A wind tunnel coordinate axis system calibration method and calibration device based on coding mark

Abstract

The present invention discloses a wind tunnel coordinate axis calibration method and a calibration device based on coding marks, the method comprising: establishing a world coordinate system; establishing a test model coordinate system, determining the coordinates of each reflective marking point; determining the coordinates of the reflective marking point in the world coordinate system, and determining the rigid body transformation relationship between the model coordinate system and the world coordinate system according to the coordinates of the reflective marking point in the model coordinate system, point cloud registration; establishing a coordinate conversion plate coordinate system, determining the coordinates of each coded marking point; determining the coordinates of the coded marking point in the world coordinate system, and determining the rigid body transformation relationship between the coordinate conversion plate coordinate system and the world coordinate system according to the coordinates of the coded marking point in the coordinate conversion plate coordinate system, point cloud registration; using the coordinate conversion plate coordinate system to calculate the model posture and displacement; determining the rigid transformation relationship between the coordinate conversion plate coordinate system and the test model coordinate system, thereby calculating the model posture and displacement in the wind tunnel coordinate system. The present invention improves the field adaptability and versatility of the calibration method.

Description

Technical Field

[0001] The invention relates to the field of optical measurement of aviation wind tunnel tests, and in particular to a wind tunnel coordinate axis system calibration method and a calibration device based on coding marks. Background Art

[0002] With the establishment of wind tunnel groups in my country and the development of flight test technology, aircraft model wind tunnel tests have put forward higher requirements for simulation authenticity and test refinement. Traditional methods are becoming increasingly incapable of meeting these requirements. The use of optical non-contact measurement methods has gradually become a trend in aerospace aircraft model tests. Optical non-contact measurement methods can accurately track the motion information during aircraft model tests, such as angle of attack measurement in continuously variable angle of attack tests, flight trajectory and attitude tracking in free flight tests, etc.

[0003] There is a key link in the test process, that is, the model coordinate system and the wind tunnel coordinate system need to be accurately aligned to ensure that the measurement data is in a unified coordinate system, remove the relative relationship in the middle, and obtain the absolute trajectory and attitude information. In principle, this link can be obtained by aligning the model point cloud existing in the two coordinate systems to obtain the rigid body transformation matrix obtained by alignment. The model coordinate system can locate the geometric center according to the design size and actual morphology of the model, and determine the model body coordinate system according to the geometric center. However, how to accurately calibrate the wind tunnel coordinate system is a puzzling problem. Traditional calibration methods, such as three-dimensional stepped calibration blocks, have problems such as large volume and weight, difficult installation and maintenance, and high requirements for the manufacturing accuracy of marking points, resulting in poor applicability and limited application occasions. In addition, the calibration of domestic wind tunnel coordinate systems generally relies on model support mechanisms, but this method is not suitable for wind tunnel tests without model support mechanisms, such as model free flight. Summary of the invention

[0004] In order to make up for the shortcomings of the above-mentioned background technology, the present invention proposes a wind tunnel coordinate axis system calibration method and a calibration device based on coding marks to solve the problems of low adaptability and difficult installation and maintenance of the wind tunnel coordinate axis system calibration method.

[0005] The technical problem of the present invention is solved by the following technical solutions:

[0006] The present invention discloses a method for calibrating a wind tunnel coordinate axis system based on coded marking points, comprising the following steps:

[0007] S1. Establish a world coordinate system;

[0008] S2. Establish the wind tunnel test model coordinate system and determine the coordinates P of each reflective mark point in the test model coordinate system m ;

[0009] S3. Determine the coordinates P of the reflective marking point in the world coordinate systemw ,According to the coordinates of the reflective marker points in the test model coordinate system, the point cloud is registered with the two point clouds to determine the rigid body transformation relationship between the test model coordinate system and the world coordinate system;

[0010] S4, establish the coordinate system of the coordinate conversion plate, and determine the coordinates P of each coded mark point in the coordinate system of the coordinate conversion plate t ;

[0011] S5. Determine the coordinates P of the coded marker point in the world coordinate system wc , according to the coordinates of the coded marker points in the coordinate system of the coordinate conversion plate, point cloud registration is performed to determine the rigid body transformation relationship between the coordinate system of the coordinate conversion plate and the world coordinate system;

[0012] S6. Use the coordinate conversion plate coordinate system instead of the wind tunnel coordinate system to calculate the test model posture and displacement;

[0013] S7. According to the rigid body transformation relationship between the test model coordinate system and the world coordinate system, the rigid body transformation relationship between the coordinate conversion plate coordinate system and the world coordinate system, and the test model position and displacement, determine the rigid body transformation relationship between the coordinate conversion plate coordinate system and the test model coordinate system, that is, the rigid body transformation relationship between the wind tunnel coordinate system and the test model coordinate system, so as to calculate the test model position and displacement in the wind tunnel coordinate system.

[0014] In some embodiments, in step S1, the step of establishing the world coordinate system is: performing camera calibration, obtaining high-precision internal and external parameters of each camera, and selecting a designated camera coordinate system to establish the world coordinate system.

[0015] In some embodiments, in step S2, establishing the wind tunnel test model coordinate system comprises the following steps:

[0016] S21, measuring the test model using a rotational inertia measurement device to obtain the center of mass position of the test model;

[0017] S22, scanning the test model with reflective marking points using a handheld scanning device to obtain a three-dimensional point cloud thereof, wherein the three-dimensional point cloud includes a point cloud of the test model and a point cloud of the reflective marking points;

[0018] S23. Taking the center of mass of the test model as the origin of the model coordinate system, determine the directions of the coordinate axes of the test model coordinate system according to the symmetry of the test model.

[0019] In some embodiments, step S3 specifically includes:

[0020] S31, take a picture of the test model, identify and reconstruct the marking points, and obtain the coordinates of the reflective marking points in the world coordinate system;

[0021] S32, performing point cloud registration according to the coordinates of the reflective marking points in the test model coordinate system and the coordinates of the reflective marking points in the world coordinate system, and determining the rigid body transformation relationship between the test model coordinate system and the world coordinate system:

[0022] P w = w R m ×P m + w T m

[0023] in, w R m Indicates the rotation transformation of the reflective mark point coordinates from the test model coordinate system to the world coordinate system. w T m Represents the translation transformation of the reflective mark point coordinates from the test model coordinate system to the world coordinate system.

