CN104154870A - Method for measuring thickness of lubricating oil film in double-color-light interference mode - 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 in a double-color-light interference mode. Red-and-green double-color-light interference tristimulus values of the thickness of the lubricating oil film between a steel ball and a glass plate are calculated, then a light interference image caused by the thickness of the lubricating oil film of the contact area of the steel ball and the glass plate under different sliding speeds and different loads is measured and recorded, a G-R modulation light intensity curve of black feature stripes closest to a contact center is analyzed, the specific series of all stripes in the whole interference image are determined, the specific film thickness distribution is obtained by calculation, and the thickness of the lubricating oil film is measured. The measurement process is simple, the measurement efficiency is high, the measuring range three times greater than that of white light interference is obtained, and the oil film thickness distribution of the whole contact area under different sliding speeds and different loads is convenient to measure.

Description

A kind of method of bi-coloured light interferometry oil film thickness

Technical field:

The invention belongs to field of optical measuring technologies, a kind of method that relates to bi-coloured light interferometry oil film thickness, particularly utilize bi-coloured light interfere and Relative light intensity principle measurement mechanical Contact Pair between nanometer to the method for sub-micrometer scale oil film thickness, be applicable to measure the film thickness distribution in the contact region of friction speed, load under elastohydrodynamic lubrication, hydrldynamic pressure lubrication and other lubricating status.

Background technology:

Between mechanical operating part, forming the oil film of adequate thickness, two surface segmentation are come, is to reduce friction, avoids the important means of wearing and tearing.At present, optical interferometry is to measure one of effective method of oil film thickness, and its utilizes the interference fringe forming to calculate oil film thickness and shape.Nineteen sixty-five, the people such as Cameron have proposed the measurement structure of ball-dish contact, utilize interference of light technology first observed to the classical shape of a hoof oil film shape with outlet constriction, opened up photoelastic stream (Optical Elastohydrodynamics) research field, by improvement, glass disc, beam splitter layer (Cr film), bed course (SiO have been determined ₂), the optical measurement configuration of lubricating oil and steel ball, wherein the introducing of light splitting Cr film has greatly improved the contrast of interference fringe, the proposition of cushion layer technique has reduced to survey thickness lower limit.According to the difference of using light source, optical interferometry is divided into monochromatic light interferometric method and White Light Interferometer, monochromatic light interferometric method judges oil film thickness by the variation of light intensity between interference fringe level time counting and analysis light and shade striped, the MBI measurement scheme that the relative light intensity method (ROII) proposing in conjunction with Huangping, Luo Jianbin etc. and the Guo Feng of Qingdao Technological University propose, resolution is 0.85nm, and range reaches 5 μ m; But need to be 0 o'clock serialograph from speed in measurement, from image history, number goes out order of interference, inefficiency so not only, and often can lose level time in high speed kinetic measurement, cause thickness erroneous judgement; White Light Interferometer utilizes the variation of hue coordinate in interference image to calculate oil film thickness, without definite interference fringe level time; But the increase with thickness, the wavelength coverage that forms constructive interference increases, the contrast of interference fringe and color saturation decay are serious, for white light interference, its the highest thickness of surveying is generally no more than 1 μ m, and the precision of measuring depends on strict calibration process, the several factors of calibration process, as the curvature of surface in contact in static demarcating and kinetic measurement will not cause the error of measurement on an equal basis.In order to guarantee that under measuring accuracy condition, raising can be surveyed maximum oil film thickness, researchist also adopts double-colored or three coloured light to measure, actual is the compromise of monochromatic light interference and white light interference, Lord etc. have proposed the pseudo-phase stepping measurement method of interfering based on three coloured light, but due to technical sophistication, be not promoted, the Guo Feng of Qingdao Technological University, State of Zhao builds in the bi-coloured light interference light intensity modulator approach > > measuring at its paper < < oil film thickness and proposes G-R bi-coloured light modulation technology, attempt with an Image Information Processing thickness, avoid monochromatic light to the inferior dependence of history image level, but only utilized a modulating wave to clap the cycle, range is only 1 μ m, can not meet the measurement demand of high thickness, in the extreme point of more crucial the is theoretical adjustment curve calculating of twin-beam and actual measurement, extreme point size deviation is larger, cause the method cannot apply in actual measurement.Therefore, explore a kind of wide range, high precision, measurement is necessary to nano/submicron lubricating oil film thickness to facilitate feasible method.

Summary of the invention:

The object of the invention is to overcome loaded down with trivial details order of interference counting and the little shortcoming of other interference technique ranges of monochromatic light in existing measuring method, seeking design provides a kind of method of bi-coloured light interferometry oil film thickness, optics range can be expanded to 4 μ m, can accurately judge the order of interference of point of fixity by a double-colored interference image, and then utilize monochromatic ruddiness light distribution to realize the dynamically efficient measurement of nano/submicron oil film thickness under variable load between Contact Pair or speed change degree operating mode according to relative light intensity method.

