JP2000351534A - Image formation device and image formation method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image formation device and an image formation method capable of forming images on both faces of a sheet with high throughput. SOLUTION: Toner images on two pages, for example, toner images corresponding to images on the second page and the fourth page are formed on an intermediate transfer belt 46, and each toner image is sequentially transferred on rear surfaces of two sheets supplied into a secondary transfer region R2 by a paper supply part 63. Moreover, two sheets on which images are formed on the rear surfaces only in this way are switch-back conveyed by a paper discharge part 64. In parallel to this operation, toner images corresponding to images on the first page and the third page are formed on the intermediate transfer belt 46. The two sheets are conveyed into the secondary transfer region R2 again through a paper resupply part 66 and the paper supply part 63 to transfer images on surfaces of each sheet sequentially.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to an image forming apparatus and an image forming method for sequentially forming images of a plurality of pages on both sides of a sheet.

[0002]

2. Description of the Related Art Many image forming apparatuses, such as printers, facsimile machines and copiers, having a structure capable of forming an image on both sides of a sheet have been conventionally provided. As such an image forming apparatus,
For example, there is an apparatus described in JP-A-10-83104. In this image forming apparatus, a toner image of each color is developed by a developing unit including a black developing device and three color developing devices, and multiple-transferred to an intermediate transfer member. Then, a color image is formed by secondarily transferring the image on the intermediate transfer body to a sheet fed from a feeding unit. Subsequently, the sheet is conveyed to a fixing unit to fix the color image on the sheet, and then discharged to a discharge unit on the upper surface of the apparatus by a discharge roller.

A reversing unit is provided as a mechanism for reversing a sheet in order to form an image on the other side of a sheet having an image fixed on one side. The reversing unit is composed of two pairs of conveying rollers provided along the sheet discharge path and a flapper, and conveys the sheet subjected to the fixing process as described above to the discharge unit side by the pair of conveying rollers. After that, the sheet is reversely conveyed by rotating the pair of conveying rollers in reverse. At the time of the reverse conveyance, the flapper is switched, and is carried into the reverse conveyance path. Thereafter, the sheet is again conveyed to the position of the registration roller pair by the reversing path conveyance roller pair.

In the conventional image forming method, when two toner images can be formed on an intermediate transfer member, images are formed on both sides of a sheet according to an image forming sequence as shown in FIG. are doing. Hereinafter, FIG.
A conventional image forming method will be described with reference to FIG.

[0005] First, the second page (the first back side image)
Is formed, developed with a Y toner image, and primarily transferred to an intermediate transfer member. Thereafter, the primary transfer is performed for the M, C, and K components. When the full-color toner image of the second page is thus formed, the secondary transfer to the first sheet that has been kept on standby by the registration roller pair is started.

[0006] The sheet on which the image of the second page is printed is conveyed to the pair of registration rollers by a reversing unit in a predetermined sequence. At the same time, the second sheet is conveyed from the cassette and conveyed to the position of the registration roller pair prior to the first sheet. During this time, 4
The primary transfer of the Y component toner images of the page (the second image on the back side) and the first page (the first image on the front side) to the intermediate transfer member is performed, and further, the M, C, and K components. Is also performed continuously. Thereafter, first, the image of the fourth page is secondarily transferred to the second sheet previously conveyed from the cassette. This sheet is conveyed to the reversing unit, and conveyed to the pair of registration rollers. As a result, the second sheet is turned upside down, and the third page is secondarily transferred to the front surface at the timing shown in FIG. On the other hand, for the first sheet, after the image of the first page is secondarily transferred, the sheet is conveyed to the discharge unit.

Thereafter, similarly, pages 6 and 3, 8
An image is generated for each of two pages, that is, the first page, the fifth page, and so on. Of the two pages of images, the previously generated image is transferred to a sheet conveyed from a cassette, and the transferred sheet is conveyed to a reversing unit. The image generated later is secondarily transferred to the sheet conveyed from the reversing unit, and the transferred sheet is carried out of the machine. When the table of the last sheet (for example, the ninth page in the case of printing five sheets and ten pages) is printed, the toner corresponding to the image on the ninth page is formed without forming two images. Only an image is formed, the image is secondarily transferred to this sheet, and the sheet is carried out of the apparatus.

[0008]

By the way, in the above conventional example, since a toner image for only two pages can be formed on the intermediate transfer member, an image is formed for every two pages, and the image formation is performed per unit time. The number of pages that can be processed, that is, the throughput is improved. However, since only the image of the second page is formed in the first image formation and only the image of the ninth page is formed in the last image formation, there is still room for improvement in terms of improving the throughput. is there.

In the above image forming apparatus, when an image of a second page, for example, an image of a fourth page and an image of a first page are continuously formed, the image of the fourth page is formed.
After the first sheet is switched back and reversed by the reversing unit, and the sheet is completely conveyed from the reversing unit to the reversing conveyance path, the first sheet on which the image of the first page is formed needs to be discharged to the discharge unit. This is one of the factors that hinder the improvement of the throughput.

The present invention has been made in view of the above problems, and has as its object to provide an image forming apparatus and an image forming method capable of forming an image on both sides of a sheet with high throughput.

[0011]

SUMMARY OF THE INVENTION The present invention relates to an image forming apparatus for sequentially forming images of a plurality of pages on both sides of a sheet. In order to achieve the above object, n pages (n.gtoreq.2) are provided.
Forming a toner image on an intermediate transfer member, sequentially transferring these toner images to n sheets, a sheet feeding means for feeding the sheet to the transfer means, and re-feeding the sheet to the sheet feeding means A sheet re-feeding means, a sheet discharging means for discharging the sheet conveyed from the transfer means to a predetermined discharge position, and reversing and conveying the sheet to the re-feeding means; Control means for controlling the paper means and the paper discharge means, and forms an n-page toner image corresponding to an image to be formed on one main surface of the continuous n sheets on the intermediate transfer body, After sequentially feeding the n sheets to the transfer unit to form an image corresponding to one main surface of each sheet, a toner image corresponding to an image to be formed on the other main surface of the n sheets Is formed on the intermediate transfer member, and
The sheets are reversed and conveyed by a sheet discharging unit toward a sheet re-feeding unit, and further fed to a transfer unit to sequentially form corresponding images on the other main surface of each sheet.

In the present invention, n pages of toner images are formed on the intermediate transfer member, and each toner image is sequentially transferred to one main surface of the n sheets fed to the transfer unit by the sheet feeding unit. . Further, the n sheets on which the image is formed only on one main surface in this way are switchback-conveyed by the paper discharging means and conveyed again to the transfer means. In this transfer means,
A toner image corresponding to an image to be formed on the other main surface of each sheet is formed on the intermediate transfer member, and is sequentially transferred to the other main surface of the n sheets re-fed to the transfer means.
As described above, image formation is continuously performed in units of n pages, thereby improving throughput.

Here, in order to reversely convey the sheet, the sheet discharging means may be constituted as follows. For example, the paper discharge unit is configured to be able to independently guide the sheet on which the image is formed by the transfer unit, and at least one of the first and second paths is connected to a paper discharge position.
Switching means for selectively switching the sheet conveyance path to the first or second path, and conveyance means for bidirectionally conveying the sheet along the longitudinal direction of each of the first and second paths. May be provided. In this case, the first and second paths function as switchback paths.

[0014] A conveying means is provided between the first drive roller disposed at a position sandwiched between the first and second paths and rotatable in the forward and reverse directions, with respect to the first drive roller so as to sandwich the first path. A first driven roller disposed opposite to the first driven roller and a second driven roller disposed opposite to the first driving roller so as to sandwich the second path.
With the configuration including the driven rollers, it is possible to simultaneously carry in and carry out the sheet to the sheet discharging means with a minimum structure, and the throughput is further improved.

[0015] Further, a carrying-in means is arranged on the opposite side of the sheet discharging position with respect to the switching means, and the conveyed sheet is conveyed to the switching means along the second path, while the sheet is conveyed to the switching means. A carrying-out means may be provided on the re-feeding means side, and the sheet conveyed along the first path from the switching means may be conveyed to the re-feeding means. In this case, the sheet is surely sent to the switching means by the carrying-in means, and the sheet conveyed from the switching means to the re-feeding means is surely carried out to the re-feeding means.

Here, by configuring the carrying-in means and the carrying-out means as follows, the number of components can be minimized. That is, a second drive roller rotatable in a predetermined direction is disposed at a position sandwiched between the first and second paths, and the fourth and fourth rollers are sandwiched between the second drive roller and the first and second paths. What is necessary is just to arrange | position the 3rd driven roller facing each. In this case, the second driving roller and the fourth driven roller constitute a carrying-out means, and the second driving roller and the third driven roller constitute a carrying-in means.

Further, the paper discharging means may be constituted as follows. That is, the paper discharge means is connected to the paper discharge position, and a paper discharge path for continuously guiding the n sheets on which images are formed by the transfer means toward the paper discharge position, and a paper discharge path along the paper discharge path. It may be configured by a conveying unit that conveys the sheet toward the sheet discharge position and that reversely conveys the sheet. In this case, the switchback operation of the sheet can be performed in one discharge path.

Further, the image forming method according to the present invention comprises:
An image forming method for sequentially forming images of a plurality of pages on both sides of a sheet, wherein in order to achieve the above object, a toner image corresponding to an image to be formed on one main surface of a continuous n sheets is intermediately transferred. A first step of forming n-sheets on a body and sequentially feeding n sheets to a transfer unit to form an image corresponding to one main surface of each sheet; and, following the first step, n sheets A toner image corresponding to an image to be formed on the other main surface is formed on the intermediate transfer body, and the n sheets on which the image is formed on the one main surface are reversely conveyed and fed again to the transfer means. A second step of sequentially forming corresponding images on the other main surface of each sheet.

According to the present invention, similarly to the invention relating to the above-described image forming apparatus, the n-page toner image formed on the intermediate transfer member is sequentially transferred to one main surface of n sheets, and then transferred to the intermediate transfer member. While forming another n-page toner image, the n sheets are switchback-conveyed by the paper discharging means, and another n-page toner image is sequentially transferred to the other main surface of each sheet. As described above, image formation is performed in units of n pages, and the throughput is improved.

Here, for example, in the first step, when a two-page toner image is formed on the intermediate transfer member by the transfer means, and each toner image is transferred to one main surface of two sheets, respectively, the second step May be executed as follows. That is, the two sheets on each of which the image is formed on one main surface by the transfer unit are respectively different first sheets.
Alternatively, the sheet may be conveyed reversely on the second switchback path.
Further, in the second step, when the preceding sheet carried into the first switchback path is carried out from the first switchback path and at the same time, the subsequent sheet is carried into the second switchback path, the two switchback operations partially overlap. Throughput is further improved.

Further, the switchback operation of n sheets may be configured as follows. That is,
The n sheets on which images have been formed in the first step are sequentially carried into the switchback path, and when all the sheets have been carried in, the sheets are carried out of the switchback path in the reverse order of the carrying order and are again transferred to the transfer means. It may be configured to feed paper.

[0022]

DETAILED DESCRIPTION OF THE INVENTION Overall Configuration of Image Forming Apparatus FIG. 1 is a diagram showing an image forming apparatus provided with one embodiment of a paper discharge device according to the present invention. This image forming apparatus includes yellow (Y), cyan (C), magenta (M),
The apparatus forms a full-color image by superimposing four black (K) toners, or forms a monochrome image using only black (K) toner. 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 form an image forming means for forming an image on a sheet. The case 1 also includes a sheet supply / discharge unit 6 for feeding a sheet to the image forming unit and discharging the image-formed sheet to a predetermined discharge position.

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 unit 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 photoreceptor 21 of the image carrier unit 2 and further primary-transferred to the intermediate transfer belt 46 of the transfer unit 4. And this primary transfer image (toner image)
Is secondarily transferred to the sheet S fed to the transfer position by the sheet supply / discharge unit 6, and then the sheet S is conveyed to the fixing unit 5 and undergoes a fixing process. The sheet S on which the fixing process has been performed is fed to a predetermined sheet discharge position by the sheet discharge unit 64 of the sheet supply and discharge unit 6. Hereinafter, after describing the configuration of each unit of the apparatus, the characteristic parts of the present invention will be described in detail.

B-1. Case 1 The upper surface of the case 1 functions as a standard paper discharge tray 11, and a paper discharge port 12 opened on the upper surface side of the case 1.
The sheet S on which an image has been formed is ejected one by one to the standard ejection tray 11 via the. The image forming apparatus can be equipped with a multi-bin unit (not shown) on the upper side and a finisher (not shown) on the side as optional. Openings 13 are provided on the top and side surfaces of case 1 for transport to the bin unit and finisher.
14 are provided.

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 a photoconductor 2 rotatable in the direction of the arrow in FIG.
1, a charging roller 22 as charging means, developing devices 23Y, 23C, 23M, 23K as developing means, and a cleaning unit 24 are arranged around the photoreceptor 21 in the direction of rotation thereof. ing. The charging roller 22 contacts the outer peripheral surface of the photoconductor 21 to uniformly charge the outer peripheral surface. The laser light L from the exposure unit 3 is directed toward the outer peripheral surface of the photoconductor 21 charged by the charging roller 22. Irradiated. This exposure unit 3
Scans and exposes the laser beam L onto the photosensitive member 21 in accordance with an image signal given from an external device such as a host computer to form an electrostatic latent image on the photosensitive member 21 corresponding to the image signal.

The electrostatic latent image thus formed is developed
Is developed with toner. That is, in this embodiment, as the developing unit 23, a developing unit 23Y for yellow, a developing unit 23C for cyan, a developing unit 23M for magenta, and a developing unit 23K for black are arranged along the photoconductor 21 in this order. Have been. These developing units 23Y and 23
C, 23M, and 23K are configured to be able to freely contact and separate from the photoreceptor 21, respectively.
One of the developing units 3M, 23C, and 23B selectively contacts the photoconductor 21, and applies a toner of a corresponding color to the surface of the photoconductor 21 to make the electrostatic latent image on the photoconductor 21 visible. I do.

The toner image developed by the developing unit 23 is primarily transferred onto the intermediate transfer belt 46 of the transfer unit 4 in a primary transfer region R1 located between the black developing unit 23K and the cleaning unit 24. The transfer unit 4
Will be described later in detail.

The cleaning section 24 is disposed at a position which is advanced from the primary transfer area R1 in the circumferential direction (the direction of the arrow in the figure). This cleaning unit 24
A cleaner blade 241 for scraping off toner remaining on the outer peripheral surface of the photoreceptor 21, and a receiving portion 2 for receiving the toner scraped off by the cleaner blade 241.
42.

B-3. Transfer Unit 4 Next, the configuration of the transfer unit 4 will be described. In this embodiment, the transfer unit 4 includes the drive rollers 41 and 4
Driven rollers 42 to 45 and these rollers 41 to 4
5, and a secondary transfer roller 48 for secondarily transferring the intermediate toner image transferred to the intermediate transfer belt 46 to the sheet S. And
When the color image is transferred to the sheet S, the photosensitive member 21
A color image is formed by superimposing the toner images of each color formed thereon on the intermediate transfer belt 46, and is transferred to the sheet S to obtain a full-color image. When a monochrome image is to be transferred to the sheet S, only a black toner image is formed on the photoreceptor 21 on the intermediate transfer belt 46 and transferred to the sheet S to obtain a monochrome image.

More specifically, the transfer unit 4
Is configured as follows. That is, as shown in the figure, the drive roller 41 is arranged on the cleaning section 24 side (the right hand side in the figure) of the primary transfer area R1. A gear is fixed to an end of the drive roller 41, and the gear is meshed with a drive gear of the photoconductor 21, so that the drive roller 41 is driven to rotate at substantially the same peripheral speed as the photoconductor 21. Then, with the rotation of the drive roller 41, the intermediate transfer belt 46 is circulated and driven at substantially the same peripheral speed as the photosensitive member 21 in the direction of the arrow shown in the figure. In addition, the driving roller 41 includes
An electrode roller 47 is in contact with the outer peripheral side via the intermediate transfer belt 46, and a primary transfer voltage is applied to a conductive layer (described later) of the intermediate transfer belt 46 via the electrode roller 47.

On the other hand, a driven roller 45 is disposed on the developing unit 23 side (the left-hand side in FIG. 1) of the primary transfer area R 1, and applies tension to the intermediate transfer belt 46 with the driving roller 41. As a result, the belt portion located between the rollers 41 and 46 is pressed against the photosensitive member 21 to form a primary transfer portion.

The driven roller 42 among the remaining rollers is a tension roller, and applies tension to the intermediate transfer belt 46 by urging means (not shown). The driven roller 43 is a backup roller that forms the secondary transfer area R2.

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 moved toward and away from the intermediate transfer belt 46 by a contact / separation mechanism (not shown), and is pressed against the intermediate transfer belt 46 during the secondary transfer. Then, in this pressed state, the secondary transfer roller 48
Is applied, and the toner image transferred to the intermediate transfer belt 46 is transferred to the sheet S fed to the secondary transfer region R2 by the paper supply / discharge unit 6 (secondary transfer).

The driven roller 44 is connected to the belt cleaner 4.
9 is a backup roller. The belt cleaner 49 includes a cleaner blade 491 that comes into contact with the intermediate transfer belt 46 to scrape off the toner remaining on the outer peripheral surface thereof, and a receiving portion 492 that receives the toner scraped by the cleaner blade 491. ing. The belt cleaner 49 can be moved toward and away from the intermediate transfer belt 46 by a contact / separation mechanism (not shown).

In this embodiment, the intermediate transfer belt 4
Reference numeral 6 denotes a three-layer structure including an insulating base made of a synthetic resin, a conductive layer formed on the insulating base, and a resistance layer formed on the conductive layer and pressed against the photoconductor 21. It has a structure. At the side edge 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 endlessly formed by connecting both ends of the belt having the three-layer structure, and is controlled so that the toner image is primarily transferred while avoiding the joint. .

B-4. Fixing unit 5 Sheet S on which the toner image has been transferred by transfer unit 4
Is a predetermined feeding path 6 by a feeding / discharging unit 6 described later.
Although the sheet is fed along a dotted line 30 (a two-dot chain line in the figure), a fixing unit 5 is disposed downstream of the secondary transfer region R2. The fixing unit 5 is formed by two fixing units 51 and 52. In the main fixing unit 51, a heat roller 511 disposed above the paper feed path 630,
The heat roller 511 includes a pressing roller 512 pressed from below and fixes the toner image transferred onto the conveyed sheet S onto the sheet S. On the other hand, in the auxiliary fixing section 52, a heat roller 521 disposed below the sheet feeding path,
And a pressure roller 522 pressed from above on the sheet S.
The habit is alleviated. The sheet S on which an image has been formed in this manner is further fed by the sheet feeding / discharging unit 6
The paper is fed to the standard paper discharge tray 11 and the multi-bin unit along 30.

B-5. The paper supply / discharge unit 6 includes a cassette 61 and a manual tray 62 capable of storing a plurality of sheets S in a stacked state, and a sheet S from the cassette 61 or the manual tray 62 along the paper supply path 630. The sheet feeding unit 63 for conveying the sheet S to the next transfer area R2 and the fixing unit 5, and the sheet S on which the image has been fixed is selectively discharged to the standard sheet discharge tray 11, the multi-bin unit or the finisher, or the sheet S conveyed is The paper discharge unit 64 that reversely feeds the paper to the re-feed unit, the switching unit 65 that selectively switches the paper discharge paths 641a and 641b of the sheet S in the paper discharge unit 64, and the sheet S conveyed from the paper discharge unit 64 Sheet S
And a paper re-feeding section 66 for feeding paper to the paper feeding section 63 again.

