Light beam pointing control system based on single CCD (Charge Coupled Device) and hierarchical positioning and tracking method

Abstract

The invention relates to a light beam pointing control system based on a single CCD (Charge Coupled Device) and a hierarchical positioning tracking method, belongs to the technical field of space laser communication, and is used for solving the problems of complex light path, error accumulation and insufficient tracking precision in a traditional light beam control system. According to the technical scheme, a single CCD detector is combined with a beam splitter unit to receive a double-light-spot image, a displacement error is eliminated through a first fast reflecting mirror, and an angle error is corrected through a second fast reflecting mirror; and light spot centroid calculation and hierarchical PID control are carried out by using an FPGA, so that dynamic adjustment of light beam pointing is realized. The system structure is simplified through a single-detector double-optical-path collaborative design, deviation accumulation is effectively inhibited through a hierarchical error compensation mechanism, the light beam pointing precision and tracking stability are remarkably improved, meanwhile, the hardware cost and the maintenance difficulty are reduced, and the system is suitable for a space optical communication system in a high-dynamic environment.

Description

Technical Field

[0001] The present invention belongs to the technical field of space laser communication and relates to a light beam pointing control system based on a single CCD and a hierarchical positioning and tracking method. Background Art

[0002] Space laser communication (SLC) is a communication method that uses light beams to transmit in free space, enabling data transmission without a physical medium (such as optical fiber or conductive cable). Combining the advantages of microwave and optical fiber communications, SLC has become an important tool in multiple communication links, including those based in space, space, and land. However, SLC faces several challenges, primarily due to its line-of-sight (LOS) link transmission, which makes communication quality susceptible to environmental factors such as atmospheric turbulence and attenuation. In SLC, high-precision beam tracking control is a key factor in ensuring system performance. Since the relative position and alignment between the transmitter and receiver cannot be completely accurate, and due to building shaking or equipment vibration, the beam's pointing direction may deviate. This deviation is called "pointing error" (PE). To maintain communication stability and efficiency, beam pointing error must be effectively controlled to ensure stable transmission in free space. To improve beam pointing accuracy, fast steering mirrors (FSMs) are often used for beam pointing adjustment. However, traditional beam pointing control systems have several issues, such as:

[0003] Limitations of Single-Reflex Mirror Systems: In some traditional systems, a single reflex mirror is often used to adjust the direction of the laser beam. However, this design can only adjust the beam within a limited range and has difficulty maintaining stability in complex environments, especially when high dynamic range or precise tracking are required, which can easily affect accuracy.

[0004] Accumulation of beam pointing errors: During beam transmission, due to the complexity of the optical path, mirror errors, and environmental factors (such as temperature changes and vibration), beam pointing errors gradually accumulate, resulting in a degradation of communication system signal quality. Therefore, a high-precision control system is required to adjust the beam pointing in real time.

[0005] Complexity of optical path design: Traditional beam-pointing control systems often use multiple detectors and complex optical path designs, which not only increase the system's size and weight, but also increase costs and maintenance difficulties. More complex optical path designs can also introduce more error sources, further impacting system stability and reliability.

[0006] Therefore, a high-precision control system is needed to adjust the direction of the light beam in real time, while simplifying the optical path system structure, reducing system complexity and lowering costs. Summary of the Invention

[0007] In light of this, the present invention aims to provide a single-CCD-based beam pointing control system and a hierarchical positioning and tracking method, aiming to address issues such as beam pointing deviation, error accumulation, and complex optical path design. This system utilizes a single CCD to receive image information from two light spots and feeds it back to an FPGA. The system achieves precise beam pointing correction through the synergistic effect of two fast-reflection mirrors and a hierarchical adjustment mechanism, significantly improving system accuracy and stability while simplifying the optical path system structure, reducing system complexity, and lowering costs.

