JP2007286508A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent charging failure by reducing, for a long time, failure in cleaning a charging roll. <P>SOLUTION: On the charging roll 13 for charging a photoreceptor drum 12, a cleaning member 50 is disposed in contact with the charging roll 13. A pressure varying device 60 is disposed on the back of the cleaning member 50 in order to partially increase the pressure of the cleaning member 50 on the charging roll 13. The pressure varying device 60 is provided with a pressing member 62 that presses the back of the cleaning member 50. A ball screw 42 is screwed with a thread in the hole 62A of the pressing member 62. When a gear 68 is rotated by the motor 70, the ball screw 64 rotates through a gear 66, and consequently the pressing member 62 moves in a longitudinal direction. This makes it possible to partially increase the pressure of the cleaning member 50 on the charging roll 13. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus such as a copying machine or a printer that employs an electrophotographic method, and in particular, an image forming apparatus including a cleaning member that cleans the surface of a charging roll that charges the surface of an image carrier such as a photoconductor. It is about.

  Conventionally, as a charging device for an image forming apparatus such as a copying machine or a printer adopting an electrophotographic method, a device using a corona discharge phenomenon such as a scorotron charger has been widely used, but a charging device using a corona discharge phenomenon is used. In this case, the generation of ozone and nitrogen oxides that have a negative effect on the human body and the global environment is a problem. In contrast, the contact charging method in which a conductive charging roll or the like is in direct contact with the photosensitive member to charge the photosensitive member generates less ozone and nitrogen oxides and has good power efficiency. It has become mainstream.

  In such a contact charging system, a cleaning device using a foaming material or a brush for cleaning while contacting the surface of the charging roll is provided. In such a cleaning device, a cleaning member such as a foam material or a brush is applied to the charging roll uniformly in the longitudinal direction. However, in reality, there is a tolerance of mounting dimensions such as the height of the cleaning member or mounting backlash. In addition, the charging roll often has a crown shape, and it is difficult to apply a pressing force at the time of cleaning uniformly in the longitudinal direction. As a result, defective cleaning often occurs partially, and there is a problem that charging failure occurs and image quality is deteriorated.

  Further, in order to make the pressing pressure of the cleaning member uniform, a large force is required, and the mechanism becomes large and the cost increases.

  On the other hand, an apparatus has been proposed in which a cleaning member that cleans only a part of a charging roll is configured to be movable, and the charging roll is cleaned by moving the cleaning member (for example, Patent Document 1 and Patent Document 2). See). However, in this apparatus, since the cleaning member partially cleans the charging roll, it takes a long time for cleaning. Generally, since charging unevenness occurs unless charging is performed after the cleaning is completed, it is necessary to wait for the end of the cleaning. Yes, the downtime of the image forming apparatus increases. In addition, the mechanism for moving the cleaning member becomes large, and the cleaning member tends to accumulate dirt, so the life is short and the reliability is poor.

Further, a configuration has been proposed in which the cleaning force is increased only at the end portion side of the cleaning member by making the thickness of both ends of the cleaning member thicker than the central portion (see, for example, Patent Document 3). However, the contamination of the charging roll may vary depending on the image density and the image forming position, so it is not sufficient to increase the cleaning force only on the end side of the cleaning member.
JP-A-8-248740 JP-A-9-101659 JP-A-9-101661

  The present invention has been made in view of the above problems, and an object of the present invention is to provide an image forming apparatus capable of reducing charging roller cleaning failure over a long period of time and suppressing image quality deterioration due to occurrence of charging failure.

  In order to solve the above-described problems, an image forming apparatus according to the first aspect of the present invention includes an image carrier that is rotationally driven, and rotates in contact with the surface of the image carrier. A charging roll to be charged, a cleaning member that contacts the surface of the charging roll and cleans the surface of the charging roll, a pressure urging means that presses the cleaning member against the charging roll, and a rear side of the cleaning member The cleaning member has a pressure variable means for applying a force for partially pressing the surface of the charging roll and for varying the pressing force in the longitudinal direction.

