JP5211028B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an electrophotographic image forming apparatus such as a copying machine, a laser printer, and a facsimile, and more particularly to an image forming apparatus including a charging member that charges the surface of a photosensitive drum in a contact state.

  In an image forming apparatus using an electrophotographic process, suitable means for uniformly charging the surface of the photosensitive drum include a corona charging method including a corona discharger and a conductive charging member typified by a charging roller. There is a contact charging system. Since many corona products such as ozone are generated in the corona discharger, components in the air are decomposed by ozone, and ion products such as NOx and SOx are generated. For this reason, in recent years, it has been recognized that the contact charging method is adopted instead of the corona charging method. This contact charging method can suppress generation of ozone, NOx, SOx, and the like by applying a DC voltage or a voltage obtained by superimposing an AC voltage on a DC voltage.

  Incidentally, as one of charging members used in the contact charging method, there is a charging roller formed by forming a roller body such as conductive rubber around a shaft. In order to ensure that the charging roller is in contact with the surface of the photoreceptor, a load in the direction of the photoreceptor is usually applied to both ends of the charging roller shaft. For this reason, the nip portion between the charging roller and the photosensitive member comes into close contact when driving is stopped, and a load is applied to the close contact portion during re-driving.

  The load at the time of re-driving is maximized at both ends of the nip portion near both ends of the shaft, which is the load position. Further, since the physical strength of the roller end is generally lower than that of the center portion, the end portion is damaged when a load is repeatedly applied to the end portion of the rubber roller. In particular, in a high-speed machine, the load at the time of driving is large, so that the end of the roller body frequently breaks.

  Therefore, various methods for preventing the adhesion between the photosensitive member and the charging roller while the driving of the image forming apparatus is stopped have been proposed. For example, Patent Document 1 discloses that the photosensitive member and the charging roller are not used when the apparatus is not used for a long time. There is disclosed a technique for preventing a plasticizer or the like exuded from a rubber portion of a charging roller from adhering to a photosensitive member by interposing a sheet member therebetween.

  Further, Patent Document 2 discloses that a contact member between a photosensitive member and a contact member (charging roller) at the time of non-image formation is provided with a developer layer (toner layer) to stop rotation of the photosensitive member. A technique for preventing the surface of a photoreceptor from being contaminated by a bleed product is disclosed.

JP-A-7-168421 JP 2007-199570 A

  However, in the method of Patent Document 1, a sheet member and its driving device are required as additional members, which leads to an increase in size and cost of the device. Further, since the method of Patent Document 2 aims to prevent bleeding of plasticizer or the like from the charging roller, it is necessary to interpose the toner layer over the entire nip portion between the photosensitive member and the charging roller. There is a possibility that uneven charging on the surface of the photosensitive member due to contamination of the photosensitive member may affect the output image. In addition, there is a problem that toner consumption other than printing increases.

  In view of the above problems, the present invention provides an image forming apparatus capable of reducing the load applied to the end of the charging member at the start of driving of the apparatus by a simple and low-cost method and suppressing damage to the end of the charging member. The purpose is to do.

  In order to achieve the above object, the present invention charges an image carrier having a photosensitive layer formed on the surface, and charging the surface of the image carrier by applying a charging bias in contact with the surface of the image carrier. An image forming unit including a charging member to be developed, a developing device that develops an electrostatic latent image formed on the surface of the image carrier into a toner image, and the image carrier uniformly charged by the charging member An image forming apparatus comprising: an exposure apparatus that writes an electrostatic latent image on the surface of the image forming apparatus; and a control unit that controls the operation of each unit including the exposure apparatus and the image forming unit. After completion, the toner carrying regions are formed in the vicinity of both ends in the longitudinal direction of the surface of the image carrier, and the toner carrying regions are stopped at the contact positions between the image carrier and both ends of the charging member. Stop spinning It is characterized by a door.

  According to the present invention, in the image forming apparatus having the above-described configuration, the control unit continuously rotates the image carrier after the image output is completed, so that the toner adheres on the image carrier in the image forming unit. Forming an area and rotating the image carrier reversely after forming the toner adhesion area to stop the toner adhesion area at a contact position between the image carrier and both ends of the charging member. .

  According to the present invention, in the image forming apparatus configured as described above, the toner adhesion region is in contact with both ends of the charging member outside the image forming region of the image carrier.

