JP6006699B2 - Image forming apparatus - Google Patents

Description

The present invention relates to an image forming equipment.

  The electrophotographic image forming apparatus includes a photosensitive drum on which a toner image is formed and a developing device for supplying toner to the photosensitive drum. The developing device includes a developing roller disposed in parallel with the photosensitive drum.

  The developing device is detachably attached to the main body of the image forming apparatus. However, since the developing roller is disposed close to the photosensitive drum as described above, the developing roller may come into contact with the photosensitive drum during the mounting operation and the detaching operation.

  On the other hand, Patent Document 1 discloses a configuration in which the developing device is removed from the apparatus main body with the developing roller retracted from the photosensitive drum in advance.

  That is, the developing device of Patent Document 1 includes a housing, a developing roller and a magnetic roller that extend in parallel to each other, and a bearing member that rotatably supports end portions of the developing roller and the magnetic roller.

  The bearing member can swing around the axis of the magnetic roller together with the developing roller. The developing roller is in contact with the photosensitive drum when the bearing member is biased by the first spring. An arm member is fixed near the magnetic roller of the bearing member.

  A shaft member extending in the axial direction of the magnetic roller is provided in the housing so as to be movable in the axial direction of the magnetic roller. The shaft member is biased by a second spring so that one end protrudes from the housing. The shaft member reciprocates while contacting the arm member, thereby swinging the arm member and the bearing member around the axis of the magnetic roller.

  The apparatus main body includes a holder part to which the developing device is attached and a cover part provided on the front side of the holder part so as to be openable and closable.

  Then, when the cover unit is closed with the developing device mounted on the holder unit, the tip of the protruding shaft member comes into contact with the back surface of the cover unit and resists the urging force of the second spring by the cover unit. Can be pushed in. At that time, the arm member and the bearing member swing as the shaft member moves, and the developing roller is pressed against and contacted with the photosensitive drum by the urging force of the first spring.

  On the other hand, when the cover portion is opened, the shaft member moves so as to protrude forward by the biasing force of the second spring. The movement of the shaft member causes the arm member and the bearing member to swing against the biasing force of the first spring, so that the developing roller is retracted from the photosensitive drum.

JP2013-125149A

  Here, in the configuration of Patent Document 1, it is desirable to increase the urging force of the first spring in order to ensure that the developing roller is in contact with the photosensitive drum.

  However, in order to move the shaft member forward by the biasing force of the second spring when the cover portion is opened, it is necessary to set the biasing force of the second spring larger than the biasing force of the first spring. Therefore, if the biasing force of the first spring is increased, the biasing force of the second spring must be further increased.

  However, when the urging force of the second spring is increased, a large force is required to close the cover portion against the urging force of the second spring, and thus there is a problem that it is difficult to close the cover portion.

  The present invention has been made in view of the above points, and the object of the present invention is to increase the urging force for urging the developing roller so that the developing roller is surely brought into contact with the photosensitive drum. In addition, the cover member can be easily closed and the shaft member can be appropriately moved when the cover portion is opened.

  An image forming apparatus according to the present invention includes a photosensitive drum, a developing device that is provided so as to be in contact with the photosensitive drum and that extends in the front-rear direction, and a magnetic roller that extends in parallel with the developing roller; The developing device is inserted and mounted from the rear end side of the developing roller, while the developing device is pulled out from the front end side of the developing roller and detached, and viewed from the front on the front side of the holder portion. A cover portion is provided that can swing between a closed position that overlaps at least a part of the developing device mounted on the holder portion and an open position that does not overlap the developing device.

  The developing device includes a bearing member that rotatably supports end portions of the developing roller and the magnetic roller and swingable about an axis of the magnetic roller, and the developing roller includes the photosensitive drum. A first urging means for urging the bearing member in a direction approaching the position, an arm member fixed to the bearing member, and extending in the front-rear direction and moving in the front-rear direction, thereby moving the arm member and the bearing member A shaft member configured to swing around the axis of the magnetic roller; and a second biasing unit that biases the shaft member forward against the biasing force of the first biasing unit. ing.

  The cover portion has an engaging portion that engages with the front end portion of the shaft member, and swings from the open position to the closed position to push the shaft member to the rear position, thereby moving the developing roller. The shaft member engaged with the engaging portion is pulled out to the front position by swinging from the closed position to the open position while being brought into contact with the photosensitive drum, and the developing roller is moved to the photosensitive drum. The front end portion of the shaft member is configured to be disengaged from the engagement portion when the shaft member is pulled out to the front position by the cover portion. Has been.

  According to this configuration, when the developing device is attached to the image forming apparatus, the developing device is attached to the holder portion by being inserted into the holder portion from the rear end side of the developing roller. At this time, the second biasing means biases the shaft member forward against the biasing force of the first biasing means. Subsequently, the cover part is swung from the open position to the closed position. Thus, the cover portion pushes the shaft member to the rear position against the urging force of the second urging means. Then, with the movement of the shaft member to the rear position, the arm member and the bearing member swing around the axis of the magnetic roller, and the developing roller receiving the urging force of the first urging means via the bearing member It approaches and contacts the photosensitive drum.

  On the other hand, when the developing device is detached from the image forming apparatus, the cover portion is swung from the closed position to the open position. As a result, the shaft member engaged with the engaging portion of the cover portion is pulled out to the front position in conjunction with the swinging motion of the cover portion while receiving the urging force of the second urging means. Then, as the shaft member moves forward, the arm member and the bearing member swing around the axis of the magnetic roller, and the developing roller separates from the photosensitive drum against the urging force of the first urging means. And it will be in the evacuation state.

  In this way, by adopting a configuration in which the shaft member is forcibly pulled out by the cover portion, even if the urging force of the first urging means is increased and the developing roller is reliably brought into contact with the photosensitive drum, the first Since the urging force of the second urging means does not need to be larger than the urging force of the first urging means, the cover portion can be easily closed against the urging force of the second urging means.

  Furthermore, the engagement state of the front end portion of the shaft member with the engaging portion is released when the shaft member is pulled out to the front position by the cover portion. Therefore, after the shaft member is reliably moved to the front position, the cover part is moved away from the shaft member to the open position. That is, according to this configuration, the shaft member can be appropriately moved when the cover portion is opened.

The cover portion has a rotation shaft that is pivotally supported by the holder portion, and the engagement portion has a bifurcated claw extending perpendicularly to the axis of the rotation shaft, and the front end of the shaft member The groove is formed with a groove that is sandwiched and engaged by the claw, the groove width of the groove is W, the thickness of the claw when viewed from the axial direction of the rotating shaft is L, and the groove When the thickness of the shaft member in the length direction is H, and the inclination angle with respect to the vertically downward direction of the claw when the shaft member moves to the front position is θ, the groove width W of the groove portion is given by (1)
W ≧ Htanθ + L / cosθ (1)
Is preferably defined by:

Temporarily, the groove width W of a groove part is W <Htan (theta) + L / cos (theta).
Since the nail | claw of an engaging part will remove | deviate from a groove part before moving a shaft member to a front position, it cannot move a shaft member to a front position reliably.

  On the other hand, in this configuration, since the groove width W of the groove portion is defined by the above formula (1), the claw of the engaging portion comes out of the groove portion after the shaft member is moved to the front position. That is, the shaft member can be reliably moved to the front position.

  According to the present invention, even when the biasing force for biasing the developing roller is increased so that the developing roller is surely brought into contact with the photosensitive drum, the cover member can be easily closed and the shaft member can be opened when the cover portion is opened. Can be moved appropriately.

FIG. 1 is a perspective view showing an appearance of the image forming apparatus. FIG. 2 is a partially cutaway front view showing the main parts of the photosensitive drum and the developing device. FIG. 3 is a front view showing the holder part and the cover part. FIG. 4 is a front view showing the holder part and the cover part. FIG. 5 is a front view showing the holder part and the cover part. FIG. 6 is an enlarged side view showing an end portion of the developing device. FIG. 7 is a side sectional view schematically showing a partial configuration of the developing device. FIG. 8 is a side view showing the developing device and the cover. FIG. 9 is a side view showing the developing device and the cover portion. FIG. 10 is a side view showing the developing device and the cover. FIG. 11 is an enlarged perspective view showing the engaging portion. FIG. 12 is an enlarged perspective view showing the front end portion of the shaft member. FIG. 13 is a perspective view showing the engaging portion engaged with the shaft member. FIG. 14 is a side view showing the shaft member pulled out by the engaging portion. FIG. 15 is a side view showing the shaft member and the claw at the front position in the present embodiment. FIG. 16 is a side view showing the shaft member and the claw at the front position in the present embodiment. FIG. 17 is a side view showing the shaft member and the claw before reaching the front position in the comparative example.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. The present invention is not limited to the following embodiment.

  FIG. 1 shows an appearance of a multifunction machine 1 as an image forming apparatus according to this embodiment. FIG. 2 shows the main parts of the photosensitive drum 11 and the developing device 13. 3 to 5 show the external appearance of the holder part 14 and the cover part 15. In FIG. 1, the illustration of the platen portion (document pressing) is omitted.

  The multifunction machine 1 is an electrophotographic image forming apparatus, and includes a housing 10 that constitutes a main body of the apparatus, as shown in FIGS. Inside the housing 10, a drum unit 12 having a photosensitive drum 11, a developing device 13 for developing an electrostatic latent image formed on the photosensitive drum 11, and the photosensitive drum 11 and the developing device 13 are detachable. The holder part 14 to hold | maintain and the cover part 15 provided in the front side of the holder part 14 are accommodated.

  As shown in FIG. 1, a front cover 17 is provided on the front side surface of the housing 10. The holder part 14 and the cover part 15 are accommodated in the housing 10 by being covered with a front cover 17.

  A scanner unit 18 that scans a document is disposed on the upper portion of the housing 10. Below the scanner unit 18, a paper discharge unit 19 that discharges the image-formed paper from the inside of the housing 10 is formed. A paper feed cassette 20 as a paper feed unit is provided below the holder unit 14. Although not shown, the housing 10 further accommodates an optical scanning unit that scans the photosensitive drum 11 by irradiating a laser beam and a fixing unit that fixes a toner image formed on the sheet to the sheet. doing.

  For example, four drum units 12 are provided corresponding to toners of four colors of yellow, magenta, cyan, and black. The drum unit 12 includes a photosensitive drum 11, a charger (not shown) and a cleaning unit (not shown) provided around the photosensitive drum 11.

  The charger charges the surface of the photosensitive drum 11. An electrostatic latent image is formed on the photosensitive drum 11 charged by the charger by being irradiated with laser light from the optical scanning unit. The cleaning unit cleans the surface of the photosensitive drum 11.

  FIG. 6 shows an enlarged end portion of the developing device 13. FIG. 7 schematically shows a partial configuration of the developing device 13. Here, the right side in FIGS. 6 and 7 is the front side, and the left side in FIG. 6 is the rear side. 2 to 5, the front side of the page is the front side, and the back side of the page is the rear side.

  For example, four developing devices 13 are provided corresponding to the four drum units 12. The developing device 13 is a hybrid developing device, and includes a developing roller 23 that extends in the front-rear direction along the photosensitive drum 11 and a magnetic roller 24 that extends in parallel with the developing roller 23. The developing roller 23 is provided so as to be in contact with the photosensitive drum 11.

  The developing device 13 forms a magnetic brush by supporting a two-component developer including carrier and toner on the surface of the magnetic roller 24, and the toner supplied from the magnetic brush to the developing roller 23 causes the surface of the developing roller 23 to be formed. A toner layer is formed. Then, the developing device 13 develops the electrostatic latent image on the surface of the photosensitive drum 11 as a toner image by causing the toner to fly from the toner layer to the photosensitive drum 11.

  As shown in FIG. 2, the developing device 13 further includes a housing 26 to which the side cover 25 is attached, and a bearing member 27 that rotatably supports the end portions of the developing roller 23 and the magnetic roller 24. . The bearing members 27 are provided on both end sides of the developing roller 23 and the magnetic roller 24, respectively. Each bearing member 27 is provided in the housing 26 so as to be swingable around the axis A of the magnetic roller 24. As a result, the developing roller 23 can be brought into contact with and separated from the photosensitive drum 11 by swinging around the axis A of the magnetic roller 24.

  The developing device 13 includes a first spring 28 as a first urging unit that urges the bearing member 27 in a direction in which the developing roller 23 approaches the photosensitive drum 11, and an arm member 29 fixed to the bearing member 27. It has.

  The first spring 28 is a compression spring. One end of the first spring 28 is engaged with the side cover 25, and the other end is engaged with the developing roller 23 in the bearing member 27. The arm member 29 is provided in the vicinity of the magnetic roller 24 in the bearing member 27 and is formed integrally with the bearing member 27. A bearing 30 is provided at the tip of the arm member 29.

  6 and 7, the developing device 13 includes a shaft member 31 that extends in the front-rear direction and is movable in the front-rear direction, and a second urging unit that urges the shaft member 31 forward. And a second spring 32.

  The shaft member 31 is supported by the housing 26 and covered with the side cover 25. FIG. 6 shows a state where the side cover 25 is removed and the shaft member 31 is exposed. In FIG. 6, the cover portion 15 is not shown.

  The shaft member 31 has a cam portion 34 that contacts the bearing 30 and guides the arm member 29 when the shaft member 31 moves in the front-rear direction. When the shaft member 31 moves forward, the cam portion 34 pushes down the bearing 30 downward in FIGS. 2 and 6 so that the developing roller 23 is detached from the photosensitive drum 11 and the arm member 29 and the bearing member. 27 is swung around the axis A of the magnetic roller 24.

  On the other hand, the cam portion 34 has the arm member 29 and the bearing so that the developing roller 23 comes into contact with the photosensitive drum 11 by guiding the bearing 30 upward in FIGS. The member 27 is swung around the axis A of the magnetic roller 24.

  The second spring 32 is a tension spring. One end of the second spring 32 engages with the housing 26, and the other end engages with the shaft member 31, thereby urging the shaft member 31 forward.

  On the other hand, the biasing force of the first spring 28 acts on the bearing member 27 in the direction in which the bearing 30 is moved upward in FIGS. 2 and 6. Therefore, the first spring 28 urges the shaft member 31 rearward in the cam portion 34 that is in contact with the bearing 30. That is, the second spring 32 urges the shaft member 31 forward against the urging force of the first spring 28.

  As shown in FIGS. 3 to 5, the holder portion 14 has a mounting hole 35 in which the developing device 13 and the drum unit 12 are mounted. The mounting hole 35 extends in the front-rear direction and opens on the front end side. The developing device 13 is inserted into the mounting hole 35 of the holder portion 14 from the rear end side of the developing roller 23 and mounted. Further, the drum unit 12 is inserted into the mounting hole 35 of the holder portion 14 from the rear end side of the photosensitive drum 11 and mounted. Thus, the developing device 13 and the drum unit 12 are mounted on the holder unit 14 side by side alternately.

On the other hand, the developing device 13 is detached from the holder portion 14 by being pulled out from the front end side of the developing roller 23. Further, the drum unit 12 is pulled out from the front end side of the photosensitive drum 11 and is detached from the holder portion 14.

  8 to 10 show the developing device 13 and the cover unit 15. In addition, illustration of the holder part 14 is abbreviate | omitted in FIGS.

  As shown in FIGS. 3 to 5 and FIGS. 8 to 10, the cover portion 15 is swingably supported by the holder portion 14. The cover portion 15 overlaps at least a part of the developing device 13 mounted on the holder portion 14 when viewed from the front on the front side of the holder portion 14 (see FIGS. 3 and 8), and overlaps the developing device 13. It is provided so as to be swingable with respect to an open position (see FIGS. 5 and 10) that does not become necessary.

  The cover portion 15 is configured to position the drum unit 12 at a predetermined position and push the shaft member 31 of the developing device 13 to the rear position by swinging from the open position to the closed position. In addition, the cover portion 15 is configured to pull out the shaft member 31 of the developing device 13 to the front position by swinging from the closed position to the open position.

  That is, the shaft member 31 is movable between the rear position and the front position. The developing roller 23 comes into contact with the photosensitive drum 11 when the shaft member 31 is pushed into the rear position. On the other hand, when the shaft member 31 moves to the front position, the developing roller 23 is retracted from the photosensitive drum 11.

  The cover portion 15 includes a cover main body 36, a support plate 37 attached to the cover main body 36, and an engagement portion 38 attached and fixed to the support plate 37. The cover body 36 has a rotation shaft 36 a that is pivotally supported by the holder portion 14. The engaging portion 38 is configured to engage with the front end portion of the shaft member 31.

  Here, FIG. 11 shows the engaging portion 38 in an enlarged manner. FIG. 12 shows the front end portion of the shaft member 31 in an enlarged manner. FIG. 13 shows the engaging portion 38 engaged with the shaft member 31. FIG. 14 shows the shaft member 31 pulled out by the engaging portion 38. In FIG. 14, the cover main body 36 is not shown.

  As shown in FIGS. 11 to 13, the engaging portion 38 is configured by a hook member that engages with the front end portion of the shaft member 31 interposed therebetween. That is, the engaging portion 38 has an attachment portion 39 attached to the support plate 37 and a bifurcated claw 40 formed integrally with the attachment portion 39. The claw 40 extends perpendicularly to the axis B of the rotation shaft 36 a of the cover body 36. On the other hand, a groove 41 is formed at the front end of the shaft member 31 so as to be sandwiched between the claws 40.

  The shaft member 31 has a distal end portion 42 on the front side of the groove portion 41 and a proximal end side portion 43 on the rear side of the groove portion 41. The width in the direction sandwiched by the claw 40 of the distal end portion 42 (hereinafter simply referred to as width) is narrower than the width of the proximal end portion 43. Furthermore, the width of the tip end portion 42 is gradually narrowed toward the front. As a result, the claw 40 of the engaging portion 38 is easily engaged with the groove portion 41 of the shaft member 31.

  Then, as shown in FIGS. 8 to 10 and 14, the cover portion 15 swings from the closed position (see FIG. 8) to the open position (see FIG. 10) around the axis B of the rotation shaft 36 a. Thus, the shaft member 31 engaged with the engaging portion 38 is configured to be pulled out to the front position.

  Further, the front end portion of the shaft member 31 is configured such that the engagement state with the engagement portion 38 is released when the shaft member 31 is pulled out to the front position by the cover portion 15.

Here, FIG.15 and FIG.16 has shown the shaft member 31 and the nail | claw 40 in the front position. As shown in FIGS. 15 and 16, the groove width of the groove portion 41 is W, the thickness of the claw 40 when viewed from the direction of the axis B of the rotation shaft 36 a of the cover portion 15 is L, and the length of the groove portion 41. The thickness of the shaft member 31 in the direction is H, and the inclination angle of the claw 40 with respect to the vertically downward direction when the shaft member 31 moves to the front position is θ. At this time, the groove width W of the groove portion 41 is expressed by the following equation (1).
W ≧ Htanθ + L / cosθ (1)
It is prescribed by.

FIG. 15 shows that W = H tan θ + L / cos θ.
FIG. 16 shows the case where W> H tan θ + L / cos θ.
The case is shown.

  With the above configuration, when the developing device 13 is mounted on the multi-function device 1, the developing device 13 is inserted into the holder portion 14 from the rear end side of the developing roller 23 as shown in FIG. 14 is attached. At this time, the second spring 32 biases the shaft member 31 forward against the biasing force of the first spring 28. And as shown, for example in FIG.10 and FIG.14, the shaft member 31 has moved to the front position.

  Subsequently, as shown in FIGS. 3 to 5 and FIGS. 8 to 10, the cover portion 15 is swung from the open position to the closed position below. By the swinging operation, the cover portion 15 pushes the shaft member 31 whose tip is in contact with the support plate 37 of the cover portion 15 backward against the urging force of the second spring 32. As a result, the shaft member 31 moves from the front position to the rear position. At this time, the claw 40 of the engaging portion 38 in the cover portion 15 is engaged with the groove portion 41 on the distal end side of the shaft member 31.

  Then, as the shaft member 31 moves backward, the arm member 29 is guided by the cam portion 34, and the arm member 29 and the bearing member 27 swing around the axis A of the magnetic roller 24. As a result, the developing roller 23 receiving the urging force of the first spring 28 via the bearing member 27 swings so as to approach the photosensitive drum 11. When the shaft member 31 moves to the rear position (see, for example, FIG. 6), the developing roller 23 contacts the photosensitive drum 11.

  On the other hand, when the developing device 13 is detached from the multifunction device 1, the cover portion 15 is swung from the closed position to the open position. Since the shaft member 31 is engaged with the engaging portion 38 of the cover portion 15 when the cover portion 15 starts to swing from the closed position, the shaft member 31 is moved forward by the cover portion 15 while receiving the urging force of the second spring 32. Pulled out.

  Then, the arm member 29 is guided by the cam portion 34 as the shaft member 31 moves forward, and the arm member 29 and the bearing member 27 swing around the axis A of the magnetic roller 24. As a result, the developing roller 23 separates from the photosensitive drum 11 against the urging force of the first spring 28 and enters a retracted state.

  The shaft member 31 stops moving forward at the front position. As shown in FIGS. 9, 10, and 14, after the shaft member 31 is pulled out to the front position, the cover portion 15 further swings toward the open position, whereby the claw 40 of the engaging portion 38 is It is disengaged from the groove 41 of the shaft member 31.

  Therefore, according to the present embodiment, the developing device 13 can be detached from the multifunction device 1 with the developing roller 23 retracted from the photosensitive drum 11.

  In addition, since the shaft member 31 is forcibly pulled out by the cover portion 15, even if the biasing force of the first spring 28 is increased and the developing roller 23 is brought into contact with the photosensitive drum 11 reliably, The urging force of the two springs 32 need not be greater than the urging force of the first spring 28. Therefore, since the urging force of the second spring 32 can be made relatively small, the cover portion 15 can be easily closed against the urging force of the second spring 32. That is, according to the present embodiment, the cover 15 can be easily closed even if the developing roller 23 is surely brought into contact with the photosensitive drum 11.

  Furthermore, since the engaging portion 38 is configured by the hook member that is engaged so as to sandwich the front end portion of the shaft member 31, the engaging portion 38 can be appropriately engaged with the shaft member 31 with a relatively simple configuration. it can.

  In addition, in this embodiment, when the shaft member 31 is pulled out to the front position by the cover portion 15, the engagement state of the front end portion of the shaft member 31 is released. Configured. That is, the groove width W of the groove portion 41 is defined so as to satisfy the above formula (1).

Here, FIG. 17 shows a comparative example that does not satisfy the condition of the above formula (1) (that is, W <H tan θ + L / cos θ
The shaft member 31 and the claw 40 before reaching the front position are shown.

As shown in FIG. 17, suppose that the groove width W of the groove portion 41 does not satisfy the condition of the above formula (1), and W <H tan θ + L / cos θ.
, The claw 40 of the engaging part 38 comes off the groove part 41 before the shaft member 31 is moved to the front position. Therefore, the shaft member 31 cannot be reliably moved to the front position.

  On the other hand, in this embodiment, since the groove width W of the groove part 41 is prescribed | regulated by said Formula (1), as shown in FIG.15 and FIG.16, the nail | claw 40 of the engaging part 38 is the shaft member 31. After moving to the forward position, it comes off from the groove 41.

  Therefore, according to this embodiment, after the shaft member 31 is reliably moved to the front position, the cover portion 15 can be detached from the shaft member 31 and swung to the open position. That is, according to the present embodiment, the shaft member 31 can be appropriately moved when the cover portion 15 is opened.

  In the above-described embodiment, the multifunction peripheral is described as an example of an image forming apparatus. However, the present invention is not limited to this, and may be another image forming apparatus such as a printer, a scanner device, or a copying machine.

As described above, the present invention is useful for imaging equipment.

1 MFP (image forming device)
11 Photosensitive drum 13 Developing device 14 Holder portion 15 Cover portion 23 Developing roller 24 Magnetic roller 27 Bearing member 28 First spring (first biasing means)
29 Arm member 31 Shaft member 32 Second spring (second biasing means)
36a Rotating shaft 38 Engaging portion 40 Claw 41 Groove portion

Claims (2)

A photosensitive drum;
A developing device provided with a developing roller provided in contact with the photosensitive drum and extending in the front-rear direction; and a magnetic roller extending in parallel with the developing roller;
The developing device is inserted and mounted from the rear end side of the developing roller, while the developing device is pulled out from the front end side of the developing roller and detached from a holder portion;
Provided to be swingable between a closed position that overlaps at least a part of the developing device mounted on the holder portion and an open position that does not overlap the developing device when viewed from the front on the front side of the holder portion. An image forming apparatus comprising a cover unit,
The developing device includes a bearing member that rotatably supports end portions of the developing roller and the magnetic roller and swingable about an axis of the magnetic roller, and the developing roller includes the photosensitive drum. A first urging means for urging the bearing member in a direction approaching the position, and extending in the front-rear direction and moving in the front-rear direction, thereby swinging the bearing member around the axis of the magnetic roller. A shaft member, and second urging means for urging the shaft member forward against the urging force of the first urging means,
The cover portion has an engaging portion that engages with a front end portion of the shaft member, and swings from the open position to the closed position to push the shaft member to the rear position, thereby causing the developing roller to move to the photosensitive member. The shaft member engaged with the engaging portion is pulled out to the front position by swinging from the closed position to the open position while being brought into contact with the body drum, and the developing roller is retracted from the photosensitive drum. Configured to let
The front end portion of the shaft member is configured to be disengaged from the engagement portion when the shaft member is pulled out to the front position by the cover portion. The image forming apparatus according to claim 1.
The cover portion has a rotation shaft that is pivotally supported by the holder portion,
The engaging portion has a bifurcated claw extending perpendicularly to the axis of the rotating shaft,
The front end portion of the shaft member is formed with a groove portion that is sandwiched and engaged with the claw,
The groove width of the groove portion is W, the thickness of the claw when viewed from the axial direction of the rotating shaft is L, the thickness of the shaft member in the length direction of the groove portion is H, and the shaft member is The groove width W of the groove part is given by the following equation (1), where θ is the inclination angle of the nail with respect to the vertical downward direction when the claw is moved to the front position.
W ≧ Htanθ + L / cosθ (1)
An image forming apparatus defined by .

Images