JP2009204995A - Image forming device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve the problem that the push up roller, if used to prevent image transfer scattering, is prone to cause defective images by damaging the back surface of the intermediate transfer belt. <P>SOLUTION: This image forming devise includes image carriers 40, 50, 60, 70 to form toner images respectively on their surfaces, an intermediate transfer belt 8 on which the toner images are transferred from the image carriers and overlapped, transfer materials 14, 15, 16, 17 respectively facing the image carriers with the intermediate transfer belt in between, and rollers 34, 35, 36, 37 to press the intermediate transfer belt to the image carriers at around the upstream of the nip sections 84, 85, 86, 87 formed with the image carriers and the intermediate transfer belt. Those rollers includes elastic layers on their surfaces at least and are disposed free to turn. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an image forming apparatus such as a printer, a copying machine, and a facsimile. For example, the present invention relates to an electrophotographic color image forming apparatus using an intermediate transfer system.

  In recent years, full-color copying machines as well as monochrome copying machines are often used as image forming apparatuses. As such a full-color copying machine, a tandem color copying machine in which a photosensitive drum is provided for each color toner is often used because of its high printing speed.

  In such a tandem type color copying machine, a toner image formed on a photosensitive drum for each color is temporarily transferred onto an intermediate transfer belt and superimposed, and then transferred onto a recording medium such as paper. Is done. The secondary transferred toner image is fixed on a sheet and discharged from the copying machine.

  Here, a toner and a reverse bias are applied to a primary transfer roller disposed opposite to the photosensitive drum with the intermediate transfer belt interposed therebetween, and primary transfer is performed by pressing by the primary transfer roller. However, when the toner image on the photosensitive drum approaches the vicinity of the nip portion, discharge may occur and so-called “transfer scattering” may occur.

  In order to prevent this “transfer scattering”, an image forming apparatus having a belt lifting roller in the vicinity of the upstream side of the nip portion is disclosed (for example, see Patent Document 1).

FIG. 7 is a view showing the vicinity of the nip portion 204 of one photosensitive drum 200 and the intermediate transfer belt 202 in the tandem type image forming apparatus disclosed in Patent Document 1. As shown in FIG. 7, an intermediate transfer belt 202 is passed through a nip portion 204 formed by the photosensitive drum 200 and the primary transfer roller 201, and the intermediate transfer belt 202 is lifted by a roller 203 on the upstream side of the nip portion 204. Is lifted to the photosensitive drum 200 side. In this way, by reducing the gap on the upstream side of the nip portion 204, “transfer scattering” is suppressed.
JP 2001-75379 A

  However, when the lifting roller 203 for suppressing “transfer scattering” is used, if a foreign object is caught between the lifting roller 203 and the back surface of the intermediate transfer belt 202, the back surface of the belt is damaged and a streak-like image defect is caused. There was a problem that would occur.

  That is, in the image forming apparatus using the intermediate transfer method, toner, paper dust, and the like adhere to exposed portions in the housing. Since a metal roller is generally used as the lifting roller 203 as in the image forming apparatus disclosed in Patent Document 1, if a foreign object is caught between the hard metal roller and the intermediate transfer belt 202, The back surface of the intermediate transfer belt 202 is damaged. When the back surface of the intermediate transfer belt 202 is scratched, a streak-like image defect occurs.

  An object of the present invention is to provide an image forming apparatus that can suppress damage to an intermediate transfer member that occurs when a push-up roller for preventing scattering of transfer is used in consideration of the problems of the conventional image forming apparatus described above. And

In order to achieve the above object, the first present invention provides:
A plurality of image carriers on which toner images are formed; and
An intermediate transfer member on which a plurality of toner images formed for each image carrier are transferred and superimposed;
A transfer member provided to face each of the plurality of image carriers with the intermediate transfer member interposed therebetween;
A roller member that presses the intermediate transfer member in the vicinity of the upstream side of at least one of the nip portions among the nip portions formed by the plurality of image carriers and the intermediate transfer member; An image forming apparatus,
The roller member is an image forming apparatus that has an elastic layer on at least a surface thereof and is rotatably arranged.

The second aspect of the present invention provides
One image carrier on which a plurality of toner images are sequentially formed on the surface;
An intermediate transfer body on which the plurality of toner images are transferred and superimposed;
A transfer member provided so as to face the image carrier with the intermediate transfer member interposed therebetween;
An image forming apparatus comprising: a roller member that presses the intermediate transfer member in the vicinity of the upstream side of the nip portion formed by the image carrier and the intermediate transfer member toward the image carrier.
The roller member is an image forming apparatus that has an elastic layer on at least a surface thereof and is rotatably arranged.

The third aspect of the present invention
In the image forming apparatus according to the first or second aspect of the present invention, the roller member has a frictional force on the surface so as not to slip when the intermediate transfer member is driven.

The fourth aspect of the present invention is
The roller member is the image forming apparatus according to any one of the first to third aspects, in which a rubber layer is formed on a surface of a metal roller.

The fifth aspect of the present invention provides
The image forming apparatus according to any one of the first to fourth aspects of the present invention, further comprising a cleaning unit for removing deposits adhering to the surface of the intermediate transfer member on the transfer member side.

The sixth aspect of the present invention provides
A cleaning unit for removing deposits adhering to the transfer member side surface of the intermediate transfer member;
The image forming apparatus according to the first or second aspect of the present invention includes a control unit that measures a rotation speed of the roller member and causes the cleaning unit to perform cleaning based on a change in the rotation speed.

The seventh aspect of the present invention
The control unit causing the cleaning unit to perform cleaning based on the change in the rotation speed is to cause the cleaning unit to perform cleaning when the rotation speed becomes lower than a predetermined rotation speed. 6 is an image forming apparatus according to a sixth aspect of the present invention;

In addition, the eighth aspect of the present invention
The control unit causes the cleaning unit to perform cleaning based on the change in the rotation speed when the difference between the rotation speeds measured at a plurality of points in time within a predetermined period is greater than a predetermined value. The image forming apparatus according to the sixth aspect of the present invention is to cause the cleaning unit to perform cleaning.

  According to the present invention, it is possible to provide an image forming apparatus that can suppress damage to the intermediate transfer member that occurs when a push-up roller for preventing transfer scattering is used.

  A copier as an example of an image forming apparatus according to the present invention will be described below with reference to the drawings.

(Embodiment 1)
FIG. 1 is a structural cross-sectional view of the front surface of a copying machine according to Embodiment 1 of the present invention.

  As shown in FIG. 1, the copying machine 1 according to the first embodiment includes a plurality of paper feed cassettes 2 for storing paper on which images are formed on the bottom. In addition, the copying machine 1 includes an original reading unit 3 that reads an image of an original with an exposure lamp, a lens, a mirror, and the like.

  The copying machine 1 according to the first embodiment is a color copying machine using a tandem method, and includes a black image forming unit 4, a yellow image forming unit 5, a cyan image forming unit 6 arranged in the horizontal direction, and A magenta image forming unit 7 is provided. An intermediate transfer belt 8 for superimposing images formed by these image forming units is disposed. Further, a secondary transfer unit 9 for transferring the toner image superimposed on the intermediate transfer belt 8 onto a sheet and a fixing unit 10 for fixing the transferred toner image on the sheet are provided.

  A registration roller 25 is provided upstream of the secondary transfer unit 9 in the paper conveyance direction (see arrow E), and is used to convey the paper between the secondary transfer unit 9 and the fixing unit 10. A conveyor belt 26 is provided. Further, a discharge roller pair 12 for discharging the paper that has passed through the fixing unit 10 to the outside of the copying machine 1 is provided on the side surface, and a discharge tray 13 on which the paper discharged by the discharge roller pair 12 is placed is provided. Is provided. In FIG. 1, the sheet conveyance direction is indicated by an arrow E.

  Next, the configuration of the image forming unit and the intermediate transfer belt 8 will be described.

  FIG. 2 is an enlarged configuration diagram in the vicinity of the intermediate transfer belt 8. In FIG. 2, the thickness of the intermediate transfer belt 8 is shown thicker than usual for easy understanding.

  As shown in FIGS. 1 and 2, the black image forming unit 4 includes a photosensitive drum 40 made of amorphous silicon, a charger 41, a developing unit 42, a cleaning unit 43, a static eliminator 44, and the like. Further, a laser scanner unit (hereinafter referred to as LSU) 46 that forms an electrostatic latent image by optically scanning the surface of the photosensitive drum 40 charged by the charger 41 of the black image forming unit 4 is a photosensitive drum. 40 is provided above. Similarly, the other image forming units 5, 6, 7 also have photosensitive drums 50, 60, 70, chargers 51, 61, 71, developing units 52, 62, 72, cleaning units 53, 63, 73, static eliminators. 54, 64, 74 and LSUs 56, 66, 76 and the like.

  Further, primary transfer rollers 14, 15, 16, and 17 are disposed so as to face the photoreceptor drums 40, 50, 60, and 70 with the intermediate transfer belt 8 interposed therebetween, and the primary transfer rollers 14, 15, 16 are arranged. , 17 are pressed against the photosensitive drums 40, 50, 60, 70 facing each other with the intermediate transfer belt 8 sandwiched between them by a spring member 31. The developing units 42, 52, 62, and 72 are provided with developing rollers 45 and 55 that are disposed in contact with the photosensitive drum in order to supply toner to the surfaces of the photosensitive drums 40, 50, 60, and 70, respectively. , 65, 75 are provided. In FIG. 2, only the photosensitive drum, the charger, and the developing roller are shown.

