JP4820737B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus such as a copying machine, a facsimile, and a printer.

  Conventionally, a plurality of image forming units as image forming units have been provided, and toner images formed on the respective image carriers are sequentially primary transferred onto an intermediate transfer belt as an endless belt, and then superimposed on the intermediate transfer belt. An image forming apparatus is known in which a toner image is secondarily transferred collectively onto a transfer material at a secondary transfer portion.

  Patent Document 1 discloses an image forming apparatus having a partial separation mode in which an intermediate transfer belt is separated from a photosensitive member other than a black photosensitive member, and a full separation mode in which the intermediate transfer belt is separated from all image carriers. Are listed.

JP 2003-186313 A

During image formation, the image carrier and the intermediate transfer belt are rotated at a constant speed. However, if there is a difference between the time required for the image carrier and the intermediate transfer belt to rise to the speed during image formation, The transfer belt may rub against the image carrier to cause fine scratches on the image carrier or the intermediate transfer belt. At the initial stage of use, even if such fine scratches occur, there is no effect on the image quality, etc., but over time, such fine scratches accumulate to form entire scratches, resulting in image defects and the tip of the cleaning blade. Will cause problems such as damage.
In particular, when a flywheel or the like is attached to the rotation shaft of the image carrier in order to suppress rotation unevenness, it takes a long time for the image carrier to rise to a predetermined speed due to inertial force. There is a tendency for the transfer belt to have a difference in time required to rise to the speed at the time of image formation.

  Therefore, when the intermediate transfer belt described in Patent Document 1 is in the all separation mode in which the intermediate transfer belt is separated from all the image carriers, the intermediate transfer belt and the image carrier are raised to a predetermined speed, and the image carrier and the intermediate transfer belt are It is also conceivable that the intermediate transfer belt is brought into contact with the image carrier at the time when the speed becomes constant. However, in the all separation mode of Patent Document 1, the tension of the intermediate transfer belt is weakened so that the belt does not wrinkle or bend in the all separation mode. For this reason, even if the driving roller is rotated to rotate the belt, the frictional force does not act between the driving roller and the belt, and the belt does not rotate.

  The present invention has been made in view of the above-described background, and an object of the present invention is to provide an image forming apparatus capable of rotationally driving an endless belt in a state where the endless belt is separated from all image carriers. Is to provide.

In order to achieve the above object, the invention of claim 1 includes an image carrier for carrying an electrostatic latent image, and latent image forming means for forming an electrostatic latent image on the image carrier, A plurality of image forming means having a developing means for developing the electrostatic latent image into a toner image, and sequentially facing the surface of each image carrier of the plurality of image forming means. An intermediate transfer belt whose surface moves endlessly, primary transfer means for primarily transferring a toner image on the image carrier onto the surface of the intermediate transfer belt, and a toner image transferred on the intermediate transfer belt in the image forming apparatus and a secondary transfer means for secondarily transferred on, and stretched the intermediate transfer belt, a plurality of stretching rollers for abutting the intermediate transfer belt to the image carrier And applying tension to the intermediate transfer belt by pressing the intermediate transfer belt A tension roller, a first swinging member for supporting a plurality of stretching rollers, leaving at least one image bearing member to separate the intermediate transfer belt from the other image bearing members, and one stretching roller , A second swing member for separating the intermediate transfer belt from at least one image carrier, a first eccentric cam for supporting and rotating the second swing member, and a second An eccentric cam, and the intermediate transfer belt is in contact with all the image carriers, and the primary transfer means primarily transfers the toner image on the image carrier onto the surface of the intermediate transfer belt and the secondary transfer. All contact mode in which the toner image transferred onto the intermediate transfer belt is secondarily transferred onto the transfer material, and a tension that allows the intermediate transfer belt to be rotationally driven, thereby applying the intermediate transfer belt to all the images. Separated from the body All apart drivable mode than said tension of the intermediate transfer belt at all apart drivable mode, and the total spaced low tension mode which is a state where the intermediate transfer belt at a lower tension is separated from all of the image bearing member that, Contact / separation means configured to be able to take, and the contact / separation means is configured to separate the intermediate transfer belt from the image carrier by separating the stretching roller from the image carrier, In addition, the distance between the tension roller and the image carrier in the fully separated driveable mode is configured to be shorter than the distance between the tension roller and the image carrier in the fully separated low tension mode. In the full contact mode, the second eccentric cam is separated from the second swinging member, and the first eccentric cam is in contact with the second swinging member, The second oscillating member is supported only by the first eccentric cam, and in the fully separated drive enable mode, the first eccentric cam is separated from the second oscillating member, and the second eccentric cam is The second rocking member is configured to support the second rocking member only by the second eccentric cam in contact with the second rocking member.
According to a second aspect of the present invention, in the image forming apparatus of the first aspect, the second eccentric cam is provided at a position farther from the fulcrum of the second oscillating member than the first eccentric cam. It is characterized by this.
According to a third aspect of the present invention, in the image forming apparatus according to the first or second aspect, the tension roller abuts on a front surface of the intermediate transfer belt, and extends from the front surface to the back surface of the intermediate transfer belt. It is characterized by applying a tension toward.
According to a fourth aspect of the present invention, in the image forming apparatus according to any one of the first to third aspects , the tension of the intermediate transfer belt in the fully-separable drive mode is 0.7 to 1 times the tension at the time of image formation. It is characterized by that.
According to a fifth aspect of the present invention, in the image forming apparatus according to any one of the first to fourth aspects, the contact / separation unit starts rotating the image carrier and the intermediate transfer belt until a predetermined speed is reached. During this period, a mode in which all separation is possible is taken.
According to a sixth aspect of the present invention, in the image forming apparatus according to any one of the first to fourth aspects, the contact / separation unit rotates the intermediate transfer belt in a rotation direction opposite to the rotation direction during image formation. This mode is characterized by taking a mode in which all separation is possible.
The invention of claim 7, said the claims in any of the image forming apparatus to claim 1 to 6, setting digits before SL on the first said swing fulcrum of the swing member in the second oscillating member To do.
The invention of claim 8, in any of the image forming apparatus according to claim 1 to 7, from the center of rotation of the front Symbol first eccentric cam the maximum distance L4 to the outer peripheral surface, and a shortest distance L5, the first (2) When the longest distance from the center of rotation of the eccentric cam to the outer peripheral surface is L6 and the shortest distance is L7, the relationship is L4>L6>L5> L7.
According to a ninth aspect of the present invention, there is provided an image carrier for carrying an electrostatic latent image, latent image forming means for forming an electrostatic latent image on the image carrier, and the electrostatic latent image. A plurality of image forming means having a developing means for developing and forming a toner image, and the surfaces of the plurality of image forming means are moved endlessly so as to face the surfaces of the respective image carriers. An image forming apparatus comprising: a transfer material conveyance belt that carries and conveys a transfer material; and a transfer unit that transfers a toner image on the image carrier to the surface of the transfer material carried on the transfer material conveyance belt A plurality of stretching rollers for stretching the transfer material conveyance belt and bringing the transfer material conveyance belt into contact with the image carrier, and pressing the transfer material conveyance belt to the intermediate transfer belt. Supports a tension roller for applying tension and a plurality of tension rollers, At least one image carrier is supported by a first swinging member for separating the transfer material transport belt from another image carrier, leaving at least one image carrier, and one tension roller. A second rocking member for separating the transfer material conveying belt; a first eccentric cam that supports and rotates the second rocking member; and a second eccentric cam; A full contact mode in which the belt abuts all image carriers, and the transfer means transfers the toner image on the image carrier onto the transfer material surface carried by the transfer material conveyance belt; and the transfer material conveyance belt Provides a tension that can be rotationally driven to separate the transfer material transport belt from all image carriers, and a tension lower than the tension of the transfer material transport belt in the fully separate drive enable mode. In the And a contact / separation means configured to be able to take a fully-separated low tension mode in which the drawing material conveyance belt is separated from all image carriers, and the contact roller is provided with the tension roller as the image carrier. The transfer material conveyance belt is configured to be separated from the image carrier by being separated from the body, and the distance between the tension roller and the image carrier in the all separation driveable mode is set to The second eccentric cam is separated from the second swinging member so as to be shorter than the separation distance between the tension roller and the image carrier in the separation low tension mode and in the full contact mode. The first eccentric cam is in contact with the second rocking member to support the second rocking member only by the first eccentric cam. One eccentric cam is the second swing The second eccentric cam is in contact with the second swinging member and is separated from the moving member, and is configured to support the second swinging member only by the second eccentric cam.

