JPH04339653A - Apparatus for inspecting printing fault - Google Patents

Abstract

PURPOSE:To detect the local fault of a pixel unit and a wide fault over a certain region. CONSTITUTION:An image is formed from the data imaged in an imaging part 1 in an image forming part 2. The contour of said image is extracted to be subjected to thickening processing to form a mask image in a mask region forming part 3. The image forming part 2 forms a standard pattern image to store said image in a standard pattern memory 4 and, thereafter, a pattern image to be inspected is formed. A comparison part 6 compares the density of the standard pattern image with that of the pattern image to be inspected and it is judged whether the difference between both images exceeds a reference value. A local fault judging part 7 outputs a local fault detection signal when the data exceeding the reference value is not contained in the mask of the mask image. A wide flaw is outputted by providing a window or a region to perform the comparison of average density.

Description

[Detailed description of the invention]

0001

[Field of Industrial Application] The present invention relates to a device for inspecting defects in printed patterns on the surface of sheets or strips that repeat at regular intervals, and particularly for inspecting stains caused by various color inks that occur on color printed matter. The present invention relates to a printing defect inspection device.

0002

2. Description of the Related Art A method of inspecting defects in such sheet or strip-shaped printed matter will be explained. One method is to image the print pattern using photosensors that are arranged perpendicularly to the running direction of the printed material and have a relatively large area compared to the amount of meandering of the printed material, and the signals from each photosensor are be stored in memory. Contamination (defects) due to changes in the signals received by each phone sensor due to the meandering of the printed material
A detection tolerance range was set and an alarm was output when the tolerance range was exceeded.

FIG. 10 is an explanatory diagram for setting this tolerance range. When the pattern shifts from A to B due to meandering of the printed material, the amount of light received by each element i and j of the photosensor changes.
The output of each element i, j changes. In this way, even if there is no defect in the printed matter, the output changes due to meandering, so it is necessary to set a tolerance range at a value larger than the width of change due to meandering.

Another method involves extracting the outline of a standard printed pattern by means such as differentiation, binarizing it, and then storing the image, which has been thickened by an amount corresponding to the meandering amount, in a memory. put. Similarly, the contour of the pattern to be inspected is extracted by differentiation or the like, subjected to binarization processing, and this image is compared with the image stored in the memory. If a binarized image of the pattern to be inspected appears in a position where there are no pixels in the image stored in the memory, a warning is output as a stain.

FIG. 11 is a diagram illustrating a stain detection method using this contour binary image, where A indicates the contour, and the diagonally shaded area B indicates the area subjected to the thickening process. When the pixels (indicated by x) of the image obtained by converting the outline of the pattern to be inspected are within the diagonal lines, it is not determined to be a stain, but if it occurs anywhere else, it is determined to be a stain.

[0006]

[Problems to be Solved by the Invention] Printing stains include fine particle-like ink splatters, or line-shaped stains that are narrow in the width direction of printed matter and long in the running direction, such as the doctor lines of a gravure printing machine. In a light-receiving element with a large pixel area, the minute dirt density is averaged with the surrounding reflection density, making detection difficult. Furthermore, the detection sensitivity is further reduced due to the deviation of the reading position due to the meandering of the printed material.

FIG. 12 is a diagram showing a light-receiving element with a large unit pixel area, where E indicates the 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 with a large area D·H.

[0008] In addition, dirt may adhere to a relatively wide area at a low density, such as dirt on a printed material. When detecting the outline of a dirt image having a low density by means such as differential processing, noise is often erroneously detected in areas other than the dirt image. This is because the differential processing outputs a large value when the rate of change in density is large, but when the density of dirt is uniformly low, only a small value is output, and if a small value is set as the reference value, The noise in some parts becomes dirt,
This is because there are many cases of false detection.

[0009] Furthermore, stains generated on color printed matter have various tones, and a light receiving element having spectral sensitivity over the entire visible region has insufficient detection sensitivity.

In FIG. 13, (a) shows the detection sensitivity of an element having uniform spectral characteristics over the entire visible region, and (b) shows the detection sensitivity only in the blue (B), green (G), and red (R) regions. FIG. 2 is a diagram illustrating detection sensitivity of an element having spectral characteristics. For example, in the case of an element that has uniform spectral characteristics over the entire visible range when receiving cyan light, the amount of change in the detection signal relative to white is 30% per area without diagonal lines, as shown in (a). Change occurs. In other words, no change occurs in the 70% indicated by diagonal lines. On the other hand, as shown in (b), B,
The following changes occur with respect to white in each of the G and R elements. B element: 0% G element: 0% R element: 100% In other words, 100% of the R element, which is a complementary color to blue-green, is detected, but the other B and G elements are not detected. In other words, the R element is (a)
It has three times the detection sensitivity of elements with uniform spectral characteristics over the entire visible region.

The present invention has been made in view of the above-mentioned problems, and an object of the present invention is to provide a printing defect inspection device that detects printing stains by classifying them into local stains and wide-area stains that are spread widely and thinly as a whole. With the goal.

0012

[Means for Solving the Problems] FIG. 1 is a first principle diagram of the present invention. In the figure, 1 is an imaging unit that inputs the printed pattern of a running strip printed with the same pattern, 2 is an image generation unit that generates a pattern image from the output of this imaging unit 1, and 3 is a differential of this pattern image density. A mask area creation unit performs spatial filter processing by an operator, performs binarization processing, and then fattening processing to create a density boundary image; 4 stores a standard pattern image generated from the standard pattern by the image generation unit 2; a standard picture memory; 5, a reference value setting unit for setting a reference value for the density difference; 6, the image generation unit 2 compares the inspection target picture image generated from the inspection target picture with the standard picture image, and determines the density difference as described above; A comparison unit 7 determines whether or not the reference value is exceeded, and if a pixel of the pattern image to be inspected that exceeds the reference value is located in an area where no pixels of the density boundary image exist, it is determined to be a defect, and a local defect signal is generated. This is a local defect determination unit that outputs the following.

FIG. 2 is a second principle diagram of the present invention. In the figure, 1 is an imaging unit that inputs the printed pattern of a running strip printed with the same pattern, 2 is an image generation unit that generates a pattern image from the output of this imaging unit 1, and 3 is a differential of this pattern image density. A mask area creation section that performs spatial filter processing by an operator, binarization processing, and fattening processing to create a density boundary image; 8 is a memory that stores the pattern image output from the image generation section; 9 is this memory A window setting unit sets a window in an area where pixels of the density boundary image do not exist based on the pattern image stored in 8, and a window setting unit 10 inputs the pattern image in the set window area from the image generation unit 2 and sets a window An in-window standard value pattern generation section 11 generates an average density value of an internal standard pattern;
12 is a reference value setting section that sets a reference value for the density difference; 13 is an average value of the density of the standard patterns within the window; and a wide area defect determination unit that outputs a wide area defect signal when the density difference between the average value of the density of the inspected pattern within the window exceeds the reference value.

FIG. 3 is a diagram showing the third principle of the present invention. In the figure, 1 is an imaging unit that inputs the printed pattern of a running strip printed with the same pattern, 2 is an image generation unit that generates a pattern image from the output of this imaging unit 1, and 3 is a differential of this pattern image density. A mask area creation unit that performs spatial filter processing by an operator, binarization processing, and fattening processing to create a density boundary image; 14 divides the pattern image generated by the image generation unit 2 into a plurality of measurement regions; an area average generation unit that calculates the average density of each measurement area; 15 a memory that stores the average density of each measurement area calculated by the area average generation unit 14 for the standard pattern image; a mask area dividing unit that divides the density boundary image created by the mask area creating unit 3 into the same sections as the measurement area; 12 a reference value setting unit that sets a reference value for the density difference; 13 an area average generating unit 14; The average density value of the measurement area of the pattern image to be inspected generated by is compared with the average density value of the corresponding measurement area of the standard pattern image stored in the memory 15, and the density difference is determined by the reference value setting section. wide area defect determination that outputs a wide area defect signal when pixels constituting the density boundary image are not included in the corresponding mask area generated by the mask area dividing unit 16 when the reference value of 12 is exceeded; Department.

Further, a color image sensor is used as the light receiving element of the image pickup section 1, and the colors are separated into red, blue, and green for subsequent processing.

[0016]

[Operation] A one-dimensional image of a standard pattern image captured by the imaging unit 1 is converted into a two-dimensional image by the image generation unit 2, a contour is extracted by differential processing and binarization processing by the mask area creation unit 3, and printing is performed on this contour. Fattening is performed to correspond to the amount of meandering of the body. There is a possibility that a pattern exists within this thickened area. A pattern to be inspected is imaged by an imaging section 1, a two-dimensional image is generated by an image generation section 2, and the density of each pixel of the standard pattern is compared with the density of each pixel of the test pattern. If there is a difference in this concentration, it may be due to dirt or dust. Therefore, the density boundary image is used as a mask, and when a density difference exceeding the standard value occurs outside of this mask (thickened area), it is determined that the defect is due to dirt or dust. It is highly likely that this is due to meandering, so it should not be determined as a defect. This allows defect inspection to be performed with high pixel resolution at each pixel level.

