JP3671779B2 - Color image forming apparatus and color image forming method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a color image forming apparatus and a color image forming method for sequentially forming color images on both main surfaces of a sheet.
[0002]
[Prior art]
Many image forming apparatuses such as printers, facsimile machines, and copiers are conventionally provided with a configuration capable of forming images on both sides of a sheet. In this type of image forming apparatus, a toner image of each color is developed by a developing unit composed of a black developing unit and three color developing units, and is transferred onto an intermediate transfer member in a multiple transfer manner. Then, the color image on the intermediate transfer member is secondarily transferred to one main surface of the sheet fed by the paper feeding unit, thereby forming a color image on the one main surface. Subsequently, after the sheet is conveyed to the fixing unit and the color image is fixed on the sheet, the single-sided image sheet on which the image is formed only on one main surface is conveyed to the refeeding unit.
[0003]
The refeed unit is provided with a switchback mechanism, and the single-sided image sheet conveyed to the refeed unit as described above is reversed by the switchback mechanism and then refeeded to the sheet feed unit. Is done. Then, after the color image is transferred to the other main surface of the single-sided image sheet as in the case of the one main surface, the sheet is conveyed to the fixing unit and the color image is fixed to the other main surface of the sheet.
[0004]
In this way, a double-sided image sheet having color images formed on both main surfaces is obtained. This double-sided image sheet is sent to a paper discharge unit and finally discharged to a paper discharge tray (discharge position).
[0005]
[Problems to be solved by the invention]
By the way, in the conventional image forming apparatus, in order to improve the throughput, color images of n pages (n ≧ 3) are formed in parallel on the intermediate transfer member, and these color images are respectively transferred to the corresponding sheets. A method has been proposed. However, there has been no room for improvement in terms of throughput improvement because no detailed examination has been made on the order of sheet conveyance and the order of arrangement of color images on the intermediate transfer member. In particular, in an apparatus that reverses a single-sided image sheet using a switchback mechanism, it is necessary to prevent sheet mutual interference at the switchback mechanism, and how to solve this problem is a major issue. ing.
[0006]
The present invention has been made in view of the above problems, and an object thereof is to provide a color image forming apparatus and a color image forming method capable of forming color images on both main surfaces of a sheet with high throughput.
[0007]
[Means for Solving the Problems]
The present invention relates to a color image forming apparatus and a color image forming method for sequentially forming color images on both main surfaces of a sheet, and is configured as follows in order to achieve the above object.
[0008]
The color image forming apparatus according to the present invention includes n image (n ≧ 3) toner images arranged side by side on an intermediate transfer member, and sequentially transferring each toner image onto a corresponding sheet, and the image forming unit A sheet feeding unit that feeds the sheet to the image forming unit, a sheet discharging unit that discharges the sheet conveyed from the image forming unit to a predetermined sheet discharge position, and a sheet conveyed from the image forming unit. And a control unit for controlling the image forming unit, the sheet feeding unit, the sheet discharging unit, and the sheet refeeding unit. The control means includes a total n of at least one first sheet having a color image formed on one main surface and at least one second sheet having no image formed on both main surfaces. While feeding sheets to the image forming means in the following transport order, color images to be transferred to the respective sheets are arranged in an arrangement order corresponding to the transport order and formed on the intermediate transfer member, For each of the first sheets, a color image corresponding to each sheet is transferred to the other principal surface, and then discharged to the discharge position by the discharge unit, and for each of the second sheets, After the color image corresponding to 1 is transferred to one main surface, the re-feeding unit re-feeds the next sheet as the next first sheet. As for the conveyance order, when only one second sheet is included in n sheets, the second sheet is in an arbitrary order, and a plurality of the second sheets are included. In such a case, it is determined that at least one first sheet is interposed between the second sheets.
[0009]
Further, the color image forming method according to the present invention includes at least one first sheet having a color image formed on one main surface and at least one second sheet having no image formed on both main surfaces. A first step of preparing a total of n sheets, and when only one second sheet is included in the n sheets, the second sheets are arranged in an arbitrary order, and a plurality of When the second sheet is included, the n sheets are fed to the transfer position in a transport order in which at least one first sheet is interposed between the second sheets. 2 steps, a color image to be transferred to each of the other main surfaces of the first sheet, and a color image to be transferred to each of the one main surfaces of the second sheet in an arrangement order corresponding to the transport order The first to be formed on the intermediate transfer body side by side While transferring the color image corresponding to the sheet to each sheet fed to the transfer position in the transport order, the first sheet after the transfer is discharged to a predetermined discharge position; The second sheet after transfer includes a fourth step of refeeding toward the transfer position as the next first sheet.
