JP4454753B2 - Image forming apparatus - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an image forming apparatus using an electrophotographic recording method, and more particularly to an image forming apparatus such as a printer, a copying machine, and a facsimile.
[0002]
[Prior 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 into practical use.
[0003]
As a typical example, a developing unit containing toner as a developer of each color is arranged on a photosensitive member as an image carrier so that it can be developed sequentially. For example, four colors of yellow, magenta, cyan, and black are provided. The rotary developing device including the developing units visualizes the electrostatic latent images of the respective colors formed on one common photosensitive member as toner images at the developing positions by the developing units, and this toner image is obtained. There is an image forming apparatus of a type that forms a multicolor toner image by repeating a process of transferring 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.
[0004]
Also, an apparatus has been devised that selectively superimposes toner images of respective colors on a photosensitive member to form a multicolor toner image on the surface of the photosensitive member and then collectively transfers the image onto a recording medium.
[0005]
Further, each color toner image is formed on a plurality of photosensitive members by a developing device of each color, and each color toner image on each photosensitive member is transferred onto a transfer material 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 transferring images on each other. Here, instead of directly transferring the toner image from each photoconductor to the recording medium (transfer material), the toner images of each color are temporarily transferred from each photoconductor onto the intermediate transfer member in sequence, and then the intermediate transfer is performed. There is also an intermediate transfer type image forming apparatus that collectively transfers a multicolor toner image on a body onto a recording medium (transfer material).
[0006]
Each of the above-described typical methods for color image forming apparatuses using the electrophotographic recording method has advantages and disadvantages, but the in-line method is advantageous from the viewpoint of speeding up in combination with recent market needs. From the viewpoint of adapting to various transfer materials such as cardboard, the intermediate transfer body method is superior.
[0007]
A conventional example of an in-line color image forming apparatus will be described with reference to a schematic cross-sectional view shown in FIG.
[0008]
As shown in FIG. 4, photosensitive drums 1 a to 1 d are arranged in parallel in the moving direction of the intermediate transfer belt 6 so as to be opposed to developing means 4 a to 4 d such as developing units containing toner of each color. Each color toner image formed on each photosensitive drum by each developing means is transferred onto the intermediate transfer member by the transfer rollers 8a to 8d in an electrostatic sequential manner, and is a four color toner in which black is added to yellow, magenta and cyan. A full color toner image is formed.
[0009]
Further, charging means 2a to 2d, exposure means 3a to 3d, and developing means 4a to 4d for forming toner images of the respective colors on the photosensitive drums are disposed around the photosensitive drums 1a to 1d. Yes.
[0010]
Further, cleaning devices 5a to 5d having cleaning blades are provided for transferring the toner image onto the intermediate transfer belt and then collecting the toner remaining on each photosensitive drum by sliding.
[0011]
Next, an image forming operation will be described. Laser beams modulated in accordance with image data from a host such as a personal computer are irradiated from exposure means 3a to 3d onto the surfaces of the photosensitive drums 1a to 1d uniformly charged by the charging rollers which are the charging means 2a to 2d. Thus, a desired electrostatic latent image is obtained for each color. The latent image is reversely developed at the developing position and visualized as a toner image by developing means 4a to 4d which are developing units containing toner of respective colors arranged opposite to the latent image. The toner image is sequentially transferred to the intermediate transfer belt 6 at each transfer position, is fed at a predetermined timing by a sheet feeding unit (not shown), and is collectively transferred to a transfer material P conveyed by the conveyance 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 a transfer medium to obtain a desired color print image.
[0012]
Here, conventionally, 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. Has been proposed. According to this, the transfer efficiency of each color toner image is improved, and this is a very effective method when transferring two or more color toner images in a superimposed manner. In particular, in the four-color full color mode, a toner image transferred from each photosensitive drum to the intermediate transfer belt is lost due to a difference in speed between each photosensitive drum and the intermediate transfer belt. By preventing the phenomenon and improving the transfer efficiency, it is possible to obtain a good image having no hue variation.
[0013]
In addition, the electrophotographic color image forming apparatus has not only a full color mode in which a full color toner image is formed using four color toners but also a mono color mode in which a black and white image is formed using only a photosensitive drum for black toner. It can be selected and switched.
[0014]
[Problems to be solved by the invention]
However, the monochromatic mode has the following problems.
