JPH0371263B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method and apparatus for inspecting patterns on printed matter.

As shown in Fig. 1, the conventional printed matter pattern inspection device extracts image information by scanning a printed matter 1 in the width direction with a line sensor camera 2, and on the other hand, uses the output of a rotary encoder 4 attached to a cylinder 3 of a conveyance system. By synchronizing the scanning of the camera 2, the sample pattern 5 (FIG. 2) is divided into a large number of small pixels arranged in a matrix.

The density of each of these pixels is sequentially compared with the corresponding small pixels of the sample pattern 6 (FIG. 2), which has been similarly divided and recorded in the memory, to detect the presence or absence of a defect.

In this kind of pattern inspection, if there is a positional shift in the width direction of the conveyance system as shown in Figure 3, the gradation obtained from the specimen will change for the 3 marked pixels out of the gradation 7 obtained from the sample. When compared with the corresponding three pixels of No. 8, it is erroneously determined that there is a defect even if there is no defect in the sample pattern.

One way to prevent this is to set a large tolerance value for the tone difference between the sample and the sample.

However, this results in a decrease in defect detection accuracy and is not necessarily a good countermeasure.

A method free from such problems involves correcting the positional deviation of the sample pattern with respect to the sample pattern, and various methods have been devised.

The first method is as shown in Japanese Patent Application No. 56-146355 filed by the applicant of the present invention, which detects the position of a pattern on a printed matter in the width direction, and detects the position change when writing sample pattern data into a reference value memory. When the data of the sample pattern and the data of the sample pattern are written in the detected value memory are different by a predetermined value or more, the sample pattern data at that time is written in the reference value memory.

However, this method requires a device for detecting positional changes in the width direction of the printed material and for correcting positional deviations according to the positional change information.
This results in problems of increased hardware complexity and higher costs.

Part 2 is shown in Special Publication No. 55-45948, etc.
This method compares a sample pixel with several pixels in the vicinity of the corresponding sample pixel.

However, this method has a problem in that it inevitably reduces inspection accuracy.

The present invention has been made in view of the above-mentioned points, and it is an object of the present invention to provide a method and device for inspecting patterns of printed matter, which can inspect patterns with high precision even if there is a positional shift in the conveyance type of printed matter, and which can be constructed at low cost. With the goal.

In order to achieve this objective, the present invention provides pattern gradation data in the width direction of the sample (hereinafter referred to as sample row data).
is compared with the corresponding widthwise pattern gradation data of the specimen (hereinafter referred to as specimen row data) to detect defects. The present invention provides a method and apparatus for performing pattern inspection using a sample row and a sample row that are most similar in phase to the sample row.

Embodiments of the present invention will be described below with reference to FIGS. 4 to 11.

4a and 4b show sample row data and sample row data; FIG. 4a shows the basic relationship between sample row data and sample row data handled in the method of the present invention; shows the relationship between sample line data and sample line data in special parts such as picture edges of printed matter.

First, according to figure a, a plurality of sample row data 10 to 16 are referred to for one sample row data 9.
These sample row data 10 to 16 are obtained by shifting the basic sample row data 13 one pixel at a time to the left and right by the expected positional shift.

Then, the sample row data 9 is changed to the sample row data 10 to
The density can be compared with the data 12 whose phase is closest to the sample row data 9 among the data 16, and defect detection is thereby performed.

Thereby, even if the sample row data 9 is misaligned in the width direction of the printed material, the data can be compared in terms of content, so defects can be detected with high accuracy.

Next, according to FIG. 2B, the sample row data 18 having the closest phase to the sample row data 17 is compared, and the gradation difference tolerance value is increased. This makes it possible to carry out defect inspection suitable for cases where the gradation difference is extremely large, such as at the edge of a picture. In other words, since the sample row data 18 is closest in phase to the sample row data 17, the phase difference between the two is 1/2.
This is the pixel width. Therefore, the tone difference between the sample and the specimen at the pixel corresponding to the edge when a positional shift of 1/2 pixel width occurs may be taken as the tolerance value for that pixel. Various methods can be used to set this permissible value for each pixel (Japanese Patent Application No. 1983-
(see No. 179599), or pixels corresponding to edges may be masked to exclude them from the determination target.

FIG. 5 shows the configuration of an apparatus for carrying out the method of the present invention, which is constructed based on the idea shown in FIG. In this configuration, the image on the printed matter 1 is scanned by the camera 2 and image information is extracted. At this time, the rotation amount of the conveyance system cylinder 3 is taken out by the rotary encoder 4 and given to the synchronization circuit 21. The synchronization circuit 21 provides its output to the camera 2, the A/D conversion circuit 22, and the address circuit 24, and performs scanning synchronization of the camera 2, A/D conversion synchronization of image information taken out by the camera 2, and sample pixel data. Address assignment for the memory 25 and pixel control data memory 26 is performed.

Therefore, even when writing sample row data to the sample pixel data memory 25, reading data from the sample pixel data memory 25 and pixel control data memory 26 for judgment operation in the judgment circuit 23 when detecting sample row data is required. However, accurate data correspondence can be obtained. Pixel control data memory 26
Data for giving an allowable value to each pixel is set in advance, and the determination circuit 23 takes into consideration the allowable value based on the pixel control data when comparing the sample row data and the sample row data.

FIG. 6 shows a more specific configuration of the determination circuit 23 in the device shown in FIG.
A shift circuit using latches L ₁ to _{L 3} for shifting SD and pixel control data MD one pixel at a time, and a shift circuit using latches L ₄ to _{L 6} for shifting sample row data TD one pixel at a time, respectively. It is formed by combining the determination element groups of determination elements JE ₁ to _{JE 3} and JE ₄ to _{JE 7} .

Each of the shift circuits performs a shift operation by applying the clock CLK used for scanning of the camera 2 (FIG. 1) to a latch circuit, and the clock CLK may be applied to each pixel.

For example, sample row data TD ₁ has latches L ₄ , L ₅ , L ₆
is shifted sequentially in synchronization with the camera scan.
TD2, TD3, TD4. Similarly, sample row data SD1 and pixel control data MD1 are stored in latches L ₁ ,
L ₂ , L ₃ are shifted sequentially in synchronization with camera scanning, and MD ₂ , MD ₃ , MD ₄ and SD ₂ , SD ₃ , SD ₄
becomes.

And sample row data TD1 is the judgment element
It is given to JE ₁ , JE ₂ , JE ₃ , and JE ₄ and compared with sample row data and pixel control data. That is, the judgment element JE ₄ makes a judgment based on the sample row data TD1 ₁ , the sample row data SD ₁ , and the pixel control data MD ₁ , and the judgment element VE ₁ makes a judgment based on the sample row data TD1, SD ₁ , and _pixel control data MD1.
Judgment by MD ₂ , also in JE ₂ TD ₁ and SD ₃ ,
Judgment is based on MD ₃ , and JE ₃ uses TD ₁ , SD ₄ , and MD ₄ . Thereby, a determination is made when the sample row data and pixel control data are delayed with respect to the sample row data.

On the other hand, when the sample row data is delayed relative to the sample row data and the pixel control data, on the other hand, determination elements JE ₅ , JE ₆ , and JE ₇ make the determination.

As a result, each of the determination elements JE ₁ to _{JE 7} compares and determines the sample row data 9 and the sample row data 10 to 16 in FIG. 4a. Each output of judgment elements JE ₁ to JE ₇ is connected to the comprehensive judgment circuit TJU.
given to. The overall judgment circuit TJU selects the minimum value among the outputs of each element, and makes a pass/fail judgment based on whether the value exceeds a threshold value.

FIG. 7 shows a more specific configuration of the determination element JE used in the determination circuit of FIG.
It consists of an absolute value detection circuit DA, a comparator CP, and a counter CT. and,
The absolute value detection circuit DA outputs the absolute value |TD−SD| of the difference between the sample row data TD and the sample row data SD. The pixel control data MD, which is the tolerance value for |TD-SD| and |TD-SD|, are compared in magnitude by a comparator CP, and the output thereof is given to a counter CT, so that |TD-SD|>
The number of pixels called MD is counted.

FIG. 8 shows a more specific configuration of the absolute value circuit of the difference in the determination element of FIG.
It consists of two adders AD ₁ and AD ₂ , an exclusive OR circuit EX, and an inverter INV, and by receiving TD as an input, -
Forms an output called SD. Since this circuit is well known, detailed explanation will be omitted.

FIG _. 9 shows in more detail the configuration of the comprehensive judgment circuit TJU in the judgment circuit _{of FIG .} The lowest value of each output J ₁ to J ₇ is detected.

Figure 10 shows the low value detection circuit MIN in Figure 9.
This shows a more specific configuration of the selector
It consists of SE and comparator CP.
This circuit detects a low value among the two inputs A and B. Therefore, the comprehensive judgment circuit in Figure 9 detects a low value by combining two of each of the seven inputs, and detects this low value. The results are compared with each other to detect a low value, and by performing another low value detection, the lowest value among the seven inputs is detected.

With the above configuration, even if the pattern on the printed matter is misaligned to some extent, it is possible to accurately determine whether the pattern is good or bad, enabling high-speed inspection and reducing the cost of the apparatus. Further, since the sample row data and the sample row data are compared, it is possible to perform an inspection with much higher precision than when comparing the patterns as a whole.

Figure 11 shows a configuration that can also deal with misalignment of printed matter in the flow direction.
Judgment circuits JC ₁ to _{JC 7} similar to the judgment circuit shown in the figure,
Shift registers SR ₁ to _{SR 6} and comprehensive judgment circuit
It is composed of TJU. shift register
SR is the number of bits equal to the number of sensor array bits of camera 2 (Fig. 1), and the sample row data SD,
The pixel control data MD and sample row data TD are delayed _one pixel at a time like the latch in _the circuit _{of FIG . 7} is given to the overall judgment circuit TJU to detect the minimum value.

As described above, the present invention prepares a predetermined number of rows of sample row data centered on the row for image information extracted from a sample print for each pixel row by row, and the sample row data is one of the sample row data. Since the quality of the printed pattern is judged based on whether the difference in density is within the allowable value or not, the pattern can be inspected with accuracy that does not pose a practical problem even if there is positional shift due to the transportation of the printed material. . Further, according to the present invention, positional deviation is allowed in the transport system, so the cost of the transport system can be reduced.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the configuration of an image information detection section of a pattern inspection device that is the object of the present invention, FIG. Fig. 3 is an explanatory characteristic diagram when a positional shift of a pattern occurs due to the print conveyance system, etc., and Fig. 4 a and b are characteristics showing the basic inspection method of the method of the present invention and the pattern edge inspection method. figure,
FIG. 5 is a block diagram showing the configuration of an apparatus for carrying out the method of the present invention, FIG. 6 is a block diagram showing a more specific configuration of the determination circuit in the apparatus of FIG. 5, and FIG. FIG. 8 is a block diagram showing a more specific configuration of the determination element in the determination circuit of FIG. 7, FIG. 6 is a block diagram showing a more specific configuration of the comprehensive judgment circuit in the judgment circuit shown in FIG.
Figure 0 is a block diagram showing a more specific configuration of the low value detection circuit in the comprehensive judgment circuit of Figure 9;
The figure is a block diagram showing a configuration that can cope with misalignment of printed matter in the flow direction. 1...Printed matter, 2...Camera, 3...Cylinder, 4...
Rotary encoder, 5, 7, 9, 17...sample picture (sample row) data, 6, 8, 10, 18...sample picture (sample row) data. TD…Sample row data,
SD...Sample row data, MD...Pixel control data, JC
...judgment circuit, JE...judgment element, L...latch,
SR...Shift register, TJU...Comprehensive judgment circuit.

Claims (1)

[Scope of Claims] 1. A pattern inspection method for determining the quality of a pattern by comparing pattern data extracted from a sample print with pattern data previously extracted from the sample print and recorded in a memory, comprising: At least one of the sample line data detected in the sample line data and the sample line data recorded in the memory is shifted relative to the other one pixel at a time within the range of the positional shift of the printed matter that can actually occur, and a plurality of data are generated. and detecting a level difference by comparing the sample row data and the sample row data using the plurality of data, and determining whether the minimum value of the level difference is within a predetermined tolerance range. A method for inspecting patterns of printed matter, characterized in that a pattern of printed matter is determined by reading the image. 2. The method according to claim 1, wherein a special level tolerance is set for the edges of the printed matter. 3. A device that generates a synchronization signal according to the conveyance speed of the printed material; a camera that scans the pattern of the printed material based on the synchronized signal to extract image information; and this camera writes the image information extracted from the sample printed material. A sample row data memory, and a sample row data from the camera and data from the sample row data memory, and by shifting the position of at least one of these two data by one pixel to cope with the expected positional shift of the printed matter. 1. A pattern inspection device for printed matter, comprising: a judgment circuit that forms a plurality of data with deviations and compares the sample row data with the sample row data using the plurality of data.