JP4564941B2 - Sheet conveyance auxiliary device and image forming apparatus - Google Patents

Description

  The present invention relates to an auxiliary conveyance device for conveying a sheet, which is a recording medium, of an image recording apparatus such as a printer, a copying machine, a fax machine, or a scanner.

  In recent years, image forming apparatuses are required to be miniaturized and to be able to use paper of various thicknesses. For example, when a sheet stacked in a horizontally installed sheet feeding tray is supplied to a desired position such as an image forming unit, the sheet occupies a range that the sheet conveyance path occupies in the horizontal direction when the sheet is conveyed without changing its direction. The image forming apparatus is increased in size in terms of a plane or a projected occupation area.

  In view of this, it has been practiced to change the transport direction by curving the sheet immediately after being fed from the sheet feed tray by the arcuate guide surface of the sheet guide. For example, the conveyance direction is changed by curving a sheet pulled out from a horizontally disposed sheet cassette vertically upward (see Patent Document 1 and Patent Document 2).

An example of such a sheet feeding mode in FIGS. As shown in FIG. 9 , in the conventional conveying apparatus that feeds the sheet P from the sheet feeding tray of the sheet feeding apparatus 2 in a substantially vertical upward direction, the sheet P stacked in the sheet feeding tray is a pickup roller. 23, separated one by one by the FRR separation type feed roller 24 and reverse roller 25, and conveyed along the lower guide plate 34. When this conveyance state is considered in detail, as shown in FIG. 10 as time passes, as the sheet conveyance proceeds, the sheet P that rubs against the lower guide plate 34 changes its traveling direction, so long as it is weak. , proceeds along the curve of the lower guide plate 34, the sheet to some extent with the strength of the hip travel path to be pressed by the upper guide plate 33 is corrected (in FIG. 10 (a) ~ (d) Reference), and reaches the pair of conveying rollers 42 along the elastically deformable guide piece 40 located at the outlet of the lower guide plate 34.

Japanese Patent Laid-Open No. 10-265070 JP 2002-274702 A

However, in the conveyance mode as shown in FIG. 9 and FIG. 10 , in the case of a particularly stiff sheet such as an envelope or a postcard, the resistance becomes larger, which causes an obstacle to sheet feeding. That is, when the state of FIG. 10 b, resulting in large transport load when the sheet P contacts the upper guide plate 33. As a result, along with a large conveyance load received by the sheet, the sheet conveyance becomes unstable, and sheet delay or non-feed occurs.

Therefore, the solution is to remove the upper guide plate by separating the position of the conveying roller pair from the feed roller (increasing the radius of curvature at the sheet conveying curved portion to cope with the bending of a stiff sheet). Can be considered. Further, as shown in FIG. 11 , the diameter of the conveying roller 43 on the inner circumference side of the conveying path is increased, and a follower roller 44 is further added immediately after the separating unit to increase the conveying force while curving the sheet. Such a configuration has also been devised. However, in such a configuration, the conveyance roller 43 must have a radius of curvature commensurate with the stiffness of the sheet to be used, and the conveyance roller is considerably large, thereby achieving space saving of the apparatus. There is a problem that it is impossible to do so, and the layout of other parts must be changed. In addition, if the upper guide plate is removed as described above, it may not be possible to reach the nip between the conveying roller and the driven roller when conveying an upward curled sheet. There is a possibility that foreign matter (toner, grease, etc.) may be scattered.

  That is, in the conventional sheet feeding form, when the sheet is conveyed while being curved, the resistance at the time of conveyance increases, so that the required torque increases, the driving force needs to be increased, and the cost increases. The sheet may be damaged such as wrinkles and scratches. In addition, there is a problem that the apparatus is enlarged to sufficiently bend the conveyance path.

  The present invention has been made in view of the above circumstances, and the object of the present invention is to reliably convey a sheet from a feed roller to a conveyance roller provided at a destination where the sheet conveyance direction is changed in a limited space. However, the object is to reduce the resistance during the conveyance.

