JP2002006582A - Image-forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image-forming device, capable of stably outputting proper image by preventing the occurrence of image defects due to deterioration of parts constituting process equipments for colors being used less frequently, in an image-forming device which uses the developer of plural colors, including a black color. SOLUTION: An electrostatic latent image for another color is formed on photoreceptor drums 11M, 11C, 11Y and 11Bk, similarly to the image information of the black color, in terms of at least one color other than the black color to such an extent that the tone of the black color will not change in an area, where only the image information of the black color exists, and the toner image of the black color and the toner image of another color are superposed and transferred to a recording medium, whereby the using circumstances of the developer having the color other than the black color are maintained on a prescribed condition.

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 such as a copying machine, a printer, and a facsimile which employs an electrophotographic system or an electrostatic recording system, and more particularly to a color image forming apparatus such as a color copier, a color printer, and a color facsimile. The present invention relates to a forming apparatus.

[0002]

2. Description of the Related Art As an example of a color image forming apparatus adopting an electrophotographic system, a four-tandem tandem type color image forming apparatus in which a photosensitive drum as a latent image carrier and a developing device are arranged one-to-one will be described. I do.

In such a color image forming apparatus, as shown in FIG. 11, photosensitive drums 111M and 111 serving as latent image carriers are used.
C, 111Y, and 111Bk.
M, 111C, 111Y, and 111Bk are respectively surrounded by magenta (M) toner, cyan (C) toner,
Four sets of recording devices 110M and 110 that form images using yellow (Y) toner and black (Bk) toner
C, 110Y, and 110Bk. These four recording devices are arranged in parallel along an intermediate transfer belt 131 which is an intermediate transfer device.

[0004] Magenta (M)
The recording apparatus 110M containing the color toner will be described as an example with reference to FIG. Note that the other recording devices 110C, 1
10Y and 110Bk have the same configuration as the recording apparatus 110M except for the toner.

[0005] In the recording device 110M, a charging bias is applied by a power supply device (not shown) as a charging device for charging the photosensitive drum 111M along the periphery of the photosensitive drum 111M rotating in the direction of arrow A. Arrow B
A charging roller 112M that rotates in the direction of the arrow, an exposure device 113M that is an exposure unit for forming an electrostatic latent image on the photosensitive drum 111M, and a developing bias for developing the electrostatic latent image on the photosensitive drum 111M with toner. Is applied by a power supply device (not shown) and rotates in the direction of arrow C.
A primary transfer roller 132M for bringing the intermediate transfer belt 131 into contact with the photosensitive drum 111M for primary transfer of the toner image on the intermediate transfer belt 131 onto the intermediate transfer belt 131; A cleaning device 116M and the like for collecting the next transfer residual toner in the waste toner container 115M are provided.

Next, a method for supplying toner to the developing sleeve 114M will be described.

First, magenta (M) toner 118M in the toner container 117M is sent to a toner supply roller 119M that is disposed below the toner container 117M and rotates in the direction of arrow D. Then, the toner supply roller 11
9M and the developing sleeve 114M contact each other,
The toner is supplied onto the developing sleeve 114M. The toner on the developing sleeve 114M is regulated and charged to an optimum layer thickness by the developing blade 120M, and the charged toner carried on the developing sleeve 114M at the optimum layer thickness is developed by a power supply device (not shown) to a developing bias. Is applied to develop the latent image on the photosensitive drum 111M.

Next, a primary transfer bias is applied to the magenta (M) toner image formed by the recording device 110M by a power supply device (not shown), and the intermediate transfer belt 1
31 is primarily transferred. Similarly, image formation of other colors is performed, and magenta (M), cyan (C),
Image formation of each color is performed in the order of yellow (Y) color and black (Bk) color, and finally, on the intermediate transfer belt 131, magenta (M) color, cyan (C) color, yellow (Y) color Thus, a multi-color toner image in which black (Bk) toner images are superimposed is completed. The toner image is supplied to a secondary transfer roller 1 by a power supply device (not shown).
By applying a secondary transfer bias to the recording paper 34, the secondary transfer is collectively performed on the recording paper P conveyed by the secondary transfer roller 134 and the intermediate transfer belt 131. The recording paper P on which a plurality of color toner images are formed is conveyed to a fixing device 136, where the toner image is fixed on the recording paper P, and a color image is discharged out of the image forming apparatus. The secondary transfer residual toner remaining on the intermediate transfer belt without being secondary-transferred to the recording paper P is transferred to the intermediate transfer belt cleaning device 13.
Collected in 5.

[0009]

In a color image forming apparatus such as a quadruple tandem system, when outputting a black-and-white image using only a black toner, the intermediate transfer member and the recording material are colored. The photosensitive drum can be kept away from the recording device containing the toner so that the intermediate transfer member and the recording paper do not come into contact with each other, and the recording device containing the color toner can be stopped.

However, in general, most of the image is composed of black and white. However, in many cases, an image colored to emphasize a part or an image using color at one point is output in many cases. In this case, the photosensitive drum, the developing sleeve, and the like must be operated while the intermediate transfer member and the recording paper are kept in contact with each other without being separated from each recording device.

