JP2019035782A - Image forming apparatus - Google Patents

Abstract

To prevent the occurrence of a dust-like abnormal image even when a sheet with a small thickness is fed.SOLUTION: An image forming apparatus comprises: a conveyance belt 61 that conveys a sheet P between a transfer nip N1 and a fixing nip N2; a motor Mt3 (driving means) that drives the conveyance belt 61; and a paper thickness sensor 93 (thickness detection means) that detects the thickness of the sheet P conveyed by the conveyance belt 61. When the thickness detected by the paper thickness sensor 93 is small, a control unit 90 controls the motor Mt3 so as to reduce a velocity ratio A/B (=surface linear velocity A of conveyance belt 61/surface linear velocity B of transfer rotating body 70) compared with that when the thickness is large.SELECTED DRAWING: Figure 3

Description

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

  2. Description of the Related Art Conventionally, image forming apparatuses such as copying machines and printers are provided with a conveyance belt (conveyance device) that conveys a sheet (paper) sent from a transfer nip such as a secondary transfer nip toward a fixing nip. Known (for example, refer to Patent Documents 1 and 2).

  Specifically, in the image forming apparatus in Patent Document 1, toner images respectively formed on a plurality of photosensitive drums by a plurality of developing devices are primarily transferred to be superimposed on the surface of the intermediate transfer belt. The toner image carried on the intermediate transfer belt (image carrier) is secondarily transferred to a sheet conveyed to a secondary transfer nip (transfer nip) position. Then, the sheet on which the toner image is secondarily transferred is conveyed toward the fixing device by a conveyance belt (conveyance device). The sheet conveyed to the fixing device is fed into the fixing nip, and the transferred toner image is fixed on the surface thereof.

  In a conventional image forming apparatus, when a sheet (thin paper) having a small thickness (paper thickness) is conveyed, a dust-like abnormal image may occur in an image formed on the sheet.

  The present invention has been made to solve the above-described problems, and it is an object of the present invention to provide an image forming apparatus in which a dust-like abnormal image hardly occurs even when a thin sheet is passed.

  The image forming apparatus according to the present invention includes an image carrier that carries a toner image, a transfer nip formed in contact with the image carrier, and a sheet conveyed to the transfer nip on the image carrier. The transfer rotator that transfers the toner image, the fixing rotator, and the pressure rotator contact each other to form a fixing nip, and the toner image transferred to the sheet conveyed to the fixing nip is fixed to the sheet. A fixing device; a conveying belt that conveys a sheet between the transfer nip and the fixing nip; a driving unit that drives the conveying belt; and a thickness detecting unit that detects the thickness of the sheet conveyed by the conveying belt; , (Surface linear velocity of the conveyor belt / Surface linear velocity of the transfer rotator) is defined as a speed ratio, when the thickness detected by the thickness detector is small, compared to when the thickness is large. It is obtained and a control unit for controlling the drive means so that the speed ratio decreases.

  According to the present invention, it is possible to provide an image forming apparatus that hardly generates a dust-like abnormal image even when a thin sheet is passed.

1 is an overall configuration diagram illustrating an image forming apparatus according to an embodiment of the present invention. It is a block diagram which expands and shows a part of image forming part. FIG. 3 is a schematic diagram illustrating an intermediate transfer belt device, a secondary transfer roller, a conveying device, and a fixing device. It is a perspective view which shows a conveying apparatus. FIG. 6 is a schematic diagram illustrating a locus of a sheet conveyed by a conveyance belt. FIG. 5 is a table showing a speed ratio of a traveling speed of a conveyance belt, a linear speed of a secondary transfer roller, and a linear speed at a fixing nip. FIG. 10 is a table showing a speed ratio of a traveling speed of a conveyance belt, a linear speed of a secondary transfer roller, and a linear speed at a fixing nip as a modification.

  Hereinafter, embodiments for carrying out the present invention will be described in detail with reference to the drawings. In addition, in each figure, the same code | symbol is attached | subjected to the part which is the same or it corresponds, The duplication description is simplified or abbreviate | omitted suitably.

First, the overall configuration and operation of the image forming apparatus 100 will be described with reference to FIGS.
FIG. 1 is a block diagram showing a printer as an image forming apparatus, and FIG. 2 is an enlarged view showing a part of the image forming unit.
As shown in FIG. 1, an intermediate transfer belt 8 (intermediate transfer member) as an image carrier is installed in the center of the image forming apparatus main body 100. Further, image forming units 6Y, 6M, 6C, and 6K corresponding to the respective colors (yellow, magenta, cyan, and black) are arranged in parallel so as to face the intermediate transfer belt 8.

  Referring to FIG. 2, an image forming unit 6Y corresponding to yellow includes a photosensitive drum 1Y as a photosensitive member, a charging unit 4Y disposed around the photosensitive drum 1Y, a developing unit 5Y, a cleaning unit 2Y, It is comprised by the lubricant supply apparatus 3, the static elimination part, etc. Then, an image forming process (charging process, exposure process, developing process, transfer process, cleaning process, charge eliminating process) is performed on the photosensitive drum 1Y, and a yellow image is formed on the photosensitive drum 1Y. Become.

  The other three image forming units 6M, 6C, and 6K have substantially the same configuration as that of the image forming unit 6Y corresponding to yellow except that the color of the toner used is different. A corresponding image is formed. Hereinafter, description of the other three image forming units 6M, 6C, and 6K will be omitted as appropriate, and only the image forming unit 6Y corresponding to yellow will be described.

Referring to FIG. 2, photosensitive drum 1Y is driven to rotate counterclockwise by a main motor. Then, the surface of the photosensitive drum 1Y is uniformly charged at the position of the charging unit 4Y (a charging process).
Thereafter, the surface of the photosensitive drum 1Y reaches the irradiation position of the laser beam L emitted from the exposure unit 7, and the width direction at this position (the vertical direction in FIG. 1 and FIG. 2 and the main scanning direction). The electrostatic latent image corresponding to yellow is formed by the exposure scanning (the exposure process).

Thereafter, the surface of the photosensitive drum 1Y reaches a position facing the developing portion 5Y, and the electrostatic latent image is developed at this position to form a yellow toner image (developing process).
Thereafter, the surface of the photosensitive drum 1Y reaches a position facing the intermediate transfer belt 8 and the primary transfer roller 9Y, and the toner image formed on the surface of the photosensitive drum 1 at this position is the surface of the intermediate transfer belt 8. Primary transfer (this is a primary transfer step). At this time, a small amount of untransferred toner remains on the photosensitive drum 1Y.

