JP5958627B1 - Sliding device - Google Patents

Abstract

An object of the present invention is to measure the film thickness of a transparent film existing between sliding surfaces without performing a complicated operation. A transparent sliding member 42 and a reflective sliding member 48 move relative to each other while receiving a load, and a liquid film 46 exists between the transparent sliding member 42 and the reflective sliding member 48 and is transparent. The sliding material 42 and the liquid film 46 are made of a material that transmits light, and the reflective sliding material 48 is made of a material that reflects light. The light from the white light source 22 is converted into light composed of monochromatic light of three wavelengths using a band-pass filter, and is transmitted through the transparent sliding material 42 and the liquid film 46 to irradiate the reflective sliding material 48. The interference is generated, and the camera 32 measures the luminance of each of the two or more lights having different wavelengths in the generated optical interference. The arithmetic device 60 calculates the film thickness of the liquid film 46 based on the brightness of each of the two or more lights measured by the camera 32. [Selection] Figure 7

Description

  The present invention relates to a sliding device that measures the film thickness of a transparent film.

  Conventionally, a sliding device specialized in oil film thickness measurement is known among the transparent film thickness measurement of a sliding surface (Non-Patent Documents 1 and 2). The basic principle of film thickness measurement is optical interferometry. In oil, a steel ball is rubbed with a transparent disk (glass, sapphire) coated with a partially reflective film (chrome) and a protective film (silica) to form an oil film between sliding surfaces. White light is irradiated to the sliding surface of the steel ball through the transparent disk. This white light has a broad spectrum and is not wavelength-controlled. Then, a part of the irradiated light is reflected by the chromium film, and the remaining light passes through the silica layer and the oil film and reflects back to the steel ball, so that an optical path difference of the light is generated and optical interference occurs. The interference color is photographed using a digital color CCD camera, and the image is captured as an RGB luminance distribution into a computer using an image acquisition board. These RGB luminance distributions are converted into HSV luminance distributions by image processing, and the distribution of H (Hue, hue) is used.

  Further, the hue distribution is converted into the film thickness distribution using a hue-film thickness calibration table experimentally created using a transparent film sample whose film thickness is known in advance.

P. M. CANN et.al, "The Development of a Spacer Layer Imaging Method (SLIM) for Mapping Elastohydrodynamic Contacts", TRIBOLOGY TRANSACTIONS, Vol. 39 (1996), 4, 915-921 “EHL Ultrathin Film Thickness Measurement System”, Internet <URL: http://mail.shima-tra.co.jp/jp/products/topics/ehl071201.pdf>

  In the technique described in Non-Patent Document 1, a hue-film thickness calibration table must be created in order to convert an interference color into a transparent film thickness. For the preparation, a transparent film with a known and continuously changing film thickness is prepared, and this is used for optical interference with a material having the same spectral reflectance, that is, the same color and reflectance as the specimen for which an oil film is to be measured. Therefore, it is necessary to cause optical interference by sandwiching it with a transparent disk. There are various ways to achieve this, but the typical method is to prepare a sphere with the same spectral reflectance as the specimen used for oil film measurement, press it against the disk, and use the sphere and disk as a transparent film. This is a method using a gap (air film thickness). Since the gap at the contact point is zero and the gap distribution from the contact point can be calculated from the curvature of the sphere, the film thickness is known, and the hue of the interference color and the film thickness can be linked. However, as shown in Non-Patent Document 1, the relationship between hue and film thickness is a complicated curve, and it is necessary to measure the gap value and the hue value at a certain fine interval. Become. In addition, the calibration curve must be recreated each time the color of the specimen, the color of the oil, or the optical system (camera, lens, illumination) changes.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to obtain a sliding device that can measure the film thickness of a transparent film without performing complicated operations.

A sliding device according to a first aspect of the present invention is a sliding device including a first sliding material, a second sliding material, a transparent film, a photodetector, a light source, and an arithmetic device, The sliding material and the second sliding material move relative to each other while receiving a load, and the transparent film exists between the first sliding material and the second sliding material, The first sliding material and the transparent film are made of a material that transmits light, and the second sliding material is made of a material that reflects light, and transmits light from the light source to the first film. The light is transmitted through the transparent film and irradiated to the second sliding material to cause optical interference, and the photodetector detects the light after the generated optical interference at a plurality of measurement points. In this case, the brightness of light having a wavelength range narrow enough to be regarded as monochromatic light is measured, and the number of wavelengths to be measured at that time is two or more. Based on the luminance of each of the two or more light measured for each of the measurement points by the output device, a relational expression representing a relationship between the thickness of the transparent film and the luminance of each of the two or more light Then, from the relational expression including the film thickness of the transparent film at each of the measurement points and the unknown variable derived from the measurement environment assumed to be the same at each of the measurement points, the transparent film at each of the measurement points A film thickness and an unknown variable derived from the measurement environment are obtained, and the transparent film is a liquid film.
A sliding device according to a second invention is a sliding device comprising a first sliding material, a second sliding material, a transparent film, a photodetector, a light source, and an arithmetic device, The sliding material and the second sliding material move relative to each other while receiving a load, and the transparent film exists between the first sliding material and the second sliding material, The first sliding material and the transparent film are made of a material that transmits light, and the second sliding material is made of a material that reflects light, and transmits light from the light source to the first film. The light is transmitted through the transparent film and irradiated to the second sliding material to cause optical interference, and the photodetector detects the light after the generated optical interference at a plurality of measurement points. In this case, the brightness of light having a wavelength range narrow enough to be regarded as monochromatic light is measured, and the number of wavelengths to be measured at that time is two or more. A relational expression representing the relationship between the brightness of each of the two or more lights and the film thickness of the transparent film, based on the brightness of each of the two or more lights measured for each of the measurement points by an output device. Then, from the relational expression including the film thickness of the transparent film at each of the measurement points and the unknown variable derived from the measurement environment assumed to be the same at each of the measurement points, the transparent film at each of the measurement points A film thickness and an unknown variable derived from the measurement environment are obtained, and the unknown variable derived from the measurement environment includes the absorption coefficient of the transparent film for each of the two or more lights, and the two or more lights of the transparent film. At least one of the refractive indices for each of the above.

In the sliding device according to the first invention and the second invention , the light from the light source is irradiated to the second sliding material through the first sliding material and the transparent film. The optical detector generates light interference, and the light detector measures the luminance of light having a narrow wavelength width to a degree that can be regarded as monochromatic light from the light after the generated light interference at a plurality of measurement points, and the wavelength to be measured at that time The number is 2 or more. And the said arithmetic unit calculates the film thickness of the said transparent film based on each brightness | luminance of the said 2 or more light measured about each of the said measurement point with the said photodetector.

  As described above, the light from the light source is transmitted through the first sliding material and the transparent film and irradiated to the second sliding material to cause optical interference. By measuring the brightness of each of the two or more lights having different values, and calculating the film thickness of the transparent film based on the brightness of each of the two or more lights measured by the photodetector. The film thickness of the transparent film can be measured without performing the above.

