JP2003302816A - Method for cleaning contact electrification means of image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent the deterioration of image quality by cleaning an electrifying roller while controlling voltage applied to an electrification means. <P>SOLUTION: A first sequence before an image forming sequence is completed, by applying electrification bias at image formation before one revolution of a photoreceptor drum when transfer materials approach to a transfer nip and controlling to provide the image forming. In a second sequence until the transfer materials, such as paper, pass through the transfer nip and the transported and discharged to a fixing device 112, similarly to the first sequence, the voltage of -100 V is applied to an electrifying roller 102, and a fouling with positive polarity on the electrifying roller 102 is returned to a photoreceptor drum 101. In this case, a cleaning bias may be applied until just before the drive of a main motor is made a halt. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for cleaning contact charging means in an electrophotographic image forming apparatus such as a copying machine or a printer.

[0002]

2. Description of the Related Art An image forming apparatus using an electrostatic latent image technique, such as a copying machine, a laser beam printer, an electronic copying machine, a facsimile machine or the like, forms an image of a subject on a surface of a photoconductor charged in advance. A spot of laser light that blinks according to the image data scans the photoconductor to form an electrostatic latent image, and the toner image converted by development is transferred onto plain paper.
An image is formed by fixing.

In order to charge the surface of the photosensitive member, conventionally, a charging charger using corona discharge which does not contact the photosensitive member has been used. This charger is excellent in that it uniformly charges the surface of the photoconductor with a predetermined polarity and potential,
There is a problem in that ozone needs to be generated by corona discharge because it requires a potential several times higher than the charging potential of the photoconductor.

In contrast to such a charger, a contact charging device for charging a charging member by contacting it with a photosensitive member requires a low potential, so that a high-voltage power supply is simplified and corona is hardly generated. Although it is gradually being used instead of a charger, since the charging member is in direct contact with the photoconductor, it is easy to pick up contaminants such as residual toner and toner additives on the photoconductor and stain them. There is a problem that the image density is deteriorated due to uneven charging and the image quality is deteriorated.

Therefore, a voltage having a positive polarity and a negative polarity is alternately applied to the charging roller with respect to the charging potential of the photosensitive drum, and the pulse bias returns the adhered substances from the charging roller to the photosensitive drum, and again by the cleaning means. A method of collecting was proposed.

[0006]

However, in the method of applying the pulse bias for alternately switching the voltage on the positive polarity side and the voltage on the negative polarity side with respect to the charging potential of the photosensitive drum, when the bias is switched to the reverse polarity side, a predetermined voltage is applied. Since it takes time to output the voltage of
There is a problem that it is difficult to obtain the desired effect.

The present invention has been made in view of the above points. By controlling the potential applied to the charging means without using a dedicated member or the like, stable charging roller cleaning is always performed and the image quality is deteriorated. The purpose is to prevent.

[0008]

To achieve the above object, the invention according to claim 1 of the present invention is directed to an image bearing member, a contact charging means for charging the surface of the image bearing member, and the image according to image information. An exposing means for forming an electrostatic latent image on the surface of a carrier, a developing means for developing the electrostatic latent image with a developer, and a developer image visualized on the surface of the image carrier. In a method of cleaning a contact charging means in an image forming apparatus having a transfer means for transferring to a sheet and a cleaning means for collecting the residual developer on the image carrier, a voltage applied to the contact charging means during non-image formation is After applying the bias applied during image formation for at least one rotation of the image carrier, the bias applied to the contact charging unit is switched to the first level to transfer the deposits of the contact charging unit onto the image carrier. The above cleaning means The first sequence for more recovery, and the voltage applied to the contact charging means at the time of non-image formation is applied to the contact charging means after applying the applied bias at the time of image formation for at least one rotation of the image carrier. Second
A second sequence of switching to a level, transferring the deposits of the contact charging means that could not be collected in the first sequence onto the image carrier, and collecting them by the cleaning means. According to a second aspect of the present invention, there is provided a method for cleaning contact charging means in an apparatus, wherein the voltage applied to the contact charging means is a high-potential DC voltage having the same polarity as the charging polarity of the image carrier at the first level, At the second level, a DC voltage or ground voltage in the vicinity of a ground potential having the same polarity as the charge polarity of the image carrier and an absolute value lower than the charge potential of the image carrier, or a ground potential having a polarity opposite to the charge polarity of the image carrier. A method for cleaning a contact charging means in an image forming apparatus according to claim 1, wherein the DC voltage is a voltage in the vicinity of the contact charging means. 3. The cleaning method for a contact charging means in an image forming apparatus according to claim 1, wherein the voltages of the first sequence and the second sequence are alternately applied at each non-image forming time. The invention according to claim 4 is characterized in that the time for applying the voltage of the first level or the second level to the contact charging means is at least within the time required for one rotation of the contact charging means. The cleaning method for contact charging means in an image forming apparatus according to any one of items 1 to 3, and the invention according to claim 5 further applies the voltage of the first level or the second level to the contact charging means. 5. The bias applied to the transfer means is set to 0 within at least the time required for the contact charging means to make one rotation in the applied time. A method for cleaning a contact charging means in the image forming apparatus according to any misalignment.

