CN111366079B - Calibration method for rapidly determining geometric positions of components in deflection measurement system - Google Patents
Calibration method for rapidly determining geometric positions of components in deflection measurement system Download PDFInfo
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- CN111366079B CN111366079B CN202010266084.9A CN202010266084A CN111366079B CN 111366079 B CN111366079 B CN 111366079B CN 202010266084 A CN202010266084 A CN 202010266084A CN 111366079 B CN111366079 B CN 111366079B
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
- G01B11/00—Measuring arrangements characterised by the use of optical techniques
- G01B11/002—Measuring arrangements characterised by the use of optical techniques for measuring two or more coordinates
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
- G01B11/00—Measuring arrangements characterised by the use of optical techniques
- G01B11/02—Measuring arrangements characterised by the use of optical techniques for measuring length, width or thickness
- G01B11/03—Measuring arrangements characterised by the use of optical techniques for measuring length, width or thickness by measuring coordinates of points
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
- G01B11/00—Measuring arrangements characterised by the use of optical techniques
- G01B11/02—Measuring arrangements characterised by the use of optical techniques for measuring length, width or thickness
- G01B11/06—Measuring arrangements characterised by the use of optical techniques for measuring length, width or thickness for measuring thickness ; e.g. of sheet material
- G01B11/0608—Height gauges
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- G—PHYSICS
- G06—COMPUTING; CALCULATING OR COUNTING
- G06T—IMAGE DATA PROCESSING OR GENERATION, IN GENERAL
- G06T7/00—Image analysis
- G06T7/80—Analysis of captured images to determine intrinsic or extrinsic camera parameters, i.e. camera calibration
Abstract
The invention relates to the technical field of optical engineering, and discloses a calibration method for quickly determining the geometric position of each part in a deflection measurement system, which comprises the following steps: the upper plane of a standard cylinder is made into a standard mirror surface, a circle of uniformly distributed black circular spot features are made on the periphery of the standard cylinder, the radius of one circular spot is smaller, the mirror surface is set into a coordinate system xOy plane, and an x axis is arranged on an axis where the circular spot is located. Firstly, the position of a standard mirror in a camera coordinate system is directly determined by utilizing a PnP method according to the imaging of the mirror circular spots, a small-size dot array pattern is displayed on a screen, a virtual image of the screen reflected by the mirror is shot by utilizing a camera, the spots displayed on the screen in the image are identified, and the position of the screen can be determined. The invention can effectively estimate the pose of each component in the measurement system, comprises the camera, the screen, the chuck and the workpiece, has simple operation and strong practicability, and has important significance for realizing high-precision deflection measurement of the optical curved surface.
Description
Technical Field
The invention relates to the technical field of optical engineering, in particular to a calibration method for quickly determining the geometric position of each part in a deflection measurement system.
Background
In modern precision measurements, interferometric methods are often used for specularly reflecting surfaces. But the measuring range is small, the measuring device is sensitive to environmental interference, and the measuring device is not suitable for measuring complex curved surfaces. In recent years, phase measurement deflection has enabled high-precision measurement of complex curved surfaces. The system is simple, has a large dynamic range and strong anti-interference capability, and is widely concerned in the field of optical engineering. The principle is that regular stripes are generated on a display, the stripes are deformed after being reflected by the measured surface, a CCD camera is used for shooting a deformation pattern, the surface gradient distribution of the measured surface shape can be calculated through the derivation of the geometric relation, and then the surface shape height is obtained through integration.
The accuracy of the deflection measurement depends directly on the quality of the geometric calibration, i.e. the determination of the relative position between the various components in the measurement system, including the camera, the workpiece, the screen, etc. The traditional geometric calibration usually adopts auxiliary instruments such as a three-coordinate measuring machine or a laser tracker, and has the disadvantages of complex operation, high cost and poor practicability. Xiao et al (opt. commun.2013; 305, 143-. However, the position of the workpiece cannot be directly determined, and the problem of 'height-slope ambiguity' inherent in deflection measurement cannot be solved. Additional detection by a laser tracker or the like is still required to determine the position of the workpiece, which is complicated to operate. Therefore, the calibration method for rapidly determining the geometric positions of all parts in the deflection measurement system is provided to solve the problems.
Disclosure of Invention
Technical problem to be solved
Aiming at the defects of the prior art, the invention provides a calibration method for quickly determining the geometric position of each part in a deflection measurement system, which has the advantages of simplicity, quickness and the like, and solves the problems that the position of a workpiece cannot be directly determined, the inherent height-slope ambiguity of deflection measurement cannot be solved, and the position of the workpiece still needs to be determined by additional detection of a laser tracker and the like.
(II) technical scheme
In order to achieve the purpose of simplicity and rapidness, the invention provides the following technical scheme: the utility model provides a calibration device of each parts geometric position in quick definite deflection measurement system, includes chuck, camera and screen, the top movable mounting of chuck has the standard component main part, the top fixedly connected with standard mirror surface of standard component main part, the outside of standard mirror surface just is located the top fixedly connected with black spot of standard component main part.
Preferably, the standard mirror has a flatness better than λ/5PV, and the standard body and the standard mirror are concentric.
Preferably, the distance and the diameter of the black circular spots are known, wherein one characteristic spot is smaller and has a diameter 2/3 times that of the other circular spots, the xOy plane of the mirror coordinate system is established at the standard mirror, the origin point is at the center of the standard mirror, and the x axis is set as the axis of the small circular spot.
Another technical problem to be solved by the present invention is to provide a calibration method for quickly determining the geometric position of each component in a deflection measurement system, which includes the following steps:
1) clamping the standard part main body by using a chuck, and adjusting the positions of a camera with known internal reference and a screen with known pixel size so that the camera can directly observe the pattern displayed by the screen;
2) the method comprises the steps that a screen displays a small-size dot array, a camera directly shoots a pattern virtual image reflected by a standard mirror surface, a circle of black circular spots on the mirror surface are recognized from the image, and a rotation matrix Rc2m and a translation vector Tc2m between a camera coordinate system and a mirror surface coordinate system are calculated by utilizing a PnP method;
3) establishing a corresponding relation between a screen dot array and dot images in a camera pattern, determining coordinates of a screen virtual image in a camera coordinate system by using a PnP method, and obtaining an actual position of a screen by using mirror reflection;
4) keeping the chuck still, replacing the standard part main body with an actually measured workpiece, clamping the workpiece in the same way, determining the transverse position of the workpiece in a mirror coordinate system by the central axis of the cylinder, and only leaving an unknown quantity of the height z;
5) and (3) optimally calculating the height of the workpiece, tracking light rays from the centers of small circular points in a camera, intersecting the nominal surface shape reflection of the workpiece with a screen plane to obtain pixel coordinates (u, v), and setting the actual pixel coordinates of the gravity centers of the circular points as (u ', v'). Taking the height h of the workpiece as a variable, and adjusting the value through numerical optimization:
and adopting a Levenberg-Marquardt method to carry out iterative solution.
(III) advantageous effects
Compared with the prior art, the invention provides a calibration method for quickly determining the geometric positions of all parts in a deflection measurement system, which has the following beneficial effects:
the calibration method for rapidly determining the geometric positions of all parts in the deflection measurement system can determine the relative geometric positions among a screen, a camera, a chuck clamp and a workpiece by only acquiring a pair of images, uses a specially designed standard part main body as a geometric reference, uses a standard plane mirror for reflection imaging to determine the pose of the screen, processes a circular spot characteristic on a plane of the screen to determine the position of the screen, transmits the X and Y transverse positions to the chuck through a cylinder below the standard part main body, determines the transverse position of the workpiece after being fixed, is an off-axis imaging system, directly causes the deflection of a reflection pattern due to the height deviation of the workpiece, so that the camera pixel reflects the light trace to the screen through the measured workpiece to perform ray tracing, reflects the height deviation of the workpiece due to the deviation from an actual display pattern, and optimizes and adjusts the height of the workpiece by using numerical values, the relative geometric position of each element in the whole system can be determined, the pose of each part of the measurement system, including a camera, a screen, a chuck and a workpiece, can be effectively estimated, and the method has important significance for realizing high-precision deflection measurement.
Drawings
FIG. 1 is a schematic structural diagram of a calibration time measurement system according to a calibration method for rapidly determining geometric positions of components in a deflection measurement system according to the present invention;
FIG. 2 is a schematic structural diagram of a customized standard component main body according to a calibration method for rapidly determining geometric positions of components in a deflection measurement system provided by the present invention;
FIG. 3 is a flow chart of a geometric calibration structure of a calibration method for rapidly determining the geometric position of each component in a deflection measurement system according to the present invention;
fig. 4 is a structural schematic diagram of tracking errors before and after optimization of height z in a calibration method for rapidly determining geometric positions of components in a deflection measurement system according to the present invention.
In the figure: 1 chuck, 2 cameras, 3 screens, 4 standard parts, 5 standard mirror surfaces and 6 black circular spots.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
Referring to fig. 1-4, a calibration device for rapidly determining the geometric position of each component in a deflection measurement system includes a chuck 1, a camera 2 and a screen 3, a standard component main body 4 is movably mounted on the top of the chuck 1, a standard mirror 5 is fixedly connected to the top of the standard component main body 4, the flatness of the standard mirror 5 is better than λ/5PV, the outer circles of the standard component main body 4 and the standard mirror 5 are coaxial, a black circular spot 6 is fixedly connected to the top of the standard component main body 4 and outside the standard mirror 5, the distance and the diameter of the black circular spot 6 are known, one of the characteristic spots is small and the diameter of the black circular spot is 2/3 times that of the other circular spots, an xOy plane of a mirror coordinate system is established at the standard mirror 5, the origin is at the center of the standard mirror 5, and the x axis is set as the axis of the.
A calibration method for rapidly determining the geometric position of each component in a deflection measurement system comprises the following steps:
1) clamping a standard part body 4 by using a chuck 1, and adjusting the positions of a camera 2 with known internal reference and a screen 3 with known pixel size so that the camera 2 can directly observe the pattern displayed on the screen 3;
2) the screen 3 displays a small-size dot array, the camera 2 directly shoots a pattern virtual image reflected by a standard mirror 5, a circle of black circular spots 6 on the mirror are identified from the image, and a rotation matrix Rc2m and a translation vector Tc2m between a coordinate system of the camera 2 and a coordinate system of the mirror are calculated by utilizing a PnP method;
3) establishing a corresponding relation between a dot array of the screen 3 and a dot image in a pattern of the camera 2, determining a coordinate of a virtual image of the screen 3 in a coordinate system of the camera 2 by using a PnP method, and obtaining an actual position of the screen 3 by using mirror reflection;
4) keeping the chuck 1 still, replacing the standard part main body 4 with an actually measured workpiece, clamping the workpiece in the same way, determining the transverse position of the workpiece in a mirror coordinate system by the central axis of the cylinder, and only leaving an unknown quantity of the height z;
5) and (3) optimally calculating the height of the workpiece, performing ray tracing from gravity center pixels of small dots in a camera, intersecting the nominal surface shape reflection of the workpiece with the plane of the screen 3 to obtain a pixel coordinate system (u, v), and setting actual pixel coordinates of the gravity centers of the dots as (u ', v'). Taking the height h of the workpiece as a variable, and adjusting the value through numerical optimization:
the problem is solved iteratively by adopting a Levenberg-Marquardt method.
The first embodiment is as follows:
in order to realize the quick and simple calibration of the deflection measurement system, the common plane reflector is made into a standard part with a reference for improvement, an aluminum alloy material is adopted, the upper part is a cylinder with the caliber of 200mm and the height of 10mm, the upper surface is turned into a mirror surface by adopting single-point diamond, and the flatness is superior to lambda/5 PV. And 24 circular spots with the diameter of 16mm are uniformly distributed on the upper surface at the position of 180mm, wherein the diameter of one circular spot is set to be 10mm, and all the circular spots are blackened as shown in figure 1. And directly acquiring the attitude of the plane mirror through the mark point on the plane mirror. The screen displays a 20 x 15 array of dots, each dot having a diameter set to 15 pixels, and the geometric calibration is accomplished according to the steps of fig. 3. An aspherical workpiece having a diameter of 130mm was measured, and light ray tracing was performed from the center of gravity of a dot imaged by a camera, and the obtained tracing deviation was as shown in fig. 4 (a). The final projection bias obtained using the Levenberg-Marquardt method to iteratively optimize the workpiece height is shown in FIG. 4(b), with the RMS of the reprojection error decreasing from 13.1 to 0.12 pixels.
The invention has the beneficial effects that: the calibration method for rapidly determining the geometric positions of all parts in a deflection measurement system can determine the relative geometric positions among a screen 3, a camera 2, a chuck 1 and a workpiece only by acquiring a pair of images, uses a specially designed standard part main body 4 as a geometric reference, uses a standard plane mirror thereof for reflection imaging, determines the pose of the screen 3, processes a round spot characteristic on a plane thereof for determining the position of the screen 3, transmits the X and Y transverse positions to the chuck 1 through a column below the standard part main body, and determines the transverse position after fixing the workpiece, while the whole measurement system is an off-axis imaging system, the height deviation of the workpiece can directly cause the deflection of a reflection pattern, therefore, the light ray tracing is performed from the pixels of the camera 2 to the screen 3 through the reflection of the measured workpiece, the height deviation of the workpiece can be reflected by the deviation of the actual display pattern, and the height of the workpiece is adjusted by numerical optimization, the relative geometric position of each element in the whole system can be determined, the pose of each part of the measurement system can be effectively estimated, the camera 2, the screen 3, the chuck 1 and the workpiece are included, the method has important significance for realizing high-precision deflection measurement, and the problems that the position of the workpiece cannot be directly determined, the 'height-slope ambiguity' inherent in the deflection measurement cannot be solved, and the position of the workpiece still needs to be determined by additional detection of a laser tracker and the like are solved.
Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that changes, modifications, substitutions and alterations can be made in these embodiments without departing from the principles and spirit of the invention, the scope of which is defined in the appended claims and their equivalents.
Claims (1)
1. A calibration method for rapidly determining geometric positions of components in a deflection measurement system is characterized in that the measurement system comprises a chuck (1), a camera (2) and a screen (3), a standard component main body (4) is movably mounted at the top of the chuck (1), a standard mirror surface (5) is fixedly connected at the top of the standard component main body (4), the flatness of the standard mirror surface (5) is better than lambda/5 PV, the outer circles of the standard component main body (4) and the standard mirror surface (5) are coaxial, black circular spots (6) are fixedly connected at the top of the standard component main body (4) and outside the standard mirror surface (5), the positions and diameters of the black circular spots (6) on the standard component main body (4) are known, one of the characteristic spots is small, the diameter is 2/3 times of the other circular spots, and an xOy plane of a mirror coordinate system is established at the standard mirror surface (5), the origin is at the center of the standard mirror surface (5), and the x axis is set as the axis of the small circular spot;
the method comprises the following steps:
1) clamping a standard part main body (4) by using a chuck (1), and adjusting the positions of a camera (2) with known internal reference and a screen (3) with known pixel size, so that the camera (2) can directly observe the pattern displayed by the screen (3);
2) the screen (3) displays a small-size dot array, the camera (2) directly shoots a pattern virtual image reflected by a standard mirror surface (5), a circle of black circular spots (6) on the mirror surface are recognized from the image, and a rotation matrix Rc2m and a translation vector Tc2m between a coordinate system of the camera (2) and a coordinate system of the mirror surface are calculated by utilizing a PnP method;
3) establishing a corresponding relation between a dot array of the screen (3) and a dot image in a pattern of the camera (2), determining a coordinate of a virtual image of the screen (3) in a coordinate system of the camera (2) by using a PnP method, and obtaining an actual position of the screen (3) by using mirror reflection;
4) keeping the chuck (1) still, replacing the standard part body (4) with an actually measured workpiece, clamping the workpiece in the same way, determining the transverse position of the workpiece in a mirror coordinate system by the central axis of the cylinder, and only leaving an unknown quantity of the height z;
5) performing optimized calculation on the height of the workpiece, performing ray tracing on gravity center pixels of small dots in a camera, intersecting a screen plane through nominal surface shape reflection of the workpiece to obtain a pixel coordinate system (u, v), setting actual pixel coordinates of the gravity centers of the dots as (u ', v'), taking the height h of the workpiece as a variable, and adjusting the value through numerical optimization:
and adopting a Levenberg-Marquardt method to carry out iterative solution.
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| CN113251953B (en) * | 2021-04-19 | 2022-07-15 | 霖鼎光学(上海)有限公司 | Mirror included angle measuring device and method based on stereo deflection technology |
| CN113362399B (en) * | 2021-07-02 | 2022-08-30 | 复旦大学 | Calibration method for positions and postures of focusing mirror and screen in deflection measurement system |
| CN114322840B (en) * | 2021-11-22 | 2024-04-12 | 昂视智能(深圳)有限公司 | 3D scanning system calibration method, device and data processing method |
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| CN105783775B (en) * | 2016-04-21 | 2018-05-11 | 清华大学 | A kind of minute surface and class minute surface object surface appearance measuring device and method |
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