JP3945092B2 - Image forming apparatus - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an image forming apparatus having a duplex mode in which images are formed on both sides of sheets such as copy paper, transfer paper, paper, and an OHP transparent sheet.
[0002]
[Prior art]
As this type of image forming apparatus, for example, there is an apparatus described in Japanese Patent Laid-Open No. 11-35209. In this image forming apparatus, a first paper discharge path for discharging a sheet after image formation toward a paper discharge tray that receives a sheet discharged after image formation is independent of the first paper discharge path. A second paper discharge path for discharging the sheet after the image formation; and a switching unit that guides the sheet after the image formation to one of the first and second paper discharge paths. When a sheet jam occurs in the first or second sheet discharge path, the sheet is guided to the other sheet discharge path by the switching unit, so that the sheet after image formation is interrupted without interrupting the image forming operation. The paper is discharged to the paper output tray. Therefore, even when a sheet jam occurs, an image can be continuously formed and discharged on the subsequent sheet, and an efficient image forming process is possible.
[0003]
Incidentally, the image forming apparatus has a plurality of image forming modes. For example, the image forming mode includes a single-side mode in which an image is formed only on one side of a sheet and a double-side mode in which an image is formed on both sides of the sheet.
[0004]
Further, when executing the duplex mode, it is necessary to reversely convey a sheet on which an image is formed on one side. Therefore, in the image forming apparatus, at least one of the first and second paper discharge paths also functions as a sheet reversing path, and various sheet conveyance processes can be executed according to the mode.
[0005]
For example, when both paper discharge paths function as reversal paths, the (first) sheet is first conveyed to one paper discharge path, and the sheet is reversed and conveyed out of the paper discharge path. The second sheet) is carried into the other paper discharge path. When the reverse conveyance of the first sheet is completed, the second sheet is subsequently conveyed out from the other paper discharge path to carry out the reverse conveyance of the second sheet. Hereinafter, this sheet conveyance process is referred to as “simultaneous carry-in / out process”.
[0006]
Further, when only one of them is to function as a reverse path, the first sheet is reversely conveyed in the paper discharge path that also functions as the reverse path, and after the reverse conveyance is completed, the second sheet in the same paper discharge path. Reverse transfer is performed. Further, in the image forming apparatus, when the reverse conveyance is performed in each paper discharge path in the reverse order to the simultaneous carry-in / out process due to the mechanical configuration, after the reverse conveyance by the other paper discharge path is completed. Otherwise, the reverse conveyance by one paper discharge path cannot be performed. Hereinafter, the sheet conveyance process in which the second sheet is reversed and conveyed after the first sheet is reversed is referred to as a “sequential reversal process”.
[0007]
In addition, when the paper discharge path and the reverse path are used together, the first sheet on which the image is formed on both sides of the paper discharge path is discharged to one side of the paper after being discharged toward the paper discharge tray. Only the (second) sheet on which an image is formed may be conveyed. Here, when the first sheet and the second sheet are continuously conveyed toward the sheet discharge tray and the discharge process of the first sheet to the sheet discharge tray is completed, the second sheet remaining in the sheet discharge path is reversed. Be transported. Hereinafter, this sheet conveyance process is referred to as “paper discharge reversal continuous process”.
[0008]
Furthermore, when a color image can be formed, the image formation mode includes a color mode for forming a color image and a monochrome mode for forming a monochrome image.
[0009]
[Problems to be solved by the invention]
As described above, the image forming apparatus has a fixed interval between images on an image carrier such as a photosensitive member or an intermediate transfer medium, despite having various image forming modes. There is a problem in terms of efficient image formation, and there remains room for improvement. Further, the sheet interval when the image-formed sheet is conveyed to the sheet discharge path has the same problem as the image interval, and there remains room for improvement in achieving efficient image formation.
[0010]
The present invention has been made in view of the above problems, and an object thereof is to provide an image forming apparatus that enables efficient image formation.
[0011]
[Means for Solving the Problems]
An image forming apparatus according to the present invention is different from each other in an image forming unit that forms an image on a sheet, a sheet feeding unit that feeds a sheet to the image forming unit, and a sheet on which an image is formed by the image forming unit. Paper is discharged via one of the first and second paper discharge paths, and each of the paper discharge paths is configured to be able to reversely convey the sheet, and has been reversely conveyed from the paper discharge means. The present invention relates to an image forming apparatus that includes a refeed unit that reverses a sheet and refeeds the sheet and a control unit that controls each part of the apparatus.
[0012]
In order to achieve the above object, the image forming unit includes an image carrier that carries an image, and a transfer unit that transfers an image on the image carrier to a sheet. At the same time as the first sheet discharge path is reversed and conveyed, and a second sheet following the first sheet is simultaneously loaded into the second sheet discharge path. While the sheet discharge is performed on one of the discharge paths, only the reverse conveyance can be performed on the other, and the control unit sets the interval between the images carried on the image carrier according to the image forming mode. It is configured to be adjustable. Then, as an image forming mode, both sides have a continuous discharge reversal process in which the first sheet is discharged via the first discharge path and then the second sheet following the first sheet is reversely conveyed by the first discharge path. When the mode is set, the control means sets the interval on the image carrier between the image to be transferred to the first sheet and the image to be transferred to the second sheet to an image interval corresponding to the continuous discharge reversal process. change. Alternatively, the control unit is configured such that the control unit can adjust the sheet conveyance interval in the sheet conveyance path between the image forming unit and the paper discharge unit according to the image forming mode, and the first sheet and the first sheet in the sheet conveyance path can be adjusted. The conveyance interval between the two sheets is adjusted to a conveyance interval corresponding to the continuous discharge reverse processing.
[0013]
As described above, in the image forming apparatus according to the present invention, (1) the interval between the images carried on the image carrier according to the image forming mode and (2) the sheet conveyance path between the image forming means and the paper discharge means. At least one of the sheet conveyance intervals is adjusted to improve the efficiency of image formation.
[0018]
DETAILED DESCRIPTION OF THE INVENTION
A. Overall configuration of image forming apparatus
FIG. 1 is a diagram showing an image forming apparatus including an embodiment of a paper discharge device 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 forming unit 2, an exposure unit 3, a transfer unit 4 and a fixing unit 5 are provided inside a case 1, and these constitute 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.
[0019]
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 forming 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.
[0020]
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.
[0021]
B-2. Image forming unit 2 and exposure unit 3
In this image forming apparatus, the image forming unit 2 is detachable from the case 1. The image forming unit 2 is provided with a photoconductor 21 that can rotate in the direction of the arrow in the figure, and further, around the photoconductor 21 along the rotation direction, a charging roller 22 as a charging unit, and a developing unit as a developing unit. Developing units 23Y, 23C, 23M, and 23K, and a cleaning unit 24 are respectively disposed. 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. .
[0022]
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.
[0023]
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.
[0024]
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.
[0025]
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.
[0026]
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.
[0027]
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.
[0028]
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.
[0029]
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).
[0030]
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).
[0031]
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. 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. .
[0032]
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.
[0033]
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 section 64 that reversely feeds the sheet, a switching section 65 that selectively switches the sheet S discharge paths 641a and 641b in the sheet discharge section 64, and a sheet S conveyed from the sheet discharge section 64 again. And a paper refeeding unit 66 that feeds the paper 63.
[0034]
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.
[0035]
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.
[0036]
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.
[0037]
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 R 2 and has undergone the fixing process in the fixing unit 5 is fed to the paper discharge unit 64. The paper discharge unit 64 has two paper discharge paths 641a and 641b. One paper discharge path (second paper discharge path) 641a extends from the fixing unit 5 to the standard paper discharge tray 11, and the other paper discharge path. A paper path (first paper discharge path) 641b extends between the paper refeed unit 66 and the multi-bin unit substantially parallel to the paper discharge path 641a. Three drive rollers 642c to 644c are disposed along the paper discharge paths 641a and 641b at a predetermined interval and sandwiched between the paper discharge paths 641a and 641b. Corresponding to the driving rollers 642c to 644c, driven rollers 642a to 644a are disposed on the paper discharge path 641a side, and driven rollers 642b to 644b are disposed on the paper discharge path 641b side. .
[0038]
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 two paper discharge paths 641a. On the other hand, a switchback exit roller pair 646 is configured by the driving roller 642c and the driven roller 642b, and functions as an unloading unit that conveys the sheet conveyed along the first sheet discharge path 641b from the sheet discharge unit 64, which will be described later. In this way, the sheet S temporarily waiting in the second paper discharge path 641a or the first paper discharge path 641b is conveyed toward the refeed unit 66.
[0039]
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. Then, the sheet S can be conveyed in the opposite direction in the both paper discharge paths 641a and 641b according to the rotation direction of the drive 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 along the second paper discharge path 641a, and at the same time, the first discharge. The sheet S can be conveyed to the refeed unit 66 side along the paper path 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.
[0040]
As described above, in this embodiment, the sheet S is moved along the second discharge path 641a by the driving roller 643c and the driven roller 643a, and by the driving roller 644c and the driven roller 644a. Second conveying means is configured to convey the sheet S toward the second sheet discharge position) and reversely convey the sheet S toward the refeed unit 66. The drive roller 643c and the driven roller 643b, and the drive roller 644c and the driven roller 644b convey the sheet S along the first paper discharge path 641b toward the multi-bin unit (first paper discharge position). In addition, a first transport unit that reversely transports the sheet S toward the refeed unit 66 is configured. 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.
[0041]
In this embodiment, each of the first and second paper discharge roller pairs 643 and 644 simultaneously carries the sheet S to the paper discharge side and the conveyance to the switching unit 65 in the paper discharge paths 641a and 641b. It functions as a carry-in / out means, and the apparatus configuration is simpler and easier to control than when the first and second transport means are provided. In this embodiment, two carry-in / out means, that is, the first and second paper discharge roller pairs 643 and 644 are provided. However, the number of carry-in / out means is arbitrary and depends on the maximum sheet size to be conveyed. May be set as appropriate.
[0042]
By the way, a third paper discharge roller pair 647 is arranged in the vicinity of the standard paper discharge tray 11 in the paper discharge path 641a. 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 paper discharge path 641a. The third paper discharge roller pair 647 stacks and discharges the sheet S conveyed along the second paper discharge path 641a to the standard paper 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.
[0043]
On the other hand, in the first paper discharge path 641b, a switching flap 648 is provided at a position immediately above the driven roller 643b constituting the first paper discharge roller pair 643, and the sheet S conveyed along the paper discharge path 641b is discharged. The destination can be switched. That is, when the switching flap 648 is located at the solid line position in the figure, the sheet S is conveyed as it is along the paper discharge path 641b and discharged toward the multi-bin unit, while the switching flap 648 is discharged. When positioned on the path 641b, the sheet S leaves the sheet discharge path 641b and is discharged to the finisher through the opening 14.
[0044]
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, there are two sheet discharge paths 641a, A switching unit 65 that switches between 641b is disposed, 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.
[0045]
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.
[0046]
The first switching flap 651 serves as switching means for guiding the sheet S that has undergone the fixing process and is conveyed by the pair of paper discharge inlet rollers 645 to one of the paper discharge paths 641a and 641b. This is for guiding the sheet S once carried into the paper discharge path 641b to the refeed unit 66. The first switching flap 651 is fixed to a shaft 653b disposed between the paper discharge 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. Therefore, 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 to the standard paper discharge tray 11 side as it is along the second paper discharge path 641a. On the other hand, when the pin 656b moves downward, the first switching flap 651 rotates counterclockwise, and the tip 651b is switched to a position directed to the second driven roller 642a side, and the second discharge inlet roller pair 645 is moved. Then, the sheet S conveyed by is guided to the opening 13 along the other first paper discharge path 641b.
[0047]
The second switching flap 652 is for guiding the sheet once carried into the second paper discharge path 641a to the refeed unit 66, and is disposed outside the guide plate 657 that guides one surface of the first paper discharge path 641b. The shaft 653a is fixed. 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 paper discharge path 641b indicated by a solid line in FIGS. On the other hand, when the pin 656a moves downward, the tip portion 652a rotates clockwise and enters the first paper discharge path 641b, and the sheet once carried into the second paper discharge path 641a is fed to the refeed unit 66. Lead.
[0048]
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.
[0049]
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.
[0050]
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 a plurality of paper discharge 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 sheet discharge paths 641a and 641b, and the sheet S waiting to be conveyed to the sheet discharge paths 641a and 641b is selectively re-feed unit 66. Can be transported. The characteristic operation will be described in detail later while showing a specific image forming sequence.
[0051]
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.
[0052]
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.
[0053]
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 forming unit controller 72 for controlling the operation of the image forming unit 2, and the exposure unit 3. An exposure unit controller 73 that controls the operation, 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 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.
[0054]
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.
[0055]
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 68 a, a clutch driver 763 is provided for the paper discharge side clutch group 68 b provided in the paper discharge unit 64, and a refeed paper provided in the refeed unit 66. The clutch driver 764 is configured to ON / OFF control the side clutch group 68c.
[0056]
Further, as described above, the paper 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.
[0057]
C. Operation of image forming apparatus
Next, the operation of the image forming apparatus configured as described above, particularly the three types of image forming sequences most relevant to the features of the present invention will be described in detail.
[0058]
C-1. First image forming sequence
This first image forming sequence is to form a monochrome image on both sides of an A4 sheet and then discharge it to the standard discharge tray 11 as a discharge destination, and will be described below with reference to FIGS. To do.
[0059]
FIG. 4 is a schematic diagram showing the first embodiment (first image forming sequence) of the image forming method according to the present invention. FIGS. 5 to 7 are diagrams schematically showing the sheet conveyance state at the timings T1, T2, and T3 in FIG. 4, respectively. In FIG. 4 (and FIGS. 8, 10, and 11 described later), the “intermediate transfer belt” column indicates a toner image that is primarily transferred to the intermediate transfer belt 46. In addition, the boundary line in the same column indicates the joint portion of the intermediate transfer belt 46. In this embodiment, the intermediate transfer belt 46 has a toner image corresponding to one sheet at the maximum A3 size or two sheets at the A4 size. The primary transfer is possible. The attributes of the primary transferred toner image are displayed with four alphanumeric characters. Each display content is as follows.
[0060]
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 “parenthesis characters” are also common to the sheet attributes shown in the “gate roller”, “first paper discharge path”, and “second paper discharge path” fields in FIG. It is used as.
[0061]
(a) First, when an image signal is input from the host computer to the control unit 7, an intermediate toner image of an image of the second page (image to be formed on the back side of the first sheet) is formed, and an A4 size sheet is formed. S1 is transported 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]
Note that the intermediate transfer belt 46 according to this embodiment (and later embodiments) can transfer two A4-size intermediate toner images at the same time. In this image sequence, however, the intermediate toner image can be transferred as necessary. The number of simultaneously formed images is switched. Further, the interval of the toner images on the intermediate transfer belt (image carrier) 46 (hereinafter referred to as “image interval”) is adjusted according to the image forming mode.
[0063]
(b) The sheet S1 on which the image of the second page has been formed in this way is conveyed to the second paper discharge path 641a connected to the standard paper discharge tray 11 that has been selected in advance as the paper discharge position.
[0064]
(c) When the sheet S1 is conveyed to the second paper discharge path 641a, the switching flap 652 of the switching unit 65 rotates in the clockwise direction in FIG. 1, and the leading end 652b is directed to the driven roller 642b side. Switch. Then, the rotation directions of the first and second paper discharge roller pairs 643 and 644 are switched, and the sheet S1 is reversely conveyed to the refeed unit 66.
[0065]
In parallel with this, an image of the fourth page (image to be formed on the second back surface) is formed on the back surface of the next sheet S2. That is, an intermediate toner image corresponding to this image is formed on the intermediate transfer belt 46, and in parallel with the intermediate toner image forming process, the next sheet S2 is conveyed from the cassette 61 or the like to the gate roller pair 637 and is put on standby. Keep it. Then, the intermediate toner image is secondarily transferred to the sheet S2 at an appropriate timing and fixed by the fixing unit 5 to form the fourth page image on the back side of the second sheet.
[0066]
(d) A first paper discharge path that connects the sheet S2 on which the image of the fourth page is formed in this way to another multi-bin unit (not shown) different from the standard paper discharge tray 11 that is selected in advance as the paper discharge position. 641b.
[0067]
In parallel with this, an image of the sixth page (image to be formed on the back side of the third sheet) is formed on the back side of the next sheet S3. That is, an intermediate toner image corresponding to this image is formed on the intermediate transfer belt 46 adjacent to the intermediate toner image of the fourth page, and the next sheet S3 is loaded in the cassette 61 in parallel with this intermediate toner image forming process. Etc. to the gate roller pair 637 and wait. Here, in this embodiment, in order to execute the simultaneous loading / unloading processing of the sheets S2 and S3 as will be described later, the fourth page image and the sixth page image are set to a reference image interval (for example, in the case of an A4 monochrome single side). Are formed in parallel on the intermediate transfer belt 46 with an image interval ΔD1 different from the image interval).
[0068]
Then, the intermediate toner image is secondarily transferred to the sheet S3 at an appropriate timing and fixed by the fixing unit 5 to form the image of the sixth page on the back side of the third sheet (timing T1). As shown in FIG. 5, the third sheet S3 thus imaged is separated from the sheet S2 previously conveyed to the first paper discharge path 641b by a sheet conveyance interval ΔSD1 corresponding to the image interval ΔD1. In this state, the paper is conveyed toward the paper discharge unit 64.
[0069]
When the leading edge of the sheet S3 is positioned at the switching unit 65, preparations for performing the simultaneous carry-in / out process are performed as follows. That is, the carry-in of the sheet S2 to the first paper discharge path 641b is completed, and the switching flap 651 of the switching unit 65 is further rotated in the clockwise direction in FIG. 1, and the leading edge 651b is moved to the first driven roller 642b side. Return to the desired position. Then, the rotation directions of the first and second paper discharge roller pairs 643 and 644 are switched, and the reverse conveyance of the sheet S2 to the refeed unit 66 is started. As described above, in this embodiment, the interval between the intermediate toner images on the intermediate transfer belt 46 is adjusted to the image interval ΔD1 in order to secure the time necessary for preparing the simultaneous carry-in / out process.
[0070]
(e) As shown in FIG. 6, the sheet S3 conveyed to the paper discharge unit 54 is conveyed to a second paper discharge path 641a connected to the standard paper discharge tray 11 that is selected in advance as a paper discharge position. At this time, since the paper discharge unit 64 is configured as described in detail above, the sheet S2 is re-feeded on the first paper discharge path 641b at the same time when the sheet S3 is carried in on the second paper discharge path 641a. It is reversed and carried out toward the part 66. As described above, according to this image forming sequence, the two sheets S2 and S3 can be transported simultaneously, the processing time required for image formation can be shortened, and the throughput can be improved.
[0071]
Note that the sheet S1 that has already been transported to the refeed unit 66 in advance is transported to the gate roller pair 637 and stands by as shown in FIG.
[0072]
(f) Next, an intermediate 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. 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 first page image on the first surface side. Thus, image formation on both sides of the sheet S1 is completed.
[0073]
In parallel with this, the sheet S2 conveyed to the re-feeding unit 66 is conveyed to the gate roller pair 637 and waits.
[0074]
(g) The sheet S1 having images formed on both sides in this way is discharged toward a preselected standard discharge tray 11.
[0075]
In parallel with this, an intermediate toner image corresponding to the image of the third page (image to be formed on the surface of the second sheet) is formed on the intermediate transfer belt 46. Then, the intermediate toner image is secondarily transferred to the sheet S2 at an appropriate timing, and is fixed by the fixing unit 5 to form the third page image on the second surface side. Thus, image formation on both sides of the sheet S2 is completed.
[0076]
Note that the third sheet S3 conveyed to the second paper discharge path 641a in the step (e) is reversely conveyed toward the refeed path 664 at an appropriate timing, and further, the gate roller following the sheet S2. Transport to pair 637 and wait.
[0077]
(h) The sheet S2 on which the images are formed on both sides is discharged toward the standard discharge tray 11 following the sheet S1 discharged in advance.
[0078]
In parallel with this, an intermediate toner image corresponding to the image of the fifth page (image to be formed on the surface of the third sheet) is formed on the intermediate transfer belt 46. Then, the intermediate toner image is secondarily transferred to the sheet S3 at an appropriate timing, and is fixed by the fixing unit 5 to form an image of the fifth page on the surface side of the third sheet. Thus, image formation on both sides of the sheet S3 is completed.
[0079]
(i) The sheet S3 having images formed on both sides in this manner is discharged toward the standard discharge tray 11 following the sheet S2 discharged in advance.
[0080]
At the same time, an intermediate toner image corresponding to the image of the eighth page (image to be formed on the back side of the fourth sheet) is formed on the intermediate transfer belt 46, and in parallel with this intermediate toner image forming process, The sheet S4 is conveyed from the cassette 61 or the like to the gate roller pair 637 and is kept waiting. Here, in this embodiment, in order to execute the discharge reversal continuous processing of the sheets S3 and S4 as will be described later, the image interval ΔD2 between the image on the fifth page and the image on the eighth page is different from the reference image interval. They are formed in parallel on the intermediate transfer belt 46 so as to be separated from each other.
[0081]
Then, the intermediate toner image is secondarily transferred to the sheet S4 at an appropriate timing and fixed by the fixing unit 5 to form an image of the eighth page on the back side of the fourth sheet.
[0082]
(j) Then, the sheet S4 on which the image is formed only on one main surface (back surface) is conveyed toward the standard paper discharge tray 11 through the second paper discharge path 641a in advance, as shown in FIG. The sheet S3 is conveyed toward the paper discharge unit 64 while being separated from the sheet S3 by a sheet conveyance interval ΔSD2 corresponding to the image interval ΔD2.
[0083]
Thereafter, when the sheet S4 is completely carried into the second paper discharge path 641, the sheet S3 is released from the nip of the third paper discharge roller pair 647 of the paper discharge unit 64, and the switching flap 652 of the switching unit 65 is illustrated. 1 is rotated clockwise to return its tip 652b to a position oriented toward the first driven roller 642b. Then, the rotation directions of the first and second paper discharge roller pairs 643 and 644 are switched, and the reverse conveyance of the sheet S4 to the refeed unit 66 is started. As described above, in this embodiment, the interval between the intermediate toner images on the intermediate transfer belt 46 is adjusted to the image interval ΔD2 in order to secure the time necessary for executing the paper discharge reversal continuous process.
[0084]
After that, the above steps (c) to (j) are repeated until all the images up to the desired page are formed on the sheet.
[0085]
As described above, in the first image forming sequence, the double-sided mode having the simultaneous carry-in / out process and the paper discharge reversal continuous process is set as the image forming mode, and the intermediate transfer belt to be formed on the continuous sheet according to this mode Since the interval between the intermediate toner images on 46 is adjusted to the image intervals ΔD1 and ΔD2, images can be efficiently formed on both sides of the sheet.
[0086]
C-2. Second image forming sequence
This second image forming sequence is to form a monochrome image on both sides of the A4 sheet and then discharge it to the standard paper discharge tray 11 as a paper discharge destination. In this respect, the second image forming sequence is common to the first image forming sequence. However, this is different from the first image forming sequence in that sequential reversal processing is performed instead of simultaneous carry-in / out processing. Hereinafter, a description will be given with reference to FIGS.
[0087]
FIG. 8 is a schematic diagram showing a second embodiment (second image forming sequence) of the image forming method according to the present invention. FIG. 9 is a diagram schematically illustrating the sheet conveyance status at timing T4 in FIG.
[0088]
(k) First, when an image signal is input to the control unit 7 from the host computer, an intermediate toner image of the second page image (image to be formed on the first back surface) is formed, and an A4 size sheet is formed. S1 is transported 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.
[0089]
(l) The sheet S1 on which the image of the second page is thus formed is conveyed to the second paper discharge path 641a connected to the standard paper discharge tray 11 that has been selected in advance as the paper discharge position.
[0090]
(m) When the sheet S1 is conveyed to the second paper discharge path 641a, the switching flap 652 of the switching unit 65 rotates in the clockwise direction in FIG. 1, and the leading end 652b is directed to the driven roller 642b side. Switch. Then, the rotation directions of the first and second paper discharge roller pairs 643 and 644 are switched, and the sheet S1 is reversely conveyed to the refeed unit 66.
[0091]
In parallel with this, an image of the fourth page (image to be formed on the second back surface) is formed on the back surface of the next sheet S2. That is, an intermediate toner image corresponding to this image is formed on the intermediate transfer belt 46, and in parallel with the intermediate toner image forming process, the next sheet S2 is conveyed from the cassette 61 or the like to the gate roller pair 637 and is put on standby. Keep it. Then, the intermediate toner image is secondarily transferred to the sheet S2 at an appropriate timing and fixed by the fixing unit 5 to form the fourth page image on the back side of the second sheet.
[0092]
(n) The sheet S2 on which the image of the fourth page is thus formed is conveyed to the second paper discharge path 641a. In parallel with this, an image of the sixth page (image to be formed on the back side of the third sheet) is formed on the back side of the next sheet S3. That is, an intermediate toner image corresponding to this image is formed on the intermediate transfer belt 46 adjacent to the intermediate toner image of the fourth page, and the next sheet S3 is loaded in the cassette 61 in parallel with this intermediate toner image forming process. Etc. to the gate roller pair 637 and wait. In this embodiment, as will be described later, in order to execute the sequential inversion processing of the sheets S2 and S3, the image on the fourth page and the image on the sixth page are separated by an image interval ΔD3 different from the reference image interval. Thus, they are formed in parallel on the intermediate transfer belt 46.
[0093]
Then, the intermediate toner image is secondarily transferred to the sheet S3 at an appropriate timing and fixed by the fixing unit 5 to form an image of the sixth page on the back side of the third sheet (timing T4). As shown in FIG. 9, the third sheet S3 thus imaged is separated from the sheet S2 previously conveyed to the second paper discharge path 641a by the sheet conveyance interval ΔSD3 corresponding to the image interval ΔD3. In this state, the paper is conveyed toward the paper discharge unit 64.
[0094]
Note that when the leading edge of the sheet S3 is positioned at the switching portion 65, the reverse conveyance of the sheet S2 is completed as follows. That is, the loading of the sheet S2 into the second paper discharge path 641a is completed, and the switching flap 652 of the switching unit 65 is further rotated in the clockwise direction in FIG. 1, and the leading edge 652b is directed to the driven roller 642b side. Move to. Then, the rotation direction of the first and second paper discharge roller pairs 643 and 644 is switched, and the sheet S2 is reversely conveyed to the refeed unit 66. As described above, in this embodiment, in order to prevent mutual interference between the preceding sheet S2 and the succeeding sheet S3, it is necessary to perform the sequential reversing process, and the sheet S3 is carried into the second sheet discharge path 641b. Prior to this, the interval of the intermediate toner image on the intermediate transfer belt 46 is adjusted to the image interval ΔD3 in order to ensure the reversal conveyance time of the sheet S2.
[0095]
(o) Since the subsequent operation is the same as the first image forming sequence, description of the operation is omitted.
[0096]
As described above, in the second image forming sequence, the duplex mode having the sequential reversing process and the paper discharge reversing continuous process is set as the image forming mode, and the intermediate transfer belt 46 to be formed on the continuous sheet according to this is set. Since the interval between the intermediate toner images is adjusted to the image intervals ΔD2 and ΔD3, images can be efficiently formed on both sides of the sheet.
[0097]
C-3. Third image forming sequence
This third image forming sequence is one in which color images are formed on both main surfaces of the A4 sheet and then discharged onto the standard paper discharge tray 11, and will be described below with reference to FIGS.
[0098]
10 and 11 are schematic views showing a third embodiment (third image forming sequence) of the image forming method according to the present invention.
[0099]
(p) First, when an image signal is input from the host computer to the control unit 7, an electrostatic latent image corresponding to an image on the second page (image to be formed on the back side of the first sheet) is formed on the photosensitive member 21. After the formation, the yellow developing device 23Y 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.
[0100]
(q) 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. Here, in this embodiment, in order to execute the simultaneous loading / unloading processing of the sheets S1 and S2, as will be described later, the second page image and the fourth page image are set to a reference image interval (for example, in the case of an A4 monochrome single side). Are formed in parallel on the intermediate transfer belt 46 with an image interval ΔD1 different from the image interval).
[0101]
(r) 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.
[0102]
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.
[0103]
(s) The sheet S1 on which the image of the second page is thus formed is conveyed to the first paper discharge path 641b connected to the multi-bin unit.
[0104]
In parallel with this, an image of the fourth page (image to be formed on the second back surface) 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. The second sheet S2 thus image-formed is directed toward the paper discharge unit 64 in a state where it is separated from the sheet S1 previously conveyed to the first paper discharge path 641b by the sheet conveyance interval ΔSD1 corresponding to the image interval ΔD1. Are transported.
[0105]
When the leading edge of the sheet S2 is positioned at the switching unit 65, preparations for performing the simultaneous carry-in / out process are performed as follows. That is, the carry-in of the sheet S1 to the first paper discharge path 641b is completed, and the switching flap 651 of the switching unit 65 is further rotated in the clockwise direction in FIG. 1, so that the leading edge 651b is moved to the first driven roller 642b side. Return to the desired position. Then, the rotation directions of the first and second paper discharge roller pairs 643 and 644 are switched, and the reverse conveyance of the sheet S1 to the refeed unit 66 is started. As described above, in this embodiment, the interval between the intermediate toner images on the intermediate transfer belt 46 is adjusted to the image interval ΔD1 in order to secure the time necessary for preparing the simultaneous carry-in / out process.
[0106]
(t) The sheet S2 transported to the paper discharge unit 64 is transported to the second paper discharge path 641a connected to the standard paper discharge tray 11 selected in advance as the paper discharge position. 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 paper discharge path 641b simultaneously with the conveyance of the sheet S2 on the second paper discharge path 641a. It is conveyed reversely toward the part 66. As described above, according to this image forming sequence, similarly to the first image forming sequence, the two sheets S1 and S2 are simultaneously conveyed, thereby improving the processing capability per unit time, that is, the throughput. Can be made.
[0107]
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.
[0108]
(u) Similarly, the yellow toner image of the image of the third page (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.
[0109]
(v) Further, a color toner image is formed on the intermediate transfer belt 46 by superimposing a cyan toner image, a magenta toner image and a black toner image on each toner image.
[0110]
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.
[0111]
Note that the second sheet S2 conveyed to the second paper discharge path 641a in the step (t) is reversely conveyed toward the refeed unit 66 at an appropriate timing, and further, the gate roller following the sheet S1. Transport to pair 637 and wait.
[0112]
(w) 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 applied to the sheet S2. Secondary transfer is performed, and fixing is performed by the fixing unit 5 to form an image of the third page on the surface side of the second sheet.
[0113]
(x) The sheet S2 having images formed on both sides in this way is discharged toward the standard discharge tray 11 following the sheet S1 discharged in advance.
[0114]
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.
[0115]
After that, the above steps (q) to (x) are repeated until all the images up to the desired page are formed on the sheet.
[0116]
As described above, according to the third image forming sequence, the double-sided mode having the simultaneous carry-in / out process is set as the image forming mode, and the intermediate on the intermediate transfer belt 46 to be formed on the continuous sheet according to this is set. Since the interval between the toner images is adjusted to the image interval ΔD1, images can be efficiently formed on both sides of the sheet.
[0117]
D. Other
The present invention is not limited to the above-described embodiment, and various modifications other than those described above can be made without departing from the spirit of the present invention. For example, the first image forming sequence is not applicable only to the image forming apparatus shown in FIG. 1, and two sheet discharge paths are provided, and a sheet can be switched back in at least one sheet discharge path. The present invention can also be applied to an image forming apparatus having a configuration.
[0118]
In the above embodiment, the two paper discharge paths 641a and 641b are both functioned as the reverse path, but the present invention can also be applied to an image forming apparatus using only one of the reverse paths. That is, even in this type of image forming apparatus, the paper discharge reversal continuous process and the sequential reversal process can be performed, and an efficient image formation is performed by adjusting the image intervals ΔD2 and ΔD3 on the intermediate transfer belt 46. be able to.
[0119]
In the above-described embodiment, the image interval on the intermediate transfer belt 46 is adjusted. However, the sheet conveyance speed in the sheet feeding unit 63 and the sheet discharge unit 64 is variable, and the sheet conveyance speed is controlled. Thus, the sheet interval may be adjusted according to the image forming mode. That is, the sheet conveyance intervals may be controlled to be the intervals ΔSD1, ΔSD2, and ΔSD3 in accordance with the image forming mode in the paper feed path from the secondary transfer region R2 to the paper discharge unit 64. Further, the control based on the sheet conveyance interval and the control based on the image interval may be combined.
[0120]
Further, although the intermediate transfer belt 46 is used as an image carrier, the present invention can also be applied to an image forming apparatus using an intermediate transfer drum. The present invention can also be applied to an image forming apparatus that directly transfers an image (toner image) on a photoreceptor to a sheet. In this case, the photoconductor corresponds to the image carrier of the present invention, and efficient image formation can be performed by adjusting the image interval on the photoconductor.
[0121]
Further, the present invention can be applied to an image forming apparatus that mounts a sheet on a transfer roller and forms an image on the sheet. That is, efficient image formation can be performed by adjusting the interval (corresponding to the “conveyance interval” of the present invention) between the sheets mounted on the transfer roller according to the image forming mode.
[0122]
Furthermore, in the above embodiment, the image forming apparatus is capable of forming a color image using four color toners, but the application target of the present invention is not limited to this, and forms only a monochrome image. Of course, the present invention can also be applied to an image forming apparatus. The image forming apparatus according to the above embodiment is a printer that forms an image given from an external device such as a host computer via a communication interface 77 on a sheet such as copy paper, transfer paper, paper, and an OHP transparent sheet. However, the present invention can be applied to all image forming apparatuses such as copying machines and facsimile machines. Further, the image forming method of the image forming apparatus according to the present invention is not limited to the electrophotographic method, and includes an ink jet method and a thermal transfer method.
[0123]
【The invention's effect】
As described above, according to the present invention, (1) the interval between the images carried on the image carrier in accordance with the image forming mode, and (2) the sheet in the sheet conveyance path between the image forming means and the paper discharge means. Since at least one of the conveyance intervals is adjusted, it is possible to improve the efficiency of image formation.
[Brief description of the drawings]
FIG. 1 is a diagram illustrating an image forming apparatus including an embodiment of a paper discharge device according to the present invention.
2 is an enlarged perspective view showing a switching unit in FIG. 1; FIG.
3 is a block diagram showing a schematic configuration of a control unit that controls the image forming apparatus of FIG. 1; FIG.
FIG. 4 is a schematic diagram showing a first embodiment (first image forming sequence) of an image forming method according to the present invention.
FIG. 5 is a diagram schematically illustrating a sheet conveyance state at a timing T1 in FIG.
6 is a diagram schematically illustrating a sheet conveyance state at a timing T2 in FIG.
7 is a diagram schematically illustrating a sheet conveyance state at a timing T3 in FIG.
FIG. 8 is a schematic diagram showing a second embodiment (second image forming sequence) of the image forming method according to the present invention.
FIG. 9 is a diagram schematically illustrating a sheet conveyance state at a timing T4 in FIG.
FIG. 10 is a schematic diagram showing a third embodiment (third image forming sequence) of the image forming method according to the invention.
FIG. 11 is a schematic diagram showing a third embodiment (third image forming sequence) of the image forming method according to the invention.
[Explanation of symbols]
2. Image forming unit (image forming means)
3. Exposure unit (image forming means)
4. Transfer unit (image forming means, transfer unit)
5. Fixing unit (image forming means)
7. Control unit (control means)
21 ... Photoconductor
46. Intermediate transfer belt (image carrier)
63: Paper feeding unit
64: Paper discharge section
66 ... Re-feed section
71: Control unit (control means)
641a, 641b ... paper discharge path
711 ... CPU (control means)
ΔD1, ΔD2, ΔD3 ... Image interval
ΔSD1, ΔSD2, ΔSD3 ... Sheet conveyance interval

Claims (3)

An image forming unit that forms an image on the sheet, a sheet feeding unit that feeds the sheet to the image forming unit, and a sheet on which the image is formed by the image forming unit are different from each other in first and second sheet discharge paths. A sheet discharge unit configured to discharge the sheet through one of the two sheet discharge paths and to allow the sheet to be reversed and conveyed, and the sheet reversed and conveyed from the sheet discharge unit to be reversed. In an image forming apparatus comprising a refeed unit for refeeding a paper unit and a control unit for controlling each part of the apparatus,
The image forming unit includes an image carrier that carries an image, and a transfer unit that transfers an image on the image carrier to a sheet,
The paper discharge means is configured to execute a simultaneous carry-in / out process of carrying the second sheet following the first sheet into the second paper discharge path at the same time as the first sheet is reversed and conveyed through the first paper discharge path. In addition, while performing sheet discharge in one of the first and second discharge paths, only reverse conveyance can be performed on the other, and
The control means can adjust the interval between images carried on the image carrier according to an image forming mode,
As the image forming mode, a discharge reversing continuous process is performed in which the first sheet is discharged via the first discharge path, and then the second sheet following the first sheet is reversely conveyed by the first discharge path. When the duplex mode is set,
The control means changes an interval on the image carrier between an image to be transferred to the first sheet and an image to be transferred to the second sheet to an image interval corresponding to the paper discharge reversal continuous process. An image forming apparatus.   The image forming apparatus according to claim 1, wherein the control unit adjusts a sheet conveyance interval in a sheet conveyance path between the image forming unit and the paper discharge unit in addition to the image interval according to an image forming mode. An image forming unit that forms an image on the sheet, a sheet feeding unit that feeds the sheet to the image forming unit, and a sheet on which the image is formed by the image forming unit are different from each other in first and second sheet discharge paths. A sheet discharge unit configured to discharge the sheet through one of the two sheet discharge paths and to allow the sheet to be reversed and conveyed, and the sheet reversed and conveyed from the sheet discharge unit to be reversed. In an image forming apparatus comprising a refeed unit for refeeding a paper unit and a control unit for controlling each part of the apparatus,
The paper discharge means is configured to execute a simultaneous carry-in / out process of carrying the second sheet following the first sheet into the second paper discharge path at the same time as the first sheet is reversed and conveyed through the first paper discharge path. In addition, while performing sheet discharge in one of the first and second discharge paths, only reverse conveyance can be performed on the other, and
The control unit can adjust a sheet conveyance interval in a sheet conveyance path between the image forming unit and the paper discharge unit according to an image forming mode,
As the image forming mode, a discharge reversing continuous process is performed in which the first sheet is discharged via the first discharge path, and then the second sheet following the first sheet is reversely conveyed by the first discharge path. When the duplex mode is set,
The image forming apparatus, wherein the control unit adjusts a conveyance interval between the first sheet and the second sheet in the sheet conveyance path to a conveyance interval corresponding to the paper discharge reversal continuous process.

Images