JP2824334B2 - Automatic color tone controller for printed materials - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an automatic control device applied to an ink supply device of a printing machine for stabilizing the color tone of a printed matter.

[0002]

2. Description of the Related Art In multicolor printing, the viscosity of ink, printing pressure, the content of dampening water in ink, and the like change due to changes in ambient temperature and humidity and changes in temperature due to heat generated by rollers of a printing machine. As a result, the color tone of the printed matter changes over time. This change in color tone increases, and sample printing (for example,
If the difference between the color and the proof print becomes extremely large, it is regarded as poor color tone. In order to prevent such poor color tone, the operator must constantly monitor the entire surface of the printed material during printing and make adjustments to maintain the color tone.

In order to improve such a situation, there have been proposed some devices for automatically controlling the color tone. Proposed devices can be broadly classified into the following two types. one,
A print monitoring strip is used. In this method, a special strip for printing monitoring containing solid patches for each ink color is printed at the same time in the margin of the printed material, the color density and color coordinates of each patch on this strip are measured, and the values are set to the target values. The ink supply amounts of the respective colors are adjusted so as to match. For example, JP-A-63-141745, JP-A-63-145035, JP-A-63-1
The inventions described in Japanese Patent Application Publication No. 66541, Japanese Patent Application Laid-Open No. 01-53845 and the like correspond to this.

Another one does not use the print monitoring strip described above. In this method, the color density and color coordinates of the printed product are directly measured, and the ink supply amounts of the respective colors are adjusted so that the values match the target values. For example, the invention described in Japanese Patent Application Laid-Open No. 01-218835 corresponds to this.

[0005]

The use of the print monitoring strip has the following three problems and has not been widely used. (1) In a printing company, printing is often performed using the entire surface of the paper for effective use of the paper, and there is often no margin for inserting a strip. (2) Putting strips in the margins themselves requires extra work time in the plate making process, which is the pre-printing process.
It is not preferable in terms of efficiency. (3) Although the area of the strip must be small for the reason of the above item (1), it involves the inaccuracy of estimating the color tone of a wide print surface from the small strip to be measured.

On the other hand, those which do not use the print monitoring strip do not have the above three problems, but have a serious problem that it is almost impossible to separate the color change by the black ink. In printing, all colors are reproduced with four inks of black, indigo, red, and yellow, so on the design, black by indigo, red, and yellow inks and black by black ink alone are mixed. ing. In such a case, simple measurement of the three color densities of red, green and blue according to the conventional method shows that indigo,
Changes in three color density detection values when the ink supply amount changes in the black part due to the appropriate overprinting of red and yellow inks, and the color when the ink supply amount changes in the black part with black ink A change in the detected density value occurs in the same manner.

[0007] For this reason, it is almost impossible to distinguish which of the causes caused the color change of an arbitrary black portion. Therefore, it is impossible to find four ink correction amounts. Generally speaking, the O.D. The three color densities (ΔB, ΔG, ΔR) of blue, green, and red with the K sheet are four ink film thickness changes (ΔK, ΔC,
ΔM, ΔY). The following is a mathematical expression.

[0008]

(Equation 1)

[0009]

(Equation 2)

[0010]

(Equation 3)

[0011] However, F _B ~F _R is a function relating the ink film thickness change each blue, green, the color change in the concentration of yellow.
In the control, contrary to the above equation, ΔB, ΔG, ΔR
It is necessary to find K, ΔC, ΔM, and ΔY, but obviously, the number of equations (3) is smaller than that of the unknowns (4) and cannot be solved. For this reason, there is no practical use of this type.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a color tone control device which solves the above-mentioned problems which occur when a print monitoring strip is not used.

[0013]

Means for Solving the Problems (1) In each of the divided sections in which the printing surface is virtually separated into n parts (n ≧ 2) in the printing direction, the divided section is set for each of blue, green, and red. A means for detecting the average color density during printing during printing. (2) The difference (3 × n) between the color density obtained for each of the divided sections and the reference color density and a plurality (usually black, indigo, red, (Yellow four colors)
Based on the image streak rate (the number of used ink colors × n) in each of the above-mentioned divided sections for each ink color, the color density of each color necessary to match the color density of the printed matter obtained every moment with the stored reference color density is obtained. Means is provided for calculating the correction amount of the ink supply film thickness by a multiple regression analysis technique.

[0014]

The color density information obtained by adopting item (1) in (Means for Solving the Problems) is the conventional color density information.
From 3 to 3n. As a result, the number of ink film thickness changes (4n) in which the number (3n) of
More). That is, it is as follows.

[0015]

(Equation 4)

However, the suffixes 1 to n indicate that they are related to the color density of each divided section. This time, conversely, the number of mathematical expressions is excessive with respect to the unknowns, but the method of multiple regression analysis described in the above (Means for solving the problem) (2) (for example, Nikka Giren Publishing Co., Ltd.) The amount of change in the ink film thickness, which is an unknown variable, that is, the amount of correction of the ink film thickness (the change in the sign of the change is inverted) is accurately calculated by an arithmetic device applying the above-mentioned method. Can be estimated.

The arithmetic unit for determining the change in the ink film thickness also inputs the image ratio in each divided section for each ink color. The functions F _{B1 to} F _Rn shown in Equation 4 are thereby obtained.
Is quantitatively determined.

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a sheet-fed printing press according to the present invention will be described with reference to FIGS. FIG. 1 is a side view showing a configuration of a color tone control device according to the present invention, FIG. 2 is a block diagram of FIG. 1, and FIG. 3 shows a state as viewed from above a printing paper. The color detection is performed on the printing paper 16 on the impression cylinder 14 of the final color (see FIG. 1).

Light from a light source 3 such as a xenon lamp irradiates the surface (printing surface) of a printing paper 16 through an optical fiber 11. Reference numeral 12 denotes a plate cylinder, 13 denotes a blanket cylinder, 15 denotes a paper discharge cylinder, and 17 denotes a power supply. The optical fiber 11 also has a role of guiding light to a limited narrow space inside the printing press, and creating a band-like light source that matches the detection area of the color line camera 1. As shown in FIG. 1, an optical fiber 11 is provided so as to irradiate at an angle of about 45 degrees with respect to the normal direction from the printing surface. On the other hand, color line camera 1
Is installed to receive the reflected light in the normal direction from the printing surface. As shown in FIG. 3, the detection area has a full width in the width direction and 1 mm to several mm in the running direction. That is, the detection area of one line is (print paper width) × (1 mm to several mm). Inside the color line camera 1, there are three light receiving sections provided with blue, green, and red filters, each corresponding to the magnitude of the blue, green, and red color densities of a minute area of 1 to several millimeters of printing paper. The generated electric signal is generated for each line. Electric signals corresponding to the magnitudes of the blue, green, and red densities of each minute area (about 1,000) of each line are sequentially sent to the color density detection device 2, where they are allocated to each ink key area, and each ink key area is assigned. Are stored at predetermined positions in three "current value memories" of blue, green, and red. As the printing paper 16 travels, the detection area of the color line camera 1 sequentially changes. As a result, the entire surface of the printing paper 16 is divided into base-like detection units, and the “current value memory” of three colors of the corresponding ink keys is obtained. (19, 20, 21 in FIG. 4). A synchronizer is required so that the signal at a certain position of the printing paper is always stored in the same memory location even when a disturbance such as a change in the machine speed occurs. The synchronization signal can be generated, for example, from a rotary encoder (R / E) (see FIG. 3) attached to the final color impression cylinder shaft. As R / E, two types of pulse signals of 1 pulse / rotation and 1,500 pulses / rotation are prepared, and they are respectively used as an input start signal (matching to the front end of the paper) and a subdivision synchronization signal. A signal is captured at a pitch of about 1 mm on the paper by a general method using such a synchronization signal, and the capturing position does not shift even if the machine speed changes.

The above "current value memory" 19, 20, 21
The average color density calculation device 4 calculates the average color density in each divided section where the printing surface is virtually divided into n (n ≧ 2) in the printing direction (printing paper running direction) for each ink key. calculate. The calculation of the average color density is performed for each of the blue, green, and red color densities. A description will be given by taking as an example the calculation from the “current value memory” (blue) of one ink key area shown in FIG. In this case, n = 4, and since the number of memories of the color density detecting device (Bi) in the minute area of each divided section is M, the average color density (B
₁ , B ₂ , B ₃ , B ₄ ) are as follows.

[0021]

(Equation 5)

However, the number i of Bi is 1, 1 from the front end of the paper.
2, 3, ... Number for the remaining two color densities
It is calculated similarly in accordance with equation (5). Thus, the average color density
The average color density signal calculated by the arithmetic unit 4 is controlled by the
Good printed matter (OK sheet) that should be the standard for
Switch 5 shown in FIG. 2 is connected to the A side
Then, it is stored in the reference color density storage device 6. Meanwhile, calculation
Printed matter whose average color density signal is controlled
Switch 5 is connected to the B side.
Is sent to the color density difference calculating device 7. This switch 5
Is installed on a light booth, for example.
Replacement is entrusted. When switch 5 is connected to A side
The switch 05 is automatically connected to the 0A side and the color density difference
Separated from the arithmetic unit 7, adjustment by opening and closing the ink key is performed
Not. On the other hand, when the switch 5 is connected to the B side,
H05 is automatically connected to the 0B side and the stored base
The signal of the quasi-color density is sent to the color density difference calculation device 7. control
Looking at the movement during the period, switches 5, 05 are each
B, 0B and are controlled.
Average color density (B₁~ R _n)signal
And the reference color density (0B₁~ 0R_n)
The signals are respectively sent to the color density difference calculation device 7. Color density
The difference calculator 7 calculates the difference between the above two color densities.
You.

[0023]

(Equation 6)

The signal of the calculated color density difference is sent to the calculating device 8 for the ink supply film thickness correction amount. Next, the content of the calculation of the ink supply film thickness correction amount by the calculation device 8 will be described. Before that, the relationship between the ink supply film thickness and the color density will be described. As an equation for quantifying this relationship, the following Yu
There is a le-Nielsen equation. (For example, it is described in "Theory of Color Reproduction" co-translated by Tsutomu Mawatari and Tatsuro Kuniji, published by the Printing Society of Japan.

[0025]

(Equation 7)

[0026] However, D is the concentration of network prints, a is dot percent (0 ≦ a ≦ 1.0), D s is the solid portion (a = 1.0 parts) ink density, and m is a screen line It is a coefficient that takes into account the amount of light diffusion in the paper, depending on the number and the type of paper. Here, solid area ink density D _s is within the range of the ink supply thickness T on the paper is not significantly changed is expressed by the following equation.

[0027]

(Equation 8)

Here, p and q are constants depending on the types of ink and paper. Substituting equation 8 into equation 7 gives

[0029]

(Equation 9)

The equation (9) is non-linear, but in the color tone control, it is sufficient to pay attention only to a small variation from a certain target color density, so that the linearization can be performed using Taylor expansion. Given that the density and the ink supply film thickness at a certain target color density point are D ₀ and T _0, and considering minute variations from the target point, ΔD and ΔT, respectively,

[0031]

(Equation 10)

## EQU1 ## By substituting this into Equation 9 and performing Taylor expansion on the right-hand side and omitting the term of (ΔT) ² or more as a minute amount, the following relational expression for minute variations ΔD and ΔT is obtained.

[0033]

[Equation 11]

Equation (11) basically holds for a halftone dot portion having an area ratio of a. However, instead of the halftone dot area ratio a, the average image ratios g _{B1 to} g _Yn of the above-described divided sections are used. Also, instead of the color density difference ΔD, the average color density differences ΔB ₁ -Δ
By considering R _n , it can be considered as a relational expression between the color density difference and the ink supply film thickness difference in each divided section. As an example, if it shows about the blue density of the division section 1,

[0035]

(Equation 12)

P_BK, P_BC, P_BM, P_BY: Each ink,
Formula 8 for blue density of indigo, red and yellow inks
Constant q_BK, Q_BC, Q_BM, Q_BY： Each ink, indigo, red, yellow in
The constant g relating to the blue density of the key, expressed by Equation 8 g_K1, G_C1, G_M1, G_Y1： Each ink, indigo, red, yellow
Average image ratio in divided section 1 (0 ≦ g ≦ 1.0) T_0BK,T_0BC,T_0BM,T_0BY:Ink, Indigo, Red, Yellow Inn
Target ink supply film thickness m for blue density_BK, M_BC, M_BM, M_BY： Each ink, indigo, red, yellow in
Constants ΔK, ΔC, ΔM, ΔY represented by Equation 7 regarding the blue density of the key: black, indigo, red, yellow in
The difference between the target ink supply film thickness and the film thickness difference ΔK, ΔC, ΔM, ΔY on the right side of this equation is
Each F_BK1,F_BC1,F _BM1,F_BY1given that,

[0037]

(Equation 13)

## EQU4 ## The above is the discussion on the blue density in the divided section 1. If the three color densities in the n divided sections are extended, the following equation is obtained.

[0039]

[Equation 14]

Since the correction amount of the ink film thickness to be obtained is obtained by inverting the sign of the ink supply film thickness difference ΔK, ΔC, ΔM, ΔY, it is necessary to obtain the ink supply film thickness difference.
In the present invention, as described above, the value is obtained by using a multiple regression analysis method in Equation (14). Specifically, each of the equations (14) is converted to 3n

[0041]

(Equation 15)

By interpreting the data as a group of data, using F _{DK to} F _DY as four explanatory variables, ΔD as a target variable, and performing multiple regression analysis on 3n data groups of Equation 14, the ink obtained is obtained. The supply film thickness differences ΔK, ΔC, ΔM, and ΔY are calculated as four partial regression coefficients. The ink supply film thickness correction amount calculating device 8 performs this multiple regression analysis and performs the ink supply film thickness difference Δ
K, ΔC, ΔM, ΔY are calculated, their signs are reversed, and the signals are sent to the ink supply amount (ink key opening / closing) adjusting device 10. Of course, before performing the multiple regression analysis, the explanatory variables F _{DK to} F _DY are calculated based on Expression 12. For this purpose, the constants (p, q, T ₀ , m) shown in Equation 12 suitable for the printing conditions are input in advance. This input data does not need to be changed unless the ink, paper, and screen ruling change significantly. The average image ratio (g) of each color in each divided section is input from the average image ratio measurement device 9. (See FIG. 2) This data is updated each time the print pattern changes. The ink supply amount (ink key opening / closing) adjusting device 10 is similar to, for example, a PID adjuster, and the ink supply film thickness correction amount (−ΔK, −Δ) sent thereto.
C, −ΔM, −ΔY) as a deviation signal, and calculates an ink key opening / closing signal that makes the deviation from the reference color density zero.
Thus, the ink key is opened and closed, and the color tone of the printing paper surface can always be matched with the reference value with sufficient accuracy for practical use.

In the above embodiment, the number of colors used for printing is four colors of black, indigo, red, and yellow, but the color tone can be similarly controlled regardless of the number of colors. However, since multiple regression analysis is used, the following condition must be satisfied when the number of divided sections is n. 3n> number of colors In some cases, the ink correction amount may be simply displayed to the operator without automatically controlling the ink supply amount as in the above-described embodiment. In this case, a display device for the ink correction amount is required instead of the ink supply amount adjusting device 10 of FIG.

[0044]

According to the present invention, there is provided an automatic color tone control apparatus for a printed material in which a print surface is virtually divided into a plurality of sections in a printing direction, and each of the divided sections is divided into blue, green, red and the like. A means for detecting the average color density during printing during printing, a means for storing a color density detected for each of the divided sections as a reference color density for a printed matter serving as a control reference, and storing the color density during the control period. A means for comparing the color density detected by the detection means with the reference color density stored in the storage means, and calculating a difference between the color density and the color density calculated by the calculation for each of the divided sections; The reference color density stored from time to time based on the average image ratio in each of the divided sections for each of the plurality of ink colors used for printing, which is obtained by measurement in advance. Required to match Means for calculating the correction amount of the ink supply film thickness of each color by the method of multiple regression analysis, and receiving the correction amount of the ink supply film thickness as a deviation signal, and adjusting the ink supply amount so as to make this deviation zero. Having the means has the following effects.

The color tone of the entire printing surface can be adjusted with sufficient accuracy for practical use.
It is always possible to automatically match that of the standard.
As a result, the printing operator is freed from the work of frequently checking the color tone. Further, according to the present invention, it is not necessary to put the print monitoring strip in the margin of the printed matter, and thus extra working time and printing paper are not required.

[Brief description of the drawings]

FIG. 1 is a side view showing a configuration of an embodiment of the present invention.

FIG. 2 is a block diagram of FIG. 1;

FIG. 3 is a diagram of the color density detection unit as viewed from above the printing paper.

FIG. 4 is a diagram of a “limited value memory” of color density.

FIG. 5 is an explanatory diagram of printing direction division of a “limited value memory”.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Color line camera 2 Color density detector 3 Light source 11 Optical fiber 16 Printing paper

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) B41F 31/02 B41F 33/14 G01J 3/50

Claims (1)

(57) [Claims] An average color density is detected during printing for each of blue, green, and red in each divided section in which a printing surface is virtually divided into a plurality of sections in a printing direction. Means, for a printed matter serving as a reference for control, the color density detected for each of the divided sections as a reference color density,
Means for storing; means for comparing the color density detected by the detecting means with the reference color density stored by the storing means every moment during the control period, and calculating the difference; Based on the difference between the color densities obtained by calculation for each and the average image ratio in each of the above-described divided sections for each of the plurality of ink colors used for printing obtained by the pre-measurement, the printed matter obtained every moment is obtained. Means for calculating the correction amount of the ink supply film thickness of each color necessary to match the color density to the stored reference color density by a method of multiple regression analysis, and receiving the correction amount of the ink supply film thickness as a deviation signal, Means for adjusting the amount of ink supplied so as to make this deviation zero.