JPH11352756A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming device constituted so that the service lives of an electrifying member and a cleaning member are prolonged and excellent images can be stably obtained. SOLUTION: This image forming device is provided with a photosensitive drum (image carrier) 2 carrying the image which should be formed on a transfer paper (medium) P, a signal generation means generating an image signal showing the image, the electrifying roller (electrifying member) 3 brought into contact with the drum 2 in order to uniformly electrify the surface of the drum 2, the cleaning member 1 cleaning the roller 3, an attachment/detachment means attaching and detaching the cleaning member 1 with respect to the roller 3, an exposure device (latent image forming means) 9 forming an electrostatic latent image at the surface of the drum 2 and a developing device (developing means) 5 attaching toner to the electrostatic latent image and developing the electrostatic latent image as a toner image by the electrical impressing of bias. Then, the cleaning timing of the roller 3 by the cleaning member 1 is changed according to the image signal generated from the signal generation means.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to an image forming apparatus such as a copying machine or a laser beam printer which employs an electrophotographic system.

[0002]

2. Description of the Related Art Conventionally, as a charging device used for charging before image exposure in an image forming apparatus such as a copying machine, a charging device utilizing a discharge phenomenon such as a scorotron charger has been widely used. A contact charging system in which a charging member is brought into direct contact with a photoreceptor and a charging voltage is applied to the charging member is also used.

For example, in a configuration in which a roller made of conductive rubber is brought into contact with a photosensitive drum and is driven to rotate with the rotation of the photosensitive drum, a voltage is supplied to a metal core serving as a rubber roller shaft to uniformly apply the photosensitive drum. Charging has been done.

In such a contact charging system, the charging member is apt to be contaminated with toner or the like, and the dirt causes uneven charging. Therefore, the roller surface is rubbed by pressing a cleaning pad to rub the dirt. In some cases, a cleaning mechanism for removing the toner is added.

[0005]

If a copying machine or the like using a contact charging system is not provided with a charging member cleaning mechanism, if the copying machine or the like is used for a long period of time, charging will be hindered by contamination. Although uneven charging does not occur due to contamination by fine powder such as an external additive contained in the toner, the potential applied to the photosensitive drum decreases because the fine powder is deposited and the overall electric resistance increases.

[0006] If unevenness occurs in the method of laminating the fine powder, the unevenness causes charging unevenness of the photoreceptor, and eventually appears as image density unevenness. For this reason, a cleaning member that rubs the charging member is installed, and a mechanism for removing the adhered substance with the cleaning member is implemented. However, since the cleaning member is pressed against the charging member, the charging member is damaged by long-term use. Or, there is a possibility that poor charging occurs due to wear.

As described above, even a charging device having a cleaning mechanism may result in poor charging.

Further, the external additive contained in the toner which causes stains on the charging member usually has a property of being charged in the opposite polarity to that of the toner. Therefore, the external additive contained in the toner is More than the white background. For this reason,
If an image with a large white background ratio is continuously output, poor charging due to contamination of the charging member will occur unless the cleaning interval is shortened. However, if the cleaning interval is too short, poor charging due to scraping of the charging member will occur. Was.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and has as its object to provide an image forming apparatus capable of extending the life of a charging member and a cleaning member and stably obtaining a good image. It is in.

[0010]

According to one aspect of the present invention, there is provided an image bearing member for carrying an image to be formed on a medium, and a signal for generating an image signal representing the image. Generating means, a charging member for contacting the image carrier to uniformly charge the surface of the image carrier, a cleaning member for cleaning the charging member, and attaching and detaching the cleaning member to and from the charging member. Attaching / detaching means, latent image forming means for forming an electrostatic latent image on the surface of the image carrier, and developing means for applying toner to the electrostatic latent image by applying an electric bias and developing the toner as a toner image The cleaning timing of the charging member by the cleaning member is changed in accordance with an image signal from the signal generation unit.

According to a second aspect of the present invention, in the first aspect of the present invention, the timing of cleaning the charging member by the cleaning member is changed in accordance with the image ratio of the image signal.

According to a third aspect of the present invention, in the second aspect of the invention, the cleaning timing of the charging member by the cleaning member is managed by the number of formed images, and the image ratio of the image signal is equal to or more than a predetermined value. In some cases, it is not counted as the number of formed images.

According to a fourth aspect of the present invention, there is provided an image carrier for carrying an image to be formed on a medium, signal generating means for generating an image signal representing the image, and storing an image ratio of the image signal. A storage device for integrating, and a charging member that contacts the image carrier to uniformly charge the image carrier surface,
A cleaning member for cleaning the charging member, attaching / detaching means for attaching / detaching the cleaning member to / from the charging member, a latent image forming means for forming an electrostatic latent image on the surface of the image carrier, and applying an electric bias In the image forming apparatus having developing means for attaching toner to the electrostatic latent image and developing the toner as a toner image, the cleaning timing of the charging member by the cleaning member is changed in accordance with the storage contents of the storage device. It is characterized by the following.

According to a fifth aspect of the present invention, in the fourth aspect of the invention, the storage device stores and integrates a difference between an image ratio of the image signal and a predetermined image ratio. .

According to a sixth aspect of the present invention, in the fifth aspect of the invention, when the value of the storage device becomes equal to or more than a predetermined value, the cleaning member cleans the charging member. .

[0016]

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

<Embodiment 1> FIG. 1 is a schematic sectional view of a main part of an image forming apparatus according to the present invention. The image forming apparatus has a photosensitive drum 2 which is an image bearing member, and a member to be charged. Roller 3 serving as a charging member in contact with photosensitive drum 2
Is arranged. Then, a charging voltage is applied to the charging roller 3 from a high voltage power supply 4.

In FIG. 1, reference numeral 9 denotes an exposing device such as a laser scanner for exposing an image according to image information of a document or the like, 5 a developing device, 6 a transfer device, 7 a cleaning device, and 8 a fixing device. is there. P is a transfer sheet, which is fed from a sheet feeding device (not shown), is conveyed to a fixing device 8 through a transfer area.

Further, reference numeral 1 denotes a cleaning member for cleaning the charging roller 3, which is pressed against the charging roller 3 as shown in FIG.

When a start button (not shown) is pressed in the image forming apparatus (electrophotographic copying machine) according to the present embodiment, a main motor (not shown) rotates to rotate the photosensitive drum 2.
Is driven to rotate, and the charging roller 3 pressed by the photosensitive drum 2 is driven to rotate with respect to the photosensitive drum 2. still,
The photosensitive drum 2 includes a photosensitive layer 2a and a conductive substrate 2b of aluminum or the like, and the conductive substrate 2b is grounded. In this embodiment, the photosensitive layer 2a has a negatively charged polarity of O
It is composed of a PC.

First, in order to uniformly charge the surface of the photosensitive drum 2, a voltage is applied to the surface of the photosensitive drum 2 by the charging roller 3 to set the surface of the photosensitive drum 2 to a predetermined potential. In the present embodiment, in order to obtain a more uniform potential, after the residual charge on the photosensitive drum 2 is reset by a pre-exposure device (not shown) before charging, the voltage from the voltage power supply 4
A superimposed voltage of a DC voltage of 750 V and an AC voltage having 1800 Vpp is applied to the charging roller 3 to bring the photosensitive drum 2 to −7
It is designed to be uniformly charged to 50V.

Next, after the charged photosensitive drum 2 is image-exposed to form an electrostatic latent image on the photosensitive drum 2, the electrostatic latent image is developed by the developing device 5 to form a visible image as a toner image. Become In the present embodiment, the charging polarity of the toner is the same as the charging polarity of the photosensitive drum 2, and a reversal developing method is used as a developing method.

After the development step, the photosensitive drum 2
The toner image formed on the transfer sheet P is transferred to the transfer sheet 6 fed at an appropriate timing by the action of the transfer device 6, and the transfer sheet P on which the toner image is transferred is fixed by the conveyance belt 15 to the fixing device 8. And the toner image is fixed in the fixing device 8. The toner remaining on the photosensitive drum 2 after the transfer is removed by the cleaning device 7 and the surface of the photosensitive drum 2 is cleaned.

The cleaning member 1 used in the present embodiment has a two-layer structure including a fine fiber surface 11 and an intermediate elastic member 12, as shown in the perspective view of FIG. 1 is supported by a support 13.

In the cleaning member 1, the fine fiber surface 1
The roller 1 is rubbed in direct contact with the charging roller 3.
The fine fibers constituting the fine fiber surface 11 have a thickness of 1
mm of Exeine (trade name, manufactured by Toray Industries, Inc.), and attached to an intermediate elastic member 12 made of a sponge-like malt plane having a thickness of 2 mm to constitute the cleaning member 1. The cleaning member 1 is made of ABS. Of the support 13.

FIG. 2 shows the details of the structure of the charging roller 3 and the cleaning member 1. When the cleaning operation of the charging roller 3 is performed, the cleaning member 1 is brought into contact with the charging roller 3 by driving means 10 such as a solenoid. When the cleaning operation is not performed, the driving unit 10 separates the charging roller 3 from the charging roller 3. The cleaning member 1 may be reciprocated in the longitudinal direction of the charging roller 3 during the cleaning operation.

Next, the timing of cleaning the charging roller 3 by the cleaning member 1 will be described.

Conventionally, the charging roller has been cleaned every predetermined number of images or every number of images (for example, 400 sheets). For example, when an image having an image ratio of 7% is output, if the cleaning interval is every 400 sheets, charging failure due to contamination of the charging roller does not occur, and charging failure due to scraping of the charging roller also occurs. Does not occur within the lifetime.

However, if an image having an image ratio of 2% is continuously output, when the cleaning interval is every 400 sheets, charging failure due to contamination of the charging roller occurs before cleaning (about 300 sheets). If the cleaning interval is set to, for example, 200 sheets to prevent this, the charging failure due to the scraping of the charging roller may occur before the photosensitive drum reaches the end of its life.

Therefore, in the present embodiment, a method is adopted in which when the image ratio is equal to or more than a predetermined value, the image is not counted as the image output sheet number for determining the cleaning interval, thereby avoiding the above problem.

Specifically, a predetermined image ratio is set to 7%,
The above problem can be avoided by setting the cleaning interval to 200 sheets. That is, since the image ratio of a normal document is 7% on average, the ratio of a document having an image ratio of 7% or more is 50%. Therefore, on average, the cleaning interval is 40
It becomes zero.

On the other hand, when 7% or less of originals are continuous, the cleaning interval is 200 sheets. By doing so, even if an image having a low image ratio is produced, poor charging due to contamination of the charging roller 3 does not occur, and poor charging due to scraping of the charging roller 3 does not occur.

Second Embodiment Next, a second embodiment of the present invention will be described.

In this embodiment, the exposure apparatus 9 shown in FIG.
And a storage device for storing and integrating the difference between the image ratio of the image signal and the predetermined image ratio.

Conventionally, the charging roller has been cleaned every predetermined number of images or every number of images (for example, 400 sheets). For example, when an image with an image ratio of 7% is output, if the cleaning interval is every 400 sheets, charging failure due to contamination of the charging roller does not occur, and charging failure due to scraping of the charging roller also occurs. Does not occur within the lifetime.

However, if an image having an image ratio of 2% is continuously output, when the cleaning interval is every 400, poor charging due to contamination of the charging roller occurs before cleaning (about 300). If the cleaning interval is set to, for example, 200 sheets in order to prevent this, a charging failure occurs due to scraping of the charging roller before the photosensitive drum reaches its end of life.

Therefore, in the present embodiment, the difference between the image ratio of the image signal and the predetermined image ratio is stored and integrated by the storage device provided in the exposure device 9, and the value exceeds the predetermined value. The charging roller 3 by the cleaning member 1
The above-mentioned problem is solved by performing cleaning.

Specifically, when the image ratio of the original is 12% or more, the charging roller 3 is hardly stained and the charging roller 3 is hardly cleaned. %It was set. As the predetermined value, the predetermined image ratio (12
%) And the difference between the image ratio of 7% (in this case, 5%) was used.

In this case, since the average value of the image ratio of a normal original is 7%, the cleaning interval is 400 sheets if the original comes on average.

On the other hand, if a document having an image ratio of 2% continues, the difference from the predetermined image ratio (12%) becomes 10%, so that the cleaning interval becomes 200 sheets.

In the manner described above, even if an image having a low image ratio is produced, a charging failure by the charging roller 3 does not occur, and a charging failure due to scraping of the charging roller 3 does not occur.

[0042]

As is apparent from the above description, according to the present invention, the storage timing for cleaning the charging member by the cleaning member is stored and integrated with the image signal from the signal generating means or the image ratio of the image signal. Is changed in accordance with the stored contents of, the life of the charging member and the cleaning member can be extended, and a good image can be stably obtained.

[Brief description of the drawings]

FIG. 1 is a sectional view of a main part of an image forming apparatus according to the present invention.

FIG. 2 is a side view of a cleaning member and a charging roller portion of the image forming apparatus according to the present invention.

FIG. 3 is a perspective view of a cleaning member of the image forming apparatus according to the present invention.

[Explanation of symbols]

 Reference Signs List 1 cleaning member 2 photosensitive drum (image carrier) 3 charging roller (charging member) 5 developing device (developing device) 9 exposing device (latent image forming device) 10 driving device (detaching device) P transfer paper (medium)

Claims (6)

[Claims] 1. An image carrier for carrying an image to be formed on a medium, signal generating means for generating an image signal representing the image, and the image carrier for uniformly charging the surface of the image carrier. A charging member for contacting the carrier, a cleaning member for cleaning the charging member, attaching / detaching means for attaching / detaching the cleaning member to / from the charging member, and a latent image for forming an electrostatic latent image on the surface of the image carrier An image forming apparatus comprising: forming means; and developing means for applying toner to the electrostatic latent image by applying an electrical bias and developing the toner as a toner image, wherein the cleaning member cleans the charging member by the signal. An image forming apparatus which changes according to an image signal from a generating unit. 2. The image forming apparatus according to claim 1, wherein a timing of cleaning the charging member by the cleaning member is changed according to an image ratio of the image signal. 3. The cleaning timing of the charging member by the cleaning member is managed by the number of formed images, and is not counted as the number of formed images when the image ratio of the image signal is a predetermined value or more. The image forming apparatus according to claim 2. 4. An image carrier for carrying an image to be formed on a medium, signal generating means for generating an image signal representing the image, a storage device for storing and integrating an image ratio of the image signal, A charging member that contacts the image carrier to uniformly charge the surface of the image carrier, a cleaning member that cleans the charging member, and a detachable unit that attaches and detaches the cleaning member to and from the charging member; An image forming apparatus comprising: a latent image forming unit that forms an electrostatic latent image on the surface of the image carrier; and a developing unit that applies toner to the electrostatic latent image by applying an electrical bias and develops the toner as a toner image. 2. The image forming apparatus according to claim 1, wherein a timing of cleaning the charging member by the cleaning member is changed according to contents stored in the storage device. 5. The image forming apparatus according to claim 4, wherein the storage device stores and integrates a difference between an image ratio of the image signal and a predetermined image ratio. 6. The image forming apparatus according to claim 5, wherein the cleaning member cleans the charging member when the value of the storage device becomes equal to or more than a predetermined value.