JP2015135431A - Belt conveyance device and image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a belt conveyance device for preventing curling tendency of a belt with a simple configuration, and an image forming apparatus.SOLUTION: In a belt conveyance device 70, a belt 7 has a peripheral length which leaves an extra length when wound on a plurality of support rollers 71, 72, 73. When in drive, tension is applied to the belt 7 between a load facing roller 73 and a drive roller 73 in a conveyance direction of the belt 7. When not in drive, the drive roller 72 can be rotated following the belt 7, thereby lessening the tension.

Description

  The present invention relates to a belt conveying device used in an image forming apparatus such as a copying machine, a printer, and a facsimile machine using an electrophotographic method or an electrostatic recording method, and the image forming device.

  Conventionally, as an electrophotographic image forming apparatus, for example, an endless transfer material carrier that carries and transports an intermediate transfer member that carries a toner image transferred from a photosensitive member or a transfer material that transfers a toner image from a photosensitive member. Some belts (hereinafter also simply referred to as “belts”) are used. In particular, so-called tandem type image formation in which a plurality of image forming units each provided with a photoconductor are arranged along the belt conveyance direction, and each image forming unit is formed by superimposing images on the belt. The device is widely used.

  A tandem type image forming apparatus that employs an intermediate transfer system having an intermediate transfer belt that is an endless belt as an intermediate transfer member will be further described as an example. In such an image forming apparatus, a toner image of each color is primarily transferred from a plurality of image forming units arranged along the conveyance direction of the intermediate transfer belt to the intermediate transfer belt, and then the toner image is recorded from the intermediate transfer belt. Secondary transfer is performed on a transfer material such as paper. The intermediate transfer belt is wound around a plurality of support rollers. Further, at least one of the plurality of support rollers is urged in a direction in which a tension is applied to the intermediate transfer belt by a spring as an urging unit.

  In order to transfer the toner image to the intermediate transfer belt and the transfer material without distortion at the primary transfer portion and the secondary transfer portion, respectively, the intermediate transfer belt has a flat shape without distortion at the primary transfer portion and the secondary transfer portion. It is necessary to be. Therefore, conventionally, the intermediate transfer belt is stretched in a flat shape by stretching the intermediate transfer belt in a state where tension is applied to a plurality of support rollers.

  However, if tension is applied to the intermediate transfer belt even when it is not driven, the intermediate transfer belt may be wrapped around the support roller when left for a long period of time. When the intermediate transfer belt is wound, the planarity of the intermediate transfer belt may be deteriorated at the primary transfer portion and the secondary transfer portion, and the toner image may not be accurately transferred. In particular, when the image forming apparatus is downsized, the diameter of the support roller is also reduced, and the intermediate transfer belt is likely to wind up significantly.

  On the other hand, Patent Document 1 proposes a method using a tension adjustment mechanism. In other words, the tension adjusting mechanism includes a tension applying member that applies tension to the intermediate transfer belt, and a tension release member that operates so that the tension applying member cannot apply tension to the intermediate transfer belt. At the time of driving, the tension applying member operates by receiving power from the driving unit of the intermediate transfer belt, and urges the intermediate transfer belt in the direction in which the tension is applied. On the other hand, when not driven, the tension releasing member operates to separate the tension applying member from the intermediate transfer belt and release the tension of the intermediate transfer belt.

JP 2005-25165 A

  However, in the above-described conventional method, it is necessary to add a tension applying member that applies tension by contacting the intermediate transfer belt during driving and a tension releasing member that releases tension during non-driving. This contributes to an increase in the size of the image forming apparatus.

  In the above, the conventional problem has been described in detail by taking a tandem type image forming apparatus having an intermediate transfer belt as an example. However, the same can be said for a configuration having an endless belt that conveys an image wound around a plurality of support rollers, not limited to the intermediate transfer method and not only the tandem type.

  SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a belt conveying device and an image forming apparatus that can suppress the belt from being wound with a simple configuration.

  The above object is achieved by the belt conveyance device and the image forming apparatus according to the present invention. In summary, the first aspect of the present invention is an endless belt that receives and conveys an image at an image receiving position, and a plurality of support rollers that support the belt, and the image receiving direction in the conveying direction of the belt. A plurality of driving rollers disposed downstream from the position and driving the belt; and a load facing roller disposed downstream from the driving roller and upstream from the image receiving position in the belt conveyance direction. A load member that sandwiches the belt between the support roller and the load-opposing roller and applies a transport load to the belt, and the belt has a remainder when wrapped around the plurality of support rollers. A circumferential length that occurs, and when the belt is driven by the drive roller, the belt between the load facing roller and the drive roller in the belt conveyance direction When the belt is tensioned and the driving of the belt by the driving roller is stopped, the driving roller can be rotated by being driven by the belt, and the tension is loosened. Device.

  According to a second aspect of the present invention, there is provided an image forming apparatus comprising the belt conveyance device of the present invention.

  According to the third aspect of the present invention, an image forming unit, an endless intermediate transfer belt on which an image formed by the image forming unit is primarily transferred by a primary transfer unit, and an image transferred to the intermediate transfer belt And a plurality of support rollers for supporting the intermediate transfer belt, wherein the intermediate transfer belt is sandwiched between the secondary transfer member and the secondary transfer member. A plurality of drive rollers for driving the intermediate transfer belt, and a load facing roller disposed downstream of the secondary transfer unit and upstream of the primary transfer unit in the conveying direction of the intermediate transfer belt. And a load member that sandwiches the intermediate transfer belt between the load opposing rollers and applies a conveyance load to the intermediate transfer belt, and the intermediate transfer belt is wound around the plurality of support rollers. Hanging A circumferential length that generates a remainder when the intermediate transfer belt is driven by the drive roller, and the intermediate transfer belt is moved between the load facing roller and the drive roller in the conveying direction of the intermediate transfer belt. When a tension is applied to the intermediate transfer belt and the driving of the intermediate transfer belt by the driving roller is stopped, the driving roller can be rotated by being driven by the intermediate transfer belt, and the tension is loosened. An image forming apparatus is provided.

  According to the present invention, it is possible to prevent the belt from being wound with a simple configuration.

1 is a schematic cross-sectional view of an image forming apparatus. FIG. 3 is a schematic cross-sectional view of an intermediate transfer device and a secondary transfer roller representing states of the intermediate transfer belt in each of an operation state and a stationary state. FIG. 6 is a schematic cross-sectional view of another example of an image forming apparatus. It is a schematic diagram showing the force which acts on an intermediate transfer belt. FIG. 10 is a schematic cross-sectional view of a main part of another example of the image forming apparatus.

  Hereinafter, the belt conveyance device and the image forming apparatus according to the present invention will be described in more detail with reference to the drawings.

Example 1
1. FIG. 1 is a schematic cross-sectional view of an image forming apparatus according to an embodiment of the present invention. The image forming apparatus 100 according to the present exemplary embodiment is a tandem type image forming apparatus that employs an intermediate transfer method.

  The image forming apparatus 100 includes, as a plurality of image forming units, first, second, third, and fourth images that respectively form yellow (Y), magenta (M), cyan (C), and black (K) images. An image forming unit PY, PM, PC, PK is included. A host device such as a computer is communicably connected to the image forming apparatus 100. The image forming apparatus 100 can form a full-color image on a transfer material (recording paper, plastic sheet, cloth, etc.) using an electrophotographic method in accordance with image information from the host device.

  In this embodiment, the configurations and operations of the image forming units PY, PM, PC, and PK are substantially the same except that the color of the toner used is different. Therefore, in the following, unless there is a particular need for distinction, Y, M, C, and K at the end of the symbol indicating that the element is for any color will be omitted, and the element will be described generally.

  The image forming unit P includes a photosensitive drum 1 that is a drum-type (cylindrical) electrophotographic photosensitive member (photosensitive member) as an image carrier. The following means are arranged around the photosensitive drum 1. First, a charging roller 2 which is a roller-shaped charging member as a charging unit is disposed. Next, an exposure apparatus 3 as an exposure unit is arranged. Next, a developing device 4 as a developing unit is arranged. Next, a primary transfer roller 5 which is a roller-shaped primary transfer member as a primary transfer unit is disposed. Next, a drum cleaning device 6 as a photosensitive member cleaning unit is disposed.

  Further, an intermediate transfer belt 7 that is an endless belt as an intermediate transfer member is disposed so as to face the photosensitive drums 1Y, 1M, 1C, and 1K of the image forming units PY, PM, PC, and PK. . The intermediate transfer belt 7 is wound around a pre-secondary transfer roller 71, a secondary transfer counter roller 72, and a cleaning counter roller 73 as a plurality of support rollers, as will be described in detail later. The primary transfer rollers 5Y, 5M, 5C, and 5K described above are disposed on the inner peripheral surface side of the intermediate transfer belt 7 at positions facing the photosensitive drums 1Y, 1M, 1C, and 1K. The primary transfer roller 5 is urged (pressed) with a predetermined pressure toward the photosensitive drum 1 via the intermediate transfer belt 7, and a primary transfer portion (primary transfer portion) where the intermediate transfer belt 7 and the photosensitive drum 1 come into contact with each other. Transfer nip) N1 is formed. That is, the intermediate transfer belt 7 is sandwiched between the photosensitive drum 1 and the primary transfer roller 5 at the primary transfer nip N1. Further, on the outer peripheral surface side of the intermediate transfer belt 7, a secondary transfer roller 8 that is a roller-like secondary transfer member as a secondary transfer unit is disposed at a position facing a secondary transfer counter roller 72 described later. ing. The secondary transfer roller 8 is urged (pressed) with a predetermined pressure toward the secondary transfer counter roller 72 via the intermediate transfer belt 7, and the secondary transfer roller 7 and the secondary transfer roller 8 come into contact with each other. A transfer portion (secondary transfer nip) N2 is formed. Further, on the outer peripheral surface side of the intermediate transfer belt 7, a belt cleaning device 9 as an intermediate transfer member cleaning unit is disposed at a position facing a cleaning counter roller 73 described later.

  In addition, the image forming apparatus 100 includes a feeding unit that supplies the transfer material S to the secondary transfer nip N2, a fixing unit that fixes the toner image on the transfer material S, and the like.

  When receiving a print start signal from the host device, the image forming apparatus 100 starts image formation. When image formation is started, the photosensitive drum 1 is rotationally driven at a predetermined peripheral speed (process speed) in the direction of arrow R1 in the drawing. The photosensitive drum 1 is rotationally driven in the direction of arrow R1 in the figure by a drive motor (not shown) as a drive source. The surface of the rotating photosensitive drum 1 is charged substantially uniformly by the charging roller 2. The surface of the charged photosensitive drum 1 is scanned and exposed by the exposure device 3 to form an electrostatic latent image (electrostatic image). The electrostatic latent image formed on the photosensitive drum 1 is developed (visualized) as a toner image by attaching toner to the developing device 4. The toner image formed on the photosensitive drum 1 is transferred (primary transfer) onto the intermediate transfer belt 7 that is rotationally driven in the direction of arrow R2 in the figure by the action of the primary transfer roller 5 in the primary transfer nip N1. ) When a full color image is formed, the above-described operations are performed in the first to fourth image forming portions PY, PM, PC, and PK, and the toner images of the respective colors are formed on the intermediate transfer belt 7 in each primary transfer nip N1. A multiple toner image transferred so as to be sequentially superimposed is formed.

The toner image formed on the intermediate transfer belt 7 is transferred (secondary transfer) onto the transfer material S by the action of the secondary transfer roller 8 in the secondary transfer nip N2. As the transfer material S, for example, high-quality paper (basis weight 75 g / m ² ) is used. The transfer material S is housed in the storage cassette 11 and is conveyed to the secondary transfer nip N2 at a timing when the printing position matches the toner image on the intermediate transfer belt 7. The transfer material S onto which the toner image has been transferred is then conveyed to a fixing device 10 as a fixing unit, and is heated and pressed at a fixing nip between a fixing roller 10a and a pressure roller 10b included in the fixing device 10. As a result, the toner image is thermally fixed on the surface of the transfer material S. Thereafter, the transfer material S on which the toner image is fixed is discharged onto the discharge tray 12. Thus, the image forming process is completed.

  The toner remaining on the photosensitive drum 1 after the primary transfer (primary transfer residual toner) is removed from the photosensitive drum 1 by the drum cleaning device 6 and collected. Further, the toner remaining on the intermediate transfer belt 7 after the secondary transfer (secondary transfer residual toner) is removed from the intermediate transfer belt 7 by the belt cleaning device 9 and collected.

  The image forming apparatus 100 of the present embodiment has a printable width of 200 mm and can print A4 size transfer material S at 40 sheets per minute.

2. Configuration of Each Part The photosensitive drum 1 is formed by coating a photosensitive layer having a thickness of 20 μm having a hole blocking layer, a charge generation layer, and a charge transfer layer on the surface of an aluminum cylinder having a diameter of 24 mm. . The aluminum cylinder is electrically grounded (connected to the ground). The photosensitive drum 1 is rotationally driven in the direction of arrow R1 in the figure at a surface speed (circumferential speed) of 240 mm / sec.

The charging roller 2 is disposed in contact with the photosensitive drum 1. The charging roller 2 includes a conductive elastic body having a thickness of 1.5 mm and a volume resistivity of about 1 × 10 ⁴ Ωcm on a metal shaft having a diameter of 5.5 mm, and a volume of 0.05 μm. And a surface layer having a specific resistivity of about 1 × 10 ¹⁰ Ωcm. During the charging operation, a charging voltage (charging bias) of −1115 V is applied to the charging roller 2 from a charging power source (not shown). When the photosensitive drum 1 is rotated, the charging roller 2 is rotated by being driven by the photosensitive drum 1 at approximately the same speed as the photosensitive drum 1. The charging roller 2 charges the photosensitive drum 1 substantially uniformly by discharging in a minute gap between the charging roller 2 and the photosensitive drum 1. The surface potential (dark portion potential) of the photosensitive drum 1 after the charging process was about −500V. Here, the surface potential of the photosensitive drum 1 was measured with a surface potential meter Model 344 manufactured by Trek.

  The exposure device 3 is a scanning exposure type (laser scanner device) having a laser light source, a polygon mirror, and a lens. The exposure device 3 scans the laser emitted from the laser light source in accordance with the rotation of the photosensitive drum 1 by a rotating polygon mirror, and irradiates the charged photosensitive drum 1 through the lens. At this time, the exposure device 3 controls the amount of laser light based on the image data. As a result, the surface of the photosensitive drum 1 is scanned and exposed based on the image data, and an electrostatic latent image based on the image data is formed on the photosensitive drum 1. The surface potential (bright portion potential) of the photosensitive drum 1 at the portion that has received the maximum light amount decreases to about −100V.

The developing device 4 has a developing roller 41 as a developer carrier. During the developing operation, the developing roller 41 contacts the photosensitive drum 1. In the developing device 4, a negatively chargeable nonmagnetic toner produced by a suspension polymerization method is accommodated as a developer in a developer container 42. The average particle size of this toner is about 6.5 μm. In order to modify the surface property of the toner, silicon oxide particles having a particle size of about 20 nm are adhered to the surface substantially uniformly in an amount of about 1.5% of the weight of the toner. Here, the average particle diameter of the toner is a volume average particle diameter measured with a laser diffraction particle size distribution analyzer LS-230 manufactured by Beckman Coulter, Inc. On the surface of the developing roller 41, the frictionally charged toner is supplied in a thin layer state. The toner carried on the developing roller 41 has a toner amount per unit area of about 0.4 mg / cm ^{2 and} a toner charge amount per unit mass of about −30 μC / g. Here, the charge amount of the toner per unit mass and the toner amount per unit area were determined as follows. That is, the toner on the developing roller 41 is sucked and collected by a suction type Faraday gauge having a filter inside. Then, the charge amount of the toner per unit mass and the toner amount per unit area were obtained from the charge measured by the Faraday gauge, the toner collection area, and the mass increase of the filter. In other words, the charge amount of toner per unit mass is obtained by dividing the charge measured by the Faraday gauge by the increase in filter mass, and the toner amount per unit area is obtained by dividing the increase in filter mass by the collection area. It was. During the developing operation, a developing voltage (developing bias) of −300 V is applied to the developing roller 41 from a developing power source (not shown). The surface potential of the portion of the electrostatic latent image that has received the maximum amount of laser light is −100 V, and an electric field is generated in the direction in which the toner is attracted to the photosensitive drum 1. On the other hand, the surface potential of the portion of the electrostatic latent image that has not been exposed to the laser is −500 V, and an electric field is generated in the direction in which the toner repels the photosensitive drum 1. Due to the electrostatic force, the toner adheres only to the exposed portion of the electrostatic latent image on the photosensitive drum 1, whereby the electrostatic latent image is developed and becomes a toner image.

  The drum cleaning device 6 has an elastic blade (cleaning blade) 61 as a cleaning member disposed in contact with the photosensitive drum 1. The primary transfer residual toner on the photosensitive drum 1 is removed from the photosensitive drum 1 by being dammed up at the contact portion between the elastic blade 61 and the photosensitive drum 1 and collected in the collecting container 62.

  In this embodiment, an image forming unit is configured by the photosensitive drum 1, the charging roller 2, the exposure device 3, the developing device 4, and the like of each image forming unit P.

  In this embodiment, the intermediate transfer belt 7, each primary transfer roller 5, a plurality of support rollers 71, 72, 73 of the intermediate transfer belt 7, a belt cleaning device 9, etc. A transfer device 70 is configured. The intermediate transfer device 70 and the secondary transfer roller 8 will be described in detail below.

3. Configuration of Intermediate Transfer Device The intermediate transfer belt 7 is configured by an endless sheet in which carbon black is dispersed in polyimide (PI) resin. The intermediate transfer belt 7 has a thickness of 65 μm and a volume resistivity of 1 × 10 ¹⁰ Ωcm. Here, the electrical resistance of the intermediate transfer belt 7 was measured at an applied voltage of 100 V by connecting a Hiresta UP dedicated probe URS probe to a resistivity meter Hiresta UP manufactured by Mitsubishi Chemical Analytech Co., Ltd. Further, ribs having a width of 5 mm and a height of 2.5 mm are bonded to both ends of the intermediate transfer belt 7 in the width direction in order to prevent the intermediate transfer belt 7 from moving in the width direction and coming off the support roller.

The primary transfer roller 5 is configured by coating a conductive shaft having a thickness of 4 mm on a metal shaft having a diameter of 6 mm. The primary transfer roller 5 is an Asker rubber hardness meter C type manufactured by Kobunshi Keiki Co., Ltd., and has a rubber hardness of 30 degrees and a volume resistivity of 10 ⁵ to 10 ⁹ Ωcm. The primary transfer roller 5 is pressed to the photosensitive drum 1 side with a total pressure of about 10N. Thereby, the primary transfer nip N1 is formed. The primary transfer roller 5 rotates following the rotation of the intermediate transfer belt 7. The primary transfer roller 5 is connected to a primary transfer power source (not shown). During the primary transfer operation, the primary transfer roller 5 has a primary transfer voltage (primary transfer bias) having a polarity opposite to the toner charging polarity (negative polarity in this embodiment) at the time of development from the primary transfer power source. Applied. In the primary transfer nip N1, an electric field is formed by the difference between the surface potential of the photosensitive drum 1 (non-exposed portion: −500V, exposed portion: −100V) and the voltage (+ 225V) applied to the primary transfer roller 5. ing. The direction of the electric field is a direction in which the negatively charged toner is directed from the photosensitive drum 1 to the intermediate transfer belt 7 regardless of the exposed portion and the non-exposed portion of the photosensitive drum 1. Due to this electric field, the toner on the photosensitive drum 1 moves to the intermediate transfer belt 7.

  The intermediate transfer belt 7 is wound around three supporting rollers including a pre-secondary transfer roller 71, a secondary transfer counter roller 72, and a cleaning counter roller 73 as a plurality of support rollers. The pre-secondary transfer roller 71, the secondary transfer counter roller 72, and the cleaning counter roller 73 are electrically grounded (connected to the ground).

The pre-secondary transfer roller 71 is configured by providing a conductive rubber layer having a volume resistivity of 10 ⁵ Ωcm or less and a thickness of 0.5 mm as a surface layer on a metal shaft having a diameter of 19 mm. The pre-secondary transfer roller 71 rotates following the rotation of the intermediate transfer belt 7.

The secondary transfer counter roller 72 has a static friction coefficient of 0.4 with respect to the intermediate transfer belt 7 as a surface layer on a metal shaft having a diameter of 18 mm, a volume resistivity of 10 ⁵ Ωcm or less, and a thickness of 1 mm. A conductive rubber layer is provided. A drive motor 74 (FIG. 2) as a drive source is connected to the secondary transfer counter roller 72. That is, the secondary transfer counter roller 72 functions as a counter electrode of the secondary transfer roller 8 and also functions as a driving roller for driving the intermediate transfer belt 7. Further, the secondary transfer roller 8 is pressed with a total pressure of about 40 N toward the secondary transfer counter roller 72 side. Thereby, the secondary transfer nip N2 is formed.

The secondary transfer roller 8 is configured by covering a metal shaft having a diameter of 8 mm with an elastic layer made of EPDM foam having a thickness of 4 mm. The secondary transfer roller 8 has a rubber hardness of 30 degrees and a volume resistivity of 10 ⁷ to 10 ⁹ Ωcm measured with a weight of 9.8 N using an Asker rubber hardness meter C type manufactured by Kobunshi Keiki Co., Ltd. As described above, when the secondary transfer roller 8 is pressed toward the secondary transfer counter roller 72, the secondary transfer nip N2 is formed. The secondary transfer roller 8 rotates following the rotation of the intermediate transfer belt 7. The secondary transfer roller 8 is connected to a secondary transfer power source (not shown). During the secondary transfer operation, a secondary transfer voltage (secondary transfer bias) having a polarity opposite to the charging polarity of the toner at the time of development is applied from the secondary transfer power source to the secondary transfer roller 8. In the secondary transfer nip N2, the negatively charged toner is transferred to the intermediate transfer belt 7 due to the difference between the electrically grounded secondary transfer counter roller 72 and the voltage (+2000 V) applied to the secondary transfer roller 8. An electric field is formed in the direction from to the secondary transfer roller 8. When the transfer material S passes through the secondary transfer nip N2, the toner image on the intermediate transfer belt 7 moves to the transfer material S by the electric field formed in the secondary transfer nip N2.

  The cleaning counter roller 73 has a rubber layer having a static friction coefficient of 0.4 and a thickness of 0.3 mm with respect to the intermediate transfer belt 7 as a surface layer on a hollow metal shaft having a diameter of 23.4 mm. It is configured. The cleaning counter roller 73 rotates following the rotation of the intermediate transfer belt 7. Further, the elastic blade 91 of the belt cleaning device 9 is pressurized to the cleaning counter roller 73 side with a total pressure of about 10N. Thereby, the cleaning nip N3 is formed.

  The belt cleaning device 9 has an elastic blade (cleaning blade) 91 as a cleaning member disposed in contact with the intermediate transfer belt 7. The secondary transfer residual toner on the intermediate transfer belt 7 is removed from the intermediate transfer belt 7 by being dammed at the contact portion between the elastic blade 91 and the intermediate transfer belt 7 and collected in the collection container 92.

  Here, the peripheral length of the intermediate transfer belt 7 is 800 mm, which is 5 mm longer than the circumscribed peripheral length 795 mm of the three support rollers 71, 72, 73. That is, the peripheral length of the intermediate transfer belt 7 is a length that causes a remainder when the intermediate transfer belt 7 is wound around a plurality of support rollers. As a result, the intermediate transfer belt 7 is wound around the three support rollers 71, 72, 73 in a state where the entire circumference is slack in a stationary state.

  When the drive motor 74 (FIG. 2) connected to the secondary transfer counter roller 72 is operated, the intermediate transfer belt 7 rotates in the direction of arrow R2 in the figure at a surface speed (peripheral speed) of 240 mm / sec which is substantially the same as that of the photosensitive drum 8. Driven. When the intermediate transfer belt 7 is in an operating state, the region from the cleaning nip N3 to the secondary transfer nip N2 in the conveyance direction (rotation direction) of the intermediate transfer belt 7 indicated by an arrow R2 in the drawing is in a tensioned state. become.

In the operation state, the intermediate transfer belt 7 is wound around the secondary transfer counter roller 72 so that the winding angle from the position in contact with the secondary transfer counter roller 72 to the secondary transfer nip N2 is 30 degrees. Yes. This angle is an angle centered on the rotation axis when viewed in the direction of the rotation axis of the secondary transfer counter roller 72. Further, this angle corresponds to a winding angle θ ₂ around the secondary transfer counter roller 72 of the intermediate transfer belt 7 described further in the second embodiment. In the operation state, the intermediate transfer belt 7 is wound around the cleaning counter roller 73 so that the winding angle from the cleaning nip N3 to a position away from the cleaning counter roller 73 is 150 degrees. This angle is an angle centered on the rotation axis when viewed in the direction of the rotation axis of the cleaning counter roller 73. Further, this angle corresponds to a winding angle θ ₁ around the cleaning facing roller 73 of the intermediate transfer belt 7 described further in the second embodiment.

4). Operation of Intermediate Transfer Device Next, the operation of the intermediate transfer device 70 in this embodiment will be described in more detail. 2A and 2B are schematic cross-sectional views of the intermediate transfer device 70 and the secondary transfer roller 8 in an operating state and a stationary state, respectively.

  In this embodiment, the intermediate transfer belt 7 is wound around three support rollers 71, 72, 73. The secondary transfer counter roller 72 is connected to a drive motor 74. In this embodiment, the drive motor 74 is a brushless DC motor.

  When the intermediate transfer belt 7 is not driven, the energization to the drive motor 74 is cut off, and the drive motor 74 can freely rotate. Therefore, both the secondary transfer roller 8 and the secondary transfer counter roller 72 forming the secondary transfer nip N2 are in a state where they can freely rotate. That is, when the intermediate transfer belt 7 is not driven, the secondary transfer counter roller 72 can rotate following the intermediate transfer belt 7. Further, as described above, the peripheral length of the intermediate transfer belt 7 is longer than the circumscribed peripheral length of the three support rollers 71, 72, 73. Therefore, as shown in FIG. 2B, the intermediate transfer belt 7 is wound around the three support rollers 71, 72, and 73 in a state where the entire circumference is slack in a stationary state. In this state, no tension is applied to the intermediate transfer belt 7 and no winding occurs.

