +25 μA from the transfer roll 4a toward the photoconductor 1. The voltage is applied so that the current flows.

The cleaning means 6 is for removing the residual toner from the photoconductor 1 after transfer, and has a cleaning blade 6a arranged in contact with the photoconductor 1.
The blade 6a is adapted to scrape off the residual toner.

When a copy start switch (not shown) is pressed, the copying machine switches from the standby mode M _S to the image forming mode M _P , and the charging means 2 uniformly charges the photoconductor 1 to -750V. By forming a latent image on the photoconductor 1 by the exposure unit 3, developing the latent image by the developing unit 4 to form a toner image, and transferring the toner image on the recording sheet P by the transfer unit 5. Form an image. Further, the photoconductor 1 has the residual toner removed by the cleaning means 6 and is prepared for the next image formation.

[0031] Immediately after in this embodiment, executing the before and the image forming mode M _P executing the image formation mode M _P, a second charging roller 2b and the transfer roll 5a
With the provision of the first cleaning mode M _C1 to clean, when continuously performing image formation mode M _P is provided with a second cleaning mode M _C2 to clean the transfer roller 5a therebetween image .

In the above-mentioned first cleaning mode M _C1 ,
With the photoconductor 1 rotated, a voltage having the same value as that in the image forming mode M _P is applied as a cleaning voltage to the first charging roll 2a, and −660V is applied to the second charging roll 2b.
A cleaning voltage higher than that (for example, -100 V) is applied, 0 V is applied to the developing roll 4a, and a voltage such that a current of -25 μA flows toward the photoconductor 1 is applied to the transfer roll 5a. Therefore, the second charging roll 2b
The photoconductor 1 is charged to about -660V at a position facing the.

Further, as shown in FIG. 3, the second charging roll 2b is aligned with the timing when the portion of the photoconductor 1 charged for the cleaning mode by the first charging roll 2a comes to the facing position. The cleaning voltage is applied. This timing is the time of non-image charging. The cleaning voltage is applied for 5 seconds at a time.

In the second cleaning mode M _C2 ,
With the photosensitive member 1 rotated, a voltage having the same value as that in the image forming mode M _P is applied as a cleaning voltage to the first charging roll 2a and the second charging roll 2b, and -600 V is applied to the developing roll 4a. A voltage such that a current of −25 μA flows toward the photoconductor is applied to the transfer roll 5a.

In this embodiment, the voltage applied to the second charging roll 2b in the first cleaning mode M _C1 is set to the cleaning voltage as shown in Table 1, and the cleaning test is conducted for each cleaning voltage. . Further, in the cleaning test, specifically, the image forming mode M _P is continuously performed 10 times as one test cycle TC ₁ , and the test cycle TC _{1 is set} to 5000.
The degree of contamination of the second charging roll 2b and the transfer roll 5a after the repetition is determined.

[0036]

[Table 1]

As a result, as shown in Table 2, when a cleaning voltage larger than -460 V is applied to the second charging roll 2b in the first cleaning mode M _C1 , that is, the charging potential of the photoconductor 1 (- 660V) and 200
It has been found that when a cleaning voltage having a potential difference of V or more and having a potential relationship opposite to that at the time of image charging is applied, the second charging roll 2b can be prevented from being soiled to an extent that it can be practically used. Further, the transfer roll 5a was prevented from being soiled to the extent that it could be practically used in any cleaning test. Further, when an image was formed using the second charging roll 2b which was judged to be practically usable in the test, uneven charging of the photoconductor 1 and black streaks and white spots on the image did not occur.

Incidentally, + 400V is applied to the second charging roll 2b.
If a cleaning voltage higher than the above is applied, charges of positive polarity are injected into the photoconductor 1 (memory effect), and the image forming mode M that is subsequently performed.
_{At P} , the charging potential of the photoconductor 1 becomes small in its absolute value, which causes a problem that the density of the image changes. In addition, +60 is applied to the second charging roll 2b.
When a cleaning voltage of 0 V was applied, the photoreceptor 1 after cleaning was charged to a potential higher than 0 V, and the developing means 4 carried out wasteful development. As a countermeasure against this, the developing means 4 may be retracted so as to widen the distance between the developing roll 4a and the photoconductor 1.

[0039]

[Table 2]

Embodiment 2 The copying machine of this embodiment is different from the copying machine of the embodiment except that the first cleaning mode M _C1 is executed even after the power switch of the copying machine is turned on and the opening / closing door of the copying machine main body is closed. The same as 1.