[0015]
In a single color mode in which a black and white image is formed using only black toner, a toner image is not formed on a photosensitive drum other than the photosensitive drum on which black toner is formed, but the other color photosensitive drum is placed on the intermediate transfer belt 6. On the other hand, if the rotation continues while maintaining the above speed difference in the 4-color full-color mode, the photosensitive drums of the other colors will rub against the cleaning blade and the intermediate transfer belt 6 unnecessarily, causing wear and scratches. Despite the fact that the toner stored in the container has not disappeared and the image has not been formed on the desired number of transfer materials, the endurance life has been reached.
[0016]
In order to avoid this, for example, in the black monochrome mode, the intermediate transfer belt 6 and the other color photosensitive drums may be appropriately separated. In this case, however, the intermediate transfer belt 6 and the other color photosensitive drums may be separated. Providing a separation mechanism for separating the two leads to a very high cost and a large apparatus.
[0017]
Accordingly, an object of the present invention is to provide an image forming apparatus capable of preventing the life of the image carrier from being unnecessarily shortened without increasing the size, complexity, and cost of the apparatus. is there.
[0018]
[Means for Solving the Problems]
According to the present invention, the above object is achieved. The present invention includes a plurality of developing a plurality of image bearing member for carrying toner images of a plurality of colors, respectively, and a plurality of charging means for charging the plurality of image carriers respectively, the toner image on the plurality of image carriers respectively And an intermediate transfer belt that contacts the plurality of image carriers and transfers a toner image from the image carrier, and after the toner remaining on the image carrier is charged by the charging unit An image forming apparatus that develops a toner image on the image carrier while being collected from the image carrier by the developing means, and a single drive motor that rotationally drives the plurality of image carriers at the same rotational speed; A control unit capable of controlling the drive motor, a first mode in which a plurality of color toner images are sequentially transferred from the plurality of image carriers onto the intermediate transfer belt , and the plurality of images. Of the carrier And a second mode for transferring only bearing member toner image of a predetermined color to the intermediate transfer belt, is a selectable, when said first mode is selected, the said plurality of image bearing members intermediate The drive motor is controlled by the control means so that the moving speed of the plurality of image carriers and the moving speed of the intermediate transfer belt are different at each transfer position where the transfer belt contacts, and the second mode is When selected, the difference between the moving speed of the plurality of image carriers and the moving speed of the intermediate transfer belt at each transfer position where the plurality of image carriers and the intermediate transfer belt are in contact is the first mode. The drive motor is controlled by the control means so as to be smaller than the difference between the moving speed of the plurality of image carriers and the moving speed of the intermediate transfer belt when The features.
[0019]
DETAILED DESCRIPTION OF THE INVENTION
Example 1
Embodiments according to the present invention will be described below with reference to the drawings.
[0020]
FIG. 1 is a schematic configuration diagram illustrating an in-line 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.
[0021]
As shown in FIG. 1, negatively charged yellow (Y), magenta (M), cyan (C), and black (Bk) toners are provided so as to be opposed to developing means 4a to 4d that contain toner. Photosensitive drums 1a to 1d as image carriers are juxtaposed in the moving direction of an intermediate transfer belt 6 as a transfer medium (intermediate transfer member).
[0022]
Charging means 2a to 2d, exposure means 3a to 3d, and developing means 4a to 4d for forming respective color toner images on the photosensitive drums 1a to 1d are arranged around the photosensitive drums 1a to 1d. ing.
[0023]
After transferring the toner image from the photosensitive drum to the intermediate transfer belt 6, the toner remaining on the photosensitive drum is charged by the charging means and electrostatically collected in the developing device at the developing position, so that no separate cleaner is used. The system is used. With such a configuration, it is possible to prevent the apparatus from becoming large and complicated. Further, in this image forming apparatus, when images are continuously formed on a plurality of transfer materials, the charged residual toner is electrostatically collected by the developing device at the developing position and simultaneously on the photosensitive drum. The formed electrostatic latent image is electrostatically attached (developed) with toner at the development position. According to this, it is possible to prevent a reduction in image formation throughput.
[0024]
The endless intermediate transfer belt 6 is suspended from a driving roller 7 and a driven roller 9 and is rotated in the direction of the arrow in the figure.
