JPH0422143B2 - - Google Patents

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a printing quality inspection device for in-line inspecting the quality of printed matter being printed in a web printing press, and in particular, to detect synchronization failures during the inspection. The present invention relates to a print quality inspection device that performs correction.

[Conventional technology]

Conventionally, printing defects on printed matter (oil stains, reverse printing,
Scratches, scratches, doubles, uneven density, misregistration,
Inspections for the presence of defects (poor color tone, wrinkles, etc.) were mainly carried out by operators through sampling inspections. However, such sampling inspections are off-line and cannot inspect all printed matter, resulting in printing defects being overlooked. Therefore, in order to objectively evaluate the quality of all printed matter being printed, we use strobe lighting that synchronizes with the printing speed and use mirrors that rotate synchronously at high speed to capture printed matter while it is being printed as a still image. Attempts are being made to evaluate. However, even in this method, quality inspection depends on the operator's judgment. This was because it was believed that the problem was that each printed matter had a different pattern, and the inspection items for printed matter had subtle differences that required relying on human vision.

Furthermore, attempts have been made to print color patches at the same time as the patterns on printed matter and automate the inspection of the color patches, thereby allowing the inspection of the printed matter to be done for them. However, with this method, if printing defects (oil drips, stains, etc.) occur in the pattern area, they will be overlooked, and it could not be said that the inspection device functioned satisfactorily.

In recent years, a system for inspecting printed matter using a line sensor has been proposed, as seen in the "Printed Material Inspection Apparatus" described in Japanese Patent Application No. 57-220515. This system samples the pattern on the web during printing at predetermined intervals, inputs the pattern as a gray level signal for each line, and compares this with a reference signal for each line of the pattern to detect defects in printed matter. inspect. This sampling/inspection timing is controlled by signals from a rotary encoder attached to one of the rollers in the printing press. In this way, since the pattern itself of the printed matter can be automatically inspected in-line, the above-mentioned drawbacks are eliminated, and this system is excellent as an inspection device. by the way,
Printing machines are classified into sheet-fed printing machines, which use cut sheets of paper one by one, and web-fed printing machines, which use paper webs wound around a winding shaft. The latter are commonly known as rotary printing presses. When the above-mentioned system is applied to this rotary printing press, the accuracy of synchronization between the sampling timing for inputting the pattern of the printed material as a grayscale signal for each line and the running speed of the printed material becomes important. In this conventional example, the position of the rotary encoder that takes the sampling timing and the position of the line sensor that samples the pattern information are different, so it is difficult to sample the pattern information of each line accurately and in synchronization from the printed matter that is running at high speed. It is difficult.

In order to solve this problem, we applied for patent application No. 58-172777.
No. (Japanese Patent Application Laid-open No. 60-63168) proposes a method for correcting synchronization failure in an offset printing press using web paper. In this method, the amount of synchronization deviation is averaged over a plurality of pictures, and this is fed back to correct the sampling timing. Here, a rotary encoder for synchronization detection is attached to the impression cylinder. However, even with this method, highly accurate synchronization cannot be obtained and the circuit configuration is complicated.

[Problem that the invention seeks to solve]

The present invention has been made in order to cope with the above-mentioned circumstances, and its object is to provide a printing quality inspection device that is used in a winding printing press and is capable of accurately inspecting the quality of printed matter in synchronization with the running of the printed matter with a simple configuration. purpose.

[Means for solving problems]

The printing quality inspection device according to the present invention is a means for detecting the time difference between a timing pulse synchronized with the running of the web and a start pulse generated in accordance with the print start position of each pattern on the running web. and means for generating a sampling pulse by delaying the timing pulse according to the time difference.

[Effect]

According to this invention, the synchronization deviation time of the timing pulse synchronized with the running of the web is detected, and the timing pulse is delayed accordingly to generate the sampling pulse, so that the timing pulse is synchronized with the running of the printed material with high precision. quality inspection.

〔Example〕

An embodiment of the printing quality inspection apparatus according to the present invention will be described below with reference to the drawings. FIG. 1 is a schematic diagram showing the entire first embodiment. Here, an embodiment adapted to an offset rotary printing press will be described. A roll of paper 10 serves as a printing unit 1.
2, and each color of ink, indigo, red, and yellow is printed in sequence. The printing unit 12 is subdivided into printing units for each color, and each printing unit consists of a plate cylinder 14, a blanket cylinder 16, 18, and a plate cylinder 20, between which the web 10 is fed. and both sides of the paper are printed at the same time. The web 10 sent out from the printing unit 12 is discharged via a dryer 30, a cooling section 32, a web path 34, and a folding device 36.

A detour 38 is formed in a part of the web path 34, a free guide roller (hereinafter referred to as a free roller) 40 is provided in the detour 38, and the web 10 is wound so as to embrace the free roller 40. . A rotary encoder 42 is attached coaxially with the free roller 40. The rotary encoder 42 generates a large number (1500 as an example) of pulse signals each time the free roller 40 rotates.
This pulse signal is supplied to the printing defect detection circuit 44 as a timing pulse. Here, the angle φ at which the web 10 embraces the free roller 40 (the angle at which the web 10 is in contact with the free roller 40)
is set at 90° or more. It has been found through experiments by the inventor that if this hugging angle is 90 degrees or more, the slip between the free roller 40 and the web 10 becomes negligibly small, and this is the state in which synchronization is most easily achieved. . As an example, FIG. 2 shows the results of an experiment on the amount of synchronization deviation on a free roller. Here, the length of one period of the pattern is 625
In the case of mm, the amount of synchronization deviation is 0.4 from peak to peak value
It can be seen that the synchronization is approximately 0.6 mm, and the synchronization is significantly improved compared to the amount of synchronization deviation in Japanese Patent Application No. 172777/1983.

Illumination light from the light source 46 is transmitted to the optical fiber array 48
irradiated through. A xenon lamp is used as the light source 46. Optical fiber array 48
converts the illumination light into a band-shaped light beam along the horizontal direction of the printed matter.

As shown in FIG. 3, the pattern 56 of the printed material on the paper roll 10 is read by the line sensor 50 line by line in the horizontal direction of the printed material, and is input to the printing defect detection circuit 44 as an image signal according to the density level. Ru. The line sensor 50 uses a charge coupled device (CCD) as a light receiving element. line sensor 5
A reflective beam sensor 52 is also provided near zero. The beam sensor 52 detects a start mark 58 printed at the printing start position of each pattern 56 that is continuously printed on the paper roll 10.
The printing position of the start mark 58 is in the side edge margin of the pattern 56, and is slightly upstream or at the same position as the upper side 60 of each pattern 56 in the conveying direction A of the printed material. The detection signal of the beam sensor 52 is sent to the printing defect detection circuit 44 as a start mark signal.
is input.

FIG. 4 is a detailed circuit diagram of the printing defect detection circuit 44. The gray level signal from the line camera 50 is A/
The memory 66 is sent to the memory 66 at predetermined intervals via the D conversion circuit 64.
is supplied to As a result, the pattern of the printed material is read line by line in the left and right direction of the printed material. memory 6
6 has a capacity to store shading data of one picture. When the printing condition becomes stable, the contents of the memory 66 are written into the memory 68 as reference value data. Start mark signal from beam sensor 52
A timing pulse REP from the SMC and rotary encoder 42 is supplied to a synchronization correction circuit 70.
The sampling pulse SCP output from the synchronization correction circuit 70 is supplied to the A/D conversion circuit 64 and also to the address controller 72. Address controller 72 provides address signals to memories 66 and 68. The A/D conversion circuit 64 samples the input signal at a timing corresponding to this sampling pulse SCP and performs A/D conversion. Data at the same address in memories 66 and 68 are compared/
A determination circuit 74 compares the two and calculates the difference between the two, thereby detecting the presence or absence of a printing defect. Comparison/
A defect display section 76 is connected to the determination circuit 74 .
The defect display unit 76 is composed of a CRT monitor, and normally displays a grayscale image of the printed matter taken by the line sensor 50. When a printing defect is detected, a predetermined mark is placed on the grayscale image of the printed matter corresponding to the detected position. , for example, display "+" marks overlapping each other.

Next, the synchronization correction circuit 70 will be explained. Here, the circumferential length of the plate cylinder 20 and the circumferential length of the free roller 40 do not match. Furthermore, the ratio between the two is not an integral multiple. Therefore, there is a lag time Δt between the start pulse STP generated by detecting the rise of the start mark signal SMC from the beam sensor 52 and the timing pulse REP output from the rotary encoder 42, as shown in FIG. exists, and this lag time Δt is 0 to t (timing pulse
It changes periodically during one cycle of REP. Therefore, if the timing pulse REP from the rotary encoder 42 is used as it is as a sampling pulse for the A/D conversion circuit 64, as described above, the grayscale data of the picture to be compared with the data in the reference value memory 68 will be one line at most. This will result in misalignment, making accurate inspection impossible.

As a way to deal with this, the first possible method is to increase the frequency of the timing pulse REP from the rotary encoder 42 and shorten its period, as shown in FIG. In this case, the actual sampling pulse SCP is this timing pulse
Divide REP by a counter (divided by 4 in this example)
It is created by According to this method, the maximum value of the shift time Δt can be reduced to the equivalent of 1/n lines (n is the number of counts). Here, in order to increase the effect, n must be increased, but in order to increase n, it is necessary to increase the response frequency of the rotary encoder 42. For example, set the line spacing to 1
mm, printing speed (traveling speed of printed matter) 9m/sec,
If the count value is 32, rotary encoder 4
The response frequency of 2 is as high as 288kHz. At present, the response frequency of the rotary encoder 42 is 50 to 200 kHz, and it is impossible to improve the accuracy of synchronization using only this method.

Therefore, in this invention, as shown in FIG.
Start pulse STP to timing pulse REP
Since the running speed of the printed material is constant during printing, the timing pulse
By delaying the timing pulse REP by the time (t - Δt) obtained by subtracting this time difference Δt from the REP period t (constant value) and generating the sampling pulse SC, the interval from the start pulse STP to the sampling pulse SC is always maintained. can be set to t (certain time).

FIG. 8 is a detailed circuit diagram of a synchronization correction circuit 70 that corrects sampling timing based on such a principle. A start mark signal SMC from the beam sensor 52 is supplied to a count start terminal of a counter 82 via a differentiating circuit 80. Differentiating circuit 80 detects the rise of start mark signal SMC and generates start pulse STP. A timing pulse REP from the rotary encoder 42 is supplied to a count stop terminal of the counter 82 . The counter 82 starts counting the clock pulse CLK when a pulse is supplied to its count start terminal, and stops counting when a pulse is supplied to its count stop terminal. Therefore, the counter 82 measures the time difference Δt between the start pulse STP and the timing pulse REP.
The count value Δt of the counter 82 is set to the latch circuit 84.
is supplied to The output of latch circuit 84 is applied to a first input of difference circuit 86.

Timing pulse REP from rotary encoder 42 is input to flip-flop 88, and flip-flop 88 is set and reset by the timing pulse. A set output and a reset output of the flip-flop 88 are supplied to a count start terminal and a count stop terminal of a counter 90, respectively. Therefore, the counter 90 measures one cycle time t of the timing pulse REP.
The count value t of the counter 90 is supplied to a latch circuit 92. The output of the latch circuit 92 is the differential circuit 8
6 is supplied to the second input terminal.

The difference circuit 86 subtracts the first input signal Δt from the second input signal t. The output signal t- of the differential circuit 86
Δt is supplied to latch circuit 94. A timing pulse REP from the rotary encoder 42 is supplied to a count start terminal of a presettable counter 98. A t-Δt signal is supplied from the latch circuit 94 to a preset terminal of the presettable counter 98. Therefore, the presettable counter 98 delays the timing pulse REP by t-Δt. In this way, the synchronization correction circuit shown in FIG. 8 corrects the sampling timing as shown in FIG. Therefore, according to the first embodiment, even if the circumferential length of the plate cylinder 20 and the circumferential length of the free roller 40 do not match, the quality can be inspected with a simple configuration and accurately in synchronization with the running of the printed matter. A quality inspection device is realized.

This invention is not limited to the above-described embodiments and can be modified in various ways. For example, the timing pulse in Figure 8 is a pulse with the same period as the sampling pulse, but as explained in Figure 6, the response frequency of the rotary encoder is set to a higher frequency than the sampling frequency, and the output pulse of the rotary encoder is frequency-divided. The signal may be a timing pulse as shown in FIG. In this case, there is an advantage that the waiting time from when the start pulse is output to when the first sampling pulse is output is shortened. Furthermore, the circuit shown in FIG. 8 may be realized by a microcomputer.

〔Effect of the invention〕

As described above, according to the present invention, there is provided a printing quality inspection device for a web printing press that has a simple configuration and is capable of accurately inspecting quality in synchronization with the running of printed matter.

[Brief explanation of drawings]

Fig. 1 is a schematic diagram of a first embodiment of the printing quality inspection device according to the present invention, Fig. 2 is a characteristic diagram showing the amount of synchronization deviation in the first embodiment, and Fig. 3 is a line sensor and beam of the first embodiment. Diagram explaining the sensor, 4th
The figure is a circuit diagram of the printing defect detection circuit of the first embodiment, FIG. 5 is a timing chart explaining that synchronization deviation occurs when detecting printing defects, and FIG. 6 is a timing chart showing an example of correcting the synchronization deviation. , FIG. 7 is a timing chart showing the principle of correcting synchronization deviation according to the first embodiment, and FIG. 8 is a circuit diagram of the synchronization correction circuit according to the first embodiment. 40...Free roller, 42...Rotary encoder, 50...Line sensor, 52...Beam sensor, 64...A/D conversion circuit, 74...Comparison/judgment circuit, 80...Differential circuit, 86... Differential circuit, 98...presettable counter.

Claims (1)

[Claims] 1. In a printing quality inspection device used in a web printing machine that continuously prints a plurality of patterns on a web, a timing pulse is generated at a constant period according to the running of the web. A pulse generating means, a means for detecting the printing start position of each pattern on the running paper roll and generating a start pulse, and a time difference between the start pulse and the first timing pulse after the start pulse is generated. means for detecting; means for inputting the timing pulse and outputting the timing pulse after the lapse of the lag time to generate a sampling pulse with a period proportional to the period of the delayed timing pulse; What is claimed is: 1. A printing quality inspection device comprising: means for sampling shading information of each pattern on a web of paper that is running; and means for performing arithmetic processing on the sampling data obtained by the sampling means to detect printing defects. 2. A patent characterized in that the pulse generating means is attached to a free roller provided in the traveling path of the web, and the sampling means samples the shading information of each pattern of the web on the free roller. A printing quality inspection device according to claim 1. 3. The printing quality inspection device according to claim 2, wherein the paper roll is wound around the free roller at an angle of 90 degrees or more. 4. The pulse generating means includes a rotary encoder coaxially attached to a free roller provided in the running path of the web, and a frequency divider that divides the output pulse signal of the rotary encoder to generate a timing pulse. The printing quality inspection device according to claim 1, characterized in that: