JP2001209234A - Color image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a small and low cost color image forming device where changeover in drive between a color mode and a single color mode such as a monochrome mode can be carried out appropriately. SOLUTION: In the color copying device 100, images are formed by all image forming units 114Y to 114K in the color mode and in a single color mode, the image is formed with only a black image forming unit 114K by separating a transfer belt 113 from photoreceptor drums 120Y to 120C by slightly moving movable supporting rolls 126Y to 126K and transfer rolls 124Y to 124C downward. That is, center positions of the photoreceptor drums 120Y to 120C are installed above a center position of a black photoreceptor 120K by a specified quantity H and the color copying device 100 with a good image quality can be made small and low cost by being able to separate the transfer belt 113 from the photoreceptor drums 120Y to 120C by only slightly moving the mobile supporting rolls 126Y to 126K and transfer rolls 124Y to 124C downward.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a color image forming apparatus, and more particularly, to a small and inexpensive color image forming apparatus which appropriately switches driving between a single color mode such as a color mode and a monochrome mode.

[0002]

2. Description of the Related Art Recently, demands for full-color image formation have been increasing, and at the same time, there has been a strong demand for high-speed image formation. As a color image forming apparatus that meets such demands, there is a so-called tandem type color image forming apparatus in which a plurality of electrophotographic writing units and image forming cartridges are juxtaposed to form a color image by superimposing images. A device is used.

[0003] This tandem type color image forming apparatus includes:
An image forming station for forming an image of each color of cyan, magenta, yellow and black is provided.The image forming station of each color includes a writing unit and an image forming cartridge, and writes a laser modulated by image data of each color. The unit irradiates the photoreceptor of the image forming cartridge to form a latent image, and the image forming cartridge of each color supplies toner of each color to the photoreceptor on which the latent image is formed to develop a toner image. The image forming cartridge of each color transfers the toner image on the photoconductor to the transfer paper conveyed on the transfer belt, and forms a color image by superimposing the toner image of each color on the transfer paper.

However, full-color image formation is not always performed, and there are still many occasions where only black-and-white images are output, such as when copying a document image, and a large proportion of black-and-white images is maintained. However, when a black-and-white image is formed by a tandem type color image forming apparatus, the cost per sheet (running cost) is much higher than when an image is formed by a black-and-white image forming apparatus. This is because an image forming unit of a color not used for forming a black-and-white image is used similarly to the case of forming a color image, and the life is counted similarly to the image forming unit for black.

Therefore, it is necessary to design a color image forming apparatus such as a color copying machine and a color printer in consideration of frequent black and white images. Conventionally, when forming a black image, a recording paper is conveyed. The paper transport surface of the belt to be separated is separated from the image forming units other than the black image forming unit by, for example, rotating the recording paper transport belt around the vicinity of the black image forming unit. There has been proposed an image forming apparatus in which a color image forming unit is not used (Japanese Patent Laid-Open No. 7-19959).
0, JP-A-9-146383 and JP-A-1
0-319664).

[0006]

However, such a conventional image forming apparatus needs to be improved in order to reduce the size and stabilize the operation of the image forming apparatus.

That is, in the above-described conventional image forming apparatus, the image forming unit other than the black image forming unit is formed by rotating the recording paper conveying belt around the vicinity of the black image forming unit. Because the transport belt is separated from the unit, if the transport belt is slightly separated from the image forming units other than the black image forming unit, the image forming unit located farthest from the black image forming unit The distance of the conveyor belt is greatly increased in proportion to the distance from the center of rotation of the conveyor belt.
In addition to the need for a mechanism for switching the sheet feeding and fixing positions as described in Japanese Patent No. 3119664, the amount of movement of the transport belt increases, the transport belt unit increases, and the image forming apparatus increases in size. There was a problem that the cost was high.

In addition, since the circumference of the transport belt changes greatly, the mechanism for maintaining the tension of the transport belt becomes complicated, and the size of the image forming apparatus is increased, and the cost is increased.

Therefore, the invention according to claim 1 is an image forming apparatus, comprising: a plurality of image forming units disposed along a transport belt;
The central position of the latent image carrier of the image forming unit other than the image forming unit involved in the single color mode is separated from the transport belt by a predetermined distance from the center position of the latent image carrier of the image forming unit involved in the single color mode. In the single-color mode, the latent image carrier and the transfer belt of the image forming units other than the image forming units involved in the single-color mode and the transfer belts of all the image forming units are located near the transfer unit. The movable support means of the image forming unit other than the image forming unit involved in the single-color mode is separated from the transport belt by a predetermined amount, among the movable support means disposed on the opposite side and closely contacting the transport belt with the latent image carrier. In the single color mode, the image forming units other than the image forming units involved in image formation in the single color mode are rotated. Small and inexpensive color that can move the means and the movable support means slightly in the direction away from the conveyor belt to separate the conveyor belt from the latent image carrier and ensure stable conveyance and transfer performance of the recording medium. It is an object to provide an image forming apparatus.