  According to the first aspect of the invention, the surface of the image carrier is charged by the charging roll that rotates in contact with the surface of the image carrier. Further, the cleaning member is pressed against the charging roll by the pressure urging means, and the surface of the charging roll is cleaned by the cleaning member. At the time of this cleaning, the pressure variable means applies a force that the cleaning member partially presses against the surface of the charging roll from the back side of the cleaning member, and also changes the pressing force in the longitudinal direction. By partially varying the cleaning pressure by the cleaning member, a large force is not required as compared with the case where the entire cleaning member is pressed against the surface of the charging roll for cleaning. In addition, a pressure necessary for cleaning can be applied to a portion where the amount of dirt attached to the charging roll is large. For this reason, the charging roll can be reliably cleaned.

  According to a second aspect of the present invention, in the image forming apparatus according to the first aspect, the pressure varying unit includes a pressing member that presses a part of the back side of the cleaning member, and the pressing member is charged with the charging member. And a moving means for moving in the longitudinal direction of the roll, wherein the force that the cleaning member presses against the surface of the charging roll is increased by the moving position of the pressing member.

  According to the second aspect of the present invention, the pressing member that presses a part on the back side of the cleaning member is provided, and the pressing member is moved in the longitudinal direction of the charging roll by the moving means. Accordingly, a cleaning pressure can be partially applied in the longitudinal direction of the charging roll, and a large force is not required as compared with the case where the entire cleaning member is pressed against the surface of the charging roll for cleaning. Further, the pressure required for cleaning can be applied to the portion where the amount of dirt attached to the charging roll is large, and the charging roll can be reliably cleaned. Moreover, since the pressing member is moved in the longitudinal direction, the configuration is simple, space saving is possible, and the cost can be reduced. In addition, by adjusting the cleaning pressure at the moving position of the pressing member, mechanical attachment crossing can be eliminated, and the reliability of the cleaning ability can be maintained over a long period.

  According to a third aspect of the present invention, in the image forming apparatus according to the second aspect, the speed at which the pressing member moves in the longitudinal direction of the charging roll is variable.

  According to the third aspect of the invention, since the speed at which the pressing member moves in the longitudinal direction of the charging roll is varied, the pressing member is moved slowly at a portion where the amount of dirt on the charging roll is large, and the cleaning pressure is set. It becomes possible to enlarge. For this reason, it is possible to concentrate on the portion where the amount of dirt attached to the charging roll is large and apply a large pressure necessary for cleaning, and it becomes possible to clean the charging roll reliably.

  According to a fourth aspect of the present invention, in the image forming apparatus according to any one of the first to third aspects, the pressure varying unit is configured such that the cleaning member is partially pressed against the surface of the charging roll. It is characterized in that the force to be changed is variable according to the process conditions.

  According to the fourth aspect of the present invention, the pressure varying means varies the force with which the cleaning member is partially pressed against the surface of the charging roll according to the process conditions. The pressure required for cleaning can be applied by concentrating on a large amount. For this reason, the charging roll can be reliably cleaned.

  According to a fifth aspect of the present invention, in the image forming apparatus according to the fourth aspect, the process condition is any one of an image density, an image forming position, a recording medium size, the number of continuous prints, a temperature and humidity, or a process speed. It is characterized by being one.

  According to the fifth aspect of the present invention, the cleaning member is a surface of the charging roll according to any one of the image density, the image forming position, the size of the recording medium, the number of continuous prints, the temperature and humidity, or the process speed. The force that is partially pressed against is varied. As a result, it is possible to concentrate on a portion where the amount of dirt attached to the charging roll is large and to apply a pressure necessary for cleaning, and it is possible to clean the charging roll reliably.

  According to a sixth aspect of the present invention, in the image forming apparatus according to any one of the first to fifth aspects, the force with which the cleaning member is pressed against the surface of the charging roll is the end of the charging roll. The part side is stronger than the center part.

  According to the sixth aspect of the present invention, the force with which the cleaning member is pressed against the surface of the charging roll has a higher cleaning ability on the end side of the charging roll because the end side of the charging roll is stronger than the center. In general, the end of the charging roll has more cloud and more fine toner, so dirt is accelerated. However, the cleaning ability of the end of the charging roll is large, so the charging roll can be reliably cleaned. It becomes possible.