According to the cleaning method of the present invention having the above-mentioned structure, the voltage applied to the contact charging means is switched as follows when the image forming apparatus is not in the developing / transferring state and the image is not formed. Remove the developer stains on the charging means. First, in the first sequence, when the above voltages are switched from the charging bias to the first level and the electric fields of the image carrier and the contact charging means are reversed from those during normal image formation, they are attached to the contact charging means. A developer having a polarity opposite to the charging polarity of the image carrier is transferred to the surface of the image carrier and the contact charging means is cleaned. The positively charged or negatively charged developer is mixed in the developer transferred to the image carrier, and the developer having the same polarity as the charged polarity of the image carrier is used as the developing / cleaning means. Be recovered.

Next, in the second sequence, the first
The developer having a polarity opposite to the charging polarity of the image carrier that has not been transferred to the photosensitive drum in the sequence moves according to the rotation of the image carrier and is collected by the cleaning member.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION An embodiment of the present invention will be described below with reference to the drawings.

FIG. 3 is a sectional view of an example of the image forming apparatus according to the present invention. The image forming apparatus shown in the figure is an electrophotographic copying machine or a laser beam printer, and in the following description, a reversal is performed using a photosensitive drum 101 having a negative charging characteristic and a toner having a negative charge. The case of developing will be described.

The image forming apparatus shown in FIG. 1 is provided with a plurality of removable cartridges in an image forming main body, and a drum type electrophotographic photosensitive member (hereinafter referred to as "photosensitive drum") 101 as an image bearing member. ing. Photosensitive drum 101
Is an image forming apparatus main body (not shown, hereinafter simply referred to as “apparatus main body”).
) Is rotatably supported and is driven to rotate in the direction of arrow A by drive means (not shown). Around the photosensitive drum 101, a charging roller 102 of a primary charger that uniformly charges the surface of the photosensitive drum 101 in a substantially sequential order along the rotation direction, and an electrostatic surface corresponding to image information on the surface of the photosensitive drum 101 after charging. An exposure device 103 for forming a latent image,
Developing device 104 for developing electrostatic latent image, photosensitive drum 101
Transfer roller 10 for transferring the toner image on a transfer material such as paper
A cleaning device 110 for removing the primary transfer residual toner on the photosensitive drum 101 is arranged.

Further, around the transfer material conveying belt 105, the transfer material conveying belt 105 attached by a jam or the like is provided.
In order to remove the toner on the surface, a transfer material transport belt cleaning device (not shown) is arranged so as to face the transfer material transport belt 105. Further, the photosensitive drum 101 is provided via the transfer material transport belt 105. The transfer roller 109 is arranged at a position opposed to.

Further, a brief supplementary explanation will be given to the above-mentioned members and the like.

The photosensitive drum 101 is constructed by providing an OPC (organic optical semiconductor) photosensitive layer having a negative charging polarity on the surface of a cylindrical metal core of aluminum.

The primary charger is a charging roller 102 arranged in contact with the surface of the photosensitive drum 101, and a minus D to the charging roller 102.
It has a power source for applying a C (direct current) bias and uniformly charges the surface of the photosensitive drum 101. Exposure device 1
Reference numeral 03 denotes, for example, a laser oscillator that emits laser light according to image information, a polygon mirror, and the like. To form.

The developing device 104 accommodates negative toner that is negatively charged by friction, and is attached to the portion of the surface of the photosensitive drum 101 where the charge of the electrostatic latent image has been removed. As a result, the electrostatic latent image is developed as a toner image. The cleaning device 110 includes a cleaning blade 110 a that is in contact with the surface of the photosensitive drum 101 and scrapes off the primary transfer residual toner adhering to the surface of the photosensitive drum 101.

Next, the operation of the image forming apparatus having the above structure will be described.

For example, the surface of the photosensitive drum 101 is DC voltage -1200V by the charging roller 102 of the primary charger.
Is applied and uniformly charged to -700V. Next, the exposure device 103 performs exposure according to the image information to form an electrostatic latent image. On the surface of the photosensitive drum 101 after the exposure, the dark portion potential VD of the unexposed portion becomes −700V and the light portion potential VL of the exposed portion becomes −100V. A developing bias of -400V is applied to the developing sleeve 104a of the developing device 104, whereby negatively charged negative toner does not adhere to the unexposed portion (hereinafter referred to as "VD portion") on the surface of the photosensitive drum 101, Exposed part (hereinafter "VL
Part) and is visualized (developed) as a toner image. The photosensitive drum 101 and the transfer roller 109 rotate at the same peripheral speed in the arrow A direction and the arrow B direction, respectively, and a primary transfer bias T1 is applied to the transfer roller 109 by a high voltage power source (not shown). As a result, the toner image on the photosensitive drum 101 is transferred from the surface of the photosensitive drum 101 to the transfer material such as paper conveyed from the paper feeding device 113 due to the potential difference between the photosensitive drum 101 and the transfer roller 109 in the transfer nip portion N. At this time, the transfer residual toner remaining on the surface of the photosensitive drum 101 without being primarily transferred to the transfer material is removed by the cleaning blade 110a of the cleaning device 110 and is stored in the waste toner container 111.

As described above, a toner image is formed on the transfer material through the charging, exposure, development and transfer processes. The transfer material is transported to the fixing device 112 by a transporting device (not shown), heated and pressure-fixed by the fixing device 112, and discharged as a print image.

Next, the charging roller cleaning sequence, which is a feature of the present invention, will be described.

The cleaning sequence will be described below with reference to the drawings. FIG. 1 is a diagram of a process sequence of this embodiment.

The driving of the photosensitive drum 101 is started, and a DC voltage of -1000V is applied to the charging roller 102 of the primary charger for one rotation of the photosensitive drum or more. As a result, the photosensitive drum 101 is uniformly charged to −500V. At this time, the transfer roller 1 that is arranged in contact with the photosensitive drum 101 to face it
When a positive voltage is applied to 09, the charge on the surface of the photosensitive drum flows out, and the potential becomes close to the ground potential, so the transfer roller 109 is set to the ground potential.

Further, the background fog and reverse fog are determined by the difference between the bias applied to the developing sleeve 104a and the charging potential of the photosensitive drum 101 (hereinafter referred to as back contrast). Therefore, in order to make it equal to the back contrast of 300 V at the time of image formation, with respect to the charging potential of -500 V of the photosensitive drum 101 during the cleaning sequence,
A bias of -200V may be applied to the developing sleeve 104a.

Next, a DC voltage of -800 V is applied to the charging roller 102. At this time, discharge is not performed between the transfer roller 109 and the photosensitive drum 101, and the charging roller 102
The negative polarity deposit is returned to the photosensitive drum 101.

From one rotation of the photosensitive drum before the transfer material such as paper rushes into the transfer nip, a charging bias at the time of image formation is applied and controlled so as to be used for image formation.

As described above, the first sequence performed before the image forming sequence is completed.

Next, in the second sequence until the transfer material such as paper passes through the transfer nip, is conveyed to the fixing device 112, and is discharged, in the same manner as the first sequence, the charging roller 102- A voltage of 100 V is applied to remove the positive polarity deposits on the charging roller 102 from the photosensitive drum 1.
Return to 01.

At this time, the cleaning bias may be applied until just before the drive of the main motor is turned off.

As described above, the first sequence / second sequence
The adhering substances returned to the photosensitive drum 101 by the sequence are removed by the cleaning blade 110a and are stored in the waste toner container 111.

By controlling as described above, plus / minus charge on the charging roller 102 is performed every time one sheet is printed.
Since the sequence of returning the minus-polarity adhered substances to the photosensitive drum is recovered by utilizing the non-image forming time, it is possible to collect the foreign substances before they are deposited on the charging roller, and the effect can be obtained regardless of the process speed. The effect is obtained regardless of the performance of the bias power source applied to the charging roller.

Next, the operation during continuous image formation will be described.

When printing one sheet, as described above, the first sequence is performed before printing and the second sequence is performed after printing.
Although the sequence is performed, the first sequence in which a voltage having a negative polarity with respect to the charging potential of the photosensitive drum 101 is applied has the same potential relationship as that in the normal image forming operation.

On the other hand, since the second sequence has a potential relationship that hardly exists during a normal image forming operation, it is more effective to control the second sequence so that it is actively used.

Therefore, as shown in FIG. 2, the second sequence is adopted for the pre-printing operation and the post-printing operation, and
The first sequence is performed between the second and third sheets, the second sequence is performed between the second and third sheets, and then the first sequence is performed.
By alternately using the sequence and the second sequence, a higher cleaning effect can be obtained.

After the cleaning sequence is started, the time t ₁ during which the bias applied to the transfer roller is turned off and the bias applied to the charging roller is the pre-cleaning bias is set to one rotation of the photosensitive drum or more, and then the first
Level, or the time t _a for applying a second level of cleaning _bias, t _b, t _c is desirably made to be a charging roller one turn or more.

In the embodiment described above, D
Although the C charging method is used, the present invention is not limited to this, and it can be realized also in an AC + DC charging method in which an AC component is superimposed on a DC voltage.

Further, although the case where the surface of the photoconductor is negatively charged has been described in the present embodiment, the surface of the photoconductor may be positively charged.

[0040]

As is apparent from the above description, according to the cleaning method of the invention described in each of the claims of the present application, the developer stain on the contact charging means can be removed without using a dedicated member or the like. Further, it is possible to obtain an image with good charging uniformity throughout the life without increasing the cost regardless of the performance of the bias power source applied to the charging roller.

[Brief description of drawings]

FIG. 1 is a diagram of a process sequence according to an embodiment of the present invention.

FIG. 2 is a diagram of a process sequence during continuous image formation, which is an embodiment of the present invention.

FIG. 3 is a sectional view of an example of an image forming apparatus according to an embodiment of the present invention.

[Explanation of symbols]

101 photosensitive drum 102 charging roller 103 exposure device 104 developing device 104a developing sleeve 105 Transfer material transport belt 109 transfer roller 110 cleaning device 110a cleaning blade 111 Waste toner container 112 fixing device 113 paper feeder N transfer nip

Claims (5)

[Claims] 1. An image carrier, a contact charging unit for charging the surface of the image carrier, an exposing unit for forming an electrostatic latent image on the surface of the image carrier according to image information, and the electrostatic latent image. Developing means for developing the image with a developer, transfer means for transferring the developer image visualized on the surface of the image carrier to a transfer target, and cleaning means for recovering the residual developer on the image carrier. When,
In the method for cleaning the contact charging means in the image forming apparatus having the above, the voltage applied to the contact charging means during non-image formation is
After the applied bias at the time of image formation is applied for at least one rotation of the image carrier, the applied bias to the contact charging means is switched to the first level, and the deposits of the contact charging means are transferred onto the image carrier. A first sequence for collecting by the cleaning means, and a voltage applied to the contact charging means during non-image formation,
After the applied bias at the time of image formation is applied for at least one rotation of the image carrier, the applied bias to the contact charging means is switched to the second level to remove the deposits of the contact charging means which could not be collected in the first sequence. A second sequence of transferring to the image carrier and collecting by the cleaning means, the cleaning method of the contact charging means in the image forming apparatus. 2. The voltage applied to the contact charging means is a high potential DC voltage having the same polarity as the charging polarity of the image carrier at the first level, and the same polarity as the charging polarity of the image carrier at the second level. And a DC voltage or a ground voltage in the vicinity of a ground potential whose absolute value is lower than the charging potential of the image carrier, or a DC voltage in the vicinity of a ground potential having a polarity opposite to the charging polarity of the image carrier. 2. A method of cleaning a contact charging means in the image forming apparatus described in 1. 3. The image forming apparatus according to claim 1, wherein the voltages of the first sequence and the second sequence are alternately applied to the contact charging means every non-image forming time. Method for cleaning contact charging means in. 4. The time for applying the voltage of the first level or the second level to the contact charging means is at least within a time required for one rotation of the contact charging means. 4. A method of cleaning a contact charging means in an image forming apparatus according to any one of 1 to 3. 5. The contact charging means is applied with the voltage of the first level or the second level at least within a time required for one rotation of the contact charging means,
The method for cleaning the contact charging means in the image forming apparatus according to claim 1, wherein the bias applied to the transfer means is set to 0.