JP6520849B2 - Image forming device - Google Patents

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 reattachment of toner to the intermediate transfer belt.

  Conventionally, an endless intermediate transfer belt rotated in a predetermined direction and a plurality of image forming units provided along the intermediate transfer belt are provided, and toner images of respective colors are formed on the intermediate transfer belt by each image forming unit. An image forming apparatus of an intermediate transfer type is known in which secondary transfer is sequentially performed on the recording medium after primary transfer by sequentially overlapping.

  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 secondary transfer. When the intermediate transfer belt does not have an elastic layer, a blade system is employed in which the cleaning blade is pressed against the surface of the intermediate transfer belt to scrape the toner.

  On the other hand, when the intermediate transfer belt has an elastic layer, the cleaning brush for mechanically and electrically collecting the toner remaining on the surface of the intermediate transfer belt, the collection roller for collecting the toner from the cleaning brush, and the toner from the collection roller surface In many cases, a cleaning device provided with a blade for scraping the toner and a transport spiral for transporting the toner scraped off from the surface of the recovery roller to the waste toner recovery container is used.

  Further, various techniques for adjusting the cleaning conditions of the intermediate transfer belt are also proposed. For example, Patent Document 1 includes an adjustment mechanism for adjusting the contact conditions of the cleaning member and the intermediate transfer belt, and the monochrome mode and the color mode are provided. There is disclosed a technique of adjusting the contact condition of the cleaning member and the intermediate transfer belt to be a condition suitable for cleaning.

  Further, according to Patent Document 2, when the color mode is switched to the monochrome mode in order to prevent the back contamination of the recording material, the pressure contact of the primary transfer unit of each image forming unit to the intermediate transfer belt is temporarily released altogether. A technique is disclosed in which the primary transfer unit of the image forming unit where image formation is to be performed is crimped to shift to the monochrome mode.

JP, 2013-83676, A Unexamined-Japanese-Patent No. 2004-341399

  Some cleaning devices have a seal member that divides the inside of the housing into the cleaning brush side and the transport spiral side. The sealing member guides the toner scraped off the surface of the collection roller by the blade to the conveying spiral side by bringing the tip into contact with the collection roller on the upstream side of the blade that scrapes the toner from the surface of the collection roller, and the cleaning brush It does not go to the side (outside of the housing). Therefore, the seal member needs to be in contact at a substantially constant contact pressure not to scrape off the toner adhering to the collection roller over the entire axial direction of the collection roller.

  However, paper dust generated from a recording medium (paper) may adhere to the intermediate transfer belt, and paper dust may adhere to the seal member via the cleaning brush and the collection roller. As a result, a gap is generated between the collection roller and the seal member, and the toner on the transport spiral side flows back from the gap to the cleaning brush side and is accumulated along the seal member. Then, when the deposited toner reattaches to the cleaning brush and the toner attached again to the cleaning brush is transferred onto the intermediate transfer belt, there is a possibility that so-called toner drop may occur and an image failure may occur.

  SUMMARY OF THE INVENTION An object of the present invention is to provide an image forming apparatus capable of effectively preventing re-adhesion 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, according to a first configuration of the present invention, there are provided a plurality of image forming units forming images of different colors, an intermediate transfer unit, a secondary transfer roller, a belt cleaning device, and a control unit. An image forming apparatus comprising: The intermediate transfer unit is formed on the image carrier so as to be opposed to the endless intermediate transfer belt moving along the image forming unit and the image carrier disposed in each image forming unit with the intermediate transfer belt interposed therebetween. A plurality of primary transfer rollers for primarily transferring the formed toner image onto the intermediate transfer belt, a drive roller for rotating the intermediate transfer belt, and the intermediate transfer belt to rotate and apply a predetermined tension to the intermediate transfer belt It has a tension roller, and a roller contact / separation mechanism that reciprocates the primary transfer roller in a direction toward or away 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 the driving of the intermediate transfer unit and the belt cleaning device. The roller contact / separation mechanism forms an image in which only one primary transfer roller forms a black image by sandwiching the intermediate transfer belt, and a color mode in which all the primary transfer rollers are in pressure contact with the image carrier across the intermediate transfer belt. It is possible to switch between a monochrome mode in which the image bearing member disposed in the unit is in pressure contact. The belt cleaning device opposes the tension roller across the intermediate transfer belt, with a housing formed with an opening facing the intermediate transfer belt and a toner storage unit for storing toner removed from the surface of the intermediate transfer belt. A cleaning member disposed at a position, a recovery roller for recovering the toner attached to the cleaning member, and a seal member disposed opposite to each other over the entire longitudinal direction of the recovery roller to separate the toner storage portion from the opening portion Have. The cleaning member is disposed at a position moved inward of the housing from the opening as compared to the color mode by the pressing force of the tension roller in the monochrome mode. The control unit can execute a transfer toner recovery mode in which toner accumulated in the vicinity of the opening of the housing is recovered by 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, by executing the transfer toner recovery mode, toner and the like deposited on the bottom surface of the seal member and the housing are recovered by the cleaning member and the recovery roller. As a result, the toner deposited on the bottom surface of the sealing member or the housing reattaches to the cleaning member, and the occurrence of toner drop due to the transfer onto the intermediate transfer belt can be effectively suppressed.

