CN1330928C - Method and apparatus for measuring profile of object by double wavelength structural light - Google Patents

Abstract

The present invention relates to a method and a device for measuring an object outline by a dual wavelength structure, which belongs to the technical field of optical measurement. Firstly, a projector generates a beam of white light which is modulated by a sine and irradiates to an object to be measured, which modulates the optical field. A camera shoots to obtain images. The phase difference of each image point on the images is calculated by the autocorrelation method. The other wavelength is modulated by the sine, and the phase difference is obtained by repeating the process. The wavelengths which are modulated twice by the sine are combined to obtain a combination wavelength and a combination phase difference, and then the depth of each image point is calculated and solves the envelope to obtain actual three-dimensional shapes of objects according to the setting continuity constraint condition of the surface of the objects. The device of the invention comprises the projector, the camera and a computer. The method and the device of the invention has the advantages that the algorithmic stability is good, the surface shape of the complicated object can be measured, and the measuring precision is higher than the prior art.

Description

A kind of method that adopts double wavelength structural light Measuring Object profile

Technical field

The present invention relates to a kind of method that adopts double wavelength structural light Measuring Object profile, belong to optics (three-dimensional) field of measuring technique.

Background technology

Optical projection formula profilometry can be divided into two big classes: direct trigonometry and phase measurement.Directly trigonometry comprises laser point by point scanning method, binocular stereo vision method, structured light method (also claiming light cross-section method) etc.Phase measurement projects to the phase place of the grid picture on the object based on measurement, and Moire technique, phase-shifting method, Fourier transform method or the like are arranged.

The binocular stereo vision method is obtained two width of cloth images of Same Scene from different perspectives, as people's eyes observing scene.Computing machine obtains the depth information of this point of object by detection and coupling to same object point two picture points on two width of cloth images.The principle of binocular vision imaging is simple, but owing to will match corresponding point in the image of the left and right sides, the actual calculation process is very complicated, and three-dimensional matching problem is the main difficult point that binocular vision is measured all the time.Lot of domestic and foreign scholar studies coupling, a lot of matching algorithms has been proposed, for example utilize conditions such as outer polar curve constraint, consistency constraint, unique constraints shape continuity constraint to dwindle matching range, and the MPG algorithm of extensive influence and multi-channel structure algorithm.KanadeT. wait the iteration matching algorithm that has proposed based on selecting template window shape, size adaptively, also have matching algorithm in addition, based on the multiple dimensioned coupling of wavelet transformation etc. based on the pyramid picture structure.

The basic thought of method of structured light is exactly the geological information in the geological information help extraction scenery that utilizes in the illumination.For surf zone smooth, that do not have obvious gray scale, texture and change of shape, can form tangible striations with structured light, make things convenient for the analysis and the processing of image.Method of structured light calculates simply, measuring accuracy is higher, is widely used in actual vision measurement system.The measuring process of method of structured light mainly comprises two steps: earlier throw controllable laser to form unique point according to measuring needs to body surface by projection light source, and obtain surface image.Press the geometric shape characteristic explain projection mode of body surface projection light pattern then, utilize the triangulation principle can try to achieve distance between unique point and the camera lens principal point, the i.e. depth information of unique point.After calibrating direction in space in world coordinate system of light source and video camera, location parameter again, can try to achieve the three-dimensional coordinate of unique point in world coordinate system.

The plot of light intensity that phase measurement adopts Sine Modulated to cross looks like to be projected on the object, and image projection then deforms along with the variation of object height to object, and the light image after the distortion has formed two-dimentional bar graph, and it has comprised the three-dimensional information of object.The light intensity representation of distortion is: I _i(x, y, δ _i)=a (x, y)+b (x, y) cos[ (x, y)+δ _i], according to result data repeatedly, the autocorrelation of using Sine Modulated solves , and (x, y), (x, y), process is separated the 3D shape that envelope obtains actual object to calculate h then.Autocorrelation can be got rid of the interference of the dry sound of high frequency, so the phase-shift method precision is very high, changes the uncertain situation of separating that exists but separate the envelope process for step.

