JP2011169950A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce the occurrence of banding or color shift, by adsorbing vibration of an intermediate transfer belt generated at a secondary transfer position, and by suppressing propagation of the vibration to a primary transfer position. <P>SOLUTION: The intermediate transfer belt 20 is revolvably stretched on a plurality of rolls including a drive roll 21, a steering roll 22, etc. A plurality of image forming units 10 are arranged in positions facing the intermediate transfer belt, to primarily transfer the toner image of each color to the intermediate transfer belt, and a secondary transfer roll 24 is arranged downstream of the image forming units. An elastic roll 26 including an elastic layer on the outer periphery thereof is pressed against the inner peripheral surface side of the intermediate transfer belt between the primary transfer position 19 and the secondary transfer position 29, thereby supporting the intermediate transfer belt while the intermediate transfer belt is displaced outward. The amount of displacement AL of the elastic roll is no less than the maximum amount of amplitude BL caused by the vibration of the intermediate transfer belt when the elastic roll is not pressed against. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an image forming apparatus.

 As an image forming apparatus that forms a toner image by transferring toner to an electrostatic latent image on an image carrier, the toner image formed on the image carrier is temporarily transferred to an intermediate transfer member, Those that transfer a toner image onto a recording medium are widely used. As the intermediate transfer member, an endless intermediate transfer belt that is stretched around a plurality of roll-shaped members such as a drive roll and a steering roll and moves around is often used.

In such an apparatus, the toner image formed on the image carrier is transferred to the intermediate transfer belt at the primary transfer position, and is conveyed to the secondary transfer position by the circular movement of the intermediate transfer belt. At the secondary transfer position, a backup roll that is in contact with the inner peripheral surface of the intermediate transfer belt and a secondary transfer roll that is pressed from the outside of the intermediate transfer belt to the backup roll via the intermediate transfer belt are arranged. The recording medium is superimposed on the intermediate transfer belt and is sandwiched between the secondary transfer roll and the backup roll.
In such an image forming apparatus, for example, Patent Literature 1 and Patent Literature 2 describe techniques for suppressing the speed fluctuation of the intermediate transfer belt and the vibration of the intermediate transfer belt.

Japanese Patent Laid-Open No. 2000-231277 JP 2004-109872 A

  An object of the present invention is to reduce the propagation of the vibration of the intermediate transfer belt generated at the secondary transfer position to the primary transfer position on the upstream side in the moving direction of the intermediate transfer belt.

In order to solve the above-mentioned problem, the invention according to claim 1 is directed to an image holding member in which a latent image due to a difference in electrostatic potential is formed on an endless peripheral surface, and toner attached to the image holding member. A developing device that forms an image, an endless intermediate transfer belt that is stretched around a plurality of roll-shaped members and that is in contact with the image carrier, and is primarily transferred to the intermediate transfer belt. A secondary transfer device that transfers the toner image to a recording sheet, and the intermediate transfer between the primary transfer position of the toner image in the moving direction of the intermediate transfer belt and the secondary transfer position facing the secondary transfer device. And an elastic member pressed against an inner peripheral surface of the belt.
The elastic member is deformed by a pressure contact force against the intermediate transfer belt, and its shape is almost restored when the pressure contact force is released, and the recovery follows the displacement caused by the vibration of the intermediate transfer belt. As long as it arises like this. Therefore, it is not limited to what has the ideal elasticity in physics.

  According to a second aspect of the present invention, in the image forming apparatus according to the first aspect, the intermediate transfer belt is stretched around the roll-shaped member and the elastic member is in a non-pressure contact state. Assuming that BL is an amount displaced outwardly in the direction perpendicular to the peripheral surface by the vibration at the position to be tried, the elastic member comes into contact with the intermediate transfer belt from the position where the intermediate transfer belt is not displaced, It is assumed that it is supported at a position displaced by BL or more outward in the direction perpendicular to the peripheral surface of the transfer belt.

  According to a third aspect of the present invention, in the image forming apparatus according to the first or second aspect, the elastic member is formed after the intermediate transfer belt is stopped in a state where the elastic member is pressed against the intermediate transfer belt. It is assumed that the residual deformation that occurs when re-driven is in pressure contact with the intermediate transfer belt such that unevenness in the driving speed of the intermediate transfer belt due to the residual deformation is not detected.

  According to a fourth aspect of the invention, there is provided the image forming apparatus according to the first, second, or third aspect, wherein the intermediate transfer belt has an inward convex shape in the vicinity of both side edges of the inner peripheral surface. It has ribs which are continuous in the direction, and the elastic member is pressed between the ribs.

  The invention according to claim 5 is the image forming apparatus according to any one of claims 1 to 4, wherein the elastic member is a roll-shaped member supported so as to be rotatable about an axis. The outer peripheral part shall be formed with the elastic material.

  The invention according to claim 6 is the image forming apparatus according to any one of claims 1 to 4, wherein the elastic member is supported while being fixed in position, and the intermediate transfer belt is supported on the surface of the elastic member. It shall move around while rubbing.

  In the image forming apparatus according to claim 1, the intermediate transfer belt generated at the secondary transfer position is compared with the case where there is no elastic member pressed against the intermediate transfer belt between the primary transfer position and the secondary transfer position. It is possible to reduce the propagation of vibration to the primary transfer position on the upstream side in the moving direction of the intermediate transfer belt.

  In the image forming apparatus according to the second aspect, the contact state between the elastic member and the secondary transfer belt can be maintained as compared with the case where this configuration is not provided.

  In the image forming apparatus according to the third aspect, it is possible to suppress the uneven transfer speed of the intermediate transfer belt as compared with the case where this configuration is not provided.

  In the image forming apparatus according to the fourth aspect, it is possible to achieve both suppression of meandering of the intermediate transfer belt and absorption of vibration of the intermediate transfer belt.

  In the image forming apparatus according to the fifth aspect, it is possible to achieve both the absorption of the vibration of the intermediate transfer belt and the reduction of the rotation of the intermediate transfer belt as compared with the case where the present configuration is not provided.

  In the image forming apparatus according to the sixth aspect, it is possible to suppress a reduction in the vibration absorption effect as compared with an apparatus that does not include this configuration.

1 is a schematic configuration diagram illustrating an image forming apparatus according to an embodiment of the present invention. It is a schematic sectional drawing which shows the state in which the elastic roll used with the image forming apparatus shown in FIG. 1 is supported. FIG. 2 is a schematic cross-sectional view illustrating a state where an elastic roll used in the image forming apparatus illustrated in FIG. 1 is in contact with an inner peripheral surface of an intermediate transfer belt. FIG. 2 is a schematic diagram illustrating a state where vibration is generated on an intermediate transfer belt at a secondary transfer position of the image forming apparatus illustrated in FIG. 1. FIG. 6 is a diagram illustrating a state in which an intermediate transfer belt vibrates. FIG. 2 is a schematic diagram illustrating a state where vibration is generated on an intermediate transfer belt at a secondary transfer position of the image forming apparatus illustrated in FIG. 1. It is a figure which shows the process in which density nonuniformity generation | occurrence | production and the generated density nonuniformity are transcribe | transferred to a recording medium. It is a schematic block diagram which shows the elastic pad which can be used instead of the elastic roll shown in FIG.1 and FIG.2.

Hereinafter, embodiments of the invention according to the present application will be described with reference to the drawings.
FIG. 1 is a schematic configuration diagram of an image forming apparatus according to an embodiment of the present invention.
This image forming apparatus is a quadruple tandem full-color image forming apparatus, and forms an image of an electrophotographic system that outputs yellow (Y), magenta (M), cyan (C), and black (K) images. Units 10Y, 10M, 10C, and 10K, and an intermediate transfer belt 20 facing these units are provided. The intermediate transfer belt 20 is stretched so as to face each of the image forming units 10, and the circumferential surface thereof is driven to rotate. In order from the upstream side in the circumferential movement direction of the intermediate transfer belt 20, an image forming unit 10Y that forms a yellow toner image, an image forming unit 10M that forms a magenta toner image, and an image forming unit 10C that forms a cyan toner image. An image forming unit 10K for forming a black toner image is arranged, and on the downstream side thereof, a secondary transfer roll 24 for performing secondary transfer is disposed so as to face the intermediate transfer belt 20. The recording sheet is fed from the sheet tray 8 to the secondary transfer position 29 via the conveyance path 9 while being sandwiched between the registration rollers 9a. A fixing device 7 is provided on the downstream side of the secondary transfer position 29 in the recording paper conveyance path 9 to heat and press the toner image and press the toner image onto the recording paper. A paper discharge tray (not shown) for storing the fixed recording paper is provided.

  Each of the image forming units 10 has a photoconductive drum 1 that functions as an image holding body with an electrostatic latent image formed on the surface, and around each photoconductive drum 1, the photoconductive drum 1 is provided. A charging device 2 that charges the surface almost uniformly; a developing device 4 that selectively transfers toner to a latent image formed on the photosensitive drum to form a toner image; and a toner image on the photosensitive drum 1 The image forming apparatus includes a primary transfer roll 5 that primarily transfers the toner onto the intermediate transfer belt 20 and a cleaning device 6 that removes transfer residual toner remaining on the photosensitive drum after transfer. Further, an exposure device 3 that generates image light based on an image signal is provided for each of the uniformly charged photoconductive drums 1, and an image is formed on the photoconductive drum 1 upstream of the position where the developing device 5 faces. An electrostatic latent image is written by irradiating light.

