A method for calibrating the pointing error of a multi-mode composite tracking and aiming system

Abstract

A method for calibrating the target pointing error of a multimode composite tracking and aiming system includes: (1) setting up an autocollimator in front of the multimode optical system and the field of view of the visible light camera, calibrating the multimode optical system and marking the zero point of the visible light camera; (2) placing a target at the maximum measurement distance of the multimode optical system and marking the position of the camera zero point in the target target; then rotating the azimuth and pitch axes of the high-precision turntable to zero, reading the imaging position of the laser emission point, and recording the system deviation of the target pointing; (3) controlling the azimuth and pitch axes of the high-precision turntable to swing to different angles, and measuring the deviation value between the tracking point of the visible light camera and the imaging position of the target laser illumination point; (4) substituting the measured value into the error calculation formula including the mirror installation deviation to form a multivariate equation system, solving for the mirror installation error of the multimode composite tracking and aiming system, and then combining the swing angles of the azimuth and pitch axes of the high-precision turntable to calculate the corresponding deviation value. The method of this invention can accurately calibrate the target pointing error of the multimode composite tracking and aiming system.

Description

Technical Field

[0001] This invention belongs to the field of accuracy calibration of space tracking and aiming systems, specifically relating to a calibration method for the deviation between the laser receiving and receiving light path direction and the turntable in a space multi-mode composite tracking and aiming system. Background Technology

[0002] Optical tracking technology has significant applications in multiple fields such as communications and aerospace, and is a crucial link in establishing and maintaining laser communication links. The tracking performance of an optical tracking system directly affects the stability and reliability of optical communication. In the aerospace field, laser removal of "space debris" creates plasma, which has advantages over other removal methods, including thorough removal, low cost, and long-distance removal.

[0003] To achieve aiming and tracking, an optical path is typically constructed within the turntable. Utilizing the characteristic of Cooder's mirrors to oscillate along their axis, the turntable and the laser beam path are aligned in direction. For example... Figure 1 The diagram shows the laser emission optical path of a multimode composite tracking system. Reflector 1 is mounted on the laser emission end and fixedly connected to it; reflector 2 is mounted at the intersection of the azimuth and elevation axes and fixedly connected to the azimuth axis, rotating with it; the multimode optical system is mounted on the elevation axis and fixedly connected to it, moving with both the azimuth and elevation axes; reflector 3 is mounted on and fixedly connected to the multimode optical system, also moving with both the azimuth and elevation axes. The laser beam emitted by the laser is reflected by mirror 1 and enters the azimuth axis. As the azimuth axis rotates, the laser beam remains parallel to the azimuth axis. After being reflected by mirror 1, the laser beam is reflected by mirror 2 and enters the elevation axis. As the elevation axis rotates, the laser beam remains parallel to the elevation axis. After being reflected by mirror 2, the laser beam is reflected by mirror 3 and becomes parallel to the optical axis of the multimode optical system, illuminating the target. The laser beam is scattered by the target and received by the laser detector within the multimode optical system for distance measurement. Simultaneously, the visible light camera within the multimode optical system measures the target's position within the tracking and aiming system. When the target moves, the visible light camera detects the change in target position, and the tracking and aiming system controls the rotation of the azimuth and elevation axes of the high-precision turntable to ensure the laser beam still points towards the target, achieving tracking and aiming. As can be seen from the working principle of the laser emission path of the multimode composite tracking and aiming system, to ensure that the direction of the emitted laser beam is consistent with the dual-axis rotation, the three mirrors need to maintain specific angles that do not change during operation. These three angles need to be adjusted.

[0004] Because the adjustment angle of the reflector deviates from the theoretical value, it causes a deviation between the turntable's swing angle and the laser emission path's pointing direction. This deviation is related to the turntable's swing angle; that is, the deviation between the turntable's swing angle and the laser emission path's pointing direction changes when the azimuth and elevation axes swing to different angles. Furthermore, optical adjustment has stability issues; after adjustment, stress release occurs in the optical path, causing changes in accuracy. The reflector angle also changes under different temperature conditions; and the optical path accuracy changes when subjected to mechanical stresses. Therefore, it is necessary to calibrate the laser emission path and the turntable's pointing direction to reduce the pointing error of the tracking and aiming system caused by optical adjustment. Figure 1 The middle represents the angular deviation between the laser beam and the optical axis of the optical system.

[0005] For the calibration of measuring instrument accuracy, the key issue is how to find the pattern of error variation in order to eliminate pointing errors and achieve higher tracking accuracy. Currently, there are no publicly available calibration methods for pointing errors in tracking systems. Summary of the Invention

[0006] The technical problem solved by this invention is to overcome the shortcomings of the prior art and provide a target pointing error calibration method for a multi-mode composite tracking and aiming system. The relationship between the laser emission optical path and the turning stage pointing deviation is obtained through theoretical modeling, and the error is calibrated based on this. The error is considered in the tracking and aiming control process to reduce the tracking and aiming pointing error, thereby achieving the goal of not losing the target.

[0007] The technical solution of this invention is: a target pointing error calibration method for a multi-mode composite tracking and aiming system, comprising the following steps:

[0008] (1) Set up the autocollimator in front of the field of view of the multimode optical system and the visible light camera, autocollimate the outer end face of the secondary mirror of the multimode optical system, and adjust the attitude of the autocollimator to bring the image back to the zero point of the autocollimator; then turn on the visible light camera and make the crosshairs of the autocollimator image in the visible light camera, and record the position of the crosshairs in the camera measurement coordinate system at this time as the zero point of the visible light camera;

[0009] (2) Place a target at the maximum measurement distance of the multimode optical system, power on the visible light camera, and image the target in the visible light camera. Mark the position of the zero point of the visible light camera in the target as (x0, y0). Then, power on the high-precision turntable, rotate the azimuth and pitch axes of the high-precision turntable to (0°, 0°) and fix them. Then, power on the laser, read the laser point imaging position (x0′, y0′) on the target, and record the system deviation of the target pointing at this time as e0 = (x0′, y0′) - (x0, y0).

[0010] (3) Control the azimuth and pitch axes of the high-precision turntable to swing to different angles and measure the deviation between the tracking point (x,y) of the visible light camera and the imaging position (x′,y′) of the target laser illumination point;

[0011] (4) Substitute the measured value from step (3) into the formula e = A3 - A3′ to form a system of multivariate equations. Solve this system of multivariate equations to obtain the mirror installation error of the multimode composite tracking system. Calculate the corresponding deviation value based on the mirror installation error and the swing angles of the azimuth and pitch axes of the high-precision turntable. Where A3 is the direction vector of the laser beam when there is an installation and adjustment error, and A3′ is the ideal direction vector of the laser beam.

[0012] Furthermore, the ideal direction vector A3′ of the emitted beam of the laser is expressed as:

[0013]

[0014] in θ1 and θ2 are the azimuth axis rotation angle and pitch axis rotation angle of the high-precision turntable, respectively. α is the verticality error of the azimuth axis and pitch axis, and R3 is the reflection matrix of the reflector 3 of the multi-mode composite tracking system.

[0015] Furthermore, the direction vector A3 when the laser's emitted beam vector has an adjustment error is represented as A3 = R3R2R1A0, where R2 and R1 are the reflection matrices of the multimode composite tracking and aiming system's reflectors 2 and 1, respectively, and A0 is the laser's emitted beam vector.

[0016] Furthermore, the reflection matrix of the multi-mode composite tracking system is as follows:

[0017]

[0018] in Let be the normal vector of the mirror.

[0019] Furthermore, the transpose N' of the normal vector of the aforementioned mirror is expressed as:

[0020]

[0021] Where d1, d2, and d3 are the heights of the three pillars supporting the reflector, and the three pillars form an isosceles triangle with a height of b and a base length of a.

[0022] Furthermore, the normal vectors N1, N2, and N3 of the reflector 1 and reflector 3 are expressed as follows:

[0023]

[0024] The upper right subscript (a left-falling stroke) indicates the vector transpose.

[0025] Furthermore, the azimuth and pitch axes of the high-precision control turntable are swung to different angles, and the angle range is determined according to the usage requirements of the multi-mode composite tracking and aiming system, with no fewer than 6 swung angle positions.

[0026] Preferably, the azimuth and pitch axes of the high-precision turntable are controlled to swing to different angles, with the pitch angle swing angle ranging from -10 degrees to 50 degrees and the azimuth axis swing angle ranging from -50 degrees to 50 degrees.