  According to the first to eighth aspects of the present invention, since the endless belt is separated from all the image carriers by applying a tension that can be driven to rotate, the endless belt is separated from all the image carriers. The endless belt can be driven to rotate. Therefore, if the intermediate transfer belt and the image carrier are in the first full separation mode until they rise to a predetermined speed, it is possible to suppress the occurrence of fine scratches due to the rubbing between the image carrier and the endless belt.

Hereinafter, an example of an embodiment in which the present invention is applied to a color electrophotographic copying machine will be described.
FIG. 1 shows an example of an embodiment of the present invention, and is a schematic configuration diagram of a tandem indirect transfer type color electrophotographic copying machine. This color electrophotographic copying machine mainly comprises a copying machine main body 100, a paper feed table 200 on which the copying machine main body is placed, a scanner 300 mounted on the copying apparatus main body, and an automatic document feeder (ADF) 400 mounted thereon. Has been.

The copying apparatus main body 100 is provided with an endless belt-like intermediate transfer belt 10 in the center. As shown in FIG. 2, the intermediate transfer belt 10 has a base layer 11 made of, for example, a base layer made of a material that hardly stretches, such as a fluorine resin or a rubber material that stretches a little, and an elastic layer 12 formed thereon. Is provided. The elastic layer 12 is made of, for example, fluorine-based rubber or acrylonitrile-butadiene copolymer rubber. The surface of the elastic layer 12 is coated with, for example, a coating layer 13 having good smoothness by coating a fluorine resin.
In the example of FIG. 1, the intermediate transfer belt 10 is wound around three support rollers 14, 15, and 16 so as to be rotated and conveyed in the clockwise direction in the drawing.
In the illustrated example, an intermediate transfer belt cleaning device 17 that removes residual toner remaining on the intermediate transfer belt 10 after image transfer is provided to the right of the second support roller 15 among the three support rollers 14, 15, 16. .
Further, among the three support rollers 14, 15, and 16, the cyan, magenta, and magenta, along the conveyance direction are placed on the intermediate transfer belt 10 that is stretched between the first support roller 14 and the second support roller 15. A tandem image forming apparatus 20 is configured by arranging four image forming units 18 of yellow and black side by side. An exposure device 21 is further provided on the tandem image forming apparatus 20 as shown in FIG.

On the other hand, a secondary transfer device 22 is provided on the opposite side of the intermediate transfer belt 10 from the tandem image forming device 20. In the illustrated example, the secondary transfer device 22 is configured by spanning a secondary transfer belt 24, which is an endless belt, between two rollers 23, and is pressed against the third support roller 16 via the intermediate transfer belt 10. The image on the intermediate transfer belt 10 is transferred to a sheet.
A fixing device 25 for fixing the transferred image on the sheet is provided beside the secondary transfer device 22. The fixing device 25 is configured by pressing a pressure roller 27 against a fixing belt 26 that is an endless belt.

The secondary transfer device 22 described above is also provided with a sheet transport function for transporting the image-transferred sheet to the fixing device 25. Of course, a transfer roller or a non-contact charger may be arranged as the secondary transfer device 22, and in such a case, it is difficult to provide this sheet conveying function together.
In the illustrated example, a sheet reversing device for reversing the sheet so as to record images on both sides of the sheet is provided below the secondary transfer device 22 and the fixing device 25 in parallel with the tandem image forming device 20 described above. 28.

Now, when making a copy using this color electrophotographic copying machine, a document is set on the document table 30 of the automatic document feeder 400. Alternatively, the automatic document feeder 400 is opened, a document is set on the contact glass 32 of the scanner 300, and the automatic document feeder 400 is closed and pressed by it.
When a start switch (not shown) is pressed, when the document is set on the automatic document feeder 400, the document is transported and moved onto the contact glass 32, and then the document is set on the other contact glass 32. At that time, the scanner 300 is immediately driven to travel the first traveling body 33 and the second traveling body 34. Then, the first traveling body 33 emits light from the light source and further reflects the reflected light from the document surface toward the second traveling body 34, and is reflected by the mirror of the second traveling body 34 and passes through the imaging lens 35. The document is placed in the reading sensor 36 and the original content is read.

  When a start switch (not shown) is pressed, one of the support rollers 14, 15, 16 is rotated by a drive motor (not shown), the other two support rollers are driven to rotate, and the intermediate transfer belt 10 is rotated and conveyed. To do. At the same time, the individual image forming means 18 rotates the photoconductor 40 to form cyan, magenta, yellow, and black monochrome images on each photoconductor 40. Then, along with the conveyance of the intermediate transfer belt 10, the monochrome images are sequentially transferred to form a composite color image on the intermediate transfer belt 10.

On the other hand, when a start switch (not shown) is pressed, one of the paper feed rollers 42 of the paper feed table 200 is selectively rotated, and the sheet is fed out from one of the paper feed cassettes 44 provided in multiple stages in the paper bank 43, and the separation roller 45. Then, the sheets are separated one by one into the paper feed path 46, transported by the transport roller 47, guided to the paper feed path 48 in the copying machine main body 100, and abutted against the registration roller 49 and stopped.
Alternatively, the sheet feed roller 50 is rotated to feed out the sheets on the manual feed tray 51, separated one by one by the separation roller 52, put into the manual feed path 53, and abutted against the registration roller 49 and stopped.

Then, the registration roller 49 is rotated in synchronization with the composite color image on the intermediate transfer belt 10, the sheet is fed between the intermediate transfer belt 10 and the secondary transfer device 22, and transferred by the secondary transfer device 22. A color image is recorded on the sheet.
The sheet after the image transfer is conveyed by the secondary transfer device 22 and sent to the fixing device 25, and heat and pressure are applied to the fixing device 25 to fix the transferred image. The paper is discharged at 56 and stacked on the paper discharge tray 57. Alternatively, it is switched by the switching claw 55 and put into the sheet reversing device 28, where it is reversed and guided again to the transfer position, and an image is recorded also on the back surface, and then discharged onto the discharge tray 57 by the discharge roller 56.

  On the other hand, the intermediate transfer belt 10 after the image transfer is removed by the intermediate transfer belt cleaning device 17 to remove residual toner remaining on the intermediate transfer belt 10 after the image transfer, so that the tandem image forming apparatus 20 can prepare for the image formation again.

