JPS6157949A - Multicolor image forming method - Google Patents

Abstract

PURPOSE:To make fixing easy and obtain colors of moderate chroma by erasing an image forming area with a turn-on/off binary at a latent image formation time so that toners are distributed digitally and properly to divided minute parts and transferring toner images obtained by development to one transfer paper while superposing one on the others. CONSTITUTION:CCDs are arranged in a line and a filter array where blue, green, and red filters are arranged repeatedly in accordance with individual CCDs is put in the front of these CCDs to constitute a color image sensor 9 of a multicolor image forming device. The color of the reflected light of an original picture is detected by outputs of one set of three continuous CCDs. This color is subjected to a desired correction, and the superposition rate of each color toner required for reproducing this corrected color is operated by an operation processing circuit, and individual LEDs of an eraser 4 are lit to erase the image forming area on a photosensitive drum 1 in a unit of the size of the LED so that toners in each part of the image have said superposition rates when images formed by four image forming processes, which are performed by inserting three color separation filters and a colorless filter to the exposure light path successively, are developed with yellow, magenta, cyan, black toners and are transferred to one transfer paper.

Description

Detailed Description of the Invention Technical Field This invention relates to multicolor image formation in which toner images of multiple colors formed on a photoconductor are superimposed and transferred onto the same transfer paper, and the colors of the image are reproduced by the superimposition ratio of each color toner. Regarding the method.

Conventional multicolor image forming apparatuses have conventionally exposed and scanned a document 31 times, each time inserting color filters of blue, green, and red, which are the three primary colors of light, in multiple exposure paths to capture the reflected light flux of the document. The electrostatic latent images obtained by color separation and exposure of the photoreceptor are developed with yellow, magenta, and cyan toners, which are the three primary colors of the subtractive color method, to form three-color toner images. It is known that the images are superimposed and transferred onto a single sheet of transfer paper to obtain a full-color copy.

Theoretically, it should be possible to reproduce all colors including black by appropriately mixing the three colors yellow, magenta, and cyan, but in reality, the spectral transmittance characteristics of color M filters and the color toner It is not always possible to reproduce the color tone, gradation, and sharpness of the original because the spectral reflectance characteristics of the original are different from ideal characteristics. There are also cases where it is desired to differentiate the color tone of the original document itself. Also, many office documents have black characters, and when printing black and white copies, they must be passed through a color separation filter.
The system in which two toner images of three colors are superimposed and transferred through multiple exposures not only does not produce a desirable black color, but also has the disadvantage that color shift is noticeable in thin letters and there is a large loss of light quantity and time.

As illustrated in FIG. 1, the present inventors have developed a multicolor image forming apparatus that solves these problems.
A developing device 13 having black toner is provided following the yellow, magenta, and cyan color development H1o, 11.12 on the downstream side with respect to the rotational direction of the exposure position 18 of the photoreceptor drum L onto which the image is projected. A half mirror 72 is provided between the lens 6 and filter 8 of the system to divide the slit exposure beam into two parts, and a color image sensor 9 extending in the width direction of the photoreceptor drum l is provided at the imaging position of the beam transmitted through the half mirror. Drum exposure position 18 and yellow developer 1
0 and a light emitting element (
We have proposed a multicolor image forming device equipped with an eraser 4 that is located from an LED (LED) array.

In front of the light receiving elements of the above color image sensor 9HCCD array, a filter array in which blue, green, and red filters are arranged repeatedly is arranged in correspondence with each light receiving element.One set of blue, green, and red filters The three colors of light emitted from the portion corresponding to the area are detected by the outputs of the three light receiving elements. One light emitting element of the eraser 4 is provided corresponding to one set of filters of the color image sensor 9, and the output of one set of light receiving elements of the color image sensor is processed by an arithmetic processing circuit to form the corresponding color. The superimposition ratio of each color toner is calculated, and image processing is performed by controlling each light emitting element of the eraser 4 to blink during fC4 exposures through four color filters 82 of blue, green, red, and colorless, respectively. , cyan, and black, and the resulting fc four-color toner image is transferred to the transfer drum 14.
By superimposing and transferring the image onto a wrapped transfer paper, an image with desired color tone, gradation, and sharpness can be obtained.