[0027] The advantages of this invention compared to the prior art are:

[0028] (1) Based on the mirror mounting method, this invention establishes a theoretical model of target pointing error with the grinding amount of the pad as input. Based on this model, the calibration error can be minimized.

[0029] (2) This invention separates the systematic error and the oscillation error along the shaft, making the calibration process clear and easy to understand, reducing the difficulty of calibration and improving the calibration efficiency;

[0030] (3) The present invention calibrates the system based on the error in the assembly and adjustment of the Kude optical path, which can improve the system's aiming accuracy and thus reduce the difficulty of the Kude optical path assembly and adjustment. Attached Figure Description

[0031] Figure 1 This is a schematic diagram of the laser output optical path of a multimode composite tracking and aiming system.

[0032] Figure 2 This is a schematic diagram showing the installation method of the reflector in a multi-mode composite tracking and aiming system;

[0033] Figure 3 This is a diagram showing the dimensions of the reflector pads;

[0034] Figure 4 This is a flowchart of the method of the present invention;

[0035] Figure 5 This is a schematic diagram of the zero-point calibration of the visible light camera according to the present invention;

[0036] Figure 6 This is a schematic diagram of the target pointing error calibration of the present invention. Detailed Implementation

[0037] The method of this invention first theoretically models the error, finding the variation law of the pointing error of the aiming system with the dual-axis oscillation. Then, it addresses... Figure 1The tracking and aiming system shown is calibrated using relevant instruments and equipment. The parameters in the theoretical model are calculated using the measured error points. Finally, the pointing error value of the tracking and aiming subsystem is calculated based on the model.

[0038] First, establish Figure 1 The theoretical model of the pointing error of the system shown.

[0039] Let N be the normal vector of a plane mirror, which can be represented in a spatial coordinate system as:

[0040]

[0041] The reflection matrix R of a plane mirror can then be expressed as:

[0042]

[0043] Let the output light vector of the laser be A0, which can be represented in spatial coordinates as:

[0044]

[0045] The laser beam vector A3 after reflection by the three mirrors can be expressed as:

[0046] A3=R3R2R1A0 (4)

[0047] Wherein, parameters R1, R2, and R3 are the reflection matrices of mirror 1, mirror 2, and mirror 3, respectively.

[0048] The mirror installation method is as follows Figure 2 As shown, the coordinate system of the reflector is defined as follows: the origin is at the midpoint of the line connecting the center of the bottom surface of cylinder 1 and cylinder 2, the X-axis points from the center of the bottom surface of cylinder 2 to the center of the bottom surface of cylinder 1, the Y-axis is the height of the isosceles triangle formed by the three cylinders, pointing from the origin to cylinder 3, and the Z-axis, X-axis, and Y-axis form a right-handed coordinate system.

[0049] Assume the distance between the centers of the bases of cylinders 1 and 2 is *a*, and the height of the isosceles triangle is *b*. Figure 3 As shown. Therefore, the spatial coordinates of the top surfaces of the three support pillars in the reflector coordinate system are DZ1=(-a / 2,0,d1)′, DZ2=(a / 2,0,d2)′, and DZ3=(0,b,d3)′. Here, d1, d2, and d3 are the heights of the three support pillars, and the upper right corner indicates transposition, converting the row vector into a column vector.

[0050] The transpose of the normal vector of the mirror supported by three pillars is N' = (DZ1-DZ3)×(DZ2-DZ3). Here, the multiplication sign means vector product. The vector product of two vectors is a vector whose direction is perpendicular to the two vectors.

[0051] Substituting the coordinates, we can see that...

[0052]

[0053] Transforming N' to the global coordinate system yields the normal vector N of the mirror. The global coordinate system Oxyz is defined as follows: Figure 1 As shown.

[0054] The coordinate rotation matrix that rotates a local coordinate system by an angle θ along the x-axis to the global coordinate system is defined as S. i,θ The coordinate rotation matrix that rotates the y-axis by an angle θ to the global coordinate system is defined as S. j,θ The coordinate rotation matrix that rotates along the z-axis by an angle θ to the global coordinate system is defined as S. k,θ Its matrix representation is:

[0055]

[0056] Let reflector 2 swing with the azimuth axis by an angle θ1; reflector 3 swing with the azimuth axis by an angle θ1, and with the pitch axis by an angle θ2; the perpendicularity errors of the azimuth and pitch axes are α. Then, based on the installation relationship of the three reflectors, the normal vectors of the reflectors in the global coordinate system are respectively...

[0057]

[0058] In this equation, subscripts 1, 2, and 3 correspond to reflector 1, reflector 2, and reflector 3, respectively. It should be noted that the angles of the coordinate rotation matrix subscripts in formulas (7), (8), and (9) are related to the spatial positional relationship of reflector 1, reflector 2, and reflector 3. The angle used in this invention example is the transformation matrix used in other examples. The transformation matrix in other examples needs to be modified according to the installation angle of the reflector. The principle is the aforementioned vector coordinate system transformation.

[0059] Substituting equations (1) to (3) and (5) to (9) into equation (4), we can obtain the expression A3 for the laser beam vector when there is an adjustment error; while the ideal direction vector expression for the laser beam is...

[0060]

[0061] Therefore, the expression for the theoretical model of the deviation between the laser emitted beam and the biaxial oscillation angle is:

[0062] e = A3 - A3′ (11)

[0063] The input variables are the verticality error α of the azimuth axis and the pitch axis (for a certain high-precision turntable, this error is constant and can be measured; for the tracking and aiming system, it is a constant), the azimuth axis tilt angle θ1, and the pitch axis tilt angle θ2. The parameters that need to be determined through calibration are the height differences of the support pillars of reflector 1, reflector 2, and reflector 3, a total of 6 (2 for each reflector, corresponding to the height differences d1-d3, d2-d3 in the last row of equation (5)).

[0064] like Figure 4 The diagram shows the calibration process of the method of the present invention, and the specific steps are as follows:

[0065] ① Calibration preparation.

[0066] Required tooling and equipment: autocollimator and its accessories; safety goggles.

[0067] ② Zero-point calibration of visible light cameras.

[0068] like Figure 5 As shown, first, the autocollimator is set up directly in front of the multimode optical system and the field of view of the visible light camera. The autocollimator is then autocollimated to the outer end face of the secondary mirror of the multimode optical system. The attitude of the autocollimator is adjusted so that the image returns to the zero point of the autocollimator. Then, the visible light camera is powered on so that the crosshairs of the autocollimator are imaged in the visible light camera. The position of the crosshairs in the camera's measurement coordinate system at this time is recorded. This position is the zero point of the visible light camera.

[0069] ③ Target pointing system error calibration.

[0070] The target pointing error is divided into two parts. One part is the systematic error formed after the mirror 3 is installed and adjusted. It is a fixed value and is represented by e0. The other part is the oscillation error along the axis and is represented by e.

[0071] like Figure 6 As shown, a target is first placed at the maximum measurement distance of the multimode optical system. The visible light camera is powered on, and the target is imaged in the visible light camera. The position of the camera zero point in the target is marked, with position coordinates (x0, y0).

[0072] Then, power on the high-precision turntable, rotate its azimuth and pitch axes to (0°, 0°) and fix them; then, power on the laser, and read the laser point imaging position (x0′, y0′) on the target. At this time, the system deviation of the target pointing is...

[0073] e0=(x0′,y0′)-(x0,y0) (12)

[0074] ④ Calibration of laser pointing along-axis oscillation error. The oscillation error e varies with the oscillation angle of the two axes, that is, e is a function of the azimuth axis oscillation angle θ1 and the pitch axis oscillation angle θ2. e is a comprehensive error, which includes the systematic error e0.

[0075] Control the azimuth and pitch axes to swing to different angles, as shown in Table 1. The angle range is determined according to the requirements of the tracking system, and at least 6 points are selected. Measure the deviation between the visible light camera tracking point (x, y) and the imaging position (x′, y′) of the target laser illumination point.

[0076] Table 1. Record of laser pointing angle as it swings along the two axes.

[0077]

[0078] ⑤ Parameter calculation.

[0079] Based on the recorded values ​​in step ④, substitute them into equation (11) to form a system of multivariate equations, and solve this system of multivariate equations. The known quantities in this system of equations are the values ​​recorded in Table 1, and the unknowns are the height differences in equation (5). By solving the system of equations (e.g., by writing a program in MATLAB to calculate), the height differences of the support pillars of reflector 1, reflector 2, and reflector 3 are calculated, resulting in a total of 6 parameters.

[0080] ⑥ Error calculation.

[0081] Substitute the six parameters calculated in step ⑤ into equation (11), and set the azimuth axis swing angle θ1 and the pitch axis swing angle θ2 to different angles to calculate the corresponding deviation values, which can be used as inputs for the target pointing control system software.

[0082] The contents not described in detail in this specification are common knowledge to those skilled in the art.

Claims

1. A method for calibrating the target pointing error of a multi-mode composite tracking and aiming system, characterized in that: Includes the following steps: (1) Set up the autocollimator in front of the field of view of the multimode optical system and the visible light camera, autocollimate the outer end face of the secondary mirror of the multimode optical system, and adjust the attitude of the autocollimator to bring the image back to the zero point of the autocollimator; then turn on the visible light camera and make the crosshairs of the autocollimator image in the visible light camera, and record the position of the crosshairs in the camera measurement coordinate system at this time as the zero point of the visible light camera; (2) Place a target at the maximum measurement distance of the multimode optical system, power on the visible light camera, and image the target in the visible light camera. Mark the position of the zero point of the visible light camera in the target as (x0, y0). Then, power on the high-precision turntable, rotate the azimuth and pitch axes of the high-precision turntable to (0°, 0°) and fix them. Then, power on the laser, read the laser point imaging position (x0′, y0′) on the target, and record the system deviation of the target pointing at this time as e0 = (x0′, y0′) - (x0, y0). (3) Control the azimuth and pitch axes of the high-precision turntable to swing to different angles and measure the deviation between the tracking point (x,y) of the visible light camera and the imaging position (x′,y′) of the target laser illumination point; (4) Substitute the measured value from step (3) into the formula e = A3 - A3′ to form a system of multivariate equations. Solve this system of multivariate equations to obtain the mirror installation error of the multimode composite tracking system. Calculate the corresponding deviation value based on the mirror installation error and the swing angles of the azimuth and pitch axes of the high-precision turntable. Where A3 is the direction vector of the laser beam when there is an installation error, and A3′ is the ideal direction vector of the laser beam. The ideal direction vector A3′ of the emitted beam of the laser is expressed as: in θ1 and θ2 are the azimuth axis rotation angle and pitch axis rotation angle of the high-precision turntable, respectively; α is the verticality error of the azimuth axis and pitch axis; and R3 is the reflection matrix of the reflector 3 of the multi-mode composite tracking and aiming system. The direction vector A3 of the laser's emitted beam vector when there is an adjustment error is represented as A3 = R3R2R1A0, where R2 and R1 are the reflection matrices of the multimode composite tracking system's mirrors 2 and 1, respectively, and A0 is the laser's emitted beam vector.

2. The target pointing error calibration method for a multi-mode composite tracking and aiming system according to claim 1, characterized in that: The reflection matrix of the multi-mode composite tracking system is as follows: in Let be the normal vector of the mirror.

3. The target pointing error calibration method for a multi-mode composite tracking and aiming system according to claim 2, characterized in that: The transpose N' of the normal vector of the aforementioned reflector is expressed as: Where d1, d2, and d3 are the heights of the three pillars supporting the reflector, and the three pillars form an isosceles triangle with a height of b and a base length of a.

4. The target pointing error calibration method for a multi-mode composite tracking and aiming system according to claim 3, characterized in that: The normal vectors N1, N2, and N3 of the reflector 1 and reflector 3 are expressed as follows: The upper right subscript (a left-falling stroke) indicates the vector transpose.

5. The target pointing error calibration method for a multi-mode composite tracking and aiming system according to claim 1, characterized in that: The azimuth and pitch axes of the high-precision control turntable are swung to different angles. The angle range is determined according to the usage requirements of the multi-mode composite tracking and aiming system, and the number of swung angle positions is not less than 6.

6. The target pointing error calibration method for a multi-mode composite tracking and aiming system according to claim 1, characterized in that: The control high-precision turntable swings its azimuth and pitch axes to different angles, with the pitch angle swing range being -10 degrees to 50 degrees and the azimuth angle swing range being -50 degrees to 50 degrees.

7. A computer system comprising a memory, a processor, and a computer program stored in the memory, characterized in that, The processor executes the computer program to implement the steps of the method of claim 1.

8. A computer program product, comprising a computer program, characterized in that, When the computer program instructions are executed by the processor, they implement the steps of the method of claim 1.

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