JPH08310706A - Sheet transfer device and image forming device for duplex modes - Google Patents

Abstract

PURPOSE: To discharge a sheet of paper in reverse side without reducing a throughput and a complex control. CONSTITUTION: A path 102 for two sides is provided with a path 117 for discharging paper which branches between a transfer roller 107 located at the lowest part in the downstream of the path 102 for two sides and the branch point 108A of a path 108 for flipping over and discharges a sheet traveling in reverse in the path 102 for two sides to the outside of the device. When the tail end of the sheet discharged in reverse side which passes a fixing roller 100 and is sent to the path 102 for two sides passes at a branch point 117A of the path 117 for discharging the paper, a pair of roller 109 for flipping over are rotated in reverse as shown by a dotted line arrow. The traveling sheet in reverse is carried into the path 117 for discharging paper and is discharged on a tray 120 for discharging paper in the outside of the device through the path 117 for discharging paper.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is provided in an image forming apparatus such as a printer, a facsimile, a copier or the like having a double-sided mode, and a sheet which has been subjected to image formation on the first side is subjected to image formation on the second side. The present invention relates to a double-sided mode sheet conveying device that conveys sheets to a re-feeding stacking means (intermediate tray) for the apparatus.

[0002]

2. Description of the Related Art FIG. 4 shows a conventional image forming apparatus (for example,
1 shows a typical configuration of a double-sided mode sheet conveying device provided in a digital color printer or the like).

The sheet after the transfer (image formation) of the toner image onto the first surface is rotated in the direction of the arrow.
In the process of passing through the nip of No. 00, the transfer toner image is fixed. Then, the sheet that has passed the fixing roller pair 100 is conveyed to the identification fixing roller pair 100 and the conveying roller pair 101 and is sent to the double-sided path 102. in this case,
The flapper 103 for switching paths is the double-sided path 10
2 is opened and the normal paper ejection path 104 is closed.

The sheet sent to the double-sided path 102 is indicated by an arrow a by a plurality of conveying roller pairs 105, 106 and 107.
It is transported like. At this time, the conveying roller pair 105, 1
06 and 107 and the reversing roller pair 109 are rotating in the direction of the solid arrow. And the leading edge of the sheet is a reversing roller pair 1.
When the sheet is nipped by 09, the sheet is conveyed at high speed in the direction of arrow a by the pair of reversing rollers 109 rotating at high speed. At this time, the peripheral speeds of the conveying roller pairs 105, 106 and 107 are also synchronized with the peripheral speed of the reversing roller pair 109. When the trailing edge of the sheet passes the branch point 108A of the reversing path 108, the pair of reversing rollers 109 reverses the rotation while maintaining the high speed rotation, and causes the sheet to flow backward so that the trailing edge side is first and is fed to the reversing path 108. Here, the sheet is turned upside down and sent to a predetermined discharge roller pair 112 corresponding to the sheet size by the transport roller pair 111, and discharged onto the intermediate tray 110 with the image forming surface facing upward by the discharge roller pair 112. To be done.

The timing at which the leading edge of the sheet moving on the double-sided path 102 is clamped by the reversing roller pair 109 and the trailing edge of the sheet moving on the double-sided path 102 passes through the branch point 108A of the reversing path 108. The timing of the determination is determined based on the information detected by the sensor lever 113 installed immediately downstream of the most downstream conveyance roller pair 107.

Further, the branch point (entrance) of the reversing path 108
108A is provided with a sheet guide member (resin sheet such as Mylar) 114 that allows a sheet that passes the double-sided path 102 to pass through but does not pass a sheet that faces the double-sided path 102 toward upstream (reverse flow).

The second sheet is re-fed from above the intermediate tray 110.
After passing the fixing roller pair 100, the sheet on which the toner image has been transferred to the surface is sent to the normal paper ejection path 104 by the identification adhering roller pair 100 and the conveyance roller pair 101, and is ejected outside the machine by the paper ejection roller pair 115. The surface of the sheet is discharged onto the sheet discharge tray 116. In this case, the flapper 103 normally opens the paper discharge path 104 and closes the double-sided path 102.

As described above, when the sheet on which the toner image has been transferred to the first surface is conveyed to the intermediate tray 110, in order to prevent wrinkles and slack from occurring in the sheet,
First, the pair of conveying rollers 105 and 10 of the double-sided path 102
The peripheral speeds of 6 and 107 are synchronized with the peripheral speed of the fixing roller pair 100. Then, the leading edge of the sheet is the reverse roller pair 109.
When it is pinched by the transport rollers 105,
The peripheral speeds of 106 and 107 are synchronized with the peripheral speed of the reversing roller pair 109.

By the way, in some laser beam printers or the like which are connected to an external computer and output information from the computer, the sheet conveying device for the double-sided mode is used to discharge the back surface.

Next, a back side sheet discharging method which has been conventionally performed by using the sheet conveying apparatus for the double sided mode will be described.

Conventionally, after the sheet passing through the fixing roller pair 100 is sent to the double-sided path 102 as shown by an arrow a, the double-sided path 102 is reversely sent as shown by an arrow b to discharge the sheet pair of discharge rollers. Output tray 116 by 115
The paper is ejected upwards.

That is, first, the sheet is conveyed by the fixing roller pair 100, the conveying roller pairs 101, 105, 106, 107 and the reversing roller pair 109. At this time, the conveying roller pairs 105, 106, 107 and the reversing roller pair 109 are rotating at the same speed in the direction of the solid arrow. Then, when the trailing edge of the sheet passes through the nip of the uppermost conveying roller pair 105, the conveying roller pairs 105, 106 and 107 and the reversing roller pair 109 are reversed as indicated by the dotted arrow to reversely flow the sheet at a high speed.

[0013]

However, in the case of the above-mentioned conventional back surface ejection method, the sheet ejected on the back surface reciprocates on the double-sided path 102, and therefore the double-sided path 102.
The next sheet can be sent to the double-sided path 102 only after the sheet that is moving back through the path exits the double-sided path 102. For this reason, when the sheet takes a long time to reciprocate in the double-sided path 102, it is necessary to increase the sheet interval (the distance between the sheets), and it is necessary to set the sheet interval in the back surface discharge mode. Throughput (the number of sheets processed per unit time) is reduced.

For example, in the case of a color image forming apparatus, the driving speed of the fixing roller pair 100 is usually changed according to the material of the sheet and the like. When a thick sheet is used, the fixing roller pair 100 is driven at a low speed. Therefore, in such a case, the time required for the sheet discharged on the back surface to reciprocate in the double-sided path 102 becomes long, and a large sheet interval must be secured.

Further, in order to carry out the back surface paper discharge by the above-mentioned conventional method, each pair of conveying rollers 10 of the double-sided path 102 is used.
The drive of 5, 106 and 107 had to be complicatedly controlled as follows.

That is, (1) until the trailing edge of the sheet passes through the nip of the conveying roller pair 105, each conveying roller pair 10
The peripheral speeds of 5, 106 and 107 are synchronized (substantially coincident) with the peripheral speed of the fixing roller pair 100. (2) When the trailing edge of the sheet passes through the nip of the conveying roller pair 105, the rotation direction of each conveying roller pair 105, 106, 107 is changed from the solid arrow direction to the dotted arrow direction. At the same time, the peripheral speed is synchronized with the peripheral speed of the reversing roller pair 109. (3) When the leading edge of the sheet is nipped by the discharge roller pair 115, the peripheral speed of each of the conveying roller pairs 105, 106, and 107 is set to the fixing roller pair 1.
00 peripheral speed.

In order to enable such control, the fixing roller pair 100, the conveying roller pair 101, and the discharge roller pair 10
1, the driving of the motor M1 is transmitted to each of the conveying roller pairs 1
The drive of the motor M2 is transmitted to 05, 106, and 107, and the drive of the motor M3 is transmitted to the reversing roller pair 109. The arrows between the motors M1, M2 and M3 indicate the relationships during the control of (1), (2) and (3).

