JP3799880B2 - Conveying device and image forming apparatus provided with the conveying device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a conveyance device for detecting a sheet conveyed along a conveyance path selected from among a plurality of conveyance paths, and an image forming apparatus including the conveyance device.
[0002]
[Prior art]
An image forming apparatus (printer, copier, facsimile machine, etc.) that forms an image on a sheet such as a copy sheet, a transfer sheet, a sheet and a transparent sheet for OHP, and discharges the formed sheet to a predetermined discharge tray ) Is provided with a plurality of conveyance paths for conveying the sheet. In addition, sensors are provided in these conveyance paths to detect the presence or absence of a sheet in each conveyance path. Conventionally, a sensor is arranged for each conveyance path, and the presence or absence of a sheet on one corresponding conveyance path is detected by one sensor. This is the same when a plurality of transport paths are provided in parallel to each other. For example, in the image forming apparatus described in Japanese Patent Laid-Open No. 11-35210, two transport paths are parallel to each other in order to discharge a sheet on which an image has been formed to a receiving portion (corresponding to a discharge tray). A dedicated sensor is provided along each conveyance path.
[0003]
[Problems to be solved by the invention]
In the conventional image forming apparatus, a dedicated sensor for detecting whether or not a sheet exists in the conveyance path is provided for each conveyance path, and the number of sensors disposed as the number of conveyance paths increases. This is one of the main factors that increase the device cost.
[0004]
The present invention has been made in view of the above-described problems, and provides a conveyance device capable of reducing the number of sensors arranged on the conveyance path and reducing the cost of the apparatus, and an image forming apparatus including the conveyance device. For the purpose.
[0005]
[Means for Solving the Problems]
In order to achieve the above object, the transport device according to the present invention is arranged so that the first transport path for guiding the transported sheet toward the first position and the first transport path at least partially overlap each other. A second conveyance path that guides the conveyed sheet toward the second position, and a switching unit that selectively switches the conveyance path of the conveyed sheet to the first or second conveyance path;
The first and second transport paths are arranged at positions where they overlap each other, and are capable of detecting the presence or absence of a sheet in each transport path and the path selection information indicating the sheet transport destination by the switching means and the output of the sensor. Determination means for determining the presence or absence of a sheet in the conveyance path selected as the conveyance destination by the switching means, and a sheet detection means for detecting a sheet conveyed along the first or second conveyance path; The sheet is disposed between the switching means and the first position, conveys the first sheet toward the first position along the first conveyance path, and the trailing edge of the sheet reaches a predetermined switchback stop position. Then, after the conveyance of the first sheet is stopped, the first sheet is disposed between the first conveying unit that reversely conveys the first sheet, the switching unit, and the second position. Same as reverse transfer And a second transport means for transporting the second sheet toward the second position along the second transport path, wherein the distance from the switchback stop position to the sensor is P, and the minimum length of the first sheet is If Lmin is set, Q is the sheet interval between the first sheet and the second sheet at the start of the reverse conveyance of the first sheet, and Lmax is the maximum length of the first and second sheets, the following inequality
(Lmax-Q) / 2 <P <Lmin
The sensor is arranged so as to satisfy the above.
[0008]
In the present invention, one sensor can detect the presence or absence of a sheet in the first and second transport paths, and the sensor output is given to the determination means. In addition to the sensor output, this determination means is provided with path selection information indicating the sheet conveyance destination by the switching means, and detects whether or not a sheet exists in the first or second conveyance path by the sensor output. In addition, the presence / absence of a sheet on the selected conveyance path is determined by determining on which conveyance path the sheet should be conveyed based on the path selection information.
[0009]
Here, in the conveying apparatus according to the present invention, the first conveying means is provided, and the first conveying path functions as the switchback path. Therefore, in order to reliably detect the sheet by the sensor, the following inequality is used.
P <Lmin
Where P is the distance from the switchback stop position to the sensor, and Lmin is the minimum length of the seat.
It is necessary to arrange the sensor so as to satisfy
[0010]
Furthermore, in the conveying apparatus according to the present invention, the (second) sheet is conveyed toward the second position along the second conveying path simultaneously with the switchback operation of the (first) sheet in the first conveying path. In order to detect the sheet reliably by the sensor, the following inequality
(Lmax-Q) / 2 <P
Where Q is the sheet interval between the first sheet and the second sheet at the start of the reverse conveyance of the first sheet, and Lmax is the maximum length of the first and second sheets.
It is necessary to arrange the sensor so as to satisfy
[0011]
The image forming apparatus according to the present invention further includes an image forming unit that forms an image on a sheet, a sheet feeding unit that feeds the sheet to the image forming unit, and A sheet discharge unit having the same configuration as that of any one of the conveying devices; and a sheet refeed unit that reverses a sheet from the sheet discharge unit and re-feeds the sheet to the sheet feed unit. The sheet on which the image is formed by the forming unit is conveyed to the sheet discharge unit along the second conveyance path, while the sheet from the sheet discharge unit is the sheet refeed unit along the first conveyance path. It is comprised so that it may convey.
[0012]
In the present invention, a paper discharge unit having the same configuration as that of the above-described transport device is provided, and it is detected by the sensor output whether or not a sheet exists in the first or second transport path, and any transport path of the sheet is detected. The presence or absence of a sheet on the selected conveyance path is determined by one sensor by determining based on the path selection information whether the sheet should be conveyed.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
A. Overall configuration of image forming apparatus
FIG. 1 is a view showing an image forming apparatus provided with an embodiment of a sheet detecting apparatus according to the present invention. This image forming apparatus forms a full color image by superposing four color toners of yellow (Y), cyan (C), magenta (M), and black (K), or uses only black (K) toner. This is an apparatus for forming a monochrome image. In this image forming apparatus, an image carrier unit 2, an exposure unit 3, a transfer unit 4 and a fixing unit 5 are provided inside a case 1, and these constitute an image forming means for forming an image on a sheet. Also provided in the case 1 is a paper feed / discharge unit 6 that feeds the sheet to the image forming means and discharges the image-formed sheet to a predetermined paper discharge position.
