BACKGROUND

[0001] There is an image forming apparatus including a channel forming member that extends longitudinally in a rotation direction of a development roller, between the development roller and an inner wall of a development device body to suppress a rise in atmospheric pressure inside the development device body and to suppress the scattering of a toner to the outside of the development device body.

BRIEF DESCRIPTION OF DRAWINGS

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

[0003] FIG. 2 is a schematic rear plan view of an example development device, in which the development device is shown without the photosensitive drum.

[0004] FIG. 3 is a schematic cross-sectional view taken along line Ill-Ill of the example development device of FIG. 2, illustrated with the photosensitive drum.

[0005] FIG. 4 is an enlarged partial view of the development device of FIG. 3.

[0006] FIG. 5 is a schematic cross-sectional view taken along line V-V of the example development device of FIG. 2, illustrated with the photosensitive drum.

[0007] FIG. 6 is an enlarged partial view of the development device of FIG. 5.

[0008] FIG. 7 is a schematic diagram illustrating a developer carried on a development roller between the development roller and a housing.

[0009] FIG. 8 is a schematic diagram illustrating an example shape of an edge of an opening of the housing. [0010] FIG. 9 is a schematic diagram illustrating another example shape of an edge of the opening of the housing.

[0011] FIG. 10 is a graph showing evaluation results of scattering of a toner.

[0012] FIG. 11 is a schematic cross-sectional view of a portion of another example development device, illustrating a space downstream the nip portion.

[0013] FIG. 12 is a schematic cross-sectional view of a portion of another example development device, illustrating a space downstream the nip portion at a center portion of the development device.

[0014] FIG. 13 is a schematic cross-sectional view of the development device of FIG. 12, illustrating the space downstream the nip portion at an end position of the development device.

DETAILED DESCRIPTION

[0015] An image forming apparatus of an example includes a development roller that is rotatable to carry a toner and that includes a center portion extending in a longitudinal direction and end portions extending from opposite ends of the center portion, a housing to accommodate the development roller and that forms an opening extending in the longitudinal direction to expose a part of the development roller, and a photosensitive drum that extends in the longitudinal direction and that faces the development roller at the opening of the housing. A position where the development roller is closest to the photosensitive drum corresponds to a nip position. A space between the development roller, the photosensitive drum and the housing is located downstream the nip position in a rotation direction of the development roller. The space has a cross-sectional area taken orthogonally to the longitudinal direction, that is smaller at each of the end portions of the development roller than at the center portion.

[0016] In some apparatuses, toner tends to scatter from ends of the development roller. In the example image forming apparatus, as described above, the space between the development roller, the photosensitive drum and the housing that is located downstream the nip position in the rotation direction of the development roller, has a cross-sectional area taken orthogonally to the longitudinal direction that is smaller at each of the end portions of the development roller than at the center portion. For this reason, the scattering of the toner can be reduced.

[0017] An image forming apparatus of another example includes a development roller that is rotatable to carry a toner and that includes a center portion extending in a longitudinal direction and end portions extending from opposite ends of the center portion, a housing to accommodate the development roller and forming an opening extending in the longitudinal direction to expose a part of the development roller, and a photosensitive drum that extends in the longitudinal direction and that faces the development roller at the opening of the housing. A position where the development roller is closest to the photosensitive drum corresponds to a nip portion. A channel is formed between the development roller, the photosensitive drum and the housing on a downstream side of the nip position in a rotation direction of the development roller. The channel is narrowed at each of the end portions of the development roller relative to the center portion. [0018] In some apparatuses, the toner tends to scatter from ends of the development roller. In the example image forming apparatus, the channel that is formed between the development roller, the photosensitive drum and the housing on the downstream side of the nip position in the rotation direction of the development roller, is narrowed at each of the end portions of the development roller relative to the center portion. For this reason, the scattering of the toner in an airflow generated through the channel by the rotation of the development roller can be reduced.

[0019] 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.

