JPH11143182A - Image forming device - Google Patents

Abstract

(57) Abstract: In an image forming apparatus using a contact type charging device of an AC application type, a good image is always output regardless of the usage status of a member to be charged and a charging member, and the usage status. And by applying an appropriate alternating current or alternating voltage in accordance with the conditions, the shaving amount of the member to be charged is reduced, and the life is extended. SOLUTION: This is an image forming apparatus for performing image formation by applying an image forming process including a step of charging a surface of a member to be charged to a surface of the member to be charged.
A contact-type charging device for charging a surface of a member to be charged by bringing a charging member 2 applied with a DC electric field superimposed on an alternating electric field into contact with the member to be charged 1 and detecting replacement of the member to be charged and the charging member. And means 100, 101, and 3 for changing an alternating electric field applied to the charging member during predetermined image formation in accordance with replacement of the charged object and the charging member. Image forming apparatus.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus for forming an image by applying an image forming process including a step of charging a surface of a member to be charged, and a charging process for the member to be charged. The means relates to an image forming apparatus that is a contact-type charging device that charges a member to be charged by bringing a charging member applied with a DC electric field superimposed on an alternating electric field into contact with the member to be charged.

[0002]

2. Description of the Related Art An image forming process including a step of charging a member to be charged (hereinafter, referred to as a photoreceptor) on a member to be charged (image bearing member) such as an electrophotographic photosensitive member or a dielectric material for electrostatic recording. Then, an electrostatic latent image corresponding to the target image information is formed, and the electrostatic latent image is visualized (toner image) with a developer.
An electrophotographic apparatus (copier, optical printer, etc.) that transfers the toner image to a transfer material, further fixes the image and outputs it as an image formed product (copy, print), and uses the photoreceptor repeatedly for image formation. Image forming apparatuses such as electrostatic recording apparatuses are known.

In such an image forming apparatus, as a device for charging a photosensitive member as a member to be charged, a corona discharge device has conventionally been widely used. In this method, a corona discharge device is disposed so as to face a photoreceptor in a non-contact manner, and the photoreceptor surface is corona-charged by exposing the photoreceptor surface to a corona shower generated from the corona discharge device to which a high voltage is applied.

In recent years, contact type charging devices have attracted attention and have been put to practical use because they have advantages such as lower power supply voltage and less ozone generation than corona discharge devices. ing.

[0005] A contact-type charging device contacts an object to be charged such as a photoreceptor with a conductive charging member (contact charging member) such as a roller type (charging roller), blade type, fur brush type or magnetic brush type. A predetermined bias voltage is applied to the charging member to charge the charged body to a predetermined polarity and potential.

There are a system in which the bias applied to the charging member is only a DC voltage (DC application system) and a system in which a DC voltage is superimposed on an AC voltage (AC application system). In particular, the latter AC application method is a method frequently used in recent years because it is easy to obtain a uniform surface potential because an AC component makes charging unevenness uniform and a DC component causes a peripheral speed to a predetermined voltage.

There are two types of contact charging mechanisms: a corona charging system and a direct charging system (charge injection charging system), and each characteristic appears depending on which one is dominant.

[0008]

By the way, in an image forming apparatus using an AC application type contact charging device,
When an image is formed, the photosensitive member or the charging member as the member to be charged is in the initial state of durability (new), and when the photosensitive member or the charging member is new.
In the state after about 00 sheets of image formation,
An alternating current value or an alternating voltage value required for uniform charging differs.

This is because the charging member and the photoreceptor are slightly lowered in resistance due to discharge and minute stains while the image formation is repeated, that is, as the image formation is repeated, so that the endurance initial state is obtained. This is because the amount of current required for uniform charging is reduced.

For this reason, if the charging condition, that is, the AC current or the AC voltage is determined according to the initial state of the photosensitive member and the charging member, an excessive AC current or an excessive AC current is obtained when about 100 sheets of image are formed. An alternating voltage will be applied.

When an excessive current or voltage is applied to the member to be charged, the surface of the photosensitive member is abraded and the life of the photosensitive member is shortened.

