JP5424163B2 - Film thickness measuring method, film thickness measuring apparatus and program - Google Patents

Description

  The present invention relates to a film thickness measuring method for measuring the film thickness of a coating film on the surface of an object to be inspected in a non-contact manner. The present invention also relates to a film thickness measuring apparatus that executes this film thickness measuring method and a program used therefor.

  For large ships such as tankers, it is obliged to paint the hull to protect the hull, and the film thickness is also specified by the Maritime Safety Committee of the International Maritime Organization (IMO). ing.

In this committee, (1) the standard value of the film thickness when drying the coating film is set to 320 μm, (2) the film thickness is 90% or more of the standard value and the remaining 10%. (3) The maximum film thickness at the time of drying determined by the specifications of the paint is not exceeded, (4) The density of the measurement points on the flat part is 1 point / 5 m. ² (5) In the stiffener, it is specified that measurement is performed at a density of 1 point / 2 to 3 m within 15 mm from the edge or welded portion. When measuring according to these conditions, for example, in a large ship, the number of measurement points reaches 100,000.

  In consideration of these points, for example, as described in Non-Patent Document 1, SI (Self Indicating) paint is used for ships. In the SI paint, the film thickness dependency of the coating film color is particularly large at the film thickness in the vicinity of the reference value. Therefore, the operator can visually confirm the unevenness of the film thickness, and can apply this evenly to a large ship. Moreover, when the color visually confirmed is different from the predetermined color, it can be easily recognized that the film thickness is different from the set value.

  However, in order to comply with the above regulations, it is necessary for the operator not only to visually check the unevenness but also to numerically check the film thickness. There are many known methods for measuring the thickness of a thin film, and among them, a method for measuring this in a non-contact and non-destructive manner is particularly simple and effective. When measuring film thickness in a non-contact manner, a method using light reflection / interference is often used.For example, as in the case of measuring the above film thickness, However, application to a much thicker sample is difficult.

  A method for measuring the film thickness of the coating film having the above-mentioned film thickness is described in Patent Document 1, for example. In this technique, the film thickness is calculated by reflecting light emitted from a light source on the sample surface and measuring the spectrum of the reflected light. Therefore, the film thickness of the SI paint applied on the steel plate can be measured in a non-contact manner.

  In addition, Non-Patent Document 2 describes a technique for measuring the film thickness of a coating film by detecting infrared radiation from the surface of the coating film heated by a laser. Furthermore, Patent Document 2 describes a technique for measuring a film thickness by oscillating a pulsed terahertz wave and utilizing interference between a reflected wave from the coating film / steel plate interface and a reflected wave from the coating film surface. Yes.

Nippon Paint Marine Co., Ltd. website (searched on February 26, 2009), Internet <URL: http://www.nippe-marine.co.jp/products/noa.html> Ken Automation website (searched on February 26, 2009), Internet <URL: http://www.kenautomation.com/optisense00.html>

JP 2001-116520 A Japanese Patent Laid-Open No. 2004-28618

  However, in the method described in Patent Document 1 for detecting reflected light, the calculated film thickness may differ depending on various external factors. For example, when light other than that emitted from the light source is incident on the sample, it is difficult to calculate an accurate film thickness.

  Further, in the techniques described in Non-Patent Document 2 and Patent Document 2 using infrared rays or terahertz waves, it is possible to calculate an accurate film thickness, but expensive laser light sources, terahertz wave oscillation sources, and the like. Since parts are required, the cost of the entire film thickness measuring device has increased.

  Therefore, it has been difficult to accurately measure the film thickness of the coating film in a non-contact manner at a low cost.

  The present invention has been made in view of such problems, and an object thereof is to provide an invention that solves the above problems.

In order to solve the above problems, the present invention has the following configurations.
A film thickness measuring method according to claim 1 of the present invention is a film thickness measuring method for measuring the film thickness of a coating film formed on the surface of an object to be inspected in a non-contact manner, and the light irradiated on the object to be inspected. A color image of only the scattered light using an imaging unit, a step of calculating a hue value as a color attribute value in a color image signal that is an output of the imaging unit, and a hue value as the color attribute value And calculating the film thickness using a mathematical expression with the value as an input value.
In the present invention, the color attribute value in the color image signal of the scattered light from the non-inspection object is calculated. The film thickness is calculated by inputting this attribute value into the equation. As light that is the source of the scattered light, light emitted from an arbitrary light source, such as an LED or a fluorescent lamp, can be used as long as the color attribute value is significantly obtained. Here, a hue (h) having particularly small illumination light dependency in relation to the film thickness is used as a color attribute value.
In the film thickness measuring method according to claim 2 of the present invention, the coating film is formed of SI (Self Indicating) paint.
In the present invention, an SI paint whose color film thickness dependency is particularly remarkable is used as a material constituting the coating film .
In the film thickness measuring method according to claim 3 of the present invention, the hue value as the attribute value is determined based on the R (Red) signal, G (Green) signal, and B (Blue) signal in the color image signal. It is characterized by calculating.
In the present invention, an hsv signal, which is a color attribute value, is calculated from an RGB signal used as an output signal for general color imaging.
Moreover, the film thickness measuring method which concerns on Claim 4 of this invention irradiates the illumination light emitted from the light source with respect to the said to-be-inspected object, It is characterized by the above-mentioned.
In the present invention, a light source for emitting illumination light that is a source of scattered light is particularly used.
According to a fifth aspect of the present invention, there is provided a program for causing a computer to execute the film thickness measuring method.
According to the present invention, the film thickness measurement method is executed on, for example, a personal computer.
A film thickness measuring apparatus according to claim 6 of the present invention is a film thickness measuring apparatus that measures the film thickness of a coating film formed on the surface of an object to be inspected in a non-contact manner, and the light irradiated to the object to be inspected. of an imaging unit only scattered light color imaging, and calculate the hue values as a color attribute value in a color image signal which is an output of the imaging unit, a formula that was input values the hue value of as the attribute value And a control unit for calculating the film thickness by using the control unit.
In the present invention, the scattered light from the non-inspection object is color-imaged by the imaging unit. The control unit calculates an attribute value of the color in the color image signal, and calculates a film thickness from the attribute value using an equation. As light that is the source of the scattered light, light emitted from an arbitrary light source, such as an LED or a fluorescent lamp, can be used as long as the color attribute value is significantly obtained. Here, the hue (h) having a particularly small dependency on the illumination light in relation to the film thickness is used as the color attribute value, and the control unit calculates the film thickness using this.
Further, in the film thickness measuring apparatus according to claim 7 of the present invention, the control unit is configured to generate the color attribute based on an R (Red) signal, a G (Green) signal, and a B (Blue) signal in the color image signal. A hue value as a value is calculated.
In the present invention, the control unit calculates an hsv signal, which is a color attribute value, from an RGB signal used as an output signal for general color imaging.
A film thickness measuring apparatus according to an eighth aspect of the present invention includes a light source that emits illumination light to the object to be inspected.
In the present invention, a light source for emitting illumination light that is a source of scattered light is particularly used.
In the film thickness measuring device according to claim 9 of the present invention, the illumination light is white light.
In the present invention, white light that is not single-wavelength light is particularly used as illumination light.
In the film thickness measuring device according to claim 10 of the present invention, the positional relationship between the imaging unit and the light source is such that at least the imaging unit does not detect the reflected light from the inspection object side of the illumination light. It comprises the structure set in the position which detects the said scattered light from the said to-be-inspected object.
In the present invention, the imaging unit is set to a position where it detects scattered light without detecting reflected light from the inspection object. Therefore, the imaging unit can capture the scattered light without being affected by the reflected light.

Since the film thickness measuring method, film thickness measuring apparatus, and program of the present invention are configured as described above, the film thickness of the coating film can be accurately measured in a non-contact manner at a low cost.
At this time, the film thickness can be measured with particularly high accuracy for the coating film composed of the SI paint.
In particular, when the hue (h) is used as the color attribute value, the film thickness can be calculated without using information relating to the illuminance or the like of the illumination light.
Moreover, if a specific light source is used to emit illumination light, the film thickness can be measured with particularly high accuracy. Or if white light is used as illumination light, a cheaper light source can be used.

It is a figure which shows the structure of the film thickness measuring apparatus used as embodiment of this invention. This is the film thickness dependence of the measured and calculated hue h (a), saturation s (b), and brightness v (c). This is a result of examining an error (rms value) between a film thickness calculated using data in a plurality of film thickness ranges and an actual film thickness. It is a figure which shows the relationship between an actual film thickness and the film thickness computed with the film thickness measuring method which concerns on embodiment of this invention. It is an example of the measurement result of distribution of the brightness v at the time of imaging reflected light in the film thickness measuring device which concerns on embodiment of this invention.

  Hereinafter, a film thickness measuring apparatus according to an embodiment for carrying out the present invention will be described. FIG. 1 is a diagram showing the configuration of the film thickness measuring apparatus 10. A film thickness measuring device 10 indicated by a region surrounded by a long broken line in FIG. 1 measures the film thickness of an SI (Self Indicating) paint described in Non-Patent Document 1 or Patent Document 1 in a non-contact manner.

  As an example of the SI paint, for example, N.P. O. There is A (trade name). In this SI paint, pigment particles having a predetermined color are contained in a resin component at a predetermined density, and a solvent is mixed. The color component is set to be thin when the coating film thickness is thin, and the color component is set to be dark when the coating film thickness is thick. The color change at this time is set to be particularly large at about 320 μm, which is the standard value of the film thickness defined by the IMO Maritime Safety Committee. In this SI paint, the resin component is solidified by evaporation of the solvent after being applied, and a stable coating film is obtained.

  In FIG. 1, a light source 11 is an LED (light emitting diode), for example, and emits illumination light 12. As the wavelength of the illumination light, a certain wavelength in the visible light region can be used, but white light can also be used. Therefore, an inexpensive light source such as a fluorescent lamp can be used in addition to the LED.

  This illumination light is applied to the sample 20. The sample 20 (inspection object) has, for example, a configuration in which a coating film 22 of SI paint is applied on a steel plate 21. It is preferable that the surface of the steel plate 21 is not a mirror surface but a surface after lapping because it is difficult to generate reflected light on the surface of the steel plate 21.

  The camera (imaging unit) 13 performs color imaging of the surface of the sample 20 irradiated with the illumination light 12. At this time, when the film thickness is measured, it is installed at the position (A) indicated by the solid line in FIG. 1 so that the reflected light 14 of the illumination light 12 does not directly enter the camera 13. Thereby, most of the light detected by the camera 13 becomes scattered light 15 from the sample 20 of the illumination light 12. However, instead of measuring the absolute value of the film thickness, for example, when detecting only the presence or absence of unevenness in the coating film, the camera 13 may be installed at the position (B) indicated by the broken line in FIG. The reflected light 14 can also be detected. That is, the position of the camera 13 is variable.

  The color image is acquired as an image signal for each of RGB (Red: Green: Blue). Each signal can be obtained by using a configuration in which Red, Green, and Blue filters are arranged for each pixel in a two-dimensional CCD image sensor, as is generally known. The number of pixels of the two-dimensional CCD image sensor is appropriately set according to the optical system of the camera 13 and the size of the location to be measured in the sample 20. Further, any light receiving element that can obtain RGB signals can be used in place of the two-dimensional CCD image sensor.

  The personal computer (control unit) 16 converts the intensity of the R signal, the G signal, and the B signal (referred to as R, G, and B, respectively) into an HSV signal of hue h, saturation s, and brightness v. As is well known, this conversion is performed according to the following equation, with MAX = max (R, G, B) and MIN = min (R, G, B).

  The personal computer 16 calculates the film thickness t of the coating film 22 from the values of h, s, and v in the scattered light. This relationship can be expressed by, for example, a cubic polynomial shown below.

Here, the coefficients a _{1 to} a ₃ , b _{1 to} b ₃ , c _{1 to} c ₃ , and d depend on the material and surface state of the base (steel plate 21), the coating film 22 (type of SI paint), or illumination light. It depends on the illuminance. Specifically, the base material and surface condition. Samples in which a plurality of film thicknesses are set for each type of SI paint and for each illuminance by illumination light are created, and from these results, these coefficients can be obtained by multiple regression analysis or the like.

  In actuality, samples 20 were prepared by applying NOA mighty 60HS buff (300 μm type) as a SI paint on a 200 mm × 300 mm steel plate (non-mirror surface) at various preset thicknesses. These samples are imaged by the camera 13 when a white LED is used as the light source 11 in the configuration of FIG. 1 and a fluorescent lamp is used as room lighting, and the hue h, saturation s, and brightness v are calculated. It was. As the camera 13, a camera having 1080 × 1600 pixels, corresponding to three RGB colors, a focal length of 55 mm, and an F value of 5.6 was used. Here, the illuminance on the surface of the sample 20 was changed by changing the number of lighting of the indoor lighting (fluorescent lamp). When all the indoor lighting (fluorescent lamps) are turned off and illumination is performed only with LEDs, this illuminance is 945 lux. It was.

  The film thickness dependence of these measured and calculated values is shown for hue h in FIG. 2 (a), saturation s in FIG. 2 (b), and brightness v in FIG. 2 (c). Here, the distance between the light source 11 and the sample was 95 cm, and the distance between the camera 13 and the sample was 132 cm.

  From this result, it is clear that these parameters have a large film thickness dependency, particularly at a film thickness of up to 400 μm. Any parameter is saturated at 400 μm or more because this is because the entire surface is covered with pigment particles at a thickness greater than this when viewed microscopically in the film thickness direction. Therefore, the saturated film thickness can be appropriately set depending on the particle diameter of the pigment particles and the density thereof. However, since the standard value of the film thickness defined by the IMO Maritime Safety Committee is 320 μm, the saturated film thickness is preferably about 400 μm.

Therefore, if the coefficients a _{1 to} a ₃ , b _{1 to} b ₃ , c _{1 to} c ₃ , and d are set to values obtained by fitting by the least square method or the like based on the measurement results for each illuminance, the equation (4) Can be used to calculate the film thickness with high accuracy. At this time, this accuracy can be improved by optimizing the film thickness range for performing the fitting. When using only (1) LED as illumination light (945 lux), when using LED and fluorescent lamp (992 lux), when using LED and fluorescence (1081 lux), used in fitting FIG. 3 shows the result of calculating this error (rms value) for each of a plurality of types of film thickness ranges. Here, four film thickness ranges of 0 to 1063 μm, 0 to 679 μm, 0 to 561 μm, and 0 to 389 μm were set. From this result, it can be confirmed that the error can be reduced particularly in the case of 0 to 389 μm.

Table 1 shows examples of values of the coefficients a _{1 to} a ₃ , b _{1 to} b ₃ , c _{1 to} c ₃ , and d obtained at this time. These coefficients are calculated for each type of SI paint to be used, for each type of steel plate 21, and for each surface condition. However, in practice, since the type of SI paint, the type of steel plate 21 and the surface condition thereof are often uniform in one hull, the same coefficient can be used even when a large number of measurement points are provided. There are many cases.

  In FIG. 4, the horizontal axis represents the actual film thickness, and the vertical axis represents the measured and calculated h, s, and v, and the error (rms) between t calculated by the equation (4) and the actual film thickness. Error). From this result, it was confirmed that the film thickness can be calculated with a small rms error by the above method. Here, in this result, only the fluorescent lamp is used as the illumination light, but the same is true even when the fluorescent lamp and the LED are used in combination.

  That is, the film thickness measurement method executed in the film thickness measurement apparatus 10 includes a step of performing color imaging of the scattered light 15 using the camera 13 and a color attribute value in the color image signal which is the output of the camera 13 as a personal computer. 16 and a step in which the personal computer 16 calculates a film thickness using a mathematical expression having the attribute value as an input value. The program for executing this film thickness measurement method may be configured to be executed by the personal computer 16. In this case, the personal computer 16 can be configured not only to process the output of the camera 16 as described above but also to control the light source 11 and the camera 13 by the personal computer 16.

  Therefore, the film thickness of the coating film can be accurately measured in a non-contact manner by the film thickness measuring device 10 or the film thickness measuring method. At this time, unlike the techniques described in Non-Patent Document 2 and Patent Document 2, an expensive laser light source or terahertz wave oscillation source is not required, and for example, an inexpensive LED (light emitting diode) or fluorescent lamp can be used. Therefore, the film thickness measuring apparatus 10 is low cost.

In addition, the saturation s (FIG. 2 (b)) and lightness v (FIG. 2 (c)) have clear dependency on illumination light (illuminance or presence / absence of LED), whereas hue h (FIG. 2 (a)) is less dependent on the illumination light than these, so the coefficients b _{1 to} b ₃ and c _{1 to} c ₃ in equation (4) are not used (all of them are set to zero), and the coefficient a It is also possible to calculate t using only h by setting _{1 to} a ₃ and d to values obtained by fitting by the least square method, etc. In this case, the values of the coefficients a _{1 to} a ₃ and d are as follows: The film thickness can be calculated with high accuracy without using information such as the illuminance of illumination light, etc. In this case, an LED as a special light source, etc. From the result shown in Fig. 2 (a), fluorescence generally used as a room lamp or the like is used. Can be used light emanating from such as illumination light. Therefore, it is possible to further lower the cost of the membrane thickness measuring device 10.

  In the above method, hue h, saturation s, and brightness v are calculated and used as color attribute values from the detected RGB signals. This color is determined based on the color of the pigment contained in the paint. If the color of the pigment is determined, this color is determined by the density of the pigment particles when viewed from the film thickness direction. On the other hand, in the methods described in Non-Patent Document 2 and Patent Document 2, the film thickness is calculated based on the thermal properties of the coating film itself and the optical properties of the coating film itself. The thermal properties and optical properties of the coating largely depend on the parts other than the pigment particles, and the parts other than the pigment particles referred to here are resin components after solidification, and resin components and solvents before solidification. It is a mixture of Therefore, these properties may be different before and after solidification (drying) of the paint, and the measured film thickness is also different before and after drying. On the other hand, in the above-described method for calculating the film thickness from the color attribute, this color is almost determined only by the pigment, and thus the calculated film thickness is substantially the same before and after drying. Therefore, the coating worker can calculate the thickness of the coating film after drying by the above method immediately after application.

  In addition, in the case where the absolute value of the film thickness of the coating film 22 is not measured but the presence / absence of a concavo-convex surface is simply detected, it is not always effective to image the scattered light. FIG. 5 shows a one-dimensional intensity distribution of brightness v obtained in the same manner as described above by installing the camera 13 at the location indicated by the broken line in FIG. Curve, deviation from this smoothing curve. Since the intensity of the reflected light 14 is particularly strongly affected by the unevenness on the surface of the coating film 22, in this case, the brightness v is particularly measured, and the user can easily recognize the unevenness by visually observing the display image of the brightness v. can do. That is, in this film thickness measuring apparatus 10, the camera 13 is installed at a position (B) indicated by a broken line in FIG. 1, and the color attribute value (especially brightness v) is detected, whereby the surface of the coating film 22 is detected. Unevenness can also be detected with high accuracy. However, only the presence or absence of unevenness is recognized in this case, and the absolute value of the film thickness is determined by installing the camera 13 at a position (A) indicated by the solid line in FIG. It can be calculated by detecting h). Such a measurement can be appropriately performed by making the positional relationship of the camera 13 with respect to the reflected light 14 variable.

  That is, in this film thickness measuring apparatus 10, by making the positional relationship of the camera 13 with respect to the reflected light 14 variable, it is possible to check the unevenness of the surface of the coating film 22 and measure the absolute value of the film thickness in an optimum state. It can be carried out. This positional relationship is configured to be selected and set at least one of a position where the camera 13 detects the reflected light 14 and a position where the camera 13 detects the scattered light 15 without detecting the reflected light 14. do it. This configuration can be realized by making the position of the camera 13 and / or the light source 11 relative to the sample 20 variable.

  In the above example, the coating film to be measured is made of SI paint, but it is obvious that the same effect can be obtained if the color is determined by the pigment to be contained. In addition, although the case where a steel plate is used as the base of the coating film is described, it is clear that the material can be used as the base of the measurement object as long as the reflected light from the base surface does not adversely affect the scattered light. It is.

In the above example, the equation (4), which is a cubic polynomial, is used to calculate the film thickness from the color attribute value, but this conversion equation can be set as appropriate. Accordingly, in the above example, the set coefficients are 10 of a _{1 to} a ₃ , b _{1 to} b ₃ , c _{1 to} c ₃ , and d. Is set.

  As described above, the film thickness measuring device and the film thickness measuring method can be preferably applied particularly to the coating film on the hull, but similarly, the film thickness of the coating film is accurately measured in a non-contact manner. In this case, in addition to the hull, the present invention can be applied to any inspection object such as an automobile vehicle or an aircraft.

DESCRIPTION OF SYMBOLS 10 Film thickness measuring device 11 Light source 12 Illumination light 13 Camera (imaging part)
14 Reflected light 15 Scattered light 16 Personal computer (control unit)
20 samples (inspection object)
21 Steel plate 22 Paint film

Claims (10)

A film thickness measurement method for measuring the film thickness of a coating film formed on the surface of an object to be inspected in a non-contact manner,
Color imaging only the scattered light of the light irradiated on the inspection object using an imaging unit;
Calculating a hue value as a color attribute value in a color image signal that is an output of the imaging unit;
Calculating the film thickness using a mathematical formula having a hue value as the color attribute value as an input value;
A film thickness measuring method comprising:   The film thickness measuring method according to claim 1, wherein the coating film is formed of an SI (Self Indicating) paint. 3. The film according to claim 1, wherein a hue value as the attribute value is calculated based on an R (Red) signal, a G (Green) signal, and a B (Blue) signal in the color image signal. Thickness measurement method. The relative inspection object, the film thickness measuring method according to any one of claims 1 to 3, characterized in that irradiates illumination light emitted from the light source. A program for causing a computer to execute the film thickness measurement method according to any one of claims 1 to 4 . It is a film thickness measuring device that measures the film thickness of the coating film formed on the surface of the inspection object in a non-contact manner,
An imaging unit for color imaging only scattered light of the light irradiated on the inspection object;
A control unit for calculating a hue value as a color attribute value in a color image signal which is an output of the imaging unit, and calculates the film thickness by using a formula that was input value the value of the hue as the attribute value,
A film thickness measuring apparatus comprising: The control unit calculates a hue value as an attribute value of the color based on an R (Red) signal, a G (Green) signal, and a B (Blue) signal in the color image signal. 6. The film thickness measuring apparatus according to 6 . The film thickness measuring apparatus according to claim 6 , further comprising a light source that emits illumination light to the object to be inspected. The film thickness measuring apparatus according to claim 8 , wherein the illumination light is white light. Positional relationship of the said imaging unit light source, at least, is set to the position where the imaging unit detects the scattered light from the inspection object without detecting reflected light from the inspection object side of the illumination light The film thickness measuring device according to claim 8 , wherein the film thickness measuring device is provided.

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