JP2023032494A - Coated film thickness measurement method, coated film thickness measurement program and coated film thickness measurement system by image - Google Patents

Abstract

To provide a coated film thickness measurement method, coated film thickness measurement program and coated film thickness measurement system by an image which can highly accurately perform non-contact and planar film thickness measurement.SOLUTION: A coated film thickness measurement method comprises: a parameter decision step S1 of estimating and deciding a scattering coefficient (S) and an absorption coefficient (K) of a coated film by emitting light to a plurality of testing pieces 1 having the coated film coated by changing the film thickness of a target coating material; a film thickness estimation expression derivation step S2 of deriving a film thickness estimation expression by applying the scattering coefficient (S) and the absorption coefficient (K) to a relational expression between reflection light intensity (R(T)) and coated film thickness (T) of the coated film based on Kubelka-Munk theory; an image acquisition step S3 of illuminating a coated film 111 with which an object 110 being the measurement object is coated to acquire reflection light as an image by imaging means 70; a coated film thickness calculation step S4 of obtaining the reflection light intensity (R(T)) from the image and applying it to the film thickness estimation expression to obtain the coated film thickness (T); and a coated film thickness provision step S5 of providing the obtained coated film thickness (T).SELECTED DRAWING: Figure 1

Description

The present invention relates to an image-based coating thickness measuring method, a coating thickness measuring program, and a coating thickness measuring system for measuring coating thickness using an image.

In shipbuilding coatings, it is particularly important to ensure that the desired coating thickness is applied. Therefore, SI paints with a "Self-indicating (SI) function" have been developed as a way for workers themselves to visually confirm whether or not they have achieved a desired coating thickness at a coating work site. . SI paint is a paint in which the color of the paint film gradually changes until it reaches a predetermined film thickness by adjusting the pigment component in the paint. It is said that the thickness can be reliably secured.
On-site coating film thickness measurements have been carried out using electromagnetic or ultrasonic film thickness gauges (for dry coatings) or wet gauges (for wet coatings).

In Patent Document 1, the degree of surface roughness (a value corresponding to the film thickness) is determined by a surface roughness determination unit, and the degree of roughness and the amount of change in the degree of roughness over time are usually determined by a first film thickness calculation means. , The coating film thickness is calculated based on the wavelength distribution and the coating conditions. A paint film thickness measuring device is disclosed which is configured to calculate the film thickness of the paint based on the wavelength distribution by a thickness calculator.
Further, in Patent Document 2, a light source for applying paint to a steel material to be coated and irradiating light on the coated surface on which the coating film is applied, a measuring instrument for measuring the color information of the reflected light, and the measuring instrument A coating film thickness measuring device is disclosed which comprises a signal processing means for converting the color information obtained in (1) into a film thickness and measures the film thickness of the spot portion of the coating surface without contact.
In addition, in Patent Document 3, a calibration curve for film thickness is calculated from the reflectance of ultraviolet rays irradiated to the surface of a standard specimen on which a transparent coating film mixed with an ultraviolet absorber is formed, and the thickness of the coating film. A transparent paint having the same composition as that of the standard specimen is applied to the surface of the base material, and the surface of the specimen is irradiated with ultraviolet rays. A coating film thickness measuring method for calculating the film thickness of a test object is disclosed.
Further, in Patent Document 4, a sheet of copper plate is sequentially fed out from a roll, a titanium oxide paint is applied in a coating section, dried in a drying oven, and then the film thickness of titanium oxide is measured with a film measuring device. In doing so, a color CCD sensor is used to image the entire length of the sheet in the width direction, and the resulting video signal is converted into gradation data for each RGB color component by the video board of the controller. The data of G or B valid for the calculation circuit compares the data of G or B with the reference value stored in the reference thickness table to obtain the applicable film thickness. A film measuring apparatus is disclosed that can accurately measure the film thickness and weight of titanium, control the coating amount in the coating section by FB (feedback) control, and maintain the film thickness constant.

JP-A-9-105612 JP-A-2001-116520 JP-A-2003-4419 JP-A-2007-61780

Film thickness measurement using an electromagnetic/ultrasonic film thickness meter or wet gauge is basically a point measurement, and surface evaluation of the coating film thickness (distribution measurement of the coating film thickness) is difficult.
Moreover, since the coating film thickness measuring device of Patent Document 1 predicts the dry film thickness after drying by calculation from the measured wet film thickness, there is a possibility that the numerical accuracy of the obtained dry film thickness is low.
Further, the coating film thickness measuring device of Patent Document 2 only measures the thickness based on the relative relationship between the color information such as the color intensity and the thickness, and there is a possibility that the thickness measurement accuracy is not sufficient.
Moreover, the film thickness measurement method of Patent Document 3 is intended for transparent coating films, and cannot be applied to opaque coating films.
Moreover, the film measuring device of Patent Document 4 is intended for the film thickness of a film-like or sheet-like base material produced at a factory, and is not applicable to shipbuilding coating or the like.
Accordingly, an object of the present invention is to provide an image-based coating thickness measurement method, a coating thickness measurement program, and a coating thickness measurement system capable of performing non-contact surface coating thickness measurement with high precision. do.