As a result, in the copying machine, even when the copying machine has not been used for a long period of time and therefore the adhered matter adheres strongly to the second charging roll 2b and the transfer roll 5a, the adhered matter is removed. Can be removed. Further, in the copying machine, the recording sheet P jams and the copying machine stops, and a considerably larger amount of toner remains on the photoconductor 1 than the toner remaining in the normal image forming mode M _P. As a result, Even if a large amount of toner adheres to the second charging roll 2b and the transfer roll 5a, all the toner can be removed.

The first cleaning mode M _C1 after the power switch of the copying machine is turned on is as shown in FIG.
It operates by using the edge signal from OFF to ON of the switch as a trigger. The first cleaning mode M _C1 after closing the opening / closing door of the copying machine main body is as shown in FIG.
It operates by using the edge signal when the door changes from the open state to the closed state as a trigger.

In this embodiment, the voltage applied to the second charging roll 2b in the first cleaning mode M _C1 is set to -100 V, and then the image forming mode M _{P is set.}
Test cycle TC is performed 10 times in succession
_{After the} test cycle TC ₁ was repeated 5000 times, a cleaning test was performed to determine the degree of contamination of the second charging roll 2b and the transfer roll 5a. As a result, the contamination of the second charging roll 2b is suppressed to a good level, and even if an image is formed using the second charging roll 2b after the test, the uneven charging of the photoconductor 1 and the black image are caused. No streaks or white spots occurred. Also, the transfer roll 5a
The dirt was suppressed to the extent that it could be put to practical use.

Embodiment 3 In the copying machine of this embodiment, when the image forming mode M _P is continuously executed 50 times or more, the image forming mode M _P is divided every 50 times and the divided time is divided. The procedure is the same as that of the first embodiment except that the first cleaning mode M _C1 is executed.

In this embodiment, the voltage applied to the second charging roll 2b in the first cleaning mode M _C1 is set to -100V, and then, as shown in FIG.
The execution of the image-forming mode M _P successively 500 times the one test cycle TC _2, the test cycle TC ₂
After repeating 100 times, a cleaning test was performed to determine the degree of contamination of the second charging roll 2b and the transfer roll 5a. As a result, the contamination of the second charging roll 2b is suppressed to a good level, and even if an image is formed using the second charging roll 2b after the test, the uneven charging of the photoconductor 1 and the black image are caused. No streaks or white spots occurred. Further, the transfer roll 5a was also prevented from being soiled to the extent that it could be put to practical use.

[0046] EXAMPLE 4 This example of the copying machine, just before executing the image formation mode M _P, and, immediately after executing the above-described image forming mode M _P, a second charging roller 2b and the transfer roll 5a A fourth cleaning mode for cleaning the second charging roll 2b and the transfer roll 5a is performed between the images when the third cleaning mode M _C3 for cleaning is performed and the image forming mode M _P is continuously performed. The cleaning process is the same as the first embodiment except that the cleaning mode M _C4 is executed.

In the third cleaning mode M _C3 ,
With the photoconductor 1 rotated, 1500 V _pp , 500
A charging voltage obtained by superposing an AC voltage of H _Z and a DC voltage of −750V is applied to the first charging roll 2a, a DC voltage of −200V is applied to the second charging roll 2b, and 0V is applied to the developing roll 4a. Is applied to the transfer roll 5a so that a current of −25 μA flows toward the photoconductor 1. Therefore, the photoconductor 1 is charged to about -750V at the position facing the second charging roll 2b.

In the fourth cleaning mode M _C4 ,
With the photoconductor 1 rotated, 1500 V _pp , 500
A charging voltage obtained by superimposing an AC voltage of H _Z and a DC voltage of −750V is applied to the first charging roll 2a, a DC voltage of −200V is applied to the second charging roll 2b, and a developing voltage is applied to the developing roll 4a. A voltage of 600 V is applied, and a voltage such that a current of -25 μA flows toward the photoconductor 1 is applied to the transfer roll 5a. Therefore, the photoconductor 1 is charged to about -750V at the position facing the second charging roll 2b.

In this embodiment, as shown in FIG. 7, the image forming mode M _P is continuously performed 10 times.
Test cycle TC ₃ times, and this test cycle T
Second charging roll 2b after repeating C ₃ 5000 times
Also, a cleaning test was performed to determine the degree of dirt on the transfer roll 5a. As a result, the contamination of the second charging roll 2b is suppressed to a good level, and even if an image is formed using the second charging roll 2b after the test, the uneven charging of the photoconductor 1 and the black image are caused. No streaks or white spots occurred. Further, the transfer roll 5a was also prevented from being soiled to the extent that it could be put to practical use.