  Further, the intermediate transfer belt 8 is provided with a layer of an elastic member such as rubber on a resin belt in order to achieve both running performance and high image quality. As shown in FIG. 2, the secondary transfer unit 9 has a secondary transfer roller 92, and the secondary transfer roller 92 forms a black image based on the rotation direction of the intermediate transfer belt 8 (see arrow A). They are disposed downstream of the unit 4 and upstream of the magenta image forming unit 7 and outside the intermediate transfer belt 8.

  Further, a driven roller 21 is provided inside the intermediate transfer belt 8 so as to face the secondary transfer roller 92. Further, a driven roller 22 is provided inside the intermediate transfer belt 8 in the vicinity of the upstream side of the magenta image forming unit 7. A driving roller 24 for driving the intermediate transfer belt 8 is provided on the downstream side of the black image forming unit 4 and inside the intermediate transfer belt 8 on the upstream side of the driven roller 21. Further, as shown in FIG. 1, the residual toner on the front surface (the surface in contact with the photosensitive drum) of the intermediate transfer belt 8 is upstream of the driven roller 22 and downstream of the driven roller 21. A cleaning device 11 for removing is arranged.

  In addition, as shown in FIG. 2, the intermediate transfer belt 8 formed by the intermediate transfer belt 8 and the photosensitive drums 40, 50, 60, and 70 in the vicinity of the upstream side of the respective nip portions 84, 85, 86, and 87. On the inside, roller members 34, 35, 36, and 37 are arranged. The intermediate transfer belt 8 is lifted by these roller members 34, 35, 36, 37, and the intermediate transfer belt 8 upstream of the nip portions 84, 85, 86, 87 and the photosensitive drums 40, 50, 60, 70. The gap is narrowed and transfer scattering is suppressed.

  A longitudinal sectional view of the roller members 34, 35, 36, 37 passing through the central axis is shown in FIG. 3A, and a transverse sectional view is shown in FIG.

  As shown in FIGS. 3A and 3B, the roller members 34, 35, 36, and 37 are elastic rubbers having a large friction on the surface of the metal core 93 that contacts the intermediate transfer belt 8. The layer 94 is provided. The roller members 34, 35, 36, and 37 are grounded, and are rotatably attached so as to follow the movement of the abutting intermediate transfer belt 8.

  The photosensitive drums 40, 50, 60, and 70 are examples of the plurality of image carriers of the present invention, and the intermediate transfer belt 8 is an example of the intermediate transfer body of the present invention. The primary transfer rollers 14, 15, 16, and 17 correspond to an example of the transfer member of the present invention, and the rubber layer 94 corresponds to an example of the elastic layer of the present invention.

  Next, an image forming method of the copying machine according to the first embodiment will be described.

  Based on the image data read by the document reading unit 3, the black image forming unit 4, yellow image forming unit 5, cyan image forming unit 6, and magenta image forming unit 7 are charged by chargers 41, 51, 61, 71. An electrostatic latent image is formed by the LSUs 46, 56, 66, 76 on the surface of the uniformly charged photoreceptor drums 40, 50, 60, 70 and visualized by the developing units 42, 52, 62, 72. Is formed (see FIG. 1). At this time, the toner on the photoconductive drums 40, 50, 60, and 70 is positively charged, and the negative voltage applied to the primary transfer rollers 14, 15, 16, and 17 and the pressing force of the primary transfer roller are used. The toner images are superimposed on the intermediate transfer belt 8 in the order of magenta, cyan, yellow, and black.

  The toner remaining on the photosensitive drums 40, 50, 60, and 70 by the primary transfer is removed by the cleaning units 43, 53, 63, and 73, and the surfaces of the photosensitive drums 40, 50, 60, and 70 are removed. Electric charges are removed by the electric devices 44, 54, 64 and 74.

  At the same time, paper is fed from the paper feed cassette 2, the paper is temporarily stopped by the registration roller 25, and sent to the secondary transfer unit 9 in accordance with the movement timing of the area on the intermediate transfer belt 8 where the toner image is formed. It is.

  The toner image superimposed on the intermediate transfer belt 8 is transferred onto the sheet by the secondary transfer roller 92, and the sheet is conveyed to the fixing unit 10 by the conveyance belt 26. Then, the sheet on which the toner image is fixed by the fixing unit 10 is discharged onto the discharge tray 13 through the discharge roller pair 12 (see FIG. 1).

  When printing of the read image data is completed, the operations of the photosensitive drums 40, 50, 60, 70, the intermediate transfer belt 8, the secondary transfer roller 92, and the like are stopped, and the image forming operation is completed.

