JPH0573585B2 - - Google Patents

Description

[Detailed description of the invention]

(Technical Field of the Invention) This invention automatically eliminates defects such as ink scattering, doctor streaks, and dust when patterns are periodically and continuously printed on packaging materials such as paper, aluminum, and plastic. This invention relates to a method that enables detection even when printing is in progress. (Technical background of the invention and its problems) Generally, it is difficult to detect defects that appear in spots when printing a pattern or the like. For this reason, the device must be stopped at the beginning or end of winding.
Only a limited number of visual inspections have been carried out. However, since it is not a 100% inspection, sometimes defective products may be mixed in, which often causes problems. In order to solve this problem, recently a pair of patterns N1 and N2 (in this case, not necessarily adjacent patterns) on a sheet N printed with the same continuous pattern as shown in Fig. An apparatus has been proposed in which a control box 14 calculates the difference between the output voltages of a pair of photosensor heads A and B after photometry is carried out by sensor heads A and B at the same time and photoelectric conversion is performed, thereby determining defects on a pattern. A concrete example of this will be explained with reference to FIG.
As shown in the figure, the reflected light from the patterns N1 and N2 is
After being input to optical sensor elements 16A and 16C through light receiving elements 15A and 15B such as optical fibers and converted into voltage, the gain is appropriately adjusted by amplifiers 16B and 16D, and the output voltage is input to differential amplifier 17. . Here, the light receiving element 15
Since A and 15B are located on the same patterns N1 and N2, if the patterns are normal, their reflected lights should be equal and the output of the differential amplifier 17 should be zero. However, it is physically impossible for them to be exactly equal, so we set the amount in advance within the allowable range, and here we set this value as the upper limit.
dmax and the lower limit is set as dmin, and input to the comparator 18 together with the output of the differential amplifier 17. If ink is scattered on one of the patterns and this exceeds the set tolerance range, the output of the comparator 18 will be "NO" and, for example, will output a "1" signal to indicate an error. If it is within the range of the upper and lower limits, it will be a "GO" of a good product and a "0" signal will be output. In this way, a method for determining defects in printed matter, etc. is realized. However, the method described above requires that the optical sensing conditions of the pair of optical sensor heads remain constant. For this reason, various preparation work is required, such as selecting optical sensor elements to match their characteristics when manufacturing the device, using a differential amplifier with good output characteristics, and preventing deterioration of the optical sensor element due to aging and damage to the sensor head during detection operation. It is necessary to manually correct for characteristic mismatches due to dirt, differential amplifier drift, etc. in advance. This is complicated and requires skill, and in order to reduce this, it is necessary to sacrifice detection accuracy and expand the dead band width, which is the allowable range of the upper limit dmax and lower limit dmin. . Therefore, the stability caused by using a pair of optical sensor heads can be eliminated, and the optical sensing conditions mentioned above during manufacturing and operation can be automatically kept constant, and furthermore, compared to a pair of optical sensor heads, There has been a demand for the development of a method for detecting defects in printed matter using a single optical sensor head that can be constructed at low cost. (Object of the invention) This invention was made in view of the above-mentioned circumstances, and an object of the invention is to automatically adjust the optical detection conditions even if there is a discrepancy in the detection characteristics due to drift or changes over time. It is an object of the present invention to provide a method for detecting defects in printed matter using a single optical sensor head that compensates for and keeps the defects constant. (Summary of the Invention) The present invention relates to a method for detecting defects in printed matter in which the same pattern is periodically and continuously printed. In a method for detecting defects in printed matter, a single optical sensor head is used facing a pair of patterns, and pulses are output from a pulse generator connected to the drive section of the plate cylinder. The difference in the output voltage of each analog signal between one pattern obtained from the optical sensor head and the next pattern that is shifted by one period is determined by one of the output voltages of the plate cylinder every time the pattern is transported one period. After processing the pulse corresponding to one rotation of the cylinder and its frequency divided pulse, and digitizing the output difference of the analog signal, the digital signal of one picture conveyed earlier is converted into a digital signal for one cycle. The difference between the digital signal for one cycle of the next pattern and the stored digital signal is determined, and this difference is extracted in a continuous pattern corresponding to the pattern to be conveyed periodically, and is registered in advance. If it is determined to be a defect, the type of defect is identified by counting the number of the pulses or frequency-divided pulses at the defective location, and the sign determination is performed with respect to a certain pattern. , the ratio determination and the type of defect are displayed. (Embodiment of the Invention) FIG. 1 is a block diagram showing an example of a device for realizing the method of this invention, which is entirely computerized, and when a predetermined key on a keyboard 1 is operated, information based on a start signal SS1 is transferred to a CRT 2. At the same time, the signal SS2 is input to the main CPU 4.
As a result, the drive unit 6 consisting of a motor etc. is driven to wind up the sheet N on which the same continuous patterns N1, N2... are printed at a predetermined pitch, and the sheet N on which the patterns N1, N2... are printed is driven. is started. When the winding is completed by a predetermined amount, the scanning head 5 detects the register mark that instructs the start of detection, and outputs the register mark signal SS3.
