JP2000044131A - Sheet carrying device and image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To preventing the breaking of a sheet tip part or feeding failures by correcting sheet curls. SOLUTION: A sheet guide 32 is disposed in the vicinity of a re-feeding roller pair 31, and a fan 34 is disposed in the vicinity of the sheet guide 32 and above a middle tray 30. If an upward curled sheet 2 is re-fed from the middle tray 30, after the tip part 2a of the curled sheet is sent to the vicinity of the sheet guide 32, the curled sheet tip part 2a is pressed to the upper surface of the middle tray 30 by air blown from the fan 34, and temporarily the curl of the sheet tip part 2a is corrected. Then, the sheet tip part 2a is sent along the upper surface of the middle tray 30 to the nip part of the re-feeding roller pair 31, and surely held by the nip part of the re-feeding roller pair 31.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a sheet curl correcting device for correcting the curl of a sheet (paper, plastic sheet, etc.) as a transfer member, and an image forming apparatus (copying machine, printer) having a sheet curl correcting function. , Facsimile, etc.).

[0002]

2. Description of the Related Art Generally, an image forming apparatus to which an electrophotographic technique is applied transfers a toner image formed on a photoreceptor to a sheet, and then heats and presses the sheet with a fixing device to convert the toner image into a sheet. Then, the sheet on which the image has been formed is discharged to a sheet discharge tray or the like.

FIG. 4 shows such an image forming apparatus.
The present invention relates to an image forming apparatus 1 including a double-sided printing unit 3 capable of printing on both sides of a sheet 2.

The image forming apparatus 1 feeds a sheet 2 fed from a sheet feed cassette 4 between a photoreceptor 6 and a transfer device 7 and transfers a toner image on the photoreceptor 6 to the sheet 2. Then, the toner image is fixed to the sheet 2 by the fixing device 15. In the double-sided printing mode, the sheet 2 on which an image is formed on one side is guided from the sheet transport path 17 to a branch path 23 which is curved and branched.
Printing unit 3 by the discharge roller pair 27 at the downstream end of the
The sheet 2 is discharged upward. At this time, the sheet 2 is discharged onto the duplex printing unit 3 in a state where the sheet 2 is turned upside down by the branch path 23.

The sheet 2 on the double-sided printing unit 3 is fed into the nip portion of the pair of re-feed rollers 31 by the sheet feed roller 35, and then sent out to the re-feed path 36 by the pair of re-feed rollers 31. The sheet is fed into the sheet supply path 5 on the upstream side of the photoconductor 6. And that sheet 2
Passes through the nip portion between the photoconductor 6 and the transfer device 7 again, and an image is formed on a surface on which no image is formed. Then, the sheet 2 printed on both front and back sides is discharged onto the sheet discharge tray 45 through the sheet transport path 17.

In the face-up discharge mode in which the single-sided printing is performed with the print side up, the single-sided printed sheet is directly discharged onto the sheet discharge tray 45 via the sheet conveying path 17.

In a face-down discharge mode in which the single-sided printing is performed with the print side down, the single-sided printed sheet 2 is transferred from the duplex printing unit 3 to the sheet discharge path 3.
7, and is discharged onto the sheet discharge tray 45.

[0008]

However, in the image forming apparatus 1 having such a duplex printing unit 3, the sheet is guided in the curved branch path 23 in the duplex printing mode as described above. Therefore, the sheet 2 heated and pressed by the fixing device 15 is forcibly bent in the curved branch path 23, so that the leading end 2
a and the rear end 2b are curled (curved).

As described above, when the sheet 2 is curled, when the sheet is re-fed from the duplex printing unit 3, the leading end of the curled sheet 2 is moved to the sheet guide 32 disposed near the pair of re-feed rollers 31. In some cases, a problem may occur in which the leading end 2a of the sheet 2 breaks due to the contact of the portion 2a.
Further, the leading end 2 of the sheet 2 curled by the sheet guide 32
a, the leading end 2a of the sheet may not be smoothly fed into the nip portion of the re-feed roller pair 31, and the re-feed may not be possible.

Accordingly, an object of the present invention is to provide a sheet conveying apparatus and an image forming apparatus capable of smoothly and reliably re-feeding a sheet without bending the sheet tip even if the sheet is curled. And

[0011]

According to a first aspect of the present invention, there is provided a branch path which guides a sheet in a state where the sheet is turned upside down from a sheet conveying path after passing through a fixing device. An intermediate tray that receives sheets discharged from the path, a sheet feed roller that moves the sheets on the intermediate tray in a predetermined direction, a pair of re-feed rollers that feeds the sheets moved by the sheet feed rollers from the intermediate tray, It is arranged near the re-feed roller pair,
A sheet guide for guiding a leading edge of a sheet moved by the sheet feed roller to a nip portion of the pair of re-feed rollers, and an intermediate tray disposed near the sheet guide and above the intermediate tray, and near the sheet guide. Air blowing means for blowing air toward the upper surface,
And a sheet conveying device comprising:

According to the present invention having the above-described configuration, when the sheet curled through the branch path is fed again from the intermediate tray and the sheet leading edge is fed to the vicinity of the sheet guide, the curled sheet leading edge is fed. The sheet is pressed against the upper surface of the intermediate tray by the air blown from the air blowing means, and the curl of the sheet leading end is temporarily corrected. Therefore, the leading end of the curled sheet is sent to the nip portion of the pair of re-feed rollers along the upper surface of the intermediate tray, and is reliably held by the nip portion of the pair of re-feed rollers.

[0013] The invention according to claim 2 is characterized in that in the middle of the branch road,
A sheet deformation correcting path for bending a sheet in a direction opposite to the bending direction of the branch path is formed.

According to such a configuration, the sheet can be provided with a stiffness in the direction opposite to the curved direction of the branch path in the middle of the branch path, so that the curl amount of the sheet can be suppressed. Therefore, according to the present invention, it is possible to more easily press the leading end of the sheet against the upper surface of the intermediate tray with the air blown from the air blowing means.

According to a third aspect of the present invention, there is provided a branch path which guides a sheet in a state where the sheet is turned upside down while being curved and branched from the sheet conveying path after passing through the fixing device, and a sheet discharged from the branch path. An intermediate tray, a sheet feed roller for moving a sheet on the intermediate tray in a predetermined direction, a pair of re-feed rollers for feeding sheets moved by the sheet feed roller from the intermediate tray, and a pair of re-feed rollers. A sheet guide that guides the leading edge of a sheet moved by the sheet feed roller to a nip portion of the pair of re-feed rollers, and is disposed near the sheet guide and above an intermediate tray;
An air blowing means for blowing air toward the upper surface of the intermediate tray near the sheet guide; a re-feeding path for returning a sheet fed from the pair of re-feeding rollers to a sheet supply path upstream of the image forming means; A sheet discharge path for guiding the sheet fed from the paper roller pair to the sheet discharge port, and, in the case of the duplex printing mode, guiding the sheet fed from the re-feed roller pair to the sheet re-feed path, and face-down discharge. An image forming apparatus, comprising: a flapper that guides a sheet fed from the pair of re-feed rollers to the sheet discharge path in a paper mode.

According to such a configuration, even if the sheet on the intermediate tray is curled along the shape of the branch path, the leading end of the sheet is pressed against the intermediate tray by the air blown from the air blowing means in the vicinity of the sheet guide. Can be Therefore, the leading end of the sheet is smoothly fed into the nip portion of the pair of sheet re-feed rollers without contacting the sheet guide. Therefore, the sheet is reliably re-fed to the re-feeding path or the sheet discharge path without breaking the leading end.

[0017]

Embodiments of the present invention will be described below in detail with reference to the drawings.

[First Embodiment] FIG. 1 is a schematic configuration diagram of an image forming apparatus 1 showing an embodiment of the present invention.
FIG. 2 is an enlarged view of a part of FIG. The image forming apparatus 1 shown in these figures includes a double-sided printing unit 3 capable of printing (image formation) on both sides of a sheet 2, and a face-up in which the sheet is discharged with one-sided printing and the print side up. The mode can be switched between a paper discharge mode, a face-down paper discharge mode in which sheets are discharged with one side printing and the print side down, and a double-sided print mode. Hereinafter, the image forming apparatus 1 having such a function will be described in detail.

The sheets 2 stacked in the paper feed cassette 4 are conveyed along a sheet supply path 5, and the sheets 2 are
The toner image formed on the surface of the photoconductor 6 is transferred to the sheet 2. The sheet 2 on the sheet cassette 4 is fed by a pickup roller 8 into a nip portion between a feed roller 10 and a reverse roller 11, and only one sheet is separated and sent out to a sheet supply path 5. The registration roller pair 1 is formed by the conveyance roller pairs 12 and 13 arranged on the way.
4 and is sent between the photoconductor 6 and the transfer device 7 by the registration roller pair 14.

The sheet on which the toner image has been transferred is sent to the fixing device 15 by the rotating photosensitive member 6 and the transfer device 7, and is heated and pressed by the fixing device 15. As a result, the toner image is fixed on one side of the sheet.

A sheet conveying device 19 is arranged downstream of the fixing device 15. And the fixing device 1
The sheet having passed through 5 is conveyed along a sheet conveying path 17 by a conveying roller pair 16 constituting a sheet conveying device 19. The cleaning device 1 is provided around the photoconductor 6.
8, a charging device 20, and a developing device 21 are arranged. An optical unit 22 that irradiates the surface of the photoconductor 6 with light and forms an electrostatic latent image on the surface of the charged photoconductor 6 is disposed above the photoconductor 6.

A branch path 23 branches from the middle of the sheet conveying path 17 on the downstream side of the fixing device 15, and a flapper 24 for switching a sheet path is disposed at the branch. The flapper 24 guides the sheet to the branch path 23 when the duplex printing mode or the face-down discharge mode is selected. The flapper 24 closes the branch path 23 and opens the sheet conveying path 17 when the face-up paper discharge mode is selected. Here, the branch path 23 is curved and branched from the sheet transport path 17 so that the sheet is turned upside down and guided onto the duplex printing unit 3.

In the middle of the branch path 23, a pair of transport rollers 25
Is arranged. Also, at the downstream end of the branch path 23,
A discharge roller pair 27 is provided. Furthermore, the branch road 23
A sensor 28 for detecting the passage of a sheet is disposed at the downstream end of the sheet and upstream of the discharge roller pair 27.

The duplex printing unit 3 receives the sheet discharged via the discharge roller pair 27 on the intermediate tray 30. At the left end of the intermediate tray 30 in the figure, a sheet re-feed roller pair 31 is disposed. A sheet guide 32 is disposed near the re-feed roller pair 31, and a sheet is knocked at a position near the sheet guide 32 and downstream of the discharge roller pair 27.
Is arranged. Further, a fan 34 as an air blowing means is arranged near the sheet guide 32 and above the intermediate tray 30.

As shown in detail in FIG. 2, the sheet guide 32 has an inclined wall 32a for guiding the leading end of the sheet to the nip portion of the pair of re-feed rollers 31. or,
The sheet striker 33 is supported by an image forming apparatus main body (not shown) so as to be rotatable around a shaft 33a.
The end of the sheet discharged from the branch path 23 is hit with the claw 33b, and the end of the sheet 2 is dropped on the intermediate tray 30. Further, the fan 34 as an air blowing means blows air toward the intermediate tray 30 near the sheet guide 32.

Sheet 2 discharged on intermediate tray 30
Is set by the sheet feed roller 35 to the re-feed roller pair 31.
Sent to the side. Here, the sheet 2 is a curved branch path 2
3 is discharged onto the intermediate tray 30 in a state of curling upward, so that the sheet feed rollers 3
When it is fed to the left side in FIG. 2 at 5, the curled tip 2a hits the sheet guide 32 and bends. However, in the present embodiment, as described above, since the curled sheet tip 2a is pressed onto the intermediate tray 30 by the air blown from the fan 34, the sheet tip 2a is moved along the intermediate tray 30 along with the refeed roller pair. 31 can be smoothly fed into the nip portion.

The sheet 2 fed to the nip portion of the pair of re-feed rollers 31 is conveyed to a re-feed path 36 or selectively conveyed to a sheet discharge path 37.
In the case of the double-sided printing mode, the sheet discharge path 37 is closed by the flapper 38, while the re-feed path 36 is opened, and the sheet is fed to the re-feed path 36. And
The sheet sent to the re-feeding path 36 is transported by a pair of transport rollers 4.
The sheets are fed into the sheet supply path 5 by 0, 41, and 42. In the face-down discharge mode, the flapper 38 closes the re-feed path 36, opens the sheet discharge path 37, and feeds the sheet to the sheet discharge path 37. The sheet sent to the sheet discharge path 37 is sent to the sheet transfer path 17 by the pair of transfer rollers 43, and is discharged from the sheet discharge port 49 onto the sheet discharge tray 45 by the pair of discharge rollers 44.

Here, the control timing of the fan 34, the sheet beater 33, and the sheet feed roller 35 shown in FIG. 2 will be described. First, when the sensor 28 detects the passage of the trailing edge of the sheet, the signal is input to the controller 46. When a predetermined time has elapsed after the detection signal from the sensor 28 has been input, the controller 46 activates the sheet strike 33, then activates the fan 34 and the motor 47.
Is operated to rotate the sheet feed roller 35, and the sheet is fed into the nip portion of the pair of re-feed rollers 31 by the sheet feed roller 35. Then, the controller 46
When a predetermined time has elapsed after the operation of the sheet feed roller 35, the operation of the fan 34 is stopped. The fan 34 operates until at least the sheet leading end 2a is nipped by the nip portion of the pair of re-feed rollers 31.

As described above, according to the present embodiment, when the sheet leading end portion 2a is sent to the vicinity of the sheet guide 32 when the curled sheet 2 is fed again from the intermediate tray 30, the sheet leading end The part 2 a is blown onto the intermediate tray 30 by air blown from the fan 34. Accordingly, the sheet leading end 2 a is smoothly fed to the nip portion of the pair of sheet re-feed rollers 31 without abutting on the sheet guide 32. Therefore, according to the present embodiment, the sheet leading end 2a does not come into contact with the sheet guide 32 and is not bent, and the sheet leading end 2a is obstructed by the sheet guide 32 and cannot be fed again. There is no. Therefore, in the present embodiment, the sheet 2
Can be reliably sent to the re-feeding path 36 or the sheet discharging path 37. That is, according to the present embodiment, the sheet conveying performance is improved.

[Second Embodiment] FIG. 3 shows a second embodiment of the present invention. The same components as those in the first embodiment are denoted by the same reference numerals, and redundant description will be omitted.

In this embodiment, a sheet deformation correcting path 48 for bending the sheet 2 in a direction opposite to the bending direction of the branch path 23 is formed in the middle of the branch path 23. A conveying roller pair 50 for conveying the sheet 2 along the sheet deformation correcting path 48 is arranged in the middle of the sheet deformation correcting path 48.

In the present embodiment, the sheet 2 sent to the curved branch path 23 is separated by the sheet deformation correcting path 48 into the branch path 2.
By curving the sheet 2 in the direction opposite to the direction 3, the curl of the sheet 2 following the branch path 23 can be suppressed, and the curl amount of the sheet 2 discharged onto the intermediate tray 30 can be reduced.

According to such a configuration, the sheet leading end 2
Since the curl amount of the sheet a is small, the curl of the sheet leading end portion 2a is easily and reliably corrected by the air blown from the fan 34, and the sheet leading end portion 2a is moved along the upper surface of the intermediate tray 30 to the nip portion of the re-feed roller pair 31. Can be sent to

In this embodiment, the sheet deformation correcting path 4 is used.
8 shows a mode in which the transport roller pair 50 is disposed in the middle, but the present invention is not limited to this. The transport roller pairs are disposed upstream and downstream of the sheet deformation correction path 48, and the sheet 2 is transported by these transport roller pairs. The sheet 2 may be conveyed and brought into sliding contact with the sheet deformation correcting path 48 to correct the curl of the sheet 2. That is, the transport roller pair 50 may not be disposed in the middle of the sheet deformation correcting path 48.

In each of the above embodiments, the fan 34 is used as the air blowing means. However, the present invention is not limited to this, and an air blowing nozzle as the air blowing means is provided. (For example, a fan). Such a configuration is effective when a space for installing the fan 34 above the intermediate tray 30 cannot be secured.

Further, in each of the above embodiments, the arm type sensor 28 is used. However, the present invention is not limited to this, and any device capable of detecting the passage of the sheet 2 may be used. May be used.

[0037]

As described above, according to the present invention, when the sheet curled upward is re-fed from the intermediate tray and the leading end of the sheet is fed to the vicinity of the sheet guide, the curled sheet leading end is blown out by air. The sheet is pressed against the upper surface of the intermediate tray by the air blown from the means, and the leading end of the sheet is sent to the nip portion of the pair of re-feed rollers along the upper surface of the intermediate tray, so that the sheet is securely nipped by the nip portion of the pair of re-feed rollers. In addition, the curled sheet leading end does not come into contact with the sheet guide and bend, and the sheet cannot be re-fed due to the curl.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of an image forming apparatus according to a first embodiment of the present invention.

FIG. 2 is a partially enlarged view of FIG.

FIG. 3 is a partially enlarged view of an image forming apparatus according to a second embodiment of the present invention.

FIG. 4 is a schematic configuration diagram of a conventional image forming apparatus.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Image forming apparatus, 2 ... Sheet, 15 ... Fixing device, 17 ... Sheet transport path, 19 ... Sheet transport apparatus, 23 ... Branch path, 30 ... Intermediate tray, 31 ... Re-feeding Roller pair, 32: sheet guide, 34: fan (air blowing means), 35: sheet feed roller,
36: re-feeding path, 37: sheet discharging path, 38: flapper, 48: sheet deformation correcting path, 49: sheet discharging port

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI theme coat ゛ (reference) G03G 15/00 510 G03G 15/00 510 3F100 F term (reference) 2C059 AA01 AA19 BB03 BB11 BB21 DD03 DD08 DD21 2H028 BA05 BA09 BA14 2H072 AB15 BA04 BB08 CA01 CB06 3F049 AA01 CA32 DA14 EA24 FA08 LA02 LA05 LA07 LB01 3F054 AA01 AB01 AC02 AC03 AC05 BA02 BB17 BB21 BB26 BH04 BH07 DA02 DA11 3F100 AA01 BA12 CA03 EA00

Claims (3)

[Claims] A branching path that guides the sheet in a state where the sheet is turned upside down after bending and branching from a sheet conveying path after passing through a fixing device; and an intermediate tray that receives a sheet discharged from the branching path. A sheet feed roller for moving a sheet on the intermediate tray in a predetermined direction; a re-feed roller pair for feeding the sheet moved by the sheet feed roller from the intermediate tray; and a sheet re-feed roller disposed near the re-feed roller pair. A sheet guide for guiding a leading end of a sheet moved by the sheet feed roller to a nip portion of the pair of re-feed rollers, and a sheet guide disposed near the sheet guide and above an intermediate tray, and disposed near the sheet guide. A sheet conveying device, comprising: air blowing means for blowing air toward the upper surface of a tray. 2. The sheet conveying apparatus according to claim 1, wherein a sheet deformation correcting path for bending a sheet in a direction opposite to a bending direction of the branch path is formed in the middle of the branch path. 3. A branch path that is curved and branched from a sheet conveyance path after passing through a fixing device and guides the sheet in a state where the sheet is turned upside down, and an intermediate tray that receives the sheet discharged from the branch path. A sheet feed roller for moving a sheet on the intermediate tray in a predetermined direction; a re-feed roller pair for feeding the sheet moved by the sheet feed roller from the intermediate tray; and a sheet re-feed roller disposed near the re-feed roller pair. A sheet guide for guiding a leading end of a sheet moved by the sheet feed roller to a nip portion of the pair of re-feed rollers; and an intermediate tray disposed near the sheet guide and above the intermediate tray, and near the sheet guide. Air blowing means for blowing air toward the upper surface; and forming an image on a sheet fed from the pair of re-feed rollers. A sheet re-feeding path for returning to a sheet supply path on the upstream side of the means, a sheet discharging path for guiding a sheet fed from the re-feeding roller pair to a sheet discharge opening, and a sheet re-feeding roller in a duplex printing mode. A flapper for guiding the sheet sent from the pair to the sheet re-feeding path, and for guiding the sheet sent from the pair of sheet re-feeding rollers to the sheet discharging path in the face-down sheet discharging mode. An image forming apparatus comprising: