JPH0257771B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a printed matter inspection method and apparatus for comparing the state of a printed matter being printed in-line with a standard state in a printing press and detecting 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. 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 printing defects (oil drips, stains, etc.) occur in the pattern area, they will be overlooked, and the inspection machine cannot be said to perform its function satisfactorily.

By the way, recently, as seen in the "printed matter inspection device" published in Japanese Patent Application Laid-open No. 56-98634 and the "printed matter inspection device" published in Japanese Patent Application Laid-Open No. 59-109832, printed matter is inspected in-line using a line sensor. A system has been proposed. By using this system, the pattern itself of printed matter can be automatically inspected in-line, so it does not have the above-mentioned drawbacks and can be expected to have excellent effects as an inspection machine.

However, this system is not without its problems, and one of the biggest causes is the phenomenon that the density of the printed matter varies overall even during steady operation as a characteristic of the printing press, and the pattern of the printed matter simply changes. This system, which compares the concentration with a reference value, has a drawback in that it is difficult to distinguish such abnormalities. The above-mentioned overall density fluctuations are caused by variations in the amount of water supplied by the inking mechanism of the printing press, the dampening device, and changes in the amount of ink in the ink fountain. It can be said that it is extremely difficult to suppress.

The overall concentration fluctuation, which is a problem to be solved in the present invention, will be explained in more detail.

FIG. 1 shows a schematic diagram of a print inspection device to which the present invention is applied. In FIG. 1, the printed matter inspection device is attached to a rotary press, but there is no problem if it is also a sheet-fed printing press.

In Fig. 1, a strip-shaped printing paper 3 fed from a roll-shaped paper roll 2 is printed in four colors (black, indigo, red, and yellow) on the front and back sides in a printing section 1, and then sent to a dryer and folded. It is transported to a machine section (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 spreads the pattern information in a direction perpendicular to the flow direction of the printed matter while timing the sampling with a rotary encoder 5 attached to the printing section. A licensor such as a CCD/MOS of the existing detection unit 4 performs main scanning, and the flow of the printed matter is transferred pixel by pixel to the processing circuit 6 as sub-scanning, thereby determining whether the printed matter is normal or abnormal. 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, it is difficult to obtain good discrimination results by simply comparing the pattern information imported from the licensor with reference information in actual printed matter. This is because the print density of the printed matter changes during printing, and it can be said that it is extremely difficult to separate overall density fluctuations that cannot be called printing failures from density fluctuations that are due to printing failures.

FIG. 2 shows an example of density fluctuations in printed matter.

Figure 2 shows the print eye every 1000 sheets after printing starts.
It is a graph obtained by measuring the reflection density (R filter transmission) at 100%. The reference density of the 100% eye area is 1.3 to 1.4, shown by the chain line, while it is clearly seen how large the density fluctuations of the actual printed matter are, shown by the solid line. The causes of this density variation include the amount of ink in the ink fountain, the periodicity of ink supply due to the ink roller configuration, the balance with dampening water, the content of the image, etc., but by finally eliminating the causes,
At present, it is extremely difficult to suppress concentration fluctuations. For this reason, unless the printed matter is inspected by excluding the influence of overall density fluctuations, the method of comparing the pattern information based on the current amount of reflected light with a reference value will improve the inspection accuracy to a level sufficient for practical use. That can be said to be difficult.

The present invention takes these conditions into consideration and aims to provide a method and apparatus for inspecting printed matter that can inspect printed matter while excluding the influence of overall density fluctuations of the printed matter.

An embodiment of the present invention will be described below with reference to the drawings.

FIG. 3 is a model representation of printing failures during inspection of printed matter. Figure A shows the concentration fluctuation detection signal in the case of a printing failure due to water or oil dripping on the printed matter using a dashed line, and the standard signal during normal operation is shown as a solid line. The concentration fluctuation detection signal when dirt occurs is shown by a dashed line, and the reference signal at normal time is shown by a solid line. In Figure 3A, in a situation where the concentration of the detection signal is generally higher than the reference signal due to the influence of the overall concentration fluctuation, a drop in the concentration due to water dripping and oil dripping can be seen. In B, while the detection signal overall decreased compared to the reference signal, a concentration protrusion due to dirt was observed.

For the models shown in Figure 3 A and B, a typical comparative inspection method is to take the difference between the detection signal and the reference signal, and if the difference value is within a certain range, it is considered normal. The cases in which this is directly applied are shown in Figure 4 A and B, respectively.

In FIGS. 4A and 4B, the chain line indicates the threshold level, and the solid line indicates the difference between the detection signal and the reference signal. In this case, printing failures can be detected by setting the threshold level appropriately, but if the overall density fluctuation becomes larger, the entire signal will exceed the threshold level. It may become impossible to distinguish, or the signal variation width due to the printing fault may be absorbed by the overall density variation width, so that even a significant printing fault may not exceed the threshold level and cannot be detected.

In order to eliminate such overall density fluctuations that have an adverse effect on printing fault determination before the determination, the present invention first uses a differential signal (for example, in the model shown in FIG. 4) that is the difference between the detection signal and the reference signal. A threshold is set for a signal obtained by taking the difference between the difference signal and a signal that is shifted (delayed) by several pixels (3 to 5 pixels).

A signal subjected to such processing is shown in FIG.
Figure 5A shows the signal shown in Figure 4A subjected to the above processing, and Figure 5B shows the signal shown in Figure 4B subjected to the same processing. . As is clear from FIG. 5, by performing the above processing, it is possible to determine the presence or absence of a printing failure (that is, to set a threshold level) while removing the influence of overall density fluctuations.

Note that although the signal obtained by this process is superficially similar to the signal obtained by performing differentiation on the signal obtained by taking the difference between the detection signal and the reference signal, the following point shows that the result is different from that obtained by differentiation. It has major advantages compared to processing.

First, since the processing according to the present invention involves only differential calculation, it has the effect that the circuit configuration in a digital circuit can be greatly simplified compared to differential calculation.

Second, as shown in Figure 6, this was captured for the density pattern DP of the picture.
In a CCD license sensor, a leak phenomenon occurs to adjacent pixels at the rise and fall of the density of a picture pattern.
As in pattern OP, a signal is output as a so-called matsuta state. When differential processing is performed on such a signal, even though there is a considerable signal difference in the original signal, almost no signal difference appears as shown in Figure 7, and the change point is due to the effect of the overall concentration fluctuation mentioned above. The problem is hidden by the printer, making it impossible to detect as a printing problem.

However, according to the method of applying the present invention, setting the number of delayed pixels to 4 pixels, and taking the difference from the signal delayed by 4 pixels, it is possible to obtain a large signal difference at the change point, as shown in FIG. Therefore, it becomes easy to set the threshold level.

In this way, by setting the number of delayed pixels to about 4 pixels according to the present invention, it is possible to reduce printing failures caused by gradual density fluctuations, as well as the effects of bleeding from CCD line sensors and MOS line sensors, and improve the overall quality of printed matter. It becomes possible to accurately detect the density change point of a printing failure while the density changes.

In this example, the change point can be detected even if the number of delayed pixels is set to 1 to 3 pixels, but the signal difference cannot be made that large and the effect is not as noticeable. Also, 6
If the difference is taken with a delay of more than one pixel, the peak time will become longer and there is a drawback that the change point will not be clear. Therefore, the preferred number of delay pixels is 3 to 5 pixels.

In addition, the overall concentration may become abnormally high,
Even when the temperature decreases, the quality of the printed matter deteriorates and must be detected as a defective printed matter. However, when the above-described processing is performed, the inspection is performed with the overall density variation removed, so that abnormalities in the overall density variation cannot be detected. In order to compensate for this, the difference value between the density detection signal from the printed matter and the reference signal is accumulated for a predetermined number of pixels, and the upper and lower limits of the accumulated value are set as the standard. A value is set, and when the accumulated value exceeds the reference value, it is determined that an overall abnormal concentration fluctuation has occurred.

By adding this so-called second process to the above-described process, both printing failures such as water drips, oil drips, stains, etc., and overall abnormal density fluctuations can be detected satisfactorily.

Next, one example of a device based on the present invention will be described.

FIG. 9 shows a block diagram of a processing circuit capable of carrying out the method of the invention. Timing pulse TMP generated by the rotary encoder 5 attached to the plate cylinder or impression cylinder of the printing section
Based on this, the timing control section 11 controls the memory control section 13 and the sampling control section 12.

The memory control section 13 controls the loading of the reference signal SSS into the reference memory 17, the difference circuit 16, and the cumulative counter 21 in accordance with the signal from the timing control section 12 and the mode switching signal MSS from the CPU 23. The sampling control section 12 provides a transfer lock and a sampling start signal to the detection section 4, which is composed of a CCD line sensor and the like. The above circuit controls the timing and switching of this processing circuit.

Next, the reference signal SIS inputted from the detection section 4 is converted into a digital signal via the A/D converter 15, and then stored in the reference memory 17 in the reference signal import mode. On the other hand, in the test mode, the digitized test signal SIS is directly transferred to the first difference circuit 16. At this time, the reference signal is output based on the control signal from the memory control section.
SSS is read and transferred to the first difference circuit 16. As a result, a differential test signal, which is the difference between both signals, is obtained.
DIS is obtained. This differential test signal DIS can be considered to have the signal state shown in FIG. 4 previously shown. After that, the difference test signal DIS is branched into three parts, one goes through the delay circuit 19 and goes to the second difference circuit 18;
One is directly transferred to the second difference circuit 18. The delay time in this case is several pixels (3 to 5 pixels) to be inspected.
Equivalent is appropriate. As a result, the second differential circuit 1
The second-order difference signal DDS obtained from 8 (corresponding to the signal state in FIG. 5) is sent to the stress hold circuit 2.
0 and is determined based on the stress hold level based on the stress hold setting signal SHC from the CPU 14. If an abnormality is detected, an abnormality signal IRS is sent to the CPU 14. On the other hand, the value of the remaining three-branched differential test signal DIS is totaled for each fixed number of pixels by an accumulation counter, and is transferred to the discrimination circuit 22 as an integrated density signal IDS.
The discrimination circuit 22 generates an abnormal signal when the range of overall concentration fluctuation exceeds a preset value.
Send IRS to CPU14.

The CPU 14 has a stress hold circuit 20
Alternatively, if an abnormal signal IRS is sent from the discrimination circuit 22, measures such as an alarm and a marking reject are taken. By employing the above-described processing circuit, it becomes possible to inspect the printed matter in a state where the influence of the overall density fluctuation of the printed matter is reduced in the printed matter inspection apparatus.

Note that the block diagram shown in FIG. 9 is only one example based on the present invention, and it is also possible to change the circuit configuration in order to obtain the same effect.

As described above, according to the present invention, the amount of ink in the ink fountain of the printing press, the periodicity of ink supply due to the ink roller configuration, the balance with dampening water, the content of the pattern, etc. Since printing defects such as water drips, oil drips, and stains can be detected while excluding the influence of overall density fluctuations, extremely accurate standards are possible.

Furthermore, it is now possible to detect when the overall density fluctuation becomes abnormally high or low, which, in combination with the detection of printing problems such as water drips, oil drips, and dirt, can improve accuracy. This makes inspection possible.

[Brief explanation of the drawing]

Fig. 1 is a schematic explanatory diagram of a printing press and inspection device to which the present invention is applied, Fig. 2 is an explanatory diagram showing an example of the overall density fluctuation of printed matter, and Fig. 3 is an explanatory diagram showing an example of the density fluctuation when a printing failure occurs. This figure shows one example. Figure A is an explanatory diagram when there is water dripping, oil dripping, etc., Figure B is an explanatory diagram when there is dirt, etc., and Figure 4 is an illustration of the inspection signal and reference signal. Figure A is an explanatory diagram showing the difference signal corresponding to Figure 3B, Figure 5B is an explanatory diagram showing the difference signal corresponding to Figure 3B, and Figure 5A is an explanatory diagram showing the difference signal corresponding to Figure 3B. The figures are explanatory diagrams showing signals processed according to the present invention, in which A corresponds to Fig. 4A, B corresponds to Fig. 4B, and Fig. 6 shows a picture pattern. FIG. 7 is an explanatory diagram showing the output signal of the CCD line sensor for , FIG. 7 is an explanatory diagram showing the signal when the output signal shown in FIG. 6 is differentiated, and FIG. 8 is the output signal shown in FIG. FIG. 9 is a block diagram of a processing circuit based on the present invention. 4...Detection unit, 5...Rotary encoder,
6...processing circuit, 6...first difference circuit, 18...
...Second differential circuit, 19...Delay circuit, 20...
Threshold hold circuit, 21...cumulative counter, 22...discrimination circuit.

Claims (1)

[Claims] 1. Image pattern information of the printed material is captured pixel by pixel, and a signal based on the detected pattern information of each pixel is compared with a reference signal of the corresponding pixel to inspect abnormalities occurring in the printed material. In this method, a difference is calculated between the detected signal and a reference signal, and a difference is calculated between the signal obtained by this difference calculation and a signal obtained by delaying the signal obtained by this difference calculation by several pixels, and this difference calculation is performed. A method for inspecting printed matter, characterized in that the value is compared with a reference value to detect the presence or absence of a printing failure. 2 In addition to the comparison result, the signal obtained by calculating the difference between the detected signal and the reference signal is accumulated for a certain number of pixels, and it is determined whether the accumulated value is within a predetermined range. The printed matter inspection method according to claim 1, wherein the printed matter is determined and the presence or absence of a printing failure is detected based on the determination result. 3. A detection unit that optically scans the pattern of the printed material in a direction perpendicular to the running direction of the printed material and detects the image information pixel by pixel, and stores the image information of each pixel of the pattern of the normal printed material as reference information. a reference information storage means, a first difference calculation means for calculating a difference between the detected image information and the reference information, and a difference signal obtained by the first difference calculation means in the scanning direction of the detection section. a delay means for delaying several pixels; a second difference calculation means for performing a difference calculation between the difference signal obtained by the first difference calculation means and the delayed difference signal obtained by the delay means; Compare the two-time difference signal obtained by the difference calculation means of No. 2 with a predetermined value,
1. A printed matter inspection apparatus, comprising: a comparison calculation means for outputting an abnormality signal indicating that a printing abnormality has occurred in a pattern when the difference signal exceeds an allowable range. 4. An accumulation means for accumulating the difference signal obtained by the first difference calculation means for one picture, and comparing the accumulation signal obtained by the accumulation means with a predetermined tolerance value, and determining whether the accumulation signal is acceptable. 4. The printed matter inspection apparatus according to claim 3, further comprising discriminating means for outputting an abnormal signal when the range is exceeded.