JP2876999B2 - Printing defect inspection equipment - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a printing defect inspection apparatus for inspecting a printed pattern defect on the surface of a sheet or a band-shaped object which is repeated at a constant cycle.

[0002]

2. Description of the Related Art As a method for inspecting a running printed matter in which the same pattern appears continuously at a constant cycle, a pattern without defects is taken as a standard pattern image, and pixels at the same position as the image of the pattern to be inspected are taken. Are compared, if a pixel range different from the standard picture image occurs, the different pixel range is determined as a print defect. However, if meandering or the like occurs due to running, even if the standard pattern and the inspection target pattern are the same, they are compared with pixels at shifted positions, and are erroneously recognized as print defects. For this reason, it is not determined based on the pixel difference within the range in which the meandering occurs, and a print defect is determined when a mismatch occurs between the pixel of the standard pattern and the pixel of the inspection target pattern beyond the range.

More specifically, a contour portion having a large change in the density of a picture one printing cycle or more before is extracted by means of differentiation or the like, binarized, and the binarized image is thickened by a width of several pixels before and after the contour. The created contour mask image is stored in the memory. One more
The picture before the printing cycle or more is stored in the memory as a standard picture. Pixels at the same position between the image of the inspection target pattern and the standard pattern are compared in density one pixel at a time. If the density difference exceeds the allowable value and is outside the contour mask image, the pixel is determined to be defective. ing. Japanese Patent Application Laid-Open No. 4-339563 discloses such a technique. Also, Japanese Patent Application Laid-Open
Japanese Patent Application Laid-Open No. 05-85534 (Japanese Patent Publication No. Hei 6-17877) shows that the tolerance of the defect judgment is changed for each measurement point in consideration of the pattern mismatch due to meandering.

[0004]

The pattern position of a printed material to be compared for inspection due to various causes such as mechanical characteristics and control characteristics of a transport mechanism for moving the printed material and the like, elongation of a printing paper, unevenness of ink thickness, etc. is one. The position is shifted from the position of the standard pattern provided before the print screen. Of the pictures to be compared, the contour is most affected by misalignment, so that the contour is covered with a mask having a width exceeding the misalignment amount to prevent false detection signals of defects. However, in this case, in the case of a pattern having many contours, adjacent mask images overlap with each other to narrow an area that can be inspected, and there is a problem that a defect is hard to be found. In addition, if the tolerance near the point where the density change is large in consideration of meandering is increased, the possibility that a defect is erroneously determined to be within the tolerance increases.

[0005] In addition, the running printing surface may be wavy in the width direction due to uneven tension in the width direction (perpendicular to the running direction) of the printed matter or partial elongation of the printing material. In this case, since unevenness in brightness occurs at the peaks and valleys of the waves, the density difference between the standard pattern image and the inspection target pattern image to be compared increases, and a false detection signal is output. In order to prevent this, it is necessary to set a large allowable value of the density difference between the pictures to be compared. If the allowable value is set to a large value as described above, an image having a defect within the allowable value is not determined to be a defect.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems, and it is possible to prevent a defect detection area from being narrowed by not using an outline mask, and to set a defect determination value with respect to a false signal due to a wave or the like of printing paper. It is an object of the present invention to provide a printing defect detection device capable of correctly determining defective printing by making a change.

[0007]

FIG. 1 is a diagram showing the principle of the first aspect of the present invention. In the figure, reference numeral 1 denotes an imaging unit for inputting a printing pattern of a running belt which repeatedly prints the same pattern,
Reference numeral 2 denotes an image generation unit for generating a picture image from the output of the imaging unit 1, and 3 detects a contour density difference representing an absolute value of a density difference of pixels separated by a predetermined distance from the image generated by the image generation unit 2. An edge memory for storing a standard pattern input to the image generator 2 and an edge memory for storing a contour density difference of the standard pattern image detected by the edge detector 3 based on the input. A black density detection unit 6 detects that the original pixel for generating the contour density difference is close to the black density at 3, and a standard pattern 6 is input to the image generation unit 2 from the black density detection unit 5 based on the input. A black density memory 7 for storing the detection result of the image, a pattern to be inspected is input to the image generation unit 2, and the original pixel for generating the contour density difference output from the black density detection unit 5 based on the input is black. To the concentration
A detection result of whether or not it is close and a corresponding contour density difference of the standard picture image stored in the black density memory 6 are generated.
Depending on whether the original pixel is close to black density or not.
If it is not close to the black density, set the first density difference setting value and
In this case, a density difference setting unit that sets a second density difference setting value larger than the first density difference setting value, and the edge detection unit 3 uses the inspection target picture image output from the image generation unit 8 to set the edge detection unit 3. The absolute value of the difference between the contour density difference generated in step (1) and the contour density difference of the standard picture image stored in the edge memory 4 corresponding to the contour density difference is obtained, and the first density difference set value or
A density difference comparing section 9 for comparing with the second density difference set value , 9 is an absolute difference between the contour density differences for each pixel of the picture image to be inspected;
If the absolute value of the difference between the contour density differences exceeds the density difference set value over the number of pixels continuously set in the horizontal direction and the vertical direction of the pattern image to be inspected sequentially, A defect determination unit that determines a horizontal or vertical pixel range of the inspection target picture image corresponding to the outline density difference of the range as a defect.

According to the second aspect of the present invention, a color image sensor is used as a light receiving element of the image pickup unit, color separation into red, blue, and green is performed, the lowest density of each color corresponds to the black density, and the subsequent processing is performed.

In the invention according to claim 3, the standard pattern is an image one print image before the test pattern, and the standard pattern moves as the test pattern sequentially moves. The standard pattern stops at the pattern before the defect occurrence pattern, and moves to the pattern where the defect disappears when the defect occurrence disappears.

[0010]

A one-dimensional image is obtained by capturing an image of a standard pattern by the image capturing unit 1, a two-dimensional image is generated by the image generating unit 2, and a pixel is separated by a certain distance (about several pixels) on the two-dimensional image by the edge detecting unit 3. Is extracted, and the edge density difference representing the density difference between pixels is stored in the edge memory 4 for one print screen while sequentially shifting the pixel position. The two original pixels from which the contour density difference has been extracted are simultaneously input to the black density detection unit 5 and compared with the black density set value to determine whether or not the density is close to that of the black pixel. It is stored in the screen black density memory 6.

Next, in the same manner as the standard pattern, a pattern to be inspected is imaged by the imaging unit 1, a two-dimensional image is generated by the image generation unit 2, and a density difference between pixels at a predetermined distance on the two-dimensional image is detected by the edge detection unit 3. Is extracted to obtain a contour density difference, and a density difference comparing unit 8 obtains a difference (absolute value of the difference) between the contour density difference and the contour density difference at a corresponding position stored in the edge memory 4. At this time, the edge memory may not detect that the edge is an edge, and may detect the edge as an edge due to dirt. On the other hand, the edge detector 3
The two pixels that generate the contour density difference are simultaneously input to the black density detection unit 5 to detect whether the density is equal to or higher than a predetermined density close to the black pixels. The detection result at the pixel position corresponding to the standard pattern stored in the black density memory 6 is output to the density difference setting unit 7 when a pixel close to a black pixel exists or does not exist. Is done. If If no pixel is present near the black pixel the density difference setting unit 7 for the first concentration difference setting value, there are pixels close to a black pixel first
The second density difference setting value having a value larger than the density difference setting value is output to the density difference comparing unit 8.

The density difference comparing section 8 compares the first or second density difference set value with the difference between the contour density differences (referred to as a double difference), and if the difference is within the set value, the pixel which has generated the contour density difference is determined. Is not a defect, and when the double difference exceeds a set value, it is assumed that the pixel that has generated the contour density difference includes a defective pixel. Even if it is not stored as an edge in the edge memory, an edge detected as an edge by the edge detection unit, that is, a stain is also determined by this. In the defect judging unit 9, the difference (double difference) between the corresponding contour density differences over the number of pixels continuously set in the horizontal direction and the vertical direction of the inspection target picture image exceeds the first or second density difference set value. In this case, it is assumed that the range of the pixel of the inspection target picture corresponding to the contour density difference is defective printing. The number of consecutive pixels in the horizontal direction corresponds to the meandering amount of the printed matter, and the number of consecutive pixels in the vertical direction corresponds to the amount of synchronization deviation in the running direction. If the number of pixels is within these numbers, it is determined that the printing is caused by meandering or out of synchronization, and is not determined to be defective printing.

Next, the operation of the black density detector 5 and the black density memory 6 will be described. FIG. 2 shows the outline of the picture image and the change in density. (A) shows an image signal (density signal) of a contour position and a standard picture. The outline position is (B)-
(E) is also supported. The dashed line indicates the black density,
The dark part is also brighter than the black density, and the density difference between the light part and the dark part is d1. (C) is (A)
The absolute value of the density difference between pixels separated by a predetermined distance from the image of the edge detection unit 3 is taken as the edge density difference, and this represents the edge density difference sequence stored in the edge memory 4. (B) is an image signal of the pattern to be inspected at the same position as (A),
When it becomes dark due to ripples in the width direction of the printing paper,
The density of the light part of the outline is reduced by darkening,
Since the dark portion has reached the black density, it does not become lower. As a result, the density difference between the bright and dark portions is d2. (D) shows the outline density difference sequence in which the image of (B) becomes the edge density difference in the edge detection unit 3. (E) shows the relationship between the difference (d1-d2) between the contour density difference between the standard picture and the picture to be inspected in the density difference comparing section 8 and the density difference setting value set in the density difference setting section 7. Since the difference (d1-d2) is an absolute value, there are cases where the standard pattern is darker and cases where the inspection target image is darker.

FIG. 3B shows a case in which the dark portion of the outline has black density, and the difference in density from the bright portion is d2. If there is no such restriction in the dark part, d2 is d1 as in (A).
And (d1−d2) becomes 0. If there is no restriction on the black density as described above, even if the brightness of the image is reduced due to the ripples on the print screen, (d1−d2) is 0 or within the allowable range. A false signal indicating that an error has occurred can be eliminated. However, as shown in (B), when the dark portion of the contour has reached the black density, the difference d2 between the bright portion and the dark portion decreases, and the value of (d1-d2) becomes larger than the actual value. For this reason, there is a case where the printing is determined to be defective printing beyond the density difference set value shown in (E). In order to avoid this, one of the two original pixels that generate the contour density difference (d1 and d2 are the density of the contour density difference) (that is, the pixel of the image signal shown in (A) and (B)) has the black density and the black density. Then, as shown in (B), since the density difference between the light and dark portions of the contour is reduced, d2 becomes smaller and d1-d2 becomes larger. Therefore, when the density difference d2 occurs in this way, that is, when any of the original pixels for generating the contour density difference has the black density, the density difference setting value is switched to a large value. For this reason, as shown in FIG. 1, the density difference set value is switched by the black pixel detection signal from the black density detection unit 5 and the black density memory 6. When the inspection target picture image is darker than the standard pattern image as shown in FIG. 2, the black density signal is output from the black density detection unit 5 to which the inspection target picture image is input as shown in FIG. Conversely, when the standard pattern image is dark and the inspection target pattern image is bright, the black density signal is output from the black density memory 6. When the black density detecting section 5 detects that the dark portion of the contour has black density, it detects when the density becomes close to black density. This is a technique to facilitate detection. As a result, it is possible to correctly determine even a false signal due to the ripple of the printing paper.

The color sensor separates the colors into red, blue, and green, and the minimum density of each color corresponds to the black density, and the inspection is performed.

It is assumed that the standard pattern has no printing defect, and the difference between the standard pattern and the standard pattern is a printing defect in the inspection target pattern. The difference between the two is detected by comparing pixels at the same position in both images. One of the printed patterns is set as a standard pattern, and the subsequent patterns are set as inspection target patterns. Since the inspection target patterns move sequentially, the standard pattern also moves following the pattern. This is because when the two patterns are separated from each other, the deviation between the two patterns increases due to meandering, elongation in the running direction, and the like. The smaller the deviation, the more accurately a print defect can be detected. For this reason, the standard pattern and the pattern to be inspected are set continuously, but when a defect occurs in the pattern to be inspected, the standard pattern remains at the pattern before the defect occurred, and when the defect disappears, it disappears. Try to transfer the standard pattern to the pattern. As a result, defect detection can be performed in a state in which the printing paper is not easily affected by meandering of the printing paper or synchronization deviation in the running direction.

[0017]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 3 is a diagram illustrating an entire apparatus including the print defect inspection apparatus according to the present embodiment. The band-shaped printed matter 21 on which the same pattern is repeatedly printed by the printing unit 20 flows through the roll 22. A mark sensor 23 is provided above the printed material 21 on one of the rolls 22 in the inspection target section. The mark sensor 23 reads a synchronization mark or a color control register mark printed in the margin of the printed material 21, and reads the signal of the printed mark 21. Used for synchronizing repeated pictures.

A rotary encoder 24 is provided on the other roll 25 in the section to be inspected, and generates a pulse signal every time the printed material 21 travels a predetermined length. There are two types of illumination. The reflection illumination 28 is used for inspecting the printed picture surface, and the transmitted illumination 26 is used for ink removal of the printed picture and the printed matter 21.
When there is a transparent part such as a film, it is used for inspection of the transparent part. The diffusion plate 27 prevents illumination unevenness of the transmitted illumination. The CCD line sensor camera 30 reads one line (one scanning line) of image data in synchronization with the pattern of the printed matter 21 illuminated by the illumination in synchronization with the pulse signal generated by the rotary encoder 24.

FIG. 4 is a block diagram of a print defect inspection apparatus according to the first embodiment. In this embodiment, R (red), G (green), B input from the CCD color line sensor camera 30 are used.
The (blue) picture signal is processed by the R processing module, the G processing module, and the B processing module. Since each module has the same configuration, a detailed configuration of the R processing module will be shown and described. The minimum density of each color is described as black density.

In FIG. 4, the picture signal is CC as light quantity.
The light is input from the D color line sensor camera 30, enters the R processing module, the G processing module, and the B processing module, and the light amount of the picture signal is logarithmically converted by the logarithmic converter 31. This is to make the output linear with respect to the density gradation and facilitate the subsequent processing. Next, in the scan converter 32, the mark sensor signal and the rotary encoder signal described with reference to FIG. 3 are input, and the fluctuation of the pattern reading cycle in the running direction caused by the fluctuation of the speed of the printed matter 21 is suppressed, which is convenient for the inspection processing. The signal is converted into a picture signal having a good constant period. The CRT controller 33 generates a periodic signal and an image memory address signal for this purpose.

The picture signal after the scan conversion is generated by a delay circuit 34 for a picture signal delayed by several pixels, and the difference from the original picture signal is obtained by a difference detector 40 to obtain a contour density difference signal.

Also, the input / output signals of the delay circuit 34 are separately inputted to comparison circuits 35 and 36, and compared with the density setting values. When each value is closer to the black density than the setting value, the binary output "1" , And “0” when far away. The density setting value is a density value larger by + α than the black density. The outputs of the comparators 35 and 36 are ORed by the OR gate 37, and if the output of any one of the comparators 35 and 36 becomes "1", "1" is output, and the result is printed by one. It can be stored in the binary memory 38 for the picture cycle. The binary memory 38 is a FIFO
While storing the binary signal in the memory of the O-structure (first-in first-out system), the binary signal stored one cycle before the print pattern is read out, and the logical sum gate 39 takes the logical sum with the output of the logical sum gate 37. Output to the selection circuit 44.

The selection circuit 44 selects a density difference set value 1 and a density difference set value 2.
If none of the input values to 5, 36 are close to black density,
That is, it is selected when the output of the OR gate 39 is “0”. The density difference setting value 2 is larger than the density difference setting value 1 and is selected when the output of the OR gate 39 is “1”. That is, the selection of the density difference setting value 2 corresponds to the case where the density difference setting value is increased when the dark portion of the outline has black density and the density difference d2 from the light portion has been reduced as described with reference to FIG.

The contour density difference signal generated by the difference detector 40 is stored in a multi-valued memory 41 having a FIFO structure, and at the same time, is stored one cycle before the printing picture cycle, and the difference from the read contour density difference signal. (Hereinafter referred to as a double difference) is obtained by the difference detector 42. The double difference and the density difference set value selected by the selection circuit 44 are compared by the comparison circuit 43. When the absolute value of the double difference exceeds the density difference set value, the comparison circuit 43 outputs "1". . The output of the comparison circuit 43 enters a size determiner 45.

In the size judging unit 45, the difference between the corresponding contour density differences (double difference) over the predetermined number of pixels continuously in the horizontal and vertical directions of the picture image to be inspected, respectively.
If it exceeds the density difference set value, it is determined that the range of the pixel of the inspection target picture corresponding to the contour density difference (the pixel of the inspection target picture for generating the contour density difference) is defective printing. As an example of continuous horizontal and vertical pixels as a reference for determination, the horizontal direction indicates the number of pixels exceeding the meandering amount per printing cycle, and the vertical direction indicates the number of pixels exceeding the amount of synchronization deviation per printing cycle. Set. The horizontal direction is 1-2 pixels and the vertical direction is n pixels. If it is determined to be defective, a signal is output to the alarm device 47, and an alarm is issued by a buzzer, light, or the like.

In the comparison circuit 43, when the double difference exceeds the density difference set value, the stored values of the binary memory 38 and the multi-value memory 41 corresponding to the standard picture are not updated, Is maintained and updated to the data of the first pattern image to be inspected at the time when it is no longer exceeded. In addition, 1 as an imaging device
Although a two-dimensional image sensor is used, a two-dimensional image sensor can also be used.

[0027]

As is clear from the above description, the present invention detects a print defect by extracting a density difference of a pattern outline and comparing a standard pattern with a pattern to be inspected. If the density is close to black (the lowest density in the case of color), a defect determination value can be selected, and a false defect signal generated by the wavy irregularities on the printing surface is eliminated to prevent a decrease in detection accuracy. . Further, since the meandering and the period shift of the printing surface are determined based on the continuous number of defective pixels, it is not necessary to provide a mask unlike the related art, and the inspection area is not reduced by the mask.

[Brief description of the drawings]

FIG. 1 is a principle diagram of the present invention.

FIG. 2 is a diagram illustrating a contour portion of a picture image and a state of density change.

FIG. 3 is an overall configuration diagram of a defective print detection device including the present embodiment.

FIG. 4 is a block diagram illustrating the configuration of the present embodiment.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 imaging unit 2 image generation unit 3 edge detection unit 4 edge memory 5 black density detection unit 6 black density memory 7 density difference setting unit 8 density difference comparison unit 9 defect determination unit 30 CCD color line sensor camera 31 logarithmic converter 32 scan conversion Device 33 CRT controller 34 delay circuit 35, 36, 43 comparison circuit 37, 39, 46 OR gate 38 binary memory 40, 42 difference detector 41, multi-valued memory 44 selection circuit 45 size judgment device 47 alarm device

Claims (3)

(57) [Claims] 1. An image pickup unit for inputting a print pattern of a running belt that repeatedly prints the same pattern, an image generation unit that generates a pattern image from an output of the image pickup unit, and an image generated by the image generation unit. An edge detection unit that detects an outline density difference representing an absolute value of a density difference between pixels separated by a predetermined distance, and a standard pattern input to the image generation unit, and a standard pattern detected by the edge detection unit based on the input. An edge memory for storing the contour density difference of the picture image, a black density detecting section for detecting that the original pixel for generating the contour density difference in the edge detecting section is close to black density, and a standard pattern for the image generating section. A black density memory for storing a detection result from the black density detection unit based on the input; and a ring output from the black density detection unit based on the input; The original pixel that generates the Guo density difference is black
The detection result of whether the degree is close to the degree and the corresponding contour density difference of the standard pattern image stored in the black density memory are generated.
If the original pixel is not close to black density according to the detection result of whether or not the original pixel is close to black density, a first density difference set value is set,
If it is close, the second density difference setting is larger than the first density difference setting value
A density difference setting unit for setting a value ; a contour density difference generated by the edge detection unit based on the inspection target picture image output from the image generation unit; and a contour density difference stored in the edge memory corresponding to the contour density difference. The absolute value of the difference from the contour density difference of the standard pattern image is obtained, and the first density difference set value or the second density difference is calculated.
A density difference comparing unit that compares the difference value with the set value , sequentially obtains the absolute value of the difference between the contour density differences for each pixel of the inspection target picture image, and continuously obtains the absolute value of the difference between the contour target density image in the horizontal direction and the vertical direction. The absolute value of the difference between the contour density differences is equal to or greater than the first density difference set value or the second density
A defect judging unit for judging a horizontal or vertical pixel range of the picture image to-be-inspected corresponding to the contour density difference exceeding the range when the difference exceeds the set value. Printing defect inspection device. 2. The method according to claim 1, wherein a color image sensor is used as a light receiving element of the image pickup unit, color separation into red, blue, and green is performed, a minimum density of each color corresponds to a black density, and subsequent processing is performed. Item 1. A print defect inspection device according to Item 1. 3. The standard pattern is an image one print image before the inspection target pattern, and moves as the inspection target pattern sequentially moves. When a defect occurs in the inspection target pattern, the standard pattern is The print defect inspection apparatus according to claim 1, wherein the print defect inspection apparatus stops at the pattern before the defect occurrence pattern, and moves to the pattern where the defect disappeared when the defect occurrence disappears.