JP3952649B2 - 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 sides 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. 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 unit and three color developing units, and is transferred onto an intermediate transfer member in a multiple transfer manner. A color image is formed by secondary transfer of the image on the intermediate transfer member onto the sheet fed from the feeding unit. Subsequently, after the sheet is conveyed to the fixing unit and the color image is fixed on the sheet, the sheet is discharged to the discharge unit on the upper surface of the apparatus by the discharge roller.
[0003]
Further, a reversing unit is provided as a mechanism for reversing the sheet so as to form an image on the other side of the sheet having the image fixed on one side. This reversing unit is composed of two pairs of conveying rollers provided along the sheet discharge path and a flapper. The sheet fixed as described above is conveyed to the discharge unit side by the pair of conveying rollers. Then, the conveying roller pair is reversely rotated and the sheet is conveyed in the reverse direction. At the time of this reverse conveyance, the flapper is switched and carried into the reverse conveyance path. Thereafter, the sheet is conveyed again to the position of the registration roller pair by the reverse path conveyance roller pair.
[0004]
By the way, in the conventional image forming apparatus, when two toner images can be formed on the intermediate transfer member, images are formed on both sides of the sheet in accordance with an image forming sequence as shown in FIG. . Hereinafter, a conventional image forming method will be described with reference to FIG.
[0005]
First, an electrostatic latent image of the Y component of the second page (first back side image) is formed, developed with a Y toner image, and primarily transferred to an intermediate transfer member. Thereafter, the M, C, and K components are also primarily transferred. Thus, when the full-color toner image of the second page is formed, the secondary transfer to the first sheet that has been waiting for the registration roller pair is started.
[0006]
The sheet on which the image of the second page is copied is conveyed to the registration roller opposite side 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 period, primary transfer of the Y component toner images of the fourth page (second back side image) and the first page (first front side image) to the intermediate transfer member is performed, and the M component, C The component and the K component are also continuously performed. After that, first, the image of the fourth page is secondarily transferred to the second sheet conveyed first from the cassette. This sheet is conveyed to the reversing unit and then conveyed to the opposite side of the registration roller. As a result, the second sheet is turned upside down, and the third page is secondarily transferred onto the front surface at the timing shown in FIG. On the other hand, for the first sheet, the image of the first page is secondarily transferred and then conveyed toward the discharge unit.
[0007]
[Problems to be solved by the invention]
Thus, in the conventional apparatus, since the reversing unit is provided along the paper discharge path, the sheet on which the image is formed only on one main surface (here, the back surface) is not after reversing and transporting by the reversing unit. Sheets with images formed on both main surfaces cannot be conveyed to the discharge section. Therefore, it is necessary to secure time for performing the reverse conveyance in the reverse unit.
[0008]
For example, the above time can be secured by widening the interval between two toner images on the intermediate transfer member. However, in order to widen the interval between the toner images, it is necessary to enlarge the intermediate transfer member, resulting in an increase in the size of the apparatus. Further, the ratio of the toner image formed on the intermediate transfer member is reduced, and the throughput is reduced accordingly.
[0009]
In addition, in order to ensure the above time, it may be possible to control the conveyance so that the sheets on which the images are formed on both main surfaces are temporarily put in the trouble of carrying in the reversing unit, but the conveyance control becomes complicated. There's a problem. Further, in this type of image forming apparatus, a fixing unit is provided in front of the reversing unit, and it is not preferable in terms of the process to make the sheet stand by at this fixing unit.
[0010]
The present invention has been made in view of the above problems, and provides a compact color image forming apparatus and a color image forming method capable of efficiently forming color images on both main surfaces of a sheet with high throughput and simple control. The purpose is to provide.
[0011]
[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 sides of a sheet, and is configured as follows to achieve the above object.
[0012]
The color image forming apparatus according to the present invention forms two pages of toner images side by side on an intermediate transfer member, and sequentially transfers each toner image onto a corresponding sheet, and supplies the sheet to the image forming unit. A sheet feeding unit for feeding paper, a sheet refeeding unit for refeeding the sheet to the sheet feeding unit, and a sheet conveyed from the image forming unit along a sheet discharge path toward a predetermined sheet discharge position. Control for controlling the sheet discharge / reverse transfer unit, the image forming unit, the sheet feed unit, the refeed unit, and the sheet discharge / reverse transfer unit that transports and reversely transports the sheet toward the refeed unit. Means. The control unit feeds the first sheet having a color image formed on one main surface and the second sheet having no image formed on both main surfaces to the image forming unit in this order, A first color image to be transferred to the other main surface of the first sheet and a second color image to be transferred to the one main surface of the second sheet are arranged in this order and formed on the intermediate transfer body, The second color image is transferred to one main surface of the second sheet following the transfer of the first color image to the other main surface of the first sheet, and the first color image is transferred. The first sheet and the second sheet on which the second color image has been transferred are transported toward the paper discharge position in close proximity in this order, and the first sheet is discharged by the paper discharge / reversing means. Following the delivery to the position The 2 wherein the sheet paper discharge-inverting conveying means and said re-feed means is re-feeding to the feeding means as the first sheet of the next.