In the method for measuring the coating thickness by the image corresponding to claim 1, the coating thickness is measured by the image, and a plurality of tests with the coating film applied by changing the thickness of the target coating material are performed. A parameter determination step for estimating and determining the scattering coefficient (S) and the absorption coefficient (K) of the coating film by irradiating the piece with light, and the scattering coefficient (S) and the absorption coefficient (K) according to the Kubelka-Munk theory A film thickness estimation formula derivation step for deriving a film thickness estimation formula by applying it to the relational expression between the reflected light intensity (R (T)) of the coating film and the coating film thickness (T) based on An image acquisition step of illuminating the applied coating film and acquiring the reflected light as an image with an imaging means, and obtaining the reflected light intensity (R (T)) from the image and applying it to the film thickness estimation formula to apply the coating thickness ( It is characterized by having a coating thickness calculation step for obtaining T) and a coating thickness providing step for providing the obtained coating thickness (T).
According to the first aspect of the present invention, non-contact planar film thickness measurement can be performed with high accuracy using an image.

According to the second aspect of the present invention, the estimation of the scattering coefficient (S) and the absorption coefficient (K) in the parameter determination step is performed by preparing a sufficient number of test pieces for the assumed film thickness and calculating the reflected light intensity It is characterized by estimating using a nonlinear least-squares method including the Levenberg-Marquard method based on the measurement results of (R(T)) and coating thickness (T).
According to the second aspect of the present invention, the scattering coefficient (S) and absorption coefficient (K) of the coating film can be accurately estimated.

According to a third aspect of the present invention, the film thickness estimation formula derivation step further comprises a fitting step of fitting the film thickness estimation formula using the actually measured film thickness of the coating film.
According to the third aspect of the present invention, the coating thickness (T) can be calculated more accurately from the thickness estimation formula fitted using the measured thickness.

The present invention according to claim 4 is characterized in that the light in the parameter determination step and the illumination in the image acquisition step are light under the same conditions.
According to the fourth aspect of the present invention, film thickness measurement can be performed under the same conditions without correcting the scattering coefficient (S) and the absorption coefficient (K) determined in the parameter determining step.

The present invention according to claim 5 is characterized in that the imaging means is a spectral camera.
According to the fifth aspect of the present invention, it is possible to obtain a spectral image in a wavelength band of a specific wavelength and accurately measure the reflected light intensity (R(T)) for each wavelength band.

In the present invention according to claim 6, a sample image acquisition step of producing a plurality of coating film samples with a known coating thickness and acquiring the coating film samples as sample images under the same conditions, and an image acquisition step A parameter correction step of acquiring a plurality of coating film samples as sample images during measurement, comparing the sample images with the sample images during measurement, and correcting the scattering coefficient (S) and the absorption coefficient (K). and
According to the sixth aspect of the present invention, by comparing the sample image of the coating film sample and the sample image during measurement and correcting the scattering coefficient (S) and the absorption coefficient (K), the sample image and the sample during measurement It is possible to accurately measure the coating thickness (T) in consideration of the difference in image measurement conditions.

The present invention according to claim 7 is characterized in that the film thickness of the coating film sample is approximately the upper limit and the approximately lower limit of the coating film of the object to be measured.
According to the seventh aspect of the present invention, even with a small number of coating film samples, the coating film thickness (T) can be accurately measured with higher accuracy.

According to an eighth aspect of the present invention, saturation is used as the reflected light intensity (R(T)).
According to the eighth aspect of the present invention, even in the visible light region, the coating thickness (T) can be measured with higher accuracy based on the saturation as the reflected light intensity (R (T)). can be done.

In the present invention according to claim 9, the target paint is a wavelength band in which the reflected light intensity (R (T)) of the coating film does not cause saturation in the range of the coating film thickness of the object to be measured. It is characterized by being a paint having
According to the ninth aspect of the present invention, by using a paint having a wavelength band that does not cause saturation of the reflected light intensity (R(T)), even in a thick film region, by selecting a wavelength band Film thickness measurements can be made possible.

In the coating thickness measurement program by image corresponding to claim 10, the program for measuring the coating thickness by the image, wherein the computer is provided with an image acquisition step in the coating thickness measurement method by the image, and the coating thickness calculation and a coating thickness providing step.
According to the tenth aspect of the present invention, the image-based coating film thickness measurement method can be performed more accurately and quickly, and the film thickness can be measured in a non-contact manner and with high accuracy.

According to an eleventh aspect of the present invention, a computer is caused to execute a film thickness estimation formula deriving step.
According to the eleventh aspect of the present invention, it is possible to accurately and quickly derive a film thickness estimation formula fitted using the measured film thickness.

According to a twelfth aspect of the present invention, a computer is caused to execute the sample image acquiring step and the parameter correcting step.
According to the twelfth aspect of the present invention, by correcting the scattering coefficient (S) and the absorption coefficient (K), the coating thickness ( T) can be measured accurately and quickly.

In a coating film thickness measurement system using an image corresponding to claim 13, the system measures the coating thickness using an image, and the scattering coefficient (S) and the absorption coefficient (K) of the coating film of the target coating material are is applied to the relational expression between the reflected light intensity (R (T)) of the coating film and the coating thickness (T) based on the Kubelka-Munk theory, and a film thickness estimation formula derivation means for deriving the film thickness estimation formula; Illuminating the coating film of the object, obtaining the reflected light as an image by the imaging means, and obtaining the reflected light intensity (R (T)) from the image and applying it to the film thickness estimation formula It is characterized by comprising coating thickness calculating means for obtaining the coating thickness (T) and coating thickness providing means for providing the obtained coating thickness (T).
According to the thirteenth aspect of the present invention, non-contact planar film thickness measurement can be performed with high accuracy using an image.

A fourteenth aspect of the present invention is characterized in that the illumination in the image acquisition means is the light under the same conditions as when the scattering coefficient (S) and the absorption coefficient (K) are obtained.
According to the fourteenth aspect of the present invention, film thickness measurement can be performed under the same conditions without correcting the calculated scattering coefficient (S) and absorption coefficient (K).

According to a fifteenth aspect of the present invention, the imaging means is a spectral camera.
According to the fifteenth aspect of the present invention, it is possible to acquire a spectral image in a wavelength band of a specific wavelength and accurately measure the reflected light intensity (R(T)) for each wavelength band.

According to the sixteenth aspect of the present invention, there is provided a sample image storage means for storing a plurality of sample images of a coating film having a known film thickness obtained under the same conditions, and a plurality of images obtained by the image obtaining means during measurement. and parameter correction means for comparing the sample image and the sample image during measurement of the coating film sample and correcting the scattering coefficient (S) and the absorption coefficient (K).
According to the sixteenth aspect of the present invention, by comparing the sample image of the coating film sample and the sample image during measurement and correcting the scattering coefficient (S) and the absorption coefficient (K), the sample image and the sample during measurement It is possible to accurately measure the coating thickness (T) in consideration of the difference in image measurement conditions.

A seventeenth aspect of the present invention is characterized in that saturation is used as the reflected light intensity (R(T)).
According to the present invention of claim 17, even in the visible light region, the coating thickness (T) can be measured with higher accuracy based on the saturation as the reflected light intensity (R (T)). can be done.

According to the coating film thickness measurement method using images of the present invention, it is possible to perform non-contact surface film thickness measurement with high accuracy using images.

In addition, the scattering coefficient (S) and the absorption coefficient (K) in the parameter determination step are estimated by preparing a sufficient number of test pieces for the assumed film thickness and reflecting the intensity of the reflected light (R (T)) and When estimating using the nonlinear least-squares method including the Levenberg-Marquard method based on the results of the measurement of the coating thickness (T), the scattering coefficient (S) and absorption coefficient (K) of the coating film are accurately estimated. can do.

Further, in the film thickness estimation formula derivation step, if there is a fitting step of fitting the film thickness estimation formula using the actually measured film thickness of the coating film, the film thickness fitted using the measured film thickness The coating thickness (T) can be calculated more accurately from the estimation formula.

Further, when the light in the parameter determination step and the illumination in the image acquisition step are the light under the same conditions, the scattering coefficient (S) and the absorption coefficient (K) determined in the parameter determination step are not corrected under the same conditions. Film thickness measurement can be performed at the base.

Further, when the imaging means is a spectrum camera, it is possible to acquire a spectrum image in a wavelength band of a specific wavelength and accurately measure the reflected light intensity (R(T)) for each wavelength band.

In addition, a sample image acquisition step in which multiple coating film samples with a known coating thickness are created and the coating film samples are acquired as sample images under the same conditions, and multiple coating film samples are also acquired in the image acquisition step. A sample image of a coating film sample when it has a parameter correction step of acquiring a sample image at the time of measurement, comparing the sample image with the sample image at the time of measurement, and correcting the scattering coefficient (S) and the absorption coefficient (K) By comparing the sample image at the time of measurement and correcting the scattering coefficient (S) and the absorption coefficient (K), considering the difference in measurement conditions between the sample image and the sample image at the time of measurement, the coating thickness (T) Accurate measurement is possible.

In addition, if the film thickness of the coating film sample is approximately the upper limit and approximately the lower limit of the coating film of the object to be measured, even if the number of coating film samples is small, the coating film thickness (T) can be measured accurately and with higher precision.

Further, when the saturation is used as the reflected light intensity (R (T)), even in the visible light region, the coating thickness (T) is based on the saturation as the reflected light intensity (R (T)). can be measured with higher accuracy.

In addition, if the target paint has a wavelength band in which the reflected light intensity (R (T)) of the coating film does not cause saturation in the range of the coating film thickness of the object to be measured. By using a paint having a wavelength band that does not cause saturation of the reflected light intensity (R (T)), it is possible to measure the film thickness even in a thick film region by selecting the wavelength band. .

