JP2004155553A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus capable of providing excellent printing efficiency when printing on one face of a paper sheet and reducing its size and weight without disturbing alignment of sheets on a paper discharge tray when printing on both faces of the paper sheet. <P>SOLUTION: This image forming apparatus is provided with a first conveyance passage 18 for supplying the sheet S fed from a first paper feeding cassette 12 to an image forming part 3, a second conveyance passage 23 for guiding the sheet S on which image is formed by the image forming part 3 into the paper discharge tray 6, a third conveyance passage 24 branched from the second conveyance passage 23 and connected with the first conveyance passage 18, and a switch-back conveyance passage 22 branched from the first conveyance passage 18 to return the sheet S advancing from a tip into the first conveyance passage 18 from a rear end. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an image forming apparatus such as a copier, a facsimile machine, a printer, and a multifunction peripheral thereof, and more particularly, to an image forming apparatus capable of performing double-sided printing on a sheet (copy paper, plastic film, or the like).
[0002]
[Prior art]
Various types of image forming apparatuses of this type have conventionally been devised and are generally known. For example, the image forming apparatus 100 shown in FIG. 2 is configured to convey the sheet sent from the paper feed cassettes 101, 102, and 103 to the image forming unit 105 via the switchback conveyance path 104, and the switchback conveyance path By inverting the sheet at 104, the intermediate tray for double-sided printing for stocking the sheet printed on one side is omitted, and the overall structure is reduced (for example, see Patent Document 1). .
[0003]
Further, the image forming apparatus 106 as shown in FIG. 3 is capable of rotating a discharge roller 108 disposed for discharging a sheet after image formation onto a discharge tray 107 in both forward and reverse directions. After most of the sheet having an image formed on one side is discharged onto the discharge tray 107 by the discharge roller 108, the conveyance path switching unit 110 is switched, and the discharge roller 108 is rotated in the reverse direction, and the sheet is discharged. The sheet is returned to the sheet conveying path 111 (switched back), and an image is formed on the back side (unprinted side) of the single-sided printed sheet conveyed through the sheet conveying path 111, so that the single-sided printed sheet is An intermediate tray for double-sided printing for stocking is omitted, and the overall structure is reduced in size (for example, see Patent Document 2).
[0004]
[Patent Document 1]
JP-A-9-110313 (paragraphs 0014, 0017 to 0022 and FIG. 1)
[Patent Document 2]
JP-A-4-28675 (paragraph number (f) and FIG. 1)
[0005]
[Problems to be solved by the invention]
However, in the first conventional example disclosed in Patent Literature 1, sheets sent from the sheet feeding cassettes 101 and 102 other than the sheet feeding cassette 103 dedicated to thick paper that performs only one-sided printing always pass through the switchback conveyance path 104. Since the paper is fed into the image forming unit 105 later, the distance from the paper feed cassettes 101 and 102 to the image forming unit 105 becomes longer, and there is a problem that printing takes time.
[0006]
Further, in the second conventional example disclosed in Patent Document 2, when performing double-sided printing, a sheet on which single-sided printing has been completed is switched back by a discharge roller 108 rotating in both forward and reverse directions. After almost the entire area excluding one end sandwiched by the paper discharge rollers 108 is discharged onto the paper discharge tray 107, the paper is returned to the sheet conveying path 111 again. Therefore, in the second conventional example, when a sheet is switched back by the discharge roller 108 during double-sided printing, there is a possibility that the alignment of the image-formed sheets already stacked on the discharge tray 107 may be disturbed. There was a need to solve such a problem.
[0007]
Therefore, the present invention can solve the problems of the prior art by devising a conveyance path for switching back the sheet, and has been downsized without having to install an intermediate tray for double-sided printing. It is an object to provide an image forming apparatus.
[0008]
[Means for Solving the Problems]
According to the first aspect of the present invention, there is provided a first conveyance path for supplying a sheet sent from a paper supply cassette to an image forming unit, and a second conveyance path for guiding a sheet on which an image has been formed by the image forming unit to a discharge tray. A third conveying path that branches off from the second conveying path and connects to the first conveying path; and a sheet that branches off from the first conveying path and enters the sheet from the front end to the first conveying path from the rear end. And a return switchback conveyance path. Here, the discharge tray broadly includes components such as a tray of a sorter, a sheet stacking unit of a post-processing apparatus that performs post-processing such as staples, a so-called internal discharge unit, etc., on which printed sheets are stacked. .
[0009]
According to a second aspect of the present invention, in the first aspect of the invention, a sheet cassette different from the sheet cassette is connected to the switchback conveyance path, and sheets fed from the sheet cassette are switched back. The sheet is conveyed to the first conveyance path via a conveyance path.
[0010]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
[0011]
(Schematic configuration of image forming apparatus)
FIG. 1 is a schematic configuration diagram of an image forming apparatus 1 according to an embodiment of the present invention. The image forming apparatus 1 shown in FIG. 1 includes a sheet supply / conveyance unit 2 for supplying / conveying a sheet (copy paper, plastic film, etc.) S, and a toner image on the sheet S conveyed by the sheet supply / conveyance unit 2. An image forming unit 3 to be formed, a fixing unit 4 for fixing the toner image formed on the sheet S by the image forming unit 3 to the sheet S, and a sheet S passing through the fixing unit 4 is discharged to the outside of the main body 5. A paper tray 6 and a discharge section 7 for discharging the paper to a post-processing device (not shown). The sheet supply / conveyance unit 2 and the image forming unit 3 will be described in detail below. In the present embodiment, the fixing unit 4 includes a fixing roller 8 and a pressure roller 10 that presses the sheet S on which a toner image is formed on the fixing roller 8. Further, the discharge unit 7 includes a paper discharge roller 11 formed by combining a pair of rollers.
[0012]
(Sheet supply / conveyance unit)
As shown in FIG. 1, in a main body 5 of the image forming apparatus 1, a first paper cassette 12 and a second paper cassette 13 are arranged in parallel in an upper stage, and the first paper cassette 12 and the second paper Below the paper cassette 13, a third paper supply cassette 14 and a fourth paper supply cassette 15 are arranged in cascade.
[0013]
The first sheet cassette 12 and the second sheet cassette 13 among the plurality of sheet cassettes 12 to 15 are large-capacity sheet cassettes, and are provided in the third and fourth sheet cassettes 14 and 15 at the lower stage. A relatively large number of sheets S can be stored. On the other hand, the lower third and fourth paper cassettes 14 and 15 are formed to be large enough to accommodate a large-sized sheet S that cannot be accommodated by the upper first and second paper cassettes 12 and 13.
[0014]
Then, the uppermost sheet S of the sheet bundle stacked in the first sheet cassette 12 and the second sheet cassette 13 is fed into the nip of the feed roller 17 by the pickup roller 16, and then sent by the feed roller 17. The paper is sent to the first transport path 18. The uppermost sheet S of the sheet bundle stacked on the third paper feed cassette 14 and the fourth paper feed cassette 15 is fed into the nip of the feed roller 21 by the pickup roller 20, and then sent by the feed roller 21. It is sent out to the switchback conveyance path 22 and further sent out to the first conveyance path 18 via the switchback conveyance path 22.
[0015]
The sheet S transport path includes a first transport path 18 that supplies the sheet S sent from the first sheet cassette 12 and the second sheet cassette 13 to the image forming unit 3 and an image formed by the image forming unit 3. A second conveyance path 23 that guides the sheet S that has passed through the fixing unit 4 to the discharge tray 7 after passing through the fixing unit 4, and a third conveyance path 24 that branches off from the second conveyance path 23 and connects to the first conveyance path 18. A switchback conveyance path 22 that branches off from the first conveyance path 18 and a fourth conveyance path that branches off from the third conveyance path 24 and returns the sheet S to a position near the upstream side of the discharge roller 11 of the second conveyance path 23. 25.
[0016]
The switchback conveyance path 22 includes a sheet introduction unit 22a that allows the sheet S to enter from the first conveyance path 18 and a sheet discharge unit 22b that returns the sheet S entered from the front end to the first conveyance path 18 from the rear end. And A first branching claw 26 is attached to a branch portion between the sheet introduction section 22a and the first transporting path 18 of the switchback transporting path 22. The first branching claw 26 is used to switch the transport path of the sheet S, and the sheet S sent from the first paper cassette 12 or the second paper cassette 13 is imaged on the first transport path 18. The sheet S, on which an image is formed on one side by the image forming unit 3, is fed directly to the forming unit 3, or is guided to the switchback conveyance path 22.
