JP2010085388A - Method and apparatus for inspecting printed matter - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an imaging method suitable for inspecting color printed matter with a high degree of accuracy regardless of differences in photosensitivity among models of camera or differences among individual ones and to provide an inspection apparatus capable of inspection with high reliability in real time. <P>SOLUTION: An inspection method includes: a first illuminating step of irradiating a first surface of printed matter with white light; a second illuminating step of irradiating the first surface of the printed matter with light in at least one predetermined type of wavelength band; a third illuminating step of irradiating a second surface of the printed matter with white light; an imaging step of taking images of the first surface of the printed matter either in synchronization with the conveyance of the printed matter or at predetermined time intervals; and an image-processing and defect-determining step of determining the presence of defects in the printed matter by using the image data on the first surface of the printed matter as obtained in the imaging step. An inspection apparatus is also provided. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

The present invention relates to a printed matter inspection method and inspection apparatus, and more particularly, to a color printed matter defect inspection method and inspection apparatus.

For example, there is a gravure printing machine as a printed material composed of colors. Hereinafter, a gravure printing machine will be described as an example.

In general, in a gravure printing machine, a belt-like printed material obtained by printing on an original fabric is conveyed, an image of the printed material is imaged by an imaging means such as a line sensor camera included in an inspection apparatus, and image data obtained at that time is obtained. Based on this, visual inspection is conducted. In such a printed matter inspection apparatus, a color camera is mainly used in order to inspect a color printed matter with high accuracy.

A general color camera forms a color image by combining images captured by three types of light receiving elements such as red (hereinafter R), green (hereinafter G), and blue (hereinafter B). The color line sensor camera has a three-line system in which light receiving elements having sensitivity to R, G, and B wavelengths are arranged in parallel, and a light beam received by arranging a spectroscopic means such as a prism inside the camera. Are divided into R, G, and B wavelengths, and two types of methods are used, namely a 3CCD system (or a 3-plate system) in which light receiving elements are arranged according to the decomposed wavelengths.

Moreover, in a gravure printing machine, not only paper but also a plurality of types of original fabrics including a special product such as a transparent plastic film and aluminum vapor deposition are printed by the same printer. For this reason, in the conventional illumination device for a printed matter inspection device, a necessary light source is selected from light sources such as irregular reflection, regular reflection, and transmission that the illumination device has every time the original of the printed matter to be inspected is switched. It was selected, and appropriate light intensity adjustment was performed to support inspection of various printed materials.

For example, Patent Document 1 has been proposed as a method for imaging a printed matter using a CCD camera or the like and inspecting the printed matter using image processing.
With the technology described in Patent Document 1, it is possible to inspect a plurality of types of original fabrics with a single inspection device, but by using a fluorescent lamp that mainly emits white light as illumination, depending on the color of the defect However, the problem is that the detection power of defects is slightly different. In addition, there has been a problem that the detection power of defects is slightly different depending on the difference in model of the light receiving sensitivity of the camera and individual differences.

Japanese Patent No. 3808937

The present invention has been devised in view of the above-described problems, and provides an imaging method suitable for inspecting a printed matter composed of colors with high accuracy regardless of differences in camera light receiving sensitivity between models and individual differences. At the same time, it is an object to provide an inspection apparatus capable of performing an inspection in real time with high reliability.

In order to achieve the above object, the invention of claim 1
A first illumination stage that irradiates the surface of the printed matter with the front surface, the back surface, or both sides thereof printed with white light;
A second illumination step of irradiating at least one type of light in a predetermined wavelength range on the printed surface;
A third illumination stage for irradiating the printed back with white light;
An imaging step of imaging the printed material surface in synchronization with conveyance or at a predetermined time interval;
Using the image data of the surface of the printed matter obtained in the imaging step, image processing / defect determining step for judging defects present in the printed matter;
A method for inspecting printed matter, comprising:
It is what.

In the invention of claim 2,
A first illuminating means for irradiating the front surface, the back surface, or the surface of the printed material printed on both sides thereof with white light;
A second illuminating means for irradiating the surface of the printed matter with at least one kind of light in a predetermined wavelength range;
A third illuminating means for irradiating the printed back with white light;
Imaging means for imaging the surface of the printed matter in synchronization with conveyance or at a predetermined time interval,
Image processing / defect determination means for determining defects present in the printed matter, using image data of the surface of the printed matter obtained by imaging in the imaging means,
An inspection apparatus for printed matter, comprising:
It is what.

In the invention of claim 3,
A first illumination stage that irradiates the surface of the printed matter with the front surface, the back surface, or both sides thereof printed with white light;
Irradiating at least one kind of light in a predetermined wavelength range on the surface of the printed matter, the second illumination stage mainly including the wavelength range of around 500 nm, around 600 nm, or both;
A third illumination stage for irradiating the printed back with white light;
An imaging step of imaging the printed material surface in synchronization with conveyance or at a predetermined time interval;
Using the image data of the surface of the printed matter obtained in the imaging step, image processing / defect determining step for judging defects present in the printed matter;
A method for inspecting printed matter, comprising:
It is what.

In the invention of claim 4,
A first illumination stage that irradiates the surface of the printed matter with the front surface, the back surface, or both sides thereof printed with white light;
Irradiating at least one kind of light in a predetermined wavelength range on the surface of the printed matter, the second illumination stage mainly including the wavelength range of around 500 nm, around 600 nm, or both;
A third illumination stage for irradiating the printed back with white light;
An imaging step of imaging the printed material surface in synchronization with conveyance or at a predetermined time interval;
Using the image data of the surface of the printed matter obtained in the imaging step, image processing / defect determining step for judging defects present in the printed matter;
An inspection apparatus for printed matter, comprising:
It is what.

As described above, according to the present invention, an imaging method suitable for inspecting a printed matter composed of color with high accuracy is provided regardless of the difference in model and individual difference in camera light reception sensitivity, and high reliability in real time. It is possible to provide an inspection apparatus capable of performing an inspection under

The schematic block diagram which shows the structure of the principal part of the inspection apparatus which concerns on this invention. Sectional drawing which shows the imaging and illumination means of this invention. The figure which shows an example of the spectral sensitivity of a monochrome camera. The figure which shows an example of the spectral sensitivity of a color camera. The figure which shows an example of the spectral intensity of a fluorescent lamp. The figure which shows a specific visibility curve. The flowchart which shows the whole schematic operation | movement of the test | inspection apparatus of this invention.

Embodiments of a printed matter inspection method and apparatus according to the present invention will be described below with reference to the drawings. FIG. 1 is a schematic configuration diagram showing a printed matter inspection apparatus according to the present invention.

The inspection apparatus of the present invention includes an imaging unit 30 that realizes an imaging stage in which the printing machine moves the printed material 10 at a predetermined speed, synchronizes with the speed of the printing machine, and images the surface of the printed material 10, and the surface of the printed material 10. Reflective illumination means 20 for realizing an illumination stage for irradiating white light and light other than white light, transmission illumination means 21 for realizing an illumination stage for irradiating the back surface of the printed matter 10 with white light, and the surface of the printed matter 10 by the imaging means 30 Control / image processing means 40 that realizes a control / image processing stage that extracts and automatically determines a defective portion existing in the printed material 10 using image data obtained by imaging the image.

The printed material 10 moves in the imaged area at a predetermined speed. At this time, a signal for each unit distance is obtained from a unit that measures the amount of movement of the printed matter 10 attached to the printing machine with high accuracy, and the signal may be divided and distributed to the control / image processing means 40 in some cases. By sending a signal, scanning imaging is performed so as not to be affected by the speed fluctuation of the printing press. When the conveyance speed of the printing press can be regarded as constant within the range of the resolution of the image pickup means 30, a method of obtaining an image only by starting image pickup by a trigger signal and image pickup at a constant time interval is also conceivable. However, it is always more reliable to take images that are synchronized with the conveyance speed of the printing press.

In addition to the speed fluctuation of the printing press, there is a possibility that the original fabric of the printed material 10 is an original fabric that tends to expand and contract, such as a plastic film. When the original fabric of the printed matter 10 is expanded or contracted, there is a possibility that the image will be affected even if imaging is performed in synchronization with the speed of the printing press. Therefore, in addition to the conveyance speed of the printing press, measurement in consideration of the expansion and contraction of the printed material 10 is necessary. Generally, the influence of expansion and contraction is often reduced by adopting a measurement method in which a part of the printed product 10 is brought into contact.

