JPH08166754A - Image forming device - Google Patents

Abstract

PURPOSE: To provide an image forming device capable of preventing transfer paper from being stained by impurity removed from a latent image carrier. CONSTITUTION: The latent image carrier 11 is constituted so that it is moved in a positive direction at the time of forming an image and moved in a reverse direction at the time of finishing forming the image, and an angle (α) equivalent to the rotational amount thereof in the reverse direction is 360 deg./πD<=α<θ. Provided that D: the outside diameter (mm) of the latent image carrier, and θ: the angle (deg.) around the center of the latent image carrier equivalent to the width of an aperture 16C formed on a cleaning device and having an upper edge where the tip of a cleaning blade 16A in the moving direction of the latent image carrier 11 is positioned and a lower edge 16D opposed to the upper edge and abutting on the surface of the latent image carrier 11 or approaching thereto through a gap equal to or under the size of developer used in processing for making a latent image a visible image. Thus, the impurity is prevented from coming off from the lower edge 16D of the aperture 16C and falling on a transfer paper carrying path located below.

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,
More specifically, it relates to an image forming apparatus using a contact type charging device.

[0002]

2. Description of the Related Art Generally, an electrophotographic system is known as one of image forming systems. In this system, an electrostatic latent image corresponding to an original image is formed by exposure on a photoconductor which is a latent image carrier. The electrostatic latent image, which has been subjected to a visible image processing with a developer, is transferred onto a transfer paper to obtain a copy. Such an electrophotographic system is widely used in copiers, printers, facsimiles and the like. In this electrophotographic system, a charging process for uniformly charging the photoconductor is executed before the process of exposing the original image. Conventionally,
As a charging method adopted in the charging step, there is a non-contact method using corona discharge.

This system has been required to be replaced because of the large amount of power consumed and the ozone generated by the discharge being harmful.

Therefore, in place of the non-contact charging method, in recent years, a conductive member such as a rubber roller mixed with a conductive material such as carbon is brought into contact with the photoconductor to direct voltage or a superimposed voltage of direct current and alternating current. A contact charging method of charging by applying a voltage has been proposed and implemented.

The contact charging method has advantages that power consumption can be reduced and ozone is hardly generated as compared with the non-contact charging method.

In the contact charging method, it is important for the photosensitive member and the charging roller in contact with the photosensitive member to make uniform contact in order to prevent uneven charging.

One of the causes of uneven charging is adhesion of impurities to the surface of the charging member used in the contact charging system. The impurities correspond to extraneous materials such as excess toner and paper dust remaining on the photoconductor.

Conventionally, as a method of removing such impurities from the photoconductor, there is a method of cleaning the photoconductor after image transfer using a scraping member such as a cleaning blade, and further, it is attached to the surface of the charging member. As a method for eliminating the impurities, a cleaning blade is used as in the case of the photoconductor.

However, in the method using the cleaning blade, since the same surface of the cleaning blade is always in contact with the surface of the photoconductor as an impurity blocking surface with respect to the moving direction of the photoconductor, the impurities deposited on the surface are kept. When the amount of the toner is increased, some of the impurities blocked by the cleaning blade may be rubbed by the movement of the photoconductor and come out from the impurity blocking surface of the cleaning blade.

Therefore, when the photoconductor faces the charging roller, the impurities adhere to the charging roller. This hinders the uniform contact of the charging roller with the photosensitive member, resulting in uneven charging. When uneven charging occurs, a part of the image formed on the photoconductor is lost.

In the past, in order to solve such a problem, after the image forming process is completed, the photosensitive member is moved in the direction opposite to that in the image forming process and accumulated on the damming surface of the cleaning blade. It has been proposed to eliminate the impurities present (for example, Japanese Patent Laid-Open No. 5-341624).

[0012]

However, the method described in the above publication has the following problems.

Generally, in a cleaning unit in which a cleaning blade is arranged, a part of the photoconductor is inserted into the unit to scrape impurities, and the scraped impurities leak to the outside of the unit. It is supposed not to. For this reason, the cleaning unit has an opening for allowing a part of the photoconductor to enter.

However, when the photoconductor is moved in the opposite direction, the scraped impurities may drop from the gap existing between the photoconductor and the lower edge of the opening.

For example, when the transfer paper transport path is installed below the cleaning unit, the drop-out impurities are deposited on the transport path and contaminate the transfer paper.

If the amount of movement of the photosensitive member in the opposite direction is large, the amount of movement in the opposite direction also increases because the charging member also follows the contacting member. For this reason, the cleaner on the charging member side
The number of times the impurities deposited on the Ning blade reach the contact position with the photoconductor also increases, and the amount of the impurities deposited on the contact position with the photoconductor increases. Moreover, if the movement ends when the impurities reach the contact position, the impurities solidify at the contact position, and charging and image formation cannot be performed on this portion, and a part of the image is lost. Will end up.

When the reverse rotation of the photoconductor is repeated as in the configuration described in the above publication, the reverse rotation amount may become unstable as the reverse rotation is repeated. As shown by the solid line in FIG. 5, this is because the transmission amount changes from the initial set amount due to the service life, the change over time, the increase in frictional engagement force, etc. with respect to the connection relationship between the mechanisms. This is because the details will decrease.

An object of the present invention is to transfer the image by the impurities removed from the latent image bearing member in view of the problem in removing impurities by the cleaning blade when the above-mentioned conventional image forming apparatus, particularly, the contact type charging device is used. An object of the present invention is to provide an image forming apparatus capable of preventing paper from being soiled.

Another object of the present invention is to provide an image forming apparatus which can prevent the reversal amount from changing over time.

Still another object of the present invention is to completely prevent the adhering of impurities to the charging device due to the reversal of the latent image carrier, and to eliminate the influence of impurities even if they do. To provide.

[0021]

To achieve this object, the invention according to claim 1 has a photoconductive layer on the surface,
A latent image carrier that can rotate forward and backward, a contact charging device that contacts the latent image carrier to uniformly charge the photoconductive layer, and an electrostatic latent image formed on the latent image carrier are visible. An image forming apparatus comprising: a cleaning device having a blade in contact with the surface of the latent image carrier for cleaning the latent image carrier after transferring the image-processed image, wherein the latent image carrier is Is moved in the forward direction at the time of image formation, and is moved in the reverse direction at the end of image formation, and the angle (α) corresponding to the rotation amount in the reverse direction is 360 ° / πD ≦ α <θ where D: Outer diameter of latent image carrier (mm) θ: The tip of the cleaning blade in the moving direction of the latent image carrier has an upper edge and a lower edge facing the upper edge, and is formed in the cleaning device. Angle around the center of the latent image carrier corresponding to the width of the opening It is characterized by being set to (deg.).

According to a second aspect of the invention, in the image forming apparatus according to the first aspect, the visible image carried on the latent image carrier is transferred below the opening formed in the cleaning blade device. It is characterized in that a part of the stretched portion of the transfer belt constituting the transport path of the transferred transfer paper is positioned.

According to a third aspect of the present invention, in the image forming apparatus according to the second aspect, the transfer belt is formed so that the length in the width direction corresponding to the direction perpendicular to the moving direction is larger than that of the cleaning blade. It is characterized by being.

According to a fourth aspect of the invention, in the image forming apparatus according to the first aspect, the latent image carrier has a variable reverse rotation amount.

According to a fifth aspect of the present invention, a latent image carrier having a photoconductive layer on its surface and movable in the forward and reverse directions, and a photoconductive layer which is in contact with the latent image carrier are uniformly formed. A contact charging device for charging and an electrostatic latent image formed on the latent image bearing member are transferred to the latent image bearing member after transfer of an image obtained by subjecting the latent image bearing member to a visible image processing to contact the surface of the latent image bearing member for cleaning. In the image forming apparatus having a blade that is, the contact charging device,
It is characterized in that it is provided so as to be able to come into contact with and separate from the latent image carrier.

According to a sixth aspect of the present invention, in the image forming apparatus according to the fifth aspect, the contact charging device is separated from the latent image carrier at the end of the image forming process using the latent image carrier. It has a feature.

The invention according to claim 7 is the invention according to claim 5 or 6.
The image forming apparatus described above is characterized in that a cleaning member that comes into contact with the surface of the contact charging device is disposed at a position where the contact charging device is separated from the latent image carrier.

[0028]

According to the first aspect of the present invention, the amount of reverse rotation of the latent image carrier is set to the opening width or less, so that the impurities blocked by the cleaning blade pass through the lower edge of the opening and move downward. It never falls.

According to the second and third aspects of the present invention, the impurities that have fallen from the lower edge of the opening adhere to the transfer belt,
It is removed by the cleaning blade that is in contact with the transfer belt.

According to the fourth aspect of the invention, the reverse rotation amount can be adjusted according to the change with time in the drive system of the latent image carrier.

In the inventions according to claims 5 to 7, after the image forming process by the latent image carrier, the surface of the charging device is cleaned while the charging device is separated.

[0032]

The details of the present invention will be described below with reference to the illustrated embodiments.

FIG. 1 is a schematic diagram for explaining the essential structure of a copying machine (one of the image forming apparatuses according to the embodiment of the present invention).

In the figure, the copying machine 10 is provided with a photosensitive drum 11 which is a latent image carrier.

The photosensitive drum 11 has a photoconductive layer made of an organic material such as OPC on the surface thereof, and as shown in FIG. 2, in the positive direction indicated by the reference symbol P and in the reverse direction indicated by the reference symbol N. Each can be rotated.

Around the photosensitive drum 11, a charging device 12 for performing an image forming process in the positive direction,
An exposure device 13, a developing device 14, a transfer device 15, and a cleaning device 16 are arranged respectively.

When rotating in the forward direction, the image forming process including the visible image transfer process by the transfer device 15 of the above-mentioned devices is executed, and at the time of reverse rotation, the cleaning device 16 is equipped with the cleaning device 16, which will be described in detail later. The impurities accumulated on the cleaning blade are removed.

In the figure, reference numeral 17 is a pre-transfer exposure lamp, and
Reference numeral 8 indicates a charge eliminating quenching lamp and reference numeral 19 indicates an eraser. Further, in the vicinity of the photoconductor drum 11, a registration roller 20 for feeding the transfer paper S toward a nip portion between the photoconductor drum 11 and the transfer device 15.
A sheet feeding device 21 including the above is provided.

The charging device 12 is composed of a conductive roller capable of rotating in contact with the photoconductive layer of the photosensitive drum 11, and is connected to a high voltage power source 12A to generate a DC voltage or a DC voltage and an AC voltage. A superposed voltage is applied to uniformly charge the photoconductive layer.

The charging device 12 can be brought into contact with and separated from the photoconductor drum 11 by a contacting / separating mechanism (not shown), and is a charging process and an exposure process which are image forming processes by the photoconductor drum 11. , Contacting the surface of the photoconductor drum 11 until the development process and the transfer process are completed,
After the transfer process is completed, it can be separated from the photosensitive drum 11. The separation time may be from the time when the charging process is completed to the time when the next charging process is performed.

A cleaning member 12B is arranged at a separated position of the charging device 12, and the surface of the charging device 12 rotating at this position can be cleaned.

The exposure device 13 has a plurality of mirrors and an imaging lens (not shown) that form an optical path for forming an image of the reflected light from the original on the original table (not shown) on the photoconductive layer. Therefore, an electrostatic latent image corresponding to the original image is formed on the photoconductive layer. In this embodiment, due to the intensity of the reflected light, the negative charge disappears in the photoconductive layer, and the portion where the charge remains is formed as an electrostatic latent image.

As the developing device 14, a magnetic brush developing device having a well-known structure is used, and the magnetic developer carried and conveyed by the developing sleeve 14A comes into contact with the electrostatic latent image on the conductive layer to form an electrostatic latent image. It is designed to perform visible image processing.

The pre-transfer exposure lamp 18 is used in order to lower the charging potential of the toner adhering to the electrostatic latent image so as not to lower the transfer efficiency even if there are environmental changes such as temperature and humidity.

The transfer device 15 includes a transfer belt 15A wound around a pair of rollers and a transfer bias roller 15B.
A transfer mechanism 15C for the transfer belt 15A and a cleaning blade 15D.

In the transfer device 15, the registration timing is set by the registration roller 20 and then the paper feeding device 2 is set.
The transfer sheet S fed from No. 1 is conveyed while being sandwiched by the nip portion formed between the transfer sheet S and the surface of the photoconductive layer of the photoconductor drum 11, and the bias voltage from the transfer bias roller 15B via the high-voltage power supply 15B1 is applied. Upon application, the visible image carried on the photoconductive layer is transferred to the transfer paper S.

