CN105423942A - Correction method for biprism defect error in bootstrap loader three-dimensional digital image correction (BSL 3D DIC) system - Google Patents

Abstract

The invention provides a correction method for a biprism defect error in a bootstrap loader three-dimensional digital image correction (BSL 3D DIC) system. The correction method comprises the steps of placing a calibration board in the visual field of a measurement system, adjusting the position and the gesture of the calibration board, acquiring the offset image of the calibration board, wherein the measurement system comprises a biprism, a bi-telecentric lens and a complementary metal oxide semiconductor (CMOS) camera; removing the biprism from the measurement system; acquiring an image in directly observing the calibration board; calculating the pixel coordinates of corresponding angle points before and after offset according to the offset image of the calibration board and the image in direct observing; performing lens distortion calibration and correction according to the pixel coordinates of the angle points in direct observing; constructing a least square function, and performing calibration on the main direction angle of the prism according to the least square function by means of the pixel coordinates of the corresponding angle points before and after offset; and inputting the calibration result into a correction mathematical model for correcting the biprism defect error. The correction method can correct the biprism defect error in the BSL 3D DIC system and furthermore improves measurement accuracy of the system.

Description

The modification method of biprism defect error in BSL 3D DIC system

Technical field

The present invention relates to photo-measuring experimental mechanics and three-dimensional digital image technical field, particularly the modification method of biprism defect error in a kind of BSL3DDIC system.

Background technology

Three-dimensional digital image correlation technique (3DDigitalImageCorrelation, 3DDIC) is a kind of important noncontact full field deformation measure method in Experimental Mechanics field.Tradition 3DDIC uses at least two image capture devices (as CCD or CMOS camera) to observe the test zone of specimen surface simultaneously, and obtains three-dimensional surface shape and the space displacement of testee by binocular (or many orders) visual theory.Comparatively two-dimensional digital image correlation technique (2DDIC), 3DDIC range of application is more wide.But need sufficient distance to obtain the test pattern of different visual angles between each camera in traditional 3DDIC optical path, experimental provision integrated level is lower; In order to obtain reliable measurement result, need during experiment to carry out Accurate Calibration to the inside and outside parameter of camera; In addition, camera properties difference, experiment time image acquisition the factor such as synchronization extent all can affect the accuracy of measurement result.Above factor limits the application and development of 3DDIC method all to some extent.

As the development of 3DDIC method, based on the one camera three-dimensional digital image correlation technique (Bi-prism-basedSingleLens3DDigitalImageCorrelation of biprism, BSL3DDIC) by placing biprism before camera, use single camera to realize three-dimensional measurement, substantially increase the integrated level of 3DDIC test macro.For the three-dimensionalreconstruction problem in BSL3DDIC method, research relevant at present provides multiple method, as: K.Genovese etc. realize the reconstruct (K.Genovese of three-dimensional appearance by demarcation and lens error correction, L.Casaletto, J.A.Rayas, V.Flores, A.Martinez, OpticsandLasersinEngineering51,278 – 285,2013).The method does not rely on the imaging model of system, but higher to the requirement of calibration result, experimentation relative complex.In addition, biprism is considered as independently optical element by L.F.Wu etc., very according to its configuration and optical parametric, propose a kind of mathematical model describing prism imaging rule, greatly reduce difficulty (L.F.Wu, the J.G.Zhu of experimental calibration, H.M.Xie, MeasurementScienceandTechnology25,115008,2014).On this basis, L.F.Wu etc. utilize two telecentric lens, further simplify above-mentioned mathematical model, reduce model error, improve measuring accuracy (L.F.Wu, the J.G.Zhu of BSL3DDIC method, H.M.Xie, AppliedOptics54 (26), 2015).

However, the configuration all giving tacit consent to biprism at present relevant research is desirable, and namely the seamed edge of biprism is parallel with rear surface perpendicular to its xsect, as shown in Fig. 1 (a).But, be subject to processing the restriction of alignment precision in process, the actual biprism used is defective mostly, this defect can be divided into face intrinsic deflection, as shown in Fig. 1 (b), from deflecting facet according to the relative position of its seamed edge and rear surface, as shown in Fig. 1 (c), and mixing deflection, as shown in Fig. 1 (d), wherein mixing deflection is situation the most general.As optical element important in BSL3DDIC system, the geometric configuration of biprism directly affects the accuracy of measurement of this system, when particularly carrying out three-dimensionalreconstruction by mathematical model, must correct this error.

Summary of the invention

The present invention is intended to solve one of technical matters in above-mentioned correlation technique at least to a certain extent.

For this reason, one object of the present invention is the modification method proposing biprism defect error in a kind of BSL3DDIC system, and the method can be revised biprism defect error, improves the accuracy of measurement of BSL3DDIC system.

To achieve these goals, embodiments of the invention propose the modification method of biprism defect error in a kind of BSL3DDIC system, comprise the following steps: S1: build measuring system, and scaling board is placed in the visual field of described measuring system, and adjust the position of described scaling board and attitude until described scaling board imaging clearly, and gather the dislocation image of described scaling board, wherein, described measuring system comprises biprism, two telecentric lens and a CMOS camera; S2: remove described biprism from described acquisition system; S3: gather image when directly observing described scaling board; S4: according to the pixel coordinate of corresponding angle point before and after the dislocation image of described scaling board and image calculating dislocation when directly observing described scaling board; S5: carry out lens distortion demarcation and correction according to the pixel coordinate of angle point during direct observation described scaling board; S6: build least square function, and utilize the pixel coordinate of corresponding angle point before and after dislocation to demarcate biprism principal stresses angle according to described least square function; And S7: build and revise mathematical model, the calibration result of biprism principal stresses angle is inputted described correction mathematical model to revise biprism defect error.

In addition, in BSL3DDIC system according to the above embodiment of the present invention, the modification method of biprism defect error can also have following additional technical characteristic:

In some instances, described scaling board is one piece of gridiron pattern scaling board, and the grid length of side of described gridiron pattern scaling board is 1.6mm.

In some instances, describedly from described acquisition system, remove described biprism, comprise further: remove the camera before and after biprism and described pair of telecentric lens, and keep the invariant position of described scaling board.

In some instances, described step S5 comprises further: judge that whether the degree of lens distortion is higher than distortion threshold value; If the degree of lens distortion is higher than described distortion threshold value, then moves described scaling board to diverse location, and gather correspondence image, with all regions making angle point farthest spread all over described correspondence image; Calculate the pixel coordinate of each angle point in each image, and matching lens distortion function; According to described lens distortion function, each pixel coordinate is revised.

In some instances, described lens distortion function is:

${\mathrm{\δ}}_x=x_u(k_1{r}^2+k_2{r}^4+k_3{r}^6+k_4{r}^8+k_5{r}^{10})+(p_0+p_2{r}^2)(2x_u^2+r^2)+r^2(s_0+s_2{r}^2),$

${\mathrm{\δ}}_y=y_u(k_1{r}^2+k_2{r}^4+k_3{r}^6+k_4{r}^8+k_5{r}^{10})+(p_1+p_3{r}^2)(2y_u^2+r^2)+r^2(s_1+s_3{r}^2),$

Wherein, δ _x, δ _ybe respectively the perturbed field of image level, vertical direction, (x _u, y _u) be undistorted pixel coordinate, k ₁, k ₂, k ₃, k ₄, k ₅, p ₀, p ₁, p ₂, p ₃, s ₀, s ₁, s ₂, s ₃for demarcating the distortion parameter obtained.

In some instances, if the degree of described lens distortion is lower than distortion threshold value, then lens distortion demarcation and correction is not carried out.

In some instances, in described step S6, described least square function is:

${\mathrm{LSF}}_1={\mathrm{\Σ}}_i{\mathrm{\Σ}}_j{\[-{\mathrm{sin\θ}}^{+}(x_{cij}^{+}-x_{cij}^0)+{\mathrm{cos\θ}}^{+}(y_{cij}^{+}-y_{cij}^0)\]}^2,$

${\mathrm{LSF}}_2={\mathrm{\Σ}}_i{\mathrm{\Σ}}_j{\[-{\mathrm{sin\θ}}^{-}(x_{cij}^{-}-x_{cij}^0)+{\mathrm{cos\θ}}^{-}(y_{cij}^{-}-y_{cij}^0)\]}^2,$

Wherein, θ ⁺and θ ^-the calibration result of biprism principal stresses angle, described θ ⁺and θ ^-make LSF ₁and LSF ₂obtain minimal value.

In some instances, described correction mathematical model is:

$x_c^{+}{\mathrm{cos\θ}}^{+}+y_c^{+}{\mathrm{sin\θ}}^{+}=-\frac{\mathrm{\η}}{P_{sz}}\[(1+A^{+}{\mathrm{tan\α}}^{+})(X{\mathrm{cos\θ}}^{+}+Y{\mathrm{sin\θ}}^{+})+A^{+}Z-A^{+}{t}_0\],$

$x_c^{-}{\mathrm{cos\θ}}^{-}+y_c^{-}{\mathrm{sin\θ}}^{-}=-\frac{\mathrm{\η}}{P_{sz}}\[(1+A^{-}{\mathrm{tan\α}}^{-})(X{\mathrm{cos\θ}}^{-}+Y{\mathrm{sin\θ}}^{-})-A^{-}Z+A^{-}{t}_0\],$

$x_c^{+}{\mathrm{sin\θ}}^{+}-y_c^{+}{\mathrm{cos\θ}}^{+}=-\frac{\mathrm{\η}}{P_{sz}}(X{\mathrm{sin\θ}}^{+}-Y{\mathrm{cos\θ}}^{+}),$

$x_c^{-}{\mathrm{sin\θ}}^{+}-y_c^{-}{\mathrm{cos\θ}}^{+}=-\frac{\mathrm{\η}}{P_{sz}}(X{\mathrm{sin\θ}}^{-}-Y{\mathrm{cos\θ}}^{-}),$

Wherein, α ⁺and α ^-represent the angle of wedge of biprism both sides wedge-shaped mirrors respectively, A ⁺and A ^-be and biprism locking angle ⁺and α ^-and the parameter that refractive index n is relevant.

In some instances, wherein,

$A^{+}=\frac{n{\mathrm{sin\α}}^{+}{\cos }^2{\mathrm{\α}}^{+}}{\sqrt{1-n^2{\sin }^2{\mathrm{\α}}^{+}}}-{\mathrm{sin\α}}^{+}{\mathrm{cos\α}}^{+},$

$A^{-}=\frac{n{\sin }^{-}{\mathrm{\αcos}}^2\mathrm{\α}-}{\sqrt{1-n^2{\sin }^2{\mathrm{\α}}^{-}}}-{\sin }^{-}{\mathrm{\αcos\α}}^{-}.$

In some instances, described step S7 comprises further: by θ ⁺and θ ^-substitute into and revise in mathematical model, and pixel coordinate is solved to the volume coordinate of corresponding object point in combination with the picture point in the testee dislocation image of DIC computing coupling, and carry out follow-up three-dimensional appearance reconstruct.

According to the modification method of biprism defect error in the BSL3DDIC system of the embodiment of the present invention, introduce the concept of biprism principal direction, the biprism that there is manufacturing deficiency is equivalent to the prism wedge that two principal directions and reference frame form an angle respectively; And when utilizing prism wedge imaging, image along prism axis to this feature of generation dislocation, by demarcating biprism principal direction, does not carry out error correction; In addition, biprism principal direction calibration process and experiment measuring process separate, do not interfere with each other, follow-up lens distortion can be carried out demarcate after completing demarcation; Further, utilize and revise mathematical model, the correction of systematic error can be realized in the process of three-dimensionalreconstruction.The method can be revised biprism defect error, improves the accuracy of measurement of system.

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

Accompanying drawing explanation

Above-mentioned and/or additional aspect of the present invention and advantage will become obvious and easy understand from accompanying drawing below combining to the description of embodiment, wherein:

Fig. 1 is several form schematic diagram of current biprism manufacturing deficiency;

Fig. 2 is the process flow diagram of the modification method of biprism defect error in BSL3DDIC system according to an embodiment of the invention;

Fig. 3 is the equivalent schematic of the biprism that there is manufacturing deficiency according to an embodiment of the invention;

Fig. 4 is according to an embodiment of the invention based on the vertical view of biprism with the one camera 3DDIC system of two telecentric lens;

Fig. 5 is the schematic diagram of the dislocation image of scaling board according to an embodiment of the invention;

Fig. 6 is the schematic diagram of the direct observed image of scaling board according to an embodiment of the invention; And

Fig. 7 is according to an embodiment of the invention for the schematic diagram of the image of lens distortion demarcation.

Embodiment

Be described below in detail embodiments of the 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.

Below in conjunction with accompanying drawing, the modification method according to biprism defect error in the BSL3DDIC system of the embodiment of the present invention is described.

First, the principle of the modification method of biprism defect error in the BSL3DDIC system of the embodiment of the present invention is described by reference to the accompanying drawings.

Specifically, in order to without loss of generality, in this example, to mix the biprism manufacturing deficiency of deflected, the principle of this modification method is described.Figure 3 shows that one piece of biprism that there is manufacturing deficiency, its bottom surface ABCD is rectangle plane.Due to manufacturing deficiency, rib UV is not parallel with bottom surface on top.For the purpose of directly perceived, set up reference frame XYZ with upper 1 O of bottom surface ABCD for initial point, make coordinate axis OZ perpendicular to bottom surface ABCD and pass through 1 K on the rib of top, and coordinate axis OX, OY are parallel with AB (CD), BC (AD) respectively.

Extend the clinoplane that coordinate axis OX is just half side, intersect at straight line EF with bottom surface ABCD.The clinoplane being set up plane GHJI and extension by coordinate axis OZ intersects at straight line GH, and makes straight line JI be parallel to straight line EF.Obviously, the body GIE-HJF that plane GHJI, plane GHFE, plane FEIJ, plane GIE and plane HJF are formed is a sphenoid.In like manner, the negative half side clinoplane of bottom surface ABCD and coordinate axis OX can be utilized to build sphenoid PMR-QNS, and wherein plane P QSR and plane GHJI intersects at straight line OK (i.e. coordinate axis OZ).For sphenoid GIE-HJF, cross the plane OKL that OK is constructed perpendicular to this sphenoid axial (direction of straight line EF), then dihedral angle KLO is the angle of wedge of this sphenoid, and its size Useable angles chi measurement obtains.Rectilinear direction perpendicular to sphenoid axis in definition plane ABCD is the principal direction of sphenoid, as: the direction of straight line OL is the principal direction of sphenoid GIE-HJF.Ideally, the principal direction of biprism both sides sphenoid is all parallel with X-axis.When there is manufacturing deficiency, biprism both sides still can be considered as two sphenoids, but there is angle respectively between its principal direction and X-axis, such as: the principal direction OL of sphenoid GIE-HJF and the angle of coordinate axis OX are θ ⁺; In like manner, the principal stresses angle of sphenoid PMR-QNS is θ ^-(θ ^-<0).Superscript "+" represents that this parameter corresponds to the just half side wedge-shaped mirrors of biprism herein, otherwise "-" represents that this parameter corresponds to biprism and bears half side wedge-shaped mirrors, lower same.Principal stresses angle is difficult to direct measurement usually, need obtain by demarcating.

Below for the one camera 3DDIC system based on biprism and two telecentric lens, the biprism principal stresses angle scaling method related in the embodiment of the present invention is described, the light path of this system is arranged as shown in Figure 4.In this system, the optical axis of two telecentric lens overlaps with the coordinate axis OZ in Fig. 3.For convenience of description, the principal direction coordinate system being initial point with O point shown in Fig. 3 is defined with coordinate axis overlap with OZ, coordinate axis respectively along the principal direction of the just half side and negative half side prism wedge of biprism.Following coordinate conversion relation is there is between principal direction coordinate system and reference frame:

$\left\{\begin{array}{c}{\tilde{X}}^{+}\\ {\tilde{Y}}^{+}\\ {\tilde{Z}}^{+}\end{array}\right\}=\left[\begin{array}{ccc}{\mathrm{cos\&theta;}}^{+}& -{\mathrm{sin\&theta;}}^{+}& 0\\ {\mathrm{sin\&theta;}}^{+}& {\mathrm{cos\&theta;}}^{+}& 0\\ 0& 0& 1\end{array}\right]\left\{\begin{array}{c}X\\ Y\\ Z\end{array}\right\},---\left(1.a\right)$

$\left\{\begin{array}{c}{\tilde{X}}^{-}\\ {\tilde{Y}}^{-}\\ {\tilde{Z}}^{-}\end{array}\right\}=\left[\begin{array}{ccc}{\mathrm{cos\&theta;}}^{-}& -{\mathrm{sin\&theta;}}^{-}& 0\\ {\mathrm{sin\&theta;}}^{-}& {\mathrm{cos\&theta;}}^{-}& 0\\ 0& 0& 1\end{array}\right]\left\{\begin{array}{c}X\\ Y\\ Z\end{array}\right\},---\left(1.b\right)$

Suppose that CMOS camera sensor plane orthogonal is in the optical axis of two telecentric lens, and the row and column of its pel array is parallel to coordinate axis OX and OY respectively, the pixel coordinate of some O in the image of collected by camera is (x _c, y _c).When not placing biprism, coordinate is that the dimensional target point of (X, Y, Z) can be determined by following formula position in the picture:

$x_c^0=x^0-x_c=-\frac{\mathrm{\&eta;}}{P_{sz}}X,---\left(2.a\right)$

$y_c^0=y^0-y_c=-\frac{\mathrm{\&eta;}}{P_{sz}}Y,---\left(2.b\right)$

(x in formula ⁰, y ⁰) be the pixel coordinate of picture point, for with (x _c, y _c) be pixel coordinate during initial point, η is the enlargement factor of two telecentric lens, P _sZfor the physical size of pixel each on cmos sensor.After placing biprism, picture point (x ⁰, y ⁰) can misplace, form the picture point with a pair dislocation, if its pixel coordinate is (x ⁺, y ⁺) and (x ^-, y ^-).With (x _c, y _c) for initial point time, its pixel coordinate with obtain by following formula:

$x_c^{+}=x^{+}-x_c,---\left(3.a\right)$

$y_c^{+}=y^{+}-y_c,---\left(3.b\right)$

$x_c^{-}=x^{-}-x_c,---\left(3.c\right)$

$y_c^{-}=y^{-}-y_c.---\left(3.d\right)$

And from (1.a) and (1.b) formula, be tied to the rotational transform be transformed to around OZ axle of principal direction coordinate system by reference coordinate, therefore in the picture, above-mentioned pixel coordinate is done following around (x _c, y _c) face in rotational transform:

${\tilde{y}}_c^{0+}=-{\mathrm{sin\&theta;}}^{+}{x}_c^0+{\mathrm{cos\&theta;}}^{+}{y}_c^0,---\left(4.a\right)$

${\tilde{y}}_c^{0-}=-{\mathrm{sin\&theta;}}^{-}{x}_c^0+{\mathrm{cos\&theta;}}^{-}{y}_c^0,---\left(4.b\right)$

${\tilde{y}}_c^{+}=-{\mathrm{sin\&theta;}}^{+}{x}_c^{+}+{\mathrm{cos\&theta;}}^{+}{y}_c^{+},---\left(4.c\right)$

${\tilde{y}}_c^{-}=-{\mathrm{sin\&theta;}}^{-}{x}_c^{-}+{\mathrm{cos\&theta;}}^{-}{y}_c^{-},---\left(4.d\right)$

In formula with represent when not placing biprism respectively, picture point longitudinal pixel coordinate value under the principal direction coordinate system of biprism both sides; with represent after placing biprism respectively, dislocation picture point with longitudinal pixel coordinate value under respective principal direction coordinate system.During owing to utilizing prism wedge imaging, image not along prism axis to misplacing, therefore is corresponding under the just half side and negative half side principal direction coordinate system of biprism, and before and after placement biprism, the displacement of picture point vertical direction is zero.Thus the pixel coordinate in (4) formula should meet following relation:

${\tilde{y}}_c^{0+}={\tilde{y}}_c^{+},---\left(5.a\right)$

${\tilde{y}}_c^{0-}={\tilde{y}}_c^{-}.---\left(5.b\right)$

Simultaneous (4), (5) formula, can according to the forward and backward picpointed coordinate of dislocation, to biprism principal stresses angle θ ⁺and θ ^-demarcate.In addition, consider and usually use multiple dimensional target point to demarcate, above-mentioned principal stresses angle obtains by least square method.

Consider the manufacturing deficiency of biprism, dimensional target point (X, Y, Z) and picture point pair corresponding with it with between relation can be represented by following correction mathematical model:

$\begin{array}{c}{x}_c^{+}{\mathrm{cos\&theta;}}^{+}+y_c^{+}{\mathrm{sin\&theta;}}^{+}=-\frac{\mathrm{\&eta;}}{P_{sz}}\&lsqb;(1+A^{+}{\mathrm{tan\&alpha;}}^{+})(X{\mathrm{cos\&theta;}}^{+}+Y{\mathrm{sin\&theta;}}^{+})+\\ A+Z-A+t0,\end{array}---\left(6.a\right)$

$\begin{array}{c}{x}_x^{-}{\mathrm{cos\&theta;}}^{-}+y_c^{-}{\mathrm{sin\&theta;}}^{-}=-\frac{\mathrm{\&eta;}}{P_{sz}}\&lsqb;(1+A^{-}{\mathrm{tan\&alpha;}}^{-})(X{\mathrm{cos\&theta;}}^{-}+Y{\mathrm{sin\&theta;}}^{-})-\\ A-Z+A-t0,\end{array}---\left(6.b\right)$

$x_c^{+}{\mathrm{sin\&theta;}}^{+}-y_c^{+}{\mathrm{cos\&theta;}}^{+}=-\frac{\mathrm{\&eta;}}{P_{sz}}(X{\mathrm{sin\&theta;}}^{+}-Y{\mathrm{cos\&theta;}}^{+}),---\left(6.c\right)$

$x_c^{-}{\mathrm{sin\&theta;}}^{+}-y_c^{-}{\mathrm{cos\&theta;}}^{+}=-\frac{\mathrm{\&eta;}}{P_{sz}}(X{\mathrm{sin\&theta;}}^{-}-Y{\mathrm{cos\&theta;}}^{-}),---\left(6.d\right)$

α in formula ⁺and α ^-represent the angle of wedge (dihedral angle) of biprism both sides wedge-shaped mirrors respectively; A ⁺and A ^-be and biprism locking angle ⁺and α ^-and the parameter that refractive index n is relevant, its expression formula is:

$A^{+}=\frac{n{\mathrm{sin\&alpha;}}^{+}{\cos }^2{\mathrm{\&alpha;}}^{+}}{\sqrt{1-n^2{\sin }^2{\mathrm{\&alpha;}}^{+}}}-{\mathrm{sin\&alpha;}}^{+}{\mathrm{cos\&alpha;}}^{+},---\left(7.a\right)$

$A^{-}=\frac{n{\sin }^{-}{\mathrm{\&alpha;cos}}^2{\mathrm{\&alpha;}}^{-}}{\sqrt{1-n^2{\sin }^2{\mathrm{\&alpha;}}^{-}}}-{\mathrm{sin\&alpha;}}^{-}{\mathrm{cos\&alpha;}}^{-};---\left(7.a\right)$

T ₀for biprism is along the thickness of OZ axle, i.e. the length of Fig. 3 middle conductor OK, can use vernier caliper measurement to obtain.Revised volume coordinate obtains by solving (6) formula.θ ⁺and θ ^-value usually less, therefore (6) formula normally ill-conditioned linear systems.In order to control the error in solving result, should solve as follows:

Step 1: simultaneous (6.c), (6.d) formula, cancellation X solves and obtains Y.

Step 2: solve the Y obtained in step 1 and substitute into (6.a), (6.b) formula, simultaneous solution X and Z.

Based on this, Fig. 2 illustrates the process flow diagram of the modification method of biprism defect error in BSL3DDIC system according to an embodiment of the invention.It should be noted that, in this example, for the one camera 3DDIC system based on biprism and two telecentric lens, the demarcation related to and modification method are further detailed, not as the restriction of establishing the present invention in the embodiment of the present invention.In addition, in view of the key content that the present invention relates to is for demarcating and modification method, therefore gives tacit consent in this example and built the measuring system shown in Fig. 4.After use said system completes measurement, with reference to shown in Fig. 2, the method comprises the following steps:

Step S1: build measuring system, and scaling board to be placed in the visual field of measuring system, and adjust the position of scaling board and attitude until scaling board imaging clearly, further, use the dislocation image of CMOS collected by camera software collection scaling board, as shown in Figure 5.Wherein, measuring system comprises biprism, two telecentric lens and a CMOS camera.Wherein, scaling board is one piece of gridiron pattern scaling board, and the grid length of side of described gridiron pattern scaling board is 1.6mm.It should be noted that, the initial point in Fig. 5 is labeled as the gauge point be produced on biprism seamed edge, is equivalent to the some K in Fig. 3.(x in Fig. 5 _c, y _c) the center that marked by initial point, position determine.

Step S2: remove biprism from acquisition system.

Further, step S2 comprises further: remove the camera before and after biprism and two telecentric lens, and keep the invariant position of scaling board.

Step S3: employing CMOS collected by camera software collection directly observes image during scaling board, such as, shown in Fig. 6.

Step S4: according to the pixel coordinate of corresponding angle point before and after the dislocation image of scaling board and image calculating dislocation when directly observing scaling board.

In conjunction with aforementioned exemplary, step S4 specifically comprises: use corner recognition algorithm, the pixel coordinate of angle point shown in the white circle in calculating chart 6 and calculated by (2) formula the pixel coordinate of the corresponding angle point in calculating chart 5 left and right sides subsequently with and calculated by (3) formula with it should be noted that, subscript " i ", " j " represent that this point is positioned at the i-th row, the jth row of angle point array herein, lower same.

Step S5: carry out lens distortion demarcation and correction according to the pixel coordinate of angle point during direct observation scaling board.

In one embodiment of the invention, step S5 comprises further:

Step S51: judge that whether the degree of lens distortion is higher than distortion threshold value.

Step S52: if the degree of lens distortion is higher than distortion threshold value, then show to need to carry out lens distortion demarcation and correction, be specially: mobile scaling board to diverse location, and gathers correspondence image, with all regions making angle point farthest spread all over correspondence image, such as, shown in Fig. 7.

Step S53: the pixel coordinate calculating each angle point in each image, and matching lens distortion function.Particularly, lens distortion function is such as:

${\mathrm{\&delta;}}_x=x_u(k_1{r}^2+k_2{r}^4+k_3{r}^6+k_4{r}^8+k_5{r}^{10})+(p_0+p_2{r}^2)(2x_u^2+r^2)+r^2(s_0+s_2{r}^2),$

${\mathrm{\&delta;}}_y=y_u(k_1{r}^2+k_2{r}^4+k_3{r}^6+k_4{r}^8+k_5{r}^{10})+(p_1+p_3{r}^2)(2y_u^2+r^2)+r^2(s_1+s_3{r}^2),$

Wherein, δ _x, δ _ybe respectively the perturbed field of image level, vertical direction, (x _u, y _u) be undistorted pixel coordinate, k ₁, k ₂, k ₃, k ₄, k ₅, p ₀, p ₁, p ₂, p ₃, s ₀, s ₁, s ₂, s ₃for demarcating the distortion parameter obtained.

Step S54: each pixel coordinate is revised according to lens distortion function.

Further, in step s 5, also comprise:

Step S55: if the degree of lens distortion is lower than distortion threshold value, namely this lens distortion can be ignored, then do not carry out lens distortion demarcation and correction.

Step S6: build least square function, and according to least square function, utilize the pixel coordinate of corresponding angle point before and after dislocation to demarcate biprism principal stresses angle.Wherein, the least square function of structure is such as:

${\mathrm{LSF}}_1={\mathrm{\&Sigma;}}_i{\mathrm{\&Sigma;}}_j{\&lsqb;-{\mathrm{sin\&theta;}}^{+}(x_{cij}^{+}-x_{cij}^0)+{\mathrm{cos\&theta;}}^{+}(y_{cij}^{+}-y_{cij}^0)\&rsqb;}^2,---\left(9.a\right)$

${\mathrm{LSF}}_2={\mathrm{\&Sigma;}}_i{\mathrm{\&Sigma;}}_j{\&lsqb;-{\mathrm{sin\&theta;}}^{-}(x_{cij}^{-}-x_{cij}^0)+{\mathrm{cos\&theta;}}^{-}(y_{cij}^{-}-y_{cij}^0)\&rsqb;}^2,---\left(9.b\right)$

Wherein, θ ⁺and θ ^-the calibration result of biprism principal stresses angle, described θ ⁺and θ ^-make LSF ₁and LSF ₂obtain minimal value.

Step S7: build and revise mathematical model, the calibration result of biprism principal stresses angle is inputted this correction mathematical model to revise biprism defect error.Wherein, the correction mathematical model that correction mathematical model and aforementioned (6) formula are shown, is specially:

$x_c^{+}{\mathrm{cos\&theta;}}^{+}+y_c^{+}{\mathrm{sin\&theta;}}^{+}=-\frac{\mathrm{\&eta;}}{P_{sz}}\&lsqb;(1+A^{+}{\mathrm{tan\&alpha;}}^{+})(X{\mathrm{cos\&theta;}}^{+}+Y{\mathrm{sin\&theta;}}^{+})+A^{+}Z-A^{+}{t}_0\&rsqb;,$

$x_c^{-}{\mathrm{cos\&theta;}}^{-}+y_c^{-}{\mathrm{sin\&theta;}}^{-}=-\frac{\mathrm{\&eta;}}{P_{sz}}\&lsqb;(1+A^{-}{\mathrm{tan\&alpha;}}^{-})(X{\mathrm{cos\&theta;}}^{-}+Y{\mathrm{sin\&theta;}}^{-})-A^{-}Z+A^{-}{t}_0\&rsqb;,$

$x_c^{+}{\mathrm{sin\&theta;}}^{+}-y_c^{+}{\mathrm{cos\&theta;}}^{+}=-\frac{\mathrm{\&eta;}}{P_{sz}}(X{\mathrm{sin\&theta;}}^{+}-Y{\mathrm{cos\&theta;}}^{+}),$

$x_c^{-}{\mathrm{sin\&theta;}}^{+}-y_c^{-}{\mathrm{cos\&theta;}}^{+}=-\frac{\mathrm{\&eta;}}{P_{sz}}(X{\mathrm{sin\&theta;}}^{-}-Y{\mathrm{cos\&theta;}}^{-}),$

Wherein, α ⁺and α ^-represent the angle of wedge of biprism both sides wedge-shaped mirrors respectively, A ⁺and A ^-be and biprism locking angle ⁺and α ^-and the parameter that refractive index n is relevant.

More specifically, $A^{+}=\frac{n{\mathrm{sin\&alpha;}}^{+}{\cos }^2{\mathrm{\&alpha;}}^{+}}{\sqrt{1-n^2{\sin }^2{\mathrm{\&alpha;}}^{+}}}-{\mathrm{sin\&alpha;}}^{+}{\mathrm{cos\&alpha;}}^{+},$

$A^{-}=\frac{n{\sin }^{-}{\mathrm{\&alpha;cos}}^2{\mathrm{\&alpha;}}^{-}}{\sqrt{1-n^2{\sin }^2{\mathrm{\&alpha;}}^{-}}}-{\mathrm{sin\&alpha;}}^{-}{\mathrm{cos\&alpha;}}^{-}.$

Based on this, step S7 comprises further: by θ ⁺and θ ^-substitute in above-mentioned correction mathematical model, and pixel coordinate is solved to the volume coordinate of corresponding object point in combination with the picture point in the testee dislocation image of DIC computing coupling, and carry out follow-up three-dimensional appearance reconstruct.

To sum up, according to the modification method of biprism defect error in the BSL3DDIC system of the embodiment of the present invention, introduce the concept of biprism principal direction, the biprism that there is manufacturing deficiency is equivalent to the prism wedge that two principal directions and reference frame form an angle respectively; And when utilizing prism wedge imaging, image along prism axis to this feature of generation dislocation, by demarcating biprism principal direction, does not carry out error correction; In addition, biprism principal direction calibration process and experiment measuring process separate, do not interfere with each other, follow-up lens distortion can be carried out demarcate after completing demarcation; Further, utilize and revise mathematical model, the correction of systematic error can be realized in the process of three-dimensionalreconstruction.The method can be revised biprism defect error, improves the accuracy of measurement of system.

In describing the invention, it will be appreciated that, term " " center ", " longitudinal direction ", " transverse direction ", " length ", " width ", " thickness ", " on ", D score, " front ", " afterwards ", " left side ", " right side ", " vertically ", " level ", " top ", " end " " interior ", " outward ", " clockwise ", " counterclockwise ", " axis ", " radial direction ", orientation or the position relationship of the instruction such as " circumference " are based on orientation shown in the drawings or position relationship, only the present invention for convenience of description and simplified characterization, instead of indicate or imply that the device of indication or element must have specific orientation, with specific azimuth configuration and operation, therefore limitation of the present invention can not be interpreted as.

In addition, term " first ", " second " only for describing object, and can not be interpreted as instruction or hint relative importance or imply the quantity indicating indicated technical characteristic.Thus, be limited with " first ", the feature of " second " can express or impliedly comprise at least one this feature.In describing the invention, the implication of " multiple " is at least two, such as two, three etc., unless otherwise expressly limited specifically.

In the present invention, unless otherwise clearly defined and limited, the term such as term " installation ", " being connected ", " connection ", " fixing " should be interpreted broadly, and such as, can be fixedly connected with, also can be removably connect, or integral; Can be mechanical connection, also can be electrical connection; Can be directly be connected, also indirectly can be connected by intermediary, can be the connection of two element internals or the interaction relationship of two elements, unless otherwise clear and definite restriction.For the ordinary skill in the art, above-mentioned term concrete meaning in the present invention can be understood as the case may be.

In the present invention, unless otherwise clearly defined and limited, fisrt feature second feature " on " or D score can be that the first and second features directly contact, or the first and second features are by intermediary indirect contact.And, fisrt feature second feature " on ", " top " and " above " but fisrt feature directly over second feature or oblique upper, or only represent that fisrt feature level height is higher than second feature.Fisrt feature second feature " under ", " below " and " below " can be fisrt feature immediately below second feature or tiltedly below, or only represent that fisrt feature level height is less than second feature.

In the description of this instructions, specific features, structure, material or feature that the description of reference term " embodiment ", " some embodiments ", " example ", " concrete example " or " some examples " etc. means to describe in conjunction with this embodiment or example are contained at least one embodiment of the present invention or example.In this manual, to the schematic representation of above-mentioned term not must for be identical embodiment or example.And the specific features of description, structure, material or feature can combine in one or more embodiment in office or example in an appropriate manner.In addition, when not conflicting, the feature of the different embodiment described in this instructions or example and different embodiment or example can carry out combining and combining by those skilled in the art.

Although illustrate and describe embodiments of the invention above, be understandable that, above-described embodiment is exemplary, can not be interpreted as limitation of the present invention, and those of ordinary skill in the art can change above-described embodiment within the scope of the invention, revises, replace and modification.

Claims (10)

1. the modification method of biprism defect error in BSL3DDIC system, is characterized in that, comprise the following steps:

S1: build measuring system, and scaling board is placed in the visual field of described measuring system, and adjust the position of described scaling board and attitude until described scaling board imaging clearly, and gather the dislocation image of described scaling board, wherein, described measuring system comprises biprism, two telecentric lens and a CMOS camera;

S2: remove described biprism from described measuring system;

S3: gather image when directly observing described scaling board;

S4: according to the pixel coordinate of corresponding angle point before and after the dislocation image of described scaling board and image calculating dislocation when directly observing described scaling board;

S5: carry out lens distortion demarcation and correction according to the pixel coordinate of angle point during direct observation described scaling board;

S6: build least square function, and utilize the pixel coordinate of corresponding angle point before and after dislocation to demarcate biprism principal stresses angle according to described least square function; And

S7: build and revise mathematical model, the calibration result of biprism principal stresses angle is inputted described correction mathematical model to revise biprism defect error.

2. the modification method of biprism defect error in BSL3DDIC system according to claim 1, it is characterized in that, described scaling board is one piece of gridiron pattern scaling board, and the grid length of side of described gridiron pattern scaling board is 1.6mm.

3. the modification method of biprism defect error in BSL3DDIC system according to claim 1, is characterized in that, describedly from described acquisition system, removes described biprism, comprises further:

Remove the camera before and after biprism and described pair of telecentric lens, and keep the invariant position of described scaling board.

4. the modification method of biprism defect error in BSL3DDIC system according to claim 1, it is characterized in that, described step S5 comprises further:

Judge that whether the degree of lens distortion is higher than distortion threshold value;

If the degree of lens distortion is higher than described distortion threshold value, then moves described scaling board to diverse location, and gather correspondence image, with all regions making angle point farthest spread all over described correspondence image;

Calculate the pixel coordinate of each angle point in each image, and matching lens distortion function;

According to described lens distortion function, each pixel coordinate is revised.

5. the modification method of biprism defect error in BSL3DDIC system according to claim 4, it is characterized in that, described lens distortion function is:

${\mathrm{\&delta;}}_x=x_u(k_1{r}^2+k_2{r}^4+k_3{r}^6+k_4{r}^8+k_5{r}^{10})+(p_0+p_2{r}^2)(2x_u^2+r^2)+r^2(s_0+s_2{r}^2),$

${\mathrm{\&delta;}}_y=y_u(k_1{r}^2+k_2{r}^4+k_3{r}^6+k_4{r}^8+k_5{r}^{10})+(p_1+p_3{r}^2)(2y_u^2+r^2)+r^2(s_1+s_3{r}^2),$

Wherein, δ _x, δ _ybe respectively the perturbed field of image level, vertical direction, (x _u, y _u) be undistorted pixel coordinate, k ₁, k ₂, k ₃, k ₄, k ₅, p ₀, p ₁, p ₂, p ₃, s ₀, s ₁, s ₂, s ₃for demarcating the distortion parameter obtained.

6. the modification method of biprism defect error in BSL3DDIC system according to claim 4, is characterized in that, if the degree of described lens distortion is lower than distortion threshold value, does not then carry out lens distortion demarcation and correction.

7. the modification method of biprism defect error in BSL3DDIC system according to claim 1, it is characterized in that, in described step S6, described least square function is:

${\mathrm{LSF}}_1={\mathrm{\&Sigma;}}_i{\mathrm{\&Sigma;}}_j{\&lsqb;-{\mathrm{sin\&theta;}}^{+}(x_{cij}^{+}-x_{cij}^0)+{\mathrm{cos\&theta;}}^{+}(y_{cij}^{+}-y_{cij}^0)\&rsqb;}^2,$

${\mathrm{LSF}}_2={\mathrm{\&Sigma;}}_i{\mathrm{\&Sigma;}}_j{\&lsqb;-{\mathrm{sin\&theta;}}^{-}(x_{cij}^{-}-x_{cij}^0)+{\mathrm{cos\&theta;}}^{-}(y_{cij}^{-}-y_{cij}^0)\&rsqb;}^2,$

Wherein, θ ⁺and θ ^-the calibration result of biprism principal stresses angle, described θ ⁺and θ ^-make LSF ₁and LSF ₂obtain minimal value.

8. the modification method of biprism defect error in BSL3DDIC system according to claim 1, it is characterized in that, described correction mathematical model is:

$x_c^{+}{\mathrm{cos\&theta;}}^{+}+y_c^{+}{\mathrm{sin\&theta;}}^{+}=-\frac{\mathrm{\&eta;}}{P_{sz}}\&lsqb;(1+A^{+}{\mathrm{tan\&alpha;}}^{+})(X{\mathrm{cos\&theta;}}^{+}+Y{\mathrm{sin\&theta;}}^{+})+A^{+}Z-A^{+}{t}_0\&rsqb;,$

$x_c^{-}{\mathrm{cos\&theta;}}^{-}+y_c^{-}{\mathrm{sin\&theta;}}^{-}=-\frac{\mathrm{\&eta;}}{P_{sz}}\&lsqb;(1+A^{-}{\mathrm{tan\&alpha;}}^{-})(X{\mathrm{cos\&theta;}}^{-}+Y{\mathrm{sin\&theta;}}^{-})-A^{-}Z-A^{-}{t}_0\&rsqb;,$

$x_c^{+}{\mathrm{sin\&theta;}}^{+}-y_c^{+}{\mathrm{cos\&theta;}}^{+}=-\frac{\mathrm{\&eta;}}{P_{sz}}(X{\mathrm{sin\&theta;}}^{+}-Y{\mathrm{cos\&theta;}}^{+}),$

$x_c^{-}{\mathrm{sin\&theta;}}^{+}-y_c^{-}{\mathrm{cos\&theta;}}^{+}=-\frac{\mathrm{\&eta;}}{P_{sz}}(X{\mathrm{sin\&theta;}}^{-}-Y{\mathrm{cos\&theta;}}^{-}),$

Wherein, α ⁺and α ^-represent the angle of wedge of biprism both sides wedge-shaped mirrors respectively, A ⁺and A ^-be and biprism locking angle ⁺and α ^-and the parameter that refractive index n is relevant.

9. the modification method of biprism defect error in BSL3DDIC system according to claim 8, is characterized in that, wherein,

$A^{+}=\frac{n{\mathrm{sin\&alpha;}}^{+}{\cos }^2{\mathrm{\&alpha;}}^{+}}{\sqrt{1-n^2{\sin }^2{\mathrm{\&alpha;}}^{+}}}-{\mathrm{sin\&alpha;}}^{+}{\mathrm{cos\&alpha;}}^{+},$

$A^{-}=\frac{n{\mathrm{sin\&alpha;}}^{-}{\cos }^2{\mathrm{\&alpha;}}^{-}}{\sqrt{1-n^2{\sin }^2{\mathrm{\&alpha;}}^{-}}}-{\mathrm{sin\&alpha;}}^{-}{\mathrm{cos\&alpha;}}^{-}.$

10. the modification method of biprism defect error in BSL3DDIC system according to claim 9, it is characterized in that, described step S7 comprises further:

By θ ⁺and θ ^-substitute into and revise in mathematical model, and in combination with the picture point in the testee dislocation image of relevant (DIC) computing coupling of digital picture to pixel coordinate, solve the volume coordinate of corresponding object point, and carry out follow-up three-dimensional appearance reconstruct.