Here, the registration roller 49 is generally used while being grounded, but it is also possible to apply a bias for removing paper dust from the sheet. In general, in the intermediate transfer method, it is difficult for paper dust to move to the photoconductor, so that it is not necessary to consider paper dust transfer and may be grounded. Further, a DC bias is applied as the applied voltage, but this may be an AC voltage having a DC offset component in order to more uniformly charge the sheet.
The paper surface after passing through the registration roller 49 to which a bias is applied in this way is slightly charged on the negative side. Therefore, in the transfer from the intermediate transfer belt 10 to the sheet, there are cases where the transfer conditions are changed and the transfer conditions are changed as compared with the case where no voltage is applied to the registration roller 49.

  In the tandem image forming apparatus 20 described above, the individual image forming means 18 includes, for example, a charging device 60, a developing device 61, and a primary device around a drum-shaped photoconductor 40 as shown in FIG. The image forming apparatus includes a transfer device 62, a photoconductor cleaning device 63, a charge removal device 64, and the like.

  The intermediate transfer belt cleaning device 17 has a cleaning blade, and removes residual toner on the surface of the intermediate transfer belt by pressing the tip of the cleaning blade against the surface of the intermediate transfer belt. For this reason, foreign substances such as toner and paper dust gradually adhere to the tip portion by continuous use. If this is left unattended, this foreign matter may be trapped between the cleaning blade and the surface of the intermediate transfer belt, resulting in poor cleaning.

  Therefore, in the present embodiment, a driving unit that can rotate the intermediate transfer belt 10 in both forward and reverse directions is provided, and the intermediate transfer belt rotates in a direction opposite to the rotation direction during image formation during non-image formation, A cleaning mode in which foreign matter adhering to the part is removed from the tip part and removed.

Next, features of the present embodiment will be described.
In the color electrophotographic copying machine according to the present embodiment, contact / separation means for contacting / separating the intermediate transfer belt 10 with respect to each photoreceptor 40 is provided. This contact / separation means has the following contact / separation operation mode. That is, a full contact mode in which the intermediate transfer belt is in contact with all the photoconductors, and a partial separation mode in which the intermediate transfer belt is separated from other photoconductors while leaving the K-color photoconductor. Further, in a state in which a tension capable of driving the intermediate transfer belt is applied, the first total separation mode, which is a full separation drive mode in which the intermediate transfer belt is separated from all image carriers, and the tension of the intermediate transfer belt This is a second full separation mode which is a full separation low tension mode in which the intermediate transfer belt is separated from all the image carriers in a weak state.

FIG. 4 is an explanatory view of the tension structure of the intermediate transfer belt 10 and shows a full contact mode in which the intermediate transfer belt 10 is in contact with all the photoconductors 40C, M, Y, and Bk. In the following description, C, M, Y, and Bk are added to the symbols for cyan, magenta, yellow, and black members, respectively.
In FIG. 4, the contact / separation means includes a first swing arm 70 and contact / separation cam 71 for simultaneously contacting / separating the intermediate transfer belt 10 to the cyan, magenta, and yellow photoconductors 40C, M, and Y. The intermediate transfer belt 10 is mainly composed of a second swing arm 80 and an eccentric cam 81 for moving the intermediate transfer belt 10 toward and away from the black photoreceptor 40Bk. The contact / separation cam 71 is rotationally driven by a first drive motor 74 that is driven and controlled by a control signal from a drive control unit 73. The eccentric cam 81 is rotationally driven by a second drive motor 86 that is driven and controlled by a control signal from the drive control unit 85.
As shown in FIG. 4, the driven roller 14 in the vicinity of the black photoconductor 40Bk is disposed on the lower side in the drawing with respect to each primary transfer roller. As a result, the intermediate transfer belt 10 is brought into contact with the photoreceptors 40C, M, Y, and Bk by the primary transfer rollers 62C, M, Y, and Bk that are stretching rollers.

  One end side of the first swing arm 70 is supported so as to be swingable by a swing support point 72 on the black primary transfer roller 62Bk side with respect to the longitudinal intermediate position of the second swing arm 80. Here, since the second swing arm 80 swings, the swing fulcrum 72 itself swings. A support roller 15 that stretches the intermediate transfer belt 10 is provided on the other end side of the first swing arm 70. Further, in the longitudinal direction of the first swing arm 70, a tension roller for bringing the intermediate transfer belt into contact with the respective photoreceptors 40Y, 40M, and C is provided between the swing support point 72 and the support roller 15. Three primary transfer rollers 62C, M, and Y for cyan, magenta, and yellow are rotated in a state where they are biased to the photoreceptors 40C, M, and Y by the pressure springs 63C, M, and Y, respectively. Supported as possible. The first swing arm 70 is closer to the support roller 15 than the middle position in the longitudinal direction, and a contact / separation cam 71 is in contact with the side opposite to the position where the three primary transfer rollers 62C, M, Y are disposed. As the contact / separation cam 71 rotates, the first swing arm 70 swings about the swing fulcrum 72. As a result, the three primary transfer rollers 62C, M, and Y are brought into contact with and separated from the three photosensitive members 40C, M, and Y, and the intermediate transfer belt 10 is integrated with the three photosensitive members 40C, M, and Y. It is possible to move it in and out.

FIG. 5 is an enlarged configuration diagram showing the vicinity of the second swing arm 80.
As shown in the figure, the second swing arm 80 is swingably supported by an intermediate transfer unit frame (not shown) around a swing fulcrum 82 on one end side, and on the other end side is an intermediate transfer. A black primary transfer roller 62Bk, which is a stretching roller for bringing the belt into contact with the black photoconductor 40K, is provided. The black primary transfer roller 62Bk is rotatably supported while being urged toward the black photosensitive member 40Bk by the pressure spring 63Bk. The second swing arm 80 is closer to the black primary transfer roller 62Bk than the intermediate position in the longitudinal direction, and an eccentric cam 81 is in contact with the side opposite to the position where the black photoreceptor 40Bk is disposed. The eccentric cam 81 has a first position A, a second position B, and a third position C that are different in distance from the rotation center of the eccentric cam 81. The relationship between the distance L1 from the rotation center of the first position A, the distance L2 from the rotation center of the second position B, and the distance L3 from the rotation center of the third position C is L1>L2> L3. It has become. Then, the second drive motor 86 is driven and controlled by the drive control unit 85 so that any one of the first position A, the second position B, and the third position C contacts the second swing arm 80. The As described above, any of the positions having different distances from the center of rotation comes into contact with the second swing arm 80 to support the second swing arm 80, so that the second swing arm 80 is different from each other. There are three possible positions.
As shown in the figure, when the first position A is in contact with and supported by the second swing arm 80, the first posture in which the intermediate transfer belt 10 is brought into contact with the black photoreceptor 40Bk is changed to the second swing arm. The moving arm 80 takes. In addition, when the second position B is in contact with and supported by the second swing arm 80, the second swing arm 80 has a second posture in which the intermediate transfer belt 10 is slightly separated from the black photoreceptor 40Bk. Take. Further, when the third position C is in contact with and supported by the second swing arm 80, the second swing arm 80 has a third posture in which the intermediate transfer belt 10 is largely separated from the black photoreceptor 40Bk. Take.

