CN101915559A - Method and system thereof for measuring three-dimensional surface shape of object by electronic speckle phase shift technology - Google Patents

Abstract

The invention relates to a method for measuring the three-dimensional surface shape of an object by an electronic speckle phase shift technology, which comprises the following steps: (1) fixing an object to be measured on a reference plane which is connected with a phase shifter and can rotate in a vertical plane; (2) enabling the object to be measured and the reference plane to deflect slightly less than 5 degrees, and generating alternately dark and bright interference fringes on the surface of the object to be measured by interference of light; and (3) applying phase shift to the surface of the object to be measured by the phase shifter to change the optical path difference of the reference light and object light; carrying out equal four-step phase shifting on the curved interference fringes obtained in the step (2), wherein the alternately dark and bright interference fringes can make corresponding translation according to the size of the applied phase shift; obtaining a wrapped phase diagram by a four-step phase algorithm, and because the phases are wrapped between -pi and pi, serializing the phases by a phase unwrapping algorithm to obtain the true phase of the object to be measured; and deriving the height distribution of the object surface according to the mapping relation between the phase and the height, and obtaining the surface shape of the object. Meantime, the invention also discloses a system of the method.

Description

Utilize the method and the system thereof of electronic speckle phase-shifting technique Measuring Object 3 d shape

Technical field

The present invention relates to a kind of 3 d shape measuring method and system of object, especially a kind of method and system thereof that utilizes electronic speckle phase-shifting technique Measuring Object 3 d shape.

Background technology

Along with the develop rapidly of computer technology, electronic technology, digital image acquisition and treatment technology, produced the electronic speckle pattern interferometry art.In recent years because the electronic speckle pattern interferometry technology has simple to operate, measurement of full field, noncontact, high precision, the low characteristics of shock insulation requirement, become a kind of comparatively ripe optical 3-dimensional surface shape measurement technology, and obtained widely using in surface shape measurement, deformation measurement, particularly the electronic speckle pattern interferometry technology has remarkable advantages in the application of Non-Destructive Testing, thermal deformation measurement and the Oral Repair of equipment.In the surface shape measurement, whether accurately the phase measurement that extracts phase information from light distribution is decision measurement result one of gordian technique, mainly contains fourier transform method and phase-shift method.Fourier transform method contrast height based on projecting grating be easy to dynamic process, but measuring accuracy is subjected to the restriction of projecting grating spatial frequency, and sensitivity is not high.Electronic speckle pattern interferometry utilizes interference of light to produce the interference modulations striped, does not need projecting grating, and the phase information of object is included in the speckle particle, and forming with the speckle is the interference fringe of carrier, thereby sensitivity is also higher.The developing direction of speckle measurement technique has determined and must develop to three-dimensional measurement.Three-dimensional phase shifting electronic speckle interference technology is that the electronic speckle pattern interferometry technology is in conjunction with the development of phase-shifting technique to three-dimensional, high precision and automation direction.The electronic speckle carrier-frequency modulation has been applied to the 3 d shape of object and has measured, and the carrier frequency modulation has the characteristics of whole audience extraction face shape information, the insensitive shortcoming of measurement of shape edge, opposite or details.Chinese patent 200620044101.X discloses a kind of based on optical fiber and phase shifting electronic speckle commercial measurement object dimensional anamorphotic system, does not measure but the electronic speckle phase-shifting technique also is applied to the 3 d shape of object always.

Summary of the invention

The objective of the invention is for overcoming above-mentioned the deficiencies in the prior art, a kind of simple structure, precision and the highly sensitive method and the system thereof that utilize electronic speckle phase-shifting technique Measuring Object 3 d shape are provided.

For achieving the above object, the present invention adopts following technical proposals:

A kind of method of utilizing electronic speckle phase-shifting technique Measuring Object 3 d shape may further comprise the steps:

1) testee is fixed on the reference planes, reference planes are connected with a phase-shifter, and reference planes make reference planes can do the rotation of spending angles less than 5 in perpendicular greater than testee;

2) testee is done the deflection of spending angles less than 5 together with reference planes, utilize interference of light, produce light and dark interference fringe on the testee surface, i.e. deflection by object utilizes electronic speckle pattern interferometry to produce interference fringe at body surface;

3) by phase-shifter the testee surface being applied phase shift changes the light path of thing light, and then cause the change of the phase differential of reference light and thing light, to step 2) interference fringe of the bending that obtains four step phase shifts such as does, these light and dark interference fringes can be done corresponding translation according to the size of adding phase shift, utilize phase-shifting technique to extract the phase information of object plane, obtain wrapped phase figure, because phase place is wrapped in (π, π), continuous phase is obtained the true phase place of testee with phase-unwrapping algorithm; Mapping relations according to phase place and height draw the height profile of object plane, thereby obtain the face shape of object.

