CN105371778A - Real-time measurement method and system for digital cutting speckle interference - Google Patents

Abstract

The embodiment of the invention provides a real-time measurement method and system for digital cutting speckle interference, and relates to the measurement field. The method comprises the steps: employing a laser as a light source, enabling polarized light outputted by the light source to be filtered and expanded through a spatial filter and a beam expander, and then enabling the light to irradiate the surface of a measurement target; enabling the light from the surface of the measurement target to pass through a first polarizing film, and forming linearly polarized light; enabling the linearly polarized light to pass through a Wollaston prism cutting apparatus, and enabling ordinary light o and extraordinary light e to pass through a second polarizing film; forming a speckle interference graph through the mutual interference of the ordinary light o and extraordinary light e; collecting an imaged speckle interference graph through a CCD (charge coupling device), and obtaining at least two collected speckle interference graphs in a time sequence; carrying out the image subtraction of at least two collected speckle interference graphs, and generating at least one subtracted speckle interference graph; and displaying at least one subtracted speckle interference graph.

Description

The method for real-time measurement that Surface profiling is interfered and system

Technical field

The present invention relates to laser speckle interference measuring field, particularly relate to method for real-time measurement and the system of the interference of a kind of Surface profiling.

Background technology

When laser is radiated at the body surface with diffuse reflective nature, superposes at spatial coherence from the light of body surface reflection, will interfere in whole space, form speck and the blackening of stochastic distribution, be called laser speckle.Early 1970s, interferometry method of laser speckle is developed, it except have holographic interferometry method noncontact, can intuitively provide except the series of advantages such as whole audience situation, also there is light path simple, less demanding to surface of test piece, lower to requirement for experiment condition, the features such as convenience of calculation.

Electronic speckle pattern interferometry (ESPI) is just widely used in diffuser surface displacement or deformation monitoring in the beginning of this century.It has, and precision is high, the whole audience, the advantages such as noncontact.ESPI technology has just been widely used since appearance. and its application has displacement and deformation measurement, strain analysis, dynamic test, nondestructive examination etc.The characteristics such as the various distortion in work machine field, vibration, impact, surfaceness, rigidity and hardness can be applied to; Detect surface or the inherent vice of compound substance, integrated circuit, pressure vessel and welding object, and may be used for the deformation measurement of civil structure and water conservancy projects.In a word, ESPI has very important status and wide prospect at machinery, building, water conservancy, electrical equipment, Aero-Space, weapon industry and biomedical sector.

The limitation of ESPI is: due to the introducing of reference light, makes the optical path difference of object light and reference light comparatively large, therefore requires higher to the coherent length of light source; In actual applications, often need the physical quantity such as strain and amount of deflection obtaining object, and ESPI can only measure ohject displacement, needs to be further processed experimental data, this has a certain impact to precision; In some application, require higher to the anti-seismic performance of measuring system, and ESPI is higher for noise signal susceptibility.For ESPI Problems existing, there is Speckle shearing interferometry.

Speckle shearing interferometry is proposed by Hung and Leendertz at first, and they are studied the speckle-shearing interferometry system based on wollaston prism and Michelson interferometer respectively.In research, they obtain speckle-shearing interferometry figure, and have set forth relative theory and key issue.After this, this technology is introduced into engineering field, and is named as Speckle shearing interferometry (Shearography).

Speckle shearing interferometry directly can be measured the first differential of displacement (strain), eliminates the differential calculation after measuring displacement, simplifies data handling procedure, has very great help to raising measuring accuracy.Its way of realization has a lot, and based in the measuring system of wollaston prism, field angle is relatively larger, and without the need to introducing reference light, and antijamming capability is comparatively strong, without the need to special shock insulation, and can test under not light protected environment, have stronger practical value.

But, in prior art, can not measure in real time object.

Summary of the invention

The embodiment provides method for real-time measurement and the system of the interference of a kind of Surface profiling, can measure in real time measurement object.

To achieve these goals, this invention takes following technical scheme.

On the one hand, the method for real-time measurement providing a kind of Surface profiling to interfere, comprising:

Use laser instrument as light source, the polarized light exported by described light source carries out filtering through spatial filter and beam expander and after expanding, is radiated at the surface of measurement target;

The reflected light on described measurement target surface, through the first polaroid, forms linearly polarized light;

Described linearly polarized light is through Wollaston prism shear, and described Wollaston prism shear makes every Shu Suoshu linearly polarized light be cut into polarization direction mutually perpendicular ordinary light o light and non-ordinary light e light;

Described ordinary light o light and described non-ordinary light e light are through the second polaroid, and described second polaroid makes described ordinary light o light consistent with described non-ordinary light e polarisation of light direction;

Described ordinary light o light and described non-ordinary light e light form speckle interference figure through mutually interfering, and described speckle interference figure images on charge coupled cell CCD through imaging lens;

Described charge coupled cell CCD gathers the described speckle interference figure of imaging, the speckle interference figure after at least two width obtained in time series gather;

Image subtraction is carried out to the speckle interference figure after described at least two width collections, generate at least one subtract each other after speckle interference figure;

Display described at least one subtract each other after speckle interference figure.

Described image subtraction is carried out to the speckle interference figure after described at least two width collections, generate at least one subtract each other after the step of speckle interference figure comprise:

Speckle interference figure after 2nd width to N width collection is deducted respectively the first width gather after speckle interference figure, obtain at least one subtract each other after speckle interference figure, N is the total quantity of speckle interference figure after gathering, N be greater than 1 natural number.

Described method also comprises:

To described at least one subtract each other after the light intensity of every bit of speckle interference figure carry out Fourier transform, obtain spectrogram;

According to described spectrogram, what obtain described measurement target is being parallel to the time-based phase changing capacity in described light source direction;

According to the time-based phase changing capacity of described measurement target, calculate described measurement target and be parallel to the displacement variable along with the time in described light source direction;

Be parallel to the displacement variable along with the time in described light source direction according to described measurement target, calculating the described measurement target of generation and be parallel to the strain in described light source direction.

Describedly be parallel to the displacement variable along with the time in described light source direction according to described measurement target, calculating and generate described measurement target and be parallel to the step of the strain in described light source direction according to following formulae discovery:

$\frac{\∂w}{\∂x}(x,y,t)=\frac{\mathrm{\Δ}(x,y,t)}{4\mathrm{\π}}\·\mathrm{\λ}\·\frac{1}{\mathrm{\Δ}x};$

Wherein, for measurement target is being parallel to the strain in described light source direction, Δ x represents the shearing displacement in x direction; λ represents the wavelength of light source; Δ (x, y, t) is being parallel to the displacement variable along with the time in described light source direction for measurement target.

On the other hand, the real-time measurement system providing a kind of Surface profiling to interfere, comprising:

Laser instrument, spatial filter and beam expander, the first polaroid, Wollaston prism shear, the second polaroid, imaging lens and charge coupled cell CCD, computing machine;

Described laser instrument is used for, as light source, and polarization light output;

Described spatial filter and beam expander are used for, and the polarized light exported by described light source carries out filtering and after expanding, is radiated at the surface of measurement target;

Described first polaroid is used for, and makes the reflected light on described measurement target surface after described first polaroid, forms linearly polarized light;

Described Wollaston prism shear is used for, and carries out Wollaston prism shearing to described linearly polarized light, makes every Shu Suoshu linearly polarized light be cut into polarization direction mutually perpendicular ordinary light o light and non-ordinary light e light;

Described second polaroid is used for, and make described ordinary light o light and described non-ordinary light e light after described second polaroid, polarization direction is consistent;

Described charge coupled cell CCD and imaging lens are used for, and described ordinary light o light and described non-ordinary light e light are interfered through mutual the speckle interference figure formed, images on charge coupled device ccd by imaging lens;

Described computing machine is used for, control the described speckle interference figure that described charge coupled cell CCD gathers imaging, speckle interference figure after at least two width obtained in time series gather, image subtraction is carried out to the speckle interference figure after described at least two width collections, generate at least one subtract each other after speckle interference figure; At least one speckle interference figure after subtracting each other described in display.

Described computing machine carries out image subtraction to the speckle interference figure after described at least two width collections, generate at least one subtract each other after speckle interference figure be specially:

Speckle interference figure after 2nd width to N width collection is deducted respectively the first width gather after speckle interference figure, obtain at least one subtract each other after speckle interference figure, N is the total quantity of speckle interference figure after gathering, N be greater than 1 natural number.

Described computing machine also for;

To described at least one subtract each other after the light intensity of every bit of speckle interference figure carry out Fourier transform, obtain spectrogram;

According to described spectrogram, what obtain described measurement target is being parallel to the time-based phase changing capacity in described light source direction;

According to the time-based phase changing capacity of described measurement target, calculate described measurement target and be parallel to the displacement variable along with the time in described light source direction;

Be parallel to the displacement variable along with the time in described light source direction according to described measurement target, calculating the described measurement target of generation and be parallel to the strain in described light source direction.

Described according to described phase changing capacity, calculate the described measurement target of generation and be parallel to the strain in described light source direction specifically according to following formula:

$\frac{\∂w}{\∂x}(x,y,t)=\frac{\mathrm{\Δ}(x,y,t)}{4\mathrm{\π}}\·\mathrm{\λ}\·\frac{1}{\mathrm{\Δ}x};$

Wherein, for measurement target be parallel in described light source direction strain, Δ x represents the shearing displacement in x direction; λ represents the wavelength of light source; Δ (x, y, t) is being parallel to the displacement variable along with the time in described light source direction for measurement target.

The technical scheme provided as can be seen from the embodiment of the invention described above, in the embodiment of the present invention, can measure measurement object in real time.

The aspect that the present invention adds and advantage will part provide in the following description, and these will become obvious from the following description, or be recognized by practice of the present invention.

Accompanying drawing explanation

In order to be illustrated more clearly in the technical scheme of the embodiment of the present invention, below the accompanying drawing used required in describing embodiment is briefly described, apparently, accompanying drawing in the following describes is only some embodiments of the present invention, for those of ordinary skill in the art, under the prerequisite not paying creative work, other accompanying drawing can also be obtained according to these accompanying drawings.

Fig. 1 is the process flow diagram of the method for real-time measurement that Surface profiling of the present invention is interfered.

Fig. 2 is the connection layout of the real-time measurement system that Surface profiling of the present invention is interfered.

Fig. 3 is the index path based on the heterodyne speckle-shearing interferometry measuring system of Wollaston prism in application scenarios of the present invention.

Fig. 4 is wollaston prism schematic diagram in application scenarios of the present invention.

Embodiment

Be described below in detail embodiments of the present invention, the example of described embodiment is shown in the drawings, and wherein same or similar label represents same or similar element or has element that is identical or similar functions from start to finish.Being exemplary below by the embodiment be described with reference to the drawings, only for explaining the present invention, and can not limitation of the present invention being interpreted as.

