JP4377872B2 - Surface inspection device - Google Patents

Description

  The present invention relates to a surface inspection apparatus, and more particularly to a surface inspection apparatus that inspects the surface of a diffractive optical change element (diffractive OVD: Optical Variable Device).

  The diffractive OVD is an element whose surface is processed to cause a light diffraction phenomenon, as represented by an embossed hologram. Therefore, it is characterized by having a pattern with vivid color caused by light diffraction and interference phenomenon. In addition, the diffractive OVD is often formed on a metal thin film and often has a metallic luster.

  Thus, the diffractive OVD has optical characteristics that are different from those of normal printing. Therefore, it is often used as a forgery prevention technique (security thread) for printed matter such as gift certificates and cards such as credit cards. The quality of security threads is greatly related to the reliability of printed materials and cards. Therefore, an inspection means for inspecting the quality of the diffractive OVD forming the security thread is important.

  Printed matter and cards with a security thread attached or printed are mechanically transported, and a counting process and a quality inspection process are performed simultaneously. In the counting process, printed matter and cards are conveyed at high speed and counting is performed. The conveyance speed may be several meters per second or more. In order to perform quality inspection simultaneously with such high-speed counting, a high-speed inspection device is required.

  In order to perform high-precision inspection in quality inspection, it is desirable to inspect the printed matter and cards in a state where they are stationary at an accurate inspection position. However, since conveyance is involved before reaching the inspection process, it is difficult to completely avoid a displacement from an accurate inspection position. Furthermore, in order to further increase the speed of the inspection process, the inspection must be performed while being transported, and the inspection object (printed matter and cards) flickers in the height direction with respect to the inspection position, and the angular deviation with respect to the transport direction. Variations such as a certain skew also occur. Such fluctuations deteriorate the accuracy of the inspection. Therefore, in the inspection of printed matter and cards in such a state, a stable inspection that is resistant to fluctuations is required.

  Thus, the inspection of the diffractive OVD needs to achieve both high speed and stability. For the purpose of this stability, for example, in Patent Document 1, a means is employed in which a light source is disposed so as to surround the entire circumference of a hologram surface, which is a kind of diffractive OVD, and the inspection light is irradiated. In the hologram illuminated in this way, diffracted light is obtained from the entire surface, and a hologram image obtained by imaging the diffracted light and a hologram image having no defect stored in advance are patterned. Compared by matching.

In this way, a minute defect is inspected over the entire surface of the hologram by inspecting for the presence or absence of a defect based on the imaging result of the diffracted light obtained from the entire surface of the hologram.
Japanese Patent Application Laid-Open No. 2004-239834

  However, when performing pattern matching between a captured hologram image and a previously stored hologram image, it is necessary to perform a complicated process such as feature extraction of the hologram image.

  In addition, in order to allow a stable inspection while tolerating fluctuations such as misalignment and skew caused by the transport device, processing involving complicated correlation operations such as a normalized correlation method, a phase-only correlation method, and geometric matching is also required.

  Such a complicated process hinders high-speed inspection, and therefore, it has been difficult to inspect the diffractive OVD with high speed and stability with a conventional inspection apparatus.

  An object of the present invention made to solve such a technical problem is to perform a stable and high-speed inspection with respect to fluctuations such as positional deviation, fluttering, and skew of the diffractive OVD in a state of being conveyed at high speed. It is to provide a surface inspection apparatus that can be used.

  A feature according to an embodiment of the present invention is that a light source that irradiates a diffractive optical change element with light including a plurality of wavelength components, a diffracted light having a first wavelength diffracted by the diffractive optical change element, and An evaluation value relating to a color difference between the diffracted light of the first wavelength and the diffracted light of the second wavelength, based on the detection result of the diffracted light of the second wavelength and the detection result of the light detecting means; And calculating means for calculating.

  ADVANTAGE OF THE INVENTION According to this invention, the surface inspection apparatus which can perform a surface inspection stably and at high speed can be provided.

Embodiments of the present invention will be described below with reference to the drawings. For convenience of explanation, in the embodiment of the present invention, it is assumed that the top is the vertical direction of the diffractive optical change element (the surface side of the diffractive optical change element). Specifically, “up” refers to the Z direction described later. That is, the direction described in the description of the embodiment of the present invention refers to the relative direction with respect to the vertical direction of the diffractive optical change element with respect to the diffractive optical change element, and the direction with respect to the direction of gravity. It is not limited to what indicates.

(First embodiment)
FIG. 1 shows a configuration of a surface inspection apparatus 100 for a diffractive optical change element (diffractive OVD) according to a first embodiment of the present invention. This surface inspection apparatus 100 is used for inspection of a diffraction type OVD 102 that is pasted or printed on a paper sheet 101. An illumination unit 201, a condensing unit 202, a light detection unit 203, and a discrimination processing unit 204 are provided. Is provided.

  The illumination unit 201 is disposed along the side surface of the diffractive OVD 102 so as to irradiate the diffractive OVD 102 with light from an obliquely upward direction. The illuminating unit 201 is a linear light source having a light emitting part that is sufficiently longer than the diffractive OVD 102. Specifically, a light source having a linear fluorescent tube or a light source having a linear halogen bulb may be used. In addition, a transmission light that realizes a linear light source by a light guide in which light from a light source is incident into the light guide by an optical transmission means such as an optical fiber and light is emitted in a linear or array form. It may be used. As a spectral characteristic of the light source, a light source including a plurality of wavelengths may be used. More preferably, a white light source having a broad spectral distribution characteristic from a wavelength in the near infrared region to a wavelength in the near ultraviolet region is preferably used.

  By irradiating light to the diffractive OVD 102 from obliquely above in this manner, diffracted light can be made incident without making specularly reflected light incident on the light detection means 203 described later.

  The condensing unit 202 is separated from the diffractive OVD 102 by a predetermined distance, and is arranged so that the center of the diffractive OVD 102 and the optical axis of the condensing unit 202 substantially intersect. The light condensing means 202 is arranged to condense the light diffracted by the diffractive OVD. Specific condensing means may be, for example, a single convex lens having a predetermined focal length or a camera lens composed of a plurality of lenses.

  The light detection means 203 is arranged on the opposite side to the diffractive OVD 102 with the light collection means 202 interposed therebetween. At this time, it is preferable to arrange at the focal position of the diffracted light condensed by the condensing means 202 or the vicinity thereof. In this embodiment, a plurality of light detection means 203 are provided. Each light detection means 203 is constituted by a plurality of color sensors. Although the present invention is not limited by the number of color sensors, in this embodiment, a case where three color sensors are used for each light detection means 203 will be described. As the color sensor, for example, a photodiode combined with a red filter, a photodiode combined with a green filter, a photodiode combined with a blue filter, or the like can be used. In this embodiment, the plurality of light detection means 203 are diffracted by the first light detection means for detecting the diffracted light of the first wavelength diffracted by the test object (diffractive OVD 102) and the test object. The second light detecting means for detecting the diffracted light of the second wavelength is configured.

As shown in FIG. 2, a single light detection unit 203 includes color sensors 301a, 301b, and 301c that detect red (R), green (G), and blue (B), which are the three primary colors of light. The light intensity detected by each of the color sensors 301 a to 301 c is converted into an electrical signal (spectral intensity signal) for each of a plurality of wavelengths and sent to the discrimination processing means 204. Here, the light detection unit 203 does not necessarily correspond to each component of red (R), green (G), and blue (B), and a color sensor that can correspond to at least two types of wavelengths can be used. . Each color sensor detects the intensity of light having wavelengths of red (R), green (G), and blue (B), which are the three primary colors of light, and spectral intensity signals I _R , I _G , I of the respective wavelengths. _B is sent to the color difference amount calculation unit 302 included in the discrimination processing unit 204. Here, the wavelength detected by the color sensor is described as being the three primary colors RGB of light, but the present invention is not limited by this wavelength selection method, and the type of diffractive OVD that is assumed, An optimal color may be selected as appropriate depending on the configuration of the inspection apparatus.

  As shown in FIG. 2, the discrimination processing unit 204 includes a color difference amount calculation unit 302, a surface state determination unit 303, and a determination result output unit 304. The color difference amount calculation unit 302 calculates a color difference amount signal (evaluation value) from the spectral intensity signals sent from the color sensors 301 a to 301 c and sends the color difference amount signal to the surface state determination unit 303.

Here, a calculation example in the color difference amount calculation unit 302 will be described using mathematical expressions. First, sets of spectral intensity signals from the color sensors 301a, 301b, and 301c are respectively (I _1R , I _1G , I _1B ), (I _2R , I _2G , I _2B ), and (I _3R , I _3G , I _3B ). For each spectral intensity signal of each color sensor, the color difference index value Q _i of the R signal and the B signal is obtained by the following equation.

Here, I _max and I _min are the maximum value and the minimum value of the spectral intensity signal output by the color sensor, and are determined by the performance of the color sensor.

Next, an average value P for each color sensor of the color difference index value Q _i is obtained by the following equation.

The distance from the average value P to the color difference index value Q _{i of} each color sensor is obtained by the following equation, and the value is used as the color difference amount signal D.

The color difference amount signal D obtained here can also be interpreted as a standard deviation indicating the degree of variation of the color difference index value Q _i . The color difference amount signal D is sent from the color difference amount calculation unit 302 to the surface state determination unit 303, and determination processing is performed. In the calculation example shown here, the means for calculating using the R and B components has been described. However, R and G, G and B, or a combination thereof may be used.

In the above description, since the case where the light detection means is configured using a plurality of color sensors is described, the color difference amount signal D is defined as in Expression (3), but a single color sensor is used. When the light detection means is configured, the color difference index value Q _i may be sent as it is to the surface state determination unit 303 as the color difference amount signal D.

  In the surface state determination unit 303, determination processing is performed as shown in the flowchart of FIG. In this determination process, the color difference amount signal D is first taken into the surface state determination unit 303 (S401). Next, the surface state determination unit 303 determines the surface state of the diffractive OVD based on the color difference amount signal D. That is, the surface state determination unit 303 compares a color difference amount signal D with a threshold value stored in advance in a storage unit (not shown) such as a memory, and determines whether the color difference amount signal D exceeds or does not exceed the threshold value. A determination is made (S402). When the color difference amount signal D exceeds the threshold value, the surface state determination unit 303 determines that the diffractive OVD is normal, and outputs a normal signal to the determination result output unit 304 (S403). On the other hand, when the color difference amount signal D does not exceed the threshold value, the surface state determination unit 303 determines that the surface of the diffractive OVD is abnormal, and outputs an abnormal signal to the determination result output unit 304 (S404). .

  These signals are finally sent from the determination result output unit 304 to, for example, a display device (not shown) combined with the surface inspection apparatus 100 of the present embodiment, and the determination result can be displayed by visual display or the like. It becomes possible. Alternatively, as shown in FIG. 4, processing such as sorting paper sheets that are sent to the conveyance sorting apparatus 121 of the inspection processing apparatus 120 including the surface inspection apparatus 100 and on which the diffractive OVD with damage or deterioration is attached. It becomes possible. For example, as the transport sorting device 121, a sorting arm (not shown) is operated based on a normal signal or an abnormal signal, and paper sheets carried out by a belt conveyor or the like are sorted by the sorting arm. There is something configured. Further, in the inspection processing device 120, a counting device 122 that counts the number of normal paper sheets and abnormal paper sheets based on a signal indicating normality or abnormality output from the determination result output unit 304 of the surface inspection apparatus 100. The number of each can also be counted.

  Below, the effect of this Embodiment is demonstrated in detail using drawing. As shown in FIG. 5, when the diffractive OVD 102 is irradiated with illumination light from an oblique direction, specularly reflected light, which is zero-order diffracted light with respect to a specific incident light, is opposite to the element surface at the same exit angle as the incident angle. Eject. However, the diffracted light beam is emitted along a specific plane or curved surface according to the angle of the light beam incident on the element surface depending on the direction and pitch of the diffraction grating constituting the diffractive OVD 102. For example, as shown in FIG. 6, when the surface is oriented perpendicular to the Z direction, the grating arrangement direction is parallel to the Y direction, and incident light rays on the YZ plane are obliquely incident on the diffraction grating. The light beam is limited to the vicinity of the YZ plane indicated by the broken line in FIG. Further, when the arrangement direction of the grating is perpendicular to the Y direction as shown in FIG. 7, the diffracted light beam is limited to the vicinity of a specific conical surface indicated by a broken line.

  Therefore, in the present embodiment, by using a linear light source as the illumination unit 201, light beams at many angles are incident on the diffractive OVD 102 in the longitudinal direction of the light source. Therefore, as shown in FIG. 8, the light beam of diffracted light is emitted in a generally wide and radial manner.

  An example in which the spread of the diffracted light is obtained by calculation and the direction cosine of the diffracted light is plotted is shown in FIG. Explaining the conditions of this calculation, here, the L component of the direction cosine (L, M, N) as an angle with respect to the coordinate system taking the Z axis in the optical axis direction is plotted on the horizontal axis and the M component is plotted on the vertical axis. ing. The grating direction of the diffraction grating is in the Y direction as shown in FIG. The pitch of the diffraction grating used in the diffractive OVD 102 is generally several hundred nanometers to several micrometers, but here, a calculation example is shown with 1 micrometer. For incident light, the angle θ of the incident light with respect to the diffraction grating surface is fixed at 45 °, and in this state, the angle φ of the incident light with respect to the X direction is changed from 0 ° to −180 °. The numbers from 0 ° to −180 ° in FIG. 9 indicate a plot of diffracted light corresponding to the angle φ of the incident light. This change corresponds to the fact that the light beam incident on the diffraction grating comes from many directions as the light source becomes longer. In addition, the wavelength of the incident light is plotted by changing every 100 nm from 400 nm (blue) to 700 nm (red). The correspondence between the wavelength and the plot point is shown in the legend of wavelength correspondence in FIG. As shown in FIG. 9, the direction cosine of the diffracted light with respect to the light beam coming from a specific direction has a linear distribution of wavelengths from the first-order diffracted light to the third-order diffracted light, and the emission direction of the diffracted light is limited. I understand that. However, it can also be seen that the diffracted light can be broadened by increasing the angle of the incident light with respect to the grating direction of the diffraction grating.

  As described above, since the diffracted light is emitted widely and radially from the diffractive OVD 102, even if the surface of the diffractive OVD 102 has an angular deviation as shown by the broken line in FIG. The light can be incident, and the light detection means 203 can detect the diffracted light. That is, it can be said that the surface inspection apparatus 100 according to the present embodiment is a stable inspection apparatus that is strong against fluctuations such as angular deviation of the diffractive OVD 102.

  The diffractive OVD 102 is often composed of a plurality of diffraction gratings having different grating pitches and grating directions. Even for such a diffractive OVD, by using a light source (illuminating means 201) from which light enters from any direction such as a linear light source, it is possible to see other than a diffraction grating having a specific grating pitch or grating direction. It is possible to eliminate the low versatility that is difficult. In other words, a diffractive OVD in which various diffraction gratings are combined can be inspected stably.

  If the diffraction grating pattern constituting the diffractive OVD 102 is normal, a light beam coming from a specific direction is diffracted by chromatic dispersion as shown in FIG. For example, as shown in FIG. 10, when the diffraction grating pattern of the diffractive OVD 102 is normal (partially enlarged in FIG. 10), the illumination light has a spectrum including three wavelengths λ1, λ2, and λ3. Is incident on the diffractive OVD 102, the diffracted light is diffracted in different directions by the light of wavelengths λ1, λ2, and λ3. On the other hand, when the diffractive OVD 102 has defects, wear, or scratches that can be visually recognized, diffracted light that has undergone wavelength dispersion decreases. For example, as shown in FIG. 11, when the diffractive OVD 102 has defects, wear, or scratches (defects, etc.) (shown partially enlarged in FIG. 11), the diffraction grating OVD 102 has a diffractive grating in some parts. This is because there is a defect in the function of the diffraction grating, such as the destruction of the regular structure or the loss of the diffraction grating. In this case, light is reflected on, for example, the material of the diffractive OVD 102 that has been changed into an irregular structure, or the surface of the paper sheet 101 to which the diffractive OVD 102 is attached. Therefore, even if illumination light having a spectrum of three wavelengths λ1, λ2, and λ3 is incident on the diffractive OVD 102, the diffuse reflection has a spectrum including the three wavelengths λ1, λ2, and λ3 in many directions. A lot of light will be emitted.

  On the other hand, when attention is paid to a cross section orthogonal to the longitudinal direction of the light source (illuminating means 201), as shown in FIG. 12, the diffractive OVD 102 having a certain width functions as a minute light source. In this cross section, the positional relationship is such that a minute light source emits light obliquely from above. Therefore, on the surface of the diffractive OVD 102, a light beam is incident at a small incident angle at a position close to the light source, and a light beam is incident at a large incident angle at a position far from the light source. As a result, in the normal diffractive OVD 102, the angle formed by the light beam that is diffracted with the light beam in the regular reflection direction and incident on the light condensing means 202 changes depending on the position. Since the diffracted light is dispersed, the wavelength changes if the angle is different. That is, the wavelength of light incident on the light condensing means 202 varies depending on the position on the surface of the diffractive OVD 102.

Therefore, if the diffractive OVD 102 is normal, the diffraction incident on each color sensor included in the light detection means 203 as shown in FIG. The wavelength of light also varies. That is, the diffracted light incident on the color sensor becomes a color close to a single color, so that the color sensor detects a color close to a single color, and the color detected by each color sensor is different. On the other hand, as described above, when the diffractive OVD 102 has an abnormality such as a defect, wear or scratch, the light incident on the color sensor is diffusely reflected light. Therefore, each color sensor has a feature of detecting light close to white including a plurality of wavelengths. This means that the features of normal diffractive OVD and the features of abnormal diffractive OVD having defects and the like are replaced with optical information. Specifically, the average value P calculated by the above equation (2) can be regarded as a color difference index value when diffused light is detected, and the color difference amount signal D in the above equation (3). Can be regarded as the standard deviation of the color difference index value Q _i .

This standard deviation becomes smaller as the difference of the color difference index value Q _i with respect to the average value P expressed by the above equation (2) becomes smaller. That is, the color difference amount signal D decreases as the detection light becomes light (diffuse reflected light) including a plurality of wavelengths close to white. Here, as described above with reference to FIG. 11, if the diffractive OVD 102 has defects, abrasion, scratches, or the like, the light incident on the color sensor becomes close to diffusely reflected light. Accordingly, the surface state determination unit 303 (FIG. 2) can determine whether or not the diffractive OVD 102 has a defect based on whether or not the color difference amount signal D exceeds the threshold (FIG. 3).

  In the discrimination processing means 204, in order to accurately capture the optical information, a normal diffraction type is calculated by a method of calculating the color difference amount from the spectral intensity signal coming from the color sensor (Equation (1) to Equation (3)). A process for discriminating between an OVD and an abnormal diffractive OVD having a defect or the like is performed. In other words, the discrimination processing means 204 captures the feature that the wavelength of light reaching the light detection means differs depending on the part of the surface of the diffractive OVD, and performs a process of discriminating between normal diffractive OVD and damaged / degraded diffractive OVD. Do it. As described above, this processing can be realized by a combination of several mathematical formulas and a threshold value, and simple and high-speed discrimination processing is possible. That is, the diffractive OVD surface inspection apparatus 100 provided by the present embodiment is a surface inspection apparatus that can accurately capture the characteristics of the diffraction grating included in the diffractive OVD 102 and can perform high-speed inspection. It can be said. Thus, even when the surface inspection apparatus 100 is combined with a high-speed conveyance apparatus, it can perform a stable inspection against fluctuations such as fluttering and skew of the paper sheet 101 that occur in the conveyance process.

(Second Embodiment)
Hereinafter, a second embodiment of the present invention will be described with reference to the drawings. In addition, about the same part as 1st Embodiment, the same code | symbol is attached | subjected and the description is abbreviate | omitted.

  FIG. 13 shows the configuration of a diffractive OVD surface inspection apparatus 200 according to the second embodiment of the present invention. The surface inspection apparatus 200 is used for inspection of the diffractive OVD 102 that is pasted or printed on a paper sheet 101. Further, the paper sheet 101 is inspected by the surface inspection apparatus 200 while being conveyed by the conveyance belt 103.

  The surface inspection apparatus 200 mainly includes an illuminating unit 201, a condensing unit 202, a light detecting unit 203, and a discrimination processing unit 204.

  The illumination means 201 is disposed along the side surface of the diffractive OVD 102 so as to irradiate the diffractive OVD 102 with light from an obliquely upward direction. The illumination means 201 is a substantially arc-shaped light source that is sufficiently longer than the diffractive OVD 102 and has an elongated light emitting portion. As the spectral characteristic of the light source, a light source including a plurality of wavelengths may be used, but it is more preferable to use a white light source having a broad spectral distribution characteristic from a wavelength in the near infrared region to a wavelength in the near ultraviolet region.

  By irradiating light to the diffractive OVD 102 from obliquely above in this manner, diffracted light can be made incident without making specularly reflected light incident on the light detection means 203 described later. In this case, it is possible to effectively prevent the regular reflection light from entering the light detection means 203 by adopting a configuration in which the substantially arc-shaped light source is disposed over 180 ° around the diffractive OVD 102. Note that the configuration of the substantially arc-shaped light source is not limited to the configuration arranged over 180 ° around the diffractive OVD 102, and may be 180 ° or more, and in short, obliquely above the diffractive OVD 102. As long as the light is incident from the light source.

  The condensing means 202 is separated from the diffractive OVD 102 by a predetermined distance, and is arranged so that the center of the diffractive OVD 102 and the optical axis of the condensing means 202 substantially intersect. At this time, the condensing means 202 preferably uses a camera lens, and the focal length and F number are selected optimally depending on the overall size of the surface inspection apparatus, the brightness of the light source, the size of the diffractive OVD 102, and the like. That's fine.

  As shown in FIG. 14, the light detection means 203 includes color / line image sensors 305 a to 305 c configured by, for example, CCDs (charge-coupled devices). Each color / line image sensor acquires an image of a component in which 305a is red (R), 305b is green (G), and 305c is blue (B). Here, the paper sheet 101 is transported by the transport belt 103. Therefore, the color line image sensor scans the surface of the diffractive OVD 102 through the diffracted light, and acquires the image data. In order to take an image in this way, it is preferable to arrange the light detection means 203 at the image forming position of the light condensing means 202 which is a camera lens.

  The color / line image sensor generally has three line sensors for imaging each component of red (R), green (G), and blue (B), which are the three primary colors of light as described above. Is. However, the line sensors do not necessarily require three lines corresponding to the respective components of red (R), green (G), and blue (B), but the number of line sensors that can correspond to at least two types of wavelengths. Should just be provided. That is, the present invention is not limited by the number of color components and the number of line sensors, and an optimal value may be selected according to the characteristics of the diffractive OVD to be inspected and the required processing speed.

  In the discrimination processing unit 204, first, the image capturing unit 306 generates three diffractive OVD image data decomposed by RGB components from signals coming from the color / line image sensors 305a to 305c.

Next, the color difference amount calculation unit 302 calculates the color difference amount D from the image data of the diffractive OVD. The calculation method will be described using mathematical expressions. First, the pixel density value in each pixel of the image data is assumed to be I (m, n). Here, m represents coordinates in the main scanning direction of the line image sensor on the image data, and n represents coordinates in the sub scanning direction. The pixel density values of the image data of the RGB components acquired by the color / line image sensors 305a to 305c are I _R (m, n), I _G (m, n), and I _B (m, n).

Here, the color difference index value Q (m, n) for each pixel of the image data is obtained by the following equation.

Here, C is an intermediate value between the maximum value and the minimum value of the pixel density value. For example, when 256-gradation image data having a pixel density value of 0 to 255 is acquired by a line image sensor, C is 128. Next, an average value P for each color / line image sensor of the color difference index value Q (m, n) is obtained by the following equation.

From this average value P, how far the color difference index ground Q (m, n) of each color sensor is located is calculated, and the sum of the obtained values is used as a color difference amount signal D. This color difference amount signal D is expressed by the following equation.

  The color difference amount signal D obtained here can also be interpreted as a standard deviation indicating the degree of variation of the color difference index value Q (m, n). The color difference amount signal D is sent from the color difference amount calculation unit 302 to the surface state determination unit 303, and determination processing is performed. In the calculation example shown here, the means for calculating using the R and B components has been described, but a calculation method combining R and G, G and B, or a combination thereof may be used.

  Similar to the first embodiment, the surface state determination unit 303 performs determination according to the flowchart shown in FIG. 3 and outputs a normal signal or an abnormal signal. These signals are finally sent from the determination result output unit to, for example, a display device (not shown) combined with the surface inspection apparatus 200 of the present embodiment, and the determination result can be displayed by visual display or the like. It becomes. Alternatively, as described above with reference to FIG. 4, processing such as sorting of paper sheets that are sent to the conveyance sorting apparatus 121 of the inspection processing apparatus 120 including the surface inspection apparatus 200 and to which the diffractive OVD having a damaged or deteriorated surface is attached. Is possible. Further, in the inspection processing device 120, a counting device 122 that counts the number of normal paper sheets and abnormal paper sheets based on a signal indicating normality or abnormality output from the determination result output unit 304 of the surface inspection apparatus 200. The number of each can also be counted.

  Thus, in the surface inspection apparatus 200 according to the second embodiment, if the diffractive OVD 102 has defects, wear, scratches, etc., the light incident on the color / line image sensor is mostly diffusely reflected. The surface state determination unit 303 (FIG. 2) can determine whether or not the diffractive OVD 102 has a defect based on whether or not the color difference signal D exceeds a threshold value (FIG. 3). .

  As described above, the surface inspection apparatus 200 according to the second embodiment can be realized by a combination of several mathematical expressions (expressions (4) to (6)) and a threshold value, and is simple. And high-speed discrimination processing is possible. In other words, the discrimination processing means 204 captures the feature that the wavelength of light reaching the light detection means differs depending on the part of the surface of the diffractive OVD, and performs a process of discriminating between normal diffractive OVD and damaged / degraded diffractive OVD. Can be done. That is, the diffractive OVD surface inspection apparatus 200 provided by the present embodiment is a surface inspection apparatus that can accurately capture the characteristics of the diffraction grating included in the diffractive OVD 102 and can perform high-speed inspection. It can be said. Thus, even when the surface inspection apparatus 200 is combined with a high-speed conveyance apparatus, the surface inspection apparatus 200 can perform a stable inspection against fluctuations such as fluttering and skew of the paper sheet 101 generated in the conveyance process.

(Other embodiments)
In the first embodiment of the present invention, an example in which a color sensor is used as the light detection unit has been described. However, a color area image sensor may be used as the light detection unit. In this case, the same determination processing means as in the second embodiment may be used. By using a color area image sensor, a spectral intensity signal can be obtained with a finer spatial resolution. Therefore, surface inspection with higher accuracy is possible.

  In the first embodiment of the present invention, an example in which a linear light source is used, and in the second embodiment, a substantially arc-shaped light source is described. However, in the present invention, either a linear light source or a substantially arc light source may be used regardless of the embodiment. A linear light source has a feature that the configuration is simple and easy to adjust, and a substantially arc-shaped light source has a feature that energy can be saved because light can be efficiently emitted. In view of these characteristics, an appropriate selection may be made according to the performance and restrictions of the system incorporating the surface inspection apparatus of the present invention.

  In the description of the embodiment of the present invention, an example in which a light source such as a straight line or an arc is used as the illumination unit 201 has been described. However, the present invention is not limited by these shapes. The light sources in which the micro light sources 501 are arranged in a linear array as shown in FIG. 15 or the micro light sources 501 are arranged in a substantially arc shape as shown in FIG. A light source may be used. Alternatively, as shown in FIG. 17, a light source in which linear light sources 502 are connected in a polygonal line may be used. Alternatively, as shown in FIG. 18, a light source may be used in which a linear light source 502 is sandwiched between two mirrors 503 facing each other so as to be an apparently long illumination unit. Alternatively, as shown in FIG. 19, a light source may be used in which the mirror 503 is disposed obliquely with respect to the linear light source 502 and becomes an illuminating unit apparently connected in a broken line shape. Alternatively, the linear light source 502 shown in FIGS. 18 and 19 may be replaced with one micro light source 501 or a micro light source array including a plurality of micro light sources. Furthermore, these linear light sources and minute light sources may be combined. For example, as shown in FIG. 20, a light source combining a minute light source 501 and a linear light source 502 may be used. In the surface inspection apparatus of the present invention, these light sources may be appropriately selected in accordance with the specifications of the diffractive OVD to be inspected and the characteristics preferentially required for the inspection apparatus. By appropriately selecting an optimal light source, it becomes possible to acquire a spectral intensity signal and image data of a diffractive OVD that is efficient and more stable, and a highly accurate inspection is possible.

In the description of the embodiment of the present invention, the color difference amount signal D is obtained by obtaining the standard deviation value of the color difference index value Q represented by the equation (1) or the equation (4) in the discrimination processing means. An example was described. However, the present invention is not limited to the definition of the color difference amount signal D. For example, the saturation S used in the HSV (Hue Saturation Value) color system may be used instead of the color difference index value Q. The saturation S is defined as follows, for example.

Here, when a color sensor is used as in the first embodiment, I _R , I _G , and I _B represent signals output from the color sensors, as in the second embodiment. When an image is captured using a color image sensor, each component of RGB of each pixel density value of the image data is represented. In Expression (7), max {I _R, I _G , I _B } means that the maximum value among I _R , I _G , and I _B is selected, and min {I _R , I _G , I _B } means that the smallest one of I _R , I _G , and I _B is selected. Expression (7) indicates that the saturation S is different when max {I _R , I _G , I _B } is 0 and when it is not 0.

  Even when this saturation S is used, the color difference amount signal D may be obtained by calculating the standard deviation value aggregated for the color sensor of saturation S or the standard deviation value aggregated for the pixels of the image data. In this way, by using the processing discriminating device that calculates the color difference signal D from the saturation, it becomes possible to discriminate the diffracted light emitted from the hologram surface and entering the color sensor in a wide color gamut. For this reason, stable inspection can be performed even with respect to changes in the pitch and pattern of the diffraction grating constituting the hologram, and a highly versatile surface inspection apparatus can be obtained.

  Furthermore, in the description of the embodiment of the present invention, an example in which the final output is a binary output of an abnormal signal and a normal signal has been described. However, the present invention is not limited by the form of the output, and may be a device that finally outputs the color difference amount calculated by the color difference amount calculation unit. As a result, the surface inspection apparatus of the present invention can be used, for example, as an apparatus that quantitatively measures the degree of deterioration or damage of the diffractive OVD, or an apparatus that collects data by performing measurements on a number of diffractive OVDs. be able to.

It is a perspective view which shows 1st Embodiment of the surface inspection apparatus which concerns on this invention. It is a block diagram which shows the light detection means and discrimination | determination processing means of the surface inspection apparatus of FIG. It is a flowchart which shows operation | movement of the surface state determination part contained in the discrimination | determination processing means of the surface inspection apparatus of FIG. It is a block diagram which shows the inspection processing apparatus containing the surface inspection apparatus which concerns on this invention. It is a figure which shows the angle relationship of the light ray which injects into a diffraction type OVD, the light ray which specularly reflects, and a diffracted light ray. It is a figure showing emitting a diffracted light beam in the limited direction. It is a figure showing emitting a diffracted light beam in the limited direction. It is a rough-line perspective view which shows the effect that the surface test | inspection apparatus based on this invention can perform the test | inspection stable with respect to the fluctuation | variation of the diffraction type OVD. It is a figure showing the breadth and chromatic dispersion of diffracted light with respect to the angle change of incident light. It is a basic diagram which shows the example of the relationship between the direction of the diffracted light beam of normal diffractive OVD, and a wavelength. It is a basic diagram which shows the example of the relationship between the direction of the diffracted light beam of a diffraction type OVD with a damage and deterioration, and a wavelength. It is a rough-line side view which shows the effect of capturing the characteristic of diffraction type OVD by being detected so that it may include a plurality of wavelengths. It is a perspective view which shows 2nd Embodiment of the surface inspection apparatus which concerns on this invention. It is a block diagram which shows the light detection means and discrimination | determination processing means of the surface inspection apparatus of FIG. It is a basic diagram which shows the illumination means which concerns on other embodiment. It is a basic diagram which shows the illumination means which concerns on other embodiment. It is a basic diagram which shows the illumination means which concerns on other embodiment. It is a basic diagram which shows the illumination means which concerns on other embodiment. It is a basic diagram which shows the illumination means which concerns on other embodiment. It is a basic diagram which shows the illumination means which concerns on other embodiment.

Explanation of symbols

100, 200 Surface inspection device 101 Paper sheet 102 Diffraction OVD
DESCRIPTION OF SYMBOLS 103 Conveying belt 120 Inspection processing apparatus 201 Illumination means 202 Condensing means 203 Light detection means 204 Discrimination processing means 301a, 301b, 301c Color sensor 302 Color difference amount calculation part 303 Surface state determination part 303 Determination result output part 305 Color / line image sensor 501 Micro light source 502 Linear light source 503 Mirror

Claims (9)

A light source that irradiates the diffractive optical change element with light including a plurality of wavelength components;
Light detecting means for detecting the diffracted light of the first wavelength and the diffracted light of the second wavelength diffracted by the diffractive optical change element;
A surface inspection comprising: a calculation unit that calculates an evaluation value related to a color difference between the diffracted light of the first wavelength and the diffracted light of the second wavelength based on a detection result of the light detection unit. apparatus.   2. The light source irradiates the light from a direction corresponding to an obliquely upward direction when the vertical direction of the diffractive optical change element is upward with respect to the diffractive optical change element. The surface inspection apparatus described in 1.   The surface inspection apparatus according to claim 2, wherein the light source is a linear light source extending in a width direction of an irradiation surface of the diffractive optical change element.   The surface inspection apparatus according to claim 2, wherein the light source is a light source having a semicircular arc shape extending along a periphery of an irradiation surface of the diffractive optical change element.   The surface inspection apparatus according to claim 1, wherein the light detection unit is a color sensor that detects a spectral intensity for each of the first and second wavelength components.   The surface inspection apparatus according to claim 1, wherein the light detection unit is an imaging unit that acquires image data for each of the first and second wavelength components. The calculation means calculates the evaluation value based on each spectral intensity of the first and second wavelength components,
6. The surface according to claim 5, further comprising discrimination means for comparing the evaluation value with a predetermined threshold and discriminating a surface state of the diffractive optical change element based on the comparison result. Inspection device. The calculation means calculates the evaluation value based on the saturation obtained from the spectral intensity for each of the first and second wavelength components,
6. The surface according to claim 5, further comprising discrimination means for comparing the evaluation value with a predetermined threshold and discriminating a surface state of the diffractive optical change element based on the comparison result. Inspection device. The calculation means calculates the evaluation value based on a pixel density of image data for each of the first and second wavelength components,
6. The surface inspection apparatus according to claim 5, further comprising a discriminating unit that compares the evaluation value with a predetermined threshold and discriminates the surface state of the test object based on the comparison result.

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