CN102967261A - 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 the 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

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

Summary of the invention

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

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

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

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

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

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

Step 4 is calculated 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 the described step 3 is specially: displacement δ equals the center of gravity horizontal ordinate of scattering hot spot

In the difference that moves forward and backward, 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 _iBe the horizontal ordinate of i picture dot of scattering hot spot, f (x _i) be the ordinate of i picture dot of scattering hot spot, n ₁Be minimum picture dot sequence number, n ₂Be maximum picture dot sequence number.

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

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

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

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

Further, calculate in the following manner described similarity coefficient $C=\frac{\underset{j=1}{\overset{m}{\mathrm{\Σ}}}[p\left(x_j\right)-\stackrel{\‾}{p}]\×[q\left(x_j^{\′}\right)-\stackrel{\‾}{q}]}{\sqrt{\underset{j=1}{\overset{m}{\mathrm{\Σ}}}{[f\left(x_j\right)-\stackrel{\‾}{f}]}^2}\sqrt{\underset{j=1}{\overset{m}{\mathrm{\Σ}}}{[g\left(x_j^{\′}\right)-\stackrel{\‾}{g}]}^2}},$ 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 the sample sub-range, x _jBe j picture dot in the sample subarea, q (x' _j) be the target sub-range, x ' _jBe j picture dot in the target sub-range, m is the 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 the testee surface away from the mobile then formula of Laser Focusing point ± choose-, if the testee surface near Laser Focusing point movement then in the formula ± choose+.

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

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

2, the present invention can in the measurement for the treatment of under the high roughness strong scattering of the displacement object plane condition, have the high and good characteristics of real-time of precision.

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

Description of drawings

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; The 2-plus lens; 3-testee surface; The 4-imaging len; The 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; The 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, may further comprise the steps:

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

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

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

Described bandwidth threshold values F is 150～250.

The square weighting gravity model appoach is specially: by the center of gravity horizontal ordinate of the scattering hot spot that moves forward and backward

Difference obtain δ, the 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,

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

Correlation method is specially:

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

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

The target sub-range of search and sample sub-range similarity coefficient maximum when searching and the peaked position of related coefficient, sample sub-range, is aided with the interpolation reason and just can records the scattering spot displacement.

In the trigonometry displacement measurement, the light intensity of the scattering hot spot that each pixel of CCD receives converts the one dimension character matrix to, when scattering hot spot during along CCD pixel orientation displacement, the digital distribution of this one dimension matrix is substantially constant, but volume coordinate corresponding to each numeral changes.Get the window function of one fixed width with signal cutout in the one dimension character matrix before displacement, get can reflect the scattering interface information data (300 picture dot width that for example comprise main peak) as the sample sub-range, use the successive objective sub-range (1-300 that seeks 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 the sample sub-range, x _jBe the picture dot in the sample subarea, q (x' _j) be the target sub-range, x ' _jBe the picture dot in the target sub-range, m is the picture dot sum.

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

The 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 the testee surface away from plus lens move then in the formula ± choose-; If testee surface near plus lens move then in the formula ± choose+;

Embodiment:

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

It is GCL-304(focal length F=20mm that imaging len is selected the model of Daheng's photoelectricity production) lens, obtain object distance and image distance is respectively 28mm and 70mm according to magnification.Scatteringangleθ is excessive then can to cause the problems such as astigmatism and distortion, and scatteringangleθ is set as 30 degree.

Plus lens focal length F=24mm.

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

Bandwidth threshold values F=180.

Testee is smooth mirror surface, and coat 80 order atomized aluminiums at smooth mirror surface and simulate rough interfaces, be in the strong scattering object plane this moment, and this testee is carried out 10 different displacements, with gravity model appoach and the inventive method data are processed respectively, the result is as shown in table 1.

Table 1 the inventive method and gravity model appoach measurement result are relatively

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

Implementation example described herein only is to the explanation for example of the present invention's spirit.Those skilled in the art can make various modifications or replenish or adopt similar mode to substitute described implementation example, but can't depart from spirit of the present invention or surmount the defined scope of appended claims.

Claims (6)

1. laser displacement measurement method based on Digital Speckle Correlation Method is specially:

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

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

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

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

2. a kind of new pattern 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 the described step 3 is specially: displacement δ equals the center of gravity horizontal ordinate of scattering hot spot

In the difference that moves forward and backward, 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 _iBe the horizontal ordinate of i picture dot of scattering hot spot, f (x _i) be the ordinate of i picture dot of scattering hot spot, n ₁Be minimum picture dot sequence number, n ₂Be maximum picture dot sequence number.

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

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

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

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

5. laser displacement measurement method according to claim 4 is characterized in that, calculates in the following manner described similarity coefficient $C=\frac{\underset{j=1}{\overset{m}{\mathrm{\Σ}}}[p\left(x_j\right)-\stackrel{\‾}{p}]\×[q\left(x_j^{\′}\right)-\stackrel{\‾}{q}]}{\sqrt{\underset{j=1}{\overset{m}{\mathrm{\Σ}}}{[f\left(x_j\right)-\stackrel{\‾}{f}]}^2}\sqrt{\underset{j=1}{\overset{m}{\mathrm{\Σ}}}{[g\left(x_j^{\′}\right)-\stackrel{\‾}{g}]}^2}},$ Wherein,

P (x _j) be the sample sub-range, x _jBe j picture dot in the sample subarea, q (x' _j) be the target sub-range, x ' _jBe j picture dot in the target sub-range, m is the picture dot sum.

6. according to claim 1 and 2 or 3 described laser displacement measurement methods, it 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 the testee surface away from the mobile then formula of Laser Focusing point ± choose-, if the testee surface near Laser Focusing point movement then in the formula ± choose+.

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