Conversely, if the charging conditions, that is, the AC current or the AC voltage, are determined according to the state after the formation of about 100 sheets of images, the charging uniformity is poor during about 100 sheets at the beginning of the endurance. A good image could not be obtained. In particular, in the case of an intermediate length such as a halftone, adverse effects due to charging non-uniformity were remarkable.

An object of the present invention is to provide an image forming apparatus using a contact-type charging device of an AC application type, regardless of the usage state (durability state) of a member to be charged and a charging member.
An object of the present invention is to always output a good image and to apply a proper alternating current or an alternating voltage according to a use condition, thereby reducing the shaving amount of the member to be charged and achieving a longer life.

[0014]

SUMMARY OF THE INVENTION The present invention is an image forming apparatus having the following configuration.

(1) An image forming apparatus for performing image formation by applying an image forming process including a step of charging a surface of a member to be charged with the surface of the member to be charged. A contact-type charging device for charging a surface of a member to be charged by bringing a charging member applied with a DC electric field superimposed on the electric field into contact with the member to be charged, wherein the member to be charged and means for detecting replacement of the charging member are provided. An image forming apparatus comprising: means for changing an alternating electric field applied to the charging member during predetermined image formation in accordance with replacement of the member to be charged and the charging member.

(2) The image forming apparatus according to (1), wherein the alternating electric field applied to the charging member is increased during a predetermined image formation in response to the exchange of the charged member and the charging member. apparatus.

(3) The means for detecting replacement of the charged member and the charging member is a power supply of the image forming apparatus or a signal for turning on / off a door switch. Image forming apparatus. (4) The image forming apparatus according to (1), wherein the means for detecting replacement of the charged object and the charged member is an input signal from a user or a serviceman.

(5) An image forming apparatus for forming an image by applying an image forming process including a step of charging the surface of the member to be charged, wherein the means for charging the member to be charged is an alternating device. A contact-type charging device that charges a charging target surface by bringing a charging member applied with a DC electric field superimposed on an electric field into contact with the charging target, and includes a unit that detects a thickness of the charging target,
An image forming apparatus comprising: means for changing an alternating electric field according to the thickness of the member to be charged.

(6) The thickness detection means of the member to be charged detects the thickness of the member to be charged from a DC current component flowing through the member to be charged when the DC voltage is kept constant. The image forming apparatus according to (5).

(7) The thickness detection means of the member to be charged detects the thickness of the member to be charged from a DC voltage component flowing through the member to be charged when the DC current is constant. The image forming apparatus according to (5).

(8) The thickness detecting means of the charged body detects the thickness of the charged body from an alternating current component flowing through the charged body when the alternating voltage is kept constant. The image forming apparatus according to (5).

(9) The charged body thickness detecting means detects the thickness of the charged body from an alternating voltage component flowing through the charged body when the alternating current is constant. The image forming apparatus according to (5).

(10) The image forming apparatus according to any one of (1) to (9), wherein the charging member is a conductive charging member having at least a high resistance layer on a surface layer.

<Operation> With the above structure, the member to be charged,
Regardless of the use condition of the charging member, always applying an optimal alternating current or alternating voltage to always output a good image, reduce shaving on the surface of the member to be charged, and achieve a longer life. Can be.

[0025]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiment 1 (FIGS. 1 to 4) (1) Schematic Configuration of Example of Image Forming Apparatus FIG. 1 is a schematic configuration diagram of an image forming apparatus of the present embodiment. The image forming apparatus of this embodiment is a laser beam printer using a transfer type electrophotographic process, a contact charging type, and a reversal developing type.

[Photoconductor] 1 is a rotating drum type electrophotographic photoconductor (hereinafter abbreviated as photoconductor) as a member to be charged (image carrier).

The photoreceptor 1 of this embodiment comprises a conductive drum base 1b of aluminum or the like and a photosensitive layer (photoconductive layer) 1a formed on the outer peripheral surface thereof, having a diameter of 30 mm and a length of 350 m.
m, a negatively charged OPC photosensitive member (negative photosensitive member), which is rotationally driven at a process speed (peripheral speed) of 100 mm / sec by a clock method a shown by an arrow. or,
The photosensitive layer 1a used had an initial thickness of 30 μm.