[0020] With reference to FIG. 1 , an example image forming apparatus 1 may use toners of four colors such as magenta, yellow, cyan and black to form a color image. The image forming apparatus 1 includes a conveying device 10, a plurality of photosensitive drums 20, a plurality of development devices 30, a transfer device 40, a fixing device 50 and a discharge device 60.

[0021] The conveying device 10 conveys a sheet (e.g., a sheet of paper) M that is a recording medium on which an image is to be formed. The plurality of photosensitive drums 20 include photosensitive drums 20M, 20Y, 20C and 20K. The photosensitive drums 20M, 20Y, 20C and 20K form electrostatic latent images for forming magenta, yellow, cyan and black toner images. Since the photosensitive drums 20M, 20Y, 20C and 20K are similar in configuration, the photosensitive drums 20M, 20Y, 20C and 20K may be collectively described as the "photosensitive drums 20" unless otherwise specified, and a single one of the photosensitive drums 20M, 20Y, 20C and 20K may be referred to herein as a "photosensitive drum 20".

[0022] The development device 30, a charging device 22, an exposure device 23 and a cleaning unit 24 are provided on a periphery of the photosensitive drum 20. The charging device 22 may charge a surface of the photosensitive drum 20 to a predetermined potential. The exposure device 23 exposes the surface of the photosensitive drum 20 to a light according to an image to be formed on the sheet M, after the surface has been charged by the charging device 22. Accordingly, an electrostatic latent image corresponding to the image to be formed on the sheet M is formed on the surface of the photosensitive drum 20. The cleaning unit 24 retrieves a toner that remains on the photosensitive drum 20.

[0023] The plurality of development devices 30 include development device 30M, 30Y, 30C and 30K. The development devices 30M, 30Y, 30C and 30K are disposed adjacent the respective photosensitive drums 20M, 20Y, 20C and 20K, to develop the electrostatic latent images formed on the surfaces of the photosensitive drums 20M, 20Y, 20C and 20K, so as to generate respective toner images. Since the development devices 30M, 30Y, 30C and 30K are similar in configuration, the development devices 30M, 30Y, 30C and 30K may be collectively described as the "development devices 30", and a single one of the development devices 30M, 30Y, 30C and 30K may be referred to herein as a "development device 30".

[0024] Each development device 30 includes a development roller 31 to supply the toner to the surface of the adjacent photosensitive drum 20. The development roller 31 supplies the toner to the surface of the photosensitive drum 20, so as to develop the electrostatic latent image formed on the surface of the photosensitive drum 20. Accordingly, a toner image corresponding to the electrostatic latent image, namely, a toner image corresponding to the image to be formed on the sheet M is formed on the surface of the photosensitive drum 20. [0025] The transfer device 40 conveys the toner images developed by development devices 30, and transfers the toner images on to the sheet M. The transfer device 40 includes an intermediate transfer belt 41 onto which the toner images formed on the surface of the photosensitive drums 20 are primarily transferred in a layered manner so as to form a single composite toner image, and which secondarily transfers the composite toner image onto the sheet M.

[0026] The fixing device 50 heats and presses the sheet M including the composite toner image, to fix the toner image to the sheet M. The discharge device 60 discharges the sheet M, to which the toner image is fixed by the fixing device 50, to the outside of the apparatus.

[0027] With reference to FIGS. 1 to 6, the development device 30 illustrated in FIG. 2 includes the development roller 31 that is rotatable, a housing 32, a first stirring conveyor 33, a second stirring conveyor 34 and a developer regulator 35.

[0028] The development roller 31 extends in a longitudinal direction D1 , and carries a developer containing a toner and a carrier. The development roller 31 is disposed to face the photosensitive drum 20 such that a gap is formed between the development roller 31 and the photosensitive drum 20, and rotates while carrying the developer on a surface thereof, the developer being accommodated in the housing 32. Namely, the development roller 31 rotates in a rotation direction D2 to convey the developer.

[0029] The development roller 31 may have a cylindrical shape, for example. The development roller 31 has a rotation axis 31A extending in the longitudinal direction D1. The development roller 31 is disposed such that the rotation axis 31A of the development roller 31 is parallel to a rotation axis 20A of the photosensitive drum 20 and an interval (or distance) between the development roller 31 and the photosensitive drum 20 is constant in the longitudinal direction D1 . The development roller 31 carries the developer on the surface, the developer being stirred by the first stirring conveyor 33 and the second stirring conveyor 34. The development roller 31 conveys the developer being carried to a development region DA to develop the electrostatic latent image on the photosensitive drum 20. The development region DA is a region located between the development roller 31 and the photosensitive drum 20, and is a region where the development roller 31 and the photosensitive drum 20 face each other. The development region DA includes a nip position NP where the development roller 31 and the photosensitive drum 20 are closest to each other. [0030] The development roller 31 includes a development sleeve 311 forming a surface layer of the development roller 31 , and a magnet 312 disposed inside the development sleeve 311 . The development sleeve 311 is a cylindrical member made of non-magnetic metal. The development sleeve 311 is rotatable about the rotation axis 31 A. For example, the magnet 312 is fixed to a shaft on the rotation axis 31 A that is fixed to the housing 32, and has a plurality of magnetic poles. For example, the development sleeve 311 is rotatably supported by the shaft, and is rotationally driven by a drive source such as a motor. The developer is carried on a surface of the development sleeve 311 by a magnetic force of the magnet 312. The development roller 31 conveys the developer in a rotation direction of the development sleeve 311 when the development sleeve 311 rotates. Incidentally, a rotation of the development roller 31 refers to a rotation of the development sleeve 311 , and the rotation direction D2 of the development roller 31 refers to the rotation direction of the development sleeve 311 .

[0031] The magnet 312 is disposed at a center portion of the development roller 31 in the longitudinal direction D1 , and is not disposed at opposite end portions of the development roller 31 in the longitudinal direction D1. For this reason, the development roller 31 has a conveying region 313 including the magnet 312, and a pair of non-conveying regions 314 that do not include the magnet 312. The conveying region 313 is located at the center portion of the development roller 31 in the longitudinal direction D1 , and the pair of nonconveying regions 314 are located at the opposite end portions of the development roller 31 in the longitudinal direction D1.

[0032] The housing 32 is a container for the development device 30, and includes a development chamber H inside. The development chamber H of the housing 32 accommodates the developer containing the toner and the carrier. In addition, the development chamber H of the housing 32 accommodates the development roller 31 , the first stirring conveyor 33, the second stirring conveyor 34 and the developer regulator 35. The housing 32 includes an opening 321 at a position where the development roller 31 faces the photosensitive drum 20, and the toner in the development chamber H is supplied from the opening 321 to the photosensitive drum 20.

[0033] A space is formed between the development roller 31 , the photosensitive drum 20 and the housing 32 by the opening 321. In the space between the development roller 31 , the photosensitive drum 20 and the housing 32, a space that is located downstream the nip position NP in the rotation direction D2 of the development roller 31 is referred to as a space S. The space S includes a space extending from the nip position NP to a downstream edge 322 of the opening 321 of the housing 32, that is surrounded by the development roller 31 , the photosensitive drum 20 and the housing 32. Namely, the development roller 31 , the photosensitive drum 20 and the housing 32 substantially delimit the space S. In addition, the space S includes a first gap S1 between the development roller 31 and the housing 32 adjacent to the downstream edge 322 of the opening 321 , and a second gap S2 between the photosensitive drum 20 and the housing 32 adjacent to the downstream edge 322 of the opening 321 (cf. FIG. 4). A surface of the housing 32 that faces the development roller 31 to form the first gap S1 is referred to as a first facing surface 323. In addition, a surface of the housing 32 that faces the photosensitive drum 20 to form the second gap S2 is referred to as a second facing surface 324.

