Single-ccd-based light beam pointing control system and hierarchical positioning tracking method

Abstract

This invention relates to a beam pointing control system and a hierarchical positioning and tracking method based on a single CCD, belonging to the field of space laser communication technology. It addresses the problems of complex optical paths, error accumulation, and insufficient tracking accuracy in traditional beam control systems. The technical solution includes: using a single CCD detector combined with a beam splitter unit to receive dual-spot images; eliminating displacement errors through a first fast-reflecting mirror and correcting angular errors through a second fast-reflecting mirror; and using an FPGA for spot centroid calculation and hierarchical PID control to achieve dynamic adjustment of the beam pointing. This invention simplifies the system structure through a single-detector dual-optical-path collaborative design, and the hierarchical error compensation mechanism effectively suppresses deviation accumulation, significantly improving beam pointing accuracy and tracking stability while reducing hardware costs and maintenance difficulty. It is suitable for space optical communication systems in highly dynamic environments.

Description

Technical Field

[0001] This invention belongs to the field of space laser communication technology, and relates to a beam pointing control system and a hierarchical positioning and tracking method based on a single CCD. Background Technology

[0002] Space Laser Communication (SLC) is a communication method that utilizes light beams to propagate in free space, enabling data transmission without physical media (such as optical fibers or conductive cables). Combining the advantages of microwave and fiber optic communication, SLC has become an important means of communication across multiple communication links, including air-based, space-based, and land-based systems. However, SLC faces several challenges, primarily due to its line-of-sight (LOS) transmission nature, which makes communication quality susceptible to environmental factors such as atmospheric turbulence and attenuation. High-precision beam tracking control is crucial for ensuring system performance in SLC. Since the relative position and alignment between the transmitter and receiver cannot be perfectly precise, and beam pointing can deviate due to building swaying or equipment vibration, this deviation is called "pointing error" (PE). To maintain communication stability and efficiency, beam pointing error must be effectively controlled to ensure stable beam transmission in free space. Fast Steering Mirrors (FSMs) are commonly used to adjust beam pointing accuracy. However, traditional beam pointing control systems have several problems, such as:

[0003] Limitations of single fast mirror systems: In some traditional systems, a single fast mirror is commonly used to adjust the direction of the laser beam. However, this design can only adjust the beam within a limited range and is difficult to maintain stability in complex environments, especially under high dynamic range or precision tracking requirements, where accuracy is easily affected.

[0004] Accumulation of beam pointing error: During beam transmission, due to the complexity of the optical path, mirror errors, and the influence of environmental factors (such as temperature changes and vibrations), the beam pointing deviation gradually accumulates, leading to a decrease in the signal quality of the communication system. Therefore, a high-precision control system is needed to adjust the beam pointing in real time.

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

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

[0007] In view of this, the purpose of this invention is to provide a beam pointing control system and a hierarchical positioning and tracking method based on a single CCD, aiming to solve problems 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 the FPGA. Through the synergistic effect of two fast-reflecting mirrors and a hierarchical adjustment mechanism, precise beam pointing correction is achieved, significantly improving the system's accuracy and stability. Simultaneously, it simplifies the optical path system structure, reduces system complexity, and lowers costs.

[0008] To achieve the above objectives, the present invention provides the following technical solution:

[0009] A beam pointing control system based on a single CCD includes:

[0010] A laser, used to emit a laser beam;

[0011] A coupler is used to receive and transmit the corrected laser beam;

[0012] The fast-reflecting mirror unit includes a first fast-reflecting mirror FSM-1 and a second fast-reflecting mirror FSM-2. The first fast-reflecting mirror FSM-1 is used to adjust the laser beam path to point towards the center of the mirror surface of the second fast-reflecting mirror FSM-2, and the second fast-reflecting mirror FSM-2 is used to adjust the laser beam path to point perpendicularly towards the center of the coupler.

[0013] The 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 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 beam from the second fast mirror to the coupler and the third beam splitter BS-3. The third beam splitter BS-3 combines the beams from the first beam splitter and the second beam splitter.

[0014] A CCD detector is used to receive the image of two light spots after they are combined by a third beam splitter.

[0015] The Field Programmable Gate Array (FPGA) is used to process the spot image data acquired by the CCD detector and drive the fast-reflecting mirror unit to perform 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 positioned in the optical path reflection direction of the first fast-reflecting mirror FSM-1;

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

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

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

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

[0022] The binarization module uses threshold segmentation to extract the spot region;

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

[0024] The centroid calculation module uses the Hough circle transform to detect the center of the light spot as the centroid coordinates.

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

[0026] The diameters D1 and D2 of the first and second light spots satisfy D1 / D2 = 1.2 to 1.5;

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

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

[0029] The 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 beam from the first beam splitter is obtained by the third beam splitter BS-3. BS3 =85%, reflectivity R of the beam from the second beam splitter BS3 =90%.

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

[0033] First-level positioning stage: By adjusting the attitude of the first fast-reflecting mirror FSM-1, the centroid coordinates of the first spot are brought to the pre-calibrated position C1, eliminating beam pointing displacement error;

[0034] Second-stage positioning: By adjusting the attitude of the second fast-reflecting mirror FSM-2, the centroid coordinates of the second spot are brought to the pre-calibrated position C2, eliminating 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 into beams again before being transmitted to the CCD.

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

[0037] Calculate the offset (Δ) between the current centroid coordinates C1' and the calibration coordinates C1 of the first light spot. x1 ,Δ y1 );

[0038] The first fast-reflecting mirror drive voltage (U) is generated using a PID algorithm. 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 These are the proportional, integral, and derivative coefficients for the first fast-reflecting mirror control, respectively.

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

[0043] Calculate the offset (Δ) between the current centroid coordinates C2' and the calibration coordinates C2 of the second spot. x2 ,Δ y2 );

[0044] The second fast-reflecting mirror driving voltage (U) is generated using a PID algorithm. 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 These are the proportional, integral, and derivative coefficients of the second fast-reflecting mirror control, respectively, and K... p2 >K p1 K d2 <K d1 .

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

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

[0050] Accumulated voting along the image gradient direction θ for the center coordinates (a, b) satisfies:

[0051] a = x ± rcosθ, b = y ± rsinθ

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

[0053] Furthermore, the Canny edge detection includes:

[0054] Calculating gradient magnitude using the Sobel operator Among them G x G y These are the gradient components in the horizontal and vertical directions, respectively;

[0055] Set a high threshold T high and low threshold T low Perform edge connections, where T high =2T low And T low Take the top 20 percentile values ​​of the image's grayscale histogram.

[0056] The beneficial effects of this invention are as follows: Through structural innovation of a single CCD detector and dual fast-reflecting mirrors working in tandem, combined with a hierarchical positioning and tracking method, this invention achieves multiple technological breakthroughs in beam pointing control systems. Firstly, the optical path design using a single detector and beam-splitter unit significantly simplifies the optical system architecture, reduces the number of components and assembly error sources, and lowers hardware costs and maintenance difficulty. Secondly, through a hierarchical error compensation mechanism, displacement error and angular error are decoupled. The first fast-reflecting mirror eliminates beam offset, and the second fast-reflecting mirror corrects residual angular deviation, effectively suppressing error accumulation and improving long-term operational stability. Thirdly, the FPGA-based real-time image processing and dual-PID independent control strategy balance fast response and high-precision adjustment, ensuring accurate beam pointing in dynamic environments. Fourthly, the optimized design of beam-splitter parameters and beam spot characteristics enhances the distinguishability and detection reliability of the dual beam spots, avoiding control failures caused by signal crosstalk. While maintaining the system's compactness, the overall solution addresses the pain points of traditional technologies, such as limited adjustment range, multiple error coupling, and insufficient environmental adaptability. It provides a highly reliable and low-cost pointing control solution for space laser communication, demonstrating significant technical practicality and industry promotion value.

[0057] Other advantages, objectives, and features of the invention will be set forth in part in the description which follows, and in part will be apparent to those skilled in the art from the following examination, or may be learned from practice of the invention. The objectives and other advantages of the invention can be realized and obtained through the following description. Attached Figure Description

[0058] To make the objectives, technical solutions, and advantages of the present invention clearer, the preferred embodiments of the present invention will be described in detail below with reference to the accompanying drawings, wherein:

[0059] Figure 1 This is a schematic diagram of a beam control system based on a single CCD.

[0060] Figure 2 A flowchart of beam hierarchical positioning and tracking based on a single CCD;

[0061] Figure 3 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;

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

[0063] Figure 5 Image of the centroid of the light spot detected by Hough circle transform; Figure 5 (a) is the centroid image of the two light spots when they separate. Figure 5 (b) is the centroid image of the two light spots when they partially overlap. Detailed Implementation

[0064] The following specific examples illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and various details in this specification can be modified or changed 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 representations of the basic concept of the present invention. Unless otherwise specified, the following embodiments and features can be combined with each other.

[0065] The accompanying drawings are for illustrative purposes only and are schematic diagrams, not actual pictures. They should not be construed as limiting the invention. To better illustrate the embodiments of the invention, some parts in the drawings may be omitted, enlarged, or reduced, and do not represent the actual product dimensions. It is understandable to those skilled in the art that some well-known structures and their descriptions may be omitted in the drawings.

[0066] In the accompanying drawings of the embodiments of the present invention, the same or similar reference numerals correspond to the same or similar components. In the description of the present invention, it should be understood that if terms such as "upper," "lower," "left," "right," "front," and "rear" indicate the orientation or positional relationship based on the orientation or positional relationship 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 orientation, or be constructed and operated in a specific orientation. Therefore, the terms used to describe positional relationships in the drawings are only for illustrative purposes and should not be construed as limiting the present invention. For those skilled in the art, the specific meaning of the above terms can be understood according to the specific circumstances.

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

[0068] The FPGA controller acquires the spot image of the light source beam in the CCD. Based on this spot image, it calculates the centroid coordinates of the first and second spots, obtaining the corresponding spot centroid offset as input to the PID algorithm. The PID algorithm generates the corresponding drive control signal for the fast-reflecting mirror, which is then converted into a drive voltage value for the fast-reflecting mirror via the DAC module. Based on this drive voltage value, the fast-reflecting mirror is controlled to rotate around its own axis to correct the directional 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 commands. The fast reflector unit consists of a first fast reflector FSM-1 and a second fast reflector FSM-2, which adjust the beam direction 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 serves as beacon light to detect beam deviation, and the other part serves as signal light coupled into the optical fiber for communication.

[0070] The beam control system is described in detail below:

[0071] The light beam from the source is reflected by the first fast-reflecting mirror FSM-1 and then incident on the first beam splitter BS-1. BS-1 splits the beam into two paths: transmitted light (accounting for 90%, i.e., T) BS1 =90%) is directed towards the second fast reflector FSM-2, and after being reflected by FSM-2, it enters the second beam splitter BS-2; the reflected light (accounting for 10%, i.e. 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: the reflected beam (accounting for 95%, i.e., R) BS2 =95%) of the light is incident perpendicularly to the center of the coupler; the transmitted light (accounting for 5%, i.e., T) BS2 =5%) incident on the third beam splitter BS-3.

[0073] The third beam splitter, BS-3, transmits 85% (T) of the reflected light from BS-1. BS3 =85%), reflecting 90% of 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] Because the beam generated by the second spot has a longer transmission path and passes through more optical elements, the light intensity and spot size of the second spot are smaller than those of the first spot. The FPGA can distinguish between the two spots during image processing.

[0075] Solid arrows indicate the beam path of the deflected beam, while dashed arrows indicate the corrected beam path.

[0076] After being reflected by the first fast mirror FSM-1 and the second fast mirror FSM-2, the light beam is projected through the second beam splitter BS-2 pointing coupler.

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

[0078] This example provides a graded beam positioning and tracking method, which can be used for... Figure 1 This is illustrated in a beam control system based on a single CCD. Figure 2 This is a flowchart of a beam hierarchical positioning and tracking method according to an embodiment of the present invention. The flowchart includes the following steps:

[0079] First, the CCD acquires the image information of the light spot and feeds it back to the FPGA. The FPGA performs image processing and calculates the centroid coordinates of the first and second light spots.

[0080] The FPGA utilizes the centroid offset (Δ) of the first light spot. x1 ,Δ y1 The first driving voltage value (U) of the first fast-reflecting mirror FSM-1 is calculated using a PID algorithm. x1 U y1 This controls the first fast-reflecting mirror FSM-1 to rotate around its own x-axis and y-axis, causing the first light spot to return to the first target position. At this time, the light source beam points to the center of the mirror surface of the second fast-reflecting mirror FSM-2, eliminating the displacement error of the beam direction. A conditional judgment is performed: if the first light spot has returned to the first target position, proceed to the next step; otherwise, repeat the step.

[0081] The FPGA utilizes the centroid offset (Δ) of the second light spot x2 ,Δ y2 The second driving voltage value (U) of the second fast-reflecting mirror FSM-2 is calculated using a PID algorithm. x2 U y2), thereby controlling the second fast steering mirror FSM-2 to rotate around its own x-axis and y-axis to return the second light spot to the second target position. Conditional judgment is carried out. If the second light spot has 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, controlling 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 into 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, 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 This is the edge image of the light spot extracted after edge detection using the Canny algorithm. Figure 4 (a) is an image of the edge of the two light spots when they are separated. Figure 4 (b) is the edge image of the light spot when the two light spots partially overlap. The generated light spot edge image is used as the input for the Hough circle transform.

[0096] Finally, the center of the light spot is detected from the edge image using Hough circle transform and considered as its centroid. 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] For each possible combination of (a,b,r), a cumulative vote is cast, and the peak value corresponds to the detected circle. The center (a,b) of the circle detected by the Hough transform is the centroid of the light spot.

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

[0100] The feedback control process includes: First, the FPGA controls FSM-1 using a PID algorithm to return the centroid coordinates C1′ of the first light spot to the calibration coordinates C1, completing the first stage of control and eliminating the displacement error in the beam direction; then, the FPGA controls FSM-2 using a PID algorithm to return the centroid coordinates C2′ of the second light spot to the calibration coordinates C2, completing the second stage of control and eliminating the angular error in the beam direction. The coupler receives the maximum optical power, and the feedback control process ends.

[0101] The input to the PID algorithm is the difference between the target position coordinates and the current actual centroid coordinates.

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

[0103] The output of the PID algorithm is a weighted sum of the proportional, integral, and derivative terms:

[0104]

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

[0106] In summary, the beam pointing control system and hierarchical positioning and tracking method proposed in this invention utilize a single CCD to receive image information from two light spots and feed it back to the FPGA. Through the synergistic effect of two fast-reflecting mirrors and a hierarchical adjustment mechanism, precise beam pointing control is achieved, which significantly improves the accuracy and stability of the system. At the same time, it simplifies the optical path system structure, reduces system complexity, and lowers 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 intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A beam pointing control system based on a single CCD, characterized in that: include: A laser, used to emit a laser beam; A coupler is used to receive and transmit the corrected laser beam; The fast-reflecting mirror unit includes a first fast-reflecting mirror FSM-1 and a second fast-reflecting mirror FSM-2. The first fast-reflecting mirror FSM-1 is used to adjust the laser beam path to point towards the center of the mirror surface of the second fast-reflecting mirror FSM-2, and the second fast-reflecting mirror FSM-2 is used to adjust the laser beam path to point perpendicularly towards the center of the coupler. The 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 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 beam from the second fast mirror to the coupler and the third beam splitter BS-3. The third beam splitter BS-3 combines the beams from the first beam splitter and the second beam splitter. A CCD detector is used to receive the image of two light spots after they are combined by a third beam splitter. The field-programmable gate array (FPGA) is used to process the spot image data acquired by the CCD detector and drive the fast-reflecting mirror unit to perform beam pointing correction through a hierarchical control algorithm. The optical path configuration of the beam splitter unit satisfies: The first beam splitter BS-1 is positioned in the optical path reflection direction of the first fast-reflecting mirror FSM-1; The second beam splitter BS-2 is positioned in the optical path reflection direction of the second fast-reflecting mirror FSM-2; The third beam splitter BS-3 simultaneously receives transmitted light from the first beam splitter and reflected light from the second beam splitter, and directs both beams toward the photosensitive surface of the CCD detector.

2. The beam pointing control system based on a single CCD according to claim 1, characterized in that: The FPGA performs image processing including: The Gaussian filter module is used to suppress noise in the spot image; The binarization module uses threshold segmentation to extract the spot region; The edge detection module extracts the edges of the light spot based on the Canny algorithm; The centroid calculation module uses the Hough circle transform to detect the center of the light spot as the centroid coordinates.

3. The beam pointing control system based on a single CCD according to claim 1, characterized in that: The two light spots received by the CCD detector have distinguishable characteristics: Diameter of the first light spot With the diameter of the second spot satisfy =1.2~1.5; Light intensity ratio of the two light spots =1.5~2.

0.

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

5. A hierarchical positioning and tracking method based on any one of claims 1 to 4, characterized in that: include: First-level positioning stage: By adjusting the attitude of the first fast-reflecting mirror FSM-1, the centroid coordinates of the first spot are brought to the pre-calibrated position C1, eliminating beam pointing displacement error; Second-stage positioning: By adjusting the attitude of the second fast-reflecting mirror FSM-2, the centroid coordinates of the second spot are brought to the pre-calibrated position C2, eliminating 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 into beams again before being transmitted to the CCD. The first-level positioning stage specifically includes: Calculate the current centroid coordinates of the first light spot. With calibration coordinates offset ; The first fast-reflecting mirror drive voltage is generated using a PID algorithm. It satisfies: in , , These are the proportional, integral, and derivative coefficients for the first fast-reflecting mirror control, respectively. The second-level positioning stage specifically includes: Calculate the offset between the current centroid coordinates C2' and the calibration coordinates C2 of the second light spot. ; The second fast-reflecting mirror driving voltage is generated using a PID algorithm. It satisfies: in , , These are the proportional, integral, and derivative coefficients of the second fast-reflecting mirror control, respectively. , .

6. The hierarchical positioning and tracking method according to claim 5, characterized in that: The Hough circle transform is used to detect the center of the first and second light spots as the centroid coordinates. The Hough circle transform detection process includes: In parameter space Establish the equation of a circle ; Along the image gradient direction Perform circle center coordinates The cumulative votes satisfy: in The coordinates of the edge points, r This is the preset radius search range.

7. The hierarchical positioning and tracking method according to claim 5, characterized in that: The edges of the first and second light spots are extracted based on the Canny algorithm. The extraction process of the Canny algorithm includes: Calculating gradient magnitude using the Sobel operator ,in , These are the gradient components in the horizontal and vertical directions, respectively; Set high threshold and low threshold Perform edge connectivity, where ,and Take the top 20 percentile values ​​of the image's grayscale histogram.

Images