JP5282450B2 - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus which prevents contamination in a white image part while reducing costs and extending a service life with respect to at least magenta, cyan and yellow image carriers. <P>SOLUTION: The four-drum tandem image forming apparatus has a color output mode and a black monochrome output mode, and is constituted so that an image carrier 2d for color other than black is separated from a transfer belt 1d1 in the black monochrome output mode. A common charging potential supply power source is used for at least magenta, cyan and yellow image carriers 2d. In the color output mode, the charging potential of at least magenta, cyan and yellow image carriers 2d are controlled to the same value, while in the black monochrome output mode, the charging potential is variably controlled. <P>COPYRIGHT: (C)2010,JPO&amp;INPIT

Description

  The present invention relates to an image forming apparatus used for image formation such as a copying machine, a printer, and a FAX.

  In color image forming apparatuses such as printers, copiers, and facsimile machines that form images using color toners, in recent years, miniaturization and cost reduction of the apparatuses have been accelerated. A general electrophotographic image forming apparatus has a charging potential supply power source according to the color of the color, and the charging potential and the developing bias according to the developing bias determined to make the density of each color constant. The charging potential is controlled to be variable so that the potential difference between the two is substantially equal. An electric field is applied between the charging potential (white image potential) and the developing bias in order to prevent the reversely charged toner from attaching to the white image portion. Generally, toner adhesion to the white image portion can be most suppressed when the development start potential is almost reached. However, if the potential difference between the charging potential and the development bias is smaller than the development start potential, the region where the regular charged toner is developed Therefore, the difference between the development bias and the development start potential is set to about −100 V to −200 V in consideration of variation variation. As a specific example, when the development bias is −250 V and the development start potential is −80 V, the charging potential on the surface of the image carrier is set to about −480 V. If this charging potential is set to the minus side, the adhesion of the reversely charged toner is further increased, and if the charging potential is set to the plus side, development is performed at a portion of the plus side with respect to -280V. When the development bias and the development start voltage are shifted to the plus side or the minus side according to the density adjustment, the set value of the charging potential is generally shifted accordingly. Here, the expression that there is an approximately optimum charging potential setting value according to the developing bias setting value of each color will be kept.

On the other hand, as a measure for reducing the cost of the apparatus, there is a method of using one power source in common with a charged potential supply power source (see, for example, Patent Document 1 and Patent Document 2). In this method, since the same charging potential supply bias is used for the four colors, the charging bias cannot be variably set for each color according to the development bias as described above. For this reason, it is necessary to predict the fluctuation range of the setting of the developing bias in advance, and to set so that the development start voltage is not exceeded in any of them. For this reason, the difference between the actually set developing bias setting value and the charged potential setting value becomes large, and the reversely charged toner is likely to adhere to the white image portion, and the fogging of the white image portion is a problem.
In order to solve this problem, for example, a measure for making the charge distribution of the toner excessively uniform is necessary (reducing the reversely charged toner), and various proposals have been made. As one of the measures that can be implemented with a simple configuration alone, yellow is the most downstream color, and for the three upstream colors, the reversely charged toner is collected on the downstream image carrier, and only the most downstream yellow is fogged. There is a measure to make the color dirty but not visually noticeable.
However, in this method, there is no downstream image carrier in the system in which the image carrier for magenta, cyan, and yellow (for CMY) is separated from the transfer belt in the black (K) single color output mode. , The problem is not solved. In addition, for black, since the toner contains a carbon component, the resistance tends to be low, and the reversely charged toner component tends to increase more than the color toner, and also visually adheres to the white image portion. In this case, there is a problem that it is more easily detected by human eyes than color toner.

JP 2004-151612 A Japanese Patent Laid-Open No. 2004-163502

Therefore, the present invention has been made in view of the above problems, and the problem is that at least for magenta, cyan, and yellow, the white image portion is stained while achieving low cost and long life. An object of the present invention is to provide an image forming apparatus that does not cause the above-described problem.
Another object of the present invention is to provide an image forming apparatus that does not cause smearing of the white image portion in the color and black monochrome output modes.
Another object of the present invention is to provide an image forming apparatus that does not cause smearing of the white image portion of the final color.

