Drum unit

Abstract

The purpose is to suppress the flow of heated air from the fuser towards the photosensitive drum. [Solution] The drum unit 50 is movable relative to the main body housing 10 of the image forming apparatus and, when positioned within the main body housing 10, is aligned with the fuser 80 in a direction perpendicular to the vertical direction. The drum unit 50 comprises a plurality of photosensitive drums 51, a first frame supporting one end of the photosensitive drum 51 in the axial direction, a second frame supporting the other end of the photosensitive drum 51 in the axial direction, and a third frame 130 connecting the first frame and the second frame. The third frame 130 constitutes the upper end of the drum unit 50 and the outer surface (rear surface F2) of the drum unit 50 on the fuser 80 side. The third frame 130 has a shielding wall W for shielding the fuser 80 from heat. The shielding wall W extends from a position above the rotation center X1 of the photosensitive drum 51 to below the rotation center X1 and extends in the axial direction.

Description

Technical Field

[0001] The present disclosure relates to a drum unit.

Background Art

[0002] Conventionally, as an image forming apparatus, there is known one including a drum unit having a plurality of photosensitive drums, a fixing device arranged at an interval in the front-rear direction with respect to the drum unit, and a duct having a wall arranged between the drum unit and the fixing device (see Patent Document 1). The wall of the duct is located above the rotation center of the photosensitive drum. The wall of the duct suppresses the flow of air heated by the fixing device toward the photosensitive drum.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] By the way, when the interval between the drum unit and the fixing device is reduced for miniaturization of the image forming apparatus, there is a possibility that the conventional duct wall cannot suppress the flow of air heated by the fixing device toward the photosensitive drum.

[0005] Therefore, an object of the present disclosure is to suppress the flow of air heated by the fixing device toward the photosensitive drum.

Means for Solving the Problems

[0006] To solve the above problems, the drum unit of the present disclosure is movable with respect to the main body housing of the image forming apparatus and is aligned with the fixing device in a direction orthogonal to the vertical direction in a state of being arranged in the main body housing. The drum unit comprises multiple photosensitive drums, a first frame, a second frame, and a third frame. The first frame supports one end of each of the photosensitive drums in the axial direction. The second frame supports the other axial ends of the multiple photosensitive drums. The third frame connects the first and second frames. The third frame forms the upper end of the drum unit and the outer surface of the drum unit on the fuser side. The third frame has a shielding wall. The shielding wall is a wall designed to shield the fuser from heat. The shielding wall extends from a position above the rotation center of the photosensitive drum down to a position below the rotation center, and extends axially.

[0007] The shielding wall of the third frame extends from a position above the rotation center of the photosensitive drum to a position below the rotation center, and extends axially, thereby suppressing the flow of air heated by the fuser towards the photosensitive drum.

[0008] Furthermore, the shielding wall may have a first portion and a second portion. The first part extends in the vertical direction. The second part extends diagonally downwards from the lower end of the first part, away from the fuser.

[0009] The second part is configured to extend diagonally downwards from the lower end of the first part, away from the fuser. For example, if the rear end of a sheet that has passed through multiple photosensitive drums curls upwards towards the shielding wall due to the stiffness of the sheet, it is possible to prevent the rear end of the sheet from coming into contact with the shielding wall.

[0010] Furthermore, the shielding wall may have ribs connected to the first and second sections.

[0011] By giving the shielding wall a rib configuration, the rigidity of the shielding wall can be increased.

[0012] Furthermore, one end and the other end of the shielding wall in the axial direction may be located inward from both ends of the photosensitive drum.

[0013] The drum unit may also further include a charger and a charging frame. The charger charges the photosensitive drum. The charging frame holds the charger. The charging frame has two walls that are separated in the axial direction. The shielding wall is located between the two walls.

[0014] The charging frame may also have an intake port for drawing in air from outside the drum unit. The shielding wall may form a first channel between the shielding wall and the charged frame through which air passing through the intake can pass.

[0015] By configuring the shielding wall to form a first channel through which air passing through the intake can pass between the shielding wall and the charged frame, the shielding wall can be cooled by the air passing through the first channel, thereby suppressing the transfer of heat from the shielding wall to the photosensitive drum.

[0016] The drum unit may also further include a cleaning roller and a cleaning frame. The cleaning roller cleans the photosensitive drum. The cleaning frame holds the cleaning rollers. The cleaning frame is held in place by two walls. The shielding wall may form a second channel between the shielding wall and the cleaning frame through which the air that has passed through the first channel can pass.

[0017] By configuring the shielding wall to form a second channel through which air that has passed through the first channel can pass between the shielding wall and the cleaning frame, the shielding wall can be cooled by the air passing through the second channel, thereby suppressing the transfer of heat from the shielding wall to the photosensitive drum.

[0018] Further, the third frame may have a recess into which a positioning shaft provided on the main body housing fits.

[0019] Also, in a state where the drum unit is attached to the main body housing, the shielding wall may be disposed at a position closer to the photosensitive drum than the positioning shaft.

[0020] Further, the third frame may have a handle at its upper end.

[0021] Further, the third frame may hold a connector that can be connected to a main body contact provided on the main body housing.

[0022] Also, the photosensitive drum may be non - detachably supported by the first frame and the second frame.

[0023] Also, the first frame and the second frame may be detachable from a developing cartridge including a developing roller.

[0024] Also, the photosensitive drum may be disposed on an endless belt for conveying a sheet. In the vertical direction, the distance from the lower end of the shielding wall to the upper surface of the endless belt may be smaller than the distance from the lower end of the shielding wall to the center of the photosensitive drum.

[0025] By setting the distance from the lower end of the shielding wall to the upper surface of the endless belt to be smaller than the distance from the lower end of the shielding wall to the center of the photosensitive drum, it is possible to further suppress the flow of the air heated by the fixing device toward the photosensitive drum.

[0026] Also, the shielding wall may be aligned with the endless belt in the vertical direction.

[0027] By setting the shielding wall to be aligned with the endless belt in the vertical direction, it is possible to further suppress the flow of the air heated by the fixing device toward the photosensitive drum.

[0028] Furthermore, the drum unit of this disclosure is aligned in a first direction with an endless belt for conveying a sheet. The drum unit comprises a first photosensitive drum, a second photosensitive drum, and a frame. The first photosensitive drum is capable of contacting the first surface of the endless belt. The second photosensitive drum can come into contact with the first surface. The frame has one end on the endless belt side in the first direction and the other end on the opposite side of the endless belt. The frame supports the first photosensitive drum and the second photosensitive drum. The frame has a third frame that forms the other end of the frame and the outer surface of the frame on the fuser side. The third frame has a shielding wall. The shielding wall is a wall that shields the fuser from heat. The shielding wall extends in the first direction and in the axial direction of the first photosensitive drum. In the first direction, the shielding wall extends from a position further from the first surface than the rotation center of the first photosensitive drum to a position closer to the first surface than the rotation center of the first photosensitive drum.

[0029] By configuring the shielding wall to extend in a first direction from a position further from the first surface than the rotation center of the first photosensitive drum to a position closer to the first surface than the rotation center of the first photosensitive drum, the shielding wall can suppress the flow of air heated by the fuser toward the first photosensitive drum.

[0030] Furthermore, in the first direction, the distance from the tip of the shielding wall in the first direction to the first surface may be smaller than the distance from the tip to the center of the photosensitive drum.

[0031] By configuring the shielding wall so that the distance from the tip to the first surface in the first direction is smaller than the distance from the tip to the center of the photosensitive drum, the flow of air heated by the fuser towards the photosensitive drum can be further suppressed.

[0032] Furthermore, the shielding wall may be aligned with the endless belt in the first direction.

