BACKGROUND

[0001] Some imaging apparatuses include a transfer belt that conveys a toner image so as to transfer the toner image to a printing medium, and a cleaning device that removes from the transfer belt, non-transferred toner particles which have not been transferred to the printing medium and remain on the transfer belt.

BRIEF DESCRIPTION OF DRAWINGS

[0002] FIG. 1 is a schematic diagram of an example imaging apparatus.

FIG. 2 is a cross-sectional view illustrating an example transfer device, FIG. 3 is a perspective view illustrating an example cleaning unit.

FIG. 4 is a cross-sectional view illustrating an example cleaning unit. FIG. 5 is a schematic diagram of a portion of an example cleaning device illustrated with toner particles.

FIG. 6 is a cross-sectional view illustrating a modified example of the cleaning unit.

FIG. 7 is a cross-sectional view illustrating another modified example of the cleaning unit.

FIG. 8 is a cross-sectional view illustrating still another modified example of the cleaning unit.

DETAILED DESCRIPTION

[0003] In the following description, with reference to the drawings, the same reference numbers are assigned to the same components or to similar components having the same function, and overlapping description is omitted. Hereinafter, an example imaging system will be described. The imaging system may be an imaging apparatus such as a printer, according to some examples, or a developing device used in the imaging apparatus or the like, according to some examples. [0004] With reference to FIG. 1, an example imaging apparatus 1 may form a color image by using respective colors of magenta, yellow, cyan, and black. The imaging apparatus 1 may include a conveying device 10 which conveys a sheet P corresponding to a printing medium, a developing device 20 which develops an electrostatic latent image, a transfer device 30 which secondarily transfers a toner image to the sheet P, a photoconductor 40 which forms an electrostatic latent image on a surface (a peripheral surface) thereof, a fixing device 50 which fixes a toner image to the sheet P, and a discharging device 60 which discharges the sheet P. [0005] The conveying device 10 conveys the sheet P which is a printing medium on which an image is to be formed, along a conveyance route R1. The sheet P is accommodated in a cassette K in a stacked state and is picked up and conveyed by a feeding roller 11. The conveying device 10 allows the sheet P to reach a transfer region R2 via the conveyance route R1 at a timing at which a toner image to be transferred to the sheet P, reaches the transfer region R2. [0006] Four developing devices 20 are provided for the respective four colors of magenta, yellow, cyan, and black. Each developing device 20 includes a developer carrier 24 which carries a toner on the photoconductor 40. In the developing device 20, a two-component developer including a toner and a carrier, is used as the developer. For example, in the developing device 20, the toner and the carrier are adjusted to a predetermined mixing ratio and are further mixed and stirred to uniformly disperse the toner so as to adjust the developer to an optimal or targeted charge amount. The developer is carried on the developer carrier 24. When the developer is conveyed with a rotation of the developer carrier 24, to a developing region facing the photoconductor 40, the toner in the developer carried on the developer carrier 24 transfers to an electrostatic latent image formed on the peripheral surface of the photoconductor 40, so as to develop the electrostatic latent image. [0007] The transfer device 30 conveys the toner image formed by the developing device 20 to the transfer region R2 where the toner image is secondarily transferred to the sheet P. The transfer device 30 includes a transfer belt 31 onto which a toner image is primarily transferred from the photoconductor 40, a suspension roller 34 which suspends (or supports) the transfer belt 31, idler rollers 35 and 36, a drive roller 37 which drives the transfer belt 31, a primary transfer roller 32 which positions the transfer belt 31 between the primary transfer roller 32 and the photoconductor 40, a secondary transfer roller 33 which positions the transfer belt 31 between the secondary transfer roller 33 and the drive roller 37, and a cleaning unit (or cleaning device) 38 which collects a toner remaining on the transfer belt 31. [0008] The photoconductor 40 is also called an electrostatic latent image carrier, a photoconductor drum, or the like. Four photoconductors 40 are provided for the four colors, respectively. The photoconductors 40 are provided along the movement direction of the transfer belt 31. The developing device 20, a charging device 