JP2002293483A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To form a thinner image forming device having improved productivity in printing work by reducing intervals for paper in an image forming part during continuous image formation and having the function of double printing. SOLUTION: A reversing path 6 provided with paper reversing means 14 is connected to the midway of a paper carrying path 4 ranging from a paper storage part 1 to the image forming part 2. The intervals for a series of paper to be carried in the image forming part 2 is reduced by switch-back of the paper in the reversing path 6, resulting in improved productivity in image forming work. Furthermore, the need for a special passage where switch-back of the paper is performed for double printing is eliminated by switch-back of the paper in the reversing path 6, to be carried via a refeed path 33 and the paper carrying path 4 to the image forming part 2 again for double printing. Thus, the thinner image forming device can be formed through the reversing path 6 is provided therein.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a double-sided printing function,
The present invention relates to an image forming apparatus having a function of reversing paper discharging, in which printed sheets are discharged in page order with the printing surface facing down.

[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.
7 will be described. This image forming apparatus includes a photoconductor 1
And an image forming unit 102 for forming an image on a sheet fed with a developing unit 101 and a developing unit 101. On the sheet discharging side of the image forming unit 102, the sheet on which the image is formed is directed to the sheet discharging unit 103. And a second conveyance path 105 through which the image-formed paper is conveyed for duplex printing or reverse discharge. At a branch point between the first transport path 104 and the second transport path 105, a switching claw 106 for switching the transport direction of the sheet discharged from the image forming unit 102 to the first transport path 104 or the second transport path 105 is provided. Have been.

[0004] At the front end of the second transport path 105,
A reversing path 107 for switching back the sheet transported on the transport path 105 is provided. In the reversing path 107, there is provided a reversing roller 108 which is movable to a contact / separation position (up / down position), and switches back the sheet by being abutted and rotated.

A re-feeding path 109 for conveying the sheet switched back in the reversing path 107 forward to the image forming unit 102 for double-sided printing is provided in front of the sheet in the conveying direction.
And a reverse discharge path 110 for discharging the paper to the paper discharge section 103 in the page order with the printing surface facing down. The re-feeding path 109 is disposed below the reversing path 107, and at a branch point between the re-feeding path 109 and the reversing sheet discharging path 110, the feeding direction of the sheet switched back in the reversing path 107 is re-supplied. A switching claw 111 for switching to the feeding path 109 or the reverse sheet discharging path 110 is provided.

When double-sided printing is performed in this image forming apparatus, the sheet on which image formation on one side has been completed is the second sheet.
The switching claw 106 is switched so as to be transported to the transport path 105, and the sheet is fed into the reversing path 107 via the second transport path 105. The switching pawl 111 is switched so that the sheet fed into the reversing path 107 is switched back by the action of the flipping roller 108 and then fed into the re-feeding path 109. Is sent to the image forming unit 102 again.
As a result, image formation (double-sided printing) is performed on the other side of this sheet, and the sheet on which double-sided printing has been performed is placed on the first transport path 1.
The sheet is ejected to the sheet ejection section 103 through the path 04.

[0007] In the case of performing reverse discharge in this image forming apparatus, the sheet on which image formation on one side has been completed is the second sheet.
The switching claw 106 is switched so as to be transported to the transport path 105, and the sheet is fed into the reversing path 107 via the second transport path 105. The switching pawl 111 is switched so that the sheet fed into the reversing path 107 is switched back by the action of the reversing roller 108 and then fed to the reversing sheet discharging path 110. Is discharged to the sheet discharge unit 103.
The paper discharged via the reverse discharge path 110 is discharged in page order with the print surface facing downward, so-called reverse discharge is performed.

[0008]

However, in the image forming apparatus shown in FIG.
7 and the re-feed path 109 must be provided in two stages, upper and lower, and the height of the image forming apparatus is increased.

SUMMARY OF THE INVENTION It is an object of the present invention to improve the productivity of a printing operation by narrowing the interval between sheets in an image forming section when image formation is performed continuously, and furthermore, to reduce the number of sheets for performing double-sided printing. An object of the present invention is to reduce the thickness of the image forming apparatus by eliminating the need for a dedicated paper conveyance path for switchback.

[0010]

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 into the reverse path is fed back to the paper transport path by switching back the paper fed into the reverse path, and the preceding sheet being 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, conveying means for conveying the paper which the fed to the re-feed path to the sheet conveying path,
Having.

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 in the sheet conveying path, and the sheet conveyed in 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, the preceding sheet sent to the sheet conveying path and the subsequent sheet fed to the reversing path are in a state where at least a part thereof is superimposed. By controlling the speed of feeding the paper to the 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 the sheets that are switched back and sent to the image forming unit can be reduced. it can. Thus, 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 reverse path, the feeding of the paper to the image forming unit can be accurately maintained at a small interval. As a result, 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 a re-feeding path, and the sheet is sent out to a sheet feeding path by a feeding means. . The sheet sent out to the sheet conveying path in this way is sent again to the reversing path, switched back in the reversing path, and then sent again to the image forming unit, where the image is formed on the other side of the sheet (both sides). Printing) is performed.
This eliminates the need for a dedicated paper transport path for switching back the paper to perform double-sided printing, and the reverse path can also be used as a paper transport path for switching back the paper for double-sided printing. Nevertheless, it is possible to prevent the image forming apparatus from being thickened, that is, to reduce the thickness of the image forming apparatus.

According to a second aspect of the present invention, in the image forming apparatus according to the first aspect, a reversing sheet discharging path branched from the middle of the re-feeding path and connected to a sheet discharging section; And a reverse discharge means for switching back the paper fed to the path toward the reverse discharge path and reversely discharging the sheet.

Therefore, when a sheet having an image formed on one side is fed to the re-feeding path, the sheet is switched back by the reversing sheet discharging means and fed to the reversing sheet discharging path, whereby the sheet is fed back. Are discharged in reverse order to the paper discharge section in the order of pages with the surface on which the image is formed facing downward.

According to a third aspect of the present invention, in the image forming apparatus according to the second aspect, the conveying means and the reverse discharge means are located downstream of a branch point of the re-feed path from the reverse discharge path. And a forward direction in which the sheet fed into the re-feeding path is pinched and conveyed toward the sheet conveying path, and the sheet is switched back from the state in which the pinched state is maintained and the reversal is performed. It is a re-feeding paper feed direction switching roller that is switchable between forward and reverse rotations in the reverse rotation direction for feeding into the paper discharge path.

Accordingly, since the re-feeding sheet feeding direction switching roller has the functions of the conveying means and the reversing paper discharging means, it is not necessary to separately provide the conveying means and the reversing paper discharging means, and the structure is simplified.

At the time of reversal discharge, the sheet fed into the re-feeding path is pinched by the re-feeding sheet feeding direction switching roller rotating in the normal rotation direction, and thereafter, the re-feeding sheet feeding direction holding the sheet. When the switching roller is driven to rotate in the reverse direction, the sheet is fed to the reverse discharge path, so that the sheet to be reversely discharged does not become free in the course of conveyance, and the paper being conveyed is free. Skew in the sheet width direction and skew caused by the occurrence of the skew are prevented.

According to a fourth aspect of the present invention, in the image forming apparatus according to the second or third aspect, in the re-feeding path, the preceding sheet which is switched back and fed to the reverse sheet discharging path and the re-feeding The next sheet conveyed in the transport path can pass.

Therefore, when the trailing end of the preceding sheet fed to the reverse sheet discharging path is located in the re-feeding path, the succeeding sheet can be fed into the re-feeding path. Even when the interval between the conveyed sheets is small, that is, when the interval between the ejected sheets of the image-formed sheet is narrow, the reverse ejection can be smoothly performed.

According to a fifth aspect of the present invention, in the image forming apparatus according to the fourth aspect, the re-feeding sheet feeding direction switching roller switches the previous sheet fed back to the reverse sheet discharging path and the re-feeding sheet. The sheet is provided outside the passing area where the subsequent sheet conveyed in the feeding path passes.

Therefore, when the re-feeding sheet feed direction switching roller is driven to rotate in the reverse direction to pinch the preceding sheet and feed it into the reversing discharge path, the succeeding sheet conveyed through the re-feed path is re-started. When the following sheet reaches the re-feeding paper feed direction switching roller, the inconvenience of reaching the feed paper feed direction switching roller does not occur, and the state of nipping the preceding sheet by the re-feeding paper feed direction switching roller has ended. . For this reason, even when the preceding sheet and the succeeding sheet pass each other in the re-feeding path, the sheet is inverted and discharged by reversing the rotation direction without moving the re-feeding sheet feeding direction switching roller. Can be performed.