[0024] In some embodiments, in step S4, the coordinate conversion plate is a highly flat rectangular calibration plate, and a plurality of coding mark points are provided on the coordinate conversion plate, each coding mark point adopts a different code to meet the coding uniqueness, and the horizontal coding mark point connection line and the vertical coding mark point connection line are kept parallel to the rectangular side of the coordinate conversion plate, and step S4 specifically includes:

[0025] S41. Determine the size of the coordinate conversion plate according to wind tunnels of different sizes, so that the size of the coordinate conversion plate is proportional to the diameter of the wind tunnel nozzle to meet the conversion accuracy of the coordinate axis system of wind tunnels with different fields of view;

[0026] S42, according to the position and direction of the coding mark point, measure the relative position relationship between the coordinates, determine the coordinate system of the coordinate conversion plate, and calculate the coordinates of each coding mark point in the coordinate system of the coordinate conversion plate.

[0027] In some embodiments, step S5 specifically includes:

[0028] S51, take a picture of the coordinate conversion plate, identify and reconstruct the coded marker points, and obtain the coordinates P of the coded marker points in the world coordinate system wc .

[0029] S52, performing point cloud registration according to the coordinates of the coded marking points in the coordinate system of the coordinate conversion plate and the coordinates of the coded marking points in the world coordinate system, and determining the rigid body transformation relationship between the coordinate system of the coordinate conversion plate and the world coordinate system:

[0030] P wc = wc R t ×P t + wc T t

[0031] in,wc R t Indicates the rotation transformation of the coded marker from the coordinate system of the coordinate conversion board to the world coordinate system. wc T t Indicates the translation transformation of the coded marker from the coordinate system of the coordinate conversion board to the world coordinate system.

[0032] In some embodiments, in step S6, the method of using the coordinate conversion plate coordinate system instead of the wind tunnel coordinate system to calculate the test model posture is:

[0033] Assume that at a certain moment during the test, an arbitrary marked point P on the test model is in the wind tunnel coordinate system S wind The lower coordinate is P wind , test model coordinate system S modle The coordinates P modle_c , in the coordinate conversion board coordinate system S temp The next position is P temp , then the following conversion relationships exist from the wind tunnel coordinate system to the test model coordinate system, and from the coordinate conversion plate coordinate system to the model coordinate system:

[0034]

[0035] in, wind R temp Indicates the rotation transformation of the marker point from the coordinate conversion plate coordinate system to the wind tunnel coordinate system. wind T temp Indicates the translation transformation of the marker point from the coordinate system of the coordinate conversion plate to the wind tunnel coordinate system. temp R modle Indicates the rotation transformation of the marking point from the test model coordinate system to the coordinate system of the coordinate conversion plate. temp T modle Indicates the translation transformation of the marking point from the test model coordinate system to the coordinate system of the coordinate conversion plate;

[0036] According to the above two equations, the transformation relations of each coordinate system exist as follows:

[0037] P wind = wind R temp × temp R modle ×P modle_c - wind R temp × temp T modle + wind T temp

[0038] thus:

[0039]

[0040] in, wind R modle Indicates the rotation transformation of the marker point from the wind tunnel coordinate system to the coordinate conversion plate coordinate system. wind T modle Indicates the translation transformation of the marker point from the wind tunnel coordinate system to the coordinate conversion plate coordinate system;

[0041] Since the coordinate axes of the wind tunnel coordinate system and the coordinate conversion plate coordinate system are parallel, that is, wind R temp =I 3×3 , where I 3×3 represents the 3×3 identity matrix,

[0042]

[0043] Therefore, the coordinate conversion plate coordinate system can be directly used instead of the wind tunnel coordinate system to calculate the test model posture.

[0044] In some embodiments, in step S6, the method of calculating the displacement of the test model using the coordinate conversion plate coordinate system instead of the wind tunnel coordinate system is:

[0045] Assume that at t0 and t1, the reflective mark point on the test model is measured in the wind tunnel coordinate system S wind Point Cloud and Model coordinate system S modle The point cloud of the reflective marker point is P modle , then the following relationship exists:

[0046]

[0047] Among them, R 0 represents the rotation transformation of the reflective mark point from the model coordinate system to the wind tunnel coordinate system at time t0, R 1 represents the rotation transformation of the reflective mark point from the model coordinate system to the wind tunnel coordinate system at time t1, T 0 represents the translation transformation of the reflective marker from the model coordinate system to the wind tunnel coordinate system at time t0, T 1 Represents the translation transformation of the reflective marker point from the model coordinate system to the wind tunnel coordinate system at time t1;

[0048] At this time, the displacement calculation formula of the test model is:

[0049] T 0-1 =T 1 -T 0

[0050] Assuming that the coordinate conversion plate coordinate system is used instead of the wind tunnel coordinate system, the point cloud of the marked point on the test model in the wind tunnel coordinate system is measured at t0 and t1 respectively: and Then there is the following point cloud coordinate transformation relationship:

[0051]

[0052] in, Indicates the coordinates of the reflective mark point at time t0 in the coordinate conversion board coordinate system, Indicates the coordinates of the reflective marking point at time t1 in the coordinate system of the coordinate conversion board;

[0053] Model displacement calculation formula:

[0054]

[0055] According to the above formula, we can get:

[0056]

[0057] in, wind T 0 temp represents the translation transformation of the marked point from the coordinate system of the coordinate conversion plate to the wind tunnel coordinate system at time t0, wind T 1 temp Indicates the translation transformation of the marked point from the coordinate system of the coordinate conversion plate to the wind tunnel coordinate system at time t1;

[0058] It can be deduced that:

[0059]

[0060] because but:

[0061]

[0062] Therefore, the coordinate conversion plate coordinate system can be directly used instead of the wind tunnel coordinate system to calculate the displacement of the test model.

[0063] The present invention also discloses a wind tunnel coordinate axis calibration device based on coded marking points, comprising:

[0064] Install the card holder;

[0065] A vertical guide rail, both ends of which are fixed to the wind tunnel through the mounting base;

[0066] A square tube adapter is arranged on the vertical guide rail, and an interference fit is adopted between the square tube adapter and the vertical guide rail;

[0067] A horizontal guide rail, wherein the horizontal guide rail is connected to the vertical guide rail via a square tube connector, an interference fit is adopted between the horizontal guide rail and the square tube adapter, and after the mounting base is fixed, the axis of the horizontal guide rail is parallel to the axis of the wind tunnel nozzle;

[0068] A round tube adapter, arranged on the horizontal guide rail;

[0069] A dual-axis level, disposed on the horizontal guide rail;

[0070] A coordinate conversion plate, wherein the coordinate conversion plate is connected to the biaxial level through the circular tube adapter, the plane where the biaxial level is located is perpendicular to the plane where the coordinate conversion plate is located, and the coordinate conversion plate is in a vertical plane; the coordinate conversion plate is used to establish a coordinate conversion plate coordinate system, and by adjusting the biaxial level, the coordinate conversion plate coordinate system and the wind tunnel coordinate system have the same direction of each coordinate axis.

[0071] In some embodiments, the coordinate conversion plate is a highly flat rectangular calibration plate, and a plurality of coding marking points are arranged on the coordinate conversion plate. Each coding marking point adopts a different code to meet the uniqueness of the code, and the horizontal coding marking point connection line and the vertical coding marking point connection line are kept parallel to the rectangular side of the coordinate conversion plate; the size of the coordinate conversion plate is proportional to the diameter of the wind tunnel nozzle.

[0072] The beneficial effects of the present invention compared with the prior art include: the wind tunnel coordinate axis system calibration method based on coded marking points provided by the present invention determines the coordinate system of the coordinate conversion plate in the wind tunnel coordinate system space through limited marking points, and can complete the wind tunnel coordinate axis system calibration by converting the coordinates of the coordinate conversion plate to the wind tunnel coordinate system, so that it is applicable to the coordinate axis system calibration of various complex working conditions and large field wind tunnels, overcoming the shortcomings of the traditional method such as insufficient flexibility. The wind tunnel coordinate axis system calibration method of the present invention has better field adaptability and stronger versatility.

[0073] The wind tunnel coordinate axis calibration device based on coded marking points provided by the present invention only needs to process a high-precision coordinate conversion plate and a small amount of auxiliary installation tooling. On-site installation and debugging are simple and convenient, and the manufacturing cost is reduced while ensuring accuracy, which greatly facilitates on-site test operations. BRIEF DESCRIPTION OF THE DRAWINGS

[0074] Figure 1 A flow chart of a wind tunnel coordinate axis system calibration method according to an embodiment of the present invention;

[0075] Figure 2 A two-dimensional design diagram of a cone test model according to an embodiment of the present invention;

[0076] Figure 3 The point cloud result of the handheld scanning device scanning the cone test model of the embodiment of the present invention;

[0077] Figure 4 A design diagram of a coordinate conversion plate according to an embodiment of the present invention;

[0078] Figure 5 Schematic diagram of a wind tunnel coordinate axis calibration device according to an embodiment of the present invention. DETAILED DESCRIPTION

[0079] The present invention is further described below with reference to the accompanying drawings and in combination with preferred embodiments. It should be noted that the embodiments and features in the embodiments of the present application can be combined with each other without conflict.

[0080] It should be noted that the directional terms such as left, right, up, down, top, and bottom in this embodiment are merely relative concepts or are based on the normal use status of the product, and should not be considered as restrictive.

[0081] When the existing high-precision three-dimensional stepped calibration block calibration technology is used to calibrate the wind tunnel coordinate axis system, there are problems such as large volume and weight of the calibration block, difficulty in installation and maintenance, and high manufacturing precision requirements for the marking points on the calibration block. The embodiment of the present invention provides a wind tunnel coordinate axis system calibration method based on coded marking points with high applicability, and the wind tunnel coordinate axis system calibration is completed by replacing the wind tunnel coordinate system with the coordinate conversion plate coordinate system. The calibration method of the embodiment of the present invention uses the coordinate conversion plate coordinate system to replace the wind tunnel coordinate system to complete the wind tunnel coordinate axis system calibration and realize the wind tunnel test model posture and displacement measurement. The embodiment of the present invention is suitable for the coordinate axis system calibration of various complex working conditions and large field of view wind tunnels, such as the wind tunnel coordinate axis system calibration of the wind tunnel of the continuous variable angle of attack experimental wind tunnel and the wind tunnel coordinate axis system calibration of the free flight experimental wind tunnel. It has the advantages of low cost, fast speed, high precision, etc., and therefore has great engineering application value.

[0082] like Figure 1 As shown, the wind tunnel coordinate axis system calibration method based on coded marking points in an embodiment of the present invention includes the following steps:

[0083] S1. Establishing a world coordinate system. The video measurement system performs camera calibration, obtains high-precision internal and external parameters of each camera, and selects a specified camera coordinate system to establish a world coordinate system.

[0084] S2. Establish the wind tunnel test model coordinate system, use a handheld scanning device to scan the test model with the marker points, obtain its three-dimensional point cloud, and determine the coordinates P of each reflective marker point in the test model coordinate system. m The test model coordinate system is determined according to the geometric characteristics of the test model point cloud.

[0085] Among them, establishing the wind tunnel test model coordinate system includes the following steps:

[0086] S21. Use a rotational inertia measurement device to measure the test model to obtain the center of mass position of the test model.

[0087] S22. Use a handheld scanning device to scan the test model with reflective marking points to obtain its three-dimensional point cloud, which includes the test model point cloud and the reflective marking point cloud.

[0088] S23. Taking the center of mass of the test model as the origin of the model coordinate system, determine the directions of the coordinate axes of the test model coordinate system according to the symmetry of the test model.

[0089] S3. Determine the coordinates P of the reflective marking point in the world coordinate system w ,According to the coordinates of the reflective marker points in the test model coordinate system, the point cloud is registered with the two point clouds to determine the rigid body transformation relationship between the test model coordinate system and the world coordinate system.

[0090] Specifically, step S3 includes:

[0091] S31, the video measurement system takes a picture of the coordinate conversion plate, identifies and reconstructs the marking points, and obtains the coordinates of the reflective marking points in the world coordinate system;

[0092] S32. Perform point cloud registration according to the coordinates of the reflective marking points in the test model coordinate system and the coordinates of the reflective marking points in the world coordinate system to determine the rigid body transformation relationship between the test model coordinate system and the world coordinate system:

[0093] P w = w R m ×P m + w T m

[0094] in, w R m Indicates the rotation transformation of the reflective mark point coordinates from the test model coordinate system to the world coordinate system. w T m Represents the translation transformation of the reflective mark point coordinates from the test model coordinate system to the world coordinate system.

[0095] S4, establish the coordinate system of the coordinate conversion plate, and determine the coordinates P of each coded mark point in the coordinate system of the coordinate conversion plate t The coordinate conversion board is provided with two rows and three columns of coded marking points. The coordinate conversion board coordinate system is determined according to the position and direction of the coded points. The coordinate conversion board is a highly flat rectangular calibration board. Each coded marking point uses a different code to meet the uniqueness of the code, and the horizontal coded marking point connection line and the vertical coded marking point connection line are kept parallel to the rectangular side of the coordinate conversion board.

[0096] Specifically, step S4 includes:

[0097] S41. Determine the size of the coordinate conversion plate according to wind tunnels of different sizes, so that the size of the coordinate conversion plate is proportional to the diameter of the wind tunnel nozzle to meet the conversion accuracy of the coordinate axis system of wind tunnels with different fields of view;

[0098] S42, according to the position and direction of the coding mark point, measure the relative position relationship between the coordinates, determine the coordinate system of the coordinate conversion plate, and calculate the coordinates of each coding mark point in the coordinate system of the coordinate conversion plate.

[0099] S5. Determine the coordinates P of the coded marker point in the world coordinate system wc ,According to the coordinates of the coded marker points in the coordinate system of the coordinate conversion plate, point cloud registration is performed to determine the rigid body transformation relationship between the coordinate system of the coordinate conversion plate and the world coordinate system.

[0100] Specifically, step S5 includes:

[0101] S51, take a picture of the coordinate conversion plate, identify and reconstruct the coded marker points, and obtain the coordinates P of the coded marker points in the world coordinate system wc .

[0102] S52, performing point cloud registration according to the coordinates of the coded marker points in the coordinate conversion plate coordinate system and the coordinates of the coded marker points in the world coordinate system, and determining the rigid body transformation relationship between the coordinate conversion plate coordinate system and the world coordinate system:

[0103] P wc = wc R t ×P t + wc T t

[0104] in, wc R t Indicates the rotation transformation of the coded marker from the coordinate system of the coordinate conversion board to the world coordinate system. wc T t Indicates the translation transformation of the coded marker from the coordinate system of the coordinate conversion board to the world coordinate system.

[0105] S6. Use the coordinate conversion plate coordinate system instead of the wind tunnel coordinate system to calculate the test model's position and displacement.

[0106] Specifically, the method of calculating the test model posture using the coordinate conversion plate coordinate system instead of the wind tunnel coordinate system is as follows:

[0107] Assume that at a certain moment during the test, an arbitrary marked point P on the test model is in the wind tunnel coordinate system S wind The lower coordinate is P wind , test model coordinate system S modle The coordinates P modle_c , in the coordinate conversion board coordinate system S temp The next position is Ptemp , then the following conversion relationships exist from the wind tunnel coordinate system to the test model coordinate system, and from the coordinate conversion plate coordinate system to the model coordinate system:

[0108]

[0109] in, wind R temp Indicates the rotation transformation of the marker point from the coordinate conversion plate coordinate system to the wind tunnel coordinate system. wind T temp Indicates the translation transformation of the marker point from the coordinate system of the coordinate conversion plate to the wind tunnel coordinate system. temp R modle Indicates the rotation transformation of the marking point from the test model coordinate system to the coordinate system of the coordinate conversion plate. temp T modle Indicates the translation transformation of the marking point from the test model coordinate system to the coordinate system of the coordinate conversion plate;

[0110] According to the above two equations, the transformation relations of each coordinate system exist as follows:

[0111] P wind = wind R temp × temp R modle ×P modle_c - wind R temp × temp T modle + wind T temp

[0112] thus:

[0113]

[0114] in, wind R modle Indicates the rotation transformation of the marker point from the wind tunnel coordinate system to the coordinate conversion plate coordinate system. wind T modle Indicates the translation transformation of the marker point from the wind tunnel coordinate system to the coordinate conversion plate coordinate system;

[0115] Since the coordinate axes of the wind tunnel coordinate system and the coordinate conversion plate coordinate system are parallel, that is, wind R temp =I 3×3 , where I 3×3 represents the 3×3 identity matrix,

[0116]

[0117] Therefore, the coordinate conversion plate coordinate system can be directly used instead of the wind tunnel coordinate system to calculate the test model posture.

[0118] Specifically, the method for calculating the displacement of the test model using the coordinate conversion plate coordinate system instead of the wind tunnel coordinate system is:

[0119] Assume that at t0 and t1, the reflective mark point on the test model is measured in the wind tunnel coordinate system S wind Point Cloud and Model coordinate system S modle The point cloud of the reflective marker points is P modle , then the following relationship exists:

[0120]

[0121] Among them, R 0 represents the rotation transformation of the reflective mark point from the model coordinate system to the wind tunnel coordinate system at time t0, R 1 represents the rotation transformation of the reflective mark point from the model coordinate system to the wind tunnel coordinate system at time t1, T 0 represents the translation transformation of the reflective marker from the model coordinate system to the wind tunnel coordinate system at time t0, T 1 Represents the translation transformation of the reflective marker point from the model coordinate system to the wind tunnel coordinate system at time t1;

[0122] At this time, the displacement calculation formula of the test model is:

[0123] T 0-1 =T 1 -T 0

[0124] Assuming that the coordinate conversion plate coordinate system is used instead of the wind tunnel coordinate system, the point cloud of the marked point on the test model in the wind tunnel coordinate system is measured at t0 and t1 respectively: and Then there is the following point cloud coordinate transformation relationship:

[0125]

[0126] in, Indicates the coordinates of the reflective mark point at time t0 in the coordinate conversion board coordinate system, Indicates the coordinates of the reflective marking point at time t1 in the coordinate system of the coordinate conversion board;

[0127] Model displacement calculation formula:

[0128]

[0129] According to the above formula, we can get:

[0130]

[0131] in,wind T 0 temp represents the translation transformation of the marked point from the coordinate system of the coordinate conversion plate to the wind tunnel coordinate system at time t0, wind T 1 temp Indicates the translation transformation of the marked point from the coordinate system of the coordinate conversion plate to the wind tunnel coordinate system at time t1;

[0132] It can be deduced that:

[0133]

[0134] because but:

[0135]

[0136] Therefore, the coordinate conversion plate coordinate system can be directly used instead of the wind tunnel coordinate system to calculate the displacement of the test model.

[0137] S7. According to the rigid body transformation relationship between the test model coordinate system and the world coordinate system, the rigid body transformation relationship between the coordinate conversion plate coordinate system and the world coordinate system, and the test model position and displacement, determine the rigid body transformation relationship between the coordinate conversion plate coordinate system and the test model coordinate system, that is, the rigid body transformation relationship between the wind tunnel coordinate system and the test model coordinate system, so as to calculate the test model position and displacement in the wind tunnel coordinate system.

[0138] The present invention also discloses a wind tunnel coordinate axis calibration device based on coded marking points, comprising:

[0139] Install the card holder;

[0140] A vertical guide rail, both ends of which are fixed on the wind tunnel through mounting brackets;

[0141] The square tube adapter is arranged on the vertical guide rail, and an interference fit is adopted between the square tube adapter and the vertical guide rail;

[0142] Horizontal guide rail: The horizontal guide rail and the vertical guide rail are connected by a square tube connector. Interference fit is adopted between the horizontal guide rail and the square tube adapter. After the mounting base is fixed, the axis of the horizontal guide rail is parallel to the axis of the wind tunnel nozzle.

[0143] The round tube adapter is arranged on the horizontal guide rail;

[0144] A dual-axis level, mounted on a horizontal guide rail;

[0145] Coordinate conversion plate, the coordinate conversion plate is connected to the dual-axis level through a round tube adapter, the plane where the dual-axis level is located is perpendicular to the plane where the coordinate conversion plate is located, and the coordinate conversion plate is in the vertical plane; the coordinate conversion plate is used to establish the coordinate system of the coordinate conversion plate, and by adjusting the dual-axis level, the coordinate system of the coordinate conversion plate and the wind tunnel coordinate system are in the same direction in each coordinate axis.

[0146] Among them, the coordinate conversion plate is a highly flat rectangular calibration plate, on which a plurality of coding marking points are arranged. Each coding marking point adopts a different code to meet the uniqueness of the coding, and the horizontal coding marking point connection line and the vertical coding marking point connection line are kept parallel to the rectangular side of the coordinate conversion plate; the size of the coordinate conversion plate is proportional to the diameter of the wind tunnel nozzle.

[0147] The specific embodiments of the present invention and their working principles are further described in detail below with reference to the accompanying drawings.

[0148] Taking the cone test model 9 as an example, the wind tunnel coordinate axis system calibration method based on coding marks in this embodiment specifically includes the following steps:

[0149] 1) Adjust the position and focal length of each camera in the wind tunnel video measurement system 1 to make the image clear and cover the motion range of the test model.

[0150] 2) Establish a world coordinate system, calibrate the camera using the video measurement system, obtain high-precision internal and external parameters of each camera, and select the specified camera coordinate system to establish the world coordinate system.

[0151] 3) Establish a wind tunnel test model coordinate system, use a handheld scanning device to scan the test model with the marker points attached, obtain its three-dimensional point cloud, and determine the coordinates of each reflective marker point in the test model coordinate system. Determine the test model coordinate system based on the geometric characteristics of the test model point cloud. The method for establishing a wind tunnel test model coordinate system includes:

[0152] 3.1) Before 3D scanning, the test model was measured using a rotational inertial measurement device to obtain the center of mass of the test model, which was located 148.36 mm from the apex of the cone on the rotation axis. Figure 2 shown.

[0153] 3.2) Scan the test model with reflective marking points with a handheld scanner to obtain the test model point cloud and the reflective marking point cloud, such as Figure 3 As shown, the two point clouds are imported into Gemogic Studio software (reverse engineering and 3D detection software).

[0154] 3.3) Take the center of mass of the test model as the origin of the model coordinate system. According to the symmetry of the test model, take the cone rotation axis as the X axis, and keep Y and Z perpendicular to each other.

[0155] 3.4) Determine the coordinates of the reflective marking point P in the test model coordinate system in the Gemogic Studio software. m :

[0156]

[0157] 4) The video measurement system takes pictures of the test model, identifies and reconstructs the reflective marker points, and obtains the coordinates of the reflective marker points in the world coordinate system. According to the coordinates of the reflective marker points in the test model coordinate system, the two point clouds are registered to obtain the rigid body transformation relationship between the test model coordinate system and the world coordinate system.

[0158] Methods for determining the rigid body transformation relationship between the test model coordinate system and the world coordinate system include:

[0159] 4.1) The video measurement system takes pictures of the test model, identifies and reconstructs the marker points, and obtains the coordinates P of the reflective marker points in the world coordinate system. w :

[0160]

[0161] 4.2) According to the coordinates of the reflective marker points in the test model coordinate system and the reflective marker points in the world coordinate system, perform point cloud registration to determine the rigid body transformation relationship between the two coordinate systems:

[0162] P w = w R m ×P m + w T m

[0163] w T m =[-731.86490 -30.20354 1201.30456]

[0164]

[0165] 5) Design a coordinate conversion plate. Design two rows and three columns of coded marking points on the coordinate conversion plate, and determine the coordinate system of the coordinate conversion plate according to the position and direction of the coded marking points.

[0166] Methods for designing a coordinate conversion plate include:

[0167] 5.1) According to wind tunnels of different sizes, determine the size of the coordinate conversion plate so that the size of the coordinate conversion plate is proportional to the diameter of the wind tunnel nozzle, so as to meet the conversion accuracy of the coordinate axis system of wind tunnels with different fields of view.

[0168] 5.2) The coordinate conversion plate must be processed into a rectangular calibration plate with high flatness. The coding marking points use different codes to meet the coding uniqueness, and keep the horizontal coding marking points and vertical coding marking points parallel to the rectangular edges.

[0169] 5.3) After design and processing, the relative position relationship between the coordinates needs to be measured, such as Figure 4 As shown, the coordinate system of the coordinate conversion plate is established at the center of the coding mark point 17, the X axis points from the coding mark point 17 to the coding mark point 15, the Y axis points from the coding mark point 17 to the coding mark point 13, and the Z axis follows the right-hand rule, and the coordinates P of each coding mark point in the coordinate system of the coordinate conversion plate are calculated. t :

[0170]

[0171] 6) The video measurement system takes a picture of the coordinate conversion plate, identifies and reconstructs the coded marker points, obtains the coordinates of the coded marker points in the world coordinate system, aligns the point cloud based on the coordinates of the coded marker points in the coordinate conversion plate coordinate system, and calculates the rigid body transformation relationship between the coordinate conversion plate and the world coordinate system.

[0172] The method for determining the rigid body transformation relationship between the coordinate system of the coordinate conversion plate and the world coordinate system includes:

[0173] 6.1) The video measurement system takes a picture of the coordinate conversion plate, identifies and reconstructs the coded marker points, and obtains the coordinates P of the coded marker points in the world coordinate system. w .

[0174] 6.2) According to the coordinates of the coded marking points in the coordinate conversion board coordinate system in step S53 and the coordinates of the coded marking points in the world coordinate system in step S61, point cloud registration is performed to determine the rigid body transformation relationship between the two coordinate systems.

[0175] P w = w R t ×P t + w T t

[0176] w T t =[273.88990 335.20322 578.30622]

[0177]

[0178] 7) The coordinate conversion plate coordinate system replaces the wind tunnel coordinate system to calculate the test model's position and displacement.

[0179] The methods for calculating the model pose and displacement by using the coordinate conversion plate coordinate system instead of the wind tunnel coordinate system include:

[0180] 7.1) The coordinate conversion plate coordinate system can replace the wind tunnel coordinate system to calculate the model attitude.

[0181] Assume that at a certain moment during the test, an arbitrary mark point P on the model is in the wind tunnel coordinate system S wind The lower coordinate is P wind , model coordinate system S modle The coordinates P modle , in the coordinate conversion board coordinate system S temp The next position is P temp , then the following conversion relationships exist between the wind tunnel coordinate system and the model coordinate system, and between the coordinate conversion plate coordinate system and the model coordinate system:

[0182]

[0183] According to the above two equations, the conversion relationships of the coordinate systems exist as follows:

[0184] P wind = wind R temp × temp R modle ×P modle - wind R temp × temp T modle + wind T temp

[0185] thus:

[0186]

[0187] Since the coordinate axes of the wind tunnel coordinate system and the coordinate conversion plate coordinate system are parallel, that is, wind R temp =I 3×3 ,

[0188]

[0189] Therefore, the coordinate conversion plate coordinate system can be directly used instead of the wind tunnel coordinate system to calculate the model pose.

[0190] 7.2) The coordinate conversion plate coordinate system can replace the wind tunnel coordinate system to calculate the model displacement

[0191] Assume that at time t0 and t1, the reflective mark point on the model is measured by the video measurement system in the wind tunnel coordinate system S wind Point Cloud and Model coordinate system S modle The point cloud of the reflective marker points is P modle , then the following relationship exists:

[0192]

[0193] At this time, the displacement calculation formula of the test model is:

[0194] T 0-1 =T 1 -T 0

[0195] Assuming that the coordinate conversion plate coordinate system is used instead of the wind tunnel coordinate system, the point cloud of the marked points on the model in the wind tunnel coordinate system is measured by the video measurement system at time t0 and t1 respectively. and Then there is the following point cloud coordinate transformation relationship:

[0196]

[0197] Model displacement calculation formula:

[0198]

[0199] According to the above formula, we can get:

[0200]

[0201] It can be deduced that:

[0202]

[0203] because but:

[0204]

[0205] Therefore, the coordinate conversion plate coordinate system can be directly used instead of the wind tunnel coordinate system to calculate the model displacement.

[0206] Therefore, the conversion relationship between the coordinate conversion plate and the object to be measured is:

[0207] P t = t R m ×P m + t T m

[0208] t T m =[-731.86490 -30.20354 1201.30456]

[0209]

[0210] in, t R mIndicates the rotation transformation of the reflective mark point from the test model coordinate system to the coordinate system of the coordinate conversion plate, t T m Represents the translation transformation of the reflective mark point from the test model coordinate system to the coordinate system of the coordinate conversion plate.

[0211] 8) According to the rigid transformation relationship between the test model coordinate system and the world coordinate system, the rigid transformation relationship between the coordinate conversion plate coordinate system and the world coordinate system, and the test model posture and displacement, the transformation relationship of each coordinate system can be obtained, and the rigid transformation relationship between the coordinate conversion plate coordinate system and the model coordinate system, that is, the rigid transformation relationship between the wind tunnel coordinate system and the model coordinate system, can be obtained. Thus, the model posture and displacement in the wind tunnel coordinate system can be calculated.

[0212] like Figure 5 As shown, this embodiment also provides a wind tunnel coordinate system calibration device based on coded marking points, including: two mounting bases 2, a vertical guide rail 3, a square tube adapter 4, a horizontal guide rail 5, two round tube adapters 6, a dual-axis level 7 and a coordinate conversion plate 8.

[0213] Both ends of the vertical guide rail 3 are fixed to the wind tunnel through two mounting sockets 2; the square tube adapter 4 is arranged on the vertical guide rail 3, and an interference fit is adopted between the square tube adapter 4 and the vertical guide rail 3; the horizontal guide rail 5 is connected to the vertical guide rail 3 through the square tube connector 4, and an interference fit is adopted between the horizontal guide rail 5 and the square tube adapter 4. After the two mounting sockets 2 are fixed, the axis of the horizontal guide rail 5 is parallel to the axis of the wind tunnel nozzle (the free flow direction is parallel to the nozzle axis); two circular tube adapters 6 and a dual-axis level 7 will be arranged on the horizontal guide rail 5; the coordinate conversion plate 8 is connected to the dual-axis level 7 through two circular tube adapters 6, the plane where the dual-axis level 7 is located is perpendicular to the plane where the coordinate conversion plate 8 is located, and the coordinate conversion plate 8 is in the vertical plane; the coordinate conversion plate 8 is used to establish the coordinate system of the coordinate conversion plate, and the coordinate axes of the coordinate system of the coordinate conversion plate and the wind tunnel coordinate system are made to have the same direction by adjusting the dual-axis level 7.

[0214] The coordinate conversion plate 8 is a highly flat rectangular calibration plate. A plurality of coding marking points are arranged on the coordinate conversion plate 8. Each coding marking point adopts a different code to meet the uniqueness of the code, and the horizontal coding marking point connection line and the vertical coding marking point connection line are kept parallel to the rectangular side of the coordinate conversion plate; the size of the coordinate conversion plate 8 is proportional to the diameter of the wind tunnel nozzle.

[0215] The wind tunnel coordinate axis system calibration method based on coding marks in the embodiment of the present invention can determine the wind tunnel coordinate axis system only by arranging a number of coding mark points on a plane, and has the advantages of good stability and strong adaptability. At the same time, a corresponding coordinate axis system calibration device is provided, and the wind tunnel coordinate system is calibrated by replacing the wind tunnel coordinate system with the coordinate conversion plate coordinate system of the calibration device, thereby ensuring high-precision test model posture measurement and providing reliable data for wind tunnel model optical tests.

[0216] The above contents are further detailed descriptions of the present invention in combination with specific preferred embodiments, and it cannot be determined that the specific implementation of the present invention is limited to these descriptions. For those skilled in the art of the present invention, several equivalent substitutions or obvious variations can be made without departing from the concept of the present invention, and the performance or use is the same, which should be regarded as belonging to the protection scope of the present invention.

Claims

1. A wind tunnel coordinate axis calibration method based on coded markers, characterized in that: The following steps are involved: S1. Establish a world coordinate system; S2. Establish the wind tunnel test model coordinate system and determine the coordinates P of each reflective mark point in the test model coordinate system m ; S3. Determine the coordinates P of the reflective marking point in the world coordinate system w ,According to the coordinates of the reflective marker points in the test model coordinate system, the point cloud is registered with the two point clouds to determine the rigid body transformation relationship between the test model coordinate system and the world coordinate system; S4, establish the coordinate system of the coordinate conversion plate, and determine the coordinates P of each coded mark point in the coordinate system of the coordinate conversion plate t ; S5. Determine the coordinates P of the coded marker point in the world coordinate system wc , according to the coordinates of the coded marker points in the coordinate system of the coordinate conversion plate, point cloud registration is performed to determine the rigid body transformation relationship between the coordinate system of the coordinate conversion plate and the world coordinate system; S6. Use the coordinate conversion plate coordinate system instead of the wind tunnel coordinate system to calculate the test model posture and displacement; S7, according to the rigid body transformation relationship between the test model coordinate system and the world coordinate system, the rigid body transformation relationship between the coordinate conversion plate coordinate system and the world coordinate system, and the test model posture and displacement, determine the rigid body transformation relationship between the coordinate conversion plate coordinate system and the test model coordinate system, that is, the rigid body transformation relationship between the wind tunnel coordinate system and the test model coordinate system, so as to calculate the test model posture and displacement in the wind tunnel coordinate system; In step S4, the coordinate conversion plate is a rectangular calibration plate with high flatness. A plurality of coding mark points are arranged on the coordinate conversion plate. Each coding mark point adopts a different code to meet the coding uniqueness, and the horizontal coding mark point connection line and the vertical coding mark point connection line are kept parallel to the rectangular side of the coordinate conversion plate. Step S4 specifically includes: S41. Determine the size of the coordinate conversion plate according to wind tunnels of different sizes, so that the size of the coordinate conversion plate is proportional to the diameter of the wind tunnel nozzle to meet the conversion accuracy of the coordinate axis system of wind tunnels with different fields of view; S42, according to the position and direction of the coding mark point, measure the relative position relationship between the coordinates, determine the coordinate system of the coordinate conversion plate, and calculate the coordinates of each coding mark point in the coordinate system of the coordinate conversion plate.

2. The wind tunnel coordinate axis calibration method based on coded marking points according to claim 1, characterized in that: In step S1, the steps of establishing the world coordinate system are: performing camera calibration, obtaining high-precision internal and external parameters of each camera, and selecting a designated camera coordinate system to establish the world coordinate system.

3. The wind tunnel coordinate axis calibration method based on coded marking points according to claim 1, characterized in that: In step S2, establishing the wind tunnel test model coordinate system includes the following steps: S21, measuring the test model using a rotational inertia measurement device to obtain the center of mass position of the test model; S22, scanning the test model with reflective marking points using a handheld scanning device to obtain a three-dimensional point cloud thereof, wherein the three-dimensional point cloud includes a point cloud of the test model and a point cloud of the reflective marking points; S23. Taking the center of mass of the test model as the origin of the model coordinate system, determine the directions of the coordinate axes of the test model coordinate system according to the symmetry of the test model.

4. The wind tunnel coordinate axis calibration method based on coded marking points according to claim 1, characterized in that: Step S3 specifically includes: S31, take a picture of the test model, identify and reconstruct the marking points, and obtain the coordinates of the reflective marking points in the world coordinate system; S32, performing point cloud registration according to the coordinates of the reflective marking points in the test model coordinate system and the coordinates of the reflective marking points in the world coordinate system, and determining the rigid body transformation relationship between the test model coordinate system and the world coordinate system: P w = w R m ×P m + w T m in, w R m Indicates the rotation transformation of the reflective mark point coordinates from the test model coordinate system to the world coordinate system. w T m Represents the translation transformation of the reflective mark point coordinates from the test model coordinate system to the world coordinate system.