  The photodetector according to the present invention measures the luminance of each of the two or more lights at a plurality of measurement points, and the arithmetic unit is configured to measure the two or more of the measurement points measured by the photodetector. A relational expression representing the relationship between the brightness of each of the two or more lights and the film thickness of the transparent film, based on the brightness of each of the light, and the film thickness of the transparent film at each of the measurement points, And a film of the transparent film at each of the measurement points by solving simultaneous equations or an optimization method for a relational expression including unknown variables derived from the measurement environment assumed to be the same at each of the measurement points. Thickness and unknown variables derived from the measurement environment can be obtained.

  The unknown variables derived from the measurement environment include the surface light intensity of each of the two or more lights and the back light intensity of each of the two or more lights when no absorption by the transparent film occurs. Can do.

  The unknown variable derived from the measurement environment may include an extinction coefficient for each of the two or more lights of the transparent film. Thereby, even if the transparent film is colored, the film thickness can be measured.

  The unknown variable derived from the measurement environment may include a refractive index for each of the two or more lights of the transparent film. Thereby, even if the transparent film is a material having a large wavelength dependency of the refractive index, such as an oil film, the film thickness can be measured.

  The above relational expression is represented by the following expression.

Here, j represents a number assigned to each of the two or more lights, i represents a number assigned to each of the plurality of measurement points, and I (i, j) is i by the photodetector. Represents the luminance of the j-th light measured at the measurement point, I ₁ (j) represents the surface light intensity of the j-th light, and I ₂ (j) represents the transparent film of the j-th light. Represents the light intensity of the back surface when no light absorption occurs, α (j) represents the extinction coefficient for the jth light of the transparent film, and n (j) represents the refractive index of the transparent film for the jth light. T (i) represents the film thickness of the transparent film at the i-th measurement point, and λ (j) represents the wavelength of the j-th light.

  The wavelengths of the two or more lights are 200 nm to 4,000 nm.

  The transparent film is a liquid film.

  The above arithmetic device is based on the luminance of each of the two or more lights measured for each of some of the plurality of measurement points by the photodetector, and for the relational expression, Solve the simultaneous equations or optimize the thickness of the transparent film at each of the measurement points and the unknown variable derived from the measurement environment, and use the photodetector to detect the remaining of the plurality of measurement points. Each of the two or more lights for each of the measurement points based on the brightness of each of the two or more lights measured for each of the measurement points and the determined unknown variable derived from the measurement environment. A candidate value for the film thickness of the transparent film at the measurement point satisfying the relational expression with respect to a wavelength is obtained, and the wavelength from the candidate value for the film thickness of the transparent film at the measurement point for each wavelength of the two or more lights. Mate between Can determine the thickness value of said transparent film in the measuring points using.

  The sliding device transmits a wavelength of each of the two or more lights provided on the optical path of the light emitted from the light source and provided between the light source and the first sliding material. It is possible to further include a band pass filter.

The above-mentioned sliding device is on the optical path of the light causing the optical interference, and is provided between the photodetector and the first sliding material, and each wavelength of the two or more lights. A band pass filter that transmits light, or an optical spectroscope that splits each of the two or more lights.
The light source can be a flash lamp.
A sliding device according to a third invention is a sliding device comprising a first sliding material, a second sliding material, a liquid film, a photodetector, a flash lamp, and an arithmetic device, The first sliding material and the second sliding material move relative to each other while receiving a load, and the liquid film exists between the first sliding material and the second sliding material. The first sliding material and the liquid film are made of a material that transmits light, and the second sliding material is made of a material that reflects light, and the light from the flash lamp is The first sliding material and the liquid film are transmitted to irradiate the second sliding material to cause optical interference, and the photodetector detects monochromatic light from the generated light interference light. The brightness of light having a wavelength width narrow enough to be considered is measured, and the number of wavelengths to be measured at that time is 2 or more, Based on the luminance of each of the measured said two or more light by the detector, to calculate the thickness of the liquid film.

  As described above, the sliding device according to the present invention transmits light from a light source through the first sliding material and the transparent film to irradiate the second sliding material to cause light interference. And measuring the brightness of each of the two or more lights having different wavelengths in the generated light interference, and based on the brightness of each of the two or more lights measured by the photodetector, the film of the transparent film By calculating the thickness, there is an excellent effect that the film thickness of the transparent film can be measured without performing complicated work.

It is a figure which shows a mode that optical interference arises. It is a figure for demonstrating the principle which measures a film thickness. It is a graph which shows the relationship between a brightness | luminance and a film thickness. It is a graph which shows the relationship between the brightness | luminance and film thickness in case an absorption coefficient is 0, and the film thickness candidate value of wavelength 470nm in case intensity | strength is 0.4. It is a graph which shows the relationship between the brightness | luminance and film thickness in case an absorption coefficient is not 0, and the film thickness candidate value of wavelength 470nm in case intensity | strength is 0.4. It is a figure for demonstrating the matching method. It is a figure which shows the structure of the film thickness measurement system which concerns on embodiment of this invention. It is a graph which shows the transmission characteristic of a 3 wavelength band pass filter. It is a functional block diagram which shows the structure of the arithmetic unit of the film thickness measurement system which concerns on embodiment of this invention. It is a figure which shows the film thickness measurement process routine performed by the arithmetic unit which concerns on embodiment of this invention. It is a schematic diagram of a silicon wafer. It is a figure which shows the interference image by the base oil film of a silicon wafer recessed part. I ₁ (j) and a result of deriving the I ₂ (j) is a diagram showing a. It is a figure which shows the result of having compared the thickness distribution of the base oil film, and the cross section of the depth distribution measured with the three-dimensional shape measuring machine. It is a figure which shows the result of having plotted the average film thickness and the average depth of a recessed part in three levels of several nm order, several tens nm order, and several hundred nm order. It is a figure which shows the interference image by the steel disc which carried out the mirror surface grinding | polishing. It is a figure which shows the position of a measurement point. I ₁ (j) and a result of deriving the I ₂ (j) is a diagram showing a. It is a figure which shows the result of having converted into the film thickness distribution from the interference image.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

<Principle of this embodiment>
<Definition of transparent film>
In the present embodiment, a film thickness measurement system capable of measuring the thickness distribution of a transparent film existing between sliding materials will be described, but before that, the definition of the transparent film will be described. In the present embodiment, the transparent film does not mean only a film that hardly causes attenuation of light due to transmission such as a water film, but a film that causes attenuation of light due to transmission such as a film of engine oil, That is, it also means a colored transparent film. Furthermore, in the meaning of the area | region which permeate | transmits the light which exists between sliding surfaces, the clearance gap between sliding surfaces when a liquid and solid are not included is also meant. A specific example is a valley portion of surface roughness when surfaces having surface roughness slide in the air or in vacuum. In the present embodiment, the transparent film means the above unless otherwise specified.

<Importance of transparent film thickness measurement>
In a sliding portion of a machine element, a transparent film is often present between sliding surfaces. For example, many sliding portions are lubricated with a liquid such as oil, and these liquids are transparent in many cases, so that a transparent film exists between the sliding surfaces. Further, a transparent film may be formed on the surface of the sliding material due to a chemical reaction between the sliding material and surrounding substances. Specific examples include a ZnDTP reaction film when steel is rubbed in engine oil and an oxide film when steel is rubbed in the atmosphere. These are all transparent. Further, there is a case where a transparent film as an object does not exist between the sliding surfaces but there is a region that transmits light. A specific example is a valley portion of surface roughness when surfaces having surface roughness slide in the air or in vacuum. Even in such a case, it is beneficial to measure the thickness distribution of the region. This is because the distribution of zero film thickness means the true contact point distribution.

  Since these transparent film thickness distributions affect the friction characteristics, measuring the transparent film thickness distribution is important in the sliding part design.

<Optical interference method>
As a method for measuring a transparent film thickness distribution, particularly an oil film thickness distribution, there is a “light interference method”. This is a method for measuring the transparent film thickness using light interference.

  The principle of optical interferometry is shown in FIG. One of the sliding materials is made of a material that transmits light, and the other sliding material is made of a material that reflects light. Hereinafter, these sliding materials are referred to as “transparent sliding material” and “reflective sliding material”, respectively. The transparent sliding material is transmitted from the light source, and light is irradiated to the other sliding material through the transparent film. At this time, the difference in refractive index between the transparent sliding material and the transparent film is appropriately set so that light is partially reflected and partially transmitted at the interface. When the difference in refractive index is small and sufficient reflection does not occur, a partial reflection film may be formed on the surface of the transparent sliding material in contact with the transparent film.

  The light transmitted through the transparent film is reflected by the reflective sliding material, passes through the transparent film and the transparent sliding material again, and returns to the light source direction. Here, the light reflected by the transparent sliding material-transparent film interface is referred to as “front light”, and the light reflected by the reflective sliding material is referred to as “back light”. The surface wave and the back surface wave cause optical interference because of the optical path difference. When the surface of the reflective sliding material is observed from the transparent sliding material side through the transparent film with a photodetector (camera or the like), optical interference is observed. Since the light interference color (wavelength and luminance) is affected by the optical path difference, that is, the transparent film thickness, information on the transparent film thickness can be obtained from the interference color. This is the principle of optical interferometry.

<Prior art issues>
The problem of the prior art is a method for converting the interference color obtained by the optical interferometry to the film thickness. Color and film thickness calibration must be experimentally created in advance, which is very cumbersome.

  Further, the hue distribution is converted into the film thickness distribution using a hue-film thickness calibration table experimentally created using a transparent film sample whose film thickness is known in advance. As described in Non-Patent Document 1, the hue is a periodic function with respect to the film thickness, and the hue of the interference color with respect to the increase in the film thickness appears in the same hue with a period of about 250 nm as the order of interference (period 250 nm). Since the period is about 250 nm, the size of the film thickness measurement range is limited to 250 nm, and the film thickness measurement range is narrow.

<Outline of Embodiment of the Present Invention>
The film thickness measurement system having the function of measuring the thickness distribution of the transparent film between the sliding surfaces according to the embodiment of the present invention is used to convert the interference color to the transparent film thickness in order to solve the problems of the prior art. It is characterized in that the “calibration” is created without the need for pre-creation by a complicated experiment. Specifically, it is created from optical formulas describing optical interference and measurement results. At this time, the created calibration is not a table but a mathematical expression.

  An outline of a method for creating the calibration formula will be described. First, the relationship between the luminance and the film thickness (optical path difference) in light interference in light of a single wavelength (hereinafter referred to as monochromatic light) can be described by a mathematical expression. This formula includes four unknown variables derived from the measurement environment (irradiation light wavelength, transparent film optical properties, reflective sliding material color, etc.), and these unknown variables are derived for use as calibration. There is a need. The feature of the embodiment of the present invention is that these unknown variables are derived from the measurement result (interference color distribution). At this time, an assumption is made that the unknown variable is constant in the interference color distribution, that is, the “interference color distribution depends only on the intensity strengthening / weakening due to interference at each wavelength”. Then, the unknown variable does not depend on the measurement point, so if you select multiple measurement points and create a sufficient number of equations, you can solve the simultaneous equations or optimize the unknown variable and film thickness in the equation by minimizing the error. Can be determined.

  Furthermore, since the previous equation describes the brightness and film thickness of monochromatic light, the photodetector will split the light after optical interference with a resolution that can be regarded as monochromatic light, and the luminance of each wavelength will be independently determined. It is necessary to measure. This includes a method in which the photodetector includes a spectroscope, and the irradiation light is composed of monochromatic light, but the latter is adopted in this embodiment. This is because there is no current spectroscope capable of obtaining a spectral spectrum for each point in a two-dimensional space such as a camera image. Therefore, the difference from the prior art is that the irradiation light is not white light having a broad spectrum but two or more monochromatic lights having known wavelengths. The photodetector measures the brightness of each monochromatic light independently. Furthermore, since an equation is required for two or more wavelengths at one measurement point in order to derive an unknown variable, the irradiation light is composed of two or more monochromatic lights.

  The basic configuration of the embodiment of the present invention is shown in FIG. In addition to the configuration of the conventional optical interferometry, it is equipped with an “optical system that independently measures the brightness of each wavelength contained in the irradiating light” and an algorithm that generates a calibration that converts the interference color into a film thickness from the measurement results. An “arithmetic unit” is required.

<Principle of generating calibration to convert interference color to film thickness>
The creation of the calibration formula from the luminance value of the interference color to the film thickness is performed in the following two steps.

In the first step, a plurality of measurement points are selected in the interference color distribution, and the unknown variable and the film thickness of the selected measurement point are derived by fitting the interference color theoretical formula and the measurement value. In the second step, the film thickness candidate value is calculated and the true value is determined by the matching method.

<Deriving unknown variables by fitting interference color theory and measured values>
In order to automatically generate calibration from the measurement results, it is necessary to derive unknown variables from the measurement results that depend on the environment in which this measurement is performed (lighting, optical properties of the transparent film, color of the reflective sliding material, etc.). is there. Specifically, at each wavelength, it is necessary to derive four unknown variables including the intensity of the surface wave, the intensity of the back surface wave when attenuation by the transparent film does not occur, the attenuation coefficient of the transparent film, and the refractive index of the transparent film. There is.

  The feature of this interference color analysis is not to derive these from the measurement results at one point but to derive them from the measurement results at a plurality of points on the assumption that they are constant in the interference color distribution. .

<Interference color theory>
Using irradiation light composed of m monochromatic lights, p measurement points in the image (corresponding to the number of pixels in the image. When using a general camera, millions to tens of millions Consider the case of measuring the transparent film thickness (which is a pixel). If the number assigned to an arbitrary measurement point is i (i = 1 to p) and the number assigned to monochromatic light is j (j = 1 to m), the luminance after interference of the wavelength j measured at the measurement point i The relationship between I (i, j) and the transparent film thickness t (i) at the measurement point i is expressed by Expression (1). Hereinafter, the expression (1) is referred to as “interference color theoretical expression”.

(1)

Where I ₁ (j) is the surface light intensity of the j-th monochromatic light, I ₂ (j) is the back-surface light intensity when no absorption of the j-th monochromatic light by the transparent film occurs, and α (j) is the transparent film The extinction coefficient for the j-th monochromatic light, n (j) is the refractive index of the transparent film for the j-th monochromatic light, and λ (j) is the wavelength of the j-th monochromatic light determined in advance.

