JP2003255653A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve the productivity by enabling image forming even when a rotary developing unit is rotated and moved. <P>SOLUTION: Since, by rotating and moving an arbitrary developing unit (yellow developing unit 4a or magenta developing unit 4b or cyan developing unit 4c) of the rotary developing unit 4 at/to the developing position of a photoreceptor drum 1 in a timing that a toner image is formed on the photoreceptor drum 1 with development by a fixed developing unit 4d, the development can be performed by the fixed developing unit 4d even when the arbitrary developing unit (yellow developing unit 4a or magenta developing unit 4b or cyan developing unit 4c) of the rotary developing unit 4 is rotated and moved at/to the developing position, the productivity can be improved. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus such as a copying machine, a printer or a facsimile which forms an image by an electrophotographic system or an electrostatic recording system, and more particularly to a fixed developing device and a plurality of movable developing devices. The present invention relates to an image forming apparatus capable of forming a color image using a container.

[0002]

2. Description of the Related Art As an image forming apparatus capable of forming a color image by a conventional electrophotographic method, for example, a color copying machine of a digital method electrically processes an image signal of a document read by a reading unit to generate a magenta ( M), cyan (C), yellow (Y), and black (K) components are separated and sent to the printer unit. At this time, since one component of magenta, cyan, yellow, and black is sent to the printer unit for each reading (original scanning), the original scanning is performed four times in total in one image forming operation. .

By scanning each original, electrostatic latent images of magenta, cyan, yellow, and black are sequentially formed on one photosensitive drum, and are sequentially developed by developing devices having toners corresponding to the electrostatic latent images of respective colors. . Then, in order to transfer the toner images of four times magenta, cyan, yellow, and black developed on the photosensitive drum onto the paper, for example, an image forming apparatus having a rotatable transfer drum that contacts the photosensitive drum at the transfer position ( In a copying machine, a sheet of paper electrostatically adsorbed on a transfer drum rotates four times, so that toner images of each color for four times are sequentially superimposed and transferred onto the sheet. That is, a full-color image for one sheet is obtained by rotating the transfer drum four times.

The circumference of the transfer drum is generally a size capable of transferring an image of the maximum size (for example, A3) of paper, and two images can be transferred if it is less than half (for example, A4) of paper. Therefore, when printing a plurality of images of that size (A4 or B5 size), two images were transferred onto the transfer drum. That is, when printing a plurality of original images of one sheet of A4 or B5 size, two developed images are transferred onto the transfer drum so that two images are formed by the above-described image forming one sequence of four rotations of the transfer drum. Since it is possible to print on this paper, productivity can be improved.

[0005]

By the way, in an image forming apparatus such as a copying machine capable of forming a color image having a single photosensitive drum and a transfer drum, a rotary developing device is used in order to downsize the apparatus. May be used. That is, a rotating body (hereinafter, referred to as a rotary developing device) having yellow (Y), magenta (M), and cyan (C) developing devices is rotated, and the developing position of the photosensitive drum is developed at each developing device timing. Development is carried out by rotating and moving. Further, as the black (K) developing device, a fixed developing device which is always in contact with the photosensitive drum is often used in consideration of productivity in the black monochromatic mode (black and white image mode).

The image transfer timing and the operation timing of the rotary developing device when forming color images of A3 size (maximum transfer size) and A4 size in the above image forming apparatus are as shown in FIG.

When forming a color image of A3 size (first round of the transfer drum), first, the yellow (Y) image developed on the photosensitive drum by the yellow (Y) developing device is transferred to a sheet on the transfer drum. Then, the rotary developing device is rotated to rotationally move the magenta (M) developing device to the developing position of the photosensitive drum.

(Second round of transfer drum) The magenta (M) image developed on the photosensitive drum by the magenta (M) developing device is transferred onto the paper on the transfer drum, and the rotary developing device is rotated to rotate the cyan (C) image. The developing device is rotationally moved to the developing position of the photosensitive drum.

(Third round of transfer drum) The cyan (C) image developed on the photosensitive drum by the cyan (C) developing device is transferred onto a sheet on the transfer drum.

(4th round of transfer drum) The black (K) image developed on the photosensitive drum by the black (K) developing device which is a fixed developing device is transferred onto the paper on the transfer drum.

By sequentially performing the transfer process by the above four rotations of the transfer drum, four color toner images (toner images of magenta, cyan, yellow and black) are sequentially superposed on the paper on the transfer drum. Transferred to form a composite color toner image corresponding to the target color image.

On the other hand, when forming a color image of A4 size, as shown in FIG. 13 shown below, two images are transferred together on two sheets.

(First round of transfer drum) First, the first yellow (Y) image (Y1 image) and the second yellow (Y) developed on the photosensitive drum by the yellow (Y) developing device.
The image (Y2 image) is transferred to each of the two sheets of paper on the transfer drum. It should be noted that when two A4 size sheets are electrostatically attracted to the surface, the amount of the toner is about one revolution of the transfer drum. Therefore, the magenta (M) developing device of the rotary developing device is exposed until the next magenta image is transferred. The drum cannot be rotated to a position where it can be developed.

(Second round of transfer drum) The magenta (M) developing device of the rotary developing device is rotationally moved to a position where development of the photosensitive drum is possible at the timing when the first magenta (M) image is to be developed, and the second sheet is developed. Only the magenta (M) image (M2 image) is transferred.

(Third round of transfer drum) The first magenta (M) image (M1 image) is transferred, and the cyan (C) developing device of the rotary developing device is rotationally moved to a position where it can be developed on the photosensitive drum.

(4th round of transfer drum) The first cyan (C) image (C1 image) and the second cyan (C) image (C2 image) are transferred onto a sheet on the transfer drum.

(5th round of transfer drum) Since the black (K) developing device is a fixed developing device, the first sheet of black (K)
Image (K1 image) and second black (K) image (K2
Image) to the paper on the transfer drum.

As described above, when an A4 size color image is formed, the image cannot be transferred when the rotary developing device is rotationally moved, so that the productivity is slightly lowered.

Further, it is conceivable to lengthen the image interval between the first and second sheets, that is, to lengthen the peripheral length of the transfer drum in order to secure the time for rotationally moving the rotary developing device. The productivity at the time of image formation with paper size is reduced.

Therefore, it is an object of the present invention to provide an image forming apparatus capable of performing image formation (transfer operation) even when the rotary developing device is rotationally moved to improve productivity.

[0021]

In order to achieve the above object, the invention according to claim 1 develops an image by developing a first image carrier and a latent image on the first image carrier. A fixed developing device that is fixedly arranged to form, a plurality of developing devices that develop the latent image on the first image carrier to form an image, and any one developing device that includes the plurality of developing devices. And a moving means for selectively moving the developing means to a developing position, and by the developing operation by the fixed developing device and the developing device mounted on the moving means,
In an image forming apparatus for sequentially superposing and transferring images formed on the first image carrier onto the second image carrier, an image is formed using both the fixed developing device and the plurality of developing devices. When continuously forming a plurality of images each having a size equal to or smaller than a half of the maximum possible size image, the developing operation by the fixed developing device is performed after the developing operation by the first developing device mounted on the moving unit. The second developing device is moved to the developing position by the moving means during the developing operation by the fixed developing device to execute the developing operation.

According to a second aspect of the invention, there is provided a first image carrier, and a fixed developing device which is fixedly arranged to develop the latent image on the first image carrier to form an image. A plurality of developing devices that develop the latent image on the first image carrier to form an image, and a moving unit that mounts the plurality of developing devices and selectively moves any one of the developing devices to a developing position. The image formed on the first image carrier is sequentially superposed on the second image carrier by the developing operation by the fixed developing device and the developing device mounted on the moving means. In the image forming apparatus for transferring, when using both the fixed developing device and the plurality of developing devices, three or more images of a size less than half of the maximum size image that can be formed are continuously formed. After the developing operation by the first developing device mounted on the moving means, the fixed developing is performed. Is carried out, the second developing device is moved to the developing position by the moving means during the developing operation by the fixed developing device to carry out the developing operation, and the developing device is mounted on the fixed developing device and the moving means. When the images obtained by the developing operation by the developing device are sequentially overlapped to form two images, and when the third image is subsequently formed, the last image is used when the second image is formed. It is characterized in that the development is carried out first by using the developing device mounted on the moving means.

Further, it is characterized in that the fixed developing means uses black toner, and the developing devices of the developing devices mounted on the moving means respectively use toners of yellow, magenta and cyan colors.

[0024]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will now be described based on the illustrated embodiments.

<First Embodiment> FIG. 1 is a schematic configuration diagram showing an image forming apparatus according to a first embodiment of the present invention. The image forming apparatus according to the present embodiment is a full-color digital copying machine using an electrophotographic method.

The image forming apparatus is provided with a digital full-color image reader section (hereinafter referred to as a reader section) A on the upper side and a digital full-color image printer section (hereinafter referred to as a printer section) B on the lower side.

In the reader unit A, the original 21 is placed on the original table glass 20 and exposed and scanned by the exposure lamp 22, so that the reflected light image from the original 21 is reflected by the mirror 23.
24, far infrared ray cut filter 25 and lens 2
A full color CCD sensor 27 is focused through 6 and a color separated image signal is obtained. At this time, a full-color CCD sensor (R, G, B sensor) 27 using a standard white plate 30
The output data (color separation image signal) of is corrected.
The standard white plate 30 exhibits almost uniform reflection characteristics from visible light to infrared light, and has a white color in the visible.

The signal processing unit 28 takes in the color-separated image signal output from the full-color CCD sensor 27, electrically processes the R, G, B signals, and magenta (M),
Cyan (C), yellow (Y), and black (K) components are decomposed and sent to the printer unit B. Further, for each document scanning (scanning) in the reader unit A, M, C,
One component of Y and K is sent to the printer unit B, and the original is scanned four times in total when forming a color image.

In the printer section B, the photosensitive drum 1 as the first image carrier is rotatably supported in the arrow direction (clockwise direction). Around the photosensitive drum 1, a charging roller 2, a developing device 3, a transfer drum 5 and the like are installed along the rotation direction thereof. A fixing device 44 is installed downstream of the transfer drum 5 in the sheet conveying direction.
The developing device 3 is composed of a rotatable developing device 4 and a black (K) developing device 4d as a fixed developing device.

The rotary developing device 4 is a yellow (Y) developing device 4.
a, magenta (M) developing device 4b, cyan (C) developing device 4
c, and contains yellow toner, magenta toner, and cyan toner, respectively. The rotary developing device 4 is
For example, when developing magenta, the magenta developing device 4b rotationally moves to the developing position of the photosensitive drum 1. The black (K) developing device (fixed developing device) 4d stores black toner and is always in contact with the photosensitive drum 1.

Further, in the present embodiment, by the control of the control unit 50, the rotary developing device 4 is rotated during the developing operation in the black (K) developing device (fixed developing device) 5 so that each developing device (yellow (Y ) Developing device 4a, magenta (M) developing device 4
b, the cyan (C) developing device 4c) can be rotationally moved to the developing position (details will be described later).

The transfer drum 5 is a cassette 40a or 4
A sheet of paper (recording medium) P as a second image carrier, which is fed from 0b and is transported through the transport units 41a and 41b, is electrostatically adsorbed on the surface of the sheet P, and is wound at the transfer position where it abuts the photosensitive drum 1. The toner images of the respective colors developed on the drum 1 are sequentially superimposed and transferred onto the paper P. In the peripheral opening area of the transfer drum 5, a sheet (not shown) made of a dielectric material to which the paper P is attracted is integrally stretched in a cylindrical shape. The transfer drum 5 used in the present embodiment is capable of winding two sheets of A4 size paper (one sheet of A3 size) and electrostatically adsorbing them. That is, the maximum image forming size of the image forming apparatus of this embodiment is A3 size.

Two sensors 5 are provided in the transfer drum 5.
a and 5b are arranged, and the flag 5c is the sensor 5
By detecting the timing of passing through a and 5b, the front end positions of the two A4 size sheets P adsorbed on the transfer drum 5 are synchronized with the front ends of the toner images formed on the photosensitive drum 1. be able to.

Next, an image forming sequence by the image forming apparatus of the present embodiment described above will be described with reference to the flowchart shown in FIG.

When a user gives an instruction to copy a plurality of originals (n sheets) from an operation unit (not shown), the control unit (CPU) 50 of the image forming apparatus performs control according to the flowchart of FIG. .

First, in step S1, if the size of the paper P attracted to the transfer drum 5 is A4 size or more, the process proceeds to step S2, and if it is less than A4 size, the process proceeds to step S4. In step S2, "color image forming sequence 1" described below is started. When the number of copies reaches n, which is the final number, the "color image forming sequence 1"
Is finished (step S3), and the "color image forming sequence 1" is repeated until the number of finished sheets reaches n.

FIG. 3 shows "color image forming sequence 1".
The flowchart of is shown. Further, FIG. 4 shows the rotation of the transfer drum 5 in the “color image forming sequence 1”, the transfer timing of the toner image of each color (yellow, magenta, cyan, black) and the rotation (movement) timing of each developing device. It is a figure.

When the "color image forming sequence 1" is started, as described above, the reader unit A reads the yellow (Y) image (step S20), and the yellow (Y) image is electrostatically formed on the photosensitive drum 1. Formation of a latent image and development by the yellow (Y) developing device 4a of the rotary developing device 4 are performed to transfer to the sheet P adsorbed on the transfer drum 5 of the first round (step S21), and then rotational development The developing device 4 is rotated to rotationally move the magenta (M) developing device 4b to the developing position (step S22).

Subsequently, similarly, the magenta (M) image is read (step S23), the electrostatic latent image of the magenta (M) image is formed, the development is performed by the magenta (M) developing device 4b, and the transfer drum 5 of the second round is used. After the transfer onto the sheet P adsorbed above (step S24), the cyan (C) developing device 4c is moved to the developing position (step S25).

Similarly, the cyan (C) image is read (step S26), the electrostatic latent image of the cyan (C) image is formed, the development is performed by the cyan (C) developing device 4c, and the transfer drum 5 on the third rotation is formed. Transfer to the paper P adsorbed on the paper (step S
27) is performed. Thereafter, the black (K) image is read (step S28), the electrostatic latent image of the black (K) image is formed, the development is performed by the black (K) developing device (fixed developing device) 4d, and the transfer drum 5 on the fourth round is moved. Transfer to the sheet P adsorbed on the sheet P (step S29).

Then, the paper P on which the full-color image obtained by superposing the yellow, magenta, cyan, and black toner images is formed is separated from the transfer drum 5 by the separation claw 42, and then the conveyance belt 43 is used. The full-color image is conveyed to the fixing device 44, heated and pressed to fix the full-color image in the fixing nip portion between the fixing roller 44a and the pressure roller 44b of the fixing device 44, and then, the discharge tray 47 is discharged via the discharge rollers 45 and 46. Is ejected.

The transfer residual toner and the like remaining on the surface of the photosensitive drum 1 after the above toner image transfer is removed by a cleaning device (not shown) and used for the next image formation. After transferring the toner image, the rotary developing device 4 is rotated to move the yellow (Y) developing device 4a to the developing position (step S30), and the "color image forming sequence 1" is ended.

On the other hand, when the size of the paper P adsorbed to the transfer drum 5 is equal to or smaller than A4 size in step S1, the process proceeds to step S4, and the "high-speed mode" which is a feature of the present invention is instructed from the operation unit (not shown). If is included, the process proceeds to step S5, and if not, the process proceeds to step S9. In step S5, it is determined whether or not the number of remaining sheets P is two or more, and if two or more, the process proceeds to step S6 to perform "two-sheet continuous transfer", which is a feature of the present invention described below, "color image formation". Sequence 2 ”is performed. Also, step S
If the number of remaining sheets P is 5, in step 5, the process proceeds to step S7 and the above-mentioned "color image sequence 1" is executed.

FIG. 5 shows the "color image forming sequence 2".
The flowchart of is shown. Further, FIG. 6 shows the rotation of the transfer drum 5 in the “color image forming sequence 2”, the transfer timing of the toner image of each color (yellow, magenta, cyan, black) and the rotation (movement) timing of each developing device. It is a figure.

When the "color image forming sequence 2" is started, the first yellow (Y1 image) image is read by the reader unit A as described above (step S32),
A sheet of toner adsorbed on the transfer drum 5 in the first round after formation of an electrostatic latent image of a yellow (Y1 image) image on the photosensitive drum 1 and development by the yellow (Y) developing device 4a of the rotary developing device 4. Transfer to P (step S33). Then, similarly, the second yellow (Y2 image) image is read by the reader unit A (step S34), and the yellow (Y2 image) is read.
Formation of an electrostatic latent image of the image on the photosensitive drum 1 and development by the yellow (Y) developing device 4a of the rotary developing device 4 to transfer the image onto the sheet P adsorbed on the transfer drum 5 in the first round. Perform (step S35). Then, the rotary developing device 4 is rotated to move the magenta (M) developing device 4b to the developing position (step S36).

Subsequently, similarly, the first black (K1 image) image is read (step S37) and the black (K1 image) is read.
(1 image) formation of an electrostatic latent image of an image, development by a black (K) developing device (fixed developing device) 4d, second transfer drum 5
Transfer to the sheet P adsorbed on the upper side (step S38).

Then, the second magenta (M2 image) image is read (step S39), an electrostatic latent image of the magenta (M2 image) image is formed on the photosensitive drum 1, and the magenta (M) image of the rotary developing device 4 is read. ) After the development by the developing device 4b, 2
Transfer to the sheet P adsorbed on the transfer drum 5 on the circumference is performed (step S40). Then, similarly, the first magenta (M1 image) image is read by the reader unit A (step S41), an electrostatic latent image of magenta (M1 image) is formed on the photosensitive drum 1, and the magenta of the rotary developing device 4 is read. (M) After the development by the developing device 4b, the transfer to the sheet P adsorbed on the transfer drum 5 in the third round is performed (step S42). Then, the rotary developing device 4 is rotated to move the cyan (C) developing device 4c to the developing position (step S43).

Then, the second black (K2 image) image is read (step S44), the electrostatic latent image of the black (K2 image) image is formed, and development is performed by the black (K) developing device (fixed developing device) 5. Transfer to the paper P adsorbed on the transfer drum 5 of the third round (step S45).

Then, the first cyan (C1 image) image is read (step S46), the electrostatic latent image of the cyan (C1 image) image is formed on the photosensitive drum 1, and the rotary developing device 4 is used.
After the development by the cyan (C) developing device 4c, the transfer to the sheet P adsorbed on the transfer drum 5 on the fourth round is performed (step S47). Then, similarly, the second cyan (C2 image) image is read by the reader unit A (step S4).
8), formation of an electrostatic latent image of a cyan (C2 image) image on the photosensitive drum 1, and a cyan (C) developing device 4c of the rotary developing device 4.
Then, the transfer to the sheet P adsorbed on the transfer drum 5 in the fourth round is performed (step S49).

The two sheets P on which the full-color images obtained by superimposing the toner images of the respective colors are respectively formed are separated from the transfer drum 5 by the separating claws 42, and then the fixing device 44 is formed by the conveying belt 43. Is transported to
The full-color image is heated and pressed in the fixing nip portion between the fixing roller 44a and the pressure roller 44b of the fixing device 44 to fix the full-color image, and then the discharge tray 4 is discharged via the discharge rollers 45 and 46.
Paper is discharged to 7. When the number of finished sheets reaches n, the "color image forming sequence 2" is finished (step S8),
If the number of finished sheets n has not been reached, the process returns to step S5.

The transfer residual toner and the like remaining on the surface of the photosensitive drum 1 after the above toner image transfer is removed by a cleaning device (not shown) and used for the next image formation.

"Color image forming sequence 2" described above
Rotation of the transfer drum 5 and transfer timing of toner images of respective colors (yellow, magenta, cyan, black) and respective developing devices (yellow (Y) developing device 4a, magenta (M) developing device 4b, cyan (C) developing device) The rotation (movement) timing of 4c) is as shown in FIG.
While the transfer drum makes one revolution, the first yellow (Y1 image) image and the second yellow (Y2 image) image are sequentially transferred.

Subsequently, while the transfer drum makes two rounds, the first black (K1 image) image and the second magenta (M2 image)
Images) Images are transferred in sequence. At this time, the transfer of the yellow (Y2 image) image is completed, and the rotary developing device 4 is rotated during the transfer process of the black (K1 image) image, so that the yellow (Y) developing device 4a moves to the magenta (M) developing device 4b.
Is moved to the developing position to prepare for developing a magenta (M2, M1 image) image. Therefore, the developing device (yellow (Y)
Image formation (toner image transfer) can be performed even when the magenta (M) developing device 4b is moved from the developing device 4a.

Subsequently, while the transfer drum makes three revolutions, the first magenta (M1 image) image and the second black (K2 image)
Images) Images are transferred in sequence. At this time, the transfer of the magenta (M1 image) image is completed, the rotary developing device 4 is rotated during the transfer process of the black (K2 image) image, and the magenta (M) developing device 4b to the cyan (C) developing device 4c are rotated. To the developing position to prepare for developing a cyan (C1, C2 image) image.

Subsequently, the first cyan (C1 image) image and the second cyan (C2 image) image are sequentially transferred while the transfer drum makes four revolutions.

If the "high speed mode" is not selected in step S4 and the "normal mode" is selected, step S9 is executed.
Proceed to.

In step S9, the number of remaining sheets P is 2
Whether the number of sheets is equal to or more than one is determined. When the number of sheets is equal to or more than 2, the process proceeds to step S10, and the "color image forming sequence 3" described below is performed. If the remaining number of sheets is one in step S9, the "color image sequence 1" described above is performed (step S11).

FIG. 7 shows "color image forming sequence 3".
The flowchart of is shown. In the "color image forming sequence 3", the rotation of the transfer drum 5, the transfer timing of the toner image of each color (yellow, magenta, cyan, black) and the rotation (movement) timing of each developing device are "conventional technology". 13 is the same as that described in FIG.

When the "color image forming sequence 3" is started, the first yellow (Y1 image) image is read by the reader unit A as described above (step S50),
The electrostatic latent image of the yellow (Y1 image) image is formed on the photosensitive drum 1, and the development is performed by the yellow (Y) developing device 4a of the rotary developing device 4, and the electrostatic latent image is adsorbed on the transfer drum 5 in the first round.
Transfer to the first sheet of paper P is performed (step S51).

Similarly, the reader unit A reads the second yellow (Y2 image) image (step S5).
2), an electrostatic latent image of a yellow (Y2 image) image is formed on the photosensitive drum 1, and development is performed by the yellow (Y) developing device 4a of the rotary developing device 4, and the electrostatic latent image is attracted onto the transfer drum 5 of the first round. Transfer to the second sheet of paper P thus formed (step S5)
3). Then, the rotary developing device 4 is rotated to move the magenta (M) developing device 4b to the developing position (step S5).
4).

Subsequently, similarly, the second magenta (M2 image) image is read (step S55) and the magenta (M2) image is read.
2 image) electrostatic latent image formation, development by magenta (M) developing device 4b, second magenta (M2 image) image on paper P attracted onto transfer drum 5 in the second round (Step S56).

Then, the first magenta (M1 image) image is read (step S57), the electrostatic latent image of the magenta (M1 image) image is formed on the photosensitive drum 1, and the magenta (M) of the rotary developing device 4 is read. ) Development by developing unit 4b
Transfer is performed to the first sheet P adsorbed on the transfer drum 5 of the circumference (step S58). Then, the rotary developing device 4 is rotated to move the cyan (C) developing device 4c to the developing position (step S59).

Similarly, the first cyan (C1 image) image is read by the reader unit A (step S6).
0), an electrostatic latent image of cyan (C1 image) is formed on the photosensitive drum 1, and development is performed by the cyan (C) developing device 4c of the rotary developing device 4, and the electrostatic latent image is adsorbed on the transfer drum 5 at the fourth lap. A cyan (C1 image) image is transferred to the first sheet P (step S61). Subsequently, similarly, the second cyan (C2 image) image is read (step S62), the electrostatic latent image of the cyan (C2 image) image is formed, the development is performed by the cyan (C) developing device 4c, and the fourth round is performed. The cyan (C2 image) image is transferred to the second sheet P adsorbed on the transfer drum 5 (step S63).

Then, the first black (K1 image) image is read (step S64), an electrostatic latent image of the black (K1 image) image is formed, and development is performed by the black (K) developing device (fixed developing device) 4d. The black (K1 image) image is transferred onto the first sheet P adsorbed on the transfer drum 5 in the fifth cycle (step S65). Then, likewise 2
Reading of the first black (K2 image) image (step S66), formation of an electrostatic latent image of the black (K1 image) image on the photosensitive drum 1, and development by the black (K) developing device (fixed developing device) 4d. The black (K2 image) image is transferred onto the second sheet of paper P adsorbed on the transfer drum 5 in the fifth cycle through the step S67.

Then, the two sheets P on which the full-color images obtained by superposing the toner images of the respective colors are respectively formed are separated from the transfer drum 5 by the separating claws 42, and then the fixing device 44 is formed by the conveyor belt 43. Is transported to
The full-color image is heated and pressed in the fixing nip portion between the fixing roller 44a and the pressure roller 44b of the fixing device 44 to fix the full-color image, and then the discharge tray 4 is discharged via the discharge rollers 45 and 46.
The sheet is ejected to 7, and the “color image forming sequence 3” is ended.

The transfer residual toner remaining on the surface of the photosensitive drum 1 after the above toner image transfer is removed by a cleaning device (not shown), and the toner is provided for the next image formation.

When the number of finished sheets reaches n, the above "color image forming sequence 3" is finished (step S
12) If the number of finished sheets has not reached n, the process returns to step S9.

As described above, in the present embodiment, the image is formed by transferring onto two sheets each of which is half (A4 size) or less of the maximum formed image size (A3 size in the present embodiment) by the image forming apparatus. In this case, by selecting "color image forming sequence 2" as the "high speed mode", the rotary developing device (yellow (Y) developing device 4a, magenta (M) developing device 4b, cyan (C) developing device 4c) is selected. The developing operation is performed by the black (K) developing device (fixed developing device) 4d even when the toner is rotated. Here, the size refers to a size in the rotation direction of the photosensitive drum 1 (paper conveyance direction), that is, a so-called sub-scanning direction.

Therefore, in the conventional case, when the toner images of the respective colors are superposed and transferred onto the two sheets of A4 size paper on the transfer drum 5, the transfer drum 5 needs to be rotated five times. In the present embodiment, the transfer drum 5
Since it only requires 4 rotations, the productivity can be improved.

<Embodiment 2> In this embodiment also, the image forming apparatus according to Embodiment 1 shown in FIG. 1 will be described. The image forming sequence is the same as in the first embodiment except for the image forming sequence in the present embodiment, and in the present embodiment, only the image forming sequence in the present embodiment will be described.

In the case of the first embodiment, "high speed mode"
In the "color image forming sequence 2" as described above, when the two-sheet continuous transfer as shown in FIG. 6 is continuously performed twice or more to form three or more images, the rotary developing device 4 is used before the second two-sheet continuous transfer is performed. Need to be rotationally moved from the cyan (C) developing device 4c for the fourth color to the yellow (Y) developing device 4a for the first color. Therefore, when continuous transfer of two sheets is continued twice or more, a time loss of one rotation of the transfer drum 5 is caused due to switching of the developing device. Therefore, in the second embodiment of the present invention, even when continuous transfer of two sheets is continued twice or more, time loss is prevented and further productivity can be improved.

Next, an image forming sequence by the image forming apparatus of the present embodiment will be described with reference to the flowchart shown in FIG.

When the user gives an instruction to copy a plurality of originals (n sheets) from an operation unit (not shown), the control unit (CPU) 50 of the image forming apparatus performs control according to the flowchart of FIG. .

First, if the size of the paper P attracted to the transfer drum 5 in step S1 is A4 size or more, the process proceeds to step S2, and if it is less than A4 size, the process proceeds to step S4. In step S2, the above-mentioned "color image forming sequence 1" is started. Then, in step S3, the number of copies is counted, and when the number of copies reaches the end number n, the "color image forming sequence 1" is ended and the end number n is reached.
When the number of sheets has not reached, the process returns to step S2, and the "color image forming sequence 1" is repeated until the number of finished sheets reaches n. Steps S1 to S3 are the same as those in the first embodiment.

On the other hand, when the size (recording size) of the paper P attracted to the transfer drum 5 is A4 size or less in step S1, the process proceeds to step S4, and the instruction from the operation unit (not shown) includes the "high speed mode". If so, the process proceeds to step S70, and if the "high speed mode" is not selected, the process proceeds to step S9.

In step S9, the number of remaining sheets P is 2
Whether the number of sheets is equal to or more than one is determined, and when the number of sheets is equal to or more than 2, the process proceeds to step S10, and the above-described "color image forming sequence 3" is performed. In step S9, the remaining number of sheets is 1
If the number is one, the "color image sequence 1" described above is performed (step S11). When the number of finished sheets reaches n in step S10, the "color image forming sequence 3" is finished (step S12). If the number of finished sheets has not reached n, the process returns to step S9. Steps S9 to S12 are the same as those in the first embodiment.

In step S70, it is determined whether or not the number of remaining sheets P is three or more. If the number is three or more, the process proceeds to step S71, the above-mentioned "color image forming sequence 2" is performed, and the process proceeds to step S72. . Also, step S
If the number of remaining sheets P is less than 3 in 70, the process proceeds to step S5.

In step S5, the number of remaining sheets P is 2
It is determined whether the number of sheets is equal to or more than one. If the number of sheets is equal to or more than two, the process proceeds to step S6, and the above-mentioned "color image forming sequence 2" is performed.
I do. If the remaining number of sheets is one in step S5, the above-mentioned "color image sequence 1" is performed (step S7). When the number of finished sheets is n in step S6, the "color image forming sequence 2" is finished (step S8). If the number of finished sheets is not reached n, the process returns to step S5. Steps S5 to S8 are the first embodiment
Is the same as.

Then, in step S72, it is determined whether or not the number of remaining sheets P is two or more at the time of image formation by the "color image forming sequence 2", and if two or more, the process proceeds to step S73. The "color image forming sequence 4" of the present embodiment described below is performed. If the number of remaining sheets is one in step S72, "color image sequence 5" of the present embodiment described below.
Is performed (step S75).

FIG. 9 shows the "color image forming sequence 4".
The flowchart of is shown. In addition, FIG. 10 illustrates the rotation of the transfer drum 5 in the “color image forming sequence 2” of the transfer drum 5 for the first to fourth rotations and the “color image forming sequence 4” of the transfer drum 5 for the fifth to eighth rotations, and each color. FIG. 6 is a diagram showing a transfer timing of toner images of (yellow, magenta, cyan, black) and a timing of rotation (movement) of each developing device.

When the "color image forming sequence 4" is started, as described above, the first cyan (C3 image) image is read by the reader unit A (step S80), and the cyan (C3 image) photosensitive drum is read. The electrostatic latent image is formed on the first sheet, and the development is performed by the cyan (C) developing device 4c of the rotary developing device 4 to transfer the image onto the sheet P adsorbed on the transfer drum 5 at the fifth round (step S81). ). Then, in the same manner, the second cyan (C4 image) image is read by the reader unit A (step S82), an electrostatic latent image of the cyan (C4 image) image is formed on the photosensitive drum 1, and the rotary developing device 4 operates. After the development by the cyan (C) developing device 4c, the transfer to the sheet P adsorbed on the transfer drum 5 in the fifth round is performed (step S8).
3). Then, the rotary developing device 4 is rotated to move the magenta (M) developing device 4b to the developing position (step S8).
4).

Subsequently, similarly, the first black (K3 image) image is read (step S85), and the black (K3 image) is read.
(3 images) formation of an electrostatic latent image of an image, development by a black (K) developing device (fixed developing device) 4d, transfer drum 5 of the sixth round
Transfer to the sheet P adsorbed on the upper side (step S86).

Then, the second magenta (M4 image) image is read (step S87), the electrostatic latent image of the magenta (M4 image) image is formed on the photosensitive drum 1, and the magenta (M) of the rotary developing device 4 is read. ) Developing by the developing device 4b 6
Transfer to the sheet P adsorbed on the transfer drum 5 of the circumference is performed (step S88). Then, similarly, the first magenta (M3 image) image is read by the reader unit A (step S89), the electrostatic latent image of the magenta (M3 image) is formed on the photosensitive drum 1, and the magenta of the rotary developing device 4 is formed. (M) After the development by the developing device 4b, the transfer to the sheet P adsorbed on the transfer drum 5 of the seventh round is performed (step S90). Then, the rotary developing device 4 is rotated to move the yellow (Y) developing device 4a to the developing position (step S91).

Then, the second black (K4 image) image is read (step S92), an electrostatic latent image of the black (K4 image) is formed, and development is performed by the black (K) developing device (fixed developing device) 4d. , Transfer to the paper P adsorbed on the transfer drum 5 in the seventh round (step S93).

Then, the first yellow (Y3 image) image is read (step S94), the electrostatic latent image of the yellow (Y3 image) image is formed on the photosensitive drum 1, and the yellow (Y) image of the rotary developing device 4 is read. ) Development by the developing device 4a
Transfer to the sheet P adsorbed on the peripheral transfer drum 5 is performed (step S95). Then, similarly, the second yellow (Y4 image) image is read by the reader unit A (step S96), the electrostatic latent image of the yellow (Y4 image) image is formed on the photosensitive drum 1, and the rotary developing device 4 is operated. After the development by the yellow (Y) developing device 4a, the transfer to the sheet P adsorbed on the transfer drum 5 in the eighth round is performed (step S9).
7).

The two sheets P on which the full-color images obtained by superposing the toner images of the respective colors are respectively formed are separated from the transfer drum 5 by the separating claws 42, and then the fixing device 44 is formed by the conveyor belt 43. Is transported to
The full-color image is heated and pressed in the fixing nip portion between the fixing roller 44a and the pressure roller 44b of the fixing device 44 to fix the full-color image, and then the discharge tray 4 is discharged via the discharge rollers 45 and 46.
Paper is discharged to 7.

Further, the transfer residual toner and the like remaining on the surface of the photosensitive drum 1 after the above toner image transfer is removed by a cleaning device (not shown) and used for the next image formation. When the predetermined number n, which is the end number, is reached, the "color image forming sequence 4" is ended (step S74), and if the predetermined number n is not reached, the process returns to step S70.

[Color image forming sequence 4] described above
Rotation of the transfer drum 5 and transfer timing of toner images of respective colors (yellow, magenta, cyan, black) and respective developing devices (yellow (Y) developing device 4a, magenta (M) developing device 4b, cyan (C) developing device) The timing of rotation (movement) of 4c) is, as shown in FIG. 10, first, on the fifth lap of the transfer drum, the first cyan (C3 image)
The image and the second cyan (C4 image) image are sequentially transferred.

Subsequently, the first black (K3 image) image and the second magenta (M4 image) image are sequentially transferred on the sixth round of the transfer drum 5. At this time, cyan (C
(4 images) image transfer is completed, the rotary developing device 4 is rotated during the transfer process of the black (K3 image) image, and the cyan (C) developing device 4c is moved to the magenta (M) developing device 4b. In preparation for developing a magenta (M4, M3 image) image. Therefore, the developing device (cyan (C) developing device 4
Image formation (toner image transfer) can be performed even when the magenta (M) developing device 4b is moved from c.

Subsequently, the first magenta (M3 image) image and the second black (K4 image) image are sequentially transferred on the seventh round of the transfer drum 5. At this time, the transfer of the magenta (M3 image) image is completed, and the rotary developing device 4 is rotated during the transfer process of the black (K4 image) image so that the magenta (M) developing device 4b moves to the yellow (Y) developing device 4a.
To the developing position to prepare for developing a yellow (Y3, Y4 image) image.

Subsequently, the first yellow (Y3 image) image and the second yellow (Y4 image) image are sequentially transferred on the eighth round of the transfer drum 5.

If the number of remaining sheets is one in step S72, the process proceeds to step S75 to execute the "color image forming sequence 5" of the present embodiment described below.

FIG. 11 shows a flowchart of the "color image forming sequence 5".

When the "color image forming sequence 5" is started, as described above, the reading of the cyan (C image) image by the reader unit A (step S100) and the cyan (C image) are performed.
Image) forming an electrostatic latent image of the image on the photosensitive drum 1 and developing by the cyan (C) developing device 4c of the rotary developing device 4
The transfer to the sheet P adsorbed on the transfer drum 5 of the circumference is performed (step S101). Then, the rotary developing device 4 is rotated to move the magenta (M) developing device 4b to the developing position (step S102).

Subsequently, similarly, the magenta (M image) image is read (step S103), the electrostatic latent image of the magenta (M image) image is formed, the development is performed by the magenta (M) developing device 4b, and the sixth transfer is performed. Transfer to the sheet P adsorbed on the drum 5 (step S104). Then, the rotary developing device 4
Is rotated to move the yellow (Y) developing device 4a to the developing position (step S105).

Then, the yellow (Y image) image is read (step S106), the electrostatic latent image of the yellow (Y image) image is formed on the photosensitive drum 1, and the yellow (Y) developing device 4a of the rotary developing device 4 is formed. Then, the transfer to the sheet P adsorbed on the transfer drum 5 on the seventh round is performed (step S107).

Then, the black (K image) image is read (step S108), the electrostatic latent image of the black (K image) image is formed, and the black (K) developing device (fixed developing device) 4
The development by d and the transfer to the sheet P adsorbed on the transfer drum 5 in the eighth round are performed (step S109).

Then, a sheet of paper P on which a full-color image obtained by superposing the toner images of the respective colors is formed.
Is separated from the transfer drum 5 by the separation claw 42 and then conveyed to the fixing device 44 by the conveying belt 43, and the full-color image is heated and applied at the fixing nip portion between the fixing roller 44a and the pressure roller 44b of the fixing device 44. After being pressed and fixed, the paper is ejected to the paper ejection tray 47 via the paper ejection rollers 45 and 46.

The transfer residual toner remaining on the surface of the photosensitive drum 1 after the above toner image transfer is removed by a cleaning device (not shown), and the toner is provided for the next image formation.

As described above, in the present embodiment, when the two-sheet continuous transfer is performed twice or more, the cyan (C) developing device 4c of the rotary developing device 4 used last in the first two-sheet continuous transfer is
It was used as the first developing device in the second two-sheet continuous transfer.

Therefore, in this embodiment, the first embodiment
In addition to the effect obtained in step 1, there is no time loss when shifting to the second two-sheet continuous transfer operation, so that the productivity can be further improved.

Further, in each of the above-described embodiments, the present invention is applied to an image forming apparatus using, as a transfer means, a transfer drum that is in contact with a photosensitive drum at a transfer portion and winds a sheet around the surface to perform transfer. However, in addition to the above, for example, instead of the sheet adsorbed on the transfer drum, a toner image of each color is transferred from the photosensitive drum onto an intermediate transfer member (intermediate transfer belt or intermediate transfer drum) as a second image carrier. The present invention can be similarly applied to an image forming apparatus having a structure in which a full-color image is transferred by superimposing them on each other and then collectively transferred to a sheet.

[0103]

As described above, according to the first aspect of the present invention, by using both the fixed developing device and the plurality of developing devices, the size of the image which can be formed is half or less than the maximum size of the image. When a plurality of images are continuously formed, the developing operation by the fixed developing device is performed after the developing operation by the first developing device mounted on the moving device, and the first moving device is operated by the moving device during the developing operation by the fixed developing device. (2) By moving the developing device to the developing position and executing the developing operation, the fixed developing device can perform the development even when the arbitrary developing device of the plurality of developing devices is moved to the predetermined developing position. Productivity can be improved.

According to the second aspect of the present invention, by using both the fixed developing device and the plurality of developing devices, an image of a size not more than half of the maximum size image that can be formed is continuously formed. When forming three or more images, the developing operation is performed by the fixed developing unit after the developing operation by the first developing unit mounted on the moving unit, and the second developing is performed by the moving unit during the developing operation by the fixed developing unit. The developing device is moved to the developing position to carry out the developing operation, and the images obtained by the developing operation by the fixed developing device and the developing device mounted on the moving means are sequentially superposed to form two images continuously. Subsequently, when forming the image of the third image, the development is carried out by first using the developing device mounted on the moving means used last when forming the image of the second image, thereby further improving the productivity. be able to.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram showing an image forming apparatus according to first and second embodiments of the present invention.

FIG. 2 is a flowchart showing an image forming sequence according to the first embodiment of the present invention.

FIG. 3 is a flowchart showing “color image forming sequence 1” in Embodiment 1 of the present invention.

FIG. 4 is a diagram showing rotation of a transfer drum, a transfer timing of a toner image of each color, and a rotation (movement) timing of each developing device in a “color image forming sequence 1” according to the first embodiment of the present invention.

FIG. 5 is a flowchart showing a “color image forming sequence 2” according to the first embodiment of the present invention.

FIG. 6 is a diagram showing the rotation of the transfer drum, the transfer timing of the toner image of each color, and the rotation (movement) timing of each developing device in the “color image forming sequence 2” according to the first embodiment of the present invention.

FIG. 7 is a flowchart showing “color image forming sequence 3” in Embodiment 1 of the present invention.

FIG. 8 is a flowchart showing an image forming sequence according to the second embodiment of the present invention.

FIG. 9 is a flowchart showing “color image forming sequence 4” in Embodiment 2 of the present invention.

FIG. 10 is a diagram showing the rotation of the transfer drum, the transfer timing of the toner image of each color, and the rotation (movement) timing of each developing device in the “color image forming sequence 4” according to the second embodiment of the present invention.

FIG. 11 is a flowchart showing “color image forming sequence 5” in Embodiment 2 of the present invention.

FIG. 12 is a diagram showing rotation of a transfer drum in a color image forming sequence in a conventional example, transfer timing of toner images of respective colors, and rotation (movement) timing of developing units.

FIG. 13 is a diagram showing rotation of a transfer drum in a color image forming sequence in a conventional example, transfer timing of toner images of respective colors, and rotation (movement) timing of developing units.

[Explanation of symbols]

1 Photosensitive drum (first image carrier) 2 charging roller 3 developing device 4 Rotating developing device (developing device) 4a Yellow developing device 4b magenta developer 4c cyan developing device 4d Black developing device (fixed developing device) 5 transfer drum 44 fixing device 50 controller A leader section B Printer section P paper (second image carrier)

   ─────────────────────────────────────────────────── ─── Continued front page    F-term (reference) 2H027 DA41 DA43 DA46 DC10 DE01                       DE07 DE09 EA03 EA04 EC01                       EC06 EC09 EC20 ED08 ED16                       ED24 EE01 EE04 EE05 EE07                       EF06 FA02 FA03 FA28 FA35                       FB07 FB14                 2H030 AD05 AD07 AD08 AD17 BB24                       BB33 BB43 BB46 BB54 BB56                       BB63 BB71

Claims (3)

[Claims] 1. A first image carrier, a fixed developing device fixedly arranged to develop a latent image on the first image carrier to form an image, and a first image carrier on the first image carrier. The fixed developing device includes: a plurality of developing devices for developing latent images to form an image; and a moving means for mounting the plurality of developing devices and selectively moving one of the developing devices to a developing position. In the image forming apparatus, the image formed on the first image carrier is sequentially superposed and transferred onto the second image carrier by a developing operation by a developing device mounted on the first image carrier and the fixing device. The first developing device mounted on the moving means when a plurality of images each having a size of half or less of the maximum image size that can be formed are continuously formed by using both the developing device and the plurality of developing devices. After the developing operation by the developing unit, the developing operation by the fixed developing unit is executed and the fixing is performed. By the moving means during the developing operation executed by the image unit by moving the second developing device at the developing position to perform a developing operation, an image forming apparatus characterized by. 2. A first image bearing member, a fixed developing device fixedly arranged to develop a latent image on the first image bearing member to form an image, and a first image bearing member on the first image bearing member. The fixed developing device includes: a plurality of developing devices for developing latent images to form an image; and a moving means for mounting the plurality of developing devices and selectively moving one of the developing devices to a developing position. In the image forming apparatus, which sequentially transfers the images formed on the first image carrier onto the second image carrier by a developing operation by a developing device mounted on the first image carrier and the fixing device, When using the developing device and the plurality of developing devices to continuously form three or more images of a size less than half of the maximum size image that can be formed, the first means mounted on the moving means. 1 After the developing operation by the developing device, carry out the developing operation by the fixed developing device. The second developing device is moved to the developing position by the moving means during the developing operation by the fixed developing device to perform the developing operation, and the developing operation is performed by the developing device mounted on the fixed developing device and the moving means. When the two images are successively formed by sequentially superposing the obtained images and subsequently forming the third image, the moving means used last when forming the second image is mounted. An image forming apparatus characterized by performing development using a developing device first. 3. The fixed developing unit uses black toner, and each developing unit of the developing units mounted on the moving unit is yellow.
The image forming apparatus according to claim 1, wherein toners of magenta and cyan are used respectively.