JP2003330245A - Color image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a color image forming apparatus constituted so that the increase of a maintenance cost can be suppressed by making the replacing cycle of an image forming device used for forming a monochromatic image nearly equivalent to that of other devices used for forming color images in the case a frequency in forming the monochromatic image is higher than a frequency in forming other color images. <P>SOLUTION: The color image forming apparatus is provided with a plurality of image forming units equipped with a latent image carrier capable of forming an image with complementary color toner and an image forming device for performing an image forming processing for the latent image carrier. The latent image carrier 4B and also the image forming device 7B in the image forming unit which is arranged in the final position in the moving direction of a transfer body 8A to which the images are successively formed by respective image forming units are transferred are made larger in size than the image carriers and the image forming devices for other image forming units positioned on this side of the final position. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus, and more particularly to a color image forming apparatus capable of forming a toner image for each color separation.

[0002]

2. Description of the Related Art An image forming apparatus has a structure for forming a color image using complementary color toner corresponding to color separation based on an original image or image information. The configuration for forming a color image is provided with a plurality of photoconductors which are latent image carriers for forming a toner image using a complementary color corresponding to color separation, and the toner images formed on the photoconductors are sequentially formed. By superposing and transferring the image on the recording paper or the intermediate transfer body, and fixing the superimposed and transferred image when the recording paper is used, and when the intermediate transfer body is used, the superimposed and transferred image is recorded on the recording paper. There is known a configuration in which a color image can be obtained by collectively transferring the image onto a sheet or the like and then fixing the image. In particular, a so-called four-tandem system in which a photoconductor and an image forming unit including a photoconductor, a charging device, a writing device, a developing device, and a cleaning device for executing an image forming process for the photoconductor are arranged side by side in a horizontal direction or a vertical direction. A structure called as is well known (for example, US Pat. No. 5,380,006, JP-A-6-13874).
4, JP-A-10-3193, JP-A 7-2
8294, JP-A-8-15949). In this case, the quadruplet corresponds to the number of toner images of yellow, magenta, cyan, which are complementary colors corresponding to color separation, and black, which are targeted for improving gradation and forming a monochrome image. .

In the color image forming apparatus using the quadruple tandem system, the image forming devices including the photoconductors provided in the image forming units are formed to have substantially the same structure, that is, to have the same size. Therefore, each image forming device has the same durable life.

[0004]

However, when a full-color image is frequently formed, the frequency of use of each image forming device becomes uniform, so that the variations in durability among the devices are not so different from each other. For example, when a monochrome image is formed more frequently than a full-color image, only a unit that forms a black image among the plurality of image forming apparatuses is used differently from other units. The formation ratio of a full-color image and a monochrome image is 4:
It has been obtained as a result of market research that the frequency of monochrome image formation is high, such as 6 to 2: 8.

When the formation frequencies of the full-color image and the monochrome image are different, the life of the image forming device in the unit forming the yellow, magenta, and cyan toner images used for forming the full-color image and the unit forming the monochrome image are different. The life of the image forming device is greatly different, and the replacement cycle is also different. For this reason, the unit used for obtaining a color image having a high formation frequency is replaced at a different time from the replacement time of other units. There is a risk that the maintenance cost of the device may increase due to variations in the period during which the device cannot be used and an increase in the frequency of replacing one unit.

In view of the above-mentioned problems in the conventional image forming apparatus, in particular, the full-color image forming apparatus having a structure using a plurality of image forming units, the image forming frequency of a single color is the formation of other color images. Provided with a color image forming apparatus having a configuration capable of suppressing an increase in maintenance cost by bringing the replacement cycle of a plastic image forming apparatus closer to that of another color image when the frequency is higher than the frequency. To do.

Another object of the present invention is to provide a color image forming apparatus having a structure capable of improving the throughput related to image formation when the frequency of image formation of a single color is high.

Another object of the present invention is to provide a color image forming apparatus having a structure capable of preventing image position deviation when an image forming unit of a plurality of colors is provided.

[0009]

The invention according to claim 1 is
In a color image forming apparatus having a structure capable of forming toner images of a plurality of colors by using complementary color toners corresponding to color separation, a latent image carrier capable of forming an image with the complementary color toners and an image forming process of the body A plurality of image forming units each having an image forming device for executing the above, and latent images in the image forming units arranged at the final position in the moving direction of the transfer body to which the images sequentially formed by the image forming units are transferred. It is characterized in that the image forming device including the image carrier is larger in size than the latent image carrier and the image forming device in the image forming unit located before the final stage.

