JP2001154420A - Color image forming apparatus and color image forming method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a compact color image forming device and a color image forming method by which a color image can be efficiently formed at both main surfaces of a sheet with a high throughput and by simple control. SOLUTION: A toner image (1st color image) which should be transferred on the front surface of the previous sheet and a toner image (2nd color image) which should be transferred on the back surface of the next sheet are formed at an intermediate transfer belt 41 by being arrayed in this turn. After the toner image (1st color image) formed at the front side of the belt 41 is transferred on the previously supplied sheet, the sheet is ejected to a standard paper ejection tray. After the toner image (2nd color image) formed at the back end side of the belt 41 continuously to the transfer of the toner image of the front side on the previously supplied sheet is transferred on the following sheet, the following sheet is inverted and carried by a paper ejection part 64 and supplied again as the next preceding sheet by a paperre-supply part 66.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a color image forming apparatus and a color image forming method for sequentially forming a color image 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 a conventional image forming apparatus, 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, 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 primary-transferred to an intermediate transfer member. Thereafter, the primary transfer is also 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 which has been kept on standby by the pair of registration rollers 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 Y-component toner images of the first page (the back side image of the second sheet) and the first page (the front side image of the first sheet) are transferred to the intermediate transfer member by the first transfer.
The next transfer is performed, and further, the M, C, and K components are continuously performed. 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 its front surface is
The second page is secondarily transferred at the timing shown in FIG. On the other hand, for the first sheet, the image of the first page is
After the next transfer, the sheet is conveyed to the discharge section.

[0007]

As described above, in the conventional apparatus, since the reversing unit is provided along the paper discharge path, a sheet on which an image is formed only on one main surface (here, the back surface) is used. Unless the sheet is reversed and conveyed, the sheet having the 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.

For example, the above time can be secured by increasing the interval between two toner images on the intermediate transfer member. However, in order to widen the interval between toner images, it is necessary to increase the size of the intermediate transfer member, which leads to 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.

In order to secure the above-mentioned time, it is conceivable to carry out transport control so that sheets having images formed on both main surfaces are temporarily put on standby while taking in the reversing unit, but the transport control is complicated. Problem. Also,
In this type of image forming apparatus, a fixing unit is provided at a position in front of the reversing unit, and it is not preferable in terms of a process to wait a sheet in the fixing unit.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and has a compact color image forming apparatus and a color image forming apparatus capable of efficiently forming a color image on both main surfaces of a sheet with high throughput and simple control. It is an object to provide a forming method.

[0011]

SUMMARY OF THE INVENTION The present invention relates to a color image forming apparatus and a color image forming method for sequentially forming a color image on both sides of a sheet. Make up.

A color image forming apparatus according to the present invention comprises:
Image forming means for forming two pages of toner images side by side on an intermediate transfer member and sequentially transferring each toner image to a corresponding sheet, sheet feeding means for feeding a sheet to the image forming means, A sheet re-feeding unit for re-feeding the sheet to the sheet feeding unit; and a sheet conveyed from the image forming unit along the sheet discharging path to a predetermined sheet discharging position. And a control unit for controlling the image forming unit, the paper feeding unit, the re-feeding unit, and the paper discharging / reversing conveying unit. The control means 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 means 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 one main surface of the second sheet are arranged in this order on the intermediate transfer body, After transferring the first color image to the other main surface of the first sheet, the first sheet is discharged to the discharge position by the discharge / reverse conveyance means, and the second color image is transferred to the second main image. After being transferred to one main surface of the sheet, the second sheet is re-fed to the sheet feeding unit as the next first sheet by the sheet discharging / reversing conveyance unit and the sheet re-feeding unit.

The color image forming method according to the present invention is characterized in that 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 are prepared. And forming 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 one main surface of the second sheet in this order to form an intermediate transfer body. Two steps, 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 A third step of transferring a second color image to one main surface of the second sheet, discharging the first sheet to which the first color image has been transferred to a predetermined discharge position, and The second sheet on which the image has been transferred is And a fourth step for transporting to the transfer position as a sheet.

