CN104180778A - 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 measurement of angle technology of optics, particularly for a kind of structured light method of testing of small angle measurement.

Technical background

Measurement of angle is that the measurement of the important component part of geometric sense measurement technology, particularly minute angle is all extremely important and acts in many fields such as Precision Machining, Aero-Space, military affairs and communications.In angle measurement technique research the earliest be mechanical type and electromagnetic type angle measurement technique, as multiteeth indexing table and circle magnetic grid etc., the major defect of these methods is mostly hand dipping, is not easy to realize robotization, measuring accuracy is restricted.Extremely people's the attention owing to having noncontact, pin-point accuracy and highly sensitive feature of optics angle-measuring method, the development of especially stable LASER Light Source makes industry spot measurement become possibility.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, optics angle-measuring method is except well-known optical dividing head method and polygon method, and conventional also have photoelectric encoder method, diffraction approach, autocollimation method, Fiber Optic Sensor, acoustooptic modulation method, circle raster method, optics internal reflection method, laser interferance method, parallel interferogram technique and loop laser method etc.These methods have feature and range of application separately.In autocollimation method, object and picture lay respectively at conjugate planes.When object rotates, object imaging point in image planes is also moved thereupon, by measuring the amount of movement of picture point, just calculates the angle that object rotates.Autocollimation method principle is simple, easy to operate, easily go, but measurement range is generally all very little, conventionally between somewhat to tens minutes, measures reliability and measuring accuracy conventionally in several rads.The application of circle grating in measurement of angle is very extensive, has also reached high accuracy in complete cycle is measured at any angle.Its shortcoming is higher to heart accuracy requirement to grating and turntable, the making processing difficulties of pin-point accuracy grating.The major advantage of optics internal reflection method small angle measurement is that volume is little, can make pocket angular instrument, but its measurement range is also very little, therefore can only be for small angle measurement.Laser interference angle measurement technique changes into the angle of directly measuring object rotation the optical path difference of measuring object reflected light and reference light.Therefore the part that can be as accurate as optical wavelength due to interferometry even 1/tens is the highest measuring method of current degree of accuracy.But very harsh to the requirement of environment, many extraneous factors, as surrounding air flows, ambient vibration etc. all can produce a very large impact measurement result, and apparatus structure is accurate, stability is bad, volume is large, thereby conventionally only as a kind of measuring basis and detection means, be difficult to in-site measurement and workshop condition and measure.The principle of work of ring laser is based on Sagnac effect.When tested measurer and ring laser synchronously rotate with respect to static photoelectric collimator, the moment coinciding at guidance axis and measurer faceted pebble normal, tested angle converts the photocurrent that produced by photoelectric auto-collimator to and triggers and the required time interval of stop pulse, interface arrangement during this time every interior to loop laser pulse reading.The shortcoming of the method is to realize kinetic measurement, and very high to measuring condition requirement, processing technology is difficult to assurance, and cost is high, strict to environmental requirement.This is also that ring laser does not obtain the main reason of widely applying, and its measurement result also can be subject to the impact of " frequency pulling " and earth rotation, and much methods are all applicable to low-angle precision measurement.

By finding out the introduction of several optics angle-measuring methods of commonly using at present, optical method is widely used in low-angle measurement, and has reached very high measuring accuracy, becomes irreplaceable low-angle detection means.The measurement requirement improving constantly for meeting some field, increasing measuring method and measuring technique be studied, exploitation constantly.Optical method has extremely important effect and application prospect widely in low-angle measurement.

Quantity of information that structured light metering method is obtained is abundant, have measure highly sensitive, precision is high and equipment cost is relatively low, anti-environmental interference ability is strong, can be used for the advantages such as workshop detection, has been widely used in optical measurement field.And for adopting method of structured light to realize the report of low-angle measurement, have no up to now report.

Summary of the invention

The present invention is a kind of method of structured light of small angle measurement, has simple in structure, easy to use, highly sensitively, to environment, without specific (special) requirements, the advantage such as can in workshop condition, detect.

Native system comprises display screen, ccd video camera and robot calculator.Computing machine produces Eigen Structure, is presented on display screen, and projects to testee or be fixed on the catoptron on object, after being reflected, by ccd video camera, is received.CCD takes and records the Eigen Structure reflecting.Namely CCD takes and records the virtual image that display screen is formed by catoptron.When catoptron rotates, the virtual image of shot by camera also can rotate.The virtual image before and after rotating is analyzed, calculated its rotational angle.According to light reflection law, half of this angle is the angle that catoptron rotates.

The present invention has following advantage:

1. the present invention, to environment without specific (special) requirements, can detect in workshop condition.

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

3. the present invention has larger measurement dynamic range.

4. the system architecture that the present invention adopts is simple, easy to use, and system element is placed without special requirement.

5. detection method of the present invention has very high sensitivity.

6. the structure pattern and the phase-shifting technique that in the present invention, adopt have quite high precision, and can effectively suppress noise and the impact of surrounding environment on testing result.

Accompanying drawing explanation

Fig. 1 is the detection method system architecture schematic diagram of mentioning in the present invention;

Fig. 2 is camera model schematic diagram;

Fig. 3 is characteristic feature 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 rotating; The virtual image before Fig. 4 a. rotates; The virtual image after Fig. 4 b. rotates.

Embodiment

As shown in Figure 1, native system is mainly to comprise ccd video camera, display screen and computing machine.Show the Eigen Structure that screen display is generated by computing machine, through testee or after being fixed on the catoptron reflection on object by ccd video camera captured and record.Namely CCD takes and records the virtual image that display screen is formed by catoptron.When catoptron rotates, the virtual image of shot by camera also can rotate.The virtual image before and after rotating is analyzed, calculated its rotational angle.According to light reflection law, half of this angle is the angle that catoptron rotates.Take below and show that screen display two dimension sine streak Eigen Structure, as example describes, has similar measuring process when showing other Eigen Structures, this example does not comprise all the elements of this patent.

First video camera is demarcated and tried to achieve intrinsic parameter.Camera imaging model as shown in Figure 2, adopts and to have considered that the non-linear camera model of aberration describes imaging relations, and the linear camera model based on perspective projection adds the aberration that causes lens distortion.World coordinate system mid point p (x, y, z), the coordinate of its picture point in plane of delineation system 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 respectively normalization matrix on u, v axle; (u ₀, v ₀) be principal point coordinate; R and T are the outer parameter of video camera, represent respectively rotation matrix and the translation matrix of the relative world coordinate system of camera coordinate system; X=x/z, Y=y/z, has represented the projecting direction that p is ordered.Can be in the hope of Intrinsic Matrix K by camera calibration.Camera calibration method is a lot, as the two-step approach of Tsai and Roger proposition, the plane reference method that Zhang Zhengyou proposes etc.

Second step, shows and takes two-dimentional sine streak Eigen Structure and carry out image processing.Generation standard two dimension sine streak Eigen Structure in computing machine, through testee or after being fixed on the catoptron reflection on object by ccd video camera captured and record.Namely CCD takes and records the virtual image that display screen is formed by catoptron, as shown in Fig. 4 (a).According to Fourier's fringe analysis method, by Fourier transform, filtering and inverse Fourier transform, the image of taking from video camera, extract the PHASE DISTRIBUTION of blocking of two orthogonal directionss.Then the pixel coordinate of estimating bright spot carries out phase unwrapping in the window of certain width to bright spot, and two-dimensional linear matching, can obtain the subpixel coordinates of local bright spot, thereby extract the location of pixels that obtains unique point.At this moment, just can adopt camera calibration method to calculate now video camera with respect to the outer parameter rotation matrix R of the virtual image ₁.

The 3rd step, rotates after catoptron, shows and takes two-dimentional sine streak Eigen Structure and carry out image processing.Rotate catoptron, ccd video camera is taken and is recorded the virtual image that now display screen is formed by catoptron, as shown in Fig. 4 (b).Repeat second step computation process, obtain video camera and with respect to catoptron, rotate the outer parameter rotation matrix R of the rear virtual image ₂.

The 4th step, calculates the catoptron anglec of rotation.According to formula 2, can obtain catoptron and rotate the rotation matrix between former and later two virtual images:

$R_{12}=R_1^{-1}{R}_2---\left(2\right)$

R wherein ₁₂be the matrix of 3 * 3, the root of its eigenwert quadratic sum is the rotational angle of the virtual image.According to flat mirror reflects principle, the rotational angle of catoptron is 1/2 of virtual image rotational angle, and the virtual image rotational angle value obtaining just can be obtained to the anglec of rotation of catoptron divided by 2, is also the anglec of rotation of object simultaneously.

Claims (6)

1. a method of structured light for small angle measurement, is characterized in that: measuring system is comprised of ccd video camera, display screen and computing machine;

First carry out camera calibration, obtain the intrinsic parameter of video camera;

Second step, produces Eigen Structure by computing machine, be presented on display screen, and project to testee or be fixed on the catoptron on object, after reflection by video camera record; Analyze to extract and to obtain the location of pixels of unique point in document image, then calculate now video camera with respect to the outer parameter rotation matrix R of the virtual image ₁;

The 3rd step, rotates after catoptron, repeats the computation process in second step, obtains video camera and with respect to catoptron, rotates the outer parameter rotation matrix R of the rear virtual image ₂;

The 4th step, calculates the anglec of rotation of object.

2. the method for structured light of small angle measurement according to claim 1, is characterized in that: by camera calibration, obtain its intrinsic parameter, adopt the nonlinear model of having considered aberration.

3. the method for structured light of small angle measurement according to claim 1, is characterized in that: Eigen Structure is two-dimentional sine streak, gridiron pattern or Gauss's dot matrix.

4. the method for structured light of small angle measurement according to claim 1, is characterized in that: analyze and extract the location of pixels that obtains unique point in document image, thereby adopt camera marking method to obtain the outer parameter rotation matrix with respect to the video camera of the virtual image.

5. the method for structured light of small angle measurement according to claim 1, is characterized in that: by the external parameters of cameras rotation matrix R with respect to the virtual image before and after rotating ₁and R ₂try to achieve the rotational angle of the virtual image:

$R_{12}=R_1^{-1}{R}_2$

R ₁₂be the matrix of 3 * 3, the root of its eigenwert quadratic sum is the rotational angle of the virtual image.

6. the method for structured light of small angle measurement according to claim 1, it is characterized in that: the rotational angle that calculates object, according to plane reflection law, the rotational angle of object is 1/2 of virtual image rotational angle, the virtual image rotational angle value obtaining just can be obtained to the anglec of rotation of catoptron divided by 2, is also the anglec of rotation of object simultaneously.