  According to the present invention, since the pressure necessary for cleaning is sufficiently applied to the portion where the amount of dirt attached to the charging roll is large, the charging roll can be reliably cleaned. For this reason, generation | occurrence | production of a charging defect can be suppressed and an image of favorable image quality can be obtained. In addition, since a large force is not required by partially applying the pressure necessary for cleaning, the configuration can be simplified, the space can be saved, and the cost can be reduced.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 shows an image forming apparatus 100 according to the first embodiment of the present invention.

  The image forming apparatus 100 performs image processing based on color image information sent from an image data input device such as a personal computer (not shown), and forms a color image on a recording sheet P by an electrophotographic method.

  The image forming apparatus 100 includes image forming units 10Y, 10M, 10C, and 10K that form toner images of respective colors of yellow (Y), magenta (M), cyan (C), and black (K). In the following, when it is necessary to distinguish YMCK, description will be made by adding any of Y, M, C, and K after the reference. When YMCK does not need to be distinguished, Y, M, C, K is omitted.

  The image forming units 10Y, 10M, 10C, and 10K are arranged so that the image forming units 10Y, 10M, 10C, and 10K move in the traveling direction of the endless intermediate transfer belt 30 that is stretched by the backup roll 34 and the plurality of stretch rolls 32. They are arranged in series in the order of 10K. Further, the intermediate transfer belt 30 is provided with primary transfer rolls 16Y, which are arranged to face the photosensitive drums 12Y, 12M, 12C, and 12K as image carriers of the image forming units 10Y, 10M, 10C, and 10K, respectively. It is inserted between 16M, 16C and 16K.

  Next, the configuration of each of the image forming units 10Y, 10M, 10C, and 10K and the image forming operation will be described using the image forming unit 10Y that forms a yellow toner image as a representative.

  The surface of the photosensitive drum 12Y is uniformly charged by the charging roll 13Y. Next, image exposure corresponding to the yellow image is performed by the exposure device 14Y, and an electrostatic latent image corresponding to the yellow image is formed on the surface of the photosensitive drum 12Y.

  The electrostatic latent image corresponding to the yellow image is developed by the toner carried on the developing roll 18Y to which the developing bias of the developing device 15Y is applied, and becomes a yellow toner image. The yellow toner image is primarily transferred onto the intermediate transfer belt 30 by the pressing force of the primary transfer roll 16Y and the electrostatic attraction force by the transfer bias applied to the primary transfer roll 16Y.

  In this primary transfer, the entire yellow toner image is not transferred to the intermediate transfer belt 30, and a part of the yellow toner image remains on the photosensitive drum 12Y as transfer residual yellow toner. Further, an external additive of toner is also attached to the surface of the photosensitive drum 12Y. After the primary transfer, the photosensitive drum 12Y passes through a position facing the cleaning device 20Y, and transfer residual toner and the like on the surface of the photosensitive drum 12Y are removed. Thereafter, the surface of the photosensitive drum 12Y is charged again by the charging roll 13Y for the next image forming cycle.

  As shown in FIG. 1, in the image forming apparatus 100, the image forming process similar to the above is performed at each image forming unit 10Y at a timing in consideration of the relative position difference between the image forming units 10Y, 10M, 10C, and 10K. , 10M, 10C, and 10K, and Y, M, C, and K color toner images are sequentially superimposed on the intermediate transfer belt 30 to form a multiple toner image.

  Then, the multiple toner images are batched from the intermediate transfer belt 30 by the electrostatic attraction force of the secondary transfer roll 36 to which the transfer bias is applied to the recording paper P conveyed to the secondary transfer position A at a predetermined timing. Then, it is transferred onto the recording paper P.

  The recording paper P to which the multiple toner images have been transferred is separated from the intermediate transfer belt 30, and then conveyed to the fixing device 31, where it is fixed to the recording paper P by heat and pressure, thereby forming a full color image.

The transfer residual toner on the intermediate transfer belt 30 that has not been transferred to the recording paper P is collected by the intermediate transfer belt cleaner 33.
As shown in FIGS. 2 and 3, a charging roll 13 that is in contact with the photosensitive drum 12 is disposed above the photosensitive drum 12. This charging roll 13 has a charging layer 13B formed around a conductive shaft 13A. A motor (not shown) is connected to the support shaft of the photosensitive drum 12, and the photosensitive drum 12 is driven to rotate counterclockwise (in the direction of arrow 2) in FIG. Further, the charging roll 13 rotates in the direction of the arrow 4 following the rotation of the photosensitive drum 12.
A cleaning member 50 that comes into contact with the surface of the charging roll 13 is provided above the charging roll 13. The cleaning member 50 is a rectangular sponge member that contacts the full width of the charging roll 13 in the longitudinal direction. The cleaning member 50 is charged at a predetermined pressure by a pressure biasing means such as a coil spring (not shown) provided at both ends of the cleaning member 50. It is pressed against the roll 13. On the back side of the cleaning member 50, a pressure variable device 60 that partially increases the pressure contact force of the cleaning member 50 to the charging roll 13 is disposed.
As shown in FIG. 2, the pressure variable device 60 is provided with a pressing member 62 that presses a part of the cleaning member 50 in the longitudinal direction. A ball screw 64 is disposed in parallel with the cleaning member 50, and a screw portion that is screwed with the ball screw 64 is provided inside an opening 62 </ b> A formed in the pressing member 62. A gear 66 is connected to the end of the ball screw 64, and the gear 66 is engaged with a gear 68 connected to a rotation shaft 70 </ b> A of the motor 70. The driving of the motor 70 is controlled by the control unit 72. For example, a stepping motor is used as the motor 70. By driving the motor 70, the gear 66 is rotated via the gear 68, and the ball screw 64 is rotated. The pressing member 62 is configured to reciprocate in the direction of the arrow 73 by the rotation of the ball screw 64.
The cleaning member 50 is made of a foam having a porous three-dimensional structure, has cavities and irregularities (hereinafter referred to as cells) inside and on the surface, and has elasticity. This cleaning member 50 is selected from materials made of foaming resin or rubber such as polyurethane, polyethylene, polyamide, olefin, melamine or polypropylene, NBR, EPDM, natural rubber and styrene butadiene rubber, chloroprene, silicone, nitrile, etc. Is done. Thereby, the cleaning member 50 having a large number of cells can be manufactured at low cost. The cleaning member 50 efficiently cleans foreign substances such as external additives by driven sliding rubbing with the photosensitive drum 12, and at the same time, the surface of the photosensitive drum 12 is not scratched by rubbing of the cleaning member 50. In order to prevent tearing and breakage over a long period of time, polyurethane that is strong in tearing and tensile strength is particularly preferably used.

  It is not particularly limited as polyurethane, but polyol such as polyester polyol, polyether polyester and acrylic polyol, 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, 4,4-diphenylmethane diisocyanate, tolidine diisocyanate, It only needs to be accompanied by a reaction of an isocyanate such as 1,6-hexamethylene diisocyanate, and a chain extender such as 1,4-butanediol or trimethylolpropane is preferably mixed. In general, foaming is performed using a foaming agent such as water, azodicarbonamide, azo compounds such as azobisisobutyronitrile. Further, auxiliary agents such as foaming aids, foam stabilizers, catalysts, etc. may be added as necessary.

  Next, details of the charging roll 13 will be described.

  This charging roll 13 is formed by sequentially forming a conductive elastic layer and a surface layer as a charging layer 13B on a conductive shaft 13A.

  The diameter of the charging roll 13 is from 7 mm to 15 mm, more preferably from 8 mm to 14 mm, and the thickness of the charging layer 13B is preferably from 2 mm to 4 mm. If the diameter is 15 mm or more, the number of times of contact with the external additive per location on the peripheral surface is reduced, and the number of discharges is reduced. This is disadvantageous from the viewpoint of miniaturization, although it has excellent long-term stability against dirt and charging performance. . If the diameter is 7 mm or less, the image forming apparatus 100 can be downsized, which is advantageous. However, the number of times of contact with the external additive per peripheral surface increases and the number of discharges increases, which is disadvantageous for long-term stability. It becomes.

  The charging roll 13 is not limited to the following configuration as long as it has a predetermined charging performance.

