CN100439857C - Displacement Field Separation Method of Large Shear Carrier Frequency Electron Speckle Interference Displacement Field - Google Patents

Abstract

The invention provides a large shear carrier frequency electron speckle interference displacement field separation method. The separation method is as follows: in the shearing electronic speckle interference system, a reference object is placed next to the measured object, and the measured object and the reference object are illuminated simultaneously with symmetrical double beams; the speckle interference is realized through a large shearing prism, and the The deflection of the reference object introduces carrier modulation stripes; according to the size of the deformation of the object, deflect the angle of the reference object appropriately to adjust the spatial frequency and realize the modulation of the displacement field; after the object is loaded, the carrier stripe is modulated by the deformation of the object and bends; In the Liye transform method, two phase diagrams containing out-of-plane and in-plane displacement information are demodulated respectively; after the two phase diagrams are enveloped, an algebraic operation is performed to separate the in-plane displacement field from the out-of-plane displacement field. The invention has the advantages of good modulation fringe quality, simple system, no reference light and the like, and can quickly and stably measure the two-dimensional component of the deformation field of the object.

Description

Displacement Field Separation Method of Large Shear Carrier Frequency Electron Speckle Interference Displacement Field

technical field

The invention relates to a separation method of frequency carrier electron speckle interference displacement field.

Background technique

Shearing electronic speckle interferometry has the advantages of simple optical path, high degree of automation, low requirements for shock resistance, and direct measurement of the derivative field of displacement. It is widely used in the field of nondestructive testing. The shearing electronic speckle interferometry technology of the large dislocation crystal prism (Wollaston prism) can realize the displacement measurement of the speckle interferometry, which has the advantages of simple system, no special introduction of reference light, and good fringe quality. In order to analyze the interference fringes of the deformation field with high precision, the phase shift method and the carrier wave method are commonly used to realize the phase measurement of the deformation field. Compared with the phase shift method, the carrier method of the interference fringe space modulation does not require precise phase shift equipment, has low requirements on the measurement environment, and has the advantage of being suitable for dynamic measurement, which is of great value in practical applications. Since optical interferometry is based on interference fringes to measure the displacement field, the quality of the interference fringes has a great influence on the measurement results. In particular, the interference fringe spatially modulated carrier method requires high-contrast fringes. The contrast of interference fringes obtained by holographic interferometry and moire interference is relatively high, and this method is widely used in holography and moiré interference. This method has also been introduced into electronic speckle interferometry, but the high noise of speckle fringes limits the development of this technique. In recent years, with the development of digital image processing technology, this method has attracted people's attention.

Contents of the invention

Aiming at the shortcomings of the existing electronic speckle interference technology, the present invention provides a large shear carrier frequency electronic speckle interference displacement field separation method capable of quickly and stably measuring the two-dimensional component of the deformation field of an object.

The separation method of large shear carrier frequency electronic speckle interference displacement field in the present invention is as follows:

In the shearing electronic speckle interference system, a reference object is placed next to the measured object, and a symmetrical double beam is used to illuminate the measured object and the reference object at the same time; the speckle interference is realized through a large shearing prism, and the deflection of the reference object is introduced into the carrier wave Modulation fringes; according to the size of the deformation of the object, deflect the angle of the reference object in an appropriate amount to adjust the spatial frequency and realize the modulation of the displacement field; after the object is loaded, the carrier fringe is bent and deformed by the modulation of the deformation of the object; using the Fourier transform method, Two phase diagrams containing out-of-plane and in-plane displacement information are obtained by demodulation respectively; after the two phase diagrams are enveloped, an algebraic operation is performed to separate the in-plane displacement field from the out-of-plane displacement field.

The invention realizes the speckle interference through the large shearing prism, so that the system is simple; the carrier modulation fringes are introduced through the deflection of the reference object, and high-quality modulation fringes are obtained, which has the advantage of high fringe contrast. According to the relationship between the spatial frequency and the deflection angle of the reference object, the modulation of the displacement field is conveniently obtained. Combined with the Fourier transform method, the in-plane displacement field can be separated from the out-of-plane displacement field by a simple phase operation. The invention proposes a method for separating displacement fields by large-shear carrier modulation, which has the advantages of good modulation fringe quality, simple system, no need for reference light, etc., and can quickly and stably measure two-dimensional components of object deformation fields.

Description of drawings

Fig. 1 is a schematic diagram of an optical path for large-shear electron speckle interference carrier frequency modulation.

FIG. 2 is a carrier fringe diagram when the object is illuminated by the front illumination light 11 .

FIG. 3 is a modulated carrier fringe diagram when the loaded illumination light 11 illuminates an object.

FIG. 4 is a carrier fringe diagram when the front illumination light 12 illuminates the object.

FIG. 5 is a modulated carrier fringe pattern after being modulated by deformation of the object when the loaded illumination light 12 irradiates the object.

FIG. 6 is a demodulated envelope phase diagram when illuminated by the illumination light 11 .

FIG. 7 is a demodulated envelope phase diagram when the illumination light 12 is illuminated.

Fig. 8 is a diagram of equal displacement distribution of the separated horizontal displacement component u field.

Fig. 9 is a diagram of equal displacement distribution of the separated out-of-plane displacement component w field.

In the figure: 1. variable beam splitter, 2. mirror 2, 3. camera, 4. lens, 5. polarizer, 6. large shear prism, 7. beam expander 1, 8. beam expander 2, 9. Reflector 1, 10, Reflector 3, 11, Illumination Light 1, 12, Illumination Light 2, 13, Measured Object, 14, Reference Object.

Detailed ways

Example

The optical path of large shear electron speckle interference carrier frequency modulation is shown in Figure 1. The laser beam is split into two beams: through variable beam splitter 1, reflector 9 and beam expander 7, it becomes illumination light 11; through variable beam splitter 1, reflector 2, reflector 10 and beam expander 8, it becomes Illumination light12. Adjusting the variable beam splitter 1 can make the intensity of the illumination light 11 and the illumination light 12 equal. A reference object 14 is fixedly placed next to the measured object 13, and both the illuminating light 11 and the illuminating light 12 can simultaneously illuminate the two objects. When the illumination light 11 or the illumination light 12 illuminates the object, the diffusely reflected light of the object passes through the large shearing prism 6 and the polarizer 5 , and then enters the camera 3 through the lens 4 .

The normal incident light beam enters the prism 6, and the prism 6 produces two misaligned images. Prism 6 and polarizer 5 are placed in front of the camera lens of camera 3 (seeing Fig. 1), if the dislocation angle of prism 6 is very large, then the two images formed by the object itself on the camera 3 target surface due to dislocation can be completely separated, and Superimposed with an image of a reference object 14 placed next to the object. When the incident light is irradiated on the measured object 13 and the reference object 14 at the same time, the camera 3 can receive the information of the object light and the reference light at the same time by using the large misalignment prism 6, but the polarization directions of the object light and the reference light are perpendicular to each other, in order to make this Two beams of polarized light with different vibration directions interfere, and a polarizer 5 is arranged behind the misalignment prism 6, and its polarization direction is 45° to the two optical axes of the misalignment prism. In this way, the coaxial polarization coherence of the object light and the reference light information on the target surface of the camera 3 is achieved, and the light intensity is almost equal, so that a good interference result is obtained.

Before the object is deformed, it is illuminated by two light beams respectively, and an unloaded original speckle image of the object is collected and stored in the computer. Subsequently, images corresponding to the two light beams are respectively illuminated and collected in other states, and each image is subtracted from the first image, and the subtracted result is displayed on the monitor in real time. During the deflection of the reference object, the carrier fringe can be introduced. When the object is deformed, the carrier fringe is modulated by the deformation of the object and bends.

After the interference fringe field is linearly modulated, it becomes dense carrier fringes containing deformation information. The modulated carrier stripe can be expressed as

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

Among them, a(x, y) is the background light intensity, b(x, y) is the fringe amplitude, b(x, y)/a(x, y) is often called fringe contrast, Δφ(x, y) is The phase change caused by the deformation of the object, that is, the phase to be sought, is a function of the spatial position. where f ₀ is the spatial frequency along the x-axis direction introduced by the deflection of the reference object. It can be known from theoretical derivation that:

${\mathrm{<span\; class="notranslate">\; f</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; \&Delta;\&alpha;</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; cos</span>}\mathrm{<span\; class="notranslate">\; \&theta;</span>}<span\; class="notranslate">\; )</span>}{\mathrm{<span\; class="notranslate">\; \&lambda;</span>}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; )</span>$

Among them, λ is the wavelength of the laser used, θ is the angle between the illumination light and the surface normal of the object, and Δα is the tiny angle of rotation of the reference object.

It can be seen from formula (1) that the phase shift of modulated interference fringes does not vary with time, but varies with space. The light intensity expression (1) of the carrier stripe in the x direction can be expressed as

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

Among them, j represents the unit of the imaginary part, and * represents the conjugate of the complex number. c(x, y) is expressed in plural form as

$\mathrm{<span\; class="notranslate">\; c</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; x</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; the\; y</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; 2</span>}}\mathrm{<span\; class="notranslate">\; b</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; x</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; the\; y</span>}<span\; class="notranslate">\; )</span>\mathrm{<span\; class="notranslate">\; exp</span>}<span\; class="notranslate">\; [</span>\mathrm{<span\; class="notranslate">\; j\&Delta;\&phi;</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; x</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; the\; y</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; ]</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 4</span>}<span\; class="notranslate">\; )</span>$

Perform Fourier transform on the light intensity I(x, y) in the x-axis direction to get

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

Among them, A(f _x , y) is obtained by transforming the background light intensity and low-frequency noise. Filter out A(f _x , y) and C ^* (f _x +f ₀ , y) with an appropriate filter, get C(f _x -f ₀ , y) and move it to the origin to become C(f _x , y), then inverse Fourier transform to get c(x, y), and the phase distribution can be obtained:

$\mathrm{<span\; class="notranslate">\; \&Delta;\&phi;</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; x</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; the\; y</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; the\; tan</span>}}^{<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}}\frac{\mathrm{<span\; class="notranslate">\; Im</span>}<span\; class="notranslate">\; [</span>\mathrm{<span\; class="notranslate">\; c</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; x</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; the\; y</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; ]</span>}{\mathrm{<span\; class="notranslate">\; Re</span>}<span\; class="notranslate">\; [</span>\mathrm{<span\; class="notranslate">\; c</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; x</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; the\; y</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; ]</span>}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 6</span>}<span\; class="notranslate">\; )</span>$

Among them, Re and Im represent to take the real part and the imaginary part of the complex number. What is obtained from formula (6) is the envelope phase of the variation of the principal value within [-π, π], which needs to be de-enveloped to be continuous.

When the illumination light 11 and the illumination light 12 respectively illuminate the object, the relationship between the light wave phase change and the deformation of the object is

$\mathrm{<span\; class="notranslate">\; \&Delta;</span>}{\mathrm{<span\; class="notranslate">\; \&phi;</span>}}_{\mathrm{<span\; class="notranslate">\; A</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; x</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; the\; y</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&pi;</span>}}{\mathrm{<span\; class="notranslate">\; \&lambda;</span>}}<span\; class="notranslate">\; [</span>\mathrm{<span\; class="notranslate">\; w</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; cos</span>}\mathrm{<span\; class="notranslate">\; \&theta;</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; u</span>}\mathrm{<span\; class="notranslate">\; sin</span>}\mathrm{<span\; class="notranslate">\; \&theta;</span>}<span\; class="notranslate">\; ]</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 7</span>}<span\; class="notranslate">\; )</span>$

$\mathrm{<span\; class="notranslate">\; \&Delta;</span>}{\mathrm{<span\; class="notranslate">\; \&phi;</span>}}_{\mathrm{<span\; class="notranslate">\; B</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; x</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; the\; y</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&pi;</span>}}{\mathrm{<span\; class="notranslate">\; \&lambda;</span>}}<span\; class="notranslate">\; [</span>\mathrm{<span\; class="notranslate">\; w</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; cos</span>}\mathrm{<span\; class="notranslate">\; \&theta;</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; u</span>}\mathrm{<span\; class="notranslate">\; sin</span>}\mathrm{<span\; class="notranslate">\; \&theta;</span>}<span\; class="notranslate">\; ]</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 8</span>}<span\; class="notranslate">\; )</span>$

where w is the out-of-plane displacement of the object deformation along the z-axis direction, and u is the in-plane displacement of the object deformation along the x-axis direction. It can be seen that what is measured is a mixed field.

The out-of-plane displacement field and the in-plane displacement field can be obtained by adding and subtracting Equation (7) and Equation (8).

${\mathrm{<span\; class="notranslate">\; \&Delta;\&phi;</span>}}_{\mathrm{<span\; class="notranslate">\; A</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; x</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; the\; y</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; \&Delta;\&phi;</span>}}_{\mathrm{<span\; class="notranslate">\; B</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; x</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; the\; y</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; 4</span>}\mathrm{<span\; class="notranslate">\; \&pi;</span>}}{\mathrm{<span\; class="notranslate">\; \&lambda;</span>}}\mathrm{<span\; class="notranslate">\; w</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; cos</span>}\mathrm{<span\; class="notranslate">\; \&theta;</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 9</span>}<span\; class="notranslate">\; )</span>$

${\mathrm{<span\; class="notranslate">\; \&Delta;\&phi;</span>}}_{\mathrm{<span\; class="notranslate">\; A</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; x</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; the\; y</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; \&Delta;\&phi;</span>}}_{\mathrm{<span\; class="notranslate">\; B</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; x</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; the\; y</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; 4</span>}\mathrm{<span\; class="notranslate">\; \&pi;</span>}}{\mathrm{<span\; class="notranslate">\; \&lambda;</span>}}\mathrm{<span\; class="notranslate">\; u</span>}\mathrm{<span\; class="notranslate">\; sin</span>}\mathrm{<span\; class="notranslate">\; \&theta;</span>}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 10</span>}<span\; class="notranslate">\; )</span>$

From equations (9) and (10), it can be seen that as long as the phase changes of the deformation of the object are obtained when the illumination light 11 and illumination light 12 are irradiated, and then simple addition and subtraction are performed on the two phase fields, the out-of-plane The displacement field is separated from the in-plane displacement field.

Using the optical path shown in Figure 1, measure and separate the displacement field of the simply supported beam. The incident angle of the two beams is 49.4°, and it is carried out on the anti-vibration table. The simply supported beam has a length of 150 mm, a height of 19.50 mm, and a thickness of 18.50 mm. It is made of plexiglass. The elastic modulus of the material is E=3.4×10 ⁹ Pa, and the Poisson's ratio is v=0.34. The loaded span is 71.00mm, and the differential load is about 75N. Silver powder is coated on the surface of the Charpy to enhance the reflectivity.

Before the object is deformed, the two light beams are illuminated separately, and an unloaded original speckle image of the object is collected and stored in the computer, and then the collected image is subtracted from the first image, and the speckle-related fringes presented after the subtraction are displayed on the monitor. device. The carrier fringe is first introduced by rotating the reference object, and then the object is loaded, and the carrier fringe is modulated by the deformation of the object to bend.

FIG. 2 is the carrier fringe obtained when the illuminating light 11 irradiates the object before loading, and FIG. 3 is the modulated carrier fringe after being bent by the modulation of the deformation of the object when the illuminating light 11 irradiates the object after loading. FIG. 4 is the carrier fringe when the illuminating light 12 irradiates the object before loading, and FIG. 5 is the modulated carrier fringe diagram after being bent by the deformation modulation of the object when the illuminating light 12 irradiates the object after loading. The deformed phase of the object is demodulated by using the Fourier transform method respectively, and Fig. 6 and Fig. 7 are the envelope phase diagrams demodulated when illuminated by the illumination light 11 and the illumination light 12 respectively. Figure 6 and Figure 7 are respectively de-enveloped to obtain a continuous phase map, and the phase map of the horizontal displacement component and the phase map of the out-of-plane displacement can be separated after the addition and subtraction of the two continuous phase maps. According to formula (9) and formula (10), the phase of the separated displacement field is transformed into a quantitative displacement field distribution. Figure 8 is the equal displacement distribution diagram of the separated horizontal displacement The isodisplacement distribution map of the surface displacement component w field. Among them, the length shown in the horizontal direction is the span of the simply supported beam (71.0mm), the vertical direction is the height of the simply supported beam (19.5mm), and the unit of the displacement component is microns.

It can be seen from the results that using the large-shear electronic speckle interferometry system, the carrier fringe introduced by the method of deflecting the reference object has high contrast and can effectively modulate the deformation field of the object. Combined with the Fourier transform method, the system can effectively separate the mixed 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; After two width of cloth position phasors are separated envelope, carry out algebraic operation the in-plane displacement field is separated with the acoplanarity displacement field.

Images