A schematic view showing an internal configuration of an image forming apparatus 100 according to a first embodiment of the present invention Enlarged view in the vicinity of the image forming portion Pa in FIG. 1 Side cross-sectional view of developing device 3a mounted on image forming apparatus 100 according to the first embodiment Side cross-sectional view of the intermediate transfer unit 30 mounted on the image forming apparatus 100 according to the first embodiment External perspective view of the belt cleaning unit 19 shown in FIG. 4 Side cross-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 accompanied by the pressure release of the primary transfer rollers 6a to 6d Block diagram showing control path of image forming apparatus 100 Timing chart showing operations of a developing toner recovery mode and a transfer toner recovery mode in the image forming apparatus 100 of the first embodiment A flowchart showing an execution procedure of the developing toner recovery mode and the transfer toner recovery mode in the image forming apparatus 100 of the first embodiment Block diagram showing a control path of the image forming apparatus 100 according to the second embodiment of the present invention A flowchart showing an execution procedure of the developing toner recovery mode and the 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 view showing 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 portion Pa in FIG.

  The image forming apparatus 100 shown in FIG. 1 is a so-called tandem type 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 disposed in order from the upstream side in the transport direction (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 formed by the respective steps of charging, exposure, development and transfer. And black images are sequentially formed.

  Photosensitive drums 1a, 1b, 1c and 1d for carrying visible images (toner images) of respective colors are disposed in these image forming portions Pa to Pd, and further rotate clockwise in FIG. An intermediate transfer belt 8 is provided adjacent to each of the image forming portions Pa to Pd.

  The photosensitive drums 1a to 1d are each composed of a raw tube which is a support (conductive base) and a photosensitive layer formed on the surface of the raw tube. In the present embodiment, the photosensitive drums 1a to 1d in which the organic photosensitive layer (OPC) is formed on the surface of the raw tube made of aluminum are used. The transfer sheet P to which the toner image is transferred is accommodated in the sheet cassette 16 at the lower portion of the main body of the image forming apparatus 100, and conveyed to the secondary transfer roller 9 through the sheet feeding roller 12a and the resist roller pair 12b. . The intermediate transfer belt 8 mainly uses a seamless belt.

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

  Next, an image forming procedure in the image forming apparatus 100 will be described. When an image formation start 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 beam (laser light) emitted from the light emission window 5a of the exposure device 5, and electrostatic latents corresponding to image signals are formed on the respective photosensitive drums 1a to 1d. Form an image. The developing devices 3a to 3d are filled with toners of respective colors of cyan, magenta, yellow and black by a predetermined amount. When the ratio of the toner in the two-component developer filled in the developing devices 3a to 3d falls below a specified value due to the formation of toner images described later, the developing devices 3a to 3d from the toner containers 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 is electrostatically attached, so that the electrostatic latent image formed by the exposure from the exposure device 5 is formed. The toner image is formed.

  Then, an electric field is applied between the primary transfer rollers 6a to 6d and the photosensitive drums 1a to 1d at a predetermined transfer voltage by the primary transfer rollers 6a to 6d, and cyan, magenta, yellow, and the like on the photosensitive drums 1a to 1d. The 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 intermediate transfer belt 8 starts to rotate clockwise with the rotation of drive roller 10 by a belt drive motor (not shown), transfer sheet P is adjacent to intermediate transfer belt 8 at a predetermined timing from registration roller 12 b. The full-color image is transferred by being conveyed to the provided secondary transfer roller 9. The transfer sheet P to which the toner image has been transferred is conveyed to the fixing unit 13. The toner remaining on the surface of the intermediate transfer belt 8 is removed by a belt cleaning unit 19.

  The transfer paper P conveyed to the fixing unit 13 is heated and pressed by the fixing roller pair 13a, the toner image is fixed on the surface of the transfer paper P, and a predetermined full-color image is formed. The transfer paper P on which the full color image is formed is discharged as it is (or after it is distributed to the reverse conveying path 18 by the branch portion 14 and the image is formed on both sides) by the discharge roller pair 15 to the discharge tray 17.

  FIG. 3 is a side cross-sectional view of the developing device 3a mounted on the image forming apparatus 100 of the first embodiment. Note that FIG. 3 shows a state as viewed from the back side of FIGS. 1 and 2, and the arrangement of each member in the developing device 3a is reversed from that in FIGS. Further, although the following description exemplifies the developing device 3a disposed in the image forming portion Pa, the configurations of the developing devices 3b to 3d disposed in the image forming portions Pb to Pd are basically the same. I omit it.

  As shown in FIG. 3, the developing device 3 a includes a developing container (casing) 20 in which a two-component developer (hereinafter, simply referred to as a developer) composed of toner and magnetic carrier is stored. The stirring and transfer chamber 21 and the supply and transfer chamber 22 are divided by the partition wall 20a. In the stirring and conveying chamber 21 and the feeding and conveying chamber 22, a stirring and conveying screw 23a for charging and charging the toner (positively charged toner) supplied from the toner container 4a (see FIG. 1) is mixed with the carrier and supplied and conveyed. The screws 23 b are rotatably disposed.

  A toner supply roller 24 (developer carrier) is disposed above the supply conveyance screw 23 b in the development container 20, and a development roller 25 is disposed to face the upper right of the toner supply roller 24. The developing roller 25 faces the photosensitive drum 1a (see FIG. 2) on the opening side (right side in FIG. 3) of the developing container 20, and the toner supply roller 24 and the developing roller 25 rotate counterclockwise in FIG. To rotate. In addition, a brush cutter blade 26 is attached to the developing container 20 along the longitudinal direction of the toner supply roller 24 (the direction perpendicular to the paper surface of FIG. 3).

