JPH0635265A - Both-side unit for image forming device - Google Patents

Abstract

PURPOSE:To print on both sides of paper at high speed. CONSTITUTION:Paper reversing paths 3 and 4 provided with switchback paths 31 and 47 are provided at two stages. By successively sorting and feeding the paper P where an image is formed on its surface and which is consecutively fed to the paths 3 and 4, the paper is surely resupplied without stacking the paper or temporarily stopping the paper in order to adjust timing at the time of switchback even when a feeding interval between the papers is made short or feeding speed is made high, so that the image is formed on both sides at high speed. By making only a paper receiving part 7 receiving the paper from a device main body 1 and a paper feeding part 8 feeding the paper to the device main body 1 in the respective paths 3 and 4 a common path, the interference of the paper going toward the device main body 1 is effectively prevented.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a duplex unit of an image forming apparatus such as a copying machine or a page printer which can print on both front and back sides of a sheet.

[0002]

2. Description of the Related Art As a double-sided unit of a conventional image forming apparatus capable of printing on both front and back sides of a paper, for example, Japanese Patent Laid-Open No.
As described in Japanese Patent Laid-Open No. 181064, a sheet (transfer sheet) after copying on one side is conveyed to a switchback path and stacked in a returning section with the front end and the rear end being exchanged, and the returning section. Counting starts when the paper first arrives in the paper, and when the count value reaches the number of copies, the paper that was first stacked in the return section is re-fed and passed through the reversing section. There is one that can be copied on both sides by reversing the front and back and making a copy on the back side.

Further, as described in Japanese Patent Laid-Open No. 57-141656, the paper after copying on one side is temporarily stopped at the stage where it is partially discharged by a paper discharge roller, and this time it is reversed. It is possible to copy an image on both sides without lowering the copying speed by transporting it and storing it in the second storing section at high speed, and then transporting it again at a predetermined timing to copy the image on the back side. There is also.

Further, as in the double-sided unit disclosed in Japanese Patent Laid-Open No. 182655/58, a double-sided copying assisting means including a sheet discharging section, a switching gate, a switchback section, a returning section and a reversing section is provided, A predetermined return position where the sheet after the image is copied on the front side can be quickly copied on the back side by increasing the copy return speed by the double-sided copy assisting means when copying the image on the back side. To increase the efficiency of double-sided copying, and further, as described in Japanese Patent Laid-Open No. 62-161641, the paper feed interval of double-sided or multi-leaf sheets is set to By providing a conveyance control unit that adjusts according to the conveyance state of the leaf body or external means, 1
Some have been designed to prevent a decrease in the maximum printable number per minute.

[0005]

However, in the case of the double-sided unit according to the above-mentioned Japanese Patent Laid-Open No. 58-181064, the sheets are once stacked on the return section and stopped, so that the processing time is equal to the stop time. However, there was a case where it was not possible to perform double-sided printing at high speed.

Further, in the case of the duplex unit according to Japanese Patent Laid-Open No. 57-141656, since the switchback path uses the same transport path as the next continuously transported paper, it precedes it. Since the next sheet had to be paused in order to avoid interference while the sheet was being switched back, it was sometimes impossible to perform double-sided printing at high speed.

Further, as in the double-sided unit according to Japanese Patent Laid-Open No. 182655/1983, the speed at which a sheet after one-sided printing is conveyed to the reversing unit is increased, and the number of Japanese Patent Laid-Open No. 62-62156 is used.
Even when the paper feed interval is adjusted according to the sheet conveyance state as in the double-sided unit according to Japanese Patent No. 161641, the processing speed is expected to be slightly increased but the processing speed is not expected to be greatly improved. There was an occasion. The present invention has been made in view of the above problems, and an object thereof is to enable printing on both sides of a sheet at high speed.

[0008]

In order to achieve the above object, the present invention provides a double-sided unit of an image forming apparatus capable of printing on both front and back sides of a sheet, which is provided with a plurality of sheet reversing paths by a switchback method. Is. Then, in the duplex unit of the image forming apparatus, the plurality of sheet reversing paths are respectively connected to the conveying paths on the apparatus body side in a state of being mounted on the apparatus body, and a sheet receiving section from the apparatus body of each sheet reversing path is provided. It is preferable that only the sheet sending-out section to the apparatus main body be a shared path.

Further, it is preferable that each of the plurality of sheet reversing paths is provided with a conveying mechanism that conveys a sheet at a plurality of sheet conveying speeds. Further, it is effective to provide a conveyance number control means for changing the number of sheets to be simultaneously conveyed in the paper reversing path according to the size of the paper to be conveyed in the paper reversing path.

[0010]

According to the double-sided unit of the image forming apparatus having the above-described structure, since the plurality of sheet reversing paths by the switchback system are provided, even if the conveying interval between the sheets is narrowed or the conveying speed is increased, Sheets that have images formed on them and are continuously fed are distributed to the multiple sheet reversing paths in sequence and fed, so that the sheets are not stacked or temporarily stopped at the time of switchback for timing adjustment. In addition, since the paper can be reliably re-fed, double-sided image formation can be performed at high speed.

Further, a plurality of sheet reversing paths are connected to the transporting path on the side of the apparatus body while being mounted on the apparatus body,
If only the paper receiving section from the apparatus main body of each paper reversing path and the paper sending section to the apparatus main body are shared paths, the paper that is switched back in each paper reversing path and heads to the conveying path on the apparatus main body side, Since the sheets only join at the portion of the small shared path, the sheets can be conveyed at a high speed without interfering with each other without stopping or decelerating the conveyance of the subsequent sheets.

Further, if each of the plurality of sheet reversing paths is provided with a conveying mechanism that conveys a sheet at a plurality of sheet conveying speeds, a plurality of sheets are conveyed in different conveying directions in each sheet reversing path. Alternatively, it is possible to freely control the conveyance of the sheet at different conveyance speeds.

Further, if the number-of-conveyed-sheets control means for changing the number of sheets to be simultaneously conveyed in the sheet reversing path according to the size of the sheet to be conveyed in the sheet reversing path is provided, it is the same in the case of short sheets in the conveying direction. Since a plurality of sheets can be simultaneously conveyed in the sheet reversing path, it is possible to efficiently process a large number of double-sided images.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT An embodiment of the present invention will be specifically described below with reference to the drawings. FIG. 1 is a system configuration diagram showing a laser beam printer which is an image forming apparatus having a duplex unit according to the present invention. The laser beam printer, which is the image forming apparatus, includes a double-sided unit 2 used when printing on both front and back surfaces of the paper P, and the double-sided unit 2 includes a plurality of paper reversing paths 3 and 4 (switchback type). 3 or more may be provided).

The double-sided unit 2 is attached to the lower side of the apparatus main body (printer main body) 1 as shown in the drawing, and the paper reversing paths 3 and 4 are connected to the conveying paths 5 and 6 on the apparatus main body 1 side, respectively. Then, only the sheet receiving section 7 from the apparatus main body 1 and the sheet sending-out section 8 to the apparatus main body 1 of each of the sheet reversing paths 3 and 4 are shared paths. A mass paper feed tray 10 is mounted on the side of the duplex unit 2, and the paper P stored in the mass paper feed tray 10 is fed into the duplex unit 2 by a paper feed roller 9, which is a duplex The inside of the unit 2 is lifted and is transported to the transport path 6 of the apparatus main body 1.

The paper P is provided inside the apparatus main body 1,
The front end side is abutted against the registration roller pair 11 in the stopped state to perform skew correction, and the skew correction is performed.
Registration roller pair 1 at the same timing as the image on 2
When 1 rotates, it is conveyed to the lower side of the photosensitive drum 12.

The surface of the photosensitive drum 12 is charged by corona discharge by the charging charger 13 while rotating clockwise, and the electrostatic latent image is formed by irradiating the surface thereof with laser light from the optical writing unit 14. It
The latent image is visualized as it passes through the developing unit 15, and is transferred by the transfer / separation unit 16 to the upper surface side of the paper P conveyed by the registration rollers 11.

The sheet P on which the image has been transferred is sent to the fixing unit 17 to fix the image, and sheet discharge in a face-down state (discharge with the image side facing down) is selected in single-sided image formation. 1 is conveyed toward the large-volume sheet discharge unit 19 by the branch claw 18 which is rotated to the position shown by the solid line in FIG. Discharged on top.

Then, the residual toner on the surface of the photosensitive drum 12 after the transfer of the image is removed by the cleaning unit 23. On the other hand, during double-sided image formation,
The sheet P that has passed through the fixing unit 17 with the image formed on one side of the branch claw 18 that has been rotated to the position shown by the phantom line in FIG.
Is guided to the transport path 5 by the branch claw 18 and is transported into the duplex unit 2 by the transport roller 24.

The double-sided unit 2 has two units as described above.
The sheet reversing paths 3 and 4 of two switchback systems are provided, and the sheet reversing path 3 on the upper side of the sheet reversing paths 3 and 4 conveys sheets at a plurality of sheet conveying speeds.
The lower sheet reversing path 4 also has conveying mechanisms 27 and 28 for conveying the sheet at a plurality of sheet conveying speeds.
Is equipped with.

