JP2001201912A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming device capable of preventing the life of an image carrier from being shortened needlessly without making the device large in size, without complicating the device, and without increasing the cost. SOLUTION: In the case of a black monochromatic mode of forming a monochromatic image, the circumferential speed of photoreceptor drums 1a to 1d is controlled so as to be higher than that in a full color mode, and the circumferential speed may become nearly equal to that of the intermediate transfer belt 6.

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 using an electrophotographic recording system, and more particularly, to an image forming apparatus such as a printer, a copying machine, a facsimile, and the like.

[0002]

2. Description of the Related Art Various color image forming apparatuses for forming a color image on a transfer material using an electrophotographic recording system have been devised, and some of them have been put to practical use.

[0003] As a typical example, a developing device containing a toner as a developer of each color is arranged on a photoreceptor as an image carrier so as to be sequentially developed.
A rotary developing device having magenta, cyan, and black developing units visualizes each color electrostatic latent image formed on one common photoconductor as a toner image at a developing position by each developing unit. A method of forming a multicolor toner image by repeating a process of transferring the toner image onto a recording medium (transfer material) such as a sheet carried and conveyed on a transfer drum or the like as a transfer material carrier every time the toner image is obtained. Image forming apparatus.

Further, there has been proposed an apparatus of a system in which toner images of respective colors are selectively superimposed sequentially on a photoreceptor, a multicolor toner image is formed on the photoreceptor surface, and then collectively transferred to a recording medium.

Further, a toner image of each color is formed on each of a plurality of photoconductors by a developing device of each color, and each color toner image on each photoconductor is transferred and carried on a transfer belt or the like as a transfer material carrier. There is a so-called in-line type image forming apparatus that forms a multicolor toner image by sequentially superimposing and transferring images on a material. Here, instead of directly transferring a toner image from each photoconductor to a recording medium (transfer material),
There is also an image forming apparatus of an intermediate transfer type in which toner images of each color are temporarily superimposed and transferred on an intermediate transfer body sequentially, and thereafter, a multicolor toner image on the intermediate transfer body is collectively transferred to a recording medium (transfer material).

[0006] Each of the typical methods of the color image forming apparatus using the above-mentioned electrophotographic recording method has advantages and disadvantages. However, from the viewpoint of speeding up along with recent market needs, an in-line method is used. The intermediate transfer member system is superior from the viewpoint that it is superior and can cope with various transfer materials such as cardboard.

A conventional example of an in-line type color image forming apparatus will be described with reference to a schematic sectional view shown in FIG.

As shown in FIG. 4, photosensitive drums 1a to 1d opposed to developing means 4a to 4d such as developing devices containing toners of the respective colors are arranged side by side in the moving direction of the intermediate transfer belt 6. I have. The toner images of the respective colors formed on the respective photosensitive drums by the respective developing means are electrostatically sequentially transferred onto the intermediate transfer body by the transfer rollers 8a to 8d, and are transferred in four colors of yellow, magenta, cyan and black. To form a full-color toner image.

Further, charging means 2a to 2d and exposure means 3a to 3d for forming toner images of respective colors on each photosensitive drum.
3d, developing means 4a to 4d
It is arranged around d.

Further, cleaning devices 5a to 5d having cleaning blades for rubbing and collecting the toner remaining on each photosensitive drum after transferring the toner image to the intermediate transfer belt are provided.

Next, the image forming operation will be described. A laser beam modulated according to image data from a host such as a personal computer is irradiated from the exposure units 3a to 3d onto the surfaces of the photosensitive drums 1a to 1d uniformly charged by the charging rollers serving as the charging units 2a to 2d. Thus, a desired electrostatic latent image is obtained for each color. This latent image is reversely developed at a developing position by developing means 4a to 4d, which are developing devices containing toners of respective colors, which are disposed to face the latent image, and are visualized as a toner image. This toner image is
At each transfer position, the image is sequentially transferred to the intermediate transfer belt 6, is fed at a predetermined timing by a sheet feeding unit (not shown), and is collectively transferred to a transfer material P conveyed by a conveying unit. The color toner image on the transfer material P is heated and melted by a fixing device (not shown), and is permanently fixed on the transfer medium to obtain a desired color print image.

