JP2017142283A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming apparatus that can effectively suppress a toner from coming off in switching from a color mode to a monochrome mode and the occurrence of soil on the back of a recording medium.SOLUTION: An image forming apparatus comprises a plurality of image forming parts, an intermediate transfer unit, a secondary transfer roller, a belt cleaning device including a cleaning member and a recovery roller, a bias application device, and a control part. The intermediate transfer unit includes an intermediate transfer belt, a plurality of primary transfer rollers, a driving roller, a tension roller, and a roller contact/separation mechanism. The control part, when switching from a color mode to a monochrome mode during continuous printing, turns off a bias applied to the recovery roller or makes its polarity the same as that of a toner before applying a bias with a reverse polarity to that of the toner to the recovery roller immediately after a position of the intermediate transfer belt corresponding to the rear end of the first image in monochrome printing passes through the belt cleaning device.SELECTED DRAWING: Figure 8

Description

  The present invention relates to an image forming apparatus provided with a mechanism for removing residual toner on the surface of an intermediate transfer belt using a cleaning member, and more particularly to a method for preventing toner from reattaching to an intermediate transfer belt.

  2. Description of the Related Art Conventionally, an endless intermediate transfer belt that rotates in a predetermined direction and a plurality of image forming units provided along the intermediate transfer belt are provided, and toner images of each color are formed on the intermediate transfer belt by the image forming units. There is known an intermediate transfer type image forming apparatus that sequentially superimposes images and performs primary transfer and then secondary transfer onto a recording medium.

  Such an intermediate transfer type image forming apparatus is provided with a belt cleaning device for removing toner remaining on the intermediate transfer belt after the secondary transfer. When the intermediate transfer belt does not have an elastic layer, a blade method is employed in which the cleaning blade is pressed against the surface of the intermediate transfer belt to scrape off the toner.

  On the other hand, when the intermediate transfer belt has an elastic layer, a cleaning brush that mechanically and electrically recovers toner remaining on the surface of the intermediate transfer belt, a recovery roller that recovers toner from the cleaning brush, and toner from the surface of the recovery roller In many cases, a cleaning device is used that has a blade that scrapes off the toner and a conveying spiral that conveys the toner scraped off from the surface of the collecting roller to a waste toner collecting container.

  Various techniques for adjusting the cleaning conditions of the intermediate transfer belt have also been proposed. For example, Patent Document 1 includes an adjustment mechanism that adjusts the contact condition between the cleaning member and the intermediate transfer belt, and includes a monochrome mode and a color mode. And a technique for adjusting the contact condition between the cleaning member and the intermediate transfer belt to be a condition suitable for cleaning.

  Further, in Patent Document 2, when switching from the color mode to the monochrome mode in order to prevent the recording material from being soiled, after all the pressure bonding of the primary transfer unit of each image forming unit to the intermediate transfer belt is once released, A technique is disclosed in which a primary transfer unit of an image forming unit where image formation is performed is pressed to shift to a monochrome mode.

JP 2013-83676 A JP 2004-341399 A

  Incidentally, some cleaning devices have a seal member that partitions the inside of the housing into a cleaning brush side and a conveying spiral side. The seal member guides the toner scraped off from the surface of the collecting roller by the blade to the conveying spiral side by bringing the tip part into contact with the collecting roller on the upstream side of the blade that scrapes the toner from the surface of the collecting roller. It does not go to the side (outside of the housing). For this reason, the seal member needs to be in contact with the contact roller with a substantially constant contact pressure so as not to scrape off the toner adhering to the recovery roller over the entire axial direction of the recovery roller.

  However, paper dust generated from the recording medium (paper) may adhere to the intermediate transfer belt, and paper dust may adhere to the seal member via a cleaning brush and a collection roller. As a result, a gap is generated between the collection roller and the seal member, and the toner on the conveying spiral side flows backward to the cleaning brush side and reattaches to the cleaning brush. Then, when the toner reattached to the cleaning brush moves onto the intermediate transfer belt, there is a possibility that a so-called toner drop occurs and an image defect occurs.

  In particular, when switching from the color mode in which all the primary transfer rollers are pressed against the photosensitive drum to the monochrome mode in which only one primary transfer roller is pressed against the photosensitive drum corresponding to the black image, the tension of the intermediate transfer belt The cleaning brush moves to the inside of the housing due to the change of. As a result, the cleaning brush comes into contact with the toner accumulated on the bottom surface of the seal member and the housing, and reattaches to the cleaning brush. Then, the toner reattached to the cleaning brush moves to the intermediate transfer belt, and after the monochrome mode is switched, the toner is dropped or the back side of the paper is smeared.

  SUMMARY OF THE INVENTION In view of the above problems, an object of the present invention is to provide an image forming apparatus that can effectively prevent the occurrence of toner drop and backside contamination of a recording medium when switching from a color mode to a monochrome mode.

  In order to achieve the above object, a first configuration of the present invention includes a plurality of image forming units that form images of different colors, an intermediate transfer unit, a secondary transfer roller, a belt cleaning device, and a bias applying device. And an image forming apparatus including a control unit. The intermediate transfer unit is disposed opposite to an endless intermediate transfer belt that moves along the image forming unit and an image carrier disposed in each image forming unit across the intermediate transfer belt, and is formed on the image carrier. A plurality of primary transfer rollers that primarily transfer the toner image onto the intermediate transfer belt, a drive roller that rotates the intermediate transfer belt, and a rotation that follows the intermediate transfer belt and applies a predetermined tension to the intermediate transfer belt. A tension roller and a roller contact / separation mechanism that reciprocates the primary transfer roller in a direction approaching or separating from the intermediate transfer belt. The secondary transfer roller secondarily transfers the toner image primarily transferred onto the intermediate transfer belt onto the recording medium. The belt cleaning device removes residual toner on the surface of the intermediate transfer belt. The bias applying device applies a bias to the belt cleaning device. The control unit controls the intermediate transfer unit, the belt cleaning device, and the bias applying device. The roller contact / separation mechanism includes a color mode in which all primary transfer rollers are pressed against the image carrier with the intermediate transfer belt interposed therebetween, and image formation in which only one primary transfer roller forms a black image with the intermediate transfer belt interposed therebetween. It is possible to switch between the monochrome mode pressed against the image carrier disposed in the section. The belt cleaning device opposes the tension roller with the intermediate transfer belt sandwiched between a housing formed with an opening facing the intermediate transfer belt, a toner accommodating portion for storing toner removed from the surface of the intermediate transfer belt. A cleaning member disposed at a position, a recovery roller that electrically recovers toner adhering to the cleaning member by applying a bias having a polarity opposite to that of the toner from a bias application device, and a longitudinal direction of the recovery roller. A seal member disposed opposite to each other and partitioning the toner containing portion and the opening. In the monochrome mode, the cleaning member is disposed at a position moved inward of the housing from the opening by the pressing force of the tension roller as compared with the color mode. When switching from the color mode to the monochrome mode during continuous printing, the control unit turns off the bias applied to the collection roller or sets the same polarity as the toner, and then prints the first sheet in the monochrome mode of the intermediate transfer belt. Immediately after the position corresponding to the rear end of the image has passed through the belt cleaning device, a bias having a polarity opposite to that of the toner is applied to the collecting roller.

  According to the first configuration of the present invention, when switching from the color mode to the monochrome mode, the bias applied to the collection roller until the position corresponding to the rear end portion of the first monochrome image of the intermediate transfer belt passes. By turning off or having the same polarity as the toner, the toner or the like accumulated in the belt cleaning device does not adhere to the cleaning member until the region corresponding to the first monochrome print image of the intermediate transfer belt passes. By applying a bias having a polarity opposite to that of the toner at the timing when the position corresponding to the rear end of the first monochrome image has passed, the toner is adhered to the cleaning member, and further, monochrome printing is performed on the intermediate transfer belt. Adhere between the first and second sheets. As a result, it is possible to effectively suppress the occurrence of toner drop and backside contamination of the recording medium in the first monochrome print.