According to a second aspect of the present invention, the angle formed between the transfer means and the movable support means of the image forming unit formed around the latent image carrier of the image forming unit involved in the single color mode is different from that of the single color mode. By moving the transfer means of the image forming unit involved in the monochrome mode to a position having the same angle in the color mode, the transport state and the transfer state of the recording medium are set to the same state in the color mode and the monochrome mode, and the color mode is changed. It is another object of the present invention to provide a color image forming apparatus capable of improving the image quality by ensuring the same transfer process conditions in the single-color mode and the stable transfer performance.

[0011]

According to a first aspect of the present invention, there is provided a color image forming apparatus, which is disposed along a transport belt for transporting a recording medium, and has a color image forming apparatus on each latent image carrier by electrophotography. The toner image is formed, and the recording medium conveyed on the transport belt by transfer means disposed at a position facing each of the latent image carriers with the transport belt interposed therebetween. A plurality of image forming units for transferring toner images to form toner images of respective colors on the recording medium, and in the color mode, rotating the latent image carriers of all the image forming units to thereby form all the latent images. A toner image is formed on a carrier and the toner images on all the latent image carriers are sequentially transferred to the recording medium conveyed on the conveyor belt to form a color image. Only the latent image carrier of the image forming unit involved in image formation is rotated to form a toner image on the latent image carrier and the recording medium conveyed on the conveyance belt to the recording medium conveyed by the image forming unit. A color image forming apparatus that forms a single-color image by transferring a toner image on the latent image carrier by a transfer unit, wherein the latent image is sandwiched between the transfer belts near the transfer unit of all of the image forming units. Movable supporting means disposed on the opposite side of the image carrier and for bringing the transport belt into close contact with the latent image carrier is provided, and the latent image carrier of an image forming unit other than the image forming unit involved in the single color mode is provided. The center position of the latent image carrier of the image forming unit involved in the single color mode is disposed at a position away from the transport belt by a predetermined amount; Movable support means of an image forming unit other than the image forming unit involved in the single-color mode among the support means is disposed so as to be movable in a direction away from the transport belt by a predetermined amount; The transfer unit of an image forming unit other than the image forming unit involved in the transfer belt is disposed so as to be movable in a direction away from the transport belt by a predetermined amount,
In the single color mode, the above object is achieved by moving the transfer unit and the movable support unit of the image forming units other than the image forming unit involved in the single color mode in a direction separated by a predetermined amount from the transport belt. are doing.

According to the above arrangement, of the plurality of image forming units arranged along the conveyor belt, the latent image carriers of the image forming units other than the image forming units involved in the monochromatic mode are moved to the center position. In the monochrome mode, the image forming unit is disposed at a position away from the center of the latent image carrier by a predetermined amount from the conveyance belt, and in the monochrome mode, image formation other than the image forming unit involved in the monochrome mode is performed. The single-color movable support means is disposed near the transfer means of the unit and the transfer means of all the image forming units on the opposite side to the latent image carrier with the transport belt therebetween, and closely contacts the transport belt with the latent image carrier. The movable support means of the image forming unit other than the image forming unit involved in the mode is moved in a direction away from the transport belt by a predetermined amount, so that the monochromatic mode is used. Sometimes, the transfer means and the movable support means of the image forming units other than the image forming units involved in the image formation in the single-color mode are slightly moved in the direction away from the transport belt to separate the transport belt from the latent image carrier. Thus, it is possible to provide a small and inexpensive color image forming apparatus capable of securing stable recording medium conveyance performance and transfer performance.

In this case, for example, as set forth in claim 2, the transfer means of the image forming unit involved in the monochromatic mode is disposed so as to be movable by a predetermined amount in a predetermined direction,
An angle between the transfer unit and the movable support unit formed around the latent image carrier of the image forming unit involved in the single-color mode is at a position where the angle is the same in the single-color mode and the color mode. The transfer unit of the image forming unit involved in the monochrome mode may be moved.

