JP2018010079A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming apparatus which can effectively prevent re-attachment of a toner removed from an intermediate transfer belt surface using a cleaning member to the intermediate transfer belt.SOLUTION: An image forming apparatus includes a plurality of image forming units, an intermediate transfer unit, a secondary transfer roller, a belt cleaning device and a control unit. The intermediate transfer unit includes an intermediate transfer belt, a plurality of primary transfer rollers, a drive roller, a tension roller and a roller contact/separation mechanism. The belt cleaning device includes a cleaning member which faces the tension roller with the intermediate transfer belt held therebetween. The control unit can execute a transfer toner recovery mode of recovering a toner accumulating in the vicinity of an opening of a housing by using the cleaning member and a recovery roller by driving the intermediate transfer belt and the belt cleaning device in a monochrome mode at the non-image formation.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 conveyance spiral side flows backward from the gap toward the cleaning brush and accumulates along the seal member. Then, when the accumulated toner is reattached to the cleaning brush and the toner reattached to the cleaning brush is transferred onto the intermediate transfer belt, there is a possibility that a so-called toner drop occurs and an image defect occurs.

  SUMMARY OF THE INVENTION In view of the above problems, an object of the present invention is to provide an image forming apparatus capable of effectively preventing re-deposition of toner removed from the surface of an intermediate transfer belt using a cleaning member to the intermediate transfer belt. .

  In order to achieve the above object, the 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, a control unit, An image forming apparatus. 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 control unit controls driving of the intermediate transfer unit and the belt cleaning 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 collection roller that collects toner adhering to the cleaning member, and a seal member that is disposed to face the entire length of the collection roller and that partitions the toner storage portion and the opening. Have. 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. The control unit can execute the transfer toner recovery mode in which the toner accumulated near the opening of the housing is recovered using the cleaning member and the recovery roller by driving the intermediate transfer belt and the belt cleaning device in monochrome mode during non-image formation. It is.

  According to the first configuration of the present invention, the toner or the like accumulated on the bottom surface of the seal member and the housing is collected by the cleaning member and the collection roller by executing the transfer toner collection mode. Accordingly, it is possible to effectively suppress the occurrence of toner drop due to the toner deposited on the bottom surface of the seal member or the housing being reattached to the cleaning member and further transferred onto the intermediate transfer belt.

1 is a schematic diagram showing an internal configuration of an image forming apparatus 100 according to a first embodiment of the present invention. Enlarged view of the vicinity of the image forming portion Pa in FIG. Side surface sectional drawing of the developing device 3a mounted in the image forming apparatus 100 of 1st Embodiment. Side sectional view of the intermediate transfer unit 30 mounted on the image forming apparatus 100 of the first embodiment. 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 operations in the developing toner recovery mode and the transfer toner recovery mode in the image forming apparatus 100 of the first embodiment. 6 is a flowchart showing an execution procedure of a developing toner recovery mode and a transfer toner recovery mode in the image forming apparatus 100 of the first embodiment. FIG. 3 is a block diagram showing a control path of an image forming apparatus 100 according to a second embodiment of the present invention. 7 is a flowchart showing an execution procedure of a developing toner recovery mode and a transfer toner recovery mode in the image forming apparatus 100 of the second 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 further rotate clockwise in FIG. An intermediate transfer belt 8 is provided adjacent to each of the image forming portions Pa to Pd.

  Each of the photosensitive drums 1a to 1d includes a base tube that is a support (conductive base) and a photosensitive layer formed on the surface of the base tube. In this embodiment, photosensitive drums 1a to 1d in which an organic photosensitive layer (OPC) is formed on the surface of an aluminum tube are used. 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 rotating direction (counterclockwise direction in FIG. 2). 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. The toner remaining on the surfaces of the photosensitive drums 1a to 1d after the primary transfer is removed by the cleaning blade 32 and the rubbing roller 33 of the cleaning devices 7a to 7d.

  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 discharged to the discharge tray 17 by the discharge roller pair 15 as it is (or after being distributed to the reverse conveyance path 18 by the branching unit 14 and the image is formed on both sides).

  FIG. 3 is a side sectional view of the developing device 3a mounted on the image forming apparatus 100 according to the first embodiment. 3 shows a state viewed from the back side of FIGS. 1 and 2, and the arrangement of each member in the developing device 3a is opposite to that in FIGS. Further, in the following description, the developing device 3a disposed in the image forming unit Pa is illustrated, but the configuration of the developing devices 3b to 3d disposed in the image forming units Pb to Pd is basically the same, and thus the description will be given. Omitted.

  As shown in FIG. 3, the developing device 3a includes a developing container (casing) 20 in which a two-component developer (hereinafter simply referred to as a developer) composed of toner and a magnetic carrier is stored. The partition wall 20a is divided into an agitating and conveying chamber 21 and a supply and conveying chamber 22. In the agitating / conveying chamber 21 and the supply / conveying chamber 22, the agitating / conveying screw 23 a and the supplying and conveying the toner (positively charged toner) supplied from the toner container 4 a (see FIG. 1) are mixed with the carrier and agitated and charged. Each screw 23b is rotatably arranged.

  In the developing container 20, a toner supply roller 24 (developer carrier) is disposed above the supply / conveying screw 23 b, and a developing roller 25 is disposed to face the toner supply roller 24 diagonally to the right. The developing roller 25 faces the photosensitive drum 1a (see FIG. 2) on the opening side (the right side in FIG. 3) of the developing container 20, and the toner supply roller 24 and the developing roller 25 are counterclockwise in FIG. Rotate to. In addition, a spike cutting blade 26 is attached to the developing container 20 along the longitudinal direction of the toner supply roller 24 (direction perpendicular to the paper surface of FIG. 3).

  The developer is agitated by the agitating / conveying screw 23a and the supply / conveying screw 23b, and circulates through the agitating / conveying chamber 21 and the supplying / conveying chamber 22 in the developing container 20 to charge the toner. It is conveyed to the roller 24. Then, a magnetic brush (not shown) is formed on the toner supply roller 24, and the thickness of the magnetic brush on the toner supply roller 24 is regulated by the earbrush blade 26, and then the toner supply roller 24 and the developing roller 25. A thin toner layer is formed on the developing roller 25 by a potential difference ΔV between Vmag (DC) applied to the toner supply roller 24 and Vslv (DC) applied to the developing roller 25 and a magnetic field.

  The toner thin layer formed on the developing roller 25 by contact with the magnetic brush on the toner supply roller 24 is conveyed to an opposing portion (opposing region) between the photosensitive drum 1 a and the developing roller 25 by the rotation of the developing roller 25. The Since Vslv (DC) and Vslv (AC) are applied to the developing roller 25, the toner flies due to a potential difference with the photosensitive drum 1a, and the electrostatic latent image on the photosensitive drum 1a is developed. .

  In the right side wall of the developing container 20 in FIG. 3, in the vicinity of the developing roller 25, a toner receiving and supporting member 27 having a triangular cross section protruding inside the developing container 20 is provided. As shown in FIG. 3, the toner receiving support member 27 is arranged along the longitudinal direction of the developing container 20 (direction perpendicular to the paper surface of FIG. 3). A wall portion that faces the developing roller 25 and is inclined downward from the developing roller 25 toward the toner supply roller 24 is formed. On the upper surface of the toner receiving support member 27, a toner receiving member 28 for receiving the toner that is peeled off from the developing roller 25 and dropped is attached along the longitudinal direction. A vibration generating device 29 is attached to a substantially central portion in the longitudinal direction of the toner receiving member 28. A vibration motor (not shown) is disposed inside the vibration generator 29, and generates vibration by driving the vibration motor. The vibration generated by the vibration generator 29 is transmitted to the toner receiving member 28.

  If the toner accumulated around the ear cutting blade 26 or the toner receiving support member 27 aggregates and adheres to the developing roller 25, the aggregated toner may move to the photosensitive drum 1a and cause image defects. Therefore, the image forming apparatus 100 according to the present embodiment supplies and conveys toner accumulated on the toner receiving member 28 by shaking the toner receiving member 28 in the developing devices 3a to 3d by the vibration generating device 29 during non-image formation. A developing toner recovery mode for recovering to the chamber 22 can be executed.

  FIG. 4 is a side sectional view of the intermediate transfer unit 30 mounted on the image forming apparatus 100 according to the first embodiment. 4 shows the intermediate transfer unit 30 as viewed from the back side in FIG. As shown in FIG. 4, 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 that are in contact with 1d, and a pressure switching roller 34. 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 is supported so that both ends of the rotation shafts of the primary transfer rollers 6a to 6d and the pressure switching roller 34 can be rotated and can be moved perpendicularly to the traveling direction of the intermediate transfer belt 8 (up and down direction in FIG. 4). A roller contact / separation mechanism 60 having a pair of support members (not shown) and a driving means (not shown) for reciprocating the press switching roller 34 in the vertical direction. 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 to a monochrome mode in which the photosensitive drum 1d is pressed against the photosensitive drum 1d via the intermediate transfer belt 8.

  Specifically, the roller contact / separation mechanism 60 moves the pressure switching roller 34 upward to move the primary transfer rollers 6a to 6d upward together with the intermediate transfer belt 8, and the primary transfer rollers 6a to 6c are moved to the photosensitive drum 1a. Separated from ~ 1c. Here, since the pressure switching roller 34 is disposed closer to the tension roller 11 than the primary transfer roller 6a, the lower surface of the intermediate transfer belt 8 (the contact surface with the photosensitive drums 1a to 1d) is a fulcrum on the drive roller 10 side. Swings up and down. Therefore, the distance between the intermediate transfer belt 8 and the photosensitive drums 1a to 1d is maximum on the photosensitive drum 1a side and minimum on the photosensitive drum 1d side.

  5 is an external perspective view of the belt cleaning unit 19 shown in FIG. 4, 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 the counter direction (counterclockwise direction in FIG. 6) with respect to the moving direction of the intermediate transfer belt 8 to thereby remove foreign matters such as toner and paper dust remaining on the intermediate transfer belt 8 (hereinafter, toner). 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. 6) while contacting the surface of the fur brush 41. A cleaning bias power supply 65 (see FIG. 8) is connected to the collection roller 43, and a cleaning bias having a polarity opposite to that of the toner (here, negative polarity) is applied when the intermediate transfer belt 8 is cleaned. The tension roller 11 is grounded (grounded) to the ground. 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. 6, the seal member 50 is disposed in the housing 40 so as to face the entire length direction of the collection roller 43 (direction perpendicular to the paper surface of FIG. 6). 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.

  Therefore, in the image forming apparatus 100 according to the present embodiment, the transfer toner collection mode for collecting the toner and the like accumulated on the sealing member 50 and the bottom surface 40c of the housing 40 using the fur brush 41 can be executed.

  Specifically, the primary transfer rollers 6a to 6c are switched to the monochrome mode in which the roller contact / separation mechanism 60 is separated from the photosensitive drums 1a to 1c. As a result, the tension applied to the intermediate transfer belt 8 from the primary transfer rollers 6a to 6d and the pressure switching roller 34 is slightly released, so that the tension roller 11 approaches the fur brush 41 as shown in FIG. 7 (FIG. 7). Move in the direction of the black arrow). Accordingly, the fur brush 41 is pressed against the tension roller 11, and the fur brush 41 approaches 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. 7). Therefore, the toner and the like accumulated on the sealing member 50 and the bottom surface 40c of the housing 40 are collected by the fur brush 41.

  FIG. 8 is a block diagram illustrating a control path of the image forming apparatus 100 according to the first embodiment. 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. Each of the power sources is controlled by a control signal from the bias control circuit 61, the charging bias power source 62 is applied to the charging rollers in the charging devices 2a to 2d, and the developing bias power source 63 is supplied to the toner supply roller 24 and the developing roller 25 in the developing devices 3a to 3d. The transfer bias power supply 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 supply 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 control signals to and receive input signals from the operation unit 70, such as a temporary storage unit 94 that stores image data and the like, a counter 95, and each device in the image forming apparatus 100. 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 RAM 93 (or ROM 92) also stores a threshold value for the number of printed sheets for determining the execution time of a toner collection mode described later. 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. 9 is a timing chart showing operations in the developing toner recovery mode and the transfer toner recovery mode in the image forming apparatus 100 of the first embodiment. 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 cleaning bias was applied to the recovery roller 43 by controlling the constant current so that the current flowing through the recovery roller 43 during cleaning of the intermediate transfer belt 8 was 30 μA.

  When the developing toner collecting mode is executed, first, driving of the color developing devices 3a to 3c and the black developing device 3d is started. In this embodiment, when the vibration generator 29 is driven, the toner supply roller 24 and the developing roller 25 are rotated (reversely rotated) in the opposite direction (clockwise direction in FIG. 3) to that during image formation.

  Next, the toner generated on the toner receiving member 37 is shaken off by operating the vibration generating device 29 after a time t1 (here, 0.4 seconds) from the start of driving of the developing devices 3a to 3d. The operation pattern of the vibration generator 29 is repeated for a predetermined number of cycles, with the operation of driving the vibration generator 29 for time t2 (drive period) and stopping for only time t3 (stop period) as one cycle. In this embodiment, t2 = 0.6 seconds and t3 = 0.2 seconds, and the time of one cycle (t2 + t3) is 0.8 seconds, and 6 cycles are repeated.

  Due to the vibration of the toner receiving member 28, the toner accumulated on the toner receiving member 28 slides down along the inclination of the toner receiving member 28 and freely falls into an area sandwiched between the toner receiving support member 27 and the toner supply roller 24. To do. Part of the toner dropped from the toner receiving member 28 adheres to the magnetic brush on the toner supply roller 24. A part of the remaining toner that has not adhered to the magnetic brush on the toner supply roller 24 is accumulated at the tip of the spike cutting blade 26, but is scraped off by the magnetic brush of the toner supply roller 24 that rotates in the reverse direction. At this time, by adjusting the magnetic force and the arrangement of the magnetic poles (regulatory poles) of the fixed magnet body facing the ear cutting blade 26 so that the ears of the magnetic brush formed on the toner supply roller 24 become longer, the ear cutting blade 26 is adjusted. The scraping effect of the toner accumulated on the tip of the toner increases.

  The toner adhering to the magnetic brush on the toner supply roller 24 rotates with the surface of the toner supply roller 24 and passes through the gap between the toner supply roller 24 and the earbrush blade 26, and is supplied to the toner at the same polarity portion of the fixed magnet body. After being peeled off from the roller 24, it is forcibly returned to the supply conveyance chamber 22.

  When the developing roller 25 and the toner supply roller 24 are rotated in the reverse direction, the developer in the developing container 20 overflows from the toner replenishing port, or the developer is biased in the developing container 20 to cause noise in the toner concentration detection sensor. May occur. Therefore, after the developing roller 25 and the toner supply roller 24 are rotated in the reverse direction, the developing roller 25 and the toner supply roller 24 are continuously rotated for a certain period of time in the same direction as the image formation (counterclockwise direction in FIG. 3) ( (Forward rotation) is preferable.

  In this embodiment, after the driving of the vibration generator 29 in the final cycle (sixth cycle in this case) is completed, the developing roller 25 and the toner supply roller 24 are turned on for a time t4 (= 0.5 seconds + 8 of the toner supply roller 24). The rotation is continued for only the rotation time of the circumference.

  When the transfer toner collection mode is executed, the pressure switching roller 34 is moved upward from the state where the four (four colors) primary transfer rollers 6a to 6d are pressed against the photosensitive drums 1a to 1d (color mode). The primary transfer rollers 6a to 6c are separated. By this separation operation, the tension of the intermediate transfer belt 8 is released and the tension roller 11 moves in a direction approaching the fur brush 41 (in the direction of the black arrow in FIG. 7), so that the fur brush 41 is pressed by the tension roller 11. It moves in the direction approaching the seal member 50 and the bottom surface 40c of the housing 40 (the direction of the white arrow in FIG. 7). In the case of this testing machine, the time t5 required for the separating operation of the primary transfer rollers 6a to 6c is 2 seconds.

  Next, the driving of the intermediate transfer belt 8 and the belt cleaning unit 19 is continued for a time t6 in a state where the three primary transfer rollers 6a to 6c are separated (monochrome mode). Since the cleaning bias applied to the collection roller 43 is ON, the toner deposited on the seal member 50 and the bottom surface 40 c of the housing 40 adheres to the fur brush 41 and is further collected from the fur brush 41 to the collection roller 43. At this time, the intermediate transfer belt 8 and the secondary transfer bias applied to the intermediate transfer belt 8 and the secondary transfer bias applied to the secondary transfer roller 9 have opposite polarities (the same polarity as the toner) at the time of image formation. Toner adhesion to the next transfer roller 9 can be suppressed. In the case of this testing machine, the time t6 is about 3.5 seconds.

  Thereafter, when the image to be formed is color, a pressing operation is performed to press the primary transfer rollers 6a to 6c against the photosensitive drums 1a to 1d in preparation for the next image formation. On the other hand, if the image to be formed is monochrome, no pressing operation is necessary.

  Even if the intermediate transfer bias has the same polarity as the toner, the toner may physically adhere to the intermediate transfer belt 8 or the reversely charged toner may adhere electrically. Therefore, the predetermined position of the intermediate transfer belt 8 moves from the belt cleaning unit 19 to the secondary transfer roller 9 during the pressing operation time t7 so that the toner attached to the intermediate transfer belt 8 does not affect the printing immediately after the pressing operation. It needs to be longer than the time to do. In the case of this testing machine, the distance from the belt cleaning unit 19 to the secondary transfer roller 9 is 438.8 mm, and the process speed is 30 sheets / min. Therefore, the intermediate transfer belt from the belt cleaning unit 19 to the secondary transfer roller 9 is used. The travel time of 8 is 2.37 seconds. Therefore, the time t7 is set to about 2.5 seconds with a slight margin. If the image to be formed is monochrome and no pressing operation is performed, printing may be started after elapse of time t7 (about 2.5 seconds).

  By executing the transfer toner recovery mode as described above, the occurrence of toner drop due to the reattachment of toner deposited on the bottom surface 40c and the seal member 50 to the intermediate transfer belt 8 is improved, but the transfer toner recovery mode is executed. The driving time of the photosensitive drum 1d during which the cleaning blade 32 (see FIG. 2) of the cleaning device 7d is pressed increases. As a result, the abrasion of the photosensitive layer on the surface of the photosensitive drum 1d becomes larger than that of the photosensitive drums 1a to 1c, and only the service life of the photosensitive drum 1d is shortened. Therefore, in order to extend the service life of the photosensitive drum 1d, the layer thickness (initial layer thickness) of the photosensitive drum 1d at the start of use is made thicker than that of the photosensitive drums 1a to 1c. preferable.

  The thickness of the photosensitive layer of the photosensitive drum 1d can be determined as follows. For example, the execution time of the transfer toner collection mode is 6.8 seconds, the execution timing of the transfer toner collection mode is every 100 sheets of color printing, and the service life (drum life) of the photosensitive drums 1a to 1d is 200k (200,000 sheets). Then, the transfer toner collection mode is executed 200,000 / 100 = 2,000 (times) throughout the service life, and the transfer toner collection mode is accumulated 6.8 × 2,000 = 1,600 (seconds). )

  Further, if the cumulative driving time of the photosensitive drums 1a to 1c through the service life is 342,800 seconds, the cumulative driving time of the photosensitive drum 1d is 342,800 + 13,600 = 356,400 (seconds), and the photosensitive drum The rate at which 1d is driven excessively is 13,600 / 342,800 × 100≈3.96 (%).

  From the above results, the initial thickness of the photosensitive layer of the photosensitive drum 1d may be 3.96% thicker than that of the photosensitive drums 1a to 1c. For example, if the initial layer thickness of the photosensitive layers of the photosensitive drums 1a to 1c is 36 μm, the initial layer thickness of the photosensitive layer of the photosensitive drum 1d is 36 × 1.0396 = 37.428 μm. Note that the above calculation method considers only wear due to excessive driving of the photosensitive drum 1d other than printing, and the photosensitive layer of the photosensitive drum 1d when the ratio of printing in monochrome mode (monochrome printing) is large. The wear of is not considered.

  Further, when printing in monochrome mode (monochrome printing) is executed, the tension of the intermediate transfer belt 8 is released and the fur brush 41 is pressed by the tension roller 11 and accumulated on the seal member 50 and the bottom surface 40c of the housing 40. Collect the toner. For this reason, it is not efficient to execute the transfer toner recovery mode immediately after monochrome printing is performed, and the wear of the photosensitive layer of the photosensitive drum 1d is promoted. Therefore, when the transfer toner recovery mode is executed according to the cumulative number of printed sheets counted by the counter 95, the count value of the counter 95 is reset by executing monochrome printing, and the transfer is performed for a predetermined period after the monochrome printing is executed. It is preferable not to execute the toner recovery mode.

  FIG. 10 is a flowchart illustrating an execution procedure of the developing toner recovery mode and the transfer toner recovery mode in the image forming apparatus 100 according to the first embodiment. The execution procedure of the transfer toner recovery mode and the development toner recovery mode in the image forming apparatus 100 of this embodiment will be described with reference to FIGS.

  When the printing operation is started by receiving a printing command from the personal computer (step S1), the control unit 90 starts counting up the number of printed sheets by the counter 95 (step S2). More specifically, both the vibration control counter and the belt separation control counter are counted up.

  Next, the control unit 90 determines whether or not monochrome printing has been executed (step S3). If monochrome printing has been executed (Yes in step S3), the count value of the belt separation control counter is reset (step S4). ). Note that the vibration control counter continues to count up.

  Next, the control unit 90 determines whether or not the printing is finished (step S5). If the printing is continued (No in step S5), the control unit 90 returns to step S2 and continues counting up. If printing has been completed (Yes in step S5), it is determined whether or not the belt separation control counter has reached a threshold value T (300 sheets in this case) (step S6). If the threshold value T has been reached (Yes in step S6), a control signal is transmitted from the control unit 90 to the vibration generator 29 and the roller contact / separation mechanism 50, and the developing toner recovery mode and transfer toner recovery shown in FIG. The mode is executed simultaneously (step S7). Thereafter, the vibration control counter and the belt separation control counter are reset (step S8), and the process ends.

  On the other hand, if the threshold value T has not been reached in step S6 (No in step S6), it is determined whether or not the vibration control counter has reached the threshold value S (100 sheets here) (step S9). When the threshold value S is reached (Yes in step S9), a control signal is transmitted from the control unit 90 to the vibration generator 29, and only the developing toner recovery mode shown in FIG. 9 is executed (step S10). When only the developing toner recovery mode is executed, it is only necessary to drive the developing devices 3a to 3d, and driving of the intermediate transfer belt 8 and the belt cleaning unit 19 and application of the intermediate transfer bias and the secondary transfer bias become unnecessary.

  Thereafter, the vibration control counter is reset (step S11), and the process ends. If the threshold value S has not been reached in step S7 (No in step S9), the process is terminated without executing any of the development toner collection mode and the transfer toner collection mode.

  According to the above control, the toner accumulated on the bottom surface 40c of the housing 40 and the seal member 50 is removed from the fur brush by releasing the pressing of the primary transfer rollers 6a to 6c and executing the transfer toner collecting mode every predetermined number of prints. It is collected by a collection roller 43 through 41. Accordingly, the toner deposited on the bottom surface 40c and the seal member 50 is prevented from moving onto the intermediate transfer belt 8, and the occurrence of toner dropping can be effectively suppressed.

  When the transfer toner recovery mode is performed, the development toner recovery mode in which the accumulated toner in the developing devices 3a to 3d is shaken off is also performed at the same time, thereby shortening the printing waiting time and improving the image forming efficiency. Here, the threshold T (300 sheets) of the belt separation control counter that determines the execution timing of the transfer toner collection mode is an integral multiple of the threshold S (100 sheets) of the vibration control counter that determines the execution timing of the development toner collection mode ( 3 times), the transfer toner recovery mode is always executed simultaneously with the development toner recovery mode, so that the print waiting time can be shortened and the driving time of the photosensitive drums 1a to 1d can be shortened. it can.

  Here, since the threshold T of the belt separation control counter is 300 sheets and the threshold S of the vibration control counter is 100 sheets, the transfer toner collection mode is executed every three development toner collection modes. However, the belt separation control counter is reset by the printing operation in the monochrome mode, and the threshold S of the number of printed sheets for executing the developing toner collecting mode varies depending on the internal temperature of the image forming apparatus 100, the number of continuous printed sheets, and the like. There are cases where the execution timing of the recovery mode and the development toner recovery mode do not match. In this case, as shown in FIG. 10, when the belt separation control counter reaches the threshold value T, the developing toner collection mode and the transfer toner collection mode are executed simultaneously, and the vibration control counter and the belt separation control counter are reset. Good.

  In addition, the threshold value T of the belt separation control counter varies depending on the printing rate, and the higher the printing rate, the larger the amount of toner collected by the belt cleaning unit 19, so the threshold value T becomes smaller. By inputting the threshold value T corresponding to the most frequently used printing rate from the operation unit 70, it is possible to set the optimal transfer toner recovery mode execution timing according to the use state.

  FIG. 11 is a block diagram showing a control path of the image forming apparatus 100 according to the second embodiment of the present invention. The image forming apparatus 100 according to the present embodiment includes a first counter 95a that counts the number of continuous prints and a second counter 95b that counts the cumulative number of prints including continuous printing and single-shot printing. The first counter 95 a includes a first vibration control counter that controls driving of the vibration generator 29 and a first belt separation control counter that controls separation of the intermediate transfer belt 8 by the roller contact / separation mechanism 60. The second counter 95 b includes a second vibration control counter that controls driving of the vibration generator 29 and a second belt separation control counter that controls separation of the intermediate transfer belt 8 by the roller contact / separation mechanism 60. Each counter can count up and reset the number of printed sheets separately. The controller 90 executes the transfer toner recovery mode and the development toner recovery mode at a predetermined timing during continuous printing or at the end of printing based on the number of prints counted by the first counter 95a and the second counter 95b. The configurations of other parts of the image forming apparatus 100 such as the developing devices 3a to 3d and the belt cleaning unit 19 are the same as those in the first embodiment.

  FIG. 12 is a flowchart illustrating an execution procedure of the developing toner recovery mode and the transfer toner recovery mode in the image forming apparatus 100 according to the second embodiment. The execution procedure of the transfer toner recovery mode and the development toner recovery mode in the image forming apparatus 100 of the present embodiment will be described with reference to FIGS. 1 to 7, 9, and 11 as necessary.

  When the printing operation is started by receiving a printing command from the personal computer (step S1), the control unit 90 starts counting up the number of printed sheets by the counter 95 (step S2). More specifically, both the first vibration control counter and the first belt separation control counter are counted up in the first counter 95a, and both the second vibration control counter and the second belt separation control counter are used in the second counter 95b. Count up.

  Next, the control unit 90 determines whether or not monochrome printing has been performed (step S3). If monochrome printing has been performed (Yes in step S3), the count values of the first and second belt separation control counters are determined. Reset (step S4). Note that the count-up of the first and second vibration control counters continues.

  Next, the control unit 90 determines whether or not the first belt separation control counter of the first counter 95a has reached the threshold value T1 (300 sheets here) (step S5). If the threshold value T1 has been reached (Yes in step S5), a control signal is transmitted from the control unit 90 to the vibration generator 29 and the roller contact / separation mechanism 50, and the developing toner recovery mode and transfer toner recovery shown in FIG. The mode is executed simultaneously (step S6). Thereafter, the first vibration control counter and the first belt separation control counter, and the second vibration control counter and the second belt separation control counter are reset (step S7).

  On the other hand, if the threshold value T1 has not been reached in step S5 (No in step S5), it is determined whether or not the first vibration control counter has reached the threshold value S1 (100 sheets here) (step S8). If the threshold value S1 has been reached (Yes in step S8), a control signal is transmitted from the control unit 90 to the vibration generator 29, and only the developing toner recovery mode shown in FIG. 9 is executed (step S9). When only the developing toner recovery mode is executed, it is only necessary to drive the developing devices 3a to 3d, and driving of the intermediate transfer belt 8 and the belt cleaning unit 19 and application of the intermediate transfer bias and the secondary transfer bias become unnecessary. Thereafter, the first vibration control counter and the second vibration control counter are reset (step S10).