The invention according to claim 6 is the invention according to claims 2 to 5
The image forming apparatus according to any one of the preceding claims, further comprising: a switching claw disposed at a branch point between the re-feeding path and the reverse sheet discharging path; and an urging body for urging the switching claw. The urging body urges the switching claw so as to position the switching claw at a position that allows the sheet switched back in the re-feeding path to be fed into the reverse sheet discharging path. The urging force is such that when the sheet discharged from the image forming unit and conveyed through the re-feeding path abuts on the switching claw, the switching claw can be moved to a position allowing the advance of the sheet. Is set to

Therefore, the switching required for conveying the paper in the re-feeding path by passing the switching claw and feeding the sheet switched back in the re-feeding path to the reverse discharge path. Switching of claws can be performed by a biasing body with a simple structure without using an electric actuator such as a solenoid,
Moreover, the switching operation of the switching claw using this biasing body is
It is reliable and can respond at high speed.

The invention according to claim 7 is the invention according to claims 2 to 5
In the image forming apparatus according to any one of the above, the reverse discharge sheet is disposed at a branch point between the re-feed path and the reverse discharge path, and is a traveling direction of a sheet conveyed through the re-feed path, and Is driven to rotate along the traveling direction of the paper conveyed along the path,
A roller having a number of protrusions on an outer peripheral portion thereof, and a roller abutting on the outer peripheral portion of the roller and arranged at a position for nipping a sheet conveyed through the re-feeding path by the roller, and a direction for conveying the nipped sheet. A first opposing roller that rotates at a distance, and is disposed at a position where the sheet is conveyed through the reversing sheet discharge path by the roller while being in contact with the outer peripheral portion of the roller, and is rotated in the direction in which the nipped sheet is conveyed. A second opposing roller,
Gripping means disposed on the re-feed path and downstream of the first opposing roller to grip and stop a sheet conveyed through the re-feed path.

Therefore, the sheet conveyed in the re-feeding path is conveyed while being nipped by the roller and the first opposing roller. By gripping the sheet by the gripping means at a predetermined timing before the rear end of the sheet nipped and transported by the roller and the first opposing roller passes through the contact portion between the roller and the first opposing roller, The conveyance of the sheet is stopped.

By continuing the rotation of the rollers even after the paper is gripped by the gripping means and the transport is stopped, the trailing end of the paper is continuously transported, and the paper is gradually moved between the gripping means and the rollers. Bend. When the trailing end of the sheet passes through the contact portion between the roller and the first opposing roller, the sheet is in a state where the trailing end is held by the protrusion of the roller, and the trailing end of the sheet held by the protrusion is the roller. Is transported to the reversing discharge path side with the rotation of. When the trailing end of the sheet curved between the gripping means and the roller is transported to a predetermined position on the reversing sheet ejection path side with the rotation of the roller, the curved sheet jumps up to cancel the curved state by its own restoring force. Then, the trailing end of the sheet is released from the holding state by the projection and enters between the roller and the second opposed roller.

The holding state of the holding means is released at a timing immediately after the trailing edge of the sheet enters between the roller and the second opposing roller, so that the sheet is conveyed while being nipped by the roller and the second opposing roller. Then, the conveyance direction is switched back, and the sheet is conveyed through the reverse sheet discharging path.

Here, in the process in which the sheet transported in the re-feeding path is switched back so that the sheet is transported in the reverse sheet discharging path, the sheet is sandwiched between the roller and the first opposing roller. It is conveyed and stopped by being grasped by the grasping means, and is conveyed while being sandwiched between the roller and the second opposing roller, and is not rubbed in contact with a member such as a branch claw. . For this reason, it is possible to prevent the paper from being rubbed and scratched, and the image formed on the paper from being rubbed and deteriorating the image quality.

Since the leading edge of the sheet (the trailing edge of the sheet before being switched back) is carried by the protrusions and is carried without causing the leading end of the sheet to be displaced in an oblique direction, the sheet is inverted. Is prevented from occurring when the sheet is transported.

According to an eighth aspect of the present invention, in the image forming apparatus according to the seventh aspect, the gripping means is a gripping pad movable to a gripping position and a grip release position.

Therefore, by moving the gripping pad to the gripping position, it is possible to reliably grip and stop the paper being conveyed in the re-feeding path, and to control the leading edge of the paper (after the paper before being switched back). By moving the gripping pad to the grip release position after the end) is conveyed to the reverse discharge path side, the sheet is transported through the reverse discharge path.

According to a ninth aspect of the present invention, in the image forming apparatus according to the seventh aspect, the gripping means is a transport roller capable of switching the rotation direction between forward and reverse directions and holding the sheet.

Therefore, the sheet can be conveyed on the re-feeding path by rotating the conveying roller in the normal rotation direction, and the sheet conveyed on the re-feeding path can be gripped by stopping the rotation of the conveying roller. The transport roller is rotated in the reverse direction after the leading edge of the sheet (the rear end of the sheet before being switched back) is conveyed to the reverse discharge path, and the sheet is reversely discharged. It can be transported on the road.

Here, by using a transport roller that can be switched between forward and reverse as the gripping means, the roller and the transport roller (gripping means) can be used when the paper transport direction is switched back.
It is no longer necessary to bend the sheet between the steps, and it is possible to prevent the sheet from being bent due to the bending.

According to a tenth aspect of the present invention, in the image forming apparatus according to any one of the first to ninth aspects, the transporting means transports the sheet in the re-feeding path to the sheet transporting path at an arbitrary timing. Can be sent out.

Therefore, the sheet fed to the re-feeding path can be sent out to the sheet feeding path at an appropriate timing, and the first image forming operation can be performed on one side of the sheet fed from the sheet storage unit. It is possible to perform so-called interleaf paper feeding in which paper feeding and paper feeding for performing image formation (double-sided printing) on the other surface of the paper conveyed through the re-feed path are mixed.

According to an eleventh aspect of the present invention, in the image forming apparatus according to any one of the first to tenth aspects, the conveying speed of the sheet conveyed through the re-feeding path is adjusted by the image forming unit. It is set faster than the process speed.

Therefore, when performing double-sided printing while performing interleaf paper feeding, the paper conveyed in the re-feeding path can be quickly sent to the connection point with the paper conveying path, and the paper is fed from the paper storage section. The distance between the sheet to be fed and the sheet conveyed through the re-feeding path and sent out to the sheet conveying path can be reduced, and the productivity of the duplex printing operation is improved.

According to a twelfth aspect of the present invention, in the image forming apparatus according to any one of the second to sixth aspects, the conveying speed of the sheet conveyed through the reverse sheet discharging path is controlled by the image forming unit. It is set faster than the process speed.

Therefore, it is possible to widen the interval between the sheets that are inverted and discharged to the sheet discharge unit, and to perform post-processing such as punching and staple binding on the sheets discharged to the sheet discharge unit. Processing can be performed easily.

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 image forming unit is an electrophotographic image forming unit.

Therefore, in an image forming apparatus having an electrophotographic image forming section, the invention according to any one of claims 1 to 12 can be realized.

According to a fourteenth aspect of the present invention, in the image forming apparatus according to any one of the first to twelfth 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 12 can be realized in an image forming apparatus having a digital electrophotographic image forming section provided with digital writing means.

[0046]

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 structure of an image forming apparatus provided with a digital electrophotographic image forming section provided with digital writing means. FIG. 2 is an enlarged front view showing a mechanism along a paper transport path. 3 is a perspective view showing an inlet roller and a branch claw, FIG. 4 is an explanatory view for explaining an operation state of the sheet reversing means, FIG. 5 is a perspective view showing a transport roller and a switching claw, and FIGS. FIG. 8 is an explanatory view showing a state of feeding a sheet to an image forming unit in the case of performing image formation by using the image forming apparatus. FIG. 8 is an explanatory view showing a state of sheet transport during double-sided printing, and FIG. FIG. 10 is a schematic diagram showing a sheet conveyance order and a sheet interval at a connection point between a sheet conveyance path and a re-feeding path. FIG. 10 is an explanatory diagram showing a sheet conveyance state at the time of reverse discharge, and FIG. 6 is a diagram showing a sheet transport operation at the time.

As shown in FIG. 1, the image forming apparatus includes:
Paper feed tray 1 as a paper storage unit for holding and stacking paper;
The image forming unit 2 forms an image on the paper fed from the paper feed tray 1 or on one surface and forms an image on the other surface of the paper fed again, and the image forming unit 2 performs image formation. A paper discharge unit 3 and the like for discharging the cut paper are provided. Further, in the image forming apparatus, there are provided a number of transport paths for transporting the paper between the paper feed tray 1, the image forming unit 2, the paper discharge unit 3, and the like.

As one of the above-described transport paths, a paper transport path 4 from the paper feed tray 1 to the image forming section 2 is provided. A branch point 5 is provided in the middle of the paper transport path 4, and a reversal path 6 branches from the branch point 5. The reversing path 6 is for switching back the sheet conveyed through the sheet conveying path 4. The sheet conveyed through the sheet conveying path 4 is once fed in, then switched back by the sheet reversing means described later, and is again returned to the sheet conveying path. 4 is sent out.