5. The wind tunnel coordinate axis calibration method based on coded marking points according to claim 1, characterized in that: Step S5 specifically includes: S51, take a picture of the coordinate conversion plate, identify and reconstruct the coded marker points, and obtain the coordinates P of the coded marker points in the world coordinate system wc ; S52, performing point cloud registration according to the coordinates of the coded marking points in the coordinate system of the coordinate conversion plate and the coordinates of the coded marking points in the world coordinate system, and determining the rigid body transformation relationship between the coordinate system of the coordinate conversion plate and the world coordinate system: P wc = wc R t ×P t + wc T t in, wc R t Indicates the rotation transformation of the coded marker from the coordinate system of the coordinate conversion board to the world coordinate system. wc T t Indicates the translation transformation of the coded marker from the coordinate system of the coordinate conversion board to the world coordinate system.

6. The method for calibrating wind tunnel coordinate axis system based on coded marking points according to claim 1, characterized in that: In step S6, the method of calculating the test model posture by using the coordinate conversion plate coordinate system instead of the wind tunnel coordinate system is: Assume that at a certain moment during the test, an arbitrary marked point P on the test model is in the wind tunnel coordinate system S wind The lower coordinate is P wind , test model coordinate system S modle The coordinates P modlec , in the coordinate conversion board coordinate system S temp The next position is P temp , then the following conversion relationships exist from the wind tunnel coordinate system to the test model coordinate system, and from the coordinate conversion plate coordinate system to the model coordinate system: in, wind R temp Indicates the rotation transformation of the marker point from the coordinate conversion plate coordinate system to the wind tunnel coordinate system. wind T temp Indicates the translation transformation of the marker point from the coordinate system of the coordinate conversion plate to the wind tunnel coordinate system. temp R modle Indicates the rotation transformation of the marking point from the test model coordinate system to the coordinate system of the coordinate conversion plate. temp T modle Indicates the translation transformation of the marking point from the test model coordinate system to the coordinate system of the coordinate conversion plate; According to the above two equations, the transformation relations of each coordinate system exist as follows: P wind = wind R temp × temp R modle ×P modle_c - wind R temp × temp T modle + wind T temp thus: in, wind R modle Indicates the rotation transformation of the marker point from the wind tunnel coordinate system to the coordinate conversion plate coordinate system. wind T modle Indicates the translation transformation of the marker point from the wind tunnel coordinate system to the coordinate conversion plate coordinate system; Since the coordinate axes of the wind tunnel coordinate system and the coordinate conversion plate coordinate system are parallel, that is, wind R temp =I 3×3 , where I 3×3 represents the 3×3 identity matrix, Therefore, the coordinate conversion plate coordinate system can be directly used instead of the wind tunnel coordinate system to calculate the test model posture.

7. The method for calibrating wind tunnel coordinate axis system based on coded marking points according to claim 1, characterized in that: In step S6, the method for calculating the displacement of the test model using the coordinate conversion plate coordinate system instead of the wind tunnel coordinate system is: Assume that at t0 and t1, the reflective mark point on the test model is measured in the wind tunnel coordinate system S wind Point Cloud and Model coordinate system S modle The point cloud of the reflective marker points is P modle , then the following relationship exists: Among them, R 0 represents the rotation transformation of the reflective mark point from the model coordinate system to the wind tunnel coordinate system at time t0, R 1 represents the rotation transformation of the reflective mark point from the model coordinate system to the wind tunnel coordinate system at time t1, T 0 represents the translation transformation of the reflective marker from the model coordinate system to the wind tunnel coordinate system at time t0, T 1 Represents the translation transformation of the reflective marker point from the model coordinate system to the wind tunnel coordinate system at time t1; At this time, the displacement calculation formula of the test model is: T 0-1 =T 1 -T 0 Assuming that the coordinate conversion plate coordinate system is used instead of the wind tunnel coordinate system, the point cloud of the marked point on the test model in the wind tunnel coordinate system is measured at t0 and t1 respectively: and Then there is the following point cloud coordinate transformation relationship: in, Indicates the coordinates of the reflective mark point at time t0 in the coordinate conversion board coordinate system, Indicates the coordinates of the reflective marking point at time t1 in the coordinate system of the coordinate conversion board; Model displacement calculation formula: According to the above formula, we can get: in, wind T 0 temp represents the translation transformation of the marked point from the coordinate system of the coordinate conversion plate to the wind tunnel coordinate system at time t0, wind T 1 temp Indicates the translation transformation of the marked point from the coordinate system of the coordinate conversion plate to the wind tunnel coordinate system at time t1; It can be deduced that: because but: Therefore, the coordinate conversion plate coordinate system can be directly used instead of the wind tunnel coordinate system to calculate the displacement of the test model.

8. A wind tunnel coordinate axis calibration device based on coded marking points, characterized in that: include: Install the card holder; A vertical guide rail, both ends of which are fixed to the wind tunnel through the mounting base; A square tube adapter is arranged on the vertical guide rail, and an interference fit is adopted between the square tube adapter and the vertical guide rail; A horizontal guide rail, wherein the horizontal guide rail is connected to the vertical guide rail via a square tube connector, an interference fit is adopted between the horizontal guide rail and the square tube adapter, and after the mounting base is fixed, the axis of the horizontal guide rail is parallel to the axis of the wind tunnel nozzle; A round tube adapter, arranged on the horizontal guide rail; A dual-axis level, disposed on the horizontal guide rail; A coordinate conversion plate, wherein the coordinate conversion plate is connected to the biaxial level through the round tube adapter, the plane where the biaxial level is located is perpendicular to the plane where the coordinate conversion plate is located, and the coordinate conversion plate is located in a vertical plane; the coordinate conversion plate is used to establish a coordinate conversion plate coordinate system, and by adjusting the biaxial level, the coordinate conversion plate coordinate system and the wind tunnel coordinate system have the same direction of each coordinate axis; The coordinate conversion plate is a highly flat rectangular calibration plate, on which a plurality of coding marking points are arranged, each coding marking point adopts a different code to meet the coding uniqueness, and the horizontal coding marking point connection line and the vertical coding marking point connection line are kept parallel to the rectangular side of the coordinate conversion plate; the size of the coordinate conversion plate is proportional to the diameter of the wind tunnel nozzle.

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