[0017]
A second branching claw 27 is attached to the junction of the sheet introduction section 22a and the sheet discharge section 22b of the switchback conveyance path 22. When the sheet S is introduced from the first conveyance path 18 to the switchback conveyance path 22, the second branch claw 27 closes the sheet discharge unit 22b, and the sheet S is moved between the sheet introduction unit 22a and the sheet discharge unit 22b. The movement of the sheet S is guided so as to smoothly pass through the junction. On the other hand, when returning the sheet S from the switchback conveyance path 22 to the first conveyance path 18, the second branch claw 27 closes the sheet introduction part 22a, and the sheet S is moved between the sheet introduction part 22a and the sheet discharge part 22b. The movement of the sheet S is guided so as to smoothly pass through the junction.
[0018]
Further, a sheet supply path 28 of the third sheet cassette 14 and a sheet supply path 30 of the fourth sheet cassette 15 are connected to the switchback path 22. A third branching pawl 31 is attached to the junction of the sheet feed path 28 and the switchback transport path 22 of the third paper feed cassette 14. The third branch claw 31 closes the sheet supply path 28 when the sheet S is introduced from the first transport path 18 to the switchback transport path 22, and the sheet S is transported smoothly along the switchback transport path 22. Move to position. On the other hand, the third branching pawl 31 opens the sheet supply path 28 when the sheet S is sent out from the third paper feed cassette 14.
[0019]
Further, a fourth branching claw 32 is attached to the junction of the sheet supply path 30 and the switchback conveyance path 22 of the fourth paper feed cassette 15. The fourth branch claw 32 closes the sheet supply path 30 when the sheet S is introduced from the first conveyance path 18 to the switchback conveyance path 22, and the sheet S is smoothly conveyed along the switchback conveyance path 22. Move to position. On the other hand, the fourth branch claw 32 opens the sheet supply path 30 when the sheet S is sent out from the fourth sheet cassette 15.
[0020]
The first transport path 18 includes a transport roller 33 that transports the sheet S sent from the second paper cassette 13 to the first paper cassette 12 side, and a sheet S that is delivered from the first paper cassette 12. A transport roller 34 for transporting downstream; a transport roller 35 disposed downstream of the junction of the first transport path 18 and the switchback transport path 22 (on the image forming unit 3 side); And a registration roller 36 that prevents the sheet S conveyed from the conveyance roller 37 from skewing and then feeds the sheet S to the image forming section 3 along the sheet conveyance direction. ing. In the switchback conveyance path 22, a conveyance roller 38 for conveying the sheet S sent from the fourth sheet cassette 15 to the third sheet cassette 14, and a sheet S sent from the third sheet cassette 14 are provided. A transport roller 40 that feeds to the first transport path 18 is disposed. In the third transport path 24, a transport roller 41 is disposed downstream of a branch from the fourth transport path 25. In the fourth transport path 25, a transport roller 42 that feeds the sheet S transported from the third transport path 24 to the nip of the paper discharge roller 11 in the second transport path 23 is disposed.
[0021]
A first sheet detection sensor 43 is disposed in the first conveyance path 18 between the conveyance roller 34 and the first branch claw 26. Further, a second sheet detection sensor 44 is disposed in the switchback conveyance path 22 between the second branch claw 27 and the conveyance roller 40. Further, a third sheet detection sensor 46 is disposed between the conveyance roller 33 and the junction of the sheet supply path 45 of the second paper feed cassette 13 and the first conveyance path 18. The detection signals of the first to third sheet detection sensors 43 to 46 are input to a control unit (not shown), and the control unit controls the driving of the transport rollers 33 and the operation of the branch claws (26). Is done.
[0022]
Here, each of the transport rollers 38 and 40 of the switchback transport path 22 can rotate in both forward and reverse directions. The transport roller 41 of the third transport path 24 and the transport rollers 33 and 34 of the first transport path 18 can rotate in both forward and reverse directions. That is, by rotating the transport rollers 38 and 40 of the switchback transport path 22 forward, the sheet S is introduced from the first transport path 18 to the switchback transport path 22 while the transport rollers 38 and 40 are rotated reversely. , The sheet S can be sent from the switchback conveyance path 22 to the first conveyance path 18. Further, by rotating the transport rollers 41, 33, and 34 of the third transport path 24 and the first transport path 18 forward, the sheet S is sent downstream of the transport rollers 41 of the third transport path 24 in the sheet transport direction. Thereafter, the sheet S can be sent to the nip of the paper discharge roller 11 via the fourth conveyance path 25 by rotating the conveyance rollers 41, 33, and 34 in the reverse direction.