According to these inventions, a single sheet discharging / reversing conveyance means discharges a double-sided image sheet having images formed on both main surfaces, and a single-sided image sheet formed with an image formed only on one main surface. The reverse transport process is performed, and the sheet discharging process and the reverse transport 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 one main surface of the second sheet are:
The intermediate transfer member is formed in this order. 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. After the transfer of the first color image, the second sheet (one-sided image sheet) is re-fed as the next first sheet after the second color image is transferred to one main surface of the second sheet. .

[0015]

FIG. 1 is a diagram showing one embodiment of an image forming apparatus according to the present invention. This image forming apparatus forms a full-color image by superimposing four color toners of yellow (Y), cyan (C), magenta (M), and black (K). When an image signal is given to the control unit 1 (FIG. 2), each unit of the engine unit E is controlled in accordance with a command from the control unit 1 to convert the image signal into a sheet S such as transfer paper, copy paper, or an OHP sheet. Form the corresponding image.

In the engine section E, a toner image can be formed on the photosensitive member 21 of the image carrier unit 2. That is, the image carrier unit 2 includes a photoconductor 21 rotatable in the direction of the arrow in FIG. 1, and further includes a charging roller 22 as a charging unit, a developing unit around the photoconductor 21 along the rotation direction. Developing devices 23Y, 23C, 23
M, 23K, and a photoreceptor cleaner blade 24 are arranged, respectively.

In this apparatus, the charging roller 22 is connected to the photosensitive member 2
After the outer peripheral surface of the photoreceptor 21 is uniformly charged by contacting the outer peripheral surface of the photoconductor 1, the laser light L is emitted from the exposure unit 3 toward the outer peripheral surface of the photoconductor 21. As shown in FIG. 1, 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, and a laser beam L from the light emitting element 31 is rotated by a high-speed motor 32. Incident on a polygon mirror 33 to be formed. The laser light L reflected by the polygon mirror 33 is transmitted to the lens 34 and the mirror 3
5, the photosensitive drum 21 is scanned in the main scanning direction (a direction perpendicular to the plane of the drawing) to form an electrostatic latent image corresponding to an image signal. 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.

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
Each of C, 23M, and 23K is configured to be able to freely contact and separate from the photoconductor 21, and the four developing units 23Y, 23M, 23C, and 23 according to instructions from the control unit.
B selectively contacts the photoconductor 21 and applies a high voltage to apply a toner of a selected color to the surface of the photoconductor 21 to apply electrostatic latent on the photoconductor 21. Reveals an image.

The toner image developed by the developing unit 23 is primarily transferred onto the intermediate transfer belt 41 of the transfer unit 4 in a primary transfer area R1 located between the black developing unit 23K and the photosensitive member cleaner blade 24. Transcribed. Further, a photosensitive member cleaner blade 24 is disposed at a position advanced in the circumferential direction (the direction of the arrow in FIG. 1) from the primary transfer region R1.
After the primary transfer, the toner remaining on the outer peripheral surface of the photoconductor 21 is scraped off.

Next, the configuration of the transfer unit 4 will be described. In this embodiment, the transfer unit 4 includes a roller 4
2 to 47; an intermediate transfer belt 41 stretched over each of the rollers 42 to 47; a secondary transfer roller 48 for secondarily transferring the intermediate toner image transferred to the intermediate transfer belt 41 to the sheet S; And a photoreceptor / belt driving unit (not shown) that rotationally drives the body 21 and the intermediate transfer belt 41 in synchronization. When the color image is to be transferred to the sheet S, the color image is formed by superimposing the toner images of each color formed on the photoreceptor 21 on the intermediate transfer belt 41, and The sheet S is taken out from the cassette 61, the manual feed tray 62 or an additional cassette (not shown) by the paper unit 63, and is conveyed to the secondary transfer area R2. Further, a full-color image is obtained by secondary-transferring a color image onto the sheet S.