41, an exposure unit (or exposure device) 42, and a cleaning device 43 are arranged in a peripheral region of the photoconductor 40. [0009] The charging device 41 is a charging roller which contacts the photoconductor 40 to uniformly charge the surface of the photoconductor 40 to a predetermined potential. The exposure unit 42 exposes the surface of the photoconductor 40 charged by the charging device 41 in response to an image formed on the sheet P. Accordingly, a potential of a portion exposed by the exposure unit 42 in the surface of the photoconductor 40 changes, so that an electrostatic latent image is formed. Four developing devices 20 are provided to generate a toner image by developing an electrostatic latent image formed on each of the photoconductor 40 by the toners supplied from toner tanks N facing the respective developing devices 20. The toner tanks N are filled with magenta, yellow, cyan, and black toners, respectively. The cleaning device 43 collects the toner remaining on the photoconductor 40 after the toner image formed on the photoconductor 40 has been primarily transferred to the transfer belt 31. [0010] The fixing device 50 conveys the sheet P to pass through a fixing nip region for heating and pressing the sheet so that the toner image secondarily transferred from the transfer belt 31 to the sheet P is adhered and fixed to the sheet P. The fixing device 50 includes a heating roller 52 which heats the sheet P and a pressing roller 54 which rotates in a driving manner while pressing the heating roller 52. The heating roller 52 and the pressing roller 54 has a cylindrical shape and the heating roller 52 includes a heat source such as a halogen lamp provided therein. A fixing nip region which is a contact region is provided between the heating roller 52 and the pressing roller 54 where a toner image is melted and fixed to the sheet P when the sheet P passes through the fixing nip region. [0011] The discharging device 60 includes discharging rollers 62 and 64 which discharge the sheet P having a toner image fixed thereto by the fixing device 50 to the outside of the apparatus. [0012] The imaging apparatus 1 further includes a control unit (or controller) 68. The control unit 68 is a computer including a processor, a storage, an input device, a display device, and the like and has a function of controlling the overall operation of the imaging apparatus 1. The storage unit of the control unit 68 stores a control program for controlling various processes performed by the imaging apparatus 1 using a processor. [0013] Next, a printing process using the imaging apparatus 1 will be described. When an image signal of a recording target image is input to the imaging apparatus 1, the control unit 68 of the imaging apparatus 1 rotates the feeding roller 11 so that the sheet P stacked in the cassette K is picked up and conveyed. Then, in a charging operation, the surface of the photoconductor 40 is uniformly charged to a predetermined potential by the charging device 41. Subsequently, in an exposing operation, a laser beam is irradiated to the surface of the photoconductor 40 by the exposure unit 42 on the basis of the received image signal so as to form an electrostatic latent image. [0014] The developing device 20 carries out a developing operation in which the electrostatic latent image is developed so as to form a toner image. In a transferring operation, the toner image which has been formed is primarily transferred from the photoconductor 40 to the transfer belt 31 in a region in which the photoconductor 40 faces the transfer belt 31. The toner images formed on four photoconductors 40 are sequentially layered on the transfer belt 31 so as to form a single layered (or composite) toner image. Then, the composite toner image is secondarily transferred to the sheet P conveyed from the conveying device 10 in the transfer region R2 in which the drive roller 37 faces the secondary transfer roller 33. [0015] The sheet P onto which the laminated toner image is secondarily transferred is conveyed to the fixing device 50. Then, in a fixing operation, the fixing device 50 heats and presses the sheet P between the heating roller 52 and the pressing roller 54 when the sheet P passes through a fixing nip region, so that the laminated toner image is melted and fixed to the sheet P. Then, the sheet P is discharged to the outside of the imaging apparatus 1 by the discharging rollers 62 and 64. [0016] FIG. 2 is a cross-sectional view illustrating an example transfer device 30. [0017] As described above, the transfer device 30 includes the transfer belt 31, the suspension roller 34, the idler rollers 35 and 36, the drive roller 37, the primary transfer roller 32, the secondary transfer roller 