CN104154870B - Method for measuring thickness of lubricating oil film by two-color light interference - Google Patents

Abstract

The invention belongs to the technical field of optical measurement, and relates to a method for measuring the thickness of a lubricating oil film by two-color light interference. The three-stimulus value of red and green two-color light interference of the thickness of the lubricating oil film between a steel ball and a glass disc is firstly calculated, and then measured and recorded at different sliding speeds. and the optical interference images caused by the thickness of the lubricating oil film in the contact area of the steel ball and the glass disc under different loading conditions, analyze the G-R modulation light intensity curve of the black characteristic stripe closest to the contact center, and determine the specificity of all the stripes in the entire interference image Series, calculate the specific film thickness distribution, and realize the measurement of lubricating oil film thickness; the measurement process is simple, the measurement efficiency is high, and the measurement range is 3 times larger than that of white light interference, which is convenient for measuring the entire contact area under different sliding speeds and different loads oil film thickness distribution.

Description

A Method for Measuring Lubricating Oil Film Thickness by Two-color Light Interferometry

Technical field:

The invention belongs to the technical field of optical measurement, and relates to a method for measuring the thickness of lubricating oil film by two-color light interference, in particular to a method for measuring the thickness of lubricating oil film on the nanometer to submicron scale between mechanical contact pairs by using the principle of two-color light interference and relative light intensity The method is suitable for measuring the film thickness distribution in the contact area of different speeds and loads under elastohydrodynamic lubrication, hydrodynamic lubrication and other lubrication states.

Background technique:

Forming an oil film of sufficient thickness between mechanical moving parts to separate the two surfaces is an important means to reduce friction and avoid wear. At present, optical interferometry is one of the most effective methods to measure the thickness of lubricating oil film. It uses the formed interference fringes to calculate the thickness and shape of the oil film. In 1965, Cameron et al. proposed the measurement structure of ball-disk contact, and used optical interference technology to observe the classic horseshoe-shaped oil film shape with outlet necking for the first time, which opened up the research field of Optical Elastohydrodynamics. After improvement, The optical measurement configuration of the glass disk, spectroscopic layer (Cr film), cushion layer (SiO ₂ ), lubricating oil and steel ball was determined. The introduction of spectroscopic Cr film greatly improved the contrast of interference fringes, and the proposed cushion layer technology The lower limit of measurable film thickness is smaller. According to the different light sources used, light interferometry is divided into monochromatic light interferometry and white light interferometry. Monochromatic light interferometry judges the oil film thickness by counting the order of interference fringes and analyzing the change of light intensity between light and dark fringes. Combined with Huang Ping, Luo The relative light intensity method (ROII) proposed by Jianbin et al. and the MBI measurement scheme proposed by Guo Feng of Qingdao Technological University have a resolution of 0.85nm and a range of 5μm; The interference order is counted in the record, which is not only inefficient, but also often loses the order during high-speed dynamic measurement, resulting in misjudgment of the film thickness; the white light interferometry uses the change of the color coordinates in the interference image to calculate the oil film thickness, without determining the interference fringe level However, with the increase of film thickness, the wavelength range of constructive interference increases, and the contrast and color saturation of interference fringes attenuate seriously. For white light interference, the highest measurable film thickness generally does not exceed 1 μm, and the measurement accuracy depends on Strict calibration process, many factors in the calibration process, such as the different curvature of the contact surface in static calibration and dynamic measurement, will cause measurement errors. In order to improve the maximum measurable oil film thickness under the condition of ensuring the measurement accuracy, researchers also use two-color or three-color light for measurement, which is actually a compromise between monochromatic light interference and white light interference. Lord et al. proposed a pseudo-phase stepping based on three-color light interference However, due to the complexity of the technology, it has not been promoted; Guo Feng and Zhao Guolei of Qingdao University of Technology proposed the GR two-color light intensity modulation technology in their paper "Double-color Interference Light Intensity Modulation Method for Oil Film Thickness Measurement", trying to use a piece of image information Dealing with film thickness, avoiding the dependence of monochromatic light on the order of historical images, but only one modulation beat cycle is used, and the range is only 1μm, which cannot meet the measurement requirements of high film thickness, and the more important thing is the modulation of theoretical calculation of double beams There is a large deviation between the extreme point of the curve and the extreme point in the actual measurement, which makes this method unable to be applied in the actual measurement. Therefore, it is necessary to explore a large-range, high-precision, convenient and feasible method to measure the thickness of nano/submicron lubricating oil film.

Invention content:

The purpose of the present invention is to overcome the disadvantages of cumbersome interference order counting of monochromatic light and the small range of other interference techniques in the existing measurement methods, and seek to design and provide a method for two-color light interferometric measurement of lubricating oil film thickness, which can extend the optical range to 4μm, the interference order of a fixed point can be accurately judged through a two-color interference image, and then use the monochromatic red light intensity distribution to realize dynamic nano/sub Efficient measurement of micron lubricant film thickness.

In order to achieve the above object, the present invention adopts the two-color light oil film lubrication test bench to realize the measurement of the lubricating oil film thickness. The two-color light oil film lubrication test bench is provided with a 3CCD color camera that captures the oil film interference image between the steel ball and the glass disc contact pair in real time. The image card is transmitted to the computer for display and storage, and the specific measurement steps include:

(1) Calculate the three-stimulus value of red-green two-color light interference corresponding to the thickness of the lubricating oil film between the steel ball and the glass disc from 1nm to 4500nm, that is, the relative light intensity distribution of red and green RG in the oil film interference system; use the principle of color addition and color complex Now the equation, the color tristimulus value obtained by the 3CCD (RGB) color camera of the 3CCD color camera with the spectral sensitivity characteristics of f _R (λ), f _G (λ), and f _B (λ) respectively is

$C=\underset{\mathrm{\λ}}{\∫}k\left(\mathrm{\λ}\right)I_h\left(\mathrm{\λ}\right)f_C\left(\mathrm{\λ}\right)\mathrm{d\λ},$ C = R, G, B

Among them, C represents the three stimulus values of R (red), G (green), and B (blue), S (λ) is the spectral energy distribution function of the red and green two-color light source used, k is the adjustment coefficient, and the value range of k is 0 Between 1 and 1, the purpose is to normalize the three stimulus values, I _h (λ) is the interference light intensity at the film thickness h on each band λ, and the interference light intensity I of the glass disk interface is according to the formula

