JP4485702B2 - Image forming apparatus, printer and copying machine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent lateral drift and skew of reversely delivery paper by a simple mechanism. SOLUTION: When reversely delivering the paper formed with an image on one face, the paper formed with the image in the one face and delivered from an image forming part is sent to a reconveying path 29, conveyed to a predetermined position toward a paper conveying path by first normal/reverse rotation conveying rollers 32 and 33 rotatively driven in a normal rotation direction, switched back by rotatively driving the first normal/reverse rotation conveying rollers 32 and 33 in a reverse rotation direction, sent to a reverse paper delivery path 31 and delivered. The paper to be reversely delivered does not become free during conveyance inside the reconveying path 29, and the lateral drift and skew caused by a free state of the paper during conveyance can be prevented.

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention can efficiently perform continuous image formation, and further has an image forming function including a duplex printing function, and a reverse sheet discharging function for discharging the printed paper in page order with the printing surface facing down. The present invention relates to an apparatus, a printer using the image forming apparatus, and a copying machine.
[0002]
[Prior art]
2. Description of the Related Art Conventionally, there has been known an image forming apparatus that has a duplex printing function and a reverse discharge function that discharges paper after printing has been printed in page order with the printing surface facing downward.
[0003]
A schematic structure of such an image forming apparatus will be described with reference to FIG. This image forming apparatus includes a sheet storage unit 101 in which sheets are stacked and held, an image forming unit 104 that forms an image on a sheet that has been fed with a photosensitive member 102 and a developing unit 103, and a sheet on which an image is formed. Is provided, and a paper transport path 106 for transporting paper is provided between the paper storage unit 101 and the image forming unit 104.
[0004]
On the paper discharge side of the image forming unit 104, a direct paper discharge path 107 through which the image-formed paper is conveyed toward the paper paper discharge unit 105, and the image-formed paper for duplex printing or reverse paper discharge A paper conveyance path 108 to be conveyed is provided. A switching claw 109 is provided at a branch point between the direct paper discharge path 107 and the paper transport path 108 to switch the transport direction of the paper discharged from the image forming unit 104 to the direct paper discharge path 107 or the paper transport path 108. Yes.
[0005]
A reversing path 110 is provided on the leading end side of the paper transport path 108 to switch back the paper transported through the paper transport path 108. In the reversing path 110, there is provided a reversing roller 111 that is movable to a contact / separation position (vertical position) and that is driven to rotate while pinching the paper so as to switch back the paper.
[0006]
In the forward direction of the sheet switched back in the reversing path 110, a re-conveying path 112 for conveying the sheet to the image forming unit 104 again for duplex printing, and the sheet with the printing surface facing downward. A reverse paper discharge path 113 for discharging the paper to the paper discharge unit 105 in the order of pages is provided. The re-conveying path 112 is disposed below the reversing path 110, and the re-conveying path 112 is arranged at the branch point between the re-conveying path 112 and the reversing discharge path 113 with the transport direction of the paper switched back in the reversing path 110. Alternatively, a switching claw 114 for switching to the reverse paper discharge path 113 is provided.
[0007]
When image formation is continuously performed by such an image forming apparatus, a sheet that is separated and fed from the sheet storage unit 101 or a sheet that is re-conveyed via the re-conveying path 112 is used as the sheet conveying path 106. Then, the images are successively sent to the image forming unit 104 to form images one after another on each sheet. Each sheet is temporarily stopped at a position in contact with the registration roller 115 and sent to the image forming unit 104 at a timing at which an image is formed at an appropriate position on the sheet.
[0008]
When performing double-sided printing in this image forming apparatus, the switching claw 109 is switched so that the paper on which image formation on one side has been completed is transported to the paper transport path 108, and the paper is transported to the paper transport path 108. Is sent into the reversing path 110. Then, the switching claw 114 is switched so that the sheet fed into the reversing path 110 is fed back into the reconveying path 112 when the sheet is switched back by the action of the reverse rolling roller 111, and the sheet is reconveyed. The image is sent again to the image forming unit 104 via the path 112 and the sheet conveyance path 106. As a result, image formation (double-sided printing) is performed on the other side of the paper, and the paper on which double-sided printing has been performed is discharged directly to the paper discharge unit 105 via the paper discharge path 107.
[0009]
When performing reverse paper discharge in this image forming apparatus, the switching claw 109 is switched so that the paper on which image formation on one side has been completed is transported to the paper transport path 108, and the paper is transported to the paper transport path. It is fed into the reversing path 110 via 108. Then, the switching claw 114 is switched so that the sheet fed into the reversing path 110 is fed back into the reversing discharge path 113 when the sheet is switched back by the action of the reverse roll roller 111, and the sheet is reversed. Paper is discharged to the paper discharge unit 105 via the paper discharge path 113. The paper is discharged in page order with the printing surface facing downward, so-called reverse paper discharge.
[0010]
Here, in the image forming apparatus as shown in FIG. 15, the paper transported through the paper transport path 108 is temporarily freed by being thrown into the reversing path 110. The formed paper is pinched by the reverse roller 111 and switched back, and sent to the reverse paper discharge path 113 or the re-conveyance path 112.
[0011]
[Problems to be solved by the invention]
However, once the paper transported through the paper transport path 108 is fed into the reversing path 110, once the paper becomes free, the paper may be laterally shifted in the paper width direction or skewed.
[0012]
For this reason, it is necessary to provide a jogger mechanism (not shown) for correcting the lateral misalignment of the paper in the reversing path 110 on the reversing path 110. When such a jogger mechanism is provided, the number of parts is reduced. Increases the complexity of the mechanism and the cost of the image forming apparatus increases.
[0013]
Further, when the jogger mechanism is not provided, the paper that has been reversely discharged on the paper discharge unit 105 varies, and the post-processing is troublesome.
[0014]
An object of the present invention is to prevent a lateral shift and skew of a sheet to be reversed and discharged by a simple mechanism.
[0015]
Another object of the present invention is to prevent lateral misalignment or skew of a reversely discharged sheet by a simple mechanism even when image formation is performed at high speed.
[0016]
[Means for Solving the Problems]
According to a first aspect of the present invention, there is provided an image forming apparatus comprising: a paper storage unit that stacks and holds paper; a separation paper feeding unit that separates and feeds paper one by one from the paper storage unit; and an image on the fed paper. An image forming unit for forming; a paper transport path from the paper storage unit to the image forming unit; a reversing path through which the paper transported through the paper transport path connected to the middle of the paper transport path is sent; At least a part of the feeding state in which the sheet sent to the reversing path is switched back and sent to the sheet conveying path, and the preceding sheet fed from the reversing path and the succeeding sheet fed to the reversing path are A sheet reversing means that can be switched to an open state that allows superposition, a re-conveying path connected between the paper discharge side of the image forming unit and the upstream side of the reversing path of the sheet conveying path; In the middle of the re-transport path And a reversing paper discharge path that is branched from the reversing paper discharge section and connected to the paper discharge section, and is provided downstream from the branch point of the reversing paper discharge path. A first forward / reverse conveyance roller that can be switched between forward and reverse rotations in a forward rotation direction for conveying toward the conveyance path and a reverse rotation direction for switching back the paper and feeding it to the reverse discharge path.
[0017]
Therefore, the sheets stacked and held in the sheet storage unit are separated and fed one by one by the separation feeding unit and conveyed on the sheet conveyance path, and the sheet conveyed on the sheet conveyance path is sent to the reversing path, Then, the sheet is reversed by the sheet reversing means, sent out from the reversing path toward the image forming unit, and the image is formed on the sheet fed into the image forming unit.
[0018]
When the paper fed into the reversing path is switched back, it is switched back by controlling the paper feeding speed to the reversing path, the paper feeding speed from the reversing path, the paper feeding timing from the reversing path, etc. Thus, the interval between sheets fed to the image forming unit can be reduced. In other words, even when there is a variation in the timing of feeding from the paper storage unit or a variation in the conveyance speed during conveyance up to the reversing path, the feeding of the paper to the image forming unit is accurately maintained at a small interval. Therefore, the productivity of the image forming operation in the image forming apparatus can be improved.
[0019]
When performing double-sided printing, an image is formed on one side and discharged from the image forming unit is sent to the re-conveying path, and the first forward / reverse conveying roller is driven to rotate in the forward direction. Send the paper to the paper transport path. The paper sent out to the paper conveyance path in this way is sent again to the reversing path, switched back on the reversing path, and then sent back to the image forming unit to form an image on the other side of the paper (double-sided printing). ) Is performed. Since the sheet sent out from the re-conveying path to the sheet conveying path is conveyed downstream from the branch point of the reverse discharge path in the re-conveying path, the state held between the first forward / reverse conveying rollers is maintained. Does not cause lateral misalignment or skew.
[0020]
When performing reverse paper discharge, an image is formed on one side and the paper discharged from the image forming unit is sent to the re-conveying path, and is rotated by the first forward / reverse conveying roller that is driven to rotate in the normal rotation direction. The paper is transported to a predetermined position toward the paper transport path. Then, after the sheet is conveyed to a predetermined position on the re-conveyance path, the first forward / reverse conveyance roller is rotationally driven in the reverse direction to switch back the sheet and send it to the reverse discharge path. Paper is discharged to the paper discharge section. At the time of this reverse paper discharge, the paper fed into the re-conveying path is nipped by a first normal / reverse conveying roller that is rotationally driven in the normal rotation direction, and then the first normal / reverse conveying roller that holds the paper. When the paper is rotated in the reverse direction, the paper is fed into the reverse paper discharge path, so that the paper that is reversely discharged is not free during the conveyance, and the paper being conveyed is free during the conveyance. A lateral shift or skew in the paper width direction caused by the state is prevented.
[0021]
According to a second aspect of the present invention, in the image forming apparatus according to the first aspect, on the downstream side of the branch point of the reverse discharge path in the re-conveyance path, the succeeding paper fed into the re-conveyance path and this A passing area is provided in which the preceding paper that is switched back in the re-conveying path and is fed into the reverse discharge path is provided, and the first forward / reverse conveying roller is provided outside the passing area.
[0022]
Therefore, while the first forward / reverse conveyance roller is rotationally driven in the reverse rotation direction and the preceding sheet is being fed from the reconveying path to the reverse discharge path, the succeeding sheet is made to pass the preceding sheet in the passing area. The paper can be fed into the re-conveying path, and even when the interval between the reversely discharged sheets becomes narrower due to the improvement in the productivity of the image forming operation, the sheets can be successively discharged in reverse.
[0023]
Since the first forward / reverse conveyance roller is provided outside the passing area between the preceding sheet and the succeeding sheet, the first forward / reverse conveyance roller is rotated in the reverse direction to reversely discharge the preceding sheet. There is no inconvenience that the succeeding sheet sent to the re-conveying path reaches the first forward / reverse conveying roller while being fed to the path, and the first is performed when the succeeding sheet reaches the first forward / reverse conveying roller. Since the preceding sheet is nipped by the forward / reverse conveying roller, the first forward / reverse conveying roller can be driven to rotate in the forward direction to sandwich the subsequent sheet. The reverse paper discharge used can be performed smoothly.
[0024]
According to a third aspect of the present invention, in the image forming apparatus according to the first or second aspect, forward / reverse switching of the first forward / reverse conveyance roller is performed by forward / reverse rotation of a motor connected to the first forward / reverse conveyance roller. This is done by switching.
[0025]
Therefore, the forward / reverse switching of the first forward / reverse conveying roller can be performed reliably and accurately.
[0026]
According to a fourth aspect of the present invention, in the image forming apparatus according to any one of the first to third aspects, the sheet conveyed on the reconveying path upstream from the branch point of the reverse sheet discharging path on the reconveying path. A sheet end detection sensor for detecting the end of the sheet is provided, and the rotation of the first forward / reverse conveyance roller is switched in the reverse direction at a preset timing after the sheet end detection by the sheet end detection sensor.
[0027]
Therefore, even when the size of the reversely discharged paper is different, the first forward / reverse conveying roller can be switched in the reverse direction at the timing when the leading end side of the reverse discharge direction of the paper reaches a predetermined position. .
[0028]
According to a fifth aspect of the present invention, in the image forming apparatus according to any one of the first to fourth aspects, in the vicinity of the branch point of the reverse paper discharge path in the re-conveyance path and downstream of the branch point, A reversing roller is provided that is driven to rotate in a direction in which the paper is fed into the reversing paper discharge path. The reversing roller is provided so as to be switched between a paper feeding state in which the paper is nipped and conveyed and an open state in which the nipping of the paper is released. ing.
[0029]
Therefore, when a small-size sheet is reversely discharged, the sheet can be fed into the reverse discharge path by the rotation of the reverse roller. Further, by switching the reversing roller to the released state, it is possible to smoothly feed the subsequent sheet to the re-conveying path during the passing conveyance.
[0030]
According to a sixth aspect of the present invention, in the image forming apparatus according to the fifth aspect, the reversing roller that is rotationally driven in a direction in which the sheet is fed into the reversal discharge path and the first forward / reverse conveying roller have the same circumference. Done synchronously with speed.
[0031]
Therefore, when the paper is fed into the reverse paper discharge path, the paper is prevented from being pulled or loosened between the reverse roller and the first forward / reverse conveyance roller, and the reverse paper discharge can be performed smoothly.
[0032]
According to a seventh aspect of the present invention, in the image forming apparatus according to the fifth or sixth aspect, a reverse discharge roller that is rotationally driven in a direction in which a sheet is conveyed to the paper discharge unit is provided on the reverse discharge path. The reverse paper discharge roller is disposed at a position for sandwiching the preceding paper that has been reversely discharged before the subsequent paper transported through the re-transport path reaches the reverse roller.
[0033]
Therefore, when the preceding sheet and the succeeding sheet are reversed and conveyed while passing, when the succeeding sheet conveyed through the re-conveying path reaches the reversing roller, the reversing roller is released for passing. Although the preceding paper that has been fed into the reverse paper discharge path before the subsequent paper reaches the reverse roller is held between the reverse paper discharge rollers, the reverse paper discharge can be performed smoothly.
[0034]
According to an eighth aspect of the present invention, in the image forming apparatus according to any one of the second to seventh aspects, within the range that is within the passing area or outside the passing area according to the size of the paper to be reversed and discharged. Second forward / reverse transport that can be switched forward / reversely between a forward rotation direction in which the paper fed into the re-transport path is transported toward the paper transport path and a reverse rotation direction in which the paper is switched back and sent to the reverse paper discharge path. A roller is provided, and the second forward / reverse conveyance roller is provided so as to be switched between a paper feeding state in which the paper is nipped and conveyed and an open state in which the nipping of the paper is released.
[0035]
Therefore, when the passing area changes with the size of the sheet and the second forward / reverse conveying roller is outside the passing area, the second forward / reverse conveying roller is made the same as the first forward / reverse conveying roller. Can be switched between the normal rotation direction and the reverse rotation direction, and the paper can be reversed and discharged. Further, when the second forward / reverse transport roller is in the passing area, the second forward / reverse transport roller is switched to the open state at a timing when the preceding paper and the subsequent application pass each other. Reverse paper discharge can be performed smoothly while passing the following paper.
[0036]
According to a ninth aspect of the present invention, there is provided a sheet storage unit that stacks and holds sheets, a separation sheet feeding unit that separates and feeds sheets one by one from the sheet storage unit, and an image that forms an image on the fed sheet. A forming unit, a sheet conveying path from the sheet storing unit to the image forming unit, a reversing path that is connected in the middle of the sheet conveying path and that is fed through the sheet conveying path, and a reversing path At least a part of the feeding state in which the fed paper is switched back and sent to the paper conveying path overlaps with the preceding paper fed from the reversing path and the subsequent paper fed to the reversing path. A sheet reversing means that can be switched between an open state to be permitted, a reconveying path connected between a paper discharge side of the image forming unit and an upstream side of the reversing path of the sheet conveying path, and the reconveying path Branched from the middle of A reversal discharge path connected to the paper discharge section and a reversal discharge path in the re-conveyance path are provided downstream of the branch point of the reversal discharge path, and the paper fed into the re-conveyance path is directed to the paper conveyance path. A forward / reverse conveyance roller that can be switched between forward and reverse rotations in a forward rotation direction in which the paper is conveyed and a reverse rotation direction in which the paper is switched back and sent to the reverse paper discharge path, and the paper is discharged on the reverse paper discharge path. A reverse discharge roller that is rotationally driven in the direction of conveyance to the paper portion, and the subsequent paper fed onto the re-conveyance path and the switch-back on the re-conveyance path to be fed into the reverse discharge path The forward / reverse transport roller is disposed outside the passing area provided on the transport path so as to pass the preceding paper, and the distance between the reverse discharge roller and the forward / backward transport roller is determined by the usable paper. Minimum paper feed length Ri is set to be smaller.
[0037]
Therefore, the sheets stacked and held in the sheet storage unit are separated and fed one by one by the separation feeding unit and conveyed on the sheet conveyance path, and the sheet conveyed on the sheet conveyance path is sent to the reversing path, Then, the sheet is reversed by the sheet reversing means, sent out from the reversing path toward the image forming unit, and the image is formed on the sheet fed into the image forming unit.
[0038]
When the paper fed into the reversing path is switched back, it is switched back by controlling the paper feeding speed to the reversing path, the paper feeding speed from the reversing path, the paper feeding timing from the reversing path, etc. Thus, the interval between sheets fed to the image forming unit can be reduced. In other words, even when there is a variation in the timing of feeding from the paper storage unit or a variation in the conveyance speed during conveyance up to the reversing path, the feeding of the paper to the image forming unit is accurately maintained at a small interval. Therefore, the productivity of the image forming operation in the image forming apparatus can be improved.
[0039]
When performing double-sided printing, a sheet on which an image is formed and discharged from the image forming unit is sent to the re-conveying path, and the normal / reverse conveying roller is driven to rotate in the normal direction. Send it out to the paper transport path. The paper sent out to the paper conveyance path in this way is sent again to the reversing path, switched back on the reversing path, and then sent back to the image forming unit to form an image on the other side of the paper (double-sided printing). ) Is performed. Since the sheet sent out from the reconveying path to the sheet conveying path is held downstream by the forward / reverse conveying roller when being conveyed downstream from the branch point of the reverse discharge path in the reconveying path, the lateral misalignment is maintained. And no skew.
[0040]
When performing reverse paper discharge, an image is formed on one side and the paper discharged from the image forming unit is sent to the re-conveying path, and the paper is fed by a forward / reverse transport roller that is driven to rotate in the forward rotation direction. It is transported to a predetermined position toward the paper transport path. Then, after the sheet is conveyed to a predetermined position on the reconveying path, the sheet is switched back by rotating the forward / reverse conveying roller in the reverse direction and sent to the reverse discharge path, and then passes through the reverse discharge path. To the paper output section. At the time of this reverse paper discharge, the paper fed into the re-conveying path is nipped by a normal / reverse conveying roller that is driven to rotate in the normal direction, and then the normal / reverse conveying roller that holds the paper in the reverse direction. When the paper is rotated, the paper is fed into the reverse paper discharge path, so that the paper to be reversely discharged is not in a free state in the middle of conveyance, and the paper in the conveyance is in a free state in the middle of the conveyance. Is prevented from causing lateral misalignment and skew in the paper width direction.
[0041]
In addition, since the forward / reverse conveyance roller is arranged outside the passing area, the forward / reverse conveyance roller does not hinder the passing of the preceding sheet and the succeeding sheet, and smoothly performs the reverse discharge. It can be done.
[0042]
In addition, since the distance between the reverse paper discharge roller and the forward / reverse conveyance roller is set to be smaller than the minimum sheet passing length of usable paper, the paper of all sizes is reversely discharged only by the function of the reverse paper discharge roller. Therefore, the reverse paper discharge mechanism can be simplified.
[0043]
According to a tenth aspect of the present invention, in the image forming apparatus according to the ninth aspect, the forward / reverse switching of the forward / reverse conveying roller is performed by forward / reverse switching of a motor connected to the forward / reverse conveying roller.
[0044]
Therefore, the forward / reverse switching of the forward / reverse conveying roller can be reliably and accurately performed.
[0045]
According to an eleventh aspect of the present invention, in the image forming apparatus according to the ninth or tenth aspect, an end portion of the sheet conveyed on the reconveying path is arranged upstream of the branch point of the reverse discharge path on the reconveying path. A paper end detection sensor for detection is provided, and the rotation of the forward / reverse conveyance roller is switched in the reverse direction at a preset timing after the paper end detection by the paper end detection sensor.
[0046]
Therefore, even when the size of the reversely discharged paper is different, the forward / reverse conveying roller can be switched in the reverse direction at the timing when the leading end side of the paper in the reverse discharge direction reaches a predetermined position.
[0047]
According to a twelfth aspect of the present invention, in the image forming apparatus according to any one of the first to eleventh aspects, the conveyance speed of the reversely discharged paper is set to be higher than the conveyance speed of the paper to the re-conveyance path. ing.
[0048]
Therefore, the passing area can be brought close to the branch point between the re-conveying path and the reverse discharge path, and the arrangement of various rollers such as the first and second forward / reverse conveying rollers, the forward / reverse conveying rollers, and the reverse discharging rollers can be arranged. The degree of freedom can be increased.
[0049]
According to a thirteenth aspect of the present invention, in the image forming apparatus according to any one of the first to twelfth aspects, a switching claw disposed at a branch point between the reconveying path and the reverse discharge path, and the reconveying path. The switching claw is urged so that the switching claw is positioned at a position where the paper switched back in is allowed to be fed into the reverse discharge path, and the re-carrying path is directed toward the paper conveying path. An urging body set to an urging force that is large enough to move the switching claw to a position that allows the paper to travel on the re-carrying path when the conveyed paper abuts the switching claw; Have
[0050]
Therefore, the switching of the switching claw necessary for the conveyance of the paper in the re-conveying path that passes through the switching claw and the feeding of the paper switched back in the re-conveying path to the reverse discharge path is performed by the solenoid. It is possible to use a biasing body with a simple structure without using such an electric actuator, such as a spring, and the switching operation of the switching claw using this biasing body can be performed at high speed and is reliable. It will be a thing.
[0051]
According to a fourteenth aspect of the present invention, in the image forming apparatus according to any one of the first to thirteenth aspects, the image forming unit is an electrophotographic image forming unit.
[0052]
Therefore, the invention according to any one of claims 1 to 13 can be realized in an image forming apparatus including an electrophotographic image forming unit.
[0053]
According to a fifteenth aspect of the present invention, in the image forming apparatus according to any one of the first to thirteenth aspects, the image forming unit is a digital electrophotographic image forming unit including a digital writing unit.
[0054]
Therefore, the invention according to any one of claims 1 to 13 can be realized in an image forming apparatus including a digital electrophotographic image forming unit including a digital writing unit.
[0055]
According to a sixteenth aspect of the present invention, there is provided a printer according to any one of the first to fifteenth aspects, an input terminal for receiving input of image data, and an image based on the image data by controlling the image forming apparatus. A control unit that causes the sheet to be formed on the sheet.
[0056]
Therefore, this printer also exhibits the same operations and effects as the invention according to any one of claims 1 to 15.
[0057]
According to a seventeenth aspect of the present invention, there is provided a copying machine that controls an image reading apparatus that reads an image of a document, the image forming apparatus according to any one of the first to fifteenth aspects, the image reading apparatus, and the image forming apparatus. And a control unit that causes the image forming apparatus to form an image on a sheet based on the image data of the document read by the image reading apparatus.
[0058]
Therefore, this copying machine also exhibits the same operations and effects as the invention according to any one of claims 1 to 15.
[0059]
DETAILED DESCRIPTION OF THE INVENTION
A first embodiment of the present invention will be described with reference to FIGS. FIG. 1 is a schematic diagram showing the overall structure of an image forming apparatus having a digital electrophotographic image forming unit, FIG. 2 is an enlarged front view showing a sheet reversing means for switching back a conveyed sheet, and FIG. FIG. 4 and FIG. 5 are explanatory views showing the state of transport of the paper to the image forming unit when image formation is continuously performed, and FIG. 6 is the paper transport during continuous image formation. FIG. 7 is an explanatory view showing the state of paper transport during duplex printing, FIG. 8 is an explanatory view showing the state of paper transport during reverse paper discharge, and FIGS. 9 through 11 are papers during reverse paper discharge. It is explanatory drawing explaining in detail the conveyance state.
[0060]
As shown in FIG. 1, in this image forming apparatus, image formation is performed on a sheet tray 1 which is a sheet storage unit in which sheets are stacked and held, a sheet fed from the sheet tray 1, or one side, and then fed again. An image forming unit 2 that forms an image on the other side of the paper that has been formed, a paper discharge tray 3 that is a paper discharge unit that discharges the paper on which the image has been formed, and the like are provided.
[0061]
In addition, the image forming apparatus is provided with a paper path from the paper fed from the paper tray 1 to the paper discharge tray 3 via the image forming unit 2. A portion from the image forming unit 2 to the image forming unit 2 is a sheet conveyance path 4.
[0062]
The paper tray 1 is provided with a separating paper feeding means 7 having a pickup roller 5 that feeds the stacked and held paper and an FRR type separation paper feeding roller 6 that separates the paper fed by the pickup roller 5 one by one. Is provided.
[0063]
The image forming unit 2 includes a photoconductor 8 on which an image is formed, a charger 9 that uniformly charges the surface of the photoconductor 8, a digital writing unit 10 that writes an electrostatic latent image on the photoconductor 8, and a photosensor. A developing device 11 that forms a toner image by attaching toner to the electrostatic latent image on the body 8, a transfer device 12 that transfers the developed toner image onto a sheet, and a cleaning that removes residual toner on the photoconductor 8. An apparatus 13 and a fixing device 14 for fixing the toner image transferred to the paper are provided.
[0064]
On the paper conveyance path 4, a first conveyance roller 15, a second conveyance roller 16, a registration sensor 17, a registration roller 18, and the like are arranged. Further, a reversing path 19 through which a sheet conveyed through the sheet conveying path 4 is fed is connected to a portion of the sheet conveying path 4 between the first conveying roller 15 and the second conveying roller 16.
[0065]
On the reversing path 19, the paper sent to the reversing path 19 is switched back and sent to the paper transport path 4, the preceding paper sent from the reversing path 19 and the succeeding paper sent to the reversing path 19. A sheet reversing means 20 that can be switched to an open state that allows at least a part of the sheet to overlap, a sheet end detection sensor that detects an end of the sheet that is fed into or sent out of the reversing path 19. 21 is provided.
[0066]
As shown in FIG. 2, the sheet reversing means 20 includes a driving roller 22 that is rotationally driven by a motor, and a driven roller 23 that is movably provided at a position that is in contact with and away from the driving roller 22 and that is rotated along with the contact. The moving roller 23 is configured to move the driven roller 23 to a position where it is in contact with or away from the driving roller 22. The moving mechanism for moving the driven roller 23 is such that the driven roller 23 is connected to one end and the other end is connected to the link 25 supported by the fulcrum 24, and is connected to the substantially central portion of the link 25. A spring 26 is urged in the direction of contact, and a solenoid 27 is connected to the link 25 to urge the driven roller 23 away from the drive roller 22.
[0067]
In FIG. 2B, the driven roller 23 is brought into contact with the driving roller 22 by the urging force of the spring 26, and the driving roller 22 is rotationally driven in the direction of the arrow so that the driving roller 22 and the driven roller 23 are sandwiched. In this state, the sheet being fed is sent out from the reverse path 19.
[0068]
FIG. 2A shows an open state in which the driven roller 23 is rotated downward by driving the solenoid 27 and a gap is generated between the driving roller 22 and the driven roller 23. In this open state, the paper is fed into the reversing path 19.
[0069]
A direct paper discharge path 28 is provided between the paper discharge side of the image forming unit 2 and the paper discharge tray 3. The paper discharge side of the image forming unit 2 and the upstream side of the reverse path 19 in the paper conveyance path 4 are provided. A re-transport path 29 is provided between the two. A switching claw 30 for switching the transport direction of the paper discharged from the image forming unit 2 to the direct paper discharge path 28 or the re-transport path 29 is provided at a branch point between the direct paper discharge path 28 and the re-transport path 29. It has been.
[0070]
The re-conveying path 29 is formed of a vertical path part 29a extending downward and a horizontal path part 29b extending in a substantially horizontal direction from the lower end part of the vertical path part 29a, and the leading end of the horizontal path part 29b is a sheet. It is connected to the conveyance path 4.
[0071]
A reverse discharge path 31 is branched from the boundary between the vertical path portion 29 a and the horizontal path portion 29 b in the middle of the re-transport path 29, and the reverse discharge path 31 is connected to the discharge tray 3.
[0072]
In the horizontal path portion 29b in the re-conveyance path 29, first forward / reverse conveyance rollers 32, 33, a second forward / reverse conveyance roller 34, and a reverse roller 35 are provided. Further, a paper rear end detection sensor 36 that is a paper end detection sensor is provided in the vertical path portion 29 a in the re-conveyance path 29. Further, a conveyance roller 37 and a switching claw 38 are provided at a branch point between the re-conveyance path 29 and the reverse discharge path 31.
The first forward / reverse transport rollers 32 and 33 are a drive roller connected to a motor (not shown) capable of switching between forward and reverse such as a stepping motor and a DC servo motor, and a driven roller always in contact with the drive roller. It is comprised by. The first forward / reverse transport rollers 32 and 33 are configured to forward-feed the sheet fed to the horizontal path portion 29b of the re-conveyance path 29 toward the sheet transport path 4, and to reverse the sheet by switching back the sheet. It is provided so that it can be switched between forward and reverse rotations in the reverse rotation direction fed into the paper path 31. The forward / reverse switching of the first forward / reverse conveying roller is performed by forward / reverse switching of the motor.
[0073]
As shown in FIG. 10, on the downstream side of the branch point of the reverse paper discharge path 31 in the horizontal path portion 29b, the preceding paper that is reversely discharged toward the reverse paper discharge path 31 when the paper is reversely discharged. A passing region “X” is provided in which A and the succeeding paper B fed to the horizontal path portion 29b pass each other. The passing area “X” changes depending on the sizes of the sheets A and B and the conveyance speed of the sheets A and B. Further, the passing area “X” changes every moment according to the transport position of the sheets A and B, and is when the illustrated passing area “X” is maximized.
[0074]
Since the first forward / reverse conveyance rollers 32 and 33 are disposed outside the passing area “X”, the first forward / reverse conveyance rollers 32 and 33 are driven to rotate in the reverse direction to reversely discharge the preceding paper A. There is no inconvenience that the subsequent paper B reaches the first forward / reverse conveyance rollers 32 and 33 while being fed into the paper path 31. When the succeeding sheet B is transported to the position of the first forward / reverse transport rollers 32, 33, the preceding sheet A is released from the nipping state by the first forward / reverse transport rollers 32, 33, and the first forward / reverse transport roller By rotating the rollers 32 and 33 in the forward rotation direction, the succeeding paper B fed to the horizontal path portion 29b can be transported downstream of the horizontal path portion 29b (in the direction of transporting to the paper transport path 4). .
[0075]
The basic structure of the second forward / reverse transport roller 34 is the same as that of the first forward / reverse transport rollers 32 and 33, and a drive roller connected to a motor capable of switching between forward and reverse rotation and a follower abutted on the drive roller. It is comprised by the roller, and it is provided so that forward / reverse switching is possible in the forward rotation direction and the reverse rotation direction. However, the second forward / reverse conveying roller 34 can be switched between a paper feeding state for nipping and conveying the paper and an open state for releasing the nipping of the paper when the driven roller contacts and separates from the driving roller. Is provided. This switching is performed by driving a solenoid (not shown).
[0076]
Further, the second forward / reverse conveyance roller 34 is arranged in a passing area or outside the passing area according to the size of the sheet to be reversed and discharged. When the preceding paper A and the succeeding paper B are passed by passing at the position of the second forward / reverse transport roller 34, the second forward / reverse transport roller 34 is switched to an open state so that the passing transport is not hindered. I am doing so.
[0077]
The reverse roller 35 is provided in the vicinity of the branch point of the reverse paper discharge path 31 in the horizontal path portion 29b. The reversing roller 35 is composed of a driving roller and a driven roller, and is driven to rotate in a direction in which the sheet is fed into the reversing paper discharge path 31. By driving the solenoid, the reversing roller is brought into contact with and separated from the driving roller. In addition, a sheet feeding state in which the sheet is nipped and conveyed and a release state in which the nipping of the sheet is released can be switched. When the reversing roller 35 is driven to rotate, the reversing roller 35 and the first and second forward / reverse conveying rollers 32, 33, 34 are driven to rotate synchronously at the same peripheral speed. This prevents the sheet to be reversely discharged from being pulled or slackened between the first and second transport rollers 32, 33, 34 and the reverse roller 35.
[0078]
The sheet trailing edge detection sensor 36 is installed in the vicinity of the branch point between the reconveying path 29 and the reverse discharge path 31 and upstream of the branching point, and detects the trailing end of the sheet conveyed through the reconveying path 29. To detect. In accordance with the detection result of the paper trailing edge detection sensor 36, the first and second forward / reverse conveyance rollers 32, 33, and 34 are switched in the reverse direction, and the reverse roller 35 and the second forward / reverse conveyance roller 34 feed the paper. Switch to state.