At a position upstream of the branch point 5 on the paper transport path 4 in the paper transport direction, a transport roller 7 driven by a motor (not shown) is provided. At the branch point 5, an inlet roller 8 driven by a motor (not shown) to feed the sheet to the reversing path 6 and a leading end of the sheet conveyed upstream of the inlet roller 8 in the conveying direction are detected. And a branch claw 10 for switching between the path of the sheet fed into the reversing path 6 and the path of the sheet fed from the reversing path 6. The entrance sensor 9 according to the present embodiment is a reflection-type optical sensor including a light emitting element (not shown) that emits light and a light receiving element (not shown) that receives light emitted by the light emitting element. When the sheet is conveyed, the light emitted from the light emitting element is reflected by the sheet, and the reflected light is received by the light receiving element to detect the sheet.

Downstream of the branch point 5 in the sheet conveying direction, an intermediate conveying roller 11 driven by a motor (not shown) to feed the sheet switched back by the reversing path 6 to the image forming section 2, A sensor 12 and a registration roller 13 for performing a registration operation for synchronizing the timing at which a sheet detected by the registration sensor 12 is sent to the image forming unit 2 with the image forming operation are provided. The registration sensor 12 is the same reflection type sensor as the entrance sensor 9 described above.

On the reversing path 6, the sheet fed into the reversing path 6 is switched back and sent out to the sheet conveying path 4, and the preceding sheet sent from the reversing path 6 and fed into the reversing path 6. And a reversing sensor 15 for detecting the leading end of the sheet fed to the reversing path 6. The reversing means 14 can be switched to an open state allowing at least a part of the succeeding sheet to overlap. I have.
This reversing sensor 15 is also a reflection type sensor similar to the entrance sensor 9 described above.

As shown in FIG. 4, the sheet reversing means 14
The reversing roller 16 is intermittently driven to rotate by a stepping motor (not shown), and is disposed at a position facing the reversing roller 16 with the reversing path 6 interposed therebetween, and is brought into contact with the outer peripheral surface of the reversing roller 16. And a driven roller 17 that is rotated. At a part of the outer peripheral portion of the reversing roller 16, a notch portion 16 a that forms a gap between the outer peripheral surface of the driven roller 17 when facing the driven roller 17 is formed. FIG. 4B shows that the outer peripheral surface of the reversing roller 16 and the outer peripheral surface of the driven roller 17 abut against each other.
Is driven in the direction of the arrow, and the driven roller 17 is rotated in the direction of the arrow, whereby the sheet is sent out to the sheet transport path 4. FIG. 4 (a)
The notch 16a faces the driven roller 17, whereby
This is an open state in which a gap is formed between the outer peripheral surface of the reversing roller 16 and the driven roller 17. In the open state, the sheet is fed into the reversing path 6. The transport speed of the sheet before it is fed into the reversing path 6 is set to be higher than the transport speed after the sheet is fed from the reversing path 6.

On the downstream side of the paper feed tray 1 in the paper transport direction,
Pickup roller 18 for taking out the stacked sheets
And a separating sheet feeding means 20 provided with a separating roller 19 of FRR system for separating the taken out sheets one by one.

The image forming section 2 includes a photosensitive member 21 on which an image is formed on a surface, and a charger 2 for uniformly charging the photosensitive member 21.
2. A digital optical writing device 23, which is a digital writing device for optically writing an electrostatic latent image on the photoconductor 21, a developing device 24 for forming a toner image by attaching toner to the electrostatic latent image on the photoconductor 21 And a transfer unit 25 for transferring the developed toner image onto the sheet, a cleaning device 26 for removing the residual toner on the photoconductor 21, a fixing unit 27 for fixing the toner image transferred on the sheet, and the like. .
In the image forming section 2, an image is formed by a digital electrophotographic process.

The branch claw 10 arranged at the branch point 5
As shown in FIG. 2, a first guide surface 10 a facing the sheet fed into the reversing path 6, a second guide surface 10 b facing the sheet fed from the reversing path 6, and a first guide surface 1
0a and the second guide surface 10b, and is formed in a substantially triangular shape having an acute-angle branch claw tip 10c opposed to the reversing path 6. As shown in FIG. 3, the branch claw 10 is fixed to a support shaft 28 arranged near and parallel to the center shaft 8a of the inlet roller 8.
Are rotatably supported by bearings (not shown).
One end of an arm 29 is fixed to an end of the support shaft 28, and one end of a spring 30 is locked to the other end of the arm 29. In the direction in which the arm 29 is rotated by the biasing force of the spring 30, a stopper 31 for regulating the rotation position of the arm 29 is provided.

The bifurcated claw 10 is rotated about the axis of the support shaft 28 together with the support shaft 28, and thereby the first switching position (the position shown by the solid line in FIG. 2) and the second switching position (the virtual position in FIG. 2). (Position shown by a line).
The first switching position is such that the paper fed into the reversing path 6 rotates the branch claw 10 against the urging force of the spring 30 due to its own stiffness, and the paper is moved between the outer peripheral surface of the entrance roller 8 and the branch claw. 10 is a rotation position when the robot is traveling between the first guide surface 10a and the first guide surface 10a. The second switching position is such that no sheet exists between the outer peripheral surface of the entrance roller 8 and the first guide surface 10 a of the branch claw 10, and the arm 29 is biased by the spring 30.
Is the rotation position when it comes into contact with the stopper 31. When the branch claw 10 is rotated to the second switching position, the branch claw tip 10c is located inside the outer peripheral portion of the entrance roller 8 as shown by a virtual line.

A paper discharge path 32 is directly connected between the paper discharge side of the image forming section 2 and the paper discharge section 3, and is upstream of the branch point 5 in the paper discharge side of the image formation section 2 and the paper transport path 4. A re-feeding path 33 is connected to the side. At the branch point between the direct discharge path 32 and the re-feed path 33 on the discharge side of the image forming section 2, the transport direction of the sheet discharged from the image forming section 2 is directly changed to the discharge path 32 or the re-feed path. Switching claw 34 for switching to road 33
Is provided.

The re-feeding path 33 is formed of a vertical portion 33a extending downward and a horizontal portion 33b bent in a direction extending substantially horizontally from the lower end of the vertical portion 33a. Is connected to the paper transport path 4.

In the middle of the re-feed path 33, the vertical portion 33a
A reverse discharge path 35 is branched from a bent portion between the sheet and the horizontal portion 33 b, and the reverse discharge path 35 is connected to the sheet discharge section 3.

In the horizontal portion 33b in the re-feeding path 33,
A two-sided printing sending state in which the sheet sent to the re-feeding path 33 rotates in the normal rotation direction to send out the sheet to the sheet feeding path 4 for the two-sided printing, and the sheet sent to the re-feeding path 33 is reversely discharged. A reversing sheet feeding direction switching roller 36 as a reversing sheet discharging means is provided, which is switchable to a reversing sheet discharging state in which the sheet is switched back to the path 35 and rotated in the reverse direction for reversing sheet discharging. I have. The re-feeding paper feed direction switching roller 36 is composed of a plurality of roller pairs 37 including a drive roller whose rotation direction is rotatable forward and reverse, and a driven roller which is movable toward and away from the drive roller. I have. Each roller pair 37 is configured such that each drive roller can be driven independently. Further, the re-feeding paper feed direction switching roller 36 nips the paper in the horizontal portion 33b to stop the conveyance, and switches the paper at an arbitrary timing according to a detection result of a paper position detection sensor (not shown). It has a function of sending out to the paper transport path 4.

At the location where the reversing sheet discharge path 35 branches off from the re-feeding path 33, the sheet transported in the direction in which the paper in the re-feeding path 33 is transferred from the vertical portion 33a to the horizontal portion 33b is rotated. A roller 38 and a switching claw 39 are provided. As shown in FIG. 5, the switching claw 39 is provided on the first guide surface 3 facing the sheet conveyed from the vertical portion 33a to the horizontal portion 33b.
9a, a second guide surface 39b facing the sheet which is switched back and heading to the reverse sheet discharge path 35, and a first guide surface 3
It is formed in a substantially triangular shape having an acute-angle switching claw tip portion 39c facing the horizontal portion 33b between the second guide surface 39b and the second guide surface 39b. The switching claw 39 is fixed to a support shaft 40 arranged near and parallel to the center shaft 38a of the transport roller 38, and the support shaft 40 is rotatable by a bearing (not shown). It is pivoted. Support shaft 4
0, one end of the arm 41 is fixed to the end of the arm 41.
Is fixed to one end of a spring 42 as an urging member. In the direction in which the arm 41 is rotated by the urging force of the spring 42, a stopper 43 for regulating the rotational position of the arm 41 is provided.