$I={\left|{\stackrel{\‾}{\mathrm{E.}}}_0^{-}\right|}^2={|{\stackrel{\‾}{\mathrm{E.}}}_0^{-1}+{\stackrel{\‾}{\mathrm{E.}}}_0^{-2}+{\stackrel{\‾}{\mathrm{E.}}}_0^{-3}+{\stackrel{\‾}{\mathrm{E.}}}_0^{-4}+\&Center\; Dot;\&Center\; Dot;\&Center\; Dot;|}^2={\left|\underset{m=1}{\overset{\∞}{\mathrm{\Σ}}}{\stackrel{\‾}{\mathrm{E.}}}_0^{-m}\right|}^2$ to calculate, where Indicates the electric vector of reflected light, m=1,2,..., the subscript 0 represents the glass medium, It is directly reflected from the interface of the glass disk, and other reflected light is reflected and projected by the layers below the glass disk; then along the thickness of the lubricating oil film from 0nm to 4500nm, the normalized light intensity of the green light is subtracted from the normalized light intensity of the red light The two-color light modulated light intensity GR is obtained by changing the light intensity, and the corresponding change relationship curve between the film thickness and the relative light intensity of G, R, and GR is drawn; There is a one-to-one relationship between the size of the extremum point of the curve and the film thickness, and the corresponding two-color light interference image presents black characteristic stripes at the boundary of each modulation beat; Red and green two-color laser light source, the calculation results show that the optical thickness corresponding to each wave beat in the GR modulation light intensity curve is 1408nm, and each wave beat contains 10 extreme points, and adjacent wave beats are not exactly the same. After calculating the normalized red and green light intensity values of the black characteristic fringe position of the two-color light interference image within the film thickness range of 4500nm, after making the GR modulation light intensity curve, take the 8th and 9th extreme points on each wave of the curve The sum of the absolute values of the light intensity SUM is used as a criterion to distinguish the first three beats. It is found that the SUM value is between 1.0 and 1.8 as the first beat, and the SUM value between 1.8 and 2.8 belongs to the second beat. The value between 2.5 and 3.2 is the third beat, and the eighth extreme point of the first three beats corresponds to the interference orders of monochromatic red light interference (4,4), (8,8), ( 12,12);

(2) Measure and record the optical interference image caused by the thickness of the lubricating oil film in the contact area between the steel ball and the glass disc when the sliding speed is greater than 0mm/s, analyze the G-R modulation light intensity curve of the black characteristic stripe closest to the contact center, and calculate the 8th The sum of the absolute values of the light intensity values of the 1st and 9th extreme points is compared with the calculated SUM value to determine the beat band, and the interference order of the red light corresponding to the position of the 8th extreme point; and then compared with the calculated SUM value Comparing the film thickness relative light intensity curve of 0-4500nm red light, the specific interference series of the central interference area at this sliding speed can be obtained, so as to determine the specific series of all fringes in the entire interference image, and then use the interference principle to calculate the specific series. The thickness distribution of the film; use the same method to continuously record the interference images of light caused by the lubricating film in the contact area of the steel ball and the glass disc at different sliding speeds, so as to obtain the interference order and film thickness distribution of the central contact area at different sliding speeds;

(3) Measure and record the interference image caused by the lubricating film in the contact area of the steel ball and the glass disc under the load applied by the loading lever, measure and obtain the G-R modulation light intensity curve of the black characteristic stripe closest to the center of the contact area under this load, and use it at the same time The sum of the absolute values of the light intensity values at the 8th and 9th extreme points determines the interference order of the red light corresponding to the position of the 8th extreme point; By comparing the light intensity curves, the specific interference series of the central interference area at this speed can be obtained, so that the specific series of all fringes in the entire interference image can be determined, and then the specific film thickness distribution can be obtained by using the interference principle to realize the lubricating oil film thickness. Measurement.

The acquisition process of the two-color modulation light intensity G-R in the present invention specifically includes: first storing the interference image through a 3CCD color camera; then recording the rotational speed and/or load, and then obtaining and storing the red light and green light intensity values in the designated area of the interference image, Output the maximum and minimum values of red light and green light intensity respectively; use the formula

$\mathrm{<span\; class="notranslate">\; G</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; R</span>}<span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; G</span>}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; G</span>}\mathrm{<span\; class="notranslate">\; max</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; G</span>}\mathrm{<span\; class="notranslate">\; min</span>}}<span\; class="notranslate">\; )</span>}{{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; G</span>}\mathrm{<span\; class="notranslate">\; max</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; G</span>}\mathrm{<span\; class="notranslate">\; min</span>}}}<span\; class="notranslate">\; -</span>\frac{{\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; R</span>}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; R</span>}\mathrm{<span\; class="notranslate">\; max</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; R</span>}\mathrm{<span\; class="notranslate">\; min</span>}}<span\; class="notranslate">\; )</span>}{{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; R</span>}\mathrm{<span\; class="notranslate">\; max</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; R</span>}\mathrm{<span\; class="notranslate">\; min</span>}}}$

Calculate the two-color difference light intensity G-R of the region.

The method for judging the 8th and 9th extremum points in the G-R modulation light intensity curve of the present invention specifically includes: first obtaining the variation of the G-R modulation light intensity at the black feature interference fringes of the interference image with the pixel point coordinates; and then finding out The position of all extreme points on the extreme point of the G-R modulation light intensity curve whose absolute value of light intensity is less than 0.5, that is, the 0 area, contains and represents the position where a wave beat ends; secondly, from the 0 area to the contact center direction, that is, the contact In the direction of the relative reduction of the sub-gap and the film thickness, a group of adjacent extreme points with approximately equal absolute values near the 0 zone are the 8th and 9th extreme points, and the G-R value less than 0 is the 8th pole Value point, greater than 0 is the ninth extreme point.

The main structure of the two-color light interference oil film lubrication test bench of the present invention includes a test bench base, a red and green two-color laser light source, a rotating frosted glass, an optical fiber, a computer, a 3CCD color camera, a coaxial lighting microscope, a glass disc, a steel ball, a loading lever, Spring tension gauge, ball holder and servo motor. A glass disk, loading lever and servo motor are installed on the base of the test bench. The glass disk is a transparent circular structure; Meter connection; steel balls are fixed on the ball bracket, lubricating oil is added to the raceway between the steel balls and the glass disc to form a lubricating oil film; the red and green two-color laser light source is placed on the base of the test bench, and the front side of the red and green two-color laser light source is placed. Rotating frosted glass, an optical fiber is installed between the rotating ground glass and the coaxial illuminating microscope, the light emitted by the red and green laser light source passes through the rotating ground glass and filtered, then enters the coaxial illuminating microscope through the optical fiber, and finally shoots vertically to the observation area of the coaxial illuminating microscope ;Use a spring tension gauge to apply load to the loading lever to realize the measurement of the thickness of the lubricating oil film under different loads; the servo motor drives the glass disk to rotate on the base of the test bench, and the speed of the corresponding experimental contact area is 0mm/s to 1.5m/s to realize the glass disk Film thickness measurement at different rotation speeds; a 3CCD color camera is connected directly above the coaxial illumination microscope, and the 3CCD color camera captures the interference image in real time, and transmits the interference image to a computer equipped with an image acquisition card for display or storage.