The transport mechanism 25 on the sheet reversing path 3 side is provided at the entrance of the switchback path 31, and a pair of switchback rollers 32 is rotated by a motor 33 in both forward and reverse directions. Further, the transport mechanism 26 uses the re-feed transport path 3
A pair of rollers 35 and 36, which are provided at a position 4 and are spaced apart from each other, are rotationally driven by a motor 37, respectively.

A branch claw 38 is provided at a branch between the switchback path 31 and the re-feeding / conveying path 34, and a branch claw 39 is not shown at the branch between the two sheet reversing paths 3 and 4. A solenoid pair is rotatably provided between the positions shown in FIGS. 2 and 3, and a pair of rollers 42, 43 rotated by a motor 41 as shown in FIG. It is provided at intervals.

A sensor 44 (for example, a reflection type photo sensor) for detecting the sheet P fed from the apparatus main body 1 into the duplex unit 2 is provided on the upstream side of the roller pair 42.
However, a sensor 45 is arranged in the conveying path between the branch claw 39 and the switchback roller 32, and a sensor 46 is arranged in the conveying path between the branch claw 38 and the switchback roller 32.

Further, the transport mechanism 2 of the lower sheet reversing path 4
7 is provided at the entrance of the switchback path 47,
The pair of switchback rollers 48 are rotated in both forward and reverse directions by the motor 49, and the transport mechanism 2 of the re-feed transport path 51.
8, roller pairs 52 and 53 are rotationally driven by a motor 54, respectively. A branch claw 55 is rotatably provided at a branch portion between the switchback path 47 and the re-feeding and conveying path 51 by a solenoid (not shown), for example.

Further, roller pairs 57 and 58 rotated by a motor 56 are provided at intervals in the carrying direction near the carrying path where the two sheet reversing paths 3 and 4 merge, and the roller pair 57 is provided. A sensor 59 is arranged in the conveying path between the roller pair and the roller pair 36, and a sensor 60 is arranged in the sheet feeding section 8 of the conveying path.

Next, referring to FIG. 4, the operation of each part when the sheet reverse path 3 on the upper side of the duplex unit 2 is used to reverse the front and back of the sheet and re-feed the sheet to the apparatus main body 1 will be described. explain. When the leading edge of the sheet P having an image formed on one side (front side) of the apparatus body 1 conveyed into the duplex unit 2 is detected by the sensor 44, the branch claw 39 is switched to the position shown in FIG. Therefore, it is conveyed to the upper sheet side sheet reversing path 3 by the conveying force of the roller pair 42 driven by the motor 41.

Then, the sensor 45 at the branching portion causes the paper P
4 is switched to the position shown by the solid line in FIG. 4 by the operation of a solenoid (not shown). Therefore, the sheet P is drawn into the switchback path 31 by the switchback roller 32 rotating in the direction of the arrow in the figure, and when the rear end is detected by the sensor 46, the motor 33 is stopped and the switchback roller 32 is stopped. Stops.

Next, when the motor 33 rotates in the reverse direction, the switchback roller 32 rotates in the direction opposite to the arrow in FIG. 4, and the branch claw 38 switches to the position shown by the phantom line in FIG. P is switched back toward the re-feeding conveyance path 34. The transport speed at this time is increased as compared with the speed at the time of paper feeding.

The sheet P is conveyed to the right in FIG. 4 by the roller pairs 35 and 36 which are rotationally driven in the direction of the arrow by the motor 37, and when the sensor 59 detects the leading edge of the sheet P, the motor 37 is moved. Is temporarily stopped, and when a re-feeding command is output from the main body side thereafter, the motor 37 is restarted at a predetermined timing, and the paper P is conveyed to the roller pair 57 driven by the motor 56. When the sensor 60 detects the trailing edge of the sheet P, the entire process of re-feeding the first sheet by the duplex unit 2 for double-sided image formation is completed.

The sheet re-feeding process by the double-sided unit 2 is the same for the lower sheet reversing path 4, so its explanation will be omitted. 1 for image formation
The branch claw 3 in which the second sheet is in the position shown in FIG. 2 as described above
Immediately after the trailing edge of the sheet 9 has passed, the branching claw 39 is switched to the position shown in FIG. 3, and the second sheet is quickly sent to the lower sheet reversing path 4, and the upper sheet reversing path 3 shown in FIG.
After the re-feeding process similar to the operation described in the above, it is reversed and conveyed to the apparatus main body 1 through the paper sending-out section 8 which is a shared path.

Then, the next third sheet is fed again into the upper sheet reversing path 3, and thereafter, the sheet is alternately fed into the upper and lower sheet reversing paths 3 and 4.
The switching timing of the branch claw 39 is determined by the sensor 44.
By switching after a predetermined time in consideration of the sheet transport speed from the timing when the leading edge of the sheet P is detected, it is possible to switch it immediately after the preceding sheet passes.

As described above, since the double-sided unit 2 is provided with the switch-back type sheet reversing path in two stages, the sheet-to-sheet conveying interval is narrow and the image forming apparatus has a high conveying speed. , The sheets that are continuously fed to the duplex unit 2 with the image formed on the front side are alternately distributed to the upper and lower sheet reversing paths 3 and 4 to be fed, thereby stacking the sheets or switching on the conveying path. It is possible to surely re-feed the sheet and form an image on the back side at high speed without temporarily stopping the conveyance to avoid interference between the sheets at the time of backing.

As shown in FIG. 4, the duplex unit 2 includes a sheet receiving portion 7 from the apparatus main body 1 to the branch point a of the upper and lower sheet reversing paths 3 and 4, and a branch point b to the apparatus main body 1. Since only the paper feeding section 8 of the above is used as the shared path, the paper which is switched back in the respective paper reversing paths 3 and 4 toward the transport path 6 on the apparatus main body side is only a part of the shared path at a short distance. Since they are only merged, the subsequent sheets can be efficiently conveyed to the apparatus body 1 at high speed without interfering with each other without stopping or decelerating the conveyance of the subsequent sheets.

Next, with reference to FIG. 5, an embodiment will be described in which a number-of-conveyed sheets control means for changing the number of sheets to be simultaneously conveyed in the sheet reversing path according to the size of the sheet to be conveyed in the sheet reversing path is described. . The duplex unit of the image forming apparatus according to this embodiment controls so as to change the number of sheets to be simultaneously conveyed in each sheet inversion path according to the size of the sheet to be conveyed in the sheet inversion path 3 or 4.

[0035] That is, (become either the same for the same in length in this embodiment) sheet reversing path 3 or 4
Paper P having a length in the transport direction that is less than half the length of the transport path of
When double-sided image formation of 1 and P 2 is performed, a switchback roller 32 driven by a motor 33 and a roller pair 35, 36 driven by a motor 37, as shown in the upper sheet reversing path 3 in FIG. Two transport mechanisms 25,
At 26, the conveyance of two sheets of paper P1 and P2 is controlled.

In this case, the condition is that the lengths of the sheets P1 and P2 are such that the transport mechanisms 25 and 26 can transport them. Further, as indicated by the sheet P3 in the sheet reversing path 4 on the lower side of FIG. 5, when the length of the sheet is more than half the length of the conveying path, the roller pair 52 driven by the motor 54, 1 using all three rollers of switchback roller 48 driven by 53 and motor 49
The sheet P3 is conveyed. In this way, the number of sheets of paper P3 that is long in the transport direction is one for each sheet reversing path.

Further, if the sheet reversing path is a conveying path having a sufficient length and driving rollers independently rotated by a large number of driving sources (motors) are provided on the conveying path, one sheet of paper is formed. It is possible to further increase the number of sheets of paper that can be processed simultaneously in the reversing path. In each of the above-described embodiments, if the transport mechanisms 25, 26, 27 and 28 in the upper and lower sheet reversing paths 3 and 4 are capable of transporting the sheets at a plurality of sheet transport speeds, respectively, the sheets are different. Since the conveyance can be freely controlled at the conveyance speed, the sheet can be efficiently inverted and re-fed.

FIG. 6 is a block diagram showing the control system in each of the above embodiments. The instruction code output from the microprocessor unit (hereinafter abbreviated as MPU) 61 of the apparatus body 1 is an interface (hereinafter abbreviated as I / F).
It is received from the MPU 64 of the duplex unit 2 from 62 via the I / F 63 of the duplex unit 2. With this command code, the duplex unit 2 can know the timing of feeding and discharging from the apparatus main body 1 and the size of the fed sheet.

The MPU 64 is provided with a ROM 65 and a RAM 66 in which a program is incorporated, and through the motor driver 67, the transport mechanisms 25, 26, which are provided in the upper and lower sheet reversing paths 3, 4 (FIG. 4). The motor group 68 for driving 27 and 28 respectively is driven and controlled, and the solenoid group 69 for switching the turning positions of the branch claws 38, 39, 55 is controlled to be turned on and off, so that each position on the conveyance path in the duplex unit 2 is controlled. A paper detection signal is input from a sensor group 71 including various sensors provided, and the position of the paper is detected by the signal.

In the embodiment of FIG. 5, this MPU6
The control unit 4 controls the number of sheets to be simultaneously conveyed in the sheet reversing path according to the size of the sheet to be conveyed in the sheet reversing path 3 or 4. Therefore, this MPU
Reference numeral 64 functions as a conveyance number control means.

[0041]

As described above, according to the present invention, since a plurality of sheet reversing paths by the switchback system are provided, even in the image forming apparatus in which the sheet conveyance interval is narrow or the sheet conveyance speed is high. By sequentially feeding the sheets of paper on which images are formed and continuously fed to the paper reversing paths, the sheets can be stacked or temporarily stopped for timing adjustment at switchback. The double-sided image formation can be performed at a high speed because the sheet can be surely re-fed without the need for performing the operation.

Further, a plurality of sheet reversing paths are connected to the conveying path on the side of the apparatus main body while being mounted on the apparatus main body,
If only the paper receiving section from the apparatus main body of each paper reversing path and the paper sending section to the apparatus main body are shared paths, the paper that is switched back in each paper reversing path and heads to the conveying path on the apparatus main body side, Since only the part of the shared path having the slight length merges, the subsequent sheets can be transported without stopping or decelerating the transportation of the subsequent sheets without interfering with each other. Therefore, higher speed can be realized.

Further, if each of the plurality of sheet reversing paths is provided with a conveying mechanism that conveys the sheet at a plurality of sheet conveying speeds, the plurality of sheets can be simultaneously controlled in each sheet reversing path. Since it can be transported in different transport directions or controlled at different transport speeds, it can be controlled freely, so that a wide range of control is possible.

Further, if the number-of-conveyed-sheets control means for changing the number of sheets to be simultaneously conveyed in the sheet reversing path according to the size of the sheet to be conveyed in the sheet reversing path is provided, it is the same in the case of short sheets in the conveying direction. Since a plurality of sheets can be simultaneously conveyed in the sheet reversing path, it is possible to efficiently process a large number of double-sided images.

[Brief description of drawings]

FIG. 1 is a system configuration diagram showing a laser beam printer which is an image forming apparatus including a duplex unit according to the present invention.

FIG. 2 is a schematic diagram showing a state in which a branching claw 39 provided at a branching portion of two sheet reversing paths of the duplex unit in FIG. 1 is rotated to a position that guides a sheet to an upper sheet reversing path side. Is.

FIG. 3 is a schematic view showing a state in which the branching claw 39 is also rotated to a position for guiding a sheet to a lower sheet reversing path.

FIG. 4 is a schematic configuration diagram showing a double-sided unit of FIG. 1 in an enlarged manner.

FIG. 5 is a schematic diagram for explaining an embodiment in which the number of sheets to be simultaneously conveyed in the sheet inversion path is changed according to the size of the sheet to be conveyed in the sheet inversion path.

FIG. 6 is a block diagram showing a control system of a duplex unit of the image forming apparatus according to the present invention.

[Explanation of symbols] 1 main body 2 double-sided unit 3,4 paper reversing path 5,6 transport path 7 paper receiving section 8 paper sending section 25, 26, 27, 28 transport mechanism 31 switchback path 64 microprocessor unit (number of transport sheets) Control means)

Claims (4)

[Claims] 1. A double-sided unit of an image forming apparatus, wherein a plurality of sheet reversing paths of a switchback system are provided in a double-sided unit of an image forming apparatus capable of printing on both front and back sides of a sheet. 2. The double-sided unit of the image forming apparatus according to claim 1, wherein the plurality of sheet reversing paths are respectively connected to a conveying path on the apparatus body side in a state where the sheet reversing paths are installed in the apparatus body. A duplex unit of an image forming apparatus, wherein only a sheet receiving section from the apparatus body and a sheet sending section to the apparatus body are shared paths. 3. The double-sided unit of the image forming apparatus according to claim 1, wherein each of the plurality of sheet reversing paths includes a conveying mechanism that conveys a sheet at a plurality of sheet conveying speeds. Double-sided unit of image forming apparatus. 4. The double-sided unit of the image forming apparatus according to claim 1, the number of sheets to be simultaneously conveyed in the sheet reversing path according to the size of the sheet to be conveyed in the sheet reversing path. A double-sided unit for an image forming apparatus, which is provided with a conveyance number control unit for changing