Patent Grant
9971298
The present invention relates to an image forming apparatus using an electrophotographic system.
An image forming apparatus, such as a copying machine, a printer, and a facsimile machine, using an electrophotographic system or an electrostatic recording system is provided with a charging means for charging a photosensitive member on which an electrostatic latent image and a developer image are to be formed. In recent years, a contact DC charging system in which a conductive charging member, instead of a corona charger, is brought into direct contact with a photosensitive member to charge uniformly the surface of the photosensitive member and suppress the generation of ozone has been widely used as the charging means. As an example of this system, a DC bias is applied to a charging roller which is a charging member, uniform discharge is performed while bringing the charging roller into rotational contact with the surface of the photosensitive member, and the surface of the photosensitive member is uniformly charged.
Meanwhile, in the contact DC charging system, the charging roller is in direct contact with the photosensitive member surface. Therefore, a toner and an external additive and the like contained in the toner are likely to adhere to the surface of the charging roller when the surface of the photosensitive member cannot be completely cleaned with a cleaning member. As a result, charging is likely to be poor. Accordingly, various means for cleaning the charging member in order to prevent contamination of the surface of the contact charging member in the abovementioned configuration have been suggested. Japanese Patent Application Publication No. 2002-108069 discloses a configuration for cleaning a contact charging member with a brush.
A cleaning device including a cleaning member such as a cleaning blade has been widely used as a means for removing and collecting residual toner from an image bearing member after a transfer step. The toner collected by the cleaning device becomes waste toner, but from the viewpoints of, for instance, environmental conservation and effective use of resources, it is desirable not to generate waste toner. Further, from the viewpoint of, for instance, miniaturizing the apparatus, it is preferable that a cleaning device be not provided. Accordingly, there is a cleanerless system (Japanese Patent No. 4510493) in which the toner remaining on the image bearing member is removed from the image bearing member by “cleaning simultaneous with development”, collected and recycled.
When the contact DC charging system using the charging roller or the like is used in the cleanerless system, the contamination of the surface of the charging roller is significant. In the cleanerless system, the toner remaining on the photosensitive member (fogging, transfer residual, external additive, etc.) gets directly to the surface of the charging roller because there is no member for cleaning the photosensitive member. As a result, the toner or the like is likely to adhere to the surface of the charging roller. Therefore, image defects such as poor charging are likely to occur. In view of this problem, the configuration disclosed in Japanese Patent Application Publication No. 2002-108069 in which the contact charging member is cleaned with a brush appears to be effective.
However, where the amount of the toner remaining on the photosensitive member increases and the amount of the toner adhered to the charging member increases, the toner may stay on the cleaning member such as a brush and cause toner scattering. When a developing cartridge is present under the cleaning member, the scattered toner often adheres to the developing cartridge and causes troubles.
It is an object of the present invention to provide a technique capable of reducing various adverse effects caused by scattering of a developer from a cleaning member for cleaning a charging member.
In order to achieve the object described above, an image forming apparatus comprising:
an image bearing member;
a charging member that charges the image bearing member;
a cleaning member that contacts the charging member and cleans the charging member;
a developer bearing member that bears a developer for developing a latent image formed on the image bearing member; and
a frame that accommodates the developer, wherein
the developer bearing member is disposed below the cleaning member so as to overlap with the cleaning member when viewed in a vertical direction and includes a base body and an elastic layer that covers the base body and has a width that accommodates, in a longitudinal direction of the developer bearing member, the entire region of the cleaning member in the longitudinal direction; and
in the longitudinal direction, the cleaning member is disposed at a position where the entire region thereof in the longitudinal direction is accommodated in the width of the elastic layer,
is provided.
In order to achieve the object above, an image forming apparatus comprising:
an image bearing member;
a charging member that charges the image bearing member;
a cleaning member that contacts the charging member and cleans the charging member;
a developer bearing member that bears a developer for developing a latent image formed on the image bearing member and is disposed below the cleaning member so as to overlap with the cleaning member when viewed in a vertical direction;
a frame that accommodates the developer; and
a shielding member which is a sheet-shaped member having magnetic properties and which is disposed in an opposing space between the cleaning member and the developer bearing member so as to have a region overlapping with the cleaning member and the developer bearing member when viewed in the vertical direction,
is provided.
Further features of the present invention will become apparent from the following description of exemplary embodiments (with reference to the attached drawings).
Hereinafter, a description will be given, with reference to the drawings, of embodiments of the present invention. However, the sizes, materials, shapes, their relative arrangements, or the like of constituents described in the embodiments may be appropriately changed according to the configurations, various conditions, or the like of apparatuses to which the invention is applied. Therefore, the sizes, materials, shapes, their relative arrangements, or the like of the constituents described in the embodiments do not intend to limit the scope of the invention to the following embodiments.
<Charging>
In the present example, the photosensitive drum as the image bearing member is a negative-polarity OPC photosensitive member having a diameter (ϕ) of 24 mm. In the present example, a contact DC charging system is used, and a charging roller 12 serving as a charging member is brought into contact with the photosensitive drum 11 with a predetermined pressure to form a charging nip c. The applied DC voltage is set to such a value that the potential difference between the surface of the photosensitive drum 11 and the charging roller 12 is equal to or higher than the discharge starting voltage, specifically, a DC voltage of −1200 V is applied as a charging bias. At this time, the surface of the photosensitive drum 11 is uniformly charged by contact charging to a charging potential (dark potential) Vd=−650 V.
<Exposure>
A laser beam scanner 3 including a laser diode, a polygon mirror, and the like is provided in the main body as an exposure unit serving as a means for forming an electrostatic latent image on the charged image bearing member. The laser beam scanner 3 outputs an intensity-modulated laser beam correspondingly to a time-series electric digital pixel signal of target image information, and the uniformly charged surface of the rotating photosensitive drum 11 is scanned and exposed by the laser beam L. The laser power is adjusted so that the potential Vl becomes −100 V when the uniformly charged surface of the photosensitive drum 11 is entirely exposed with the laser beam.
<Development>
The developing device 2 as the developing means having the developing member supplies a developer to the electrostatic latent image formed on the photosensitive drum. In this example, a negative-charging magnetic toner is used as the magnetic developer. The development can be performed with a developing sleeve as the developing member, to which a developing bias (Vdc) −300 V is applied from a developing bias power source (not shown in the figure) serving as a voltage applying means for applying a voltage to the developing member.
<Transfer>
A transfer roller 4 of medium resistance which serves as a contact transfer means is used as a transfer means for transferring the developer image visualized by the developing means to the transfer medium. The transfer roller is brought into pressure contact with the photosensitive drum 11 in a predetermined manner to form a transfer nip b. In the transfer roller 4 used in this example a medium resistance foamed layer 4b is formed on a core metal 4a. The transfer roller has a roller resistance value of 5×108Ω, and transfer is performed by applying a voltage of +2.0 kV to the core metal 4a.
<Fixing>
A fixing device 5 of a thermal fixing type is used as a fixing means. A recording material P which has passed through the transfer portion and to which the toner image has been transferred is separated from the surface of the rotating photosensitive drum 11 and introduced into this fixing device 5. The recording material is then heated and pressurized at a fixing nip e and discharged outside the apparatus as an image formed product (print copy).
<Cleanerless System>
Next, the cleanerless system of this example will be described in detail. In the present example, the untransferred developer remaining on the image bearing member after the transfer by the transfer means is collected by the developing means simultaneously with the development. Thus, the developer remaining on the image bearing member after the transfer of the developer image to the recording material is moved through the developer bearing member to a frame containing the developer and collected. In other words, the so-called cleanerless system is used in which a cleaning member for removing the untransferred toner which has not been transferred and remains on the photosensitive drum 11 from the photosensitive drum 11 is not provided.
The untransferred toner remaining on the photosensitive drum 11 after the transfer step is charged negatively in the same manner as the photosensitive drum 11 by an electric discharge in the space before the contact region (charging nip c) of the charging roller 12 and the photosensitive drum 11. The untransferred toner charged negatively passes by the charging roller 12 without adhering thereto due to the relationship of the potential difference (the surface potential of the photosensitive drum=−650 V, the charging roller potential=−1200 V) at the charging nip.
The untransferred toner that has passed through the charging nip c reaches a laser irradiation position. Since the amount of the untransferred toner is not so large as to shield the laser beam of the exposure means, the untransferred toner does not affect the step of forming the electrostatic latent image on the photosensitive drum. The toner that has passed through the laser irradiation position d and the toner on the non-exposed portion (the surface of the photosensitive drum not subjected to laser irradiation), in the contact region (developing nip a) between the developing sleeve 21 and the photosensitive drum 11, are collected by an electrostatic force to the developing sleeve 21 (developing potential −300 V). The toner on the exposed portion (the surface of the photosensitive drum subjected to laser irradiation) continues to be present on the photosensitive drum 11, as it is, without being collected by the electrostatic force. However, part of the toner may be collected by a physical force caused by the difference in peripheral speed between the developing sleeve 21 and the photosensitive drum 11. At this time, since the potential applied to the developing sleeve 21 is −300 V, the potential difference (Vback) with the photosensitive drum surface potential of −650 V is 350 V.
As described above, the toner which has not been transferred to the paper and remains on the photosensitive drum 11 is largely collected by the developing device 2. The toner collected by the developing device 2 is mixed with the toner remaining in the developing chamber 27 and reused.
<Developing Device>
Next, the configuration of the developing device 2 will be described in detail. The developing sleeve 21 serving as a developer bearing member is rotatably supported by the developing device 2 and is rotationally driven with respect to the photosensitive member at a peripheral speed of 140%. A magnet roller 22 serving as a magnetic force generating member is fixedly arranged on the inside (inner side) of a cylinder of the developing sleeve 21.
The magnetic one-component black developer (negative charging characteristic) T serving as a magnetic developer in the developing device is stirred by a stirring member 28 inside the developing device and conveyed to the vicinity of the developing sleeve 21. The conveyed developer T is supplied to the surface of the developing sleeve by the magnetic force of a magnet roller. The developer supplied to the surface of the developing sleeve is uniformly thinned by passing by the developing blade 23 and triboelectrically charged to a negative polarity. The developer is then conveyed to the developing position where it contacts the photosensitive drum 11 to develop the electrostatic latent image.
The toner sealing portion 24 is made of felt, has a width of 4 mm, a thickness of 5 mm, and an Asker C hardness of 45°, and is attached to the developing device 2 with a double sided tape. Measurement of Asker C hardness is carried out under the condition of a load of 100 g by bringing a pushing needle of an Asker C type hardness meter (manufactured by Kobunshi Keiki Co., Ltd.) against the surface of the toner sealing portion 24. When the developing sleeve 21 is set at a predetermined position and a seal pressing member 35 is inserted from the side opposite to the developing blade 23, as shown in
<Charging Device>
Next, the configuration of the charging device 1 will be described in detail. The photosensitive drum 11 serving as an image bearing member is rotationally driven in the clockwise direction indicated by an arrow at a constant peripheral speed of 100 mm/sec (=process speed PS, printing speed). The charging roller 12 is configured of a core metal part 12a having a diameter (ϕ) of 6 mm and a rubber layer having a thickness of 2 mm. In this example, a charging roller gear is provided on the core metal 2a of the charging roller 12, and the charging roller gear is engaged with the drum gear provided at the end portion of the photosensitive drum 11. Therefore, as the photosensitive drum 11 is rotationally driven, the charging roller 12 is also rotationally driven. The peripheral speed of the surface of the charging roller 12 is set to be 115% or 120% of the peripheral speed of the surface of the photosensitive drum 11. There is a charging power source as a voltage applying means for applying a charging bias to the charging roller 12, and in this example, a DC voltage is applied from the charging power source to the core metal 2a. Since a cleanerless system is used in this example, contamination of the charging roller 12 by the toner or an external additive contained in the toner causes a problem. Accordingly, in the present example, a configuration is used in which the charging roller contamination is suppressed by a brush member 8 as the cleaning member.
The relationship between the charging roller 12 and the brush member 8 and the effect thereof will be described hereinbelow in detail with reference to
With the above configuration, the toner attached to the surface of the charging roller 12 is negatively polarized by rubbing against the brush bristles 8c of the brush member 8. As a result, the toner is separated from the charging roller by the charging bias (−1200 V) and collected by the developing device 2 through the photosensitive drum 11 simultaneously with the development.
The features of this example will be described hereinbelow. In the present example, in order to suppress image defects which are due to toner scattering from the brush member, the longitudinal width of the brush member is set to be within the longitudinal width of the conductive elastic rubber layer of the developing sleeve in the image forming apparatus.
When the amount of the toner remaining on the photosensitive member increases due to an increase in the transfer residue caused by toner degradation in long-term use or an increase in fogging toner caused by a high-temperature and high-humidity environment, it becomes difficult to charge negatively the entire toner adhered to the charging roller at the time of contact with the brush member 8. As a result, part of the toner in contact with the brush member 8 may stay in the brush bristles 8c of the brush member 8. The toner staying in the brush bristles 8c spreads in the longitudinal direction of the brush member 8 and stays in the entire brush. As a result, when the bristles of the brush cannot retain the toner remaining thereon, the toner falls down and scatters. Where the developing configuration is below the brush member 8, as in the present example, the scattered toner sometimes adheres to the aluminum base tube 21a of the developing sleeve 21. Since the aluminum base tube 21a is peripherally supported by the bearings 25 provided at the developing frame, when the toner adheres to the aluminum base tube, the adhered toner is rubbed against the bearings and may be fixedly attached to the aluminum base tube. As a result, image defects occur due to an abnormal rise in rotational torque or uneven rotation of the developing sleeve.