In this device, the image portion determined to be black by the color image sensor 9 is statically removed by the eraser in the image forming process that performs yellow, magenta, and cyan development, and is not developed with color toner, and in the image forming process that performs black toner development. The other portions are neutralized by the eraser, and only the black image portion is erased by the black toner, resulting in a pure black image with no sharp color shift. In addition, various color corrections can be performed according to preset processing programs.

In FIG. 3, 2 is a static eliminator, 3 is a charger, 15 is a pre-transfer static eliminator, 16 is a pre-cleaning static eliminator, and 17 is a cleaning unit.

Now, the color of each part of the image reproduced on the copy is determined by the superimposition ratio of each color toner in that part.

In the conventional multicolor image forming apparatus using the color separation image superimposition transfer method mentioned at the beginning, the original image is separated using a color separation filter, an analog latent image is formed on the photoreceptor, and the image is developed with toner. , continuous toner images are formed in the front, rear, left and right directions. Therefore, for example, the green portion of the image is reproduced with a layer of cyan toner C uniformly superimposed on a layer of yellow toner Y, as shown in FIG. Further, for a certain color, the three colors yellow, magenta, and cyan are uniformly superimposed at a ratio corresponding to the color.

However, color toners used in electrophotographic image forming apparatuses such as copiers are not transparent, and therefore, when they are overlaid all over, the resulting colors are muddy and lack saturation.

Further, toner having multiple layers has a disadvantage of poor fixing properties.

Purpose: In view of the above problems of conventional multicolor image forming apparatuses, the present invention solves the above problems using a multicolor image forming apparatus proposed by the present inventors as shown in FIG. An object of the present invention is to provide a multicolor image forming method.

Structure In order to achieve the above object, the present invention divides a pixel of an appropriate size into a plurality of minute parts, and each color toner constituting a certain color is divided into a predetermined ratio of one pixel as a whole constituting that color. Thus, when forming a latent image for each color image, on/off binary erasure is performed in units of the fine portions so that the divided fine portions are digitally appropriately distributed as either 1 or 0. It is characterized in that by superimposing and transferring toner images obtained by developing a blue color onto a sheet of transfer paper, the toner is partially superimposed within the above-mentioned pixels as shown in FIG.

In this way, the color of a certain part of the image is reproduced by partially overlapping each color toner within pixels of an appropriate thickness, making it easier to fix and creating a color with appropriate saturation. You can get the color. Also, when looking at the pixel as a whole, the ratio of each color toner is a predetermined ratio to form that color, so if the size of the pixel is appropriately determined, color unevenness will not be noticeable when viewed with the naked eye. do not have.

An example of a method for partially overlapping two colors of toner within one pixel will be described below.

Now, the color image sensor 9 of the multicolor image forming apparatus shown in FIG. C.C.
Blue, green, and red correspond to D (B in the figure).

It is assumed that the filter array is constructed by stacking filter arrays in which filters (indicated by G and R) are repeatedly arranged.

Therefore, from the output of the following three CCDs, 0.1
It is possible to detect the color of the reflected light of the original image with a width of 25 mm. The arithmetic processing circuit calculates the charge ratio of each color toner necessary to reproduce this color with the desired correction, and then inserts three color separation filters and a colorless filter into each path of the dew point. 4 times O image formation excessive N, yellow,
When developing with magenta, cyan, and black toners and superimposing them and transferring them onto a single sheet of transfer paper, each LED of the eraser 4 is made to emit light so that each part of the image has the above-mentioned toner superimposition ratio, and the photoreceptor drum 1 is Erase the image head in units of LED size.

As shown in FIG. 5, the eraser 4 has one light emitting surface of 0.
It is formed by arranging 125mm square LEDs in a row, and each LE
Although it is possible to change the light quantity of D, in order to stabilize the brightness, it is preferable to perform a binary operation of blinking and blinking.

Therefore, as shown in FIG. 6, for example, each LED of the eraser
The irradiation range 101 is arranged in 4 columns vertically and horizontally in a total of 16 squares, and an O-5m square area 100 is considered as one pixel, and sections are divided according to the toner superimposition ratio for each color image forming process. Equation (1) By appropriately dispersing charges and driving the eraser 4 so as to leave charges and erase other sections, the required toner superimposition ratio for one pixel as a whole can be obtained. In this case, as mentioned above, it is necessary to make sure that the toners of each superimposed color do not completely overlap in the same section, and that no section completely overlaps, that is, it is necessary to overlap them partially. It is.