  The developer is stirred by the stirring and conveying screw 23a and the feeding and conveying screw 23b, and is circulated in the stirring and conveying chamber 21 and the feeding and 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 magnetic brush on the toner supply roller 24 is regulated in layer thickness by the blade cutting blade 26, and then the toner supply roller 24 and the developing roller 25 are The toner thin 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 conveyed to the opposite portion.

  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 the facing portion (facing region) of the photosensitive drum 1 a and the developing roller 25 by the rotation of the developing roller 25 Ru. Since Vslv (DC) and Vslv (AC) are applied to the developing roller 25, the toner flies due to the potential difference with the photosensitive drum 1a, and the electrostatic latent image on the photosensitive drum 1a is developed. .

  In the vicinity of the developing roller 25 on the right side wall in FIG. 3 of the developing container 20, a toner receiving and supporting member 27 having a triangular cross-sectional shape which protrudes to the inside of the developing container 20 is provided. As shown in FIG. 3, the toner receiving and supporting member 27 is disposed along the longitudinal direction of the developing container 20 (the direction perpendicular to the sheet of FIG. 3), and the upper surface of the toner receiving and supporting member 27 A wall portion facing the developing roller 25 and inclined downward from the developing roller 25 toward the toner supply roller 24 is configured. A toner receiving member 28 is attached to the upper surface of the toner receiving and supporting member 27 along the longitudinal direction to receive toner that is pulled off from the developing roller 25 and falls. A vibration generator 29 is attached to a substantially central portion of the toner receiving member 28 in the longitudinal direction. 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.

  When the toner accumulated around the blade cutting blade 26 and the toner receiving and supporting member 27 coagulates and adheres to the developing roller 25, the coagulated toner may be transferred to the photosensitive drum 1a and an image failure may occur. Therefore, in the image forming apparatus 100 of the present embodiment, the toner receiving member 28 in the developing devices 3a to 3d is vibrated by the vibration generating device 29 at the time of non-image formation to shake the toner deposited on the toner receiving member 28 It is possible to execute a developing toner recovery mode for recovering into the chamber 22.

  FIG. 4 is a side cross-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 rear side of FIG. As shown in FIG. 4, the intermediate transfer unit 30 includes the intermediate transfer belt 8 wound around the downstream drive roller 10 and the upstream tension roller 11, and the photosensitive drums 1 a through the intermediate transfer belt 8. It has primary transfer rollers 6 a to 6 d in contact with 1 d and a pressure switching roller 34. Further, at a position facing the tension roller 11, a belt cleaning unit 19 for removing the toner remaining on the surface of the intermediate transfer belt 8 is disposed. The detailed configuration of the belt cleaning unit 19 will be described later.

  The intermediate transfer unit 30 is capable of rotating both ends of the rotation shafts of the primary transfer rollers 6a to 6d and the pressure switching roller 34, and movably vertically (vertically in FIG. 4) with respect to the traveling direction of the intermediate transfer belt 8. The roller contact / separation mechanism 60 has a pair of supporting members (not shown) and a drive means (not shown) for reciprocating the pressing switching roller 34 in the vertical direction. The roller contact / separation mechanism 60 only has a color mode in which the four primary transfer rollers 6a to 6d are in pressure contact with the photosensitive drums 1a to 1d (see FIG. 1) via the intermediate transfer belt 8, and only the primary transfer roller 6d. The mode can be switched to the monochrome mode in which the photosensitive drum 1 d is in pressure contact with the intermediate transfer belt 8.

  Specifically, the roller contact / separation mechanism 60 moves the pressing switching roller 34 upward to move the primary transfer rollers 6a to 6d together with the intermediate transfer belt 8 to move the primary transfer rollers 6a to 6c to the photosensitive drum 1a. Separate 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 (contact surface with the photosensitive drums 1a to 1d) is fulcrum on the drive roller 10 side. Swing up and down as. Therefore, the distance between the intermediate transfer belt 8 and the photosensitive drums 1a to 1d is maximized on the photosensitive drum 1a side and is minimized 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 an internal configuration of the belt cleaning unit 19. As shown in FIG. The belt cleaning unit 19 includes a fur brush 41, a recovery roller 43, a blade 45, and a transport spiral 47 in the housing 40, and the fur brush 41, the recovery roller 43, and the transport spiral 47 are cleaned at one end of the housing 40. A drive input gear train 48 is disposed for inputting a drive force from a drive motor (not shown).

  The fur brush 41 is disposed opposite to the tension roller 11 via the intermediate transfer belt 8 on the side of the opening 40 a of the housing 40. The fur brush 41 rotates in the counter direction (counterclockwise direction in FIG. 6) with respect to the movement direction of the intermediate transfer belt 8 to remove foreign matters such as toner and paper dust remaining on the intermediate transfer belt 8 (hereinafter referred to as toner Scrape etc). The brush portion of the fur brush 41 in contact with the collection roller 43 is formed of conductive fibers having a resistance value of about 1 to 900 MΩ.

  The collection roller 43 rotates in the opposite direction (clockwise direction in FIG. 6) to the fur brush 41 while contacting the surface of the fur brush 41, thereby collecting toner and the like attached to the fur brush 41. A cleaning bias power supply 65 (see FIG. 8) is connected to the collection roller 43, and a cleaning bias of the opposite polarity (here, negative polarity) to the toner is applied when the intermediate transfer belt 8 is cleaned. Further, the tension roller 11 is grounded (grounded) to the ground. As a result, toner and the like scraped off the intermediate transfer belt 8 are electrically and mechanically collected by the brush portion of the fur brush 41, and further electrically moved 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 swinging end side (the rotation shaft 41 a side) of the bearing member 51 is urged in the upper right direction in FIG. 6 by the compression spring 49.

  The blade 45 contacts the collection roller 43 from the upstream side (the counter direction with respect to the movement direction of the surface of the collection roller 43) with respect to the rotation direction of the collection roller 43 and scrapes off the toner etc. collected by the collection roller 43 Clean the roller 43. The transport spiral 47 is disposed in the toner storage portion 40b of the housing 40, and transports the toner scraped off by the blade 45 from the recovery roller 43 to a waste toner recovery container (not shown) outside the housing 40. .

  As shown in FIG. 6, in the housing 40, the seal member 50 is disposed to face the entire area in the longitudinal direction of the recovery roller 43 (the direction perpendicular to the sheet of FIG. 6). The seal member 50 is a sheet-like member formed of, for example, polyurethane or the like, and is in contact with the collection roller 43 at a predetermined contact pressure. The contact pressure of the seal member 50 needs to be set so that the toner or the like scraped off by the blade 45 does not go toward the recovery roller 43 again without scraping off the toner adhering to the recovery roller 43.

  As described above, when the paper dust attached to the intermediate transfer belt 8 adheres to the seal member 50 via the fur brush 41 and the recovery roller 43, a gap is generated between the recovery roller 43 and the seal member 50. The toner or the like in the toner storage portion 40 b flows back to the opening 40 a side and is deposited on the seal member 50 and the bottom surface 40 c of the housing 40. Then, when the deposited toner and the like reattach to the fur brush 41 and transfer onto the intermediate transfer belt 8, there is a possibility that toner may be dropped.

  Therefore, in the image forming apparatus 100 according to the present embodiment, it is possible to execute a transfer toner recovery mode in which toner and the like deposited on the seal member 50 and the bottom surface 40c of the housing 40 are recovered using the fur brush 41.

  Specifically, the roller contact / separation mechanism 60 switches the primary transfer rollers 6a to 6c to the monochrome mode in which the primary transfer rollers 6a to 6c are 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. Move in the direction of the black arrow). Along with this, 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 biasing force of the compression spring 49 (the direction of the white arrow in FIG. 7). The toner and the like deposited on the seal member 50 and the bottom surface 40 c of the housing 40 are collected by the fur brush 41.

  FIG. 8 is a block diagram showing a control path of the image forming apparatus 100 of the first embodiment. In addition, since various controls of each part of the apparatus are performed when using the image forming apparatus 100, the control path of the entire image forming apparatus 100 is complicated. Therefore, the parts of the control path that are necessary for the implementation of the present invention will be mainly described here.

  The bias control circuit 61 is connected to the charging bias power supply 62, the developing bias power supply 63, the transfer bias power supply 64, and the cleaning bias power supply 65, and operates each of these power supplies in response to an output signal from the control unit 90. The respective power supplies are controlled by a control signal from the bias control circuit 61, the charging bias power supply 62 is applied to the charging rollers in the charging devices 2a to 2d, and the developing bias power supply 63 is applied to the toner supply roller 24 and the developing roller 25 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 indicating various states, to indicate the state of the image forming apparatus 100, and to display the image formation state and the number of print copies. Various settings of the image forming apparatus 100 are performed from a printer driver of a personal computer.

  In addition, in the operation unit 70, a start button instructed by the user to start image formation, a stop / clear button used when canceling the image formation, etc., and various settings of the image forming apparatus 100 are defaulted. The reset button etc. which are used for are provided.

  The control unit 90 includes a central processing unit (CPU) 91 as a central processing unit, a read only memory (ROM) 92 as a read only storage unit, a random access memory (RAM) 93 as a read / write storage unit, A temporary storage unit 94 for storing image data etc., a counter 95, and a plurality (two in this case) for transmitting control signals to each device in the image forming apparatus 100 and receiving input signals from the operation unit 70. At least an I / F (interface) 96.

  The ROM 92 stores a control program for the image forming apparatus 100, data necessary for control, and other data that can not be changed during use of the image forming apparatus 100. The RAM 93 stores necessary data generated during control of the image forming apparatus 100, data temporarily required to control the image forming apparatus 100, and the like. The RAM 93 (or the ROM 92) also stores a threshold for the number of printed sheets for determining the execution time of the 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 accumulates and counts the number of printed sheets.

  Further, the control unit 90 transmits a control signal from the CPU 91 to each part and apparatus in the image forming apparatus 100 through the I / F 96. Further, each portion, a signal indicating the state from the device or an input signal is transmitted to the CPU 91 through the I / F 96. 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 of the developing toner recovery mode and the transfer toner recovery mode in the image forming apparatus 100 according to the first embodiment. In addition, using a color printer (Ecosys P 6040, manufactured by KYOCERA Document Solutions Inc.) as shown in FIG. 1 as a testing machine, a urethane elastic layer is laminated on a polyvinylidene fluoride (PVDF) base layer as an intermediate transfer belt 8. Further, an elastic belt (manufactured by Okura Kogyo Co., Ltd.) in which a coat layer made of polytetrafluoroethylene (PTFE) was further laminated was used.

  The belt cleaning unit 19 includes a fur brush 41 (SA-7, manufactured by Toei Sangyo Co., Ltd.) made of conductive acrylic, a recovery roller 43 whose surface is anodized, and a polyurethane rubber (1577 E, manufactured by Bando Chemical Industries, Ltd.) And a sealing member 50 of thermoplastic polyurethane (made by Shidam Co., Ltd.) with a thickness of 0.05 mm lined with 0.3 mm stainless steel foil. In addition, a cleaning bias was applied to the collection roller 43 by performing constant current control so that the current flowing to the collection roller 43 was 30 μA at the time of cleaning of the intermediate transfer belt 8.

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

  Next, the toner generated on the toner receiving member 37 is shaken off by operating the vibration generator 29 after 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 such that the vibration generator 29 is driven for a time t2 (driving period) and stopped for a time t3 (stop period) as one cycle, and is repeated for a predetermined number of cycles. In this embodiment, t2 = 0.6 seconds, t3 = 0.2 seconds, and one cycle (t2 + t3) is repeated for six cycles at 0.8 seconds.

  Due to the vibration of the toner receiving member 28, the toner deposited on the toner receiving member 28 slides downward along the slope of the toner receiving member 28 and freely falls to the area sandwiched between the toner receiving support member 27 and the toner supply roller 24. Do. A part of the toner dropped from the toner receiving member 28 adheres to the magnetic brush on the toner supply roller 24. A portion of the remaining toner that did not adhere to the magnetic brush on the toner supply roller 24 is deposited on the tip of the spike blade 26 but scraped off by the magnetic brush of the counter-rotating toner supply roller 24. At this time, the ear cutting blade 26 is adjusted by adjusting the magnetic force and the arrangement of the magnetic poles (regulating poles) of the fixed magnet facing the ear cutting blade 26 so that the spikes of the magnetic brush formed on the toner supply roller 24 become long. The scraping effect of the toner accumulated on the tip of the

  The toner adhering to the magnetic brush on the toner supply roller 24 rotates along the surface of the toner supply roller 24, passes through the gap between the toner supply roller 24 and the blade cutting blade 26, and supplies the toner at the same polarity part of the fixed magnet body After being separated from the roller 24, it is forcibly returned to the feeding and conveying chamber 22.

  When the developing roller 25 and the toner supplying roller 24 are reversely rotated, the developer in the developing container 20 overflows from the toner replenishing port, or the developing agent is biased in the developing container 20, and the noise of the toner concentration detection sensor It may occur. Therefore, after the developing roller 25 and the toner supply roller 24 are reversely rotated, the developing roller 25 and the toner supply roller 24 are rotated in the same direction (the counterclockwise direction in FIG. It is preferable to make it forward rotate.

  In the present embodiment, after driving of the final cycle (the sixth cycle here) of the vibration generating device 29 is completed, the developing roller 25 and the toner supply roller 24 are operated for a time t4 (= 0.5 seconds + eight of the toner supply roller 24). The forward rotation is continued only for the rotation time).

  When executing the transfer toner recovery mode, the pressure switching roller 34 is moved upward from the state (color mode) in which the four (four-color) primary transfer rollers 6a to 6d are pressed by the photosensitive drums 1a to 1d. A separation operation of the primary transfer rollers 6a to 6c is performed. By this separation operation, the tension of the intermediate transfer belt 8 is released, and the tension roller 11 moves in the direction in which the tension roller 11 approaches the fur brush 41 (the direction of the black arrow in FIG. 7). It moves in the direction approaching the sealing 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 test machine, the time t5 required for the separation operation of the primary transfer rollers 6a to 6c is 2 seconds.

  Next, driving of the intermediate transfer belt 8 and the belt cleaning unit 19 is continued for a time t6 in a state (monochrome mode) in which the three primary transfer rollers 6a to 6c are separated. 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, by setting the intermediate transfer bias applied to the intermediate transfer belt 8 and the secondary transfer bias applied to the secondary transfer roller 9 to the reverse polarity (the same polarity as that of the toner) at the time of image formation, the intermediate transfer belt 8 and the second transfer The adhesion of toner to the next transfer roller 9 can be suppressed. In the case of this tester, time t6 is about 3.5 seconds.

  Thereafter, when the image to be formed is a color, a pressing operation is performed to press the primary transfer rollers 6a to 6c to the photosensitive drums 1a to 1d in preparation for the next image formation. On the other hand, when the image to be formed is monochrome, the pressing operation is unnecessary.

  Even if the intermediate transfer bias has the same polarity as that of the toner, the toner may be physically attached to the intermediate transfer belt 8 or the oppositely charged toner may be electrically attached. Therefore, in the pressing operation time t7, the predetermined position of the intermediate transfer belt 8 moves from the belt cleaning unit 19 to the secondary transfer roller 9 so that the toner attached to the intermediate transfer belt 8 does not affect the printing immediately after the pressing operation. It should be longer than the time you In the case of this test machine, since 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 / minute, the intermediate transfer belt from the belt cleaning unit 19 to the secondary transfer roller 9 The movement time of 8 is 2.37 seconds. Therefore, time t7 is about 2.5 seconds with some allowance. When the image to be formed is monochrome and the pressing operation is not performed, the printing may be started after the time t7 (about 2.5 seconds) has elapsed.

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

  How thick the photosensitive layer of the photosensitive drum 1d is to be made 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 life time (drum life) of the photosensitive drums 1a to 1d is 200 k (200,000 sheets). Assuming that the number of times of execution of the transfer toner recovery mode through the lifetime is 200,000 / 100 = 2,000 (times), the cumulative execution time of the transfer toner recovery mode is 6.8 × 2,000 = 13,600 (seconds). ).

  Also, assuming that the cumulative driving time of the photosensitive drums 1a to 1c throughout the lifetime 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 1d is The rate at which 1d is driven extra is 13,600 / 342, 800 × 100 ≒ 3.96 (%).

  From the above results, the initial layer thickness of the photosensitive layer of the photosensitive drum 1d may be made 3.96% thicker than that of the photosensitive drums 1a to 1c. For example, when 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. The above calculation method takes into consideration only the wear due to excessive driving of the photosensitive drum 1 d other than printing, and the photosensitive layer of the photosensitive drum 1 d when the ratio of printing (monochrome printing) in monochrome mode is high. Wear is not considered.

  When printing in monochrome mode (monochrome printing) is performed, the tension of the intermediate transfer belt 8 is released, and the fur brush 41 is pressed against the tension roller 11 and deposited on the seal member 50 and the bottom surface 40 c of the housing 40. Collect the toner. Therefore, it is not efficient to execute the transfer toner recovery mode immediately after the monochrome printing is performed, and further, the abrasion of the photosensitive layer of the photosensitive drum 1d is promoted. Therefore, when the transfer toner collection 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 transfer is performed for a predetermined period after monochrome printing is performed. Preferably, the toner recovery mode is not performed.

  FIG. 10 is a flowchart showing the procedure of executing the developing toner recovery mode and the transfer toner recovery mode in the image forming apparatus 100 according to the first embodiment. An 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 9 as necessary.

  When the printing operation is started by receiving the 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 monochrome printing is performed (step S3), and when monochrome printing is performed (Yes in step S3), resets the count value of the belt separation control counter (step S4). ). The count up of the vibration control counter continues.

  Next, the control unit 90 determines whether or not printing is completed (step S5), and if printing is continued (No in step S5), the process returns to step S2 and continues counting up. If the printing is completed (Yes in step S5), it is determined whether the belt separation control counter has reached a threshold T (300 sheets in this case) (step S6). When the threshold value T is 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 the transfer toner recovery shown in FIG. The mode is simultaneously executed (step S7). Thereafter, the vibration control counter and the belt separation control counter are reset (step S8), and the process is ended.

  On the other hand, if the threshold value T is not reached in step S6 (No in step S6), it is determined whether the vibration control counter has reached the threshold value S (100 sheets in this case) (step S9). If the threshold value S is reached (Yes in step S9), a control signal is transmitted from the control unit 90 to the vibration generating device 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, only the driving of the developing devices 3a to 3d is sufficient, and the driving of the intermediate transfer belt 8 and the belt cleaning unit 19 and the 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 is ended. When the threshold value S is not reached in step S7 (No in step S9), the processing is ended without executing any of the developing toner recovery mode and the transfer toner recovery mode.

  According to the above control, the toner deposited on the bottom surface 40c of the housing 40 and the seal member 50 is a fur brush by releasing the pressing of the primary transfer rollers 6a to 6c every predetermined number of printed sheets and executing the transfer toner recovery mode. It is recovered by the recovery roller 43 via 41. Accordingly, the transfer of the toner accumulated on the bottom surface 40c and the seal member 50 onto the intermediate transfer belt 8 is suppressed, and the generation of the toner drop can be effectively suppressed.

  When the transfer toner recovery mode is performed, the print waiting time can be shortened and the image forming efficiency can be improved by simultaneously performing the developing toner recovery mode in which the accumulated toner in the developing devices 3a to 3d is shaken. Here, the threshold T (300 sheets) of the belt separation control counter that determines the execution timing of the transfer toner recovery 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 recovery mode (100 sheets). Since the transfer toner recovery mode is always executed simultaneously with the developing toner recovery mode by setting it to 3 times, printing waiting time can be shortened and driving time of the photosensitive drums 1a to 1d can be shortened. it can.

  Here, since the threshold value T of the belt separation control counter is 300 sheets and the threshold value S of the vibration control counter is 100 sheets, the transfer toner collection mode is executed every three developing 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 printing sheets for executing the developing toner recovery mode fluctuates with the in-machine temperature of the image forming apparatus 100 and the number of continuous printing sheets. There are cases where the execution timings of the recovery mode and the development toner recovery mode do not coincide. Also in this case, as shown in FIG. 10, when the belt separation control counter reaches the threshold T, the developing toner collection mode and the transfer toner collection mode are simultaneously executed to reset the vibration control counter and the belt separation control counter. Good.

  Further, the threshold T of the belt separation control counter changes the appropriate value depending on the printing rate, and the threshold T decreases because the amount of toner collected by the belt cleaning unit 19 increases as the printing rate increases. By inputting the threshold value T corresponding to the printing rate to be used most frequently from the operation unit 70, it is possible to set the execution timing of the transfer toner recovery mode optimum for 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 has a first counter 95a for counting the number of continuously printed sheets, and a second counter 95b for counting the number of accumulated printed sheets including continuous printing and single-shot printing. The first counter 95 a has a first vibration control counter that controls the drive of the vibration generator 29 and a first belt separation control counter that controls the separation of the intermediate transfer belt 8 by the roller contact / separation mechanism 60. The second counter 95 b has a second vibration control counter that controls the drive of the vibration generator 29 and a second belt separation control counter that controls the 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 control unit 90 executes the transfer toner collection mode and the development toner collection mode at predetermined timing during continuous printing or after the completion of printing, based on the number of printed sheets counted by the first counter 95a and the second counter 95b. The configuration of the other parts of the image forming apparatus 100, such as the developing devices 3a to 3d and the belt cleaning unit 19, is the same as that of the first embodiment.

  FIG. 12 is a flowchart showing the procedure of executing the developing toner recovery mode and the transfer toner recovery mode in the image forming apparatus 100 according to the second embodiment. An 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 the 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 count up in the first counter 95a, and both the second vibration control counter and the second belt separation control counter in the second counter 95b. Count up the

  Next, the control unit 90 determines whether monochrome printing is performed (step S3), and when monochrome printing is performed (Yes in step S3), the count values of the first and second belt separation control counters It resets (step S4). Note that counting 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 T1 (here, 300 sheets) (step S5). When the threshold value T1 is 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 the transfer toner recovery shown in FIG. The mode is simultaneously executed (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, when the threshold value T1 is not reached in step S5 (No in step S5), it is determined whether the first vibration control counter has reached the threshold value S1 (here, 100 sheets) (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 generating device 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, only the driving of the developing devices 3a to 3d is sufficient, and the driving of the intermediate transfer belt 8 and the belt cleaning unit 19 and the 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 is completed (step S11), and if printing is continued (No in step S11), the process returns to step S2 and continues counting up. When the printing is completed (Yes in step S11), it is determined whether the second belt separation control counter of the second counter 95b has reached the threshold T2 (300 sheets in this case) (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 the transfer toner recovery shown in FIG. The mode is simultaneously executed (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, when the threshold value T2 is not reached in step S12 (No in step S12), it is determined whether the second vibration control counter has reached the threshold value S2 (here, 100 sheets) (step S15). When the threshold value S2 is reached (Yes in step S15), a control signal is transmitted from the control unit 90 to the vibration generating device 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, only the driving of the developing devices 3a to 3d is sufficient, and the driving of the intermediate transfer belt 8 and the belt cleaning unit 19 and the 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 is not reached in step S15 (No in step S15), the processing is ended without executing any of the developing 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 end of the printing operation, and the printing operation is performed even during continuous printing when the predetermined number of continuous printings is continued. Interrupt the transfer toner recovery mode. As a result, when continuous printing of a large number of sheets continues, the transfer toner collection mode is executed without waiting for the end of the printing operation, so that the occurrence of toner drop can be suppressed more effectively. Further, as in the first embodiment, when the transfer toner recovery mode is performed, the developing toner recovery mode is also performed at the same time, so that the printing waiting time can be shortened and the image forming efficiency can be improved.

  Furthermore, when printing in monochrome mode is executed and toner accumulated on the seal member 50 and the bottom surface 40c of the housing 40 is recovered by the fur brush 41, the count value of the belt separation control counter is reset, and the transfer toner recovery mode is Not run. Therefore, execution of unnecessary transfer toner collection mode is suppressed, and printing waiting time is shortened to improve image forming efficiency, and friction with the cleaning blade 32 and the rubbing roller 33 (all refer to FIG. 2). It is also possible to suppress the abrasion of the photosensitive layer of the photosensitive drum 1d due to the above.

  Here, since the threshold values T1 and T2 of the first and second belt separation control counters are 300 sheets and the threshold values S1 and S2 of the first and second vibration control counters are 100 sheets, transfer is performed every three times in the developing toner recovery mode. The toner recovery mode is to be executed. However, since the threshold values S1 and S2 of the number of printed sheets for executing the developing toner recovery mode fluctuate depending on the in-machine temperature of the image forming apparatus 100, the number of continuous printing sheets, etc. In some cases. Also in that case, as shown in FIG. 12, the developing toner recovery mode and the transfer toner recovery mode are simultaneously executed when the first and second belt separation control counters reach the threshold values T1 and T2, and the first and second The vibration control counter and the first and second belt separation control counters may be reset.

  Others 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, although the belt cleaning unit 19 including the fur brush 41 is illustrated in each of the above-described embodiments, the present invention can be similarly applied to a configuration using a cleaning roller instead of the fur brush 41.

  In each of the above embodiments, the transfer toner recovery mode is performed in synchronization with the developing toner recovery mode of the developing devices 3a to 3d. However, the invention is not limited to this, and may be synchronized with other control of the image forming apparatus 100. You may do so. For example, as control executed by the image forming apparatus 100 at the time of non-image formation, a cleaning mode for cleaning the light emission window 5a of the exposure device 5, and the developing devices 3a to 4d immediately before the toner containers 4a to 4d become empty. In the case of having a toner replenishment mode for forcibly replenishing the toner to 3d, and a toner ejection mode for forcibly ejecting the toner carried on the developing roller 25 in the developing devices 3a to 3d onto the photosensitive drums 1a to 1d, The recovery mode can be synchronized with at least one of the cleaning mode, the toner replenishment mode, and the toner discharge mode. Further, the transfer toner recovery mode can also be executed when a no-paper feed state occurs in which the sheets in the sheet cassette 16 are exhausted.

  Further, the present invention is applicable not only to the tandem type color printer as shown in FIG. 1, but also to various image forming apparatuses using an intermediate transfer belt and its cleaning device such as a color copier and a color multifunction 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 using the present invention, it is possible to provide an image forming apparatus capable of effectively preventing reattachment of the toner removed from the surface of the intermediate transfer belt to the intermediate transfer belt using the cleaning member.

Pa to Pd Image forming unit 1a to 1d Photosensitive drum (image carrier)
3a to 3d developing devices 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 conveyance spiral 50 seal member 51 bearing member 60 roller contact and separation mechanism 61 bias control circuit (bias application device)
64 Transfer bias power supply (bias application device)
90 control unit 95 counter (number of printed sheets counting unit)
95a 1st counter (1st counting section)
95b Second Counter (Second Count Unit)
100 image forming devices

Claims (11)

A plurality of image forming units forming images of different colors;
An endless intermediate transfer belt moving along the image forming unit, and an image carrier disposed in each of the image forming units with the intermediate transfer belt interposed therebetween, and 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 drive roller for rotating the intermediate transfer belt, and the intermediate transfer belt to rotate while rotating with a predetermined tension on the intermediate transfer belt An intermediate transfer unit having: a tension roller for applying the toner; and a roller contacting / separating mechanism for reciprocating the primary transfer roller in a direction toward or away 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 provided with
The roller contact / separation mechanism has a color mode in which all the primary transfer rollers are in pressure contact with the image carrier across the intermediate transfer belt, and only one primary transfer roller across the intermediate transfer belt is black. It is possible to switch between a monochrome mode in which the image bearing member disposed in the image forming unit for forming an image is in pressure contact with the image bearing member,
The belt cleaning device
A housing in which an opening facing the intermediate transfer belt and a toner storage portion for storing the 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 opposite to the entire area in the longitudinal direction of the collection roller and partitioning the toner storage portion and the opening portion;
Have
The cleaning member is disposed at a position moved inward of the housing from the opening compared to the color mode by the pressing force of the tension roller in the monochrome mode.
The control unit recovers the toner deposited in the vicinity of the opening of the housing by driving the intermediate transfer belt and the belt cleaning device in the monochrome mode during non-image formation, using the cleaning member and the recovery roller. An image forming apparatus capable of executing a transfer toner recovery mode. The printing apparatus further includes a print sheet count unit that counts the number of print sheets in the color mode.
The control unit executes the transfer toner collection mode when the number of printed sheets in the color mode counted by the number of printed sheets reaches a predetermined number T after the previous execution of the transfer toner collection mode. The image forming apparatus according to claim 1, characterized in that   The control unit executes printing in the monochrome mode until the number of sheets printed in the color mode counted by the number of printed sheets reaches the predetermined number T after the previous execution of the transfer toner collection mode. 3. The image forming apparatus according to claim 2, wherein the count value of the number-of-printed-sheet counting unit is reset. The print sheet number counting unit has a first count unit that counts the continuous print number, and a second count unit that counts the cumulative print number including continuous printing and single-shot printing.
The control unit is configured such that the number of printed sheets counted by the first count unit reaches a predetermined number T1 after execution of the transfer toner collection mode last time, or the number of printed sheets counted by the second count unit is predetermined When the number of sheets T2 is reached, the transfer toner recovery mode is executed, and after execution of the transfer toner recovery mode, count values of the first count unit and the second count unit are reset. The image forming apparatus according to claim 1.   The control unit counts the number of printed sheets in the color mode counted by the first counting unit after the previous execution of the transfer toner collection mode until the number of printed sheets in the color mode reaches a predetermined number T1, or the second counting unit When printing in the monochrome mode is executed before the number of printed sheets in the color mode reaches the predetermined number T2, the count values of the first count unit and the second count unit are reset. 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 bearing member disposed in the image forming portion forming a black image has a thicker layer thickness of the photosensitive layer than the image bearing member disposed in the image forming portion forming an image other than black. The image forming apparatus according to any one of claims 1 to 5, wherein   The layer thickness of the photosensitive layer is determined on the basis of the cumulative driving time in the monochrome mode in the endurance period of the image carrier of the image carrier disposed in the image forming unit for forming a black image. The image forming apparatus according to claim 6, wherein The image forming unit is
A toner receiving member disposed opposite to the image carrier and having a developing roller for supplying toner to the image carrier in a region facing the image carrier, and a toner receiving surface for receiving the toner falling from the developing roller A vibration generating device for vibrating the toner receiving member;
A developing device for developing an electrostatic latent image formed on the image carrier,
It is possible to execute 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 accumulated on the toner receiving surface,
The image forming apparatus according to any one of claims 2 to 7, wherein the control unit executes the transfer toner recovery mode simultaneously with the developing toner recovery mode. The image forming unit includes a developing roller that is disposed to face the image carrier and supplies toner to the image carrier in a region facing the image carrier, and the image forming portion is formed on the image carrier. Equipped with a developing device for developing an electrostatic latent image
An exposure device 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 supplied 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;
And further
The control unit performs the transfer toner collection mode, an exposure cleaning that cleans the light emission window of the exposure device, a toner replenishment from the toner storage container to the developing device, and a forcing of the toner from the developing roller to the image carrier 9. The image formation according to any one of claims 2 to 8, wherein the image formation is performed simultaneously with at least one of ejection and occurrence of a recording medium non-supplyable state in which the recording medium in the recording medium storage cassette has run out. apparatus. A bias applying device for applying a bias to the primary transfer roller and the secondary transfer roller,
10. The method according to claim 1, wherein the bias applying device applies a bias of the same polarity as the toner to the primary transfer roller and the secondary transfer roller while the transfer toner recovery mode is being performed. The image forming apparatus according to claim 1.   The image forming apparatus according to any one of claims 1 to 10, wherein the intermediate transfer belt is formed by laminating a plurality of layers including an elastic layer.

Images