JPH0511554B2 - - Google Patents

Description

Detailed Description of the Invention [Industrial Application Field] The present invention is used in a printing press to compare the state of a printed matter being printed in-line with a standard state, and detect disturbances and synchronization that occur when abnormalities in the printed matter are detected. The present invention relates to a printed matter inspection device that prevents erroneous judgments due to defects.

[Prior Art] Conventionally, the mainstream method for inspecting printed matter has been to rely on human vision off-line. 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. 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 was done. However, these methods were not systems that could be called inspection machines in that they relied on human vision for inspection. Furthermore, attempts have been made to print color patches at the same time as the patterns on the printed matter and to inspect the color patches instead of inspecting the printed matter. However, with this method,
If a printing problem (oil dripping, stains, etc.) occurs in the pattern, it will be overlooked, and the inspection machine cannot be said to be functioning satisfactorily.

On the other hand, a system has recently been proposed in which printed matter is inspected in-line using a line-shaped sensor, as seen in Japanese Patent Application No. 57-220515 entitled "Printed Material Inspection Apparatus." This method will be explained with reference to Fig. 4. 1 is a plate cylinder, 2 is a blanket cylinder, 3 is an impression cylinder, 4
is a printing paper, and when the printing paper 4 passes between a blanket cylinder 2 and an impression cylinder 3, the pattern on the plate cylinder 1 is transferred to the printing paper 4 via the blanket cylinder. Further, 5 is a line-shaped camera (multiple light receiving elements), and the line-shaped camera 5
The pattern on the printing paper 4 immediately after passing between the blanket cylinder 2 and the impression cylinder 3 is scanned in the width direction (A-B direction),
It is designed to continuously detect the shading of the pattern in the same width direction. Reference numeral 6 denotes a signal processing device, and the signal processing device 6 receives the pattern shading detection signal from the line camera 5 and the normal shading value of the pattern stored in advance in the signal processing device 6 from a rotary encoder 7. After the timing pulse of The detection signal obtained at that time is output to notify the operator and at the same time mark the defective printed paper.

[Problems to be Solved by the Invention] As described above, conventionally, the line-shaped camera 5 scans a printed matter and the pattern information is obtained as a grayscale value detection signal and is stored in the signal processing device 6 in advance. The normal density values are taken in by timing pulses from the rotary encoder 7, and after alignment, they are compared, and it is determined whether the comparison results are within the allowable range or not, and print quality defects (white spots, oil drips, etc.) are detected. , scratches, etc.), but when scanning pattern information using only the timing pulse from the rotary encoder 7, there is no problem as long as it is perfectly synchronized. However, in actual inspection, the timing pulse from the rotary encoder 7 Because the position of the image information detection part is different from the position of the image information detection part, it becomes very difficult to synchronize due to the effects of printing speed fluctuations, tension fluctuations, elastic deformation and plastic deformation of the printing paper, etc. Furthermore, due to electrical noise, Since disturbance is added to the detection signal, there is a problem in that if the judgment is made only by simple comparison, an erroneous judgment may occur, that is, it may be judged that there is a defect even though it is not defective. Currently, the amount of synchronization deviation has been suppressed to a minute value of about 0.1 mm, but in actual print inspection equipment, in order to detect minute printing failures, for example, all AY versions (horizontal)
When dealing with a printed matter (880 mm x 625 mm in height), it is desirable that one pixel of the picture information taken in from a detection unit such as a line sensor is 2 mmφ or less.
However, if the diameter is less than 1 mm, the amount of information to be handled will be enormous, making it unreasonable in terms of printing speed.
For this reason, the appropriate size of the detection pixel is 1 mmφ to 2 mmφ, but the above-mentioned synchronization deviation amount of about ±0.1 mm poses a major problem in defect determination.

In other words, the scanning lines sampled in accordance with the timing pulses from the rotary encoder will vary each time the signal is taken in, as shown in FIG. That is, in one scan, pixel information was captured along scanning lines n, n+1, ..., but in the next scan,
There will be some pixels for which it is impossible to determine printing defects by comparing pixel information along scanning lines n', n'+1, . . . with a reference signal. This means that it may not be possible to determine whether the density of each pixel has changed due to a synchronization shift or whether the density has changed due to a printing defect. Furthermore, since electrical noise is mixed into the signal as a disturbance, some pixels are generated whose gradation values are considerably different from the normal gradation values stored in advance. This causes a misjudgment. What is important for such an inspection device is to have a high inspection accuracy, that is, to be able to detect minute changes in concentration.
The goal is to eliminate false judgments, but these two items are contradictory.

The present invention solves the above-mentioned conventional problems and, for a pixel determined to be abnormal (defect) as a result of comparison, considers printing characteristics and determines the presence or absence of abnormality (spatial isolation) in surrounding pixels adjacent to the pixel. By checking whether there is an abnormality (time isolation) in past pixels at the same position as that pixel, we can improve inspection accuracy and
It is an object of the present invention to provide a printed matter inspection device that can prevent erroneous judgments due to disturbances, synchronization shifts, etc.

[Means for Solving the Problems] The printed matter inspection device according to the present invention compares picture information for each pixel obtained by capturing the picture of a printed matter pixel by pixel with reference information for each corresponding pixel stored in advance. In a print inspection device that performs calculations and determines whether or not the comparison result is within an allowable range to inspect abnormalities that occur in printed matter, pixels that are determined to be abnormal or erroneous determination candidates based on the comparison results are stored. The present invention is characterized in that it is equipped with an abnormality memory, an isolated point circuit comprising means for checking the presence or absence of abnormality in surrounding pixels of the pixel, and means for checking the presence or absence of abnormality in past pixels at the same position as the pixel.

[Operation] According to the present invention, the pattern information for each pixel and its reference information are compared and calculated, and based on the result after the determination, if the pixel is determined to be defective, if it is misdetermined due to disturbance, it is determined that the pattern information for each pixel is incorrect due to the randomness of the disturbance. Since it is thought to be isolated from surrounding pixels, check the isolation, and if it is not isolated, it is a true defect, and if it is isolated, it is a micro defect such as a hitch (a type of scratch that appears on planographic prints). In order to distinguish this from the previous pixel, it is checked whether the defect has occurred continuously before that pixel. In this case, minute defects such as hits will continue to occur unless the cause is removed, so when there is no continuity, it is determined that it is a disturbance such as a synchronization shift or electrical noise, and it is not output as a defect.
Misjudgment can be prevented.

[Embodiment] FIG. 1 is a block diagram showing the configuration of an embodiment of the present invention, in which 11 is a detection section, 12 is a timing circuit, 13 is an A-D converter, 14 is a frame memory, 15 is a reference memory, 16 is a comparison circuit, 17
is a discrimination circuit, 18 is an isolated circuit, 19 is a CPU, 2
0 is alarm, marking and reject, 2
1 indicates abnormal memory, and 22 indicates memory control.

In FIG. 1, a detection unit 1 consisting of a line sensor etc. installed in the positional relationship shown in FIG.
1 and a timing circuit 12, the timing of taking in the printed matter is determined, and the analog signal of the taken-in picture is transferred to the frame memory 14 as a digitally converted digital target signal by an A-D converter 13. First, when taking in the reference, the timing is taken and the reference signal is taken in from the frame memory 14 to the reference memory 15. Next, at the time of inspection, the data is stored once in the A-D converter and frame memory 14, the timing is taken, and the data is sequentially stored in the comparison circuit 16.
Transfer to. This transfer timing is controlled by the memory control 22, and at the same time the reference signal is also transferred from the reference memory 15 to the comparison circuit 16. As a result, the reference signal and the test signal are sent to the comparison circuit 16. The comparison method includes, for example, calculating the difference between the detected signal and the reference signal, and then comparing the signal obtained by this difference calculation with the difference calculation, as described in the specification of Japanese Patent Application No. 172778/1983, for example. For example, a difference is calculated between the signal obtained by the method and a signal delayed by several pixels, and this difference calculation value is compared with a reference value. Based on the result of this difference comparison, a determination circuit 17 determines whether there is an abnormality (defect) in the printed matter according to a preset threshold value. As a result of the determination, if a point (pixel) exceeding the threshold value is detected, the position information of that point is stored in the abnormality memory 21. Note that this abnormality memory 21 stores determination results for several past sheets. The points stored in the abnormality memory 21 include not only true defects but also points caused by the above-mentioned synchronization deviation and electrical noise. These are distinguished by the next isolated point circuit 18. Therefore, the isolated point circuit 18 first checks whether or not there is an abnormality in the surrounding pixels adjacent to the pixel determined to be abnormal in the entire printed matter.
For example, if a pixel in the shaded area in FIG. 2 is determined to be defective by the discriminating circuit 17, but there are no pixels around that pixel that are determined to be defective, this is considered an erroneous determination candidate. Not considered, CPU1
9 does not immediately output an alarm, marking, or reject signal, and when there is a defect in ~, it is determined to be a true defect, and the CPU 19 outputs an alarm, marking, or reject signal. Here, instead of checking all of the pixels, it may be sufficient to check only the pixels. Next, the abnormality memory 21
Check past discrimination results. In other words, the continuity of abnormality is checked for a plurality of past pixels at the same position as the pixel that has been determined as an erroneous determination candidate. The reason for this is that once defects (scratches, stains, etc.) in printed matter occur, they continue to occur in the same location. For example, as shown in Figure 3, if an erroneous judgment candidate occurs at the diagonal line point (point A) of the No.
Check whether there is an erroneous determination candidate at point A on the No.-1 sheet. If there is no false positive candidate in No.-1, A
The point is determined to be a true misjudgment, that is, it is not a defect.
Of course, at that time, the CPU 19 does not output any alarm, marking, or reject signals.
Furthermore, if there is an erroneous judgment candidate at point A on the No. 1 sheet, there is a strong possibility that this pixel is not an erroneous judgment but a true printing defect. No.
- Check the continuity of the third sheet and the past few sheets, and if any point A from the past several sheets exists in the abnormal memory 21, that is, it is a defect candidate, point A is determined to be a true defect. , alarm, marking, reject 20, etc. Here, checks for past erroneous judgment candidates and abnormal pixels are No.-1, No.-
2. Not limited to No.-3, No.-1 and No.-3
It may be checked at any time, or it may be checked at appropriate intervals. In this way, based on the results of comparison calculations, we further check the isolation of the abnormal state from surrounding pixels, past erroneous judgment candidates, and continuity with the abnormal pixel to prevent erroneous judgments due to disturbances such as synchronization shifts and electrical noise. A highly accurate and highly reliable printed matter inspection device can be realized. The above explanation is
This is based on some embodiments of the present invention, and even if the isolated point circuit 18 is manufactured as a hardware,
Even if the isolated point circuit 18 is integrated with the CPU 19 and isolated point processing is performed by software, various modifications can be made without departing from the spirit of the present invention.

[Effects of the Invention] According to the present invention, the pattern information of a printed matter is scanned by a line sensor and sent to the signal processing device as a grayscale signal, and the same is sent to the signal processing device as a reference signal for each corresponding pixel stored in advance. In a device that performs comparison calculations and determines whether or not the comparison result is within an allowable range to inspect abnormalities (defects) that occur in printed matter, the inspection accuracy is increased and false judgments due to disturbances and synchronization deviations are within an acceptable range. Excellent effects such as being able to prevent only erroneous judgments without increasing the number of errors can be achieved.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the configuration of an embodiment of the present invention, FIG. 2 is a diagram showing an example of spatial isolation in an embodiment of the invention, and FIG. 3 is an example of temporal isolation. FIG. 4 is a schematic diagram showing a printed matter inspection apparatus, and FIG. 5 is a model diagram of out-of-synchronization. 11...Detection unit, 14...Frame memory, 1
5... Reference memory, 16... Comparison circuit, 17...
Discrimination circuit, 18... isolated point circuit, 19... CPU.

Claims (1)

[Claims] 1 Compare and calculate the pattern information for each pixel obtained by capturing the pattern of the printed matter pixel by pixel with pre-stored reference information for each corresponding pixel, and check whether the comparison result is within the allowable range. In print inspection equipment that distinguishes and inspects abnormalities that occur on printed matter,
an abnormality memory for storing pixels that are determined to be abnormal or erroneous determination candidates; and a means for checking whether pixels surrounding the same pixel are abnormal, using the abnormality memory, for a pixel determined to be abnormal based on the comparison result; 1. A printed matter inspection device comprising: an isolated point circuit comprising means for checking the presence or absence of an abnormality in a plurality of past pixels at the same position.