[0079]
The transport roller 37 is a roller that is rotationally driven in a direction to transport the paper in the re-transport path 29 from the vertical path portion 29a toward the horizontal path portion 29b. It functions to feed from the vertical path portion 29 a to the horizontal path portion 29 b and to feed the reversely discharged paper to the reverse paper discharge path 31. As shown in FIG. 3, the switching claw 38 faces the first guide surface 38 a that faces the sheet conveyed from the vertical path portion 29 a to the horizontal path portion 29 b, and the sheet that is switched back to the reverse discharge path 31. Formed in a substantially triangular shape having a second guide surface 38b and a switching claw tip portion 38c that is sandwiched between the first guide surface 38a and the second guide surface 38b and protrudes acutely toward the downstream side of the horizontal path portion 29b. Has been. The switching claw 38 is fixed to a support shaft 39 disposed in the vicinity of the center shaft 37a of the transport roller 37 in parallel with the center shaft 37a, and the support shaft 39 is rotatable by a bearing (not shown). It is pivotally supported. One end of an arm 40 is fixed to the end of the support shaft 39, and one end of a spring 41 that is an urging member is locked to the other end of the arm 40. In addition, a stopper 42 for restricting the rotation position of the arm 40 is provided in the direction in which the arm 40 is rotated by the biasing force of the spring 41.
[0080]
The switching claw 38 is rotatably provided at the first switching position and the second switching position by rotating around the axis of the supporting shaft 39 together with the supporting shaft 39. In the first switching position, the paper traveling from the vertical path portion 29a toward the horizontal path portion 29b rotates the switching claw 38 against the urging force of the spring 41 by its own waist strength, and the paper is conveyed. This is a rotation position when the roller 37 is traveling between the outer peripheral surface of the roller 37 and the first guide surface 38 a of the switching claw 38. In the second switching position, there is no sheet between the outer peripheral surface of the transport roller 37 and the first guide surface 38 a of the switching claw 38, and the arm 40 is rotated by the biasing force of the spring 41 to contact the stopper 42. It is the position when When the switching claw 38 is rotated to the second switching position, the switching claw tip portion 38 c is located inside the outer peripheral portion of the transport roller 37, and the switched back sheet is directed toward the reverse discharge path 31. The sheet guided and switched back is restricted from entering the vertical path portion 29a.
[0081]
The reverse paper discharge path 31 is provided with a reverse paper discharge roller 43 that is rotationally driven in the direction of reverse paper discharge to the paper discharge tray 3. This reverse paper discharge roller 43 is a preceding paper that is reversely discharged before the leading edge (see FIGS. 9 to 11) of the subsequent paper B transported through the re-transport path 29 reaches the position of the reverse roller 35. The paper is disposed at a position where it reaches the reverse paper discharge roller 43. As a result, even if the reverse roller 35 is switched to the open state for the passing conveyance of the preceding paper A and the succeeding paper B, the leading edge of the preceding paper A is already held by the reverse paper discharge roller 43. Therefore, the reverse paper discharge of the paper can be continued smoothly. When the paper is reversed and discharged by the reverse discharge roller 43 and the first and second forward / reverse transfer rollers 32, 33, and 34, the transfer speed is the transfer when the paper is sent to the re-transport path 29. High speed is set according to the speed. This setting is performed by changing the rotation speed of the motor between forward rotation and reverse rotation.
[0082]
Further, the image forming apparatus includes an image forming operation in the image forming unit 2, a separating and feeding unit 7, first and second transport rollers 15 and 16, a registration roller 18, a switching claw 30, and first and second forward / reverse rotations. The driving of the conveying rollers 32, 33, 33, the reverse roller 35, the reverse paper discharge roller 43, and the like, the detection results of various sensors such as the paper edge detection sensor 21, the registration sensor 17, and the paper rear edge detection sensor 36, and the image forming mode A control unit (not shown) is provided for controlling according to the settings (single-sided printing mode, double-sided printing mode, reverse paper discharge mode, etc.).
[0083]
In such a configuration, when the start key is pressed after the continuous image forming mode is set, sheets are fed one after another from the sheet tray 1. These sheets are conveyed along the sheet conveying path 4 toward the image forming unit 2, and are sent to the reversing path 19 on the way, switched back by the sheet reversing means 20, and sent out from the reversing path 19. The paper sent out from the reversing path 19 is sent to the image forming unit 2 through the paper transport path 4 and image formation on the paper is performed.
[0084]
When the sheet conveyed through the sheet conveying path 4 is sent to the reversing path 19 to be switched back, the sheet feeding speed to the reversing path 19, the sheet feeding speed from the reversing path 19, and the sheet feeding timing from the reversing path 19 By controlling the above, it is possible to reduce the interval between sheets that are switched back and sent to the image forming unit 2, thereby improving the productivity of the image forming operation. For example, as shown in the diagram of FIG. 6, the sheet is conveyed from the sheet tray 1 to the reversal stop position in the reversing path 19 at a high conveyance speed Va, and is sent from the reversal stop position at a low conveyance speed Vb. The sheet interval in the image forming unit 2 can be reduced.
[0085]
FIG. 4 shows a state in which the preceding paper a is being sent out from the reversing path 19, and the paper reversing means 20 is in a sending state as shown in FIG. The succeeding paper “b” is transported through the paper transport path 4 and is sent to the reversing path 19.
[0086]
FIG. 5 shows a state in which the preceding paper “a” is conveyed to a position where the leading end of the paper a comes into contact with the registration roller 18 and the subsequent paper “b” is fed into the reverse path 19. After the preceding paper a is sent out from the reversing path 19 and its leading end is nipped by the second conveying roller 16, the driven roller 23 is separated from the driving roller 22, and the paper reversing means 20 is as shown in FIG. Then, the succeeding sheet b is fed into the reverse path 19 through the space between the driven roller 23 and the driving roller 22 which are separated. The succeeding paper b is fed into the reversing path 19 so that the trailing edge side of the preceding paper a and the leading edge side of the succeeding paper b overlap in the reversing path 19.
[0087]
FIG. 7 is an explanatory diagram for explaining the flow of a sheet when duplex printing is performed on the sheet. The paper on which the image is formed on one side in the image forming unit 2 is transported through the re-transport path 29 as indicated by an arrow, and the paper is first and second forward / reversely transported to be rotated in the forward rotation direction. It is conveyed as it is by the rollers 32, 33, and 34, and sent out to the paper conveyance path 4. After the sheet is fed to the sheet conveyance path 4, it is conveyed in the same way as the sheet fed from the sheet tray 1, sent to the reverse path 19, switched back, and sent to the image forming unit 2 again. When a sheet on which an image is formed on one side is sent again to the image forming unit 2, the sheet is switched back by the reverse path 19 so that the other side of the sheet faces the photosensitive member 8. Thus, image formation (double-sided printing) is performed on the other surface.
[0088]
FIG. 8 to FIG. 11 are explanatory diagrams for explaining the flow of paper when a paper having an image formed on one side is reversely discharged. The sheet on which the image is formed on one side is conveyed through the reconveying path 29 as indicated by the arrow, and reaches the horizontal path portion 29b. The paper that has reached the horizontal path portion 29b is switched back by the horizontal path portion 29b and sent to the reverse paper discharge path 31, and is reversely discharged onto the paper discharge tray 3 with the surface on which the image is formed facing downward. Details of the reverse paper discharge are as shown in FIGS.
[0089]
FIG. 9 shows a state in which the reverse paper discharge of the preceding paper A sent into the horizontal path portion 29b is started, and the subsequent paper B is conveyed in the vertical path portion 29a toward the horizontal path portion 29b. It is. At this time, both the first and second forward / reverse conveying rollers 32, 33, and 34 are rotationally driven in the reverse direction, and the reverse roller 35 is also rotationally driven in the same direction to feed the paper A into the reverse discharge path 31. I'm trying.
[0090]
FIG. 10 shows a state in which the preceding sheet A and the succeeding sheet B are passed and conveyed in the horizontal path portion 29b. At this time, the second forward / reverse conveyance roller 34 and the reverse roller 35 located in the passing area “X” are switched to the open state so as not to prevent the subsequent paper B from being fed into the horizontal path portion 29b. It has become. The leading sheet A is nipped by the reverse paper discharge roller 43 at the leading end side, so that the conveying force from the first / second forward / reverse conveying rollers 32, 33, 34 and the reverse roller 35 is not applied. Even in such a case, the conveyance toward the paper discharge tray 3 is favorably performed.