Since each of the conveying roller pairs 105, 106 and 107 changes the peripheral speed and the rotation direction, the motor M is used.
2 is a motor capable of changing the driving speed and the driving direction. Similarly, since the reversing roller pair 109 changes the peripheral speed and the rotating direction, the motor M3 is also a motor capable of changing the driving speed and the driving direction.

Therefore, the present invention has been made in view of the above-mentioned circumstances, and does not reduce the throughput, does not complicate the control and drive structure, and can eject the back side paper. An object of the present invention is to provide a sheet conveying device for double-sided mode which can be performed.

[0020]

SUMMARY OF THE INVENTION According to the present invention, there is provided a double-sided path for transporting a sheet having an image formed on the first side toward a re-feeding stacking means, and a branch from a downstream portion of the double-sided path. And a reversing path for reversing the sheet conveyed through the double-sided path, and a reversal conveying means for reversing the sheet conveyed through the double-sided path and feeding it to the reversing path. The present invention relates to a double-sided mode sheet conveying device.

In order to achieve the above object, the present invention provides a sheet which is branched at a part of the double-sided path just upstream of a branch point of the reversing path and which flows backward in the double-sided path. It is characterized in that it has a paper discharge path for discharging paper to.

Further, when the trailing edge of the sheet conveyed through the double-sided path has passed the branch point of the sheet discharge path, the reversing conveying means reversely flows the sheet and sends it to the sheet discharge path. It is characterized by

[0023]

According to the sheet conveying apparatus of the present invention having the above-mentioned structure, the sheet conveyed to the double-sided path for discharging the back side is backflowed by the reversing conveying means and sent to the sheet discharging path. Then, the back side of the sheet is discharged from the sheet discharge path to the outside of the machine.

Therefore, since the sheet discharged on the back side does not reciprocate in the main part of the double-sided path, the next sheet can be continuously fed to the double-sided path.

As a result, for example, even when the fixing means is driven at a low speed, it is not necessary to take a large space between sheets,
Throughput does not decrease.

Further, the sheet of the back side sheet discharged into the double-sided path is discharged to the outside of the machine by the reversing conveying means, and the sheet conveying means of the double-sided path does not participate in the sheet discharging. .

As a result, the control of the sheet conveying means on the double-sided path is not complicated.

[0028]

An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 shows the structure of a double-sided mode sheet conveying device according to the present invention.

In describing the structure of the present double-sided mode sheet conveying device, the same members and the like as those of the conventional double-sided mode sheet conveying device (FIG. 4) are designated by the same reference numerals and are structurally and functionally Descriptions of those that do not change are omitted.

In the sheet conveying device for the double-sided mode, the branch point 1 between the conveying roller pair 107 and the reversing path 108 is set.
08A, the double-sided path 102 has a sheet discharge path 117 that discharges a sheet that flows back through the double-sided path 102 to the outside of the machine. A sheet guide member (a resin such as Mylar) that allows a sheet that goes downstream in the double-sided path 102 to pass through but does not pass a sheet that goes upstream (backflows) in the double-sided path 102 at a branch point 117A of the sheet discharging path 117. A sheet) 119 is provided.

The paper discharge path 117 includes a pair of paper discharge rollers 11.
8 are provided, and the sheets discharged to the outside of the apparatus by the pair of discharge rollers 118 are stacked on the discharge tray 120.

In the sheet conveying device for the double-sided mode,
The drive of the motor M4 is transmitted to the fixing roller pair 100, the conveying roller pair 101, the paper discharge roller pair 115, and the conveying roller pairs 105, 106, and 107. In this case, the pair of conveying rollers 105, 106, 107 is connected to the motor M via a clutch (for example, a one-way rotating clutch) 123.
4 drive is transmitted. Further, the drive of the motor M5 capable of forward and reverse rotation is transmitted to the reverse roller pair 109 and the paper discharge roller pair 118.

Next, the operation of the sheet conveying device for the double-sided mode will be described in the order of the normal sheet discharge mode, the double-sided mode, and the rear sheet discharge mode. <Operation in normal paper ejection mode> Normal paper ejection mode designation key 1
When the normal paper discharge mode is designated by 26, the CPU 12
5 turns on the motor M4 and turns off the clutch 123. Further, the CPU 125 controls a solenoid (not shown) of the flapper 103 so that the flapper 103 opens the normal paper ejection path 104.

As a result, the fixing roller pair 100, the conveying roller pair 101, and the discharge roller pair 115 rotate in the direction of the arrow, and the image-formed sheet that has passed through the fixing roller pair 115 is transferred onto the discharge tray 116 outside the machine. The paper is ejected with the image forming side facing up. <Operation in Duplex Mode> When the duplex mode is designated by the duplex mode designation key 128, the CPU 125 causes the motor M to operate.
4, M5 and clutch 123 are turned on. Also, CP
U125 controls the solenoid of the flapper 103 so that the flapper 103 opens the double-sided path 102.

As a result, the fixing roller pair 100, the conveying roller pair 101, the paper discharge roller pair 115, and the conveying roller pair 10
5, 106, 107, the reversing roller pair 109, and the discharge roller pair 118 rotate in the direction of the solid line arrow, and the fixing roller pair 10
The first-side image-formed sheet that passed 0 is double-sided pass 1
Sent to 02.

When the leading edge of the sheet moving on the double-sided path 102 is nipped by the pair of reversing rollers 109, the CPU 125 turns off the clutch 123 and sets the pair of conveying rollers 106, 107, 108 in a rotation-free state. Let Therefore, the sheet is conveyed at high speed by the pair of reversing rollers 109.

When the trailing edge of the sheet passes the branch point 108A of the reversing path 108, the CPU 125 changes the driving direction of the motor M5 to reverse the pair of reversing rollers 109 in the direction of the dotted arrow. As a result, the sheet flows backward and is sent to the reversing path 108. Here, the sheet is turned upside down, and is conveyed to a predetermined discharge roller pair 112 corresponding to the sheet size by the conveyance roller pair 111, and the image formation surface is turned upward by the discharge roller pair 112 and the intermediate tray 1 is turned on.
10 is discharged.

The CPU 125 is installed immediately downstream of the conveying roller pair 107 at the timing when the leading edge of the sheet is nipped by the reversing roller pair 109 and when the trailing edge of the sheet passes the branch point 108A of the reversing path 108. The determination is made based on the information detected by the sensor lever 113. The position at a distance B from the sensor lever 113 is the passing position of the branch point 108A. <Operation in back side paper ejection mode> Back side paper ejection mode designation key 1
When the back surface discharge mode is designated by 27, the CPU 12
5 turns on the motors M4, M5 and the clutch 123. Further, the CPU 125 controls the solenoid of the flapper 103 so that the flapper 103 opens the double-sided path 102.

As a result, the fixing roller pair 100, the conveying roller pair 101, the paper discharge roller pair 115, and the conveying roller pair 10
5, 106, 107, the reversing roller pair 109, and the discharge roller pair 118 rotate in the direction of the solid line arrow, and the fixing roller pair 10
The image-formed sheet that has passed 0 is sent to the double-sided path 102.

When the leading edge of the sheet moving on the double-sided path 102 is nipped by the reversing roller pair 109, the CPU 125 turns off the clutch 123 and sets the conveying roller pairs 106, 107 and 108 in a rotation-free state. Let Therefore, the sheet is conveyed at high speed by the pair of reversing rollers 109.

When the trailing edge of the sheet passes the branch point 119A of the sheet discharging path 117, the CPU 125 changes the driving direction of the motor M5 to reverse the reverse roller pair 109 in the direction of the dotted arrow. As a result, the sheet flows backward and is sent to the paper discharge path 117. The sheet sent to the sheet discharge path 117 is discharged onto the sheet discharge tray 120 outside the apparatus with the image forming surface facing downward by the sheet discharge roller pair 118 rotating in the direction of the dotted arrow.

It should be noted that the CPU 125 detects the timing when the leading edge of the sheet is nipped by the reversing roller pair 109 and the timing when the trailing edge of the sheet passes the branch point 117A of the sheet discharging path 117 based on the information detected by the sensor lever 113. I judge it. The position at a distance A from the sensor lever 113 is the passing position of the branch point 117A.

Arrows c and d show the flow of the sheet in the back surface discharge mode.

FIG. 2 shows an example of the overall configuration of a color image forming apparatus (digital color printer) equipped with the double-sided mode sheet conveying device of the present invention.

Color This image forming apparatus has a digital color image reader section in the upper part of the image forming apparatus main body and a digital color image printer section in the lower part.

In the reader unit, the original 30 is placed on the original table glass 31 and exposed and scanned by the exposure lamp 32, so that the reflected light image from the original 30 is condensed by the lens 33 on the full color sensor 34, and color separation is performed. Get the image signal. The color-separated image signal is processed by a video processing unit (not shown) through an amplifier circuit (not shown), and is sent to the printer section.

In the printer section, the photosensitive drum 1 as an image bearing member is rotatably supported in the direction of the arrow, and a pre-exposure lamp 11, a corona charger 2, a laser exposure optical system 3, and a potential sensor 12 are provided around the photosensitive drum 1. , Four developing devices 4y, 4c, 4m, 4Bk of different colors, on-drum light amount detecting means 1
3, the transfer device 5, and the cleaning device 6 are arranged.

In the laser exposure optical system 3, the image signal from the reader section is converted into an optical signal by a laser output section (not shown), and the converted laser light is reflected by the polygon mirror 3a, and the lens 3b and the mirror. It is projected onto the photosensitive drum 1 through 3c.

At the time of image formation in the printer section, the photosensitive drum 1 is rotated in the direction of the arrow, and the photosensitive drum 1 after the charge is removed by the pre-exposure lamp 11 is uniformly charged by the charger 2 and light is separated for each separated color. The image E is irradiated to form a latent image.

Next, a predetermined developing device is operated to develop the latent image on the photosensitive drum 1 to form a toner image based on resin on the photosensitive drum 1. The developing device is an eccentric cam 24.
By the operations of y, 24c, 24m, and 24Bk, the photosensitive drum 1 is selectively approached according to each separated color.

Further, the sheet S supplied with the toner image on the photosensitive drum 1 from the cassette 35 or 36 to the position facing the photosensitive drum 1 via the transport system 37 and the transfer device 5.
Transfer to. In this example, the transfer device 5 includes a transfer drum 5a,
Transfer charger 5b, suction charger 5c for electrostatically attracting the sheet S, suction roller 5g facing the charger, and inner charger 5
d, a recording material carrying sheet 5f made of a dielectric material is integrally stretched in a cylindrical shape in an opening area of a peripheral surface of a transfer drum 5a which is rotatably supported and has an outer charger 5e. ing. The recording material carrying sheet 5f uses a dielectric sheet such as a polycarbonate film.

As the drum-shaped transfer device, that is, the transfer drum 5a is rotated, the toner image on the photosensitive drum 1 is transferred onto the sheet S carried on the recording material carrying sheet 5f by the transfer charger 5b.

In this way, a desired number of color images are transferred to the sheet S sucked and conveyed to the recording material carrying sheet 5f to form a full color image.

In the case of forming a full-color image, when the transfer of the four color toner images is completed in this way, the sheet S is separated from the transfer drum 5a by the action of the separation claw 8a, the separation push-up roller 8b and the separation charger 5h. After the transfer, the photosensitive drum 1 is subjected to the image forming process again after cleaning the residual toner on the surface with the cleaning device 6.

Further, in order to prevent the powder from being scattered and adhered on the recording material carrying sheet 5f of the transfer drum 5a and the oil being adhered on the sheet, the brush 14 is interposed via the fur brush 14 and the recording material carrying sheet 5f. The backup brush 15 facing the sheet, the oil removing roller 16 and the recording material carrying sheet 5
Cleaning is performed by the action of the backup brush 17 that faces the roller 16 via f. Such cleaning should be done before or after image formation, or jam (paper jam)
When it occurs, it will be done at any time.

Further, in this example, the eccentric cam 25 is operated at a desired timing and the cam follower 5i integrated with the transfer drum 5f is operated, whereby the gap between the recording material carrying sheet 5a and the photosensitive drum 1 is changed. Can be set arbitrarily. For example, during standby or when the power is off, the transfer drum and the photosensitive drum are separated from each other.

As described above, the sheet S separated from the transfer drum 5a is sent to the fixing roller pair 100. Then, the toner image is fixed on the sheet surface by being heated and pressed in the process of passing through the identification fixing roller pair 100.

Sheet S that has passed through the fixing roller pair 100
In the normal paper discharge mode, the paper is discharged onto the paper discharge tray 116 outside the machine through the paper discharge path 104. Further, in the case of the back surface paper discharge mode, the paper is discharged onto the paper discharge tray 120 outside the machine through the double-sided path 102 and the paper discharge path 117. In the double-sided mode, the sheet is discharged onto the intermediate tray 110 through the double-sided path 102 and the reverse path 108.

Sheets S stacked on the intermediate tray 110
Are fed by the sheet re-feeding roller 47 in order from the uppermost sheet S. Then, the fed-out sheets S are separated one by one by the separation roller pair 48, and again by the conveyance roller pairs 43, 44, 45.
Sent to. After that, the toner image is transferred to the second surface of the sheet S, and when the sheet S passes through the fixing roller pair 100, the sheet S is discharged onto the sheet discharge tray 116 outside the machine through the normal sheet discharge path 104. .

FIG. 3 shows another example of the overall structure of a color image forming apparatus (digital color printer) equipped with the double-sided mode sheet conveying device of the present invention.

The present color image forming apparatus has two cassette paper feeding units 50 and 51 and one manual paper feeding unit 58, and the sheet S is selectively selected from these paper feeding units 50, 51 and 58. Will be delivered.

In each of the sheet feeding units 50, 51 and 58, the sheets S stacked on the cassettes 50A and 51A or the tray 58A are fed out by the sheet feeding roller 52 in order from the uppermost sheet. Then, the sheet S fed out by the sheet feeding roller 52 is sent to the registration roller pair 57 in which only the uppermost sheet is separated by the separation roller pair 53 including a feed roller and a retard roller and the rotation of which is stopped.

In this case, the sheet S fed from the cassettes 50A and 51A having a long distance to the registration roller pair 57 is relayed to the plurality of conveyance roller pairs 54 to 56 and sent to the registration roller pair 57.

Sheet S sent to registration roller pair 57
When the leading edge of the sheet hits the nip of the registration roller pair 57 to form a predetermined loop, the movement is temporarily stopped. By forming this loop, the skewed state of the sheet S is corrected.

A long conveying belt (endless belt) 59 is installed in a substantially horizontal state downstream of the registration roller pair 57. The conveyor belt 59 rotates counterclockwise. A plurality of photosensitive drums 60 to 6 carrying color toner images of different colors are provided on the conveyor belt 59.
3 are sequentially arranged along the sheet conveying direction.

Here, the most upstream photosensitive drum 60 carries a magenta toner image, the next photosensitive drum 61 carries a cyan toner image, and the next photosensitive drum 62 carries a yellow toner image. Then, the most downstream photosensitive drum 63 carries a black toner image.

In this color image forming apparatus, a plurality of originals are sequentially set at predetermined positions on the original plate (platen glass) 72 by an automatic original feeder (not shown). Then, the color image of the document set on the document table 72 is read by the reading optical system 73. The read color image is decomposed into color components of magenta, cyan, yellow, and black by the CCD element 74 and temporarily stored in an image memory (not shown).

The image information stored in the image memory is the
The photosensitive drums 60 to 6 which are sequentially rotated clockwise for each color component by the writing optical system 75 including the scanner.
Written on 3.

First, the projection of the laser light LM based on the image of the magenta component is started on the most upstream photosensitive drum 60, and an electrostatic latent image is formed on the photosensitive drum 60. This electrostatic latent image is visualized by magenta toner supplied from the developing device 64.

Next, the projection of the laser beam LC based on the image of the cyan component is started on the photosensitive drum 61, and an electrostatic latent image is formed on the photosensitive drum 61. This electrostatic latent image is visualized by the cyan toner supplied from the developing device 65.

Next, laser light L on the photosensitive drum 61
After a lapse of a predetermined time from the start of the projection of C, the projection of the laser beam LY based on the image of the yellow component is started on the photosensitive drum 62 to form an electrostatic latent image on the photosensitive drum 62. This electrostatic latent image is visualized by the yellow toner supplied from the developing device 66.

Next, the laser light L on the photosensitive drum 62
After a lapse of a predetermined time from the start of Y projection, the laser beam LB based on the image of the black component is started to be projected on the photosensitive drum 63 to form an electrostatic latent image on the photosensitive drum 63. This electrostatic latent image is visualized by the black toner supplied from the developing device 67.

Around the photosensitive drums 60 to 63, primary chargers 68 to 71 for uniformly charging the photosensitive drums 60 to 63, and the photosensitive drum 60 after the toner image transfer.
Cleaners 72 to 75 and the like for removing the toner adhering to the upper surfaces of 63 to 63 are installed.

The sheet S sent to the registration roller pair 57 and corrected in the skewed state starts rotation at a timing at which the toner image on the most upstream photosensitive drum 60 and the sheet front end are aligned with each other. It is sent onto the conveyor belt 59 rotating counterclockwise by the pair 57.

The sheet S sent onto the conveyor belt 59 is transferred by the conveyor belt 59 to the downstream side, and the transfer portion between the photosensitive drum 60 and the transfer charger 76, the photosensitive drum 61 and the transfer charger 77. Transfer section between and photosensitive drum 6
2 and the transfer charger 78, and the transfer portion between the photosensitive drum 63 and the transfer charger 79 are sequentially passed, whereby toner images of magenta, cyan, yellow, and black are formed on the sheet surface. Are overlaid and transferred.

The most downstream photosensitive drum 63 and the transfer charger 79
The sheet S that has passed the transfer portion between the
To the fixing roller pair 35. Then, while the sheet S passes through the nip of the fixing roller pair 100, it is heated and pressed to fix the transferred toner image on the sheet surface.

Sheet S that has passed through fixing roller pair 100
In the normal paper discharge mode, the paper is discharged onto the paper discharge tray 116 outside the machine through the paper discharge path 104. Further, in the case of the back surface paper discharge mode, the paper is discharged onto the paper discharge tray 120 outside the machine through the double-sided path 102 and the paper discharge path 117. In the double-sided mode, the sheet is discharged onto the intermediate tray 110 through the double-sided path 102 and the reverse path 108.

Sheets S stacked on the intermediate tray 110
Are sequentially fed by the re-feed roller pair 80 from the uppermost sheet S. The fed-out sheets S are separated one by one by the separation roller pair 81, one by one by the conveyance roller pair 81, and the conveyance roller pair 56.
Is again sent to the registration roller pair 57. After that, the toner image is transferred to the second surface of the sheet S,
After passing through the fixing roller pair 100, the normal paper discharge path 10
The sheet is discharged to the sheet discharge tray 116 outside the machine through the sheet No. 4.

[0080]

As described above, in the double-sided mode sheet conveying device of the present invention, the sheet that has branched from the upstream side of the branch point of the reversing path and flows backward in the double-sided path is discharged to the outside of the machine. A paper discharge path for paper is provided, and when the trailing edge of the back-side discharged sheet fed to the double-sided path has passed the branch point of the paper discharge path, the reversing conveyance means is reversed to discharge the reverse sheet. Since the paper is fed to the paper path, there is an advantage that the throughput is not reduced even when the back surface paper is discharged, and the control is not complicated.

[Brief description of drawings]

FIG. 1 is a vertical cross-sectional side view showing the configuration of a double-sided mode sheet conveying device according to an embodiment of the present invention.

FIG. 2 is a vertical cross-sectional side view showing an example of the overall configuration of a color image forming apparatus (laser beam printer) provided with a double-sided mode sheet conveying device of the present invention.

FIG. 3 is a vertical cross-sectional side view showing another example of the overall configuration of a color image forming apparatus (laser beam printer) provided with the double-sided mode sheet conveying device of the present invention.

FIG. 4 is a vertical cross-sectional side view showing a configuration of a sheet conveying device for a double-sided mode of a conventional example.

[Explanation of symbols]

1, 60 to 63 Photosensitive drum (image forming means) 100 Fixing roller pair (fixing means) 102 Double-sided path (path) 104 Normal paper discharge path (path) 105 to 107 Conveying roller pair (sheet conveying means) 108 Reversing Path 108A Reversal path branch point 109 Reversal roller pair (reversal conveyance means) 110 Intermediate tray (refeed stacking means) 113 Sensor lever (sheet detection means) 114, 119 Sheet guide member 117 Ejection Paper path (path) 117A Branch point of paper discharge path 118 Paper discharge roller pair (paper discharge means) 123 Clutch (clutch means) M4 motor (first drive source) M5 motor (second drive source)

Claims (11)

[Claims] 1. A double-sided path for conveying a sheet on which an image has been formed on the first side toward a re-feed stacking means, and a double-sided path branched from a downstream portion of the double-sided path. Sheet conveyance for double-sided mode, which comprises a reversal path for reversing the conveyed sheet and a reversal conveying means for reversing the conveyed sheet through the double-sided path and feeding it to the reversal path. In the apparatus, the double-sided path has a sheet discharge path that branches at a portion immediately upstream of a branch point of the reversal path and discharges a sheet that flows backward through the double-sided path to the outside of the machine. A sheet conveying device for double-sided mode. 2. When the trailing edge of the sheet conveyed through the double-sided path passes through the branch point of the sheet discharge path, the reversal conveying means reversely flows the sheet and feeds the sheet into the sheet discharge path. 2. The sheet conveying device for double-sided mode according to claim 1, wherein. 3. The double-sided mode sheet transporting apparatus according to claim 1, wherein a plurality of sheet transporting means for transporting a sheet downstream are installed in the double-sided path. 4. The sheet discharge path is branched between the sheet conveying unit located at the most downstream side of the double-sided path and the branch point of the reversing path. Sheet transport device for double-sided mode. 5. The double-sided mode sheet transporting device according to claim 3, wherein the drive of the first drive source is transmitted to the respective sheet transporting means of the double-sided path via the clutch means. 6. The sheet conveying apparatus for a double-sided mode according to claim 1, wherein the sheet discharging path is provided with a sheet discharging unit that discharges the sheet to the outside of the machine. 7. The double-sided mode sheet conveying device according to claim 6, wherein the driving of a second drive source capable of forward and reverse rotation is transmitted to the reversing conveying unit and the sheet discharging unit. 8. A sheet guide member at a branch point of the reversing path and the sheet discharging path of the double-sided path, which allows a sheet going from upstream to downstream but not a sheet going from downstream to upstream. The sheet conveying device for double-sided mode according to claim 1, wherein the sheet conveying device is provided. 9. The double-sided mode sheet according to claim 1, wherein the double-sided path is provided with sheet detecting means for setting a timing for switching the driving direction of the reversing transporting means. Transport device. 10. The double-sided mode sheet transport according to claim 1, wherein the double-sided path is branched from a normal paper-discharge path for normally discharging the sheet that has passed through the fixing unit to the outside of the apparatus. apparatus. 11. An image forming unit that forms a toner image on a fed sheet, a fixing unit that fixes the toner image formed by the image forming unit, and a sheet that has passed through the fixing unit is re-fed. Re-loading loading means for temporarily loading for storage, and any one of claims 1 to 10.
2. An image forming apparatus, comprising: the double-sided mode sheet transporting device.