[0013]
Further, the color image forming method according to the present invention includes a first step of preparing a first sheet having a color image formed on one main surface thereof and a second sheet having no image formed on both main surfaces thereof; A second step in which a first color image to be transferred to the other main surface of the first sheet and a second color image to be transferred to the one main surface of the second sheet are arranged in this order on the intermediate transfer member; The first sheet and the second sheet are continuously fed to a transfer position to transfer the first color image on the intermediate transfer member to the other main surface of the first sheet, and the second color A third step of transferring the image to the one main surface of the second sheet, and a sheet discharging / transferring the sheet on which the color image is transferred toward a predetermined discharge position, and reversely conveying the sheet toward the transfer position. The first color image is converted by the reverse conveying means. The copied first sheet and the second sheet on which the second color image has been transferred are conveyed toward the discharge position while being close to each other in this order, and the first sheet is moved to the discharge position. Subsequent to paper discharge, there is a fourth step in which the second sheet is reversely conveyed and conveyed toward the transfer position.
[0014]
In these inventions, a single sheet discharge / reverse conveyance unit discharges a double-sided image sheet having images formed on both main surfaces, and a reverse conveyance process of a single-sided image sheet on which only one main surface is formed. However, the paper discharge process and the reverse conveyance process are performed as follows. That is, the first color image to be transferred to the other main surface of the first sheet and the second color image to be transferred to the one main surface of the second sheet are arranged in this order on the intermediate transfer member. Then, after the first color image is transferred to the other main surface of the first sheet, the first sheet (double-sided image sheet) is discharged to a discharge position. Further, following the transfer of the first color image, the second color image is transferred to one main surface of the second sheet, and then the second sheet (single-sided image sheet) is re-fed as the next first sheet. .
[0015]
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.
[0016]
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.
[0017]
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.
[0018]
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.
[0019]
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.
[0020]
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.
[0021]
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.
[0022]
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.
[0023]
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 transported to the paper discharge unit 64 along the paper feed path, and then discharged to the standard paper discharge tray (paper discharge position).
[0024]
Further, a switching flap 65 is provided on the fixing unit 5 side of the paper discharge unit 64. When the switching flap 65 is positioned at a solid line position in the figure, the sheet S conveyed through the fixing unit 5 is provided. Can be drawn into the paper discharge path 641, and when further conveyed, it is discharged to the standard paper discharge tray as described above. On the other hand, after the switching flap 65 is switched to the broken line position in the figure, the sheet S on the paper discharge path 641 can be reversely conveyed toward the paper refeeding section 66 by driving the rollers of the paper discharge unit 64 in reverse. It is configured as follows. As described above, the paper discharge unit 64 functions as a paper discharge / reverse conveyance unit of the present invention.
[0025]
The re-feeding unit 66 that receives the sheet S reversed and conveyed from the paper discharge unit 64 has a plurality of roller pairs. Then, by returning the sheet S to the pair of gate rollers 631 along the refeeding path, the non-image forming surface of the sheet S can face the intermediate transfer belt 41 and the image can be secondarily transferred to the surface in the sheet feeding unit 63. It becomes.
[0026]
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.
[0027]
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.
[0028]
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.
[0029]
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.
[0030]
Next, a double-sided color printing operation of the image forming apparatus configured as described above will be described with reference to FIGS.
[0031]
3 and 4 are schematic views showing the operation of the image forming apparatus shown in FIG. 5 to 7 are diagrams schematically showing a sheet conveyance state. 3 and 4, the “intermediate transfer belt” column 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, two toner images of A4 size can be primarily transferred onto the intermediate transfer belt 41. . The attributes of the primary transferred toner image are indicated by four alphanumeric characters. Each display content is as follows.
[0032]
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.
[0033]
(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).
[0034]
(b) Following this yellow toner image, a cyan toner image, a magenta toner image and a black toner image are superimposed on the yellow toner image transferred to the intermediate transfer belt 41 to form a color toner image (color image). It is formed on the intermediate transfer belt 41. Along with the formation of the intermediate toner image, the A4 size sheet S1 is conveyed from the cassette 61 or the like to the gate roller pair 631, and is kept waiting. 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 the second page image on the back side of the first sheet.
[0035]
(c) The single-sided image sheet S1 on which the image of the second page is formed on one side is once transported to the paper discharge unit 64, and then the switching flap 65 is switched from the solid line position to the broken line position, and the refeed unit 66 Inverted and transported toward. In parallel with the reverse conveyance of the sheet S1, a yellow toner image corresponding to the image of the first page (image to be formed on the surface of the first sheet) is formed on the intermediate transfer belt 41.
[0036]
(d) Similarly, the yellow toner image of the fourth page image (image to be formed on the back side of the second sheet) is formed side by side with the yellow toner image of the first page. At the same time, the sheet S1 conveyed to the refeed unit 66 is conveyed toward the gate roller pair 631 and waits.
[0037]
(e) Further, a cyan toner image, a magenta toner image, and a black toner image are superimposed on each toner image to form a color toner image on the intermediate transfer belt 41. Then, as shown in FIG. 4, the leading color toner image of the intermediate toner image formed in this way is secondarily transferred to the sheet S1 at an appropriate timing and fixed by the fixing unit 5 to be the first surface side. The first page image is formed. Thus, image formation on both sides of the sheet S1 is completed.
[0038]
(f) The double-sided image sheet S1 having images formed on both sides in this way is conveyed to the paper discharge unit 64 and discharged toward the standard paper discharge tray. At the same time, the remaining image on the intermediate transfer belt 41 is left. The intermediate toner image is secondarily transferred to the sheet S2 and fixed by the fixing unit 5 to form the third page image on the second surface side. At this time, the switching flap 65 has returned to the solid line position in FIG.
[0039]
(g) As shown in FIG. 5, the single-sided image sheet S2 on which the image is formed on one side follows the two-sided image sheet S1 that has been transported in advance and is transported toward the standard paper discharge tray. In parallel with this, a yellow toner image corresponding to the image of the third page (image to be formed on the surface of the second sheet) is formed on the intermediate transfer belt 41.
[0040]
(h) When the double-sided image sheet S1 is discharged to the discharge tray (discharge position), as shown in FIG. 6, the switching flap 65 is immediately switched from the solid line position in FIG. It is reversed and conveyed toward the portion 66.
[0041]
(i) Similarly, in parallel with the reverse conveyance of the sheet S2, the yellow toner image corresponding to the image on the sixth page (image to be formed on the back surface of the third sheet) is replaced with the yellow toner on the third page. The image is formed on the intermediate transfer belt 41 along with the image. At the same time, the sheet S2 conveyed to the refeed unit 66 is conveyed toward the gate roller pair 631 and waits.
[0042]
(j) Furthermore, a cyan toner image, a magenta toner image, and a black toner image are superimposed on each toner image to form two color toner images, that is, an image on the third page and an image on the sixth page in this order. Are formed side by side on the intermediate transfer belt 41. The leading toner image of the color toner image thus formed is secondarily transferred to the sheet S2 at an appropriate timing and fixed by the fixing unit 5 to form the third page image on the second surface side. (FIG. 7). Thus, image formation on both sides of the sheet S2 is completed.
[0043]
Thereafter, the same steps as the above steps (f) to (j) are repeated until all the images up to the desired page are formed on the sheet.
[0044]
As described above, in this embodiment, the toner image (first color image) to be transferred to the front surface of the previous sheet (corresponding to “the other main surface of the first sheet” of the present invention) and the back surface of the next sheet A toner image (second color image) to be transferred (corresponding to “one main surface of the second sheet” of the present invention) is formed on the intermediate transfer belt 41 in this order. Then, the toner image (first color image) formed on the leading side of the intermediate transfer belt 41 is transferred to the preceding sheet and then discharged to the standard discharge tray, while following the transfer of the leading toner image. After the toner image (second color image) formed on the end side is transferred to the next sheet, the next sheet is reversely conveyed by the paper discharge unit 64. As described above, the sheet to be discharged (double-sided image sheet) is configured to be conveyed to the paper discharge unit 64 prior to the sheet to be reversed (single-sided image sheet). The double-sided image sheet can be discharged without receiving it. Therefore, it is not necessary to form two toner images apart from each other on the intermediate transfer belt 41 more than necessary, and the intermediate transfer belt 41 can be suppressed to a minimum size, and the apparatus can be miniaturized. Further, since two toner images can be efficiently formed on the intermediate transfer member, the throughput can be increased as compared with the conventional example.
[0045]
In particular, in this embodiment, as shown in FIG. 5, for example, the double-sided image sheet (first sheet) S1 and the single-sided image sheet (second sheet) S2 are conveyed in close proximity, and the double-sided image sheet S1 is the standard output. Since the single-sided image sheet S2 is reversed and conveyed to the refeed unit 66 as soon as it is discharged to the paper tray, the first half of the sheet discharge process and the sheet reverse transfer process (in the discharge unit 64). The process of pulling the single-sided image sheet) can be performed in parallel, and higher throughput can be obtained.
[0046]
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-described embodiment, the case where two pages of A4 size color toner images are formed on the intermediate transfer belt 41 has been described. However, two color toner images of other sizes are formed side by side on the intermediate transfer belt 41. The present invention can also be applied to an image forming apparatus and a color image forming method.
[0047]
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.
[0048]
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.
[0049]
【The invention's effect】
As described above, according to the present invention, the first color image to be transferred to the other main surface of the first sheet and the second color image to be transferred to the one main surface of the second sheet are arranged in this order in the middle. 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, and the second color image is transferred after the transfer of the first color image. Is transferred to one main surface of the second sheet, and then the second sheet is re-feeded as the next first sheet. The first sheet on which is formed can be discharged. Therefore, it is not necessary to form two toner images on the intermediate transfer member more than necessary, the intermediate transfer member can be suppressed to a minimum size, and the apparatus can be miniaturized. Further, since two toner images can be efficiently formed on the intermediate transfer member, the throughput can be increased as compared with the conventional example.
[0050]
Further, if the first sheet and the second sheet are conveyed in close proximity, and the second sheet is reversed and conveyed immediately after the first sheet is discharged to the discharge position, the sheet discharge process is performed. And the first half of the sheet reverse conveyance process (the process of drawing the second sheet into the paper discharge / reverse conveyance means) can be performed in parallel, and higher throughput can be obtained.
[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.
FIG. 5 is a diagram schematically illustrating a sheet conveyance state.
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 schematic diagram illustrating a conventional image forming method.
[Explanation of symbols]
1 ... Control unit (control means)
2 ... Image carrier unit 3 ... Exposure unit 4 ... Transfer unit 41 ... Intermediate transfer belt (intermediate transfer member)
63: Paper feed unit (paper feed means)
64 ... Paper discharge section (paper discharge / reverse conveying means)
66 ... Refeeding section (refeeding means)
641... Discharge path S, S1 to S3.

Claims (2)

In a color image forming apparatus that sequentially forms color images on both sides of a sheet,
Image forming means for forming toner images for two pages 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 refeed unit for refeeding the sheet to the sheet feed unit;
A sheet discharging / reversing conveying unit that conveys a sheet conveyed from the image forming unit along a sheet discharging path toward a predetermined sheet discharging position, and reversely transports the sheet toward the re-feeding unit;
A control unit for controlling the image forming unit, the sheet feeding unit, the refeed unit, and the sheet discharge / reverse conveyance unit;
The control means feeds, in this order, the first sheet having a color image formed on one main surface and the second sheet having no image formed on both main surfaces to the image forming means. A first color image to be transferred to the other main surface of one sheet and a second color image to be transferred to the one main surface of the second sheet are arranged in this order and formed on the intermediate transfer member, and Following the transfer of one color image to the other main surface of the first sheet, the second color image is transferred to one main surface of the second sheet, and the first color image is transferred to the first main surface. The sheet and the second sheet on which the second color image has been transferred are conveyed toward the discharge position while being close to each other in this order, and the first sheet is moved to the discharge position by the discharge / reverse unit. Following the discharge, the second sheet Color image forming apparatus according to claim to refeeding to said feeding means as the first sheet of the next by the paper discharge-inverting conveying means and said sheet refeeding means. In a color image forming method for sequentially forming color images on both sides of a sheet,
A first step of preparing a first sheet having a color image formed on one main surface thereof and a second sheet having no image formed on both main surfaces;
A second step in which a first color image to be transferred to the other main surface of the first sheet and a second color image to be transferred to the one main surface of the second sheet are arranged in this order on the intermediate transfer member; ,
The first sheet and the second sheet are continuously fed to a transfer position to transfer the first color image on the intermediate transfer member to the other main surface of the first sheet, and the second color image A third step of transferring the first main surface of the second sheet;
The first sheet on which the first color image has been transferred by a sheet discharge / reverse conveying unit that conveys the sheet on which the color image is transferred toward a predetermined sheet discharge position and reversely conveys the sheet toward the transfer position. And the second sheet on which the second color image has been transferred are conveyed toward the discharge position while being close to each other in this order, and the first sheet is discharged to the discharge position. And a fourth step of conveying the second sheet in the reverse direction and conveying it toward the transfer position.

Images