[0034] A seal 325 is attached to the housing 32. The seal 325 is disposed upstream the nip position NP in the rotation direction D2 of the development roller 31 , and a tip portion of the seal 325 abuts the photosensitive drum 20. For this reason, the seal 325 seals a space between the photosensitive drum 20 and the housing 32 on an upstream side of the nip position NP in the rotation direction D2 of the development roller 31 .

[0035] The first stirring conveyor 33 and the second stirring conveyor 34 stir the developer which includes the carrier that is magnetic and the toner that is not magnetic, to frictionally charge the carrier and the toner. In addition, the first stirring conveyor 33 and the second stirring conveyor 34 convey the developer while stirring the developer. The first stirring conveyor 33 is disposed in a first conveying path 331 disposed below the development chamber H, and the second stirring conveyor 34 is disposed in a second conveying path 341 disposed below the first conveying path 331. The first conveying path 331 and the second conveying path 341 extend in the longitudinal direction D1 , and communicate with each other at opposite end portions in the longitudinal direction D1. The first stirring conveyor 33 is a supply auger that stirs the developer and that supplies the developer to the development roller. The second stirring conveyor 34 is an admix auger that stirs the developer to convey the developer between the first conveying path 331 and the second conveying path 341 .

[0036] The developer regulator 35 limits a thickness of the developer transported by the development roller 31 . Namely, the developer regulator 35 limits a carrying amount of the developer carried on the development roller 31. The developer regulator 35 is disposed in the vicinity of the development region DA on an upstream side of the development region DA in the rotation direction D2 of the development roller 31. The developer regulator 35 forms a predetermined gap between the developer regulator 35 and the development roller 31 . Accordingly, when the development roller 31 rotates, the developer regulator 35 limits a layer thickness of the developer carried on a peripheral surface of the development roller 31 , to level the layer thickness to a uniform layer thickness. A conveyance amount of the developer that is conveyed to the development region DA by the development roller 31 can be adjusted by adjusting an interval (or distance) between the developer regulator 35 and the development roller 31.

[0037] When the development roller 31 rotates, air is taken into the development chamber H by the developer carried on the surface of the development roller 31 , and the atmospheric pressure of the development chamber H (internal pressure of the housing 32) increases. When the atmospheric pressure of the development chamber H increases, air of the development chamber H is discharged from the opening 321 of the housing 32. In this case, the seal 325 seals the space between the photosensitive drum 20 and the housing 32 on the upstream side of the nip position NP in the rotation direction D2 of the development roller 31 . Consequently, the air discharged from the development chamber H to the opening 321 flows to a downstream side of the nip position NP in the rotation direction D2 of the development roller 31.

[0038] FIG. 7 illustrates the developer that may be carried on the development roller 31 between the development roller 31 and the housing 32. A hatched portion in FIG. 7 indicates the developer. With reference to FIG. 7, in the conveying region 313, the developer is carried on the development roller 31 by the magnetic force of the magnet 312. However, the magnetic force (or magnetic field) of the magnet 312 is curved outwardly at opposite end portions of the conveying region 313 in the longitudinal direction D1 , so that the amount of the developer carried at the end portions of the development roller 31 is reduced, forming a rounded profile of the carried developer that extends into the nonconveying regions 314. For example, even when a gap between the development roller 31 and the housing 32 at a center portion of the conveying region 313 in the longitudinal direction D1 is filled with the developer carried on the development roller 31 , gaps between the development roller 31 and the housing 32 at the opposite end portions of the conveying region 313 in the longitudinal direction D1 may not be filled with the developer carried on the development roller 31 . As a result, the air discharged from the development chamber H to the opening 321 tends to flow more easily at the respective non-conveying regions 314 and along the opposite end portions of the conveying region 313 in the longitudinal direction D1 , than along the conveying region 313, and the toner accommodated in the development chamber H is more likely to scatter to the outside of the development device 30 along with the flow of the air.

[0039] With reference to FIGS. 2 to 7, the example development roller 31 includes a center portion 315 extending in the longitudinal direction D1 , and end portions 316 and 316 extending from opposite ends of the center portion 315. The center portion 315 is located at the center portion of the development roller 31 in the longitudinal direction D1 , and extends in the longitudinal direction D1. The end portions 316 and 316 are adjacent to the center portion 315, and extend from the opposite ends of the center portion 315 in the longitudinal direction D1. Then, in order to reduce the scattering of the toner, the space S has a cross- sectional area taken orthogonally to the longitudinal direction D1 , that is smaller at each of the end portions 316 and 316 of the development roller 31 than at the center portion 315. Namely, the cross-sectional area of the space S taken orthogonally to the longitudinal direction D1 at each of the end portions 316 and 316 of the development roller 31 is smaller than the cross-sectional area of the space S taken orthogonally to the longitudinal direction D1 at the center portion 315 of the development roller 31 .

[0040] In addition, a channel C is formed between the development roller 31 , the photosensitive drum 20 and the housing 32 on the downstream side of the nip position NP in the rotation direction D2 of the development roller 31 . The channel C is a channel of the air that is discharged from the development chamber H to the opening 321 because of a rise in the internal pressure of the housing 32 caused by the rotation of the development roller 31 , so as to extend at least partially in the space S. The channel C extends from the first gap S1 between the first facing surface 323 of the housing 32 and the development roller

31 to the second gap S2 between the second facing surface 324 of the housing

32 and the photosensitive drum 20 through the downstream edge 322 of the opening 321 of the housing 32. Then, in order to reduce the scattering of the toner in an airflow generated through the channel C by the rotation of the development roller 31 , the channel C is narrowed at each of the end portions 316 and 316 of the development roller 31 relative to the center portion 315. Namely, the channel C is narrower at each of the end portions 316 and 316 of the development roller 31 than at the center portion 315 of the development roller 31 . [0041] Each end portion 316 of the development roller 31 includes, in addition to the corresponding non-conveying region 314, an area 313A. The areas 313A and 313A are located at the opposite end portions of the conveying region 313 in the longitudinal direction D1. Namely, the cross-sectional area of the space S has a change point in the conveying region 313, and a boundary portion between each of the areas 313A and 313A and the center portion 315 corresponds to the change point. The cross-sectional area of the space S is smaller and the channel C is narrower outside the boundary portions, namely at each of the end portions 316 and 316 of the development roller 31 , than at the center portion 315. In other words, each end portion 316 of the development roller 31 includes the corresponding area 313A of the conveying region 313. The cross-sectional area of the space S that is smaller is taken at each of the areas 313A and 313A of the conveying region 313 within the respective end portions 316 and 316 of the development roller 31. Similarly, the channel C is narrowed adjacent to each of the areas 313A and 313A of the conveying region 313 within the respective end portions 316 and 316 of the development roller 31 .

[0042] With reference to FIGS. 4 and 6, the space S has a width W that extends from the nip position NP to the downstream edge 322 of the opening 321 of the housing 32. The downstream edge 322 is a closest position where the opening 321 of the housing 32 is closest to the nip position NP on the downstream side of the nip position NP in the rotation direction D2 of the development roller 31 . In addition, the channel C is formed in the space S. Then, an end width EW (width W) of the space S at each of the end portions 316 and 316 of the development roller 31 (cf. FIG. 6) is narrower than a center width CW (width W) of the space S at the center portion 315 of the development roller 31 (cf. FIG. 4). Accordingly, the space S is smaller at each end portion 316 than at the center portion 315 of the development roller 31. In addition, the channel C is narrower at each end portion 316 than at the center portion 315 of the development roller 31.

[0043] FIG. 8 is a schematic diagram illustrating an example of the opening 321 of the housing 32. The opening 321 of the housing 32 illustrated in FIG. 8 has a stepped shape to narrow the space S from the center width CW to the end width EW. Namely, the opening 321 of the housing 32 includes an opening center portion 321 A extending adjacent the center portion 315 of the development roller 31 and opening end portions 321 B and 321 B extending adjacent the end portions 316 and 316 of the development roller 31 on the downstream side of the nip position NP in the rotation direction D2 of the development roller 31 . The opening center portion 321 A and the opening end portions 321 B and 321 B extends in the longitudinal direction D1. The opening center portion 321 A and the opening end portions 321 B and 321 B form the stepped shape in which a first distance from the nip position NP to the opening center portion 321 A in a direction orthogonal to the longitudinal direction D1 corresponds to the center width CW and a second distance from the nip position NP to each of the opening end portions 321 B and 321 B in the direction orthogonal to the longitudinal direction D1 corresponds to the end width EW.

[0044] For example, with reference to FIGS. 6 and 8, the housing 32 includes protrusions 326 at opposite ends of the opening 321 adjacent to the end portions 316 and 316 of the development roller 31 , to form the stepped shape that narrows the space S from the center width CW to the end width EW Accordingly, the stepped shape to narrow the space S from the center width CW to the end width EW can be formed by the protrusion 326.

[0045] FIG. 9 is a schematic diagram illustrating another example of the opening 321 of the housing 82. The opening 321 of the housing 82 illustrated in FIG. 9 is shaped to gradually narrow the width W of the space S from the center width CW to the end width EW. Namely, the opening 321 of the housing 32 includes an opening center portion 321 C (corresponding substantially to the center portion 315 of the development roller 31 ) and opening end portions 321 D and 321 D (corresponding substantially to the end portions 316 and 316 of the development roller 31 ) on the downstream side of the nip position NP in the rotation direction D2 of the development roller 31 . At least a part of at least one of the opening center portion 321 C and the opening end portions 321 D and 321 D extends slantingly or curvedly (e.g., non-parallel) relative to the longitudinal direction D1. Accordingly, the opening center portion 321 C and each of the opening end portions 321 D and 321 D are connected to each other such that a minimum distance from the nip position NP to the opening center portion 321 C in the direction orthogonal to the longitudinal direction D1 is CW and a maximum distance from the nip position NP to each of the opening end portions 321 D and 321 D in the direction orthogonal to the longitudinal direction D1 is EW

[0046] The scattering of the toner to the outside of the development device 30 was evaluated. In this evaluation, the center width CW of the space S at the center portion 315 of the development roller 31 was fixed at 7.8 mm, and the end width EW of the space S at each of the end portions 316 and 316 of the development roller 31 was changed according to Test Examples 1 to 6 which will be described. The end width EW of Test Example 1 was set to 4.7 mm, the end width EW of Test Example 2 was set to 5.0 mm, the end width EWof Test Example 3 was set to 5.6 mm, the end width EW of Test Example 4 was set to 5.9 mm, the end width EW of Test Example 5 was set to 7.8 mm, and the end width EW of Test Example 6 was set to 7.8 mm. In Test Examples 1 to 4, the end width EW was set to be smaller than the center width CW, and in Test Examples 5 and 6, the end width EW was set to be the same as the center width CW. The toner of the development chamber H tends to scatter to the outside of the development device 30 through the channel C when the development roller 31 rotates. For this reason, a portion of the second facing surface 324 of the housing 32 that faces one end portion 316 of the development roller 31 was set as an evaluation target surface, and the amount of scattering of the toner to the outside of the development device 30 was evaluated by a ratio of a toner contamination region to the evaluation target surface. The ratio was defined as a ratio of an area of a region where toner adherence is observed, to a total area of the evaluation target surface. Evaluation results are shown in FIG. 10. In the graph of FIG. 10, the horizontal axis represents the end width EW of the space S at each of the end portions 316 and 316 of the development roller 31 , and the vertical axis represents the ratio of the toner contamination region to the evaluation target surface.

[0047] With reference to FIG. 10, in the Test Examples 5 and 6 in which the end width EW was set to be the same as the center width CW, the ratio of the toner contamination region was much higher than 20%. On the other hand, in any of Test Examples 1 to 4 in which the end width EW was set to be smaller than the center width CW, the ratio of the toner contamination region was much lower than 20%.

[0048] As described above, in the examples of image forming apparatus 1 , the space S between the development roller 31 , the photosensitive drum 20 and the housing 32 that is located downstream the nip position NP in the rotation direction D2 of the development roller 31 , has the cross-sectional area taken orthogonally to the longitudinal direction that is smaller at each of the end portions 316 and 316 of the development roller 31 than at the center portion 315. Consequently, the air flow discharged from the development chamber H at the end portions 316 and 316 of the development roller 31 is reduced. Accordingly, the scattering of the toner can be reduced.

[0049] In addition, the magnetic force (or magnetic field) of the magnet 312 is curved outwardly at the opposite end portions of the conveying region 313 in the longitudinal direction D1 , so that the amount of the developer carried at the end portions of the development roller 31 is reduced. However, the end portions 316 and 316 of the development roller 31 also include the respective areas 313A and 313A of the conveying region 313. For this reason, the scattering of the toner from the areas 313A and 313A of the conveying region 313 can also be reduced. [0050] In addition, in the width that extends from the nip position NP to the downstream edge 322 of the opening 321 of the opening 321 of the housing 32, the end width EW of the space S at each of the end portions 316 and 316 of the development roller 31 is narrower than the center width CW of the space S at the center portion 315 of the development roller 31. Consequently, the air flow discharged from the development chamber H at each of the end portions 316 and 316 of the development roller 31 is reduced. Accordingly, the scattering of the toner can be reduced. Moreover, even when the width W of the space S is narrowed, a distance between the housing 32 and the development roller 31 and a distance between the housing 32 and the photosensitive drum 20 do not change greatly. For this reason, a greater error margin can be tolerated in the manufacturing of each component by adjusting the cross-sectional area of the space S taken orthogonally to the longitudinal direction using the width W of the space S, and accordingly, the ease of production is improved.

[0051] Although various examples have been described and illustrated in the present disclosure, it should be understood that the arrangements and details can also be changed in other examples.

[0052] For example, in an example development device 30a illustrated in FIG. 11 , a width of the first gap S1 between the development roller 31 and the housing 32 adjacent to the downstream edge 322 of the opening 321 may be changed in the longitudinal direction D1 to reduce the scattering of the toner. In addition, in an example development device 30b illustrated in FIG. 12, a width of the second gap S2 between the photosensitive drum 20 and the housing 32 adjacent to the downstream edge 322 of the opening 321 may be changed in the longitudinal direction D1 to reduce the scattering of the toner.

[0053] In the development device 30a illustrated in FIG. 11 , the first gap

51 has a width W1 corresponding to a closest distance between the housing 32 and the development roller 31 in the direction orthogonal to the longitudinal direction D1. The width W1 (end width) of the first gap S1 at each of the end portions 316 and 316 of the development roller 31 is narrower than the width W1 (center width) of the first gap S1 at the center portion 315 of the development roller 31. Such a configuration can be obtained, for example, by forming protrusions similar to the protrusions 326 of the development device illustrated in FIG. 6 on the first facing surface 323 of the housing 32 at positions corresponding to the end portions 316 and 316 of the development roller 31 .

[0054] In the development device 30b illustrated in FIGS. 12 and 13, the second gap S2 extends in the longitudinal direction D1. The second gap S2 includes a center position S21 that is aligned with the center portion 315 of the development roller 31 , and end positions S22 that are aligned with the end portions 316 and 316 of the development roller 31. In addition, the second gap

52 has a width W2 corresponding to a closest distance between the housing 32 and the photosensitive drum 20 in the direction orthogonal to the longitudinal direction D1 . Additionally, the width W2 is narrower at each of the end positions S22 of the second gap S2 than at the center position S21 of the second gap S2. Such a configuration can be obtained, for example, by forming protrusions 327 similar to the protrusions 326 of the development device illustrated in FIG. 6 on the second facing surface 324 of the housing at positions corresponding to the end positions S22.

[0055] 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.