A pulse generator 7 consisting of a pulse encoder etc. linked to the drive unit 6 generates pulses corresponding to one rotation of one cylinder of the plate cylinder connected to the drive unit 6 in correspondence with one period of the image, and The frequency-divided pulse signal SS5 is input to the main CPU 4 and is further stored in the storage section 3. On the other hand, the optical sensor A in the single optical sensor head facing the pattern N1
1 (optical sensors A1, A2, etc. depending on the size of the picture)
In order to detect whether the corresponding detection area within the pattern N1 is normal or not, the reflected light from the pattern is collected and photoelectrically converted into a voltage signal SS8. after that,
The analog signal SS9 is input to the amplifier 8, which is made up of an IC, etc., and the gain is properly adjusted.The A/D converter 9 converts the analog amount into a digital signal SS10, which is an equivalent digital amount, and is input to the local CPU 11. After internal processing,
The signal SS11 is output to the storage unit 10, and the processed signal SS12 is input to the main CPU 4, where it is collectively processed. In this case, the digital signal is stored for one cycle of one picture (one cylinder), and the difference between the digital signals delayed by one cycle of the next picture is always calculated, for example, picture N1 and picture N2 to be sent next. By taking the signal difference between the two and finally recognizing and processing the temporal pattern of this difference in the main CPU 4, it is possible to obtain pattern detection information (for example, how defective is the density and color of a certain area, etc.). can. In addition, a large number of optical sensors A1 to AN are grouped together in a single optical sensor head A according to the size of the pattern N1, and the pattern N of these printed matter
The detection information for 1 and N2 is sent to local CPU 1.
After processing in step 1, the main CPU 4 performs overall processing, so that even if the output of the optical sensor head A fluctuates due to some reason during operation, this method can always be detected.
The system uses CRT2 to visualize the content and monitor it step by step. In such a configuration, its operation is shown in Figure 2~
This will be explained with reference to FIG. FIG. 2 is a flowchart showing an example of the operation, and FIG. 3 is a timing chart showing a situation in which a pattern is detected according to this flowchart. Before operation, a sheet N on which the same patterns N1, N2, N3, etc. are printed periodically as shown in FIG. It is placed in a state where it is transported by cylinder. In this state, first, by operating a predetermined key on the keyboard 1, the drive unit 6 is driven and the sheet N is wound up, and the patterns N1,
N2, N3, ... sequentially move in the S direction for one cycle of one pattern, and when the register mark instructing the start of detection is identified, pulses are counted, and the light is positioned on the first pattern N1 as shown in the figure. Sensor head A
Detection is started (step S1). In this case, the detection area of optical sensor head A is set to 1 of 1 pattern.
By using the optical sensors A1 to AN facing one picture so that the settings can be made in cycles, the output waveforms of adjacent pictures, for example N1 and N2, will also be out of phase by one cycle of one picture. become.
Therefore, if information about one pattern is always stored and this information is compared with other adjacent patterns, information on the differences between the two can be easily obtained (in this case, the speed of transport of the pattern and the sensor head As long as the synchronization with the output processing from A is maintained constant, the positional relationship of the pair of pictures to be compared does not necessarily have to be adjacent). The method of this invention focuses on this point. By the way, in general, if the pattern is good like pattern N1, a standard waveform such as A(t) between t0 and t1 in FIG. If there are spot defects a and b in some parts, compared to the good product, the bright part a will have a convex shape as shown in A(t) between t1 and t2 in the same figure B, and the dark part b will have a concave shape. (See Figure 3 A, B, and C). Hereinafter, an arbitrary i-th pattern Ni will be explained with reference to a mathematical formula. In this way, the i-th picture Ni is sent onto the optical sensor head A, and the reflected light is photoelectrically converted by a pair of optical sensors Ai, and the output waveform ai(t) between (ti-ti-1)
(Step S2, Figure 3B). Next 1
The pattern is divided into n parts (therefore, the size of one pulse is not a unit of time but a unit of length), and sampling is performed for each divided section (step S3), and the output is the analog quantity described above. The waveform is digitized (step S4), and the n of the i-th pattern Ni is
Digital quantity C=Cij as j division interval during division
(Pj) is determined (Step S5, Figure 3C). This is temporarily stored in the storage unit 10 in order to use it for the next calculation.
Write it to RAM and store it, and set it to D=-1, (Pj) (hereinafter, if it will be played back after being stored, mark it) (Steps S6 and S7, Fig. 3 D), then next step. When the sheet N is conveyed for one cycle of one picture and the next picture Ni+1 is placed on the optical sensor head A, the difference in digital amount C=Cij (Pj) is calculated in the same way as described above and stored in the storage unit 10. D (step) stored and played back
S8) and this stored value C are processed in the local CPU 11, and the difference C−D=dij(Pj)=Cij(Pj)−
(i-1)j(Pj) is obtained (step S9, FIG. 3E). Next, the upper limit of the allowable range for determining whether the pattern is normal is determined as the dead image upper limit dmax, and if E: eij (Pj) = | dij (Pj) | - dmax ≧ 0, continue processing, and if ≦ 0, continue processing. If so, the process returns to step S5 and -1 is set as dij (steps S10, S11, S12). After that, pattern N
The pulse numbers are determined by comparing the j-th pulse numbers to determine whether the results obtained by performing the same detection with the single optical sensor head A are the same. That is, if Pi=, the process is continued, and if Pj≠, it is assumed that a positional shift in detection has occurred, and the process is carried forward (step S13). In this way, in order to check whether the pattern Ni is a good product or how defective it is, sign determination and ratio determination are performed. In other words, if it is a defective product, the positive and negative signs are always output with the wrong signs, so for example, the pattern judgment shown in the table below is performed (step S14,
S15).

[Table] Here, patterns corresponding to various defects are registered in advance in the internal storage section of the main CPU 4, and it is determined which pattern corresponds to the defect (step S16). This makes it possible to identify what kind of defects exist in the pattern Ni. If not applicable, preparations are made to update the memory of the carryover portion (step S17). If applicable (step S18), parts that are unnecessary for the determination, such as the last 0 of the output pattern of a, -a, 0 in the sign determination in Table 1, are unnecessary for the determination, and are removed to avoid incorrect processing. is deleted to clear the RAM of the storage unit 10, and preparations are made to update the memory for the next pattern (Ni+1) (step S19). Next, in order to check whether the entire defect detection system is operating normally, after detecting a certain number of patterns N1 to Ni, the number of defects is detected. That is, the total amount Σ| of |ei|
Find ei | (step S20) and set the main
Comparison processing Σ|ei|-e with the total upper limit e registered and set in the internal storage of the CPU 4 is performed (step S21), and if Σ|ei|-e≧0, a defect has occurred. It is determined that this is not a printing error but is caused by a misalignment or meandering of the sheet N, and the machine is re-inspected (step S22).
Furthermore, if Σ|ei|-e<0, it is determined to be a normal printing error and is transmitted to the main CPU 4, and this information is displayed on the CRT 2 (step
S23). At the same time, it is determined whether the defects in the patterns N1, N2, etc. are within the acceptable range for the product, and whether they are major, medium, or minor defects; in other words, whether the defects are continuous or one-off. In order to do this, the above pattern is divided into n, and the defective parts are checked for the pulses in the adjacent sections centered around the j-divided section...Pj-1, Pj, Pj+1... (step
S24), if there is a defect, count the number of adjacent pulses (step S25), and if only Pj is counted due to a spot defect, such as dust, etc. (step S27), or if there is a narrow defect, e.g. Is this a case where Pj-1, Pj, Pj+1 are counted due to doctor's lines etc. (step S28), or is it a case where a wide area defect, for example, a stain of ink, etc., spreads over a wide area and...Pj-1, Pj, Pj+1... are connected? If a large number of defects are counted (step S29), it is determined to which type the defect belongs (step S29).
S26), the number of defects occurring in one period of the pattern is counted (steps 30, S31, S32), and the location and type of defects are displayed on the CRT 2 to notify defect information of the pattern (step S33). Furthermore, in order to detect the next pattern (Ni+1), a signal is sent to the main CPU 4 for general processing (step S34), and the drive unit 6 rotates by one cylinder. By the way, in parallel with this, the process after the above-mentioned memory update preparation (step S19) is 1.
This will be performed continuously for one cycle of the pattern, but if an error occurs during the process and processing is not possible, return to sampling division (step S3).
When the process is completed, the carried over/erased data of the pattern Ni is cleared from the RAM of the storage unit 3, and the process returns to register mark identification (step S1) to detect the next pattern (Ni+1), and the pattern Ni and The same processing will be performed. In this way, by repeatedly processing steps S1 to S36 in the flowchart of FIGS. 2A to C for all the patterns N1, N2, N3, . . . , NN,
That is, by sequentially storing one period of one pattern in the optical sensor head A and performing comparison/update processing, the patterns N1, N2,...NN consecutively printed on the sheet N are stored.
Defect information will be displayed on a CRT2 or the like. Now, in the case of the above-mentioned detection, the detection output of the optical sensor head A does not fluctuate, but the drift of the amplifier 8 or the optical sensor A1 to
Even if the detection characteristics change due to aging of the AN, by using the above method, the changes can be automatically corrected and accurate detection output can be obtained.
That is, FIG. 4 is a timing chart for explaining this situation. As shown in the figure, if the optical sensor head A is lifted by f relative to the reference amount, this can be calculated by performing calculations one after another. Since the deviation f is accumulated as an error and magnified, the conventional method causes overestimation. However, according to the method of the present invention, steps S9 (C-D) are performed according to the flowchart of FIG.
By performing the arithmetic processing, the deviation f due to the drift of the differential amplifier 8 or aging of the optical sensors A1 to AN is canceled out, and the pattern defects (a, b and b in Fig. 4E) are automatically corrected. c, etc.) will be extracted. That is, Optical sensor head A: Output waveform A(t)
...(Step S2) D:(t) ...(Step S8) C-D:(t)-A(t) ...(Step S9) Here, a deviation f occurs and A(t)→A(t )+f, A(t)→(t)+f, so C-D={A(t)+f}-{(t)+f}=A(t)-(
t) ... (Step S9) Therefore, even if the detection characteristics vary due to the deviation f due to any factor, it is canceled out in the arithmetic processing process, and only the defects a, b, c, etc. of the desired pattern are found. To explain this with reference to the timing chart in Figure 4, for example, between t1 and t2, the output waveform varies by A(t) + f for the shift f, and as shown in the figure, after A/D conversion, is digitized, and even if the deviation f changes as described above (Fig. 4 C, D),
In the arithmetic processing C-D (step S9), only the defect information of the same pattern as shown in FIG. 3E without the above-mentioned variation as shown in FIG. 4E is obtained. Therefore,
Even if there is a change in the detection characteristics due to the drift of the amplifier 8 or the aging of the optical sensor A1...AN during operation of the device, the method of the present invention automatically corrects it through internal processing, so it always remains the same. Accurate detection will be performed. By using a pair of photosensor heads A in both of the above two cases, even if noise components due to fluctuations etc. are mixed in during the calculation process, only the image defect information can be obtained in the end. Therefore, high accuracy can be achieved as a method for detecting defects in printed matter. (Effects of the Invention) As described above, according to the method of the present invention, in a method for detecting defects in printed matter in which the same pattern is periodically and continuously printed,
It has many advantages such as being inexpensive, requiring no maintenance during operation, automatically detecting the types of defects in printed matter with high accuracy, and visually displaying them in color.

[Brief explanation of the drawing]

Fig. 1 is a block diagram showing an example of an apparatus for realizing the method of this invention, Fig. 2 is a flowchart for explaining the method of this invention, and Figs. 3 and 4 are timing diagrams for explaining the method of this invention. The chart, FIGS. 5A and 5B, and FIG. 6 are diagrams for explaining a method for detecting defects in printed matter for detecting defects in printed matter when the same pattern is continuously printed. 1...Keyboard, 2...CRT, 3...Storage unit, 4...Main CPU, 5...Scanning head, 6...Drive unit, 7...Pulse generator, A
1, A2, ~AN... optical sensor, 8... amplifier,
9...A/D converter, 10...Storage unit, 11...
Local CPU, N1, N2, ~NN...Picture, N
...Sheet with a pattern printed on it, A... Optical sensor head, 14... Control box, 15A and 15B
...Photodetector, 16A and 16C...Photosensor element, 16B and 16D...Amplifier, 17...Differential amplifier, 18...Comparator.

Claims (1)

[Claims] 1. In a method for detecting defects in printed matter in which the same pattern is periodically and continuously printed, a single optical sensor head is used facing a pair of patterns to drive the plate cylinder. A pulse is output from a pulse generator connected to the optical sensor head, and the difference in output voltage of each analog signal between one picture obtained from the optical sensor head and a picture shifted by one cycle to be conveyed next is determined by the output voltage difference of each analog signal. Each time the pattern is conveyed one cycle, the pulse corresponding to one rotation of one cylinder of the plate cylinder and its frequency division pulse are processed, and the output difference of the analog signal is digitized, and then The digital signal of one carried picture is stored for one period, the difference between the digital signal of one cycle of the next picture and the stored digital signal is calculated, and this difference is applied to the periodically carried picture. Correspondingly, the pulses are continuously patterned and extracted, and the sign and ratio are determined with respect to the pre-registered pattern. If it is determined to be a defect, the number of the pulses or frequency-divided pulses at the defective location is counted. 1. A method for detecting defects in printed matter, characterized in that the type of defect is identified by displaying the sign determination, the ratio determination, and the type of defect.