BACKGROUND

[0001] An image forming apparatus may use a two-component developer containing toner and carrier particles. In such an image forming apparatus, an electrostatic latent image formed on a photosensitive drum is developed by toner and a developed toner image is transferred to a transfer belt. It is likely that carrier particles, in addition to toner particles, adhere to the surface of the photosensitive drum and the surface of the transfer belt.

BRIEF DESCRIPTION OF DRAWINGS

[0002] FIG. 1 is a schematic diagram of an example carrier removal device.

[0003] FIG. 2 is a schematic diagram of an example image forming apparatus.

[0004] FIG. 3 is a schematic diagram showing a vicinity of an example lubricant roller (carrier removal device) provided in the image forming apparatus. [0005] FIG. 4 is a graph showing a relationship between the number of cycles and the amount of wear of a photosensitive drum in a test image forming apparatus.

[0006] FIG. 5 is a graph showing a relationship between the number of cycles and the amount of wear of a photosensitive drum in an example image forming apparatus.

[0007] FIG. 6 is a schematic diagram of another example carrier removal device.

[0008] FIG. 7 is a schematic diagram showing the vicinity of an example belt cleaning device provided in the image forming apparatus.

DETAILED DESCRIPTION

[0009] 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.

[0010] FIG. 1 is a diagram schematically showing a carrier removal device according to an example. As shown in FIG. 1 , an example carrier removal device 2 includes a magnetic body 3 which forms a pickup pole and a release pole and a roller sleeve 5 which rotates around the magnetic body 3 in a direction indicated by an arrow 5a. The magnetic body 3 is fixed and does not rotate. The roller sleeve 5 faces a conveyance body 4 having a surface 4a rotating in a direction indicated by an arrow 4b. In FIG. 1 , the roller sleeve 5 is spaced away from the surface 4a of the conveyance body 4, however, in other examples, the roller sleeve 5 may be in contact with the surface 4a of the conveyance body 4. The pickup pole of the magnetic body 3 forms a magnetic field in a region 6 including the surface 4a of the conveyance body 4 so that a magnetic field is applied to carrier particles 9 adhering to the surface 4a of the conveyance body 4. The release pole of the magnetic body 3 forms a magnetic field in a region 7 on the downstream side of the pickup pole in the rotational direction of the roller sleeve 5. The roller sleeve 5 draws the carrier particles 9 from the surface 4a of the conveyance body 4 to the roller sleeve 5, by the action of the magnetic force of the pickup pole and releases the drawn (or transferred) carrier particles 9 by the action of the magnetic force of the release pole. That is, the carrier removal device 2 removes the carrier particles 9 from the surface 4a of the conveyance body 4 by causing the carrier particles 9 to be transferred from the conveyance body 4 to the roller sleeve 5 of the carrier removal device 2, and removes the carrier particles 9 from the surface of the roller sleeve 5. Hereinafter, an example of an image forming apparatus including the carrier removal device will be described.

[0011] FIG. 2 is a diagram schematically showing an example image forming apparatus. FIG. 3 is a diagram schematically showing the periphery (or vicinity) of an example carrier removal device provided in the image forming apparatus. An image forming apparatus 1 shown in FIG. 2 is a device which forms a color image by using cyan, magenta, yellow, and black colors. The image forming apparatus 1 includes a conveying device 10 which conveys a sheet 15 corresponding to a printing medium, photosensitive drums 40C, 40M, 40Y, and 40K which are examples of the image carriers to form respective electrostatic latent images, developing devices 20C, 20M, 20Y, and 20K located adjacent the photosensitive drums 40C, 40M, 40Y, and 40K to develop the respective electrostatic latent images with toner of the colors of cyan, magenta, yellow, and black, respectively, a transfer device 30 to which the toner images of the respective colors are primarily transferred and which secondarily transfers the toner images to the sheet 15, a fixing device 50 which fixes the toner images to the sheet 15, and a discharge device 60 which discharges the sheet 15. The photosensitive drums 40C, 40M, 40Y, and 40K have similar configurations and any one thereof may be referred to herein as a photosensitive drum 40. The developing devices 20C, 20M, 20Y, and 20K have similar configurations and any one thereof may be referred to herein as a developing device 20. The developing device 20, a lubricant roller 100, a cleaning blade 43, a charging roller 41 , and an exposure unit (or exposure device) 42 are provided around the corresponding photosensitive drum 40.

[0012] The conveying device 10 conveys the sheet 15 which is a print medium on which an image is to be formed along a conveyance path 12. The sheet 15 is stored in a stacked state (in a stack of sheets 15) in a cassette 17, and is subsequently picked up from the stack and conveyed by a feeding roller 11. The conveying device 10 guides the sheet 15 to reach a transfer region 13 through the conveyance path 12 at a timing at which the toner image to be transferred to the sheet 15 reaches the transfer region 13.

[0013] The developing devices 20C, 20M, 20Y, and 20K are provided for the respective four colors of toner. Each developing device 20 includes a developing roller 21 which carries toner to the adjacent photosensitive drum 40. In the developing device 20, a two-component developer containing nonmagnetic toner and magnetic carrier particles is used as the developer. In the developing device 20, the toner and the carrier particles are adjusted to a targeted mixing ratio. The toner and the carrier particles are mixed and stirred, to disperse the toner, and the developer to which the optimum charge amount is applied is adjusted. The developer is carried on the developing roller 21. Then, when the developer is conveyed to a developing region facing the photosensitive drum 40 by the rotation of the developing roller 21 , the toner contained in the developer carried on the developing roller 21 is transferred to the electrostatic latent image formed on the surface of the photosensitive drum 40 and the electrostatic latent image is developed to form a toner image with the corresponding color of toner. [0014] The transfer device 30 receives the toner images formed on the respective photosensitive drums 40C, 40M, 40Y, and 40K, in a layered manner so as to form a single layered toner image, and conveys the layered toner image to the transfer region 13 where the layered toner image is secondarily transferred to the sheet 15. The transfer device 30 includes a transfer belt 31 (conveyance belt) which is an endless belt to which the toner image is primarily transferred from the respective photosensitive drums 40C, 40M, 40Y, and 40K, in a layered manner so as to form a single layered toner image, a suspension roller 34 which supports the transfer belt 31 , idler rollers 35 and 36, a drive roller 37 which drives the transfer belt 31 , primary transfer rollers 32C, 32M, 32Y, and 32K which interpose the transfer belt 31 between the primary transfer rollers 32C, 32M, 32Y, and 32K and the photosensitive drums 40C, 40M, 40Y, and 40K, and a secondary transfer roller 33 which interposes the transfer belt 31 between the secondary transfer roller 33 and the drive roller 37.

[0015] The photosensitive drum 40 may be referred to as an electrostatic latent image carrier. The photosensitive drums 40C, 40M, 40Y, and 40K are provided for the four respective colors, and are arranged along the moving direction of the transfer belt 31. The circumferential surface of each photosensitive drum 40 forms a rotatable surface 40a. The photosensitive drum 40 shown in FIG. 3 rotates clockwise around an axis extending orthogonally to the view of the figure. As described above, the toner (e.g., toner particles) is transferred from the developing roller 21 to the surface 40a of the photosensitive drum 40. When the toner is transferred, the carrier particles may move from the developing roller 21 to the surface 40a of the photosensitive drum 40. The carrier particles transferred to the surface 40a may remain on the surface 40a while being separated from the toner when the toner image is primarily transferred to the transfer belt 31 . In this case, the surface 40a of the photosensitive drum 40 conveys the carrier particles in a rotational direction. Additionally, a part of the carrier particles transferred to the surface 40a may move to the transfer belt 31 together with the toner when the toner image is primarily transferred to the transfer belt 31.

[0016] The lubricant roller 100 is provided along the circumference of the photosensitive drum 40. The lubricant roller 100 is located between the developing roller 21 and the cleaning blade 43 along the circumference of the photosensitive drum 40. The lubricant roller 100 is located on the upstream side of the cleaning blade 43 in the rotational direction of the photosensitive drum 40. The lubricant roller 100 may rotate to follow the rotation of the photosensitive drum 40. The lubricant roller 100 carries the lubricant supplied from a lubricant source 150. The lubricant roller 100 applies the carried lubricant to the surface 40a of the photosensitive drum 40. The example lubricant roller 100 is described further below.