Here, conventionally, in order to improve the transfer efficiency of the toner image from the photosensitive drum to the intermediate transfer belt,
A method has been proposed in which the peripheral speed of the photosensitive drum and the peripheral speed of the intermediate transfer belt at each transfer position have a speed difference.
According to this, the transfer efficiency of each color toner image is improved, and this is a very effective method when transferring toner images of two or more colors in a superimposed manner. In particular, in the four-color full-color mode, by providing a speed difference between each photosensitive drum and the intermediate transfer belt, the toner image transferred from each photosensitive drum to the intermediate transfer belt is hollow, so-called hollow. By preventing the phenomenon and improving the transfer efficiency, it is possible to obtain a good image with no color change.

In addition, in an electrophotographic color image forming apparatus, not only a full color mode in which a full color toner image is formed using four color toners, but also a monochromatic image in which a black and white image is formed using only a black toner photosensitive drum. The color mode can be selected and switched.

[0014]

However, the single color mode has the following problems.

In a single color mode in which a black-and-white image is formed using only black toner, no toner image is formed on a photosensitive drum of a color other than the photosensitive drum on which black toner is formed. If the belt 6 continues to rotate while maintaining the above speed difference in the four-color full-color mode, the photosensitive drums of the other colors needlessly rub against the cleaning blade and the intermediate transfer belt 6, resulting in wear and damage. As a result, the life of the developing device may be extended even though the toner stored in the developing device is not exhausted or the image is not formed on a desired number of transfer materials. .

In order to avoid this, for example, it is conceivable to appropriately separate the intermediate transfer belt 6 from the photosensitive drums of other colors in the black monochromatic mode. Providing a separation mechanism for separating the photosensitive drum from the photosensitive drum greatly increases the cost and the size of the apparatus.

Therefore, an object of the present invention is to increase the size of the device,
An object of the present invention is to provide an image forming apparatus that can prevent the life of an image carrier from being unnecessarily shortened without increasing complexity and cost.

[0018]

According to the present invention, the above object is achieved. The present invention provides an image forming apparatus comprising: a plurality of image carriers each carrying a plurality of color toner images; and a transfer medium on which the toner images are transferred from the image carriers in contact with the plurality of image carriers. In the apparatus, a first mode in which a plurality of color toner images are sequentially transferred from the plurality of image carriers to the transfer medium at respective transfer positions in a superimposed manner, and a predetermined mode among the plurality of image carriers is A second mode of transferring a single-color toner image to the transfer medium,
When the first mode is selected, the moving speed of the plurality of image carriers at each transfer position and the moving speed of the transfer medium are different, and when the second mode is selected, each of the transfer positions is different. Wherein the difference between the moving speed of the plurality of image carriers and the moving speed of the transfer medium is smaller than the difference between the moving speed of the plurality of image carriers and the moving speed of the transfer medium in the first mode. It is characterized by being performed.

[0019]

(Embodiment 1) An embodiment according to the present invention will be described below with reference to the drawings.

FIG. 1 is a schematic configuration diagram illustrating an in-line type color image forming apparatus according to the present invention. Members having the same functions as those of the image forming apparatus of FIG. 4 described in the conventional example are denoted by the same reference numerals.

As shown in FIG. 1, yellow (Y), magenta (M), cyan (C), black (B
k) Photosensitive drum 1 as an image carrier, which is disposed opposite developing means 4a to 4d such as a developing device containing toner.
a to 1d are arranged side by side in the moving direction of the intermediate transfer belt 6 as a transfer medium (intermediate transfer body).

Charging means 2a to 2d and exposure means 3 for forming toner images of respective colors on the photosensitive drums 1a to 1d
a to 3d and the developing means 4a to 4d
~ 1d.

After the toner image is transferred from the photosensitive drum to the intermediate transfer belt 6, the toner remaining on the photosensitive drum is charged by charging means and electrostatically collected in a developing device at a developing position, so that a cleaner is separately provided. Uses a system that is not used. With such a configuration, it is possible to prevent the apparatus from becoming large and complicated. Further, in the present image forming apparatus, when an image is continuously formed on a plurality of transfer materials, at the developing position, the charged residual toner is electrostatically collected by a developing device and simultaneously placed on a photosensitive drum. The formed electrostatic latent image is electrostatically attached (developed) with toner at a developing position. According to this, it is possible to prevent a decrease in throughput of image formation.

The endless intermediate transfer belt 6 is suspended by a driving roller 7 and a driven roller 9, and is configured to rotate in a direction indicated by an arrow in FIG.

Next, the image forming operation will be described. A laser beam modulated in accordance with image data from a host such as a personal computer is exposed on the surfaces of the photosensitive drums 1a to 1d, which are uniformly charged to a negative polarity by charging rollers as the charging units 2a to 2d. Irradiated from 3d, a desired electrostatic latent image is obtained for each color. This latent image is reversely developed at a developing position by developing means 4a to 4d, which are developing devices containing toners of respective colors, which are disposed to face the latent image, and are visualized as a toner image. The toner image is sequentially transferred to the intermediate transfer belt 6 at each transfer position, fed at a predetermined timing by a feeding unit (not shown), and transferred by a feeding unit P (transfer paper).
And are electrostatically transferred together. The color toner image on the transfer material P is heated and melted by a fixing device (not shown), and is permanently fixed on the transfer material P to obtain a desired color print image.

In this embodiment, in order to improve the transfer efficiency of the toner image from the photosensitive drum to the intermediate transfer belt, there is a speed difference between the peripheral speed of the photosensitive drum and the peripheral speed of the intermediate transfer belt at each transfer position. We apply the method to make it. According to this, the transfer efficiency of each color toner image is improved, and particularly when toner images of two or more colors are transferred in a superimposed manner, it is very effective and suppresses a change in color due to a decrease in transfer efficiency. Can be.

Further, in the image forming apparatus of this embodiment, not only the full color mode in which a full color toner image is formed using four color toners (using each photosensitive drum) but also the black toner only (black toner) is used. And a monochrome mode for forming a black-and-white image (using only the photosensitive drum). Such mode switching is controlled by a CPU (not shown) as a control means by a user's mode designation.

Further, as shown in FIG.
d, the charging units 2a to 2d and the developing units 4a to 4d are integrated with each other to form process cartridges 20a to 20d as units detachable from the apparatus main body.

In this embodiment, a drive motor for rotating each of the photosensitive drums 1a to 1d is provided, and the peripheral speed of each photosensitive drum can be independently controlled by the CPU.

Here, first, in the full-color mode, transfer is performed sequentially in the order of yellow, magenta, cyan, and black. At each transfer position, it is preferable that the peripheral speed of the intermediate transfer belt 6 is different from the peripheral speed of the photosensitive drums 1a to 1d by 0.5 to 3.5%. 5% difference in peripheral speed
The peripheral speed of the intermediate transfer belt 6 is higher than the peripheral speed of the photosensitive drum. Note that the same effect can be obtained even if the peripheral speed of the photosensitive drum is higher than the peripheral speed of the intermediate transfer belt 6. That is, assuming that the peripheral speed of the photosensitive drum and the peripheral speed of the intermediate transfer belt are V1 and V2 at each transfer position, 0.5 <{(V1-V2) / V2} × 100 <3.5 or 0.5. <{(V2-V1) / V1} × 100 <3.
5 is preferably satisfied.

By setting the peripheral speeds of the photosensitive drums 1a to 1d and the intermediate transfer belt as described above, a change in tint due to a decrease in transfer efficiency is suppressed, and a good image is obtained.

Next, in the black monochrome mode for forming a monochrome image, the peripheral speed of the photosensitive drums 1a to 1d is changed from that in the full color mode. In the case of this embodiment, the photosensitive drum 1
The peripheral speeds a to 1d are controlled by the CPU so as to be faster than that in the full-color mode and to be substantially equal to the intermediate transfer belt 6 at the transfer position. However, it is impossible to achieve perfect constant velocity, and the peripheral speed difference is 0.3%.
Within this range, it is referred to as “constant velocity” in this embodiment. That is, the peripheral speed of the photosensitive drums 1a to 1d at the transfer position is V3, and the peripheral speed of the intermediate transfer belt 6 at the transfer position is V4.
Assuming that {(V3-V4) / V4} × 100 <0.3 or {(V4-V3) / V3} × 100 <0.3, the peripheral speed difference from the intermediate transfer belt is Damage to the photosensitive drum was almost eliminated.

In a mode in which toner images of two or more colors are superimposedly transferred onto the intermediate transfer belt, when the transfer efficiency of the toner image transferred from the photosensitive drum to the intermediate transfer belt is lowered, the change in the tint is caused. Therefore, it is necessary to make a peripheral speed difference between each photosensitive drum and the intermediate transfer belt.However, in the case of the mode in which only a black toner image is transferred to the intermediate transfer belt, Since images are not superimposed to form a color, even if there is no difference in peripheral speed between the photosensitive drum for black and the intermediate transfer belt, it does not appear as a color change in the image. is there.

With such a configuration, it is also possible to use one drive motor for rotating the photosensitive drums of each color, and to simplify the control device (control circuit) for controlling the rotation of the drive motors. Size, further miniaturization, and cost reduction can be achieved.

Further, the length of the toner image formed on the photosensitive drum in the sub-scanning direction may be adjusted in advance so that the image formed on the transfer material P does not expand or contract.

In particular, in the image forming apparatus according to this embodiment,
As in the conventional example, a system without a separate cleaner is used.Since there is no damage to the photosensitive drum by the cleaning blade, it is more abraded and scratched by rubbing with the intermediate transfer belt, and the life of the photosensitive drum is affected. However, the present invention has solved this problem.

In the black monochrome mode for forming a black and white image, there is no need to form a color image by superimposing and transferring toners using only the photosensitive drum for black. The peripheral speed of the transfer belt may be increased. In this case, the peripheral speeds of the intermediate transfer belt and the photosensitive drum maintain the above relationship.

In this embodiment, the following method is employed to confirm that the peripheral speed of the photosensitive drum at the transfer position is different from the peripheral speed of the intermediate transfer belt. First, a predetermined test toner image is formed on the photosensitive drum (for example, two line toner images extending in the main scanning direction are formed at a predetermined distance in the sub-scanning direction).
Before transferring the test toner image to the intermediate transfer belt, the length A (corresponding to the above-described predetermined distance) between the line toner images in the rotation direction (sub-scanning direction) of the photosensitive drum is measured. . Next, the line toner image and the line toner image on the intermediate transfer belt in the moving direction of the intermediate transfer belt after the test toner image is primarily transferred to the intermediate transfer belt and before the secondary transfer to the transfer material. And measure the length B between them.

Here, tapes were used for measuring the lengths A and B, respectively. This tape is a transparent polyester tape No. manufactured by Nichiban Co., Ltd. 550 (#
25) and the width is 18 mm.

More specifically, when measuring A, the test toner image on the photosensitive drum before the primary transfer is transferred to the tape, and this is transferred to a predetermined sheet (for example, a scaled sheet).
Then, the length A of the test toner image is measured. Similarly, B is also used for transferring the test toner image to the intermediate transfer belt.
After the completion of the next transfer and before the second transfer, a test toner image is transferred to the tape, and the tape is attached to the predetermined paper, and the length B of the test toner image is measured.

Finally, the peripheral speed difference between the photosensitive drum and the intermediate transfer belt at the transfer position can be obtained from the measured lengths A and B.

As another method, the transfer speed of the transfer material in the secondary transfer nip (substantially equal to the peripheral speed of the transfer belt 8 in the present embodiment) using a laser beam is used. Of the intermediate transfer drum 7 can be measured.

It should be noted that the present invention is not limited to this as long as there is a suitable measuring method other than the above measuring method.

In the above, the black single-color mode has been described. However, the present invention is not limited to this, and the same can be applied to each of the single-color modes of yellow, magenta, and cyan.