In addition to the invention described in claim 1, the invention described in claim 2 is characterized in that the image forming unit arranged at the final position is a unit capable of forming a monochrome image.

According to a third aspect of the present invention, in addition to the first aspect of the present invention, the transfer body is composed of a transfer belt having a spreading surface facing the image forming units, and the transfer belt faces the image forming units. A transfer device facing the latent image carrier of the image forming unit located at the final position is disposed near the image forming unit located on the rearmost side in the moving direction of the spreading surface, across the transfer belt. It is characterized by that.

The invention according to claim 4 is the invention according to claim 1 or 2.
In addition to the invention described above, the image forming units other than the image forming unit for monochrome image formation arranged at the final position in the moving direction of the transfer body are the above-mentioned at the time of image formation using only the monochrome image forming unit. It is characterized in that it can be separated from the transfer body.

According to a fifth aspect of the invention, in addition to the first aspect of the invention, the image forming surface of the latent image carrier of the image forming unit arranged at the final position in the moving direction of the transfer body is the above-mentioned. It is characterized in that the length of the transfer body along the moving direction is an integral multiple of at least twice the length of the image forming surface of the latent image carrier in another image forming unit.

According to a sixth aspect of the present invention, in addition to the invention according to any one of the first to third aspects, a latent image bearing of an image forming unit arranged at a final position in the moving direction of the transfer body is carried. The length of the image forming surface of the body along the moving direction of the transfer body is an integer greater than or equal to twice the length of the image forming surface of the latent image carrier of another image forming unit in the moving direction of the transfer body. When the transfer body is a belt, the peripheral length of the belt drive roller is doubled and image formation is performed along the moving direction of the belt in the latent image carrier of the image forming unit arranged at a position other than the final position. The surface length is equal to or an integral multiple of the length of the surface, and in addition, the installation interval of the latent image carrier in the image forming unit other than the final position in the moving direction of the belt is set in the latent image carrier other than the final position in the latent image carrier. Of the latent image carrier of the image forming unit arranged at the final position and the latent image carrier of the image forming unit arranged immediately before the final position. The installation interval is set to the length of the image forming surface along the moving direction of the belt in the latent image carrier of the image forming unit arranged at the final position, or 1/2 or an integral multiple thereof, and the total length of the belt is set. It is characterized in that the lengths of the image forming surfaces of the latent image carriers of the image forming units other than the final position are set to different numbers.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to embodiments shown in the drawings. FIG. 1 is a schematic view showing a color image forming apparatus according to an example for explaining an embodiment of the invention. In FIG. 1, a color image forming apparatus 1 includes an image forming unit 2 capable of forming an image for each color separation.
(For the sake of convenience, the initials Y, M, C, and B, which mean yellow, magenta, cyan, and black, are attached to the reference numeral 2 for display) are juxtaposed in the horizontal direction, and these image forming units 2Y, 2M, and 2C are arranged side by side. An exposure unit 3 is arranged below 2B.

Each image forming unit 2Y, 2M, 2C, 2
Each of the units B has the same configuration, and the configuration will now be described on behalf of the unit 2C that forms a cyan image. The image forming unit 2C is provided with a photosensitive drum 4C which is a latent image carrier, and a charging device 5C for performing an image forming process along the direction of the arrow around the photosensitive drum 4C. Exposure unit 3
An incident portion 6C of the writing light from, a developing device 7C, a transfer device 8, and a cleaning device 9C are arranged.

Each image forming unit 2C, 2M, 2Y, 2
Photoconductor drums 4C, 4M, 4Y, and 4 provided in B
B is each of these image forming units 2C, 2M, 2Y, 2
The transfer belt 8A faces a transfer device 8 having a transfer belt 8A as a transfer body having a spreading surface parallel to the juxtaposition direction of B, and the transfer belt 8A is a driving roller 8A1 and a driven roller arranged on both sides of the juxtaposition direction. The image forming units 2C, 2M, 2Y, and 2B are wound around 8A2 to move in the order in which toner images can be transferred.

The transfer device 8 includes a primary transfer bias roller 8B arranged at a position facing the photosensitive drums 4C, 4M, 4Y, and 4B across the transfer belt 8A, and each image formation on the transfer belt 8A. A secondary transfer bias roller 8C that faces the drive roller 8A that is located near the image forming unit 2B that is disposed at the final position in the moving direction of the spreading surface that faces the unit is provided. Transfer belt 8
The image transfer to A is a primary transfer step in which toner images of respective colors are sequentially superimposed and transferred, and the image transfer using the secondary transfer bias roller 8C is a recording sheet S fed from the sheet feeding device 10.
Corresponds to a secondary transfer process in which a superimposed transfer image is collectively transferred.

After the secondary transfer process of the transfer belt 8A, the toner remaining on the belt surface is removed by the belt cleaning device 11 arranged on the driven roller 8A2 side. Further, at the time of cleaning, a static eliminator for eliminating residual charges on the surface of the belt may be provided as needed.

The paper feeding device 10 is provided with a paper feeding cassette 10A for accommodating the recording paper S and a manual feeding tray 10B capable of manually feeding paper, and the recording paper is conveyed from the paper feeding cassette 10A and the manual feeding tray 10B. A registration roller 10C is provided at a position where the paths meet.

After passing through the secondary transfer bias roller 8C, the transfer image is fixed on the recording sheet S by the fixing device 12,
The direction switching claw 14 sets the paper ejection mode in which the paper is ejected onto the paper ejection tray 1A by the paper ejection roller 13 and the double-sided copy mode in which the paper is reversed and conveyed again toward the registration rollers 10C via the re-conveyance path RR. It is like this.

The color image forming apparatus 1 having the above-mentioned configuration
In each of the image forming units 2Y, 2M, 2C, 2B
Of these, the image forming unit arranged at the final position in the moving direction of the transfer belt 8A facing each of these image forming units, in other words, the secondary transfer bias roller 8C.
The photosensitive drum 4B in the image forming unit 2B arranged closest to the image forming unit 2B and the developing device 7B and the cleaning device 9B, which are the image forming devices related to the photosensitive drum 4B, are the image forming units 2C and 2M of other colors. Two
It is larger than the Y model.

Since this embodiment has the configuration as described above,
Since the image forming unit 2B for monochrome image formation arranged at the final position in the moving direction of the spreading surface of the transfer belt 8A facing the image forming unit is formed larger than the other image forming units, By suppressing the increase in the peripheral length of the drum 4B, the capacity of the developer, and the increase in the frequency of contact with the cleaning member with respect to the stress latent image bearing member in the developer circulation cycle, damage caused by the increase is shortened, and the life span is extended. Then, it is possible to set the same replacement cycle as that of the image forming units of other colors. As a result, it is possible to suppress the maintenance cost by increasing the durability of the molding unit, which has a high frequency of image formation, and prevents the replacement degree from increasing.

In the configuration shown in FIG. 1, the sheet feeding device 1
The conveyance path of the recording paper S fed from 0 is set in a substantially vertical direction, and the secondary transfer process is performed in the middle of the conveyance path 2
Since the position where the next transfer bias roller 8C and the transfer belt 8A face each other is provided, when forming a monochrome image, the recording paper passes a position facing another image forming unit other than the monochrome image forming unit. Since the conveyance path length is shortened, the throughput at the time of monochrome image formation can be improved.

The transfer belt 8A included in the transfer device 8 can be separated from image forming units other than the monochrome image forming unit 2B when forming a monochrome image.
That is, inside the transfer belt 8A, the pressing roller 15 for pressing the transfer belt 8A against the peripheral surface of the photosensitive drum 4B in the monochrome image forming unit 2B is arranged, and the transfer belt 8A has the pressing roller 15A. With this position as a fulcrum, it can be separated from image forming units other than monochrome images by an elevating device (not shown) as shown in FIG. In this case, the transfer belt 8
Similarly, the primary transfer bias roller 8B and the belt cleaning device 11 attached to A are separated from each other. With such a configuration, the transfer belt 8 is moved from the image forming units other than the monochrome image forming unit only when forming the monochrome image.
By separating A, other colors (colors other than monochrome)
It is possible to prevent the transfer body from being damaged by an inadvertent external force when the image forming unit comes into contact with the transfer body.