FIG. 2 is a schematic diagram showing an embodiment of the reflective illumination means 20 and the transmission illumination means 21 according to claims 1 and 3 of the present invention.

An imaging lens 32 is attached to the imaging means 30, and the printed material 10 to be imaged is arranged in the vertical direction. In the gravure printing machine, since the printed material 10 is manufactured in a roll shape, the conveyance speed is often a constant speed. In this case, since the imaging target always passes under the imaging means 30, the imaging means 30 mainly selects a line sensor in many cases, but the area depends on the type of printing press, particularly the form of conveyance. You can select the camera. Further, although the image pickup means 30 is arranged perpendicular to the printed material 10, in the case of a line sensor camera, an illumination system that can obtain an appropriate image can be realized, and each pixel is arranged in the horizontal direction of the line sensor. 2 may be arranged in a direction inclined by θ in FIG. 2 (direction of an angle other than 90 ° with respect to the printed material 10), for example, as long as the printed material 10 at the same distance can be imaged.

The reflective illumination unit 20 includes a first illumination unit 22 that is disposed between the printed material 10 and the imaging unit 30 and that irradiates the surface of the printed material 10 with white light, and a second illumination unit 23 that irradiates light other than white light. ing. Any type of the reflective illumination means 20 may be used as long as the amount of light capable of obtaining an image that can be appropriately processed can be ensured. However, when a line sensor is used for the imaging means 30, a linear shape is used. An illumination system capable of irradiation is suitable. Specifically, a fluorescent lamp, a transmission light, an LED illumination or the like is selectively used. Further, the reflection illumination means 20 may be arranged to select one of them depending on the original fabric of the printed matter 10 while arranging irregular reflection, regular reflection, or both, or both, but the type of printing machine (printing method) Any arrangement may be selected depending on the material. Further, in order for the imaging unit 30 to receive an optimal amount of light, two or more first illumination units 22 that emit white light and two or more second illumination units 23 that emit light other than white light may be arranged. . In addition, when a fluorescent lamp is employed for the reflective illumination unit 20, a reflective member may be disposed around the reflective illumination unit 20 to increase the amount of light.

The reflective illumination means 20 is provided with an imaging slit 31. Specifically, as long as there is no influence on the amount of light received by the image pickup means 30, it may be either a gap or a transparent member such as glass or transparent acrylic.

The transmitted illumination means 21 is arranged between the imaging means 30 and the transmitted illumination means 21 in such a positional relationship that the printed product 10 is arranged, and a third illumination unit 24 that irradiates the back surface of the printed product 10 with white light. I have. Any kind of transmitted illumination means 21 may be used as long as the amount of light capable of obtaining an image that can be appropriately processed can be secured. However, when a line sensor is used for the image pickup means 30, a linear shape is used. An illumination system capable of irradiation is suitable. Specifically, a fluorescent lamp, a transmission light, an LED illumination or the like is selectively used. In addition, as a method for ensuring the maximum light amount, the transmitted illumination unit 20 can be arranged linearly with respect to the imaging unit 30. It is not necessary to have a typical arrangement. In addition, the transmission illumination means 21 may not be used when using a raw material with particularly low transparency depending on the type of printing press (printing method) and the raw material. However, it is suitable that the transmission illumination means 21 can be switched between ON and OFF, for example, when it is attached to a printing press where it is uncertain what kind of fabric will be conveyed. Further, two or more third illumination means 24 for irradiating white light may be disposed in order to cause the imaging means 30 to receive an optimal amount of light. In addition, when a fluorescent lamp is used for the transmission illumination unit 20, a reflection member may be disposed around the transmission illumination unit 20 to increase the amount of light.

FIG. 3 shows an example of the spectral sensitivity of a monochrome line sensor (hereinafter referred to as a monochrome camera). As shown in FIG. 3, the monochrome camera relies on the sensitivity of one type of element for brightness information. When the color printed matter 10 is imaged with a monochrome camera, there is a case where there is no difference in output gradation values even when different colors are combined. On the other hand, in the case of a color camera, light is received by three types of elements having sensitivity to R, G, and B, respectively. Since the information of the printed matter 10 can be reflected, it is more suitable for imaging the colored printed matter 10 than a monochrome camera.

FIG. 4 is an example of spectral sensitivities for R, G, and B of a color line sensor (hereinafter referred to as a color camera). The relative ratio of R, G, and B is preferably as close as possible to the ratio of human eye sensitivity (visual sensitivity), but at present, there are many points depending on the element itself, and it is difficult to make them completely coincide. In the color camera of FIG. 4, R is the highest and B is the lowest.

Therefore, many color cameras have a white balance adjustment function for adjusting an error between elements. This adjusts the error between elements based on the imaging result of a white object. When such adjustment is performed, an error between elements can be eliminated from the white imaging result. However, the actual correction only increases or decreases the resulting output for each wavelength as a whole. The larger the increase or decrease, the more the noise component, the less sensitive the brightness difference, etc. It is inevitable that there will be an impact. This may cause adverse effects such as differences in the detection powers of R, G, and B, and the inability to detect defects having subtle brightness differences.

FIG. 5 is an example of the spectral intensity of a white fluorescent lamp. White illumination that emits white light has its own spectral characteristics depending on the type of fluorescent lamp, LED, etc., but basically there is no difference in having R, G, and B spectral intensity. . This also applies to illumination that emits white light other than fluorescent lamps. Although it is possible to adjust the light intensity of the white illumination, it increases or decreases the overall light intensity, and the R, G, and B light intensity cannot be increased or decreased individually. As described above, when a reflection optical system is configured with only white illumination, if a variation in the spectral sensitivity of the camera occurs, it is difficult to absorb the variation with the optical system.

Accordingly, in the first and second aspects of the present invention, the second illuminating unit 23 is arranged, and the second illuminating unit 23 irradiates one or more kinds of light in a predetermined wavelength region other than the white light, thereby providing a camera. Variation of the spectral sensitivity of the light can be adjusted by the spectral intensity of the illumination light. Such second illumination means 23 can emit light such as R, G, and B that emit light in a single color, illumination that can emit R and G at the same time, or yellow, etc., in accordance with the image sensor of the camera. Can be used. Any combination may be used as long as the illumination can be selected so that the relative ratio of the spectral sensitivity of the camera to be used matches the visibility. Two or more second illumination means 23 may be arranged, and each may be a combination of different wavelengths.

Fig. 6 is based on the light with a wavelength of 555 nm that the human eye feels most strongly, and expresses the degree of feeling of brightness at other wavelengths as a ratio. It shows the standard relative luminous sensitivity (specific luminous sensitivity) curve agreed by CIE).

When the sensitivity of the human eye is reproduced by an R, G, B image sensor as shown in FIG. 6, if a color camera as shown in FIG. 4 is used, the sensitivity around 500 nm and 600 nm, which is the boundary between the wavelengths, is human. It can be seen that it tends to be weaker than the eyes. So far, when the defect is yellow (including around 600 nm), the defect detection ability is weak. This is due to the difference in sensitivity between the color camera and the human eye in this wavelength range, and although it is a defect that can be detected visually, it cannot be detected from an image captured by the color camera.

Therefore, in claims 3 to 4 of the present invention, not only the wavelength region of the second illumination means 23 is set so that the balance of the intensity of R, G, and B of the entire illumination light matches the spectral sensitivity of the camera, but also the color. Illumination mainly including wavelength ranges of around 500 nm, around 600 nm, or both in order to fill the sensitivity difference between the camera and the human eye was used as the second illumination means 23. When both wavelength ranges are mainly included, it is considered that the balance of the intensity of R, G, and B cannot be adjusted independently. Therefore, it is desirable to prepare two types of around 500 nm and around 600 nm separately. In addition, as a method for realizing illumination mainly including the specified wavelength range, it is desirable to use illumination means that can emit light only in the specified wavelength range. However, the wavelength range other than the specified wavelength range can be excluded by a special filter or the intensity other than the specified wavelength range can be used. If is sufficiently smaller than the specified wavelength range, the realization method is not particularly concerned.

If it is possible to match the variations in camera sensitivity of R, G, and B, fill the sensitivity difference between the color camera and the human eye, and secure a sufficient amount of light to obtain an image that can be processed appropriately, The reflective illumination unit 20 may be configured by only the second illumination unit 23. However, the actual inspection apparatus for printed matter 10 is often conveyed at high speed, and it is difficult to secure the required brightness without white light as the first illumination means 22. From such a current situation, in the present embodiment, the reflection illumination unit 20 includes two types of illumination units 22 and 23.

FIG. 7 is a flowchart showing the overall operation of the control / image processing means 40. The printed material 10 moves at a predetermined conveying speed, synchronizes with the conveying speed of the printing press and the expansion and contraction of the printed material, and the surface of the printed material 10 is imaged by the imaging means 30 (step S1).

This image data is sent to the control / image processing means 40, and information on the printed matter is extracted from this image data (step S2). Further, defect detection / determination processing is executed using the extracted information (step S3). This defect detection / determination process is executed for all the printed materials 10, and then the entire operation is completed (step S4, YES).

In the defect detection / determination process (step S3), the obtained image is binarized and multi-valued to extract a defective part, or a reference image is held in advance as master data. By performing image processing such as pattern matching with the obtained image data and difference processing, defects of various printed materials 10 can be detected.

As described above, by using the illumination means of this embodiment and matching variations in camera sensitivity, it is possible to reduce noise components and easily capture minute differences in brightness, and to fill in sensitivity differences between color cameras and human eyes. Thus, it becomes possible to improve the detection power of defects near 500 nm and 600 nm, which has been considered to have a weak detection power of defects. Therefore, it becomes possible to inspect a printed matter composed of colors with high accuracy regardless of the difference in camera light receiving sensitivity between models and individual differences.

10 .. Printed material 20 .. Reflective illumination means 21 .. Transmitted illumination means 22... First illumination means 23 .. 2nd illumination means 24 .. 3rd illumination means 30. Slit 32 ··· lens 40 for imaging · · control and image processing means

Claims (4)

A first illumination stage that irradiates the surface of the printed matter with the front surface, the back surface, or both sides thereof printed with white light;
A second illumination step of irradiating at least one type of light in a predetermined wavelength range on the printed surface;
A third illumination stage for irradiating the printed back with white light;
An imaging step of imaging the printed material surface in synchronization with conveyance or at a predetermined time interval;
Using the image data of the surface of the printed matter obtained in the imaging step, image processing / defect determining step for judging defects present in the printed matter;
A method for inspecting printed matter, comprising: A first illuminating means for irradiating the front surface, the back surface, or the surface of the printed material printed on both sides thereof with white light;
A second illuminating means for irradiating the surface of the printed matter with at least one kind of light in a predetermined wavelength range;
A third illuminating means for irradiating the printed back with white light;
Imaging means for imaging the surface of the printed matter in synchronization with conveyance or at a predetermined time interval,
Image processing / defect determination means for determining defects present in the printed matter, using image data of the surface of the printed matter obtained by imaging in the imaging means,
An inspection apparatus for printed matter, comprising: A first illumination stage that irradiates the surface of the printed matter with the front surface, the back surface, or both sides thereof printed with white light;
Irradiating at least one kind of light in a predetermined wavelength range on the surface of the printed matter, the second illumination stage mainly including the wavelength range of around 500 nm, around 600 nm, or both;
A third illumination stage for irradiating the printed back with white light;
An imaging step of imaging the printed material surface in synchronization with conveyance or at a predetermined time interval;
Using the image data of the surface of the printed matter obtained in the imaging step, image processing / defect determining step for judging defects present in the printed matter;
A method for inspecting printed matter, comprising: A first illuminating means for irradiating the front surface, the back surface, or the surface of the printed material printed on both sides thereof with white light;
Irradiating at least one kind of light in a predetermined wavelength range on the surface of the printed matter, the second illumination stage mainly including the wavelength range of around 500 nm, around 600 nm, or both;
A third illuminating means for irradiating the printed back with white light;
Imaging means for imaging the surface of the printed matter in synchronization with conveyance or at a predetermined time interval,
Image processing / defect determination means for determining defects present in the printed matter, using image data of the surface of the printed matter obtained by imaging in the imaging means,
An inspection apparatus for printed matter, comprising:

Images