Compared with other optical interference oil film thickness measurement methods, the present invention can accurately judge the interference series at the minimum film thickness in the lubricating contact area through the G-R modulation light intensity analysis of the characteristic fringes of a two-color interference image, and then can directly follow the monochromatic The multi-beam interference principle of light calculates the film thickness h. The measurement process is simple and the measurement efficiency is high. It avoids the loss of the number of interference order counts that rely on the acceleration process of monochromatic light under high-speed conditions. The obtained value is 3 times larger than that of white light interference. The measurement range can reach 4μm; it is convenient to measure the oil film thickness distribution of the entire contact area under different sliding speeds and different loads, and provides a new method for the measurement of lubricating oil film thickness between contact pairs in lubrication research and engineering practice.

Description of drawings:

Fig. 1 is the schematic diagram of the assembled structure principle of the two-color varnish oil film lubrication test bench used in the present invention, including test bench base 101, red and green two-color laser light source 102, rotating frosted glass 103, optical fiber 104, computer 105, 3CCD color camera 106, coaxial Illumination microscope 107, glass disc 108, steel ball 109, loading lever 110, spring tension gauge 111, ball holder 112 and servo motor 113.

Fig. 2 is the spectral sensitivity characteristic response curve of used 3CCD color camera when the present invention is realized, wherein 21 is the spectral response curve f _B (λ) of blue light, 22 is the spectral response curve f _G (λ) of green light, and 23 is red light The spectral response curve f _R (λ).

Fig. 3 is the spectral energy distribution function of the red and green two-color laser light source used in the realization of the present invention.

Fig. 4 is a graph showing the relationship between the film thickness of the calculation database and the normalized red and green light intensities R, G and relative modulation light intensity G-R when the present invention is implemented.

Fig. 5 is a red-green two-color light interference image showing black characteristic fringes at the end of the beat wave generated by a wedge-shaped gap with a thickness of 0-4500nm calculated during the implementation of the present invention.

Fig. 6 is a static interference image taken by a 3CCD color camera according to the embodiment of the present invention.

Fig. 7 is a G-R distribution diagram of the relative modulated light intensity along the increasing direction of the steel ball radius with the center as the starting point of the measured ball-on-disk Hertzian contact interference image according to the embodiment of the present invention.

Fig. 8 is a comparison chart of the ball-on-disk Hertzian contact measurement results of the present invention and the classical Hertzian contact theory, in which 71 is the theoretical curve of Hertzian contact, and 72 is the experimentally measured curve of the two-color light interference method.

Fig. 9 is a dynamic oil film interference image taken with a 3CCD color camera according to an embodiment of the present invention.

10 is an analysis diagram of G-R relative modulated light intensity along the direction of increasing radius indicated by image pixel coordinates for the first group of black characteristic stripes closest to the contact center according to an embodiment of the present invention.

Fig. 11 is a schematic diagram of multi-beam interference generation of the multi-layer film measuring system used in the present invention.

detailed description:

The present invention will be further described below by way of embodiments and in conjunction with the accompanying drawings.

Example:

The main structure of the two-color light interference oil film lubrication test bench used in this embodiment includes a test bench base 101, a red and green two-color laser light source 102, a rotating frosted glass 103, an optical fiber 104, a computer 105, a 3CCD color camera 106, a coaxial illumination microscope 107, a glass Disc 108, steel ball 109, loading lever 110, spring tension gauge 111, ball holder 112 and servo motor 113, glass disc 108, loading lever 110 and servo motor 113 are installed on the test bench base 101, glass disc 108 is a transparent circle Shaped structure; a ball holder 112 is placed above one end of the loading lever 110, and the bottom of the other end is connected with a spring tension gauge 111; a steel ball 109 is fixed on the ball holder 112, and 30ml of lubrication is added to the raceway between the steel ball 109 and the glass disc 108 oil to form a lubricating oil film; the red and green two-color laser light source 102 is placed on the test bench base 101, the front side of the red and green two-color laser light source 102 is placed with a rotating ground glass 103, and an optical fiber 104 is arranged between the rotating ground glass 103 and the coaxial illumination microscope 107 , the light emitted by the red and green two-color laser light source 102 passes through the rotating frosted glass 103 and is filtered, then is introduced into the coaxial illumination microscope 107 through the optical fiber 104, and finally shoots vertically to the observation area of the coaxial illumination microscope 107; Apply load to realize the measurement of lubricating oil film thickness under different loads; the servo motor 113 drives the axis of the glass disc 108 to rotate on the test bench base 101, and the corresponding speed of the experimental contact area is 0mm/s to 1.5m/s, realizing the glass disc at different speeds. Measurement of film thickness: a 3CCD color camera 106 is connected directly above the coaxial illumination microscope 107, and the 3CCD color camera 106 captures the interference image in real time, and transmits the interference image to the computer 105 equipped with an image acquisition card for display or storage.

The experimental environment temperature of the present embodiment is 20 ± 1 ℃, and relative humidity is 50% ± 5%. The diameter of the steel ball 109 is 25.4mm, and the spherical surface of the steel ball 109 is a precision grinding and polishing surface with high reflectivity, and the surface roughness Ra is less than 8nm; the central wavelength of the red and green two-color laser light source 102 is 653nm and 532nm respectively; the lubricating film is Air, with a refractive index of 1.0; 3CCD color camera 106 captures the interference image between the steel ball 109 and the glass disc 108 contact pair, and transmits it to the computer 105 for display and storage through the image card. The specific measurement steps include:

S101: Calculate the three-stimulus value of red-green two-color light interference corresponding to the thickness of the lubricating air film between the steel ball 109 and the glass disc 108 from 1nm to 4500nm, that is, the relative light intensity distribution of red and green RG in the oil film interference system; use the principle of color addition and color To reproduce the equation, the color tristimulus values obtained by the 3CCD (RGB) color camera 106 with the spectral sensitivity characteristics shown in Fig. 2 being respectively f _R (λ), f _G (λ), and f _B (λ) are

$C=\underset{\mathrm{\&lambda;}}{\&Integral;}k\left(\mathrm{\&lambda;}\right)I_h\left(\mathrm{\&lambda;}\right)f_C\left(\mathrm{\&lambda;}\right)\mathrm{d\&lambda;},$ C = R, G, B

Wherein, C represents R, G, B tri-stimulus value, S (λ) is the spectral energy distribution function (as shown in Figure 3) of red and green two-color laser light source 102 used, k is adjustment coefficient, and the value range of k is 0 between 1 and 1, the purpose is to normalize the values of the three stimuli, and I _h (λ) is the corresponding interference light intensity when the film thickness on each band λ is h, due to the high reflection of the multilayer film medium and the surface of the steel ball The rate leads to multi-beam interference, and the interference light intensity of the final glass interface is according to $I={\left|{\stackrel{\&OverBar;}{\mathrm{E.}}}_0^{-}\right|}^2={|{\stackrel{\&OverBar;}{\mathrm{E.}}}_0^{-1}+{\stackrel{\&OverBar;}{\mathrm{E.}}}_0^{-2}+{\stackrel{\&OverBar;}{\mathrm{E.}}}_0^{-3}+{\stackrel{\&OverBar;}{\mathrm{E.}}}_0^{-4}+\&CenterDot;\&CenterDot;\&CenterDot;|}^2={\left|\underset{m=1}{\overset{\&infin;}{\mathrm{\&Sigma;}}}{\stackrel{\&OverBar;}{\mathrm{E.}}}_0^{-m}\right|}^2$ calculation, where (m=1,2,…) represents the electric vector of the reflected light, the subscript 0 represents the glass medium, only It is directly reflected from the chrome-glass interface, and other reflected light is reflected and projected by the layers below the chrome-glass; in this way, on the basis of multi-beam interference, considering the wavelength, bandwidth and 3CCD color camera response of red and green light sources, a A complete set of color and chromaticity calculation algorithms for lubricating oil film thickness two-color light interference; along the air film thickness increasing from 0nm to 4500nm, the normalized light intensity of green light minus the normalized light intensity of red light is used to obtain the two-color difference value Light intensity GR, so as to draw the relationship curve between the film thickness and the relative light intensity of G, R, and GR, as shown in Figure 4; , there is a one-to-one relationship between the size of the extremum point of the curve and the film thickness, and the corresponding two-color light interference image presents black characteristic stripes at the boundary of each modulation beat, as shown in Figure 5; Red and green two-color laser light sources 102 with central wavelengths of 653nm and 532nm respectively, the calculation results show that the optical thickness corresponding to each beat in the GR modulation light intensity curve is 1408nm, and each beat contains 10 extreme points, adjacent The wave beats are not exactly the same. For the black characteristic fringe position of the two-color light interference image within the film thickness range of 4500nm, calculate the normalized red and green light intensity values to draw a GR modulation light intensity curve, and take the eighth on each wave beat of the curve The sum of the absolute value of the light intensity of the ninth extreme point and the SUM is used as a criterion to distinguish the first three beats. Considering the model color calculation error and the image noise problem in the actual measurement application, there is always a SUM value between 1.0 and 1.8 between 1.8 and 2.8 is the second wave, and the SUM value between 2.5 and 3.2 is the third wave, and the 8th extreme point of the first three waves corresponds to The interference orders of monochromatic red light interference are (4,4), (8,8), (12,12);

S102: Load the loading lever 110 through the spring tension gauge 111, keep the load between the steel ball 109 and the glass disc 108 at 2N, and after the coaxial illumination microscope 107 focuses until the image is clear, use the 3CCD color camera 106 to take and save the interference image as Figure 6, analyze the G-R modulation light intensity of the first group of black characteristic stripes closest to the contact center along the direction of increasing radius, as shown in Figure 7, and calculate the sum of the absolute values of the light intensity values at the 8th and 9th extreme points at the same time Compared with the theoretically calculated SUM value criterion, because 1.52 is between 1.0 and 1.8, it is known that this area belongs to the first beat band, and the position coordinates of the eighth extreme point correspond to the red light The interference order is (4,4); then along the radius to the center of the contact area, according to the light intensity of the red light, there are 4 interference constructive points and 4 interference destructive points, so the specific interference order of the contact center can be obtained The number is (0,0), so that the specific series of all fringes in the entire interference image can be determined, and then the specific film thickness distribution is calculated by using the principle of relative light intensity of monochromatic light, as shown in Figure 8, and Figure 8 shows the proposed method The measured results are in good agreement with the calculated values of the classical Hertzian contact theory;

S103: Add 30ml of PB1300 lubricating oil to the glass plate 108. The density of the lubricating oil is 896kg·m ^-3 , the dynamic viscosity at 20°C is 117Pa·s, and the refractive index is 1.502; The load between the ball 109 and the glass disc 108 is 10N. After adjusting the focal length of the coaxial illuminating microscope 107 until the image is clear, start the servo motor 113 and set the rotation speed at 2.22mm/s; use the 3CCD color camera 106 to shoot and save the interference image as As shown in Figure 9, analyze the GR modulation light intensity of the first group of black characteristic stripes closest to the contact center along the direction of increasing radius, see Figure 10, and calculate the light intensity of the 8th extreme point A and the 9th extreme point B at the same time The sum of the absolute values of the values is 2.25, and its size is between 1.8 and 2.8, so it is known that this area belongs to the second beat band, and thus it is known that the coordinates of the eighth extreme point correspond to the interference order of red light as ( 8,8), due to the continuous change of the film thickness, according to the light intensity change of the red light at the center of the contact area, the specific interference series of the central interference area can be obtained by counting the number of interference constructive points and interference destructive points , and then the specific series of all fringes in the entire interference image can be determined, and then the film thickness value of any region of interest in the image can be calculated by using the principle of relative light intensity of monochromatic light.

The acquisition process of normalized red-green light intensity R, G and red-green two-color relative difference light intensity G-R described in this embodiment specifically includes:

S201: storing the interference image through the 3CCD color camera 106;

S202: Obtain and store the rotation speed and load in a file;

S203: Obtaining the red light and green light intensity values of the designated area of the image and saving them to a file;

S204: output the maximum and minimum values of the red light and green light intensity in the specified area;

S205: Using the formula

$G=\frac{{2I}_G-(I_{G\max }+I_{G\min })}{I_{G\max }-I_{G\min }},R=\frac{{2I}_R-(I_{R\max }+I_{R\min })}{I_{R\max }-I_{R\min }}$ and

$\mathrm{<span\; class="notranslate">\; G</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; R</span>}<span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; G</span>}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; G</span>}\mathrm{<span\; class="notranslate">\; max</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; G</span>}\mathrm{<span\; class="notranslate">\; min</span>}}<span\; class="notranslate">\; )</span>}{{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; G</span>}\mathrm{<span\; class="notranslate">\; max</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; G</span>}\mathrm{<span\; class="notranslate">\; min</span>}}}<span\; class="notranslate">\; -</span>\frac{{\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; R</span>}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; R</span>}\mathrm{<span\; class="notranslate">\; max</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; R</span>}\mathrm{<span\; class="notranslate">\; min</span>}}<span\; class="notranslate">\; )</span>}{{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; R</span>}\mathrm{<span\; class="notranslate">\; max</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; R</span>}\mathrm{<span\; class="notranslate">\; min</span>}}}$

Calculate the normalized red and green light intensities R, G and the two-color relative difference light intensity G-R of the region.

The method for judging the 8th and 9th extremum points in the G-R modulation light intensity curve of the present invention specifically includes: first obtaining the variation of the G-R modulation light intensity at the black feature interference fringes of the interference image with the pixel point coordinates; and then finding out All extreme points on the extreme point of the G-R modulation light intensity curve whose absolute value of light intensity is less than 0.5, the position of these points with very small G-R light intensity value, that is, the 0 zone, contains and represents the position where a wave beat ends; secondly , from zone 0 to the contact center, that is, the direction in which the contact gap and film thickness are relatively reduced, a group of adjacent extreme points with approximately equal absolute values near zone 0 are the 8th and 9th extreme points , where the G-R value less than 0 is the 8th extreme point, and the value greater than 0 is the 9th extreme point.

References for the calculation of multi-beam interference light intensity involved in this embodiment "Guo Feng, Huang Bolin; Large-scale measurement system for micro-nano lubricating film thickness, Acta Tribology 2004, volume 17, third issue, page 521; namely Guo F. and Wong PL, A wide range measuring system for thin lubricating film: from nano to micro thickness, Tribology Letters, 2004, Vol.17, No.3.521", as shown in Figure 11, the optical oil film measurement system is a glass , chromium, oil and steel composed of 4-layer dielectric optical system, each dielectric layer is marked as q=0~3, at the boundary between q and q+1, all light reflection electric vectors and light transmission electric vectors propagate according to incident and reflection Directions are synthesized into two categories, denoted as and The superscript plus or minus sign represents the direction of propagation, and the subscript represents the number of the medium in which the light propagates (such as 0 for glass), is the electric vector propagating to the steel at the interface between oil and steel, represents the electric vector of the incident light, Represents the electric vector of the outgoing light; the refractive index of the medium q is recorded as

${\stackrel{\&OverBar;}{\mathrm{no}}}_q={\mathrm{no}}_q-{\mathrm{ik}}_q,$ q=0~3

Where n _q is the real part of the refractive index, k _q is the attenuation coefficient, for optically transparent media, the attenuation coefficient is zero; at the junction of the medium layer q and q+1, the effective reflection coefficient is written as

${\stackrel{\&OverBar;}{R}}_q=\frac{{\stackrel{\&OverBar;}{\mathrm{E.}}}_q^{-}}{{\stackrel{\&OverBar;}{\mathrm{E.}}}_q^{+}},$ q=0~3

Reflection coefficient and The following relationship exists:

${\stackrel{<span\; class="notranslate">\; \&OverBar;</span>}{\mathrm{<span\; class="notranslate">\; R</span>}}}_{\mathrm{<span\; class="notranslate">\; q</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; =</span>\frac{{\stackrel{<span\; class="notranslate">\; \&OverBar;</span>}{\mathrm{<span\; class="notranslate">\; r</span>}}}_{\mathrm{<span\; class="notranslate">\; q</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; +</span>{\stackrel{<span\; class="notranslate">\; \&OverBar;</span>}{\mathrm{<span\; class="notranslate">\; R</span>}}}_{\mathrm{<span\; class="notranslate">\; q</span>}}\mathrm{<span\; class="notranslate">\; exp</span>}<span\; class="notranslate">\; (</span><span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; i</span>}\mathrm{<span\; class="notranslate">\; 2</span>}\stackrel{<span\; class="notranslate">\; \&OverBar;</span>}{\mathrm{<span\; class="notranslate">\; \&delta;</span>}}\mathrm{}}_{\mathrm{<span\; class="notranslate">\; q</span>}}<span\; class="notranslate">\; )</span>}{\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; +</span>{\stackrel{<span\; class="notranslate">\; \&OverBar;</span>}{\mathrm{<span\; class="notranslate">\; r</span>}}}_{\mathrm{<span\; class="notranslate">\; q</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}}{\stackrel{<span\; class="notranslate">\; \&OverBar;</span>}{\mathrm{<span\; class="notranslate">\; R</span>}}}_{\mathrm{<span\; class="notranslate">\; q</span>}}\mathrm{<span\; class="notranslate">\; exp</span>}<span\; class="notranslate">\; (</span><span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; i</span>}\mathrm{<span\; class="notranslate">\; 2</span>}\stackrel{<span\; class="notranslate">\; \&OverBar;</span>}{\mathrm{<span\; class="notranslate">\; \&delta;</span>}}}_{\mathrm{<span\; class="notranslate">\; q</span>}}<span\; class="notranslate">\; )</span>}$

in q is the thickness of the dielectric layer q, λ is the wavelength of the incident light, is the Fresnel reflection coefficient, because there is no transmission but only reflection on the surface of the steel ball, so there is According to the above formula, it can be obtained sequentially The reflectance or interference intensity of a layered system is defined as the ratio of the radiant energy of reflected light to the radiant energy of incident light, or the intensity ratio of reflected light to incident light, according to the formula Calculate and obtain the multi-beam interference light intensity or reflectivity, and assign values to the oil film thickness d ₂ sequentially starting from 0 nm, that is, the relationship between film thickness and multi-beam interference light intensity is obtained.

The interference order of any point in the interference image involved in this embodiment is defined as (δ, β), wherein the dark interference order of the point between the nth dark fringe and the n+1th dark fringe is δ=n, The bright interference order of the point between the nth bright fringe and the n+1th bright fringe is β=n; if the two-color light interference is used to judge the interference order (δ) of a certain reference point in the interference image corresponding to the red light ,β), because the film thickness changes continuously, the interference order also changes continuously with the ebb and flow of red light interference, so the interference order of other points in the interference image can be determined.

The monochromatic light multi-beam interference relative light intensity principle involved in this embodiment measures the film thickness reference "Wang Xuefeng, Guo Feng, Yang Peiran; Nano/micron elastodynamic oil film thickness measurement system, Journal of Tribology, 2006, volume 26, phase 2 , pp. 150-154", in optical interference, the interference intensity changes with the film thickness at a period of λ/(2n), where λ is the wavelength and n is the refractive index of the medium. For any oil film thickness h, there is a unique corresponding interference level The second is (β=0, δ=0) or (β=0, δ=1) oil film thickness h ₀ (there is defined as 0-level oil film thickness), the two have the same interference intensity, and their relationship conforms to the following Mode

$\mathrm{<span\; class="notranslate">\; h</span>}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; h</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; \&beta;</span>}\frac{\mathrm{<span\; class="notranslate">\; \&lambda;</span>}}{\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; no</span>}}$

In the formula: h is the thickness of the oil film, _h0 is the thickness of the 0th grade oil film, that is, the thickness of the oil film when β=0, λ is the wavelength, n is the refractive index of the lubricating oil, β is the nth bright streak and the n+1th grade The bright interference order of the points between the bright fringes; the relationship curve between the zero-order film thickness h ₀ and the normalized interference intensity can be calculated from the multi-beam interference light intensity. Therefore, calculating the film thickness through multi-beam interference is to extract the normalized light intensity of the image, find out the corresponding 0-level film thickness according to the increasing interval, and then add the integer period film thickness of βλ/2n to obtain the final film thickness; the measurement point The acquisition of interference order β is the key. For monochromatic light measurement, it is obtained by gradually increasing the entrainment speed from 0 and increasing the film thickness. The camera needs to record the whole process, but the high-speed oil film change may cause order loss. Causes errors in film thickness calculation; this embodiment analyzes the interference order at any point in the interference image through the characteristic fringes of the two-color light, without relying on historical records, thereby avoiding the cumbersome counting of interference orders and possible loss of orders.

In this embodiment, according to the interference principle of light, when the optical path difference Δ of two beams of coherent light is an even multiple of the half wavelength of the incident light, the two light waves are superimposed and strengthened, and bright fringes appear; when the optical path difference Δ of two beams of coherent light is When the incident light is an odd multiple of the half-wavelength, the two light waves are superimposed and weakened, resulting in dark fringes; if the optical path difference increases continuously from 0, light and dark interference fringes will be produced, and the degree of light and dark is expressed by light intensity, which is not difficult to understand. The fixed film thickness corresponds to a unique light intensity value, but the fixed light intensity value corresponds to multiple periodic film thicknesses, so the concept of interference order is proposed to distinguish; in the film thickness measurement system, the surface of the steel ball 109 and the glass The two beams of light reflected on the surface of the disk 108 come from the same incident light, which satisfies the coherence condition of light, and the film thickness between the steel ball 109 and the glass disk 108 changes continuously, so light and dark interference fringes will be produced.

The calculation equation of the color reproduction described in this embodiment is referring to "Yu Daoyin, Tan Hengying; Mechanical Industry Press 2006, the 80th page"; Utilize " Red-Green-Blue " model and color reproduction equation, to spectral sensitivity characteristic The color tristimulus values obtained by the camera sensors of f _R (λ), f _G (λ), and f _B (λ) respectively are

$C=\underset{\mathrm{\&lambda;}}{\&Integral;}k\left(\mathrm{\&lambda;}\right)I_h\left(\mathrm{\&lambda;}\right)f_C\left(\mathrm{\&lambda;}\right)\mathrm{d\&lambda;},$ C = R, G, B

Among them, C represents the tristimulus value of R, G, and B colors, S(λ) is the spectral energy distribution function of the red and green two-color light source used, k is the normalization coefficient, and the value range of k is between 0 and 1, and I _h (λ) is the intensity of interference light at the height of film thickness h in each wavelength band λ.

The color addition principle described in this embodiment is referred to " Yu Daoyin, Tan Hengying; Machinery Industry Press 2006, the 79th page "; The matching equation is expressed as F=R+G+B; according to the substitution rate of Grassmann color mixing, if there are two color lights R1, G1, B1 and R2, G2, B2 are added and mixed, then the tristimulus of the mixed light value is

$\left\{\begin{array}{c}\mathrm{<span\; class="notranslate">\; R</span>}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}\\ \mathrm{<span\; class="notranslate">\; G</span>}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; G</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; G</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}\\ \mathrm{<span\; class="notranslate">\; B</span>}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; B</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; B</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}\end{array}\right.$

The tristimulus value of a mixed color is the sum of the tristimulus values of each component color.

The color computer reproduction method described in this embodiment is referred to "Zhou Guangmei, Guo Feng, Li Hongsheng; Research on the characteristics of lubricating oil film two-color light interferometry system, Acta Optics Sinica 2012, volume 32, issue 3, article number 0312006", color reproduction Using the "RGB" color system, set a mixed color value to color the graph through the values of the three primary colors when drawing, and the format is as follows:

Mixed color value = RGB(red value, green value, blue value)

The "red value", "green value" and "blue value" here are all integers, ranging from 0 to 255, representing the intensity of each color in the mixed color. When the color is reproduced by the computer, it is necessary to linearly process the tristimulus values R, G, and B into a color code that can be accepted by the computer.

For the Hertzian contact deformation used in this embodiment, refer to: Yang Peiran; Numerical Analysis of Fluid Lubrication, National Defense Industry Press, 1998, page 49, in the contact area of Hertz point contact, the two surfaces are pressed against each other, and the gap is 0, outside the contact area , increasing along the radius x from the contact center, the gap H after deformation is

$\mathrm{<span\; class="notranslate">\; h</span>}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; 4</span>}\mathrm{<span\; class="notranslate">\; W</span>}}{\mathrm{<span\; class="notranslate">\; \&pi;</span>}{\mathrm{<span\; class="notranslate">\; E.</span>}}^{<span\; class="notranslate">\; \&prime;</span>}}<span\; class="notranslate">\; [</span>\frac{<span\; class="notranslate">\; |</span>\mathrm{<span\; class="notranslate">\; x</span>}<span\; class="notranslate">\; |</span>}{\mathrm{<span\; class="notranslate">\; b</span>}}\sqrt{\frac{{\mathrm{<span\; class="notranslate">\; x</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}{{\mathrm{<span\; class="notranslate">\; b</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; ln</span>}<span\; class="notranslate">\; (</span>\frac{<span\; class="notranslate">\; |</span>\mathrm{<span\; class="notranslate">\; x</span>}<span\; class="notranslate">\; |</span>}{\mathrm{<span\; class="notranslate">\; b</span>}}<span\; class="notranslate">\; +</span>\sqrt{\frac{{\mathrm{<span\; class="notranslate">\; x</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}{{\mathrm{<span\; class="notranslate">\; b</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; ]</span>$

Among them, E' is the equivalent elastic modulus of the two surfaces, b is the half-width of the contact area, calculated according to the following formula

$\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{{\mathrm{<span\; class="notranslate">\; E.</span>}}^{<span\; class="notranslate">\; \&prime;</span>}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; (</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; v</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}{{\mathrm{<span\; class="notranslate">\; E.</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}}<span\; class="notranslate">\; +</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; v</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}{{\mathrm{<span\; class="notranslate">\; E.</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}}<span\; class="notranslate">\; )</span>$

$\mathrm{<span\; class="notranslate">\; b</span>}<span\; class="notranslate">\; =</span>\sqrt{\frac{\mathrm{<span\; class="notranslate">\; 8</span>}\mathrm{<span\; class="notranslate">\; WR</span>}}{\mathrm{<span\; class="notranslate">\; \&pi;</span>}{\mathrm{<span\; class="notranslate">\; E.</span>}}^{<span\; class="notranslate">\; \&prime;</span>}}}$

Among them, R is the radius of the steel ball, v ₁ and v ₂ are the Poisson's ratio of the upper and lower contact surfaces, E ₁ and E ₂ are the elastic modulus of the upper and lower contact surfaces, all of which can be obtained by looking up the table.

The acquisition steps of the interference image described in this embodiment are as follows:

(1). Turn on the air conditioner in the room where the two-color light oil film lubrication test bench is located, adjust the temperature to 20±1°C, and the relative humidity to 50%±5%, and start the experiment after the temperature and humidity are constant;

(2). Turn on the power supply of computer 105, red and green two-color laser light source 102, servo motor 113 and 3CCD color camera 106;

(3). Apply 30 milliliters of lubricating oil on the surface of the glass disc 108, apply a predetermined load on the loading lever 101, make the steel ball 109 contact with the surface of the glass disc 108, from the center of the contact area along the steel ball radius increase direction, the steel ball 109 The gap with the glass disk 108 is gradually increasing. When coherent light is incident, it conforms to the principle of interference and will produce interference fringes;

(4). Start the computer 105 equipped with the 3CCD color camera 106 supporting image acquisition card, open the image acquisition software, click on the real-time acquisition image, let the two-color laser pass through the rotating frosted glass 103 filter, and enter the coaxial illumination microscope 107 through the optical fiber 104 , aim the coaxial illuminating microscope 107 at the ball-disk contact area, and adjust the focus until the image is clear;

(5). Start the servo motor 113, the servo motor 113 drives the glass disc 108 to rotate, and adjust to the speed to be tested, use the image acquisition software to save the required acquisition image, and analyze the RGB light intensity in the image area where the film thickness needs to be measured value, calculate the normalized relative light intensity values R, G and the relative modulation light intensity difference G-R of the area to be measured;

(6). For the same loading load, adjust the rotating speed of the glass disc 108; or the rotating speed of the same glass disc 108, adjust the loading load, can capture the interference image and analyze the G-R relative modulation light intensity difference in the required film thickness measurement area .

Claims (3)

1. A method for measuring lubricating oil film thickness by two-color light interference, characterized in that the measurement of lubricating oil film thickness is realized by using a two-color light interference oil film lubrication test bench, and its specific measurement steps include: (1) Calculate the three-stimulus value of red-green two-color light interference corresponding to the thickness of the lubricating oil film between the steel ball and the glass disc from 1nm to 4500nm, that is, the relative light intensity distribution of red and green RG in the oil film interference system; use the principle of color addition and color complex According to the equation, the color tristimulus values obtained by 3CCD color cameras with spectral sensitivity characteristics respectively f _R (λ), f _G (λ) and f _B (λ) are $\mathrm{<span\; class="notranslate">\; C</span>}<span\; class="notranslate">\; =</span>\underset{\mathrm{<span\; class="notranslate">\; \&lambda;</span>}}{<span\; class="notranslate">\; \&Integral;</span>}\mathrm{<span\; class="notranslate">\; k</span>}\mathrm{<span\; class="notranslate">\; S</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; \&lambda;</span>}<span\; class="notranslate">\; )</span>{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; h</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; \&lambda;</span>}<span\; class="notranslate">\; )</span>{\mathrm{<span\; class="notranslate">\; f</span>}}_{\mathrm{<span\; class="notranslate">\; C</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; \&lambda;</span>}<span\; class="notranslate">\; )</span>\mathrm{<span\; class="notranslate">\; d</span>}\mathrm{<span\; class="notranslate">\; \&lambda;</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; C</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; R</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; G</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; B</span>}$ Among them, C represents the three stimulus values of R (red), G (green), and B (blue), S (λ) is the spectral energy distribution function of the red and green two-color light source used, k is the adjustment coefficient, and the value range of k is 0 Between 1 and 1, the purpose is to normalize the three stimulus values, I _h (λ) is the interference light intensity at the film thickness h on each band λ, and the interference light intensity I of the glass disk interface is according to the formula to calculate, where Indicates the electric vector of reflected light, m=1,2,..., the subscript 0 represents the glass medium, It is directly reflected from the interface of the glass disk, and other reflected light is reflected and projected by the layers below the glass disk; then along the thickness of the lubricating oil film from 0nm to 4500nm, the normalized light intensity of the green light is subtracted from the normalized light intensity of the red light The two-color modulated light intensity GR is obtained by normalizing the light intensity, and the corresponding change relationship curve between the film thickness and the relative light intensity of G, R, and GR is drawn; There is a one-to-one relationship between the size of the extremum point of the curve and the film thickness, and the corresponding two-color light interference image presents black characteristic stripes at the boundary of each modulation beat; Red and green two-color laser light source, the calculation results show that the optical thickness corresponding to each wave beat in the GR modulation light intensity curve is 1408nm, and each wave beat contains 10 extreme points, and adjacent wave beats are not exactly the same. After calculating the normalized red and green light intensity values of the black characteristic fringe position of the two-color light interference image within the film thickness range of 4500nm, after making the GR modulation light intensity curve, take the 8th and 9th extreme points on each wave of the curve The sum of the absolute values of the light intensity SUM is used as a criterion to distinguish the first three beats. It is found that the SUM value is between 1.0 and 1.8 as the first beat, and the SUM value between 1.8 and 2.8 belongs to the second beat. The value between 2.5 and 3.2 is the third beat, and the eighth extreme point of the first three beats corresponds to the interference orders of monochromatic red light interference (4,4), (8,8), ( 12,12); (2) Measure and record the optical interference image caused by the thickness of the lubricating oil film in the contact area between the steel ball and the glass disc when the sliding speed is greater than 0mm/s, analyze the G-R modulation light intensity curve of the black characteristic stripe closest to the contact center, and calculate the 8th at the same time The sum of the absolute values of the light intensity values of the 1st and 9th extreme points is compared with the calculated SUM value to find out the wave segment to which it belongs, and the interference order of the red light corresponding to the position of the 8th extreme point; and then calculated with the obtained Comparing the film thickness relative light intensity curve of 0-4500nm red light, the specific interference series of the central interference area at this sliding speed can be obtained, so as to determine the specific series of all fringes in the entire interference image, and then calculated by using the interference principle Specific film thickness distribution; use the same method to continuously record the interference images of light caused by the lubricating film in the contact area of the steel ball and the glass disc at different sliding speeds, so as to obtain the interference order and film thickness distribution of the central contact area at different sliding speeds; (3) Measure and record the interference image caused by the lubricating film in the contact area of the steel ball and the glass disc under the load applied by the loading lever, measure and obtain the G-R modulation light intensity curve of the black characteristic stripe closest to the center of the contact area under this load, and use it at the same time The sum of the absolute values of the light intensity values at the 8th and 9th extreme points determines the interference order of the red light corresponding to the position of the 8th extreme point; Comparing the light intensity curves, the specific interference series of the central interference area at this speed can be obtained, so as to determine the specific series of all fringes in the entire interference image, and then use the interference principle to calculate the specific film thickness distribution to realize the measurement of lubricating oil film thickness ; The main structure of the two-color light interference oil film lubrication test bench includes a test bench base, a red and green two-color laser light source, a rotating frosted glass, an optical fiber, a computer, a 3CCD color camera, a coaxial lighting microscope, a glass disc, a steel ball, a loading lever, and a spring tension Gauge, ball holder and servo motor, the base of the test bench is equipped with a glass disk, loading lever and servo motor, the glass disk is a transparent circular structure; a ball holder is placed above one end of the loading lever, and the other end is connected to the spring tension gauge ;Steel balls are fixed on the ball support, and lubricating oil is added to the raceway between the steel balls and the glass disc to form a lubricating oil film; the red and green two-color laser light source is placed on the base of the test bench, and the front side of the red and green two-color laser light source is placed with a rotating ground glass There is an optical fiber between the rotating ground glass and the coaxial illuminating microscope. The light emitted by the red and green laser light source passes through the rotating ground glass and is filtered. The spring tension gauge applies load to the loading lever to measure the thickness of the lubricating oil film under different loads; the servo motor drives the glass plate to rotate on the base of the test bench, and the corresponding speed of the experimental contact area is 0mm/s to 1.5m/s, realizing different speeds of the glass plate The measurement of the lower film thickness; a 3CCD color camera is connected directly above the coaxial illumination microscope, and the 3CCD color camera captures the interference image in real time, and transmits the interference image to a computer equipped with an image acquisition card for display or storage. 2. The method for measuring lubricating oil film thickness by two-color light interferometry according to claim 1, wherein the acquisition process of said two-color modulation light intensity G-R specifically comprises: first storing the interference image by a 3CCD color camera; then recording the rotational speed and/or load, and then obtain and store the red light and green light intensity values in the specified area of the interference image, and output the maximum and minimum values of the red light and green light intensity respectively; use the formula $\mathrm{<span\; class="notranslate">\; G</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; R</span>}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; 2</span>}{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; G</span>}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; G</span>}\mathrm{<span\; class="notranslate">\; m</span>}\mathrm{<span\; class="notranslate">\; a</span>}\mathrm{<span\; class="notranslate">\; x</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; G</span>}\mathrm{<span\; class="notranslate">\; m</span>}\mathrm{<span\; class="notranslate">\; i</span>}\mathrm{<span\; class="notranslate">\; no</span>}}<span\; class="notranslate">\; )</span>}{{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; G</span>}\mathrm{<span\; class="notranslate">\; m</span>}\mathrm{<span\; class="notranslate">\; a</span>}\mathrm{<span\; class="notranslate">\; x</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; G</span>}\mathrm{<span\; class="notranslate">\; m</span>}\mathrm{<span\; class="notranslate">\; i</span>}\mathrm{<span\; class="notranslate">\; no</span>}}}<span\; class="notranslate">\; -</span>\frac{\mathrm{<span\; class="notranslate">\; 2</span>}{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; R</span>}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; R</span>}\mathrm{<span\; class="notranslate">\; m</span>}\mathrm{<span\; class="notranslate">\; a</span>}\mathrm{<span\; class="notranslate">\; x</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; R</span>}\mathrm{<span\; class="notranslate">\; m</span>}\mathrm{<span\; class="notranslate">\; i</span>}\mathrm{<span\; class="notranslate">\; no</span>}}<span\; class="notranslate">\; )</span>}{{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; R</span>}\mathrm{<span\; class="notranslate">\; m</span>}\mathrm{<span\; class="notranslate">\; a</span>}\mathrm{<span\; class="notranslate">\; x</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; R</span>}\mathrm{<span\; class="notranslate">\; m</span>}\mathrm{<span\; class="notranslate">\; i</span>}\mathrm{<span\; class="notranslate">\; no</span>}}}$ Calculate the two-color modulation light intensity G-R of the region. 3. The method for measuring the thickness of lubricating oil film by two-color light interferometry according to claim 1, characterized in that the method for judging the 8th and 9th extreme points in the G-R modulation light intensity curve specifically comprises: first obtaining an interference image The G-R modulation light intensity at the black characteristic interference fringes varies with the pixel coordinates; then find out the positions of all extreme points on the extreme point of the G-R modulation light intensity curve whose absolute value of light intensity is less than 0.5, that is, the 0 area, including and Represents the position where a wave beat ends; secondly, from zone 0 to the contact center, that is, the direction in which the contact gap and film thickness are relatively reduced, a group of adjacent extreme points with approximately equal absolute values near zone 0 are are the 8th and 9th extreme points, where the G-R value is less than 0 is the 8th extreme point, and the value greater than 0 is the 9th extreme point.