JP2000241357A - Apparatus for inspecting contamination of printed matter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an apparatus for inspecting a contamination of printed matter by using a camera capable of photographing the pattern printed on a web running at a high speed. SOLUTION: A three-plate type line sensor camera 6 for taking the image of a web 1, on which the same pattern is printed, running at a high speed and a contamination detecting part 9 analyzing the image photographed by the three-plate type line sensor camera 6 to detect the contamination of the pattern are provided. The three-plate type line sensor camera 6 has a right-angled three-color spectral prism reflecting the blue color of incident light by its first inclined surface, reflecting the red color of the light passed through the first slope by its second slope, and emitting the green color passed through the first and second slopes and respective sensors receiving blue, red and green colors.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a stain inspection apparatus for detecting a print stain on a web running at a high speed on which the same pattern is printed.

[0002]

2. Description of the Related Art A line sensor is used as an image sensor for picking up a picture in order to detect a print stain on a web running at a high speed on which the same picture is printed. This is because a two-dimensional image can be obtained by the one-dimensional line sensor by moving the subject relatively to the camera in a direction perpendicular to the width direction of the line sensor. When a monochrome image is obtained, a single line sensor for detecting luminance may be used, but several methods are used to obtain a color image. Conventionally, a camera used for a printed smear inspection apparatus uses a three-color one-line CCD color sensor or a three-color three-line CCD color sensor.

FIG. 7 is a diagram for explaining the structure of a camera using a CCD color line sensor for one line of three colors. The light that has passed through the lens is converted into a three-color, one-line color CCD (Charge
RGB (red, green, blue) colors are extracted by a Coupled Device and output as R, G, and B signals. As shown, the three-color, one-line color CCD has a structure in which light receiving elements for detecting R, G, and B are repeatedly arranged in this order.

FIG. 8 is a view for explaining the configuration of a camera using a CCD color line sensor of three colors and three lines. 3
The three-line color CCD has R, G, B
Line sensors R of light receiving elements for detecting respective colors,
G and B are arranged. The outputs of the R line sensor, G line sensor, and B line sensor are output simultaneously.

[0005]

The above-mentioned technologies have the following problems. In the CCD color line sensor of one line of three colors shown in FIG. 7, since the light receiving elements for detecting the three colors of R, G, and B are repeatedly arranged on one line of CCD, the spatial color resolution is poor. Also, the fidelity of reproducibility on the monitor screen at the edge of the subject is poor. Furthermore, since it is difficult to obtain a CCD sensor that operates at high speed, it has been difficult to accurately detect a stain on a picture printed on a web running at high speed. In the three-color, three-line CCD color line sensor shown in FIG. 8, since the three colors R, G, and B are not on the same line, an image is reproduced when the camera and the subject are moving relative to each other in a direction perpendicular to the line sensor. In this case, a shift occurs between the three colors. This is because the positions of the R, G, and B color CCDs are different.
Is due to the different location of the subject.
Further, since there is no CCD sensor that operates at a high speed, it is difficult to accurately detect a stain on a pattern printed on a web that runs at a high speed.

SUMMARY OF THE INVENTION The present invention has been made in consideration of the above-described problems, and has as its object to provide a stain inspection apparatus for printed matter using a camera capable of accurately capturing a picture printed on a web running at high speed. And

[0007]

In order to achieve the above object, according to the first aspect of the present invention, there is provided a three-plate line sensor camera for picking up an image of a web running at high speed on which the same pattern is printed, and an image pick-up by the three-plate line sensor camera. And a dirt detection unit that detects the dirt on the pattern by analyzing the image thus obtained. The three-panel line sensor camera reflects the blue light of the incident light on the first inclined surface and intersects perpendicularly with the first inclined surface. A right-angle three-color spectral prism that reflects the red light of the light that has passed through the first inclined surface on the two inclined surfaces and emits the green light that has passed through the first inclined surface and the second inclined surface; A line sensor for receiving green light.

The line sensor scans the subject from left to right to obtain this one-dimensional image. However, when the subject is relatively moved in the direction perpendicular to the scanning direction, the currently obtained one-dimensional image and the preceding one-dimensional image are obtained. It is different from the obtained one-dimensional image. A two-dimensional image can be obtained by arranging the one-dimensional images repeatedly obtained in this manner in the order in which they were obtained. Although the one-dimensional images of R and B are reflected once by the prism, the two-dimensional image obtained by the above method is a normal image that is not inverted. The line sensor only needs to be able to detect the luminance of the separated colors, so a monochrome line sensor may be used. A high-speed monochrome line sensor is commercially available at a low price. Since light from the same position of the subject is split into three colors by the prism, there is no color shift. The image obtained by such a three-plate line sensor camera is compared with a normal image with no stain by the stain detection unit, and if there is a difference, it is determined as stain.

According to a second aspect of the present invention, the right-angled three-color spectral prism has a main body in which a blue-reflecting film is attached to one of the isosceles right triangles and a red-reflecting film is attached to the other isosceles triangle. A prism and the same length as the passing path from which light parallel to the bottom is attached to one of the equal sides at right angles to the bottom of the main prism, passes through one of the equal sides, is reflected by the other equal side, and exits outside the base. A first sub-prism, and a second sub-prism attached to the other equilateral side in parallel with the base and having the same length as a passage path from the other equilateral side to the outside of the base after being reflected. ing.

With this configuration, the exit surface of the first sub prism, the exit surface of the main prism, and the exit surface of the second sub prism are
Since the optical path lengths from the incident point on one of the equal sides become equal and the respective line sensors need to be set at the same distance from these surfaces, alignment adjustment becomes easy.

According to a third aspect of the present invention, the three-plate line sensor camera includes a first mirror inclined at 45 degrees to a vertical line of the web, and a first mirror disposed orthogonally to the first mirror. The image of the second mirror of the optical system including the second mirror that reflects the reflected image of the light is incident.

The first mirror reflects the incident light at right angles, and the second mirror reflects the incident light.
The reflected light is reflected at a right angle by the mirror, so that the emitted light returns to the incident light. By using an optical system that guides the emitted light to a three-plate line sensor camera, the distance between the subject and the camera can be significantly reduced. Because of this shortening, it is possible to use a standard lens with a long focal length and widen the field of view without using a wide-angle lens as the objective lens of the camera, so that images can be obtained over a wide range without distortion. Can be. Further, the apparatus can be made compact.

[0013]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a diagram showing a configuration of an embodiment of the present invention. The same pattern is repeatedly printed on the web 1 by a plate cylinder or the like (not shown). The roller 2 transports the web 1 at high speed in the direction of the arrow. One of the rollers 2 is provided with an encoder 3 which is directly connected to the shaft or via a gear to detect a rotation angle and output it as a pulse. Lighting device 5
Is a three-plate line sensor camera 6 using a fluorescent lamp or the like.
Illuminates the area to be imaged. The reflected light from the imaging area is reflected at right angles by the first mirror 7, further reflected at right angles by the second mirror 8, and is incident on the three-panel line sensor camera 6. As a result, the distance between the camera 6 and the imaging area can be significantly reduced. The print stain inspection device 9 takes in the picture of the web 1 from the output of the encoder 3 and compares it with the reference picture to detect the print stain of the picture.

FIG. 2 is a block diagram showing the configuration of the print smear inspection apparatus 9. As shown in FIG. The image generation unit 10 performs shading correction on an image signal captured by the three-plate line sensor camera 6. Further, a picture in the running direction of the web 1 is read from a signal of the encoder 3 and converted into a picture signal having a fixed period. The standard image storage memory 11 stores an image of a picture pattern free from print stains. This standard image may be a previously captured image of a picture without print stains, but if the currently captured image has no print stains, the image may be updated to that image. The comparison unit 12 compares the currently captured image with the standard image and detects the difference. If there is no difference, the stain determination unit 13 determines that there is no print stain, and if there is a difference, determines whether the difference is print stain.

FIG. 3 is a diagram showing an optical system of the three-plate line sensor camera 6. As shown in FIG. Reference numeral 21 denotes a lens that collects light from a subject. Reference numeral 22 denotes a right-angle three-color spectral prism, which includes a main prism 23, a first sub-prism 24, and a second sub-prism 25. The main prism 23 is a triangular prism having a cross section of a right-angled isosceles triangle, with the incident side being one equilateral 23a, the emitting side being the other equilateral 23b, and 23c being the base. A first coating 26 that reflects the B (blue) color and transmits the other color is deposited on one equal side 23a, and the first coating 26 reflects the R (red) color and transmits the other color on the other equal side. Two coatings 27 are deposited. These coatings are called dichroic mirrors.

A first sub-prism 24 is mounted on one of the equilateral sides 23a at right angles to the bottom side 23c.
A second sub-prism 25 is attached to 3b in parallel with the bottom side 23c. The intersection of the incident light A with one of the equal sides 23a is a, the intersection with the other equal side 23b is b, the emission point from the first sub-prism 24 is c, the emission point from the main prism 23 is d, and the second Assuming that the emission point from the prism 25 is e, the lengths ac, abd, and abe have the same length 3L.
Thereby, the passing lengths of the R, G, and B colors passing through the prism are all the same. The exit surface c from the first sub-prism 24,
A color correction filter 28 is attached to the exit surface d from the main prism 23 and the exit surface e from the second sub-prism 25, and functions to adjust imperfect spectral characteristics only by color separation by the coatings 26 and 27.

The three line sensors 29 are arranged at a fixed distance from the respective color correction filters 28, and the light passing distances from the point a are all the same. The line sensor 29 uses a commercially available high-speed monochrome CCD. Since each line sensor 29 only needs to detect the luminance of each color and convert it into an electric signal, it is not necessary to use a color line sensor.
In order to reproduce an image, each of these electric signals is input to the corresponding R electron gun, G electron gun, and B electron gun of the cathode ray tube of the monitor, and the corresponding color of the three-color phosphor screen is generated by the electron beam of each color. It should be done.

FIG. 4 shows a camera circuit configuration of the present embodiment. CCD denotes the line sensor 29 of FIG. The drive circuit 30 includes each line sensor 29 and devices 31 connected thereto,
Synchronize 32. The video signal processing circuit 31 performs signal processing such as amplification of the signal of the line sensor 29, clipping at a level higher than the specified level of the video signal, clamping so that the black level does not fluctuate, and gamma correction for correctly reproducing the gradation of the subject. Do. The A / D converter 32 converts an analog signal into a digital signal. In this way, the R,
G and B digital signals are output.

FIG. 5 is an explanatory view in which a two-dimensional image can be obtained by the three-plate line sensor camera of the present invention. When the object S is viewed as shown in the figure, the image viewed at the position A and the light reflected once by the mirror B
The top and bottom of the image viewed from the position are reversed. Therefore, FIG.
2D image sensor (2D CC)
When D) is used, an operation of inverting the B and R images up and down with respect to G is required. In order to avoid this, a prism that mirror-reflects B and R twice is usually used. However, when the subject relatively moves in a direction orthogonal to the scanning direction of the line sensor using a CCD line sensor (one-dimensional image sensor) as in the present invention, only point K in the figure is viewed. That is, each pixel of the CCD sees the distribution of brightness in the horizontal direction (direction perpendicular to the paper surface) at the K position as shown in FIG.
Next, when the subject moves and the K1 point comes to the K point position, CC
D indicates the horizontal brightness distribution at point K1 at that position.
That is, the R, G, and B CCD line sensors simultaneously display the K point for three colors, display the next moved K1 point, and further display the K2 point. This is repeated to form a two-dimensional screen, so that there is no upward or downward reversal of the R and B images, and a normal two-dimensional image can be obtained.

Since the three-plate line sensor camera 6 requires a color separation prism, as shown in FIG.
In addition to the aberration of 1, the aberration of the color separation prism 22 is also added, and the image quality in the peripheral portion of the screen is easily deteriorated. On the other hand, the image quality of the imaging lens 21 is generally inferior to the wide-angle type, and the image quality tends to be further deteriorated when combined with the color separation prism 22. Therefore, it is necessary to use a standard lens that improves the image quality as much as possible. A three-panel line sensor camera has approximately three times the spatial color separation capability of a three-color one-line camera, so if the spatial color separation capability important for inspection is constant, the field of view of one camera can be widened. It is possible. However, if a standard lens is used instead of a short-focus wide-angle lens, the distance between the inspection surface and the camera is inevitably increased, and a large space is required for mounting the inspection apparatus. Therefore, by providing the first mirror 7 and the second mirror 8 as shown in FIG. 1, the distance between the three-plate line sensor camera 6 and the web 1 can be shortened, and the apparatus can be made compact.

[0021]

As is clear from the above description, the present invention has the following effects. By using a camera having a large spatial resolution capability for each color, it is possible to accurately detect print stains. Since a commercially available high-speed monochrome CCD is used, a clear image of an object moving at high speed can be obtained, and a high-speed line print stain inspection can be performed. Since the three color line sensors each output an image at the same location, it is also possible to inspect the print stain on the web 1 running on a curved surface such as a roll surface. By using the mirror, the installation space of the camera can be reduced without deteriorating the image quality, and the whole apparatus can be made compact.

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration of an embodiment of the present invention.

FIG. 2 is a block diagram of a print smear inspection apparatus.

FIG. 3 is a diagram showing a configuration of a rectangular three-color spectral prism used in the present invention.

FIG. 4 is a camera circuit diagram of the embodiment.

FIG. 5 is an explanatory diagram in which a two-dimensional image of the camera of the present invention becomes a normal image.

FIG. 6 shows components of a CCD line sensor.

FIG. 7 is a diagram illustrating a configuration of a color camera using a three-color one-line CCD.

FIG. 8 is a diagram showing a configuration of a color camera using a three-color three-line CCD.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Web 2 Roller 3 Encoder 5 Illumination device 6 Three-plate line sensor camera 7 1st mirror 8 2nd mirror 9 Printing dirt inspection device 10 Image processing part 11 Standard image storage memory 12 Comparison part 13 Dirt judgment part 21 Lens 22 Right angle three Color spectral prism 23 Main prism 23a One equilateral 23b The other equilateral 23c Bottom 24 First sub-prism 25 Second sub-prism 26 First coating 27 Second coating 28 Color correction filter 29 Line sensor 30 Drive circuit 31 Video signal processing circuit 32 A / D converter

Claims (3)

[Claims] 1. A three-plate line sensor camera for capturing an image of a web running at high speed on which the same pattern is printed, a dirt detection unit for analyzing a picture taken by the three-plate line sensor camera and detecting dirt on the pattern, The three-panel line sensor camera reflects the blue of the incident light on the first inclined surface,
A right-angle three-color spectral prism that reflects the red light of the light that has passed through the first inclined surface and emits the green light that has passed through the first and second inclined surfaces at a second inclined surface that is orthogonal to the first inclined surface. And a line stain sensor for receiving the blue, red, and green light, respectively. 2. The main prism, wherein the right-angled three-color spectral prism has a blue-reflecting film adhered to one isosceles right-angled isosceles triangle and a red-reflective film adhered to the other isosceles triangle. Are attached to the bottom of the main prism at right angles to the first side, and the first sub-path has the same length as the passing path from which light parallel to the bottom passes through one of the equal sides, is reflected by the other equal side, and exits outside the bottom. A prism and a second sub-prism attached to the other equilateral side in parallel with the base and having the same length as a passage path from the other equilateral side to the outside of the base after being reflected. The printed matter inspection apparatus according to claim 1. 3. The three-panel line sensor camera has a first mirror inclined by 45 degrees with respect to a vertical line of the web,
3. An image of a second mirror of an optical system comprising a second mirror disposed orthogonal to the first mirror and reflecting a reflection image of the first mirror, is incident thereon. Print stain inspection equipment.