For example, assume that the color detected by the color image sensor 9 is green, and the toner ratio obtained by processing by the arithmetic processing circuit is 12/16 for cyan and 10/16 for yellow. In this case, these toners? Ii of 0.5 angle
! To partially overlap within i+ element, add cyan toner to 16
It is sufficient to scatter the yellow toner appropriately (meaning randomly) in 12 of the sections, and to spread the yellow toner appropriately in 10 of the 16 sections. The probability that two randomly scattered toner colors will overlap completely is actually zero, and the probability that they will not overlap completely is also zero, so the two toners will partially overlap and the expected result will not be achieved. can get.

A dither matrix method is one of the methods for appropriately distributing each color toner to several sections among the 16 sections. As shown in Fig. 7(a), the dither matrix is a matrix in which one number from 1 to 16 is arbitrarily placed in each section corresponding to the 16 sections of one pixel; for example, one for cyan and one for yellow. Prepare 3 completely different things. In order to leave two out of the 16 sections, it is sufficient to apply toner to the sections for which the result of subtracting l from the number of each section is 1 or more. In other words, instead of erasing that section, you only need to erase other sections.

If you want to leave 10 sections, just subtract 6 from the number of each section.

The 71st ffi (b) explains this, where the black circled portions are not erased and the white circled portions are erased. The above operation is performed by storing the no<turn of the dither matrix in ROIVf and comparing it with the output of the arithmetic processing circuit. If the above erase is performed and the cyan toner and yellow toner are developed and superimposed and transferred onto one sheet of transfer paper, the cyan toner and yellow toner will partially overlap, forming one pixel 100, as shown in FIG. 7(c). As a whole, an image with the required superimposition ratio is obtained. (c) In the figure, the mark Δ is cyan toner, and the mark ○ is yellow toner.

Within a 0-51+Lm square pixel, there are parts that are only cyan, parts that are only yellow, and parts where these overlap, but when viewed with the naked eye from a normal clear viewing distance of about 30 cm, these The parts blend together seamlessly, giving the desired color saturation and depth.

In the above example, the green color in which cyan toner and yellow toner are combined at a superimposition ratio of 12:10 has been described.
The same method can be used for other colors and when 2M tatami mats of three or more colors are used.

Effects As described above, according to the present invention, by partially superimposing the toners of each color to make the three colors of each part of the image appear, an image with appropriate saturation can be reproduced and fixing can be facilitated.

[BRIEF DESCRIPTION OF THE DRAWINGS] FIG. 1 is a sectional view showing an example of the configuration of a multicolor image forming apparatus suitable for carrying out the present invention, and FIG. 2 is a toner superimposition diagram obtained by a conventional multicolor image forming method. FIG. 3 is a microscopic cross-sectional view of the torch-overlapping portion obtained by the method of the present invention, and FIG. 4 is a schematic diagram of the light-receiving part of the color image sensor of the apparatus shown in FIG. , FIG. 5 is a schematic diagram of the light emitting part of the eraser of the device shown in FIG. 1, FIG. 6 is an explanatory diagram of one pixel in the present invention, and FIG. 7 is an explanation explaining one embodiment of the method of the present invention. It is a diagram. 1...Photoconductor, 4...Eraser 9...Color image sensor 10-13...Developer for each color 100...Pixel 101...Minute parts constituting the pixel Fig. 1 Fig. 2 Figure 3

Claims (1)

[Claims] In a multicolor image forming method in which toner images of multiple colors formed on a photoconductor each time multiple exposures are superimposed and transferred to the same transfer paper, and the color of the image is reproduced by the superimposition ratio of each color toner, an appropriate size is used. A pixel is divided into a plurality of minute parts, and the toner of each color constituting a certain color is appropriately distributed to the divided minute parts so that one pixel as a whole has a predetermined superimposition ratio constituting that color. When forming a latent image corresponding to each color image, on/off binary erasing is performed on each of the fine portions, and the toner images obtained by development are superimposed and transferred, so that the toner is partially superimposed within the pixel. A multicolor image forming method characterized by: