JP5354374B2 - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus which can suppress deterioration of durability of a toner image carrying belt and suppressing speed variation of the toner image carrying belt when a sheet type member enters a transfer nip. <P>SOLUTION: When it is unnecessary to suppress the speed variation of a primary transfer area T1 of an intermediate transfer belt 2, such as, when an image is not formed or when an image is formed on plain paper, a bite amount of an abutting roller 41 at the intermediate transfer belt 2 is adjusted to 0[mm] by a bite amount adjusting mechanism 35. Meanwhile, when it is necessary to suppress the speed variation of the primary transfer area T1 of the intermediate transfer belt 2, such as, when an image is formed on cardboard, the abutting roller 41 is allowed to bite at the intermediate transfer belt 2 by a predetermined amount by the bite amount adjusting mechanism 35. <P>COPYRIGHT: (C)2011,JPO&amp;INPIT

Description

  The present invention relates to an image forming apparatus such as a copying machine, a printer, and a facsimile machine that employs an image forming method such as an electrophotographic method, an electrostatic recording method, an ionography method, and a magnetic recording method. More specifically, the present invention relates to an image forming apparatus that obtains a final image by transferring a toner image on a toner image carrying belt such as an intermediate transfer belt to a sheet-like member.

  In recent years, in a color image forming apparatus, a toner image on a photosensitive drum is primarily transferred onto an intermediate transfer belt, which is a toner image carrying belt, in a primary transfer portion, and four color toner images on the intermediate transfer belt are secondary-transferred. An intermediate transfer system that performs secondary transfer to a sheet-like member at the transfer nip is often employed. This intermediate transfer belt type image forming apparatus has the advantage that it can be used with various types of sheet-like members such as thin paper, thick paper, postcards and envelopes, and is highly versatile. However, when a single-sheet member having a thickness of a certain level or more enters the secondary transfer nip, the speed of the intermediate transfer belt that has been driven at a constant speed fluctuates for a short time, and the primary transfer is performed. There was a problem that the image was disturbed in the part.

  More specifically, as shown in FIG. 24, when the leading end of the sheet-like member S enters the secondary transfer nip, the secondary transfer nip is pushed wide by the thickness of the sheet-like member S. When the secondary transfer nip is expanded by the thickness of the sheet-like member S, a load is suddenly applied to the driving of the secondary transfer counter roller 116, and the rotation of the secondary transfer counter roller 116 is temporarily delayed. As a result, the belt amount fed from the driving roller 114 around which the upstream end of the secondary transfer nip upstream stretch surface is wound is larger than the belt amount fed by the secondary transfer counter roller 116. As a result, the stretch surface on the upstream side of the secondary transfer nip becomes loose. On the other hand, the amount of belt sent out by the driven roller 115 by the driving force of the driving roller 114 is larger than the amount of belt sent by the secondary transfer counter roller 116. As a result, the stretched surface between the secondary transfer counter roller 116 and the driven roller 115 of the intermediate transfer belt 110 (hereinafter referred to as the secondary transfer nip downstream stretched surface) is pulled to the opposite side of the belt moving direction. The tension on the secondary transfer nip downstream tension surface increases. Then, the driven roller 115 is pulled and decelerated in the direction opposite to the belt moving direction, and an area between the driven roller 115 and the driving roller 114 of the intermediate transfer belt (hereinafter referred to as a primary transfer area) is opposite to the belt moving direction. And the speed of the intermediate transfer belt in the primary transfer nip is reduced. Therefore, when the image is transferred from the photosensitive drum 104 to the intermediate transfer belt 110 at the primary transfer portion while this deceleration occurs, the image is disturbed due to the speed fluctuation.

  Such a defect assumes the speed fluctuation waveform of the intermediate transfer belt that occurs at the time of entry before the sheet-like member enters the secondary transfer nip, and controls the drive roller drive so as to cancel the assumed speed fluctuation waveform. It is known to avoid by feedforward control.

  However, the speed fluctuation waveform of the intermediate transfer belt differs depending on changes in the waist of the sheet-like member, the secondary transfer pressure, the secondary transfer roller hardness, and the like. For this reason, in the case of the feedforward control, the assumed speed fluctuation waveform to be canceled differs from the actual speed fluctuation waveform, and there is a possibility that the belt speed fluctuation is deteriorated.

  Such a problem can also be avoided by suppressing the stretching surface on the downstream side of the secondary transfer nip of the intermediate transfer belt from being pulled to the side opposite to the belt moving direction. It has been known.

  In Patent Document 1, when the sheet-like member enters the secondary transfer nip, a tension is applied to the downstream side of the secondary transfer nip of the intermediate transfer belt that becomes tensioned by a spring from the outside so as to bend the belt inward. An image forming apparatus is described in which a tension roller for biasing is provided, and the tension roller adjusts the tension of the stretched surface on the downstream side of the secondary transfer nip of the intermediate transfer belt. Specifically, when the tension surface of the secondary transfer nip downstream tension surface of the intermediate transfer belt is pulled to the opposite side of the belt movement direction and the tension of the secondary transfer nip downstream tension surface increases, the tension roller is displaced outward. Thus, the tension on the stretched surface on the downstream side of the secondary transfer nip is reduced.

  However, in the image forming apparatus of Patent Document 1, when the sheet-like member enters the secondary transfer nip, the intermediate transfer belt is stretched by a predetermined tension on the stretched surface on the downstream side of the secondary transfer nip. When the sheet-like member enters the secondary transfer nip, a load is suddenly applied to the driving of the secondary transfer counter roller, the rotation temporarily slows down, and the tension on the stretched surface on the downstream side of the secondary transfer nip increases. After that, the tension roller is displaced and the tension on the stretching surface downstream of the secondary transfer nip is weakened. Therefore, immediately after the sheet-like member enters the secondary transfer nip, a force is applied to pull the downstream transfer nip downstream stretched surface opposite to the belt moving direction, and the tension is applied to the secondary transfer nip downstream stretch. It reaches the tension surface on the downstream side of the surface. As a result, it was not possible to sufficiently suppress disturbance in the image at the primary transfer portion or the like. Further, in the image forming apparatus described in Patent Document 1, in order to reduce the size of the apparatus, the intermediate transfer belt is stretched by being bent inward by 90 ° or more on the stretching surface on the downstream side of the secondary transfer nip. For this reason, local stress is generated at a position where the intermediate transfer belt is bent inward by 90 ° or more, and there is a problem that it is difficult to obtain durability of the intermediate transfer belt due to this local stress.

  The present applicant has proposed an image forming apparatus of Japanese Patent Application No. 2008-221817 in order to suppress the speed fluctuation of the primary transfer portion of the intermediate transfer belt. The image forming apparatus supports a contact roller that is a contact member that contacts the intermediate transfer belt in the vicinity of the secondary transfer roller, and a secondary transfer roller, and the secondary member when the sheet-like member enters the secondary transfer nip. In conjunction with the displacement of the transfer roller, interlocking means for displacing the contact roller in the direction of decreasing the tension of the intermediate transfer belt is provided. Specifically, the contact roller is in contact with the secondary transfer nip downstream stretch surface of the intermediate transfer belt. The interlocking means is swingably supported by the apparatus main body, and when the sheet-like member enters the secondary transfer nip and the secondary transfer roller is pushed down, the interlocking means swings, and the contact roller The secondary transfer nip is displaced in the direction of decreasing the tension on the downstream tension surface. When the sheet-like member starts to bite into the secondary transfer nip, the secondary transfer roller starts to be pushed down, so that an increase in tension when the sheet-like member enters the secondary transfer nip can be suppressed by the interlocking means.

  In this configuration, as will be apparent from a verification experiment to be described later, as the amount of the contact roller that bites into the intermediate transfer belt increases, the effect of suppressing an increase in tension when the sheet-like member enters the secondary transfer nip is more effective. High, it is possible to suppress the speed fluctuation of the intermediate transfer belt when the sheet-like member enters the secondary transfer nip. However, when the amount of biting of the contact roller into the intermediate transfer belt is increased, the intermediate transfer belt bends similarly to Patent Document 1, so that local stress is generated in the intermediate transfer belt and the durability of the intermediate transfer belt is increased. There is a problem of getting worse. On the other hand, if the amount of biting of the contact roller into the intermediate transfer belt is reduced, the effect of suppressing the increase in tension cannot be sufficiently obtained when the paper is thick, and the effect of suppressing the speed fluctuation of the intermediate transfer belt is sufficiently obtained. There is also the problem of disappearing.

  In the above, an intermediate transfer type image forming apparatus in which the toner image carrying belt is an intermediate transfer belt has been described. However, when transferring a toner image on the intermediate transfer belt to a sheet-like member for image quality improvement, image transfer is performed. Even in a transfer simultaneous fixing type image forming apparatus that simultaneously performs image fixing and image fixing, the same problem may occur in the transfer section. Also in this case, when a sheet-like member having a thickness of a certain level or more enters the transfer fixing unit, the speed of the intermediate transfer belt that has been driven at a constant speed is reduced for a short time until the primary transfer unit etc. This can cause a problem that the image is disturbed.

  Even in the direct transfer type image forming apparatus in which the toner image carrying belt is a photosensitive belt and the toner image on the photosensitive belt is directly transferred to the sheet-like member at the transfer portion, the same problem occurs in the transfer portion. Can occur. In this case, when a sheet-like member having a thickness of a certain degree or more enters the transfer portion, the speed fluctuation of the photosensitive belt that has been driven at a constant speed until then occurs. Due to the speed fluctuation of the photosensitive belt, a deviation occurs between the exposure light irradiation timing for forming the latent image and the timing when the surface of the photosensitive belt passes the exposure position, and the positional deviation of the latent image formed on the photosensitive belt is shifted. A malfunction that occurs may occur.

  The present invention has been made in view of the above problems, and an object of the present invention is to suppress the deterioration of the durability of the toner image carrying belt and to change the speed of the toner image carrying belt when the sheet-like member enters the transfer nip. It is an object of the present invention to provide an image forming apparatus capable of suppressing the above.

