CN1971207A - Large-shearing carrier-frequency electronic speckle interference displacement field separating method - Google Patents

Abstract

A separating method for large shear carrier speckle interference displacement field is provided. The separating method is: in the system of shear electron speckle interference, mounts a reference beside the object to be measured, use symmetrical double light beam to illuminate the measuring object and the reference; the speckle interference is realized via large shear optical prism, the deflection of inference is introduced to the carrier modulation stripe; according to the value of deformation, deflects the angular of reference to adjust the spatial frequency to realize the modulation of displacement field; bending deformation of the carrier strip of measuring object is occurred by the deformation of the object; using the method of Fourier transformation, two phase diagrams containing the information of the separation surface and the inner surface displacement is obtained by demodulation; after enveloping the two-phase graphic analysis, the inner surface displacement field and the separation surface field are separated by algebraic computation. The advantages of invention are high quantity of modulation stripe, simple structure and don't need reference light. It can measure dichotomic component of the deformation field of body fast and stably.

Description

Large-shearing carrier-frequency electronic speckle interference displacement field separating method

Technical field

The present invention relates to the separation method of carrier-frequency electronic speckle interference displacement field.

Background technology

Requiring that the shearing electronic speckle interference technology has that light path is simple, automaticity is high, shockproof be low, the direct advantages such as derivative field of Displacement Measurement, is widely used in the Non-Destructive Testing field.Utilize the shearing electronic speckle interference technology of big shearing crystal prism (Wollaston prism) then can realize the displacement measurement of speckle interference, advantage such as having system simply, does not need to introduce specially reference light, and the striped quality is good.Be the interference fringe of high accuracy analysis deformation field, phase-shift method commonly used and carrier wave method realize the phase measurement of deformation field.Compare with phase shifting method, the carrier method of interference fringe spatial modulation does not need accurate phase shift apparatus, and is low to the environmental requirement of measuring, and has the advantage of suitable kinetic measurement, and important value is arranged in actual applications.Because interference of light metering all is based on interference fringe and carries out that displacement field measures, the quality of interference fringe is very big to the influence of measurement result.Particularly interference fringe spatial modulation carrier method more needs the high-contrast striped.The interference fringe contrast that holographic interferometry and moire interference obtain is than higher, and this method is used more in holography and moire interference.This method also is introduced in the electronic speckle pattern interferometry, but the strong noise of speckle striped has limited the development of this technology.In recent years, along with development of digital image, this method has caused people's attention again.

Summary of the invention

The present invention is directed to the deficiency that existing electronic speckle pattern interferometry technology exists, provide a kind of can be fast, the large-shearing carrier-frequency electronic speckle interference displacement field of the Measuring Object deformation field two dimensional component method of separating stably.

Large-shearing carrier-frequency electronic speckle interference displacement field separating method of the present invention is:

In the shearing electronic speckle interference system, will testee the next door place a reference substance, with symmetric double light beam throw light on simultaneously respectively testee and reference substance; Realize speckle interference by big shearing prism, carrier modulation stripe is introduced in reference substance deflection; According to the size of deformation of body, an amount of deflection reference substance angle to regulate spatial frequency, realizes the modulation of displacement field; Testee loading back carrier fringe is subjected to the modulation of deformation of body and occurs bending and deformation; Utilize fourier transform method, demodulation obtains comprising two width of cloth position phasors from face and in-plane displacement information respectively; Behind the two phase diagram envelope, carry out algebraic operation the in-plane displacement field is separated with the acoplanarity displacement field.

The present invention realizes speckle interference by the big prism of shearing, and makes system simple; Carrier modulation stripe is introduced in deflection by reference substance, has obtained high-quality modulation stripe, has the high advantage of fringe contrast.Relation according between spatial frequency and the reference substance deflection angle obtains the modulation of displacement field easily.In conjunction with Fourier transformation method, can the in-plane displacement field be separated with the acoplanarity displacement field by the phase computing of simple position.The present invention proposes big shearing carrier modulation and separate the method for displacement field, it is good to have the modulation stripe quality, and system is simple, does not need advantages such as reference light, can be fast, Measuring Object deformation field two dimensional component stably.

Description of drawings

Fig. 1 is big shearing electronic speckle interference carrier frequency modulation light path synoptic diagram.

Fig. 2 is the carrier fringe figure when loading front lit light 11 illuminated objects.

Fig. 3 is the modulated carrier bar graph when loading back lighting light 11 illuminated objects.

Fig. 4 is the carrier fringe figure when loading front lit light 12 illuminated objects.

Fig. 5 is the modulated carrier bar graph that is subjected to when loading back lighting light 12 irradiating objects after the deformation of body modulation bends.

The envelope position phasor that Fig. 6 demodulates when throwing light on for illumination light 11.

The envelope position phasor that Fig. 7 demodulates when throwing light on for illumination light 12.

Fig. 8 is the distribution plan such as displacement such as grade of isolated horizontal shift component u field.

Fig. 9 is the distribution plan such as displacement such as grade of isolated acoplanarity displacement component w field.

Among the figure: 1, variable spectroscope, 2, catoptron 2,3, video camera, 4, lens, 5, polaroid, 6, shear prism greatly, 7, beam expanding lens 1,8, beam expanding lens 2,9, catoptron 1,10, catoptron 3,11, illumination light 1,12, illumination light 2,13, testee, 14, reference substance.

Embodiment

Embodiment

Big shearing electronic speckle interference carrier frequency modulation light path as shown in Figure 1.Laser beam becomes two bundles through beam split: through variable spectroscope 1, catoptron 9 and beam expanding lens 7, become illumination light 11; Through variable spectroscope 1, catoptron 2, catoptron 10 and beam expanding lens 8, become illumination light 12.Regulate variable spectroscope 1, can make illumination light 11 and illumination light 12 isocandelas.Testee 13 next door fixed placement one reference substance 14, illumination light 11 and illumination light 12 two objects that all can throw light on simultaneously.When illumination light 11 or illumination light 12 illuminated objects, diffusing through excessive shearing prism 6, polaroid 5 of object enters video camera 3 through lens 4 again.

The light beam of normal incidence enters prism 6, and prism 6 produces the picture of two dislocation.Prism 6 and polaroid 5 are placed the camera lens front (see figure 1) of video camera 3, if the error angle of prism 6 is very big, then object self can separate at two pictures that video camera 3 target surfaces form fully owing to misplace, and superimposed with a picture of the reference substance 14 that is placed on the object next door.When incident light is radiated on testee 13 and the reference substance 14 simultaneously, can make the information of 3 while of video camera accepted thing light and reference light with big shearing prism 6, but the polarization direction of thing light and reference light is vertical mutually, for making the different polarized light interference of this two bundle direction of vibration, also will arrange a polaroid 5 behind dislocation prism 6, its polarization direction is at 45 with two optical axises of dislocation prism.Make thing light and reference light information realize that on the target surface of video camera 3 coaxial polarization is relevant like this, and light intensity is almost equal, thereby good result of interference is arranged.

Throws light on respectively by two light beams before the deformation of body, gather the original speckle image that an amplitude object do not load respectively and deposit in the computing machine.Subsequently, corresponding two light beams throw light on respectively and gather the image of object at other states, and each width of cloth image and first width of cloth image subtraction, and the result after subtracting each other is presented on the monitor in real time.Reference substance deflection during this time can be introduced carrier fringe, when object has distortion, carrier fringe be subjected to object distortion modulation and bend.

The interference fringe field becomes carrier fringe intensive, that contain deformation information after the linearity modulation.The carrier fringe of being modulated can be expressed as

I(x，y)＝a(x，y)+b(x，y)cos[Δφ(x，y)+2πf ₀x] (1)

Wherein, a (x y) is the background light intensity, b (x y) is streak amplitude, and b (x, y)/(x y) often is called fringe contrast to a, and (x, the y) phase change that causes for deformation of body promptly wait to ask a phase to Δ φ, and they all are the functions of locus.F in the formula ₀Be reference substance deflection introduce along the axial spatial frequency of x.By theoretical derivation as can be known:

$f_0=\frac{\mathrm{\Δ\α}(1+\cos \mathrm{\θ})}{\mathrm{\λ}}---\left(2\right)$

Wherein, λ is used Wavelength of Laser, and θ is the angle of illumination light and body surface normal, and Δ α is the minute angle that reference substance rotates.

By (1) formula as can be known, the phase-shift phase of the interference fringe of being modulated does not change in time, but with spatial variations.The light intensity expression (1) of carrier fringe on the x direction can be expressed as

I(x，y)＝a(x，y)+c(x，y)exp(j2πf ₀x)+c ^*(x，y)exp(-j2πf ₀x) (3)

Wherein, j represents imaginary part unit, and * represents the conjugation of plural number.C (x y) represents with plural form, for

$c(x,y)=\frac{1}{2}b(x,y)\exp \[\mathrm{j\Δ\φ}(x,y)\]---\left(4\right)$

(x, y) carrying out Fourier transform can obtain to light intensity I at the x direction of principal axis

H(f _x，y)＝A(f _x，y)+C(f _x-f ₀，y)+C ^*(f _x+f ₀，y) (5)

Wherein, A (f _x, y) obtain by background light intensity and low-frequency noise conversion.With suitable wave filter with A (f _x, y) and C ^*(f _x+ f ₀, y) filter, obtain C (f _x-f ₀, it is moved on to initial point after y) and becomes C (f _x, y), do again inverse fourier transform obtain c (x y), can obtain PHASE DISTRIBUTION:

$\mathrm{\Δ\φ}(x,y)={\tan }^{-1}\frac{\mathrm{Im}\[c(x,y)\]}{\mathrm{Re}\[c(x,y)\]}---\left(6\right)$

Wherein, Re and Im represent to get real and imaginary part.The envelope position phase of the variation that is main value in [π, π] that is obtained by formula (6), need separate the envelope computing could be with its serialization.

When illumination light 11 and illumination light 12 difference illuminated objects, phase of light wave changes and the deformation of body pass is

$\mathrm{\Δ}{\mathrm{\φ}}_A(x,y)=\frac{2\mathrm{\π}}{\mathrm{\λ}}\[w(1+\cos \mathrm{\θ})+u\sin \mathrm{\θ}\]---\left(7\right)$

$\mathrm{\Δ}{\mathrm{\φ}}_B(x,y)=\frac{2\mathrm{\π}}{\mathrm{\λ}}\[w(1+\cos \mathrm{\θ})-u\sin \mathrm{\θ}\]---\left(8\right)$

Wherein w be deformation of body along the acoplanarity displacement on the z direction of principal axis, u is that deformation of body is along the in-plane displacement on the x direction of principal axis.What as seen, measure is mixing field.

With formula (7) and formula (8) addition with subtract each other, can get acoplanarity displacement field and in-plane displacement field.

$\mathrm{\Δ}{\mathrm{\φ}}_A(x,y)+\mathrm{\Δ}{\mathrm{\φ}}_B(x,y)=\frac{4\mathrm{\π}}{\mathrm{\λ}}w(1+\cos \mathrm{\θ})---\left(9\right)$

$\mathrm{\Δ}{\mathrm{\φ}}_A(x,y)-\mathrm{\Δ}{\mathrm{\φ}}_B(x,y)=\frac{4\mathrm{\π}}{\mathrm{\λ}}u\sin \mathrm{\θ}---\left(10\right)$

By formula (9) and formula (10) as seen, as long as the phase change of deformation of body when obtaining illumination light 11 and illumination light 12 irradiations respectively, then simple plus and minus calculation is carried out mutually in this two width of cloth position, just acoplanarity displacement field and in-plane displacement field can be separated.

Use light path shown in Figure 1, the measurement of free beam being carried out displacement field with separate, the incident angle of two light beams is 49.4 °, carries out on vibration isolators.The freely-supported beam length is 150mm, highly is 19.50mm, and thickness is 18.50mm, and organic glass is made, and the elastic modulus of material is E=3.4 * 10 ⁹Pa, Poisson ratio is v=0.34.The span that loads is 71.00mm, and difference is carried the about 75N of heap(ed) capacity.Be coated with silver powder on the free beam surface to strengthen reflectivity.

The first two light beam of deformation of body throws light on respectively, gather the original speckle image that an amplitude object do not load respectively and deposit in the computing machine, subsequently the image of Cai Jiing respectively with first width of cloth image subtraction, the relevant striped of the speckle that presents after subtracting each other is presented on the monitor.At first the rotary reference thing is introduced carrier fringe, and object loads then, and carrier fringe is subjected to the modulation of deformation of body and bends.

Fig. 2 is the carrier fringe that obtains when loading front lit light 11 irradiating objects, and Fig. 3 is subjected to the modulated carrier striped after the modulation of deformation of body bends when being loading back lighting light 11 irradiating objects.Fig. 4 is the carrier fringe when loading front lit light 12 irradiating objects, and Fig. 5 is the modulated carrier bar graph that is subjected to when loading back lighting light 12 irradiating objects after the deformation of body modulation bends.Utilize the Fourier transform method to demodulate deformation of body position phase respectively, the envelope position phasor that Fig. 6 and Fig. 7 demodulate when being respectively illumination light 11 and illumination light 12 illuminations.Fig. 6 and Fig. 7 are separated envelope respectively obtain continuous position phasor, two continuous phasor additions, subtract that the back is separable to go out horizontal shift component position phasor and acoplanarity displacement position phasor.According to formula (9) and formula (10), become quantitative displacement field to distribute isolated displacement field phase transition, Fig. 8 is the distribution plan such as displacement such as grade of isolated horizontal shift component u field, Fig. 9 is the distribution plan such as displacement such as grade of isolated acoplanarity displacement component w field.Wherein, length shown in the horizontal direction is the span (71.0mm) of free beam, and vertical direction is freely-supported depth of beam (19.5mm), and the unit of displacement component is a micron.

By the result as seen, utilize big shearing electronic speckle interference system, the carrier fringe contrast height that the method for deflection reference substance is introduced, the effectively deformation field of modulated object.In conjunction with Fourier transformation method, this system can effectively separate mixing field.

Claims (1)

1, a kind of large-shearing carrier-frequency electronic speckle interference displacement field separating method is characterized in that this method is:

In the shearing electronic speckle interference system, will testee the next door place a reference substance, with symmetric double light beam throw light on simultaneously respectively testee and reference substance; Realize speckle interference by big shearing prism, carrier modulation stripe is introduced in reference substance deflection; According to the size of deformation of body, an amount of deflection reference substance angle to regulate spatial frequency, realizes the modulation of displacement field; Testee loading back carrier fringe is subjected to the modulation of deformation of body and occurs bending and deformation; Utilize fourier transform method, demodulation obtains comprising two width of cloth position phasors from face and in-plane displacement information respectively; Behind the two phase diagram envelope, carry out algebraic operation the in-plane displacement field is separated with the acoplanarity displacement field.

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