JP4221970B2 - Image forming apparatus - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an electrophotographic image forming apparatus such as a copying machine or a printer, and more particularly to an image forming apparatus using a belt unit such as an intermediate transfer belt or a paper transport belt.
[0002]
[Prior art]
Conventionally, in an image forming apparatus that forms a color image, a toner image formed on a photosensitive drum is transferred onto a recording medium carried by an intermediate transfer belt or a conveyance belt, or a toner image transferred onto an intermediate transfer belt. A method is widely used in which the toner image is secondarily transferred onto a recording medium, and the toner image on the transferred recording medium is heated and pressed to fix the toner image on the recording medium.
[0003]
In particular, in a tandem type image forming apparatus in which a plurality of photosensitive drums are arranged, a belt and a plurality of rolls that stretch the belt are supported by a frame body, and a fixing device is assembled to the frame body to form an integral conveyance unit. And a unit that is detachable from the image forming apparatus so that it can be pulled out when a jam occurs or during maintenance and inspection (Japanese Patent Laid-Open No. 5-35008). etc).
[0004]
However, in the tandem type image forming apparatus, if the position where the belt is brought into contact with the plurality of photosensitive drums is deviated, color misregistration occurs in the multiple transferred image, the image quality is deteriorated, and the frame is supported. There is a problem that the member is deformed or damaged.
[0005]
In JP-A-8-171248, positioning accuracy and reproducibility for positioning a belt module in which a belt and a plurality of rolls that stretch the belt are supported by a frame with respect to a plurality of photosensitive drums are ensured. In addition, a technique is disclosed in which the conveyance direction of an unfixed toner image between the belt module and the fixing device is made the same, and the adverse effect on the belt caused by a transfer material loop caused by the speed difference between the belt module and the fixing device is disclosed.
[0006]
If this technique is used, it is considered that the positioning accuracy and the like are improved.
[0007]
[Problems to be solved by the invention]
However, according to the technique disclosed in Japanese Patent Application Laid-Open No. 8-171248, in order to support the frame body, two through shafts are provided in the belt module, and the belt module is moved up and down, so that a plurality of photosensitive drums can be supported. However, there are problems that the mechanism is complicated and that a large space is required, such as four spring coils that absorb vibration applied to the belt module on the penetrating shaft.
[0008]
In view of the above circumstances, an object of the present invention is to provide an image forming apparatus including a belt module that has a simple structure, is easy to install, and has high positioning accuracy.
[0009]
[Means for Solving the Problems]
An image forming apparatus of the present invention that achieves the above object includes a plurality of arranged photosensitive drums on which toner images are formed,
An endless belt that moves via each position in contact with each of the plurality of photosensitive drums and receives transfer of toner images formed on the plurality of photosensitive drums directly or on a recording medium carried thereon; and A transfer roll for transferring a toner image formed on the plurality of photosensitive drums facing each of the plurality of photosensitive drums across the endless belt to the endless belt or to a recording medium carried by the endless belt. A transfer unit having
A transfer drawer that moves the endless belt between a position contacting the plurality of photosensitive drums and a position separating the endless belt by raising and lowering the transfer unit;
In the image forming apparatus for forming an image by finally transferring and fixing the toner image on the endless belt onto a recording medium,
The transfer unit has four placement portions for placing the transfer unit on the transfer drawer,
The transfer drawer includes a support member that supports four placement portions of the transfer unit and absorbs vibration of the transfer unit, and a cam device that raises and lowers the support member.
[0010]
As described above, the transfer unit having the endless belt and the transfer roll has the placement portions at four places, and the placement portion can be positioned on the transfer drawer to perform front-rear and left-right positioning. A transfer drawer cam device having a cam device for raising and lowering a support member raises and lowers the transfer unit and presses an endless belt against a plurality of photosensitive drums by an elastic support member that supports the mounting portion to perform vertical positioning. Therefore, the structure of the transfer unit and the transfer drawer can be simplified, the incorporation into the image forming apparatus can be facilitated, and the positioning accuracy can be increased.
[0011]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described.
[0012]
FIG. 1 is a schematic configuration diagram illustrating an image forming apparatus according to the first embodiment.
[0013]
The image forming apparatus shown in FIG. 1 has four photoreceptors 1 on which Y (yellow), M (magenta), C (cyan), and K (black) toner images are formed while rotating in the direction of arrow A. Each of the four photoconductors 1 is in contact with a paper conveying belt 9 that is laid across a drive roll 7 and a driven roll 8 and circulates in the direction of arrow B. Around each photoconductor 1, a charger 2, an exposure device 3, a developing device 4, and a cleaning device 5 are provided. Each photoconductor 1 is uniformly charged by the charger 2 while rotating in the direction of arrow A. The uniformly charged photoreceptor 1 is irradiated with an exposure beam modulated based on an image signal separated into each color from the exposure device 3 to form an electrostatic latent image. Each color toner image is formed on the photoreceptor 1 by being developed with each color toner in the developing device 4.
[0014]
The four photoconductors 1 on which the toner images of each color of YMCK are formed face the transfer roll 6 at each transfer position with the paper transport belt 9 interposed therebetween. The paper transport belt 9 carries the paper P fed from the paper tray 33 and transports the paper P to each transfer position. The four photoreceptors 1 on which the toner images of each color of YMCK are formed rotate in the direction of arrow A, and when the toner image is rotated to the transfer position, the formed toner images are conveyed on the sheet P on which the sheet conveying belt 9 has been conveyed. Each timing is adjusted so as to be transferred.
[0015]
The toner images of each color of YMCK are successively multiplex-transferred onto one sheet P on the sheet transport belt 9, and the sheet P on which all the YMCK color toner images are superimposed and transferred is fixed by a heating roll 31 and a pressure roll 32. Heated and pressurized by the apparatus 30, an image composed of a fixed toner image is formed on the paper P.
[0016]
A cleaning device 5 is provided at a position in contact with the surface of the photoconductor 1 after the toner image formed on the photoconductor 1 is transferred to the paper P and before the next image forming cycle. The surface of the photoreceptor 1 is cleaned and prepared for the next image forming cycle. Further, the toner on the paper transport belt 9 is cleaned by the belt cleaning device 17.
[0017]
In the present embodiment, the drive roll 7 and the driven roll 8, the paper transport belt 9 that circulates and moves in the direction of arrow B across the drive roll 7 and the driven roll 8, and the four photosensitive 1 sandwiching the paper transport belt 9. And a transfer roll 6 facing each other are integrated to form a transfer unit. This transfer unit forms a drawer unit that is detachably supported by the image forming apparatus, and the paper transport belt 9 carries the paper P fed from the paper tray 33 and transports the paper to each transfer position. When a jam occurs, or when inspection or repair is performed, the drawer unit can be pulled out from the image forming apparatus.
[0018]
FIG. 2 is a perspective view showing the drawer unit of the present embodiment.
[0019]
The drawer unit shown in FIG. 2 is driven by a driving roll 7 and moves via a position in contact with four photosensitive drums (not shown) to carry toner images formed on the four photosensitive drums (not shown). A sheet conveying belt 9 that receives a transfer onto a recording medium, and a recording in which the sheet conveying belt 9 carries toner images formed on the four photosensitive drums while facing the four photosensitive drums with the sheet conveying belt 9 interposed therebetween. A transfer unit 40 having a transfer roll that does not appear in the drawing to be transferred to the medium, and a transfer that moves the sheet transport belt 9 between a position where it contacts the four photosensitive drums and a position where it is separated by moving the transfer unit 40 up and down. The drawer 41 is configured.
[0020]
The transfer drawer 41 is provided with a positioning notch 41a of the transfer unit 40 and a handle 42c for rotating the cam of the cam device 42 that partially appears in the figure, on the front side surface of the figure, and does not appear in the figure. On the side surface side, two pins 41b are provided on the right and left ends of the frame member 41c that supports the cam device 42, respectively. Further, the transfer unit 40 is provided with a positioning shaft 40a at the center of the side surface on the front side surface in the drawing, and two legs 40b for leaning the transfer unit 40 on the side surface not shown in the drawing. Yes.
[0021]
The transfer unit 40 is mounted on the transfer drawer 41, and the positioning shaft 40 a is engaged with the positioning notch 41 a of the transfer drawer 41, so that the transfer unit 40 is fixed to the transfer drawer 41. The fixed drawer unit is fixed to the frame of the image forming apparatus by fitting the pin 41b of the transfer drawer 41 to a fitting portion (not shown) provided in the frame of the image forming apparatus. The transfer unit 40 can be inspected and repaired by pulling the drawer unit out of the image forming apparatus, removing the transfer unit 40 from the transfer drawer 41, and leaning on the three legs 40b of the transfer unit 40.
[0022]
The structure in which the transfer unit 40 is placed on the transfer drawer 41 in this manner simplifies the structure of the drawer unit, facilitates the incorporation of the unit, and allows the transfer unit 40 to be positioned with high accuracy.
[0023]
FIG. 3 is a diagram showing the transfer unit of the present embodiment.
[0024]
The transfer unit 40 shown in FIG. 3 includes a positioning shaft 40a at the center of the side surface on the front side surface in the figure, and three legs 40b on which the transfer unit 40 is leaned on the side surface not shown in the figure. Further, a position restricting member 40c that is provided in the four corners on the transfer drawer 41 and that contacts when the transfer unit 40 is abutted against a frame (not shown) that fixes the photosensitive drum appears in the drawing. There are two each on the non-side surface and the near side surface in the figure.
[0025]
Since the position restricting member 40c includes the spherical surface portion 40e, if the position restricting member provided on the frame side (not shown) for fixing the photosensitive drum includes only a flat surface portion having no spherical surface portion, the transfer is performed. The unit 40 and a frame (not shown) for fixing the photosensitive drum can be brought into point contact with the position regulating member 40c.
[0026]
As described above, if the transfer unit 40 and the frame (not shown) for fixing the photosensitive drum are brought into point contact at four points, the transfer unit 40 is not displaced in the horizontal direction. The drum can be reliably positioned.
[0027]
FIG. 4 is a diagram showing a transfer drawer of the present embodiment.
[0028]
The transfer drawer 41 shown in FIG. 4 is provided on each of the left and right sides of the transfer drawer 41 and absorbs the vibration that the transfer unit 40 contacts with the photosensitive drum, and a cam device 42 that moves the support member 41d up and down. The frame member 41c that supports both the support member 41d and the cam device 42 is provided.
[0029]
The support member 41d extends in the width direction of the paper transport belt 9, and rises with a plate-like portion 41e that elastically supports the placing portion 40d at both ends A and B, and a central portion C of the plate-like portion 41e being bent. And a rising portion 41f. The center portion C has rigidity because it has a rising portion 41f that is bent and rises, while both ends A and B are elastic because they are composed only of the plate-like portion 41e. Therefore, both ends A and B of the support member 41d bend to press the transfer unit 40 against the photosensitive drum, and absorb vibration received by the photosensitive drum coming into contact with the paper transport belt 9.
[0030]
The cam device 42 includes a cam 42a that moves the support member 41d up and down by rotating, a drive member 42b that rotates the cam 42a by performing linear motion, and a handle 42c that linearly moves the drive member 42b by rotating. I have.
[0031]
After the transfer unit 40 is mounted on the transfer drawer 41 and the drawer unit is mounted on the image forming apparatus, the cam 42a is rotated by rotating the handle 42c in the direction opposite to the arrow D direction to raise the support member 41d. Thus, the transfer unit 40 is pressed against the photosensitive drum (position in the figure). When pulling out the drawer unit from the image forming apparatus, the cam 42a is rotated by rotating the handle 42c in the direction of arrow D, and the support member 41d is lowered.
[0032]
FIG. 5 is a diagram illustrating a part of the support member and the cam device.
[0033]
In FIG. 5, the support member 41d extends in the width direction of the paper conveying belt, and a plate-like portion 41e that elastically supports the placing portion 40d at both ends A and B and a central portion C of the plate-like portion 41e are bent. And a rising portion 41f rising up. The center portion C has rigidity because it has a rising portion 41f that is bent and rises, while both ends A and B are elastic because they are composed only of the plate-like portion 41e. Further, a long hole 41g is opened in the rising portion 41f of the central portion C, and the support member 41d is fastened by a screw 41h so as to be movable up and down through the long hole 41g.
[0034]
On the other hand, the cam 42a of the cam device 42 is a support member at the center portion C of the central portion C having rigidity of the support member 41d and contacting the plate-like portion 41e connected to the rising portion 41f provided with the long hole 41g and having rigidity. 41d is moved up and down.
[0035]
When the mounting portion 40d of the transfer unit 40 is placed on both ends A and B and the support member 41d is raised, both ends A and B are bent to press the transfer unit 40 against the photosensitive drum, and the support member 41d is The vibration received from the photosensitive drum via the transfer unit 40 is absorbed.
[0036]
As described above, the support member 41d has the central portion C having rigidity and both ends A and B having elasticity, and the central portion C having rigidity receives the lifting force from the cam device 42 and has both ends A having elasticity. , B share the role of pressing the transfer unit 40, so that the structure of the transfer drawer is simplified.
[0037]
Next, a second embodiment will be described.
[0038]
The second embodiment is different from the first embodiment in that it includes an intermediate transfer belt instead of the paper conveyance belt and a secondary transfer roll that re-transfers the toner image on the intermediate transfer belt to a recording medium. However, since the other points are the same, the differences will be described.
[0039]
FIG. 6 is a schematic configuration diagram illustrating an image forming apparatus according to the second embodiment.
[0040]
The image forming apparatus shown in FIG. 6 includes four photosensitive drums 11Y, 11A, 11B, 11Y, 11Y, 11Y, Y, Magenta (M), Cyan (C), and black (K) toner images, respectively. 11M, 11C, and 11K are juxtaposed. Further, an intermediate transfer belt 21 that is stretched around a drive roll 22, a driven roll 23, a tension roll 24, and a counter roll 25 and circulates in the B direction while contacting each of the four photosensitive drums 11Y, 11M, 11C, and 11K. I have. Around each photosensitive drum 11, each of the charging devices 12 </ b> Y, 12 </ b> M, 12 </ b> C, and 12 </ b> K that charges the photosensitive drum 11, exposure light is applied to the photosensitive drum 11 that is charged based on the image data separated for each color. Each of the exposure devices 13Y, 13M, 13C, and 13K that forms an electrostatic latent image by irradiating (LB), and the electrostatic latent image is developed with toners of the respective colors of YMCK from a close position to form a toner image. Each of the developing devices 14Y, 14M, 14C, and 14K and the intermediate transfer belt 21 are opposed to the respective photosensitive drums 11, and the toner image formed on the photosensitive drum 11 is primarily transferred to the intermediate transfer belt 21. Next transfer rolls 27Y, 27M, 27C, 27K, and cleaning members 16Y for cleaning toner remaining on the photosensitive drum 11 after transfer with a conductive brush and blade 16M, 16C, is equipped with a 16K. Further, a secondary transfer roll 28 that faces the opposing roll 25 across the intermediate transfer belt 21 and secondarily transfers the toner image on the intermediate transfer belt 21 to the paper P, and chutes the paper P conveyed from a paper tray (not shown). 34, a registration roll 35 fed to the secondary transfer roll 28, a paper guide member 37 for guiding the paper P coming out of the secondary transfer roll 28 to the conveying belt 36, and the paper P on which the paper toner image has been secondarily transferred. A conveyance belt 36 that conveys the toner image on the paper P conveyed by the conveyance belt 36 and a fixing device 30 that includes a heating roll 31 and a pressure roll 32 that fix the toner image on the paper P are provided. The secondary transfer roll 28 includes a cleaning device 28a, and the intermediate transfer belt includes a belt cleaning device 38.
[0041]
The surface of the photosensitive drum 11 uniformly charged by the charger 12 is irradiated from the exposure device 13 with exposure light (LB) that has been subjected to pulse width modulation based on image data decomposed for each color, thereby causing electrostatic latent An image is formed, and the electrostatic latent image is developed with each color toner of the developing device 14 to form each color toner image on the surface of the photosensitive drum 11. Each color toner image on the photoconductive drum 11 is sequentially multiplex-transferred onto the intermediate transfer belt 21 by the primary transfer roll 27, and each color toner image that has been multiplex-transferred is transferred onto the paper P by the secondary transfer roll 28. The toner image on the paper P is further fixed on the paper by the fixing device 30 to form an image composed of the fixed toner image.
[0042]
In the present embodiment, the intermediate transfer belt 21 that is stretched around the drive roll 22, the driven roll 23, the tension rolls 24, and the opposing roll 25 and circulates in the direction of the arrow B, and the four photoconductors 11 across the intermediate transfer belt 21. And a transfer roll 27 that is opposed to each other to form a transfer unit, and a secondary transfer roll can be detachably attached to the transfer unit. The transfer unit with the secondary transfer roll attached forms a drawer unit, and the drawer unit may, for example, cause a jam when the toner image is secondarily transferred from the intermediate transfer belt 21 to the paper P. When inspecting and repairing, it can be pulled out from the image forming apparatus.
[0043]
FIG. 7 is a perspective view illustrating a transfer unit according to the second embodiment.
[0044]
The transfer unit 40 shown in FIG. 7 is driven by the drive roll 22 and moves through positions where it contacts four photosensitive drums (not shown), and the toner images formed on the four photosensitive drums are sequentially transferred. Intermediate transfer belt 21 and a transfer roll that does not appear in the figure, which transfers the toner images formed on the four photosensitive drums to the intermediate transfer belt, facing each of the four photosensitive drums across the intermediate transfer belt. Further, a secondary transfer roll 28 for retransferring the toner image transferred onto the intermediate transfer belt 21 onto the recording medium is detachably attached to the transfer unit 40.
[0045]
Further, the transfer unit 40 is provided with a positioning shaft 40a at the center of the front side surface in the drawing, and two legs 40b on which the transfer unit 40 is leaned on the side surface not shown in the drawing. Further, a position restricting member 40c that is provided in the four corners on the transfer drawer 41 and that contacts when the transfer unit 40 is abutted against a frame (not shown) that fixes the photosensitive drum appears in the drawing. There are two each on the side surface not present and on the front side surface in the figure.
[0046]
Since the position restricting member 40c includes the spherical surface portion 40e, if the position restricting member provided on the frame side (not shown) for fixing the photosensitive drum includes only a flat surface portion having no spherical surface portion, the transfer is performed. The unit 40 and a frame (not shown) for fixing the photosensitive drum can be brought into point contact with the position regulating member 40c.
[0047]
As described above, since the transfer unit 40 in which the secondary transfer roll is incorporated and the frame (not shown) for fixing the photosensitive drum are brought into point contact at four locations, the transfer unit 40 is not displaced in the horizontal direction. The unit 40 can be reliably positioned on the four photosensitive drums, and the secondary transfer roll 28 can be detachably attached to the transfer unit 40, so that the intermediate transfer belt and the secondary transfer roll can also be positioned. Simultaneously and easily.
[0048]
FIG. 8 is a front view showing the periphery of the transfer drawer of the second embodiment.
[0049]
In FIG. 8, there is a transfer drawer 41 on which the transfer unit 40 is placed, and below that, a recording medium on which the toner image is secondarily transferred from the intermediate transfer belt 21 by the secondary transfer roll 28 is conveyed toward the fixing device 30. And a sheet guide member 37 that guides the recording medium that has come out of the secondary transfer roll 28 to the sheet conveyance belt 36.
[0050]
The transfer drawer 41 is provided on each of the left and right sides. The transfer drawer 41 presses the transfer unit 40 against the photosensitive drum, and also supports a support member 41d that absorbs vibration received by the transfer unit 40 from the photosensitive drum, and a cam device 42 that raises and lowers the support member 41d. And a frame member 41c that supports both the support member 41d and the cam device 42.
[0051]
The support member 41d spreads in the width direction of the intermediate transfer belt, and is bent at the center portion C of the plate-like member 41e and the plate-like member 41e having elasticity for placing the placement portion 40d of the transfer unit 40 on both ends A and B. And a rising portion 41f having rigidity.
[0052]
The cam device 42 includes a cam 42a that moves up and down the plate-like member 41e connected to the rising portion 41f having the rigidity of the support member 41d by rotating, a drive member 42b that rotates the cam 42a by performing a linear motion, and an arrow D. A handle 42c that linearly moves the drive member 42b by manually rotating in the direction is provided.
[0053]
By placing the transfer unit 40 with the secondary transfer roll attached on the transfer drawer 41 and attaching the drawer unit to the image forming apparatus, the handle 42c is manually rotated in the direction opposite to the arrow D direction. The transfer unit 40 is pressed against the photosensitive drum by rotating the cam 42a and raising the support member 41d (position in FIG. 9). Then, when pulling out the drawer unit from the image forming apparatus, the cam 42a is rotated by manually rotating the handle 42c in the direction opposite to the arrow D direction, and the support member 41d is lowered.
[0054]
As described above, the support member 41d has the central portion C having rigidity and both ends A and B having elasticity, and the central portion C having rigidity receives the lifting force from the cam device 42 and has elasticity at the same time. Since both ends A and B press the transfer unit 40 and play two roles, the structure of the transfer drawer can be simplified.
[0055]
【The invention's effect】
As described above, according to the image forming apparatus of the present invention, the transfer unit is configured by the endless belt such as the sheet conveying belt or the intermediate transfer belt and the transfer roll, and the four units for moving the transfer unit up and down are mounted. Since the mounting portion is provided, it is possible to perform front-rear and left-right positioning by placing the mounting portion on the transfer drawer, and a transfer drawer cam device having a support member and a cam device for raising and lowering the support member. The transfer unit can be moved up and down, and the endless belt can be pressed against a plurality of photosensitive drums by an elastic support member that supports the mounting portion, so that the vertical positioning can be performed, thereby simplifying the structure of the entire belt module. Further, it can be easily incorporated into the image forming apparatus, and the positioning accuracy can be improved.
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram illustrating an image forming apparatus according to a first embodiment.
FIG. 2 is a perspective view showing a drawer unit of the present embodiment.
FIG. 3 is a diagram illustrating a transfer unit of the present embodiment.
FIG. 4 is a diagram showing a transfer drawer of the present embodiment.
FIG. 5 is a view showing a part of a support member and a cam device.
FIG. 6 is a schematic configuration diagram illustrating an image forming apparatus according to a second embodiment.
FIG. 7 is a perspective view illustrating a transfer unit according to a second embodiment.
FIG. 8 is a front view showing the periphery of a transfer drawer according to the second embodiment.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Photoconductor 2 Charger 3 Exposure device 4 Developing device 5 Cleaning device 6 Transfer roll 7,22 Drive roll 8,23 Followed roll 9 Paper conveyance belt 11,11Y, 11M, 11C, 11K Photosensitive drum 12,12Y, 12M, 12C, 12K charging device 13, 13Y, 13M, 13C, 13K exposure device 14, 14Y, 14M, 14C, 14K developing device 16, 16Y, 16M, 16C, 16K cleaning member 21 intermediate transfer belt 24 tension roll 25 opposing roll 27, 27Y, 27M, 27C, 27K Primary transfer roll 28 Secondary transfer roll 30 Fixing device 31 Heating roll 32 Pressure roll 33 Paper tray 34 Chute 35 Registration roll 36 Transport belt 37 Paper guide member 38 Belt cleaning device 40 Transfer unit 40a Shuff 40b Leg 40c Position regulating member 40d Placement portion 40e Spherical surface portion 41 Transfer drawer 41a Positioning cutout portion 41b Pin 41c Frame member 41d Support member 41e Plate member 41f Rising portion 41g Long hole 41h Screw 42 Cam device 42a Cam 42b Drive member 42c handle

Claims (3)

A plurality of photoconductor drums arranged to form a toner image;
An endless belt that moves via each position in contact with each of the plurality of photosensitive drums and receives a transfer of a toner image formed on the plurality of photosensitive drums directly or on a recording medium carried thereon; and A transfer roll for transferring a toner image formed on the plurality of photosensitive drums facing each of the plurality of photosensitive drums across the endless belt to the endless belt or to a recording medium carried by the endless belt. A transfer unit having
A transfer drawer that moves the endless belt between a position contacting the plurality of photosensitive drums and a position separating the endless belt by raising and lowering the transfer unit, and finally records a toner image on the endless belt In an image forming apparatus for forming an image by transferring and fixing on a medium,
The transfer unit has four placement portions for placing the transfer unit on the transfer drawer,
The transcription drawer is
A pair of supporting members extending along the width direction of the endless belt, each supporting member sharing the four mounting portions of the transfer unit two by two, and each supporting member is the mounting portion A support member having a plate-like portion that supports each one at both ends, a rising portion that rises by bending the central portion of the plate-like portion, and a cam device that is connected to the rising portion and raises and lowers the support member And the support member absorbs vibration of the transfer unit by pressing the transfer unit against the photosensitive drum while both ends are bent when the support member is raised by the cam device. The transfer unit, wherein the endless belt is an intermediate transfer belt that directly transfers a toner image formed on the plurality of photosensitive drums, and transfers the toner image on the intermediate transfer belt onto a recording medium. The image forming apparatus according to claim 1, further comprising a secondary transfer roll that is detachably attached to the transfer unit and that moves up and down integrally with the transfer unit in a state of being attached to the transfer unit. A frame for fixing the plurality of photosensitive drums;
Each of the transfer unit and the frame has four position restricting members that restrict contact positions of the belt and the plurality of photosensitive drums that come into contact with the transfer unit and the frame. there, the one spherical portion of the position regulating member in contact with each other and the other by having a flat portion, of claim 1, wherein each four position regulating member which is a shall be point contact Image forming apparatus.

Images