  As the material of the shaft 13A, free-cutting steel, stainless steel or the like is used, and the material and surface treatment method are appropriately selected according to the use such as slidability, and the material having no conductivity is generally plated. It may be processed by an appropriate process and a conductive process may be performed.

  The conductive elastic layer constituting the charging layer 13B of the charging roll 13 may be, for example, an elastic material such as rubber having elasticity, a conductive material such as carbon black or ionic conductive material for adjusting the resistance of the conductive elastic layer, or the like. Accordingly, materials that can be usually added to rubber, such as softeners, plasticizers, curing agents, vulcanizing agents, vulcanization accelerators, anti-aging agents, and fillers such as silica and calcium carbonate, may be added. It is formed by coating the peripheral surface of the conductive shaft 13 </ b> A with a mixture in which materials normally added to rubber are added. As a conductive agent for the purpose of adjusting the resistance value, a material in which a material that conducts electricity using electrons and / or ions as a charge carrier, such as carbon black or an ionic conductive agent blended in a matrix material, is used. it can. The elastic material may be a foam.

  The elastic material constituting the conductive elastic layer is formed, for example, by dispersing a conductive agent in a rubber material. Rubber materials include isoprene rubber, chloroprene rubber, epichlorohydrin rubber, butyl rubber, urethane rubber, silicone rubber, fluorine rubber, styrene-butadiene rubber, butadiene rubber, nitrile rubber, ethylene propylene rubber, epichlorohydrin-ethylene oxide copolymer rubber, epichlorohydrin-ethylene oxide. -Allyl glycidyl ether copolymer rubber, ethylene-propylene-diene terpolymer rubber (EPDM), acrylonitrile-butadiene copolymer rubber, natural rubber and the like, and blended rubbers thereof. Among these, silicone rubber, ethylene propylene rubber, epichlorohydrin-ethylene oxide copolymer rubber, epichlorohydrin-ethylene oxide-allyl glycidyl ether copolymer rubber, acrylonitrile-butadiene copolymer rubber, and blended rubbers thereof are preferably used. These rubber materials may be foamed or non-foamed.

  As the conductive agent, an electronic conductive agent or an ionic conductive agent is used. Examples of electronic conductive agents include carbon blacks such as ketjen black and acetylene black; pyrolytic carbon, graphite; various conductive metals or alloys such as aluminum, copper, nickel, and stainless steel; tin oxide, indium oxide, titanium oxide Examples thereof include fine powders such as various conductive metal oxides such as tin oxide-antimony oxide solid solution and tin oxide-indium oxide solid solution; Examples of ionic conductive agents include perchlorates and chlorates such as tetraethylammonium and lauryltrimethylammonium; alkali metals such as lithium and magnesium; perchlorates and chlorates of alkaline earth metals Can be mentioned.

  The surface layer constituting the charging layer 13B is formed to prevent contamination due to foreign matters such as toner, and the surface layer material may be any of resin, rubber, etc. It is not limited. Polyester, polyimide, copolymer nylon, silicone resin, acrylic resin, polyvinyl butyral, ethylene tetrafluoroethylene copolymer, melamine resin, fluoro rubber, epoxy resin, polycarbonate, polyvinyl alcohol, cellulose, polyvinylidene chloride, polyvinyl chloride, polyethylene And ethylene vinyl acetate copolymer. Of these, polyvinylidene fluoride, a tetrafluoroethylene copolymer, polyester, polyimide, and copolymer nylon are preferably used from the viewpoint of contamination of the external additive.

  The surface layer can contain a conductive material to adjust the resistance value. The conductive material preferably has a particle size of 3 μm or less. In addition, as a conductive agent for the purpose of adjusting the resistance value, it electrically conducts electrons and / or ions as charge carriers, such as carbon black, conductive metal oxide particles, or ionic conductive agent blended in the matrix material. What disperse | distributed material etc. can be used.