Further, according to the program for measuring the coating thickness by image of the present invention, the coating thickness measuring method by the image can be executed more accurately and quickly, and the coating thickness can be measured in a non-contact and highly accurate manner.

Further, when the computer is caused to execute the film thickness estimation formula deriving step, the film thickness estimation formula fitted using the measured film thickness can be derived accurately and quickly.

Further, when the computer executes the sample image acquisition step and the parameter correction step, the difference in measurement conditions between the sample image and the sample image during measurement is corrected by correcting the scattering coefficient (S) and the absorption coefficient (K). With this in mind, the coating thickness (T) can be measured accurately and quickly.

Further, according to the coating film thickness measurement system using images of the present invention, non-contact surface film thickness measurement can be performed with high accuracy using images.

Further, when the illumination in the image acquisition means is light under the same conditions as when obtaining the scattering coefficient (S) and the absorption coefficient (K), the obtained scattering coefficient (S) and absorption coefficient (K) are corrected. film thickness can be measured under the same conditions.

Further, when the imaging means is a spectrum camera, it is possible to acquire a spectrum image in a wavelength band of a specific wavelength and accurately measure the reflected light intensity (R(T)) for each wavelength band.

In addition, a sample image storage means for storing a plurality of sample images of a coating film having a known film thickness acquired under the same conditions, If a parameter correction means for comparing the sample image and the sample image and correcting the scattering coefficient (S) and the absorption coefficient (K) is provided, the sample image of the coating film sample and the sample image at the time of measurement are compared and scattering is performed. By correcting the coefficient (S) and the absorption coefficient (K), the coating thickness (T) can be accurately measured in consideration of the difference in measurement conditions between the sample image and the sample image during measurement.

Further, when the saturation is used as the reflected light intensity (R (T)), even in the visible light region, the coating thickness (T) is based on the saturation as the reflected light intensity (R (T)). can be measured with higher accuracy.

FIG. 1 is a flowchart of a first coating thickness measurement method using an image according to an embodiment of the present invention; Functional block diagram showing the coating thickness measurement system using the same image as a means of realizing functions A diagram showing the predicted value of the KM theory based on the value determined by parameter estimation for the color change (chroma) of the same paint Graph showing "film thickness-reflected light intensity" when the values of the same scattering coefficient (S) and absorption coefficient (K) are changed Flow chart of the second coating thickness measurement method using the same image

A coating thickness measuring method, a coating thickness measuring program, and a coating thickness measuring system according to an embodiment of the present invention will be described.
FIG. 1 is a flow chart of a first coating thickness measuring method using an image, and FIG. 2 is a functional block diagram showing a coating thickness measuring system using an image as a function realizing means.
The coating thickness measurement system shown in FIG. 2 is a system for measuring coating thickness from an image, and includes a thickness estimation formula derivation means 10, an image acquisition means 20, a coating thickness calculation means 30, a coating thickness Equipped with providing means 40, sample image storage means 50, parameter correction means 60, imaging means 70, input means 80, and display means 90, a part of the coating thickness measurement method using images is executed.
The computer 100 is provided with image acquiring means 20, coating thickness calculating means 30, coating thickness providing means 40, sample image storing means 50, and parameter correcting means 60 as functions. Program is installed.
The film thickness estimation formula derivation means 10 converts the scattering coefficient (S) and the absorption coefficient (K) of the coating film of the paint to be measured into the reflected light intensity (R (T) of the coating film based on the Kubelka-Munk theory ) and the coating film thickness (T) to derive the film thickness estimation formula.
The image acquiring means 20 illuminates the coating film 111 of the object 110 to be measured, and acquires the reflected light as an image by the imaging means 70 .
The coating thickness calculation means 30 obtains the reflected light intensity (R(T)) from the acquired image and applies it to the thickness estimation formula to obtain the coating thickness (T).
The coating thickness providing means 40 provides the obtained coating thickness (T) to the display means 90 .

As shown in FIG. 1, the first coating film thickness measurement method first irradiates light on a plurality of test pieces 1 having a coating film coated with a target coating film with a different thickness, and the coating The scattering coefficient (S) and absorption coefficient (K) of the film are estimated and determined (S1: parameter determination step). The plurality of test pieces 1 are obtained by applying the paint whose coating thickness is to be measured with different film thicknesses for each test piece 1, and the film thickness is known.
The scattering coefficient (S) and absorption coefficient (K) are parameters that are assumed to take different values for each paint.
The scattering coefficient (S) is the rate of increase in reflectance with respect to an increase in coating thickness (T). As an extreme example, in the case of a transparent coating film, the scattering coefficient (S)=0 (no reflection of light within the coating film). For example, the intensity of reflected light from pigment particles in paint can be evaluated by the scattering coefficient (S). Even with the same pigment particles, the scattering coefficient (S) is considered to increase as the content increases, and the scattering coefficient (S) is also considered to increase when highly reflective pigment particles are used.
The absorption coefficient (K) is the rate of decrease in transmittance with respect to the increase in coating thickness (T), and is like the attenuation of light incident on the coating film 111 . Since each resin has a different absorption spectrum, the value of the absorption coefficient (K) differs for each type of resin, and it is assumed that the manner of attenuation also differs depending on the wavelength band of incident light.

The parameter determination step S1 can also be performed in a laboratory experiment or the like, and the scattering coefficient (S) and absorption coefficient (K) of the coating film can be obtained in advance in the laboratory experiment before film thickness measurement on site. If the scattering coefficient (S) and absorption coefficient (K) are measured in advance for a combination of paints and light sources to be measured, various conditions such as the imaging equipment and light source 120 can be set to the same conditions as in laboratory experiments. By adjusting the shooting conditions such as this, it becomes possible to measure the film thickness distribution with one-shot shooting at the site.
A processing procedure in the parameter determination step S1 is, for example, as follows.
1) Prepare a sufficient number of test pieces 1 for the film thickness range to be measured, irradiate each prepared test piece 1 with light from a light source, and photograph the test piece 1 using a spectrum camera or the like.
2) Based on the image acquired by photographing, data of "film thickness-reflected light intensity" is created.
3) Using the created "film thickness - reflected light intensity" data, parameter estimation is performed using a nonlinear least squares method such as the Levenberg-Marquard method, etc., and the scattering coefficient (S) and absorption coefficient ( K) is determined.
Thus, in the parameter determination step S1, the scattering coefficient (S) and the absorption coefficient (K) are determined by preparing a sufficient number of test pieces 1 for the assumed film thickness, and based on the measurement results, the Levenberg- The scattering coefficient (S) and the absorption coefficient (K) of the coating film can be accurately estimated by using the nonlinear least-squares method including the Marquard method.

式（１）の逆関数は次式（２）と書け、式（２）が膜厚推定式となる。なお、ｌｎは自然対数である。

After the parameter determination step S1, the obtained scattering coefficient (S) and absorption coefficient (K) are input to the computer 100 using the input means 80. FIG. Input means 80 is, for example, a keyboard, a mouse, or the like. The computer 100 applies the scattering coefficient (S) and the absorption coefficient (K) to the relational expression between the reflected light intensity (R (T)) of the coating film and the coating thickness (T) based on the Kubelka-Munk theory. An estimation formula is derived (S2: film thickness estimation formula derivation step).
In the film thickness estimation formula derivation step S2, the film thickness estimation formula derivation means 10 models the relationship between "film thickness-reflected light intensity" using the Kubelka-Munk theory. The Kubelka-Munk theory is a theory that associates the intensity of light incident on a substance with the intensity of light reflected, and is widely used for color matching of paints. According to the Kubelka-Munk theory, the relational expression between the film thickness (T) and the reflected light intensity (R(T)) is given by the following equation (1).

The inverse function of the formula (1) can be written as the following formula (2), and the formula (2) becomes the film thickness estimation formula. Note that ln is the natural logarithm.

Here, FIG. 3 is a diagram showing the predicted values of the KM theory based on the values determined by parameter estimation for the color change (chroma) of the paint. Saturation). Note that saturation can also be said to be reflected light intensity (R(T)) in the visible light region.
"Measured data" in FIG. 3 is a value measured by a commercially available electromagnetic film thickness meter, and shows the average value and standard deviation of 30 measurements performed on one test piece 1 . From FIG. 3, it can be seen that the color change of the coating film is well captured. As the film thickness increases, it asymptotically approaches a constant value (corresponding to color saturation), and the estimation error increases in a region close to the value (R _∞ ) when the reflected light intensity (R(T)) converges. The value (R _∞ ) when the reflected light intensity (R(T)) converges depends on the values of the scattering coefficient (S) and the absorption coefficient (K). In this way, by using the saturation as the reflected light intensity (R (T)), even in the visible light region, the coating thickness (T ) can be measured with higher accuracy. That is, the coating thickness (T) can be determined based on the KM theory even in the visible light region by using chroma. Therefore, the coating thickness (T) can be measured with high accuracy without using a spectrum camera. Alternatively, the coating thickness (T) may be measured by combining the reflected light intensity (R(T)) obtained by a spectral camera or hyperspectral camera and the saturation obtained in the visible light band. Note that if there are color samples of about two types of film thickness, it is possible to estimate the film thickness from an image.
Further, the film thickness estimation formula derivation step S2 includes a fitting step S2-1 for fitting the film thickness estimation formula using the actually measured film thickness of the coating film 111. FIG. "KM fitting" in FIG. 3 is the result of estimating the parameters of the KM theory (formula (1)) by the LM method and fitting to "Measured data". By fitting the film thickness estimation formula in this way, the coating thickness (T) can be calculated more accurately from the film thickness estimation formula (2) fitted using the measured film thickness.
The scattering coefficient (S) and the absorption coefficient (K) vary depending on the material of the coating film 111 (coating components such as pigments and resins), measurement conditions (shooting equipment, light source 120, etc.), and the wavelength of the reflected light. (The shape of the fitting function in FIG. 3 changes for each wavelength).