[0008] In order to achieve the above object, the present invention provides the following technical solutions:

[0009] A single CCD-based beam pointing control system, comprising:

[0010] a laser for emitting a laser beam;

[0011] a coupler for receiving and transmitting the rectified laser beam;

[0012] A fast mirror unit, comprising a first fast mirror FSM-1 and a second fast mirror FSM-2, wherein the first fast mirror FSM-1 is used to adjust the laser light path to point to the center of the mirror surface of the second fast mirror FSM-2, and the second fast mirror FSM-2 is used to adjust the laser light path to point vertically to the center of the coupler;

[0013] A beam splitter unit includes a first beam splitter BS-1, a second beam splitter BS-2, and a third beam splitter BS-3. The first beam splitter BS-1 splits the light beam from the first fast mirror to the third beam splitter BS-3 and the second fast mirror FSM-2. The second beam splitter BS-2 splits the light beam from the second fast mirror to the coupler and the third beam splitter BS-3. The third beam splitter BS-3 combines the light beams from the first beam splitter and the second beam splitter.

[0014] A CCD detector is used to receive the two beam spot images after being combined by the third beam splitter;

[0015] A Field Programmable Gate Array (FPGA) is used to process the light spot image data collected by the CCD detector and drive the fast mirror unit to perform light beam pointing correction through a hierarchical control algorithm.

[0016] Furthermore, the optical path configuration of the beam splitter unit satisfies:

[0017] The first beam splitter BS-1 is arranged in the light path reflection direction of the first fast reflection mirror FSM-1;

[0018] The second beam splitter BS-2 is arranged in the light path reflection direction of the second fast reflection mirror FSM-2;

[0019] The third beam splitter BS-3 simultaneously receives the transmitted light from the first beam splitter and the reflected light from the second beam splitter, and directs the two beams of light toward the photosensitive surface of the CCD detector.

[0020] Furthermore, the FPGA performs image processing including:

[0021] Gaussian filter module, used to suppress noise in the spot image;

[0022] Binarization processing module uses threshold segmentation to extract the spot area;

[0023] Edge detection module, extracts the edge of the light spot based on the Canny algorithm;

[0024] The center of mass calculation module detects the center of the light spot as the center of mass coordinate through Hough circle transform.

[0025] Furthermore, the two light spots received by the CCD detector have distinguishable characteristics:

[0026] The diameter D1 of the first light spot and the diameter D2 of the second light spot satisfy D1 / D2=1.2-1.5;

[0027] The light intensity ratio of the two light spots is I1 / I2 = 1.5~2.0.

[0028] Furthermore, the reflection / transmission ratio of the beam splitter is configured as follows:

[0029] Transmittance T of the first beam splitter BS-1 BS1 =90%, reflectivity R BS1 =10%;

[0030] The reflectivity R of the second beam splitter BS-2 BS2 =95%, transmittance T BS2 =5%;

[0031] The transmittance T of the third beam splitter BS-3 to the beam from the first beam splitter BS3 =85%, the reflectivity R of the beam from the second beam splitter BS3 =90%.

[0032] A hierarchical positioning and tracking method based on the system comprises:

[0033] The first stage of positioning: by adjusting the posture of the first fast reflection mirror FSM-1, the coordinates of the center of mass of the first light spot reach the pre-calibrated position C1, eliminating the beam pointing displacement error;

[0034] Second-stage positioning: By adjusting the posture of the second fast-reflecting mirror FSM-2, the coordinates of the second light spot's centroid reach the pre-calibrated position C2, eliminating the beam pointing angle error;

[0035] The first light spot is the light spot that is directly transmitted to the CCD through the first beam splitter, and the second light spot is the light spot that is reflected by the second beam splitter and then split twice to the CCD.

[0036] Furthermore, the first level positioning stage specifically includes:

[0037] Calculate the offset (Δ x1 ,Δ y1 );

[0038] The first fast mirror driving voltage (U x1 ,U y1 ), which satisfies:

[0039] U x1 =K p1 ·Δx1+K i1 ·∫Δx1dt+K d1 d(Δx1) / dt

[0040] U y1 =K p1 ·Δy1+K i1 ·∫Δy1dt+K d1 ·d(Δy1) / dt

[0041] where K p1 , K i1 , K d1 They are the proportional, integral and differential coefficients of the first fast reflex mirror control respectively.

[0042] Furthermore, the second level positioning stage specifically includes:

[0043] Calculate the offset (Δ x2 ,Δ y2 );

[0044] The second fast mirror driving voltage (U x2 ,U y2 ), which satisfies:

[0045] U x2 =K p2 ·Δx2+Ki2 ∫Δx2dt+K d2 d(Δx2) / dt

[0046] U y2 =K p2 ·Δy2+K i2 ·∫Δy2dt+K d2 ·d(Δy2) / dt

[0047] where K p2 , K i2 , K d2 are the proportional, integral and differential coefficients of the second fast mirror control, and K p2 >K p1 , K d2 <K d1 .

[0048] Furthermore, the detection process of the Hough circle transform includes:

[0049] Establish the circle equation (xa) in parameter space (a,b,r) 2 +(yb) 2 =r 2 ;

[0050] Cumulative voting of the circle center coordinates (a, b) along the image gradient direction θ satisfies:

[0051] a=x±rcosθ,b=y±rsinθ

[0052] Where (x, y) is the edge point coordinate, and r is the preset radius search range.

[0053] Furthermore, the Canny edge detection includes:

[0054] Sobel operator is used to calculate the gradient amplitude Among them G x , G y are the gradient components in the horizontal and vertical directions respectively;

[0055] Set the high threshold T high and low threshold T low Make edge connections, where T high =2T low , and T low Take the first 20% quantile of the image grayscale histogram.

[0056] The beneficial effects of the present invention are as follows: the present invention has achieved multiple technological breakthroughs in the light beam pointing control system through the structural innovation of the coordinated control of a single CCD detector and a dual fast reflex mirror, combined with a graded positioning and tracking method. First, the optical path design of a single detector combined with a beam splitter unit significantly simplifies the optical system architecture, reduces the number of components and assembly error sources, and reduces hardware costs and maintenance difficulties. Second, through a graded error compensation mechanism, the displacement error and the angle error are decoupled, the first fast reflex mirror first eliminates the beam offset, and then the second fast reflex mirror corrects the residual angle deviation, effectively suppressing the error accumulation effect and improving long-term working stability. Third, the FPGA-based real-time image processing and dual PID independent control strategy take into account both fast response and high-precision adjustment to ensure accurate tracking of the light beam pointing in a dynamic environment. Fourth, the optimized design of the beam splitter parameters and the light spot characteristics enhances the discrimination and detection reliability of the dual light spots, avoiding control failures caused by signal crosstalk. While maintaining the compactness of the system, the overall solution solves the pain points of limited adjustment range, multiple error coupling and insufficient environmental adaptability in traditional technologies, providing a highly reliable and low-cost pointing control solution for space laser communications, with significant technical practicality and industry promotion value.

[0057] Other advantages, objects, and features of the present invention will be described in part in the following description and, in part, will be apparent to those skilled in the art upon examination of the following description or may be learned from practice of the present invention. The objects and other advantages of the present invention may be realized and obtained through the following description. BRIEF DESCRIPTION OF THE DRAWINGS

[0058] In order to make the purpose, technical solutions and advantages of the present invention more clear, the present invention will be described in detail below with reference to the accompanying drawings, in which:

[0059] Figure 1 Schematic diagram of the beam control system based on a single CCD;

[0060] Figure 2 This is a flow chart of beam classification positioning and tracking based on a single CCD;

[0061] Figure 3 is the original image of the light spot received by the CCD; Figure 3 (a) is the original image when the two spots are separated. Figure 3 (b) is the original image when the two light spots partially overlap;

[0062] Figure 4 It is the spot edge image extracted after Canny algorithm edge detection; Figure 4 (a) is the edge image of the light spot when the two light spots are separated. Figure 4 (b) is the edge image of the light spot when the two light spots partially overlap;

[0063] Figure 5 It is the centroid image of the light spot detected by Hough circle transform; Figure 5 (a) is the centroid image of the two light spots when they are separated. Figure 5 (b) is the centroid image of the two light spots when they partially overlap. DETAILED DESCRIPTION

[0064] The following describes the embodiments of the present invention by means of specific examples, and those skilled in the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and the details in this specification can also be modified or changed in various ways based on different viewpoints and applications without departing from the spirit of the present invention. It should be noted that the illustrations provided in the following embodiments are only schematic illustrations of the basic concept of the present invention, and the following embodiments and features in the embodiments can be combined with each other without conflict.

[0065] Among them, the accompanying drawings are only for illustrative purposes and represent only schematic diagrams rather than actual pictures, and should not be understood as limiting the present invention. In order to better illustrate the embodiments of the present invention, some parts of the accompanying drawings may be omitted, enlarged or reduced, and do not represent the dimensions of actual products. For those skilled in the art, it is understandable that some well-known structures and their descriptions may be omitted in the accompanying drawings.

[0066] The same or similar numbers in the drawings of the embodiments of the present invention correspond to the same or similar parts; in the description of the present invention, it should be understood that if there are terms such as "upper", "lower", "left", "right", "front", "back", etc. indicating directions or positional relationships, they are based on the directions or positional relationships shown in the drawings. They are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific direction, be constructed and operate in a specific direction. Therefore, the terms describing the positional relationship in the drawings are only used for illustrative purposes and cannot be understood as limiting the present invention. For ordinary technicians in this field, the specific meanings of the above terms can be understood according to specific circumstances.

[0067] Figure 1 FIG. 1 is a schematic diagram of a beam control system based on a single CCD according to the present invention. Figure 1 As shown, the system includes an FPGA controller, a fast reflection mirror unit, a CCD and a beam splitter unit.

[0068] The FPGA controller is used to capture the light spot image of the light source beam on the CCD. Based on this light spot image, it calculates the center of mass coordinates of the first and second light spots. The corresponding center of mass offsets are used as inputs to the PID algorithm. The PID algorithm then generates a drive control signal for the corresponding quick-reflection mirror. The DAC module then converts this drive control signal into a drive voltage value for the quick-reflection mirror. Based on this drive voltage value, the quick-reflection mirror is controlled to rotate around its own axis to correct the directivity deviation of the light source beam.

[0069] Furthermore, the FPGA is the core control component of the entire system, responsible for receiving and processing signals and issuing control instructions. The fast mirror unit consists of a first fast mirror FSM-1 and a second fast mirror FSM-2, which adjusts the direction of the light beam by rotating around its own x-axis or y-axis. The CCD is used to detect the spot position of the light source beam and provide feedback signals to the FPGA. The beam splitter unit consists of a first beam splitter BS-1, a second beam splitter BS-2, and a third beam splitter BS-3, which splits the light source beam into two parts, one part is used as a beacon light to detect beam offset, and the other part is used as signal light to couple into the optical fiber for communication.

[0070] The following is a detailed description of the beam control system:

[0071] The light beam from the light source is reflected by the first fast reflector FSM-1 and then enters the first beam splitter BS-1. BS-1 splits the light beam into two paths: the transmitted light (accounting for 90%), i.e. T BS1 =90%) points to the second fast mirror FSM-2, and is reflected by FSM-2 and incident on the second beam splitter BS-2; the reflected light (accounting for 10%, namely R BS1 =10%) is directly incident on the third beam splitter BS-3.

[0072] The second beam splitter BS-2 splits the beam from FSM-2 into two paths: reflected light (accounting for 95%, namely R BS2 =95%) is incident vertically to the center of the coupler; the transmitted light (5%, i.e. T BS2 =5%) is incident on the third beam splitter BS-3.

[0073] The third beam splitter BS-3 transmits 85% of the reflected light from BS-1 (T BS3 =85%), and reflects 90% of the transmitted light from BS-2 (R BS3 =90%), and finally the two beams are combined to the photosensitive surface of the CCD detector to form the first light spot (from the reflected light of BS-1) and the second light spot (from the transmitted light of BS-2).

[0074] Since the light beam generated by the second light spot has a longer transmission path and passes through more optical elements, the light intensity and spot size of the second light spot are smaller than those of the first light spot. The FPGA can distinguish the two light spots during image processing.

[0075] The solid arrows represent the beam path with the beam shifted, and the dashed arrows represent the beam path after correction.

[0076] The light beam from the light source is reflected by the first fast reflection mirror FSM-1 and the second fast reflection mirror FSM-2, and then projects through the second beam splitter BS-2 toward the coupler.

[0077] According to an example of the present invention, a beam grading positioning tracking method is provided. It should be noted that the steps shown in the flowchart of the accompanying drawings can be executed in a computer system such as a set of computer executable instructions, and although a logical order is shown in the flowchart, in some cases, the steps shown or described can be executed in an order different from that shown here.

[0078] In this example, a beam classification positioning tracking method is provided, which can be used to Figure 1 A single CCD-based beam control system is shown. Figure 2 1 is a flow chart of a beam classification positioning and tracking method according to an embodiment of the present invention. The flow chart includes the following steps:

[0079] First, the CCD acquires the light spot image information and feeds it back to the FPGA, where the image is processed and the centroid coordinates of the first light spot and the second light spot are calculated.

[0080] FPGA uses the centroid offset of the first light spot (Δ x1 ,Δ y1 ), the first driving voltage value (U x1 ,U y1 ), thereby controlling the first fast-reflection mirror (FSM-1) to rotate about its own x- and y-axes, returning the first light spot to the first target position. The light source beam is now directed toward the center of the second fast-reflection mirror (FSM-2), eliminating beam pointing errors. A conditional check is performed: if the first light spot has returned to the first target position, the next step is performed; otherwise, the current step is repeated.

[0081] FPGA uses the centroid offset of the second spot (Δ x2 ,Δ y2 ), the second driving voltage value (U x2 ,U y2) so as to control the second fast steering mirror FSM-2 to rotate around its own x-axis and y-axis, and make the second light spot return to the second target position. A condition judgment is carried out. If the second light spot has already returned to the second target position, the beam tracking is completed; otherwise, this step is repeated.

[0082] Furthermore, the system uses FPGA for image processing and feedback control. Figure 3 is the original image of the light spot received by the CCD, Figure 3 (a) is the original image when the two light spots are separated, Figure 3 (b) is the original image when the two light spots partially overlap. The image resolution is 320×256.

[0083] Among them, the image processing process includes:

[0084] First, receive the light spot image from the CCD, and perform Gaussian filtering on the image. The Gaussian filtering process is mainly used to smooth the image and suppress noise. A two-dimensional Gaussian function is used to generate a convolution kernel, and the image is convolved. The Gaussian function is:

[0085]

[0086] where σ is the standard deviation, which controls the degree of smoothing. The kernel size is (2k + 1)×(2k + 1), and usually k = 3σ. The convolution formula is:

[0087]

[0088] Then convert the grayscale image to a binary image to segment the light spot area. Set a threshold T, and perform threshold segmentation on the filtered image I filtered as follows:

[0089]

[0090] Then perform edge detection through the Canny algorithm to extract the light spot edge. Use the Sobel operator to calculate the gradients G x and G y :

[0091]

[0092] The gradient magnitude and direction are:

[0093]

[0094] Retain the local maximum gradient value along the gradient direction θ and suppress non-maximum values. By setting high thresholds T1 and T2, the pixels are divided into strong edges (G≥T1), weak edges (T2≤G≤T1), and non-edges (G<T2), and only the weak edges connected to the strong edges are retained to obtain the edge image.

[0095] Figure 4 It is the spot edge image extracted after Canny algorithm edge detection. Figure 4 (a) is the edge image of the light spot when the two light spots are separated. Figure 4 (b) is the edge image of the light spot when the two light spots partially overlap. The generated edge image of the light spot is used as the input of the Hough circle transform.

[0096] Finally, the center of the light spot is detected from the edge image by Hough circle transform and regarded as the center of mass. The equation of the circle is: (xa) 2 +(yb) 2 =r 2 , the parameter space is (a,b,r). For each edge point (x,y), search for possible circle centers along the gradient direction θ:

[0097] a=x±rcosθ,b=y±rsinθ

[0098] Votes are accumulated for each possible (a, b, r) combination, and the peak corresponds to the detected circle. The center of the circle (a, b) detected by Hough transform is the center of mass of the light spot.

[0099] Figure 5 is the centroid image of the light spot detected by Hough circle transform, Figure 5 (a) is the centroid image of the two light spots when they are separated. Figure 5 (b) shows the centroid image of the two spots when they partially overlap. Each spot is calibrated with an independent circular outline, with its center explicitly marked by a red cross (+ sign). This coordinate point is the centroid of the spot. The larger spot in the CCD image is the first spot, and the smaller spot is the second spot. The coordinates of the centroid of the first spot are C1′, and the coordinates of the centroid of the second spot are C2′.

[0100] The feedback control process involves: first, the FPGA controls FSM-1 using a PID algorithm to return the first light spot's centroid coordinate C1' to the calibrated coordinate C1, completing the first-level control and eliminating the displacement error in the beam's pointing direction. Then, the PID algorithm controls FSM-2 to return the second light spot's centroid coordinate C2' to the calibrated coordinate C2, completing the second-level control and eliminating the angular error in the beam's pointing direction. The feedback control process ends when the coupler receives maximum optical power.

[0101] The input of the PID algorithm is the difference between the target position coordinate value and the current actual center of mass coordinate value:

[0102] e(t)=r(t)-y(t)

[0103] The output of the PID algorithm is the weighted sum of the proportional term, the integral term, and the differential term:

[0104]

[0105] K p , K i and K d are the proportional, integral and differential gain parameters respectively, u(t) is the control signal of the fast mirror, which is converted into the driving voltage value of the fast mirror through the DAC module.

[0106] In summary, the present invention proposes a beam pointing control system and a hierarchical positioning and tracking method based on a single CCD, which utilizes a single CCD to receive the image information of two light spots and feeds it back to the FPGA. The precise beam pointing control is achieved through the synergistic effect of two fast-reflecting mirrors and a hierarchical adjustment mechanism, which significantly improves the accuracy and stability of the system, while simplifying the optical path system structure, reducing system complexity, and lowering costs.

[0107] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not limiting. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present invention can be modified or replaced by equivalents without departing from the purpose and scope of the technical solutions, which should all be included in the scope of the claims of the present invention.

Claims

1. A beam pointing control system based on a single CCD, characterized by: include: a laser for emitting a laser beam; a coupler for receiving and transmitting the rectified laser beam; A fast mirror unit, comprising a first fast mirror FSM-1 and a second fast mirror FSM-2, wherein the first fast mirror FSM-1 is used to adjust the laser light path to point to the center of the mirror surface of the second fast mirror FSM-2, and the second fast mirror FSM-2 is used to adjust the laser light path to point vertically to the center of the coupler; A beam splitter unit includes a first beam splitter BS-1, a second beam splitter BS-2, and a third beam splitter BS-3. The first beam splitter BS-1 splits the light beam from the first fast mirror to the third beam splitter BS-3 and the second fast mirror FSM-2. The second beam splitter BS-2 splits the light beam from the second fast mirror to the coupler and the third beam splitter BS-3. The third beam splitter BS-3 combines the light beams from the first beam splitter and the second beam splitter. A CCD detector is used to receive the two beam spot images after being combined by the third beam splitter; A Field Programmable Gate Array (FPGA) is used to process the light spot image data collected by the CCD detector and drive the fast mirror unit to perform light beam pointing correction through a hierarchical control algorithm.

2. The single CCD-based beam pointing control system according to claim 1, characterized in that: The optical path configuration of the beam splitter unit satisfies: The first beam splitter BS-1 is arranged in the light path reflection direction of the first fast reflection mirror FSM-1; The second beam splitter BS-2 is arranged in the light path reflection direction of the second fast reflection mirror FSM-2; The third beam splitter BS-3 simultaneously receives the transmitted light from the first beam splitter and the reflected light from the second beam splitter, and directs the two beams of light toward the photosensitive surface of the CCD detector.

3. The single CCD-based beam pointing control system according to claim 1, characterized in that: The FPGA performs image processing including: Gaussian filter module, used to suppress noise in the spot image; Binarization processing module uses threshold segmentation to extract the spot area; Edge detection module, extracts the edge of the light spot based on the Canny algorithm; The center of mass calculation module detects the center of the light spot as the center of mass coordinate through Hough circle transform.

4. The single CCD-based beam pointing control system according to claim 1, characterized in that: The two light spots received by the CCD detector have distinguishable characteristics: The diameter D1 of the first light spot and the diameter D2 of the second light spot satisfy D1 / D2=1.2-1.5; The light intensity ratio of the two light spots is I1 / I2 = 1.5~2.

0.

5. The single CCD-based beam pointing control system according to claim 1, characterized in that: The reflection / transmission ratio of the beam splitter is configured as: Transmittance T of the first beam splitter BS-1 BS1 =90%, reflectivity R BS1 =10%; The reflectivity R of the second beam splitter BS-2 BS2 =95%, transmittance T BS2 =5%; The transmittance T of the third beam splitter BS-3 to the beam from the first beam splitter BS3 =85%, the reflectivity R of the beam from the second beam splitter BS3 =90%.

6. A hierarchical positioning and tracking method based on the system of any one of claims 1 to 5, characterized in that: include: The first stage of positioning: by adjusting the posture of the first fast reflection mirror FSM-1, the coordinates of the center of mass of the first light spot reach the pre-calibrated position C1, eliminating the beam pointing displacement error; Second-stage positioning: By adjusting the posture of the second fast-reflecting mirror FSM-2, the coordinates of the second light spot's centroid reach the pre-calibrated position C2, eliminating the beam pointing angle error; The first light spot is the light spot that is directly transmitted to the CCD through the first beam splitter, and the second light spot is the light spot that is reflected by the second beam splitter and then split twice to the CCD.

7. The hierarchical positioning and tracking method according to claim 6, wherein: The first level positioning stage specifically includes: Calculate the offset (Δ x1 ,Δ y1 ); The first fast mirror driving voltage (U x1 ,U y1 ), which satisfies: U x1 =K p1 ·Δx1+K i1 ·∫Δx1dt+K d1 ·d(Δx1) / dt U y1 =K p1 ·Δy1+K i1 ·∫Δy1dt+K d1 ·d(Δy1) / dt where K p1 , K i1 , K d1 They are the proportional, integral and differential coefficients of the first fast reflex mirror control respectively.

8. The hierarchical positioning and tracking method according to claim 7, wherein: The second level positioning stage specifically includes: Calculate the offset (Δ x2 ,Δ y2 ); The second fast mirror driving voltage (U x2 ,U y2 ), which satisfies: U x2 =K p2 ·Δx2+K i2 ·∫Δx2dt+K d2 ·d(Δx2) / dt U y2 =K p2 ·Δy2+K i2 ·∫Δy2dt+K d2 ·d(Δy2) / dt where K p2 , K i2 , K d2 are the proportional, integral and differential coefficients of the second fast mirror control, and K p2 >K p1 , K d2 <K d1 .

9. The hierarchical positioning and tracking method according to claim 6, characterized in that: The detection process of the Hough circle transform includes: Establish the circle equation (xa) in parameter space (a,b,r) 2 +(yb) 2 =r 2 ; Cumulative voting of the circle center coordinates (a, b) along the image gradient direction θ satisfies: a=x±rcosθ,b=y±rsinθ Where (x, y) is the edge point coordinate, and r is the preset radius search range.

10. The hierarchical positioning and tracking method according to claim 6, characterized in that: The Canny edge detection includes: Sobel operator is used to calculate the gradient amplitude Among them G x , G y are the gradient components in the horizontal and vertical directions respectively; Set the high threshold T high and low threshold T low Make edge connections, where T high =2T low , and T low Take the first 20% quantile of the image grayscale histogram.

Images