[0010]
In these inventions, a color image corresponding to the other main surface of the first sheet is transferred to the other main surface, and color images are formed on both main surfaces. As a result, a double-sided image sheet is obtained and discharged to a predetermined discharge position. On the other hand, when a color image corresponding to one main surface of the second sheet is transferred to the one main surface, the front and back are reversed and then fed again to the transfer position as the next first sheet. Here, if another sheet is conveyed while the sheet is reversed with respect to one second sheet, the two sheets interfere with each other.
[0011]
Therefore, in the present invention, when a plurality of second sheets are included in n sheets, the sheet conveyance order is set so that at least one or more first sheets are interposed between the second sheets. Is set. Therefore, a time margin is created between the reversing operation of the second sheet and the reversing operation of the next second sheet as much as the first sheet is interposed, and the second sheets are prevented from interfering with each other. .
[0012]
In addition, when only one second sheet is included in n sheets, sheet interference due to sheet reversal does not occur, and therefore the second sheets can be fed in an arbitrary order.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 is a diagram showing an embodiment of an image forming apparatus according to the present invention. This image forming apparatus is an apparatus that forms a full color image by superposing four color toners of yellow (Y), cyan (C), magenta (M), and black (K), and is supplied from an external device such as a host computer. When an image signal is supplied to the control unit 1 (FIG. 2), each part of the engine unit E is controlled in accordance with a command from the control unit 1 to convert the image signal to the sheet S such as transfer paper, copy paper, or OHP sheet. A corresponding image is formed.
[0014]
In the engine unit E, a toner image can be formed on the photoconductor 21 of the image carrier unit 2. That is, the image carrier unit 2 includes a photosensitive member 21 that can rotate in the direction of the arrow in FIG. 1, and further, a charging roller 22 as a charging unit and a developing unit around the photosensitive member 21 along the rotating direction. Developing units 23Y, 23C, 23M, and 23K, and a photoreceptor cleaner blade 24 are disposed.
[0015]
In this apparatus, the charging roller 22 contacts the outer peripheral surface of the photoconductor 21 to uniformly charge the outer peripheral surface, and then the laser light L is emitted from the exposure unit 3 toward the outer peripheral surface of the photoconductor 21. As shown in the figure, the exposure unit 3 includes a light emitting element 31 such as a semiconductor laser that is modulated and driven in accordance with an image signal. The laser light L from the light emitting element 31 is rotationally driven by a high speed motor 32. Is incident on the polygon mirror 33. The laser beam L reflected by the polygon mirror 33 scans the photoconductor 21 via the lens 34 and the mirror 35 in the main scanning direction (direction perpendicular to the paper surface of the figure) and corresponds to the image signal. An electrostatic latent image is formed. Reference numeral 36 denotes a horizontal synchronization reading sensor for obtaining a synchronization signal in the main scanning direction, that is, a horizontal synchronization signal HSYNC.
[0016]
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 photosensitive member 21, and according to instructions from the control unit, the four developing units 23Y, 23M, 23C, and 23B. One of the developing devices selectively contacts the photoconductor 21 and a high voltage is applied to apply toner of the selected color to the surface of the photoconductor 21 so that an electrostatic latent image on the photoconductor 21 is applied. To manifest.
[0017]
The toner image developed by the developing unit 23 is primarily transferred onto the intermediate transfer belt 41 of the transfer unit 4 in the primary transfer region R1 located between the black developing device 23K and the photoreceptor cleaner blade 24. . A photoreceptor cleaner blade 24 is disposed at a position advanced in the circumferential direction (in the direction of the arrow in FIG. 1) from the primary transfer region R1, and remains on the outer peripheral surface of the photoreceptor 21 after the primary transfer. Scrape off the toner.
[0018]
Next, the configuration of the transfer unit 4 will be described. In this embodiment, the transfer unit 4 includes rollers 42 to 47, an intermediate transfer belt 41 stretched over the rollers 42 to 47, and an intermediate toner image transferred to the intermediate transfer belt 41 on the sheet S. A secondary transfer roller 48 for next transfer, and a photoconductor / belt drive unit (not shown) that drives the photoconductor 21 and the intermediate transfer belt 41 to rotate synchronously are provided. When a color image is transferred onto the sheet S, the color toner images formed on the photosensitive member 21 are superimposed on the intermediate transfer belt 41 to form a color image, and the paper supply / discharge unit 6 supplies the color image. The sheet S is taken out from the cassette 61, the manual feed tray 62, or an additional cassette (not shown) by the paper portion 63 and conveyed to the secondary transfer region R2. Further, a full color image is obtained by secondary transfer of the color image onto the sheet S.
[0019]
Note that toner remaining on the outer peripheral surface of the intermediate transfer belt 41 after the secondary transfer is removed by a cleaner blade 491 provided in the belt cleaner 49. In other words, the belt cleaner 49 is disposed so as to face the roller 46 with the intermediate transfer belt 41 interposed therebetween, and the cleaner blade 491 comes into contact with the intermediate transfer belt 41 at an appropriate timing and remains on the outer peripheral surface thereof. Scrape off the toner.
[0020]
A sensor 40 for detecting the reference position of the intermediate transfer belt 41 is disposed in the vicinity of the roller 43, and obtains a synchronization signal in the sub-scanning direction substantially perpendicular to the main scanning direction, that is, a vertical synchronization signal VSYNC. Functions as a vertical synchronization reading sensor.
[0021]
As described above, in this embodiment, an image in which four color toner images are superimposed by the image carrier unit 2, the exposure unit 3, and the transfer unit 4, that is, a color image is formed and transferred to the sheet S. These components constitute the image forming means of the present invention. Then, the sheet S on which the color image has been transferred by the image forming unit is moved downstream of the secondary transfer region R2 along a predetermined paper feed path (two-dot chain line) by the paper feed unit 63 of the paper feed / discharge unit 6. The toner image on the sheet S which is conveyed to the fixing unit 5 disposed and is conveyed is fixed to the sheet S. Then, the sheet S is further conveyed to the switching unit 65 along the sheet feeding path, and is selectively conveyed to the paper discharge unit 64 or the refeed unit 66 by the switching unit 65.
[0022]
The sheet S conveyed to the paper discharge unit 64 is further conveyed along the paper discharge path 641 and discharged to a standard paper discharge tray (paper discharge position).
[0023]
On the other hand, the sheet S conveyed to the refeed unit 66 is conveyed into the switchback mechanism 662 along the reverse path 661 while being guided by the switching mechanism 660. Then, after the sheet S is switched back in the switchback mechanism 662, the switching mechanism 660 switches the conveyance path of the sheet S to the refeeding path 663, and the sheet S that has been reversed and conveyed from the switchback mechanism 662. Is returned to the gate roller pair 631 along the refeed path 663. In this way, the non-image forming surface (the other main surface) of the sheet S in the paper feeding unit 63 faces the intermediate transfer belt 41, and the image can be secondarily transferred to the surface.
[0024]
FIG. 2 is an electrical configuration diagram of the image forming apparatus shown in FIG. In this image forming apparatus, when an image signal is given to the main controller 11 of the control unit 1 from an external device such as a host computer, the engine controller 12 is configured as shown in FIG. Then, each part of the engine part E is controlled to form an image corresponding to the image signal on the sheet S.
[0025]
The engine controller 12 has a CPU 121, and as an input signal from the engine unit E, a horizontal synchronization signal HSYNC from the horizontal synchronization read sensor 36, a vertical synchronization signal VSYNC from the vertical synchronization read sensor 40, and a fixing unit. The temperature signal indicating the fixing temperature is received from the temperature sensor 51 provided in the circuit 5. Further, based on these input signals and various information, the CPU 121 sends a photoconductor / belt drive unit 41a for rotationally driving the photoconductor 21 and the intermediate transfer belt 41 in synchronization with each other, and a drive command signal for driving control. To the belt drive control circuit 122, and the photoreceptor / belt drive control circuit 122 controls the photoreceptor / belt drive unit 41 a using the DC motor as a drive source to control the rotational speed of the photoreceptor 21 and the conveyance of the intermediate transfer belt 41. The speed V is controlled.
[0026]
In addition to the photoconductor / belt drive control circuit 122, the engine controller 12 further includes a transfer roller separation / contact control circuit 123 and a belt cleaner separation / contact control circuit 124 as dedicated control circuits for controlling the transfer unit 4. I have. The transfer roller separation / contact control circuit 123 controls the secondary transfer roller drive unit 48a based on a command signal from the CPU 121 to bring the secondary transfer roller 48 into contact with the intermediate transfer belt 41 at an appropriate timing. On the other hand, the belt cleaner separation / contact control circuit 124 gives a CB signal to the belt cleaner drive unit 49a based on a command signal from the CPU 121 to control the belt cleaner drive unit 49a, and intermediately transfers the cleaner blade 491 at an appropriate timing. The belt 41 is separated and abutted.
[0027]
Reference numeral 113 in the figure denotes an image memory provided in the main controller 11 for storing an image given from an external device such as a host computer via the interface 112, and reference numeral 125 controls the engine unit E. Is a RAM for temporarily storing control data for the CPU 121 and calculation results in the CPU 121, and a reference numeral 126 is a ROM for storing calculation programs executed by the CPU 121.