[Charging] 2 is a charging roller as a contact charging member (primary charging device). The charging roller 2 is a roller having a composite layer structure of a central metal core 2a, an elastic conductive layer 2b formed concentrically on the outer periphery thereof in a roller shape, and a resistance layer 2c further formed on the outer peripheral surface thereof.

The elastic conductive layer 2b is made of, for example, 10 ⁴ Ωcm
It is a single layer or a composite layer of the following conductive rubber (such as EPDM).

The resistance layer 2c is a single layer or a composite layer of hydrin rubber or resin (trade name, nylon resin, carbon dispersion) having a thickness of about 10 ⁷ to 10 ¹¹ Ωcm and about 100 μm or less. The resistance layer 2c serves to prevent leakage to the photoconductor, prevent bleeding of the plasticizer in the elastic conductive layer 2b, and the like.

The charging roller 2 has both ends of a cored bar 2a rotatably supported by a bearing member (not shown), and is arranged in parallel with the drum type photosensitive member 1 and is attached to the photosensitive member 1 by pressing means (not shown). In this case, the photosensitive drum 1 is rotated in a counterclockwise direction by the rotation of the photosensitive member 1.
It rotates following. The pressure nip n between the photoreceptor 1 and the charging roller 2 is a charging portion (charging area).

Reference numeral 3 denotes a charging bias application power supply (power supply for a charging member). When a predetermined bias voltage is applied from the power supply 3 to the metal core 2a of the charging roller 2, the outer peripheral surface of the rotary photosensitive member 1 is contact-charged. In such a manner, charging is uniformly performed to a predetermined polarity and potential.

The present embodiment is an AC application method in which a bias voltage (AC + DC) obtained by superimposing a DC voltage on an AC voltage is applied to the charging roller 2.

The AC current component is set so that the photosensitive member 1 and the charging roller 2 can secure uniform charging in an initial state. In this embodiment, in order to uniformly charge the surface of the photoconductor 1, a DC voltage component: a constant voltage of −750 V, an AC current component: a constant current control of 1200 μA is applied to the charging roller 2, -730 V was obtained as the surface potential (charge potential, dark potential).

[Exposure] Exposure 4 of the target image information is performed on the charged surface of the rotating photoreceptor 1 by the exposure means 5 to form an electrostatic latent image of the image information.
The exposing unit 5 is a laser beam scanning exposing unit, a slit exposing unit for document images, and the like. In this embodiment, it is a laser beam scanning exposure unit.

[Current Image] Next, the developing device 6 applies a developer to the electrostatic latent image forming surface of the rotating photoreceptor 1 to develop the electrostatic latent image as a toner image. In the case of the present embodiment, the negative latent toner (negative toner) adheres to the exposed light portion of the electrostatic latent image, so that the electrostatic latent image is reversely developed.

The developing device 6 in this embodiment is a device of a jumping developing system using one-component magnetic toner. 6
a is a non-magnetic developing sleeve, and 0.3 mm
, And are driven to rotate in the counterclockwise direction of the arrow c. 6b is the developing sleeve 6a
This is a non-rotating magnet roller inserted and arranged.

With the rotation of the developing sleeve 6a, a toner (not shown) contained in the developing device is applied as a thin layer on the outer peripheral surface thereof, and is held by the magnetic force of the magnet roller 6b, so that the photosensitive member 1 and the developing sleeve 6a Is transported to the developing site 6c, which is a portion facing the above. In this embodiment, a superimposed voltage of DC component: -500 V AC component: frequency 1800 Hz, V _PP 1400 V is applied to the developing sleeve 6 a from the developing bias applying power source 8 (power source for developing member).

As a result, the toner flies at the developing site 6c, and the electrostatic latent image on the surface of the rotating photosensitive member 1 is subjected to jumping development.

[Transfer] 7 is a transfer roller as transfer means. The transfer roller 7 includes a central core 7a and a medium-resistance elastic layer 7b formed concentrically and integrally with the outer periphery of the core 7a. The transfer roller 7 in this embodiment is
The conductive rubber roller has a resistance of 5 × 10 ⁸ Ω and a diameter of 16 m.

The transfer roller 7 has both ends of the metal core 2a rotatably supported by bearing members (not shown).
The photosensitive member 1 is arranged in parallel with the drum-type photosensitive member 1 and is pressed against the photosensitive member 1 with a predetermined pressing force by a pressing means (not shown). It is driven and rotated clockwise d. The pressure contact nip 7c between the photoconductor 1 and the transfer roller 7 is a transfer portion.

The transfer material P is supplied from a paper supply unit (not shown).
At a predetermined timing, the photosensitive drum 1 is fed to a transfer portion 7c which is a pressure nip portion between the photosensitive member 1 and the transfer roller 7. That is, when the leading end of the toner image formed on the surface of the rotary photoreceptor 1 reaches the transfer portion 7c, the transfer material P is transferred to the transfer portion 7c at the timing when the leading end of the transfer material P also reaches the transfer portion 7c. Is sent to

The surface of the transfer material P fed to the transfer portion 7c is brought into close contact with the rotary photoreceptor 1 and is conveyed while nipping the transfer portion. Further, during a period from when the leading end of the transfer material P reaches the transfer portion 7c to when the rear end of the transfer material P exits the transfer portion 7c, the transfer bias applying power source 10 is applied to the metal core 7a of the transfer roller 7.
A predetermined direct current bias having a polarity opposite to that of the toner is applied from a (transfer member power supply) as a transfer bias. In this embodiment, a DC voltage of +3500 V was applied.

In the process in which the transfer material P is nipped and conveyed by the transfer portion 7c, the toner image on the rotary photosensitive member 1 is transferred to the transfer material P by the action of the transfer electric field formed by the transfer roller 7 and the transfer portion. The image is sequentially transferred by the pressing force at 7c.

The transfer material P, which has passed through the transfer portion 7c and has been separated from the surface of the rotary photoreceptor 1, is conveyed to a fixing device (not shown) to fix the toner image, and then discharged outside the apparatus main body. Or, for example, if an image is also formed on the back surface, the sheet is conveyed to the re-conveying unit to the transfer site.

[Cleaning] After the transfer material is separated, the surface of the rotating photoreceptor 1 is removed to remove residual contaminants such as toner (transfer residual toner) and paper dust remaining on the photoreceptor 1 without being transferred to the transfer material P. The surface is cleaned by the cleaning blade 9a of the cleaning device 9, and the entire surface is exposed (pre-exposed) by the static eliminator (static elimination lamp) 11, and is initialized by erasing the electrical memory, and is repeatedly used for image formation. Is done.

In this embodiment, the charging roller 2 and the transfer roller 7 are driven and rotated by the photosensitive member 1. However, a gear or the like may be attached, and the driving may be forcibly driven by a driving means such as a motor.

(2) Control of Charging Bias When an image is formed using the image forming apparatus having the above-described configuration, as shown in FIG. It can be seen that 1a is being scraped.

At this time, the charging roller 2 as a contact charging member
The AC current component of the charging bias is 1200 μA. The thickness of the photosensitive layer 1a in this embodiment is initially 30 μm.
m, the remaining thickness of the photosensitive layer 1a became about 10 μm at the time of 50,000 sheets on the side of A4. When the thickness of the photosensitive layer is less than 10 μm, the photoreceptor in this embodiment cannot be charged, and a good image cannot be formed.

FIG. 3 shows the relationship between the number of formed images and the alternating current value required to ensure uniform charging. From this, it can be seen that the required amount of alternating current is reduced to 960 μA after the number of image formation exceeds 100.

FIG. 4 shows the relationship between the number of formed images and the shaved amount of the photosensitive layer when the AC current component is 960 μA. I understand.

When the photosensitive member 1 and the charging member 2 are replaced, it is necessary to turn off / on the power supply of the image forming apparatus or the door switch.

Therefore, in this embodiment, more specifically, after the power supply of the image forming apparatus main body or the door switch is turned on in response to the power supply or the door switch off / on signal, 150 sheets of image formation are performed. During this period, an AC current value of 1200 μA was applied to the charging roller 2 serving as a charging member, and thereafter, 960 μA of an AC current was applied to form an image. A good image could be provided.