[0025]
Next, an 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 uniformly charged to a negative polarity by the charging rollers as the charging units 2a to 2d. Irradiated from 3d, a desired electrostatic latent image is obtained for each color. The latent image is reversely developed at the developing position and visualized as a toner image by developing means 4a to 4d which are developing units containing toner of respective colors arranged opposite to the latent image. This toner image is sequentially transferred to the intermediate transfer belt 6 at each transfer position, is fed at a predetermined timing by a sheet feeding unit (not shown), and is collectively applied to a transfer material P (transfer sheet) conveyed by the conveyance unit. Is transferred electrostatically. 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.
[0026]
In this embodiment, in order to improve the transfer efficiency of the toner image from the photosensitive drum to the intermediate transfer belt, a method of giving a speed difference between the peripheral speed of the photosensitive drum and the peripheral speed of the intermediate transfer belt at each transfer position. Applicable. According to this, the transfer efficiency of each color toner image is improved, and in particular, when transferring two or more color toner images in a superimposed manner, it becomes very effective and suppresses variation in color due to a decrease in transfer efficiency. Can do.
[0027]
Further, in the image forming apparatus of this embodiment, not only the full color mode for forming a full color toner image (using each photosensitive drum) using four color toners but also only black toner (photosensitive for black toner). A mono color mode for forming a monochrome image (using only the drum) can be selected and switched. Such mode switching is controlled by a CPU (not shown) as a control means in accordance with user mode designation.
[0028]
Further, as shown in FIG. 2, the photosensitive drums 1a to 1d, the charging units 2a to 2d, and the developing units 4a to 4d are integrated to form a process cartridge 20a to a unit that can be attached to and detached from the apparatus main body. It is in the form of 20d.
[0029]
In this embodiment, drive motors for rotating the respective photosensitive drums 1a to 1d are provided, and the peripheral speeds of the respective photosensitive drums can be independently controlled by the CPU.
[0030]
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%. A peripheral speed difference of 5% is provided, and the peripheral speed of the intermediate transfer belt 6 is faster than the peripheral speed of the photosensitive drum. The same effect can be obtained even if the peripheral speed of the photosensitive drum is made faster than the peripheral speed of the intermediate transfer belt 6. That is, at each transfer position, if the peripheral speed of the photosensitive drum is V1 and the peripheral speed of the intermediate transfer belt is V2,
0.5 <{(V1-V2) / V2} × 100 <3.5
Or, 0.5 <{(V2-V1) / V1} × 100 <3.5
Is preferably satisfied.
[0031]
By setting the peripheral speeds of the photosensitive drums 1a to 1d and the intermediate transfer belt as described above, a change in color due to a decrease in transfer efficiency is suppressed, and a good image is obtained.
[0032]
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 the present embodiment, the peripheral speed of the photosensitive drums 1a to 1d is made higher than that in the full color mode, and is controlled by the CPU so that the speed is substantially constant at the intermediate transfer belt 6 and the transfer position. However, perfect constant speed is not feasible, and if the peripheral speed difference is within 0.3%, it will be called “constant speed” in this embodiment. That is, if 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,
{(V3-V4) / V4} × 100 <0.3
Or {(V4−V3) / V3} × 100 <0.3
If this holds, damage to the photosensitive drum due to the difference in peripheral speed from the intermediate transfer belt is almost eliminated.
[0033]
In the mode in which toner images of two or more colors are transferred onto the intermediate transfer belt in an overlapped manner, if the transfer efficiency of the toner image transferred from the photosensitive drum to the intermediate transfer belt is reduced, it becomes a variation in color. Since it appears in the image, it is necessary to create a peripheral speed difference between each photosensitive drum and the intermediate transfer belt, but in the mode in which only the black monochrome toner image is transferred to the intermediate transfer belt, the toner images are This is because the color is not formed in an overlapping manner, so that even if a peripheral speed difference is not provided between the black photosensitive drum and the intermediate transfer belt, it does not appear in the image as a change in color.
[0034]
In addition, with such a configuration, it is possible to use one drive motor that rotationally drives the photosensitive drums of the respective colors, and the control device (control circuit) that controls the rotation of the drive motor can be simplified and updated. The size can be reduced and the cost can be reduced.
[0035]
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 stretch or shrink.