In addition, a fluorine-based or silicone-based resin is used for the surface layer. In particular, it is preferably composed of a fluorine-modified acrylate polymer. Further, fine particles may be added to the surface layer. As a result, the surface layer becomes hydrophobic and acts to prevent the adhesion of foreign matter to the charging roll 13. Further, insulating particles such as alumina and silica are added to give unevenness to the surface of the charging roll 13, thereby reducing the burden at the time of rubbing against the photosensitive drum 12 and charging roll 13 and the photosensitive drum. It is also possible to improve the mutual wear resistance.
In the image forming apparatus 100 having the above configuration, when the motor 70 is driven by the control unit 72, the gear 66 is rotated via the gear 68, and the ball screw 64 is rotated. As the ball screw 64 rotates, the pressing member 62 reciprocates in the direction of the arrow 73. By moving the pressing member 62 in the longitudinal direction of the cleaning member 50, the pressing force of the cleaning member 50 against the charging roll 13 is partially increased. For this reason, a large cleaning pressure can be applied depending on the position of the pressing member 62, and the cleaning ability of the cleaning member 50 can be increased. Accordingly, a large force for pressing the entire cleaning member 50 against the charging roll 13 is not required. Further, the pressure required for cleaning can be applied to the portion where the amount of dirt attached to the charging roll 13 is large, and the charging roll can be reliably cleaned. In addition, since the pressing member 62 is moved in the longitudinal direction, the configuration is simple, space saving is possible, and cost can be reduced. In addition, since the cleaning pressure is adjusted according to the moving position of the pressing member 62, the mechanical attachment crossing can be eliminated and the reliability of the cleaning ability can be improved, and the life of the cleaning member 50 can be extended.
Here, using the image forming apparatus 100 of the present embodiment, an experiment was performed to measure the cleaning efficiency and the pressing force for achieving the cleaning efficiency of 100%. Further, as a comparative example, a similar experiment was performed using an apparatus (an example in which only the cleaning member 50 is used) in which the cleaning member is pressed against the entire length of the charging roll with a constant pressure.
The cleaning efficiency is an area ratio in which the entire area of the charging roll 13 is cleaned. The area ratio is determined by measuring the amount of dirt before and after the charging roll 13 (amount with respect to the area) after the cleaning member 50 is pressed and driven for a certain period of time by attaching a certain amount of dirt to the charging roll 13. It is calculated.
As shown in FIG. 4, in the image forming apparatus 100 of the present embodiment, the cleaning efficiency is 100%, and the pressing force to make the cleaning efficiency 100% is about 0.000588 N / mm ² (6 gf / cm ² ). Met. On the other hand, in the apparatus of the comparative example, the cleaning efficiency was 60%, and the pressing force to make the cleaning efficiency 100% was about 0.0049 N / mm ² (50 gf / cm ² ). Therefore, in the image forming apparatus 100 according to the present embodiment, the cleaning efficiency of the charging roll 13 is improved, and the cleaning pressure is partially increased by the pressing member 62, so that a large pressing force is not required for the entire cleaning member 50. .

  In the image forming apparatus 100, the speed at which the pressing member 50 moves in the longitudinal direction of the charging roll 13 may be varied by changing the rotation speed of the motor 70. For example, the pressing force of the cleaning member 50 can be partially increased by moving the pressing member 50 slowly. As a result, it is possible to concentrate on the portion where the amount of dirt attached to the charging roll 13 is large and apply a large pressure necessary for cleaning, and the charging roll 13 can be reliably cleaned.

  In addition, the pressing member 62 may be moved to a predetermined position in accordance with the process conditions of the image forming apparatus 100 by the control unit 72 to increase the pressure contact force of the cleaning member 50 to the charging roll 13. Examples of the process conditions include one or more of image density, image forming position, size of recording paper P, number of continuous prints, temperature and humidity, and process speed.

  Specifically, the pressing member 62 is moved to a portion where the image density is high, and the pressure contact force of the cleaning member 50 is made larger than that where the image density is low. Further, the pressing member 62 is moved to the image forming position of the photosensitive drum 12 so that the pressing force of the cleaning member 50 is made larger than the position where no image is formed. Further, the pressing member 62 is moved to the paper passing portion based on the paper size detected by a sensor (not shown), and the pressure contact force of the cleaning member 50 is made larger than that of the non-paper passing portion. Further, the pressing member 62 is moved in the longitudinal direction when the number of continuous prints counted by a counter (not shown) is large, and the pressure contact force of the cleaning member 50 is increased as compared with when the number of continuous prints is small. Further, based on the temperature / humidity detected by a temperature / humidity sensor (not shown), the pressing member 62 is moved in the longitudinal direction when the temperature and humidity are high, and the pressing force of the cleaning member 50 is made larger than when the temperature and humidity is low. Further, when the process speed is high, the pressing member 62 is moved in the longitudinal direction, and the pressure contact force of the cleaning member 50 is made larger than when the process speed is low. By performing the control as described above, the pressing member 62 can be moved to a portion where the amount of dirt on the charging roll 13 is likely to increase, and the pressure contact force of the cleaning member 50 can be intensively increased. Thereby, the surface of the charging roll 13 can be reliably cleaned.

  Next, an image forming apparatus according to a second embodiment of the present invention will be described.

  In addition, the same code | symbol is attached | subjected to the member same as 1st Embodiment, and the overlapping description is abbreviate | omitted.

As shown in FIG. 5, in this image forming apparatus, a charging roll 113 is disposed on the lower side of the photosensitive drum 112, and an exposure device 114 and a developing device 115 are arranged along the rotation direction of the photosensitive drum 112. In addition, a primary transfer roll 116 disposed with the intermediate transfer belt 130 interposed therebetween, and a cleaning device 120 are disposed.
As shown in FIGS. 5 and 6, a cleaning member 150 that contacts the surface of the charging roll 113 is provided below the charging roll 113. The cleaning member 150 is a rectangular sponge member that contacts the full width of the charging roll 13 in the longitudinal direction, and is pressed against the charging roll 113 with a predetermined pressure. A pressure variable device 160 that partially increases the pressure contact force of the cleaning member 150 to the charging roll 113 is disposed on the back side of the cleaning member 150.
The pressure variable device 160 is provided with a pressing roll 152 that presses a part of the cleaning member 50 in the longitudinal direction. The pressing roll 152 is supported by a substantially U-shaped support member 154 so as to be rotatable about a support shaft 153. A protrusion 155 is formed in the lower part of the support member 154, and a ball screw 156 is screwed into a screw part formed in the opening 155A of the protrusion 155. A pair of rails 164 that hold the support member 154 so as not to rotate are provided on both sides of the lower portion of the support member 154 so that the support member 154 can move along the rail 164.
Further, as shown in FIG. 6, a gear 158 is connected to the end of the ball screw 156. The gear 158 is meshed with a gear 164 connected to the rotation shaft 162 </ b> A of the motor 162.
As shown in FIG. 7, the pressing roll 152 has flanges 152 </ b> A at both edges. As shown in FIG. 5, the pressing roll 152 is disposed so that both sides of the cleaning member 50 are accommodated inside the flange 152 </ b> A, and comes off the cleaning member 50 when the pressing roll 152 moves while rotating. It is prevented.
In such an image forming apparatus, when the motor 162 is driven, the gear 158 is rotated via the gear 164 and the ball screw 156 is rotated. The rotation of the ball screw 156 causes the pressing roll 152 to reciprocate in the direction of the arrow 166 while rotating. By moving the pressing roll 152 in the longitudinal direction of the cleaning member 150, the pressing force of the cleaning member 150 to the charging roll 113 is partially increased, and the cleaning capability of the cleaning member 150 is increased. For this reason, the pressure required for cleaning can be applied to the portion where the amount of dirt attached to the charging roll 113 is large, and the charging roll 113 can be reliably cleaned. In addition, since it is not necessary to apply a large pressure contact force to the entire area of the cleaning member 150, the configuration is simple, space saving is possible, and cost can be reduced. In addition, the sliding resistance with the cleaning member 150 can be reduced by rotating the pressing roll 152. Further, since the cleaning pressure is adjusted according to the moving position of the pressing roll 152, the mechanical attachment intersection is eliminated, the reliability of the cleaning capability can be improved, and the life of the cleaning member 150 is extended.

