JPS63109470A - Method for setting exposure in color electrophotographic copying machine - Google Patents

Abstract

PURPOSE:To prevent color mixture by specifying exposure to be applied to a photosensitive body in accordance with the potential of a dark part of a photosensitive body, the density of necessary colors and the density of unnecessary colors. CONSTITUTION:The quantity E0 of exposure irradiated to the photosensitive body is set based on a shown equality I at the time of color separation and exposure. In the equality I, S is the sensitivity of the photosensitive body, VDDP is the potential of the dark part of the photosensitive body, DW is the density of a necessary color, and DU is the density of an unnecessary color. Consequently, the potential contrast between the potential of an electrostatic latent image based on unnecessary colors and the potential of an electrostatic latent image based on unnecessary colors can be set to its maximum value, the color mixture of respective colors can be suppressed and the latitude of respective colors in development can be expanded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an electrophotographic copying machine, and more particularly to an exposure amount setting method for a color electrophotographic copying machine.

[Prior art] ゛When obtaining color images using powder using electrophotographic methods, etc.
The desired color is obtained by subtractive color mixing by overlapping four toner colors, usually cyan, magenta, and yellow, and in some cases black.

In such a method, image formation using toners of three primary colors is performed by overlappingly recording each color toner, and when reproducing secondary colors for the three primary colors, such as green, red, and blue, the primary A secondary color is obtained by laminating two types of color toners.

For example, when reproducing a recorded image, the colors are separated using a blue filter and exposed to form an electrostatic latent image corresponding to the yellow component. This electrostatic latent image is developed with yellow toner and the yellow toner image is transferred to transfer paper.Next, the electrostatic latent image obtained by color separation using a red filter is developed with cyan toner and the yellow toner image is transferred to a transfer paper. Obtain a toner image.

This cyan toner image is superimposed on the yellow toner image described above to obtain a secondary color toner image, and this is fixed to obtain a recorded image.

Color toner images produced by such electrophotography are usually formed on white paper, and are recognized as colors by irradiation with white light. For example, the reason why yellow and cyan toner layers appear to overlap on white paper in a recorded image is as follows. The white light passes through the yellow and cyan toner layers, is reflected by the white paper, and passes through the two toner layers again to reach the eye. When white light passes through two toner layers, 40
The light around 0~500r+g+ is absorbed, the cyan toner layer absorbs the light around 600~700n*, and the remaining 5
Only light around 00 to 600n■ reaches the eyes and appears green.

[Problem that the invention seeks to solve]

In a color electrophotographic copying machine that obtains a color image using the method described above, when copying a color original, especially a printed original, yellow and magenta on the original are printed.

Since the color separation efficiency of yellow and blue (the combination of cyan and magenta is obtained by combining them) is as low as 16 to 18%, the electrostatic contrast is as small as about 170 V or less for selenium (Se) based sensitive materials. For this reason, for example, when separating blue color, yellow is developed using the static images corresponding to magenta and blue on the original as latent images, and magenta is reproduced as red, and blue (cyan + magenta) is reproduced as black. There was a problem. A similar problem occurs when green color is separated; in this case, magenta is developed on the electrostatic latent image corresponding to green (cyan + yellow) on the document, and green is expressed as black.

The present invention was devised to solve the above-mentioned problems, and by setting the amount of exposure to the photoreceptor according to the dark potential of the photoreceptor, the necessary color density, and the unnecessary color density, the difference between each color can be improved. The purpose is to prevent color mixing.

[Means and actions for solving the problem] The exposure amount setting method of a color electrophotographic copying machine separates the light from the original using red, green, and blue filters, exposes the photoreceptor, and then processes the copying process for each color. In a color electrophotographic copying machine that performs multicolor copying by repeating the above-mentioned color separation and exposure, the exposure 11. 1 -7 voop 3 10-"+10-" However, S: Photoreceptor sensitivity VDDP: Dark area potential of photoreceptor Ri: Necessary color density U: Unnecessary color density.

In the present invention, the potential contrast between the potential of the electrostatic latent image of the desired color and the potential of the electrostatic latent image of the unnecessary color on the document is determined by determining the amount of exposure irradiated to the photoreceptor based on the above formula. Maximum value. Therefore, by developing these electrostatic latent images, a color copy image with high contrast, that is, with little color mixture, can be obtained.

〔Example〕

DETAILED DESCRIPTION OF THE INVENTION Hereinafter, features of the present invention will be specifically described based on examples with reference to the drawings.

FIG. 2 shows a color electrophotographic copying machine to which the present invention is applied. Around a drum-shaped photoreceptor 1, a charger 2, an exposure light source 3 such as an exposure lamp, a color filter assembly 4, a yellow developer 5Y, A magenta developer 5M, a cyan developer 5C, a transfer drum 6, a cleaner 7, etc. are arranged. Further, a fixing device 8 is provided close to the transfer drum 6 to fix the transferred image.

Selenium (Se), cadmium sulfide (CdS), and the like are used as the photoreceptor 1, and here, a photoreceptor 1 using selenium will be described as an example.

The photoreceptor 1 is charged by a charger 2 and then exposed by an exposure light source 3 to reach a yellow developing device 5Y.

Color electrophotographic copying machines separate documents into three colors.
Color filter assembly 4 between exposure light source 3 and photoreceptor 1
is provided with red, green and blue filters, which can be switched. For example, an electrostatic latent image formed by exposure to light through a blue filter is developed with yellow toner, and an electrostatic latent image formed by exposure to light through green and red filters is similar. The latent image is magenta.

Developed with cyan toner.

Although the exposure amount and the potential of a latent image will be described here with respect to exposure with light that has passed through a blue filter, the same applies to exposure with light that has passed through green and red filters.

In connection with the exposure light source 3, for example an exposure lamp, a variable resistor is provided to control the current flowing into the exposure lamp, and an exposure ff as shown in FIG. 3 is attached to the variable resistor.
By rotating the i-adjustment dial 9, the exposure amount can be adjusted. Therefore, the potential v1 in the yellow developing device 5Y of the latent image formed by exposure with the light that has passed through the blue filter is changed by turning the exposure adjustment dial 9.

Now, a blank sheet of paper is placed as a document on the document support table (not shown) of the color electrophotographic copying machine shown in FIG. 2, and a probe for measuring surface potential is attached in place of the yellow developer 5Y. here,
Turn the exposure amount adjustment dial 9 shown in FIG.
By reading the numerical values on the scale provided on the exposure adjustment dial 9 and the measured values by the surface electrometer, the exposure as shown in FIG. 1 is obtained! The relationship between the scale of the l adjustment dial 9 and the dark area surface potential VDDP of the photoreceptor in the yellow developing device 5Y is obtained. For the convenience of the following explanation, the intercept of the straight line in FIG. 1 with the Y-axis is assumed to be VvD, and the slope of the straight line, that is, the sensitivity of the photoreceptor, is assumed to be S.

Next, the blue separation density of the solid yellow portion and solid blue portion of the printed document can be measured using a printed color sample using a densitometer equipped with a commercially available color separation filter. Let the density of the yellow solid portion, which is the necessary color, measured here be DW, and the density of the blue solid portion, which is the unnecessary color, be Dll.

Using the Y-ring intercept JVDDP, the slope S of the straight line, the yellow solid area density GW, and the blue solid area density Dll obtained as above, the photoreceptor irradiation exposure amount (relative value) Eo is determined as 510-I
Set the position of the exposure 1 adjustment dial 9 so that the value determined by '''+1O-1l'' is obtained.

By setting the exposure amount based on this formula (11),
The potential contrast (V) between the potential V of the electrostatic latent image of the required color (yellow in this case) of the original and the potential vu of the electrostatic latent image of the unnecessary color (blue in this case). -0 expression +1 where Vu is set to maximum value
The reason why the maximum contrast can be obtained by the exposure 11Eo determined by ) will be explained below.

First, the potential V of the required color. and the potential Vt+ of the unnecessary color, Vw = (-JVDDP-5EoxlO-")"V
Since LI −(?VDDP−5EoxlO−”)t, 9−vu= +V[1DP−2(SEoXlo−”) JVDDP
+(SEoXlo-”)”)-(VDDP-2(S
E6X10-Du)? VDDP+ (SE, xlO-
u)”)=-2SEA ?VDDP (10-”-1
0-Du)+ (SEA)"(10-""-10-1l
u'li...(2) In equation (2), DW>DO, so 10-ow-t IQ-111't< Q
It is.

Therefore, V@-V becomes an upwardly convex quadratic function with respect to Eo. Therefore, E gives the maximum value of equation (2).

is obtained from the conditions for setting the differential function of equation (2) to 0, as shown below.

d(Vw Vu) = −2S (10−”−10−”) x (, rvoop 5Eo(10→”+10−■
))=O S 10-"+10-" That is, the formula Tl+ is obtained. And this formula (11
The maximum contrast can be obtained by setting the exposure amount Eo based on . Also, the contrast V at this time
@-VLl becomes IQ-DM+IQ-@11.

In this way, the square root yvo of the dark potential VDDP of the photoreceptor
By setting the exposure lEo for the photoreceptor according to the required color density DW and unnecessary color density DU, color mixing between the respective colors can be prevented, and the latitude of each color in development can be widened.

Furthermore, a good color image without color mixture can be obtained regardless of the influence of external disturbances.

Next, a specific example for controlling the exposure amount will be described.

FIG. 4 shows a first embodiment of the exposure amount control n circuit.

When the exposure light source 3 is one light, it is normally necessary to readjust the exposure adjustment dial 9 shown in FIG. 3 to a predetermined setting value every three copying cycles for red, green, and blue. be. In the embodiment shown in FIG. 4, exposure amount adjustment variable resistors 10R, IOC, and 10B are provided for each color, respectively.

Each variable resistor 10R, 10G is controlled by a changeover switch 11 driven by a cycle count signal indicating each cycle.

10B are sequentially switched. Therefore, the exposure cycle is detected every time, and the current flowing into the exposure light source 3 is switched according to the exposure cycle.

Therefore, it is possible to automatically switch the set exposure amount in each copying cycle.

Further, when there are two or more exposure light sources, by providing a plurality of exposure mm adjusting means, it becomes possible to automatically switch to the set exposure amount for each copying cycle. However, in the case of two lights, it is necessary to use the same means as in the first embodiment shown in FIG. 4 for the exposure light source used in two of the three copy cycles. be.

FIG. 5 shows a second embodiment of the exposure amount control circuit, which is applied when there are three exposure light sources.

In the second embodiment, each exposure light source 3R, 3G, 3B
Exposure lU4 adjustable variable resistor 10R, IOC, I, respectively
OB is connected, and the variable resistors 10R, IOC, and 10B are sequentially switched by a changeover switch 11 driven by a cycle count signal, as in the first embodiment.

(Effects of the Invention) As described above, in the present invention, the exposure amount is set according to the dark area potential of the photoreceptor, the necessary color density, and the unnecessary color density based on the equation (11). This formula sets the potential contrast of the electrostatic latent image of the necessary color and unnecessary color of the document formed on the photoreceptor during each color separation and exposure to the maximum value, so the electrostatic latent image formed based on this condition is When developed, a color copy image with high contrast, that is, with little color mixture, can be obtained.

[Brief explanation of the drawing]

Figure 1 shows the photoreceptor surface potential and exposure Il! A graph showing the relationship with the scale of the adjustment dial, FIG. 2 is a schematic sectional view of a color electrophotographic copying machine to which the present invention is applied, FIG. 3 is a front view of the exposure adjustment dial, and FIG. 4 is a diagram showing the relationship between the exposure light source and FIG. 5 is a block diagram of the exposure amount switching control circuit when there is one exposure light source, and FIG. 5 is a block diagram of the exposure amount switching control circuit when there are three exposure light sources. l: Photoconductor 2: Charger 3.3R, 3G, 38: Exposure light source 4: Color filter assembly 5Y, 5M, 5C
:Developer 6:Transfer drum 7:Cleaner 8:Fixer 9;Exposure! Adjust dial 10R, IOC, IOB: Variable resistor patent applicant
Fuji Xerox Co., Ltd. agent Masu Tegori (and 2 others) Figure 1 Exposure adjustment dial scale m2 Figure opening 6

Claims (1)

[Claims] 1. A color electrophotographic copying machine that performs multicolor copying by color-separating original light using red, green, and blue filters to expose a photoreceptor and repeating the copying process for each color,
Exposure amount E applied to the photoreceptor during color separation and exposure
_O to E_O=1/S(√VDDP)/(10^-^D^W+
10^-^D^U) However, the exposure amount setting method for a color electrophotographic copying machine is characterized in that S: photoconductor sensitivity VDDP: photoconductor dark potential DW: required color density DU: unnecessary color density. .