  Next, examples will be described below.

  In the first embodiment, the photosensitive drums 40, 50, 60, and 70 have a diameter of 30 mm, and the length of the intermediate transfer belt 8 between the photosensitive drums is set to 100 mm. In addition, as the roller members 34, 35, 36, and 37, as shown in FIGS. 3A and 3B, a rubber core 94 having a thickness of 1.5 mm is formed on the surface of a metal core 93 having a diameter of 8 mm. Use. The rubber layer 94 is made of rubber having an Asker C hardness of 40 to 55 degrees and a dynamic friction coefficient with the back surface resin of the intermediate transfer belt 8 of 1.5 or more.

  FIG. 4 is an enlarged view of a contact portion between the intermediate transfer belt 8 and the photosensitive drums 40 and 50 and the roller members 34 and 35 in this embodiment.

  As shown in FIG. 4, the position of the intermediate transfer belt 8 on the upper surface side in the center of the contact portion with the roller member 35 is J, and the center position of the nip portion 85 between the intermediate transfer belt 8 and the photosensitive drum 50 is K. And Further, the position on the upper surface side of the center of the contact portion of the intermediate transfer belt 8 with the roller member 34 is L, and the position of the center of the nip portion 84 between the intermediate transfer belt 8 and the photosensitive drum 40 is M. The length between JK and LM is set to 25 mm, and the length between KL is set to 75 mm. The contact position Ha between the roller member 35 and the intermediate transfer belt 8 is set to be 2 mm higher than the contact position Hb between the primary transfer roller 15 and the intermediate transfer belt 8. The other photosensitive drums and roller members are arranged in the same manner.

  In this embodiment, the photosensitive drums 40, 50, 60 are used to reduce the adhesion between the photosensitive drums 40, 50, 60, 70 and the intermediate transfer belt 8 for the purpose of preventing the image from being lost. , 70 is set to 200.0 mm / sec, and the peripheral speed of the drive roller 24 is set to 200.2 mm / sec. Here, the peripheral speeds of the driving roller 24 and the photosensitive drums 40, 50, 60, and 70 refer to the speeds on the respective roller surfaces.

  As shown in FIGS. 3A and 3B, since the elastic rubber layer 94 is formed on the surface of the roller members 34, 35, 36, and 37, the intermediate transfer belt 8 and the roller member 34, Even if an adherent such as toner or paper dust adheres between 35, 36, and 37, the rubber layer 94 can absorb irregularities due to the adherent, and thus the back surface of the intermediate transfer belt 8 can be prevented from being damaged.

  Further, by using the roller members 34, 35, 36, and 37 having the configurations shown in FIGS. 3A and 3B, the color caused by the slip between the intermediate transfer belt 8 and the roller members 34, 35, 36, and 37 can be obtained. Misalignment can also be prevented.

  In the conventional image forming apparatus, in FIG. 7, when a resin such as polyimide is used as the intermediate transfer belt 202, the dynamic friction coefficients between the surface of the metal lifting roller 203 and the back surface of the resin intermediate transfer belt 202 are compared. In some cases, the coefficient of dynamic friction between the metal lifting roller 203 and its bearing is approximately the same as the coefficient of dynamic friction between metals (about 0.2 to 0.4).

  At this time, when the torque due to the frictional force between the lifting roller 203 and the back surface of the intermediate transfer belt 202 is smaller than the torque due to the frictional force between the shaft of the lifting roller 203 and its bearing, the lifting roller 203 is moved to the intermediate transfer belt. A slip occurs between the intermediate transfer belt 202 and the lifting roller 203 without being driven to rotate.

  As described above, when the frictional force between the lifting roller 203 and the back surface of the intermediate transfer belt 202 is small, the lifting roller 203 not only rotates following the intermediate transfer belt 202 but also slips. When the rotation is shifted from the driven rotation 202 to the slip, the speed of the intermediate transfer belt 202 becomes unstable, and color misregistration may occur.

  In the example of the first embodiment, the roller members 34, 35, 36, and 37 are formed with a rubber layer 94 having a large dynamic friction coefficient on the surface thereof. Since it rotates at substantially the same speed as the back surface of the transfer belt 8, color misregistration due to slippage of the roller members 34, 35, 36, and 37 hardly occurs. At this time, the circumferential speeds of the roller members 34, 35, 36, and 37 are considered to be the speeds of the intermediate transfer belt 8 at the respective positions, and values between 200.0 and 200.2 mm / sec.

