JP4432364B2 - Image forming apparatus - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an image forming apparatus such as a copying machine or a printer, and more particularly to improvement of an image forming apparatus that transfers images on a plurality of image carriers onto a belt member or a recording material on the belt member.
[0002]
[Prior art]
Conventionally, as an example of this type of image forming apparatus, for example, a so-called tandem color image forming apparatus adopting an electrophotographic method, each color component (for example, yellow (Y), magenta (M), cyan (C), A plurality of image bearing members such as a photosensitive drum for forming a black (K) toner image are arranged and temporarily transferred to the same location on the intermediate transfer member by a primary transfer device (primary transfer). After that, the multiple toner images are collectively transferred (secondary transfer) to a recording material by a secondary transfer device, and then the toner remaining on the intermediate transfer member is removed by a cleaning device.
As this type of intermediate transfer member, a belt-like intermediate transfer member is frequently used because of its structural advantages such as high layout flexibility and small footprint in the apparatus, and the advantages of adapting to various recording materials. Has been.
[0003]
By the way, in this type of tandem color image forming apparatus, for example, in an image forming apparatus configured to selectively execute a single color mode and a plurality of color modes, the image forming apparatus is used for image formation when the single color mode is executed. Since the unexposed photosensitive drum and the intermediate transfer belt are in contact with each other, the following problems occur.
For example, when the photosensitive drum that is not used for image formation continues to contact the intermediate transfer belt, the intermediate transfer belt continues to be rubbed and the life of the photosensitive drum is likely to be shortened. If the developer remaining on the photosensitive drum continues to contact or approach the intermediate transfer belt, the developer remaining on the photosensitive drum adheres to the surface of the intermediate transfer belt, and the developer is removed. There was also a risk of wasted consumption.
Therefore, in order to solve the above problem, for example, when the single color mode is selected, an area corresponding to the photosensitive drum to be used is left in the intermediate transfer belt, and the intermediate transfer belt portion corresponding to the unused photosensitive drum is retracted. An image forming apparatus in which an unused photosensitive drum and an intermediate transfer belt are arranged in a non-contact manner has been proposed (see Patent Document 1 and Patent Document 2).
[0004]
[Patent Document 1]
JP 2001-242680 A (column of embodiment of the invention, FIG. 2)
[Patent Document 2]
JP 2000-181184 A (column of embodiment of the invention, FIG. 6)
[Patent Document 3]
JP 2002-148899 A (Example column)
[0005]
[Problems to be solved by the invention]
However, in these proposed image forming apparatuses, since the unused photosensitive drum and the intermediate transfer belt are arranged in a non-contact manner, belt deflection, waviness, curling, and the like during running of the intermediate transfer belt, There is a possibility of contact with the retracted roll and other components, and image defects due to wear of the belt and parts and unnecessary charging may occur.
In order to prevent such image defects, it is necessary to reliably maintain the distance between the retracted roll and other components and the intermediate transfer belt, and it is necessary to increase the retracted amount. May lead to
Such a technical problem is not limited to the intermediate transfer type image forming apparatus, and similarly occurs in an image forming apparatus using a recording material conveying belt for conveying a recording material.
The present invention is intended to solve the above technical problems, and has an image forming apparatus that selects a single color mode or a plurality of color modes with a simple configuration, less component consumption, and no image defects. A device is provided.
[0006]
[Means for Solving the Problems]
  That is, according to the present invention, as shown in FIGS. 1 (a) and 1 (b), a plurality of image carriers 1 (specifically 1a to 1d) for forming and supporting the respective color component images and the image carriers 1 are applied. An endless belt member 2 that is circulated and conveyed in contact with the plurality of image carriers 1, and an image on the image carrier 1 on the belt member 2 or a recording material held on the belt member 2 is provided. The transfer member 3 (specifically 3a to 3d) for transferring the image and a plurality of image forming modes are selectively switched, and all or a part of the image carrier 1 is used according to the selected image forming mode. When the image forming mode selecting means 4 for performing image forming processing and the image forming mode using a part of the image carrier 1 are selected, the contact state between the image carrier 1 to be used and the belt member 2 is maintained. In order to bring the non-use image carrier 1 and the belt member 2 into a non-contact state, the image carrier 1 And a retraction mechanism 5 for retracting the tension trajectory of the belt member 2 partially against the belt member 2, the image bearing member 1 side is formed bent in the opposite direction at both ends thereofReturn deformableAn image carrier having a bent portion 2a, the bent portion 2a being set so that both ends of the transfer member 3 are positioned in the region of the bent portion 2a, and being used when an image forming mode is selected. 1 andSaidBetween the transfer member 3It extends along the shape of the transfer member 3 against which the belt member 2 is pressed.It is characterized by being.
  Reference numeral 7 denotes a tension roll that stretches the belt member 2, and reference numeral 8 denotes a tension roll that functions as one of the tension rolls and applies tension to the belt member 2.
[0007]
In such technical means, the image carrier 1 may be appropriately selected as a photoconductor, a dielectric, etc. as long as it can carry an image, and the form thereof is either a drum shape or a belt shape. Also good. The belt member 2 includes an intermediate transfer member and a recording material transport member.
In this case, the belt member 2 is retracted when the image forming mode is selected, and the image carrier 1 is retracted from the viewpoint of the positional accuracy before and after the image carrier 1 is retracted and the complexity of the retracting mechanism. Not considered.
[0008]
  Further, the belt member 2 in this embodiment is preferably a rigid belt, and may be a metal belt. The belt member 2 may be an elastic belt as long as the belt member 2 has the bent portions 2a at both ends, which is a feature of the present case.
  Further, the bent portions 2a at both ends of the belt member 2 are located beyond the maximum image forming area, and both ends of the transfer member 3 are positioned in the bent portion 2a. LikeIn the present invention, a mode in which both ends of the transfer member 3 are positioned in the region of the bent portion 2a is employed.In this case, since the bent portion 2a is outside the image forming area, or even if the belt member 2 comes into contact with the transfer member 3 retracted during traveling, the belt member 2 contacts only with the bent portion 2a. A good image can be formed without the possibility of unnecessary contact charging in the image forming area. The bent portions 2a at both ends of the belt member 2 may be linear or curved as long as the shape extends in the direction opposite to the image carrier 1 side.
[0009]
In this aspect, the retract mechanism 5 is configured to be controlled by the control device 9 with the information from the image forming mode selection means 4 being below.
The retract mechanism 5 includes a retract member 6 that can be retracted with respect to the belt member 2, and is configured such that when the retract member 6 is retracted, the transfer member 3 to be retracted is also retracted. It is more preferable to reduce the size of the retract mechanism 5 or the device.
Furthermore, although the retract mechanism 5 is comprised by the single or several retract member 6, the aspect comprised by the single retract member 6 is preferable from a viewpoint of size reduction of an apparatus.
Since the retract member 6 in this embodiment is normally in contact with the belt member 2, it is preferable that the retract member 6 is made of a conductive member and grounded in order to prevent contact charging with the belt member 2.
In order to prevent contact charging between the belt member 2 and the transfer member 3 after being retracted, the retract mechanism 5 in this aspect preferably retracts the retracting member 6 as well as the retracting member 6. Although it is preferable to make the retracting amount of the transfer member 3 larger than the retracting amount, the present invention is not limited to this, and the tension of the belt member 2 retracted by retracting the stretching locus of the belt member 2 by retracting the retracting member 6. Accordingly, the belt member 2 and the image carrier 1 may be separated by pressing the transfer member 3.
[0010]
  In addition, the width of the belt member 2 in this aspect isIt is wider than the width of the transfer member 3,From the width of the retracting member 6NarrowThen, even if the retract member 6 and the transfer member 3 come into contact with the belt member 2, it does not come into contact with the image forming region, and contact charging and sliding wear can be prevented.
  Furthermore, the transfer member 3 in this embodiment may be in the form of a roll or other shape (for example, corotron).
  In particular, in this aspect, an image forming apparatus using the belt member 2 as an intermediate transfer member is suitable.
[0011]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be described in detail based on embodiments shown in the accompanying drawings.
Embodiment 1
FIG. 2 is an explanatory diagram showing Embodiment 1 of a tandem color image forming apparatus to which the present invention is applied.
In this embodiment, the tandem color image forming apparatus forms toner images of four color components (Y (yellow), M (magenta), C (cyan), and K (black)) in this embodiment. Four image forming units 20 (specifically 20a to 20d) are arranged in parallel, and each color component toner image formed by the image forming unit 20 is transferred onto the intermediate transfer belt 32 by a primary transfer unit 22 (specifically, 22a to 22d) are sequentially transferred first, and each color component toner image on the intermediate transfer belt 32 is secondarily transferred to a recording sheet at a secondary transfer portion, and this recording sheet is guided to a fixing device 38. It is.
