JPH07306964A - Device for discriminating normal/defective condition of paper - Google Patents

Abstract

PURPOSE:To recognize a microprint without a picture detector having a high resolution by generating moire stripes on the microprint and detecting the picture of moire stripes and subjecting them to space frequency analysis to recognize the microprint. CONSTITUTION:This discriminating device is provided with a carrying part 2, a photo-interrupter 3, an optical system 4, an area sensor (picture detecting means) 5, a lattice plate (interference fringe generating means) 6, and a strobe illumination device (an illuminating means and an intermittent light emitting light source) 7. A lattice is put on the microprint printed on paper 9 to generate moire stripes having a space frequency higher than that of the microprint. These moire stripes are subjected to space frequency analysis to recognize the microprint. Consequently, the optical system 4 and the line sensor 5 which have lower resolutions than those required for direct picture recognition of the microprint can be used.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a sheet quality determining device for optically determining the quality of a sheet on which a microprint is printed.

[0002]

2. Description of the Related Art Generally, very fine characters and patterns (hereinafter referred to as microprints) may be printed on a paper sheet. Since the line width of this microprint is very small (for example, several tens of μm), advanced technology is required to print the microprint on a large number of paper sheets with uniform quality. Therefore, it is possible to identify whether or not the microprint is printed according to the standard, and use the identification result as a reference for determining the quality of the sheet.

However, since it is difficult to visually and accurately recognize the microprint, it is necessary to use an image recognition technique in order to make a pass / fail determination of the paper sheet without error.

As a general fine image input technique, a magnifying optical system and an image detector (area sensor, line sensor, etc.)
And a method of capturing a magnified image of an input object in an image detector, a method of scanning a minute laser spot and capturing reflected light in a photodetector, and the like.

A moire phenomenon is known as a general optical phenomenon. And this moire phenomenon is, for example,
Optical Technology Contact by Yoshizawa, Vol.29. No.7 (1991) p4
~ P10.

[0006]

By the way, for example, when a method using a magnifying optical system is adopted, it is necessary to capture an image of a relatively large area in the detector for image processing and statistical processing in the subsequent stage. Become. Especially when a character string is printed, it is desirable to input images of a plurality of characters. However, in order to satisfy this condition, 100
A large and expensive area sensor with 10,000 pixels or more is required.
Therefore, the cost is high.

In consideration of the size (line width and outer shape) of the microprint, the imaging optical system is required to have a resolution of 10 to 20 μm. However, if the resolution of the optical system is satisfied, the depth of field of the optical element is very shallow (± 0.0
5 mm). That is, it is necessary to use a high resolution area sensor and keep the flatness of the paper sheet within ± 0.05 mm. Therefore, even if the technique of capturing the enlarged image in the image detector is simply applied, the cost becomes high and it is difficult to obtain a good determination result.

This also applies to the laser scanning method, and it is more difficult to obtain a good discrimination result considering the relative movement of the paper sheet and the light beam. It is an object of the present invention to provide a paper sheet quality determination device capable of recognizing a microprint without using a high-resolution image detector.

[0009]

In order to achieve the above object, the invention of claim 1 is a paper sheet supporting means for supporting a paper sheet having a microprint, and a moire fringe for generating a moire fringe on the microprint. The image forming apparatus includes a generating unit, an image detecting unit for detecting an image of the moire fringes, and a microprint recognizing unit for recognizing the microprint by analyzing the spatial frequency of the Moire fringes. And the invention of claim 1 is
The microprint can be recognized without using a high resolution image detector.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIGS. 1 and 2 show an embodiment of the present invention, in which reference numeral 1 is a paper sheet quality determination device (hereinafter referred to as a determination device).

The discriminating apparatus 1 includes a conveying section (paper sheet supporting means) 2, a photo interrupter 3, an optical system 4, an area sensor (image detecting means) 5, a lattice plate (interference fringe generating means) 6,
And strobe lighting device (illuminating means, intermittent light source) 7
Is equipped with. Of these, the transport unit 2 has a conveyor 8. The conveyor 8 supports the rectangular paper sheet 9 and supports the paper sheet 9 with the longitudinal direction thereof oriented in the traveling direction. Then, the conveyor 8 horizontally conveys the paper sheet 9 at a constant speed, as indicated by an arrow A in FIG. Here, it is possible to adopt various general ones as the transport unit 2.

A microprint 10 composed of a plurality of characters is printed on the paper surface of the paper sheet 9 handled in this embodiment, as shown in an enlarged view in FIG. The line width of each character is, for example, several tens of μm or less.

The photo interrupter 3 has a light projecting section 11 and a light receiving section 12. The light projecting unit 11 and the light receiving unit 12 are arranged with the passage of the paper sheet 9 in between, and light (not shown) emitted from the light projecting unit 11 is taken into the light receiving unit 12. When the paper sheet 9 is passing between the light projecting unit 10 and the light receiving unit 11, the light of the light projecting unit 11 is blocked by the paper sheet 9 and does not enter the light receiving unit 12. Then, the light receiving unit 12 outputs an electric signal according to the presence / absence of light incident.

The area sensor 5 uses a CCD element. Further, the area sensor 5 is arranged above the conveyor 8 and the light receiving surface of the CCD is directed toward the conveyor 8. The optical system 4 is arranged between the area sensor 5 and the conveyor 8. The strobe illumination device 7 is obliquely directed to the conveyor 8 and illuminates the paper sheet 9 conveyed by the conveyor 8 at a predetermined timing. The illuminated image of the paper sheet 9 is input to the area sensor 5 via the optical system 4.

The grid plate 6 is arranged between the conveyor 8 and the optical system 4. The lattice plate 6 is made of transparent glass, and the lattice surface of the lattice plate 6 is printed with lattices at predetermined intervals. Then, the image of the paper sheet 9 passes through the lattice plate 6 and is taken into the area sensor 5.

Further, the discriminating device 1 is provided with an arithmetic control system 13 shown in FIG. This arithmetic control system 13
Is a photo interrupter 3, a delay circuit 14, a trigger circuit 15, an area sensor 5, an image processing unit 16, and an FFT.
(High-speed Fourier transform) analyzer 17, comparator 1
8 and a result display unit 19. Further, the strobe lighting device 7 is connected to the trigger circuit 15 in parallel with the area sensor 5. Image processing unit 16, F
The FT analyzer 17 and the comparator 18 constitute the microprint recognition means 20.

The output signal of the photo interrupter 3 is sent to the trigger circuit 15 via the delay circuit 14, and the trigger circuit 15 causes the area sensor 5 and the strobe lighting device 7 to operate synchronously. The image data output from the area sensor 5 is sent to the image processing unit 16, and the data processed by the image processing unit 16 is Fourier transformed by the FFT analyzer 17. A portion of the output signal of the FFT analyzer 17 corresponding to the intensity of the specific frequency is compared with a predetermined threshold Th by the comparator 18, and the result display section displays the result of the quality judgment of the paper sheet 9 based on the comparison result. 19 is displayed. As the result display unit 19, various general output devices such as a display device and a printer device can be used.

Next, the operation of the discriminating apparatus 1 will be described. First, as shown in FIG. 1, the paper sheet 9 is conveyed at a constant speed by the conveyor 8 with the paper surface facing up and down, and the passage sensor 4
Sent to. When the front end of the paper sheet 9 reaches the photo interrupter 3, the output signal of the photo interrupter 3 changes.
Further, the output signal of the photo interrupter 3 is delayed by the delay circuit 14 and input to the trigger circuit 15, which causes the area sensor 5 and the strobe lighting device 7 to operate in synchronization.

The delay time of the delay circuit 14 is set based on the distance from the front end of the paper sheet 9 to the microprint 10 and the conveying speed of the conveyor 8. That is, when the microprint 10 reaches a predetermined position, the strobe lighting device 7 illuminates the paper sheet 9 (particularly, the portion where the microprint 10 is printed).

The image of the microprint 10 is guided to the area sensor 5 by the optical system 4. Micro print 10
Since the image of 3 is transmitted through the lattice plate 6, the image of the microprint 10 overlaps the image of the lattice 21 printed on the lattice plate 6 as shown in FIG. 3A. Each microprint character 2
Since 2 is composed of a plurality of line elements, the microprint 10 and the grid 21 intersect each other, so that FIG.
Moire fringes 23 are generated as schematically shown in FIG.
Then, the moire fringes 23 are imaged on the area sensor 5 by the optical system 4. In addition, here, the intervals between the lines of the grid 21 are substantially uniform, and the value is the microprint character 2.
Although the distance between the two line elements substantially matches, moire fringes are generated even if they do not match, which is not a problem.

Since the lattice plate 6 and the paper sheet 9 are vertically separated from each other, the moire fringes 23 are considered to be spatially localized. For this reason, the arrangement of the optical system 4, the area sensor 5 and the lattice plate 6 is such that the moire fringes 23 are arranged in the area sensor 5
It is set so that it can form an image. In the present embodiment, the light receiving surface of the area sensor 5 faces the paper surface of the paper sheet 9 substantially in parallel.

The output of the area sensor 5 is sent to the image processing section 16. Then, in the image processing unit 16, FIG.
As shown in (a) or FIG. 5 (a), the profile of the image density is measured with respect to the observed moire fringes 23,
The measurement result is output to the FFT analyzer 17.

As shown in FIG. 3B, the spacing D between the generated moire fringes 23 is larger than the line spacing and the grid spacing d of the microprint characters 22, and the spatial frequency (line-pairs / mm) of the moire fringes 23 is large. ) Is a microprint 10 or a grid 21
Smaller than. When the lattice spacing of the grid 21 and the stripe spacing of the microprint characters 22 are the same, the line spacing of the microprint characters 22 and the lattice spacing are both d, and the angle between them is θ, and the shading period of the profile T Is represented as follows.

[0024]

[Equation 1]

In FIG. 3 (b), the grating 21,
The arrangement of the line elements of the microprint character 22 is shown in a simplified manner in order to avoid complicated illustration of the relationship between the microprint character 22 and the moire fringes 23.

The FFT analyzer 17 extracts the periodic component of the moire fringe 22 as shown in FIG. 4B or 5B, and the output of the FFT analyzer 17 is sent to the comparator 18. In the comparator 18, the intensity of the periodic component fm of moire fringes is compared with a preset threshold value Th. Then, as shown in FIG. 4B, when the intensity of the periodic component fm exceeds Th, the paper sheet at that time is determined to be good. Further, when the intensity of the periodic component of the moire fringes observed is different from f _m (in this case, f _i ) as shown in FIG. 5B, or when the periodic component f _m is smaller than Th, then The paper sheet is determined to be no. Then, the determination result is displayed on the result display unit 19.

In the discriminating apparatus 1 as described above, the grid 21 is superposed on the microprint 10 printed on the paper sheet 9 to form moire fringes 23 having a spatial frequency larger than that of the microprint 10. And this moire stripe 2
3 is subjected to spatial frequency analysis to recognize the microprint 10. Therefore, it becomes possible to use the optical system 4 and the line sensor 5 having a lower resolution than in the case where the microprint 10 is directly image-recognized. Then, the required photographing conditions are relaxed, and as a result, the cost is reduced.

Further, since the demand for resolution is loosened, the depth of field becomes deep. Therefore, a clear image is obtained. Further, since the image of the moire fringe 23 having a large spatial frequency is detected, the amount of data can be reduced as compared with the case where the image of the microphone reprint 10 is directly detected. Signal processing such as data compression is also easy. The amount of data handled is
The larger the area captured by the area sensor 5, the larger the area.

The present invention is not limited to the above-mentioned embodiment, but can be variously modified. For example, in this embodiment, the grid 21 is printed on the grid plate 6, but the grid may be carved on the grid plate 6. Further, a plastic material may be adopted as the material of the lattice plate 6.

Further, in this embodiment, the lattice plate 6 is arranged between the optical system 4 and the paper sheet 9, but as shown in FIG. 6, the first lattice plate 6 is arranged between the lattice plate 6 and the paper sheet 9. The optical system 32 may be arranged, the grating plate 6 may be arranged at the image forming position of the microprint 10, and the line sensor 5 may be arranged at the image forming position of the image of the grating 21. In this case, the image of the moire fringes is formed on the line sensor 5 by the second optical system 33.

As shown in FIG. 7, the moire fringes 23 are formed by using the pixel array of the area sensor 5 without using the grid plate 6.
May be generated. Here, in FIG. 7, only a partial vertical arrangement of pixels is shown in order to avoid complication of the drawing.

In this embodiment, the image detector is C
Although the area sensor 5 using a CD is used, a line sensor may be used. It is also possible to use a photodiode 42 as an image detector as shown in FIG. However, in this case, in order to capture the grayscale image of the region where the moire fringes 22 are generated in the photodiode 42,
A means 43 for scanning the light by moving the paper sheet 9 and the light source relatively is required. Furthermore, as a light source, an incandescent lamp 44
Etc. using a continuous light source.

Further, as in the discriminating device 51 of FIG. 9, even if a lattice image is projected on the paper sheet 9, moire fringes can be generated. In this case, the projection device (projection means) 52,
The enlargement / reduction optical system 53 is added, and the lattice plate 6 is arranged between the projection device (projection means) 52 and the enlargement / reduction optical system 53.

Further, as shown in FIG. 10 or FIG. 11, the microprint 10 is recorded by using an interferometer or the like.
Moire fringes can be obtained even if the interference patterns of the light 54 are overlapped. In these cases, the grid plate becomes unnecessary.

The discriminator 61 shown in FIG. 10 is provided with a moire fringe generating means 62 using a Michelson interferometer. The moire fringe generating means 62 is a laser oscillator 63 as a monochromatic light source and an optical interference means. 64 is provided. The light interference means 64 has a half mirror 65 and a mirror 66. Further, reference numeral 67 is a beam expander.

On the other hand, the discriminating device 71 of FIG. 11 is provided with a moire fringe generating means 72 utilizing a Mach-Zehnder interferometer, and the moire fringe generating means 72 includes a laser oscillator 63 as a monochromatic light source and an optical source. The interference means 73 is provided. The light interference means 73 is a half mirror 65 and a mirror 66.
have.

[0037]

As described above, according to the present invention, a paper sheet supporting means for supporting a paper sheet having a microprint, a lattice providing means for superimposing a lattice on the microprint to generate moire fringes, and an image of the moire fringes. An image detecting means for detecting the micro-printing and a micro-print recognizing means for recognizing the micro-print by analyzing the spatial frequency of the moire fringes are provided.

Therefore, the invention of claim 1 has an effect that a microprint can be recognized without using a high-resolution image detector. Further, there is an effect that the microprint can be recognized without being influenced by the conveyance failure or the undulation of the surface that occurs when the sheet is conveyed.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing a paper sheet quality determination device according to an embodiment of the present invention.

FIG. 2 is a block diagram showing an arithmetic control system of a paper sheet quality determination device according to an embodiment of the present invention.

FIG. 3A is an explanatory diagram showing an example of a microprint and a grid, and FIG. 3B is a line and grid of microprint characters;
9A and 9B are explanatory diagrams showing the relationship between moire fringes.

4A and 4B relate to measurement of good paper sheets, where FIG. 4A is a graph showing an example of an output of an area sensor, and FIG. 4B is a graph showing an output of an FFT analyzer.

5A and 5B relate to measurement of defective paper sheets, where FIG. 5A is a graph showing an example of an output of an area sensor, and FIG. 5B is a graph showing an output of an FFT analyzer.

FIG. 6 is a configuration diagram showing a modified example of the paper sheet quality determination device.

FIG. 7 is an explanatory diagram showing a modified example of the method for observing moire fringes.

FIG. 8 is a configuration diagram showing another modified example of the paper sheet quality determination device.

FIG. 9 is a configuration diagram showing another modified example of the paper sheet quality determination device.

FIG. 10 is a configuration diagram illustrating another modified example of the paper sheet quality determination device.

FIG. 11 is a configuration diagram showing another modified example of the paper sheet quality determination device.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Paper sheet quality determination device, 2 ... Conveying part (paper sheet supporting means), 4 ... Optical system, 5 ... Area sensor (image detecting means), 6 ... Lattice plate (lattice providing means), 7 ... Strobe lighting device (Illumination means), 9 ... paper sheet, 10 ... microprint, 13 ... arithmetic control system, 20 ... microprint recognition means, 21 ... lattice, 22 ... microprint characters, 23 ...
Moire fringes, 31 ... Paper quality determination device, 32 ... First optical system, 33 ... Second optical system, 41 ... Paper quality determination device, 42 ... Photodiode (image detection means), 44 …
Incandescent light bulb (illuminating means), 51 ... Paper quality determination device, 5
2 ... Projection device (projection means), 54 ... Moire fringe generation means,
61 ... Paper quality determination device, 62 ... Moire fringe island generation means, 63 ... Laser oscillator (monochromatic light source), 64 ... Optical interference means, 71 ... Paper quality determination device, 72 ... Moire fringe generation means, 73 ... Optical interference means.

Claims (12)

[Claims] 1. A paper sheet supporting means for supporting a paper sheet having a microprint, a moire fringe generating means for generating a moire fringe on the microprint, an image detecting means for detecting an image of the moire fringe, and the moire. A paper quality judging device comprising a microprint recognizing means for recognizing the microprint by spatial frequency analysis of stripes. 2. A sheet quality determining apparatus according to claim 1, wherein the moire fringe generating means is a lattice plate on which a lattice is formed and which transmits an image of a microprint. 3. The sheet quality determining apparatus according to claim 1, wherein the moire fringe generating means has a projecting means and a lattice plate. 4. A sheet quality determining apparatus according to claim 1, wherein the moire fringe generating means has a monochromatic light source and an optical interference means. 5. The sheet quality determining apparatus according to claim 2, further comprising an optical system arranged between the lattice plate and the image detecting means to guide the image of the moire fringes to the image detecting means. 6. A first optical system for forming a microprint image on a lattice plate and a second optical system for forming a moire fringe image on an image detecting means. 2. A sheet quality determination device described in 2. 7. The paper sheet quality determining apparatus according to claim 1, further comprising illumination means for illuminating the microprint. 8. The paper sheet pass / fail judgment device according to claim 6, wherein the illumination means emits light intermittently. 9. The sheet quality determining apparatus according to claim 6, wherein the illumination means continuously emits light. 10. The sheet quality determining apparatus according to claim 1, wherein the image detecting means is an area sensor. 11. The image detecting means is a photodiode which scans at least a line.
The described sheet quality determination device. 12. An area sensor having a large number of vertically and horizontally arranged pixels, wherein moire fringes are formed by a combination of a pixel array of the area sensor and a lattice, and the area sensor is also used as a moire fringe generating means. 11. The paper sheet quality determination device according to claim 10.