According to the above arrangement, the angle formed by the transfer means and the movable support means of the image forming unit, which is formed around the latent image carrier of the image forming unit involved in the single color mode, is different between the single color mode and the color mode. Since the transfer unit of the image forming unit involved in the single color mode is moved to the same angle in the color mode and the single color mode, the transfer state and the transfer state of the recording medium are set to the same state in the color mode and the single color mode. Thus, the transfer process conditions can be made the same, stable transfer performance can be secured, and the image quality can be improved.

[0015]

Preferred embodiments of the present invention will be described below in detail with reference to the accompanying drawings. It should be noted that the embodiments described below are preferred embodiments of the present invention, and therefore, various technically preferable limitations are added. However, the scope of the present invention is not limited to the following description. The embodiments are not limited to these embodiments unless otherwise specified.

1 to 4 show an embodiment of the color image forming apparatus of the present invention. FIG. 1 shows a color copying apparatus to which the embodiment of the color image forming apparatus of the present invention is applied. FIG.

In the color copying apparatus 100, an image forming unit 102 is mounted on a base 101, and an image reading unit 103 is mounted on the image forming unit 102.

The image reading unit 102 includes a contact glass 1
The image of the original set on the original 04 is color-separated for each predetermined color by the reduction optical system 105, incident on the photoelectric conversion unit 106 for each color, photoelectrically converted by the photoelectric conversion unit 106, and the image of the original is converted into color. The data is read and output to a control unit of the color copying apparatus 100 (not shown).

In the image forming section 102, a paper cassette 108 for accommodating a plurality of recording papers (recording medium) 107 is detachably attached. , And are sent out to the registration roller pair 110.

The image forming unit 102 includes an endless belt-like transfer belt 113 stretched over a driving roller 111 and a driven roller 112, and images of yellow, magenta, cyan, and black arranged along the transfer belt 113. Forming units 114Y, 114M, 114C, 114
K, a suction roller 115, a charge removing unit 116, a cleaning unit 117, a fixing unit 118, a discharge roller 119, and the like.

The transfer belt (transport belt) 113 is formed in an endless belt shape as described above, and is stretched while being engaged with the drive roller 111 and the driven roller 112. By being rotationally driven by a driving mechanism such as a motor, it is rotationally driven in a counterclockwise direction in FIG.

The pair of registration rollers 110 is provided for the sheet feeding roller 1.
After adjusting the timing of the recording paper 107 sent from the feeding roller 09, the recording paper 107 is sent to the suction roller 115 and
Reference numeral 15 electrostatically attracts the recording paper 107 sent from the registration roller pair 109 to the transfer belt 113.

The transfer belt 113 sequentially transports the recording paper 107 electrostatically attracted by the attraction roller 115 to each of the image forming units 114Y, 114M, 114C, and 114K, and each of the image forming units 114Y, 114M, and 114K.
C, the recording paper 107 on which the image of each color is transferred and the toner of each color is transferred from the driving roller 111 to the fixing unit 11.
Separated and sent out to 8.

The fixing section 118 heats and presses the fixing roller 118a and the pressure roller 118b heated to a predetermined fixing temperature to fix the toner on the recording paper 107 to the recording paper 107 and sends out the toner to the discharge roller 119. , Discharge roller 11
9 discharges the fixed recording paper 107 onto a discharge tray (not shown).

Each of the above image forming units 114Y and 114
M, 114C and 114K are driven by an unillustrated drive mechanism as shown in FIG.
Photoconductor drums (latent image carriers) 120Y, 120M, 120C, 120K, charging units 121Y, 121M, 121C, 121K, optical writing unit 1
22Y, 122M, 122C, 122K, developing unit 123
Y, 123M, 123C, 123K, transfer rollers (transfer means) 124Y, 124M, 124C, 124K and cleaning units 125Y, 125M, 125C, 125K
Etc., and the charging units 121Y, 121M, 121
C, 121K, optical writing units 122Y, 122M, 122
C, 122K, developing units 123Y, 123M, 123C,
123K, transfer rollers 124Y, 124M, 124C,
124K and cleaning units 125Y, 125M, 12
5C and 125K are photosensitive drums 120Y and 120M,
It is arranged around 120C and 120K.

The image forming units 114Y, 114M, 1
14C, 114K are charging units 121Y, 121M, 12
1C and 121K, the photosensitive drums 120Y and 120
M, 120C, and 120K are uniformly charged, and the optical writing unit 1
The photosensitive drums 120Y, 120M, 120C, which are uniformly charged by 22Y, 122M, 122C, 122K,
A laser beam modulated by the image data read by the image reading unit 103 is applied to the image forming unit 120K to form an electrostatic latent image on the photosensitive drums 120Y, 120M, 120C, and 120K. Developing units 123Y, 123M, 123C, 12
3K is an optical writing unit 122Y, 122M, 122C, 12
The photosensitive drums 120Y, 1Y on which an electrostatic latent image is formed at 2K
A toner image is formed on each of 20M, 120C, and 120K with each color toner.

Transfer rollers 124Y, 124M, 124
C, 124K are photosensitive drums 120Y, 120M, 1
When the recording paper 107 is conveyed by the transfer belt 113 between the photosensitive drums 120C and 120K, the photosensitive drums 120Y and 120K
The toner images of the respective colors on 120M, 120C, and 120K are transferred to recording paper 107.

Cleaning units 125Y, 125M, 12
5C and 125K are the photosensitive drums 120 on which transfer has been completed.
Y, 120M, 120C, and 120K are cleaned of residual toner, and the cleaned photosensitive drums 120Y, 120M, 120C, and 120K are uniformly charged by the charging units 121Y, 121M, 121C, and 121K, and are re-imaged. Served for formation.

The transfer rollers 124Y, 124M, 12
4C and 124K, the transfer rollers 124Y, 124M, and 124C of the yellow, magenta, and cyan image forming units 114Y, 114M, and 114C are vertically moved by a predetermined amount by a driving mechanism (not shown) as shown in FIGS. In a color mode in which a color image is formed, the transfer belt 113 is moved slightly upward to move the transfer belt 113 to the photosensitive drum 1 as shown in FIG.
In the monochrome mode in which an image is formed in black and white by bringing the transfer belt 113 into close contact with the photoconductor drums 120Y, 120M, and 120C by a predetermined distance as shown in FIG. Pull apart.

Each of the image forming units 114Y,
114M, 114C and 114K have transfer rollers 124
Transfer belt 1 than Y, 124M, 124C, 124K
13, movable support rollers (movable support means) 126Y, 126M, 126C, 126K
Are provided, and the black image forming unit 113 is provided.
A movable support roller 127 is further provided downstream of the K transfer roller 124K. The movable support rollers 126Y, 126M, 126C, and 126K are disposed so as to be movable by a predetermined amount in the vertical direction, as shown in FIGS. That is, the movable support rollers 126Y, 126Y
6M, 126C and 126K move upward in the color mode as shown in FIG.
3 is the photosensitive drums 120Y, 120M, 120C, 12
In the monochrome mode, the transfer belt 113 is moved downward to separate the transfer belt 113 from the photosensitive drums 120Y, 120M, and 120C by a predetermined distance, as shown in FIG.

On the other hand, the recording paper 10 is
The transfer belt 116 that has sent out the fixing belt 118 to the fixing unit 118 further rotates counterclockwise, and after being neutralized by the neutralizing unit 116, is cleaned by the cleaning unit 117 and again.
The next recording paper 107 is attracted by the suction roller 115, and the recording paper 107 is separated from the image forming units 114Y and 114Y.
It is transported along 4M, 114C and 114K.

Then, the image forming unit 114Y,
Of the image forming units 114Y, 114M, 114M, 114C and 114K, yellow, magenta and cyan
114C is the photosensitive drum 120Y, 120M, 1
The center position of 20C is located above the center position of the black photoconductor 120K by a predetermined amount H as shown by H in FIG. 1 (a state separated from the transfer belt 113). , The photosensitive drums 120Y, 120
M and 120C are disposed above the black photosensitive drum 120K, so that the movable support rollers 126Y, 126M, 126C and 126
K and the transfer rollers 124Y, 124M, and 124C are disposed in a state of being located above the transfer roller 124K and the movable support roller 127 by a predetermined amount H, and as described above, from the state shown in FIG. It is arranged so as to be able to move slightly downward by a predetermined amount to the state position shown in FIG.

The black photosensitive drum 120K
Is the conveyance distance of the recording paper 107 between the magenta photosensitive drum 120M and the cyan photosensitive drum 120C, the cyan photosensitive drum 120C and the black photosensitive drum 1
As shown in FIG. 3, the center positions of the yellow, magenta, and cyan photoconductor drums 120Y, 120M, and 120C and the black photoconductor 120K are set so that the conveyance distance of the recording paper 107 between the photoconductors 120K and 20K is the same. The vertical position distance H from the center position and the conveying direction distance W of the recording paper 107 between the cyan photosensitive drum 120C and the black photosensitive drum 120K are set.

Further, the color copying apparatus 1 of the present embodiment
00 denotes a black transfer roller 12 as shown in FIG.
4K in the color mode and the single color mode in the transfer belt 11
The movable support roller 127 disposed between the transfer roller 124K and the drive roller 111 is moved in the vertical direction by a predetermined amount.

