JP2003300309A - Method for automatically registering print - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for registering a print which can improve a registering accuracy by a method for calculating an accurate register mark position even in the high speed printing case in which a register mark is not printed in a complete shape, which can maintain further reduction in a spoilage and a high quality and which can particularly suitable for an automatic control and hence can contribute to an improvement in a production efficiency. <P>SOLUTION: A method for automatically registering the print comprises the steps of detecting straight lines of two colors of central cross-shaped register marks, having the cross-shaped register marks of the colors at the center and the cross-shaped register marks at four corners of a printing sheet by using a Hough transformation; and automatically register correction controlling the crossing points of the two lines as the color register mark positions. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of calculating a register mark position by an automatic register control device and performing printing registration.

[0002]

2. Description of the Related Art Recently, there has been a great demand for color printing, and multicolor printing has become common.

On the other hand, as the speed of printing presses has increased, it has become difficult for humans to match the register, which is the relative positioning of color plates, and the automatic register control device has become an indispensable device. . An automatic register control device is a device that generally reads a register mark printed on a paper surface, calculates the position of the register mark, and corrects the register shift.

This register mark has at least 1 for each color.
It is printed, and using this, it is judged whether any color is misregistered with respect to the color of the register mark reference,
If misregistration has occurred, correct it.

In correcting the misregistration, the accuracy of calculating the register mark position is important. On the other hand, in the current printing press, the register mark is not always printed in perfect form. Specifically, the shape may be deformed due to the ink not adhering to the image area or the ink adhering to the non-image area.

Particularly, in offset printing, the ink and water are usually used to separate the image area and the non-image area. Therefore, if the balance of ink and water is not always constant, the shape of the register mark will change with time. It tends to change.

Further, the current register mark position calculating method calculates the barycentric position of the area of the read register mark as the register mark position. That is,
This is a calculation method assuming that the shape of the register mark is uniformly deformed in all directions.

However, a rotary printing machine is used for high-speed printing, and there is a printing direction. Therefore, the actual change in the shape of the register mark is directional, and if the center of gravity of the printed register mark is taken as the position of the register mark, the accuracy will drop. Therefore, in the actual printing site, the print operator constantly samples the printed matter,
Since it is necessary to constantly compensate for the relative position between colors, there is a demand for labor saving by further improving the accuracy of the automatic register control device.

[0009]

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and an object of the present invention is to achieve high printing even in the case of high-speed printing in which register marks are not printed in perfect form. By using an accurate register mark position calculation method, it is possible to improve register accuracy.
It is an object of the present invention to provide a printing registration method capable of further reducing waste paper and maintaining high quality, and particularly suitable for automatic control, and thus contributing to improvement of production efficiency.

[0010]

According to a first aspect of the present invention for solving the above problems, a register mark provided on a printing sheet is recognized by using Hough transform, and the recognized register mark position is printed. It is an automatic printing registration method characterized by being used for automatic registration correction control of.

According to a second aspect of the present invention, the register mark of the printing paper is provided with a cross-shaped register mark of each color at the center and cross-shaped register marks of each color at the four corners. This is an automatic print registration method characterized by detecting two straight lines of each color by using Hough transform, and performing automatic register correction control of printing by using an intersection point of these two straight lines as a register mark position of each color.

A third aspect of the present invention is the automatic print registration method according to claim 1, wherein the printing is high-speed rotary printing.

Here, the Hough transform is one of figure detection methods. When a figure existing in the image space can be expressed by parameters, all the points plotted in the image space are converted into the parameter space. If you convert it to and input it, the input value of the parameter of the figure you want to detect becomes the maximum value,
The figure of that parameter is detected. (US Patent No. 30
(See No. 69654)

As shown in FIG. 3, a straight line ρt lacking in the xy plane
= Xcos θt + y sin θt (constant: ρt, θt, parameter: x, y) on the point (x1, y1), (x2, y
Suppose only 2) is present. At this time, the point (x
1, y1) is a straight line equation, ρ = x1 cos θ + y1
sin θ (constant: x1, y1, parameter: ρ, θ), and the combination of (ρ, θ) draws one curve on the ρθ plane. This parameter conversion is called Hough conversion. Then, the curve ρ = x1 cos θ + y1 sin θ and the curve ρ =
x2cosθ + y2sinθ is (ρt, θ
intersect at t). In the image on the xy plane, (x1, y1) ~
When there are n points from (xi, yi) to (xn, yn), all n points are converted to the ρθ plane, and the curve ρ = x
If n icos θ + yisin θ are drawn and the intersecting coordinates (ρ, θ) are counted every time the curves intersect, n
When the Hough transformation of all the points is completed, the coordinate (ρt, θt) with the largest count is raised, and ρt = xcosθ
t + ysin θt is a straight line composed of the most points in the image. From the principle of this Hough transform, the obtained straight line is surely extracted even if the line is missing or there are extra points.

