CN102426007A - High-precision method for measuring attitude angle of triaxial air bearing table and measurement device thereof - Google Patents

Abstract

The invention provides a method and a device for measuring a high-precision attitude angle of a three-axis air bearing platform. Guide rails and blackout curtains are installed around the bottom of the three-axis air flotation table. The artificial lighting system is installed on the liftable platform. The bottom guide rails of the three-axis air flotation table are used to install blackout curtains. On the plane, the digital CCD camera is installed on the liftable platform. The steps of the measurement method include calibrating the digital CCD camera; the digital CCD camera collects the image of the marker and transmits it to the computer responsible for image processing; performs sub-pixel positioning on the marker point on the marker, and obtains the precise coordinates of the marker point in the image; Calculate the relative attitude angle between the marker and the digital CCD camera. The measuring device of the present invention is easy to install, has high measuring precision, and can complete the high-precision attitude measurement of the air bearing platform. The invention is also used for the precise measurement of the attitude angle of the single-axis turntable.

Description

Method and device for measuring high-precision attitude angle of three-axis air bearing platform

(1) Technical field

The invention relates to space technology, in particular to a method and device for measuring a high-precision attitude angle of a three-axis air bearing platform.

(2) Background technology

The three-axis air bearing platform relies on the air film formed between the air bearing and the bearing seat by compressed air to make the simulation platform float, so as to realize the relative motion condition of approximately frictionless, so as to simulate the impact of space vehicles such as satellites in outer space. The mechanical environment with small disturbance torque. As a space vehicle motion simulator, the three-axis air bearing platform is an important means and method in the process of space vehicle development for the full physical simulation experiment of the satellite control system to test the performance of the system.

During the test, the three-axis air-floor table needs to dynamically provide the attitude information such as the angle and angular velocity of the air-floor table through the attitude measurement system in order to complete the closed-loop control. (such as resolvers, inductive synchros, photoelectric code discs, gratings, etc.) are not applicable to the measurement of the three-axis air bearing table, and new measurement methods and devices need to be considered. And in the current practical application, the measurement accuracy of the measurement system is directly related to the effect of the simulation test.

After searching the literature, it was found that the Chinese invention patent application number: 200610010260.2, the patent name is the three-axis air bearing platform attitude angle measurement device and its measurement method, the patent is installed above the three-axis air bearing platform with a CCD camera, on the air bearing table surface A measurement LED cursor system is installed, using computer vision theory combined with the distance information of the measurement cursor point to calculate the relative motion parameters of the air bearing table surface relative to the camera, but due to the defects in the system construction, the measurement accuracy is limited, which affects its actual scope of use.

Chinese invention patent application number: 200410009086.7, the patent name is: Rigid body space pose measurement device and its measurement method. The external contact measurement method cannot be allowed, because the contact brings interference to the air bearing table, so this method is not suitable for the attitude information measurement of the three-axis air bearing table.

In the document "Study on the single-frame servo angle measurement system of three-axis air bearing platform" (published in Acta Astronautics. 1996, 17(4): 71-74), Zhang Xiaoyou, Liu Dun of Harbin Institute of Technology and Beijing Institute of Control Engineering Li Jisu et al. proposed a single-frame servo measurement scheme. In this system, an arc arm that can rotate around the vertical line in the center of the air-floor table is installed on the base of the air-floor table, and a movable carriage is installed on it. The attitude information of the air bearing table is measured by the rotation of the sensitive arc arm and the movement of the carriage. When the system needs to add a complex mechanical system and sensor system, the mechanism is complicated, and its accuracy is limited by the mechanical device and sensor, which can only reach 0.01°, which is difficult to achieve high precision.

(3) Contents of the invention

The object of the present invention is to provide a high-precision attitude angle measurement method and device for a three-axis air bearing platform.

The purpose of the present invention is achieved in this way: a high-precision attitude angle measuring device for a three-axis air flotation table, which is composed of a three-axis air flotation table top, a three-axis air flotation table spherical air bearing, and a three-axis air flotation table bearing base It is composed of seat, marker, digital CCD camera, artificial lighting system, blackout curtain, guide rail and liftable platform for installing camera and artificial light source. The guide rail and blackout curtain are installed around the bottom of the three-axis air bearing table, and the artificial lighting system is installed On the liftable platform, the bottom guide rail of the three-axis air bearing table is used to install the shading curtain, which is used to form a closed visual measurement space during measurement, and the marker is fixed on the bottom plane of the three-axis air bearing table. The angular movement of the former is exactly the same. The liftable platform for installing the camera and artificial light source is installed on the bearing base of the three-axis air bearing, and the digital CCD camera is installed on the liftable platform.

The present invention is a measurement method realized by the high-precision attitude angle measurement device of the three-axis air bearing platform, the steps are as follows:

Step 1: Calibrate the digital CCD camera;

Step 2: Close the shading curtain to form a closed image acquisition environment, and turn on the artificial light source;

Step 3: The digital CCD camera collects the image of the marker and transmits it to the computer responsible for image processing;

Step 4: The computer processes the image information of the marker, performs sub-pixel positioning on the marker points on the marker, and obtains the precise coordinates of the marker points in the image;

Step 5: Calculate the relative attitude angle between the marker and the digital CCD camera according to the principle of computer vision.

The invention provides a high-precision attitude angle measuring device and a measuring method for a three-axis air-floating platform capable of dynamically measuring attitude angle information of a three-axis air-floating platform without causing interference to the air-floating platform. Install markers at the bottom of the three-axis air flotation table, and install guide rails and shading curtains around the bottom of the three-axis air flotation table; install a liftable platform on the base of the three-axis air flotation table, and install on the platform A digital CCD camera and a light source, the camera is connected with the image acquisition card in the computer through a data cable. The camera used in the present invention is installed on the body of the three-axis air flotation table, the marker is installed on the bottom of the three-axis air flotation table, and the space distance between the camera and the marker is shortened. Artificial light sources, artificial light source feature points and blackout curtains are added to establish a closed image acquisition environment and eliminate the interference of external light sources. The present invention adopts a calibration template-type measuring feature device, which has higher precision compared with a measuring cursor system composed of light-emitting diodes. The camera lens uses an object-space telecentric lens, which is suitable for precise visual measurement.

The high-precision attitude measurement method of the three-axis air-floating platform of the present invention has simple installation of measuring equipment and high measurement accuracy, and can measure the high-precision attitude measurement of the air-floating platform. The invention is also used for the precise measurement of the attitude angle of the single-axis turntable.

(4) Description of drawings

Figure 1 is a schematic diagram of the composition of the attitude angle measurement system of the three-axis air bearing platform;

Figure 2 is a schematic diagram of the location of the measurement feature mark and the camera;

Figure 3 is a flow chart of the angle measurement of the three-axis air bearing platform.

(5) Specific implementation methods

The present invention will be further described below with examples in conjunction with the accompanying drawings.

Embodiment 1: in conjunction with Fig. 1, a kind of three-axis air-floating table high-precision attitude angle measuring device of the present invention, it is made of three-axis air-floating table top (1), three-axis air-floating table spherical surface air bearing (2), Three-axis air bearing base (3), marker (4), digital CCD camera (5), artificial lighting system (6), blackout curtains, guide rails (7) and liftable lifts for installing cameras and artificial light sources The platform (8) is composed of guide rails and blackout curtains installed around the bottom of the three-axis air flotation table (1), the artificial lighting system is installed on the liftable platform, and the guide rails at the bottom of the three-axis air flotation table are used to install blackout curtains It is used to form a closed visual measurement space during measurement. The marker (4) is fixed on the bottom plane of the three-axis air bearing table (1), and the angular movement of the two is exactly the same. The lifting platform (8) is installed on the three-axis air bearing base (3), and the digital CCD camera (5) is installed on the liftable platform (8).

The invention discloses a method for measuring a high-precision attitude angle of a three-axis air bearing platform, the steps of which are as follows:

Step 1: Calibrate the digital CCD camera;

Step 2: Close the shading curtain to form a closed image acquisition environment, and turn on the artificial light source;

Step 3: The digital CCD camera collects the image of the marker and transmits it to the computer responsible for image processing;

Step 4: The computer processes the image information of the marker, performs sub-pixel positioning on the marker points on the marker, and obtains the precise coordinates of the marker points in the image;

Step 5: Calculate the relative attitude angle between the marker and the digital CCD camera according to the principle of computer vision.