[0012]
Each image forming unit 20 includes a photosensitive drum 21 (specifically, 21a to 21d), and around the photosensitive drum 21, a charging roll 23 (specifically, charging the photosensitive drum 21). 23a to 23d), a laser exposure device (not shown) for writing an electrostatic latent image on the photosensitive drum 21, and each color component toner is accommodated to visualize the electrostatic latent image on the photosensitive drum 21. An electrophotographic device such as a developing device (not shown), a primary transfer device 22 for transferring each color component toner image on the photosensitive drum 21 to the intermediate transfer belt 32, and a cleaner for removing residual toner on the photosensitive drum 21, etc. It is arranged.
[0013]
Further, the intermediate transfer belt 32 is stretched and circulated on a plurality of stretching rolls 25 to 31. For example, the stretching roll 31 is used as a driving roll and the other stretching rolls 25 to 30 are driven. Further, the tension roll 27 is made to function as a tension roll that applies tension to the intermediate transfer belt 32.
Reference numeral 24 denotes a retract roll for retracting the trajectory of the intermediate transfer belt 32, and changes the trajectory of the intermediate transfer belt 32 by moving back and forth between a position contacting the intermediate transfer belt 32 and a position separating from the position. It is configured to be able to.
[0014]
In this embodiment, a portion of the intermediate transfer belt 32 that faces the stretching roll 29 is set as a secondary transfer portion, and the secondary transfer roll is provided on the surface of the secondary transfer portion of the intermediate transfer belt 32. A transfer bias is applied between the secondary transfer roll 33 and a tension roll 29 (functioning as a backup roll) facing the secondary transfer roll 33.
[0015]
Also, around the secondary transfer roll 33, a registration roll 34 that regulates the recording sheet, an upstream conveyance guide 35, a downstream conveyance guide 36, a conveyance roll 37, and a fixing device 38 are disposed.
Reference numerals 39 and 40 are blades and scrapers for removing residual toner on the intermediate transfer belt 32, reference numeral 41 is a sensor for detecting the movement of the intermediate transfer belt 32, and reference numeral 42 is a meander of the intermediate transfer belt 32. Reference numeral 43 denotes an edge sensor for detecting a home position sensor.
[0016]
In the present embodiment, as shown in FIG. 3, the retract mechanism includes a retract roll 24 that changes the stretching locus of the intermediate transfer belt 32, a support mechanism 46 that supports the retract roll 24, and a drive to the support mechanism 46. It is comprised with the driving force transmission mechanism 70 which transmits force.
The support mechanism 46 supports the retract roll 24 and is disposed at one end of the retract arm 47 that rotates about the reference numeral 47 a and a direction in which the retract roll 24 is pressed against the intermediate transfer belt 32. And a stopper 49 that suppresses the rotation of the retract arm 47.
[0017]
Further, as shown in FIGS. 4 to 7, the driving force transmission mechanism 70 includes a large number of gears, shafts, and the like that transmit the driving force from the driving motor 71 to the retract arm 47.
As shown in the drawing, a gear 72 is mounted on the drive motor 71, and another gear 74 is mounted on the shaft of a gear 73 that meshes with the gear 72. At a position facing the gear 74, there is a worm gear 75 mounted on the shaft 76 and meshes with the gear 74. Further, eccentric cams 77 are provided at both ends of the shaft 76, and protrusions 78 are provided on the outer surface of the eccentric cam 77. The end of the retract arm 47 is in pressure contact with the circumferential surface of the eccentric cam 77.
Accordingly, the shaft 76 is rotated by the rotation of the drive motor 71 and the eccentric cam 77 is rotated, so that the retract arm 47 is rotated and the retract roll 24 is retracted from the intermediate transfer belt 32.
Reference numeral 79 denotes a rotating piece fixed to the shaft 76 so as to monitor the rotation state of the shaft 76, and reference numeral 80 denotes a sensor for detecting the moving state of the rotating piece 79.
