JP2007322559A - Charger, photoreceptor drum unit, and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To surely prevent the electrostatic charge unevenness of a photoreceptor drum 41 due to the setting of a charged brush 47. <P>SOLUTION: The charger 42 arranged in a recording section 13 of the image forming apparatus includes the charged brush 47. The charged brush 47 includes a revolving shaft 56, and a number of conductive bristles 57 disposed around the revolving shaft 56. The bristles 57 are subjected to hair skewing processing in such a manner that at least their tips face rhombic. The bristles 57 are configured to part from the surface of the photoreceptor drum 41 during the stoppage of the brush and to be brought into contact with the surface of the photoreceptor drum 41 by the centrifugal force during the rotation of the brush (selection figure). The charger 42 includes a cover 59 having an arcuate inner wall surface 58 covering an outer side of the chaged brush 47. The radius n of the arcuate inner wall surface 58 is set smaller than the radius r2 of the hair end circles during the brush rotation and is more specifically set equal to the radius r1 of the hair end circles during the stoppage of the brush (r<r2, r=r1). <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a charging device, a photosensitive drum unit, and an image forming apparatus including a charging brush including a large number of conductive hairs for charging a photosensitive drum.

In Patent Document 1, the charging brush of the brush charger is subjected to a slanting process so that the brush charger is attached to the image forming apparatus and is not brought into contact with the photosensitive member until the charging operation is started. A configuration in which the brush is brought into contact with the photosensitive member by centrifugal force or electrostatic attraction force. According to Patent Document 1, it is possible to prevent the contact brush from being lowered due to the charging brush.
JP-A-2005-173185 (FIG. 2 (a), FIG. 2 (b), 0013-0015, etc.)

  However, for example, in an image forming apparatus used in an office, printing requests frequently occur, and it is necessary to rotate the brush charger each time. In this case, in the configuration of the above-mentioned Patent Document 1, since the strong centrifugal force acts on the charging brush for a long time, the hairs of the inclined hair are weakened. It comes in contact.

  As a result, the brush charger eventually becomes partially damaged, causing charging unevenness and jitter, causing distortion of the image, and particularly causing shading unevenness in a halftone image. I was sorry.

Means and effects for solving the problems

  The problems to be solved by the present invention are as described above. Next, means for solving the problems and the effects thereof will be described.

  According to a first aspect of the present invention, a charging device having the following configuration is provided. That is, a charging brush that charges the surface of the photosensitive drum by rotating while contacting the photosensitive drum is provided. The charging brush includes a rotation shaft, and a plurality of conductive hair bodies provided around the rotation shaft and having at least a tip thereof directed obliquely. The hair is separated from the surface of the photosensitive drum when the rotating shaft is stopped, and is brought into contact with the surface of the photosensitive drum by centrifugal force when the rotating shaft is rotated. A cover having an arc inner wall surface covering the outside of the charging brush is provided, and the radius of the arc inner wall surface is smaller than the radius of the tip circle when the rotating shaft rotates.

  In this configuration, when the rotary shaft is rotated, the hair at the position facing the arc inner wall surface of the cover is forcibly brought down by the arc inner wall surface. Therefore, even if the rotating shaft is driven for a long time, the degree of oblique hair does not weaken, so that the hair can be reliably separated from the surface of the photosensitive drum when the rotating shaft is stopped. As a result, settling of the charging brush can be prevented and an image with good image quality can be stably formed.

  In the charging device, it is preferable that the radius of the inner wall surface of the arc is equal to the radius of the tip circle when the rotating shaft is stopped.

  Thereby, even when the rotating shaft rotates, the hair body is forcibly tilted by the arc inner wall surface of the cover so that the locus of the hair tip of the hair body coincides with the hair tip circle when the rotating shaft stops. Accordingly, since the hair body reliably maintains the original degree of oblique hair, the hair body can be reliably separated from the surface of the photosensitive drum when the rotating shaft is stopped.

  In the charging device, it is preferable that the tip of the hair is tilted in a direction along a circumferential surface movement direction of the rotating photosensitive drum.

  As a result, the hair does not stretch against the rotation of the charging brush, so that the charging brush can be smoothly rotated to rub the surface of the photosensitive drum and be charged satisfactorily.

  In the charging device, a guide wall surface is preferably disposed on at least one end side of the arc inner wall surface, and the guide wall surface is preferably smoothly connected to the arc inner wall surface.

  This prevents the hair from hitting the end of the inner wall surface of the arc so that it is damaged or cut off, so that charging unevenness and current leakage can be avoided.

  According to a second aspect of the present invention, there is provided a photosensitive drum unit including the charging device and the photosensitive drum.

  According to a third aspect of the present invention, there is provided an image forming apparatus comprising the charging device and the photosensitive drum.

  According to these configurations, it is possible to prevent the charging brush from being set and to stably form an image with good image quality.

  Next, embodiments of the invention will be described. FIG. 1 is a partial sectional view of a front view showing an overall configuration of a multifunction peripheral according to an embodiment of the present invention. FIG. 2 is an enlarged front sectional view showing a state of a recording unit in a power-off state of the multifunction peripheral. 3 is an enlarged front cross-sectional view showing a state of a recording unit that is driven with the power supply of the multifunction peripheral being turned on, and FIG. 4 is an enlarged view of a main part showing a state of a rotating charging brush.

  A multifunction machine 1 as an electrophotographic image forming apparatus shown in FIG. 1 is configured to have both a facsimile function and a copy function. A document reading unit 11 on which a facsimile transmission document or a copy document can be set is provided on the upper portion of the housing 10 of the multifunction machine 1. In addition, a paper feeding unit 12 that can be stocked in a state where papers 2 as recording media are stacked is provided at the lower part of the housing 10. A recording unit 13, a fixing unit 14, and a paper discharge unit 15 are arranged side by side in the middle portion of the housing 10.

  The document reading unit 11 includes an auto document feeder and a flat bed, and is configured to read a document with a CCD sensor. The paper feed unit 12 includes two paper feed trays that can be pulled out to the front side (the front side in FIG. 1), that is, an upper tray 21 and a lower tray 22.

  In the upper tray 21, a plurality of sheets 2 are stacked on a plate-shaped flapper 31 that is rotatably provided. A fan-shaped paper feed roller 32 is disposed above the flapper 31. Then, while pushing up the flapper 31 upward by a biasing spring (not shown), the paper feed roller 32 is driven in the direction of the arrow in FIG. 1, so that the uppermost sheet 2 is separated and picked up one by one, It is sent out toward the recording unit 13. The lower tray 22 also has a paper feed mechanism having the same configuration as that of the upper tray 21.

  As illustrated in FIG. 1, a curved sheet conveyance path 16 that extends from the sheet feeding unit 12 to the sheet discharge unit 15 via the recording unit 13 and the fixing unit 14 is provided inside the housing 10 of the multifunction device 1. It is configured. In the paper transport path 16, a feed roller 33 is disposed downstream of the paper feed roller 32, and a registration roller 34 is disposed further downstream. Further, driven rollers are provided so as to face the feed roller 33 and the registration roller 34, respectively, and each driven roller is urged against the feed roller 33 and the registration roller 34. With this configuration, the feed roller 33 and the registration roller 34 respectively rotate and drive the paper 2 while nipping the driven roller, thereby conveying the paper 2 to the recording unit 13 on the downstream side.

  An enlarged view of the recording unit 13 is shown in FIG. 2, and as shown in FIG. 2, the recording unit 13 as an image forming unit includes a charging device 42, an LED head 43, and a developing device around a photosensitive drum 41. 44, a transfer roller 45, and a memory removal brush 46 are arranged.

  The photosensitive drum 41 is configured by forming an organic photoreceptor layer on the outer peripheral surface of a cylinder made of aluminum. The charging brush 47 has a structure in which a large number of conductive hairs 57 are planted on the surface of a rotating shaft 56 made of a metal shaft, and a high voltage is applied from a high voltage power source (not shown). Drive is transmitted to the rotation shaft 56 from a gear (not shown) attached to the end of the photosensitive drum, and is configured to be able to rotate.

  The bristle body 57 is subjected to an appropriate oblique hair treatment, and is tilted so that its tip is inclined from the radial direction to one side in the circumferential direction. As the oblique hair treatment method, for example, a straight-hair brush formed by radially planting linear brush hair (hair body 57) on the rotating shaft 56 is used as a pipe having an inner diameter of the diameter after the oblique hair. It is conceivable to insert the steel plate while rotating it, and in this state, introduce high temperature steam into the pipe and braze it.

  A cover 59 is provided so as to cover the outside of the charging brush 47. The cover 59 is made of, for example, a synthetic resin, and an arcuate inner wall surface 58 that can come into contact with the hair body 57 of the charging brush 47 is formed therein.