[0014]
When an image signal is given to the control unit 7 from an external device such as a host computer, the control unit 7 controls each part of the device to form an image corresponding to the image signal on the sheet S. That is, in this image forming apparatus, a toner image is formed on the photosensitive member 21 of the image carrier unit 2 and is further primarily transferred to the intermediate transfer belt 46 of the transfer unit 4. Then, after the primary transfer image (toner image) is secondarily transferred to the sheet S fed to the transfer position by the paper supply / discharge unit 6, the sheet S is conveyed to the fixing unit 5 and subjected to a fixing process. . The fixed sheet S is fed to a predetermined paper discharge position by the paper discharge unit 64 of the paper supply / discharge unit 6. Hereinafter, after describing the configuration of each part of the apparatus, the characteristic part of the present invention will be described in detail.
[0015]
B. Configuration of each part
B-1. Case 1
The upper surface portion of the case 1 functions as a standard paper discharge tray 11, and the sheets S on which images have been formed one by one through the paper discharge port 12 opened on the upper surface side portion of the case 1. It is configured so as to be discharged. The image forming apparatus can be optionally equipped with a multi-bin unit (not shown) on the upper side and a finisher (not shown) on the side. Openings 13 and 14 are provided on the upper surface and the side surface of the case 1 for conveyance to the bin unit and the finisher, respectively.
[0016]
B-2. Image carrier unit 2 and exposure unit 3
In this image forming apparatus, the image carrier unit 2 is detachable from the case 1. The image carrier unit 2 is provided with a photoconductor 21 that can rotate in the direction of the arrow in the figure, and further, a charging roller 22 as a charging unit and a developing unit around the photoconductor 21 along the rotation direction. The developing units 23Y, 23C, 23M, and 23K, and the cleaning unit 24 are arranged. The charging roller 22 is in contact with the outer peripheral surface of the photosensitive member 21 to uniformly charge the outer peripheral surface. The laser light L is emitted from the exposure unit 3 toward the outer peripheral surface of the photosensitive member 21 charged by the charging roller 22. Irradiated. The exposure unit 3 scans and exposes the laser beam L onto the photoconductor 21 in accordance with an image signal supplied from an external device such as a host computer, and forms an electrostatic latent image corresponding to the image signal on the photoconductor 21. .
[0017]
The electrostatic latent image thus formed is developed with toner by the developing unit 23. That is, in this embodiment, as the developing unit 23, a yellow developing unit 23Y, a cyan developing unit 23C, a magenta developing unit 23M, and a black developing unit 23K are arranged along the photoconductor 21 in this order. Has been. These developing units 23Y, 23C, 23M, and 23K are configured so as to be able to come into contact with and separate from the photoconductor 21, respectively, and the four developing units 23Y, 23Y, One of the developing units 23M, 23C, and 23B selectively abuts on the photoconductor 21, and the toner of the corresponding color is applied to the surface of the photoconductor 21 to reveal the electrostatic latent image on the photoconductor 21. To do.
[0018]
The toner image developed by the developing unit 23 is primarily transferred onto the intermediate transfer belt 46 of the transfer unit 4 in the primary transfer region R1 located between the black developing device 23K and the cleaning unit 24. The structure of the transfer unit 4 will be described in detail later.
[0019]
A cleaning unit 24 is disposed at a position advanced from the primary transfer region R1 in the circumferential direction (the arrow direction in the figure). The cleaning unit 24 includes a cleaner blade 241 that scrapes off toner remaining on the outer peripheral surface of the photoconductor 21 after the primary transfer, and a receiving unit 242 that receives toner scraped off by the cleaner blade 241. Yes.
[0020]
B-3. Transfer unit 4
Next, the configuration of the transfer unit 4 will be described. In this embodiment, the transfer unit 4 is transferred to the driving roller 41, the four driven rollers 42 to 45, the intermediate transfer belt 46 stretched over the rollers 41 to 45, and the intermediate transfer belt 46. And a secondary transfer roller 48 for secondary transfer of the intermediate toner image onto the sheet S. When a color image is transferred to the sheet S, the color toner images formed on the photoreceptor 21 are superimposed on the intermediate transfer belt 46 to form a color image, which is then transferred to the sheet S to be a full color. Get an image. When a monochrome image is transferred to the sheet S, only a black toner image is formed on the intermediate transfer belt 46 on the photosensitive member 21 and transferred to the sheet S to obtain a monochrome image.
[0021]
More specifically, the transfer unit 4 is configured as follows. That is, as shown in the figure, the drive roller 41 is disposed on the cleaning unit 24 side (right hand side in the figure) of the primary transfer region R1. A gear is fixed to the end of the drive roller 41, and the gear is engaged with the drive gear of the photoconductor 21, so that the drive roller 41 is rotationally driven at substantially the same peripheral speed as the photoconductor 21. As the drive roller 41 rotates, the intermediate transfer belt 46 is circulated and driven in the direction indicated by the arrow at the same peripheral speed as that of the photosensitive member 21. An electrode roller 47 is in contact with the drive roller 41 from the outer peripheral side via an intermediate transfer belt 46, and a conductive layer (to be described later) of the intermediate transfer belt 46 via the electrode roller 47. A primary transfer voltage is applied.
[0022]
On the other hand, a driven roller 45 is disposed on the developing unit 23 side (left-hand side in the figure) of the primary transfer region R 1, and applies tension to the intermediate transfer belt 46 between the driving roller 41. As a result, the belt portion located between the rollers 41 and 46 is pressed against the photoreceptor 21 to form a primary transfer portion.
[0023]
Of the remaining rollers, the driven roller 42 is a tension roller, and applies tension to the intermediate transfer belt 46 by a biasing means (not shown). The driven roller 43 is a backup roller that forms the secondary transfer region R2.
[0024]
A secondary transfer roller 48 is opposed to the backup roller 43 with the intermediate transfer belt 46 interposed therebetween. The secondary transfer roller 48 can be brought into and out of contact with the intermediate transfer belt 46 by a contact / separation mechanism (not shown), and is pressed against the intermediate transfer belt 46 at the time of secondary transfer. In this pressure contact state, a secondary transfer voltage is applied to the secondary transfer roller 48 and the toner image transferred to the intermediate transfer belt 46 is fed to the secondary transfer region R2 by the paper feed / discharge unit 6. Transferred to the sheet S (secondary transfer).
[0025]
The driven roller 44 is a backup roller for the belt cleaner 49. The belt cleaner 49 includes a cleaner blade 491 that contacts the intermediate transfer belt 46 and scrapes off toner remaining on the outer peripheral surface thereof, and a receiving portion 492 that receives the toner scraped off by the cleaner blade 491. ing. The belt cleaner 49 can be brought into and out of contact with the intermediate transfer belt 46 by a contact and separation mechanism (not shown).
[0026]
In this embodiment, the intermediate transfer belt 46 is an insulating base made of a synthetic resin, a conductive layer formed on the insulating base, and formed on the conductive layer and pressed against the photoreceptor 21. It has a three-layer structure composed of a resistance layer. At the side edge portion of the intermediate transfer belt 46 having the three-layer structure, the resistance layer is removed in a strip shape, and the conductive layer is exposed in a strip shape. The electrode roller 47 is in contact with the exposed portion, so that the intermediate transfer belt 46 is contacted. On the other hand, a primary transfer voltage is applied. The intermediate transfer belt 46 is finished in an endless manner by joining both end portions of the belt having the three-layer structure, and is controlled so that the toner image is primarily transferred while avoiding the joint portion. .
[0027]
B-4. Fixing unit 5
The sheet S on which the toner image has been transferred by the transfer unit 4 is fed along a predetermined paper feed path 630 (two-dot chain line in the figure) by a paper feed / discharge unit 6 which will be described later. The fixing unit 5 is disposed on the downstream side. The fixing unit 5 is formed by two fixing portions 51 and 52. The main fixing unit 51 includes a heat roller 511 disposed on the upper side of the paper feed path 630 and a pressure roller 512 pressed against the heat roller 511 from the lower side, and is conveyed. The toner image transferred to the sheet S is fixed to the sheet S. On the other hand, the auxiliary fixing unit 52 includes a heat roller 521 disposed on the lower side of the sheet feeding path and a pressure roller 522 pressed against the heat roller 521 from the upper side. The habit of the sheet S generated at 51 is alleviated. In this way, the sheet S on which an image has been formed is further fed by the paper feed / discharge unit 6 along the paper feed path 630 toward the standard paper discharge tray 11 or the multi-bin unit.
[0028]
B-5. Feed / discharge unit 6
The paper supply / discharge unit 6 includes a cassette 61 and a manual feed tray 62 that can store a plurality of sheets S in a stacked state, and a sheet S from the cassette 61 or the manual feed tray 62 along the paper feed path 630 and the secondary transfer region R2 and The sheet feeding unit 63 that transports the sheet to the fixing unit 5 and the fixed sheet S are selectively discharged to the standard sheet discharge tray 11, the multibin unit, or the finisher, or the sheet S that has been transported is on the refeed unit side. A sheet discharge unit 64 that reversely feeds the sheet S, a switching unit 65 that selectively switches the conveyance paths 641a and 641b of the sheet S in the sheet discharge unit 64, and a sheet S conveyed from the sheet discharge unit 64 again. A refeed unit 66 that feeds paper to the unit 63.
[0029]
B-5-1. Paper feed unit 63
The sheet feeding unit 63 is provided with a pickup roller 631 so as to come into contact with the uppermost sheet S among the sheets S stored in the cassette 61 in order to carry out the sheet S from the cassette 61. A separation roller pair 632 is provided on the outlet side (right hand side in FIG. 1) of the cassette 61 in order to reliably separate the sheets S carried out from the cassette 61 one by one by the pickup roller 631. Thus, the sheets S stored in the cassette 61 can be reliably taken out one by one toward the secondary transfer region R2. Such a configuration of taking out the sheet S is the same on the manual feed tray 62 side. In other words, the sheets S stored in the manual feed tray 62 are carried out of the manual feed tray 62 by the pickup roller 633 and further sent out by the separation roller pair 634 one by one toward the secondary transfer region R2.
[0030]
The sheet S fed from the cassette 61 is fed to the gate roller pair 637 via the second and third relay roller pairs 635 and 636, while the sheet S fed from the manual feed tray 62 is fed to the third relay roller pair 636. And is fed to the gate roller pair 637 through the third relay roller pair 636. In this image forming apparatus, a cassette can be added to the lower part of the apparatus as an option, and sheets fed into the case 1 from the extension cassette (not shown) through the opening 15 are the same as described above. In order to feed the gate roller pair 637, a first relay roller pair 638 is disposed in the vicinity of the opening 15.
[0031]
The sheet S fed from the cassette 61, the manual feed tray 62, or the additional cassette as described above to the gate roller pair 637 is subjected to registration processing by the gate roller pair 637, and then at a predetermined timing, the secondary transfer region R2, That is, the paper is fed between the intermediate transfer belt 46 and the secondary transfer roller 48. As described above, in this embodiment, the paper feed unit 63 is formed by the components 631 to 638, and the cassette 61, the manual feed tray 62 and the additional cassette to the secondary transfer region R 2 and the paper discharge unit 64. A conveyance path of the sheet S is a sheet feeding path 630.
[0032]
B-5-2. Paper discharge unit 64
The sheet S (image-formed sheet) on which the toner image has been transferred in the secondary transfer region R2 and has undergone fixing processing in the fixing unit 5 is fed to the paper discharge unit 64. The paper discharge unit 64 has two transport paths 641a and 641b. One transport path (second transport path; second switchback path) 641a extends from the fixing unit 5 to the standard paper discharge tray 11, and The other transport path (first transport path; first switchback path) 641b extends between the re-feed unit 66 and the multi-bin unit substantially parallel to the transport path 641a. Three drive rollers 642c to 644c are arranged along these transport paths 641a and 641b at a predetermined interval and sandwiched between the transport paths 641a and 641b. Corresponding to the driving rollers 642c to 644c, driven rollers 642a to 644a are disposed on the conveyance path 641a side, and driven rollers 642b to 644b are disposed on the conveyance path 641b side.
[0033]
Of the three driving rollers, the driving roller 642c provided in the vicinity of the fixing unit 5 and the refeed unit 66 is configured to rotate only in the counterclockwise direction on the paper surface of FIG. As described above, in the paper discharge unit 64, the drive roller 642c and the driven roller 642a constitute a paper discharge entrance roller pair 645, which functions as a carry-in means for pulling the fixed sheet S into the paper discharge unit 64. The sheet S is conveyed toward the standard paper discharge tray 11 along the second conveyance path 641a. On the other hand, a switchback exit roller pair 646 is constituted by the driving roller 642c and the driven roller 642b, and functions as unloading means for conveying the sheet conveyed along the first conveying path 641b from the sheet discharge unit 64, which will be described later. In this way, the sheet S temporarily waiting in the second transport path 641a or the first transport path 641b is transported toward the refeed unit 66.
[0034]
Unlike the drive roller 642c, the remaining drive rollers 643c and 644c can be rotated forward and backward, and the first and second paper discharge roller pairs 643 and 644 are configured at the positions where the drive rollers 643c and 644c are disposed, respectively. is doing. In addition, the sheet S can be conveyed in a direction opposite to each other through the conveying paths 641a and 641b according to the rotation direction of the driving rollers 643c and 644c. For example, when the driving rollers 643c and 644c rotate counterclockwise on the paper surface of FIG. 1, the sheet S can be conveyed toward the standard paper discharge tray 11 side along the second conveyance path 641a, and at the same time, the first conveyance path. The sheet S can be conveyed to the refeed unit 66 side along 641b. Note that when the rotation direction of the drive rollers 643c and 644c is reversed, the sheet S is conveyed in the direction reversed from the above.
[0035]
As described above, in this embodiment, the sheet S is moved along the second conveyance path 641a by the driving roller 643c and the driven roller 643a, and by the driving roller 644c and the driven roller 644a (the first discharge tray 11 (the first discharge tray 11)). Second conveying means for conveying the sheet S toward the second position) and reversely conveying the sheet S toward the sheet refeeding section 66 is configured. Further, the driving roller 643c and the driven roller 643b, and the driving roller 644c and the driven roller 644b convey the sheet S along the first conveying path 641b toward the multi-bin unit (first position). First conveying means for conveying S in a reverse direction toward the sheet refeeding section 66 is configured.
[0036]
Further, in this embodiment, the driving roller is shared in configuring the first and second conveying means, but a dedicated driving roller may be provided for each. In this embodiment, the first conveying means is composed of two pairs of rollers (643b and 643c; 644b and 644c), and the second conveying means is also composed of two pairs of rollers (643a and 643c; 644a and 644c). However, the number of sets is arbitrary, and at least one set may be provided to convey the sheet S.
[0037]
In this embodiment, each of the first and second paper discharge roller pairs 643 and 644 simultaneously carries the sheet S on the conveyance paths 641a and 641b to the paper discharge side and the switching unit 65. It functions as a means, and the device configuration is simpler and easier to control than when the first and second transport means are provided. In this embodiment, the two conveying units, that is, the first and second paper discharge roller pairs 643 and 644 are provided. However, the number of conveying units is arbitrary and is appropriately determined according to the maximum sheet size to be conveyed. You only have to set it.
[0038]
Incidentally, a third paper discharge roller pair 647 is disposed in the transport path 641a in the vicinity of the standard paper discharge tray 11. In the third paper discharge roller pair 647, a driving roller 647c and a driven roller 647a are rotatably arranged so as to sandwich the conveyance path 641a. The third sheet discharge roller pair 647 stacks and discharges the sheet S conveyed along the second conveyance path 641 a to the standard sheet discharge tray 11. Although not shown in FIG. 1, a corrugation roller is attached to at least one of the rotation shafts of the drive roller 647c and the driven roller 647a, and the sheet S is in a direction substantially perpendicular to the sheet discharge direction. The sheet is curled and removed by applying a forcing force.
[0039]
On the other hand, in the first conveyance path 641b, a switching flap 648 is provided at a position directly above the driven roller 643b constituting the first sheet discharge roller pair 643, and the sheet discharge destination of the sheet S conveyed along the conveyance path 641b is set. Switching is possible. In other words, when the switching flap 648 is located at the solid line position in the drawing, the sheet S is conveyed as it is along the conveyance path 641b and discharged toward the multi-bin unit, while the switching flap 648 is conveyed to the conveyance path 641b. When positioned above, the sheet S leaves the conveyance path 641 b and is discharged to the finisher through the opening 14.
[0040]
Further, between the first discharge roller pair 643 configured as described above, the discharge inlet roller pair 645 and the switchback outlet roller pair 646, the conveyance path of the sheet S is divided into two conveyance paths 641a and 461b. A switching unit 65 that switches between the two is provided, and the conveyance path of the sheet S is selectively switched by controlling the switching unit 65. More specifically, the switching unit 65 is configured as follows.
[0041]
B-5-3. Switching unit 65
FIG. 2 is an enlarged perspective view showing the switching unit of FIG. As shown in the drawing, the switching unit 65 includes a first switching flap 651 and a second switching flap 652. And it is comprised as follows in order to drive each switching flap 651,652 respectively.
[0042]
The first switching flap 651 serves as switching means for guiding the sheet S, which has undergone the fixing process and is conveyed by the pair of paper discharge inlet rollers 645, to either one of the conveying paths 641a and 641b, and the first conveying. This is for guiding the sheet S once carried into the path 641b to the refeed unit 66. The first switching flap 651 is fixed to a shaft 653b disposed between the transport paths 641a and 641b. An arm 654b is fixed to one end of the shaft 653b, and a pin 656b of a solenoid 655b is connected to the tip of the arm 654b. Accordingly, when the pin 656b is in the upwardly moved position, the first switching flap 651 is at a position where the tip 651b is directed toward the first driven roller 642b as shown by the solid line in FIG. The sheet S conveyed by the roller pair 645 is guided as it is toward the standard paper discharge tray 11 side along the second conveyance path 641a. On the other hand, when the pin 656b moves downward, the first switching flap 651 rotates counterclockwise and switches to a position where the tip 651b is directed to the second driven roller 642a side, and the second discharge inlet roller pair 645 is moved. The sheet S that has been conveyed is guided toward the opening 13 along the other first conveyance path 641b.
[0043]
The second switching flap 652 is for guiding the sheet once transported to the second transport path 641a to the refeed unit 66, and is disposed outside the guide plate 657 that guides one surface of the first transport path 641b. It is fixed to the shaft 653a. An arm 654a is fixed to one end of the shaft 653a, and a pin 656a of a solenoid 655a is connected to the tip of the arm 654a. Therefore, when the pin 656a is in the upwardly moved position, the second switching flap 652 is in a position retracted from the first conveyance path 641b indicated by a solid line in FIGS. On the other hand, when the pin 656a is moved downward, the leading end portion 652a of the pin 656a rotates clockwise and enters the first transport path 641b, and the sheet once transported to the second transport path 641a is guided to the refeed unit 66.
[0044]
The guide plate 657 is provided with a notch 657a facing the second switching flap 652, and when the second switching flap 652 is rotated in the clockwise direction, the leading end portion 652a enters the notch 657a. , Toward the nip portion 646b between the driving roller 642c and the driven roller 642b. On the other hand, when the first switching flap 651 rotates counterclockwise, its tip 651b enters the notch 657a.