Embodiment 2: In combination with Fig. 1-Fig. 3, the present invention mainly consists of the following parts: three-axis air-flotation table top (1), three-axis air-floation table spherical air bearing (2), three-axis air-flotation table bearing base (3), marker (4), digital CCD camera (5), artificial light source (6), blackout curtain guide rail (7), for installing the liftable platform (8) of camera and artificial light source. The marker (4) is fixed on the bottom plane of the three-axis air bearing table top (1), and the angular movement of the two is exactly the same. The liftable platform (8) is installed on the three-axis air bearing base (3), and can be moved up and down to a suitable position for fixing as required. The camera (5) is installed on the liftable platform (8) to collect image information of each mark on the marker (4), and the artificial light source (6) provides constant and reliable lighting for image collection. The camera is a black and white digital CCD camera, which is connected to the computer using CameraLink to prevent interference. Camera resolution is considered in conjunction with marker size. The lens is a telecentric lens on the object side; the geometric structure and number of markers are determined by the measurement accuracy of the system and the selected algorithm. One implementation is that the three feature points are arranged in a straight line and installed to form an isosceles triangle in the height direction; Figure 2 is a schematic diagram of the location of the camera and feature points. The material of the template can be made of glass, metal, aluminum substrate and other materials, and the precision can reach 0.0005 micron.

Embodiment 3: basic work flow of the present invention is as shown in Figure 3, and concrete processing method is:

1. Calibrate the camera: collect the image of the calibration board and use it as a calibration image to calibrate the camera. The number is more than 4; extract the calibration image and determine the image coordinates of each calibration point on the calibration board; according to the physical size of the calibration board, Determine the world coordinates of each calibration point on the calibration board; for the ideal central perspective imaging model of the camera, according to the above data, use the least square method to obtain the homography matrix H, which reflects the relationship between the world coordinate system and the image coordinate system; The corresponding matrix H can be solved to obtain the internal parameters of the camera, so as to obtain the parameters of the ideal perspective model of the camera; on the basis of the ideal central perspective imaging model of the camera, the distortion parameters can be obtained by using the maximum likelihood method, so as to establish the actual imaging model of the camera. Complete the calibration process.

2. Close the blackout curtain to form a closed image acquisition environment, and turn on the artificial light source;

3. Acquisition of images of measurement feature devices (i.e. markers);

4. The computer processes the image information of the marker, performs sub-pixel positioning on the marker points on the marker, and obtains the precise coordinates of the marker points in the image. The image coordinates of the marked points in the marker are represented by their centers, and the precise positioning of the centers of each marked point requires the following steps:

(1) Image preprocessing to remove image noise.

(2) Image segmentation, counting the pixel values of all pixels in the image, determining the segmentation threshold, and binarizing and classifying each pixel according to the threshold. Due to the noise in the image, there will be some burrs on the edge of the cursor after binarization. In order to eliminate the influence of these burrs, morphological filtering is performed.

(3) Extract cursor features. According to the image segmentation results, the cursor feature pixels are determined by using the 8-neighborhood region growing method.

(4) Cursor sub-pixel positioning. Sub-pixel positioning requires two basic conditions: first, the target is composed of multiple points, and has certain geometric and gray distribution characteristics; second, the specific position of the target positioning reference point on the target must be clarified. In the present invention, these two conditions are met, and the centroid method can be used to perform sub-pixel level high-precision positioning of the cursor. The cursor is characterized by a circle, and it is suitable to use the centroid method to determine the coordinates of the cursor center when positioning. Calculate the centroid of the cursor feature according to the centroid formula. When the size of the characteristic area of the cursor is moderate, the accuracy of the centroid method can reach 0.2 to 0.5 pixels.

5. According to the principle of computer vision, calculate the relative attitude angle between the marker and the camera.

The process of using the camera to measure the attitude angle of the three-axis air bearing platform is the inverse process of recovering its three-dimensional structure from the two-dimensional image of the marked point, and the following coordinate system is involved in this process:

(1) The base coordinate system of the air bearing table

(2) The coordinate system of the air bearing table surface

(3) Camera coordinate system

(4) Image plane coordinate system

(5) Measuring characteristic device coordinate system

Since the conversion relationship between the coordinate system of the air bearing table surface and the coordinate system of the measuring feature device is a specific quantity that can be determined in advance, and there is also a definite conversion relationship between the camera coordinate system and the base coordinate system of the air bearing table, so the gas The relative rotation parameters between the coordinate system of the floating platform and the base coordinate system of the air bearing platform can be obtained by calculating the relative rotation parameters between the camera coordinate system and the measurement feature coordinate system.

The basic principle of the present invention to visually measure the attitude angle of the three-axis air bearing platform is as follows:

As shown in Figure 2, where AK is perpendicular to AC, AJ is perpendicular to AB, and both AK and AJ are on plane ABC, straight line L passes through point A and is perpendicular to plane ABC, straight line L and ray AK form plane α, straight line L and The ray AJ constitutes the plane β, and the spatial region between the plane α and the plane β is called V. When the camera is in space V or W, the coordinates of the three feature points A, B, and C in the camera coordinate system can be uniquely solved.

The coordinates of feature points A, B, and C in the coordinate system of the measuring device are known, assuming that the coordinates of feature points A, B, and C in the camera coordinate system are X _{A, c} = x _{A, c} , y _{A , c} , z _{A, c} ) ^T , X _{B, c} = x _{B, c} , y _{B, c} , z _{B, c} ) ^T , X _c = x _{C, c} , y _{C, c} , z _{C, c} ) ^T , the coordinates in the coordinate system of the measuring device are x _{A, m} = (x _{A, m} , y _{A, m} , z _{A, m} ) ^T , X _{B, m} = (x _{B, m} , y _{B, m} , z _{B, m} ) ^T , X _{C, m} = (x _{C, m} , y _{C, m} , z _{C, m} ) ^T , then the camera coordinate system O _c x _c y _c z _c and the measurement feature device coordinate system O _m The relationship between x _m y _m z _m is as follows: rotation matrix R

[x _{A, c} X _{B, c} X _{C, c} ] = R[x _{A, m} X _{B, m} X _{C, m} ] (1)

From X _{A, c} , X _{B, c} , X _{C, c} and X _{A, m} , X _{B, m} , X _{C, m} can be calculated to obtain unit column vector n _{A, c} , n _{B, c ,} n _{C, c} and n _{A, m} , n _{B, m} , n _{C, m} , then the rotation matrix R:

R=[n _{A, c} n _{B, c} n _{C, c} ] [n _A, m n _{B, m} n _{C, m} ] ^-1 (2)

The three-axis rotation angle between the camera coordinate system and the measurement feature coordinate system can be decomposed from the rotation matrix R, and the specific derivation is as follows:

$\mathrm{<span\; class="notranslate">\; R</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; \&gamma;</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; \&beta;</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; \&alpha;</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>\left[\begin{array}{ccc}{\mathrm{<span\; class="notranslate">\; r</span>}}_{\mathrm{<span\; class="notranslate">\; 11</span>}}& {\mathrm{<span\; class="notranslate">\; r</span>}}_{\mathrm{<span\; class="notranslate">\; 12</span>}}& {\mathrm{<span\; class="notranslate">\; r</span>}}_{\mathrm{<span\; class="notranslate">\; 13</span>}}\\ {\mathrm{<span\; class="notranslate">\; r</span>}}_{\mathrm{<span\; class="notranslate">\; twenty\; one</span>}}& {\mathrm{<span\; class="notranslate">\; r</span>}}_{\mathrm{<span\; class="notranslate">\; twenty\; two</span>}}& {\mathrm{<span\; class="notranslate">\; r</span>}}_{\mathrm{<span\; class="notranslate">\; twenty\; three</span>}}\\ {\mathrm{<span\; class="notranslate">\; r</span>}}_{\mathrm{<span\; class="notranslate">\; 31</span>}}& {\mathrm{<span\; class="notranslate">\; r</span>}}_{\mathrm{<span\; class="notranslate">\; 32</span>}}& {\mathrm{<span\; class="notranslate">\; r</span>}}_{\mathrm{<span\; class="notranslate">\; 33</span>}}\end{array}\right]<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 3</span>}<span\; class="notranslate">\; )</span>$

Then when cosβ≠0, the calculation formula of each Euler angle can be obtained as follows:

$\left\{\begin{array}{c}\mathrm{<span\; class="notranslate">\; \&beta;</span>}<span\; class="notranslate">\; =</span><span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; arctan</span>}\frac{{\mathrm{<span\; class="notranslate">\; r</span>}}_{\mathrm{<span\; class="notranslate">\; 31</span>}}}{\sqrt{{{\mathrm{<span\; class="notranslate">\; r</span>}}_{\mathrm{<span\; class="notranslate">\; 11</span>}}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; +</span>{{\mathrm{<span\; class="notranslate">\; r</span>}}_{\mathrm{<span\; class="notranslate">\; twenty\; one</span>}}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}}\\ \mathrm{<span\; class="notranslate">\; \&alpha;</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; arctan</span>}\frac{{\mathrm{<span\; class="notranslate">\; r</span>}}_{\mathrm{<span\; class="notranslate">\; 32</span>}}}{{\mathrm{<span\; class="notranslate">\; r</span>}}_{\mathrm{<span\; class="notranslate">\; 33</span>}}}\\ \mathrm{<span\; class="notranslate">\; \&gamma;</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; arctan</span>}\frac{{\mathrm{<span\; class="notranslate">\; r</span>}}_{\mathrm{<span\; class="notranslate">\; twenty\; one</span>}}}{{\mathrm{<span\; class="notranslate">\; r</span>}}_{\mathrm{<span\; class="notranslate">\; 11</span>}}}\end{array}\right.<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 4</span>}<span\; class="notranslate">\; )</span>$

Embodiment 4: In conjunction with Fig. 1, the present invention installs markers at the bottom of the table top of the three-axis air flotation table, and installs guide rails and shading curtains around the bottom of the three-axis air flotation table table; The platform can be raised and lowered, and a digital CCD camera and a light source are installed on the platform, and the camera is connected with the image acquisition card in the computer through a data line. The digital CCD camera is installed on the body of the three-axis air flotation table, and the marker is installed on the bottom of the three-axis air flotation table, and the space distance between the camera and the marker is shortened. Artificial light sources, artificial light source feature points and blackout curtains are added to establish a closed image acquisition environment and eliminate the interference of external light sources. The present invention adopts a calibration template-type measuring feature device, which has higher precision compared with a measuring cursor system composed of light-emitting diodes. The camera lens uses an object-space telecentric lens, which is suitable for precise visual measurement. The marker is installed at the bottom of the three-axis air bearing table, and there are marks required for measurement on the template, and the geometric shape, geometric structure and number of the marks are different according to the needs.

The artificial lighting system is installed on the liftable platform. The selection of the artificial lighting system needs to be based on the field of view of the lens, the distance between the lighting system and the cursor system, the shape and color of the cursor, and the imaging objective lens to determine the appropriate lighting. device. Its liftable platform is installed on the base of the three-axis air bearing table, and the slide rail at the bottom of the three-axis air bearing table is used to install blackout curtains, which are used to form a closed visual measurement space during measurement.

Claims (2)

1. three-axis air-bearing table high-precision attitude angle measuring device; It is by three-axis air-bearing table table top (1), three-axis air-bearing table sphere air-bearing (2), three-axis air-bearing table bearing base (3), marker (4), digital ccd video camera (5), artificial light system (6), window-blind, guide rail (7) and be used to install that the liftable platform (8) of video camera and artificial light source forms; It is characterized in that: mounting guide rail and window-blind around three-axis air-bearing table table top (1) bottom; The artificial light system is installed on the liftable platform; Three-axis air-bearing table table top bottom guide track is used to install window-blind; Window-blind is used for when measuring, forming the vision measurement space of sealing, and marker (4) is fixed on the base plane of three-axis air-bearing table table top (1), and both angular motions are identical; The liftable platform (8) that is used to install video camera and artificial light source is installed in three-axis air-bearing table bearing base (3), and digital ccd video camera (5) is installed on the liftable platform (8).

2. three-axis air-bearing table high-precision attitude angle measuring method of realizing by the described three-axis air-bearing table high-precision attitude angle measuring of claim 1 device, it is characterized in that: step is following:

Step 1: digital ccd video camera is demarcated;

Step 2: close window-blind and form the sealing image capture environment, open artificial light source;

Step 3: digital ccd video camera is gathered the image of marker and is transferred to the computing machine of being responsible for Flame Image Process;

Step 4: the image information of Computer Processing marker, the gauge point on the marker is carried out sub-pixel positioning, obtain the accurate coordinates of gauge point in image;

Step 5: according to principle of computer vision, the relative attitude angle between calculation flag device and the digital ccd video camera.

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