[0033] By configuring the shielding wall to align with the endless belt in the first direction, the flow of air heated by the fuser towards the photosensitive drum can be further suppressed. [Effects of the Invention]

[0034] This can suppress the flow of heated air from the fuser towards the photosensitive drum. [Brief explanation of the drawing]

[0035] [Figure 1] This is a cross-sectional view showing an image forming apparatus according to an embodiment. [Figure 2] This is a perspective view showing a process unit. [Figure 3] This is a perspective view showing the drum unit. [Figure 4] This is a perspective view showing the drum unit with the third frame removed. [Figure 5] This is a perspective view of the third frame from the front. [Figure 6] This is a perspective view showing the drum unit with the charging frame and cleaning frame removed. [Figure 7] This is a cross-sectional view showing a magnified view of the structure around the shielding wall. [Figure 8] This diagram shows the relationship between the narrow section of the shielding wall and the photosensitive drum. [Modes for carrying out the invention]

[0036] Next, the embodiments will be described in detail with reference to the drawings as appropriate. As shown in Figure 1, the image forming apparatus 1 comprises a main body housing 10, a sheet supply unit 20, an image forming unit 30, and a sheet discharge unit 90.

[0037] The main casing 10 includes a front cover 11 and an output tray 12. The front cover 11 opens and closes the opening on the front side of the main casing 10. The rear cover 13 opens and closes the opening on the rear side of the main casing 10.

[0038] The sheet supply unit 20 comprises a sheet tray 21 and a supply mechanism 22. The sheet tray 21 holds sheets S such as paper. The supply mechanism 22 supplies the sheets S in the sheet tray 21 to the image forming unit 30.

[0039] The image forming unit 30 comprises an exposure apparatus 40, a process unit PU, a transfer unit 70, and a fuser 80.

[0040] The exposure apparatus 40 is located on top of the process unit PU. The exposure apparatus 40 emits a light beam to expose the surface of the photosensitive drum 51.

[0041] The process unit PU is located between the sheet tray 21 and the exposure device 40. The process unit PU comprises a drum unit 50 and a plurality of developing cartridges 60.

[0042] The drum unit 50 comprises a plurality of photosensitive drums 51, a plurality of chargers 52 corresponding to the plurality of photosensitive drums 51, and a plurality of cleaning rollers 53. In this embodiment, the drum unit 50 comprises four photosensitive drums 51, four chargers 52, and four cleaning rollers 53. One of the four photosensitive drums 51 corresponds to the first photosensitive drum, and one of the remaining three corresponds to the second photosensitive drum. Of the four photosensitive drums 51, the photosensitive drum 51 located closest to the fuser 80 corresponds to the first photosensitive drum.

[0043] As shown in Figure 7, the charger 52 has a charging wire 52A and a grid electrode 52B. The charger 52 charges the photosensitive drum 51. The cleaning roller 53 cleans the photosensitive drum 51.

[0044] Returning to Figure 1, the drum unit 50 is movable relative to the main housing 10. More specifically, the drum unit 50 is movable in the front-rear direction between an image forming position inside the main housing 10 and an extended position outside the main housing 10, through an opening in the main housing 10 that is opened by opening the front cover 11. When the drum unit 50 is in the image forming position, printing is possible.

[0045] When the drum unit 50 is positioned in the image forming position within the main housing 10, it is aligned with the fuser 80 in a direction perpendicular to the vertical direction. More specifically, when the drum unit 50 is positioned in the image forming position, it is aligned with the fuser 80 in the front-to-back direction. When the drum unit 50 is positioned in the image forming position, it is located in front of the fuser 80.

[0046] Multiple developing cartridges 60 each contain toner of a different color. Each developing cartridge 60 includes a developing roller 61 and a supply roller 62.

[0047] The transfer unit 70 is located between the sheet tray 21 and the process unit PU. The transfer unit 70 comprises a drive roller 71, a driven roller 72, a conveyor belt 73 as an example of an endless belt, and a plurality of transfer rollers 74.

[0048] The conveyor belt 73 is an endless belt for conveying the sheet S. The conveyor belt 73 is aligned with the drum unit 50 in the vertical direction, which is an example of the first direction.