1 is a schematic diagram showing an internal configuration of an image forming apparatus 100 according to an embodiment of the present invention. Enlarged view of the vicinity of the image forming portion Pa in FIG. Side sectional view of the intermediate transfer unit 30 mounted on the image forming apparatus 100 External perspective view of the belt cleaning unit 19 shown in FIG. Side surface sectional view showing the internal configuration of the belt cleaning unit 19 Side surface sectional view showing the moving direction of the tension roller 11 and the fur brush 41 when the primary transfer rollers 6a to 6d are pressed. Block diagram showing a control path of the image forming apparatus 100 Timing chart showing an example of switching operation from the color mode to the monochrome mode in the image forming apparatus 100 of the present embodiment A flowchart showing switching control from the color mode to the monochrome mode in the image forming apparatus 100 of the present embodiment.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a schematic diagram illustrating a configuration of an image forming apparatus 100 according to an embodiment of the present invention, and FIG. 2 is an enlarged view of the vicinity of an image forming unit Pa in FIG.

  An image forming apparatus 100 shown in FIG. 1 is a so-called tandem color printer, and has the following configuration. In the main body of the image forming apparatus 100, four image forming portions Pa, Pb, Pc, and Pd are sequentially arranged from the upstream side in the transport direction (the right side in FIG. 1). 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.

  These image forming portions Pa to Pd are provided with photosensitive drums 1a, 1b, 1c and 1d which carry visible images (toner images) of the respective colors, and are further illustrated by a driving means (not shown). 1, an intermediate transfer belt 8 that rotates in the clockwise direction is provided adjacent to each of the image forming portions Pa to Pd. The toner images formed on the photosensitive drums 1a to 1d are sequentially transferred onto the intermediate transfer belt 8 that moves while being in contact with the photosensitive drums 1a to 1d. As an example, the image is transferred onto the transfer paper P at one time, and further fixed on the transfer paper P in the fixing unit 13, and then discharged from the main body of the image forming apparatus 100. An image forming process for each of the photosensitive drums 1a to 1d is executed while rotating the photosensitive drums 1a to 1d in the counterclockwise direction 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 main body of the image forming apparatus 100, and is conveyed to the secondary transfer roller 9 via the paper feed roller 12a and the registration roller pair 12b. . As the intermediate transfer belt 8, a belt having no seam (seamless) is mainly used.

  Next, the image forming units Pa to Pd will be described. Hereinafter, the image forming unit Pa will be described in detail. However, the image forming units Pb to Pd have basically the same configuration, and thus the description thereof is omitted. As shown in FIG. 2, a charging device 2a, a developing device 3a, and a cleaning device 7a are disposed around the photosensitive drum 1a along the drum rotation direction (counterclockwise direction in FIG. 1). A primary transfer roller 6 a is disposed with 8 interposed therebetween. Further, a belt cleaning unit 19 facing the tension roller 11 with the intermediate transfer belt 8 interposed therebetween is disposed on the upstream side in the rotation direction of the intermediate transfer belt 8 with respect to the photosensitive drum 1a.

  Next, an image forming procedure in the image forming apparatus 100 will be described. When the start of image formation is input by the user, first, the surfaces of the photosensitive drums 1a to 1d are uniformly charged by the charging devices 2a to 2d. Next, the surfaces of the photosensitive drums 1a to 1d are irradiated with light beams (laser light) emitted from the light emission window 5a of the exposure apparatus 5, and electrostatic latent images corresponding to image signals are respectively formed on the photosensitive drums 1a to 1d. Form an image. The developing devices 3a to 3d are filled with predetermined amounts of cyan, magenta, yellow, and black toners, respectively. In addition, when the ratio of the toner in the two-component developer filled in each developing device 3a to 3d falls below a specified value due to the formation of a toner image described later, each developing device 3a to 3d is transferred from the toner container 4a to 4d. Toner is replenished. The toner in the developer is supplied onto the photosensitive drums 1a to 1d by the developing devices 3a to 3d and electrostatically adheres to the electrostatic latent image formed by the exposure from the exposure device 5. A toner image is formed.

  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 cyan, magenta, yellow, and yellow on the photosensitive drums 1a to 1d. 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 7a to 7d in preparation for the subsequent formation of a new electrostatic latent image.

  When the intermediate transfer belt 8 starts to rotate in the clockwise direction as the driving roller 10 is rotated by a belt drive motor (not shown), the transfer paper P is adjacent to the intermediate transfer belt 8 from the registration roller 12b at a predetermined timing. The full color image is transferred to the secondary transfer roller 9 provided. The transfer paper P onto which the toner image is transferred is conveyed to the fixing unit 13. The toner remaining on the surface of the intermediate transfer belt 8 is removed by the belt cleaning unit 19.

  The transfer paper P conveyed to the fixing unit 13 is heated and pressed by the fixing roller pair 13a to fix the toner image 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, it is discharged as it is onto the discharge tray 17 by the discharge roller 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 13 is once projected from the discharge roller 15 to the outside of the apparatus. Thereafter, the transfer paper P is distributed to the paper transport path 18 by the branching portion 14 by rotating the discharge roller 15 in the reverse direction, and is transported again to the secondary transfer roller 9 with the image surface reversed. Then, after the next image formed on the intermediate transfer belt 8 is transferred by the secondary transfer roller 9 to the surface of the transfer paper P where the image is not formed and conveyed to the fixing unit 13 to fix the toner image. , And discharged to the discharge tray 17.

  FIG. 3 is a side sectional view of the intermediate transfer unit 30 mounted on the image forming apparatus 100. FIG. 3 shows a state in which the intermediate transfer unit 30 is viewed from the back side in FIG. As shown in FIG. 3, the intermediate transfer unit 30 includes an intermediate transfer belt 8 stretched between a downstream drive roller 10 and an upstream tension roller 11, and the photosensitive drums 1 a to 1 d via the intermediate transfer belt 8. Primary transfer rollers 6a to 6d in contact with 1d. A belt cleaning unit 19 for removing toner remaining on the surface of the intermediate transfer belt 8 is disposed at a position facing the tension roller 11. The detailed configuration of the belt cleaning unit 19 will be described later.

  The intermediate transfer unit 30 includes a pair of support members (not shown) that rotatably supports both ends of the rotation shafts of the primary transfer rollers 6 a to 6 d, and the support members reciprocate perpendicularly to the traveling direction of the intermediate transfer belt 8. A roller contact / separation mechanism 60 having drive means (not shown) for movement is provided. The roller contact / separation mechanism 60 includes only a color mode in which the four primary transfer rollers 6a to 6d are pressed against the photosensitive drums 1a to 1d (see FIG. 1) via the intermediate transfer belt 8, and only the primary transfer roller 6d. It is possible to switch between a monochrome mode in which the photosensitive drum 1d is pressed through the intermediate transfer belt 8 and a retract mode in which all of the four primary transfer rollers 6a to 6d are separated from the intermediate transfer belt 8.

  4 is an external perspective view of the belt cleaning unit 19 shown in FIG. 3, and FIG. 5 is a side sectional view showing the internal configuration of the belt cleaning unit 19. The belt cleaning unit 19 includes a fur brush 41, a collection roller 43, a blade 45, and a conveyance spiral 47 in the housing 40, and the fur brush 41, the collection roller 43, and the conveyance spiral 47 are cleaned at one end of the housing 40. A drive input gear train 48 for inputting a drive force from a drive motor (not shown) is disposed.

  The fur brush 41 is disposed opposite to the tension roller 11 via the intermediate transfer belt 8 on the opening 40 a side of the housing 40. The fur brush 41 rotates in a counter direction (counterclockwise direction in FIG. 5) with respect to the moving direction of the intermediate transfer belt 8, thereby causing foreign matter (hereinafter referred to as toner) remaining on the intermediate transfer belt 8 such as toner and paper dust. Etc.). The brush portion of the fur brush 41 that contacts the collection roller 43 is formed of conductive fibers having a resistance value of about 1 to 900 MΩ.

  The collection roller 43 collects toner and the like attached to the fur brush 41 by rotating in a direction opposite to the fur brush 41 (clockwise direction in FIG. 5) while contacting the surface of the fur brush 41. A cleaning bias power supply 65 (see FIG. 7) is connected to the collection roller 43. As a result, the toner or the like scraped off from the intermediate transfer belt 8 is electrically and mechanically collected on the brush portion of the fur brush 41 and further moved electrically to the collection roller 43.

