JP2011008143A - Belt unit and image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To introduce tension by the operation of driving an extended endless belt by continuously releasing the tension of the belt in order to prevent residual deformation from being generated in the extended endless belt.SOLUTION: The endless belt 20 is extended around a plurality of rollers 21, 22 and 23, the support shaft 28 of the second roller 22 supported so as to be movable is biased by a compression spring 24, and thereby tension is introduced into the belt. A rotation shaft 26 supported parallel to the support shaft of the second roller is provided with a pressing member 25 pressed against the second roller via the belt, thereby holding the second roller so as to be displaced in a direction in which the tension of the belt decreases. The pressing member is supported so as to be rotatable, and rotated accompanied by the movement of the belt in its circumferential direction, thereby releasing a pressing force exerted on the second roller.

Description

  The present invention relates to a belt unit and an image forming apparatus using the belt unit.

  A belt unit in which an endless belt is stretched by a plurality of rollers and driven in the circumferential direction is, for example, an electrophotographic type or electrostatic recording type image forming apparatus, an intermediate transfer member, a recording paper transport device, an electrostatic latent unit. Used as a photoreceptor belt or the like on which an image is formed. In such a belt unit, a belt in which a film-like member formed of synthetic resin or the like is endless is often used.

  In such a belt, tension is introduced in the circumferential direction when the belt is driven in a circular manner, but a belt having a mechanism for releasing or introducing the tension in the circumferential direction according to the situation or the like is disclosed in, for example, Patent Document 1 to Patent Document 4. Proposed to each of up to.

In the tension applying mechanism described in Patent Document 1, the first roller for driving the belt is movable, and when the first roller is driven, the driving roller itself causes the belt to be driven by the driving force. It moves to the position where it extends.
In the transfer belt device described in Patent Document 2, a bearing of a roller that stretches the transfer belt is movable, and the transfer belt is elastically pressed against the transfer belt. Then, the bearing is pressed by the pressure release member, and the roller is retracted to release the pressure on the transfer belt.
In the image forming apparatus described in Patent Document 3, a tension release roller contacts an inner peripheral surface of a transfer belt wound around a plurality of rollers. The tension release roller is driven so as to advance and retreat by a cam, and can apply tension to the transfer belt or remove tension.
The image forming apparatus described in Patent Document 4 includes a tension applying unit that applies a predetermined tension to an endless belt. The tension applying unit is configured to bring the tension roller supported by the swing arm into contact with the inner peripheral surface of the belt and drive the swing arm to advance and retract the tension roller with respect to the belt.

Japanese Utility Model Publication No. 5-50475 JP 7-295395 A Japanese Patent Laid-Open No. 11-352790 JP 2005-25165 A

  SUMMARY OF THE INVENTION An object of the present invention is to provide a belt unit that can put a belt in a state in which tension is released into a state in which tension is applied by an operation of driving the belt, and an image forming apparatus using the belt unit. And

  In order to solve the above-mentioned problem, the invention according to claim 1 is provided with a belt whose surface can be moved in a state where tension is applied, and a support shaft that spans the belt and rotates about an axis. A rotating member supported so as to be movable; an urging means for urging the rotating member in a direction in which the belt tension is applied; and a state in which the rotating member is displaced in a direction in which the belt tension decreases. A holding member that holds the belt via the belt, wherein the holding member releases a state where the rotating member is displaced by the movement of the belt, and tension is applied to the belt by the biasing means. A belt unit is provided.

  The invention according to claim 2 is a belt in which a surface is movable in a state where tension is applied, and a rotating member on which the belt is stretched and a support shaft that rotates about an axis line is movably supported. And an urging means for urging the rotating member in a direction in which the belt tension is applied; and a restraining member for constraining a state in which the rotating member is displaced in a direction in which the belt tension decreases. The restraint member releases a state where the rotation member is displaced by the rotation of the rotation member, and a tension is applied to the belt by the biasing means.

  According to a third aspect of the present invention, there is provided a belt whose surface is movable in a state in which tension is applied, and a rotating member on which the belt is stretched and a support shaft that rotates about an axis line is movably supported. Biasing means for biasing the rotating member in a direction in which the belt tension is applied, and contact with the surface of the belt in a state in which the rotating member is displaced in a direction in which the belt tension decreases. A member, and a restraining member that restrains the state in which the rotating member is displaced in a direction in which the tension of the belt decreases, and the restraining member is moved by the movement of the belt, A belt unit is provided in which a state in which the belt is displaced in a decreasing direction is released, and tension is applied to the belt by the biasing means.

  According to a fourth aspect of the present invention, in the belt unit according to the first aspect, the holding member is rotatably supported and is rotated by the movement of the belt.

  The invention according to claim 5 is the belt unit according to claim 4, wherein the holding member rotates in a direction in which gravity acts.

  According to a sixth aspect of the present invention, in the belt unit according to any one of the first, fourth, and fifth aspects, the tension of the holding member is reduced by a frictional force with the belt. The state displaced in the direction to be released shall be released.

  The invention according to claim 7 is the belt unit according to any one of claims 1, 4, 5, and 6, wherein the holding member has a contact portion with the belt. It should be softer.

  The invention according to claim 8 is the belt unit according to claim 2 or 3, wherein the restraining member is rotatably supported and is rotated by the rotation of the rotating member.

  The invention according to claim 9 is the belt unit according to claim 8, wherein the restraining member rotates in a direction in which gravity acts.

  The invention according to claim 10 is the belt unit according to any one of claims 2, 3, 8, and 9, wherein the restraining member is provided on an axis of the rotating member. The state in which the belt is displaced in the direction in which the belt tension decreases is released by the gear and the gear provided on the restraining member.

  According to an eleventh aspect of the present invention, in the belt unit according to the third aspect, the contact member is rotatably supported and is rotated by the movement of the belt.

  The invention according to claim 12 is the belt unit according to claim 11, wherein the contact member rotates in a direction in which gravity acts.

  The invention according to claim 13 is the belt unit according to any one of claims 3, 11, and 12, wherein the contact member and the restraining member are supported by the same support shaft. It shall be.

  An invention according to a fourteenth aspect is the image forming apparatus having the belt unit according to any one of the first to thirteenth aspects, wherein the rotating member is tensioned to the belt when the image forming apparatus is shipped. An image forming apparatus is provided in which the rotating member is released in a direction in which the rotating member is displaced in a direction in which the belt tension is reduced by driving the belt at the start of use.

  In the belt unit according to the first aspect, the belt in a state in which the tension is released can be in a state in which the tension is applied by the operation of driving the belt.

  In the belt unit according to the second aspect, the belt in which the tension is released can be brought into a state in which the tension is applied by the operation of driving the belt.

  In the belt unit according to the third aspect, the belt in a state where the tension is released can be brought into a state where the tension is applied by the operation of driving the belt.

  In the belt unit according to the fourth aspect, the tension can be applied to the belt by rotating the holding member.

  In the belt unit according to the fifth aspect, after releasing the state in which the rotating member is displaced, the holding member holds the position by its own weight.

  In the belt unit according to the sixth aspect, the configuration can be simplified as compared with the case where the configuration is not provided.

  In the belt unit according to the seventh aspect, the belt is less likely to be damaged as compared with the case where the contact portion with the belt is hard.

  In the belt unit according to the eighth aspect, the tension can be applied to the belt by rotating the restraining member.

  In the belt unit according to the ninth aspect, after releasing the displaced state of the rotating member, the restraining member holds its position under its own weight.

  In the belt unit according to the tenth aspect, the state in which the rotating member is displaced using the meshing of the gear is released, and the belt can be in a state in which tension is applied.

  In the belt unit according to the eleventh aspect, the tension can be applied to the belt by rotating the contact member.

  In the belt unit according to the twelfth aspect, the contact member holds its position under its own weight after releasing the displaced state of the rotating member.

  In the belt unit according to the thirteenth aspect, the belt unit can be made smaller as compared with the case where the contact member and the restraining member are not supported by the same support shaft.

  In the image forming apparatus according to the fourteenth aspect, a tension is applied by an operation of driving the belt at the time of use with the belt used in a condition where the tension is applied at a state where the tension is reduced from that at the time of use. State.

1 is a schematic configuration diagram of an image forming apparatus according to an embodiment of the present invention. FIG. 2 is a schematic cross-sectional view showing a belt unit used in the image forming apparatus shown in FIG. 1 in a state in which the belt tension is released and a state in which the belt is in tension. FIG. 3 is a partial plan view of the belt unit shown in FIG. 2. It is a schematic side view which shows the state by which the tension | tensile_strength of the belt unit which is other embodiment of this invention was cancelled | released, and the tension | tensile_strength was introduce | transduced into the belt. FIG. 5 is a partial plan view of the belt unit shown in FIG. 4. It is a schematic side view which shows the state by which the tension | tensile_strength of the belt unit which is other embodiment of this invention was cancelled | released, and the tension | tensile_strength was introduce | transduced into the belt. FIG. 7 is a partial plan view of the belt unit shown in FIG. 6. It is a schematic block diagram of the image forming apparatus which is other embodiment of this invention.

Embodiments of the present invention will be described below with reference to the drawings.
FIG. 1 is a schematic configuration diagram of an image forming apparatus according to an embodiment of the present invention.
This image forming apparatus is a quadruple tandem full-color image forming apparatus, and forms an image of an electrophotographic system that outputs yellow (Y), magenta (M), cyan (C), and black (K) images. Units 10Y, 10M, 10C, and 10K, and an intermediate transfer belt 20 facing these units are provided. The intermediate transfer belt 20 is stretched so as to face each of the image forming units 10, and the circumferential surface thereof is driven to rotate. In order from the upstream side in the circumferential movement direction of the intermediate transfer belt 20, an image forming unit 10Y that forms a yellow toner image, an image forming unit 10C that forms a cyan toner image, and an image forming unit 10M that forms a magenta toner image. An image forming unit 10K for forming a black toner image is arranged, and on the downstream side thereof, a secondary transfer roller 1 for performing secondary transfer is disposed so as to face the intermediate transfer belt 20. The recording sheet is fed from the sheet tray 2 through the conveyance path 3 to the secondary transfer portion while being sandwiched between the registration rollers 4. A fixing device 5 that heats and pressurizes the toner image to press the toner image on the recording sheet is provided downstream of the secondary transfer portion in the recording sheet conveyance path, and the toner image is fixed further downstream. A paper discharge tray 6 is provided for storing the recording sheet paper.

  Each of the image forming units 10 includes a photoconductive drum 11 that functions as an image holding body with an electrostatic latent image formed on the surface thereof, and around each photoconductive drum 11, A charging device 12 that charges the surface substantially uniformly; a developing device 13 that selectively transfers toner to a latent image formed on the photosensitive drum to form a toner image; and a toner image on the photosensitive drum 11 Are provided with a primary transfer roller 14 for primary transfer of the toner onto the intermediate transfer belt 20 and a cleaning device 15 for removing residual toner remaining on the photosensitive drum after transfer. In addition, an exposure device 16 that irradiates image light based on an image signal is provided on four uniformly charged photosensitive drums 11, and the photosensitive drum 11 is statically positioned upstream of the position where the developing device 13 faces. An electric latent image is written.

  The photoconductor drum 11 is formed by laminating an organic photoconductor layer on the peripheral surface of a cylindrical member made of metal, and the metal portion is electrically grounded. Further, a bias voltage may be applied.

The charging device 12 has a roller in which a stainless steel cylindrical metal core is covered with a rubber layer, and an electric resistance value is adjusted by mixing conductive powder such as carbon into the rubber layer. . This roller is supported so as to rotate in contact with the photosensitive drum 11, and a charging voltage is applied. As a result, a discharge is generated in a minute gap with respect to the photosensitive drum 11, and the surface of the photosensitive drum is charged to a desired voltage.
Instead of the charging device 12, a device for charging the surface of the photosensitive drum by corona discharge can be used.

  The exposure device 16 generates a flashing laser beam based on an image signal, and scans this in the main scanning direction (axial direction) of each photosensitive drum 11 by a polygon mirror. Thereby, an electrostatic latent image corresponding to an image of each color is formed on the surface of each photoconductive drum 11.

  The developing device 13 uses a two-component developer containing toner and a magnetic carrier, and includes a developing roller 13 a at a position close to the photosensitive drum 11. The developing roller 13 a has a thin layer of two-component developer formed on the peripheral surface thereof, and rotates to convey the two-component developer to a position facing the photosensitive drum 11. In addition, the toner consumed as a result of image formation is replenished from the toner cartridge 7 according to the amount consumed.

  The primary transfer roller 14 is formed by coating the outer peripheral surface of a metal core material with a conductive rubber material. The primary transfer roller 14 is in contact with the inner peripheral surface of the intermediate transfer belt 20, and the photosensitive drums 11Y, 11M, 11C, and 11K. They are arranged at opposite positions. A transfer bias voltage is applied between the primary transfer rollers 14Y, 14M, 14C, and 14K and the photosensitive drums 11Y, 11M, 11C, and 11K, and passes through positions that face the photosensitive drums 11Y, 11M, 11C, and 11K. The toner image on the photosensitive drum is electrostatically transferred to the intermediate transfer belt 20.

  The cleaning device 15 removes transfer residual toner adhering to the photosensitive drum 11 with a cleaning blade and a cleaning brush arranged in contact with the peripheral surface of the photosensitive drum 11.

  The fixing device 5 includes a heating roller 5a having a built-in heating source, and a pressure roller 5b arranged in parallel with the heating roller 5a, and these are pressed against each other to form a nip portion. . The recording sheet to which the toner image has been transferred is fed into the nip portion and heated and pressurized between the heated heating roller 5a and the pressure roller 5b, and the toner image is pressed onto the recording sheet. Has become.

  The intermediate transfer belt 20 is formed by forming a film-like member made of a resin material such as polyimide, polyamideimide, polycarbonate, or fluorine resin in an endless manner. The resin material is adjusted to have a predetermined surface resistivity by dispersing a substance for imparting conductivity such as carbon or an ion conductive substance. This intermediate transfer belt is stretched around a first support roller 21, a second support roller 22, and a third support roller 23 that are rotatably supported by a support frame 27, and is provided in the present invention. The belt unit which is embodiment is comprised. Then, when the first support roller 21 is driven to rotate, the surface of the intermediate transfer belt moves around in the direction of arrow A shown in FIG.

  The first support roller 21 receives a rotational driving force from a drive motor (not shown), and rotates to move the intermediate transfer belt 20 around. The secondary transfer roller 1 is pressed against the first support roller 21 with the intermediate transfer belt 20 interposed therebetween, so that the toner image on the intermediate transfer belt is transferred onto the recording sheet conveyed from the sheet tray 6. It has become.

  As shown in FIGS. 2 and 3, the support shaft 28 of the second support roller 22 is supported by a bearing 29, and the bearing 29 is urged by a compression spring 24 in a direction to apply tension to the intermediate transfer belt 20. Has been. As a result, a predetermined tension that allows the intermediate transfer belt 20 to move stably is introduced by the repulsive force of the compression spring 24.

  A pressing member 25 is disposed at a position facing the second support roller 22 with the intermediate transfer belt 20 in between, and is supported by a rotation shaft 26 parallel to the axis of the second support roller 22. It can be rotated around the rotation axis. As shown in FIG. 2A, the pressing member 25 includes an arm portion 25a provided so as to protrude from the rotating shaft 26, and a pad 25b made of an elastic member provided at the tip thereof. The pad 25b is brought into contact with the non-image area where the image of the intermediate transfer belt 20 is not transferred, and the intermediate transfer belt 20 can be pressed against the second support roller 22 from the outer peripheral surface side of the intermediate transfer belt 20. It has become. When the pressing member 25 is pressed against the second support roller 22 via the intermediate transfer belt 20, the amount of deformation of the compression spring 24 increases due to the pressing force, and the second support roller 22 moves backward to perform intermediate transfer. The tension of the belt 20 is relaxed. Further, since the pressing member 25 is supported by the rotating shaft 26, the pressing member 25 is rotated by a frictional force when the intermediate transfer belt 20 moves in the circumferential direction, and the pressing force to the intermediate transfer belt 20 and the second support roller 22. Is to be canceled.

Such an image forming apparatus operates as follows.
When the image forming apparatus is manufactured and shipped at the factory, the pad 25 b of the pressing member 25 is pressed against the second support roller 22 via the intermediate transfer belt 20. As a result, the compression spring 24 that urges the second support roller 22 is in a position where the second support roller 22 is displaced in a state in which the deformation is greater than when the intermediate transfer belt 20 is stretched. Then, when the pressing member 25 presses the intermediate transfer belt 20 against the second support roller 22 from the outer peripheral surface side of the intermediate transfer belt 20, the second support roller 22 is displaced in a direction in which the tension of the intermediate transfer belt 20 decreases. Hold the position. As a result, the tension of the intermediate transfer belt 20 is reduced compared to when it is stretched, and is almost not introduced as shown in FIG. As a result, the residual deformation following the shape of the peripheral surface of the roller is reduced on the intermediate transfer belt 20 even at the positions wound around the support rollers 21, 22, and 23.

