JP2002274730A - Image forming apparatus, printer and copier - Google Patents

Abstract

(57) [Problem] To provide a simple mechanism for preventing lateral displacement and skew of a sheet to be reversely discharged. When a sheet on which an image is formed on one side is reversely discharged, the sheet on which an image is formed on one side and discharged from an image forming unit is sent to a re-conveying path, and the sheet is forwarded. First forward / reverse transport rollers 32, 3 driven to rotate in the forward direction
3, the sheet is conveyed to a sheet conveying path to a predetermined position, and then the first forward / reverse conveying rollers 32 and 33 are driven to rotate in the reverse direction to switch back the sheet to the reverse sheet discharging path 31. Feed in and eject. Prevents the laterally displaced or skewed paper in the width direction caused by the paper being inverted being not discharged in the middle of the conveyance in the re-conveying path 29 and being freed in the middle of the conveyance. it can.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention enables efficient continuous image formation, and furthermore, a function of double-sided printing,
The present invention relates to an image forming apparatus having a reversal sheet discharging function of discharging a sheet on which printing has been performed with the print surface facing down in the order of pages, a printer and a copier using the image forming apparatus.

[0002]

2. Description of the Related Art Conventionally, there has been known an image forming apparatus having a function of double-sided printing, and a function of reversing paper discharge in which a printed sheet is discharged in a page order with the print surface facing down.

FIG. 1 shows a schematic structure of such an image forming apparatus.
5 will be described. The image forming apparatus includes a sheet storage unit 101 in which sheets are stacked and held, an image forming unit 104 that includes a photoconductor 102, a developing unit 103, and the like, and forms an image on a sheet that has been fed, and an image-formed sheet. The paper transport path 10 through which the paper is transported is provided between the paper storage unit 101 and the image forming unit 104.
6 are provided.

[0006] On the paper discharge side of the image forming unit 104, a direct paper discharge path 107 in which the paper on which the image has been formed is conveyed toward the paper discharge unit 105, and the paper on which the image has been formed is printed on both sides or reversed. And a paper transport path 108 for transporting the paper. A switching claw 109 for switching the transport direction of the paper discharged from the image forming unit 104 to the direct paper discharge path 107 or the paper transport path 108 is provided at a branch point between the direct paper discharge path 107 and the paper transport path 108. I have.

[0005] A reversing path 110 for switching back the sheet conveyed through the sheet conveying path 108 is provided at the leading end side of the sheet conveying path 108. In the reversing path 110, there is provided a reversing roller 111 which is movable to a contact / separation position (up / down position), switches the paper back by being nipped and rotationally driven.

A re-conveying path 112 for conveying the sheet switched back in the reversing path 110 to the image forming unit 104 again for double-sided printing is provided in front of the conveying direction of the sheet switched back.
And a reverse discharge path 113 for discharging the paper to the paper discharge unit 105 in page order with the print surface facing down. The re-conveying path 112 is disposed below the reversing path 110, and at a branch point between the re-conveying path 112 and the reversing discharge path 113, the conveying direction of the sheet switched back in the reversing path 110 is changed to the re-conveying path 112. Alternatively, a switching claw 114 for switching to the reverse discharge path 113 is provided.

In the case where image formation is continuously performed by such an image forming apparatus, a sheet separated and fed from the sheet storage unit 101 or a sheet re-conveyed through the re-conveying path 112 is used. The image forming unit 10 passes through the transport path 106 one after another.
4 to form an image on each sheet one after another. Each sheet is temporarily stopped at a position where it comes into contact with the registration roller 115, and sent to the image forming unit 104 at a timing when an image is formed at an appropriate position on the sheet.

When performing double-sided printing in this image forming apparatus, the switching claw 109 is switched so that the sheet on which image formation on one side has been completed is conveyed to the sheet conveying path 108, and the sheet is The sheet is fed into the reversing path 110 via the conveyance path 108. When the sheet fed into the reversing path 110 is switched back by the action of the flipping roller 111, the switching claw 114 is switched so that the sheet is fed to the re-conveying path 112, and the sheet is re-conveyed. The sheet is sent to the image forming unit 104 again via the path 112 and the sheet conveying path 106. As a result, image formation (double-sided printing) is performed on the other side of the sheet, and the sheet on which double-sided printing has been performed is discharged directly to the sheet discharging unit 105 via the sheet discharging path 107.

In the case of performing reverse discharge in this image forming apparatus, the switching claw 109 is switched so that the sheet on which image formation on one side has been completed is conveyed to the sheet conveying path 108, and the sheet is discharged. The sheet is fed into the reversing path 110 via the sheet conveying path 108. Then, when the sheet fed into the reversing path 110 is switched back by the action of the flipping roller 111, the switching claw 114 is switched so that the sheet is fed to the reversing sheet discharging path 113, and the sheet is turned over. The paper discharge unit 105 is passed through the paper discharge path 113
Paper. The paper is discharged in a page order with the print surface facing downward, that is, so-called reverse discharge.

Here, in the image forming apparatus as shown in FIG. 15, the sheet conveyed through the sheet conveying path
10, the sheet is temporarily set in a free state by being thrown into the reversing path 110, and the sheet once set in the free state in the reversing path 110 is nipped by the reversing roller 111 to be switched back. Sending.

[0011]

However, the paper transport path 1
When the sheet conveyed through the sheet 08 is sent to the reversing path 110 and once becomes free, the sheet may be laterally shifted or skewed in the sheet width direction.

For this reason, it is necessary to provide a jogger mechanism (not shown) for correcting the lateral deviation of the sheet in the reversing path 110 on the reversing path 110. When such a jogger mechanism is provided, As a result, the number of parts increases and the mechanism becomes complicated, and the cost of the image forming apparatus increases.

When no jogger mechanism is provided,
The paper that has been inverted and discharged onto the paper discharge unit 105 is uneven, and the post-processing takes time and effort.

SUMMARY OF THE INVENTION An object of the present invention is to prevent a laterally displaced or skewed sheet to be inverted and discharged by a simple mechanism.

Another object of the present invention is to prevent a laterally displaced or skewed sheet to be inverted and discharged by a simple mechanism even when an image is formed at a high speed.

[0016]

According to an aspect of the present invention, there is provided an image forming apparatus, comprising: a sheet storage section for stacking and holding sheets; and a separation sheet feeding section for separating and feeding sheets one by one from the sheet storage section. An image forming unit that forms an image on a fed sheet, a paper transport path from the paper storage unit to the image forming unit, and a paper transport path that is connected in the middle of the paper transport path and transported along the paper transport path. Path, into which the paper fed to the reverse path is fed back to the paper transport path by switching back the paper fed to the reverse path, and the preceding sheet fed from the reverse path and fed into the reverse path. A sheet reversing means that can be switched to an open state that allows at least a part of the subsequent sheet to overlap, and between a sheet discharge side of the image forming unit and an upstream side of the reversing path of the sheet conveying path. Connected to A feed path, a reverse discharge path branched from the middle of the re-conveyance path and connected to the sheet discharge section, and a re-conveyance path provided downstream of a branch point of the reverse discharge path in the re-conveyance path. A first forward / reverse transport roller capable of switching between forward and reverse rotation in a forward rotation direction for transporting the paper fed to the transport path toward the paper transport path and a reverse rotation direction for switching back the paper and feeding the paper to the reverse discharge path. And

Therefore, the sheets stacked and held in the sheet storage section are separated and fed one by one by the separating sheet feeding means and conveyed through the sheet conveying path, and the sheet conveyed through the sheet conveying path is sent to the reversing path, After being temporarily stopped in the reversing path, the sheet is switched back by the sheet reversing means, sent out from the reversing path to the image forming section, and an image is formed on the sheet sent to the image forming section.

When the sheet fed into the reversing path is switched back, by controlling the speed of feeding the sheet to the reversing path, the speed of feeding the sheet from the reversing path, the timing of feeding the sheet from the reversing path, and the like, The interval between sheets that are switched back and sent to the image forming unit can be reduced. In other words, even if there is a variation in the timing of feeding paper from the paper storage unit or a variation in the transport speed during transport to the reversing path, the feeding of the paper to the image forming unit is accurately maintained at a small interval. Therefore, the productivity of the image forming operation in the image forming apparatus can be improved.