Thereafter, the surface of the photosensitive drum 1Y reaches a position facing the cleaning unit 2Y, and untransferred toner remaining on the photosensitive drum 1Y at this position is collected in the cleaning unit 2Y by the cleaning blade 2a (cleaning). Process.)
Here, inside the cleaning unit 2Y, a lubricant supply device 3 (a lubricant supply device for a photoconductor) including a lubricant supply roller 3a, a solid lubricant 3b, a compression spring 3c (biasing member), and the like is provided. Has been. Then, the lubricant supply roller 3a rotating in the clockwise direction in FIG. 2 scrapes the lubricant little by little from the solid lubricant 3b, and the lubricant is supplied to the surface of the photosensitive drum 1Y by the lubricant supply roller 3a. It will be.
Finally, the surface of the photosensitive drum 1Y reaches a position facing the neutralization unit, and the residual potential on the photosensitive drum 1 is removed at this position.
Thus, a series of image forming processes performed on the photosensitive drum 1Y is completed.

The image forming process described above is performed in the other image forming units 6M, 6C, and 6K in the same manner as the yellow image forming unit 6Y. That is, a laser beam L based on image information is irradiated from the exposure unit 7 disposed above the image forming unit onto the photosensitive drums 1M, 1C, and 1K of the image forming units 6M, 6C, and 6K. Is done. Specifically, the exposure unit 7 emits laser light L from a light source, and irradiates the photosensitive drum through a plurality of optical elements while scanning the laser light L with a polygon mirror that is rotationally driven. Note that a plurality of LEDs arranged in the width direction may be used as the exposure unit 7.
Thereafter, the toner images of the respective colors formed on the photosensitive drums 1M, 1C, and 1K through the developing process by the developing units 5M, 5C, and 5K are superimposed on the intermediate transfer belt 8 and primarily transferred. In this way, a color image is formed on the intermediate transfer belt 8.

Here, the intermediate transfer belt 8 serving as an image carrier is stretched and supported by a plurality of roller members 16 to 22, 80, and is driven by rotation of one roller member (drive roller 16) by a drive motor Mt1. It is moved endlessly in the direction of the arrow in FIG.
The four primary transfer rollers 9Y, 9M, 9C, and 9K respectively sandwich the intermediate transfer belt 8 with the photosensitive drums 1Y, 1M, 1C, and 1K to form a primary transfer nip. Then, a transfer voltage (primary transfer bias) having a polarity opposite to the polarity of the toner is applied to the primary transfer rollers 9Y, 9M, 9C, and 9K.
The intermediate transfer belt 8 travels in the direction of the arrow, and sequentially passes through the primary transfer nips of the primary transfer rollers 9Y, 9M, 9C, and 9K. In this way, the toner images of the respective colors on the photosensitive drums 1Y, 1M, 1C, and 1K are primarily transferred so as to overlap the surface of the intermediate transfer belt 8 (this is a primary transfer process).

  Thereafter, the intermediate transfer belt 8 on which the toner images of the respective colors are primarily transferred and overlapped reaches a position facing the secondary transfer roller 70 as a transfer rotator. At this position, the secondary transfer counter roller 80 sandwiches the intermediate transfer belt 8 and the secondary transfer belt 72 between the secondary transfer roller 70 and forms a secondary transfer nip N1 (see FIG. 5A). doing. The four color toner images formed on the intermediate transfer belt 8 are secondarily transferred onto the sheet P conveyed to the position of the secondary transfer nip N1 (secondary transfer process). At this time, the untransferred toner that has not been transferred to the sheet P remains on the intermediate transfer belt 8.

Thereafter, the intermediate transfer belt 8 reaches the position of the intermediate transfer cleaning unit 10. At this position, deposits such as untransferred toner adhered to the surface of the intermediate transfer belt 8 are removed.
Further, the intermediate transfer belt 8 reaches the position of a lubricant supply device 30 as an intermediate transfer lubricant supply device. At this position, the lubricant is supplied to the surface of the intermediate transfer belt 8.
Thus, a series of transfer processes performed on the intermediate transfer belt 8 is completed.

Here, referring to FIG. 1, a sheet P conveyed to the position of the secondary transfer nip is fed from a sheet feeding unit 26 disposed below the apparatus main body 100 to a sheet feeding roller 27, a registration roller pair 28, and the like. It is conveyed via.
Specifically, the sheet feeding unit 26 stores a plurality of sheets P such as sheets. When the paper feed roller 27 is driven to rotate counterclockwise in FIG. 1, the uppermost sheet P is fed toward the rollers of the registration roller pair 28 via the first conveyance path K1. The

  The sheet P conveyed to the registration roller pair 28 (timing roller pair) temporarily stops at the position of the roller nip of the registration roller pair 28 that has stopped rotating. Then, the registration roller pair 28 is rotationally driven in synchronization with the color image on the intermediate transfer belt 8, and the sheet P is conveyed toward the secondary transfer nip N1. Thus, a desired color image is transferred onto the sheet P.

Thereafter, the sheet P on which the color image has been transferred at the position of the secondary transfer nip N1 is sent out from the secondary transfer nip N1 and then conveyed to the position of the fixing device 50 by the conveyance belt 61 (conveyance device 60). Then, at the position of the fixing nip N2 (see FIG. 5A), the color image transferred on the surface is fixed on the sheet P by the heat and pressure of the fixing belt 51 and the pressure roller 54 (fixing). Process.)
Thereafter, the sheet P is discharged out of the apparatus by the pair of discharge rollers via the second conveyance path K2. The sheets P discharged out of the apparatus by the pair of discharge rollers are sequentially stacked on the stack unit as an output image.
Thus, a series of image forming processes in the image forming apparatus is completed.

Next, the configuration and operation of the developing unit 5Y (developing device) in the image forming unit will be described in more detail with reference to FIG.
The developing unit 5Y includes a developing roller 51Y that faces the photosensitive drum 1Y, a doctor blade 52Y that faces the developing roller 51Y, two conveying screws 55Y disposed in the developer container, and a toner concentration in the developer. A density detection sensor 56Y for detecting The developing roller 51Y includes a magnet fixed inside, a sleeve rotating around the magnet, and the like. In the developer accommodating portion, a two-component developer G composed of a carrier and toner is accommodated.

The developing unit 5Y configured as described above operates as follows.
The sleeve of the developing roller 51Y rotates in the direction of the arrow in FIG. The developer G carried on the developing roller 51Y by the magnetic field formed by the magnet moves on the developing roller 51Y as the sleeve rotates. Here, the developer G in the developing section 5Y is adjusted so that the ratio of the toner (toner concentration) in the developer G is within a predetermined range. Specifically, when a low toner density state is detected by the toner density sensor installed in the developing unit 5Y, new toner is introduced from the toner container 58 into the developing unit 5Y so that the toner density falls within a predetermined range. To be replenished.
Thereafter, the toner replenished from the toner container 58 into the developer accommodating portion is circulated through the two separated developer accommodating portions while being mixed and stirred together with the developer G by the two conveying screws 55Y (see FIG. 2). It is the movement in the direction perpendicular to the paper.) The toner in the developer G is attracted to the carrier by frictional charging with the carrier, and is carried on the developing roller 51Y together with the carrier by the magnetic force formed on the developing roller 51Y.

The developer G carried on the developing roller 51Y is conveyed in the direction of the arrow in FIG. 2 and reaches the position of the doctor blade 52Y. The developer G on the developing roller 51Y is conveyed to a position facing the photosensitive drum 1Y (development region) after the developer amount is made appropriate at this position. The toner is attracted to the latent image formed on the photosensitive drum 1Y by the electric field formed in the development area. Thereafter, the developer G remaining on the developing roller 51Y reaches the upper portion of the developer accommodating portion as the sleeve rotates, and is detached from the developing roller 51Y at this position.
The toner container 58 is detachably (replaceable) with respect to the developing unit 5Y (image forming apparatus 100). When the new toner stored in the toner container 58 becomes empty, the toner container 58 is removed from the developing unit 5Y (image forming apparatus 100) and replaced with a new one.

Next, the intermediate transfer belt device in the present embodiment will be described in detail with reference to FIG.
Referring to FIG. 3, the intermediate transfer belt device includes an intermediate transfer belt 8 as an image carrier, four primary transfer rollers 9Y, 9M, 9C, and 9K, a driving roller 16, a driven roller 17, a pre-transfer roller 18, Tension roller 19, cleaning counter roller 20, lubricant counter roller 21, backup roller 22, intermediate transfer cleaning unit 10, lubricant supply device 30 as an intermediate transfer lubricant supply device, secondary transfer counter roller 80, and transfer rotator Secondary transfer roller 70 and the like.

  The intermediate transfer belt 8 (image carrier) is in contact with four photosensitive drums 1Y, 1M, 1C, and 1K that respectively carry toner images of respective colors to form a primary transfer nip. The intermediate transfer belt 8 mainly includes eight roller members (a driving roller 16, a driven roller 17, a pre-transfer roller 18, a tension roller 19, a cleaning counter roller 20, a lubricant counter roller 21, a backup roller 22, and a secondary transfer counter roller 80. It is stretched and supported by.

In the present embodiment, the intermediate transfer belt 8 includes PVDF (vinylidene fluoride), ETFE (ethylene-tetrafluoroethylene copolymer), PI (polyimide), PC (polycarbonate), etc. in a single layer or multiple layers. A conductive material such as carbon black is dispersed. The intermediate transfer belt 8 is adjusted so that the volume resistivity is in the range of 10 ⁶ to 10 ¹³ Ωcm and the surface resistivity on the back side of the belt is in the range of 10 ⁷ to 10 ¹³ Ωcm. The intermediate transfer belt 8 is set to have a thickness in the range of 20 to 200 μm. In the present embodiment, the thickness of the intermediate transfer belt 8 is set to about 60 μm, and the volume resistivity is set to about 10 ⁹ Ωcm.
If necessary, a release layer can be coated on the surface of the intermediate transfer belt 8. At that time, materials used for the coating are ETFE (ethylene-tetrafluoroethylene copolymer), PTFE (polytetrafluoroethylene), PVDF (vinylidene fluoride), PEA (perfluoroalkoxy fluororesin), FEP (four A fluororesin such as fluorinated ethylene-hexafluoropropylene copolymer) or PVF (vinyl fluoride) can be used, but is not limited thereto.

The primary transfer rollers 9Y, 9M, 9C, and 9K are in contact with the corresponding photosensitive drums 1Y, 1M, 1C, and 1K via the intermediate transfer belt 8, respectively. Specifically, the yellow primary transfer roller 9Y contacts the yellow photosensitive drum 1Y via the intermediate transfer belt 8, and the magenta primary transfer roller 9M passes through the intermediate transfer belt 8 for magenta. The primary transfer roller 9C for cyan contacts the photosensitive drum 1C for cyan via the intermediate transfer belt 8, and the primary transfer roller 9K for black (for black) contacts the photosensitive drum 1M. It is in contact with the black (black) photosensitive drum 1K via the intermediate transfer belt 8. Each of the primary transfer rollers 9Y, 9M, 9C, and 9K is an elastic roller having a conductive sponge layer formed on a core metal, and has a volume resistance of 10 ⁶ to 10 ¹² Ω (preferably 10 ⁷ to 10 ⁷ 10 ⁹ Ω).

  The driving roller 16 is positioned downstream of the four photosensitive drums in the running direction of the intermediate transfer belt, and the inner transfer belt 8 is wound on the inner periphery of the intermediate transfer belt 8 at a winding angle of about 120 degrees. It arrange | positions so that it may contact | abut on a surface. The driving roller 16 is rotationally driven in the clockwise direction in FIG. 3 by a driving motor Mt1 controlled by the control unit 90. As a result, the intermediate transfer belt 8 travels in a predetermined traveling direction (clockwise in FIG. 3).

  The driven roller 17 is located in the intermediate transfer belt 8 at a position upstream of the four photosensitive drums in the running direction of the intermediate transfer belt 8 with the intermediate transfer belt 8 wound at a winding angle of about 180 degrees. It arrange | positions so that it may contact | abut to a surrounding surface. In the intermediate transfer belt 8, a portion from the driven roller 17 to the driving roller 16 is set to be substantially horizontal. The driven roller 17 is driven to rotate clockwise in FIG. 3 as the intermediate transfer belt 8 travels.

The tension roller 19 is in contact with the outer peripheral surface of the intermediate transfer belt 8. The pre-transfer roller 18, the cleaning counter roller 20, the lubricant counter roller 21, the backup roller 22, and the secondary transfer counter roller 80 are in contact with the inner peripheral surface of the intermediate transfer belt 8.
An intermediate transfer cleaning unit 10 (cleaning blade) is installed between the secondary transfer counter roller 80 and the lubricant counter roller 21 so as to contact the cleaning counter roller 20 via the intermediate transfer belt 8.
A lubricant supply device 30 (intermediate transfer lubricant supply device) is installed between the cleaning counter roller 20 and the tension roller 19 so as to contact the lubricant counter roller 21 via the intermediate transfer belt 8. The lubricant supply device 30 includes a lubricant supply roller, a solid lubricant, a compression spring, and the like, similarly to the lubricant supply device 3 for the photosensitive drum. Then, the lubricant supply roller rotating counterclockwise in FIG. 3 scrapes the lubricant little by little from the solid lubricant, and the lubricant is supplied to the surface of the intermediate transfer belt 8 by the lubricant supply roller. Become.
All of the roller members 17 to 22 and 80 excluding the drive roller 16 are driven to rotate clockwise in FIG. 3 as the intermediate transfer belt 8 travels.

Referring to FIG. 3, secondary transfer opposing roller 80 is in contact with secondary transfer roller 70 via intermediate transfer belt 8 and secondary transfer belt 72. The secondary transfer counter roller 80 has an NBR having a volume resistance of about 10 ⁷ to 10 ⁸ Ω and a hardness (JIS-A hardness) of about 48 to 58 degrees on the outer peripheral surface of a cylindrical metal core made of stainless steel or the like. An elastic layer made of rubber (layer thickness is about 5 mm) is formed.

  In the present embodiment, the secondary transfer counter roller 80 is electrically connected to the power supply unit 91 (bias output means), and the secondary transfer bias becomes a high voltage of about −5 kV from the power supply unit 91. Is applied. The secondary transfer bias applied to the secondary transfer counter roller 80 is used to secondary-transfer the toner image primarily transferred onto the surface of the intermediate transfer belt 8 onto the sheet P conveyed to the secondary transfer nip. And a secondary transfer bias (DC voltage) having the same polarity as that of the toner (in this embodiment, a negative polarity). As a result, the toner carried on the toner carrying surface (outer circumferential surface) of the intermediate transfer belt 8 is electrostatically moved from the secondary transfer counter roller 80 side to the secondary transfer roller 70 side by the secondary transfer electric field. Become.

The secondary transfer roller 70 as a transfer rotator is in contact with the toner carrying surface (outer peripheral surface) of the intermediate transfer belt 8 to form a secondary transfer nip through which the sheet P is conveyed. The secondary transfer roller 70 is driven to rotate counterclockwise in FIG. 3 by a drive motor Mt2 controlled by the control unit 90. As a result, the sheet P sandwiched in the secondary transfer nip is transported toward the transport device 60 together with the intermediate transfer belt 8 that is rotationally driven in the clockwise direction in FIG.
The secondary transfer roller 70 is formed by forming (coating) an elastic layer having a hardness (Asker C hardness) of about 40 to 50 degrees on a cored bar made of stainless steel, aluminum, or the like. The elastic layer of the secondary transfer roller 70 is made of a solid or foamed sponge by dispersing a conductive filler such as carbon or containing an ionic conductive material in a rubber material such as polyurethane, EPDM, or silicone. Can be formed. In this embodiment, the elastic layer is set to have a volume resistance of about 10 ^6.5 to 10 ^7.5 Ω in order to suppress concentration of transfer current.
It is also possible to improve the releasability of the roller surface with respect to the toner by forming a release layer such as a semiconductive fluororesin or urethane resin on the surface of the secondary transfer roller 70.

Hereinafter, the configuration and operation of the image forming apparatus 100, which are characteristic in the present embodiment, will be described in detail with reference to FIGS.
As described above with reference to FIG. 3 and the like, the image forming apparatus 100 according to the present embodiment includes an intermediate transfer belt 8 as an image carrier, a secondary transfer roller 70 as a transfer rotating body, a fixing device 50, A conveying belt 61 (conveying device 60) is installed.
A secondary transfer roller 70 serving as a transfer rotator is in contact with an intermediate transfer belt 8 (image carrier) that carries a toner image to form a transfer nip N1 (secondary transfer nip). The secondary transfer roller 70 is for transferring the toner image on the intermediate transfer belt 8 to the sheet P conveyed to the secondary transfer nip N1.

  3 and 5, the fixing device 50 includes a fixing belt 51 as a fixing rotator, a heating roller 52, a fixing auxiliary roller 53, a pressure roller 54 as a pressure rotator, an upper guide plate 55, a lower guide plate 55, and a lower guide plate 55. It comprises a guide plate 56 and the like. In the fixing device 50, the fixing belt 51 (fixing rotator) and the pressure roller 54 (pressure rotator) are in contact with each other to form a fixing nip N2, and the image is transferred to the sheet P conveyed to the fixing nip N2. The toner image is fixed on the sheet P.

Specifically, the fixing belt 51 is stretched and supported by a heating roller 52 and a fixing auxiliary roller 53. The heating roller 52 is a hollow structure, and a heater (heating source) is installed therein. The fixing auxiliary roller 53 is in pressure contact with the pressure roller 54 via the fixing belt 51, and a fixing nip N <b> 2 is formed between the fixing belt 51 and the pressure roller 54. The pressure roller 54 is driven to rotate counterclockwise in FIGS. 3 and 5 by a drive motor Mt4 controlled by the control unit 90. As a result, the fixing belt 51, the auxiliary fixing roller 53, and the heating roller 52 are driven to rotate in the clockwise direction in FIGS.
The fixing belt 51 is heated by the heating roller 52 heated by the heater, and the toner image on the sheet P is fixed at the fixing nip N2 by the heat from the fixing belt 51 and the nip pressure at the fixing nip N2. It will be.

An upper guide plate 55 is installed on the upstream side of the fixing nip N2 in the fixing device 50 so as to face the transfer surface of the sheet P (the surface on which an unfixed toner image is carried). A lower guide plate 56 is disposed so as to face the non-transfer surface (the surface on which an unfixed toner image is not carried) of the sheet P.
The upper guide plate 55 has a plurality of rib-like protrusions extending in the conveyance direction formed on the guide surface at intervals in the width direction, and an unfixed toner image on the sheet P is rubbed against the rib-like protrusions. It is arranged not to be able to.
The lower guide plate 56 is formed with a plurality of rib-like protrusions extending in the conveyance direction on the guide surface at intervals in the width direction, and has a large resistance when guiding the sheet P to the fixing nip N2. It is arranged not to become.

3 to 5, the conveying device 60 includes a conveying belt 61, a driving roller 62, a driven roller 63, a suction fan 64, and the like.
The conveyance belt 61 conveys the sheet P between the secondary transfer nip N1 (transfer nip) and the fixing nip N2. Specifically, the conveyance belt 61 is an endless belt that conveys the sheet P fed from the secondary transfer nip N1 (transfer nip) toward the fixing nip N2, and is formed of a rubber material. The transport belt 61 is held by a casing of the transport device 60 through two roller members 62 and 63 so as to be able to travel. A motor Mt3 (belt motor) is installed as a driving means for driving the conveyor belt 61.

  Specifically, the transport belt 61 is stretched and supported by a plurality of roller members (a driving roller 62 and a driven roller 63). The driving roller 62 and the driven roller 63 are rotatably held in the casing of the transport device 60. The motor Mt3 as the driving means is a variable speed motor that rotationally drives one roller member (the driving roller 62) among the plurality of roller members. When the driving roller 62 is driven to rotate counterclockwise in FIGS. 3 and 5 by the motor Mt3, the transport belt 61 and the driven roller 63 are also rotated counterclockwise. Then, the rotational speed of the driving roller 62 is varied by the control of the motor Mt3 by the control unit 90, so that the traveling speed A (surface linear speed) of the conveyor belt 61 is variably controlled to a desired speed. As a result, the sheet P delivered from the secondary transfer nip N1 is conveyed by the conveyance belt 61 toward the fixing nip N2 (fixing device 50) at a desired traveling speed A (conveyance speed).

Here, with reference to FIG. 5A, in the present embodiment, the conveyance belt 61 has a belt conveyance surface (a belt surface facing the sheet P and the upper surface of the belt) of 2. It is arranged so as to be positioned below a virtual plane S connecting the next transfer nip N1 and the fixing nip N2.
That is, the transport belt 61 (transport device 60) is not disposed so as to block the virtual plane S, but is disposed below and away from the virtual plane S.
With this configuration, the sheet P delivered from the secondary transfer nip N1 is conveyed by the conveyance belt 61 while being placed on the conveyance belt 61 by its own weight, and then slid onto the upper guide plate 55. It is guided to the fixing nip N2 so as to follow the inclination of the lower guide plate 56 without contact. Accordingly, the transportability of the sheet P from the secondary transfer nip N1 to the fixing nip N2 is improved.

Also, as shown in FIG. 4, a rib 65 protruding from the belt conveying surface of the conveying belt 61 toward the conveying path (upward) is provided in the conveying device 60 in the present embodiment in the conveying direction (traveling direction). It is formed so as to extend.
Specifically, in the present embodiment, the conveyance belt 61 is divided into three in the width direction (the direction perpendicular to the conveyance direction and the direction perpendicular to the paper surface of FIGS. 3 and 5). Each of the transport belts 61 divided into three has a length in the width direction set to about 80 mm. By dividing the conveyance belt 61 in the width direction, even if the accuracy of the parallelism and roundness of the two roller members 62 and 63 is not so high, the belt is less likely to be shifted. In this embodiment, the conveyance belt 61 divided into three is used, but a conveyance belt divided into two or four or more can also be used.
A rib 65 (the length in the width direction is set to about 1 mm) is formed between the adjacent conveyance belt 61 and the conveyance belt 61 so as to protrude upward by about 2 mm from the belt conveyance surface. ing.
By providing the ribs 65 in this way, even if toner or paper dust adheres to the casing of the transport device 60, the deposits are on the back surface of the sheet P (the surface facing the transport device 60). It becomes difficult to adhere (becomes difficult to get dirty on the back). Furthermore, by providing the rib 65 between the transport belt 61 and the transport belt 61, it is possible to prevent a problem that the adjacent transport belts 61 interfere with each other.

As shown in FIG. 4, a plurality of hole portions 61 a are formed in the entire area of the transport belt 61.
The transport device 60 is provided with a suction fan 64 that sucks the sheet P on the belt transport surface from the inner peripheral surface side of the transport belt 61 through the plurality of holes 61a. That is, the sheet P on the transport belt 61 is sucked by the suction fan 64 in the direction of the white arrow in FIG. 5A and is transported while being in close contact with the transport belt 61 to some extent. By providing the suction fan 64 in this way, the transportability of the sheet P by the transport belt 61 is improved.
In addition, a plurality of groove portions extending in the width direction are formed in the conveyance belt 61 at intervals in the circumferential direction. This groove is for improving the grip force of the conveyance belt 61 against the sheet P.

Here, the image forming apparatus 100 according to the present embodiment assumes that the linear velocity (surface linear velocity) of the secondary transfer roller 70 (transfer rotator) in the secondary transfer nip N1 (transfer nip) is B and the fixing nip N2. When the linear velocity (surface linear velocity) of the pressure roller 54 (or the fixing belt 51) is C, a relationship of B> C is established.
That is, the rotation speeds of the two drive motors Mt2 and Mt4 are set so that the linear velocity B of the sheet P in the secondary transfer nip N1 is larger than the linear velocity C of the sheet P in the fixing nip N2.

In order to convey the sheet P satisfactorily between the secondary transfer nip N1 and the fixing nip N2 without causing a jam or an abnormal image, the sheet P is conveyed in a slack state between them. This is necessary.
If the sheet P is conveyed while being pulled between the secondary transfer nip N1 and the fixing nip N2 having a high nip pressure, a drive failure occurs in each of the nips N1 and N2 via the sheet P. . Specifically, the rotation unevenness of the fixing belt 51 and the pressure roller 54 is transmitted to the secondary transfer roller 70, and the rotation unevenness causes an abnormal image such as a horizontal streak image called banding during the secondary transfer process. In addition, the sheet P that is strongly pulled between the nips flickers at the moment when the sheet P passes through the secondary transfer nip N1, and the toner image on the sheet P comes into contact with the upper guide plate 55, and an abnormal image such as a cosmetic image appears. Will occur.
On the other hand, in the present embodiment, the linear velocity B of the sheet P in the secondary transfer nip N1 is set to be larger than the linear velocity C of the sheet P in the fixing nip N2, and FIG. As described above, since the sheet P is conveyed in a relaxed state between the secondary transfer nip N1 and the fixing nip N2, the above-described problems are less likely to occur. Specifically, in this embodiment, the linear velocity C of the pressure roller 54 (or the fixing belt 51) in the fixing nip N2 is 0 than the linear velocity B of the secondary transfer roller 70 in the secondary transfer nip N2. The rotational speeds of the two drive motors Mt2 and Mt4 are set as fixed values so as to be about 7% slower.

Here, referring to FIGS. 1 and 3, the image forming apparatus 100 according to the present embodiment has a paper thickness as a thickness detection unit that detects the thickness (paper thickness) of the sheet P conveyed by the conveyance belt 61. A sensor 93 is installed.
Specifically, the paper thickness sensor 93 (thickness detection means) is a distance measuring sensor disposed so as to face the conveyance guide plate in the vicinity of the paper feed unit 26. Then, the thickness of the sheet P fed from the paper feed unit 26 and conveyed while being in close contact with the conveyance guide plate is optically and directly detected by the paper thickness sensor 93. The installation position of the paper thickness sensor 93 is not limited to the vicinity of the paper feed unit 26, and may be in the transport path from the paper feed unit 26 to the transport device 60. It can also be configured to detect at a detection position outside the sheet feeding unit 26 before setting the sheet P.