[0023]
(Image forming unit)
The image forming unit 3 includes a drum-shaped photoconductor 47, and a charging device 48, an exposure device 50, a developing device 51, a transfer device 52, a cleaning device 53, and the like arranged around the photoconductor 47. In the image forming section 3 having such a configuration, the photosensitive member 47 is rotationally driven in a direction indicated by an arrow A at a predetermined process speed (peripheral speed) by a driving unit (not shown). Charged uniformly. An electrostatic latent image is formed on the surface of the charged photoconductor 47 by the exposure device 50. Here, based on image information from a scanner unit (not shown) or another image forming apparatus, a computer, a scanner, or the like connected by a communication unit such as a network, the exposure device 50 To remove an electric charge in a laser beam irradiated portion on the surface of the photoreceptor 47 to form an electrostatic latent image according to image information. The electrostatic latent image formed on the surface of the photoreceptor 47 is developed by the developing device 51 as a toner image by electrostatically adhering charged toner.
[0024]
(Description of operating state)
Hereinafter, the case of single-sided printing and the case of double-sided printing will be described separately. The first to fourth branch claws 26, 27, 31, and 32 are turned off when the solid line positions in FIG. 1 are turned off, and turned on when switching the sheet S conveyance path in FIG. Further, in the transport path of the sheet S formed in a loop by the first transport path 18, the second transport path 23, and the third transport path 24, three sheets of A4 landscape size can be accommodated at the same time. It is assumed that The following description is an example of a case where the sheet S is sent out from the first sheet cassette 12.
[0025]
In the case of single-sided printing, the sheet S sent from the first paper feed cassette 12 is sent to the image forming unit 3 through the first transport path 18, and the toner image is transferred by the image forming unit 3, and the toner image is transferred. Is fixed by being heated and pressed by the fixing unit 4, passes through the second conveyance path 23, and is discharged to the outside of the main body 5 (for example, the discharge tray 6) by the discharge roller 11 with the image forming surface facing upward ( Ejected up face). In the case of this one-sided printing, the sheet S sent from the third paper feed cassette 14 or the fourth paper feed cassette 15 is fed into the first feed path 18 from the sheet discharge section 22 b of the switchback feed path 22. The processing is performed in the same manner as for the sheet S sent from the first sheet cassette 12 or the second sheet cassette 13.
[0026]
Here, when the sheet S is discharged with the image forming surface down (down face), the sheet S discharged from the fixing unit 4 is fed into the third transport path 24 and the first transport path 18. Thereafter, the sheet S is sent out from the rear end side to the fourth transport path 25, and the sheet S, which has been turned upside down, is discharged to the outside of the main body 5 (for example, on the discharge tray 6) by the discharge rollers 11.
[0027]
In the case of double-sided printing, first, three sheets S are successively sent out from the first paper feed cassette 12 to the first transport path 18 at a predetermined timing. The sheet S sent from the first paper cassette 12 is sent to the image forming unit 3 through the first conveyance path 18, and after the toner image is formed on one side by the image forming unit 3, the toner image is Is fixed in the fixing unit 4. Then, the sheet S discharged from the fixing unit 4 to the second transport path 23 is guided to the third transport path 24 and further guided to the first transport path 18. When the third sheet detection sensor 46 detects the leading end of the sheet S guided to the first conveyance path 18, the first branching claw 26 is switched from the ON state to the OFF state (the position indicated by the solid line in FIG. 1), and is switched to the single-sided state. One printed sheet S is introduced into the switchback conveyance path 22. Thereafter, when the rear end of the sheet S is detected by the second sheet detection sensor 44, each of the conveying rollers 38 and 40 rotates in the reverse direction (to convey the sheet S upward in FIG. 1), and The two-branch claw 27 is switched to the ON state, and the sheet S is sent from the rear end side to the first transport path 18 via the sheet discharge section 22 b of the switchback transport path 22. As a result, the front and back of the sheet S are reversed, and the back side on which the image is not formed faces the photoconductor 47.
[0028]
When the first sheet S is sent out from the switchback conveyance path 22, the rear end of the first sheet S (the rear end in the conveyance direction on the switchback conveyance path 22) is detected by the second sheet detection sensor 44. Then, the transport rollers 38, 40 rotate forward (rotate in a direction to introduce the sheet S into the switchback transport path 22), and the second branch claw 27 is turned off. Then, the second sheet S on which single-sided printing has been performed is introduced into the switchback conveyance path 22, and the second sheet S is first conveyed in a state where the second sheet S is turned upside down similarly to the first sheet S described above. Returned to Road 18.
[0029]
When the second sheet S is sent out from the switchback conveyance path 22, the rear end of the second sheet S (the rear end in the conveyance direction on the switchback conveyance path 22) is detected by the second sheet detection sensor 44. Then, the transport rollers 38, 40 rotate forward (rotate in a direction to introduce the sheet S into the switchback transport path 22), and the second branch claw 27 is turned off. Then, the third sheet S on which single-sided printing has been performed is introduced into the switchback conveyance path 22, and the third sheet S is turned upside down in the same manner as the first and second sheets S described above. It is returned to one transport path 18.
[0030]
When the third sheet S is sent out from the switchback conveyance path 22, the rear end of the third sheet S (the rear end in the conveyance direction on the switchback conveyance path 22) is detected by the second sheet detection sensor 44. Then, the first branch claw 26 is switched to the OFF state, and the fourth to sixth sheets S are sequentially sent out from the first sheet cassette 12 to the first conveyance path 18 at a predetermined timing, and Print processing is performed in the same manner as in the case of the first to third sheets S.
[0031]
The sheet S sent out from the switchback conveyance path 22 is sent to the image forming unit 3 after the skew is corrected by the registration roller 36, and a toner image is formed on the back side where the image is not formed. The toner image is fixed by the fixing unit 4. The sheet S discharged from the fixing unit 4 passes through the second transport path 23 and is discharged to the outside of the main body 5 (for example, the discharge tray 6) by the discharge roller 11 with the back surface facing upward.
[0032]
(Effects of the present embodiment)
In the image forming apparatus 1 of the present embodiment configured as described above, since it is not necessary to install an intermediate tray for double-sided printing, it is of course possible to reduce the size and weight of the entire structure. In the case of single-sided printing, the sheets S sent from the first sheet cassette 12 and the second sheet cassette 13 can be conveyed to the image forming unit 3 without passing through the switchback conveyance path 22, and all the sheets are switched back. The printing time can be reduced as compared with the first conventional example configured to pass through.
[0033]
Further, in the image forming apparatus 1 of the present embodiment, since the switchback conveyance path 22 also serves as a conveyance path of the sheet S sent from the third paper supply cassette 14 and the fourth paper supply cassette 15, There is no need to separately provide a transport path for reversing the front and back sides, so that the configuration inside the main body 5 can be simplified, and at the same time, there is a problem (such as alignment of sheets stacked on the paper discharge tray) as in the second conventional example. Malfunction).
[0034]
Further, in the image forming apparatus 1 of the present embodiment, the switchback conveyance path 22 is provided in the main body 5 as described above, and when the sheet S is turned upside down, as in the second conventional example, Therefore, there is no possibility that the user accidentally pulls out the sheet S (sheet on which both-side printing is not completed) S on which only one side is printed from the main body 5 because the sheet S is not discharged to the outside.
[0035]
【The invention's effect】
As described above, according to the present invention, when printing is performed on only one side of a sheet, the sheet can be conveyed to the image forming unit without passing through the switchback conveyance path, so that printing efficiency can be improved, and both sides of the sheet can be improved. When printing on paper, the sheet is temporarily not discharged onto the paper output tray and then switched back (reversed), which may disturb the alignment of the printed sheets stacked on the paper output tray. Absent.
[0036]
Further, according to the present invention, since the switchback conveyance path also functions as a conveyance path for the sheet sent from the paper feed cassette, the intermediate tray for double-sided printing can of course be omitted. Space can be effectively used, and the overall structure can be reduced in size and weight.
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram of an image forming apparatus according to an embodiment of the present invention.
FIG. 2 is a schematic configuration diagram of an image forming apparatus according to a first conventional example.
FIG. 3 is a schematic configuration diagram of an image forming apparatus according to a second conventional example.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Image forming apparatus, 3 ... Image forming part, 6 ... Discharge tray, 12 ... 1st paper feed cassette, 13 ... 2nd paper feed cassette, 14 ... 3rd paper feed cassette, 15 ... ... Fourth paper cassette, 18... First transport path, 22... Switchback transport path, 23... Second transport path, 24.

Claims (2)

A first conveyance path for supplying the sheet sent from the paper supply cassette to the image forming unit;
A second conveyance path for guiding a sheet on which an image is formed by the image forming unit to a paper discharge tray;
A third transport path branched from the second transport path and connected to the first transport path;
A switchback conveyance path that branches from the first conveyance path and returns the sheet that has entered from the front end to the first conveyance path from the rear end;
An image forming apparatus comprising: A paper cassette different from the paper cassette is connected to the switchback transport path,
2. The image forming apparatus according to claim 1, wherein the sheet fed from the sheet cassette is transported to the first transport path via the switchback transport path.

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