[0049] Multiple photosensitive drums 51 are arranged on a conveyor belt 73. The multiple photosensitive drums 51 can contact the upper surface F1 of the conveyor belt 73, which is an example of a first surface. Specifically, when the drum unit 50 is in the image forming position, the multiple photosensitive drums 51 are in contact with the upper surface F1. In the process of the drum unit 50 moving from the image forming position to the withdrawal position, the multiple photosensitive drums 51 move away from the upper surface F1.

[0050] The drive roller 71 and driven roller 72 rotate the conveyor belt 73. The transfer roller 74 is located inside the conveyor belt 73. The transfer roller 74 sandwiches the conveyor belt 73 between itself and the photosensitive drum 51.

[0051] The fuser 80 includes a heating roller 81 and a pressure roller 82. The heating roller 81 heats the sheet S. The pressure roller 82 sandwiches the sheet S between itself and the heating roller 81.

[0052] The charger 52 charges the surface of the photosensitive drum 51. The exposure device 40 exposes the surface of the photosensitive drum 51. As a result, an electrostatic latent image is formed on the photosensitive drum 51. The developing roller 61 supplies toner to the photosensitive drum 51. As a result, a toner image is formed on the photosensitive drum 51.

[0053] The sheet supply unit 20 transports the sheet S between the photosensitive drum 51 and the transfer roller 74. The toner image on the photosensitive drum 51 is transferred to the sheet S. The sheet S, on which the toner image has been transferred, is transported between the heating roller 81 and the pressure roller 82. As a result, the fuser unit 80 heat-fixes the toner image to the sheet S.

[0054] The sheet discharge unit 90 has a conveyor roller 91 and a discharge roller 92. The conveyor roller 91 conveys the sheet S to the discharge roller 92. The discharge roller 92 discharges the sheet S onto the discharge tray 12.

[0055] As shown in Figures 2 and 3, the drum unit 50 further comprises a frame 100. The frame 100 is a rectangular frame having a rectangular hole that penetrates vertically. The frame 100 has a lower end E1, an upper end E2, and a rear surface F2. The lower end E1 is one end of the frame 100 on the side of the conveyor belt 73 in the vertical direction. The upper end E2 is the other end of the frame 100 on the side opposite to the conveyor belt 73 in the vertical direction. The lower end E1 and upper end E2 of the frame 100 are also the lower end and upper end of the drum unit 50.

[0056] In other words, the lower end E1 is the bottom surface of the frame 100, which appears as a rectangular frame when viewed from below. Similarly, the upper end E2 is the top surface of the frame 100, which appears as a rectangular frame when viewed from above.

[0057] The rear surface F2 is the outer surface of the frame 100 on the side facing the fuser 80. The rear surface F2 is also the outer surface of the drum unit 50 on the side facing the fuser 80.

[0058] The frame 100 comprises a first frame 110, a second frame 120, a third frame 130, and a fourth frame 140. The lower ends of the first frame 110, the second frame 120, the third frame 130, and the fourth frame 140 each constitute the lower end E1 of the frame 100. The upper ends of the first frame 110, the second frame 120, the third frame 130, and the fourth frame 140 each constitute the upper end E2 of the frame 100.

[0059] As shown in Figure 6, the first frame 110 supports one axial end of the plurality of photosensitive drums 51. In this embodiment, the first frame 110 supports the right end of the plurality of photosensitive drums 51.

[0060] The second frame 120 supports the other axial ends of the plurality of photosensitive drums 51. In this embodiment, the second frame 120 supports the left end of the plurality of photosensitive drums 51.

[0061] Each photosensitive drum 51 is non-removably supported by the first frame 110 and the second frame 120. The first frame 110 and the second frame 120 are detachable from the developing cartridge 60 (see Figures 2 and 3).

[0062] As shown in Figure 3, the third frame 130 connects the rear ends of the first frame 110 and the second frame 120. The fourth frame 140 connects the front ends of the first frame 110 and the second frame 120. The rear surface of the third frame 130 constitutes the rear surface F2 of the frame 100.

[0063] The third frame 130 has a handle 131 at its upper end. The handle 131 is a part that the user can grasp. Below the handle 131, a hole 132 is formed that penetrates in the front-to-back direction.

[0064] The third frame 130 holds the connector CN. The connector CN can be connected to a main body contact (not shown) provided on the main body housing 10. The connector CN is electrically connected to a charger 52 or the like via a relay board, harness, etc. The main body contact is electrically connected to a control unit (not shown) via a harness, etc.

[0065] As shown in Figure 4, the third frame 130 further has recesses 133. There is one recess 133 on the right side and one on the left side of the third frame 130. As shown in Figure 7, the main housing 10 is provided with a positioning shaft SF for positioning the drum unit 50 in the front-rear direction.

[0066] The positioning shaft SF is a metal shaft that extends in the left-right direction. When the drum unit 50 is positioned at the image forming position, the positioning shaft SF enters the recess 133.

[0067] As shown in Figures 6 and 7, the drum unit 50 further comprises a plurality of charging frames 200 and a plurality of cleaning frames 300. The charging frame 200 is the frame that holds the charger 52. The charging frame 200 is located axially between the first frame 110 and the second frame 120. The charging frame 200 is supported by the first frame 110 and the second frame 120.

[0068] The charging frame 200 has two walls 210 that are spaced apart in the axial direction. Each wall 210 protrudes backward.

[0069] The cleaning frame 300 is a frame that holds the cleaning roller 53. The cleaning frame 300 has two walls 310 that are spaced apart in the axial direction. Each wall 310 protrudes backward. Each wall 310 is located between the two walls 210 of the charging frame 200. Each wall 310 is held by the two walls 210 of the charging frame 200.

[0070] As shown in Figure 7, the third frame 130 further includes a shielding wall W. The shielding wall W is a wall for shielding the heat from the fuser unit 80. The shielding wall W extends from a position above the rotation center X1 of the photosensitive drum 51 to below the rotation center X1.

[0071] When the drum unit 50 is mounted on the main housing 10, more specifically when the drum unit 50 is positioned in the image formation position, the shielding wall W is positioned closer to the photosensitive drum 51 than to the positioning shaft SF. More specifically, the shielding wall W is positioned between the center X2 of the photosensitive drum 51 and the positioning shaft SF in the front-to-back direction.

[0072] The shielding wall W is aligned with the conveyor belt 73 in the vertical direction. In the vertical direction, the distance L1 from the lower end of the shielding wall W to the upper surface F1 of the conveyor belt 73 is smaller than the distance from the lower end of the shielding wall W to the rotation center X1 of the photosensitive drum 51.

[0073] The shielding wall W has a first section W1, a second section W2, a third section W3, and a rib W4. The first part, W1, extends in the vertical direction. The second part W2 extends diagonally downward from the lower end of the first part W1, away from the fuser 80. When viewed from above, the second part W2 coincides with the rotation center X3 of the drive roller 71.

[0074] The third part W3 extends in the front-to-back direction from the lower end of the second part W2 toward the photosensitive drum 51. Rib W4 is connected to the first section W1, the second section W2, and the third section W3. Rib W4 protrudes from the first section W1 toward the photosensitive drum 51. Rib W4 protrudes upward from the second section W2 and the third section W3.

[0075] As shown in Figure 3, the shielding wall W extends in the axial direction. The first portion W1 has a wide portion W11 and a narrow portion W12.

[0076] The narrow section W12 has a shorter axial length than the wide section W11. The narrow section W12 protrudes from the axial center of the lower end of the wide section W11. As shown in Figure 8, one end and the other end of the narrow section W12 in the axial direction are located inward from both ends of the photosensitive drum 51.

[0077] The narrow section W12 is located between the two walls 210 of the charging frame 200. More specifically, the narrow section W12 is located between the two walls 310 of the cleaning frame 300.

[0078] As shown in Figure 5, the narrow section W12 has the same axial length as the second section W2 and the third section W3. The second section W2 extends from the lower end of the narrow section W12. The shielding wall W has multiple ribs W4 as described above. The multiple ribs W4 are spaced apart in the axial direction.

[0079] As shown in Figure 6, the charging frame 200 further has an intake port 220 for drawing in air from outside the drum unit 50. The first frame 110 has a vent port 111 facing the intake port 220 of the charging frame 200. When a fan (not shown) inside the main housing 10 rotates, as shown in Figure 7, air from outside the drum unit 50 flows through the vent port 111 and the intake port 220 toward the charging wire 52A.

[0080] The shielding wall W forms a first channel FP1 through which air passing through the intake port 220 can pass, between the shielding wall W and the charged frame 200. The shielding wall W forms a second channel FP2 through which air passing through the first channel FP1 can pass, between the shielding wall W and the cleaning frame 300.

[0081] As described above, the following effects can be obtained according to this embodiment. The shielding wall W of the third frame 130 extends from a position above the rotation center X1 of the photosensitive drum 51 to below the rotation center X1, and extends in the axial direction. This configuration allows the shielding wall W to suppress the flow of air heated by the fuser 80 toward the photosensitive drum 51.

[0082] The second part W2 is configured to extend diagonally downwards from the lower end of the first part W1, away from the fuser 80. This configuration prevents the rear end of the sheet S from coming into contact with the shielding wall W when the sheet S, having passed through multiple photosensitive drums 51, curls upwards towards the shielding wall W due to the stiffness of the sheet S.

[0083] By configuring the shielding wall W to have ribs W4, the rigidity of the shielding wall W can be increased.

[0084] The shielding wall W is configured to form a first flow path FP1 through which air passing through the intake port 220 can pass between the shielding wall W and the charged frame 200. This allows the shielding wall W to be cooled by the air passing through the first flow path FP1, thereby suppressing the transfer of heat from the shielding wall W to the photosensitive drum 51.

[0085] The shielding wall W is configured to form a second channel FP2 between the shielding wall W and the cleaning frame 300, through which air that has passed through the first channel FP1 can pass. This allows the shielding wall W to be cooled by the air passing through the second channel FP2, thereby suppressing the transfer of heat from the shielding wall W to the photosensitive drum 51.

[0086] By configuring the distance L1 from the lower end of the shielding wall W to the upper surface F1 of the conveyor belt 73 to be smaller than the distance X1 from the lower end of the shielding wall W to the rotation center of the photosensitive drum 51, the flow of air heated by the fuser 80 toward the photosensitive drum 51 can be further suppressed.

[0087] By arranging the shielding wall W to be aligned vertically with the conveyor belt 73, the flow of air heated by the fuser 80 toward the photosensitive drum 51 can be further suppressed.

[0088] This disclosure is not limited to the embodiments described above and can be used in various forms as illustrated below. The image forming apparatus is not limited to printers; it may also be a copier or a multifunction device, for example.

[0089] The shape of the shielding wall is not limited to the shape of the embodiment described above. For example, the shielding wall may have only the first portion described above, or it may have only the first portion and the second portion described above. The first portion is not limited to a structure having a wide portion and a narrow portion, but may, for example, be simply formed in the shape of a rectangular plate.

[0090] The charger may be, for example, a charging roller. The endless belt may be, for example, an intermediate transfer belt. The fuser may, for example, be configured to include a heating roller, an endless belt, and a rubber pad that sandwiches the belt between the heating roller.

[0091] The first direction is not limited to the vertical direction; for example, it may be a direction that is inclined diagonally with respect to the vertical direction.

[0092] Each photosensitive drum may be detachably supported from the frame. Each photosensitive drum, along with a charger and other components, constitutes a drum cartridge, and the drum cartridge may be detachably supported by a frame.

[0093] Each photosensitive drum may be detachably supported within a frame as a process cartridge integrated with a developing cartridge. The image forming apparatus may be a monochrome image forming apparatus. In this case, the frame may be configured to support one photosensitive drum and one developing cartridge.

[0094] The elements described in the above embodiments and modifications may be implemented in any combination. [Explanation of symbols]

[0095] 1. Image forming apparatus 10 Main Unit 50 Drum Units 51 Photosensitive drum 80 Fuser 110 First Frame 120 Frame 2 130 3rd Frame W shielding wall X1 Rotation Center

Claims

1. A drum unit that is movable relative to the main housing of an image forming apparatus and, when positioned within the main housing, is aligned with the fuser in a direction perpendicular to the vertical direction, Multiple photosensitive drums, A first frame supporting one end of each of the photosensitive drums in the axial direction, A second frame supporting the other ends of the multiple photosensitive drums in the axial direction, A third frame connecting the first frame and the second frame, the third frame comprising the upper end of the drum unit and the outer surface of the drum unit on the fuser side, The 3rd frame is A drum unit characterized by having a shielding wall for shielding the heat of the fuser, which extends from a position above the rotation center of the photosensitive drum to below the rotation center and extends in the axial direction.

2. The aforementioned shielding wall is, The first part extends in the vertical direction, The drum unit according to claim 1, further comprising a second portion extending diagonally downward from the lower end of the first portion in a direction away from the fuser.

3. The drum unit according to claim 2, characterized in that the shielding wall has ribs connected to the first portion and the second portion.

4. The drum unit according to claim 1, characterized in that one end and the other end of the shielding wall in the axial direction are located inward from both ends of the photosensitive drum.

5. A charger for charging the photosensitive drum, The charging frame for holding the aforementioned charger further comprises The charging frame has two walls separated in the axial direction, The drum unit according to claim 1, characterized in that the shielding wall is located between the two walls.

6. The charging frame has an intake port for taking in air from outside the drum unit, The drum unit according to claim 5, characterized in that the shielding wall forms a first flow path between the shielding wall and the charged frame through which air passing through the intake port can pass.

7. A cleaning roller for cleaning the photosensitive drum, A cleaning frame for holding the cleaning roller, further comprising a cleaning frame held by two walls, The drum unit according to claim 6, characterized in that the shielding wall forms a second channel through which air that has passed through the first channel can pass between the shielding wall and the cleaning frame.

8. The drum unit according to claim 1, characterized in that the third frame has a recess into which a positioning shaft provided in the main body housing is inserted.

9. The drum unit according to claim 8, characterized in that, when the drum unit is mounted on the main body housing, the shielding wall is positioned closer to the photosensitive drum than the positioning shaft.

10. The drum unit according to claim 1, characterized in that the third frame has a handle at its upper end.

11. The drum unit according to claim 1, characterized in that the third frame holds a connector that can be connected to a main body contact provided on the main body housing.

12. The drum unit according to claim 1, characterized in that the photosensitive drum is irremovably supported by the first frame and the second frame.

13. The drum unit according to claim 1, characterized in that the first frame and the second frame are detachable from a developing cartridge equipped with a developing roller.

14. The photosensitive drum is placed on an endless belt for transporting the sheet. The drum unit according to claim 1, characterized in that, in the vertical direction, the distance from the lower end of the shielding wall to the upper surface of the endless belt is smaller than the distance from the lower end of the shielding wall to the center of the photosensitive drum.

15. The drum unit according to claim 14, characterized in that the shielding wall is aligned vertically with the endless belt.

16. An endless belt for transporting sheets and drum units arranged in a first direction, A first photosensitive drum that can come into contact with the first surface of the endless belt, A second photosensitive drum that can come into contact with the first surface, A frame having one end on the side of the endless belt in the first direction and the other end on the opposite side of the endless belt, supporting the first photosensitive drum and the second photosensitive drum, the frame having a third frame that constitutes the other end of the frame and the outer surface of the frame on the fuser side, Equipped with, The drum unit is characterized in that the third frame is a shielding wall for shielding the heat of the fuser, extending in the first direction and in the axial direction of the first photosensitive drum, and in the first direction, having a shielding wall that extends from a position further from the first surface than the rotation center of the first photosensitive drum to a position closer to the first surface than the rotation center of the first photosensitive drum.

17. The drum unit according to claim 16, characterized in that, in the first direction, the distance from the tip of the shielding wall in the first direction to the first surface is smaller than the distance from the tip to the center of the photosensitive drum.

18. The drum unit according to claim 16, characterized in that the shielding wall is aligned with the endless belt in a first direction.

Images