JP2621690B2 - 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 an apparatus for inspecting a printed pattern on a surface of a sheet or a band-shaped object which is repeated at a predetermined cycle, and particularly to an apparatus for inspecting stains caused by various colored inks on a color printed matter. The present invention relates to a printing defect inspection device.

[0002]

2. Description of the Related Art A method of inspecting a sheet or a strip of a printed object for defects will be described. One method is to use a photosensor arranged in a direction perpendicular to the running direction of the print object and having a relatively large area compared to the meandering amount of the print object to image a print pattern and to output a signal from each photosensor. Is stored in the memory. Dirt (defect) in anticipation of the change in the signal received by each phone sensor due to meandering of the printed object
An allowable range for detection was set, and an alarm was output when the allowable range was exceeded.

FIG. 10 is a diagram for explaining the setting of the allowable range. When the pattern shifts from A to B due to the meandering of the printing object, the light receiving amounts of the elements i and j of the photo sensor change. The output of j changes. As described above, even if there is no defect in the printed matter, the output changes due to meandering. Therefore, it is necessary to provide an allowable range with a value larger than the change width due to meandering.

In another method, an outline of a standard print pattern is extracted by means of differentiation or the like, binarized, and an image subjected to a fattening process corresponding to a meandering amount is stored in a memory. deep. Similarly, the pattern to be inspected is extracted by differentiation or the like, binarized, and this image is compared with the image stored in the memory. When a binarized image of the picture to be inspected appears at a position where there is no pixel in the image stored in the memory, an alarm is output as dirt.

FIG. 11 is a diagram for explaining a method of detecting dirt using the binarized outline image. A indicates the outline, and a range B indicated by oblique lines indicates a range where the processing is made thicker. When the pixel (indicated by x) of the image obtained by binarizing the contour of the inspection target pattern is within the oblique line, it is not determined that the pixel is dirty.

[0006]

The printing stains include minute particulate ink splashes or linear stains such as doctor lines of a gravure printing machine which are narrow in the width direction of the printed matter and long in the running direction. In a light receiving element having a large pixel area, the minute dirt density is averaged with the surrounding reflection density, making detection difficult. In addition, the detection sensitivity further decreases due to the shift of the reading position due to the meandering of the printed matter.

FIG. 12 is a diagram showing a light receiving element having a large unit pixel area. E indicates a light receiving element, and D and H indicate its width and height. d indicates the amount of meandering to the left or right. The width D of the light receiving element needs to be larger than the maximum value of the meandering amount d. As D increases, H also increases, resulting in a light receiving element having a large area D · H.

[0008] Further, there is a case where stains with a low density adhere to a relatively large area such as stains on a printing ground. When detecting the outline of a stain image having a low density by means such as differentiation processing, noise is often erroneously detected in a region other than the stain image. This means that the differential processing has a large value when the rate of change of density is large, but when the density is uniformly low, only a small value is output. As the noise of the part becomes dirty,
This is because erroneous detection increases.

In addition, stains generated on color prints have various color tones, and a light-receiving element having a spectral sensitivity over the entire visible region has insufficient detection sensitivity.

FIG. 13A shows the detection sensitivity of an element having uniform spectral characteristics over the entire visible region, and FIG. 13B shows only the blue (B), green (G), and red (R) regions. FIG. 4 is a diagram illustrating detection sensitivity of an element having spectral characteristics. For example, in the case of an element having uniform spectral characteristics over the entire visible region when receiving blue-green (cyan) color, the amount of change in the detection signal with respect to white as shown in FIG. Changes occur. In other words, there is no change in 70% indicated by oblique lines. On the other hand, as shown in FIG.
The following changes occur with respect to white in each of the R elements. B element 0% G element 0% R element 100%, that is, 100% of the R element that is a complementary color of blue-green is detected, but the other B and G elements are not detected. That is, the R element has three times the detection sensitivity of the element having uniform spectral characteristics over the entire visible region of (a).

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems, and provides a print defect inspection apparatus which detects print stains by classifying them into local stains and wide-area stains which are wide and thin widely. With the goal.

[0012]

[0013]

FIG . 2 is a block diagram of the first embodiment of the present invention.
It illustrates the principle of a. In FIG. 1, reference numeral 1 denotes an image pickup unit for inputting a printed pattern of a running belt on which the same pattern is printed, 2 an image generation unit for generating a pattern image from an output of the image pickup unit 1,
Reference numeral 3 denotes a mask area creating unit for creating a density boundary image by subjecting the picture image density to a spatial filtering process by a differential operator, binarizing the picture image, and then performing a fattening process. Reference numeral 8 denotes a picture image output from the image generating unit. A storage memory 9 is a window setting unit for setting a window in a region where no pixel of the density boundary image is present from the picture image stored in the memory 8, and a window setting unit 10 is for setting the picture image in the set window area to the above-mentioned. An in-window standard value pattern generation unit for inputting from the image generation unit 2 and generating an average value of the density of the in-window standard pattern, an input unit 11 inputs a pattern image in the set window area from the image generation unit 2 and In-window inspection pattern generation unit that generates an average value of the density of the inspection pattern in the window,
12 is a reference value setting unit that sets a reference value of the density difference, 13 is a case where the density difference between the average value of the density of the standard pattern in the window and the average value of the density of the inspection pattern in the window exceeds the reference value, This is a wide area defect determination unit that outputs a wide area defect signal.

[0014]

Further, a color image sensor is used as a light receiving element of the image pickup unit 1 to separate the color into red, blue, and green, and the subsequent processing is performed.

[0016]

A one-dimensional image obtained by capturing the standard picture image by the image capturing unit 1 is converted into a two-dimensional image by the image generating unit 2, and the contour is extracted by the differentiation process and the binarizing process by the mask area generating unit 3, and is printed on the contour. A fattening process corresponding to the amount of meandering of the body is performed. There is a possibility that a picture is present in the area subjected to the fattening processing.

The window setting section 9 sets a window in a region where no pixel of the density boundary image exists, that is, in a region other than the mask. The difference between the average density in the window of the standard picture image and the average density in the window of the test picture image is compared. If the difference is equal to or more than the reference value, it is determined that the test picture in this window is entirely dirty. As a result, it is possible to detect a wide-area defect such as a stain on a printing ground, in which a relatively large area is stained with low density. Since the window is set other than the mask, the influence of the meandering of the print is eliminated.

[0018]

Further, by performing color separation into red, blue, and green with a color sensor for inspection, the detection sensitivity is improved up to three times at the maximum as compared with the case of a light receiving element having spectral sensitivity over the entire visible region.

[0020]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 4 is a diagram illustrating an entire apparatus including the print defect inspection apparatus according to the present embodiment. The strip-shaped printed matter 21 on which the same pattern is 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, 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 22 'in the section to be inspected, and generates a pulse signal every time the printed material 21 travels a predetermined length. There are two illuminations. When the printed matter 21 is transparent such as a film, the illumination light is guided from the transmitted light source 25 to the printed matter 21 through the optical light guide 26 and the diffusion plate 27. The diffusion plate 27 prevents illumination unevenness of the transmitted illumination. When the printed matter 21 is opaque like paper, illumination is guided from the reflected light source 28 to the printed matter 21 through the optical light guide 29. The CCD color line sensor camera 30 reads pixel data of one line (one scanning line) in synchronization with the pulse signal generated by the rotary encoder 24 from the picture of the printed matter 21 illuminated by the illumination. Figure 1 is a station
It is a principle figure which detects a part defect. In the figure, 1 is the same
Enter the print pattern of the running belt that printed one pattern
The imaging unit 2 generates a picture image from the output of the imaging unit 1.
The image generation unit 3 is a differential operator for calculating the pattern image density.
And then thickening after binarization
Create mask area to create density boundary image by processing
And 4, the standard generated by the image generating unit 2 from the standard pattern.
Standard picture memory for storing picture images, 5 for density difference
A reference value setting unit 6 for setting a value is detected by the image generation unit 2.
Inspection target picture image generated from the inspection target picture and the standard picture
Compare pattern images and check if the density difference exceeds the reference value
The comparing unit 7 for determination determines the pixel size of the picture image to be inspected.
Pixels exceeding the reference value are pixels of the density boundary image.
If it is in an area that does not exist, it is determined to be defective and a local defect signal is generated.
This is a local defect determination unit that outputs.