Those skilled in the art of the present technique are appreciated that unless expressly stated, and singulative used herein " ", " one ", " described " and " being somebody's turn to do " also can comprise plural form.Should be further understood that, the wording used in instructions of the present invention " comprises " and refers to there is described feature, integer, step, operation, element and/or assembly, but does not get rid of and exist or add other features one or more, integer, step, operation, element, assembly and/or their group.Should be appreciated that, when we claim element to be " connected " or " coupling " to another element time, it can be directly connected or coupled to other elements, or also can there is intermediary element.In addition, " connection " used herein or " coupling " can comprise wireless connections or couple.Wording "and/or" used herein comprises one or more arbitrary unit listing item be associated and all combinations.

Those skilled in the art of the present technique are appreciated that unless otherwise defined, and all terms used herein (comprising technical term and scientific terminology) have the meaning identical with the general understanding of the those of ordinary skill in field belonging to the present invention.Should also be understood that those terms defined in such as general dictionary should be understood to have the meaning consistent with the meaning in the context of prior art, unless and define as here, can not explain by idealized or too formal implication.

For ease of the understanding to the embodiment of the present invention, be further explained explanation below in conjunction with accompanying drawing for several specific embodiment, and each embodiment does not form the restriction to the embodiment of the present invention.

As shown in Figure 1, be the method for real-time measurement that a kind of Surface profiling of the present invention is interfered, comprise:

Step 11, use laser instrument as light source, the polarized light exported by described light source carries out filtering through spatial filter and beam expander and after expanding, is radiated at the surface of measurement target;

Step 121, the reflected light on described measurement target surface, through the first polaroid, forms linearly polarized light;

Step 13, described linearly polarized light is through Wollaston prism shear, and described Wollaston prism shear makes every Shu Suoshu linearly polarized light be cut into polarization direction mutually perpendicular ordinary light o light and non-ordinary light e light; Ordinary o light is separated in space with unusual e light, and therefore on object, the very e light of any ordinary o light and another point after the shearing can at space coincidence.That is, object is a bit divided into 2 points after wollaston prism; 2 of space become a bit after wollaston prism.

Step 14, described ordinary light o light and described non-ordinary light e light are through the second polaroid, and described second polaroid makes described ordinary light o light consistent with described non-ordinary light e polarisation of light direction;

Step 15, described ordinary light o light and described non-ordinary light e light form speckle interference figure through mutually interfering, and described speckle interference figure images on charge coupled cell CCD through imaging lens;

Step 16, described charge coupled cell CCD gathers the described speckle interference figure of imaging, the speckle interference figure after at least two width obtained in time series gather;

Step 17, carries out image subtraction to the speckle interference figure after described at least two width collections, generate at least one subtract each other after speckle interference figure;

Step 18, display described at least one subtract each other after speckle interference figure.

Step 17 comprises:

Speckle interference figure after 2nd width to N width collection is deducted respectively the first width gather after speckle interference figure, obtain at least one subtract each other after speckle interference figure, N is the total quantity of speckle interference figure after gathering, N be greater than 1 natural number.

Described method also comprises:

Step 19, to described at least one subtract each other after the light intensity of every bit of speckle interference figure carry out Fourier transform, obtain spectrogram;

Step 110, according to described spectrogram, what obtain described measurement target is being parallel to the time-based phase changing capacity in described light source direction;

Step 111, according to the time-based phase changing capacity of described measurement target, calculates described measurement target and is being parallel to the displacement variable along with the time in described light source direction;

Step 112, is being parallel to the displacement variable along with the time in described light source direction according to described measurement target, calculates the described measurement target of generation and is being parallel to the strain in described light source direction.

Step 112 is according to following formulae discovery:

$\frac{\∂w}{\∂x}(x,y,t)=\frac{\mathrm{\Δ}(x,y,t)}{4\mathrm{\π}}\·\mathrm{\λ}\·\frac{1}{\mathrm{\Δ}x};$

Wherein, for measurement target is being parallel to the strain in described light source direction, Δ x represents the shearing displacement in x direction; λ represents the wavelength of light source; Δ (x, y, t) is being parallel to the displacement variable along with the time in described light source direction for measurement target.In this step, set up coordinate system in advance, to be parallel to light source direction for X-axis, perpendicular to the plane setup Y-axis of light source direction and Z axis.

As shown in Figure 2, be the real-time measurement system that a kind of Surface profiling of the present invention is interfered, comprise:

Laser instrument 21, spatial filter and beam expander 22, first polaroid 23, Wollaston prism shear 24, second polaroid 25, imaging lens 26 and charge coupled cell CCD27, computing machine 28;

Described laser instrument 21 for, as light source, export polarized light;

Described spatial filter and beam expander 22 for, the polarized light exported by described light source carries out filtering and after expanding, is radiated at the surface of measurement target;

Described first polaroid 23 for, make the reflected light on described measurement target surface after described first polaroid, formed linearly polarized light;

Described Wollaston prism shear 24 for, Wollaston prism shearing is carried out to described linearly polarized light, makes every Shu Suoshu linearly polarized light be cut into polarization direction mutually perpendicular ordinary light o light and non-ordinary light e light;

Described second polaroid 25 for, make described ordinary light o light and described non-ordinary light e light after described second polaroid, polarization direction is consistent;

Described charge coupled cell CCD27 and imaging lens 26 for, by described ordinary light o light and described non-ordinary light e light through mutually interfering the speckle interference figure formed, image on charge coupled device ccd by imaging lens;

Described computing machine 28 for, control the described speckle interference figure that described charge coupled cell CCD gathers imaging, speckle interference figure after at least two width obtained in time series gather, image subtraction is carried out to the speckle interference figure after described at least two width collections, generate at least one subtract each other after speckle interference figure; At least one speckle interference figure after subtracting each other described in display.

Described computing machine carries out image subtraction to the speckle interference figure after described at least two width collections, generate at least one subtract each other after speckle interference figure be specially:

Speckle interference figure after 2nd width to N width collection is deducted respectively the first width gather after speckle interference figure, obtain at least one subtract each other after speckle interference figure, N is the total quantity of speckle interference figure after gathering, N be greater than 1 natural number.

Described computing machine 28 also for;

To described at least one subtract each other after the light intensity of every bit of speckle interference figure carry out Fourier transform, obtain spectrogram;

According to described spectrogram, what obtain described measurement target is being parallel to the time-based phase changing capacity in described light source direction;

According to the time-based phase changing capacity of described measurement target, calculate described measurement target and be parallel to the displacement variable along with the time in described light source direction;

Be parallel to the displacement variable along with the time in described light source direction according to described measurement target, calculating the described measurement target of generation and be parallel to the strain in described light source direction.

Described according to described phase changing capacity, calculate the described measurement target of generation and be parallel to the strain in described light source direction specifically according to following formula:

$\frac{\∂w}{\∂x}(x,y,t)=\frac{\mathrm{\Δ}(x,y,t)}{4\mathrm{\π}}\·\mathrm{\λ}\·\frac{1}{\mathrm{\Δ}x};$

Wherein, for measurement target be parallel in described light source direction strain, Δ x represents the shearing displacement in x direction; λ represents the wavelength of light source; Δ (x, y, t) is being parallel to the displacement variable along with the time in described light source direction for measurement target.

The present invention does not need the displacement of specifically measuring object, can obtain the deformation gradient of object.

Application scenarios of the present invention is below described.

The method for real-time measurement that Surface profiling based on Wollaston prism of the present invention is interfered, comprises following step:

Step one: select output frequency to be that the laser instrument of ω is as light source;

Step 2: the linearly polarized light of output carries out filtering through spatial filter and beam expander and after expanding, is radiated at the surface of measurement target.Linearly polarized light has three relatively independent measurement subsystems, be respectively X in face, Y-direction measurement subsystem and from face Z-direction measurement subsystem.This measuring system can be measured from face Z-direction.

Step 3: the reflected light after light is radiated at measurement target surface carries measurement target surface deformation information.Reflected light, through the first polaroid P1, makes the polarization direction of reflected light consistent.

Step 4: the linearly polarized light after polaroid P1 is through shear.Shear used in this measuring system is Wollaston prism, and after Wollaston prism, light beam is cut into the two mutually perpendicular o light in bundle polarization direction and e light.

Step 5: the two bundle mutually perpendicular o light in polarization direction and e light are through the second polaroid P2, and polarization direction is consistent, two bundle polarized lights interfere formation speckle interference figure mutually.

Step 6: image on CCD by this speckle interference figure, carries out gathering and data processing with computing machine.

Step 7: utilize image subtraction program, all deducts the first width every piece image that the second width starts, obtains the figure after subtracting each other.Can Real Time Observation conoscope image on computers, there is butterfly plaque-like striped in the defective region of measurement target, the information such as the defect of object can be obtained in real time by observing butterfly macules.

Step 8: carry out Fourier transform to the speckle pattern that CCD obtains with computing machine, obtains spectrogram, obtains the time-based phase changing capacity of object, thus calculate the first order derivative of time-based deformation and the strain of object by spectrogram.

Current Surface profiling measurement mechanism all cannot complete the real-time measurement to object.The present invention is by a set of time domain cutting speckle measuring system, complete the direct measurement to object the Grade of Distance, and the Real Time Observation to measurement target defect, there is feature that is real-time, accurate, anti-interference, can the defect of inspected object in real time, directly measure the strain of object.

That is, the present invention is directed to Problems existing in speckle-shearing interferometry measurement, propose the real-time direct measuring method of the strain of a kind of object and defect.A kind of Surface profiling based on Wollaston prism of the present invention interferes method for real-time measurement, in conjunction with the advantage of temporal speckle, the real time dynamic measurement that Surface profiling is interfered can be completed, not only have outside untouchable, the advantage such as high precision, high sensitivity and measurement of full field of measurement, also may correspond to straighten and connect measurement and the feature such as structure is simple, become the effective tool measuring the object informations such as ohject displacement, strain, defect, vibrations and roughness.In addition, along with the develop rapidly in the fields such as mechanical industry, Aero-Space and national defense industry, speckle interference measuring technique is had higher requirement, can the defect displacement of real―time precision measurment testee and strain (displacement gradient) very important, the present invention solves this problem well.

Below invention thought of the present invention and principle are introduced.

1. the Grade of Distance is measured:

Single beam throws light under little shearing displacement condition, and Surface profiling interference system can measure the Grade of Distance.When light path illumination direction and x-z with y-z two planes are all parallel, measuring system is to two in-plane displacement Graded factor with all insensitive, wherein, for light is in y-z plane, in-plane displacement gradient when shear direction is x direction, for light is in x-z plane, in-plane displacement gradient when shear direction is x direction.Therefore, the Grade of Distance can be isolated separately in the case be light in x-y plane, the Grade of Distance when shear direction is x direction.Adopt similar light path arrangement, after adjustment shear direction, just can obtain etc. the Grade of Distance of multiple directions, be light in x-y plane, the Grade of Distance when shear direction is y direction.

2. an internal strain is measured:

Face internal strain can be represented by formula 2-1:

$\begin{array}{cc}& {\mathrm{\ϵ}}_x=\frac{\∂u}{\∂x}\\ {\mathrm{\ϵ}}_y=\frac{\∂v}{\∂y}& \end{array}---\left(2-1\right)$

${\mathrm{\γ}}_{xy}=\frac{\∂v}{\∂x}+\frac{\∂u}{\∂y}$

Wherein, ε _x, ε _yand ε _zbe respectively normal strain, u, v, w are the displacement in x, y, z direction respectively;

be light in x-z plane, in-plane displacement gradient when shear direction is x direction;

be light in y-z plane, in-plane displacement gradient when shear direction is y direction;

be light in y-z plane, in-plane displacement gradient when shear direction is x direction;

be light in x-z plane, in-plane displacement gradient when shear direction is y direction.

Under single beam lighting condition, the factor of the Grade of Distance can not be zero, so can not isolate in-plane displacement gradient.But, under twin-beam lighting condition, can by this factor cancellation.Suppose that illumination twin-beam is about y-z plane symmetry, then the phase place change that two-beam produces can be expressed as:

${\mathrm{\Δ}}_1=\left(\frac{2\mathrm{\π}}{\mathrm{\λ}}\right)(\left(\sin \mathrm{\α}\right)\frac{\∂u}{\∂x}+(1+cos\mathrm{\α})\frac{\∂\mathrm{\ω}}{\∂x})\mathrm{\Δ}x---(2-2)$

${\mathrm{\Δ}}_2=\left(\frac{2\mathrm{\π}}{\mathrm{\λ}}\right)((-sin\mathrm{\α})\frac{\∂u}{\∂x}+(1+cos\mathrm{\α})\frac{\∂\mathrm{\ω}}{\∂x})\mathrm{\Δ}x---(2-3)$

Equation (2-2) and (2-3) subtract each other, and obtain the difference Δ of phase place change _d:

${\mathrm{\Δ}}_d={\mathrm{\Δ}}_1-{\mathrm{\Δ}}_2=\left(\frac{4\mathrm{\π}}{\mathrm{\λ}}\right)\left(sin\mathrm{\α}\right)\left(\frac{\∂u}{\∂x}\right)\mathrm{\Δ}x---(2-4)$

Wherein, Δ ₁it is the phase place change that light beam produces; Δ ₂it is the phase place change that the second bundle light produces; Δ _dfor the phase differential of two-beam;

be light in x-y plane, the Grade of Distance when shear direction is x direction;

Δ x is the shearing displacement in x direction.

Phase difference _dwith the normal strain component ε in equation 1-1 _xcorresponding.After illumination direction and shear direction are regulated, separable go out any direction face in normal strain, and can to calculate shearing strain.

3. strain and space displacement gradient:

Stain vector S can be expressed from the next:

$S=\left[\begin{array}{ccc}{\mathrm{\ϵ}}_x& {\mathrm{\γ}}_{xy}& {\mathrm{\γ}}_{xz}\\ {\mathrm{\γ}}_{yx}& {\mathrm{\ϵ}}_y& {\mathrm{\γ}}_{yz}\\ {\mathrm{\γ}}_{zx}& {\mathrm{\γ}}_{zy}& {\mathrm{\ϵ}}_z\end{array}\right]$

$=\left[\begin{array}{ccc}\frac{\∂u}{\∂x}& \frac{1}{2}\left(\frac{\∂u}{\∂y}+\frac{\∂v}{\∂x}\right)& \frac{1}{2}\left(\frac{\∂u}{\∂z}+\frac{\∂w}{\∂x}\right)\\ \frac{1}{2}\left(\frac{\∂v}{\∂x}+\frac{\∂u}{\∂y}\right)& \frac{\∂v}{\∂y}& \frac{1}{2}\left(\frac{\∂v}{\∂z}+\frac{\∂w}{\∂y}\right)\\ \frac{1}{2}\left(\frac{\∂w}{\∂x}+\frac{\∂u}{\∂z}\right)& \frac{1}{2}\left(\frac{\∂w}{\∂y}+\frac{\∂v}{\∂z}\right)& \frac{\∂w}{\∂z}\end{array}\right]---3-1)$

Wherein, ε _x, ε _yand ε _zfor normal strain, γ _xy, γ _xz, γ _yx, γ _yz, γ _zxand γ _zyfor shear strain.Because the space displacement gradient about z direction directly can not be measured by Surface profiling interferometry, therefore, only have in strain matrix directly measure by Surface profiling interferometry.The present invention is to the Grade of Distance measure, it can be reflected in speckle-shearing interferometry striped.

Wherein, u, v, w are the displacement in x, y, z direction respectively;

be light in x-z plane, in-plane displacement gradient when shear direction is x direction;

be light in x-z plane, in-plane displacement gradient when shear direction is y direction;

be light in y-z plane, in-plane displacement gradient when shear direction is x direction;

be light in y-z plane, in-plane displacement gradient when shear direction is y direction;

be light in x-y plane, the Grade of Distance when shear direction is x direction;

be light in x-y plane, the Grade of Distance when shear direction is y direction.

4. striped formation basic theory and explanation

Cutting speckle image intensity can be expressed from the next:

Wherein, I is the testee surface speckle pattern light intensity that CCD image planes receive; I ₀for background light intensity; γ is the modulation visibility of speckle pattern, for random phase distribution.

After body surface generation miniature deformation, I can respective change be I (t):

Wherein, Δ (t) represents the time dependent phase place change because deformation produces.

Due to random phase the unknown, so directly cannot find out useful information from speckle image.But, if two width speckle patterns are carried out subtraction, random phase will be eliminated, the pattern after subtracting each other will be rendered as the bar graph comprising deformation data:

Wherein, the corresponding number of cycles Δ of dark fringe=2n π (n=0,1,2 ...), the corresponding semiperiod Δ of bright fringes=(2n+1) π (n=0,1,2 ...).

Δ in formula is the phase place change produced due to deformation in t.

The phase place of speckle interference figure is determined by formula (4-4):

Wherein, λ is optical maser wavelength, and n is medium refraction index, and L is the optical path difference of two-beam line, for phase constant.

To the differentiate of (4-4) formula, can obtain:

$\mathrm{\Δ}\mathrm{\φ}=\frac{\∂\mathrm{\φ}}{\∂\mathrm{\λ}}\mathrm{\Δ}\mathrm{\λ}+\frac{\∂\mathrm{\φ}}{\∂n}\mathrm{\Δ}n+\frac{\∂\mathrm{\φ}}{\∂L}\mathrm{\Δ}L=-\frac{2\mathrm{\π}nL}{{\mathrm{\λ}}^2}\mathrm{\Δ}\mathrm{\λ}+\frac{2\mathrm{\π}L}{\mathrm{\λ}}\mathrm{\Δ}n+\frac{2\mathrm{\π}n}{\mathrm{\λ}}\mathrm{\Δ}L---\left(4-5\right)$

Wherein, Δ φ represents phase changing capacity, Δ λ, and Δ n and Δ L then represents the variable quantity of optical maser wavelength, medium refraction index and two-beam linear light path difference respectively.

Due under common experimental conditions, the change of optical maser wavelength and medium refraction index (in air n=1) can be left in the basket, so (4-5) formula can be reduced to:

$\mathrm{\Δ}\mathrm{\φ}=\frac{2\mathrm{\π}}{\mathrm{\λ}}\mathrm{\Δ}L=\frac{2\mathrm{\π}}{\mathrm{\λ}}(A\mathrm{\Δ}u+B\mathrm{\Δ}v+C\mathrm{\Δ}w)---(4-6)$

Wherein, Δ u, Δ v and Δ w represent three components of displacement vector respectively, and A, B and C are geometric relationship factor of influence, and they are by light source coordinates S (x _s, y _s, z _s) and camera coordinates O (x _o, y _o, z _o) determine, definition is as follows:

$\begin{array}{c}A=\frac{\left(x-x_0\right)}{\sqrt{x_0^2+y_0^2+z_0^2}}+\frac{\left(x-x_s\right)}{\sqrt{x_s^2+y_s^2+z_s^2}}\\ B=\frac{\left(y-y_0\right)}{\sqrt{x_0^2+y_0^2+z_0^2}}+\frac{\left(y-y_s\right)}{\sqrt{x_s^2+y_s^2+z_s^2}}\\ C=\frac{\left(z-z_0\right)}{\sqrt{x_0^2+y_0^2+z_0^2}}+\frac{\left(z-z_s\right)}{\sqrt{x_s^2+y_s^2+z_s^2}};\end{array}---\left(4-7\right)$

When shearing occurs in x direction, (4-7) formula can be rewritten as:

$\mathrm{\Δ}\mathrm{\φ}=\frac{2\mathrm{\π}}{\mathrm{\λ}}\left(A\frac{\mathrm{\Δ}u}{\mathrm{\Δ}x}+B\frac{\mathrm{\Δ}v}{\mathrm{\Δ}x}+C\frac{\mathrm{\Δ}w}{\mathrm{\Δ}x}\right)\mathrm{\Δ}x---(4-8)$

Wherein Δ x represents the distance of two points on object plane that image planes are interfered mutually, the shearing displacement namely on x direction.

Under little shearing displacement condition, the Difference Terms in differential term expression (4-8) can be used:

$\mathrm{\Δ}\mathrm{\φ}=\frac{2\mathrm{\π}}{\mathrm{\λ}}\left(A\frac{\∂u}{\∂x}+B\frac{\∂v}{\∂x}+C\frac{\∂w}{\∂x}\right)\mathrm{\Δ}x---(4-9)$

Wherein with represent displacement component u, v and w partial derivative in the x direction respectively, namely displacement component is at the spatial gradient in x direction.

If shear and occur in y direction, then formula (2-11) is corresponding becomes:

$\mathrm{\Δ}\mathrm{\φ}=\frac{2\mathrm{\π}}{\mathrm{\λ}}\left(A\frac{\∂u}{\∂y}+B\frac{\∂v}{\∂y}+C\frac{\∂w}{\∂y}\right)\mathrm{\Δ}y---(4-10)$

Wherein Δ y represents the shearing displacement of measuring system in y direction.

If illumination and receiving trap are all parallel to z-axis, then sensitive factor A and B can be regarded as 0.Therefore, according to formula (4-10), coordinate is that the point of (x, y) can be expressed as at the Grade of Distance of t and the relation of phase place change:

$\frac{\∂w}{\∂x}(x,y,t)=\frac{\mathrm{\Δ}(x,y,t)}{4\mathrm{\π}}\·\mathrm{\λ}\·\frac{1}{\mathrm{\Δ}x}---(4-11)$

Wherein, Δ x represents the shearing displacement in x direction, and λ represents optical maser wavelength.According to formula (4-11), known the Grade of Distance is directly proportional to phase changing capacity.

Reference path figure, in time executing stressed to measurement object, measuring object can deform, and comprises xyz tri-directions.Native system can measure the distortion in z direction.Applying pressure is a lasting process, and the time is longer, and the power of applying is larger, and the distortion of z is larger.Δ (x, y, t) measures the displacement variable of object in z-axis direction along with the time.

Concerning one occur lateral shift disk, stripe represents respectively with can be regarded as the level line of the Grade of Distance.

5. the relation of phase place and change in displacement, is shown in formula.

$\mathrm{\Δ}\mathrm{\φ}=\frac{2\mathrm{\π}}{\mathrm{\λ}}\mathrm{\Δ}L---(5-1)$

Δ φ is phase place, and Δ L is the displacement of being referred to as.

6. line strain

When in rectangular coordinate, cell cube of getting is regular hexahedron, the length of three orthogonal seamed edges before being deformed after knots modification and the ratio of former length, be defined as line strain, represent with ε.A bit be respectively ε in the line strain in x, y, z direction _x, ε _x, ε _y, ε _z.Line strain is just to extend, and shortens to negative.

7. shear strain

Two orthogonal seamed edges of cell cube, right angle knots modification after deformation, is defined as angular strain or shear strain, represents with γ.A bit in x-y direction, the shear strain in z-x direction, y-z direction, point adding Wei γ _xy, γ _yz, γ _zx.Shear strain is just reduced to right angle, otherwise is negative.

8. as shown in Figure 4, wollaston prism is bonded by two pieces of orthogonal right-angle prisms of optical axis.Because prism material is biaxial crystal (as quartz), the light of vertical incidence will be cut into the two-beam line propagated along different directions.

The light entering wollaston prism from left side can be regarded as the combination of the orthogonal two-beam line of direction of vibration (ordinary light o light and extraordinary ray e light).When it impinges perpendicularly on left side right-angle prism, because incident direction is vertical with optical axis, so the direction of propagation deviation does not occur, but because birefringece crystal is for the refractive index difference of two-beam, so o light and e light are respectively with v _oand v _epropagate.When o light and e light are transmitted to adhesive interface, because right side prismatic light direction of principal axis opposing left prism have rotated 90 °, so time on the left of o light in prism and e light become e light and o light respectively, refractive index is also by n _oand n _ebecome n _eand n _o.Wollaston material is used to be quartz herein, for quartz, n _o<n _e, according to refraction law, on adhesive interface, e depends the propagation of nearly normal direction alone, and o light is propagated away from normal direction, and therefore, two-beam separates certain angle in the prism of right side, and direction of vibration is mutually vertical.When two-beam line shines air from wollaston prism, birefringence will be there is.According to Snell's law, the angle expression formula of two-beam line is:

θ＝2sin ^-1[(n _e-n _o)tanβ](8-1)；

Wherein, θ is splitting angle; β is the angle of wedge of wollaston prism.

The shearing displacement Δ x=2*L*tan (θ) in x direction, L are the distance of Wollaston prism to CCD, by measuring the θ of L and acquisition, can obtain the shearing displacement in x direction.

From wollaston prism beam splitting principle, any on object plane will present two pictures misplaced in image planes, and namely produce shearing, shear direction is determined by the optical axis direction of wollaston prism.Two-beam due to outgoing is the orthogonal line polarisation of direction of vibration, therefore, this two-beam be made to produce and interfere, must add a polaroid, make the polarization direction of its polarization direction and two-beam all at 45 ° after prism.

Due to the two-beam Xian Gong road after being sheared by wollaston prism, so this element has extremely strong antijamming capability.In addition, compare other shears, its optical efficiency is higher, and field range is larger.The shortcoming of wollaston prism is Phasor comparison difficulty, is not suitable for utilizing four-stepped switching policy to calculate.Sequence speckle interference service time technology herein, without the need to carrying out phase-shift operations, avoids the shortcoming of phase shift difficulty when using wollaston prism.Therefore, adopt wollaston prism as shear herein.

One of ordinary skill in the art will appreciate that: accompanying drawing is the schematic diagram of an embodiment, the module in accompanying drawing or flow process might not be that enforcement the present invention is necessary.

As seen through the above description of the embodiments, those skilled in the art can be well understood to the mode that the present invention can add required general hardware platform by software and realizes.Based on such understanding, technical scheme of the present invention can embody with the form of software product the part that prior art contributes in essence in other words, this computer software product can be stored in storage medium, as ROM/RAM, magnetic disc, CD etc., comprising some instructions in order to make a computer equipment (can be personal computer, server, or the network equipment etc.) perform the method described in some part of each embodiment of the present invention or embodiment.

Each embodiment in this instructions all adopts the mode of going forward one by one to describe, between each embodiment identical similar part mutually see, what each embodiment stressed is the difference with other embodiments.Especially, for device or system embodiment, because it is substantially similar to embodiment of the method, so describe fairly simple, relevant part illustrates see the part of embodiment of the method.Apparatus and system embodiment described above is only schematic, the wherein said unit illustrated as separating component or can may not be and physically separates, parts as unit display can be or may not be physical location, namely can be positioned at a place, or also can be distributed in multiple network element.Some or all of module wherein can be selected according to the actual needs to realize the object of the present embodiment scheme.Those of ordinary skill in the art, when not paying creative work, are namely appreciated that and implement.

The above; be only the present invention's preferably embodiment, but protection scope of the present invention is not limited thereto, is anyly familiar with those skilled in the art in the technical scope that the present invention discloses; the change that can expect easily or replacement, all should be encompassed within protection scope of the present invention.Therefore, protection scope of the present invention should be as the criterion with the protection domain of claim.

Claims (8)

1. a method for real-time measurement for Surface profiling interference, is characterized in that, comprising:

Use laser instrument as light source, the polarized light exported by described light source carries out filtering through spatial filter and beam expander and after expanding, is radiated at the surface of measurement target;

The reflected light on described measurement target surface, through the first polaroid, forms linearly polarized light;

Described linearly polarized light is through Wollaston prism shear, and described Wollaston prism shear makes every Shu Suoshu linearly polarized light be cut into polarization direction mutually perpendicular ordinary light o light and non-ordinary light e light;

Described ordinary light o light and described non-ordinary light e light are through the second polaroid, and described second polaroid makes described ordinary light o light consistent with described non-ordinary light e polarisation of light direction;

Described ordinary light o light and described non-ordinary light e light form speckle interference figure through mutually interfering, and described speckle interference figure images on charge coupled cell CCD through imaging lens;

Described charge coupled cell CCD gathers the described speckle interference figure of imaging, the speckle interference figure after at least two width obtained in time series gather;

Image subtraction is carried out to the speckle interference figure after described at least two width collections, generate at least two subtract each other after speckle interference figure;

Display described at least one subtract each other after speckle interference figure.

2. method according to claim 1, is characterized in that, describedly carries out image subtraction to the speckle interference figure after described at least two width collections, generate at least one subtract each other after the step of speckle interference figure comprise:

Speckle interference figure after 2nd width to N width collection is deducted respectively the first width gather after speckle interference figure, obtain at least one subtract each other after speckle interference figure, N is the total quantity of speckle interference figure after gathering, N be greater than 1 natural number.

3. method according to claim 1, is characterized in that, described method also comprises:

To described at least one subtract each other after the light intensity of every bit of speckle interference figure carry out Fourier transform, obtain spectrogram;

According to described spectrogram, what obtain described measurement target is being parallel to the time-based phase changing capacity in described light source direction;

According to the time-based phase changing capacity of described measurement target, calculate described measurement target and be parallel to the displacement variable along with the time in described light source direction;

Be parallel to the displacement variable along with the time in described light source direction according to described measurement target, calculating the described measurement target of generation and be parallel to the strain in described light source direction.

4. method according to claim 3, it is characterized in that, describedly be parallel to the displacement variable along with the time in described light source direction according to described measurement target, calculating and generate described measurement target and be parallel to the step of the strain in described light source direction according to following formulae discovery:

$\frac{\&part;w}{\&part;x}(x,y,t)=\frac{\mathrm{\&Delta;}(x,y,t)}{4\mathrm{\&pi;}}\&CenterDot;\mathrm{\&lambda;}\&CenterDot;\frac{1}{\mathrm{\&Delta;}x};$

Wherein, for measurement target is being parallel to the strain in described light source direction, Δ x represents the shearing displacement in x direction; λ represents the wavelength of light source; Δ (x, y, t) is being parallel to the displacement variable along with the time in described light source direction for measurement target.

5. a real-time measurement system for Surface profiling interference, is characterized in that, comprising:

Laser instrument, spatial filter and beam expander, the first polaroid, Wollaston prism shear, the second polaroid, imaging lens and charge coupled cell CCD, computing machine;

Described laser instrument is used for, and as light source, exports polarized light;

Described spatial filter and beam expander are used for, and the polarized light exported by described light source carries out filtering and after expanding, is radiated at the surface of measurement target;

Described first polaroid is used for, and makes the reflected light on described measurement target surface after described first polaroid, forms linearly polarized light;

Described Wollaston prism shear is used for, and carries out Wollaston prism shearing to described linearly polarized light, makes every Shu Suoshu linearly polarized light be cut into polarization direction mutually perpendicular ordinary light o light and non-ordinary light e light;

Described second polaroid is used for, and make described ordinary light o light and described non-ordinary light e light after described second polaroid, polarization direction is consistent;

Described charge coupled cell CCD and imaging lens are used for, and described ordinary light o light and described non-ordinary light e light are interfered through mutual the speckle interference figure formed, images on charge coupled device ccd by imaging lens;

Described computing machine is used for, control the described speckle interference figure that described charge coupled cell CCD gathers imaging, speckle interference figure after at least two width obtained in time series gather, image subtraction is carried out to the speckle interference figure after described at least two width collections, generate at least one subtract each other after speckle interference figure; At least one speckle interference figure after subtracting each other described in display.

6. system according to claim 5, is characterized in that, described computing machine carries out image subtraction to the speckle interference figure after described at least two width collections, generate at least one subtract each other after speckle interference figure be specially:

Speckle interference figure after 2nd width to N width collection is deducted respectively the first width gather after speckle interference figure, obtain at least one subtract each other after speckle interference figure, N is the total quantity of speckle interference figure after gathering, N be greater than 1 natural number.

7. system according to claim 5, is characterized in that, described computing machine also for;

To described at least one subtract each other after the light intensity of every bit of speckle interference figure carry out Fourier transform, obtain spectrogram;

According to described spectrogram, what obtain described measurement target is being parallel to the time-based phase changing capacity in described light source direction;

According to the time-based phase changing capacity of described measurement target, calculate described measurement target and be parallel to the displacement variable along with the time in described light source direction;

Be parallel to the displacement variable along with the time in described light source direction according to described measurement target, calculating the described measurement target of generation and be parallel to the strain in described light source direction.

8. system according to claim 7, is characterized in that, described according to described phase changing capacity, calculates the described measurement target of generation and is being parallel to the strain in described light source direction specifically according to following formula:

$\frac{\&part;w}{\&part;x}(x,y,t)=\frac{\mathrm{\&Delta;}(x,y,t)}{4\mathrm{\&pi;}}\&CenterDot;\mathrm{\&lambda;}\&CenterDot;\frac{1}{\mathrm{\&Delta;}x};$

Wherein, for measurement target be parallel in described light source direction strain, Δ x represents the shearing displacement in x direction; λ represents the wavelength of light source; Δ (x, y, t) is being parallel to the displacement variable along with the time in described light source direction for measurement target.