  The photoconductor drum 1 is formed by laminating an organic photoconductor layer on the peripheral surface of a cylindrical member made of metal, and the metal portion is electrically grounded. Further, a bias voltage may be applied.

The charging device 2 includes an electrode wire that is stretched with a space from the peripheral surface of the photosensitive drum 1 that is a member to be charged, and a voltage is applied between the electrode wire and the photosensitive drum 1. The surface of the photosensitive drum 1 is charged by generating corona discharge.
In the present embodiment, the device for charging by corona discharge is used as described above, but a contact or non-contact charging device such as a solid discharger, a roll shape or a blade shape can also be used.

  The cleaning device 6 removes transfer residual toner adhering to the photosensitive drum with a cleaning blade and a cleaning brush arranged in contact with the peripheral surface of the photosensitive drum 1.

  The exposure device 3 generates a blinking laser beam based on an image signal, and scans this in the main scanning direction (axial direction) of each photosensitive drum 1 by a polygon mirror. As a result, electrostatic latent images corresponding to the images of the respective colors are formed on the surfaces of the respective photosensitive drums 1.

  The developing device 4 uses a two-component developer containing toner and a magnetic carrier. The developing device 4 includes a developing roll 4a at a position close to the photosensitive drum 1, and two developing rollers 4a are arranged on the circumferential surface of the rotating developing roll 4a. A thin layer of component developer is formed. In addition, the toner consumed as a result of image formation is replenished according to the amount consumed.

The primary transfer roll 5 is obtained by coating a metal core material with an outer peripheral surface with a conductive rubber material. For each of the image forming units 10Y, 10M, 10C, and 10K, the photosensitive drums 1Y, 1M, 1C, and 1K It is arranged on the back side of the intermediate transfer belt 20 at the opposite position. A transfer bias voltage is applied between the primary transfer rolls 5Y, 5M, 5C, 5K and the photosensitive drums 1Y, 1M, 1C, 1K, and the primary transfer rolls 5Y, 5M, 5C, 5K and the photosensitive drums 1Y, 1Y, 1Y, The toner image on the photosensitive drum is electrostatically transferred to the intermediate transfer belt 20 that passes through the primary transfer position facing 1M, 1C, and 1K.
Further, primary transfer rolls 5Y, 5M, and 5C for transferring a yellow image, a magenta image, and a cyan image are supported so as to be able to retreat from a state in which they are pressed against the photosensitive drum 1 via the intermediate transfer belt 20. When the corresponding color toner image is formed on the photosensitive drum 1, it is pressed against the photosensitive drum 1 via the intermediate transfer belt 20, and when the corresponding color toner image is not formed, it is indicated by a broken line in FIG. As shown, they are separated.

  The fixing device 7 includes a heating roll 7a having a built-in heating source, and a pressure roll 7b pressed against the heating roll 7a, which are arranged in parallel to contact each other to form a nip portion. ing. The recording sheet to which the toner image has been transferred is fed into the nip portion and heated and pressurized between the heated heating roll 7a and the pressure roll 7b, and the toner image is pressed onto the recording sheet. Has become.

For example, the intermediate transfer belt 20 has a predetermined surface resistivity in which a material for imparting conductivity such as carbon or an ion conductive material is dispersed in a resin material such as polyimide, polyamideimide, polycarbonate, or fluorine resin. The film-like member adjusted so as to be endless is formed. Then, the drive roll 21 that is rotationally driven, the steering roll 22 that adjusts the deviation in the width direction of the intermediate transfer belt 20, and the backup roll 23 are stretched to move around in the direction of arrow A shown in FIG. It is supposed to be.
The drive roll 21 receives a rotational driving force from a drive motor (not shown), and rotates to move the intermediate transfer belt 20 around.
A secondary transfer roll 24 is arranged at a position facing the backup roll 23 and the intermediate transfer belt 20 so as to transfer the toner image on the intermediate transfer belt onto the recording sheet conveyed from the sheet tray 8. ing.
At both ends in the width direction of the intermediate transfer belt, ribs 20a for suppressing meandering of the circular movement are provided as shown in FIG. The rib 20a protrudes inward from the inner peripheral surface of the intermediate transfer belt and is continuous in the circumferential direction. The peripheral surfaces of the drive roll 21, the steering roll 22, and the backup roll 23 that stretch the intermediate transfer belt 20 are on both sides. The two ribs provided at the edge of the intermediate transfer belt 20 are pressed against the inner peripheral surface of the intermediate transfer belt 20.

  A toner removing device 25 is disposed at a position facing the drive roll 21 and the intermediate transfer belt 20, and a cleaning blade 25 a provided in the toner removing device 25 contacts the intermediate transfer belt 20 to perform intermediate transfer. The transfer residual toner adhering to the belt is scraped off and removed.

Between the primary transfer position 19 and the secondary transfer position 29, an elastic roll 26 having an outer peripheral portion formed of an elastic material is supported in contact with the inner peripheral surface of the intermediate transfer belt 20.
The elastic roll 26 as an elastic member is formed with an elastic layer 26b made of foamed resin or foamed rubber on the outer peripheral surface of a shaft 26a made of a metal such as SUS or iron or a resin having heat resistance. It rotates following the circular movement. The elastic roll 26 is supported at a position where the intermediate transfer belt 20 stretched between the steering roll 22 on the upstream side and the backup roll 23 on the downstream side is pushed outward in the direction perpendicular to the peripheral surface.

The position for supporting the elastic roll 26 is set as follows.
If the position of the intermediate transfer belt 20 is stretched between the upstream side steering roll 22 and the downstream side backup roll 23 and the elastic roll 26 is not in pressure contact, the reference position 27 is set. The position 27 is supported at a position where the displacement amount in the direction perpendicular to the peripheral surface of the intermediate transfer belt 20 from the position in contact with the intermediate transfer belt at position 27 is AL.
The displacement AL is set as follows.
In the image forming apparatus according to the present embodiment, when a recording paper having the maximum basis weight (g / m ² ) that can be used is passed through the secondary transfer position 29 without the elastic roll 26 being pressed against the intermediate transfer belt 20. The intermediate transfer belt 20 vibrates. At this time, a maximum amplitude amount (maximum displacement amount from a position in a state in which no vibration is caused) on the outer side perpendicular to the circumferential surface of the intermediate transfer belt 20 at a position where the elastic roll 26 is to be pressed is defined as BL. The elastic roll 26 is supported at a position where the displacement amount AL from the position where the intermediate transfer belt 20 located at the reference position 27 is in contact with the intermediate transfer belt 20 without causing a displacement is equal to or greater than the maximum amplitude amount BL.

That is, as shown in FIG. 2, the displacement AL is the maximum amplitude BL in the direction in which the center 26c-1 of the elastic roll contacting the intermediate transfer belt 20 at the reference position 27 is pressed against the intermediate transfer belt 20. The elastic roll 26 is supported by moving to the position 26c-2 as described above.
The displacement amount AL is set so that the deformation amount of the elastic layer 26b formed on the outer peripheral surface of the elastic roll 26 falls within the elastic deformation range. In other words, when the elastic roll 26 that has been stopped is driven, the elastic roll 26b does not undergo any residual deformation, or even if it occurs, the elastic roll is such that the unevenness in the speed of the intermediate transfer belt due to the residual deformation cannot be observed. Is pressed against the intermediate transfer belt.

  By supporting the elastic roll 26 in this way, even when the thick paper having the maximum basis weight enters the secondary transfer position 29 and vibration occurs in the intermediate transfer belt 20, the elastic layer 26b of the elastic roll. Is kept in contact with the intermediate transfer belt 20 without being separated. That is, when the elastic roll 26 is pressed against the intermediate transfer belt 20 so that the displacement amount becomes AL, the elastic roll 26 is elastically deformed and the displacement amount of the intermediate transfer belt 20 is CL. Even when vibration occurs in the intermediate transfer belt 20 and a displacement BL having the maximum amplitude occurs, the elastic roll 26 is elastically restored in shape and follows the displacement of the intermediate transfer belt 20. .

In the present embodiment, as the elastic roll, a roll having a diameter of 18 mm in which the peripheral surface of the shaft 26a made of metal, resin, or the like is coated with foam rubber (hardness 35 ° [Asker C]) as an elastic layer is used. Further, in this image forming apparatus, the elastic roll 26 is arranged so that the maximum amplitude BL of the intermediate transfer belt 20 when the elastic roll 26 is not pressed is 3 mm and the displacement AL of the elastic roll is 3.5 mm. Yes. At this time, the tension of the intermediate transfer belt 20 is 60 N (6.12 kgf).
The diameter of the elastic roll 26, the material and hardness of the elastic layer, the tension of the intermediate transfer belt 20, and the like can be set as appropriate based on the recording paper that can pass through the image forming apparatus.

As shown in FIG. 3, the elastic roll 26 is pressed between ribs 20 a provided at both edge portions on the inner peripheral surface of the intermediate transfer belt 20.
The rib 20a is made of the same material as the intermediate transfer belt 20, is provided so as to protrude from the inner peripheral surface of the intermediate transfer belt, and is continuous in the circumferential direction. Therefore, when the elastic roll 26 is pressed against the rib, the cross section of the intermediate transfer belt 20 is deformed, and a portion that does not come into contact with the elastic roll 26 is generated. In order to prevent this, the circumferential surface of the elastic roll 26 that comes into contact with the intermediate transfer belt 20 is formed so that the width is narrower than the interval between the ribs 20a as shown in FIG. When the end of the elastic roll 26 and the rib 20a come into contact with each other due to the meandering of the intermediate transfer belt 20, the contact pressure between the inner peripheral surface of the intermediate transfer belt 20 and the elastic layer 26b of the elastic roll 26 fluctuates to absorb vibration. The effect may be reduced. Therefore, the length of the elastic roll 26 in the axial direction is preferably set to be about 5 mm shorter than the width between the ribs 20 a provided at both ends of the intermediate transfer belt 20 in the width direction.