  According to the present invention, in the image forming apparatus configured as described above, the width of the toner adhesion region in the circumferential direction of the image carrier is substantially equal to the width of the contact region between the image carrier and both ends of the charging member. It is characterized by.

  According to the present invention, in the image forming apparatus configured as described above, the charging member is a charging roller in which a roller body is formed of a conductive rubber on an outer peripheral surface of a metal shaft.

  According to the first configuration of the present invention, when the image forming process is stopped, the toner layer is always present only at the contact position between the image carrier and both ends of the charging member, and the image carrier is driven again. In this case, the load applied to the end of the charging member due to the friction between the image carrier and the charging member can be reduced, and damage to the end of the charging member can be suppressed. Further, wasteful toner consumption other than printing can be suppressed as much as possible.

  Further, according to the second configuration of the present invention, in the image forming apparatus having the first configuration, the image carrier is continuously rotated after the image output is completed, so that the image forming unit can be placed on the image carrier. A cleaning member or a transfer member is formed by forming a toner adhesion region and rotating the image carrier reversely after forming the toner adhesion region to stop the toner adhesion region at the contact position between the image carrier and both ends of the charging member. The toner adhesion region can be quickly moved to the contact position between the image carrier and the charging member without separating the toner from the surface of the image carrier.

  According to the third configuration of the present invention, in the image forming apparatus having the first or second configuration, the toner adhesion region is in contact with both ends of the charging member outside the image forming region of the image carrier. Thus, it is possible to eliminate the influence on the output image due to the toner adhering to the charging member.

  According to the fourth configuration of the present invention, in the image forming apparatus having any one of the first to third configurations, the width of the toner adhering region in the circumferential direction of the image carrier is set to the image carrier and the charging member. By making the width of the contact area with both ends of the toner substantially equal, the toner consumption can be minimized to prevent the end of the charging member from being damaged.

  According to the fifth configuration of the present invention, in the image forming apparatus having any one of the first to fourth configurations, as a charging member, a roller body made of conductive rubber that is particularly easy to adhere to the surface of the image carrier. By using the charging roller having the above, it is possible to effectively prevent the end of the roller body from being damaged with a large load applied at the start of driving and low rigidity.

1 is a schematic cross-sectional view showing the overall configuration of an image forming apparatus of the present invention. Partial enlarged view around the image forming unit Pa in FIG. 1 is a block diagram showing a control path of an image forming apparatus of the present invention. Side view of the image forming portion Pa showing a state immediately after the image forming process is completed and the toner adhesion region T is formed on the photosensitive drum 1a. A plan view of the relationship between the photosensitive drum 1a and the charging roller 21 as seen from the right side of FIG. FIG. 4 is a side view showing a state where a predetermined time has elapsed from the state of FIG. 4 and the toner adhesion region T has moved in the direction of the charging roller 21. A plan view of the relationship between the photosensitive drum 1a and the charging roller 21 as seen from the right side of FIG. FIG. 6 is a side view showing a state in which a predetermined time has elapsed from the state of FIG. 6 and the photosensitive drum 1 a has stopped with the toner adhesion region T interposed at the contact positions with both ends of the charging roller 21. A plan view of the relationship between the photosensitive drum 1a and the charging roller 21 as seen from the right side of FIG.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a schematic cross-sectional view of an image forming apparatus equipped with the developing device of the present invention. Here, a tandem color image forming apparatus is shown. In the main body of the color printer 100, four image forming portions Pa, Pb, Pc, and Pd are arranged in order from the right side in FIG. These image forming portions Pa to Pd are provided corresponding to images of four different colors (cyan, magenta, yellow, and black), and cyan, magenta, and yellow are respectively performed by charging, exposure, development, and transfer processes. And a black image are sequentially formed.

  The image forming portions Pa to Pd are provided with photosensitive drums 1a, 1b, 1c, and 1d that carry visible images (toner images) of the respective colors, and are further driven by a driving unit (not shown). The intermediate transfer belt 8 that rotates clockwise is provided adjacent to the image forming portions Pa to Pd. The toner images formed on the photosensitive drums 1a to 1d are sequentially transferred and superimposed on the intermediate transfer belt 8 that moves while contacting the photosensitive drums 1a to 1d, and then the secondary transfer roller 9. Is transferred onto a transfer paper P as an example of a recording medium, and further fixed on the transfer paper P in the fixing unit 7 and then discharged from the apparatus main body. An image forming process for each of the photosensitive drums 1a to 1d is executed while rotating the photosensitive drums 1a to 1d counterclockwise in FIG.

  The transfer paper P onto which the toner image is transferred is accommodated in a paper cassette 16 at the lower part of the apparatus, and drives a secondary transfer roller 9 and an intermediate transfer belt 8 described later via a paper feed roller 12a and a registration roller pair 12b. It is conveyed to the nip between the rollers 11. A sheet made of dielectric resin is used for the intermediate transfer belt 8, and a (seamless) belt having no seam is mainly used. Further, a blade-like belt cleaner 19 for removing toner remaining on the surface of the intermediate transfer belt 8 is disposed on the downstream side in the moving direction of the intermediate transfer belt 8 when viewed from the secondary transfer roller 9.

  Next, the image forming units Pa to Pd will be described. There are charging devices 2a, 2b, 2c and 2d for charging the photosensitive drums 1a to 1d and image information on the photosensitive drums 1a to 1d around and below the photosensitive drums 1a to 1d, which are rotatably arranged. The exposure device 4 for exposing the toner, the developing devices 3a, 3b, 3c and 3d for forming toner images on the photosensitive drums 1a to 1d, and the developer (toner) remaining on the photosensitive drums 1a to 1d are removed. Cleaning devices 5a, 5b, 5c and 5d are provided.

  When image data is input from a host device such as a personal computer, first, the surfaces of the photosensitive drums 1a to 1d are uniformly charged by the charging devices 2a to 2d, and then light is irradiated according to the image data by the exposure device 4. The electrostatic latent images corresponding to the image data are formed on the respective photosensitive drums 1a to 1d. Each of the developing devices 3a to 3d is filled with a predetermined amount of a two-component developer containing toner of each color of cyan, magenta, yellow, and black. In addition, when the ratio of the toner in the two-component developer filled in each of the developing devices 3a to 3d is less than a predetermined value due to the formation of a toner image, which will be described later, each developing device 3a to The toner is replenished in 3d. The toner in the developer is supplied onto the photosensitive drums 1a to 1d by the developing devices 3a to 3d and electrostatically attached to the electrostatic latent image formed by exposure from the exposure device 4. A toner image is formed.

  Then, the primary transfer rollers 6a to 6d apply an electric field at a predetermined transfer voltage between the primary transfer rollers 6a to 6d and the photosensitive drums 1a to 1d, and yellow, cyan, magenta, and yellow on the photosensitive drums 1a to 1d are applied. A black toner image is primarily transferred onto the intermediate transfer belt 8. These four color images are formed with a predetermined positional relationship predetermined for forming a predetermined full-color image. Thereafter, the toner remaining on the surfaces of the photosensitive drums 1a to 1d is removed by the cleaning devices 5a to 5d in preparation for the subsequent formation of a new electrostatic latent image.

  The intermediate transfer belt 8 is stretched between an upstream conveyance roller 10 and a downstream drive roller 11, and the intermediate transfer belt 8 rotates clockwise as the drive roller 11 is rotated by a drive motor (not shown). When the rotation starts, the transfer paper P is conveyed from the registration roller pair 12b to the secondary transfer roller 9 provided adjacent to the intermediate transfer belt 8 at a predetermined timing, and the full color image is transferred. The transfer paper P onto which the toner image is transferred is conveyed to the fixing unit 7.

  The transfer paper P conveyed to the fixing unit 7 is heated and pressurized by the fixing roller pair 13 so that the toner image is fixed on the surface of the transfer paper P, and a predetermined full color image is formed. The transfer paper P on which the full-color image is formed is distributed in the transport direction by the branching portion 14 that branches in a plurality of directions. When an image is formed on only one side of the transfer paper P, the image is directly discharged onto the discharge tray 17 by the discharge roller pair 15.

  On the other hand, when images are formed on both sides of the transfer paper P, a part of the transfer paper P that has passed through the fixing unit 7 is once protruded from the discharge roller pair 15 to the outside of the apparatus. Thereafter, the transfer paper P is distributed to the paper conveyance path 18 by the branching section 14 by rotating the discharge roller pair 15 in the reverse direction, and is re-conveyed to the registration roller pair 12b with the image surface reversed. Then, after the next image formed on the intermediate transfer belt 8 is transferred to the surface of the transfer paper P on which the image is not formed by the secondary transfer roller 9 and conveyed to the fixing unit 7 to fix the toner image. The paper is discharged from the discharge roller pair 15 to the discharge tray 17.

  FIG. 2 is an enlarged view of the vicinity of the image forming portion Pa in FIG. Since the image forming units Pb to Pd have basically the same configuration, description thereof is omitted. Around the photosensitive drum 1a, a charging device 2a, a developing device 3a, a cleaning device 5a, and a charge eliminating lamp 20 are disposed along the drum rotation direction (counterclockwise in FIG. 2), and the intermediate transfer belt 8 is interposed therebetween. The primary transfer roller 6a is arranged.

  The charging device 2 a includes a charging roller 21 that contacts the photosensitive drum 1 a to charge the drum surface, and a charging cleaning roller 23 for cleaning the charging roller 21. As the charging roller 21, for example, a roller body 21b (see FIG. 4) having a conductive rubber layer such as epichlorohydrin rubber formed on the outer peripheral surface of a metal shaft 21a (see FIG. 4) is used. The charging roller 21 is pressed against the photosensitive drum 1a by applying a predetermined pressure to both ends of the shaft 21a, and is driven to rotate as the photosensitive drum 1a rotates.

  The developing device 3a is a two-component developing type having two agitating and conveying screws 25, a magnetic roller 27, and a developing roller 29, and a toner thin film is applied to the developing roller 29 using a magnetic brush standing on the surface of the magnetic roller 27. A layer is formed, and a developing bias having the same polarity (positive) as the toner is applied to the developing roller 29 to cause the toner to fly on the drum surface.

  The cleaning device 5 a includes a rubbing roller 30, a cleaning blade 31, and a collection screw 33. The rubbing roller 30 is pressed against the photosensitive drum 1a with a predetermined pressure, and is driven to rotate in the same direction on the contact surface with the photosensitive drum 1a by a driving means (not shown). The speed is controlled faster than the peripheral speed of 1a (1.2 times here). Examples of the rubbing roller 30 include a structure in which a foam layer made of EPDM rubber and having an Asuka C hardness of 55 ° is formed as a roller body around a metal shaft. The material of the roller body is not limited to EPDM rubber, but may be rubber or foam rubber body of other materials, and those having an Asuka C hardness in the range of 10 to 90 ° are preferably used.

  A cleaning blade 31 is fixed in contact with the photosensitive drum 1a on the surface of the photosensitive drum 1a downstream of the contact surface with the rubbing roller 30 in the rotation direction. As the cleaning blade 31, for example, a polyurethane rubber blade having a JIS hardness of 78 ° is used, and is attached at a predetermined angle with respect to the tangential direction of the photosensitive member at the contact point. The material, hardness, dimensions, the amount of biting into the photosensitive drum 1a, the pressure contact force, and the like of the cleaning blade 31 are appropriately set according to the specifications of the photosensitive drum 1a. Residual toner removed from the surface of the photosensitive drum 1 a by the rubbing roller 30 and the cleaning blade 31 is discharged to the outside of the cleaning device 5 a as the recovery screw 33 rotates.

  A neutralizing lamp 20 is disposed between the cleaning device 5a and the charging device 2a. The neutralization lamp 20 removes residual charges on the surface of the drum by irradiating the surface of the photosensitive drum 1a with light.

  Next, the control path of the image forming apparatus of the present invention will be described. FIG. 3 is a block diagram showing an example of a control path used in the image forming apparatus of the present invention. In addition, since various controls of each part of the apparatus are performed when the color printer 100 is used, the control path of the entire color printer 100 becomes complicated. Therefore, here, a portion of the control path that is necessary for the implementation of the present invention will be mainly described.

  The control unit 90 includes a central processing unit (CPU) 91 as a central processing unit, a read only memory (ROM) 92 that is a read-only storage unit, a random access memory (RAM) 93 that is a read / write storage unit, A plurality of (two in this case) that transmit control signals to and receive input signals from the operation unit 60, such as a temporary storage unit 94 that stores image data and the like, a counter 95, and each device in the color printer 100. At least an I / F (interface) 96 is provided. Further, the control unit 90 can be arranged at an arbitrary location inside the apparatus main body.

  The ROM 92 stores control programs for the color printer 100, data necessary for control, and the like that are not changed during use of the color printer 100. The RAM 93 stores necessary data generated during the control of the color printer 100, data temporarily required for the control of the color printer 100, and the like. The counter 95 integrates and counts the number of printed sheets, the driving time t1, and the charging bias application time t2.

  The control unit 90 transmits a control signal from the CPU 91 to the respective units and devices in the color printer 100 through the I / F 96. In addition, a signal indicating the state and an input signal are transmitted from each part or device to the CPU 91 through the I / F 96. Examples of the parts and devices controlled by the control unit 90 include, for example, the image forming units Pa to Pd, the exposure device 4, the primary transfer rollers 6a to 6d, the fixing unit 7, the secondary transfer roller 9, the image input unit 40, and bias control. Examples include the circuit 41, the operation unit 50, and the like.

  The image input unit 40 is a receiving unit that receives image data transmitted from the personal computer or the like by the color printer 100. The image signal input from the image input unit 40 is converted into a digital signal and then sent to the temporary storage unit 94.

  The motor control circuit 41 is connected to the drum motor 42, the developing motor 43, the cleaning motor 44, the belt driving motor 45, and the primary transfer driving motor 46, and controls the driving of the motors 42 to 46 by the output signal from the control unit 90. .

  Each of these motors 42 to 46 is controlled by a control signal from a motor control circuit 41, the drum motor 42 is for the photosensitive drums 1a to 1d, and the developing motor 43 is for the stirring and conveying screw 25, the magnetic roller 27 in the developing devices 3a to 3d, The developing roller 29, the cleaning motor 44 is the rubbing roller 30 in the cleaning devices 5a to 5d, the belt drive motor 45 is the intermediate transfer belt 8 and the secondary transfer roller 9, and the primary transfer drive motor 46 is the primary transfer roller 6a to 6a. 6d is driven at a predetermined linear velocity.

  The bias control circuit 50 is connected to the charging bias power source 51, the developing bias power source 52, and the transfer bias power source 53, and operates each of these power sources according to an output signal from the control unit 90. A predetermined bias is applied to the charging devices 2a to 2d, the magnetic roller 27, the developing roller 29, the primary transfer rollers 6a to 6d, and the secondary transfer roller 9 according to a control signal from the control circuit 50.

  The operation unit 60 is provided with a liquid crystal display unit 61 and an LED 62. The liquid crystal display unit 61 and the LED 62 indicate the state of the color printer 100, and display the image forming status and the number of copies to be printed. Yes. Various settings of the color printer 100 are performed from a printer driver of a personal computer.

  In addition, the operation unit 60 is provided with a stop / clear button used when canceling image formation and the like, a reset button used when various settings of the color printer 100 are set to the default state, and the like.

  In the color printer 100 shown in FIG. 1, the charging roller 21 made of conductive rubber comes into close contact with the photosensitive drums 1a to 1d when a long time has passed after the driving of the apparatus is stopped. Therefore, when the apparatus is re-driven and the photosensitive drums 1a to 1d start to rotate, a load is applied to the nip portion between the photosensitive drums 1a to 1d and the charging roller 21, and the end of the weak roller may be damaged. there were.

  Therefore, in the present invention, when the driving of the apparatus is stopped, areas where toner is adhered (hereinafter referred to as toner adhesion areas) are formed in the vicinity of both ends in the longitudinal direction of the surfaces of the photosensitive drums 1a to 1d, and the toner adheres. The region is stopped at the contact position between the photosensitive drums 1 a to 1 d and both ends of the charging roller 21. In the following, referring to FIGS. 1 to 3 as necessary, the procedure for driving the image forming unit (photosensitive drum, charging roller and developing device) and the exposure device after the image formation is completed until the driving of the device is stopped. Will be described. In the following description, the image forming unit Pa is taken as an example, but the same applies to the image forming units Pb to Pd, and the description thereof is omitted.

  FIG. 4 is a side view showing the state of the image forming portion Pa immediately after the image forming process is completed and the toner adhesion region T is formed on the photosensitive drum 1a. FIG. FIG. 5 is a plan view of the relationship with a roller 21 as viewed from the right side of FIG. 4 (developing device 3a side). In FIG. 4, for convenience of explanation, the cleaning device 5a, the primary transfer roller 6a, the intermediate transfer belt 8, and the charge eliminating lamp 20 are omitted (the same applies to FIGS. 6 and 8 described later). FIG. 5 shows only the photosensitive drum 1a, the charging roller 21 and the developing roller 29, and only the outline of the developing roller 29 is indicated by a broken line so that the position of the toner adhesion region T on the photosensitive drum 1a can be seen. (The same applies to FIGS. 7 and 9 described later).

  When the image forming process is completed, the control unit 90 transmits a control signal to each unit of the apparatus, and continues the rotation of the photosensitive drum 1a and the charging of the drum surface by the charging device 2a even after the completion of the image formation. Then, an electrostatic latent image is formed at a predetermined position by light irradiation of the exposure device 4 (see FIG. 1). On the other hand, the developing bias is continuously applied to the magnetic roller 27 and the developing roller 29 of the developing device 3a. When the electrostatic latent image passes through the developing device 3a due to the rotation of the photosensitive drum 1a, toner adheres to the electrostatic latent image from the developing roller 29, and as shown in FIGS. 4 and 5, the length of the surface of the photosensitive drum 1a is increased. A toner adhesion region T is formed outside the image forming region near both ends in the direction. The dimension L of the toner adhesion region T in the circumferential direction of the photosensitive drum 1a is set to be substantially equal to the width of the contact region in the circumferential direction of the photosensitive drum 1a and the charging roller 21.

  6 is a side view showing a state of the image forming unit Pa after a predetermined time has elapsed from the state of FIG. 4, and FIG. 7 is a view of the relationship between the photosensitive drum 1a and the charging roller 21 as seen from the right side of FIG. It is a top view. As shown in FIGS. 6 and 7, the toner adhesion region T is moved in the direction of the charging roller 21 by rotating the photosensitive drum 1a in the direction opposite to the normal time (direction of arrow A in FIG. 6). Then, the control unit 90 transmits a control signal to the motor control circuit 41 to stop the driving of the drum motor 42 (both see FIG. 3), so that the toner adhesion region T stops at the contact position with the charging roller 21. Thus, the rotation of the photosensitive drum 1a is stopped. At this time, the control signal is also transmitted to the bias control circuit 50 (see FIG. 3), and the application of the charging bias to the charging roller 21 and the application of the developing bias to the magnetic roller 27 and the developing roller 29 are also stopped.

  Note that the photosensitive drum 1a does not stop immediately even when the drum motor 42 stops, but stops by rotating in the direction of arrow A by a predetermined distance due to inertia. Therefore, the drum motor 42 is stopped at such a timing that the toner adhesion region T stops at the contact position with the charging roller 21 in consideration of the rotation amount due to the inertia of the photosensitive drum 1a.

  FIG. 8 is a side view showing a state in which a predetermined time has elapsed from the state of FIG. 6 and the photosensitive drum 1a has stopped with the toner adhesion region T interposed between the charging roller 21 and the both end portions. FIG. 9 is a plan view of the relationship between the photosensitive drum 1a and the charging roller 21 as viewed from the right side of FIG. As shown in FIGS. 8 and 9, when the image forming process is finished and the driving of the apparatus is stopped, the toner adhesion region T is always at the contact position between the photosensitive drums 1 a to 1 d and both ends of the charging roller 21. Therefore, the releasability between the photosensitive drums 1a to 1d and both ends of the charging roller 21 is improved.

  Therefore, the load applied to both ends of the charging roller 21 when the apparatus is re-driven is reduced, and the damage to both ends of the charging roller 21 is effective without providing an additional member or increasing the amount of toner consumption. Can be prevented. The toner adhesion areas T on the surfaces of the photosensitive drums 1a to 1d are collected by the cleaning devices 5a to 5d (see FIG. 2) when the image forming process is resumed. Further, when toner adheres to the charging roller 21, it is removed by the charging cleaning roller 23. However, since the toner adhesion region T is formed outside the image forming regions of the photosensitive drums 1a to 1d, the toner is applied to the charging roller 21. Even if it adheres, there is no possibility of adversely affecting the output image.

