JP2002296848A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the productivity of image forming work by narrowing the intervals of forms fed in continuous image formation and to improve the productivity of image forming work by narrowing the intervals of forms even in both side printing in the interleaving system. SOLUTION: In the case of both side printing in the interleaving system, a means is provided which changes the time required for re-feed in which a form fed from a form storage part 1 and passes a junction A between a re-feed line 29 and a form carrying line 4 is returned to the junction A again through an image forming part 2 and the re-feed line 29, and this time required for re-feed is made shorter to narrow the intervals of forms, thereby enhancing the productivity of image forming work at the time of both side printing in the interleaving system.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to an image forming apparatus capable of efficiently performing continuous image formation and performing double-sided printing by an interleaf method.

[0002]

2. Description of the Related Art Conventionally, an image forming apparatus having a function of performing double-sided printing by an interleaf method is known.
The schematic structure of such an image forming apparatus will be described with reference to FIG.

This image forming apparatus includes a paper storage unit 101 for storing and stacking sheets, an image forming unit 104 for forming an image on fed paper provided with a photoreceptor 102 and a developing unit 103, and the like. Paper discharge unit 1 from which discharged paper is discharged
The paper transport path 106 for transporting the paper is provided between the paper storage unit 101 and the image forming unit 104.

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

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

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

In the case of performing interleaf type double-sided printing with this image forming apparatus, a sheet fed from the sheet storage unit 101 and having an image formed on one side (front side) in the image forming unit 104 is a sheet of paper. Conveying path 108, reversing path 11
0, the sheet is sent again to the image forming unit 104 via the re-feeding path 112, and the image is formed on the other surface (back surface). Paper on which image formation (double-sided printing) has been performed on the front and back sides
The sheet is directly discharged to the sheet discharge unit 105 via the sheet discharge path 107.

Here, when continuous image formation is performed by the image forming apparatus as shown in FIG. 15, when two sheets are fed to the image forming section 104 in a state of being overlapped, one image is converted into two sheets. The image forming operation is interrupted when the sheet is formed over the sheet or when the sheet size detecting sensor detects that the sheet size is abnormal.

Therefore, when image formation is performed continuously, it is necessary to feed the paper with a sufficiently large interval between the front and rear sheets in order to prevent the sheets sent to the image forming unit 104 from overlapping. There is. More specifically, slips when paper is separately fed from the paper storage unit 101, aging and environmental changes of paper transport speed when paper is transported through the paper transport path 106, and variations in stopping time for registration, etc. In consideration of the above, at the time of continuous image formation, paper is fed with a space of several tens mm between the front and rear sheets. Therefore, when image formation is performed continuously, the time during which image formation is not actually performed is lengthened, and the productivity of the image formation operation is reduced.

Therefore, the applicant of the present application has
As an image forming apparatus capable of increasing the productivity of an image forming operation when image forming is continuously performed, a reversing path and a sheet reversing unit are provided in the middle of a sheet conveying path in which sheets are conveyed toward an image forming unit. The provided image forming apparatus is described in Japanese Patent Application
No. 1-239672 and Japanese Patent Application No. 2000-230153.

According to the image forming apparatus provided with the reversing path and the sheet reversing means, the sheet conveyed along the sheet conveying path and fed into the reversing path is temporarily stopped in the reversing path and then switched back. It is sent to the image forming unit. And
When performing this switchback, the sheet is switched back and sent to the image forming unit by controlling the speed of feeding the sheet to the reversing path, the speed of feeding the sheet from the reversing path, the timing of feeding the sheet from the reversing path, and the like. The distance between the sheets to be printed can be reduced, thereby improving the productivity of the image forming operation.

In the case where the above-described reversing path is provided, if the paper is switched back on the reversing path during double-sided printing, the re-feeding path 112 as shown in FIG. The sheet on which the image formation on the front side has been completed can be directly sent from the reversing path 110 to the sheet conveying path 106.