[0045]
In addition, since the rotation drive mechanism of the switching flap 648 is the same as that of the first and second switching flaps 651 and 652, the description thereof is omitted here.
[0046]
As described above, in this embodiment, the paper discharge unit is configured by incorporating the switching unit 65 into the paper discharge unit 64 having the plurality of transport paths 641a and 641b. According to this paper discharge device, an image has already been formed. The sheet S can be selectively conveyed to one of the two conveyance paths 641a and 461b, and the sheet S waiting to be conveyed on the conveyance paths 641a and 461b can be selectively conveyed to the refeed unit 66. It has become. The characteristic operation will be described in detail later while showing a specific image forming sequence.
[0047]
B-5-4. Refeed unit 66
Returning to FIG. 1, the configuration of the paper refeed unit 66 will be described. The sheet refeeding unit 66 conveys the sheet S conveyed from the switchback exit roller pair (carrying means) 646 to the gate roller pair 637 of the sheet feeding unit 63 along the sheet refeeding path 664. It is composed of three refeed roller pairs 661 to 663 arranged along a refeed path 664. In each of the refeed roller pairs 661 to 663, a driving roller is disposed below the refeeding path 664, and a driven roller is disposed in contact with the driving roller. In this manner, the sheet S conveyed from the paper discharge unit 64 is returned to the gate roller pair 637 along the refeed path 664 so that the non-image forming surface of the sheet S moves the intermediate transfer belt 46 in the paper supply unit 63. The image can be secondarily transferred to the surface.
[0048]
B-6. Control unit 7
FIG. 3 is a block diagram showing a schematic configuration of a control unit that controls the image forming apparatus of FIG. The control unit 7 stores a CPU 711 for performing various arithmetic processes and control commands for controlling the entire apparatus, a RAM 712 for temporarily storing control data and calculation results, a calculation program executed by the CPU 711, and the like. The control part 71 which has ROM713 to perform is provided. The control unit 71 is connected to an external device such as a host computer via a communication interface 77, and an image signal or the like can be input from the external device via the communication interface 77. The image signal is also directly input to the image memory 78 via the communication interface 77, and image data based on the image signal can be stored.
[0049]
In addition to the communication interface 77, the control unit 71 includes an image memory 78, an operation display unit 79 including operation buttons and a display panel, an image carrier unit controller 72 for controlling the operation of the image carrier unit 2, and an exposure unit. 3, an exposure unit controller 73 that controls the operation of the transfer unit 4, a transfer unit controller 74 that controls the operation of the transfer unit 4, a fixing unit controller 75 that controls the operation of the fixing unit 5, and a paper supply / discharge unit that controls the operation of the paper supply / discharge unit 6. It is electrically connected to the paper unit controller 76 and gives a control command to each part of the apparatus to control the entire apparatus. In this embodiment, since the features of the invention are closely related to the sheet S conveying operation, the configuration of the paper supply / discharge unit controller 76 will be described in further detail.
[0050]
As shown in the figure, the paper supply / discharge unit controller 76 is disposed in each part of the motor driver 761, the three clutch drivers 762 to 764, the solenoid driver 765, and the paper supply / discharge unit 6, and detects the sheet S. And a sensor group 766. Among these, the motor driver 761 is for driving and controlling a drive motor 67 which is a drive source of the paper supply / discharge unit 6, and the driving force of the drive motor 67 is the paper feed unit 63, the paper discharge unit 64, and the re-feed. The sheet S is conveyed to the section 66 and conveyed.
[0051]
Further, in the paper feed unit 63, the paper discharge unit 64, and the re-feed unit 66, the driving force is transmitted to a part of the rollers via a clutch (not shown), A clutch driver 762 is provided for the paper feed side clutch group 68a, a clutch driver 763 is provided for the paper discharge side clutch group 68b provided in the paper discharge unit 64, and a refeed paper provided in the paper refeed unit 66. The clutch driver 764 is configured to ON / OFF control the side clutch group 68c.
[0052]
Further, as described above, the discharge section 64 is provided with the three switching flaps 641, 642, and 648, and is driven to rotate by flap switching solenoid groups (solenoids 655a, 655b, etc.). In the embodiment, a solenoid driver 765 is provided to control the flap switching solenoid group. Then, according to the image forming sequence, the control unit 71 determines to which transport path the sheet is transported, and each solenoid driver 765 is in accordance with a command indicating this determination content (corresponding to the selected path information of the present invention). The sheet conveyance destination by the switching unit 65 is switched by switching the solenoid.
[0053]
Further, the sensor 766j (FIG. 1) in the sensor group 766 is a position where the first and second transport paths 641b and 641a overlap each other, and the following conditional expression:
(Lmax-Q) / 2 <P <Lmin
However,
Lmax: maximum sheet length,
Lmin: minimum sheet length,
P: distance from switchback stop position to sensor 766j,
Q: interval between successive sheets (sheet interval),
It is the sensor arrange | positioned so that it may satisfy | fill. The sensor 766j is integrally provided with a projector and a light receiver. The sensor 766j emits light from the light projector to the first and second transport paths 641b and 641a, and the light reflected by the sheet is received by the light receiver. Thus, it is possible to detect whether or not the sheet S exists in the first or second transport path 641b, 641a.
[0054]
As described above, this embodiment is configured such that the sheet S is conveyed along the conveyance path selected from the first and second conveyance paths 641b and 641a disposed so as to overlap each other. The sensor 766j detects whether or not a sheet exists in each of the conveyance paths 641b and 641a, and the control unit 71 selects based on the path selection information indicating which conveyance path the sheet should be conveyed to. The presence / absence of a sheet in the conveyance path is determined. The specific determination operation and the position where the sensor 766j is disposed will be described in detail in the next section “C. Operation of Image Forming Apparatus”.
[0055]
C. Operation of image forming apparatus
Next, the operation of the image forming apparatus configured as described above, in particular, one of the image forming sequences most relevant to the features of the present invention will be exemplified and described in detail. This image forming sequence is to form a color image on both main surfaces of the A4 sheet and then discharge it to the standard paper discharge tray 11, and will be described below with reference to FIGS.
[0056]
4 and 5 are schematic diagrams showing an image forming sequence of the image forming apparatus of FIG. FIG. 6 is a diagram schematically showing the sheet conveyance state at the timing T1 in FIG. 4 and 5, the column “intermediate transfer belt” indicates a toner image that is primarily transferred to the intermediate transfer belt 46. Further, the boundary line in the same column indicates the joint portion of the intermediate transfer belt 46. In this embodiment, two toner images can be primarily transferred to the intermediate transfer belt 46 with a maximum A4 size. . The attributes of the primary transferred toner image are displayed with four alphanumeric characters. The contents of each display are as follows.
[0057]
Number: Number of sheets;
English letters: F ... Front side, B ... Back side;
Parentheses: page number;
Parenthesis English letters: K ... Black, Y ... Yellow, M ... Magenta, C ... Cyan;
The display contents other than “parentheses” are also common to the sheet attributes shown in the “gate roller”, “first transport path”, and “second transport path” fields in FIG. It is used.
[0058]
(a-1) First, when an image signal is input from the host computer to the control unit 7, an electrostatic latent image corresponding to the image on the second page (image to be formed on the back surface of the first sheet) on the photoreceptor 21. After the image is formed, the yellow developing device 23 </ b> Y is selectively brought into contact with the photoconductor 21 to form a yellow toner image on the surface of the photoconductor 21. Then, the toner image is primarily transferred onto the intermediate transfer belt 46.
[0059]
(a-2) Similarly, the yellow toner image of the fourth page image (the image to be formed on the back side of the second sheet) is formed side by side with the yellow toner image of the second page.
[0060]
(b-1) Further, a cyan toner image, a magenta toner image, and a black toner image are superimposed on each toner image to form a color intermediate toner image on the intermediate transfer belt 46.
[0061]
Then, along with the formation of the intermediate toner image, the A4 size sheet S1 is conveyed from the cassette 61 or the like to the gate roller pair 637 and is kept waiting. Then, the intermediate toner image is secondarily transferred to the sheet S1 at an appropriate timing and fixed by the fixing unit 5 to form the second page image on the back side of the first sheet.
[0062]
(b-2) The sheet S1 on which the image of the second page is thus formed is conveyed to the first conveyance path 641b connected to the multi-bin unit. At this time, the control unit 71 gives the solenoid driver 765 path selection information indicating that the sheet S1 should be conveyed to the first conveyance path 641b, and the switching unit 65 causes the leading ends 651b and 652a of the switching flaps 651 and 652 to be the second. Are switched to be directed toward the driven roller 642a.
[0063]
When the sheet S1 is conveyed to the first conveyance path 641b and the leading end thereof passes the sensor 766j, the sensor 766j detects the sheet S1, and the sensor output changes. Therefore, the control unit 71 detects that the sheet S1 has been conveyed to the conveyance paths 641a and 641b in response to the change in the sensor output. Here, it is impossible to determine to which transport path 641a and 641b the sheet S1 has been transported by only the output information of the sensor 766j. In this embodiment, however, the sheet can be placed in the first transport path 641b in advance. Since it is known that S1 is conveyed based on the route selection information, the control unit 71 can determine the presence or absence of a sheet on the first conveyance route 641b based on the sensor output and the route selection information.
[0064]
When the trailing end of the sheet S1 reaches the switchback stop position SP, the conveyance of the sheet S1 is stopped and the sheet S1 is stopped.
[0065]
In parallel with the conveyance of the sheet S1 to the first conveyance path 641b, an image of the fourth page (an image to be formed on the back surface of the second sheet) is formed on the back surface of the next sheet S2. That is, following the sheet S1, the next sheet S2 is conveyed from the cassette 61 or the like to the gate roller pair 637 and kept waiting, and the intermediate toner image on the intermediate transfer belt 46 is secondarily transferred to the sheet S2 at an appropriate timing. Then, the image is fixed by the fixing unit 5 and an image of the fourth page is formed on the back side of the second sheet.
[0066]
(c-1) The sheet S2 on which the image of the fourth page is thus formed is conveyed to the second conveyance path 641a connected to the standard paper discharge tray 11 that is selected in advance as the paper discharge position, as shown in FIG. At this time, since the paper discharge unit 64 is configured as described in detail above, the sheet S1 is re-feeded on the first conveyance path 641b simultaneously with the conveyance of the sheet S2 on the second conveyance path 641a side. Inverted and transported toward. At this time, in order to convey the next sheet S2 to the second conveyance path 641a, the control section 71 gives path selection information to that effect to the solenoid driver 765, and turns the switching flap 651 of the switching section 65 in the clockwise direction in FIG. It rotates to return its tip 651b to a position oriented toward the first driven roller 642b.
[0067]
Then, as shown in FIG. 6, when the leading end of the sheet S2 reaches a position separated from the switchback stop position SP by the distance Q toward the fixing unit 5, the first and second discharge roller pairs 643 and 644 rotate. The direction is switched and rotationally driven to reversely convey the sheet S1 to the refeed unit 66. After a while, when the leading end of the sheet S1 passes the sensor 766j, the output of the sensor 766j changes.
[0068]
On the other hand, on the second conveyance path 641a side, when the next sheet S2 is conveyed from the fixing unit 5 side and the leading end reaches the sensor 766j, the sensor 766j detects the sheet S2 and the sensor output changes. For this reason, the control unit 71 detects that the sheet S2 has been conveyed to the conveyance paths 641a and 641b in response to the change in the sensor output, but the sheet S2 is conveyed to the second conveyance path 641a in advance as described above. Since it is known based on the route selection information, the control unit 71 can determine the presence / absence of a sheet on the second conveyance route 641a based on the sensor output and the route selection information.
[0069]
When the trailing end of the sheet S2 reaches the switchback stop position SP, the conveyance of the sheet S2 is stopped and the sheet S2 is stopped.
[0070]
As described above, according to this embodiment, only one sensor 766j is provided for the two transport paths 641a and 641b. However, by using the path selection information in addition to the sensor output, the transport path 641a and 641b can be used within the transport path. The presence or absence of a sheet can be detected. Accordingly, it is possible to reliably detect the presence or absence of a sheet in the plurality of transport paths with fewer sensors.
[0071]
In addition, according to this image forming sequence, the two sheets S1 and S2 are conveyed simultaneously, whereby the processing capacity per unit time, that is, the throughput can be improved. Further, when two sheets are simultaneously conveyed by one path of the paper discharge unit 64 (for example, when simultaneously conveyed by one path as described in Japanese Patent Publication No. 61-11865), the sheets are However, this image forming apparatus transports both sheets through separate transport paths 641a and 641b, so that the above problem does not occur and the sheet is prevented from being soiled. be able to.
[0072]
In parallel with the sheet conveyance, a yellow toner image corresponding to the image of the first page (image to be formed on the surface of the first sheet) is formed on the intermediate transfer belt 46.
[0073]
(c-2) Similarly, the yellow toner image of the third page image (image to be formed on the surface of the second sheet) is formed side by side with the yellow toner image of the first page. At the same time, the sheet S1 conveyed to the refeed unit 66 is conveyed toward the gate roller pair 637 and is put on standby.
[0074]
(d-1) Further, a cyan toner image, a magenta toner image, and a black toner image are superimposed on each toner image to form a color intermediate toner image on the intermediate transfer belt 46.
[0075]
Then, the intermediate toner image thus formed is secondarily transferred to the sheet S1 at an appropriate timing, and is fixed by the fixing unit 5 to form the first page image on the first sheet side. Thus, image formation on both sides of the sheet S1 is completed.
[0076]
Note that the second sheet S2 conveyed to the second conveyance path 641a in the step (c-1) is reversed and conveyed toward the refeed unit 66 at an appropriate timing, and further, the gate following the sheet S1. It conveys to the roller pair 637 and waits.
[0077]
(d-2) The sheet S1 on which the images are formed on both sides is discharged toward the standard discharge tray 11, and at the same time, the intermediate toner image formed on the intermediate transfer belt 46 is transferred to the sheet. Secondary transfer is performed at S2, and fixing is performed by the fixing unit 5, so that an image of the third page is formed on the surface side of the second sheet.
[0078]
(e-1) The sheet S2 having images formed on both sides in this manner is discharged toward the standard discharge tray 11 following the sheet S1 discharged in advance.
[0079]
In parallel with this, a yellow toner image corresponding to the image of the sixth page (image to be formed on the back side of the third sheet) is formed on the intermediate transfer belt 46.
[0080]
Thereafter, the above steps (a-2) to (e-1) are repeated until all the images up to the desired page are formed on the sheet.
[0081]
As described above, in this embodiment, one sensor 766j is provided for the first and second transport paths 641b and 641a overlapping each other, and the control unit 71 is based on the output of the sensor 766j and the selected path information. The presence / absence of a sheet in each conveyance path is determined, and the sheet detection apparatus according to the present invention is configured by the sensor 766j and the control unit 71 functioning as a determination unit. In this embodiment, the following conditional expression
(Lmax-Q) / 2 <P <Lmin
The sensor 766j is disposed so as to satisfy the following reason, for the following reason. Hereinafter, the reason why the distance P is set shorter than the minimum sheet length Lmin and the reason why the distance P is set longer than the distance ((Lmax−Q) / 2) will be described.
[0082]
When the second transport path 641b functions as a switchback path as described above, if the sensor 766j is set longer than the minimum sheet length Lmin from the switchback stop position SP, the leading edge of the sheet reaches the sensor 766j. Previously, the trailing edge of the sheet reaches the switchback stop position SP and the sheet conveyance is stopped, and the presence or absence of the sheet by the sensor 766j cannot be detected. Therefore, the distance P must be zero or more and shorter than the minimum sheet length Lmin. That is, the following inequality
P <Lmin
Must be satisfied (disposition condition 1).
[0083]
The following reason will be described with reference to FIGS. When the next sheet S2 is transported to the second transport path 641a simultaneously with the switchback of the sheet S1 from the first transport path 641b, as shown in FIG. 6, the distance between the sheets S1 and S2 at the start of the switchback. (Sheet interval) is the interval Q. Then, as time elapses, the trailing edge of the sheet S1 and the leading edge of the sheet S2 overlap, and as the sheet conveyance further proceeds, the leading edge of the sheet S1 and the leading edge of the sheet S2 overlap as shown in FIG. At this time, the distance from the switchback stop position SP to the leading ends of the sheets S1 and S2 is (Lmax−Q) / 2.
[0084]
Here, assuming that the sensor 766j is disposed closer to the switchback stop position SP than the position where the leading ends of the sheets S1 and S2 coincide with each other, the sheet detection is performed at a position where the sheets S1 and S2 overlap. Even if the sheet S1 is transported to the refeed unit 66 and its leading end passes through the sensor 766j, a part of the next sheet S2 has already reached the sensor 766j at that time. Therefore, the sensor 766j cannot continuously detect the sheet and determine the sheet switching.
[0085]
On the other hand, when the sensor 766j is arranged on the opposite side of the switchback stop position SP from the position where the leading ends of the sheets S1 and S2 coincide with each other, that is, the following inequality
(Lmax-Q) / 2 <P
7, as shown in FIG. 7, the leading edge of the sheet S1 passes through the sensor 766j as the sheet S1 is reversed and conveyed to the refeeding section 66 side, and the leading edge of the next sheet S2 is obtained. Has not reached the sensor 766j, and the output of the sensor 766j returns to a state where no sheet is detected. When the sheet conveyance further proceeds and the next sheet S2 is conveyed to the first conveyance path 641a, the leading end of the sheet S2 reaches the sensor 766j and the output of the sensor 766j changes to be the same as in the case of the sheet S1. Thus, the sheet S2 is detected. Accordingly, when the next sheet S2 is transported to the second transport path 641a simultaneously with the switchback operation of the sheet S1 in the first transport path 641b, the distance P is set to the distance ((Lmax−Q) / 2. ) Must be set longer than (positioning condition 2).
[0086]
When the next sheet is transported to the second transport path 641a after the switchback operation in the first transport path 641b is completed, the disposition condition 2 is not an essential requirement and the disposition condition 1 is satisfied. As long as the sheet is present on the first and second transport paths 641b and 641a, it can be reliably detected.
[0087]
When the transport path 641b does not function as a switchback path, the sheet is directed toward the multi-bin unit on the first transport path 641b side, and toward the standard discharge tray 11 on the second transport path 641a side. Since it is only transported in one direction, the sensor 766j may be disposed at any position as long as the transport paths 641a and 641b overlap each other.
[0088]
In the above embodiment, the first transport path 641b functions as a switchback path. However, when the second transport path 641a functions as a switchback path, the arrangement condition 1 is satisfied as described above. By disposing the sensor 766j in the first and second sheets, it is possible to reliably detect the presence or absence of sheets on the first and second transport paths 641b and 641a even when the switchback operation is performed on the second transport path 641a.
[0089]
In the above embodiment, the first transport path 641b functions not only as a sheet discharge path for discharging a sheet to the multi-bin unit (first position) but also as a switchback path. However, the present invention is not limited to this, and the present invention can also be applied to an apparatus in which the first transport path functions only as a switchback path.