Such an image forming apparatus operates as follows.
When the image forming operation is started, the photosensitive drum 1 is driven to rotate, and the charging device 2 charges the surface of each photosensitive drum 1 almost uniformly to a potential of about -600V to -800V. The exposure device 3 outputs a flashing laser beam based on the image data, and scans the photosensitive layer on the surface of the photosensitive drum 1. As a result, the potential at the laser light irradiation position is attenuated, and a latent image due to the difference in electrostatic potential is formed on the surface of the photosensitive drum 1.

  The electrostatic latent image formed on the photosensitive drum 1 in this way is conveyed to a developing position facing the developing roll 4a by the rotation of the photosensitive drum 1. When passing through the developing position, the toner adhering to the developing roll 4a is electrostatically transferred to the latent image portion on the surface of the photosensitive drum, and a toner image is formed.

  At the primary transfer position 19, the photosensitive drum 1 and the primary transfer roll 5 are opposed to each other via the intermediate transfer belt 20, and a transfer bias voltage is applied between them. When the toner image developed on the surface of each photosensitive drum 1 is conveyed to the primary transfer position 19, electrostatic force acts on the toner in the electric field formed between the photosensitive drum 1 and the primary transfer roll 5. Then, the toner image on the surface of the photosensitive drum 1 is transferred to the surface of the intermediate transfer belt 20. At this time, the transfer bias voltage applied to the primary transfer roll 5 has a polarity (+) opposite to the polarity (−) of the toner.

  In this way, the intermediate transfer belt 20 is transferred so that the toner images of the respective colors are superimposed while sequentially facing the respective image forming units 10. The intermediate transfer belt 20 on which the toner images of all colors have been transferred in multiple layers is transported in the direction of arrow A shown in FIG. 1 and is placed opposite to the backup roll 23 that contacts the inner surface of the intermediate transfer belt 20. It is conveyed to the contact portion with the secondary transfer roll 24 that has been made.

A recording sheet is conveyed between the secondary transfer roll 24 and the intermediate transfer belt 20 at a predetermined timing, and a secondary transfer bias voltage is applied between the secondary transfer roll 24 and the backup roll 23. . At this time, the transfer bias voltage applied to the secondary transfer roll 24 has a polarity (−) opposite to the polarity (+) of the toner, and an electrostatic force acts on the toner within the formed electric field. The toner image on the surface is transferred to the recording paper.
Thereafter, the recording paper is fed into the fixing device 7 where the toner image is heated and pressurized, and the color-superposed toner image is fixed on the surface of the recording paper.
In this way, the recording sheet on which the color image has been fixed is conveyed toward the discharge unit, and a series of color image forming operations is completed.

  In the above process, when a thick paper having a large basis weight is used as the recording paper, when the thick paper enters the secondary transfer position 29, an impact is applied to the intermediate transfer belt 20 in a direction perpendicular to the peripheral surface and the intermediate transfer belt 20. Generates vibration in the moving direction. That is, as shown in FIG. 4, the load increases rapidly at the moment when the leading end of the thick paper P is sandwiched between the secondary transfer roll 24 and the intermediate transfer belt 20. Thereby, as shown in FIG. 5, the intermediate transfer belt vibrates greatly immediately after the thick paper P is sandwiched. Further, the thick paper P is conveyed in a state of being sandwiched between the secondary transfer roll 24 and the intermediate transfer belt 20, and as shown in FIG. 6, the rear end portion passes through the registration roll 9a and the restraint is released. The At this time, the rear end portion of the thick paper P jumps upward and hits the intermediate transfer belt 20 to vibrate the intermediate transfer belt 20 so as to be displaced in a direction perpendicular to the peripheral surface. Further, when the rear end of the thick paper P passes through the opposite portion between the secondary transfer roll 24 and the backup roll 23, the load is suddenly changed, and vibration is generated in the intermediate transfer belt.

  When the vibration of the intermediate transfer belt 20 thus generated is propagated to the primary transfer positions 19Y, 19M, 19C, and 19K of the image forming units 10Y, 10M, 10C, and 10K, the primary transfer positions 19Y, 19M, Density unevenness called so-called banding is generated in an image transferred at 19C and 19K. An image in which such density unevenness occurs is conveyed to the secondary transfer position 29 by the circular movement of the intermediate transfer belt 20 and appears in the image as stripe-like or band-like density unevenness when transferred to the recording paper. That is, as shown in FIG. 7, the intermediate transfer belt 20 vibrates when the first thick paper enters the secondary transfer position 29, and the density unevenness generated in the image primarily transferred by this vibration is the secondary transfer. The image is transferred to the position 29 and transferred onto the rear portion of the image to be transferred onto the first thick paper or onto the recording paper following this thick paper, resulting in density unevenness in the image. In the example shown in FIG. 7, the density unevenness caused by the vibration when the first thick paper enters the primary transfer position appears on the second thick paper. Also. Density unevenness caused by vibration when the trailing edge of the first thick paper passes through the secondary transfer position and when the second thick paper enters the secondary transfer position appears on the third thick paper.

  On the other hand, in the present embodiment, the elastic roll 26 is disposed on the upstream side of the secondary transfer position 29 in the circumferential movement direction of the intermediate transfer belt 20 and is in pressure contact with the inner peripheral surface of the intermediate transfer belt 20. As a result, when thick paper is passed and vibration occurs in the intermediate transfer belt 20 at the secondary transfer position 29, it propagates to the pressure contact position of the elastic roll 26, and the elastic layer 26 b of the elastic roll 26 is deformed. Therefore, propagation of the vibration to the primary transfer positions 19Y, 19M, 19C, and 19K provided between the drive roll 21 and the steering roll 22 is suppressed.

Further, when the elastic layer 26b of the elastic roll is pressed against the intermediate transfer belt 20 beyond the range of the elastic deformation range, residual deformation occurs in the elastic layer 26b when the intermediate transfer belt 20 is driven again from a stopped state. There is a case. When the intermediate transfer belt 20 rotates in a state where residual deformation has occurred, the intermediate transfer belt 20 is displaced in a direction perpendicular to the peripheral surface as the elastic roll 26 rotates. This displacement causes a change in the circumferential movement speed and causes a color registration shift (color shift).
On the other hand, in the image forming apparatus of the present embodiment, the elastic roll is pressed against the intermediate transfer belt 20 so that the elastic layer 26b is not deformed, so that the driving is started when the intermediate transfer belt 20 is stopped. In this case, the intermediate transfer belt 20 is not displaced in the direction perpendicular to the peripheral surface.
Further, the intermediate transfer belt 20 does not move away from the elastic roll 26 when vibration occurs, and vibration is transmitted to the elastic roll 26 when vibration occurs.

In this embodiment, the elastic roll 26 is supported so as to rotate as the intermediate transfer belt 20 rotates. However, the elastic roll 26 may be supported so that the rotation is constrained without following the movement of the intermediate transfer belt 20. it can.
This fixed elastic roll has the same configuration as the elastic roll 26, and is formed by forming an elastic layer made of an elastic material such as foamed resin or foamed rubber on the outer periphery of a shaft made of metal or resin, The supported position is fixed. Further, unlike the elastic roll 26, the rotation is restricted, and the intermediate transfer belt 20 moves around so as to rub the surface of the fixed elastic roll. The position at which the fixed elastic roll is disposed is set in the same manner as the elastic roll 26 and is supported at a position where the displacement amount AL is greater than at least the maximum amplitude BL of the intermediate transfer belt 20.

  In the fixed elastic roll whose rotation is restricted in this way, when the vibration generated in the intermediate transfer belt 20 is propagated at the secondary transfer position, the elastic layer is deformed by the rotation of the fixed elastic roll being restricted. It becomes easy.

Further, as shown in FIG. 8, instead of the elastic roll 26 or the fixed elastic roll, an elastic pad 30 pressed against the inner peripheral surface of the intermediate transfer belt 20 can be used as an elastic member.
The elastic pad 30 is made of foamed resin or foamed rubber that undergoes elastic deformation, and has a primary transfer position 19 and a secondary transfer position 29 by a pedestal 31 made of a metal such as SUS or iron or a heat-resistant resin. And is supported between. Then, the elastic pad 30 is pressed against the inner peripheral surface of the intermediate transfer belt 20 to push the intermediate transfer belt 20 toward the outer peripheral surface, and the intermediate transfer belt 20 that circulates rubs the surface of the elastic pad 30.

The position where the elastic pad 30 is supported is determined in the same manner as the elastic roll 26 and the fixed elastic roll, and this image is determined from the position where the elastic pad 30 is in contact with the intermediate transfer belt stretched without being pressed. The recording paper having the maximum basis weight that can be passed through the forming apparatus is in a position in pressure contact with the intermediate transfer belt with a displacement DL larger than the maximum amplitude BL of vibration generated in the intermediate transfer belt 20. At this time, the material of the elastic pad 30 is selected and the tension of the intermediate transfer belt 20 is adjusted so that the amount of deformation of the elastic pad 32 falls within the range of the elastic deformation region. No deformation occurs.
The elastic pad 30 as described above is deformed when vibration occurs in the intermediate transfer belt 20.

Next, an effect confirmation test using the image forming apparatus including the elastic roll or the fixed elastic roll according to the present embodiment and observing the occurrence of banding and color registration shift (color shift) will be described.
[Experiment 1]
Table 1 shows an image forming apparatus provided with an elastic roll 26 according to the present embodiment between a primary transfer position 19 and a secondary transfer position 29, and an intermediate transfer instead of a metal idler roll instead of the elastic roll 26. The result of having observed the presence or absence of banding using the image forming apparatus press-contacted to the belt is shown.
In this experiment, the first recording paper (Colotech + Gloss Coat paper “Trademark of Xerox Corporation”, basis weight: 280 g / m ² , the reference of the intermediate transfer belt when an elastic roll or the like is not pressed on each of the image forming apparatuses. Maximum amplitude from position to outer peripheral surface side (hereinafter referred to as “runout amount”): 1.5 mm), second recording paper (Elite Gloss paper “Trademark of Xerox Corporation”, basis weight: 300 g / m ² , intermediate 3 of transfer belt runout (1.7 mm) and third recording paper (PC Green 100 (trademark of Oji Paper Co., Ltd.), basis weight: 350 g / m ² , runout of intermediate transfer belt: 2.5 mm) Each type of recording paper was continuously run to form an image with a full halftone of 40%.
The runout amount of the intermediate transfer belt when the third recording paper (PC green 100) having the maximum basis weight used in this experiment is passed is 2.5 mm. In this experiment, the displacement from the reference position 27 is used. An elastic roll and an idler roll were respectively arranged so that the amount AL was 2 mm.

As shown in Table 1, in the image forming apparatus provided with the elastic roll according to the present embodiment, the deflection amount of the intermediate transfer belt when entering the secondary transfer position is smaller than the displacement amount 2 mm of the elastic roll 26. Banding did not occur when the first recording paper (Colotech + Gloss Coat paper) and the second recording paper (Elite Gloss paper) were passed, but the deflection amount was more than the displacement AL2 mm of the elastic roll 26. When large third recording paper (PC Green 100) was passed, some banding occurred.
On the other hand, in an image forming apparatus provided with an idler roll on which no elastic layer is formed, banding occurs on all recording sheets even though the idler roll is disposed at a position displaced by 2 mm from the reference position. Therefore, it can be seen that the vibration of the intermediate transfer belt 20 generated at the secondary transfer position 29 can not be absorbed by the idler roll regardless of the basis weight of the recording paper, and the vibration is propagated to the primary transfer position 19.
As described above, the vibration of the intermediate transfer belt 20 generated at the secondary transfer position 29 is caused by the pressure contact with the intermediate transfer belt by setting the displacement AL of the elastic roll, that is, the elastic member, to be equal to or greater than the shake amount BL of the intermediate transfer belt 20. It can be seen that propagation to is suppressed.

[Experiment 2]
Next, the occurrence of banding and color registration was tested by changing the displacement AL of the elastic roll.
In this experiment, the displacement AL of the elastic roll 26 is arranged to be 1 mm, 2 mm, 3 mm, 4 mm, 5 mm and 6 mm from the reference position 27, and the first recording paper (Colotech + Gloss Coat paper, basis weight: 280 g). / M ² , the amount of deflection of the intermediate transfer belt: 1.5 mm) and the third recording paper (PC Green 100, basis weight: 350 g / m ² , amount of deflection of the intermediate transfer belt: 2.5 mm) % Images were formed.

As shown in Table 2, the first recording paper (Colotech + Gloss Coat paper) with an intermediate transfer belt runout of 1.5 mm has some banding when the elastic roll displacement AL is 1 mm. However, no banding occurred when the displacement AL was 2 mm or more.
In the case of the third recording paper (PC Green 100) in which the deflection amount of the intermediate transfer belt is 2.5 mm, banding occurs when the elastic roll displacement amount AL is 1 mm, and in the case of 2 mm, banding occurs in part. When it is 3 mm or more, banding does not occur.

Next, the presence or absence of color misregistration, that is, color registration misalignment occurring in a color image formed by superimposing a plurality of color images was checked.
In both the first recording paper (Colotech + Gloss Coat paper) and the third recording paper (PC Green 100), when the displacement amount AL of the elastic roll 26 is 5 mm, a color registration misalignment occurs in part, resulting in 6 mm. It happened for almost all images.
The cause of the color registration misalignment is that although the elastic roll 26 is disposed with a displacement amount AL that is greater than or equal to the deflection amount of the intermediate transfer belt 20, the elastic roll 26 is moved beyond the range of the elastic deformation region of the elastic layer 26b. It is considered that residual deformation occurred in the elastic layer 26b due to the pressure contact.

  From the above results, the elastic roll 26 has a displacement amount AL larger than the shake amount BL of the intermediate transfer belt 20 due to passing the thick paper having the maximum basis weight capable of forming an image with the image forming apparatus. It is understood that the elastic layer 26b of the elastic roll in this case needs to be set so as to be within the elastic deformation range.

[Experiment 3]
Next, a description will be given of an experiment comparing the banding occurrence state between an image forming apparatus including a fixed elastic roll whose rotation is constrained and an image forming apparatus including an elastic roll that rotates following the circumferential movement of the intermediate transfer belt.
In an image forming apparatus that supports a fixed elastic roll and a rotatable elastic roll so that the displacement AL of each roll is 2 mm, the first recording paper (Colotech + Gloss Coat paper, basis weight: 280 g / m ² , Intermediate transfer belt shake amount: 1.5 mm), second recording paper (Elite Gloss paper, basis weight: 300 g / m ² , intermediate transfer belt shake amount: 1.7 mm) and third recording paper (PC green) 100, basis weight: 350 g / m ² , half-amplitude of intermediate transfer belt: 2.5 mm), and each recording sheet is continuously run to obtain an image with a full halftone of 40%. Formed.

As a result, as shown in Table 3, in the image forming apparatus provided with the fixed elastic roll, no banding occurred on all the recording sheets passed. On the other hand, in the image forming apparatus provided with an elastic roll driven by the rotation of the intermediate transfer belt, banding occurred in part when the PC green 100 was passed.

1: Photosensitive drum, 2: Charging device, 3: Exposure device, 4: Development device, 5: Primary transfer roll, 6: Cleaning device, 7: Fixing device, 8: Sheet tray, 9: Transport path, 9a: Resist roll,
10: Image forming unit, 19: Primary transfer position,
20: Intermediate transfer belt, 20a: Rib of intermediate transfer belt, 21: Drive roll, 22: Steering roll, 23: Backup roll, 24: Secondary transfer roll, 25: Toner removal device,
26: elastic roll, 26a: elastic roll shaft, 26b: elastic layer of elastic roll, 26c: axial center of elastic roll, 27: reference position when the elastic roll is not pressed against the stretched intermediate transfer belt 29: secondary transfer position, 30: elastic pad, 31: pedestal,
AL: displacement amount of the elastic roll, BL: maximum amplitude amount of the intermediate transfer belt, CL: displacement amount of the intermediate transfer belt when the elastic roll is pressed, DL: displacement amount of the base of the elastic pad

Claims (6)

An image carrier in which a latent image due to a difference in electrostatic potential is formed on an endless peripheral surface;
A developing device for forming a toner image by attaching toner to the image carrier;
An endless intermediate transfer belt, which is stretched around a plurality of roll-shaped members, and is contacted with the image carrier to primarily transfer the toner image;
A secondary transfer device for transferring the toner image primarily transferred to the intermediate transfer belt to a recording sheet;
An elastic member pressed against the inner peripheral surface of the intermediate transfer belt between a primary transfer position of the toner image in the moving direction of the intermediate transfer belt and a secondary transfer position facing the secondary transfer device. An image forming apparatus.   An amount by which the intermediate transfer belt, which is stretched around the roll-shaped member and the elastic member is in a non-pressure-contact state, is displaced outward in a direction perpendicular to the peripheral surface by the vibration at a position where the elastic member is to be pressed-contacted. Assuming BL, the elastic member is supported at a position displaced from the position where the intermediate transfer belt is not displaced by contact with the intermediate transfer belt by a distance of BL or more outward in the direction perpendicular to the peripheral surface of the intermediate transfer belt. The image forming apparatus according to claim 1, wherein:   The elastic member is configured such that residual deformation that occurs when the intermediate transfer belt is rested in a state where the elastic member is in pressure contact with the intermediate transfer belt and then is driven again is uneven driving speed of the intermediate transfer belt due to the residual deformation. 3. The image forming apparatus according to claim 1, wherein the image forming apparatus is pressed against the intermediate transfer belt so as not to be detected. The intermediate transfer belt has ribs that are convex inward and continuous in the circumferential direction near the edges on both sides of the inner peripheral surface.
The image forming apparatus according to claim 1, wherein the elastic member is pressed between the ribs.   The said elastic member is a roll-shaped member supported so that rotation around an axis line was possible, Comprising: The outer peripheral part is formed with the elastic material, The any one of Claim 1 to 4 characterized by the above-mentioned. The image forming apparatus described. 5. The elastic member according to claim 1, wherein the elastic member is supported at a fixed position, and the intermediate transfer belt rotates while rubbing the surface of the elastic member. Image forming apparatus.

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