JP2000247524A - Switchback device for duplex printable image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To straight correct the face directional distortion and switch back a sheet continuously without requiring any space between sheets by providing an advance/discharge part set so as to have a positional relation for guiding both sides of a sheet and having a plurality of bins. SOLUTION: This device has an advance/discharge part 71 having a plurality of bins nipped between opposed upper guide parts 712a-712b and lower guide parts 713a-713g and having sheet outlet and inlet ports 714a-714g. The gap between the upper guide parts 712a-712g and the lower guide part 713a-713g, or the gap between the opposed inner surfaces for passing a sheet in the bin is set to a prescribed space of the degree to which one sheet can pass without any force. The sheet outlet and inlet ports 714a-714g are properly switched by an advance/discharge part switching means 72 to carry the sheet toward an upstream carrying passage 24 or a downstream carrying passage 25.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a copying machine, a laser printer, a facsimile, and the like, and more particularly to a switchback device of an image forming apparatus using an electrophotographic technique.

[0002]

2. Description of the Related Art A conventional switchback device of an image forming apparatus capable of performing double-sided printing will be described with reference to FIG. The conventional switchback device 7 includes a reversing tray 73; a switchback roller 741, switchback roller driving means (not shown), a separation arm 742, an arm shaft 743, a separation solenoid 744, and a separation arm. Force member 7
A sheet moving means 74 comprising a spring 45 and a separation spring 746;
A hitting guide 751, a hitting guide shaft 752, a hitting solenoid 753, a hitting guide urging member 754, and a hitting spring 755.
And the like.

Next, the operation of a conventional switchback device will be described. First, in a state of waiting for a sheet, the rotation of the switchback roller 741 is stopped, and the switchback roller 741 is retracted from the reversing tray 73.
1 is also in a retracted state (shown by a broken line). Here, when the sheet is conveyed from the upstream side conveyance path 24, the conveyed sheet is made to enter the switchback device 7 by driving the pair of entry rollers (241, 242). When the leading edge of the paper comes under the switchback roller 741,
The switchback roller 741 is connected to the reversing tray 73.
The sheet is brought rightward in the figure by contacting the upper sheet and transmitting the rotation drive (CCW direction in the angle in the figure) of the switchback roller. When the entire sheet enters the switchback device 7, the hitting guide 75 hits the rear end of the sheet in the direction of the reversing tray 73 to move the sheet along the reversing tray 73. Subsequently, the rotation direction of the switchback roller 741 is in the opposite direction (CW in the angle shown in the figure).
Direction), and the sheet is delivered to the pair of discharge rollers (251, 252) of the downstream transport path 25 and discharged from the switchback device 7.

[0004]

However, according to such a conventional method, the rear end of the sheet from the upstream transport path 24 curls due to the image forming apparatus having the fixing device. If it is, the downstream transport path 25
The paper jam, broken paper ears, and other problems occurred.

The above problem can be solved by a method in which both sides of the sheet are guided one by one and transferred from the upstream side transport path 24 to the downstream side transport path 25. However, since the distance between the sheets is required, the printing speed is reduced. Problem.

[0006]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention provides a switchback device for an image forming apparatus capable of performing double-sided printing. A paper moving means, wherein the entrance / ejection unit has at least two or more N bins which also serve as an entrance into which the paper enters and an exit through which the paper is discharged, and one of the bins is one of the bins. A first state in which the n-th bin is directed to the upstream transport path, an n-th state in which the n-th bin is directed to the upstream transport path, and the (n-1) th bin is directed to the downstream transport path; The (N + 1) th state in which the second bin is directed to the downstream side transport path can be taken, and the opposing guide portions of the respective bins have a positional relationship of guiding both sides of the sheet passing therethrough, and the bin switching means includes: The entrance / exit section is the first The state can be switched from the state to the (N + 1) th state, and the sheet moving means conveys the sheet entering the switchback device to the inside of the reversing tray, and then reverses the sheet conveying direction to change the sheet rear end side. And a switchback device for an image forming apparatus capable of performing double-sided printing, wherein

