CN104180778B - Structured light method for small-angle measurement - Google Patents

Abstract

Disclosed is a structured light method for small-angle measurement. A measuring system comprises a CCD camera, a display screen and a computer. A feature pattern is displayed on the display screen and projected onto a measured object or a reflector fixed on the object, and the pattern is reflected and then shot by the camera. The reflected feature pattern is shot by the CCD camera, and in other words, a virtual image formed through the reflector on the display screen is shot by the CCD camera. When the object rotates, the virtual image shot by the camera rotates too. The rotating angle of the virtual image can be calculated by analyzing the virtual image before and after rotation. According to the light reflection law, the rotating angle of the object is half of the rotating angle of the virtual image. The measuring system is simple in structure, convenient to use, high in sensitivity, free of special requirements for the environment, and capable of conducting detection in a workshop.

Description

A kind of method of structured light of small angle measurement

Technical field

The present invention relates to a kind of optical angle measurement technique, especially for a kind of structure optical tests of small angle measurement Method.

Technical background

Angular surveying is the important component part of geometric sense measurement technology, and the particularly measurement of minute angle adds accurate Many fields such as work, Aero-Space, military affairs and communication are all extremely important and act on.Study earliest in angle measurement technique Be mechanical type and electromagnetic type angle measurement technique, such as multiteeth indexing table and circle magnetic grid etc., the major defect of these methods is mostly handss Work measures it is not easy to realize automatization, and certainty of measurement is restricted.Optics angle-measuring method is due to having noncontact, high accuracy The attention of with highly sensitive feature and extremely people, the development of especially stable LASER Light Source makes industry spot measurement become May.Therefore, make the application of optics angle-measuring method more and more extensive, various new optics angle-measuring methods also arise at the historic moment.At present, light Learn angle-measuring method in addition to well-known optical dividing head method and polygon method, conventional also has photoelectric encoder method, diffraction Method, autocollimation method, Fiber Optic Sensor, acousto-optic modulation method, Circular gratings method, optical internal-reflection method, laser interferance method, parallel interferogram technique with And loop laser method etc..These methods have respective feature and range of application.In such as autocollimation method, position distinguished by object and picture In conjugate planes.When object rotates, object formed picture point in image planes is also moved therewith, by measuring picture point Amount of movement just to calculate object rotation angle.Autocollimation method principle is simple, easy to operate, easy, but measurement range is general All very littles, generally rather to tens/, Measurement reliability and certainty of measurement are generally in several rads.Circular gratings are in angle Application in measurement widely, has also reached high accuracy in complete cycle measures at any angle.Its shortcoming is to light Grid are higher to heart accuracy requirement with turntable, and the fabrication and processing of high accuracy grating is difficult.Optical internal-reflection method low-angle is surveyed The major advantage of amount is small volume, can make pocket clinometer, but its measurement range also very little, therefore it is only used for little angle Degree measurement.The angle that laser interference angle measurement technique rotates direct measurement object changes into Measuring Object reflected light and reference light Optical path difference.Because interferometry can be as accurate as the part even 1/tens of optical wavelength, it is therefore current essence Exactness highest measuring method.But the requirement to environment is extremely harsh, many extraneous factors, such as surrounding air flowing, environment Vibration etc. all can produce a very large impact to measurement result, and apparatus structure is accurate, stability is bad, volume is big, thus generally It is only used as a kind of measuring basiss and detection meanss, be difficult to in-site measurement and workshop condition measurement.The work of ring laser Principle is based on sagnac effect.When tested measurer and ring laser are with respect to static photoelectric collimator synchronous axial system, The moment coinciding with measurer faceted pebble normal in guidance axis, tested angle is converted into being touched by the photoelectric current that photoelectric auto-collimator produces Send out and time interval needed for stop pulse, interface arrangement here every interior to loop laser pulse reading.The shortcoming of the method It is to realize kinetic measurement, measuring condition is required very high, processing technique is difficult to ensure that, high cost, strict to environmental requirement. This is also the main reason that ring laser does not obtain widely applying, and its measurement result also suffers from " frequency pulling " With the impact of earth rotation, a lot of methods are applied both to low-angle accurate measurement.