FIG. 5 is a block diagram of a print defect inspection apparatus according to the first embodiment. In this embodiment, R (red), G (green), B (blue) input from the CCD color line sensor camera 30
Processing signal, R processing module, G processing module, B
Process in the processing module. Since each module has the same configuration, a detailed configuration of the R processing module will be shown and described.

In FIG. 5, the picture signal is CC as light quantity.
Input from the D color line sensor camera 30, enter the R processing module, G processing module, B processing module,
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. 4 are input, and the fluctuation of the pattern reading cycle in the running direction caused by the fluctuation of the speed of the printed material is suppressed, and the pattern signal is converted into a pattern signal having a certain period convenient for the inspection processing. I do. CR
The T controller 33 generates a periodic signal and an image memory address signal for this purpose.

The picture signal after the scan conversion is stored in a standard picture memory 34.
At the same time, a spatial filter process 35, a binarization process 36, and a fattening process 37 are performed by the differential operator to create a density boundary image, and the image is stored in the binary memory 38.

The inspection picture signal 39 subsequently read from the CCD color line sensor camera 30 is subjected to a logarithmic conversion 31 and a scan conversion 32 in the same manner as described above, and stored in the standard picture memory 34 for each pixel and the density detected by the difference detector 40. The difference is taken, and this is compared with the set individual allowable value 41, which is an allowable value, by the comparator 42. When the difference exceeds the set individual allowable value 41, the comparison result P is output. The comparison result P is ANDed with the inverted signal of the binary memory 38 by the AND gate 43 to check the overlap with the density boundary pixel, and outputs the detection signal P when it does not overlap.

On the other hand, the standard picture signal of the scan conversion is taken into the picture memory 45 by a memory image update signal from the CPU 44. The contents of the picture memory 45 are converted by a D / A converter 46 into analog video signals.

The window and the position of the window are CR
It is created by the window position setting unit 47 and the window generator 48 from the horizontal / vertical synchronization signal and the image address signal generated by the T controller 33, and is synchronized with the image reading timing of the picture memory 45. The window signal is D
The analog video signal from the A / A converter 46 is mixed with the analog video signal by the mixer 49 and displayed on the CRT display 50. A window position is set by selecting an area of the pattern image reflected on the CRT display 50 where the density change is small.

When the CPU 44 reads the window position from the window position setting device 47, the picture memory 45 reads the density data of M pixels × N pixels constituting the window at the window position, and stores the average density value in the internal memory of the CPU 44. Store.

FIG. 6 shows a window of M × N pixels displayed on a CRT display. Usually, a plurality of windows are provided. Similarly, the average density value of the standard pattern is obtained for all windows, and when the average density value is stored in the internal memory of the CPU 44, an update signal is output from the CPU 44 to the pattern memory 45, and the next inspection pattern signal after scan conversion is stored in the pattern memory.
Take in at 45.

The CPU 44 reads the density data of M × N pixels in the window area from the picture memory 45, finds an average density value, and compares the average density value with the average density value of the pixels in the standard picture window stored in the internal memory of the CPU 44. A density difference is calculated, and when the density difference is larger than the set average allowable value 51, a stain signal is generated.

The OR signal of the dirt signal and the detection signal P from the AND gate 43 is calculated by an OR gate 52.
At 53, the logical sum of the output of each of the G processing module and the B processing module is calculated, and the result is output from the alarm signal unit 54 as a dirt alarm signal.

Next, a second embodiment will be described. In the second embodiment, a small area is automatically set instead of the window processing in the first embodiment to detect a wide area defect. FIG.
Is a principle diagram for automatically setting a small area and detecting a wide area defect.
You. In the figure, 1 is a running belt on which the same pattern is printed.
An imaging unit 2 for inputting a print pattern of a body is designated by 2
An image generation unit that generates a pattern image from the output, 3 is this pattern
The image density is spatially filtered by the differential operator,
After the binarization process, the thickening process is performed to obtain the density boundary image.
A mask area creation unit to be created is generated by the image generation unit 2.
The pattern image to be formed is divided into a plurality of measurement areas, and each measurement area
Area average generation unit that calculates the average value of the density of
Each measurement calculated by the area average generation unit 14 for the pattern image
A memory for storing the average value of the density of the region, 16 is the mask
The density boundary image created by the area creating unit 3 is referred to as the measurement area.
The mask area dividing part, which divides the mask into the same sections,
A reference value setting unit for setting a reference value;
The density flat of the measurement area of the inspection target picture image generated in 14
Correspondence between the average value and the standard picture image stored in the memory 15
The average value of the density of the measurement area to be measured.
If the value exceeds the reference value of the reference value setting section 12,
In the corresponding mask area generated by the mask area dividing unit 16
Does not include the pixels constituting the density boundary image
This is a wide area defect determination unit that outputs a wide area defect signal. FIG.
FIG. 9 is a block diagram showing the configuration of the second embodiment, in which components denoted by the same reference numerals as in FIG. 5 have the same functions.

Hereinafter, the description of the present embodiment will be made on points different from the first embodiment. The picture signal scanned and converted by the scan converter 32 is divided by the area averaging processor 55 into small areas having an area of M pixels × N pixels, and a density average value of M × N pixels is obtained in each small area to obtain a standard value. It is stored in the picture memory 56.

FIG. 8 shows an area averaging processor 55 of 5 × 5 pixels.
FIG. 3 is a diagram showing an example of the configuration of FIG. The picture signal after the scan conversion enters a 5 pixel × 5 pixel averaging circuit 550 as a serial signal similar to a video signal and is sequentially stored in a line memory M1 having a storage capacity for one line. In synchronization with this, the stored contents of the line memories M1 to M4 are sequentially read out and entered into the 5 × 5 pixel averaging circuit 550, where the averaging results of 25 pixels are sequentially output by the pipeline. The output data is latched by a strobe signal generated every fifth line and every fifth pixel and stored in the standard picture memory 56. The strobe signal is output for each pixel per line.
Output 5x5 pixel averaged data for each pixel
Is also good.

The inspection pattern signal subsequently read from the CCD color line sensor camera 30 compares the density with the image stored in the standard pattern memory 34 for each pixel in the logarithmic conversion 31, the scanning conversion 32, and the pixel as in the case of the standard pattern. The difference is detected 40, the set individual allowable value 41 is compared with the magnitude 42, and the comparison result is ANDed with the inverted signal of the binary memory 38 by ANDC 61,
If the pixel does not overlap with the density boundary pixel, the result of the logical product is output as the detection signal P.

At the same time, the inspection picture signal undergoes an area averaging process 55 to generate an average density value 57 of a small area of the inspection picture.
Then , a difference detection 58 with the corresponding small area density average value of the standard pattern stored in the standard pattern memory 56 is performed, and a comparison 60 of the set average allowable value 59 and the size is performed.
Is exceeded, the comparison result Q is output.

The density boundary image stored in the binary memory 38 is also subjected to the same small area division processing as that of the area averaging processor 55 by the area division processor 62, and the density boundary image is stored in each small area. Is present, all the small area M × N pixels are output as density boundary pixels.

FIG. 9 shows an area dividing processor 62 of 5 × 5 pixels.
FIG. 3 is a diagram showing an example of the configuration of FIG. The output of the binary memory 38 is a serial signal similar to a video signal and is a 5.times.5 pixel OR circuit 62.
At the same time, the data is sequentially stored in a line memory R1 having a storage capacity for one line. At the same time, the stored contents of the line memories R1 to R4 are sequentially read out, and when they enter the 5 × 5 pixel OR circuit 620, the OR result of 25 pixels is sequentially output by the pipeline.

The output data is latched by a strobe signal generated every fifth line and every fifth pixel, and a logical product of the inverted data and the comparison result Q is obtained by an AND gate 63 to obtain a detection signal Q. At this time, in order to match the positions of the pixels of the two signals input to the AND gate 63, the phase of the strobe for latching the output data is shown in FIG.
Alternatively, the adjustment is performed by the fifth line detection circuit and the fifth pixel detection circuit in FIG. Note that the strobe signal is applied to one pixel per line.
5x5 pixel average processing data for each pixel
May be stored.

The detection signal 1 from the AND gate 61 and the detection signal Q from the AND gate 63 are ORed by the OR gate 64, and the OR of the G processing module and the B processing module is ORed by the AND gate 65. Warning signal 66
Output as

[0041]

As is apparent from the above description, according to the present invention, a mask is provided in order to eliminate the influence of meandering of a printed matter, a stain in an area other than the mask is detected, and the stain is removed in pixel units. Local defect detection to detect,
A small area is taken out, and a wide area defect detection for detecting an overall stain having a small density change in the area is performed. For wide area defect detection, a method of setting an area by providing a window and a method of automatically setting an area have also been realized.

[Brief description of the drawings]

FIG. 1 is a principle diagram for detecting a local defect .

FIG. 2 is a principle diagram according to claim 1 ;

FIG. 3 is a principle diagram for automatically setting a small area and detecting a wide area defect .

FIG. 4 is an overall configuration diagram of a defect detection apparatus including the present embodiment.

FIG. 5 is a block diagram showing the configuration of the first embodiment.

FIG. 6 is a diagram illustrating window setting.

FIG. 7 is a block diagram showing a configuration of a second embodiment.

FIG. 8 is a block diagram illustrating a specific example of an area averaging processor.

FIG. 9 is a block diagram showing a specific example of a region division processor.

FIG. 10 is an explanatory diagram for determining an allowable range of the photosensor due to meandering of a printed matter.

FIG. 11 is an explanatory diagram of a mask.

FIG. 12 is an explanatory diagram of a light receiving element having a large unit pixel area.

FIG. 13 is a diagram illustrating a comparison between an element having uniform spectral characteristics over the entire visible region and an element having spectral characteristics of red, blue, and green regions.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Image pick-up part 2 Image generation part 3 Mask area creation part 4 Standard picture memory 5, 12 Reference value setting part 6 Comparison part 7 Local defect judgment part 8, 15 memory 9 Window setting part 10 Standard picture generation part in window 11 Inspection in window Picture generation unit 13 Wide area defect judgment unit 14 Area average generation unit 16 Mask area division unit

 ──────────────────────────────────────────────────続 き Continuation of front page (72) Inventor Nobuyuki Kojima 2951-4 Ishikawacho, Hachioji-shi, Tokyo Nireco Co., Ltd. (56) References JP-A-61-153548 (JP, A)

Claims (2)

(57) [Claims] 1. An image pickup section for inputting a print pattern of a running belt on which the same pattern is printed, an image generation section for generating a pattern image from an output of the image pickup section, and a spatial filter by a differential operator for determining the density of the pattern image. A mask area creating unit that creates a density boundary image by performing a process, binarizing and then a fattening process, a memory that stores a pattern image output by the image generating unit, and a pattern image stored in the memory. A window setting unit for setting a window in an area where pixels of the density boundary image do not exist; and a picture image in the set window area is input from the image generation unit to generate an average value of density of a standard picture in the window. A standard image generation unit in a window, and a pattern image in the set window area is input from the image generation unit, and an average value of the density of the inspection pattern in the window is generated. An in-window inspection pattern generation unit, a reference value setting unit for setting a reference value of a density difference, and a density difference between the average value of the density of the standard pattern in the window and the average value of the density of the inspection pattern in the window. A print defect inspection device, comprising: a wide area defect determination unit that outputs a wide area defect signal when a reference value is exceeded. 2. The print defect inspection apparatus according to claim 1, wherein a color image sensor is used as a light receiving element of the image pickup unit, and color separation into red, blue, and green is performed and subsequent processing is performed.