JPS5845059A - Detection of color shift in offset printing - Google Patents

Abstract

PURPOSE:To detect color shift of each plate by such an arrangement wherein original plates in which symbols for all colors are arranged are pasted to a printing plate of each color so that they perpendicularly cross with each other and distances between lines on the original plates are optically detected and memorized and the detected values of a printed sheet are compared and calculated. CONSTITUTION:Original plates 5 in which lines a-d, each representing the symbol of one color, being arranged with an equal space provided are pasted to the upper lower, left and right margins of printing plates 1-4, each representing a separated color, so that they perpendicularly cross with each other. Next, the plate 1 is set at a specified position of a detection base 6, a detection camera 7 is made to scan so that it crosses lines a-d, the distance between lines is converted into digital value and memorized as a reference value. Next, printing is performed by plates 1-4 and the distance between 4 lines at the margins of a sheet are detected by the same manner and they are compared and calculated by the previously memorized reference values and the results of the detection are converted into numerical values and they are displayed on a CRT as error data. The positional registration of plates 1-4 can be easily and accurately accomplished by adjusting the position of plates 2-4.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for detecting color misregistration in offset printing, which accurately detects color misregistration in multicolor offset printing, thereby ensuring correct and precise positional adjustment of plates for each color. .

Generally, when performing multicolor printing using offset printing, a plate is prepared in advance for each color, and the blank paper to be printed is passed through each plate one after another, and one color is superimposed one after another. I am getting a printed copy.

However, it is extremely troublesome and difficult to adjust the position of the plates at the beginning of printing so that the colors of the multicolored plates do not overlap or shift.

For this reason, at present, 10 marks are placed for each color in the top, bottom, left, and right margins of each plate, and color deviations in the vertical and horizontal directions can be visually detected from the 10 marks of different colors on printed matter printed with each plate. The system detected the color shift, adjusted the position of the plate of that color by the amount corresponding to the color shift, and repeated the same procedure until all the 10 marks of each color matched with each other.

However, it is difficult to accurately adjust the color shift of thin lines of 0.1 mm or less by visual inspection alone, and there is currently no equipment that can accurately detect this. Because the color shift was adjusted beforehand, long experience and skill were required.

The present invention has been made in view of such conventional problems, and involves attaching in advance an original plate with symbols such as lines or figures for each color arranged on a plurality of plates separated into each color of the manuscript. The data obtained by optically measuring the distance between lines on the original plate in advance and the data obtained by optically measuring the distance between lines on the printed matter that has passed through each plate are calculated, and a numerical value based on the error data is calculated. C
It is an object of the present invention to provide a method for detecting color misregistration in offset printing, which can be displayed on an RT screen or on a digital display and used as accurate position adjustment data for each plate.

An embodiment of the present invention will be specifically described below with reference to the drawings.

Fang 1 is a plate for four-color offset printing (
11[21[31F41], and each of these editions (11~[
4) is a version of the manuscript separated into each color.

Each of these plates (1) to (4) has a sheet-like original plate (5) as shown in Figure 2, which has lines α, h, c, and d for each color arranged at equal intervals as symbols. One sheet is pasted horizontally and vertically on the top, bottom, left and right margins of plates (1) to (4).

Next, the plates (1) and C plate +21 (any one of 31141 may be used) are set at the set position of the detection table (6) as shown in Figure 3, and the detection camera ( 7
) is moved to take a scanning photograph across each line αjA a ' a d, and the distance between each line a, b, c, d is detected as reference data, which is converted into a digital signal and sent to the detection table (6). It is stored in a storage circuit such as a non-volatile RAM provided therein.

It is recorded on a magnetic tape section (8) or displayed on a CRT (9). (II is an operation key that commands the operation of this memory, etc.

Next, each of the plates (11 to (4)) is set in a printing machine, and paper or the like is passed through these plates (1) to (4) to produce a printed matter that is approximately the same as the original in which each color is superimposed. Then, a total of four lines α, b, c, and d, one for each plate, are imprinted on the margins of this printed matter.

Then, the printed matter was set on the detection stand +61 shown in Figure 3 in the same way as for the plate (11).

The previously described detection camera (7) scans the images a, b, c, and d, detects the distance between these lines, and compares and calculates the detected data with reference data stored in the previous storage circuit. , the calculation output is digitized and CR is used as error data.
Display it on T or store it in memory. Note that if one of the four colors is determined as a reference color, differences in other colors can be automatically displayed, recorded, or printed based on a memory circuit and an arithmetic circuit.

In this way, by adjusting the position of each plate (2) to (4) based on the numerical value of the error data calculated and tabulated/red, the alignment of each plate (1) to (4) can be easily and accurately. I can do it.

Figure 4 shows the signal system circuit as a block diagram.
(111 is a memory circuit that stores the line distance on the original plate (5) as reference data, and a21 is a memory circuit that stores detection data of the line distance imprinted on the printed material. Both memory circuits (111 (12 + The data is processed by the arithmetic circuit (131
, the data corresponding to the error in the distance between both lines is compared and calculated, and the calculated output is recorded in another memory circuit (141), or the printing machine (151 is activated or the display ( The signal system circuit can be configured to handle either digital signals or analog signals, and the line-to-line distance detection means can also be used for detection cameras such as television cameras. In addition, various optical means may be used, such as a combination of a light emitting element and a light receiving element, or one that projects and reflects a laser beam.

As explained above, according to the present invention, at least one original plate having, for example, lines for each color arranged at equal intervals as a symbol is pasted on each of a plurality of plates in a direction orthogonal to each other, and The distance between each line on the original plate is detected while being scanned by an optical means, and this is temporarily stored, and the copy of each line on the printed material printed by the plate is scanned by the optical means to determine the distance between the lines. Detect.

This detected data and the stored data are compared and calculated, and the error in the distance between drawing lines is displayed as a numerical value on the display means, thereby quickly and accurately detecting the color shift in the image of each plate. Therefore, use this as position adjustment data for each version.

It is possible to accurately position each plate.

[Brief explanation of the drawing]

Figure 1 is a front view of each plate in the present invention, Figure 2 is a front view of the original plate with rigid positioning lines to be pasted on each plate, and Figure 3 is a front view of the original plate.
The figure is a schematic perspective view of the detection table, and Figure 4 is a block circuit diagram of a signal system for color shift detection. +I l F21 (31+41... version, (5)...
・Original plate with detailed drawings, (6)...Detection stand, (7)...
Optical means (camera). (8)...Magnetic tape section, (9)...CR1', (
II...operation key, all...storage means, 031.
...Arithmetic means, (151...Display means. Fig. 1 Fig. 3 Fig. 4

Claims (1)

[Claims] On a plurality of plates on which the original is distributed into each color, a small number of original plates (one at a time) on which symbols for each color have been arranged in advance are pasted in directions orthogonal to each other, and the distance between each line on the original plate is scanned by optical means. and storing the detected data in a storage means, and scanning a copy of each of the symbols on the printed matter printed by the plurality of plates with the optical means to detect the distance between the lines; Color shift in offset printing characterized in that the detection output and the memory output of the storage means are compared and calculated by the calculation means, and the error output for each color of both signals is numerically displayed by the display means. Detection method.