Process unit and image forming apparatus

Abstract

This suppresses image defects caused by foreign matter adhering to the electrostatic roller. [Solution] An image forming apparatus comprising: a rotatable image carrier; a charging roller positioned to contact the surface of the image carrier and charge the surface; an exposure apparatus for irradiating the image carrier with light to form a latent image on the surface of the image carrier; a brush unit having a brush including a substrate and brush fibers; a brush holding portion for holding the substrate; and an extension portion extending from one end of the brush holding portion in the direction of the rotation axis of the charging roller in a direction intersecting the direction of the rotation axis; and a frame for supporting the extension portion, wherein, when viewed in the direction of the rotation axis, the extension portion overlaps with the optical path of light from the exposure apparatus toward the image carrier.

Description

Technical Field

[0001] The present invention relates to a process unit used in an image forming apparatus and an image forming apparatus that forms an image on a recording material.

Background Art

[0002] Patent Document 1 describes that in a cleanerless image forming apparatus, a brush-shaped cleaning member is arranged to remove toner adhering to a charging roller.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] The cleaning member in the above document is mainly for removing toner adhering to the charging roller. However, when foreign substances such as dust adhere to the charging roller, charging failure due to the foreign substances may occur, and for example, image defects called black spots may occur.

[0005] An object of the present invention is to provide a process unit and an image forming apparatus capable of suppressing image defects caused by foreign substances adhering to a charging roller.

Means for Solving the Problems

[0006] One aspect of the present invention is an image forming apparatus comprising: a rotatable image carrier; a charging roller positioned to contact the surface of the image carrier and to charge the surface; an exposure apparatus for irradiating the image carrier with light to form a latent image on the surface of the image carrier; a brush unit having a plate-shaped substrate and brush fibers protruding from the substrate and in contact with the surface of the charging roller; a brush holding portion for holding the substrate; and an extension portion extending from one end of the brush holding portion in the direction of the rotation axis of the charging roller in a direction intersecting the direction of the rotation axis; and a frame for supporting the extension portion, wherein, when viewed in the direction of the rotation axis, the extension portion overlaps with the optical path of the light from the exposure apparatus toward the image carrier.

[0007] Another aspect of the present invention is a process unit comprising: a rotatable image carrier; a charging roller positioned to contact the surface of the image carrier and charge the surface; a brush including a plate-shaped substrate and brush fibers protruding from the substrate and contacting the surface of the charging roller; a brush holding portion for holding the substrate; and a swinging support portion extending from one end of the brush holding portion in the direction of the rotation axis of the charging roller in a direction intersecting the direction of the rotation axis; and a frame that swingably supports the swinging support portion, wherein when a cross section passing through the center of the brush in the direction of the rotation axis and perpendicular to the direction of the rotation axis is viewed in the direction of the rotation axis, at least a part of the swinging support portion protrudes downstream in the direction of rotation with respect to a virtual straight line passing through the center of the image carrier and the most downstream end of the brush holding portion in the cross section in the direction of rotation of the image carrier during image formation. [Effects of the Invention]

[0008] According to the present invention, it is possible to provide a process unit and an image forming apparatus that can suppress image defects caused by foreign matter adhering to the charging roller. [Brief explanation of the drawing]

[0009] [Figure 1]Cross-sectional view of a process unit and a scanner unit according to an embodiment. [Figure 2] A schematic diagram (a) and a perspective view (b) of an image forming apparatus according to an embodiment. [Figure 3] A perspective view of an image forming apparatus according to an embodiment. [Figure 4] (a) A cross-sectional view of the process unit according to the embodiment, and (b) a schematic diagram showing the arrangement of the photosensitive drum and process components. [Figure 5] A perspective view (a) of the drum unit according to the embodiment, and enlarged views (b, c) of a part of the drum unit. [Figure 6] A perspective view showing a part of a drum unit according to an embodiment. [Figure 7] Rear view (a), cross-sectional view (b, c), and side view (d-g) of the drum unit according to the embodiment. [Figure 8] Perspective views (a, b) of a photosensitive drum and a charging roller according to an embodiment. [Figure 9] Diagrams (a-e) illustrating the brush unit according to the embodiment. [Figure 10] Diagrams (a, b) illustrating the brush unit according to the embodiment. [Figure 11] Diagrams (a, b) illustrating the brush unit according to the embodiment. [Figure 12] Rear view (a), cross-sectional views (b, c), and enlarged views of a portion of the cross-section (d-g) of the drum unit according to the embodiment. [Figure 13] Rear view (a) and cross-sectional views (b, c) of the drum unit according to the embodiment. [Figure 14] Schematic diagrams of brush units according to one embodiment (a) and comparative examples (b, c). [Figure 15] Diagrams (a, b) illustrating the brush unit according to the embodiment. [Figure 16] A perspective view (a) of a process unit according to an embodiment, and a magnified view of a part thereof (b). [Modes for carrying out the invention]

[0010] Hereinafter, embodiments according to the present disclosure will be described with reference to the drawings.

[0011] (Image forming apparatus) Using FIGS. 2(a), 2(b), and 3, the outline of an image forming apparatus 1 according to an embodiment will be described. FIG. 2(a) is a schematic diagram of an image forming apparatus 1 according to an embodiment. FIGS. 2(b) and 3 are perspective views of the image forming apparatus 1.

[0012] An image forming apparatus generally refers to a device that forms an image on a recording material P by an electrophotographic image forming unit. Examples of image forming apparatuses include electrophotographic copiers, laser beam printers, LED printers, electrophotographic facsimiles, and the like. The image forming apparatus 1 of the present embodiment is a monochrome laser beam printer that forms an image on a recording material P based on image information input from an external device. The recording material P includes various sheet materials of different materials such as paper such as plain paper and thick paper, plastic films such as overhead projector sheets, special-shaped sheets such as envelopes and index papers, and cloth.

[0013] In the following description and drawings, the direction of the rotation axis of the image carrier (photosensitive drum 21) included in the image forming apparatus 1 is taken as the X direction. The vertical direction (gravity direction) when the image forming apparatus 1 is installed on a horizontal plane is taken as the Z direction. The direction intersecting both the X direction and the Z direction is taken as the Y direction. The X direction, Y direction, and Z direction are preferably orthogonal to each other.

[0014] In the present embodiment, on one end side of the process unit 20 in the X direction, an input coupling portion 51a (described later) that receives the driving force of a driving source (motor) disposed in the apparatus main body 1A is disposed. Therefore, one end side in the X direction (the side indicated by the arrow X in the figure) may be referred to as the "driving side", and the other end side in the X direction (the opposite side of the arrow X) may be referred to as the "non-driving side".

[0015] As shown in Figures 2(a)(b) and 3, the image forming apparatus 1 comprises an apparatus body 1A, an image forming unit 10, a fixing unit 70, a pickup roller 65 as a feeding unit, and a pair of discharge rollers 80 as a discharge unit. The image forming unit 10 includes a process unit 20 as a process unit, a scanner unit 11 as an exposure apparatus, and a transfer roller 12 as a transfer unit.

[0016] The main body 1A of the device is a housing (structural frame) that includes frame members such as sheet metal frames that constitute the frame of the image forming apparatus 1, and cover members that form the external surface of the image forming apparatus 1. The image forming unit 10, fixing unit 70, pickup roller 65, and discharge roller pair 80 are housed or supported in the main body 1A of the device.

[0017] Figure 4(a) is a cross-sectional view of the process unit 20. Figure 4(b) is a schematic diagram of the photosensitive drum 21 and the process components arranged around it. The process unit 20 of this embodiment includes a drum unit 25 including the photosensitive drum 21 and a developing unit 30 including a developing roller 31.

[0018] The drum unit 25 includes a photosensitive drum 21, a charging roller 22, a pre-exposure section 23, a paper dust collection brush 24 which is a brush unit for the photosensitive drum 21, a brush unit 40 for the charging roller 22, and a drum frame 26. The developing unit 30 includes a developing roller 31, a developing container 32, a supply roller 33, a stirring member 34, and a developing blade 35. When the brush unit 40 for the charging roller 22 is referred to as the first brush unit, the brush unit for the photosensitive drum 21 can be referred to as the second brush unit.

[0019] The photosensitive drum 21 functions as an image carrier that holds a latent image (electrostatic latent image) and a toner image (developer image). The photosensitive drum 21 is a photoreceptor molded into a cylindrical (drum) shape. The photosensitive drum 21 of this embodiment has a cylindrical base made of aluminum and a photosensitive layer formed on the base of a negatively charged organic photoreceptor. The photosensitive drum 21 is rotated by the motor of the apparatus body 1A at a predetermined circumferential speed (process speed) in a predetermined rotational direction (direction indicated by arrow Q in Figures 4(a) and 4(b)) during image formation.

[0020] As shown in Figure 4(b), the charging section Q1 is defined as the position where the surface 21a of the photosensitive drum 21 and the charging roller 22 face each other. The exposure section Q2 is defined as the position where the laser light from the scanner unit 11 is irradiated onto the surface 21a of the photosensitive drum 21. The developing section Q3 is defined as the position where the surface 21a of the photosensitive drum 21 and the developing roller 31 face each other. The transfer section Q4 is defined as the position where the surface 21a of the photosensitive drum 21 and the transfer roller 12 face each other. The brush contact section Q5 is defined as the position where the surface 21a of the photosensitive drum 21 and the paper dust collection brush 24 come into contact. The charging section Q1, exposure section Q2, developing section Q3, transfer section Q4, and brush contact section Q5 are arranged in this order in the rotation direction (Q) of the photosensitive drum 21 during image formation. In other words, in this embodiment, the rotation direction of the photosensitive drum 21 during image formation is such that a point on the surface 21a of the photosensitive drum 21 passes through the charging section Q1, the exposure section Q2, the developing section Q3, the transfer section Q4, and the brush contact section Q5 in that order.

[0021] The charging roller 22 is positioned to contact the photosensitive drum 21. In this embodiment, the charging roller 22 can contact and separate from the photosensitive drum 21, and the image forming operation is performed with the charging roller 22 in contact with the photosensitive drum 21. The charging roller 22 is rotatable in a direction that follows the photosensitive drum 21 (counterclockwise in Figure 4(a)).

[0022] The charging roller 22 charges the surface 21a of the photosensitive drum 21 by applying a charging voltage from a charging power supply provided in the main body 1A of the device. In this embodiment, the photosensitive drum 21 is negatively charged by the charging roller 22.

[0023] The pre-exposure section 23 is positioned downstream of the brush contact section Q5 and upstream of the charging section Q1 in the rotation direction (Q) of the photosensitive drum 21. The pre-exposure section 23 irradiates light onto the surface 21a of the photosensitive drum 21 to remove surface charge in order to generate a stable discharge in the charging section.

[0024] The paper dust collection brush 24 (brush unit for the photosensitive drum 21) has a brush portion 24a made of pile fabric or the like, and a support member that supports the brush portion 24a and is fixed to the drum frame 26. The paper dust collection brush 24 blocks foreign matter such as paper dust adhering to the surface 21a of the photosensitive drum 21 at the brush contact portion Q5, thereby suppressing the occurrence of image defects caused by foreign matter. On the other hand, the paper dust collection brush 24 allows toner adhering to the surface 21a of the photosensitive drum 21 to pass through the brush contact portion Q5.

[0025] The brush unit 40 for the electrostatic roller 22 has a brush 41 that can come into contact with the surface 22a of the electrostatic roller 22. The brush 41 can scrape off foreign matter such as paper dust and sand that has adhered to the surface 22a of the electrostatic roller 22. The detailed configuration and operation of the brush unit 40 will be described later.

[0026] The scanner unit 11 irradiates the photosensitive drum 21 with laser light corresponding to image information input from an external device, and exposes the photosensitive drum 21 by scanning the surface 21a of the photosensitive drum 21 using a polygon mirror (scanning optical system). This exposure process forms an electrostatic latent image on the surface 21a of the photosensitive drum 21 corresponding to the image information. Note that the exposure device is not limited to the scanner unit 11 that emits laser light, but may also be an LED exposure device, for example. An LED exposure device is an exposure device that uses an LED array, in which multiple LEDs are arranged along the rotation axis direction of the photosensitive drum 21 (the main scanning direction in the exposure process), as a light source.

[0027] The developing unit 30 includes a developing roller 31 as a developer carrier for holding the developer, a developing container 32 which forms the frame of the developing unit 30, a supply roller 33 capable of supplying developer to the developing roller 31, an agitator 34, and a developing blade 35. The developing roller 31, the supply roller 33, and the agitator 34 are rotatably supported by the developing container 32. The developing roller 31 is positioned at the opening of the developing container 32 so as to face the photosensitive drum 21. The supply roller 33 is in rotatable contact with the developing roller 31, and the toner, which is the developer contained in the developing container 32, is supplied (applied) to the surface of the developing roller 31 by the supply roller 33. Note that the supply roller 33 is not necessarily required if a configuration is in place that can supply sufficient toner to the developing roller 31.

[0028] The developing unit 30 of this embodiment uses a contact developing method. That is, the toner layer supported on the developing roller 31 comes into contact with the surface 21a of the photosensitive drum 21 in the developing section Q3 (developing area) where the photosensitive drum 21 and the developing roller 31 face each other. A developing voltage is applied to the developing roller 31 by a developing power supply. Under the developing voltage, the toner supported on the developing roller 31 is transferred from the developing roller 31 to the drum surface according to the potential distribution of the surface 21a of the photosensitive drum 21, thereby developing the electrostatic latent image into a toner image. In this embodiment, an inversion developing method is employed. That is, in the charging process, toner adheres to the area of ​​the surface 21a of the photosensitive drum 21 that has been charged, and in the exposure process, the amount of charge has decreased due to light irradiation, thereby forming a toner image.