If it is often necessary to operate each recording apparatus while using little toner, some components constituting the recording apparatus gradually deteriorate. Specifically, in a cleaning device for collecting the primary transfer residual toner on the photosensitive drum, a situation occurs in which the amount of toner supplied to the cleaning device becomes extremely small. When the toner supply becomes extremely low, the friction between the photosensitive drum and the cleaning blade increases, and the torque required to rotate the photosensitive drum increases, and the friction between the photosensitive drum and the cleaning blade increases. When the edge of the cleaning blade is chipped or the edge of the cleaning blade is turned up, the primary transfer residual toner is not scraped off from the chipped or turned up portion by the cleaning blade but slips through, and cleaning failure may occur. There is.

In view of the above, the present invention prevents the occurrence of image defects due to deterioration of components constituting process equipment for colors that are not frequently used in an image forming apparatus using a plurality of color developers including a black color. It is another object of the present invention to provide an image forming apparatus capable of stably outputting a good image.

[0013]

Means for Solving the Problems The main invention according to the present application is a latent image carrier capable of carrying an electrostatic latent image on its surface, a charging means for charging the surface of the latent image carrier, Exposure means for forming an electrostatic latent image on the surface of the latent image carrier by exposing the surface thereof in accordance with image information, and applying the developer to the latent image carrier to form the electrostatic latent image thereon. What is claimed is: 1. An image forming apparatus comprising: a developing unit that visualizes a developer image; and a transfer unit that transfers the developer image to a recording medium, wherein the exposing unit includes an image decomposed for each of a plurality of colors including a black color. By exposing the surface of the latent image carrier after charging according to the information, an electrostatic latent image for each color is formed on the surface, and the developing unit performs the developing for each color for a plurality of colors including black. And a plurality of developing devices disposed opposite to the latent image carrier. Each developing device applies a developer of each color to the latent image carrier in accordance with the color of the image image report, thereby converting the electrostatic latent image into a developer image of each color, and the transfer unit transfers the latent image to the latent image. In an image forming apparatus capable of recording an image corresponding to the image information on the recording medium by sequentially superimposing and transferring the developer images of each color formed on the carrier onto a recording medium, using the developer of each developing device A developer use status detecting means for detecting the situation is provided. Based on the developer use status detected by the developer use status detection means, the color of the black color does not change in an area where the image information is only black. For at least one other color other than the black color, the exposure unit forms an electrostatic latent image for the other color on the latent image carrier in the same manner as the black color image information, and the transfer unit performs the black color Same as above for developer image By transferring overlapping the other colors of developer images, developer usage of the developing devices other than black color is an image forming apparatus characterized by being configured to be maintained at a predetermined condition.

[0014]

Embodiments of the present invention will be described below with reference to the accompanying drawings.

(First Embodiment) First, a first embodiment of the present invention will be described.

FIG. 1 is a sectional view of a color image forming apparatus showing an example of the image forming apparatus according to the first embodiment of the present invention.

In this color image forming apparatus, as shown in FIG. 1, photosensitive drums 11M, 11C, 1
1Y, 11Bk, and the photosensitive drums 11M, 11C, 1
Around 1Y and 11Bk, four sets of recording apparatuses 10M, which form images using magenta (M) toner, cyan (C) toner, yellow (Y) toner, and black (Bk) toner, respectively. 10C, 10Y, and 10Bk are provided. These four recording devices are arranged in parallel along an intermediate transfer belt 31 which is an intermediate transfer device.

Magenta (M)
FIG. 2 shows an example of the recording apparatus 10M containing the color toner.
This will be described with reference to FIG. The other recording devices 10C, 10Y,
10Bk has the same configuration as the recording apparatus 10M except for the toner.

In the recording device 10M, a charging bias is applied by a power supply device (not shown) as a charging device for charging the photosensitive drum 11M along the periphery of the photosensitive drum 11M rotating in the direction of arrow A. A charging roller 12M serving as charging means rotating in the direction of arrow B, an exposure device 13M serving as exposure means for forming an electrostatic latent image on the photosensitive drum 11M, and a toner developing means for developing the electrostatic latent image on the photosensitive drum 11M. Is applied by a power supply device (not shown) and intermediate transfer for primary transfer of the toner image on the developing sleeve 14M and the photosensitive drum 11M as the developing means rotating in the direction of arrow C onto the intermediate transfer belt 31. A primary transfer roller 32M for bringing the belt 31 into contact with the photosensitive drum 11M, and a primary transfer residual toner remaining on the photosensitive drum 11M without primary transfer. A cleaning device 16M or the like for collecting the waste toner container 15M is arranged.

Next, a method for supplying toner to the developing sleeve 14M will be described.

First, a magenta (M) toner 18M in a toner container 17M is provided at a lower portion of the toner container 17M and rotates in a direction indicated by an arrow D in a toner supply roller 19M.
Sent to M. Then, the toner is supplied onto the developing sleeve 14M by the contact between the toner supply roller 19M and the developing sleeve 14M. The toner on the developing sleeve 14M is regulated and charged to an optimum layer thickness by the developing blade 20M, and the charged toner carried on the developing sleeve 14M with the optimum layer thickness is developed by a power supply device (not shown). Is applied to the photosensitive drum 1
Used for developing 1M of latent image.

