JPH03264359A - Device for inspecting printed matter - Google Patents

Abstract

PURPOSE:To make it possible to detect defective printings without fail even if positions thereof move by calculating an accumulated value in accordance with a check width decided by a doctor stroke information of a printing machine. CONSTITUTION:A data processing circuit for checking is divided into two sections. A first checking section comprises a reference value memory 12, an allowable value memory 13, a difference circuit 14, and a comparison circuit 15, wherein checking is performed by comparing an image information and a reference image information of a pattern at every picture element with respect to overall patterns of a printed matter. A second checking section comprises an auxiliary CPU 17 wherein checking is performed by performing an accumulative operation of a picture element positioned in a low concentration area obtainable by a predetermined sampling, i.e., in the same place with respect to the cross direction of a paper, with an image information of several picture elements adjacent thereto, and then, comparing it with a predetermined allowable value. According to a printed matter check device 10, a check width is decided based on a doctor stroke information of a printing machine. The accumulated value, which is calculated based on the check width by comparing an inputted image information and the reference image information, is compared with a reference accumulated value stored previously, so that minor print defects in size or concentration difference can be checked precisely without fail regardless of deviations of defective printings caused by the doctor stroke.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a printed matter inspection device that compares the pattern of a printed matter being printed inline with reference information to detect printing defects.

[Prior Art] Conventionally, inspection of printed matter for printing defects (stains, doctor streaks, ink splatters, dust, etc.) has mainly been carried out by sampling inspection performed by an operator. However, such sampling inspections are offline, and the quality of all printed matter cannot be inspected, and printing defects may be overlooked. Therefore, in order to objectively evaluate the quality of all printed matter being printed, we use strobe lighting that is synchronized with the printing speed and use mirrors that rotate synchronously at high speed. Attempts are being made to evaluate.

However, even in this method, quality inspection is dependent on the operator. This was because it was thought that the problem was that the patterns of printed matter were different one by one, and that inspection items for printed matter had subtle differences that had to rely on human vision.

In addition, attempts have been made to print color marks along with patterns on printed matter and automate the inspection of the color marks, thereby allowing printed matter to be inspected on behalf of the user. However, with this method, if a printing defect occurs in the pattern area, it will be overlooked, and it could not be said that it fully functions as an inspection device.

Therefore, in recent years, various printed matter inspection apparatuses such as those described below have been proposed.

(1) JP-A-59-109832 and JP-A-59-
Japanese Patent No. 128418 describes a printed matter inspection device that uses a line sensor to inspect printed matter in an offset printing machine. Since this printed matter inspection device can automatically inspect the entire pattern of printed matter in-line, it does not have the above-mentioned drawbacks and can be expected to have excellent effects as an inspection device. This inspection device roughly stores the pattern information of printed matter in a standard state as reference information in the reference memory, and during inspection, it uses methods such as differences to compare the pattern information sequentially taken in by the line sensor with the reference information. ), and the inspection device determines that a printing defect exists when these differences exceed an allowable range.

(2) Japanese Patent Application Laid-Open No. 146133/1984 also includes a method of adding the density difference of each pixel of the sensor to several surrounding pixels and comparing it with reference information so that printing defects with small density differences can also be detected. A printed matter quality defect inspection device that is also used is described. This inspection device adds density differences between a plurality of pixels adjacent in the sensor scanning direction (paper width direction).

(3) Japanese Patent Publication No. 1-47823 discloses that in order to detect doctor streaks, etc., the densities of one sheet of pixels arranged vertically along the conveyance direction of the paper are summed, compared with reference information, and printed matter is An inspection device for determining the quality of a product is described.

[Issue 8 to be solved by the invention] However, even if the inspection device in (1) above is capable of detecting printing defects that occur in offset printing, it is difficult to detect printing defects that occur in, for example, gravure printing, especially size For defects with a small density or defects with a small density difference, it is difficult for the sensor of the inspection device to detect the density difference from the reference information, and it is often impossible for such an inspection device to detect printing defects.

Specifically speaking about gravure printing, thin line-like printing defects called doctor streaks or two-twos (hereinafter simply referred to as two-twos) occur.

The situation is shown in FIG. 3, where doctor streaks 31 and two-twos 32 are generated on the paper 3 after printing in the form of parallel lines along the paper conveyance direction. The doctor streaks 31 occur continuously on many sheets, but the number of two-twos 32 may occur on only one or two sheets if there are few. Doctor streaks and two-two do not necessarily occur with the same four colors of ink in color printing, but they also occur with various colors and densities when several colors of ink are mixed. Therefore, it is sometimes difficult for the sensor of an inspection device to detect the density difference of these printing defects even on a blank sheet of paper, and it is often even more difficult to detect them in a pattern.

When a high-density doctor streak 31 and a low-density two-two 32 occur on the paper 3 in FIG.
Line sensor も(
An example of the signal output when photographing is shown in Fig. 4. Fig. 4 shows the case (a) when the printed matter is normal on line Ll and the case (b) when doctor streaks 41 and two-two 42, which are printing defects, occur.
, and when the printed matter is normal on line L2 (c)
This is the case (d) in which printing defects such as doctor streaks 41' and 2-2'42' occur.

As mentioned above, although doctor streaks can be detected to some extent in density on a blank sheet of paper, almost no difference in density can be detected in a picture.

Two-two, which originally has no density difference, is completely undetectable in the image.

The above inspection device (2) can detect printing defects with small density differences in offset printing because there is a certain level of flooring not only in the conveyance direction of the paper but also in the width direction. However, since the printing defects in gravure printing as described above are in the form of very thin lines, they are still difficult to detect.

In the inspection device (3) above, printing defects such as doctor streaks in gravure printing are moved in position in the width direction of the paper due to the doctor stroke mechanism of the printing machine.

As a result, the inspection pixels are shifted, making it difficult to detect the printing defect.

In addition, when inspecting a single image by dividing it into fine pixels, the number of calculations becomes enormous, and the inspection may not be able to keep up with the printing speed of the gravure printing machine. Since the sum of the densities is calculated regardless of whether they are high or low, if a stain-like printing defect (when the density becomes high) and density fluctuations in the pattern area (when the density becomes low) occur at the same time, the defect is determined. Detection becomes difficult.

In this way, there are differences in the characteristics of printing defects (shape, density difference, number of sheets, etc.) due to differences in the principles and structures of printing machines.
Highly accurate testing cannot be expected by using the same testing method alone.

[Means for Solving the Problems] The present invention has been made to solve the above problems, and includes a manual means for inputting printed matter as image information, and a first means for storing image information serving as a reference for the printed matter. storage means, inspection width determination means for determining an inspection width based on doctor stroke information of the printing press, and comparison of image information input from the input means with reference image information stored in the first storage means. A cumulative calculation means for calculating a value as a cumulative value based on the test width, a second storage means for storing a reference cumulative value, and a cumulative value obtained by the cumulative calculation means and the second storage means. This is a printed matter inspection apparatus characterized by comprising a comparison means for comparing the reference cumulative value stored in the printed matter with a reference cumulative value stored in the printed matter and determining the quality of the printed matter.

Further, the cumulative calculation means is characterized in that the cumulative value is calculated for the sampled low concentration region.

[Operation] According to the print inspection device according to the present invention, the inspection width is determined based on the doctor stroke information of the printing press, and the ratio of input image information and reference image information is compared with a reference cumulative value stored in advance. By doing so, printing defects that are small in size or have a small density difference can be reliably and accurately inspected without being affected by the deviation of printing defects due to doctor strokes.

[Embodiment] Hereinafter, an embodiment of a printed matter inspection apparatus according to the present invention will be described with reference to the drawings.

FIG. 1 is a brochure diagram showing the circuit configuration thereof, and FIG. 2 is a schematic diagram showing an example of how the printed matter inspection device is installed in a rotogravure rotary press.

As shown in FIG. 2, in the gravure rotary press, a strip-shaped paper 3 is supplied to a printing section 5 from a roll-shaped paper roll 2 attached to a paper feeding section.

In this embodiment, the printing unit 5 is composed of two units that print in one color on the front and back sides, but when performing normal color printing, it prints eight units in four colors (black, indigo, red, and yellow) on the front and back sides. Consists of units. Paper 3 after printing is folded II
6, and before being folded or cut, the line sensor 7 reads the pattern as image information. A rotary encoder 8 is attached to the guide roller on which the line sensor 7 is located, and the rotary encoder 8 outputs a clock pulse in synchronization with the rotation of the guide roller as the paper 2 is conveyed. The clock pulses of the rotary encoder 8 are manually input to the inspection device 10, and the image information of the pattern when the line sensor 7 scans one line on the paper 3 in the direction perpendicular to the conveying direction is input to the inspection device W10 according to the clock pulses. be done. In this way, the image of the printed matter becomes image information for one line each time the paper 3 is conveyed at a fixed pitch, and eventually the entire image is input to the inspection device 10. In addition, line sensors and rotary encoders are installed for the front 7a, 8a and the back 7b, 8b.
The patterns on both the front and back sides are input to the inspection device 10.

Next, the circuit configuration of the inspection device 10 will be explained with reference to FIG.

The circuits that perform data processing for inspection include a reference value memo IJ 12, which performs inspection by comparing image information of the image and reference image copying information for each pixel on the entire image of the printed matter, a tolerance memory 13, a difference circuit 14, and a comparison circuit. 15, the low-density area obtained by predetermined sampling, that is, the pixels located at the same position in the width direction of the paper, and the pixel information of several adjacent pixels are calculated. , and a second inspection part of the sub-CPU 17 that performs inspection by comparing with a preset tolerance value.

The clock pulse CK from the rotary encoder 8 is also supplied to the sampling controller 16.

The sampling controller 16 outputs a line synchronization signal LS to the line sensor 7 and a sample signal SS to other circuits in synchronization with the clock pulse CK. Line sensor 7-1
Line scanning is performed for each line synchronization signal LS, and thereby the scanning position is determined along the conveyance direction of the printed material.

Finally, the first inspection part will be explained.

Video signal I for each line output from line sensor 7
s is supplied to a reference value memory 12 and a difference circuit 14 as digital video data 10(i+j) via an A/D converter 11. The writing and reading addresses (i, j) of the reference value memory 12 are controlled by the sample signal SS output by the sampling controller 16. The reference value memory 12 stores, as reference information, reference data RD(i, j) for each pixel from the video data 10(i,
). Here, the reference data RD(ij) may be determined from the video data of a pattern of one printed matter or from the results of an average calculation or the like from the video data of a plurality of sheets. Base! 1! After the reference data RD is stored in the value memory 12 and the inspection is started, the reference data RD(i.

J) and video data ID (i, j) are input to the difference circuit 14. The difference circuit 14 determines the magnitude of the difference (absolute value of the difference) for each pixel and outputs it to the comparison circuit 15 as difference data DD(i,j). On the other hand, the tolerance memory 13, which stores information on the inspection tolerance range in advance, stores tolerance data AD of each pixel representing the inspection tolerance according to the sample signal SS.
(i+j) is output to the comparison circuit 15. Here, the method of setting the allowable data AD(IIJ) in the allowable value memory 13 may be a method in which variations in the density of normal printed matter are investigated in advance and a value larger than that value is set.

Comparison circuit I5 calculates difference data DO(i, j) for each pixel.
Compare the size of the allowable data 80 (i, j),
If the difference data DD (+, j) is larger, it is determined that a printing defect has occurred and an error signal E1 is output to the CPU 1B.

Next, the second inspection part will be explained using FIG.

This part is for detecting printing defects (doctor streaks, two-two) peculiar to gravure printing machines. Usually, a doctor mechanism for gravure printing includes a doctor stroke mechanism that swings a doctor blade left and right. Therefore, the printing defect also moves in the width direction to some extent along the conveyance direction of the paper. Therefore, in order to detect the above-mentioned printing defects, it is necessary to determine the inspection unit width in accordance with the fluctuation width of the doctor stroke.

For example, as shown in Figure 7-a, when the width of the inspection pixel of the line sensor is approximately 3.01, and the doctor stroke is set to 25 rotations and the stroke cycle is set to 20 revolutions, the cumulative calculation is performed. If it is performed at several locations the length of three sheets of paper, the amount of movement of the doctor between those three sheets is approximately 7
．． It can be calculated as 51. Therefore, the inspection width can be determined to be 3 pixels. Thereafter, the inspection is performed for each inspection unit width, and the average value, added value, etc. of pixels included within the width is set as inspection data 5ID(n, +++). However, n and m correspond to the width direction and conveyance direction of the paper, respectively. 7th-
As shown in figure b, the inspection data 5ID (n, m) is the adjacent inspection data 5ID (n-1, m), 510 (n+
1. II) to share a predetermined number of pixels. The width and period of the doctor stroke may be determined manually by the printing machine using the signal KS and automatically determined by the inspection device, or may be input from the operation panel (Sl). Reference data RD (i, j) from the reference value memory 12 and video data 10 (i, j) from the A/D converter 11 are manually input to the sub CPU 17 (S2). From this reference data RD (i, j), select a blank part of the paper or a part with low density, that is, a part in the low density area, and select it as an inspection line (S3). By determining the position of the inspection line, the reference for each inspection unit is determined. The value becomes the reference data RD(i, j
) is calculated and stored as reference data SRD (n, m) (S4).Although multiple inspection lines are required for one pattern in order to cope with a small number of defects,
You only need about 5 pieces. Furthermore, if it is not possible to secure an inspection line over the entire width of the paper due to the pattern, only the part that does not cover the pattern may be used as the inspection line, as shown in FIG. In this case, the line must be selected so that all positions in the width direction of the paper can be detected.The position of the inspection line may be input from the operation panel or automatically determined by the inspection device. . Next, video data 10 (i, j
), enter the test data 5ID from this data.
(n, m) is calculated (S6). This inspection data 5ID
(n, s+) and reference data 5liD (n, s) to (1
), the absolute value of the difference is cumulatively calculated the same number of times for each inspection width located at the same position in the width direction of the paper (S7).

SUM, Σ l 510(n, m+1)-SR
D (n, s + I) l - (1) I turtle 0 Compare this calculation result with the preset tolerance value (SS), and if the calculation result exceeds the tolerance value, output error signal E2 to CPU1B. (S9). CPU1
8 notifies that a printing defect has occurred through an alarm or the like by inputting error signals El and E2.

In this way, in this embodiment, in addition to the inspection data processing of the conventional inspection device, the inspection data processing for gravure printing is also used, so that highly accurate inspection is possible even in the gravure printing machine.

The present invention is not limited to the embodiments described above,
For example, although the second inspection section of the inspection device is configured with software, it can also be implemented with a circuit having a similar function.

[Effects of the Invention] As explained above, according to the present invention, the cumulative value is calculated based on the inspection width determined by the doctor stroke information of the printing machine, so the position of the printing defect does not move due to the doctor stroke mechanism. This has the effect that it can be reliably detected.

[Brief Description of the Drawings] Fig. 1 is a block diagram showing the circuit configuration of an embodiment of the present invention;
Figure 2 is a schematic diagram of a gravure printing machine equipped with a printed matter inspection device, Figure 3 is a schematic diagram showing printing defects in gravure printing, and Figure 4 is a line sensor signal for printed matter with and without printing defects. FIG. 5 is a flowchart showing the flow of the second inspection means of this embodiment, FIG. 6 is a model diagram of inspection line selection, and FIG. 7-(a) shows the inspection width setting method. Model diagram, FIG. 7-(b) is a model diagram showing the configuration of the inspection width. 7... Line sensor 8... Rotary encoder 11... A/D converter 12... Reference memory 1
3...Tolerance value memory 14...Differential circuit 15...
・Comparison circuit 16...Sampling controller 17...Sub CPU 1 B...CPU 1st
Figure 3 Figure 4 Figure 6 C(A) Funeral diagram 11n C'q) Figure 7

Claims (2)

[Claims] (1) An input means for inputting printed matter as image information, a first storage means for storing reference image information of the printed matter, and an inspection width determining means for determining an inspection width based on doctor stroke information of the printing press. and cumulative calculation means for calculating a comparison value between the image information input from the input means and the reference image information stored in the first storage means as a cumulative value based on the inspection width; a second storage means for storing cumulative values; and a comparison means for comparing the cumulative value obtained by the cumulative calculation means with a reference cumulative value stored in the second storage means to determine the quality of the printed matter. A printed matter inspection device comprising: (2) The printed matter inspection apparatus according to claim 1, wherein the cumulative calculation means calculates a cumulative value for a sampled low-density region.