[0029] Furthermore, in this embodiment, a toner with a particle size of approximately 6 μm and a normal polarity (normal charging polarity) of negative polarity is used. As an example, the toner used in this embodiment is a polymerized toner produced by a polymerization method. In addition, the toner in this embodiment does not contain magnetic components, and the toner is supported on the developing roller 31 mainly by intermolecular forces and electrostatic forces (mirror image forces), making it a so-called non-magnetic one-component developer. However, a one-component developer containing magnetic components may also be used. Furthermore, the one-component developer may contain additives (for example, wax or silica fine particles) to adjust the fluidity and charging performance of the toner in addition to toner particles. Alternatively, a two-component developer composed of a non-magnetic toner and a magnetic carrier may be used as the developer. When a magnetic developer is used, for example, a cylindrical sleeve with a magnet placed inside is used as the developer carrier (developing roller).

[0030] The developing container 32 functions as a toner storage section that houses toner (developer). Inside the developing container 32, a toner storage chamber 36 is formed for storing toner. The agitator 34 is positioned inside the toner storage chamber 36. The agitator 34 rotates, driven by the motor of the main body 1A, to agitate the toner in the developing container 32 and to transport the toner toward the developing roller 31 and the supply roller 33. The agitator 34 also passes through the developing section Q3 without being used for development, and then circulates the toner stripped from the developing roller 31 within the developing container 32, homogenizing the toner in the developing container 32. Note that the agitator 34 is not limited to a rotating form. For example, an oscillating agitator may be used.

[0031] The developing blade 35 is positioned at the opening of the developing container 32 together with the developing roller 31. The developing blade 35 regulates the amount of toner carried on the developing roller 31. In other words, the toner supplied to the surface of the developing roller 31 is uniformly thinned as it passes through the area opposite the developing blade 35 as the developing roller 31 rotates. In addition, as the toner supplied to the surface of the developing roller 31 passes through the area opposite the developing blade 35, its charge is increased to a negative polarity due to triboelectric charging.

[0032] The developing unit 30 of this embodiment includes a shielding member 37 positioned above the developing blade 35. The shielding member 37 shields the area between the developing roller 31 and the developing blade 35, and between the photosensitive drum 21 and the developing roller 31, to prevent foreign matter from entering when the brush 41 scrapes off foreign matter adhering to the aforementioned charging roller 22. The shielding member 37 is positioned below the contact position between the brush 41 and the charging roller 22, and above the area between the developing roller 31 and the developing blade 35, and between the photosensitive drum 21 and the developing roller 31. The shielding member 37 is supported by the developing container 32 and extends from the upper surface of the developing container 32 to a position close to the surface 21a of the photosensitive drum 21. The shielding member 37 substantially isolates the space between the drum unit 25 and the developing unit 30 and the space where the developing roller 31 is located, in the cross-section shown in Figure 4(a), except for a small gap between the shielding member 37 and the surface 21a of the photosensitive drum 21. The shielding member 37 may be a member fixed to the developing container 32 with screws or adhesive, or it may be integrally formed with the resin member constituting the developing container 32.

[0033] The term "process unit" is not limited to one comprising all the components of the process unit 20 in this embodiment, but may include an image carrier (photosensitive drum) and at least one process component. A process component is a component that acts on the image carrier to perform processes such as charging, exposure, development, transfer, and cleaning in an electrophotographic process. For example, a drum unit 25, which includes a photosensitive drum 21 and a charging roller 22, is an example of a process unit when a developing unit 30 is detachably attached to the drum unit 25. The charging roller 22, developing roller 31, and brush unit (paper dust collection brush 24) for the photosensitive drum 21 in this embodiment are examples of process components.

[0034] (Image formation process) Next, the image forming operation of the image forming apparatus 1 will be described. The image forming operation is a series of operations in which the image forming apparatus 1 transports recording material P one sheet at a time and forms an image on the recording material P using the process unit 20. When the image forming apparatus 1 receives image information and instructions to execute the image forming operation from an external device connected to it, the control unit of the image forming apparatus 1 starts the image forming operation.

[0035] When the image forming operation starts, the photosensitive drum 21 is rotated in the image forming unit 10, and the surface 21a of the photosensitive drum 21 is uniformly charged to a predetermined polarity and potential in the charging unit Q1 by applying voltage to the charging roller 22. The scanner unit 11 irradiates the photosensitive drum 21 with laser light based on the input image information. As a result, the charged surface 21a of the photosensitive drum 21 is exposed in the exposure unit Q2, and an electrostatic latent image is formed on the surface 21a of the photosensitive drum 21. The developing roller 31 carries toner as a developer and rotates, supplying it to the photosensitive drum 21 in the developing unit Q3. As a result, the electrostatic latent image is developed into a toner image (developer image).

[0036] In parallel with the operation of the image forming unit 10, one sheet of recording material P is fed at a time from the recording material storage unit (tray, cassette) located at the bottom of the main body 1A by the pickup roller 65. The feeding timing of the recording material P is controlled so that the recording material P enters the transfer unit Q4 at the same time that the toner image formed on the photosensitive drum 21 reaches the transfer unit Q4. As the recording material P passes through the transfer unit Q4, the toner image is transferred from the photosensitive drum 21 to the recording material P by applying voltage to the transfer roller 12.

[0037] The recording material P that has passed through the transfer section Q4 is transported to the fixing section 70, where it undergoes image fixing. Specifically, the fixing section 70 heats and pressurizes the toner image on the recording material P while transporting it by gripping it with the nip portions of a pair of rotating bodies such as a fixing roller pair. The recording material P that has passed through the fixing section 70 is discharged to the outside of the device body 1A by a pair of discharge rollers 80 and loaded onto a discharge tray 81, which is a loading section formed on the upper part of the device body 1A.

[0038] In this embodiment, the image forming apparatus 1 does not include a cleaning member for recovering (removing) toner that was not transferred to the recording material P (transfer target) in the transfer section Q4 (transfer residue toner) from the photosensitive drum 21. In this embodiment, the transfer residue toner adhering to the surface area on the photosensitive drum 21 that has passed through the transfer section Q4 is recovered by the developing roller 31 in the developing section Q3 after passing through the brush contact section Q5 and the charging section Q1. This type of method is called a cleanerless method or a developing and cleaning method.

[0039] More specifically, the paper dust collection brush 24 blocks foreign matter such as paper dust adhering to the photosensitive drum 21 from the recording material P at the brush contact area Q5, while allowing the transfer residue toner to pass through. Furthermore, as the transfer residue toner passes through the charging area Q1, the toner particles charged with the opposite polarity to the normal polarity and toner particles with a charge amount close to zero are supplied with the normal polarity charge, thereby increasing the charge amount of the transfer residue toner.

[0040] Subsequently, the behavior of the residual toner as it passes through the developing unit Q3 differs depending on the region on the surface 21a of the photosensitive drum 21. In this embodiment, since an inversion development method is employed, the surface potential (bright area potential) of the photosensitive drum 21 in the region exposed in the exposure unit Q2 (bright area region) is on the non-normal polarity side with respect to the potential of the developing roller 31 to which the developing voltage is applied. Therefore, the residual toner adhering to the bright area remains on the surface 21a of the photosensitive drum 21 without being transferred to the developing roller 31 in the developing unit Q3, and becomes part of the toner image together with the toner supplied from the developing roller 31. On the other hand, the surface potential (dark area potential) of the photosensitive drum 21 in the region not exposed in the exposure unit Q2 (dark area region) is on the normal polarity side with respect to the potential of the developing roller 31 to which the developing voltage is applied. Therefore, the residual toner adhering to the dark area is transferred to the developing roller 31 in the developing unit Q3 and collected in the developing container 32. The transfer residue toner collected in the developing container 32 is mixed with the toner already present in the developing container 32 to become uniform, and then used again for developing.

[0041] In the cleanerless system, foreign matter adhering to the photosensitive drum 21 in the transfer section Q4 is not removed by the cleaning member. Even if the paper dust collection brush 24 blocks the foreign matter as in this embodiment, some of the foreign matter may slip through the paper dust collection brush 24. Therefore, as described below, it is preferable to use a brush unit 40 for the charging roller 22 to reduce the occurrence of image defects caused by the adhesion of foreign matter to the charging roller 22.

[0042] (Toner replenishment and cartridge replacement) This section describes toner replenishment and cartridge replacement in the image forming apparatus 1 of this embodiment. As shown in Figures 2(b) and 3, a top cover 82 that can be opened and closed is provided on the upper part of the apparatus body 1A. At least a portion of the upper surface of the top cover 82 is formed as an output tray 81 for loading. An opening / closing member 83 is attached to the top cover 82, which is supported so as to be openable and closable around a pivot axis 83a that extends in the front-rear direction (Y direction) of the apparatus. In addition, an opening 82a that opens upward is formed in the output tray 81 of the top cover 82.

[0043] As shown in Figures 2(a) and 3, the image forming apparatus 1 is provided with a mounting section 106 on which a toner pack 100, which serves as a replenishment container, can be attached. The mounting section 106 has an opening (toner receiving port) that can communicate with the toner discharge port of the toner pack 100, and a shutter that can open and close the toner receiving port. The mounting section 106 may be part of the process unit 20, or it may be fixed to the apparatus body 1A.

[0044] The opening / closing member 83 is configured to move between a closed position, which closes the opening 82a to prevent the toner pack 100 from being mounted on the mounting section 106, and an open position, which opens the opening 82a to allow the toner pack 100 to be mounted on the mounting section 106. When the opening / closing member 83 is in the open position, the mounting section 106 is exposed to the outside of the image forming apparatus 1 through the opening 82a. In the closed position, the opening / closing member 83 functions as part of the discharge tray 81 and can support the recording material P discharged into the discharge tray 81. In addition, a groove 82b provided in the top cover 82 allows the user to easily place their fingers on the opening / closing member 83.

[0045] In this embodiment, a direct replenishment method is employed that allows toner to be supplied to the developing unit 30 inside the image forming apparatus 1 from outside the image forming apparatus 1. In other words, the user can replenish toner to the developing unit 30 from the toner pack 100 mounted on the mounting section 106 while the process unit 20, including the developing unit 30, is mounted on the apparatus body 1A. With the toner pack 100 mounted on the mounting section 106 of the image forming apparatus 1, at least a portion of the toner pack 100 is exposed to the outside of the image forming apparatus 1.

[0046] The direct replenishment method has the following advantages compared to the method of replacing the entire process unit 20 (process cartridge method). First, it improves usability because it eliminates the need to remove the process unit 20 from the image forming apparatus 1 and replace it with a new process cartridge when the toner level in the process unit 20 becomes low. Also, it is cheaper to replenish the toner in the developing container 32 than to replace the entire process unit 20. Furthermore, the direct replenishment method reduces costs because it does not require the replacement of various rollers, gears, etc., compared to the method of replacing only the developing unit 30 of the process unit 20 (developing cartridge method).

[0047] In this embodiment, the process unit 20 is configured as a process cartridge that can be attached to and detached from the main body 1A of the device. The user can remove the process unit 20 from the main body 1A by opening an opening / closing member provided on the main body 1A and replace it with a new process unit 20.

[0048] The configuration of the brush unit 40 described below may also be applied to image forming apparatuses using process cartridges or developing cartridges. Furthermore, the process unit 20 is not limited to a cartridge that can be attached to or detached from the apparatus body 1A, but may be fixed to the apparatus body 1A in a manner that does not anticipate replacement by the user. In other words, the "process unit" in this disclosure may be shipped attached to the apparatus body 1A during the manufacture of the image forming apparatus 1 and can be used without replacement until, for example, the image forming apparatus 1 reaches the end of its lifespan.

[0049] (Drum unit) The configuration of the drum unit 25 will be explained using Figures 4(a) to 8(b). Figure 5(a) is a perspective view of the drum unit 25. Figure 5(b) is a perspective view of the non-driven end of the drum unit 25 as seen from the center of the drum unit 25 in the longitudinal direction. Figure 5(c) is a perspective view of the driven end of the drum unit 25 as seen from the center of the drum unit 25 in the longitudinal direction. Figure 6 is a perspective view of the drum unit 25 (excluding the drum frame 26, the driven-side cover member 43, and the non-driven-side cover member 44). Figure 7(a) is a rear view of the drum unit 25 (excluding the driven-side cover member 43 and the non-driven-side cover member 44) as seen from the upstream side in the Y direction. Figures 7(b) and 7(c) are cross-sectional views of the drum unit 25 along the CC line in Figure 7(a). Figures 7(d) and 7(e) are side views of the drum unit 25 as seen in the direction of arrow D in Figure 7(a). Figures 7(f) and 7(g) are side views of the drum unit 25 as seen in the direction of arrow E in Figure 7(a). Figures 8(a) and 8(b) are schematic diagrams illustrating the contact and separation of the photosensitive drum 21 and the charging roller 22. Figures 7(b), 7(d), 7(f) and 8(b) show the state in which the charging roller 22 is in contact with the photosensitive drum 21, while Figures 7(c), 7(e), 7(g) and 8(a) show the state in which the charging roller 22 is separated from the photosensitive drum 21.

[0050] As shown in Figures 4(a) and 5(a), the drum unit 25 includes a photosensitive drum 21, a charging roller 22, a paper dust collection brush 24, a drum frame 26, a drive-side cover member 43, a non-drive-side cover member 44, and a brush unit 40. The drum unit 25 also includes a drive-side bearing 45 and a non-drive-side bearing 46 (Figures 5(b) and 5(c)), charging roller biasing members 48 and 49 (Figures 7(d) and 7(f)), charging roller separation members 28 and 29 (Figures 7(d) to 7(g)), and a charging roller electrical contact 47 (Figure 6).

[0051] The drum unit 25 extends in a long, slender shape along the rotation axis of the photosensitive drum 21. Similarly, the charging roller 22 extends in a long, slender shape along the rotation axis of the photosensitive drum 21. Therefore, in the following description, the direction parallel to the rotation axis 21X of the photosensitive drum 21 (the X direction) may be referred to as the longitudinal direction of the drum unit 25, the longitudinal direction of the photosensitive drum 21, or the longitudinal direction of the charging roller 22.