  Further, the thickness of both ends of the cleaning member 150 is formed to be thicker than that of the central portion, and the force with which the cleaning member 150 is pressed against the surface of the charging roll 113 is made stronger at the end portion than the central portion of the charging roll 113. good. By increasing the cleaning pressure on the end side of the charging roll 113, the cleaning ability on the end side of the charging roll 113 is increased. In general, the end side of the charging roll 113 has more cloud and more fine toner, so that dirt is accelerated. For this reason, the charging roll 113 can be reliably cleaned by increasing the cleaning ability on the end side of the charging roll 113.

  In the above embodiment, the cleaning members 50 and 150 are formed of foamed resin. However, the present invention is not limited to this configuration, and may be a brush, for example. Further, the cleaning members 50 and 150 may be configured so as to be able to contact and separate from the charging roll instead of being normally contacted.

  The image forming apparatus 100 shown in FIG. 1 has a configuration in which image forming units 10Y, 10M, 10C, and 10K of yellow, magenta, cyan, and black are arranged in parallel along the moving direction of the intermediate transfer belt 30. The configuration is not limited to this. For example, the present invention can be applied to a cleaning member for a charging roll even in a configuration in which a toner image is formed on a photosensitive drum by repeating a four-cycle operation using a rotary developing device.

1 is a schematic configuration diagram illustrating an image forming apparatus according to a first embodiment of the present invention. FIG. 2 is a perspective view showing a charging roll cleaning member and a pressure variable device used in the image forming apparatus shown in FIG. 1. FIG. 2 is a configuration diagram illustrating a charging roll cleaning member and a pressure variable device used in the image forming apparatus illustrated in FIG. 1. FIG. 2 is a diagram illustrating a cleaning efficiency and a pressing force for setting the cleaning efficiency to 100% in the image forming apparatus illustrated in FIG. 1 and a comparative apparatus. FIG. 6 is a configuration diagram illustrating a charging roll cleaning member and a pressure variable device used in an image forming apparatus according to a second embodiment of the present invention. FIG. 6 is a side view showing a charging roller cleaning member and a pressure variable device used in the image forming apparatus shown in FIG. 5. It is a perspective view which shows the pressing roll used for the image forming apparatus shown in FIG.

Explanation of symbols

10Y, 10M, 10C, 10K Image forming units 12Y, 12M, 12C, 12K Photosensitive drum 13 Charging roll 13A Shaft 13B Charging layer 50 Cleaning member 60 Pressure variable device (pressure variable means)
62 Pressing member 64 Ball screw 66 Gear 68 Gear 70 Motor 72 Control unit 100 Image forming device 112 Photosensitive drum 113 Charging roll 150 Cleaning member 152 Pressing roll (pressing member)
153 Support shaft 154 Support member 154A Protruding portion 155 Rail 156 Ball screw 158 Gear 160 Pressure variable device (pressure variable means)
162 Motor 164 Gear P Recording paper

Claims (6)

A rotationally driven image carrier;
A charging roll that rotates in contact with the surface of the image carrier and charges the image carrier;
A cleaning member that contacts the surface of the charging roll and cleans the surface of the charging roll;
Pressure urging means for pressing the cleaning member against the charging roll;
Pressure varying means for applying a force that the cleaning member partially presses against the surface of the charging roll from the back side of the cleaning member and that varies the pressing force in the longitudinal direction;
An image forming apparatus comprising: The pressure variable means includes a pressing member that presses a part of the rear side of the cleaning member, and a moving means that moves the pressing member in the longitudinal direction of the charging roll,
The image forming apparatus according to claim 1, wherein the force that the cleaning member presses against the surface of the charging roll is increased according to the movement position of the pressing member.   The image forming apparatus according to claim 2, wherein a speed at which the pressing member moves in a longitudinal direction of the charging roll is variable.   4. The pressure varying unit according to claim 1, wherein the force by which the cleaning member partially presses the surface of the charging roll varies according to a process condition. 5. Image forming apparatus.   The image forming apparatus according to claim 4, wherein the process condition is any one of an image density, an image forming position, a size of a recording medium, the number of continuous prints, a temperature and humidity, or a process speed.   6. The image forming apparatus according to claim 1, wherein the force with which the cleaning member comes into pressure contact with the surface of the charging roll is stronger at the end of the charging roll than at the center. .

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