After the secondary transfer, toner remaining on the outer peripheral surface of the intermediate transfer belt 41 is removed by a cleaner blade 491 provided in the belt cleaner 49. That is, the belt cleaner 49
Is disposed opposite to the roller 46 with the intermediate transfer belt 41 interposed therebetween. At an appropriate timing, the cleaner blade 491 comes into contact with the intermediate transfer belt 41 to scrape toner remaining on the outer peripheral surface thereof. Drop.

A sensor 40 for detecting a reference position of the intermediate transfer belt 41 is disposed near the roller 43, and a synchronization signal in a sub-scanning direction substantially orthogonal to the main scanning direction, that is, a vertical synchronization signal It functions as a vertical synchronization reading sensor for obtaining VSYNC.

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 unit of the present invention. Then, the sheet S on which the color image has been transferred by the image forming unit is located 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 conveyed to the fixing unit 5 is fixed to the sheet S. Then, after the sheet S is further conveyed to the paper discharge unit 64 along the paper supply path, the sheet S is discharged to a standard paper discharge tray (paper discharge position).

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 FIG. 2, the switching flap 65 is conveyed via the fixing unit 5. Paper sheet S
When the sheet is further conveyed, the sheet is discharged to the standard sheet discharge tray as described above. On the other hand, when the switching flap 65 is switched to the position indicated by the broken line in FIG. 7 and the rollers of the paper discharge section 64 are driven to reverse, the sheet S on the paper discharge path 641 can be reversely conveyed toward the re-feed section 66. It is configured as follows. As described above, the paper discharge unit 64 functions as the paper discharge / reverse transport unit of the present invention.

The re-feeding unit 66 that receives the sheet S reversely conveyed from the sheet discharging unit 64 has a plurality of roller pairs. Then, by returning the sheet S to the gate roller pair 631 along the re-feeding path, the non-image forming surface of the sheet S in the sheet feeding unit 63 faces the intermediate transfer belt 41, and the image can be secondarily transferred to the surface. Becomes

FIG. 2 is an electrical configuration diagram of the image forming apparatus shown in FIG. When an image signal is supplied from an external device such as a host computer to the main controller 11 of the control unit 1, the image forming apparatus responds to a command from the main controller 11.
2 controls each part of the engine unit E configured as shown in FIG. 1 to form an image corresponding to the image signal on the sheet S.

The engine controller 12 has a CPU 1
And a horizontal synchronization signal HSYNC from the horizontal synchronization reading sensor 36 as an input signal from the engine unit E.
Also, the vertical synchronization signal VSYNC is output from the vertical synchronization read sensor 40.
And a temperature sensor 51 provided in the fixing unit 5.
, Respectively.
In addition, based on these input signals and various information,
The CPU 121 supplies a photoconductor / belt drive control circuit 122 with a photoconductor / belt drive unit 41a that rotationally drives the photoconductor 21 and the intermediate transfer belt 41 in synchronization with each other. Belt drive control circuit 1
The rotation speed of the photoconductor 21 and the conveyance speed V of the intermediate transfer belt 41 are controlled by controlling the photoconductor / belt driving unit 41 a using a DC motor as a driving source.

The engine controller 12 includes a transfer roller separation / contact control circuit 123 and a belt cleaner separation / contact control circuit in addition to the photoconductor / belt drive control circuit 122 as dedicated control circuits for controlling the transfer unit 4. 1
24 is further provided. The transfer roller separation / contact control circuit 123 controls the secondary transfer roller driving section 48a based on a command signal from the CPU 121 to perform the transfer at an appropriate timing.
The next transfer roller 48 is brought into contact with and separated from the intermediate transfer belt 41. On the other hand, the belt cleaner separation / contact control circuit 124 controls the belt cleaner drive unit 49a by giving the CB signal to the belt cleaner drive unit 49a based on the command signal from the CPU 121, and transfers the cleaner blade 491 to the intermediate transfer at an appropriate timing. The belt 41 is brought into contact with and separated from the belt 41.

Reference numeral 113 in the figure is an image memory provided in the main controller 11 for storing an image provided from an external device such as a host computer via the interface 112, and reference numeral 125 is an engine unit E. Is a RAM for temporarily storing control data for controlling the operation, calculation results in the CPU 121, and the like, and a reference numeral 126 is a ROM for storing a calculation program executed by the CPU 121 and the like.

Next, the double-sided color printing operation of the image forming apparatus configured as described above will be described with reference to FIGS.

FIGS. 3 and 4 are schematic views showing the operation of the image forming apparatus shown in FIG. FIG. 5 to FIG. 7 are diagrams schematically showing a sheet conveyance state. In FIGS. 3 and 4, the column of “intermediate transfer belt” indicates a toner image primarily transferred to the intermediate transfer belt 41.
Also, the boundary line in the same column indicates a joint portion of the intermediate transfer belt 41, and in this embodiment, the intermediate transfer belt 41
Is capable of primary transfer of two A4 size toner images. The attributes of the primary transferred toner image are indicated by four alphanumeric characters. The contents of each display are as follows.

Numerical characters: sheet number; English characters: F: front surface, B: back surface; parenthesized numeral: page number; parenthesis: K: black, Y: yellow, M: magenta, C: cyan; In the "Gate roller" and "Paper discharge path" columns, the upper row shows the sheet number, and the lower row shows the image forming status.

(A) First, when an image signal is input to the control unit 1 from the host computer, an electrostatic image corresponding to a second page image (an image to be formed on the back surface of the first sheet) is formed on the photosensitive member 21. After forming the latent image, the developing unit 2 for yellow
3Y 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).

(B) Subsequent to the 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 toner image). image)
Is formed on the intermediate transfer belt 41. Along with the formation of the intermediate toner image, the sheet S1 of A4 size
1 and the like to the gate roller pair 631 and are kept on standby. Then, the intermediate toner image is secondarily transferred onto the sheet S1 at an appropriate timing, and is
The image of the second page is formed on the back side of the sheet.

(C) Once the single-sided image sheet S1 on which the image of the second page is formed on one side is once conveyed to the paper discharge unit 64, the switching flap 65 is switched from the solid line position to the broken line position, and re-feeding is performed. The sheet is conveyed reversely toward the paper section 66. In parallel with the reversal conveyance of the sheet S1, 1
A yellow toner image corresponding to the image of the page (the image to be formed on the surface of the first sheet) is formed on the intermediate transfer belt 41.

(D) 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 first page. At the same time, the sheet S conveyed to the re-feeding unit 66
1 is conveyed toward the gate roller pair 631 and is put on standby.

(E) Further, a color toner image is formed on the intermediate transfer belt 41 by superimposing a cyan toner image, a magenta toner image, and a black toner image on each toner image. Then, as shown in FIG. 4, the leading color toner image of 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 fix the front surface of the first sheet. To form an image of the first page. Thus, the image formation on both sides of the sheet S1 is completed.

(F) The double-sided image sheet S1 on which images are formed on both sides is conveyed to the paper discharge unit 64 and discharged toward the standard paper discharge tray, and at the same time, on the intermediate transfer belt 41. The second intermediate toner image is secondarily transferred onto the sheet S2 and fixed by the fixing unit 5 to form a third page image on the second surface side. At this time, the switching flap 65 has returned to the solid line position in FIG.

(G) The single-sided image sheet S2 having an image formed on one side in this manner is closely followed to the previously conveyed double-sided image sheet S1 and directed toward the standard paper output tray as shown in FIG. Transport. In parallel with this, a yellow toner image corresponding to the image of the third page (the image to be formed on the second surface) is formed on the intermediate transfer belt 41.

(H) When the double-sided image sheet S1 is discharged to the discharge tray (discharge position), the switching flap 65 is immediately switched from the solid line position in FIG. 1 to the broken line position as shown in FIG. The sheet is conveyed reversely toward the sheet re-feeding section 66.

(I) Similarly, in parallel with the reverse conveyance of the sheet S2, the 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 copied to the third page. Intermediate transfer belt 41 side by side with the yellow toner image
Formed. At the same time, the sheet S2 being conveyed to the re-feeding section 66 is conveyed toward the gate roller pair 631 and is made to stand by.

(J) Further, 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, a third page image and a sixth page image. Are formed on the intermediate transfer belt 41 in this order. Then, 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 a third page image on the second surface side. (FIG. 7). Thus, the image formation on both sides of the sheet S2 is completed.

Thereafter, the above step (f) is repeated until all images up to the desired page are formed on the sheet.
Steps similar to (j) are repeated.

As described above, in this embodiment,
Toner image (first color image) to be transferred to the previous sheet surface (corresponding to “the other main surface of the first sheet” of the present invention)
And a toner image (second color image) to be transferred to the next sheet back surface (corresponding to “one main surface of the second sheet” of the present invention) are formed in this order and formed on the intermediate transfer belt 41. I have. Then, the toner image (first color image) formed on the front side of the intermediate transfer belt 41 is transferred to the previous sheet and then discharged to the standard paper output tray. The toner image formed on the end side (second
After transferring the color image) to the next sheet, the next sheet is reversed and conveyed by the paper discharge unit 64. As described above, the sheet to be discharged (double-sided image sheet) is conveyed to the sheet discharge section 64 prior to the sheet to be reversely conveyed (single-sided image sheet). The double-sided image sheet can be discharged without receiving the sheet. Therefore, it is not necessary to form two toner images apart from each other on the intermediate transfer belt 41 more than necessary.
Can be suppressed to the minimum size, and the device can be downsized. 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.

In particular, in this embodiment, as shown in FIG. 5, for example, as shown in FIG. 5, a double-sided image sheet (first sheet) S1 and a single-sided image sheet (second sheet) S2 are conveyed in a state of being close to each other. When the sheet is discharged to the standard discharge tray, the single-sided image sheet S2 is immediately reversed and conveyed to the re-feeding unit 66, so that the sheet discharge processing and the first half of the sheet reversal conveyance processing (discharge) The process of drawing the single-sided image sheet into the unit 64) can be performed in parallel, and higher throughput can be obtained.

The present invention is not limited to the above-described embodiment, and various changes other than those described above can be made without departing from the gist of the present invention. For example, in the above-described embodiment, a case has been described in which two pages of an A4 size color toner image are formed on the intermediate transfer belt 41. However, a color image in which two color toner images of other sizes are formed side by side on the intermediate transfer belt 41 is described. The present invention can be applied to an image forming apparatus and a color image forming method.

In the above embodiment, the intermediate transfer belt 41 is used as the intermediate transfer member. However, transfer media other than the intermediate transfer belt (transfer drum, transfer belt, transfer sheet, intermediate transfer drum, intermediate transfer sheet, reflection medium, The present invention can also be applied to a color image forming apparatus and method for forming a color image by transferring a toner image to a type recording sheet or a transparent storage sheet.

Further, in the above-described embodiment, an image provided from an external device such as a host computer via the interface 112 is copied to a copy sheet, a transfer sheet, a sheet, and an OH.
The present invention relates to an electrophotographic color image forming apparatus such as a copying machine or a facsimile machine, that is, a color image forming a color image by superimposing a plurality of color toners. The present invention can be applied to all forming apparatuses.

[0049]

As described above, according to the present invention, the first
A first color image to be transferred to the other main surface of the sheet;
A second color image to be transferred to one main surface of the sheet is arranged in this order to form an intermediate transfer body, and after transferring the first color image to the other main surface of the first sheet, the first sheet is discharged. , And following the transfer of the first color image,
After the second color image is transferred to one main surface of the second sheet, the second sheet is re-fed as the next first sheet. The first sheet having an image formed on the main surface can be discharged. Therefore, it is not necessary to form two toner images apart from each other more than necessary on the intermediate transfer body, and the intermediate transfer body can be suppressed to a minimum size, and the apparatus can be downsized. 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.

Further, if the first sheet and the second sheet are conveyed in a state of being close to each other, and the first sheet is discharged to the discharge position, the second sheet is immediately reversed and conveyed. The paper discharge process and the first half of the sheet reversal transport process (the process of pulling the second sheet into the paper discharge / reverse transport unit) can be performed in parallel, and higher throughput can be obtained.

[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 a block diagram illustrating a schematic configuration of a control unit that controls the image forming apparatus of FIG.

FIG. 3 is a schematic diagram illustrating an operation of the image forming apparatus illustrated in FIG. 1;

FIG. 4 is a schematic view showing an operation of the image forming apparatus shown in FIG.

FIG. 5 is a diagram schematically showing a sheet conveyance state.

FIG. 6 is a diagram schematically illustrating a sheet conveyance state.

FIG. 7 is a diagram schematically illustrating a sheet conveyance state.

FIG. 8 is a schematic view showing a conventional image forming method.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Control unit (control means) 2 ... Image carrier unit 3 ... Exposure unit 4 ... Transfer unit 41 ... Intermediate transfer belt (intermediate transfer body) 63 ... Paper supply part (paper supply means) 64 ... Paper discharge part (paper discharge) · Reversing conveyance means) 66: re-feeding section (re-feeding means) 641: paper discharge path S, S1 to S3: sheet

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) G03G 21/14 B41J 3/00 S 21/00 384 G03G 21/00 372 F term (Reference) 2C062 RA06 2H027 DA32 EB04 EB06 ED17 ED19 ED24 EE05 EE07 EF09 FA13 FA28 ZA07 2H028 BA06 BA16 BB04 BB06 2H030 AD05 AD08 AD17 BB02 BB23 BB42 3F100 AA02 CA15 DA11 EA15

Claims (4)

[Claims] 1. A color image forming apparatus for sequentially forming a color image on both sides of a sheet, an image in which two pages of toner images are formed side by side on an intermediate transfer member, and each toner image is sequentially transferred to a corresponding sheet. Forming means, sheet feeding means for feeding a sheet to the image forming means, re-feeding means for re-feeding a sheet to the sheet feeding means, and a sheet being conveyed from the image forming means along a sheet discharging path. A sheet discharging / reversing conveying means for conveying the sheet to a predetermined sheet discharging position and reversing and conveying the sheet toward the re-feeding means; the image forming means, the sheet feeding means, and the re-feeding means And a control unit for controlling the sheet discharging / reversing / conveying unit, wherein the control unit includes a first sheet having a color image formed on one main surface and a second sheet having no image formed on both main surfaces.
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 one main surface of the second sheet while feeding the sheet to the image forming means in this order. Are arranged in this order on the intermediate transfer member, and after the first color image is transferred to the other main surface of the first sheet, the first sheet is discharged by the discharge / reverse transport means. And the second sheet is transferred to one main surface of the second sheet, and then the second sheet is transferred as the next first sheet by the sheet discharging / reversing / transporting means and the sheet re-feeding means. A color image forming apparatus, wherein the sheet is fed again to the sheet feeding unit. 2. The paper discharge apparatus according to claim 1, wherein the control unit controls the discharge of the sheet while keeping the first sheet on which the first color image is transferred and the second sheet on which the second color image is transferred close in this order. 2. The color image forming apparatus according to claim 1, wherein the second sheet is conveyed toward a position, and when the first sheet is discharged to the discharge position, the second sheet is reversely conveyed to the sheet re-feeding unit. 3. 3. A color image forming method for sequentially forming a color image on both sides of a sheet, comprising: a first sheet having a color image formed on one main surface thereof;
A first step of preparing a second sheet on which images are not formed on both main surfaces; a first color image to be transferred to the other main surface of the first sheet; and a transfer to one main surface of the second sheet A second step of arranging a second color image to be formed in this order on an intermediate transfer member, and continuously feeding the first sheet and the second sheet to a transfer position and forming the intermediate transfer member on the intermediate transfer member. A third step of transferring a first color image to the other main surface of the first sheet, and transferring the second color image to one main surface of the second sheet; and the step of transferring the first color image A fourth step of discharging the first sheet to a predetermined discharge position and transporting the second sheet on which the second color image has been transferred to the transfer position as a next first sheet. A color image forming method. 4. In the fourth step, the first sheet and the second sheet are conveyed toward the paper discharge position while being close to each other, and the first sheet is discharged to the paper discharge position. 4. The color image forming method according to claim 3, wherein the second sheet is reversed and conveyed toward the transfer position.