In sum, prior art is owing to adopt proprietary projection arrangement at present, and the 3-D scanning mode is confined to monotechnics, and precision index exists the barrier that is difficult to go beyond aspect indivedual.Binocular method matching problem is very complicated, causes error to be difficult to control.The striped distance of structured light method can not be infinitely small, and precision is restricted.Phase method is owing to exist the arc tangent conversion in the computation process, obtaining one group separates, under the body surface continuity constraint, can find unique suitable separating, but the scope that this step that has limited the object under test surface consecutive point degree of depth changes, the applicability of product is restricted bigger.

Summary of the invention

The objective of the invention is to propose a kind of method and device that adopts double wavelength structural light Measuring Object profile, the light of crossing by the Sine Modulated of liquid crystal projection apparatus projection different wave length is to body surface, obtain to have the two-dimensional image data of projected light information by video camera, restore the depth information of object again according to the projected image Pixel Information.

The method of the employing double wavelength structural light Measuring Object profile that the present invention proposes may further comprise the steps:

(1) projector produces a branch of white light after Sine Modulated, and the brightness value of this white light is: ${\mathrm{Iout}}_i(m,n,{\mathrm{\δ}}_i)=\cos [\frac{m}{p}\×2\mathrm{\π}+{\mathrm{\δ}}_i],$ p ₁Be the wavelength of Sine Modulated, m, n are the coordinate of light field on reference planes, δ _iBe phase-shift phase, ${\mathrm{\δ}}_i\∈(-\frac{\mathrm{\π}}{2},\frac{\mathrm{\π}}{2});$

(2) with above-mentioned white light to object under test, above-mentioned light field is modulated by object under test, the brightness value of each pixel is on the image that camera obtains: I _i(x, y, δ _i)=a (x, y)+b (x, y) cos[ (x, y)+δ _i], x wherein, y are the coordinate of each pixel in the image that obtains of above-mentioned shooting, (x y) is the background light intensity of environment on the image to a, and (x y) is the optical feature value on testee surface to b, and (x y) is the phase differential that testee produces modulation back, illumination light field, δ to  _iBe phase-shift phase, camera is parallel with described reference planes with the line of projector;

(3) phase differential that uses correlation method to calculate each pixel on the above-mentioned image is:

Δ  ₁(x, y)= (x _A, y)- (x _C, y), x wherein _CBe the coordinate of each pixel on the above-mentioned image at the phase place equivalent point before the testee modulation on the reference planes, x _ABe the coordinate of each pixel on the above-mentioned image at the phase place equivalent point after the testee modulation on the reference planes;

(4) with p ₂Be the wavelength of Sine Modulated, repeating step (1) (2) (3) obtains Δ  ₂(x, y),

(5) wavelength to above-mentioned twice Sine Modulated makes up, and obtains combined wave length to be $p=\frac{p_1{p}_2}{p_1-{\mathrm{<figure-callout\; id="2"\; label="p"\; filenames="C20051013288600091.png,C20051013288600101.png"\; state="\{\{state\}\}">p</figure-callout>}}_2},$ Then on the above-mentioned image in combination back the phase differential of each pixel be Δ  (x, y)=Δ  ₂(x, y)-Δ  ₁(x, y);

(6) phase differential after the combination that obtains according to aforementioned calculation calculates the degree of depth of each pixel Wherein L is the distance between projector and camera and the reference planes, and d is the distance between projector and the camera, and p is the wavelength of Sine Modulated;

(7) according to the continuity constraint condition of the body surface of setting, the depth z of above-mentioned each pixel is separated envelope, obtain the actual 3D shape of object.

The device of the employing double wavelength structural light Measuring Object profile that the present invention proposes comprises:

(1) projector is used to produce a branch of white light after Sine Modulated, and the brightness value of this white light is: ${\mathrm{Iout}}_i(m,n,{\mathrm{\&delta;}}_i)=\cos [\frac{m}{p}\&times;2\mathrm{\&pi;}+{\mathrm{\&delta;}}_i],$ p ₁Be the wavelength of Sine Modulated, m, n are the coordinate of light field on reference planes, δ _iBe phase-shift phase, ${\mathrm{\&delta;}}_i\&Element;(-\frac{\mathrm{\&pi;}}{2},\frac{\mathrm{\&pi;}}{2}),$ Be connected with computing machine;

(2) camera, be used for taking the image at the illumination light field object under test of above-mentioned white light, camera is parallel with described reference planes with the line of projector, and the distance between projector and camera and the reference planes is L, distance between projector and the camera is d, is connected with computing machine;

(3) computing machine is used to control projector and produces the white light with ad hoc structure, and handles behind the image of reception camera.

The method and the device thereof of the employing double wavelength structural light Measuring Object profile that the present invention proposes have following characteristics and advantage:

1, the calculating to phase differential is easy to the influence of unfavorable factors such as filtering environmental light to measurement result in the inventive method, so algorithm stability is good.

2, the inventive method is very strong to the correct reducing power of object surfaces step situation to be measured, therefore can the surface measurements shape complex objects more.

3, use method and apparatus of the present invention, 3D shape that can clear reproduction object under test, measuring accuracy is higher than prior art.

Description of drawings

Fig. 1 is the principle schematic of the inventive method.

Fig. 2 is the light path synoptic diagram in the inventive method.

Fig. 3 separates the envelope synoptic diagram in the inventive method.

Fig. 4 is the structural representation of apparatus of the present invention.

Among Fig. 1～Fig. 4, the 1st, projector, the 2nd, camera, the 3rd, object under test, 3a is the lip-deep observation station of object under test, the 4th, reference planes, the 5th, the face such as y such as grade at light path place, the 6th, observation station 3a is at the phase place equivalent point before the object under test modulation on the reference planes 4, the 7th, observation station 3a arrives the intersection point of reference planes 4, and the 8th, observation station 3a is at the phase place equivalent point after the object under test modulation on the reference planes 4, the 9th, computing machine, the 10th, projector is to the connecting line of computing machine, and the 11st, camera is to the connecting line of computing machine.D among Fig. 2 is the distance between the entrance pupil of of projector and camera, the 1st, projector and camera go out the distance of entrance pupil to reference planes.Among Fig. 3, A is the object under test surface configuration, and B is the surface configuration that main value that phase-shifting method is obtained differs calculating, and C is the object that there is the step situation on another surface, and D is the surface configuration that object C obtains through phase-shifting method.

Embodiment

The method of the employing double wavelength structural light Measuring Object profile that the present invention proposes, at first projector produces a branch of white light after Sine Modulated, and the brightness value of this white light is: ${\mathrm{Iout}}_i(m,n,{\mathrm{\&delta;}}_i)=\cos [\frac{m}{p}\&times;2\mathrm{\&pi;}+{\mathrm{\&delta;}}_i],$ p ₁Be the wavelength of Sine Modulated, m, n are the coordinate of light field on reference planes, δ _iBe phase-shift phase, ${\mathrm{\&delta;}}_i\&Element;(-\frac{\mathrm{\&pi;}}{2},\frac{\mathrm{\&pi;}}{2});$ To object under test, light field is modulated by object under test with white light, and the brightness value of each pixel is on the image that camera obtains: I _i(x, y, δ _i)=a (x, y)+b (x, y) cos[ (x, y)+δ _i], x wherein, y are the coordinate of each pixel in the image that obtains of above-mentioned shooting, (x y) is the background light intensity of environment on the image to a, and (x y) is the optical feature value on testee surface to b, and (x y) is the phase differential that testee produces modulation back, illumination light field, δ to  _iBe phase-shift phase, camera is parallel with described reference planes with the line of projector; Use the phase difference  of each pixel on the correlation method computed image ₁(x, y)= (x _A, y)- (x _C, y), x wherein _CBe the coordinate of each pixel on the image at the equivalent point before the testee modulation on the reference planes, x _ABe the coordinate of each pixel on the image at the equivalent point after the testee modulation on the reference planes; With p ₂Be the wavelength of Sine Modulated, repeat said process, obtain Δ  ₂(x, y); Wavelength to twice Sine Modulated makes up, and obtains combined wave length to be $p=\frac{p_1{p}_2}{p_1-{\mathrm{<figure-callout\; id="2"\; label="p"\; filenames="C20051013288600091.png,C20051013288600101.png"\; state="\{\{state\}\}">p</figure-callout>}}_2},$ Then on the image of combination back the phase differential of each pixel be Δ  (x, y)=Δ  ₂(x, y)-Δ  ₁(x, y); According to the phase differential after the combination that calculates, calculate the degree of depth of each pixel

Wherein L is the distance between projector and camera and the reference planes, and d is the distance between projector and the camera, and p is the wavelength of Sine Modulated; According to the continuity constraint condition of the body surface of setting, the depth z of each pixel is separated envelope, obtain the actual 3D shape of object.

The device of the employing double wavelength structural light Measuring Object profile that the present invention proposes, its structure comprises as shown in Figure 4: projector 1, be used to produce a branch of white light after Sine Modulated, the brightness value of this white light is: ${\mathrm{Iout}}_i(m,n,{\mathrm{\&delta;}}_i)=\cos [\frac{m}{p}\&times;2\mathrm{\&pi;}+{\mathrm{\&delta;}}_i],$ P is the wavelength of Sine Modulated, and m, n are the coordinate of light field on reference planes, δ _iBe phase-shift phase, ${\mathrm{\&delta;}}_i\&Element;(-\frac{\mathrm{\&pi;}}{2},\frac{\mathrm{\&pi;}}{2});$ Camera 2 is used for taking the image at the illumination light field object under test of white light, and camera is parallel with described reference planes with the line of projector, and the distance between projector and camera and the reference planes is 1, and the distance between projector and the camera is d; Computing machine 3 is used to control projector and produces the white light with ad hoc structure, and handles behind the image of reception camera.

In one embodiment of the present of invention, the model of used projector is: PB2245, to produce by BenQ company, and the model of used camera is: DH-HV series colorful digital output video camera, to produce by company of Daheng, used computing machine is the P4 compatible.

Below introduce an embodiment of the inventive method in detail.

At first, as shown in Figure 1, projector 1 projection Sine Modulated is crossed the white light of brightness.This illumination light field brightness value as shown in the formula, be known, export by the computer control projector.

${\mathrm{Iout}}_i(x,y,{\mathrm{\&delta;}}_i)=\cos [\frac{x}{p}\&times;2\mathrm{\&pi;}+{\mathrm{\&delta;}}_i],$ As can be seen, light intensity value and y are irrelevant from formula, and the y direction is first-class bright.P is a wavelength, δ _iBe phase-shift phase, ${\mathrm{\&delta;}}_i\&Element;(-\frac{\mathrm{\&pi;}}{2},\frac{\mathrm{\&pi;}}{2}).$

After illumination light arrived on the object, light field was modulated, the image after camera is taken, brightness value as shown in the formula:

I _i(x，y，δ _i)＝a(x，y)+b(x，y)cos[(x，y)+δ _i]

Phase shift scanning is continuously repeatedly taken, and each frame phase shift 2 π/N gathers the N frame altogether.Use I ₁, I ₂, I ₃I _NExpression then can observe the image calculating from N phase shift to the N frame brightness value of same point according to correlation method:

Use correlation method and can greatly eliminate I _i(x, y, δ _i)=a (x, y)+b (x, y) cos[ (x, y)+δ _i] a in the formula (and x, y) and b (x, y) for the adverse effect of measuring, the phase differential that extracts can have very high precision.Obtain Δ  (x, y) after, then can obtain observation station 3a to the distance of reference planes 4 this depth information just, as shown in Figure 2, some 3a for body surface, when reference planes are not placed object, then the same point on the image is a point 6, then putting 6 phase place is this phase place before the testee modulation on the image, and has placed after the object, and the phase place of putting 3a changes, produced phase shift, it is identical to put 8 phase place on phase place after some 3a changes and the reference surface, so phase differential has: Δ  (x, y)= (x ₈, y)- (x ₆, y),  (x in the formula ₆, y),  (x ₈, y) be respectively the phase place of the light field of Sine Modulated at point 6, point 8, so can get:

Δ  (x, y)=2 π | x ₆₈|/p, p is the wavelength of Sine Modulated in the formula, x ₆₈For putting 6 to the distance of putting 8.Can draw by the triangle similarity relation:

Z in the formula _3a7Be the depth information value of a 3a to reference planes 4.