[0052] As shown in Figures 5(a) to 5(c), a drive-side cover member 43 is attached to one end (drive side) of the drum frame 26 extending in the X direction, and a non-drive-side cover member 44 is attached to the other end (non-drive side) of the drum frame 26. The drive-side cover member 43 and the non-drive-side cover member 44 are fixed to the drum frame 26 by screwing or adhesive. The drive-side cover member 43 forms at least a part of the end face of one end (drive side) of the drum unit 25, and the non-drive-side cover member 44 forms at least a part of the end face of the other end (non-drive side) of the drum unit 25. The drum frame 26, drive-side cover member 43, and non-drive-side cover member 44, which are connected to each other, constitute the frame of the drum unit 25. Furthermore, the drum frame 26, drive-side cover member 43, and non-drive-side cover member 44, which are connected to each other, together with the frame of the developing unit 30, constitute the frame of the process unit 20.

[0053] The photosensitive drum 21 is rotatably supported around the rotation axis 21X (Figure 5(a)) by the drive-side cover member 43 and the non-drive-side cover member 44.

[0054] As shown in Figures 5(a) and 6, a drum drive member 51 is provided on one longitudinal end (drive side) of the photosensitive drum 21. In this embodiment, the drum drive member 51 rotates integrally with the outer circumference of the photosensitive drum 21 that contacts the charging roller 22. The drum drive member 51 has an input coupling part 51a which serves as a drive input part that receives a driving force (rotational force) from the main body 1A to rotate the photosensitive drum 21.

[0055] With the process unit 20 mounted on the apparatus body 1A, the input coupling portion 51a of the drum drive member 51 engages with the output coupling portion of the apparatus body 1A. Through the engagement of the output coupling portion and the input coupling portion 51a, driving force is transmitted from the motor of the apparatus body 1A to the photosensitive drum 21, causing the photosensitive drum 21 to rotate in a predetermined rotational direction (Q).

[0056] The charging roller 22 is rotatably supported by a drive-side bearing 45 and a non-drive-side bearing 46 of a bearing member. When the drive-side bearing 45 is referred to as the first bearing member, the non-drive-side bearing 46 can be referred to as the second bearing member. The charging roller 22 rotates around a rotation axis 22X (Figure 6) which is substantially parallel to the rotation axis 21X of the photosensitive drum 21.

[0057] The drive-side bearing 45 and the non-drive-side bearing 46 are supported on the drum frame 26 in such a manner that they are movable relative to the drum frame 26 in a direction intersecting the longitudinal direction of the photosensitive drum 21. As the drive-side bearing 45 and the non-drive-side bearing 46 move, the charging roller 22 is movable in directions toward and toward the photosensitive drum 21 (arrows S and T in Figures 7(b) and 7(c)).

[0058] Specifically, the drive-side bearing 45 and the non-drive-side bearing 46 in this embodiment are positioned between two guides 26d (Figures 7(b) and 7(c)) provided on the drum frame 26. Figures 7(b) and 7(c) show two guides 26d corresponding to the non-drive-side bearing 46, but the drum frame 26 is provided with two guides corresponding to the drive-side bearing 45. The drive-side bearing 45 and the non-drive-side bearing 46 have grooves 45g (Figure 6) formed therein that engage with the guides 26d. The two guides 26d extend in directions perpendicular to the longitudinal direction of the photosensitive drum 21 (arrows S and T). The drive-side bearing 45 and the non-drive-side bearing 46 are movable along the extending direction of the two guides 26d.

[0059] The electrostatic roller biasing members 48 and 49 are positioned at both longitudinal ends of the electrostatic roller 22. The electrostatic roller biasing member 48 on the drive side is positioned between the drive side bearing 45 and the drum frame 26 (Figure 7(f)(g)). The electrostatic roller biasing member 49 on the non-drive side is positioned between the non-drive side bearing 46 and the drum frame 26 (Figure 7(d)(e)). The electrostatic roller biasing members 48 and 49 bias the drive side bearing 45 and the non-drive side bearing 46 in the direction that the electrostatic roller 22 approaches the photosensitive drum 21 (arrow T in Figure 7(b)).

[0060] As shown in Figure 6, a drive input gear 22G is attached to the drive-side end of the charging roller 22. The drive input gear 22G meshes with the gear portion of the drum drive member 51 described above. Therefore, when the photosensitive drum 21 is rotated, the charging roller 22 in this embodiment rotates in the direction that follows the photosensitive drum 21 (arrow R in Figures 6 and 7(b) to (g)) due to the driving force transmitted via the drum drive member 51 and the drive input gear 22G.

[0061] Furthermore, the charging roller 22 is not limited to being rotated by drive transmission via the drum drive member 51 and the drive input gear 22G, but may also be configured to rotate by the frictional force acting between the surfaces 21a and 22a of the photosensitive drum 21 and the charging roller 22.

[0062] As shown in Figure 4(a), the paper dust collection brush 24 is fixed to the drum frame 26 so as to be in contact with the photosensitive drum 21.

[0063] (Separation of the electrostatic rollers) The configuration relating the contact and separation of the charging roller 22 with respect to the photosensitive drum 21 will now be described. The image forming apparatus 1 of this embodiment is equipped with a mechanism that allows the charging roller 22 to be kept separated from the photosensitive drum 21 from the time the image forming apparatus 1 is shipped from the apparatus body 1A until it reaches the user.

[0064] Specifically, as shown in Figure 8(a), the charging roller separation members 28 and 29 are provided at both longitudinal ends of the charging roller 22. One charging roller separation member 28 is positioned at the drive-side end of the charging roller 22, and the other charging roller separation member 29 is positioned at the non-drive-side end of the charging roller 22. The charging roller separation members 28 and 29 are rotatable around the rotation axis 22X of the charging roller 22 and are rotatable relative to the charging roller 22.

[0065] As shown in Figures 8(a) and 8(b), each of the charging roller separating members 28 and 29 has contact ribs 28a and 29a, force receiving protrusions 28b and 29b, and levers 28c and 29c.

[0066] The contact ribs 28a and 29a are formed to protrude outward beyond the outer diameter of the charging roller 22. The contact ribs 28a and 29a are capable of contacting the surface 21a of the photosensitive drum 21 outside the area where the surface 22a of the charging roller 22 contacts the surface 21a of the photosensitive drum 21 in the longitudinal direction (X direction) of the charging roller 22. As shown in Figures 8(a) and 7(c), 7(e), and 7(g), when the contact ribs 28a and 29a are in contact with the surface 21a of the photosensitive drum 21, a predetermined gap d1 is formed between the surface 22a of the charging roller 22 and the surface 21a of the photosensitive drum 21. In addition, the charging roller separation members 28 and 29 receive the biasing force of the charging roller biasing members 48 and 49. In other words, the contact ribs 28a and 29a come into contact with the surface 21a of the photosensitive drum 21, so that the charging roller 22 is held in a position separated from the photosensitive drum 21 (separated position) against the biasing force of the charging roller biasing members 48 and 49.

[0067] As shown in Figures 8(a) and 8(b), the force-receiving protrusions 28b and 29b are located at both longitudinal ends of the photosensitive drum 21. The drum drive member 51, located at one end of the photosensitive drum 21, has a protrusion 51b that can engage with the force-receiving protrusion 28b of the drive-side charging roller separation member 28. The other end of the photosensitive drum 21 has a drum flange 52 that rotates integrally with the photosensitive drum 21. The drum flange 52 has a protrusion 52b that can engage with the force-receiving protrusion 29b of the non-drive-side charging roller separation member 29.

[0068] The force-receiving projection 28b of the charging roller separation member 28 and the projection 51b of the drum drive member 51 are positioned at the same location in the longitudinal direction (X direction) of the charging roller 22. The force-receiving projection 29a of the charging roller separation member 29 and the projection 52b of the drum flange 52 are positioned at the same location in the longitudinal direction (X direction) of the charging roller 22. Furthermore, the drum drive member 51 and the drum flange 52 in this embodiment have multiple sets (specifically, four sets) of projections 51b and 52b, with each set consisting of one projection 51b and one projection 52b having equal rotational phases with respect to the rotation axis 21X of the photosensitive drum 21.

[0069] After the image forming apparatus 1 is installed at the user's location, during the initialization process of the image forming apparatus 1, the charging roller 22 is brought into contact with the photosensitive drum 21. Specifically, during the initialization process, the photosensitive drum 21 is rotated in a predetermined rotational direction (Q) by the driving force from the motor of the apparatus body 1A. Then, as shown in Figure 8(b), the protrusions 51b and 52b of either the drum drive member 51 or the drum flange 52, which rotate integrally with the photosensitive drum 21, come into contact with and press against the force-receiving protrusions 28b and 29b of the charging roller separation members 28 and 29. As a result, the charging roller separation members 28 and 29 rotate in the direction indicated by the arrow R.

[0070] The rotation of the charging roller separation members 28 and 29 releases the contact between the contact ribs 28a and 29a and the surface 21a of the photosensitive drum 21. Then, as shown in Figures 7(b), (d), and (f), the biasing force of the charging roller biasing members 48 and 49 causes the drive-side bearing 45 and the non-drive-side bearing 46 to slide in the direction indicated by arrow T, moving the charging roller 22 to a position where it contacts the photosensitive drum 21 (contact position).

[0071] When the charging roller separation members 28 and 29 are assembled to the drum unit 25, they are assembled at a predetermined phase (Figure 8(a)) that holds the charging roller 22 in a separated position. However, if for any reason the charging roller separation members 28 and 29 rotate from the predetermined phase, the operator can return the charging roller separation members 28 and 29 to the predetermined phase by gripping and operating the levers 28c and 29c of the charging roller separation members 28 and 29.

[0072] The mechanism described above allows the charging roller 22 to be kept away from the photosensitive drum 21, for example, from the time the image forming apparatus 1 is shipped until it reaches the user. This suppresses deformation of the charging roller 22 caused by being pressed against the photosensitive drum 21 for a long period of time while stationary, and reduces the risk of image defects caused by deformation of the charging roller 22. Furthermore, the configuration in which the charging roller 22 automatically contacts the photosensitive drum 21 as the photosensitive drum 21 rotates after the image forming apparatus 1 reaches the user shortens the waiting time before the user can start using the image forming apparatus 1.

[0073] (Conductive path of the electrostatic roller) The configuration of the conductive path for the charging roller 22 in the drum unit 25 will now be described. As shown in Figure 6, the charging roller electrical contact 47 is located on one end (drive side) of the drum unit 25 in the longitudinal direction (X direction) of the charging roller 22 and is electrically connected to the charging roller 22.

[0074] Specifically, the charging roller electrical contact 47 has a first contact portion 47a that can contact the electrical contact (body-side contact portion) of the device body 1A, and a second contact portion 47b that contacts one end of the driving-side charging roller biasing member 48. The charging roller biasing member 48 is, for example, a compression coil spring made of metal wire and is conductive. The other end of the charging roller biasing member 48 is in contact with the driving-side bearing 45. The driving-side bearing 45 is made of a resin material mixed with a conductive material such as carbon and is conductive. The driving-side bearing 45 also holds, for example, the conductive shaft portion (metal shaft) of the charging roller 22. Therefore, the charging roller electrical contact 47 of this embodiment is electrically connected to the charging roller 22 via the charging roller biasing member 48 and the driving-side bearing 45.

[0075] With the process unit 20 mounted on the main body 1A, the first contact portion 47a of the charging roller electrical contact 47 contacts the main body side contact portion of the main body 1A. The main body side contact portion is electrically connected to a charging power supply on a high-voltage substrate located on the main body 1A. Therefore, the charging voltage from the charging power supply can be applied to the charging roller 22 via the main body side contact portion and the conductive path from the charging roller electrical contact 47 to the charging roller 22.

[0076] (Brush unit) A brush unit 40 for the electrostatic roller 22 will now be described. The brush unit 40 has a brush 41 (Figure 4(a)) equipped with brush fibers 41a, and is configured so that the brush fibers 41a come into contact with the surface 22a of the electrostatic roller 22. The brush 41 can scrape off foreign matter adhering to the surface 22a of the electrostatic roller 22 with the brush fibers 41a.

[0077] While the image forming apparatus 1 is in use, foreign matter such as sand and dust may adhere to the surface 22a of the charging roller 22. For example, if the image forming apparatus 1 is used in an environment with a large amount of airborne sand and dust (outdoors or a similar environment), sand and dust are more likely to adhere to the charging roller 22. There is not just one path for foreign matter to enter; for example, in the transfer section Q4, it may adhere from the recording material P to the photosensitive drum 21 and then from the photosensitive drum 21 to the charging roller 22, or it may be taken into the apparatus body 1A along with the outside air and carried by the airflow to reach the charging roller 22.

[0078] If foreign matter adheres to the surface 22a of the charging roller 22, image defects may occur due to charging failure. For example, if foreign matter such as sand and dust adheres to a certain location on the surface 22a of the charging roller 22, and the rotation of the charging roller 22 causes the foreign matter to repeatedly pass through the charging section Q1, the foreign matter may become embedded in the surface 22a. In this case, a point-like charging defect occurs at the location corresponding to the foreign matter, and as a result, periodic point-like image defects may occur in the image output by the image forming operation at intervals corresponding to the circumference of the charging roller 22. Such image defects are also called black spots.

[0079] By arranging the brush unit 40 for the charging roller 22, foreign matter adhering to the surface 22a of the charging roller 22 can be scraped off by the brush fibers 41a of the brush 41. The brush 41 prevents foreign matter such as sand and dust from remaining in a specific location on the surface 22a of the charging roller 22, making it less likely for image defects such as black spots caused by the adhesion of foreign matter to occur. Furthermore, even when the image forming apparatus 1 is used in an environment with a large amount of airborne sand and dust, for example, it becomes possible to maintain high image quality over a long period of time.

[0080] The brush unit 40 will be explained in detail using Figures 9(a) to 11. The brush 41 extends in a long, narrow shape along the longitudinal direction (X direction) of the charging roller 22. In the following explanation, the longitudinal direction (X direction) of the charging roller 22 may be referred to as the longitudinal direction of the brush 41. The direction perpendicular to the longitudinal direction (X direction) of the brush 41 and along the base material of the brush 41 (W direction in the figure) may be referred to as the short direction of the brush 41. In addition, the direction perpendicular to both the longitudinal direction (X direction) and the short direction (W direction) of the brush 41 (V direction in the figure) may be referred to as the height direction of the brush 41. The V and W directions do not necessarily coincide with the Y and Z directions mentioned above.

[0081] Figure 9(a) is a view of the brush unit 40 from the opposite side of the charging roller 22 in the height direction (V direction) of the brush 41. Figure 9(b) is a view of the brush unit 40 in the short direction (W direction). Figure 9(c) is a view of the brush unit 40 from the side of the charging roller 22 in the height direction (V direction) of the brush 41. Figure 9(d) is a perspective view of the brush unit 40. Figure 9(e) is a perspective view of the brush base 42. Figure 10(a) is a perspective view of the brush unit 40. Figure 10(b) is an exploded view of the non-driven end of the brush unit 40. Figure 11 is a perspective view showing the brush 41 and the brush electrical contact 50.

[0082] As shown in Figures 9(d) and 10, the brush unit 40 includes a brush 41, a brush base 42, a brush electrical contact 50, and brush biasing members 53 and 54.

[0083] The brush 41 comprises brush fibers 41a (brush bristles), a sheet-like base 41b that supports the brush fibers 41a, and a plate-like support member 41c that supports the base 41b. The base 41b and the support member 41c constitute a plate-like base material. The brush fibers 41a protrude from the base material to one side in the thickness direction of the base material (the thickness direction of the support member 41c).

[0084] The brush 41 of this embodiment is formed by attaching a pile fabric to a support member 41c using, for example, an adhesive. The brush fibers 41a are, for example, conductive yarn piles made of nylon fibers containing carbon as a conductive agent, and the base 41b is a base fabric into which the conductive yarn piles are woven. The support member 41c is, for example, a sheet metal member. Alternatively, the brush 41 of this embodiment can also be said to consist of a brush body including the brush fibers 41a and the base 41b, and a support (support member 41c) that supports the brush body.

[0085] Furthermore, the brush 41 is not limited to a combination of pile fabric and sheet metal member. For example, the brush 41 may have a resin base material with a plurality of holes formed therein, and bundles of brush fibers 41a implanted in each of the holes of the base material. In other words, the base material of the brush 41 is not limited to a combination of a base 41b (a part that directly supports the brush fibers 41a) and a support member 41c (a part that supports the base 41b), but may also be an integrally molded part that supports the brush fibers 41a.

[0086] The brush base 42 is an example of a holding member for holding the brush 41. The brush base 42 includes a main unit portion 42a as a brush holding portion for holding the brush 41, and swinging support portions 42n and 42r as supported portions supported by the drum frame 26. In this embodiment, the main unit portion 42a holds the base material (particularly the support member 41c) of the brush 41. The swinging support portions 42n and 42r swing integrally with the main unit portion 42a.

[0087] In this embodiment, an example is described in which the main unit portion 42a and the swing support portions 42n and 42r are integrally formed. However, the swing support portions 42n and 42r may be separate components from the main unit portion 42a and fixed to the main unit portion 42a with screws or adhesive. Furthermore, the "holding member" does not necessarily have to be composed of a single component, as in the example in which the swing support portions 42n and 42r, which are separate components from the main unit portion 42a, are fixed to the main unit portion 42a.

[0088] The brush base 42 has a drive-side position restricting portion 42j and non-drive-side position restricting portions 42k and 42m, which serve as restricting portions (contact portions) for restricting the position of the brush unit 40. The drive-side bearing 45 and non-drive-side bearing 46 have contact portions (45a, 46a, and 46b) that contact the drive-side position restricting portion 42j and non-drive-side position restricting portions 42k and 42m, respectively, as will be described later. In other words, the drive-side bearing 45 and non-drive-side bearing 46 in this embodiment function as restricting members (positioning members) that restrict the position of the brush base 42 by contacting the brush base 42 (holding member). When the drive-side position restricting portion 42j is called the first restricting portion, the non-drive-side position restricting portions 42k and 42m can be called the second restricting portion. The position restriction of the brush unit 40 will be described later.

[0089] The main unit portion 42a of the brush base 42 extends along the longitudinal direction (X direction) of the brush 41, over substantially the entire length of the region where the brush fibers 41a are arranged. The brush 41, brush electrical contacts 50, and brush biasing members 53 and 54 are arranged in the main unit portion 42a. The oscillating support portions 42n and 42r are arranged on both outer sides of the main unit portion 42a in the longitudinal direction (X direction) of the brush 41. One oscillating support portion 42n is located on the driving side, and the other oscillating support portion 42r is located on the non-driving side.

[0090] The brush base 42 is movably supported by the drum frame 26 (Figures 5(b)(c) and 6) and is movable in a direction toward and toward the charging roller 22. In other words, the brush unit 40 is movable so that the brush base 42 (brush holding part) moves toward and toward the charging roller 22. In this embodiment, the brush unit 40 is swingable (rotatable) relative to the drum frame 26 by the engagement of support holes 42p and 42s provided in the brush base 42 with support shafts 26a and 26b provided in the drum frame 26. In addition, in this embodiment, the brush unit 40 is biased by brush biasing members 53 and 54 so that the base material of the brush 41 (41b, 41c) and the brush base 42 move toward the charging roller 22.

[0091] The main unit portion 42a of the brush base 42 is provided with width regulating grooves 42g, 42h, and 42i for regulating the position of the brush 41 in the short direction (W direction) of the brush 41. In this embodiment, the brush base 42 is provided with width regulating grooves 42g, 42h, and 42i at three locations on the main unit portion 42a in the longitudinal direction (X direction) of the brush 41: the drive side end, the center, and the non-drive side end. The number and arrangement of the width regulating grooves 42g, 42h, and 42i may be changed. The inner width of the width regulating grooves 42g, 42h, and 42i is set to be approximately equal to the width of the brush 41 in the short direction (W direction) of the brush 41 (in particular, the width of the support member 41c). When the brush 41 engages with the width regulating grooves 42g, 42h, and 42i, the position of the brush 41 relative to the brush base 42 in the short direction (W direction) is regulated (positioned).

[0092] Furthermore, in this embodiment, the drum frame 26 is provided with a longitudinal regulating rib 26c (Figure 5(b)), and the main unit portion 42a of the brush base 42 is provided with a longitudinal regulating groove 42f (see also Figure 10(a)). The longitudinal regulating rib 26c protrudes in a direction intersecting the longitudinal direction (X direction) of the brush 41. By engaging the longitudinal regulating rib 26c with the longitudinal regulating groove 42f, the position of the brush unit 40 relative to the drum frame 26 is regulated (positioned) in the longitudinal direction (X direction) of the brush 41. Alternatively, the brush base 42 may be provided with a longitudinal regulating rib (convex portion) that protrudes in a direction intersecting the longitudinal direction (X direction), and the drum frame 26 may be provided with a longitudinal regulating groove (recess) that engages with this longitudinal regulating rib.

[0093] As shown in Figure 9(e), brush seating surfaces 42b and 42c are provided at both ends of the main unit portion 42a in the longitudinal direction (X direction) of the brush 41. The brush seating surfaces 42b and 42c protrude toward the brush 41 in the height direction (V direction) of the brush 41 compared to the surface 42z between the brush seating surfaces 42b and 42c. The brush 41 is fixed to the brush base 42 by a support member 41c being bonded to the brush seating surfaces 42b and 42c by an adhesive or other method. When the brush 41 is fixed to the brush seating surfaces 42b and 42c, the surface 42z between the brush seating surfaces 42b and 42c on the main unit portion 42a does not basically come into contact with the brush 41.

[0094] In other words, the main unit portion 42a (brush holding portion) has opposing surfaces (42b, 42c, 42z) that face the support member 41c (sheet metal member) in the thickness direction of the base material (41b, 41c) of the brush 41. The opposing surfaces include a brush seating surface 42b (first seating surface portion) to which one end of the sheet metal member is fixed in the rotation axis direction (X direction) of the charging roller, and a brush seating surface 42c (second seating surface portion) to which the other end of the sheet metal member is fixed in the rotation axis direction (X direction) of the charging roller. The opposing surfaces also include a surface 42z (unfixed portion) formed in the region between the first seating surface portion and the second seating surface portion in the rotation axis direction (X direction) of the charging roller, to which the sheet metal member is not fixed.

[0095] In this embodiment, the brush base 42 is a molded product (resin molded part), and some deformation may occur during molding. For example, the brush base 42 may warp, such that the central part of the brush base 42 in the longitudinal direction (X direction) protrudes towards the brush 41 side or the opposite side in the height direction (V direction). In addition, the brush base 42 may twist, such that the orientation of the brush seating surfaces 42b and 42c differs between one end and the other end in the longitudinal direction (X direction).

[0096] Therefore, by having a highly rigid metal support member 41c in the brush 41, and by having both ends of the support member 41c fixed to the brush seating surfaces 42b and 42c of the brush base 42, deformation of the brush base 42 can be corrected. In other words, the warping and twisting of the brush base 42 can be corrected by making it conform to the support member 41c, which is more rigid than the brush base 42. This suppresses the influence of shape errors in the brush base 42 on the position and shape of the brush 41, and allows the brush fibers 41a to make stable contact with the charging roller 22.

[0097] As shown in Figures 9(d) and 10(a), the swing support portions 42n and 42r (first extension portion and second extension portion) of the brush base 42 extend (project) to one side in the short direction (W direction) of the brush 41 relative to the main unit portion 42a. Support holes 42p and 42s are formed at the tips of the swing support portions 42n and 42r. The drum frame 26 is provided with support shafts 26a and 26b (Figures 5(b) and 5(c)) which engage with the holes. The brush unit 40 is swingably supported relative to the drum frame 26 by the engagement of the support holes 42p and 42s with the support shafts 26a and 26b of the drum frame 26, respectively. Both support shafts 26a and 26b extend in the direction of the rotation axis of the charging roller 22 (the longitudinal direction of the brush 41, the X direction). The imaginary straight line passing through the centers of the support shafts 26a and 26b is the pivot axis of the brush unit 40.

[0098] When the drive-side oscillating support portion 42n and support shaft 26a are referred to as the first oscillating support portion and the first support portion, respectively, the non-drive-side oscillating support portion 42r and support shaft 26b can be referred to as the second oscillating support portion and the second support portion, respectively. Also, when the support hole 42p and support shaft 26a are referred to as the first hole portion and the first shaft portion, respectively, the support hole 42s and support shaft 26b can be referred to as the second hole portion and the second shaft portion, respectively. In this embodiment, the support shafts 26a and 26b (shaft portions) are arranged in the drum frame 26 and the support holes 42s and 42p (hole portions) are formed in the brush unit 40, but it is also possible to form the holes in the drum frame 26 and arrange the shaft portions that engage with the holes in the brush unit 40.

[0099] Furthermore, the oscillating support parts 42n and 42r are provided with openings 42q and 42t, where support holes 42p and 42s open in a direction intersecting the oscillating axis of the brush unit 40. In other words, the support holes 42p and 42s are formed as an arc shape with a portion of the circumference around the oscillating axis of the brush unit 40 cut out by the provision of openings 42q and 42t. The opening direction V1 of the drive-side opening 42q and the opening direction V2 of the non-drive-side opening 42t are different from each other. By providing openings 42q and 42t, the support holes 42p and 42s can be more easily engaged with the support shafts 26a and 26b when attaching the brush unit 40 to the drum frame 26.

[0100] As shown in Figures 10(a) and 10(b), the brush biasing members 53 and 54 are attached to one end and the other end of the main unit portion 42a in the longitudinal direction (X direction) of the brush 41. Specifically, the first end 53a of the drive-side brush biasing member 53 is attached to the shaft portion 42d provided at one end of the main unit portion 42a. One end of the non-drive-side brush biasing member 54 is attached to the shaft portion 42e (Figure 9(a)) provided at the other end of the main unit portion 42a.

[0101] The brush electrical contact 50 has a first portion 50a with a hole formed therein that engages with the shaft portion 42d, and a second portion 50b extending from the first portion 50a in the longitudinal direction (X direction) of the brush 41. The brush electrical contact 50 is formed, for example, by punching and bending a single sheet metal member.

[0102] The first part 50a is planar in shape, substantially perpendicular to the height direction (V direction) of the brush 41, and its hole engages with the shaft portion 42d. It is supported by being sandwiched between the first end 53a of the brush biasing member 53 and the brush base 42. The other end (second end 53b) of the brush biasing member 53 is in contact with the third contact portion 47c provided on the aforementioned electrostatic roller electrical contact 47 (see also Figure 6).

[0103] As shown in Figures 11(a) and 11(b), the tip of the second portion 50b of the brush electrical contact 50 is provided with a contact portion 50c that abuts against the side surface 41d of the support member 41c of the brush 41 in the short direction (W direction). The second portion 50b is provided with one or more bent portions 50b1 that utilize the elasticity (springiness) of the sheet metal to more reliably bring the contact portion 50c into contact with the side surface 41d of the support member 41c. The contact portion 50c is pressed against the side surface 41d of the support member 41c by the elasticity (springiness) of the second portion 50b of the brush electrical contact 50.

[0104] With the above configuration, the brush 41 is electrically connected to the main body side contact portion of the device body 1A via the charging roller electrical contact 47, the brush biasing member 53, and the brush electrical contact 50. Furthermore, since the brush 41 is electrically connected to the charging roller 22 via the brush electrical contact 50, the potential of the brush 41 is equal to that of the charging roller 22. In other words, a charging voltage is applied to both the brush 41 and the charging roller 22 via the brush electrical contact 50 from the charging power supply of the device body 1A.

[0105] Foreign matter adhering to the charged roller 22 may be electrically charged. Therefore, if there is a potential difference between the brush 41 and the charged roller 22, the foreign matter may be electrostatically pressed against the charged roller 22 as it passes through the contact area between the charged roller 22 and the brush 41, making it difficult for the brush 41 to scrape off the foreign matter. If the brush 41 and the charged roller 22 are at the same potential, the brush 41 will be able to easily scrape off foreign matter adhering to the surface 22a of the charged roller 22, regardless of whether the foreign matter is charged or not.

[0106] Furthermore, if the charging roller 22 and the brush 41 are electrically connected, the same advantages can be obtained regardless of the specific configuration of the conductive path. In this embodiment, an example has been described in which the conductive path from the charging roller electrical contact 47, which is a contact member exposed to the outside of the process unit 20, to the charging roller 22 and the conductive path to the brush 41 are branched. However, this is not the only example; for example, a conductive path from the charging roller 22 to the brush 41 may be configured by arranging conductive members such as wires that electrically connect the drive-side bearing 45 and the support member 41c of the brush 41 in the oscillating support part 42n and the main unit part 42a. Alternatively, a similar conductive path may be configured by forming a part of the oscillating support part 42n and the main unit part 42a from conductive resin.

[0107] (Brush unit position restriction) The positional control of the brush unit 40 will be explained using Figures 12(a) to (g). Figure 12(a) is a view of the drum unit 25 from the upstream side in the Y direction (rear view). Figure 12(b) is a cross-sectional view of the drum unit 25 along the GG line in Figure 12(a). Figure 12(c) is a cross-sectional view of the drum unit 25 along the FF line in Figure 12(a). Figure 12(d) is an enlarged view of a part of Figure 12(b) (the area where the brush unit 40 and the non-drive side bearing 46 are in contact). Figure 12(e) is an enlarged view of a part of Figure 12(c) (the area where the brush unit 40 and the drive side bearing 45 are in contact). Figure 12(f) shows the state in which the brush unit 40 has rotated around the support shafts 26a and 26b from the state in Figure 12(d). Figure 12(g) is an enlarged view of a part of Figure 12(b) (near the support shaft 26b).

[0108] As described above, the brush unit 40 is movable relative to the charging roller 22. The brush base 42 (holding member) is configured to be movable in the direction of movement in which the base material (41b, 41c) of the brush 41 moves toward and away from the charging roller 22 (Figure 12(b)(c)). In this embodiment, the brush base 42 is movable (oscillated) relative to the charging roller 22 in the direction of rotation (arrow U) around the support shafts 26a, 26b, respectively, by engaging the support holes 42p, 42s with the support shafts 26a, 26b of the drum frame 26.

[0109] Here, the "direction of movement" of the brush base 42 is any direction that has a component perpendicular to the tangent to the arc centered on the rotation axis of the charging roller 22. For example, the "direction of movement" may be a linear direction intersecting the arc centered on the rotation axis of the charging roller 22, or a rotational direction around an axis parallel to the rotation axis of the charging roller 22 and spaced apart from the rotation axis of the charging roller 22. Furthermore, the "direction of movement" is not limited to a linear direction along a single straight line or a direction along a single arc, but may also be a direction along a curve formed by combining multiple line segments and / or multiple curved sections. For example, when the brush base 42 moves while being guided by a guide shape such as a groove provided in the drum frame 26, the "direction of movement" may be a direction along the guide shape.

[0110] In this embodiment, the brush unit 40 is biased by brush biasing members 53 and 54 in the direction indicated by arrow U in the figure in the rotational direction around the support shafts 26a and 26b. The brush unit 40 is positioned (contains) its position in the rotational direction around the support shafts 26a and 26b by contacting the drive-side bearing 45 and the non-drive-side bearing 46.

[0111] In the longitudinal direction (X direction) of the brush 41, the support hole 42p on one side (the drive side) and the support shaft 26a are fitted together so that they can slide smoothly (Figure 12(b)). In other words, the inner diameter of the support hole 42p is set to be approximately equal to the outer diameter of the support shaft 26a, and the inner surface of the support hole 42p (first hole portion) is in slidable contact with the outer surface of the support shaft 26a (first shaft portion). In contrast, on the other side (the non-drive side), a gap d2 is formed between the outer surface of the support shaft 26b and the inner surface of the support hole 42s, as shown in Figure 12(g). In other words, the inner diameter of the support hole 42s (second hole portion) is set to be larger than the outer diameter of the support shaft 26b (second shaft portion), and the difference between the inner diameter of the support hole 42s and the outer diameter of the support shaft 26b is greater than the difference between the inner diameter of the support hole 42p and the outer diameter of the support shaft 26a. The function of gap d2 will be described later.

[0112] Let's explain the position restriction of the brush unit 40 in more detail. At one end (drive side) of the brush unit 40 in the longitudinal direction (X direction) of the brush 41, as shown in Figure 12(e), the drive side position restricting portion 42j provided on the main unit portion 42a of the brush base 42 comes into contact with the drive side contact portion 45a of the drive side bearing 45. As mentioned above, the drive side bearing 45 is movable relative to the drum frame 26 in the direction in which the charging roller 22 approaches and moves away from the photosensitive drum 21 (arrows S, T), but it is positioned by the contact between the charging roller 22 and the photosensitive drum 21. Therefore, the contact between the drive side position restricting portion 42j and the drive side contact portion 45a stops the swinging of the brush base 42 in the direction of arrow U due to the biasing force of the brush biasing members 53 and 54. As mentioned above, there is no gap in the engagement between the support hole 42s and the support shaft 26a. Therefore, on the drive side, the position of the brush unit 40 (the position of the brush base 42) is determined based on the center of the support shaft 26a and the contact position of the drive side position regulating part 42j and the drive side contact part 45a.

[0113] On the other hand, at the other end (non-driven side) of the brush unit 40, as shown in Figure 12(d), the non-driven side position restricting parts 42k and 42m provided on the main unit part 42a of the brush base 42 come into contact with the non-driven side contact parts 46a and 46b of the non-driven side bearing 46. As mentioned above, the non-driven side bearing 46 is movable relative to the drum frame 26 in the direction in which the charging roller 22 approaches and moves away from the photosensitive drum 21 (arrows S and T), but is positioned by the contact between the charging roller 22 and the photosensitive drum 21. Therefore, the contact between the non-driven side position restricting parts 42k and 42m and the non-driven side contact parts 46a and 46b stops the rotation of the brush unit 40 in the direction of arrow U due to the biasing force of the brush biasing members 53 and 54.

[0114] Here, the other end (non-driven side) of the brush unit 40 is provided with two restricting surfaces (non-driven side position restricting sections 42k and 42m) that face in different directions when viewed in the longitudinal direction (X direction) of the brush 41. When the non-driven side position restricting section 42k is called the first restricting surface, the non-driven side position restricting section 42m can be called the second restricting surface. The non-driven side position restricting section 42k (first restricting surface) contacts the non-driven side contact section 46a (first contact section) of the non-driven side bearing 46, and the non-driven side position restricting section 42m (second restricting surface) contacts the non-driven side contact section 46b (second contact section) of the non-driven side bearing 46. This makes it possible to accurately determine the position of the brush unit 40 (position of the brush base 42) on the non-driven side in a direction perpendicular to the longitudinal direction (X direction) of the brush 41.

[0115] More specifically, in this embodiment, the position of the brush unit 40 is determined by the convex shape of the non-drive side bearing 46 fitting into the concave shape (groove shape) formed by the non-drive side position restricting portions 42k and 42m. In other words, the convex shape of the non-drive side bearing 46, including the non-drive side contact portions 46a and 46b, fits into the bottom portion 42v of the concave shape formed by the non-drive side position restricting portions 42k and 42m. This positions the brush unit 40 in a direction perpendicular to the longitudinal direction (X direction) of the brush 41.

[0116] The gap d2 between the non-driven support hole 42s and the support shaft 26b (Figure 12(g)) allows the convex shape of the non-driven bearing 46 to engage more reliably with the concave shape formed by the non-driven position restricting parts 42k and 42m. In other words, even if the brush base 42 has some warping or twisting, the gap d2 allows for displacement of the support hole 42s relative to the support shaft 26b, thus allowing the convex shape of the non-driven bearing 46 to engage more reliably with the concave shape of the brush base 42.

[0117] Incidentally, as the brush unit 40 rotates around the support shafts 26a and 26b, there may be cases where only one of the non-driven side position restricting parts 42k and 42m comes into contact with the non-driven side contact part 46a or 46b, as shown in Figure 12(f). In the example in Figure 12(f), the non-driven side position restricting part 42k and the non-driven side contact part 46a are in contact, while the non-driven side position restricting part 42m and the non-driven side contact part 46b are not in contact.

[0118] However, the concave shape formed by the non-drive side position restricting portions 42k and 42m is formed to be concave toward the upstream side in the rotational direction (arrow U) in which the brush unit 40 rotates around the support shafts 26a and 26b according to the biasing force of the brush biasing members 53 and 54. Therefore, as the brush unit 40 swings in the swinging direction indicated by arrow U according to the biasing force of the brush biasing members 53 and 54, the convex shape of the non-drive side bearing 46 slides over the non-drive side position restricting portion 42k toward the bottom 42v of the concave shape. As a result, even if the situation temporarily becomes as shown in Figure 12(f), thereafter, as shown in Figure 12(d), the convex shape of the non-drive side bearing 46 is in contact with both the non-drive side position restricting portions 42k and 42m and engages with the concave shape.

[0119] As explained above, the position of the brush base 42 is restricted when the restricting portion (drive-side position restricting portion 42j, non-drive-side position restricting portion 42k, 42m) of the brush base 42 (holding member) comes into contact with the bearing member (drive-side bearing 45, non-drive-side bearing 46). Since the position of the brush base 42 is restricted by the contact between the bearing member holding the charging roller 22 and the restricting portion, the brush 41 can come into contact with the charging roller 22 with a more stable penetration amount.

[0120] The amount of penetration of the brush 41 into the charging roller 22 refers to the distance that the tip of the brush fiber 41a, assuming the charging roller 22 is not present, penetrates inward relative to the virtual cylindrical surface along the actual surface 22a of the charging roller 22. For example, the amount of penetration of the brush 41 is defined as the difference between the sum of the outer diameter of the charging roller 22 and the amount of protrusion of the brush fiber 41a into the base material (41b, 41c) (brush bristle length), and the shortest distance from the rotation axis of the charging roller 22 to the base material (41b, 41c) of the brush 41 in the state shown in Figures 12(b) and (c).

[0121] The amount of penetration of the brush 41 into the charging roller 22 may vary from product to product due to dimensional tolerances of the parts, etc., and may also vary depending on the position in the longitudinal direction (X direction). In such cases, the function of the brush 41 in scraping off foreign matter adhering to the surface 22a of the charging roller 22 may be reduced, potentially causing image defects. In contrast, according to this embodiment, the brush 41 can be made to contact the charging roller 22 with a more stable amount of penetration. As a result, it becomes easier to maintain the charging performance of the charging roller 22 over a long period of time, and the possibility of image defects can be reduced.

[0122] Furthermore, on the non-driven side, a gap d2 is provided between the support hole 42s and the support shaft 26b, and the position of the brush unit 40 is restricted by the contact between the non-driven side position restricting parts 42k, 42m and the non-driven side contact parts 46a, 46b. As a result, even if the drum frame 26 is twisted at one end and the other end in the longitudinal direction (X direction) due to dimensional tolerances of the parts or variations during assembly, twisting of the brush unit 40 can be suppressed. This also reduces variations in the amount of penetration of the brush 41 into the charging roller 22.

[0123] On the drive side, it is preferable that the drive side position restricting portion 42j and the drive side contact portion 45a have a shape that allows for point contact. This makes it possible to suppress changes in the contact position between the drive side position restricting portion 42j and the drive side contact portion 45a, even if there is an inclination on the surface of the drive side position restricting portion 42j or the surface of the drive side contact portion 45a due to shape errors of the parts, etc. As a result, variations in the amount of penetration of the brush 41 into the charging roller 22 can be further reduced. Specifically, in this embodiment, the drive side contact portion 45a is planar in shape that intersects with the direction in which the brush 41 approaches and moves away from the charging roller 22 (the direction perpendicular to the base portion 41b), and the drive side position restricting portion 42j has a substantially arc shape when viewed in the longitudinal direction (X direction).

[0124] For similar reasons, on the non-driven side, it is preferable that the non-driven side position restricting portion 42k and the non-driven side contact portion 46a are in point contact, and it is preferable that the non-driven side position restricting portion 42m and the non-driven side contact portion 46b are in point contact. In this embodiment, the non-driven side position restricting portions 42k and 42m are planar, and the non-driven side contact portions 46a and 46b are substantially arc-shaped. Furthermore, the non-driven side position restricting portions 42k and 42m are substantially orthogonal to each other when viewed in the longitudinal direction (X direction).

[0125] In this embodiment, the rigidity of the support member 41c of the brush 41 is used to suppress twisting of the brush unit 40 (twisting of the brush base 42). If the configuration allows twisting of the brush unit 40, and the brush base 42 only contacts one of the drive-side bearing 45 and the non-drive-side bearing 46, then variations in the amount of penetration of the brush 41 into the charging roller 22 will occur. To avoid this, it is conceivable to increase the biasing force of the brush biasing members 53 and 54, but this raises concerns that the contact pressure of the charging roller 22 against the photosensitive drum 21 will become uneven in the longitudinal direction (X direction). In other words, the difference in biasing force between the drive-side and non-drive-side charging roller biasing members 48 and 49 and the difference in biasing force between the drive-side and non-drive-side brush biasing members 53 and 54 are superimposed, which may cause variations in the contact pressure of the charging roller 22 against the photosensitive drum 21. Variations in the contact pressure of the charging roller 22 against the photosensitive drum 21 can cause problems such as uneven potential of the photosensitive drum 21, resulting in uneven image density, and uneven wear of the photosensitive drum 21. Therefore, from the viewpoint of suppressing variations in the contact pressure of the charging roller 22 against the photosensitive drum 21, it is preferable that the biasing force of the brush biasing members 53 and 54 be small.

