JPH0431307B2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention is a quality inspection of printed matter that automatically inspects for off-printing of patterns such as pictures and characters on printed matter, and for various stains, scratches, etc. that occur on printed matter. Regarding equipment.

[Prior Art] Normally, printed matter is inspected by a printing press operator who takes out the printed matter at appropriate intervals and visually inspects the printed matter. However, such an inspection is time-consuming, and the detection is delayed, and by the time the defect is noticed, a considerable number of defective prints have already been printed, resulting in a poor printing yield. Additionally, this requires an operator to constantly monitor the printing press, so in a factory where several printing presses are in operation, a number of operators corresponding to the number of printing presses are required. .

Although various automatic inspection apparatuses have been announced with the aim of solving this drawback and improving the yield of printed matter and saving labor, the current situation is that none of them are necessarily satisfactory in terms of inspection accuracy.

These automatic inspection devices utilize an optical method, and the principle thereof will be explained with reference to FIG. In the figure, 11 is a plate cylinder, 12 is a blanket cylinder, and 13 is an impression cylinder. When the printing paper 14 passes between the blanket cylinder 12 and the impression cylinder 13, the printed pattern of the plate cylinder 11 is printed on the printing paper 14. It is beginning to be transcribed. The surface of the printing paper 14 to which the printed pattern has been transferred is scanned in a line shape (indicated by A-B in the figure) by a line-shaped camera 15. This line camera 15 converts the optical density of the printed pattern into an electrical signal and outputs it as a video signal, and the video signal is sent to a signal processing device 16. In addition,
This part may be of any type as long as it has an equivalent function; for example, it may be a contact type line sensor that is often used in facsimiles and the like. The signal processing device 16 compares the input video signal with a normal printing pattern previously stored in a memory mechanism included therein, and based on this difference, detects quality defects occurring on the printing paper 14, such as dirt, scratches, etc. Detects white spots etc.
It has a function of outputting a signal informing the operator of this fact, or, if the cause of the defect is known, outputting an operation signal to eliminate the cause of the defect.

[Problems to be Solved by the Invention] The key point in a quality defect inspection device for printed matter using such an optical method is to correctly compare and judge the detected gray level signal with the gray level signal during normal printing. It is in. Conventionally, the detection limit size of the defect to be inspected is relatively large, for example, several mm.
It has been applied to many objects such as the above-mentioned ink stains, and the inspection speed is relatively slow.

However, as printing becomes more sophisticated and faster in recent years, the requirements for inspection tend to become more and more sophisticated. In other words, the situation has come to be such that an inspection device capable of supporting an inspection limit dimension of 1 mm or less and an inspection speed of 5 m/sec or more is desired. In such a situation, the image information representing the reference image stored in the reference value memory is compared with the image information in the current value memory that is updated every moment, that is, the image information to be inspected, and the printed matter is determined based on the difference. When detecting printing defects that occur in the printing process, it is important to consider how the amount of error in both cases corresponds to the defect determination.

First, as a means to obtain synchronization between the contents of the reference value memory and the contents of the current value memory, a rotation angle detector such as a rotary encoder is attached to the plate cylinder or impression cylinder, and the tip of the printed image or the inspection is detected from the rotation angle. How to obtain image information for each dimension, and the start mark printed in the margin at the top of the image when printing.
Methods have been proposed in which image information is obtained for each operation time based on the passing time from the previous start mark to the next start mark using optical or other means of detection. Since the purpose of this paper is to propose a printed matter quality inspection apparatus having a speed correction function, detailed explanation thereof will be omitted here.

By implementing the synchronization deviation correction method described above, it is possible to ensure synchronization between the reference value image and the current value image, but a certain temporal operation interval within one pattern changes due to changes in the operating speed of the printing press. For,
The camera's exposure time will vary. For this reason, in charge storage type solid-state devices such as CCD and MOS,
The level of the obtained detection signal fluctuates, and a simple comparison process in printing defect determination cannot be used. In addition, good inspection accuracy cannot be expected in defect determination by comparing the amount of error that occurs during the comparison process with a threshold value that is unrelated to information such as the signal level or the portion of the image.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a quality inspection device for printed matter that can inspect printed matter for deprinting, etc. with high precision.

[Means and effects for solving the problems] The present invention includes a current memory that stores image information input from an optical detector, and a system that transfers and stores the contents of the current memory as is when the image information is correct. or a reference memory that directly stores image information from the optical detector, and the signal level of the reference memory content or the current memory content is determined from the printing speed information when obtaining the current memory content and the reference memory content. In an apparatus that has a function of performing a speed correction calculation and detects quality defects in printed matter by comparing the current memory contents that are updated every moment with the reference memory contents, the reference memory that has undergone the speed correction calculation is A tolerance table for selecting tolerance values used for defect determination based on image information, and a comparison between the amount of error and the tolerance value when an error occurs when comparing the current memory contents with the reference memory contents. The gist of the present invention is to include a means for determining quality defects in printed matter based on the relationship, and it is possible to perform highly accurate quality inspection by correcting fluctuations in the pattern detection signal due to changes in printing speed.

[Embodiment of the Invention] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. In FIG. 1, 21 is a plate cylinder, 22 is a blanket cylinder, 23 is an impression cylinder, and the printing paper 24 has a blanket cylinder 2.
When passing between the plate cylinder 2 and the impression cylinder 23, the printed pattern of the plate cylinder 21 is transferred. The surface of the printing paper 24 to which the printed pattern has been transferred is scanned in a line shape (indicated by A-B in the figure) by a line-shaped camera 25. This line camera 25 converts the optical shading of the printed pattern into an electrical signal and outputs it as a video signal, and the video signal is sent to a signal processing device 26. The signal processing device 26 compares the input video signal with a normal printing pattern previously stored in a memory mechanism included therein, and detects quality defects occurring on the printing paper 24, such as dirt, scratches, etc., based on the difference. If it detects white spots etc. and outputs a signal to notify the operator, or if the cause of the defect is known,
It has a function of outputting an operation signal to eliminate the cause of the occurrence.

A rotation angle detector (pulse generator) 27 is attached to the blanket cylinder 22 . This rotation angle detector 27 generates a pulse number proportional to the rotation speed of the blanket cylinder 22. This signal is sent to the signal processing device 26, and based on this signal, the signal processing device 26 generates a printing speed signal. It is becoming possible to obtain Note that this rotation angle detector 2
7 may be attached to the plate cylinder 21 or the pressure cylinder 23.

FIG. 2 shows a block diagram of a printed matter inspection apparatus mainly including the signal processing device 26. As shown in FIG. In the figure, picture position information from a rotation angle detector 27 and a start mark detector 31 is processed by a synchronization circuit 29. This synchronization circuit 29
outputs a scanning start signal and an address generation signal to the line camera 25 and the address generation circuit 30 from the leading edge of the printed pattern for each inspection dimension or for each scanning time. As a result, the reference image stored in the reference value memory 31 and the current value memory 32
It is synchronized with the current image that is stored in and updated every moment.

Further, the image information from the line camera 25 is digitized by the A/D converter 33, further averaged by the averaging circuit 34, and then stored in the current value memory 32. The content of the current image stored in the current value memory 32 and the content of the reference image stored in the reference memory 31 are selected based on address information generated by the address generation circuit 30, and are selected by the difference calculation circuit 35.
and is output to the speed correction calculation circuit 36. The speed correction calculation circuit 36 performs a speed correction calculation on the signal level of the reference image based on the printing speed when the reference image was stored and the printing speed at the time of inspection. The contents of the reference image subjected to the speed correction calculation are output to the difference calculation circuit 35 and the tolerance table 37.

The difference calculation circuit 35 compares the contents of the reference image subjected to the speed correction calculation and the current image, which is updated moment by moment, for each constituent image of the image, and outputs the amount of deviation to the abnormality determination circuit 38. Note that the difference calculation here includes a method that simply compares the pixels of two images, or a method that calculates the difference between a certain pixel and a pixel several pixels apart in the same image and calculates the difference between the two images. Although methods for comparison have been proposed, the main purpose of the present invention is to propose an overall configuration of a printed matter quality inspection apparatus having a printing speed correction function, so detailed explanation thereof will be omitted.

The tolerance table 37 selects a tolerance according to the part of the reference image and the signal level based on the content of the reference image subjected to the speed correction calculation and the information attached thereto, and outputs it to the abnormality determination circuit 38. As a result,
It is possible to prevent deterioration in the accuracy of abnormality determination due to the speed difference between the reference image and the inspection image. Abnormality determination circuit 38
compares the allowable error from the allowable value table 37 and the error amount from the difference calculation circuit 35, and if the error amount is larger than the allowable error, notifies the CPU 39 that a printing defect has occurred. CPU39 is
From the abnormality occurrence report from the abnormality determination circuit 38 and the address information from the address generation circuit 30, it is possible to know in which position of the printed pattern the abnormality has occurred, and to generate an alarm according to predetermined procedures in each process.・Issuing commands such as marking/reject 40.

In addition, in Fig. 2, a speed correction calculation is performed on the reference image, and the tolerance value table 37 is searched with the result to obtain the permissible error. , the signal level between both images may be matched due to a change in operating speed of the printing press, etc., and the allowable error may be searched for using the current image data after speed correction calculation.

With the above configuration, the difference calculation between the current image and the reference image is performed without being affected by increases or decreases in the signal level of the inspection image (current image) due to changes in the operating speed of the printing press, etc. By comparing the allowable error retrieved from the optimum allowable value table 37 according to the operating speed of the printer and the error amount calculated by the difference calculation, the quality of printed matter can be inspected with high precision.

It should be noted that the present invention is not limited to the above-mentioned embodiments, and can be programmed using a similar circuit configuration or a microcomputer.

[Effects of the Invention] As described above, the present invention has a speed correction function that corrects fluctuations in the pattern detection signal due to changes in printing speed, so the printed matter can be inspected with high precision. We can provide quality inspection equipment.

[Brief explanation of drawings]

FIG. 1 is a perspective view showing the configuration of a printed matter quality inspection device according to an embodiment of the present invention, FIG. 2 is a block diagram showing the circuit configuration of the device shown in FIG. 1, and FIG. 3 is a conventional printed matter quality inspection device. It is a perspective view showing the composition of an inspection device. 24...Printing paper, 25...Line camera, 2
6... Signal processing device, 27... Rotation angle detector,
28...Start mark detector, 29...Synchronization circuit, 30...Address generation circuit, 31...Reference value memory, 32...Current value memory, 33...A/
D converter, 34...Averaging circuit, 35...Difference calculation circuit, 36...Speed correction calculation circuit, 37...
... Tolerance table, 38 ... Abnormality determination circuit, 39
……CPU.

Claims (1)

[Scope of Claims] 1. A current memory that stores image information input from the optical detector, and when the image information is correct, the contents of the current memory are transferred and stored as they are, or the image from the optical detector is stored. and a reference memory that directly stores information, and the signal level of the reference memory content or the current memory content is changed from the printing speed information when obtaining the current memory content and the reference memory content to the gray level due to the print speed fluctuation. In a device that detects quality defects in printed matter by comparing the constantly updated current memory contents and reference memory contents, the device has a function of performing speed correction calculations to correct fluctuations in image information. A device for storing a tolerance value corresponding to a signal level, and for selecting a tolerance value used for defect determination according to a signal level of image information in the current memory or reference memory subjected to the speed correction calculation. If an error occurs when comparing the current memory content and the reference memory content with the tolerance table, the quality defect of the printed matter is determined based on the magnitude relationship between the amount of error and the tolerance value selected from the tolerance table. 1. A quality inspection device for printed matter, comprising means for making a determination.