[0091]
FIG. 11 shows a state in which the trailing edge of the preceding sheet A enters the reverse sheet discharge path 31 and the succeeding sheet B is conveyed toward the sheet conveying path 4 along the horizontal path portion 29b. The first and second forward / reverse conveying rollers 32, 33, 34 are all driven to rotate in the forward direction, and the reverse roller 35 is in an open state. When it is determined based on the detection result of the paper trailing edge detection sensor 36 that the succeeding paper B has been sent to the predetermined position of the horizontal path portion 29b, the state shifts to the state shown in FIG. The paper B is switched back by the driven first and second forward / reverse conveying rollers 32, 33, 34 and the reverse roller 35, and the feeding of the paper B to the reverse paper discharge path 31 is started. Therefore, the paper that is switched back by the horizontal path portion 29b and sent to the reverse paper discharge path 31 does not become free in the middle of the conveyance, and the paper conveyed in the re-conveyance path 29 is free in the middle of the conveyance. Therefore, it is possible to prevent lateral misalignment and skew in the paper width direction that occur due to a state of being unfavorable.
[0092]
If the reversely discharged paper is of a long size, the second forward / reverse transport roller 34 and the reverse roller 35 can be dispensed with, and only the first forward / reverse transport rollers 32 and 33 are used for the reverse rotation. Paper can be discharged. However, if the paper is of a short size, the second forward / reverse conveyance roller 34 or the reverse roller 35 is used to reverse the paper so that the leading edge of the paper is fed to the reverse paper discharge roller 43. The paper is fed into the reverse paper discharge path 31 to the nipped position.
[0093]
Next, a second embodiment of the present invention will be described with reference to FIG. In addition, the same part as the part demonstrated in FIG. 1 thru | or FIG. 11 is shown with the same code | symbol, and description is also abbreviate | omitted.
[0094]
The basic structure of the present embodiment is the same as that of the first embodiment, and the forward / reverse conveying rollers 44 and 45 are arranged on the horizontal path portion 29b.
[0095]
The forward / reverse conveying rollers 44 and 45 are constituted by a driving roller connected to a motor (not shown) that can be switched between forward and reverse such as a stepping motor and a DC servo motor, and a driven roller that is always in contact with the driving roller. Has been. The forward / reverse transport rollers 44 and 45 are forward rotation directions for transporting the paper fed to the horizontal path portion 29 b toward the paper transport path 4, and reverse rotation directions for switching the paper back and feeding it to the reverse paper discharge path 31. The forward / reverse switching is performed by forward / reverse switching of the motor.
[0096]
Further, the forward / reverse conveying rollers 44 and 45 are disposed outside the passing area “X” in the horizontal path portion 29b.
[0097]
On the reverse paper discharge path 31, there is provided a reverse paper discharge roller 43 that is rotationally driven in a direction to convey the paper fed onto the reverse paper discharge path 31 to the paper discharge tray 3. The distance “L” between the reverse paper discharge roller 43 located on the side and the forward / reverse conveyance roller 44 is smaller than the minimum sheet passing length (sheet length along the conveyance direction) usable in this image forming apparatus. Is set.
[0098]
In such a configuration, according to the present embodiment, when performing double-sided printing, the forward / reverse conveyance rollers 44 and 45 are driven to rotate in the forward rotation direction, and the sheet fed to the horizontal path portion 29b is rotated forward / reversely. The paper is nipped by the transport rollers 44 and 45 and transported toward the paper transport path 4.
[0099]
When reverse paper discharge is performed, the paper fed into the horizontal path portion 29b is sandwiched between forward and reverse transport rollers 44 and 45 that are driven to rotate in the forward direction, and the rear end of the paper has the switching claw 38 interposed therebetween. The paper is conveyed to the passing position, and then the rotation direction of the forward / reverse conveyance rollers 44 and 45 is switched to the reverse direction, and the paper is switched back and sent to the reverse paper discharge path 31. Therefore, the paper that is switched back by the horizontal path portion 29b and sent to the reverse paper discharge path 31 does not become free in the middle of the conveyance, and the paper conveyed in the re-conveyance path 29 is free in the middle of the conveyance. Therefore, it is possible to prevent lateral misalignment and skew in the paper width direction that occur due to a state that is not stable.
[0100]
Further, the distance “L” between the reverse paper discharge roller 43 located closest to the switching claw 38 and the forward / reverse conveyance roller 44 is set to be smaller than the minimum paper passing length of the paper usable in this image forming apparatus. Regardless of the size of the paper to be reversely discharged, by rotating the forward / reverse conveying rollers 44 and 45 in the reverse direction, the paper that is switched back is surely reached to the position where it is held by the reverse paper discharge roller 43. The second forward / reverse conveying roller 34 and the reverse roller 35 having the contact / separation mechanism described in the first embodiment are not necessary. As a result, the mechanism for switching back and discharging paper in the horizontal path portion 29b has a simple structure and is downsized.
[0101]
Next, a third embodiment of the present invention will be described with reference to FIG. FIG. 13 is a block diagram showing a schematic structure of the printer 51 according to the present embodiment. The printer 51 controls the image forming apparatus 52 described in the first or second embodiment, the input terminal 53 that receives input of image data from an external device such as a personal computer, and the image forming apparatus 52. And a control unit 54 for forming an image on the sheet based on the image data.
[0102]
Therefore, according to the printer 51, the same operation and effect as those described in the first or second embodiment can be obtained.
[0103]
Next, a fourth embodiment of the present invention will be described with reference to FIG. FIG. 14 is a block diagram showing a schematic configuration of the copying machine 61 according to the present embodiment. The copying machine 61 controls the image reading device 62 that reads an image of a document, the image forming device 52 described in the first or second embodiment, the image reading device 62, and the image forming device 52. The image forming apparatus 52 includes a control unit 63 that causes the image forming apparatus 52 to form an image on the paper based on the image data of the document read by the image reading apparatus 62.
[0104]
Therefore, according to the copying machine 61, the same operations and effects as those described in the first or second embodiment can be obtained.
[0105]
【The invention's effect】
According to the image forming apparatus of the first aspect of the present invention, when the paper on which the image is formed on one side is reversely discharged, the image is formed on the one side and discharged from the image forming unit. The sheet is fed into the re-conveying path, and the sheet is conveyed to a predetermined position toward the sheet conveying path by the first forward / reverse conveying roller that is rotationally driven in the forward rotation direction, and then the first forward / reverse conveying roller is moved in the reverse direction. By rotating the paper, the paper is switched back, sent to the reverse paper discharge path, and discharged, so the paper that is reversely discharged is not free during the transfer, and the paper being transferred is not being transferred. Lateral misalignment and skew in the paper width direction caused by the free state can be prevented, and this lateral misalignment and skew can be prevented by a simple mechanism of switching the rotation direction of the first forward / reverse conveying roller. It is possible.
[0106]
According to the second aspect of the present invention, in the image forming apparatus according to the first aspect, the first forward / reverse conveying roller is provided outside the passing area between the preceding sheet and the succeeding sheet in the reconveying path. In this case, the preceding sheet and the succeeding sheet can be reversed and discharged at high speed while being conveyed in the passing area. At this time, the first forward / reverse conveying roller is driven to rotate in the reverse direction to reversely discharge the preceding sheet. It is possible to prevent the occurrence of inconvenience that the subsequent sheet sent to the re-conveying path reaches the first forward / reverse conveying roller while being fed to the paper path, and the rotation of the first forward / reverse conveying roller is reversed to the normal direction. The paper can be reversed and discharged smoothly while switching between directions.
[0107]
According to a third aspect of the present invention, in the image forming apparatus according to the first or second aspect, the forward / reverse switching of the first forward / reverse transport roller is the forward / reverse rotation of the motor connected to the first forward / reverse transport roller. Since it is performed by switching, the forward / reverse switching of the first forward / reverse transport roller can be performed reliably and accurately.
[0108]
According to a fourth aspect of the present invention, in the image forming apparatus according to any one of the first to third aspects, the sheet conveyed on the reconveying path upstream from the branch point of the reverse sheet discharging path on the reconveying path. A sheet trailing edge detection sensor for detecting the trailing edge of the sheet is provided, and the rotation of the first forward / reverse conveying roller is switched in the reverse direction at a preset timing after the sheet trailing edge is detected by the sheet trailing edge detection sensor. Even when the reversely discharged paper size is different, the first forward / reverse conveying roller can be switched in the reverse direction at the timing when the leading end side of the paper in the reverse discharge direction reaches a predetermined position, that is, Even if the size of the paper to be reversed is different, it can be reversed and discharged at the same timing.
[0109]
According to the fifth aspect of the present invention, in the image forming apparatus according to any one of the first to fourth aspects, in the vicinity of the branch point of the reverse discharge path in the re-conveyance path and downstream of the branch point, A reversing roller is provided that is driven to rotate in the direction in which the paper is fed into the reversing paper discharge path. Therefore, when paper of a small size is reversely discharged, the paper can be fed into the reverse discharge path by the rotation driving of the reverse roller, and by switching the reverse roller to the release state, Subsequent paper can be fed smoothly.
[0110]
According to the sixth aspect of the present invention, in the image forming apparatus according to the fifth aspect, the rotational driving of the reverse roller and the first forward / reverse transport roller when the paper is fed into the reverse discharge path is synchronized at the same peripheral speed. Therefore, the sheet fed into the reverse discharge path can be prevented from being pulled or slackened between the reverse roller and the first forward / reverse conveyance roller, and the reverse discharge can be performed smoothly.
[0111]
According to the seventh aspect of the present invention, in the image forming apparatus according to the fifth or sixth aspect, the reverse discharge roller that is rotationally driven in a direction to convey the paper to the paper discharge unit is provided on the reverse discharge path, Since the reverse paper discharge roller is arranged at a position where the preceding paper that is reversely discharged before the subsequent paper transported on the re-transport path reaches the reverse roller, the reverse paper discharge roller is disposed. When the succeeding sheet reaches the reversing roller, the preceding sheet to be reversed and discharged can be sandwiched by the reversing sheet discharge roller to release the reversing roller. The reverse paper discharge performed while passing each other smoothly can be performed.
[0112]
According to the eighth aspect of the present invention, in the image forming apparatus according to any one of the second to seventh aspects, the image forming apparatus is within a passing area or outside the passing area depending on the size of the paper to be reversed and discharged. The paper can be forward / reversely switched between a normal rotation direction in which the paper fed into the re-conveying path is conveyed toward the paper conveyance path and a reverse rotation direction in which the paper is switched back and sent to the reverse paper discharge path. A second forward / reverse transport roller is provided that can be switched between a paper feed state for nipping and transporting the sheet and an open state for releasing the nipping of the sheet. The paper can be smoothly reversed and discharged, and the second forward / reverse conveyance roller is switched to the released state, so that subsequent paper can be fed smoothly during low-pass conveyance. Ukoto can.
[0113]
According to the image forming apparatus of the ninth aspect of the present invention, when the paper on which the image is formed on one side is reversely discharged, the image is formed on the one side and discharged from the image forming unit. The paper is fed into the re-conveying path, and the paper is conveyed to a predetermined position toward the paper conveying path by the forward / reverse conveying roller that is rotationally driven in the forward direction, and then the forward / reverse conveying roller is rotationally driven in the reverse direction. The paper is switched back and sent to the reverse paper discharge path for paper discharge, so that the paper that is reversely discharged is not free during the transport, but the paper being transported is free during the transport. Therefore, it is possible to prevent lateral deviation and skew in the paper width direction, and to prevent this lateral deviation and skew by a simple mechanism of switching the rotation direction of the forward and reverse conveying rollers. . In addition, since the forward / reverse conveying roller is disposed outside the passing area, the forward / reverse conveying roller does not interfere with the passing of the preceding sheet and the succeeding sheet, and does not interfere with the reverse discharge. Since the distance between the reverse discharge roller and the forward / reverse conveyance roller is set to be smaller than the minimum sheet passing length of usable paper, all the operations are performed only by the reverse discharge roller. It becomes possible to reversely discharge a sheet of a size, and a mechanism for moving the forward / reverse conveying roller according to the sheet size is not required, and the reverse discharge mechanism can be further simplified.
[0114]
According to the tenth aspect of the present invention, in the image forming apparatus according to the ninth aspect, the forward / reverse switching of the forward / reverse conveying roller is performed by forward / reverse switching of the motor connected to the forward / reverse conveying roller. Switching between forward and reverse rotation of the forward / reverse conveying roller can be performed reliably and accurately.
[0115]
According to the eleventh aspect of the present invention, in the image forming apparatus according to the ninth or tenth aspect, the trailing edge of the sheet conveyed on the reconveying path is located upstream from the branch point of the reverse discharge path in the reconveying path. A sheet trailing edge detection sensor is provided to detect and the forward / reverse conveying roller is switched in the reverse direction at a preset timing after the sheet trailing edge is detected by the sheet trailing edge detection sensor. Even when the paper is different, the forward / reverse conveying roller can be switched in the reverse direction at the timing when the leading end of the paper in the reverse paper discharge direction reaches a predetermined position, that is, the paper size for reverse paper discharge is different. Even in this case, the paper can be reversed and discharged at the same timing.
[0116]
According to a twelfth aspect of the present invention, in the image forming apparatus according to any one of the first to eleventh aspects, the conveyance speed of the reversely discharged paper is set to be higher than the paper feeding speed to the re-conveyance path. Therefore, the passing area can be brought close to the branch point between the re-conveying path and the reverse discharge path, and thereby the first and second forward / reverse conveyance rollers, the forward / reverse conveyance rollers, the reverse discharge rollers, etc. The degree of freedom of arrangement of various rollers can be increased.
[0117]
According to a thirteenth aspect of the present invention, in the image forming apparatus according to any one of the first to twelfth aspects, the switching claw disposed at a branch point between the reconveying path and the reverse discharge path, and the inside of the reconveying path The switching claw is urged so that the switching claw is positioned at a position that allows the switched back sheet to be fed into the reverse discharge path, and the sheet conveyed on the reconveying path toward the sheet conveying path And a biasing member set to a biasing force that is large enough to move the switching claw to a position that allows the paper to travel along the re-carrying path when it abuts the switching claw. Use an electrical actuator such as a solenoid to switch the switching claw required for transporting the paper in the re-transport path and feeding the paper switched back in the re-transport path to the reverse discharge path. Without biasing body with simple structure Ukoto can, moreover, it is possible to switch operation of the switching claw with the biasing body made reliable enables high-speed response.
[0118]
According to the fourteenth aspect of the present invention, in the image forming apparatus according to any one of the first to thirteenth aspects, since the image forming section is an electrophotographic image forming section, the electrophotographic image forming section is provided. The invention according to any one of claims 1 to 13 can also be realized in the image forming apparatus.
[0119]
According to the fifteenth aspect of the present invention, in the image forming apparatus according to any one of the first to thirteenth aspects, the image forming unit is a digital electrophotographic image forming unit provided with a digital writing unit. The invention according to any one of claims 1 to 13 can also be realized in an image forming apparatus including a digital electrophotographic image forming unit including means.
[0120]
According to the printer of the sixteenth aspect of the present invention, the image forming apparatus according to any one of the first to fifteenth aspects, an input terminal for receiving input of image data, and image data input by controlling the image forming apparatus Therefore, this printer also exhibits the same operations and effects as those of any one of the first to fifteenth aspects of the invention.
[0121]
According to the copying machine of the seventeenth aspect of the present invention, the image reading device for reading an image of the original, the image forming device according to any one of the first to fifteenth aspects, the image reading device and the image forming device are controlled. Since the image forming apparatus includes a control unit that causes the image forming apparatus to form an image on the paper based on the image data of the document read by the image reading apparatus, the copier also includes the invention according to any one of claims 1 to 15. The same operation and effect are exhibited.
[Brief description of the drawings]
FIG. 1 is a schematic diagram illustrating an overall structure of an image forming apparatus including a digital electrophotographic image forming unit according to a first embodiment of the present invention.
FIGS. 2A and 2B are enlarged front views showing a sheet reversing unit, in which FIG. 2A shows an open state, and FIG.
FIG. 3 is a perspective view showing a conveyance roller and a switching claw.
FIG. 4 is an explanatory diagram illustrating a conveyance state of a sheet to an image forming unit when image formation is continuously performed.
FIG. 5 is an explanatory diagram illustrating a state of conveyance of a sheet to an image forming unit when image formation is continuously performed.
FIG. 6 is a diagram showing a sheet conveying operation during continuous image formation.
FIG. 7 is an explanatory diagram illustrating a sheet conveyance state during duplex printing.
FIG. 8 is an explanatory diagram illustrating a conveyance state of a sheet during reverse paper discharge.
FIG. 9 is an explanatory diagram illustrating in detail a state of paper conveyance during reverse paper discharge.
FIG. 10 is an explanatory diagram for explaining in detail the state of conveyance of paper during reverse paper discharge.
FIG. 11 is an explanatory diagram illustrating in detail a state of paper conveyance during reverse paper discharge.
FIG. 12 is a schematic diagram illustrating an arrangement state of forward / reverse conveyance rollers, reverse discharge rollers, and the like according to the second embodiment of the present invention.
FIG. 13 is a block diagram of a printer according to a third embodiment of this invention.
FIG. 14 is a block diagram of a copying machine according to a fourth embodiment of this invention.
FIG. 15 is a schematic diagram showing the overall structure of a conventional image forming apparatus having a duplex printing function and a reverse paper discharge function.
[Explanation of symbols]
1 Paper storage
2 Image forming unit
3 Paper output section
4 Paper transport path
7 Separation paper feeding means
19 Inversion road
20 Paper reversing means
29 Re-transport path
31 Reverse paper discharge path
32, 33 First forward / reverse conveying roller
34 Second forward / reverse conveying roller
35 Reverse roller
36 Paper edge detection sensor
43 Reverse paper discharge roller
44, 45 Forward / reverse transport roller
52 Image forming apparatus
53 Input terminal
55 Control unit
62 Image reader
63 Control unit

Claims (17)

A paper storage section for stacking and holding paper;
A separation sheet feeding means for separating and feeding sheets one by one from the sheet storage unit;
An image forming unit that forms an image on the fed paper;
A paper conveyance path from the paper storage unit to the image forming unit;
A reversing path that is connected in the middle of the sheet conveying path and into which the sheet conveyed through the sheet conveying path is sent;
At least a part of the feeding state in which the sheet fed to the reversing path is switched back and sent to the sheet conveying path, and the preceding sheet fed from the reversing path and the succeeding sheet fed to the reversing path are A paper reversing means switchable to an open state allowing the superposition;
A re-conveying path connected between the paper discharge side of the image forming unit and the upstream side of the reversing path of the paper conveying path;
A reverse discharge path branched from the middle of the re-transport path and connected to the paper discharge section;
Provided downstream from the branch point of the reversing paper discharge path in the re-conveyance path, the normal rotation direction for conveying the sheet sent to the re-conveyance path toward the sheet conveyance path and the sheet are switched back. A first forward / reverse conveyance roller that can be switched between forward and reverse rotations in the reverse rotation direction fed into the reverse discharge path;
An image forming apparatus. On the downstream side of the branch point of the reversing paper discharge path in the reconveying path, the succeeding sheet fed to the reconveying path and the preceding paper that is switched back on the reconveying path and sent to the reversing paper discharge path. The image forming apparatus according to claim 1, wherein a passing area where the sheet passes is provided, and the first forward / reverse conveying roller is provided outside the passing area. The image forming apparatus according to claim 1, wherein the forward / reverse switching of the first forward / reverse conveyance roller is performed by forward / reverse switching of a motor connected to the first forward / reverse conveyance roller. A paper end detection sensor for detecting the end of the paper conveyed on the reconveying path is provided upstream of the reversal discharge path branch point in the reconveying path, and after the paper end is detected by the paper end detecting sensor. The image forming layer according to any one of claims 1 to 3, wherein the rotation of the first forward / reverse conveying roller is switched in the reverse direction at a preset timing. A reversing roller is provided near the branch point of the reversal discharge path in the re-conveying path and downstream of the branch point, and is driven to rotate in a direction to feed the paper into the reversal discharge path. 5. The image forming apparatus according to claim 1, wherein the image forming apparatus is switchable between a sheet feeding state in which the sheet is nipped and conveyed and an open state in which the nipping of the sheet is released. The image forming apparatus according to claim 5, wherein the reverse roller and the first forward / reverse conveyance roller that are rotationally driven in a direction in which the sheet is fed into the reverse discharge path are synchronously performed at the same peripheral speed. A reverse paper discharge roller that is rotationally driven in a direction to transport the paper to the paper paper discharge unit is provided on the reverse paper discharge path, and before the subsequent paper transported through the re-transport path reaches the reverse roller. 7. The image forming apparatus according to claim 5, wherein the reverse discharge roller is disposed at a position where the preceding paper that has been reversely discharged is sandwiched. The forward rotation direction for transporting the sheet fed into the re-conveying path toward the sheet conveying path within the range that is within the passing area or outside the passing area according to the size of the reversely discharged sheet and the sheet A second forward / reverse conveyance roller that can be switched between forward and reverse rotations in the reverse direction to be fed back to the reverse discharge path, and the second forward / reverse conveyance roller sandwiches the sheet and conveys the sheet. The image forming apparatus according to claim 2, wherein the image forming apparatus is provided so as to be switchable to an open state in which the pinching is released. A paper storage section for stacking and holding paper;
A separation sheet feeding means for separating and feeding sheets one by one from the sheet storage unit;
An image forming unit that forms an image on the fed paper;
A paper conveyance path from the paper storage unit to the image forming unit;
A reversing path that is connected in the middle of the sheet conveying path and into which the sheet conveyed through the sheet conveying path is sent;
At least a part of the feeding state in which the sheet fed to the reversing path is switched back and sent to the sheet conveying path, and the preceding sheet fed from the reversing path and the succeeding sheet fed to the reversing path are A paper reversing means switchable to an open state allowing the superposition;
A re-conveying path connected between the paper discharge side of the image forming unit and the upstream side of the reversing path of the paper conveying path;
A reverse discharge path branched from the middle of the re-transport path and connected to the paper discharge section;
Provided downstream from the branch point of the reversing paper discharge path in the re-conveyance path, the normal rotation direction for conveying the sheet sent to the re-conveyance path toward the sheet conveyance path and the sheet are switched back. A forward / reverse conveyance roller that can be switched between forward and reverse rotations in the reverse rotation direction fed into the reverse discharge path;
A reverse paper discharge roller provided on the reverse paper discharge path and rotationally driven in a direction to convey the paper to the paper paper discharge unit;
Have
The succeeding sheet fed on the reconveying path and the preceding sheet switched back on the reconveying path and sent to the reversing discharge path pass outside the passing area provided on the conveying path. Forward and reverse transport rollers are arranged,
An image forming apparatus in which a distance between the reverse discharge roller and the forward / reverse conveyance roller is set to be smaller than a minimum sheet passing length of usable paper. The image forming apparatus according to claim 9, wherein the forward / reverse switching of the forward / reverse conveyance roller is performed by forward / reverse switching of a motor coupled to the forward / reverse conveyance roller. A paper end detection sensor for detecting the end of the paper conveyed on the reconveying path is provided upstream of the reversal discharge path branch point in the reconveying path, and after the paper end is detected by the paper end detecting sensor. The image forming layer according to claim 9 or 10, wherein the rotation of the forward / reverse conveying roller is switched in the reverse direction at a preset timing. The image forming apparatus according to claim 1, wherein a conveyance speed of the reversely discharged paper is set to be higher than a paper feeding speed to the re-conveyance path. The switching claw disposed at the branch point between the re-conveying path and the reverse paper discharge path, and the switching to a position that allows the paper switched back in the re-conveyance path to be fed into the reverse paper discharge path. The switching claw is urged so that the claw is positioned, and when the sheet conveyed on the reconveying path toward the sheet conveying path comes into contact with the switching claw, the sheet advances in the reconveying path. The image forming apparatus according to claim 1, further comprising: an urging body set to an urging force having a magnitude such that the switching claw moves to a position where the switching claw is allowed to move. The image forming apparatus according to claim 1, wherein the image forming unit is an electrophotographic image forming unit. 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. An image forming apparatus according to any one of claims 1 to 15,
An input terminal for receiving input of image data;
A control unit for controlling the image forming apparatus to form an image on a sheet based on the image data;
Having a printer. An image reading device for reading an image of a document;
An image forming apparatus according to any one of claims 1 to 15,
A control unit that controls the image reading apparatus and the image forming apparatus and causes the image forming apparatus to form an image on a sheet based on image data of the original read by the image reading apparatus;
Copier with.

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