JPH0465786B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention is an inspection method for running printed matter that compares the state of printed matter being printed in-line with a standard state in a printing machine and reduces false judgments due to synchronization deviation that occur when detecting abnormalities in printed matter. Regarding the method. [Prior Art] Conventionally, printed matter has been mainly inspected off-line by relying on human vision. This means that each printed item has a different pattern,
This comes from the fact that inspection items on printed matter have been thought to involve subtle differences that require reliance on human vision. Recently, 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 is being done. However, in that this attempt relies on human vision for inspection, it is not a system that can be called an inspection machine. In addition, by printing color patches at the same time as the printed image and inspecting these color patches,
Attempts are also being made to have printed materials inspected on their behalf. However, with this method, if printing defects (oil dripping, stains, etc.) occur in the pattern area, they will be overlooked, and it could not be said that the inspection machine is fully functioning. Furthermore, a system has recently been proposed that inspects printed matter 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 system, the pattern itself of printed matter can be automatically inspected in-line, so it can be expected to have excellent effects as an inspection machine without the drawbacks of the above-mentioned examples. [Problems to be Solved by the Invention] However, the above system handles a large amount of image data at high speed, which causes various problems. Especially fluctuations in printing speed,
Printing speed and synchronization of inspection become major issues in maintaining inspection accuracy. This problem will be explained below with reference to the schematic configuration diagram of the printed matter inspection apparatus shown in FIG. Although FIG. 4 shows the case where the printed matter inspection device is attached to a sheet-fed printing press, the same applies if it is attached to a rotary press. In Figure 4, the sheet-shaped printing paper is
After printing in, for example, four colors (yellow, red, indigo, black) in the printing section 1, the paper is sent to the paper discharge section. The printed matter inspection device checks the timing of sampling using a rotary encoder 2 attached to the printing section in order to inspect the printing condition after printing in four colors.
The pattern information of each pattern 3 printed on printing paper is scanned and processed line by line by a line sensor such as a solid-state image sensor (hereinafter referred to as CCD) of a detection unit 4 extending in a direction perpendicular to the print conveyance direction. The signal is taken into the circuit 5, and the density level is compared with the reference signal in the processing circuit 5, and based on this result, it is determined whether the printing condition is normal or abnormal. As a result, if the printing condition is determined to be abnormal, an alarm
It becomes possible to deal with this by means such as marking and redirecting. However, if the pattern information is scanned using only the timing pulse from the rotary encoder 2, there will be no problem as long as the period is perfect, but in actual inspection, the position of the rotary encoder that takes the timing and the position of the pattern information detection section may be different. Therefore, synchronization becomes extremely difficult due to the effects of printing speed fluctuations, tension fluctuations, elastic deformation and plastic deformation of the printing paper, etc. The current amount of synchronization deviation has been suppressed to a minute value of around 0.1 mm. However, in actual printed matter inspection equipment, in order to detect minute printing defects such as white spots and stains,
When targeting printed matter, it is desirable that one pixel of the pattern information taken in from the detection unit 4 such as a CCD line sensor is 2 mmφ or less. However, 1
Since the amount of information to be handled becomes enormous below mmφ,
This becomes difficult due to the print speed. Therefore, the size of the inspection pixel of printed matter is 1mmφ to 2mmφ
is appropriate, but the amount of synchronization deviation mentioned above is ±
A thickness of about 0.1 mm is a big problem in signal processing. In other words, the scanning lines sampled in accordance with the timing pulses from the rotary encoder 2 differ from each other every time the signal is taken in, as shown in FIG. In other words, in one scan, pixel information is captured along scanning lines n, n+1, n+2, etc., but in the next scan, pixel information is captured along scanning lines n', n'+1, n'+2,... This results in cluttered pixel information. In this state, it may be impossible to determine printing defects by comparing the detected pixel information and the reference signal. This means that the density of each pixel changes due to the synchronization shift, and for some pixels it is not clear whether the density change was due to a printing defect or due to the synchronization shift. Therefore, it is sufficient to mask such pixels and exclude them from the inspection target. Therefore, in general, the contour portion, that is, the pixels obtained by a spatial filter used in digital image processing technology, is masked. As an example of the spatial filter, if the pixel density of an arbitrary image is distributed as shown in _{FIG .} or a ₂₁ −a ₁₁
The larger absolute value of each of these values is taken as the amount of density change for that pixel, and the area where the amount is larger is masked. Also, for left and right, a ₁₀ −a ₁₁ or a ₁₂
It is sufficient to use the larger absolute value of −a ₁₁ . In view of the above, an object of the present invention is to provide a method for inspecting running printed matter that can prevent erroneous judgments due to synchronization errors. [Means for Solving the Problems] Therefore, the present invention has been proposed to print a pattern on a sheet of paper by holding it in the grip and conveying it with a claw. Inspection of running printed matter that detects each pattern with a detector, converts this detected pattern information into a digital signal, and compares this converted signal with a predetermined reference value to check for abnormalities that occur in printed matter. In the method, a pixel with a large density change between adjacent pixels of the digitalized picture information is found, the pixel is divided into a plurality of regions in the conveying direction of the sheet, and these pixels are divided into each region. This masking level is set so that the area at the end of the grip is lower than the area at the beginning of the grip, and pixels whose density changes are equal to or higher than the set masking level. This is an inspection method for running printed matter in which the printed matter is masked and excluded from the inspection target. [Operation] Therefore, the mask level is high at the beginning of the paper being held in the mouth, and gradually lowered toward the end of the paper being held in the mouth.
Misjudgments due to synchronization errors can be eliminated, only printing defects can be detected, and there is no need to mask more pixels than necessary.
Inspection accuracy improves. [Example] The method of the present invention will be described below, but first an overview thereof will be described. That is, the method of the present invention does not apply a uniform mask level over the entire printed matter only to the outline of the pattern, as in the conventional method, but takes into consideration the behavior of the paper in the printing machine. In the case of sheet-fed printed matter, the amount of synchronization is generally determined by the amount of synchronization between the beginning of gripping the paper, that is, the side where the nail grips the paper, and the end of gripping, that is, the free end opposite to the beginning of gripping, as shown in Figure 1. There is a tendency for the end of the mouth to gradually become larger. The reason for this is that the printing paper stretches, shrinks,
It is thought that the amount of synchronization deviation increases in the latter half of the paper due to turbulence. It is also known that in the case of rotary presses, the amount of synchronization deviation is large in the latter half of the image. Therefore, when inspecting running printed matter, the level of masking, that is, the value that determines which value of the above-mentioned density change should be masked, is determined by dividing the running printed matter into multiple areas in the print conveyance direction depending on the printed matter. This is a method of inspection. Therefore, the mask level is high at the beginning of paper gripping and gradually lowered, eliminating misjudgments due to synchronization errors and detecting only printing defects.
This eliminates the need to mask more pixels than necessary, improving inspection accuracy. As an example of this, if the area is divided into three areas as shown in Figure 2, hold each area in your mouth and start from the beginning (1),
(2) and (3). Furthermore, the density of each pixel is converted into an 8-bit digital amount by an analog A-digital D converter (A/D converter). In other words, there are 256 levels from 0 to 255. Therefore, the amount of change in density, that is, the difference in density between each pixel, is expressed as a digital quantity.For example, the following table shows.

〔Effect of the invention〕

According to the present invention described above, a pixel with a large amount of change in density between adjacent pixels of picture information obtained by digitization is found, and the pixel is divided into a plurality of regions in the conveyance direction of a sheet, and each region is Set a masking level to mask these against the masking level, and set this masking level so that the area at the end of the grip is lower than the area at the beginning of the grip, and the amount of density change above this set masking level. Since the pixels that correspond to the above are masked and excluded from the inspection target, it is possible to prevent erroneous judgments due to synchronization deviation, and to provide a method for inspecting running printed matter that improves inspection accuracy.

[Brief explanation of drawings]

Fig. 1 is a diagram showing the synchronization deviation amount and the positional relationship of paper for explaining the method of the present invention, Fig. 2 is a diagram showing an example of dividing and masking the paper for explaining the method of the present invention, and Fig. 3 The figure is a block diagram showing an example of a signal processing circuit of a running print inspection device for carrying out the method of the present invention, FIG. 4 is a schematic configuration diagram for explaining a conventional print inspection device, and FIG. FIG. 6 is a model diagram of out-of-synchronization for explaining the problem in the figure. FIG. 6 is a diagram showing the relationship between the conventional density change calculation method and out-of-synchronization. 11...detection section, 12...timing circuit, 1
3...A/D converter, 14...Frame memory, 15...Reference memory, 16...Concentration change calculation circuit, 17...Mask memory, 18...Difference circuit, 19...Memory control, 20... Discrimination circuit, 21...Central processing unit.

Claims (1)

[Scope of Claims] When printing a pattern by holding a sheet of paper in your mouth and conveying it with a claw, as the sheet of paper is being conveyed, the pattern of the sheet of paper is detected pixel by pixel by a detector, The detected pattern information is converted into a digital signal, and the converted signal is compared with a predetermined reference value to inspect for abnormalities occurring in the printed matter. Find a pixel with a large amount of density change between adjacent pixels of information, divide the pixel into a plurality of regions in the conveyance direction of the sheet, and set a masking level for masking these for each region. This masking level is set so that the area at the end of the grip is lower than the area at the beginning of the grip, and pixels whose density changes are greater than or equal to the set masking level are masked and excluded from the inspection target. A method for inspecting running printed matter.