JPS63111057A - Printing quality inspection device - Google Patents

Abstract

PURPOSE:To enable the quality inspection of a printed matter to be executed by controlling the meandering of printing paper precisely by a simple structure, by providing a means in which the meandering control signal of a web is emitted by operating a phase shift amount by sensing a web width direction edge position of a start mark in an image signal being inputted. CONSTITUTION:When the flow direction edge of a start mark 58 is sensed with a beam sensor 52, the beam sensor 52 supplies a start pulse to a printing defect sensing circuit 44. A line sensor 50 reads each pattern 56 at each line in the lateral direction of the printed matter and supplies it to the printing defect sensing circuit 44 as an image signal corresponding to a variable density level. The printing defect sensing circuit 44 senses a printing quality of each pattern by comparing an input image signal with a reference signal. At that time, signals from the line sensor 50 and the beam sensor 52 are also supplied to a controller 80, a control motor 82 is controlled and a pair of meandering control rollers 84, 86 are tilted.

Description

[Detailed Description of the Invention] [Industrial Application Field] This invention inputs the pattern of the printed material being printed on the rolling paper stamp 111 using a line sensor and compares it with a reference pattern signal to check the quality of the printed material. The present invention relates to a print quality inspection device that performs in-line inspection, and particularly relates to a print quality inspection device that corrects a phase shift of a picture signal in the scanning direction of a line sensor due to meandering of a web during inspection.

[Conventional technology]

Conventionally, printing defects in printed matter (oil stains, backing, rubbing,
Sampling inspections by operators have been the mainstream for inspections for the presence of defects (hits, doubles, density unevenness, misregistration, poor color tone, wrinkles, etc.). However, such sampling inspections are off-line and cannot inspect all printed matter, so printing defects may be overlooked. Therefore, in order to objectively evaluate the quality of all printed matter being printed, we use strobe lighting synchronized with the printing speed and use mirrors that rotate synchronously at high speed to evaluate the printed matter as a still image while it is being printed. Attempts are being made to do so. However, even in this method, quality inspection depends on the operator's judgment. This was because it was thought 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 the human visual angle.

In addition, attempts have been made to print color batches at the same time as the patterns on printed matter and automate the inspection of the color patches, thereby allowing printed matter to be inspected on behalf of the user. However, with this method, if a printing defect occurs in the pattern area, it will be overlooked, and it could not be said that the function of the inspection device is fully fulfilled.

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 filed by the present applicant. This system samples the pattern on the paper roll being printed at predetermined intervals, inputs the pattern as a shading signal for each line, inputs this as a shading signal for each line of the pattern, and inputs this as a shading signal for each line of the pattern. The printed product is inspected for defects by comparing it with a line-by-line reference signal. This sampling/inspection timing is controlled by signals from a rotary encoder attached to one of the rollers in the printing press. Since this system can automatically inspect the pattern itself of printed matter in-line, it does not have the above-mentioned drawbacks and is excellent as an inspection device.

By the way, printing machines are classified into sheet-fed printing machines that use cut sheets of paper one by one, and web printing machines that 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 start of sampling, which inputs the image of the printed material as an image signal for each line, uses the actual printed material image or the start mark printed at the same time, and starts sampling for each line. The sampling starts at the same position.

Furthermore, the sampling timing for each line is controlled by a signal from a rotary encoder. Ensuring the synchronization accuracy of this sampling timing leads to an improvement in the inspection accuracy of the inspection device. In other words, if the pixel-by-pixel image data obtained by inputting an image signal represents a pattern portion that differs from place to place on each image, inspection becomes impossible.

Here, regarding ensuring the synchronization accuracy of the sampling timing regarding the running direction of printed matter (hereinafter referred to as the flow direction),
This problem can be solved without any problems by utilizing the inventions of Japanese Patent Application No. 58-172777 and Japanese Patent Application No. 257797 filed by the applicant of the present application.

However, these inventions do not describe how to ensure synchronization accuracy in a direction perpendicular to the flow direction, that is, in the scanning direction of the line sensor (hereinafter referred to as the scanning direction).

The main cause of impeding synchronization accuracy in the scanning direction is meandering of the printing paper.