That is, a part of a figure (a line in the present invention) is missing (ink does not reach the image area in the present invention) or a part of a figure (a line in the present invention). There is noise (in the present invention, ink adheres to non-image areas)
Even if it is done, the figure is accurately detected, so it is a detection method that is robust to the measurement environment. Since this Hough transform can detect a general figure, it is not necessary to limit it to a straight line that intersects the register marks.

[0016]

BEST MODE FOR CARRYING OUT THE INVENTION (Preparation of Experiment) First, as shown in FIG. The cross-shaped register mark 10 formed by combining straight lines and the diamond-shaped register mark 20 are printed and provided at different positions for each color. At the same time, the cross-shaped register mark 30 in which straight lines are combined at the four corners of the printing paper 1 is printed at the same position for each color.
Next, after registering, the central register mark positions used in the examples and comparative examples are read by an automatic registering device, and printed matter is mass-produced by each automatic registering method.

Example First, two straight lines of each color were detected by using the Hough transform for each mark of the cross register mark 10 in the center of the printing paper 1. A camera of an actual automatic registering device captures a binary image in which the cross shape of the register mark is missing, the print is dirty, and optical and electrical noises are included. All the captured points were Hough-transformed, a curve was drawn on the ρθ plane, and the intersecting coordinates (ρ, θ) were counted every time the curves intersected.

Since two straight lines are extracted, two coordinates with large counts appear on the ρθ plane, and since the captured image has optical and electrical noise, the coordinates around the coordinates with large counts are present. As for the coordinates, the closer the coordinates are to the larger count number, the larger the count number is. As a result, there are two peaks with different counts locally on the ρθ plane.
Therefore, two straight lines can be obtained by obtaining the coordinates of the two extreme points.

The coordinate with the maximum count number (eg (ρt, θt)) on the ρθ plane is the apex of one mountain. From the captured xy image, ρt = xcos θt + y sin θt
All the points in the vicinity are deleted, the remaining points are subjected to Hough transform again, and the coordinate with the maximum count number on the ρθ plane (for example,
(Ρs, θs)), and ρt = xcos θt + ysi
nθt, ρs = xcosθs + ysinθs is the equation of the straight line obtained. Next, the intersection point was obtained from the equation of these two straight lines, and this intersection point became the position of the register mark.

Finally, it is determined how to perform control from the position of each register mark. In 10 of FIG. 1, there is a color having two register marks (here, M), and since the positions of the two register marks of this color are used as a reference, the register adjustment of this color is not performed. The other three color register marks are calculated in which direction and how much they are displaced from the two reference color register marks, and by adjusting the position and phase of the roller, the top, bottom, left, right, and twist with respect to the reference color. Automatic registration correction control was performed to add position corrections such as.

After the printing is completed, the cross-shaped register marks 30 at the four corners of the sample printed on the printing paper are measured, and the center position of the register mark of the other color from the center position of the register mark of the reference color (here, M) is measured. It was measured whether they were apart. This result shows that all three color register marks other than the reference colors at the four corners are within the range of 50 μm from the center position of the reference color register mark.
It was 9.97%.

<Comparative Example> The center of gravity of the diamond-shaped register mark 20 provided at the center of the printing paper 1 was calculated, and the center of gravity was set as the position of each color register mark, and automatic register correction control was performed. After the printing is completed, the cross-shaped register marks 30 at the four corners of the sample printed on the printing paper 1 are measured, and the center position of the register mark of the other color is separated from the center position of the register mark of the reference color (here, M). It was measured. This result shows that all three color register marks other than the reference colors at the four corners are within the range of 50 μm from the center position of the reference color register mark.
It was 9.6%.

[0023]

By using the register mark position calculation method of the present invention, highly accurate registration can be maintained as compared with the conventional automatic registration in which the center of gravity is calculated, and the occurrence of waste paper due to misregistration can be further reduced. The production efficiency can be further improved.

[0024]

[Brief description of drawings]

FIG. 1 is an explanatory diagram of a printing sheet provided with various register marks.

FIG. 2 is an enlarged explanatory view of four-corner register marks in FIG.

FIG. 3 is an explanatory diagram of a straight line calculation method using Hough transform.

[Explanation of symbols]

1 ... Printing paper 10 ... Cross register mark 20 ... Diamond register mark 30 ... Cross register mark

Claims (3)

[Claims] 1. An automatic print registration method, wherein a register mark provided on a printing paper is recognized by using Hough transform, and the recognized register mark position is used for automatic register correction control of printing. 2. The register mark of the printing paper is provided with a cross register mark of each color at the center and cross register marks of each color at the four corners, and the cross register mark at the center is two lines for each color by Hough conversion. Is detected and the intersection of the two straight lines is used as the register mark position for each color to perform automatic registration correction control for printing. 3. The automatic print registration method according to claim 1, wherein the printing is high-speed rotary printing.