Process unit and image forming apparatus

Abstract

To provide a process unit that can uniformly electrify a photoreceptor drum.SOLUTION: A process unit comprises: a photoreceptor drum 13 on a surface of which a toner image is formed; an electrifying roller 50 that is brought into pressure contact with the photoreceptor drum 13 to electrify the photoreceptor drum; a cleaning roller 60 that is brought into pressure contact with the electrifying roller 50 to clean the electrifying roller; and an urging member 80 that urges the electrifying roller 50 or the cleaning roller 60. The central axis of the photoreceptor drum 13 is arranged at a position not overlapping a central axis line TL passing through the central axis of the electrifying roller 50 and the central axis of the cleaning roller 60. An urging direction of the urging member 80 is on the same straight line as the central axis line TL.SELECTED DRAWING: Figure 4

Description

[Technical field]

[0001] The present invention relates to a process unit for transferring a toner image and an image forming apparatus. [Background technology]

[0002] Conventionally, in electrophotographic image forming apparatuses, a toner image is formed by charging the surface of a photosensitive drum to cause toner to adhere thereto, and this toner image is transferred to a sheet of paper to form an image. In recent years, various methods for charging a photosensitive drum have been proposed, and for example, a contact charging method in which a conductive charging roller is brought into direct contact with the photosensitive drum has been adopted (for example, see Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2007-121544 A Summary of the Invention [Problem to be solved by the invention]

[0004] The image forming apparatus described in Patent Document 1 includes a charging roll that charges a member to be charged, a cleaning member that cleans the charging roll, a holding member that maintains the relative positions of the charging roll and the cleaning member substantially constant, a housing in which the holding member is slidably attached, and a biasing means that biases the holding member toward the member to be charged, thereby pressing the charging roll against the member to be charged.

[0005] In the above-mentioned image forming apparatus, the charging roll has a difference in the load applied between both ends held by the holding member and the central portion that is far from the holding member, which may cause distortion of the shaft.The image forming apparatus is configured such that the biasing means biases the holding member along the direction in which the charged body and the charging roll face each other, and as a result of the difference in the distance to the charged body caused by shaft distortion, the nip width between the charged body and the charging roll becomes uneven, which may cause the photosensitive body potential to change.

[0006] The present invention has been made to solve the above-mentioned problems, and has an object to provide a process unit and an image forming apparatus that can uniformly charge a photosensitive drum without reducing the efficiency of transmission of the pressure contact force to the charging roller. [Means for solving the problem]

[0007] The process unit according to the present invention is a process unit for transferring a toner image, and includes a photosensitive drum on whose surface a toner image is formed, a charging roller for charging the photosensitive drum by pressing the photosensitive drum against the charging roller, and a cleaning roller for cleaning the charging roller by pressing the charging roller against the charging roller. a charging roller biasing member for biasing the charging roller; and a cleaning roller biasing member for biasing the cleaning roller. a central axis of the photosensitive drum is disposed at a position not overlapping with a central axis passing through a central axis of the charging roller and a central axis of the cleaning roller; Charge biasing member The biasing direction is on the same straight line as the central axis. The cleaning roller is longer than the charging roller in the width direction of the photosensitive drum. It is characterized by:

[0008] The process unit according to the present invention may be configured to include a bearing portion that supports the central axis of the charging roller and the central axis of the cleaning roller, and the distance between the central axis of the charging roller and the central axis of the cleaning roller is fixed by the bearing portion.

[0012] In the process unit according to the present invention, the charging roller and the cleaning roller may be arranged lower than the photosensitive drum in a height direction.

[0013] In the process unit according to the present invention, the charging roller may be configured to have a crown shape.

[0014] The image forming apparatus according to the present invention is characterized by including the process unit according to the present invention. Effect of the Invention

[0015] According to the present invention, since the charging roller is not biased straight toward the central axis of the photosensitive drum, it is possible to reduce the deviation of the contact position with the photosensitive drum caused by shaft distortion of the charging roller, and it is possible to uniformly charge the photosensitive drum without reducing the efficiency of transmission of the pressure contact force to the charging roller. [Brief description of the drawings]

