JPS6112344A - Apparatus for inspecting printed matter - Google Patents

Abstract

PURPOSE:To certainly detect all of printing abnormalities, by removing an abnormality signal caused by the phase shift of the boundary part between the low and high density parts of a picture pattern by utilizing an optical shading-off phenomenon and adding differential signals with respect to picture patterns of plural continuous sheets to perform judgement. CONSTITUTION:An optical system is adjusted so that focus gets out of the light receiving surface of the photoelectric converter element provided to a detection part 4. By this adjustment, a reference signal and a detection signal gradually change (signals become obtuse) at a boundary part and, therefore, if the differential of both signals is taken, the pulse generated by a phase lens can be suppressed to a level considerably smaller than a tolerant range having a height and width accompanied by an optical shading-off amount, the density differential at the boundary part and a phase shift amount and the effect of phase shift can be removed. Therefore, signals obtained by the operation of differential corresponding to a definite number of sheets are added to perform treatment for discriminating whether the addition treatment result is present in the tolerant range.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a printed matter inspection method for in-line comparing a printed matter with a standard state and detecting an abnormality in the printed matter.

Conventionally, the mainstream method for inspecting printed matter has been offline and relying on human vision. This is one printed item.
This stems from the fact that the dot pattern is different from the other, and the subtle differences in inspection items on printed matter that require reliance on human vision have been thought to be a problem. On the other hand, in response to the desire to evaluate printed matter while it is being printed, efforts are being made to use strobe lighting that is synchronized with the printing speed and to use mirrors that rotate synchronously at high speed to determine the printed matter that is being printed as a still image. An attempt was made. 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 inspect the color batches, thereby allowing the inspection of the printed matter to be performed on behalf of the user. 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 function properly.

On the other hand, a system has recently been proposed in which printed matter is inspected in-line using a line sensor, as shown in Japanese Patent Application No. 57-220515 [Print Inspection Apparatus J]. 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, the invention is not without its problems; for example, during printing, the pattern on the printing paper may be out of phase in the vertical and horizontal directions due to tension fluctuations, drying temperature changes, and other factors. In-line inspection is hampered by the problem that it is difficult to distinguish false abnormal signals caused by phase shifts in inspection images from true abnormal signals.

For this reason, a method for correcting synchronization defects in inspection of single-run printed matter according to Japanese Patent Application No. 58-172777 has been proposed, and by utilizing the same invention, the phase shift in the machine direction in a rotary printing press can be minimized. This makes it possible to perform inspections while suppressing

However, there are cases in which simply utilizing the above invention is not sufficient.

In other words, there is a danger that a slight phase shift will be detected as a large signal difference at the edge of a photograph, etc. in a printed image, that is, at the boundary between the white part of the paper and the high density part of the ink. .

For example, if we assume that we are performing pixel detection from 1 to 1 on the boundary between a white background (0% dot) and a solid dot ioo%,
A phase shift of 0.01% will generate an abnormal signal of 10% level.

In this case, it can be said that it is extremely difficult to distinguish between a true abnormal signal due to a printing abnormality and a false abnormal signal due to a phase shift.

In order to solve this problem, a method has been proposed in which the tolerance of the inspection signal for the edge part is made more relaxed than for other parts, as seen in the "Inspection method for printed matter" published in Japanese Patent Application Laid-Open No. 58-81165. In the above proposal, if a defect occurs in the edge portion, there is a small possibility that the defect will be overlooked, which is insufficient for practical use. The present invention solves these problems, and by using the present invention, it is possible to distinguish between a false abnormal signal at the edge of a picture caused by a phase shift and a true abnormal signal due to an abnormality in printed matter, and to obtain more accurate signals. The purpose is to enable inspection.

Hereinafter, the present invention will be described in detail based on some examples.

FIG. 1 is a schematic diagram showing the configuration of a printed matter inspection apparatus according to the present invention. Figure 1 shows an example of installation on a rotary printing press.
There is no problem with sheet-fed printing machines. In FIG. 1, printing paper (
3) is printed in four colors (yellow, red, indigo, and black) on both sides in the printing section (1), and then transported to a dryer and a folding machine (not shown). In order to inspect the printing condition after printing in four colors on both sides, the printed matter inspection device uses a rotary encoder (5) installed in the printing section (1) to determine the timing of inspection sampling and reads the pattern information on the printing paper. Detection part (4)
The line sensor inputs the pattern information to the processing circuit (6), and it is judged whether the pattern information matches the reference information or not.

As a result, if it is determined that the printing condition is abnormal, it becomes possible to take measures such as alarms, markings, and rejects.

However, as mentioned above, printing paper (
3) The above pattern is affected by tension fluctuations, drying temperature fluctuations, etc., and it is impossible to completely eliminate the phase shift using only the timing pulse from the rotary encoder (5).

For this reason, as shown in FIG. 2, in boundary areas where the density difference is large, false abnormal signals due to phase shifts are likely to occur. In other words, Fig. 2 (a) and (n) show that the areas including the boundaries where the difference in density of the picture is large when a phase shift occurs is detected based on the rotary encoder (5) K (if detected at the same timing). It shows the level of the reference signal and the level of the test signal, and as shown in the figure, based on the phase difference (a difference e in the signal acquisition timing occurs,
Assuming that a comparative inspection is performed using the difference between the reference signal and the inspection signal, the difference signal exceeds the tolerance range S, as shown in Figure 2 (C), and therefore the printed matter in this area may be normal. Otherwise, it will be erroneously determined to be abnormal.

In the present invention, the focus h! -Adjust the optical system so that the object is out of focus (out of focus). As a result, the reference signal and test signal shown in Figures 2A and 2B gradually change at the boundary, as shown in Figures 6A and 6B, respectively. Therefore, if we take the difference, as shown in Figure 6, the pulse generated by the phase shift has an optical blur, a density difference at the boundary, and a height and width that correspond to the phase shift. This can be suppressed to a level considerably smaller than the range S, and the influence of phase shift can be eliminated.

However, simply measuring optically out of focus will not detect true printing abnormalities, such as abnormalities with a small area and a difference in level. That is, the reference signal is as shown in Figure 4 (a).
When the signal is flat as shown in Figure 4 (b), when it is in focus, it can be perceived as a small abnormal signal with a considerable level difference from the reference signal, as shown by the dotted line in Figure 4 (b). Because the printing abnormality is out of focus, it is detected as a poor abnormal signal (dull signal) with a gradual level difference as shown in the solid line, and even if the difference is taken, it falls within the allowable range S as shown in Figure 4 (C). It becomes undetectable.

In order to eliminate such defects, the following processing is performed in the present invention.

In other words, the difference between the reference signal and the test signal detected when the focus is out of focus and the test signal is calculated, the signals obtained by the difference calculation are added for a certain number of images, and the addition result is within the allowable range. Performs processing to determine whether or not.

Considering that the phase shift occurs randomly with respect to the pattern position, for example, in five consecutive prints, a phase shift occurs by one page in the scanning direction, a phase shift occurs by one page in the reverse scanning direction, and so on. Assume that the phase shift of the six images is sufficiently small.

The reference signal at the boundary between the optically low-density area and the high-density area is as shown in FIG. As shown in Figure (b), a phase shift in the scanning direction is represented by I, a phase shift in the reverse scanning direction is represented by m, and a sufficiently small phase shift is represented by n. By calculating the difference between each inspection signal for these five pictures and the reference signal shown in Figure 5 (A), and adding the results of this difference calculation, the 5th
As shown in Figure (c), no signal exceeding the allowable range appears. This is because the phase shift does not tend to advance or lag, but rather occurs randomly. False abnormal signals h' caused by Do not exceed the tolerance level.

On the other hand, printing abnormalities that occur in small areas and have different levels, such as cypress and ink splatter, tend to occur on multiple sheets in succession at the same position of the image. For example, as shown in Fig. 6 (a), for five consecutive pictures, there is a phase shift in the scanning direction of one picture, as shown in Fig. 6 (b), with respect to a flat reference signal. If a printing abnormality with a difference in level occurs in a small area in a state where a phase shift occurs, with one sheet having a phase shift in the direction and three sheets having almost no phase shift, as shown in Fig. 6 (b). Because the optical system is out of focus, it is detected as a signal with a gradual and small level difference. Here, 0, p, and q indicate detection signals in a state where there is almost no phase shift when a phase shift occurs in the scanning direction, when a phase shift occurs in the reverse scanning direction, and when there is almost no phase shift.

The test signal shown in Figure 6 (b) and Figure 6 (a)
By calculating the difference between the reference signal shown in Figure 6(c) and adding the values for 5 images, it is possible to extract the abnormal signal with a large level difference in the area where the printing abnormality occurs, as shown in Fig. 6 (c), and the tolerance range S can be extracted. It is possible to determine whether or not a printing abnormality has occurred with sufficient accuracy.

In other words, an abnormal signal that did not exist in the reference signal is detected as a signal with a gradual and small level difference depending on the optical quantity, but the signal after the difference calculation is composed of components in the same direction. There is no difference. (As a result, by adding multiple pictures in chronological order, it becomes possible to compensate for the deficiencies caused by controlling the focus of the optical system.

In addition, the number of additional sheets of the above-mentioned chronological pattern is 4 to 4, taking into account the nature of continuous occurrence of printing failures and the characteristics of phase shift.
It is preferable to set the number to about 10, and after addition, a comparison is made with the allowable range S, and the addition result is refreshed each time.

In addition, in order to dull the detection signal, an optical quantity phenomenon was used, but there are other methods that can be considered, such as using an electrical method. If no processing is performed, it is difficult to obtain a signal in only one direction (XO-Y), which has the drawback of complicating the configuration, so it is preferable to use an optical system as in the present invention.

In addition to the difference calculation in the above-mentioned processing, the signal after the difference calculation and the signal after this difference calculation are delayed by several pixels, as seen in the "Inspection method for printed matter" in Japanese Patent Application No. 58-172778. It is also possible to perform further differential processing (so-called second-order difference) between the added signal and the added signal before the addition calculation.

Next, an example of a processing circuit for realizing the printed matter inspection method of the present invention will be explained based on FIG.

Here, an optical quantity is used to dull the input signal, and an optical system (not shown) is adjusted and held in an out-of-focus state.

A detection unit (4) using a CCD line sensor etc. detects the information of the picture printed on the printing paper at the sampling timing calculated by the sampling control circuit f15 based on the pulses generated by the rotary encoder 5). Depending on the signal, the input car is conducted.

Since the input image signal IS is an analog signal, A
/D converter (force). When the printing operator presses the instruction button from the operation stand to set the current printed matter as a reference, the digitized input signal is converted into a digital signal through the reference memory (8 ), and is used repeatedly as a reference signal when testing is started.

When the test starts, the input signal is sent to the A/D converter (
7) and is directly transferred to the differential circuit (9). At this moment,
The memory control circuit (14) addresses the reference memory (8) while specifying the address of the reference memory (8).
) is read out and transferred to the differential circuit (9) at the same time as the input signal, the differential circuit (9) outputs 1
A difference signal D S /l'' between the test signal and the reference signal 1 is output.

Now, let's compare the reference signal and the test signal.

The method is not limited to only the difference method, and the above-mentioned second-order difference method may also be used.
The circuit configuration proposed in No. 778 can be applied, and other circuit configurations that can obtain similar results may also be used.

Subsequently, the difference signal DS is stored in the addition memo IJ-(10) and simultaneously stored in the addition memo IJ-(16) by the addition circuit (16).
The value in 10) is added and transferred to the comparator circuit 01), where it is checked by the CPU (12) whether it exceeds the specified tolerance range. When testing the first picture, the value of the addition memory (10) is 0. If an abnormality is found in the first pattern, the comparison circuit (error signal ES!1'' from 1υ; transferred to CPU (121, means for eliminating alarms, markings, rejects, etc. 03) is used to deal with defective printed matter. can do.

Here, if no abnormality is found in the first pattern, the difference signal of the first pattern stored at the same address by the memory control circuit circle is called from the addition memory 〇〇) for the difference signal of the next pattern. , both are added in the adder circuit (16), and the result is sent to the comparator circuit (16).
1), and the same inspection as above is performed. Further, this addition result is stored in the addition memo IJ-(10). Thereafter, after the addition, storage and inspection are repeated up to a predetermined number of symbols, the contents of the addition memo IJ-(10) are refreshed and the above process is repeated.

Here, these additions, recordings, and erasures are controlled by the memory control circuit a (a) 2, and the addition of patterns is controlled by the memory control circuit a (a).
P U (+2 allows memory control circuit (14
1 can be instructed.

Note that the processing circuit shown in FIG. 7 is an embodiment for realizing the method of the present invention, and there is no problem in using other circuit configurations or software processing.

As described above, according to the printed matter inspection method according to the present invention, the low density of the pattern is determined by using the optical quantity phenomenon. It is possible to remove false abnormal signals caused by phase shifts at the boundary with the high 1 density, and also to add up the difference signals for multiple consecutive pictures and check whether the results are within the allowable range. Since the configuration is configured to determine whether or not the printing is negative, all printing abnormalities including printing abnormalities that appear as signals with a large level difference in a small area can be reliably detected even in a state where a phase shift exists.

[Brief explanation of the drawing]

The drawings show one embodiment of the present invention, and FIG. 1 is a schematic diagram of a printed matter inspection apparatus to which the present invention is applied, and FIG. A model diagram of the false abnormal signal that is emitted. Figure 5 is a model diagram showing the relaxation of phase shift by using optical quantities. Figure 4 shows the influence of optical quantities on small-area defects. Model diagram: Figure 5 is a model diagram showing the effect of mitigating the occurrence of abnormal signals due to phase shift by using addition memory, and Figure 6 is a model diagram showing the effect of mitigating the occurrence of abnormal signals caused by phase shift by using addition memory. FIG. 7 is a block diagram showing an embodiment of a processing circuit for carrying out the print inspection method of the present invention.

Claims (1)

[Claims] (1) A method for inspecting abnormalities occurring in printed matter by capturing picture information of a printed matter pixel by pixel and comparing an inspection signal based on the detected picture information for each pixel with a reference signal for each corresponding pixel, Adjusting an optical system constituting the detection unit so that the test signal and the reference signal can be detected as dull signals, and performing a difference calculation with at least the reference signal on the test signal captured via the optical system, A method for inspecting printed matter, characterized in that the calculation results are added for each corresponding pixel of a plurality of consecutive printed materials, and it is determined whether or not this added signal is within a predetermined tolerance range.