To achieve these goals, the present invention adopts bi-coloured light film lubrication testing table to realize the measurement of oil film thickness, on bi-coloured light film lubrication testing table, be provided with the 3CCD color camera of catching in real time the oil film interference image between steel ball and glass disc Contact Pair, through image card, be transferred to Computer display and storage, its concrete measuring process comprises:

(1), calculate the corresponding red and green color interference of light tristimulus values from 1nm to 4500nm of oil film thickness between steel ball and glass disc, the red green RG relative light intensity of oil film interference system distributes; Utilize color to be added principle and color reproduction equation, sensitive property of spectrum is respectively to f _r(λ), f _g(λ), f _b(λ) color tristimulus values that 3CCD (RGB) color camera of 3CCD color camera obtains is

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

Wherein, C represents R (red), G (green), B (indigo plant) tristimulus values, and S (λ) is the spectral power distribution function of red and green color light source used, k is adjustment factor, the span of k is between 0 to 1, and object is to make the equal normalization of tristimulus values, I _h(λ) for the upper thickness of each wave band λ is the interference light intensity at h place, the interference light intensity I at glass disc interface is according to formula

$I={\left|{\stackrel{\&OverBar;}{E}}_0^{-}\right|}^2={|{\stackrel{\&OverBar;}{E}}_0^{-1}+{\stackrel{\&OverBar;}{E}}_0^{-2}+{\stackrel{\&OverBar;}{E}}_0^{-3}+{\stackrel{\&OverBar;}{E}}_0^{-4}+\&CenterDot;\&CenterDot;\&CenterDot;|}^2={\left|\underset{m=1}{\overset{\&infin;}{\mathrm{\&Sigma;}}}{\stackrel{\&OverBar;}{E}}_0^{-m}\right|}^2$ Calculate, wherein represent catoptrical electricity vector, m=1,2 ..., subscript 0 represents glass medium, direct glass disc boundary reflection, other reflected light all pass through reflection and the projection of the following layer of glass disc, then along oil film thickness, from 0nm, be increased to 4500nm, the normalization light intensity that the normalization light intensity of green glow is deducted to ruddiness obtains bi-coloured light modulation light intensity G-R, and draws out the corresponding variation relation curve map of thickness and G, R, G-R relative light intensity with this, G-R modulation light intensity curve presents the feature of modulating wave to the variation of thickness, the size of this curve extreme point and thickness exist relation one to one, and corresponding bi-coloured light interference image presents black feature striped at each modulating wave bat boundary with it, the centre wavelength adopting is respectively to the red and green color LASER Light Source of 653nm and 532nm, result of calculation shows in G-R modulation light intensity curve that it is 1408nm that each ripple is clapped corresponding optical thickness, each ripple is clapped and is all comprised 10 extreme points, adjacent ripple is clapped not identical, after being calculated to the strong value of normalization red-green glow, the black feature fringe position of bi-coloured light interference image within the scope of the 4500nm thickness calculating makes after G-R modulation light intensity curve, the absolute value sum SUM that gets upper the 8th and the 9th the extreme point light intensity value of each ripple bat of curve distinguishes first three ripple as criterion and claps, find that SUM value is first wave bat between 1.0 to 1.8, SUM value belongs to Second Wave and claps between 1.8 to 2.8, SUM value is that the 3rd ripple is clapped between 2.5 to 3.2, the order of interference that wherein the corresponding monochromatic ruddiness of the 8th extreme point of first three ripple bat is interfered is respectively (4, 4), (8, 8), (12, 12),

(2) the optical interference picture that steel ball when, survey record sliding speed is greater than 0mm/s and glass disc contact region lubricating oil film thickness cause, the G-R modulation light intensity curve of the black feature striped that analysis is nearest apart from contact center, calculate the 8th and the 9th extreme point light intensity value absolute value sum simultaneously and contrast with the SUM value calculating under clap wave band, and the order of interference of the 8th the corresponding ruddiness in extreme point position; Then contrast with the thickness relative light intensity curve of the 0～4500nm ruddiness calculating, draw the concrete interference level of interference region, this sliding speed Xia center, thereby determine streaky concrete progression in whole interference image, then utilize principle of interference to calculate concrete film thickness distribution; Utilize the steel ball of the different sliding speeds of same procedure continuous recording and the interference of light image that glass disc contact region lubricating film causes, thereby obtain different sliding speed Xia center contact region order of interference and film thickness distribution;

(3) interference image that, under survey record loading lever imposed load condition, steel ball and glass disc contact region lubricating film cause, the G-R modulation light intensity curve of the black feature striped that the center, distance contact region under this load of measuring is nearest utilizes the 8th and the 9th extreme point light intensity value absolute value sum to judge the order of interference of the 8th extreme point position correspondence ruddiness simultaneously; Then draw the concrete interference level of interference region, this speed Xia center with thickness-relative light intensity curve comparison of the 0～4500nm ruddiness calculating, thereby can determine streaky concrete progression in whole interference image, then utilize principle of interference to calculate concrete film thickness distribution, realize the measurement of oil film thickness.

The acquisition process of double-colored modulation light intensity G-R of the present invention specifically comprises: first by 3CCD color camera storage interference image; Record again rotating speed and/or load, then obtain ruddiness and green glow light intensity value the storage of interference image appointed area, export respectively maximal value and the minimum value of ruddiness and green glow light intensity; Utilize formula

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

Calculate the double-colored difference light intensity G-R in described region.

In G-R modulation light intensity curve of the present invention, the determination methods of the 8th and the 9th extreme point specifically comprises: the variation of first obtaining the G-R modulation light intensity pixel coordinate at interference image black characteristic interference striped place; Then find out the position that light intensity absolute value on the extreme point of G-R modulation light intensity curve is less than all extreme points of 0.5, i.e. 0th district, comprises and represents that a ripple claps the position of finishing; Secondly, from 0th district to contact center direction, the Contact Pair gap direction that reduce relative to thickness, is the 8th and the 9th extreme point near the nearest approximately equalised one group of adjacent extreme point of order of magnitude in 0th district, wherein G-R value be less than 0 be the 8th extreme point, be greater than 0 be the 9th extreme point.