According to the present invention, there is provided a sheet conveyance auxiliary device arranged on the inner peripheral side of a sheet conveyance curved path, wherein the sheet conveyance auxiliary device is configured by at least two rollers wound around a belt. and having a rotary member constitutes at least a part of the sheet conveying curved path by a guide member disposed on the outer peripheral side of the sheet conveying curved path, opposed to the guide member disposed on the outer peripheral side of the sheet conveying curved path This is solved by the belt surface defining the inner peripheral side of the sheet conveying curved path and the at least two rollers together defining the inner peripheral side of the sheet conveying curved path via the belt .

Sheet conveyance downstream of the rollers of the two rollers to be wound around the belts is, if also serves as one of the first conveying roller pair of the sheet conveying path located downstream of the sheet conveying curved path, more preferably .

  Furthermore, it is advantageous if the roller on the upstream side of the sheet conveyance among the two rollers around which the belt is wound is configured to be able to retract from the sheet conveyance curved path against the spring means. Of the two rollers wound around the belt, the roller on the downstream side of the sheet conveyance is preferably used as a drive source to rotate the belt. It is also preferable to provide teeth on the inner peripheral surface of the belt and mesh with the outer peripheral teeth of the roller on the downstream side of the sheet conveyance.

  It is preferable that the belt is configured so that only the central portion in the direction orthogonal to the sheet conveying direction is in contact with the sheet. If the central part in the direction perpendicular to the sheet conveying direction on the outer peripheral surface of the belt is convex, or if the central part in the longitudinal axis direction of the roller around which the belt is wound is convex, only the central part of the belt is the sheet Get in touch with. It is also preferable that at least the surface of the belt is made of a conductive material.

According to the first aspect of the present invention, it is possible to reduce the conveyance resistance of the curved conveyance path when bending and conveying a stiff sheet, and to prevent conveyance failure such as skew feeding in the sheet feeding to the downstream side of the sheet conveyance. be able to. According to the invention of claim 2, it is possible to feed the sheet smoothly to the transport nip of the sheet over preparative conveyance downstream, it is possible to suppress displacement or paper jam of the transfer timing.

  If the belt is configured so that only the belt center in the direction perpendicular to the sheet conveying direction is in contact with the sheet, the sheet is rubbed against the edge of the belt when conveying the sheet, resulting in a rubbing trace. Can be prevented. By using a conductive material for the belt surface, it is possible to avoid unnecessary static electricity when a slip occurs between the belt and a stable sheet conveyance.

Hereinafter, the present invention will be described as an embodiment in which the present invention is applied to a tandem color laser printer (hereinafter referred to as a printer) which is an electrophotographic image forming apparatus.
The image forming unit 3 of the printer 1 shown in FIG. 1 is arranged so as to be inclined so that the side that receives the sheet as the transfer material that has been fed is the lower side and the paper discharge side of the sheet that has completed image formation is the upper side. A transfer / conveying device 10 is provided. The transfer conveying device 10 has an endless transfer belt 12 wound around a plurality of rollers, in this example, four support rollers 11, and any one of the support rollers 11 is counterclockwise in FIG. The transfer belt 12 is rotationally driven in the sheet conveying direction X by being rotationally driven in the direction. Four image forming units 4M, 4C for magenta (M), cyan (C), yellow (Y), and black (Bk) in order from the bottom along the upper running side of the transfer belt 12, that is, in the sheet conveying direction X. , 4Y, 4Bk are arranged in parallel. The order of the colors of the image forming units 4M, 4C, 4Y, and 4Bk is arbitrary and can be changed as appropriate. However, the black image forming unit 4Bk that is expected to form a monochromatic image is the most upstream or most downstream in the transport direction X. It is desirable to be at the end. The transfer belt 12 constitutes an example of a transfer material carrier that carries and conveys a transfer material. Instead of the transfer belt 12, for example, a transfer material carrier configured in a drum shape or the like may be used. it can.

  Each of the image forming units 4M, 4C, 4Y, and 4Bk has a photosensitive drum 5 as an image carrier, and the photosensitive drum 5 in contact with the transfer belt 12 is a driving unit (not a transfer device). (Not shown) is driven to rotate clockwise in the figure. Around the photosensitive drum 5, a charging roll 6, a cleaning device 9, a developing device 7 and the like as a charging unit are provided, and a toner image on the photosensitive member is transferred to a sheet at an opposing position across the transfer belt 12. For this purpose, a transfer roll 14 is disposed. Instead of the transfer roll, a transfer device including a transfer brush, a transfer blade, or a transfer charger may be employed. A space between the charging roll 6 and the developing device 7 is an optical writing position where the photosensitive drum 5 is irradiated with laser light from the optical writing device 8 disposed above the image forming unit. In each of the image forming units 4M, 4C, 4Y, and 4Bk, the photosensitive member 5 and some elements that form a toner image on the surface thereof are each configured as a process cartridge that is detachably attached to the apparatus main body 1. ing.

  Each color developing device 7 in each of the image forming units 4M, 4C, 4Y, 4Bk is a two-component developing device using a developer composed of toner and carrier, and is supplied to each color developing device 7 according to the amount of consumed toner. Each color toner is individually stored in four cartridges, and in particular, the cartridge storing black toner is larger than the other three cartridges. The four toner cartridges are juxtaposed in the lateral direction of the apparatus in the color printer of this example, and are shown as cartridges 20 in the upper right corner in FIG. In FIG. 1, since the three cartridges other than those for black toner appear to overlap, only one is shown by a solid line, and the cartridge for black toner is shown by a two-dot chain line.

  On the other hand, a cassette 21 of the sheet feeding device 2 is disposed in the lower part of the apparatus main body 1, and sheets (not shown) are stacked on a bottom plate 22 disposed in the cassette 21. The pickup roller 23 that is in contact with the upper surface of the uppermost sheet is driven to rotate counterclockwise, whereby the uppermost sheet is fed, and the fed sheet is upstream of the transfer belt 12 in the sheet conveying direction. Is temporarily abutted against a registration roller 13 provided on the side, and is sent out at a predetermined timing by the rotation thereof, carried on the transfer belt 12 and conveyed in the direction of the arrow X, and the toner between each photoconductor 5 and the transfer belt 12 Passes the image transfer position.

  Accordingly, the magenta image forming unit 4M for the image forming operation as the first image forming unit drives an LD (laser diode) (not shown) to the photosensitive drum 5 charged by the charging roll 6. Then, optical writing of an optical image developed with magenta toner is performed by the optical writing device 8 that irradiates the polygon mirror 8a with laser light and guides the reflected light onto the photosensitive drum 5 through a cylinder lens or the like. By this writing, an electrostatic latent image is formed on the photosensitive drum 5 based on image data sent from a host machine such as a personal computer, and the latent image becomes a visible image of magenta toner by the developing device 7. Then, at the toner image transfer position, the visible image of the magenta toner is transferred to the recording sheet by the action of the transfer roll 14 disposed on the back side of the transfer belt 12.

  In the same manner as the above image forming operation, in the other image forming units 4C, 4Y, and 4Bk, visible images are formed by the respective toners on the surfaces of the respective photosensitive drums 5, and these visible images are conveyed by the transfer belt 12. Each time the sheet to be transferred arrives at each transfer position, it is transferred in an overlapping manner. Therefore, in the color printer 1, a full-color image is transferred onto a sheet in a short time that is almost the same as that in monochrome. The transferred sheet is separated from the transfer belt 12 and fixed by the fixing device 15. The sheet after fixing is normally discharged outside the apparatus as it is. At this time, the sheet is reversed and discharged on the back side to a discharge tray 16 provided on the upper surface of the apparatus body 1. Backside paper discharge is an almost indispensable condition for the printer to arrange prints in page order.

  Next, the sheet conveyance auxiliary device according to the present invention disposed between the sheet feeding device 2 and the conveyance path to the registration roller 13, particularly the conveyance roller in the vertical conveyance path (in FIG. 1, it is omitted for the sake of space). ). Details of the apparatus are shown in FIGS. Between the FRR separation type sheet feeding mechanism including the pickup roller 23, the feed roller 24, and the reverse roller 25 and the sheet vertical conveyance path, that is, the sheet conveyance from the sheet feeding portion of the sheet feeding apparatus to the sheet vertical conveyance path In the curved path, the conveying belt 30 extends from the first belt pulley 27 that also constitutes the first conveying roller of the sheet vertical conveying path and the second belt pulley 28 attached to the idler shaft to one side (upper portion) of the curved path. It is arranged in. The conveyor belt 30 is made of a conductive material, and prevents static electricity that may be generated by rubbing against the sheet.

  Further, a driven roller 31 disposed at the entrance of the sheet vertical conveyance path via the conveyance belt 30 is in contact with the first belt pulley 27. The first belt pulley 27, the second belt pulley 28, and the conveyance belt 30 constitute a sheet conveyance assist device. The driving means (the motor M in FIG. 2c) of the first belt pulley 27 causes the conveyance belt 30 to be a sheet. Rotates in the transport direction.

The sheet conveyance curved path is defined by an upper guide plate 33 and a lower guide plate 34, and the vertical conveyance path is formed by the lower vertical piece of the lower guide plate 34, the vertical conveyance guide plate 35, and the upper guide plate 33. A path is defined by the upper vertical piece. The sheet conveying portion of the conveying belt 30 is disposed so as to protrude from the upper guide plate 33 to the sheet conveying curved path (specifically, the nip position between the conveying belt 30 and the driven roller 31 and the leading end of the sheet P). Is arranged so that the conveying belt 30 protrudes at a position of the upper guide plate 33 that intersects with a straight line connecting a position that contacts the outer peripheral guide member (the lower guide plate 34 or the vertical conveying guide plate 35). ) When the sheet P is conveyed, the sheet P does not contact the upper guide plate 33 but contacts the conveying belt 30, and the conveying force is caused by the conveying belt 30, particularly by the belt portion around the second belt pulley 28. To be added. Accordingly, the leading edge of the sheet can be moved and guided to the nip portion between the conveying belt 30 and the driven roller 31 by the conveying force of the feed roller 24 and the conveying belt 30. Higher stiffness of the sheet is strong, at the time the state of FIG. 10 b of the conventional example previously described in the contact pressure is increased, it is possible to perform the conveying force assist.

  The second belt pulley 28 may be configured so as to be in a fixed state as shown in FIG. 2a. However, an elastic means a (FIG. 2c) such as a spiral spring or a leaf spring is attached, and as shown in FIG. The second belt pulley 28 may be retracted in the A direction when the above contact pressure is applied. Specifically, as shown in FIG. 2c, a plurality of first belt pulleys 27 arranged in the sheet width direction are fixed on a common shaft, and the opposed driven rollers 31 are also provided on the common shaft. The driven roller 31 is biased toward the first belt pulley 27 (toward the conveyor belt 30) by an unillustrated elastic means so as to have a predetermined nip pressure. Therefore, when the driving force of the driving means (motor M) is transmitted to the first belt pulley 27 through the shaft and rotated in the direction of the arrow in the figure, the driven roller 31 is rotated in the direction of the arrow in the figure. Similarly to the above, a plurality of second belt pulleys 28 are also arranged in the seat width direction and are rotatably attached to a common shaft. The shaft is urged by the elastic member a in a direction opposite to the A direction (retracting direction). Therefore, when the first belt pulley 27 rotates, the second belt pulley 28 is rotated in the direction of the arrow in the figure by the conveyor belt 30 and swings so that the second belt pulley 28 side protrudes and retracts from the upper guide plate 33. It becomes possible.

  2A and 2B, in which the first belt pulley 27, the second belt pulley 28, and the conveyance belt 30 constitute the sheet conveyance auxiliary device, the first belt pulley 27 or its conveyance belt portion is the first conveyance in the vertical conveyance path. As shown in FIG. 3a, the sheet conveying auxiliary device is compactly composed of a first belt pulley 27 ′ having a small diameter, a second belt pulley 28 ′, and a conveying belt 30 as shown in FIG. It is also possible to arrange a separate roller 32 that is paired with the driven roller 31 of the second roller 31. The second belt pulley 28 'may be configured to be in a fixed state as shown in FIG. 3a, but is provided with elastic means a (FIG. 3c) such as a spiral spring or a leaf spring, as shown in FIG. 3b. The second belt pulley 28 'may be retracted in the A direction when a predetermined contact pressure or more is applied. Specifically, as shown in FIG. 3c, a plurality of rollers 32 arranged in the sheet width direction are fixedly provided on a common shaft, and the opposed driven rollers 31 are similarly provided on a common shaft, not shown. The driven roller 31 is urged against the roller 32 by the elastic means so as to have a predetermined nip pressure. Therefore, when the driving force of the driving means (motor M) is transmitted to the roller 32 through the shaft and rotated in the direction of the arrow in the figure, the driven roller 31 is rotated in the direction of the arrow in the figure. Similarly to the above, a plurality of first belt pulleys 27 ′ and second belt pulleys 28 ′ are also arranged in the seat width direction, and each is rotatably attached to a common shaft. The shaft of the first belt pulley 27 ′ is rotated in the direction of the arrow in the drawing when the driving force of the driving means (motor M) is transmitted through a plurality of gears. On the other hand, the shaft of the second belt pulley 28 'is urged by the elastic member a in a direction opposite to the A direction (retracting direction). Therefore, when the first belt pulley 27 ′ rotates, the second belt pulley 28 ′ is rotated in the direction of the arrow in the drawing by the transport belt 30, and the second belt pulley 28 ′ protrudes / retreats from the upper guide plate 33. Can be swung.

At this time, the position at which the second belt pulley 28 ′ protrudes is the same as described with reference to FIG. 2 b, the nip position between the roller 32 and the driven roller 31, and the guide member (the lower guide plate 34 having the outer periphery of the sheet P). Alternatively, it is the position of the upper guide plate 33 that intersects the straight line connecting the position where it contacts the vertical conveyance guide plate 35). Accordingly, when the sheet P is conveyed, the sheet P does not contact the upper guide plate 33 but contacts the conveying belt 30, and the conveying force is generated by the conveying belt 30, particularly by the belt portion around the second belt pulley 28 ′. It is added to the sheet P. Thereby, the leading edge of the sheet can be moved and guided to the nip portion between the roller 32 and the driven roller 31 by the conveying force of the feed roller 24 and the conveying belt 30. Higher stiffness of the sheet is strong, at the time the state of FIG. 10 b of the conventional example previously described in the contact pressure is increased, it is possible to perform the conveying force assist.

A cross section of the belt pulley is shown in FIG. By rounding the end portion of the conveyance belt 30, the belt end portion is not rubbed against the sheet during sheet conveyance, so that no rubbing trace due to the belt edge portion is generated on the sheet. In addition to the rounded configuration, a similar effect can be achieved by providing a taper that reduces the belt thickness toward the outer end. FIG. 5 shows another configuration of the belt pulley. The pulley 27 is configured to have a small end diameter so that a central portion in a direction orthogonal to the sheet conveying direction is convex. For this reason, the belt 30 follows the outer contour of the pulley, so that the belt end portion is not rubbed against the sheet during sheet conveyance. With such a configuration, it is possible to provide an effect of stopping the belt .

FIG. 6 shows details of the configuration of the conveyor belt unit. A conveyor belt 30 wound around a first belt pulley 27 fixed to the conveyor roller drive shaft 37 and a second belt pulley 28 that is disposed on an idler shaft 38 and is rotatably installed at the center of the idler shaft is a first belt. The pulley 27 rotates in the rotation direction. In this case, the first belt pulley 27 may be a flat pulley and the conveyor belt 30 may be a flat belt to transmit the drive by frictional contact. However, the first belt pulley 27 may be a timing pulley, and the back surface of the conveyor belt may be a timing belt. It is even better if the belt is rotated by meshing the teeth. Further, when the idler shaft is disposed so as to be rotatable with respect to the conveying device, the idler shaft and the belt pulley may be fixed and the idler shaft and the second belt pulley may be rotated integrally. The conveyor belt surface is made of EP rubber suitable for sheet conveyance. Further, it is more preferable that not only the surface of the conveyor belt but also the whole is made of EP rubber.

7 and 8 show an example in which the sheet conveyance auxiliary device is attached to the image forming apparatus. FIG. 7 shows a mode in which the sheet conveyance auxiliary device also serves as the first conveyance means (conveyance roller) in the vertical conveyance path. FIG. 7 is an outline of the state in which the vertical conveyance guide plate 35 and the driven roller 31 in FIG. 2 are omitted, and the surface of the conveyance belt 30 near the first belt pulley 27 in the three sheet conveyance auxiliary devices can be seen. . In this example, three sheet conveyance assisting devices are distributed in the sheet width direction, but the number is arbitrary including one, and is determined from the configuration of the entire image forming apparatus.

In the example of FIG. 8 , three normal conveyance rollers 33 that are paired with the driven roller 31 in the vertical conveyance path are arranged, and two sheet conveyance auxiliary devices are arranged therebetween. With this configuration, the main sheet conveying force at the entrance of the vertical conveying path is given by the conveying roller 33, and the auxiliary conveying force is given by the conveying belt 30. In the case of this example, a conveyor belt is arranged between the three conveyance rollers 33. However, when there is only one conveyance roller, two places on both sides of the sheet width, and when there are two conveyance rollers, between them or outside both sides. Etc., arranged in combination.

  Further, it is possible to adopt an appropriate configuration for the number of conveyor belts, the diameter of pulleys around which the conveyor belts are wound, the driving method of the conveyor belts, and the like. Moreover, the material of a conveyance belt is an example, and can use an appropriate thing. The separation method in the paper separation unit of the paper supply means is not limited to the FRR method, and any separation method may be used. In addition, in the above-described embodiment, the conveyance belt is disposed at the center in the sheet width direction and at an equal interval from the center in the sheet width direction. Is possible. Moreover, although the conveyance belt is intermittently arranged in the sheet width direction, a belt extending in the entire width direction may be used.

  In addition, when the present invention is applied to an image forming apparatus, not only the sheet turning portion immediately after the sheet separating portion of the sheet feeding means, but also the portion where the sheet after fixing is turned and the sheet conveying direction are changed (turned). The present invention can be applied to a portion where the sheet is turned at an appropriate place, such as a portion where the sheet is discharged to the paper discharge portion, a portion where the sheet conveyance direction is changed (turned) and the sheet is guided to the double-side portion. In addition, the image forming method is arbitrary, and can be applied to an apparatus such as an ink jet method.

  Furthermore, the present invention can be applied not only to an image forming apparatus but also to a portion where a sheet is turned in an apparatus having a function of conveying a sheet (sheet) such as a scanner or an automatic document feeder (ADF).