The transfer belt 15A is separated from the photoconductive layer of the photosensitive drum 11 at the time of non-transfer, but at the time of transfer,
The contact / separation mechanism 15C is displaced toward the photoconductor drum 11 by a solenoid 15C2 whose operation is controlled by the control plate 15C1. The excess toner adhering to the transfer belt 15A and impurities such as fibers of transfer paper or paper dust are removed by a cleaning blade 15D provided in contact with the transfer belt 15A. The electrode plate denoted by reference numeral 15E is provided to stabilize the current flowing from the transfer bias roller 15B to the photosensitive member side and stabilize the transfer performance.

The transfer paper S on which the visible image on the photoconductive layer is transferred by the transfer device 15 is conveyed by the transfer belt 15A, is brought to the fixing roller 22, and is discharged to a paper discharge tray (not shown).

The cleaning device 16 includes the photosensitive drum 1
Cleaning blade 16A in contact with the photoconductive layer 1
And a conveying screw 16B for collecting the excess toner on the photoconductive layer scraped off by the cleaning blade 16A toward the developing device 14.

As shown in FIG. 2, the cleaning device 16 has an opening 16C formed at a position facing the photosensitive drum 11.

The opening 16C is opposed to the tip of the cleaning blade 16A in the rotation direction of the photosensitive drum 11 and the lower edge 1 which is in contact with the surface of the photosensitive drum 11 so as to face it.
It is configured in the range of 6D. The lower edge of the opening 16D
Is not limited to the case where the photosensitive drum 11 is brought into contact with the photosensitive drum 11 as described above. It is possible.

Transfer belt 15A in transfer device 15
Has a length in the width direction corresponding to a direction perpendicular to the moving direction thereof longer than that of the cleaning blade 16A, and as shown in FIG.
A part of the stretched portion is positioned below the opening 16C. Thus, even if there is an impurity that has fallen from the position of the opening 16C, it can be received, and the received impurity can be scraped off by the cleaning blade 15D that is in contact with itself. .

The photosensitive drum 11 is designated by the symbol P in FIG.
The reverse rotation amount in the direction indicated by is set to the following relationship.

Now, in FIG. 2, when the angle corresponding to the amount of rotation of the photosensitive drum 11 in the reverse direction is (α),
The following relationships are being established.

360 ° / πD ≦ α <θ where D: outer diameter of the photosensitive drum 11 (mm) θ: the tip of the cleaning blade in the moving direction of the latent image carrier is located at the upper edge and this upper edge It is formed in the cleaning device and has a lower edge which is opposed to the surface of the latent image carrier and is adjacent to the surface of the latent image carrier with a gap smaller than the size of the developer used for the visible image processing of the latent image. An angle (de) around the center of the latent image carrier corresponding to the width of the opening
g. ).

In this embodiment, when the outer diameter of the photosensitive drum 11 is 60 mm, the rotation amount in the reverse direction is set to 1 to 5 mm, and the angle (α) corresponding to this rotation amount is
It is set to 1.9 to 9.55 °, which is smaller than the value of the right term of the above equation. In this case, the opening width is set so that impurities do not drop from the lower edge of the opening toward the transfer belt 15A.

The reverse rotation amount (α) in the reverse direction never becomes larger than the angle (θ) corresponding to the opening width, which prevents the impurities from passing through the opening lower edge 16D. .

The photosensitive drum 11 can change the amount of reverse rotation.

The photosensitive drum 11 is driven by a stepping motor which is also used for the transfer belt 15A and various rollers, and the position and the rotation amount are controlled by the number of steps output to the stepping motor. It is supposed to be done. The photoconductor drum 11 is configured such that the driving force to the rotating shaft is transmitted through a speed reducing mechanism (not shown) connected to the stepping motor. The same amount of rotation as in the initial state may not be obtained with the number of steps in the initial condition due to an increase in sliding resistance or the like in the moving part. Therefore, in the stepping motor control unit (not shown), as shown in FIG. 3, pulse width modulation (P
The amount of rotation is adjusted by WM). As a result, in FIG. 5, the state in which the amount of rotation in the opposite direction decreases over time (the state indicated by the solid line) is prevented, as indicated by the chain double-dashed line. Such adjustment of the amount of rotation in the reverse direction is not limited to the time when a state different from a preset initial condition occurs in the control unit of the stepping motor, as well as, for example, in the copying machine 10. A switch capable of selecting the adjustment mode may be arranged in the operation unit (not shown), and the pulse width may be changed according to the number of times the switch is turned on.

The forward / reverse rotation timing of the photosensitive drum 11 is shown in FIG.
Is shown in.