The switching claw 39 is rotated about the axis of the support shaft 40 together with the support shaft 40, so that the first switching position and the second
It is provided rotatably at the switching position. The first switching position is such that the paper advancing from the vertical portion 33a to the horizontal portion 33b rotates the switching claw 39 against the urging force of the spring 42 due to its own stiffness, and the paper is transported by the transport roller 38.
Is a rotating position when the switching claw 39 is traveling between the outer peripheral surface and the first guide surface 39a. The second switching position is the rotation position illustrated in FIGS. 1 and 5 and the like. When no paper exists between the outer peripheral surface of the transport roller 38 and the first guide surface 39a of the switching claw 39, the spring 42 This is the rotation position when the arm 41 is in contact with the stopper 43 due to the urging force. When the switching claw 39 is rotating to the second switching position,
The switching claw tip portion 39c is located inside the outer peripheral portion of the transport roller 38, restricts the switched back sheet from entering the vertical portion 33a, and guides the sheet toward the reverse discharge path 35.

In the horizontal portion 33b which is a part of the re-feeding path 33, it is possible that the sheet which is switched back and sent to the reversing sheet discharging path 35 and the sheet which goes from the vertical portion 33a to the horizontal portion 33b can pass each other. Have been. More specifically, the re-feeding mode in which the height and width of the horizontal portion 33b have dimensions that allow two sheets to pass each other, and have been switched to the reverse discharge state in which the preceding paper is fed to the reverse discharge path 35. The paper feed direction switching roller 36 (i.e., each roller pair 37) separates the drive roller and the driven roller at the timing when the subsequent paper enters the horizontal portion 33b and becomes free, and the horizontal portion 3
3b is allowed to be sent.

The transport speed of the paper transported through the re-feeding path 33 is set to be higher than the image forming process speed in the image forming section 2. For example, if the image forming process speed is 330
mm / s, whereas the speed at the time of being conveyed through the re-feeding path 33 is 560 mm / s. In addition, the reversing discharge path 3
5 is set to be faster than the image forming process speed in the image forming unit 2.

In such a configuration, the paper sheets stacked and held on the paper feed tray 1 are separated and fed one by one by the separation paper feeding means 20, and the separated paper sheets are continuously fed along the paper transport path 4. Sent out.

When the leading edge of the paper sent out along the paper transport path 4 reaches the branch point 5 and is detected by the entrance sensor 9, the entrance roller 8 is driven to rotate. Further, the branch claw 1 whose leading end portion of the sheet is rotated to the second switching position with respect to the branch point 5
When the sheet hits the first guide surface 10a, the sheet is pushed up by the strength of the waist and pivots to the second switching position, and the sheet is moved between the first guide surface 10a and the outer peripheral surface of the entrance roller 8. It is sent to the reversing path 6 through the gap. When the sheet is fed into the reversing path 6, the sheet reversing means 14 is in an open state as shown in FIG.

When the trailing edge of the sheet fed to the reversing path 6 passes between the first guide surface 10 a and the outer peripheral surface of the entrance roller 8, the branch pawl 10 is automatically switched to the second switching position by the biasing force of the spring 30. Rotate to the position. When the branch claw 10 is rotated to the second switching position, the branch claw tip 10 c of the branch claw 10 is positioned inside the outer peripheral surface of the entrance roller 8, and the sheet is sent out from the reverse path 6. In this case, the leading end of the sheet is reliably prevented from entering between the outer peripheral surface of the entrance roller 8 and the first guide surface 10 a of the branch claw 10, and the sheet from the reversing path 6 toward the image forming unit 2 is prevented. Sending can be performed smoothly.

When the sheet is fed from the reversing path 6 by the sheet reversing means 14, the reversing roller 16 is driven to rotate counterclockwise as shown by an arrow in FIG. This is performed by the driven roller 17 being in contact therewith being rotated and the sheet being nipped by the reversing roller 16 and the driven roller 17 to apply a conveying force to the sheet.

The sheet fed from the reversing path 6 is pinched by the intermediate conveying roller 11 at its leading end, and the application of the conveying force from the sheet reversing means 14 is released at the timing when the conveying force is applied from the intermediate conveying roller 11. Then, the sheet reversing means 14 is opened as shown in FIG. When the sheet reversing means 14 enters the open state as shown in FIG. 4A, the feeding of the subsequent sheet to the reversing path 6 is permitted.

The sheet nipped by the intermediate transport roller 11 is transported by the intermediate transport roller 11 to a location where the sheet is brought into contact with the registration roller 13 and is rotated at a predetermined timing. The sheet is sent to the image forming unit 2 and an image is formed on the sheet.

FIGS. 6 and 7 are explanatory views for explaining the flow of sheets when sheets are continuously conveyed to form an image. At the same time that the preceding sheet a is sent out from the reversing path 6 to the sheet conveying path 4, the succeeding sheet b is conveyed toward the reversing path 6. The preceding sheet a is initially provided with a conveying force by the sheet reversing means 14, and after the sheet reversing means 14 is stopped in the open state shown in FIG. It is transported to the forming section 2. On the other hand, the subsequent sheet b is given a conveying force by the conveying roller 7 and the entrance roller 8, and the sheet reversing means 14 is turned on as shown in FIG.
Is sent to the reversing path 6 when the open state shown in FIG. That is, the feeding of the sheet b to the reversing path 6 is performed while the sheet reversing means 14 is in the open state and the sheet a is being sent out from the reversing path 6 while the trailing end of the preceding sheet a in the reversing path 6 And the trailing end of the succeeding sheet b (the leading end when the sheet is switched back and fed).

Then, the preceding sheet a is sent out from the reversing path 6 and the succeeding sheet a is generated at a timing when an appropriate small interval is generated between the trailing end of the sheet a and the leading end in the sending direction of the succeeding sheet b. By sending a from the reversing path 6, the interval between the sheets a and b before and after being conveyed in the image forming unit 2 can be kept at a small interval, and the productivity of the image forming operation can be improved.

FIG. 11 is a diagram showing the paper transport operation during continuous image formation. The sheet is transported at a transport speed “Va” by the transport roller 7 and the entrance roller 8 from the sheet feeding tray 1 to the reversal stop position in the reversal path 6, and is intermediate with the reversal roller 16 from the reversal stop position to the image forming unit 2. The sheet is transported by the transport rollers 11 at a transport speed “Vb” equal to the image forming speed. The transport speed “Va” is
It is set to a value faster than the transport speed “Vb”.

FIG. 8 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 the re-feeding path 33 as shown by the arrow, and the sheet is conveyed as it is by the re-feeding sheet feed direction switching roller 36 to be conveyed. Sent to Road 4. After the sheet is sent to the sheet conveying path 4, the sheet is conveyed in the same manner as the sheet fed from the sheet feeding tray 1, sent to the reversing path 6, switched back, and sent to the image forming unit 2 again. . When the sheet on which an image is formed on one side is sent again to the image forming unit 2, the sheet is reversed by the switchback in the reversing path 6, so that the other side of the sheet is (The surface on which no image is formed) faces the photoreceptor 21, and the image can be formed (double-sided printing) on the other surface.

Here, the switchback of the sheet necessary for performing the duplex printing is performed using the reversing path 6 provided for improving the productivity of the image forming operation without using a dedicated sheet conveying path. Therefore, the thickness of the image forming apparatus can be prevented from being increased despite the provision of the reversing path 6, that is, the thickness of the image forming apparatus can be reduced.

When double-sided printing is performed by this image forming apparatus, paper feeding for forming the first image on one side of the paper fed from the paper feeding tray 1 and the re-feeding path 33 In this case, the so-called inter-leaf paper feeding is performed while mixing paper feeding for forming an image on the other surface of the paper conveyed with the paper. In this duplex printing by interleaf feeding, first, a plurality of (for example, two or three) sheets are continuously fed from the sheet feeding tray 1 and a predetermined page order is placed on one side of the sheets. (For example, in the case of two sheets,
(3 page order, 3 sheets, 1, 3, 5 page order)
Image formation. The first sheet on which image formation is performed on one side and conveyed through the re-feeding path 33 is
3b, the sheet on which the image is formed on one side is sent to the sheet conveying path 4 by the re-feeding sheet feed direction switching roller 36, and the sheet is alternately fed with the sheet fed from the sheet feed tray 1. The sheet is conveyed through the sheet conveying path 4. And
The paper on which double-sided printing has been completed is directly conveyed through the paper discharge path 32 and discharged to the paper discharge unit 3, and only paper on which an image is formed on one side is image-formed on the other side (double-sided printing). )
Is fed into the re-feeding path 33 in preparation for.

Here, since the conveying speed of the paper conveyed through the re-feeding path 33 is set faster than the image forming process speed in the image forming section 2, the duplex printing is performed while performing the interleaf feeding. In this case, the sheet conveyed through the re-feeding path 33 can be quickly sent to the connection point with the sheet feeding path 4, and the sheet fed from the sheet feeding tray 1 and the sheet fed through the re-feeding path 33 are conveyed. The interval between the sheet fed to the sheet transport path 4 and the sheet can be reduced, and the productivity of the duplex printing operation can be improved.

FIG. 9 shows a connection point between the paper transport path 4 and the re-feed path 33 at the time of two-sided printing by the two-sheet interleaf system in which two sheets are first continuously fed from the paper feed tray 1. FIG. 4 is a schematic diagram showing a sheet conveyance order and a sheet interval in FIG. The circled number attached to each paper indicates paper feed tray 1.
Indicates the order of the paper when the paper is fed from, and the characters of “front” attached to the circled number mean that the paper has an image formed on the front surface.

Further, in FIG. 9, “T” indicates that the trailing end of the paper (for example, paper) fed from the paper feed tray 1 passes through the connection point between the paper transport path 4 and the re-feed path 33. Then, it is the required re-feeding time required for the leading edge of the sheet “front” to reach the connection point via the image forming unit 2 and the re-feeding path 33.

The required re-feeding time “T” can be expressed by the following equation (1) in the case of a two-sheet interleaf. In the case of a two-sheet interleaf, two sheets pass through a connection point between the sheet transport path 4 and the re-feed path 33 during “T”. T = (2D + 3X) / V (1) where D: paper length X: paper interval at connection point V: paper transport speed at connection point The re-feeding required time “T” is n In the case of a sheet interleaf, it can be expressed by the following equation (2). In the case of a three-sheet interleaf, four sheets pass through the connection portion during "T". T = [2 (n-1) D + (2n-1) X] / V (2) Here, if the re-feeding required time "T" becomes longer, the paper interval "X" becomes inevitably longer, and The sheet interval at the time of leaf type double-sided printing is widened, and the productivity of the image forming operation is reduced.

Therefore, by shortening the time "T" for the re-feeding station, it is possible to narrow the sheet interval at the time of double-sided printing of the interleaf system, thereby increasing the productivity of the image forming operation.

In order to shorten the re-feeding station time "T", it is conceivable to increase the speed of "V" in the equations (1) and (2). The speed of “V” can be increased by setting the transport speed of the paper transported through the re-feed path 33 to be higher than the process speed in the image forming unit 2.

Regarding the value of the transport speed “V”, the desired paper interval “X” and the re-feeding station time “T” are determined in advance from the paper size and the number of interleaves. The transport speed “V” is obtained by searching from the set data table and substituting those numerical values into Expression (1) or Expression (2). These calculations are performed by a control unit provided in the image forming apparatus.

In order to shorten the time "T" for the re-feeding station, it is conceivable to shorten the time required from the reversing path 6 to the registration roller 13. That is, the stop time when the sheet on the reversing path 6 is switched back is shortened, and the transport speed from the reversing path 6 to the registration roller 13 is increased.

Regarding the values of the transport speed and the stop time, if the required time from the image forming unit 2 to the connection point is determined, the re-feeding station time “T” is used. The predetermined time is subtracted, and a stop time and a transport speed necessary for transporting the sheet from the reversing path 6 to the registration roller 13 within the time obtained by the subtraction are calculated. These calculations are performed in the control unit.

FIG. 10 is an explanatory diagram for explaining the flow of a sheet in the case where a sheet having an image formed on one side is inverted and discharged. The sheet on which the image has been formed on one side is transported through the re-feeding path 33 as shown by the arrow, and reaches the horizontal portion 33b. Then, the sheet is switched back by the re-feeding sheet feed direction switching roller 36, and is discharged to the sheet discharge section 3 via the reverse discharge path 35, and the surface on which the image is formed is formed by the switch back. The sheets are ejected to the sheet ejection section 3 in the order of the lower pages.

Here, a switching claw 39 urged by a spring 42 is located at a second switching position at a branch point between the re-feeding path 33 and the reverse sheet discharging path 35. Paper is transported by the switching claw 39 depending on the strength of its own waist.
Is rotated to the first switching position and enters the horizontal portion 33b. When the trailing edge of the sheet passes through the position of the switching claw 39, the switching claw 3
9 automatically returns to the second switching position by the urging force of the spring 42, so that when the sheet is switched back and fed into the reverse discharge path 35, the sheet is reliably guided to the reverse discharge path 35. Therefore, it is possible to prevent the sheet from entering the vertical portion 33a and causing a sheet jam. In addition, the switching of the switching claw 39 can be performed by a simple structure using the spring 42 without using an electric actuator such as a solenoid. Moreover, the switching operation of the switching claw 39 using the spring 42 is reliable and can be performed at high speed.

In the horizontal portion 33b, the sheet which is switched back and sent to the reversing sheet discharge path 35 is connected to the vertical portion 3b.
It is possible for the paper going from 3a to the horizontal part 33b to pass. For this reason, at the time of reverse discharge, the preceding sheet whose leading end portion has passed through the position of the switching claw 39 and has been sent to the reverse discharge path 35 is transported by a transport roller or the like provided on the reverse discharge path 35. Immediately after the sheet is nipped and the conveying force is applied, the re-feeding sheet feeding direction switching roller 36 is set in the separated state, and the subsequent sheet can be fed to the horizontal portion 33b by passing through the location of the switching claw 39. Therefore, even when the interval between the sheets conveyed in the re-feed path 33 is small, that is, even when the interval between the discharged sheets of the image-formed sheet is narrow, the reverse discharge can be smoothly performed.

Further, since the conveyance speed of the sheet conveyed through the reverse discharge path 35 is set to be faster than the image forming process speed in the image forming section 2, the sheet is conveyed through the reverse discharge path 35 to discharge the sheet. It is possible to widen the interval between the sheets that are inverted and discharged to the unit 3. Therefore, when post-processing such as punching and staple binding is performed on the paper discharged to the paper discharge unit 3, the subsequent processing can be easily performed.

Next, a second embodiment of the present invention will be described with reference to FIG.
This will be described with reference to FIGS. The same portions as those described in the first embodiment are denoted by the same reference numerals, and description thereof is omitted (the same applies to the following embodiments).

In the horizontal portion 33b of the re-feeding path 33,
First forward / reverse transport rollers 50, 5, which are transport means and reverse paper discharge means, and are re-feeding paper transport direction switching rollers.
1, a second forward / reverse transport roller 52 as a transport unit and a reverse discharge unit, and a reversing roller 53 as a reverse discharge unit. In addition, the vertical portion 3 in the re-feed path 33
A paper edge detection sensor 54 is provided in 3a. Further, at a branch point between the re-feeding path 33 and the reverse discharge path 35,
A transport roller 38 and a switching claw 39 are provided.

The first forward / reverse transport rollers 50 and 51 are always in contact with a drive roller connected to a forward / reverse switchable motor (not shown) such as a stepping motor or a DC servomotor. And a driven roller. The first forward / reverse transport rollers 50 and 51 are provided with a forward rotation direction for transporting the paper fed to the horizontal portion 33b of the re-feeding path 33 toward the paper transport path 4 and a switchover of the paper for reverse discharge. It is provided so as to be switchable between forward and reverse rotation in the reverse rotation direction to be fed into the paper path 35. The forward / reverse switching of the first forward / reverse transport rollers 50 and 51 is performed by forward / reverse switching of the motor.

As shown in FIG. 13, when the sheet is inverted and discharged, the sheet is inverted and discharged toward the inverted sheet discharge path 35 downstream of the branch point of the horizontal portion 33b with the inverted sheet discharge path 35. A passing area “X” where the preceding sheet A and the succeeding sheet B sent to the horizontal portion 33b pass each other is provided. The passing area “X” changes depending on the size of 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 50, 51
Are arranged outside the passing area “X”. For this reason, while the first forward / reverse transport rollers 50 and 51 sandwich the preceding paper A and feed the paper A to the reverse discharge path 35, the subsequent paper B is transported to the first forward / reverse transport roller 50. , 5
Inconvenience of reaching 1 does not occur. Subsequent paper B
Is transported to the position of the first forward / reverse transport rollers 50 and 51, the preceding sheet A is
0, 51, the first forward / reverse transport rollers 50, 51 are driven to rotate in the forward direction so that the succeeding sheet B sent to the horizontal section 33b is downstream of the horizontal section 33b ( Direction to transport toward paper transport path 4)
To a predetermined position. Therefore, the first forward / reverse transport rollers 50 and 51 do not need to be separated from each other even when the reversed paper is passed by the horizontal portion 33b, and only need to switch the rotation direction while maintaining the contact state. , Simple structure.

The second forward / reverse transport roller 52 has the same basic structure as the first forward / reverse transport rollers 50 and 51, and has a drive roller connected to a motor capable of switching between forward and reverse rotation, and abuts against the drive roller. 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 52 can be switched between a paper feed state in which the paper is nipped and transported and a released state in which the paper is nipped by the driven roller being brought into contact with and separated from the drive roller. Is provided. This switching is performed by driving a solenoid (not shown).

Further, the second forward / reverse transport roller 52 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 transport roller 52, the second forward / reverse transport roller 52 is switched to the open state and the low-speed transport is not hindered. Like that.

The reversing roller 53 is provided near the branch point of the reversing discharge path 35 in the horizontal portion 33b. The reversing roller 53 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 into the reversing discharge path 35. The driving roller drives the driven roller to contact and separate from the driving roller. 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. Also, when the reversing roller 53 is driven to rotate (when the sheet is reversed and discharged toward the reversing discharge path 35), the reversing roller 53 and the first
The second forward / reverse transport rollers 50, 51, and 52 are synchronously driven to rotate at the same peripheral speed. As a result, the sheets to be reversed and discharged are transferred to the first and second forward / reverse transport rollers 50 and 5.
Pulling or loosening between the first and second rollers 52 and the reversing roller 53 is prevented.

The paper edge detection sensor 54 is installed near the branch point between the re-feeding path 33 and the reversing sheet discharging path 35 and upstream of the branch point, and the sheet conveyed through the re-feeding path 33 is provided. Detects the trailing end. The first and second forward / reverse transport rollers 50, 51, 5
The rotation direction of No. 2 is switched from the normal rotation direction to the reverse rotation direction,
Then, the reversing roller 53 and the second forward / reverse transport roller 52 are switched to the contact state.

[0099] In the reverse paper discharge path 35, paper is
(See FIG. 1 and the like) is provided with a reverse discharge roller 55 that is driven to rotate in the reverse discharge direction. Before the leading edge of the succeeding sheet B conveyed along the re-feed path 33 reaches the position of the reversing roller 53, the reversing sheet discharging roller 55 is used to move the preceding sheet A to be reversed and ejected. It is arranged at a position reaching 55. Thereby, when the reversing roller 53 is switched to the open state for the passing conveyance of the preceding sheet A and the succeeding sheet B, the leading end of the preceding sheet A can be held by the reversing discharge roller 55, Can be smoothly continued. The reversing discharge roller 55 and the first and second forward / reverse transport rollers 50, 51, 52
When the sheet is inverted and discharged, the transport speed is set higher than the transport speed when the sheet is fed into the re-feeding path 33. This setting is performed by, for example, changing the number of rotations of the motor between forward rotation and reverse rotation.

In such a configuration, FIG. 12 shows that the reverse sheet discharge of the preceding sheet A sent into the horizontal section 33b has started, and the succeeding sheet B has passed through the vertical section 33a in the horizontal section 3a.
3b. At this time, the first and second forward / reverse transport rollers 50, 51, 52 are both driven to rotate in the reverse direction, and the reverse roller 53 is also driven to rotate in the same direction, so that the sheet A is fed into the reverse sheet discharge path 35. I am trying to do.

FIG. 13 shows a state in which the preceding sheet A and the succeeding sheet B are being conveyed by passing each other in the horizontal section 33b. At this time, the second region located in the passing area “X”
The forward / reverse transport roller 52 and the reversing roller 53 are switched to the open state, so that the subsequent sheet B is not prevented from being fed into the horizontal portion 33b. Since the leading end side of the preceding sheet A is nipped by the reversing discharge roller 55, the first and second forward / reverse transport rollers 50, 5
Even when the conveying force from the rollers 1 and 52 and the reversing roller 53 is not applied, the sheet is properly conveyed toward the sheet discharge unit 3.

FIG. 14 shows that the preceding sheet A also enters the reverse discharge path 35 at the trailing end, and the subsequent sheet B
Is transported toward the paper transport path 4 side.
The first and second forward / reverse transport rollers 50, 51, and 52 are all driven to rotate in the forward direction, and the reverse roller 53 is open. Then, the subsequent sheet B is transferred to the horizontal portion 33b.
That the sheet has been fed to the predetermined position.
When the determination is made based on the detection result of FIG. 4, the state shown in FIG. 12 is reached, and the paper B is rotated by the first and second forward / reverse transport rollers 50, 51, 52 and the reverse roller 53 that are driven to rotate in the reverse direction.
Is switched back, and feeding of the sheet B to the reverse sheet discharging path 35 is started. Therefore, the sheet that has been switched back in the horizontal section 33b and sent to the reverse sheet discharge path 35 does not enter a free state in the course of switching the conveyance direction, and the sheet conveyed through the re-feed path 33 is conveyed. Lateral shift and skew in the sheet width direction caused by the free state on the way can be prevented.

If the sheet to be reversed and discharged has a long size, the second forward / reverse transport roller 52 and the reverse roller 53 can be dispensed with.
Reversal discharge can be performed using only 0 and 51.

Next, a third embodiment of the present invention will be described with reference to FIG.
5 will be described. Re-feeding path 33 and reverse sheet discharging path 35
The roller 60 and the first opposing roller 61
, A second opposing roller 62, a gripping pad 63 as a gripping means, and a detection sensor 64.

The roller 60 has a part of the outer peripheral portion,
3 and a reversing discharge path 35, which are connected to a motor (not shown) to advance the sheet conveyed in the re-feed path 33 and the sheet conveyed in the reversal discharge path 35. It is driven to rotate along the traveling direction. The roller 60 has a cylindrical roller body 60a and a number of protrusions 60b radially provided on the outer periphery of the roller body 60a, and these protrusions 60b are formed of an elastic body.

The first opposing roller 61 is in contact with the outer peripheral portion of the roller 60 and is arranged at a position where the sheet conveyed by the roller 60 through the re-feed path 33 is pinched, and the direction in which the pinched sheet is conveyed. It is turned around. Further, at a position where the first opposing roller 61 contacts the roller 60, the projection 60b of the elastic body is bent to substantially the same position as the outer peripheral surface of the roller body 60a.

The second opposing roller 62 is in contact with the outer peripheral portion of the roller 60, and by this roller 60, the reverse discharge path 35
Is arranged at a position where the sheet to be conveyed is pinched, and is rotated in the direction in which the pinched sheet is conveyed. Further, at a position where the second opposing roller 62 contacts the roller 60, the projection 60b of the elastic body is bent to substantially the same position as the outer peripheral surface of the roller body 60a.

The detection sensor 64 is disposed upstream of the first opposing roller 61 in the direction in which the sheet is conveyed, and detects the end (leading end and rear end) of the sheet being conveyed.

The grip pad 63 is connected to an actuator such as a solenoid, and moves to a grip position for gripping and stopping the paper on the re-feed path 33 and a grip release position for releasing the gripped and stopped state. It is provided freely.

In such a configuration, when performing the reverse discharge, the sheet conveyed through the re-feed path 33 is sandwiched between the roller 60 rotating in the direction of the arrow and the first opposing roller 61, and advances. The gripping pad 63 is moved to the gripping position immediately after the paper 64 detects the trailing edge of the paper and before the trailing edge of the paper passes through the contact portion between the roller 60 and the first opposing roller 61. The transport is stopped by being gripped. Even after the paper is gripped by the grip pad 63, the rotation of the roller 60 is continued, so that the rear end side of the paper is continuously transported on the re-feed path 33, and the paper is Curves gradually between. When the trailing edge of the sheet passes through the contact portion between the roller 60 and the first opposing roller 61, the sheet is moved by the trailing edge (the leading edge when the sheet is switched back and conveyed through the reverse sheet discharging path 35). 60 are held by the projections 60b,
The trailing end of the sheet held by the protrusion 60b is carried to the reverse sheet discharging path 35 side with the rotation of the roller 60. When the rear end of the sheet curved between the grip pad 63 and the roller 60 is transported to a predetermined position on the reversing sheet discharge path 35 side with the rotation of the roller 60, the curved sheet changes its curved state due to its own restoring force. The paper jumps up so that the rear end of the paper
Ob is released from the holding state, and enters between the roller 60 and the second opposing roller 62.

By releasing the gripping state of the gripping pad 63 immediately after the rear end of the sheet enters between the roller 60 and the second opposing roller 62, the sheet is released by the roller 60 and the second opposing roller 62. The sheet is nipped and conveyed, and is conveyed through the reverse sheet discharging path 35 with the conveyance direction switched back.

Here, in the process in which the transport direction is switched back so that the paper transported through the re-feeding path 33 is transported through the reverse discharge path 35, the paper is transported by the roller 60 and the first
The sheet is conveyed while being pinched by the opposing roller 61, and is stopped by being held by the holding pad 63.
And is conveyed while being nipped by the second opposing roller 62,
There is no rubbing in contact with a hard member such as a branch claw. For this reason, it is possible to prevent the paper from being rubbed and scratched, and the image formed on the paper from being rubbed and deteriorating the image quality.

At the time of switchback, the leading edge of the sheet (the trailing edge of the sheet before switchback) is set to the protrusion 60b.
Is transported without causing the leading end of the paper to be displaced in an oblique direction, thereby preventing skew.

Next, a fourth embodiment of the present invention will be described with reference to FIG.
6 will be described. The basic structure of the present embodiment is the same as that of the third embodiment, and is different from the third embodiment in that, instead of the gripping pad 63, a transport roller 70 whose rotation direction can be switched between forward and reverse is used as the gripping means. It is.