[0018]
In the present embodiment, the protruding portion 78 of the eccentric cam 77 further engages with the groove 64a of the gantry 64 on which the primary transfer device 22 is supported, and is configured to be slidable therein. The gantry 64 is provided with an elongated hole 64b along the traveling direction of the intermediate transfer belt 32. A sliding piece 66 mounted on the fixed piece 65 is fitted into the elongated hole 64b, and the gantry 64 moves in one direction. It adopts a configuration that makes it possible.
[0019]
In this embodiment, as shown in FIG. 3, three primary transfer units 22 (specifically 22a to 22c) are installed on the same mount 64, and the other primary transfer unit 22 (specifically 22d). It has a different form.
Further, the primary transfer device 22 includes a primary transfer roll 62 (specifically 62a to 62d) and an elastic member such as a spring engaged with shafts at both ends of the primary transfer roll 62. The primary transfer roll 62 is urged upward in the figure (photosensitive drum 21 side).
Furthermore, the movable pieces 63 (specifically 63a to 63c) are fitted to the shafts at both ends of the three primary transfer rolls 62 (specifically 62a to 62c). The upward movement is suppressed. One end of the movable piece 63 is locked to the gantry 64, and is configured to rotate around the rotation axis by the movement of the gantry 64.
Therefore, the primary transfer unit 22 is configured as a mechanism that retracts in conjunction with the retracting of the retract roll 24.
[0020]
The intermediate transfer belt 32 in the present embodiment is a rigid belt mainly composed of a polyimide resin, containing oxidized carbon black in the polyimide resin, and having a surface roughness (Ra) of about 1. 5 μm or less and a belt thickness of 100 μm are used. At both ends, there are bent portions 32a (see FIG. 10B) that are bent in a substantially straight line in the opposite direction to the photosensitive drum 21 side. A polyimide resin belt is produced by supplying and spreading a polyamic acid solution on the inner surface of a cylindrical mold to form a coating, curing it until it can be held as a belt by heating, and then removing the belt from the mold to make a metal cylinder. It replaces with an outer surface and is implemented through the process of performing an imide conversion reaction by heating (for example, refer patent document 3).
[0021]
Next, the operation of the image forming apparatus according to the present embodiment will be described.
Now, when the image selection in the full color (four color) mode is performed, the image forming apparatus according to the present embodiment, as shown in FIG. 2, the photosensitive drum 21 disposed in the image forming unit 20 of each color. (Specifically, 21a to 21d) are in contact with the intermediate transfer belt 32.
At this time, predetermined toner images of the respective colors are created on the photosensitive drum 21, and the toner images on the photosensitive drum 21 are stretched by applying a predetermined bias voltage to the primary transfer unit 22. It is electrostatically transferred onto an intermediate transfer belt 32 that is circulated and conveyed using the roll 31 as a drive roll.
The toner image that has been multiplex-transferred onto the intermediate transfer belt 32 is subjected to secondary transfer onto the recording sheet that has been transported through the recording sheet transport path 45 by a secondary transfer device including a secondary transfer roll 33 and a backup roll 29. The toner image transferred onto the recording sheet is then fixed by the fixing device 38.
[0022]
Here, when the single color mode (specifically, black) is selected, the retract roll 24 is operated, and as shown in FIG. 8, the intermediate transfer belt 32 is moved to the photosensitive drums 21a to 21c and the primary transfer units 22a to 22c. (The locus of the intermediate transfer belt 32 shown by the solid line in FIG. 8 is taken). Note that the phantom lines in the figure indicate the locus of the intermediate transfer belt 32 in the full color mode.
The intermediate transfer belt 32 that has been switched to the monochrome mode has a short trajectory between the drive roll 31 and the tension roll 25, so that a bend occurs, but this bend is absorbed by the tension roll 27.
[0023]
The toner image formed on the black photosensitive drum 21d is transferred onto the intermediate transfer belt 32 by the primary transfer unit 22d, and is transferred onto the recording sheet transported through the recording sheet transport path 45 by the secondary transfer device. The toner image that has been secondarily transferred to the recording sheet and then transferred onto the recording sheet is then fixed by a fixing device 38.
[0024]
Furthermore, paying attention to the retract mechanism which is a characteristic point of the present embodiment, the operation will be described in detail with reference to FIGS.
When the selection mode is switched from the color mode to the single color mode (specifically, black), a signal is transmitted from the control device (not shown) to the drive motor 71 to operate the retract mechanism, and the retract mechanism starts to operate.
When the drive motor 71 starts to rotate, the shaft 76 on which the worm gear 75 is mounted rotates via the gears 72 to 74, and thus the eccentric cams 77 at both ends of the shaft 76 rotate. Therefore, the retract arm 47 in pressure contact with the eccentric cam 77 lifts its end in the direction of the intermediate transfer belt 32 and rotates via the central shaft 47a. Therefore, the retract roll 24 moves in the direction opposite to the photosensitive drum 21 side, and the intermediate transfer belt 32 is separated from the photosensitive drum 21.
[0025]
On the other hand, since the protrusion 78 provided on the eccentric cam 77 moves the groove 64a of the gantry 64 to the left side shown in FIG. 5, the plurality of projections 67 provided on the gantry 64 allow the movable piece 63 (specifically, 63a to 63c) rotate. As a result, the primary transfer roll (specifically 62a to 62c) moves in a direction away from the intermediate transfer belt 32.
The drive motor 71 is stopped by a passing signal of the sensor 80 by the rotating piece 79.
[0026]
FIGS. 9A to 9C are explanatory views schematically showing the amount of movement of the retract arm 47 and the amount of movement of the movable piece 63 performed by the rotation of the eccentric cam 77.
If the eccentric cam 77 is rotated 180 °, the amount of movement α of the rotating shaft of the eccentric cam 77 (specifically, the amount of movement of the retract arm 47 by the eccentric cam 77) and the amount of movement β of the protrusion 78 ( Specifically, the relationship with the movement amount of the movable piece 63 is expressed as shown in FIG.
As shown in FIG. 9B, the movement amount α lowers the retract roll 47 by γ (specifically, retracts in the direction opposite to the photosensitive drum 21). Further, as shown in FIG. 9C, the moving amount β of the movable piece 63 lowers the primary transfer roll 62 by δ.
In this embodiment, since γ <δ, the retract amount of the primary transfer device 22 (specifically, the primary transfer roll 62) is larger than the retract amount of the retract roll 24. ing.
[0027]
Here, the intermediate transfer belt 32, which is another feature of the present embodiment, will be described.
10A and 10B are cross-sectional views showing the relationship between the photosensitive drum 21, the intermediate transfer belt 32, and the primary transfer unit 22 at the primary transfer site, and FIG. 10A shows the selected image formation. FIG. 10B shows a state in the image forming unit that is not selected.
In FIG. 10A, the intermediate transfer belt 32 is in close contact with the photosensitive drum 21 and the primary transfer device 22 (specifically, the primary transfer roll), and the bent portion at the end of the intermediate transfer belt 32 is straight. In FIG. 10B, the intermediate transfer belt 32 is separated from the photosensitive drum 21 and the primary transfer device 22 (specifically, the primary transfer roll). The shape of the portion 32a also appears.
[0028]
For this reason, a sufficient nip area is formed in a portion requiring primary transfer, and unnecessary contact charging is prevented because the portion not requiring primary transfer does not contact the photosensitive drum 21 and the primary transfer device 22. Image defects can be prevented.
Further, since the intermediate transfer belt 32 has the bent portions 32a at both ends, the intermediate transfer belt 32 has a shape that increases the rigidity of the intermediate transfer belt 32 (a shape that increases the surface rigidity), and the swell and flutter during traveling of the intermediate transfer belt 32 are reduced. . Further, since the end portion of the primary transfer device 22 is positioned at the bent portion 32a, even if the intermediate transfer belt 32 contacts the primary transfer device 22 during traveling, no contact charge is generated.
Needless to say, since the bent portion 32a is located beyond the effective image area, there is no particular problem in image formation.
[0029]
  As described above, when forming an image in the single color mode, the three color photosensitive drums 21 are retracted from the intermediate transfer belt 32, and the means related to image formation such as a charger and a cleaning device are also stopped or frequencyd. Therefore, unnecessary wear and tear can be prevented, and the service life can be extended.
  Further, since the intermediate transfer belt 32 is provided with the bent portion 32a, undulation and fluttering during running of the intermediate transfer belt 32 can be reduced, and the influence on image defects such as contact charging can be prevented. . Even if the primary transfer device 22 and the intermediate transfer belt 32 are in contact with each other, both ends of the primary transfer device 22 are in contact with each other at the bent portion 32a of the intermediate transfer belt 32, so there is no unnecessary contact charging and image formation. Since it does not affect the process, it is possible to prevent image defects.