[0017] The lubricant source 150 is provided to be in contact with the lubricant roller 100. The lubricant source 150 comes into contact with the lubricant roller 100 so that the lubricant is carried on the lubricant roller 100. The lubricant source 150 has a bar shape which extends in the axial direction of the lubricant roller 100 (a direction orthogonal to the view of FIG. 2). The lubricant source 150 is provided to come into contact with the lubricant roller 100. The lubricant source 150 may be biased by a biasing member such as a spring to be pressed against the lubricant roller 100. The lubricant roller 100 scrapes the lubricant source 150 at the contact position with the lubricant source 150 and supplies the scraped lubricant to the surface 40a at the contact position with the photosensitive drum 40. The lubricant source 150 is formed of, for example, zinc stearate, barium stearate, or lead stearate.

[0018] The cleaning blade 43 collects the toner remaining on the photosensitive drum 40. The cleaning blade 43 collects the toner (residual toner) remaining on the photosensitive drum 40 after the toner image is primarily transferred from the photosensitive drum 40 to the transfer belt 31 . The cleaning blade 43 is formed of an elastic body such as urethane rubber. The cleaning blade 43 is held by a holding member 43a to be swingable (e.g., pivotable) and is pressed against the surface 40a of the photosensitive drum 40 by applying a load to the holding member 43a due to the elastic force of the elastic member 43b. The cleaning blade 43 removes the residual toner on the surface 40a of the photosensitive drum 40 by coming into contact with the surface 40a of the photosensitive drum 40. Further, the cleaning blade 43 flattens the lubricant applied to the surface 40a of the photosensitive drum 40 by the lubricant roller 100 and spreads the lubricant on the surface 40a of the photosensitive drum 40 substantially uniformly.

[0019] The charging roller 41 is provided adjacent the photosensitive drum 40. The charging roller 41 is a charging member that charges the surface of the photosensitive drum 40 to a predetermined potential. The charging roller 41 rotates to follow the rotation of the photosensitive drum 40. A cleaning roller 41 a is provided adjacent the charging roller 41 . The cleaning roller 41 a is a cleaning member that cleans the surface of the charging roller 41 .

[0020] With reference to FIG. 2, the exposure unit 42 exposes the surface of the photosensitive drum 40 charged by the charging roller 41 to a light, in response to an image to be formed on the sheet 15. Accordingly, a portion of the surface of the photosensitive drum 40 that is exposed to the light, changes in potential so that an electrostatic latent image is formed on the surface of the photosensitive drum 40.

[0021] Toner tanks 18C, 18M, 18Y, and 18K respectively face the developing devices 20C, 20M, 20Y, and 20K. The toner tanks 18C, 18M, 18Y, and 18K respectively store cyan, magenta, yellow, and black toners. The toner tanks 18C, 18M, 18Y, and 18K have similar configurations and any one thereof may be referred to herein as a toner tank 18. The toner in the toner tank 18 is supplied to the corresponding developing device 20. The developing device 20 develops the electrostatic latent image formed on the photosensitive drum 40 with the toner supplied from the toner tank 18 to generate a corresponding toner image. [0022] The fixing device 50 fixes the toner image to the sheet 15 by passing the sheet 15 through a fixing nip region for heating and pressing the sheet. The fixing device 50 includes a heating roller 52 which heats the sheet 15 and a pressing roller 54 which presses the sheet against the heating roller 52 while driving the heating roller to rotate. A fixing nip region is provided between the heating roller 52 and the pressing roller 54. The discharge device 60 includes discharge rollers 62 and 64 which discharge the sheet 15 including the fixed toner image to the outside of the image forming apparatus 1 .

[0023] The image forming apparatus 1 further includes a control unit (or controller) 80. The control unit 80 has a function of controlling the operation of the image forming apparatus 1. The control unit 80 includes a storage unit (or storage device) and a processor. The storage unit (or storage device) of the control unit 80 stores a control program (e.g., data and instructions) that is executable by the processor for controlling operations of the image forming apparatus 1 .

[0024] Next, a printing process using the image forming apparatus 1 will be described. When an image signal of an image to be recorded is input to the image forming apparatus 1 , the control unit 80 of the image forming apparatus 1 rotates the feeding roller 11 and picks up and conveys the sheet 15 stacked in the cassette 17. In a charging operation, the surface of the photosensitive drum 40 is charged to a predetermined potential by the charging roller 41. In an exposing operation, the exposure unit 42 irradiates the surface of the photosensitive drum 40 with a laser beam on the basis of the input image signal to form an electrostatic latent image.

[0025] In a developing operation, the developing device 20 develops the electrostatic latent image formed on the surface of the photosensitive drum 40 to form a toner image on the surface of the photosensitive drum 40. In a transfer operation, toner image is primarily transferred from the photosensitive drum 40 to the transfer belt 31 at a region where the photosensitive drum 40 faces the transfer belt 31. The respective toner images formed on four photosensitive drums 40 are sequentially layered on the transfer belt 31 to form a single layered toner image. The layered toner image is secondarily transferred to the sheet 15 conveyed from the conveying device 10 at the transfer region 13 where the drive roller 37 and the secondary transfer roller 33 face each other.

[0026] The sheet 15 to which the layered toner image is transferred is conveyed to the fixing device 50. The fixing device 50 heats and presses the sheet 15 in the fixing nip region when the sheet 15 passes through the fixing nip region between the heating roller 52 and the pressing roller 54. In a fixing operation, the fixing device 50 fixes the layered toner image to the sheet 15 by heating and pressing the layered toner image. Then, the sheet 15 is discharged to the outside of the image forming apparatus 1 by the discharge rollers 62 and 64.

[0027] Next, the lubricant roller 100 which is the carrier removal device will be further described. As shown in FIG. 3, the lubricant roller 100 includes a magnetic body 110 and a roller sleeve 120. The magnetic body 110 is, for example, a cylindrically molded plastic magnet, and is fixed to a housing 101 that stores the lubricant roller 100. That is, the magnetic body 110 does not rotate. The roller sleeve 120 has a cylindrical shape and stores the magnetic body 110 in the inner space. The roller sleeve 120 is supported by the housing 101 or the magnetic body 110 to rotate around the magnetic body 110 while storing (or housing) the magnetic body 110 inside the roller sleeve 120. The roller sleeve 120 may be driven to rotate by a drive source such as a motor. The roller sleeve 120 in the example shown in the drawing rotates counterclockwise, for example, around an axis extending orthogonally to the view of FIG. 3.

[0028] The example roller sleeve 120 includes a base 121 (tubular base) and an application layer 125. The base 121 is formed in a cylindrical shape by a material that substantially does not shield magnetism. The material that substantially does not shield magnetism includes a material that does not shield at least a part of magnetism, that is, a material that at least partially transmits magnetism (e.g., at least partially transmits the magnetic field of the magnetic body 110). For example, the base 121 may be formed of a non-magnetic metal. Examples of the material of the base 121 include aluminum, stainless steel, and the like. The application layer 125 is formed of a material that substantially does not shield magnetism, and covers the entire outer circumferential surface of the base 121. The application layer 125 may be an elastic body that can adhere to the surface 40a of the photosensitive drum 40, and is formed of, for example, a foam (foam layer). The application layer 125 may be a sponge-like elastic body. An example of the sponge-like elastic body includes urethane foam. As described above, the application layer 125 of the roller sleeve 120 scrapes the lubricant source 150 at a contact position 125a (first contact position) with the lubricant source 150 and supplies the scraped lubricant to the surface 40a at a contact position 125b (second contact position) with the photosensitive drum 40.

[0029] The magnetic pole formed by the magnetic body 110 includes a pickup pole 111 and a release pole 113. The pickup pole 111 forms a magnetic field 111a which draws the carrier particles from the surface 40a of the photosensitive drum 40 onto the roller sleeve 120. In an example, the pickup pole 111 is set to correspond to a region facing the photosensitive drum 40 of the roller sleeve 120, that is, the contact position 125b of the roller sleeve 120 that contacts the photosensitive drum 40. The magnetic field 111 a which is formed by the pickup pole 111 covers the contact position 125b of the roller sleeve 120 that contacts the photosensitive drum 40. In an example, the pickup pole 111 may be an N pole.