B-5-1. Paper Feed Unit 63 The paper feed unit 63 is provided with a pickup roller 631 so as to come into contact with the uppermost sheet S of the sheets S stored in the cassette 61 in order to carry out the sheets S from the cassette 61. And this pickup roller 63
A separation roller pair 632 is provided on the outlet side (the right-hand side in FIG. 1) of the cassette 61 in order to surely separate the sheets S carried out from the cassette 61 by one.
Thus, the sheets S stored in the cassette 61 are
The sheets can be taken out toward the secondary transfer region R2 without fail. The configuration for taking out the sheet S is the same on the manual feed tray 62 side. That is, the sheet S stored in the manual feed tray 62
Is the manual feed tray 62 by the pickup roller 633.
Are transported to the secondary transfer region R2 one by one by the separation roller pair 634.

The sheet S sent 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 manual tray 6
The sheet S sent out of the second relay roller pair 636
, And are fed to the gate roller pair 637 via 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. Sheets fed into the case 1 from an additional cassette (not shown) through the opening 15 can be provided in the same manner as described above. Opening 15 to feed to gate roller pair 637
, A first relay roller pair 638 is provided.

As described above, the gate roller pair 63 is removed from the cassette 61, the manual feed tray 62 or the additional cassette.
7 is fed to the gate roller pair 637.
Then, the sheet is fed at a predetermined timing to the secondary transfer region R2, that is, 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, the additional cassette, the secondary transfer area R2, and the paper discharge unit 6
The conveyance path of the sheet S up to 4 is a sheet feeding path 630.

B-5-2. Sheet discharging section 64 The toner image is transferred in the secondary transfer area R2, and the sheet S (image-formed sheet) subjected to the fixing process by the fixing unit 5 is fed to the sheet discharging section 64. This paper discharge unit 64 is 2
One of the paper discharge paths (second paper discharge path; second switchback path) 6
41a extends from the fixing unit 5 to the standard paper discharge tray 11, and the other paper discharge path (first paper discharge path; first switchback path) 641b is substantially parallel to the paper discharge path 641a. It extends between the multi-bin unit. Three drive rollers 642c to 644c are arranged at predetermined intervals along these paper discharge paths 641a and 641b, and are sandwiched between the paper discharge paths 641a and 641b. In addition, each of the drive rollers 642c to 642c
The driven roller 6 corresponding to the paper discharge path 641a
42a to 644a are provided, and driven rollers 642b to 644b are provided, respectively, on the paper discharge path 641b side.

The driving roller 642c provided in the vicinity of the fixing unit 5 and the sheet re-feeding section 66 among the three driving rollers is configured to rotate only in the counterclockwise direction on the sheet of FIG. As described above, the paper discharge unit 64
In the embodiment, the driving roller 642c and the driven roller 642a form a sheet discharge entrance roller pair 645, and the fixed sheet S
Functions as a carrying-in means for drawing the
The sheet S is transferred along the discharge path 641a to the standard discharge tray 1
Conveyed toward 1. On the other hand, the driving roller 642c and the driven roller 642b form a switchback exit roller pair 646.
And functions as an unloading unit that conveys the sheet conveyed along the first paper discharge path 641b from the paper discharge unit 64, and as described later, the second paper discharge path 641a or the first paper discharge path 641b. Sheet S temporarily waited at
Is transported toward the re-feeding section 66.

The remaining drive rollers 643c and 644c are
Unlike the drive roller 642c, the drive roller 642c can be rotated forward and backward, and constitutes the first and second paper discharge roller pairs 643, 644 at the positions where the drive rollers 643c, 644c are disposed. Then, the driving rollers 643c, 644
The sheet S can be conveyed in opposite directions on both the paper discharge paths 641a and 641b in accordance with the rotation direction of c. For example, the driving rollers 643c and 644c in FIG.
Is rotated counterclockwise, 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 sheet S is re-fed along the first paper discharge path 641b. It can be transported to the part 66 side. When the rotation direction of the driving rollers 643c and 644c is reversed, the sheet S is conveyed in a direction opposite to the above.

As described above, in this embodiment,
The driving roller 643c and the driven roller 643a, and the driving roller 644c and the driven roller 644a transfer the sheet S along the second discharge path 641a to the standard discharge tray 111.
Second transport means for transporting the sheet S toward the (second paper discharge position) and reversely transporting the sheet S toward the re-feeding unit 66 are provided. The driving roller 643c and the driven roller 643b, and the driving roller 644c and the driven roller 6
44b, the sheet S is conveyed to the multi-bin unit (first discharge position) along the first discharge path 641b,
Further, a first sheet S that reversely conveys the sheet S toward the re-feeding unit 66
Conveying means are respectively constituted. And these first
The second conveying means constitutes the conveying means according to the present invention.

Further, in this embodiment, the drive rollers are shared in forming the first and second transport means, but dedicated drive rollers may be provided respectively. Further, in this embodiment, the first transporting means is a pair of rollers (643b and 643c; 644b and 644).
c), and the second conveying means is also composed of two pairs of rollers (643a and 643c; 644a and 644c). The number of each pair is arbitrary, and at least one or more sets are provided for each. S may be conveyed.

In this embodiment, the first and second
Each of the discharge roller pairs 643 and 644 is connected to the discharge path 6
It functions as a transport unit that simultaneously transports the sheet S to the paper discharge side and transports the sheet S to the switching unit 65 in the first and second transport units 41a and 641b. The apparatus configuration is simpler than when the first and second transport units are provided. , Control becomes easy. Further, in this embodiment, two transport means, that is, the first and second discharge roller pairs 643 and 644 are provided.
The number of conveying means is arbitrary, and may be appropriately set according to the maximum sheet size to be conveyed.

In the discharge path 641a, the third discharge roller pair 64 is located near the standard discharge tray 11.
7 are provided. This third paper discharge roller pair 647 is
Drive rollers 647c sandwich the paper discharge path 641a.
And a driven roller 647a are rotatably arranged. The third discharge roller pair 647 is connected to the second discharge path 641.
a of the sheet S conveyed along the first paper discharge tray 1
1. Stack and discharge. Although not shown in FIG. 1, a corrugation roller is attached to at least one of the rotation shafts of the driving roller 647c and the driven roller 647a, and a direction substantially orthogonal to the sheet discharging direction is attached to the sheet S. To reduce and remove sheet curl.

On the other hand, in the first paper discharge path 641b, a switching flap 648 is provided immediately above the driven roller 643b constituting the first paper discharge roller pair 643, and the paper discharge path 641b is provided.
The discharge destination of the sheet S conveyed along b can be switched. That is, when the switching flap 648 is located at the solid line position in FIG.
When the switching flap 648 is positioned on the paper discharge path 641b while the sheet S is conveyed as it is along the paper 41b and discharged to the multi-bin unit, the sheet S is discharged to the paper discharge path 641b.
b, and is discharged to the finisher via the opening 14.

Further, between the first discharge roller pair 643 configured as described above, the discharge inlet roller pair 645 and the switchback exit roller pair 646, the sheet S is transported by two discharge paths. A switching unit 65 for switching between the paths 641a and 461b is provided. By controlling the switching unit 65, the transport path of the sheet S is selectively switched. More specifically, the switching unit 65 is configured as follows.

B-5-3. Switching Section 65 FIG. 2 is an enlarged perspective view showing the switching section of FIG. The switching unit 65 includes a first switching flap 651 as shown in FIG.
And a second switching flap 652. And
In order to drive each switching flap 651, 652, respectively,
It is configured as follows.

The first switching flap 651 serves as a switching means for guiding the sheet S, which has been subjected to the fixing process and conveyed by the pair of discharge rollers 645, to one of the discharge paths 641a and 641b. The sheet S once conveyed to the first sheet ejection path 641b is
It is intended to lead to. This first switching flap 651
Is fixed to a shaft 653b disposed between the paper ejection 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 a tip of the arm 654b. Therefore, when the pin 656b is in the upwardly moved position, the first switching flap 651 is located 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 directly transferred to the second discharge path 64
It is guided toward the standard paper discharge tray 11 along 1a. On the other hand, when the pin 656b moves down, the first switching flap 65
1 rotates counterclockwise, the leading end 651b is switched to a position to be directed to the second driven roller 642a side, and the sheet S conveyed by the second discharge inlet roller pair 645 is transferred to the other first roller. Opening 1 along discharge path 641b
Guide towards 3.

The second switching flap 652 is for guiding the sheet once conveyed to the second discharge path 641a to the re-feed section 66, and is provided with a guide plate 657 for guiding one surface of the first discharge path 641b. It is fixed to a shaft 653a disposed outside. An arm 654a is fixed to one end of the shaft 653a, and a pin 656a of a solenoid 655a is connected to a tip of the arm 654a. Therefore, when the pin 656a is at the position where the pin 656a is moved upward, the second switching flap 652 is at a position retracted from the first paper discharge path 641b shown by a solid line in FIGS. On the other hand, the pin 65
When 6a moves down, it turns clockwise to move its tip portion 6a.
52a enters the first discharge path 641b, and guides the sheet once conveyed to the second discharge path 641a to the re-feed section 66.

The guide plate 657 has a second switching flap 65.
2 is provided, and when the second switching flap 652 rotates clockwise, the leading end portion 652a enters the notch 657a to allow the drive roller 642c and the driven roller 642b to rotate. Nip part 64
Head to 6b. On the other hand, when the first switching flap 651 rotates counterclockwise, the tip 651b of the first switching flap 651 is notched 657.
a.

The rotation driving mechanism of the switching flap 648 includes first and second switching flaps 651, 65.
2 is the same as that of FIG.

As described above, in this embodiment, the paper discharging device is configured by incorporating the switching unit 65 into the paper discharging unit 64 having the plural paper discharging paths 641a and 641b. According to this paper discharging device, The sheet S on which an image has been formed can be selectively conveyed to one of the two discharge paths 641a and 461b, and the discharge paths 641a and 461b.
The sheet S waiting to be conveyed to the sheet re-feeding unit 66 can be selectively conveyed. The characteristic operation will be described later in detail while showing a specific image forming sequence.

B-5-4. Returning to FIG. 1, the configuration of the re-feeding unit 66 will be described.
The re-feeding section 66 transports the sheet S transported from the switchback exit roller pair (conveying means) 646 to the gate roller pair 637 of the paper feeding section 63 along the re-feeding path 664. It is composed of three pairs of re-feed rollers 661 to 663 arranged along the re-feed path 664. In each of the pair of re-feed rollers 661 to 663, a drive roller is provided below the re-feed path 664, and a driven roller is provided so as to face and contact the drive roller. In this way, the sheet S conveyed from the sheet discharge unit 64 is moved along the re-feed path 664 by the gate roller pair 6.
By returning to 37, the non-image forming surface of the sheet S in the sheet feeding unit 63 faces the intermediate transfer belt 46, and the image can be secondarily transferred to the surface.

B-6. Control Unit 7 FIG. 3 is a block diagram illustrating a schematic configuration of a control unit that controls the image forming apparatus of FIG. This control unit 7
Includes a CPU 711 for performing various arithmetic processes and control commands for controlling the entire apparatus, a RAM 712 for temporarily storing control data, arithmetic results, and the like.
RO for storing arithmetic programs and the like performed by CPU 711
M713. The control unit 71 is connected to an external device such as a host computer via a communication interface 77, and can input image signals and the like 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, so that image data based on the image signal can be stored.

The control unit 71 includes a communication interface 77
Besides, 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,
An exposure unit controller 73 for controlling the operation of the exposure unit 3, a transfer unit controller 74 for controlling the operation of the transfer unit 4, a fixing unit controller 75 for controlling the operation of the fixing unit 5, and controlling the operations of the paper supply / discharge unit 6. It is electrically connected to the paper supply / discharge unit controller 76 and gives a control command to each section of the apparatus to control the entire apparatus. In this embodiment, since the features of the present invention are closely related to the operation of conveying the sheet S, the configuration of the sheet supply / discharge unit controller 76 will be described in further detail.

The paper supply / discharge unit controller 76 includes:
As shown in the figure, a motor driver 761, three clutch drivers 762 to 764, a solenoid driver 76
5 and a sensor group 766 that is disposed in each section of the paper supply / discharge unit 6 and detects the sheet S. Among them, the motor driver 761 is for controlling the driving of a driving motor 67 which is a driving source of the paper supply / discharge unit 6, and the driving force of the driving motor 67 is applied to the paper supply unit 63 and the paper
4 and the sheet S is conveyed to the re-feed section 66 to convey the sheet S.

In the sheet feeding section 63, the sheet discharging section 64, and the sheet re-feeding section 66, the driving force is transmitted to a part of the rollers via a clutch (not shown). 63
The clutch driver 762 controls the paper feed side clutch group 68a provided in the paper discharge unit, the clutch driver 763 controls the paper discharge side clutch group 68b provided in the paper discharge unit 64, and the The clutch driver 764 controls ON / OFF of the paper feed side clutch group 68c, respectively.

Further, in the paper discharge section 64, the three switching flaps 641, 642, 648 are provided as described above, and are rotated by a flap switching solenoid group (solenoids 655a, 655b, etc.). In this embodiment, a solenoid driver 765 is provided to control the flap switching solenoid group.

C. Operation of Image Forming Apparatus Next, the operation of the image forming apparatus configured as described above, particularly, two types of image forming sequences most relevant to the features of the present invention will be described in detail.