  In the present embodiment, the paper thickness sensor 93 is used as a thickness detection unit that detects the thickness (paper thickness) of the sheet P. However, the operation panel 92 installed on the exterior of the apparatus main body 100 as the thickness detection unit. (See FIGS. 1 and 3). Specifically, information on the sheet P set in the paper feeding unit 26 (at least information on the paper thickness) by the operation of the operation panel 92 (for example, a touch button for selecting the paper thickness is displayed) by the user. Is input), the control unit 90 detects the paper thickness of the sheet P.

In this embodiment, when the surface linear velocity of the conveyor belt 61 is A and the surface linear velocity of the secondary transfer roller 70 (transfer rotator) is B, and the speed ratio is A / B, the paper thickness sensor When the thickness of the sheet P detected by 93 (thickness detection means) is thin, the control unit 90 reduces the belt ratio so that the speed ratio A / B is smaller than that when the sheet P is thick. The motor Mt3 (driving means) is controlled.
Specifically, the control unit 90 causes the speed ratio A / B described above to be smaller when the thickness detected by the paper thickness sensor 93 is equal to or smaller than the predetermined value X as compared with the case where the thickness exceeds the predetermined value X. The motor Mt3 is controlled. Specifically, in the present embodiment, when thin paper having a basis weight of 100 gsm or less is conveyed, the motor Mt3 is controlled so that the above-described speed ratio A / B is 0.996, and the basis weight is 100 gsm. When the sheet P other than the thin paper exceeding is transported, the motor Mt3 is controlled so that the above-described speed ratio A / B becomes 1.006.

More specifically, in the present embodiment, the surface linear velocity B (the number of rotations of the drive motor Mt2) of the secondary transfer roller 70 is set so as not to change regardless of the thickness of the conveyed sheet P. When the thickness of the sheet P detected by the thickness sensor 93 (thickness detection means) is small, the traveling speed A (surface linear velocity) of the conveying belt 61 is slower than when the thickness of the sheet P is thick. The controller 90 controls the belt motor Mt3 (driving means).
Specifically, in the present embodiment, the control unit 90 sets the thickness detected by the paper thickness sensor 93 to a predetermined value X (in this embodiment, a value corresponding to the basis weight 100 gsm of the sheet P). .) In the following cases, the motor Mt3 is controlled so that the traveling speed A of the conveyor belt 61 becomes slower than when the thickness exceeds the predetermined value X.

Such control is performed when a sheet P other than thin paper (basis paper, cardboard, etc.) having a basis weight exceeding 100 gsm is passed, and the leading edge of the sheet P has entered the position of the conveyance belt 61. In order to prevent the sheet P from jumping up, it is necessary to set the traveling speed of the conveying belt 61 faster than the linear speed B of the secondary transfer nip N1, but the traveling speed of the conveying belt 61 set as such is set. When a thin paper having a basis weight of 100 gsm or less is conveyed, as shown in FIG. 5B, a thin paper (sheet P) that is weak due to a large linear velocity difference between the fixing device 50 and the conveying device 60. ) Would be greatly bent. A part of the thin paper (sheet P) that is greatly bent in this way comes into the space between the lower guide plate 56 and the conveyor belt 61 (the part surrounded by the broken line in FIG. 5B). In the vicinity thereof, the rib 65 of the conveying device 60 and the rib-like protrusions of the lower guide plate 56 are rubbed with a strong force to be frictionally charged. It becomes an abnormal image.
On the other hand, in the present embodiment, when the thin sheet P (thin paper) is passed, the motor Mt3 is controlled so that the speed ratio A / B (traveling speed A of the conveyor belt 61) is reduced. Therefore, the above-described problems are alleviated without causing a large deflection between the fixing device 50 and the conveying device 60.

More specifically, with reference to FIG. 6, in this embodiment, the traveling speed (surface linear speed) of the conveying belt 61 is A, and the linear speed (surface line) of the secondary transfer roller 70 in the secondary transfer nip N1. The control unit 90 detects the sheet detected by the paper thickness sensor 93 when the speed) is B and the linear speed (surface linear speed) of the pressure roller 54 (or the fixing belt 51) in the fixing nip N2 is C. When the thickness of P exceeds a predetermined value X, the motor Mt3 is controlled so that the relationship A>B> C is established. Further, when the thickness of the sheet P detected by the paper thickness sensor 93 is equal to or less than the predetermined value X, the control unit 90 controls the motor Mt3 so that the relationship B>A> C is established. FIG. 6 shows the speed ratio of A and C, where the linear speed B at the secondary transfer nip N1 is 100.
In particular, in the present embodiment, the control unit 90 determines the traveling speed of the conveyor belt 61 when the thickness detected by the paper thickness sensor 93 is equal to or less than the predetermined value X as compared to when the thickness exceeds the predetermined value X. The motor Mt3 is controlled so as to be slower by 1.0% or more.
By performing such control, the jumping of the sheet P when the leading edge of the sheet P enters the position of the conveying belt 61 is reduced, and the abnormal image of the dust when the thin paper is passed as the sheet P is reduced. Occurrence can be reduced.

Further supplementary explanation will be given.
As described above, the relationship between the linear velocity B in the secondary transfer nip N1 and the linear velocity C in the fixing nip N2 is B> C in order to prevent the sheet P from being pulled between the nips. It has become a relationship.
On the other hand, the relationship between the linear velocity B in the secondary transfer nip N1 and the running velocity A (linear velocity) of the conveying belt 61 when a sheet P other than thin paper is passed is a relationship of A> B. It is preferable. This is because the sheet P other than thin paper has a certain degree of rigidity, so that the leading end of the sheet P contacts the conveying belt 61 when the traveling speed A of the conveying belt 61 becomes slower than the linear velocity B in the secondary transfer nip N1. This is because the brake is applied at the moment, and the sheet P jumps up. Then, as the sheet P jumps up like this, the sheet P blurs at the secondary transfer nip N1, and a horizontal stripe-like jitter image is generated. In particular, when thick paper having high rigidity is passed as the sheet P, such a problem becomes remarkable.
In the present embodiment, in order to prevent such a problem, the traveling speed A of the conveying belt 61 when a sheet P other than thin paper is passed is compared with the linear speed B in the secondary transfer nip N1. , It is set to be about 0.6% faster. Since the traveling speed A of the transport belt 61 is faster than the linear speed B in the secondary transfer nip N1, when the highly rigid sheet P comes into contact with the transport belt 61, the transport belt 61 does not generate a brake. The sheet P is delivered smoothly.

In contrast, when thin paper with low rigidity is passed as the sheet P, the leading edge of the sheet P is conveyed even if the traveling speed A of the conveyor belt 61 is slower than the linear speed B in the secondary transfer nip N1. Since the sheet P bends so as to absorb the impact at the moment of contact with the belt 61, the sheet P does not jump up.
However, when a thin paper having low rigidity is passed as the sheet P, if the traveling speed A of the conveyor belt 61 is set faster than the linear speed B in the secondary transfer nip N1, the traveling speed A of the conveyor belt 61 is set. Will become very fast with respect to the linear velocity C in the fixing nip N2, and as described above with reference to FIG. 5B, the rigidity between the conveying device 60 and the fixing device 50 is increased. A low thin paper (sheet P) will be greatly bent, and a dust-like abnormal image will be generated. Specifically, when a halftone image is printed, a black streak-like image is formed at a position corresponding to the rib 65 of the image.
On the other hand, in the present embodiment, when thin paper having low rigidity is passed as the sheet P, the motor is set so that the traveling speed A of the conveyor belt 61 is slower than the linear speed B in the secondary transfer nip N1. Since Mt3 is controlled, the speed difference between the traveling speed A of the transport belt 61 and the linear speed C at the fixing nip N2 is also reduced, and a thin paper (sheet) having low rigidity between the transport apparatus 60 and the fixing apparatus 50 is used. The problem that P) is greatly bent is reduced. Therefore, the occurrence of dust-like abnormal images when thin paper is passed is also reduced.
In addition, when the thin paper is passed, the relationship of B> C is maintained even when the relationship of B> A is satisfied, so that the sheet P is not pulled between the two nips N1 and N2.
In addition, as a result of experiments and simulations performed by the inventor of the present application, when the thickness detected by the paper thickness sensor 93 is equal to or smaller than a predetermined value X (corresponding to a basis weight of 100 gsm), the thickness exceeds the predetermined value X. It has been found that by reducing the traveling speed of the conveyor belt 61 by 1.0% or more, the occurrence of dust-like abnormal images during thin paper feeding can be stably reduced.

<Modification>
FIG. 7 is a table showing a speed ratio of the traveling speed of the conveyance belt 61, the linear speed of the secondary transfer roller 70, and the linear speed at the fixing nip N2, as a modified example. FIG. 7 is a diagram corresponding to FIG. 6.
1 and 3, a temperature / humidity sensor 94 is installed inside the image forming apparatus 100 as temperature / humidity detection means for detecting the temperature / humidity inside.
In the modification, the control unit 90 has an absolute humidity based on the temperature / humidity detected by the temperature / humidity sensor 94 (temperature / humidity detecting means) equal to or lower than a threshold value W (absolute humidity corresponding to 10 ° C. and 15%). In some cases, the motor Mt3 (driving means) is controlled so that the traveling speed A of the transport belt 61 is slower than when the absolute humidity exceeds the threshold value W.
Specifically, in the modification, as shown in FIG. 7, when the thickness of the sheet P detected by the paper thickness sensor 93 exceeds a predetermined value X, the motor Mt3 is set so that the relationship A>B> C is established. Is controlling. Further, when the thickness of the sheet P detected by the paper thickness sensor 93 is equal to or less than the predetermined value X, the motor Mt3 is controlled so that the relationship B>A> C is established. At this time, the absolute humidity obtained by the calculation unit of the control unit 90 based on the temperature detected by the temperature / humidity sensor 94 and the relative humidity is equal to or less than the threshold value W (the absolute humidity corresponding to 10 ° C. and 15%). When this happens, the traveling speed A of the conveyor belt 61 is further reduced while maintaining the relationship of B>A> C.
This is a low-temperature and low-humidity environment where the absolute humidity is lower than the absolute humidity (threshold W) corresponding to 10 ° C. and 15%. When thin paper is passed as the sheet P, the absolute humidity exceeds the threshold W ( The moisture content of the sheet P is larger than when thin paper is passed in a normal temperature and normal humidity environment, a high temperature and high humidity environment, etc.), and the sheet P is greatly bent as shown in FIG. This is because, by rubbing against 65 or the like, a larger frictional charge is generated, and the degree of the dusty abnormal image is deteriorated.
On the other hand, in the modified example, when thin paper is passed as a sheet P in a low-temperature and low-humidity environment, the traveling speed A of the transport belt 61 is set to be lower and the transport device 60 and the fixing device 50 Since the sheet P (thin paper) is prevented from being bent so much, the occurrence of dust-like abnormal images can be reduced.
In the modification, the temperature / humidity sensor 94 (temperature / humidity detection means) is configured to detect the temperature / humidity inside the image forming apparatus main body 100. It can also be configured to detect temperature and humidity. In such a case, the moisture absorption state of the sheet P to be passed can be detected with higher accuracy.

As described above, the image forming apparatus 100 according to the present embodiment has the conveyance belt 61 that conveys the sheet P between the transfer nip N1 and the fixing nip N2, and the motor Mt3 (driving unit) that drives the conveyance belt 61. In addition, a paper thickness sensor 93 (thickness detection means) that detects the thickness of the sheet P conveyed by the conveyance belt 61 is provided. When the thickness detected by the paper thickness sensor 93 is small, the speed ratio A / B (= surface linear velocity A of the conveying belt 61 / surface linear velocity B of the transfer rotating body 70) is compared with the case where the thickness is large. The motor Mt3 is controlled by the control unit 90 so that becomes smaller.
As a result, even when a thin sheet P is passed, the occurrence of dust-like abnormal images is reduced.

In the present embodiment, the present invention is applied to the image forming apparatus 100 using the secondary transfer roller 70 as a transfer rotating body. On the other hand, the present invention can also be applied to an image forming apparatus using a secondary transfer belt as a transfer rotator.
In the present embodiment, the present invention is applied to the image forming apparatus 100 using the intermediate transfer belt 8 (intermediate transfer member) as an image carrier and the secondary transfer roller 70 as a transfer rotating member. Applied. In contrast, a photosensitive drum (photosensitive member) as an image carrier on which a toner image developed by the developing unit is formed without an intermediate transfer member such as an intermediate transfer belt or an intermediate transfer drum, and a photosensitive drum A transfer rotator for transferring a toner image on a photosensitive drum to a sheet conveyed to the transfer nip to form a transfer nip, so-called direct transfer type image formation The present invention can also be applied to an apparatus. As the transfer rotator, a transfer belt or a transfer roller can be used.
In the present exemplary embodiment, the present invention is applied to the image forming apparatus 100 using the fixing belt 51 as a fixing rotating body and the pressure roller 54 as a pressing rotating body. In contrast, the present invention can also be applied to an image forming apparatus using a fixing roller as a fixing rotator and an image forming apparatus using a pressure belt as a pressure rotator.
Even in such cases, the same effects as those of the present embodiment can be obtained.

In the present embodiment, the traveling speed A of the conveyor belt 61 is configured to be variable in two stages. In the modification, the traveling speed A of the conveyor belt 61 is configured to be variable in three stages. Depending on the thickness of P and the temperature / humidity (absolute humidity), the traveling speed of the conveyor belt can be varied in multiple stages by a greater number.
Further, a calculation formula for obtaining the optimum traveling speed of the conveyance belt 61 from the thickness and temperature / humidity (absolute humidity) of the sheet P is stored in the storage unit, and the sheet P is conveyed according to the detected thickness and temperature / humidity (absolute humidity). It is also possible to calculate the optimum traveling speed of the belt 61 and vary the traveling speed.
Even in such cases, the same effects as those of the present embodiment can be obtained.

  In the present embodiment, the surface linear velocity B of the secondary transfer roller 70 (transfer rotator) is not changed regardless of the thickness of the sheet P being conveyed. The drive motor Mt2 can also be configured such that the surface linear velocity B of the secondary transfer roller 70 (transfer rotator) varies depending on the thickness. For example, when the thick paper is conveyed as the sheet P, the drive motor Mt2 can be controlled so that the surface linear velocity B of the secondary transfer roller 70 is halved compared to the case where the thin paper is conveyed as the sheet P. . As described above, even when the drive motor Mt2 is controlled by the control unit 90, when the thickness of the sheet P is thin, the control unit so that the speed ratio A / B is smaller than that when the sheet P is thick. By controlling the motor Mt3 (driving means) by 90, the same effect as that of the present embodiment can be obtained.

In the present embodiment, the motor Mt2 for driving the secondary transfer roller 70 (transfer rotator) may be configured not to be installed. In this case, the secondary transfer roller 70 is driven to rotate as the intermediate transfer belt 8 travels. Therefore, the surface linear velocity B of the secondary transfer roller 70 becomes equal to the surface linear velocity of the intermediate transfer belt 8 driven by the drive motor Mt1.
Even in such a case, the same effect as that of the present embodiment can be obtained.

  It should be noted that the present invention is not limited to the present embodiment, and it is obvious that the present embodiment can be modified as appropriate within the scope of the technical idea of the present invention, other than suggested in the present embodiment. is there. In addition, the number, position, shape, and the like of the constituent members are not limited to the present embodiment, and the number, position, shape, and the like suitable for implementing the present invention can be achieved.

  In the present specification and the like, “sheet” refers to a sheet-like recording medium (image forming) such as coated paper, label paper, OHP sheet, metal sheet, film, plastic film, cloth, etc. To include all of the target media).

1Y, 1M, 1C, 1K photoconductor drum (photoconductor),
8 Intermediate transfer belt (image carrier),
50 fixing device,
51 fixing belt (fixing rotating body),
54 Pressure roller (pressure rotator),
60 conveying device,
61 Conveyor belt,
61a hole,
62 Drive roller (roller member),
63 driven roller (roller member),
64 suction fan,
65 ribs,
70 Secondary transfer roller (transfer rotator),
90 control unit,
93 Paper thickness sensor (thickness detection means),
94 Temperature / humidity sensor (temperature / humidity detection means),
100 Image forming apparatus (image forming apparatus main body),
Mt3 motor (drive means, belt motor),
S virtual plane, P sheet (paper).

JP2012-226209A JP 2012-83414 A

Claims (10)

An image carrier for carrying a toner image;
A transfer rotator that contacts the image carrier to form a transfer nip, and transfers a toner image on the image carrier to a sheet conveyed to the transfer nip; and
A fixing device in which a fixing rotator and a pressure rotator are in contact with each other to form a fixing nip, and a toner image transferred to the sheet conveyed to the fixing nip is fixed to the sheet;
A conveying belt that conveys a sheet between the transfer nip and the fixing nip;
Drive means for driving the conveyor belt;
Thickness detecting means for detecting the thickness of the sheet conveyed by the conveying belt;
When (surface linear velocity of the conveyor belt / surface linear velocity of the transfer rotating body) is defined as a speed ratio, the speed is higher when the thickness detected by the thickness detecting means is smaller than when the thickness is thicker. A control unit for controlling the driving means so as to reduce the ratio;
An image forming apparatus comprising:   The control unit controls the drive unit so that the speed ratio is smaller when the thickness detected by the thickness detection unit is equal to or less than a predetermined value, compared to when the thickness exceeds the predetermined value. The image forming apparatus according to claim 1. When the traveling speed of the conveying belt is A, the linear speed of the transfer rotator in the transfer nip is B, and the linear speed of the fixing rotator or the pressure rotator in the fixing nip is C,
The controller is
When the thickness detected by the thickness detector exceeds the predetermined value, a relationship of A>B> C is established,
3. The image forming apparatus according to claim 2, wherein when the thickness detected by the thickness detecting unit is equal to or less than the predetermined value, the driving unit is controlled so that a relationship of B>A> C is established. apparatus.   When the thickness detected by the thickness detector is equal to or less than the predetermined value, the control unit causes the traveling speed of the conveyor belt to be slower by 1.0% or more than when the thickness exceeds the predetermined value. The image forming apparatus according to claim 3, wherein the driving unit is controlled as described above.   The image forming apparatus according to claim 2, wherein the predetermined value is a value corresponding to a basis weight of 100 gsm of the sheet. A temperature / humidity detecting means for detecting the temperature / humidity inside the image forming apparatus main body or in the vicinity of the sheet feeding unit storing the sheet,
When the absolute humidity based on the temperature / humidity detected by the temperature / humidity detection means is equal to or lower than the threshold, the control unit drives the drive so that the speed ratio is slower than when the absolute humidity exceeds the threshold. 6. The image forming apparatus according to claim 1, wherein the image forming apparatus is controlled.   7. The conveyance belt according to claim 1, wherein the conveyance belt is disposed such that a belt conveyance surface thereof is positioned below a virtual plane connecting the transfer nip and the fixing nip. The image forming apparatus described in 1.   The conveyance device that holds the conveyance belt so as to be able to travel is formed such that a rib protruding from a belt conveyance surface of the conveyance belt toward a conveyance path extends in a conveyance direction. Item 8. The image forming apparatus according to Item 7. The transport belt has a plurality of holes,
The transport device that holds the transport belt so as to travel includes a suction fan that sucks a sheet on the belt transport surface from the inner peripheral surface side of the transport belt through the plurality of holes. The image forming apparatus according to claim 1. The conveyor belt is stretched and supported by a plurality of roller members,
The drive means is a motor with a variable rotational speed that rotationally drives one of the plurality of roller members.
The relationship B> C is established, where B is the linear velocity of the transfer rotator at the transfer nip and C is the linear velocity of the fixing rotator or the pressure rotator at the fixing nip. The image forming apparatus according to claim 1, wherein the image forming apparatus is an image forming apparatus.

Images