CN102494614B - High-precision digital speckle related measurement method - Google Patents
High-precision digital speckle related measurement method Download PDFInfo
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- CN102494614B CN102494614B CN201110359343.3A CN201110359343A CN102494614B CN 102494614 B CN102494614 B CN 102494614B CN 201110359343 A CN201110359343 A CN 201110359343A CN 102494614 B CN102494614 B CN 102494614B
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Abstract
A high-precision digital speckle related measurement method adopts a measuring device consisting of a CW (continuous wave) laser, a collimated beam expander, a converging lens, a CCD (charge coupled device) camera and a computer for measurement, and is realized through adopting the following steps: filtering speckle images arranged in a generation plane of a to-be-tested object before and after the displacement and recorded by the CCD camera, so as to obtain the complex signal distribution of light intensity; performing interpolation after analyzing the phase position distribution, so as to obtain the phase position distribution matrix with the sub-pixel accuracy; utilizing the phase position vortex topological charge numbers plus 1 and minus 1 to replace the original phase position values, and replacing other points with 0, so as to build two sparse matrixes; and finally performing related operation to the two sparse matrixes so as to obtain the in-plane displacement information of the to-be-tested object. The method can realize the high computational efficiency and high measuring accuracy at the same time, has the characteristics of compactness in optical path, simplicity and feasibility, and is suitable for the real-time and on-line detection in the field of photoelectric nondestructive detection.
Description
Technical field
The present invention relates to a kind of digital speckle correlation measurement method of the measurement object plane intrinsic displacement that is applied to the fields such as photoelectricity Non-Destructive Testing, a kind of high-precision digital speckle related measurement method specifically.
Background technology
Laser speckle refers in the time that Ear Mucosa Treated by He Ne Laser Irradiation is on rough object surface, the light and dark spot that diffuses and form after reflection space is interfered mutually.Speckle has carried testee information, by can obtain the change information of testee to the analysis of speckle field.Digital speckle correlation measurement method is progressively to grow up after twentieth century eighties, for measuring the non-contact optical measuring method of object plane intrinsic displacement.It has that light path is simple, measurement of full field, noncontact and measurement environment is required to the advantages such as low; Thereby be widely used at field of non destructive testing.
In digital speckle correlation measurement method, in the situation that other conditions are identical, measuring accuracy is directly proportional to counting of correlation computations, and calculating is counted more, and measuring accuracy is higher; And calculate increasing of counting, the counting yield of related operation is reduced; Therefore, realize Computationally efficient and high measurement accuracy is a difficult problem to be solved in this technology simultaneously.
In the counting yield research of digital speckle correlation measurement method, mostly concentrate on the best relevant search of How to choose subarea, as: document [photoelectric project 34,53-58 (2007], document [Optics Express 16,7037-7048 (2008)] and document [Optics and Lasers in Engineering 45,967-974 (2007)] etc.Even but finding after the size of best relevant search subarea, in the time of large displacement, to calculate and count still very highly, counting yield can not meet the requirement of measuring in real time in a lot of engineerings.In the measuring accuracy research of digital speckle correlation measurement method, mainly contain method of interpolation, Surface Fitting and gradient algorithm etc., these traditional digital speckle correlation measurement methods are all based on speckle field gray scale correlation computations, by improving algorithm, although its precision can reach sub-pix, it is low that counting yield also becomes thereupon.
Aspect the patent documentation of digital speckle correlation measurement, (Granted publication number is CN101158679B to patent " bone trabecular extraction and mechanical property measuring method and measurement mechanism thereof ", Granted publication day is 2011.04.27), a kind of method and device that utilizes Digital Speckle Correlation Method to measure bone trabecular mechanical property disclosed, this patent is the new application of digital speckle correlation measurement method, and does not pay close attention to measuring accuracy and the counting yield of the method itself; (publication number is CN101788427A to patent " a kind of device for detecting mechanical property of multifunctional film ", open day is 2010.07.28), this device adopts Digital Speckle Correlation Method to measure deformation of thin membrane, moves a layer method in conjunction with Bubbling method and improvement, can obtain the mechanical property of films and coatings; This device is also to utilize speckle intensity map directly to carry out relevant search, and its measuring accuracy and counting yield are not all analyzed in detail.
To sum up analyze knownly, in existing disclosed background technology, realize Computationally efficient and high measurement accuracy is a technical barrier to be solved in digital speckle correlation measurement method simultaneously always.
Summary of the invention
The object of the invention is the deficiency for solving the problems of the technologies described above, a kind of high-precision digital speckle related measurement method is provided, the method can realize the measurement of the nano level high resolution precision of in-plane displacement when high-level efficiency is calculated.
Deficiency for solving the problems of the technologies described above of the present invention, the technical scheme adopting is: the measurement mechanism that utilization of the present invention is made up of continuous wave laser, collimator and extender device, convergent lens, CCD camera and computing machine is measured, light beam working direction at this continuous wave laser is provided with collimator and extender device and testee successively, light beam is after testee scattering, after convergent lens is assembled, light beam enters CCD camera imaging, then be stored into computing machine, measuring process is as follows:
1, with the Speckle Intensity figure before CCD cameras record testee generating plane intrinsic displacement and after displacement
,
, for guaranteeing measuring accuracy, the mean diameter that should make the speckle particle in speckle pattern is 5 Pixels, speckle image is of a size of 1024 × 1024 Pixels; By two width Speckle Intensity figure
with
be stored into computing machine and carry out subsequent treatment;
2, with the special complex filter of Gauss-Hull rice, to the Speckle Intensity figure before testee generating plane intrinsic displacement and after displacement
,
carry out filtering, the light intensity complex signal that obtains them distributes
with
;
3, then, distribute according to light intensity complex signal
with
obtain its PHASE DISTRIBUTION
with
, right
with
carry out bicubic spline interpolation, obtain having the PHASE DISTRIBUTION matrix of sub-pixel precision
with
;
4, according to the definition of phase vortex, utilize formula
to PHASE DISTRIBUTION matrix
with
carry out the search of phase vortex point, wherein,
for comprising the contour integral of this search point; In the time of s=+1, this vortex is positive vortex, and in the time of s=-1, this vortex is negative vortex; Replace PHASE DISTRIBUTION matrix with+1 or-1
with
in the numerical value of original this point, matrix
with
in other numerical value a little replace with 0; Two phase vortex matrixes that represent that testee generating plane intrinsic displacement is forward and backward are finally obtained
x 1(
x,
y) and
x 2(
x,
y); Because 0 value accounts for the overwhelming majority in these two matrixes, so, these two matrixes
x 1(
x,
y) and
x 2(
x,
y) be sparse matrix;
5, selecting size is that the subarea of 51 × 51 Pixels is as region of search, to two forward and backward sparse matrixes of object generating plane intrinsic displacement
x 1(
x,
y) and
x 2(
x,
y) carry out related operation, obtain speckle field and exist
the in-plane displacement with sub-pixel precision of direction
, the enlargement factor of imaging optical path is
m, the in-plane displacement amount that testee occurs is
.
First the present invention utilizes the Speckle Intensity image of former and later two states of CCD cameras record testee generating plane intrinsic displacement, then utilize rice special complex filter in Gauss-Hull to carry out filtering to this two width image and obtain the complex signal distribution of light distribution, and then obtain the PHASE DISTRIBUTION of speckle field; PHASE DISTRIBUTION is carried out interpolation and is obtained having to the PHASE DISTRIBUTION matrix of sub-pixel precision, then determine position and topological charge number ± 1 of each vortex point according to the definition of phase vortex, in PHASE DISTRIBUTION matrix, utilize respectively+1 or-1 to replace original phase value, the numerical value of other points is replaced with 0, has so just constructed two sparse matrixes; Finally, these two sparse matrixes are carried out to related operation, obtain the in-plane displacement information of testee.
Principle of work of the present invention is:
In digital speckle correlation measurement, utilize the forward and backward two width Speckle Intensity gray-scale maps of CCD cameras record object generating plane intrinsic displacement, use respectively
,
represent; Then be stored into computing machine and carry out related operation.Speckle pattern before generating plane intrinsic displacement
in centered by center point P point, get size as the subarea A of n × n is as relevant search subarea; When after testee generation deformation, subarea A moves to the position of subarea B, and P point moves to P ' point.By statistics Xue Zhi, the related coefficient maximum of these two sample spaces of A and B; Utilize standardization autocovariance related function to ask its related coefficient,
Wherein,
when from P ' of P point search
the displacement producing in direction,
for the related coefficient of this point,
be respectively each pixel gray scale in the speckle image of the forward and backward acquisition of generating plane intrinsic displacement,
be respectively relevant search subarea A, the average gray value of B; Determine the position of subarea B according to the maximal value of related coefficient, finally obtain speckle field move rear P '
x,
ythe displacement of direction
; In formula (1),
.
In digital speckle correlation measurement, the speckle pattern of CCD cameras record is the surface of intensity distribution, has lost phase information; First the present invention converts speckle intensity distributions by Gauss-Hull rice is special
being redeveloped into complex signal distributes
,
(2)
Wherein,
for
fourier transform,
be respectively
the frequency of direction, step (
f) be step function, be defined as,
(3) in formula,
ffor
xthe frequency of direction
f x or
ythe frequency of direction
f y .
The complex signal that obtains speckle pattern light intensity distributes
after, extract its PHASE DISTRIBUTION
(4)
Wherein, arg (...) represent plural number to ask phase angle.
Obtain after its PHASE DISTRIBUTION, utilize bicubic spline interpolation, obtain having the PHASE DISTRIBUTION of sub-pixel precision
.Then, determine the position of each phase vortex point by following formula
(5)
Wherein,
for comprising the contour integral of this search point, s is topological charge number, is an integer.In normal state speckle field, s gets ± and 1; In the time of s=+1, phase place increases counterclockwise around this point, is positive vortex; In the time of s=-1, phase place increases clockwise around this point, is negative vortex.Utilize+1 or-1 to remove to replace phasing matrix
in the numerical value of this point,
in other use a little 0 value to replace, last, formed a vortex distribution matrix with sub-pixel precision
x(
x,
y).Because the value of most points in this matrix is 0, so
x(
x,
y) be sparse matrix.
Utilize (2)-(5) formula, to the forward and backward Speckle Intensity figure of object generating plane intrinsic displacement
,
process, obtain representing two sparse matrixes of the forward and backward information of object generating plane intrinsic displacement
x 1(
x,
y) and
x 2(
x,
y); Then, select suitable search subarea to these two sparse matrixes
x 1(
x,
y) and
x 2(
x,
y) carry out related operation, obtain speckle field and exist
direction has the displacement of sub-pixel precision
; If the enlargement factor of imaging optical path is
m, the in-plane displacement amount of testee is
.While being correlated with due to sparse matrix, 0 value point does not participate in computing, therefore, has improved greatly the efficiency of correlation computations.
Compared with conventional art, advantage of the present invention: the inventive method has simple, feature fast and accurately, and its measuring accuracy can reach tens nanometers, and meanwhile, its counting yield improves more than 10 times than traditional Digital Speckle Correlation Method phase specific energy.That is to say that the object that this method realizes is: can when high-level efficiency is calculated, realize the measurement of the nano level high resolution precision of in-plane displacement.Can be widely used in the fields such as photoelectricity Non-Destructive Testing, be particularly suitable for real-time, the high precision reliable measurements of the micro-displacement in these fields.
Accompanying drawing explanation
Fig. 1 is the structural representation of measurement mechanism in the present invention.
Reference numeral: 1, continuous wave laser, 2, collimator and extender device, 3, testee, 4, convergent lens, 5, CCD camera, 6, computing machine.
Embodiment
The measurement mechanism that utilization of the present invention is made up of continuous wave laser 1, collimator and extender device 2, convergent lens 4, CCD camera 5 and computing machine 6 is measured, as shown in the figure, the continuous wave laser 1 of wherein selecting is He-Ne laser instrument, and optical maser wavelength is 632.8nm, and power is 10mW.First according to above-mentioned structural arrangement optical path figure, the laser beam that continuous wave laser 1 sends becomes directional light after collimator and extender device 2, is radiated on testee 3; Laser beam, through after testee 3 scatterings, forms speckle light field in echo area; After convergent lens 4, enter 5 imagings of CCD camera, be then stored into computing machine 6 and process, concrete measuring process is as follows:
First, record before testee 3 generating plane intrinsic displacements with CCD camera 5 and displacement after Speckle Intensity figure
,
, for guaranteeing measuring accuracy, the mean diameter that should make the speckle particle in speckle pattern is 5 Pixels, speckle image is of a size of 1024 × 1024 Pixels; Two width Speckle Intensity figure are stored into computing machine 6 and carry out subsequent treatment;
Adopt with the special complex filter of Gauss-Hull rice, to the Speckle Intensity figure before testee 3 generating plane intrinsic displacements and after displacement
,
carry out filtering, the light intensity complex signal that obtains them distributes
,
;
Then, distribute according to light intensity complex signal
with
obtain its PHASE DISTRIBUTION
with
, right
with
carry out bicubic spline interpolation, obtain having the PHASE DISTRIBUTION matrix of sub-pixel precision
with
;
According to the definition of phase vortex, utilize formula
to PHASE DISTRIBUTION matrix
with
carry out the search of phase vortex point, wherein,
for comprising the contour integral of this search point; In the time of s=+1, this vortex is positive vortex, and in the time of s=-1, this vortex is negative vortex; Replace PHASE DISTRIBUTION matrix with+1 or-1
with
in the numerical value of original this point, matrix
with
in other numerical value a little replace with 0; Two phase vortex matrixes that represent that testee generating plane intrinsic displacement is forward and backward are finally obtained
x 1(
x,
y) and
x 2(
x,
y); Because 0 value accounts for the overwhelming majority in these two matrixes, so, these two matrixes
x 1(
x,
y) and
x 2(
x,
y) be sparse matrix;
Selecting size is that the subarea of 51 × 51 Pixels is as region of search, to two forward and backward sparse matrixes of testee 3 generating plane intrinsic displacements
x 1(
x,
y) and
x 2(
x,
y) carry out related operation, obtain speckle field and exist
the in-plane displacement with sub-pixel precision of direction
, the enlargement factor of the convergent lens 4 of selecting is 10 times, the in-plane displacement amount that testee 3 occurs is
;
The pixel size of the CCD camera 5 of selecting is 10mm, and the measuring accuracy of this inventive method is 0.01mm, i.e. 10nm; Under the identical condition of the hardware configuration of computing machine 6, the counting yield of this inventive method is 10 times of conventional digital speckle correlation technique counting yield.
Our experiments show that: the counting yield of the inventive method can improve more than 10 times, meanwhile, its measuring accuracy can reach the resolution below 10nm; In addition, this inventive method also has succinct, the simple feature of light path, be suitable for field of industrial production in real time, online detect.
Claims (1)
1. a high-precision digital speckle related measurement method, the method is utilized by continuous wave laser (1), collimator and extender device (2), convergent lens (4), the measurement mechanism that CCD camera (5) and computing machine (6) form is measured, be provided with successively collimator and extender device (2) and testee (3) in the light beam working direction of this continuous wave laser (1), light beam is after testee scattering, after convergent lens (4) is assembled, light beam enters CCD camera (5) imaging, then be stored into computing machine (6), described continuous wave laser (1) is He-Ne laser instrument, optical maser wavelength is 632.8nm, power is 10mW, the pixel size of described CCD camera (5) is 10mm, it is characterized in that: measuring process is as follows:
Speckle Intensity figure before step 1, use CCD cameras record testee generating plane intrinsic displacement and after displacement
,
, for guaranteeing measuring accuracy, the mean diameter that should make the speckle particle in speckle pattern is 5 Pixels, speckle image is of a size of 1024 × 1024 Pixels; By two width Speckle Intensity figure
with
be stored into computing machine and carry out subsequent treatment, in this step, the Speckle Intensity figure of CCD cameras record is stored into computing machine and carries out related operation, the speckle pattern before generating plane intrinsic displacement
in centered by center point P point, get size as the subarea A of n × n is as relevant search subarea; When after testee generation deformation, subarea A moves to the position of subarea B, and P point moves to P ' point,
By statistics Xue Zhi, the related coefficient maximum of these two sample spaces of A and B; Utilize standardization autocovariance related function to ask its related coefficient,
(1)
Wherein,
when from P ' of P point search
the displacement producing in direction,
for the related coefficient of this point,
be respectively each pixel gray scale in the speckle image of the forward and backward acquisition of generating plane intrinsic displacement,
be respectively relevant search subarea A, the average gray value of B; Determine the position of subarea B according to the maximal value of related coefficient, finally obtain speckle field move rear P '
x,
ythe displacement of direction
; In formula (1),
;
Step 2, the special complex filter of use Gauss-Hull rice, to the Speckle Intensity figure before testee generating plane intrinsic displacement and after displacement
,
carry out filtering, the light intensity complex signal that obtains them distributes
with
, wherein
(2), in formula (2)
for
fourier transform,
be respectively
the frequency of direction, step (
f) be step function, be defined as,
(3), in formula (3)
ffor
xthe frequency of direction
f x or
ythe frequency of direction
f y ;
Step 3, then, distributes according to light intensity complex signal
with
obtain its PHASE DISTRIBUTION
with
, right
with
carry out bicubic spline interpolation, obtain having the PHASE DISTRIBUTION matrix of sub-pixel precision
with
;
Step 4, according to the definition of phase vortex, utilize formula
to PHASE DISTRIBUTION matrix
with
carry out the search of phase vortex point, wherein,
for comprising the contour integral of this search point; In the time of s=+1, this vortex is positive vortex, and in the time of s=-1, this vortex is negative vortex; Replace PHASE DISTRIBUTION matrix with+1 or-1
with
in the numerical value of original this point, matrix
with
in other numerical value a little replace with 0; Two phase vortex matrixes that represent that testee generating plane intrinsic displacement is forward and backward are finally obtained
x 1(
x,
y) and
x 2(
x,
y); Because 0 value accounts for the overwhelming majority in these two matrixes, so, these two matrixes
x 1(
x,
y) and
x 2(
x,
y) be sparse matrix;
Step 5, to select size be that the subarea of 51 × 51 Pixels is as region of search, to two forward and backward sparse matrixes of object generating plane intrinsic displacement
x 1(
x,
y) and
x 2(
x,
y) carry out related operation, obtain speckle field and exist
the in-plane displacement with sub-pixel precision of direction
, the enlargement factor of imaging optical path is
m, the in-plane displacement amount that testee occurs is
.
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CN103020907B (en) * | 2012-12-04 | 2015-08-26 | 上海交通大学 | Based on the DSPI striped filtering system of two-dimensional ensemble empirical mode decomposition |
CN103383353B (en) * | 2013-07-02 | 2015-04-22 | 河南科技大学 | Optical vortices-based dynamic speckle test method |
CN104634281A (en) * | 2015-02-15 | 2015-05-20 | 上海理工大学 | Drum machine and measuring method |
CN105157588B (en) * | 2015-09-05 | 2018-01-26 | 辽宁工程技术大学 | A kind of multidimensional Synchronous fluorimetry measuring method of strain localization band spacing development law |
CN110631487B (en) * | 2019-11-08 | 2020-12-11 | 济南大学 | Method for measuring transverse micrometric displacement by utilizing laser speckle autocorrelation technology |
CN111856480B (en) * | 2020-07-29 | 2023-11-10 | 南京工程学院 | Rapid detection method and detection system for equipment displacement |
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