[0028]
Next, a double-sided color printing operation of the image forming apparatus configured as described above will be described with reference to FIGS.
[0029]
3 to 5 are schematic diagrams showing the operation of the image forming apparatus shown in FIG. 6 to 9 are diagrams schematically illustrating the sheet conveyance status. 3 to 5, the column “intermediate transfer belt” indicates a toner image that is primarily transferred to the intermediate transfer belt 41. Further, the boundary line in the same column indicates the joint portion of the intermediate transfer belt 41. In this embodiment, the toner image for three pages can be primarily transferred to the intermediate transfer belt 41 in A4 size. . The attributes of the primary transferred toner image are indicated by four alphanumeric characters. The contents of each display are as follows.
[0030]
Number: Sheet number;
English letters: F ... Front side, B ... Back side;
Parentheses: page number;
Parenthesis English letters: K ... Black, Y ... Yellow, M ... Magenta, C ... Cyan;
In the “Gate roller” and “Discharge path” fields in the figure, the sheet number is shown in the upper row and the image forming status is shown in the lower row.
[0031]
(a) First, when an image signal is input from the host computer to the control unit 1, an electrostatic latent image corresponding to an image on the second page (an 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 to the intermediate transfer belt 41 (FIG. 3).
[0032]
Further, after forming an electrostatic latent image corresponding to the image of the fourth page (image to be formed on the back side of the second sheet) separated by one page, the yellow developing unit 23Y is selectively set to the photosensitive member. 21, a yellow toner image is formed on the surface of the photoreceptor 21. Then, the toner image is primarily transferred to the intermediate transfer belt 41. Thus, two yellow toner images are formed side by side on the intermediate transfer belt 41 while being separated by one page.
[0033]
(b) Subsequent to these yellow toner images, a cyan toner image, a magenta toner image, and a black toner image are superimposed on each yellow toner image transferred to the intermediate transfer belt 41 to obtain two color toner images ( A color image) is formed on the intermediate transfer belt 41. Along with the formation of the intermediate toner image, the A4 size sheet S1 on which both main surfaces are not formed is conveyed from the cassette 61 or the like to the gate roller pair 631, and is kept waiting. Then, at an appropriate timing, the leading intermediate toner image (“1-B- (2)” in the figure) is secondarily transferred to the sheet S1 and fixed by the fixing unit 5 to the back side of the first sheet. The second page image is formed. In this way, a sheet (hereinafter referred to as “single-sided image sheet”) S1 having a color image transferred only on the back surface (one main surface) is obtained. This single-sided image sheet corresponds to the “first sheet” of the present invention. Further, a sheet in which an image is not formed on both main surfaces as described above is referred to as “image-free sheet”, and this corresponds to the “second sheet” of the present invention.
[0034]
As is clear from the description here, even if the sheet S1 is the same, the non-image sheet changes to the single-sided image sheet as the printing process proceeds. Therefore, in order to distinguish these clearly, in the following description, for the single-sided image sheet (first sheet), “(1)” is added at the end of the reference sign, while for the non-image sheet (second sheet). Add “(2)” to the end of the code.
[0035]
(c) The single-sided image sheet S1 (1) is conveyed to the switchback mechanism 662 of the refeed unit 66, where it is reversed. Then, in order to transfer the color image of the first page to the front surface (one main surface) of the single-sided image sheet S1 (1), it is transported toward the paper feed unit 63 as the next first sheet, and the next transfer processing is performed. Prepare.
[0036]
Further, in parallel with the reverse conveyance of the single-sided image sheet S1 (1), the A4 size non-image sheet S2 (2) is sent out from the cassette 61 or the like, and the intermediate toner image on the rear end side (shown in FIG. (2-B- (4))) is secondarily transferred to the sheet S2 (2) and fixed by the fixing unit 5 to form an image of the fourth page on the back side of the second sheet. In this way, a single-sided image sheet S2 (1) is obtained.
[0037]
(d) This single-sided image sheet S2 (1) is also conveyed to the switchback mechanism 662 of the refeed unit 66, and is switched back in the same manner as the previous single-sided image sheet S1 (1). In this embodiment, as described above, an interval of one page is provided between the two sheets S1 (1) and S2 (1), so both sheets S1 (1) and S2 ( Sheet transport can be performed without the mutual interference of 1). Then, the sheet S2 (1) is conveyed as the next first sheet toward the sheet feeding unit 63 to prepare for the next transfer process.
[0038]
(e) In parallel with the reverse conveyance of the sheet S2 (1), the following three pages of yellow toner images, that is,
A yellow toner image corresponding to the image on the first page (image to be formed on the surface of the first sheet),
A yellow toner image corresponding to the image on page 6 (image to be formed on the back side of the third sheet),
A yellow toner image corresponding to the image on the third page (image to be formed on the surface of the second sheet),
Are arranged on the intermediate transfer belt 41 in this arrangement order.
[0039]
(f) Subsequent to these yellow toner images, a cyan toner image, a magenta toner image, and a black toner image are superimposed on each yellow toner image transferred to the intermediate transfer belt 41 to obtain two color toner images ( A color image) is formed on the intermediate transfer belt 41. In this way, three color images, namely
-Color image of the first page (corresponding to the “first color image” of the present invention),
-6th page color image (corresponding to "second color image" of the present invention),
-Color image of the third page (corresponding to the “third color image” of the present invention),
Are arranged on the intermediate transfer belt 41 in this arrangement order.
[0040]
Further, as shown in FIG. 4, in parallel with this, the first single-sided image sheet (first first sheet) S1 (1) and the third non-image sheet (second sheet) S3 (2) And the second single-sided image sheet (later first sheet) S2 (1) are sequentially conveyed to the secondary transfer region (transfer position) R2 in this conveyance order, and the following steps (g) to (i) Transfer process with.
[0041]
(g) First, the single-sided image sheet S1 (1) is fed to the secondary transfer region R2 at an appropriate timing, and the color image of the first page formed at the leading position of the intermediate transfer belt 41 is displayed on the single-sided image sheet S1. Transfer to the surface (the other main surface) of (1) to obtain a double-sided image sheet S1 having color images formed on both main surfaces. The double-sided image sheet S1 is conveyed to the paper discharge unit 64 by the switching unit 65, and further discharged to the standard paper discharge tray by the paper discharge unit 64 (see FIG. 6).
[0042]
(h) Subsequent to the transfer of the color image to the single-sided image sheet S1 (1), the non-image sheet S3 (2) is fed to the secondary transfer region R2 at an appropriate timing and placed at the intermediate position of the intermediate transfer belt 41. The formed color image of the sixth page is transferred to the back surface (one main surface) of the imageless sheet S3 (2) to obtain a single-sided image sheet S3 (1). The single-sided image sheet S3 (1) is conveyed by the switching unit 65 to the switchback mechanism 662 of the refeed unit 66 (see FIG. 6). Then, the switchback inversion of the single-sided image sheet S3 (1) is executed here. Then, in order to transfer the color image of the fifth page to the front surface (one main surface) of the single-sided image sheet S3 (1), it is conveyed toward the paper supply unit 63 to prepare for the next transfer process. Thus, in this embodiment, the single-sided image sheet S3 (1) is conveyed toward the paper feeding unit 63 as the next first sheet.
[0043]
(i) Following the transfer of the color image to the non-image sheet S3 (2), the single-sided image sheet S2 (1) is fed to the secondary transfer region R2 at an appropriate timing and fed to the intermediate transfer belt 41. The color image of the third page formed at the rear end position is transferred to the surface (the other main surface) of the single-sided image sheet S2 (1) to obtain a double-sided image sheet S2 in which color images are formed on both main surfaces. (See FIG. 6). As with the double-sided image sheet S1, the double-sided image sheet S2 is conveyed to the paper discharge unit 64 by the switching unit 65, and further discharged to the standard paper discharge tray by the paper discharge unit 64.
[0044]
(j) In parallel with the sheet S2 discharge operation, the following three pages of yellow toner images, that is,
A yellow toner image corresponding to the image on page 8 (image to be formed on the back side of the fourth sheet),
A yellow toner image corresponding to the image on page 5 (image to be formed on the surface of the third sheet),
A yellow toner image corresponding to the image on page 10 (image to be formed on the back side of the fifth sheet),
Are arranged on the intermediate transfer belt 41 in this arrangement order.
[0045]
(k) Following these yellow toner images, a cyan toner image, a magenta toner image, and a black toner image are superimposed on each yellow toner image transferred to the intermediate transfer belt 41 to obtain two color toner images ( A color image) is formed on the intermediate transfer belt 41. In this way, three color images, namely
-Color image on page 8 (corresponding to "fourth color image" of the present invention),
-Color image of the fifth page (corresponding to the “fifth color image” of the present invention),
-10th page color image (corresponding to "sixth color image" of the present invention),
Are arranged on the intermediate transfer belt 41 in this arrangement order.
[0046]
Further, as shown in FIG. 5, in parallel with this, the fourth non-image sheet (first second sheet) S4 (2) and the third single-sided image sheet (first sheet) S3 (1) And the fifth non-image sheet (the second second sheet) S5 (2) are sequentially conveyed to the secondary transfer region (transfer position) R2 in this conveyance order, and the following steps (l) to (n) Transfer process with.
[0047]
(l) First, the imageless sheet S4 (2) is fed to the secondary transfer region R2 at an appropriate timing and the color image of the eighth page formed at the leading position of the intermediate transfer belt 41 is displayed as the imageless sheet S4. Transfer to the back surface (one main surface) of (2) to obtain a single-sided image sheet S4 (1). The single-sided image sheet S4 (1) is conveyed by the switching unit 65 to the switchback mechanism 662 of the refeed unit 66, where the switchback is reversed (see FIG. 7). Then, in order to transfer the color image of the seventh page to the front surface (one main surface) of the single-sided image sheet S4 (1), it is conveyed toward the paper supply unit 63 (see FIG. 8). Thus, the next transfer process is prepared. As described above, in this embodiment, the single-sided image sheet S4 (1) is conveyed toward the paper feeding unit 63 as the next first sheet (first first sheet).
[0048]
(m) Following the transfer of the color image to the non-image sheet S4 (2), the single-sided image sheet S3 (1) is fed to the secondary transfer region R2 at an appropriate timing to the intermediate position of the intermediate transfer belt 41. The formed color image of the fifth page is transferred to the front surface (the other main surface) of the single-sided image sheet S3 (1) to obtain a double-sided image sheet S3 in which color images are formed on both main surfaces (see FIG. 7). . The double-sided image sheet S3 is transported to the paper discharge unit 64 by the switching unit 65 and discharged to the standard paper discharge tray by the paper discharge unit 64 (see FIG. 8), similarly to the double-sided image sheets S1 and S2.
[0049]
(n) Following the transfer of the color image to the single-sided image sheet S3 (1), the non-image sheet S5 (2) is fed to the secondary transfer region R2 at an appropriate timing and the rear end position of the intermediate transfer belt 41 The color image of the 10th page formed on the sheet is transferred to the back surface (one main surface) of the imageless sheet S5 (2) to obtain a single-sided image sheet S5 (1) (see FIG. 8). The single-sided image sheet S5 (1) is conveyed by the switching unit 65 to the switchback mechanism 662 of the paper refeeding unit 66, where the switchback is reversed (see FIG. 9). Then, in order to transfer the color image of the ninth page to the front surface (one main surface) of the single-sided image sheet S5 (1), it is conveyed toward the paper supply unit 63 to prepare for the next transfer process. As described above, in this embodiment, the single-sided image sheet S5 (1) is conveyed toward the paper feeding unit 63 as the next first sheet (the subsequent first sheet).
[0050]
In the following, a first printing process that executes the same processes as the processes (e) to (i) and a second printing process that executes the same processes as the processes (j) to (n) are performed. A double-sided image sheet is sequentially formed repeatedly and discharged to a standard discharge tray.
[0051]
As described above, according to this embodiment, three pages of color images can be formed in parallel on the intermediate transfer belt 41, and three sheets can be sequentially fed to form an image in units of three pages. Printing processing can be performed with high throughput.
[0052]
In addition, when two sheets with no image (second sheet) are included in three sheets that are continuously fed, mutual interference in the switchback mechanism 662 becomes a problem. In the form, the problem is solved by configuring as described above. That is, in such a case, for example, as shown in FIG. 5, in the second printing process including the steps (i) to (n), the single-sided image sheet (the first image sheet between the non-image sheets S4 (2) and S5 (2) 1 sheet) S3 (1) is interposed, and the sheet is fed to the secondary transfer region (transfer position) R2 in this conveying order. For this reason, in the switchback mechanism 662, there is an interval for one page between the sheets S4 (1) and S5 (1), and as a result, both sheets in the switchback mechanism 662 as shown in FIGS. The sheet can be conveyed without causing mutual interference between S4 (1) and S5 (1).
[0053]
When only three sheets without images (second sheet) are included in three sheets that are continuously fed, the process includes steps (e) to (i) as shown in FIG. 4, for example. In the first printing process, a problem in the second printing process (mutual interference of sheets in the switchback mechanism 662) does not occur. Therefore, in the above embodiment, the arrangement order of color images (sheet conveyance order) in the first printing process is the order shown in FIG.
First color image 1-F; first sheet (single-sided image sheet) S1 (1),
Second color image 3-B; second sheet (sheet without image) S3 (2),
Third color image 2-F; first sheet (single-sided image sheet) S2 (1),
However, it may be changed to the order shown in FIGS.
[0054]
In the above embodiment, first, color images are transferred to the two non-image sheets S1 and S2 to create single-sided image sheets S1 (1) and S2 (1), which are used in the first printing process. Although it is the first sheet, as shown in FIG. 4D, first, a color image is transferred to one sheet without image S1 (2) to create a single-sided image sheet S1 (1). May be used as the next first sheet. In this case, a double-sided image sheet is sequentially created by repeating the second printing process and the first printing process following the creation of the single-sided image sheet S1 (1). Can be discharged.