By at present commonly use several optics angle-measuring methods introduction can be seen that optical method low-angle measurement in Have been obtained for being widely applied, and reached very high certainty of measurement, become irreplaceable low-angle detection meanss.For Meet the measurement requirement that some fields improve constantly, increasing measuring method and e measurement technology are constantly studied, open Send out.Optical method has in low-angle measurement and extremely important acts on and be widely applied prospect.

The informative that structure light metering method obtains, has that measurement sensitivity is high, high precision is relative with equipment cost Relatively low, environment resistant interference performance is strong, the advantages of can be used for workshop and detect, has been widely used in field of optical measurements.And For the report realizing low-angle measurement using method of structured light, have no report so far.

Content of the invention

The present invention is a kind of method of structured light of small angle measurement, has that structure is simple, easy to use, sensitivity is high, right Environment no particular/special requirement, the advantages of can be detected in workshop condition.

The system includes display screen, ccd video camera and electronic computer.Computer produces Eigen Structure, is shown in display On screen, and project to testee or be fixed on reflecting mirror on object, received by ccd video camera after being reflected.Ccd shoots Record the Eigen Structure reflecting.Namely ccd shoots and records the virtual image that display screen is formed by reflecting mirror.Work as reflecting mirror When rotating, the virtual image of shot by camera also can rotate.The virtual image before and after rotating is analyzed, calculates its turn Dynamic angle.According to light reflection law, the half of this angle is the angle that reflecting mirror rotates.

The present invention has a following advantage:

1. the present invention, to environment no particular/special requirement, can be detected in workshop condition.

2., without special optical element in the present invention, cost is very cheap.

3. the present invention has larger measurement dynamic range.

4. the system structure that the present invention adopts is simple, easy to use, places no special requirement to system element.

5. detection method has very high sensitivity.

6. the structure pattern employed in the present invention and phase-shifting technique have at a relatively high precision, and can effectively suppress The impact to testing result of noise and surrounding.

Brief description

Fig. 1 is the detection method system structure diagram mentioned in the present invention；

Fig. 2 is camera model schematic diagram；

Fig. 3 is typical characteristic pattern shape；Fig. 3 a. gridiron pattern；Fig. 3 b. Gauss dot matrix；Fig. 3 c. two dimension sine streak；

Fig. 4 is video camera shooting virtual image schematic diagram before and after rotation；The virtual image before Fig. 4 a. rotation；The virtual image after Fig. 4 b. rotation.

Specific embodiment

As shown in figure 1, the system mainly includes ccd video camera, display screen and computer.Display screen display is by calculating The Eigen Structure that machine generates, by ccd shot by camera and remember through testee or after the reflecting mirror reflection that is fixed on object Record.Namely ccd shoots and records the virtual image that display screen is formed by reflecting mirror.When reflecting mirror rotates, video camera is clapped The virtual image taken the photograph also can rotate.The virtual image before and after rotating is analyzed, calculates its rotational angle.Fixed according to light line reflection Rule, the half of this angle is the angle that reflecting mirror rotates.With display screen display two dimension sine streak Eigen Structure it is below Example illustrates, and has similar measurement process when showing other Eigen Structures, and this example does not include all of this patent Content.

First demarcation is carried out to video camera and try to achieve intrinsic parameter.Camera imaging model is as shown in Fig. 2 using considering aberration Non-linear camera model imaging relations are described, that is, based on perspective projection linear camera model add cause camera lens abnormal The aberration becoming.World coordinate system midpoint p (x, y, z), coordinate in plane of delineation system for its picture point is (u, v).Perspective Projection imaging relation can be expressed as:

$\mathrm{\λ}\left[\begin{array}{c}u\\ v\\ 1\end{array}\right]=\left[\begin{array}{ccc}{f}_u& 0& u_0\\ 0& f_v& v_0\\ 0& 0& 1\end{array}\right]\left[\begin{array}{cc}r& t\end{array}\right]\left[\begin{array}{c}x\\ y\\ 1\end{array}\right]=k\left[\begin{array}{cc}r& t\end{array}\right]\left[\begin{array}{c}x\\ y\\ 1\end{array}\right]---\left(1\right)$

In formula, λ is the non-zero proportions factor, and k is camera Intrinsic Matrix, f_uWith f_vRepresent normalization matrix on u, v axle respectively； (u₀,v₀) based on point coordinates；R and t is the outer parameter of video camera, represents the rotation that camera coordinate system is relative to world coordinate system respectively Torque battle array and translation matrix；X=x/z, y=y/z, illustrate the projecting direction of p point.Can be in the hope of internal reference by camera calibration Matrix number k.Camera calibration method is a lot, the two-step method that such as tsai and roger proposes, plane reference method that Zhang Zhengyou proposes etc..

Second step, shows and shoots two-dimentional sine streak Eigen Structure and carry out image procossing.Generate mark in a computer Quasi- two dimension sine streak Eigen Structure, is clapped through testee or after the reflecting mirror reflection that is fixed on object by ccd video camera Take the photograph and record.Namely ccd shoots and records the virtual image that display screen is formed by reflecting mirror, such as shown in Fig. 4 (a).According to Fourier Fringe analysis method, by Fourier transformation, filtering and inverse Fourier transform, extracts two from the image that video camera shoots Orthogonal direction block PHASE DISTRIBUTION.Then estimate the pixel coordinate of bright spot, bright spot is carried out in the window of one fixed width Phase unwrapping, and two-dimensional linear matching, can obtain the subpixel coordinates of local bright spot, thus extracting the picture obtaining characteristic point Plain position.At this moment it is possible to using camera calibration method be calculated now video camera with respect to the outer parameter spin moment of the virtual image Battle array r₁.

3rd step, after rotating reflecting mirror, shows and shoots two-dimentional sine streak Eigen Structure and carry out image procossing.Rotate Reflecting mirror, ccd video camera shoots and records the virtual image that now display screen is formed by reflecting mirror, such as shown in Fig. 4 (b).Repeat second Step calculating process, obtains the outer parameter spin matrix r that video camera is with respect to the virtual image after reflecting mirror rotation₂.

4th step, calculates the reflecting mirror anglec of rotation.Reflecting mirror can be obtained according to formula 2 and rotate the rotation between former and later two virtual images Torque battle array:

$r_{12}=r_1^{-1}{r}_2---\left(2\right)$

Wherein r₁₂For the matrix of 3 × 3, the rotational angle of the root as virtual image of its eigenvalue quadratic sum.According to plane Mirror principle of reflection, the rotational angle of reflecting mirror is the 1/2 of virtual image rotational angle, by the virtual image obtaining angle of rotation angle value divided by 2 just Can get the anglec of rotation of reflecting mirror, be also the anglec of rotation of object simultaneously.

Claims (5)

1. a kind of method of structured light of small angle measurement it is characterised in that: measuring system is by ccd video camera, display screen and calculating Machine forms；

Carry out camera calibration first, obtain the intrinsic parameter of video camera；

Second step, produces Eigen Structure by computer, and display on a display screen, and projects to testee or is fixed on object Reflecting mirror, recorded by video camera after reflection；The location of pixels obtaining recording characteristic point in image is extracted in analysis, then calculates Obtain now video camera with respect to the outer parameter spin matrix r of the virtual image₁；

3rd step, after rotating reflecting mirror, repeats the calculating process in second step, obtains video camera empty with respect to after reflecting mirror rotation The outer parameter spin matrix r of picture₂；

4th step, is calculated the anglec of rotation of object；

Wherein, by the external parameters of cameras spin matrix r with respect to the virtual image before and after rotating₁And r₂Try to achieve the angle of rotation of the virtual image Degree:

$r_{12}=r_1^{-1}{r}_2$

r₁₂For the matrix of 3 × 3, the rotational angle of the root as virtual image of its eigenvalue quadratic sum.

2. small angle measurement according to claim 1 method of structured light it is characterised in that: obtained by camera calibration Its intrinsic parameter, using the nonlinear model considering aberration.

3. small angle measurement according to claim 1 method of structured light it is characterised in that: Eigen Structure is that two dimension is sinusoidal Striped, gridiron pattern or Gauss dot matrix.

4. small angle measurement according to claim 1 method of structured light it is characterised in that: analysis extraction obtain record figure The location of pixels of characteristic point in picture, thus obtain the outer parameter rotation of the video camera with respect to the virtual image using camera marking method Matrix.

5. small angle measurement according to claim 1 method of structured light it is characterised in that: calculate object angle of rotation Degree, according to plane reflection law, the rotational angle of object is the 1/2 of virtual image rotational angle, by the virtual image obtaining angle of rotation angle value Divided by 2 anglecs of rotation that just can get reflecting mirror, it is also the anglec of rotation of object simultaneously.