  The first support roller 21 is rotationally driven at the same time as the image forming apparatus is installed at the position where it is used and the image forming operation is started or before the image forming operation is started. At this time, the intermediate transfer belt 20 is not tensioned and is not strongly wound around the first support roller 21, but the secondary transfer roller 1 is pressed against the intermediate transfer belt 20. The intermediate transfer belt 20 is driven in the circumferential direction by the frictional force of the portion. As the intermediate transfer belt 20 moves in the circumferential direction, the pressing member 25 pressed against the second support roller 22 rotates in the direction in which gravity acts (the direction of the arrow shown in FIG. 2B). The pressing force on the second support roller 22 is released. As a result, the second support roller 22 moves toward the intermediate transfer belt 20 by the repulsive force of the compression spring 24, and applies tension to the intermediate transfer belt 20. In this state, the first support roller 21 is rotationally driven, so that the intermediate transfer belt 20 stably rotates in a state where tension is applied in the circumferential direction. Here, after the second support roller 22 is released from the displaced state, the pressing member 25 hangs down by its own weight and does not come into contact with the intermediate transfer belt 20 again. In addition, since the constant tension is always applied by the compression spring 24 after the displacement of the second support roller 22 is released, it is more stable than the configuration in which the tension is applied every time the intermediate transfer belt is driven. A certain tension is applied.

  When the image forming operation is started, the photosensitive drums 11 are rotationally driven, and the surface of each photosensitive drum 11 is charged almost uniformly by the charging device 12. The exposure device 16 outputs a flashing laser beam based on the image data, and scans the photosensitive layer on the surface of the photosensitive drum 11. As a result, the potential at the irradiation position of the laser beam is attenuated, and a latent image due to the difference in electrostatic potential is formed on the surface of the photosensitive drum 11.

  The electrostatic latent image formed on the photosensitive drum 11 in this way is conveyed to a developing position facing the developing roller 13a by the rotation of the photosensitive drum 11. When passing through the developing position, the toner adhering to the developing roller 13a is electrostatically transferred to the latent image portion on the surface of the photosensitive drum, and a toner image is formed.

  In the primary transfer portion, the photosensitive drum 11 and the primary transfer roller 14 face each other via the intermediate transfer belt 20, and a transfer bias voltage is applied between them. When the toner image developed on the surface of each photoconductive drum 11 is conveyed to the primary transfer portion, an electrostatic force acts on the toner in an electric field formed between the photoconductive drum 11 and the primary transfer roller 14, The toner image on the surface of the photosensitive drum 11 is transferred to the surface of the intermediate transfer belt 20.

  In this way, the intermediate transfer belt 20 is transferred so that the toner images of the respective colors are superimposed while sequentially facing the respective image forming units 10. The intermediate transfer belt 20 on which the toner images of all the colors have been transferred in multiple turns is conveyed in the direction of arrow A shown in FIG. 1 and is opposed to the first support roller 21 that contacts the inner surface of the intermediate transfer belt 20. Then, it is conveyed to a contact portion with the secondary transfer roller 1 arranged in this manner.

A secondary transfer bias voltage is applied between the secondary transfer roller 1 and the first support roller 21, and the recording sheet is fed between the secondary transfer roller 1 and the intermediate transfer belt 20 at a predetermined timing. . The toner images on the intermediate transfer belt 20 are collectively transferred to the recording sheet.
The recording sheet to which the toner image has been transferred is sent to the fixing device 5, where the toner image is heated and pressurized, and the color-superposed toner image is fixed on the surface of the recording sheet.

Next, a belt unit according to another embodiment of the present invention will be described with reference to FIGS.
In this belt unit, the intermediate transfer belt 30 is stretched around a first support roller 31, a second support roller 32, and a third support roller 33 in the same manner as the belt unit shown in FIG. Is. The second support roller 31 is urged by the compression spring 34 in the direction in which the intermediate transfer belt 30 is stretched, and can be retracted when the pressing member 35 is pressed. As with the belt unit shown in FIG. 2, the pressing member 35 is supported by a rotation shaft 36 parallel to the second support roller 32, and the rotation shaft 36 is supported by a support frame 37 via a bearing 38. It can be rotated around.

  In the belt unit of this embodiment, the arm portion 35 a of the pressing member 35 is fixed on the axis of the rotating shaft 36 and rotates together with the rotating shaft 36. Further, a partial gear 39 provided with teeth only in a part in the circumferential direction is fixed near both ends of the rotating shaft 36. On the other hand, a drive transmission gear 41 is fixed to the support shaft 40 of the second support roller 32 and meshes with the partial gear 39 fixed to the rotary shaft 36.

  The partial gear 39 has a fan-shaped shape extending from a joint base portion 39a fixed to the rotary shaft 36, and teeth that mesh with the drive transmission gear 41 are formed along the periphery of the tip portion. When the pressing member 35 is pressed against the peripheral surface of the second support roller 32, it is set so as to mesh with the drive transmission gear 41, and the rotating shaft 36 rotates to rotate the pressing member 35. In the state where the pressure on the second support roller 32 is released, the meshing between the partial gear 39 and the drive transmission gear 41 is also released as shown in FIG. At this time, the range in which the teeth of the partial gear 39 are formed has a shape protruding in a fan-like narrow range, so that the meshing with the teeth of the drive transmission gear 41 is released, so that FIG. ), The distance between the rotation shaft 36 and the support shaft 40 that supports the second support roller 32 can be approached. Since the partial gear 39 rotates in the direction in which gravity acts, the partial gear 39 hangs down due to its own weight after releasing the displaced state of the second support roller 22 and comes into contact with the drive transmission gear 41 again. There is no.

In such a belt unit, the second support roller 32 can be held in a state of being retracted to a position where the tension of the intermediate transfer belt 30 is relaxed. At this time, the second support roller 32 is engaged with the pressing member 35 and the drive transmission gear 41. It resists the elastic repulsion force of the compression spring 34 with both of the partial gears 39. Thereby, the load of the pressing member 35 is reduced, and the deformation of the pad 35b provided at the tip can be reduced. Further, when the intermediate transfer belt 30 is driven to rotate, a force in the direction of rotating around the rotation shaft 36 is applied to the tip of the pressing member 35, and the intermediate transfer belt 30 is pressed by the pressing member 35. A rotational force is applied to the second support roller 32. When the second support roller 32 rotates, a rotational driving force is transmitted from the support shaft 40 to the rotary shaft 36 via the drive transmission gear 41 and the partial gear 39. When the rotating shaft 36 rotates, the pressing contact of the pressing member 35 to the second support roller 32 is released, and the meshing between the drive transmission gear 41 and the partial gear 39 is released. As a result, the restraint of the second support roller 32 held at the retracted position is released, and the intermediate transfer belt 30 is moved to a position where it is stretched.
Therefore, when the belt unit or the image forming apparatus using the belt unit is shipped, the second support roller 32 is moved backward to leave the intermediate transfer belt 30 in a relaxed state, and when the intermediate transfer belt 30 is driven for the first time, the intermediate transfer belt 30 is moved. Tension can be introduced into the belt 30.

6 and 7 are a schematic side view and a partial plan view showing a belt unit according to another embodiment of the present invention.
Similarly to the belt unit shown in FIG. 2, this belt unit also has an intermediate transfer belt 50 stretched between a first support roller 51, a second support roller 51, and a third support roller 52, and is driven to rotate. The The second support roller 52 is urged by the compression spring 54 in the direction in which the intermediate transfer belt 50 is stretched, and the pressing member 55 fixed to the rotary shaft 56 is pressed against the intermediate transfer belt 50. Sometimes, the intermediate transfer belt is retracted in the direction of loosening the tension.

  In the belt unit of this embodiment, in the vicinity of both ends of the rotation shaft 56 to which the pressing member 55 is fixed, the support shaft 60 is brought into contact with the support shaft 60 of the second support roller 52 and moved backward. A restraining arm 59 for holding is provided. The restraining arm 59 includes a base portion 59a fixed to the rotation shaft 56, an arm portion 59b projecting from the base portion 59a toward the support shaft 60, and an abutting portion made of an elastic material provided at the tip of the arm portion 59b. 59c. The contact portion 59c has a concave contact surface with the support shaft 60, and can hold the support shaft 60 in a stable state.

  The restraining arm 59 is fixed to the rotary shaft 56 so as to protrude toward the support shaft of the second support roller 52 when the pressing member 55 is in a position where the press member 55 is pressed by the second support roller 52. Yes. Accordingly, the second support roller 52 is held in the retracted position together with the pressing member 55, and the tension of the intermediate transfer belt can be maintained in a relaxed state.

  Further, when the intermediate transfer belt 50 is driven to rotate, a rotational force is transmitted to the pressing member 55 and the second support roller 52 that are supported so as to sandwich the intermediate transfer belt 50. When the second support roller 52 rotates, a rotational force is transmitted to the restraining arm 59 that is in contact with the support shaft 60, and the rotating shaft 56 to which the restraining arm 59 is fixed is rotated. The rotating shaft 56 is rotated by the rotational force transmitted from the pressing member 55 and the rotational force transmitted from the second support roller 52 via the restraining arm 59, and the support shaft 60 formed by the pressing member 55 and the restraining arm 59. The second support roller 52 is moved in a direction to apply tension to the intermediate transfer belt 50 by the compression spring 54. As a result, tension is introduced into the intermediate transfer belt 50, and the intermediate transfer belt 50 moves around by the driving of the first support roller 51.

  Such a belt unit or an image forming apparatus using the belt unit presses the pressing member 55 against the second support roller 52 through the intermediate transfer belt until it is used after being manufactured. Further, the restraining arm 59 is brought into contact with the support shaft 60 of the second support roller, and the second support roller 52 is moved backward so that the intermediate transfer belt is relaxed. When the intermediate transfer belt 50 is first driven, the restriction of the second support roller 52 by the pressing member 55 and the restraining arm 59 can be released and the intermediate transfer belt 50 can be stretched.

FIG. 8 is a schematic configuration diagram of an image forming apparatus according to another embodiment of the present invention.
The image forming apparatus includes four electrophotographic image forming units 70 as in the image forming apparatus shown in FIG. 1, and these are arranged in the vertical direction. Each image forming unit 70 includes a photoconductive drum 71, a charging device 72, a developing device 73, a transfer device 74, and a cleaning device 75. Each photoconductive drum 71 has an exposure device 76. The image light is irradiated from. A belt unit 80 is provided so that each photosensitive drum 71 and the endless belt 81 face each other. The belt unit 80 receives the recording sheet conveyed from the sheet tray 94 on the outer peripheral surface of the belt 81. It adheres to and is transported. Then, the toner images are sequentially transferred and superimposed on the recording sheet conveyed from each of the photosensitive drums 71 when passing the position facing the image forming unit 70.

  A fixing device 91 is provided at a position where the recording sheet, which is conveyed while being adhered to the belt 81 and onto which the toner image has been transferred, is peeled off from the belt 81, and both sides of the sheet discharge tray 92 and the recording sheet are provided downstream. A transport path 93 is provided.

The belt unit 80 includes an endless belt 81 and a first support roller 82 and a second support roller 83 that stretch the endless belt 81. The belt 80 is arranged in a direction indicated by an arrow in FIG. It is a circular drive. Similar to the belt unit shown in FIGS. 2 and 3, the second support roller 83 is urged by a compression spring (not shown) and applies tension to the belt 80. A rotation shaft 84 is supported in parallel with the support shaft of the second support roller at a position facing the second support roller 83, and a pressing member 85 is attached. The pressing member 85 is pressed against the second support roller 83 via the belt 81 wound around the second support roller 83 and retracts the second support roller 83 against the elastic repulsion force of the compression spring. Thus, the belt 81 force is loosened. As the specific structure of the pressing member 85 and the like that function in this manner, the same structure as that shown in FIGS. 2 and 3 can be adopted.
Further, the mechanism for holding the belt in a relaxed state and the mechanism for releasing the belt tension and introducing the tension to the belt are the belt unit shown in FIGS. 4 and 5, or FIGS. The same mechanism as the belt unit shown in FIG.
On the other hand, the opposing roller 86 is pressed against the first support roller 82 via the belt 80, and the belt is pressed against the surface of the first support roller 82 even when the tension of the belt is loosened. The belt can be driven around.

Even in such an image forming apparatus, the pressing member 85 can be pressed against the support roller 83 of the belt unit 80 and the support roller 83 can be moved backward so that no tension is introduced into the belt 81. Then, when the belt 81 is driven, the restraint at the position where the second support roller 83 is retracted by the pressing member 85 is released, and tension is applied to the belt 81 so that the recording sheet can be conveyed. it can.
Further, when the belt unit having the restraint releasing mechanism shown in FIGS. 4 and 5 is adopted as the belt unit, the pressure member is pressed against the support roller, the drive transmission gear and the partial gear as shown in FIG. , The tension is not introduced into the belt, and the tension can be introduced when the driving of the belt is started. Similarly, when the belt unit having the restraint releasing mechanism shown in FIGS. 6 and 7 is adopted, the pressing member is pressed against the support roller, and the support shaft is restrained by the restraining arm as shown in FIG. Thus, the belt can be held in a tension-free state, and tension can be introduced into the belt by driving the belt.

1: secondary transfer roller, 2: sheet tray, 3: transport path, 4: registration roller, 5: fixing device, 6: paper discharge tray, 7: toner cartridge,
10: Image forming unit 11: Photoconductor drum 12: Charging device 13: Developing device 14: Primary transfer roller 15: Cleaning device 16: Exposure device
20: intermediate transfer belt, 21: first support roller, 22: second support roller, 23: third support roller, 24: compression spring, 25: pressing member, 26: rotating shaft, 27: support frame, 28: support shaft, 29: bearing,
30: Intermediate transfer belt, 31: First support roller, 32: Second support roller, 33: Third support roller, 34: Compression spring, 35: Pressing member, 36: Rotating shaft, 37: Support frame, 38: bearing, 39: partial gear,
40: support shaft, 41: drive transmission gear,
50: Intermediate transfer belt 51: First support roller 52: Second support roller 53: Third support roller 54: Compression spring 55: Pressing member 56: Rotating shaft 57: Support frame 58: Bearing, 59: Restraint arm, 60: Support shaft,
70: image forming unit, 71: photosensitive drum, 72: charging device, 73: developing device, 74: primary transfer roller, 75: cleaning device, 76: exposure device,
80: belt unit, 81: belt, 82: first support roller, 83: support roller, 84: rotating shaft, 85: pressing member, 86: counter roller,
91: fixing device, 92 discharge tray, 93: conveyance path for both sides, 94: sheet tray

Claims (14)

A belt whose surface is movable while tension is applied;
A rotating member on which the belt is passed and a support shaft that rotates about an axis is supported movably;
An urging means for urging the rotating member in a direction in which the tension of the belt is applied;
A holding member that holds, via the belt, a state in which the rotating member is displaced in a direction in which the belt tension decreases.
The holding unit releases a state where the rotating member is displaced by the movement of the belt, and tension is applied to the belt by the urging means. A belt whose surface is movable while tension is applied;
A rotating member on which the belt is passed and a support shaft that rotates about an axis is supported movably;
An urging means for urging the rotating member in a direction in which the tension of the belt is applied;
A restraining member that restrains a state in which the rotating member is displaced in a direction in which the tension of the belt decreases,
The belt unit, wherein the restraining member releases a state in which the rotating member is displaced by the rotation of the rotating member, and tension is applied to the belt by the biasing means. A belt whose surface is movable while tension is applied;
A rotating member on which the belt is passed and a support shaft that rotates about an axis is supported movably;
An urging means for urging the rotating member in a direction in which the tension of the belt is applied;
A contact member that contacts the surface of the belt in a state where the rotating member is displaced in a direction in which the tension of the belt decreases;
A restraining member that restrains a state in which the rotating member is displaced in a direction in which the tension of the belt decreases,
When the contact member moves due to the movement of the belt, the restraining member releases the state in which the tension of the belt is reduced, and tension is applied to the belt by the biasing means. A belt unit characterized by that.   The belt unit according to claim 1, wherein the holding member is rotatably supported and rotates by movement of the belt.   The belt unit according to claim 4, wherein the holding member rotates in a direction in which gravity acts.   6. The belt unit according to claim 1, wherein the holding member releases a state in which the holding member is displaced in a direction in which the tension of the belt decreases due to a frictional force with the belt. .   The belt unit according to any one of claims 1, 4, 5, and 6, wherein the holding member has a softer contact portion with the belt.   4. The belt unit according to claim 2, wherein the restraining member is rotatably supported and is rotated by the rotation of the rotating member.   The belt unit according to claim 8, wherein the restraining member rotates in a direction in which gravity acts.   The said restraining member cancels | releases the state displaced in the direction which the tension | tensile_strength of the said belt reduces with the gear provided on the axis line of the said rotation member, and the gear provided in this restraining member, The claim | claim. The belt unit according to any one of claims 3, 8, and 9.   The belt unit according to claim 3, wherein the contact member is rotatably supported and rotates by movement of the belt.   The belt unit according to claim 11, wherein the contact member rotates in a direction in which gravity acts.   The belt unit according to any one of claims 3, 11, and 12, wherein the contact member and the restraining member are supported by the same support shaft. An image forming apparatus comprising the belt unit according to any one of claims 1 to 13,
When the image forming apparatus is shipped, the rotating member is displaced in a direction in which the belt tension decreases, and when the belt is driven at the start of use, the rotating member is displaced in a direction in which the belt tension decreases. An image forming apparatus for canceling the state.

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