C-1. First Image Forming Sequence This first image forming sequence is to form a color image on both main surfaces of an A4 sheet and then discharge the sheet to the standard paper output tray 11. Hereinafter, FIGS. It will be described with reference to FIG.

FIGS. 4 and 5 are schematic views showing a first embodiment (first image forming sequence) of the image forming method according to the present invention. FIG. 6 is a diagram schematically showing the sheet conveyance status at the timing T1 in FIG. In FIGS. 4 and 5 (and FIGS. 7 and 8 described later), the column of “intermediate transfer belt” indicates a toner image primarily transferred to the intermediate transfer belt 46. In addition, the boundary line in the same column indicates a joint portion of the intermediate transfer belt 46. In this embodiment, two toner images of a maximum A4 size can be primarily transferred to the intermediate transfer belt 46. . The attributes of the primary transferred toner image are indicated by four alphanumeric characters. The contents of each display are as follows.

Numerical characters: number of sheets; English characters: F: front surface, B: back surface; parenthesis numbers: page numbers; parenthesis: K: black, Y: yellow, M: magenta, C: cyan; The display contents other than "English characters" are also used in common for the sheet attributes shown in the "gate roller", "first discharge path" and "second discharge path" columns in FIG. ing.

(A-1) First, when an image signal is input from the host computer to the control unit 7, an image of the second page (an image to be formed on the back surface of the first sheet) is formed on the photosensitive member 21.
After the formation of the electrostatic latent image corresponding to the above, the yellow developing unit 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 to the intermediate transfer belt 46.

(A-2) Similarly, the yellow toner image of the image of the fourth page (the image to be formed on the back surface of the second page) is formed side by side with the yellow toner image of the second page.

(B-1) Further, a color intermediate 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.

Along with the formation of the intermediate toner image, A
The four-size sheet S1 is conveyed from the cassette 61 or the like to the gate roller pair 637 and is kept on standby. Then, the intermediate toner image is secondarily transferred to the sheet S1 at an appropriate timing, and is fixed by the fixing unit 5 to form a second page image on the back side of the first sheet.

(B-2) The sheet S1 on which the image of the second page is formed is conveyed to the first sheet discharge path 641b connected to the multi-bin unit 8.

In parallel with this, the image of the fourth page (the 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, after the sheet S1, the next sheet S2 is transferred from the cassette 61 or the like to the gate roller pair 637.
The intermediate toner image on the intermediate transfer belt 46 is secondarily transferred to the sheet S2 at an appropriate timing, and is fixed by the fixing unit 5, and is transferred to the back side of the second sheet.
An image for the page is formed.

(C-1) The sheet S2 on which the image of the fourth page has been formed in this manner is, as shown in FIG. 6, a second paper discharge path 641a which leads to the standard paper discharge tray 11 which is previously selected as a paper discharge position. Transport to At this time, since the sheet discharging unit 64 is configured as described above in detail, the sheet S1 is re-fed on the first sheet discharging path 641b at the same time when the sheet S2 is conveyed on the second sheet discharging path 641a. The sheet is reversely conveyed toward the section 66. As described above, according to the image forming sequence, the two sheets S1 and S2 are simultaneously conveyed, whereby the processing capacity per unit time, that is, the throughput can be improved.

Further, in this way, the two sheets are discharged
4 at the same time (for example,
In the case where the sheets are simultaneously conveyed along one path as described in JP-A-1-118565), there is a problem that the sheets are stained due to the rubbing between the sheets. However, in this image forming apparatus, both sheets are separately discharged. Route 641a,
Since the sheet is conveyed at 641b, the above problem does not occur, and the sheet can be prevented from being stained.

In parallel with the sheet conveyance, a yellow toner image corresponding to the image of the first page (the image to be formed on the first surface) is formed on the intermediate transfer belt 46.

(C-2) Similarly, the yellow toner image of the image of the third page (the 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 being conveyed to the sheet re-feeding section 66 is conveyed toward the gate roller pair 637 and is made to stand by.

(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.

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 an image of the first page on the front side of the first sheet. Thus, the image formation on both sides of the sheet S1 is completed.

In step (c-1), the second discharge path 641a
The second sheet S2 conveyed to the re-feeding section 66 at an appropriate timing is conveyed reversely, and further conveyed to the gate roller pair 637 following the sheet S1 and is put on standby.

(D-2) The sheet S 1 on which images are formed on both sides is discharged toward the standard paper discharge tray 11, and the intermediate toner formed on the intermediate transfer belt 46 in parallel with the discharge. The image is secondarily transferred to the sheet S2 and fixed by the fixing unit 5 to form a third page image on the front side of the second sheet.

(E-1) The sheet S2 on which images are formed on both sides is discharged toward the standard discharge tray 11 following the previously discharged sheet S1.

At the same time, a yellow toner image corresponding to the image of the sixth page (the image to be formed on the back surface of the third sheet) is formed on the intermediate transfer belt 46.

Thereafter, the above steps (a-t) are repeated until all images up to the desired page are formed on the sheet.
2) to (e-1) are repeated.

As described above, in the first image forming sequence, image formation is continuously performed in units of two pages, and the image is formed on more sheets per unit time than in the conventional example. And the throughput can be improved.

When two pages of images on the intermediate transfer body are successively formed on two sheets in succession, in the conventional example, the preceding sheet is switchback-reversed by the reversing unit, and the reversing unit is moved to the reversing conveyance path. While the subsequent sheet cannot be conveyed until the sheet is completely loaded, in this embodiment, two sheets can be conveyed simultaneously as described above, which is advantageous in improving the throughput. It is.

C-2. Second Image Forming Sequence This second image forming sequence is for forming a color image on both main surfaces of an A4 sheet and then discharging the same to the standard paper output tray 11. Hereinafter, FIGS. It will be described with reference to FIG.

FIGS. 7 and 8 are schematic views showing a second embodiment (second image forming sequence) of the image forming method according to the present invention. 9 and FIG.
FIG. 8 is a diagram schematically illustrating a sheet conveyance state at timings T2 and T3 in FIG. 7.

(F-1) First, when an image signal is input from the host computer to the control unit 7, an image of the fourth page (an image to be formed on the back surface of the second sheet) is formed on the photosensitive member 21.
After the formation of the electrostatic latent image corresponding to the above, the yellow developing unit 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 to the intermediate transfer belt 46.

(F-2) Similarly, the yellow toner image of the image of the second page (the image to be formed on the back of the first sheet) is formed side by side with the yellow toner image of the fourth page.

(G-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.

Along with the formation of the intermediate toner image, A
The four-size sheet S2 is conveyed from the cassette 61 or the like to the gate roller pair 637 and is kept on standby. Then, the intermediate toner image is secondarily transferred onto the sheet S2 at an appropriate timing, and is fixed by the fixing unit 5 to form the image of the fourth page on the back side of the second sheet.

(G-2) The sheet S2 on which the image of the fourth page is formed is conveyed to the second paper discharge path 641a connected to the standard paper discharge tray 11.

In parallel with this, the image of the second page (the image to be formed on the back of the first sheet) is formed on the back of the next sheet S1. That is, after the sheet S2, the next sheet S1 is transferred from the cassette 61 or the like to the gate roller pair 637.
The intermediate toner image on the intermediate transfer belt 46 is secondarily transferred to the sheet S1 at an appropriate timing, and is fixed by the fixing unit 5 so that the intermediate toner image is fixed on the back side of the first sheet.
An image for the page is formed.

(H-1) The sheet S1 on which the image of the second page is formed is conveyed to the second sheet discharge path 641a following the preceding sheet S2, as shown in FIG. When the two sheets S2 and S1 are completely conveyed into the second discharge path 641a, the switching flap 6 of the switching section 65
52 rotates clockwise in FIG. 1 and FIG. 9, and the leading end 652b is switched to a position directed toward the first driven roller 642b. Then, the rotation direction of the first and second paper discharge roller pairs 643, 644 is switched, and the sheet S
1, S2 are sequentially reversed and conveyed to the re-feeding section 66 in the reverse order of the loading order.

In parallel with the sheet conveyance, a yellow toner image corresponding to the image of the first page (the image to be formed on the surface of the first sheet) is formed on the intermediate transfer belt 46.

(H-2) Similarly, the yellow toner image of the image of the third page (the 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 being conveyed to the sheet re-feeding section 66 is conveyed toward the gate roller pair 637 and is made to stand by.

(I-1) Further, a color intermediate 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.

Then, the intermediate toner image thus formed is secondarily transferred to the sheet S1 at an appropriate timing and fixed by the fixing unit 5 to form an image of the first page on the front side of the first sheet. Thus, the image formation on both sides of the sheet S1 is completed.

The sheet S2 conveyed to the sheet re-feeding section 66 following the sheet S1 in the step (h-1) is conveyed to the gate roller pair 637 after the sheet S1 at an appropriate timing and is made to stand by. .

(I-2) The sheet S1 on which images are formed on both sides in this way is discharged toward the standard paper discharge tray 11, and in parallel therewith, the intermediate toner formed on the intermediate transfer belt 46 is discharged. The image is secondarily transferred to the sheet S2 and fixed by the fixing unit 5 to form a third page image on the front side of the second sheet.

(J-1) The sheet S2 on which images are formed on both sides is discharged toward the standard discharge tray 11 following the previously discharged sheet S1.

At the same time, a yellow toner image corresponding to the image of the eighth page (the image to be formed on the back surface of the fourth sheet) is formed on the intermediate transfer belt 46.

Thereafter, the above steps (f-f) are repeated until all images up to the desired page are formed on the sheet.
2) to (j-1) are repeated.

As described above, also in the second image forming sequence, image formation is continuously performed in units of two pages, similarly to the first image forming sequence.
Images can be formed on more sheets per unit time than in the conventional example, and the throughput can be improved.

Further, when two pages of images on the intermediate transfer member are successively formed on two sheets in succession, in the conventional example, the preceding sheet is switchback-reversed by the reversing unit, and the reversing unit is moved to the reversing conveyance path. While the succeeding sheet cannot be conveyed until after the sheet is completely loaded, in the present embodiment, after the preceding sheet is loaded into the paper discharge path 641a, the subsequent sheet is The sheet can be immediately and continuously loaded into the sheet discharge path 641a, which is advantageous in improving the throughput.

D. Others The present invention is not limited to the above embodiments,
Various changes other than those described above can be made without departing from the gist of the invention. For example, the first
The image forming sequence of (1) is not only applicable to the image forming apparatus shown in FIG. For example, JP-A-11-3
The present invention is also applicable to the image forming apparatuses described in JP-A-5209 and JP-A-11-35210.

Further, the second image forming sequence is not necessarily applicable only to the image forming apparatus shown in FIG. That is, in this image forming sequence, 1
The switchback operation and the paper discharge operation are performed in one paper discharge path 641a, and the paper discharge path 641b is not used at all. Therefore, an image forming apparatus having only one sheet discharge path, for example, a conventional example (Japanese Patent Laid-Open No. 10-83104)
The second image forming sequence can also be applied to the apparatus described in Japanese Patent Application Laid-Open Publication No. H10-175,036.

In applying the second image forming sequence to the image forming apparatus shown in FIG.
1b, the switchback operation may be performed, and the paper discharge operation may be performed in the second paper discharge path 641a. When a sheet having images formed on both main surfaces is discharged to the multi-bin unit, a switchback operation and a discharge operation may be performed in the first discharge path 641b, or a second operation may be performed. The switchback operation may be performed in the first paper discharge path 641a, while the paper discharge operation may be performed in the first paper discharge path 641b.

In the above embodiment, a toner image of two pages of the A4 sheet is formed on the intermediate transfer belt 46,
These images are successively and sequentially transferred to two sheets to form an image in units of two pages. However, it is necessary to form an n-page (n ≧ 2) toner image on the intermediate transfer belt 46. In this case, n sheets can be sequentially fed to the secondary transfer area R2 to perform image formation in units of n pages.

In the above description, the case where an image is formed in units of n pages in an image forming apparatus having one or two paper discharge paths has been described. However, the number of paper discharge paths is limited to one or two. However, three or more may be provided.

In the above embodiment, the intermediate transfer belt 46 is used as the intermediate transfer member. However, it is understood that the present invention can be applied to an image forming apparatus using an intermediate transfer drum as in the conventional example. Not even.

Further, in the above, in order to explain the features of the present invention, the image forming sequence for forming a color image on both sides of the sheet S has been described in detail as an embodiment. The present invention is not limited to the double-sided mode, and can be applied to a monochrome double-sided mode.

[0112]

As described above, according to the image forming apparatus and the image forming method of the present invention, as described above, an image is continuously formed on a sheet in units of n pages (n ≧ 2). With such a configuration, images can be formed on both sides of the sheet with excellent throughput.

Further, when two sheets having an image formed on one main surface thereof by the transfer means are reversely conveyed through different first and second switchback paths, the preceding sheet carried into the first switchback path is replaced with the first sheet. By configuring so that the subsequent sheet is carried in to the second switchback path at the same time as the sheet is carried out from one switchback path, the two switchback operations partially overlap to further improve the throughput.