In FIG. 1, reference numeral 100 denotes a main control circuit (CPU) of the image forming apparatus, which performs necessary sequence control of the image forming apparatus. The control of the charging bias applied to the charging roller 2 is also performed. That is, the main control circuit 100
Based on the ON signal S after the power switch or the door switch is turned on, the driver 101 is operated via the driver 101 so that 1200 μA as an AC current value is applied to the charging roller 2 during 150 sheets of image formation. To control the charging bias application power supply 3 and thereafter to control so that an AC current of 960 μA is applied.

<Embodiment 2> In this embodiment, in the image forming apparatus of the embodiment 1, an appropriate attachment / detachment detecting means A (not shown) such as a micro switch for detecting attachment / detachment of the photosensitive member 1 and the charging member 2 is used. After the detachment detection unit A detects the detachment of the photoreceptor 1 and the charging member 2 by the main control circuit 100, the AC current value of the charging roller 2 is changed to 1200 μA during the formation of 150 images. , The charging bias application power supply 3 was controlled via the driver 101, and thereafter, the control was performed such that an AC current of 960 μA was applied.

When an image was formed under the above control,
The uniformity of charging could be secured up to over 70,000 sheets, and a good image could be provided.

In the first embodiment, if the power supply of the image forming apparatus main body is turned off / on before the image formation of 150 sheets has been completed, the uniformity of charging is obtained when the photosensitive member 1 is over 50,000 sheets as in the conventional example. Although it could not be secured, in the present embodiment, it was possible to stably provide a good image for a long period regardless of the power-off / on interval.

<Embodiment 3> This embodiment is directed to the image forming apparatus of Embodiment 1 in which the photosensitive member 1 and the charging member 2 are provided.
Immediately after the replacement, an installation mode (such as an ON operation of a dedicated switch) for inputting an installation signal to the main control circuit 100 by a user or a serviceman is provided. Is input through the driver 101 to control the charging bias application power supply 3 through the driver 101 so that 1200 μA is applied to the charging roller 2 as an AC current value during the image formation of 150 sheets. Thereafter, the AC current of 960 μA is applied. It was controlled to be applied.

When an image was formed under the above control,
As in Example 2, the charging uniformity could be secured up to more than 70,000 sheets, and a good image could be provided.

In the second embodiment, when the photosensitive member and the charging member 2 are detached during use, the alternating current value is increased from the time of the next image formation until the image formation of 150 sheets is completed again. However, in the present embodiment, it is possible to more reliably apply the alternating current value according to the usage state of the photoconductor 1 and the charging member 2.

<Embodiment 4> (FIGS. 5 and 6) In the present embodiment, a means 102 for detecting the thickness of the photosensitive layer 1a of the photosensitive member 1 is provided as shown in FIG. did.

That is, as shown in FIG. 6, the thickness of the photosensitive layer 1a and the DC current component flowing into the photosensitive member 1 include an AC current value applied to the charging member 2 of a predetermined value or more.
If it is more than μA, there is a one-to-one relationship. At this time, the surface potential of the photoconductor 1 is -730V.

In order to detect this DC current component, a parallel circuit comprising a resistor 103 having a resistance value of 10 kΩ and a capacitor 104 having a capacitance of 1000 pF is inserted in series between the charging member 2 and the power supply 3 for the charging device. By calculating the DC current component from the voltage generated at both ends of 103,
This was used as the thickness detecting means 102 of the photosensitive layer 1a. Reference numeral 105 denotes a voltmeter that detects a voltage generated at both ends of the resistor 103. The detected voltage information of the voltmeter 105 is input to the main control circuit 100 to calculate a DC current component.

The control system 100 including the detecting means 102
1010, the AC current value of the charging bias for the charging member 2 is set to 960 μA, and the photosensitive member 1 is charged to a predetermined potential, -730 V in the present embodiment, during the pre-multiple rotation of the image forming apparatus when the power is turned on. The direct current component at the time of processing is detected. If the detected current is 22 μA or less, one
During the image formation of 50 sheets, the AC current component applied to the charging member 2 is set to 1200 μA, the rest is set to 960 μA, and when the detected current is 22 μA or more, the AC current applied to the charging member 2 from the first sheet after the power is turned on. The components were set to 960 μA to perform image formation.