Bi-coloured light of the present invention interferes the agent structure of film lubrication testing table to comprise testing table base, red and green color LASER Light Source, rotation frosted glass, optical fiber, computing machine, 3CCD color camera, coaxial-illuminating microscope, glass disc, steel ball, loading lever, spring tension meter, ball holder and servomotor, on testing table base, install and be equipped with glass disc, load lever and servomotor, glass disc is transparent circular configuration; The top, one end that loads lever is equipped with ball holder, and other end below is connected with spring tension meter; In ball holder, be fixed with steel ball, on the raceway between steel ball and glass disc, add lubricating oil to form lubricating oil film; Red and green color LASER Light Source is placed on testing table base, the front side of red and green color LASER Light Source is placed with rotation frosted glass, between rotation frosted glass and coaxial-illuminating microscope, be provided with optical fiber, the light that red and green color LASER Light Source is sent is through rotating after frosted glass filtering, through optical fiber, import coaxial-illuminating microscope, final vertical sand shooting is to the microscopical viewing area of coaxial-illuminating; By spring tension meter, to loading lever imposed load, realize the measurement of oil film thickness under different loads; Servomotor drives glass disc rotation on testing table base, corresponding experiment contact region rotating speed be 0mm/s to 1.5m/s, realize the measurement of thickness under glass disc different rotating speeds; Directly over coaxial-illuminating microscope, be connected with 3CCD color camera, 3CCD color camera is caught interference image in real time, and interference image is transferred to demonstration or preservation in the computing machine that image pick-up card is housed.

The present invention compares with the measuring method of other optical interference oil film thicknesses, by the G-R modulation Intensity Analysis of a double-colored interference image feature striped, accurately judge the interference level at minimum thickness place, lubricating contact district, and then can directly according to monochromatic multiple-beam interference principle, calculate thickness h, its measuring process is simple, measurement efficiency is high, avoid monochromatic light under high-speed working condition, to rely on the order of interference counting loss problem of accelerator picture record, get than the range of large 3 times of white light interference, can reach 4 μ m; The oil film thickness of being convenient to measure whole contact region under different sliding speeds and different loads distributes, in Study on Lubrication and engineering reality between Contact Pair oil film thickness measurement a kind of new method is provided.

Accompanying drawing explanation:

Fig. 1 is bi-coloured light film lubrication testing table package assembly principle schematic used in the present invention, comprising testing table base 101, red and green color LASER Light Source 102, rotation frosted glass 103, optical fiber 104, computing machine 105,3CCD color camera 106, coaxial-illuminating microscope 107, glass disc 108, steel ball 109, loading lever 110, spring tension meter 111, ball holder 112 and servomotor 113.

Fig. 2 is the sensitive property of spectrum response curve of the present invention's 3CCD color camera used while realizing, wherein the 21 spectral response curve f that are blue light _b(λ), the 22 spectral response curve f that are green glow _g(λ), the 23 spectral response curve f that are ruddiness _r(λ).

Fig. 3 is the spectral power distribution function of the present invention's red and green color LASER Light Source used while realizing.

Fig. 4 is the present invention's computational data storehouse thickness and the strong R of normalization red-green glow, G and the relative graph of a relation of modulating light intensity G-R while realizing.

Fig. 5 is the red and green color optical interference picture that Pai Bo end that 0-4500nm thickness wedge gap that the present invention calculates while realizing produces presents black feature striped.

Fig. 6 is the static interferogram picture that the embodiment of the present invention is taken with 3CCD color camera.

Fig. 7 is surveyed ball dish hertz contact interference image by the embodiment of the present invention take center as starting point, increases the relative modulation light intensity G-R distribution plan of direction along steel ball radius.

Fig. 8 is ball dish hertz contact measurement result of the present invention and classical hertz of contact theory comparison diagram, and wherein 71 is a hertz contact theory curve, and 72 test and record curve for bi-coloured light interference technique.

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

Figure 10 is that the embodiment of the present invention G-R that radius that first group of nearest black feature striped of contact center represent along image pixel coordinate increases direction that adjusts the distance modulates light intensity analysis chart relatively.

Figure 11 is that the multiple-beam interference of the present invention's multilayer film measuring system used produces schematic diagram.

Embodiment:

Below by embodiment, also the invention will be further described by reference to the accompanying drawings.

Embodiment:

The bi-coloured light that the present embodiment adopts interferes the agent structure of film lubrication testing table to comprise testing table base 101, red and green color LASER Light Source 102, rotation frosted glass 103, optical fiber 104, computing machine 105,3CCD color camera 106, coaxial-illuminating microscope 107, glass disc 108, steel ball 109, load lever 110, spring tension meter 111, ball holder 112 and servomotor 113, on testing table base 101, install and be equipped with glass disc 108, load lever 110 and servomotor 113, glass disc 108 is transparent circular configuration; The top, one end that loads lever 110 is equipped with ball holder 112, and other end below is connected with spring tension meter 111; In ball holder 112, be fixed with steel ball 109, on the raceway between steel ball 109 and glass disc 108, add 30ml lubricating oil to form lubricating oil film; Red and green color LASER Light Source 102 is placed on testing table base 101, the front side of red and green color LASER Light Source 102 is placed with rotation frosted glass 103, between rotation frosted glass 103 and coaxial-illuminating microscope 107, be provided with optical fiber 104, the light that red and green color LASER Light Source 102 is sent is through rotating after frosted glass 103 filtering, through optical fiber 104, import coaxial-illuminating microscope 107, final vertical sand shooting is to the viewing area of coaxial-illuminating microscope 107; By 111 pairs of spring tension meters, load the measurement that lever 110 imposed loads are realized oil film thickness under different loads; Servomotor 113 drives the axle rotation of glass disc 108 on testing table base 101, corresponding experiment contact region rotating speed be 0mm/s to 1.5m/s, realize the measurement of thickness under glass disc different rotating speeds; Directly over coaxial-illuminating microscope 107, be connected with 3CCD color camera 106,3CCD color camera 106 is caught interference image in real time, and interference image is transferred to demonstration or preservation in the computing machine 105 that image pick-up card is housed.

The experimental situation temperature of the present embodiment is 20 ± 1 ℃, and relative humidity is 50% ± 5%; Glass disc 108 is K9 glass disc, and the surface of glass disc 108 adds chromium plating film, and reflectivity is 20%, and roughness Ra is 4nm; The diameter of steel ball 109 is 25.4mm, the accurate polishing surface that the sphere of steel ball 109 is high reflectance, and surface roughness Ra is less than 8nm; The centre wavelength of red and green color LASER Light Source 102 is respectively 653nm and 532nm; Composite lubricating film is air, and refractive index is 1.0; 3CCD color camera 106 is caught the interference image between steel ball 109 and glass disc 108 Contact Pair, is transferred to computing machine 105 shows and storage through image card, and concrete measuring process comprises:

S101: calculate the corresponding red and green color interference of light tristimulus values from 1nm to 4500nm of lubricated air film thickness between steel ball 109 and glass disc 108, the red green RG relative light intensity of oil film interference system distributes; Utilize color to be added principle and color reproduction equation, sensitive property of spectrum shown in Fig. 2 is respectively to f _r(λ), f _g(λ), f _b(λ) color tristimulus values that 3CCD (RGB) color camera 106 obtains is

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

Wherein, C represents R, G, B tristimulus values, and S (λ) is the spectral power distribution function (as shown in Figure 3) of red and green color LASER Light Source 102 used, and k is adjustment factor, and the span of k is between 0 to 1, and object is to make the equal normalization of tristimulus values, I _h(λ) corresponding interference light intensity while being h for the upper thickness of each wave band λ, because the high reflectance of multilayer film medium and steel ball surface causes multiple-beam interference, the interference light intensity of final glass interface according to $I={\left|{\stackrel{\&OverBar;}{E}}_0^{-}\right|}^2={|{\stackrel{\&OverBar;}{E}}_0^{-1}+{\stackrel{\&OverBar;}{E}}_0^{-2}+{\stackrel{\&OverBar;}{E}}_0^{-3}+{\stackrel{\&OverBar;}{E}}_0^{-4}+\&CenterDot;\&CenterDot;\&CenterDot;|}^2={\left|\underset{m=1}{\overset{\&infin;}{\mathrm{\&Sigma;}}}{\stackrel{\&OverBar;}{E}}_0^{-m}\right|}^2$ Calculate, wherein (m=1,2 ...) representing catoptrical electricity vector, subscript 0 represents glass medium, only has directly, from the reflection of chromium-glass interface, other reflected light all pass through reflection and the projection of the following layer of chromium-glass, so just, on multiple-beam interference basis, consider red and green color optical source wavelength, bandwidth and the response of 3CCD color camera, generate the color colourity computational algorithm that a set of complete oil film thickness bi-coloured light is interfered, along air thickness, from 0nm, be increased to 4500nm, the normalization light intensity that the normalization light intensity of green glow is deducted to ruddiness obtains double-colored difference light intensity G-R, draws out the corresponding variation relation curve map of thickness and G, R, G-R relative light intensity, as shown in Figure 4 with this, G-R curve presents the feature of modulation to the variation of thickness, within the scope of certain thickness, there is relation one to one in the size of the extreme point of this curve and thickness, the interference image of corresponding bi-coloured light presents black feature striped at each modulating wave bat boundary with it, as shown in Figure 5, for the centre wavelength adopting, be respectively the red and green color LASER Light Source 102 of 653nm and 532nm, result of calculation shows in G-R modulation light intensity curve that it is 1408nm that each ripple is clapped corresponding optical thickness, each ripple is clapped and is all comprised 10 extreme points, adjacent ripple is clapped not identical, black feature fringe position to bi-coloured light interference image within the scope of 4500nm thickness, after calculating the strong value of normalization red-green glow, make G-R modulation light intensity curve, the absolute value sum SUM that gets upper the 8th and the 9th the extreme point light intensity value of each ripple bat of curve distinguishes first three ripple as criterion and claps, consider the image noise problem in the model color error of calculation and actual measurement application, all the time have SUM value is first wave bat between 1.0 to 1.8, SUM value belongs to Second Wave and claps between 1.8 to 2.8, SUM value is that the 3rd ripple is clapped between 2.5 to 3.2, and the order of interference that first three ripple is clapped the corresponding monochromatic ruddiness interference of the 8th extreme point is respectively (4, 4), (8, 8), (12, 12),

S102: load lever 110 by 111 pairs of spring tension meters and load, keeping the load between steel ball 109 and glass disc 108 is 2N, after coaxial-illuminating microscope 107 is focused and is known to image, with 3CCD color camera 106, take and preserve interference image as Fig. 6, the analysis first group black feature striped nearest apart from contact center increases the G-R modulation light intensity of direction along radius, as shown in Figure 7, calculate the 8th and the 9th extreme point light intensity value absolute value sum is 1.52 simultaneously, the SUM value criterion calculating with theory contrasts, because 1.52 between 1.0 and 1.8, therefore learn that this region belongs to first and claps wave band, and the order of interference of the 8th the corresponding ruddiness of extreme point position coordinate is (4, 4), then along partly radially contact region center position according to the light intensity of ruddiness, change, having 4 interference to grow mutually point disappears a little mutually with 4 interference, therefore show that the concrete interference level of contact center is (0,0), thereby can determine streaky concrete progression in whole interference image, then utilize monochromatic light Relative light intensity principle to calculate concrete film thickness distribution as shown in Figure 8, Fig. 8 shows that the measurement result of institute's put forward the methods and classical hertz contact theory calculated value have good anastomose property,

S103: add 30ml PB1300 lubricating oil on glass disc 108, the density of this lubricating oil is 896kgm ^-3, in the time of 20 ℃, kinetic viscosity is 117Pas, refractive index is 1.502, with spring tension meter 111, continue to load, making the load between steel ball 109 and glass disc 108 is 10N, regulates coaxial-illuminating microscope 107 focal lengths to clear picture, starts servomotor 113, and setting rotating speed is 2.22mm/s, with 3CCD color camera 106, take and preserve interference image as shown in Figure 9, the analysis first group black feature striped nearest apart from contact center increases the G-R modulation light intensity of direction along radius, see Figure 10, calculate the 8th extreme point A and the 9th extreme point B light intensity value absolute value sum is 2.25 simultaneously, its size is between 1.8 and 2.8, therefore learn that this region belongs to second count wave band, the order of interference of knowing thus the 8th the corresponding ruddiness of extreme point position coordinate is (8, 8), because thickness changes continuously, to center, contact region, according to the light intensity of ruddiness, change, number goes out to have the interference number that long point disappears a little mutually with interference mutually can obtain the concrete interference level of interference region, center, and then can determine streaky concrete progression in whole interference image, then utilize monochromatic light Relative light intensity principle to calculate the film thickness value in any care region in image.

Described in the present embodiment, the acquisition process of the strong R of normalization red-green glow, G and red and green color relative difference light intensity G-R specifically comprises:

S201: by 3CCD color camera 106 storage interference images;

S202: obtain and store rotating speed and load to file;

S203: obtain ruddiness and the green glow light intensity value of image appointed area and be saved in file;

S204: maximal value and the minimum value of ruddiness and green glow light intensity in output specified region;

S205: utilize formula

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

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

Calculate the strong R of normalization red-green glow, G and the double-colored relative difference light intensity G-R in described region.

In G-R modulation light intensity curve of the present invention, the determination methods of the 8th and the 9th extreme point specifically comprises: the variation of first obtaining the G-R modulation light intensity pixel coordinate at interference image black characteristic interference striped place; Then find out all extreme points that on the extreme point of G-R modulation light intensity curve, light intensity absolute value is less than 0.5, the position of the point that these G-R light intensity values are very little, i.e. 0th district, comprises and has represented that a ripple claps the position of finishing; Secondly, from 0th district to contact center direction, the Contact Pair gap direction that reduce relative to thickness, is the 8th and the 9th extreme point near the nearest approximately equalised one group of adjacent extreme point of order of magnitude in 0th district, wherein G-R value be less than 0 be the 8th extreme point, be greater than 0 be the 9th extreme point.

The computing reference document of the multiple-beam interference light intensity that the present embodiment relates to " Guo Feng, golden cypress woods; The large range measuring system of micro-nano lubricated thickness, tribology journal 2004, the 17 volumes, the third phase, the 521st page; Be Guo F.and Wong P.L., 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; optics measuring of oil film system is 4 layers of Medium Optics system that are comprised of glass, chromium, oil and steel; each dielectric layer is labeled as q=0～3; at the boundary of q and q+1, all light reflection electric vectors and light transmission electric vector, by incident and synthetic two classes of reflections propagate direction, are denoted as respectively with subscript plus sige or minus sign represent the direction of propagation, and subscript represents that light propagates in medium wherein number (as 0 being glass), oil and the electric vector of steel boundary to steel propagation, represent the electric vector of incident light, represent the electric vector of emergent light; The refractive index of medium q is designated as

${\stackrel{\&OverBar;}{n}}_q=n_q-{\mathrm{ik}}_q,$ q＝0～3

N wherein _qreal part refractive index, k _qbe attenuation coefficient, for optically transparent medium, attenuation coefficient is zero; At the intersection of dielectric layer q and q+1, effective reflection coefficient writing

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

Reflection coefficient with there is following relation:

${\stackrel{\&OverBar;}{R}}_{q-1}=\frac{{\stackrel{\&OverBar;}{r}}_{q-1}+{\stackrel{\&OverBar;}{R}}_q\exp (-{i2\stackrel{\&OverBar;}{\mathrm{\&delta;}}\mathrm{}}_q)}{1+{\stackrel{\&OverBar;}{r}}_{q-1}{\stackrel{\&OverBar;}{R}}_q\exp (-{i2\stackrel{\&OverBar;}{\mathrm{\&delta;}}}_q)}$

Wherein q is the thickness of dielectric layer q, and λ is incident light wavelength, fei Nier reflection coefficient, because not having transmission to only have reflection at steel ball surface, therefore have according to above formula, can obtain successively the reflectance of hierarchical system or interference strength are defined as the ratio of reflected light radiation energy to incident light radiation energy, or the strength ratio of reflected light to incident light, by formula calculate and obtain multiple-beam interference light intensity or reflectivity, from 0nm, start to oil film thickness d ₂assignment successively, obtains the relation of thickness and multiple-beam interference light intensity.

The order of interference of any point in the interference image that the present embodiment relates to is defined as (δ, β), the dark order of interference of wherein putting between n level dark fringe and n+1 level dark fringe is δ=n, and the bright order of interference of putting between n level bright fringes and n+1 level bright fringes is β=n; If interfere the order of interference (δ that judges certain reference point in the interference image that ruddiness is corresponding by bi-coloured light, β), because thickness changes continuously, the growth and decline that order of interference is interfered along with ruddiness are also continuous variations, therefore can determine the order of interference of other point in interference image.

The monochromatic light multiple-beam interference Relative light intensity principle that the present embodiment relates to is measured thickness list of references " Wang Xuefeng, Guo Feng, Yang Peiran; Nano/micron bullet stream oil film thickness measuring system, tribology journal 2006, the 26th volume, the 2nd phase, 150th～154 pages ", in the interference of light, interference strength be take λ/(2n) with thickness and is changed in the cycle; λ is wavelength; n is medium refraction index, and to arbitrary oil film thickness h, all unique corresponding order of interference is the oil film thickness h of (β=0; δ=0) or (β=0, δ=1) ₀(this place is defined as 0 grade of oil film thickness), both have identical interference strength, and its relation meets following formula

$h=h_0+\mathrm{\&beta;}\frac{\mathrm{\&lambda;}}{2n}$

In formula: h is oil film thickness, h ₀0 grade of oil film thickness, i.e. the oil film thickness of β=0 o'clock, λ is wavelength, and n is the refractive index of lubricating oil, and β is the bright order of interference of putting between n level bright fringes and n+1 level bright fringes; 0 grade of thickness h ₀can be calculated by multiple-beam interference light intensity with the relation curve of normalized interference strength.So calculating thickness by multiple-beam interference is exactly the normalization light intensity of extracting image, according to increasing range lookup, go out 0 grade of corresponding thickness, then class adds that the number of cycles thickness of β λ/2n obtains final thickness; Wherein obtaining of measurement point order of interference β is crucial, monochromatic light is measured, by increasing Entrainment Velocity since 0 gradually, increased thickness and obtain, need whole process under cameras record, but oil film at a high speed changes, may there is the inferior loss of level, cause thickness miscount; The present embodiment goes out the order of interference of any point in interference image by the feature fringe analysis of bi-coloured light, and does not rely on historical record, thus the level time loss of avoiding the loaded down with trivial details of order of interference counting and may occurring.

The present embodiment, according to interference of light principle, when the optical path difference Δ of two bundle coherent lights is the even-multiple of incident light half-wavelength, is strengthened after two light wave stacks, occurs bright fringes; When the optical path difference Δ of two bundle coherent lights is the odd-multiple of incident light half-wavelength, after two light wave stacks, weaken, there is dark fringe; If optical path difference increases continuously from 0, will produce light and dark interference fringe, the degree of light and shade light strong representation, be understood that, the light intensity value that fixing thickness is corresponding unique, but corresponding periodic a plurality of thickness of fixing light intensity value, the concept that therefore proposes order of interference is distinguished; In membrane thickness measuring system from the two-beam of steel ball 109 surface and glass disc 108 surface reflections from a branch of incident light, meet the coherent condition of light, and the thickness between steel ball 109 and glass disc 108 changes continuously, so can produce light and dark interference fringe.

Described in the present embodiment, the accounting equation of color reproduction is referring to " Yu Daoyin, Tan Hengying; China Machine Press 2006, the 80th page "; Utilize " Red-Green-Blue " model and color reproduction equation, sensitive property of spectrum is respectively to f _r(λ), f _g(λ), f _b(λ) color tristimulus values that camera sensor obtains is

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

Wherein, C represents R, G, B color tristimulus values, and S (λ) is the spectral power distribution function of red and green color light source used, and k is normalization coefficient, the span of k between 0 to 1, I _h(λ) interference light intensity that is h height for the upper thickness of each wave band λ.

Described in the present embodiment, color is added principle referring to " Yu Daoyin, Tan Hengying; China Machine Press 2006, the 79th page "; The RGB tristimulus values of color mixture is the corresponding tristimulus values sum of each component color, and color F matching equation is expressed as F=R+G+B; According to the replacement rate of Jim Glassman blend of colors, if there are two color of light R1, G1, B1 and R2, G2, after B2 is added and mixes, the tristimulus values of mixed light is

$\left\{\begin{array}{c}R=R_1+R_2\\ G=G_1+G_2\\ B=B_1+B_2\end{array}\right.$

The tristimulus values of color mixture is each component color tristimulus values sum.

Described in the present embodiment, color computing machine reproducing method is referring to " Zhou Guangmei, Guo Feng, Li Hongsheng; The characteristic research of lubricating oil film bi-coloured light interferometer measuration system, Acta Optica 2012, the 32nd volume, the 3rd phase, article numbering 0312006 ", color reproduction adopts " RGB " color system; during mapping, by trichromatic value, a kind of blend color value being set is pattern coloring, and form is as follows:

Blend color value=RGB (red value, green value, blue valve)

Here " red value ", " green value ", " blue valve " are integer, and span is 0～255, represent the intensity of each color in blend color.When computer color reappears, tristimulus values R, G, B need to be carried out to linear process, become the color code that can accept for computing machine.