Further, n sheets on which an image has been formed on one main surface by the transfer means are sequentially and continuously carried into the switchback path, and when all the sheets have been carried in, the order is reversed. Even in the case where the sheet is carried out from the switchback path and fed to the transfer unit again, the subsequent sheet can be carried into the switchback path without waiting for the sheet to be carried out from the switchback path. Thus, the throughput can be improved as compared with the conventional example.

[Brief description of the drawings]

FIG. 1 is a diagram showing one embodiment of an image forming apparatus according to the present invention.

FIG. 2 is an enlarged perspective view showing a switching unit of FIG.

FIG. 3 is a block diagram illustrating a schematic configuration of a control unit that controls the image forming apparatus of FIG. 1;

FIG. 4 is a schematic diagram showing a first embodiment (first image forming sequence) of the image forming method according to the present invention.

FIG. 5 is a schematic diagram showing a first embodiment (first image forming sequence) of the image forming method according to the present invention.

FIG. 6 is a diagram schematically illustrating a sheet conveyance state at a timing T1 in FIG. 4;

FIG. 7 is a schematic view showing a second embodiment (second image forming sequence) of the image forming method according to the present invention.

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 T2 in FIG. 7;

FIG. 10 is a diagram schematically illustrating a sheet conveyance state at a timing T3 in FIG. 7;

FIG. 11 is a schematic view illustrating a conventional image forming method.

[Explanation of symbols]

2 Image carrier unit 3 Exposure unit 4 Transfer unit 5 Fixing unit 6 Paper supply / discharge unit 7 Control unit 11 Standard paper discharge tray (paper discharge position) 63 Paper supply unit (paper supply means) 64 ... Paper discharge section (paper discharge means) 65... Switching section (paper discharge means) 66... Re-feed section (re-feed means) 71... Control section 630. The second switchback path) 641b: paper discharge path (first paper discharge path; first switchback path) 643, 644: paper discharge roller pair (conveying means) 642c to 644c: drive rollers 643a, 644a (second) ) Driven rollers 643b, 644b (first) driven rollers 645: paper discharge inlet roller pair (conveying means) 646: switchback outlet roller pair (conveying means) 664: sheet re-feeding path S, S1 to S4: sheets

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) G03G 15/16 G03G 15/16 3F100 21/00 370 21/00 370 F term (Reference) 2H027 ED17 ED19 ED24 EF09 2H028 BA05 BA09 BB02 2H032 BA09 BA18 BA23 CA12 3F053 EA03 EB04 EC02 EC06 ED03 ED17 LA03 LA04 LB03 3F054 AA01 AC02 BJ04 CA35 DA02 DA14 3F100 AA02 BA02 BA17 EA03 EA10 EA13 EA15

Claims (10)

[Claims] 1. An image forming apparatus for sequentially forming a plurality of pages of images on both sides of a sheet, wherein an n-page (n ≧ 2) toner image is formed on an intermediate transfer member,
Transfer means for sequentially transferring these toner images to n sheets, sheet feed means for feeding a sheet to the transfer means, re-feed means for re-feeding the sheet to the sheet feed means, A sheet discharging unit for discharging the sheet conveyed from the unit to a predetermined sheet discharging position and reversely conveying the sheet to the re-feeding unit; the transfer unit, the sheet feeding unit, the re-feeding unit, and A control unit for controlling a paper discharge unit, wherein the control unit forms on the intermediate transfer body an n-page toner image corresponding to an image to be formed on one main surface of the continuous n sheets. After sequentially feeding the n sheets to the transfer means and forming images corresponding to one main surface of each sheet, respectively, the image to be formed on the other main surface of the n sheets is Forming a corresponding toner image on the intermediate transfer member In both cases, the n sheets are reversely conveyed toward the re-feeding unit by the sheet discharging unit, and are further fed to the transfer unit to sequentially form corresponding images on the other main surface of each sheet. And an image forming apparatus. 2. The sheet discharging means is configured to be capable of independently guiding a sheet on which an image has been formed by the transfer means, and at least one of the first and second paths leading to the sheet discharging position. Switching means for selectively switching the sheet conveyance path to the first or second path; and conveying the sheet bidirectionally along the longitudinal direction of each path in each of the first and second paths. The image forming apparatus according to claim 1, further comprising: 3. The first driving roller disposed between the first and second paths, the first driving roller being rotatable in a forward and reverse direction, and the first driving roller being disposed between the first path and the second path. 3. A first driven roller disposed opposite to a roller, and a second driven roller disposed opposite to the first driving roller so as to sandwich the second path.
The image forming apparatus as described in the above. 4. A loading means disposed on the opposite side of the sheet discharging position with respect to the switching means and transporting the conveyed sheet toward the switching means along the second path; And an unloading means disposed on the refeeding means side with respect to the means, and transporting the sheet conveyed along the first path from the switching means to the refeeding means. 4. The image forming apparatus according to 2 or 3. And a second driving roller disposed in a position sandwiched between the first and second paths and rotatable in a predetermined direction, and the second driving roller sandwiching the second path. A third driven roller disposed opposite to the driving roller, and the unloading means opposes the second driving roller and the second driving roller so as to sandwich the first path. The image forming apparatus according to claim 4, further comprising a fourth driven roller disposed. 6. The paper discharge means is connected to the paper discharge position, and a paper discharge path for continuously guiding the n sheets on which images are formed by the transfer means toward the paper discharge position. 2. The image forming apparatus according to claim 1, further comprising a conveying unit configured to convey the sheet toward the discharge position along the discharge path and to reversely convey the sheet. 7. An image forming method for sequentially forming a plurality of pages of images on both sides of a sheet, wherein a toner image corresponding to an image to be formed on one main surface of a continuous n sheets is formed on an intermediate transfer member. A first step of sequentially feeding the n sheets to the transfer unit to form images corresponding to one main surface of each sheet, and following the first step, the n sheets A toner image corresponding to an image to be formed on the other main surface of the intermediate transfer member, and the n sheets on which the image is formed on one main surface are reversely conveyed and supplied again to the transfer means. And a second step of sequentially forming corresponding images on the other main surface of each sheet by paper. 8. In the first step, a two-page toner image is formed on the intermediate transfer member by the transfer unit, and each toner image is transferred onto one main surface of two sheets, respectively. 8. The image forming method according to claim 7, wherein, in the step, the two sheets having the image formed on one main surface by the transfer unit are reversely conveyed through different first and second switchback paths. 9. In the second step, the preceding sheet carried into the first switchback path is carried out from the first switchback path, and at the same time, the subsequent sheet is placed in the second switchback path.
The image forming method according to claim 8, wherein the image is transferred to a switchback path. 10. In the second step, the n sheets on which images are formed in the first step are sequentially loaded into a switchback path, and when all the sheets are loaded, the order reverse to the loading order. 8. The image forming method according to claim 7, wherein the sheet is carried out from the switchback path and fed again to the transfer unit.