When performing double-sided printing, a sheet on which an image is formed on one side and discharged from the image forming unit is sent to the re-conveying path, and the first forward / reverse conveying roller is driven to rotate in the normal direction. As a result, the paper is sent to the paper transport path.
The sheet sent out to the sheet conveying path in this way is sent again to the reversing path, switched back on the reversing path, sent again to the image forming section, and forming an image on the other side of the sheet (double-sided printing). ) Is performed. When the sheet sent from the re-conveying path to the sheet conveying path is conveyed downstream from the branch point of the reversing sheet discharging path in the re-conveying path, the first sheet is fed.
Since the state of being held by the forward / reverse transport rollers is maintained, lateral displacement and skew do not occur.

In the case of performing the reverse discharge, a sheet on which an image is formed on one side and discharged from the image forming section is sent to the re-conveying path, and the first normal-reverse conveying is driven to rotate in the normal direction. The roller conveys the sheet toward a sheet conveying path to a predetermined position. Then, after the sheet is conveyed to a predetermined position on the re-conveying path, the sheet is switched back by rotating the first forward / reverse conveying roller in the reverse direction and fed to the reversing sheet discharging path. Then, the paper is discharged to the paper discharge section. At the time of the reverse discharge, the sheet fed into the re-conveying path is nipped by the first forward / reverse rotation conveying roller which is driven to rotate in the normal direction, and thereafter, the first forward / reverse rotation conveying roller nipping the sheet. Is rotated in the reverse direction so that the sheet is fed to the reverse discharge path, so that the sheet to be reversely discharged does not become free during the conveyance, and the sheet being conveyed becomes free during the conveyance. A lateral shift and a skew in the paper width direction caused by the state are prevented.

According to a second aspect of the present invention, in the image forming apparatus according to the first aspect, a downstream portion of the re-conveying path downstream of a branch point of the reversing sheet discharging path is fed to the re-conveying path. A passing area where a sheet and a preceding sheet which is switched back on the re-conveying path and sent to the reverse sheet discharging path is provided, and the first forward / reverse conveying roller is provided outside the passing area.

Accordingly, while the first forward / reverse transport roller is driven to rotate in the reverse direction to feed the preceding sheet from the re-transport path to the reverse discharge path, the succeeding sheet and the preceding sheet are passed in the passing area. The paper can be fed into the re-conveying path while passing each other, and even if the interval between the papers to be reversed is narrowed due to the improvement in the productivity of the image forming work, the papers can be successively reversed and discharged. it can.

Since the first forward / reverse transport roller is provided outside the passing area between the preceding sheet and the succeeding sheet, the first forward / reverse transport roller is driven to rotate in the reverse direction to feed the preceding sheet. There is no inconvenience that the subsequent sheet sent to the re-conveying path when the sheet is fed to the reverse sheet discharging path reaches the first forward / reverse conveying roller.
When the sheet reaches the forward / reverse transport roller, the state of nipping the preceding sheet by the first forward / reverse transport roller has been completed.
The first forward / reverse transport roller can be driven to rotate in the forward direction to pinch subsequent paper, and the reverse discharge using the first forward / reverse transport roller can be performed smoothly.

According to a third aspect of the present invention, in the image forming apparatus according to the first or second aspect, the first forward / reverse transport roller is switched between forward / reverse rotation by a motor connected to the first forward / reverse transport roller. This is performed by switching between normal and reverse rotations.

Therefore, the switching between the forward and reverse rotation of the first forward / reverse transport roller can be performed reliably and accurately.

The invention described in claim 4 is the first to third aspects of the present invention.
In the image forming apparatus according to any one of the above, a sheet edge detection sensor that detects an end of a sheet conveyed through the re-conveyance path is provided upstream of a branch point of the reversing sheet discharge path in the re-conveyance path. The rotation of the first forward / reverse transport roller is switched in the reverse direction at a preset timing after the detection of the sheet edge by the sheet edge detection sensor.

Therefore, even if the size of the sheet to be reversely discharged is different, the first forward / reverse transport roller is switched to the reverse direction at the timing when the leading end of the sheet in the reverse discharge direction reaches a predetermined position. be able to.

The invention according to claim 5 is the invention according to claims 1 to 4
In the image forming apparatus according to any one of the above, in the vicinity of a branch point of the reversing sheet discharge path in the re-conveying path and downstream of the branch point, a rotational drive is performed in a direction to feed a sheet to the reversing sheet discharging path. The reversing roller is provided so as to be switchable between a sheet feeding state in which the sheet is nipped and conveyed and an open state in which the sheet is nipped to be released.

Therefore, when a small-sized sheet is to be inverted and discharged, the sheet can be fed to the inverted discharge path by rotating the reversing roller. In addition, by switching the reversing roller to the release state, it is possible to smoothly feed the succeeding sheet into the re-conveying path during the passing conveyance.

According to a sixth aspect of the present invention, in the image forming apparatus of the fifth aspect, the reversing roller and the first forward / reverse transport roller, which are driven to rotate in a direction for feeding the sheet into the reversing sheet discharge path, , At the same peripheral speed.

Therefore, when the sheet is fed to the reversing discharge path, the sheet is prevented from being pulled or loosened between the reversing roller and the first forward / reverse transport roller, and the reversing sheet can be smoothly discharged.

According to a seventh aspect of the present invention, in the image forming apparatus according to the fifth or sixth aspect, a reverse discharge roller that is driven to rotate in a direction for transporting a sheet to the sheet discharge portion is provided on the reverse discharge path. The reverse discharge roller is disposed at a position where the subsequent sheet conveyed through the re-conveyance path sandwiches the preceding sheet that has been reversely discharged before reaching the reverse roller.

Therefore, when the reverse sheet is discharged while the preceding sheet and the subsequent sheet are conveyed by passing each other, and when the subsequent sheet conveyed on the re-conveyance path reaches the reversing roller, the reversing roller is used for the passing sheet. Although the sheet must be released, the preceding sheet sent to the reversing sheet discharge path before the subsequent sheet reaches the reversing roller is sandwiched by the reversing sheet discharging roller, so that the reversing sheet can be smoothly discharged. .

[0034] The invention described in claim 8 is the invention according to claims 2 to 7.
In the image forming apparatus according to any one of the above, the sheet fed to the re-conveying path within the range that is within the passing area or outside the passing area depending on the size of the sheet to be reversely discharged, the paper conveying path And a second forward / reverse transport roller capable of switching between forward / reverse rotation in a forward direction for transporting the paper toward the reverse direction and a reverse direction for switching the sheet back and sending the sheet to the reverse sheet discharge path. It is provided to be switchable between a paper feed state in which the paper is nipped and conveyed and an open state in which the paper is nipped to be released.

Therefore, when the passing area changes due to the difference in the sheet size and the second forward / reverse transport roller is outside the passing area, the second forward / reverse transport roller is replaced with the first forward / reverse transport roller. In the same manner as described above, switching between the normal rotation direction and the reverse rotation direction is performed, and the reverse discharge of the sheet can be performed. Further, when the second forward / reverse transport roller is in the passing area, the second forward / reverse transport roller is switched to the open state at a timing when the preceding paper and the subsequent application pass each other, so that the leading paper and the preceding paper are switched. The reversal ejection performed while passing the succeeding paper can be performed smoothly.

According to a ninth aspect of the present invention, there is provided a paper storage unit for stacking and holding paper, a separation paper feeding unit for separating and feeding paper one by one from the paper storage unit, and forming an image on the fed paper. An image forming unit, a paper transport path from the paper storage unit to the image forming unit, a reversing path that is connected in the middle of the paper transport path and feeds the paper transported through the paper transport path, A sending state in which the sheet sent to the reversing path is switched back and sent to the sheet conveying path,
A sheet reversing means that can be switched to an open state that allows at least a part of a preceding sheet fed from the reversing path and a succeeding sheet fed to the reversing path to overlap with each other; A re-conveying path connected between the sheet discharging side and the upstream side of the reversing path of the sheet conveying path, and a reversing sheet discharging path branched from the middle of the re-conveying path and connected to the sheet discharging unit. A forward direction in which the sheet fed to the re-conveying path is provided downstream of the branch point of the reversing sheet discharging path in the re-conveying path, and the sheet is switched back. A forward / reverse transport roller capable of switching between forward and reverse rotation in a reverse direction for feeding the paper into the reverse paper discharge path; and a reverse discharge roller provided on the reverse paper discharge path and rotationally driven in a direction for transporting the paper to the paper discharge section. Paper rollers,
And a passing area provided on the transport path so that a succeeding sheet fed on the re-feed path and a preceding sheet switched back on the re-feed path and fed to the reverse discharge path pass each other. The forward / reverse transport roller is disposed outside the printer, and the distance between the reverse discharge roller and the forward / reverse transport roller is set to be smaller than the minimum sheet passing length of usable paper.

Therefore, the sheets stacked and held in the sheet storage section are separated and fed one by one by the separating sheet feeding means and conveyed through the sheet conveying path. The sheet conveyed through the sheet conveying path is sent to the reversing path, After being temporarily stopped in the reversing path, the sheet is switched back by the sheet reversing means, sent out from the reversing path to the image forming section, and an image is formed on the sheet sent to the image forming section.

When the paper fed into the reversing path is switched back, by controlling the speed of feeding the paper to the reversing path, the speed of feeding the paper from the reversing path, the timing of feeding the paper from the reversing path, and the like, The interval between sheets that are switched back and sent to the image forming unit can be reduced. In other words, even if there is a variation in the timing of feeding paper from the paper storage unit or a variation in the transport speed during transport to the reversing path, the feeding of the paper to the image forming unit is accurately maintained at a small interval. Therefore, the productivity of the image forming operation in the image forming apparatus can be improved.

In the case of performing double-sided printing, a sheet on which an image is formed on one side and ejected from the image forming unit is sent to the re-conveying path, and the forward / reverse conveying roller is driven to rotate in the normal direction. The sheet is sent out to the sheet transport path. The sheet sent out to the sheet conveying path in this way is sent again to the reversing path, switched back on the reversing path, sent again to the image forming section, and forming an image on the other side of the sheet (double-sided printing). ) Is performed. When the sheet sent from the re-conveying path to the sheet conveying path is conveyed downstream from the branch point of the reversing sheet discharging path in the re-conveying path, the sheet is held by the forward / reverse conveying rollers. And no skew.

In the case of performing the reverse discharge, the sheet on which an image is formed on one side and discharged from the image forming unit is sent to a re-conveying path, and is rotated by a normal-reverse conveying roller which is driven to rotate in a normal direction. The paper is transported to a paper transport path to a predetermined position. Then, after the sheet is conveyed to a predetermined position on the re-conveying path, the sheet is switched back by rotating the forward / reverse conveying roller in the reverse direction, sent to the reverse sheet discharging path, and passed through the reverse sheet discharging path. Paper to the paper discharge section. At the time of this reverse discharge, the sheet fed into the re-conveyance path is pinched by the forward / reverse feed roller that is driven to rotate in the normal direction, and then the forward / reverse feed roller holding the sheet is rotated in the reverse direction. Since the sheet is fed to the reverse discharge path by being driven to rotate, the sheet to be reversely discharged does not become free during the conveyance, and the paper being conveyed becomes free during the conveyance. This prevents lateral displacement and skew in the paper width direction caused by this.

In addition, since the forward / reverse transport rollers are arranged outside the passing area, the forward / reverse transport rollers do not hinder the passing of the preceding sheet and the succeeding sheet, and do not cause the reverse discharge. Paper can be made smoothly.

Further, since the distance between the reversing discharge roller and the forward / reverse transport roller is set to be smaller than the minimum sheet passing length of usable paper, all sizes of paper can be removed only by the function of the reversing discharge roller. It is possible to perform reverse discharge, and the mechanism of reverse discharge can be simplified.

According to a tenth aspect of the present invention, in the image forming apparatus according to the ninth aspect, the switching between the forward and reverse rotation of the forward / reverse transport roller is performed by switching the forward / reverse rotation of a motor connected to the forward / reverse transport roller. Will be

Therefore, the forward / reverse rotation of the forward / reverse transport roller can be reliably and accurately switched.

The eleventh aspect of the present invention provides the ninth or the first aspect.
0, a sheet edge detection sensor for detecting an end of a sheet conveyed through the re-conveying path is provided upstream of a branch point of the reversing sheet discharging path in the re-conveying path. The rotation of the forward / reverse transport roller is switched in the reverse direction at a preset timing after the detection of the sheet edge by the edge detection sensor.

Therefore, even if the size of the sheet to be reversely discharged is different, the forward / reverse transport roller can be switched to the reverse direction at the timing when the leading end of the sheet in the reverse direction reaches the predetermined position. it can.

According to a twelfth aspect of the present invention, in the image forming apparatus according to any one of the first to eleventh aspects, the transport speed of the sheet to be reversed and discharged is higher than the speed of feeding the sheet into the re-conveying path. Is set to

Therefore, the passing area can be made closer to the branch point between the re-conveying path and the reversing sheet discharging path, and the first and second paths can be set.
It is possible to increase the degree of freedom of arrangement of various rollers such as a forward / reverse transport roller, a forward / reverse transport roller, and a reverse discharge roller.

According to a thirteenth aspect of the present invention, in the image forming apparatus according to any one of the first to twelfth aspects, the switching claw disposed at a branch point between the re-conveying path and the reverse sheet discharging path; Urging the switching claw so that the switching claw is located at a position that allows the sheet switched back in the re-conveying path to be sent to the reverse sheet discharging path;
The size at which the switching claw moves to a position that allows the sheet to travel along the re-conveying path when the sheet conveyed toward the sheet conveying path on the re-conveying path abuts on the switching claw. And an urging member set to the urging force of

Therefore, switching of the switching claw necessary for conveying the paper in the re-conveying path by passing through the switching claw and for feeding the sheet switched back in the re-conveying path to the reverse discharge path is performed. It can be performed by an urging member having a simple structure without using an electric actuator such as a solenoid, for example, a spring, and the switching operation of the switching claw using this urging member can be performed at a high speed. It will be sure.

According to a fourteenth aspect of the present invention, in the image forming apparatus according to any one of the first to thirteenth aspects, the image forming section is an electrophotographic image forming section.

Therefore, the invention according to any one of claims 1 to 13 can be realized in an image forming apparatus provided with an electrophotographic image forming section.

According to a fifteenth aspect of the present invention, in the image forming apparatus according to any one of the first to thirteenth aspects, the image forming unit is a digital electrophotographic image forming unit having a digital writing unit.

Therefore, the invention according to any one of claims 1 to 13 can be realized in an image forming apparatus having a digital electrophotographic image forming section having digital writing means.

According to a sixteenth aspect of the present invention, there is provided a printer according to any one of the first to fifteenth aspects, an input terminal for receiving input of image data, and controlling the image forming apparatus to generate the image data. And a control unit for causing an image to be formed on a sheet based on the image.

Therefore, this printer also has the same functions and effects as the invention according to any one of the first to fifteenth aspects.

According to a seventeenth aspect of the present invention, there is provided a copying machine for reading an image of an original, an image forming apparatus according to any one of the first to fifteenth aspects, and the image reading apparatus and the image forming apparatus. A control unit for controlling the image forming apparatus to form an image on a sheet based on image data of the document read by the image reading apparatus.

Therefore, in this copying machine, the same operation as the invention according to any one of claims 1 to 15,
It works.

[0059]

FIG. 1 shows a first embodiment of the present invention.
This will be described with reference to FIG. FIG. 1 is a schematic diagram showing the overall structure of an image forming apparatus having a digital electrophotographic image forming section, FIG. 2 is an enlarged front view showing a sheet reversing means for switching back a conveyed sheet, and FIG. FIG. 4 and FIG. 5 are perspective views showing a conveying roller and a switching claw, FIG. 4 and FIG. 5 are explanatory views showing a state of conveying a sheet to an image forming unit when image formation is continuously performed, and FIG. FIG. 7 is an explanatory view showing the transport state of the sheet during duplex printing, FIG. 8 is an explanatory view showing the transport state of the sheet during reverse discharge, and FIGS. 9 to 11 are the sheets during reverse discharge. FIG. 4 is an explanatory diagram for explaining the transport state of the first embodiment in detail.

In this image forming apparatus, as shown in FIG.
A paper tray 1 serving as a paper storage unit in which paper is stacked and held;
An image forming unit 2 that forms an image on the other side of a sheet fed from the paper tray 1 or an image formed on one side and fed again, and discharges the sheet on which the image has been formed A paper discharge tray 3 or the like, which is a paper discharge unit to be used, is provided.

Further, this image forming apparatus is provided with a paper path through which the paper fed from the paper tray 1 reaches the paper discharge tray 3 via the image forming section 2. A portion from the paper tray 1 to the image forming section 2 is a paper transport path 4.

The paper tray 1 is provided with a pickup roller 5 for sending out the stacked and held sheets, and a separation feed roller 6 of the FRR type for separating the sheets sent out by the pickup roller 5 one by one. Paper means 7 is provided.

The image forming section 2 includes a photosensitive member 8 on which an image is formed on its surface, a charger 9 for uniformly charging the surface of the photosensitive member 8, and a digital writing means for writing an electrostatic latent image on the photosensitive member 8. 10, a developing unit 11 for forming a toner image by attaching toner to an electrostatic latent image on the photoconductor 8, a transfer unit 12 for transferring the developed toner image onto paper, and a residual toner on the photoconductor 8 A cleaning device 13 for removing, a fixing device 14 for fixing the toner image transferred to the sheet, and the like are provided.

The first transport roller 1 is located on the paper transport path 4.
5, a second transport roller 16, a registration sensor 17, a registration roller 18, and the like are arranged. Further, a reversing path 19 into which the sheet conveyed through the sheet conveying path 4 is fed is connected to a portion of the sheet conveying path 4 between the first conveying roller 15 and the second conveying roller 16.

On the reversing path 19, the sheet fed to the reversing path 19 is switched back and sent out to the sheet transport path 4, and the preceding sheet sent from the reversing path 19 and fed into the reversing path 19. Sheet reversing means 20 that can be switched to an open state that allows at least a part of the next sheet to be overlapped with the next sheet, and a sheet edge that detects an end of the sheet fed into or out of the reversing path 19. A section detection sensor 21 is provided.

As shown in FIG. 2, the paper reversing means 20 is movably provided at a position where the driving roller 22 is driven to rotate by a motor and comes into contact with and separates from the driving roller 22, and is rotated when it abuts. Driven roller 23, driven roller 2
3 comprises a moving mechanism for moving the drive roller 3 to a position where the drive roller 3 comes into contact with or separates from the drive roller 22. The moving mechanism for moving the driven roller 23 includes a link 25 having one end connected to the driven roller 23 and the other end connected to a substantially central portion of the link 25 supported by the fulcrum 24 to drive the driven roller 23 to the driving roller 22.
26, link 2 biasing in the direction of contact with
5 and a solenoid 27 for urging the driven roller 23 in a direction to separate the driven roller 23 from the driving roller 22.

FIG. 2B shows that the driven roller 23 is brought into contact with the drive roller 22 by the urging force of the spring 26, and the drive roller 22 is driven to rotate in the direction of the arrow. This is a feeding state in which the nipped paper is sent out from the reversing path 19.

FIG. 2A shows an open state in which the driven roller 23 is rotated downward by the driving of the solenoid 27, and a gap is formed between the driving roller 22 and the driven roller 23.
In the open state, the sheet is fed into the reversing path 19.

A paper discharge path 28 is provided directly between the paper discharge side of the image forming section 2 and the paper discharge tray 3, and the paper discharge side of the image forming section 2 and the upstream side of the reversing path 19 in the paper transport path 4. A re-conveying path 29 is provided between the two sections. At the branch point between the direct discharge path 28 and the re-conveyance path 29, the conveying direction of the sheet discharged from the image forming unit 2 is set to the direct discharge path 28.
Alternatively, a switching claw 30 for switching to the re-transport path 29 is provided.

The re-transport path 29 is formed by a vertical path section 29a extending downward and a horizontal path section 29b extending substantially horizontally from the lower end of the vertical path section 29a.
The leading end of b is connected to the sheet transport path 4.

In the middle of the re-transport path 29,
a from the boundary between the horizontal path section 29a and the reverse paper discharge path 31.
The reverse discharge path 31 is connected to the discharge tray 3.

In the horizontal path portion 29b of the re-transport path 29, first forward / reverse transport rollers 32, 33, second forward / reverse transport roller 34, and reverse roller 35 are provided.
Further, a sheet trailing edge detection sensor 36 which is a sheet edge detecting sensor is provided in the vertical path portion 29a in the re-transport path 29. Further, a first forward / reverse transport roller 32, 33 provided with a transport roller 37 and a switching claw 38 at a branch point between the re-transport path 29 and the reverse discharge path 31, includes a stepping motor, a DC servo motor, and the like. And a driven roller connected to a motor (not shown) capable of switching between forward and reverse rotation, and a driven roller constantly in contact with the driving roller. The first forward / reverse transport rollers 32 and 33 rotate in a forward direction in which the sheet fed to the horizontal path portion 29 b of the re-feed path 29 is transported toward the sheet transport path 4, and switch the sheet back to reverse discharge. It is provided so as to be capable of switching between forward and reverse rotation in the reverse rotation direction to be fed into the paper path 31. The forward / reverse switching of the first forward / reverse transport roller is performed by forward / reverse switching of the motor.

As shown in FIG. 10, when the sheet is inverted and discharged, the sheet is inverted and discharged toward the inverted sheet discharge path 31 downstream of the branch point of the inverted sheet discharge path 31 in the horizontal path portion 29b. A passing area “X” is provided in which the preceding sheet A and the succeeding sheet B sent to the horizontal path portion 29b pass each other. It should be noted that the passing area “X” corresponds to the sheets A and B
And the transport speed of the sheets A and B. The passing area “X” changes every moment according to the transport position of the sheets A and B, and is when the passing area “X” shown in FIG.

Then, the first forward / reverse transport rollers 32, 33
Is located outside the passing area “X”, the first
While the forward / reverse transport rollers 32, 33 are driven to rotate in the reverse direction to feed the preceding sheet A to the reverse discharge path 31, the succeeding sheet B reaches the first forward / reverse transport rollers 32, 33. The inconvenience described above does not occur. When the succeeding sheet B is transported to the position of the first forward / reverse transport rollers 32, 33, the preceding sheet A is transported to the first forward / reverse transport rollers 32, 33.
3 has been released, and the subsequent sheet B sent to the horizontal path portion 29b is driven downstream of the horizontal path portion 29b by rotating the first forward / reverse transport rollers 32, 33 in the forward direction. (The direction in which the sheet is conveyed to the sheet conveying path 4).

The second forward / reverse transport roller 34 has the same basic structure as the first forward / reverse transport rollers 32 and 33, and is in contact with a drive roller connected to a forward / reverse switching motor. The driven rollers are provided so as to be switchable between the normal rotation direction and the reverse rotation direction. However, the second forward / reverse transport roller 34 can be switched between a paper feed state in which the paper is nipped and transported and an open state in which the paper is nipped by moving the driven roller toward and away from the drive roller. Is provided. This switching is performed by driving a solenoid (not shown).

The second forward / reverse transport roller 34 is
Depending on the size of the sheet to be reversed and discharged, the sheet is arranged within the passing area or outside the passing area. When the preceding sheet A and the succeeding sheet B are conveyed by passing each other at the position of the second forward / reverse conveying roller 34, the second forward / reverse conveying roller 34 is switched to the open state, and the passing conveyance is not hindered. Like that.

The reversing roller 35 is provided near a branch point of the reversing discharge path 31 in the horizontal path portion 29b. The reversing roller 35 is composed of a driving roller and a driven roller, and is a roller that is driven to rotate in a direction to feed the sheet to the reversing sheet discharging path 31. The reversing roller 35 contacts and separates the driven roller from the driving roller by driving a solenoid. And a sheet feeding state in which the sheet is nipped and conveyed, and an open state in which the sheet is nipped to be released. When the reversing roller 35 is driven to rotate, the reversing roller 35 and the first and second forward / reverse transport rollers 32, 33, and 34 are driven to rotate synchronously at the same peripheral speed. As a result, the sheets to be reversed and discharged are transported by the first and second transport rollers 32, 33, 3
Between the reversing roller 4 and the reversing roller 35, pulling or loosening is prevented.

The paper trailing edge detection sensor 36 is connected to the re-conveying path 29
The reverse end of the sheet conveyed along the re-conveying path 29 is installed near the branch point between the sheet and the reverse sheet discharging path 31 and upstream of the branch point. In accordance with the detection result of the sheet trailing edge detection sensor 36, the first and second forward / reverse transport rollers 32, 3
3, 34 are switched in the reverse direction, and the reversing roller 35 and the second forward / reverse transport roller 34 are switched to the sheet feeding state.

The transport roller 37 is a roller that is driven to rotate so as to transport the paper in the re-transport path 29 from the vertical path section 29a to the horizontal path section 29b.
The function of feeding the sheet from the vertical path portion 29a to the horizontal path portion 29b and feeding the sheet to be reversed and discharged to the reverse discharge path 31 are provided by the switch 7 and the switching claw 38. Switching claw 38
3, as shown in FIG.
b, a first guide surface 38a facing the sheet conveyed to
A second guide surface 38b facing the sheet which is switched back and heads to the reverse discharge path 31 and an acute angle toward the downstream side of the horizontal path portion 29b sandwiched between the first guide surface 38a and the second guide surface 38b. And a substantially triangular shape having a switching claw tip 38c protruding therefrom. And this switching claw 38
Is fixed to a support shaft 39 arranged near and parallel to the central shaft 37a of the transport roller 37,
9 is rotatably supported by a bearing (not shown). One end of an arm 40 is fixed to an end of the support shaft 39,
The other end of the arm 40 is engaged with one end of a spring 41 as an urging body. In the direction in which the arm 40 is rotated by the urging force of the spring 41, a stopper 42 is provided for regulating the rotational position of the arm 40.

The switching claw 38 is rotated about the axis of the support shaft 39 together with the support shaft 39 to thereby switch the first switching position to the second switching position.
It is provided rotatably at the switching position. In the first switching position, the sheet traveling from the vertical path section 29a to the horizontal path section 29b rotates the switching claw 38 against the urging force of the spring 41 due to its own waist strength, and the sheet is conveyed. The rotation position is when the roller 37 is traveling between the outer peripheral surface of the roller 37 and the first guide surface 38a of the switching claw 38. In the second switching position, no paper exists between the outer peripheral surface of the transport roller 37 and the first guide surface 38 a of the switching claw 38, and the arm 40 is rotated by the urging force of the spring 41 to abut the stopper 42. It is the position when you did. When the switching claw 38 is rotated to the second switching position, the switching claw tip 38 c is positioned inside the outer peripheral portion of the transport roller 37 to position the switched back sheet toward the reverse discharge path 31. The guided and switched back paper is restricted from entering the vertical path portion 29a.

In the reverse discharge path 31, the sheets are discharged from the discharge tray 3.
Discharge roller 4 which is driven to rotate in the direction of reverse discharge
3 are provided. The reversing paper discharging roller 43 is used to move the leading edge of the succeeding paper B (see FIGS. 9 to 11) conveyed through the re-conveying path 29 before the reversing paper is discharged before reaching the position of the reversing roller 35. The sheet is disposed at a position where the sheet reaches the reverse sheet discharging roller 43. As a result, even if the reversing roller 35 is switched to the open state for passing the preceding sheet A and the succeeding sheet B, the leading end of the preceding sheet A is already nipped by the reversing sheet discharging roller 43. Therefore, the reverse discharge of the sheet can be smoothly continued. When the sheet is inverted and discharged by the reversing sheet discharging roller 43 and the first and second forward / reverse conveying rollers 32, 33, and 34, the conveyance speed is determined when the sheet is fed into the re-conveying path 29. High speed is set depending on the speed. This setting
This is performed by changing the number of rotations of the motor between the forward rotation and the reverse rotation.

In this image forming apparatus, the image forming operation in the image forming section 2, the separation sheet feeding means 7, the first and second
Conveyance rollers 15 and 16, registration roller 18, switching claw 3
0, the first and second forward / reverse transport rollers 32, 33, 33, the reversing roller 35, the reversing discharge roller 43, and the like are driven by the paper edge detection sensor 21, the registration sensor 17, the paper rear edge detection sensor 36, and the like. A control unit (not shown) is provided which controls according to the detection results of various sensors and the setting of an image forming mode (one-sided printing mode, two-sided printing mode, reverse sheet discharging mode, etc.).

In such a configuration, when the start key is pressed after the continuous image forming mode is set, the paper is fed from the paper tray 1 one after another. These sheets are conveyed along the sheet conveying path 4 toward the image forming section 2, are fed into the reversing path 19 on the way, are switched back by the sheet reversing means 20, and are sent out from the reversing path 19.
The sheet sent from the reversing path 19 is sent to the image forming unit 2 via the sheet conveying path 4, and the image is formed on the sheet.

The sheet conveyed through the sheet conveying path 4 is moved to the reversing path 1
9 to switch back, the reverse path 19
By controlling the speed at which the paper is fed into the printer, the speed at which the paper is fed from the reversing path 19, the timing at which the paper is fed from the reversing path 19, and the like, the interval between the sheets that are switched back and sent to the image forming unit 2 is reduced. Therefore, the productivity of the image forming operation can be improved. For example, as shown in the diagram of FIG. 6, the paper is transported at a high transport speed Va from the paper tray 1 to the reversal stop position in the reversal path 19, and is sent out at a low transport speed Vb from the reversal stop position. In addition, the paper interval in the image forming unit 2 can be reduced.

FIG. 4 shows a state in which the preceding sheet a is sent out from the reversing path 19, and the sheet reversing means 20 is
As shown in (b), it is in the sending state. The subsequent sheet b is conveyed along the sheet conveying path 4 and is about to be sent to the reversing path 19.

FIG. 5 shows a state in which the preceding sheet a has been transported to a position where the leading end of the sheet a contacts the registration roller 18 and the succeeding sheet b has been fed into the reversing path 19. The preceding sheet a is sent out from the reversing path 19 and its leading end is
After being nipped by the transport roller 16, the driven roller 23 separates from the drive roller 22, and the sheet reversing means 20 moves to the position shown in FIG.
The driven roller 23 which is in the open state as shown in FIG.
The subsequent sheet b is fed into the reversing path 19 through the space between the sheet and the drive roller 22. The feeding of the succeeding sheet b to the reversing path 19 is performed such that the trailing end of the preceding sheet a and the leading end of the succeeding sheet b overlap in the reversing path 19.

FIG. 7 is an explanatory diagram for explaining the flow of a sheet when duplex printing is performed on the sheet. The sheet on which image formation has been performed on one surface in the image forming unit 2 is conveyed through a re-conveying path 29 as indicated by an arrow, and the sheet is firstly and secondly rotated in the normal direction. Rollers 32, 3
The sheet is conveyed as it is by 3 and 34 and sent out to the sheet conveying path 4. After the sheet is sent to the sheet conveyance path 4, the sheet is conveyed in the same manner as the sheet fed from the sheet tray 1, is sent to the reversing path 19, and is switched back.
It is sent to the image forming unit 2 again. When the sheet on which the image is formed on one side is sent to the image forming unit 2 again,
Since the sheet is switched back in the reversing path 19, the other surface of the sheet faces the photoreceptor 8, and image formation (double-sided printing) is performed on the other surface.

FIG. 8 to FIG. 11 are explanatory views for explaining the flow of sheets when the sheet on which an image is formed on one side is inverted and discharged. The sheet on which the image has been formed on one surface is conveyed through the re-conveying path 29 as shown by the arrow, and reaches the horizontal path section 29b. The paper that has reached the horizontal path portion 29b is
The sheet is switched back in the horizontal path section 29b and is turned over.
And the sheet is inverted and discharged onto the sheet discharge tray 3 with the surface on which the image is formed facing downward. The details of the reverse discharge are shown in FIGS. 9 to 11.

FIG. 9 shows that the reverse sheet discharge of the preceding sheet A sent into the horizontal path section 29b has been started, and the succeeding sheet B is conveyed in the vertical path section 29a toward the horizontal path section 29b. It is in the state that it is. At this time, the first and second forward / reverse transport rollers 32, 33, and 34 are all driven to rotate in the reverse direction, and the reverse roller 35 is also driven to rotate in the same direction.
The sheet A is about to be sent to the reverse sheet discharging path 31.

FIG. 10 shows a state in which the preceding sheet A and the succeeding sheet B are being conveyed by passing each other in the horizontal path section 29b. At this time, the second forward / reverse transport roller 34 and the reversing roller 35 located within the passing area “X” have been switched to the open state, and the succeeding sheet B is fed to the horizontal path section 29b.
It does not prevent you from being sent to. Since the leading end side of the preceding paper A is nipped by the reversing discharge roller 43, the first and second forward / reverse transport rollers 32,
Even when the conveyance force from the rollers 33 and 34 and the reversing roller 35 is not applied, the conveyance toward the paper discharge tray 3 is favorably performed.

FIG. 11 shows that the trailing edge of the preceding sheet A enters the reverse discharge path 31 and the succeeding sheet B
b is being conveyed toward the paper conveyance path 4.
The first and second forward / reverse transport rollers 32, 33, and 34 are all driven to rotate in the forward direction, and the reverse roller 35 is open. Then, the subsequent sheet B is transferred to the horizontal path section 29.
When it is determined that the sheet has been fed to the predetermined position b based on the detection result of the sheet trailing edge detection sensor 36, the state shifts to the state of FIG. 9 and the first and second forward / reverse transports that are driven to rotate in the reverse direction. The sheet B is switched back by the rollers 32, 33, and 34 and the reversing roller 35, and the feeding of the sheet B to the reversing discharge path 31 is started. Therefore, the horizontal road portion 29b
The paper fed back to the reversing paper discharge path 31 after being switched back does not enter a free state in the middle of the conveyance, and the paper conveyed in the re-conveyance path 29 enters a free state in the middle of the conveyance. The resulting lateral displacement and skew in the paper width direction can be prevented.

If the sheet to be reversely discharged has a long size, the second forward / reverse transport roller 34 and the reverse roller 35 can be dispensed with.
Reversal discharge can be performed using only the sheets 2 and 33. However, when the sheet is of a short size, when the sheet is reversed and discharged, the leading end of the sheet is transmitted to the reversed discharge roller 43 by using the second forward / reverse transport roller 34 or the reverse roller 35. The sheet is fed into the reversing sheet discharge path 31 to the position where the sheet is nipped.

Next, a second embodiment of the present invention will be described with reference to FIG.
2 will be described. 1 to 11 are denoted by the same reference numerals, and description thereof will be omitted.

The basic structure of this embodiment is the same as that of the first embodiment, and forward and reverse transport rollers 44 and 45 are arranged on the horizontal path 29b.

The forward / reverse transport rollers 44 and 45 are a driving roller connected to a forward / reverse switching motor (not shown) such as a stepping motor or a DC servo motor, and a driven roller constantly contacting the driving roller. It is composed of The forward / reverse transport rollers 44 and 45 are connected to the horizontal path 2
9b is provided so as to be switchable between a normal rotation direction in which the paper fed to the paper transport path 4 is transported toward the paper transport path 4 and a reverse rotation direction in which the paper is switched back and sent to the reverse paper discharge path 31. The forward / reverse switching is performed by the forward / reverse switching of the motor.

The forward / reverse transport rollers 44 and 45 are arranged outside the passing area "X" in the horizontal path portion 29b.

On the reverse discharge path 31, this reverse discharge path 3
1 is provided with a reverse discharge roller 43 which is driven to rotate in a direction of transporting the sheet fed to the discharge tray 3 to the reverse discharge roller 43 and the forward / reverse transport roller located closest to the switching claw 38 side. The distance “L” from the image forming apparatus 44 is set to be smaller than the minimum sheet passing length (sheet length along the conveyance direction) that can be used in this image forming apparatus.

In such a configuration, according to the present embodiment, when performing double-sided printing, the forward and reverse
4 and 45 are rotated in the normal rotation direction, and the sheet fed to the horizontal path portion 29 b is conveyed toward the sheet conveyance path 4 while being nipped by the forward and reverse rotation conveyance rollers 44 and 45.

In the case of performing the reverse discharge, the paper fed into the horizontal path portion 29b is sandwiched between forward and reverse transport rollers 44 and 45 which are driven to rotate in the normal rotation direction, and the rear end of the paper is switched. The sheet is conveyed to a position where it passes through the claw 38, and thereafter, the rotation direction of the forward / reverse rotation conveyance rollers 44 and 45 is switched to the reverse direction, and the sheet is switched back and sent to the reverse sheet discharge path 31. Therefore, the sheet that has been switched back in the horizontal path section 29b and sent to the reverse discharge path 31 does not enter a free state in the middle of the conveyance, and the re-conveyance path 2
9 can be prevented from being displaced or skewed in the paper width direction caused by the paper being conveyed 9 being free during the conveyance.

The distance "L" between the reverse discharge roller 43 and the forward / reverse transport roller 44 located closest to the switching claw 38 side.
Is set to be smaller than the minimum length of paper that can be used in this image forming apparatus.
By rotating the sheet 5 in the reverse direction, the switched back sheet can be surely conveyed to a position nipped by the reversing sheet discharging roller 43, and the second sheet having the contact / separation mechanism described in the first embodiment is provided. (2) The forward / reverse transport roller 34 and the reverse roller 35 become unnecessary. As a result, the mechanism for switching back the paper in the horizontal path portion 29b and discharging it in reverse has a simple structure and is downsized.

Next, a third embodiment of the present invention will be described with reference to FIG.
3 will be described. FIG. 13 is a block diagram showing a schematic structure of a printer 51 according to the present embodiment. The printer 51 controls the image forming apparatus 52 described in the above-described first or second embodiment, an input terminal 53 that receives input of image data from an external device such as a personal computer, and controls the image forming apparatus 52. And a control unit 54 for forming an image based on the image data on a sheet.

Therefore, according to this printer 51,
The same operation and effect as those described in the first or second embodiment can be obtained.

Next, a fourth embodiment of the present invention will be described with reference to FIG.
4 will be described. FIG. 14 is a block diagram showing a schematic configuration of a copying machine 61 according to the present embodiment. The copier 61 includes an image reading device 62 that reads an image of a document.
And the image forming apparatus 52 described in the first or second embodiment, the image reading apparatus 62 and the image forming apparatus 5
And a controller 63 for controlling the image forming apparatus 52 to perform image formation based on the image data of the document read by the image reading apparatus 62 on the sheet by the image forming apparatus 52.

Therefore, according to the copying machine 61, the same operation and effect as those described in the first or second embodiment can be obtained.

[0105]

According to the image forming apparatus of the first aspect of the present invention, when a sheet having an image formed on one surface is inverted and discharged, the image is formed on one surface and the image is formed on the image forming unit. Is transported to a re-conveying path, and the sheet is conveyed to a predetermined position toward the sheet conveying path by a first forward / reverse conveying roller that is driven to rotate in the normal direction, and then the first forward / reverse conveying is performed. By rotating the roller in the reverse rotation direction, the sheet is switched back, and is sent to the reversing sheet discharge path to discharge the sheet.Therefore, the sheet to be reversed and discharged does not become free in the middle of the conveyance. It is possible to prevent lateral displacement and skew in the paper width direction caused by the paper being in a free state during transport, and to prevent the lateral displacement and skew by switching the rotation direction of the first forward / reverse transport roller. Simple It can be carried out by the mechanism.

According to the second aspect of the present invention, in the image forming apparatus according to the first aspect, the first forward / reverse transport roller is provided outside the passing area of the preceding sheet and the succeeding sheet in the re-feed path. Therefore, it is possible to reversely discharge the preceding sheet at a high speed while passing the preceding sheet and the succeeding sheet in the passing area at this time. At this time, the first forward / reverse transport roller is driven to rotate in the reverse direction and the preceding sheet is rotated. Can be prevented from occurring when the next sheet fed to the re-conveying path reaches the first forward / reverse conveying roller when the sheet is fed to the reverse sheet discharging path, and the rotation of the first forward / reverse conveying roller is rotated forward. It is possible to smoothly perform the reverse discharge of the sheet while switching between the direction and the reverse rotation direction.

According to the third aspect of the present invention, in the image forming apparatus according to the first or second aspect, the first forward / reverse transport roller is switched between forward and reverse rotation by the motor connected to the first forward / reverse transport roller. The switching between the forward and reverse rotation of the first forward / reverse transport roller can be performed reliably and accurately.

According to a fourth aspect of the present invention, in the image forming apparatus according to any one of the first to third aspects, the re-conveying path is conveyed upstream of a branch point of the reversing discharge path in the re-conveying path. A paper trailing edge detection sensor for detecting the trailing edge of the sheet to be fed is provided, and the rotation of the first forward / reverse transport roller is switched in the reverse direction at a preset timing after the detection of the trailing edge of the sheet by the sheet trailing edge detection sensor. Therefore, even if the size of the sheet to be reversely discharged is different, the first forward / reverse transport roller can be switched to the reverse direction at the timing when the leading end side of the sheet in the reverse discharge direction reaches a predetermined position. That is, even if the size of the paper to be inverted and discharged is different, the inverted paper can be discharged at the same timing.

According to a fifth aspect of the present invention, in the image forming apparatus according to any one of the first to fourth aspects, the vicinity of the branch point of the reversing sheet discharge path in the re-conveying path and the downstream side of the branch point. A reversing roller, which is rotationally driven in a direction to feed the paper into the reversing discharge path, is provided on the side, and the reversing roller can be switched between a paper feeding state in which the paper is nipped and conveyed and an open state in which the paper is nipped to be released. Since it is provided,
When a small-sized sheet is inverted and discharged, the sheet can be sent to the inverted sheet discharge path by rotating the reversing roller, and the sheet can be fed to the reverse sheet by switching the reversing roller to the released state, so that the succeeding sheet during the passing conveyance can be performed. Can be smoothly delivered.

According to the sixth aspect of the present invention, in the image forming apparatus according to the fifth aspect, when the sheet is fed to the reverse sheet discharging path, the rotation of the reversing roller and the first forward / reverse transport roller is performed by the same rotation. Since the paper is fed synchronously at the speed, the paper fed to the reverse paper discharge path can be prevented from being pulled or loosened between the reverse roller and the first forward / reverse transport roller, and the reverse paper discharge can be performed smoothly. Can be.

According to the seventh aspect of the present invention, in the image forming apparatus according to the fifth or sixth aspect, the reversing discharge roller, which is rotationally driven in a direction for transporting the sheet to the paper discharge unit, is provided on the reversing discharge path. Since the reverse paper discharge roller is disposed at a position where the preceding paper that is reversely discharged before the subsequent paper conveyed through the re-conveyance path reaches the reverse roller, the preceding paper is nipped by the reverse paper discharge roller. When the succeeding sheet conveyed by the sheet reaches the reversing roller, the preceding sheet to be reversed and discharged can be sandwiched by the reversing sheet discharging roller to release the reversing roller. The reversal ejection performed while the sheet is conveyed by passing the sheet can be smoothly performed.

According to an eighth aspect of the present invention, in the image forming apparatus according to any one of the second to seventh aspects, the image forming apparatus falls within the passing area or outside the passing area depending on the size of the sheet to be reversely discharged. Within the range, it is possible to switch between forward and reverse rotation between a forward rotation direction in which the paper fed to the re-feeding path is transported toward the paper transport path and a reverse rotation direction in which the paper is switched back and sent to the reverse discharge path, Further, since a second forward / reverse transport roller is provided which can be switched between a paper feed state for nipping and transporting the paper and an open state for releasing the nipping of the paper, the second forward / reverse transport roller is used. In addition, it is possible to smoothly perform the reverse discharge of small-sized paper, and to switch the second forward / reverse transport roller to the release state, thereby feeding the succeeding paper during low-speed transport. It can be carried out smoothly.

According to the image forming apparatus of the ninth aspect, when the sheet on which the image is formed on one side is to be inverted and discharged, the image is formed on one side and discharged from the image forming section. The paper sheet is sent to the re-conveying path, and the paper is conveyed to a predetermined position toward the paper conveying path by the forward / reverse conveying roller that is driven to rotate in the normal direction, and then the normal / reverse conveying roller is rotated in the reverse direction. When driven, the paper is switched back and sent to the reverse paper discharge path to discharge the paper.Therefore, the paper to be reversely discharged does not become free during the conveyance, and the paper being conveyed becomes free during the conveyance. And the skew in the paper width direction caused by the normal state can be prevented, and the prevention of the lateral shift and skew is performed by a simple mechanism that switches the rotation direction of the forward and reverse rotation transport rollers. It is possible. In addition, since the forward / reverse transport rollers are arranged outside the passing area,
The forward / reverse transport roller can smoothly perform reverse discharge without hindering the passing of the preceding sheet and the succeeding sheet, and furthermore, the forward / reverse transport roller and the forward / reverse transport roller Is set to be smaller than the minimum paper passing length of usable paper, it is possible to reversely discharge all sizes of paper only by the function of the reverse discharge roller, and correct the paper according to the paper size. There is no need for a mechanism for moving the reverse transport roller toward and away from the roller, and the mechanism for reversing and discharging paper can be further simplified.

According to the tenth aspect, the ninth aspect is provided.
In the image forming apparatus described above, the switching of the forward / reverse rotation of the forward / reverse rotation transport roller is performed by switching the forward / reverse rotation of the motor connected to the forward / reverse rotation transport roller. Can be done accurately.

According to the eleventh aspect, in the ninth aspect,
11. The image forming apparatus according to claim 10, further comprising a sheet rear end detection sensor for detecting a rear end of a sheet conveyed through the re-conveyance path upstream of a branch point of the reversing sheet discharge path in the re-conveyance path. The forward / reverse transport roller is switched in the reverse rotation direction at a preset timing after the detection of the trailing edge of the sheet by the trailing edge detection sensor. The forward / reverse transport roller can be switched in the reverse direction at the timing when the leading end side in the paper direction reaches a predetermined position, that is, even if the size of the paper to be reversed is different, the reverse discharge is performed at the same timing. Can be paper.

According to the twelfth aspect, according to the first aspect,
The image forming apparatus according to any one of claims 1 to 11,
Since the conveyance speed of the sheet to be reversed and discharged is set to be higher than the speed of feeding the sheet to the re-conveyance path, the passing area can be made closer to the branch point between the re-conveyance path and the reversal discharge path, Accordingly, it is possible to increase the degree of freedom in the arrangement of various rollers such as the first and second forward / reverse transport rollers, forward / reverse transport rollers, and reverse discharge rollers.

According to the thirteenth aspect, the first aspect is provided.
13. The image forming apparatus according to any one of claims 12 to 12, wherein
The switching claw is arranged at a branch point between the re-conveying path and the reversing discharge path, and the switching claw is located at a position allowing the sheet switched back in the re-conveying path to be fed to the reversing discharging path. The switching claw is urged to a position where the sheet conveyed on the re-conveying path toward the sheet conveying path abuts on the switching claw, and the sheet is allowed to proceed on the re-conveying path. Since it has a biasing member set to a biasing force of a moving size, the sheet is transported in the re-conveying path by passing through the switching claw, and the reverse discharging path of the sheet switched back in the re-conveying path. The switching of the switching claw required for feeding into the device can be performed by an urging body having a simple structure without using an electric actuator such as a solenoid, and switching using this urging body is also possible. Fast and reliable nail switching operation It can be.

According to the invention set forth in claim 14, claim 1 is
13. The image forming apparatus according to any one of claims 13 to 13, wherein
Since the image forming unit is an electrophotographic image forming unit, the invention according to any one of claims 1 to 13 can be realized in an image forming apparatus including the electrophotographic image forming unit.

According to the fifteenth aspect, the first aspect is provided.
13. The image forming apparatus according to any one of claims 13 to 13, wherein
Since the image forming section is a digital electrophotographic image forming section provided with digital writing means, an image forming apparatus provided with a digital electrophotographic image forming section provided with digital writing means is also provided. Any one of the inventions can be realized.

According to the printer of the present invention, an image forming apparatus as set forth in any one of claims 1 to 15, an input terminal for receiving an input of image data, and an input terminal for controlling the image forming apparatus. Since the printer has a control unit for forming an image based on the image data on a sheet, the same operation and effect as the invention according to any one of claims 1 to 15 can be obtained in this printer.

According to the copying machine of the seventeenth aspect,
An image reading apparatus for reading an image of a document, an image forming apparatus according to any one of claims 1 to 15, and an image based on image data of the document read by the image reading apparatus by controlling the image reading apparatus and the image forming apparatus. Since the image forming apparatus has a control unit for causing the image forming apparatus to perform the formation on paper, the same operation and effect as those of the invention according to any one of claims 1 to 15 can be obtained in this copying machine.

[Brief description of the drawings]

FIG. 1 is a schematic diagram illustrating an entire structure of an image forming apparatus including a digital electrophotographic image forming unit according to a first embodiment of the present invention.

FIG. 2 is an enlarged front view showing a sheet reversing unit;
(A) is an open state, and (b) is a sheet sending state.

FIG. 3 is a perspective view showing a transport roller and a switching claw.

FIG. 4 is an explanatory diagram illustrating a state in which a sheet is transported to an image forming unit when image formation is performed continuously.

FIG. 5 is an explanatory diagram illustrating a state in which a sheet is transported to an image forming unit when image formation is performed continuously.

FIG. 6 is a diagram illustrating a sheet conveyance operation during continuous image formation.

FIG. 7 is an explanatory diagram illustrating a sheet conveyance state during duplex printing.

FIG. 8 is an explanatory diagram illustrating a sheet conveyance state during reverse sheet ejection.

FIG. 9 is an explanatory diagram for explaining in detail a sheet conveyance state at the time of reverse sheet ejection.

FIG. 10 is an explanatory diagram for explaining in detail a sheet conveyance state at the time of reverse discharge.

FIG. 11 is an explanatory diagram for explaining in detail a sheet conveyance state during reverse discharge.

FIG. 12 is a schematic diagram illustrating an arrangement of a forward / reverse transport roller, a reverse discharge roller, and the like according to a second embodiment of the present invention.

FIG. 13 is a block diagram of a printer according to a third embodiment of the present invention.

FIG. 14 is a block diagram of a copying machine according to a fourth embodiment of the present invention.

FIG. 15 is a schematic diagram showing the entire structure of a conventional image forming apparatus having a double-sided printing function and a reverse sheet discharging function.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 paper storage section 2 image forming section 3 paper discharge section 4 paper transport path 7 separation paper feed means 19 reverse path 20 paper reverse means 29 re-transport path 31 reverse discharge path 32, 33 first forward / reverse transport roller 34 second Forward / reverse transport roller 35 Reverse roller 36 Paper edge detection sensor 43 Reverse discharge roller 44, 45 Forward / reverse transport roller 52 Image forming device 53 Input terminal 55 Control unit 62 Image reading device 63 Control unit

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 3F053 BA03 BA12 BA14 BA18 BA21 BA29 LA03 LA07 LB03 3F100 AA02 BA05 BA13 CA12 CA13 CA14 DA04 DA05 EA03 EA04 EA05 EA06 EA17

Claims (17)

[Claims] A sheet storage unit for stacking and holding sheets of paper; a separating sheet feeding unit for separating and feeding sheets one by one from the sheet storage unit; and an image forming unit for forming an image on the fed sheets. A paper transport path from the paper storage section to the image forming section, a reverse path connected in the middle of the paper transport path to which a sheet transported through the paper transport path is fed, A feeding state in which a sheet is switched back and sent to the sheet transport path, and an opening allowing at least a part of a preceding sheet fed from the reversing path and a subsequent sheet fed to the reversing path to overlap with each other. A sheet reversing means that can be switched to a state, a re-conveying path connected between a sheet discharging side of the image forming unit and an upstream side of the reversing path of the sheet conveying path, and from the middle of the re-conveying path. Forked paper A reversing discharge path connected to a paper unit, and a reversing discharge path provided in the re-conveying path downstream of a branch point of the reversing discharging path, for conveying the sheet fed to the re-conveying path toward the sheet conveying path. An image forming apparatus comprising: a first forward / reverse transport roller capable of switching between forward and reverse rotations in a forward rotation direction and a reverse rotation direction in which the sheet is switched back and sent to the reverse discharge path. 2. A downstream sheet of the re-conveying path downstream of a branch point of the reversing sheet discharging path, and a subsequent sheet fed to the re-conveying path and the sheet being switched back by the re-conveying path to form the reversing sheet discharging path. 2. The image forming apparatus according to claim 1, wherein a passing area is provided in which the preceding sheet fed to the sheet is passed, and the first forward / reverse transport roller is provided outside the passing area. 3. The switching of the first forward / reverse transport roller between forward and reverse rotation is performed by switching the forward / reverse rotation of a motor connected to the first forward / reverse transport roller.
The image forming apparatus as described in the above. 4. A sheet end detection sensor for detecting an end of a sheet conveyed through the re-conveyance path is provided upstream of a branch point of the reversing sheet discharge path in the re-conveyance path. The image forming layer according to any one of claims 1 to 3, wherein the rotation of the first forward / reverse transport roller is switched in the reverse direction at a preset timing after the detection of the paper edge. 5. A reversing roller, which is rotatably driven in a direction to feed a sheet to the reversing sheet discharge path, near a branch point of the reversal sheet discharging path in the re-conveying path and downstream of the branch point. The image forming apparatus according to claim 1, wherein the reversing roller is provided so as to be switchable between a sheet feeding state in which the sheet is nipped and conveyed and an open state in which the sheet is nipped to be released. 6. The reversing roller and the first forward / reverse transport roller, which are rotationally driven in a direction for feeding the sheet into the reversing discharge path, are synchronously performed at the same peripheral speed.
The image forming apparatus as described in the above. 7. A reversing discharge roller, which is rotatably driven in a direction for conveying a sheet to the sheet discharge unit, is provided on the reversing discharge path, and a subsequent sheet conveyed on the re-conveying path is a reversing roller. The image forming apparatus according to claim 5, wherein the reverse discharge roller is disposed at a position where the preceding sheet that has been reversely discharged before reaching the sheet is nipped. 8. A paper transporting device for transporting a sheet fed to the re-conveying path toward the paper conveying path within a passing area or outside the passing area according to the size of the sheet to be reversely discharged. There is provided a second forward / reverse transport roller capable of switching forward / reverse rotation in a forward direction and a reverse direction in which the paper is switched back and sent to the reverse discharge path. The second forward / reverse transport roller sandwiches and transports the paper. The image forming apparatus according to any one of claims 2 to 7, wherein the image forming apparatus is provided so as to be switchable between a sheet feeding state in which the sheet is fed and an open state in which the sheet is released. 9. A sheet storage unit for stacking and holding sheets, a separation sheet feeding unit for separating and feeding sheets one by one from the sheet storage unit, and an image forming unit for forming an image on the fed sheets. A paper transport path from the paper storage unit to the image forming unit, a reversing path that is connected in the middle of the paper transport path and feeds the paper conveyed through the paper transport path, A feeding state in which a sheet is switched back and sent to the sheet transport path, and an opening allowing at least a part of a preceding sheet fed from the reversing path and a subsequent sheet fed to the reversing path to overlap with each other. A sheet reversing means that can be switched to a state, a re-conveying path connected between a sheet discharging side of the image forming unit and an upstream side of the reversing path of the sheet conveying path, and from the middle of the re-conveying path. Forked paper A reversing discharge path connected to a paper unit, and a reversing discharge path provided in the re-conveying path downstream of a branch point of the reversing discharging path, for conveying the sheet fed to the re-conveying path toward the sheet conveying path. A forward / reverse transport roller capable of switching forward / reverse rotation in a forward direction and a reverse direction in which the paper is switched back and sent to the reverse discharge path; and the paper discharge unit provided on the reverse discharge path to discharge the paper. A reversing paper discharge roller that is driven to rotate in the direction of conveying the paper to the re-conveying path, and a preceding sheet that is switched back on the re-conveying path and sent to the reversing paper discharging path. The forward / reverse transport roller is disposed outside a passing area provided on the transport path so that the paper passes each other. Paper length Image forming apparatus is set smaller. 10. The image forming apparatus according to claim 9, wherein the switching between the forward and reverse rotation of the forward / reverse transport roller is performed by switching the forward / reverse rotation of a motor connected to the forward / reverse transport roller. 11. A sheet end detection sensor for detecting an end of a sheet conveyed through the re-conveying path is provided upstream of a branch point of the reversing sheet discharging path in the re-conveying path. 11. The image forming layer according to claim 9, wherein the rotation of the forward / reverse transport roller is switched in the reverse direction at a preset timing after the detection of the paper edge. 12. The image forming apparatus according to claim 1, wherein a conveying speed of the sheet to be reversed and discharged is set to be higher than a feeding speed of the sheet to the re-conveying path. 13. A switching claw disposed at a branch point between the re-conveying path and the reversing sheet discharging path, and allowing a sheet switched back in the re-conveying path to be sent to the reversing sheet discharging path. The switching claw is urged so that the switching claw is located at a position where the sheet is conveyed toward the sheet conveyance path on the re-conveying path. The image forming apparatus according to any one of claims 1 to 12, further comprising: an urging body set to an urging force having a magnitude enough to move the switching claw to a position where the urging member is allowed to move on the re-conveying path. 14. The image forming apparatus according to claim 1, wherein the image forming unit is an electrophotographic image forming unit. 15. The image forming apparatus according to claim 1, wherein the image forming unit is a digital electrophotographic image forming unit including a digital writing unit. 16. An image forming apparatus according to claim 1, an input terminal for receiving input of image data, and controlling the image forming apparatus to form an image based on the image data on a sheet. And a control unit for causing the printer to perform the operation. 17. An image reading apparatus for reading an image of a document, the image forming apparatus according to claim 1, and controlling the image reading apparatus and the image forming apparatus to read the image by the image reading apparatus. And a control unit for causing the image forming apparatus to form an image based on image data of the original document on a sheet.