  The cover 59 for storing the charging brush 47 is formed in a circular arc shape (substantially C-shape) in cross section, and the side facing the photosensitive drum 41 is open. Guide walls 66 and 67 for guiding the hair tips of the hair bodies 57 are provided at the edges of the open portion of the cover 59. The guide wall surfaces 66 and 67 are formed in an arc shape and are smoothly connected to the end of the arc inner wall surface 58.

  FIG. 2 shows a state in which the power source of the multi-function device 1 is turned off. At this time, the rotating shaft 56 stops without rotating (brush stopped state). If there is no print request for a long time even when the power of the multifunction device 1 is turned on, a controller (not shown) of the multifunction device 1 controls to stop driving each unit such as the recording unit 13 in order to save power. The rotating shaft 56 is also stopped in this case. In this brush stopped state, as shown in FIG. 2, the bristle body 57 is separated from the surface of the photosensitive drum 41 even in the open portion of the cover 59 to form an appropriate gap.

  On the other hand, when the MFP 1 is turned on and a facsimile document is received or copied, the recording unit including the photosensitive drum 41 and the rotating shaft 56 of the charging brush 47 as shown in FIG. Thirteen various rollers and shafts are driven to rotate. As shown in FIG. 3, in a state where the rotating shaft 56 is rotating (brush rotating state), the hair body 57 changes its posture to the upright side by centrifugal force in the open portion of the cover 59, so Contacts the surface of the photosensitive drum 41.

  As described above, a high voltage is applied to the charging brush 47 from a high voltage power source. As a result, the hair 57 rubs the peripheral surface (surface) of the photosensitive drum 41, so that the surface of the photosensitive drum 41 is uniformly charged.

  FIG. 4 is an enlarged view of the charging device 42 in the brush rotating state. As shown in FIG. 4, the arc inner wall surface 58 of the cover 59 is arranged concentrically with the rotating shaft 56. The radius r of the arc inner wall surface 58 is set to be smaller than the radius r2 of the hair tip circle c2 when the charging brush 47 rotates to bring the hair body 57 into an upright state (r <r2). Furthermore, the radius r of the arc inner wall surface 58 is configured to be equal to the radius r1 of the tip circle c1 when the brush is stopped (r = r1).

  Here, the hair tip circle c2 when the charging brush 47 is rotated is that when the hair body 57 is slightly upright due to centrifugal force when the cover 59 is removed and the charging brush 47 is rotated. A circle connecting the tips of the hairs 57. Further, the brush tip circle c1 in a brush stopped state refers to a circle connecting the tips of the hairs 57 when the charging brush 47 is stopped. Accordingly, it goes without saying that the tip circle c2 in the brush rotating state becomes larger than the tip circle c1 in the brush stopped state due to centrifugal force (r2> r1).

  Consider the case where the rotary shaft 56 is rotationally driven with the above configuration. At this time, the bristle body 57 at the position facing the arc inner wall surface 58 of the cover 59 is prevented by the arc inner wall surface 58 from slightly rising due to centrifugal force. Therefore, it is possible to prevent the fallen wrinkles of the hair body 57 provided by the oblique hair processing from being weakened by the centrifugal force. Moreover, since the radius r of the arc inner wall surface 58 is equal to the radius r1 of the hair tip circle c1 when the brush is stopped (r = r1), the hair ends of the hairs 57 are stopped when the rotation is stopped again. The cover 59 is securely brazed so as not to protrude from the tip circle c1.

  On the other hand, the bristle body 57 located in the open portion of the cover 59 comes into contact with the surface of the photosensitive drum 41 while being slightly raised by a centrifugal force accompanying the rotation. When the charging brush 47 further rotates, the bristle member 57 moves away from the surface of the photosensitive drum 41 and immediately comes into contact with the guide wall surface 66 of the cover 59 to gradually strengthen the falling posture again. Since the guide wall surface 66 is smoothly connected to the end of the arc inner wall surface 58, no sharp edge appears at the end of the arc inner wall surface 58, and the bristle body 57 is the end of the arc inner wall surface 58. It is prevented from being damaged or cut by hitting. In addition, since the guide wall surface 67 is smoothly connected also to the edge part on the opposite side of the circular arc inner wall surface 58, the hair body 57 is not damaged or cut | disconnected also in this part.

  As shown in FIG. 4, the falling direction of the bristle body 57 (the tip tilting direction and the brazing direction) is a direction along the circumferential surface movement direction of the rotating photosensitive drum 41. Therefore, when both are rotationally driven so that the peripheral surface of the charging brush 47 and the peripheral surface of the photosensitive drum 41 are rubbed in the opposite directions (FIG. 4), the eyes of the charging brush 47 become so-called order. The charging brush 47 can be smoothly rotated without the body 57 stretching and resisting rotation.

  As shown in FIG. 3, the LED head 43 as an exposure unit is disposed on the downstream side of the charging brush 47 (refers to the downstream side in the rotation direction of the photosensitive drum 41, hereinafter the same), and includes a light emitting diode (LED). ) Are arranged side by side in the paper width direction. The LED head 43 selectively emits light corresponding to the image data of the facsimile original received via the telephone line or the image data read by the original reading unit 11. As a result, the surface of the photosensitive drum 41 is selectively exposed, and an electrostatic latent image is formed by eliminating the charge energy of the exposed portion.

  The developing device 44 is disposed on the downstream side of the LED head 43 and includes a toner container 61 that stores non-magnetic one-component toner, and a stirring blade 62 that is rotationally driven inside the toner container 61 for stirring the toner. It has. Further, the developing device 44 includes a supply roller 63 disposed inside the toner container 61, a development roller 64 disposed in contact with both the supply roller 63 and the photosensitive drum 41, and an outer periphery of the development roller 64. And a regulating blade 65 disposed so as to come into contact with the surface.

  With this configuration, the supply roller 63 and the developing roller 64 are rotationally driven so as to rub the circumferential surfaces in opposite directions. Further, the tip of the regulating blade 65 rubs against the peripheral surface of the developing roller 64 that is rotationally driven. As a result, the toner in the toner container 61 is frictionally charged and adheres to the surface of the developing roller 64 due to a potential difference. The toner t on the surface of the developing roller 64 is adjusted by the regulating blade 65 so that the adhesion thickness is uniform, and is sent to the photosensitive drum 41 side by the rotation of the developing roller 64.

  Thereafter, at the contact portion between the photosensitive drum 41 and the developing roller 64, the toner t on the surface of the developing roller 64 is selectively applied to the photosensitive drum 41 only in the portion corresponding to the exposed portion of the photosensitive drum 41 by the LED head 43. Move to the surface. As a result, a toner image is formed on the surface of the photosensitive drum 41.

  The transfer roller 45 is disposed on the downstream side of the developing unit 44 and disposed on the opposite side of the photosensitive drum 41 with the sheet transport path 16 (sheet 2) interposed therebetween. A high voltage from a high voltage power source is applied to the transfer roller 45. Therefore, the toner image formed on the surface of the photosensitive drum 41 moves so as to approach the transfer roller 45 side by the rotation of the photosensitive drum 41, and is transferred to the paper 2 by the electric field attraction force. However, the toner t of the toner image is not completely transferred onto the paper 2, and the toner that has not been transferred remains on the surface of the photosensitive drum 41 as a residual toner (untransferred toner) tr.

  The memory removal brush 46 is disposed on the downstream side of the transfer roller 45, and the tip of the brush contacts the surface of the photosensitive drum 41 and a predetermined bias voltage is applied. With this configuration, the residual toner tr on the surface of the photosensitive drum 41 is uniformly diffused (dispersed) on the surface of the photosensitive drum 41 by the memory removal brush 46. Since the bias voltage is applied to the memory removal brush 46 as described above, the residual toner tr is more effectively dispersed.

  The residual toner tr diffused on the surface of the photosensitive drum 41 as described above passes through the charging brush 47 on the downstream side as the photosensitive drum 41 rotates. Although the residual toner tr may be attached to the hair 57 side as the hair 57 of the charging brush 47 rubs the surface of the photosensitive drum 41, the hair 57 is covered as shown in FIG. 59, the remaining toner tr adhering to the bristle body 57 is shaken off and falls. Similarly, the paper dust that has adhered to the surface of the photosensitive drum 41 and has moved to the hair body 57 is also shaken off when the hair body 57 hits the guide wall surface 66. Due to this flicker effect, it is possible to prevent foreign matters such as residual toner tr from adhering and accumulating on the charging brush 47 side and adversely affecting the charging effect.

  As shown in FIG. 3, the residual toner tr that has passed through the charging brush 47 further passes through the LED head 43. The residual toner tr in the portion exposed by the LED head 43 is transferred onto the paper 2 together with the toner t from the developing roller 64. The residual toner tr in the unexposed portion moves to the surface of the developing roller 64 due to a potential difference and is collected by the developing device 44 (cleanerless method).

  Of the configuration of the recording unit 13 described above (FIG. 3), at least the photosensitive drum 41, the charging brush 47, the cover 59, and the memory removal brush 46 are housed in a synthetic resin housing 51 and integrated as a photosensitive drum unit 52. It can be handled. At least the stirring blade 62, the supply roller 63, the developing roller 64, and the regulating blade 65 are attached to the toner container 61 made of synthetic resin, and can be handled as a toner cartridge 68 integrally. . The photosensitive drum unit 52 and the toner cartridge 68 are configured to be detachable from the multifunction machine 1 and can be exchanged as necessary.

  The toner image transferred onto the sheet 2 in the recording unit 13 as described above is removed from the potential by the charge eliminating brush 55 disposed in the vicinity of the transfer roller 45. The sheet 2 is sent to the fixing unit 14 on the downstream side of the sheet conveyance path 16 by the rotation of the photosensitive drum 41.

  As shown in FIG. 1, the fixing unit 14 includes a heat roller 71 that incorporates a heat source (such as a halogen lamp) and is rotationally driven, and a press roller 72 that is disposed to face the heat roller 71. ing. The press roller 72 is pressed against the heat roller 71 by a biasing spring (not shown). With this configuration, when the sheet 2 passes between the heat roller 71 and the press roller 72, the toner t of the toner image is melted and fixed to the sheet 2 by the heat of the high temperature heat roller 71 and the pressure by the press roller 72. . The fixing unit 14 is provided with a separation claw 73 for preventing the paper 2 from being wrapped around the heat roller 71 while being attached thereto.

  The paper discharge unit 15 includes a paper discharge roller 77 that is driven to rotate, and a paper discharge tray 78 that stocks the discharged paper 2. With this configuration, the sheet 2 sent from the fixing unit 14 is nipped between the sheet discharge roller 77 and a driven roller disposed opposite thereto, and is discharged onto the sheet discharge tray 78.

  As described above, in the multifunction machine 1 of the present embodiment, the charging device 42 of the recording unit 13 includes the charging brush 47, and the charging brush 47 rotates while contacting the photosensitive drum 41, whereby the surface of the photosensitive drum 41. Is configured to be charged. The charging brush 47 includes a rotating shaft 56 and a plurality of conductive hair bodies 57 that are provided around the rotating shaft 56 and brazed so that at least a tip thereof is directed obliquely. ing. The hair 57 is separated from the surface of the photosensitive drum 41 when the rotation shaft 56 is stopped (FIG. 2), while the hair 57 is rotated by centrifugal force when the rotation shaft 56 is rotated (FIGS. 3 and 4). It is configured to contact the surface. Further, the charging device 42 includes a cover 59 having an arc inner wall surface 58 that covers the outside of the charging brush 47, and the radius r of the arc inner wall surface 58 has a bristle when the rotating shaft 56 rotates as shown in FIG. It is configured to be smaller than the radius r2 of the tip circle (r <r2).

  As a result, during rotation of the rotary shaft 56 (FIG. 4), the bristle body 57 at a position other than the position exposed from the cover 59 and rubbing the surface of the photosensitive drum 41 faces the arc inner wall surface 58 of the cover 59, The arc wall surface 58 is forced to fall down. Therefore, even if the rotary shaft 56 is driven to rotate for a long time, the degree of oblique hair does not weaken. Therefore, the hair body 57 is reliably separated from the surface of the photosensitive drum 41 when the rotary shaft 56 is stopped (FIG. 2). be able to. As a result, settling of the charging brush 47 can be prevented and charging unevenness, jitter, and driving unevenness can be avoided, so that an image with good image quality can be stably formed.

  In the charging device 42, the radius r of the arc inner wall surface 58 is equal to the radius r1 of the tip circle when the rotary shaft is stopped (r = r1).

  Thereby, the hair body 57 at the time of brush rotation is regulated by the arc inner wall surface 58 of the cover 59 so that the locus of the hair tip coincides with the hair tip circle c1 when the brush is stopped. Accordingly, the hair body 57 reliably keeps the level of the oblique hair that has been brazed, so that the hair body 57 can be reliably separated from the surface of the photosensitive drum 41 when the rotating shaft is stopped.

  In addition, a slanting process is performed so that the tip of the bristle body 57 is tilted along the direction in which the peripheral surface of the rotating photosensitive drum 41 moves.

  As a result, the bristle body 57 does not resist the rotation of the charging brush 47, so that the charging brush 47 can be smoothly rotated to rub the surface of the photosensitive drum 41 and be charged satisfactorily.

  Further, guide wall surfaces 66 and 67 are disposed on both ends of the arc inner wall surface 58, and the guide wall surfaces 66 and 67 are smoothly connected to the arc inner wall surface.

  Accordingly, the hair 57 is prevented from being damaged or cut off by the end of the arc inner wall surface 58 when the hair 57 enters or exits the cover 59 as the rotating shaft 56 rotates. Therefore, it is possible to extend the life of the charging brush 47 and to prevent uneven charging and current leakage due to the broken hair body 57.

  The embodiment described above can be modified as follows, for example.

  Instead of planting the hair body 57 radially on the rotating shaft 56 and brazing the tip portion diagonally, for example, the hair body 57 is changed to a structure in which hair is planted on the rotating shaft 56 so that the root portion of the hair body is inclined from the radial direction. can do.

  The guide wall surfaces 66 and 67 can be formed on a planar guide wall surface that is tangentially connected to the arc inner wall surface 58 instead of being formed in an arc shape in cross section. Further, the guide wall surfaces 66 and 67 on one side can be omitted.

  The recording unit 13 exemplified above can be applied not only to the multifunction machine 1 but also to a facsimile machine, a copier, a printer, and the like.

1 is a partial cross-sectional view of a front view illustrating an overall configuration of a multifunction peripheral according to an embodiment of the present invention. FIG. 3 is an enlarged front cross-sectional view illustrating a state of a recording unit in a power-off state of the multifunction machine. FIG. 3 is an enlarged front cross-sectional view showing a state of a recording unit that is powered on and driven by a multifunction peripheral. The principal part enlarged view which shows the mode of the rotating charging brush.

Explanation of symbols

1 MFP (image forming device)
2 Paper 10 Case 11 Document reading unit 12 Paper feed unit 13 Recording unit 14 Fixing unit 15 Paper discharge unit 16 Paper transport path 21 Upper tray 22 Lower tray 31 Flapper 32 Paper feed roller 33 Feed roller 34 Registration roller 41 Photosensitive drum 42 Charging Device 43 LED head 44 Developer 45 Transfer roller 46 Memory removal brush 47 Charging brush 51 Housing 52 Photosensitive drum unit 55 Static elimination brush 56 Rotating shaft 57 Hair body 58 Arc inner wall surface 59 Cover 61 Toner container 62 Stirring blade 63 Supply roller 64 Development roller 65 Restriction blades 66, 67 Guide wall surface 68 Toner cartridge 71 Heat roller 72 Press roller 73 Separation claw 77 Paper discharge roller 78 Paper discharge tray c1 Brush tip circle when the brush stops c2 Brush tip circle when the brush rotates r Arc inner wall Surface radius r1 Tip radius when brush is stopped r2 Tip radius when brush is rotated t Toner tr Residual toner (untransferred toner)

Claims (6)

In a charging device comprising a charging brush that charges the surface of the photosensitive drum by rotating while contacting the photosensitive drum,
The charging brush is
A rotation axis;
A plurality of conductive hairs provided around the rotating shaft and at least a tip thereof being directed obliquely;
With
The hair is separated from the surface of the photosensitive drum when the rotating shaft is stopped, and is configured to contact the surface of the photosensitive drum by centrifugal force when the rotating shaft rotates.
A charging device comprising: a cover having an arc inner wall surface covering the outside of the charging brush, wherein the radius of the arc inner wall surface is smaller than the radius of the tip circle when the rotating shaft rotates. The charging device according to claim 1,
The charging device according to claim 1, wherein a radius of the inner wall surface of the arc is equal to a radius of a tip circle when the rotating shaft is stopped. The charging device according to claim 1 or 2,
The charging device according to claim 1, wherein a direction in which the tip of the bristle body falls is a direction along a circumferential surface movement direction of the rotating photosensitive drum. The charging device according to any one of claims 1 to 3, wherein
A charging device, wherein a guide wall surface is disposed on at least one end side of the arc inner wall surface, and the guide wall surface is smoothly connected to the arc inner wall surface.   A photosensitive drum unit comprising: the charging device according to claim 1; and the photosensitive drum. An image forming apparatus comprising: the charging device according to claim 1; and the photosensitive drum.

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