In the black monochrome mode, the CP is set such that the peripheral speed difference between the peripheral speed of the photosensitive drums 1a to 1d and the peripheral speed of the intermediate transfer belt 6 at each transfer position becomes substantially zero.
The control was performed by U, but the present invention is not limited to this. Each photosensitive drum 1a to 1d at each transfer position in the black monochrome mode
The peripheral speed difference between the peripheral speed of the intermediate transfer belt and the peripheral speed of the intermediate transfer belt at each transfer position in the four-color full-color mode. If the speed difference is made smaller, it is possible to prevent an unnecessary decrease in the durable life of each photosensitive drum in the same manner as described above. The peripheral speed difference between the peripheral speed of each photosensitive drum and the peripheral speed of the intermediate transfer belt in the black monochromatic mode is because the photosensitive drum and the intermediate transfer belt do not rub and wear due to the peripheral speed difference. Most preferably, it is zero.

(Embodiment 2) In Embodiment 1, an image forming apparatus for temporarily transferring a toner image from a photosensitive drum to an intermediate transfer member has been described. In this embodiment, however, a photosensitive drum as shown in FIG. An image forming apparatus for directly transferring a toner image to a transfer material carried and conveyed on a transfer belt will be described.

By replacing the peripheral speed of the intermediate transfer belt in the first embodiment with the peripheral speed of the transfer belt (the transport speed of the transfer material P carried and transported on the transfer belt) in the present embodiment, the present embodiment is also implemented. The present invention can be applied in the same manner as in Example 1.

Next, the present embodiment will be described with reference to FIG. 3 for parts different from the image forming apparatus shown in FIG. Members having the same functions as those in FIG. 1 are denoted by the same reference numerals, and description thereof will be omitted.

Each of the photosensitive drums 1a to 1d has a transfer belt 6
0 are juxtaposed. The transfer belt 60 is wound around a driving roller 70 and a tension roller 90, and carries the transfer material P and conveys it to each transfer position. Further, cleaning devices 5a to 5d having cleaning blades for scraping and cleaning the toner remaining on the photosensitive drum are provided.

The image forming process will be briefly described. Each color toner image formed on each of the photosensitive drums 1a to 1d is fed at a predetermined timing, and is transferred onto a transfer material P carried on a transfer belt 60 by a transfer roller 8a. When a predetermined voltage (positive polarity) is applied to .about.8d, electrostatic transfer is performed at each transfer position in order. The transfer rollers 8a to 8d also have a function of pressing the transfer material P together with the transfer belt so as to contact the photosensitive drums 1a to 1d with a predetermined pressure.

Each color toner image transferred to the transfer material P is heated and pressed by a fixing device (not shown) to be fixed on the transfer material P to become a permanent image.

Also in this embodiment, by controlling the peripheral speed of the photosensitive drum by the control means (CPU) for each image forming mode, that is, in the four-color full-color mode,
A desired peripheral speed difference is provided between each photosensitive drum and the transfer belt (and the transfer material). In the single color mode, the peripheral speed difference between each photosensitive drum and the transfer belt (and the transfer material) is set to four colors full color. By setting the value smaller than that in the case of the mode, and preferably to zero, it is possible to prevent the durable life of the photosensitive drum from being unnecessarily reduced due to the rubbing between the photosensitive drum and the transfer belt (and the transfer material). .

In particular, in the market, in addition to the full-color mode, a black single-color mode for forming a black-and-white image is often selected, so that the present invention is effective.

Further, even in the system in which the cleaning device for the photosensitive drum is provided as in the present embodiment, the abrasion of the photosensitive drum by the transfer belt 60 can be greatly reduced as in the first embodiment. became.

[0055]

As described above, according to the present invention,
Without increasing the size, complexity and cost of the equipment,
It is possible to prevent the life of the image carrier from becoming unnecessarily short.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of an image forming apparatus according to the present invention.

FIG. 2 is a schematic configuration diagram of a process cartridge.

FIG. 3 is a schematic configuration diagram of an image forming apparatus according to the present invention.

FIG. 4 is a schematic configuration diagram of a conventional image forming apparatus.