Next, a primary transfer bias is applied to the magenta (M) color toner image formed by the recording device 10M by a power supply device (not shown), and the intermediate transfer belt 31
The primary transfer is performed thereon. Similarly, image formation of other colors is performed, and image formation of each color is performed in the order of magenta (M), cyan (C), yellow (Y), and black (Bk). On the intermediate transfer belt 31, magenta (M), cyan (C), yellow (Y),
A plurality of color toner images in which the black (Bk) color toner images are superimposed are completed. Then, the secondary transfer roller 3 applies a secondary transfer bias to the secondary transfer roller 34 by a power supply device (not shown).
Paper P conveyed by the belt 4 and the intermediate transfer belt 31
And the secondary transfer is performed collectively. The recording paper P on which a plurality of color toner images are formed is conveyed to the fixing device 36, where the toner image is fixed on the recording paper P, and a color image is discharged out of the image forming apparatus. Further, the secondary transfer residual toner remaining on the intermediate transfer belt without being secondary-transferred to the recording paper P is collected by the intermediate transfer belt cleaning device 35.

Next, a description will be given of a method of calculating the printing rate, which is the amount of image information of each toner, in the present embodiment.

In this embodiment, the printing rate of the toner is calculated using the number of print dots in each printing apparatus and the operating state of the printing apparatus.

First, a method of counting the number of print dots will be described.

As shown in FIG. 3, the host computer (S
Data to be printed out from 2) is sent as an electric signal to an image signal processing unit in the image forming apparatus. This data is converted to magenta (M) color and cyan (C) by the image signal processing unit.
Color (Y) and black (Bk) (S3). Then, the dot data of the image signal separated for each of the magenta (M), cyan (C), and yellow (Y) colors is counted by the dot number counting means, and the number of dots formed in the image is calculated. Ask (S
4). Then, the number of dots counted this time is added to the total number of dots, which is the total number of print dots of each color (S
5). Then, the total number of dots for each color is stored in a non-volatile memory (not shown) (S6).

Next, a method of detecting the operation status of each recording apparatus will be described.

As a method of detecting the operation status of each of the magenta (M), cyan (C), and yellow (Y) recording devices, the number of rotations of the photosensitive drum 11M of the magenta (M) recording device 10M is determined. Used. This is the magenta (M) color,
This is because the rotation speeds of the photosensitive drums of cyan (C) and yellow (Y) are the same. First, the rotation speed of the photosensitive drum 11M is measured by the photosensitive drum rotation speed measurement unit 21M (S
7). Then, the measured photosensitive drum rotation speed is added to the total photosensitive drum rotation speed which is the sum of the photosensitive drum rotation speeds (S
8) The value of the total number of photosensitive drum rotations is stored in the nonvolatile memory (S9).

Next, a method of calculating the printing ratio of each toner will be described.

First, a predetermined total number of photosensitive drum rotations is set as a check rotation in order to obtain the toner printing rate at regular intervals. If the total photosensitive drum rotational speed is equal to or less than the check rotational speed, the process returns to step 2 (S2) and the same operation as above is repeated. If the total photosensitive drum rotational speed becomes equal to or greater than the check rotational speed (S10), The printing rate for each color is obtained by retrieving the total number of dots of magenta (M), cyan (C), and yellow (Y) stored in the above-described nonvolatile memory and the total number of photosensitive drum rotations (S
11).

The printing ratio is calculated using the following equation.

Printing rate = total number of dots / (printable area width ×
Photosensitive drum circumference x total number of photosensitive drum rotations x resolution) x 10
0 (%) Next, a method of determining whether the printing rate is extremely low (hereinafter, referred to as a low printing rate) and an image forming method in the case of a low printing rate will be described.

First, the printing rate obtained by the above equation is compared with a low printing rate constant preset as a threshold value for determining whether or not the printing rate is low (S12). Magenta (M)
Color, cyan (C) color, and yellow (Y) color, if the printing rate is equal to or higher than the low printing rate constant, black (B)
k) The black (Bk) color toner is set to be used for the dots for printing the color (S13), and the total number of photosensitive drum rotations, magenta (M), cyan (C), and yellow (Y) are set.
The total number of dots of each color is reset to zero (S15).

Further, magenta (M) color, cyan (C) color,
When the printing rate of any one of the yellow (Y) colors falls below the low printing rate constant, the dots for printing the black (Bk) color include not only the black (Bk) toner but also the magenta (M) color. , Cyan (C) color and yellow (Y) color, the printing rate of which is lower than the low printing rate constant is set so as to print (S14), the total photosensitive drum rotation speed and magenta (M). The total number of dots of each color, cyan (C), and yellow (Y) is reset to zero, and the process ends (S1).
5).

The device of this embodiment is 600 dpi (dot)
per inch) color laser beam printer and letter size paper (216 mm
X279mm) printable area is 206mm x 269m
When converted to dots with m, the total number of dots is 4,866 dots × 6,354 dots = 30,918,564 dots. The outer diameter of the photosensitive drum 11M was 30 mm, the number of rotations for checking the photosensitive drum was set to 100, and the low printing rate constant was set to 1.5%.

A durability test was performed using the image forming apparatus of this embodiment.

In the durability test, a sample image composed of a magenta (M) color, a cyan (C) color, and a yellow (Y) color with a printing rate of 1% and a black (Bk) color with a printing rate of 4% was used. The test was performed in an environment at a temperature of 15 ° C. and a humidity of 10%.

As a result, no cleaning failure occurred even after printing 5,000 sheets as shown in Table 1. When the cleaning blade was observed after the end of the durability test,
No chipping or curling of the edge of the cleaning blade occurred.

[Table 1]

As a comparative example, the image data is black (B
A durability test was performed using only the black (Bk) toner for the k) color dots and using the same sample image as that used in the present embodiment. As shown in Table 1, about 1000 sheets were printed. When printing was completed, poor cleaning occurred, and when the cleaning blade was observed, it turned up at the edge of the cleaning blade.

In this embodiment, the low printing rate constant is set to 1.
Although set to 5%, it is desirable to set to about 2.5%.

In the present embodiment, the number of rotations of the photosensitive drum is used as a method of detecting the operation state of the recording apparatus.
The rotation speed of the developing roller, the charging bias application time, the developing bias application time, or the like may be used.

As described above, when the printing rate is low, the image data is printed not only on black (Bk) toner but also on magenta (M) toner, cyan (C) toner, and black (Bk) toner. By using the yellow (Y) toner having a printing rate lower than the specified printing rate in a superposed manner, an image having a lower printing rate is generated than when only the black (Bk) toner is used. Cleaning defects can be suppressed.

(Second Embodiment) Next, a second embodiment of the present invention will be described. Note that the same components as those of the first embodiment are denoted by the same reference numerals, and description thereof is omitted.

In this embodiment, the image data is black (B
k) not only black (Bk) toner but also magenta (M) toner, cyan (C) toner,
By using a total of four yellow (Y) toners in a superimposed manner, it is possible to suppress poor cleaning occurring in an image having a low printing ratio and minimize the change in the color of black (Bk) dots. It is characterized in that it is kept to a minimum.

An image control method in the case of a low printing rate, which is a feature of this embodiment, will be described. Note that the configuration of the image forming apparatus of this embodiment and the method of calculating the printing rate are the same as those of the first embodiment.

As shown in FIG. 4, in the present embodiment, the value of the printing rate obtained in the same manner as in the first embodiment and the low value set as the threshold value for determining whether or not the printing rate is low. The printing rate constant is compared (S32). Magenta (M) color,
If any one of the printing rates of the cyan (C) color and the yellow (Y) color falls below the low printing rate constant, the black (B)
k) In addition to black (Bk) toner, a total of four toners of magenta (M), cyan (C), and yellow (Y) toners are used for dots for printing colors. Setting (S34), magenta (M) color,
When all the printing rates of the cyan (C) color and the yellow (Y) color are equal to or higher than the low printing rate constant, the setting is made such that the black (Bk) color toner is used for the dots for printing the black (Bk) color ( S33). Then, the total number of dots of magenta (M), cyan (C), and yellow (Y) is reset to zero, and the process ends (S35).

As in the first embodiment, in this embodiment, a durability test was performed under the same conditions as in the first embodiment. As a result, no cleaning failure occurred even after printing 5,000 sheets.

In addition to the black (Bk) toner, magenta (M) toner, cyan (C) toner,
FIG. 5 shows the results obtained by examining the tint of black (Bk) dots using a total of four yellow (Y) toners.

FIG. 5 is a diagram schematically showing an L ^* a ^* b ^* color system chromaticity diagram. In FIG. 5, the + a ^* direction is red in the red direction and the redness increases as the value of a ^* increases. Becomes stronger, and -a ^*
In the green direction, the greenness becomes stronger as the value of a ^* becomes smaller, the + b ^* direction becomes more yellowish in the yellow direction as the value of b ^* becomes larger, and the b ^* direction becomes b ^* in the blue direction ^. As the value of becomes smaller, blueness becomes stronger. In the present embodiment, since L ^* is targeted at a low value of 30 or less because black is targeted, the deviation of the values of a ^* and b ^* is about 5 in absolute value, respectively. In FIG. 5, the corresponding part is shown in an enlarged manner.

Next, the respective marks shown in FIG. 5 will be described. White circles (）) indicate the case of only the black (Bk) toner, and black circles (ブ ラ ッ ク) indicate the magenta (M) ) When the color toner is superimposed, the white star (*) is the black (Bk) color and the cyan (C) toner is superimposed, and the black star (★) is the black (Bk) toner and the yellow (Y) toner Are overlapped with black (Bk) toner, magenta (M) toner, cyan (C) toner, and yellow (Y) toner.

In this embodiment, the density on the image data is 1
If it is 00%, it is output at the maximum image density, and if the density on the image data is 0%, it is output at the minimum image density. During that time, an image processing apparatus is used in which the density on the image data and the output image density change linearly. , The density of the black (Bk) color on the image data is 100%, and the other colors (magenta (M) color,
The density on the image data of cyan (C) and yellow (Y) was set to 30%.

FIG. 5 shows that the black (Bk) toner, the magenta (M) toner, the cyan (C) toner, and the yellow (Y) toner are the most superimposed on the black (Bk) toner.
k) It was found that the color was close to the color. In the present embodiment, the density on the black (Bk) color image data is set to 100%.
The same result was obtained when the density on the black (Bk) color image data was set to 80%.

As described above, when the image data is black (B
k) not only black (Bk) toner but also magenta (M) toner, cyan (C) toner,
Using a total of four toners of the yellow (Y) toner in a superimposed manner can reduce cleaning defects that occur in an image with a low printing ratio, compared to using only the black (Bk) toner. Further, it has become possible to further minimize the change in color.

(Third Embodiment) Next, a third embodiment of the present invention will be described. Note that the same components as those of the first embodiment are denoted by the same reference numerals, and description thereof is omitted.

In this embodiment, the image data is black (B
k) not only black (Bk) toner but also magenta (M) toner, cyan (C) toner,
By superimposing and using the yellow (Y) toner having a low printing ratio, a cleaning failure that occurs in an image with a low printing ratio is suppressed, and furthermore, the black (B)
k) By setting the image forming order such that the color toner is formed on the top surface of the recording paper, the black (B)
k) It is characterized by minimizing a change in the tint of a color dot.

The features of the configuration of the image forming apparatus according to the present embodiment will be described. Note that the printing rate calculation method and the image control method in the case of a low printing rate according to the present embodiment are the same as those in the first embodiment.

In the image forming apparatus according to the present embodiment, as shown in FIG.
From the left side of FIG. 6, a black (Bk) color recording device, a magenta (M) color recording device, a cyan (C) color recording device, and a yellow (Y) color recording device are arranged in this order. That is, image formation is performed in the order of black (Bk), magenta (M), cyan (C), and yellow (Y). Finally, the toner images are superimposed on the intermediate transfer belt 31 in the order of black (Bk), magenta (M), cyan (C), and yellow (Y). Then, the toner image is subjected to a secondary transfer bias applied to the secondary transfer roller 34 by a power supply device (not shown) on the recording paper P conveyed by the secondary transfer roller 34 and the intermediate transfer belt 31, The secondary transfer is performed collectively. From the recording paper P side, the recording paper P on which the toner images are superimposed in the order of yellow (Y), cyan (C), magenta (M), and black (Bk) is conveyed to the fixing device 36, and the recording paper P The fixing of the toner image to P is performed, and a color image is discharged out of the image forming apparatus.

As in the first embodiment, a durability test was performed in this embodiment with the same settings as in the first embodiment. As a result, no cleaning failure occurred even after printing 5,000 sheets.

In addition to the black (Bk) toner, magenta (M) toner, cyan (C) toner,
Black (B) with yellow (Y) toner superimposed
k) When examining the tint of the color dot, the tint was as shown in FIG.

FIG. 7 is also a diagram schematically showing an L ^* a ^* b ^* color system chromaticity diagram similarly to FIG. 5, and the corresponding portions are enlarged and shown. In FIG. 7, black diamonds (◆) indicate black (B
k) When only the color toner is used, the black circle (●) indicates that the black (Bk) toner is superimposed on the magenta (M) toner, and the white circle (印) indicates the black (Bk) toner. When the magenta (M) toner is superimposed on the toner, the white star (*) is black (Bk) on the cyan (C) toner.
When color toners are superimposed, the white square mark (□) is black (B)
k) When the cyan (C) toner is superimposed on the color toner, a black star (★) indicates when the black (Bk) toner is superimposed on the yellow (Y) toner, and a white triangle (△) Is a case where the yellow (Y) toner is superimposed on the black (Bk) toner.

In this embodiment, similarly to the second embodiment, the density on the black (Bk) color image data is set to 100%.
%, Other colors (magenta (M), cyan (C),
The density on the yellow (Y) image data was set to 30%.

From FIG. 7, it was found that the color tone of the black (Bk) toner becomes closer to that of the black (Bk) toner by moving the black (Bk) toner upward (far from the recording paper). In this embodiment, the density on the black (Bk) color image data is fixed to 100%, but the same result can be obtained even when the density on the black (Bk) color image data is 80%. Was.

As described above, when the image data is black (B
k) not only black (Bk) toner but also magenta (M) toner, cyan (C) toner,
By superimposing and using the yellow (Y) toner having a low printing rate, it is possible to suppress the cleaning failure that occurs in an image with a low printing rate, and to record the black (Bk) toner. By setting the order of development to be transferred to the top surface of the paper, it is possible to minimize the change in the tint of black (Bk) dots.

(Fourth Embodiment) Next, a fourth embodiment of the present invention will be described. Note that the same components as those of the first embodiment are denoted by the same reference numerals, and description thereof is omitted.

In the present embodiment, when the type of paper is plain paper, in addition to the black (Bk) toner, dots of the low printing rate are added to the dots for printing black (Bk) on the image data. When the paper type is an OHP sheet, in addition to the black (Bk) toner on the dots for printing black (Bk) color on the image data,
This is characterized in that toner of a color having a low printing rate is superimposed at a density higher than that of plain paper.

An image control method in the case of a low printing rate, which is a feature of this embodiment, will be described with reference to FIG. Note that the configuration of the image forming apparatus of the present embodiment and the method of calculating the printing rate
This is the same as in the first embodiment.

As shown in FIG. 9, in the present embodiment, the printing rate value determined in the same manner as in the first embodiment and a threshold value for determining whether or not the printing rate is low are set. A comparison is made with the low printing rate constant (S52). Magenta (M)
A case will be described in which any one of the printing rates among the colors, cyan (C) and yellow (Y), becomes lower than the low printing rate constant.

First, the paper type of the recording paper P is determined by the paper type determination device 37 (S54). Then, when the recording paper P is detected as an OHP sheet, it is set to print in the OHP sheet mode (S56). If the paper type is plain paper, the plain paper mode is selected (S57), and the dots for printing black (Bk)
Magenta (M) in addition to black (Bk) toner
The color, cyan (C) color, and yellow (Y) color are set so that toners having a printing ratio of a low printing ratio constant or less are superposed. In the OHP mode, in addition to the black (Bk) toner, the printing ratio among the magenta (M), cyan (C), and yellow (Y) colors is low for the dots for printing the black (Bk) color. The toner having a rate constant or less is superimposed. At this time, the density of the superimposed image data is set higher than that of plain paper. Then, the total number of dots of magenta (M), cyan (C), and yellow (Y) is reset to zero, and the process ends (S37).

If the density on the image data is 100%, the image is output at the maximum image density. If the density on the image data is 0%, the image is output at the minimum image density. When the type of paper is plain paper, the printing rate of any one of magenta (M), cyan (C), and yellow (Y) is If the printing rate constant is equal to or less than the low printing rate constant, the original image data has a density of 100% for the dots of black (Bk) on the black (Bk) color image data, magenta (M) color, and cyan (C). ), The density on the image data of yellow (Y) is set to 30%, and when the type of paper is an OHP sheet, the density on the image data of black (Bk) is 100%, and the density on the magenta (M) ) Color, cyan (C) color, yellow (Y) color printing rate within has set the density of the color image data of which falls below the low printing rate constant at 60%.

Also in this embodiment, a durability test was performed on plain paper and an OHP sheet under the same conditions as in the first embodiment. As a result, as shown in Table 2, 5000 sheets of both plain paper and OHP sheets were used.
No cleaning failure occurred even when the sheet was printed. When the cleaning blade was observed after the end of the durability test, the edge of the cleaning blade was not chipped or turned up.

[Table 2]

As a comparative example, a durability test similar to that described above was performed using only black (Bk) toner for dots of black (Bk) image data.
As shown in Table 2, when about 1,000 sheets were printed, poor cleaning occurred, and the edge of the cleaning blade turned up.

Further, an endurance test was carried out using a sample image in which the printing ratio of the black job was lowered. Specifically, magenta (M), cyan (C), and yellow (Y)
A durability test was performed using a sample image in which the printing ratio of black (Bk) was 2% at a printing ratio of 2%. As a result, as shown in Table 3, in the case of plain paper, poor cleaning occurred when 4000 sheets were printed, but in the case of OHP sheets, no poor cleaning occurred even after 5000 sheets were printed.

[Table 3]

When the type of paper is an OHP sheet, the light transmitted through the OHP may be blocked to reproduce the black (Bk) color. Is reproduced by setting the density on the black (Bk) color image data to 100%, light can be sufficiently blocked.
Even when another color was superimposed thereon, little change in tint occurred, and black (Bk) color dots could be reproduced.

In the present embodiment, the number of rotations of the photosensitive drum is used as a method of detecting the operating state of the recording apparatus. However, the number of rotations of the developing roller, the charging bias application time, the developing bias application time, and the like are used. May be.

In the present embodiment, the low printing constant is set to 1.5%, but it is preferable to set the low printing constant to about 2.5% or less. Further, in the present embodiment, the paper type discriminating apparatus is used for discriminating the paper type. However, a paper specifying means for specifying the paper type by a user from software, a main body panel or the like may be used.

As described above, when the printing rate is low, the image data is printed not only with black (Bk) toner but also with magenta (M), cyan (C), and yellow ( Y) By superimposing and printing toner of a color equal to or less than the low printing constant of the color, it is possible to suppress a cleaning defect that occurs in an image having a low printing ratio.

Further, by providing the OHP sheet mode, when the OHP sheet is used, it is possible to consume a larger amount of the toner of the low printing rate while suppressing the change in the color tone than when using the plain paper. This makes it possible to more effectively suppress poor cleaning occurring in an image having a low printing ratio.

(Fifth Embodiment) Next, a fifth embodiment of the present invention will be described. Note that the same components as those of the first embodiment are denoted by the same reference numerals, and description thereof is omitted.

In the present embodiment, when the type of paper is plain paper, if there is a toner with a low printing rate, only black (Bk) toner is used for dots for printing black (Bk) on image data. Instead, the color shift on plain paper is reduced by superimposing all the colors of magenta (M), cyan (C), and yellow (Y),
If the type of paper is an OHP sheet, black (Bk) dots are printed on the image data in black (Bk).
k) In addition to the color toner, only the toner of the color with a low printing rate is superimposed.

An image control method in the case of a low printing rate, which is a feature of this embodiment, will be described with reference to FIG. Note that the configuration of the image forming apparatus of this embodiment and the method of calculating the printing rate are the same as those of the first embodiment.

As shown in FIG. 10, in the present embodiment, the printing rate value determined in the same manner as in the first embodiment and a threshold value for determining whether or not the printing rate is low are set. The low printing rate constant is compared (S62). A case in which the printing rate of any one of the magenta (M), cyan (C), and yellow (Y) colors is equal to or less than the low printing rate constant will be described.

First, the paper type of the recording paper P is determined by the paper type determination device 37 (S64). When the recording paper P is detected as an OHP sheet, the printing is set in the OHP sheet mode. In addition to the black (Bk) toner, the magenta (M) The color, cyan (C) color, and yellow (Y) color are set so that only the toner whose printing rate is equal to or less than the low printing rate constant is superimposed (S65).
If the paper type is plain paper, set it to plain paper mode,
Black (Bk) dots are printed on black (Bk)
k) In addition to the color toners, magenta (M), cyan (C), and yellow (Y) toners are superposed (S66). In the OHP sheet mode, the printing rate of the toner to be superimposed on the black (Bk) toner is set to be higher than that of the plain paper. Then, the total number of dots of magenta (M), cyan (C), and yellow (Y) is reset to zero, and the process ends (S67).

If the density on the image data is 100%, the image is output at the maximum image density. If the density on the image data is 0%, the image is output at the minimum image density. When the type of paper is plain paper, the printing rate of any one of magenta (M), cyan (C), and yellow (Y) is If the printing rate constant is equal to or less than the low printing rate constant, the original image data has a density of 100% for the dots of black (Bk) on the black (Bk) color image data, magenta (M) color, and cyan (C). ), The density on the image data of yellow (Y) is set to 30%, and when the type of paper is an OHP sheet, the density on the image data of black (Bk) is 100%, and the density on the magenta (M) ) Color, cyan (C) color, yellow (Y) color printing rate within has set the density of the color image data of which falls below the low printing rate constant at 60%.

Also in this embodiment, a durability test was performed under the same conditions as in the first embodiment. As a result, the occurrence of the cleaning failure was such that the magenta (M), cyan (C), and yellow (Y) colors had a printing rate of 1%, and the black (Bk) color had a printing rate of 4%. When the sample image is used, even if the paper type is plain paper, OHP
In the case of a sheet, no cleaning failure occurred even after printing 5,000 sheets. When the cleaning blade was observed after the end of the durability test, the edge of the cleaning blade was not chipped or turned up. or,
Magenta (M), cyan (C), and yellow (Y) colors have a printing rate of 1% and black (Bk) colors have a printing rate of 2%. If the paper type was plain paper, cleaning failure occurred when 4000 sheets were printed, but O
In the case of HP sheets, cleaning failure did not occur even after printing 5,000 sheets.

When the type of paper is an OHP sheet, the light transmitted through the OHP may be cut off to reproduce the black (Bk) color. Is reproduced by setting the density on the black (Bk) color image data to 100%, light can be sufficiently blocked.
Even when another color was superimposed thereon, little change in tint occurred, and black (Bk) color dots could be reproduced.

In the present embodiment, the number of rotations of the photosensitive drum is used as a method of detecting the operation state of the recording apparatus. However, the number of rotations of the developing roller, the charging bias application time, the developing bias application time, and the like are used. May be.

In the present embodiment, the low printing constant is set to 1.5%, but it is preferable to set the low printing constant to about 2.5% or less. Further, in the present embodiment, the paper type discriminating apparatus is used for discriminating the paper type. However, a paper specifying means for specifying the paper type by a user from software, a main body panel or the like may be used.

As described above, when the type of paper is plain paper and there is a toner with a low printing rate, black (Bk) dots are printed on the image data.
k) In addition to the color toner, all the colors of magenta (M), cyan (C), and yellow (Y) are superimposed and printed. When the type of paper is an OHP sheet, the image is printed. On the data, low printing is achieved by superimposing black (Bk) color toner on the dots for printing black (Bk) color and toner of low printing rate color more than when the paper type is plain paper. In addition, it is possible to more effectively suppress the cleaning failure that occurs in the image having a low ratio, and to minimize the change in the black (Bk) color tint regardless of the type of paper, whether plain paper or OHP sheet. It became possible to suppress.

[0089]

As described above, according to the invention of the present application, parts constituting a process device for a color which is not frequently used in an image forming apparatus using a plurality of color developers including a black color. Image defects due to deterioration of the image can be prevented, and a good image can be stably output.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view illustrating a schematic configuration of an image forming apparatus according to a first embodiment of the present invention.

FIG. 2 is a cross-sectional view illustrating a schematic configuration of a recording device provided in the image forming apparatus of FIG.

FIG. 3 is a flowchart illustrating a method of determining whether an image information amount for each color is equal to or less than a predetermined amount and an image control method according to the first embodiment of the present invention.

FIG. 4 is a flowchart illustrating a method for determining whether an image information amount of each color is equal to or less than a predetermined amount and an image control method according to the second embodiment of the present invention.

FIG. 5 is an L ^* a ^* b ^* color system chromaticity diagram of each color developer according to the second embodiment of the present invention.

FIG. 6 is a sectional view illustrating a schematic configuration of an image forming apparatus according to a third embodiment of the present invention.

FIG. 7 is an L ^* a ^* b ^* color system chromaticity diagram of each color developer according to the third embodiment of the present invention.

FIG. 8 is a cross-sectional view illustrating a schematic configuration of an image forming apparatus according to a fourth embodiment of the present invention.

FIG. 9 is a flowchart illustrating a method for determining whether an image information amount for each color is equal to or less than a predetermined amount and an image control method according to a fourth embodiment of the present invention.

FIG. 10 is a flowchart illustrating a method for determining whether an image information amount for each color is equal to or less than a predetermined amount and an image control method according to a fifth embodiment of the present invention.

FIG. 11 is a cross-sectional view illustrating a schematic configuration of a conventional image forming apparatus.

12 is a cross-sectional view illustrating a schematic configuration of a recording device provided in the image forming apparatus of FIG.

[Explanation of symbols]

11M, 11C, 11Y, 11Bk Photosensitive drum (latent image carrier) 12M Charging roller (charging means) 13M Exposure device (exposure means) 14M Developing sleeve (developing means) 21M Photosensitive drum rotation number measuring section (developer use state detecting means) ) 34 Secondary transfer roller (transfer means) P Recording paper (recording medium)

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 2H027 DA44 DB01 DC02 DD07 EB04 EC06 EC14 EE06 EF06 FA28 ZA07 2H030 AB02 AD11 AD13 AD16 BB32 BB63 5C074 AA02 AA15 BB02 BB26 CC26 DD24 DD28 EE08 EE11 FF15 GG09 GG12

Claims (8)

[Claims] 1. A latent image carrier capable of carrying an electrostatic latent image on a surface, a charging means for charging the surface of the latent image carrier, and a surface of the charged latent image carrier corresponding to image information. Exposing means for forming an electrostatic latent image on the surface by exposing to light; developing means for visualizing the electrostatic latent image as a developer image by applying a developer to the latent image carrier; An image forming apparatus comprising: a transfer unit that transfers a developer image onto a recording medium, wherein the exposure unit is configured to charge the latent image carrier after charging according to image information decomposed for each of a plurality of colors including a black color. An electrostatic latent image for each color is formed on the surface by exposing the surface, and the developing means is disposed to face the latent image carrier for each color for a plurality of developers including a black color. A plurality of developing devices, each developing device corresponding to the color of the image information. The electrostatic latent image is made into a developer image of each color by applying a developer of each color to the latent image carrier, and the transfer unit transfers the developer image of each color formed on the latent image carrier to a recording medium. An image forming apparatus capable of recording an image corresponding to the image information on the recording medium by sequentially superimposing and transferring the images on the recording medium, comprising: a developer use status detecting unit configured to detect a developer use status of each developing device; Based on the developer use state detected by the use state detection unit, in an area where the image information is only the black color, at least one other color other than the black color to the extent that the black color does not change, the exposure unit Forms an electrostatic latent image for another color on the latent image carrier in the same manner as the black image information, and the transfer unit superimposes the black developer image on the other color developer image as described above. By transcribing, An image forming apparatus comprising the developer usage of the developing device of the non-rack color is set to be maintained at a predetermined condition. 2. The developer according to claim 1, wherein the other color developer other than the black color developer is at least one of a magenta color developer, a cyan color developer, and a yellow color developer. Image forming apparatus. 3. The developer use status means is capable of detecting the amount of image information in each of the other colors, and at least when the amount of image information in at least one of the other colors becomes equal to or less than a predetermined value. For colors whose amount is less than the predetermined value,
The image forming apparatus according to claim 1, wherein an electrostatic latent image similar to black image information is formed on the latent image carrier. 4. The developer use status means is capable of detecting the amount of image information in each of the other colors, and when the amount of image information in at least one of the other colors becomes equal to or less than a predetermined value, the developer use status means. 4. The image forming apparatus according to claim 1, wherein an electrostatic latent image similar to black image information is formed on the latent image carrier for all colors. 5. 5. The recording medium according to claim 1, wherein the black developer image and the other color developer image are superimposedly transferred such that the black developer image is transferred to the uppermost surface of the recording medium. Item 5. The image forming apparatus according to any one of items 4. 6. A developer image of another color transferred in a region where image information is only a black color and superimposed on a black developer image when the recording medium is an OHP sheet rather than plain paper. The image forming apparatus according to claim 1, wherein the developer amount is set to be large. 7. A developer image of another color, which is transferred over a black developer image in an area where image information is only black, when all the recording media other than black are used when the recording medium is plain paper. 7. The developer image according to claim 1, wherein the developer image is a color developer image.
The image forming apparatus according to claim 1. 8. The developer use status means is capable of detecting the amount of image information in each of the other colors, and the image information is transferred in a region where only the black color is superimposed on the black developer image. When the recording medium is an OHP sheet and the amount of image information in at least one of the other colors becomes a predetermined value or less when the recording medium is an OHP sheet, the color of the image information amount is a predetermined value or less. 8. An electrostatic latent image similar to image information is formed on a latent image carrier.
The image forming apparatus according to claim 1.