JP4007041B2 - Automatic printing register method - Google Patents

Description

[0001]
[Technical field to which the invention belongs]
The present invention relates to a method for calculating a register mark position by an automatic registration control device and performing printing registration.
[0002]
[Prior art]
Recently, there is a great demand for color printing, and multi-color printing is becoming common.
[0003]
On the other hand, as printing presses have increased in speed, it has become difficult for humans to register the relative position of color plates, and automatic register control devices have become indispensable devices. The automatic registration control device is a device that generally reads a register mark printed on a paper surface, calculates a position of the register mark, and corrects a registration error.
[0004]
At least one register mark is printed for each color, and using this, it is determined whether any color is misregistered with respect to the register mark reference color. If there is misregistration, correction is performed. .
[0005]
Here, when correcting the misregistration, the calculation accuracy of the register mark position is important.
On the other hand, in the current printing press, the register mark is not always printed completely. Specifically, the shape may be deformed due to ink not being applied to the image area or ink being applied to the non-image area.
[0006]
In particular, offset printing usually uses ink and water to separate the image area from the non-image area, so if the ink and water balance is not always constant, the shape of the register mark will change over time. Tend.
[0007]
Further, in the current register mark position calculation method, the barycentric position of the area of the read register mark is calculated as the register mark position. That is, the calculation method is based on the premise that the shape of the register mark is uniformly deformed in all directions.
[0008]
However, a rotary printing press is used for high-speed printing, and there is a printing direction. Therefore, the actual change in the shape of the register mark has directionality, and if the center of gravity of the printed register mark is set as the position of the register mark, the accuracy is lowered.
For this reason, in an actual printing site, it is necessary for the printing operator to always sample the printed matter and always compensate for the relative position between the colors, and labor saving is required by further improving the accuracy of the automatic register control device.
[0009]
[Problems to be solved by the invention]
The present invention has been made in view of the above-described problems, and the object of the present invention is to provide a highly accurate register mark position calculation method even in the case of high-speed printing in which register marks are not printed completely. Therefore, it is possible to improve the registration accuracy, further reduce paper loss and maintain high quality, and is particularly suitable for automatic control, thus providing a printing registration method that can contribute to the improvement of production efficiency. That is.
[0010]
[Means for Solving the Problems]
The first invention of the present invention for solving the above problems is to recognize register marks provided on the printing paper, the recognized print automatic registration of the register mark position Ru used for automatic register correction control of the print a method, register marks to be printed on substantially center of the printing paper K, C, M, to different positions cross register mark of the reference color selected from among colors of the cross register mark and the color group of Y A printing step, and a position calculating step for detecting two straight lines of the cross register mark for each cross register mark using a Hough transform and calculating an intersection of the two straight lines as each register mark position; Calculating the amount of misregistration that calculates the amount of misregistration of the register marks of the other three colors with the position of the two cross register marks as the reference color as the reference Step and includes a position correcting step of performing other three colors positional correction based on the positional deviation amount, a print automatic registration method characterized by.
[0011]
According to a second aspect of the present invention, the register mark printing step includes a step of printing K, C, M, and Y color cross register marks at four corners of the printing paper, and after the position correcting step. Measuring the cross register marks at the four corners of the printing paper, and calculating the misregistration amount of the position of the other register mark with respect to the position of the cross register mark of the reference color. Is the method.
[0012]
According to a third aspect of the present invention, in the printing automatic registration method according to claim 1, the printing is high-speed rotary printing.
[0013]
Here, the Hough transform is one of the graphic detection methods, and when a graphic existing in the image space can be expressed by a parameter, all the points plotted in the image space are converted into the parameter space. , The input value of the parameter of the figure to be detected becomes a maximum value, and the figure of the parameter is detected. (See U.S. Pat. No. 3,069,654)
[0014]
As shown in FIG. 3, it is assumed that only points (x1, y1) and (x2, y2) on a straight line ρt = xcos θt + ysin θt (constants: ρt, θt, parameters: x, y) lacking in the xy plane exist. To do. At this time, the equation of the straight line including the point (x1, y1) is ρ = x1 cos θ + y1 sin θ (constants: x1, y1, parameters: ρ, θ), and the combination of (ρ, θ) is one on the ρθ plane. Draw a curve. This parameter conversion is called Hough conversion. The curve ρ = x1 cos θ + y1 sin θ and the curve ρ = x2 cos θ + y2 sin θ intersect at (ρt, θt) on the ρθ plane.
When n points from (x1, y1) to (xi, yi) to (xn, yn) exist in the image on the xy plane, all the n points are converted to the ρθ plane, and the curve ρ = xicosθ + yisinθ is obtained. Every time n curves are drawn and the intersected curves are counted, the intersected coordinates (ρ, θ) are counted. When the Hough transform of all n points is completed, the coordinate (ρt, θt) with the largest count is obtained. As a result, ρt = x cos θt + ysin θt is a straight line composed of the most points in the image. From the principle of the Hough transform, the obtained straight line is surely extracted even if the line is missing or there is an extra point.
[0015]
That is, a part of a figure (a line in the present invention) is missing (in the present invention, ink does not reach the image area), or a part of a figure (a line in the present invention) has noise. This is a detection method that is robust to the measurement environment because the figure is accurately detected even when the ink is deposited on the non-image area in the present invention.
The Hough transform is not limited to a straight line that intersects the register marks because it can detect a general graphic.
[0016]
DETAILED DESCRIPTION OF THE INVENTION
(Preparation for experiment)
First, as shown in FIG. 1, a cross register mark 10 in which straight lines are combined at the center of the printing paper 1 by offset printing using a dampening solution of four colors K, C, M, and Y, as shown in FIG. The rhombus register mark 20 is printed and provided at a different position for each color. At the same time, cross-shaped register marks 30 in which straight lines are combined at the four corners of the printing paper 1 are printed at the same positions for the respective colors. Next, after registering, the center register mark position used in the embodiment and the comparative example is read by the automatic registering apparatus, and the printed matter is mass-produced by each automatic registering method.
[0017]
<Example>
First, Hough transform was used for each mark of the cross register mark 10 in the center of the printing paper 1 to detect two straight lines of each color. The camera of an actual automatic registration device is captured as a binary image in which the cross shape of the register mark is missing, there are print stains, and optical and electrical noise is included. All the captured points were subjected to Hough transform, a curve was drawn on the ρθ plane, and the intersected coordinates (ρ, θ) were counted each time the curves intersected.
[0018]
Since two straight lines have been extracted, two coordinates with large counts appear on the ρθ plane, and the captured image contains optical and electrical noise. The coordinates closer to the coordinates having a larger count number have a larger count number. As a result, two peaks having different count numbers are locally formed on the ρθ plane, and obtaining the coordinates of the two extreme points results in obtaining two straight lines.
[0019]
The coordinate with the maximum count number (for example, (ρt, θt)) on the ρθ plane is the apex of one mountain. All the points in the vicinity of ρt = x cos θt + ysin θt are deleted from the captured xy image, the remaining points are subjected to the Hough transform again, and the coordinates with the maximum count number (for example, (ρs, θs)) are obtained on the ρθ plane, xcosθt + ysinθt and ρs = xcosθs + ysinθs are obtained as straight line equations.
Next, an intersection point was obtained from the two straight line equations, and this intersection point became the position of the register mark.
[0020]
Finally, it is determined how to apply control from the position of each register mark. In FIG. 1, there is a color having two register marks (here, M), and since the position of the two register marks of this color is used as a reference, the color registration is not adjusted. For the other three color register marks, calculate how much the register marks are shifted from the two positions of the reference color, and adjust the position and phase of the roller to adjust the top, bottom, left, and right sides of the reference color. Automatic registration correction control that adds position correction such as was performed.
[0021]
After printing is finished, the cross register marks 30 at the four corners of the sample printed on the printing paper are measured, and how far the register mark center position of the other color is away from the register mark center position of the reference color (here, M). Was measured.
As a result, 99.97% of the register marks of all three colors other than the reference colors at the four corners are within the range of 50 μm from the center position of the register marks of the reference color.
[0022]
<Comparative example>
The center of gravity of the rhombus 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 finished, the cross register marks 30 at the four corners of the sample printed on the printing paper 1 are measured, and how far the register mark center position of the other color is away from the register mark center position of the reference color (here, M). Measured.
As a result, 99.6% of the register marks of all three colors other than the reference color at the four corners are within the range of 50 μm from the center position of the register mark of the reference color.
[0023]
【The invention's effect】
By using the register mark position calculation method of the present invention, it is possible to maintain highly accurate registration compared to the conventional automatic registration that calculates the center of gravity, further reducing the occurrence of waste paper due to misregistration, and further improving production efficiency Can be made.
[0024]
[Brief description of the drawings]
FIG. 1 is an explanatory diagram of printing paper provided with various register marks.
FIG. 2 is an explanatory diagram enlarging the four-corner register mark of FIG. 1;
FIG. 3 is an explanatory diagram of a straight line calculation method using Hough transform.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Printing paper 10 ... Cross register mark 20 ... Rhombus register mark 30 ... Cross register mark

Claims (3)

Recognize the register mark formed on the printing paper, a printing automatic registration method Ru with register mark position said recognized automatically register correction control of the print,
A register mark printing step for printing K, C, M, and Y color cross register marks and a reference color cross register mark selected from the color group at different positions in the approximate center of the printing paper;
For each cross register mark, a Hough transform is used to detect two straight lines of the cross register mark and calculate an intersection of the two straight lines as each register mark position;
A misregistration amount calculating step of calculating misregistration amounts of the other three color register marks with reference to the positions of the two cross register marks that are the reference colors;
And a position correction step of correcting the positions of the other three colors based on the amount of positional deviation. The register mark printing step includes a step of printing K, C, M, and Y color cross register marks at four corners of the printing paper,
After the position correcting step, the method includes a step of measuring the cross register marks at the four corners of the printing paper and calculating a shift amount of the position of the other register mark with respect to the position of the cross register mark of the reference color. The automatic printing registration method according to claim 1 .   The automatic printing registration method according to claim 1, wherein the printing is high-speed rotary printing.

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