[0016] [Figure 1] 1 is a schematic configuration diagram showing an image forming apparatus according to a first embodiment of the present invention. [Diagram 2] FIG. 1 is a schematic front view showing a process unit according to a first embodiment of the present invention. [Diagram 3] FIG. 2 is an enlarged perspective view showing an end portion of a process unit. [Figure 4] 3 is a schematic side view showing the relationship between the positions of the photosensitive drum, the charging roller, and the cleaning roller and the urging direction. FIG. [Figure 5A] 5 is a schematic side view showing the positions and biasing directions of a photosensitive drum and a charging roller in a comparative example. FIG. [Figure 5B] FIG. 5B is a schematic front view showing the photosensitive drum and the charging roller in FIG. 5A. [Figure 6A] FIG. 2 is a schematic side view showing the positions and biasing directions of the photosensitive drum and the charging roller in the first embodiment of the present invention. [Figure 6B] FIG. 6B is a schematic front view showing the photosensitive drum and the charging roller in FIG. 6A. [Figure 7] 13 is a schematic side view showing the position of a biasing member in a modified example. FIG. [Figure 8] FIG. 6 is a schematic front view showing a process unit according to a second embodiment of the present invention. [Figure 9] FIG. 11 is a schematic side view showing the biasing direction in the first arrangement example. [Figure 10] FIG. 11 is a schematic side view showing the biasing direction in the second arrangement example. [Figure 11] FIG. 13 is a schematic side view showing the biasing direction in the third arrangement example. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0017] (First embodiment) An image forming apparatus according to a first embodiment of the present invention will now be described with reference to the drawings.

[0018] FIG. 1 is a schematic diagram showing the configuration of an image forming apparatus according to a first embodiment of the present invention.

[0019] The image forming apparatus 1 forms multi-color and monochrome images on a specified sheet of paper in accordance with image data transmitted from outside, and is configured to include an exposure device 11, a developing device 12, a photosensitive drum 13, a cleaner device 14, a charger 15, an intermediate transfer belt device 16, a fixing device 17, a paper feed cassette 18, and a paper output tray 19.

[0020] The image data handled by this image forming apparatus corresponds to a color image using each of the colors black (K), cyan (C), magenta (M), and yellow (Y). Therefore, four developing devices 12, photoconductor drums 13, chargers 15, and cleaner devices 14 are provided so as to form four types of latent images corresponding to each color, and are set to black, cyan, magenta, and yellow, respectively, and these constitute four image stations.

[0021] The photoconductor drum 13 is disposed at approximately the center of the image forming apparatus 1. The charger 15 uniformly charges the surface of the photoconductor drum 13 to a predetermined potential. The exposure device 11 exposes the surface of the photoconductor drum 13 to light to form an electrostatic latent image. The development device 12 develops the electrostatic latent image on the surface of the photoconductor drum 13 to form a toner image on the surface of the photoconductor drum 13. Through the above-mentioned series of operations, a toner image of each color is formed on the surface of each photoconductor drum 13. The cleaner device 14 removes and collects residual toner on the surface of the photoconductor drum 13 after development and image transfer. The structure of the photoconductor drum 13 and the vicinity of the charger 15 will be described in detail with reference to FIG. 2, which will be described later.

[0022] The intermediate transfer belt device 16 is disposed above the photosensitive drum 13, and includes an intermediate transfer belt 21, an intermediate transfer belt drive roller 22, an intermediate transfer belt driven roller 23, an intermediate transfer roller 24, an intermediate transfer belt cleaning device 25, and a tension roller 26. Four intermediate transfer rollers 24 are provided corresponding to the image stations for each color of YMCK.

[0023] The intermediate transfer belt drive roller 22, the intermediate transfer belt driven roller 23, the intermediate transfer roller 24, and the tension roller 26 are configured to tension the intermediate transfer belt 21 and move the surface of the intermediate transfer belt 21 in a predetermined direction (the direction of the arrow C in the figure).

[0024] The intermediate transfer belt 21 rotates in the direction of arrow C, and residual toner is removed and collected by the intermediate transfer belt cleaning device 25. The toner images of each color formed on the surface of each photosensitive drum 13 are sequentially transferred and superimposed to form a color toner image on the surface of the intermediate transfer belt 21.

[0025] A nip area is formed between the transfer roller 27a of the secondary transfer device 27 and the intermediate transfer belt 21, and the paper P conveyed through the sheet conveying path S is sandwiched in the nip area and conveyed. When the paper P passes through the nip area, the toner image on the surface of the intermediate transfer belt 21 is transferred to the paper P.

[0026] The paper feed cassette 18 is a cassette for storing paper P to be used for image formation, and is provided below the exposure device 11. The paper discharge tray 19 is provided above the image forming unit 1a, and is a tray for placing paper P on which an image has been formed.

[0027] In the image forming apparatus 1, the paper P in the paper feed cassette 18 is sent to the paper discharge tray 19 through the sheet transport path S, the secondary transfer device 27, and the fixing device 17. Along the sheet transport path S, a paper feed roller 31, a registration roller 32, a pre-registration roller 33, the fixing device 17, and a paper discharge roller 34 are arranged.

[0028] The paper feed roller 31 is provided near an end of the paper feed cassette 18, and supplies the paper P one sheet at a time from the paper feed cassette 18 to the sheet transport path S. The registration roller 32 temporarily holds the paper P being transported from the paper feed cassette 18, and transports the paper P to the transfer roller 27a at a timing when the leading edge of the toner image on the photosensitive drum 13 and the leading edge of the paper P are aligned. The pre-registration roller 33 is a small roller for assisting in the transport of the paper P.

[0029] The fixing device 17 is a belt fixing type fixing device, in which a fixing belt 173 is wound around a plurality of rollers (here, a fixing roller 171 and a heating roller 172). The fixing belt 173 is configured to transfer heat from the heating roller 172 to the fixing roller 171. In the fixing device 17, a pressure roller 174 is pressed against the fixing roller 171 via the fixing belt 173. The fixing device 17 receives the paper P on which an unfixed toner image has been formed, and conveys the paper P by sandwiching it between the fixing belt 173 and the pressure roller 174. After the fixing, the paper P is discharged onto the paper discharge tray 19 by the paper discharge rollers 34.

[0030] In this embodiment, the fixing device 17 is a fixing device of a belt fixing type, but is not limited to this, and may be a type in which the pressure roller 174 directly presses the fixing roller 171 .

[0031] In the image forming apparatus 1, the photoconductor drum 13 and the charger 15 are part of a process unit 40. Next, the process unit 40 according to the first embodiment of the present invention will be described with reference to the drawings.

[0032] Fig. 2 is a schematic front view showing a process unit according to a first embodiment of the present invention, and Fig. 3 is an enlarged perspective view showing an end of a part of the process unit. In Fig. 2, the housing 41 and the bearing unit 70 are hatched to make the structure of each part easier to understand. In Fig. 3, the photosensitive drum 13, the charging roller 50, the cleaning roller 60, and the bearing unit 70 at one end of the process unit 40 are shown in order to make the drawing easier to see.

[0033] The process unit 40 according to the first embodiment of the present invention includes a photoconductor drum 13, a charging roller 50, and a cleaning roller 60. In the image forming apparatus 1 shown in Fig. 1, a toner image is transferred from the photoconductor drum 13 to a sheet of paper via the intermediate transfer belt 21, but the present invention is not limited to this, and the toner image may be transferred directly from the photoconductor drum 13 to a sheet of paper, in which case a nip area is formed by pressing a transfer roller 27a against the photoconductor drum 13. Accordingly, the process unit 40 may also include a transfer roller 27a.

[0034] The photosensitive drum 13 is supported by the housing 41 at both ends in the width direction W of the central shaft (photosensitive shaft 13a).

[0035] The charging roller 50 is located below the photoconductor drum 13 in the height direction Z, and both ends in the width direction W of the central shaft (charging shaft 50a) are supported by bearings 70. In this embodiment, the charging roller 50 is made of epichlorohydrin rubber and has a diameter of Φ12, and the charging shaft 50a has a diameter of Φ6. The charging roller 50 may also be in a crown shape with projections and recesses so that the diameter at the center in the width direction W is larger than at both ends.

[0036] The cleaning roller 60 is located below the charging roller 50 in the height direction Z, and both ends in the width direction W of the central shaft (cleaning shaft 60a) are supported by bearings 70. In this embodiment, the cleaning roller 60 is made of urethane sponge and has a diameter of Φ11.3, and the cleaning shaft 60a has a diameter of Φ6.

[0037] The bearings 70 are provided at both ends in the width direction W, and support the charging shaft 50a and the cleaning shaft 60a while keeping the distance between them fixed. Two urging members 80 are provided between the bearings 70 and the housing 41, corresponding to the two bearings 70, and the two urging members 80 urge the corresponding bearings 70 upward. In this embodiment, the urging members 80 are coil springs with a spring load of 600 gf. In this way, since the charging roller 50 and the cleaning roller 60 are both axially supported by the bearings 70, the cleaning roller 60 can be stably pressed against the charging roller 50, and stable cleaning performance can be maintained.

[0038] The bearing portion 70 and the housing 41 may each be provided with a groove or a protrusion to restrict the direction in which the bearing portion 70 moves to the biasing direction of the biasing member 80 .

[0039] In this embodiment, the photoconductor drum 13 has a photoconductor shaft 13a connected to a drive unit (not shown) and rotates by the transmitted driving force. The charging roller 50 is in pressure contact with the photoconductor drum 13 and rotates in response to the drive of the photoconductor drum 13 to charge the photoconductor drum 13. The cleaning roller 60 is in pressure contact with the charging roller 50 and rotates in response to the rotation of the charging roller 50 to clean dirt from the charging roller 50.

[0040] Next, the relationship between the positions of the photosensitive drum 13, the charging roller 50, and the cleaning roller 60 and the direction in which they are urged by the urging member 80 will be described with reference to FIGS. 4 to 6B.

[0041] FIG. 4 is a schematic side view showing the relationship between the positions of the photosensitive drum, the charging roller, and the cleaning roller and the biasing direction.

[0042] 4 shows a schematic diagram of the positional relationship between the photosensitive drum 13, charging roller 50, cleaning roller 60, and urging member 80 as viewed from one end, and does not include the housing 41 and the bearing portion 70. In FIG. 4, the urging member 80 is separated from the charging shaft 50a and the cleaning shaft 60a, but the urging force is transmitted to both of them via the bearing portion 70.

[0043] As shown in FIG. 4, the charging shaft 50a is not located directly below the photoconductor shaft 13a, but is located at a position shifted along the circumferential surface of the photoconductor drum 13 (lower right in FIG. 4). The cleaning shaft 60a is located directly below the charging shaft 50a. The dashed line in FIG. 4 indicates a first auxiliary line HL1 passing through the photoconductor shaft 13a and the charging shaft 50a, and the two-dot chain line indicates a central axis TL passing through the charging shaft 50a and the cleaning shaft 60a. That is, the photoconductor shaft 13a is located at a position that does not overlap with the central axis TL, and the cleaning shaft 60a is located at a position that does not overlap with the first auxiliary line HL1. The urging member 80 is provided along the central axis TL and is arranged so that the central axis TL passes through its center. That is, the urging direction of the urging member 80 is on the same straight line as the central axis TL. In this embodiment, the central axis TL and the first auxiliary line HL1 intersect with each other, and the angle between them (inclination angle θ) is set to 10 to 15°.

[0044] In a configuration in which the photoconductor drum 13 is charged by the charging roller 50, when shaft distortion occurs in the charging roller 50, a difference in nip width occurs between both ends and the center, and the photoconductor potential may change. In the present embodiment, the biasing direction of the biasing member 80 is inclined with respect to the first auxiliary line HL1, thereby suppressing the effect on the nip width.

[0045] Therefore, the relationship between the positions of the photosensitive drum 13 and the charging roller 50 and the urging direction will be described with reference to Figures 5A to 6B, which show a comparative example having a conventional structure and this embodiment. Note that Figures 5A to 6B focus on the photosensitive drum 13 and the charging roller 50, and omit the cleaning roller 60 and the urging member 80. Also, in Figures 5B and 6B, in order to clarify the change in the shape of the charging roller 50, the way in which the charging roller 50 is bent is shown more emphasized than in the actual structure.

[0046] FIG. 5A is a schematic side view showing the positions and biasing directions of a photosensitive drum and a charging roller in a comparative example, and FIG. 5B is a schematic front view showing the photosensitive drum and charging roller of FIG. 5A.

[0047] 5A and 5B, the charging shaft 50a is located directly below the photoconductor shaft 13a and is configured to urge the charging shaft 50a directly upward. In other words, the urging force from the urging member 80 (first urging force F1) overlaps with the first auxiliary line HL1.

[0048] In the charging roller 50, both ends in the width direction W are supported by a shaft, and since there is a difference in the load applied thereto compared to the central portion, the charging roller 50 is bent along the biasing direction as shown in FIG. 5B. That is, while both ends of the charging roller 50 are in contact with the photoconductor drum 13, in the central portion, a floating occurs between the charging roller 50 and the photoconductor drum 13 by the amount of the bending. As a result, although the nip width is as designed at both ends in the width direction W, the nip width at the central portion is narrowed, and a difference in charging potential occurs. The difference in charging potential affects the amount of toner adhesion, leading to changes in image quality and deterioration of cleaning performance.

[0049] FIG. 6A is a schematic side view showing the positions and biasing directions of the photosensitive drum and the charging roller in the first embodiment of the present invention, and FIG. 6B is a schematic front view showing the photosensitive drum and the charging roller in FIG. 6A.

[0050] In the first embodiment of the present invention, as described above, the charging shaft 50a is located at a position slightly shifted from directly below the photoconductor shaft 13a, and is configured to urge the charging shaft 50a directly upward. In other words, the urging force from the urging member 80 (the second urging force F2) intersects with the first auxiliary line HL1.

[0051] In the present embodiment, as shown in FIG. 6B, the charging roller 50 is bent, but since the direction in which the charging shaft 50a and the photosensitive shaft 13a face each other (the direction of the first auxiliary line HL1) is offset from the direction in which the bending occurs (the direction of the second spring force F2), the floating caused by the bending is reduced.

[0052] As described above, in this embodiment, the charging roller 50 is not biased straight toward the central axis of the photosensitive drum 13. This makes it possible to reduce the misalignment of the contact position with the photosensitive drum 13 caused by shaft distortion of the charging roller 50, and enables the photosensitive drum 13 to be uniformly charged without reducing the efficiency of transmission of the pressure contact force to the charging roller 50.

[0053] 4 shows a configuration in which the urging member 80 urges along the height direction Z, but the present invention is not limited thereto, and it is sufficient that the photoconductor shaft 13a, the charging shaft 50a, and the cleaning shaft 60a are arranged so that the central axis TL and the first auxiliary line HL1 intersect. In other words, the charging shaft 50a may be located directly below the photoconductor shaft 13a, and in this case, the urging member 80 may urge in a direction inclined with respect to the height direction Z.

[0054] The charging roller 50 and the cleaning roller 60 are preferably disposed below the photosensitive drum 13 in the height direction Z. In other words, even if the shafts are distorted downward due to their own weight, the charging roller 50 and the cleaning roller 60 are biased upward away from the central axis of the photosensitive drum 13, so that a uniform nip width can be maintained.

[0055] In addition, by adopting a crown-shaped charging roller 50, shaft distortion can be alleviated and the nip width can be made uniform. However, without being limited thereto, the charging roller 50 may be a straight shape with a uniform diameter.

[0056] 7, the biasing member 80 may be disposed so that the central axis TL passes through the side end of the biasing member 80, and the biasing center of the biasing member 80 may be on the same straight line as the central axis TL. In other words, if the central axis TL passes through the biasing member 80 so as to be parallel to the biasing direction, the biasing direction of the biasing member 80 can be considered to be on the same straight line as the central axis TL. The load from the biasing member 80 may be adjusted so that it is applied to the charging shaft 50a and the cleaning shaft 60a by the bearing 70.

[0057] Second embodiment Next, an image forming apparatus (process unit) according to a second embodiment of the present invention will be described with reference to the drawings. Note that the structure of the image forming apparatus according to the second embodiment is substantially the same as that of the first embodiment, so the same reference numerals are used and the description and drawings are omitted.

[0058] Fig. 8 is a schematic front view showing a process unit according to a second embodiment of the present invention. In Fig. 8, the housing 41, the charging bearing 71, and the cleaning bearing 72 are hatched to make the structure of each part easier to understand.

[0059] The second embodiment of the present invention differs from the first embodiment in that the charge shaft 50a and the cleaning shaft 60a are supported separately. Specifically, in the second embodiment, a charge bearing portion 71 and a cleaning bearing portion 72 are provided instead of the bearing portion 70. The charge bearing portion 71 supports both ends of the charge shaft 50a, and the cleaning bearing portion 72 supports both ends of the cleaning shaft 60a.

[0060] The urging member in this embodiment is composed of a charge urging member 81 that urges the charge roller 50, and a cleaning urging member 82 that urges the cleaning roller 60. Specifically, the charge urging member 81 is provided between the charge bearing portion 71 and the housing 41, and the cleaning urging member 82 is provided between the cleaning bearing portion 72 and the housing 41. In this way, the charge roller 50 and the cleaning roller 60 are urged separately, so that the force and direction of urging each can be freely designed according to the arrangement of each part.

[0061] In this embodiment, the urging direction can be made different between the charging urging member 81 and the cleaning urging member 82. Therefore, a first to a third arrangement example in which the urging direction is different will be described with reference to Figs. 9 to 11. In the second embodiment, the photosensitive drum 13, the charging roller 50, and the cleaning roller 60 are arranged in the same manner as in the first embodiment, and a description thereof will be omitted, together with the relationship with the central axis line TL and the first auxiliary line HL1.

[0062] FIG. 9 is a schematic side view showing the biasing direction in the first arrangement example.

[0063] In the first arrangement example, the charging urging member 81 and the cleaning urging member 82 are both provided along the central axis TL, and the urging directions of the charging members are aligned with the central axis TL. Although the charging urging member 81 and the cleaning urging member 82 have the same urging direction, the charging roller 50 and the cleaning roller 60 are individually urged, and therefore the loads on each of them can be appropriately designed.

[0064] FIG. 10 is a schematic side view showing the biasing direction in the second arrangement example.

[0065] The dashed line in FIG. 10 indicates a second auxiliary line HL2 passing through the photoconductor shaft 13a and the cleaning shaft 60a. In the second arrangement example, the charge biasing member 81 is provided along the central axis TL, and the corresponding biasing direction overlaps with the central axis TL. The cleaning biasing member 82 is provided along the second auxiliary line HL2, and the corresponding biasing direction overlaps with the second auxiliary line HL2. With this configuration, the cleaning biasing member 82 applies a biasing force toward the photoconductor drum 13, while the biasing force from the charge biasing member 81 is directed in a direction shifted from the photoconductor drum 13, so that the influence of shaft distortion of the charging roller 50 can be mitigated.

[0066] FIG. 11 is a schematic side view showing the biasing direction in the third arrangement example.

[0067] In the third arrangement example, the charging urging member 81 is provided along the first auxiliary line HL1, and the corresponding urging direction overlaps with the first auxiliary line HL1. The cleaning urging member 82 is provided along the central axis TL, and the corresponding urging direction overlaps with the central axis TL. With this configuration, the urging force from the cleaning urging member 82 applied to the charging roller 50 via the cleaning roller 60 can urge the charging roller 50 in a direction that reduces the misalignment of the contact position between the charging roller 50 and the photosensitive drum 13.

[0068] It should be noted that the embodiments disclosed herein are illustrative in all respects and are not intended to provide a basis for a restrictive interpretation. Therefore, the technical scope of the present invention is not interpreted solely by the above-described embodiments, but is defined by the claims. Furthermore, all modifications within the scope and meaning equivalent to the claims are included. [Explanation of symbols]

[0069] 1. Image forming device 13 Photoconductor drum 13a Photoconductor shaft (center shaft of photoconductor drum) 15 Charger 40 Process Unit 41 Case 50 Charging roller 50a Charging shaft (central shaft of charging roller) 60 Cleaning roller 60a Cleaning shaft (central shaft of cleaning roller) 70 Bearing section 71 Charged bearing part 72 Cleaning bearing part 80 biasing member 81 Charged energizing member 82 Cleaning biasing member TL center axis W Width direction Z height direction

Claims

1. A process unit for transferring a toner image, a photoconductor drum on whose surface a toner image is formed; a charging roller that presses against the photosensitive drum to charge the photosensitive drum; a cleaning roller that presses against the charging roller to clean it; a charge biasing member for biasing the charge roller; a cleaning biasing member for biasing the cleaning roller, the central axis of the photosensitive drum is disposed at a position not overlapping with a central axis passing through the central axis of the charging roller and the central axis of the cleaning roller; The biasing direction of the charge biasing member is aligned with the central axis line, the cleaning roller is supported on the photosensitive drum by a support member that supports the photosensitive drum and the cleaning roller. The cleaning roller is longer than the charging roller in the width direction of the central axis of the photosensitive drum. A process unit characterized by:

2. 2. The process unit according to claim 1, The charging roller and the cleaning roller are disposed lower than the photosensitive drum in the height direction. A process unit characterized by:

3. 3. The process unit according to claim 1, further comprising: The charging roller is crown-shaped. A process unit characterized by:

4. 4. An image forming apparatus comprising the process unit according to claim 1.

Images