  The rotation shafts 41 a and 43 a of the fur brush 41 and the collection roller 43 are rotatably supported by the bearing member 51, and the fur brush 41 can swing around the rotation shaft 43 a of the collection roller 43. Further, the rocking end side (rotating shaft 41a side) of the bearing member 51 is urged by the compression spring 49 in the upper right direction in FIG.

  The blade 45 contacts the collection roller 43 from the upstream side with respect to the rotation direction of the collection roller 43 (counter direction with respect to the moving direction of the surface of the collection roller 43) and scrapes off the toner collected by the collection roller 43 for collection. Clean the roller 43. The conveying spiral 47 is disposed in the toner accommodating portion 40 b of the housing 40, and conveys the toner scraped off from the collecting roller 43 by the blade 45 to a waste toner collecting container (not shown) outside the housing 40. .

  As shown in FIG. 5, a seal member 50 is disposed in the housing 40 so as to face the entire longitudinal direction of the collection roller 43. The seal member 50 is a sheet-like member made of polyurethane or the like, for example, and is in contact with the collection roller 43 with a predetermined contact pressure. The contact pressure of the seal member 50 needs to be set so that the toner adhering to the collection roller 43 is not scraped off, and the toner scraped off by the blade 45 does not face the collection roller 43 again.

  As described above, when the paper dust adhered on the intermediate transfer belt 8 adheres to the seal member 50 via the fur brush 41 and the collection roller 43, a gap is generated between the collection roller 43 and the seal member 50. Then, the toner or the like in the toner storage portion 40 b flows back to the opening 40 a side and accumulates on the seal member 50 or the bottom surface 40 c of the housing 40. Then, when the accumulated toner or the like reattaches to the fur brush 41 and moves onto the intermediate transfer belt 8, there is a possibility that toner drops may occur.

  In particular, when the color mode is changed from the color mode to the monochrome mode by the roller contact / separation mechanism 60, the tension applied to the intermediate transfer belt 8 is slightly released by separating the primary transfer rollers 6a to 6c from the intermediate transfer belt 8. As shown, the tension roller 11 moves in the direction approaching the fur brush 41 (the black arrow direction in FIG. 6). Accordingly, the fur brush 41 is pressed by the tension roller 11 and moves in a direction approaching the seal member 50 and the bottom surface 40c of the housing 40 against the urging force of the compression spring 49 (the white arrow direction in FIG. 6). The toner accumulated on the seal member 50 and the bottom surface 40 c of the housing 40 is collected by the fur brush 41. As a result, toner or the like is transferred from the fur brush 41 to the intermediate transfer belt 8, and after switching to the monochrome mode, toner drop or back-stain on the transfer paper occurs when the first sheet is printed.

  Therefore, in this embodiment, when the color mode is switched to the monochrome mode, the cleaning bias applied to the collection roller 43 is turned off while the area corresponding to the first monochrome print of the intermediate transfer belt 8 passes the belt cleaning unit 19. And A cleaning bias is applied when the rear end of the first monochrome print sheet passes the belt cleaning unit 19.

  FIG. 7 is a block diagram illustrating a control path of the image forming apparatus 100. It should be noted that since various control of each part of the apparatus is performed when the image forming apparatus 100 is used, the control path of the entire image forming apparatus 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 bias control circuit 61 is connected to the charging bias power source 62, the developing bias power source 63, the transfer bias power source 64, and the cleaning bias power source 65, and operates each of these power sources by an output signal from the control unit 90. In accordance with a control signal from the bias control circuit 61, each of the power sources is charged to the charging roller in the charging devices 2a to 2d, and the developing bias power source 63 to the toner supply roller and the developing roller in the developing devices 3a to 3d. The transfer bias power source 64 applies a predetermined bias to the primary transfer rollers 6 a to 6 d and the secondary transfer roller 9, and the cleaning bias power source 65 applies a predetermined bias to the collection roller 43 in the belt cleaning unit 19.

  The image input unit 66 is a receiving unit that receives image data transmitted from the personal computer or the like to the image forming apparatus 100. The image signal input from the image input unit 66 is converted into a digital signal and then sent to the temporary storage unit 94.

  The operation unit 70 is provided with a liquid crystal display unit 71 and LEDs 72 that indicate various states, and displays the state of the image forming apparatus 100 and displays the image forming status and the number of copies to be printed. Various settings of the image forming apparatus 100 are performed from a printer driver of a personal computer.

  In addition, the operation unit 70 includes a start button for instructing the user to start image formation, a stop / clear button used when the image formation is stopped, and various settings of the image forming apparatus 100 in a default state. A reset button or the like is provided for use.

  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 readable / writable storage unit, A plurality of (two in this case) that transmit a control signal to each device in the temporary storage unit 94, the counter 95, and the image forming apparatus 100 for storing image data and the like, and receive an input signal from the operation unit 50. The I / F (interface) 96 is provided.

  The ROM 92 stores a control program for the image forming apparatus 100, data necessary for control, and the like that are not changed during use of the image forming apparatus 100. The RAM 93 stores necessary data generated during the control of the image forming apparatus 100, data temporarily required for controlling the image forming apparatus 100, and the like. The temporary storage unit 94 temporarily stores the image signal input from the image input unit 66 and converted into a digital signal. The counter 95 counts the accumulated number of printed sheets.

  In addition, the control unit 90 transmits a control signal from the CPU 91 to the respective units and apparatuses in the image forming apparatus 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 5, the belt cleaning unit 19, the roller contact / separation mechanism 60, the bias control circuit 61, the image input unit 66, and the operation unit 70. Etc.

  FIG. 8 is a timing chart showing an example of the switching operation from the color mode to the monochrome mode in the image forming apparatus 100 of the present embodiment. FIG. 9 is a timing chart from the color mode to the monochrome mode of the image forming apparatus 100 of the present embodiment. It is a flowchart which shows switching control. A procedure for switching from the color mode to the monochrome mode in the image forming apparatus 100 of the present embodiment will be described using FIGS. 8 and 9 with reference to FIGS. 1 to 7 as necessary.

  A color printer (Ecosys P6040, manufactured by Kyocera Document Solutions) as shown in FIG. 1 is used as a test machine, and a urethane elastic layer is laminated on a base layer made of polyvinylidene fluoride (PVDF) as an intermediate transfer belt 8. Further, an elastic belt (manufactured by Okura Kogyo Co., Ltd.) on which a coat layer made of polytetrafluoroethylene (PTFE) was laminated was used.

  The belt cleaning unit 19 includes a fur brush 41 made of conductive acrylic (SA-7, manufactured by Toei Sangyo Co., Ltd.), a recovery roller 43 whose surface is anodized, polyurethane rubber (1577E, manufactured by Bando Chemical Co., Ltd.). No. 45, and a sealing member 50 of 0.05 mm thick thermoplastic polyurethane (manufactured by Seadam) lined with a 0.3 mm stainless steel foil. Further, the current flowing through the collection roller 43 during the cleaning of the intermediate transfer belt 8 was set to 30 μA.

  First, printing in the color mode (hereinafter referred to as color printing) is started by receiving a printing command from the personal computer (step S1). At this time, a cleaning bias is applied to the collection roller 43 of the belt cleaning unit 19. Next, the control unit 90 determines whether or not a command for switching to the monochrome mode has been received (step S2). If a command to switch to monochrome mode has not been received (No in step S2), color printing is continued.

  When the instruction to switch to the monochrome mode is received (Yes in Step S2), the control unit 90 transmits a control signal to the roller contact / separation mechanism 60 to separate the primary transfer rollers 6a to 6c from the photosensitive drums 1a to 1c. A three-color separation operation is performed (step S3). By the three-color separation operation, the tension of the intermediate transfer belt 8 is released and the tension roller 11 moves in the direction approaching the fur brush 41 (in the direction of the black arrow in FIG. 6), so that the fur brush 41 presses against the tension roller 11. Then, it moves in the direction approaching the seal member 50 and the bottom surface 40c of the housing 40 (the white arrow direction in FIG. 6).

  Next, the control unit 90 determines whether or not a portion corresponding to the rear end portion of the final image of color printing has passed through the belt cleaning unit 19 on the intermediate transfer belt 8 (step S4). Then, the cleaning bias is turned off at a timing (T1 in FIG. 8) when a portion corresponding to the rear end of the final image of color printing has passed the belt cleaning unit 19 (step S5). As a result, the toner accumulated in the housing 40 does not adhere to the fur brush 41.

  If the cleaning bias is turned off before the color mode is switched to the monochrome mode, that is, the three-color separation operation is completed, the toner remaining on the intermediate transfer belt 8 may not be sufficiently removed by color printing. Therefore, it is preferable that the timing when the cleaning bias is turned off is after the three-color separation operation is completed.

  Further, the control unit 90 determines whether or not a position corresponding to the rear end portion of the first image in monochrome mode (hereinafter referred to as monochrome printing) on the intermediate transfer belt 8 has passed through the belt cleaning unit 19. Judgment is made (step S6). Then, a cleaning bias is applied at a timing (T2 in FIG. 8) when a portion corresponding to the rear end of the first monochrome print image passes the belt cleaning unit 19 (step S7). As a result, toner or the like accumulated in the housing 40 adheres to the fur brush 41. The toner or the like adhering to the fur brush 41 is collected by the collecting roller 43, but a part of the toner or the like is on the intermediate transfer belt 8 at a portion corresponding to the interval between the first and second monochrome prints (between sheets). Transition.

  Thereafter, monochrome printing is started (step S8), and the control for switching from the color mode to the monochrome mode is terminated. The toner or the like transferred from the fur brush 41 onto the intermediate transfer belt 8 is subjected to a primary transfer roller 6d (photosensitive member) after a time t1 from the application of the cleaning bias, that is, immediately after the image of the first monochrome print is first transferred. It passes through the drum 1d). Here, the time t1 is a time required for the predetermined region of the intermediate transfer belt 8 to move the distance from the belt cleaning unit 19 to the primary transfer roller 6d.

  According to the above control, even when the fur brush 41 contacts the toner or the like accumulated in the belt cleaning unit 19 when switching from the color mode to the monochrome mode, it corresponds to the first monochrome print image of the intermediate transfer belt 8. The toner does not adhere to the fur brush 41 until the area to be passed passes. Then, by applying a cleaning bias at the timing when the region corresponding to the first image of monochrome printing passes, toner or the like is adhered between the first and second monochrome printing of the intermediate transfer belt 8. Thereby, it is possible to effectively suppress the occurrence of toner drop and back stain on the transfer paper P in the first monochrome printed image.

  In addition, it is possible to continuously apply a cleaning bias when switching from the color mode to the monochrome mode and collect the toner and the like accumulated in the belt cleaning unit 19 on the intermediate transfer belt 8, but in this case, monochrome Before starting printing, it is necessary to drive (age) the intermediate transfer belt 8 for a predetermined time to remove the collected toner and the like. According to the control of the present embodiment, since the aging operation of the intermediate transfer belt 8 is not required, it is possible to improve the image forming efficiency by collecting the accumulated toner and shortening the printing waiting time.

  Note that switching from the color mode to the monochrome mode is performed relatively frequently, and the toner deposited on the housing 40 and the seal member 50 adheres to the fur brush 41 at each switching. Therefore, the amount of toner transferred from the fur brush 41 to the intermediate transfer belt 8 is only within the range between the first and second monochrome prints (between sheets), and there is a possibility of affecting the second monochrome print image. Absent.

  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, in the above embodiment, the belt cleaning unit 19 including the fur brush 41 is illustrated, but the present invention can be similarly applied to a configuration using a cleaning roller instead of the fur brush 41.

  In the above embodiment, the cleaning bias applied to the collection roller 43 when switching from the color mode to the monochrome mode is turned OFF, and the cleaning bias is applied at the timing when the region corresponding to the first image of monochrome printing has passed. However, a bias having the same polarity as the toner may be applied to the collection roller 43 instead of turning the cleaning bias OFF.