FIG. 3 shows the result of plotting the theoretical equation of interference color under the conditions of I ₁ = I ₂ = 1/4, α = 0, n = 1, λ = 470 nm, 560 nm, and 600 nm. Thus, if an unknown variable can be derived, a calibration curve of color (luminance value of each monochromatic light) and film thickness can be obtained.

<Derivation of interference color theory>
The interference color theory formula is derived from a combination of optical formulas. First, consider interference due to light of one wavelength at one point in space. When light having two optical path differences becomes dominant with respect to interference as in this measurement, the brightness of the interference light is expressed by Equation (2) (Non-patent Document 3 (Hect Optics II-Wave Engineering) -See 4th edition, Maruzen, P.157 (2002)).

(2)

Here, I ₁ and I ₂ are the luminances of the surface wave and the back wave, respectively, and δ is the phase difference [rad.] Of the two waves.

  The phase difference [rad.] Of the two waves is obtained by dividing the optical path difference [m] by the wavelength [m] and multiplying by 2π. In this measurement system, since the optical path difference is twice the optical film thickness of the transparent film, assuming that the physical film thickness of the transparent film is t and the refractive index of the transparent film is n, δ is expressed by the following equation (3): expressed.

(3)

  Substituting equation (3) into equation (2) yields equation (4).

(4)

  Next, the absorption (brightness attenuation) of interference light by the transparent film is considered. The attenuation of light is expressed by Equation (5) (see Non-Patent Document 4 (Hectonics I-Fundamentals and Geometric Engineering-4th Edition, Maruzen, P.197 (2002))).

(5)

Here, α is an extinction coefficient, and L is a distance (transmission distance) through which light passes through the transparent film. In Expression (5), the light transmitted through the transparent film is I ₂ , and the transmission distance is twice the physical film thickness, so I ₂ may be I ₂ e ^{−α * 2t} . Then, equation (6) is derived.

(6)

Next, it will be described which function of each unknown variable is measurement point i or wavelength j. As described above, the characteristics of this analysis method are “surface wave intensity I ₁ ”, “back surface wave intensity I ₂ when attenuation by the transparent film does not occur”, “transparent film attenuation coefficient α”, “transparent film” The refractive index n of is assumed to be constant in the plane. This is an assumption that holds within a range where there is no practical problem on many sliding surfaces except when there is color unevenness of the sliding material. Even if there is color unevenness, if the measurement points used to determine unknown variables are set only in the same color and the film thickness distribution is also in the same color, there is no problem in the analysis value, and there is color unevenness However, the effectiveness of this measurement method is not impaired.

From this assumption, in Equation (6), I ₁ , I ₂ , α, and n do not depend on the measurement point i, but depend on the wavelength j, and thus are functions of only j. On the other hand, since the film thickness t does not depend on the wavelength j but depends on the measurement point i, it is a function of only i. The measured interference brightness depends on both i and j. When these ideas are introduced into the equation (6), an interference color theoretical equation can be obtained.

<Conditions for the number of measurement points from which unknown variables can be derived>
The number of unknown variables is assumed to be X (X = 1 to 4. In the above case, the number of unknown variables is 4, but if the number of unknown variables is found experimentally, the number decreases, and X is assumed). If the number of measurement points is k and the number of wavelengths is m, the number of unknown variables is Xm + k. Since m luminance values are obtained from one point, the necessary condition is X × m + k ≦ m × k, and it is understood that the number of measurement points satisfying the following equation (8) is necessary.

(8)

  In the present embodiment, since the unknown variable X = 4 and the number of wavelengths m = 3 that do not depend on the measurement point, 6 points can be obtained. Of course, unknown variables can be obtained with higher accuracy when there are more measurement points.

  It can also be seen that if the number of wavelengths m = 1, the condition is not satisfied even if the number of measurement points k is increased, regardless of the number X of unknown variables. Therefore, two or more wavelengths are essential for using this measurement method.

<Derivation of unknown variable that minimizes error between measured value and interference color theory using least squares fitting>
After selecting the number of measurement points satisfying the equation (8), a relational expression of the measurement luminance value, the four unknown variables, and the film thickness is created at each measurement point according to the interference color theory equation. By performing fitting so that the square sum of the error between the measured value and the interference color theory formula is minimized in these relational expressions (the least squares method), four unknown variables and the film thickness at each measurement point are derived simultaneously. . When optimization using the least square method is performed, the optimum value to be derived is the global minimum, but the local minimum is selected depending on the initial value setting. Therefore, in order to improve the analysis accuracy, when an unknown variable is derived, an initial value close to the true value of the film thickness is input for each selected measurement point. These initial values include the oil film thickness distribution on the sliding surface and the surrounding color information, and the color chart shown in Fig. 3 (the trend of color change with increasing film thickness does not change significantly even if the measurement environment changes). Considering this, it is possible to input a value approximately close to the true value. Empirically, it has been found that even if the initial value differs from the true value by about ± 100 nm, it reaches the true value, and the setting of the initial value does not require such strictness. In order to improve the analysis accuracy, it is also important to set the film thickness measurement range appropriately, that is, not to set it wider than necessary.

<Calculation of film thickness candidate value and determination of true value by matching method (second step)>
In the first step method, the calculation load increases as the number of measurement points used to derive unknown variables increases. Therefore, the entire area of the image (several millions to tens of millions because the number of measurement points = the number of camera pixels) is the first step. It is unsuitable to analyze only with this. Therefore, the number of measurement points used for derivation of unknown variables in the first step is limited to several tens, and in the second step, the unknown variables derived in the first step are used to calculate the remaining measurement points from the brightness of each wavelength. Conversion to film thickness is performed. Specifically, from the derived unknown variable and the brightness value of each point / wavelength, the film thickness candidate value in Equation (1) is obtained for each measurement point, and the true value is determined using the matching method between wavelengths. It is a technique to do. In the second step, the film thickness values at a plurality of measurement points are not determined simultaneously as in the first step, but the film thickness values at each measurement point are determined one by one.

<Calculation of film thickness candidate value>
Here, since I ₁ (j), I ₂ (j), α (j), and n (j) are already known by the first step, the relationship between film thickness t and luminance I is obtained using equation (1). Becomes known. FIG. 4 shows the relationship between film thickness t and luminance I when attenuation by the transparent film does not occur (α = 0), and FIG. 5 shows film thickness t and luminance when attenuation by the transparent film occurs (α> 0). The relationship of I is shown. 4 and 5 show the film thickness candidate values at a wavelength of 470 nm when the intensity is 0.4. In the case where no attenuation occurs, the film thickness candidate value can be analytically obtained by substituting α = 0 into equation (1) and modifying equation (7). On the other hand, when attenuation occurs, an equation for analytically obtaining a film thickness candidate value has not been found, and must be obtained by numerical calculation. Of course, if an analytically obtained expression is found, it may be used.

(7)

<Estimation of film thickness by phase matching method between wavelengths>
The true value is determined from the film thickness candidate values calculated as described above using the matching method (see Non-Patent Document 5 (Ato, AIST Metrology Standards Report, Vol. 4, No. 1 (2005))). To do. As shown in FIG. 6, the matching method is a method of selecting a value having the smallest difference in film thickness candidate values of three wavelengths as the true value of the film thickness. Even in the coincidence method, since film thicknesses with close candidate values of three wavelengths appear periodically, it is important to set the film thickness measurement range appropriately, that is, not to set it wider than necessary in order to improve the analysis accuracy. is there. In addition, three monochromatic lights are used this time. However, as the number of wavelengths increases, the period (interval) in which the film thicknesses with similar candidate values between wavelengths appear increases, so the analysis accuracy improves.