33, and the cleaning unit 38. The transfer belt 31 conveys the toner image primarily transferred from the photoconductor 40 to the transfer region R2 and secondarily transfers the toner image to the sheet P in the transfer region R2. The transfer belt 31 is an endless belt which moves in a circulating manner by the suspension roller 34, the idler rollers 35 and 36, and the drive roller 37. The transfer belt 31 includes a front surface (or outer surface) 31a which conveys a toner image primarily transferred from the photoconductor 40 and a back surface (or inner surface) 31b which is opposite to the front surface 31a. The front or outer surface 31a constitutes the outer peripheral surface of the transfer belt 31 and the back or inner surface 31b constitutes the inner peripheral surface of the transfer belt 31. [0018] The transfer belt 31 is suspended on (or supported by) the suspension roller 34, the idler rollers 35 and 36, and the drive roller 37 from the inside (the side of the inner surface 31b). The suspension roller 34, the idler rollers 35 and 36, and the drive roller 37 are rotatable around their respective axes. The drive roller 37 rotates in a driving manner around the axis by power supplied from an electric motor and the suspension roller 34 and the idler rollers 35 and 36 rotate in a driven manner as the drive roller 37 rotates in a driving manner. The transfer belt 31 rotates in a rotation direction (or rotational direction) C illustrated in FIG.2 as the drive roller 37 rotates in a driving manner. [0019] The primary transfer roller 32 is provided so as to press against the photoconductor 40 from the inner peripheral side of the transfer belt 31. The secondary transfer roller 33 is disposed in parallel to the drive roller 37 with the transfer belt 31 interposed therebetween and is provided so as to press against the drive roller 37 from the outer peripheral side of the transfer belt 31. Accordingly, the secondary transfer roller 33 forms the transfer region R2 between the secondary transfer roller 33 and the transfer belt 31. The toner image primarily transferred onto the transfer belt 31 is secondarily transferred to the sheet P in the transfer region R2 which is formed between the drive roller 37 and the secondary transfer roller 33. [0020] The cleaning unit 38 collects the toner remaining on the transfer belt 31 after the toner image formed on the transfer belt 31 has been secondarily transferred to the sheet P. The cleaning unit 38 is provided on the downstream side of the transfer region R2 in the rotation direction C of the transfer belt 31. FIG. 3 is a perspective view illustrating an example of the cleaning unit 38 and FIG. 4 is a cross-sectional view of the example cleaning unit 38, taken along a plane that is orthogonal to the rotation axis of the drive roller 37. [0021] The cleaning unit 38 illustrated in FIGS. 3 and 4 includes a first cleaning device 70, a second cleaning device 80, and a collection container 90. [0022] The first cleaning device 70 may be an electrostatic cleaning device that collects toner particles remaining on the transfer belt 31 by the use of an electrostatic force. The first cleaning device 70 is provided adjacent to the transfer belt 31 on the downstream side of the transfer region R2 in the rotation direction C of the transfer belt 31. The first cleaning device 70 includes a first roller 71 and a first blade 72. [0023] The second cleaning device 80 may be an electrostatic cleaning device that collects toner particles remaining on the transfer belt 31 by an electrostatic force. The second cleaning device 80 is provided adjacent to the transfer belt 31 on the downstream side of the first cleaning device 70 in the rotation direction C of the transfer belt 31. The second cleaning device 80 includes a second roller 81 and a second blade 82. [0024] The first roller 71 may be a substantially cylindrical metallic roller. The first roller 71 is provided on the downstream side of the transfer region R2 in the rotation direction C and rotates around an axis by receiving power from an electric motor while contacting the outer surface 31a of the transfer belt 31. The rotation direction of the first roller 71 may be the same as the rotation direction C of the transfer belt 31. Accordingly, the first roller 71 and the transfer belt 31 may move in opposite tangential directions at a point of contact between the first roller 71 and the transfer belt 31, or at a position of closest distance between the first roller 71 and the transfer belt 31. The first roller 71 is charged by bias power during an image forming operation, as will be described further below. The first roller 71 attracts and collects, by electrostatic force, toner particles remaining on the transfer belt 31 that have not been transferred in the transfer region R2. Hereinafter, the toner particles collected by the first roller 71 among the non-transferred toner on the transfer belt 31 are also referred to as "first toner particles T1" (see FIG.5). [0025] The first blade 72 may have a plate shape and may be formed of a conductive material such as metal or conductive urethane. The first blade 72 is provided on the downstream side of the first roller 71 in the conveyance direction of the first toner particles T1 on the first roller 71. The first blade 72 is disposed at a position contacting or adjacent to the upper portion of the first roller 71 to scrape off the first toner particles T1 adhered to the surface of the first roller 71 so that the first toner particles T1 are separated from the first roller 71. The first blade 72 is disposed so as to overlap at least a part of the second roller 81 in the horizontal direction, e.g., along the rotation direction C of the transfer belt 31. Accordingly, the first toner particles T1 separated from the first roller 71 drop onto the second roller 81 after being accumulated on the first blade 72. [0026] The second roller 81 may be a substantially cylindrical metallic roller. With reference to FIG. 4, the second roller 81 is provided between the drive roller 37 and the suspension roller 34 in the horizontal direction, that is, the downstream side of the first roller 71 along the rotation direction C of the transfer belt 31. The second roller 81 rotates around an axis by receiving power from an electric motor while contacting the outer surface 31a of the transfer belt 31. The rotation direction of the second roller 81 may be the same as the rotation direction C of the transfer belt 31. Accordingly, the second roller 81 and the transfer belt 31 may move in opposite tangential directions at a point of contact between the second roller 81 and the transfer belt 31, or at a position of closest distance between the second roller 81 and the transfer belt 31. The second roller 81 is charged by receiving bias power during an image forming operation, as will be described further below. The second roller 81 attracts and collects, by electrostatic force, toner particles remaining on the transfer belt 31 that have not been collected by the first roller 71. Hereinafter, the toner particles collected by the second roller 81 among the non-transferred toner on the transfer belt 31 will be referred to as "second toner particles T2" (see FIG. 5). In addition, the second roller 81 receives the first toner particles T1 that drop from the first blade 72 and collects the toner particles together with the second toner particles T2. [0027] The second blade 82 may have a plate shape and may be formed of a conductive material such as metal or conductive urethane. The second blade 82 is provided on the downstream side of the second roller 81 in the conveyance direction of the second toner particles T2 on the second roller 81. The second blade 82 is supported on the bottom surface (or surface of a bottom wall) of the collection container 90. The second blade 82 is disposed at a position contacting or adjacent to the surface of the second roller 81 to scrape off the first toner particles T1 and the second toner particles T2 adhered to the surface of the second roller 81 so that the first toner particles T1 and the second toner particles T2 are separated from the second roller 81. [0028] The collection container 90 is provided on the downstream side of the first cleaning device 70 and the second cleaning device 80 in the rotation direction C of the transfer belt 31. The collection container 90 is a container opening toward the second cleaning device 80 and defines a collection chamber 90s and a toner conveyance path 90c therein. The collection chamber 90s stores the non-transferred toner particles collected by the first cleaning device 70 and the second cleaning device 80. The toner conveyance path 90c extends between the second cleaning device 80 and the collection chamber 90s and guides the toner particles collected by the first cleaning device 70 and the second cleaning device 80 to the collection chamber 90s. [0029] Additionally, the collection chamber 90s is provided with a conveyor device and the non-transferred toner particles collected by the collection chamber 90s may be conveyed to a toner cartridge by the conveyor device as waste toner or recycled toner. [0030] A power supply (or power supply unit or power supply device) 98 is electrically connected to the first cleaning device 70 and the second cleaning device 80. The power supply unit 98 charges the first roller 71 and the second roller 81 by applying a voltage to each of the first roller 71 and the second roller 81 through the first blade 72 and the second blade 82. The power supply unit 98 is connected to the control unit 68 of the imaging apparatus 1 so as to communicate therewith to control the voltage applied to the first roller 71 and the second roller 81 in response to the control signal from the control unit 68. [0031] As an example, the power supply unit 98 may apply a voltage to the first roller 71 and the second roller 81 so that the first roller 71 and the second roller 81 are charged to the potentials of different polarities during an image forming operation. For example, the power supply unit 98 applies voltages of different polarities to the first roller 71 and the second roller 81 by negatively charging the first roller 71 and positively charging the second roller 81. Accordingly, the toner particles charged to different polarities on the transfer belt 31 can be collected by using the first roller 71 and the second roller 81. [0032] In addition, the cleaning unit 38 may further include support rollers 95 and 96. The support rollers 95 and 96 are provided adjacent to the first cleaning device 70 and the second cleaning device 80 and rotate in a driven manner by the rotation of the transfer belt 31 while contacting the inner surface 31b of the transfer belt 31. In an example illustrated in FIG. 4, the support rollers 95 and 96 are provided below the first blade 72 and the second blade 82, respectively. The support rollers 95 and 96 support the transfer belt 31 from below so as to prevent the transfer belt 31 from being loosened. [0033] The movement of the toner particles collected by the example cleaning unit 38 will be described. [0034] The toner image primarily transferred from the photoconductor 40 to the outer surface 31a of the transfer belt 31 is conveyed in the rotation direction C by the transfer belt 31 and is secondarily transferred from the transfer belt 31 to the sheet P in the transfer region R2. The toner particles remaining on the outer surface 31a of the transfer belt 31 that have not been transferred from the transfer belt 31 to the sheet P, are conveyed to pass through the transfer region R2 and move toward the first roller 71. [0035] When the toner particles on the transfer belt 31 move to a region facing the first roller 71, a portion of the toner particles is collected by the first roller 71 by the use of an electrostatic force. For example, the first toner particles T1 which are charged to the polarity opposite to the first roller 71 among the toner particles that remain on the transfer belt 31, is adhered to the first roller 71. As illustrated in FIG. 5, the first toner particles T1 adhered to the first roller 71 move to a region facing the first blade 72 in accordance with the rotation of the first roller 71 and are scraped off by the first blade 72 so as to be separated from the first roller 71. [0036] The toner particles which are not collected by the first roller 71 are conveyed past the first roller 71 on the conveyor belt 31, and move toward the second roller 81. When the toner particles on the transfer belt 31 move to a region facing the second roller 81, another portion of the toner particles is collected by the second roller 81 by the use of an electrostatic force. For example, the second toner particles T2 that are charged to the polarity opposite to the second roller 81 among the toner particles that remain on the transfer belt 31, are adhered to the second roller 81. [0037] As described above, since the first blade 72 is disposed so as to overlap at least a part of the second roller 81 in the horizontal direction, the first toner particles T1 separated from the first roller 71 by the first blade 72 accumulate on the first blade 72 and drop onto the second roller 81. Accordingly, the second roller 81 receives the first toner particles T1. Accordingly, the first toner particles T1 are collected by the second roller 81 together with the second toner particles T2. With reference to FIG. 5, when the first toner particles T1 and the second toner particles T2 which are collected by the second roller 81 move to a region facing the second blade 82 in accordance with the rotation of the second roller 81, the toner particles are scraped off from the second roller 81 by the second blade 82. [0038] The first toner particles T1 and the second toner particles T2 which are separated from the second roller 81 pass through the toner conveyance path 90c and are collected by the collection chamber 90s. The non-transferred first and second toner particles T1 and T2 which are collected by the collection chamber 90s are conveyed into, for example, a toner cartridge by the conveyor device as waste toner or recycled toner. [0039] In the cleaning unit 