[0007]

The entrance / ejection unit is positioned so as to guide both sides of the sheet passing therethrough. Even if the sheet is curled, it is guided by both the upper guide unit and the lower guide unit to straighten the deflection in the surface direction. Be corrected. Further, since a plurality of bins are provided, it is possible to continuously switch back the sheets without having to keep the distance between the sheets.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The operation of an image forming apparatus capable of double-sided printing to which one embodiment of the present invention is applied to print images on both sides will be described with reference to FIG. In the drawing, sheets fed one by one from a sheet feeding cassette 1 by a sheet feeding roller 11 are fed through a conveyance path 21, where the leading ends thereof are adjusted by a registration unit 3, and stand by, and are sent to an image forming unit 4 at a predetermined timing. The toner image formed by the image forming unit 4 is conveyed, and is transferred to the first surface of the sheet by the transfer unit 45. The sheet on which the unfixed toner image has been transferred to the first surface is conveyed to the nip portion between the heat roller 51 and the pressure roller 52 of the fixing device 5 by the conveyance path 23, and the two rollers pinch and heat the sheet. The unfixed toner image on the first surface is fixed. Next, the sheet having the image on the first surface is transported by the branching means 6 to the transport path 24.
Is transferred to the switchback device 7 via the switchback device 7, the transfer direction is changed in the switchback device 7, and the transfer is performed to the transfer path 25. Subsequently, the sheet having an image on the first surface is again adjusted in the leading end by the registration unit 3 via the conveyance path 26 and waits, and is conveyed to the image forming unit 4 at a predetermined timing, and is formed by the image forming unit 4. The transferred toner image is transferred to the second surface of the sheet by the transfer unit 45. The sheet on which the unfixed toner image has been transferred to the second surface is transferred to the transport path 2.
By 3, the toner is conveyed to a nip portion between the heat roller 51 and the pressure roller 52 of the fixing device 5, and the unfixed toner image on the second surface is fixed by being nipped and heated by the two rollers. The sheet on which images have been printed on both sides up to this point is discharged to the discharge tray 9 via the discharge unit 8 by the branching unit 6.

Since the image forming apparatus capable of performing both-side printing according to the embodiment of the present invention employs a circulation system, printing on the first side of the seven sheets of paper that have been fed, and then printing on the second side of the seven sheets of paper. This is a method of printing and discharging.

Further, the configuration of a switchback device in an image forming apparatus capable of performing double-sided printing employing the embodiment of the present invention will be described in detail with reference to FIGS.

The switchback device 7 has an upper guide portion (712a to 712g) and a lower guide portion (713a to 713g).
713g) and the paper entrances (714a to 714g).
g), an entry / exit unit 7 including a shaft 715 and a switching gear 716.
1, entry / exit switching means 72;
Sheet movement including a switchback roller 741, switchback roller driving means (not shown), a separation arm 742, an arm shaft 743, a separation solenoid 744, a separation arm urging member 745, and a separation spring 746. Means 7
4 and the like.

More specifically, the gap between the upper guides (712a to 712g) 711 and the lower guides (713a to 713g) of the entrance / ejection unit 71, that is, the gap between the inner surfaces of the bins where the sheets pass, is Even if a sheet of paper is able to pass between the guides without difficulty, and the passing paper is curled, the sheet is bent straight in the surface direction until it is transferred to the next downstream transport path 25. The distance is such that the distance can be corrected, and about 1 mm to 5 mm is appropriate. The upper guide portion (712a
To 712 g) and the lower guide portion (713a to 713g).
It is preferable to provide ribs on the opposite surface at appropriate intervals in the transport direction in order to improve the slip of the paper. The entry / ejection unit 71 is driven by the entry / exit switching means 72 about the shaft 715 to move the paper entrance 714a to the upstream transport path in the first state and the paper entrance 714b to the paper entrance 714b. A second state in which the paper entrance / exit 714a is directed to the downstream transportation path, and the paper entrance / exit 714c is directed to the upstream transportation path, and the paper entrance / exit 714d is directed to the downstream transportation path. To the third state, and similarly to the fourth to
A seventh state and finally an eighth state in which the sheet entrance 714g is directed to the downstream-side transport path.

The ingress / ejection switching means 72 uses a stepping motor whose rotation angle can be controlled, and transmits the rotation of a gear 721 of the shaft of the stepping motor to the switching gear 716 of the ingress / ejection unit 71, thereby obtaining The first to eighth states can be switched.

The reversing tray 73 includes a sheet conveying surface 731 and a sheet contact portion 732. If the paper transport surface 731 is provided with ribs at appropriate intervals, the transport of the paper can be performed smoothly. The sheet contact portion is a sheet moving unit 74.
Is not absolutely necessary in the switchback device having the
Is the paper transport surface 73 according to the size of the paper being transported.
1 is movable in the paper transport direction, and the paper contact portion 7
The position of the sheet contact portion 732 is determined so that the length from the surface No. 32 to the entrance 714 of the sheet is substantially the same as the length of the sheet in the transport direction, and based on a sheet size detection signal or operator setting information, etc. The sheet contact portion 732 is positioned by being driven by a rack and pinion 733 and a stepping motor 734.

The switchback roller 741 may be used as a normal paper feed roller or transport roller made of EPDM, CR rubber, urethane rubber, natural rubber, or the like.
The sheet is controlled so that it can rotate in either of the CCW directions, and conveys the sheet delivered from the upstream conveying path 24.

A mechanism relating to the separation and contact of the sheet moving means 74 with respect to the sheet will be described. The switchback roller 7
Reference numeral 41 denotes an arm shaft 7 while being instructed by the detachment arm 742.
It is rotatable around 43, and can take a contact state and a retracted state with respect to the sheet. The switchback roller 741 is normally in a retracted state. At this time, since the contact / separation solenoid 744 is OFF, the contact / separation spring 741 is turned off.
6 urges the separation arm 742 via the separation arm urging member 745 in a direction to retract the switchback roller 741. When the sheet on the reversing tray 73 is transported, the switchback roller 741 is in contact with the switchback roller 741.
Is turned on, the separation / contact arm urging member 745 is turned on.
Of the contact arm 742 is released, and as a result, the switchback roller 741 comes into contact with the paper side by a load due to its own weight.

Next, the operation of the present switchback device is shown in FIG.
It will be described based on. First, in a state of waiting for a sheet, the rotation of the switchback roller 741 is stopped, and the sheet is retracted from the reversing tray 73. The ingress / ejection section 71 connects the sheet entrance 714a to the upstream transport path 2
This is a first state directed in four directions. FIG. 5A shows a state of waiting for the entry of the first sheet as described above.

When the sheet is conveyed from the upstream conveyance path 24, the conveyed sheet is made to enter the switchback device 7 by driving the pair of entry rollers (241, 242). FIG. 5B shows a state in which the first sheet enters the switchback device 7 as described above.

Next, when the leading edge of the first sheet comes under the switchback roller 741, the movement of the separation / contact arm 742 causes the switchback roller 7 to move.
Reference numeral 41 contacts the sheet on the reversing tray 72 and conveys the rotational drive (CCW direction in the angle in the figure) of the switchback roller 741 to move the sheet to the right in the figure. At this time, the switchback roller 741 When the leading end of the conveyed sheet reaches the sheet contact portion via the sheet conveying surface of the conveying tray 73, the sheet stops. When the entire first sheet enters the switchback device 7, the entry / ejection unit 71 causes the entry / exit switching unit 72 to direct the sheet entrance 714 b toward the upstream transport path 24, and The second state is established in which the paper entrance 714a is directed toward the downstream transport path 25.
Subsequently, the switchback roller 74 that has stopped the first sheet at the same time as the second sheet enters the sheet entrance 714b from the upstream side transport path 24.
1 is rotated in the reverse direction (CW direction in the angle shown) to convey the sheet to the left in the figure, and to deliver the sheet to the discharge roller pair (251, 252) of the downstream side conveyance path 25, and to perform the switchback. It is discharged from the device 7. When the sheet is delivered to the pair of discharge rollers (251, 252) of the downstream transport path 25, the switchback roller 741 is in a retracted state by the separation / contact means, stops rotating, and the next sheet comes. Wait for. FIG. 5C shows a state in which the second sheet enters while discharging the first sheet as described above.

Similarly, FIG. 5D shows a state in which the third sheet enters while discharging the second sheet.
FIG. 5E shows a state in which the seventh sheet enters while discharging the sixth sheet.

FIG. 5F shows a state in which the seventh sheet is being discharged, and the entrance / discharge unit 71 is in an eighth state. When the ejection of the seventh sheet is completed, the entrance / ejection unit 71 is switched to the entrance / ejection unit switching unit 72.
As a result, the first state is established, and the apparatus waits for the next first sheet to enter again. FIG. 5 (g) shows a state in which the seventh sheet is discharged, and the first sheet is waiting to enter again.

In the embodiment of the present invention, the entrance / ejection unit 7
1 has seven bins 711. This is because the image forming apparatus capable of double-sided printing according to the present embodiment is of a circulation type, and therefore, seven sheets of paper are circulated in the image forming apparatus. I did this. To explain in more detail,
This is a method of printing on the first side of a sheet of paper and subsequently printing and discharging on the second side of the seven sheets of paper. Since these sheets are printed with an image on the second side and discharged, there is a time margin before a new sheet arrives at the switchback device 7, and the entrance / ejection unit is in the eighth state. Although it takes time from the first state to the first state, the printing speed is not affected. That is,
Although it depends on the paper size, a switch using the technique of the present invention will not cause a reduction in printing speed if it has an entrance / ejection unit having the same number of bins 711 as the number of papers circulating in the image forming apparatus. Back device.

[0023]

According to the present invention, when performing duplex printing, it is possible to reduce the problem of paper jams and broken edges of the paper caused around the switchback device due to the curl of the paper. It can be reduced without dropping.

[Brief description of the drawings]

FIG. 1 is a schematic diagram of a switchback device of the present invention.

FIG. 2 is an image forming apparatus capable of performing double-sided printing employing the switchback device of the present invention.

FIG. 3 is an image forming apparatus capable of performing double-sided printing employing the switchback device of the present invention.

FIG. 4 is a perspective view of the switchback device of the present invention.

FIG. 5 is a schematic view of the operation of the switchback device of the present invention.

FIG. 6 is a schematic view of a conventional switchback device.

[Explanation of symbols]

 41; photosensitive drum 42; main charging device 43; laser optical unit 44; developing device 46;

Claims (1)

[Claims] 1. A switchback device for an image forming apparatus capable of performing double-sided printing, comprising: an entrance / ejection unit; an entrance / ejection switching unit; a reversing tray; and a paper moving unit; A first state in which at least two or more N bins that also serve as an entrance for paper entry and an exit for paper ejection are provided, and the first bin of the bins is directed to the upstream transport path; The n-th state in which the n-th bin is directed to the upstream transport path and the (n-1) -th bin is directed to the downstream transport path, and the (N + 1) -th state in which the N-th bin is directed to the downstream transport path. The guide portions of the respective bins are in a positional relationship of guiding both sides of the sheet passing therethrough, and the bin switching means is configured to
The discharge unit can switch from the first state to the (N + 1) th state, and the sheet moving unit conveys the sheet entering the switchback device to the inside of the reversing tray, and then reverses the sheet conveying direction. A switchback device for an image forming apparatus capable of performing double-sided printing, wherein the sheet is discharged from the rear end side of a sheet.