  When the intermediate transfer belt 7 is driven, the drive motor 74 is energized to operate it. The intermediate transfer belt 7 is sandwiched between the secondary transfer roller 8 and the secondary transfer counter roller 72 at the secondary transfer nip N2. When the drive motor 74 is operated, the intermediate transfer belt 7 is driven in the direction of arrow R2 (counterclockwise in the figure). Further, the intermediate transfer belt 7 is sandwiched between the elastic blade 91 of the belt cleaning device 9 and the cleaning counter roller 73 at the cleaning nip N3. As a result, a conveyance load (running load) is applied to the intermediate transfer belt 7. When driving of the intermediate transfer belt 7 is started, the slack from the cleaning nip N3 of the intermediate transfer belt 7 to the secondary transfer nip N2 is wound up. When the intermediate transfer belt 7 further rotates, slippage between the intermediate transfer belt 7 and the elastic blade 91 occurs regularly at the cleaning nip N3, and the entire intermediate transfer belt 7 starts to rotate. At this time, as shown in FIG. 2A, the region from the cleaning nip N3 to the secondary transfer nip N2 in the conveyance direction of the intermediate transfer belt 7 is in a tensioned state. On the other hand, in the conveyance direction of the intermediate transfer belt 7, the area from the secondary transfer nip N2 to the cleaning nip N3 is in a slack state.

  As described above, when the intermediate transfer belt 7 is driven, the intermediate transfer belt is in the primary transfer nip N1 and the secondary transfer nip N2 in the region from the cleaning nip N3 to the secondary transfer nip N2 in the conveyance direction of the intermediate transfer belt 7. 7 is stretched flat. Therefore, in the primary transfer nip N1 and the secondary transfer nip N2, the toner images can be primary and secondary transferred, respectively, without distortion. On the other hand, when the intermediate transfer belt 7 is driven, the intermediate transfer belt 7 rotates in a slack state in the region from the secondary transfer nip N2 to the cleaning nip N3 in the conveyance direction of the intermediate transfer belt 7. Then, when entering the cleaning nip N3, the belt is pressed by the elastic blade 91 of the belt cleaning device 9 and enters the region stretched flat again.

  Here, when the intermediate transfer belt 7 is driven while being stretched around a plurality of support rollers, if there is a difference in the circumferential length in the width direction of the intermediate transfer belt 7, the tension on the shorter circumferential side becomes stronger. For this reason, even if several support rollers are arrange | positioned in parallel, a shift | offset | difference force works to the longer one from the short circumference. In the conventional configuration, for example, when the intermediate transfer belt 7 having both peripheral lengths of 790 mm and 792 mm is stretched and driven on three support rollers, the following may occur. That is, the intermediate transfer belt 7 may move in the width direction, get over the rib adhered to the end portion, and the intermediate transfer belt 7 may come off from the three support rollers. On the other hand, in the configuration of this embodiment, tension is applied only to the region from the cleaning nip N3 to the secondary transfer nip N2 in the conveyance direction of the intermediate transfer belt 7. Therefore, a difference in tension due to a difference in circumferential length with respect to the width direction of the intermediate transfer belt 7 does not occur or is remarkably suppressed. In the configuration of the present embodiment, for example, even when the intermediate transfer belt 7 having both peripheral lengths of 800 mm and 802 mm is used, the intermediate transfer belt 7 does not come off from the three support rollers.

  When the image formation is completed, the energization to the drive motor 74 is cut off, and the secondary transfer counter roller 8 is again in a state where it can freely rotate. Then, the primary transfer roller 5, the pre-secondary transfer roller 71, the secondary transfer counter roller 72, and the secondary transfer roller 8 are rotated in reverse by being driven by the intermediate transfer belt 7 due to the tension difference of the intermediate transfer belt 7. Then, the intermediate transfer belt 7 is pulled back from the slack side of the region from the secondary transfer nip N2 to the cleaning nip N3 in the conveying direction of the intermediate transfer belt 7 to the tension side of the region from the cleaning nip N3 to the secondary transfer nip N2. . As a result, as shown in FIG. 2B, the intermediate transfer belt 7 returns to a state where the entire circumference is loosened.

  As described above, the intermediate transfer device 70 as the belt conveying device of the present embodiment includes the intermediate transfer belt 7 that is an endless belt that receives and conveys an image at the primary transfer nip N1 as an image receiving position. The intermediate transfer device 70 includes a plurality of support rollers that support the belt 7. The plurality of support rollers include the following. First, there is a driving roller (secondary transfer counter roller) 72 that is disposed downstream of the primary transfer nip N1 in the conveyance direction of the belt 7 and drives the belt 7. Further, a load facing roller (cleaning facing roller) 73 disposed downstream of the driving roller 72 and upstream of the primary transfer nip N1 in the conveying direction of the belt 7. In addition, the intermediate transfer device 70 includes a load member (elastic blade) 91 that sandwiches the belt 7 with the load facing roller 73 and applies a conveyance load to the belt 7. The belt 7 has a circumferential length that generates a remainder when wound around a plurality of support rollers. Further, when the belt 7 is driven by the driving roller 72, tension is applied to the belt 7 between the load facing roller 91 and the driving roller 72 in the conveying direction of the belt 7. Further, when the driving of the belt 7 by the driving roller 72 is stopped, the driving roller 72 can be rotated by being driven by the belt 7 and the tension is relaxed.

  Accordingly, a tension is partially applied to the intermediate transfer belt 7 at the time of image formation so that an image can be formed without distortion, and the intermediate transfer belt 7 is in a slack state at the time of non-image formation.

  As described above, according to this embodiment, it is possible to apply tension to the intermediate transfer belt 7 only during driving without adding a special tension applying member or tension releasing member, and release the tension when not driving. Thereby, it is possible to suppress the winding of the intermediate transfer belt 7 and to suppress image defects caused by the winding of the intermediate transfer belt 7. That is, according to the present embodiment, the tension of the intermediate transfer belt 7 when not driven can be reduced more than when driven with a simple configuration. Thereby, it is possible to prevent the intermediate transfer belt 7 from being wound when not driven.

Example 2
Next, another embodiment of the present invention will be described. The basic configurations and operations of the belt conveyance device and the image forming apparatus of the present embodiment are the same as those of the first embodiment. Therefore, elements having the same or corresponding functions and configurations as those of the image forming apparatus according to the first embodiment are denoted by the same reference numerals, and detailed description thereof is omitted.

  FIG. 3 is a schematic cross-sectional view of the image forming apparatus of this embodiment. In this embodiment, a shaft torque applying member 75 of 0.08 Nm is attached to the rotating shaft of the cleaning counter roller 73 as an applying means for applying a load torque to the cleaning counter roller 73. Other configurations and operations are the same as those in the first embodiment.

  Consider the tension acting on the intermediate transfer belt 7 with reference to FIG. The tension T1 applied to the intermediate transfer belt 7 at the time of driving is obtained by Expression 1 from FIG. 4 (a) showing the balance of forces around the load-side cleaning counter roller 73.

  Next, from FIG. 4B showing the balance of forces around the secondary transfer counter roller 72 on the drive side, the maximum intermediate transfer belt 7 of which the secondary transfer counter roller 72 can drive the intermediate transfer belt 7 without slipping. The tension T2 is obtained by Expression 2.

  The greater the tension applied to the intermediate transfer belt 7, the higher the stability of the intermediate transfer belt 7 against disturbances such as vibration. In the case of the first embodiment, the tension T1 that acts on the intermediate transfer belt 7 at the time of driving calculated by the above formula 1 is 11N. However, the maximum tension T2 of the intermediate transfer belt 7 that can be driven without slipping the secondary transfer counter roller 72 obtained by the above formula 2 is 20 N, and the tension has a surplus force. Therefore, in this embodiment, a shaft torque applying member 75 of 0.08 Nm is attached to the cleaning facing roller 73. As a result, the tension T1 applied to the intermediate transfer belt 7 during driving is 17.5 N, and the stability of the intermediate transfer belt 7 is increased.

From the viewpoint of improving the conveyance stability of the intermediate transfer belt 7, it is preferable that the value of the tension T1 is as close as possible to the value of the tension T2 within a range smaller than the value of the tension T2. That is, when the belt 7 is driven by the driving roller 72, the tension applied to the belt 7 between the load facing roller 73 and the driving roller 72 in the conveying direction of the belt 7 is defined as T1 (N). Further, the maximum tension of the belt 7 that the drive roller 72 can drive without slipping the belt 7 is T2 (N). At this time,
T2 × 0.8 ≦ T1 <T2
It is preferable to satisfy. When the tension T1 is smaller than the tension T2, typically, the above-described preferable range is obtained by providing an applying means for applying a load torque to the rotating shaft of the load facing roller as in this embodiment. be able to.

  As described above, according to the present embodiment, the same effects as those of the first embodiment can be obtained, and the tension acting on the intermediate transfer belt 7 at the time of driving can be increased, so that the stability of the intermediate transfer belt 7 with respect to vibration or the like can be improved. it can.

Others While the present invention has been described with reference to specific embodiments, the present invention is not limited to the above-described embodiments.

  For example, in the above-described embodiments, the case where the present invention is applied to an intermediate transfer type image forming apparatus has been described. However, the present invention is not limited to this, and the present invention is similarly applied to a direct transfer type image forming apparatus. Can be applied. FIG. 5 is a schematic cross-sectional view of a main part of a direct transfer type image forming apparatus. In FIG. 5, elements that are the same as or correspond to those in the intermediate transfer type image forming apparatus shown in FIG. The image forming apparatus of FIG. 5 is an endless belt as a transfer material carrier that carries and conveys a transfer material, instead of the intermediate transfer device 70 provided with the intermediate transfer belt 7 in the image forming apparatus of FIG. A transfer device 270 including a transfer material carrying belt (conveying belt) 207 is included. The toner image formed in the image forming unit is transferred to the transfer material S that is carried and conveyed by the transfer material carrying belt 207 in the transfer nip N as an image receiving position. In the image forming apparatus of FIG. 5, the transfer device 270 includes a drive roller 272 and a load facing roller 273 as a plurality of support rollers that support the transfer material carrying belt 207. A driving motor (not shown) as a driving source is connected to the driving roller 272, and the elastic blade 291 of the belt cleaning device 209 is pressed to the load facing roller 273 via the transfer material carrying belt 207. Further, the peripheral length of the transfer material carrying belt 207 is longer than the circumscribed peripheral length of the two support rollers 272 and 273. As a result, tension is applied to the transfer material carrying belt 207 between the cleaning nip N3 and the drive roller 272 in the conveying direction of the transfer material carrying belt 207 during driving. Further, at the time of driving, the transfer material carrying belt 207 between the drive roller 272 and the cleaning nip N3 in the conveying direction of the transfer material carrying belt 207 is in a loose state. Further, in the stationary state, the driving roller 273 can freely rotate, and the transfer material carrying belt 207 is in a state where the entire circumference is slack. Accordingly, the transfer material carrying belt 207 in the transfer nip N is stretched in a flat state when the transfer material carrying belt 207 is driven, and the transfer material carrying belt 207 is not driven when the transfer material carrying belt 207 is not driven. It is possible to loosen the tension.

  The image forming apparatus is not limited to a tandem type having a plurality of image forming units (image receiving positions). For example, a plurality of developing devices are provided for a single photoconductor, and each time a toner image is formed on the photoconductor, the image is transferred to a transfer material on an intermediate transfer belt or a transfer material carrying belt. There is something that forms. The present invention can also be applied to such an image forming apparatus, and the same effects as those of the above-described embodiments can be obtained.

  Moreover, although the above-mentioned Example demonstrated the case where a load member was a blade-shaped member, it is not limited to this. The load member may be a roller-like member, a brush-like member, or the like as a cleaning member that removes deposits such as toner from the belt. The load member is not limited to the cleaning member, and may be, for example, a blade-like member, a roller-like member, or a brush-like member as a toner charging member that charges the toner attached to the belt. In this case, the load member may be connected to a power source for applying a voltage thereto.

DESCRIPTION OF SYMBOLS 1 Photosensitive drum 5 Primary transfer roller 7 Intermediate transfer belt 8 Secondary transfer roller 9 Belt cleaning device 70 Intermediate transfer device 71 Pre-secondary transfer roller 72 Secondary transfer counter roller (drive roller)
73 Cleaning counter roller (load counter roller)
91 Elastic blade (load member)

Claims (11)

An endless belt for receiving and conveying images at an image receiving position;
A plurality of supporting rollers for supporting the belt, the driving roller being arranged downstream of the image receiving position in the belt conveying direction and driving the belt; and the downstream of the driving roller in the belt conveying direction. And a plurality of supporting rollers provided on the upstream side of the image receiving position, and a plurality of supporting rollers.
A load member that sandwiches the belt with the load-opposing roller and applies a conveying load to the belt;
Have
The belt has a circumferential length that generates a surplus when it is wound around the plurality of support rollers. When the belt is driven by the drive roller, the belt moves from the load facing roller in the belt conveyance direction. Tension is applied to the belt up to the driving roller, and when the driving of the belt by the driving roller is stopped, the driving roller can be rotated by being driven by the belt and the tension is released. A belt conveyance device.   2. The belt conveyance according to claim 1, wherein the driving roller sandwiches the belt between a transfer member that transfers an image transferred to the belt to a transfer material at the image receiving position. apparatus.   The belt conveying device according to claim 1, wherein the load member is a cleaning member that removes deposits from the surface of the belt. T1 (N) is the tension applied to the belt when the belt is driven by the driving roller, and T2 (N) is the maximum belt tension that the driving roller can drive without slipping the belt. The following formula
T2 × 0.8 ≦ T1 <T2
The belt conveying device according to any one of claims 1 to 3, wherein the belt conveying device is satisfied.   The belt conveying device according to claim 1, further comprising an applying unit that applies load torque to a rotation shaft of the load facing roller.   An image forming apparatus comprising the belt conveyance device according to claim 1. Image forming means;
An endless intermediate transfer belt on which an image formed by the image forming means is primarily transferred at a primary transfer portion;
A secondary transfer member for secondary transfer of the image transferred to the intermediate transfer belt to a transfer material at a secondary transfer portion;
A plurality of support rollers for supporting the intermediate transfer belt, the drive roller driving the intermediate transfer belt while sandwiching the intermediate transfer belt with the secondary transfer member, and the conveying direction of the intermediate transfer belt A plurality of support rollers provided with load opposing rollers disposed downstream of the secondary transfer unit and upstream of the primary transfer unit,
A load member that sandwiches the intermediate transfer belt with the load facing roller and applies a conveyance load to the intermediate transfer belt;
Have
The intermediate transfer belt has a circumferential length that generates a surplus when wound around the plurality of support rollers. When the intermediate transfer belt is driven by the drive roller, the intermediate transfer belt is moved in the conveyance direction of the intermediate transfer belt. When tension is applied to the intermediate transfer belt between the load facing roller and the drive roller, and the drive of the intermediate transfer belt by the drive roller is stopped, the drive roller follows the intermediate transfer belt. An image forming apparatus characterized in that the tension can be relaxed.   The image forming apparatus according to claim 7, wherein the load member is a cleaning member that removes deposits from the surface of the intermediate transfer belt.   A plurality of the image forming units are provided between the load facing roller and the driving roller in the conveyance direction of the intermediate transfer belt, and the intermediate transfer belt is provided in a primary transfer unit corresponding to each image forming unit. 9. The image forming apparatus according to claim 7, wherein the image is primarily transferred. When the intermediate transfer belt is driven by the drive roller, the tension applied to the intermediate transfer belt is T1 (N), and the maximum intermediate transfer that the drive roller can drive without slipping the intermediate transfer belt When the belt tension is T2 (N),
T2 × 0.8 ≦ T1 <T2
The image forming apparatus according to claim 7, wherein:   The image forming apparatus according to claim 7, further comprising an applying unit that applies a load torque to a rotation shaft of the load facing roller.

Images