CN102967261B - Laser displacement measuring method based on digital speckle correlation method (DSCM) - Google Patents

Abstract

The invention discloses a laser displacement measuring method based on a DSCM. The method includes that lasers are vertically shot into a moving measured object surface through focusing; scattered light at incident spots on the measured object surface is received and is imaged on the sensitive surface of a charge coupled device (CCD) through an imaging lens to obtain scattering spots; when the signal bandwidth of the scattering spots is smaller than or equal to a bandwidth threshold, the measured object surface is indicated to be a weak scattering interface, and displacements of the scattering spots on the CCD are measured by using an average weighted centroid method; when the signal bandwidth of the scattering spots is larger than the bandwidth threshold, the measured object surface is indicated to be a strong scattering interface, and displacements of the scattering spots on the CCD are measured by using a correlation method; and the displacement of the measured object is calculated according to the displacements of the scattering spots on the CCD. According to the method, accurate measurement of displacements of various roughness object surfaces is achieved, and the measurement is rapid and accurate.

Description

A kind of laser displacement measurement method based on Digital Speckle Correlation Method

Technical field

The present invention relates to displacement sensing fields of measurement, be specifically related to a kind of laser displacement measurement method based on Digital Speckle Correlation Method, be applicable to strong scattering, rough interfaces displacement measurement.

Background technology

Laser triangulation displacement transducer is a kind of important sensor of non-cpntact measurement displacement, is widely used in the measurements such as three-D profile, thickness, width, material level and vibration.The diffuse reflection hot spot that laser beam projects is formed to tested object plane by it, as transducing signal, the optical receiver diffusing of collecting being converged to focal plane by lens imaging principle forms picture point.This receiver can be light spot position detector (CCD), also available position Sensitive Apparatus PSD.When using laser triangulation law theory to measure the displacement of body surface, in weak scattering situation, after hardware filtering and software filtering, the gravity center shift of spot signal before and after displacement can be obtained by gravity model appoach, obtain the shift value of hot spot on CCD, and then obtain the actual displacement value of object plane.But body surface is more coarse, when there is strong scattering, the upper received measuring point scattering hot spot of CCD will be submerged in speckle noise, at this moment take to suppress the technical measures of speckle effect by poor effect.

Summary of the invention

The object of the invention is the problems referred to above being to exist for prior art, a kind of laser displacement measurement method based on Digital Speckle Correlation Method is provided,, the method can realize the displacement measurement under the very coarse condition of tested object plane, and has and measure rapidity and accuracy.

Above-mentioned purpose of the present invention is achieved through the following technical solutions:

Based on a laser displacement measurement method for Digital Speckle Correlation Method, be specially:

Testee surface during step 1 laser line focus vertical incidence moves;

Step 2 receives the scattered light at incident luminous point place, testee surface, and the sensitive area being imaged on CCD by imaging len obtains scattering hot spot;

Step 3 when the signal bandwidth of scattering hot spot is less than or equal to bandwidth threshold values F, then shows that testee surface is weak scattering interface, adopts average weighted gravity model appoach to measure the displacement δ of scattering hot spot on CCD; When the signal bandwidth of scattering hot spot is greater than bandwidth threshold values F, then shows that testee surface is strong scattering cross section, adopt the displacement δ of correlation measurement scattering hot spot on CCD;

Step 4 calculates the displacement of testee according to the displacement δ of scattering hot spot on CCD.

Further, described bandwidth threshold values F span is 150 ~ 250.

Further, the average weighted gravity model appoach in described step 3 is specially: displacement δ equals the center of gravity horizontal ordinate of scattering hot spot in movable difference, the center of gravity horizontal ordinate of scattering hot spot computing formula is

$\stackrel{\‾}{x}=\frac{\underset{i=n_1}{\overset{n_2}{\mathrm{\Σ}}}{x}_i{f}^2\left(x_i\right)}{\underset{i=n_1}{\overset{n_2}{\mathrm{\Σ}}}{f}^2\left(x_i\right)}$

Wherein, x _ifor the horizontal ordinate of i-th picture dot of scattering hot spot, f (x _i) be the ordinate of i-th picture dot of scattering hot spot, n ₁for minimum picture dot sequence number, n ₂for maximum picture dot sequence number.

Further, the correlation method in described step 3 is specially:

Read the light intensity of the scattering hot spot before testee displacement, and one dimension picture dot light intensity matrix before converting displacement to, in displacement last dimension picture dot light intensity matrix, choose the sample sub-range comprising main peak information;

Read the light intensity of the scattering hot spot after testee displacement, and one dimension picture dot light intensity matrix after converting displacement to, after displacement, choose multiple target sub-range identical with sample sub-range width in one dimension picture dot light intensity matrix;

Search and the maximum target sub-range of sample sub-range similarity coefficient, and be aided with interpolation processing and obtain scattering spot displacement.

Further, described similarity coefficient is calculated in the following manner $C=\frac{\underset{j=1}{\overset{m}{\mathrm{\Σ}}}[p\left(x_j\right)-\stackrel{\‾}{p}]\×[q\left(x_j^{\′}\right)-\stackrel{\‾}{q}]}{\sqrt{\underset{j=1}{\overset{m}{\mathrm{\Σ}}}{[f\left(x_j\right)-\stackrel{\‾}{f}]}^2}\sqrt{\underset{j=1}{\overset{m}{\mathrm{\Σ}}}{[g\left(x_j^{\′}\right)-\stackrel{\‾}{g}]}^2}},$ Wherein, $\stackrel{\‾}{p}=\underset{j=1}{\overset{m}{\mathrm{\Σ}}}p\left(x_j\right)/m,$ $\stackrel{\‾}{q}=\underset{j=1}{\overset{m}{\mathrm{\Σ}}}q\left(x_j^{\′}\right)/m,$ P (x _j) be sample sub-range, x _jfor the picture dot of the jth in sample subarea, q (x' _j) be target sub-range, x ' _jfor the picture dot of the jth in target sub-range, m is picture dot sum.

Further, described step 4 adopts the displacement of direct-injection type trigonometric calculations testee, is specially: the displacement of testee wherein, l is object distance, and l' is image distance, and θ is scattering angle, and φ is the angle of CCD and incident light; If testee surface is moved away from Laser Focusing point, in formula ± choose-, if testee surface is moved near Laser Focusing point, in formula ± choose+.

The present invention compared with prior art, has the following advantages:

1, the present invention is according to the size of bandwidth threshold values, judges weak scattering interface and strong scattering cross section, automatically adopts gravity model appoach to carry out survey calculation, automatically adopt Digital Speckle Correlation Method to calculate when object plane to be measured is strong scattering interface when object plane to be measured is weak scattering interface.This just compensate for that conventional laser trigonometry displacement transducer is coarse at height, gravity model appoach lost efficacy in strong reflection object plane situation, the defect that measuring result error is large.Achieve the accurate measurement to the displacement of various roughness object plane.

2, the present invention can treat the measurement under displacement object plane high roughness strong scattering condition, has the advantages that precision is high and real-time is good.

3, the present invention uses simply, and easy to operate, cost is low.

Accompanying drawing explanation

Fig. 1 is the inventive method process flow diagram;

Fig. 2 is for implementing measurement mechanism structural drawing of the present invention.

Wherein, 1-laser instrument; 2-plus lens; 3-testee surface; 4-imaging len; 5-CCD(charge coupled cell); φ-be the angle of CCD and incident light; δ-the displacement of scattering hot spot on CCD; L '-image distance; L-object distance; θ-scattering angle; The displacement of Δ-testee.

Embodiment

Below in conjunction with accompanying drawing, technical scheme of the present invention is described in further detail.

With reference to Fig. 1 and 2, the present invention is based on the laser displacement measurement method of Digital Speckle Correlation Method, comprise the following steps:

Step 1 uses laser instrument 1 to send laser, and laser, after plus lens 2 focuses on, impinges perpendicularly on testee surface 3.

Step 2 receiver lens receives the scattered light from the incident luminous point place on testee surface, and is imaged on the sensitive area of CCD5 by imaging len 4, obtains scattering hot spot.

Step 3 sets bandwidth threshold values F, the i.e. inter-pixel distance of CCD, analyze the signal bandwidth of scattering hot spot, adopt average weighted gravity model appoach to measure the displacement δ of scattering hot spot on CCD when the signal bandwidth of scattering hot spot is less than or equal to bandwidth threshold values F, adopt the displacement δ of correlation measurement scattering hot spot on CCD when the signal bandwidth of scattering hot spot is greater than bandwidth threshold values F.

Described bandwidth threshold values F is 150 ~ 250.

Square weighting gravity model appoach is specially: by the center of gravity horizontal ordinate of movable scattering hot spot difference obtain δ, center of gravity horizontal ordinate based on following formula:

$\stackrel{\‾}{x}=\frac{\underset{i=n_1}{\overset{n_2}{\mathrm{\Σ}}}{x}_i{f}^2\left(x_i\right)}{\underset{i=n_1}{\overset{n_2}{\mathrm{\Σ}}}{f}^2\left(x_i\right)}$

Wherein, for the center of gravity horizontal ordinate of scattering hot spot, x _ifor scattering hot spot i-th picture dot horizontal ordinate, f/ (x _i) for scattering hot spot a fourth picture dot ordinate, n ₁for minimum picture dot sequence number, n ₂for maximum picture dot sequence number.

Correlation method is specially:

Read the light intensity of the scattering hot spot before testee displacement, and one dimension pixel light intensity matrix before converting displacement to, in displacement last dimension pixel light intensity matrix, choose the sample sub-range comprising main peak information;

Read the light intensity of the scattering hot spot after testee displacement, and one dimension pixel light intensity matrix after converting displacement to, after displacement, choose the target sub-range identical with sample sub-range width in one dimension pixel light intensity matrix;

Search the target sub-range maximum with sample sub-range similarity coefficient, when searching the position with sample sub-range related coefficient maximal value, being aided with interpolation reason and just can recording scattering spot displacement.

In trigonometry displacement measurement, the light intensity of the scattering hot spot that each pixel of CCD receives converts one dimension character matrix to, when scattering hot spot is along the orientation displacement of CCD pixel, the digital distribution of this one dimension matrix is substantially constant, but the volume coordinate of each numeral correspondence changes.The window function of one fixed width is got by signal cutout in one dimension character matrix before displacement, get can reflect scattering interface information data (such as comprising 300 picture dot width of main peak) as sample sub-range, use the successive objective sub-range (1-300 finding same widths in the one dimension character matrix of related operation after displacement, 2-301,3-302,, 10251-10550).By the computing of one dimension digital correlation, similarity coefficient C is based on following formula:

$C=\frac{\underset{j=1}{\overset{m}{\mathrm{\Σ}}}[p\left(x_j\right)-\stackrel{\‾}{p}]\×[q\left(x_j^{\′}\right)-\stackrel{\‾}{q}]}{\sqrt{\underset{j=1}{\overset{m}{\mathrm{\Σ}}}{[f\left(x_j\right)-\stackrel{\‾}{f}]}^2}\sqrt{\underset{j=1}{\overset{m}{\mathrm{\Σ}}}{[g\left(x_j^{\′}\right)-\stackrel{\‾}{g}]}^2}}$

Wherein: p (x _j) be sample sub-range, x _jfor the picture dot in sample subarea, q (x' _j) be target sub-range, x ' _jfor the picture dot in target sub-range, m is picture dot sum.

Step 4 obtains the displacement of testee according to δ and direct-injection type trigonometry.

Direct-injection type trigonometry is based on following formula:

$\mathrm{\Δ}=\frac{l\×\mathrm{\δ}\×\sin \mathrm{\φ}}{l^{\′}\×\sin \mathrm{\θ}\±\×\sin (\mathrm{\θ}+\mathrm{\φ})}$

Wherein, l is object distance, and l ' is image distance, and θ is scattering angle; φ is the angle of CCD and incident light, if testee surface is moved away from plus lens, in formula ± choose-; If testee surface is moved near plus lens, in formula ± choose+;

Embodiment:

Laser instrument is selected and is adopted power adjustable laser device (model DI650-1-3) as light source, and its output power is 1mw, and therefore the range of adjustment of laser power is 0-1mw.The optical signal receiver adopted is TCD1501D line array CCD, its maximum drive frequency is 6MHZ, simulation frequency is 1MHZ, when driving chip Counter Value meter to 4570 time, produce full signal, sampling period (1/ driving frequency) is multiplied by Counter Value and is optical-integral-time, and thus the optical-integral-time of circuit is 0.77ms-4.57ms.When the signal that CCD receives is too weak, need to carry out signal amplification, in circuit design, adopt 20k Ω digital potentiometer to carry out the adjustment of enlargement ratio, pre-resistor is 1k Ω, therefore regulates the range of adjustment of CCD gain amplifier to be 1-20 times.

The model that imaging len selects Daheng photoelectricity to produce is GCL-304(focal length F=20mm) lens, obtain object distance according to magnification and image distance is respectively 28mm and 70mm.Scatteringangleθ is excessive, can cause the problem such as astigmatism and distortion, and scatteringangleθ is set as 30 degree.

Plus lens focal length F=24mm.

CCD selects TCD1501D, picture dot distance 4um, and length is 55mm, is highly 66mm.

Bandwidth threshold values F=180.

Testee is smooth mirror surface, and on smooth mirror surface, coat 80 order atomized aluminiums simulation rough interfaces, be now in strong scattering object plane, 10 different displacements are carried out to this testee, process data by gravity model appoach and the inventive method respectively, result is as shown in table 1.

Table 1 the inventive method compares with gravity model appoach measurement result

The experimental data of upper table shows, apply the inventive method when strong scattering interface and be better than gravity model appoach result, result of calculation is accurate to micron order, and error is within 2%.

Concrete embodiment described herein is only to the explanation for example of the present invention's spirit.Those skilled in the art can make various amendment or supplement or adopt similar mode to substitute to described concrete embodiment, but can't depart from spirit of the present invention or surmount the scope that appended claims defines.

Claims (6)

1., based on a laser displacement measurement method for Digital Speckle Correlation Method, be specially:

Testee surface during step 1 laser line focus vertical incidence moves;

Step 2 receives the scattered light at incident luminous point place, testee surface, and the sensitive area being imaged on CCD by imaging len obtains scattering hot spot;

Step 3 when the signal bandwidth of scattering hot spot is less than or equal to bandwidth threshold values F, then shows that testee surface is weak scattering interface, adopts average weighted gravity model appoach to measure the displacement δ of scattering hot spot on CCD; When the signal bandwidth of scattering hot spot is greater than bandwidth threshold values F, then shows that testee surface is strong scattering cross section, adopt the displacement δ of correlation measurement scattering hot spot on CCD;

Step 4 calculates the displacement of testee according to the displacement δ of scattering hot spot on CCD.

2. a kind of laser displacement measurement method based on Digital Speckle Correlation Method according to claim 1, is characterized in that, described bandwidth threshold values F span is 150 ~ 250.

3. laser displacement measurement method according to claim 1 and 2, is characterized in that, the average weighted gravity model appoach in described step 3 is specially: displacement δ equals the center of gravity horizontal ordinate of scattering hot spot in movable difference, the center of gravity horizontal ordinate of scattering hot spot computing formula is

$\stackrel{\‾}{x}=\frac{\underset{i=n_1}{\overset{n_2}{\mathrm{\Σ}}}{x}_i{f}^2\left(x_i\right)}{\underset{i=n_1}{\overset{n_2}{\mathrm{\Σ}}}{f}^2\left(x_i\right)}$

Wherein, x _ifor the horizontal ordinate of i-th picture dot of scattering hot spot, f (x _i) be the ordinate of i-th picture dot of scattering hot spot, n ₁for minimum picture dot sequence number, n ₂for maximum picture dot sequence number.

4. laser displacement measurement method according to claim 1 and 2, is characterized in that, the correlation method in described step 3 is specially:

Read the light intensity of the scattering hot spot before testee displacement, and one dimension picture dot light intensity matrix before converting displacement to, in displacement last dimension picture dot light intensity matrix, choose the sample sub-range comprising main peak information;

Read the light intensity of the scattering hot spot after testee displacement, and one dimension picture dot light intensity matrix after converting displacement to, after displacement, choose multiple target sub-range identical with sample sub-range width in one dimension picture dot light intensity matrix;

Search and the maximum target sub-range of sample sub-range similarity coefficient, and be aided with interpolation processing and obtain scattering spot displacement.

5. laser displacement measurement method according to claim 4, is characterized in that, calculates described similarity coefficient in the following manner $C=\frac{\underset{j=1}{\overset{m}{\mathrm{\Σ}}}[p\left(x_j\right)-\stackrel{\‾}{p}]\×[q\left({x^{\′}}_j\right)-\stackrel{\‾}{q}]}{\sqrt{\underset{j=1}{\overset{m}{\mathrm{\Σ}}}{[f\left(x_j\right)-\stackrel{\‾}{f}]}^2}\sqrt{\underset{j=1}{\overset{m}{\mathrm{\Σ}}}{[g\left({x^{\′}}_j\right)-\stackrel{\‾}{g}]}^2}},$ Wherein, p (x _j) be sample sub-range, x _jfor the picture dot of the jth in sample subarea, q (x' _j) be target sub-range, x ' _jfor the picture dot of the jth in target sub-range, m is picture dot sum.

6. laser displacement measurement method according to claim 1 and 2, is characterized in that, described step 4 adopts the displacement of direct-injection type trigonometric calculations testee, is specially: the displacement of testee wherein, l is object distance, and l' is image distance, and θ is scattering angle, and φ is the angle of CCD and incident light; If testee surface is moved away from Laser Focusing point, in formula ± choose-, if testee surface is moved near Laser Focusing point, in formula ± choose+.