<System configuration>
A film thickness measurement system 10 according to an embodiment of the present invention will be described with reference to FIGS.

  As shown in FIG. 7, the film thickness measurement system 10 includes an optical system 20, a sliding system 40, and a calculation device 60.

<Optical system>
The optical system 20 includes a white light source 22, a light guide 24, a three-wavelength band pass filter 26, a half mirror 28, a lens 30, and a camera 32.

  The white light emitted from the white light source 22 is incident on the light guide 24 and is composed of monochromatic light of three wavelengths transmitted through a three-wavelength bandpass filter 26 that is provided in the middle of the light guide 24 and transmits three wavelengths. The irradiated light is reflected by the half mirror 28 and is incident on the sliding system 40.

  The light reflected by the sliding system 40 passes through the half mirror 28 and enters the camera 32.

  The camera 32 measures the luminance of each of the three wavelengths of light in the optical interference generated in the sliding system 40.

  The major difference between the embodiment of the present invention and the prior art is that the irradiated light is composed of monochromatic light having a known wavelength. In the present embodiment, three wavelengths having wavelengths of 470 nm, 560 nm, and 600 nm are selected as monochromatic light constituting the irradiation light. This is because a general color camera is used as a photodetector in consideration of the RGB spectral sensitivity of a general color camera. Irradiation light composed of these monochromatic lights is realized by transmitting white light (xenon flash lamp) having a broad spectrum only at a specific wavelength using a three-wavelength bandpass filter 26. FIG. 8 shows an example of the transmission spectrum of the three-wavelength bandpass filter 26. The full width at half maximum (FWHM) of each monochromatic light is about 10 nm. When using this measurement method, the smaller the full width at half maximum, the better. However, reasonable results are obtained even when monochromatic light with a full width at half maximum of 10 nm is used. In this embodiment, the bandpass filter is used to configure the irradiation light only from the monochromatic light. However, it may be realized by combining a light source that emits monochromatic light, for example, an LED or a laser.

  In this embodiment, the case where these visible lights are used as the wavelength of light to be irradiated will be described as an example, but this measurement principle is not limited to visible lights, and light having an arbitrary wavelength (electromagnetic wave) However, this measurement principle is valid. However, light below 200 nm is called vacuum ultraviolet light and is absorbed by the atmosphere, so it is difficult to handle. In addition, light (middle infrared to far infrared, radio waves) of 4000 nm or more is radiated from an object at room temperature due to radiation, so that it is difficult to distinguish between interference light and radiation light, and there are obstacles to analysis. Therefore, the wavelength range constituting monochromatic light is preferably 200 nm to 4000 nm.

  In this embodiment, the number of monochromatic lights is 3, but as will be described later, this measurement principle is valid if the number of monochromatic lights is 2 or more.

  In the present embodiment, a 3CCD digital color camera (AT200-CL manufactured by JAI) is used as the camera 32. This is to avoid overlapping of spectral sensitivity, that is, light of 470 nm (Blue) or 600 nm (Red) is counted as luminance by the light receiving element of 560 nm (Green). Note that this overlap of spectral sensitivities can be corrected, and if corrected, cameras with overlapping spectral sensitivities (such as a 1CCD camera) can also be used.

  Imaging is taken into the arithmetic unit 60 via a frame grabber. The image taken in the arithmetic unit 60 is not converted to HSV, but is used for analysis as an RGB luminance distribution, that is, as a luminance distribution of monochromatic light having wavelengths of 470 nm, 560 nm, and 600 nm. The RGB bit depth of imaging is 8 bits (256 gradations).

  In this embodiment, a case where a camera which is a two-dimensional photodetector is used as an example of the photodetector will be described as an example. However, the principle of this measurement is not limited to the case where a two-dimensional detector is used. As will be described later, in order to apply this measurement principle, data of multiple measurement points is required as a condition in the same plane, but even if multiple points are measured in the time direction using a one-dimensional detector, the condition is satisfied. It is.

<Sliding system>
The sliding system 40 includes a transparent sliding material 42, a partially reflective film 44, a transparent protective film 45, a liquid film 46, a reflective sliding material 48, and a sliding test machine 50.

  The liquid film 46 exists between the transparent sliding material 42 and the reflective sliding material 48, and the transparent protective film 45 and the liquid film 46 provided on the opposite side of the transparent sliding material 42 from the optical system 20 side are the liquid film 46. The reflective sliding member 48 and the liquid film 46 are in contact with each other.

  The transparent sliding material 42 and the liquid film 46 transmit light of three wavelengths, and the reflective sliding material 48 reflects light of three wavelengths. The incident irradiation light from the optical system 20 is transmitted through the transparent sliding material 42 and the liquid film 46 and irradiated to the reflective sliding material 48 to cause optical interference.

  The sliding tester 50 rotates the transparent sliding member 42, and the transparent sliding member 42 and the reflective sliding member 48 move relative to each other while receiving a load.

  In the present embodiment, a lubricating oil film is used as the liquid film 46. The type of lubricating oil is a hydrocarbon base oil (Yubase4 manufactured by SK Lubricants (R)). It is colorless and transparent and does not absorb light. In the present embodiment, the liquid film 46 is used as the transparent film. However, the present measurement principle can be applied as long as it meets the definition of the transparent film described above, and is not limited to the liquid film.

In the present embodiment, single crystal sapphire, which is a material that is transparent to visible light and has high strength and high wear resistance, is used as the transparent sliding member 42. Since visible light is used in this embodiment, it is limited to a transparent body for visible light such as sapphire or quartz glass, but if the wavelength range of monochromatic light to be used is changed, the usable material is also changed, This measurement method is not limited to a material transparent to visible light. For example, when the infrared light region is used as the wavelength of the monochromatic light, the present principle can also be realized by using silicon or germanium as the transparent sliding material 42 and using an infrared camera as the photodetector. In this embodiment, since the reflection between the sapphire and the lubricating oil was not sufficient, the surface of the transparent sliding member 42 made of sapphire was coated with a chromium partial reflection film 44. Further, a 150 nm (physical film thickness) coating of a transparent protective film 45 of silica (SiO ₂ ) was applied on the partial reflection film 44. The purpose of this is to prevent the partial reflection film 44 of chrome from being peeled off during sliding, and to offset the oil film thickness in the plus direction (to raise the bottom). This is because the transparent protective film 45 of silica is transparent to visible light, and thus the measured film thickness value is a value obtained by adding the silica film thickness in addition to the oil film thickness. The aim of offsetting is shown below.

  The measurement method of this embodiment performs conversion from luminance to film thickness using a calibration formula for luminance and film thickness. This change in luminance becomes a cosine curve as shown in equations (1) and 3. Then, the change in luminance with respect to the change in film thickness becomes scarce at the peak and bottom of the curve, and the analysis accuracy (robustness against resolution and noise) decreases. Even if the luminance value of one wavelength is peak or bottom, it does not matter if the luminance value of other wavelengths is other than that (slope part), but if all three wavelengths are at the peak or bottom, the analysis accuracy will be lowered. Become. Since such a region appears in the vicinity of 0 nm or 120 nm in FIG. 3, in order to avoid such a region, a transparent protective film 45 of silica is coated, and the oil film thickness is offset by 150 nm (physical film thickness). ing.

  In the present embodiment, mirror-polished carbon steel is used as the reflective sliding member 48. The surface roughness and material of the reflective sliding member 48 are not limited as long as optical interference can be generated.

  In this embodiment, a disk-on-disk type sliding tester is used as the sliding tester 50 as shown in FIG. The disk-on-disk type sliding tester is a test in which a rotating transparent sliding material 42 is pressed against a disk test piece which is a reflective sliding material 48 with a predetermined load, and friction is performed under a continuous sliding condition in a surface contact mode. Machine. The friction coefficient and vertical load can be measured simultaneously with the transparent film thickness distribution on the sliding surface.

<Calculation device>
The arithmetic unit 60 includes a CPU, a ROM that stores a program for a film thickness measurement processing routine, which will be described later, a RAM that stores data, and a bus that connects these. The arithmetic device 60 measures the film thickness based on the image input from the camera 32 and outputs the measurement result by the output unit 70.

  When the arithmetic device 60 is described with function blocks divided for each function realizing means determined based on hardware and software, as shown in FIG. 9, an image acquisition unit 62, an unknown variable derivation unit 64, and a film thickness value determination A portion 66 is provided.

  The image acquisition unit 62 acquires an image representing the light interference distribution input from the camera 32, and obtains the luminance of each measurement point (each pixel) for each of the three wavelengths.

  Based on the image acquired by the image acquisition unit 62, the unknown variable deriving unit 64 represents a relationship between the luminance of each of the three wavelengths and the film thickness of the liquid film 46 for each of some measurement points. For the above equation (1), which is a relational expression including an unknown variable derived from the measurement environment that is assumed to be the same in the thickness and the thickness of the liquid film 46 at the measurement point, the least square method The thickness of the liquid film 46 at each of some measurement points and an unknown variable derived from the measurement environment are obtained by an optimization method such as the above.

  Based on the image acquired by the image acquisition unit 62 and the obtained unknown variable derived from the measurement environment, the film thickness value determination unit 66 applies the three wavelengths according to the above equation (7). Then, a candidate value of the film thickness of the liquid film 46 at the measurement point that satisfies the relational expression of the above equation (1) is obtained, and a matching method between wavelengths is obtained from the candidate value of the film thickness of the liquid film 46 at the measurement point for the three wavelengths. Is used to determine the film thickness value of the liquid film 46 at the measurement point.

<Operation of film thickness measurement system>
Next, the operation of the film thickness measurement system 10 according to the present embodiment will be described.

  First, when the transparent sliding member 42 is rotated by the sliding tester 50 and the transparent sliding member 42 and the reflective sliding member 48 are moving relative to each other while receiving a load, the white light from the white light source 22 is detected. Light is incident on the three-wavelength band-pass filter 26, and the irradiation light composed of monochromatic light of three wavelengths transmitted through the three-wavelength band-pass filter 26 is reflected by the half mirror 28 and incident on the sliding system 40. A part of the irradiation light composed of monochromatic light of three wavelengths is reflected at the interface between the partial reflection film 44 and the liquid film 46, and a part of the irradiation light composed of monochromatic light of three wavelengths is a part of the transparent sliding material 42. When light interference occurs due to reflection at the interface with the reflective film 44, the optical interference distribution is imaged by the camera 32, and an image is input to the arithmetic device 60 each time the camera 32 captures an image.

  Then, a film thickness measurement processing routine shown in FIG. 10 is executed by the arithmetic device 60 for each of the input images.

  First, in step 100, the brightness of each of the three wavelengths at each measurement point (each pixel) is acquired from the processing target image input from the camera 32.

In step 102, for each of some measurement points, for each of the three wavelengths, the relational expression (1) using the brightness of the measurement point acquired in step 100 is prepared and optimized. By the method, the surface light intensity I ₁ (j) of each monochromatic light of the three wavelengths, the back surface light intensity I ₂ (j) when the liquid film 46 does not absorb the monochromatic light of each of the three wavelengths, The absorption coefficient α (j) for each monochromatic light of three wavelengths, the refractive index n (j) for each monochromatic light of the three wavelengths of the liquid film 46, and the film thickness t ( i) is determined.

In the next step 104, a target measurement point is selected from the remaining measurement points. In step 106, the luminance of the three wavelengths of the measurement point acquired in step 100, the surface light intensity I ₁ (j) of each of the three wavelengths of monochromatic light obtained in step 102, and the monochromatic light of each of the three wavelengths. Back light intensity I ₂ (j) when no light absorption by the liquid film 46 occurs, the light absorption coefficient α (j) for each of the monochromatic light of the three wavelengths of the liquid film 46, and each of the monochromatic light of the three wavelengths of the liquid film 46 A candidate value for the film thickness of the liquid film 46 at the target measurement point that satisfies the relational expression of the above expression (1) using the refractive index n (j) is calculated according to the above expression (7) for each of the three wavelengths. To do.

  In step 108, the film thickness value of the liquid film 46 at the target measurement point is determined from the candidate value of the film thickness of the liquid film 46 at the target measurement point calculated for each of the three wavelengths in step 106.

  In step 110, it is determined whether or not the processing in steps 104 to 108 has been completed for all remaining measurement points. If there is a measurement point that has not been subjected to the processing of step 104 to step 108 among the remaining measurement points, the process returns to step 104 and the measurement point is selected as the target measurement point. On the other hand, when the processing of step 104 to step 108 is completed for all remaining measurement points, the process proceeds to step 112.

  In step 112, the film thickness of each liquid film 46 at some measurement points calculated in step 102 and the film thickness of each liquid film 46 at some measurement points determined in step 108 are as follows. The output is performed by the output unit 70, and the process ends.

<Experimental example>
<Verification of transparent film thickness under static conditions>
In order to show the effectiveness of the measurement technique in the present embodiment, it is necessary to show the validity of the derived transparent film thickness. Therefore, samples with known film thicknesses were measured by the measurement method of the present embodiment, and their film thickness values were compared.

<Sample and interference elephant>
A transparent film having a known film thickness was prepared by putting a base oil into a recess having a known depth. This is because the transparent film thickness is the same as the depth of the recess if it is a static measurement in which the transparent film is not slid. A recess having a known depth was prepared by etching a silicon wafer. FIG. 11 shows a schematic diagram of a silicon wafer. The shape in the direction of the surface of the dent was a square with a side of about 700 μm, and three levels of depth levels of several nm, several tens of nm, and several hundreds of nm were used. Base oil was put into the concave portion of the silicon wafer and pressed against the transparent sliding material, and an interference image at that time was taken.

  On the other hand, a white interference type three-dimensional shape measuring machine (Newview manufactured by Zygo (R)) was used for measuring the depth of the dent. The measurement was performed in the atmosphere.

  FIG. 12 shows an interference image by a base oil film in a silicon wafer recess (depth several hundred nm order). Note that FIG. 12 is an image obtained by cutting out only the periphery of the recess from the imaging.

<Derivation of unknown variable>
In order to derive unknown variables, 19 measurement points were selected from the entire imaging including the recess. Here, since the transparent film used in this experiment is a base oil and has no absorption in the visible light range (attenuation coefficient ≈ 0), the attenuation coefficient α (j) is zero in advance (α (470nm) = α (560nm) = α (600nm) = 0) Also, since the refractive index is not wavelength-dependent, the refractive index n (j) of the transparent film at all wavelengths was set to 1.46 (n (470 nm) = n (560 nm) = n (600 nm) = 1.46). Therefore, the derived variables are two variables I ₁ (j) and I ₂ (j).

FIG. 13 shows the result of deriving I1 (j) and I2 (j) using the algorithm described in the above embodiment. The luminance values of I ₁ and I ₂ mean luminance values in 8 bits (256 gradations). In this way, variables could be derived from the luminance values at a plurality of measurement points without the need for experimental calibration. Using these variables, the base oil film with the recesses on the order of several nm and several tens of nm was also analyzed.

<Comparison result>
FIG. 14 shows the result of comparing the thickness distribution of the base oil film by the recesses on the order of several hundred nm and the cross section of the depth distribution measured by a three-dimensional shape measuring machine. It turns out that both agree well. FIG. 15 shows the results of plotting the average film thickness and the average depth of the recesses at three levels of several nm order, several tens nm order, and several hundred nm order. If these are the same value, they are arranged on a straight line of Y = X shown in FIG. In FIG. 15, the plots are arranged on a straight line of Y = X at three levels, and measured using the white interference type three-dimensional shape measuring instrument and the measurement method of the present embodiment. The transparent film thickness was in good agreement. From this result, it can be seen that the transparent film thickness calculated from the measurement method of the present embodiment is appropriate.

  In addition, the conventional technique can only analyze the optical film thickness in the range of 250 nm. When the optical film thickness of 250 nm is converted into a physical film thickness, the lubricating oil (refractive index: 1.46) used this time is approximately 170 nm. In the measurement using a recess of the order of several hundred nm, it is possible to measure a film thickness of about 230 nm. Therefore, it can be seen that the measurement method of this embodiment can analyze a wider film thickness range than the conventional technique.

<Measurement of transparent film thickness during sliding>
Next, the result of measuring the film thickness using a general lubricating oil film as the transparent film present on the sliding surface will be described.

<Sample>
Mirror-polished steel (carbon steel) was used as the reflective sliding material. The shape was a Φ5 mm disk. However, the sliding surface is not a perfect plane, but has a medium-high shape (spherical shape) with a very large curvature (equivalent to SR1000) by special polishing. This is for preventing the contact at the end of the test piece, which is not desirable as a sliding test, and for calculating the transparent film thickness by elastic fluid lubrication calculation described later. As the transparent film, a base oil film was used as before. The sliding conditions are a sliding speed of 3.0 m / s, a load of 2000 N, and an oil temperature of 80 ° C.

  FIG. 16 shows an interference image by a mirror-polished steel disk. A horseshoe-like pattern is observed, but this is a fluid film thickness distribution between a flat plate called a horseshoe shape and a sphere, called a horseshoe shape. It is known to become thinner. In this experimental example, the range enclosed by the frame in the figure was analyzed.

<Derivation of unknown variable>
The measurement points used for derivation of the unknown variable are 51 points shown in FIG. In FIG. 17, the reason why many measurement points are selected in the left part (region where the optical film thickness is around 450 nm) is that the luminance value of each wavelength corresponds to the above-described peak / bottom at this film thickness. (470nm is the peak and 560nm and 600nm is the bottom). In such a place, it is necessary to select many measurement points in order to derive an appropriate unknown variable.

Using these 51 measurement points, as in the previous static test, I ₁ (j) and I ₂ (j) were obtained with an absorption coefficient of zero and a refractive index of 1.46. The result is shown in FIG.

<Oil film thickness distribution>
FIG. 19 shows the result of conversion from the interference image to the film thickness distribution using the unknown variable of FIG. First, focusing on the qualitative distribution shape, it becomes a horseshoe shape, and it can be seen that this is a reasonable shape as the oil film thickness distribution on the sliding surface. Next, attention is paid to a quantitative film thickness value. The average film thickness at the central portion that is the maximum on the sliding surface was about 400 nm, and the film thickness at the left and right end portions that was the minimum was about 140 nm. From this, it can be seen that, similar to the static measurement result described above, the interference image can be converted into the film thickness distribution in a film thickness range wider than that of the prior art.

<Comparison with film thickness by lubrication calculation>
In order to examine the validity of the film thickness value, we compared it with the average film thickness at the center by elastohydrodynamic lubrication (EHL) calculation. For the EHL calculation, a commonly used Chittenden-Dowson equation was used (Non-Patent Document 6 (Chittenden, RJ, Dowson, D., Dunn, JF, Taylor, CM: Proc. Roy. Soc. London, A397 (1985) 271)). The Chittenden-Dowson equation is shown in the following equation (9).

(9)

Where R _x is the composite radius of curvature (sliding direction) [mm], R _y is the composite radius of curvature (sliding orthogonal direction) [mm], W is the vertical load [N], u is the average sliding speed [m / s], h _c is the central oil film thickness [μm], β is the pressure viscosity index [Pa-1], η ₀ is the atmospheric pressure viscosity [Pa · s], and E is the synthetic elastic modulus. [Pa]. The pressure viscosity index was calculated with reference to the results of Non-Patent Document 7 (Hata et al., Tribologist, Vol. 55 No. 9 (2010)). The oil temperature at that time was calculated as 80 ° C.

  Under this test condition, the average oil film thickness at the center is 415 nm, which is almost consistent with the analysis result. Therefore, it can be seen that the measurement method of the present embodiment is also effective for the transparent film thickness during sliding. Note that the experimental value is smaller than the calculated value because of the influence of temperature. In the calculation, the set oil temperature of 80 ° C. was used, but in the experiment, the oil temperature on the sliding surface was 80 ° C. or higher due to sliding.

  As described above, according to the film thickness measurement system according to the embodiment of the present invention, the light from the white light source is changed to light composed of monochromatic light of three wavelengths using a bandpass filter, and transparent sliding is performed. The light and the liquid film are transmitted and irradiated to the reflective sliding material to cause optical interference. In the generated optical interference, the brightness of each of the three wavelengths of light is measured, and each of the measured three wavelengths of light is measured. By measuring the film thickness of the liquid film based on the brightness of the liquid, it is possible to measure the film thickness of the liquid film without performing complicated work such as prior interference color / brightness-film thickness calibration by experiment Can do. Moreover, the film thickness measurement range can be improved.

  Moreover, even if the transparent film is colored, the film thickness can be measured by including the absorption coefficient for each of the three wavelengths of light of the transparent film as an unknown variable. Moreover, even if the transparent film is made of a material such as an oil film, the film thickness can be measured by including the refractive index of each of the three wavelengths of the transparent film as an unknown variable.

  In the above-described embodiment, the case where the film thickness is calculated by solving the simultaneous equations or calculating the film thickness by the optimization method from the relational expression of the above expression (1) for some measurement points has been described as an example. It is not limited to this. When the number of measurement points is small, the film thickness may be calculated for all measurement points by solving simultaneous equations from the relational expression (1) or by an optimization method.

  Moreover, although the case where the irradiation light which permeate | transmitted the 3 wavelength band pass filter injects into a sliding system was demonstrated to the example, it is not limited to this. For example, white light from a white light source may be incident on a sliding system, and reflected light from the sliding system may be captured by a camera via a three-wavelength bandpass filter or a spectroscope.

DESCRIPTION OF SYMBOLS 10 Film thickness measurement system 20 Optical system 22 White light source 26 Three wavelength band pass filter 28 Half mirror 32 Camera 40 Sliding system 42 Transparent sliding material 44 Partial reflection film 45 Transparent protective film 46 Liquid film 48 Reflective sliding material 50 Sliding Testing machine 60 Arithmetic device 62 Image acquisition unit 64 Unknown variable derivation unit 66 Film thickness value determination unit

Claims (11)

A sliding device including a first sliding material, a second sliding material, a transparent film, a photodetector, a light source, and an arithmetic device,
The first sliding material and the second sliding material move relative to each other while receiving a load,
The transparent film exists between the first sliding material and the second sliding material,
The first sliding material and the transparent film are made of a material that transmits light,
The second sliding material is made of a material that reflects light,
Irradiating light from the light source through the first sliding material and the transparent film and irradiating the second sliding material to cause light interference;
The photodetector measures the luminance of light having a wavelength range narrow enough to be regarded as monochromatic light from the generated light-interfered light at a plurality of measurement points, and the number of wavelengths measured at that time is two or more. ,
The arithmetic unit is configured to calculate the brightness of each of the two or more lights and the film thickness of the transparent film based on the brightness of each of the two or more lights measured for each of the measurement points by the photodetector. A relational expression representing a relation, wherein the measurement point is determined from a relational expression including a film thickness of the transparent film at each of the measurement points, and an unknown variable derived from a measurement environment assumed to be the same at each of the measurement points. Determining the film thickness of the transparent film in each of the above , and an unknown variable derived from the measurement environment,
The sliding device , wherein the transparent film is a liquid film . A sliding device including a first sliding material, a second sliding material, a transparent film, a photodetector, a light source, and an arithmetic device,
The first sliding material and the second sliding material move relative to each other while receiving a load,
The transparent film exists between the first sliding material and the second sliding material,
The first sliding material and the transparent film are made of a material that transmits light,
The second sliding material is made of a material that reflects light,
Irradiating light from the light source through the first sliding material and the transparent film and irradiating the second sliding material to cause light interference;
The photodetector measures the luminance of light having a wavelength range narrow enough to be regarded as monochromatic light from the generated light-interfered light at a plurality of measurement points, and the number of wavelengths measured at that time is two or more. ,
The arithmetic unit is configured to calculate the brightness of each of the two or more lights and the film thickness of the transparent film based on the brightness of each of the two or more lights measured for each of the measurement points by the photodetector. A relational expression representing a relation, wherein the measurement point is determined from a relational expression including a film thickness of the transparent film at each of the measurement points, and an unknown variable derived from a measurement environment assumed to be the same at each of the measurement points. Determining the film thickness of the transparent film in each of the above , and an unknown variable derived from the measurement environment ,
The unknown device derived from the measurement environment includes at least one of an absorption coefficient of the transparent film for each of the two or more lights and a refractive index of the transparent film for each of the two or more lights . Before SL arithmetic device based on the luminance of each of the two or more light measured for each of the measurement points by the light detector, and the thickness of the brightness and the transparent film of each of the two or more light In relation to the relational expression including unknown variables derived from the measurement environment assumed to be the same at each of the measurement points, and the film thickness of the transparent film at each of the measurement points, The sliding device according to claim 1 or 2 , wherein an unknown variable derived from the measurement environment and a film thickness of the transparent film at each measurement point are obtained by solving simultaneous equations or by an optimization method. The measurement environment from the unknown variables, the surface light intensity of each of the two or more light, and said each of two or more light, the transparent film according to claim 1 wherein including a back surface light intensity when the light absorption does not occur due to 4. The sliding device according to any one of items 3 . The relational expression, the sliding device according to any one of claims 1 to 4 represented by the following formula.

Here, j represents a number assigned to each of the two or more lights, i represents a number assigned to each of the plurality of measurement points, and I (i, j) is i by the photodetector. Represents the luminance of the j-th light measured at the measurement point, I ₁ (j) represents the surface light intensity of the j-th light, and I ₂ (j) represents the transparent film of the j-th light. Represents the light intensity of the back surface when no light absorption occurs, α (j) represents the extinction coefficient for the jth light of the transparent film, and n (j) represents the refractive index of the transparent film for the jth light. T (i) represents the film thickness of the transparent film at the i-th measurement point, and λ (j) represents the wavelength of the j-th light. The sliding device according to any one of claims 1 to 5 , wherein wavelengths of the two or more lights are 200 nm to 4,000 nm. The arithmetic unit is configured for the relational expression based on the luminance of each of the two or more lights measured for each of some of the plurality of measurement points by the photodetector. Solve the equation or optimize the thickness of the transparent film at each of the measurement points and determine unknown variables derived from the measurement environment by an optimization method.
Based on the brightness of each of the two or more lights measured for each of the remaining measurement points of the plurality of measurement points by the photodetector, and the obtained unknown variable derived from the measurement environment, For each measurement point, a candidate value for the film thickness of the transparent film at the measurement point satisfying the relational expression for each wavelength of the two or more lights is obtained, and the measurement for each wavelength of the two or more lights is performed. from the membrane candidate value of the thickness of the transparent film at a point, sliding according to any one of claims 1 to 6 for determining the thickness values of the transparent film in the measuring points using the matching method between the wavelengths Moving device. A band-pass filter that is on the optical path of the light emitted from the light source and is provided between the light source and the first sliding material and transmits each wavelength of the two or more lights. The sliding device according to any one of claims 1 to 7 . A bandpass filter that is provided on the optical path of the light causing the optical interference and is provided between the photodetector and the first sliding material, and transmits each wavelength of the two or more lights; Alternatively, the sliding device according to any one of claims 1 to 7 , further comprising an optical spectrometer that splits the light into each of the two or more lights.   The sliding device according to any one of claims 1 to 9, wherein the light source is a flash lamp. A sliding device comprising a first sliding material, a second sliding material, a liquid film , a photodetector, a flash lamp , and an arithmetic device,
The first sliding material and the second sliding material move relative to each other while receiving a load,
The liquid film exists between the first sliding material and the second sliding material,
The first sliding material and the liquid film are made of a material that transmits light,
The second sliding material is made of a material that reflects light,
Irradiating the light from the flash lamp through the first sliding material and the liquid film and irradiating the second sliding material to cause light interference;
The photodetector measures the luminance of light having a narrow wavelength width so that it can be regarded as monochromatic light from the generated light after interference, and the number of wavelengths to be measured at that time is two or more,
The arithmetic device calculates the film thickness of the liquid film based on the brightness of each of the two or more lights measured by the photodetector.