When an image was formed under the above control,
As in the case of Examples 2 and 3, charging uniformity could be ensured up to 70,000 sheets, and a good image could be provided.

In the present embodiment, the life of the photosensitive member 1 can be more reliably prolonged than in the first embodiment, the configuration is inexpensive as compared with the second embodiment, and the user and the service are provided as in the third embodiment. The life of the photoconductor 1 can be extended without putting a burden on the man.

The above-described detection of the thickness of the photosensitive layer 1a is not limited to the multi-rotation before the image forming apparatus is turned on when the power is turned on. Was.

Further, in this embodiment, the thickness of the photosensitive layer 1a is detected by the value of the DC current at the time of the constant DC voltage, but the present invention is not limited to this. Either AC voltage or AC current value at AC constant voltage,
Alternatively, two or more can be used in combination.

In the structure of the present invention, 150
Although the alternating current is increased between sheets, the present invention is not limited to this, and is determined by the material and configuration of the charging member 1 and the photoconductor 2 and the configuration of the image forming apparatus such as the process speed. Things.

Further, it goes without saying that the configurations of the respective embodiments may be used independently or in combination of two or more.

In the above description, “at the time of multi-rotation before” of the image forming apparatus is a start-up (start-up) operation period (warming period) of the image forming apparatus. This is a step of driving the main motor of the apparatus by turning on the apparatus power to rotate the photoreceptor 1 to execute a preparation operation of required process equipment. After the previous multi-rotation process has been completed, the main motor is temporarily stopped to stop the rotation of the photoconductor, and the apparatus stands by until an image formation start signal is input.
Enter the state.

In the "pre-rotation period", when an image formation start signal is input to the image forming apparatus in the standby state, the main motor is driven again to rotate the photosensitive member 1 again, and the image forming apparatus is operated for a while. This is a step of executing a predetermined pre-image forming operation. When the predetermined pre-rotation process is completed, the apparatus subsequently proceeds to an image formation execution process.

<Others> 1) The image forming apparatus according to the embodiment is an apparatus for an electrophotographic process using an electrophotographic photosensitive member as a member to be charged, but is not limited thereto. For example, an apparatus such as an electrostatic recording process using an image forming apparatus may be used. in this case,
After uniformly charging the dielectric surface to the predetermined polarity and potential,
A static elimination means such as a static elimination needle head and an electron gun selectively erases electricity to write and form an electrostatic latent image corresponding to target image information.

The member to be charged is not limited to the drum type, but may be a belt type,
Any type such as a web type and a sheet type is available.

2) The contact charging member is not limited to the roller type.
Any form and structure can be used. As the waveform of the AC component, a sine wave, a rectangular wave, a triangular wave, or the like can be used as appropriate. It may be a rectangular wave formed by periodically turning on / off the DC power supply.

3) In contact charging in which charging by discharge is dominant, the charging member does not necessarily have to be in contact with the member to be charged, and the charging member and the member to be charged are interposed therebetween by the voltage between the gap and the correction Paschen curve. Charging is performed (proximity charging) if there is a small gap (gap) that satisfies the determined dischargeable condition and faces in a non-contact manner. In the present invention, such a proximity charging mode is also included in the category of contact charging.

4) The developing device 6 employs a developing principle other than the embodiment.
It may be of the type. A reversal development system or a regular development system may be used.

5) The transfer device may be blade transfer, corona discharge transfer, or the like. An image forming apparatus that forms not only a single-color image but also a multi-color or full-color image by multiple transfer or the like using an intermediate transfer body such as a transfer drum or a transfer belt may be used.

6) A toner image corresponding to the required image information is formed on the member 1 to be charged, the toner image forming section is positioned in the reading / displaying section, and the image is displayed. An image display device in which an image is transferred to a transfer material and output as a hard copy, or the toner image is removed from the surface of the charged object without being transferred to the transfer material, and the charged object is repeatedly used for forming a display image. (Image display device). The image forming apparatus of the present invention includes such an image display device.