In the figure, when rotating in the forward direction, a normal image forming process is executed. In this case, a pulse signal that causes the stepping motor to rotate in the forward direction is output.

The image forming process is executed by the rotation in the forward direction, and when the process is completed, the output of the pulse signal to the stepping motor is stopped, and then the pulse signal for performing the reverse rotation is output. To be done.

Since this embodiment has the above-mentioned structure,
When the image forming process is executed, the photosensitive drum 11 is rotated in the forward direction. When the image forming process is executed, an electrostatic latent image is formed on the photosensitive drum 11 by the developing device 1.
The visible image processing is performed by 4, and the visible image is transferred to the transfer sheet S fed from the sheet feeding device 22. The cleaning blade 16A of the cleaning device 16 scrapes off impurities such as excess toner and paper dust remaining on the surface of the photosensitive drum 11 that has completed the transfer process. In this case, the photosensitive drum 11 is scraped off by the cleaning blade 16A with a part of the surface of the photosensitive drum 11 being inserted into the opening 16C formed in the cleaning device 16. Since the lower edge 16D of the opening 16C is in contact with the surface of the photoconductor drum 11, the impurities scraped off are
It is prevented from falling downward and is collected in the cleaning device 16.

Assuming that the surface of the photosensitive drum 11 and the opening 16 are
There is a slight gap between the cleaning blade 15 and the lower edge of C, and the impurities dropped downward from this gap are placed on the transfer belt 15A and are in contact with the transfer belt 15A.
Scraped by D. As a result, the transfer belt 15
Even if there are impurities that have fallen on A, they are all removed from the transfer belt 15A, and therefore the backside of the transfer paper S that is conveyed next does not become dirty.

When the image forming process is completed, the charging device 12 is separated from the surface of the photosensitive drum 11 and the photosensitive drum 11 is stopped.

The surface of the charging device 12 is cleaned by a cleaning member 12B provided at a position separated from the photoconductor drum 11 to remove the attached impurities. The photoconductor drum 11 starts rotating in the opposite direction by reversing the output form of the pulse signal to the stepping motor.

The amount of reverse rotation at this time is based on the above-mentioned relational expression, and therefore, the stepping motor also receives a pulse signal corresponding to the amount of reverse rotation.

When the photosensitive drum 11 rotates in the opposite direction,
The impurities accumulated on the damming surface of the cleaning blade 16A for scraping impurities are dragged and discharged in accordance with the rotation of the photosensitive drum 11, and fall into the cleaning device 16. However, as shown in FIG. 2, when some of the impurities fall downward from the gap existing between the surface of the photoconductor drum 11 and the lower edge 16D of the opening 16C of the cleaning device 16, the transfer described above is performed. It is eliminated by cleaning on the belt 15A side.

The dropping of impurities is a phenomenon in which foreign matter accumulated on the upstream side of the lower edge 16D of the opening abutting on the photosensitive drum 11 is dropped by the impact when the photosensitive drum 11 is reversed. Even in such a case, the transfer sheet S located below the opening is completely cleaned in the conveyance path, so that the transfer sheet S is not contaminated. Moreover, the length of the transfer belt 15A in the width direction is determined by the cleaning blade 1.
Since it is longer than that of 6A, the impurities dropped from the opening lower edge 16D can be almost completely dropped onto the transfer belt 15A, so that it may drop to a position other than the transfer belt 15A and contaminate the periphery. It can be prevented.

According to the above-described embodiment, when the rotation amount of the photoconductor drum 11 in the reverse direction becomes particularly fine depending on the outer diameter of the photoconductor drum 11, the reverse rotation amount is also set. Accordingly, we have to reduce it considerably,
Although it is difficult to control the drive system, it is possible to prevent the transfer belt S from collecting stains on the transfer sheet S on the conveyance path even if the reverse rotation amount cannot be minimized by enabling the transfer belt 15A to collect the falling impurities. Will be possible.

[0071]

As described above, according to the first aspect of the present invention, the amount of the reverse rotation of the latent image carrier is set to be equal to or less than the opening width, so that the impurities blocked by the cleaning blade are removed from the lower edge of the opening. Since it does not pass through and fall downward,
It is possible to prevent impurities from falling into the transfer path of the transfer sheet located below the latent image carrier and prevent the transfer sheet from being transferred along the transfer path from being contaminated.

According to the second and third aspects of the present invention, the impurities that have fallen from the lower edge of the opening adhere to the transfer belt and are removed by the cleaning blade that is in contact with the transfer belt. It is possible to completely prevent the backside from being soiled.