In the superincumbent solution procedure, separating of phase differential to separating set, if get the calculating that main value carries out the back, then the result needs phase place to remove parcel, as shown in Figure 3, A is a cross section of object under test real surface shape among the figure, and B gets the surface configuration that the phase difference calculating behind the main value obtains, separating of depth information is fixed in the scope as can be seen, so just need wait according to the constraint condition of the continuous character in object under test surface and recover.But when step taking place,, shown in C among Fig. 3, separate the depth information that calculates before the envelope so shown in D at 2, then can't correctly restore true form as C if adjacent degree of depth difference surpasses the upper limit of span in the reality for the surface.In order to avoid the appearance of this situation as far as possible, a feasible method is to enlarge span, actual step is within the scope gets final product.But the size of span is relevant with wavelength, and p is big more, and span is big more, but p is big more, and the illumination light field is even more, is unfavorable for error control, and this also is to enlarge the drawback that wavelength causes merely.The present invention proposes the dual wavelength method, uses twice close illumination light field of wavelength to obtain two cover phase-shifting method data, carries out certain reorganization, does not influence the quality of light field under the prerequisite of increase span.

By Δ  (x, y)=2 π | x ₆₈|/p

Obtain 2 π | x ₆₈|=Δ  (x, y) p

Dual wavelength can get: 2 π | x ₆₈|=Δ  ₁(x, y) p ₁

2π·|x ₆₈|＝Δ ₂(x，y)·p ₂

Two formulas comprehensively have:

So can remember work: Δ  (x, y)=Δ  ₂(x, y)-Δ  ₁(x, y)

$p=\frac{p_1{p}_2}{p_1-{\mathrm{<figure-callout\; id="2"\; label="p"\; filenames="C20051013288600091.png,C20051013288600101.png"\; state="\{\{state\}\}">p</figure-callout>}}_2}$

I.e. 2 π | x ₆₈|=Δ  (x, y) p

At this moment, if p ₁, p ₂Very approaching, then Zu He wavelength p is just very big, uses the calculation of parameter depth information of combination.Then for finding the solution It is big that the span of the degree of depth becomes, and the illumination light field remains the small wavelength Sine Modulated, does not have the uniform problem of light field, well solved the problem that the depth information step of consecutive point overruns and can't reduce.Through separating the actual three-dimensional shape data that to obtain object behind the envelope.

Claims (1)

1, a kind of method that adopts double wavelength structural light Measuring Object profile is characterized in that this method may further comprise the steps:

(1) projector produces a branch of white light after Sine Modulated, and the brightness value of this white light is:

${\mathrm{Iout}}_i(m,n,{\mathrm{\&delta;}}_i)=\cos [\frac{m}{p}\&times;2\mathrm{\&pi;}+{\mathrm{\&delta;}}_i],$ p ₁Be the wavelength of Sine Modulated, make Sine Modulated wavelength p get p ₁And p ₂, m, n are the coordinate of light field on reference planes, δ _iBe phase-shift phase, ${\mathrm{\&delta;}}_i\&Element;(-\frac{\mathrm{\&pi;}}{2},\frac{\mathrm{\&pi;}}{2});$

(2) with above-mentioned white light to object under test, above-mentioned light field is modulated by object under test, the brightness value of each pixel is on the image that camera obtains: I _i(x, y, δ _i)=a (x, y)+b (x, y) cos[ (x, y)+δ _i], x wherein, y is the coordinate of each pixel in the image that obtains of above-mentioned shooting, (x y) is the background light intensity of environment on the image, b (x to a, y) be the optical feature value on testee surface, (x is the phase differential that testee produces modulation back, illumination light field y) to , and camera is parallel with described reference planes with the line of projector;

(3) use correlation method to calculate the phase difference  of each pixel on the above-mentioned image ₁(x, y)= (x _A, y)- (x _C, y), x wherein _CBe the coordinate of each pixel on the above-mentioned image at the equivalent point before the testee modulation on the reference planes, x _ABe the coordinate of each pixel on the above-mentioned image at the equivalent point after the testee modulation on the reference planes;

(4) with p ₂Be the wavelength of Sine Modulated, repeating step (1) (2) (3) obtains Δ  ₂(x, y),

(5) wavelength to above-mentioned twice Sine Modulated makes up, and obtains combined wave length to be $p_{12}=\frac{p_1{p}_2}{p_1-p_2}$ , then on the above-mentioned image in combination back the phase differential of each pixel be Δ  (x, y)=Δ  ₂(x, y)-Δ  ₁(x, y);

(6) phase differential after the combination that obtains according to aforementioned calculation calculates the degree of depth of each pixel , wherein L is the distance between projector and camera and the reference planes, d is the distance between projector and the camera;

(7) according to the continuity constraint condition of the body surface of setting, the depth z of above-mentioned each pixel is separated envelope, obtain the actual 3D shape of object.

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