  In this embodiment, the rubber layer 94 is made of rubber having an Asker C hardness of 40 to 55 degrees and a dynamic friction coefficient with the back surface resin of the intermediate transfer belt 8 of 1.5 or more. When rubber having a thickness of 4 mm or more and an Asker C hardness of 35 degrees or less is used for the rubber layer 94 with respect to the diameter 8 mm of the metal core 93, the rubber layer 94 is too thick and the Asker C hardness is too small. There is a risk that the speed of the intermediate transfer belt 8 becomes unstable due to the expansion and contraction of 94.

  On the other hand, if the rubber layer 94 is as thin as less than 1 mm and the hardness is as high as Asker C hardness of 60 degrees or more, the unevenness cannot be absorbed when adhering matter is attached to the back surface of the intermediate transfer belt 8, and sufficient damage is caused. The prevention effect cannot be obtained.

  In the first embodiment, as shown in FIG. 3A, the rubber layer 94 of the roller members 34, 35, 36, and 37 is described as being formed on the entire roller portion of the metal core 93. However, the width of the rubber layer 94 only needs to be greater than or equal to the width of the intermediate transfer belt 8. A portion where the rubber layer 94 contacts the intermediate transfer belt 8 in the roller portion of the metal core 93 as shown in the longitudinal sectional view of the roller member of the other configuration of the first embodiment shown in FIG. What is necessary is just to be formed.

  In the first embodiment, the roller members 34, 35, 36, and 37 are configured such that the rubber layer 94 is provided on the surface of the metal core 93, but have the same hardness as the metal instead of the metal core 93. Other materials may be used, and other materials having the same hardness and frictional force may be used instead of the rubber layer 94. The surface of the roller members 34, 35, 36, and 37 has the same hardness and frictional force as the rubber layer 94, not limited to those made of two materials such as the metal core 93 and the rubber layer 94. If so, a configuration in which three or more materials are laminated may be used.

  In the first embodiment, the roller members 34, 35, 36, and 37 are disposed so as to lift the intermediate transfer belt 8. However, the roller members 34, 35, 36, and 37 are appropriately changed depending on the arrangement of the photosensitive drum and the intermediate transfer belt. . In short, it is only necessary to determine the position of the roller member so as to narrow the gap between the photosensitive drum and the intermediate transfer belt in the vicinity of the upstream side of the nip portion.

  In the first embodiment, the rollers are provided in the vicinity of all upstream sides of the four nip portions 84, 85, 86, 87 formed by the four photosensitive drums 40, 50, 60, 70 and the intermediate transfer belt 8. The members 34, 35, 36, and 37 are provided. If there is a nip portion where “transfer scattering” is difficult to occur due to, for example, the charge amount of the toner used being low, the nip portion It is not necessary to provide a roller member upstream. For example, the configuration may be such that one roller member is provided only upstream of one nip portion.

  Further, in the first embodiment, rubber having an Asker C hardness of 40 to 55 degrees and a coefficient of dynamic friction with the back surface resin of the intermediate transfer belt 8 on the surfaces of the roller members 34, 35, 36, and 37 is 1.5 or more. Although the layer 94 is formed, if the Asker C hardness is 40 to 55 degrees, even if the coefficient of dynamic friction with the back surface resin of the intermediate transfer belt 8 is small, it is provided on the surface of the roller member instead of the rubber layer 94. It is good also as a structure. In this case, although the effect of preventing the occurrence of color misregistration due to the slip between the intermediate transfer belt 8 and the roller member cannot be obtained, the effect of preventing the damage due to the adhered matter on the back surface of the intermediate transfer belt 8 can be obtained. .

(Embodiment 2)
FIG. 5 is an enlarged configuration diagram in the vicinity of the intermediate transfer belt of the copying machine according to the second embodiment of the present invention. Unlike the tandem copying machine of the first embodiment, the copying machine of the second embodiment is a one-drum copying machine.

  In the copying machine according to the second embodiment, as shown in FIG. 5, one photosensitive drum 100 and development that supplies four types of toners of black, yellow, cyan, and magenta to the photosensitive drum 100 for each color. A device 101 is provided. The developing device 101 includes a black developing device 101K, a yellow developing device 101Y, a cyan developing device 101C, and a magenta developing device 101M, and each developing device is moved to a developing position facing the photosensitive drum 100 by rotating. By moving sequentially, toner images of opposite colors are formed on the surface of the photosensitive drum 100.

  One photosensitive drum 100 corresponds to an example of one image carrier of the present invention.

  Further, an intermediate transfer belt 102 is provided for superimposing toner images for each color. Inside the intermediate transfer belt 102, a primary transfer roller 103 is provided at a position facing the photosensitive drum 100. In addition, a driving roller 104, a driven roller 105, and a roller member 106 are also provided. The driven roller 105 is disposed at a position facing the secondary transfer roller 107 for secondary transfer of the toner image on the intermediate transfer belt 102 to the sheet, and the drive roller 104 is rotated in the rotational direction of the intermediate transfer belt 102 ( With reference to the arrow H), it is provided downstream of the primary transfer roller 103 and upstream of the driven roller 105. Note that the sheet conveyance direction is indicated by an arrow I.

  A roller member 106 is disposed in the vicinity of the upstream side of the nip portion 108 formed between the photosensitive drum 100 and the intermediate transfer belt 102. Similar to the roller members 34, 35, 36, and 37 of the first embodiment, the roller member 106 is provided to narrow the gap between the photosensitive drum 100 and the intermediate transfer belt 102 in the vicinity of the upstream side of the nip portion 108. Yes.

  Further, this roller member 106 has elastic frictional friction on the surface of the metal core, like the roller members 34, 35, 36, and 37 of the first embodiment as shown in FIGS. 3 (a) and 3 (b). A rubber layer having a large coefficient is formed, and is rotatably attached so as to follow the intermediate transfer belt 102.

  In the copying machine of the second embodiment, a toner image of one color is formed on the surface of the photosensitive drum 100, and after the toner image is primarily transferred to the intermediate transfer belt 102, the toner image of the other color is exposed to light. It is formed on the surface of the body drum 100, and is primary-transferred over the previously transferred toner image. In this manner, toner images are sequentially formed on the photosensitive drum 100 and are primarily transferred onto the intermediate transfer belt 102 so as to be primary transferred, whereby a color toner image is formed on the intermediate transfer belt 102 and the secondary transfer roller 107. Is transferred to a recording medium such as paper.

  Since an elastic rubber layer is formed on the surface of the roller member 106, even if toner or paper dust adheres between the intermediate transfer belt 102 and the roller member 106, the unevenness due to the adhered matter is rolled into the roller. Since it can be absorbed by the rubber layer on the surface of the member 106, it is possible to prevent the back surface of the intermediate transfer belt 102 from being damaged as in the case of the first embodiment.

  Further, since the dynamic friction coefficient of the roller layer surface of the roller member 106 is large, the roller member 106 is driven by friction with the intermediate transfer belt 102 and rotates at substantially the same speed as the back surface of the intermediate transfer belt 102. Misalignment can also be prevented.

  Thus, the present invention can be applied to a one-drum type copying machine as in the second embodiment.

(Embodiment 3)
FIG. 6 is an enlarged configuration diagram in the vicinity of the intermediate transfer belt of the copying machine according to the third embodiment of the present invention. The copier of the third embodiment is a tandem type copier similar to that of the first embodiment. In FIG. 6, the same components as those of the copier of the first embodiment shown in FIG. The same symbols are used.

  The copying machine of the third embodiment is different from the configuration of the first embodiment in that a control unit 30 and a back surface cleaning blade 38 are provided in addition to the configuration of FIG. Since the image forming method is the same as that of the copying machine of the first embodiment, description thereof is omitted. The difference from the first embodiment is that it has a function of cleaning the back surface of the intermediate transfer belt 8. Hereinafter, a different part from the copying machine of Embodiment 1 is demonstrated.

  As shown in FIG. 6, the copying machine according to the third embodiment includes a back surface cleaning blade 38 for removing deposits on the back surface of the intermediate transfer belt 8. If the cleaning blade is kept in contact with the intermediate transfer belt 8 at all times, the speed of the intermediate transfer belt 8 becomes unstable due to the behavior of the cleaning blade. Therefore, in the third embodiment, the cleaning blade is brought into contact only when cleaning is performed. Thus, the back surface cleaning blade 38 is provided with a contact / separation mechanism.

  Further, the copying machine of the third embodiment includes a control unit 30 that controls the contact / separation mechanism of the back surface cleaning blade 38 based on the rotational speeds of the roller members 34, 35, 36, and 37.

  The back surface cleaning blade 38 is an example of the cleaning unit of the present invention.

  As shown in FIGS. 3A and 3B, the roller members 34, 35, 36, and 37 have a rubber layer 94 having a large dynamic friction coefficient formed on the surface thereof, and are rotatably attached. Since it rotates following the intermediate transfer belt 8 without slipping, the peripheral speeds of the roller members 34, 35, 36, and 37 are equal to the moving speed of the intermediate transfer belt 8. Since the peripheral speeds can be calculated from the rotational speeds of the roller members 34, 35, 36, and 37, the moving speed of the intermediate transfer belt 8 can be acquired from the rotational speeds of the roller members 34, 35, 36, and 37. A change in the moving speed of the intermediate transfer belt 8 can also be detected by a change in the rotation speed of the roller members 34, 35, 36, and 37.

  When it is determined that the back surface of the intermediate transfer belt 8 needs to be cleaned based on the change in the rotation speed of the roller members 34, 35, 36, and 37, the control unit 30 moves the back surface cleaning blade 38 of the intermediate transfer belt 8. Control to perform cleaning by contacting the back surface.

  Specifically, the control unit 30 determines that the average rotation speed of the roller members 34, 35, 36, and 37 in a predetermined period (for example, a period in which the intermediate transfer belt 8 makes one round) is slower than the predetermined rotation speed. In this case, it is determined that slip has occurred between the driving roller 24 and the intermediate transfer belt 8, and the rear surface cleaning blade 38 is controlled to perform cleaning. As a deposit such as toner adheres to the back surface of the intermediate transfer belt 8, the friction between the driving roller 24 and the intermediate transfer belt 8 becomes small and slips easily, and the moving speed of the intermediate transfer belt 8 is slow. Therefore, the magnitude of the slip between the drive roller 24 and the intermediate transfer belt 8 can be determined from the rotational speed of the roller members 34, 35, 36, and 37.

  Further, the control unit 30 changes the rotational speed of the roller members 34, 35, 36, and 37 within a predetermined short period (for example, a period during which the intermediate transfer belt 8 moves a distance of 25 mm from the roller member to the photosensitive drum). However, when the amount of change exceeds a predetermined amount of change, it is determined that an adhering substance such as paper dust has adhered, and also in this case, the rear surface cleaning blade 38 is controlled to perform cleaning. If a deposit of a certain size or more adheres to the back surface of the intermediate transfer belt 8, the moving speed of the intermediate transfer belt 8 suddenly changes when the portion with the deposit on the intermediate transfer belt 8 passes. From the sudden change in the rotational speed of the roller members 34, 35, 36, and 37, it can be determined that the deposit has adhered to the back surface of the intermediate transfer belt 8.

  For example, the rotational speeds of the roller members 34, 35, 36, and 37 are measured every minute period, and the difference between the two rotational speeds measured continuously is greater than or equal to a predetermined magnitude, or a short period (for example, The difference between the maximum value and the minimum value of the measured values of a plurality of rotational speeds measured within a distance of 25 mm from the roller member to the photosensitive drum during a period in which the intermediate transfer belt 8 moves) is equal to or greater than a predetermined value. A sudden change in the rotation speed can be determined.

  Note that the rotational speeds of the roller members 34, 35, 36, and 37 can be detected, for example, by measuring the number of rotations within a predetermined period. It can also be detected by measuring the time required for rotation at a predetermined rotational speed.

  Further, when the control unit 30 determines whether or not the back surface of the intermediate transfer belt 8 needs to be cleaned, the peripheral speed is obtained from the rotational speed acquired from the roller members 34, 35, 36, and 37, and the peripheral speed value is obtained. You may make it determine based on. Further, instead of acquiring the rotational speeds of the roller members 34, 35, 36, and 37, the peripheral speeds of the roller members 34, 35, 36, and 37 are acquired, and the determination is made based on the peripheral speeds. Good.

  Further, since the moving speed of the intermediate transfer belt 8 can be accurately detected by measuring the rotational speeds of the roller members 34, 35, 36, and 37, the controller 30 rotates the roller members 34, 35, 36, and 37. Based on the change in speed, the rotational speed of the drive roller 24 and the photosensitive drums 40, 50, 60, and 70 may be feedback controlled.

  Note that no slip occurs between the driving roller 24 and the intermediate transfer belt 8, and even if slip occurs between the roller members 34, 35, 36, 37 and the intermediate transfer belt 8, the roller members 34, 35. , 36 and 37 can be used to control the back surface cleaning blade 38.

  In this case, when slip occurs with the intermediate transfer belt 8, the rotational speed measured by the roller members 34, 35, 36, and 37 is slower than the reference rotational speed when no slip occurs. Therefore, the magnitude of the slip between the roller members 34, 35, 36, 37 and the intermediate transfer belt 8 can be determined based on the difference between the measured rotational speed and the reference rotational speed. Therefore, the control unit 30 may control the rear surface cleaning blade 38 to perform cleaning when it is determined that the rotational speed has decreased and the slip amount has increased.

  However, in this case, since the accurate moving speed of the intermediate transfer belt 8 cannot be detected from the number of rotations of the roller members 34, 35, 36, and 37, the rotation of the driving roller 24 cannot be feedback-controlled as described above. .

  In this case, the roller members 34, 35, 36, and 37 may have elastic surfaces with Asker C hardness of about 40 to 55 degrees, and dynamic friction with the back surface resin of the intermediate transfer belt 8. The coefficient may be small.

  In the third embodiment, the back surface cleaning blade 38 is used as an example of the cleaning unit of the present invention. However, a brush-like cleaning member may be used.