According to the fourth aspect of the present invention, since the reverse rotation amount can be adjusted according to the change over time in the drive system of the latent image carrier, the reverse rotation amount can be maintained at a predetermined amount regardless of the change over time. Thus, it is possible to completely prevent the impurities scraped off by the cleaning blade from coming out downward from the lower edge of the opening of the cleaning device and dropping.

According to the fifth to seventh aspects of the invention, since the surface of the charging device is cleaned after the image forming process by the latent image carrier while the charging device is separated, uneven charging due to impurities adhering to the charging device is eliminated. It is possible to obtain an image without defects.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing a main configuration of a copying machine which is one of embodiments of the present invention.

FIG. 2 is a local layout diagram for explaining the relationship between a photoconductor drum that forms a latent image carrier and a cleaning device in the copying machine shown in FIG.

FIG. 3 is a diagram for explaining the content of drive control for a photosensitive drum that forms a latent image carrier.

FIG. 4 is a timing chart for explaining a drive control state of a photosensitive drum that forms a latent image carrier.

FIG. 5 is a diagram for explaining a state of a change over time regarding a rotation amount of a photosensitive drum that forms a latent image carrier and a means for correcting this.

[Explanation of symbols]

 10 Copier as one of image forming apparatus 11 Photoreceptor drum forming latent image carrier 12 Charging roller forming contact type charging device 12B Cleaning member 15 Transfer device 15A Transfer belt 15D Cleaning blade 16 Cleaning device 16A Cleaning blade 16C Opening 16D Opening lower edge α Rotation amount of the photoconductor drum in the reverse direction θ Opening width along the rotation direction of the photoconductor drum D External diameter of the photoconductor drum

Claims (7)

[Claims] 1. A latent image carrier having a photoconductive layer on its surface and capable of rotating in the normal and reverse directions, and a contact charging device for contacting the latent image carrier to uniformly charge the photoconductive layer. A cleaning in which a blade in contact with the surface of the latent image carrier is arranged to clean the latent image carrier after transferring an image obtained by subjecting the electrostatic latent image formed on the latent image carrier to a visible image. In the image forming apparatus including the device, the latent image carrier is moved in the forward direction at the time of image formation and is moved in the reverse direction at the end of image formation, and the angle (α) corresponding to the rotation amount in the reverse direction is set. ) Is 360 ° / πD ≦ α <θ where D: outer diameter (mm) of latent image carrier θ: the tip of the cleaning blade in the moving direction of the latent image carrier is located at the upper edge and Faces the surface of the latent image carrier facing each other or for visible image processing of the latent image. The developing device has a lower edge which is adjacent to the developer by a gap not larger than the size of the developer and is set to an angle (deg.) Around the center of the latent image carrier corresponding to the width of the opening formed in the cleaning device. An image forming apparatus characterized in that 2. The image forming apparatus according to claim 1, wherein an opening formed in the cleaning device is below the opening.
A cleaning blade that constitutes a conveyance path of the transfer paper on which the visible image carried on the latent image carrier is transferred, and is in contact with a cleaning blade that removes impurities such as excess developer and paper dust attached to itself The image forming apparatus is characterized in that a part of the extending portion of the transfer belt is located. 3. The image forming apparatus according to claim 2, wherein the transfer belt is formed so that the length in the width direction corresponding to the direction perpendicular to the moving direction is larger than that of the cleaning blade. Image forming apparatus. 4. The image forming apparatus according to claim 1, wherein the latent image carrier has a variable reverse rotation amount. 5. A latent image carrier having a photoconductive layer on its surface and movable in forward and reverse directions, and a contact charging device for contacting the latent image carrier to uniformly charge the photoconductive layer. A blade contacting the surface of the latent image carrier for cleaning the latent image carrier after transferring an image obtained by subjecting the electrostatic latent image formed on the latent image carrier to a visible image. In the image forming apparatus, the contact charging device is provided so as to be able to come into contact with and separate from the latent image carrier. 6. The image forming apparatus according to claim 5, wherein the contact charging device is separated from the latent image carrier at the end of the image forming process using the latent image carrier. . 7. The image forming apparatus according to claim 5 or 6, wherein a cleaning member that abuts on the surface of the contact charging device is arranged at a position where the contact charging device is separated from the latent image carrier. An image forming apparatus characterized by the above.