Further, the window setting section 9 sets a window in an area where there are no pixels of the density boundary image, that is, in an area other than the mask. The difference between the average density within the window of the standard picture image and the average density within the window of the inspection picture image is compared, and if the difference is greater than the reference value, it is determined that the inspection picture within this window is entirely dirty. This makes it possible to detect wide-area defects, such as stains on printed material, in which stains are adhered to a relatively wide area at a low density. Since a window is set in addition to the mask, the influence of meandering of the printed material is eliminated.

In addition, the area average generation unit 14 divides the pattern image into a plurality of areas and compares the average density of the standard pattern and the average density of the pattern to be inspected for each measurement area, and the difference in density is determined as the standard. If the value is greater than the value, in order to eliminate the influence of the meandering of the printing material, it is checked whether the pixels of the density boundary image are included in the mask area of the same section, and if the pixels are not included, it can be determined that there is wide-area staining. Thereby, the processing of the area average generation unit 14 can be automated. In the case of second-principle diagrams, automation is difficult because it is necessary to display a window on a CRT display and set the window at a position where there are no pixels of the density boundary image.

Furthermore, by using a color sensor to separate the colors into red, blue, and green for inspection, the detection sensitivity can be improved up to three times as compared to the case of a light-receiving element having spectral sensitivity over the entire visible region.

[0020]

Embodiments Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 4 is a diagram showing the entire apparatus including the printing defect inspection apparatus of this embodiment. A strip-shaped printed material 21 printed with the same pattern by the printing unit 20 flows through a roll 22. A mark sensor 23 is provided above the printed matter 21 on one roll 22 in the inspection target section, and reads a synchronization mark or a register mark for color control printed on the margin of the printed matter 21, and sends the signal to the printed matter 21.
Used to synchronize repeated patterns.

[0021] Also, the other roll 22' in the section to be inspected
A rotary encoder 24 is provided above, and the printed matter 21
A pulse signal is generated every time the vehicle travels a predetermined length. There are two types of illumination, and when the printed matter 21 is transparent like a film, illumination light is guided from a transmitted light source 25 to the printed matter 21 through an optical light guide 26 and a diffuser plate 27. The diffuser plate 27 prevents uneven illumination of transmitted illumination. If the printed material 21 is opaque, such as paper, illumination is guided from the reflective light source 28 to the printed material 21 through an optical light guide 29. The CCD color line sensor camera 30 reads one line of pixel data (one scanning line) of the pattern of the printed matter 21 illuminated by illumination in synchronization with the pulse signal generated by the rotary encoder 24 .

FIG. 5 shows a block diagram of the printing defect inspection apparatus of the first embodiment. In this embodiment, the R (red), G (green), and B (blue) pattern signals inputted from the CCD color line sensor camera 30 are processed by the R processing module, the G processing module, and the G processing module.
Processed by B processing module. Since each module has the same configuration, we will show the detailed configuration of the R processing module.
explain.

In FIG. 5, the picture signal is represented by CC as the amount of light.
It 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 proportional to the density gradation and to facilitate subsequent processing. Next, the scan converter 32 inputs the mark sensor signal and rotary encoder signal explained in FIG. Converts to a pattern signal with a constant period. The CRT controller 33 generates a periodic signal and an image memory address signal for this purpose.

The picture signal after scan conversion is stored in the standard picture memory 3.
At the same time, a density boundary image is created by performing spatial filter processing 35, binarization processing 36, and thickening processing 37 using a differential operator, and is stored in a binary memory 38.

The inspection pattern signal 39 subsequently read from the CCD color line sensor camera 30 is subjected to logarithmic conversion 31 and scan conversion 32 in the same manner as described above. The difference is taken and this is used as a set individual tolerance value 41 which is a tolerance value and a comparator 42
Compare the size with , and if it exceeds the set individual tolerance value 41,
A 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, and the overlap with the density boundary pixel is checked, and if there is no overlap, the detection signal P is output.

On the other hand, the standard picture signal for scan conversion is sent to the CPU 44.
The image is taken into the pattern memory 45 by the memory image update signal from . The contents of the picture memory 45 are stored in the D/A converter 46.
is converted into an analog video signal by

[0027] The window and the window position are CR.
It is created by the window position setter 47 and window generator 48 from the horizontal/vertical synchronization signal and the image address signal generated by the T controller 33, and is sent to the picture memory 45.
It is synchronized with the image readout timing. The window signal is mixed with the analog video signal from the D/A converter 46 in a mixer 49 and displayed on a CRT display 50. The window position is set by selecting an area where the density of the pattern image shown on the CRT display 50 is less varied.

When the CPU 44 reads the window position from the window position setter 47, the CPU 44 reads the density data of M pixels×N pixels constituting the window at the window position from the picture memory 45, and stores this 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. A plurality of windows are usually provided. For all windows, the average density value of the standard pattern is calculated in the same way and stored in the internal memory of the CPU 44.The CPU 44 then outputs an update signal to the pattern memory 45, and the next scan-converted test pattern signal is stored in the pattern memory. 45.

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

The dirt signal and the detection signal P from the AND gate 43 are logically summed at the OR gate 52, and further logically summed with the respective outputs of the G processing module and the B processing module at the OR gate 53, and the result is output as an alarm. Signal 5
4 is output as a dirt alarm signal.

Next, a second embodiment will be explained. The second embodiment detects wide-area defects by automatically setting small regions instead of the window processing in the first embodiment. FIG. 7 is a block diagram showing the configuration of the second embodiment, and parts having the same symbols as those in FIG. 5 have the same functions.

The present embodiment will be explained below with respect to the points that are different from the first embodiment. The image signal scan-converted by the scan converter 32 is divided into small areas having an area of M pixels x N pixels by the area averaging processor 55, and the average density value of M x N pixels within each small area is determined and standardized. It is stored in the picture memory 56.

FIG. 8 shows a 5 pixel×5 pixel area averaging processor 5.
5 is a diagram showing a configuration example of No. 5; FIG. The image signal after scan conversion is a serial signal similar to a video signal and is simultaneously input to a 5 pixel x 5 pixel averaging circuit 550 and 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 processing circuit 550, whereupon the average processing results of 25 pixels are sequentially outputted by the pipeline. The output data is latched by a strobe signal generated every 5th line and 5th pixel and stored in the standard picture memory 5.
6 is stored.

The inspection pattern signal subsequently read from the CCD color line sensor camera 30 undergoes logarithmic conversion 31, scan conversion 32, and density comparison with the image stored in the standard pattern memory 34 for each pixel, as in the case of standard patterns. Difference detection 40
The comparison result is ANDed with the inverted signal of the binary memory 38 using an ANDCAD 61. If the pixel does not overlap with the density boundary pixel,
The AND result is output as a detection signal P.

At the same time, the test pattern signal undergoes area averaging processing 55 to generate a small area density average value 57 of the test pattern, and the corresponding small area density average value of the standard pattern stored in the standard pattern memory 56 is generated. A difference detection 58 with the value is performed, and a comparison 60 of magnitude with a set average allowable value 59 is performed, and if the set average allowable value 59 is exceeded, a comparison result Q is output.

The density boundary image stored in the binary memory 38 is also divided by the area averaging processor 55.The same small area dividing process is performed by the area dividing processor 62, and density boundary pixels are divided into each small area. exists, all M×N pixels in the small area are output as density boundary pixels.

FIG. 9 shows a 5 pixel x 5 pixel area division processor 6.
2 is a diagram showing a configuration example of No. 2. FIG. The output of the binary memory 38 is a serial signal similar to a video signal that enters the 5×5 pixel OR circuit 620 and is simultaneously stored sequentially in the line memory R1 having a storage capacity for one line. At the same time, the contents of the line memories R1 to R4 are sequentially read out,
When entering the 5×5 pixel OR circuit 620, the pipeline sequentially outputs the OR result of 25 pixels.

The output data is latched by a strobe signal generated on the fifth line and every fifth pixel, and the AND gate 63 calculates the AND of the inverted data and the comparison result Q described above to obtain the detection signal Q. At this time, in order to align the pixel positions of the two signals input to the AND gate 63, the phase of the strobe that latches the output data is adjusted by the fifth line detection circuit and the fifth pixel detection circuit in FIG. 8 or 9. Ru.

The detection signal 1 from the AND gate 61 and the detection signal Q from the AND gate 63 are logically summed by an OR gate 64, and then logically summed with the G processing module and the B processing module by an AND gate 65. The result is output as an alarm signal 66.

[0041]

As is clear from the above description, the present invention provides a mask to eliminate the influence of meandering printed matter, detects dirt in areas other than this mask, and detects dirt in pixel units. Local defect detection to be detected;
Wide-area defect detection is performed by extracting a small area and detecting overall contamination with small density changes within that area. In addition, for wide-area defect detection, we have realized a method of setting a window to define the area and a method of automatically setting the area.

[Brief explanation of drawings]

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

FIG. 2 is a second principle diagram of the present invention.

FIG. 3 is a third principle diagram of the present invention.

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

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

FIG. 6 is a diagram illustrating window settings.

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

FIG. 8 is a block diagram showing a specific example of a region averaging processor.

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

FIG. 10 is an explanatory diagram that defines the allowable range of the photosensor due to meandering of printed matter.

FIG. 11 is an explanatory diagram of a mask.

FIG. 12 is an explanatory diagram of a light receiving element with 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 in each of the red, blue, and green regions.

[Explanation of symbols]

1 Imaging section 2 Image generation section 3 Mask area creation section 4 Standard picture memory 5, 12 Standard value setting section 6 Comparison section 7 Local defect determination section 8,15 Memory 9 Window settings section 10 In-window standard pattern generation section 11 In-window inspection pattern generation section 13 Wide area defect determination section 14 Area average generation unit 16 Mask area division part

Claims (4)

[Claims] 1. An imaging section that inputs a printed pattern of a traveling strip printed with the same pattern, an image generation section that generates a pattern image from the output of this imaging section, and a spatial filter that uses a differential operator to calculate the density of this pattern image. a mask area creation unit that performs processing and binarization processing and then thickening processing to create a density boundary image; a standard pattern memory that stores the standard pattern image generated from the standard pattern by the image generation unit; and a density difference a reference value setting unit that sets a reference value for the image, and a comparison unit that compares the standard pattern image with the image to be inspected generated from the pattern to be inspected by the image generation unit and determines whether the difference in density exceeds the reference value. and a local defect determination unit that determines that a pixel exceeding the reference value among the pixels of the pattern image to be inspected is defective and outputs a local defect signal if the pixel exceeds the reference value in an area where no pixel of the density boundary image exists. A printing defect inspection device characterized by: 2. An imaging section that inputs a printed pattern of a traveling strip printed with the same pattern, an image generation section that generates a pattern image from the output of this imaging section, and a spatial filter that uses a differential operator to calculate the density of this pattern image. A mask area creation unit that processes and binarizes and then thickens to create a density boundary image, a memory that stores the pattern image output from the image generation unit, and a pattern image stored in this memory. A window setting unit sets a window in an area where no pixels of the density boundary image exist, and a pattern image within the set window area is inputted from the image generation unit to generate an average value of the density of the standard pattern in the window. an in-window standard pattern generation section; an in-window inspection pattern generation section that receives a pattern image within the set window area from the image generation section and generates an average value of the density of the in-window inspection pattern; and a density difference standard. a reference value setting unit for setting a value; and a wide area defect that outputs a wide area defect signal when 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. A printing defect inspection device comprising: a determining section. 3. An imaging section that inputs a printed pattern of a traveling strip printed with the same pattern, an image generation section that generates a pattern image from the output of this imaging section, and a spatial filter using a differential operator to calculate the density of this pattern image. a mask area creation unit that performs processing, binarization processing, and then fattening processing to create a density boundary image; and a mask area creation unit that divides the picture image generated by the image generation unit into a plurality of measurement areas and averages the density of each measurement area. an area average generation unit that calculates the value, a memory that stores the average density value of each measurement area calculated by the area average generation unit for the standard picture image, and a density boundary image created by the mask area creation unit. a mask area dividing unit that divides the measurement area into the same sections; a reference value setting unit that sets a reference value for the density difference; and a density average value of the measurement area of the pattern image to be inspected generated by the area average generation unit. , Compare the density average value of the corresponding measurement area of the standard pattern image stored in the memory, and if the density difference exceeds the reference value of the reference value setting unit, the correspondence generated by the mask area dividing unit. and a wide area defect determination section that outputs a wide area defect signal when the pixels constituting the density boundary image are not included in the mask area. 4. A color image sensor is used as a light-receiving element of the imaging unit, and the colors are separated into red, blue, and green for subsequent processing. printing defect inspection equipment.