1 is a schematic configuration diagram of an image forming apparatus. It is a figure showing an example of a sheet conveyance auxiliary device concerning the present invention. It is a figure which shows the example which can be partially retracted of the sheet | seat conveyance auxiliary | assistance apparatus which concerns on this invention. It is a schematic perspective view explaining the drive means of the 1st belt pulley in the sheet conveyance auxiliary | assistance apparatus in FIG. It is a figure which shows another example of the sheet | seat conveyance auxiliary | assistance apparatus which concerns on this invention. It is a figure which shows another example of the sheet conveyance auxiliary | assistance apparatus which can be partially retracted. It is a schematic perspective view explaining the drive means of the 1st belt pulley in the sheet conveyance auxiliary | assistance apparatus in FIG. It is an example of composition of a pulley which is a roller which hangs around a belt. It is another structural example of the pulley which is a roller which hangs around a belt. It is a perspective view which shows the structure of a belt part. FIG. 3 is a schematic perspective view illustrating an example in which the sheet conveyance auxiliary device of the present invention is attached to the image forming apparatus conveyance device. FIG. 6 is a schematic perspective view illustrating another example in which the sheet conveyance auxiliary device of the present invention is attached to the image forming apparatus conveyance device. It is a schematic block diagram which shows the conventional sheet conveying apparatus. It is a figure explaining the mode in the case of conveying a firm sheet | seat by a curved conveyance path, and the change with time is shown from (a) to (d). It is the schematic which shows the conventional sheet conveying apparatus of another structure.

Explanation of symbols

23 pickup roller 24 feed roller 25 reverse roller 27 transport roller 28 idler shaft 30 transport belt 31 driven roller 33 upper guide plate 34 lower guide plate 35 vertical transport guide plate

Claims (11)

A sheet transport assisting device which is disposed on the inner peripheral side of the sheet conveying curved path, said sheet transport auxiliary device, which has a rotating member that at least two rollers is configured is wound around a belt, a sheet conveying The guide member arranged on the outer peripheral side of the curved path constitutes at least a part of the sheet conveying curved path, and the belt surface facing the guide member arranged on the outer peripheral side of the sheet conveying curved path is the inner circumference of the sheet conveying curved path A sheet conveyance assisting device characterized in that the at least two rollers define an inner circumferential side of the sheet conveyance curved path through the belt . The roller on the downstream side of the sheet conveyance among the two rollers wound around the belt also serves as one of the first conveyance roller pair of the sheet conveyance path positioned on the downstream side of the sheet conveyance curved path. Item 2. The sheet conveyance assisting device according to Item 1 . Sheet conveyance upstream side of the roller of the two rollers which are wrapped around the belt, to claim 1 or 2, characterized in that against the spring means is constructed to be retracted from the sheet conveying curved path The sheet conveyance auxiliary device according to the description. The sheet conveyance auxiliary device according to any one of claims 1 to 3 , wherein a roller on a downstream side of the sheet conveyance rotates the belt as a driving source among the two rollers wound around the belt. 5. The sheet conveyance assisting apparatus according to claim 4 , wherein teeth are provided on an inner circumferential surface of the belt and meshed with outer circumferential teeth of a roller on a downstream side of the sheet conveyance. The belt sheet transport auxiliary device according to any one of claims 1 to 5, characterized in that it is configured to contact only the central portion of the sheet in the direction perpendicular to the sheet conveying direction. The sheet conveyance auxiliary device according to claim 6 , wherein the outer peripheral surface of the belt has a convex central portion in a direction orthogonal to the sheet conveyance direction. The sheet conveyance assisting device according to claim 6 , wherein a central portion in a longitudinal axis direction of the roller wound around the belt is convex. The sheet conveyance auxiliary device according to claim 1 , wherein at least a surface of the belt is made of a conductive material. Image forming apparatus having a sheet conveying auxiliary device according to any one of claims 1-9. The image forming apparatus according to claim 10, wherein the sheet conveyance assisting device is arranged immediately downstream of the sheet feeding device.

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