38, the first toner particles T1 remaining on the transfer belt 31 are collected by the first cleaning device 70 and the second toner particles T2 that are conveyed past the first cleaning device 70 are collected by the second cleaning device 80. The second cleaning device 80 receives the first toner particles T1 from the first cleaning device 70 and sends (or conveys, or transfers, or directs) the first toner particles T1 and the second toner particles T2 to the collection chamber 90s. [0040] In the cleaning unit 38, the first toner particles T1 and the second toner particles T2 which are respectively collected by the first cleaning device 70 and the second cleaning device 80 are sent (or conveyed) to the collection chamber 90s through the common toner conveyance path 90c, to reduce the installation space of the cleaning unit 38 as compared with a case in which individual (or separate) toner conveyance paths are formed between the first cleaning device 70 and the collection chamber 90s, and between the second cleaning device 80 and the collection chamber 90s. In addition, the first toner particles T1 and the second toner particles T2 are collected through the common toner conveyance path 90c, to suppress the possibility of toner clogging as compared with a case in which the toner particles are collected through a plurality of toner conveyance paths. [0041] A modified example of the cleaning unit mounted on the imaging apparatus will be described. [0042] FIG.6 is a cross-sectional view illustrating an example cleaning unit (or cleaning device) 38A according to a modified example. The cleaning unit 38A is different from the cleaning unit 38 illustrated in FIG. 4, for example, in that a first cleaning device 70A is provided instead of the first cleaning device 70. The first cleaning device 70A includes a first roller 71A and a flicker member 72A. [0043] The first roller 71A is a conductive brush roller and includes a shaft portion 71A1 and a brush portion 71A2 connected to the shaft portion 71A1. The first roller 71A receives power from the electric motor and rotates around an axis while the brush portion 71A2 contacts the outer surface 31a of the transfer belt 31. The first roller 71A is charged by receiving bias power from a power supply such as the power supply unit 98 (cf. FIG. 4), during an image forming operation. The first roller 71A collects the toner particles remaining on the transfer belt 31 that have not been transferred to the sheet P, by attracting the toner particles to adhere to the brush portion 71A2 in the transfer region R2 by the use of an electrostatic force. [0044] The flicker member 72A is provided at a position to contact the brush portion 71A2, when the brush portion 71A2 rotates around the shaft portion 71A1 so that the first toner particles T1 adhered to the brush portion 71A2 are separated from the first roller 71A. The first toner particles T1 separated from the first roller 71A are accumulated onto the flicker member 72A and are subsequently dropped onto the second roller 81. [0045] Similarly to the cleaning unit 38 illustrated in FIG. 5, the second roller 81 of the cleaning unit 38A collects the second toner particles T2 remaining on the transfer belt 31 that have not been collected by the first roller 71A, by the use of an electrostatic force, receives the first toner particles T1 separated from the first roller 71A by the flicker member 72A, and sends (or conveys, or transfers, or directs) the first toner particles T1 and the second toner particles T2 to the collection chamber 90s. In the cleaning unit 38A, the first toner particles T1 and the second toner particles T2 which are respectively collected by the first cleaning device 70A and the second cleaning device 80, are sent to the collection chamber 90s through the common toner conveyance path 90c, to reduce the installation space of the cleaning unit 38A. [0046] Another modified example of the cleaning unit will be described. [0047] FIG. 7 is a cross-sectional view illustrating an example cleaning unit 38B. The cleaning unit 38B is different from the cleaning unit 38 illustrated in FIG.4, for example, in that a first cleaning device 70B is provided instead of the first cleaning device 70. The first cleaning device 70B includes a contact roller 73 in addition to the first roller 71 and the first blade 72. [0048] The first roller 71 may be a substantially cylindrical metallic roller that rotates around an axis by receiving power from the electric motor and that is separated (or spaced apart) from the transfer belt 31. The contact roller 73 is interposed between the transfer belt 31 and the first roller 71. The contact roller 73 may be a substantially columnar conductive sponge roller that rotates around an axis by receiving power from the electric motor and that contacts the outer surface 31a of the transfer belt 31 and the surface of the first roller 71. The contact roller 73 is charged by receiving bias power from a power supply such as the power supply unit 98 (cf. FIG. 4), during an image forming operation. [0049] The contact roller 73 collects the toner particles remaining on the transfer belt 31 that have not been transferred to the sheet P in the transfer region R2 by the use of an electrostatic force. The toner particles collected by the contact roller 73 adhere to the first roller 71 by the use of an electrostatic force when the toner particles are moved to a region facing the first roller 71. The first toner particles T1 adhered to the first roller 71 are scraped off from the first roller 71 by the first blade 72 when the toner particles are moved to a region facing the first blade 72 in accordance with the rotation of the first roller 71. [0050] Similarly to the cleaning unit 38 illustrated in FIG. 5, the second roller 81 of the cleaning unit 38B collects the second toner particles T2 remaining on the transfer belt 31 that have not been by the contact roller 73, by the use of an electrostatic force, receives the first toner particles T1 separated from the first roller 71 by the first blade 72, and conveys the first toner particles T1 and the second toner particles T2 to the collection chamber 90s. In the cleaning unit 38B, the first toner particles T1 and the second toner particles T2 which are respectively collected by the first cleaning device 70B and the second cleaning device 80 are sent to the collection chamber 90s through the common toner conveyance path 90c, to reduce the installation space of the cleaning unit 38B. [0051] In addition, in the cleaning unit 38B, the toner particles on the transfer belt 31 are leveled by the conductive sponge contact roller 73, to increase the recovery rate of the toner particles on the transfer belt 31. Additionally, the contact roller 73 is not limited to the conductive sponge roller. For example, the contact roller 73 may be a brush roller. [0052] Another modified example of the cleaning unit will be described. [0053] FIG. 8 is a cross-sectional view illustrating a cleaning unit 38C according to another modified example. The cleaning unit 38C is different from the cleaning unit 38 illustrated in FIG. 4, for example, in that the cleaning unit is located in the vicinity of the suspension roller 34. [0054] The cleaning unit 38C illustrated in FIG. 8 includes a first cleaning device 70C, a second cleaning device 80C, and a collection container 90C. The first cleaning device 70C is provided in the vicinity of the suspension roller 34 and includes a first roller 71C, a first blade 72C, and a contact roller 73C. The second cleaning device 80C is provided on the downstream side of the first cleaning device 70C in the rotation direction C of the transfer belt 31 and includes a second roller 81C and a second blade 82C. [0055] The first roller 71C may be a substantially cylindrical metallic roller that rotates around an axis by receiving power from the electric motor while being separated from the transfer belt 31. The first roller 71C is charged by receiving bias power from a power supply such as the power supply unit 98 (cf. FIG. 4), during an image forming operation. The first blade 72C may be a plate member formed of a conductive material such as metal or conductive urethane. The first blade 72C is disposed at a position contacting or adjacent to the upper portion of the first roller 71C and scrapes off the first toner particles T1 adhered to the surface of the first roller 71C so as to separate the first toner particles T1 from the first roller 71C. The first blade 72C is disposed so as to overlap at least a part of the second roller 81C in the horizontal direction. [0056] The contact roller 73C is interposed between the transfer belt 31 and the first roller 71C. The contact roller 73C may be a substantially columnar sponge roller and rotates by receiving power from the electric motor while contacting the outer surface 31a of the transfer belt 31 and the surface of the first roller 71C. The contact roller 73C is charged by receiving bias power from a power supply such as the power supply unit 98 (cf. FIG. 4), during an image forming operation. [0057] The contact roller 73C collects the toner particles remaining on the transfer belt 31 that have not been transferred to the sheet P in the transfer region R2, by the use of an electrostatic force. The first roller 71C receives the toner particles collected by the contact roller 73C and conveys the toner particles toward the first blade 72C. The first blade 72C scrapes off the first toner particles T1 adhered to the first roller 71C from the first roller 71C. The first toner particles T1 which are scraped off from the first roller 71C by the first blade 72C drop onto the second roller 81C. [0058] The second roller 81C may be a substantially cylindrical metallic roller that positions the transfer belt 31 between the second roller 81C and the suspension roller 34. For example, the second roller 81C is provided so as to face the suspension roller 34. The second roller 81C rotates around an axis by receiving the power from the electric motor and contacts the outer surface 31a of the transfer belt 31. The second roller 81C is charged by receiving bias power from the power supply unit 98 as will be described later during an image forming operation. The second roller 81C collects the toner particles remaining on the transfer belt 31 that has not been collected by the first cleaning device 70C, by the use of an electrostatic force. In addition, the second roller 81C receives the first toner particles T1 separated from the first roller 71C from the first blade 72C and collects the first toner particles together with the second toner particles T2. [0059] The second blade 82C may have a plate shape and may be formed of a conductive material such as metal or conductive urethane. The second blade 82C is provided on the downstream side of the second roller 81C in the conveyance direction of the second toner particles T2 on the second roller 81C. The second blade 82C is supported on the bottom surface (or surface of a bottom wall) of the collection container 90C. The second blade 82C is positioned to contact or to be adjacent to the surface of the second roller 81C, in order to scrape off the first toner particles T1 and the second toner particles T2 adhered to the surface of the second roller 81 so as to separate the first toner particles T1 and the second toner particles T2 from the second roller 81. [0060] The collection container 90C is provided on the downstream side of the second cleaning device 80C in the rotation direction C of the transfer belt 31. The collection container 90C is open toward the second cleaning device 80C and defines the collection chamber 90s and the toner conveyance path 90c therein. The collection chamber 90s stores the non-transferred toner particles collected by the first cleaning device 70C and the second cleaning device 80C. The toner conveyance path 90c extends between the second cleaning device 80 and the collection chamber 90s to guide the toner particles collected by the first cleaning device 70C and the second cleaning device 80C to the collection chamber 90s. [0061] In the cleaning unit 38C, the first toner particles T1 present on the transfer belt 31 are collected by the first cleaning device 70C, and the second toner particles T2 conveyed past the first cleaning device 70 are collected by the second cleaning device 80C. The second cleaning device 80C receives the first toner particles T1 from the first cleaning device 70C and sends (or conveys, or transfers, or directs) the first toner particles T1 and the second toner particles T2 to the collection chamber 90s. [0062] Similarly to the cleaning unit 38 illustrated in FIGS.4 and 5, the second roller 81C of the cleaning unit 38C collects the second toner particles T2 remaining on the transfer belt 31 that have not been collected by the contact roller 73C, by the use of an electrostatic force, receives the first toner particles T1 separated from the first roller 71C by the first blade 72C, and conveys the first toner particles T1 and the second toner particles T2 to the collection chamber 90s. In the cleaning unit 38C, the first toner particles T1 and the second toner particles T2 which are respectively collected by the first cleaning device 70C and the second cleaning device 80C, are sent to the collection chamber 90s through the common toner conveyance path 90c, to suppress the installation space of the cleaning unit 38C. [0063] It is to be understood that not all aspects, advantages and features described herein may necessarily be achieved by, or included in, any one particular example. Indeed, having described and illustrated various examples herein, it should be apparent that other examples may be modified in arrangement and detail is omitted. [0064] For example, in the cleaning unit 38 illustrated in FIG. 4, voltages of different polarities are applied from the power supply unit 98 to the first roller 71 and the second roller 81, however voltage of the same polarity may be applied to the first roller 71 and the second roller 81. In addition, the polarity of the voltage applied from the power supply unit 98 to the first roller 71 and the second roller 81 may be changed in response to time.