The features of the present invention, which is a means for solving the above problems, are listed below.
The image forming apparatus of the present invention has a tandem configuration in which image forming apparatuses of respective colors including image carriers for the respective colors are arranged to face an endless belt, and the image forming apparatus has at least a color output mode and a black monochrome output mode. The image forming apparatus for each color includes a charging unit and a developing unit respectively opposed to the image carrier for each color, and uses one common charging potential supply power source for the charging unit. In the color output mode, the output value of the charging potential supply power source is determined in correspondence with the developing bias having the highest absolute value among the developing biases used in the developing means, and the image carrier for each color The charging means is controlled so that the charging potentials of the two are equal to each other, and in the black single color output mode, the charging bias is adjusted in accordance with the developing bias used in the developing means for black. By determining the output value of the charging potential power supply, a charging potential of the image bearing member for black with variably controlled to control so as to separate the said endless belt from the image bearing member for a color other than black, the color output mode, the final color of the toner image to be transferred to the endless belt you being a yellow.

The image forming apparatus of the present invention is an image forming apparatus having a tandem configuration in which image forming apparatuses of respective colors including image carriers for the respective colors are arranged to face endless belts, and the image forming apparatuses of the respective colors are images for the respective colors. Each of the charging means and the developing means arranged to face the carrier, respectively, uses one common charging potential supply power for the charging means included in the color image forming device, and produces black. One charging potential supply power source is used for the charging device included in the image device, and the final color for transferring the toner image to the endless belt is yellow, corresponding to the developing bias used in the developing means for yellow. The output value of the one charging potential supply power source is determined, and the output value of the one charging potential supply power source is determined in correspondence with the developing bias used in the developing means for black. To.

Also, the image forming apparatus of the present invention, further, characterized by a black most upstream color toner image is transferred to the endless belt.
The image forming apparatus of the present invention, further, characterized by that it is a configuration with a secondary transfer portion.
The image forming apparatus of the present invention is further characterized in that the endless belt is a belt that also serves to suck and convey recording paper.

The image forming apparatus as the means for solving the above has the following effects.
In the present invention, since a common charging potential supply power source is used for at least the magenta, cyan, and yellow (CMY) image carriers, the cost of the apparatus can be reduced. In addition, in order to achieve a long life of the CMY image carrier, the charging potential is developed for the fogging of the white image portion, which is a side effect when the endless belt is separated in the black monochrome output mode. It can be reduced by making it variable according to the bias. That is, at least for CMY, it is possible to prevent the white image portion from being stained while achieving cost reduction and long life.
In the present invention, in the color output mode, the most downstream color is yellow, so that the toner that causes the fogging of the white image portion having the reverse charge polarity can be collected by the downstream color image carrier. With regard to the final color, it is possible to prevent the white image portion from being stained in the color output mode by setting the yellow color to be visually inconspicuous so that a slight amount of fogging of the white image portion is not a problem. it can.

In the present invention, with respect to the final color having no downstream color, the reversely charged toner transferred to the endless belt directly becomes a stain on the white image portion. By setting the charging potential (at least for magenta, cyan, and yellow, since they are common power supplies, the same charging potential is used), it is possible to prevent the white image portion of the final color from being stained. For the three upstream colors, there is no problem because the reversely charged toner that contributes to the contamination of the white image portion can be collected by the final color image carrier.
According to the present invention, in the black monochrome output mode, the black charging potential is determined according to the black development bias, thereby preventing the white image portion from being stained in the black monochrome output mode. That is, in the black monochrome output mode, the CMY image carrier and the endless belt are separated from each other, so that the black image carrier becomes the most downstream image carrier, and the downstream image carrier as in the color output mode. Thus, the problem that the reversely charged toner cannot be collected can be solved. By the way, in the color output mode, when the KMCY common charging power supply is used, when the charging potential is set so as to reduce the adhesion of the black reverse charging toner, the other three colors are reversed in the white image portion. Such a setting cannot be made because adhesion of charged toner increases.

