JP2003207970A - Multicolor image forming device and its method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a tandem type multicolor image forming device by which the internal part of the device is simplified and the image forming of a job where color image data are mixed with monochromatic image data is efficiently performed in a short time without increasing a cost and also to provide a multicolor image forming method. <P>SOLUTION: The device is provided with an image forming mode changeover means which performs changeover between a first image forming mode to allow whole photoreceptor drums to be brought into contact with a carrier belt when a color image is formed and a second image forming mode to allow only the most upper stream side photoreceptor drum to be brought into contact with the carrier belt in the case of monochromatic image forming. When monochromatic image data are mixed with multicolor image data in the image forming job consisting of a plurality of sheets, image forming mode changeover times are detected based on the co-existing state and image forming by combining the first and second image forming modes is selected when a total image data changeover times are equal to or less than prescribed times. When the total times exceed the prescribed times, the first image forming mode is selected for image forming. <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 a multicolor image forming apparatus such as a copying machine, a facsimile, a printer, etc., which transfers a multicolor image or monochromatic image of various colors formed on an image carrier, The present invention relates to a multicolor image forming apparatus and a multicolor image forming method for forming a multicolor image or a single color image.

[0002]

2. Description of the Related Art Conventionally, electrostatic latent images corresponding to images of different colors (for example, C: cyan, M: magenta, Y: yellow, K: black) are formed for the purpose of speeding up image output. A tandem-type multi-image forming apparatus, in which four image forming stations each having an image carrier are arranged in parallel along the conveying direction of the recording material, and a multicolor image can be formed on the recording material by passing the recording material once. Color image forming apparatuses are in widespread use.

In this multicolor image forming apparatus, not only multicolor image formation but also black and white image formation using only a single color developer, especially a black developer, can be performed. In addition, in a multi-color image forming apparatus for both multi-color / black-and-white image formation, it is generally reported that the image formation amount in black and white is larger than that in multi-color image formation.

In a tandem type multicolor image forming apparatus, it is not necessary to use all four image forming stations when forming a black and white image. Therefore, in order to prevent deterioration of the image carrier of the unused image forming stations. The rotation of the unused image carrier is stopped.

Specifically, when a tandem type multicolor image forming apparatus is used to form a black-and-white image, when the rotation of an image carrier not used for image formation is stopped, a recording material is used in each image forming station. When the sheet is conveyed, it is necessary to stop the rotation of the image carrier and the recording material in a non-contact state so as not to disturb the black image by the stopped image carrier. Either the image carrier or the transfer / transport carrier that is in motion is moved so that the stopped image carrier and the recording material do not come into contact with each other.

As a result, the life of the image carrier in the image forming station is extended and the running cost of the color image forming apparatus is reduced.

[0007]

However, in the above-mentioned conventional multicolor image forming apparatus, the stopped image carrier and the transfer material as a recording material are brought into non-contact state, or vice versa. In order to bring the carrier and the transfer material into contact with each other,
Although it is necessary to move the image carrier or the transporting means for transporting the transfer material in the contact / separation direction such as ascending / descending, this movement cannot be performed instantaneously, which takes several seconds.

Moreover, switching from the second image forming mode (monochromatic image forming mode) for performing monochromatic image formation (monochrome image forming) to the first image forming mode (multicolor image forming mode) for performing multicolor image formation. In this case, since only the most upstream image forming station is used in the second image forming mode, if the transfer material (recording material / intermediate transfer carrier) passes through the most upstream image forming station. While it is possible to switch the image forming mode, when switching from the first image forming mode for forming a multi-color image to the second image forming mode for forming a single color image,
In this image forming mode, all the image forming stations are used to form an image, so switching cannot be performed until the transfer material passes through the image forming station located on the most downstream side, and it takes extra time. Therefore, it takes several seconds for this movement.

As described above, in addition to the time required for moving the conveying means in the contact and separation directions such as raising and lowering, the most upstream image forming station when switching from the second image forming mode to the first image forming mode is performed. The time required for the transfer material to pass through and the time for the transfer material to pass through the image forming station located on the most downstream side when switching from the first image forming mode to the second image forming mode are required. Therefore, if the image forming mode is switched every time the type of the actual image changes, it takes a very long time and efficient image formation cannot be performed.

Further, when the image data of the job for executing image formation is mixed image data of multi-color and single color, the image carrier of the image forming station stopped during the image formation of the same job. It is necessary to switch between a single-color image forming mode in which the transfer medium and the transfer material conveying means are not in contact with each other, and a multi-color image forming mode in which the image carriers of all image forming stations are used. There is a problem that it takes a long time to complete the image formation.

In view of this, in Japanese Patent Laid-Open No. 11-133697, multicolor image data and monochromatic image data are separately formed and images are formed in the respective modes, and then the order of the image formed objects is returned to the original state. A multicolor image forming apparatus that improves efficiency is disclosed.

With this configuration, even when monochromatic image data and multicolor image data are mixed in a plurality of image forming jobs, it is possible to shorten the time required to complete all the image formation in the same job. The deterioration of the image carrier can be suppressed.

However, since the multicolor image forming apparatus of the above publication requires an intermediate tray or the like for temporarily accommodating a plurality of image formed objects on which images have been previously formed, In addition to being complicated, the cost of the device is increased.

Further, the multicolor image forming apparatus having no intermediate tray separates the multicolor image data and the single color image data into respective modes (a mode in which all image carriers are used and a specific image carrier is used only). When the image formation is performed in the mode (in the mode), the formation order of the image-formed products is different, and it is necessary to rearrange them later, which is very troublesome.

The present invention has been made in view of the above points, and an object of the present invention is to make the inside of the apparatus simple and to obtain the multicolor image data and the single color image data without increasing the cost. It is an object of the present invention to provide a tandem-type multicolor image forming apparatus and a multicolor image forming method capable of efficiently performing image formation of mixed jobs without a troublesome work such as rearranging.

[0016]

In order to achieve the above object, according to the present invention, a plurality of image forming stations, each of which is arranged in parallel along the transporting direction of a transfer material and has an image carrier, is formed. A multi-color image is formed by all the image forming stations by bringing the image carriers of all the image forming stations into contact with the conveying means during multi-color image formation. In the image forming mode of No. 1 and the conveying means for the image carriers of the other image forming stations remaining so as to bring only the image carrier of the image forming station located on the most upstream side into contact with the transfer material when forming an image in a single color. A second image forming mode in which a single color image is formed by the most upstream image forming station by separating the image forming station, and an image forming mode switching unit, etc. It assumes a multicolor image forming apparatus and multi-color image forming method to switch I. When the single-color image data and the multi-color image data are mixed in the image forming job for a plurality of sheets, the image formation in the first image forming mode, or the first and second image forming modes is performed according to the mixed state. The image formation in which the image formation modes are combined is selected by the image formation mode switching means or the like.

According to this specific matter, the mixed state of the monochromatic image data and the multicolor image data is recognized based on the image forming job, and the number of times the image forming mode is switched is detected from the recognition result, or the image forming mode is switched. The time required for image formation including the time required for image formation is calculated, and it is determined whether to switch the image formation mode according to the detection result or the calculation result. By performing the single-color image formation in the image formation mode, the number of times the image formation mode is switched is reduced and the time required for image formation is controlled to be the shortest. As a result, it is possible to always perform the most efficient image formation, and eliminate the very troublesome work of rearranging the formation order of the image formed objects by eliminating the need for an intermediate tray and the like, and a simple and low-cost configuration. It is possible to obtain the multicolor image forming apparatus.

When the image formation in the second image formation mode is performed at a speed faster than the image formation in the first image formation mode, the second image formation mode for the monochromatic image formation is performed. It goes without saying that the image forming speed is increased, and the time required for image formation can be more effectively shortened even when the single-color and multi-color image forming modes are combined. Moreover, since the image quality is not significantly degraded when the image forming speed is increased in the monochromatic image formation as compared with the multicolor image formation, it is possible to efficiently perform the image formation without the image quality degradation. Become.

In particular, the following constitution is given as a more concrete indication of the selection criterion by the image forming mode switching means.

That is, the number of times the image forming mode is switched is detected based on the mixed state of the single color image data and the multicolor image data, and the number of times the multicolor image data is switched to the single color image data and the multicolor image data is changed to the multicolor image data. When the total number of times of switching to image data and the total number of times are less than or equal to a predetermined number,
While the image formation in which the first and second image formation modes are combined is selected, the image formation in the first image formation mode is selected when the total number of times exceeds a predetermined number.

According to this specific matter, when the number of times the type of image data (monochromatic image data, multicolor image data) changes is less than a predetermined number, the image forming mode is switched every time the type of image changes. However, since the image forming efficiency does not decrease, image formation is performed by combining the first and second image forming modes. On the other hand, when the number of times the type of image changes exceeds a predetermined number of times, by performing image formation in the first image forming mode (multicolor image formation),
It is possible to shorten the time required for switching and always perform efficient image formation.

On the other hand, the continuous number of monochromatic image data is detected based on the mixed state of the monochromatic image data and the multicolor image data, and when the continuous number of the monochromatic image data is equal to or more than a predetermined number, While selecting the image formation in which the first and second image formation modes are combined, the image formation in the first image formation mode is selected when the number of continuous single color image data is less than the predetermined number. ing.

According to this specific matter, when the number of continuous single-color image data is a predetermined number or more, the first image forming mode for forming a multi-color image and the second image forming mode for forming a single-color image are formed. Both are switched to form an image. On the other hand, when the number of consecutive single color image data is less than the predetermined number, efficient image formation can be performed by performing image formation in the first image formation mode in which multicolor image formation is performed. It will be possible. This is because if the number of consecutive monochromatic image data is less than the predetermined number, the first
Since the number of times the second image forming mode is switched increases, the time required for switching the image forming mode increases, and the image forming time can be shortened if all the images are formed in the first image forming mode. Is. Therefore, when the number of continuous single color image data is less than the predetermined number determined in consideration of the image forming efficiency, the image forming time is reduced by processing all the image forming in the first image forming mode. It can be shortened.

[0024]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is an explanatory view showing the configuration of a digital color copying machine as a multicolor image forming apparatus according to this embodiment.

In FIG. 1, a copying machine 1 is of a multi-function type and has the functions of a facsimile machine and a printer in addition to the functions of a copying machine.

First, the structure of the copying machine 1 will be described.
As shown in FIG. 1, the copying machine 1 includes a RADF 112, a scanner unit 110, an image forming unit 210, and a paper feeding mechanism 21.
1 is provided, and an operation panel (not shown) is further provided.

The RADF 112 is a document feeder in the copying machine 1, and is a double-sided automatic document feeder (RADF; R).
everaging Automatic Document
It has a function as tFeeder).

That is, the RADF 112 conveys the document set at a predetermined position onto the document table 111 in the scanner section 110. Then, after the document image is read by the scanner unit 110, it has a function of carrying out to a predetermined take-out position. Also, R
The ADF 112 also has a function of reversing the original after the original image is read by the scanner unit 110 and conveying the original to the original table 111 again. As a result, in the copying machine 1, it is possible for the scanner unit 110 to read the images on both sides of the document.

Further, the RADF 112 is a document table 111.
It can be opened and closed freely. Therefore, the user
When using the RADF 112, this RADF 112
While the RADF is closed while the RADF is opened, the document can be placed directly on the document table 111.

The scanner section 110 is for reading an image of a document conveyed by the RADF 112,
An image input device in the copying machine 1. In addition to the document table 111, the scanner unit 110 includes a first scanning unit 113, a second scanning unit 114,
It has an optical lens 115 and a CCD 116.

The scanning units 113 and 114 are used for the document table 1.
By moving back and forth in parallel with 11, the platen 11
It is for reading an image of a document placed on the sheet 1.

The first scanning unit 113 has an exposure lamp 113a for exposing the original image, and a first mirror 113b for deflecting the reflected light image from the original in a predetermined direction. Then, it is set so as to reciprocate in parallel with the document table 111 at a predetermined scanning speed while maintaining a constant distance from the lower surface of the document table 111.

Further, the second scanning unit 114 has the first scanning unit
It has second and third mirrors 114a and 114b for deflecting the reflected light image deflected by the mirror 113b in the direction in which the optical lens 115 is located. And
The second scanning unit 114 includes the first scanning unit 11
3, a constant speed relationship is maintained, and reciprocating movement is performed in parallel with the document table 111.

The optical lens 115 includes the first to third mirrors 1
The reflected light image from the document deflected by 13b, 114a and 114b is reduced and imaged at a predetermined position on the CCD 116.

The CCD 116 photoelectrically converts the formed reflected light image to generate an image and information of an electric signal and outputs it to the image forming section 210 (CCD; cha).
Rage coupled device) line sensor.

Further, the CCD 116 can read a color image. That is, the CCD 11
6 can generate image information of line data that is color-separated for each color component of R (red), G (green), and B (blue) from a color reflected light image.

The image information generated by the CCD 116 is further transferred to an image processing unit (see FIG. 2) described later and subjected to a predetermined image processing, and then the image forming unit 210.
Is output to.

The image forming section 210 uses a sheet P as a transfer material based on the image information output from the CCD 116.
It is for printing images on. The image forming section 210 is composed of a black image transfer section 301, a yellow image transfer section 302, a magenta image transfer section 303, and a cyan image transfer section 304.

The transfer units 301 to 304 have substantially the same structure, and transfer the black image, the yellow image, the magenta image, and the cyan image to the sheet P based on the image information. Is set to.

The transfer units 301 to 304 have LSUs 227a to 227d and first to fourth image forming stations Sa to Sd, respectively.

Pixel signals corresponding to the black component, the yellow component, the magenta component and the cyan component in the image information are input to the LSU (laser beam scanner unit) 227a to 227d, respectively. Then, each of the LSUs 227a to 227d, based on these image signals, the photosensitive drums 222a to 222d in the first to fourth image forming stations Sa to Sd.
It is set to expose (described later) and generate an electrostatic latent image.

Also, these LSUs 227a to 227d
Has a semiconductor laser diode (not shown) for generating a dot-shaped laser beam modulated according to image information, and a laser controller for controlling the power of the semiconductor laser diode and the timing of light generation. .

Further, the LSUs 227a to 227d are the Bolgon mirrors 240a to 240d and the f-θ lens 241.
a-241d and mirrors 242a-242d, 243
a to 243d.

The polygon mirrors 240a to 240d have a function of deflecting the laser beam emitted from the semiconductor laser element in the main scanning direction. Also, each of the above f-
The θ lens and the mirror are the Borgon mirrors 240a-2
This is for forming an image of the laser beam deflected by 40d on the surfaces of the photoconductor drums 222a to 222d as image carriers.

The first to fourth image forming stations S
a to Sd generate toner images corresponding to respective colors based on the laser beams emitted from the LSUs 227a to 227d, and sequentially transfer the toner images to the sheet P. These image forming stations Sa to Sd are provided on the photosensitive drum 222.
a to 222d, and chargers 223a to 223a to
223d, developing devices 224a to 224d, transfer dischargers 225a to 225d, and cleaning devices 226a to 226d.
226d is arranged around the photosensitive drums 222a to 222d along the arrow F direction.

Each of the photosensitive drums 222a to 222d is a drum-shaped transfer roller having a photosensitive material on its surface, and is set so as to be rotationally driven in the arrow F direction. The chargers 223a to 223d are provided on the photoconductor drum 222.
It is a scorotron type corona discharger for uniformly charging a to 222d.

The developing devices 224a to 224d contain toners of black, yellow, magenta and cyan, respectively. The toner has a function of developing the electrostatic latent image formed on the photoconductor drums 222a to 222d with these toners to form a toner image.

The transfer dischargers 225a to 225d transfer the toner images on the photosensitive drums 222a to 222d to the sheet P.
It is a corona discharger for transferring to. The powers (potentials) of the transfer dischargers 225a to 225d are controlled by a power controller (not shown). Further, the cleaning devices 226a to 226d
After the transfer to the sheet P, the photosensitive drums 222a to 222a
It has a function of removing the toner remaining on 2d.

The axial length of the photosensitive drums 222a to 222d is set to be slightly longer than the width of the sheet P. Therefore, electrostatic latent image and toner image (image)
Is formed not on the entire surface of the photoconductor drums 222a to 222d but only on the central region. So, in the following,
The image forming area of each of the photoconductor drums 222a to 222d is set as an image area, and the end area where no image is formed is set as a non-image area.

The sheet feeding mechanism 211 conveys the sheet P to a predetermined position of the image forming section 210 in order to transfer the toner image of each color generated by the image forming section 210 to the sheet P. Further, the paper feeding mechanism 211 has a function of discharging the sheet P to the outside after the toner image is transferred.

The sheet feeding mechanism 211 includes a sheet cassette 25.
1, a take-out roller 250, a plurality of conveyance rollers 252, registration rollers 212, a transfer conveyance belt mechanism 213 as a conveyance means, a fixing device 217, a conveyance direction switching gate 218, a paper discharge roller 219, and a paper discharge tray 220.

The sheet cassette 251 is for accommodating a cut sheet-shaped sheet P used in the copying machine 1. The take-out roller 252 is a pickup roller for taking out the sheets P one by one from the sheet cassette 251. Further, the transport rollers 252, ...
The sheet P output from the sheet cassette 251 is sent to the main transport path L and is transported on the main transport path L.

The pre-registration detection switch is the conveyance roller 2
This is for detecting that the sheet P conveyed by 52, ... Has passed a predetermined position on the main conveyance path L and outputting a predetermined detection signal.

The registration roller 212 temporarily holds the sheet P conveyed on the main conveyance path L.
Further, it has a function of feeding the toner images on the photoconductor drums 222a to 222d to the transfer / conveying belt mechanism 213 in time with the image forming stations Sa to Sd so that the toner images can be satisfactorily transferred onto the sheet P.

In other words, the registration roller 212 causes the leading edge of the toner image on the photosensitive drums 222a to 222d to be pressed against the leading edge of the printing range of the sheet P based on the detection signal output from the pre-registration detection switch. It is set so as to send P to the transfer / transport belt mechanism 213.

The transfer / transport belt mechanism 213 has a drive roller 214, a driven roller 215, a transport belt 216, a suction charger 228, a charge eliminator 229, and an auxiliary roller 231.

The conveyor belt 216 is stretched between the driving roller 214 and the driven roller 215, and each roller 214,
215 is designed to be frictionally driven in the direction of arrow Z. Then, it has a function of electrostatically adsorbing the sheet P fed by the registration rollers 212 and conveying it to each of the image forming stations Sa to Sd and the fixing device 217.

Digital color copying machine 1 of this embodiment
Conveys the conveyor belt 216 to the photosensitive drums 222a to 222.
It can be brought into contact with or separated from d, and can be switched between formation of a single color image and formation of a color image. Such contact / separation control of the transport belt 216 will be described in detail later.

The attraction charger 228 is provided at the first image forming station Sa located on the most upstream side of the sheet P in the conveying direction.
And a brush provided between the registration roller 212 and the registration roller 212 for charging the surface of the conveyor belt 216. That is, in the copying machine 1, the conveyance belt 216 is charged and the sheet P is electrostatically adsorbed to prevent the sheet from being displaced during conveyance.

The static eliminator 229 is provided between the fourth image forming station Sd located on the most downstream side of the sheet P in the transport direction and the fixing device 217, and removes the surface of the transport belt 216 by an alternating current. It is for doing.

That is, each image forming station Sa to
The toner images of the respective colors are transferred and superposed on the sheet P conveyed to Sd. Then, when the transfer by each of the image forming stations Sa to Sd is completed, the sheet P is set by the static eliminator 229 to be sequentially peeled from the transport belt 216 from the leading end portion thereof and guided to the fixing device 217. There is.

The fixing device 217 heat-fixes the unfixed toner image transferred onto the sheet P. And
The sheet P that has been subjected to the heat fixing process is guided by the conveyance guide 218, and the sheet P after fixing is discharged to the discharge tray 220.

In the above description, LSU 227a ...
By 227d, a laser beam is scanned and exposed to perform optical writing on the photoconductor. But LS
Instead of U227a to 227d, a writing optical system (LED is composed of a light emitting diode array and an imaging lens array.
Head) may be used. LED head is LSU22
Compared with 7a to 227d, the size is smaller and there is no moving part and there is no sound. Therefore, it can be preferably used in an image forming apparatus such as a tandem type digital color copying machine which requires a plurality of optical writing units.

Next, the image processing section of the digital color copying machine 1 will be described with reference to FIG. Figure 2
FIG. 3 is a block diagram showing a state in which a central processing unit (CPU) 50 mounted on the digital color copying machine 1 controls the operation of the digital color copying machine 1.

As shown in FIG. 2, the digital color copying machine 1 includes an operation board unit 40, a double-sided automatic document feeder 41, an image reading section 42, an image forming section 43, and an image processing section 4.
4, a CCD 45, an image data input unit 46, an image data output unit 47, an image memory 48, an image data communication interface 49 (I / F) for communicating with an external terminal, and a central processing unit 50.

The central processing unit 50 is connected to the operation board unit 40 composed of an operation panel capable of mutual communication, the double-sided automatic document feeder 41, the screen reading section 42, the image forming section 43, and the image processing section 44, and the both sides thereof. The automatic document feeder 41, the screen reading unit 42, the image forming unit 43, and other drive mechanism units constituting the digital color copying machine 1 are managed by sequence control, and control signals are output to each unit.

The operation board unit 40 is provided with an operation panel, and the central processing unit 50 is in a state capable of mutual communication.
The digital color copying machine 1 is operated in accordance with the set mode by transferring to the central processing unit 50 a control signal indicating the content of the copying mode set and inputted by the operator through the operation panel. Are controlled.

In addition to this, it is possible to set the initial state (default) of the digital color copying machine 1 and change the setting of the control value for each image forming mode from the operation panel. You can change the settings by entering the hidden code and so on. Therefore, when the color image formation is frequently performed according to the user's request, the default image formation mode is set to perform the image formation using the first to fourth image forming stations Sa to Sd. On the contrary, when monochromatic image formation is frequently performed, the image forming mode in which the image formation is performed using only the first image forming station Sa can be set.

Further, the operation board unit 40 is transferred from the central processing unit 50 with control signals indicating various operating states of the digital color copying machine 1, and the operator can determine what state the apparatus is currently in by the control signals. As shown in FIG.

The contact / separation control of the conveyor belt 216 in the digital color copying machine 1 of this embodiment will be described below with reference to FIGS. 3 and 4.

In addition to the members described above, the digital color copying machine 1 includes, as shown in FIGS. 3 and 4, a separation / contact drive unit 253, a holding roller 255, and motors M1 to M6.
Is equipped with.

The contact / separation mechanism section 253 is the central processing unit 5.
It is adapted to be driven by a command from the image forming mode switching means MC provided at 0. Further, in the separation / contact driving unit 253, an eccentric shaft 256 is inserted in an oval insertion hole, and the rotation of the eccentric shaft 256 causes the conveyor belt 216 to separate from or contact the photosensitive drums 222b to 222d. It becomes possible to do.

Further, the driving roller 214 is the motor M1.
Further, the photosensitive drums 222a to 222d are connected to the motors M3 to M6, respectively, and the motors M1 to M6 are controlled by the central processing unit 50.

In the digital color copying machine 1 of this embodiment, when the color image forming mode (first image forming mode) is performed, as shown in FIG.
16 and the first to fourth image forming stations Sa to S
The photosensitive drums 222a to 222d of d are brought into contact with each other to form an image.

On the other hand, when the monochromatic image forming mode (second image forming mode) is carried out, as shown in FIG. 4, the image forming should be carried out only by the first image forming station Sa located on the upstream side again. , The conveyor belt 216 is the transfer discharger 2
25a, which is in contact only with another transfer discharger 225b.
It is separated from ~ 225d.

At this time, the distance between the photosensitive drum 222b of the second image forming station Sb and the conveyor belt 216, which are close to the fulcrum 255 serving as the rotation axis, is about 2 mm.
The distance between the photosensitive drum 222d of the fourth image forming station Sd on the farthest downstream side and the conveying belt 216 is set to be about 10 mm.

As described above, during monochromatic image formation such as monochromatic image formation, only the photoconductor drum 222a of the first image forming station Sa on the most upstream side for image formation is brought into contact with the transfer discharger 225a. By controlling, the image quality of a single color image is improved, and at the same time, the photoconductor drums 222 of all the image forming stations Sa to Sd are constantly operated.
Compared with an image forming apparatus that forms an image in a state in which a to 222d are in contact with the transfer dischargers 225a to 225d,
The product life of the unused photosensitive drums 222b to 222d can be extended.

The separation operation of the conveyor belt 216 at this time is performed by the transfer conveyor belt mechanism 213 by a detector (not shown).
The position may be controlled by the number of rotation steps of the motor M2 with reference to the position, or two detectors may be used so that the contact position and the separated position can be detected.

Any of the above-mentioned separated / contacted states may be set as the default state. Settings can be input from the operation board unit 40 or the like according to the usage status of the user.

Such contact / separation switching is performed by appropriately rotating the motor M2 in response to a command from the central processing unit 50 to rotate the conveyor belt 216 about the axis of the holding roller 255. In the separated state, the motors M4 to M connected to the photosensitive drums 222b to 222d of the separated second to fourth image forming stations Sb to Sd.
6 is controlled to be stopped by the central processing unit 50.

Here, when switching between the color image forming mode (first image forming mode) and the single color image forming mode (second image forming mode), the second to fourth image forming stations Sb to Sd are operated. Photoconductor drum 222b
.About.222d and the transfer dischargers 225b to 225d will be described in more detail with reference to FIGS.

For example, when the mode is switched from the monochromatic image forming mode to the color image forming mode, the drive switching of the photosensitive drums 222b to 222d and the conveying belt 216 are performed.
It is necessary to switch between contact and separation with.

That is, the photosensitive drums 222b to 222d of the second to fourth image forming stations Sb to Sd.
In order to avoid abrasion due to sliding between the conveyor belt 216 and
The photosensitive drums 222b to 222d are rotated to a predetermined rotation speed, and the conveyor belt 216 is moved to bring them into contact with each other.

Conventionally, the contact operation is performed after the sheet P in the monochromatic image forming mode is separated from the conveyor belt 216. This is because when mode switching is performed with at least the sheet P remaining on the conveyor belt 216 during image formation, the effect of the sheet P on the conveyor belt 216 on the image, specifically, streaks on the image occurs. It was thought that there was a risk of

That is, from the start of image formation in the single-color image forming mode to the completion of switching to the color image forming mode, the time required for image formation of the black component image, cyan, magenta, and yellow in which image formation is not performed thereafter are performed. The time required for the sheet P to pass through the image forming portion of each color and disappear from the conveyor belt 216, and the rotation of the photosensitive drums 222b to 222d and the movement of the transfer conveyor belt mechanism 213 are included. It takes time to contact.

In the digital color copying machine 1 of the present embodiment, when the image formation of the black component on the sheet P is completed, the photosensitive drums 222b to 222d of cyan, magenta, and yellow are rotated to transfer the transfer belt. Mechanism 2
Start the movement of 13.

As an example, the photosensitive drums 222a to 222d of the first to fourth image forming stations Sa to Sd.
The rotation speed of 222d is a constant speed rotation of about 100 mm / s. It should be noted that from the start of the rotation operation of the photosensitive drums 222b to 222d until the predetermined rotation speed is reached and from the constant speed rotation to the stop, it is performed in a relatively short time of several hundred ms after the control signal is output. You can

The cyan, magenta, and yellow photoconductor drums 222b to 222 of the transfer / transport belt mechanism 213 are also provided.
The contact / separation operation with respect to 2d requires about 5 to 8 seconds because of the large number of parts constituting the transfer / transport belt mechanism 213 and the large size and weight.

In FIG. 5, after the image formation of the black component is completed,
Cyan, magenta, and yellow photoconductor drums 222
b to 222d start rotating, and the transfer / conveying belt mechanism 213
Shows the state immediately before the movement (state in the monochromatic image forming mode).

Here, each of the photosensitive drums 222a to 22a
The distance L1 between 2d is 100 mm, the photosensitive drum 222b
The distance L2 between the eccentric shaft 256 and the eccentric shaft 256 is set to be 50 mm. From this state, first, the transfer / conveying belt mechanism 213 starts to move. The conveyor belt 216 has a fulcrum 25
The drive roller side moves around 5. The black component photosensitive drum 222a is always in contact with the conveyor belt 216, but the other cyan, magenta, and yellow photosensitive drums 222b to 222d are in contact with the conveyor belt 216 in the color image forming mode. However, there is no contact in the monochrome image forming mode. Further, in the single-color image forming mode, the photosensitive drums 222b to 222d for cyan, magenta, and yellow colors have their rotation operations stopped.

FIG. 6 shows a state in which the sheet P has passed through the cyan photosensitive drum 222b after the transport belt 216 started to move. Even at this time, the photosensitive drums 222b to 22b of cyan, magenta, and yellow
2d is not in contact with the conveyor belt 216. Then, as shown in FIG. 7, the cyan, magenta, and yellow photosensitive drums 222b are not provided until the sheet P passes through the yellow photosensitive drum 222d.
~ 222d simultaneously contacts the conveyor belt 216.

As a result, the sheet P becomes the photosensitive drum 22.
When the passage of 2d is completed, it is possible to immediately start the color image formation. The stopped photosensitive drums 222b to 222d of cyan, magenta, and yellow colors start rotating between the state of FIG. 5 and the state of FIG. 7, and the state of FIG. The speed is controlled to be the same as the speed of the transport belt 216 until just before the photosensitive drum 222d that has been separated contacts the transfer belt 216.

As an example, the cyan photosensitive drum 222b and the conveyor belt 21 near the fulcrum 255 when separated from each other.
6 is set to be about 2 mm, and the gap between the yellow photosensitive drum 222d far from the fulcrum 255 and the conveyor belt 216 is set to be about 10 mm. The distance L1 between the photosensitive drums 222a to 222d is 100 m.
m and L2 are fulcrum points 255 near the middle of the cyan photosensitive drum 222b and the black photosensitive drum 222a.
Since it is provided, it is set to 50 mm.

In this case, after the transfer of the black image to the sheet P is completed, it takes only 1.5 seconds until the trailing edge of the sheet P passes through the fourth photosensitive drum 222d. At this time, the sheet P on the conveyor belt 216 and the photosensitive drums 222b to
The gap with 222d is 60% to 70% of the gap when the transfer / conveying belt mechanism 213 starts moving. Therefore, immediately after the transfer of the black image to the sheet P is completed (the sheet P is the black photosensitive drum 2
Immediately after being completely separated from 22a), the raising of the transfer / conveying belt mechanism 213 can be started.

As described above, the photosensitive drum 22
The time required for 2a to 222d to reach a predetermined rotation speed is
It is shorter than the time required to complete the movement of the transfer / transport belt mechanism 213. Therefore, even if the photoconductor drums 222a to 222d start to rotate after the transfer / conveying belt mechanism 213 starts moving, when the photoconductor drums 222a to 222d contact each other, the rotation speed of the photoconductor drums 222a to 222d reaches a constant speed. Therefore, the surfaces of the photosensitive drums 222a to 222d and the conveyor belt 216 do not rub against each other.

When the rotation time of the photoconductor drums 222a to 222d is set as short as possible, the timing at which the photoconductor drums 222a to 222d contact the conveyor belt 216 and the photoconductor drums 222a to 222d are kept at a constant speed. The photosensitive drum 22 is calculated by the time until
The rotation start timing of 2a to 222d can be set. The separation / contact operation of the conveyor belt 216 is controlled with reference to the position of the transfer conveyor belt mechanism 213 by a detector (not shown).

As described with reference to FIGS. 2 and 3, the motor M1 for driving the conveyor belt 216, the motor M2 for moving the separation / contact mechanism, and the photosensitive drums 222a to 222d of the respective colors.
The operation timings of the respective motors M3 to M6 for rotating are controlled by the same control unit. Furthermore, by using each of these motors M1 to M6 as stepping motors,
The speed control and the position control can be controlled with open loop with high accuracy, and the timing of each operation can be easily achieved.

As described above, in the digital color copying machine 1 of the present embodiment in which the separation / contact state is switched depending on the image forming mode, in particular, as shown in FIG. 8, single color image data and color image data are included in an image print job. In the case where both and are mixed, the image formation is performed for the total of 14 originals by selectively using the single-color image forming mode and the color image forming mode. In FIG. 8, ▲ indicates switching to the color image forming mode, and ∇ indicates switching to the single color image forming mode.

As shown in FIG. 8A, the color image 3
When the image formation of one sheet, ten single color images and one color image is continuously performed, after the image formation of three color images, the re-upstream side photosensitive drum 222a and the transfer discharger 225 are brought into contact with each other. As described above, the control for changing the image forming mode is performed. After forming 10 monochromatic images, all the photoconductor drums 222a to 222d are transferred to the transfer discharger 2 again.
It is controlled so as to come into contact with 25a to 225d.

Further, as shown in FIG. 8B, three color images, four single color images, two color images, and one single color image 4
When the image formation of one sheet and one color image is continuously performed, the image forming modes are switched when the color is changed to the single color and when the single color is changed to the color, and the photosensitive drums 222b to 222d are transferred. Discharger 225b
The image formation is performed by separating and contacting with the .about.225d.

Subsequently, as shown in FIG. 8C, when the image formation of three monochromatic images, ten color images, and one monochromatic image is continuously performed, three monochromatic images are formed. rear,
The image forming mode is switched to the color image forming mode to form a color image, and the remaining one monochromatic image is formed in the color image forming mode.

Further, as shown in FIG. 8D, when the image formation of 10 monochromatic images, 1 color image, 2 monochromatic images, and 1 color image is continuously performed, the monochromatic image 1
After forming 0 images, the image forming mode is switched to the color image forming mode. The remaining color / monochromatic images are all formed in the color image forming mode.

As shown in (c) and (d) of FIG.
The time required for switching the image forming mode, that is, the transfer discharger 2 for the photosensitive drums 222b to 222d
Considering the time required to contact / separate 25b to 225d,
When it is more efficient to perform the single-color image formation in the color image formation mode, the image formation in the color image formation mode enables the image formation with the shortest image formation time.

The method of calculating the image forming time and selecting the image forming mode so as to maximize the efficiency will be specifically described with reference to Tables 1 to 3 as follows. is there.

[0106]

[Table 1] Time required for image formation in color image formation mode,
Table 1 shows the time required for image formation in the monochromatic image forming mode, the time Td required for switching from the color image forming mode to the monochromatic image forming mode, and the time Tu required for switching from the monochromatic image forming mode to the color image forming mode. As shown, it is 8 seconds and 5 seconds, respectively.

In this embodiment, since the image forming speed in the color image forming mode is set to be half the image forming speed in the single color image forming mode, the image forming time per sheet in the color image forming mode is set. The image forming time per sheet in the single-color image forming mode is Tc, and Tb is 3 seconds / sheet and 1.5 seconds / sheet as shown in Table 1, respectively.

As described above, since the image forming speed in the monochromatic image forming mode for forming a monochromatic image is set higher than that in the color image forming mode, the case where only the monochromatic image is formed or the both image forming modes are combined. However, the time required for image formation can be shortened more effectively.

Regarding the switching time of the image forming mode, the switching time Td (8 seconds) from the color image forming mode to the monochromatic image forming mode is longer because all image forming stations are used in the color image forming mode. Since the image formation is performed by using the transfer material, switching cannot be performed until the transfer material passes through the image forming station located on the most downstream side.
This is because it takes an additional 3 seconds in addition to the time for switching the image forming mode from the single color image forming mode to the color image forming mode.

[0110]

[Table 2] Then, as shown in Table 2, the number of image formations in the color image formation mode, the number of image formations in the single color image formation mode,
The number of times of switching from the color image forming mode to the monochrome image forming mode and the number of times of switching from the monochrome image forming mode to the color image forming mode are NC sheet, Nb sheet and Nd respectively.
If the number of sheets is Nu, then each image formation shown in FIGS. 8A to 8D will take time as shown in Table 3 below.

[0111]

[Table 3] As shown in Table 3, when forming an image as shown in FIG. 8A, the number of times the image forming mode is switched is better when the image forming mode is switched to the image forming mode corresponding to the original image. Since it is as small as twice for 14 originals, the image forming time can be shortened as compared with the case where the image is formed only in the color image forming mode for about 2 seconds.

On the contrary, during the image formation shown in FIG. 8B, the number of times the image forming mode is switched increases to four. Therefore, it is possible to perform image formation for 14 seconds only in the color image forming mode. The image forming time can be shortened as compared with the case where the image is formed while switching the mode to the image forming mode corresponding to the original image.

At the time of image formation shown in FIG. 8C, when the image formation is performed only in the color image formation mode, as compared with the case where the image formation is performed while switching to the image formation mode corresponding to the original image, By forming a single color image in the color image forming mode, the image forming time can be minimized. In the image formation shown in FIG. 8D, when the image formation is performed only in the color image formation mode, the image formation may be performed depending on the situation as compared with the case where the image formation is performed while switching to the image formation mode corresponding to the original image. The image forming time can be shortened most by combining the single color image forming in the color image forming mode without switching the image forming mode.

According to this situation, for example, when the number of times the type of image (monochromatic image, color image) changes is less than a predetermined number of times, the image forming mode is changed each time the type of image changes. Since the image forming efficiency does not decrease even after switching, image formation is performed by combining the two image forming modes, and when the number of times the type of image changes exceeds a predetermined number, the color image forming mode (color image forming mode) is performed. The image formation may be performed as it is. As a result, it is possible to prevent an inefficient image formation due to an increase in the time required to switch the image formation mode, and it is possible to always perform an efficient image formation.

Further, when the monochromatic image data continues for a predetermined number of times or more, both the monochromatic image forming mode and the color image forming are switched to form an image, and when the monochromatic image formation does not continue for a predetermined number of times or more. Alternatively, the image formation may be performed in the color image formation mode in which the color image formation is performed. As a result, when monochromatic image formation does not continue for a predetermined number of times or more, the number of times the image forming mode is switched increases, so the time required to switch the image forming mode increases, and all the image formation in the color image forming mode is performed. The image forming time can be shortened by performing the above. Therefore, when the monochromatic image data is not continuous for a predetermined number of times determined in consideration of the image forming efficiency, the image forming time can be shortened by processing all the image forming in the color image forming mode.

Here, one example of the image forming method in the digital color copying machine 1 of the present embodiment as described above will be explained based on the flowcharts of FIGS. 9 and 10.

First, when the image forming mode is selected in consideration of the number of times the image forming mode is switched, after inputting the image data in step ST1 of the flowchart of FIG. 9, the kind of image data is selected in step ST2. Determine. Next, in step ST3, the number of times the image forming mode is switched, that is, the total number of times of switching from the single color image forming mode to the color image forming mode and the number of times of switching from the color image forming mode to the single color image forming mode is equal to or greater than a predetermined number. Or not. If the determination in step ST3 is YES, that is, the total number of times is greater than or equal to the predetermined number, in step ST4, the photosensitive drums 222a of all the image forming stations Sa to Sd are detected.
A color image forming mode for rotating the first to 222 d is selected, and all images are formed in the color image forming mode in step ST5. Then, in step ST6, it is determined whether or not there is the next image data, and the process is repeated until there is no more next image data, and then step ST7.
Then, the default mode is set and the image formation is completed.

On the other hand, if the determination in step ST3 is NO, that is, the total number of times is less than the predetermined number of times, step S3 is performed.
At T8, the optimum image forming mode according to the type of image data of the first page is selected from the color image forming mode and the single color image forming mode, and at step ST9, image formation is performed in the color image forming mode or the single color image forming mode. . Then, in step ST10, it is determined whether or not there is the next image data. If there is no next image data, the process proceeds to step ST7. On the other hand, if the determination in step ST10 is YES with the next image data, it is determined in step ST11 whether the image data is of a different type from the image data formed in the previous page.

If the determination in step ST11 is NO, which is the same type of image data as the previous page, the process returns to step ST9 to perform image formation in the same image mode, while the image of a type different from the previous page is used. If YES in step ST12, in step ST12, the optimum image forming mode according to the type of image data of the next page is selected from the color image forming mode and the single color image forming mode, and in step ST13, the color image forming mode is selected. Alternatively, image formation is performed in the monochromatic image formation mode. afterwards,
In step ST14, it is determined whether or not there is next data, and if there is no next data, the process proceeds to step ST7.

On the other hand, if the determination in step ST14 is YES with the next data, it is determined in step ST15 whether the image data is of a different type from the image data formed on the previous page. If the determination in step ST15 is NO, which is the same type of image data as the previous page, the process returns to step ST13 to perform image formation in the same image mode, while the image data is of a type different from the previous page. If YES, the process returns to step ST12, and the optimum image forming mode corresponding to the type of image data of the next page is selected from the color image forming mode and the single color image forming mode. Here again, the optimum image forming mode according to the type of image is repeatedly selected until the next image data is exhausted.

As described above, the number of times the image forming mode is switched is calculated, the total number of times of switching is compared with a predetermined number, and the image forming mode is selected so that the image forming time is the shortest. It is possible to shorten the time required to switch between, and always perform efficient image formation.

In this case, the user may previously input the predetermined number of times using the operation panel or the like. For example, in the case of (a) and (b) of FIG. 8, the image formation can be performed most efficiently by setting the predetermined number of times to three times.

Next, the case where the image forming mode is selected in consideration of the time required for image formation will be described.

Step ST2 of the flowchart of FIG.
In step 1, after inputting image data, step ST2
At 1, the type of image data is determined. Next, in step ST23, the time required for image formation is calculated, and in step ST24, it is determined whether the image formation by switching the image formation modes is slower than the image formation in the color image formation mode. judge.

If the determination in step ST24 is YES that the image forming mode is switched to form an image later, in step ST25, the photosensitive drums 222a to 222d of all the image forming stations Sa to Sd are formed.
The color image forming mode for rotating is selected, and in step ST26, all images are formed in the color image forming mode. Then, in step ST27, it is determined whether or not there is the next data, and the process is repeated until there is no more next data. Then, in step ST28, the default mode is set and the image formation is completed.

On the other hand, when the determination in step ST24 is NO in which it is faster to switch the image forming modes to form an image, in step ST29, the optimum image forming mode corresponding to the type of the image data of the first page is selected. Select from color image formation mode and single color image formation mode,
In step ST30, image formation is performed in the color image formation mode or the single color image formation mode. Then, in step ST31, it is determined whether or not there is the next data. If there is no next data, the above step S31 is performed.
Proceed to T28. On the other hand, the determination in step ST31 is
If the next data is YES, step ST32
At, it is determined whether the image data is of a different type from the image data formed on the previous page.

If the determination in step ST32 is NO, which is the same type of image data as the previous page, the process returns to step ST30 and the image formation is performed in the same image mode as the image of the previous page. If YES as the data, in step ST33, the optimum image forming mode according to the type of image data of the next page is selected from the color image forming mode and the single color image forming mode, and in step ST34, the color image forming mode is selected. Alternatively, image formation is performed in the monochromatic image formation mode. Then, in step ST35, it is determined whether or not there is the next data. If there is no next data, the process proceeds to step ST28.

On the other hand, if the determination in step ST35 is YES with the next data, it is determined in step ST36 whether the image data is of a different type from the image data formed on the previous page. If the determination in step ST36 is NO, which is the same type of image data as the previous page, the process returns to step ST34 to perform image formation in the same image mode, while the image data is of a type different from the previous page. If YES, the process returns to step ST33, and the optimum image forming mode corresponding to the type of image data of the next page is selected from the color image forming mode and the single color image forming mode. Here again, the optimum image forming mode according to the type of image is repeatedly selected until the next image data is exhausted.

As described above, by calculating the image forming time and selecting the image forming mode so that the image forming time is the shortest, the time required for switching the image forming modes is shortened and the image is always most efficiently imaged. Forming can take place.

As described above, since the image forming mode is selected in accordance with the degree of mixing of the monochromatic image data and the color image data to form the image, the intermediate tray or the like is not necessary and the order of forming the image formed products is eliminated. It is possible to eliminate the very troublesome work of rearranging the items, and obtain the digital color copying machine 1 having a simple and low-cost configuration.

The present invention is not limited to the above embodiment, and includes various other modifications. For example, although the tandem type color image forming apparatus has been described in the above embodiment, as shown in FIG. 11, the second intermediate transfer belt 301 is provided between the driving roller 214 and the driven roller 215. Through the intermediate transfer belt mechanism 300 capable of contacting / separating from the photosensitive drums 222b-222d of the fourth image forming stations Sb-Sd, and carrying the toner image transferred onto the intermediate transfer belt 301 as a carrying means. Even in the digital color copying machine 1'which adopts the intermediate transfer method in which the sheet P conveyed on the belt 302 is transferred by the secondary transfer roller 302a, the same structure is obtained by using the same configuration as described above. The effect of can be obtained.

[0132]

As described above, in the present invention, the mixed state of monochromatic image data and multicolor image data is recognized based on the image forming job, and the number of times the image forming mode is switched is detected from the recognition result. Or calculate the time required to form an image including the time required to switch the image forming mode, and determine whether to switch the image forming mode according to the detection result or the calculation result. By performing the single-color image formation in the first image formation mode for forming the image, the number of times the image formation mode is switched is controlled so that the time required for the image formation is minimized. It is possible to obtain a multicolor image forming apparatus having a simple and low-cost configuration, which can form an image well and does not require an intermediate tray or the like.

By performing the image formation in the second image formation mode at a speed faster than the image formation in the first image formation mode, the image in the second image formation mode for monochromatic image formation is formed. Even when the formation speed is increased and the single-color and multi-color image formation modes are combined, the time required for image formation can be more effectively shortened. Moreover, even if the image forming speed is increased during the monochromatic image formation, the image formation can be efficiently performed without deteriorating the image quality.

Further, the number of times the image forming mode is switched is detected based on the mixed state of the monochromatic image data and the multicolor image data, and when the number of times the type of the image data changes exceeds a predetermined number, the first By performing image formation in the image formation mode, it is possible to shorten the time required for switching and always perform efficient image formation.

On the other hand, based on the mixed state of the monochromatic image data and the multicolor image data, when the number of consecutive monochromatic image data is less than the predetermined number, the image formation is performed in the first image forming mode. By doing so, the time required to switch the image forming mode can be shortened.

[Brief description of drawings]

FIG. 1 is a sectional view of a digital color copying machine according to an embodiment of the present invention as viewed from the front.

FIG. 2 is a block diagram showing a configuration of an image processing unit in a digital color copying machine.

FIG. 3 is a cross-sectional view of a main part of a copying machine showing a contact state of a conveyor belt when a color image forming mode is selected.

FIG. 4 is a cross-sectional view of essential parts of the copying machine showing a separated state of the conveyor belt when the single-color image forming mode is selected.

FIG. 5 is a diagram illustrating a case of switching to a monochromatic image forming mode,
FIG. 6 is a cross-sectional view of a main part of a copying machine showing in more detail the separated state between the photoconductor drums of the second to fourth image forming stations and the transfer discharger.

FIG. 6 is a main part of a copying machine showing in detail the separated state between the photoconductor drums of the second to fourth image forming stations and the transfer discharger during the switching between the monochromatic image forming mode and the color image forming mode. FIG.

FIG. 7 is a cross-sectional view of essential parts of the copying machine showing in further detail the contact state between the photoconductor drums of the second to fourth image forming stations and the transfer discharger at the time of switching to the color image forming mode.

FIG. 8A is an explanatory diagram illustrating switching of image forming modes in the case where image formation of three color images, ten single color images, and one color image is continuously performed.
(B) 3 color images, 4 single color images, 2 color images
FIG. 9 is an explanatory diagram illustrating switching of image forming modes when image formation of one sheet, four monochrome images, and one color image is continuously performed. (C) is 3 single color images, 1 color image
FIG. 9 is an explanatory diagram illustrating switching of image forming modes when image formation of 0 sheets and one monochrome image is continuously performed. (D) is an explanatory diagram for explaining switching of image forming modes in the case where image formation of 10 single color images, 1 color image, 2 single color images, and 1 color image is continuously performed.

FIG. 9 is a flowchart showing a procedure of an image forming method when the image forming mode is selected in consideration of the number of times the image forming mode is switched.

FIG. 10 is a flowchart showing a procedure of an image forming method when an image forming mode is selected in consideration of a time required for image formation.

FIG. 11 is a cross-sectional view of a digital color copying machine according to a modified example of the present embodiment as seen from the front.

[Explanation of symbols]

222a to 222d Photoreceptor drums (image carrier) Sa to Sd First to fourth image forming stations 213 Transfer transport belt mechanism (transport means) 302 Transport belt (transport means) 1,1 'Digital color copying machine (multicolor Image forming apparatus) MC Image forming mode switching means P sheet (transfer material)

Continued front page    F-term (reference) 2H027 DA21 DA46 DE02 DE07 EC06                       EC19 ED02 ED16 EE03 EE04                       EE06 EF06 EF09 FA28 FB18                       FC02 GB14 ZA07                 2H030 AB02 AD06 AD09 AD17 BB02                       BB23 BB42 BB44 BB56                 2H200 FA02 FA09 FA13 FA20 GA12                       GA29 GA34 GA47 GB25 HA12                       HB03 HB29 JA02 JB06 JB13                       JB17 JB18 JB20 JB26 JB41                       JB49 KA03 KA07 LA14 LA19                       LA23 LA24 LA27 PA11 PA20                       PB39                 5C074 AA20 BB26 DD11 DD12 DD24                       DD28 EE04 EE08 EE20 FF15                       HH02

Claims (10)

[Claims] 1. A plurality of image forming stations, each of which is arranged in parallel along a transfer material conveyance direction and is provided with an image carrier, and a conveying means for conveying a transfer material on which an image is formed.
First, a multicolor image is formed by all the image forming stations by bringing the image carriers of all the image forming stations into contact with the conveying means at the time of forming images in the multicolor.
While the image forming mode is switched to another image forming mode, the conveying means for the image carriers of the other image forming stations that remain so that only the image carrier of the image forming station located on the most upstream side remains in contact with the transfer material at the time of image formation with a single color. In the multi-color image forming apparatus, the image forming mode switching means switches to a second image forming mode in which a single color image is formed by the most upstream side image forming station. When single-color image data and multi-color image data are mixed in an image forming job for a plurality of sheets, image formation in the first image forming mode or first and second images is performed according to the mixed state. A multicolor image forming apparatus, characterized in that image formation combining a forming mode is selected. 2. The multicolor image forming apparatus according to claim 1, wherein the image forming mode switching means calculates the image forming time based on a mixed state of the single color image data and the multicolor image data,
A multicolor image forming apparatus characterized in that image formation in the first image forming mode or image forming combining the first and second image forming modes is selected according to the calculation result. 3. The multicolor image forming apparatus according to claim 1 or 2, wherein the image forming mode switching means selects an image forming mode based on a mixed state of single color image data and multicolor image data. It is characterized in that the number of times of switching is detected, and image formation in the first image forming mode or image forming combining the first and second image forming modes is selected according to the detection result. Multicolor image forming apparatus. 4. The multicolor image forming apparatus according to claim 1, wherein the image formation in the second image forming mode is performed more than the image formation in the first image forming mode. A multicolor color image forming apparatus characterized by being performed at a high speed. 5. The multicolor image forming apparatus according to any one of claims 1 to 4, wherein the image forming mode switching means is based on a mixed state of single color image data and multicolor image data. Detecting the number of times the image forming mode is switched, the total number of times of switching from multicolor image data to monochromatic image data and of switching from monochromatic image data to multicolor image data is less than or equal to a predetermined number, While the image formation combining the first and second image forming modes is selected, when the total number of times exceeds a predetermined number, the image forming in the first image forming mode is selected. Multi-color image forming apparatus. 6. The multicolor image forming apparatus according to any one of claims 1 to 4, wherein the image forming mode switching means is based on a mixed state of monochromatic image data and multicolor image data. When the continuous number of single color image data is detected and the number of continuous single color image data is equal to or larger than a predetermined number, the image formation combining the single color image data and the multi color image data is selected, while the single color image data is selected. The multicolor image forming apparatus is characterized in that the image formation in the first image forming mode is selected when the number of consecutive sheets is less than the predetermined number. 7. A multicolor image forming apparatus, comprising: a plurality of image forming stations, each of which is arranged in parallel along a transfer material conveying direction and provided with an image carrier, and a conveying means for conveying a transfer material on which an image is formed. The first image forming mode in which multi-color image formation is performed by all the image forming stations by bringing the image carriers of all the image forming stations into contact with the conveying means during image formation by the By separating the conveying means from the image carriers of the other image forming stations that remain so that only the image carriers of the image forming stations located on the side are in contact with the transfer material, a single color by the image forming station on the most upstream side is formed. In the multi-color image forming method in which the mode is switched to the second image forming mode for forming an image, during the image forming job for a plurality of sheets. When the single-color image data and the multi-color image data are mixed, the image formation in the first image formation mode or the image formation in which the first and second image formation modes are combined is performed depending on the mixed state. A multicolor image forming method characterized by being carried out. 8. The multicolor image forming method according to claim 7, wherein the image formation in the second image formation mode is performed at a faster speed than the image formation in the first image formation mode. And a multicolor image forming method. 9. The multicolor image forming method according to claim 7 or 8, wherein the number of times the image forming mode is switched is detected based on a mixed state of single color image data and multicolor image data. The first and second image forming modes are combined when the total number of times of switching from color image data to single color image data and number of times of switching from single color image data to multicolor image data is less than or equal to a predetermined number. A multicolor image forming method, wherein while the image is formed, when the total number of times exceeds a predetermined number, the image is formed in the first image forming mode. 10. The multicolor image forming method according to claim 7, wherein the number of consecutive single color image data is based on a mixed state of the single color image data and the multicolor image data. Is detected, and when the number of continuous single-color image data is equal to or more than a predetermined number, image formation is performed by combining the single-color image data and the multi-color image data, while the continuous number of single-color image data is the predetermined number. A multicolor image forming method, wherein when the number is less than 1, the image is formed in the first image forming mode.