In order to achieve the above object, a first aspect of the present invention provides a toner image carrying belt which is stretched by a plurality of stretching rollers and carries a toner image on its surface and moves endlessly, and among the plurality of stretching rollers. And a transfer roller that forms a transfer nip for transferring the toner image on the toner image carrying belt to a sheet-like member, in the vicinity of the transfer roller. A contact member that is in contact with a region downstream of the transfer nip of the toner image carrier belt in the toner image carrier belt movement direction, the contact member and the transfer roller, and supports the transfer of the sheet-like member. Interlocking means for displacing the contact member in a direction in which the tension of the toner image carrying belt decreases in conjunction with the displacement of the transfer roller when entering the nip, and the toner image carrying of the contact member. It is characterized in that provided the biting amount adjusting means for adjusting the amount of engagement against the belt.
According to a second aspect of the present invention, in the image forming apparatus according to the first aspect, the interlocking unit is configured so that the transfer roller is pressed toward the tension roller facing the transfer roller with the toner image carrying belt interposed therebetween. The pressing means for pressing the pressing member, the pressing force adjusting means for adjusting the pressing force of the pressing means to the interlocking means, and the biting amount of the contact member after the adjustment by the biting amount adjusting means with respect to the toner image carrying belt And a pressing force adjustment control means for controlling the pressing force adjusting means based on the detected amount of biting to adjust the pressing force of the pressing means to the interlocking means. It is.
According to a third aspect of the present invention, in the image forming apparatus of the second aspect, the pressing force adjustment control means pushes the interlocking member against the interlocking member as the amount of biting of the contact member into the toner image carrying belt increases. The pressing force adjusting means is controlled so that the pressure increases.
According to a fourth aspect of the present invention, in the image forming apparatus of the first aspect, the biting amount adjusting means detects the displacement of the transfer roller when the biting amount of the contact member with respect to the toner image carrying belt is adjusted. Displacement detecting means, pressing means for pressing the interlocking means so that the transfer roller is pressed to the tension roller side facing the transfer roller across the toner image carrying belt, and the interlocking of the pressing means A pressing force adjusting means for adjusting the pressing force to the means, and the pressing force adjusting means is controlled based on the detection result of the displacement detecting means to adjust the pressing force of the pressing means to the interlocking means. And a pressing force adjustment control means.
According to a fifth aspect of the present invention, in the image forming apparatus according to the fourth aspect, the pressing force adjustment control unit is configured to perform a pressing operation based on a detection result of the displacement detection unit so that the transfer roller is positioned at a predetermined position. The pressure adjusting means is controlled.
According to a sixth aspect of the present invention, in the image forming apparatus according to any one of the first to fifth aspects, the biting amount adjusting means is controlled on the basis of the thickness of the sheet-like member conveyed to the transfer nip. A biting amount adjustment control means for adjusting the biting amount of the contact member with respect to the toner image carrying belt is provided.
According to a seventh aspect of the present invention, in the image forming apparatus according to the sixth aspect, the biting amount adjustment control means is configured such that the thickness of the sheet-like member conveyed to the transfer nip increases as the thickness of the contact member increases. The biting amount adjusting means is controlled such that the biting amount with respect to the toner image carrying belt is increased.
The invention according to claim 8 is the image forming apparatus according to claim 6 or 7, further comprising a thickness detecting means for detecting the thickness of the sheet-like member upstream of the transfer nip in the sheet-like member conveyance direction, The image forming apparatus, wherein the bite amount adjustment control unit controls the bite amount adjustment unit based on a detection result of the thickness detection unit.
According to a ninth aspect of the present invention, in the image forming apparatus according to any one of the first to eighth aspects, the image forming apparatus further includes a heating unit that is provided in the vicinity of the transfer nip and heats the toner image carrying belt or the sheet-like member. The toner image on the toner image carrying belt is transferred to the sheet-like member at the nip and fixed at the same time.

According to the present invention, by providing the biting amount adjusting means for adjusting the biting amount of the contact member with respect to the toner image carrying belt, if the biting amount is adjusted as follows, the durability of the toner image carrying belt is deteriorated. And the fluctuation in the speed of the toner image carrying belt when the sheet-like member enters the transfer nip can be suppressed. That is, when the thickness of the sheet-like member conveyed to the transfer nip is thin, the sheet-like member conveyed to the transfer nip is adjusted by the biting amount adjusting means so that the biting amount of the contact member with respect to the toner image carrying belt is reduced. When the thickness of the toner is thick, the biting amount adjusting means adjusts so that the biting amount of the contact member with respect to the toner image carrying belt increases.
As described above, by adjusting the amount of contact of the contact member into the toner image carrying belt, a thick sheet-like member that greatly increases the tension of the toner image carrying belt when entering the transfer nip of the sheet-like member is obtained. When transported to the transfer nip, the amount of biting of the abutting member into the intermediate transfer belt is adjusted so that the effect of suppressing an increase in tension when the sheet-like member enters the transfer nip can be sufficiently obtained. The speed fluctuation of the image bearing belt can be suppressed. On the other hand, when a thin sheet-like member with a small speed fluctuation of the toner image carrying belt when the sheet-like member enters the transfer nip is conveyed to the transfer nip, the amount of biting of the contact member into the toner image carrying belt is reduced. Therefore, the bending of the toner image carrying belt by the contact member is alleviated, and the local stress applied to the toner image carrying belt can be weakened.

  According to the present invention, it is possible to suppress the deterioration of the durability of the toner image carrying belt and to suppress the speed fluctuation of the toner image carrying belt when the sheet-like member enters the transfer nip.

1 is a schematic configuration diagram of an image forming apparatus according to an embodiment. The figure which shows the speed fluctuation of a drive roller and a driven roller. FIG. 3 is an explanatory diagram schematically showing a transfer paper on which a toner image in which positional deviation has occurred is transferred. (A) The figure which showed transmission of the force when a sheet | seat entered the prenip part. (B) is an enlarged explanatory view of the vicinity of the secondary transfer nip when the paper enters the prenip portion, and (c) is a graph for explaining the speed fluctuation when the paper enters the prenip portion. (A) The figure which showed transmission of the force when a sheet | seat penetrates into this nip part. FIG. 6B is an enlarged explanatory view of the vicinity of the secondary transfer nip when the sheet enters the main nip portion. (C) is a graph for explaining the speed fluctuation when the paper enters the main nip portion. Explanatory drawing of the mechanism in which both a drive roller and an entrance roller decelerate by paper sheet nip entry. FIG. 6A is a diagram illustrating transmission of force when the pre-nip region of the intermediate transfer belt returns. (B) is an enlarged explanatory view of the vicinity of the secondary transfer nip when the pre-nip region of the intermediate transfer belt returns. (C) is a graph for explaining the speed fluctuation caused when the pre-nip region of the intermediate transfer belt returns. Data investigating the relationship between the speed fluctuation of the driven roller and the driving roller and the displacement of the tension roller and the secondary transfer roller. The graph which investigated the relationship between the amount of biting of the contact roller with respect to the intermediate transfer belt and the speed fluctuation of the driven roller when the leading edge of the paper entered the main nip. 1 is a schematic configuration diagram of an image forming apparatus according to Embodiment 1. FIG. The schematic block diagram of a bite-in amount adjustment mechanism. The schematic block diagram of a pressing force adjustment mechanism. FIG. 3 is a control block diagram of the image forming apparatus according to the first exemplary embodiment. FIG. 3 is a control flow diagram of biting amount adjustment according to the first embodiment. FIG. 6 is a control flow diagram of biting amount adjustment according to the second embodiment. FIG. 10 is a schematic configuration diagram of an image forming apparatus according to a modification of the second embodiment. FIG. 9 is a control flow diagram for adjusting the amount of biting in a modification of the second embodiment. FIG. 4 is a schematic configuration diagram of an image forming apparatus according to a third embodiment. Control block diagram in image forming apparatus of embodiment 3 The block diagram of the said microprocessor for implementing said feedback control based on the displacement information of secondary transfer roller displacement information. FIG. 6 is a schematic configuration diagram of an image forming apparatus according to a fourth embodiment. FIG. 10 is a schematic configuration diagram of an image forming apparatus according to a modified example of Embodiment 4. FIG. 10 is a schematic configuration diagram of an image forming apparatus according to a fifth embodiment. FIG. 4 is a schematic diagram illustrating a state in which a tension state of an intermediate transfer belt is changed when a sheet-like member enters a secondary transfer nip.

Hereinafter, an embodiment of an image forming apparatus to which the present invention is applied will be described.
FIG. 1 is a main part configuration diagram showing the image forming apparatus. In this figure, the image forming apparatus includes four process units 100Y, 100, M, and K for forming yellow (Y), magenta (M), cyan (C), and black (K) toner images. ing. In addition, a sheet conveyance path including a plurality of guide plates for conveying a recording sheet in the apparatus, a registration roller pair 9, a fixing device 15, an optical writing unit (not shown), a transfer unit 50, and the like are also provided.

  This image forming apparatus has a so-called tandem configuration in which four process units 100Y, 100C, 100M, and 100K are arranged along an endless movement direction with respect to an intermediate transfer belt 2 described later. The process units 100Y, 100C, 100M, and 100K for each color have a common support using the photoreceptors 1Y, 1C, 1M, and 1K, which are latent image carriers, and various devices disposed around the photoreceptors as one unit. It can be attached to and detached from the printer unit main body. The configuration is the same except that the colors of the toners used are different.

  Taking the Y process unit 100Y as an example, a charging device 103Y, a developing device 101Y, a cleaning device 102Y, and the like are provided around the photoreceptor 1Y as a toner image carrier. The photosensitive member 1Y of the process unit 100Y is driven to rotate counterclockwise in the drawing by a driving unit (not shown). The charging device 103Y uniformly charges the peripheral surface of the rotationally driven photoreceptor 1Y to the same polarity as the toner charging polarity. An optical writing unit (not shown) drives a laser diode based on the image information, and irradiates the rotating charged photoconductor 1Y while deflecting the laser light in the direction of the rotation axis. Perform the scanning process. Thereby, an electrostatic latent image based on the Y image information is formed on the photoreceptor 1Y. As the photoreceptor 1 </ b> Y, a drum-like member is used in which a photosensitive layer is formed by applying a photosensitive organic photosensitive material to a base tube made of aluminum or the like. However, an endless belt may be used.

  The developing device 101Y develops the electrostatic latent image on the photoreceptor 1Y using a two-component developer (hereinafter simply referred to as developer) containing a magnetic carrier (not shown) and non-magnetic Y toner. Instead of the two-component developer, a type that develops with a one-component developer not containing a magnetic carrier may be used.

  The Y toner image formed on the photoreceptor 1Y by development is transferred to the front surface of the intermediate transfer belt 2 at a Y primary transfer nip described later. The transfer residual toner adhering to the photoreceptor 1Y after the Y toner image is transferred in this way is removed from the surface of the photoreceptor 1Y by the drum cleaning device 102Y. Prior to this cleaning, the surface of the photoreceptor 1 </ b> Y is discharged by receiving light from a discharge lamp (not shown).

  Although the Y process unit 100Y has been described, M, C, and K toner images are similarly formed on the surfaces of the photoreceptors 1M, C, and K in the M, C, and K process units.

  A transfer unit 50 is disposed below the four process units 100Y, 100C, 100M, and 100K. The transfer unit 50 has an intermediate transfer belt 2 as a toner image carrying belt. The intermediate transfer belt 2 is stretched by stretching rollers such as a driving roller 3, a secondary transfer counter roller 5, a tension roller 6, a driven roller 7, and an entrance roller 4. The intermediate transfer belt 2 is moved endlessly in the clockwise direction in the figure by the rotational driving of the driving roller 3 while being in contact with the photoreceptors 1Y, 1C, 1M, and 1K. As a result, primary transfer nips for Y, C, M, and K where the photoreceptors 1Y, 1C, 1M, and 1K contact the intermediate transfer belt 2 are formed.

  In the vicinity of the primary transfer nips for Y, C, M, and K, the intermediate transfer belt 2 is transferred to the photoreceptors 1Y, C, M, and K by primary transfer rollers 104Y, 104, M, and K disposed inside the belt loop. It is pushing toward. A primary transfer bias is applied to these primary transfer rollers 104Y, 104C, 104M, and 104K by a power source (not shown). As a result, a primary transfer electric field for electrostatically moving the toner images on the photoreceptors 1Y, 1C, 1M, and 1K toward the intermediate transfer belt 2 is formed in the primary transfer nips for Y, C, M, and K. Yes.

  In the drawing, a toner image is sequentially applied to each of the primary transfer nips on the front surface of the intermediate transfer belt 2 that sequentially passes through the primary transfer nips for Y, C, M, and K with endless movement in the clockwise direction. Overlaid and primary transferred. By this primary transfer of superposition, a four-color superposed toner image (hereinafter referred to as a four-color toner image) is formed on the front surface of the intermediate transfer belt 2.

  A secondary transfer roller 8 serving as an abutting member is disposed below the intermediate transfer belt 2 in the drawing, and a portion of the intermediate transfer belt 2 that is wound around the secondary transfer counter roller 5 is contacted from the belt front surface. A secondary transfer nip is formed in contact therewith. Thus, a secondary transfer nip is formed in which the front surface of the intermediate transfer belt 2 and the secondary transfer roller 8 are in contact with each other. The shaft center of the secondary transfer roller 8 is located upstream of the shaft center of the secondary transfer counter roller 5 in the paper transport direction. The secondary transfer roller 8 may be driven to rotate counterclockwise in the drawing by a motor (not shown), or may be configured to rotate around the intermediate transfer belt 2.

  A secondary transfer bias having the same polarity as the toner is applied to the secondary transfer counter roller 5 in the belt loop by a power source (not shown). On the other hand, the secondary transfer roller 8 outside the belt loop is grounded. Thereby, a secondary transfer electric field is formed in the secondary transfer nip.

  A registration roller pair 9 is disposed on the right side of the secondary transfer nip in the drawing. In parallel with image formation, the paper feed roller 18 is rotated to feed out the paper 19 as a sheet-like member from the paper feed cassette 20, separated one by one by the separation roller 17, and fed into the paper conveyance path, and conveyed by the conveyance roller 16. Then, it stops against the registration roller 9. Alternatively, the paper on the manual feed portion is fed out, put into the paper conveyance path, and abutted against the registration roller 9 and stopped.

  The sheet 19 sandwiched between the registration rollers is sent to the secondary transfer nip at a timing that can be synchronized with the four-color toner image on the intermediate transfer belt 2. In the secondary transfer nip, the four-color toner images on the intermediate transfer belt 2 are collectively transferred to a sheet as a sheet-like member due to the influence of the secondary transfer electric field and the nip pressure, and become a full color image combined with the white color of the sheet.

  On the front surface of the intermediate transfer belt 2 that has passed through the secondary transfer nip, untransferred toner that has not been transferred to the paper at the secondary transfer nip adheres. This untransferred toner is cleaned by a belt cleaning device (not shown) that contacts the intermediate transfer belt 2.

  The sheet 19 that has passed through the secondary transfer nip is fed toward the fixing device 15 by the conveyance force between the intermediate transfer belt 2 and the conveyance belt 11. The fixing device 15 is configured by pressing the pressure roller 12 against a fixing belt 13 a stretched between a fixing roller 13 and a heating roller 14. The fixing belt 13a is heated by an IH coil (not shown) in the heating roller 14, and is heated to a temperature necessary for image fixing. On the other hand, the pressure roller 12 also incorporates a heater (not shown) and is used for preheating during standby. The unfixed image on the paper is fixed on the paper 19 by applying heat and pressure at the nip portion between the fixing belt 13 a and the pressure roller 12. The heater of the fixing device 15 does not have to use an IH coil, and may be a system constituted by a pair of heat rollers.

  The fixing device 15 applies heat and pressure to fix the transferred image, and then the paper is discharged to a paper discharge tray (not shown). Alternatively, the image is again guided to the transfer position by a double-side reversing mechanism (not shown), and an image is recorded and fixed on the back surface, and then discharged to a paper discharge tray.

  The secondary transfer roller 8 that is in contact with the intermediate transfer belt 2 to form a secondary transfer nip includes a metal cored bar and an elastic member such as rubber coated on the peripheral surface thereof. In the secondary transfer nip, the portion of the intermediate transfer belt 2 that is wound around the secondary transfer counter roller 5 bites into the elastic member on the surface of the secondary transfer roller 8. Thereby, a wide secondary transfer nip is formed.

Next, problems of the intermediate transfer belt 2 of the conventional image forming apparatus will be described.
When the sheet 19 enters the secondary transfer nip, a driving roller 3 and a driven roller 7 that stretch a region (hereinafter referred to as a primary transfer region) that contacts the photoreceptors 1Y, C, M, and K of the intermediate transfer belt 2 are Then, the speed fluctuation as shown in FIG. 2 occurs. Such a phenomenon is particularly noticeable when a thick paper is passed (in this case, a continuous weight of 220 [kg] paper, a basis weight of 256 [g / m2] paper or more is assumed).

  On the other hand, the photoreceptors 1Y, 1C, 1M, and 1K are driven to rotate at substantially the same speed even when entering the secondary transfer nip of the paper leading edge. A speed difference occurs between them. Due to this speed difference, a transfer position shift occurs in the primary transfer nip.

FIG. 3 is an explanatory diagram schematically showing a sheet 19 on which a toner image having a misalignment is transferred as a final image when a monochrome image is formed.
A toner image including a transfer position shift in the primary transfer nip that occurs when the leading edge of the sheet enters the secondary transfer nip is defined on the sheet 19 at a position L from the leading edge of the sheet, where L is the distance from the primary transfer nip to the secondary transfer nip. Transfer or transfer / fixing. For this reason, as shown in FIG. 3, the final image on the sheet 19 to be discharged is locally a portion I2 that is lighter than the portion I1 of the normal image and a portion I3 that is darker than the normal image portion I1. The resulting image has uneven density.
Note that, when images of a plurality of colors are formed, the distances from the primary transfer nip to the secondary transfer nip are different for each color, so that images having different distances L from the leading edge of the paper to the density unevenness are output for each color. .
As described above, in order to prevent the transfer position shift in the primary transfer portion that occurs when the paper enters, it is necessary to suppress the speed fluctuations of the driving roller 3 and the driven roller 7 when the paper enters. The mechanism by which the speed fluctuations of the driving roller 3 and the driven roller 7 occur will be described below.

In the present image forming apparatus, as shown in FIG. 1, the axial center of the secondary transfer roller 8 is located upstream of the axial center of the secondary transfer counter roller 5 in the sheet conveying direction. Therefore, the nip where the outer peripheral surface of the intermediate transfer belt 2 contacts the secondary transfer roller 8 has the following two nip portions. That is, the inner peripheral surface of the intermediate transfer belt 2 is in a secondary transfer nip (hereinafter referred to as a main nip portion) that is in contact with the secondary transfer counter roller 5 and upstream of the secondary transfer nip in the sheet conveying direction. The inner peripheral surface of the intermediate transfer belt 2 has a nip portion that is not in contact with the secondary transfer counter roller 5 (hereinafter referred to as a pre-nip portion).
As described above, since the image forming apparatus according to the present embodiment has the main nip portion and the pre-nip portion, the speed fluctuations of the driving roller 3 and the driven roller 7 are roughly divided into the following three fluctuations. .

(1) Speed fluctuation due to the leading edge of the paper 19 entering the pre-nip portion FIG. 4 is an explanatory diagram of speed fluctuation that occurs when the paper 19 enters the pre-nip section.
When the leading edge of the sheet enters the pre-nip portion, a stretch region (hereinafter referred to as pre-nip region T3) between the secondary transfer counter roller 5 and the entrance roller 4 which is a stretch surface on the upstream side of the transfer nip of the intermediate transfer belt 2 is pushed inward. It is. When the pre-nip region of the intermediate transfer belt 2 is pushed inward, the portion on the upstream side in the intermediate transfer belt moving direction from the contact portion of the pre-nip region T3 with the front end of the sheet moves as shown in FIG. Pull in the direction. As a result, as shown in FIG. 4B, the inlet roller 4 receives a pulling force I2 in the same direction as the belt moving direction, and the inlet roller 4 receives a torque E2 in the same direction as the rotational direction. As a result, the entrance roller 4 is accelerated. Further, as indicated by an arrow F (2) in FIG. 4A, the force I2 pulling in the same direction as the belt moving direction is transmitted to the driving roller 3 via the intermediate transfer belt 2, and is rotated to the driving roller 3 in the rotational direction. As shown by the thick line in FIG. 4C, the driving roller 3 is accelerated. Finally, as shown by an arrow F (2) in FIG. 4A, a force I2 pulling in the same direction as the belt moving direction is transmitted to the driven roller 7 via the intermediate transfer belt 2. As a result, the driven roller 7 is accelerated as indicated by the bold line in FIG.

  Further, the downstream portion of the intermediate transfer belt 2 in the intermediate transfer belt moving direction from the contact portion of the pre-nip region T3 of the intermediate transfer belt 2 with the front end of the sheet is pulled in the direction opposite to the belt moving direction. As a result, as shown in FIG. 4B, the secondary transfer counter roller 5 is subjected to a pulling force I1 in the direction opposite to the belt moving direction, and the secondary transfer counter roller 5 is reverse to the rotation direction. Torque E1 is applied. Thereby, the secondary transfer counter roller 5 is decelerated. Further, the force I1 pulling in the direction opposite to the belt moving direction is transmitted to the tension roller 6 and the driven roller 7 via the intermediate transfer belt 2 as indicated by an arrow F (1) in FIG. Considering the transmission path, the force I2 pulling in the same direction as the belt moving direction is transmitted to the driven roller 7, and before the driven roller 7 is accelerated, the driven roller 7 is decelerated by the force I1 pulling in the direction opposite to the belt moving direction. Should do. However, as shown in FIG. 4C, the driven roller 7 is not decelerated by the force I1 pulling in the direction opposite to the belt moving direction. In this experiment, because the secondary transfer roller 8 was driven by another motor, the force I1 pulling in the direction opposite to the belt moving direction was extinguished by the rotational driving force of the secondary transfer roller 8. It is done.

  As shown in FIG. 4B, the primary transfer region T1 of the intermediate transfer belt 2 is accelerated by the driving roller 3 being accelerated by the force I2 that is pulled in the belt moving direction. As a result, as shown in FIG. 3, a portion I2 having a lighter color than the portion I1 of the normal image is generated.

(2) Speed fluctuation due to the leading edge of the paper 19 entering the main nip part FIG. 5 is an explanatory diagram of the speed fluctuation that occurs when the leading edge of the paper enters the main nip part, which is the secondary transfer nip.
The speed fluctuation due to the leading edge of the paper 19 entering the main nip portion is caused by the secondary transfer counter roller 5 being pushed by the leading edge of the paper 19 pushing down the secondary transfer roller 8 when the leading edge of the paper 19 enters the main nip portion. It is a phenomenon that slows down.
Here, the mechanism by which the secondary transfer counter roller 5 decelerates will be described with reference to FIG.
As shown in FIG. 6, in order for the leading edge of the sheet 19 to enter the nip portion, the leading edge of the sheet 19 needs to push down the secondary transfer roller 8 by an amount corresponding to the thickness of the sheet 19. As shown in the figure, the secondary transfer roller 8 is urged in the direction of arrow A in the figure by the urging coil spring 10b. In order to push down the secondary transfer roller 8, the force (arrow B in the figure) that the leading edge of the paper 19 pushes down the secondary transfer roller 8 needs to exceed the urging force of the urging coil spring 10b. The force B that pushes down the leading edge of the sheet 19 is a conveying force that conveys the leading edge of the sheet to the right side in the figure, and the conveying force is the rotational driving force C of the secondary transfer counter roller 5. In other words, when the leading edge of the sheet 19 comes into contact with the secondary transfer roller 8, the secondary transfer counter roller 5 has not only torque for conveying the belt but also the leading edge of the sheet to push down the secondary transfer roller 8. Necessary torque is generated. As a result, as shown in FIG. 5B, the rotational load (arrow D1 in the figure) of the secondary transfer counter roller 5 increases, and the secondary transfer counter roller 5 decelerates. In this experiment, the secondary transfer roller 8 is driven to rotate. For this reason, the rotational driving force of the secondary transfer roller 8 also acts as a force at which the leading edge of the sheet 19 pushes down the secondary transfer roller 8, and the secondary transfer roller 8 only has a secondary transfer roller 8 that pushes down the secondary transfer roller 8. The torque applied to the transfer counter roller 5 is reduced.

  On the other hand, the entrance roller 4 is also decelerated similarly to the secondary transfer counter roller 5. This is because when the leading edge of the paper 19 enters the main nip portion, the paper 19 does not advance until the leading edge of the paper 19 pushes down the secondary transfer roller 8, and therefore the belt due to the frictional force between the intermediate transfer belt 2 and the paper. A traveling load J2 is generated. Due to this travel load, torque D2 in the direction opposite to the rotation direction acts on the entrance roller 4, and the entrance roller 4 similarly decelerates. The belt running load J2 is transmitted to the driving roller 3 via the intermediate transfer belt 2 as shown by an arrow F (3) in FIG. However, the belt traveling load transmitted to the driving roller 3 is canceled by the driving force of the motor that drives the driving roller 3 to rotate, and is not transmitted to the driven roller 7 upstream of the driving roller 3 in the belt moving direction.

  When the secondary transfer counter roller 5 decelerates, a stretch region (hereinafter referred to as a tension control region T2) between the secondary transfer counter roller 5 and the driven roller 7 which is a stretch surface on the downstream side of the transfer nip of the intermediate transfer belt 2 is a belt moving direction. As shown by an arrow F (4) in FIG. 5A, a force J1 in the direction opposite to the belt moving direction is transmitted to the tension roller 6 and the driven roller 7. When the force J1 pulling in the direction opposite to the belt moving direction is transmitted to the driven roller 7, the driven roller 7 is decelerated as shown by the thick line in FIG. As the driven roller 7 decelerates, the primary transfer region T1 of the intermediate transfer belt 2 is pulled in the direction opposite to the belt moving direction, and torque in the direction opposite to the rotation direction of the driving roller 3 is applied. As a result, the drive roller 3 decelerates as indicated by the thick line in FIG. As described above, as the driven roller 7 and the driving roller 3 are decelerated, the primary transfer region T1 of the intermediate transfer belt 2 is decelerated, and a darker portion I3 is generated than the normal image portion I1 as shown in FIG. It is.

(3) Speed fluctuation due to return of pre-nip region T3 of the intermediate transfer belt 2 after entering the front end main nip FIG. 7 is an explanatory diagram of fluctuation due to return of the pre-nip region T3 of the intermediate transfer belt 2 after entering the front end main nip. is there.
As shown in FIG. 7B, when the leading edge of the sheet pushes down the secondary transfer roller 8 and enters the main nip portion, the intermediate transfer belt 2 that has been pushed inward by the leading edge of the sheet 19 so far. The pre-nip region T3 is restored. As a result, a phenomenon opposite to the above (1) speed fluctuation due to entry of the pre-nip portion occurs. That is, a force G1 that pushes the belt in the same direction as the belt movement direction is generated on the downstream side in the belt movement direction from the position where the leading edge of the paper in the pre-nip region T3 is pushing the belt. On the other hand, a force G2 that pushes the belt in the direction opposite to the belt moving direction is generated on the upstream side of the belt moving direction from the position where the leading edge of the paper in the pre-nip region T3 presses the belt. The force G2 for pushing the belt in the direction opposite to the belt moving direction is transmitted to the entrance roller 4 and the drive roller 3 through the intermediate transfer belt 2 as shown by an arrow F (6) in FIG. As a force G2 that pushes the inlet roller 4 in the direction opposite to the belt moving direction is generated, a torque H1 in the direction opposite to the inlet roller rotation direction is generated in the inlet roller 4 as shown in FIG. Slows down. Similarly, torque in the direction opposite to the rotation direction of the drive roller is generated in the drive roller 3, and the speed of the drive roller 3 decreases as shown by the thick line in FIG.

  On the other hand, the force G1 for pushing the belt in the direction opposite to the belt moving direction is, as shown by an arrow F (5) in FIG. 7A, via the intermediate transfer belt 2, the secondary transfer counter roller 5, the tension roller 6, It is transmitted to the driven roller 7. When the force G1 for pushing the belt in the direction opposite to the belt moving direction is transmitted to the secondary transfer counter roller 5, as shown in FIG. 7B, the torque in the same direction as the rotation direction of the secondary transfer counter roller 5 is obtained. H2 is generated and the secondary transfer counter roller 5 is accelerated. Similarly, a torque in the same direction as the rotation direction of the driven roller 7 is generated in the driven roller 7, and the speed of the driven roller 7 increases as shown by a thick line in FIG. 7C.

  In FIG. 7C, the driving roller 3 and the driven roller 7 fluctuate even after the speed fluctuates due to the return of the intermediate transfer belt 2. This is because the torsional vibration is generated in the shaft of the driving roller 3 to which the driving force of the driving motor is transmitted due to the speed fluctuation of the driving roller 3 in the above (1) to (3), and the intermediate transfer belt 2 is returned by the torsional vibration. Even after the speed fluctuation due to the above, it is considered that the speed fluctuation occurred in the driving roller 3 and the driven roller 7.

FIG. 8 shows data obtained by examining the relationship between the speed fluctuation of the driven roller 7 and the driving roller 3 and the displacement of the tension roller 6 and the secondary transfer roller 8.
As shown in FIG. 8, it can be seen that the linear velocity of the driven roller 7 starts to drop, that is, the tension roller 6 starts to be suddenly displaced in the belt outer direction almost simultaneously with the start of the main nip entry variation of (2). This means that the tension roller 6 is pushed down to the outside of the belt due to an increase in belt tension between the secondary transfer counter roller 5 and the driven roller 7 of the intermediate transfer belt 2. If the tension roller 6 is not provided, there is no relaxation of tension due to the tension roller 6 being pushed down to the outside of the belt, so that the load torque generated when the front end of the paper enters the main roller nip propagates to the driven roller 7 with almost no loss. Thus, the deceleration of the driven roller 7 increases.
On the other hand, if the belt tension in the tension control region T2 of the intermediate transfer belt 2 is weak when the front end of the sheet is in the main nip portion, the force J1 is applied to the tension control region T2 of the intermediate transfer belt 2 in the direction opposite to the belt moving direction. Even if (see FIG. 5B) works, the force can be made difficult to propagate to the driven roller 7 and the driving roller 3. As a result, the speed reduction of the driven roller 7 and the driving roller 3 can be suppressed, and the speed reduction of the primary transfer region T1 of the intermediate transfer belt 2 can be suppressed. Therefore, as shown in FIG. 3, it is possible to suppress the occurrence of a portion I3 having a darker color than the portion I1 of the normal image.

  Further, it can be seen that the secondary transfer roller 8 starts to be displaced in the belt outer direction (downward in the drawing) almost simultaneously with the tension roller 6 starting to be displaced in the belt outer direction. Therefore, if the belt tension in the tension control region T2 can be weakened in conjunction with the displacement of the secondary transfer roller 8, the load torque for decelerating the secondary transfer counter roller 5 can hardly be transmitted to the driven roller 7, and the driven roller 7 Thus, the speed reduction of the drive roller 3 can be suppressed, and the speed reduction of the primary transfer region T1 of the intermediate transfer belt 2 can be suppressed.

  Therefore, in the present embodiment, as shown in FIG. 1, a contact roller 41 as a contact member that contacts the intermediate transfer belt 2 in the region from the secondary transfer roller 8 to the tension roller 6 is provided. 8 and the abutting roller 41 are supported, the abutting roller 10 is displaced in the belt outer direction in conjunction with the displacement of the secondary transfer roller 8, and the interlocking member 10 as an interlocking means for weakening the belt tension in the tension control region T2 is provided. Provided.

  The rotation shaft of the secondary transfer roller 8 is rotatably supported by a bearing (not shown) fixed to the interlocking member 10. The interlocking member 10 is supported so as to swing about the swinging shaft 10 a, and the rotation shaft of the secondary transfer roller 8 and the secondary transfer opposing roller 5 are moved along with the swinging of the interlocking member 10. Change the distance to the rotation axis.

  One end of a biasing coil spring 10b as a pressing means is fixed to the interlocking member 10. By the biasing coil spring 10b, the interlocking member 10 is given a biasing force in the counterclockwise direction around the swing shaft 10a, and the secondary transfer roller 8 is pressed against the intermediate transfer belt 2.

  A cam abutting surface with which the eccentric cam 10c abuts is provided at the end of the interlocking member 10 opposite to the swing shaft 10a. When the eccentric cam 10c is rotationally driven by a cam motor (not shown), the interlocking member 10 is rotated little by little in the clockwise direction in the drawing so as to push down the interlocking member 10 against the biasing force of the biasing coil spring 10b. Then, the distance between the axes of the secondary transfer roller 8 and the secondary transfer counter roller 5 gradually increases. Along with this, the size of the secondary transfer nip gradually decreases, and eventually the secondary transfer roller 8 is separated from the intermediate transfer belt 2.

  Further, the interlocking member 10 has a support arm 10d on the opposite side of the swing shaft 10a, and the shaft of the contact roller 41 described above is fixed to the support arm 10d at the tip of the support arm 10d (not shown). The bearings are rotatably supported. The contact roller 41 pushes the intermediate transfer belt 2 inward, and the arrangement position is set so that the contact roller 41 bites into the intermediate transfer belt 2.

  When the thick paper enters the main nip portion (secondary transfer nip), the secondary transfer roller 8 is pushed down by the paper 19 against the pressing force of the biasing coil spring 10b. When the secondary transfer roller 8 is pushed down by the sheet 19, the interlocking member 10 rotates counterclockwise in the figure around the swing shaft 10a, and the contact roller 41 supported by the interlocking member 10 is supported. Also move. In the present embodiment, the moving direction of the contact roller 41 is a direction of retreating from the intermediate transfer belt 2 that has been pushed in. The movement of the contact roller 41 loosens the tension control region T2 downstream of the secondary transfer nip. Therefore, the tension control region T2 can reduce the force that pulls the driven roller 7 in the direction opposite to the belt moving direction. Speed reduction can be suppressed. As a result of the speed reduction of the driven roller 7 being suppressed, the force that the driven roller 7 pulls the driving roller 3 in the direction opposite to the belt moving direction is reduced, and the speed reduction of the driving roller 3 is suppressed. As a result, the speed reduction of the primary transfer region T1 of the intermediate transfer belt 2 is suppressed, and the density reduction can be suppressed.

Since the deceleration fluctuation occurs due to the entry of the thick paper 19 for a very short time of several milliseconds, the timing at which the contact roller 41 moves must be precisely matched with the timing at which the deceleration fluctuation occurs. In the present embodiment, since both the contact roller 41 and the secondary transfer roller 8 are supported by the interlocking member 10, the movement of the secondary transfer roller 8 and the movement of the contact roller 41 are simultaneous. Thereby, the timing at which the contact roller 41 is retracted from the intermediate transfer belt 2 and the belt tension in the tension control region T2 is weakened can be made the same as the timing at which the deceleration fluctuation occurs. 1, the same effect can be obtained. However, in the case of the configuration shown in FIG. 1, there is no toner image downstream of the secondary transfer nip where the contact roller 41 is to be arranged. There is no problem even if the roller comes into contact with the surface of No. 2, and the outside is brought into contact with the outside for ease of removing each device from the image forming apparatus during maintenance.

  Up to this point, the description has been made of the deceleration fluctuation when the thick paper 19 enters the main nip portion (secondary transfer nip). However, in the present embodiment, when the rear end of the thick paper 19 comes out of the main nip portion. It is also effective against acceleration fluctuations. When the rear end of the thick paper 19 passes through the nip portion, the load on the secondary transfer counter roller 5 is instantaneously reduced. As a result, the driven roller 7 and the driving roller 3 are also accelerated. In this embodiment, the contact roller 41 moves to the intermediate transfer belt 2 in conjunction with the return of the secondary transfer roller 8 to the position where it contacts the intermediate transfer belt 2. I will bite in. As a result, the contact roller 41 pulls the intermediate transfer belt moving direction downstream side of the contact roller 41 to the opposite side to the intermediate transfer belt moving direction, and the acceleration fluctuation of the driven roller 7 can be suppressed. As a result, speed fluctuations in the primary transfer region T1 of the intermediate transfer belt 2 can be suppressed.

In the above embodiment, while the sheet 19 passes through the main nip portion, the secondary transfer roller 8 remains lowered by the sheet thickness, and the contact roller 41 is not separated from the intermediate transfer belt 2 but is in the retracted state. Retained. Since the belt path is larger than before the contact roller 41 is retracted, the belt remains slack if it remains as it is.
However, in the above-described embodiment, the contact roller 41 is provided separately from the tension roller 6, and the contact roller 41 is retracted and the tension roller 6 pressurizes the intermediate transfer belt when the belt path length is increased. Since the belt moves in the direction of pushing in the belt 2, the belt does not remain loose. That is, the contact roller 41 is retracted simultaneously with the entry of the sheet 19 into the main nip portion, the intermediate transfer belt 2 is loosened, and the propagation of the deceleration fluctuation is prevented, and then the path of the intermediate transfer belt 2 by the tension roller 6. The length is maintained in the same manner as before the retracting of the contact roller 41. If the tension roller 6 pushes the looseness of the intermediate transfer belt 2 at the same time when the contact roller 41 is retracted from the intermediate transfer belt 2 when the main nip portion enters the leading edge of the sheet 19, the contact roller Although the effect of the roller 41 is lost, the reaction of the tension roller 6 is slightly delayed with respect to the fluctuation of the belt tension, so that the effect of the contact roller 41 is not diminished.

Next, features of the present embodiment will be described.
FIG. 9 is a graph in which the relationship between the amount of biting of the contact roller 41 with respect to the intermediate transfer belt 2 and the speed fluctuation of the driven roller 7 when the leading end of the paper 19 enters the main nip is examined.
FIG. 9 shows a state in which the contact roller 41 is in contact with the intermediate transfer belt 2 (biting amount: 0 mm), a state in which the contact roller 41 is intruded into the intermediate transfer belt by 3 [mm], and the contact roller 41 is in the middle This is a result of calculation by simulation of a belt speed fluctuation when the sheet 19 is plunged into the main nip portion in a state where the transfer belt 2 is bitten by 5 [mm]. The speed fluctuation in FIG. 9 is a speed fluctuation when a sheet having a basis weight of 359 [g / m ² ] is entered into the main nip portion. Further, when the contact roller 41 bites into the intermediate transfer belt 2, the interlocking member 10 rotates counterclockwise in the figure due to the reaction force of the intermediate transfer belt 2, and the transfer nip pressure decreases. For this reason, in order to compensate for the decrease of the transfer nip pressure corresponding to the amount of biting of the contact roller 41, the fulcrum of the urging coil spring 10b is displaced further toward the tension side to change the spring pressure, so that the transfer nip pressure is maintained under the same conditions. I have to.

  As shown in FIG. 9, when the contact roller 41 bites into the 3 [mm] intermediate transfer belt 2, the linear velocity fluctuation rate of the driven roller 7 falls, and the biting amount of the contact roller 41 is 0 [mm]. When the contact roller 41 is cut into the 5 [mm] intermediate transfer belt by about 15 [%] compared to the case, the amount of biting of the contact roller 41 is about 35 compared with the case where the contact roller 41 is 0 [mm]. [%]Decrease. In this way, it can be understood that if the amount of biting of the intermediate transfer belt 2 by the contact roller 41 is increased, the effect of suppressing the speed fluctuation when the sheet enters the main nip portion is high.

  However, when the amount of biting of the contact roller 41 into the intermediate transfer belt 2 is increased, bending deformation of the intermediate transfer belt 2 increases, local stress is generated, the load on the intermediate transfer belt 2 increases, and the intermediate transfer belt 2 increases. There is a problem that the durability of the transfer belt 2 is deteriorated. On the other hand, if the amount of biting of the contact roller 41 into the intermediate transfer belt 2 is reduced in order to reduce the load on the intermediate transfer belt 2, the effect of suppressing the speed fluctuation can be sufficiently obtained on a thin sheet. However, the effect of suppressing the speed fluctuation cannot be sufficiently obtained when using thick paper.

  Therefore, in the present invention, the amount of biting of the contact roller 41 with respect to the intermediate transfer belt 2 can be adjusted, and the amount of biting is adjusted according to printing conditions and paper thickness, thereby reducing the load on the intermediate transfer belt 2. On the other hand, the speed fluctuation at the time of entering the paper main nip can be suppressed satisfactorily. Hereafter, it demonstrates concretely using each Example of this invention.

[Example 1]
The image forming apparatus according to the first exemplary embodiment includes a high image quality mode and a low image quality mode. In the high image quality mode, printing is performed by causing the contact roller 41 to bite into the 5 mm intermediate transfer belt 2. In the low image quality mode, the contact roller 41 is set to be separated from the intermediate transfer belt 2 for printing. In the first embodiment, the contact roller 41 is separated from the intermediate transfer belt 2 even during standby (non-image formation).

FIG. 10 is a schematic configuration diagram of the image forming apparatus according to the first embodiment.
The image forming apparatus according to the first exemplary embodiment includes a biting amount adjustment control unit including a drive command unit 25 and an adjustment control unit 28, and a biting amount adjustment mechanism 35 serving as a biting amount adjustment unit illustrated in FIG. .

FIG. 11 is a schematic configuration diagram of the biting amount adjustment mechanism 35.
As shown in FIG. 11, a bearing 33 on which the shaft of the contact roller 41 is rotatably supported is attached to a support arm 10d of the interlocking member 10 so as to be slidable in a direction perpendicular to the surface of the intermediate transfer belt 2. Yes. The biting amount adjustment mechanism 35 includes an eccentric cam 32 that contacts the lower surface of the bearing 33 and a biting amount adjustment drive motor 30 that rotationally drives the eccentric cam 32. Further, the biting amount adjustment drive motor 30 is controlled by the adjustment control unit 28 shown in FIG. The biting amount adjusting drive motor 30 uses a motor capable of adjusting the rotation angle, such as a stepping motor.

Further, when the amount of biting of the contact roller 41 with respect to the intermediate transfer belt 2 is increased, the interlocking member 10 rotates counterclockwise in the drawing due to the reaction force of the intermediate transfer belt 2 and the transfer nip pressure is reduced. Table 1 below shows the amount of vertical displacement (second) of the secondary transfer roller 8 when the amount of biting of the contact roller 41 into the intermediate transfer belt 2 is changed without changing the biasing force of the biasing coil spring 10b. (Next transfer lowering amount) and transfer nip pressure are shown. The secondary falling amount is a measured value by experiment, and the transfer nip pressure is a calculated value by simulation.

  As can be seen from Table 1, when the contact roller 41 is bitten into the intermediate transfer belt 2, the secondary transfer roller 8 is pushed down and the transfer nip pressure decreases. For example, when the contact roller 41 is made to bite into the intermediate transfer belt 2 by 3 [mm], it can be seen that the transfer nip pressure is reduced from 101.7 [N] to 80.2 [N].

  For this reason, in the image forming apparatus according to the first embodiment, the pressing force adjusting mechanism 55, which is the pressing force adjusting unit shown in FIG. 12, for adjusting the pressing force of the biasing coil spring 10b to the interlocking member 10, and the pressing force adjusting unit. And a pressing force adjustment control means including a drive command unit 25 and an adjustment control unit 28.

FIG. 12 is a schematic configuration diagram of the pressing force adjusting mechanism 55.
As shown in FIG. 12, the pressing force adjusting mechanism 55 has a support member attached to the other end of the urging coil spring 10b and slidable in the expansion / contraction direction of the urging coil spring 10b with respect to the side plate 34 of the apparatus body. 45. The pressing force adjustment mechanism 55 includes an eccentric cam 51 that contacts the surface of the support member 45 on the biasing spring side, and a press adjustment drive motor 52 that rotationally drives the eccentric cam 51. The pressing adjustment drive motor 52 is controlled by the adjustment control unit 28 shown in FIG. As the pressing adjustment drive motor 52, a motor capable of adjusting a rotation angle such as a stepping motor is used.

FIG. 13 is a control block diagram of the image forming apparatus according to the first embodiment.
The drive command unit 25 includes a memory 27 and a microprocessor 26. The microprocessor 26 performs various processes based on a program stored in the memory 27. When a predetermined signal (position switching setting ON / OFF signal) is input from the control unit (not shown) to the microprocessor 26 of the drive command unit 25, the microprocessor 26 contacts the memory 27 stored in advance. A drive voltage value corresponding to the position of the roller 41 (5 [mm] biting position / separating position) is taken out. And it sends to the 1st drive driver 29a which controls the bite amount adjustment drive motor 30 of the adjustment control part 28, and the bite amount adjustment drive motor 30 is rotated. Further, the microprocessor 26 takes out a driving voltage value corresponding to the position of the support member 45 (position corresponding to 5 [mm] biting / position corresponding to separation) stored in the memory 27 in advance. And it sends to the 2nd drive driver 29b which controls the press adjustment drive motor 52 of the adjustment control part 28, and rotates the press adjustment drive motor 52. FIG.

FIG. 14 is a control flowchart of the amount of biting adjustment according to the first embodiment.
The position switching setting is set to ON in the high image quality mode, and the position switching setting is set to OFF in the low image quality mode. Switching between the high image quality mode and the low image quality mode is performed by the user operating an operation unit (not shown) of the apparatus main body or operating a personal computer (PC).
First, a control unit (not shown) checks whether the position switching setting is ON when a print job is input (S1). When the position switching setting is ON (YES in S1), the biting control for causing the contact roller 41 to bite into the intermediate transfer belt 2 by 5 [mm] is performed (S2). Specifically, a command is transmitted from a control unit (not shown) to the drive command unit 25 and the adjustment control unit 28, and the contact roller 41 is displaced to a position where the contact roller 41 bites into the intermediate transfer belt 2 by 5 [mm]. Further, the urging force of the urging coil spring 10b is increased by displacing the support member 45 so that the transfer nip pressure does not decrease. As a result, even when printing is started and the sheet is passed through the secondary transfer nip, the image is printed without unevenness of density due to the above-described suppression effect. When the printing operation is completed (YES in S5), the biting control is turned off (S6). Specifically, a command is transmitted from a control unit (not shown) to the drive command unit 25 and the adjustment control unit 28, and the contact roller 41 is displaced to a position away from the intermediate transfer belt 2. Further, the supporting member 45 is displaced to reduce the urging force of the urging coil spring 10b.
On the other hand, when the position switching setting is OFF (low image quality mode) (NO in S1), printing is performed in a state where the contact roller 41 is separated from the intermediate transfer belt 2 without performing control of the biting amount adjustment. .

  As described above, in the first embodiment, the contact roller 41 bites into the intermediate transfer belt 2 only when the printing operation is performed in the high image quality mode. The intermediate transfer belt 2 cannot be bent and deformed by the roller 41. Therefore, no local stress is generated by the contact roller 41 when the apparatus is on standby or during a printing operation in the low image quality mode, so that the load on the intermediate transfer belt 2 does not increase. Therefore, the durability of the intermediate transfer belt 2 can be improved. Further, in the high image quality mode, printing is performed by causing the contact roller 41 to bite into the intermediate transfer belt 2 by 5 [mm], and therefore the intermediate transfer belt 2 when the sheet enters the main nip (secondary transfer nip). Speed reduction of the primary transfer region T1 is suppressed, density reduction can be suppressed, and a high-quality image can be obtained.

[Example 2]
Next, Example 2 will be described.
In the first embodiment, in the high image quality mode, the paper is printed while being displaced in the belt inner direction with respect to any paper. However, since the intermediate transfer belt 2 hardly fluctuates in speed at the time of entering the main nip portion (secondary transfer nip) with a thin paper, when using such a thin paper, the contact roller When printing is performed with 41 being separated from the intermediate transfer belt 2, the burden on the intermediate transfer belt 2 is reduced.
Therefore, in the image forming apparatus according to the second embodiment, the amount of biting of the contact roller 41 into the intermediate transfer belt 2 is adjusted according to the thickness of the sheet conveyed to the main nip (secondary transfer nip). .

FIG. 15 is a control flowchart of the biting amount adjustment according to the second embodiment.
In the second embodiment, a cardboard mode and a plain paper mode are provided. Switching between these modes is performed by a user operating an operation unit (not shown) of the apparatus body or operating a personal computer (PC). Switch.
As shown in FIG. 15, in the thick paper mode (YES in S11), after the biting control for causing the contact roller 41 to bite into the intermediate transfer belt 2 by 5 [mm] as in the first embodiment (S12), printing is performed. (S13 to S14), and when printing is completed (YES in S15), the contact roller 41 is separated from the intermediate transfer belt 2 (S16). On the other hand, in the plain paper mode (NO in S11), printing is performed with the contact roller 41 being separated from the intermediate transfer belt 2.

Also, three modes such as a plain paper mode, a medium thick paper mode, and a super thick paper mode may be used. In this case, for example, as shown in Table 2 below, the biting amount of the contact roller 41 with respect to the intermediate transfer belt 2 is set to 3 [mm] in the middle thick paper mode, and in the super paper thick paper mode, The amount of biting of the contact roller 41 with respect to the intermediate transfer belt 2 is set to 5 [mm]. In this way, by providing a plurality of thick paper modes, it is not necessary to increase the contact pressure of the contact roller 41 more than necessary while obtaining the effect of suppressing the speed fluctuation according to each paper thickness.

  In the above description, the user selects the mode. In this case, when the user sets a mistake, for example, when printing is performed using plain paper but the thick paper mode is set, the intermediate transfer belt is used. 2 is wasted load. Further, if printing is performed using thick paper but the plain paper mode is set, density unevenness occurs and a deteriorated image is printed. Therefore, the position switching operation may be performed after detecting the thickness of the actually conveyed paper.