[0030] The release pole 113 forms magnetic fields 113a and 113b for releasing the carrier particles from the roller sleeve 120 of the lubricant roller 100. In an example, the release pole 113 is disposed on the downstream side of the pickup pole 111 in the rotational direction of the roller sleeve 120. That is, the release pole 113 is set to a position on the downstream side of the contact position 125b of the roller sleeve 120 that contacts the photosensitive drum 40, in the rotational direction of the lubricant roller 100. The magnetic fields 113a and 113b formed by the release pole 113 do not cover the surface 40a of the photosensitive drum 40. Further, the release pole 113 is set to the upstream side of the contact position 125a where the roller sleeve 120 contacts the lubricant source 150, in the rotational direction of the lubricant roller 100. In the example shown in the drawing, the release pole 113 is formed by two magnetic poles 113a and 113b having the same polarity and positioned adjacent to each other in the circumferential direction. The polarity of these magnetic poles may be, for example, an S pole. The carrier particles drawn (or transferred) to the roller sleeve 120 by the action of the pickup pole 111 are released from the roller sleeve 120 at a position where the magnetic field 113a and the magnetic field 113b are switched, namely a boundary where the magnetic field changes from the magnetic field 113a to the magnetic field 113b. The release position in the example shown in the drawings is positioned within the lower half of the roller sleeve 120 in the vertical direction (e.g., in the direction of gravity).

[0031] As described above, the example magnetic body 110 is a plastic magnet. For example, the magnetic body 110 is formed by molding a resin mixed with magnetic powder into a cylindrical shape and magnetizing the magnetic powder by applying a strong magnetic field to the molded product. Due to such a manufacturing method, in the magnetic body 110 of the example shown in the drawings, a magnetic pole 117 having the same polarity as the pickup pole 111 is formed at a position facing the pickup pole 111 and a magnetic pole 119 having the same polarity as the release pole 113 is formed at a position facing the release pole 113.

[0032] As described above, the example image forming apparatus 1 includes the photosensitive drum 40 which has the rotatable surface 40a and the lubricant roller 100 (carrier removal device) which is disposed adjacent to the photosensitive drum 40 and includes the magnetic body 110 and the roller sleeve 120 rotating around the magnetic body 110. The magnetic body 110 includes the pickup pole 111 which is disposed in a region facing the photosensitive drum 40 in the roller sleeve 120 to draw the carrier particles from the surface 40a onto the roller sleeve 120, and the release pole 113 which is disposed on the downstream side of the pickup pole 111 in the rotational direction of the roller sleeve 120 to release the carrier particles from the roller sleeve 120.

[0033] In the above-described image forming apparatus 1 , the surface 40a of the photosensitive drum 40 may be worn by the cleaning blade 43 (e.g., due to friction). In this case, a deviation of the pressing force of the cleaning blade 43 with respect to the surface 40a of the photosensitive drum 40 may cause a deviation in the amount of wear of the photosensitive drum 40 in the axial direction of the photosensitive drum 40. Further, since the carrier particles remaining on the surface 40a of the photosensitive drum 40 are held by the lubricant roller 100, the carrier particles may be rubbed against the surface 40a of the photosensitive drum 40 so as to further cause wear in the surface 40a of the photosensitive drum 40. [0034] When the amount of wear of the photosensitive drum 40 deviates in the axial direction, the surface potential of the photosensitive drum 40 also deviates. That is, a film covering the surface 40a of the photosensitive drum 40 is worn, such that the surface potential of the portion having a relatively thin film thickness increases and the surface potential of the portion having a greater film thickness decreases. In this case, since the carrier particles are discharged from the developing device 20 to the portion having a high surface potential, the amount of the carrier particles held by the lubricant roller 100 at the portion having a high surface potential, increases. Therefore, in the region in the surface 40a of the photosensitive drum 40 where the surface potential is high and the film thickness is relatively thin, the wear due to the carrier particles held by the lubricant roller 100 can be increased.

[0035] As described above, in the example image forming apparatus, the lubricant roller 100 includes the magnetic body 110 having the pickup pole 111 and the release pole 113. Accordingly, the carrier particles carried on the surface 40a of the photosensitive drum 40 may be collected by the lubricant roller 100 and subsequently released from the lubricant roller 100. In this way, since the carrier particles remaining on the surface 40a of the photosensitive drum 40 do not remain on (are not held by) the lubricant roller 100, so as to suppress the wear of the surface 40a of the photosensitive drum 40 due to the carrier particles.

[0036] FIG. 4 is a graph showing a relationship between the number of cycles and the amount of wear of a photosensitive body in a test image forming apparatus without the magnetic body 110. FIG. 5 is a graph showing a relationship between the number of cycles and the amount of wear of a photosensitive body in an example image forming apparatus including the magnetic body 110. The number of cycles is a value that is an index of the number of printed sheets. That is, FIGS. 4 and 5 show changes in the film thickness of the surface of the photosensitive body over time. "Front" and "rear" in the graph refer to opposite end portions in the axial direction of the photosensitive body, respectively. In FIGS. 4 and 5, the amount of wear due to the cleaning blade is greater on the front end portion than on the rear end portion. When the lubricant roller does not include the magnetic body, the wear on the front end portion tends to increase as shown in FIG. 4. On the other hand, when the lubricant roller 100 includes the magnetic body 110, the wear on the front side is less likely to progress as shown in FIG. 5. In a comparison of the graphs of FIGS. 4 and 5, when the number of cycles is 4000, the difference in the amount of wear between the front and the rear is about 20% in FIG. 4, whereas the difference is suppressed to about 10% in FIG. 5.

[0037] In an example, the pickup pole 111 is disposed at the contact position 125b in which the roller sleeve 120 contacts the rotatable surface 40a of the photosensitive drum 40 and the release pole 113 is offset from the contact position 125b in the rotational direction of the roller sleeve 120. In this configuration, the roller sleeve 120 collects the carrier particles by the action of the pickup pole 111 at the contact position 125b contacting the surface 40a. The collected carrier particles are conveyed to a position offset in the rotational direction in accordance with the rotation of the roller sleeve 120 and are released. The release position in the example shown in the drawings is included in the lower half of the roller sleeve 120 in the vertical direction. Therefore, the released carrier particles can be dropped below the roller sleeve 120. For example, the carrier particles may be collected in a collection container provided below the roller sleeve 120.

[0038] In an example, the photosensitive drum 40 which is the conveyance body, has a cylindrical shape which includes a circumferential surface forming the rotatable surface 40a. In this case, the roller sleeve 120 forms the lubricant roller 100 which applies the lubricant to the circumferential surface of the photosensitive drum 40, the pickup pole 111 of the magnetic body 110 is set to draw the carrier particles from the photosensitive drum 40 to the lubricant roller 100, and the release pole 113 is set to release the carrier particles from the lubricant roller 100. In this configuration, the lubricant roller 100 can function as the carrier removal device. Therefore, an increase in the number of parts is suppressed and an increase in size is suppressed.

[0039] The lubricant roller 100 contacts the lubricant source 150 at the contact position 125a to receive the lubricant and further contacts the photosensitive drum 40 at the contact position 125b to apply the lubricant. The pickup pole 111 is disposed at the contact position 125b of the lubricant roller 100 and the release pole 113 is disposed on the downstream side of the contact position 125b and the upstream side of the contact position 125a in the rotational direction of the lubricant roller 100. In this configuration, since the carrier particles drawn (or transferred) to the lubricant roller 100 are released before reaching the contact position 125a with the lubricant source 150, the carrier particles are inhibited from contacting the lubricant source 150.

[0040] Although various examples have been described and shown herein, but it should be understood that other examples can be modified in their arrangement and details.

[0041] For example, the pattern of the magnetic pole formed on the magnetic body 110 is not limited to the form illustrated in FIG. 3. For example, FIG. 6 is a diagram showing another example of the lubricant roller 100 as the carrier removal device. The magnetic body 110 shown in FIG. 6 has the pickup pole 111 and the release pole 113 as the magnetic poles and does not include the magnetic poles 117 and 119. The pickup pole 111 is set to correspond to the contact position 125b of the roller sleeve 120 that contacts the photosensitive drum 40. The magnetic field 111 a formed by the pickup pole 111 covers the contact position 125b of the roller sleeve 120 that contacts the photosensitive drum 40. The release pole 113 is formed from the downstream end of the pickup pole 111 to the upstream end of the pickup pole 111 in the rotational direction of the roller sleeve 120. The magnetic field 113a and the magnetic field 113b formed by the release pole 113 are switched at the position on the upstream side of the contact position 125a between the roller sleeve 120 and the lubricant source 150 in the rotational direction of the lubricant roller 100. The carrier particles collected by the roller sleeve 120 are released at the switching position between the magnetic field 113a and the magnetic field 113b, that is, the upstream position of the contact position 125a.

[0042] Further, although the examples of the carrier removal device that have been described with reference to shown in FIG. 3 and the like serve as the lubricant roller, in other examples, the carrier removal device may be included in the image forming apparatus in a different form. FIG. 7 is a diagram schematically showing the periphery (or vicinity) of an example belt cleaning device provided in an image forming apparatus. As shown in FIG. 7, the example image forming apparatus includes the belt cleaning device for removing the toner remaining on the transfer belt 31 .

[0043] The belt cleaning device includes a first conductive roller 200, a diffusion roller 230, and a second conductive roller 240 in this order from the upstream side in the moving direction of the transfer belt 31 . The transfer belt 31 moves (rotates) counterclockwise in the view of FIG. 7. The first conductive roller 200 interposes the transfer belt 31 between the first conductive roller 200 and an adjacent auxiliary roller 201. A predetermined voltage is applied to the first conductive roller 200 in order to align the charge of the toner on the transfer belt 31 with (or set the charge to) a predetermined polarity (e.g., a negative polarity). A cleaning blade 225 which contacts the first conductive roller 200 to scrape off the toner of the surface of the first conductive roller 200 is disposed adjacent the first conductive roller 200. The diffusion roller 230 diffuses the toner on the transfer belt 31 and reduces the adhesive force of the toner on the transfer belt 31 . For example, the diffusion roller 230 may be a brush roller. A cleaning blade 230a which contacts the diffusion roller 230 to scrape off the toner adhering to the diffusion roller 230 is disposed adjacent the diffusion roller 230.

[0044] The second conductive roller 240 interposes the transfer belt 31 between the second conductive roller 240 and an adjacent auxiliary roller 241 . A voltage of a polarity (e.g., a positive polarity) opposite to the polarity of the voltage applied to the first conductive roller 200, is applied to the second conductive roller 240 in order to collect the toner having the same polarity as the first conductive roller 200 (e.g., negative polarity), from the transfer belt 31. A cleaning blade 240a which contacts the second conductive roller 240 to scrape off the toner of the surface is disposed adjacent the second conductive roller 240. With such a configuration, the toner remaining on the transfer belt 31 is charged to the negative polarity by the first conductive roller 200, is diffused by the diffusion roller 230, and is collected by the second conductive roller 240. Additionally, since the toner on the transfer belt 31 is finally removed by the second conductive roller 240, the second conductive roller 240 can be said to be a cleaning device on its own.

[0045] In the cleaning device with such a configuration, the first conductive roller 200 may serve as the carrier removal device. The example first conductive roller 200 includes a magnetic body 210 and a roller sleeve 220. The magnetic body 210 is, for example, a plastic magnet molded into a cylindrical shape, and is fixed so as to not rotate about an axial direction. The roller sleeve 220 has a cylindrical shape and stores the magnetic body 210 in an inner space. The roller sleeve 220 is rotatable relative to the magnetic body 210 so as to rotate independently from the magnetic body 210 while housing the magnetic body 210. The roller sleeve 220 may be driven by a drive source such as a motor to rotate. The roller sleeve 220 of the example shown in the drawing rotates counterclockwise, for example, about an axis extending orthogonally to the view of FIG. 7.

[0046] The roller sleeve 220 is formed in a cylindrical shape by a conductive material that substantially does not shield magnetism. For example, the roller sleeve 220 may be formed of a non-magnetic metal. Examples of the material of the roller sleeve 220 include aluminum, stainless steel, and the like. [0047] The magnetic pole formed by the magnetic body 210 includes a pickup pole 211 and a release pole 213. The pickup pole 211 forms a magnetic field 211a which draws the carrier particles from the surface of the transfer belt 31 onto the roller sleeve 220. In an example, the pickup pole 211 is positioned in a region facing the transfer belt 31 of the roller sleeve 220, that is, the contact position of the roller sleeve 220 that contacts the transfer belt 31 . The magnetic field 211 a which is formed by the pickup pole 211 covers the contact position of the roller sleeve 220 that contacts the transfer belt 31 . In an example, the pickup pole 211 may be an N pole.

[0048] The release pole 213 forms magnetic fields 213a and 213b for releasing the carrier particles from the roller sleeve 220 of the first conductive roller 200. In an example, the release pole 213 is disposed on the downstream side of the pickup pole 211 in the rotational direction of the roller sleeve 220. The magnetic fields 213a and 213b which are formed by the release pole 213 do not cover the surface 40a of the transfer belt 31 . In the example shown in the drawing, the release pole 213 is formed by two magnetic poles having the same polarity and adjacent to each other in the circumferential direction so that the magnetic fields 213a and 213b are formed. The polarities of these magnetic poles may be, for example, N poles. The carrier particles drawn to the roller sleeve 220 by the action of the pickup pole 211 are released from the roller sleeve 220 at a position in which the magnetic field 213a and the magnetic field 213b are switched. The switching position of the magnetic field 213a and the magnetic field 213b is set to the upstream position of the cleaning blade 225 in the rotational direction of the first conductive roller 200. The pickup pole 211 is formed at the contact position in which the roller sleeve 220 contacts the conveyance surface of the transfer belt 31 and the release pole 213 is disposed at a position substantially facing the contact position of the roller sleeve 220 that contacts the transfer belt 31 . That is, the release pole 213 corresponds to a position in which the contact position of the roller sleeve 220 that contacts the transfer belt 31 is rotated by 180° about the axis of the roller sleeve 220. In the magnetic body 210, the release pole 113 having the same polarity as the pickup pole 211 is formed at a position facing the pickup pole 211 and a magnetic pole 217 is formed between the pickup pole 211 and the release pole 213 that contacts the rotational direction. Further, a magnetic pole 219 is formed between the release pole 213 and the pickup pole 211 that contacts the rotational direction. The polarities of the magnetic poles 217 and 219 are S poles opposite to the polarities of the pickup pole 211 and the release pole 213.

[0049] As described above, since the first conductive roller 200 which is the carrier removal device is provided adjacent to the transfer belt 31 , it is possible to more efficiently remove the carrier particles on the transfer belt 31 . Accordingly, the transfer belt 31 is better protected from a damage caused by the carrier particles. Further, since the first conductive roller 200 serves as the carrier removal device, an increase in the number of parts is suppressed and an increase in size of the device may be suppressed.

[0050] The pickup pole 211 of the magnetic body 210 is set to draw the carrier particles from the transfer belt 31 to the roller sleeve 220. The release pole 213 is set to release the carrier particles from the roller sleeve 220 at a position facing the pickup pole 211. Therefore, since the carrier particles are released at a position farthest from the transfer belt 31 , the carrier particles released from the roller sleeve 220 are inhibited from returning to the transfer belt 31.

[0051] The first conductive roller 200 is disposed on the upstream side of the second conductive roller 240 that is provided on the upstream side of the photosensitive drum 40, in the rotational direction of the transfer belt 31. Therefore, it is possible to suppress the carrier particles from damaging the transfer belt 31 at the contact position between the second conductive roller 240 and the transfer belt 31 .

[0052] Further, in the examples shown in FIG. 3 and the like, an example in which the magnetic body 110 has a cylindrical shape is shown. However, the shape of the magnetic body is not particularly limited if the magnetic body can form the pickup pole and the release pole. For example, the magnetic body may be a cylindrical plastic magnet disposed on an outer periphery of a cylindrical core metal around the core metal. Further, the magnetic body may include a plurality of divided magnets.

[0053] Further, the size of the roller sleeve 120 of the lubricant roller 100 is not particularly limited. For example, the diameter of the roller sleeve 120 may be the same as the diameter of the developing roller 21 and when the developing roller 21 includes a sleeve, the sleeve of the developing roller 21 and the roller sleeve 120 may be the same part (e.g., formed as a single component).

[0054] 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.