  Further, it is not necessary to retract the retracted parts more than necessary, and it is not necessary to provide a part such as a stopper for preventing the intermediate transfer belt 32 from coming into contact with the retracted parts.
[0030]
In the present embodiment, the black photosensitive drum 21d is shown to have the same size as the other photosensitive drums 21 (specifically, 21a to 21c). It is also possible to increase the speed of the intermediate transfer belt 32 and improve the image forming processing speed when the monochromatic mode is selected.
In the present embodiment, the retracting direction of the retract roll 24 is the rotating direction. However, the retracting direction of the retract roll 24 may be a rectilinear direction. If so, there is no problem.
Further, in the present embodiment, the primary transfer unit 22 is also retracted in a mechanically linked manner with the retract roll 24. For example, when the selection mode is switched, the primary transfer unit 22 is individually set based on the signal. Even if it is the structure to evacuate, it does not change that it is the structure to evacuate in conjunction.
[0031]
Embodiment 2
  FIG. 11 is an explanatory view showing Embodiment 2 of a tandem color image forming apparatus to which the present invention is applied.
  In this figure, the present embodiment is configured in substantially the same manner as the image forming apparatus in the first embodiment, but the number of image forming units 20 is different from that in the first embodiment. The forming unit 20 e is disposed at an adjacent position on the downstream side of the drive roll 31. The second retract roll50Is disposed between the image forming units 20e and 20a. In addition, the same code | symbol is attached | subjected to the component similar to Embodiment 1, and the detailed description is abbreviate | omitted.
[0032]
  The operation of the image forming apparatus in the present embodiment will be described with reference to FIG.
  When the selection is switched from the transparent color + full color mode to the transparent color + black mode, the retract mechanism operates, and the primary transfer device 22 (specifically, 22a to 22c) retracts in conjunction with the retracting of the retract roll 24. As a result, the intermediate transfer belt 32 is separated from the photosensitive drums 21a to 21c as shown by a locus indicated by a solid line. Note that the phantom lines in the figure indicate the locus of the intermediate transfer belt 32 when the transparent color and full color mode are selected.
  In the present embodiment, unlike retracting the retract roll 24, the second retract roll50Shows an example that does not work, but this second retract roll50The intermediate transfer belt 32 can also be separated from the transparent photosensitive drum 21e.
[0033]
As described above, when forming an image in the single color + transparent color mode, the three color photosensitive drums 21 are retracted from the intermediate transfer belt 32 and the units related to image formation such as a charger and a cleaning device are also stopped. Or, since the frequency is reduced, unnecessary consumption of them can be prevented, and the life can be extended.
Further, since the intermediate transfer belt 32 is provided with a bent portion 32a (see FIG. 10B), undulation and fluttering during running of the intermediate transfer belt 32 can be reduced, and the influence on image defects such as contact charging can be reduced. It is also possible to prevent this.
Further, it is not necessary to retract the retracted parts more than necessary, and it is not necessary to provide a part such as a stopper for preventing the intermediate transfer belt 32 from coming into contact with the retracted parts.
[0034]
Embodiment 3
FIG. 13 is an explanatory view showing Embodiment 3 of a tandem color image forming apparatus to which the present invention is applied.
In this figure, the present embodiment is configured in substantially the same manner as the image forming apparatus in the first embodiment, but the retracted primary transfer units 22a to 22c are not linked to the retract mechanism in the first embodiment. Different. In addition, the same code | symbol is attached | subjected to the component similar to Embodiment 1, and the detailed description is abbreviate | omitted.
[0035]
The operation of the image forming apparatus according to the present embodiment will be described with reference to FIG.
When the selection is switched from the full color mode to the single color mode, the retract mechanism is activated, and the locus of the intermediate transfer belt 32 is changed in a direction away from the photosensitive drums 21a to 21c as indicated by a solid line in the figure. Note that the phantom lines in the figure indicate the locus of the intermediate transfer belt 32 when full color is selected.
In other words, the intermediate transfer belt 32 that has maintained the locus like a virtual line by the retract roll 24 is changed to a locus that is stretched by the tension roll 25 and the drive roll 31.
The change in the locus of the intermediate transfer belt 32 causes the primary transfer units 22a to 22c to be separated from the respective photosensitive drums 21a to 21c as they are.
At this time, the elastic force of an elastic body (specifically, a spring or the like) that urges the primary transfer units 22a to 22c toward the intermediate transfer belt 32 is attached to such a degree that it can follow the change in the locus of the intermediate transfer belt 32. Since it is composed of power, the primary transfer unit 22 is in contact with the intermediate transfer belt 32 both when the full color mode and the single color mode are selected.
[0036]
In this embodiment, the primary transfer device 22 and the intermediate transfer belt 32 are always in contact with each other. However, the primary transfer device 22 and the intermediate transfer belt 32 are not in contact with the unnecessary photosensitive drum 21. Since this contact occurs at the bent portion 32a (see FIG. 10B) of the intermediate transfer belt 32, the image forming area of the intermediate transfer belt 32 and the primary transfer device 22 do not come into contact with each other. Since there is no contact charging and it does not affect the image forming process, it is possible to prevent image defects.
[0037]
Embodiment 4
FIG. 15 is an explanatory view showing Embodiment 4 of a tandem color image forming apparatus to which the present invention is applied.
In this figure, the present embodiment is configured in substantially the same manner as the image forming apparatus of the first embodiment, but an image is directly formed on a recording sheet such as paper by an image forming unit 20 (specifically, 20a to 20d). Unlike the first embodiment, the sheet transfer belt 51 is wound around a number of stretching rolls instead of the intermediate transfer belt in that the transfer is performed.
Further, an adsorption roll 52 for applying a charge for adsorbing the recording sheet to the sheet conveyance belt 51 is disposed at a position facing the drive roll 31 via the sheet conveyance belt 51, and the recording sheet of the adsorption roll 52 is arranged. A registration roll 53 for controlling the orientation of the recording sheet is disposed on the upstream side of the conveyance route, and a fixing device 54 is disposed on the downstream side of the recording sheet conveyance route of the black photosensitive drum 21d. In addition, the same code | symbol is attached | subjected to the component similar to Embodiment 1, and the detailed description is abbreviate | omitted.
[0038]
The operation of the image forming apparatus in the present embodiment will be described with reference to FIG.
In the drawing, the orientation of the recording sheet is controlled by the registration roll 53 and then adsorbed onto the sheet conveying belt 51 via the adsorption roll 52. Then, the toner images of the respective colors are transferred onto the recording sheet along the locus indicated by the imaginary line, and the toner images on the recording sheet are fixed by the fixing device 54.
Here, when the selection is switched from the full color mode to the single color mode, the retract roll 24 is retracted, and the primary transfer device 22 (specifically, 22a to 22c) interlocked with the retract roll 24 is retracted, and the virtual of FIG. The sheet conveying belt 51 changes its locus from a line to a solid line. For this reason, the three photosensitive drums 21 a to 21 c are separated from the sheet conveying belt 51.
[0039]
As described above, when forming an image in the single color mode, the three color photosensitive drums 21 are retracted from the sheet conveying belt 51, and the units related to image formation such as a charger and a cleaning device are also stopped or frequencyd. Therefore, unnecessary wear and tear can be prevented, and the service life can be extended.
Further, since the sheet conveying belt 51 has a bent portion, undulation and fluttering during traveling of the sheet conveying belt 51 can be reduced, and the influence on image defects such as contact charging can be prevented.
Further, it is not necessary to retract the retracted parts more than necessary, and it is not necessary to provide a part such as a stopper for preventing the sheet conveying belt 51 from coming into contact with the retracted parts.
[0040]
【The invention's effect】
  As described above, according to the present invention, when an image forming mode that uses a part of an image carrier is selected, the contact state between the image carrier to be used and the belt member is maintained, and an unused image carrier is used. In order to keep the body and the belt member in a non-contact state, the tension locus of the belt member with respect to the image carrier is partially retracted, so that both the monochrome mode image and the multiple color mode image are supported, The operation frequency of the image carrier unnecessary for image formation can be reduced, and the life of the image carrier can be increased accordingly.
  In particular, in the present invention, both ends of the belt member are bent in the opposite direction to the image carrier side.Return deformableSince it has a bent part and both ends of the transfer member are positioned in the area of the bent part, the surface rigidity of the belt member is improved, so that the swell and fluttering during running can be reduced, and further the transfer Since the contact portion with the member becomes the bent portion, it is also possible to prevent the influence on image defects such as contact charging.
  Further, it is not necessary to retract the retracted parts more than necessary, and it is not necessary to provide a part such as a stopper for preventing the belt member from contacting the retracted part.
  Furthermore, the bent portion is between the image carrier used and the transfer member.Along the shape of the transfer member that presses the belt memberExtendIs a thingTherefore, the contact state between the image carrier and the belt member can be maintained well between the used image carrier and the transfer member.
[Brief description of the drawings]
FIGS. 1A and 1B are explanatory views showing an outline of an image forming apparatus according to the present invention.
FIG. 2 is an explanatory diagram showing Embodiment 1 of a tandem type image forming apparatus to which the present invention is applied.
FIG. 3 is an explanatory diagram showing a retract mechanism in the first embodiment.
FIG. 4 is a first explanatory view showing a main part of a retract mechanism.
FIG. 5 is a second explanatory view showing a main part of the retract mechanism.
FIG. 6 is a third explanatory view showing the main part of the retract mechanism.
FIG. 7 is a fourth explanatory view showing the main part of the retract mechanism.
FIG. 8 is an explanatory diagram showing an operation in the first embodiment.
FIGS. 9A, 9B, and 9C are explanatory diagrams showing a retraction amount in the first embodiment. FIGS.
FIGS. 10A and 10B are explanatory views showing a cross section around the intermediate transfer belt in the first embodiment. FIGS.
FIG. 11 is an explanatory diagram showing Embodiment 2 of a tandem type image forming apparatus to which the present invention is applied.
FIG. 12 is an explanatory diagram showing an operation in the second embodiment.
FIG. 13 is an explanatory view showing Embodiment 3 of a tandem type image forming apparatus to which the present invention is applied.
FIG. 14 is an explanatory diagram showing the operation in the third embodiment.
FIG. 15 is an explanatory view showing Embodiment 4 of a tandem type image forming apparatus to which the present invention is applied;
FIG. 16 is an explanatory diagram showing an operation in the fourth embodiment.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 (1a-1d) ... Image carrier, 2 ... Belt member, 2a ... Bending part, 3 (3a-3d) ... Transfer member, 4 ... Image formation mode selection means, 5 ... Retract mechanism, 6 ... Retract member, 7 ... tension roll, 8 ... tension roll, 9 ... control device

Claims (9)

A plurality of image carriers that form and carry each color component image, an endless belt member that is circulated and conveyed in contact with the image carrier, and a belt member or a belt provided for each of the plurality of image carriers. A transfer member that transfers an image on the image carrier to a recording material held on the member and a plurality of image forming modes are selectively switched, and all or one of the image carriers is selected according to the selected image forming mode. When the image forming mode selection means for performing image forming processing using the image forming section and the image forming mode using a part of the image carrier, the contact state between the image carrier to be used and the belt member is maintained. A retract mechanism that partially retracts the tension locus of the belt member relative to the image carrier so as to bring the unused image carrier and the belt member into a non-contact state,
The belt member has a bendable portion which is bent back and deformed in opposite directions to the image carrier side at both ends, and the bend portion is formed in the region of the bend portion. it ends in which extend along the shape of the transfer member for pressing said belt member at between said transfer member and the image bearing member to be used at the time of image formation mode selection while being set to be positioned in An image forming apparatus. The image forming apparatus according to claim 1.
2. The image forming apparatus according to claim 1, wherein the bent portions at both end portions of the belt member are located at portions exceeding the maximum image forming region. The image forming apparatus according to claim 1.
The retraction mechanism includes a retract member that is retractable with respect to a belt member. The image forming apparatus according to claim 1.
An image forming apparatus, wherein the retract mechanism includes a retract member that is retractable with respect to the belt member, and an interlocking mechanism that retracts the transfer member in conjunction with the retracting operation of the retract member. The image forming apparatus according to claim 3.
The retraction mechanism comprises a single retraction member. The image forming apparatus according to claim 3.
The retract member is a conductive member and is grounded. The image forming apparatus according to claim 3.
An image forming apparatus, wherein the retracting amount of the transfer member is larger than the retracting amount of the retracting member. The image forming apparatus according to claim 1.
An image forming apparatus, wherein the width of the belt member is narrower than the width of the retracting member. The image forming apparatus according to claim 1.
The image forming apparatus, wherein the belt member is an intermediate transfer member.

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