That is, in the color mode, the black movable support roller 126K, the transfer roller 124K, and the movable support roller 127 have the movable support roller 126K positioned above and the movable support roller 127 positioned below as indicated by the solid line. The transfer roller 124K is located in the right direction in FIG. 4 (upstream in the transport direction of the recording paper 107). In the monochrome mode, the black movable support roller 126K, the transfer roller 124K, and the movable support roller 127 are indicated by broken lines. As shown, the movable support roller 126K is located below, the movable support roller 127 is located above, and the transfer roller 124K is located leftward (downstream in the transport direction of the recording paper 107) in FIG.

The angle between the center of the black photosensitive drum 120K and the center of the movable support roller 126K and the transfer roller 124K in the color mode is D, and the angle between the center of the photosensitive drum 120K and the transfer roller 124K and the movable support roller 127 is D. The angle formed by the center is F, the angle formed by the center of the black photosensitive drum 120K and the center of the movable support roller 126K and the transfer roller 124K in the monochromatic mode is D ′, and the center of the photosensitive drum 120K and the transfer roller 124 are defined.
When the angle between K and the center of the movable support roller 127 is F ′, the black movable support roller 126K, the transfer roller 124K, and the movable support roller are set so that the angle D = the angle D ′ and the angle F = the angle F ′. The moving distance in the color mode and the monochrome mode is set at 127.

Next, the operation of the present embodiment will be described. The color copying apparatus 100 according to the present embodiment includes image forming units 114Y and 114 for yellow, magenta, and cyan.
M, 114C photoconductor drums 120Y, 120M, 12
The center position of 0C is set to the black image forming unit 114.
The movable support roller 126Y is disposed so as to be located above the center position of the K photoconductor 120K by a predetermined amount H and makes the transfer belt 113 closely contact each of the photoconductor drums 120Y, 120M, 120C, and 120K. , 126M,
126C, 126K, movable support roller 127 and transfer rollers 124Y, 124M, 124C, 124K.
Movable support rollers 126Y, 126M, 126C, 126
K and the transfer rollers 124Y, 124M, and 124C are disposed in a state of being located above the transfer roller 124K and the movable support roller 127 by a predetermined amount, and are disposed so as to be movable downward by a predetermined amount. And the movable support rollers 126Y, 126M, 126 in the monochrome mode.
C, 126K and transfer rollers 124Y, 124M, 12
The feature is that the 4C is moved up and down to form an image using only the necessary image forming units 114Y, 114M, 114C and 114K.

That is, in the color copying apparatus 100, in the color mode, the movable support rollers 126Y, 126M, 126C, 126K and the transfer rollers 124Y, 124M, 124C move upward, as shown in FIG. All transfer rollers 124Y, 124M, 124
C and 124K transfer the transfer belt 113 to the photosensitive drum 120
Y, 120M, 120C, and 120K.

In this state, when copying is started, a drive motor (not shown) rotates, and the drive roller 111 rotates.
The transfer belt 113 rotates counterclockwise.

The transfer cassette 113 is attached to the paper feed cassette 10.
8, the recording paper 107 separated one by one by the paper feed roller 109 and sent to the registration roller pair 110 is adjusted in timing by the registration roller pair 110, and then sent out between the suction roller 115 and the transfer belt 113. ,
The suction roller 115 electrostatically attracts the transfer belt 113 to the transfer belt 113.

On the other hand, each image forming unit 114Y, 11
4M, 114C, and 114K are photosensitive drums 120Y, 120M, 120C, and 120 that are driven to rotate clockwise.
K is uniformly charged by the charging units 121Y, 121M, 121C, and 121K, and the optical writing units 122Y, 122M, and 1K.
The photosensitive drums 120 </ b> Y, 120 </ b> M, 120 </ b> C, and 120 </ b> K uniformly charged by 22 </ b> C and 122 </ b> K are irradiated with a laser modulated by image data, and the
An electrostatic latent image is formed on each of 20Y, 120M, 120C, and 120K. Image forming units 114Y, 114M, 114
C and 114K are photosensitive drums 1 on which an electrostatic latent image is formed
Developing section 123 at 20Y, 120M, 120C, 120K
Y, 123M, 123C, and 123K adhere toners of respective colors to form toner images of the respective colors.