[0055]
In the above embodiment, the image is formed in units of three pages. However, the number of unit pages is not limited to “3”, and may be any number of three or more. However, in order to obtain the same effect as the above embodiment, that is, the effect of performing the printing process at a high throughput while preventing the mutual interference of the single-sided image sheets with the switchback mechanism 662, the conveyance order is set as follows. There is a need to. That is, the conveyance order needs to be set so that at least one single-sided image sheet (first sheet) is interposed between the non-image sheets (second sheet).
[0056]
For example, when the number of unit pages is “4”, as shown in FIGS. 11A and 11B, one first sheet S2 is provided between the second sheets S3 (2) and S4 (2). (1) is interposed, or two first sheets S1 (1) and S2 (1) are interposed between the second sheets S3 (2) and S4 (2) as shown in FIG. In this way, the sheet conveyance order is set, and color images to be transferred to the respective sheets may be arranged and formed on the intermediate transfer belt 41 in an arrangement order corresponding to the conveyance order.
[0057]
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, in the above embodiment, the case where three pages of A4 size color toner images are formed on the intermediate transfer belt 41 has been described. However, the color toner images of other sizes are formed on the intermediate transfer belt 41 by n pages (n ≧ 3). The present invention can also be applied to a color image forming apparatus and a color image forming method that are formed side by side.
[0058]
In the above embodiment, the intermediate transfer belt 41 is used as the intermediate transfer member. However, a transfer medium other than the intermediate transfer belt (transfer drum, transfer belt, transfer sheet, intermediate transfer drum, intermediate transfer sheet, reflection type recording sheet). Alternatively, the present invention can be applied to a color image forming apparatus and method for forming a color image by transferring a toner image to a transmissive memory sheet or the like.
[0059]
Further, in the above embodiment, the printer prints an image given from an external device such as a host computer via the interface 112 on a sheet such as copy paper, transfer paper, paper, and an OHP transparent sheet. The present invention can be applied to electrophotographic color image forming apparatuses such as copying machines and facsimile machines, that is, color image forming apparatuses in general that form a color image by superposing a plurality of color toners.
[0060]
【The invention's effect】
As described above, according to the present invention, n pages (n ≧ 3) of color images are formed in parallel on the intermediate transfer member, and n sheets are sequentially fed to form images in units of n pages. Therefore, the image forming process can be performed with a high throughput. In addition, even when n sheets continuously fed include two second sheets, at least one or more first sheets are interposed between the second sheets. By setting the sheet conveyance order, it is possible to prevent the occurrence of mutual interference between the second sheets when the switchback is reversed.
[Brief description of the drawings]
FIG. 1 is a diagram showing an embodiment of an image forming apparatus according to the present invention.
2 is a block diagram showing a schematic configuration of a control unit that controls the image forming apparatus of FIG. 1; FIG.
3 is a schematic diagram showing an operation of the image forming apparatus shown in FIG.
4 is a schematic diagram showing an operation of the image forming apparatus shown in FIG. 1. FIG.
5 is a schematic diagram illustrating an operation of the image forming apparatus illustrated in FIG. 1. FIG.
FIG. 6 is a diagram schematically illustrating a sheet conveyance state.
FIG. 7 is a diagram schematically illustrating a conveyance state of a sheet.
FIG. 8 is a diagram schematically illustrating a conveyance state of a sheet.
FIG. 9 is a diagram schematically illustrating a sheet conveyance state.
FIG. 10 is a diagram showing another embodiment of the image forming apparatus according to the present invention.
FIG. 11 is a diagram showing another embodiment of the image forming apparatus according to the present invention.
[Explanation of symbols]
1 ... Control unit (control means)
2 ... Image carrier unit
3. Exposure unit
4 ... Transcription unit
41. Intermediate transfer belt (intermediate transfer member)
63: Paper feed unit (paper feed means)
64 ... Paper discharge section (paper discharge means)
66 ... Refeeding section (refeeding means)
662 ... Switchback mechanism
S1 to S3 (sheets with color images formed on both main surfaces)
S1 (1) -S5 (1) ... Single-sided image sheet (first sheet)
S1 (2) -S5 (2) ... No image sheet (second sheet)

Claims (5)

In a color image forming apparatus that sequentially forms color images on both main surfaces of a sheet,
Image forming means for forming n pages (n ≧ 3) of toner images side by side on an intermediate transfer member, and sequentially transferring each toner image to a corresponding sheet;
A paper feeding means for feeding a sheet to the image forming means;
A paper discharge means for discharging the sheet conveyed from the image forming means to a predetermined paper discharge position;
A refeed unit that reverses the sheet conveyed from the image forming unit and then refeeds the sheet;
A control means for controlling the image forming means, the paper feed means, the paper discharge means and the refeed means;
The control means includes a total of n sheets of at least one first sheet having a color image formed on one main surface and at least one second sheet having no image formed on both main surfaces. Sheets are fed to the image forming means in the following conveyance order, while color images to be transferred to the sheets are arranged in an arrangement order corresponding to the conveyance order and formed on the intermediate transfer member,
For each of the first sheets, a color image corresponding to each sheet is transferred to the other principal surface and then discharged to the discharge position by the discharge unit.
For each of the second sheets, a color image corresponding to each sheet is transferred to one main surface thereof, and then fed again to the paper feeding unit as the next first sheet by the paper feeding unit. A color image forming apparatus.
The transport order is such that when only one second sheet is included in n sheets, the second sheet is in an arbitrary order, and when a plurality of the second sheets are included. Is determined such that at least one of the first sheets is interposed between the second sheets.   The control means feeds the first sheet and the second sheet alternately to the image forming means, while the color image to be transferred to the other main surface of the first sheet and one of the second sheets The color image forming apparatus according to claim 1, wherein a color image to be transferred to a main surface is formed alternately on the intermediate transfer member. The intermediate transfer member is configured to be able to form toner images for three pages side by side,
The color image forming apparatus according to claim 1, wherein the control unit alternately executes the following first and second printing processes.
In the first printing process, the first sheet, the second sheet, and the first sheet that is different from the first sheet are fed to the image forming unit in this order, A first color image to be transferred to the other main surface of the first sheet; a second color image to be transferred to one main surface of the second sheet; and a second color image to be transferred to the other main surface of the subsequent first sheet. Three color images are arranged in this order and formed on the intermediate transfer member,
After the first color image is transferred to the other main surface of the first sheet, the first sheet is discharged to the discharge position by the discharge unit;
Further, following the transfer of the first color image to the first sheet, the second color image is transferred to one main surface of the second sheet, and then the second sheet is transferred by the refeeding unit. Refeeding the sheet feeding means as the first sheet of the next second printing process;
Further, following the transfer of the second color image to the second sheet, the third color image is transferred to the other main surface of the subsequent first sheet, and then the subsequent first sheet is transferred to the paper discharge means. Is a process for discharging the sheet to the discharge position.
In the second printing process, the previous second sheet, the first sheet, and a second sheet that is different from the previous second sheet are fed to the image forming unit in this order, A fourth color image to be transferred to one main surface of the second sheet, a fifth color image to be transferred to the other main surface of the first sheet, and a first color image to be transferred to one main surface of the subsequent second sheet. 6 color images are arranged in this order and formed on the intermediate transfer member,
After the fourth color image is transferred to one main surface of the previous second sheet, the previous second sheet is re-supplied by the re-feeding unit to the paper feeding unit as a first sheet for the next first printing process. Feed
Further, following the transfer of the fourth color image to the second sheet, the fifth color image is transferred to the other main surface of the first sheet, and then the first sheet is transferred by the paper discharge unit. Paper is ejected to the paper ejection position,
Further, following the transfer of the fifth color image to the first sheet, the sixth color image is transferred to one main surface of the subsequent second sheet, and then the subsequent second sheet is re-feeded. The sheet is fed again to the sheet feeding means as the first sheet of the next first printing process by the means. In a color image forming method for sequentially forming color images on both main surfaces of a sheet,
On the other hand, a total of n sheets comprising at least one first sheet having a color image formed on the main surface and at least one second sheet having no image formed on both main surfaces are prepared. 1 process,
When only one second sheet is included in n sheets, the second sheet is arranged in an arbitrary order, and when a plurality of second sheets are included, the second sheet is included. A second step of feeding the n sheets to the transfer position in a conveying order such that at least one or more of the first sheets are interposed between
An intermediate transfer member in which a color image to be transferred to each of the other principal surfaces of the first sheet and a color image to be transferred to each of the one principal surfaces of the second sheet are arranged in an arrangement order corresponding to the conveyance order A third step of forming
While transferring the color image corresponding to the sheet to each sheet fed to the transfer position in the conveying order, the first sheet after the transfer is discharged to a predetermined discharge position, and after the transfer, A color image forming method comprising: a fourth step of refeeding the second sheet as the next first sheet toward the transfer position. In the second step, the first sheet and the second sheet are alternately fed to the image forming unit,
In the third step, a color image to be transferred to the other main surface of the first sheet and a color image to be transferred to the one main surface of the second sheet are alternately arranged on the intermediate transfer member. The color image forming method according to claim 4.

Images