FIG. 16 is a schematic configuration diagram of the image forming apparatus according to the second embodiment in which the thickness detection sensor 46 is arranged.
As shown in FIG. 16, a thickness detection sensor 46 serving as a thickness detection means is arranged upstream of the registration roller pair 9 in the sheet conveyance direction so that the thickness is detected before registration is started. A displacement sensor can be used as the thickness detection sensor. Since the height of the front surface of the sheet is displaced depending on the thickness of the sheet, the output value of the displacement sensor changes. Therefore, the thickness of the paper can be detected based on the output value of the displacement sensor. As the displacement sensor, an optical or other non-contact displacement sensor may be used, or a contact displacement sensor may be used.

FIG. 17 is a control flowchart of the amount of biting adjustment according to a modification of the second embodiment.
As shown in the figure, when a paper feed process is performed in which a print job is input and the paper 19 is fed to the registration roller pair 9, the paper thickness is detected by the thickness detection sensor 46 (S21 to S22). . When the detection result of the thickness detection sensor 46 exceeds the threshold value, it is determined that the sheet is thick paper, and control is performed so that the contact roller 41 bites into the intermediate transfer belt 2. On the other hand, when the detection result of the thickness detection sensor 46 is equal to or smaller than the threshold value, printing is performed without performing control for causing the contact roller 41 to bite into the intermediate transfer belt 2.

[Example 3]
Next, Example 3 will be described.
In the first and second embodiments, the position of the support member 45 for compensating for the transfer nip pressure that decreases with the amount of biting of the contact roller 41 into the intermediate transfer belt 2 is determined in advance. However, when the amount of biting of the contact roller 41 is not one step or two steps but a plurality of values is given, feedback is performed so that the secondary transfer roller 8 is always in a predetermined position rather than preliminarily determined at the time of design. It is more efficient to control. Further, because there is a possibility that a predetermined transfer nip pressure cannot be secured at the position of the support member 45 determined at the time of design due to environmental fluctuations, it is effective to perform feedback control.

  For this reason, in the third embodiment, the displacement of the secondary transfer roller 8 when the contact roller 41 bites into the intermediate transfer belt 2 is detected, and the interlocking member 10 of the urging coil spring 10b is detected based on the detection result. The urging force is adjusted to perform feedback control for returning the position of the secondary transfer roller 8 (transfer nip pressure) to a predetermined position.

FIG. 18 is a schematic configuration diagram of an image forming apparatus according to the third embodiment.
As illustrated in FIG. 18, the image forming apparatus according to the third embodiment includes a secondary transfer roller displacement sensor 24 serving as a displacement detection unit in the image forming apparatus according to the first embodiment. Further, the secondary transfer roller displacement sensor 24 is connected to the drive command unit 25 and the adjustment control unit 28. In the third embodiment, the displacement of the secondary transfer roller 8 is detected by detecting the displacement of the interlocking member 10.

FIG. 19 is a control block diagram of the image forming apparatus according to the third embodiment. The control block diagram shown in FIG. 19 shows only the characteristic points of the third embodiment. Although not shown in FIG. 19, the drive command unit 25 has a control (not shown) as in the first embodiment. A signal of biting amount information is input from the unit, and a command value is transmitted to the first drive driver 29a of the adjustment control unit 28.
A signal of displacement information measured by the secondary transfer roller displacement sensor 24 is input to the microprocessor 26 in the drive command unit 25. In the memory 27, the amount of biting of the contact roller 41 with respect to the intermediate transfer belt 2 is 0 (when the contact roller 41 is not in contact with the intermediate transfer belt), and the secondary transfer roller 8 contacts the intermediate transfer belt 2 with a predetermined transfer nip pressure. The secondary transfer roller position (position of the interlocking member 10) when in contact is stored as a target value.

  When the displacement information signal measured by the secondary transfer roller displacement sensor 24 is input to the microprocessor 26 in the drive command unit 25, the microprocessor 26 stores the target value stored in the memory 27, Comparison with the measured value measured by the secondary transfer roller displacement sensor 24 is performed. Then, a control command value (drive voltage value) that eliminates the deviation from the target value is generated, and the command value (drive voltage) is sent to the second drive driver 29 b of the adjustment control unit 28.

FIG. 20 is a block diagram of the microprocessor 26 for performing the feedback control based on the secondary transfer roller displacement information.
An output signal of the secondary transfer roller displacement sensor 24, that is, information P (i−1) of the displacement amount of the secondary transfer roller 8 is given to a calculation unit (subtractor) 37. The calculation unit 37 calculates a difference e (i) between a target value Ref (i) of the displacement amount of the secondary transfer roller, which is a control target value, and information P (i-1) of the displacement amount of the secondary transfer roller. To do. The difference e (i) is input to the control controller unit 38. The controller section 38 includes a low-pass filter 39 for removing high frequency noise and a proportional element (gain Kp) 40. In the control controller unit 38, a driving voltage u (i) used for driving the pressing adjustment driving motor 52 is obtained. The obtained drive voltage u (i) is transmitted to the adjustment control unit 28. The adjustment control unit 28 generates a drive signal by the second drive driver 29 b based on the drive voltage u (i) and outputs the drive signal to the press adjustment drive motor 52. The driving force of the pressure adjustment driving motor 52 thus controlled to drive rotates the eccentric cam 51 to drive the support member 45, and changes the biasing force of the biasing coil spring 10b to the interlocking member 10. Then, the interlocking member 10 rotates about the swing shaft 10a, and the secondary transfer roller 8 moves to a predetermined target position. The feedback loop control operation described above is repeated. Here, the control system is an example, and any other PID control system, modern control system, robust control system, or the like may be used.

  Thus, by installing the secondary transfer roller displacement sensor 24 and performing feedback control on the target value, the position of the secondary transfer roller can be accurately maintained and the transfer nip pressure can be secured.

[Example 4]
Next, Example 4 will be described.
In the fourth embodiment, the toner image on the intermediate transfer belt is transferred to the paper 19 at the secondary transfer nip, and at the same time, the fixing is performed.

FIG. 21 is a schematic configuration diagram of an image forming apparatus according to the fourth embodiment.
As shown in FIG. 21, a heating device 21 serving as a heating unit is provided in the vicinity of the secondary transfer nip and upstream of the secondary transfer nip in the sheet-like member conveyance direction. The heating device 21 heats the sheet 19 to a temperature sufficient to fix the toner, and the transfer and fixing are simultaneously performed in the secondary transfer nip.

  FIG. 22 is a modification of the fourth embodiment. In this modification, the intermediate transfer belt 2 is heated by the heating device 21, the toner on the intermediate transfer belt 2 is melted, and transfer and fixing are simultaneously performed in the secondary transfer nip.

  In the fourth embodiment shown in FIGS. 21 and 22, as in the first to third embodiments, the amount of biting of the contact roller 41 into the intermediate transfer belt is adjusted based on the paper thickness and the like. As a result, while reducing the load on the intermediate transfer belt 2, a decrease in the speed of the primary transfer region T1 is suppressed, and a decrease in density can be suppressed.

[Example 5]
Next, Example 5 will be described.
In the fifth embodiment, the toner image on the photosensitive belt is transferred to the paper 19 at the transfer nip.

FIG. 23 is a schematic configuration diagram of an image forming apparatus according to the fifth embodiment.
In the image forming apparatus of Example 5, yellow (Y), magenta (M), cyan (C), and black (K) are formed on a belt-like photoreceptor (hereinafter referred to as photoreceptor belt 1) as a toner image carrying belt. The toner images are sequentially superimposed during one rotation of the photosensitive belt 1 to form a color image.

  On the outer peripheral surface of the photoreceptor belt 1, the Y-color image forming unit 110 </ b> Y, the C-color image forming unit 110 </ b> C, the M-color image forming unit 110 </ b> M, and the K-color image forming unit 110 </ b> K Are sequentially arranged at regular intervals.

  First, the photosensitive belt 1 that moves endlessly at a predetermined linear velocity as the driving roller 3 rotates is uniformly charged by the charging device 103Y in the image forming unit 110Y. When the photosensitive belt 1 is exposed with a laser beam Ly of an optical writing unit (not shown) modulated by the yellow information of the image, the potential of the exposed portion is reduced to form a yellow electrostatic latent image. The electrostatic latent image is formed on the photosensitive belt 1 as a yellow toner image by the developing device 101Y. Further, the endless movement of the photosensitive belt 1 moves the surface of the photosensitive belt 1 on which the Y color toner image is formed to the image forming unit 110C. Then, after being recharged by the charging device 103C and exposed with the laser beam Lc, the developing device 101C develops the C color toner image so as to overlap the Y color toner image. Subsequently, the surface of the photosensitive belt 1 on which the developed two-color superimposed toner image of Y color and C color is formed by the endless movement of the photosensitive belt 1 sequentially passes through the imaging unit 110M and the imaging unit 110K. Then, the M color toner image and the K color toner image are successively developed so as to overlap the superimposed toner image on the photosensitive belt 1.

  The four-color superimposed toner image formed on the photosensitive belt 1 proceeds to the primary transfer portion, the toner image and the paper are combined at the primary transfer nip, and the four colors on the photosensitive belt 1 are applied by applying a bias to the primary transfer roller 104. The toner images are transferred onto the paper at once.

  Also in the fifth embodiment shown in FIG. 23, the amount of biting of the contact roller 41 into the photosensitive belt 1 is adjusted based on the paper thickness and the like, similarly to the first to third embodiments. As a result, it is possible to suppress a decrease in the speed of the photosensitive belt 1 while reducing the load on the photosensitive belt 1 and to suppress a positional shift of a latent image formed on the photosensitive belt 1.