The image forming units 114Y, 114M, 1
14C and 114K are transfer rollers 124Y and 124M,
124C, 124K and each photosensitive drum 120Y, 120
When the recording paper 107 is conveyed by the transfer belt 113 between the recording paper 107 and the transfer rollers
The toner images of the respective colors on the photoconductor drums 120Y, 120M, 120C, and 120K are sequentially transferred to the recording paper 107 by the Y, 124M, 124C, and 124K, and the photosensitive members that have been transferred by the cleaning units 125Y, 125M, 125C, and 125K. Body drum 120Y, 120M, 120
C, 120K to remove the residual toner remaining on the photosensitive drums 120Y, 120K.
M, 120C, and 120K to the charging units 121Y, 121
M, 121C, and 121K uniformly charge, and the image is formed again.

The color copying apparatus 100 transfers the recording paper 107 on which the toner images of each color have been transferred to the transfer belt 11.
3 to the drive roller 111,
The recording paper 107 is sent out to the fixing unit 118 in the portion. The color copier 100 uses the drive roller 111 to move the recording paper 10
Then, the transfer belt 116 that has sent the sheet 7 to the fixing unit 118 is further rotated counterclockwise, and after the charge is removed by the charge removing unit 116, it is cleaned by the cleaning unit 117, and the next recording paper 107 is again cleaned by the suction roller 115. Let it adsorb,
The recording paper 107 is transferred to each image forming unit 114Y, 114
It is transported along M, 114C and 114K.

The color copying apparatus 100 transfers the recording paper 107 conveyed to the fixing section 118 to the fixing roller 1.
The toner image on the recording paper 107 is fixed on the recording paper 107 by applying heat and pressure by a roller 18a and a pressure roller 118b, and is discharged onto a discharge tray (not shown) by a discharge roller 119.

In the monochromatic mode, the color copying apparatus 100 is in the state shown in FIG.
6Y, 126M, 126C, 126K and transfer roller 1
24Y, 124M, and 124C have moved slightly downward to separate the transfer belt 113 from the yellow, magenta, and cyan photosensitive drums 120Y, 120M, and 120C.

At this time, the center positions of the photosensitive drums 120Y, 120M, and 120C of the yellow, magenta, and cyan image forming units 114Y, 114M, and 114C are aligned with the photosensitive member 12 of the black image forming unit 114K.
Since the movable support roller 126Y is disposed above the center position of 0K by a predetermined amount H, the movable support roller 126Y,
126M, 126C, 126K and transfer roller 124
The transfer belt 113 is separated from the yellow, magenta, and cyan photosensitive drums 120Y, 120M, and 120C by moving the Y, 124M, and 124C slightly downward.

Therefore, the movable supporting rollers 126Y, 1
26M, 126C, 126K and the transfer roller 124Y,
The moving mechanism of the rollers 124M and 124C can be made small and inexpensive, the color copier 100 can be made small and inexpensive, and the conveyance performance of the recording paper 107 can be made good. .

In the monochrome mode, the transfer roller 124C for cyan and the transfer roller 124K for black are used.
Movable support roller 1 for black disposed between
26Y is also moved downward, so that the yellow, magenta, and cyan photosensitive drums 120Y, 120M,
The recording paper 107 conveyed away from 0C can be smoothly conveyed between the photosensitive drum 120K for black and the transfer roller 124K.

In the monochrome mode, a drive motor (not shown) rotates, the drive roller 111 rotates, and the transfer belt 113 rotates counterclockwise. This transfer belt 1
13, the recording paper 107 separated one by one from the paper supply cassette 108 by the paper supply roller 109 and adjusted in timing by the registration roller pair 110 is sent out between the suction roller 115 and the transfer belt 113, and Is electrostatically attracted to the transfer belt 113.

On the other hand, the image forming units 114Y and 114
M, 114C and 114K are image forming units 114K
Only the black photosensitive drum 120K is driven to rotate clockwise. This photosensitive drum 120
K is uniformly charged by the charging unit 121K, and the optical writing unit 122
A laser modulated by image data is applied to the photosensitive drum 120K uniformly charged with K to form an electrostatic latent image on the photosensitive drum 120K. The image forming unit 114K includes a photosensitive drum 120 on which an electrostatic latent image is formed.
Attach black toner to the K at the developing unit 123K,
A black toner image is formed.

The image forming unit 114K includes a transfer belt 1 between the transfer roller 124K and the photosensitive drum 120K.
When the recording paper 107 is conveyed by 13, the black toner image on the photosensitive drum 120K is transferred onto the recording paper 107 by the transfer roller 124K, and is left on the transferred photosensitive drum 120K by the cleaning unit 125K. The remaining toner is cleaned, and the cleaned photosensitive drum 120K is uniformly charged by the charging unit 121K, and is again subjected to image formation.

The color copying apparatus 100 conveys the recording paper 107 on which the black toner image has been transferred to the drive roller 111 by the transfer belt 113, and sends the recording paper 107 to the fixing unit 118 at the drive roller 111. The color copying apparatus 100 further rotates the transfer belt 116 that has sent the recording paper 107 to the fixing unit 118 by the driving roller 111 in a counterclockwise direction, removes the charge by the charge removing unit 116, and then cleans by the cleaning unit 117. The next recording paper 107 is again sucked by the suction roller 115, and the image forming units 114Y and 114 from which the recording paper 107 is isolated.
M, 114C, the image forming unit 114
Transfer to K.

Then, the color copying apparatus 100 transfers the recording paper 107 conveyed to the fixing unit 118 to the fixing roller 1.
The toner image on the recording paper 107 is fixed on the recording paper 107 by applying heat and pressure by a roller 18a and a pressure roller 118b, and is discharged onto a discharge tray (not shown) by a discharge roller 119.

The color copying apparatus 100 includes a magenta photosensitive drum 120M and a cyan photosensitive drum 120M.
As shown in FIG. 3, the transport distance of the recording paper 107 between C and C and the transport distance of the recording paper 107 between the cyan photosensitive drum 120C and the black photosensitive drum 120K are the same. , Yellow, magenta, and cyan photoconductor drums 120Y, 120M, and 120C, and the vertical position distance H between the center position of the black photoconductor 120K and the recording of the cyan photoconductor drum 120C and the black photoconductor drum 120K. A distance W in the transport direction of the paper 107;
Is set.

Therefore, when the drive roller 111 is eccentric, the conveyance speed unevenness due to the eccentricity of the drive roller 111 is reduced by the image forming units 114Y, 114M,
The same can be caused at 114C and 114K, and image displacement can be canceled to improve image quality.

Further, the color copying apparatus 1 of the present embodiment
In the color mode, as shown in FIG. 4, the black movable support roller 126K, the transfer roller 124K, and the movable support roller 127 are positioned such that the movable support roller 126K is located above the movable support roller 126K as indicated by the solid line. Roller 12
7, the transfer roller 124K is located to the right in FIG. 4, and in the monochrome mode, the black movable support roller 126K, the transfer roller 124K, and the movable support roller 127 are movable as shown by the broken lines. Support roller 126
K is located below, the movable support roller 127 is located above, and the transfer roller 124K is located leftward in FIG.

The angle between the center of the black photosensitive drum 120K and the center of the movable support roller 126K and the transfer roller 124K in the color mode is D, and the angle between the center of the photosensitive drum 120K and the transfer roller 124K and the movable support roller 127 is The angle formed by the center is F, the angle formed by the center of the black photosensitive drum 120K and the center of the movable support roller 126K and the transfer roller 124K in the monochromatic mode is D ′, and the center of the photosensitive drum 120K and the transfer roller 124 are defined.
When the angle between K and the center of the movable support roller 127 is F ′, the black movable support roller 126K, the transfer roller 124K, and the movable support roller are set so that the angle D = the angle D ′ and the angle F = the angle F ′. The moving distance in the color mode and the monochrome mode is set at 127.

Therefore, the positional relationship between the contact point between the recording paper 107 and the black photosensitive drum 120K and the transfer point can be kept unchanged between the color mode and the monochrome mode. It is possible to prevent the toner from entering the transfer area in a state where it is not in close contact with the drum 120K, thereby preventing the occurrence of problems such as transfer dust. As a result, image quality can be improved.

Although the invention made by the inventor has been specifically described based on the preferred embodiments, the invention is not limited to the above-described embodiment, and various modifications can be made without departing from the gist of the invention. It goes without saying that it is possible.

[0060]

According to the color image forming apparatus of the present invention, of the plurality of image forming units arranged along the transport belt, the image forming units other than the image forming unit involved in the single color mode. The central position of the latent image carrier is disposed at a position away from the transport belt by a predetermined amount from the central position of the latent image carrier of the image forming unit involved in the monochrome mode, and in the monochrome mode, The transfer unit of the image forming unit other than the image forming unit involved in the mode and the transfer unit of all the image forming units are disposed on the opposite side of the latent image carrier with the transport belt interposed therebetween and carry the latent image carrier. The movable support means of the image forming unit other than the image forming unit involved in the monochrome mode among the movable support means to be in close contact with the body is separated from the transport belt by a predetermined amount. In the single-color mode, the transfer means and the movable support means of the image forming units other than the image forming units involved in the image formation in the single-color mode are slightly moved in the direction slightly separated from the transport belt to carry the latent image. It is possible to provide a small and inexpensive color image forming apparatus capable of separating a conveyance belt from a body and securing stable recording medium conveyance performance and transfer performance.

According to the color image forming apparatus of the present invention, the transfer means and the movable supporting means of the image forming unit formed around the latent image carrier of the image forming unit involved in the single color mode are used. Since the transfer unit of the image forming unit involved in the single-color mode is moved to a position where the angle to be formed is the same angle in the single-color mode and the color mode, the transfer state and the transfer state of the recording medium are the same in the color mode and the single-color mode. In this state, the transfer process conditions can be made the same in the color mode and the single-color mode, so that stable transfer performance can be secured and the image quality can be improved.

[Brief description of the drawings]

FIG. 1 is a schematic front sectional view of a color copying apparatus to which an embodiment of a color image forming apparatus according to the present invention is applied in a color mode.

FIG. 2 is a schematic front sectional view of the color copying apparatus of FIG. 1 in a single color mode.

3 is an enlarged front view of the vicinity of a photosensitive drum from black to magenta for explaining a positional relationship between a photosensitive drum of black and a photosensitive drum of another color in the color copying apparatus of FIG. 1;

FIG. 4 is an enlarged front view of the vicinity of a black photosensitive drum showing a change in the positions of a movable support roller, a transfer roller, and a movable support roller for black in FIG.

[Explanation of symbols]

REFERENCE SIGNS LIST 100 color copying apparatus 101 pedestal unit 102 image forming unit 103 image reading unit 107 recording paper 108 paper feed cassette 109 paper feed roller 110 registration roller pair 111 drive roller 112 driven roller 113 transfer belt 114Y, 114M, 114C, 114K image forming unit 115 Suction roller 116 Static elimination unit 117 Cleaning unit 118 Fixing unit 119 Ejection roller 120Y, 120M, 120C, 120K Photoconductor drum 121Y, 121M, 121C, 121K Charging unit 122Y, 122M, 122C, 122K Optical writing unit 123Y, 123M, 123C, 123K developing unit 124Y, 124M, 124C, 124K transfer roller 125Y, 125M, 125C, 125K cleaning unit 126Y, 126M, 126C, 126K, 1 27 Movable support roller

Claims (2)

[Claims] An image forming unit that forms a toner image of each color on each of the latent image carriers by an electrophotographic method and sandwiches each of the latent image carrying units with the conveying belt interposed therebetween; The toner image on the latent image carrier is transferred to the recording medium conveyed on the conveyance belt by a transfer unit disposed at a position facing the body to form a toner image of each color on the recording medium. A plurality of image forming units are provided, and in the color mode, the latent image carriers of all the image forming units are rotated to form toner images on all the latent image carriers, and are transported on the transport belt. The toner images on all the latent image carriers are sequentially transferred to the recording medium to form a color image, and in the single color mode, the latent image carrier of the image forming unit involved in image formation in the single color mode is formed. Is rotated to form a toner image on the latent image carrier and transfer the toner image on the latent image carrier to the recording medium conveyed on the conveyor belt by the transfer unit of the image forming unit. A color image forming apparatus for forming a single-color image, wherein the transfer belt is disposed near the transfer unit of all the image forming units on the opposite side to the latent image carrier with the transfer belt therebetween. The image forming unit includes a movable supporting unit that is in close contact with an image carrier, and the center position of the latent image carrier of an image forming unit other than the image forming unit involved in the single color mode is related to the single color mode. The latent image carrier is disposed at a position away from the transport belt by a predetermined amount from the center position of the latent image carrier, and the image forming unit of the movable support means that is involved in the monochrome mode. The movable support means of the image forming unit other than the image forming unit is disposed so as to be movable in a direction away from the transport belt by a predetermined amount, and the image forming unit of the transfer means other than the image forming unit involved in the monochrome mode. A transfer unit disposed movably in a direction away from the transport belt by a predetermined amount, and in the single-color mode, the transfer unit and the movable support unit of an image forming unit other than the image forming unit involved in the single-color mode A color image forming apparatus, which is moved in a direction away from the transport belt by a predetermined amount. 2. The apparatus according to claim 1, wherein said transfer means of said image forming unit which is involved in said single color mode is disposed so as to be movable in a predetermined direction by a predetermined amount, and said latent image carrier of said image forming unit which is involved in said single color mode is centered. The transfer unit of the image forming unit involved in the single-color mode is moved to a position where the angle between the transfer unit and the movable support unit is the same in the single-color mode and the color mode. 2. The color image forming apparatus according to claim 1, wherein: