Echo tracking system and single-input double-output coupling type laser pointing control method

Abstract

The invention relates to the technical field of photoelectric tracking, and particularly provides an echo tracking system and a single-input double-output coupling type laser pointing control method.The system is composed of an echo receiving unit, a photoelectric imaging unit, a tracking control unit and a laser emitting unit, and echo signals are predicted through the photoelectric imaging unit; and the tracking control unit is guided to carry out echo tracking, an output signal of the photoelectric imaging unit is converted into an angle control instruction, the angle control instruction is respectively transmitted to the coarse tracking actuator and the fine tracking actuator, image rotation caused by coarse tracking motion is eliminated through decoupling operation, and two stages of execution devices are controlled to carry out tracking on the basis of decoupling. The illumination light path and the imaging light path adopt a common light path design, and decoupling operation is performed on the coarse tracking actuator and the fine tracking actuator, so that image rotation caused by coarse tracking is eliminated, the tracking precision is improved, the size of the tracking system is greatly reduced, and use scenes with strict requirements on the size and the precision are met.

Description

Technical Field

[0001] This invention relates to the field of photoelectric tracking technology, specifically providing an echo tracking system and a single-input dual-output coupled laser pointing control method. Background Technology

[0002] Acquisition, tracking, and aiming (ATP) systems are widely used in laser communication, military defense, astronomical observation, and aerial mapping. To achieve high tracking accuracy, ATP systems generally employ a compound axis structure. A compound axis ATP system has two motion actuation components, referred to as coarse tracking and fine tracking. Coarse tracking has a larger stroke and serves as the first stage of tracking; fine tracking, as the second stage of tracking to compensate for the tracking residuals of coarse tracking, generally has a smaller stroke and a higher bandwidth.

[0003] Composite-axis ATP systems can be categorized into dual-detector and single-detector types based on their implementation. As the name suggests, the dual-detector type uses one detector to control one actuator to complete optical closed-loop control. This control structure is inherently self-decoupled; as long as each control loop is stable, the entire system is stable during operation. Although the dual-detector ATP system is simple in its control structure, it is difficult to apply in environments with stringent requirements for size, weight, and power consumption. Firstly, the additional coarse-tracking detector increases the complexity of the overall optical structure. Secondly, it prevents the overall size from being compressed to a suitable level. Furthermore, during optical assembly and adjustment, the optical axes of both detectors need to be aligned, increasing the construction period and cost.

[0004] Single-detector systems use one detector to control two motion actuators in a closed-loop optical control system. This control method involves motion coupling between the two control loops. To stabilize the entire control system and theoretically achieve the same accuracy as a dual-detector system, a decoupling controller needs to be built between the two control sub-loops. Theoretically, this allows for the design of a single-detector control system. However, in practice, implementing a single-detector control system faces certain technical challenges. Firstly, there is the limitation of the field of view. To obtain a high-frequency position signal, the field of view of the fine-tracking detector is limited by current hardware capabilities and cannot be very large. This places demands on the accuracy of the first-stage tracking; if the first-stage tracking error is too large, the second-stage tracking stroke will be limited, potentially causing the target to wobble out of the field of view and resulting in tracking failure. Secondly, there are problems caused by the optical system: the movement of the first-stage tracking actuator can cause image rotation in the target image, which, if severe, can completely destabilize the tracking. Thirdly, due to atmospheric transmission, the detector image flickers, and the resulting output signal fluctuations can also cause tracking instability. Therefore, it is necessary to propose an echo tracking system and its application using a single-input dual-output coupled laser pointing control method. Summary of the Invention

[0005] To address the aforementioned problems, this invention provides an echo tracking system and a single-input dual-output coupled laser pointing control method, effectively solving the engineering challenges of single-detector type composite axis tracking systems. It is applicable to high-precision composite axis tracking in environments with strict requirements on size and weight.

[0006] The echo tracking system provided by the present invention includes: an echo receiving unit, an optoelectronic imaging unit, a tracking control unit, and a laser emitting unit;

[0007] The echo receiving unit includes an off-axis beam expander primary mirror, an off-axis beam expander secondary mirror, a fast reflector, and a spatial beam splitter.

[0008] The laser emitting unit is located on one side of the space beam splitter and is used to emit the detection laser; the photoelectric imaging unit is located on the other side of the space beam splitter and is used to collect the echo signal reflected by the target from the detection laser and predict the echo signal corresponding to the midpoint between two frames of echo signals. The photoelectric imaging unit outputs the inter-frame prediction signal and the collected signal to guide the tracking control unit to perform echo tracking.

[0009] The tracking control unit includes a decoupling controller, a coarse tracking actuator, a fine tracking actuator, and a coarse tracking mirror. The decoupling controller decouples the output signal of the photoelectric imaging unit and uses the decoupling signal to control the coarse tracking actuator and the fine tracking actuator. The coarse tracking actuator drives the coarse tracking mirror to adjust its pose, and the fine tracking actuator drives the fast mirror to adjust its pose.

[0010] The detection laser passes sequentially through a spatial beam splitter, a fast reflector, an off-axis beam expander secondary mirror, an off-axis beam expander primary mirror, and a coarse tracking reflector before being directed toward the target. The echo signal reflected from the target then passes sequentially through a coarse tracking reflector, an off-axis beam expander primary mirror, an off-axis beam expander secondary mirror, a fast reflector, and a spatial beam splitter before being directed toward the photoelectric imaging unit.

[0011] Preferably, the detection laser emitted by the laser emitting unit is in the infrared band, visible light band, or ultraviolet band.

[0012] Preferably, the photoelectric imaging unit includes a front imaging lens group and a photodetector, and the imaging position is adjusted by the front imaging lens group.

[0013] Preferably, the coarse tracking mirror is a two-dimensional pendulum mirror that can be driven independently for azimuth and pitch angles; the coarse tracking actuator is a DC torque motor that drives the two-dimensional pendulum mirror to rotate around the azimuth and pitch axes.

[0014] Preferably, the precision tracking actuator is a piezoelectric ceramic or voice coil motor that drives the fast-reflecting mirror to rotate.

[0015] A single-input dual-output coupled laser pointing control method includes the following steps:

[0016] S1: Integrate the echo signal on the target surface of the photodetector, extract the center coordinates of the echo signal using the centroid algorithm, and obtain the acquired signal;

[0017] S2: Predict the position of the inter-frame echo signal on the target surface of the photodetector using the Kalman filter algorithm to obtain the predicted signal;

[0018] S3: The photoelectric imaging unit outputs the acquired signal and the prediction signal to the tracking control unit. The tracking control unit converts the output signal of the photoelectric imaging unit into angle control commands that the coarse tracking actuator and the fine tracking actuator need to execute. The decoupling controller decouples the angle control commands to obtain the coarse tracking decoupling signal.

[0019] S4: Calculate the image rotation angle caused by the coarse tracking decoupling signal, obtain the correction angle of the image rotation angle through rotation transformation, and use the coarse tracking decoupling signal and the correction angle as the coarse tracking angle of the coarse tracking actuator.

[0020] S5: Based on the coarse tracking angle, the fine tracking angle of the fine tracking actuator is obtained through decoupling calculation of a single detector.

[0021] Preferably, the process of S2 is as follows:

[0022] S21: The function of the change in echo signal coordinates on the calibration target surface and the rotation angles of the coarse and fine tracking actuators:

[0023] (Δx,Δy)=f1(Δθ AC ,Δθ EC ,Δθ AF ,Δθ EF );

[0024] Where Δx and Δy are the coordinate changes of the echo signal on the target surface, and Δθ AC ,Δθ EC Δθ represents the changes in azimuth and pitch angles of the coarse tracking actuator, respectively. AF ,Δθ EF These represent the changes in the azimuth and pitch angles of the precision tracking actuator, respectively.

[0025] S22: The function of the rate of change of echo signal coordinates on the calibration target surface and the angular velocities of the coarse and fine tracking actuators:

[0026]

[0027] in, w represents the rate of change of the coordinates of the echo signal on the target surface. AC ,w ECThese represent the azimuth and pitch angular velocities of the coarse tracking actuator, respectively. AF ,w EF These represent the azimuth and pitch angular velocities of the precision tracking actuator, respectively.

[0028] S23: The inter-frame echo signal predicted according to the Kalman filter algorithm is:

[0029]

[0030] Where, x k ,y k , The coordinates and rate of change of the k-th frame echo signal on the target surface are represented by x. k+1 / 2 ,y k+1 / 2 , Let f represent the coordinates and coordinate change rate of the inter-frame prediction signal of the echo signals in frames k and (k+1) on the target surface, where T represents the time interval between frames k and (k+1). 1k f represents the change in coordinates of the k-th frame echo signal on the target surface. 2k This represents the rate of change of the coordinates of the k-th frame echo signal on the target surface.

[0031] Preferably, in S4, the image rotation angle caused by the coarse tracking decoupling signal is calculated by the BP neural network that has completed the fitting training.

[0032] Preferably, the fitting and training process of the BP neural network is as follows:

[0033] Collect the azimuth and pitch angles of the coarse tracking actuator corresponding to different image rotation angles;

[0034] The azimuth and elevation angles are used as inputs to the BP neural network, and the rotation angle is used as the output of the BP neural network for fitting and training.

[0035] Preferably, a three-loop control system consisting of a position loop, a speed loop, and a current loop is used to drive the coarse tracking actuator to perform coarse tracking angle; a two-loop control system consisting of a position loop and a current loop is used to drive the fine tracking actuator to perform fine tracking angle.

[0036] Compared with the prior art, the present invention can achieve the following beneficial effects:

[0037] This invention, by predicting the inter-frame position of the echo signal, effectively increases the overall sampling frequency of the detector. It also uses the acquired and predicted signals to guide the tracking control unit to drive the coarse and fine tracking actuators, greatly increasing the stability and tracking accuracy of the system. Furthermore, by using a laser pointing control method to decouple the single-input dual-output control structure, it eliminates the image rotation caused by coarse tracking motion through an algorithm, avoiding the need for an additional de-rotation mechanism and reducing the size and complexity of the echo tracking system.

[0038] This invention employs a two-dimensional long-stroke pendulum mirror for coarse target tracking, which not only reduces the system size and weight, making the system structure more compact, but also improves the rigidity of the tracking device. The system's first-order modal response can reach over 200Hz, and its rotational inertia is small, greatly enhancing its potential control bandwidth. Furthermore, compared to traditional vertical axis designs, the two-dimensional long-stroke pendulum mirror does not require "circle drawing" adjustments. This type of adjustment is typically used to ensure that the tracker can respond uniformly in all directions, but the adjustment process may introduce adjustment errors. The two-dimensional pendulum mirror of this invention simplifies the adjustment process and reduces potential adjustment errors.

[0039] The detection optical path and imaging optical path of the present invention adopt a common optical path design, so that the tracking accuracy is approximately equivalent to the laser irradiation accuracy of the entire system.

[0040] This invention uses a spatial beam splitter for beam splitting design, which reduces the equipment's dependence on lens coating processes and lowers the technical difficulty and cost. Attached Figure Description

[0041] Figure 1 This is an optical structure diagram of an echo tracking system provided according to an embodiment of the present invention;

[0042] Figure 2 This is a control structure block diagram of a single-input dual-output coupled laser pointing control method provided in an embodiment of the present invention.

[0043] The reference numerals in the figures include:

[0044] First plane mirror 1-1, second plane mirror 1-2, off-axis beam expander primary mirror 2-1, off-axis beam expander secondary mirror 2-2, fast mirror 2-3, spatial beam splitter 2-4, imaging front lens group 3-1, imaging detector 3-2, laser 4-1. Detailed Implementation

[0045] In the following description, embodiments of the invention will be described with reference to the accompanying drawings. In the description below, the same modules are denoted by the same reference numerals. Where the same reference numerals are used, their names and functions are also the same. Therefore, their detailed description will not be repeated.

[0046] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and do not constitute a limitation thereof.

[0047] like Figure 1 As shown, this embodiment of the invention provides an echo tracking system, mainly composed of an echo receiving unit, a photoelectric imaging unit, a tracking control unit, and a laser emitting unit. The laser emitting unit emits a probe laser, and its main component is a laser 4-1. The probe laser emitted by laser 4-1 can be in the infrared, visible, or ultraviolet bands, etc. The probe laser emitted by laser 4-1 passes through a portion of the structure in the echo receiving unit and the tracking control unit and then illuminates the target, generating an echo signal laser based on the cat's eye effect. The echo signal returns along the original optical path and enters the photoelectric imaging unit for imaging. Specifically, the echo receiving unit includes an off-axis beam expander primary mirror 2-1, an off-axis beam expander secondary mirror 2-2, a fast reflector 2-3, and a spatial beam splitter 2-4, arranged sequentially along the echo optical path. The off-axis beam expander primary mirror 2-1 and the off-axis beam expander secondary mirror 2-2 are both parabolic mirrors used to focus the laser echo. This off-axis beam expander system allows for a compact overall structure while compressing the laser divergence angle and increasing the system resolution. The fast reflector 2-3 is a small-aperture, micro-stroke, high-bandwidth movable reflector with adjustable spatial angle, serving as the driving device for precise tracking. The spatial beam splitter 2-4 functions as a semi-transparent, semi-reflective mirror, enabling a common optical path design for both the emitted and echo optical paths. This common optical path design allows the tracking accuracy to be approximately equivalent to the laser illumination accuracy of the entire echo system. Furthermore, during the imaging of the echo signal, the spatial beam splitter 2-4 can separate the echo signal from the beam, ensuring the separation of the echo and emitted optical paths and preventing mutual interference.

[0048] The tracking control unit includes a decoupling controller, a coarse tracking actuator, a fine tracking actuator, and a coarse tracking mirror. The decoupling controller is a software functional module used to decouple the output signal of the photoelectric imaging unit. The coarse tracking mirror is an optical element of the optical system, located in front of the output end of the off-axis beam expander primary mirror 2-1. In this embodiment, a two-dimensional pendulum mirror with independently driveable azimuth and elevation angles is selected as the coarse tracking mirror, namely the first plane mirror 1-1 in the figure. The first plane mirror 1-1 is connected to the fine tracking actuator. The coarse tracking actuator can employ two orthogonal rotating shaft DC torque motors. The fine tracking actuator can drive the first plane mirror 1-1 for a large stroke, controlling its spatial angle and rotational speed. Compared to traditional tracking turntables, the two-dimensional pendulum mirror and DC torque motors have lower rotational inertia, resulting in a higher system bandwidth. Therefore, the mechanism design of the two-dimensional pendulum mirror and DC torque motors is simpler, and the system's resonant frequency peak is much larger than the control bandwidth, reducing the risk of system resonance caused by motion control.

[0049] Furthermore, to match the light output direction or echo direction, a second plane mirror 1-2 can be set to adjust the light output direction or echo direction. In this embodiment, the second plane mirror 1-2 is set between the transmission optical path of the first plane mirror 1-1 and the off-axis beam expander primary mirror 2-1. Alternatively, the second plane mirror 1-2 can be used as a fine tracking mirror with adjustable spatial angle and rotation speed, and the first plane mirror 1-1 can be used as a mirror to change the light propagation direction. The fine tracking actuator is connected to the fast mirror 2-3 and is used to perform small-stroke fine adjustments on the fast mirror 2-3, compensate for the coarse tracking structure, and improve tracking accuracy. In this embodiment of the invention, the fine tracking actuator is a piezoelectric ceramic, and the controller of the piezoelectric ceramic is preferably a DSPF28335 control chip. The piezoelectric ceramic can convert control electrical signals into mechanical energy. When a voltage is applied, the piezoelectric ceramic will deform, thereby driving the fast mirror 2-3 to rotate, so as to achieve the purpose of fine tracking of the target. In addition, a voice coil motor can also be used as a precision tracking actuator. However, compared with a voice coil motor, piezoelectric ceramics have a faster response speed and can drive the fast reflector 2-3 to rotate faster. Furthermore, piezoelectric ceramics can remain at zero position when the power is off, which improves the stability of the system.

[0050] The photoelectric imaging unit is mainly used to acquire echo signals and image them to obtain target information. The photoelectric imaging unit is located on the right side of the space beam splitter 2-4, meaning the photoelectric imaging unit and the laser emission unit are respectively located on opposite sides of the space beam splitter 2-4. Along the echo optical path, the photoelectric imaging unit sequentially includes an imaging front lens group 3-1 and an imaging detector 3-2. The imaging detector 3-2 operates in the same wavelength band as the laser 4-1. The imaging detector 3-2 can be a CCD array or a CMOS array. The imaging front lens group 3-1 adjusts the imaging position of the echo signal by movement, ensuring the intersection point falls on the target surface of the imaging detector 3-2. The position of the echo signal spot on the target surface of the imaging detector 3-2 is output to the tracking control unit, which is then guided by the output signal of the imaging detector 3-2 to perform echo tracking. Because the imaging detector 3-2 has a limited acquisition frequency for the echo signal spot on the target surface, its output signal is discrete, with each sample corresponding to one frame of output signal. When the acquisition frequency is low, signal discontinuity is inevitable, leading to problems such as stuttering or reversal in the tracking actuator. Therefore, this embodiment of the invention also uses a Kalman filter algorithm to predict the echo signal corresponding to the midpoint between two frames of echo signals. The acquired signal and the predicted signal are output together in chronological order to guide the tracking control unit for echo tracking, which is equivalent to increasing the overall sampling frequency of the imaging detector 3-2. Inter-frame prediction greatly improves the tracking stability of the echo system.

[0051] Based on the above structure, the spatial relative positions of the optical elements involved in laser propagation in the echo tracking system, as well as the propagation process of the laser in the emission optical path and the echo optical path, are described as follows:

[0052] Laser 4-1 is positioned directly above spatial beam splitter 2-4. Spatial beam splitter 2-4 has a spatial tilt angle of 45 degrees and provides partial transmission and reflection of laser light incident on its surface. The probe laser emitted by laser 4-1 first illuminates spatial beam splitter 2-4. Spatial beam splitter 2-4 reflects part of the light onto the surface of fast reflector 2-3. The spatial angle of fast reflector 2-3 can be adjusted. Fast reflector 2-3 reflects the probe laser towards off-axis secondary beam expander 2-2. Off-axis secondary beam expander 2-2 reflects the probe laser towards off-axis primary beam expander 2-1. Off-axis primary beam expander 2-1 reflects the probe laser towards second plane mirror 1-2. Second plane mirror 1-2 reflects the probe laser towards first plane mirror 1-1. First plane mirror 1-1 reflects the probe laser out.

[0053] After the output detection laser illuminates the target, it generates an echo laser, i.e., an echo signal, based on the cat's eye effect. The echo signal is reflected by the first plane mirror 1-1 to the second plane mirror 1-2. The second plane mirror 1-2 reflects the echo signal to the off-axis beam expander primary mirror 2-1. The off-axis beam expander primary mirror 2-1 focuses the echo signal and reflects it further to the off-axis beam expander secondary mirror 2-2. The off-axis beam expander secondary mirror 2-2 reflects the echo signal to the fast reflector 2-3. The fast reflector 2-3 reflects the echo signal to the spatial beam splitter 2-4. Part of the light is transmitted through the spatial beam splitter 2-4 and directed to the imaging front lens group 3-1. The imaging front lens group 3-1 converges the echo signal and, by moving the focus, makes the focal point fall on the target surface of the imaging detector 3-2, thus completing the acquisition of the echo signal.

[0054] Based on the above echo tracking system, this embodiment of the invention also proposes a single-input dual-output coupled laser pointing control method, including the following steps:

[0055] After the echo signal enters the photoelectric imaging unit through the echo receiving optical unit, the imaging detector 3-2 integrates and reads the echo signal on the target surface. Since the echo signal on the target surface is in the form of a light spot image, the center coordinates of the light spot are extracted using the centroid algorithm. The center coordinates of the light spot are then used as the position coordinates of the echo signal.

[0056] S2: To improve the continuity and smoothness of the output signal of the photoelectric imaging unit, the position of the inter-frame echo signal on the target surface of the photodetector is predicted using the Kalman filter algorithm. While the Kalman filter algorithm is a mature technology, its application in a signal tracking system, effectively increasing the detector's sampling frequency, is an innovative design. The specific process is as follows:

[0057] S21: The coordinate change of the echo signal on the calibration target surface is a function of the rotation angles of the coarse and fine tracking actuators.

[0058] (Δx,Δy)=f1(Δθ AC ,Δθ EC ,Δθ AF ,Δθ EF );

[0059] Where Δx and Δy are the coordinate changes of the echo signal on the target surface, i.e., the center coordinate difference between two adjacent frames of the spot image, and Δθ AC ,Δθ EC Δθ represents the changes in azimuth and pitch angles of the coarse tracking actuator, respectively. AF ,Δθ EF Δθ represents the changes in azimuth and pitch angles of the precision tracking actuator, respectively. AC ,Δθ EC ,Δθ AF ,ΔθEF It is obtained through the angle measuring elements on the coarse tracking actuator and the fine tracking actuator. The angle measuring elements can be grating encoders.

[0060] S22: The function of the rate of change of echo signal coordinates on the calibration target surface and the angular velocities of the coarse and fine tracking actuators:

[0061]

[0062] in, w represents the rate of change of the coordinates of the echo signal on the target surface. AC ,w EC These represent the azimuth and pitch angular velocities of the coarse tracking actuator, respectively. AF ,w EF These represent the azimuth and pitch angular velocities of the precision tracking actuator, respectively. AC ,w EC ,w AF ,w EF It is obtained through the velocity measuring elements on the coarse tracking actuator and the fine tracking actuator. The velocity measuring elements can be laser gyroscopes, quartz gyroscopes or MEMS gyroscopes.

[0063] S23: The inter-frame echo signal predicted according to the Kalman filter algorithm is:

[0064]

[0065] Where, x k ,y k , The coordinates and rate of change of the k-th frame echo signal on the target surface are represented by x. k+1 / 2 ,y k+1 / 2 , Let f represent the coordinates and coordinate change rate of the inter-frame prediction signal of the echo signals in frames k and (k+1) on the target surface, where T represents the time interval between frames k and (k+1). 1k This represents the change in coordinates of the k-th frame echo signal on the target surface, i.e., the function value calibrated in S21, f. 2k This represents the rate of change of the coordinates of the k-th frame echo signal on the target surface, which is the function value calibrated in S22.

[0066] S3: The photoelectric imaging unit arranges the predicted signal in chronological order among the acquired signals and outputs it to the tracking control unit. The communication protocol between the photoelectric imaging unit and the tracking control unit is RS422. The tracking control unit converts the position signal of the echo signal output by the photoelectric imaging unit on the target surface into angle control commands executable by the coarse tracking actuator and the fine tracking actuator, and inputs the angle control commands to the decoupling controller. The decoupling controller first decouples and obtains the current coarse tracking decoupling signal to prepare for the next step of image rotation angle correction.

[0067] S4: Since executing according to the coarse tracking decoupling signal will cause image rotation of the light spot image on the target surface, this embodiment of the invention also corrects the image rotation angle through an algorithm. Specifically: the coarse tracking decoupling signal is input into the BP neural network that has completed fitting training. The BP neural network outputs the image rotation angle caused by the coarse tracking decoupling signal. Then, a rotation transformation is performed through a two-dimensional rotation matrix to calculate the correction angle that can correct the output image rotation angle. The coarse tracking decoupling signal and the correction angle are superimposed as the coarse tracking angle of the coarse tracking actuator. The coarse tracking actuator drives the first planar reflector 1-1 to rotate according to the coarse tracking angle. Figure 2 As shown, the coarse tracking control method is as follows: the coarse tracking angle is transmitted to the coarse tracking actuator, and the coarse tracking actuator is driven to rotate the first plane reflector 1-1 according to the coarse tracking angle through the traditional three-closed-loop control of position loop, speed loop and current loop and combined with the feedforward controller.

[0068] Backpropagation (BP) neural networks can directly use existing network topologies, typically around 10 layers. The fitting and training process of a BP neural network is as follows:

[0069] Collect image rotation data of the first plane mirror 1-1 at different coarse tracking angles, including: the azimuth and elevation angles of the first plane mirror 1-1, and the image rotation angle on the target surface at this time;

[0070] The azimuth and elevation angles are used as inputs to the BP neural network, and the rotation angle is used as the output of the BP neural network for iterative fitting training. When the output of the BP neural network meets the accuracy requirements, the network training is completed.

[0071] S5: The decoupling controller for the fine tracking actuator is a traditional single-input, single-output, single-detector decoupling control. This control design is a mature technology. After coarse tracking is completed, single-detector control decoupling is performed based on the position information of fast reflectors 2-3. After decoupling calculation, the fine tracking angle is obtained. The fine tracking process does not need to consider image rotation or other issues; it only needs to track the target position output by the photoelectric imaging system. Figure 2As shown, the fine tracking control method is as follows: the fine tracking angle is transmitted to the fine tracking actuator, and the fine tracking actuator is driven by the dual closed-loop control of the traditional position loop and current loop to drive the fast reflector 2-3 to rotate according to the fine tracking angle, so that the line of sight of the system equipment points to the target.

[0072] Although embodiments of the present invention have been shown and described above, it is to be understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions, and variations to the above embodiments within the scope of the present invention.

[0073] The specific embodiments of the present invention described above do not constitute a limitation on the scope of protection of the present invention. Any other corresponding changes and modifications made in accordance with the technical concept of the present invention should be included within the scope of protection of the claims of the present invention.

Claims

1. An echo tracking system, characterized by The application relates to a laser tracking system. The laser tracking system comprises an echo receiving unit, an optoelectronic imaging unit, a tracking control unit and a laser emitting unit. The echo receiving unit comprises an off-axis beam expander primary mirror, an off-axis beam expander secondary mirror, a fast mirror and a spatial beam splitter. The laser emitting unit is arranged on one side of the spatial beam splitter and is used for emitting probe laser. The optoelectronic imaging unit is arranged on the other side of the spatial beam splitter and is used for collecting echo signals of the probe laser reflected by a target and predicting echo signals corresponding to middle moments of two frames of echo signals. The optoelectronic imaging unit outputs interframe prediction signals and collection signals to guide the tracking control unit to perform echo tracking.

2. The echo tracking system of claim 1, wherein, The tracking control unit comprises a decoupling controller, a coarse tracking executor, a fine tracking executor and a coarse tracking mirror.

3. The echo tracking system of claim 1, wherein, The decoupling controller decouples output signals of the optoelectronic imaging unit and controls the coarse tracking executor and the fine tracking executor by using decoupled signals.

4. The echo tracking system of claim 1, wherein, The coarse tracking executor drives the coarse tracking mirror to adjust a pose.

5. An echo tracking system as claimed in claim 4, characterized in that The fine tracking executor drives the fast mirror to adjust a pose.

6. A single input dual output coupled laser pointing control method, characterized in that, The probe laser sequentially passes through the spatial beam splitter, the fast mirror, the off-axis beam expander secondary mirror, the off-axis beam expander primary mirror and the coarse tracking mirror and is emitted to the target. The echo signals reflected by the target sequentially pass through the coarse tracking mirror, the off-axis beam expander primary mirror, the off-axis beam expander secondary mirror, the fast mirror and the spatial beam splitter and are emitted into the optoelectronic imaging unit. The probe laser emitted by the laser emitting unit is in an infrared wave band, a visible light wave band or an ultraviolet wave band. The optoelectronic imaging unit comprises an imaging front lens group and a photoelectric detector. The imaging position is adjusted by the imaging front lens group. The coarse tracking mirror is a two-dimensional swing mirror which can be independently driven in an azimuth angle and a pitch angle.

7. The single-input dual-output coupled laser pointing control method of claim 1, wherein, The coarse tracking executor is a direct current torque motor which drives the two-dimensional swing mirror to rotate around an azimuth axis and a pitch axis. The fine tracking executor is a piezoelectric ceramic or a voice coil motor which drives the fast mirror to rotate. The application further discloses a laser tracking method. S1: integral collection of echo signals on a target surface of a photoelectric detector, extraction of center coordinates of the echo signals by using a centroid algorithm and acquisition of collection signals; S2: prediction of positions of interframe echo signals on the target surface of the photoelectric detector by using a Kalman filtering algorithm and acquisition of prediction signals; S3: output of the collection signals and the prediction signals to the tracking control unit by the optoelectronic imaging unit, conversion of the output signals of the optoelectronic imaging unit into angle control instructions required by the coarse tracking executor and the fine tracking executor by the tracking control unit, decoupling of the angle control instructions by the decoupling controller and acquisition of coarse tracking decoupled signals; S4: calculation of image rotation angles caused by the coarse tracking decoupled signals, acquisition of correction angles for correcting the image rotation angles by using rotation transformation and taking the coarse tracking decoupled signals and the correction angles as coarse tracking angles of the coarse tracking executor; S5: acquisition of fine tracking angles of the fine tracking executor based on the coarse tracking angles by using single-detector decoupling calculation. The process of S2 is as follows: S21: calibration of a function of a coordinate variation of echo signals on a target surface and rotation angles of the coarse tracking executor and the fine tracking executor. (Δx,Δy) = f1(Δθ AC ,Δθ EC ,Δθ AF ,Δθ EF ) wherein Δx, Δy are coordinate change amounts of the echo signal on the target surface, Δθ AC , Δθ EC respectively represent change amounts of the azimuth angle and the elevation angle of the coarse tracking executor, Δθ AF , Δθ EF respectively represent change amounts of the azimuth angle and the elevation angle of the fine tracking executor; S22: calibrate the echo signal coordinate change speed on the target surface as a function of the coarse tracking actuator and the fine tracking actuator angular velocity: wherein, denotes the speed of the change of the echo signal coordinate on the target surface, w AC denotes the azimuthal and the elevation speed of the coarse tracking actuator, respectively, w EC denotes the azimuthal and the elevation speed of the coarse tracking actuator, respectively, w AF denotes the azimuthal and the elevation speed of the coarse tracking actuator, respectively, w EF denotes the azimuthal and the elevation speed of the coarse tracking actuator, respectively, w S23: predict the inter-frame echo signal according to the Kalman filter algorithm: wherein x k ,y k , represents the coordinates and coordinate change speed of the echo signal of the kth frame on the target surface, x k+1 / 2 ,y k+1 / 2 , represents the coordinates and coordinate change speed of the inter-frame prediction signal of the echo signal of the kth frame and the k+1th frame on the target surface, T represents the time interval of the kth frame and the k+1th frame, f 1k represents the coordinate change amount of the echo signal of the kth frame on the target surface, and f 2k represents the coordinate change speed of the echo signal of the kth frame on the target surface.

8. The single-input dual-output coupled laser pointing control method of claim 1, wherein, In the S4, the BP neural network which is trained by fitting calculates the image rotation angle caused by the coarse tracking decoupling signal.

9. The single-input dual-output coupled laser pointing control method of claim 8, wherein, The fitting training process of the BP neural network is: Collect the azimuth and elevation angles of the coarse tracking actuator corresponding to different image rotation angles; Fit and train the azimuth and elevation angles as the input of the BP neural network and the image rotation angle as the output of the BP neural network.

10. The single-input dual-output coupled laser pointing control method of claim 1, wherein, The coarse tracking actuator is driven to execute the coarse tracking angle by adopting the three-closed-loop control of the position loop, the velocity loop and the current loop; the fine tracking actuator is driven to execute the fine tracking angle by adopting the double-closed-loop control of the position loop and the current loop.

Images