[0090]
In the above-described embodiment, the present invention is applied to a device that discharges a sheet on which an image is formed at a position where the first and second transport paths 641b and 641a are different from each other. As described in the publication, the present invention can also be applied to an apparatus in which two transport paths are connected to the same paper discharge position.
[0091]
In the above embodiment, a so-called reflection type sensor that is integrally provided with a projector and a light receiver is used as the sensor 766j. However, the projector and the light receiver are opposed to each other with the first and second transport paths 641b and 641a interposed therebetween. A so-called transmission type sensor may be used. Further, as the sensor 766j, a contact type sensor may be used instead of the non-contact type.
[0092]
In the above embodiment, the present invention is applied to the paper supply / discharge unit (conveyance device) 6 that has two conveyance paths 641a and 641b and conveys the sheet. However, the conveyance apparatus has three or more conveyance paths. Even if the present invention is applied, the same effect can be obtained.
[0093]
Furthermore, in the above embodiment, the present invention is applied to a color image forming apparatus, but the present invention can also be applied to a monochrome image forming apparatus. Further, the image forming method of the image forming apparatus to which the sheet detecting apparatus according to the present invention can be applied is not limited to the electrophotographic method, and includes an ink jet method and a thermal transfer method.
[0094]
【The invention's effect】
As described above, according to the present invention, the sensor detects whether or not a sheet exists in each conveyance path, and determines which conveyance path the sheet should be conveyed based on the path selection information. As a result, the presence / absence of a sheet on the selected conveyance path is determined, so that the number of sensors arranged on the conveyance path can be reduced, and the cost of the apparatus can be reduced.
[0095]
Further, when the first sheet is conveyed toward the first position along the first conveyance path between the switching unit and the first position, and the trailing end of the sheet reaches a predetermined switchback stop position, The following inequality is also used when a first conveying unit that reversely conveys the first sheet is provided after the conveyance of the first sheet is stopped and the first conveying path functions as a switchback path.
P <Lmin
Where P is the distance from the switchback stop position to the sensor, and Lmin is the minimum length of the seat.
By arranging the sensor so as to satisfy the above, the presence or absence of the sheet can be reliably detected.
[0096]
Further, the second conveying unit conveys the second sheet along the second conveying path toward the second position simultaneously with the reverse conveyance of the first sheet by the first conveying unit between the switching unit and the second position. Even when the second sheet is conveyed toward the second position simultaneously with the switchback operation, the following inequality is used:
(Lmax-Q) / 2 <P
Where Q is the sheet interval between the first sheet and the second sheet at the start of the reverse conveyance of the first sheet, and Lmax is the maximum length of the first and second sheets.
By arranging the sensor so as to satisfy the above, the presence or absence of the sheet can be reliably detected.
[Brief description of the drawings]
FIG. 1 is a diagram illustrating an image forming apparatus provided with an embodiment of a sheet detection apparatus according to the present invention.
FIG. 2 is an enlarged perspective view showing a switching unit in FIG. 1;
3 is a block diagram showing a schematic configuration of a control unit that controls the image forming apparatus of FIG. 1; FIG.
4 is a schematic diagram illustrating an image forming sequence of the image forming apparatus in FIG. 1. FIG.
5 is a schematic diagram illustrating an image forming sequence of the image forming apparatus in FIG. 1;
FIG. 6 is a diagram schematically illustrating a sheet conveyance state at a timing T1 in FIG.
7 is a diagram schematically illustrating a sheet conveyance state in the image forming apparatus of FIG. 1. FIG.
[Explanation of symbols]
2 ... Image carrier unit
3. Exposure unit
4 ... Transcription unit
5. Fixing unit
6 ... paper supply / discharge unit (conveyance device)
7 ... Control unit
11: Standard paper discharge tray (first position)
63: Paper feeding unit
64: Paper discharge section
65 ... switching part
66 ... Re-feed section
71 ... Control unit (determination means)
641a (Second) transport path
641b (first) transport path
651, 652 ... switching flaps
766j ... Sensor
P ... Distance from the switchback stop position to the sensor
Q ... (sheet) interval
S1 ... (first) sheet
S2 ... (second) sheet
SP ... Switchback stop position

Claims (5)

A first conveyance path for guiding the conveyed sheet toward the first position;
A second transport path arranged to at least partially overlap the first transport path and guiding the transported sheet toward the second position;
Switching means for selectively switching the conveyance path of the conveyed sheet to the first or second conveyance path;
A sensor capable of detecting the presence / absence of a sheet in each of the conveyance paths by being arranged at a position where the first and second conveyance paths overlap each other, path selection information indicating a sheet conveyance destination by the switching unit, and the sensor Determining means for determining the presence or absence of a sheet in the conveyance path selected as the conveyance destination by the switching means based on the output of the output, and for detecting a sheet conveyed along the first or second conveyance path Sheet detection means,
Arranged between the switching means and the first position, conveys the first sheet toward the first position along the first conveyance path, and the trailing end of the sheet stops at a predetermined switchback. A first conveying means for reversing and conveying the first sheet after stopping the conveyance of the first sheet when reaching the position;
The second sheet is disposed between the switching unit and the second position, and is directed to the second position along the second conveyance path simultaneously with the reverse conveyance of the first sheet by the first conveyance unit. Second conveying means for conveying
The distance from the switchback stop position to the sensor is P, the minimum length of the first sheet is Lmin, and the sheet interval between the first sheet and the second sheet at the start of reverse conveyance of the first sheet is Assuming that Q is L and the maximum length of the first and second sheets is Lmax, the following inequality (Lmax−Q) / 2 <P <Lmin
A conveying device characterized in that the sensor is disposed so as to satisfy the above.   The transport apparatus according to claim 1, wherein the first and second positions are the same paper discharge position.   The transport apparatus according to claim 1, wherein the first and second positions are different discharge positions.   The transport apparatus according to claim 1, wherein the first transport path is a switchback path, and the second position is a paper discharge position for discharging a sheet on which an image is formed. An image forming means for forming an image on a sheet;
A paper feeding means for feeding a sheet to the image forming means;
A paper discharge unit having the same configuration as that of the transport device according to claim 1,
A sheet reversing unit for reversing the sheet from the sheet discharging unit and refeeding the sheet to the sheet feeding unit;
The sheet on which the image is formed by the image forming unit is conveyed to the sheet discharge unit along the second conveyance path, while the sheet from the sheet discharge unit is re-supplied along the first conveyance path. An image forming apparatus conveyed to a paper means.

Images