JPH0339464B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a printed matter inspection device for in-line comparing the state of a printed matter being printed with a standard state in a printing press to detect abnormalities in the printed matter. Conventionally, the mainstream method for inspecting printed matter has been offline and relying on human vision. This stems from the fact that each piece of printed matter has a different pattern, and because inspection items for printed matter have been thought to involve subtle differences that require reliance on human vision. On the other hand, in response to the desire to evaluate printed matter while it is being printed, attempts have been made to use strobe lighting that is synchronized with the printing speed and to use mirrors that rotate synchronously at high speed to judge printed matter that is being printed as a still image. It has been done. but,
These systems could not be called inspection machines in that they relied on human vision for inspection. In addition, attempts have been made to print color patches at the same time as the pattern on the printed matter and inspect the color patches, thereby allowing the inspection of the printed matter to be carried out on behalf of the user. However, with this method, if printing defects (oil dripping, stains, etc.) occur in the pattern area, they will be overlooked, and it cannot be said that the inspection machine is fully functioning. On the other hand, a system has recently been proposed in which printed matter is inspected in-line using a line sensor, as seen in the "Printed Material Inspection Apparatus" disclosed in Japanese Patent Application No. 57-220515. By using this method, the pattern itself of the printed matter can be automatically inspected in-line, so it is free from the various drawbacks found in the above-mentioned inspection methods, and can be expected to have excellent effects as an inspection machine. FIG. 1 shows a schematic diagram of a printed matter inspection apparatus to which the present invention is applied based on the above proposal. In FIG. 1, the printed matter inspection device is attached to a rotary printing press, but there is no problem even if it is a sheet-fed printing press. 1st
In the figure, a strip-shaped printing paper 3 is fed from a roll-shaped paper roll 2 in a printing section 1 in four colors (black, black,
After each print (indigo, red, and yellow) is applied, the paper is transported to a dryer and a folding machine (not shown). In order to inspect the printing condition after four colors have been printed on the front and back sides, the printed matter inspection device extends the pattern information in a direction perpendicular to the printed matter conveying direction while timing the sampling with a rotary encoder 5 attached to the printing section. A line sensor such as a CCD in the detection unit 4 scans one line at a time and inputs it to the processing circuit 6.The processing circuit 6 compares the density level with a reference signal, and based on this result, determines whether the printing condition is normal or not.
Perform work to determine abnormalities. As a result, if it is determined that the printing condition is abnormal, it becomes possible to take measures such as alarms, markings, rejects, etc. However, this method is not without its problems. In other words, in normal color printing, the printed matter to be inspected is overprinted with printing inks of four colors: black, indigo, red, and yellow, but printing problems occur in only one color of ink. Even in such cases, the inspection equipment must have the ability to detect such abnormalities. In order to solve this problem, R (red; wavelength
600-700nm), G (green; wavelength 500-600n)
m), B (blue violet; wavelength 400-500n)
Using the three-color color separation filter (m), the signal light from the printed matter is separated into wavelength bands, and these are input to three CCD cameras, R, G,
Rotate the B filter and input it to one CCD camera and process the R, G, B signals as a time series, or try to achieve a similar effect by blinking the R, G, and B light sources alternately. Methods have been proposed to date. Some of these conventional techniques will be explained in more detail. FIG. 2 shows a typical example of a method for separating signal light from printed matter into wavelength bands. Second
As is clear from the figure, the printing paper 3 being conveyed is irradiated with an illumination light source 12, and the reflected light is split into three parts via a half mirror 7, and an R filter 8, a G filter 9, and a B filter 10 are provided for each. The image information is inputted to the CCD line sensor 11 via a photoelectric converter, and after photoelectric conversion, the image information is transferred to a processing circuit (not shown). However, this method has the drawback that three sets of CCD line sensors are required, which not only makes the entire device large and expensive, but also makes the processing system complicated. FIG. 3 shows an example of a configuration in which R, G, and B filters are rotated to extract R, G, and B signals in time series. The printing paper 3 is illuminated by an illumination light source 12, and the reflected light is passed through a rotating filter 13.
is input to the CCD line sensor 11 via
It is transferred as image information to the photoelectric conversion post-processing circuit. Here, the rotating filter 13 includes three filters: an R filter 8', a G filter 9', and a B filter 10'.
As the rotary filter rotates, the picture information is transmitted to the CCD line sensor 11 in chronological order as shown in FIG. It will be transferred sequentially. However, this method has the problem that it is very difficult to accurately control synchronization of the rotating filter and printing paper, separation of signals, etc. In this way, the reflected light from printed matter is divided into R, G, B
Although a method of separating the colors into three colors and detecting printing failures for each color can achieve high detection accuracy, it requires large-scale equipment, is expensive, and requires a large memory capacity. This includes various major problems at the practical stage, such as the required control system becoming complicated. In view of such prior art, the present invention provides a printed matter inspection device that can be expected to have high detection accuracy in detecting printing failures of multicolor printed matter, and can also be made compact, inexpensive, and simple. The purpose is to The present invention will be explained in detail below based on embodiments of the drawings. FIG. 5 shows a schematic diagram of the apparatus according to the invention.
A multicolored printed matter 3 traveling in the direction of arrow B is illuminated uniformly in the width direction by a light source 12, and the reflected light from this printed matter 3 is passed through an optical filter 17 and then transmitted to one CCD.
The light is received by the line sensor 11 such as
By inputting an electrical signal corresponding to the amount of light received from 1 into a processing circuit 6 and comparing this signal with a reference signal stored in a memory, it is possible to detect a printing failure of a printed matter. The optical filter may be installed between the printed matter and the line sensor or between the light source and the printed matter. Here, looking at an example of the spectral sensitivity characteristics of a CCD line sensor, as shown in Fig. 6, the sensitivity is low in the B component in the wavelength band of 400 to 500 nm, and the spectral sensitivity ratio is almost the B component, which has a peak at 700 nm; G component;
It is understood that the characteristics are such that the R component is 1:1.3:1.5. Figure 6 shows the spectral sensitivity characteristics of a CCD line sensor.
Almost similar spectral sensitivity characteristics can be seen in photoelectric conversion elements such as photodiodes. On the other hand, an example of the spectral characteristics of the reflected light of printing ink is as shown in FIG. It is understood that the two inks are not completely separated and separated, but that they mutually influence other inks. Now, the spectral characteristics of the illumination light source that illuminates printed materials are
Uniform between 400 and 700nm, and the reflectance of the blank area is
Assuming that it is uniformly 90% from 400nm to 700nm,
When the reflectance of a solid print of each ink printed on such white paper is determined based on FIG. 7, it is as shown in Table 1 below.

[Table] Therefore, as mentioned above, the spectral sensitivity ratio of the CCD line sensor is 1:1.3:1.5 for each of the B, G, and R components.
From this ratio and the ratio of B, G, and R components of the blank area and solid printing of each ink shown in Table 1,
When calculating the output ratio of the CCD line sensor for the blank area and the solid printing of each ink, assuming that the blank area is 1, the output ratio is: blank area: yellow ink: red ink: blue ink ≒ 1: 0.78: 0.54: 0.33. As can be understood from this result, even in solid printing, yellow ink has an output difference of only 0.22 from the white paper area, and compared to other inks, it is possible to detect printing defects even though the fluctuation range of the output level is very small. For example, if yellow ink and indigo ink vary in density by the same density difference with respect to the standard density of a normal printed matter, the output of the CCD line sensor that detects this would be In this case, the variation of yellow ink appears to be less than 1/2 of that of blue ink depending on the above output ratio.
If we attempt to conduct an inspection by capturing reflected light from printed matter directly into the license plate, it can be said that the current situation is that it is extremely difficult to detect printing defects that occur with yellow ink compared to printing defects with other inks. Note that the above phenomenon causes slight differences in the output ratio from the line sensor depending on the type of line sensor, the color temperature of the illumination light source, the hue of the ink, etc., but the basic characteristics are generally the same, so yellow ink printing failure may occur. However, it remains difficult to detect. Therefore, it is necessary to balance the output of the line sensor for yellow ink, red ink, and indigo ink.
An optical filter 5 having spectral transmission characteristics such that the transmittance has a peak in a wavelength band of 500 nm is disposed between the line sensor and the printed material. By arranging the optical filter 5 in this way, the reflected light from the printed matter 3 illuminated by the illumination light source 12 passes through the filter 5 and enters the line sensor, and the output ratio from the line sensor 11 is yellow. The ink can also have a sufficiently different ratio to the blank area, and the detection accuracy can be improved to the same level as other inks. This will be explained in detail using a specific example. The optical filter shown in Fig. 8 has spectral transmission characteristics such as 90% transmittance for B component, 10% transmittance for G component, and 20% transmittance for R component. . In this specific example, the transmittance of the B component is 9 times that of the G component and 4.5 times that of the R component, that is, the spectral transmittance ratio is 9:1:2. The basis for this will be explained below, but it should be noted that the transmittance peak basically exists in the B component. The average transmittance of the optical filter at 400 to 500 nm is x ₁ , the average transmittance at 500 to 600 nm is x ₂ , 600
Let _x3 be the average transmittance at ~700 nm. The output of the line sensor for yellow ink is calculated from the spectral sensitivity ratio of the line sensor and the spectral reflection characteristics of yellow ink as described above: (0.25×1) x ₁ + (0.83×1.3) x ₂ + (0.9×1.5) x It can be calculated using the formula ₃ , and similarly for red ink and indigo ink, respectively (0.37×1)x ₁ + (0.21×1.3)x ₂ + (0.8×1.5)x ₃ (0.56×1)x ₁ + It can be obtained from the formula: (0.26×1.3)x ₂ + (0.16×1.5)x ₃ . Since these are equal, 0.25x ₁ +1.08x ₂ +1.35x ₃ =A 0.37x ₁ +0.27x ₂ +1.20x ₃ =A 0.56x ₁ +0.34x ₂ +0.24x ₃ =A. Solving this equation, x ₁ : x ₂ : x ₃ = 9:1:2
Therefore, in this case, an optimum spectral transmittance ratio of 9:1:2 for each of the B, G, and R components can be obtained. Note that this calculation is an integral calculation using a straight line approximation, so more precisely, it is an integral calculation using a computer.
It is desirable to obtain the transmittance ratio every 10 nm. Therefore, by designing an actual filter based on the desired spectral transmittance ratio of 9:1:2, an optical filter having a spectral transmittance as shown in FIG. 8 can be obtained as an example. be. By using such an optical filter, the output ratio from the CCD line sensor is as follows: blank area: yellow ink; red ink; indigo ink = 1:0.5:0.5:0.5, making it possible to balance the output of each color ink. Moreover, since the ratio is sufficiently different from that of the blank paper portion, it is possible to provide similarly high detection accuracy for each color ink. Note that this specific example depends on the spectral sensitivity characteristics of the CCD line sensor shown in Fig. 6 and the spectral reflection characteristics of the ink shown in Fig. 7, but other line sensors or other types may be used. Even with yellow ink, the characteristics are generally similar to those shown in Figure 6 or Figure 7, and although the spectral transmittance ratio of the specific optical filter changes slightly, it is still difficult to detect printing defects in yellow ink. Gender also exists. Therefore, as an optical filter, the wavelength band
If it has a spectral transmission characteristic that has a transmittance peak at 400 nm to 500 nm and has enough transmittance to obtain the output necessary for inspection in other visible light wavelength bands, it is possible to prevent printing problems with yellow ink. This makes it possible to overcome the difficulty of detection. The optical filter that is actually used has a transmittance of the B component that is about twice that of other components, which significantly improves the output ratio of the line sensor, making it difficult to detect printing failures in yellow ink. It has been confirmed that gender can be overcome. In accordance with the gist of the present invention, if a currently commercially available optical filter is selected, Latten No. 38 or Latten No. 79 manufactured by Kodak Co., Ltd. can be used. Figure 9 shows the spectral characteristics 21 of the above-mentioned Ratten No. 38 and the spectral characteristics 22 of Ratten No. 79, both of which have a transmittance peak in the B component, and the transmittance of the B component is higher than that of the G component. By using such an optical filter as the optical filter 17 shown in FIG. 5, the difficulty in detecting impression disturbance in yellow ink can be reduced. It has been experimentally confirmed that this can be overcome. In addition, the line sensor is infrared (700nm or more)
However, since a smearing phenomenon occurs, it is desirable to use an infrared cut filter in combination. Figure 10 shows an infrared cut filter alone and a combination of Latten No. 38 and an infrared cut filter according to the present invention, each attached to a CCD line sensor.
The output of the CCD line sensor for solid printing of each ink was measured. Although the amount of light is reduced by using the filter of Ratten No. 38, the gain is adjusted by the amplifier, and the white background level of both is the same. As a result, by using the Ratuten No. 38 filter, the output difference between yellow ink and white background was increased by 2.5 times, and detection accuracy was significantly improved compared to the case of using only the conventional infrared cut filter. In addition, the same effect can be seen for red ink, which is approximately 1.7 times more effective. Although the indigo ink was 0.75 times larger, the output difference was still greater than that of the red ink, so there was no problem with detection. In this way, it has been experimentally confirmed that the output ratio of each color ink from the CCD licensor can be improved by using Ratten No. 38, which is a type of optical filter having the above-mentioned characteristics.

[Table] The output signal from the line sensor is input to the processing circuit 6, where it is compared with a reference signal and it becomes possible to detect printing failures.・Various methods such as integration can be considered, but this is discussed in the patent application 1986-1051.
No., Japanese Patent Application No. 57-220515, etc., and since this is not the gist of the present invention, a detailed explanation will be omitted. As described above, according to the present invention, the presence or absence of printing failure in multicolor printed matter can be detected with high accuracy for each color using a single line sensor, and the device can be made smaller, less expensive, and easier to process. This has effects such as simplification.

[Brief explanation of the drawing]

FIG. 1 is a model diagram showing a schematic configuration of a printed matter inspection device, FIGS. 2, 3, and 4 are model diagrams showing conventional methods and signal forms, and FIG. This is a model diagram showing the configuration when using a filter for inspection equipment, and Figure 6 is a CCD
FIG. 7 is a diagram showing the spectral sensitivity curve of the line sensor, FIG. 7 is a diagram showing the spectral reflection characteristics of each color printing ink, and FIG. It is a diagram representing
FIG. 9 is a diagram showing the spectral transmittance of an optical filter that can be put to practical use as a filter for a printed matter inspection device. 3...Printing paper, 11...CCD line sensor,
4...detection unit, 17...filter for print inspection device, 5...rotary encoder.

Claims (1)

[Claims] 1 In a device that illuminates a traveling multicolored printed matter, receives the reflected light from this multicolored printed matter on a line sensor, converts it into an electrical signal, and inspects the printed matter based on the electrical signal from the licensor, the reflected light from the printed matter is A line sensor that receives light is installed, and a wavelength band of 400 nm is installed between this line sensor and the printed matter.
A printed matter inspection device characterized by disposing an optical filter having a spectral transmittance in the range of 500 nm to 500 nm that is larger than that in the other visible light wavelength range of 500 nm to 700 nm.