  The present invention is not limited to the tandem type color printer as shown in FIG. 1, and can be applied to various image forming apparatuses using an intermediate transfer belt and its cleaning device, such as a color copying machine and a color composite machine. .

  The present invention is applicable to an image forming apparatus having a mechanism for removing residual toner on the surface of an intermediate transfer belt using a cleaning member. By utilizing the present invention, it is possible to provide an image forming apparatus capable of effectively preventing toner drop and backside contamination of a recording medium when switching from a color mode to a monochrome mode.

Pa to Pd Image forming section 1a to 1d Photosensitive drum (image carrier)
3a to 3d Developing device 6a to 6d Primary transfer roller 8 Intermediate transfer belt 9 Secondary transfer roller 19 Belt cleaning unit (belt cleaning device)
30 Intermediate transfer unit 40 Housing 41 Fur brush (cleaning member)
43 Collection roller 45 Blade 47 Conveying spiral 50 Seal member 51 Bearing member 60 Roller contact / separation mechanism 61 Bias control circuit (bias application device)
65 Cleaning bias power supply (bias application device)
90 control unit 100 image forming apparatus

Claims (4)

A plurality of image forming units for forming images of different colors;
An endless intermediate transfer belt that moves along the image forming unit and an image carrier disposed in each of the image forming units with the intermediate transfer belt interposed therebetween are formed on the image carrier. A plurality of primary transfer rollers for primary transfer of a toner image onto the intermediate transfer belt, a driving roller for rotating the intermediate transfer belt, and rotation driven by the intermediate transfer belt and a predetermined tension on the intermediate transfer belt An intermediate transfer unit comprising: a tension roller for applying a roller; and a roller contact / separation mechanism for reciprocating the primary transfer roller in a direction approaching or separating from the intermediate transfer belt;
A secondary transfer roller for secondary transfer of the toner image primarily transferred onto the intermediate transfer belt onto a recording medium;
A belt cleaning device for removing residual toner on the surface of the intermediate transfer belt;
A bias applying device for applying a bias to the belt cleaning device;
A control unit for controlling the intermediate transfer unit, the belt cleaning device, and the bias applying device;
In an image forming apparatus comprising:
The roller contact / separation mechanism includes a color mode in which all the primary transfer rollers are pressed against the image carrier with the intermediate transfer belt interposed therebetween, and only one primary transfer roller has a black color with the intermediate transfer belt interposed therebetween. It is possible to switch between a monochrome mode pressed against the image carrier disposed in the image forming unit that forms an image,
The belt cleaning device includes:
A housing in which an opening facing the intermediate transfer belt and a toner containing portion for storing toner removed from the surface of the intermediate transfer belt are formed;
A cleaning member disposed at a position facing the tension roller across the intermediate transfer belt;
A collection roller that electrically collects toner adhering to the cleaning member by applying a bias having a polarity opposite to that of the toner from the bias application device;
A seal member disposed oppositely over the entire longitudinal direction of the collection roller, and partitioning the toner storage portion and the opening;
Have
In the monochrome mode, the cleaning member is disposed at a position moved from the opening to the inside of the housing by the pressing force of the tension roller compared to the color mode.
When switching from the color mode to the monochrome mode during continuous printing, the control unit turns off the bias applied to the collection roller or sets the same polarity as the toner, and then performs the monochrome transfer mode in the intermediate transfer belt. An image forming apparatus, wherein a bias having a polarity opposite to that of the toner is applied to the collecting roller immediately after a position corresponding to a rear end portion of the first printed image of the first sheet passes through the belt cleaning device.   The control unit is required for the position corresponding to the rear end portion of the image of the final print in the color mode of the intermediate transfer belt to move the distance to the belt cleaning device after passing through the secondary transfer roller. The image forming apparatus according to claim 1, wherein a bias applied to the collection roller when the time has elapsed is turned off or has the same polarity as the toner.   The image forming apparatus according to claim 2, wherein the control unit turns off a bias applied to the collection roller after the switching from the color mode to the monochrome mode is completed or has the same polarity as the toner.   The image forming apparatus according to claim 1, wherein the intermediate transfer belt is formed by laminating a plurality of layers including an elastic layer.

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