  Next, the control unit 90 determines whether or not printing has been completed (step S11). If printing has continued (No in step S11), the process returns to step S2 to continue counting up. If printing has been completed (Yes in step S11), it is determined whether or not the second belt separation control counter of the second counter 95b has reached a threshold value T2 (here, 300 sheets) (step S12).

  If the threshold value T2 has been reached (Yes in step S12), a control signal is transmitted from the control unit 90 to the vibration generator 29 and the roller contact / separation mechanism 50, and the developing toner recovery mode and transfer toner recovery shown in FIG. The mode is executed simultaneously (step S13). Thereafter, the first vibration control counter and the first belt separation control counter, and the second vibration control counter and the second belt separation control counter are reset (step S14).

  On the other hand, if the threshold value T2 has not been reached in step S12 (No in step S12), it is determined whether or not the second vibration control counter has reached the threshold value S2 (here, 100 sheets) (step S15). If the threshold value S2 has been reached (Yes in step S15), a control signal is transmitted from the control unit 90 to the vibration generator 29, and only the developing toner recovery mode shown in FIG. 9 is executed (step S16). When only the developing toner recovery mode is executed, it is only necessary to drive the developing devices 3a to 3d, and driving of the intermediate transfer belt 8 and the belt cleaning unit 19 and application of the intermediate transfer bias and the secondary transfer bias become unnecessary.

  Thereafter, the first vibration control counter and the second vibration control counter are reset (step S17). If the threshold value S2 has not been reached in step S15 (No in step S15), the process is terminated without executing any of the development toner collection mode and the transfer toner collection mode.

  According to the above control, the transfer toner recovery mode is executed when the number of printed sheets exceeds the predetermined number after the completion of the printing operation, and when the predetermined number of continuous printing continues, the printing operation is performed even during continuous printing. Interrupt and execute the transfer toner recovery mode. As a result, when continuous printing of a large number of sheets continues, the transfer toner recovery mode is executed without waiting for the end of the printing operation, so that the occurrence of toner drop can be more effectively suppressed. Similarly to the first embodiment, when the transfer toner recovery mode is performed, the developing toner recovery mode is also performed at the same time, thereby shortening the printing waiting time and improving the image forming efficiency.

  Further, when printing in the monochrome mode is executed and the toner accumulated on the seal member 50 and the bottom surface 40c of the housing 40 is collected by the fur brush 41, the count value of the belt separation control counter is reset, and the transfer toner collection mode is set. Not executed. Accordingly, the unnecessary transfer toner collection mode is suppressed, so that the printing waiting time is shortened to improve the image forming efficiency, and the friction with the cleaning blade 32 and the rubbing roller 33 (see FIG. 2). It is also possible to suppress wear of the photosensitive layer of the photosensitive drum 1d.

  Here, the threshold values T1 and T2 of the first and second belt separation control counters are set to 300 sheets, and the threshold values S1 and S2 of the first and second vibration control counters are set to 100 sheets. The toner recovery mode is executed. However, the threshold values S1 and S2 for the number of printed sheets for executing the developing toner collecting mode vary depending on the in-machine temperature of the image forming apparatus 100, the number of continuous printed sheets, and the like. In some cases. Also in this case, as shown in FIG. 12, when the first and second belt separation control counters reach the threshold values T1 and T2, the development toner collection mode and the transfer toner collection mode are executed simultaneously, and the first and second toner collection modes are executed simultaneously. The vibration control counter and the first and second belt separation control counters may be reset.

  In addition, the present invention is not limited to the above embodiments, and various modifications can be made without departing from the spirit of the present invention. For example, in each of the above embodiments, the belt cleaning unit 19 including the fur brush 41 is illustrated, but the present invention can be similarly applied to a configuration in which a cleaning roller is used instead of the fur brush 41.

  In each of the above embodiments, the transfer toner collection mode is performed in synchronization with the development toner collection mode of the developing devices 3a to 3d. However, the present invention is not limited to this, and is synchronized with other controls of the image forming apparatus 100. You may make it perform. For example, as control executed by the image forming apparatus 100 during non-image formation, a cleaning mode for cleaning the light exit window 5a of the exposure apparatus 5, from the toner containers 4a to 4d to the developing device 3a immediately before the toner containers 4a to 4d are emptied. Toner having a toner supply mode for forcibly supplying toner to 3d, and a toner discharge mode for forcibly discharging the toner carried on the developing roller 25 in the developing devices 3a to 3d onto the photosensitive drums 1a to 1d. The collection mode can be performed in synchronization with at least one of the cleaning mode, the toner supply mode, and the toner discharge mode. In addition, the transfer toner recovery mode can be executed when a paper-free state in which the paper in the paper cassette 16 runs out occurs.

  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 the toner removed from the surface of the intermediate transfer belt using the cleaning member from being reattached to the intermediate transfer belt.

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)
29 Vibration generator 30 Intermediate transfer unit 34 Pressure switching roller 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)
64 Transfer bias power supply (bias application device)
90 control unit 95 counter (printing number counting unit)
95a First counter (first count section)
95b Second counter (second counter)
100 Image forming apparatus

Claims (11)

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 control unit that controls driving of the intermediate transfer unit and the belt cleaning 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 for collecting the toner adhering to the cleaning member;
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.
The control unit collects toner accumulated in the vicinity of the opening of the housing using the cleaning member and the collection roller by driving the intermediate transfer belt and the belt cleaning device in the monochrome mode during non-image formation. An image forming apparatus capable of executing a transfer toner recovery mode. A print number counting unit for counting the number of prints in the color mode;
The control unit executes the transfer toner recovery mode when the number of prints in the color mode counted by the print number counting unit reaches a predetermined number T after the previous execution of the transfer toner recovery mode. The image forming apparatus according to claim 1, wherein:   The controller executes the printing in the monochrome mode until the number of printed sheets in the color mode counted by the printed sheet counting section reaches a predetermined number T after the previous execution of the transfer toner collecting mode. The image forming apparatus according to claim 2, wherein the count value of the printed sheet count unit is reset. The printed sheet count unit has a first count unit that counts the number of continuously printed sheets, and a second count unit that counts the cumulative number of printed sheets including continuous printing and single-shot printing,
The controller is configured such that when the number of printed sheets counted by the first counting unit reaches a predetermined number T1 after the previous execution of the transfer toner collecting mode, or the number of printed sheets counted by the second counting unit is predetermined. 3. The transfer toner recovery mode is executed when the number T2 is reached, and the count values of the first count unit and the second count unit are reset after the transfer toner recovery mode is executed. The image forming apparatus described in 1.   The control unit counts the number of prints in the color mode counted by the first count unit after the execution of the transfer toner recovery mode last time until the predetermined number T1 is reached or by the second count unit. The count values of the first count unit and the second count unit are reset when printing in the monochrome mode is executed until the number of printed sheets in the color mode reaches a predetermined number T2. The image forming apparatus according to claim 4. The image carrier has a support and a photosensitive layer laminated on the surface of the support,
The image carrier disposed in the image forming unit that forms a black image has a greater thickness of the photosensitive layer than the image carrier disposed in the image forming unit that forms an image other than black. The image forming apparatus according to claim 1, wherein the image forming apparatus is an image forming apparatus.   The thickness of the photosensitive layer of the image carrier disposed in the image forming unit that forms a black image is determined based on the cumulative driving time in the monochrome mode during the durability period of the image carrier. The image forming apparatus according to claim 6. The image forming unit includes:
A toner receiving member that is disposed to face the image bearing member and has a developing roller that supplies toner to the image bearing member in a region facing the image bearing member, and a toner receiving surface that receives toner falling from the developing roller. A vibration generating device that vibrates the toner receiving member;
And a developing device for developing the electrostatic latent image formed on the image carrier,
A developing toner recovery mode in which the toner receiving member is vibrated by the vibration generating device during non-image formation to shake off the toner deposited on the toner receiving surface;
The image forming apparatus according to claim 2, wherein the control unit executes the transfer toner collection mode simultaneously with the development toner collection mode. An exposure apparatus for irradiating the image carrier with light to form an electrostatic latent image based on image information;
A toner storage container for storing toner to be replenished to the developing device;
A recording medium storage cassette for storing a recording medium on which the toner image on the intermediate transfer belt is secondarily transferred;
Further comprising
The image forming unit is disposed opposite to the image carrier, and includes a developing roller that supplies toner to the image carrier in a region facing the image carrier, and is formed on the image carrier. A developing device for developing an electrostatic latent image;
The control unit is configured to perform the transfer toner recovery mode, exposure cleaning for cleaning a light exit window of the exposure device, supply of toner from the toner container to the developing device, and forcing of toner from the developing roller to the image carrier. 9. The image formation according to claim 2, wherein the image forming is performed simultaneously with at least one of ejection and occurrence of a recording medium supply impossible state in which the recording medium in the recording medium accommodation cassette is exhausted. apparatus. A bias application device for applying a bias to the primary transfer roller and the secondary transfer roller;
10. The bias of the same polarity as the toner is applied to the primary transfer roller and the secondary transfer roller by the bias application device during execution of the toner recovery mode. The image forming apparatus described.   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.

Images