7) A process cartridge detachable type in which any process equipment such as the member to be charged 1, the charging member 2, the developing device 6, the cleaning device 9 and the like can be collectively attached to and detached from the image forming apparatus main body. It can be something.

[0081]

As described above, according to the present invention, A
In an image forming apparatus using a C-type contact type charging device, a good image is always output regardless of the usage state (durability state) of a member to be charged (image carrier) and a charging member.
In addition, by applying an appropriate alternating current or an alternating voltage according to a use situation, the shaved amount of the member to be charged can be reduced, and a longer life can be realized.

[Brief description of the drawings]

FIG. 1 is a schematic diagram illustrating a schematic configuration of an image forming apparatus according to a first exemplary embodiment.

FIG. 2 is a diagram showing the relationship between the number of formed images and the shaving amount of a photosensitive layer when an alternating current component is 1200 μA.

FIG. 3 is a diagram showing a relationship between the number of formed images and an alternating current value necessary for ensuring uniform charging.

FIG. 4 is a diagram showing the relationship between the number of formed images and the shaved amount of a photosensitive layer when an AC current component is 960 μA.

FIG. 5 is a block diagram of a control system in an image forming apparatus according to a fourth embodiment.

FIG. 6 is a view showing the relationship between the thickness of a photosensitive layer and a DC current value (at the time of photoconductor surface potential: -730 V).

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 charged object (image carrier, photoreceptor) 2 contact charging member (charging roller) 3 power supply for charging member (AC + DC) 5 image exposure device 6 developing device 7 transfer member (transfer roller) 8 power supply for developing member 9 cleaning device 10 Power supply for transfer member 11 Exposure device for static elimination (pre-exposure)

Claims (10)

[Claims] 1. An image forming apparatus for forming an image by applying an image forming process including a step of charging a surface of a member to be charged to a surface of the member to be charged. A contact-type charging device for charging a surface of a member to be charged by bringing a charging member applied with a DC electric field superimposed thereon into contact with the member to be charged, and having means for detecting replacement of the member to be charged and replacement of the charging member. An image forming apparatus comprising: means for changing an alternating electric field applied to the charging member during predetermined image formation in accordance with replacement of the charged member and the charging member. 2. The image forming apparatus according to claim 1, wherein an alternating electric field applied to the charging member is increased during a predetermined image formation in response to replacement of the member to be charged and the charging member. . 3. The image forming apparatus according to claim 1, wherein the means for detecting replacement of the member to be charged and the charging member is a power supply of the image forming apparatus or an on / off signal of a door switch. Image forming device. 4. The image forming apparatus according to claim 1, wherein the means for detecting replacement of the member to be charged and the charging member is an input signal from a user or a service person. 5. An image forming apparatus for performing image formation by applying an image forming process including a step of charging a surface of a member to be charged to a surface of the member to be charged, wherein the charging means for the member to be charged includes an alternating electric field. A charging member to which a charging member applied with a DC electric field superimposed thereon is brought into contact with a member to be charged to charge the surface of the member to be charged, and has a means for detecting the thickness of the member to be charged; An image forming apparatus comprising: means for changing an alternating electric field according to a thickness of a body. 6. The apparatus according to claim 1, wherein said means for detecting the thickness of the member to be charged detects the thickness of the member to be charged from a DC current component flowing through said member when the DC voltage is constant. Item 6. The image forming apparatus according to Item 5. 7. The apparatus according to claim 1, wherein said means for detecting the thickness of said member to be charged detects said thickness of said member to be charged from a DC voltage component flowing through said member when said DC current is constant. Item 6. The image forming apparatus according to Item 5. 8. The apparatus according to claim 1, wherein said means for detecting the thickness of the member to be charged detects the thickness of the member to be charged from an alternating current component flowing through said member when the alternating voltage is constant. Item 6. The image forming apparatus according to Item 5. 9. The object-to-be-charged thickness detecting means detects the thickness of the object-to-be-charged from an alternating voltage component flowing through the object-to-be-charged when an alternating current is kept constant. Item 6. The image forming apparatus according to Item 5. 10. The image forming apparatus according to claim 1, wherein the charging member is a conductive charging member having at least a high resistance layer on a surface layer.