A kind of system that utilizes electronic speckle phase-shifting technique Measuring Object 3 d shape, it comprises laser instrument, phase-shifter and camera, each components and parts position relation is as follows: laser instrument is corresponding with semi-transparent reflection mirror I, semi-transparent reflection mirror I is corresponding with beam expanding lens I and catoptron I respectively, catoptron I, catoptron II are corresponding successively with catoptron III, catoptron III is corresponding with beam expanding lens II, and beam expanding lens II is corresponding with semi-transparent reflection mirror II, and semi-transparent reflection mirror II is corresponding with camera; Beam expanding lens I is corresponding with the testee on being arranged at reference planes, and reference planes are connected with a phase-shifter, and testee is corresponding with lens, and lens are corresponding with semi-transparent reflection mirror II.

The present invention utilizes electronic speckle pattern interferometry Measuring Object face shape, and the small deflection by object produces parallel interference fringe at body surface.Because be subjected to the modulation of the height of object plane, parallel interference fringe limpens, adopt phase-shifting technique to extract object plane 3 d shape information.This method produces interference fringe with speckle interference, and therefore measuring object plane has highly sensitive advantage, owing to adopt phase-shifting technique to extract phase information, measuring accuracy is also high.

Description of drawings

Fig. 1 is the schematic diagram of electronic speckle pattern interferometry Measuring Object face shape;

Fig. 2 is the electronic speckle pattern interferometry system light path figure of Measuring Object face shape;

Fig. 3 is the interference fringe picture that the deflection object plane is introduced;

Fig. 4 is wrapped phase figure;

Fig. 5 separates the parcel phase diagram;

Fig. 6 is the measured object 3 d shape grid chart that phase-shift method obtains;

Fig. 7 is the object plane contour map;

1. testees wherein, 2. reference planes, 3. laser instrument, 4. semi-transparent reflection mirror I, 5. catoptron I, 6. catoptron II, 7. catoptron III, 8. beam expanding lens I, 9. beam expanding lens II, 10. phase-shifter, 11. lens, 12. semi-transparent reflection mirror II, 13. cameras.

Embodiment

The present invention is further described below in conjunction with drawings and Examples.

Shown in Fig. 1-7, a kind of method of utilizing electronic speckle phase-shifting technique Measuring Object 3 d shape may further comprise the steps:

1) testee 1 is fixed on the reference planes 2, reference planes 2 are connected with a phase-shifter 10, and reference planes 2 are greater than testee 1, make reference planes 2 can do minor rotation less than 5 degree angles in perpendicular;

2) with testee 1 together with reference planes 2 do less than 5 the degree angles small deflection, utilize interference of light, produce light and dark interference fringe on testee 1 surface, promptly utilize electronic speckle pattern interferometry to produce interference fringe at body surface by the small deflection of object; This interference fringe causes the variation of interference fringe phase place owing to the modulation that is subjected to the body surface height limpens, and the elevation information of object is included in the crooked interference fringe;

3) applying phase shift by 10 pairs of testee 1 surfaces of phase-shifter changes the light path of thing light, and then cause the change of the phase differential of reference light and thing light, to step 2) interference fringe of the bending that obtains four step phase shifts such as does, these light and dark interference fringes can be done corresponding translation according to the size of adding phase shift, utilize phase-shifting technique to extract the phase information of object plane, obtain wrapped phase figure, because phase place is wrapped in (π, π), continuous phase is obtained the true phase place of testee with four step phase-unwrapping algorithms; Mapping relations according to phase place and height draw the height profile of object plane, thereby obtain the face shape of object.

The ultimate principle of phase-shifting technique Measuring Object face shape is the phase differential between the two bundle coherent lights in the optical interference circuit to be introduced equally spaced phase differential change, when phase differential changes, interference fringe is also done corresponding translation, makes in the interference field light intensity of arbitrfary point be varies with cosine and moves.One of gordian technique of surface shape measurement is the phase place of extract surface.

1. the phase-shift method phase measurement principle is as follows:

The interference fringe that speckle interference forms is a thing light and reference light is superimposed forms, and the light vibration of thing light and reference light is expressed as respectively:

Wherein, A _ObWith

Amplitude and the phase place of representing thing light respectively, A _RefWith

Amplitude and the phase place of representing reference light respectively.The later light vibration of reference light and thing optical superposition can be expressed as:

E＝E _ob+E _ref (3)

＝Acos(ωt+φ)

What it closed amplitude square is:

(4)

Therefore the light intensity of interference field is:

(5)

That is:

$I(x,y,t)=I_{\mathrm{ob}}(x,y)+I_{\mathrm{ref}}(x,y)$ (6)

$+2\sqrt{I_{\mathrm{ob}}(x,y)I_{\mathrm{ref}}(x,y)}\cos \mathrm{\φ}(x,y)$

When reference surface is the plane, suppose that its phase place equals zero, (x y) is the phase differential of object plane and reference surface, just the phase place of object under test to φ.Be connected to phase-shifter on the object plane, can apply phase shift to object plane the optical path difference of thing light is changed, and then cause the change of the phase differential of reference light and thing light, this moment, the light intensity of interference field was:

$I(x,y,t)=I_{\mathrm{ob}}(x,y)+I_{\mathrm{ref}}(x,y)$ (7)

$+2\sqrt{I_{\mathrm{ob}}(x,y)I_{\mathrm{ref}}(x,y)}\cos [\mathrm{\φ}(x,y)+\mathrm{\δ}\left(t\right)]$

Apply after the phase shift, the additive phase that the phase differential of reference light and thing light is introduced by the phase place and the phase-shifter of object determines that jointly δ (t) is the phase place that phase-shifter is introduced.If object plane is done four step phase shifts, makes that each phase-shift phase is δ _i(t), corresponding variation will take place in the phase differential of reference light and thing light after the introducing phase shift, inevitably will produce error owing to measure, and adopts the equidistant phase shift time error minimum of introducing of full cycle, so the phase-shift phase in per step is

N=4, so phase-shift phase is for being

The interference field light intensity is respectively after doing four step phase shifts:

$I_1=I_{\mathrm{ob}}(x,y)+I_{\mathrm{ref}}(x,y)+$ (8)

$2\sqrt{I_{\mathrm{ob}}(x,y)I_{\mathrm{ref}}(x,y)}\cos \left[\mathrm{\φ}(x,y)\right]$

${\mathrm{<figure-callout\; id="2"\; label="I"\; filenames="HDA0000023997590000012.png"\; state="\{\{state\}\}">I</figure-callout>}}_2=I_{\mathrm{ob}}(x,y)+I_{\mathrm{ref}}(x,y)+$

$2\sqrt{I_{\mathrm{ob}}(x,y)I_{\mathrm{ref}}(x,y)}\cos [\mathrm{\&phi;}(x,y)+\frac{\mathrm{\&pi;}}{2}]$ (9)

$I_3=I_{\mathrm{ob}}(x,y)+I_{\mathrm{ref}}(x,y)+$ (10)

$2\sqrt{I_{\mathrm{ob}}(x,y)I_{\mathrm{ref}}(x,y)}\cos [\mathrm{\&phi;}(x,y)+\mathrm{\&pi;}]$

$I_4=I_{\mathrm{ob}}(x,y)+I_{\mathrm{ref}}(x,y)+$

$2\sqrt{I_{\mathrm{ob}}(x,y)I_{\mathrm{ref}}(x,y)}\cos [\mathrm{\&phi;}(x,y)+\frac{3\mathrm{\&pi;}}{2}]$ (11)

The plot of light intensity of the expression object plane that the plot of light intensity of expression reference surface is later with doing four step phase shifts is subtracted each other respectively, phase place in the plot of light intensity that obtains only comprises the phase information of object and the additive phase that phase-shifter is introduced, and reference surface has been cut, therefore can obtain the phase place of object:

$\mathrm{\&phi;}=\arctan \frac{I_4-I_2}{I_1-I_3}---\left(12\right)$

The phase place that is obtained by phase-shift method is to be wrapped in that (the true phase place that must utilize phase-unwrapping algorithm to launch to obtain object plane just can be done further processing, recovers three-D profile for π, π) the phase place main value in the scope.

2. the principle of electronic speckle pattern interferometry Measuring Object face shape

As shown in Figure 1, L and C are respectively the photocentres of laser instrument and camera CCD, and both are at a distance of d.The C-L line is parallel with reference surface, and at a distance of s.When measured object did not exist, laser directly projected on the reference surface, and reference light and thing Light Interference Streaks are parallel to each other, when measured object, and the interference fringe distortion.If originally the position of striped is at the B place, because the blocking of object moves on to the A point of object, and the position of being ordered by the observed A of CCD is on the D point.Therefore since object block the optical path difference that has produced the BD distance, as long as corresponding phase differential is φ obtain every bit produces on the object plane phase differential just can calculate the whole audience height profile h (x, y).Get by similar triangles

$h=\frac{\mathrm{\&phi;\&lambda;<figure-callout\; id="2"\; label="s"\; filenames="HDA0000023997590000012.png"\; state="\{\{state\}\}">s</figure-callout>}}{2\mathrm{\&pi;d}+\mathrm{\&phi;\&lambda;}}---\left(13\right)$

Wherein φ is the phase place of object,

, so just PHASE DISTRIBUTION has been changed into height profile.

As shown in Figure 2, utilize the system of electronic speckle phase-shifting technique Measuring Object 3 d shape, it comprises laser instrument 3, phase-shifter 10 and camera 13, each components and parts position relation is as follows: laser instrument 3 is corresponding with semi-transparent reflection mirror I4, semi-transparent reflection mirror I4 is corresponding with beam expanding lens I8 and catoptron I5 respectively, catoptron I5, catoptron II6 are corresponding successively with catoptron III7, catoptron III7 is corresponding with beam expanding lens II9, beam expanding lens II9 is corresponding with semi-transparent reflection mirror II12, and semi-transparent reflection mirror II12 is corresponding with camera 13; Beam expanding lens I8 is corresponding with the testee 1 on being arranged at reference plate 2, and reference plate 2 is connected with a phase-shifter 10, and testee 1 is corresponding with lens 11, and lens 11 are corresponding with semi-transparent reflection mirror II12.

Electronic speckle pattern interferometry systematic survey object surfaces face shape as shown in Figure 2, measured object is a bead spherical crown, with He-Ne laser as light source through being radiated at behind the beam expanding lens on the spherical crown surface.Spherical crown is fixed on the reference planes 2 that can do minor rotation in perpendicular, reference planes 2 are connected the realization phase shift with phase-shifter 10, reference light and thing light are through realizing coaxial interference on CCD (camera) optical axis behind the square glass prism, the deflection object plane can be seen light and dark interference fringe shown in Figure 3 by CCD.Make striped limpen because of body surface has certain height, the elevation information of object is included in the crooked interference fringe.When incident angle big more, reference light light intensity and thing light light intensity more near the time, the striped bending is obvious more, fringe contrast is good more, measurement effect is also just good more.

The interference fringe that obtains such as is done at four step phase shifts, and these light and dark interference fringes can be done certain translation according to the size of adding phase shift, utilize phase-shifting technique can extract the phase information of object plane, obtain wrapped phase figure shown in Figure 4.Since phase place be wrapped in (π, π) between, need obtain the true phase place of spherical crown to continuous phase with phase-unwrapping algorithm, as shown in Figure 5.Can draw the height profile of object plane according to mapping relations (13) formula of phase place and height.Fig. 6 is the 3 d shape grid chart of the spherical crown that obtained by phase-shift method, and Fig. 7 is the contour map of object plane.

By the result as can be seen, utilize the surperficial face shape that the electronic speckle pattern interferometry phase-shift method can Measuring Object.Produce parallel interference modulations striped with electronic speckle pattern interferometry, though the sparse phase place that also can access object of striped through exact solution, so measuring accuracy is higher.But because the systematic error of phase changer makes measurement result be subjected to certain influence.

Theoretical analysis and experiment show that phase shifting electronic speckle interference technology can Measuring Object face shape.Owing to be to adopt the method for speckle interference to produce interference fringe, so this method Measuring Object face shape has highly sensitive advantage, owing to adopt phase-shifting technique to extract phase information, measuring accuracy is also high.

Claims (2)

1. a method of utilizing electronic speckle phase-shifting technique Measuring Object 3 d shape is characterized in that, may further comprise the steps:

1) testee is fixed on the reference planes, reference planes are connected with a phase-shifter, and reference planes are greater than testee, and reference planes can be done the rotation less than 5 degree angles in perpendicular;

2) testee is done the deflection of spending angles less than 5 together with reference planes, utilize interference of light, produce light and dark interference fringe on the testee surface, i.e. deflection by object utilizes electronic speckle pattern interferometry to produce interference fringe at body surface;

3) by phase-shifter the testee surface being applied phase shift changes the light path of thing light, and then cause the change of the phase differential of reference light and thing light, to step 2) interference fringe of the bending that obtains four step phase shifts such as does, these light and dark interference fringes can be done corresponding translation according to the size of adding phase shift, utilize phase-shifting technique to extract the phase information of object plane, obtain wrapped phase figure, because phase place is wrapped in (π, π), continuous phase is obtained the true phase place of testee with phase-unwrapping algorithm; Mapping relations according to phase place and height draw the height profile of object plane, thereby obtain the face shape of object.

2. system that utilizes electronic speckle phase-shifting technique Measuring Object 3 d shape, it is characterized in that: it comprises laser instrument, phase-shifter and camera, each components and parts position relation is as follows: laser instrument is corresponding with semi-transparent reflection mirror I, semi-transparent reflection mirror I is corresponding with beam expanding lens I and catoptron I respectively, catoptron I, catoptron II are corresponding successively with catoptron III, catoptron III is corresponding with beam expanding lens II, beam expanding lens II is corresponding with semi-transparent reflection mirror II, and semi-transparent reflection mirror II is corresponding with camera; Beam expanding lens I is corresponding with the testee on being arranged at reference planes, and reference planes are connected with a phase-shifter, and testee is corresponding with lens, and lens are corresponding with semi-transparent reflection mirror II.

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