  4 and 5, after the toner adhesion region T is formed, the photosensitive drums 1 a to 1 d are rotated forward (counterclockwise in FIG. 4) to move the toner adhesion region T to the charging roller 21. Although a method is also conceivable, in this case, the intermediate transfer belt 8 or the toner transfer region T may be prevented from being scraped off by the intermediate transfer belt 8, the rubbing roller 30, the cleaning blade 31, or the like contacting the photosensitive drums 1 a to 1 d. A mechanism for separating the cleaning devices 5a to 5d is required. Therefore, as described above, after the toner adhesion region T is formed, it is preferable to move the toner adhesion region T to the charging roller 21 by reversely rotating the photosensitive drums 1a to 1d.

  Further, as shown in FIG. 2, the photosensitive drums 1a to 1d and the developing roller 29 are arranged in a non-contact state, and a jumping development type is developed in which toner is ejected from the developing roller 29 side to the photosensitive drums 1a to 1d. In this case, the electrostatic latent image located slightly outside the both end portions of the developing roller 29 can be developed. However, in order to reliably form the toner adhesion region T at a position overlapping both ends of the charging roller 21, it is desirable that the dimension in the longitudinal direction of the developing roller 29 is at least equal to or greater than that of the charging roller 21.

  In addition, this invention is not limited to the said embodiment, A various change is possible in the range which does not deviate from the meaning of this invention. For example, the size and shape of the toner adhesion region T, the toner layer thickness, and the like are appropriately set according to the contact area and adhesion between the photosensitive drums 1a to 1d and the charging roller 21, the load applied to the shaft 21a of the charging roller 21, and the like. Just do it.

  Further, the present invention is not limited to the tandem type color printer shown in FIG. 1, and is provided with a charging roller such as an analog or digital type monochrome copying machine, a monochrome printer, a rotary or tandem type color copying machine, a facsimile or the like. Of course, the present invention can be applied to a contact charging type image forming apparatus.

  The present invention can be used in an image forming apparatus including a charging member that charges the surface of a photosensitive drum in a contact state. By utilizing the present invention, an image forming apparatus capable of relieving the load applied to the end portion of the charging member due to friction between the image carrier and the charging member when the image bearing member is driven again, and suppressing damage to the end portion of the charging member. It can be provided, and the life extension of the charging member can be promoted.

  In particular, when applied to an image forming apparatus equipped with a charging roller made of conductive rubber, it reduces the risk of damage to the end of the charging roller, which has high adhesion to the photoreceptor and low rigidity, thereby extending the life of the apparatus. Thus, maintenance can be improved.

Pa to Pd Image forming section 1a to 1d Photosensitive drum (image carrier)
2a to 2d charging device 3a to 3d developing device 4 exposure device 5a to 5d cleaning device 6a to 6d primary transfer roller 8 intermediate transfer belt 9 secondary transfer roller 20 static elimination lamp 21 charging roller (charging member)
21a Shaft 21b Roller body 90 Control unit 100 Color printer T Toner adhesion area

Claims (5)

An image carrier having a photosensitive layer formed on the surface;
A charging member that charges the surface of the image carrier by applying a charging bias in contact with the surface of the image carrier;
A developing device for developing the electrostatic latent image formed on the surface of the image carrier into a toner image;
An image forming unit including:
An exposure device for writing an electrostatic latent image on the surface of the image carrier uniformly charged by the charging member;
Control means for controlling the operation of each part of the apparatus including the exposure apparatus and the image forming unit;
In an image forming apparatus comprising:
The control means forms a toner adhesion region in the vicinity of both ends in the longitudinal direction of the surface of the image carrier after completion of image output, and the toner adhesion region is a contact position between the image carrier and both ends of the charging member. An image forming apparatus, wherein the rotation of the image carrier is stopped so as to stop.   The control means continuously rotates the image carrier after the image output is completed, thereby forming the toner adhesion region on the image carrier in the image forming unit, and after forming the toner adhesion region. 2. The image forming apparatus according to claim 1, wherein the image carrier is rotated in the reverse direction to stop the toner adhesion region at a contact position between the image carrier and both ends of the charging member.   The image forming apparatus according to claim 1, wherein the toner adhesion region is in contact with both end portions of the charging member outside the image forming region of the image carrier.   4. The width of the toner adhesion region in the circumferential direction of the image carrier is substantially equal to the width of a contact region between the image carrier and both ends of the charging member. An image forming apparatus according to claim 1.   5. The image forming apparatus according to claim 1, wherein the charging member is a charging roller in which a roller body is formed of a conductive rubber on an outer peripheral surface of a metal shaft.

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