JPH0367505B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a printed matter inspection method 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. However, these methods were not systems that could be called inspection machines in that they relied on human vision for inspection. Attempts have also been made to print a color patch at the same time as the pattern on the printed matter and inspect the color patch, 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 drips, stains, etc.) occur in the pattern area, they will be overlooked, and the inspection machine cannot be said to be functioning satisfactorily.

On the other hand, recently, patent application No. 1051 of 1982 or
As seen in ``Print Inspection Apparatus'' published in No. 220515, a system has been proposed in which printed matter is inspected in-line using a line sensor. By using this method, the pattern itself of the 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, there is a growing demand for not only detecting printing failures but also automatically analyzing the causes of printing failures. In other words, even if you respond to defective printed matter detected by an inspection machine by using alarms, markings, or rejects, it is possible to process the defective printed matter from discovery to removal, but the cause of the printing failure cannot be quickly discovered. Otherwise, it will take time to remove the cause of the printing failure, and there is a risk that a large number of defective copies will be produced. Therefore, there is a need for a function that can classify and display to the operator the type of printing failure that has occurred. When such a function works effectively, the operator can quickly eliminate the cause of printing failure, and the amount of paper waste is reduced.

Therefore, an object of the present invention is to provide a printed matter inspection method that makes it possible to determine the types of printing defects (ink stains, water drips, oil drips, scratches, etc.) that occur on printed matter. be.

The present invention will be explained in detail below with reference to the drawings.

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 even if it is a sheet-fed printing press.

In FIG. 1, a strip-shaped printing paper 3 fed from a roll-shaped paper roll 2 is sent to the printing section 1 in four colors (black, black,
After each color (indigo, red, and yellow) is printed, the paper is transported to a dryer and a folding machine (not shown). The printed matter inspection device inspects the printing condition after the front and back sides have been printed in four colors, so the rotary encoder 5 installed in the printing section measures the sampling timing, and the image information is sent from a licensor such as a CCD in the detection section 4. Each divided pixel is input to the processing circuit 6 and a judgment operation is performed. 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.

Furthermore, in the present invention, by performing the following processing on the detection signal from the detection unit 4, it is possible to automatically analyze the cause of printing failures,
For example, a display function is added to display oil drips, water drips, ink stains, scratches, etc. Here, we will explain the classification of oil drips, water drips, ink stains, and scratches, and will omit explanations of other factors.

Figure 2 shows the reference signal when each printing failure occurs.
A model diagram of the BS (indicated by a solid line) and the detection signal DS (indicated by a dashed-dotted line) is shown. As shown in FIG. 2A, water dripping and oil dripping have the characteristic of causing printing failure over a wide area and reducing the density. In addition, as shown in Figure 2B, ink stains
It is understood that sheep have the characteristic of increasing the concentration over a wide range, and as shown in Figure 2 (c), sheep have the characteristic of causing multiple failures from small areas, which can cause both concentration increases and concentration decreases.

It is the task of the present invention to accurately detect and classify these printing faults. For this reason, the present invention first extracts a signal whose level changes only in the abnormality part of the printed matter by performing a difference between the detection signal and the reference signal, and second, the level change of the difference signal obtained as a result of the difference. Detection of the rise and fall of the part, for example, differential processing is performed. Printing failures can be classified based on the signals obtained as a result.

FIG. 3 is a model diagram showing the state of the signal DIS after performing the difference between the detection signal and the reference signal described above.

Figure 3 A, B, and C correspond to Figure 2 A, B, and C, respectively, and correspond to water drips, oil drips, ink stains, and scratches. As is clear from FIG. 3, by such differential processing, it is possible to obtain a signal in which a sudden signal change is observed only in the portion where the printing failure has occurred.

Further, FIG. 4 shows a signal obtained by performing differential processing, for example, in a differentiating circuit on the signal after differential processing as described above. Note that the dotted line indicates the threshold level. According to FIG. 4, each signal waveform has characteristics unique to the cause of the occurrence, with respect to the threshold level provided for detecting the occurrence of each printing failure. That is, as shown in FIG. 4A, for water dripping and oil dripping, after a pulse exceeding the lower threshold level is generated, a pulse appears at the upper threshold level after a certain time delay. As shown in FIG. 4B, in the case of ink contamination, on the contrary, a pulse is generated at the upper threshold and then a pulse is generated at the lower threshold. Furthermore, in the case of a hitch, as shown in FIG. 4A, pulse generation can be observed on the opposite side with almost no time delay after pulse generation at either the upper or lower threshold. This is because while the image information captured by the line sensor of the detection unit 4 is 1 to 2 m/mφ per pixel, the size of the hit is about 1 to 4 m/mφ, and no time delay phenomenon occurs. by.

Therefore, the first pulse that appears for one printing fault crosses either the upper or lower threshold, i.e. the rising, falling sequence, and the two rising, falling pulses that appear for one printing fault. It becomes possible to determine the type of printing failure from the two pieces of time data.

Note that the detection of rising and falling edges of printing faults by the differential processing described above is not limited to literal differential processing, and may be performed using other processing methods that can achieve the same purpose, such as differential processing. It is also possible to use a method of detecting rising and falling edges by differentiating a signal obtained by delaying the post-detection signal by several pixels and a detection signal that is not subjected to delay processing.

Furthermore, although this deviates from the spirit of the present invention, it is possible to pass the input image information through R (red), G (green), and B (blue violet) filters as three-branch signals, and determine whether any signal is abnormal. By classifying whether the problem occurred, it is possible to determine whether the problem occurred with yellow, red, indigo, or black ink. In other words, if an abnormality occurs in the signal that has passed through the R filter, it will be indigo ink, if the signal has gone through the G filter, it will be red ink, if the signal has gone through the B filter, it will be yellow ink, and if it occurs in all the R, G, and B signals, it will be black ink. This is how it is determined.

As described above, by separating into three signals of RGB, it becomes possible to classify each ink by color.

Next, one embodiment of the method of the present invention will be explained based on the block diagram of FIG. Although FIG. 5 shows a block diagram of a processing circuit that can implement the method of the present invention, the present invention is not limited to this embodiment, and the circuit configuration may be modified within the scope of the spirit of the present invention. It is possible to change the information or process it using software.

As shown in FIG. 1, a timing control section 17 controls a memory control section 16 and a sampling control section 18 based on a timing pulse TMP generated by a rotary encoder 5 attached to the printing section. The memory control unit 16 receives the signal from the timing control unit 17 and the mode switching signal from the CPU 14.
Reference signal SSS to reference memory 8 according to MSS
and controls the differential circuit 9 (reference signal import mode and inspection mode). The sampling control unit 18 uses a transfer clock to provide a sampling start signal to the CCD line sensor of the detection unit 4. Timing and switching are controlled by the above circuit.

Next, the inspection signal SIS input from the CCD line sensor of the detection section 4 is converted into a digital signal via the A/D converter 7, and then stored in the reference memory 8 in the reference signal import mode. On the other hand, in the test mode, the digitized test signal SIS is directly transferred to the difference circuit 9. At this time, the reference signal SSS is read out based on the control signal from the memory control section and simultaneously transferred to the difference circuit 9. The test signal SIS at this time is used as the reference signal.
The relationship of SSS is as shown in FIG. 2, for example. As a result, a differential test signal DIS as shown in FIG. 3, which is the difference between the two signals, is obtained.

This differential test signal DIS is transferred to the differentiating circuit 10 and subjected to differential processing to become a differential test signal DDS. The differential test signal DDS has a good signal form as shown in the model diagram of FIG. 4, for example. This differential test signal DDS is branched into two and transferred to an upper limit threshold circuit 11 and a lower limit threshold circuit 12. Upper and lower threshold values are set in both threshold circuits based on a threshold setting signal SHC from the CPU 14. When a pulse exceeding this upper/lower limit threshold level is generated, a pulse signal indicating that the upper/lower limit has been exceeded is sent from the upper/lower threshold circuit 11 or the lower threshold/hold circuit 12 to the counter 13. The odd-numbered signal sent is used as a start signal, and the even-numbered signal sent is used as a stop/reset signal for counting.

The counter 13 outputs the abnormality detection signal IRS.
A distinction is made as to whether the pulse signal from the upper threshold threshold circuit 11 is used as the count start signal or the pulse signal from the lower threshold threshold circuit 12 is used as the count start signal, and the count amount is transferred to the CPU 14. . CPU14
Then, based on the abnormality detection signal IRS, it is determined whether the abnormality has occurred due to oil dripping, water dripping, ink stains, or scratches based on the following discrimination criteria. That is, the pulse signal from the lower limit threshold hold circuit 12 is used as the start signal,
Those that use the pulse signal from the upper limit threshold circuit 11 that is generated after a certain time delay as a stop/reset signal can be considered to be water dripping or oil dripping;
The lower limit threshold hold circuit 1 uses the pulse signal from 1 as a start signal and generates it after a certain time delay.
If the pulse signal from 2 is used as a stop/reset signal, it can be considered as ink stain.
Furthermore, a pulse signal from either the upper limit threshold hold circuit 11 or the lower limit threshold hold circuit 12 is used as a start signal, and immediately after that, a pulse signal from either the lower limit threshold hold circuit 12 or the upper limit threshold hold circuit 11 is generated. It can be determined that a signal that uses the pulse signal as a stop/reset signal is a hit.

Furthermore, the even-numbered pulse signals sent to the counter 13 from the upper threshold threshold circuit 11 and the lower threshold threshold circuit 12 are not treated as stop signals and reset signals as described above, but are made to act only as stop signals. If the reset signal is, for example, a pulse signal that is emitted by detecting the end of one picture, the cumulative amount of printing defects (cumulative count) such as water drips, oil drips, ink stains, and scratches on one picture can be used as the reset signal. If we adopt a method that determines a printing failure when the value of this cumulative amount exceeds a predetermined level, it is possible to detect small It is possible to appropriately deal with cases where the entire picture becomes defective due to the occurrence of many abnormalities.

Furthermore, the detection unit 4 divides the detection signal into three colors of circles R, G, and B, and passes each through the processing circuit as described above.
If the abnormality occurrence signal IRS is input to the CPU 14 separately, it can be determined whether the abnormality has occurred in black, indigo, red, or yellow ink.

As a result, the CPU 14 can display to the printing press operator the presence or absence of a printing failure, the cause of the occurrence, and the color of the ink that has occurred on the display circuit 15, and the operator can quickly remove the printing failure by following the instructions on the display circuit. , printing paper loss can be minimized.

As detailed above, according to the present invention, it is possible to not only detect whether or not a printing fault has occurred in a printed matter, but also to determine the type of printing fault, that is, whether the detected printing fault is ink stain. This makes it possible to determine whether it is oil dripping or water dripping, etc., and can quickly discover the cause of printing failures.
This allows for smooth removal of the cause of the occurrence and enables more efficient printing work.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram showing the schematic configuration of a printed matter inspection device, FIG. 2 is a signal model diagram of a printing failure, FIG. 3 is a signal model diagram after differential processing, and FIG. 4 is a signal model diagram after differential processing. FIG. 5 shows a block diagram of a processing circuit according to one embodiment of the present invention. 4...Detection section, 8...Reference memory, 6...Rotary encoder, 9...Differential circuit, 10...Differential circuit, 14...CPU.

Claims (1)

[Claims] 1. In a method for inspecting abnormalities occurring in printed matter by comparing a detection signal obtained by optically scanning a traveling printed matter with a reference signal, the printed matter is detected by calculating a difference between the detection signal and the reference signal. Extract the signal whose level changes only in the abnormality occurrence part, detect the rise and fall of the level change part of the signal obtained by difference calculation, and determine the order of occurrence of the rise and fall of the level change part, and the rise and fall of the level change part. A printed matter inspection method characterized by determining the type of printing failure based on the time between falling edges.