The present embodiment hertz juxtaposition metamorphose used is referring to Yang Peiran; Fluid lubrication numerical analysis, National Defense Industry Press 1998, the 49th page, in the contact region of hertz point contact, two surfaces compress mutually, and gap is 0, outside contact region, from contact center along radius x, increases, and distortion post gap H is

$H=\frac{4W}{\mathrm{\&pi;}{E}^{\&prime;}}[\frac{\left|x\right|}{b}\sqrt{\frac{x^2}{b^2}-1}-\ln (\frac{\left|x\right|}{b}+\sqrt{\frac{x^2}{b^2}-1})]$

Wherein, E' is the equivalent elastic modulus on two surfaces, and b is contact region half-breadth, according to following formula, calculates

$\frac{1}{E^{\&prime;}}=\frac{1}{2}(\frac{1-v_1^2}{E_1}+\frac{1-v_2^2}{E_2})$

$b=\sqrt{\frac{8\mathrm{WR}}{\mathrm{\&pi;}{E}^{\&prime;}}}$

Wherein, R is steel ball radius, v ₁, v ₂for the Poisson ratio of upper and lower surface in contact, E ₁, E ₂elastic modulus for upper and lower surface in contact, all can obtain by tabling look-up.

Described in the present embodiment, the obtaining step of interference image is as follows:

(1). open bi-coloured light film lubrication testing table place room air conditioner, regulate temperature for being 20 ± 1 ℃, relative humidity 50% ± 5%, starts experiment after temperature and humidity is constant;

(2). open the power supply of computing machine 105, red and green color LASER Light Source 102, servomotor 113 and 3CCD color camera 106;

(3). on glass disc 108 surfaces, smear 30 milliliters of lubricating oil, on loading lever 101, apply predetermined load, make steel ball 109 and glass disc 108 Surface Contacts, from center, contact region along steel ball radius, increase direction, gap between steel ball 109 and glass disc 108 is increasing gradually, when coherent light incident, meet principle of interference, will produce interference fringe;

(4). start the computing machine 105 that 3CCD color camera 106 matching Image Acquisition Boards are housed, open image capture software, click real-time image acquisition, allow two-color laser pass after 103 filtering of rotation frosted glass, through optical fiber 104, incide in coaxial-illuminating microscope 107, by coaxial-illuminating microscope 107 alignment with the ball dish contact regions, focus to clear picture;

(5). start servomotor 113, servomotor 113 drives glass disc 108 to rotate, and be adjusted to the rotating speed that needs test, with image capture software, preserve required collection image, and analyze the rgb light need to measure thickness image-region and be worth by force, calculate normalization relative light intensity value R, the G and the relative light intensity difference G-R that modulates that need measured zone;

(6). to same loaded load, regulate the rotating speed of glass disc 108; Or the rotating speed of same glass disc 108, regulates loaded load, the G-R that all can catch interference image and analyze required film thickness measured zone modulates light intensity difference relatively.

Claims (4)

1. a method for bi-coloured light interferometry oil film thickness, is characterized in that adopting bi-coloured light film lubrication testing table to realize the measurement of oil film thickness, and its concrete measuring process comprises:

(1), calculate the corresponding red and green color interference of light tristimulus values from 1nm to 4500nm of oil film thickness between steel ball and glass disc, the red green RG relative light intensity of oil film interference system distributes; Utilize color to be added principle and color reproduction equation, sensitive property of spectrum is respectively to f _r(λ), f _g(λ), f _b(λ) color tristimulus values that 3CCD (RGB) color camera of 3CCD color camera obtains is

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

Wherein, C represents R (red), G (green), B (indigo plant) tristimulus values, and S (λ) is the spectral power distribution function of red and green color light source used, k is adjustment factor, the span of k is between 0 to 1, and object is to make the equal normalization of tristimulus values, I _h(λ) for the upper thickness of each wave band λ is the interference light intensity at h place, the interference light intensity I at glass disc interface is according to formula

$I={\left|{\stackrel{\&OverBar;}{E}}_0^{-}\right|}^2={|{\stackrel{\&OverBar;}{E}}_0^{-1}+{\stackrel{\&OverBar;}{E}}_0^{-2}+{\stackrel{\&OverBar;}{E}}_0^{-3}+{\stackrel{\&OverBar;}{E}}_0^{-4}+\&CenterDot;\&CenterDot;\&CenterDot;|}^2={\left|\underset{m=1}{\overset{\&infin;}{\mathrm{\&Sigma;}}}{\stackrel{\&OverBar;}{E}}_0^{-m}\right|}^2$ Calculate, wherein represent catoptrical electricity vector, m=1,2 ..., subscript 0 represents glass medium, direct glass disc boundary reflection, other reflected light all pass through reflection and the projection of the following layer of glass disc, then along oil film thickness, from 0nm, be increased to 4500nm, the normalization light intensity that the normalization light intensity of green glow is deducted to ruddiness obtains double-colored modulation light intensity G-R, and draws out the corresponding variation relation curve map of thickness and G, R, G-R relative light intensity with this, G-R modulation light intensity curve presents the feature of modulating wave to the variation of thickness, the size of this curve extreme point and thickness exist relation one to one, and corresponding bi-coloured light interference image presents black feature striped at each modulating wave bat boundary with it, the centre wavelength adopting is respectively to the red and green color LASER Light Source of 653nm and 532nm, result of calculation shows in G-R modulation light intensity curve that it is 1408nm that each ripple is clapped corresponding optical thickness, each ripple is clapped and is all comprised 10 extreme points, adjacent ripple is clapped not identical, after being calculated to the strong value of normalization red-green glow, the black feature fringe position of bi-coloured light interference image within the scope of the 4500nm thickness calculating makes after G-R modulation light intensity curve, the absolute value sum SUM that gets upper the 8th and the 9th the extreme point light intensity value of each ripple bat of curve distinguishes first three ripple as criterion and claps, find that SUM value is first wave bat between 1.0 to 1.8, SUM value belongs to Second Wave and claps between 1.8 to 2.8, SUM value is that the 3rd ripple is clapped between 2.5 to 3.2, the order of interference that wherein the corresponding monochromatic ruddiness of the 8th extreme point of first three ripple bat is interfered is respectively (4, 4), (8, 8), (12, 12),

(2) the optical interference picture that steel ball when, survey record sliding speed is greater than 0mm/s and glass disc contact region lubricating oil film thickness cause, the G-R modulation light intensity curve of the black feature striped that analysis is nearest apart from contact center, calculate the 8th and the 9th extreme point light intensity value absolute value sum simultaneously and contrast with the SUM value calculating under clap wave band, and the order of interference of the 8th the corresponding ruddiness in extreme point position; Then contrast with the thickness relative light intensity curve of the 0～4500nm ruddiness calculating, draw the concrete interference level of interference region, this sliding speed Xia center, thereby determine streaky concrete progression in whole interference image, then utilize principle of interference to calculate concrete film thickness distribution; Utilize the steel ball of the different sliding speeds of same procedure continuous recording and the interference of light image that glass disc contact region lubricating film causes, thereby obtain different sliding speed Xia center contact region order of interference and film thickness distribution;

(3) interference image that, under survey record loading lever imposed load condition, steel ball and glass disc contact region lubricating film cause, the G-R modulation light intensity curve of the black feature striped that the center, distance contact region under this load of measuring is nearest utilizes the 8th and the 9th extreme point light intensity value absolute value sum to judge the order of interference of the 8th extreme point position correspondence ruddiness simultaneously; Then draw the concrete interference level of interference region, this speed Xia center with thickness-relative light intensity curve comparison of the 0～4500nm ruddiness calculating, thereby determine streaky concrete progression in whole interference image, then utilize principle of interference to calculate concrete film thickness distribution, realize the measurement of oil film thickness.

2. the method for bi-coloured light interferometry oil film thickness according to claim 1, is characterized in that the acquisition process of described double-colored modulation light intensity G-R specifically comprises: first by 3CCD color camera storage interference image; Record again rotating speed and/or load, then obtain ruddiness and green glow light intensity value the storage of interference image appointed area, export respectively maximal value and the minimum value of ruddiness and green glow light intensity; Utilize formula

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

Calculate the double-colored modulation light intensity G-R in described region.

3. the method for bi-coloured light interferometry oil film thickness according to claim 1, is characterized in that the determination methods of the 8th and the 9th extreme point in described G-R modulation light intensity curve specifically comprises: the variation of first obtaining the G-R modulation light intensity pixel coordinate at interference image black characteristic interference striped place; Then find out the position that light intensity absolute value on the extreme point of G-R modulation light intensity curve is less than all extreme points of 0.5, i.e. 0th district, comprises and represents that a ripple claps the position of finishing; Secondly, from 0th district to contact center direction, the Contact Pair gap direction that reduce relative to thickness, is the 8th and the 9th extreme point near the nearest approximately equalised one group of adjacent extreme point of order of magnitude in 0th district, wherein G-R value be less than 0 be the 8th extreme point, be greater than 0 be the 9th extreme point.

4. the method for bi-coloured light interferometry oil film thickness according to claim 1, the agent structure that it is characterized in that described bi-coloured light interference film lubrication testing table comprises testing table base, red and green color LASER Light Source, rotation frosted glass, optical fiber, computing machine, 3CCD color camera, coaxial-illuminating microscope, glass disc, steel ball, loading lever, spring tension meter, ball holder and servomotor, on testing table base, install and be equipped with glass disc, load lever and servomotor, glass disc is transparent circular configuration; The top, one end that loads lever is equipped with ball holder, and other end below is connected with spring tension meter; In ball holder, be fixed with steel ball, on the raceway between steel ball and glass disc, add lubricating oil to form lubricating oil film; Red and green color LASER Light Source is placed on testing table base, the front side of red and green color LASER Light Source is placed with rotation frosted glass, between rotation frosted glass and coaxial-illuminating microscope, be provided with optical fiber, the light that red and green color LASER Light Source is sent is through rotating after frosted glass filtering, through optical fiber, import coaxial-illuminating microscope, final vertical sand shooting is to the microscopical viewing area of coaxial-illuminating; By spring tension meter, to loading lever imposed load, realize the measurement of oil film thickness under different loads; Servomotor drives glass disc rotation on testing table base, corresponding experiment contact region rotating speed be 0mm/s to 1.5m/s, realize the measurement of thickness under glass disc different rotating speeds; Directly over coaxial-illuminating microscope, be connected with 3CCD color camera, 3CCD color camera is caught interference image in real time, and interference image is transferred to demonstration or preservation in the computing machine that image pick-up card is housed.