式（３）を少し変形すると、Ｒ_∞は（Ｋ／Ｓ）のみの関数として表されることが分かる。つまり、散乱係数（Ｓ）と吸収係数（Ｋ）の値が変化した場合でも散乱係数（Ｓ）と吸収係数（Ｋ）の比が一定値であれば、図４に示すようにＲ_∞は一定値になる。 SI paint (Self Indication paint) used for painting ballast tanks on ships is made so that the color change is saturated at a film thickness of 320 μm, which is required by the IMO (International Maritime Organization) paint performance standards (PSPC). Therefore, in the film thickness region of 320 μm or more, even if the film thickness increases, the color does not change and the film thickness cannot be distinguished with the naked eye.
However, depending on the wavelength of the reflected light, for example, the reflected light intensity (R(T)) does not saturate even when the film thickness exceeds 320 μm in a certain wavelength band. is assumed. Therefore, the target paint is a paint having a wavelength band in which the reflected light intensity (R(T)) of the coating film 111 does not cause saturation in the range of the film thickness of the coating film 111 of the object 110 to be measured. By using a wavelength band in which the reflected light intensity (R(T)) does not saturate, it is possible to measure film thickness in a thick film region (320 μm or more) where the film thickness cannot be identified with the naked eye. is also possible.
Here, FIG. 4 is a graph showing "film thickness-reflected light intensity" when the values of the scattering coefficient (S) and the absorption coefficient (K) are changed. Line A shows the original values of the scattering coefficient (S) and the absorption coefficient (K) calculated in the parameter determination step S1, and line B shows the scattering coefficient (S) and the absorption coefficient (K) of the original values, respectively. Line C shows the case where the scattering coefficient (S) and the absorption coefficient (K) are each 0.5 times the original value. In either case, the value converges to a constant value, but the smaller the value of the scattering coefficient (S) and the absorption coefficient (K), the larger the film thickness value that converges. In other words, by combining the material of the coating film 111 and the wavelength band so that the scattering coefficient (S) and the absorption coefficient (K) are small, it is possible to measure the film thickness even in a range exceeding 320 μm.
The value (R _∞ ) when the reflected light intensity (R(T)) converges is expressed by the following equation (3).

A slight modification of equation (3) shows that R _∞ can be expressed as a function of (K/S) only. That is, even if the values of the scattering coefficient (S) and the absorption coefficient (K) change, if the ratio of the scattering coefficient (S) and the absorption coefficient (K) is constant, R _∞ is constant as shown in FIG. be a value.

After the film thickness estimation formula derivation step S2, the coating film 111 applied to the object 110 to be measured is illuminated from the light source 120, and the reflected light is acquired as an image by the imaging means 70 (S3: image acquisition step ).
In the image acquisition step S3, the image acquisition means 20 captures an image of the object 110 in a range of, for example, 1 cm square to 100 cm square. The photographing distance is set in a predetermined range of, for example, about 1.0 m to 2.0 m, and the focal length is arbitrary.
Here, when the light in the parameter determination step S1 and the illumination in the image acquisition step S3 are the same light conditions, the conditions of the light irradiated to the test piece 1 and the light irradiated to the object 110 Since the conditions are the same, film thickness measurement can be performed under the same conditions without correcting the scattering coefficient (S) and the absorption coefficient (K) determined in the parameter determination step S1. As the light source used in the parameter determination step S1 and the light source 120 used in the image acquisition step S3, it is preferable to use, for example, a diffused light source for photographing with little unevenness in light intensity. Also, the light source used in the parameter determination step S1 and the light source 120 used in the image acquisition step S3 may be the same light source.
The light irradiated in the parameter determination step S1 and the illumination in the image acquisition step S3 may be white light, light containing a specific wavelength, light of a specific wavelength, or the like. Any light that can obtain (R(T)) can be used.

In this embodiment, the imaging means 70 used in the image acquisition step S3 is a spectrum camera. Thereby, it is possible to obtain a spectrum image of a wavelength band of a specific wavelength, and accurately measure the reflected light intensity (R(T)) for each wavelength band of about several types.
In addition, as a simple method for measuring the intensity of reflected light (R(T)) in several wavelength bands, the image pickup means 70 can transmit only light in a specific wavelength band to a visible light camera such as a general digital camera. It is also possible to photograph with a band-pass filter that allows transmission.
Further, as described above, the scattering coefficient (S) and the absorption coefficient (K) are different for each wavelength of reflected light. can be. Therefore, it is preferable to use a multi-wavelength spectroscopic camera (hyperspectral camera) capable of measuring spectra of a plurality of wavelengths as the imaging means 70 . Thereby, for example, a film thickness of 320 μm or more can be measured with higher accuracy. By using a spectral camera with a large number of bands or a hyperspectral camera, there is a possibility that a color sample (sample) becomes unnecessary. It should be noted that a light field camera capable of obtaining an image whose focus has been changed after photographing or a stereoscopic image can be used alone or in combination with a spectral camera or a hyperspectral camera.

After the image acquisition step S3, the reflected light intensity (R(T)) is obtained from the image and applied to the film thickness estimation formula to obtain the coating thickness (T) (S4: coating thickness calculation step).
Since the scattering coefficient (S) and the absorption coefficient (K), which are parameters, are obtained in the parameter determination step S1 and are known, the light intensity sensor detects the reflected light intensity (R(T)) from the surface of the coating film 111. By measuring , the coating thickness (T) can be obtained from the equation (2) using the coating thickness calculation means 30 .

After the coating thickness calculation step S4, the determined coating thickness (T) is provided from the coating thickness providing means 40 to the display means 90 (S5: coating thickness providing step).
The display means 90 is, for example, a printer, a monitor, or the like connected to the computer 100, and processes and outputs information regarding the coating thickness (T) provided from the coating thickness providing means 40. FIG.

Next, a coating thickness measuring method different from the flow shown in FIG. 1 will be described. FIG. 5 is a flow chart of the second coating thickness measuring method using images. The same parts as in the flow of the first method for measuring coating thickness are denoted by the same reference numerals, and the description thereof is omitted.
In the second coating thickness measurement method, the sample image storage means 50 and the parameter correction means 60 shown in FIG. 2 are also used. The sample image storage means 50 stores the sample images 3 obtained by obtaining the images of a plurality of coating film samples 2 having known film thicknesses under the same conditions. In addition, the parameter correction means 60 compares the sample image 4 and the sample image 3 during measurement of the plurality of coating film samples 2 acquired by the image acquisition means 20 during measurement, and the scattering coefficient (S) and the absorption coefficient (K ) is corrected.

If the conditions of the image acquisition step S3 (at the time of on-site photography) are different from the conditions of the parameter determination step S1 (at the time of laboratory experiments), several coating film samples 2 with known film thicknesses are placed on the object 120 ( By taking an image at the same time as the object to be photographed (stored in the same image), the reflected light intensity (R (T)) from the coating film sample 2 is referred to, and the scattering coefficient (S) and absorption coefficient of the parameters (K) can be corrected. That is, it is possible to correct the difference in photographing conditions between the parameter determination step S1 and the image acquisition step S3.
Therefore, as shown in FIG. 5, in the second coating thickness measuring method, a sample image acquisition step S6 and a parameter correction step S7 are executed.
In the sample image acquisition step S6, a plurality of coating film samples 2 having a known paint film thickness are produced, the coating film samples 2 are acquired as sample images 3 under the same conditions, and stored in the sample image storage means 50. do.
In the parameter correction step S7, the parameter correction means 60 also acquires a plurality of coating film samples 2 as the measurement sample images 4 in the image acquisition step S3, compares the sample images 3 and the measurement sample images 4, Correct the coefficient (S) and the absorption coefficient (K).
As a result, by comparing the sample image 3 of the coating film sample and the sample image 4 at the time of measurement and correcting the scattering coefficient (S) and the absorption coefficient (K), the measurement conditions of the sample image 3 and the sample image 4 at the time of measurement are corrected. Considering the difference, the film thickness distribution of the coating film thickness (T) can be accurately measured. In addition, in order to correct the scattering coefficient (S) and the absorption coefficient (K), automatic detection of each coating sample 2 in the photographed image and recognition and classification processing linked to the film thickness are necessary. Each coating film sample 2 is preferably attached with an identification marker such as a QR code (registered trademark).
Moreover, it is preferable that the film thickness value of the coating film sample 2 is selected such that the difference is large within the film thickness range to be measured. Therefore, the film thickness of the coating film sample 2 is set to substantially the upper limit and substantially the lower limit of the coating film 111 of the object 110 to be measured. As a result, even with a small number of coating film samples, the film thickness distribution of the coating film thickness (T) can be accurately measured with higher accuracy. For example, when the film thickness range to be measured is 0 to 450 μm, coating film samples 2 of 50 μm and 400 μm are prepared.

As described above, according to the image-based coating film thickness measuring method and the image-based coating film thickness measuring system of the present invention, non-contact surface film thickness measurement can be performed with high accuracy using images. .
In addition, using a program for measuring the coating thickness by image, the computer 100 is caused to execute the image acquisition step S3, the coating thickness calculation step S4, and the coating thickness providing step S5 in the coating thickness measurement method. The coating film thickness measurement method can be performed more accurately and quickly, and the film thickness can be measured non-contact and with high accuracy.
Further, by causing the computer 100 to execute the film thickness estimation formula derivation step S2, it is possible to accurately and quickly derive the film thickness estimation formula fitted using the measured film thickness.
Further, by causing the computer 100 to execute the sample image acquisition step S6 and the parameter correction step S7, the scattering coefficient (S) and the absorption coefficient (K) are corrected, thereby measuring the sample image 3 and the sample image 4 during measurement. The coating thickness (T) can be measured quickly and accurately considering the difference in conditions.

According to the present invention, by constructing an approximation function based on the Kubelka-Munk theory and deriving a film thickness estimation formula, it is possible to accurately estimate the coating thickness of shipbuilding coatings and other coatings.