Regarding ensuring synchronization accuracy regarding the scanning direction, see Japanese Patent Application Laid-Open No. 59
There is an invention according to No.-40241. Here, a method has been proposed in which inspection is performed by shifting image data in the scanning direction pixel by pixel of a line sensor.

Generally, the field of view per pixel of a line sensor serving as an inspection source is often set to 1 to 211 m square. For this reason, the deviation of the image in the scanning direction due to the meandering of the printing paper is 1 to 2
This invention is effective when the thickness is equal to or larger than mm.

However, actual rotary printing presses are equipped with a control device to prevent paper meandering, and the amount of pattern deviation in the scanning direction is 0.4 to 0.5 in peak-to-peak value.
(2), which is very small, and the invention described above has no effect at all. This 0.4 to 0.5 mm deviation of the pattern in the scanning direction is not much of a problem when performing a rough inspection, but it is necessary to detect misregistration of 0.1 to 0.2 mm, doubles, etc. In order to perform highly accurate inspection, it is necessary to further improve the synchronization accuracy in the scanning direction.

[Problem that the invention seeks to solve]

This invention was made to deal with the above-mentioned circumstances,
In a print quality inspection device that is used in web printing presses and inspects the quality of printed matter by inputting each pattern of the printed matter line by line using a line sensor and comparing it with a reference image, when inputting the line sensor, The purpose is to accurately prevent phase shift in the scanning direction with a simple configuration.

[Means for solving problems]

The printing quality inspection device according to the present invention includes a means for detecting a running deviation of the web paper in the scanning direction based on an image signal from a start mark printed together with a pattern on the web paper, and a means for detecting a running deviation of the web paper in the scanning direction based on an image signal from a start mark printed together with a pattern on the web paper, and and means for controlling the meandering of the printing paper accordingly.

[Effect]

According to the print quality inspection device according to the present invention, the deviation of the pattern in the scanning direction of the printing paper is measured from the position of the actually printed pattern, and the meandering of the printing paper is controlled according to the deviation. quality inspection becomes possible.

〔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 entirety of one embodiment.

Here, an example adapted to a rotary offset printing press will be described. A roll of paper is fed into the paper feed unit 10.
The image is supplied to the printing unit 12, and patterns in each color of ink, indigo, red, and yellow are sequentially printed. The printing unit 12 is subdivided into printing units for each color, and each printing unit includes a plate cylinder 14, a blanket cylinder 16, 18, and a plate cylinder 20.
A web of paper is fed between the blanket cylinders 16, 18 and both sides of the paper are printed simultaneously. A first meandering control section 66 is provided between the paper feeding unit 10 and the printing unit 12.

Details of the first meandering control section 66 are shown in FIG. A pair of meandering control rollers 10.72 are arranged in parallel along the running direction of the web, and these meandering control roller pairs 70.72 are simultaneously tilted by a control motor 74 to adjust the running position of the web to the left and right. It is now possible to do so. control motor 14
The rotation angle is determined by the controller 78 based on the output of an optical sensor 76 provided at a position corresponding to the edge of the web in the running direction.

The paper roll sent out from the printing unit 12 is sent to the dryer 3.
0, is discharged via a cooling section 32, a web bath 34, and a folding device 36.

A detour 38 is formed in a part of the web bus 34, a free guide roller (hereinafter referred to as a free roller) 40 is provided in the detour 38, and the web is wound so as to embrace the free roller 40. There is. A rotary encoder 42 is attached coaxially with the free roller 40. A large number of rotary encoders 42 (
- generates a pulse signal of, for example 1500). This pulse signal is used as a timing pulse by the printing defect detection circuit 4.
4. Illumination light from a light source 46 is irradiated through an optical fiber array 48. 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.

A line sensor 50 and a beam sensor 52 are provided on the free roller 40. The line sensor 50 uses a charge coupled device (COD) as a light receiving element.

The beam sensor 52 is a reflective beam sensor.

Output signals from the line sensor 50 and beam sensor 52 are supplied to a printing defect detection circuit 44 .

FIG. 3 is a diagram showing objects to be read by the run sensor 50 and the beam sensor 52. Each pattern 56 is printed consecutively on the paper roll. A start mark 58 is printed at the printing start position of each picture 56. start mark 58
The printing position is the side edge margin of each pattern 56, and each pattern 5
It is located at a slightly upstream position or at the same position as the upper side 60 of 6 in the conveying direction A of the printed matter. Further, the start mark 58 consists of a part along the scanning direction and a part along the flow direction.

When the beam sensor 52 detects the edge of the start mark 58 in the machine direction, it supplies a start pulse to the printing defect detection circuit 44 .

The line sensor 50 detects each pattern 56 at one point in the left and right direction of the printed matter.
Each line is read and supplied to the printing defect detection circuit 44 as an image signal corresponding to the density level. Print defect detection circuit 4
4 reads the output of the line sensor 50 while synchronizing the flow direction with a start pulse.

The output of the line sensor 50 is sampled by the timing pulse from the rotary encoder 42 and read into the print hole detection circuit 44 as a signal for each pixel.

The printing defect detection circuit 44 inputs an image signal of a good printed pattern as a reference signal at the start of operation, and inspects the printing quality of each pattern by comparing the input image signal of each pattern with the reference signal.

A second meandering control section 68 is provided immediately before the free roller 40. The second meandering control section 68 has almost the same configuration as the first meandering control section 66 shown in FIG. Signals from the sensor 50 and the beam sensor 52 are supplied to the controller 80, and the control motor 82 is controlled based on the signals, and the pair of meandering 1iIJ1
1 roller 84,86 is tilted.

Next, the operation of this embodiment will be explained. Similar to the invention of Japanese Patent Application No. 60-257797, this embodiment inspects the print quality of each pattern by comparing the input image signal of each pattern with a reference signal. Regarding the input timing of each pattern in the flow direction, see the above-mentioned patent application No. 60-2577.
Similar to the invention of No. 97, sufficient accuracy is ensured by synchronizing with the start pulse from the beam sensor 52.

The input timing of each picture in the scanning direction is synchronized as follows. As shown in the third factor, the start mark 58 consists of a part along the scanning direction and a part along the flow direction, so the beam sensor 52 detects the edge of the start mark 58 in the flow direction, and the line sensor 50 Since the image signal for several lines after the start of output sampling includes a portion of the start mark 58 along the flow direction, it is possible to synchronize the scanning direction.

FIG. 4 shows an example of a digitized image signal near the start mark portion of the second line after the start of sampling by the start pulse. The X-axis shows the pixel number, and the y-axis shows the image signal. Since the image signal is A/D converted with 8 bits,
The value is 0 to 255.

Here, the value of the image signal for the blank portion is large, and the value of the image signal for the start mark portion printed in black is small.

In the example of FIG. 4, the n, n+1, and n+2 pixels correspond to the blank section, the n+4, n+5, and n+6 pixels correspond to the start mark printed in black ink, and the n+
The third pixel corresponds to the boundary between the blank page and the start mark.

Here, in order to determine the pixel number of the pixel corresponding to the boundary between the blank paper and the start mark, first decide approximately the position where the start mark will be printed on the printed material, and select multiple (10 to 20 pixels). A pixel that does not belong to either the average value of the image signal level of the blank page or the average value of the signal level of the start mark may be selected from the candidate pixels. Let NS be the pixel number corresponding to the edge when image data serving as a reference image is captured for inspection. Furthermore, in the reference image data, the value of the image data of the pixel NS is assumed to be LS. Let px be the dimension of a pixel in the scanning direction.

Next, the value of the image data of the i-th pixel NS under inspection is
-i. From the above, the phase shift amount Δpx& of the i-th image data in the scanning direction from the reference image is expressed as follows.

Δpx −Px ・(Li −LS )/(LW−Lb
)...(1) Here, LW is the average level of the blank paper, and lb is the average level of the start mark. The direction in which the pixel number increases is defined as positive.

Therefore, if the second meandering control section 68 moves the printing paper by -ΔPx in the scanning direction, the synchronization of the inspection image in the scanning direction can be ensured with sufficiently high accuracy.

The operation of the controller 80 for determining the phase shift amount ΔPx based on this principle will be explained with reference to the flowchart of FIG. This flowchart starts when a start pulse from the beam sensor 52 is input. In step S1, the image data of the second line after the start of sampling is read into the buffer. Here, k-2 to k-5 are suitable.

In step S2, image data of one pixel from the first pixel of the data on the k-th line is read into another buffer. here,
1 is determined from the position of the start mark, and j is 10 to 2.
0 is appropriate.

In step S3, the average value 1w of the image data of the blank section is calculated. To calculate the average value LW, it is sufficient to calculate the simple average of the values exceeding a certain value among the image data of the i-i+jth pixel. Normally, the blank level is set to about 200 in the case of a full range of 266 gradations in order to avoid abnormalities in image data due to light saturation. As a result, the appropriate value for the blank portion is approximately 180. Similarly, in step S4, the average value Lb of the image data of the black ink portion of the start mark is calculated. At this time, the appropriate value is approximately 30.

In step S5, it is determined whether the data being processed is reference data or test data. If the data being processed is reference data, the pixel number Ns of the edge pixel is determined as shown in step S6. Here, if there is only one pixel that is not included in the above-mentioned blank page area and start mark area, the pixel number NS can be easily determined. However, optical blur and COD
Due to transfer omission, there may be multiple edge pixel candidates. If two candidates remain, calculate the difference between mW and Lb, and set the pixel number of the pixel with the larger difference to N.
Let it be S. If three candidates remain, the middle pixel is set as the edge pixel.

In step S7, the image data LS of the determined pixel number NS is stored.

If the data being processed is test data, the stored NS and LS are read out, as shown in step S8. In step S9, inspection data 1-i of pixel number NS is read.

In step S10, Δpx
Calculate.

Here, as mentioned above, if there are three or more candidates, L
The accuracy is improved by using Ns-1 and Ns-1st image data instead of W and Lb.

The resolution of the detection section of conventional meandering control devices is 0.1~
0.2 ass, and in the present invention, the pixel is approximately 1
If one angle is used, the resolution is theoretically 1256 gams, which greatly improves the detection accuracy of meandering control.

In step S11, a control signal corresponding to the detected deviation amount of the pattern in the scanning direction is supplied to the control motor 82 to correct the meandering of the web. After this, the operation moves to inspection of print quality by the print defect detection circuit 44.

As explained above, according to this embodiment, the meandering of the web can be controlled with extremely high precision, each pattern can be input in synchronization in both the flow direction and the scanning direction, and the print quality can be inspected with high precision. . Note that although the meandering control has been described as control by a program using a microcomputer, the same function may be realized by a circuit configuration. Furthermore, the web meandering control section is not limited to the above-mentioned example, and a unique control rams may be added.

However, according to equation (1), a phase shift larger than the length of one pixel in the scanning direction cannot be corrected by one control. For example, when automatically splicing paper rolls, there are cases where the printing paper moves more than the pixel size (1 to 2+n), but in this case, the edge number selected using the method described above is different from the standard data. , the direction and amount of movement may be determined based on the pixel number.

Alternatively, if the edge pixel numbers are different, the inspection may be interrupted and control of the meandering of the printing paper may be left to a conventional meandering control device. Of course, in this case as well, correction is possible by executing the operation of the flowchart in FIG. 5 over a plurality of pictures.

〔Effect of the invention〕

As explained above, according to the present invention, there is provided a printing quality inspection device for web printing lines that can inspect the quality of printed matter by accurately controlling the meandering of the printing paper in the scanning direction with a simple configuration. can.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of an embodiment of the printing quality inspection apparatus according to the present invention, FIG. 2 is a perspective view showing the specific configuration of the meandering control section in FIG. 1, and FIG. 3 is a crawl-in sensor and a beam sensor. FIG. 4 is a model diagram showing the state of the image signal near the start mark, and FIG.
The figure is a flowchart showing the operation of this embodiment. 34...Web bus 40...Free roller 44...Printing defect detection circuit 50...Line sensor 52...Beam sensor 66.68...Meandering control section 80...Controller 82... Control motor 84.86...Meandering control roller Fig. 2 Fig. 3

Claims (1)

[Claims] means for generating a start pulse by detecting a start mark printed in advance at the beginning of each pattern while the printed material is running; A means for inputting an image signal of each pattern based on the generation of pulses and inspecting the print quality of each pattern by comparing it with a reference image signal, and a means for inspecting the print quality of each pattern by inputting an image signal of each pattern based on the generation of a pulse. 1. A printing quality inspection device comprising means for detecting an edge position, calculating an amount of phase shift in the width direction of a web, and generating a meandering control signal for the web based on the calculation result.