[0013]

SUMMARY OF THE INVENTION However, Japanese Patent Application No.
When performing interleaf type duplex printing in an image forming apparatus provided with a reversing path and sheet reversing means proposed in Japanese Patent Application No. 239672, Japanese Patent Application No. 2000-230153, etc. The interval between the edge and the leading edge of the sheet on which an image is formed on the front surface and re-fed for image formation on the back surface tends to be greatly increased, and the productivity of the interleaf type double-sided printing decreases.

Such a phenomenon occurs for the following reasons.

This is because the provision of the reversing path and the sheet reversing means narrows the interval between the sheets and makes it impossible to feed the sheet re-fed for forming an image on the back surface.

The re-feeding path 112 becomes unnecessary, and the path on which the sheet on which image formation has been completed on one surface (front side) is conveyed is shortened. Therefore, the number of sheets that can be held in the path This is because (the number of interleaves) decreases, and the feeding of the re-feeded paper cannot be made in time.

An object of the present invention is to increase the productivity of image forming work by narrowing the interval between sheets fed during continuous image formation, and to reduce the interval between sheets even during interleaf type double-sided printing. This is to increase the productivity of the image forming operation by narrowing the width.

[0018]

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 switched back and sent out to the paper transport path, and the preceding sheet sent out 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 The paper path, the paper fed from the paper storage unit at the time of duplex printing of the interleaf system and passed through the confluence of the re-feed path and the paper transport path is the image forming unit and the re-feed path Means for changing the required re-feeding time until returning to the junction again via

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

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

In the case of performing the interleaf type double-sided printing, a sheet having an image formed on one side (front side) is sent to an image forming unit via a re-feeding path, a sheet conveying path, and a reversing path. Double-sided printing is performed by forming an image on the other side (back side).

Here, in this interleaf type double-sided printing, the interval between sheets can be shortened by changing the required re-feeding time so that the image in the interleaf type double-sided printing can be shortened. The productivity of the forming operation can be increased.

According to a second aspect of the present invention, in the image forming apparatus of the first aspect, the means for changing the required re-feeding time is a resist disposed at a position immediately before the image forming section from the reversing path. The time required to reach the roller is changed.

Therefore, by changing the time required to convey the sheet from the reversing path to the registration roller, the time required for re-feeding can be shortened and the sheet interval can be shortened. It is possible to increase the productivity of the image forming operation at the time of the double-sided printing of the system.

According to a third aspect of the present invention, in the image forming apparatus of the first aspect, the means for changing the required re-feeding time changes a process speed.

Therefore, by changing the process speed to a high speed, the time required for re-feeding can be shortened and the paper interval can be shortened. Productivity can be increased.

According to a fourth aspect of the present invention, in the image forming apparatus of the first aspect, the means for changing the required re-feeding time changes a transport speed of a sheet transported through the re-feeding path. It is.

Therefore, by changing the conveyance speed of the paper conveyed through the re-feeding path to be high, the time required for re-feeding can be shortened, and the paper interval can be shortened.
Thereby, the productivity of the image forming operation at the time of the interleaf type double-sided printing can be increased.

According to a fifth aspect of the present invention, in the image forming apparatus of the first aspect, the means for changing the required re-feeding time is a resist disposed at a position immediately before the image forming section from the reverse path. This is a combination of at least two of the change of the required time to the roller, the change of the process speed, and the change of the transport speed of the sheet transported through the re-feeding path.

Therefore, the time required for re-feeding can be reduced, the process speed can be changed to be high, and the transport speed of paper conveyed through the re-feed path can be changed to be high. By combining at least two of the above, it is possible to shorten the time required for refeeding and shorten the paper interval, thereby increasing the productivity of image forming work in interleaf type duplex printing. it can.

[0031]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One 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, FIG. FIG. 4 is an explanatory view showing the state of paper transport to the image forming section when image formation is performed continuously, FIG. 5 is a diagram showing the paper transport operation during continuous image formation, and FIGS. FIG. 14 is an explanatory view showing a sheet conveyance state during duplex printing by a leaf method (two-sheet interleaf method). FIG. FIG. 3 is a schematic diagram showing a sheet conveyance order and a sheet interval.

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

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

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

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

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

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

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

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

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

A paper discharge path 28 is provided directly between the paper discharge side of the image forming section 2 (the side that has passed the fixing section 14) and the paper discharge tray 3, and the paper discharge side of the image forming section 2 and the paper transport. A re-feeding path 29 is provided at a portion of the path 4 upstream of the reversing path 19. A switching claw 30 for switching the transport direction of the sheet discharged from the image forming unit 2 to the direct discharge path 28 or the re-feed path 29 is provided at a branch point between the direct discharge path 28 and the re-feed path 29. Is provided.

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

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

On the horizontal road portion 29b, the horizontal road portion 29
a re-feeding means 32 driven so as to convey the sheet fed onto the sheet conveying path 4 toward the sheet conveying path 4;
A reversing sheet discharging means 33 for switching back the sheet fed above and sending it to the reversing sheet discharging path 31 is provided.

At the location where the reversing sheet discharge path 31 branches off from the re-feeding path 29, the paper in the re-feeding path 29 is moved to the vertical path portion 29a.
A transport roller 34 and a switching claw 35 are provided, which are rotationally driven in a direction in which the paper is transported to the horizontal path portion 29b from the roller.
The switching claw 35 is provided rotatably in a direction of coming into contact with and separating from the transport roller 34, and is urged by an urging body such as a spring in a direction in which it comes into contact with the outer peripheral surface side of the transport roller 34. Allow the paper to travel from the vertical path 29a to the horizontal path 29b, and allow the paper switched back in the horizontal path 29b to enter the reverse discharge path 31.

The image forming apparatus includes an image forming operation in the image forming section 2, a separation sheet feeding means 7, a first and a second
Conveyance rollers 15 and 16, registration roller 18, switching claw 3
0, the driving of the re-feeding means 32, the reversing paper discharging means 33, etc., is controlled by the detection results of the paper edge detection sensor 21, the registration sensor 17, other sensors, etc., the image forming mode (simplex printing mode, duplex printing mode, reversing A control unit (not shown) for controlling according to the setting of the paper discharge mode or the like is provided. As one of the means realized by the processing in the control unit, the paper tray 1
From the paper feeding path 29 and having passed through the junction A between the re-feeding path 29 and the sheet transport path 4, re-feeded until returning to the junction A again via the image forming section 2 and the re-feeding path 29. Means for changing the required time “T” are provided.

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

When the paper fed into the reversing path 19 is switched back, the speed at which the sheet is fed into the reversing path 19, the speed at which the sheet is fed out from the reversing path 19,
By controlling the timing at which paper is fed from the printer, the interval between sheets that are switched back and sent to the image forming unit 2 can be reduced, and
The productivity of the image forming operation can be improved. For example, as shown in the diagram of FIG. 5, the paper is transported at a high transport speed Va from the paper tray 1 to the reversal stop position in the reversal path 19, and is sent out at a low transport speed Vb from the reversal stop position. In addition, the paper interval in the image forming unit 2 can be reduced.

FIG. 3 shows a state in which the preceding sheet a is sent out from the reversing path 19, and the sheet reversing means 20 is
As shown in (b), it is in the sending state. The subsequent sheet b is conveyed along the sheet conveying path 4 and is about to be sent to the reversing path 19.

FIG. 4 shows a state in which the preceding sheet a has been conveyed to a position where the leading end of the sheet a contacts the registration roller 18 and the succeeding sheet b has been fed to a stop position in the reversing path 19. After the preceding sheet a is sent out from the reversing path 19 and its leading end is nipped by the second transport roller 16, the driven roller 23 separates from the drive roller 22 and the sheet reversing means 20
2A, and the succeeding sheet b is fed into the reversing path 19 through the space between the driven roller 23 and the driving roller 22 which are separated from each other. The feeding of the succeeding sheet b to the reversing path 19 is performed such that the trailing end of the preceding sheet a and the leading end of the succeeding sheet b overlap in the reversing path 19.

FIGS. 6 to 13 are explanatory views for explaining the flow of paper during double-sided printing using the two-sheet interleaf system in which A3 size paper is transported in a vertically long state. In FIGS. 6 to 13 and FIG. 14, the circled number given to each sheet indicates the order of the fed sheets.
The characters “front” and “back” attached to the encircled numerals indicate that an image is formed on the front surface and the back surface, respectively. For example, “front” means that the third sheet of paper is fed and an image is formed on the surface.

In the two-sided printing by the two-sheet interleaf method, first, two sheets of paper are continuously fed from the sheet tray 1 (see FIG. 6), and one side (front side) of those sheets is used. (See FIGS. 7 and 8). From the third sheet, image formation on the other side (back side) of the sheet conveyed through the re-feed path 29 and one side (front side) of the sheet newly fed from the sheet tray 1 are performed. ) Are alternately performed with the image formation (FIGS. 9 to 1).
3).

FIG. 14 is a schematic diagram showing the sheet conveying order and the sheet interval at the junction A of the sheet conveying path 4 and the re-feeding path 29 during the two-sheet interleaf type double-sided printing.
“T” indicates a sheet fed from the sheet tray 1 (for example,
The required re-feeding time required after the trailing edge of the sheet passes through the junction A until the leading edge of the sheet reaches the junction A via the image forming unit 2 and the re-feeding path 29 It is.

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 exist between “T”. T = (2D + 3X) / V (1) where D: paper length X: paper interval at merging point A V: paper conveying speed at merging point A Also, the required re-feeding time “T” is , N interleaves can be expressed by the following equation (2). In the case of three interleaves, 4 is set between "T".
There are sheets of paper. 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 in the 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). That is, the transport speed of the sheet re-fed through the re-feeding path 29 by the re-feeding means 32 or the like is increased.

Regarding the value of the transport speed “V”, the desired paper interval “X” and the re-feeding station time “T” are determined in advance based on 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 in the control unit.

In order to shorten the time "T" for the re-feeding station, it is conceivable to shorten the time required from the reversing path 19 to the registration roller 18. That is, the stop time when the paper in the reversing path 19 is switched back is shortened,
The purpose is to increase the transport speed from the reversing path 19 to the registration roller 18.

The values of the transport speed and the stop time are determined by the image forming unit 2 from the confluence point A.
If the required time is determined, the predetermined time is subtracted from the re-feeding station time "T", and the sheet is conveyed from the reversing path 19 to the registration roller 18 within the time obtained by the subtraction. Calculate the stop time and the transport speed required for this. These calculations are performed in the control unit.

In order to shorten the re-feeding station time “T”, it is conceivable to increase the process speed in the image forming section 2. The process speed is changed by changing the rotation speed of the photoconductor 8, the writing speed of the digital writing unit 10, the rotation speed of the transfer unit 12, the rotation speed of the fixing unit 14, and the like.

Regarding the value of the process speed, if it is determined that the time required to convey portions other than the image forming section 2 is determined, the re-feeding station time "T" is used. The required time is subtracted, and the process speed is calculated so that the sheet passes through the image forming unit 2 within the time obtained by the subtraction. These calculations are performed in the control unit.

[0062]

According to the image forming apparatus of the first aspect of the present invention, in the interleaf type double-sided printing, the interval between sheets can be shortened by changing the required re-feeding time. Thereby, the productivity of the image forming operation at the time of the interleaf type double-sided printing can be improved.

According to the second aspect of the present invention, in the image forming apparatus according to the first aspect, the time required for transporting the sheet from the reversing path to the registration roller is changed to reduce the time required for re-feeding. The time can be shortened to shorten the paper interval, thereby increasing the productivity of the image forming operation in the interleaf type double-sided printing.

According to the third aspect of the present invention, in the image forming apparatus according to the first aspect, by changing the process speed to a high speed, the time required for re-feeding is shortened and the paper interval is shortened. Therefore, the productivity of the image forming operation at the time of the interleaf type double-sided printing can be improved.

According to the fourth aspect of the present invention, in the image forming apparatus according to the first aspect, by changing the transport speed of the paper transported in the re-feeding path to a high speed, the re-feeding is required. The time can be shortened to shorten the paper interval, thereby increasing the productivity of the image forming operation in the interleaf type double-sided printing.

According to the fifth aspect of the present invention, in the image forming apparatus of the first aspect, it is possible to change the time required for re-feeding, change the process speed to a high speed, and By changing at least two of changing the conveyance speed of the paper conveyed in the feeding path to be high, the re-feeding time can be reduced and the paper interval can be shortened. It is possible to increase the productivity of the image forming operation at the time of the interleaf type double-sided printing.

[Brief description of the drawings]

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

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

FIG. 3 is an explanatory diagram illustrating a sheet conveyance state during continuous image formation in which sheets are continuously fed.

FIG. 4 is an explanatory diagram illustrating a sheet conveyance state during continuous image formation in which sheets are continuously fed.

FIG. 5 is a diagram illustrating a sheet conveyance operation during continuous image formation.

FIG. 6 is an explanatory diagram illustrating a sheet conveyance state during two-sided printing using the two-sheet interleaf method.

FIG. 7 is an explanatory diagram illustrating a sheet conveyance state during double-sided printing using the two-sheet interleaf method.

FIG. 8 is an explanatory diagram illustrating a sheet conveyance state during double-sided printing using the two-sheet interleaf method.

FIG. 9 is an explanatory diagram illustrating a sheet conveyance state during two-sided printing using the two-sheet interleaf method.

FIG. 10 is an explanatory diagram illustrating a sheet conveyance state during two-sided printing using the two-sheet interleaf method.

FIG. 11 is an explanatory diagram illustrating a sheet conveyance state during two-sided printing using the two-sheet interleaf method.

FIG. 12 is an explanatory diagram illustrating a sheet conveyance state during two-sided printing using the two-sheet interleaf method.

FIG. 13 is an explanatory diagram illustrating a sheet conveyance state during two-sided printing using the two-sheet interleaf method.

FIG. 14 illustrates a state at a junction of a sheet conveyance path and a re-feeding path.
FIG. 4 is a schematic diagram illustrating a sheet conveyance order and a sheet interval in a two-sheet interleaf type double-sided printing.

FIG. 15 is a schematic diagram showing the entire structure of a conventional image forming apparatus having a double-sided printing function by an interleaf method.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Paper storage part 2 Image formation part 4 Paper conveyance path 7 Separation paper supply means 18 Registration roller 19 Reversal path 20 Paper reversal means 29 Re-feed path A Confluence point

Continued on the front page F term (reference) 2H027 ED16 ED17 EE02 EE03 FA13 2H028 BA06 BA09 BA16 BB04 3F049 AA10 CA01 DA12 EA10 LA02 LA07 LB03 3F100 AA02 BA05 CA11 CA12 DA01 EA04 EA06 EA14

Claims (5)

[Claims] A sheet storage unit for stacking and holding sheets of paper; a separating sheet feeding unit for separating and feeding sheets one by one from the sheet storage unit; and an image forming unit for forming an image on the fed sheets. A paper transport path from the paper storage section to the image forming section, a reverse path connected in the middle of the paper transport path to which a sheet transported through the paper transport path is fed, A feeding state in which a sheet is switched back and sent to the sheet transport path, and an opening allowing at least a part of a preceding sheet fed from the reversing path and a subsequent sheet fed to the reversing path to overlap with each other. A sheet reversing means switchable 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 an interleaf type double-sided printing Sometimes said Re-feeding of paper fed from the paper storage unit and passing through the junction of the re-feeding path and the paper transport path until returning to the junction again through the image forming unit and the re-feeding path Means for changing the required time. 2. The means for changing the required re-feeding time comprises:
The image forming apparatus according to claim 1, wherein a time required from the reversing path to a registration roller disposed immediately before the image forming unit is changed. 3. The means for changing the required re-feeding time comprises:
2. The image forming apparatus according to claim 1, wherein the process speed is changed. 4. The means for changing the required re-feeding time comprises:
2. The image forming apparatus according to claim 1, wherein a conveying speed of a sheet conveyed through the re-feeding path is changed. 5. The means for changing the required re-feeding time,
At least a change in a required time from the reversing path to a registration roller disposed immediately before the image forming unit, a change in a process speed, and a change in a conveyance speed of a sheet conveyed through the re-feeding path. 2. The image forming apparatus according to claim 1, wherein two or more are combined.