FIG. 2 shows a modified example of the structure of the transfer belt 8A shown in FIG. 1. In FIG. 2, the image forming units 2C, 2M, 2Y, and 2B are reversed from the structure shown in FIG. Is shown above. In this configuration, a belt cleaning device (for convenience, indicated by reference numeral 11 ') is arranged near the monochrome image forming unit 2B.

Next, another embodiment of the present invention will be described. Another embodiment is characterized in that a belt is used as a transfer device to prevent image position deviation when images are transferred from a plurality of image forming units. 1 and 2, the peripheral lengths of the photosensitive drums 4Y, 4M, and 4C in the image forming units 2Y, 2M, and 2C other than the modeling unit for forming a monochrome image are set to the driving roller 8A1 of the transfer belt 8A. And the peripheral length of the photosensitive drum 4B of the image forming unit for monochrome image formation is set to be twice or an integral multiple of the peripheral length of the photosensitive drums of the other image forming units. Further, the photosensitive drum of the image forming unit 2C positioned immediately before the image forming unit for monochrome image formation in the moving direction of the photosensitive drum 4B of the image forming unit for monochrome image formation and the transfer belt 8A facing the image forming unit. 4C is set to the peripheral length of the photosensitive drum 4B of the monochrome image forming unit 2B or 1/2 or an integral multiple, and the installation interval of the photosensitive drums between the image forming units other than the monochrome image is set for each photosensitive drum. The peripheral length is set so that the entire length of the transfer belt 8A is set to an integral multiple of the peripheral length of the photosensitive drum of the image forming unit other than the monochrome image forming unit.

In the present embodiment, by setting the above-mentioned dimensional relationship, even if the eccentricity of the photosensitive drum or the driving roller 8A1 of the transfer belt 8A occurs, the image generated during one rotation of each photosensitive drum and roller. Since the phases of the transfer start positions can be matched, it is possible to eliminate the image shift due to the shift of the image transfer start position.
This makes it possible to prevent the occurrence of abnormal images such as color shift.

[0029]

According to the inventions of claims 1 and 2,
Among the plurality of image forming units, the latent image carrier and the image forming device of the image forming unit arranged at the final position in the moving direction of the transfer member are larger than those of other image forming devices, and in particular, In the second aspect of the invention, since the image forming unit at the final position is a unit capable of forming a monochrome image, the latent image is formed by increasing the size of the image forming unit of a color that is more frequently formed than other colors. The length of the image forming surface of the carrier, the capacity of the developer, the increase in the frequency of contact with the cleaning member with the stress latent image carrier during the developer circulation cycle is suppressed, and the life is shortened by reducing damage. It is possible to lengthen and set the same exchange cycle as that of the image forming units of other colors. As a result, it is possible to improve the durability of the image forming unit with high image forming frequency, prevent the replacement degree from increasing, and reduce the maintenance cost.

According to the third aspect of the present invention, when the transfer member is composed of a belt, the belt is sandwiched in the vicinity of the image forming unit located on the rearmost side in the moving direction of the expanding surface facing the belt. Since the transfer device is provided, the final transfer can be performed without passing through another image forming unit, and the throughput at the time of forming an image of a single color can be improved.

According to the fourth aspect of the invention, when only the image forming unit for forming a monochrome image is used, the image forming units of other colors can be separated from the transfer body, so that images of other colors are formed. It is possible to prevent the transfer body from being damaged by an inadvertent external force when the forming unit contacts the transfer body.

According to the fifth and sixth aspects of the present invention, the image forming surface of the latent image carrier of the image forming unit arranged at the final position in the moving direction of the transfer body is along the moving direction of the transfer body. The length of each image forming unit is set to an integral multiple of 2 times or more of that of the latent image bearing member in another image forming unit, and the installation interval of the latent image bearing member in each image forming unit is regulated so that each image forming unit It is possible to eliminate the image position shift by aligning the image transfer start phases of the above.

[Brief description of drawings]

FIG. 1 is a schematic view showing a color image forming apparatus according to an example for explaining an embodiment of the invention.

FIG. 2 is a schematic diagram showing a partially modified example of the color image forming apparatus shown in FIG.

FIG. 3 is a view showing a separated state of transfer bodies in the color image forming apparatus shown in FIG.