1 Test piece 2 Coating film sample 3 Sample image 4 Sample image during measurement 10 Film thickness estimation formula derivation means 20 Image acquisition means 30 Coating thickness calculation means 40 Coating thickness providing means 50 Sample image storage means 60 Parameter correction means 70 Imaging means 100 Computer 110 Object 111 Coating film S1 Parameter determination step S2 Film thickness estimation formula derivation step S2-1 Fitting step S3 Image acquisition step S4 Coating thickness calculation step S5 Coating thickness provision step S6 Sample image acquisition step S7 Parameter correction step

Claims (17)

A method for measuring a coating thickness by an image,
A plurality of test pieces having a coating film coated with the target coating film with different thicknesses are irradiated with light, and the scattering coefficient (S) and absorption coefficient (K) of the coating film are estimated and determined. a parameter determination step;
Film thickness estimation by applying the scattering coefficient (S) and the absorption coefficient (K) to the relational expression between the reflected light intensity (R (T)) and the coating thickness (T) of the coating film based on the Kubelka-Munk theory A film thickness estimation formula derivation step for deriving a formula;
an image acquisition step of illuminating the coating film applied to the object to be measured and acquiring the reflected light as an image with an imaging means;
A coating thickness calculation step of obtaining the reflected light intensity (R (T)) from the image and applying it to the thickness estimation formula to obtain the coating thickness (T);
and a coating thickness providing step of providing the calculated coating thickness (T). Estimation of the scattering coefficient (S) and the absorption coefficient (K) in the parameter determination step involves preparing a sufficient number of test pieces for the assumed film thickness, and obtaining the reflected light intensity (R ( T)) and the coating thickness (T) is estimated using a nonlinear least squares method including the Levenberg-Marquard method based on the measurement result of the coating thickness (T). Method. 3. The method according to claim 1, wherein the film thickness estimation formula derivation step further comprises a fitting step of fitting the film thickness estimation formula using the actually measured film thickness of the coating film. A method of measuring coating thickness using images of 4. The coating thickness measuring method according to any one of claims 1 to 3, wherein the light in the parameter determination step and the illumination in the image acquisition step are set to light under the same conditions. . 5. The coating thickness measuring method according to any one of claims 1 to 4, wherein said imaging means is a spectrum camera. A sample image acquisition step of producing a plurality of coating film samples coated with the paint and having a known film thickness and acquiring the coating film samples as sample images under the same conditions; A parameter correction step of acquiring a film sample as a sample image during measurement, comparing the sample image with the sample image during measurement, and correcting the scattering coefficient (S) and the absorption coefficient (K). 6. The method for measuring coating thickness by image according to any one of claims 1 to 5. 7. The image-based coating thickness measurement according to claim 6, wherein the coating film thickness of the coating film sample is substantially the upper limit and the substantially lower limit of the coating film of the object to be measured. Method. 8. The coating thickness measuring method according to any one of claims 1 to 7, wherein saturation is used as the reflected light intensity (R(T)). The target paint is a paint having a wavelength band in which the reflected light intensity (R(T)) of the coating film does not saturate in the range of the film thickness of the coating film of the object to be measured. 9. The method for measuring coating thickness by image according to any one of claims 1 to 8, characterized in that: A program for measuring the coating thickness from an image,
to the computer,
The image acquisition step, the coating thickness calculation step, and the coating thickness providing step in the coating thickness measurement method using an image according to any one of claims 1 to 9 are executed. A paint thickness measurement program based on images. to the computer;
11. The image-based coating film thickness measurement program according to claim 10, wherein the film thickness estimation formula deriving step in claim 1 is executed. to the computer;
11. The image-based coating thickness measurement program according to claim 10, wherein said sample image acquisition step and said parameter correction step in claim 6 are executed. A system for measuring coating thickness by an image,
The relationship between the reflected light intensity (R (T)) and the coating thickness (T) of the coating film based on the Kubelka-Munk theory for the scattering coefficient (S) and the absorption coefficient (K) of the coating film of the target paint A film thickness estimation formula derivation means for applying the formula to derive a film thickness estimation formula;
an image acquiring means for illuminating the coating film of the object to be measured and acquiring the reflected light as an image with an imaging means;
A coating thickness calculation means for obtaining the reflected light intensity (R (T)) from the image and applying it to the thickness estimation formula to obtain the coating thickness (T);
and a coating thickness providing means for providing the calculated coating thickness (T). 14. The system for measuring coating thickness by images according to claim 13, wherein said illumination in said image acquisition means is light under the same conditions as those used when said scattering coefficient (S) and said absorption coefficient (K) are obtained. . 15. The coating thickness measuring system according to claim 13 or 14, wherein said imaging means is a spectrum camera. A sample image storage means for storing a plurality of sample images of a coating film having a known film thickness obtained under the same conditions, and measuring the plurality of coating film samples obtained by the image acquisition means during measurement. 16. The apparatus according to any one of claims 13 to 15, further comprising parameter correction means for comparing the time sample image and the sample image and correcting the scattering coefficient (S) and the absorption coefficient (K). A coating thickness measurement system based on the image described in the paragraph. 17. The coating thickness measuring system according to any one of claims 13 to 16, wherein saturation is used as said reflected light intensity (R(T)).

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