[Explanation of symbols]

 Reference Signs List 1 photosensitive drum 2 charging means 4 developing means 5 cleaning device 6 intermediate transfer belt 20 process cartridge 60 transfer belt P transfer material

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Hiroaki Ogata 3-30-2 Shimomaruko, Ota-ku, Tokyo Inside Canon Inc. (72) Inventor Yasunari Watanabe 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon (72) Inventor Genki Adachi 3-30-2 Shimomaruko, Ota-ku, Tokyo F-term in Canon Inc. (reference) 2H030 AA06 AB02 AD03 AD07 AD16 BB02 BB23 BB32 BB42 BB44 BB46 BB53 BB54 BB63 2H032 AA05 BA09 BA18 BA23 BA26 CA01 CA13 2H034 AA05 AA06 BF01 2H077 AA37 AD06 BA10 DB14 DB15 DB25 EA24 GA13

Claims (17)

[Claims] 1. An image comprising: a plurality of image carriers each carrying a plurality of color toner images; and a transfer medium on which the toner images are transferred from the image carriers in contact with the plurality of image carriers. A first mode in which a plurality of color toner images are sequentially transferred from the plurality of image carriers to the transfer medium at respective transfer positions in the forming apparatus;
A second mode for transferring a single-color toner image from a predetermined image carrier among the plurality of image carriers to the transfer medium, and wherein the first mode is selected, The moving speed of the plurality of image carriers at each transfer position is different from the moving speed of the transfer medium. When the second mode is selected, the moving speed of the plurality of image carriers at each transfer position and the moving speed of the plurality of image carriers are different. The image forming apparatus according to claim 1, wherein a difference between the moving speed of the transfer medium and the moving speed of the transfer medium in the first mode is smaller than a difference between the moving speeds of the plurality of image carriers in the first mode. 2. The image forming apparatus according to claim 1, wherein the image forming apparatus has a single driving source for driving the plurality of image carriers. 3. The image forming apparatus according to claim 1, wherein the single-color toner image is a black toner image. 4. The image forming apparatus according to claim 1, wherein when the second mode is selected, a moving speed of the plurality of image carriers is substantially equal to a moving speed of the transfer medium. apparatus. 5. When the second mode is selected, the moving speed of each image carrier at each transfer position is set to V
1. Assuming that the transfer speed of the transfer medium is V2, {(V1-V2) / V2} × 100 <0.3 or {(V2-V1) / V1} × 100 <0.3 holds. The image forming apparatus according to claim 4, wherein 6. When the first mode is selected, the moving speed of each of the image carriers at each of the transfer positions is set to V
3. Assuming that the transfer speed of the transfer medium is V4, 0.5 <{(V3-V4) / V4} × 100 <3.5 or 0.5 <{(V4-V3) / V3} × 100 < 3.
The image forming apparatus according to claim 1, wherein the following condition is satisfied. 7. The image forming apparatus according to claim 1, wherein the transfer medium is a transfer material carried and transported by a transfer material carrier. 8. The image forming apparatus according to claim 1, wherein the toner image transferred to the transfer medium is transferred to a transfer material. 9. The image forming apparatus according to claim 1, wherein the transfer medium is transferred from a side of the transfer medium opposite to a side on which the toner image is transferred in order to transfer the toner images on the image carriers to the transfer medium. 9. The image forming apparatus according to claim 1, further comprising a plurality of pressing members for pressing each of said image carriers. 10. The image forming apparatus according to claim 9, wherein a voltage is applied to each of said pressing members during image transfer. 11. The image forming apparatus has a plurality of developing means for developing a latent image on each of the image carriers with toner, and the toner remaining on each of the image carriers is collected by each of the developing means. The image forming apparatus according to claim 1, wherein: 12. The image forming apparatus according to claim 11, wherein said developing means develops a latent image on each of said image carriers with toner at the same time as collecting toner remaining on each of said image carriers. Image forming apparatus. 13. The image forming apparatus according to claim 1, wherein the image forming apparatus includes a plurality of cleaning units that contact the respective image carriers and clean the toner remaining on the respective image carriers. 12. The image forming apparatus according to any one of 12 14. The image forming apparatus according to claim 13, wherein the cleaning unit includes a cleaning blade that contacts the image carrier. 15. The image forming apparatus according to claim 1, wherein the image forming apparatus includes the respective image carriers, and includes a plurality of units that can be attached to and detached from the apparatus main body. . 16. The image forming apparatus according to claim 15, wherein each of the units includes a developing unit that develops a latent image on the image carrier with toner. 17. The image forming apparatus according to claim 15, wherein each of the units includes a charging unit configured to charge a surface of the image carrier in order to form a latent image on the image carrier. .