[Explanation of symbols]

1 Color image forming apparatus 2Y, 2M, 2C Image forming unit 2B for colors other than monochrome images Monochrome image forming units 4Y, 4M, 4C Photoreceptor drum 4B which is a latent image carrier in image forming units other than monochrome images Monochrome image Photosensitive drum 7B, which is a latent image carrier included in the forming unit, developing device 9B, which is one of the image forming devices included in the monochrome image forming unit, and cleaning device 8 which is another one of the image forming devices included in the monochrome image forming unit Transfer device 8A Transfer belt 8A1 that forms a transfer member Drive roller for the transfer member

Continued front page    (72) Inventor Seiji Hoshino             1-3-3 Nakamagome, Ota-ku, Tokyo, stock             Company Ricoh F term (reference) 2H035 CA07 CB01                 2H200 FA12 FA16 GA12 GA23 GA34                       GA47 GB12 GB25 GB43 HB12                       HB22 JA02 JA16 JA18 JB13                       JC03 JC12 LA07 LA14 LA24                       LB12                 2H300 EA01 EB01 EB04 EB07 EB12                       EC01 EC05 ED09 EF03 EF08                       EG02 EG05 EH16 EH26 EJ09                       EJ47 EJ58 EK03 EL01 EL05                       FF02 FF08 FF17 GG08 GG29                       GG49 HH12 HH14 HH30

Claims (6)

[Claims] 1. A color image forming apparatus having a structure capable of forming toner images of a plurality of colors by using complementary color toners corresponding to color separation, and a latent image carrier capable of forming an image with the complementary color toners. A plurality of image forming units equipped with an image forming device for executing the image forming process for deceasing, and arranged at the final position in the moving direction of the transfer body to which the images sequentially formed by the image forming units are transferred. A color image forming apparatus, wherein an image forming device including a latent image carrier in an image forming unit is configured to be larger than a latent image carrier and an image forming device in an image forming unit located before the final stage. 2. The color image forming apparatus according to claim 1, wherein the image forming unit arranged at the final position is
A color image forming apparatus, which is a unit capable of forming a monochrome image. 3. The color image forming apparatus according to claim 1, wherein the transfer body is composed of a transfer belt having a spreading surface facing the image forming units, and the spreading surface facing the image forming unit is moved. A transfer device facing the latent image carrier of the image forming unit disposed at the final position is disposed near the image forming unit located at the rearmost side in the direction with the transfer belt interposed therebetween. Color image forming apparatus. 4. The color image forming apparatus according to claim 1, wherein the image forming unit other than the image forming unit for forming a monochrome image, which is arranged at the final position in the moving direction of the transfer body, is the monochrome image. A color image forming apparatus capable of being separated from the transfer body when forming an image using only a forming unit. 5. The color image forming apparatus according to claim 1, wherein a moving direction of the transfer body on an image forming surface of a latent image carrier of an image forming unit arranged at a final position in a moving direction of the transfer body. The color image forming apparatus is characterized in that the length along the length is an integral multiple of at least twice the length of the image forming surface of the latent image carrier in the other image forming unit. 6. A color image forming apparatus according to claim 1, wherein an image is formed on a latent image carrier of an image forming unit arranged at a final position in a moving direction of the transfer body. The length of the surface along the moving direction of the transfer body is an integer multiple of 2 times or more of the length of the image forming surface in the moving direction of the transfer body in the latent image carrier of another image forming unit. When the transfer body is a belt, the circumferential length of the belt driving roller is the same as the length of the image forming surface along the moving direction of the belt in the latent image carrier of the image forming unit other than the final position. Or an integral multiple, and in addition, the installation interval of the latent image carrier in the image forming unit other than the final position in the moving direction of the belt is included in the image forming unit other than the final position. The installation interval between the latent image carrier of the image forming unit which is equal to the length of the image forming surface along the moving direction and which is arranged at the final position and the latent image carrier of the image forming unit which is arranged immediately before the final position. Is the length of the image forming surface along the moving direction of the belt on the latent image carrier of the image forming unit arranged at the final position, or 1/2 or an integral multiple of this, and the total length of the belt is A color image forming apparatus characterized in that the length of the image forming surface of the latent image carrier of the image forming unit other than the position is set to a different number.