In such a configuration, when the sheet is conveyed through the re-feeding path 33 at the time of reverse sheet ejection, the conveying roller 70 is driven to rotate in the direction of arrow a. Then, at a predetermined timing after the trailing edge of the sheet conveyed in the re-feed path 33 is detected by the detection sensor 64, for example, the trailing edge of the sheet passes through the contact portion between the roller 60 and the first opposing roller 61. The rotation direction of the transport roller 70 is switched at the timing after the rotation to drive the transport roller 70 in the direction of arrow b.

As a result, the sheet is sent to the roller 60 side, and the leading end of the sheet (the rear end when the sheet is being conveyed through the re-feed path 33) is held by the projection 60b, and the rotation of the roller 60 is performed. As a result, the sheet is conveyed to the reversing sheet discharge path 35 side, and the leading end of the sheet enters between the roller 60 and the second opposing roller 62. The tip is the roller 60 and the second opposing roller 62
The sheet that has entered the abutting portion with the sheet is nipped by the roller 60 and the second opposing roller 62 to be provided with a conveying force, and is conveyed through the reverse sheet discharging path 35.

Here, by using the transport roller 70 that can be switched between forward and reverse as the gripping stop means, it is necessary to curve the paper between the roller 60 and the transport roller 70 when switching back the transport direction of the paper. This prevents the sheet from being bent due to the bending.

When the rotation direction of the transport roller 70 is switched, the paper transport speed of the transport roller 70 rotating in the direction of transporting the paper on the re-feeding path 33 is adjusted by the roller 60.
The speed is reduced from the paper transport speed of
May be switched.

Thus, when the rotation of the transport roller 70 is stopped and the sheet is gripped and stopped,
The sheet can be gently curved between the transport roller 70 and the roller 60. Further, it is possible to control the end of the sheet so as not to separate from the roller 60 at the time of the reverse sheet ejection, and it is possible to reduce the time for switching back the sheet.

[0120]

According to the image forming apparatus of the first aspect of the present invention, the sheet fed to the image forming section is fed to the reversing path to be switched back.
Since the preceding sheet sent to the sheet conveying path and the subsequent sheet sent to the reversing path are at least partially overlapped, the feeding speed of the sheet to the reversing path and the feeding speed of the sheet from the reversing path, By controlling the timing of feeding the sheet from the reversing path and the like, the sheet feeding timing from the sheet storage unit and the conveyance speed during conveyance to the reversing path may vary. Can be accurately maintained at a small interval to improve the productivity of the image forming operation, and furthermore, a sheet on which an image is formed on one side and discharged from the image forming unit is re-feeded. When the sheet is fed again to the image forming unit to perform double-sided printing, the reversing path can also be used as a sheet conveying path for switching back the sheet for double-sided printing. It is not necessary to provide a dedicated paper transport path for switching back the paper in order to perform surface printing, and it is possible to prevent the image forming apparatus from being thickened despite the provision of the reversing path, that is, to reduce the thickness of the image forming apparatus. it can.

According to the second aspect of the present invention, in the image forming apparatus according to the first aspect, the re-feeding path, which is branched from the middle of the re-feeding path and is connected to the sheet discharging unit, And a reversing sheet discharging means for switching back the sheet fed to the path toward the reversing sheet discharging path and reversing and discharging the sheet.
When a sheet having an image formed on one side is sent to the re-feeding path, the sheet is switched back by the reverse sheet discharging means and sent to the reverse sheet discharging path, whereby an image is formed on the sheet. The sheets can be inverted and discharged to the sheet discharge section in the order of the pages with the surfaces facing down.

According to the third aspect of the present invention, in the image forming apparatus according to the second aspect, the conveying means and the reverse discharge means are located downstream of a branch point of the re-feed path and the reverse discharge path. A forward direction in which the sheet fed into the re-feeding path is pinched and conveyed toward the sheet conveying path, and the sheet is switched back from the state in which the pinched state is maintained to the reverse sheet discharging path. Since the re-feeding paper feed direction switching roller is switchable between forward and reverse rotations in the feeding reverse direction, the re-feeding paper feed direction switching roller has a function of a transport unit and a reverse discharge unit. There is no need to provide a separate paper means, and the structure can be simplified. Also, at the time of reverse discharge, the sheet fed into the re-feeding path is pinched by the re-feeding sheet feeding direction switching roller rotating in the normal rotation direction, and thereafter, the re-feeding sheet feeding direction switching roller holding the sheet is rotated. Since the sheet is fed to the reverse discharge path by being driven to rotate in the reverse direction, the sheet to be reversely discharged does not become free during the conveyance,
It is possible to prevent a lateral shift and a skew in the sheet width direction caused by the free state of the sheet being conveyed.

According to the fourth aspect of the present invention, in the image forming apparatus according to the second or third aspect, in the re-feeding path, the preceding sheet which is switched back and fed to the reverse sheet discharging path and the re-feeding path. Since the succeeding sheet conveyed in the path can pass each other, when the trailing end of the preceding sheet fed to the reverse discharge path is located in the re-feed path, the subsequent sheet is re-feeded. , And even when the interval between sheets conveyed along the re-feed path is small, that is, even when the interval between sheets of paper on which an image is formed is narrow, reverse sheet ejection can be performed smoothly. .

According to the fifth aspect of the present invention, in the image forming apparatus according to the fourth aspect, the re-feeding sheet feeding direction switching roller is connected to the preceding sheet fed back to the reverse sheet discharging path after being switched back. Since the re-feeding paper feeding direction switching roller is driven in the reverse rotation direction, the re-feeding paper feeding direction switching roller is held in the outside of the passing area where the succeeding sheet conveyed in the feeding path passes, and the reversing sheet discharging path is nipped. When the subsequent paper reaches the re-feeding paper feed direction switching roller, the inconvenience that the subsequent paper conveyed in the re-feeding path reaches the re-feeding paper feed direction switching roller does not occur. Since the state of sandwiching the preceding sheet by the re-feeding sheet feed direction switching roller has been completed, even if the preceding sheet and the succeeding sheet pass each other in the re-feeding path,
By reversing the rotation direction without moving the re-feeding paper feed direction switching roller forward and backward, the paper can be inverted and discharged.

According to a sixth aspect of the present invention, in the image forming apparatus according to any one of the second to fifth aspects, the switching claw disposed at a branch point between the re-feeding path and the reverse discharge path,
An urging body for urging the switching claw, wherein the urging body positions the switching claw at a position that allows the sheet switched back in the re-feeding path to be sent to the reverse sheet discharging path. When the paper ejected from the image forming unit and conveyed through the re-feeding path abuts against the switching claw, the switching claw is biased to the position where the advance of the sheet is permitted. The paper is transported in the re-feeding path by passing the switching claw, and the sheet is switched back in the re-feeding path to the reversing discharge path. The switching of the switching claw required for the feeding can be performed by an urging body having a simple structure without using an electric actuator such as a solenoid, and the switching claw using the urging body can be switched. Switching operation can be assured and can respond at high speed. That.

According to the seventh aspect of the present invention, in the image forming apparatus according to any one of the second to fifth aspects, the image forming apparatus is disposed at a branch point between the re-feeding path and the reverse discharge path, and The roller is driven to rotate in the traveling direction of the sheet conveyed and along the traveling direction of the sheet conveyed through the reverse discharge path, and is brought into contact with a roller having a number of protrusions on an outer peripheral portion and an outer peripheral portion of the roller. A first opposing roller which is disposed at a position for nipping paper conveyed through the re-feeding path by the roller and rotates in the direction in which the nipped paper is conveyed; A second opposing roller that is arranged at a position for nipping the paper conveyed through the reversing discharge path and rotates in the direction in which the nipped paper is conveyed, and is disposed downstream of the first opposing roller on the re-feeding path. The paper conveyed along the re-feed path Since having a gripping means for,
In the process of switching the transport direction so that the paper transported in the re-feed path is transported in the reverse paper discharge path, the paper does not come into contact with a member such as a branch claw and is rubbed. Also, it is possible to prevent the paper from being rubbed and scratched, and to prevent the image formed on the paper from being rubbed and the image quality from deteriorating. Further, since the leading edge of the sheet is conveyed to the reversing discharge path side while being held by the protrusion, the leading end of the sheet is conveyed without causing a shift in the oblique direction. Occurrence can be prevented.

According to the eighth aspect of the present invention, in the image forming apparatus according to the seventh aspect, since the holding means is a holding pad movable to a holding position and a holding release position, the holding pad is moved to the holding position. By moving the sheet, the sheet being conveyed along the re-feeding path can be gripped and stopped.

According to the ninth aspect of the present invention, in the image forming apparatus according to the seventh aspect, since the gripping means is a transporting roller capable of switching the rotation direction between forward and reverse and nipping the paper, By stopping the rotation, the sheet being conveyed along the re-feeding path can be gripped and stopped.

According to the tenth aspect, the first aspect is provided.
10. The image forming apparatus according to any one of claims 9 to 9, wherein the conveying unit can feed the sheet in the re-feeding path to the sheet feeding path at an arbitrary timing. Can be fed to the paper transport path at an appropriate timing, and paper feeding for performing the first image formation on one side of the paper fed from the paper storage unit and paper feeding in the re-feeding path can be performed. It is possible to perform a sheet feeding in which a sheet feeding for performing image formation (double-sided printing) on the other side is mixed, that is, a so-called interleaf sheet feeding.

According to the eleventh aspect, according to the first aspect,
The image forming apparatus according to any one of claims 1 to 10,
Since the transport speed of the paper transported in the re-feeding path is set faster than the image forming process speed in the image forming unit,
When performing double-sided printing while performing interleaf paper feeding, the paper conveyed through the re-feed path can be quickly sent to the connection point with the paper conveyance path, and the paper fed from the paper The interval between the sheet conveyed along the feeding path and the sheet conveyed to the sheet conveying path can be reduced, and the productivity of the double-sided printing operation can be improved.

According to the twelfth aspect, the second aspect is provided.
In the image forming apparatus according to any one of the above items (1) to (6), the conveying speed of the sheet conveyed through the reverse sheet discharging path is set higher than the image forming process speed in the image forming unit.
It is possible to widen the interval between the sheets to be inverted and discharged to the sheet discharge unit, and to easily perform the subsequent processing when performing post-processing such as punching and stapling on the sheets discharged to the sheet discharge unit. be able to.

According to the thirteenth aspect, according to the first aspect,
13. The image forming apparatus according to any one of claims 12 to 12, wherein
Since the image forming unit is an electrophotographic image forming unit,
In an image forming apparatus having an electrophotographic image forming section, the invention according to any one of claims 1 to 12 can be realized.

According to the fourteenth aspect of the present invention, the first aspect is provided.
13. The image forming apparatus according to any one of claims 12 to 12, wherein
Since the image forming section is a digital electrophotographic image forming section provided with digital writing means, the image forming apparatus having a digital electrophotographic image forming section provided with digital writing means is provided. Any one of the inventions can be realized.

[Brief description of the drawings]

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

FIG. 2 is an enlarged front view showing a mechanism portion along a paper transport path.

FIG. 3 is a perspective view showing an entrance roller and a branch claw.

FIGS. 4A and 4B are explanatory diagrams illustrating an operation state of the sheet reversing unit, where FIG. 4A is an open state and FIG.

FIG. 5 is a perspective view showing a transport roller and a switching claw.

FIG. 6 is an explanatory diagram illustrating a state in which a sheet is fed to an image forming unit when image formation is performed continuously.

FIG. 7 is an explanatory diagram illustrating a state in which a sheet is fed to an image forming unit when image formation is performed continuously.

FIG. 8 is an explanatory diagram illustrating a sheet conveyance state during duplex printing.

FIG. 9 is a schematic diagram illustrating a sheet conveyance order and a sheet interval at a connection point between a sheet conveyance path and a re-feeding path during two-sided interleaf printing.

FIG. 10 is an explanatory diagram illustrating a sheet conveyance state during reverse sheet ejection.

FIG. 11 is a diagram illustrating a sheet conveyance operation during continuous image formation.

FIG. 12 is an explanatory diagram illustrating a sheet conveyance state at the time of reverse sheet ejection according to the second embodiment of the present invention.

FIG. 13 is an explanatory diagram illustrating a sheet conveyance state during reverse sheet ejection.

FIG. 14 is an explanatory diagram illustrating a sheet conveyance state during reverse discharge.

FIG. 15 is a schematic diagram showing a mechanism for switching back a sheet for reverse sheet ejection according to a third embodiment of the present invention.

FIG. 16 is a schematic diagram showing a mechanism for switching back a sheet for reverse sheet ejection according to a fourth embodiment of the present invention.

FIG. 17 is a schematic diagram illustrating the structure of a conventional image forming apparatus.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Paper storage part 2 Image formation part 3 Paper discharge part 4 Paper conveyance path 6 Reversing path 14 Paper reversing means 20 Separation paper supply means 23 Digital writing means 33 Re-feeding path 35 Reversing discharging path 36 Conveying means, Reversing discharging Means, re-feeding paper feed direction switching roller 39 switching claw 42 urging body 50, 51 transport means, reversing discharge means, re-feeding paper feed direction switching roller 52 transport means, reversing discharge means 53 reversing discharge means 60 roller 60b Projection 61 First opposing roller 62 Second opposing roller 63 Holding means, holding pad 70 Holding means, transport roller

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Seiji Hoshino 1-3-6 Nakamagome, Ota-ku, Tokyo Inside Ricoh Company (72) Inventor Hiromichi Matsuda 1-3-6 Nakamagome, Ota-ku, Tokyo Stock F term in Ricoh Company (reference) 3F053 BA03 BA04 BA11 BA12 EA03 EA05 EB01 EC02 ED25 GA05 GA18 LA02 LB03 3F100 AA04 CA12 CA15 EA03

Claims (14)

[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 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 the paper is switched back and sent to the paper transport path, and an opening that allows at least a part of the preceding paper fed from the reverse path and the subsequent paper fed to the reverse path to overlap with each other. A sheet reversing means that can be switched to a state, a re-feeding 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 a re-feeding path. Front the sent paper An image forming apparatus having a transfer means for transferring to the sheet conveying path, a. 2. A reversing sheet discharging path branched from the middle of the re-feeding path and connected to a sheet discharging section, and a sheet fed to the re-feeding path is switched to the reversing sheet discharging path. The image forming apparatus according to claim 1, further comprising: a reversing sheet discharging unit that reverses and discharges the sheet. 3. The image forming apparatus according to claim 2, wherein:
A forward rotation direction that is provided downstream of a branch point of the refeeding path with the reversing sheet discharging path, and that pinches the sheet fed to the refeeding path and conveys the sheet toward the sheet conveying path; 3. The image forming apparatus according to claim 2, wherein the image forming apparatus is a re-feeding sheet feeding direction switching roller capable of switching between forward and reverse rotations in a reverse rotation direction in which the sheet is switched back from the state in which the sandwiched state is maintained and sent to the reverse sheet discharging path. 4. In the re-feeding path, a preceding sheet that is switched back and sent to the reverse sheet discharging path and a subsequent sheet conveyed in the re-feeding path can pass each other. 4. The image forming apparatus according to 2 or 3. 5. The re-feeding sheet feeding direction switching roller,
5. A sheet which is switched back and sent to the reversing sheet discharging path and a subsequent sheet conveyed in the re-feeding path are provided outside a passing area where the sheets pass each other.
The image forming apparatus as described in the above. 6. A switching claw disposed at a branch point between the re-feeding path and the reverse sheet discharging path, and an urging member for urging the switching claw. The switching claw is urged to position the switching claw at a position that allows the sheet switched back in the re-feeding path to be fed into the reverse sheet discharging path, and the urging force is applied to the image forming apparatus. When the sheet discharged from the unit and conveyed through the re-feeding path contacts the switching claw, the switching claw is set to a size that allows the switching claw to move to a position that allows the sheet to advance. The image forming apparatus according to claim 2. 7. A traveling direction of a sheet conveyed through the re-feeding path and a traveling direction of a sheet conveyed through the reversing sheet-discharging path, which is disposed at a branch point between the re-feeding path and the reverse sheet discharging path. A roller having a large number of protrusions on the outer peripheral portion, which is driven to rotate in the direction, and disposed at a position where the roller is held in contact with the outer peripheral portion of the roller and the sheet conveyed through the re-feeding path is nipped by the roller. A first opposing roller that rotates in the direction of transporting the nipped paper; and a roller that abuts on an outer peripheral portion of the roller and is located at a position where the roller conveys the inverted paper discharge path by the roller. A second opposing roller that rotates in the direction in which the conveyed sheet is conveyed, and a sheet that is disposed on the re-feed path and downstream of the first opposing roller and grips the sheet that is conveyed through the re-feed path. And a gripping means for stopping. 6. The image forming apparatus according to any one of 5. 8. The image forming apparatus according to claim 7, wherein the gripping means is a gripping pad movable to a gripping position and a gripping release position. 9. The image forming apparatus according to claim 7, wherein said gripping means is a transport roller whose rotation direction is switchable between normal and reverse directions, and which holds a sheet. 10. The image forming apparatus according to claim 1, wherein said transport means is capable of sending out the paper in said re-feed path to said paper transport path at an arbitrary timing. 11. The image forming apparatus according to claim 1, wherein a conveying speed of the sheet conveyed through the re-feeding path is set higher than an image forming process speed in the image forming unit. . 12. The image forming apparatus according to claim 2, wherein a conveying speed of a sheet conveyed through the reverse sheet discharging path is set higher than an image forming process speed in the image forming unit. . 13. The image forming apparatus according to claim 1, wherein the image forming unit is an electrophotographic image forming unit. 14. 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.