In order to solve the abovementioned problem, the entire longitudinal region of the brush member 8 is arranged to be accommodated in the entire longitudinal region of the conductive elastic rubber layer 21c of the developing sleeve 21.
In Example 2, the image forming apparatus of Example 1 is used and a spacer member for keeping a predetermined distance between the sleeve 21 and the photosensitive drum 11 is provided at both ends of the developing sleeve (both sides of the conductive elastic rubber layer 21c). This spacer member is widely used in electrophotographic printers in order to keep the developing nip c constant. Where the toner adheres to the spacer member, the distance between the photosensitive drum and the developing sleeve does not become constant in the circumferential direction. Therefore, the developing nip c changes. As a result, an image defect called step unevenness in which the density varies with a developing sleeve period may occur.
Example 3 of the present invention will be described hereinbelow using the above-described image forming apparatus shown in
In the cleanerless system, since there is no member for cleaning the photosensitive member, all the toner which has not been transferred to the paper and remains on the photosensitive drum 11 reaches the charging roller 12. Most of the toner is negatively charged by rubbing against the charging roller 12 and collected by the developing sleeve 21, without adhering to the charging roller 12, but part of the toner cannot be provided with negative polarity by rubbing against the charging roller 12 and adheres to the charging roller 12. The toner which has adhered to the charging roller 12 is thereafter charged negatively by rubbing against the brush member 8 in a nip f (
However, when the amount of the toner remaining on the photosensitive member increases due to an increase in the transfer residue caused by toner degradation due to approach to the limit of endurance (long-term use) or an increase in fogging toner caused by a high-temperature and high-humidity environment, it becomes difficult to charge negatively the entire toner adhered to the charging roller at the time of contact with the brush member 8. As a result, part of the toner may stay in the brush bristles 8c of the brush member 8. The toner staying in the brush bristles 8c spreads in the longitudinal direction of the brush member 8 and stays in the entire brush. As a result, when the bristles of the brush cannot retain the toner remaining thereon, the toner falls down and scatters. Where the developing configuration is below the brush member 8, as in the present example, the scattered toner sometimes adheres to the developing sleeve 21. In particular, when the toner adheres to the longitudinal position B (see
In order to solve the above problem, as shown in
In the configuration of Example 4, in addition to the shielding member of the image forming apparatus of Example 3, another shielding member is also provided on the developing device side, such that two shielding members are arranged.
In Example 3, a toner scattering shielding member is provided on the charging device side, as shown in
As a result of disposing two shielding members as described above, the opportunity to shield with the toner scattering shielding member 15 increases even when the toner scattered from the brush member 8 cannot be shielded by the toner scattering shielding member 14. Therefore, toner scattering to the toner sealing member 24 can be further reduced.
<Effects of the Examples>
As described above, according to the present examples, it is possible to reduce the influence on image formation produced by toner scattering from the brush member in the configuration in which the charging member is cleaned with a cleaning member such as a brush member.
Features of the abovementioned examples can be combined with each other as much as possible. For example, a configuration may be used in which the shielding member is disposed in the opposing space between the cleaning member and the developing sleeve, while arranging the members so that the entire region of the cleaning member in the longitudinal direction is accommodated in the longitudinal width of the elastic layer of the developing sleeve.
While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions.
This application claims the benefit of Japanese Patent Application No. 2016-144613, filed Jul. 22, 2016 which is hereby incorporated by reference herein in its entirety.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2016-144613 | Jul 2016 | JP | national |
| Number | Name | Date | Kind |
|---|---|---|---|
| 5987277 | Okabe | Nov 1999 | A |
| 6215967 | Takeda | Apr 2001 | B1 |
| 7251441 | Hagiwara et al. | Jul 2007 | B2 |
| 9086670 | Matsuda | Jul 2015 | B2 |
| 9317008 | Handa | Apr 2016 | B2 |
| Number | Date | Country |
|---|---|---|
| 2002-108069 | Apr 2002 | JP |
| 4510493 | Jul 2010 | JP |
| Number | Date | Country | |
|---|---|---|---|
| 20180024495 A1 | Jan 2018 | US |