In the present invention, by providing an independent charging potential supply power source only for black, it is possible to set the condition that toner adhesion to the white image portion for black in the color output mode can be reduced. That is, when black color is visually attached to the white image portion, it has a characteristic that it is easily regarded as an abnormal image, and contains more carbon than other color colors, creating a reversely charged toner in terms of charging characteristics. The problem that the white image portion is likely to be smudged due to the characteristic that it is easily performed can be solved.
According to the present invention, since the transfer process is performed twice before the toner moves to the recording paper, the fog stain in the white image portion is easily collected by the downstream image carrier or the like as compared with the direct transfer. Therefore, a bold setting, that is, a setting in which the fogging of the white image portion is poor on the image carrier other than the final color is possible.
According to the present invention, in the direct transfer, the fog stain of the white image portion of the image carrier is directly put on the paper, and thus the fog stain of the white image portion is likely to be abnormal. Therefore, the endless belt may suck and convey the recording paper. It is particularly effective to be a belt that also serves as a belt.

In the present invention, with respect to the final color having no downstream color, the reversely charged toner transferred to the endless belt is directly contaminated with the white image portion. By setting the charging potential (at least magenta, cyan, and yellow are the same power supply because they are common power sources), it is possible to prevent the white image portion for the final color from being stained. For the three upstream colors, there is no problem because the reversely charged toner that contributes to the smear of the white image portion can be collected by the image carrier for the final color.
In the present invention , the CMY three-color image carrier is disposed downstream of the black image carrier, and the process of collecting the reversely charged toner three times is performed. Reduced. That is, when black color is visually attached to the white image portion, it has a characteristic that it is easily regarded as an abnormal image, and contains more carbon than other color colors, creating a reversely charged toner in terms of charging characteristics. Since the white image portion is likely to be stained because of the characteristic that it is easily performed, this problem can be solved.
According to the present invention, by providing an independent charging potential supply power source only for black, it is possible to set the apparatus under conditions that can reduce toner adhesion to the white image portion for black, which is more problematic.

  The best mode for carrying out the present invention will be described below with reference to the drawings. Note that it is easy for a person skilled in the art to make other embodiments by changing or correcting the present invention within the scope of the claims, and these changes and modifications are included in the scope of the claims. The following description is an example of the best mode of the present invention, and does not limit the scope of the claims.

The present inventor has found the following means in order to solve the conventional problems.
(First means)
The charging potential setting control is changed between the color output mode and the black monochrome output mode. In the color output mode, the charging potential target value for YCMK is the same. With this setting, it is not possible to obtain an optimal charging potential when the development bias and development start voltage for each color are different.Therefore, this setting cannot be advantageous for adhesion of reversely charged toner in the white image area, but the final color is yellow. The problem is solved by the conventional method that makes it visually inconspicuous. On the other hand, since the CMY image carrier is not driven in the black monochrome output mode, the most advantageous charging potential setting for the adhesion of the reversely charged toner to the white image portion corresponding to the black developing bias setting value is performed. This solved the problem. Further, in the configuration shown in claim 5, by using one charging potential supply power source for CMY and another charging potential supply power source for black, abnormalities are detected most visually, including in the color output mode. The problem was solved by reducing the adhesion of reversely charged toner to the white image area for black.

(Second means)
After setting the final color to yellow, the development bias setting value is determined in correspondence with the development bias for the color having the highest absolute value among the colors using the common charging potential supply power source. In the case of a method in which the charging potential is fixed, in all the assumed development bias setting values, consideration must be given so that the potential difference between the charging potential and the development bias does not exceed the development start voltage. Adversely charged toner to the white image area is slightly reduced by corresponding to the developing bias for higher colors, and the reverse charged toner to the white image area for all colors including the final color without the downstream image carrier. It was possible to adhere with no problem.

FIG. 1 shows an embodiment of an image forming apparatus of the present invention. The process cartridges 2Y, 2M, 2C, and 2K are attached to the image forming apparatus 1 in a detachable manner. The image forming apparatus 1 includes an optical system 1a, a paper feed roller 1b, a paper feed cassette 1c that stores recording paper 3, a transfer unit 1d, a fixing roller 1e, and the like. On the other hand, the process cartridge 2 includes a charging roller 2a, a developing unit, a toner storage unit 2b, a cleaning unit, a waste toner collecting unit 2c, an image carrier (also referred to as a photosensitive member) 2d, and the like. The optical system 1a includes a polygon motor, a polygon mirror, an Fθ lens, a laser diode, a mirror, and the like.
An outline of the operation of the image forming apparatus 1 will be described. The recording paper 3 stored in the paper feed cassette 1c is conveyed to the image carrier 2d by the paper feed roller 1b. The image carrier 2d is rotationally driven. At that time, the image carrier 2d is charged by the charging roller 2a, and laser light is irradiated from the optical system 1a to form an electrostatic latent image on the image carrier 2d.
The electrostatic latent image is visualized by toner when passing through the developing means and the toner storage portion 2b. The visible image is primarily transferred from the image carrier 2d to the transfer unit 1d, and secondarily transferred to the recording paper 3 conveyed from the transfer unit 1d. That is, the image forming apparatus 1 has a secondary transfer unit. Then, the recording paper 3 is conveyed to the fixing roller 1e, and the visible image on the recording paper 3 is fixed and discharged outside the image forming apparatus 1.
FIG. 2 is a perspective view of the process cartridge 2 mounted on the image forming apparatus main body. The process cartridge 2 includes a charging roller 2a, a developing unit, a toner storage unit 2b, a cleaning unit, a waste toner collecting unit 2c, and an image carrier 2d integrated (AIO). The waste toner collecting unit 2c is provided in the process cartridge.

FIG. 3 and FIG. 4 are configuration diagrams of a charging potential supply power source for the charging roller 2a. FIG. 3 shows a configuration having one charging potential supply power source for image formation for YCMK. As shown in the figure, the transfer belt 1d1, which is an endless belt of the transfer unit 1d, is stretched around three rollers. On the transfer belt 1d1, four image carriers 2d for YCMK are arranged in alignment. A charging potential supply power source is connected to each image carrier 2d via a cable. FIG. 4 shows a configuration having one charging potential supply power source for black and one common charging potential supply power source for CMY. Other configurations are the same as those in FIG. The present invention uses a common charging potential supply power source for at least the magenta, cyan and yellow image carriers, and at least the charging potential for the magenta, cyan and yellow image carriers in the color output mode. Therefore, the present invention can be implemented using any of the devices shown in FIGS. 3 and 4 because the same potential is controlled and the charging potential is variably controlled in the black monochrome output mode.
There are two charging potential supply power sources, one for magenta, cyan and yellow, and the other for black. The charging potential supply power for magenta, cyan and yellow corresponds to the developing bias for yellow. The charging potential for black is made to correspond to the developing bias for black, and the output of the charging potential supply power source is determined.

  FIG. 5 is a graph showing the relationship between the developing bias for setting the surface of the image carrier to a predetermined charging potential and the amount of toner attached to the white image portion. In this figure, when the developing bias is 0V from -80V, the toner adhesion amount suddenly increases as the developing bias increases, and normal development is performed. Therefore, a bias of −80 V when the straight line that rises rapidly is extended becomes the approximate development start point (bias). On the other hand, it can be seen that the toner adhesion amount of the white image portion gradually increases as the developing bias goes to the minus side from -80V. This is because the reversely charged toner has moved to the white image portion because the electric field attracting the reversely charged toner has increased.

  FIG. 6 shows an example of a direct transfer configuration in which transfer is performed while the recording paper 3 is sucked and conveyed by the transfer belt 1d1. In the color output mode, a bias is applied to the charging roller indicated by 2a in FIG. 1 from a charging potential supply power source common to the four colors, as in FIG. 3, and the charging potential of the image carrier is determined. In this embodiment, for example, a supply bias of about −1200 V is applied to the charging roller 2 a so that the charging potential Vc on the surface of the image carrier 2 d is −500 V. This applied bias is variable by a table when the environment changes, and can be controlled so that Vc is always constant. The development bias Vb is determined by reading the density of the pattern written on the transfer belt 1d1 with a sensor. For example, when there is a color having a Vb value of −200V and a color having −100V, the amount of toner contamination on the white paper portion is larger when Vb is −100V than the relationship of the graph of FIG. This is because the reversely charged toner is more easily moved by the electric field. If the value of Vc is set low in advance, this time, when the Vb value is set high, the development start voltage is exceeded, and the entire surface is developed.

  In the case of using Vc fixed in this way, simple setting is possible, but it is necessary to limit the width of Vb that becomes the most minus side and to determine it. As a side effect, particularly when the toner deteriorates, the charge amount drops, and Vb is set to be low, the toner stain of the white image portion occurs. In this regard, the image can be recovered by the downstream image carrier by applying a normal transfer electric field during transfer on the downstream image carrier. Specifically, in the case of FIG. 6 (FIG. 3), the toner stain on the white image portion of the black (K) toner is the image carrier for magenta (M), cyan (C), or yellow (Y) downstream thereof. Recovered by 2d. Similarly, magenta and cyan are collected by the downstream yellow image carrier 2d. Since there is no downstream image carrier only for yellow (Y), it cannot be collected, but there is no problem because it is a visually inconspicuous color.

  In the black monochrome output mode, as shown in FIG. 7, the transfer belt 1d1 and the CMY image carrier are separated from each other, and the black (K) image carrier and the transfer belt 1d1 rotate. At this time, the charging potential Vc on the surface of the image carrier is desirably determined according to the developing bias Vb. Vb is determined by reading the density of the pattern written on the transfer belt 1d1 with a sensor, as in the color output mode. For example, when Vb = −250V, the charged potential Vc on the surface of the image carrier 2d is obtained using Vb = −150V so as not to exceed the development start voltage including fluctuations. Therefore, Vc = −400V is set. Vb is updated every time the density of black (K) is sensed, and Vc is reset every time. This makes it possible to be closer to the development start point where the amount of toner adhering to the white image portion is smaller than when the charged potential Vc on the surface of the image carrier 2d is fixed at -500 V from the relationship of FIG. It is possible to make the toner stain on the white image portion inconspicuous in the monochrome output mode.

In FIGS. 6 and 7, since the same charging potential supply power is used for the four colors, this is a simple method with low cost. The configuration change between FIG. 6 and FIG. 7 is performed by controlling the position of the roller that stretches the transfer belt 1d1. That is, as described with reference to FIG. 1, a four-tandem configuration, a color output mode and a black monochrome output mode, and a configuration in which the image carrier 2d other than black and the transfer belt 1d1 are separated in the black monochrome output mode. It becomes.
In the color output mode of FIG. 6, the most negative Vb value is determined, and the Vc value is set in correspondence with the Vb value. For example, when the values of the developing bias Vb determined by the density sensor are black (K) = − 200 V, magenta (M) = − 250 V, cyan (C) = 220 V, yellow (Y) = − 210 V, magenta (M ) Is applied with a developing bias Vb = −150 V to determine the charging potential Vc on the surface of the image carrier 2d. Therefore, the value of Vc is set to -400V. By setting in this way, the amount of toner adhering to the white image portion can be closer to the development start point than when Vc is fixed at −500 V, so that the toner adhering to the white image portion can be reduced. Can do. That is, in this configuration, the final color is yellow, and the developing bias for the color having the highest absolute value among the colors using the common charging potential supply power (magenta (M) = − 250 V) The development bias setting value is determined in accordance with. In the case of a method in which the charging potential is fixed, in all the assumed development bias setting values, consideration must be given so that the potential difference between the charging potential and the development bias does not exceed the development start voltage. Corresponding to the developing bias for higher colors, the adhesion of the reversely charged toner to the white image portion is slightly reduced, and the reversely charged toner is applied to the white image portion for all colors including the final color having no downstream image carrier. Adhesion was able to be made into a level with no problem.

FIG. 1 is an explanatory view showing an embodiment of the image forming apparatus of the present invention. FIG. 2 is a perspective view of the process cartridge mounted on the image forming apparatus main body. FIG. 3 is an explanatory diagram showing a configuration of a charging potential supply power source for the charging roller, and shows a configuration having one charging potential supply power source for image formation for YCMK. FIG. 4 is an explanatory diagram showing a configuration of a charging potential supply power source for the charging roller, showing a configuration having one charging potential supply power source for black and one charging potential supply power source for CMY. . FIG. 5 is a graph showing the relationship between the developing bias for setting the surface of the image carrier to a predetermined charging potential and the amount of toner attached to the white image portion. FIG. 6 is an explanatory diagram showing an example (in the color output mode) of a direct transfer configuration in which transfer is performed while conveying a recording sheet. FIG. 7 is an explanatory diagram showing an example of a direct transfer configuration in which transfer is performed while conveying a recording sheet (in black monochrome output mode).

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Image forming apparatus 1a Optical system 1b Paper feed roller 1c Paper feed cassette 1d Transfer unit 1d1 Transfer belt 1e Fixing roller 2 Process cartridge 2a Charging roller 2b Toner storage part 2c Waste toner collection part 2d Image carrier 3 Recording paper

Claims (5)

In an image forming apparatus having at least a color output mode and a black monochromatic output mode, the image forming apparatus for each color including an image carrier for each color is disposed opposite to an endless belt.
The image forming apparatuses for the respective colors each include a charging unit and a developing unit that are respectively opposed to an image carrier for each color, and use one common charging potential supply power source for the charging unit,
In the color output mode, the output value of the charging potential supply power source is determined in correspondence with the developing bias having the highest absolute value among the developing biases used in the developing unit, and the image carrying for each color is carried out. Controlling the charging means so that the charging potential of the body is the same, and
In the black monochrome output mode, the charging potential of the black image carrier is variably controlled by determining the output value of the charging potential supply power source corresponding to the developing bias used in the developing means for black. Controlling the endless belt to be separated from an image carrier for a color other than black ,
An image forming apparatus according to claim 1, wherein the final color of the toner image transferred to the endless belt in the color output mode is yellow . In an image forming apparatus having a tandem configuration in which image forming apparatuses for each color including an image carrier for each color are arranged opposite to an endless belt,
The image forming devices for the respective colors each include a charging unit and a developing unit that are respectively arranged to face the image carrier for each color,
One charging potential supply power source is used for the charging means included in each color image forming device, and one charging potential supply power source is used for the charging device included in the black image forming device. use,
The final color for transferring the toner image to the endless belt is yellow,
Determining an output value of the one common charging potential supply power source corresponding to the developing bias used in the developing means for yellow, and
An image forming apparatus, wherein an output value of the one charging potential supply power source is determined in correspondence with a developing bias used in a black developing unit . The image forming apparatus according to claim 2.
An image forming apparatus, wherein the most upstream color of the toner image transferred to the endless belt is black . The image forming apparatus according to any one of claims 1 to 3 ,
An image forming apparatus having a secondary transfer portion . The image forming apparatus according to any one of claims 1 to 3 ,
The image forming apparatus according to claim 1, wherein the endless belt is a belt that also serves to suck and convey the recording paper .

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