[0126] According to this embodiment, since twisting of the brush unit 40 (twisting of the brush base 42) is suppressed, the biasing force of the brush biasing members 53 and 54 can be reduced while improving the positional accuracy of the brush 41 relative to the charging roller 22.

[0127] Furthermore, in this embodiment, it has been explained that the charging roller 22 is movable between a contact position and a separation position relative to the photosensitive drum 21. In this configuration, by bringing the restricting portion of the brush unit 40 into contact with the bearing member of the charging roller 22 and restricting the position of the brush holding portion, it is possible to improve the positional accuracy of the brush holding portion relative to the charging roller 22, even though the charging roller 22 is movable.

[0128] According to this embodiment, the brush unit 40 moves in conjunction with the movement of the charging roller 22 between the contact position and the separated position due to the contact between the regulating portion and the bearing member. This allows the charging roller 22 to contact and separate from the photosensitive drum 21 without being obstructed by the brush unit 40.

[0129] (Details of the brush unit) Here, the factors that affect the variation in the amount of penetration of the brush 41 into the charged roller 22 will be explained using Figures 13(a)-(c), 14(a)-(c), and 15(a)(b).

[0130] Figure 13(a) is a rear view of the drum unit 25 as seen from the upstream side in the Y direction. Figures 13(b) and (c) are cross-sectional views of the drum unit 25 along the HH line in Figure 13(a). Figure 13(b) shows the state in which the charging roller 22 is in contact position, and Figure 13(c) shows the state in which the charging roller 22 is in separated position. Figure 14(a) is a conceptual diagram showing the rotation trajectory of the brush unit 40 according to this embodiment. Figures 14(b) and (c) are conceptual diagrams showing the rotation trajectory of the brush unit 40' according to a comparative example, respectively.

[0131] The following description will focus on one end (drive side) of the brush unit 40 in the longitudinal direction (X direction), but the same explanation basically applies to the other end of the brush unit 40.

[0132] As shown in Figures 13(b) and 13(c), when viewed in the longitudinal direction (X direction) of the brush 41, the brush oscillation center of the brush unit 40 (the oscillation center of the brush base 42) is defined as P1. In this embodiment, the brush oscillation center P1 is the center of the support shaft 26a of the drum frame 26. The point at which the biasing force of the brush biasing member 53 acts on the brush base 42 is called the point of application of the biasing force P2, or simply point P2. The contact position where the drive-side position restricting part 42j and the drive-side contact part 45a come into contact is called the contact point of the restricting part P3, or simply point P3. The contact point of the restricting part P3 is the point at which the brush unit 40 receives a reaction force from the drive-side bearing 45 when the brush base 42 is pressed against the drive-side bearing 45 by the biasing force of the brush biasing member 53. The contact position where the brush fibers 41a come into contact with the charging roller 22 is called the brush contact point P4, or simply point P4. The brush contact point P4 is the point at which the brush unit 40 receives the reaction force from the charging roller 22 when the brush fibers 41a are in contact with the surface 22a of the charging roller 22 by a predetermined amount of penetration. The brush fibers 41a are in contact with the surface 22a of the charging roller 22 over a predetermined contact area in the rotational direction of the charging roller 22.

[0133] As shown in Figure 13(b), in this embodiment, in the tangential direction t of the surface 22a of the charging roller 22 at the brush contact point P4, the contact point P3 of the restricting part is located between the brush contact point P4 and the brush oscillation center P1. Also in this embodiment, in the tangential direction t, the point of application of the biasing force P2 is located between the brush contact point P4 and the brush oscillation center P1. Furthermore, in this embodiment, in the tangential direction t, the point of application of the biasing force P2 is located closer to the brush oscillation center P1 than the contact point P3 of the restricting part. Therefore, in this embodiment, in the tangential direction t, the brush contact point P4, the contact point P3 of the restricting part, the point of application of the biasing force P2, and the brush oscillation center P1 are arranged in this order.

[0134] Using Figures 14(a) to 14(c), we will explain the effect of the distance from the brush oscillation center P1 to the brush contact point P4 on the stability of contact between the brush 41 and the charged roller 22.

[0135] Figure 14(a) is a schematic diagram showing a brush unit 40 according to one embodiment of this embodiment. In this embodiment, the distance from the brush oscillation center P1 to the brush contact point P4 is L1. Figures 14(b) and (c) are schematic diagrams showing a brush unit 40' according to a comparative example in which the distance L2 from the brush oscillation center P1' to the brush contact point P4' is shorter than that of the embodiment in Figure 14(a) (L1>L2). In common to each example in Figures 14(a) to (c), the lengths L3 of the brush bases 42 and 42' in the tangential direction t are assumed to be equal. Also, except for the order of points P1', P2', P3', and P4' and the arrangement of the brush biasing member 53', the configuration of the brush unit 40' according to the comparative example in Figures 14(b) and (c) is the same as that of the embodiment in Figure 14(a).

[0136] In the embodiment shown in Figure 14(a), the trajectory traced by the tip of the brush fiber 41a when the brush unit 40 oscillates around the brush oscillation center P1 is defined as the rotation trajectory C1. The rotation trajectory C1 is a circular arc passing through the brush contact point P4 and centered at the brush oscillation center P1. Similarly, in the comparative examples shown in Figures 14(b) and (c), the trajectory traced by the tip of the brush fiber 41a when the brush unit 40' oscillates around the brush oscillation center P1' is defined as the rotation trajectory C2.

[0137] As shown in Figures 14(a) to (c), in the embodiment where the distance L1 from the brush oscillation center P1 to the brush contact point P4 is longer, the curvature of the rotation trajectory C1 is smaller compared to the comparative example where the distance L2 from the brush oscillation center P1' to the brush contact point P4' is shorter. In other words, the rotation trajectory C1 of the brush 41 in the embodiment has a gentler curve than the rotation trajectory C2 of the comparative example.

[0138] The smaller the curvature of the rotation trajectory C1, the more stable the contact of the brush 41 with the charging roller 22. That is, the angle of the brush unit 40 around the brush oscillation center (angle of the brush base 42) when the brush 41 is in contact with the charging roller 22 can fluctuate due to the influence of dimensional tolerances of the parts constituting the brush unit 40 and assembly tolerances of the drum unit 25. In this case, the larger the curvature of the rotation trajectory (smaller radius of curvature), the greater the change in the contact angle of the brush 41 with respect to the change in the angle of the brush unit 40. Conversely, the smaller the curvature of the rotation trajectory (larger radius of curvature), the greater the change in the contact angle of the brush 41 with respect to the change in the angle of the brush unit 40. The contact angle of the brush 41 is the angle between the tangential direction t of the charging roller 22 and the thickness direction of the base material (41b, 41c) of the brush 41.

[0139] When the contact angle of the brush 41 changes, the amount of penetration of the brush 41 into the charging roller 22 changes depending on the position of the charging roller 22 in the direction of rotation, and the contact pressure between the brush fibers 41a and the charging roller 22 changes. As a result, the function of the brush 41 in scraping off foreign matter attached to the charging roller 22 may be impaired. Conversely, if the change in the contact angle of the brush 41 can be kept small, the amount of penetration of the brush 41 into the charging roller 22 can be maintained at a value close to the desired value.

[0140] In other words, the longer the distance L1, the smaller the curvature of the rotational trajectory C1 of the brush 41, and the less the amount of contact of the brush 41 with the charging roller 22 is affected by part tolerances, etc. As a result, the stability of contact between the brush 41 and the charging roller 22 can be improved.

[0141] While it is possible to reduce the curvature of the rotational trajectory of the brush 41 by increasing the length L3 of the brush base 42, this would lead to an increase in the size of the device.

[0142] According to this embodiment, in the tangential direction t of the charging roller 22 at the brush contact point P4, the contact point P3 of the restricting portion is located between the brush contact point P4 and the brush oscillation center P1 (Figure 14(a)). In other words, when viewed in the direction of the rotation axis of the charging roller 22, in the tangential direction t, the contact position (P3) between the brush base 42 (holding member) and the drive-side bearing 45 (restricting member) is located between the contact position (P4) and the oscillation axis (P1) of the brush base 42.

[0143] Therefore, compared to a comparative example (Figure 14(b)) in which the contact point P3 of the regulating part is not located between the brush contact point P4 and the brush oscillation center P1, the curvature of the rotation trajectory C1 of the brush 41 can be reduced even if the length L3 of the brush base 42 is the same. This improves the stability of the contact of the brush 41 with respect to the charging roller 22. In other words, according to this embodiment, it is possible to improve the stability of the contact of the brush 41 with respect to the charging roller 22 while avoiding an increase in the size of the device.

[0144] Furthermore, according to this embodiment, in the tangential direction t of the charging roller 22 at the brush contact point P4, both the contact point P3 of the restricting portion and the point of application of the biasing force P2 are located between the brush contact point P4 and the brush oscillation center P1 (Figure 14(a)). In other words, in the view along the rotation axis of the charging roller 22, in the tangential direction t, the point of application (P2) of the biasing force of the brush biasing member 53 to the brush base 42 (holding member) is located between the contact position (P4) and the oscillation axis (P1).

[0145] Therefore, compared to the comparative example (Figure 14(c)) in which the point of application of the biasing force P2 is not located between the brush contact point P4 and the brush oscillation center P1, the curvature of the rotation trajectory C1 of the brush 41 can be reduced even if the length L3 of the brush base 42 is the same. Thus, the curvature of the rotation trajectory C1 can be reduced as much as possible under the constraint of the length L3 of the brush base 42.

[0146] Incidentally, as described above using Figures 7(a) to 8(b), the charging roller 22 in this embodiment is configured to be able to come into contact with and separate from the photosensitive drum 21. The movement of the brush unit 40 accompanying the movement of the charging roller 22 will be explained using Figures 15(a) and 15(b).

[0147] Figures 15(a) and 15(b) are schematic diagrams of the photosensitive drum 21, charging roller 22, and brush unit 40 according to this embodiment. Figure 15(a) shows the state in which the charging roller 22 is in contact position. Figure 15(b) shows the state in which the charging roller 22 is in separated position.

[0148] When the charging roller 22 is moved in the direction of arrow S from the contact position to the separated position by the charging roller separation members 28 and 29, the drive-side bearing 45 and the non-drive-side bearing 46 also move in the direction of arrow S (Figure 15(b)). As a result, the drive-side position restricting portion 42j and the non-drive-side position restricting portions 42k and 42m of the brush base 42 are pressed against the contact portions (45a, 46a, and 46b) of the drive-side bearing 45 and the non-drive-side bearing 46, causing the brush base 42 to oscillate around the brush oscillation center P1. Note that while Figures 15(a) and (b) show the drive-side position restricting portion 42j and the drive-side contact portion 45a of the drive-side bearing 45, the non-drive-side position restricting portions 42k and 42m of the brush base 42 also press against the non-drive-side contact portions 46a and 46b on the non-drive side.

[0149] When the charged roller 22 moves from the contact position to the separated position, the direction of oscillation of the brush base 42 (arrow R1) is the direction in which the brush 41 moves away from the charged roller 22 (clockwise direction in Figures 15(a) and (b)).

[0150] In this embodiment, the contact point P3 of the regulating part is positioned closer to the brush oscillation center P1 than the brush contact point P4. In other words, the distance from the brush contact point P4 to the brush oscillation center P1 is shorter than the distance from the contact point P3 of the regulating part to the brush oscillation center P1.

[0151] Therefore, the amount of movement of the base material (41b, 41c) of the brush 41 while the charging roller 22 moves from the contact position to the separated position is greater than the amount of movement of the contact point P3 of the restricting part while the charging roller 22 moves from the contact position to the separated position. Consequently, when the charging roller 22 is in the separated position (Figure 15(b)), the amount of penetration of the brush 41 into the charging roller 22 is reduced compared to when the charging roller 22 is in the contact position (Figure 15(a)). The reason for comparing the amount of movement of the base material (41b, 41c) of the brush 41 rather than the amount of movement of the brush contact point P4 is that the brush fibers 41a may be in contact with the charging roller 22 in the separated position shown in Figure 15(b).

[0152] As mentioned above, from the time the image forming apparatus 1 is shipped from the apparatus body 1A until it reaches the user, the charging roller 22 is held in a separated position, and during the initialization process to make the image forming apparatus 1 ready for use, the charging roller 22 is moved to a contact position. In this configuration, by keeping the amount of penetration of the brush 41 small when the charging roller 22 is in the separated position, deformation of the brush fibers 41a can be suppressed. Then, when the charging roller 22 is moved to the contact position, the brush 41 can be brought into contact with the charging roller 22 with an penetration amount close to the desired amount.

[0153] (Positional relationship between the brush unit and the laser beam path) The positional relationship between the brush unit 40 and the optical path of the laser beam L emitted from the scanner unit 11 will be explained primarily using Figures 1 and 16(a) and 16(b). Figure 1 is a cross-sectional view of the scanner unit 11 and the process unit 20. Figure 16(a) is a perspective view of the process unit 20, and Figure 16(b) is an enlarged view of a part of it. In Figures 1 and 16(a) and 16(b), the optical path, which is the space through which the laser beam L emitted from the scanner unit 11 toward the photosensitive drum 21 passes, is illustrated as a virtual three-dimensional shape.

[0154] As described above, the scanner unit 11, acting as an exposure device, scans and exposes the surface of the photosensitive drum 21 by irradiating it with laser light L corresponding to image information input from an external device using a scanning optical system including a polygon mirror. In addition, in the rotation direction during image formation (arrow Q in Figures 4(a) and 4(b)), the charging unit Q1, exposure unit Q2, and developing unit Q3 are arranged in this order. That is, as shown in Figure 1, the scanner unit 11 irradiates the surface 21a of the photosensitive drum 21 with laser light L directed downstream of the charging unit Q1 and upstream of the developing unit Q3 in the rotation direction (Q) of the photosensitive drum 21. The laser light L irradiated from the scanner unit 11 reaches the surface 21a of the photosensitive drum 21 by passing through the space S1 between the drum unit 25 and the developing unit 30.

[0155] Here, the brush unit 40 has a main unit portion 42a (brush holding portion) that holds the base material (41b, 41c) of the brush 41 as described above, and swing support portions 42n and 42r that are supported by the drum frame 26. The swing support portion 42n is an extension portion (first extension portion) that extends from one end (drive side) of the main unit portion 42a in the longitudinal direction (X direction) of the brush 41 in a direction intersecting the longitudinal direction. The swing support portion 42r is an extension portion (second extension portion) that extends from the other end (non-drive side) of the main unit portion 42a in the longitudinal direction (X direction) of the brush 41 in a direction intersecting the longitudinal direction. In this embodiment, the swing support portions 42n and 42r, as supported portions, are swingably supported by the drum frame 26. Furthermore, the main unit section 42a (brush holding section) oscillates together with the oscillating support sections 42n and 42r around the oscillating axis, thereby moving the base material (41b, 41c) of the brush 41 closer to and further away from the charging roller 22.

[0156] As explained using Figures 14(a) to (c), the longer the distance L1 from the brush oscillation center P1 to the brush contact point P4, the smaller the curvature of the rotational trajectory C1 traced by the brush 41, allowing the brush 41 to stably contact the charging roller 22. In other words, to make the brush 41 contact the charging roller 22 more stably, it is advantageous for the amount of protrusion of the oscillation support parts 42n and 42r (extensions) relative to the main unit part 42a to be large when viewed in the longitudinal direction (X direction) of the brush 41.

[0157] However, simply increasing the protrusion amount of the oscillating support parts 42n and 42r (extensions) may necessitate rearranging the components in the process unit 20 to avoid interference with the oscillating support parts 42n and 42r. This could potentially lead to an increase in the size of the process unit 20.

[0158] Therefore, in this embodiment, we propose a configuration that utilizes the space outside the optical path of the laser beam L in the longitudinal direction (X direction) of the brush 41 to increase the amount of protrusion of the oscillating support parts 42n and 42r (extension parts).

[0159] As shown in Figure 1, the laser beam L is irradiated onto the photosensitive drum 21 through a space S1 located downstream of the drum unit 25 and upstream of the developing unit 30 in the rotation direction (Q) of the photosensitive drum 21. Here, the optical path of the laser beam L is set so as not to interfere with the main unit part 42a (brush holding part) at least at the center of the brush 41 (cross-sectional position in Figure 1) in the rotation axis direction (X direction, main scanning direction during exposure) of the charging roller 22. On the other hand, as shown in Figures 16(a) and 16(b), even if a component is placed in a position that overlaps with space S1 in the X direction view, as long as it is outside the optical path of the laser beam L in the rotation axis direction (X direction) of the charging roller 22, it will not affect the irradiation of the laser beam L.

[0160] Therefore, as shown in Figure 1, the oscillating support portion 42n in this embodiment extends in the direction toward the developing unit 30 from the main unit portion 42a, that is, in the direction toward the downstream side in the rotation direction (Q) of the photosensitive drum 21. In other words, with respect to a virtual straight line IL1 passing through the center 21o of the photosensitive drum 21 and the endpoint 42a1 of the main unit portion 42a (brush holding portion) in the cross-section of Figure 1, at least a part of the oscillating support portion 42n protrudes downstream in the rotation direction (Q) of the photosensitive drum 21. Here, the cross-section of Figure 1 represents a view in the direction of the rotation axis of the charging roller 22, showing a cross-section that passes through the center of the brush 41 in the rotation axis direction (X direction) and is perpendicular to the rotation axis direction. Also, the endpoint 42a1 of the main unit portion 42a is the most downstream end of the main unit portion 42a in the rotation direction (Q) of the photosensitive drum 21 in the cross-section of Figure 1.

[0161] As described above, according to this embodiment, the oscillating support portion 42n (extension portion) extends downstream in the rotational direction (Q) of the photosensitive drum 21 from one longitudinal end of the main unit portion 42a (brush holding portion). This configuration allows for efficient use of space within the process unit 20. Specifically, the amount of protrusion of the oscillating support portion 42n can be increased without obstructing the optical path of the laser beam L.

[0162] Therefore, according to this embodiment, the brush 41 can be brought into more stable contact with the charging roller 22 while avoiding an increase in the size of the process unit 20. Furthermore, because the brush 41 is brought into more stable contact with the charging roller 22, foreign matter can be more easily scraped off the surface of the charging roller 22, which in turn contributes to an improvement in image quality.

[0163] In particular, in this embodiment, when viewing the cross-sections of the process unit 20 and the scanner unit 11 from the viewpoint shown in Figure 1, the oscillating support portion 42n overlaps with the optical path of the laser beam L. Here, "overlapping when viewed in a predetermined direction" means that when each element is projected perpendicularly onto a virtual plane orthogonal to the predetermined direction, the projected area of ​​one element and the projected area of ​​the other element overlap at least partially. The positional relationship in which the oscillating support portion 42n overlaps with the optical path of the laser beam L allows for more efficient use of space within the process unit 20.

[0164] Furthermore, the positional relationship between the space S1 through which the laser beam L passes and the oscillating support portion 42n can also be described as follows. In the cross-section shown in Figure 1, space S1 is formed between the downstream end face of the drum unit 25 in the rotation direction (Q) of the photosensitive drum 21 and the upstream end face 300 of the developing container 32 (the housing frame of the developing unit 30) in the rotation direction (Q). In this embodiment, the downstream end face of the drum unit 25 in the cross-section of Figure 1 is mainly formed by the charging roller 22, the main unit portion 42a of the brush base 42, and the drum frame 26. Therefore, it is preferable that the oscillating support portion 42n overlaps with the space downstream of the aforementioned virtual straight line IL1 in the rotation direction (Q) of the photosensitive drum 21 and upstream of the upstream end face 300 of the developing container 32. This configuration allows for more efficient use of the space within the process unit 20.

[0165] Furthermore, the positional relationship between the space S1 through which the laser beam L passes and the oscillating support part 42n can also be described as follows. When viewing the cross-section of Figure 1 in the direction of the rotation axis (X direction) of the charging roller 22, consider a virtual straight line IL2 that passes through the center 21o of the photosensitive drum 21 and the upstream end 30A of the developing container 32 (housing frame) in the cross-section of Figure 1. In order to prevent the laser beam L from being blocked by the developing container 32, at least a portion of the optical path of the laser beam L passes through the region upstream of the virtual straight line IL2 in the rotation direction (Q) of the photosensitive drum 21. Therefore, it is preferable that the oscillating support part 42n overlaps with the region downstream of the virtual straight line IL1 (first virtual straight line) and upstream of the virtual straight line IL2 (second virtual straight line) in the rotation direction (Q) of the photosensitive drum 21. This configuration allows for more efficient use of the space within the process unit 20.

[0166] Furthermore, the endpoint 42a1 of the main unit portion 42a (brush holding portion) may not be the part that protrudes furthest downstream in the rotation direction (Q) of the photosensitive drum 21 in the entire drum unit 25 excluding the photosensitive drum 21. In the case of the drum unit 25 of this embodiment, in the cross-section of Figure 1, the furthest downstream end 25A of the drum unit 25 (image carrier unit) excluding the photosensitive drum 21 in the rotation direction (Q) of the photosensitive drum 21 is part of the surface 22a of the charging roller 22. Let IL3 be a virtual straight line passing through the center 21o of the photosensitive drum 21 and the end 25A of the drum unit 25. In order to prevent the laser beam L from being blocked by members of the drum unit 25 other than the photosensitive drum 21, at least a part of the optical path of the laser beam L passes through the region downstream of the virtual straight line IL3 and upstream of the virtual straight line IL2 in the rotation direction (Q) of the photosensitive drum 21. Therefore, it is preferable that the oscillating support portion 42n overlaps with the region downstream of the virtual straight line IL3 (third virtual straight line) and upstream of the virtual straight line IL2 (second virtual straight line) in the rotation direction (Q) of the photosensitive drum 21. For example, if a part of the drum frame 26 protrudes downstream of the charging roller 22 in the rotation direction (Q) of the photosensitive drum 21 in the cross-section of Figure 1, the virtual straight line IL3 is defined with respect to the end of the drum frame 26 instead of the charging roller 22.

[0167] Furthermore, as shown in Figure 1, it is preferable to extend the oscillating support portion 42n to a position where the support hole 42p (hole portion) of the oscillating support portion 42n and the support shaft 26a (shaft portion) of the drum frame 26 overlap with the optical path of the laser beam L. This makes it possible to reduce the curvature of the rotational trajectory C1 of the brush 41. Similarly, it is preferable that the support hole 42p (hole portion) of the oscillating support portion 42n and the support shaft 26a (shaft portion) of the drum frame 26 protrude downstream with respect to the virtual straight line IL1 in the rotational direction (Q) of the photosensitive drum 21.

[0168] In the above explanation, the swing support portion 42n (first extension portion) at one end of the main unit portion 42a (brush holding portion) was used as an example, but the same explanation applies to the swing support portion 42r (second extension portion) at the other end. That is, when viewed from the opposite side of the viewpoint in Figure 1 in the direction of the rotation axis (X direction) of the charging roller 22, the swing support portion 42r (second extension portion) overlaps with the optical path of the laser beam L going from the scanner unit 11 to the photosensitive drum 21. This configuration allows for more efficient use of space within the process unit 20.

[0169] (modified version) In the above-described embodiment, an example was given in which the brush base 42 abuts against contact portions provided on the drive-side bearing 45 and the non-drive-side bearing 46 using the biasing force of the brush biasing members 53 and 54 (biasing members). However, the embodiment is not limited to this, and for example, the biasing members may be omitted, and the brush base 42 abuts against the contact portions provided on the drive-side bearing 45 and the non-drive-side bearing 46 by gravity acting on the brush unit 40.

[0170] Furthermore, the regulating member for restricting the position of the brush unit 40 may be provided separately from the bearing member that rotatably supports the charging roller 22. For example, the regulating portion (42j, 42k, 42m) provided on the brush base 42 may contact a protrusion provided on the drum frame 26, thereby restricting the position of the brush unit 40 in the rotational direction around the brush oscillation center P1.

[0171] In the embodiment described above, the position of the brush 41 relative to the charging roller 22 is restricted by the brush base 42 of the brush unit 40 contacting the drive-side bearing 45 and the non-drive-side bearing 46. However, the configuration is not limited to this, and for example, the position of the brush 41 relative to the charging roller 22 may be restricted by the support member 41c of the brush 41 contacting the drive-side bearing 45 and the non-drive-side bearing 46.

[0172] (Other embodiments) In the embodiments described above, an image forming apparatus 1 using a direct transfer method was illustrated, in which a toner image is transferred from an image carrier (photosensitive drum 21) to a recording material P, which is the transfer target. However, the technology of this disclosure may also be applied to an image forming apparatus using an intermediate transfer method, in which a toner image is first transferred from the image carrier (photosensitive drum 21) to an intermediate transfer target, and then the toner image is transferred from the intermediate transfer target to the recording material P. Furthermore, the technology of this disclosure is not limited to monochrome image forming apparatuses, but may also be applied to color image forming apparatuses that use multiple colors of toner.

[0173] In the above-described embodiment, an image forming apparatus 1 equipped with a cleanerless process unit 20 was explained. However, the process unit 20 may also have a cleaning member such as a cleaning blade that recovers (removes) residual toner from the photosensitive drum 21. Even in this case, foreign matter that slips through the cleaning member and reaches the charged section Q1, or foreign matter contained in the outside air taken into the image forming apparatus 1, may adhere to the charging roller 22. Therefore, even in a configuration in which the process unit 20 has a cleaning member, the occurrence of image defects caused by the adhesion of foreign matter to the charging roller 22 can be reduced by arranging the brush unit 40 described in the embodiment.

[0174] Summary of this disclosure This disclosure includes at least the following: (Composition 1) A rotatable image carrier, A charging roller is positioned to contact the surface of the image carrier and charge the surface, An exposure apparatus for irradiating the image carrier with light in order to form a latent image on the surface of the image carrier, A brush unit comprising: a brush including a plate-shaped base material and brush fibers protruding from the base material and in contact with the surface of the charging roller; a brush holding portion for holding the base material; and an extension portion extending from one end of the brush holding portion in the direction of the rotation axis of the charging roller in a direction intersecting the rotation axis direction; A frame supporting the extension portion, Equipped with, When viewed in the direction of the rotation axis, the extension overlaps with the optical path of the light from the exposure apparatus toward the image carrier. An image forming apparatus characterized by the following: (Configuration 2) The extension is pivotable around the pivot axis relative to the frame, The brush holding portion is configured to move closer to and further away from the charging roller by oscillating together with the extension portion around the pivot axis. The image forming apparatus according to configuration 1, characterized in that it is a picture forming apparatus. (Composition 3) Either the extension or the frame has a shaft portion that extends in the direction of the rotation axis, The extension portion and the other of the frame have holes that engage with the shaft portion. When viewed in the direction of the rotation axis, the shaft portion and the hole portion overlap with the optical path. The image forming apparatus according to configuration 2, characterized in that... (Composition 4) The biasing member further comprises a biasing member for biasing the holding member, including the brush holding portion and the extension portion, so that the base material approaches the charging roller. When viewed in the direction of the rotation axis of the charging roller, the point of application of the biasing force of the biasing member to the holding member is located between the contact position and the oscillation axis, in the tangential direction of the charging roller at the contact position between the brush fibers and the charging roller. The image forming apparatus according to configuration 2 or 3, characterized by the above. (Composition 5) The system further comprises a restricting member that contacts the retaining member at a contact position and restricts the position of the retaining member in the rotational direction around the pivot axis, When viewed in the direction of the rotation axis, the contact position is located between the contact position and the pivot axis in the tangential direction. The image forming apparatus according to configuration 4, characterized in that... (Composition 6) The regulating member is a bearing member that rotatably supports the charging roller. The image forming apparatus according to configuration 5, characterized by the features described herein. (Composition 7) When the extension is designated as the first extension, The brush unit further has a second extension that extends from the other end of the brush holding portion in the direction of the rotation axis in a direction intersecting the direction of the rotation axis and is supported by the frame, When viewed in the direction of the rotation axis, the second extension overlaps with the optical path. An image forming apparatus according to any one of configurations 1 to 6 characterized by the above. (Composition 8) When the brush unit is designated as the first brush unit, The image carrier is further provided with a second brush unit that has a brush that contacts the surface of the image carrier downstream of the transfer section where the image is transferred from the image carrier to the transfer target and upstream of the charging section where the image carrier faces the charging roller, in the rotation direction of the image carrier during image formation, and which collects foreign matter adhering to the image carrier. An image forming apparatus according to any one of configurations 1 to 7, characterized by the above. (Composition 9) The developing unit further comprises a toner storage section for storing toner and a developing roller for carrying the toner and supplying it to the image carrier, The toner that was not transferred from the image carrier to the transfer target is collected in the toner storage section by the developing roller. An image forming apparatus according to any one of configurations 1 to 8 characterized by the above. (Composition 10) A rotatable image carrier, A charging roller is positioned to contact the surface of the image carrier and charge the surface, A brush unit comprising: a brush including a plate-shaped base material and brush fibers protruding from the base material and in contact with the surface of the charging roller; a brush holding portion for holding the base material; and a swinging support portion extending from one end of the brush holding portion in the direction of the rotation axis of the charging roller in a direction intersecting the rotation axis direction; A frame that supports the aforementioned swingable support portion, Equipped with, When a cross-section passing through the center of the brush in the direction of the rotation axis and perpendicular to the direction of the rotation axis is viewed in the direction of the rotation axis, at least a portion of the oscillating support portion protrudes downstream in the direction of rotation with respect to a virtual straight line passing through the center of the image carrier and the downstream end of the brush holding portion in the cross-section in the direction of rotation of the image carrier during image formation. A process unit characterized by the following features. (Composition 11) The developing unit further comprises a developing roller that supplies toner to the image carrier, and a housing frame having a space for housing the toner, When viewed in the direction of the rotation axis, the swing support portion overlaps with the space downstream of the virtual straight line in the direction of rotation in the cross-section, and with the space upstream of the end face of the housing frame facing upstream in the direction of rotation. A process unit according to configuration 10, characterized by the above. (Composition 12) The developing unit further comprises a developing roller that supplies toner to the image carrier, and a housing frame having a space for housing the toner, Let the aforementioned virtual line be the first virtual line. When the cross-section is viewed in the direction of the rotation axis, if the second imaginary straight line is defined as the imaginary straight line passing through the center of the image carrier and the upstream end of the housing frame in the rotation direction within the cross-section, The rocking support portion overlaps with a region downstream of the first virtual line and upstream of the second virtual line in the direction of rotation. A process unit according to configuration 10 or 11, characterized by the above. (Composition 13) The image carrier unit further comprises the image carrier, the charging roller, the brush unit, and the frame, When the cross-section is viewed in the direction of the rotation axis, if the third imaginary straight line is defined as the imaginary straight line passing through the center of the image carrier and the downstream end of the portion of the cross-section obtained by removing the image carrier from the image carrier unit in the direction of rotation, When viewed in the direction of the rotation axis, the rocking support portion overlaps with the region downstream of the third virtual line and upstream of the second virtual line in the direction of rotation. The process unit according to configuration 12, characterized by the features described above. (Composition 14) Either the swinging support portion or the frame has a shaft portion extending in the direction of the rotation axis, The other of the swinging support portion and the frame has a hole that engages with the shaft portion. When viewed in the direction of the rotation axis, the shaft portion and the hole portion protrude downstream in the rotation direction relative to the virtual straight line. A process unit according to any one of configurations 10 to 13, characterized by the above. (Composition 15) The biasing member further comprises a biasing member for biasing the holding member, including the brush holding portion and the swinging support portion, so that the substrate approaches the charging roller. When viewed in the direction of the rotation axis of the charging roller, the point of application of the biasing force of the biasing member to the holding member is located between the contact position and the oscillation axis of the holding member, in the tangential direction of the charging roller at the contact position between the brush fibers and the charging roller. A process unit according to any one of configurations 10 to 14, characterized by the above. (Composition 16) The system further comprises a restricting member that contacts the retaining member at a contact position and restricts the position of the retaining member in the rotational direction around the pivot axis, When viewed in the direction of the rotation axis, the contact position is located between the contact position and the pivot axis in the tangential direction. A process unit according to configuration 15, characterized by the features described herein. (Composition 17) The regulating member is a bearing member that rotatably supports the charging roller. The process unit according to configuration 16, characterized by the features described above. (Composition 18) When the brush unit is designated as the first brush unit, The image carrier is further provided with a second brush unit that has a brush that contacts the surface of the image carrier downstream of the transfer section where the image is transferred from the image carrier to the transfer target and upstream of the charging section where the image carrier faces the charging roller, in the rotation direction of the image carrier during image formation, and which collects foreign matter adhering to the image carrier. A process unit according to any one of configurations 10 to 17, characterized by the above. (Composition 19) The developing unit further comprises a toner storage section for storing toner and a developing roller for carrying the toner and supplying it to the image carrier, The toner that was not transferred from the image carrier to the transfer target is collected in the toner storage section by the developing roller. A process unit according to any one of configurations 10 to 18, characterized by the above. (Composition 20) A process unit described in any one of configurations 10 to 19, The main body of the device, The process unit, which is mounted on the main body of the apparatus, is used to form an image on the recording material. An image forming apparatus characterized by the following: [Explanation of symbols]

[0175] 11…Exposure unit (scanner unit) / 20…Process unit / 21…Image carrier (photosensitive drum) / 22…Charging roller / 40…Brush unit / 41…Brush / 41a…Brush fibers / 41b, 41c…Substrate (base, support member) / 42…Holding member (brush base) / 42a…Brush holding part (main unit part) / 42n, 42r…Extended part, oscillating support part / 45, 46…Bearing members (drive-side bearing, non-drive-side bearing) / 53, 54…Biasing member (brush biasing member)

Claims

1. A rotatable image carrier, A charging roller is positioned to contact the surface of the image carrier and charge the surface, An exposure apparatus for irradiating the image carrier with light in order to form a latent image on the surface of the image carrier, A brush unit comprising: a brush including a plate-shaped base material and brush fibers protruding from the base material and in contact with the surface of the charging roller; a brush holding portion for holding the base material; and an extension portion extending from one end of the brush holding portion in the direction of the rotation axis of the charging roller in a direction intersecting the rotation axis direction; A frame supporting the extension portion, Equipped with, When viewed in the direction of the rotation axis, the extension overlaps with the optical path of the light from the exposure apparatus toward the image carrier. An image forming apparatus characterized by the following:

2. The extension is pivotable around the pivot axis relative to the frame, The brush holding portion is configured to move closer to and further away from the charging roller by oscillating together with the extension portion around the pivot axis. The image forming apparatus according to feature 1.

3. Either the extension or the frame has a shaft portion that extends in the direction of the rotation axis, The extension portion and the other of the frame have holes that engage with the shaft portion. When viewed in the direction of the rotation axis, the shaft portion and the hole portion overlap with the optical path. The image forming apparatus according to feature 2.

4. The biasing member further comprises a biasing member for biasing the holding member, including the brush holding portion and the extension portion, so that the base material approaches the charging roller. When viewed in the direction of the rotation axis of the charging roller, the point of application of the biasing force of the biasing member to the holding member is located between the contact position and the oscillation axis, in the tangential direction of the charging roller at the contact position between the brush fibers and the charging roller. The image forming apparatus according to feature 2.

5. The system further comprises a restricting member that contacts the retaining member at a contact position and restricts the position of the retaining member in the rotational direction around the pivot axis, When viewed in the direction of the rotation axis, the contact position is located between the contact position and the pivot axis in the tangential direction. The image forming apparatus according to feature 4.

6. The regulating member is a bearing member that rotatably supports the charging roller. The image forming apparatus according to feature 5.

7. When the extension is designated as the first extension, The brush unit further has a second extension that extends from the other end of the brush holding portion in the direction of the rotation axis in a direction intersecting the direction of the rotation axis and is supported by the frame, When viewed in the direction of the rotation axis, the second extension overlaps with the optical path. The image forming apparatus according to feature 1.

8. When the brush unit is designated as the first brush unit, The image carrier is further provided with a second brush unit that has a brush that contacts the surface of the image carrier downstream of the transfer section where the image is transferred from the image carrier to the transfer target and upstream of the charging section where the image carrier faces the charging roller, in the rotation direction of the image carrier during image formation, and which collects foreign matter adhering to the image carrier. The image forming apparatus according to feature 1.

9. The developing unit further comprises a toner storage section for storing toner and a developing roller for carrying the toner and supplying it to the image carrier, The toner that was not transferred from the image carrier to the transfer target is collected in the toner storage section by the developing roller. The image forming apparatus according to feature 1.

10. A rotatable image carrier, A charging roller is positioned to contact the surface of the image carrier and charge the surface, A brush unit comprising: a brush including a plate-shaped base material and brush fibers protruding from the base material and in contact with the surface of the charging roller; a brush holding portion for holding the base material; and a swinging support portion extending from one end of the brush holding portion in the direction of the rotation axis of the charging roller in a direction intersecting the rotation axis direction; A frame that supports the aforementioned swingable support portion, Equipped with, When a cross-section passing through the center of the brush in the direction of the rotation axis and perpendicular to the direction of the rotation axis is viewed in the direction of the rotation axis, at least a portion of the oscillating support portion protrudes downstream in the direction of rotation with respect to a virtual straight line passing through the center of the image carrier and the downstream end of the brush holding portion in the cross-section in the direction of rotation of the image carrier during image formation. A process unit characterized by the following features.

11. The developing unit further comprises a developing roller that supplies toner to the image carrier, and a housing frame having a space for housing the toner, When viewed in the direction of the rotation axis, the swing support portion overlaps with the space downstream of the virtual straight line in the direction of rotation in the cross-section, and with the space upstream of the end face of the housing frame facing upstream in the direction of rotation. The process unit according to feature 10.

12. The developing unit further comprises a developing roller that supplies toner to the image carrier, and a housing frame having a space for housing the toner, Let the aforementioned virtual line be the first virtual line. When the cross-section is viewed in the direction of the rotation axis, if the second imaginary straight line is defined as the imaginary straight line passing through the center of the image carrier and the upstream end of the housing frame in the rotation direction within the cross-section, The rocking support portion overlaps with a region downstream of the first virtual line and upstream of the second virtual line in the direction of rotation. The process unit according to feature 10.

13. The image carrier unit further comprises the image carrier, the charging roller, the brush unit, and the frame, When the cross-section is viewed in the direction of the rotation axis, if the third imaginary straight line is defined as the imaginary straight line passing through the center of the image carrier and the downstream end of the portion of the cross-section obtained by removing the image carrier from the image carrier unit in the direction of rotation, When viewed in the direction of the rotation axis, the swing support portion overlaps with a region downstream of the third virtual line and upstream of the second virtual line in the direction of rotation. The process unit according to feature 12.

14. Either the swinging support portion or the frame has a shaft portion extending in the direction of the rotation axis, The other of the swinging support portion and the frame has a hole that engages with the shaft portion. When viewed in the direction of the rotation axis, the shaft portion and the hole portion protrude downstream in the rotation direction relative to the virtual straight line. The process unit according to feature 10.

15. The biasing member further comprises a biasing member for biasing the holding member, including the brush holding portion and the swinging support portion, so that the base material approaches the charging roller. When viewed in the direction of the rotation axis of the charging roller, the point of application of the biasing force of the biasing member to the holding member is located between the contact position and the oscillation axis of the holding member, in the tangential direction of the charging roller at the contact position between the brush fibers and the charging roller. The process unit according to feature 10.

16. The system further comprises a restricting member that contacts the retaining member at a contact position and restricts the position of the retaining member in the rotational direction around the pivot axis, When viewed in the direction of the rotation axis, the contact position is located between the contact position and the pivot axis in the tangential direction. The process unit according to feature 15.

17. The regulating member is a bearing member that rotatably supports the charging roller. The process unit according to feature 16.

18. When the brush unit is designated as the first brush unit, The image carrier is further provided with a second brush unit that has a brush that contacts the surface of the image carrier downstream of the transfer section where the image is transferred from the image carrier to the transfer target and upstream of the charging section where the image carrier faces the charging roller, in the rotation direction of the image carrier during image formation, and which collects foreign matter adhering to the image carrier. The process unit according to feature 10.

19. The developing unit further comprises a toner storage section for storing toner and a developing roller for carrying the toner and supplying it to the image carrier, The toner that was not transferred from the image carrier to the transfer target is collected in the toner storage section by the developing roller. The process unit according to feature 10.

20. A process unit according to any one of claims 10 to 19, The main body of the device, The process unit, which is mounted on the main body of the apparatus, is used to form an image on the recording material. An image forming apparatus characterized by the following:

Images