FIG. 6 illustrates a partial separation mode in which the intermediate transfer belt 10 is separated from the other three photosensitive members 40C, M, and Y while leaving the black photosensitive member 40Bk among the four photosensitive members 40C, M, Y, and Bk. FIG.
When the contact / separation cam 71 is rotated halfway from the state of FIG. 4, the first swing arm 70 swings downward in the figure around the swing fulcrum 72, and the three for cyan, magenta and yellow are swung. The primary transfer rollers 62C, M, and Y are separated from the corresponding three photoreceptors 40C, M, and Y, and the intermediate transfer belt 10 is separated from the three photoreceptors 40C, M, and Y. As a result, the partially separated mode shown in FIG. 6 is achieved, and a black monochrome image can be formed.
In the partially separated mode, the intermediate transfer belt 10 contacts only the black photoreceptor 40Bk and is separated from the other three photoreceptors 40C, M, and Y. Therefore, the three photoreceptors 40C, M are separated. , Y can prevent deterioration of the photoreceptor due to contact with the intermediate transfer belt 10. Further, since the operations of the other three photoconductors 40C, M, and Y other than the black photoconductor 40Bk can be stopped, not only these photoconductors 40C, M, and Y but also these image forming means 18 are used. The service life of the charging device 60, the developing device 61, the cleaning device 63, etc. (see FIG. 3) can be extended.

FIG. 7 is a diagram showing a second total separation mode in which the intermediate transfer belt 10 is largely separated from the photosensitive member and the tension applied to the intermediate transfer belt is weakened.
From the state of FIG. 6, when the eccentric cam 81 is rotated and the position where it abuts and supports the second swing arm 80 is the third position C, the second swing arm 80 is centered on the swing fulcrum 82. By swinging, the second swing arm 80 shifts to the third posture. At this time, the black primary transfer roller 62Bk is lowered downward and away from the black photoreceptor 40Bk, and the intermediate transfer belt 10 is largely separated from the black photoreceptor 40Bk. As a result, the intermediate transfer belt 10 is greatly separated from all the photoconductors 40C, M, Y, and Bk.
Further, at this time, the first swing arm 70, one end of which is supported by the second swing arm 80, has its swing fulcrum 72 side lowered to the lower side in the figure, so that the first swing arm 70 is substantially omitted from the state of FIG. It will move down in parallel. If the swing fulcrum 72 of the first swing arm 70 is not connected to the second swing arm 80, the first swing arm 70 is inclined to the lower left side in the figure, and the yellow primary transfer roller 62Y. Is closest to the yellow photoconductor 40Y, and the distance between the intermediate transfer belt 10 and the yellow photoconductor 40Y is smaller than those of the other two photoconductors 40C and 40M. Further, the amount of decrease in the tension of the intermediate transfer belt 10 is small, and the effect of preventing the curl wrinkle by weakening the tension cannot be obtained sufficiently. In this embodiment, when the intermediate transfer belt 10 is separated from all the photoreceptors 40C, M, Y, and Bk, the first swing arm 70 moves downward in a substantially parallel manner. As compared with the configuration in which only one end side of the belt is swung, the distance between the intermediate transfer belt 10 and each of the photoreceptors 40C, M, and Y can be made substantially constant. Further, the belt tension of the intermediate transfer belt 10 can be reduced as compared with the full contact mode.

  Further, as the second swing arm 80 swings the black primary transfer roller 62Bk away from the black photosensitive member 40Bk, the entire first swing arm 70 moves to the right side in the drawing, so the first swing The support roller 15 disposed at the end of the moving arm 70 opposite to the swing fulcrum 72 moves to the right, and the tension of the intermediate transfer belt 10 is weakened. Although the intermediate transfer belt 10 is in a state where tension is applied by the tension roller 83, the tension spring 84 extends and the urging force of the tension roller 83 is weakened, so that the belt tension can be weakened. Therefore, when the intermediate transfer belt 10 is largely separated from all the photoconductors 40C, M, Y, and Bk, it is possible to prevent the tension of the intermediate transfer belt 10 from being weakened and to generate curl wrinkles or permanent distortion on the belt.

FIG. 8 is a diagram illustrating a first full separation mode in which the amount of separation of the intermediate transfer belt 10 from the photoconductor is smaller than that in the second full separation mode.
From the state shown in FIG. 6, when the eccentric cam 81 is rotated and the position where it abuts and supports the second swing arm 80 is set to the second position B, the second swing arm 80 is centered on the swing support point 82. By swinging, the second swing arm 80 shifts from the first posture to the second posture. At this time, as shown in the drawing, the black primary transfer roller 62Bk is further away from the black photoconductor 40Bk than in the full contact mode or the partial separation mode, and the intermediate transfer belt 10 is all of the photoconductors 40C, M,. It is separated from Y and Bk. Further, it is located closer to the black photoconductor 40Bk than in the second full separation mode, and the separation amount of the intermediate transfer belt 10 from the photoconductor is smaller than in the second full separation mode.
At this time, in the first swing arm 70, one end of which is supported by the second swing arm 80, the swing fulcrum 72 side lowers in the figure than the state shown in FIG. The support roller 15 disposed at the end opposite to the moving fulcrum 72 also moves to the right. However, since these movement amounts are smaller than the movement amounts in the second full separation mode, the tension spring 84 extends as in the second full separation mode, and the tension on the intermediate transfer belt 10 by the tension roller 83 is increased. There is no significant weakening. As a result, a sufficient frictional force between the driving roller and the intermediate transfer belt 10 can be secured, and the intermediate transfer belt 10 can be driven to rotate even in the full separation mode in which the intermediate transfer belt is separated from all the photosensitive members. Can do.

Here, the separation amount of the intermediate transfer belt 10 from the photosensitive member is adjusted so that the tension of the intermediate transfer belt 10 in the first full separation mode is 0.7 to 1 times the tension in the full contact mode. ing. This is because when the tension of the intermediate transfer belt is less than 0.7 times the tension in the full contact mode, the belt moves in the belt contact direction when the belt is driven to rotate in the full contact mode and in the first full separation mode. It was confirmed from the experiment shown below that the belt shift direction may be different when it is rotationally driven. If the belt shift direction in the full contact mode is different from the belt shift direction in the second full separation mode, the following problems occur.
This will be described more specifically with reference to FIG. FIG. 9A is an explanatory diagram of a state in which the intermediate transfer belt 10 is stretched around the support roller 14, and FIGS. 9B to 9D are enlarged views of a portion A. In the partial separation mode or the full contact mode, the intermediate transfer belt 10 is driven to rotate and moves toward the left side in the figure, and as shown in FIG. The intermediate transfer belt 10 is prevented from being displaced in the axial direction of the support roller 14 by abutting the support roller end surface 14a. However, when the belt tension in the first full separation mode is less than 0.7 times that in the full contact mode, when the intermediate transfer belt 10 is driven to rotate, the reverse direction in the full contact mode is reversed. 9C, the detent 10a of the intermediate transfer belt 10 is separated from the end surface 14a of the support roller 14, and a gap S is generated. As described above, when the intermediate transfer belt 10 is rotated again in the full contact mode in the state where the gap S is generated, as shown in FIG. 9D, until the detent 10a hits the support roller end surface 14a in the drawing. Move to the left (arrow B direction). If the toner images formed on the photoreceptors 40C, M, Y, and Bk are superimposed on the intermediate transfer belt 10 during this movement, color misregistration occurs in the axial direction.

The contents of the experiment conducted by the present inventors will be described below.
The inventors swung the belt tension between 0.5 and 1.5 [N / cm], and examined the speed in the first full separation mode and the direction of the belt. The belt tension is a value obtained by dividing the load applied to the intermediate transfer belt 10 by the tension spring 84 by the belt width, and the belt shift direction when the belt tension is 1.5 [N / cm] is positive. In this embodiment, the belt tension in the all contact mode is 1.5 [N / cm]. As a result, when the belt tension is 1.5 [N / cm], 1.1 [μm / s], when 1.0 [N / cm], 0.2 [μm / s], 0 When it was .9 [N / cm], it was -0.3 [[mu] m / s].
Thus, when the belt tension is 0.9 [N / cm], the belt is shifted in the opposite direction to the full contact mode (1.5 N / cm), and the above-described problem occurs. Further, when the belt tension is 1.0 [N / cm], which is about 0.7 times the belt tension in the full contact mode, the belt is shifted in the opposite direction to the full contact mode (1.5 N / cm). The above-mentioned problem does not occur. Therefore, in this embodiment, the intermediate transfer belt 10 is separated from the photosensitive member so that the tension of the intermediate transfer belt 10 in the first full separation mode is 0.7 to 1 times the tension in the full contact mode. By adjusting the amount, the belt shift direction when the intermediate transfer belt 10 is rotationally driven in the first separation mode is the same as that when the intermediate transfer belt 10 is rotationally driven in the full contact mode and the first full separation mode. The belt direction can be made the same. As a result, even if the intermediate transfer belt 10 is rotationally driven in the first full separation mode, the detent is not separated from the end face of the support roller, and the positional deviation in the axial direction can be suppressed.

Next, switching between the above modes will be described. FIG. 10 is a flowchart showing an example of switching between the above modes.
In the initial setting immediately after the color electrophotographic copying machine is turned on, the second full separation mode is set (S1). Then, it is determined whether or not the copy button has been turned on (S2). If the copy button has been turned on (YES in S2), the drive control unit 85 drives the second drive motor 86 to rotate, and the second cam of the eccentric cam 81 is driven. The position in contact with the swing arm 80 is changed from the third position C to the second position B, and the first separation mode is set (S3). In the first separation mode, it is checked whether or not the image to be formed is a full-color image. If the image is a full-color image, all the photoconductors 40Y, 40M, 40C, and Bk and the intermediate transfer belt 10 are driven. When all the photoconductors 40Y, 40M, 40C, and Bk and the intermediate transfer belt 10 reach the same speed, the position of the eccentric cam 81 that contacts the second swing arm 80 is changed from the second position B to the second position A. At the same time, the contact / separation cam 71 is rotated halfway to enter the full contact mode (S6). When the full contact mode is entered, full color image formation is performed. Specifically, toner images are formed on the Y, M, C, and K photoconductors, transferred onto the intermediate transfer belt 10 in sequence, and the superimposed images transferred to the intermediate transfer belt 10 are collectively recorded on a recording sheet. The image is transferred, the transferred image on the recording paper is fixed, and discharged outside the apparatus.
On the other hand, when forming a black image, the black photoconductor 40Bk and the intermediate transfer belt 10 are driven, and when the black photoconductor 40Bk and the intermediate transfer belt 10 reach the same speed, the partial separation mode is set. A black image is formed. Specifically, a toner image is formed on the black photoconductor 40Bk, transferred to the intermediate transfer belt 10, and then transferred to the recording paper, the transferred image on the recording paper is fixed, and discharged outside the apparatus. .

  When the black image or the color image is formed, it is checked whether or not there is a next image. If there is, the steps after S4 are performed. On the other hand, if there is no next image, the intermediate transfer belt 10 and the photoconductor 40 are rotationally driven, the first full separation mode is set, and when the intermediate transfer belt 10 is completely separated from the photoconductor 40, the photoconductor 40 is obtained. Then, the driving of the intermediate transfer belt 10 is stopped. When the predetermined time has elapsed, the second full separation mode is set and the tension of the intermediate transfer belt 10 is released.

As described above, in this embodiment, until the photosensitive member 40 and the intermediate transfer belt 10 rotate at a constant speed, the first separation mode that can be driven even in a state where the intermediate transfer belt 10 is separated from the photosensitive member 40 is set. Even if there is a time difference in rising between the photoconductor 40 and the intermediate transfer belt 10, fine scratches do not occur on the photoconductor 40 and the intermediate transfer belt 10.
Further, even when the driving of the photoconductor 40 and the intermediate transfer belt 10 is stopped, the driving is stopped after the first full separation mode is set. A flywheel or the like is attached to the photoconductor 40 to prevent rotation unevenness, and the inertia force is large, so that the stop time is longer than that of the intermediate transfer belt 10. For this reason, if the photosensitive member 40 and the intermediate transfer belt 10 are stopped in a state where the photosensitive member 40 and the intermediate transfer belt 10 are in contact with each other, the intermediate transfer belt 10 and the photosensitive member 40 are rubbed to cause fine scratches. May occur. For this reason, when the photosensitive member 40 and the intermediate transfer belt 10 are stopped after the first full separation mode is set, fine scratches do not occur on the photosensitive member 40 and the intermediate transfer belt 10.

  Further, when image formation is not performed for a long period of time, the second full separation mode is set and the tension applied to the intermediate transfer belt 10 is loosened, so that curling and permanent distortion is prevented from occurring on the intermediate transfer belt 10. it can. Further, when forming a black image, the intermediate transfer belt 10 is separated from the Y, M, and C photoconductors 40Y, M, and C in a partial separation mode. As a result, the operations of the other three photoconductors 40C, M, Y other than the black photoconductor 40Bk can be stopped, so that not only these photoconductors 40C, M, Y but also these image forming means. The service life of the 18 charging devices 60, the developing device 61, the cleaning device 63, and the like can be extended.

In the present embodiment, the foreign matter adhering to the tip of the cleaning blade of the intermediate transfer belt cleaning device 17 is rotated by rotating the intermediate transfer belt 10 in the direction opposite to the rotation direction during image formation during non-image formation. It has a cleaning mode in which it is peeled off from the tip. If the photosensitive member is not separated from the intermediate transfer belt 10 in this cleaning mode, the following problems occur. In other words, if the photosensitive member 40 is stopped when the intermediate transfer belt 10 is rotated in the reverse direction, the intermediate transfer belt 10 rubs against the photosensitive member 40 and fine scratches are formed on the photosensitive member 40 and the intermediate transfer belt 10. Will occur. Therefore, the driving means for rotationally driving the photosensitive member 40 is also a driving means that can be driven to rotate both forward and reverse as in the case of the intermediate transfer belt 10, and the photosensitive member 40 can also be reversely rotated when the intermediate transfer belt 10 rotates reversely. Conceivable. However, in this case, the following problems occur. That is, if there is a difference in the speed rise between the photoconductor 40 and the intermediate transfer belt 10, the intermediate transfer belt 10 rubs against the photoconductor 40 and fine scratches are generated. Further, when the cleaning blade for cleaning the photoconductor 40 is in contact with the trading system, there is a problem that the blade is caught when the photoconductor 40 is rotated in the reverse direction. Furthermore, the photosensitive member driving means needs to be a driving means that can be driven to rotate in both forward and reverse directions, which may increase the cost of the apparatus.
Therefore, in this embodiment, the cleaning mode is executed after the first full separation mode is set.

FIG. 11 is a processing flow of the cleaning mode.
As shown in the figure, the cleaning mode is started at the time of non-image formation such as after a predetermined number of images have been formed. First, when the cleaning mode is started, the first separation mode is set (S21), and the intermediate transfer belt 10 is completely separated from the photoreceptor 40 in a state where tension is applied. When in the first full separation mode, the intermediate transfer belt 10 is driven to rotate backward (S22), and the paper dust and toner adhering to the tip of the cleaning blade are removed. Then, after driving for a predetermined time (YES in S23), the initial second full separation mode is set (S25), and the process ends.

  As described above, when the intermediate transfer belt 10 is driven to rotate in the reverse direction in the cleaning mode, the intermediate transfer belt 10 is moved in the first total separation mode in which the intermediate transfer belt 10 is completely separated from the photosensitive member with the tension applied. The intermediate transfer belt 10 can be driven to rotate in the reverse direction while being separated from the photoconductor. Thereby, it is possible to prevent the photoconductor 40 and the intermediate transfer belt 10 from being finely scratched during the cleaning mode. Further, since there is no need to reversely rotate the photoconductor 40, the driving means for driving the photoconductor 40 can be a simple driving means that only performs forward rotation, and the cost increase can be suppressed. Further, even when the cleaning blade for cleaning the photoconductor 40 comes into contact with the trading system, the blade does not get caught during the cleaning mode.

[Modification 1]
Next, Modification 1 of the contacting / separating means will be described.
FIG. 12 is an enlarged configuration diagram illustrating the feature points of the first modification of the present embodiment.
In the first modification, as shown in FIG. 12, two eccentric cams 81a and 81b having different sizes allow the second swing arm 80 to take three different postures. The first eccentric cam 81a is larger than the second eccentric cam 81b, and the longest position D and the shortest position E from the rotation center of the outer peripheral surface are the longest position F and the shortest position G of the second eccentric cam 81b. Longer than. Further, the distance from the longest position F of the second eccentric cam 81b to the rotation center is longer than the distance from the shortest position E of the first cam 81a to the rotation center. That is, the distance from the rotation center of the first eccentric cam 81a to the position D is L4, the distance to the position E is L5, the distance from the rotation center of the second eccentric cam 81b to the position F is L6, and the distance to the position G is L6. When the distance is L7, the magnitude relationship is L4>L6>L5> L7.

The state shown in the drawing is a state in which the intermediate transfer belt 10 is in contact with the black photoconductor 40Bk. At this time, the position D of the first eccentric cam 81a is in contact with the second swing arm 80.
When the first full separation mode shown in FIG. 8 is set, the drive control unit 85 controls the second drive motor 86a so that the position E of the first eccentric cam 81a faces the second swing arm 80, The second drive motor 86a is controlled so that the position F of the second eccentric cam 81b faces the second swing arm 80. Since the distance L6 from the center of rotation of the second eccentric cam 81b to the position F is longer than the distance L5 from the center of rotation of the first eccentric cam 81b to the position E, the position F of the second eccentric cam 81b is the second. It contacts the swing arm 80. Further, since the distance L6 from the center of rotation of the second eccentric cam 81b to the position F is shorter than the distance L4 from the center of rotation of the first eccentric cam 81a to the position D, the second swing arm 80 is From the state shown in FIG. 12, it swings clockwise around the swing fulcrum 82 and takes the second posture. As a result, the black primary transfer roller 62Bk is lowered downward and away from the black photoreceptor 40Bk, and the intermediate transfer belt 10 is separated from the black photoreceptor 40Bk.

In the second total separation mode shown in FIG. 7, the drive control unit 85 controls the motor 86a so that the position E of the first eccentric cam 81a faces the second swing arm 80, and the second The motor 86 b is controlled so that the position G of the eccentric cam 81 b faces the second swing arm 80. Since the distance L5 from the center of rotation of the first eccentric cam 81a to the position E is longer than the distance L7 from the center of rotation of the second eccentric cam 81b to the position G, the position E of the first eccentric cam 81a is the second. It contacts the swing arm 80. In addition, since the distance L5 from the center of rotation of the first eccentric cam 81a to the position E is shorter than the distance L6 from the center of rotation of the second eccentric cam 81b to the position F, the second swing arm 80 is From the second posture, it swings clockwise in the drawing around the swing fulcrum 82 and takes the third posture. As a result, the black primary transfer roller 62Bk is further lowered further away from the black photoconductor 40Bk, and the intermediate transfer belt 10 is greatly separated from the black photoconductor 40Bk.
As described above, in the first modification, the two swing cams 80 can have three different postures by the two eccentric cams 81a and 81b having different sizes.

[Modification 2]
Next, modification 2 of the contacting / separating means will be described.
FIG. 13 is an enlarged configuration diagram of the tension roller 83, showing a characteristic part of the contacting / separating means of the second modification.
As shown in the figure, the contacting / separating means of the second modification is provided with a moving mechanism for moving the tension roller 83 to the intermediate transfer belt side. By this moving mechanism, a tension capable of driving the intermediate transfer belt 10 is applied when the intermediate transfer belt 10 is separated from all the photosensitive members. That is, in the second modification, the eccentric cam 81 that supports the second swing arm 80 has the same configuration as the contact / separation cam 71 that supports the first swing arm 70, and the second swing arm 80 has an intermediate configuration. Eccentric cam so that the transfer belt 10 can take two postures: a first posture in which the transfer belt 10 is brought into contact with the black photoconductor 40Bk, and a third posture in which the intermediate transfer belt 10 is largely separated from the black photoconductor 40Bk. The rotation of 81 is controlled. In the first full separation mode, the intermediate transfer belt 10 is moved away from the photoreceptors 40Y, M, C, and Bk by moving the tension roller 83 toward the intermediate transfer belt by the moving mechanism. A driveable tension is applied to the belt 10.
More specifically, as shown in FIG. 13, when the intermediate transfer belt 10 is driven away from all the photoconductors 40Y, M, C, and Bk, the second swing arm 80 is moved to the third posture. The intermediate transfer belt 10 is greatly separated from the photoreceptors 40Y, 40M, 40C, and 40B. Next, the eccentric cam 180 is rotated nearly 90 degrees from the state of FIG. 13A to the state of FIG. 19B. Thereby, the bearing 83a of the tension roller 83 is pressed via the tension spring 84, and the tension roller 83 is moved to the intermediate transfer belt side. As a result, in the state where the intermediate transfer belt 10 is separated from all the photoconductors, the first total separation mode in which a driveable tension is applied to the intermediate transfer belt 10 can be taken.

  On the other hand, when changing from the first full separation mode to the second full separation mode in which the intermediate transfer belt 10 is separated from all the photoconductors in a state where the tension on the intermediate transfer belt 10 is weakened, the state shown in FIG. The eccentric cam 180 is rotated in the state of FIG. 13A, and the tension roller 83 is moved away from the intermediate transfer belt 10.

  In the above description, the image forming apparatus including the intermediate transfer belt 10 has been described. However, the present invention is also applicable to an image forming apparatus configured to sequentially transfer a plurality of image carriers onto a transfer material on a transfer material conveyance belt. Can do.

FIG. 14 is an explanatory diagram of a stretch structure of the transfer material conveyance belt 90 of the color electrophotographic copying machine using the transfer material conveyance belt. The transfer material conveyance belt 90 is attached to all the photoreceptors 40C, M, Y, and Bk. A full contact mode in contact is shown.
In FIG. 14, a first swing arm 91 and a first contact / separation cam 92 are provided so that the transfer material transport belt 90 is simultaneously brought into contact with and separated from the cyan photoreceptor 40C, magenta photoreceptor 40M, and yellow photoreceptor 40Y. Is provided. In addition, a second swing arm 93 and a second contact / separation cam 94 are provided to bring the transfer material transport belt 90 into and out of contact with the black photosensitive member 40Bk. A swing support point 95 of the first swing arm 91 is supported on the second swing arm 93, and a swing support point 96 of the second swing arm 93 is supported on a transfer unit frame (not shown).
Further, a transfer material guide 98 and a transfer material conveyance roller pair 99 are provided on the upstream side in the conveyance direction of the transfer paper P with respect to the transfer portion between the black photoconductor 40Bk and the black transfer roller 97Bk, and the cyan photoconductor 40C. And a cyan transfer roller 97C, a fixing device (not shown) is provided downstream of the transfer portion in the transfer sheet conveyance direction.
The configuration in which the transfer material conveyance belt 90 is moved toward and away from each of the photoconductors 40C, M, Y, and Bk to be in the partially separated mode or the first and second fully separated modes is the same as that described above. Since it is the same, detailed explanation is omitted.

  Even in the image forming apparatus configured to sequentially transfer from the plurality of image carriers shown in FIG. 14 to the transfer material on the transfer material conveyance belt, the transfer material can be obtained by taking the second full separation mode when the apparatus is stopped. It is possible to suppress wrinkles on the conveyor belt 90. Further, by taking the first full separation mode until the photosensitive member and the transfer conveyance belt 90 rise up to the speed at which an image is formed on the transfer material, the transfer material conveyance belt rubs against the photosensitive member, and the photosensitive member It is possible to suppress the body and the transfer material transport belt 90 from being finely scratched.

  As described above, according to the image forming apparatus of the present embodiment, as the contact / separation mode of the contact / separation unit, all tensions are applied to the intermediate transfer belt in a state where the intermediate transfer belt 10 that is an endless belt can be driven. A first fully separated mode, which is a fully separated driveable mode for separating from the photoreceptor, is provided. Therefore, in the first full separation mode, the frictional force sufficiently acts between the driving roller and the belt, and the intermediate transfer belt 10 is in a state where the intermediate transfer belt 10 is separated from all the photoconductors 40Y, M, C, and Bk. Can be driven to rotate.

  Further, the tension of the intermediate transfer belt 10 in the first full separation mode is set to 0.7 to 1 times the tension when the intermediate transfer belt 10 forms an image. As a result, the belt shift direction when the intermediate transfer belt is driven to rotate in the first full separation mode can be made the same as the intermediate transfer belt shift direction during image formation. As a result, it is possible to suppress the occurrence of axial color misregistration during image formation after the intermediate transfer belt 10 is rotationally driven in the first full separation mode.

  In addition, by starting the driving of the photosensitive member and the intermediate transfer belt until the predetermined speed is reached, the first full separation mode is set. And fine scratches due to rubbing with the intermediate transfer belt do not occur.

  In addition, when the intermediate transfer belt is driven to rotate in a direction opposite to the rotation direction during image formation, the first full separation mode is set, so that the intermediate transfer belt rubs against the photosensitive member when the intermediate transfer belt is rotated reversely. There is nothing. Therefore, fine scratches due to rubbing between the photosensitive member and the intermediate transfer belt do not occur.

  In addition, according to the image forming apparatus of the present embodiment, the second is a fully separated low tension mode in which the intermediate transfer belt is separated from all the image carriers with a lower tension than the tension of the intermediate transfer belt in the first fully separated mode. It has a full separation mode. Therefore, when the same part of the belt is wound around the roller for a long period of time, such as when the apparatus is in a resting state, if the second full separation mode is set, curling and permanent distortion of the intermediate transfer belt can be reduced, Image unevenness due to curl wrinkles or permanent distortion can be reduced.

  Further, in the first full separation mode, the separation distance between the primary transfer roller, which is a stretching roller for stretching the intermediate transfer belt and bringing the intermediate transfer belt into contact with the photosensitive member, is set to the second distance. The distance between the primary transfer roller and the photosensitive member in the all separation mode is shorter. When the primary transfer roller is separated from the photoconductor, the intermediate transfer belt pressed against the photoconductor by the primary transfer roller is bent. However, in the first full separation mode, since the separation distance between the primary transfer roller and the photosensitive member is short, the amount of bending of the intermediate transfer belt is small, and this bending is absorbed by the tension roller, and the intermediate transfer belt is moved again. A drivable tension is applied. On the other hand, in the second full separation mode, since the separation distance between the primary transfer roller and the photosensitive member is long, the amount of bending of the intermediate transfer belt is large, and this bending is not absorbed by the tension roller. As a result, the belt tension applied in the second full separation mode can be made weaker than the belt tension applied in the first full separation mode.

Further, the contact / separation means is used for contacting and separating the intermediate transfer belt 10 from cyan, magenta, and yellow photoreceptors 40C, M, and Y as other image carriers while leaving the black photoreceptor 40Bk as at least one image carrier. The first swing arm 70 and the second swing arm 80 for contacting and separating the intermediate transfer belt 10 from at least the black photosensitive member 40Bk, and the swing support point 72 of the first swing arm 70. Is provided on a second swing arm 80 as a second swing member. Therefore, by swinging the second swing arm 80, the first swing arm 70 swings the swing support point 72 itself on the second swing arm 80, so that the first swing arm 70 is substantially parallel. It is possible to move to. Therefore, compared to the case where the swing fulcrum 72 itself of the first swing arm 70 does not swing, the amount of separation of the yellow primary transfer roller 62Y disposed near the swing fulcrum 72 is not insufficient. The intermediate transfer belt 10 can be separated from the cyan, magenta, and yellow photoconductors 40C, M, and Y substantially evenly.
Further, the second swing arm can take a first posture in which at least one photoconductor and the intermediate transfer belt can come into contact with each other, and a second and third posture in which the distance from the intermediate transfer belt to the photoconductor is different from each other. Configured. As a result, the contact / separation means includes a full contact mode and a partial separation mode in which the intermediate transfer belt contacts the photoconductor, a first full separation mode in which the intermediate transfer belt is slightly separated from the photoconductor, and the intermediate transfer belt from the photoconductor. A second full separation mode that is largely separated can be taken.

  Further, the eccentric cam rotates so that any one of the first, second, and third positions that are different from the rotation center of the eccentric cam that supports and rotates the second rocking arm comes into contact with the rocking member. Is controlled. Accordingly, the second swing arm can take three different postures with a simple configuration.

Further, the first eccentric cam supporting the second swing arm and the second eccentric cam are provided. The longest distance from the center of rotation of the first eccentric cam to the outer peripheral surface is L4, and the shortest distance is L5. 2 When the longest distance from the center of rotation of the eccentric cam to the outer peripheral surface is L6 and the shortest distance is L7, the relationship is L4>L6>L5> L7. By bringing the position D of the outer peripheral surface where the distance from the center of rotation of the first eccentric cam becomes L4 with the second swing arm, the second swing arm can be brought into the first posture. Further, the position E of the outer peripheral surface where the distance from the center of rotation of the first eccentric cam is L5 is opposed to the second swing arm, and the outer peripheral surface where the distance from the center of rotation of the second eccentric cam is L6. By bringing the position F into contact with the second oscillating arm, the second oscillating arm can be brought into the second posture, which is the posture taken in the first full separation mode. Further, the position G of the outer peripheral surface where the distance from the center of rotation of the second eccentric cam is L7 is opposed to the second swing arm, and the outer surface of the outer peripheral surface where the distance from the center of rotation of the first eccentric cam is L5. By bringing the position E into contact with the second oscillating arm, the second oscillating arm can be brought into the third attitude, which is the attitude that is taken in the second fully separated mode.
Thus, the two eccentric cams allow the second swing arm to take three different postures.

1 is a schematic configuration diagram of a main part of a color electrophotographic copying machine according to an embodiment. Sectional drawing of an intermediate transfer belt. The elements on larger scale of an image formation means. FIG. 4 is an explanatory diagram of a full contact mode in which the intermediate transfer belt is in contact with all the photoconductors. The expansion block diagram around the 2nd swing arm. FIG. 4 is an explanatory diagram of a partially separated mode in which the intermediate transfer belt is separated from other photoreceptors while leaving a black photoreceptor. FIG. 6 is an explanatory diagram of a second full separation mode in which the intermediate transfer belt is greatly separated from all the photoconductors. FIG. 4 is an explanatory diagram of a first full separation mode in which the intermediate transfer belt is slightly separated from all the photoconductors. (A) is explanatory drawing of the state in which the intermediate transfer belt is stretched around the support roller. ((B)-(d) is the A section enlarged view. The flowchart for demonstrating an example of switching of each mode. The figure which shows the processing flow of cleaning mode. The figure which shows the modification 1 of an approach / separation means. The figure which shows the modification 2 of an approach / separation means. FIG. 4 is an explanatory diagram of a full contact mode in which a transfer material transport belt is in contact with all the photoconductors.

Explanation of symbols

10 Intermediate transfer belt 17 Belt cleaning device 18Bk, 18Y, 18M, 18C Image forming unit 22 Secondary transfer device 40Bk, 40Y, 40M, 40C Photosensitive drum 62Bk, 62Y, 62M, 62C Primary transfer roller 70, 91 First swing Arms 72, 95 Swing fulcrum of first swing arm 80, 93 Second swing arm 97Bk, 97Y, 97M, 97C Transfer roller

Claims (9)

An image carrier for carrying an electrostatic latent image;
Latent image forming means for forming an electrostatic latent image on the image carrier;
A plurality of image forming means having a developing means for developing the electrostatic latent image into a toner image, and sequentially facing the surface of each image carrier of the plurality of image forming means. An intermediate transfer belt whose surface moves endlessly;
Primary transfer means for primarily transferring the toner image on the image carrier onto the surface of the intermediate transfer belt;
An image forming apparatus including a secondary transfer unit that secondarily transfers the toner image transferred onto the intermediate transfer belt onto a transfer material;
A plurality of stretching rollers for stretching the intermediate transfer belt and bringing the intermediate transfer belt into contact with the image carrier;
A tension roller that presses the intermediate transfer belt and applies tension to the intermediate transfer belt;
A first oscillating member for supporting a plurality of stretching rollers and leaving the intermediate transfer belt away from other image carriers, leaving at least one image carrier;
A second swing member that supports one tension roller and separates the intermediate transfer belt from at least one image carrier, and a first eccentric member that supports and rotates the second swing member. A cam and a second eccentric cam;
The intermediate transfer belt is in contact with all the image carriers, and the primary transfer unit primarily transfers the toner image on the image carrier onto the surface of the intermediate transfer belt, and the secondary transfer unit performs the transfer onto the intermediate transfer belt. A full contact mode for secondarily transferring the toner image transferred to the transfer material;
An all-separation driveable mode in which the intermediate transfer belt is separated from all image carriers by applying tension that the intermediate transfer belt can be rotationally driven; and
A contact configured to be able to be in a fully separated low tension mode in which the intermediate transfer belt is separated from all the image carriers with a lower tension than the tension of the intermediate transfer belt in the fully separated driveable mode. A separation means,
The contact / separation means is configured to separate the intermediate transfer belt from the image carrier by separating the stretch roller from the image carrier, and the stretch roller in the fully separated driveable mode. A distance between the image carrier and the image carrier is shorter than a distance between the tension roller and the image carrier in the fully separated low tension mode, and
In the full contact mode, the second eccentric cam is separated from the second swing member, and the first eccentric cam is in contact with the second swing member so that only the first eccentric cam is present. The second oscillating member is supported by the first oscillating cam so that the first eccentric cam is separated from the second oscillating member, and the second eccentric cam is the second oscillating member. The image forming apparatus is configured to support the second swinging member only by the second eccentric cam in contact with the second eccentric cam .   The image forming apparatus according to claim 1.
  An image forming apparatus, wherein the second eccentric cam is provided at a position farther from a fulcrum of swinging of the second swinging member than the first eccentric cam.   The image forming apparatus according to claim 1 or 2,
The image forming apparatus, wherein the tension roller is in contact with a front surface of the intermediate transfer belt and applies tension from the front surface to the back surface of the intermediate transfer belt. The image forming apparatus according to any one of claims 1 to 3 ,
An image forming apparatus, wherein the tension of the intermediate transfer belt in the all-separation driveable mode is set to 0.7 to 1 times the tension at the time of image formation. The image forming apparatus according to claim 1 to 4,
The contacting / separating means includes
An image forming apparatus, wherein the image carrier and the intermediate transfer belt are in a fully-separable drive mode until the image transfer member and the intermediate transfer belt start rotating and rise to a predetermined speed. The image forming apparatus according to claim 1 to 4,
The contacting / separating means includes
An image forming apparatus, wherein when the intermediate transfer belt is rotationally driven in a rotation direction opposite to a rotation direction at the time of image formation, a fully separated drive possible mode is taken. The image forming apparatus according to claim 1 to 6,
Image forming apparatus characterized by digits set before Symbol first on the second swing member swinging fulcrum of the swinging member. The image forming apparatus according to claim 1,
The maximum distance L4 from the center of rotation of the front Symbol first eccentric cam to the outer surface, the shortest distance and L5, the longest distance to the outer peripheral surface from the center of rotation of said second eccentric cam L6, and the shortest distance L7 When
An image forming apparatus configured to satisfy a relationship of L4>L6>L5> L7.   An image carrier for carrying an electrostatic latent image;
Latent image forming means for forming an electrostatic latent image on the image carrier;
A plurality of image forming means having a developing means for developing the electrostatic latent image into a toner image, and sequentially facing the surface of each image carrier of the plurality of image forming means. A transfer material conveyance belt that carries the transfer material by carrying the endlessly moved surface; and
An image forming apparatus comprising: a transfer unit configured to transfer the toner image on the image carrier to the surface of the transfer material carried on the transfer material conveyance belt;
  A plurality of stretching rollers for stretching the transfer material conveyance belt and bringing the transfer material conveyance belt into contact with the image carrier;
A tension roller that applies pressure to the intermediate transfer belt by pressing the transfer material conveying belt;
A first swinging member for supporting a plurality of stretching rollers, leaving at least one image carrier, and separating the transfer material transport belt from other image carriers;
  A second swing member that supports one tension roller and separates the transfer material transport belt from at least one image carrier, and a first swing member that supports and rotates the second swing member. An eccentric cam and a second eccentric cam;
  A full contact mode in which the transfer material transport belt is in contact with all image carriers, and a toner image on the image carrier is transferred to the transfer material surface carried by the transfer material transport belt by the transfer means;
  All-separation drive possible mode in which the transfer material conveyance belt is applied with a tension that can be rotationally driven and the transfer material conveyance belt is separated from all image carriers, and
  A configuration in which the transfer material conveyance belt can be separated from all image carriers with a lower tension than the tension of the transfer material conveyance belt in the all separation driveable mode. Equipped with
The contacting / separating means is configured to separate the transfer roller from the image carrier by separating the stretch roller from the image carrier, and the stretch in the fully separated driveable mode. A separation distance between the roller and the image carrier is configured to be shorter than a separation distance between the tension roller and the image carrier in the full separation low tension mode; and
In the full contact mode, the second eccentric cam is separated from the second swing member, and the first eccentric cam is in contact with the second swing member so that only the first eccentric cam is present. The second oscillating member is supported by the first oscillating cam so that the first eccentric cam is separated from the second oscillating member, and the second eccentric cam is the second oscillating member. The image forming apparatus is configured to support the second swinging member only by the second eccentric cam in contact with the second eccentric cam.

Images