As described above, the image forming apparatus according to the present embodiment includes the intermediate transfer belt 2 that is a toner image carrying belt that is stretched by a plurality of stretching rollers and carries a toner image on the surface and moves endlessly, and the plurality of stretching rollers. And a secondary transfer roller 8 serving as a transfer roller for forming a transfer nip for transferring the toner image on the intermediate transfer belt 2 onto a sheet 19 serving as a sheet-like member. Yes. Further, the contact roller 41 as a contact member that contacts the intermediate transfer belt 2 in the vicinity of the secondary transfer roller 8, and the contact roller 41 and the secondary transfer roller 8 are supported, so that the sheet 19 enters the secondary transfer nip. In conjunction with the displacement of the secondary transfer roller 8 at that time, an interlocking member 10 serving as interlocking means for displacing the contact roller 41 in a direction in which the tension of the intermediate transfer belt 2 decreases is provided. Further, a biting amount adjusting mechanism 35 as a biting amount adjusting means for adjusting the biting amount of the contact roller 41 with respect to the intermediate transfer belt 2 is provided.
By having such a configuration, when it is not necessary to suppress the speed fluctuation of the primary transfer region T1 of the intermediate transfer belt 2 during non-image formation or when an image is formed on plain paper, the middle of the contact roller 41 is used. Only when it is necessary to suppress the speed fluctuation of the primary transfer region T1 of the intermediate transfer belt 2 such as when the amount of biting into the transfer belt 2 is set to 0 [mm] and an image is formed on thick paper, the contact roller 41 is set in the middle. It is possible to bite into the transfer belt 2. This suppresses the speed fluctuation of the primary transfer region T1 of the intermediate transfer belt when the sheet enters the secondary transfer nip (main nip) while suppressing the load on the intermediate transfer belt 2 by the contact roller 41 as much as possible. And density unevenness can be suppressed.

The interlocking member 10 is supported in a swingable manner, and a pressing force adjusting mechanism 55 serving as a pressing force adjusting means for adjusting the pressing force applied to the interlocking member 10 by the urging coil spring 10b serving as the pressing means. A pressing force adjustment control means (consisting of a drive command unit 25 and an adjustment control unit 28) for controlling the pressing force adjustment mechanism 55 based on the amount of biting of the contact roller 41 with respect to the intermediate transfer belt 2 is provided.
Then, the pressing force adjustment control unit controls the pressing force adjustment mechanism 55 so that the pressing force to the interlocking member 10 increases as the amount of biting of the contact roller 41 into the intermediate transfer belt 2 increases.
Accordingly, it is possible to suppress the secondary transfer nip pressure from being reduced by the interlocking member 10 rotating due to the reaction force of the intermediate transfer belt 2 generated by the contact roller 41 being bitten into the intermediate transfer belt 2. Transfer defects due to a decrease in transfer nip pressure when the amount of biting is increased can be suppressed.

  According to the image forming apparatus of the third embodiment, the biting amount adjusting mechanism 35 detects the displacement of the secondary transfer roller 8 when the biting amount of the contact roller 41 with respect to the intermediate transfer belt 2 is adjusted. A secondary transfer roller displacement sensor 24 serving as a displacement detection means is provided. The pressing force adjustment control unit controls the pressing force adjustment mechanism 55 of the biasing coil spring 10b to the interlocking member 10 based on the detection result of the secondary transfer roller displacement sensor 24. Specifically, the pressing force adjustment control unit controls the pressing force adjustment mechanism 55 based on the detection result of the secondary transfer roller displacement sensor 24 so that the secondary transfer roller 8 is positioned at a predetermined position. As a result, a relationship between the amount of biting of the contact roller 41 into the intermediate transfer belt 2 and the pressing force of the biasing coil spring on the interlocking member for positioning the secondary transfer roller 8 at a predetermined position is tested in advance. There is no need to store the relationship in a memory or the like. As a result, the amount of biting of the contact roller 41 into the intermediate transfer belt 2 and the pressing force of the urging coil spring for positioning the secondary transfer roller 8 at a predetermined position due to environmental changes and usage over time are applied to the interlocking member. The secondary transfer roller 8 can be positioned at a predetermined position after adjusting the biting amount, and the transfer nip pressure can be kept constant.

  Further, according to the image forming apparatus of the second embodiment, the biting amount adjustment control means (configured by the drive command unit 25 and the adjustment control unit 28) for controlling the biting amount adjustment mechanism 35 is a sheet conveyed to the transfer nip. Based on the thickness, the biting amount adjusting mechanism 35 is controlled to adjust the biting amount of the contact roller 41 with respect to the intermediate transfer belt 2. Specifically, as the thickness of the sheet 19 conveyed to the secondary transfer nip increases, the amount of biting of the contact roller 41 with respect to the intermediate transfer belt 2 is increased. Thus, when an image is formed on a thick sheet having a large influence of the speed fluctuation of the intermediate transfer belt 2 when entering the secondary transfer nip, the amount of biting of the intermediate transfer belt 2 by the contact roller 41 is large. It is possible to satisfactorily suppress the speed fluctuation of the intermediate transfer belt primary transfer region T1 when the sheet enters the secondary transfer nip. Further, when an image is formed on a thin sheet that is less affected by the speed fluctuation of the intermediate transfer belt 2 when entering the secondary transfer nip, the amount of biting of the intermediate transfer belt 2 by the contact roller 41 is small. While reducing the load caused by the contact roller 41 of the intermediate transfer belt 2, it is possible to satisfactorily suppress the speed fluctuation of the intermediate transfer belt primary transfer region T1 when the sheet enters the secondary transfer nip.

  Further, a thickness detection sensor 46 serving as a thickness detection means for detecting the thickness of the paper is provided upstream of the secondary transfer nip in the paper conveyance direction, and the biting amount adjustment control means is based on the detection result of the thickness detection sensor 46. The amount of biting of the contact roller 41 with respect to the intermediate transfer belt 2 may be adjusted. This eliminates the need for the user to input the thickness information of the paper to be transported or to set the mode based on the thickness of the paper to be transported. Thereby, a user's erroneous input and setting are prevented, and the amount of biting according to the paper thickness can be reliably adjusted.

  Further, the image forming apparatus according to the fourth embodiment includes the heating device 21 that is provided in the vicinity of the secondary transfer nip and is a heating unit that heats the intermediate transfer belt 2 or the sheet 19, and performs intermediate transfer at the secondary transfer nip. Even the image forming apparatus configured to transfer the toner image on the belt 2 to the paper 19 and fix the toner image at the same time can obtain the above-described effects.

1Y, C, M, K: Photoconductor 2: Intermediate transfer belt (toner image carrying belt)
3: Driving roller 4: Entrance roller 5: Secondary transfer counter roller 6: Tension roller 7: Driven roller 8: Secondary transfer roller 10: Interlocking member 10a: Oscillating shaft 10b: Energizing coil spring 10d: Support arm 19: Paper 21: Heating device 24: Secondary transfer roller displacement sensor 25: Drive command unit 26: Microprocessor 27: Memory 28: Adjustment control unit 29a: First drive driver 29b: Second drive driver 30: Biting amount adjustment drive motor 35: Biting amount adjustment mechanism 41: contact roller 45: support member 46: thickness detection sensor 50: transfer unit 52: pressure adjustment drive motor 55: pressure adjustment mechanism

JP-A-2005-338884

Claims (9)

A toner image carrying belt which is stretched by a plurality of stretching rollers and carries a toner image on the surface and moves endlessly;
Image forming comprising: a transfer roller that faces one of the plurality of stretching rollers across the toner image carrying belt and forms a transfer nip for transferring the toner image on the toner image carrying belt to a sheet-like member In the device
A contact member that is in contact with a region on the downstream side of the transfer direction of the toner image carrier belt with respect to the transfer nip of the toner image carrier belt in the vicinity of the transfer roller;
The abutting member and the transfer roller are supported, and the abutting member is displaced in a direction in which the tension of the toner image carrying belt decreases in conjunction with the displacement of the transfer roller when the sheet-like member enters the transfer nip. Interlocking means,
An image forming apparatus comprising: a biting amount adjusting means for adjusting a biting amount of the contact member with respect to the toner image carrying belt. The image forming apparatus according to claim 1.
A pressing unit that presses the interlocking unit so that the transfer roller is pressed to the tension roller side facing the transfer roller with the toner image carrying belt interposed therebetween;
A pressing force adjusting means for adjusting the pressing force of the pressing means to the interlocking means;
The amount of biting of the contact member after adjustment by the biting amount adjusting unit with respect to the toner image carrying belt is detected, and the pressing force adjusting unit is controlled based on the detected amount of biting to the interlocking unit of the pressing unit. An image forming apparatus, comprising: a pressing force adjustment control unit that adjusts the pressing force. The image forming apparatus according to claim 2.
The pressing force adjusting control unit controls the pressing force adjusting unit so that the pressing force to the interlocking member increases as the amount of biting of the contact member into the toner image carrying belt increases. Forming equipment. The image forming apparatus according to claim 1.
Displacement detecting means for detecting displacement of the transfer roller when the amount of biting of the contact member with respect to the toner image carrying belt is adjusted by the amount of biting adjustment;
A pressing unit that presses the interlocking unit so that the transfer roller is pressed to the tension roller side facing the transfer roller with the toner image carrying belt interposed therebetween;
A pressing force adjusting means for adjusting the pressing force of the pressing means to the interlocking means;
An image forming system comprising: a pressing force adjusting control unit that controls the pressing force adjusting unit based on a detection result of the displacement detecting unit to adjust a pressing force of the pressing unit to the interlocking unit. apparatus. The image forming apparatus according to claim 4.
The image forming apparatus according to claim 1, wherein the pressing force adjusting control unit controls the pressing force adjusting unit based on a detection result of the displacement detecting unit so that the transfer roller is positioned at a predetermined position. The image forming apparatus according to claim 1,
There is provided a biting amount adjustment control means for controlling the biting amount adjusting means based on the thickness of the sheet-like member conveyed to the transfer nip and adjusting the biting amount of the contact member with respect to the toner image carrying belt. An image forming apparatus. The image forming apparatus according to claim 6.
The biting amount adjustment control means adjusts the biting amount adjustment means so that the biting amount of the contact member with respect to the toner image carrying belt increases as the thickness of the sheet-like member conveyed to the transfer nip increases. An image forming apparatus that controls the image forming apparatus. The image forming apparatus according to claim 6 or 7,
Thickness detection means for detecting the thickness of the sheet-like member is provided on the upstream side of the transfer nip in the sheet-like member conveyance direction,
The image forming apparatus, wherein the bite amount adjustment control unit controls the bite amount adjustment unit based on a detection result of the thickness detection unit. The image forming apparatus according to claim 1,
A heating unit provided in the vicinity of the transfer nip, for heating the toner image carrying belt or the sheet-like member;
An image forming apparatus configured to transfer and fix a toner image on the toner image carrying belt to a sheet-like member at the transfer nip.

Images