Dynamic platform laser fast stable scanning system and method based on cascaded rotating grating

Abstract

The application belongs to the field of space optical scanning and laser control technology, and particularly relates to a moving platform laser fast stable scanning system and method based on a cascade rotating grating, which comprises a signal processing and scanning control module, a cascade rotating grating execution mechanism, a motor driving module and an inertial attitude measurement module. An equal-pitch Archimedes spiral scanning mode is adopted to generate a continuous coverage scanning track, and a high-density discretization track subdivision strategy is adopted to make each expected pointing point participate in closed-loop control. The signal processing and scanning control module realizes dynamic compensation of scanning pointing through a coordinate conversion model according to platform attitude information collected by the inertial attitude measurement module, and adopts a linear active disturbance rejection control algorithm for real-time estimation and compensation. Through the above technical solutions, the application can reduce the equivalent moment of inertia, improve the system response bandwidth, expand the maximum scanning field of view, reduce the scanning track tracking error, and improve the scanning stability under the condition of a dynamic platform.

Description

Technical Field

[0001] This invention belongs to the field of space optical scanning and laser control technology, and particularly relates to a fast and stable laser scanning system and method for a moving platform based on a cascaded rotating grating. Background Technology

[0002] Laser scanning technology, as a core means of acquiring space optical information, plays an irreplaceable and crucial role in target search, space exploration, laser communication, and lidar detection. With the continuous development of aerospace, optoelectronic detection, and space information technology, the application scenarios of laser scanning systems are constantly expanding. In particular, dynamic platform environments such as airborne, vehicle-mounted, and shipborne systems place more stringent demands on scanning technology. In these application scenarios, the system not only needs to achieve large-area, rapid scanning but also needs to maintain stable coverage of the scanning field of view under conditions of platform attitude disturbances. This directly affects the completeness of target search, the reliability of lidar detection, and the success rate of establishing laser communication links, thus becoming a core technological bottleneck restricting the performance improvement of laser scanning systems for dynamic platforms.

[0003] Traditional laser scanning systems mostly employ a two-dimensional mechanical turntable structure to achieve beam deflection. This technology achieves two-dimensional scanning functionality through a combination of azimuth and pitch axes. From a technical principle perspective, the mechanical turntable solution has significant advantages such as mature control methods and an intuitive and easy-to-understand structure, meeting the basic needs of laser scanning applications for a considerable period. However, with the continuous improvement of scanning speed and accuracy requirements, the inherent shortcomings of the mechanical turntable solution have gradually become apparent.

[0004] Due to the significant rotational inertia of the mechanical turntable, insufficient response speed is prone to occur during high-speed scanning. Specifically, when scanning commands change abruptly, the actuator cannot respond quickly due to its large inertia, resulting in the actual scan trajectory lagging behind the expected trajectory. Simultaneously, vibration during mechanical rotation significantly reduces scanning accuracy, especially in applications requiring high angular resolution, where vibration-induced errors can lead to missed or misjudged targets. When the system operates in dynamic platform environments such as airborne or shipborne systems, the platform's pitch, yaw, and roll attitude disturbances further affect the stability of the beam pointing, causing field-of-view drift and discontinuities in area coverage. In severe cases, this can even lead to missed targets, which is often unacceptable in actual combat or detection applications.

[0005] To overcome the limitations of mechanical turntable solutions in terms of response speed and size, rotating grating scanning technology has received widespread attention in recent years. Based on grating diffraction theory, rotating gratings utilize the periodic structure of the grating to induce diffraction deflection of the incident laser beam. By controlling the rotation angle of the grating, continuous deflection of the beam direction can be achieved. Compared to traditional mechanical turntable solutions, rotating grating systems offer significant advantages such as compact structure, low moment of inertia, fast response speed, and high scanning accuracy, demonstrating excellent technical adaptability in applications requiring rapid scanning. The rotating dual-grating system, as a typical implementation, achieves two-dimensional beam deflection using two coaxial rotating gratings. The relative rotation angle of the two sets of gratings controls the direction of the diffracted beam in two dimensions, thus achieving rapid scanning within a relatively small volume.

[0006] However, traditional dual-grating structures have inherent limitations in scanning range. Due to the limitation of the diffraction angle range of a single grating, when the scanning range needs to be further expanded, the system is prone to insufficient coverage in the edge regions, failing to meet the application requirements of large-area search and detection. More importantly, most existing research on rotating grating scanning technology focuses on beam deflection control under static platform conditions, with relatively little research on stable scanning under dynamic platform disturbance conditions. In the actual operation of a dynamic platform, the platform's attitude disturbance is continuous and constantly changing, making it difficult for traditional scanning control methods designed for static conditions to effectively cope with this complex operating condition.

[0007] At the control strategy level, traditional laser scanning systems commonly employ PID control to track the scanning trajectory. This method achieves tracking control of the desired trajectory through a combination of proportional, integral, and derivative components. Its advantages lie in its simple structure and mature parameter tuning methods. However, the performance of a PID controller is highly dependent on the setting of control parameters. In practical engineering applications, control parameters are usually tuned based on a specific operating point of the system. When the system's operating point changes significantly during scanning, a PID controller with fixed parameters struggles to simultaneously maintain dynamic performance across the entire field of view.

[0008] Specifically, as the scan moves from the center of the field of view to the edge, the system's dynamic characteristics change. Fixed-parameter PID controllers may experience increased tracking delay, increased overshoot, and amplified scanning field of view errors. This performance degradation is particularly pronounced under dynamic platform disturbance conditions. Rapid changes in platform attitude can continuously interfere with beam pointing, and PID controllers lack the ability to effectively suppress such time-varying disturbances, thus failing to meet the stringent requirements for rapid and stable scanning under dynamic platform conditions.

[0009] Based on the analysis of the existing technical solutions above, the core technical challenge facing dynamic platform laser scanning systems lies in how to achieve both high dynamic response speed and effective suppression of platform attitude disturbances while maintaining a large scanning field of view. Traditional mechanical turntable solutions are insufficient to meet high-speed scanning requirements due to excessive inertia, traditional rotating grating solutions are inadequate in terms of scanning range and dynamic disturbance compensation capabilities, and traditional PID control strategies lack sufficient robustness when facing time-varying operating points and continuous disturbances.

[0010] Therefore, this invention proposes a novel laser scanning system and method that can take into account a large scanning field of view, high dynamic response, and dynamic platform stability compensation capability, so as to achieve rapid, stable, and continuous scanning in dynamic environments. Summary of the Invention

[0011] The purpose of this invention is to address the technical problems existing in current dynamic platform laser scanning systems, such as limited scanning range, significant impact from dynamic disturbances, insufficient scanning stability, and slow response speed and difficulty in miniaturization of traditional mechanical turntables. This invention proposes a rapid and stable laser scanning system and method for dynamic platforms based on cascaded rotating gratings. This system can achieve wide-range, high-precision, continuous, and stable laser scanning field of view coverage under dynamic motion conditions such as airborne, vehicle-mounted, and shipborne applications, and is suitable for applications such as lidar detection, laser communication, target search, and space beam control.

[0012] To solve the above-mentioned technical problems, the present invention adopts the following technical solution: Firstly, a fast and stable laser scanning system for a moving platform based on a cascaded rotating grating is provided, including a signal processing and scanning control module, a cascaded rotating grating actuator, a motor drive module, an inertial attitude measurement module, a laser emission module, a laser receiving module, and a host computer module. The modules interact and work together through standard communication interfaces and communication protocols. The cascaded rotating grating actuator consists of four rotating gratings, including a first grating G1, a second grating G2, a third grating G3, and a fourth grating G4. The four gratings are arranged sequentially along the same optical axis, and the grating plane is set perpendicular to the optical axis. The first grating G1 and the second grating G2 constitute a first group of rotating grating modules, and the third grating G3 and the fourth grating G4 constitute a second group of rotating grating modules; the two gratings in each group are installed symmetrically in opposite directions at 180°, that is, the second grating G2 is installed with a 180° rotation relative to the first grating G1, and the fourth grating G4 is installed with a 180° rotation relative to the third grating G3.

[0013] Through the 180° reverse symmetrical mounting structure, each group of gratings forms an equivalent grating with half the effective period, thereby effectively improving the beam diffraction deflection angle and expanding the system's scanning field of view while maintaining a compact system structure. The first and second groups of rotating grating modules are each controlled by an independent drive motor, and the deflection and scanning of the laser beam in two-dimensional space is achieved by adjusting the relative rotation angle of the two groups of gratings.

[0014] The signal processing and scanning control module is used to generate a continuous coverage scanning trajectory for the target area, and ensures the accuracy of the scanning trajectory based on a preset high-density discretization trajectory subdivision strategy.

[0015] The inertial attitude measurement module is used to measure the pitch, yaw, and roll attitude information of the dynamic platform in real time. It integrates a three-axis accelerometer, a three-axis gyroscope, and a magnetometer; the sampling frequency is no less than 200Hz, and the attitude measurement accuracy is better than 0.01 degrees. After receiving the data output from the inertial attitude measurement module, the signal processing and scan control module first preprocesses the gyroscope, accelerometer, and magnetometer data, including zero-bias compensation, noise filtering, and data normalization. It then calculates the platform's attitude information in real time, obtaining the platform's roll angle φ and pitch angle. i and yaw angle ψ .

[0016] After obtaining the platform attitude angles, the signal processing and scan control module establishes the coordinate transformation relationship between the inertial coordinate system and the platform coordinate system, and constructs the corresponding attitude rotation matrix. Based on this rotation matrix, the preset scan trajectory in inertial space is transformed to the platform coordinate system in real time, thereby obtaining the actual target pointing direction under platform disturbance conditions.

[0017] Furthermore, the beam elevation angle and azimuth angle are calculated based on the converted target pointing information, and the target rotation angles corresponding to the two sets of equivalent gratings are solved using the inverse kinematic model of the cascaded rotating grating. Finally, the control module sends the calculated target rotation angles to the motor drive module to achieve platform attitude disturbance compensation and beam stabilization scanning control.

[0018] The signal processing and scanning control module establishes the coordinate transformation relationship between the inertial coordinate system and the platform coordinate system based on the inertial measurement results, performs attitude compensation and grating inverse solution calculation, obtains the target rotation angles corresponding to the two sets of rotating gratings, and generates motor drive commands. The motor drive module controls the two sets of rotating gratings to rotate continuously, so that the emitted laser beam scans stably along a predetermined trajectory.

[0019] Preferably, the signal processing and scanning control module integrates a trajectory generation unit, a coordinate transformation unit, a grating inverse decoding unit, and a control algorithm execution unit. The trajectory generation unit calculates the continuous scanning trajectory based on the geometric range of the target area, the instantaneous field of view of the detector, and the preset scanning overlap rate, and generates the continuous coverage scanning trajectory using the equal pitch Archimedean spiral scanning method. The coordinate transformation unit establishes the transformation relationship between the inertial coordinate system and the platform coordinate system, and calculates the target scanning trajectory in the inertial space to the grating line-of-view coordinate system in real time. The grating inverse kinematics unit calculates the required rotation angles of the two sets of equivalent gratings based on the direction of the target beam. The control algorithm execution unit runs an active disturbance rejection control algorithm, generates motor drive commands, and outputs them to the motor drive module.

[0020] Preferably, the trajectory generation unit generates a continuous spiral scan trajectory of the target area using a constant pitch Archimedean spiral scanning method: The expression for the Archimedes spiral in polar coordinates is: p= a • i ; in, r Polar radius, i Polar angle, a The pitch coefficient of the helix; The formula for calculating the scanning pitch is: p =(1- or )• i beam ; Where η is the scan overlap rate. i beam The instantaneous field of view of the detector.

[0021] Preferably, the signal processing and scanning control module employs a high-density discretization trajectory subdivision strategy, dividing the continuous trajectory according to the system control cycle. T s Perform equal-interval sampling to generate a dense sequence of desired pointing points, where the spatial angular displacement between adjacent desired pointing points satisfies: Δ s = v · T s ; in, v For the desired scanning angular velocity, T s For the system control period, Δ s This represents the spatial angular displacement between adjacent desired pointing points.

[0022] The discretization step size is much smaller than the scanning pitch, ensuring that the discrete trajectory can accurately describe the continuous scanning trajectory. Compared to the traditional two-point scanning method, which only performs closed-loop control on the start and end points and generates grating angle commands through open-loop interpolation in the intermediate process, this invention uses high-density trajectory subdivision to ensure that each desired pointing point participates in closed-loop control. This effectively avoids the problem of intermediate trajectory deviation caused by the mismatch of the dual grating speeds, thus improving the stability and control accuracy of the scanning trajectory.

[0023] Preferably, the coordinate transformation unit transforms the target scan vector v in inertial space. I By rotation matrix R I→B Target scan vector v converted to platform coordinates B The conversion formula is: ; The rotation matrix R I→B The pitch angle, yaw angle, and roll angle are calculated and generated from the output of the inertial attitude measurement module.

[0024] Preferably, the control algorithm execution unit adopts a linear active disturbance rejection control algorithm, which consists of three parts: a linear extended state observer, a linear state error feedback control law, and a disturbance compensation quantity. The specific process of the linear active disturbance rejection control algorithm is as follows: First, the control algorithm execution unit receives the target rotation angle command output by the grating inverse decoding unit, reads the actual grating rotation angle fed back by the encoder, and calculates the deviation between the target rotation angle and the actual rotation angle. The target rotation angle serves as the desired input of the control system, and the actual rotation angle serves as the feedback input.

[0025] The grating motor and load are equivalent to a second-order system. The system state includes the grating rotation angle, grating angular velocity, and total system disturbance. The total system disturbance includes factors such as platform attitude disturbance, motor friction, load changes, model uncertainties, and external vibrations.

[0026] The linear extended state observer estimates the grating rotation angle, grating angular velocity, and total system disturbance in real time based on the actual grating rotation angle, control input, and observation error. Its discrete form is as follows: x̂1( k +1)=x̂1( k )+ T s ·x̂2( k )– β 1· e ( k ); x̂2( k +1)=x̂2( k )+T s ·x̂3( k )– β 2. e + b 0 · u ( k ); x̂3( k +1)=x̂3( k )- T s · β 3· e ( k ); in, x̂ 1 represents the estimated grating rotation angle. x̂ 2 represents the estimated angular velocity of the grating. x̂ 3 represents the estimated total system disturbance. e ( k )=x̂1( k )- x ( k ) represents the observation error. x ( k () represents the actual grating rotation angle fed back by the encoder. T s To control the period, β1, β2, and β3 are the observer gains. b 0 represents the estimated system control gain. u ( k () represents the control input from the previous moment.

[0027] The control algorithm execution unit constructs the state error feedback control quantity based on the target turning angle command and the state estimate output by the observer: u 0 ( k )= k p ·[ r ( k )- x̂ 1( k )]- k d · x̂ 2( k ); in, r ( k () represents the target rotation angle command for the current control cycle. k p and k dThe state error feedback gain is parameterized based on the controller bandwidth. Finally, the state error feedback control quantity is compensated based on the total system disturbance estimated by the extended state observer to obtain the final control input. u ( k )= u 0( k )- x̂ 3( k ) / b 0; The motor drive module drives the rotating grating to move continuously according to the final control input, so that the actual grating rotation angle follows the target rotation angle command. Through the above process, the control system can estimate and compensate for platform disturbances, motor execution errors and model uncertainties in real time in each control cycle, thereby improving the scanning stability and disturbance rejection capability of the cascaded rotating grating under dynamic platform conditions.

[0028] Preferably, the laser emitting module includes a laser body, a driving power supply, and a collimating optical system; the laser body adopts a solid-state laser with a wavelength of 1053nm, an output power of not less than 10W, and a beam quality factor M. 2 The laser beam output is less than 1.5 mrad; the collimating optical system collimates the laser beam into a parallel beam with a diameter of 50 mm and a divergence angle of less than 0.5 mrad; the laser receiving module includes a receiving optical system and a photodetector. The receiving optical system adopts a transmission optical structure with an effective aperture of 80 mm, a field of view of 6 degrees, and a focal length of 200 mm; the photodetector uses a silicon photodiode array with 512×512 pixels and a single pixel size of 15 μm×15 μm; the motor drive module uses a permanent magnet DC torque motor with a rated torque of 5 N•m, a peak torque of up to 15 N•m, and a rotor inertia of 0.01 kg•m. 2 The motor shaft is equipped with a photoelectric angle encoder with an angle resolution of not less than 0.001 degrees and the system control cycle is set to 1ms.

[0029] Secondly, a method for rapid laser stabilization scanning of a moving platform based on a cascaded rotating grating is provided. This method is implemented using a rapid laser stabilization scanning system for a moving platform based on a cascaded rotating grating and includes the following steps: Step 1: Based on dual GPS information and the platform's current attitude, complete the initial pointing to the target area; Step 2: Generate a continuous coverage scan trajectory based on the target area range, the detector's instantaneous field of view, and the scan overlap rate; Step 3: The signal processing and scanning control module outputs the target pointing information corresponding to the scanning trajectory in real time according to the control cycle; Step 4: The inertial attitude measurement module acquires the platform's pitch, yaw, and roll attitude information in real time and performs dynamic compensation for the scanning direction; Step 5: Calculate the target rotation angle of the two sets of rotating gratings based on the compensated target direction, and generate motor drive commands; Step 6: Control the continuous motion of the cascaded rotating grating to achieve laser-stabilized scanning under dynamic platform conditions; Step 7: Receive the target beacon beam and determine the target acquisition status. After completing target acquisition, switch to stable tracking mode.

[0030] The beneficial effects of this invention include: First, by replacing the traditional large-inertia mechanical turntable with a coaxial rotating grating structure, the equivalent rotational inertia of the rotating parts is reduced, which can effectively improve the dynamic response speed and scanning stability of the system, and the system response bandwidth is improved compared with the traditional mechanical turntable.

[0031] Second, by adopting a cascaded rotating grating structure, the equivalent grating period is reduced without changing the grating period and the system's degrees of freedom, thereby expanding the system's maximum scanning field of view and effectively solving the problem of limited scanning field of view in traditional dual-grating structures.

[0032] Third, dynamic platform attitude compensation is performed. The platform attitude information is acquired in real time through the inertial attitude measurement module, and the inertial space scanning trajectory is calculated to the platform coordinate system using the coordinate transformation model. This achieves real-time stable compensation of the scanning field of view under platform disturbance conditions, resulting in higher accuracy of attitude disturbance compensation.

[0033] Fourth, a high-density discretization trajectory subdivision strategy is adopted to discretize the continuous scanning trajectory into a dense sequence of desired pointing points. The angular displacement between adjacent pointing points is much smaller than the scanning pitch, so that each pointing point participates in closed-loop control. This fundamentally avoids the deviation of the intermediate trajectory caused by the mismatch of the grating speed in the traditional two-point scanning, and the scanning trajectory tracking error is effectively reduced compared with the traditional method.

[0034] Fifth, the active disturbance rejection control method is adopted to realize the real-time observation and compensation of the total disturbance of the system. The signal processing and scanning control module estimates the platform vibration disturbance, motor execution error and model uncertainty online through the linear extended state observer, and superimposes the disturbance estimate into the control input, which effectively improves the system's disturbance rejection capability. The scanning stability under dynamic platform conditions is effectively improved compared with traditional PID control. Attached Figure Description

[0035] Figure 1 This is a schematic diagram of the architecture of the dynamic platform laser rapid stabilization scanning system based on cascaded rotating gratings of the present invention.

[0036] Figure 2This is a schematic diagram of the beam deflection principle of the cascaded rotating grating actuator of the present invention.

[0037] Figure 3 This is a schematic diagram of the cascaded rotating grating stable scanning experimental system of the present invention. Detailed Implementation

[0038] The following is in conjunction with the appendix Figure 1~Figure 3 The present invention will be further described in detail below: Example 1 See appendix Figure 1 As shown, the dynamic platform laser rapid stabilization scanning system based on cascaded rotating gratings includes a signal processing and scanning control module, a cascaded rotating grating actuator, a motor drive module, an inertial attitude measurement module, a laser emission module, a laser receiving module, and a host computer module. The modules interact and work collaboratively with each other through standard communication interfaces and communication protocols.

[0039] The cascaded rotating grating actuator consists of four rotating gratings: a first grating G1, a second grating G2, a third grating G3, and a fourth grating G4. These four gratings are arranged sequentially along the same optical axis, with the grating planes perpendicular to the optical axis. The first grating G1 and the second grating G2 form a first group of rotating grating modules, and the third grating G3 and the fourth grating G4 form a second group of rotating grating modules. Within each group, two gratings are installed symmetrically in opposite directions at 180° intervals; that is, the second grating G2 is rotated 180° relative to the first grating G1, and the fourth grating G4 is rotated 180° relative to the third grating G3.

[0040] Because the polarization rotation of circularly polarized light is reversed after passing through a polarization grating, the diffraction deflection components of adjacent gratings are superimposed in the same direction in space, thus forming an equivalent half-period structure. According to the grating diffraction equation sin... i =λ / Λ; in, i λ is the deflection angle, λ is the wavelength of light, and Λ is the grating period; this structure can increase the beam deflection angle and realize the expansion of the scanning field of view.

[0041] The axial mounting distance between two gratings in the same group should be as small as possible to reduce lateral offset and adjustment errors during beam propagation between the two gratings, preferably 1–5 mm. The axial mounting distance between the first and second rotating grating modules should be minimized while meeting the space requirements for the drive motor, bearing support, and mechanical assembly. This reduces lateral displacement of the beam during free propagation after the first grating is deflected, minimizes optical axis deviation and accumulation of adjustment errors, and prevents beam cutoff at the second grating during large-angle scanning, thereby improving the accuracy and scanning stability of the beam deflection model. The preferred spacing between the two rotating grating modules is 10 mm–50 mm.

[0042] Through the 180° reverse symmetrical mounting structure, each group of gratings forms an equivalent grating with half the effective period, thereby effectively improving the beam diffraction deflection angle and expanding the system's scanning field of view while maintaining a compact system structure. The first and second groups of rotating grating modules are each controlled by an independent drive motor, and the deflection and scanning of the laser beam in two-dimensional space is achieved by adjusting the relative rotation angle of the two groups of gratings.

[0043] The signal processing and scanning control module is used to generate a continuous coverage scanning trajectory for the target area, and ensures the accuracy of the scanning trajectory based on a preset high-density discretization trajectory subdivision strategy.

[0044] The inertial attitude measurement module is used to measure the pitch, yaw, and roll attitude information of the dynamic platform in real time. It integrates a three-axis accelerometer, a three-axis gyroscope, and a magnetometer; the sampling frequency is no less than 200Hz, and the attitude measurement accuracy is better than 0.01 degrees. The signal processing and scanning control module establishes the coordinate transformation relationship between the inertial coordinate system and the platform coordinate system based on the inertial measurement results, performs attitude compensation and inverse grating calculations to obtain the target rotation angles corresponding to the two sets of rotating gratings, and generates motor drive commands. The motor drive module controls the two sets of rotating gratings to rotate continuously, ensuring that the emitted laser beam scans stably along a predetermined trajectory.

[0045] The system works as follows: The laser emission module outputs a collimated laser beam, which is incident on the cascaded rotating grating actuator along the system's optical axis. The four rotating gratings are coaxially cascaded, as shown below. Figure 2 As shown, G1 and G2 constitute the first set of rotating grating modules, and G3 and G4 constitute the second set of rotating grating modules. The two sets of gratings are driven to rotate continuously by independent motors. By changing the relative angular positions of the two equivalent gratings, the laser beam can be rapidly deflected in two-dimensional space.

[0046] During the system initialization phase, the signal processing and scanning control module first completes the initial pointing of the target area based on the dual GPS information and the platform's current attitude information, so that the center of the scanning field of view is quickly aligned with the vicinity of the target area, thereby reducing the invalid search time and improving the scanning efficiency.

[0047] After initial pointing, the system enters the area coverage scanning phase. The signal processing and scanning control module generates a continuous coverage scanning trajectory based on the target area size, the detector's instantaneous field of view, and a preset scanning overlap rate. This embodiment employs a constant-pitch Archimedean spiral trajectory, allowing the scanning field of view to continuously expand outward from the center, achieving uninterrupted coverage of the target area. By setting a certain scanning overlap amount, the probability of missed scans caused by dynamic disturbances and pointing errors can be effectively reduced.

[0048] To ensure the continuity and smoothness of the scanning trajectory during high-speed motion, the system employs a trajectory discrete output method based on control cycles. The signal processing and scanning control module updates the continuous scanning trajectory in real time at fixed time intervals, outputting the target pointing angle corresponding to the current moment within each control cycle, thus forming a continuously changing desired scanning command. Compared to the traditional method of only controlling the start and end points of the trajectory, this method can effectively reduce trajectory distortion caused by inconsistent motor speeds during the scanning process.

[0049] Meanwhile, the inertial attitude measurement module measures the platform's pitch, yaw, and roll angles in real time and transmits the attitude information to the signal processing and scan control module. Based on the real-time attitude data, the signal processing and scan control module dynamically corrects the target scanning direction, transforming the target scanning trajectory in inertial space to the platform coordinate system. This achieves scan stability compensation under platform disturbance conditions, ensuring that the scanning field of view always covers the target area.

[0050] After obtaining the compensated target orientation, the signal processing and scanning control module further calculates the target rotation angle corresponding to the two sets of rotating gratings and generates motor drive commands. The motor drive module controls the two sets of rotating gratings to rotate continuously, so that the emitted laser beam scans stably along a predetermined trajectory.

[0051] When the system enters the target acquisition phase, the beacon laser installed at the target end emits a target beam towards the system. After the target beam is focused by the receiving optical system, the photodetector outputs a target deviation signal. The signal processing and scanning control module determines whether the target has entered the current scanning field of view based on this error signal. Once the target is successfully acquired, the system can switch from area coverage scanning mode to stable tracking mode, thereby establishing a stable laser communication link or target tracking link.

[0052] To improve disturbance rejection performance in dynamic environments, this implementation employs a linear active disturbance rejection control algorithm to control the rotating grating actuator. The controller utilizes an extended state observer to estimate the total system disturbance in real time and performs online compensation for platform vibration, motor disturbance, and model uncertainties to improve the system's dynamic response speed and scanning stability.

[0053] In another embodiment of this invention, the signal processing and scanning control module integrates a trajectory generation unit, a coordinate transformation unit, a grating inverse decoding unit, and a control algorithm execution unit. The trajectory generation unit calculates the continuous scanning trajectory based on the geometric range of the target area, the instantaneous field of view of the detector, and the preset scanning overlap rate, and generates the continuous coverage scanning trajectory using the equal pitch Archimedean spiral scanning method. The trajectory generation unit generates a continuous spiral scanning trajectory for the target area using a constant pitch Archimedean spiral scanning method. The expression for the Archimedes spiral in polar coordinates is: p= a • i ; in, r Polar radius, i Polar angle, a The pitch coefficient of the helix; Scanning pitch p With the helix pitch coefficient a The relationship is: p =2 πa ; The formula for calculating the scanning pitch is: p =(1- or )• i beam ; Where η is the scan overlap rate. i beam The instantaneous field of view of the detector.

[0054] The scanning overlap rate is defined as the proportion of overlap between adjacent scanning fields of view in the radial direction. When the detector's instantaneous field of view angle is... i beam At that time, the intervals between adjacent scan trajectories are preserved. or · i beam If the overlapping region is not covered, then the scanning pitch is the remaining non-overlapping portion, i.e.: p=θ beam -eth beam =(1- η ) ibeam ; By adjusting the scan overlap rate or It can balance scanning time and coverage integrity, avoiding missed scans caused by platform disturbances or pointing errors.

[0055] The coordinate transformation unit establishes the transformation relationship between the inertial coordinate system and the platform coordinate system, and calculates the target scanning trajectory in the inertial space to the grating line-of-view coordinate system in real time. The coordinate transformation unit transforms the target scan vector v in inertial space. I By rotation matrix R I→B Target scan vector v converted to platform coordinates B The conversion formula is: ; The rotation matrix R I→B The pitch, yaw, and roll angles output by the inertial attitude measurement module are used to calculate and generate the following: First, establish an inertial coordinate system. and platform coordinate system The inertial coordinate system is fixed to the geographic reference system, while the platform coordinate system is fixedly connected to the cascaded rotating grating system. The inertial attitude measurement module outputs the platform's roll angle in real time. ϕ Pitch angle i and yaw angle ψ .

[0056] in: Roll: ; Looking up and down: ; yaw: ; ; The target scanning direction vector in the inertial coordinate system is represented as: ; in, α The azimuth angle in the inertial frame. β The pitch angle is given in the inertial frame. Then, the target scanning direction vector in the platform coordinate system is obtained through coordinate transformation. .

[0057] Through the above coordinate transformation, the target scanning trajectory in inertial space is calculated in real time to the grating line-of-sight coordinate system, realizing scanning pointing compensation under dynamic platform conditions, thereby ensuring that the scanning field of view can still stably cover the target area under platform motion conditions.

[0058] The grating inverse kinematics unit calculates the required rotation angles of the two sets of equivalent gratings based on the direction of the target beam. The control algorithm execution unit runs an active disturbance rejection control algorithm, generates motor drive commands, and outputs them to the motor drive module.

[0059] The control algorithm execution unit adopts a linear active disturbance rejection control algorithm, which consists of three parts: a linear extended state observer, a linear state error feedback control law, and a disturbance compensation quantity. The observation equation of the linear extended state observer is: x̂1( k +1)=x̂1( k )+ T s ·x̂2(k)– β 1· e ; x̂2( k +1)=x̂2( k )+ T s ·x̂3(k)– β 2· e + b 0 · u ( k ); x̂3( k +1)=x̂3( k )- T s · β 3· e ; in, x̂ 1 represents the system state estimate. x̂ 2 represents the estimated value of the system state derivative. x̂ 3 represents the estimated total system disturbance. e β1, β2, and β3 are the state observation error and the observer gain coefficients, respectively. b 0 represents the nominal value of the control gain. u ( k ) is the control input; The mathematical expression for the linear state error feedback control law is: u ( k )= k p ·( r - x̂ 1) - k d · x̂ 2; in, k p This is the proportional gain coefficient. k d The differential gain coefficient, r This represents the desired state of the system. The disturbance compensation amount is generated by adjusting the gain of the total system disturbance x̂3 estimated in real time by the linear extended state observer and then superimposed on the control input.

[0060] The specific compensation amount is x̂3 / b 0 This compensation amount is directly added to the control quantity output by the state error feedback control law to form the final control command. u ( k The output is sent to the motor drive module.

[0061] Through the aforementioned control structure, the controller can estimate the total system disturbance in real time and dynamically compensate for platform attitude disturbances, motor execution errors, and model uncertainties, achieving stable scan control without relying on a high-precision mathematical model. The controller's discrete state update frequency is set to 1kHz, consistent with the system control cycle.

[0062] The host computer module is responsible for connecting to the human-machine interface, enabling the configuration of scanning task parameters, monitoring of the scanning process, and post-processing and storage of scanning data. This module uses an industrial-grade embedded computer, equipped with an Intel Core i7 processor, 16GB of memory, and a 512GB solid-state drive. A real-time operating system is used to ensure deterministic task scheduling.

[0063] The host computer module and the signal processing and scanning control module are connected via Gigabit Ethernet, using a custom binary format for communication. Scanning task parameters, including target area range, scan overlap rate, scan time, and laser power, are configured by the host computer module and then transmitted to the signal processing and scanning control module for execution. Scanning process monitoring data, including the current scan trajectory, platform attitude, and scan progress, are displayed in real time on the human-machine interface.

[0064] In this embodiment, the signal processing and scanning control module employs a high-density discretization trajectory subdivision strategy, dividing the continuous trajectory according to the system control cycle. T s Perform equal-interval sampling to generate a dense sequence of desired pointing points, where the spatial angular displacement between adjacent desired pointing points satisfies: Δ s = v ·T s ; in, v For the desired scanning angular velocity, T s For the system control period, Δ s This represents the spatial angular displacement between adjacent desired pointing points.

[0065] The discretization step size is much smaller than the scanning pitch, ensuring that the discrete trajectory can accurately describe the continuous scanning trajectory. Each desired pointing point is transformed by coordinates and inversely solved by the grating, serving as a closed-loop command input to the control system. Compared with the traditional two-point scanning method, which only performs closed-loop control on the start and end points and generates grating rotation commands through open-loop interpolation in the intermediate process, this invention uses high-density trajectory subdivision to ensure that each desired pointing point participates in closed-loop control. This effectively avoids the problem of intermediate trajectory deviation caused by the mismatch of the rotation speeds of the two sets of gratings, significantly improving the stability and control accuracy of the scanning trajectory.

[0066] Example 2 Based on Example 1, the laser emission module includes a laser body, a driving power supply, and a collimating optical system; the laser body adopts a solid-state laser with a wavelength of 1053nm, an output power of not less than 10W, and a beam quality factor M. 2 Less than 1.5; the collimating optical system collimates the laser output beam into a parallel beam, with a collimated beam diameter of 50 mm and a divergence angle of less than 0.5 mrad.

[0067] The laser receiving module includes a receiving optical system and a photodetector. The receiving optical system adopts a transmission optical structure with an effective aperture of 80mm, a field of view of 6 degrees, and a focal length of 200mm. The photodetector uses a silicon photodiode array with 512×512 pixels and a single pixel size of 15μm×15μm. The motor drive module uses a permanent magnet DC torque motor with a rated torque of 5N•m and a peak torque of up to 15N•m. The motor rotor inertia is 0.01kg•m. 2 The motor shaft is equipped with a photoelectric angle encoder with an angle resolution of not less than 0.001 degrees and the system control cycle is set to 1ms.

[0068] A method for rapid laser stabilization scanning of a moving platform based on a cascaded rotating grating is implemented using a rapid laser stabilization scanning system for a moving platform based on a cascaded rotating grating, and includes the following steps: Step 1: Establish a mathematical model for beam deflection based on the diffraction characteristics of a cascaded rotating grating, and establish an analytical relationship between the target direction and the grating rotation angle. The grating diffraction deflection formula is: sin( i m ) = sin( ii ) + m • l / d in i m For the first m First-order diffraction angle, i i Angle of incidence l The wavelength of the laser. d The grating period is 6528nm. The grating period used in this invention is 6528nm. By combining two sets of gratings installed symmetrically in opposite directions at 180°, an equivalent grating with an equivalent period of 3264nm is formed, thereby expanding the maximum diffraction deflection angle to about twice the original value.

[0069] Step 2: Generate a continuous coverage scan trajectory based on the target area. The scanning parameters are determined based on the geometric dimensions of the target area, the instantaneous field of view of the detector, and the preset scan overlap rate. A continuous scan trajectory is then generated using a constant pitch Archimedean spiral scanning method.

[0070] Step 3: Employing a high-density discretization trajectory subdivision strategy, the continuous scan trajectory is sampled at equal intervals according to the control cycle to generate a dense sequence of desired pointing points. The spatial angular displacement between adjacent desired pointing points satisfies Δ s = v•T s ;in, v For the desired scanning angular velocity, T s For the system control period, Δ s This represents the spatial angular displacement between adjacent desired pointing points.

[0071] Step 4: Utilize the inertial attitude measurement module to acquire the dynamic platform's pitch, yaw, and roll angle attitude information in real time. Transform the inertial space scan trajectory to the grating line-of-sight coordinate system using a coordinate transformation model. The coordinate transformation formula is as follows: .

[0072] Step 5: Solve for the rotation angles of the two sets of equivalent gratings using the inverse grating model. The inverse grating model calculates the required relative rotation angle difference between the two sets of gratings based on the deflection direction of the target beam, and the drive motor controls the grating actuator to move continuously according to this angle command.

[0073] Step Six: The linear active disturbance rejection control algorithm is used to drive the grating actuator. The controller estimates the total system disturbance in real time through a linear extended state observer and adds the disturbance estimate to the control input to achieve dynamic compensation for platform attitude disturbances, motor execution errors, and model uncertainties.

[0074] Step 7: Through the above process, continuous and stable coverage of the target area by the scanning field of view is achieved under dynamic platform disturbance conditions. During the scanning process, the laser receiving module continuously detects the target beacon beam. When the target spot is detected to enter the receiving field of view, the system determines that the target has been captured and can switch to the stable tracking mode.

[0075] Example 3 Based on Example 1 or Example 2, build as follows Figure 3 The cascaded rotating grating stable scanning experimental system shown is mainly composed of a laser source, a beam expander module, a cascaded rotating grating module, an inertial measurement unit (IMU), a signal processing and scanning control module, and a beam detection device. The laser operates at a wavelength of 1053 nm and, after being expanded by the beam expander module, is incident on the cascaded rotating grating module to achieve beam deflection and scanning.

[0076] The cascaded rotating grating module consists of four gratings with a grating period of 6528nm and an effective aperture of 50mm. The four gratings are divided into two independent control modules, with two gratings in each group arranged symmetrically in opposite directions at 180° to achieve a halved equivalent period and expand the system's scanning field of view.

[0077] The signal processing and scan control module uses an STM32 embedded platform to implement trajectory planning, coordinate transformation, inverse kinematics calculation, and active disturbance rejection control algorithms. The actuator is driven by a permanent magnet DC torque motor with an encoder angle resolution of 0.001° and a system control cycle of 1ms. The inertial measurement unit (IMU) measures the platform's attitude information in real time and sends the measurement results to the controller for platform disturbance compensation and scan stabilization control.

[0078] The scanning area is covered by an Archimedean spiral trajectory with equal pitch. The scanning radius is set to 10°, the detector field of view is 3°, the scanning overlap rate is set to 20%, and the corresponding scanning pitch is 2.4°. The controller discretizes the scanning trajectory according to a fixed control cycle, outputting a small angle increment in each control cycle to achieve continuous and smooth scanning.

[0079] To verify the system's stable scanning capability under dynamic platform conditions, the laser source, beam expander module, cascaded rotating grating module, IMU, and controller were mounted as a whole on a six-degree-of-freedom swing table. The swing table was used to simulate platform attitude disturbances, with a pitch axis disturbance amplitude of 5° and a frequency of 0.2Hz, a yaw axis disturbance amplitude of 1.5° and a frequency of 0.2Hz, and a roll axis disturbance amplitude of 3° and a frequency of 0.1Hz, plus random noise disturbances.

[0080] During the experiment, the IMU measures the platform's attitude changes in real time. The controller corrects the rotation angles of the two sets of gratings in real time based on the measured attitude disturbances, achieving dynamic and stable scanning. The scanned laser beam is imaged on the far-field target surface and then acquired by an infrared camera. The image of the light spot is transmitted to the host computer through the imaging lens. The host computer displays the scanning trajectory in real time and analyzes and evaluates the scanning error and stable scanning performance.

Claims

1. A rapid and stable laser scanning system for a moving platform based on a cascaded rotating grating, characterized in that, It includes a signal processing and scanning control module, a cascaded rotating grating actuator, a motor drive module, and an inertial attitude measurement module. The modules interact and work together through standard communication interfaces and protocols. The cascaded rotating grating actuator consists of four rotating gratings, including a first grating G1, a second grating G2, a third grating G3, and a fourth grating G4. The four gratings are arranged sequentially along the same optical axis, with the grating planes perpendicular to the optical axis. The first grating G1 and the second grating G2 form a first group of rotating grating modules, and the third grating G3 and the fourth grating G4 form a second group of rotating grating modules. Within each group, two gratings are installed in a 180° reverse symmetrical arrangement. This 180° reverse symmetrical arrangement structure causes the diffraction deflection components of adjacent gratings to be superimposed in the same direction in space, forming an equivalent grating with half the effective period. The first and second sets of rotating grating modules are each controlled by an independent drive motor. The deflection and scanning of the laser beam in two-dimensional space is achieved by adjusting the relative rotation angle of the two sets of gratings. The signal processing and scanning control module is used to generate a continuous coverage scanning trajectory for the target area, and ensures the accuracy of the scanning trajectory based on a preset high-density discretization trajectory subdivision strategy. The inertial attitude measurement module is used to measure the pitch, yaw, and roll attitude information of the dynamic platform in real time. The signal processing and scanning control module also establishes the coordinate transformation relationship between the inertial coordinate system and the platform coordinate system based on the inertial measurement results, performs attitude compensation and grating inverse calculation, obtains the target rotation angles corresponding to the two sets of rotating gratings, and generates motor drive commands. The motor drive module controls the two sets of rotating gratings to rotate continuously, so that the emitted laser beam can scan stably along a predetermined trajectory; The signal processing and scanning control module integrates a trajectory generation unit, a coordinate transformation unit, a grating inverse decoding unit, and a control algorithm execution unit. The trajectory generation unit calculates the continuous scanning trajectory based on the geometric range of the target area, the instantaneous field of view of the detector, and the preset scanning overlap rate, and generates the continuous coverage scanning trajectory using the equal pitch Archimedean spiral scanning method. The coordinate transformation unit establishes the transformation relationship between the inertial coordinate system and the platform coordinate system, and calculates the target scanning trajectory in the inertial space to the grating line-of-view coordinate system in real time. The grating inverse kinematics unit calculates the required rotation angles of the two sets of equivalent gratings based on the direction of the target beam. The control algorithm execution unit runs an active disturbance rejection control algorithm, generates motor drive commands, and outputs them to the motor drive module. The control algorithm execution unit adopts a linear active disturbance rejection control algorithm, which includes three parts: a linear extended state observer, a linear state error feedback control law, and a disturbance compensation quantity. The specific process of the linear active disturbance rejection control algorithm is as follows: The control algorithm execution unit receives the target rotation angle command output by the grating inverse decoding unit, reads the actual grating rotation angle fed back by the encoder, and calculates the deviation between the target rotation angle and the actual rotation angle; the target rotation angle serves as the desired input of the control system, and the actual rotation angle serves as the feedback input. The grating motor and load are equivalent to a second-order system, and the system states include the grating rotation angle, the grating angular velocity, and the total system disturbance. The linear extended state observer estimates the grating rotation angle, grating angular velocity, and total system disturbance in real time based on the actual grating rotation angle, control input, and observation error. Its discrete form is as follows: x̂1( k +1)=x̂1( k )+ T s ·x̂2( k )– β 1· e ( k ); x̂2( k +1)=x̂2( k )+ T s ·x̂3( k )– β 2· e + b 0 · u ( k ); x̂3( k +1)=x̂3( k )- T s · β 3· e ( k ); in, x̂ 1 represents the estimated grating rotation angle. x̂ 2 represents the estimated angular velocity of the grating. x̂ 3 represents the estimated total system disturbance. e ( k )= x̂ 1( k )- x ( k ) represents the observation error. x ( k () represents the actual grating rotation angle fed back by the encoder. T s To control the period, β1, β2, and β3 are the observer gains. b 0 represents the estimated system control gain. u ( k () represents the control input from the previous moment; The control algorithm execution unit constructs the state error feedback control quantity based on the target turning angle command and the state estimate output by the observer: u 0 ( k )= k p ·[ r ( k )- x̂ 1( k )]- k d · x̂ 2( k )； in, r ( k () represents the target rotation angle command for the current control cycle. k p and k d The state error feedback gain is parameterized based on the controller bandwidth. Based on the total system disturbance estimated by the extended state observer, the state error feedback control quantity is compensated to obtain the final control input: u ( k )= u 0( k )- x̂ 3( k ) / b 0； in, u ( k () is the final control input; The motor drive module drives the rotating grating to move continuously according to the final control input, so that the actual grating rotation angle follows the target rotation angle command.

2. The laser rapid stabilization scanning system for a moving platform based on a cascaded rotating grating according to claim 1, characterized in that, The trajectory generation unit generates a continuous spiral scanning trajectory for the target area using a constant pitch Archimedean spiral scanning method. The expression for the Archimedes spiral in polar coordinates is: ρ= a • θ ； in, ρ Polar radius, θ Polar angle, a The pitch coefficient of the helix; Scanning pitch p With the helix pitch coefficient a The relationship is: p =2 πa ； The formula for calculating the scanning pitch is: p =(1- η )• θ beam ； Where η is the scan overlap rate. θ beam The instantaneous field of view of the detector.

3. The laser rapid stabilization scanning system for a moving platform based on a cascaded rotating grating according to claim 1, characterized in that, The signal processing and scanning control module employs a high-density discretization trajectory subdivision strategy, dividing the continuous trajectory according to the system control cycle. T s Perform equal-interval sampling to generate a dense sequence of desired pointing points, where the spatial angular displacement between adjacent desired pointing points satisfies: D s = v · T s ; in, v For the desired scanning angular velocity, T s For the system control period, Δ s This represents the spatial angular displacement between adjacent desired pointing points.

4. The laser rapid stabilization scanning system for a moving platform based on a cascaded rotating grating according to claim 1, characterized in that, The coordinate transformation unit transforms the target scan vector v in inertial space. I By rotation matrix R I→B Target scan vector v converted to platform coordinates B The conversion formula is: ； The rotation matrix R I→B The pitch angle, yaw angle, and roll angle are calculated and generated from the output of the inertial attitude measurement module.

5. The laser rapid stabilization scanning system for a moving platform based on a cascaded rotating grating according to claim 1, characterized in that, It also includes a laser emitting module and a laser receiving module: The laser emitting module includes a laser body, a driving power supply, and a collimating optical system. The laser body is a solid-state laser; The collimating optical system collimates the laser output beam into a parallel beam; The laser receiving module includes a receiving optical system and a photodetector. The receiving optical system adopts a transmission optical structure; the photodetector adopts a silicon photodiode array. The motor drive module uses a permanent magnet DC torque motor; A photoelectric angle encoder is installed on the end of the motor shaft.

6. A method for rapid and stable laser scanning of a moving platform based on a cascaded rotating grating, implemented using the rapid and stable laser scanning system for a moving platform based on a cascaded rotating grating as described in any one of claims 1-5, characterized in that... Includes the following steps: Step 1: Based on dual GPS information and the platform's current attitude, complete the initial pointing to the target area; Step 2: Generate a continuous coverage scan trajectory based on the target area range, the detector's instantaneous field of view, and the scan overlap rate; Step 3: The signal processing and scanning control module outputs the target pointing information corresponding to the scanning trajectory in real time according to the control cycle; Step 4: The inertial attitude measurement module acquires the platform's pitch, yaw, and roll attitude information in real time and performs dynamic compensation for the scanning direction; Step 5: Calculate the target rotation angle of the two sets of rotating gratings based on the compensated target direction, and generate motor drive commands; Step 6: Control the continuous motion of the cascaded rotating grating to achieve laser-stabilized scanning under dynamic platform conditions; Step 7: Receive the target beacon beam and determine the target acquisition status. After completing target acquisition, switch to stable tracking mode.

Images