By the way, in the copying machine of the first embodiment, when the image forming mode M _P is continuously executed, the second charging roll 2b is cleaned between the images (hereinafter referred to as an inter-image portion). If you try to do it, wasteful development will occur in the inter image part,
This is not the case in this embodiment. In order to avoid the useless development in the copying machine of the first embodiment, a method of turning off the developing bias (turning it off) or retracting the developing means 4 can be considered. These methods are not practical because the period in which they face the second charging roll 2b is very short.

Further, in the copying machine as shown in FIG.
Since only one charging roll 9 and the transfer roll 5a are provided, the photosensitive member 1 must be charged by the other roll when cleaning one roll, and the two rolls 9 and 5a are cleaned at the same time. However, in this embodiment, the two rolls 2b and 5a can be cleaned at the same time.

Further, in the copying machine as shown in FIG. 10, it is necessary to perform cleaning of the charging roll 9 and cleaning of the transfer roll 5a in time series. Although it is almost impossible to clean 5a, in this embodiment,
Since the cleaning of the charging roll 2b and the cleaning of the transfer roll 5a can be performed at the same time, the charging roll 2b and the transfer roll 5 are formed by using the inter-image part.
a can be cleaned.

[0053]

In the image forming apparatus of the present invention, the cleaning mode for cleaning the second contact charging means is provided, and in the cleaning mode, the image carrier is set to a predetermined potential in the first contact charging means. A cleaning voltage for charging is applied, and a cleaning voltage having a potential difference of 200 V or more from the charging potential of the image carrier and having a potential relationship opposite to that at the time of image charging is applied to the second contact charging means,
Since the adhering matter adhered to the surface of the second contact charging means during image charging is transferred onto the image carrier, the adhering matter can be removed from the second charging roll, and the material can be removed over a long period of time. A charging roll can be used.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of a copying machine according to a first embodiment of the present invention.

2A and 2B are explanatory views of the charging potential of the photoconductor by the charging unit of FIG. 1A.
Is after charging by the second charging roll).

FIG. 3 is an operation sequence in a cleaning test of the copying machine shown in FIG.

FIG. 4 is an example (No. 1) of an operation sequence of the copying machine according to the second embodiment of the present invention.

FIG. 5 is an example (No. 2) of the operation sequence of the copying machine according to the second embodiment of the present invention.

FIG. 6 is an operation sequence in a cleaning test of the copying machine according to the third embodiment of the present invention.

FIG. 7 is an operation sequence in a cleaning test of the copying machine according to the fourth embodiment of the present invention.

FIG. 8 is a schematic configuration diagram of a copying machine in which the inventors conducted an experiment prior to the embodiment of the present invention.

9 is an explanatory diagram of a problem in the copying machine of FIG.

FIG. 10 is a schematic configuration diagram of a conventional copying machine.

[Explanation of symbols]

1: photoconductor (image carrier), 2a: first charging roll (contact charging means arranged on the upstream side in the moving direction of the image carrier),
2b: second charging roll (contact charging means arranged on the downstream side in the moving direction of the image carrier), _MP : image forming mode,
M _S : Standby mode, M _C1 , M _C2 , M _C3 , M _C4 : Cleaning mode.

Claims (2)

[Claims] 1. A contact charging means provided on the upstream side in the moving direction of the image carrier, comprising a movable image carrier and two contact charging means arranged in contact with the image carrier. Applies a charging voltage obtained by superimposing an AC voltage and a DC voltage, and applies only the DC voltage to the contact charging means arranged on the downstream side in the moving direction of the image carrier to bring the image carrier to a predetermined potential. An image forming apparatus that forms an image by charging is provided with a cleaning mode for cleaning a contact charging means arranged on the downstream side in the moving direction of the image carrier, and in the cleaning mode, the movement of the image carrier is performed. A cleaning voltage for charging the image bearing member to a predetermined potential is applied to the contact charging unit disposed on the upstream side in the direction, and an image is applied to the contact charging unit disposed on the downstream side in the moving direction of the image bearing member. Charge potential of carrier and 200V or more An image forming apparatus, wherein a cleaning voltage having the above potential difference and having a potential relationship opposite to that at the time of image charging is applied. 2. The image forming apparatus according to claim 1, wherein the contact charging unit executes the cleaning mode when the image carrier is not charged to form an image.