[0036]
In particular, the image forming apparatus according to the present embodiment uses a system that does not include a separate cleaner as in the conventional example, and there is no damage to the photosensitive drum by the cleaning blade. As a result, the scratches were larger and the life of the photosensitive drum was affected, but this problem was solved by the present invention.
[0037]
Further, 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 a black photosensitive drum. Peripheral speed may be increased. In this case, the peripheral speeds of the intermediate transfer belt and the photosensitive drum maintain the above relationship.
[0038]
In this embodiment, in order to confirm that there is a difference in the peripheral speed between the peripheral speed of the photosensitive drum and the peripheral speed of the intermediate transfer belt at the transfer position, the following method was adopted. 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 the test toner image is transferred to the intermediate transfer belt, a length A (corresponding to the predetermined distance) between the line toner image and the line toner image in the rotation direction (sub-scanning direction) of the photosensitive drum is measured. . Next, after the primary transfer of the test toner image to the intermediate transfer belt and before the secondary transfer to the transfer material, the line toner image and the line toner image on the intermediate transfer belt in the moving direction of the intermediate transfer belt are transferred. The length B between is measured.
[0039]
Here, in order to measure length A and B, the tape was used, respectively. This tape is a transparent polyester tape No. 1 manufactured by Nichiban Co., Ltd. 550 (# 25) and the width is 18 mm.
[0040]
Specifically, when measuring A, the test toner image on the photosensitive drum before the primary transfer is transferred to the tape, and this is pasted on a predetermined sheet (for example, one with a scale). Then, the length A of the test toner image is measured. Similarly for B, after the primary transfer of the test toner image to the intermediate transfer belt is completed and before the secondary transfer, the test toner image is transferred to the tape and affixed to the predetermined paper. The length B of the toner image is measured.
[0041]
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.
[0042]
As another method, the transfer speed of the transfer material in the secondary transfer nip portion (almost equal to the peripheral speed of the transfer belt 8 in the present embodiment) using laser light is intermediate transfer in the secondary transfer nip portion. The peripheral speed of the drum 7 can be measured.
[0043]
In addition, if there exists a suitable measuring method other than the said measuring method, it will not restrict to this.
[0044]
Although the black single color mode has been described above, the present invention is not limited to this, and the same can be applied to the single color modes of yellow, magenta, and cyan.
[0045]
In the black monochrome mode, the CPU controls 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 to be almost zero. It is not limited. The difference in peripheral speed between the peripheral speed of the photosensitive drums 1a to 1d and the peripheral speed of the intermediate transfer belt at each transfer position in the black single color mode is determined as the photosensitive drums 1a to 1d at the transfer positions in the four-color full color mode. If the peripheral speed difference between the peripheral speed and the peripheral speed of the intermediate transfer belt is smaller than that, it is possible to prevent an unnecessary decrease in the durable life of each photosensitive drum as described above. Note that the difference in peripheral speed between the peripheral speed of each photosensitive drum and the peripheral speed of the intermediate transfer belt in the black monochrome mode is because the photosensitive drum and the intermediate transfer belt do not slide and wear due to the difference in peripheral speed. Most preferably it is zero.
[0046]
(Example 2)
In the first embodiment, the image forming apparatus that once transfers the toner image from the photosensitive drum to the intermediate transfer member has been described. However, in this embodiment, the transfer carried from the photosensitive drum to the transfer belt as shown in FIG. An image forming apparatus that directly transfers a toner image to a material will be described.
[0047]
By replacing the peripheral speed of the intermediate transfer belt in the first embodiment with the peripheral speed of the transfer belt in this embodiment (conveying speed of the transfer material P carried and transported on the transfer belt), this embodiment also has the same structure as in the first embodiment. Similarly, the present invention can be applied.
[0048]
Next, with respect to the present embodiment, parts different from the image forming apparatus shown in FIG. 1 will be described with reference to FIG. Members having the same functions as those in FIG. 1 are denoted by the same reference numerals and description thereof is omitted.
[0049]
The photosensitive drums 1 a to 1 d are arranged side by side along the transfer belt 60. The transfer belt 60 is wound around the drive roller 70 and the tension roller 90, and carries the transfer material P and conveys it to each transfer position. In addition, cleaning devices 5a to 5d including a cleaning blade that scrapes and cleans toner remaining on the photosensitive drum are provided.
[0050]
The image forming process will be briefly described. The color toner images formed on the photosensitive drums 1a to 1d are fed at a predetermined timing, and transferred to the transfer material P carried on the transfer belt 60 to the transfer rollers 8a to 8d. By applying a predetermined voltage (positive polarity), the images are electrostatically transferred in an overlapping manner at each transfer position. 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.
[0051]
Each color toner image transferred to the transfer material P is heated and pressed by a fixing device (not shown) to be fixed to the transfer material P to be a permanent image.
[0052]
Also in this embodiment, the peripheral speed of the photosensitive drum is controlled by the control means (CPU) for each image forming mode, that is, in the four-color full-color mode, each photosensitive drum, transfer belt (and transfer material), and In the single color mode, the difference in peripheral speed between each photosensitive drum and the transfer belt (and transfer material) is smaller than that in the four-color full color mode, preferably zero. As a result, it is possible to prevent the durable life of the photosensitive drum from being unnecessarily lowered due to the friction between the photosensitive drum and the transfer belt (and the transfer material).
[0053]
In particular, in the market, the black single color mode for forming a black and white image is often selected in addition to the full color mode, so that the present invention is effective.
[0054]
Further, even in a system in which a cleaning device for a photosensitive drum is provided as in the present embodiment, it is possible to significantly reduce the rubbing scratches on the photosensitive drum caused by the transfer belt 60 as in the first embodiment.
[0055]
【The invention's effect】
As described above, according to the present invention, it is possible to prevent the life of the image carrier from being unnecessarily shortened without increasing the size, complexity, and cost of the apparatus.
[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]
DESCRIPTION OF SYMBOLS 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

Claims (6)

A plurality of image carriers each carrying a plurality of color toner images; a plurality of charging means for charging each of the plurality of image carriers; and a plurality of developing means for developing a toner image on each of the plurality of image carriers. has an intermediate transfer belt to which the toner image is transferred from said image bearing member in contact with said plurality of image bearing members, by the developing unit the toner remaining on the image bearing member after charged by the charging unit an image forming apparatus for developing a toner image on said image bearing member while recovering from said image bearing member,
A single drive motor for rotating the plurality of image carriers at the same rotational speed; and a control unit capable of controlling the drive motor, and a plurality of color toner images are obtained from the plurality of image carriers. A first mode in which the image is sequentially superimposed on the intermediate transfer belt, and a second mode in which a toner image of a predetermined color is transferred to the intermediate transfer belt from only a predetermined image carrier among the plurality of image carriers. Is selectable,
When the first mode is selected, the moving speed of the plurality of image carriers and the moving speed of the intermediate transfer belt are different at each transfer position where the plurality of image carriers and the intermediate transfer belt are in contact with each other. The drive motor is controlled by the control means,
When the second mode is selected , the difference between the moving speed of the plurality of image carriers and the moving speed of the intermediate transfer belt at each transfer position where the plurality of image carriers and the intermediate transfer belt are in contact with each other is The drive motor is controlled by the control means so as to be smaller than the difference between the moving speed of the plurality of image carriers and the moving speed of the intermediate transfer belt when the first mode is selected. an image forming apparatus comprising. 2. The moving speed of the intermediate transfer belt when the second mode is selected is higher than the moving speed of the intermediate transfer belt when the first mode is selected. Image forming apparatus. The image forming apparatus according to claim 1, wherein the predetermined image carrier is singular. 4. The image forming apparatus according to claim 3 , wherein a black toner image is formed on the predetermined image carrier. When the second mode is selected, assuming that the moving speed of the plurality of image carriers at the respective transfer positions is V1, and the moving speed of the intermediate transfer belt is V2.
{(V1-V2) / V2} × 100 <0.3
Or {(V2−V1) / V1} × 100 <0.3
The image forming apparatus according to any one of claims 1 to 4, characterized in that hold. When the first mode is selected, the moving speed of the plurality of image carriers at the respective transfer positions is V3, and the moving speed of the intermediate transfer belt is V4.
0.5 <{(V3-V4) / V4} × 100 <3.5
Or 0.5 <{(V4-V3) / V3} × 100 <3.5
The image forming apparatus according to any one of claims 1 to 5, characterized in that hold.

Images