A high-precision unmanned aerial vehicle three-axis normal installation fresnel spherical mirror holder system

Abstract

The application discloses a high-precision unmanned aerial vehicle three-axis normal installation Fresnel spherical mirror holder system, which comprises a fixing and damping unit, a three-axis servo driving unit and a support frame unit.The fixing and damping unit is rigidly fixed on the top platform of the unmanned aerial vehicle body and provides damping function.The three-axis servo driving unit realizes the yaw axis, the roll axis and the pitch axis of the Fresnel spherical mirror load to rotate omnidirectionally and the decoupling control of attitude stability augmentation.The rotation axes of the three axes are perpendicular to each other and converge at the optical center of the load.The support frame unit bears and fixes the Fresnel spherical mirror load and inhibits the vibration amplification effect through the topologically optimized hollow truss structure.The integrated control unit collects the state data of the holder system and the unmanned aerial vehicle, calculates the target control quantity of the sunlight directional reflection, outputs the control signal to the three-axis servo driving unit and realizes the high-precision attitude control of the Fresnel spherical mirror and the sunlight directional reflection.The system provides core technical support for the stereoscopic monitoring of the unmanned aerial vehicle constellation networking.

Description

Technical Field

[0001] This invention belongs to the field of UAV optical remote sensing technology, specifically relating to a high-precision UAV three-axis upright Fresnel spherical reflector gimbal system. Background Technology

[0002] In recent years, high-precision, high-spatial-resolution monitoring of carbon pollutants in industrial emission zones and wide-area environments has become strategically crucial. Unmanned aerial vehicle (UAV) remote sensing, with its advantages of high mobility, wide coverage, and flexible deployment, has become a core tool for monitoring carbon pollutants. However, traditional passive UAV spectral remote sensing relies on atmospheric scattered light as its observation source, which is weak, easily affected by aerosols and weather, and struggles to capture the weak absorption characteristics of trace carbon pollutants, resulting in extremely low spectral signal-to-noise ratios that severely limit the accuracy of gas inversion. Therefore, introducing high-flux, highly stable direct sunlight as the observation source is key to overcoming the bottlenecks of passive UAV remote sensing technology.

[0003] To address the aforementioned issues, patent application CN118914076A proposed a detection scheme involving a ground-mounted reflector and a UAV-mounted spectrometer. This scheme uses a ground-based reflector to reflect direct sunlight onto the UAV payload in the air. However, in actual UAV operations, the ground-based reflector is fixed in its deployment and cannot be dynamically adjusted to follow the UAV's operating area. This makes it difficult to continuously provide a stable high-bearing-flux input to the moving payload, limiting the signal enhancement effect. Furthermore, the ground-based device lacks deployment flexibility, resulting in insufficient system detection efficiency and inversion accuracy, and making it difficult to achieve a significant breakthrough in signal-to-noise ratio.

[0004] Therefore, to fundamentally address the core bottlenecks of insufficient light flux and low signal-to-noise ratio in traditional UAV passive remote sensing, a high-precision UAV three-axis Fresnel spherical mirror gimbal system is needed. This system would fix the receiver spectrometer on the ground for upward observation, while the Fresnel spherical mirror would be carried aboard the UAV. This method can accurately reflect high-flux direct sunlight to the ground-based spectrometer, significantly enhancing the spectral signal while achieving high temporal resolution and a high detection signal-to-noise ratio.

[0005] However, mounting large-size spherical mirrors on UAVs still faces several core technological bottlenecks: conventional undermount gimbals are obstructed by rotors and landing gear, making it impossible to achieve unobstructed omnidirectional observation for upward-looking solar tracking; existing upright gimbals lack stiffness optimization and vibration reduction design, resulting in a high center of gravity and amplified rotor upwash and fuselage vibrations, significantly reducing line-of-sight stability under large loads. Furthermore, existing airborne mirrors mostly employ static fixed-angle or simple servo control, lacking a complete control system for the three-dimensional dynamic reflection optical path, making them prone to beam misses under wind disturbances and maneuvering conditions, and unable to achieve stable directional reflection over long distances. In addition, traditional plane mirrors and solid spherical mirrors suffer from uncontrollable beam divergence and excessive weight, making them unsuitable for UAV mounting and difficult to balance high-throughput beam expansion with UAV payload limitations.

[0006] In summary, to overcome the core bottlenecks of weak scattered light signals and low signal-to-noise ratio in traditional UAV remote sensing, and to solve the problems of mechanical rigidity, dynamic spatial optical path calculation, and lightweight optical payload design of existing UAV gimbals, there is an urgent need for a high-precision three-axis upright Fresnel spherical mirror gimbal system mounted on a small UAV platform. This system would ultimately achieve high temporal resolution and high signal-to-noise ratio for refined detection of carbon pollutants, while also providing core technical support for UAV constellation networking and three-dimensional monitoring. Summary of the Invention

[0007] In view of the defects and technological gaps in the existing technology, the purpose of this invention is to provide a high-precision UAV three-axis upright Fresnel spherical reflector gimbal system, which can solve the problems of obstruction of the upward field of view and insufficient load adaptability of traditional under-mounted gimbals, and realize omnidirectional unobstructed observation; it can make up for the defects of insufficient stiffness, amplification of vibration disturbance, and poor line-of-sight stability of existing upright gimbals, and ensure the high stability of Fresnel spherical reflectors; it can overcome the technical bottlenecks of static optical path limitations, airborne attitude coupling interference, and easy spot miss in airborne reflection systems, and realize dynamic long-range optical path reconstruction and high-precision directional reflection of sunlight; at the same time, it can solve the airborne adaptation problem of the difficulty in balancing the beam expansion performance and lightweight of traditional spherical reflectors, ensure high light flux input, comprehensively improve the reliability of the system in complex environments, and provide core technical support for high temporal resolution and high signal-to-noise ratio fine detection of carbon pollution gases in industrial emission areas.

[0008] To achieve the above-mentioned objectives, embodiments of the present invention provide a high-precision UAV three-axis upright Fresnel spherical reflector gimbal system, comprising: The fixing and damping unit is used to rigidly fix the gimbal system to the top platform of the drone fuselage and provide damping function, isolating the drone fuselage vibration and rotor system disturbance; The three-axis servo drive unit is used to decouple the omnidirectional rotation and attitude stabilization of the three rotation axes of the Fresnel spherical mirror load: yaw axis, roll axis, and pitch axis. The rotation axes of the three rotation axes are perpendicular to each other and intersect at the optical center of the load, forming a standard three-axis gimbal. The supporting frame unit is used to bear the load of the fixed Fresnel spherical mirror and suppresses the vibration amplification effect through the topology-optimized hollow truss structure. The integrated control unit is used to collect status data of the gimbal system and the UAV, calculate the target control quantity for directional reflection of sunlight, and output control signals to the three-axis servo drive unit to achieve high-precision attitude control and directional reflection of sunlight of the Fresnel spherical mirror.

[0009] In the system, the fixing and damping unit serves as the main load-bearing component of the gimbal system, used to install and support the Fresnel spherical mirror load, the three-axis servo drive unit, and the integrated control unit. Simultaneously, it isolates the UAV fuselage from vibrations and aerodynamic disturbances, ensuring the static stability of the Fresnel spherical mirror load. Preferably, the fixing and damping unit includes a gimbal base and distributed damping shock absorbers. The gimbal base is equipped with standard mounting holes that are compatible with the top interface of the drone, which are used to rigidly fix the gimbal system to the top platform of the drone fuselage. The distributed damping shock absorbers are arranged in multiple groups, preferably four groups, evenly and symmetrically distributed along the circumference of the gimbal base. The distribution circle of the shock absorbers is coaxial with the center of gravity of the Fresnel spherical mirror. Each group of distributed damping shock absorbers is located between the gimbal base and the yaw axis motor fixing component, that is, both ends of the shock absorber are rigidly connected to the gimbal base and the yaw axis motor fixing component, respectively, forming an X / Y / Z three-dimensional omnidirectional vibration isolation structure. The damping coefficient of the distributed damping shock absorbers matches the excitation frequency range of the UAV rotor, and is used to isolate the low-frequency vibration of the UAV fuselage from the high-frequency disturbance of the rotor system. That is, it isolates the high-frequency vibration transmitted by the UAV fuselage and the aerodynamic disturbance caused by the rotor upwash in a wide frequency range, suppresses the vibration-induced micro-deformation of the Fresnel spherical mirror surface and the line-of-sight jitter, and provides a stable installation reference for the long-distance high-precision directional reflection of the gimbal system and the Fresnel spherical mirror.

[0010] Preferably, the three-axis servo drive unit includes a yaw axis drive assembly, a roll axis drive assembly, and a pitch axis drive assembly arranged in pairs perpendicularly. All three drive assemblies use integrated FOC direct drive motors and support three-loop control of position, speed, and torque to achieve high-precision rotation and stabilization of the three axes. The yaw axis can achieve 360° omnidirectional rotation, and the roll and pitch axis travels both cover ±90° to counteract the influence of UAV attitude changes on the Fresnel spherical mirror pointing, achieving unobstructed omnidirectional observation.

[0011] More preferably, the yaw axis drive assembly includes a yaw axis motor fixing component, a yaw axis direct drive motor, a yaw axis output seat, and a yaw axis output seat cover. The lower end face of the yaw axis motor fixing component is rigidly connected to the shock absorber, and the upper end face is rigidly fixed to the stator end of the yaw axis direct drive motor. The rotation axis of the yaw axis direct drive motor is parallel to the vertical axis of the UAV fuselage, which is used to realize the horizontal 360° omnidirectional yaw rotation of the load. The rotor end of the yaw axis direct drive motor is rigidly connected to the yaw axis output seat, and the yaw axis output seat is connected to the yaw axis output seat cover. The formed intermediate channel is used to pass through the roll shaft arm and realize the clamping and fixing of the roll shaft arm. The roll axis drive assembly includes a roll axis arm, a roll axis direct drive motor, a roll axis output seat, and a roll axis output seat cover. The rotation axis of the roll axis direct drive motor is perpendicular to the rotation axes of the yaw axis and the pitch axis, which is used to adjust the roll angle of the load. The roll stroke covers ±90°. The stator end of the roll axis direct drive motor is rigidly fixed to the end of the roll axis arm, and the rotor end is rigidly connected to the roll axis output seat. The pitch axis arm is clamped and fixed between the roll axis output seat and the roll axis output seat cover. The pitch axis drive assembly includes a pitch axis arm, a pitch axis direct drive motor, and a pitch axis output component. The pitch axis direct drive motor is horizontally arranged, and its rotation axis is completely perpendicular to the yaw axis rotation axis. It is used to adjust the pitch angle of the load, and the pitch travel covers ±90°. The stator end of the pitch axis direct drive motor is rigidly fixed to the end of the pitch axis arm, and the rotor end is rigidly connected to the pitch axis output component. The pitch axis output component is rigidly connected to the Fresnel spherical mirror support frame unit.

[0012] Preferably, the Fresnel spherical mirror support frame unit includes a pitch axis connecting frame, a Fresnel spherical mirror support frame, a Fresnel spherical mirror reinforcement, and a Fresnel spherical mirror; The pitch axis connecting frame is rigidly connected to the spherical reflector support frame at both ends, and is also rigidly fixed to the pitch axis output component of the three-axis servo drive unit. The Fresnel spherical mirror support frame adopts a hollow truss-type topology optimization structure based on fluid transmission path optimization. Gradient reinforcing ribs are set in the main load-bearing directions of bending and torsion resistance. The thickness of the ribs decreases gradually along the force flow attenuation direction. The non-load-bearing area adopts a hollow weight reduction design. The two ends of the support frame are rigidly connected to the pitch axis drive assembly, and the middle part is used to fix the large-size Fresnel spherical mirror. While ensuring structural rigidity, the structural weight is greatly reduced, the system center of gravity distribution is optimized, the vibration amplification effect of the cantilever structure is suppressed, and a second-level vibration suppression structure is formed. The Fresnel spherical mirror reinforcement is rigidly attached to the back of the Fresnel spherical mirror through a multi-point distributed fixing method.

[0013] Furthermore, the hollow truss-type topology optimization structure takes maximum structural stiffness and minimum mass as optimization objectives, and takes the surface accuracy requirements of the Fresnel spherical reflector and the weight of the UAV payload as constraints. Gradient reinforcing ribs are set on the force transmission path from the Fresnel spherical reflector load to the pitch axis output component. The thickness of the ribs decreases gradually along the force flow attenuation direction. The non-main load-bearing force flow sparse area adopts a fully hollow weight reduction design. While ensuring the bending and torsional stiffness of the spherical reflector mounting surface, it reduces the structural self-weight and the rotational inertia of the cantilever end, suppresses the vibration amplification effect of the upright cantilever configuration, and improves the line-of-sight stability accuracy of the Fresnel spherical reflector.

[0014] Preferably, the integrated control unit includes a main control system, a high-frequency inertial measurement unit, and a communication interface module; The high-frequency inertial measurement unit is installed at the optical center of the Fresnel spherical mirror back plate and is used to collect motion data such as the three-axis attitude angle, angular velocity and acceleration information of the Fresnel spherical mirror in real time, so as to provide feedback data for stabilization control. The main control system communicates and interconnects with the three-axis servo drive unit and the UAV flight control system through a communication interface module. It synchronously acquires the UAV's RTK positioning data, real-time flight attitude, and spatiotemporal reference data. The system calculates the target control quantity for directional sunlight reflection using a solar directional reflection algorithm. Based on the target control quantity and the attitude and motion data of the Fresnel spherical mirror, the system outputs a control signal to the three-axis servo drive unit after processing by a stabilization control algorithm. This enables real-time stabilization of the Fresnel spherical mirror's line of sight, target tracking control, and directional sunlight reflection.

[0015] More preferably, calculating the target control quantity for directional reflection of sunlight includes: Multi-source spatiotemporal information synchronization and reference coordinate system establishment: Real-time acquisition of the absolute geographic coordinates of the UAV and the target, and the real-time flight attitude angles of the UAV relative to the navigation coordinate system, including the solar azimuth angle. α s and elevation angle β s Construct the rotation matrix from the navigation coordinate system to the body coordinate system. ; The navigation coordinate system adopts the North-East-West (NED) coordinate system, denoted as the N system; the Fresnel spherical mirror coordinate system is denoted as the M system; and the UAV's body coordinate system is denoted as the B system. The UAV's three-dimensional spatial coordinates are obtained through the onboard RTK and flight control system. And the heading angle of the aircraft in the N-series. Pitch angle Roll angle Construct the rotation matrix from the N-system to the B-system. Simultaneously, the target's three-dimensional coordinates are obtained through a cooperative communication link. .

[0016] Spatial vector calculation: Based on the current UTC time, UAV location information, and solar attitude information, the unit vector of solar incident light in the geographic coordinate system is calculated using an astronomical ephemeris algorithm. The target pointing unit vector is calculated by combining the spatial coordinate difference between the UAV and the target. ; The solar incident light unit vector calculation uses the SPA solar position algorithm to calculate the current azimuth of the sun in the N system. α s and elevation angle β s Construct a unit vector pointing in the direction of the sun. : Target pointing to unit vector The unit vector pointing from the center of the Fresnel spherical mirror to the target. The calculation formula is as follows: In the formula The installation offset between the geometric center of the gimbal and the center of the drone's RTK antenna has been pre-calibrated and compensated for the spatial distance between the drone and the target.

[0017] Ideal reflective surface normal vector extraction: Based on the three-dimensional spatial light reflection law, the unit vector sum of the solar incident light unit vector and the target pointing unit vector is normalized to obtain the ideal reflective surface unit normal vector in the geographic coordinate system. ; In the formula, The normal vector is the magnitude of the sum of the incident solar ray vector and the target pointing vector. This refers to the ideal orientation that a Fresnel spherical mirror must maintain in absolute geographic space.

[0018] Body attitude compensation transformation: through rotation matrix Transform the unit normal vector of the ideal reflective surface in the geographic coordinate system to the body coordinate system to obtain the unit normal vector of the ideal reflective surface in the body coordinate system. To eliminate the optical path pointing error introduced by the attitude deflection of the UAV body; This rotational transformation maps the ideal normal vector of the absolute geographic space to the body coordinate system that rotates in real time with the UAV, eliminating the interference of the UAV's roll, pitch, and heading attitude changes on the Fresnel spherical mirror's pointing direction.

[0019] Inverse kinematics solution for a three-axis upright gimbal: Based on the linkage structure characteristics and rotation sequence of the upright three-axis gimbal, the inverse kinematics of the unit normal vector of the ideal reflector in the body coordinate system is analyzed to output the target given angles of the gimbal's heading, roll, and pitch motors. ψ g , ϕ g , θ g And form the target control quantity; The rotation sequence of a standard three-axis gimbal is yaw - roll - pitch. After establishing the gimbal linkage coordinate system, the forward kinematic equation of the Fresnel spherical mirror normal vector is: In the formula, , , These are the joint angles for the gimbal's yaw, roll, and pitch axes, respectively. , , These are the rotation matrices for the corresponding axes. n 0 is the initial normal vector of the Fresnel spherical mirror when the three axes of the gimbal are zeroed; let By using analytical inversion, the unique corresponding three-axis target given angle can be calculated.

[0020] Dynamic directional projection: The given angle of the three-axis target is fed back to the main control system, which drives the upright three-axis gimbal to overcome disturbances and inter-axis coupling torque, track the given angle of the target in real time and maintain the attitude of the Fresnel spherical mirror, so as to realize high-precision directional projection of the solar beam and dynamic long-range optical path reconstruction.

[0021] Preferably, the system further includes: The consistency of the normal vector obtained by forward kinematics calculation of the forward kinematics equation with the unit normal vector of the ideal reflective surface in the body coordinate system is checked. When the deviation between the two exceeds the preset threshold, the inverse kinematics calculation is performed again. The attitude compensation of the Fresnel mirror is achieved by using accelerometer and gyroscope data calculated by high-frequency inertial measurement unit (such as high-frequency inertial sensor) to realize real-time correction of the given angle error of the control target.

[0022] Preferably, the Fresnel spherical mirror is a traditional spherical mirror whose continuous spherical surface is decomposed into a set of concentric ring working surfaces with the same curvature as the reference spherical surface, so as to achieve a significant weight reduction while fully retaining the optical characteristics of beam expansion and field of view control of the spherical mirror; The Fresnel spherical mirror's structural parameters are determined through a parameter optimization method based on the geometric constraints of collaborative detection: under the paraxial approximation, the Fresnel spherical mirror is equivalent to an ideal spherical mirror. By combining the theoretical field-of-view model of the spherical mirror with the Gaussian equation under the paraxial approximation, the optimal radius of curvature suitable for the collaborative detection mission is analytically obtained. Combined with the weight reduction constraint mapping of the airborne payload, the optimal number of Fresnel rings is obtained, thereby achieving directional beam expansion and reflection of sunlight.

[0023] More preferably, the lightweight design process of the Fresnel spherical mirror under paraxial approximation conditions specifically includes: (1) Constructing a theoretical field-of-view model: Under the paraxial approximation, let the half-aperture of the spherical mirror be... , radius of curvature The theoretical field of view of a spherical mirror is derived using Gauss's formula. for: (2) Constructing the system detection geometric constraint model: Let the observation distance between the spherical reflector and the target receiver be... The effective active area radius of the target receiver is The error angle of the integrated device for gimbal and UAV flight control system is... Establish geometric constraint equations to ensure full beam coverage: (3) Analyze the optimal radius of curvature: Solve the equations in steps (1) and (2) simultaneously to obtain the optimal radius of curvature that meets the task requirements. : (4) Ring number mapping matching: Combining the airborne load weight reduction design constraints, the optimal radius of curvature is mapped to the optimal number of Fresnel rings required for processing.

[0024] Compared with the prior art, the beneficial effects of the present invention include at least the following: 1. This invention designs a three-axis gimbal mechanical configuration mounted on the top of the UAV as a three-axis servo drive unit, which solves the field of view obstruction problem caused by the fuselage, rotor and landing gear of the traditional undermount gimbal, realizes unobstructed observation of the entire ±90° pitch range, and breaks through the limitation of landing gear installation space. It can be adapted to special operation payloads such as large-size and heavy Fresnel spherical reflectors, greatly expanding the application scenarios of UAV payloads.

[0025] 2. This invention designs a high-rigidity, lightweight mechanical structure with two-stage vibration isolation and topology optimization. The first-stage distributed damping shock absorption component isolates the fuselage from rotor disturbances, while the second-stage hollow truss frame suppresses the aerodynamic vibration amplification effect of the cantilever structure. This significantly improves the bending and torsional stiffness of the structure while reducing its weight, effectively solving the problems of aerodynamic disturbance amplification and insufficient line-of-sight stabilization accuracy of existing upright gimbals.

[0026] 3. This invention constructs an intelligent main control system based on the UAV-gimbal coupling dynamics model. It adopts an integrated FOC direct drive motor to realize three-closed-loop control. With the help of Kalman filter data denoising, it can cancel aerodynamic disturbance torque and multi-axis motion coupling torque in real time, effectively suppress stick-slip vibration and inter-axis coupling interference, and greatly improve the dynamic response speed and control accuracy of the gimbal in complex environments.

[0027] 4. This invention proposes a fully decoupled dynamic spatial sunlight directional reflection method. Through multi-coordinate system mapping and rotation matrix transformation, the attitude change of the UAV body is completely decoupled from the absolute spatial optical path pointing. Even when the UAV encounters gusts and tilts violently, the motor rotation angle can still be calculated in real time after compensation, and the absolute spatial pointing of the reflected beam can be kept stable. This breaks through the limitations of the existing static optical path, solves the pain points of light spot wandering and miss target in traditional airborne reflection systems, and realizes high-precision real-time reconstruction of dynamic long-range optical paths.

[0028] 5. This invention proposes a parameter optimization design method for Fresnel spherical mirrors. Based on Gaussian optics theory and cooperative detection geometric constraints, it solves for the optimal radius of curvature and Fresnel ring number of the spherical mirror to meet operational requirements. The Fresnel spherical mirror designed using this method combines beam-expanding performance with lightweight characteristics, effectively ensuring sufficient light flux input for ground-based spectrometers, significantly reducing payload weight, adapting to the carrying constraints of small UAVs, and achieving synergistic optimization of optical performance, system fault tolerance, and airborne lightweighting. Attached Figure Description

[0029] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0030] Figure 1 This is a schematic diagram of the overall structure of the high-precision UAV three-axis upright Fresnel spherical mirror gimbal system according to an embodiment of the present invention; Figure 2 This is a front view of the high-precision UAV three-axis upright Fresnel spherical mirror gimbal system according to an embodiment of the present invention; Figure 3 This is a top view of the high-precision UAV three-axis upright Fresnel spherical mirror gimbal system according to an embodiment of the present invention; Figure 4 This is a schematic diagram of the Fresnel spherical mirror design for a UAV three-axis upright Fresnel spherical mirror gimbal system provided in an embodiment of the present invention; Figure 5 This is a schematic diagram illustrating the directional solar reflection principle of the UAV three-axis upright Fresnel spherical reflector gimbal system provided in this embodiment of the invention; Figure 6 This is a flowchart of a method for directional solar reflection of a UAV three-axis upright Fresnel spherical mirror gimbal system provided in an embodiment of the present invention. Detailed Implementation

[0031] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and do not limit the scope of protection of this invention.

[0032] The inventive concept of this invention is to overcome the core bottlenecks in UAV remote sensing monitoring of carbon pollution gases, namely low signal-to-noise ratio of scattered light and surface reflection pollution caused by ground-based reflector solutions. Addressing the pain points of existing UAV undermount gimbals that obstruct the upward-looking field of view, easy drift and miss of reflected light spots, and the difficulty in balancing the beam-expanding performance and lightweight design of traditional reflectors, this invention provides a high-precision UAV three-axis upright Fresnel spherical reflector gimbal system and a method for directional reflection of sunlight. The top-mounted three-axis gimbal configuration avoids field-of-view obstruction and accommodates large-size Fresnel spherical reflector loads. A high-rigidity, lightweight structure with two-stage vibration isolation and topology optimization suppresses aerodynamic disturbances and fuselage vibration transmission, improving line-of-sight stability accuracy. A multi-coordinate system dynamically decoupled directional reflection algorithm eliminates the interference of fuselage attitude deflection on the reflected light path, ultimately achieving high-precision, high-stability directional reflection of sunlight under all UAV flight attitudes, providing core support for high signal-to-noise ratio, refined remote sensing detection of carbon pollution gases.

[0033] Based on the above inventive concept, this embodiment provides a high-precision UAV three-axis upright Fresnel spherical reflector gimbal system, such as... Figure 1 As shown, the system includes a multi-rotor UAV platform 1, a gimbal mounting adapter 2, and a three-axis upright Fresnel spherical mirror gimbal system 3. The multi-rotor UAV platform 1 provides the system with a flight carrier, power supply support, and a complete communication link. The gimbal mounting adapter 2 is rigidly fixed to the top mounting plane of the multi-rotor UAV platform 1. The three-axis upright Fresnel spherical mirror gimbal system 3 is rigidly fixed to the gimbal mounting adapter 2 via a gimbal base, forming an upright mounting configuration on the top of the UAV, avoiding obstruction of the payload's field of view by the fuselage, rotor, and landing gear.

[0034] like Figure 2 and Figure 3 As shown, the three-axis upright Fresnel spherical mirror gimbal system 3 consists of four parts: a fixing and damping unit, a three-axis servo drive unit, a Fresnel spherical mirror support frame unit, and an integrated control unit.

[0035] In this embodiment, the fixing and damping unit serves as the installation reference for the entire gimbal system, enabling a rigid connection between the gimbal and the drone fuselage while isolating fuselage vibrations and rotor system disturbances. Figure 2 As shown, the fixing and vibration damping unit includes a gimbal base 4 and a distributed damping shock absorber 5. The gimbal base 4 is a plate structure made of 7075 aviation aluminum alloy, with standard mounting holes on its end face. It can be adapted to the top mounting interface of different models of multi-rotor UAVs via the gimbal mounting adapter 2, enabling quick assembly and disassembly of the gimbal and universal compatibility. The distributed damping shock absorber 5 consists of four sets of damping silicone rubber omnidirectional damping balls evenly distributed along the circumference of the gimbal base. It is an integrated structure, with its upper and lower ends rigidly connected to the gimbal base 4 and the yaw axis motor fixing component 6, respectively. The four sets of damping balls are symmetrically distributed in a rectangular shape, forming a distributed elastic support structure that can achieve omnidirectional vibration isolation in the X / Y / Z spatial directions. This effectively suppresses low-frequency attitude vibrations transmitted from the UAV fuselage and isolates high-frequency blade disturbances from the rotor system, constituting the first-level vibration isolation structure of the system.

[0036] In this embodiment, the three-axis servo drive unit is the execution core of the gimbal system, used to realize the three-axis omnidirectional rotation and attitude stabilization control of the Fresnel spherical mirror load. It includes a yaw axis drive component, a roll axis drive component, and a pitch axis drive component. The rotation axes of the three rotation axes are perpendicular to each other and intersect at the optical center of the Fresnel spherical mirror load, realizing the decoupled control of the three-axis motion and avoiding the line-of-sight deviation caused by multi-axis motion coupling.

[0037] like Figure 2 As shown, the yaw axis drive assembly includes a yaw axis motor mount 6, a yaw axis direct drive motor 7, a yaw axis output mount 8, and a yaw axis output mount cover 9. The lower end face of the yaw axis motor mount 6 is rigidly connected to the distributed damping shock absorber 5, and the upper end face is rigidly fixed to the stator end of the yaw axis direct drive motor 7, providing a high-precision and high-stability installation reference for the three-axis servo drive unit. The rotation axis of the yaw axis direct drive motor 7 is parallel to the vertical axis of the UAV fuselage, used to achieve 360° omnidirectional yaw rotation of the load.

[0038] The yaw axis direct drive motor 7 is an integrated FOC direct drive brushless motor, integrating the motor stator, motor rotor, 16-bit absolute magnetic encoder, and built-in integrated drive board. The lower end of the motor stator is rigidly fixed to the yaw axis motor mounting bracket 6, and the upper end of the motor rotor is rigidly connected to the yaw axis output bracket 8. The built-in absolute magnetic encoder can collect the rotor's angle and speed information in real time, providing high-precision position feedback for closed-loop control. The built-in integrated drive board is equipped with an FOC vector control circuit, supports CAN bus communication, and can independently realize three-loop control of the motor's position, speed, and torque. The yaw axis output bracket cover 9 is rigidly connected to the yaw axis output bracket 8, with the roll shaft arm 10 clamped and fixed in the middle. The overall center of gravity distribution of the system can be optimized by adjusting the clamping position.

[0039] like Figure 2 As shown, the roll axis drive assembly includes a roll axis arm 10, a roll axis direct drive motor 11, a roll axis output seat 12, and a roll axis output seat cover 13. The rotation axis of the roll axis direct drive motor 11 is perpendicular to the rotation axes of the yaw axis and the pitch axis, which is used to adjust the roll angle of the load. The roll travel covers ±90°, which can counteract the attitude changes of the UAV in the roll direction in real time and maintain the spatial stability of the load's line of sight. Among them, the roll axis direct drive motor 11 adopts an integrated FOC direct drive motor of the same model as the yaw axis. Its motor stator is rigidly fixed to the end of the roll axis arm 10, and the motor rotor is rigidly connected to the roll axis output seat 12. The pitch axis arm 14 is clamped and fixed between the roll axis output seat 12 and the roll axis output seat cover 13. By rotating the roll axis direct drive motor 11, the pitch axis assembly and the Fresnel spherical reflector load are driven to achieve rotation and stabilization control in the roll direction.

[0040] like Figure 2 As shown, the pitch axis drive assembly includes a pitch axis arm 14, a pitch axis direct drive motor 15, and a pitch axis output component 16. The pitch axis direct drive motor 15 is horizontally arranged, with its rotation axis completely perpendicular to the yaw axis rotation axis. It is used to adjust the pitch angle of the load, with a pitch travel covering ±90°, solving the problem of obstructed viewing field of view in traditional undermount gimbals and achieving unobstructed omnidirectional observation. The pitch axis direct drive motor 15 uses an integrated FOC direct drive motor of the same model. Its stator is rigidly fixed to the end of the pitch axis arm 14, and its rotor is rigidly connected to the pitch axis output component 16. The pitch axis output component 16 is rigidly connected to the Fresnel spherical mirror support frame unit. The rotation of the pitch axis direct drive motor 15 drives the Fresnel spherical mirror support frame and the Fresnel spherical mirror load to achieve rotation and stabilization control in the pitch direction.

[0041] In this embodiment, the Fresnel spherical mirror support frame unit is the core load-bearing structure for the spherical mirror load, used to connect the pitch axis drive assembly and the spherical mirror, while also providing installation space for the integrated control unit. Figure 3As shown, the Fresnel spherical mirror support frame unit includes a pitch axis connecting frame 17, a Fresnel spherical mirror support frame 19, a Fresnel spherical mirror reinforcement 20, and a Fresnel spherical mirror 21. The pitch axis connecting frame 17 is rigidly connected at both ends to two sets of Fresnel spherical mirror support frames 19, and rigidly fixed on both sides to the pitch axis output component 16 and the pitch axis arm 14, forming the main load-bearing structure of the frame. The Fresnel spherical mirror support frame 19 is rigidly connected to the Fresnel spherical mirror reinforcement 20, and the Fresnel spherical mirror reinforcement 20 is rigidly attached to the back of the Fresnel spherical mirror 21. This multi-point distributed fixing method avoids uneven stress on the large-size Fresnel spherical mirror, preventing deformation and ensuring the surface accuracy of the Fresnel spherical mirror.

[0042] The Fresnel spherical reflector support frame is constructed entirely of T700 carbon fiber composite material. Through topology optimization, it is designed as a hollow truss structure. Gradient reinforcing ribs are installed along the main load-bearing directions for bending and torsion resistance. Non-load-bearing areas utilize a hollow, weight-reducing design, forming a multi-chamber truss structure. This structure significantly reduces structural weight while ensuring bending and torsional stiffness, optimizes the overall system center of gravity distribution, and brings the load center of gravity as close as possible to the triaxial rotation center. Simultaneously, it effectively suppresses the aerodynamic vibration amplification effect of the cantilever structure, constituting the system's second-level vibration suppression structure. In this embodiment, the Fresnel spherical reflector 21 has a diameter of 0.25m, a coating band covering the 280nm-450nm ultraviolet-visible light band, and a surface accuracy better than λ / 10@632.8nm, enabling efficient directional reflection of sunlight.

[0043] like Figure 4 As shown, the Fresnel spherical mirror used in this embodiment is a lightweight optical spherical reflecting element designed based on the Fresnel principle. Its core design logic is as follows: the continuous reflecting surface of a traditional spherical mirror is radially decomposed into a set of concentrically arranged annular reflecting working surfaces. Each annular working surface retains the same curvature characteristics as the reference sphere, while eliminating the substrate thickness that contributes nothing to the optical design. This achieves significant weight reduction of the optical element while fully preserving the optical characteristics of the spherical mirror, such as beam expansion, field-of-view adjustment, and parallel light convergence, perfectly adapting to the load-bearing limitations of small UAVs. Under paraxial approximation conditions, this Fresnel spherical mirror can be equivalent to an ideal spherical mirror, and the design and solution of core parameters such as the field of view and radius of curvature can be completed using the Gaussian formula. The specific steps are as follows: (1) Constructing a theoretical model: Under the paraxial approximation, the Fresnel spherical mirror is equivalent to an ideal spherical mirror. Let the semi-aperture of the spherical mirror be... The radius of curvature is The theoretical field of view of the spherical mirror is derived using Gauss's formula. for: (2) Constructing the system detection geometric model: The observation distance between the Fresnel spherical mirror and the target receiver spectrometer is set as... The effective active area radius of the target receiver is The integrated error angle of the gimbal and flight control system is set as follows: To ensure that the reflected beam is within the range of errors... Under the premise of still being able to completely cover the target activity area, establish geometric constraint equations: (3) Analyze the radius of curvature: Solve the equations in steps (1) and (2) above to calculate the optimal radius of curvature of the reflector that meets the requirements of the current collaborative detection mission. : (4) Structural weight reduction and ring number mapping: Based on the radius of curvature obtained analytically In conjunction with the design constraints for reducing airborne load, the radius of curvature is mapped to the optimal number of Fresnel rings for machining.

[0044] In this embodiment, the integrated control unit serves as the control and sensing core of the gimbal system, used to achieve closed-loop stabilization control of the three-axis servo drive components, communication and interaction with the UAV flight control system, multi-source sensing data fusion, and real-time calculation of the solar directional reflection algorithm. Figure 3 As shown, the integrated control unit 18 specifically includes a main control system, an inertial measurement unit (such as an inertial sensor IMU), and a communication interface module. The high-frequency IMU is installed at the center of the backplate of the Fresnel spherical mirror 21, aligned with the optical center of the Fresnel spherical mirror. It can collect motion data such as three-axis attitude angles, angular velocities, and acceleration information of the Fresnel spherical mirror load in real time, providing high-precision feedback data for stabilization control. The main control system achieves low-latency communication with the built-in drive boards of the three-axis motors via a CAN bus, and interacts with the UAV flight control system in real time via a UART serial port. It receives RTK positioning data and flight attitude data from the UAV and target pointing commands from the ground station. After processing by the solar directional reflection algorithm and the stabilization control algorithm, the system outputs control signals to the three-axis servo drive components to achieve real-time stabilization of the Fresnel spherical mirror's line of sight, target tracking control, and solar directional reflection. The communication interface module includes a CAN bus interface, a UART serial port, an Ethernet interface, and a PWM input / output interface, which can realize bidirectional communication and data transmission with the UAV flight control system, the ground control station, and the airborne payload, supporting remote control and real-time status data feedback.

[0045] In complex aerial flight environments, the Fresnel mirror coordinate system ( ) and UAV body coordinate system ( As the drone rolled ( ), pitch ( ) and heading ( The coordinates of a geographic navigation system change and deflect constantly, and are not equivalent to an absolute geographic navigation coordinate system. ).like Figure 5 As shown, to ensure the sun's beam is accurately projected onto the target point, calculations must first be performed in an absolute coordinate system. The system calculates the unit vector pointing towards the sun using the real-time acquired solar azimuth angle. The unit vector pointing towards the target is calculated by the spatial relative position of the UAV and the target. According to the law of reflection, the incident ray and the reflected ray are on opposite sides of the normal and coplanar with it. Therefore, the normal vector of an ideal Fresnel spherical mirror is... It must bisect the angle formed by the two vectors mentioned above, thus obtaining the angle. and angle .

[0046] However, the upright three-axis gimbal is mounted on the tilted drone body, therefore it must be transformed by rotation matrix. The ideal normal vector in the geographic coordinate system Mapped to the body coordinate system, we get .this This refers to the relative spatial vector that the three motors of the gimbal need to point in together after eliminating interference from the drone's flight attitude. Finally, through the inverse kinematics equations of the gimbal, this vector is decomposed into the given input values ​​of the three joint angles: heading, roll, and pitch.

[0047] The core of achieving high-precision attitude control and directional sunlight reflection of a Fresnel spherical mirror lies in completely eliminating the coupling interference of UAV attitude deflection on the spatial pointing of the Fresnel spherical mirror through multi-coordinate system dynamic rotation transformation, thereby achieving high-precision directional sunlight reflection under all UAV attitudes during flight. Figure 6 As shown, the specific implementation steps are as follows: Step S1: Synchronization of multi-source spatiotemporal information and establishment of reference coordinate system Coordinate system establishment: The system establishes a Northeast-East (NED) navigation coordinate system, denoted as the N-system, with the UAV's position at power-on time as the origin. ), as the reference coordinate system for absolute geographic space; at the same time, a UAV body coordinate system is established, denoted as the B system ( The origin is the UAV's center of mass. The X-axis points forward along the fuselage nose, the Y-axis points to the right along the fuselage right wing, and the Z-axis points downward along the fuselage vertically. The B-frame deflects in real time with the UAV's flight attitude. A Fresnel mirror coordinate system, namely the M-frame, is also established. The origin is the geometric center of the Fresnel spherical mirror, the X and Y axes are perpendicular to the mirror plane, and the Z axis is perpendicular to the mirror screen.

[0048] Acquiring UAV pose: Real-time acquisition of the UAV's current three-dimensional spatial coordinates, equipped with a Fresnel spherical mirror, is achieved via an onboard RTK positioning module and the UAV flight control system. and the body in Attitude angles (heading angles) under the system Pitch angle Roll angle ), constructing a navigation coordinate system To the body coordinate system rotation matrix .

[0049] Target location acquisition: High-precision three-dimensional absolute geographic coordinates of the target to be reflected are obtained through a cooperative communication link. .

[0050] Acquiring high-precision time and environmental parameters: The time synchronization of various sensing modules, control terminals and UAV flight control system is achieved through the spatiotemporal synchronization unit, ensuring the consistency of the time reference for spatial vector calculation, that is, obtaining the current accurate UTC time, and also obtaining the UAV's position information, specifically including the longitude, latitude and altitude of its location.

[0051] Step S2: Spatial Vector Solution Spatial vector calculation specifically includes solar incident light vector calculation and target pointing vector calculation.

[0052] Solar incident light vector calculation: Built-in SPA high-precision solar position algorithm; input current UTC time and UAV position interest, calculate the current solar position. Azimuth of the system and elevation angle This allows us to construct the unit vector of solar incident light pointing from the optical center of the Fresnel spherical mirror towards the sun. : Target pointing vector calculation: based on the UAV's current coordinates with target coordinates Calculate the target pointing unit vector from the optical center of the Fresnel spherical mirror to the target. : In the formula, The distance between the optical center of the Fresnel spherical mirror and the target is the straight-line distance in space. In this embodiment, the installation offset between the geometric center of the gimbal and the center of the UAV RTK antenna and the optical center of the Fresnel spherical mirror has been calibrated and compensated before leaving the factory, eliminating the calculation error caused by the installation deviation.

[0053] Step S3: Extraction of the normal vector of the ideal reflecting surface According to the law of reflection of light in three-dimensional space, the incident ray, the reflected ray, and the normal to the reflecting surface are coplanar, and the normal bisects the angle between the incident ray and the reflected ray. In this embodiment... and Both are unit vectors, therefore in Under the given conditions, the unit normal vector of the ideal reflecting surface of a Fresnel spherical mirror is... It can be obtained by normalizing the vector sum of two vectors, and the calculation formula is: In the formula, Let be the magnitude of the sum of the incident solar ray vector and the target pointing vector; the resulting normal vector. This refers to the ideal orientation that a Fresnel mirror must maintain in absolute geographical space, which is the core benchmark for achieving precise directional reflection of sunlight.

[0054] Step S4: UAV body attitude compensation transformation Because the three-axis gimbal is rigidly mounted on the top of the drone's fuselage, the gimbal's base will deflect in real time with the drone's flight attitude. If the gimbal is directly controlled using the ideal normal vector in the geographic coordinate system, the Fresnel spherical mirror will deviate from its pointing direction according to the drone's attitude, causing the reflected light spot to miss its target. Therefore, it is necessary to perform a coordinate system rotation transformation to map the unit normal vector of the ideal reflector surface in absolute geographic space to the drone's body coordinate system, which deflects in real time with the drone, thus eliminating the coupling error introduced by the drone's attitude deflection. The calculation formula is as follows: in, The rotation matrix of the navigation system to the machine system constructed in step S1 is generated by the real-time attitude angles issued by the UAV flight controller. The solution is obtained. The transformed... Let be the unit normal vector of the ideal reflecting surface in the body coordinate system, representing the relative orientation that the Fresnel spherical mirror normal should maintain relative to the real-time deflection of the UAV body.

[0055] Step S5: Inverse kinematics calculation of the three-axis positive mount gimbal In this embodiment, a linkage coordinate system is established for the upright three-axis gimbal (rotation sequence: Yaw-Roll-Pitch), and the gimbal linkage coordinate system is established based on this rotation sequence. Let the three joint angles of the gimbal be the target yaw angles. Target roll angle and target pitch angle When the three axes of the gimbal are zeroed, the initial normal vector of the Fresnel spherical mirror is... n 0 Along the positive Z-axis of the machine system.

[0056] The initial normal vector of the Fresnel spherical mirror (when the three axes of the gimbal are zeroed) is set to the positive Z-axis or the positive X-axis (set to...). Based on the DH parameter method, after three-axis rotation, the forward kinematic equation of its terminal normal vector in the machine system is: In the formula, , , These are the rotation matrices corresponding to the yaw, roll, and pitch axes, respectively. N kinematics Let be the actual normal vector of the Fresnel spherical mirror in the machine system after three-axis rotation. Let ,in The ideal normal vector under the machine system obtained in step S4 is inverted analytically to calculate the unique corresponding given angle of the three-axis target: Through this inverse kinematics calculation, the ideal normal vector in the body coordinate system is directly converted into the target control angle of the gimbal's three-axis motor. The calculation process involves minimal computation and can be performed in real time within the embedded main control chip. Step S6: Closed-loop feedback control and dynamic fixed projection. The gimbal three-axis target given angle obtained from step S5. The desired input value is used as the control loop. This desired input value is fed back to the main control system, which has a built-in Kalman filter unit to fuse and denoise the attitude data acquired by the IMU and the rotation angle data acquired by the high-precision motor encoder, effectively suppressing measurement noise and random disturbances. After data processing, the data is fed back to the three-axis motor to achieve directional control of the three-axis gimbal. Based on the UAV-gimbal coupled dynamics model, the system calculates and compensates for wind resistance disturbance torque, multi-axis motion coupling torque, and motor friction torque in real time based on the given target angle. An FOC vector control framework is used to drive the three-axis direct-drive motor, achieving three-loop cascaded control of the torque loop, velocity loop, and position loop. The Fresnel spherical reflector attitude is fixed and tracks the target angle in real time. Even under complex conditions such as strong wind resistance, high-frequency rotor vibration, and high-maneuver UAV flight, the Fresnel reflector attitude remains highly stable and precise. Ultimately, a stable dynamic optical path is constructed in the air between the sun, the reflector, and the target, achieving high-precision directional projection of sunlight.

[0057] The high-precision UAV three-axis upright Fresnel spherical reflector gimbal system and solar directional reflection method provided in the above embodiments fundamentally solve the problems of field-of-view obstruction and insufficient load adaptability of traditional undermount gimbals by using a three-axis gimbal configuration mounted upright on the top of the UAV, achieving ±90° omnidirectional unobstructed observation; through a high-rigidity and lightweight structure with two-stage vibration isolation and topology optimization, aerodynamic disturbance amplification and fuselage vibration transmission are effectively suppressed, significantly improving the line-of-view stability accuracy; through the optimized Fresnel spherical reflector, the directional beam expansion performance of solar light and the requirements of airborne lightweighting are taken into account, ensuring sufficient light flux input to the target receiver; through fully decoupled multi-coordinate system dynamic transformation and inverse kinematics solution algorithm, the coupling interference of UAV body attitude deflection on the reflected light path is eliminated, solving the pain points of spot migration and miss target in traditional airborne reflection systems. In this embodiment, the gimbal system has a stable line of sight and high pointing accuracy for directional reflection of sunlight, enabling stable directional projection of sunlight over long distances. This provides core hardware and algorithm support for scenarios such as hyperspectral remote sensing of carbon pollution gases, and also provides core technical support for UAV constellation networking and three-dimensional monitoring.

[0058] The specific embodiments described above illustrate the technical solution and beneficial effects of the present invention in detail. It should be understood that the above description is only the most preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, additions, and equivalent substitutions made within the scope of the principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A high-precision UAV three-axis upright Fresnel spherical mirror gimbal system, characterized in that, include: The fixing and damping unit is used to rigidly fix the gimbal system to the top platform of the drone fuselage and provide damping function, isolating the drone fuselage vibration and rotor system disturbance; The three-axis servo drive unit is used to decouple the omnidirectional rotation and attitude stabilization of the three rotation axes of the Fresnel spherical mirror load: yaw axis, roll axis, and pitch axis. The rotation axes of the three rotation axes are perpendicular to each other and intersect at the optical center of the load, forming a standard three-axis gimbal. The supporting frame unit is used to bear the load of the fixed Fresnel spherical mirror and suppresses the vibration amplification effect through the topology-optimized hollow truss structure. The integrated control unit is used to collect status data of the gimbal system and the UAV, calculate the target control quantity for directional reflection of sunlight, and output control signals to the three-axis servo drive unit to achieve high-precision attitude control and directional reflection of sunlight of the Fresnel spherical mirror.

2. The high-precision UAV three-axis upright Fresnel spherical mirror gimbal system according to claim 1, characterized in that, The fixing and damping unit includes a gimbal base and a distributed damping shock absorber. The gimbal base is equipped with standard mounting holes that are compatible with the top interface of the drone, which are used to rigidly fix the gimbal system to the top platform of the drone fuselage. Multiple sets of distributed damping shock absorbers are set up and are evenly and symmetrically distributed along the circumference of the gimbal base. The distribution circle of the shock absorbers is coaxial with the center of gravity of the Fresnel spherical mirror, forming an X / Y / Z three-dimensional omnidirectional vibration isolation structure. The damping coefficient of the distributed damping shock absorbers matches the excitation frequency range of the UAV rotor, which is used to isolate the low-frequency vibration of the UAV fuselage from the high-frequency disturbance of the rotor system.

3. The high-precision UAV three-axis upright Fresnel spherical mirror gimbal system according to claim 2, characterized in that, The three-axis servo drive unit includes a yaw axis drive assembly, a roll axis drive assembly, and a pitch axis drive assembly arranged in pairs perpendicularly. All three drive assemblies use an integrated FOC direct drive motor and support three closed-loop control of position, speed, and torque to achieve high-precision rotation and stabilization of the three axes. The yaw axis can achieve 360° omnidirectional rotation, and the travel of the roll axis and pitch axis both cover ±90°.

4. The high-precision UAV three-axis upright Fresnel spherical mirror gimbal system according to claim 3, characterized in that, The yaw axis drive assembly includes a yaw axis motor mounting component, a yaw axis direct drive motor, a yaw axis output seat, and a yaw axis output seat cover. The lower end face of the yaw axis motor mounting component is rigidly connected to the shock absorber, and the upper end face is rigidly fixed to the stator end of the yaw axis direct drive motor. The rotation axis of the yaw axis direct drive motor is parallel to the vertical axis of the UAV fuselage, which is used to realize the horizontal 360° omnidirectional yaw rotation of the load. The rotor end of the yaw axis direct drive motor is rigidly connected to the yaw axis output seat, and the yaw axis output seat is connected to the yaw axis output seat cover. The formed intermediate channel is used to pass through the roll shaft arm and realize the clamping and fixing of the roll shaft arm. The roll axis drive assembly includes a roll axis arm, a roll axis direct drive motor, a roll axis output seat, and a roll axis output seat cover. The rotation axis of the roll axis direct drive motor is perpendicular to the rotation axes of the yaw axis and the pitch axis, which is used to adjust the roll angle of the load. The roll stroke covers ±90°. The stator end of the roll axis direct drive motor is rigidly fixed to the end of the roll axis arm, and the rotor end is rigidly connected to the roll axis output seat. The pitch axis arm is clamped and fixed between the roll axis output seat and the roll axis output seat cover. The pitch axis drive assembly includes a pitch axis arm, a pitch axis direct drive motor, and a pitch axis output component. The pitch axis direct drive motor is horizontally arranged, and its rotation axis is completely perpendicular to the yaw axis rotation axis. It is used to adjust the pitch angle of the load, and the pitch travel covers ±90°. The stator end of the pitch axis direct drive motor is rigidly fixed to the end of the pitch axis arm, and the rotor end is rigidly connected to the pitch axis output component. The pitch axis output component is rigidly connected to the Fresnel spherical mirror support frame unit.

5. The high-precision UAV three-axis upright Fresnel spherical mirror gimbal system according to claim 1, characterized in that, The Fresnel spherical mirror support frame unit includes a pitch axis connecting frame, a Fresnel spherical mirror support frame, a Fresnel spherical mirror reinforcement, and a Fresnel spherical mirror; The pitch axis connecting frame is rigidly connected to the spherical reflector support frame at both ends, and is also rigidly fixed to the pitch axis output component of the three-axis servo drive unit. The spherical mirror support frame adopts a hollow truss topology optimization structure based on fluid transmission path optimization. Gradient reinforcing ribs are set in the main load-bearing directions of bending and torsion resistance. The thickness of the ribs decreases gradually along the force flow attenuation direction. The non-load-bearing area adopts a hollow weight reduction design. The middle part is used to fix a large-size Fresnel spherical mirror. The Fresnel spherical mirror reinforcement is rigidly attached to the back of the Fresnel spherical mirror through a multi-point distributed fixing method.

6. The high-precision UAV three-axis upright Fresnel spherical reflector gimbal system according to claim 1, characterized in that, The integrated control unit includes a main control system, a high-frequency inertial measurement unit, and a communication interface module; The high-frequency inertial measurement unit is installed at the optical center of the Fresnel spherical mirror back plate and is used to collect the attitude and motion data of the Fresnel spherical mirror in real time. The main control system communicates and interconnects with the three-axis servo drive unit and the UAV flight control system through a communication interface module. It synchronously acquires the UAV's RTK positioning data, real-time flight attitude, and spatiotemporal reference data. The system calculates the target control quantity for directional sunlight reflection using a solar directional reflection algorithm. Based on the target control quantity and the attitude and motion data of the Fresnel spherical mirror, the system outputs a control signal to the three-axis servo drive unit after processing by a stabilization control algorithm. This enables real-time stabilization of the Fresnel spherical mirror's line of sight, target tracking control, and directional sunlight reflection.

7. The high-precision UAV three-axis upright Fresnel spherical mirror gimbal system according to claim 1 or 6, characterized in that, Solving for the target control variables of directional reflection of sunlight includes: Multi-source spatiotemporal information synchronization and reference coordinate system establishment: real-time acquisition of the absolute geographic coordinates of the UAV and the target and the real-time flight attitude angle of the UAV relative to the navigation coordinate system, and construction of the rotation matrix from the navigation coordinate system to the body coordinate system; Spatial vector calculation: Based on the current UTC time, UAV location information, and solar attitude information, the solar incident light unit vector in the geographic coordinate system is calculated using the astronomical ephemeris algorithm, and the target pointing unit vector is calculated by combining the spatial coordinate difference between the UAV and the target. Ideal reflective surface normal vector extraction: Based on the three-dimensional spatial light reflection law, the unit vector of the solar incident light and the target pointing unit vector are summed and normalized to obtain the ideal reflective surface unit normal vector in the geographic coordinate system; Body attitude compensation transformation: By using a rotation matrix, the unit normal vector of the ideal reflective surface in the geographic coordinate system is transformed to the body coordinate system to obtain the unit normal vector of the ideal reflective surface in the body coordinate system, so as to eliminate the optical path pointing error introduced by the UAV body attitude deflection; Inverse kinematics solution for a three-axis gimbal: Based on the linkage structure characteristics and rotation sequence of the three-axis gimbal, the inverse kinematics analytical solution is performed on the unit normal vector of the ideal reflective surface in the body coordinate system, and the target given angles of the gimbal's heading, roll, and pitch three-axis motors are output and combined to form the target control variables. Closed-loop feedback control and dynamic directional projection: The given angle of the three-axis target is fed back to the main control system, which drives the upright three-axis gimbal to overcome disturbances and inter-axis coupling torque, track the given angle of the target in real time and maintain the attitude of the Fresnel spherical reflector, so as to realize high-precision directional projection of the solar beam and dynamic long-range optical path reconstruction.

8. The high-precision UAV three-axis upright Fresnel spherical mirror gimbal system according to claim 7, characterized in that, The system also includes: The consistency of the normal vector obtained by forward kinematics calculation of the forward kinematics equation with the unit normal vector of the ideal reflector in the body coordinate system is checked. When the deviation between the two exceeds the preset threshold, the inverse kinematics calculation is performed again. The attitude compensation of the Fresnel mirror is achieved by using accelerometer and gyroscope data calculated by the high-frequency inertial measurement unit, so as to realize the real-time correction of the given angle error of the control target.

9. The high-precision UAV three-axis upright Fresnel spherical mirror gimbal system according to claim 1, characterized in that, The Fresnel spherical mirror is a traditional spherical mirror whose continuous spherical surface is decomposed into a set of concentric ring working surfaces with the same curvature as the reference spherical surface. It achieves a significant weight reduction while fully retaining the optical characteristics of spherical mirror beam expansion and field of view control. The Fresnel spherical mirror's structural parameters are determined through a parameter optimization method based on the geometric constraints of collaborative detection: under the paraxial approximation, the Fresnel spherical mirror is equivalent to an ideal spherical mirror. By combining the theoretical field-of-view model of the spherical mirror with the Gaussian equation under the paraxial approximation, the optimal radius of curvature suitable for the collaborative detection mission is analytically obtained. Combined with the weight reduction constraint mapping of the airborne payload, the optimal number of Fresnel rings is obtained, thereby achieving directional beam expansion and reflection of sunlight.

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