  INDUSTRIAL APPLICABILITY The image forming apparatus according to the present invention has an effect of suppressing damage to the intermediate transfer member that occurs when a push-up roller for preventing transfer scattering is used. A printer, a copier, and a facsimile machine using the intermediate transfer method It is useful as an image forming apparatus.

1 is a cross-sectional configuration diagram of a front surface of a copying machine according to a first embodiment of the present invention. FIG. 2 is an enlarged configuration diagram in the vicinity of an intermediate transfer belt of the copying machine according to the first embodiment of the present invention. (A) Longitudinal sectional view passing through the central axis of the roller member of Embodiment 1 of the present invention, (b) Cross sectional view of the roller member of Embodiment 1 of the present invention, (c) Embodiment of the present invention 1 is a longitudinal sectional view of a roller member having another configuration passing through the central axis. The enlarged view which shows the contact part of an intermediate transfer belt, a photoreceptor drum, and a roller member of the copying machine in the Example of Embodiment 1 of this invention. Cross-sectional configuration diagram of the front surface of the copying machine according to the second embodiment of the present invention FIG. 4 is an enlarged configuration diagram in the vicinity of an intermediate transfer belt of a copying machine according to a third embodiment of the present invention. Partial enlarged view showing the vicinity of the nip portion between the photosensitive drum and the intermediate transfer belt in the conventional image forming apparatus.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Copier 2 Paper feed cassette 3 Original reading part 4 Black image forming part 5 Yellow image forming part 6 Cyan image forming part 7 Magenta image forming part 8 Intermediate transfer belt 9 Secondary transfer part 10 Fixing part 11 Cleaning device 12 Discharge roller pair 13 Discharge tray 14, 15, 16, 17 Primary transfer roller 21, 22 Driven roller 24 Drive roller 25 Registration roller 26 Conveyor belt 30 Control unit 34, 35, 36, 37 Roller member 38 Back surface cleaning blade 40, 50, 60, 70 Photoconductor drum 41, 51, 61, 71 Charger 42, 52, 62, 72 Developer 43, 53, 63, 73 Cleaning unit 44, 54, 64, 74 Charger 45, 55, 65, 75 Developing roller 46 56, 66, 76 LSU
84, 85, 86, 87 Nip part 100 Photosensitive drum 101 Developing device 102 Intermediate transfer belt 103 Primary transfer roller 104 Drive roller 105 Followed roller 106 Roller member 107 Secondary transfer roller 108 Nip part

Claims (8)

A plurality of image carriers on which toner images are formed; and
An intermediate transfer member on which a plurality of toner images formed for each image carrier are transferred and superimposed;
A transfer member provided to face each of the plurality of image carriers with the intermediate transfer member interposed therebetween;
A roller member that presses the intermediate transfer member in the vicinity of the upstream side of at least one of the nip portions among the nip portions formed by the plurality of image carriers and the intermediate transfer member; An image forming apparatus,
The image forming apparatus, wherein the roller member has an elastic layer on at least a surface thereof and is rotatably arranged. One image carrier on which a plurality of toner images are sequentially formed on the surface;
An intermediate transfer body on which the plurality of toner images are transferred and superimposed;
A transfer member provided so as to face the image carrier with the intermediate transfer member interposed therebetween;
An image forming apparatus comprising: a roller member that presses the intermediate transfer member in the vicinity of the upstream side of the nip portion formed by the image carrier and the intermediate transfer member toward the image carrier.
The image forming apparatus, wherein the roller member has an elastic layer on at least a surface thereof and is rotatably arranged.   The image forming apparatus according to claim 1, wherein the roller member has a frictional force on the surface so that the roller member is driven without slipping when the intermediate transfer member is driven.   The image forming apparatus according to claim 1, wherein the roller member has a rubber layer formed on a surface of a metal roller.   5. The image forming apparatus according to claim 1, further comprising a cleaning unit configured to remove deposits attached to the surface of the intermediate transfer member on the transfer member side. A cleaning unit for removing deposits adhering to the transfer member side surface of the intermediate transfer member;
The image forming apparatus according to claim 1, further comprising: a control unit that measures a rotation speed of the roller member and causes the cleaning unit to perform cleaning based on a change in the rotation speed.   The control unit causing the cleaning unit to perform cleaning based on the change in the rotation speed is to cause the cleaning unit to perform cleaning when the rotation speed becomes lower than a predetermined rotation speed. The image forming apparatus according to claim 6.   The control unit causes the cleaning unit to perform cleaning based on the change in the rotation speed when the difference between the rotation speeds measured at a plurality of points in time within a predetermined period is greater than a predetermined value. The image forming apparatus according to claim 6, wherein the cleaning unit is configured to perform cleaning.

Images